Servo control apparatus that performs dual-position feedback control

• US 7,915,848 B2
• Filed: 03/03/2010
• Issued: 03/29/2011
• Est. Priority Date: 05/20/2009
• Status: Active Grant

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Toyozawa, Yukio, Maeda, Kazuomi, Okita, Tadashi, Iwashita, Yasusuke
• Primary Examiner(s): Benson; Walter
• Assistant Examiner(s): COLON SANTANA, EDUARDO
• Application Number:
  US12/716,764
• Publication Number:
  US 20100295495A1
• Time in Patent Office: 391 Days
• Field of Search: 318/560, 318/567, 318/569, 318/600, 318/625, 318/632, 318/638, 318/661, 700/13, 700/186, 700/188, 700/193
• US Class Current: 318/560
• CPC Class Codes: G05B 19/19 characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path
• CPC Class Codes: G05B 2219/37297 Two measurements, on driving motor and on slide or on both sides of motor
• CPC Class Codes: G05B 2219/41141 Position error compensation as function of speed to compensate detection delay
• CPC Class Codes: G05B 2219/41418 Select feedback signal between detected position of motor and of driven load
• CPC Class Codes: G05B 2219/42152 Learn, self, auto tuning, calibrating, environment adaptation, repetition

Abstract

A servo control apparatus that performs dual-position feedback control and thereby achieves a reduction in position error according to the purpose of machining. The servo control apparatus includes: a first position detector for detecting the position of a motor; a second position detector for detecting the position of a driven load; a first position error calculator for calculating a first position error based on a position command and motor position feedback; a second position error calculator for calculating a second position error based on the position command and driven load position feedback; a third position error calculator for calculating a third position error to be used for position control, by adding to the first position error a difference taken between the first position error and the second position error and passed through a time constant circuit; a selector for selecting either the second position error or the third position error for output; and a learning controller for learning an output of the selector, and for outputting an amount of compensation to be applied to the third position error.

Claims

1. A servo control apparatus that performs dual-position feedback control, comprising:

a first position detector for detecting position of a servo motor;

a second position detector for detecting position of a load being driven by said servo motor;

a first position error calculator for calculating a first position error based on a position command for said driven load and on position feedback from said first position detector;

a second position error calculator for calculating a second position error based on said position command for said driven load and on position feedback from said second position detector;

a third position error calculator for calculating a third position error to be used for position control, by adding to said first position error a difference taken between said first position error and said second position error and passed through a time constant circuit;

a selector for selecting either said second position error or said third position error for output; and

a learning controller for learning an amount of compensation necessary to bring said second position error close to zero when said second position error is output from said selector, and learning an amount of compensation necessary to bring said third position error close to zero when said third position error is output from said selector, and for outputting either one of said learned amounts of compensation as an amount of compensation to be applied to said third position error.

2. A servo control apparatus as claimed in claim 1, wherein said selector makes said selection, based on either an external signal or on the position of said driven load.

3. A servo control apparatus as claimed in claims 1 or 2, wherein when calculating said first position error, said first position error is compensated by applying an amount of compensation proportion to speed of said servo motor to compensate for a delay in detection by said first position detector, and when calculating said second position error, said second position error is compensated by applying an amount of compensation proportion to speed of said driven load to compensate for a delay in detection by said second position detector.