Control system for regulating motor speed

Claim 2

A control system for regulating the speed of a motor having a rotatable rotor and windings that define poles of the motor, the control system comprising: a variable frequency drive that produces a drive signal that is provided to the windings of the motor to cause rotation of the rotor; speed means for providing a speed signal that indicates the actual speed of the rotor; monitor means for receiving the speed signal and generating monitor signals that indicate motor performance relative to a speed profile of desired :motor speed during operation of the motor; and control means for receiving the monitor signals and comparing the monitor signals with predetermined expected values, and for indicating a failure condition if an unexpected value is obtained and if the unexpected value persists for greater than a predetermined time interval.

Claim 3

A control system as defined in claim 1, wherein the monitor means generates monitor signals that indicate when the speed of the motor exceeds a minimum full speed, when the actual speed of the motor is below a maximum slow speed, and when the motor is properly decelerating.

Claim 4

A control system as defined in claim 1, wherein the control means generates command signals in response to the motor speed profile and the monitor signals, and wherein the command signals are provided to the variable frequency drive and determine the drive signal generated by the variable frequency drive.

Claim 5

A control system as defined in claim 3, wherein the control means restarts a timer count for an unexpected signal combination whenever the signal combination assumes an unexpected value.

Claim 6

A control system as defined in claim 4, wherein the monitor means generates monitor signals that indicate when the motor is exceeding a minimum full speed, when the motor is below a maximum slow speed, and when the motor is properly decelerating.

Claim 7

A control system as defined in claim 1, further including a contactor switch that connects and disconnects the motor from the drive signals produced by the variable frequency drive.

Claim 8

A control system as defined in claim 6, wherein the control means generates command signals in response to the motor speed profile and the monitor signals, and wherein the variable frequency drive receives the command signals and in response generates the drive signals, and the contactor switch receives the command signals and in response opens and closes.

Claim 9

A control system as defined in claim 7, wherein the monitor means generates monitor signals that indicate when the speed of the motor exceeds a minimum full speed, when the speed of the motor is below a maximum slow speed, and when the speed of the motor is within a decreasing ramp speed interval.

Claim 10

A control system as defined in claim 8, wherein the monitor means generates monitor signals comprising: a Ramping-Down-or-Stopped monitor signal that has a high value when the motor speed is within a decreasing ramp speed interval or when the motor speed is less than a maximum low speed, and has a low value otherwise; a Full-Speed monitor signal that has a high value when the motor speed is greater than a minimum Full-Speed and has a low value otherwise; and a Forward/Normal-Speed monitor signal that has a high value when the motor speed is greater than the maximum low speed value and is less than a maximum full speed value.

Claim 11

A control system as defined in claim 9, wherein the control means generates command signals that comprise: a Motor Run command signal that commands the variable frequency drive to generate motor drive signals; a Full-Speed command signal that is high when the control means determines that the motor should be driven at its full speed and has a low value when the control means determines that the motor should be driven at an intermittent speed; an Emergency Stop command signal that has a low value when the control means determines that the motor should be halted immediately, and has a high value when the control means determines that the motor should be provided with drive signals; and a Power-Disconnect command signal that is high when the control means determines that the motor should be provided with drive signals.

Claim 12

A control system as defined in claim 10, wherein the control means indicates a plurality of failure modes that comprise: a Motor-Failed-to-Run failure mode that is indicated if the Motor Run command signal has a low value and Contactor monitor signal has a high value and if this combination persists for greater than a predetermined time interval; a Motor-Failed-to-Stop failure mode that is indicated if the Motor Run command signal has a high value and the contactor monitor signal has a low value, and if this combination persists for greater than a predetermined time interval; a Motor-Failed-to-Run failure mode that is indicated if the Motor Run command signal has a low value, the Full-Speed command signal has a low value, and the Forward/Normal-Speed monitor signal has a high value, and if this combination persists for greater than a predetermined time interval; a Motor-Failed-to-Run-Full-Speed failure mode that is indicated if the Motor Run command signal has a low value, the Full-Speed command signal has a low value, and the Full-Speed monitor signal has a high value, and if this combination persists for greater than the time ordinarily necessary for the motor to reach full speed from a stopped condition; a Motor-Running-in-Reverse failure mode that is indicated if the Ramping-Down-or-Stopped monitor signal has a high value, the Full-Speed monitor signal has a high value, and the Forward/Normal-Speed monitor signal has a high value, and if this combination persists for greater than a predetermined input update time for the control means; a Motor-Running-Overspeed failure mode that is indicated if the Full-Speed monitor signal has a low value and the Forward/Normal-Speed monitor signal has a high value, and if this condition persists for greater than an input update time interval for the control means; a Motor-Failed-to-Decelerate failure mode that is indicated if the Motor Run command signal has a low value, the Full-Speed command signal has a high value, and the Ramping-Down-or-Stopped monitor signal has a high value, and if this combination of values persists for a time interval greater than is necessary for the speed means to indicate a reduction in motor speed from its full speed to its low speed; a Motor-Failed-to-Stop failure mode that is indicated if the Motor Run command signal is high and the Forward/Normal-Speed monitor signal is low, and if this combination of values persists for greater than a predetermined time interval in which the motor ordinarily can decrease from its full speed to its low speed; and a Motor-Failed-to-Accelerate failure mode that is indicated if the Motor Run command signal is low, the Full-Speed command signal is low, and the Ramping-Down-or-Stopped monitor signal is low, and if this combination of values persists for a time interval greater than the time it ordinarily takes for the motor to ramp up to full speed.

Claim 13

A control system as defined in claim 1, wherein the speed means comprises an electronic tachometer including: signal means for producing a current signal that corresponds to the current in at least one pole of the motor; filter means for removing frequency components of the current signal greater than a predetermined maximum value of the motor speed profile to provide a filtered signal; and pulse means for providing a pulse signal that indicates the frequency of the filtered signal.

Claim 14

A control system as defined in claim 12, wherein the filter means comprises a low-pass filter that filters out frequency components greater than approximately 75 Hz.

Claim 15

A control system as defined in claim 13, wherein the low-pass filter includes resistive and capacitive elements coupled to an amplifier element.

Claim 16

A control system as defined in claim 12, wherein the pulse means comprises a zero-crossing detector that produces a transition at each zero-crossing of the filtered signal.

Claim 17

A control system as defined in claim 15, wherein the zero-crossing detector comprises a resistive element coupled to an operational amplifier.

Claim 18

A control system as defined in claim 12, wherein the signal means comprises a current sensor that is coupled to one pole of the motor.

Claim 19

A control system for regulating the speed of a motor, comprising: an electronic tachometer coupled to the motor, said electronic tachometer producing a tachometer output that represents the speed of the motor; a monitor that receives said tachometer output and stores in memory a motor speed profile that represents desired motor speed during operation of the motor, said monitor comparing said tachometer output with said motor speed profile, and producing an error signal if a difference between said tachometer output and said motor speed profile exceeds predetermined expected values; and, a timer coupled to receive said error signal and that indicates a failure condition if an unexpected value is obtained and persists for greater than a predetermined time interval.

Claim 20

A control system for regulating the speed of a motor, comprising: an electronic tachometer coupled to the motor, said electronic tachometer producing a tachometer output that represents the speed of the motor; a monitor that receives said tachometer output and stores in memory a motor speed profile that represents desired motor speed during operation of the motor, said monitor comparing said tachometer output with said motor speed profile, and producing an error signal if a difference between said tachometer output and said motor speed profile exceeds predetermined expected values; and, a timer coupled to receive said error signal and that indicates a failure condition if an unexpected value is obtained and persists for greater than a predetermined time interval.

Claim 21

A control system according to claim 18, wherein: the motor has a rotor that rotates relative to windings that define poles of the motor; said electronic tachometer includes a detector coupled to one of the windings so as to produce a varying electronic signal representative of the motor's phase, and, a pulse circuit that is coupled to said detector to receive said varying electronic signal and that produces said tachometer output as a pulsed output signal having a first state when said varying electronic signal matches a predefined one of a voltage and current level and a different state when said varying electronic signal does not match said predefined one; said monitor determines the speed of the motor in dependence upon the frequency with which said tachometer output has said first state.

Claim 22

A control system for regulating the speed of a motor having a rotatable rotor and windings that define poles of the motor, said control system comprising: a variable frequency drive that produces a drive signal that is provided to the windings of the motor to cause rotation of the motor; a computer that controls operation of said variable frequency drive to run, accelerate, decelerate the motor within a predetermined motor speed profile; an electronic tachometer that electronically taps at least two windings of the motor and that produces at least one pulsed output signal that represents change of polarity of current of a phase of the motor and at least one output signal that indicates direction of rotation of the rotor; and control logic, coupled to receive said output signals from said electronic tachometer, that stores in memory a motor speed profile that represents desired motor speed during operation of the motor, including error bounds for each of desired acceleration and deceleration, compares motor speed to said motor speed profile that represents desired motor speed during operation of the motor, produces an error signal if a difference between said tachometer output and said motor speed profile exceeds said error bounds, and, indicates a failure condition an unexpected value is obtained and persists greater than a predetermined time interval.

Claim 23

A control system for regulating the speed of a motor having a rotatable rotor and windings that define poles of the motor, said control system comprising: a variable frequency drive that produces a drive signal that is provided to the windings of the motor to cause rotation of the motor; a computer that controls operation of said variable frequency drive to run, accelerate, decelerate the motor within a predetermined motor speed profile; an electronic tachometer that electronically taps at least two windings of the motor and that produces at least one pulsed output signal that represents change of polarity of current of a phase of the motor and at least one output signal that indicates direction of rotation of the rotor; and control logic, coupled to receive said output signals from said electronic tachometer, that stores in memory a motor speed profile that represents desired motor speed during operation of the motor, including error bounds for each of desired acceleration and deceleration, compares motor speed to said motor speed profile that represents desired motor speed during operation of the motor, produces an error signal if a difference between said tachometer output and said motor speed profile exceeds said error bounds, and, indicates a failure condition an unexpected value is obtained and persists greater than a predetermined time interval.