CNC Servo Torque Release During Deceleration to Prevent Overshoot
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Solution Overview
Problem
The existing CNC systems face issues with torque limitation of servo motors, leading to insufficient acceleration and deceleration, resulting in overshoot and potential machine interference, as well as position deviation and excessive error alarms.
Innovation Solution
A numerical control system that includes an in-deceleration torque limit release unit to release torque limitation only during deceleration and an acceleration/deceleration time constant calculation unit to optimize torque output, allowing for precise position control and eliminating overshoot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If torque limitation is applied to the servo motor, then damage from machine interference is minimized, but acceleration and deceleration become insufficient causing overshoot
Solution Approach 1:
The torque limit is made dynamic by releasing it only during deceleration when overshoot risk exists, rather than maintaining a static torque limit throughout all operations. This allows the system to adapt torque characteristics to specific operational phases, preventing overshoot during deceleration while maintaining adequate torque during acceleration.
Solution Approach 2:
The control unit predicts the command position in advance and determines whether torque limit release is needed before deceleration occurs. By performing position prediction and torque limit decision-making ahead of time, the system can prepare appropriate torque characteristics to prevent overshoot without waiting for actual deceleration to begin.
2Reliability
If torque limitation is applied to the servo motor, then safety is improved, but position control precision deteriorates due to excessive error alarms
Solution Approach 1:
The torque limit setting is dynamically adjusted based on the predicted command position and actual position relationship. When the predicted position exceeds the actual position by a threshold during deceleration, the torque limit is released to prevent overshoot, thereby maintaining position control precision while preserving safety benefits during normal operation.
Solution Approach 2:
The system uses feedback from position detection to determine whether torque limit release is necessary. By continuously monitoring the relationship between predicted command position and actual position, the control unit can make informed decisions about torque limit release timing, ensuring position precision is maintained while safety is preserved.
Data Source
AI summary
Provided is a numerical control system of an industrial machine that makes it possible to eliminate overshoot occurred at the time of stopping, thereby preventing interference of the machine, for example, in a case in which the torque of a motor such as a servomotor used in a feed axis of a machine tool is limited by a command unit of a CNC. A numerical control system of an industrial machine includes a command unit and a control unit configured to control driving of a motor of the industrial machine in accordance with a command from the command unit, and to perform position control by receiving a command of an end point position from the command unit or without receiving a command of the end point position from the command unit, and the control unit includes an in-deceleration torque limit release unit that, in a case of performing torque limitation of the motor, releases the torque limitation only during deceleration.