Active deceleration circuit for a brushless DC motor
First Claim
1. A method of driving a brushless dc motor comprising the steps of:
- a. sensing a phase of a rotor of the motor;
b. applying current to windings of the motor according to a sequence of drive states for inducing a continuous torque on the rotor in a first direction of rotation of the rotor wherein each commutation from a current drive state to a next drive state occurs according to the phase of the rotor; and
c. skipping one commutation whereby a torque is induced on the rotor in a direction opposite the first direction.
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Accused Products
Abstract
A circuit for driving a brushless dc motor includes an active deceleration circuit for rapidly slowing the motor. A phase locked loop senses a position of the rotor for commutating from a drive state to a next drive state in a sequence of drive states at an appropriate time for maintaining torque on the rotor in the direction of rotation. Thus, the rotor "chases" the energized windings. A speed control loop controls current in the windings and, thus, motor speed. When the speed of the motor exceeds a desired speed by more than a threshold amount, rather than commutating to a next drive state in the sequence, the circuit skips a commutation. By skipping one commutation, the current drive state is maintained while the rotor continues to turn, due to its own inertia, such that the rotor "passes up" the current drive state. This results in a torque on the rotor in a direction opposite rotation. When the phase locked loop indicates an appropriate time for commutating to a next drive state, the circuit transitions to the next drive state in the sequence. Therefore, the current drive state continues to remain one commutation behind the normally appropriate drive state, maintaining the reverse torque. Accordingly, during deceleration, the energized windings "chase" the rotor. When the rotor slows sufficiently, the energized windings will "catch up" to the rotor such that the current drive state will be the appropriate drive state for again inducing a torque on the rotor in the direction of rotation.
66 Citations
27 Claims
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1. A method of driving a brushless dc motor comprising the steps of:
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a. sensing a phase of a rotor of the motor; b. applying current to windings of the motor according to a sequence of drive states for inducing a continuous torque on the rotor in a first direction of rotation of the rotor wherein each commutation from a current drive state to a next drive state occurs according to the phase of the rotor; and c. skipping one commutation whereby a torque is induced on the rotor in a direction opposite the first direction. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A circuit for driving a brushless dc motor, the circuit comprising:
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a. a phase locked loop for commutating to a next drive state in a sequence of drive states wherein a torque on a rotor of the motor is maintained in a direction of rotation; b. a speed control loop coupled to the phase locked loop for sensing a speed of the rotor for controlling a level of the torque; and c. a deceleration circuit coupled to the speed control loop for skipping exactly one commutation wherein the torque on the rotor is maintained in a direction opposite rotation after the speed of the rotor exceeds a desired speed. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16)
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17. A circuit for driving a brushless dc motor, the circuit comprising:
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a. means for sensing a rotational speed of the motor; b. means for forming a clock signal having a frequency related to the rotational speed wherein the means for forming is coupled to the means for sensing; c. means for commutating from a drive state to a next drive state in a sequence of drive states wherein each commutation corresponds to one pulse of the clock signal wherein the means for commutating is coupled to the means for forming; and d. means for blanking exactly one pulse of the clock signal when the rotational speed exceeds a desired speed by a predetermined amount wherein the means for blanking is coupled to the means for commutating. - View Dependent Claims (18, 19, 20, 21)
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22. A method of driving a brushless dc motor comprising the steps of:
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a. sensing a phase of a rotor of the motor; b. applying current to windings of the motor according to a sequence of drive states for inducing a torque on the rotor in a first direction of rotation of the rotor wherein each commutation from a current drive state to a next drive state occurs according to the phase of the rotor; and c. skipping one commutation whereby the phase of the rotor passes up the sequence of drive states and a torque is induced on the rotor in a direction opposite the first direction. - View Dependent Claims (23, 24)
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25. A method of driving a brushless dc motor comprising the steps of:
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a. sensing a phase of a rotor of the motor; b. applying current to windings of the motor according to a sequence of drive states for inducing a torque on the rotor in a first direction of rotation of the rotor wherein each commutation from a current drive state to a next drive state occurs according to the phase of the rotor; and c. skipping a commutation whereby a torque is induced on the rotor in a direction opposite the first direction and wherein when the torque is induced on the rotor in a direction opposite the first direction, the current in the windings is in a same direction as when inducing the torque on the rotor in the first direction. - View Dependent Claims (26)
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27. A circuit for driving a brushless dc motor, the circuit comprising:
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a. means for sensing a rotational speed of the motor; b. means for forming a clock signal having a frequency related to the rotational speed wherein the means for forming is coupled to the means for sensing; c. means for commutating from a drive state to a next drive state in a sequence of drive states wherein each commutation corresponds to one pulse of the clock signal wherein the means for commutating is coupled to the means for forming; and d. means for blanking a pulse of the clock signal when the rotational speed exceeds a desired speed by a predetermined amount wherein the means for blanking is coupled to the means for commutating, wherein the means for blanking comprises a one pulse blanking circuit having a first input, a second input and an output, wherein the clock signal is coupled to the first input, a signal applied to the second input has a first logic value when the rotational speed does not exceed the desired speed by the predetermined amount and a second logic value when the rotational speed does exceed the desired speed by the predetermined amount and wherein the output provides the clock signal except that when the second input transitions from the first logic value to the second logic value, one pulse of the clock signal is blanked.
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Specification