Method and apparatus for braking a polyphase DC motor

• US 6,548,973 B1
• Filed: 01/08/1998
• Issued: 04/15/2003
• Est. Priority Date: 01/15/1997
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Jeffrey, Edward N., Chloupek, James E.
• Primary Examiner(s): SALATA, ANTHONY J
• Application Number:
  US09/004,399
• Time in Patent Office: 1,923 Days
• Field of Search: 318/375, 318/376, 318/466-470, 360/73.03, 360/74.1, 360/74.4, 360/74.6
• US Class Current: 318/375
• CPC Class Codes: G11B 19/06 by counting or timing of machine operations
• CPC Class Codes: G11B 19/20 Driving; Starting; Stopping; Control thereof
• CPC Class Codes: G11B 19/22 Brakes other than speed-regulating brakes

Abstract

A circuit (10) for braking a polyphase dc motor (12) includes a circuit (38) for producing an output signal indicating that the motor has slowed at least to an actual rotational speed and a braking circuit (42-44, 26-28) to brake the motor (12) when the output signal indicates that the motor has slowed at least to an actual rotational speed. The circuit (38) for producing an output signal indicating that the motor (12) has slowed at least to an actual rotational speed includes a first counter (70) for counting pulses of a speed signal, which may be a standard tach signal. The first counter (70) produces a first output when the first counter (70) reaches a first predetermined pulse count. A second counter (72) counts clock pulses from a clock generator (48) to produce a second output when the second counter (72) reaches a second predetermined pulse count. The first output is connected to restart the first (70) and second (72) counters, and the second output provides an indication when the frequency of the speed signal is lower than a desired ratio to the clock pulse frequency.

Claims

1. A method for braking a polyphase dc motor, comprising:

generating a speed signal indicating a spinning velocity of the motor;

upon a loss of power that energizes the motor, determining from the speed signal that the motor has slowed at least to an actual predetermined spinning velocity;

and activating a tach braking circuit to brake the motor by using clock pulses when the motor speed has been determined to have reached said predetermined spinning velocity.

2. The method of claim 1 wherein said step of determining from the speed signal that the motor speed has slowed at least to an actual predetermined spinning velocity comprises:

counting pulses of said speed indicating signal;

counting pulses of said clock pulses;

comparing said counted speed signal pulses and said counted clock pulses;

and generating a digital brake signal to activate said braking circuit when said counted clock pulses exceed said counted speed signal pulses.

3. The method of claim 2 further comprising restarting said counting pulses of said speed indicating signal and said counting pulses of said clock pulses if a number of said speed indicating pulses reaches a first predetermined number before a number of said clock pulses reaches a second predetermined number.

4. The method of claim 1 wherein said step of activating a braking circuit when the motor speed has been determined to have reached said predetermined spinning velocity comprises:

causing driver transistors for said motor to connect coils of said motor to a predetermined constant potential.

5. The method of claim 4 wherein said step of causing driver transistors for said motor to connect coils of said motor to a predetermined constant potential comprises causing driver transistors for said motor to connect coils of said motor to ground.

6. The method of claim 4 wherein said step of causing driver transistors for said motor to connect coils of said motor to a predetermined constant potential comprises causing driver transistors for said motor to connect coils of said motor to a supply voltage.

7. A circuit from braking a polyphase dc motor, comprising:

a circuit for producing an output signal indicating that said motor has slowed at least to an actual rotational speed;

and a tach braking circuit to brake said motor by using clock pulses when said output signal indicates that said motor has slowed at least to an actual rotational speed.

8. The circuit of claim 7 wherein said circuit for producing an output signal indicating that said motor has slowed at least to an actual rotational speed and said braking circuit are powered by a back-emf generated by said motor when power is disconnected.

9. The circuit of claim 7 wherein said circuit for producing an output signal indicating that said motor has slowed at least to an actual rotational speed comprises a circuit for comparing a frequency of a speed signal with a clock pulse frequency.

10. The circuit of claim 9 wherein said circuit for comparing a frequency of a speed signal with a clock pulse frequency comprises:

a first counter for counting pulses of said speed signal, said first counter producing a first output when said first counter reaches a first predetermined pulse count;

a second counter for counting said clock pulses, said second counter producing a second output when said second counter reaches a second predetermined pulse count;

said first output being connected to restart said first and second counters, and said second output providing an indication when said frequency of said speed signal is lower than a desired ratio to said clock pulse frequency.

11. The circuit of claim 7 wherein said braking circuit comprises circuitry to cause driver transistors for said motor to connect coils of said motor to a predetermined constant potential when said output signal provides an indication that said frequency of said speed signal is lower than said clock pulse frequency.

12. The circuit of claim 11 wherein said circuitry to cause driver transistors for said motor to connect coils of said motor to a predetermined constant potential comprises circuitry to cause driver transistors for said motor to connect coils of said motor to ground.

13. The circuit of claim 11 wherein said circuitry to cause driver transistors for said motor to connect coils of said motor to a predetermined constant potential comprises circuitry to cause driver transistors for said motor to connect coils of said motor to a supply voltage.

14. The circuit of claim 11 wherein said driver transistors are FET devices, and wherein said circuitry to cause driver transistors for said motor to connect coils of said motor to a predetermined constant potential comprises latches to apply a voltage to gates of said FET devices when said output signal provides an indication that said frequency of said speed signal is lower than a desired ratio to said clock pulse frequency.

15. A circuit for braking a polyphase dc motor, comprising:

a circuit for comparing a frequency of a speed signal with a clock pulse frequency and for producing an output signal to provide an indication when said frequency of said speed signal is lower than a desired ratio to said clock pulse frequency;

and a tach braking circuit to brake said motor by using clock pulses when said output signal provides an indication that said frequency of said speed signal is lower than said clock pulse frequency.

16. The circuit of claim 15 wherein said circuit for producing an output signal indicating that said motor has slowed at least to an actual rotational speed and said tach braking circuit are powered by a back-emf generated by said motor, when power is disconnected.

17. The circuit of claim 15 wherein said circuit for comparing a frequency of a speed signal with a clock pulse frequency comprises:

a first counter for counting pulses of said speed signal, said first counter producing a first output when said first counter reaches a first predetermined pulse count;

a second counter for counting said clock pulses, said second counter producing a second output when said second counter reaches a second predetermined pulse count;

said first output being connected to restart said first and second counters, and said second output providing an indication when said frequency of said speed signal is lower than a desired ratio to said clock pulse frequency.

18. The circuit of claim 15 wherein said tach braking circuit comprises circuitry to cause driver transistors for said motor to connect coils of said motor to a predetermined constant potential when said output signal provides an indication that said frequency of said speed signal is lower than a desired ratio to said clock pulse frequency.

19. The circuit of claim 18 wherein said circuitry to cause driver transistors for said motor to connect coils of said motor to a predetermined constant potential comprises circuitry to cause driver transistors for said motor to connect coils of said motor to ground.

20. The circuit of claim 18 wherein said circuitry to cause driver transistors for said motor to connect coils of said motor to a predetermined constant potential comprises circuitry to cause driver transistors for said motor to connect coils of said motor to a supply voltage.

21. The circuit of claim 18 wherein said driver transistors are FET devices, and wherein said circuitry to cause driver transistors for said motor to connect coils of said motor to a predetermined constant potential comprises latches to apply a voltage to gates of said FET devices when said output signal provides an indication that said frequency of said speed signal is lower than a desired ratio to said clock pulse frequency.