Method and apparatus for determining reverse rotation of a polyphase DC motor

A circuit for generating a reverse rotation signal in the operation of a polyphase dc motor having a plurality of driving coils, comprising:

• a comparator having a first input coupled to receive the back emf of one of said driving coils when in a floating state, having a second input coupled to a reference voltage, and having an output;
• circuitry for determining an anticipated direction in which said back emf will cross the reference voltage based upon a commutation sequence of the polyphase dc motor, and for producing a slope signal indicating the anticipated direction;
• and
• circuitry, having an input coupled to the output of the comparator and having an input coupled to receive the slope signal, for generating the reverse rotation signal responsive to a transition at the output of the comparator not corresponding to the anticipated direction indicated by the slope signal.

A circuit for operating a polyphase dc motor having a plurality of driving coils, comprising:

• a driver for applying drive signals to said driving coils;
• an incrementable sequencer for controlling said driver to apply said drive signals in a commutative sequence to said driving coils in which at least one of said coils is selected to float without drive signals during a portion of said commutative sequence;
• a back emf amplifier for amplifying the back emf on said selected at least one floating coil;
• circuitry for determining an anticipated direction the back emf on said selected at least one floating coil will cross a reference voltage;
• a reference voltage crossing detector for determining when the back emf on said selected at least one floating coil crosses the reference voltage from the anticipated direction;
• a synchronizing circuit to determine which of said plurality of coils should be said at least one floating coil and to connect said determined coil to said back emf amplifier;
• circuitry responsive to said reference voltage crossing detector to increment said sequencer in said commutative sequence;
• and circuitry responsive to said reference voltage crossing detector for producing a signal when said back emf of said selected at least one floating coil crosses the reference voltage in a direction other than the anticipated direction.

A method for operating a polyphase dc motor having a plurality of driving coils and having a rotor, comprising the steps of:

• determining the actual instantaneous position of the rotor of the motor by comparing the back emf of a coil to a reference voltage at a time when the coil is in a floating state and by detecting the direction in which the back emf of the coil crosses the reference voltage;
• generating a reference voltage crossing direction signal indicating the direction in which the back emf crosses the reference voltage;
• determining a desired rotor position precedent to executing a desired commutation sequence by generating an anticipated slope direction signal indicating the direction in which the back emf is anticipated to cross the reference voltage in the desired commutation sequence;
• executing said desired commutation sequence responsive to the actual instantaneous position of the rotor corresponding to the desired rotor position;
• comparing the signal indicating the anticipated slope direction signal to the reference voltage crossing direction signal;
• and
• generating a reverse rotation signal responsive to the anticipated slope direction signal not matching the reference voltage crossing direction signal.

A method for operating a polyphase dc motor having a plurality of driving coils, comprising:

• applying drive signals to said driving coils in a commutative sequence in which at least one of said coils is selected to float without drive signals during a portion of said commutative sequence;
• amplifying a back emf signal on said selected at least one floating coil;
• determining an anticipated direction that the back emf on said selected at least one floating coil will cross a reference voltage to provide an anticipated slope direction indicating signal;
• determining when the back emf on said selected at least one floating coil crosses the reference voltage to provide a reference voltage crossing indicating signal;
• and producing a signal when said back emf of said selected at least one floating coil crosses the reference voltage in a direction other than the anticipated direction.