Method and apparatus for operating polyphase dc motors

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;
• a reference voltage crossing detector for determining when the back emf on said selected at least one floating coil crosses a reference voltage;
• 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 mask circuitry to inhibit said detection circuitry from determining when the back emf on said at least one floating coil crosses a reference voltage for a predetermined mask time after said sequencer has been incremented.

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

• determining when a back emf of at least one coil at a time when said at least one coil is in a floating state prior to a desired commutation sequence crosses a reference voltage from a predetermined direction to determine the actual position of the rotor of the motor;
• determining a desired rotor position precedent to executing a desired commutation sequence;
• executing said desired commutation sequence when said circuit for determining the actual position of the rotor detects that the rotor is actually in the desired rotor position;
• inhibiting the detection of a reference voltage crossing of said back emf for a predetermined time after said back crosses a reference voltage by:
• providing an up counter and first and second down counters, the count of said second down counter enabling the detection of the reference voltage crossing;
• providing a source of clock pulses connected to clock said up and down counters;
• controlling said second down counter in relationship to the count of said first down counter;
• loading a count from said up counter into said first and second down counters when said reference voltage crossing detector detects a reference voltage crossing and then resetting said up counter.

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

• circuitry for determining the position of the rotor of the motor for determining a desired coil commutation sequence;
• a back emf amplifier switchably connected to individual coils when said individual coils are in a floating state;
• reference voltage crossing circuitry for determining when the output of said back emf amplifier crosses a reference voltage;
• delay circuitry for delaying a coil commutation operation for a predetermined delay period, said predetermined delay period being initiated by said reference voltage crossing circuitry when the output of said back emf amplifier crosses the reference voltage, said delay circuitry comprising:
• an up counter and a down counter;
• a source of clock pulses connected to clock said up and down counters;
• an output from said down counter being connected to inhibit said reference voltage crossing circuitry until a count in said down counter is reached;
• and
• means for loading a count from said up counter into said down counter and then for resetting said up counter when said reference voltage crossing circuitry detects a reference voltage crossing for selectively varying said predetermined delay period in dependence upon the speed of the rotor.