Motor control circuit for regulating a D.C. motor

• US 6,025,683 A
• Filed: 12/23/1998
• Issued: 02/15/2000
• Est. Priority Date: 12/23/1998
• Status: Expired due to Term

• Current Assignee: Stryker Corporation
• Original Assignee: Stryker Corporation
• Inventors: Philipp, Chris
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US09/220,167
• Time in Patent Office: 419 Days
• Field of Search: 318/139, 318/255, 318/256, 318/257, 318/268, 318/798-801, 318/807, 318/810, 318/811, 318/258, 388/937
• US Class Current: 318/257
• CPC Class Codes: H02P 7/2913 whereby the speed is regulated by measuring the motor speed and comparing it with a given physical value
• CPC Class Codes: Y10S 388/937 Hand tool

Abstract

A motor control chip (62) for asserting the control signals used to regulate the energization of the windings of a DC motor. The motor control chip includes a tachometer (94) that receives pulsed signals that vary with the rotation of the motor rotor and that produces a pulse width modulated tachometer signal as a function of the motor speed. A pulse width modulator (90) receives the tachometer signal and an analog signal representative of the user-selected motor speed. Based on the received input signals, the pulse width modulator produces a variable speed control signal. A forward/reverse oscillator (92) receives user-set signals indicating if the motor should be run in the forward or reverse directions or in an oscillatory pattern. Based on the received signals, the forward/reverse oscillator asserts a forward/reverse signal having an appropriate signal state or cycle. A motor decoder (98) receives the signals produced by the pulse width oscillator and the forward/reverse oscillator. The motor decoder then asserts the control signals that regulate when power switches selectively tie the motor windings to either a power source or ground.

Claims

1. A motor control circuit for regulating the speed of a motor having a rotor, a plurality of windings located around the rotor and configured to generate a pulsed signal representative of the rotational position of the rotor, said circuit comprising:

a tachometer for receiving the pulsed signal from the motor and producing a pulse width modulated TACHOMETER signal having an on duty cycle that is proportional to the frequency at which the pulsed signal is generated;

,

a pulse width modulator for receiving the TACHOMETER signal and a USER_-- SPEED signal representative of a user-selected speed, said pulse width modulator configured to generated a pulse width modulated SPEED_-- CONTROL_PWM signal that has an on-duty cycle proportional to the difference between an integral of the TACHOMETER signal and the USER_-- SPEED signal; and

a motor driver for receiving the pulsed signal from the motor and the SPEED_-- CONTROL_PWM signal for producing a plurality of HIGH_-- SIDE_-- CONTROL signals, each HIGH_-- SIDE_-- CONTROL signal being asserted to cause a separate one of the motor windings to be connected to a power source, and a plurality of LOW_-- SIDE_-- CONTROL signals, each LOW_-- SIDE_-- CONTROL signal being asserted to cause a separate one of the motor windings to be connected to ground, wherein the motor driver sequentially asserts the HIGH_-- SIDE_-- CONTROL signals and the LOW_-- SIDE_-- CONTROL signals as a function of the pulsed signal and the on-duty cycle of the SPEED_-- CONTROL_PWM signal.

2. The motor control circuit of claim 1, wherein said pulse width modulator includes:

an amplifier circuit for receiving the TACHOMETER signal and the USER_-- SPEED signal for producing an analog SPEED_-- CONTROL signal as a function of the difference between the USER_-- SPEED signal and the TACHOMETER signal; and

a convertor circuit for receiving the SPEED_-- CONTROL signal and producing the SPEED_-- CONTROL_PWM signal so that the SPEED_-- CONTROL_PWM signal has an on-period directly proportional to the magnitude of the SPEED_-- CONTROL signal.

3. The motor control circuit of claim 2, wherein:

said pulse width modulator includes a comparator for comparing the SPEED_-- CONTROL signal to a reference signal, and based on the comparison, said comparator asserts a BRAKE signal; and

said motor driver receives the BRAKE signal and is configured so that, upon receiving the BRAKE signal, said motor driver inhibits assertion of the HIGH_-- SIDE_-- CONTROL signals and asserts the LOW_-- SIDE_-- CONTROL signals to cause deceleration of the motor rotor.

4. The motor control circuit of claim 1, wherein:

the motor generates a plurality of pulsed signals representative of the rotational position of the motor rotor; and

said tachometer includes;

a pulse detection circuit receiving the pulsed signals and that produces a pulse train representative of the rise and fall of the pulse signals; and

a pulse generator for producing a train of constant width pulses as the TACHOMETER signal, said pulse generator being configured to receive the pulse train from said pulse detection circuit, said pulse generator configured to produce the constant width pulses forming the TACHOMETER signal at a frequency proportional to the frequency of the pulses forming the pulse train from said pulse detection circuit.

5. The motor control circuit of claim 4, wherein said pulse detection circuit includes:

a plurality of edge detector circuits, each said edge detector circuit being connected to receive a separate set of pulsed signals from the motor and to produce pulsed output signals based on the transitions of the received pulse signals; and

an adding circuit connected to said edge detector circuits for receiving the pulse output signals therefrom for producing the pulse train based on the sum of the pulsed output signals.

6. A direction control oscillator for generating motor control signals indicating if a motor rotor should operate in a forward state, a reverse state or oscillate between the forward and reverse states, said direction control oscillator including:

a first logic circuit connected to receive a first user-generated direction signal indicating that the motor should operate in the forward state and a second user-generated direction signal indicating that the motor should operate in the reverse state, said first logic circuit configured to generate a MOTOR_-- ENABLE signal when either the first user-generated direction signal or the second user-generated direction signal is received;

a second logic circuit connected to receive the first user-generated direction signal and the second user-generated direction signal, said second logic circuit configured to generate a FORWARD/REVERSE signal wherein;

when only the first user-generated direction signal is received, a FORWARD/REVERSE state signal is generated;

when only the second user-generated signal is received, a FORWARD/REVERSE state signal is generated; and

, when both the first and second user-generated direction signals are received, the FORWARD/REVERSE signal is cyclically transitioned between the FORWARD/REVERSE state signal and the FORWARD/REVERSE state signal; and

a third logic circuit connected to receive the first and second user-generated direction signals and the MOTOR_-- ENABLE signal, said third logic circuit configured to selectively forward the MOTOR_-- ENABLE signal or a MOTOR_-- ENABLE signal, wherein, when both the first and second user-generated direction signal are received, after each state transition of the FORWARD/REVERSE signal, said third logic circuit forwards the MOTOR_-- ENABLE signal for a select period of time before forwarding the MOTOR_-- ENABLE signal.

7. The direction control oscillator of claim 6, wherein said third logic circuit is connected to receive a TACHOMETER signal representative of rotor speed, and said third logic circuit is configured so that after each state transition of the FORWARD/REVERSE signal when both the first and second user-generated direction signals are received, said third logic circuit forwards the MOTOR_-- ENABLE signal until the TACHOMETER signal indicates the motor rotor has stopped turning and, after the TACHOMETER signal indicates that the motor rotor has stopped turning, said third logic circuit forwards the MOTOR_-- ENABLE signal.

8. The direction control oscillator of claim 6, wherein said third logic circuit is connected to receive a BRAKE_-- ENABLE signal and said third logic circuit is configured to generate a BRAKE_-- ON signal when said BRAKE_-- ENABLE signal is received and, when both the first and second user-generated direction signal are received, after each state transition of the FORWARD/REVERSE signal, said third logic circuit also generates the BRAKE_-- ON signal for a select period of time.

9. The direction control oscillator of claim 8, wherein, when said third logic circuit receives the first and second user-generated direction signals, said third logic circuit forwards the MOTOR_-- ENABLE signals and transmits the BRAKE_-- ON signal at the same time.

10. The direction control oscillator of claim 8, wherein said third logic circuit is connected to receive a TACHOMETER signal indicating if the motor rotor is turning, and said third logic circuit is configured so that when the first, and second user-generated direction logic signals are received, after each state transition of the FORWARD/REVERSE signal, said third logic circuit transmits the BRAKE_-- ON signal until the TACHOMETER signal indicates the motor rotor has stopped turning and, after the TACHOMETER signal indicates that the motor rotor has stopped turning, said third logic circuit transmits a BRAKE_-- ON signal.

11. A motor driver circuit for a motor having a plurality of windings and, a rotor, wherein the motor generates a plurality of pulsed signals that are representative of the rotational position of the rotor, said driver circuit including:

a first gate array for receiving the pulsed signals from the motor, a MOTOR_-- ENABLE signal indicating that the motor is to be actuated and a BRAKE_-- ON signal indicating that the motor is to be braked, said first gate array configured to sequentially assert a plurality of HIGH_-- DRIVER signals to cause the motor windings to be individually tied to a power supply when the MOTOR_-- ENABLE signal and a BRAKE_-- ON signal are received, wherein said first gate array sequentially asserts the HIGH_-- DRIVER signals based on the state of the pulsed signals;

a second gate array for receiving the pulsed signals from the motor, the MOTOR_-- ENABLE signal and a pulse width modulated SPEED_-- CONTROL signal, said second gate array configured to sequentially assert variable LOW_-- DRIVER signals that have a variable on duty-cycle to tie the motor windings to ground when the MOTOR_-- ENABLE signal is asserted, wherein said second gate array asserts the LOW_-- DRIVER signals individually based on the state of the pulsed signals, and so that the on duty-cycle of the LOW_-- DRIVER signals is a function of the duty cycle of the SPEED_-- CONTROL signal.

12. The motor driver circuit of claim 11, further including:

a brake circuit configured to receive the BRAKE_-- ON signal and the HIGH_-- DRIVER signals, said brake circuit being configured to assert a BRAKE_-- ACTUATE signal when the BRAKE_-- ON signal is asserted and the HIGH_-- DRIVER signals are not asserted; and

wherein said second gate array is configured to receive said BRAKE_-- ACTUATE signal and to simultaneously assert each said LOW_-- DRIVER signal when said BRAKE_-- ACTUATE signal is asserted.

13. The motor driver circuit of claim 11, further including:

a comparator for receiving a signal representative of current flow through the motor windings, said comparator configured to generate a CURRENT_-- LIMIT signal when the current flow through the windings exceeds a set amount;

a timer configured to receive the CURRENT_-- LIMIT signal and to assert a CURRENT_-- BLOCK signal for a set period of time after the CURRENT_-- LIMIT signal is received, and

wherein said second gate array is configured to receive said CURRENT_-- BLOCK signal and to inhibit assertion of the LOW_-- DRIVER signals when said CURRENT_-- BLOCK signal is received.

14. An integrated circuit for regulating the operation of a motor having a variable speed rotor, a plurality of windings that are selectively tied to a power source or ground, wherein the motor generates at least one pulsed signal representative of the rotational position of the rotor, said integrated circuit comprising:

a tachometer for receiving the pulsed signal from the motor said tachometer including;

a current source;

a switch array for selectively tieing a first capacitor to said current source or ground, wherein said switch array is configured to tie the capacitor to the current source for a fixed period of time after each pulsed signal is received; and

a first pulse generator connected to the first capacitor for producing TACHOMETER_PWM pulses as a function of the voltage across the capacitor;

a pulse width modulator including;

an amplifier having a first input to which integrated TACHOMETER_PWM pulses are applied, a second input to which an analog, user-set USER_-- SPEED signal is applied, said amplifier producing a SPEED_-- CONTROL signal as a function of the difference between the USER_-- SPEED signal and the integrated TACHOMETER_PWM pulses; and

a second pulse generator connected to the amplifier for receiving the SPEED_-- CONTROL signal, said second pulse generator configured to produce a pulsed SPEED_-- CONTROL_PWM signal, wherein the SPEED_-- CONTROL_PWM signal has an on duty-cycle proportional to the magnitude of the SPEED_-- CONTROL signal; and

a motor driver responsive to the SPEED_-- CONTROL_PWM signal and the pulsed signal from the motor for sequentially asserting HIGH_-- SIDE_-- CONTROL signals to tie the windings of the motor to a power source and variable on duty-cycle LOW_-- SIDE_-- CONTROL signals to tie the windings of the motor to ground, wherein, said motor driver sequentially asserts the HIGH_-- SIDE_-- CONTROL and the LOW_-- SIDE_-- CONTROL signals as a function of the pulsed signal and varies the on duty-cycle of the LOW_-- SIDE_-- CONTROL signals as a function of the on duty-cycle of the SPEED_-- CONTROL_PWM signal.

15. The integrated circuit of claim 14, further including:

a forward/reverse controller for receiving a user-set forward signal when the motor is to be run in a forward direction and a user-set reverse signal when the motor is to be run in a reverse direction, wherein, said forward/reverse controller is configured to assert a MOTOR_-- ENABLE signal when either the forward signal or the reverse signal is received and a FORWARD/REVERSE signal, the FORWARD/REVERSE signal being in a FORWARD/REVERSE signal state when the forward signal is received and in a FORWARD/REVERSE signal state when the reverse signal is received; and

wherein said motor driver receives the MOTOR_-- ENABLE signal and the FORWARD/REVERSE signal and is further configured to inhibit assertion of the HIGH_-- SIDE_-- CONTROL signals when a MOTOR_-- ENABLE signal is received and further regulates the sequence in which the HIGH_-- SIDE_-- CONTROL and the LOW_-- SIDE_-- CONTROL signals are asserted as a function of the state of the FORWARD/REVERSE signal.

16. The integrated circuit of claim 15, wherein said forward/reverse controller is configured so that, when both the user-set forward signal and the user-set reverse signal are received, said forward/reverse controller causes the FORWARD/REVERSE signal to cyclically transition between the FORWARD/REVERSE signal state and the FORWARD/REVERSE signal state.

17. An integrated circuit for regulating the operation of a motor having a rotor and a plurality of windings that are selectively tied to a power source or ground, said integrated circuit comprising:

a pulse width modulator for receiving a signal representative of the speed of the motor rotor and an analog, user-set USER_-- SPEED signal, said pulse width modulator configured to produce a pulse width modulated SPEED_-- CONTROL_PWM signal that has an on duty-cycle that varies as a function of the speed of the motor and the USER_-- SPEED signal;

a forward/reverse controller for receiving a user-set forward signal when the motor is to be run in a forward direction and a user-set reverse signal when the motor is to be run in a reverse direction, wherein, said forward/reverse controller is configured to assert a MOTOR_-- ENABLE signal when either the forward signal or the reverse signal is received and a FORWARD/REVERSE signal, the FORWARD/REVERSE signal being in a FORWARD/REVERSE signal state when the forward signal is received and in a FORWARD/REVERSE signal state when the reverse signal is received and, wherein;

when both the user-set forward signal and the user-set reverse signal are received, said forward/reverse controller causes the FORWARD/REVERSE signal to cyclically transition between the FORWARD/REVERSE signal state and the FORWARD/REVERSE signal state; and

said forward/reverse controller is further configured to receive a motor speed signal indicating if the motor rotor is turning and, when both the user-set forward signal and the user-set reverses signal are received, with each signal state transition of the FORWARD/REVERSE signal, said forward reverse controller asserts a MOTOR_-- ENABLED signal until the rotor speed signal indicates that the motor rotor has stopped turning; and

a motor driver responsive to the SPEED_-- CONTROL_PWM signal and a signal representative of the rotational position of the motor rotor for sequentially asserting HIGH_-- SIDE_-- CONTROL signals to tie the windings of the motor to a power source and LOW_-- SIDE_-- CONTROL signals that have a variable on duty-cycle to tie the windings of the motor to ground, wherein, said motor driver sequentially asserts the HIGH_-- SIDE_-- CONTROL and the LOW_-- SIDE_-- CONTROL signals as a function of the rotational position of the motor rotor and varies the on duty-cycle of the LOW_-- SIDE_-- CONTROL signals as a function of the on duty-cycle of the SPEED_-- CONTROL_PWM signal and wherein said motor driver receives the MOTOR_-- ENABLE signal and the FORWARD/REVERSE signal and is further configured to inhibit assertion of the HIGH_-- SIDE_-- CONTROL signals when a MOTOR_-- ENABLE signal is received and further regulates the sequence in which the HIGH_-- SIDE_-- CONTROL and the LOW_-- SIDE_-- CONTROL signals are asserted as a function of the state of the FORWARD/REVERSE signal.

18. The integrated circuit of claim 17, further including a tachometer circuit for receiving the signals representative of the rotational position of the rotor for generating a TACHOMETER signal representative of motor speed and, wherein, said pulse width modulator receives the TACHOMETER signal as the signal representative of the speed of the motor.

19. The integrated circuit of claim 18, wherein:

said tachometer circuit includes;

a current source;

a switch array for selectively tieing a first capacitor to said current source or ground, wherein said switch array is configured to tie the capacitor to the current source for a fixed period of time after each signal representative of motor rotor position is received; and

a first pulse generator connected to the first capacitor for producing TACHOMETER_PWM pulses as a function of the voltage across the capacitor; and

said pulse width modulator receives the TACHOMETER_PWM pulses as the TACHOMETER signal.

20. An integrated circuit for regulating the operation of a motor having a rotor and a plurality of windings that are selectively tied to a power source or ground, said integrated circuit comprising:

a pulse width modulator for receiving a signal representative of the speed of the motor rotor and an analog, user-set USER_-- SPEED signal, said pulse width modulator configured to;

produce a pulse width modulated SPEED_-- CONTROL_PWM signal that has a variable on duty-cycle that varies as a function of the speed of the motor and the USER_-- SPEED signal; and

to produce a BRAKE signal whenever the speed of the rotor is exceeding the user-set speed by a selected amount; and

a motor driver responsive to the SPEED_-- CONTROL_PWM signal, the BRAKE signal and a signal representative of the rotational position of the motor rotor for sequentially asserting HIGH_-- SIDE_-- CONTROL signals to tie the windings of the motor to a power source and LOW_-- SIDE_-- CONTROL signals that have a variable on duty-cycle to tie the windings of the motor to ground, wherein, said motor driver sequentially asserts the HIGH_-- SIDE_-- CONTROL and the LOW_-- SIDE_-- CONTROL signals as a function of the rotational position of the motor rotor and varies the on duty-cycle of the LOW_-- SIDE_-- CONTROL signals as a function of the on duty-cycle of the SPEED_-- CONTROL_PWM signal and wherein, when said motor driver receives the BRAKE signal, said motor driver selectively asserts and negates the HIGH_-- SIDE_-- CONTROL and the LOW_-- SIDE_-- CONTROL signals to cause braking of the motor rotor.

21. The integrated circuit of claim 20, wherein said motor driver is configured to cause the braking of the motor by inhibiting assertion of the HIGH_-- SIDE_-- CONTROL signals and simultaneously asserting a plurality of the LOW_-- SIDE_-- CONTROL signals.

22. The integrated circuit of claim 21, wherein said motor driver is further configured so that, while said HIGH_-- SIDE_-- CONTROL signals are being asserted, said motor driver inhibits the assertion of the plurality of the LOW_-- SIDE_-- CONTROL signals required to cause braking of the motor rotor.

23. The integrated circuit of claim 20, further including a tachometer circuit for receiving signals representative of the rotational position of the rotor for generating a TACHOMETER signal representative of motor speed and, wherein, said pulse width modulator receives the TACHOMETER signal as the signal representative of the speed of the motor.