CNC Tool Mount Detection with Ball Screw Thermal Expansion Correction
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Solution Overview
Problem
Existing numerical control devices struggle to accurately determine the mounted state of a tool on a main shaft due to variations in torque peak positions caused by the expansion and contraction of the feed shaft, which can be misinterpreted as changes in the tool's mounted state, leading to potential inaccuracies in cutting operations.
Innovation Solution
A numerical control device that includes an estimation part to measure the expansion and contraction of the feed shaft, a first acquisition part to measure motor torque, and a determination part to accurately determine the tool's mounted state by correcting torque peak angles based on these measurements, thereby distinguishing between shaft expansion and the actual tool state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the feed shaft expands and contracts due to temperature change, then the peak position of the torque differential value varies, but this causes inaccurate determination of the tool's mounted state
Solution Approach 1:
The system continuously monitors the peak position of the torque differential value and compares it against reference ranges. When the peak position falls outside the expected range due to feed shaft expansion/contraction, the system detects this deviation and adjusts or flags the mounted state determination accordingly, preventing false conclusions about tool mounting quality
Solution Approach 2:
The patent introduces a dynamic reference range for the peak position that accounts for temperature-induced variations. Instead of using a fixed peak position threshold, the system adapts the acceptable range based on observed variations, allowing accurate mounted state determination even when the peak position shifts due to feed shaft expansion or contraction
2Reliability
If the numerical control device uses torque differential value to determine tool mounted state, then it can detect mounting status, but feed shaft expansion causes false variations in peak position
Solution Approach 1:
The patent introduces an intermediary reference range that acts as a buffer between the raw torque differential value and the mounted state determination. This reference range absorbs the harmful effects of feed shaft expansion by providing a tolerance band, allowing the system to distinguish between legitimate mounted state changes and temperature-induced variations
Solution Approach 2:
The system converts the harmful effect of feed shaft expansion into useful information by using the peak position variations as an indicator. By establishing reference ranges that accommodate expected thermal variations, the system learns the normal behavior pattern and can more accurately detect actual anomalies in tool mounting, turning a source of error into a calibration opportunity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device ensures precise determination of the tool's mounted state, reducing errors and maintaining cutting accuracy by accounting for shaft expansion and contraction, thus enhancing operational reliability.
Implementation Method 1
The feed shaft expands and contracts in the up-down direction due to a temperature change thereof
Data Source
AI summary
A numerical control device estimates the expansion and contraction amount of a ball screw. The numerical control device acquires a rotation angle and disturbance force of a Z-axis motor. The numerical control device acquires the torque of the Z-axis motor to acquire the disturbance force included in the torque. The numerical control device determines the mounted state of a tool on a main shaft on the basis of the expansion and contraction amount of the ball screw, and a peak angle decided by a change in a differential value, which is the time differential of the disturbance force.