Current sensing module for a variable speed AC motor drive for use with a treadmill

• US 5,747,955 A
• Filed: 09/19/1997
• Issued: 05/05/1998
• Est. Priority Date: 03/31/1995
• Status: Expired due to Fees

• Current Assignee: BowFlex, Inc.
• Original Assignee: Quinton Instrument Co. (Cardica Incorporated)
• Inventors: Pipinich, Victor, Rotunda, John T., Hass, Lester A.
• Primary Examiner(s): Wysocki, Jonathan
• Application Number:
  US08/934,044
• Time in Patent Office: 228 Days
• Field of Search: 318/432, 318/434, 318/798-815, 388/903, 388/904, 388/930, 361/23, 361/30, 361/31, 361/42-50, 361/51, 361/87, 361/93, 361/94-97, 482/4, 482/6, 482/7, 482/54
• US Class Current: 318/434
• CPC Class Codes: A63B 22/025 electrically, e.g. D.C. motors with variable speed control
• CPC Class Codes: H02H 7/0833 for electric motors with control arrangements
• CPC Class Codes: H02P 27/047 V/F converter, wherein the voltage is controlled proportionally with the frequency
• CPC Class Codes: H02P 27/08 with pulse width modulation

Abstract

A current sensing module for use with a variable speed AC motor control drive system for use with devices such as treadmills and including a module to sense the current of pulse width modulated signals provided to an AC motor wherein the current sensing module includes a fast sense circuit to sense excessive current conditions in the pulse width modulated signals and a slow sense circuit to sense average current values in excess of desired values over a predetermined period of time to protect the AC motor from damage caused by the increased frictional resistance to the rotation of the walk belt on the treadmill deck as the walk belt and treadmill deck wear out.

Claims

1. An AC drive motor system for a treadmill having a microprocessor module, predriver module and driver module therein to provide pulse width modulated signals to a drive motor and a current sensing circuit therein, the circuit including;

a fast sense circuit for detecting the occurrence of a first current in excess of a predetermined value for an AC drive motor system to prevent rapid damage to said AC drive motor system wherein said fast sense circuit senses the current of pulse width modulated signals between the driver module and the drive motor wherein said signals have controlled cycles and when said current of said sensed signal is greater than a predetermined threshold, said fast sense circuit sends a fault signal to said predriver module to close a switch for the remainder of said cycle of said sensed signal; and

a slow sense circuit to detect the occurrence of a second current in excess of a predetermined value which is caused by a gradual fault condition wherein said fault condition results from the increased frictional resistance to the rotation of the walk belt of a treadmill on a treadmill deck.

2. The current sensing circuit of claim 1 wherein the slow sense circuit monitors the average current value of the current supplied to an AC motor over a predetermined time period such that when the average current value exceeds a preselected motor current rating for said AC motor, the sensing circuit shuts down said AC drive motor system to prevent damage to said AC motor by sending a fault signal to the microprocessor.

3. The current sensing circuit of claim 2 wherein said slow sense circuit filters out transient current values which exceed said preselected motor current rating and which do not trigger the fast sense circuit to prevent the inadvertent shut down of said AC drive motor system.

4. The current sensing circuit of claim 1 wherein said slow sense circuit and said fast sense circuit monitor the current of pulse width modulated signals supplied to said AC motor by the driver module.

5. The current sensing circuit of claim 4 wherein said pulse width modulated signals are formed by a pulse width modulated signal generator.

6. The current sensing circuit of claim 5 wherein said slow sense circuit and said fast sense circuits monitor three phases of pulse width modulated signals to said AC motor.

7. The current sensing circuit of claim 1 wherein said slow sense circuit and said fast sense circuit generate signals which are received by a microprocessor module as a fault signal to cause the shut down of said AC drive motor system until said AC drive motor system is reset if further faults are received.

8. The current sensing circuit of claim 1 wherein said slow sense circuit and said fast sense circuit generate further signals which are received by a controller module as a fault signal to notify the user of the shut down of said AC drive motor system.

9. The current sensing circuit of claim 1 wherein said slow sense circuit and said fast sense circuit generate signals which are in addition to a voltage dissipation circuit having voltage dissipation circuitry to dissipate excess bus voltage in said AC drive motor system.

10. An AC drive motor system for a treadmill having a current sensing circuit therein, the circuit including

a fast sense circuit for detecting the occurrence of a first current of a pulse width modulated signal in excess of the predetermined value for an AC drive motor system to prevent damage to said AC drive motor system wherein said fast sense circuit sends a fault signal to a predriver module to shut down a switch for the remainder of the cycle of said sensed first current of said pulse width modulated signal;

and

a slow sense circuit which monitors the average current value between a driver module and the AC motor of said AC drive motor system to detect the occurrence of a gradual fault condition where the average current exceeds a predetermined value over a predetermined period of time and wherein said average current value is less than said predetermined value for said fast sense circuit.

11. The AC drive motor system of claim 10 wherein said slow sense current senses the increase in operating current required by said AC motor as a result of increased frictional resistance to the rotation of the walk belt of the treadmill over the treadmill deck.

12. The AC drive motor system of claim 10 wherein said fast sense circuit senses is triggered by current values in excess of 20 A.

13. The AC drive motor system of claim 10 wherein said slow sense circuit senses is triggered by current values in excess of 7.5 A.

14. The AC drive motor system of claim 10 wherein said fast sense circuit includes a differential amplifier.

15. The AC drive motor system of claim 10 wherein said slow sense circuit responds in the range of seconds and the response of said fast sense circuit is less than one second.

16. The current sensing circuit of claim 10 wherein said slow sense circuit and said fast sense circuit monitor the current of said pulse width modulated signals between said driver module of said AC drive motor system and said AC motor to determine if said sensed currents as sensed by said slow sense circuit and said fast sense circuit are above certain different predetermined thresholds.

17. The current sensing circuit of claim 10 further including a filter of approximately 3 Hz therein to remove the noise caused by footfalls of a user.

18. A method of detecting the presence of potentially damaging over current situations with an AC motor having a variable speed drive motor controller system comprising the steps of:

providing a DC current to the system;

pulse width modulating the DC current to produce a drive signal which appears to an AC motor as an alternating current signal of a predetermined frequency and voltage;

sensing the current of the drive signal with a slow sense circuit and a fast sense circuit wherein the slow sense circuit monitors the average current value over a predetermined period of time and the fast sense circuit monitors the non-averaged value of the current supplied to the AC motor and the fast sense circuit sends a first fault signal to a first portion of the system to discontinue the remainder of the cycle of the sensed signal and wherein a further fault signal is sent to another portion of the system by the fast sense circuit to shut down the AC motor when multiple fault signals are generated by the fast sense circuit.

19. The method of claim 18 wherein a fault signal is generated by the slow sense circuit when the average current value exceeds a predetermined value over a predetermined period of time and the fault signal generated by the slow sense circuit causes the system to shut down the AC motor.

20. The method of claim 19 wherein the fast sense circuit generates said fault signals in response to the sensing of a current in excess of a predetermined current value which is greater than the average current value which generates a fault signal from the slow sense circuit.

21. The method of claim 20 wherein the fault signals generated by the fast sense circuit and the slow sense circuits are received by a predriver module and a microprocessor module.