Whether in the hospital, the lab, or in the home, maxon motors can be found on medical devices everywhere. Their RE13, for instance, is an integral part of the pipette system shown here, providing specific torque, smoothness, and accuracy needed for the application.

As the need for faster, less intrusive medical surgeries increases, along with the interest in smaller and more compact, home-use devices, the motor industry has kept up by producing smaller and more efficient motors. The circuitry that supports many smaller medical devices has, along with other industries, become smaller and more interactive with other devices. This has ushered in the use of low-power devices across the board.

Battery-operated devices such as infusion pumps for insulin delivery, sleep-apnea devices, and heart monitors require particular motor characteristics in order to operate efficiently and for long periods of time without running down the battery. Similarly, hand tools used in surgery, rack-mounted monitors, and data recorders and printers require the use of small, efficient motors for low-power, quiet, and vibration-less operation.

Back to basics

An electric motor drive essentially converts incoming electric power into outgoing mechanical energy. The goal is for no energy to be stored in the drive train itself, which means that the mechanical power that comes out of the system must first be fed into it—so that the power becomes a constant value that characterizes the motor drive system.

The culprit to providing such a perfect system, however, is the losses that show up in the configuration. Losses occur during the transformation of the energy, which in the simplest case is defined by the efficiencies of the corresponding components used. This means that more electrical energy must be fed into a system than can ultimately be used, or find its way to the output.

The physical manifestation of power transfer always consists of the product of two basic components. The first element is electric power (battery or low-power supply), which is a function of current times voltage. And the second element is mechanical power (typically rotation for motors), which is a function of angular velocity or speed of rotation times torque.

maxon provides a complete line of motors and motor controls for the medical market including their EC series, which is particularly suited for use in medical devices.

The best representation of such a device that could provide perfect power transfer would be where the electrical component current is proportional to the mechanical component torque (force), and the voltage is closely related to the speed of the rotation of the motor (its velocity). Successful drives must satisfy both power component requirements individually. It must achieve the required speed of rotation and simultaneously meet the demand for torque.

As with any high-technology device, these basic assumptions can be very misleading. This can often be seen in the selection of a brushless DC motor for a medical device. These motors are assigned a high power rating because of the high maximum speeds they can deliver, but if high speed of rotation isn’t necessary for the application—which most often is the case when used for infusion pumps—a mistaken selection can occur.

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