Coordinate Measuring Machine Thermal Error Compensation
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Solution Overview
Problem
Existing coordinate measuring machines face challenges in accurately measuring workpieces due to thermal expansion and contraction, especially when workpieces are at different temperatures from the environmental temperature of the measuring apparatus, leading to inaccuracies in comparison with reference workpieces.
Innovation Solution
A method involving measuring a reference workpiece at a non-ambient temperature, generating an error map or look-up table to correct dimensional values, and maintaining the reference workpiece's temperature to match production workpieces, ensuring accurate comparisons and corrections across varying temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measurements are taken on a coordinate measuring machine at environmental temperature, then the measuring apparatus is stable and easy to operate, but the measurements become inaccurate when the workpiece temperature differs from the environmental temperature due to thermal expansion and contraction
Solution Approach 1:
The patent changes the temperature parameter of the reference workpiece to match the actual workpiece temperature. By measuring the reference workpiece at the same non-ambient temperature as the production workpieces and generating temperature-specific error maps, the system adapts to different temperature conditions while maintaining measurement accuracy through parameter matching between reference and actual workpieces.
2Measurement precision
If the reference workpiece is kept in the thermal environment of the machine tool, then the temperature match improves, but the machining process heat still causes temperature differences between reference and production workpieces
Solution Approach 1:
The system uses the actual production workpiece itself as the reference by measuring the first workpiece and using its measured values to create the error map. This self-referential approach ensures that the reference temperature automatically matches the production workpiece temperature, eliminating the need for separate reference workpiece temperature control and ensuring perfect temperature consistency.
Solution Approach 2:
The patent performs preliminary measurement of a reference workpiece at the same non-ambient temperature before measuring production workpieces. By pre-establishing the error map at the actual operating temperature, the system prepares the temperature compensation data in advance, ensuring that when production workpieces are measured, the compensation is already optimized for the current thermal conditions.
3Measurement precision
If measurements are performed on the machine tool itself, then the reference workpiece remains in thermal environment, but the machine tool is idle during measurement reducing productivity
Solution Approach 1:
The patent introduces a separate coordinate measuring machine as an intermediary device that can operate independently from the machine tool. This allows the reference workpiece to be measured and error maps to be generated on a dedicated measuring apparatus while the machine tool continues machining operations, eliminating the idle time conflict while maintaining the ability to perform temperature-matched measurements.
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 improves the accuracy of dimensional measurements by accounting for thermal variations, ensuring valid comparisons and corrections, thereby enhancing the validity and precision of workpiece inspections.
Implementation Method 1
Thermal expansion and contraction affects the measurement of workpieces
Implementation Method 2
Thermal expansion and contraction affects the measurement of workpieces
Data Source
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AI summary
A series of nominally identical workpieces (10) is received from a manufacturing process and measured on a measuring apparatus (10,16,20; 40). They are received at a non-ambient temperature because of heat introduced during the manufacturing process, but they are placed on the measuring apparatus in a repeatable manner, e.g. by a robot (48), such that their non-ambient temperatures when measured are repeatable. One of the workpieces (10) is measured as a reference workpiece at the non-ambient temperature, and these measurements are compared to calibrated values obtained from an external source, in order to generate an error map or error function. The error map or error function is used to correct measurements of subsequent workpieces (10) of the series which are measured at the repeatable non-ambient temperature.