Load Torque Drop Position Measurement for NC Machine Tools
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Solution Overview
Problem
Current position measuring apparatuses in NC machine tools face inaccuracies due to response delays and high costs associated with touch probes, with load monitoring schemes offering limited accuracy of around 100 to 200 μm and longer machine cycle times.
Innovation Solution
A position measuring apparatus that includes a load increasing unit to elevate the load torque above a detectable threshold, followed by a sudden drop to cancel the abutment state, and a monitoring unit to capture position information when the load torque falls below a second value, significantly reducing response delays and improving accuracy to around 50 μm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional load monitoring scheme is used with a stylus fed at high speed, then productivity is improved, but measurement precision deteriorates due to response delay
Solution Approach 1:
Instead of detecting position by monitoring load increase when the stylus touches the target (conventional approach), this invention inverts the approach by monitoring load decrease when the stylus is retracted from the target. The stylus is fed at high speed to maintain productivity, then rapidly retracted, and the position is determined by detecting the load decrease signal, thereby eliminating response delay while maintaining high feed rates
Solution Approach 2:
The stylus is fed to a position slightly beyond the target position before retraction begins. This preliminary positioning ensures that the stylus is already in contact with the target and experiencing load before retraction starts, so that when retraction occurs, the load decrease signal is immediately generated without delay, enabling accurate position detection while maintaining high productivity
2Measurement precision
If a touch probe is used to improve measurement precision, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
This invention creates a functional copy of the touch probe's measurement capability using the existing load monitoring system. By detecting load decrease during stylus retraction instead of requiring specialized touch probe hardware, the system achieves comparable measurement precision (about 50 μm) while maintaining the simplicity and low cost of the conventional load monitoring apparatus
Solution Approach 2:
The invention changes the detection parameter from load increase (conventional approach) to load decrease (new approach). This parameter change transforms the measurement mechanism to work with high-speed retraction instead of slow approach, achieving high precision without requiring expensive touch probe hardware, thereby reducing device complexity while improving measurement capability
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
This approach allows for precise position measurement with reduced response delays and lower costs compared to touch probe systems, achieving higher accuracy and shorter machine cycle times while maintaining a low-cost, user-friendly load monitoring scheme.
Implementation Method 1
a detecting unit that detects the position of the measurement target by reading a fluctuation in the load torque of the feed motor
Implementation Method 2
a load increasing unit capable of increasing the load torque of the feed motor to a predetermined first value in a state in which the position detecting jig abuts the measurement target, the first value being above a threshold that is detectable by the apparatus
Implementation Method 3
a canceling unit that, when the load torque of the feed motor has become greater than or equal to the first value, cancels the abutment state between the measurement target and the position detecting jig to thereby cause a sudden drop in the load torque of the feed motor
Data Source
AI summary
It is possible to, with a position measuring apparatus in a NC machine tool, a NC lathe, or the like that uses a load monitoring scheme, significantly reduce a response delay on the detecting jig side than those in the conventional apparatuses, and consequently measure the position of a measurement target with high accuracy. A measurement target (e.g., an advanceable and retractable center) is caused to abut a position detecting jig at the advanced end of the measurement target. In such a state, retracting and advancing motions of the measurement target are created to increase the load torque of a feed motor to a level sufficiently higher than the load torque that is detectable by the apparatus. After that, the abutment state between the measurement target (center) and the jig is canceled to cause a sudden drop in the load torque of the feed motor. Accordingly, it is possible to, even with a position measuring apparatus that uses a relatively low-cost load monitoring scheme, significantly reduce a response delay than those in the conventional apparatuses, and consequently measure a position with higher accuracy.