Position feedback device with prediction

• US 7,456,599 B2
• Filed: 05/31/2005
• Issued: 11/25/2008
• Est. Priority Date: 05/31/2005
• Status: Active Grant

• Current Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: Quan, Juntao, Piefer, Richard W., Rehm, Thomas J.
• Primary Examiner(s): Ro; Bentsu
• Application Number:
  US11/141,596
• Publication Number:
  US 20060267529A1
• Time in Patent Office: 1,274 Days
• Field of Search: 318/432, 318/565, 318/569, 318/603, 318/605, 318/609, 318/610, 318/618, 318/625, 318/626, 318/638, 318/41, 318/66, 318/77, 318/85
• US Class Current: 318/625
• CPC Class Codes: B41F 13/004 Electric or hydraulic features of drives
• CPC Class Codes: B41P 2213/734 each printing unit being driven by its own electric motor, i.e. electric shaft
• CPC Class Codes: G05B 19/232 with speed feedback only
• CPC Class Codes: G05B 2219/37181 Encoder delivers sinusoidal signals
• CPC Class Codes: G05B 2219/37436 Prediction of displacement, relative or absolute, motion
• CPC Class Codes: G05B 2219/45187 Printer
• CPC Class Codes: G05B 2219/50218 Synchronize groups of axis, spindles

Abstract

An apparatus for use with an encoder feedback device includes a comparator, a counter, and a prediction unit. The encoder feedback device is coupled to rotate with a rotating load and operable to generate at least one feedback position signal indicative of movement of the rotating load. The comparator is operable to receive the feedback position signal and generate a first position signal including a plurality of edges based on the feedback position signal. The counter is operable to receive the first position signal and count the edges to periodically generate position values at a predetermined update interval. The prediction unit is operable to receive a position data request at a first time and predict a position of the rotating load at the first time as a function of at least a subset of the position values generated prior to the first time and a misalignment between the first time and the predetermined update interval to generate an aligned position signal.

Claims

1. An apparatus for use with an encoder feedback device coupled to rotate with a rotating load and operable to generate at least one feedback position signal indicative of movement of the rotating load, comprising:

a comparator operable to receive the feedback position signal and generate a first position signal including a plurality of edges based on the feedback position signal;

a counter operable to receive the first position signal and count the edges to periodically generate position values at a predetermined update interval; and

a prediction unit operable to receive a position data request at a first time and predict a position of the rotating load at the first time as a function of at least a subset of the position values generated prior to the first time and a misalignment between the first time and the predetermined update interval to generate an aligned position signal.

2. The apparatus of claim 1, wherein the counter is operable to generate a course component of the position values based on the counted edges, and the apparatus further comprises an incremental position estimator operable determine a fine component of the position values based on the feedback position signal generated by the encoder.

3. The apparatus of claim 2, wherein the feedback position signal comprises a first channel signal and a second channel signal, and the incremental position estimator is operable to calculate a ratio between the first channel signal and the second channel signal, and determine the fine component based on the arctangent of the ratio.

4. The apparatus of claim 1, wherein the subset includes the two most recent position values, and the prediction unit is operable to determine a velocity of the motor as a function of the two most recent position values and the predetermined update interval and predict the position of the motor based on the most recent position value and the determined velocity.

5. The apparatus of claim 4, wherein the prediction unit is operable to multiply the determined velocity by the difference between the first time and the predetermined update interval to determine a position offset and add the position offset to the most recent position value to generate the predicted position.

6. The apparatus of claim 1, further comprising a position regulator operable to receive the aligned position signal and a reference position signal and control the motor based on the difference between the reference position signal and the predicted position signal.

7. The apparatus of claim 1, further comprising:

a velocity filter and operable to receive the aligned position signal and generate a feedback velocity signal based on the aligned position signal; and

a velocity regulator operable to receive the feedback velocity signal and a reference velocity signal and control the motor based on the difference between the reference velocity signal and the feedback velocity signal.

8. An electronic line shaft, comprising:

a signal source operable to generate a reference velocity signal;

a virtual encoder coupled to the signal source and operable to generate a reference position signal based on the reference velocity signal; and

a master drive unit operable to receive the feedback position signal, the reference velocity signal, and the reference position signal, comprising;

a motor;

a first encoder associated with the motor to generate at least one feedback position signal indicative of rotation of the motor;

a motor controller operable to provide a torque input signal to the motor;

a feedback unit, comprising;

a comparator operable to generate a first position signal including a plurality of edges based on the position feedback signal;

a counter operable to count the edges to periodically generate position values at a predetermined update interval; and

a prediction unit operable to receive a position data request at a first time and predict a position of the drive at the first time as a function of at least a subset of the position values generated prior to the first time and a misalignment between the first time and the predetermined update interval to generate an aligned position signal.

9. The electronic line shaft of claim 8, further comprising at least one slave drive unit operable to receive the reference velocity and reference position signals in a synchronous manner with respect to the master drive unit.

10. The electronic line shaft of claim 8, wherein the counter is operable to generate a course component of the position values based on the counted edges, and the feedback unit further comprises an incremental position estimator operable determine a fine component of the position values based on the feedback position signal generated by the first encoder.

11. The electronic line shaft of claim 10, wherein the feedback position signal comprises a first channel signal and a second channel signal, and the incremental position estimator is operable to calculate a ratio between the first channel signal and the second channel signal, and determine the fine component based on the arctangent of the ratio.

12. The electronic line shaft of claim 8, wherein the subset includes the two most recent position values, and the prediction unit is operable to determine a velocity of the motor as a function of the two most recent position values and the predetermined update interval and predict the position of the motor based on the most recent position value and the determined velocity.

13. The electronic line shaft of claim 12, wherein the prediction unit is operable to multiply the determined velocity by the difference between the first time and the predetermined update interval to determine a position offset and add the position offset to the most recent position value to generate the predicted position.

14. The electronic line shaft of claim 8, wherein the master drive further comprises a position regulator coupled to the prediction unit and operable to receive the aligned position signal and the reference position signal and provide a control signal to the motor controller for adjusting the torque input signal based on the difference between the reference position signal and the predicted position signal.

15. The electronic line shaft of claim 8, wherein the master drive unit further comprises:

a velocity filter operable to receive the aligned position signal and generate a feedback velocity signal based on the aligned position signal; and

a velocity regulator operable to receive the feedback velocity signal and the reference velocity signal and provide a control signal to the motor controller for adjusting the torque input signal based on the difference between the reference velocity signal and the feedback velocity signal.

16. A method for determining position of a rotating load, comprising:

receiving at least one feedback position signal indicative of movement of the rotating load;

generating a first position signal including a plurality of edges based on the feedback position signal;

counting the edges to periodically generate position values at a predetermined update interval;

receiving a position data request at a first time; and

predicting a position of the rotating load at the first time as a function of at least a subset of the position values generated prior to the first time and a misalignment between the first time and the predetermined update interval to generate an aligned position signal.

17. The method of claim 16, wherein counting the edges further comprises counting the edges to generate a course component of the position values, and the method further comprises determining a fine component of the position values based on the feedback position signal.

18. The method of claim 17, wherein the feedback position signal comprises a first channel signal and a second channel signal, and determining the fine component further comprises:

calculating a ratio between the first channel signal and the second channel signal; and

calculating the arctangent of the ratio to determine the fine component.

19. The method of claim 16, wherein the subset includes the two most recent position values, and the method further comprises:

determining a velocity of the motor as a function of the two most recent position values and the predetermined update interval; and

predicting the position of the motor based on the most recent position value and the determined velocity.

20. The method of claim 19, wherein predicting the position further comprises:

multiplying the determined velocity by the difference between the first time and the predetermined update interval to determine a position offset; and

adding the position offset to the most recent position value to generate the predicted position.

21. A printing system including a plurality of printing stations for processing a web, comprising:

a signal source operable to generate a reference velocity signal;

a virtual encoder operable to generate a reference position signal based on the reference velocity signal; and

a plurality of drive units for moving the web through the printing stations in accordance with the reference position signal and the reference velocity signal, each of the drive units comprising;

a motor;

a first encoder operable to generate at least one feedback position signal indicative of rotation of the motor;

a motor controller operable to provide a torque input signal to the motor;

a feedback unit, comprising;

a comparator operable to generate a first position signal including a plurality of edges based on the position feedback signal;

a counter operable to count the edges to periodically generate position values at a predetermined update interval; and

a prediction unit operable to receive a position data request at a first time and predict a position of the drive at the first time as a function of at least a subset of the position values generated prior to the first time and a misalignment between the first time and the predetermined update interval to generate an aligned position signal.

22. The printing system of claim 21, wherein one of the plurality of drive units is designated as a master drive unit, and the remaining drive units are designated as slave drive units, further comprising a synchronization unit operable to receive the reference velocity signal and the reference velocity signal and distribute the reference velocity signal and the reference velocity signal to at least the slave drive units, the slave drive units being operable to process the reference velocity signal and the reference position signal synchronously with respect to the master drive unit.