Medical device makers and key suppliers are increasingly teaming to develop healthcare innovations. This is the case with several recent motion control developments by BEI Kimco engineers.These are found in a ventilator system, an optical positioning control application; and an ophthalmic lens grinding tool.

Valve control for critical care

In this case, the challenge was meeting a valve control actuator requirement for a medical ventilator system. The customer was using a stepper motor and lead screw mechanical arrangement to produce the linear motion required for the application.

However, speed wasn’t as high as desired and the overall package was cumbersome. Additionally, the customer wanted higher reliability and reduced power consumption.

The first step in meeting this challenge was to design a self-aligned, housed actuator capable of producing 15 N of peak force within a 40.6mm diameter size. The second challenge was to meet the aggressive speed requirement. In order to get there, it was necessary to use different bobbin materials.

To accomplish these goals, engineers developed the voice coil actuator (VCA) LA16 series with a patented magnetic spring. This eliminated the need for a mechanical return spring or alternative option. Over time, mechanical type springs exhibit wear and tear, resulting in a reduced spring constant that causes undesirable performance deviations, especially critical for medical equipment operation. The magnetic spring design was an important design element to support maximum battery life and the fail-safe valve mechanism.

The resulting performance characteristics included a 6mm stroke, a peak force of 60 N, and a continuous force of 17 N. Its outside diameter is just 40.6 mm and its length is 46 mm.

The new ventilator uses two LA16 Actuators to support different functions within the ventilator. One actuator controls the diaphragm valves that regulate the air pressure within the patient’s lungs during the inhalation and exhalation cycles. The second actuator operates a safety valve that diverts the air flow around the ventilator in the event of a system malfunction or power failure. Both actuators incorporate the magnetic spring that establishes the preferred or home position.

By using the newly developed actuators, the customer was able to increase the valve actuation speed and simplify the assembly because of the direct drive advantage. Other benefits were better resolution and control.

Near-zero outgassing levels achieved

Another technological advancement resulted from a voice coil actuator requirement needed for an optical positioning control application.

The customer was using a mechanism based on a gear motor and fixtures to mount the lens. Outgassing was an issue for them and the speed to move the lens was limited.

Key to the optical focusing mechanism design was a voice coil actuator that would produce near-zero outgassing levels. The actuator would move the lens attached to the coil assembly, which in turn would provide precise focus to the system. The operation must be accomplished without contaminating the lens.

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The challenges were to design and develop an actuator 38 mm in diameter with a 12 mm middle hole, with low outgassing materials, while maintaining the peak force of 66 N, which was necessary to move the lens at the desired speed.

To achieve near zero emissions, a linear voice coil actuator without adhesives or inks was developed; all parts were manufactured and assembled by mechanical means utilizing clean manufacturing processes, thereby eliminating any substance that could cause outgassing. High-energy neodymium iron boron (NeFeB) magnets were incorporated for operating efficiencies, and a thermocouple was integrated to monitor and control the coil temperature. With the additional customer specification for an optical clear aperture, the design also included 6.4 mm of stroke and a 12 mm middle hole. The resulting high performance VCA measured 38.1 mm in diameter and 39.6 mm in length (at mid-stroke).

In this application, following several different product interactions, BEI Kimco engineers were able to exceed customer expectations. The low outgassing actuator is part of high-quality, expensive equipment and it must perform at those levels. The specially designed VCA eliminated the outgassing problem and allowed the customer to simplify the system by mounting the lens directly in the moving coil of the actuator, thus eliminating the fixtures. Speed was also increased. High-quality optical devices demand low outgassing levels to minimize contamination. The devices also require high-precision actuation for exact motion control positioning.

Cutting-edge component for cutting tool performance

Another application involved a VCA for a cutting tool utilized in an ophthalmic lens grinding application. This application required an actuator with high force/acceleration capabilities and high-speed position control to meet the desired cutting tool performance.

The customer had been using a BLDC motor and lead screw mechanical arrangement to produce the linear motion, but was dissatisfied with the results. BEI Kimco engineers were confronted with providing a voice coil actuator capable of producing 1370 N of peak force with a maximum acceleration of 1500 m/s^2 and a diameter no larger than 110 mm. Another important requirement was reliable operational performance at ambient temperature of 40°C.

To meet these requirements, BEI Kimco developed the voice coil actuator model LA43-67-000A. This un-housed actuator features an exceptional actuator constant (KA) of 28.02 N/watt^0.5, achieved by the patented optimal design configuration and the use of strong, high-energy rare-earth magnets. Compact in size, the device measures only 108 mm in diameter and 170 mm in length (at mid-stroke).

Utilization of the LA43-67-000A voice coil actuator also allowed automatic calibration with accurate and fast alignment of the turning system without operator assistance, eliminating the need for manual adjustment and providing a significant time-savings advantage. By using VCAs, instead of the motor and lead screw technology, the customer was able to design a smaller and lighter system with fewer components and therefore less failure modes. The new system was also quieter and offered higher acceleration and more precise movement.

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High acceleration and high system precision are the two main advantages made possible by using voice coil actuators. The high force/low moving mass actuator allowed the customer to design a fast tool capable of delivering one of the highest productivity freeform lens turning processes in the industry.

Cast removal system

Supplying a motor that would meet the requirements for a revolutionary new cast removal system for a leading medical device manufacturer was another technology challenge that led to innovation.

The system was developed as part of the manufacturer’s continuing goal to develop products that reduce trauma for pediatric pat ient s . The new tool has provided an al ternat ive to the autopsy saw method used for 40-year s , whi ch e x p o s e the patient to extremely high temperature and noise levels. The new approach uses a proprietary feed wheel that fractures or breaks apart, rather than cut s the cas t material.

The motor was designed to deliver consistently high torques to drive through several layers of cast material It was also critical for the motor to be compact, lightweight, and capable of extended battery operation. To meet these requirements, BEI Kimco developed the high-performance size 23 BLDC motor with customized housing and shaft. The high-torque-density design delivers continuous power levels approaching 1 HP at speeds up to 20K RPM. Its compact size of 2.3-in. OD x 3.0-in. L, with operating efficiencies in excess of 85%, resulted in a motor powerful enough to drive the feed wheel, yet small enough to support the ergonomics of the final product for a cool running, comfortable patient solution. The motor’s competitive price point easily allowed volume production of the new cast removal device.

“It was extremely satisfying to be involved in a project that ultimately reduced trauma for children needing cast removal,” says Walter Smith, BEI Kimco’s senior applications engineer/project manager for motors.