The voice coil actuator (VCA) LA16 series with a magnetic spring was developed by BEI Kimko to meet the valve control actuator requirement for a medical ventilator system.

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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