# US 8,058,827 B2 · Motor control apparatus having a function to calculate amount of cogging torque compensation

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- Number: US 8,058,827 B2
- Document ID: US8058827B2
- Status: Granted
- Kind: B2
- Application number: 12/880,108
- Filed: 2010-09-12
- Published: 2011-06-23
- Granted: 2011-11-15
- Earliest claimed: 2009-12-22
- Assignees: Fanuc Corporation
- Inventors: Yasusuke Iwashita; Tadashi Okita; Junichi Tezuka; Kazuyuki Sugiyama
- Web page: https://patentgrep.com/patent/US8058827B2

## CPC

- H02P 6/10: Arrangements for controlling torque ripple, e.g. providing reduced torque ripple
- 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)
- H02P 23/14: Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage
- G05B 2219/41138: Torque compensation
- H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- 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

A motor control apparatus that can calculate a proper amount of cogging torque compensation even in cases where components due to other factors than cogging torque (for example, components due to gravitational torque, etc.) are superimposed on a torque command being output during constant slow-speed feed operation. The motor control apparatus includes: a torque command monitoring unit which monitors a torque command when the motor is caused to operate at a constant speed; an approximation calculation unit which calculates a torque command approximation component by approximation from the torque command monitored over an interval equal to an integral multiple of the cogging torque period of the motor; a second torque command calculation unit which calculates a second torque command by subtracting the torque command approximation component from the torque command; a second torque command frequency analyzing unit which extracts frequency components, each at an integral multiple of the fundamental frequency of the cogging torque, by performing frequency analysis on the thus calculated second torque command; and a cogging compensation amount calculation unit which calculates the amount of cogging compensation from the amplitude and phase of the extracted frequency components.

## Claims

### Claim 1

A motor control apparatus for controlling a motor used in a machine tool, comprising:
a torque command monitoring unit configured to monitor a torque command when said motor is caused to operate at a constant speed;
an approximation calculation unit configured to calculate a torque command approximation component by approximation from said torque command monitored by said torque command monitoring unit over an interval equal to an integral multiple of a cogging torque period of said motor;
a second torque command calculation unit configured to calculate a second torque command by subtracting from said torque command monitored by said torque command monitoring unit said torque command approximation component calculated by said approximation calculation unit;
a second torque command frequency analyzing unit configured to extract frequency components, each at an integral multiple of a fundamental frequency of cogging torque, by performing frequency analysis on said second torque command calculated by said second torque command calculation unit; and
a cogging compensation amount calculation unit configured to calculate the amount of cogging compensation from the amplitude and phase of said frequency components extracted by said second torque command frequency analyzing unit.

### Claim 2 (depends on 1)

A motor control apparatus as claimed in claim 1, wherein said approximation calculation unit performs said approximation by using a polynomial whose order is less than a cogging torque frequency of said motor.

### Claim 3

A motor control apparatus for controlling a motor used in a machine tool, comprising:
a torque command monitoring unit configured to monitor a torque command when said motor is caused to operate at a constant speed;
a motor position monitoring unit configured to monitor motor position;
a gravitational torque calculation unit configured to calculate a gravitational torque component at each motor position monitored by said motor position monitoring unit;
a second torque command calculation unit configured to calculate a second torque command by subtracting said gravitational torque component calculated by said gravitational torque calculation unit from said torque command monitored by said torque command monitoring unit over an interval equal to an integral multiple of a cogging torque period of said motor;
a second torque command frequency analyzing unit configured to extract frequency components, each at an integral multiple of a fundamental frequency of cogging torque, by performing frequency analysis on said second torque command calculated by said second torque command calculation unit; and
a cogging compensation amount calculation unit configured to calculate the amount of cogging compensation from the amplitude and phase of said frequency components extracted by said second torque command frequency analyzing unit.