Controller for servomotor

• US 7,531,981 B2
• Filed: 02/08/2007
• Issued: 05/12/2009
• Est. Priority Date: 02/16/2006
• Status: Active Grant

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Okita, Tadashi, Iwashita, Yasusuke, Kawamura, Hiroyuki, Takayama, Kenichi
• Primary Examiner(s): Ro; Bentsu
• Assistant Examiner(s): Luo; David S
• Application Number:
  US11/703,797
• Publication Number:
  US 20070188123A1
• Time in Patent Office: 824 Days
• Field of Search: 318/560, 318/625, 318/630, 318/567, 318/569
• US Class Current: 318/625
• CPC Class Codes: G05B 19/404 characterised by control arrangements for compensation, e.g. for backlash, overshoot, tool offset, tool wear, temperature, machine construction errors, load, inertia G05B19/19, G05B19/41 take precedence

Abstract

A controller for a servomotor capable of improving accuracy of positioning and quality of a machined surface by switching modes of correction of a position command or the like, and reducing a shock at the time of switching. A correction amount generating section obtains a correction amount based on a value of a correction factor such as machine temperature. When the external signal is in ON state, a position command or the like is corrected by the correction amount obtained by the correction amount generating section and sent via switches. A correction amount holding section holds the correction amount obtained by the correction amount generating section. When the external signal turns to OFF state, the connection of the switches is changed so that correction is performed by the correction amount held in the correction amount holding section. When the connection of the switches is changed, the correction amount does not change rapidly, so that the machine does not suffer a shock. In positioning, the external signal is turns to ON state, so that the positioning is carried out accurately by performing correction by the correction amount sent from the correction amount generating section. When a high-quality machined surface is required, the external signal is turned to OFF state so that the correction amount does not change to achieve improvement in the quality of a machined surface.

Claims

1. A controller for controlling a servomotor for driving a controlled object using a position command, a position deviation and a velocity command, comprising:

detecting means for detecting a magnitude of a fluctuation factor of the controlled object;

correction means for determining a correction amount for correcting one of the position command, the position deviation and the velocity command based on the magnitude of the fluctuation factor detected by said detecting means during the control of the servomotor, and performing the correction by the correction amount; and

switching means for selectively switching performing/non-performing of the correction by said correction means according to an external signal,

wherein the controller is adapted to control a plurality of servomotors in synchronism, said correcting means includes monitoring means for monitoring respective torques of the servomotors, and determines the correction amount based on a difference between the monitored torques.

2. A controller for controlling a servomotor according to claim 1, wherein the controller is adapted to control two servomotors in synchronism, said monitoring means monitors current commands for the two servomotors, and said correcting means determines the correction amount based on a difference between the monitored current commands.

3. A controller for controlling a servomotor for driving a controlled object using a position command, a position deviation and a velocity command, comprising:

detecting means for detecting a magnitude of a fluctuation factor of the controlled object;

correcting means for correcting one of the position command, the position deviation and the velocity command by a correction amount;

determining means for determining and updating the correction amount based on the magnitude of the fluctuation factor detected by said detecting means during the control of the servomotor; and

switching means for selectively suspending/resuming the updating of the correction amount by said determining means according to an external signal.

4. A controller for controlling a servomotor according to claim 3, wherein said determining means includes a correction amount holding section for holding a value of the correction amount immediately before the updating of the correction amount is suspended, and said correcting means performs the correction using the value of the correction amount held by the correction amount holding section while the updating of the correction amount is suspended.

5. A controller for a servomotor according to claim 4, wherein said determining means determines the correction amount to be continuously changed using the value of the correction amount held by the correction amount holding section, when the updating of the correction amount is resumed.

6. A controller for a servomotor according to claim 5, wherein said determining means comprises a correction amount generating section including a filter, and the value of the correction amount held by the correction amount holding section is used as an initial output value of the filter so that the correction amount continuously changes when the updating of the correction amount is resumed.

7. A controller for controlling a servomotor according claim 3, wherein the controller is adapted to control a plurality of servomotors in synchronism, said detecting means includes monitoring means for monitoring torques of the servomotors, and said determining means determines the correction amount based on a difference between the monitored torques.

8. A controller for a servomotor according to claim 7, wherein the controller is adapted to control two servomotors in synchronism, said monitoring means monitors current commands for the two servomotors, and said determining means determines the correction amount based on a difference between the monitored current commands.