Motors on the Go
With an influx of wireless, portable medical devices continuing to hit the market, often used by patients in their home or on the go, suppliers need to accommodate designers’ needs for smaller, more energy efficient device components. Since motors are becoming an integral part of more and more types of devices, this article looks at these factors and what developers are doing to address them.
Motors are becoming an integral part of a variety of medical devices. Driving everything from surgical robots, drug delivery pumps, ventilators, and imaging devices to surgical tools, hemodialysis machines, analyzers and diagnostic equipment, and anesthesia monitors, there are a wide array of products from which medical device designers can choose. Of course, that also makes the selection process all the more challenging. Adding into the equation the fact that many of today’s devices are being made portable and being used by patients in their homes or on their person and the selection process becomes even a greater obstacle to success.
Motor solutions for today’s portable devices are exhibiting the latest innovations in energy savings, miniaturization, and thermal management. Looking ahead, as more devices move inside the body, motor technologies will achieve even greater levels of these attributes.
When it comes to portable medical devices, whether used in hospitals or made directly for patients, component suppliers must have power at the front of their minds. It is one of the most important considerations when dealing with these types of technologies. Therefore, motor suppliers need to achieve extremely high levels of efficiency for any solution that’s intended to be used in a portable device.
Ken Wyman, GM of Allied Motion Technologies, reflects on this need, “Allied Motion is continually striving to make products that are more compact and more efficient, especially given the medical devices are increasingly battery-fed. We have found that beyond the use of, for example, rare-earth materials and switching from brush to brushless motors, application of design techniques aimed at maximizing power efficiency in our electronic drive and controller products, especially when they are integrated into our motors, is critically important.”
Looking at stepper motor specifically, Jim Nimitz, sales engineer at Lin Engineering, said, “Generally, larger stepper motors are able to produce more torque with less current, but as medical devices drive to become more compact while maintaining efficiency, stepper motors needed to adapt. Motor manufacturers have started designing motors to reach peak efficiency at the customer’s operating speed in addition to achieving required torque. By making changes to the internal winding’s wire gauge and the amount of wire turns per coil, the peak efficiency can be shifted to different motor speeds. Medical devices can get the best ratio of power in to power out from the motor and reduce the overall draw on power by designing the motor around the device’s operating speed.”
“Piezoelectric ultrasonic motors are three to ten times smaller than DC or stepper motors,” explains David Henderson, CTO and co-CEO at New Scale Technologies. He continues, “The newest piezo motors use advanced ceramic materials that operate at a few volts…directly from a battery.” This type of technology enables even greater levels of power savings while still offering the advantage of motion in medical devices.
While power is critically important, so is providing the necessary footprint while still offering enough torque for the application. Considering the limited resources available for power, this can be very tricky. Motor component suppliers are often providing some level of customization (if not an entirely custom motor solution) when it comes portable medical devices to get the design factors correct.
“In medical devices the most common goal is to reduce the size and weight of the device without adding cost,” states Jonathan Martha, medical segment manager at Portescap. “As devices become more mobile, battery capability, specifically providing the necessary current at rated voltage to hit peak speed and torque throughout the duration of a procedure, inevitably becomes a gating factor limiting some new breakthrough concepts. To help combat this, motor efficiency has increasingly been one of the most important design factors focused on in new motor and gearing designs at Portescap.”
“Recent technology has helped improve the performance of stepper motors, allowing for greater torque generation at higher operating speeds. As a result, medical devices are not limited by the motor’s loss in torque at higher speeds and can carry out their operations faster,” adds Nimitz. “More torque at higher speeds also allows medical devices to use smaller motors and maintain the required performance.”
While heat generation and management in medical devices is always a concern, it’s an even greater factor when dealing with products that may be worn by a patient. While cooling technology can be used, it will be limited due to form factor considerations and concerns on where venting would occur. Therefore, motor manufacturers are tasked with attempting to manage heat in their motors without requiring additional components.
Chuck Lewin, founder and VP of engineering at Performance Motion Devices, addresses this issue in greater detail. “The amount of generated heat and vibration is directly related to the efficiency and accuracy of the motor drive technique. Specifically, the cost of computation for executing advanced motor coil drive schemes such as field oriented control has dropped remarkably via the availability of DSPs (Digital Signal Processor). Sensor costs have also dropped, and this has made more accurate encoders available that are smaller and have much more precision. All of these electronics improvements have allowed the controls to drive motors more efficiently and with less vibration.”
Adding his own input, Don Labriola, president of Quicksilver Controls says, “Size, cost, precision, and speed are important, but specific to medical, there is a strong interest in keeping the motor cool to minimize evaporation, as well as to prevent upsetting thermal control for reactions.”
New Application Areas
New realms of medical device technology are always exciting. It’s one of the aspects that makes this wonderful industry so interesting. However, when combining miniaturization with implantable solutions, rarely do you find a more fascinating area of future medical technology innovations. In many of these developments, motors will play a key role.
When asked about this area of medicine and what impact motors will have on this type of technology, Steffen Zeller, sales manager for maxon medical, shared his insights. “High impact for curing the patient. Small ‘submarine’ devices like pills that travel through the body and make diagnoses, local drug delivery, etc., can become reality. In general, it will be a huge advantage to increase the quality of life for a patient combined with a much faster recovery time.”
Siddarth Desai, VP of R&D at Pro-Dex suggested that a greater level of understanding of the body’s natural functions is required to make truly innovation technologies in this sector. “Implantable motor technologies require the understanding of the actual body part that is being simulated. An implantable dialysis system replacing the kidney must be able to pump blood and work without fail. Similarly, a simulated heart will have to work truly as a pump driven by a motor. This is the future of motor technology!”
Motor solutions will continue to get smaller, more efficient, run cooler, and enable greater healthcare technologies that are used in hospitals, by patients, and even inside the body. While this is already happening today, the advancements to come may be even more impactful. Closing with a final thought from Desai, a remarkable level of motor technology has yet to emerge.
“Much has been done in the advancement of powered systems, but there is one area where a significant change can still occur. Most of the devices currently manufactured are autoclavable, reusable instruments. With pressure from the Sunshine Act and budgets being restricted, capital equipment investments are under greater scrutiny. Informed motor manufacturers may be wise to develop an innovative solution to provide disposable motors such that the device can be fully disposable. This trend is being lightly traded, however, it can be a major disruptive innovation in the space.”