Liquid crystal displays have been increasingly becoming popular as displays for information, image and the like. The liquid crystal displays have advantages of providing thin profile, small placing area and the like when compared with CRT (Cathode Ray Tube) displays.
Liquid crystal displays according to the present invention can be used in, for example, a display or monitor for a personal computer, a monitor for factory automation (FA), a home television set, a terminal monitor in a hospital, a library, a museum and the like, a monitor for an air traffic control tower and the like, a monitor used for reference of newspapers, documents in public offices and the like, a personal monitor in a school and a supplementary private school, a personal monitor for utilizing various media, a monitor in amusement facilities such as pachinko facilities, and the like. The liquid crystal displays according to the present invention can also be used as a light valve for projector type liquid crystal displays.
A recent liquid crystal display has image quality substantially equal to that of a CRT display. However, a viewing angle of the liquid crystal display is much narrower than that of the CRT display. Therefore, enlarging a viewing angle is one of the most important concerns in a liquid crystal display.
As a technology for enlarging a viewing angle of a liquid crystal display, there is considered using a liquid crystal display element which has a plurality of domains having different alignment directions in each pixel to obtain a wide viewing angle. Such prior art is disclosed in, for example, Japanese examined patent publication No. 58-43723, “Liquid Crystal Display Element”, Japanese patent laid-open publication No. 59-211019, “Liquid Crystal Display Device”, and Japanese patent laid-open publication No. 63-106624 (Japanese patent publication No. 2692693), “Liquid Crystal Display Panel”.
Referring to a “Liquid Crystal Display Panel” disclosed in Japanese patent laid-open publication No. 63-106624 as a prior art example, among the Japanese publications mentioned above, an explanation will be made on a prior art technology.
FIG. 28 is a plan view showing a conventional liquid crystal display according to this prior art example. FIG. 28 corresponds to FIG. 1 described in the Japanese patent laid-open publication. No. 63-106624. FIG. 29 corresponds to FIG. 2 described in the Japanese patent laid-open publication No. 63-106624. FIG. 30 corresponds to FIG. 3 described in the Japanese patent laid-open publication No. 63-106624. FIG. 30 is a cross sectional view taken on line a-a′ of FIG. 28, and shows a cross section of one pixel of the conventional liquid crystal display device, that is, a liquid crystal display element.
With reference to FIGS. 28 through 30, a structure of the conventional liquid crystal display device will be described.
On a lower glass substrate 122, there are formed a transparent lower display electrode 120 which is provided corresponding to each pixel, and a lower alignment film or layer 110 formed on the transparent lower display electrode 120.
On the lower glass substrate 122, there is also formed a thin film transistor (TFT) 113 for driving the transparent lower display electrode 120.
On an upper glass substrate 121, there are formed a transparent upper display electrode 111 and a upper alignment film or layer 109. The alignment films 109 and 110 are both made of polyimide.
A pixel B formed between the opposing transparent electrodes 111 and 120 has, for example, a square shape of 200 μm (micrometers) square, and a plurality of such pixels B are disposed in a matrix. At the center portion of the transparent display electrode, there is disposed a band shaped spacer 123 made of polyimide. As a result thereof, each pixel B is divided into a region X131 and a region Y132 by the band shaped spacer 123. These divided regions X131 and Y132 are formed as shown schematically in FIG. 16 which corresponds to FIG. 2 of Japanese patent laid-open publication No. 63-106624. That is, the upper glass substrate 121 and the opposing lower glass substrate 122 are respectively rubbed in directions shown by arrows.
In order to show an effect of improvement in viewing angle dependence of viewing quality realized by this prior art liquid crystal display, FIG. 31 shows a plan perspective view which illustrates rubbing directions and direction of twist of liquid crystal alignment between the upper and lower substrates when a direction of observation is changed by 45 degrees in bearing angle. In FIG. 31, there are shown divided regions X131, divided regions Y132, rubbing directions 1311 and 1312 in a first substrate, rubbing directions 1312 and 1322, and a twist angle 127 of liquid crystal alignment between the upper and lower substrates.
FIG. 32 is a cross sectional view taken on line b-b′ of FIG. 31 and showing a rising direction of aligning force at the surface of a substrate and a rising direction of liquid crystal alignment by an electric field between the upper and lower substrates. In FIG. 32, a twist of liquid crystal molecules is not illustrated. In FIG. 32, there are shown liquid crystal material 105, a direction of rising 106 of liquid crystal alignment caused by an electric field, the upper glass substrate 121, a lower glass substrate 122, a region X131, and a region Y132.
In this prior art liquid crystal display, as shown in FIG. 31, with respect to liquid crystal alignment in each of the divided regions or domains, a direction of spiral twist is the same, but as shown in FIG. 32, directions of angles from the substrate surface, i.e., pretilt angles, differ from each other. Because of the difference of the angles from the substrate surface, when a voltage is applied between the upper and lower electrodes, direction 106 of rising up of liquid crystal molecules, which is also called direction of tilt, differ from each other as shown in FIG. 31. Therefore, when light is irradiated from a direction which is inclined from the direction perpendicular to the substrate, optical characteristics of respective domains compensate with each other. As a result thereof, when the voltage is applied, viewing angle dependence is compensated with each other between domains having mutually different alignments in each pixel between the upper and lower substrates, and optical characteristics having small viewing angle dependency can be realized. Especially, when an image having gray shades is displayed, a phenomenon of gray shade inversion is not observed.
Other liquid crystal display panels are also known which function based on the same principle as that of the above-mentioned liquid crystal display panel and which can be fabricated by smaller number of steps than that of the above-mentioned liquid crystal display panel. Such liquid crystal display panels are described in “SID '92 Digest of U.S.A., p. 798”, “Japan Display '92 Digest, p. 591”, “SID '93 Digest of U.S.A., p. 269”, and the like.
In these examples, as in the first example, with respect to alignment of molecules of the liquid crystal material in each of the divided domains, direction of twist of a spiral is the same, but an angle to the substrate surface differs from each other. However, these liquid crystal display panels differ from the first example in a direction of aligning force applied to molecules of the liquid crystal material at the surface of the substrate and magnitude of angle of the aligning force.
In order to clarify the difference between these examples and the first example, perspective plan views and cross sectional views for each of these examples. The perspective plan views show directions of rubbing and directions of twist of alignment of liquid crystal molecules between upper and lower substrates. The cross sectional views show directions of rising up of the alignment force at the surface of the substrate and directions of rising up of alignment of liquid crystal between the upper and lower substrates caused by an electric field.
FIG. 33 is a plan perspective view showing directions of rubbing and directions of twist of alignment of liquid crystal molecules between upper and lower substrates, in the prior art example shown in “SID '92 Digest of U.S.A., p. 798”. FIG. 34 is a cross sectional view taken on line c-c′ of FIG. 33, and shows directions of rise of the aligning force at the surface of the substrate and directions of rise of alignment of liquid crystal molecules between the upper and lower substrates caused by an electric field.
An explanation will be made on the liquid crystal display element shown in FIG. 33 and FIG. 34. In the plan perspective view of FIG. 33, there are shown a divided domain X131, a divided domain Y132, a rubbing direction 1311 in the domain X on an upper glass substrate, a rubbing direction 1312 in the domain X on a lower glass substrate, a rubbing direction 1321 in the domain Y on the upper glass substrate, a rubbing direction 1322 in the domain Y on the lower glass substrate, and twist angle 127 of the liquid crystal alignment. Also, in the cross sectional view of FIG. 34, there are shown the upper glass substrate 121, the lower glass substrate 122, the divided domain X131, the divided domain Y132, liquid crystal material 105, direction 106a of rise of alignment of liquid crystal molecules caused by an electric field in the domain X, and direction 106b of rise of alignment of liquid crystal molecules caused by an electric field in the domain Y.
In this example, rubbing direction of the upper substrate is one direction, i.e., the same direction, in both of the divided domains, and rubbing direction of the lower substrate is one direction, i.e., the same direction, in both of the divided domains. However, materials of the upper and lower substrates are changed between the domain X and the domain Y. Therefore, as shown in FIG. 34, in the domain X131, the angle of liquid crystal molecules from the surface of the lower substrate 122 is higher (larger) than the angle of liquid crystal molecules from the surface of the upper substrate 121. In the domain Y132, the angle of liquid crystal molecules from the surface of the lower substrate 122 is lower (smaller) than the angle of liquid crystal molecules from the surface of the upper substrate 121. Therefore, in the domain X131, the direction 106a of rise of liquid crystal alignment caused by an electric field becomes a direction of aligning force at the lower glass substrate 122, when a voltage is applied to this liquid crystal display element. In this case, in the domain Y132, the direction 106b of rise of liquid crystal alignment caused by an electric field becomes a direction of aligning force at the upper glass substrate 121.
FIG. 35 is a plan perspective view showing directions of rubbing and directions of twist of alignment of liquid crystal molecules between upper and lower substrates, in the prior art example shown in “Japan Display '92 Digest, p. 591”. FIG. 36 is a cross sectional view taken on line d-d′ of FIG. 35, and shows directions of rise of the aligning force at the surface of the substrate and directions of rise of alignment of liquid crystal molecules between the upper and lower substrates caused by an electric field.
An explanation will be made on the liquid crystal display element shown in FIG. 35 and FIG. 36. In the plan perspective view of FIG. 35, there are shown a divided domain X131, a divided domain Y132, a rubbing direction 1311 in the domain X on an upper glass substrate, a rubbing direction 1312 in the domain X on a lower glass substrate, a rubbing direction 1321 in the domain Y on the upper glass substrate, a rubbing direction 1322 in the domain Y on the lower glass substrate, and twist angle 127 of the liquid crystal alignment. Also, in the cross sectional view of FIG. 36, there are shown the upper glass substrate 121, the lower glass substrate 122, the divided domain X131, the divided domain Y132, liquid crystal material 105, direction 106 of rise of alignment of liquid crystal molecules caused by an electric field.
In this example, rubbing direction of the upper substrate is one direction, i.e., the same direction, in both of the divided domains, and rubbing directions of the lower substrate have two different directions. Also, as shown in FIG. 36, in both the domain X131 and the domain Y132, the angle of liquid crystal molecules from the surface of the lower substrate 122 is higher (larger) than the angle of liquid crystal molecules from the surface of the upper substrate 121. However, in the lower glass substrate 122, directions of aligning force differ between the domain X131 and the domain Y132. Therefore, in both the domain X131 and the domain Y132, the direction 106 of rise of alignment of liquid crystal molecules caused by an electric field becomes a direction of aligning force at the lower glass substrate 122, when a voltage is applied to this liquid crystal display element.
FIG. 37 is a plan perspective view showing directions of rubbing and directions of twist of alignment of liquid crystal molecules between upper and lower substrates, in the prior art example shown in “SID '93 Digest of U.S.A, p. 269”. FIG. 38 is a cross sectional view taken on line e-e′ of FIG. 37, and shows directions of rise of the aligning force at the surface of the substrate and directions of rise of alignment of liquid crystal molecules between the upper and lower substrates caused by an electric field.
An explanation will be made on the liquid crystal display element shown in FIG. 37 and FIG. 38. In the plan perspective view of FIG. 37, there are shown a divided domain X131, a divided domain Y132, a rubbing direction 1311 in the domain X on an upper glass substrate, a rubbing direction 1312 in the domain X on a lower glass substrate, a rubbing direction 1321 in the domain Y on the upper glass substrate, a rubbing direction 1322 in the domain Y on the lower glass substrate, and twist angle 127 of the liquid crystal alignment. Also, in the cross sectional view of FIG. 38, there are shown the upper glass substrate 121, the lower glass substrate 122, the divided domain X131, the divided domain Y132, liquid crystal material 105, direction 106 of rise of alignment of liquid crystal molecules caused by an electric field.
In this example, rubbing direction of the upper substrate is one direction, i.e., the same direction, in both of the divided domains, and rubbing direction of the lower substrate is also one direction, i.e., the same direction, in both of the divided domains. Also, in both the domain X131 and the domain Y132, the angle of liquid crystal molecules from the surface of the lower substrate 122 is the same as the angle of liquid crystal molecules from the surface of the upper substrate 121. However, in each of the domain X131 and the domain Y132, directions of aligning force differ between the upper substrate 121 and the lower substrate 122. When no voltage is applied to this liquid crystal display element, alignment of liquid crystal molecules at the central portion is held horizontal. When a voltage is applied to this liquid crystal display element, the direction 106 of rise of alignment of liquid crystal molecules is determined by electric field having slant directions as shown in FIG. 38.
In these three prior art examples, by adopting structural improvement as shown in FIG. 33 through FIG. 38, the number of process steps is decreased from that of the above-mentioned prior art. In any of these methods, as shown in FIG. 34, FIG. 36 and FIG. 38, when a voltage is applied, directions of rise of liquid crystal molecules differ from each other in respective domains. Therefore, when light is irradiated from a direction slanted from the normal of the substrate, optical characteristics of both regions are mutually compensated. As a result thereof, viewing angle dependency in the condition a voltage is applied is mutually compensated between regions having different alignments in each pixel between the upper and lower substrates, so that optical characteristics having reduced viewing angle dependency.
On the other hand, there is a commonly known thin film transistor (TFT) type liquid crystal display which uses usual twisted nematic (TN) type liquid crystal display mode. Also, among such commonly known liquid crystal display, there is a liquid crystal display in which liquid crystal alignment is controlled by forming a slit or slits in a pixel electrode of an opposing substrate. Such liquid crystal display is disclosed in Conference Record of the 1991 International Display Research Conference, p. 239 and an explanation will be made on such liquid crystal display.
FIG. 39, which corresponds to FIG. 1(b) of the above-mentioned document, shows a cross sectional view of a part, i.e., one pixel, of the liquid crystal display disclosed in the above-mentioned document. FIG. 40, which corresponds to FIG. 7(a) of the above-mentioned document, illustrates electric field in lateral direction in such liquid crystal display. Also, FIG. 41, which corresponds to FIG. 1(a) of the above-mentioned document, shows a cross sectional view of a part, i.e., one pixel, of the commonly known liquid crystal display which uses usual TN type liquid crystal display mode. FIG. 29, which corresponds to FIG. 7(b) of the above-mentioned document, illustrates electric field in such liquid crystal display.
First, an explanation will be made on the liquid crystal display shown in FIG. 39 and FIG. 40. In the cross sectional view of FIG. 39, there are shown an upper glass substrate 221, a lower glass substrate 222, a signal electrode line 215, a lower transparent electrode, that is, a pixel electrode, 220, an upper transparent electrode, that is, an opposing electrode 219, a black mask 231, a color layer 232, an overcoat 233, a lower silicon nitride film 204, and an upper silicon nitride film 241.
On the upper glass substrate 221, there are disposed, on the side facing toward the lower glass substrate 222, the black mask 231 for shutting out the light, the color layer 232 for passing the light of predetermined color, the overcoat 233 for protecting the black mask 231 and the color layer 232, and the opposing electrode 219.
On the lower glass substrate 222, there are disposed, on the side facing toward the upper glass substrate 221, the signal electrode line 215, the lower silicon nitride film 204 for covering the lower glass substrate 222 and the signal electrode line 215, the pixel electrode 220 formed on the lower silicon nitride film 204, and the upper silicon nitride film 241 covering whole portion on the lower glass substrate 222.
In FIG. 40, electric field 202 is shown by arrows which is produced when a voltage is applied to the liquid crystal display element having the structure shown in FIG. 39.
Next, an explanation will be made on the commonly known TN type liquid crystal display element shown in FIG. 41 and FIG. 42. In the cross sectional view of FIG. 41, there are shown an upper glass substrate 221, a lower glass substrate 222, a signal electrode line 215, a lower transparent electrode, that is, a pixel electrode, 220, an upper transparent electrode, that is, an opposing electrode 229, a black mask 231, a color layer 232, an overcoat 233, a lower silicon nitride film 204, and an upper silicon nitride film 241.
On the upper glass substrate 221, there are disposed, on the side facing toward the lower glass substrate 222, the black mask 231 for shutting out the light, the color layer 232 for passing the light of predetermined color, the overcoat 233 for protecting the black mask 231 and the color layer 232, and the opposing electrode 229.
On the lower glass substrate 222, there are disposed, on the side facing toward the upper glass substrate 221, the signal electrode line 215, the lower silicon nitride film 204 for covering the lower glass substrate 222 and the signal electrode line 215, the pixel electrode 220 formed on the lower silicon nitride film 204, and the upper silicon nitride film 241 covering whole portion on the lower glass substrate 222.
In FIG. 42, electric field 202 is shown by arrows which is produced when a voltage is applied to the liquid crystal display element having the structure shown in FIG. 41.
In the prior art liquid crystal display element shown in FIG. 39 and FIG. 40, disturbance of liquid crystal alignment, which is called disclination and which is caused by lateral electric field produced between a pixel electrode and a wiring electrode such as a scanning electrode line, a signal electrode line and the like, can be reduced.
Here, the first problem in the above-mentioned prior art liquid crystal display element is that disturbance of alignment which is called disclination and which is caused by lateral electric field between the wiring electrode and the pixel electrode. This is because, potential of the wiring electrode such as the scanning electrode line, the signal electrode line and the like gives large influence on the electric field. Thereby, relatively large lateral electric field is produced and liquid crystal alignment is changed by such lateral electric field. In order to reduce the disclination, it was necessary to provide a slit in the opposing electrode by patterning it.
The second problem in the above-mentioned prior art liquid crystal display element is that, when pressure is applied from the outside to the liquid crystal display panel having such liquid crystal display element by pressing the panel by a finger or by a pen point, alignment of liquid crystal molecules is easily disturbed, or alignment division collapses or becomes defective.
This is because, the prior art liquid crystal display panel does not have sufficient mechanical strength and cell gap of the liquid crystal display panel changes easily by the pressure applied thereto, so that alignment of the liquid crystal molecules is changed.
Also, it is impossible to easily and simply realize division of a pixel region into a plurality of domains having different alignment to obtain a wide viewing angle.
There are other Japanese patent applications each relating to realizing a wide viewing angle in a liquid crystal display.
One of such applications is Japanese patent laid-open publication No. 7-104282 and entitled “Liquid Crystal Display and Method of Manufacturing the Same”. This application provides a liquid crystal display and a method of manufacturing the same in which a liquid crystal portion is divided or partitioned by high polymer material into a plurality of liquid crystal regions, and in which liquid crystal molecules or high polymer material in the liquid crystal regions are driven to various modes depending on the alignment condition, or to a mode in which the liquid crystal region is aligned into symmetry with respect to an axis.
This liquid crystal display comprises a plurality of liquid crystal regions each of which has an electrode, is disposed between a pair of substrates, at least one of the substrates being transparent, and is surrounded by the high polymer material. This liquid crystal display also comprises a light control layer which is disposed between the surface of at least one substrate and an electrode formed on the substrate, which controls an intensity of incident light by changing transmittance and which has locally different film thickness. Also, the space between the electrodes on respective surfaces of the pair of substrates varies corresponding to the change of the film thickness of the light control layer. By such structure, mechanical strength is improved, and also viewing characteristic, contrast and color reproductivity are improved.
Another one of such applications is Japanese patent laid-open publication No. 7-333612 and entitled “Liquid Crystal Display Device”. This application provides a liquid crystal display device having a wide viewing angle by averaging angle dependency of optical transmittance. The liquid crystal display device disclosed in this application has a pair of opposing substrates each of which comprises a transparent electrode formed on the surface thereof and an alignment film formed on the transparent electrode, and a liquid crystal layer of liquid crystal molecules filling the space between the substrates. When a voltage is not applied to the transparent electrodes, in a plane perpendicular to the direction of the thickness of the liquid crystal layer, there are a first liquid crystal domain in which direction of alignment of liquid crystal molecules is approximately constant and a second liquid crystal domain in which direction of alignment of liquid crystal molecules differs from that of the first liquid crystal domain. These two liquid crystal domains are realized by providing uneven portions at alignment layer formed on at least one of the substrate.
In a conventional liquid crystal display of a twisted nematic (hereafter referred to as “TN”) type which is widely used, when an electric field is not applied to liquid crystal molecules, a direction of an alignment vector of the liquid crystal molecules is parallel to a surface of a substrate and this condition corresponds to the condition in which “white” is displayed. When a voltage is applied to the liquid crystal display, the direction of the alignment vector varies toward a direction of an electric field according to a voltage applied. Thereby, the condition in which “white” is displayed is gradually changed to the condition in which “black” is displayed.
However, because of behavior peculiar to liquid crystal molecules in a condition a voltage is applied, there occurs a problem that the TN type liquid crystal display has a narrow viewing angle. This problem of narrow viewing angle is prominent in a direction toward which liquid crystal molecules rise when medium gray is displayed.
As a method of improving viewing angle characteristics, there are proposed some liquid crystal displays disclosed in Japanese patent laid-open publication No. 4-261522, Japanese patent laid-open publication No. 6-43461 and Japanese patent laid-open publication No. 10-333180.
In these liquid crystal displays, viewing angle characteristics are improved by using a structure shown in FIG. 44A, FIG. 44B and FIG. 44C. A liquid crystal display panel of the structure shown in these drawings comprises an upper substrate having a color filter substrate 501 and having a common electrode 502 and an alignment layer 503 which are formed on the color filter substrate and which have a slit 517 formed in the common electrode 502 and the alignment layer 503. Also, there is provided a lower substrate having a substrate 507, a pixel electrode 504 formed on the substrate 507 and an alignment layer 503 formed on the pixel electrode 504. A space between the upper substrate and the lower substrate is filled with liquid crystal molecules 508 which are homeotropic aligned and which form a liquid crystal layer. The liquid crystal display panel shown in FIG. 44A, FIG. 44B and FIG. 44C is put between a pair of polarizers disposed such that polarizing axes or transmission axes of these polarizers have right angles with each other. When a voltage is applied between the common electrode 502 and the pixel electrode 504, an electric field having slant components is produced. Therefore, more than one liquid crystal domains having different alignment directions are produced in each pixel, and thereby viewing angle characteristics are improved. The shape of the slit can be, for example, a rectangle as shown in FIG. 44B, or can be x-shape as shown in FIG. 44C.
In the liquid crystal display disclosed in Japanese patent laid-open publication No. 4-261522, directions of inclination of liquid crystal molecules when an electric field is applied thereto are controlled to obtain a high contrast ratio. Also, as disclosed in Japanese patent laid-open publication No. 6-43461, it is possible to use an optical compensation film to improve viewing angle characteristics of black area.
Further, in Japanese patent laid-open publication No. 6-43461, not only in a liquid crystal display panel having homeotropic alignment, but also in a liquid crystal display panel having TN alignment, each pixel is divided into more than one domains by using an electric field having slant and different components to improve viewing angle characteristics.
In Japanese patent laid-open publication No. 10-333180, a technology is disclosed in which thin film transistors, gate lines and drain lines are disposed under display electrodes, in order to prevent an electric field from the thin film transistors, the gate lines and the drain lines from affecting slant electric field components produced by using a common electrode having opening portions.
In Japanese patent laid-open publication No. 10-20323, there is disclosed a liquid crystal display in which more than one kind of minute domains coexist in a liquid crystal layer. One of substrates of liquid crystal display panel of this liquid crystal display has opening portions, and there is provided a second electrode in each of the opening portions. A voltage is applied to the second electrode to produce an electric field having slant components. Thereby, domains having different alignment directions are produced in each pixel and wide viewing angle characteristics are obtained. This publication mainly concerns a liquid crystal display having TN type cell.
Japanese PCT patent laid-open publication No. 5-505247 discloses a liquid crystal display of In-Plain-Switching (IPS) system or mode in which, in order to rotate liquid crystal molecules while keeping the liquid crystal molecules in a direction parallel to substrates of liquid crystal display panel, two electrodes are disposed on one of the substrates. A voltage is applied to between the two electrodes and, thereby, an electric field parallel to the substrates is produced. In such IPS system, a long axis of each of liquid crystal molecules does not rise from the substrate when the voltage is applied. Therefore, when a viewing angle is changed, variation of birefringence or double refraction of liquid crystal is relatively small and, therefore, wide viewing angle characteristics are obtained.
Also, in each of “Journal of Applied Physics”, Vol. 45, No. 12 (1974) 5466 and Japanese patent laid-open publication No. 10-186351, there is disclosed a liquid crystal display which has the above-mentioned IPS mode and in which liquid crystal molecules having a positive anisotropy of permittivity are aligned as homeotropic alignment. The liquid crystal molecules are rotated toward a direction parallel to the substrate by using an electric field parallel to the substrate. In this case, because of directions of the electric field, the liquid crystal molecules which are homeotropic aligned are grouped into two domains. The two domains have different alignment directions of liquid crystal molecules and, therefore, it is possible to obtain a liquid crystal display having wide viewing angle characteristics.
Japanese patent laid-open publication No. 10-186330 proposes a liquid crystal display in which square wall structures are produced by using a photosensitive material, and a pixel is formed by using each of such structures as a basic unit. When a voltage is applied to produce an electric field, liquid crystal molecules having a negative anisotropy of permittivity are rotated toward different directions in a pixel.
However, in the above-mentioned technology in which slits are provided in the common electrode, it is necessary to perform a microfabrication process, such as photolithography and the like, of the common electrode 502 which is not required in the fabrication process of the usual TN type liquid crystal display. In addition to this, there is a problem that a very precise assemble technology is required for precisely combine the upper substrate 501 and the lower substrate 507. This problem is especially important in an active matrix type liquid crystal display which uses switching elements such as TFT's and the like.
That is, in a usual active matrix type liquid crystal display, active elements such as thin film diodes and the like are formed on one of transparent substrates. Therefore, it is only necessary to perform a microfabrication process, such as photolithography and the like, on one of the substrate on which active elements are formed. It is not necessary to perform such microfabrication process on the other substrate which is usually called a “common electrode”, but it is only necessary to form an electrode on whole area of the other substrate.
However, in the above-mentioned prior art technologies, it is also necessary to perform a microfabrication process, such as photolithography and the like, on the “common electrode” on which, usually, it is not necessary to perform such microfabrication process. Therefore, fabrication process becomes complicated, and a high precision alignment and assemble technology is required for the upper substrate 501 and the lower substrate 507.
When the thin film transistors, the gate lines and the drain lines are disposed under the display electrodes, as described in Japanese patent laid-open publication No. 10-333180, an aperture ratio becomes deteriorated.
Also, in the liquid crystal display described in Japanese patent laid-open publication No. 10-20323, it is necessary to apply a voltage to each of second electrodes when driving the liquid crystal display and, therefore, a special drive technology is required. Further, an additional process is required in which a voltage is applied to the second electrodes in order to obtain divided alignment directions.
In the IPS type liquid crystal display and in the liquid crystal display in which vertically aligned liquid crystal molecules are rotated down by using the lateral electric field, there is a problem that an aperture ratio is deteriorated. Also, in these liquid crystal displays, when a cell gap of each pixel is narrowed to obtain high operating speed, a high drive voltage is required.
In the IPS type liquid crystal display and in the liquid crystal display in which vertically aligned liquid crystal molecules are rotated down by using the lateral electric field, there is still another problem as follows. That is, in such prior art liquid crystal displays, since a color filter layer is disposed between a layer in which liquid crystal molecules are disposed and an opposing substrate, especially when switching elements are formed by using a TFT structure, an electric field produced by applying a voltage between the source electrode and the common electrode affects the color filter layer, and deteriorates display characteristics.
That is, in coloring matter constituting the color filter layer, sodium ions are included as impurities. Therefore, when an electric field is applied to the color filter, electric charges are stored in the color filter layer and the color filter layer is charged up. If the color filter layer is charged up, an unnecessary electric field is always applied to the liquid crystal molecules under the charged up portion of the color filter layer. Therefore, such electric field affects display characteristics, especially color irregularity.
In the liquid crystal display which has square walls disclosed in Japanese patent laid-open publication No. 10-186330, it is necessary to fabricate the walls by using photolithography, in order to realize divided alignment directions. Therefore, a manufacturing process becomes complicated.


Many vessel-mountable sonar systems are known in the art. Examples of such systems include depth sounder(s), simple obstacle avoidance sonar(s), side scan sonar(s), mechanical scanning sonar(s), and manual pole mount(s). The display methods of these vessel-mountable sonar systems do not adequately facilitate navigation with the sonar imageries, and these systems are difficult to understand and challenging to operate while the vessel is moving. In addition, these vessel-mountable sonar systems do not have the capability to provide high definition resolution imaging from a moving platform on the vessel.
U.S. Pat. No. 7,035,166 discloses a sonar system comprising at least one sonar emitter, an array of sonar sensors configured to receive an echo from an outgoing signal generated by the sonar emitter and generate a raw data signal; at least one roll, tilt, and yaw sensor, an input from a sensor determining the latitude and longitude position of the sonar emitter; and circuitry adapted to collect the raw signal data, process the raw signal data to provide image data. The image is rotated responsively to the roll, tilt and yaw orientation of the sonar system as determined by the respective sensors. The roll, tilt and yaw sensor and image processing allows successive display of multiple images from successive transmissions to be oriented with the same fixed frame of reference in a direction relative to the earth.
U.S. Pat. No. 7,173,879 discloses a sonar system comprising a broad beam transmitter, a phased array receiver, a processor which utilizes a non-Fourier based beamformer, and correlation based processing techniques to extract valid targets from the beamformed data where the number of targets to search for is based on the values attained from an Adaptive Target Population Estimator processing technique. The values of the eigenvalues and the slope of successive eigenvalues are used to determine the number of targets to be searched for by the beamformer.
U.S. Pat. No. 7,123,546 discloses a sonar system comprising at least 2 transmitters with varying field of views, a receive system with a field of view which encompasses all the field of views generated by the transmitters, a control system designed to switch electronics between transmitters, and processing parameters set to correspond to the transmitters where the controller allows for the transmission and reception of a single ping before the next transmission, allowing each transmission to be differentiated in time.


The present invention relates to the filtration field, and more particularly, to an improved centrifugal filtration apparatus for filtering and concentrating a solution. The improvement comprises eliminating any retentate pockets below the filter and instead employing a port on the filtrate side of the filter that is above the bottom level of the filter, thereby not permitting filtering to dryness.
The filtration of fluids may be accomplished through the use of filtration devices which utilize microporous filters to filter and concentrate a macro-molecular solution is well known. This technique has been used in centrifugal filtration apparatuses that rely on centrifugal forces to create pressure in the apparatus to force solutions through a filter which separates liquid solutions into filtrate and concentrate.
There are certain drawbacks, however, associated with conventional centrifugal filtration apparatus. While many apparatus designs can prevent filtering to dryness in certain applications, they do not in other applications, such as a swinging bucket centrifuge. Those that work in both a fixed angle centrifuge and a swinging bucket centrifuge without filtering to dryness may present the problem of either retaining a different amount of concentrate when used in a fixed angle centrifuge than they will when used in a swinging bucket centrifuge or retaining a different amount of concentrate when used in fixed angle centrifuges with different fixed angles.
Some of the conventional centrifugal filtration apparatus require a second spin to remove the retained concentrate (i.e. dead stop volume). In these apparatus it is difficult or impossible to remove the retained concentrate from the concentrate tube with a pipette.
Another problem with some of the conventional centrifugal filtration apparatus is that as the concentrate volume approaches its final retained volume, the active filter area approaches zero. Therefore, the filtration rate will slow dramatically as the concentrate volume approaches its final retained volume.
Another problem with the conventional centrifugal filtration apparatus is that they are open systems (i.e. they contain a venting means that vents to the atmosphere in the centrifuge).
Yet another problem with some of the conventional centrifugal filtration apparatus is that they are not scaleable (i.e. they are designed to be used as small volume centrifugal filters, or large volume centrifugal filters, not both).
Certain types of filtration devices, such as that disclosed in U.S. Pat. No. 4,632,761 to Bowers et alia, are capable of preventing filtration to dryness and contain a dead stop feature which causes filtration to cease while there is concentrate remaining within the apparatus. This device, however, filters to dryness when spun at a 90xc2x0 angle and therefore the dead stop feature will not work if the device is spun in a swinging bucket centrifuge. Also, in this type of filtration device, the amount of concentrate remaining after dead stop is dependent upon the angle of the centrifuge rotor. The filter surface area in this type of device is limited by the diameter of the device, and the surface area is relatively small when compared to the volume of liquid solution within the housing. Another problem with this type centrifugal filtration apparatus is that is an open system (i.e. it contains a venting means that vents to the atmosphere in the centrifuge). This type of filtration device is conductive to clogging because the heaviest and denser molecules within the liquid solution are forced into the membrane filter. Accordingly, this device is limited because it will filter to dryness when spun in a swinging bucket centrifuge, it will filter to different dead stop volumes when used in fixed angle rotors with different angles, it is an open system and will vent potentially harmful gases to atmosphere during filtration, and its active filter surface area is limited by the diameter of the device.
The types of filtration devices disclosed in U.S. Pat. No. 4,722,792 to Miyagi et alia are capable of preventing filtration to dryness and contain a dead stop feature which causes filtration to cease while there is concentrate remaining within the apparatus. In this type of filtration device, the amount of concentrate remaining after dead stop is dependent upon the angle of the centrifuge rotor. Therefore, the dead stop volume will be different when the device is used in a swinging bucket rotor centrifuge than it will be when used in a fixed angle rotor, and will also be different when the device is used in fixed angle rotor centrifuges of different rotor angle. This means that the results obtained from this type of device when used in one type of centrifuge rotor cannot be compared to the results obtained from this type of device when used in another type of centrifuge rotor. Another problem with this type centrifugal filtration apparatus is that is an open system (i.e. it must contain a venting means that vents to the atmosphere in the centrifuge). Another problem with this type of centrifugal filtration apparatus is that the filtration rate starts out high because of its relatively large filter surface area. However, as the concentrate volume approaches its dead stop volume, the active filter area approaches zero. Therefore, the filtration rate will slow dramatically as the concentrate volume approaches its final retained volume. Accordingly, this device is limited because it will filter to different dead stop volumes when used in centrifuge rotors with different angles, it is an open system and will vent potentially harmful gases to atmosphere during filtration, and the filtration rate will slow dramatically as the concentrate volume approaches the dead stop volume.
The types of filtration devices disclosed in U.S. Pat. No. 5,112,484 to Zuk are capable of preventing filtration to dryness and contain a dead stop feature which causes filtration to cease while there is concentrate remaining within the apparatus. In this type of filtration device, the amount of concentrate remaining after dead stop is dependent upon the angle of the centrifuge rotor. Therefore, the dead stop volume will be different when the device is used in a swinging bucket rotor centrifuge than it will be when used in a fixed angle rotor, and will also be different when the device is used in fixed angle rotor centrifuges of different rotor angle. This means that the results obtained from this type of device when used in one type of centrifuge rotor cannot be compared to the results obtained from this type of device when used in another type of centrifuge rotor. Another problem with this type centrifugal filtration apparatus is that is an open system (i.e. it must contain a venting means that vents to the atmosphere in the centrifuge). Another problem with this type of centrifugal filtration apparatus is that as the concentrate volume approaches its final retained volume, the active filter area approaches zero. Therefore, the filtration rate will slow dramatically as the concentrate volume approaches its final retained volume. Although the retained concentrate can be removed from this device with a pipette, the retained concentrate is best removed from this type of device using the concentrate cup with a second spin. This type of device is not well suited to filter small volumes. Accordingly, this device is limited because it will filter to different dead stop volumes when used in centrifuge rotors with different angles, it is an open system and will vent potentially harmful gases to atmosphere during filtration, the filtration rate will slow dramatically as the concentrate volume approaches the dead stop volume, it is not designed to filter small volumes, and it is not easy to remove the dead stop volume with a pipette.
The types of filtration devices disclosed in U.S. Pat. No. 5,490,927 to Herczeg are capable of preventing filtration to dryness and contain a dead stop feature which causes filtration to cease while there is concentrate remaining within the apparatus. In this type of filtration device, the amount of concentrate remaining after dead stop is dependent upon the angle of the centrifuge rotor. Therefore, the dead stop volume will be different when the device is used in a swinging bucket rotor centrifuge than it will be when used in a fixed angle rotor, and will also be different when the device is used in fixed angle rotor centrifuges of different rotor angle. This means that the results obtained from this type of device when used in one type of centrifuge rotor cannot be compared to the results obtained from this type of device when used in another type of centrifuge rotor. Another problem with this type centrifugal filtration apparatus is that is an open system (i.e. it must contain a venting means that vents to the atmosphere in the centrifuge). This type of device is not well suited to filter small volumes. This type of device utilizes the entire filter surface area until the dead stop volume is reached when used in a swinging bucket centrifuge. However when this type of device is used in a fixed angle rotor centrifuge the active filter area will approach zero as the concentrate volume approaches its final retained volume. Therefore, the filtration rate will slow dramatically as the concentrate volume approaches its final retained volume when used in a fixed angle centrifuge. This type of device requires a second spin to remove the retained concentrate solution. Accordingly, this device is limited because it will filter to different dead stop volumes when used in centrifuge rotors with different angles, it is an open system and will vent potentially harmful gases to atmosphere during filtration, the filtration rate will slow dramatically as the concentrate volume approaches the dead stop volume when used in a fixed angle rotor centrifuge, it is not designed to filter small volumes, and it requires a second spin to remove the retained concentrate solution.
Finally, the art discloses the use of a lower retentate pocket to address the issue of filtering to dryness with centrifugal filtration devices. U.S. Pat. No. 5,647,990 to Vassarotti reveals a device having a concentrate retention pocket located at the bottom of a pre-filtration chamber, below the level of the filter membrane. Fluid flows through the filter into filtrate outlet channels, exiting these channels into the filtrate reservoir. These exit channels do not collect filtrate.
It is therefore an object of the present invention to provide a filtration device that may be used in a swinging bucket centrifuge, as well as a fixed angle centrifuge, without filtering to dryness.
It is also an object of the present invention to provide a filtration device that will filter to approximately the same dead stop volume when used in either a swinging bucket rotor centrifuge, or when used in a fixed angle rotor centrifuge.
It is also an object of the present invention to provide a filtration device having a relatively high filtration membrane surface area thereby enabling filtration to occur at a higher rate.
It is also an object of the present invention to provide a filtration device that continues to use a relatively high filtration membrane surface area until the dead stop volume is attained, thereby enabling filtration to occur at a higher rate throughout the entire filtration process.
It is also an object of the present invention to provide a filtration device, which minimizes the clogging of the semi-permeable membrane thereby maximizing filter efficiency.
It is also an object of the present invention to provide a filtration device from which the retained concentrate solution can be easily removed with a pipette.
It is also an object of the present invention to provide a filtration device which can be used as a closed system (i.e. does not vent to atmosphere), or that can be used as an open system (i.e. vents to atmosphere).
It is a further object of the present invention to provide a filtration device, which can be manufactured as a disposable small volume device, or as a disposable large volume device.
The foregoing problems of the prior art are solved, and the objects of the present invention are achieved, by use of a filtration apparatus constructed in accordance with the principles of the present invention.
In accordance with the present invention, the filtration apparatus for filtering and concentrating a solution includes a concentrate tube, which is divided into two sections. The upper cylindrical section acts primarily as a reservoir for unfiltered solution and directs unfiltered solution from the upper section into the lower section of the concentrate tube. The upper section is shaped so that all of the solution in the upper section will flow into the lower section regardless of the centrifuge rotor angle. The lower section of the concentrate tube is mainly rectangular, but may be triangular shaped at the bottom. The volume of the lower section is made as small as possible to insure that the entire filter surface area is used to filter the maximum amount of solution. The lower section may contain a pipette tip channel to facilitate the removal of the retained concentrate with a pipette. The lower section is open on one side, or two sides.
A micro-porous membrane or membranes may be sealed to the lower section in several ways. First, the membrane can cover the open side of the lower section of the concentrate tube, or the membranes can cover the open sides of the lower section of the concentrate tube. Alternately the micro-porous membrane may be sealed to the filter cover, or covers. A second alternative is to seal the micro-porous membrane or membranes between the filter cover and a filter sealing gasket or gaskets. A third alternative is to seal the micro-porous membrane between the filter cover and the concentrate tube using a compression rib that compresses a portion of the outer periphery of the micro-porous filter between the filter cover and the concentrate tube.
A filter cover is sealed to the open side of the lower portion of the concentrate tube, or two filter covers are sealed to the two open sides of the lower portion of the concentrate tube. The filter cover or covers contain a filter support means such as filter support ribs. The filter cover or covers also contains a filtrate outlet port. The position of the filtrate outlet port or ports determines the retained concentrate volume. The concentrate tube may contain a port or ports to allow displaced filtrate air to flow into the upper part of the concentrate tube to replace the filtered solution that flows from the concentrate tube into the filtrate tube.
The means for collecting the filtrate may include a filtrate tube. The concentrate tube may be sealed into the filtrate tube. The filtrate tube cap may contain a means to nest the concentrate storage tube.


In online gaming, game hosting services and game developers have created a number of ways to track and personalize the online gaming experience. One drawback of existing systems is that many of the features have grown up independent of each other. Games send blobs of data about gamers back and forth to a central service, but the service has no way to understand and aggregate the data outside of the game context. Games can host their own Websites, but the data displayed there is not universally accessible to other games.
In a sense, then, the service and games offer two parallel communities that offer great—but separated—resources for gamers. First, in the game community, while playing a game, the gamer can see the community of others who play the specific game, the leaderboards for that game, and his personal achievements in that game. A game can tell a gamer, from the Service data, if a Friend is online, but it can't tell the gamer what, exactly that Friend is doing on the Service or when he will be available.
Second, in the service community, the service knows a gamer player's history, all of the games he's played, the amount of time he spends online, the size of his Friends list and all of the games that Friends have played or are playing, the Friends invites sent and received, the Messages sent and received, and all of the Feedback the gamer has given and received.
Systems have tried to leverage these on-line communities to match various players to allow them to play multi-player games. Nevertheless, in general such systems, which typically emphasize skill or experience in a single game or small family of games, do not allow groups of players who are likely to enjoy shared interaction based on a variety of personal considerations to form a group outside of the game context and then collectively engage in a multiplayer game.
Further, because matchmaking interfaces have typically been part of each individual game's code, gamers have not had the ability to create a match with other players in one game and then roam with that group of players to another game.


1. Field of the Invention
The present invention relates to an optical actuator for controlling position of a focusing lens that focuses a laser beam on a disk surface. The optical actuator drives the focusing lens in three directions including focusing, tracking and tilting directions.
2. Description of the Background Art
An Optical actuator drives a focusing lens which forms a beam spot on an information disk, such as a DVD (digital versatile disk) or a CD (compact disk). By driving a focusing lens in a focusing direction, which is orthogonal to the disk surface, and a tracking direction, which is parallel to a radial direction of the disk. The optical actuator controls position of the focusing lens, so that the beam spot is formed on a pit line of the disk accurately. Furthermore, when the disk surface tilts or wobbles with respect to an optical axis of the focusing lens due to disk warpage, the optical actuator performs tilt control by pivotally rotating the focusing lens on an axis along the tangential direction or on an axis-along the radial direction of the disk.
FIG. 10 is a diagram illustrating a conventional optical actuator described in Japanese Patent Laid-Open No. 2001-297460. A focusing lens 101 is fixed to a lens holder 102. Six blade springs 103a–103c, and 103d–103f (103e and 103f are not shown) are fixed to each side of the lens holder 102. Print coils 104a and 104b are fixed to another side of the lens holder 102. A suspension holder 106 and permanent magnets 107a–107d are fixed to a base 105. The print coil 104a is disposed between the permanent magnets 107a and 107b, and the print coil 104b is disposed between the permanent magnets 107c and 107d. The blade springs 103a–103c and 103d–103f are connected to the suspension wires 108a–108c and 108d–108f (108e and 108f are not shown), each of which are fixed to the suspension holder 106.
When a current is supplied to focusing coils built in the print coils 104a and 104b so as to generate electro-magnetic forces in a vertical condition, the lens holder 102 is controlled in the focusing direction Fo. When a current is supplied to tracking coils built in the print coils 104a and 104b so as to generate electro-magnetic forces in the radial direction, the lens holder 102 is controlled in a tracking direction Tk. When a current is supplied to the focusing coils so as to generate electro-magnetic forces having opposite direction in each of the print coils 104a and 104b, rotational moment on an axis in the tracking direction Tk occurs to the lens holder 102. As a result, the lens holder 102 is driven in the tilting direction Ti.
When the lens holder 102 moves in the tilting direction, each of the blade springs 103a and 103c is warped or stretched, and the tilt control becomes unstable. Furthermore, the structure using blade springs requires higher cost and many assembly steps.
It is therefore, a primary object of the invention to provide an optical actuator which is able to perform the tilt control stably and can be produced with low cost.


Hospitals, clinics, and other healthcare providers continually face a need for donated blood to help in treating patients. It is often difficult to notify and educate the public regarding donations. Donors may not become repeat donors due to a lack of information and access. Operators and administrators may introduce inefficiencies in their operation and management of blood collection instruments due to a lack of information and access.


This invention relates in general to bird feeders and animal feeders, and is more particularly directed to demand feeders for agricultural birds, e.g., fowl such as chickens, ducks, turkeys, peafowl, or many other exotic or native birds, or small animals like cats and rabbits.
The invention is more particularly concerned with a feeder that dispenses feed on demand from a raised hopper onto a feed tray or catch dish that is suspended beneath the hopper, where the dispensing occurs by action of the bird or birds feeding, i.e., by action of the birds pecking and grabbing at food on the feed tray.
It is a significant object of the invention to create a bird feeder that is simple, easy to use, refill, and clean, and which allows for choice of a wide variety of feed types, from small grain, such as millet seed or mash, to larger particles such as pellets, corn, or dog food.
The bird feeder provides on-demand gravity feed and engages the birds in pecking and grabbing activities which helps stimulate normal, healthy behavior. The on-demand feeder also reduces over-feeding and eliminates food waste, dispensing feed only when needed.


Seagoing vessels are required in various types of offshore operations, including scientific surveys and oil and gas drilling and production. Such vessels are typically configured as drillships, barges and jack-up rigs, as well as supply and service ships.
Both active and passive techniques have been proposed for damping the natural oscillatory displacement of vessels to achieve roll and pitch stabilization in seas having periodic wave motion. Such techniques have utilized water tanks on the vessels and various arrangements of blowers, pumps, valves actuators, roll and pitch sensors, and electronic control circuits for moving water in the tanks to counteract oscillatory roll and pitch motion. A common objective of heretofore known systems has been to make the natural frequency of oscillatory flow of water in the tanks approximately the same as the natural frequency of oscillations of the vessel, thereby to "tune" the tanks to the vessel. Once tuned, the damping action is achieved by causing the flow pattern of water in the tanks to be approximately 90.degree. out of phrase with the natural oscillations of the vessel. The forces produced by the water in the tanks then tend to counteract the roll and pitch forces on the vessel.
Prior systems that attempt to achieve stabilization in the manner described above have the disadvantage that large counteracting, damping forces must be produced in order for the system to be effective. The equipment required to provide the large counteracting forces is complex and expensive. In active systems, high power blowers and pumps are typically required. Passive systems generally require high-capacity valves, special stabilizing tank configurations and control circuits for timing the flow of water in the tanks.


Recently, digital discs have been widely used in many fields. For example, a CD (abbreviation of Compact Disc) is used for digital audio records. A CD-ROM (ROM; abbreviation of Read Only Memory) is used for data memories. An LV (abbreviation of Laser Vision) disc is used for video records. In those digital discs, recorded data or information are reproduced at a speed specified to each kind of the digital discs. Thus, reproduction apparatus of digital discs are designed to reproduce the digital discs at the sole reproduction speed, i.e., a standard speed specified to each of the digital discs.
Referring now to FIG. 1, an example is shown of the conventional reproduction system for digital discs, e.g., a CD dubbing system. The CD reproduction system is provided for carrying out a dubbing from CD players to analog tape recorders.
In FIG. 1, the CD reproduction system comprises a CD player 10 and an analog tape recorder, e.g., a cassette tape recorder 11. The CD player 10 includes a CD reproducing mechanism section 12, a clock generator 13 and a signal processor 14.
The CD reproducing mechanism section 12 comprises a disc drive motor 15, a disc turntable 16 and a pickup device 17. The clock generator 13 generates a clock pulse Pck with a prescribed frequency Fck. The clock pulse Pck is applied to the signal processor 14.
The signal processor 14 comprises a servo control section 14a and an information signal reproducing section 14b. The servo control section 14a is coupled to the disc drive motor 15 and the pickup device 17 for supplying servo control signals thereto, as described later in brief. The information signal reproducing section 14b is coupled to the pickup device 17 for receiving an RF signal (RF; abbreviation of Radio Frequency) Srf read from a CD 18 and sent to the CD reproducing mechanism section 14.
The disc drive motor 15 drives the disc turntable 16 under the servo control of the servo control section 14a. The pickup device 17 shifts in the radial direction of the CD 18 under the servo control of the servo control section 14a. Thus, the pickup device 17 traces a record track on the CD 18 in a CLV (Constant Linear Velocity) speed. The pickup device 17 reads the CD 18 during the tracing of the record track of the CD 18 so that an RF signal Srf corresponding to the digital data recorded on the CD 18 is output from the pickup device 17.
The pickup device 17 outputs the RF signal Srf corresponding to the digital data, as described above. The RF signal Srf is applied to the information signal reproducing section 14b of the signal processor 14. A data slice circuit (not shown) in the information signal reproducing section 14b slices the RF signal Srf at a prescribed threshold level so that the RF signal Srf is shaped to the original digital data.
The servo control section 14a of the signal processor 14 generates two servo control data SCm and SCp and a bit synchronizing signal BS from the reproduced digital data. A motor servo control data SCm is applied to the disc drive motor 15, as described before. A pickup servo control data SCp is applied to the pickup device 17, as described before. The servo controls for both the disc drive motor 15 and the pickup device 17 are carried out in using the digital data obtained from the output of the pickup device 17, i.e., the RF signal Srf, and also the clock pulse Pck applied from the clock generator 13.
The information signal reproducing section 14b of the signal processor 14 demodulates an analog data AD from the reproduced digital data under the control of the clock pulse Pck. The analog data AD is applied to the cassette tape recorder 11. The cassette tape recorder 11 then records the analog data AD.
The conventional reproduction apparatus of digital discs, however, have a drawback that a reproduction of the digital discs takes a relatively long time the same as a standard record time provided for each of the digital discs.


1. Field of the Invention
The present invention is related to wireless tracking systems and methods. More specifically, the present invention relates to a system and method for mitigating multipath errors associated with the wireless tracking of objects by utilizing tags that transmit signals at various power levels.
2. Description of the Related Art
The ability to quickly determine the location of objects located within a facility is becoming a necessity of life. To the uninformed observer, the placement of transponders, also known as tags, on numerous non-stationary objects whether in an office or home would appear to be an unnecessary use of resources. However, the uninformed observer fails to appreciate the complexity of modern life and the desire for efficiency, whether at the office or home.
For example, in a typical hospital there are numerous shifts of employees utilizing the same equipment. When a new shift arrives, the ability to quickly locate medical equipment not only results in a more efficient use of resources, but also can result in averting a medical emergency. Thus, the tracking of medical equipment in a hospital is becoming a standard practice.
The tracking of objects in other facilities is rapidly becoming a means of achieving greater efficiency. A typical radio frequency identification system includes at least multiple tagged objects each of which transmits a signal, multiple receivers for receiving the transmissions from the tagged objects, and a processing means for analyzing the transmissions to determine the locations of the tagged objects within a predetermined environment. The tags can also receive signals.
Several prior art references discloses various tracking systems.
McKee et al., U.S. Pat. No. 6,915,135 discloses a system for determining presence, identity and duration of presence in a given area (a table in a restaurant) of an object (tag attached to a waiter).
Lester, U.S. Pat. No. 3,805,265 discloses a location system that uses line-of-sight radiant wave energy for signal transmission.
Schwengler U.S. Pat. No. 7,050,819, is directed at the problem of adequate power for a mobile telephone for a two-way communication function or a regeneration function as a node of a mesh network.
Christ, U.S. Pat. No. 5,977,913, discloses a radiofrequency system that is utilized within a prison and allows for an individual to be located after an alarm is triggered by the individual.
Zodnik, U.S. Patent Publication Number 2004/0147232, discloses wall-mounted (RJ-11 or RJ-45) wireless transceivers configured to only track the location of a self-identified wireless communication device in order to communicate the location of the self-identified wireless communication device to an emergency service such as 911.
One exemplary method triangulates the strongest received signals to determine the location of a tagged object. This method is based on the assumption that the receivers with the strongest received signals are the ones located closest to the tagged object. However, such an assumption is sometimes erroneous due to common environmental obstacles. Multipath effects can result in a further located receiver having a stronger received signal from a tagged object than a more proximate receiver to the tagged object, which can result in a mistaken location determination. The prior art has disclosed various means for overcoming multipath effects.
Tekinay, U.S. Pat. No. 6,259,894 for a Method For Improved Line-Of-Sight Signal Detection Using RF Model Parameters, discloses a method for reducing time-shift due to multipathing for a RF signal in an RF environment.
Close, U.S. Pat. No. 3,869,673 for a Method And Apparatus For Measuring Multipath Distortion, discloses a method for indicating multipath distortion in a received signal.
Lennen, U.S. Pat. No. 5,402,450 for a Signal Timing Synchronizer, discloses a method and apparatus for reducing the effects of multipath induced distortions on the accuracy of detecting the time of arrival of a received signal.
Fortune et al., U.S. Pat. No. 5,450,615 for a Prediction Of Indoor Electromagnetic Wave Propagation For Wireless Indoor Systems, discloses techniques for predicting RF propagation within a structure.
Other prior art references have disclosed the use of varying energy levels. For instance, Nakanishi, U.S. Pat. No. 5,451,847 for a Variable Energy Radio Frequency Quadrupole Linac discloses changing radio frequency energy levels to emitted focused and accelerated beams.
Kaewell, Jr. et al., U.S. Pat. No. 7,082,286 for a Path Searcher Using Reconfigurable Correlator Sets discloses producing a path profile for a user based on sorted output energy levels.
Fernabdez-Cobaton et al., U.S. Pat. No. 6,697,417 for a System And Method Of Estimating Earliest Arrival Of CDMA Forward And Reverse Link Signals discloses a mobile station receiver that detects the arrival times and energy levels of received signals, and constructs a searcher histogram and a finger histogram associated with each pilot signal.
The prior art has yet to resolve mistaken location calculations based on multipath effects for objects tracked within an indoor facility.


In recent years, airbag devices have become standard equipment for most vehicles. The airbag device is a safety device activated upon an emergency event such as a vehicle collision and inflated and deployed by gas pressure to receive and protect an occupant. There are different kinds of airbag devices for various installation locations or uses. For example, a front airbag is provided in the center of the steering at the driver seat in order to protect the occupant of the front seat against an impact mainly in the front-back direction, and a passenger airbag is provided in the vicinity of a front passenger seat at locations including the instrument panel. In addition, a side curtain airbag that is inflated and deployed along the side windows is provided at the side door area near the roof in order to protect occupants of the front and back seats against a side collision and a subsequent roll over (turn over).
In an occupant protecting device disclosed in Japanese Patent Application Publication No. 2014-034356, a side airbag to be inflated and deployed immediately next to an occupant is provided on each side of a seat. According to the above mentioned reference, occupant's movement to the side opposite to the collision side (one side in the vehicle widthwise direction) that may be caused by reaction against movement to the collision side (the other side in the vehicle widthwise direction) in a collision can be restricted.
[PTL 1]
The airbag device described above is adapted to mainly cope with collisions in various directions such as frontal and side collisions, and airbags for a driver's seat and passenger seats are designed individually to cope with a frontal collision. For a side collision, separate airbags are used depending on the body parts to be protected by the airbags, for example the head is protected by a side curtain airbag, and the chest and abdomen are protected by side airbags. These airbags are supported by reaction force surfaces on the vehicle body side such as side surfaces of the vehicle interior and therefore have high occupant restraining capabilities even when the airbags receive the weight of an occupant in restraining the occupant. However, in order to cope with collisions in more varied directions, additional airbags are used. Such additional airbags may not always secure appropriate reaction force surfaces on the vehicle body side depending on where these airbags are installed, additional spaces for these airbags are not always easily available, and the vehicle weight and device cost might increase as a result.
In view of the problem, it is an object of the present invention to provide an occupant restraining device capable of coping with a plurality of collision directions without additional airbags.


This section provides background information related to the present disclosure which is not necessarily prior art.
It is known to provide a surgical jig having a cutting guide, which assists a surgeon in making accurate and repeatable cuts during surgery. The accuracy of a cut made using a cutting guide is mainly determined by the successful positioning and fastening of the cutting guide in the operative area. Typically, a stylus is attached to the cutting guide, which references from a reference point or marker on the body, for example, a bone. The stylus is either free to translate and/or rotate relative to the cutting guide, so that it may be adjusted, or is rigidly fixed to the cutting guide. An attachment mechanism mounts the stylus to the cutting guide, and a locking mechanism locks the stylus in a desired position relative to the attachment mechanism and hence the cutting guide. Once in the operating position, the jig can be attached to, for example, a bone using pins and/or bone screws.
The use of a stylus to position a cutting guide is common in joint replacement surgery. For example, during a total or partial knee replacement operation, it is necessary to resect the proximal tibia to a specific level. Existing tibial styli reference from the tibial plateau. This area of the joint is subject to considerable wear and, in a knee requiring joint replacement is likely to be damaged. Therefore, the tibial plateau does not provide a reliable reference position. It is desirable to provide a stylus assembly that enables referencing from an area of undamaged bone, which would provide a more reliable reference position.
Once a stylus has been used to position a cutting guide, the stylus is usually removed, in order to increase the working space available to the surgeon. A problem of existing arrangements is that the removal of the stylus can cause unintentional and unnoticed movement of the cutting guide. This leads to inaccurate positioning of the cutting guide, with the result that the surgeons' incisions are misdirected. It is therefore also desirable to provide a stylus assembly which can be removed with the minimum of handling.


The invention relates to an integrated circuit comprising at least one level of metallization, the level of metallization being provided with tracks and comprising metal portions of at least two different thicknesses.
A level of metallization usually comprises metal tracks of small thickness, for example 1 micron, and small width, for example 1 micron. These metal tracks are used to transfer logic data. To manufacture inductors with an inductance of several nanohenrys, a separate level of metallization may be provided which is employed only for this purpose. In order to reduce the resistance of these inductors, particularly the direct-current resistance, use is made of inductors having a large width of, for example, 20 .mu.m, and a large thickness of, for example, 2.5 .mu.m.
However, it is rather unsatisfactory to use a level of metallization only for inductors as a large area of this level of metallization remains unused. For this reason it would be desirable to take measures enabling said level of metallization to also comprise tracks for the transfer of logic data, said tracks having a small width. However, it is very difficult to manufacture tracks which are narrow and thick.


(1) Field of the Invention
The present invention relates to a device which releases a development affecting gas for affecting the development of plant materials and to a method for use of the device. In particular, the present invention relates to a method for initiating ripening or retarding ripening of a fruit or vegetable, particularly with ethylene.
(2) Description of Related Art
Ethylene and other growth affecting gases have been used in storage rooms to modify the natural growth rate of plant materials including whole plants and plant parts such as fruits and vegetables. Such storage room systems are described in U.S. Pat. Nos. 3,620,765 to McDonnell et al; 3,924,010 to Erb; Re 28,995 to Burg. and 4,764,389 to LaBarge. These systems can only be used by wholesalers and others dealing in bulk fruits and vegetables.
The prior art has described various forms of packaging to inhibit or accelerate growth of fruits or vegetables. U.S. Pat. Nos. 3,069,274 to Concannon; 3,798,333 to Cummin; 4,528,228 to Clevenger and 4,622,229 to Toshitsugu are illustrative of such packaging. The common concept is the provision of a gas to facilitate ripening or the removal of a gas (ethylene) by the package to retard ripening of the fruit or vegetable. Such packaging can be expensive and the effect on development is subject to variation depending upon the handling and storage of the fruit or vegetable.
The prior art has described the treatment of plants to prevent fungal or other microorganism infection of cut or exposed portions. Illustrative is U.S. Pat. No. 2,923,632 to Castberg. Such treatments can only be used where the portion of the plant being treated is not eaten. Further, unless the fungicide or other chemical is safe for food purposes, it is difficult to obtain approval to market such devices. In any event, such devices are not used to affect the development (ripening or retarded ripening) of the plant material.
The prior art has described numerous chemicals for producing ripening in the manner of ethylene. They are particularly set forth by Kays, S. and Beaudry, R. in Acta Horticulturae 201 77-115 (1987). Burg, S. et al., Plant Physiol. 42 144-152 (1987) describes various unsaturated organic compounds as substitutes for ethylene to provide ripening of fruits and vegetables. Alternatively, carbon dioxide and other carbon-oxygen gases have been used to retard ripening of fruits and vegetables.
The problem has been to provide a convenient, on demand method and means for initiating the ripening and/or retardation of ripening of the fruit or vegetable.


I. Field of the Invention
The invention relates generally to the utilization of dimethyl ether and the production of hydrogen and carbon oxides. More specifically, the invention relates to a process for catalytically reacting dimethyl ether in the presence of steam.
II. Description of the Prior Art
The conversion of low molecular weight alkanes, such as methane, to synthetic fuels or chemicals has received increasing attention as low molecular weight alkanes are generally available from secure and reliable sources. For example, natural gas wells and oil wells currently produce vast quantifies of methane. In addition, low molecular weight alkanes are generally present in coal deposits and may be formed during mining operations, in petroleum processes, and in the gasification or liquefaction of coal, tar sands, oil shale, and biomass.
Many of these alkane sources are located in relatively remote areas, far from potential users. Accessibility is a major obstacle to effective and extensive use of remotely situated methane, ethane and natural gas. Costs associated with liquefying natural gas by compression or, alternatively, constructing and maintaining pipelines to transport natural gas to users are often prohibitive. Consequently, methods for converting low molecular weight alkanes to more easily transportable liquid fuels and chemical feedstocks are desired and a number of such methods have been reported.
The reported methods can be conveniently categorized as direct oxidation routes or as indirect syngas routes. The direct oxidative routes convert lower alkanes to products such as methanol, gasoline, and relatively higher molecular weight alkanes. In contrast, the indirect syngas routes involve the production of synthesis gas as an intermediate product.
Routes are known for converting methane to dimethyl ether. For example, methane is steam reformed to produce synthesis gas. Thereafter, dimethyl ether and methanol can be manufactured simultaneously from the synthesis gas, as described in U.S. Pat. No. 4,341,069 issued to Bell et al. The '069 Patent recommends a dimethyl ether synthesis catalyst having copper, zinc, and chromium co-precipitated on a gamma-alumina base. Interestingly, the '069 Patent states that dimethyl ether product can be charged as power generator fuel to a combustor of a gas turbine-prime mover arrangement, either alone or simultaneously with synthesis gas.
Alternatively, methane is converted to methanol and dimethyl ether is subsequently manufactured from methanol by passing a mixed vapor containing methanol and water over an alumina catalyst, as described in an article by Hutchings in New Scientist (Jul. 3, 1986)35.
Having a relatively low vapor pressure, dimethyl ether is readily transportable. Moreover, dimethyl ether can be economically produced in relatively small quantities, as compared to materials such as compressed natural gas which require economies of scale associated with large cryogenic plants to be produced competitively. On the other hand, synthesis gas reportedly produces very little atmospheric pollution when combusted with air as fuel. Therefore, a practical process for converting dimethyl ether to synthesis gas on a commercial scale would be attractive to, among others, natural gas producers situated far from fuel consumers.
Known processes for producing synthesis gas typically react hydrocarbons with steam at elevated temperature over a catalyst. Generally, more complex hydrocarbons are converted to methane which is then steam reformed to produce hydrogen or synthesis gas.
United Kingdom Patent Application GB 2213496 A listing Lywood as inventor describes the production of hydrogen-containing gas streams by an endothermic catalyzed reforming between methane and steam. The '496 Application proposes the following equations for the steam reforming of methane: EQU CH.sub.4 +H.sub.2 O.fwdarw.CO+3H.sub.2 1. EQU CH.sub.4 +2H.sub.2 O.fwdarw.CO.sub.2 +4H.sub.2 2. EQU CH.sub.4 +CO.sub.2 .fwdarw.2CO+2H.sub.2 3.
U.S. Pat. No. 4,592,903 issued to Osman et al., states that carbon monoxide can be endothermically converted to carbon dioxide and hydrogen through a reaction termed a water-gas shift, represented by the equation: EQU CO+H.sub.2 O.fwdarw.CO.sub.2 +H.sub.2 4.
Reportedly, the "shift" reaction, can be accomplished in two shift conversion vessels operating at different temperatures to maximize yield. The '903 patent states that a temperature of from about 600 to 900 degrees F. and a pressure of about 300 to 1,000 psig is effective in a high-temperature shift converter containing a supported, chromium-promoted iron catalyst. The '903 Patent further states that a low-temperature shift conversion takes place over a catalyst comprising a mixture of zinc and copper oxides at a temperature of from about 400 to 500 degrees F. and a pressure of from about 300 to about 1,000 psig.
It is important to distinguish between the steam reforming of hydrocarbons, as described above, and the partial oxidation of hydrocarbons. The partial oxidation of methane produces two moles of diatomic hydrogen for each mole of methane reacted. In contrast, the steam reforming of methane produces three moles of diatomic hydrogen per mole of reacted methane.
The partial oxidation of methane is described, for example, in U.S. Pat. No. 4,618,451 issued to Gent. The '451 Patent states that methane is reacted with oxygen from an air separation plant, the proportion of oxygen being less than sufficient for complete combustion. A hot gas containing hydrogen and carbon monoxide is said to be produced. The '451 patent also states that steam or nitrogen can be present during the combustion to act as a temperature modifier and to avoid soot formation. Additional hydrocarbon is reportedly injected into the hot gas, and the resulting gas mixture is reacted over a steam reforming catalyst.
A particular class of partial oxidation processes for converting methane or natural gas to synthesis gas are known as autothermal processes. By convention, the autothermal process includes an exothermic oxidation step and an endothermic steam reforming step which are in approximate heat balance. For example, U.S. Pat. No. 5,112,257 issued to Kobylinski and assigned to the assignee of the present invention, describes an autothermal process for converting natural gas to synthesis gas which includes the steps of mixing natural gas with air, subjecting a resulting mixture to simultaneous partial oxidation and steam reforming reactions, and subsequently reacting unconverted alkanes with water in the presence of a catalyst having steam reforming activity.
Processes which produce hydrogen or hydrogen-containing mixtures by reacting a single-carbon saturated alcohol, methanol, with steam are collectively termed methanol steam reforming processes. U.S. Pat. No. 4,091,086 issued to Hindin et al. describes a process for producing hydrogen by reacting steam with methanol in the presence of a catalytic composition at elevated temperatures. The '086 Patent reports states that methanol can be converted to hydrogen in a single-stage reaction over a catalytic composition comprising zinc oxide, copper oxide, thorium oxide, and aluminum oxide. Moreover, the '086 Patent states, without citing authority or presenting evidence in support, that the composition catalyzes a purported methanol decomposition. The purported decomposition is described as producing significant amounts of carbon monoxide which are immediately consumed in a water gas shift reaction.
U.S. Pat. No. 4,743,576 issued to Schneider et al. describes a catalyst for the production of synthesis gas or hydrogen from aqueous methanol by dissociation or steam reforming. The catalyst reportedly contains a noble metal component on an oxide carrier which comprises an oxide of cerium or titanium and, also, an oxide of zirconium or lanthanum.
U.S. Pat. No. 4,865,624 issued to Okada describes a process for reacting methanol with steam including a decomposition reaction zone regulated at a temperature between 250 and 300 degrees C. and a conversion reaction zone regulated between 150 and 200 degrees. The '624 patent postulates an alleged methanol decomposition for producing hydrogen and carbon monoxide directly from methanol. The conversion reaction zone described in the '624 Patent is apparently intended to promote the well-known water gas shift reaction.
An integrated turbo-electric power generation system which incorporates methanol reforming as a source of fuel and as a means of heat recovery is described in sales literature circulated by the New Energy and Industrial Technology Development Organization under the authority of the Ministry of International Trade and Industry of Japan cerca 1985. The sales literature states that methanol and steam are passed through catalysts at temperatures in the range of 250 to 350 degrees C. to produce hydrogen and carbon dioxide in an endothermic reaction. The hydrogen-containing gas is reportedly combusted with air to drive a turbine. The sales literature indicates that the reforming reactor charge and the combustion air stream can be heat exchanged with the turbine exhaust to promote energy efficiency.
Despite some earlier speculation regarding the existence of a direct methanol decomposition mechanism, practitioners generally agree that methanol steam reforming proceeds by a mechanism which does not involve the direct decomposition of methanol to hydrogen and carbon monoxide. Rather, it is accepted that the steam reforming of methanol creates methyl format and formic add as intermediaries. For example, an article by Jiang et al., Applied Catalysis A: General, 97 (1993) 145-158 Elsevier Science Publishers B. V., Amsterdam, cites studies and presents experimental data indicating that steam reforming of methanol proceeds via dehydrogenation to methyl formate, hydrolysis of methyl formate to formic acid, and decomposition of formic acid to carbon dioxide and hydrogen. According to the Jiang et al. article, no carbon monoxide production was detected while passing methanol over a copper, zinc oxide and alumina catalyst at temperatures below 250 degrees C. The Jiang et al. article reports that significant amounts of carbon monoxide were formed only at temperatures over 300 degrees C. Moreover, the Jiang et al. article states that methanol steam reforming proceeds in accord with the following equations: EQU 2CH.sub.3 OH.fwdarw.CH.sub.3 OCHO+2H.sub.2 5. EQU CH.sub.3 OCHO+H.sub.2 O.fwdarw.CH.sub.3 OH+HCOOH 6. EQU HCOOH.fwdarw.CO.sub.2 +H.sub.2 7.
UK Patent Application GB 2085314 A listing Twigg as inventor describes a catalytic process for reacting a hydrocarbon with steam in net endothermic conditions to produce a gas containing carbon oxides and hydrogen. The process is reportedly carried out using a catalyst comprising the product of thermally decomposing and reducing intimately associated compounds of nickel and/or cobalt and at least one difficultly reducible metal. Reportedly, the catalyst also comprises a water-insoluble compound of an alkali metal oxide with an acidic or amphoteric oxide or mixed oxide.
The '314 Application states that the alkali metal, usually sodium or potassium, is chosen on the basis of the vapor pressure of its hydroxide form, so as to be available as an alkaline metal hydroxide to catalyze a reaction between carbon deposited on the catalyst and steam. The '314 Application speculates that the starting hydrocarbon can be any of those proposed for use with a catalytic steam/hydrocarbon reaction including methane, natural gas, liquified petroleum gas, naphtha, methanol, dimethyl ether, and isobutyraldehyde. However, as explained below the presence of potassium hydroxide actually hinders the reaction of dimethyl ether and steam.
In order to better utilize remotely situated sources of natural gas, to transport the energy inherent in natural gas in a safer and more economic manner, and to provide a fuel which creates very little atmospheric pollution when combusted in air, a commercially practical method for transforming dimethyl ether and steam to synthesis gas is desired. Preferably, the improved method is suitable for integration into modem power generation schemes.


A conventional fixing structure of a door weather strip for a car is described with reference to FIGS. 1 to 3. In some cases, insert clips 30 have been used for fixing a molding part 11 of a weather strip 10 to a door panel 1 of a car, which forms a corner part of the weather strip 10.
The insert clip 30 has a clip part 31 protruded from the center thereof so as to fix the weather strip 10 to the door panel 1, and a catch part 32 provided at the upper portion of the clip part 31 for preventing the insert clip 30 from coming off from the weather strip 10 or from rotating.
However, in the conventional fixing structure of a door weather strip, since the molding part 11 of the weather strip 10 is fixed to the door panel 1 with the insert clip 30, the fixed structure of the insert clip 30 and the weather strip 10 is incomplete that the insert clip 30 and the weather strip 10 are not firmly integrated with each other.
Accordingly, there arises a problem that a gap 33 is produced between the insert clip 30 and the weather strip 10 thereby lowering a sealing property between the weather strip 10 and the door panel 1. Further, there arises another problem that the insert clip 30 moves from its proper position in the weather strip 10 thereby lowering an external appearance.


1. Field of the Invention
This invention relates to plastic containers for rubbish, and the like, and is directed more particularly to a wheeled container having improved wheel mounting means.
2. Description of the Prior Art
Wheeled containers for rubbish, refuse, and the like, are generally well-known. See, for example, U.S. Pat. No. 1,014,475, issued January 1912, to Chester L. Holloway; U.S. Pat. No. 3,366,397, issued Jan. 30, 1968, to Charles F. Zeilstra et al; U.S. Pat. No. 4,351,539, issued Sep. 28, 1982, to Michael S. Rodolakis; U.S. Design Pat. No. 218,359, issued Aug. 11, 1970, to William J. Marsh; and U.S. Design Pat. No. 231,184, issued Apr. 9, 1974, to Thomas E. Brown et al.
Such containers typically are molded of plastics material. Wheel assemblies for such containers often include two wheels mounted on a single rigid axle, usually of metal. The container may be molded with axle holes therein or axle holes may be cut in the container after molding. The axle usually is inserted through the two holes. One wheel may be fixed to the axle before attachment of the axle to the container but the remaining wheel must be fixed to the axle after the axle is in place. Alternatively, there may be molded in a bottom surface of the container a groove for receiving the axle. In such case, an axle with both wheels fixed thereto may be placed in the groove. The groove is then closed, at least in part, by a bracket, or the like, fixed to the container by fasteners.
There is a need for such a container having a wheel assembly which may be pre-assembled and mounted, as is, on the container quickly and easily without the need to bore holes in the container, attach wheels to axles (other than during pre-assembly of the wheel assemblies), or attach axle-retaining brackets to the container.


Semiconductor power devices have conventionally become the focus of attention, which are mainly used for systems in various power electronics fields such as motor control systems and power conversion systems.
As semiconductor power devices of this type, SiC semiconductor devices having a trench-gate structure have been proposed, for example.
For example, Patent Literature 1 discloses a field effect transistor including an n+-type SiC substrate, an n−-type epitaxial layer (drift region) formed on the SiC substrate, a p-type body region formed at a surface side of the epitaxial layer, an n+-type source region formed at a surface side within the body region, a grid-shaped gate trench formed in a manner penetrating through the source region and the body region to reach the drift region, a gate insulating film formed on the inner surface of the gate trench, a gate electrode embedded in the gate trench, a source trench formed in a manner penetrating through the source region and the body region to reach the drift region at a position surrounded by the grid-shaped gate trench, and a source electrode formed in a manner entering the source trench