US 5,294,877 A · Circuit and method for detecting deceleration rates of a polyphase DC motor

Abstract

A circuit for operating a polyphase dc motor includes first circuitry for determining when the back emf of the floating driving coils crosses zero. A first counter counts a time period between a first set of zero crossings, and a second counter is loaded with the count reached by the first counter. The second counter counts a time period between a subsequently occurring set of zero crossings. If the second counter reaches zero before the occurrence of a third zero crossing, a warning signal is generated. A method for determining if a deceleration rate of a polyphase dc motor exceeds a predetermined threshold includes measuring a first period between a first set of zero crossings of the back emf of the floating driving coils, and comparing the measurement of the first period with a subsequent period between a subsequent set of zero crossings. If the subsequent period is larger than the first period by a predetermined amount a warning signal is produced. The first period is measured by counting up from zero at a first predetermined rate from a first zero crossing until a second zero crossing occurs. The comparison of the measurement of the first period with a subsequent period is done by counting down at a second predetermined rate from the count reached in the up count when the second zero crossing occurred. And the warning signal is produced if the down count reaches a zero before a third zero crossing occurs.

Claims22

Dependent claims

A circuit for determining if a deceleration rate of a polyphase de motor having a plurality of driving coils and a moving rotor exceeds a predetermined threshold, comprising:

a back emf detector to selectively produce a back emf signal from said driving coils when said driving coils are sequentially switched into a floating state;
a reference voltage crossing detector to determine when said back emf signal produced by said back emf detector crosses a reference voltage;
a pulse generator for producing first and second non-overlapping pulses when said reference voltage crossing detector determines that said back emf has crossed the reference voltage, said second pulse occurring after said first pulse;
an up counter connected to be reset by the second pulse produced by said pulse generator;
a down counter connected to be loaded with the count existent in said up counter by said first pulse from said pulse generator;
first and second clock pulse sources, the frequency of the first clock pulses being less than the frequency of said second clock pulses, the first and second clock pulses being delivered respectively to said up and down counters to be counted thereby;
a circuit connected to said down counter to determine if the down counter has reached a predetermined count prior to the occurrence of another reference voltage crossing subsequent to the reference voltage crossing that loaded the count of said up counter into said down counter.

4 more elements

A circuit for determining if a deceleration rate of a polyphase dc motor having a plurality of driving coils and a moving rotor exceeds a predetermined threshold, comprising:

a back emf detector to selectively produce back emf signals from said driving coils when said driving coils are sequentially switched into floating states;
a reference voltage crossing detector to determine when said back emf signals produced by said back emf detector cross a reference voltage;
a pulse generator for producing first and second non-overlapping pulses when said reference voltage crossing detector determines that said back emf has crossed the reference voltage, said second pulse occurring after said first pulse;
a first counter connected to be reset by the second pulse produced by said pulse generator;
a second counter connected to be loaded with the count existent in said up counter by said first pulse from said pulse generator;
first and second clock pulse sources, the frequency of the first clock pulses being less than the frequency of said second clock pulses, the first and second clock pulses being delivered respectively to said first and second counters to be counted thereby;
a circuit connected to said second counter to determine if the second counter has reached a predetermined count prior to the occurrence of another reference voltage crossing subsequent to the reference voltage crossing that loaded the count of said first counter into said second counter.

4 more elements

Dependencies are inferred from the claim text.

Circuit and method for detecting deceleration rates of a polyphase DC motor

Life of this patent

Circuit and method for detecting deceleration rates of a polyphase DC motor

Life of this patent

Abstract

Claims22