Encoder Eccentricity Correction for Motion Control Systems

Abstract

Correction of rotary encoder eccentricity in an image forming device having a motor controller using period and position pulse train feedback signals. A motor includes an encoder disc rotating with the motor and at least two encoder sensors disposed at different circumferential positions about the encoder disc. A controller may use a high speed clock to calculate a corrected speed count based on speed counts determined from the number of clock cycles that elapse per cycle of pulse trains from the encoders. The controller may also calculate a corrected position count based at least partly on one or more position counts determined from the number of clock cycles that elapse between periodic sampling points and transitions of encoder pulse trains. The corrected position count may also be calculated based on a position count and one or more speed counts.

1 - 21 . (canceled) 
   
   
       22 . An apparatus comprising:
 a motor having an encoder disc operatively coupled thereto, the encoder disc rotating in conjunction with the motor;   a first encoder sensor disposed at a first circumferential position about the encoder disc, the first encoder sensor generating a first pulse train indicative of the speed of the encoder disc;   a second encoder sensor disposed at a second circumferential position about the encoder disc, the second circumferential position being different than the first circumferential position, the second encoder sensor generating a second pulse train indicative of the speed of the encoder disc;   a clock generator operative to generate a periodic clock signal having a frequency greater than the first and second pulse trains; and   a controller operative to generate a plurality of sampling points, the controller further operative to calculate a corrected position count based upon a number of cycles of the periodic clock signal that elapse between one of the plurality of sampling points and a transition of the first pulse train.   
   
   
       23 . The apparatus of  claim 22  wherein the controller is further operative to calculate a corrected speed count based at least partly upon an average of a number of cycles of the periodic clock signal that elapse per cycle of the first and the second pulse trains. 
   
   
       24 . The apparatus of  claim 23  wherein the first encoder sensor and the second encoder sensor are disposed substantially 180 encoder disc degrees apart from one another. 
   
   
       25 . The apparatus of  claim 22  wherein the controller is further operative to generate a plurality of second sampling points, the controller further operative to calculate the corrected position count based at least partly on an average of: the number of cycles of the periodic clock signal that elapse between one of the plurality of sampling points and the transition of the first pulse train, and a number of cycles of the periodic clock signal that elapse between one of the plurality of second sampling points and a transition of the second pulse train. 
   
   
       26 . The apparatus of  claim 25  wherein the first encoder sensor and the second encoder sensor are disposed substantially 180 encoder disc degrees apart from one another. 
   
   
       27 . The apparatus of  claim 22  further comprising a third encoder sensor disposed at a third circumferential position about the encoder disc, the third encoder generating a third pulse train indicative of the speed of the motor. 
   
   
       28 . The apparatus of  claim 27  wherein the controller is further operative to calculate the corrected position count based at least partly on a number of cycles of the periodic clock signal that elapse per cycle of the first, second, and third pulse trains. 
   
   
       29 . The apparatus of  claim 28  wherein the first encoder sensor and the second encoder sensor disposed substantially 180 encoder disc degrees apart from one another and the third encoder sensor is disposed to lag the first encoder sensor and lead the second encoder sensor by substantially 90 encoder disc degrees. 
   
   
       30 . The apparatus of  claim 22  wherein the encoder disc is operatively coupled to a photosensitive unit. 
   
   
       31 . An apparatus, comprising:
 a motor;   an encoder operatively coupled to the motor;   a first encoder sensor associated with the encoder, the first encoder sensor generating a first pulse train indicative of the speed of the encoder disc;   a clock generator operative to generate a periodic clock signal having a frequency greater than a frequency of the first pulse train; and   a controller operative to generate a plurality of sampling points, the controller further operative to calculate a corrected position count based upon a number of cycles of the periodic clock signal that elapse between one of the plurality of sampling points and a transition of the first pulse train, and adjusting a speed of the motor based upon the corrected position count.   
   
   
       32 . The apparatus of  claim 31 , further comprising:
 a second encoder sensor associated with the encoder and positioned relative to the first encoder sensor, the second encoder sensor generating a second pulse train indicative of the speed of the encoder disc;   wherein the controller calculates a corrected speed count by averaging a first speed count and a second speed count, the first speed count and the second speed count determined by counting a number of cycles of the clock signal that elapse per cycle of pulse trains received from first and second encoder sensors, respectively, adjusts the speed of the encoder and maintains a substantially constant value for the corrected speed count to effect speed control.   
   
   
       33 . The apparatus of  claim 32 , wherein the corrected position count is calculated based at least partly upon a ratio of a position count error and speed count error, the position count error being relative to the number of cycles of the periodic clock signal that elapse between the one of the sampling points and the transition of the first pulse train and the speed count error being relative to the corrected speed count. 
   
   
       34 . The apparatus of  claim 31 , further comprising a second encoder sensor disposed at a circumferential position about the encoder that is different from a circumferential position of the first encoder sensor, the second encoder sensor generating a second pulse train indicative of the speed of the encoder disc, wherein the controller is operative to generate a plurality of second sampling points and calculate the corrected position count based upon a number of cycles of the clock signal that elapse between a second sampling point and a transition of the second pulse train. 
   
   
       35 . The apparatus of  claim 34 , wherein the first and second encoder sensors are disposed on the encoder substantially 180 rotary degrees apart from one another. 
   
   
       36 . The apparatus of  claim 34 , further comprising a third encoder sensor associated with the encoder and disposed relative to the first and second encoder sensors, the third encoder sensor generating a third pulse train indicative of the speed of the encoder disc, wherein the controller calculates the corrected position count based on number of cycles of the clock signal that elapse per cycle of the first, second and third pulse trains. 
   
   
       37 . An apparatus, comprising:
 a motor;   an encoder operatively coupled to the motor;   a first encoder sensor associated with the encoder, the first encoder sensor generating a first pulse train indicative of the speed of the encoder disc;   a second encoder sensor associated with the encoder and positioned relative to the first encoder sensor, the second encoder sensor generating a second pulse train indicative of the speed of the encoder disc;   a clock generator operative to generate a periodic clock signal having a frequency greater than a frequency of the first and second pulse trains; and   a controller operative to determine a first speed count and a second speed count by counting a number of clock cycles that elapse per cycle of the first and second pulse trains, respectively, to determine a first position count by counting a number of clock cycles that elapse between a periodic command pulse and a transition of the first pulse train, to calculate a corrected speed count based upon the fist and second speed counts, to calculate a corrected position count based on the first position count, and to adjust a speed of the motor based upon the corrected speed count and the corrected position count.   
   
   
       38 . The apparatus of  claim 37 , wherein the controller further calculates a second position count by counting a number of clock cycles that elapse between a second periodic command pulse and a transition of the second pulse train, wherein the corrected position count is calculated based upon the second position count.