# US 4,916,375 A · Servomotor control apparatus

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- Number: US 4,916,375 A
- Document ID: US4916375A
- Status: Granted
- Kind: A
- Application number: 07/243,032
- Filed: 1988-08-04
- Granted: 1990-04-10
- Earliest claimed: 1986-12-12
- Assignees: Fanuc Corporation
- Inventors: Mitsuo Kurakake; Keiji Sakamoto
- Web page: https://patentgrep.com/patent/US4916375A

## CPC

- G05D 17/02: characterised by the use of electric means
- 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)
- G05B 2219/41036: Position error in memory, lookup table for correction actual position
- G05B 2219/41084: Compensation speed axis with changing, reversing direction, quadrant circle
- G05B 2219/41426: Feedforward of torque
- G05D: SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G)

## Abstract

The invention is a servomotor control apparatus for controlling the positioning of a movable element of an industrial robot or NC machine tool. An NC unit or a robot controller detects displacement from a movable element that is to be positioned, such as a table, forms a position command regarding a servomechanism, and has a correction circuit (A) which receives quadrant data (BLF) regarding a backlash correction command. When there is a quadrant reversal for each axis of the movable element, frictional torque corresponding to the axis is stored and a torque correction command (FR) corresponding thereto is outputted. A torque command of a fully-closed loop servo system for performing control based on a fed back position detection signal is corrected by the torque correction command. The servomotor control apparatus can be applied to semi-closed loop servo system in which a backlash correction is possible, and not just to a fully-closed loop servo system.

## Claims

### Claim 1

A servomotor control apparatus for controlling movement of a mechanical load in response to a position command and to a backlash correction command for correcting backlash at the mechanical load, comprising:
position detecting means for detecting a position of the mechanical load;
discriminating means for discriminating, based on the backlash correction command, a time at which an operating quadrant of the mechanical load reverses;
correcting means for receiving offset data corresponding to frictional resistance of the mechanical load, and for generating a corrected torque command based on the offset data, the detected position and the position command when the quadrant reverses; and
control means for driving and controlling the mechanical load based on the corrected torque command.

### Claim 2 (depends on 1)

A servomotor control apparatus according to claim 1, wherein said position signal detecting means comprises an optical linear scale.

### Claim 3 (depends on 1)

A servomotor control apparatus according to claim 1, wherein said correcting means comprises means for storeing the offset data corresponding to a frictional resistance value for each axis of the mechanical load.

### Claim 4 (depends on 1)

A servomotor control apparatus according to claim 1, wherein said control means comprises either a semi-closed loop servo system or a fully-closed loop servo system, and the corresponding means comprises a means for generating a corrected torque command based on the backlash correction command or on the offset data.

### Claim 5 (depends on 1)

A servomotor Control apparatus according to claim 1, wherein the mechanical load is a machine tool or an industrial robot having a plurality of servo systems.

### Claim 6 (depends on 1)

A servomotor control apparatus according to claim 1, wherein said discriminating means includes:
means for determining, based upon the backlash correction command, a time at which a quadrant in the velocity-torque characteristic for an axis of the mechanical load reserves.