Control circuit and method for negative pressure wound treatment apparatus
A negative pressure wound therapy apparatus can include a wound dressing, a fluid collection container, a vacuum pump comprising a pump motor, and tubing. Additionally, the apparatus can include a pressure sensor that measures a pressure in the tubing. One or more tubes can channel a fluid between the wound dressing, the fluid collection canister, and the pump. In addition, first and second control circuits can be provided for controlling the pump motor without using a processor. The first control circuit can generate a difference signal between a desired pressure input and a pressure sensor input, and can further generate a motor control signal responsive to the difference signal. Moreover, a second control circuit can provide an override signal based at least in part on the difference signal and at least one reference signal. The override signal beneficially overrides the motor control signal to prevent the pump motor from stalling.
1. A negative pressure wound therapy apparatus comprising:
a negative pressure source configured to aspirate fluid from a wound covered by a wound dressing, the negative pressure source comprising a motor;
a pressure sensor configured to measure pressure in a fluid flow path connecting the negative pressure source to the wound dressing; and
a control circuitry configured to:
determine a difference between a negative pressure set point and pressure measured by the pressure sensor;
cause the negative pressure source to operate in a first mode responsive to the difference not satisfying a threshold indicative of stalling of the motor; and
cause the negative pressure source to operate in a second mode responsive to the difference satisfying the threshold indicative of stalling of the motor.
2. The negative pressure wound therapy apparatus of claim 1 , wherein the control circuitry is configured to cause of the negative pressure source to switch operation from the second mode to first mode responsive to the difference no longer satisfying the threshold indicative of stalling of the motor.
3. The negative pressure wound therapy apparatus of claim 1 , wherein the first mode comprises varying a duty cycle of the motor responsive to the difference.
4. The negative pressure wound therapy apparatus of claim 3 , wherein the first mode comprises proportional integral (PI) control.
5. The negative pressure wound therapy apparatus of claim 3 , wherein the control circuitry is configured to increase the duty cycle responsive to an increase in the difference.
6. The negative pressure wound therapy apparatus of claim 1 , wherein the control circuitry is further configured to provide an indication of high pressure responsive to pressure measured by the pressure sensor satisfying a high pressure threshold.
7. The negative pressure wound therapy apparatus of claim 6 , wherein the indication of high pressure comprises deactivating the negative pressure source.
8. The negative pressure wound therapy apparatus of claim 1 , wherein the control circuitry is further configured to provide an indication of a leak responsive to pressure measured by the pressure sensor satisfying a low pressure threshold.
9. The negative pressure wound therapy apparatus of claim 1 , further comprising a canister configured to store fluid aspirated from the wound.
10. A method of operating a negative pressure wound therapy apparatus, the method comprising:
by a control circuitry:
determining a difference between a negative pressure set point and pressure measured in a fluid flow path connecting a negative pressure source comprising a motor to a wound covered by a wound dressing;
at a first time, determining that the difference does not satisfy a threshold indicative of stalling of the motor;
causing the negative pressure source to operate in a first mode responsive to determining that the difference does not satisfy the threshold indicative of stalling of the motor;
at a second time, determining that the difference satisfies the threshold indicative of stalling of the motor; and
causing the negative pressure source to operate in a second mode responsive to determining that the difference satisfies the threshold indicative of stalling of the motor.
11. The method of claim 10 , further comprising:
at a third time, determining that the difference no longer satisfies the threshold indicative of stalling of the motor; and
causing of the negative pressure source to switch operation from the second mode to first mode responsive to determining that the difference no longer satisfies the threshold indicative of stalling of the motor.
12. The method of claim 11 , wherein the first mode comprises varying a duty cycle of the motor responsive to the difference.
13. The method of claim 12 , wherein the first mode comprises proportional integral (PI) control.
14. The method of claim 13 , further comprising increasing the duty cycle responsive to an increase in the difference.
15. The method of claim 14 , further comprising:
determining that a measured pressure satisfies a high pressure threshold; and
turning off the negative pressure source responsive to determining that the measured pressure satisfies the high pressure threshold.
16. The method of claim 10 , further comprising:
determining that a measured pressure satisfies a low pressure threshold; and
providing an indication of a leak responsive to determining that the measured pressure satisfies the low pressure threshold.