Occlusion detection using pulse-width modulation and medical device incorporating same
View Patent ↗Apparatus are provided for motor control systems and related medical devices. In one embodiment, a control system includes a motor having a rotor, a modulation module coupled to the motor, and a control module coupled to the modulation module. The modulation module generates a modulated voltage that is applied to the motor and rotates the rotor to deliver fluid via a fluid path. The control module adjusts a duty cycle of the modulated voltage to achieve a commanded rotation of the rotor and detects an occlusion condition in the fluid path based on the duty cycle.
1. An infusion device, comprising:
a motor having a rotor;
a stopper mechanically coupled to the rotor, the stopper being displaced to deliver fluid via a fluid path in response to rotation of the rotor;
a modulation module coupled to the motor, the modulation module generating a modulated voltage applied to the motor, the modulated voltage oscillating between a first voltage and a second voltage, the modulated voltage being equal to the first voltage for a percentage of a time interval, the percentage corresponding to a duty cycle; and
a control module coupled to the modulation module to adjust the duty cycle to achieve a commanded rotation of the rotor and detect an occlusion condition in the fluid path based on the duty cycle.
2. The infusion device of claim 1 , wherein the control module detects the occlusion condition in response to changes to the duty cycle indicative of an occlusion in the fluid path.
3. The infusion device of claim 1 , wherein the control module determines the commanded rotation based on a commanded displacement of the stopper.
4. The infusion device of claim 1 , wherein the commanded rotation is based on an amount of the fluid to be delivered.
5. The infusion device of claim 1 , further comprising a reservoir in fluid communication with the fluid path, the reservoir having the fluid contained therein, wherein the stopper is disposed within the reservoir to deliver the fluid from the reservoir via the fluid path.
6. The infusion device of claim 1 , further comprising a sensor to obtain a measured displacement that is influenced by rotation of the rotor, wherein the control module is coupled to the sensor and adjusts the duty cycle for the modulated voltage in response to a difference between the measured displacement and an expected displacement corresponding to the commanded rotation.
7. The infusion device of claim 6 , wherein:
the motor comprises a stepper motor;
the sensor comprises an incremental position sensor to detect incremental rotations of the rotor;
the measured displacement comprises a measured number of the incremental rotations after the motor is operated to provide the commanded rotation; and
the expected displacement comprises an expected number of the incremental rotations expected to be detected by the incremental position sensor after the motor is operated to provide the commanded rotation.
8. The infusion device of claim 1 , wherein the control module:
determines an observed value for a duty cycle metric based on the duty cycle; and
detects the occlusion condition when the observed value exceeds a reference value.
9. The infusion device of claim 8 , wherein the observed value comprises a derivative of the duty cycle.
10. The infusion device of claim 8 , wherein the observed value comprises an amount of change to the duty cycle over a preceding time interval.
11. An infusion device, comprising:
a stepper motor having a rotor;
a stopper mechanically coupled to the rotor, the stopper being displaced to deliver fluid via a fluid path in response to rotation of the rotor;
a modulation module coupled to the stepper motor, the modulation module generating a modulated voltage applied to the stepper motor, the modulated voltage oscillating between a supply voltage and a reference voltage, the modulated voltage being equal to the supply voltage for a percentage of a time interval, the percentage corresponding to a duty cycle; and
a control module coupled to the modulation module to adjust the duty cycle to achieve a commanded rotation of the rotor and detect an occlusion condition in the fluid path based on the duty cycle.
12. A system for detecting occlusion in a fluid path, the system comprising:
a motor having a rotor, rotation of the rotor resulting in delivery of fluid via the fluid path;
a modulation module coupled to the motor, the modulation module generating a modulated voltage applied to the motor, the modulated voltage oscillating between a first voltage and a second voltage, the modulated voltage being equal to the first voltage for a percentage of a time interval, the percentage corresponding to a duty cycle; and
a control module coupled to the modulation module to adjust the duty cycle to achieve a commanded rotation of the rotor and detect an occlusion condition in the fluid path based on the duty cycle.
13. The system of claim 12 , wherein the control module detects the occlusion condition in response to changes to the duty cycle indicative of an occlusion in the fluid path.
14. The system of claim 12 , wherein the control module detects the occlusion condition when a change to the duty cycle over a preceding time interval exceeds a reference value indicative of an occlusion in the fluid path.
15. The system of claim 12 , wherein the commanded rotation corresponds to an amount of fluid to be dispensed via the fluid path.
16. The system of claim 12 , further comprising a fluid reservoir in fluid communication with the fluid path, the fluid reservoir including a stopper coupled to the rotor, wherein rotation of the rotor displaces the stopper to deliver the fluid from the fluid reservoir via the fluid path.
17. The system of claim 12 , wherein the modulated voltage comprises a square wave having a magnitude equal to the first voltage for the percentage of the time interval and equal to the second voltage for a remaining percentage of the time interval.
18. The system of claim 12 , wherein the modulated voltage comprises a square wave, the duty cycle corresponding to a width of the square wave.
19. The system of claim 12 , wherein the first voltage is a supply voltage and the second voltage is a ground voltage.
20. The system of claim 19 , further comprising an energy source coupled to the modulation module, the energy source providing the supply voltage.
21. The system of claim 12 , wherein the control module:
determines an observed value for a duty cycle metric based on the duty cycle; and
detects the occlusion condition when the observed value exceeds a reference value.
22. The system of claim 21 , wherein the control module determines the observed value by determining a derivative of the duty cycle.
23. The system of claim 12 , further comprising a sensor to obtain a measured displacement that is influenced by rotation of the rotor, wherein the control module is coupled to the sensor to adjust the duty cycle in response to a difference between an expected displacement and the measured displacement, wherein the expected displacement is based on the commanded rotation of the rotor.
24. The system of claim 23 , wherein the commanded rotation is influenced by an amount of the fluid to be delivered via the fluid path.
25. The system of claim 23 , wherein the control module increases the duty cycle in response to the difference between the expected displacement and the measured displacement.