Motors for Portable Medical Devices
Different motor technologies offer different motion solutions with distinct advantages for different types of portable medical devices. These motion solutions are contributing to new portable medical devices that are smaller, lighter, more powerful, and often cheaper than ever before — and designed for global distribution.
New slotless, brushless motors
A new slotless, brushless motor design from Portescap called the ECS Series is targeting applications in respiratory therapy ranging from hospital invasive ventilators to home care bi-level respiratory machines, where high-speed motor operation and highly dynamic control are required to quickly adjust the pressure output of the ventilation system.
Jonathan Martha, North American medical segment manager for Portescap, told Design News:
Primary improvements have been made to the stator and magnetic circuit to enable lower iron losses and increase efficiency, responsiveness, and life. By improving motor efficiency, we have been able to significantly reduce the temperature rise of the motor in operation. In terms of responsiveness, we have been able to dramatically reduce the lag time for a respirator or ventilator to respond when a patient requests air, how quickly the device is able to deliver. Plus in terms of efficiency, we have been able to achieve up to and above a 90 percent efficient motor.
One customer is using these slotless motors to design a new ventilator which will potentially eliminate the need for the motor cooling system and fan electronics altogether. The motor’s improved efficiency has reduced the temperature rise enough to remove the cooling mechanism. Eliminating the cooling system would reduce the cost, size, and weight of the end device.
Since power considerations are important and higher efficiencies require less current input to achieve the same output, applications are able to achieve a higher power output. This allows design engineers to make some trade-offs, and potentially lower the power source to lower costs. With a battery-operated mobile device, battery technology continues to improve, but it is still one of the limiting factors of most portable medical devices. By drawing less current and putting less stress on that battery, that is definitely a benefit.
Dave Beckstoffer, project manager for Portescap, told us:
Higher motor efficiency ripples through the entire design of portable devices. But more than anything, it offers increased flexibility for the design engineer. The motor is not the only device in the system that is drawing power. If before the application had x amount of power from a 9V battery, for example, then suddenly if the motor rather than using one volt of that now is using half of a volt, additional features and functionality can be added into the system using that additional power that has opened itself up.
Other applications for slotless motors include infusion-type diabetic pumps where there has been a migration from coreless motors to using brushless operation due to overall improvements in the price to performance of brushless motors. The major differentiator for brushless motors is that applications are able to achieve much higher speeds and longer life. Typical brushless speeds range from -10,000 to 50,000 RPM, and can reach up to 100,000 RPM, compared to brush motors speeds that are typically 12,000 RPM or lower.