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Solenoids > Application Examples: Solenoids in Medical Ventilation
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| Solenoids in Medical Ventilation |
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The latest rotary actuator available from Ledex®, the Ultimag®, solved a difficult problem in the medical market. The application involves a ventilator used by people who have difficulty breathing while they are asleep. These devices provide positive air pressure to a sleeping patient during inhalation and then an open vent during exhalation.
The application involves rotating a 4-way valve back and forth. In one direction, the device provides positive air pressure to a patient with the vent to the outside blocked off. This is the inhalation cycle. In the other position, the positive air pressure is blocked off and the vent to the outside is opened. This is the exhalation cycle.
The valve will rides on air bearings to eliminate friction. The load is inertial and requires about 26 oz.in. of torque to rotate 40° in 10ms. The valve must then remain in this position for about 2 seconds before being rotated to the opposite position, also in 10ms.
The major task hurdle is to move the load in both directions with 26 oz.in. of torque. Using a standard uni-directional BTA requires a spring of 26 oz.in. in one direction and 52 oz.in. of torque in the other.
The standard Size 5 Ultimag with 45° stroke meets the application requirements. A bi-polar PWM signal is used to operate the solenoid at 25% to obtain the fast response, and then PWM is used to reduce to continuous duty to hold for the required 2 seconds.
The competition for this device was a DC brushless motor which would require rather extensive control electronics.
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