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;
• a drive signal supply circuit for supplying drive signals to said driver, said drive signal supply circuit including circuitry for selectively removing all drive signals from said driver;
• an incrementable sequencer for generating commutative sequence signals for delivery to said drive signal supply circuit for application to said driving coils, said commutative sequence signals operative to cause each of said coils to selectively float without drive signals during a portion of said commutative sequence;
• an internal commutation bus to receive the commutation sequence signals from said incrementable sequencer prior to said drive signal supply circuit;
• a back emf amplifier for amplifying the back emf on said selected floating coil;
• a zero crossing detector for determining when the back emf on said selected floating coil crosses zero;
• a synchronizing circuit connected to receive said sequence signals from said internal commutation bus for determining which of said plurality of coils should be floating and to connect said determined coil to said back emf amplifier;
• circuitry responsive to said zero 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 floating coil crosses zero 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 the back emf of at least one coil at a time when said at least one coil is in a floating state prior to said desired commutation sequence crosses zero 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, based upon sequence signals at an output of a sequence generating circuit;
• executing said desired commutation sequence when said circuit for determining the actual instantaneous position of the rotor detects that the rotor is actually in the desired rotor position;
• inhibiting the detection of a zero crossing of said back emf for a predetermined time after said back crosses zero;
• providing an up counter and first and second down counters,
• providing a source of clock pulses connected to clock said up and down counters;
• inhibiting said clock pulses to said second down counter until said first down counter has reached a predetermined count;
• loading a count from said up counter into said first and second down counters when said zero crossing detector detects a zero crossing and then resetting said up counter.

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

• a sequence generator for generating sequence signals at an output, said sequence signals for driving said driving coils in a predetermined commutation sequence;
• a drive signal supply circuit for supplying drive signals for application to the driving coil;
• an internal commutation bus to receive the commutation sequence signals from said sequencer prior to said drive signal supply circuit;
• circuitry for determining the position of the rotor of the motor;
• a back emf amplifier switchably connected in accordance with said sequence signals at said output of said sequence generator to individual coils when said individual coils are in a floating state;
• zero crossing circuitry for determining when the output of said back emf amplifier crosses zero in response to said sequence signals;
• mask circuitry for inhibiting said zero crossing circuitry for a predetermined time after a change of commutation sequence, said mask 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 zero 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 sad up counter when said zero crossing circuitry detects a zero crossing to vary the predetermined time of said mask circuitry in dependence upon the speed of the rotor.