Adaptive brake timing for a brushless motor

1. A method performed by a drive circuit for a brushless motor that includes a rotor and a coil structure comprising at least one coil, the method comprising:

receiving a request to drive the rotor in a forward direction;

sensing a residual direction of the rotor;

sensing a residual speed of the rotor;

at least partially in response to the sensed residual direction being a reverse direction opposite the forward direction,

determining a time period as a function of the sensed residual speed, for applying a brake to the motor to slow the rotor,

applying the brake for the determined time period, and

after lapse of the determined time period, initiate driving the rotor to rotate in the forward direction.

2. The method of claim 1 , comprising, applying the brake electrically, by draining energy from the coil structure.

3. The method of claim 1 , comprising, applying the brake frictionally, by controlling a braking device to apply friction against the rotor or against a component fixed to the rotor.

4. The method of claim 1 , comprising, determining the time period as a function of the sensed residual speed, for applying a brake to the motor to stop the rotor.

5. The method of claim 1 , comprising, determining the time period as a function of the sensed residual speed, at least partially in response to both the sensed residual direction being the reverse direction and the sensed residual speed exceeding a predetermined non-zero threshold.

6. The method of claim 1 , comprising, determining the time period as a linear function of the sensed residual speed.

7. The method of claim 1 , comprising, determining the time period as proportional to the sensed residual speed.

8. The method of claim 1 , comprising, sensing the residual direction of the rotor at least partially based on identifying a sequence of outputs from magnetic-field sensors that sense a magnetic field generated by the rotor.

9. The method of claim 1 , comprising, sensing the residual direction of the rotor at least partially based on inductive position sensing.

10. The method of claim 1 , comprising, sensing the residual speed of the rotor at least partially based on an output of a magnetic field sensor.

11. The method of claim 7 , comprising, sensing the residual speed of the rotor at least partially based on an output of a Hall effect magnetic field sensor.

12. The method of claim 1 , comprising, sensing the residual speed of the rotor at least partially based on a back electromotive force (EMF) of the coil structure.

13. The method of claim 1 , comprising, after the lapse of the determined time period, initiating driving the rotor to rotate in the forward direction by applying a predetermined sequence of pulses to the coil structure.

14. The method of claim 1 , further comprising, after the lapse of the determined time period but before driving the rotor in the forward direction,

sensing a second residual speed of the rotor;

at last partially in response to the sensed second residual speed exceeding a threshold speed,

determining, as a function of the sensed second residual speed, a second time period for applying the brake, and

applying the brake for the determined second time period, wherein the initiating of driving the rotor is performed upon lapse of the second time period.

15. The method of claim 1 , further comprising:

determining the speed of the rotor during application of the brake by measuring induced current flowing through the coil structure.

16. A drive circuit for a brushless motor that includes a rotor and a coil structure comprising at least one coil, the drive circuit comprising:

an input configured to receive a request to drive the rotor in a forward direction;

a direction sense module configured to sense a residual direction of the rotor;

a speed sense module configured to sense a residual speed of the rotor; and

a processor configured to, at least partially in response to the residual direction being a reverse direction opposite the forward direction,

determine a time period, as a function of the speed, for applying a brake to the motor to slow the rotor,

apply the brake for the determined time period, and

after lapse of the determined time period, initiate driving the rotor in the forward direction.

17. The drive circuit of claim 16 , wherein the processor is configured to:

in response to the sensed residual speed being zero, apply a predetermined pulse sequence to the coil structure to accelerate the rotor using a first control scheme while the rotor speed is within a lower speed range and using a second control scheme while the rotor speed is within a higher speed range; and

in response to the sensed residual direction being forward direction and the sensed residual speed being within the higher speed range, start applying the predetermined pulse sequence of using the second control scheme instead of the first control scheme.

18. The drive circuit of claim 16 , wherein the processor is configured to determine the time period as a linear function of the sensed speed, and wherein the drive circuit is configured to enable a slope of the linear function to be programmable.

19. The drive circuit of claim 16 , further comprising:

at least one driver configured to be activated by the controller to apply the brake by draining energy from the coil structure.

20. A non-transitory data storage medium containing software instructions configured to be executed by a drive circuit to control a brushless motor that includes a rotor and a coil structure comprising at least one coil, by:

receiving a request to drive the rotor in a forward direction;

sensing a residual direction of the rotor;

sensing a residual speed of the rotor;

at least partially in response to the sensed residual direction being a reverse direction opposite the forward direction,

determining a time period as a function of the sensed residual speed, for applying a brake to the motor to slow the rotor,

applying the brake for the determined time period, and

after lapse of the determined time period, initiate driving the rotor to rotate in the forward direction.