# US 12,759,104 B2 · Machine tool and control device for machine tool

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- Number: US 12,759,104 B2
- Document ID: US12759104B2
- Status: Granted
- Kind: B2
- Application number: 18/839,593
- Filed: 2023-01-26
- Published: 2025-06-19
- Granted: 2026-10-13
- Earliest claimed: 2022-03-24
- Assignees: Citizen Watch Co., Ltd.; Citizen Machinery Co., Ltd.
- Applicants: Citizen Watch Co., Ltd.; Citizen Machinery Co., Ltd.
- Inventors: Erisha Hayashi
- Web page: https://patentgrep.com/patent/US12759104B2

## CPC

- B23Q 17/0961: {by measuring power, current or torque of a motor}
- B23Q: DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING (tools of the kind used in lathes or boring machines B23B27/00); MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT

## Abstract

A machine tool includes a driver that drives a main spindle for holding a workpiece rotatably, a servo motor that drives a tool for machining the workpiece held on the main spindle, a power source that supplies electric power to at least the driver and the servo motor, a current detector that detects a current value to be inputted into the servo motor, a storage that stores an upper limit of the current value to be inputted into the servo motor, and a controller that controls the servo motor to execute driving control of the tool. When a current value detected by the current detector exceeds the upper limit of the current value immediately after starting the main spindle, the controller changes an acceleration/deceleration time constant from a first time constant to a second time constant that is lower in power consumption than the first time constant, thereby controlling the servo motor.

## Claims

### Claim 1

A machine tool comprising:
a driver that drives a main spindle for holding a workpiece rotatably;
a servo motor that drives a tool for machining the workpiece held on the main spindle;
a power source that supplies electric power to at least the driver and the servo motor;
a current detector that detects a current value to be inputted into the servo motor;
a storage that stores an upper limit of the current value to be inputted into the servo motor; and
a controller that controls the servo motor to execute driving control of the tool, wherein
when a current value detected by the current detector exceeds the upper limit of the current value immediately after starting the main spindle, the controller changes an acceleration/deceleration time constant from a first time constant to a second time constant that is lower in power consumption than the first time constant, thereby controlling the servo motor.

### Claim 2 (depends on 1)

The machine tool according to claim 1, further comprising a voltage detector that detects a source voltage value inputted from the power source, wherein
when the current value detected by the current detector is equal to or less than the upper limit of the current value and the source voltage value detected by the voltage detector is equal to or less than a threshold voltage value immediately after starting the main spindle, the controller changes the acceleration/deceleration time constant from the first time constant to a third time constant that is lower in power consumption than the first time constant and higher in power consumption than the second time constant, thereby controlling the servo motor.

### Claim 3

A control device for a machine tool including a driver that drives a main spindle for holding a workpiece rotatably, a servo motor that drives a tool for machining the workpiece held on the main spindle, and a power source that supplies electric power to at least the driver and the servo motor, the control device comprising:
a current detector that detects a current value to be inputted into the servo motor;
a storage that stores an upper limit of the current value to be inputted into the servo motor; and
a controller that controls the servo motor to execute driving control of the tool, wherein
when a current value detected by the current detector exceeds the upper limit of the current value immediately after starting the main spindle, the controller changes an acceleration/deceleration time constant from a first time constant to a second time constant that is lower in power consumption than the first time constant, thereby controlling the servo motor.

### Claim 4 (depends on 3)

The control device for a machine tool according to claim 3, further comprising a voltage detector that detects a source voltage value inputted from the power source, wherein
when the current value detected by the current detector is equal to or less than the upper limit of the current value and the source voltage value detected by the voltage detector is equal to or less than a threshold voltage value immediately after starting the main spindle, the controller changes the acceleration/deceleration time constant from the first time constant to a third time constant that is lower in power consumption than the first time constant and higher in power consumption than the second time constant, thereby controlling the servo motor.