|A miniature voice coil actuator from BEI Kimco Magnetics is suitable for portable medical device applications.|
It's not news that medical devices are continuing to shrink, but this smaller-is-better trend would be unthinkable without the development of components small enough to drive them. Contributing to the development of miniaturized components for such portable medical devices as patient-worn drug-dispensing units and surgical hand tools, BEI Kimco Magnetics has designed the Model LA05-05-000A--a miniature voice coil actuator (VCA) that the company claims is approximately 0.13 in. smaller than competing models.
"The VCA represents a breakthrough for two reasons," states Miguel Hermosillo, BEI Kimco's applications engineer for VCAs. "First, it's very small, and second, it's very light. Portable devices that are attached to the patient's body need to be as small and light as possible." Featuring a diameter of 0.5 in., a length at midstroke of 0.5 in., force of 2.5 oz, and an actuator constant of 1.904 N per square-root watt, the compact component is designed to meet the tight packaging constraints of increasingly miniaturized medical devices.
Several technological hurdles had to be overcome to develop the VCA, however. First among them was learning how to handle the component's small-gauge wire. "Because it is easy to break a small-gauge wire, the tension applied to it must be carefully monitored," Hermosillo explains. "And while a larger-gauge wire can be stretched without affecting its performance, stretching a very thin wire can effectively decrease its cross-section." A change of that magnitude can result in higher resistance and greater voltage and power loss, he adds.
In addition, producing a layered winding with uniform turns and properly sized air gaps is technologically challenging in a product of this size, according to Hermosillo. He notes that mounting the magnets so as to avoid misalignments and undersized air gaps is also demanding in miniature components. "If improper placement of the magnet causes a misalignment, the result can be a much smaller air gap than expected. And if the air gap is too small, moving parts can touch stationary parts, causing a potential failure."
The LA05-05-000A creates linear motion, but unlike other electromechanical actuators, it is a single-component product that does not use a brushless dc motor and lead screw to convert rotational motion into linear motion. "Our VCA provides direct-drive linear motion, eliminating the use of a brushless motor and lead screw," Hermosillo says. "As a result, it requires fewer parts than other electromechanical systems." This arrangement is also more accurate than systems incorporating lead screws, he adds. "When you convert from rotary motion to linear motion using a lead screw, unwanted play is always a factor."
Because it is small, the VCA is already being used in such medical applications as surgical hand tools, which move at high speeds and accelerate rapidly. It is also being incorporated into a miniature dispensing system approximately the size of a smartphone. "The original idea for this system was to use a brushless dc motor and a lead screw to create the necessary linear movement to open and close the valve," Hermosillo says. "But by using our voice coil actuator instead, we have gained space, shrunk the weight of the device, and reduced the number of components."
BEI Kimco Magnetics