Overload prevention device for permanent magnet DC motors
A method, apparatus or computer program implements an overload prevention approach involving monitoring a speed of a motor; detecting an overload condition of the motor based on the monitored speed; and controlling an operation of the motor according to the detected overload condition.
1. A method comprising:
monitoring a speed of a motor;
detecting a load condition of the motor based on the monitored speed to determine the detecting comprising comparing the monitored speed to a first speed threshold and depending on the comparison calculating an average speed over time or over a number of speed measurements and determining whether the load condition exists or not based on a comparison of the calculated average speed to an average speed threshold; and
controlling an operation of the motor according to the detected load condition.
2. The method according to claim 1 , wherein the detecting operation detects the existence of the load condition when the calculated average speed is less than the average speed threshold which reflects a minimum operating speed.
3. The method according to claim 1 , wherein the first threshold or the average speed threshold is adjusted according to an input voltage and/or ambient temperature.
4. The method according to the claim 1 , wherein the monitoring operation generates a pulse having a pulse having a width that reflects a speed of the motor, and the comparing operation compares the width of the generated pulse to the first threshold.
5. The method according to claim 1 , wherein the monitoring operation generates pulses having widths that reflect a speed of the motor, and the comparison operation compares an average width of the plurality of generated pulses over a predetermined period or number of measurements to the average speed threshold to determine whether the load condition exists or not.
6. The method according to claim 1 , wherein the monitoring operation monitors the speed of the motor with a non-contact sensor configuration.
7. The method according to claim 6 , wherein the non-contact sensor configuration comprises a hall-effect device arranged to sense magnet field generated by a magnet connected to a shaft of the motor.
8. The method according to claim 6 , wherein the non-contact sensor configuration comprises an optical sensor.
9. The method according to claim 1 , wherein the controlling prevents operation of the motor while the load condition persists.
10. The method according to claim 1 , wherein the load condition comprises and end of stroke of the motor.
11. The method according to claim 1 , wherein the load condition comprises a mid stroke stall or overload.
12. An apparatus comprising:
a sensor for monitoring a speed of a motor;
a detector module for detecting a load condition of the motor based on the monitored speed to determine a stroke state of the motor, the detector module comparing the monitored speed to a first speed threshold and depending on the comparison calculating an average speed over time or over a number of speed measurements and determining whether the load condition exists or not based on a comparison of the calculated average speed to an average speed threshold;
a control module for controlling an operation of the motor according to the detected load condition.
13. The apparatus according to claim 12 , wherein the detector module detects the load condition when the calculated average speed is less than the average speed threshold, which reflects a minimum operating speed.
14. The apparatus according to claim 12 , wherein the first threshold or the average speed threshold is adjusted according to an input voltage and/or ambient temperature.
15. The apparatus according to claim 12 , wherein the sensor generates a pulse having a width that reflects a speed of the motor, and the detector module compares the width of the generated pulse to the first threshold.
16. The apparatus according to claim 12 , wherein the sensor generates pulses having widths that reflect a speed of the motor, and the detector module compares an average width of the plurality of generated pulses over a predetermined period or number of measurements to the average speed threshold to determine whether the load condition exists or not.
17. The apparatus according to claim 12 , wherein the sensor monitors the speed of the motor with a non-contact sensor configuration.
18. The apparatus according to claim 17 , wherein the non-contact sensor configuration comprises a hall-effect device that senses the magnetic field of a magnet connected to a shaft of the motor.
19. The apparatus according to claim 17 , wherein the non-contact sensor configuration comprises an optical sensor.
20. The apparatus according to claim 12 , wherein the controller module prevents operation of the motor while the load condition persists.
21. The apparatus according to claim 20 , further comprising a relay to turn off the motor when the load condition is detected based on a command from the controller module.
22. The apparatus according to claim 12 , further comprising a printed circuit board including the detector and controller modules.
23. A tangible computer medium having computer executable code which when executed by a processor performs the following method:
monitoring a speed of a motor;
detecting a load condition of the motor based on the monitored speed to determine a stroke state of the motor, the detecting comprising comparing the monitored speed to a first speed threshold and depending on the comparison calculating an average speed over time or over a number of speed measurements and determining whether the load condition exists or not based on a comparison of the calculated average speed to an average speed to an average speed threshold; and
controlling an operation of the motor according to the detected load condition.