Method to reduce midrange resonance during operation of a multi-phase step motor

Abstract

The frequency of the pulse width modulator within a step motor control circuit is increased above a base frequency under defined conditions to enable more accurate construction of the phase current waveform for reducing mid-range resonance. The PWM frequency is stepped between frequencies by a fixed amount above the base frequency, to reduce the excitation of system harmonics and prevent step motor operational instability.

1 . A method for reducing midrange resonance in a step motor system comprising: 
 determining a present operating frequency of a pwm oscillator within a motor controller circuit;    comparing said present operating frequency to a predetermined pwm oscillator base frequency; and    increasing said present pwm oscillator operating frequency above said predetermined pwm oscillator base frequency when said present operating frequency is below said predetermined pwm oscillator base frequency and decreasing said present pwm oscillator operating frequency when said present pwm oscillator operating frequency is above base frequency to thereby improve creation of phase current within said motor controller circuit;    
   
   
       2 . (canceled)  
   
   
       3 . The method of  claim 1  wherein said present pwm oscillator operating frequency defines a signal having a front slope.  
   
   
       4 . The method of  claim 3  wherein said present operating frequency is determined upon occurrence of said front slope signal.  
   
   
       5 . The method of  claim 3  wherein said pwm oscillator frequency is adjusted upon cessation of said front slope signal.  
   
   
       6 . A method for reducing midrange resonance in a step motor system comprising: 
 synchronizing a pwm oscillator signal within a motor controller circuit to a step motor operating current waveform generated by said controller circuit to thereby prevent interaction between an input signal to said motor controller circuit and said pwm oscillator signal thereby reducing midrange step motor operating current resonance.    
   
   
       7 . A circuit for constructing a phase current waveform in a step motor comprising: 
 a set point generator connecting with a pwm oscillator for providing front-slope and sign data to said pwm oscillator;    a bridge control logic connecting with said pwm oscillator and an H bridge, said bridge control logic-arranged for providing a step motor operating current defining an operating current waveform, for connecting a pwm signal with said step motor bridge control logic, for determining a pwm frequency during a portion of said operating current waveform, for decreasing said pwm frequency when said pwm frequency exceeds a predetermined value, for increasing said pwm frequency when said frequency is less than said predetermined value, and    synchronizing said pulse width modulator to said step motor operating current thereby controlling step motor phase current through said H bridge to a step motor coil to thereby reduce occurrence of system harmonics of said step motor phase current.    
   
   
       8 . (canceled)