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Global leading provider of quality and high-precision drive systems.
Archive | June 2012
in DC servo motor, Robotics, Automation
Rib Spreading Tool Gets Robotic Update
It may sound unbelievable, but some tools that physicians use to perform invasive surgery were originally developed in the 1930s and have gone through minimal updating since. Most often, these tools have been efficient enough to do the job, even if patients took a long time to heal. This is especially true when a surgeon has to enter the chest cavity for heart or lung operations. To date, there are two primary methods used to open a space large enough for a doctor to work inside the chest: a thoracotomy or a sternotomy.
The thoracotomy is where an incision is made between two ribs to gain access. For a sternotomy, the surgeon saws through the sternum and then spreads it apart. In both cases, the surgeon pries apart the ribs or sternum using a hand-cranked, stepping mechanical jack called a thoracic retractor. Large forces are needed to spread the ribs. In fact, the Physcient team discovered that the forces necessary to separate the ribs are roughly equal to the weight of the person being operated on, which means that using a thoracic retractor can result in broken bones, crushed nerves, wrenched joints, and torn ligaments. All of these factors offer adverse post-surgical effects that can be ongoing.
Physcient has developed technologies that are expected to greatly reduce the damage of thoracic retraction. "Two of the concerns we ran into," said Chuck Pell, cofounder (with Hugh Crenshaw) of Physcient, "were that we had to maintain the same footprint as other thoracic retractors being used in the operating room today, plus we had to be able to sterilise the tool repeatedly, to be used for literally hundreds of cycles." The company's Assuage Smart Retractor was designed to apply technology to solve a longstanding problem without changing surgeons' procedures.
According to Pell: "We both (he and Crenshaw) studied biomechanics, and it is that understanding of how creatures move that we use to translate into technology. We recently turned that knowledge to surgical tools, and are finding it very interesting. Many of the tools used in surgery today were invented prior to biomechanics becoming a mature science."
According to the National Heart, Lung, and Blood Institute, more than half a million heart surgeries are performed every year. Add to that number another hundred thousand lung surgeries, and the need for better tools quickly becomes apparent. Because of the antiquated design of thoracic retractors being used today and the number of surgeries being performed, the incidents of rib fractures has continued to increase.
Crenshaw and Pell recognised that there had been little research pertaining to the forces generated by rib spreaders in the past, and brought together a team to measure the effects and produce the technology to greatly reduce damage. Bones can flex quite a bit before breaking, often due to the rate at which the spreader moves — a sudden bend like that delivered by a hand-cranked thoracic retractor can cause a rib to snap. Bone fibers need a little time to adjust.
By placing sensors in the Assuage rib spreader, it's easier to detect whether fibres begin to break down. This information is then fed back into the tool so that it responds instantly to tissue events. This closed-loop feedback to the motor must have a high degree of precision and be completely reliable to be used inside medical devices.
Physcient designed a prototype rib spreader around a motor manufactured by Maxon. One of the more important specifications for the motor was the lack of cogging that often occurs at very low speeds. The rib spreader has to be able to move smoothly without jerking motions that can cause undue damage to the patient. DC brushless motors easily operate from a battery, and an onboard controller and sensor system helps to maintain a controlled spreading process. In order to handle the high forces necessary, Physcient selected high-torque motors.
"The motors we use from Maxon not only have to handle the greatest retraction forces ever measured in the medical industry, they also have to be precise in order to reduce damage to ligaments and soft tissues," Pell said.
Maxon manufactures a complete line of motors from 6mm to 90mm for a wide variety of applications. They are electronically commutated for minimal electrical noise. The company's DC brushless motors have no mechanical brushes to wear out, which allows them to provide long motor life. By being designed using high-grade, preloaded ball bearings, an additional benefit in longevity is added to the motor. Maxon motors provide a low-profile design ideal for applications requiring a small footprint.
The Physcient Assuage Smart Retractor takes into consideration the physics of bone and tissue. As with most cardiothoracic research, tests were run on pigs, which are biomechanically similar to humans. The Physcient team built a prototype that used two rows of curved metal fingers, meant to cradle a single rib. As the retractor automatically spreads the ribs, sensors provide feedback to the Maxon motor, providing smooth opening. In the experiments, Physcient's retractor greatly reduced tissue trauma, reduced pain, improved breathing, and resulted in better overall recovery.
Once the team at Physcient produces the Assuage rib spreader, it plans to look into other medical equipment that hasn't changed over many years. Its aim has always been patient-oriented through offering the right tools for the surgeons, and it plans to automate and upgrade the entire surgical toolkit. Physcient plans to bring Assuage Smart Retractor to market in 2013.
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New Formulae Handbook for Drive Technology
maxon motor provides effective help for drive selection.
The extensive collection with illustrations and descriptions includes formulae, terminology and explanations of the calculations that are relevant for drive systems. A flow chart provides assistance in selecting the right drive for each purpose
The Formulae Handbook lists the most important formulae in relation to all components of the drive system. It makes use of a flow chart that supports quick selection of the correct drive. Numerous illustrations and the clear descriptions of the symbols on the respective page make it easier for the reader to understand the formulae.
Roughly speaking, it is a collection of the most important formulae from the maxon catalog, as well as from the book "The selection of high-precision microdrives", published by maxon academy. The author of the book, Dr. Urs Kafader, Head of the maxon academy, gave the initiative to compile the Formulae Handbook to Jan Braun, technical instructor at the maxon academy. The book "The selection of high-precision microdrives" contains extensive know-how from the 50-year long success story of maxon DC drives with low power (below approx. 500 W). The new Formulae Handbook is intended for engineers, lecturers and students, as a perfect supplement to the above-mentioned book.
The Formulae Handbook consists of 58 pages in A5 format and is available free of charge in German and English.
maxon motor Group presents good results again
maxon motor Group again achieved good results in 2011 – Revenue doubled since 2001 – Strengthened market leadership in the field of high-precision drive technology – Well-filled product pipeline – Cautiously optimistic look at the future.
Sachseln/OW (CH). – The 2011 business year proved to be very positive for the maxon motor Group. Building on the excellent results of the year before, maxon increased the revenue to 339.6 million Swiss francs. The cash flow amounts to 37 million Swiss francs, allowing the company to finance all investments using own funds only. At the end of 2011, maxon employed more than 2,000 persons at the locations in Sachseln (Switzerland), Sexau (Germany) and Veszprém (Hungary). The export share at maxon is 81.5%. Due to the uncertain economic development worldwide, maxon is hesitant to make predictions for the current business year.
"2011 was characterised by currency declines and massive increases in the prices of commodities, especially magnets. In spite of these obstacles, we reached our targets," said Karl-Walter Braun, majority shareholder of the maxon motor Group, at the annual results media conference. The company exports to all important markets of the world. The largest increases were achieved in Northern America, Scandinavia, as well as Germany and Italy. In Asia, maxon was able to keep the revenue stable, in spite of the decline of the Asian currencies and the events in Fukushima. In Switzerland, maxon recorded very good results. The diversified company is well-established in the fields of medical technology and industrial automation, as well as in the aerospace industries, etc. "With around 2,000 employees, we are large enough to implement ambitious projects, yet still manageable enough to react and decide quickly," says Jürgen Mayer, President of the Board of Directors.
maxon, two-time winner of the Innovation Prize awarded by the Central Switzerland Chamber of Commerce, has introduced various new motors to the market, with a continuing trend towards miniaturisation. In 2011, as before, the investments for research and development are at a very high level, with 8.3% of the revenue being dedicated to this area. "Currently the product pipeline is filled with many promising developments, and with our expertise, we will generate true innovations for new markets," says Eugen Elmiger, CEO. "In the perpetually dynamic market environment, we can maintain our position by constantly introducing new products featuring Swiss precision into the market," states Elmiger. The micro motors are, for example, used in intelligent leg prosthesis systems, in deep drilling and in implantable medication delivery systems.
Cautious look at the future
"The prospects for a positive development of the global economy are intact – if only it wasn't for the euro and the euro crisis," says Karl-Walter Braun. "In this unpredictable situation, we can count on our solid financial basis and the high-quality technological products that are needed all around the world and are used in a wide range of applications."
A change occurred on the management level; the employment contract with Armin Lederer, Head of Operations, has been dissolved, due to difference of opinion regarding the strategic direction of the company. His successor will be announced in due course.
The digital positioning controller EPOS3 70/10 EtherCAT meets the highest demands in real-time positioning of synchronized multi-axis systems. Extremely compact in size, the EPOS3 possesses a wide nominal power supply voltage range from 11 to 70 VDC and delivers a continuous output current of 10 A, during acceleration and deceleration even up to 25 A. Designed for DC and EC motors with a power range up to 700 Watt, it provides outstanding uniform running for motors equipped with incremental encoders.
Humanoid Robot Fights Fires on Ships
Agility, speed, strength, and balance are all qualities needed to fight fires, especially when those fires are shipboard. Such feats are difficult for humans, let alone humanoid robots. But that's just what the RoMeLa labs at Virginia Tech are working on.
"The SAFFiR [Shipboard Autonomous Firefighting Robot] will be able to carry and operate fire extinguishers, fire hoses, throw PEAT [propelled extinguishing agent technology] canisters, as well as interact with humans and find fires. We've already built the legs of the robot and are working on the rest of it," said Derek Lahr, a PhD candidate and project manager.
The SAFFiR's legs are a highly compact amalgamation of motors, pulleys, wire harnesses, and controllers that allow the robot not only to walk, but also to walk while on a ship as it pitches and rolls through waves. Key concerns while designing the SAFFiR included the need to control the robot's locomotion from both a purely mechanical stance and a balance standpoint. For example, if the ship pitches forward, the robot might need to speed its leg movement and produce a longer stride length to keep itself from getting off balance.
Lahr said that by using maxon motors' EPOS controls, the project engineers were able to interconnect all operations easily. "For six degrees of freedom in each leg, we use six motors. That's 12 motors being used in just the legs section of the SAFFiR." Both speed and torque were necessary, since at different parts of a stride, the leg will alternately move fast and free and then slow and more controlled.
Lahr and his team used multiple 30mm maxon motors for the legs. Wherever possible, they designed in 100W motors to help reduce the weight of the unit. The motors provide the largest amount of mass in the robot, so any reduction in weight was a plus. "Maxon motors actually provide the highest power to weight ratio we could find in a brushless motor anywhere," Lahr said. "And humanoid robots can be more sensitive to weight than an airplane."
For certain critical joints like those in the knees, 200W motors were used. The knees of the robot, just like human knees, take the brunt of the load, especially when squatting or kneeling. They also have to move the fastest while walking. Those joints needed the additional torque and speed combination available with the larger wattage units.
At this point in the design testing phase, the robot is tethered much of the time, but the engineers have tested and confirmed the use of a pair of 10 amp/hour lithium polymer batteries (about the size of a small brick) will be able to power the robot for at least a half-hour with a 20A average current draw. This includes all the motors, sensors, and controls.
Because the robot operates off a closed-loop system and uses 12 motors just in the legs (there will be another 12 in the arms and hands, as well as two in the neck), Lahr and his team needed controllers that could handle the load. "We chose maxon's EPOS 50/5 controllers for the joints, aside from two EPOS 24/5 controllers used for less demanding degrees of freedom," he said.
One of the main reasons the team chose to use the EPOS (Easy Positioning System) series controllers was that they came equipped to use the CANopen bus system. "Several of us were familiar with CANopen from other applications, so we were attracted by the familiar operating and programming needs of the system software from the beginning," Lahr said. This makes the EPOS embedded controllers well suited for multi-axis distributed controls that also feature electronic gearing, PVT, step and direction, and point-to-point positioning.
The EPOS controls are used in two different modes — position control mode and force control mode. Position control allows for higher-level controllers to read position data from the sensors and closely regulate the specific position of the leg, so that corrections can be incorporated while walking. Force control mode is the latest thing in locomotion, according to Lahr. "It combines current control circuitry with load cell feedback to create a 'pure force' actuator, which allows the leg to swing freely," he said. "The EPOS controllers allow us to switch modes on-the-fly."
This is important so that the leg impact doesn't harm any of the actuators. "We can switch from position control to force control at the last millisecond, so that we can accurately control stride length and impact power," he said. An additional benefit of using the maxon controllers is that they come with EPOS Studio (a GUI-based free software package provided by maxon), which provides a simple utility to program the controllers and helps the user to bug-check software before implementing it into the CANopen system.
In general, EPOS controllers have been designed using advanced 32-bit DSP technology, which provides users like Lahr and his team the extended functionality of a miniature embedded controller. The units were specifically developed to meet demanding size and performance requirements often found in robotic, medical, and semiconductor applications.
This closeup shows four 30mm brushless motors manufactured by maxon motors.
Tethered to a power system, the SAFFiR walks while packing more than 12 maxon motors and 10 EPOS controller
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