Motor health monitoring and medical device incorporating same

1. A method of detecting degradation in a drive system including a motor, the method comprising:

applying a modulated voltage to the motor;

adjusting a duty cycle of the modulated voltage to achieve a commanded rotation of a rotor of the motor; and

identifying a degradation condition based on the duty cycle.

2. The method of claim 1 , wherein identifying the degradation condition comprises identifying the degradation condition when the duty cycle exceeds a reference value indicative of degradation in the drive system.

3. The method of claim 2 , further comprising determining the reference value as an average of the duty cycle over a preceding time interval.

4. The method of claim 1 , wherein identifying the degradation condition comprises:

determining an observed value for a duty cycle metric based on the duty cycle; and

identifying the degradation condition when the observed value exceeds a reference value indicative of degradation in the drive system.

5. The method of claim 4 , wherein identifying the degradation condition comprises identifying when the observed value exceeds the reference value by a fixed duty cycle percentage.

6. The method of claim 4 , wherein identifying the degradation condition comprises identifying when the observed value exceeds the reference value by a fixed percentage of the reference value.

7. The method of claim 4 , wherein determining the observed value comprises determining an average of the duty cycle over a preceding interval.

8. The method of claim 7 , wherein identifying the degradation condition comprises identifying when the average of the duty cycle over the preceding interval exceeds a historical average duty cycle for the drive system.

9. The method of claim 1 , wherein identifying the degradation condition comprises identifying the degradation condition in response to changes of the duty cycle indicative of degradation in the drive system.

10. The method of claim 1 , wherein adjusting the duty cycle comprises:

operating the motor to produce the commanded rotation while applying the modulated voltage;

determining an expected displacement based on the commanded rotation;

obtaining a measured displacement influenced by rotation of the rotor after operating the motor to produce the commanded rotation; and

increasing the duty cycle in response to a difference between the expected displacement and the measured displacement.

11. The method of claim 10 , wherein:

obtaining the measured displacement comprises obtaining a measured number of incremental rotations of the rotor using an incremental position sensor; and

determining the expected displacement comprises determining an expected number of incremental rotations expected to be detected by the incremental position sensor in response to operating the motor to produce the commanded rotation while applying the modulated voltage.

12. The method of claim 1 , further comprising determining the commanded rotation based on a commanded dosage of fluid to be delivered by an infusion device including the drive system.

13. A method of detecting degradation in a drive system including a motor, the method comprising:

applying a modulated voltage to the motor, the modulated voltage oscillating between a first voltage and a second voltage and being equal to the first voltage for a percentage of a time interval corresponding to a duty cycle;

adjusting the duty cycle of the modulated voltage to achieve a commanded rotation of a rotor of the motor; and

identifying a degradation condition based on the duty cycle.

14. The method of claim 13 , wherein identifying the degradation condition comprises detecting the degradation condition when the duty cycle exceeds a reference value.

15. The method of claim 14 , further comprising dynamically determining the reference value during operation.

16. The method of claim 13 , wherein identifying the degradation condition comprises detecting the degradation condition when the duty cycle gradually increases over a period of time.

17. The method of claim 13 , wherein adjusting the duty cycle comprises increasing the duty cycle in response to a difference between an expected displacement and a measured displacement that is influenced by rotation of the rotor of the motor, wherein the expected displacement is based on the commanded rotation of the rotor.

18. A method of operating an infusion device and detecting degradation in a drive system of the infusion device during operation of the infusion device, the drive system including a motor having a rotor and the infusion device including a shaft mechanically coupled to the rotor and displaced to deliver fluid in response to rotation of the rotor, the method comprising:

applying a modulated voltage to the motor, the modulated voltage oscillating between a first voltage and a second voltage and the modulated voltage being equal to the first voltage for a percentage of a time interval corresponding to a duty cycle;

adjusting the duty cycle of the modulated voltage to achieve a commanded rotation of the rotor of the motor; and

identifying a degradation condition based on the duty cycle.

19. The method of claim 18 , further comprising:

operating the motor to provide the commanded rotation of the rotor while the modulated voltage is applied to the motor; and

after operating the motor to provide the commanded rotation, obtaining a measured displacement that is influenced by rotation of the rotor from a sensor, wherein adjusting the duty cycle comprises adjusting the duty cycle in response to a difference between an expected displacement corresponding to the commanded rotation and the measured displacement.

20. The method of claim 19 , further comprising converting a commanded dosage into a commanded displacement of the shaft, wherein the commanded rotation corresponds to the commanded displacement of the shaft.