Method and apparatus for improving speed measurement quality in multi-pole machines

Abstract

A method and apparatus for improving the speed measurement quality in systems having multi-pole machines is taught. The method compensates for pole misalignment by moving average techniques.

1 . A method for use with multi-pole machines, said method comprising: 
 detecting a first time at which a first pole passes a first stator position;    detecting a second time at which a second pole passes the first stator position;    determining an elapsed time between the first and the second times;    recalling at least one historical elapsed time between the first and the second poles passing the first stator position;    calculating an average time based on the elapsed time and the at least one historical elapsed time; and    calculating a rotational quantity on the basis of the average time.    
   
   
       2 . The method of  claim 1 , wherein calculating a rotational quantity on the basis of the average comprises: 
 multiplying the average time by a number of poles.    
   
   
       3 . The method of  claim 1 , wherein the rotational quantity comprises at least one of an angular velocity and an angular acceleration.  
   
   
       4 . The method of  claim 3  wherein the angular velocity comprises at least one of radians per unit time, degrees per unit time, and revolutions per unit time.  
   
   
       5 . The method of  claim 3  wherein the angular acceleration comprises: 
 radians per unit time 2 , degrees per unit time 2 , and revolutions per unit time 2 .    
   
   
       6 . The method of  claim 1  wherein said detecting a first time at which a first pole passes a first stator position comprises: 
 starting a count upon detection of a first polarity pole by a first sensor held stationary relative to the stator.    
   
   
       7 . The method of  claim 6  wherein said detecting a second time at which a second pole passes the first stator position comprises: 
 stopping a count upon detection of a second polarity pole by the first sensor held stationary relative to the stator.    
   
   
       8 . The method of  claim 1  wherein said recalling at least one historical elapsed time between the first and the second poles passing the first stator position comprises: 
 recalling a number of historical elapsed times between the first and the second poles passing the first stator position sufficient to constitute at least a part of one mechanical rotation of a rotor.    
   
   
       9 . The method of  claim 1  further comprising: 
 controlling an electric motor responsive to the rotational quantity.    
   
   
       10 . A multi-pole machine system, said system comprising: 
 means for detecting a first time at which a first pole passes a first stator position and a second time at which a second pole passes the first stator position;    means for determining an elapsed time between the first and the second times;    means for recalling at least one historical elapsed time between the first and the second poles passing the first stator position;    means for calculating an average time based on the elapsed time and the at least one historical elapsed time; and    means for calculating a rotational quantity on the basis of the average time.    
   
   
       11 . The system of  claim 10 , wherein said means for calculating a rotational quantity on the basis of the average comprises: 
 means for multiplying the average time by a number of poles.    
   
   
       12 . The system of  claim 10 , wherein the rotational quantity comprises revolutions per unit time.  
   
   
       13 . The system of  claim 10  wherein said means for detecting a first time at which a first pole passes a first stator position and a second time at which a second pole passes the first stator position comprises: 
 means for starting a count upon detection of a first polarity pole by a first sensor held stationary relative to the stator.    
   
   
       14 . The system of  claim 10  wherein said means for detecting a first time at which a first pole passes a first stator position and a second time at which a second pole passes the first stator position comprises: 
 means for stopping a count upon detection, by a first sensor held stationary relative to the stator, of a second polarity pole.    
   
   
       15 . The system of  claim 10  wherein said means for recalling at least one historical elapsed time between the first and the second poles passing the first stator position comprises: 
 means for recalling a number of historical elapsed times between the first and the second poles passing the first stator position sufficient to constitute at least a part of one mechanical rotation of a rotor.    
   
   
       16 . The system of  claim 10  further comprising: 
 means for controlling an electric motor responsive to the rotational quantity.    
   
   
       17 . The system of  claim 16  further comprising: 
 an electric motor operably coupled to said means for controlling the electric motor; and    at least one of an automobile, a locomotive, an aircraft, and a watercraft operably coupled to said electric motor.    
   
   
       18 . An apparatus having a capability of determining a speed of a multi-pole, the apparatus comprising: 
 at least one magnetic pole position sensor positioned to detect a passing of each pole and configured to provide a pulse in a pulsed signal in response to each passing of each pole; and    a controller for measuring a time between a rising edge of one pulse and a rising edge of a next pulse in the pulsed signal and storing a total time in one revolution of a motor, the controller comprising a buffer for storing substantially all time values measured from pulse to pulse.    
   
   
       19 . The apparatus of  claim 18  wherein the controller is further comprised of a timer for measuring the time between the rising edges of one pulse and the next pulse.  
   
   
       20 . The apparatus of  claim 19  wherein the controller further comprises an overflow counter for extending the size of the timer.  
   
   
       21 . The apparatus of  claim 18  further comprising a buffer for storing all time values measured from pulse to pulse in the pulsed signal, wherein each time value measured is equivalent to the value of the counter multiplied by the extended value of the timer plus the value of the timer capture by an interrupt.  
   
   
       22 . The apparatus of  claim 18  wherein a sum total of all time values measured and stored in a buffer is substantially equivalent to a time to complete one revolution of the machine  
   
   
       23 . The apparatus of  claim 22  further comprising means for calculating a moving average speed measurement of the motor by inverting the sum total of all time values measured and multiplying a result of the inverting by a number of ticks of a timer over a prescribed period of time, thereby providing a motor frequency.  
   
   
       24 . The apparatus of  claim 18  further comprising: 
 an electric motor operably coupled to said controller and said at least one magnetic pole sensor; and    at least one of an automobile, a locomotive, an aircraft, and a watercraft operably coupled to said electric motor.