The present invention relates to an emergency-stop circuit, which is an integral part of the typical industrial machine. More particularly, this invention relates to a centralized switching system and method for an emergency stop circuit.
In industrial equipment, the traditional emergency-stop circuit consists of a xe2x80x9cself-latchingxe2x80x9d relay that contains a number of closed (kill) switches which are connected in series, and when any one of the switches is opened, the relay is de-energized. Power is restored when all kill switches are closed, and a xe2x80x9cmotors-onxe2x80x9d momentary switch (e.g., push-button switch) manually closes the contacts of the relay. The relay contacts are the last link in the serial chain of switches that energizes the coil of the relay. It is self-latching in the sense that when the motors-on switch is released, the contacts are in the coil energizing circuit that keep them closed in the first place. The coil energizing circuit is referred to herein as the emergency-stop circuit.
A robust, traditional circuit may have many kill switches in the emergency-stop circuit. These switches are typically distributed all over the machine. For example, lever-type switches are installed on door panels, so that power is killed (i.e., shut off) when one of the doors opens. This is referred to as the normally open configuration (NO), which means that the switch must be tripped to conduct. This kind of kill switch is the first to be defeated in practice. It is often taped or strapped closed so that a door may remain open during operation of the machine. (A common purpose for the defeat is debugging by a maintenance technician.) When there are several doors defeated in this manner located throughout a large machine, the probability is higher than desirable for a maintenance technician to inadvertently leave a switch defeated and return the machine to what will be unsafe use. Also, the cycle of taping/strapping and removal thereof causes wear and tear on the lever-type switch for which it was not designed.
Other types of kill switches used in the industry include over-travel switches. These switches normally operate in the closed configuration (NC), which means that tripping of the switch opens the circuit. These switches include lever-type, magnetic, infrared, or the like. To defeat over-travel switches, the switches are temporarily removed, terminals jumpered, mounting screws loosened, and brackets are slid out of the way. This also creates opportunity for mistakenly leaving kill switches defeated (or misaligned) throughout the machine when it is returned to service.
Another example of a kill switch is an air pressure switch sensing an air line that delivers required air to an air bearing spindle. In a demonstrating test, or debug mode, the machine may be run without the spindle running (no air supplied or air temporarily unavailable). This requires the jumpering of the kill switch during such time. Afterwards, forgetting to re-enable the switch allows running of the spindle without air, which leads to hardware damage.
Evidently, safe use of the traditional emergency-stop circuit requires experience and diligence on the part of the maintenance technician who attempts to temporarily bypass sections of the circuit in order to test or debug the system. Oversight due to distribution of the switches over numerous parts of the machine/device can cause him to forget to re-enable a kill switch before returning equipment back to duty.
Additionally, in order to test and debug, the technician must also disable certain devices whose power is controlled by the emergency-stop circuit. There is no straightforward, universal way to do this other than disconnecting the power to the device. This may be easy in some cases or not possible, very cumbersome, or unsafe in others.
A final consideration for these testing and debugging methods is the time required for a technician to trace through a machine in order to determine where to disable a kill switch or where to disconnect power to a device. Additionally, managerial time may be spent generating documentation in order to aid the technician""s task. This becomes apparent when one considers a factory floor that possesses a vast array of one-of-a-kind machines, all of which utilize some variant of the traditional emergency-stop circuit. Here, hypothetically, each circuit possesses essentially the same topology but utilizes different components that are located in different places and connected by a slightly different wiring scheme.
In spite of this, implementation of traditional emergency-stop circuits that are intrinsically xe2x80x9csafexe2x80x9d is certainly feasible and has been done for many years. There are reasons for the apparent success. It is a simple circuit, even though it is distributed throughout the machine. It well established. There are few components. But these are also the reasons why the circuit has not matured.
Typically, experienced engineers are reluctant to add new parts and kill switches to the circuit in an effort to xe2x80x9ckeep it simple.xe2x80x9d In developing prototypes or one-of-a-kind machines, important kill switches such as a watchdog circuit and a computer ready are often omitted. Also, some kill switches having solid state outputs (e.g. NPN) do not fit into the serially connected topology. Each requires an extra part, such as an intermediate electro-mechanical relay, whose contacts are in the kill switch chain, and whose coil is controlled by the solid state output. Because of this, sensors employing solid state outputs are avoided, and their less reliable mechanical counterparts are used instead.
Essentially, there is a mindset among skilled engineers concerning the altering of the traditional circuit""s topology. Typically, the skilled engineer begins a new project assuming that he will use the traditional circuit. Valuable time is spent on other areas and is not devoted to re-engineering the architecture for the traditional circuit or evaluating its expanded role in the project. In fact, it is not obvious to the skilled engineer to change the traditional circuit in any way in order to add functionality that can be safely incorporated within it. Such functionality, if implemented, is therefore left to be distributed throughout the remainder of the system, intermingled with unsafe subsystems such as the computer.
When implemented, for example, secondary outputs, such as amplifier xe2x80x9cenablexe2x80x9d or xe2x80x9cinhibitxe2x80x9d signals, are not usually incorporated into an emergency-stop circuit. If driven at all, a software program running on a computer having optically isolated digital outputs usually drives them. Furthermore, other feedback signals, such as xe2x80x9cstatusxe2x80x9d or xe2x80x9cfaultxe2x80x9d signals, are not used in emergency-stop circuits as kill inputs. This is generally because each signal is in a non-conducting state when the circuit is killed, which prevents the traditional circuit from restarting. If used at all, these feedback signals are likewise connected to the computer for the purposes of monitoring.
Designing in this way fosters subtle system-wide shortcomings, which can permit potentially unsafe or undesirable operation. Resulting failures or odd performance is not attributed to the emergency-stop circuit, since its simple circuitry and lack of substantial functionality are not directly responsible. Consequently, effort is typically not expended to evaluate its functionality.
One of the shortcomings becomes apparent when the traditional system enters into a power-loss period, which generally begins when the emergency-stop circuit is killed and ends when all residual power has been dissipated. During this brief period (e.g., 2 sec.), uncontrolled motion of motors can occur for some designs, because the motors are not being controlled, yet they are still technically powered by residual power in the system. In order to suppress this, designers have used the computer-controlled secondary outputs (enable, inhibit) in conjunction with the emergency-stop circuit to simultaneously cut power and disable the connected devices. This works in most cases, but is tedious to design, not flexible, and application specific. One case when this design fails is when the building power fails, which causes the computer to also cease functioning. Here the inhibit signal may not get to the device, which again creates an environment for briefly uncontrolled motion.
Most of the examples found in existing technology are concerned with passive monitoring of the emergency-stop circuit. This approach is useful in determining which kill input was responsible for stopping the circuit, but it does not provide any configuration options for startup or power-loss periods. The following patents, each of which is incorporated herein by reference, demonstrate this approach: U.S. Pat. No. 4,263,647 to Merrell, et al, entitled xe2x80x9cFault Monitor for Numerical Control Systemxe2x80x9d; U.S. Pat. No. 5,451,879 to Moore, entitled xe2x80x9cElectromechanical Relay Monitoring System with Status Clockingxe2x80x9d; U.S. Pat. No. 4,616,216 to Meirow, et al., entitled xe2x80x9cEmergency Stop Monitorxe2x80x9d; and U.S. Pat. No. 5,263,570 to Stonemark, entitled xe2x80x9cConveyor Belt Emergency Stop Indicator Light System.xe2x80x9d Configuration options do exist in the above noted patents but only in the form of providing cascaded inputs and outputs so that multiple groups of sensors may be monitored. Other patents of interest include the following: U.S. Pat. No. 4,912,384 to Kinoshita, et al., entitled xe2x80x9cEmergency Stop Control Circuitxe2x80x9d discloses the traditional active portion of the emergency-stop circuit; U.S. Pat. No. 5,319,306 to Schuyler entitled xe2x80x9cPortable Electrical Line Tester Using Audible Tones to Indicate Voltagexe2x80x9d discloses circuits that provide audio status in the form of line testers, where the leads are brought into contact after the line is energized to check it.
Traditional approaches to supplying power to motors during a power-loss period (period beginning with the loss of AC motor power and ending with either the total loss of all stored DC motor power or the loss of regulation of any associated logic power supply, whichever comes first) have focused on coarse (non-servo) control or decelerating motors to full stop. However, no approach exists that relates to fields employing emergency-stop circuitry.
Other patents in this general field are also noted. For example, U.S. Pat. No. 5,278,454 to Strauss, et al. discloses an invention related to the heating, ventilation, and air conditioning field. It describes a motion control system that senses a loss of incoming power and utilizes a dedicated pre-charged circuit to act as a short duration power supply to effect gross motion of a motor to close a damper. U.S. Pat. No. 5,426,355 to Zweighaft, et al., entitled xe2x80x9cPower-Off Motor Deceleration Control Systemxe2x80x9d discloses an invention related to the tape drive industry in which a motion control system whose amplifier stores a dedicated internal PWM signal responsible for supplying open-loop deceleration commands for a given configuration of the tape drive system that is experiencing a power-loss period. U.S. Pat. No. 4,481,449 to Roda entitled xe2x80x9cPower Fail Servo Systemxe2x80x9d discloses an invention that also relates to the tape drive field which describes the use of several xe2x80x9cpower failxe2x80x9d signals that work in harmony to decelerate the motor towards full stop and uses the technique of dynamic braking to harness excess power in the storage capacitor. A signal exists in this example which monitors the logic power supply and appropriately disables (free wheels) the motor once the supply is out of regulation.
The present invention solves the problems in the art by providing a centralized programmable emergency-stop circuit that controls the flow of the power necessary for a machine to move its working elements. The invention possesses various levels of programmability that facilitate use of the same circuit across a wide variety of industrial applications and designs, as well as across a wide variety of operational scenarios for the same machine.
The circuit of the present invention includes various types of custom programmable kill inputs. These inputs are signals that, subject to their programming, can kill an energized emergency-stop circuit or prevent a killed circuit from energizing (startup). A given kill input can also be programmed to be ignored totally, to kill when inactive, or to also prevent startup when inactive. A given kill input can be programmed so that it only affects the energized circuit and does not restrict startup, and consequently, it may be inactive at startup. Such a programmed kill input is referred to herein as a xe2x80x9cfalling-type,xe2x80x9d because once it does go active, it is the active-to-inactive or falling transition that kills the circuit. Additional programming for the kill inputs exists such as digital filter parameters, clock selection, and the like, as well as time-out options for the falling-type kill inputs, which require them to go active within some period after startup.
The present invention also provides programming options to specify conditions for a motors-on signal to energize the circuit and for the control of secondary outputs. While the primary output of the circuit controls the flow of bulk power to working elements, it is the secondary outputs that connect in parallel to the working elements in order to inhibit or enable them. The method of programming secondary outputs determines their behavior, i.e., whether they are disabled entirely for the session, enabled only when the circuit is energized, or enabled based on one of the kill input signals. This latter setting permits a computer to keep a device enabled during a power-loss period, so that a reactionary movement can be effected which drains residual power left in the dying system.
In order to improve an emergency-stop circuit that controls the flow of bulk power needed for a machine to move its elements, it is the object of this invention to provide additional features and programmability that improves performance during the period immediately following the application of electrical power needed to power circuit logic. Specifically, it is the object of the invention to inhibit energizing the circuit for a prescribed interval of time. Additionally, it is the object of the invention to provide programmability so that the interval may be changed.
In order to further improve performance during the period immediately following the application of electrical power needed to power circuit logic, it is the object of the invention to provide additional features and programmability. Specifically, it is the object of the invention to provide circuitry that determines whether the circuit has been energized at least once. Furthermore, it is the object of the invention to provide further additional circuitry that drives a dedicated power-up/reset error code which indicates electrical power has just been applied to the circuit logic. The power-up/reset error code therefore supersedes the conventional error code that is generated from all possible kill input sources. Additionally, it is the object of the invention to provide a clear signal capable of clearing the power-up/reset error code (so that the conventional error code may be revealed) and also capable of refreshing conventional error codes thereafter. It is also the object of the invention to provide programmability so that a set of clear input sources may be pre-selected from all available input sources.
Finally, in order to further improve performance during the period immediately following the application of electrical power needed to power circuit logic, it is the object of the invention to provide additional features and programmability. Specifically, it is the object of the invention to employ a start signal that when inactive inhibits the initial energizing of the circuit. Activation of the start signal occurs in response to the final cycle of a specified number of deactivation and reactivation cycles of a ready-type input signal, and deactivation of the start signal occurs when the circuit is energized. Additionally, it is the object of the invention to provide programmability so that (1) the ability of the start signal to inhibit energizing is optional, (2) the specified number of cycles can be adjusted, and (3) a set of ready-type input signals may be pre-selected from all available input sources.
It is also the object of the invention to further employ the same start signal in subsequent energizing cycles in order to further improve performance. Specifically, a second specified number of deactivation and reactivation cycles is required in order to activate the start signal. Additionally, it is the object of the invention to provide programmability so that the second specified number of cycles can be adjusted.
In order to improve an emergency-stop circuit that controls the flow of bulk power needed for a machine to move its elements, it is the object of this invention to provide additional features and programmability that improves how the circuit is commanded to energize. Specifically, it is the object of the invention to provide for additional nominal requirements for the activation of a motors-on signal, such as (1) requiring it to be previously inactive and (2) requiring it to be active for a prescribed interval or longer. Additionally, it is the object of the invention to provide programmability so that (1) the interval may be changed, (2) the requirement to be previously inactive is optional, and (3) a set of motors-on-type input sources may be pre-selected from all available input sources. Finally, it is the object of the invention to provide programmability so that (1) a set of monitor contact-type input sources may be pre-selected from all available input sources, where each monitor contact signal is active when the circuit is killed and the associated, downstream monitored relay has fully disengaged and (2) the requirement for a given monitor contact signal to be active for the motors-on signal to be active is optional.
In order to further improve the manner in which the circuit is energized, it is the object of the invention to employ a second start signal that when inactive inhibits the energizing of the circuit. Activation of the start signal occurs when all kill input sources are active, where programmability provides for a set of kill sources to be selected from all available input sources. Deactivation of the start signal occurs when the circuit is energized or when one or more of the kill input sources become inactive. Additionally, it is the object of the invention to provide status for the start signal. Furthermore, it is the object of the invention to accommodate watchdog-type kill input sources that toggle on-and-off repeatedly at a rate faster than a prescribed value, where the toggling is the requirement for the watchdog-type kill input to be active. It is also the object of the invention to provide programmability for this so that (1) the requirement for toggling is optional and (2) the minimum rate is programmable. Finally, it is the object of the invention to include in the generation of the start signal an additional, dedicated kill input source that indicates whether an internal circuit error exists.
In order to further improve an emergency-stop circuit that controls the flow of bulk power needed for a machine to move its elements, it is the object of this invention to provide additional features and programmability that improves performance during the period immediately following energizing (right after it is started). Specifically, it is the object of the invention to provide audio status for a prescribed interval. Additionally, it is the object of the invention to provide programmability so that the interval may be changed.
In order to improve an emergency-stop circuit that controls the flow of bulk power needed for a machine to move its elements, it is the object of this invention to provide additional features and programmability that improves the manner in which the circuit is de-energized (killed) or prevented from energizing. Specifically, it is the object of the invention to employ a kill signal that when active de-energizes the circuit or prevents it from energizing. Activation of the kill signal occurs when one or more kill sources become inactive, where programmability provides for a second set of kill sources to be selected from all available input sources. Deactivation of the kill signal occurs when all kill sources from the second set become active. Additionally, it is the object of the invention to include in the generation of the kill signal an additional, dedicated kill input source that indicates whether an internal circuit error exists.
In order to further improve performance for the manner in which the circuit is de-energized (killed) or prevented from energizing, it is the object of the invention to provide additional programmability so that pre-selected additional input sources can be dynamically added to the second set of kill sources at some point of time after the circuit becomes energized and subsequently removed at such time that the circuit is de-energized. A given, dynamically added input source may be programmed to be added immediately after the input source becomes active. Additionally, or alternatively, it can be added after a prescribed interval of time following the energizing of the circuit. It is also the object to provide programmability so that this prescribed interval can be adjusted.
In order to further improve performance for the manner in which the circuit is de-energized (killed) or prevented from energizing, it is the object of the invention to provided additional programmability so that one of the dynamically added input sources is dedicated to sensing the presence of the bulk power controlled by the circuit. Additionally, it is the object that this input source is an alternating-current type that generates a strobing signal indicative of the active state of the bulk power, where the strobing occurring at a rate faster than a prescribed value is the requirement that the kill input source is active. Finally, it is the object that the minimum rate is programmable.
In order to further improve an emergency-stop circuit that controls the flow of bulk power needed for a machine to move its elements, it is the object of this invention to provide additional features and programmability that improves performance during the period immediately following de-energizing (right after it is killed). Specifically, it is the object of the invention to inhibit the re-energizing of the circuit for a prescribed interval of time after it is killed. Additionally, it is the object of the invention to provide programmability so that the interval for the dying period may be changed. Also, it is the object to provide audio or visual status during the dying period.
In order to further improve an emergency-stop circuit whose primary output controls the flow of bulk power needed for a machine to move its elements and whose secondary output controls the enable or inhibit of an element, it is the object of this invention to provide additional features and programmability for the circuit so that the source of the secondary output may be selected from a set of available sources. Specifically, it can be selected from the following sources: (1) none so that the element is always disabled, (2) from a signal that is active when the circuit is energized so that the element is enabled only when the circuit is energized, or (3) a dedicated enable-type input source, so that the element is enabled whenever the enable-type input source is active. It is also the object of the invention to provide additional programmability for the third case, which places a programmable pair of restrictions on when the enable-type input source has an effect so that it is used when (1) the circuit is energized or in the dying period that immediately follows de-energizing and otherwise, the element is disabled and (2) a watchdog-type input source is active and otherwise, the element is disabled. The requirement for the watchdog-type input source to be active is that it must toggle on-and-off repeatedly at a rate faster than a prescribed value. Finally, it is the object of the invention to provide additional programmability so that (1) the minimum rate for the watchdog-type input is programmable, (2) the enable-type input source may be pre-selected from all available input sources, and (3) the watchdog-type input source may be pre-selected from all available input sources.
Accordingly, it is the object of the present invention to provide a programmable emergency-stop circuit that allows various options for the manner in which kill inputs affect the system and further provides options for the manner in which outputs are activated and deactivated. Furthermore, it is an object of the invention to provide programmability to specify the manner and timing for dynamically adding a given input source to the active set of kill inputs. Finally, it is an object of the invention to emp e circuitry that generally avoids software or a microprocessor, so that new functionality coupled with programmability may be safely incorporated within the emergency-stop circuit.
One important feature of the invention is its state machine, which provides a framework from which the invention operates. Defined by a set of internal signals that includes start and kill-type signals, the state machine specifies when the circuit may be energized, when it is killed, and when startup is inhibited. The internal signals are generated as a programmable function of time and input source states. Other features include audio status for startup and kill, requirements for startup that ensures desired energizing, requirements for a computer ready signal that ensures synchronization with software running on a computer, provisions for a dedicated error-code that identifies power glitches, and the safe oversight of a power-loss period during which a servo-controlled reflex action may be implemented.
The primary advantage for using the invention is that a centralized single circuit can be programmed and employed in a wide variety of machine designs. For a given machine design, for example, the circuit can be reprogrammed and thereby adapted to a different set of operational scenarios. When designing a machine or a plurality of machine/devices, the designer is able to associate any given input source with a desired kill input type that specifies how the input source affects the system. Furthermore, once operational in the field, for example, the machine will require maintenance, and to assist this, the circuit can be definitively reprogrammed from a central location so that certain inputs are temporarily but safely ignored and certain outputs are forced disabled during the maintenance operation.
Other advantages of the invention are related to timing, filtering, and synchronization. One such advantage is the accuracy, and hence repeatability, that can be applied to timing the motors-on button""s active period as well as to the timing of the start-up delay that prevents the immediate re-start during the DYING state of a freshly killed circuit. The use of timing and other related digital filters significantly reduces the susceptibility of the circuit to background noise. It is also an advantage from a system performance standpoint that the emergency-stop circuit causes the computer program and, thereby, the entire system to be in synchronization via several novel methods.
The invention will now be described, by way of example and not by way of limitation, with reference to the accompanying sheets of drawings and other objects, features and advantages of the invention will be apparent from this detailed disclosure and from the appended claims. All patents, patent applications, provisional applications, and publications referred to or cited herein, or from which a claim for benefit of priority has been made, are incorporated by reference in their entirety to the extent they are not inconsistent with the explicit teachings of this specification.


This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/US98/24404 which has an International filing date of Nov. 17, 1998, which designated the United States of America.
1. Field of the Invention
A method and composition of matter for use as polymeric topcoats for articles and vehicles, such as, aircrafts, naval vessels, clothing and other industrial applications. With regard to an aircraft, xe2x80x9ccold-soakxe2x80x9d of the aircraft wing fuel tank leads to localized wing ice formation under certain environmental conditions. Also, ice forms on the xe2x80x9cpleading edgesxe2x80x9d of the aircraft which detach and enter the jet engines or otherwise influence aerodynamic performance of aircraft wings. Conventional polymer paints and coatings contain a volatile organic content (VOC) that is under increasing regulation by EPA.
2. Background of the Invention
Since 1986, the limit for volatile organic content (VOC) of aerospace topcoatings as set by California Rule 1124 has dropped from around 700 g/l to its present limit of 420 g/l or even lower values. Increasing concern over the impact of organic compounds on the quality of life and environment can be expected to lead to further reduction in permissible VOC in coming years. Achieving durable, functional coatings that comply with the VOC regulations and satisfy functional coating requirements is becoming challenging for the aircraft industry and coating suppliers.
The southern California environmental control agencies require a maximum of 420 grams/liter of volatile organic compounds (VOC) from a coating material. The cyclic prepolymer coatings will reduce the VOC emissions during coating operation to less than 1 gram/liter of coating material. These new coating processes will provide a coatings technology that is environmentally compliant for the future, whereas existing solvent-borne technologies are compliant on a year-to-basis with a questionable future.
Conventional aircraft coatings used on commercial and military aircraft can be either water based or solvent based. Solvent based coatings are the most widely used. Typical solvents such as xylene, toluene and chlorinated aliphatic hydrocarbons, are required in order to control drying times, pigment distribution and surface smoothness of these coatings. These compounds all have unacceptably high VOC. Furthermore, xylene is a carcinogenic compound and the others are suspected hazardous materials both of which present serious employer liability issues. The EPA is strongly advocating a reduction of all solvents with the exception of water to reduce VOC and eliminate potential carcinogens. A water based coating is a natural alternative and has been developed for primer coatings but has yet to produce satisfactory performance as a topcoating. They contain small but significant amounts of VOC.
Historically, coating formulations meet the requirements by using xe2x80x9cexemptxe2x80x9d solvents, or by reclassifying coatings into other categories. Newer approaches for formulations and applications of coatings represented by the approach of the present invention can achieve a reduction of VOC well below 420 g/l, perhaps approaching as low as 0 g/l. This is achieved by using a new polymeric coating technology that will meet the most severe restrictions that are anticipated in the year 2010 less than 100 g/l.
High solids deposition processes are based on water reducible, flame and plasma spray coating processes to implement low VOC coatings and deposition processes through a highly focussed research and development program.
Plasma spray and flame spray processes and flourinated polymer coatings have advantages because current solvent systems have definite limits for reduction of VOC. Although water-reducible systems have potential for further VOC reduction, they have a significant VOC content and may also exhibit adherence problems. A xe2x80x9csuper-critical fluid spray coating systemxe2x80x9d is capable of reducing VOC by 30-70 percent depending on the type of resins and polymers in the parent coating system. However, the equipment is expensive, complex and bulky, and the pigmentation of coatings using this process is limited.
Plasma spraying consists of depositing a coating by flowing a powder coating-inert gas mixture through an electric arc plasma. The thermoplastic powder liquefies and flows on the surface. The advantage of this coating process over air spraying of solvent-borne and water-borne coatings is that no solvent or VOC is produced. Also, many materials can be applied with low surface energies, such as chloro- and fluoropolymers which cannot be air sprayed. The disadvantage is that the process produces an ignition source which is hazardous around aircraft and flammable vapors and liquids. The actual cost of the plasma spray coating process is higher than conventional coating processes, but the service life of the plasma sprayed coating is longer and the coating can be thicker to compensate for wear. Lifecycle costs may be lower than conventional coatings. Typical foot-wear on the surface will not damage these coatings.
The plasma spray process is a mature technology and equipment is available for use. These coatings can be applied directly to aircraft aluminum surfaces to provide a non-icing surface. Limited colors are available in stock powders, but can be formulated for any color. In order to achieve an optimal coating it also will be necessary to formulate binders and pigments with specific properties.
For a thixotropic powder, particles need to coalesce quickly, (tc needs to be short) since xcex7 is time dependent after deformation. The instantaneous viscosity, xcex7, and particle radius, rp, should be small and the surface tension, xcex3, large. For flattening, xcex7, and particularly rp should be small; and xcex3 and particularly h should be large. (Additives may be able to reduce the surface tension, but viscosity seems the primary driver.) Low xcex7 necessitates low molecular weight and higher temperatures, or slower catalysis rate.
Specific flatteners, pigments and other additives are necessary to make an effective topcoat from a resin (binder) promoting coating adhesion, providing ultra-violet (UV) radiation protection and color. These additives must be balanced against the requirements for coalescence and flattening, as increasing content of particulate in the coating increases viscosity. Several specific texts on paint chemistry for the production of a topcoat are available to guide coating formulation.
Two generic types of coatings are relevant, aircraft topcoatings and industrial maintenance (IM) coatings. Requirements for aircraft topcoatings are stringent. Typically, aircraft topcoat requirements are specified by the military specifications MIL-C-83286B, xe2x80x9cAliphatic Isocyanate Urethane Coating for Aerospace Applicationsxe2x80x9d, MIL-C-85285, xe2x80x9cHigh Solids Polyurethanesxe2x80x9d, or Boeing Military Specifications such as BMS 10-60, xe2x80x9cProtective Enamel.xe2x80x9d
An EPA reports summarizes the competitive low VOC coating processes and chemistries available in 1991; the principal ones being powder, waterborne, radiation curable and high solids coatings. The summary of this older reference still appears to represent a good economic and technical assessment of coating possibilities. This report also emphasizes that VOC from coating stripping operation is also considered one of the VOC consequences of the selection of method of coating. Table 1 summarizes coating/application methods and issues in this report.
Besides the genre of application for coatings, the actual deposition method is an important element in controlling VOC. High solids coatings, for example, achieve low VOC by eliminating the solvent classically used for coalescence, flow and flattening. They rely instead on mechanisms such as thermal or kinetic energy to achieve these ends water-based coatings replace organic solvents with water.
The EPA sets forth VOC requirements for industrial maintenance coatings, namely, primers, sealers, topcoats, etc., used in outdoor aggressive environments on structures such as bridges, ships, and hydraulic structures. The proposed VOC limit was 350 g/l; and the 2004 limit (proposed) was 300 g/l.
This reports describes in detail the VOC measurement methodology (EPA Reference Method 24, a distillation of ASTM standard test methods) and describes the calculation of VOC emissions. Manufacturers claim that the ASTM D-2369 can produce inordinately high VOC levels, particularly in marine and architectural coatings, as it requires the coating to be heated to 110 C. (230 F.) where excessive loss of volatile components by coating decomposition may occur.
Camouflage topcoatings must meet low VOC requirements and also very stringent chemical agent resistance requirements. These requirements consist of resistance to chemical decontamination/wash as well as other severe requirements.
The baseline coating is a two components solvent-borne polyester/polyisocyanate binder system that is lead, chromium, 1,1,1 trichlorethane free. This candidate new xe2x80x9clow VOCxe2x80x9d coating is a waterborne/dispersible/reducible coating using polyisocyanates and polyesters from Miles, Inc. including Bayhydrol XP-7044 WD polyester, Bayhydur XP-7007 WD polyisocyanate and de-ionized water reducer as needed.
Typical fillers are cobalt green spinet, chromium oxide, magnesium ferrite and carbazole violet pigments with diatomaceous silica, magnesium silicate and amorphous silica extender pigments. These pigments are added to the polyester component and polyisocyanate is diluted with suitable solvent to meet viscosity of both components and meeting stoichiometry.
This coating met all requirements of specification except CAR (chemical agent resistance). VOC is estimated to be xcx9c300 g/l. A fundamental problem of these WB/WD/WR coatings is film porosity that allows chemical agents to penetrate the coating. The CPVC (critical pore volume content) appears to determine gloss. A high CPVC value in the candidate coating is a problem for CAR. The author of the study cites the strategy for improving the CPVC is use of additives to improve wetting/flow/dispersion in this WB/WD/WR system.
It would appear that a well designed, low VOC aircraft topcoat may also met CARC requirements.
Table 2 outlines the basic performance characteristics of aircraft coatings.
Regulatory bodies tend to restrict the use of deposition systems that have low transfer efficiency. The California AQMD regulations require minimum transfer efficiencies of 60-85% and maximum gun tip gas pressure of 10 psi. Currently, only HVLP and electrostatic spray processes can meet these requirements.
Existing levels of corrosion protection should be maintained with new low VOC topcoatings. Corrosion (aqueous) requires the presence of water, cations and oxygen. strontium chromate is an important additive to inhibit corrosion. Coating strategy has been to achieve a physical barrier between the substrate and the external environment to prevent moisture and radiation induced coating degradation.
Since moisture egress is a virtual certainty, coating adhesion becomes a very important coating characteristic. The mechanism of adhesion is either chemical or physical. Although chemical pretreatment of the surface substrate can enhance secondary chemical bonding, and in some cases even achieve primary bonding, the major adhesion mechanism is the mechanical interlocking of the coating with the microscopic surface roughness created in anodizing.
The practical lifetime of a military or commercial coating is 4-8 years. This lifetime requirement imposes significant demand for resistance to environmental degradation.
Traditionally an epoxy primer and polyurethane topcoat are used for aircraft applications. Epoxy primer/polyurethane topcoatings are highly refined to meet the military requirements. Since epoxides are brittle and have very low UV stability, they are used as a primer and the external coating provides the UV protection. The epoxide coatings provide superior resistance to moisture penetration and subsequent corrosion. The combination of the two also has very low water absorption, vapor transmission rate and UV resistance.
Aliphatic isocyanate and polyester are highly developed UV resistant topcoatings and their literature is well documented. Typical aircraft topcoats have a dry film thickness of 0.002+/xe2x88x920.0003 inch (50.8+/xe2x88x927.8 micrometers). Set and hard dry time is typically 2 and 6 hours, respectively. Fully developed properties may not be attained until about 7 days aging.
Fillers such as talc and mica are used to provide an oriented distribution to serve as secondary radiation and physical barriers, silica and metal silicates, carbonates and sulfates are added as physical fillers that reduce gloss and increase opacity.
Water-borne coatings are one approach to compliant coatings. The primary strategy is to achieve a solution of emulsion of polymer powders whose surfaces are modified with hydrophilic groups. The major difficulty with water-borne coatings is that the use of water as a solvent leads to more porous coatings and adhesion problems related to organic surface contamination.
High solids or powder coatings are also one route to achieving low VOC levels. One approach is to reduce the solvent content of the coating, but this shortens pot life and greatly increases viscosity. These factors increase surface roughness. By moving to lower molecular weight resins, one can achieve improved viscosity and flatter coatings. However, polyisocyanate cured powders have shorter pot life and reduced flexibility due to the more rapid and extensive cross linking due to the lower molecular weight. One strategy to improve this is to use polymers with very narrow molecular weight distribution.
An EPA study and a follow-up publication evaluated six (6) coatings. The six types are solvent-borne polyurethane, waterborne epoxy primer w/latex topcoat, solvent alkyd primer/waterborne acrylic, 2 component polysiloxane topcoat, water reducible alkyd primer/acrylic topcoat and solvent alkyd primer/solvent alkyd enamel (standard baseline). The study compared impact, adhesion, pencil hardness and solvent tests and outdoor exposure tests of these coatings. The VOC data from candidate coatings in this study is useful for aerospace topcoats. Of particular interest in this assessment of IM coatings is the determination that a two component polysiloxane coating with a low VOC of about 84 g/l performed extremely well. These two studies showed the polysiloxane coatings exhibited the best VOC levels and performance in environmental testing.
A second study is also grouped in the IM coatings discussion. Although the study intended to coat F-15 aircraft, only ground vehicles were coated. It consisted of an evaluation of supercritical spray coating and a high pressure-low volume (HPLV) process called ULV (ultra low volume) spraying. The polyurethane coatings had a baseline VOC of about 420 g/l which is too high for current requirements. The study found the supercritical coating process to be unacceptable for field use, and found that the ULV process reduced emissions by about 50%, primarily by reducing the total paint sprayed in the coating process. This result shows that both the coating process itself as well as the formulation of the coating can have significant impact on total VOC emission. This study attempted to spray high solids coatings unsuccessfully. The major problem encountered was very slow drying. This was a result of an improper level of catalysts in the coating.
IM coatings for bridges using principally an epoxy mastics and silicone rubbers, that are not particularly relevant to aircraft topcoats, were evaluated. Cyclic salt-fog/freeze provided a relatively rapid method to differentiate coating performance in a short time period. Specific VOC content was not stated, but all the evaluated coatings were at or below 340 g/l. A xe2x80x9clow-VOCxe2x80x9d acrylic aliphatic polyurethane topcoat exhibited the best gloss retention.
The basic objectives of this invention are to produce a polymeric binder or matrix for a coating with extremely low, or zero VOC content that can be used as a top coat for many applications and in aircraft applications to achieve specific coating characteristics to prevent icing of aircraft wings. Icing on critical aircraft surfaces may create a condition which might impair the stability of the aircraft. The specific areas are referred to as xe2x80x9ccold-soakxe2x80x9d areas and some other areas on the xe2x80x9cleading edgesxe2x80x9d of the wings and engine nacelles. The present invention eliminates the adhesion of ice on these surfaces. Environmental icing due to weather is a related problem, but is not the direct problem concerning the present invention.
Ice will not adhere to the surface of certain polymer coatings with low surface energy such as Teflon. This is a consequence of the high contact angle between the water droplet and the surface that establishes a non-wetting surface. One objective of the present invention is to implement such coatings and a deposition process. Effective implementation will also result in a coating formulation and deposition process, with a very low VOC emission.
Coatings formulations for prevention of icing problems includes the following properties:
Low surface energies to prevent icing.
Adhesive to aircraft surfaces.
Protection of substrates from corrosion.
Resistance to jet fuel and hydraulic fluids.
Other properties for coatings specifications.
Coating materials are selected for low surface energy properties and general coating properties. The coating materials are polymerized fluoropolymers that possess good low temperature properties, e.g., do not embrittle at xe2x88x9245xc2x0 C., and do not soften at elevated temperatures of 90xc2x0 C.
Two parallel benefits of this approach may be achieved. The coating process is potentially adaptable for coating an entire aircraft or other commercial item. The combination of the coating process and the coating formulation reduces volatile organic compounds (VOC) well below the current Environmental Protection Agency (and California) limits for the forseeable future.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.


The use of ink jet printers for printing information on a recording media is well established. Printers employed for this purpose may be grouped into those that continuously emit a stream of fluid droplets, and those that emit droplets only when corresponding information is to be printed. The former group is generally known as continuous inkjet printers and the latter as drop-on-demand inkjet printers. The general principles of operation of both of these groups of printers are very well recorded. Drop-on-demand inkjet printers have become the predominant type of printer for use in home computing systems, whereas continuous inkjet systems find major application in industrial and professional environments. Typically, continuous inkjet systems produce higher quality images at higher speeds than drop-on-demand systems.
Continuous inkjet systems typically have a print head that incorporates a fluid supply system for fluid and a nozzle plate with one or more nozzles fed by the fluid supply. The fluid is jetted through the nozzle plate to form one or more thread-like streams of fluid from which corresponding streams of droplets are formed. Within each of the streams of droplets, some droplets are selected to be printed on a recording surface, while other droplets are selected not to be printed, and are consequently guttered. A gutter assembly is typically positioned downstream from the nozzle plate in the flight path of the droplets to be guttered.
In order to create the stream of droplets, a droplet generator is associated with the print head. The droplet generator stimulates the stream of fluid within and just beyond the print head, by a variety of mechanisms known in the art, at a frequency that forces continuous streams of fluid to be broken up into a series of droplets at a specific break-off point within the vicinity of the nozzle plate. In the simplest case, this stimulation is carried out at a fixed frequency that is calculated to be optimal for the particular fluid, and which matches a characteristic drop spacing of the fluid jet ejected from the nozzle orifice. The distance between successively formed droplets, S, is related to the jet velocity, v, and the stimulation frequency, f, by the relationship: v=fS. U.S. Pat. No. 3,596,275, issued to Sweet, discloses three types of fixed frequency generation of droplets with a constant velocity and mass for a continuous inkjet recorder. The first technique involves vibrating the nozzle itself. The second technique imposes a pressure variation on the fluid in the nozzle by means of a piezoelectric transducer placed typically within the cavity feeding the nozzle. A third technique involves exciting a fluid jet electrohydrodynamically (EHD) with an EHD droplet stimulation electrode.
Additionally, continuous inkjet systems employed in high quality printing operations typically require small closely spaced nozzles with highly uniform manufacturing tolerances. Fluid forced under pressure through these nozzles typically causes the ejection of small droplets, on the order of a few pico-liters in size, traveling at speeds from 10 to 50 meters per second. These droplets are generated at a rate ranging from tens to many hundreds of kilohertz. Small, closely spaced nozzles, with highly consistent geometry and placement can be constructed using micro-machining technologies such as those found in the semiconductor industry. Typically, nozzle channel plates produced by these techniques are typically made from materials such as silicon and other materials commonly employed in micromachining manufacture (MEMS). Multi-layer combinations of materials can be employed with different functional properties including electrical conductivity. Micro-machining technologies may include etching. Therefore through-holes can be etched in the nozzle plate substrate to produce the nozzles. These etching techniques may include wet chemical, inert plasma or chemically reactive plasma etching processes. The micro-machining methods employed to produce the nozzle channel plates may also be used to produce other structures in the print head. These other structures may include ink feed channels and ink reservoirs. Thus, an array of nozzle channels may be formed by etching through the surface of a substrate into a large recess or reservoir which itself is formed by etching from the other side of the substrate.
FIG. 1 schematically illustrates a prior art conventional electrohydrodynamic (EHD) stimulation means used to excite a jet of conductive fluid into a stream of droplets. Fluid supply 10 contains conductive fluid 12 under pressure which forces ink through nozzle channel 20 in the form of a conductive fluid jet 22. Conductive fluid 12 is grounded or otherwise connected through an electrical pathway. A prior art droplet stimulation electrode 15 is approximately concentric with an exit orifice 21 of nozzle channel 20 as shown in cross-section in FIG. 1A. Droplet stimulation electrode 15 typically includes a conductive electrode structure 13 produced from a variety of conductive materials, including a surface metallization layer, or from one or more layers of a semiconductor substrate doped to achieve certain conductivity levels. Prior art conductive electrode structure 13 is electrically connected to a stimulation signal driver 17 that produces a potential waveform of chosen voltage amplitude, period and functional relationship with respect to time in accordance to a stimulation signal 19. In FIG. 1, an example of a stimulation signal 19 comprises a uni-polar square wave with a 50% duty cycle. The resulting EHD stimulation is a function of the square of field strength created at the surface of the conductive fluid 12 near exit orifice 21. The resulting EHD stimulation induces charge in the conductive fluid jet 22 and creates pressure variations along the jet. Conductive electrode structure 13 is covered by one or more insulating layers 24 which are necessary to isolate droplet stimulation electrode 15 from conductive fluid 12 in order to prevent field collapse, excessive current draw and/or resistive heating of conductive fluid 12. The conductive fluid 12 must be sufficiently conductive to allow charge to move through the fluid from the grounded fluid supply 10 in order to electrohydrodynamically stimulate conductive fluid jet 22 to form droplets that subsequently form at break-off point 26. Since conductive fluids are employed, a non-uniform distribution of charge cannot be supported in the fluid jet column outside of the stimulating electric field. The electrohydrodynamic stimulation effect occurs due to the momentary induction of charge in conductive fluid 12 at nozzle orifice 20 that creates the pressure variation in fluid jet 22. For a correctly chosen frequency of the stimulation signal 19, the perturbation arising from the pressure variations will grow on the conductive fluid jet 22 until break-off occurs at the break-off point 26.
Various means for distinguishing or characterizing printing droplets from non-printing droplets in the continuous stream of droplets have been described in the art. One commonly used practice is that of electrostatic charging and electrostatic deflecting of selected droplets as described in U.S. Pat. No. 1,941,001, issued to Hansell, and U.S. Pat. No. 3,373,437, issued to Sweet et al. In these patents, a charge electrode is positioned adjacent to the break-off point of fluid jet. Charge voltages are applied to this electrode thus generating an electric field in the region where droplets separate from the fluid. The function of the charge electrode is to selectively charge the droplets as they break off from the fluid jet.
Referring back to FIG. 1, a typical prior art electrostatic droplet characterizing means includes charging electrode 30. Conductive fluid 12 is employed such that a current return path exists through the fluid supply 10 (e.g. through grounding). A charge is induced in a specific droplet under the influence of the field generated by charge electrode 30. This droplet charge is locked in on the droplet when it separates from the fluid jet 22. Charging electrode 30 is electrically connected to charge electrode driver 32. The charging electrode 30 is driven by a time varying voltage. The voltage attracts charge through conductive fluid 12 to the end of the fluid stream where it becomes locked-in or captured on charged droplets 34 once they break-off from the jet 22.
A high level of conductivity of fluid 12 is required to effectively charge droplets formed in these prior art systems. Prior art inkjet print heads that employ electrostatic droplet characterizing means typically use conductive fluid 12 conductivities on the order of 5 mS/cm. These conductivity levels permit induction of sufficient charge on charged droplets 34 to allow downstream electrostatic deflection. The conductivity required for droplet charging is typically much greater than that for droplet stimulation. Typically, a conductive fluid suitable for charging can also be stimulated using EHD principles. The selective charging of the droplets in conventional electrostatic prior art inkjet systems allows each droplet to be characterized. That is, the conductive inks permit charges of varying levels and polarities to be selectively induced on the droplets such that they can be characterized for different purposes. Such purposes may include selectively characterizing each of the droplets to be used for printing or to not be used for printing.
Again referring to the prior art system shown in FIG. 1, a potential waveform produced by the charging electrode driver 32 will determine how the formed droplets will be characterized. The potential waveform will determine which of the formed droplets will be selected for printing and which of the formed droplets will not be selected for printing. Droplets in this example are characterized by charging as shown by charged droplets 34 and uncharged droplets 36. Since a specific droplet characterization is dependant upon whether that droplet is printed with or not, the potential waveform will typically be based at least in part on a print-data stream provided by one or more systems controllers (not shown). The print-data stream typically comprises instructions as to which of the specific droplets within the stream of droplets are to be printed with, or not printed with. The potential waveform will therefore vary in accordance with the image content of the specific image to be reproduced.
Additionally, the potential waveform may also be based on methods or schemes employed to improve various printing quality aspects such as the placement accuracy of droplets selected for printing. Guard drop schemes are an example of these methods. Guard drop schemes typically define a regular repeating pattern of specific droplets within the continuous stream of droplets. These specific droplets, which may be selected to print with if required by the print-data stream, are referred to as “print-selectable” droplets. The pattern is additionally arranged such that additional droplets separate the print-selectable droplets. These additional droplets cannot be printed with regardless of the print-data stream and are referred to as “non-print selectable” droplets. This is done so as to minimize unwanted electrostatic field effects between the successive print-selectable droplets. Guard drop schemes may be programmed into one or more systems controllers (not shown) and will therefore alter the potential waveform so as to define the print-selectable droplets. The voltage waveform will therefore characterize printing droplets from non-printing droplets by selectively charging individual droplets within the stream of droplets in accordance with the print data stream and any guard drop scheme that is employed.
Again referring to the prior art system shown in FIG. 1, electrostatic deflection plates 38 placed near the trajectory of the characterized droplets interact with charged droplets 34 by steering them according to their charge and the electric field between the plates. In this example, charged droplets 34 that are deflected by deflection plates 38 are collected on a gutter 40 while uncharged droplets 36 pass through substantially un-deflected and are deposited on a receiver surface 42. In other systems, this situation may be reversed with the deflected charged droplets being deposited on the receiver surface 42. In either case, further complications arise from the fact that the charging electrode driver 32 must be synchronized with stimulation signal driver 17 to ensure that optimum charge levels are transferred to droplets, thus ensuring accurate droplet printing or guttering as the architecture of the recorder may dictate. These synchronization constraints arise as result of charging or characterizing those conductive fluid droplets at a place and time separate from their stimulation. Although prior art electrostatic characterization and deflection systems are advantageous in that they permit large droplet deflection, they have the disadvantage that they have been used primarily only with conductive fluids, thus limiting the applications of these systems.
A wide range of fluid properties is desirable in commercial inkjet applications. Jetted inks may be made with pigments or dyes suspended or dissolved in fluid mediums comprised of oils, solvents, polymers or water. These fluids typically have a large range of physical properties including viscosity, surface tension and conductivity. Some of these fluids are considered to be non-conductive fluids, and thus have insufficient levels of conductivity so as to be employed in continuous inkjet systems that rely on the selective electrostatic charging and deflection of conductive fluid droplets.
Various systems and methods for stimulating a non-conductive fluid medium to form a series of droplets and for characterizing the series of droplets to form “printing” droplets and “non-printing” droplets have been proposed. For example, U.S. Pat. No. 3,949,410, issued to Bassous et al., teaches use of a monolithic structure useful for the EHD stimulation of conductive fluid droplets in a jet stream emitted from a nozzle.
U.S. Pat. No. 6,312,110, issued to Darty, and U.S. Pat. No. 6,154,226, issued to York et al., teach the construction of various inkjet print heads wherein droplets are not stimulated from a stream of non-conductive fluid. Rather, the print heads comprises EHD pumps within the print head nozzles themselves. Droplets are ejected from the fluid supply in a similar fashion to drop-on-demand printers.
U.S. Pat. No. 4,190,844, issued to Taylor, teaches a use of a first pneumatic deflector for deflecting non-printing ink droplets towards a droplet catcher. A second pneumatic deflector either creates an “on-off” basis for line-at-a-time printing, or a continuous basis for character-by-character printing.
U.S. Pat. No. 6,079,821, issued to Chwalek et al., teaches a use of asymmetric heaters to both create and deflect individual droplets formed in a continuous inkjet recorder. Deflection of the droplets occurs by the asymmetrical heating of the jetted stream.
U.S. Pat. No. 4,123,760, issued to Hou, teaches the use of deflection electrodes upstream of a break-off point from which droplets are formed from a corresponding jetted fluid stream. Droplets produced by the stream are steered to different laterally separated printing locations by applying a cyclic differential charging signal to the deflection electrodes. This causes a deflection of the unbroken fluid stream which directs the droplets towards their desired printing positions.
It can be seen that there is a need to provide an apparatus and method of stimulating or forming a non-conductive fluid droplet or droplets from a jet of non-conductive fluid.


1. Field of the Invention
The present invention relates to a fuel cell system.
2. Description of Related Art
In recent years, fuel cells, which generate electricity by using hydrogen (fuel gas) supplied to anodes and air containing oxygen (oxidizer gas) supplied to cathodes, has been developed and are expected as electric power sources for vehicles (e.g., fuel cell electric vehicles), etc.
As the electricity generation by such the fuel cell progresses, water vapor (water) is generated at the cathode of each MEA (Membrane Electrode Assembly) of the fuel cell, and part of the generated water permeates the MEA and then cross-leaks to the anode channel (fuel gas channel). Also, part of the cross-leaked water remains in the anode channel and adheres to the surface of the MEA, etc. The water adhering to the surface of the MEA obstructs the supply of hydrogen (fuel gas) to the anode (catalysts forming the anode). Consequently, the voltage (output) of the fuel cell can fall below a target voltage and electricity generation status of the fuel cell can degenerate to a poor condition.
In a technique proposed to solve the above problem, when the electricity generation status of a fuel cell has degenerated to a poor condition as above, gas and moisture remaining in the anode channel are purged (discharged) to the outside by temporarily raising the gas pressure in the anode channel and then briefly opening a purge valve (discharge valve) placed downstream of the anode channel (see JP 2008-112585 A).


Spare tires on motor vehicles are rarely thought of by the vehicle user until such time that they are needed. When that happens, the vehicle user often finds out that the spare tire is flat or at least severely under inflated. Consequently, in order to be sure that a spare tire is fully inflated, the vehicle user must check the pressure therein from time to time, and this quite often requires removal of the tire from the trunk or moving it around in the trunk, either of which requires considerable effort. This problem is only exacerbated if the tire is secured to the trunk or if the trunk contains other things which must also be moved or removed during the process.
U.S. Pat. No. 3,019,831 to Morrello attempts to solve the aforementioned problem by attaching a pressure hose to the valve stem on the spare tire inside of a trunk and has a pressure hose leading to a valve stem which extends to the outside of the vehicle body and is attached to the vehicle body so that the pressure can be checked at the same time the other tires on the vehicle are checked. It also permits inflation without opening the trunk of the car. While this approach to solving the problem is good in certain respects, it does require alteration to the body of the vehicle and also presents an unsightly valve stem sticking out of the side of the vehicle body. This valve stem extension can catch car wash brushes and can involve considerable expense in drilling through the body of a car and putting it into place.
Consequently, there is a need for an apparatus for maintaining proper inflation of a spare tire without requiring modification to the body of a vehicle.


1. Field of the Invention
This invention relates to a novel method for the production of a halogen-containing phthalocyanine compound. More particularly, this invention relates to a method for the production of a halogen-containing phthalocyanine compound manifesting the absorption of heat ray and/or the absorption in a near infrared region, excelling in solubility in a solvent, and having excellent light-fastness.
The phthalocyanine compound which is obtained by the method contemplated by this invention excels in a heat ray-absorbing property and, therefore, is useful as a heat ray-absorbing dye. Since the phthalocyanine compound obtained by the method according to this invention absorbs light in a near infrared region having a wavelength in the range of 600-1000 nm, it can manifest excellent effects when it is used as a near infrared absorption dye and a near infrared sensitizer for writing or reading in an optical recording medium using a semiconductor laser, a liquid crystal display device, and an optical character reader, as a photothermal modifier for thermal transfer and a thermal paper, thermal stencil printing, as a near infrared absorption filter as for plasma display panel (PDP), as an asthenopia inhibitor, as a near infrared absorbing material for a photoconductive material, or as a color separation filter for an image pickup tube, as a color filter for liquid crystal display, as a selective absorption filter for a color braun tube, as a color toner, as a toner dye for flash fixing, as an ink jet ink, as an indelible bar code ink, also as a microorganism inactivating agent, as a photosensitive dye for oncotherapy, as a heat ray-shielding agent for automobiles and buildings, and as a discriminating agent for resin sorting.
2. Description of Related Art
The needs for a near infrared absorbent dye have been mounting in consequence of the expansion of the field of the applications thereof. As regards the near infrared absorption dye to be used as a near infrared absorption dye and a near infrared sensitizer for writing or reading in an optical recording medium using a semiconductor laser, a liquid crystal display device, and an optical character reader, as a photothermal modifier for thermal transfer and a thermal paper, thermal stencil printing, as a near infrared absorption filter as for plasma display panel (PDP), as an asthenopia inhibitor, as a near infrared absorbing material for a photoconductive material, or as a color separation filter for an image pickup tube, as a color filter for liquid crystal display, as a selective absorption filter for a color braun tube, as a color toner, as a toner dye for flash fixing, as an ink jet ink, as an indelible bar code ink, also as a microorganism inactivating agent, as a photosensitive dye for oncotherapy, as a heat ray-shielding agent for automobiles and buildings, and as a discriminating agent for resin sorting, methods for the production of materials which satisfy wholly such characteristics as light-fastness, heat-resistance, and solubility (or compatibility with a resin) have been studied hitherto. None of the methods developed to date, however, has proved advantageous for commercial applications.
The methods for producing such phthalocyanine compounds have been disclosed in JP-A-2000-63693, JP-A-2000-169743, JP-B HEI-07(1995)-103318, and U.S. 2003/0234995 A1, for example.
JP-A-2000-69693 discloses a method which comprises inducing the reaction of tetrafluorophthalonitrile with vanadium trichloride by using α-methyl naphthalene or benzonitrile solely while introducing an oxygen-containing gas such as a gas obtained by diluting air into the resultant reaction solution. Since the solvent, α-methyl naphthalene, to be used in this method is very expensive and since the reaction of this method necessitate the introduction of a hot oxygen-containing gas and, therefore, entails a possibility of the introduced gas entraining the expensive solvent and dispersing it outside the reaction system and threatening the danger of explosion, this method hardly deserves to be rated as favorable for commercialization. JP-A-2000-169743 discloses the reaction of tetrafluorophthalonitrile and vanadium trioxide in benzonitrile as a solvent in the presence of paratoluene sulfonic acid and calcium carbonate at 150° C. This official gazette recommends to use as an organic solvent in the reaction an inert substance having no reactivity with the starting materials and the reaction vessel and, for the purpose of preventing the reaction vessel from corrosion, to perform the reaction of a metal oxide and paratoluene sulfonic acid at relatively low temperature. The present inventors' review of this method, however, has revealed that this method is not appropriate because the phthalocyanine compound produced thereby as aimed at occasionally fails to manifest the performance as claimed.
JP-B-HEI 07(1995)-103318 discloses a novel phthalocyanine compound and a method for the production thereof and claims to produce a fluorine-containing phthalocyanine compound by reacting a corresponding phthalonitrile compound with vanadium chloride in an inert solvent or an aprotic solvent. Though only ethylene glycol cited as a reaction solvent is an example of an inert solvent, no other alcohols cannot be found anywhere. The working examples cited therein include the synthesis of phthalocyanine in a current of nitrogen. This synthesis is found to use benzonitrile exclusively as an inert solvent. U.S. 2003/0234995 A1 discloses the reaction of a substituted phthalonitrile compound with vanadium chloride using benzonitrile and octanol under reflux. Since the reaction is effected without using an inert gas such as nitrogen, the yield is as low as 63.2 mol %.


(1) Field of the Invention
This invention relates to a thin film transistor (TFT) substrate and a method for fabricating such a TFT substrate and, more particularly, to a stagger type TFT substrate fabricated through a plurality of exposure processes using a plurality of kinds of masks and a method for fabricating such a stagger type TFT substrate.
(2) Description of the Related Art
In recent years improvement in the performance of liquid crystal display units has been required greatly to obtain high brilliance, high intensity and high definition. In particular, the study and development of TFT substrates included in liquid crystal panels used in them are proceeding. In addition, today liquid crystal display units must be manufactured by efficient, more simplified processes from the viewpoint of corporate profits. Furthermore, consideration must be given to the environment on the earth in utilizing electric power and raw materials in these manufacturing processes.
Currently, TFT substrates are manufactured mainly by a reverse stagger system. TFT substrates are formed through a plurality of exposure processes by the use of a plurality of masks. In this case, at least five masks are used for forming a gate bus-line layer, an operation island layer, a drain bus-line layer, a protection film layer, and a pixel electrode layer on TFT substrates. That is to say, to manufacture reverse-stagger type TFT substrates, as many as five exposure processes must be performed. Therefore, to improve efficiency in the manufacture of such reverse-stagger type TFT substrates, a method, for example, for reducing the number of the exposure processes from five to three by the use of a half tone mask is proposed (see, for example, Japanese Unexamined Patent Publication No. 2001-311965).
By the way, there is another system, which is called a stagger system, for manufacturing TFT substrates. By adopting this system, TFT substrates which differ from reverse-stagger type TFT substrates in structure can be formed. Compared with reverse-stagger type TFT substrates, stagger type TFT substrates have, for example, the following advantages. Layers included in stagger type TFT substrates can be formed continuously. In addition, an interface treatment process is not necessary for manufacturing stagger type TFT substrates.
Conventionally, however, a plurality of exposure processes must be performed with five to eight masks to manufacture stagger type TFT substrates. Accordingly, manufacturing efficiency is low and it takes many a day to complete TFT substrates. Moreover, many (kinds of) masks are used and a plurality of exposure processes are performed. This increases the probability that a display defect will occur due to, for example, dust. As stated above, problems, such as manufacturing efficiency, a yield, and manufacturing costs, which will arise at the time of manufacturing stagger type TFT substrates remain unresolved.


The invention relates to a spring device for the motion drive of a movable component from a rest position into a displaced position. The inventive spring device includes a preloaded spring and a gas spring. The movable component is loaded into the displaced position by the preloaded spring. A pressurized gas-filled cylinder of the gas spring include a first end closed by a first end plate and a second end closed by a second end plate and the interior of which is subdivided by an axially displaceable piston into a first working chamber and a second working chamber. The first working chamber and the second working chamber are connected to each other via a restrictor, and the piston has a piston rod which is led through the first working chamber and is led to the outside through the first end plate in a sealed manner, the piston rod having a free end being fixed to the movable component or a stationary component.
In such spring devices, the extension force is composed of a sum of the force of the preloaded spring and the force component of the gas spring that is present in the extension direction, which is primarily intended to effect damping of the extension movement of the piston rod. The damping force depends on the pressure of the gas in the cylinder. As the pressure rises, the damping force also rises.
As resistances of the components to be moved increase, the forces of the spring must also increase. This alone requires a high expenditure of force for the manual movement of the movable component out of the displaced position into the rest position. If increased damping of the movement from the rest position into the displaced position is also intended to be provided, the increased damping further increases the required expenditure of force.


Within the past few years special types of light weight fracture braces have been used for the treatment of tibia fractures after the initial period of treatment in a cast of plaster of paris. The cast is used initially to immobilize the fracture. The plaster cast is uncomfortable because it is heavy and is not removable during its long period of use. It also limits the mobility of the patient. After the plaster cast is removed the special light weight fracture braces can be worn to increase patient mobility while providing the support necessary to prevent twisting, or other undue stress on the tibia during the healing process. These fracture braces are light in weight because they are commonly made of plastic; and they are usually designed to be removed, adjusted, and reused on the patient. Some of these light weight fracture braces include a foot plate attached to the bottom of a tibia brace in the form of a jacket or the like that wraps around the tibia. The foot plate is secured to the tibia supporting jacket through flexion joints that permit limited rotational motion of the ankle. This brace allow the patient a limited amount of mobility while the brace is worn. Thus, the light weight fracture braces provide a substantial benefit to the patient during the healing process when compared with a plaster cast.
Problems have been experienced with prior light weight fracture braces. The supporting jackets of these braces are commonly applied from rear to front of the patient's leg. This allows the patient's foot to be held in a normal position while the jacket is being placed on the patient's leg. On the other hand, if the jacket is applied from front to rear, the prior braces require too much movement of the patient's foot. It is best if the patient's foot is not moved from its normal position when the brace is applied. The braces applied from rear to front use the fatty tissue of the calf in the back of the tibia for attaching the brace to the leg. The jacket has an opening at the front so that the main portion of the jacket can be wrapped around the calf, often while the front opening is adjusted at the front of the tibia. It is difficult to make a brace that conforms well to the size and shape of the fatty tissue of the calf for all patients while ensuring that the size of the jacket is easily adjusted at the front of the tibia. In many cases the point of adjustment in front of the tibia applies undue pressure to the bony prominence along the front of the patient's tibia. Tibia supporting jackets made of hard plastic also are especially uncomfortable when tightened against the bony front portion of the patient's tibia. Another problem is that many of these prior art fracture braces are not always comfortable when the tibia supporting jacket is tightened. They are not designed to ensure that torque is uniformly applied to the patient's leg when the straps on the tibia supporting jacket are wrapped around the jacket and tightened. The tibia supporting jacket is often crumpled or too bulky when tightened. In either case the brace can be highly uncomfortable for the patent.
This invention provides an orthosis that overcomes the problems associated with the prior art light weight fracture braces. The tibia supporting jacket of the orthosis can be applied from front to rear of the patient's tibia. The adjustment is in the rear of the jacket, along the fatty tissue of the patient's calf. The front of the jacket thus can provide continuous padding along the bony prominence along the front of the patient's tibia, while the adjustment at the rear of the jacket along the patient's calf is much more comfortable than the prior art braces in which the jacket is applied from rear to front. The orthosis also can be applied from front to rear while leaving the patient's foot in the normal position. In addition, the tibia supporting jacket can be applied and tightened without torquing the patient's leg one way or the other. The jacket is held in a neutral position around the tibia when tightened to its fullest extent, and the jacket also folds together and is tightened in such a way the the material does not crumple or become bulky. The result is an orthosis which is comfortable to wear while still providing the required amount of support. In addition to providing the support necessary for fractures of the tibia, the orthosis also can be used as a means of support for ankle sprains.


The present invention relates to fuel gas burners for cooking appliances and particularly burners of the type employed in cooktop or rangetop applications where a receptacle or cooking vessel is seated on the surface of the burner for heating of the foodstuffs or liquid within the vessel. Cooktop burners are typically ignited by the user opening a rotary valve in the supply line to provide a flow of the fuel gas to the burner whereupon a set of switch contacts are simultaneously closed for electrically energizing an igniter having an electrode disposed to provide a spark in the stream of fuel air mixture emanating from a port in the burner. If an alternating current voltage is employed for the spark ignitor, upon ignition of the fuel air mixture and the presence of flame about the ignitor electrode, the phenomenon of flame rectification occurs; and, the change in the current may be electrically detected as an indication or proof of the presence of flame. This technique has been widely employed for combining the function of the ignitor with that of a flame sensor and providing electrical circuitry which could respond to the change in alternating current to turn off the sparking voltage to the ignitor. It is also known to provide circuitry which, upon the loss of flame, electrically detects the change of a current in the electrode and reenergizes the ignitor spark voltage automatically. However, if transient air currents extinguish the flame about an annular plural port burner on only a portion of the periphery, the flame sensor may not be able to determine whether the flame has been totally extinguished and an annoying reenergization of the ignitor occurs. The condition may also occur where variations in the line pressure of the fuel gas cause major fluctuations in the flame.
Thus, it has long been desired to provide a way or means of preventing flame loss in the region of the flame sensing ignitor when flame is being sustained in other regions of the burner and to generally stabilize the flow from the flame generating ports in the burner. It has further been desired to improve the effectiveness of a spark ignitor for a cooktop burner and to provide such functions in a burner which is sufficiently low in manufacturing cost to remain competitive in the high-volume domestic appliance marketplace.


The invention relates to a method of improving a surface of a semiconductor substrate, wherein the surface at least partially includes silicon.
In semiconductor device production, it is more and more important to provide semiconductor substrates of a very high quality. Defects of semiconductor substrates can be of very different origin and may occur in the bulk material of wafers or layers or on the surface of a structure. Deficient wafers, such as wafers or layers with holes or scratches on their surface or with oxide precipitates or so-called “HF-defects”, which are present in or on a wafer and will be apparent by an HF-etch step, are mostly not suitable for further use.
To improve the surface characteristic of a defective wafer, a wafer treatment of a wafer surface such as an etching step or a chemical mechanical polishing (“CMP”) step can be used to remove or to reduce the number or the size of defects at or near the wafer surface. Typical etchants are halogen bearing compounds such as HCl, HBr, HI, HF, and others. The etchant can also be a fluorine bearing compound such as SF6, or CxFx. Moreover or in addition, it is possible to treat a defect containing wafer thermally, preferably in a hydrogen bearing environment, to smooth it and to diminish its defects. The thermal treatment can be performed in a furnace or in a tool for rapid thermal processing (“RTP”). According to another approach disclosed in U.S. Pat. No. 6,287,941 B1, a defective wafer such as a cleaved film can be subjected to a combination of etching and deposition at very high temperature using a combination of etchant and deposition gases to result in a better surface quality.
Although such methods lead, in the first instance, to a superficial improvement of the surface condition of a defective wafer by smoothing, abrasion or defect covering of the respective wafer, the known methods are mostly very laborious and the corresponding defects cannot really be repaired. Thus, there remains a need to process defective wafers to increase surface quality.


Known commercial mobile communication systems typically include a plurality of fixed base stations arranged in patterns whereby each base station transmits and receives over a plurality of frequencies. A mobile station within range of the base station can communicate with the external world (e.g., via the Public Switched Telephone Network (“PSTN”)) through the base station using the frequencies. The area surrounding a base station in which mobile stations communicate with that base station is often referred to as a cell, with the base station generally positioned toward the center of the cell. Examples of known commercial mobile communications systems having cells include cellular communications systems, Personal Communications Systems (“PCS”), Global System for Mobile communication (“GSM”) systems, IS-136/Digital-American Mobile Phone systems (hereinafter “IS-136” or “D-AMPS”), and so on.
In an IS-136 system, a mobile station can communicate with the base station via a carrier frequency pair that includes two different (but paired) frequencies. The first frequency of the pair is the downlink (or forward) frequency where information is transmitted from the base station to the mobile station, and the second frequency of the pair is the uplink (or reverse) frequency where information is transmitted from the mobile station to the base station. Each carrier frequency pair is often referred to as a carrier or a channel, although the term channel is also used in different ways when a carrier can carry multiple channels (e.g., time-division multiple access (“TDMA”) channels, code-division multiple access (“CDMA”) channels, and so on). An IS-136 system can have 416 carriers, of which 395 carriers are available to carry voice traffic between a mobile station and a base station.
The carriers used by a base station are separated from one another in frequency to minimize interference. A cell's carriers are carefully selected so that adjoining cells do not transmit or receive on the same carrier frequencies. A mobile system operator can allocate to a base station a set of carriers with frequencies that are each separated from the next carrier by an integral number. For example, FIG. 1 shows a known frequency reuse pattern for base station cells, where each cell is assigned a set of carriers. Each cell can be allocated one of seven sets of carriers, where a cluster of seven cells as a whole is allocated all of the carriers. Thus, the frequency reuse pattern illustrated in FIG. 1 is typically referred to as having n=7 clusters. The cells are arranged and frequency sets can be allocated by assigning a first carrier set (e.g., carrier set 1) to a central cell 111 of a first cluster, and then assigning different carrier sets (e.g., carrier sets 2–7) to the cells of the first cluster surrounding that central cell. Thus, cell 111 can have carrier set 1, cell 112 can have carrier set 2, cell 113 can have carrier set 3, cell 114 can have carrier set 4, cell 115 can have carrier set 5, cell 116 can have carrier set 6, and cell 117 can have carrier set 7. Each of the carrier sets are also respectively allocated to the cells 141–147 of a fourth cluster adjacent to cells 111–117 of the first cluster. Portions of other adjacent clusters—such as cells 125 and 126 of a second cluster, cells 131 and 134–137 of a third cluster, and so on—are also illustrated.
The assignment of carriers to carrier sets, and the assignment of carrier sets to cells, can be based on the number of different carrier sets (e.g., seven, four, and three carrier sets) and the number of available carriers. An IS-136 system having 395 voice carriers and using a frequency reuse pattern illustrated in FIG. 1 can have approximately 57 carriers per carrier set and cell. With seven different carrier sets, carrier set 1 can include carriers 1, 8, 15, 22, 29, 36 and so on; carrier set 2 can include carriers 2, 9, 16, 23, 30, 37 and so on; carrier set 3 can include carriers 3, 10, 17, 24, 31, 38 on so on; and so forth with respect to carrier sets 4–7.
FIGS. 2 and 3 illustrate other known frequency reuse patterns. In particular, FIG. 2 illustrates a frequency reuse plan having n=3 clusters. A first cluster can have three cells 211–213. Six clusters—such as a second cluster having cells 221–223, a third cluster having cells 231–233, a fourth cluster having cells 241–243, and so on—can be located adjacent the first cluster. Each cell of each cluster can be allocated a third of the available system carriers. FIG. 3 illustrates a frequency reuse plan having n=4 clusters. A first cluster can have four cells 411–114. Six clusters—such as a second cluster having cells 321–324, a third cluster having cells 331–334, a fourth cluster having cells 341–344, and so on—can be located adjacent the first cluster. Each cell of each cluster can be allocated a fourth of the available system carriers.
To allow a mobile station to transmit and receive communications as the mobile station moves from one cell to another, each cell is normally positioned with its area of coverage overlapping the areas of coverage of a number of adjacent and surrounding cells. As a mobile station moves from an area covered by a first base station to an area covered by another base station, mobile station communications (e.g., a voice call, a data link, etc) are transferred from the first base station to the other base station in an area where the coverage from the two cells overlaps. The transfer of a mobile station from communicating with one base station to communicating with a second base station is typically called hand-off.
A cell can have at least two types of radio coverage. A first type of cell radio coverage is omnidirectional (i.e., azimuthally), where the cell has an antenna set that can communicate with mobile stations via each carrier of the carrier set allocated to the cell. A second type of cell radio coverage is sectored. FIG. 4 shows an illustration of a sectored cell. Cell 411 includes a plurality of sectors, including sectors 401, 402 and 403. Sectors are often referred to as an alpha sector, a beta sector, and a gamma sector. Cells are typically divided into three sectors, with each sector having an antenna set that covers a 120° sector. In a cell having three sectors, each sector antenna set can communicate with mobile stations via one-third of the carriers of the carrier set allocated to the cell so that each sector communicates over different carriers as compared to the other sectors of the cell.
Notwithstanding the use of frequency reuse patterns, interference between like carriers of different cells can occur. For example, referring again to FIG. 1, even though cell 131 is a knight's move away from cell 111 (i.e., cell 131 is up two cells and over one cell from cell 111), there can be interference between the carriers of cell 111 and cell 131. For example, within portions of cells 113, 137, and 136, there can be interference between a carrier 1 of cell 111 and a carrier 1 of cell 131. Such interference is typically called co-channel interference.
Co-channel interference can be caused by antenna patterns, power levels, carrier scattering, and wave diffraction that differ from cell to cell. Buildings, structures, mountains, foliage, and other physical objects can cause carrier signal strength to vary over the area covered by a cell. As a result, the boundaries (i.e., edges) at which the signal strength of a carrier falls below a level sufficient to support communications with a mobile station can vary widely from cell to cell. Thus, cells adjacent one another do not typically form anything like the precise geometric patterns illustrated in FIGS. 1–3. Cell coverages, however, must overlap to allow mobile stations to be handed-off between cells, and such overlapping, among other factors, can lead to co-channel interference.
In an IS-136 system, mobile stations are instructed to measure the signal strengths of various carriers and report the measured signal strengths to the mobile system. For example, referring again to FIG. 1, as a mobile station in communication with the base station of cell 111 moves through cell 111 toward cells 112 and 113, the mobile station can be instructed to measure the signal strengths of certain carriers of cells 111, 112, and 113 and report the measured carrier signal strengths to the mobile system via the base station of cell 111. When the signal strength reported by the mobile station with respect to the cell 111 carrier drops below a certain threshold (e.g., as the mobile station approaches the intersection of cells 111, 112, and 113), the mobile system will pick one carrier of the carriers measured and reported by the mobile station and instruct the mobile station to use that carrier for communications (e.g., instruct the mobile station to begin communicating with the base station of cell 113 or cell 112 via the appropriate carrier). In known IS-136 systems, mobile stations can monitor and report the carrier strengths of neighboring surrounding cells.
Mobile system operators generate frequency reuse plans to, among other things, reasonably minimize co-channel interference and reasonably maximize the likelihood that mobile stations will be successfully handed-off to a next cell as it moves away from its current cell. A first method of generating a mobile system frequency reuse plan is to use a frequency reuse pattern as illustrated in FIGS. 1–3. The efficiency of a frequency reuse plan can be increased by modifying the frequency reuse plan based on knowledge (subjective and/or objective) of the terrain covered by the frequency reuse plan. For example, FIG. 5 illustrates a frequency reuse pattern that has been modified based on terrain characteristics. A first cluster includes cells 511–517. A mountain range 501 abuts the edge of the first cluster at the exterior edges of cells 513 and 514. The mountain range 501 attenuates the carrier signals transmitted by cells 512, 511, and 515. Thus, cells 522, 521, and 525 can use the same carrier sets used by cells 512, 511, and 515 with a reasonable minimization of co-channel interference. By reusing the carrier sets in a more compact manner, the frequency reuse plan illustrated in FIG. 5 is more efficient than the frequency reuse pattern illustrated in FIG. 1. A more efficient frequency reuse plan allows for greater system utilization (e.g., more mobile stations can be supported).
Frequency reuse plans can also be based on predictive methods using computer modeling. A computer model can predict carrier propagation areas based on antenna height, transmitter power, terrain characteristics, and so forth. Measured carrier data can also be used to create and modify frequency reuse plans. In an IS-136 system, mobile stations report received carrier strengths to the mobile switch coupled to the base stations. The reported carrier strength data can be used to determine how far carriers propagate.
Carrier propagation and co-channel interference can also be measured by receivers that measure received carrier strength as they are driven throughout areas of the mobile system during a so-called “drive test.” For example, during a drive test a specific test carrier is transmitted at each cell or sector of a cell involved in the interference testing. A scanning receiver is driven over the roads, highways and traveled byways of the system. The scanning receiver scans and measures the strength of the test carrier signal transmitted by each cell at the points of possible interference, and location determination equipment (e.g., a Global Positioning System (“GPS”) unit, a Loran unit, etc.) records the position of the scanning receiving. These strength measurements are then plotted and the expected interference points from different cells may be viewed graphically to determine whether sufficient interference exists to change the channel sets assigned to a particular area. This method of performing a drive test is often referred to as a “key-up” drive test because the test carrier is continuously “keyed-up” at each cell so as to be measured. A test carrier does not carry subscriber communications.
U.S. Pat. No. 5,926,762 (“the '762 patent”) describes another type of drive test in which a unique test carrier at each cell site is transmitted such that each cell site is transmitting a different test carrier. A scanning receiver is driven over the roads, highways and traveled byways of the system to measure the strength (typically the received signal power) of each test carrier transmitted by each of the cell sites while location determination equipment records the position of the scanning receiver. According to the '762 patent, transmitting a different test carrier at each cell eliminates interference that can complicate strength measurements when a single carrier is keyed-up at multiple cells for a drive test.
These known methods of performing drive tests to measure carrier strengths and predict co-channel interference require test carriers to be keyed-up to continuously transmit. Whether a single test carrier is keyed-up at a plurality of cells, or different test carriers are keyed-up at different cells, each method requires keying-up a test carrier. When a test carrier is keyed-up, it is not available to carry subscriber communications (e.g., voice traffic), and system capacity is diminished. Thus, key-up drive tests are typically conducted during the evening when demand for system capacity is lowest. In view of the foregoing, it can be appreciated that a substantial need exists for systems and methods that can advantageously provide for determining mobile communication system telephone carrier frequency propagation characteristics.