Tapping NC Control with Adaptive Spindle Acceleration Learning
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Solution Overview
Problem
Existing numerical control methods for machine tools that synchronize spindle and feed axis during tapping suffer from feed/return errors and increased synchronization errors due to variations in induction motor torque, which affect precision and machining time.
Innovation Solution
A numerical control apparatus that includes an acceleration learning block to output a smaller initial command acceleration based on the spindle motor's state quantity, such as motor current value or secondary resistance identified value, to prevent excessive command acceleration and reduce synchronization errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the command acceleration is calculated based on maximum torque without considering motor state variations, then the machining time is shortened, but the synchronization error between spindle and feed axis increases
Solution Approach 1:
The patent applies dynamics by making the command acceleration variable rather than fixed. The acceleration learning block dynamically adjusts the initial command acceleration based on real-time motor state quantities (current, secondary resistance) to match the actual maximum torque capacity of the spindle motor under varying conditions, thereby preventing synchronization errors while maintaining high-speed machining capability
Solution Approach 2:
The patent changes the parameter of command acceleration from a fixed calculated value to a dynamically adjusted value. By monitoring motor state quantities and adjusting the initial command acceleration accordingly, the system adapts to variations in maximum torque caused by temperature changes, field current stability, and secondary resistance variations, thus preventing synchronization errors
2Speed
If the initial command acceleration is set to the calculated maximum acceleration, then high-speed machining is achieved, but feed/return errors occur due to tracking errors
Solution Approach 1:
The patent applies preliminary action by outputting a smaller initial command acceleration before the actual machining begins. This preliminary reduced acceleration allows the spindle motor to stabilize and establishes accurate synchronization between the spindle and feed axis before high-speed machining starts, preventing feed/return errors while still enabling subsequent high-speed operation
Solution Approach 2:
The system dynamically transitions from a smaller initial command acceleration to the calculated maximum acceleration after synchronization is established. This dynamic adjustment allows the system to achieve both high-speed machining and high precision by separating the acceleration phase from the machining phase
3Manufacturing precision
If the acceleration is kept constant throughout the tapping process, then synchronization errors are reduced, but the machining time increases
Solution Approach 1:
The patent segments the acceleration process into two distinct phases: an initial phase with smaller acceleration for synchronization, and a subsequent phase with calculated maximum acceleration for high-speed machining. This segmentation allows the system to achieve both synchronization accuracy and high productivity by applying different acceleration levels at different stages
Data Source
AI summary
A numerical control apparatus of a machine tool that performs tapping, includes a numerical control, an acceleration learning block, an acceleration/deceleration processing unit that applies an acceleration/deceleration process to the command acceleration and the position command value to calculate a post-acceleration/deceleration position command value, a position control unit that calculates a speed command value based on the post-acceleration/deceleration position command value, a speed/torque control unit that calculates a motor torque command value from the speed command value, and a current control unit that calculates a motor current value of a spindle motor from the motor torque command value. The acceleration learning block outputs, as the command acceleration A, an initial command acceleration A[0] which is smaller than the calculated command acceleration, in accordance with a state quantity of the spindle motor, to the acceleration/deceleration processing unit.