CTE Measurement Using Reference Gauge and Temperature Chamber
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Solution Overview
Problem
Current methods for measuring the coefficient of thermal expansion (CTE) of dimension reference gauges, such as step gauges, are costly and inaccurate, especially for long lengths, due to the need for expensive optical interferometers and the limitations of coordinate measuring machines in maintaining high accuracy over large lengths.
Innovation Solution
A method using a temperature-controlled chamber and a coordinate measuring machine with a reference gauge to measure the CTE of dimension reference gauges by comparing the length changes at different temperatures, allowing for accurate measurements without the need for expensive optical interferometers and enabling the measurement of various lengths and section lengths within the gauge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical interferometer is used to measure the CTE of dimension reference gauges, then the measurement precision is improved, but the equipment cost increases significantly
Solution Approach 1:
A reference gauge with known dimensional accuracy is introduced as an intermediary standard. The coordinate measuring machine measures both the dimension reference gauge and the reference gauge, and through comparative calculation, determines the CTE. This intermediary reference gauge enables accurate CTE measurement without requiring expensive optical interferometer equipment.
Solution Approach 2:
Instead of directly measuring absolute lengths with high-precision optical interferometers, the method copies the measurement approach by using a reference gauge with known dimensions. The coordinate measuring machine measures the reference gauge under the same thermal conditions, creating a reference measurement that can be compared with the dimension reference gauge measurement to calculate CTE, thereby avoiding the need for expensive direct high-precision measurement equipment.
2Device complexity
If a coordinate measuring machine is used to measure long lengths, then the equipment cost is reduced, but the measurement precision deteriorates
Solution Approach 1:
The patent replaces the direct mechanical measurement approach with a computational method. Instead of relying on the coordinate measuring machine's mechanical accuracy over long distances, the system uses temperature-controlled environmental chambers to maintain dimensional stability and employs computational algorithms to calculate CTE from multiple measurements taken at different temperatures, thereby compensating for the machine's limited long-distance measurement precision.
Solution Approach 2:
The measurement approach changes from measuring absolute length to measuring relative length changes at different temperatures. By controlling temperature as a parameter and measuring dimensional changes relative to a reference gauge rather than absolute dimensions, the system achieves accurate CTE measurement even with a coordinate measuring machine that has limited precision for long lengths.
3Reliability
If the temperature variation and length variation are measured to calculate CTE, then the CTE value is obtained, but the measurement uncertainty increases due to tolerance in CTE indicated in calibration certificates
Solution Approach 1:
The patent implements a feedback mechanism where the coordinate measuring machine repeatedly measures both the dimension reference gauge and the reference gauge at different temperatures. These measurements feed into a calculation system that determines CTE while accounting for measurement uncertainties. The process can be repeated multiple times to reduce uncertainty through statistical analysis, and the system provides feedback on measurement quality to ensure reliability.
Solution Approach 2:
The reference gauge is pre-calibrated with known dimensional accuracy before the CTE measurement process. This preliminary action establishes a reliable reference standard that reduces measurement uncertainty. By having the reference gauge's dimensions accurately known in advance, the system can more precisely determine the dimension reference gauge's CTE through comparison, thereby reducing overall measurement uncertainty despite tolerances in calibration certificates.
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 highly accurate and cost-effective measurement of CTE across different lengths and sections of dimension reference gauges, improving measurement precision and reducing equipment costs by using a coordinate measuring machine and a reference gauge within a temperature-controlled environment.
Implementation Method 1
CTE of an object including a dimension reference gauge is obtained by changing the temperature of the object and measuring a length variation of the object due to the temperature change
Implementation Method 2
a CTE α is given by a formula α=(ΔL/L)·(1/ΔT), where ΔT=T−To (T: a current temperature, To: a reference temperature) represents the temperature variation, and ΔL=L−Lo (L: a length of the object at the current temperature T, Lo: a length of the object at the reference temperature To) represents the length variation (thermal expansion)
Data Source
AI summary
A measurement target and a reference gauge are placed in parallel in an inside of a temperature-controlled chamber. After an interior temperature of the temperature-controlled chamber is set at a first temperature, a relative measurement of a length from a first surface to a second surface of the measurement target is performed with reference to a length from a first reference surface to a second reference surface of the reference gauge. Then, the interior temperature of the temperature-controlled chamber is set at a second temperature and a relative measurement of the length from the first surface to the second surface is similarly performed with reference to the length from the first reference surface to the second reference surface. A CTE of the measurement target is calculated based on the length of the measurement target at the first temperature and the length of the measurement target at the second temperature.