CMM Reader Head Temperature Sensing for Thermal Compensation
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Solution Overview
Problem
Existing multi-axis tool positioning systems, such as CMMs, suffer from precision loss due to temperature deviations and gradients caused by local heat sources and varying thermal expansion coefficients of different materials, leading to deformation and reduced accuracy, especially when not installed in controlled environments.
Innovation Solution
Integration of a position encoder with a temperature sensor into the reader head that collects both displacement and local temperature data, allowing for real-time compensation of thermal effects by deriving actual displacement data using a computing unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If CMMs are installed in controlled environments with low vibration and strictly controlled temperature, then measurement precision is maintained, but device complexity and ease of operation are reduced due to stringent environmental requirements
Solution Approach 1:
The system continuously monitors temperature parameters and dynamically adjusts displacement measurements based on thermal expansion coefficients. By changing the operational parameters (temperature compensation values) rather than requiring fixed environmental conditions, the CMM can operate in varied environments while maintaining precision.
Solution Approach 2:
Temperature sensors provide continuous feedback about the thermal state of the CMM structure. This feedback is processed by the computing unit to calculate and apply real-time compensation to displacement measurements, enabling the system to adapt to environmental changes automatically.
2Measurement precision
If multiple temperature sensors are distributed throughout the CMM structure to capture temperature gradients, then thermal compensation accuracy is improved, but device complexity and wiring complexity increase
Solution Approach 1:
The reader head serves multiple functions: it reads the scale for displacement measurement and simultaneously houses temperature sensors for thermal monitoring. This multi-functionality reduces the need for separate sensor wiring and integration points, simplifying the overall system architecture while maintaining comprehensive temperature monitoring capability.
Solution Approach 2:
The temperature sensing function is merged with the existing reader head structure. By combining displacement measurement and temperature monitoring in a single integrated component, the system reduces wiring complexity and eliminates the need for separate sensor installations throughout the CMM structure.
3Measurement precision
If contact temperature sensors are used to measure scale temperature, then measurement accuracy is improved, but the scale precision is reduced due to mechanical contact and stress
Solution Approach 1:
The system replaces mechanical contact temperature sensors with non-contact or minimally invasive sensing approaches integrated into the reader head. This substitution eliminates mechanical stress on the scale while still providing accurate temperature measurements through proximity-based or integrated sensing methods.
Solution Approach 2:
The reader head acts as an intermediary between the temperature measurement function and the scale. By positioning temperature sensors in the reader head rather than in direct contact with the scale, the system mediates the measurement process to avoid applying mechanical stress to the precision scale while still capturing accurate thermal data.
4Device complexity
If fixed pre-set position temperature measurements are used, then device complexity is reduced, but spatial resolution and thermal gradient detection are insufficient
Solution Approach 1:
The system transitions from static, fixed-position temperature monitoring to dynamic, continuous temperature measurement along the scale. As the reader head moves during measurement operations, temperature sensors continuously record thermal data at multiple positions, providing high spatial resolution without requiring a complex fixed sensor array.
Solution Approach 2:
Temperature measurement is performed continuously during the normal measurement operation rather than at discrete fixed points. The reader head collects temperature data continuously as it traverses the scale, providing comprehensive spatial resolution while utilizing the existing operational motion of the system.
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
Enhances precision and simplifies metrology setups by providing accurate displacement data with thermal compensation, enabling CMMs to operate outside controlled environments with improved robustness and reduced wiring complexity.
Implementation Method 1
The temperature sensor has a temperature sensor field of view associated with the scale and configured to measure local temperature values
Data Source
Figure 1a~1b
Figure 2~3
Figure 4a~5
AI summary
The invention relates to a position encoder configured to provide a relative displacement data of a first member of a CMM with respect to a second member of the CMM. The encoder comprises a scale with a plurality of scale element positioned on the first member and a reader head positioned on the second member. The reader head is configured to acquire scale position data regarding the position of at least a part of the scale elements. The reader head further comprises a temperature sensor to acquire local temperature data regarding the scale. The displacement of the members is derived based on the scale position and local temperature data.