CMM Touch Probe Offset Compensation Circuit
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Solution Overview
Problem
Existing touch probe systems face challenges in accurately distinguishing between workpiece contact signals and rest-state signal drifts due to factors like temperature, orientation, and vibrations, leading to limitations in amplification and compensation methods that can result in asymmetric trigger signals and delayed measurement operations.
Innovation Solution
A touch probe circuit incorporating a displacement sensor, an offset compensation controller, and a difference amplifier to provide varying offset compensation for rest-state signal variations, using a feedback loop and digital converters to generate a low-pass filtered signal that continues compensation during workpiece contact, ensuring accurate signal isolation and rapid correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high pass filtering is used to isolate workpiece contact signals from rest state drift, then signal isolation is improved, but amplification capability deteriorates due to power supply saturation
Solution Approach 1:
The patent extracts the rest-state signal component from the total sensor signal using a dedicated extraction circuit that separates the drift component from the workpiece contact signal component. This allows the extracted rest-state component to be compensated independently without affecting the amplification of the contact signals.
Solution Approach 2:
The patent introduces an intermediary offset compensation signal that acts as a mediator between the rest-state drift and the workpiece contact signals. This compensation signal is added to the extracted rest-state component to create a corrected signal that can be amplified without saturation while maintaining signal isolation.
2Speed
If auto-zero circuits operate at high speed to stabilize amplifier outputs, then stabilization speed is improved, but workpiece contact signals are nullified before reaching trigger levels
Solution Approach 1:
The patent implements dynamic control of the auto-zero circuit operation, enabling it to switch between high-speed stabilization mode during rest state and disabled mode during workpiece contact. This dynamic operation allows fast stabilization when needed while preventing nullification of contact signals.
Solution Approach 2:
The patent uses feedback from the trigger signal determination circuit to control the auto-zero circuit operation. When a workpiece contact is detected, the feedback signal disables the auto-zero circuit to prevent nullification of contact signals, while enabling fast stabilization during rest state.
3Measurement precision
If dummy sensors are used to compensate temperature drift, then temperature compensation is improved, but device complexity increases and other drift causes are not addressed
Solution Approach 1:
The patent creates a universal offset compensation system that handles multiple sources of rest-state drift (temperature, orientation, vibrations, hysteresis) through a single integrated circuit architecture. The system uses the actual displacement sensor to extract and compensate all drift components, eliminating the need for multiple dummy sensors and making the solution applicable to various touch probe models.
4Measurement precision
If incremental correctors are used to adjust reference values, then rest state drift compensation is improved, but measurement throughput decreases due to slow correction sequences
Solution Approach 1:
The patent performs preliminary extraction of the rest-state signal component continuously during operation, preparing the compensation signal in advance. This allows rapid application of offset compensation when workpiece contact occurs, eliminating slow correction sequences and improving measurement throughput.
Data Source
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AI summary
A touch probe circuit comprises a displacement sensor having a sensor signal responsive to touch probe stylus displacement, an offset compensation controller, and a difference amplifier. The offset compensation controller provides a varying offset compensation signal to compensate drift in a rest-state signal component of the sensor signal. The difference amplifier inputs the offset compensation signal and the sensor signal and amplifies the difference therebetween to provide an offset compensated displacement signal, which is output to a touch trigger signal generating circuit that provides a touch signal when the stylus touches a workpiece, and is also output to the offset compensation controller. The offset compensation controller portion provides a feedback loop that inputs the offset compensated displacement signal and outputs a responsive low pass filtered offset compensation signal to the difference amplifier, in order to provide the offset compensated displacement signal.