Coordinate Positioning Machine With Thermally Isolated Metrology Frame
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Solution Overview
Problem
Existing coordinate positioning machines face accuracy issues due to thermal expansion differences between drive and metrology frames, leading to distortion and inconsistent measurements across varying temperatures.
Innovation Solution
The implementation of a metrology frame with a lower coefficient of thermal expansion than the drive frame, coupled via a coupling arrangement that prevents or reduces the transfer of thermal distortion from the drive frame to the metrology frame, using materials like carbon fibre or INVAR, and a separate drive and metrology arrangement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the drive frame and metrology frame are made from the same material, then the structure is simpler and easier to manufacture, but thermal expansion differences cause distortion and measurement inaccuracies when temperature varies
Solution Approach 1:
The machine is divided into two separate frames: a drive frame that supports the drive mechanism and a metrology frame that supports the measurement system. These frames are thermally decoupled to prevent thermal expansion from the drive frame from affecting the metrology frame, thereby maintaining measurement precision while allowing each frame to be optimized independently
Solution Approach 2:
A thermal barrier or isolation mechanism is introduced between the drive frame and metrology frame to prevent thermal distortion transfer. This intermediary element allows the two frames to be physically connected while thermally isolating them, resolving the contradiction between structural simplicity and measurement accuracy
2Adaptability or versatility
If a hexapod drive arrangement is used, then the moveable structure can be positioned in six degrees of freedom, but the complexity of the drive system increases and thermal effects become more significant
Solution Approach 1:
The drive system is segmented into six independent linear actuators, each controlling one degree of freedom of the moveable structure. This modular approach allows for precise control while simplifying the overall system architecture and reducing thermal interference compared to a fully coupled hexapod mechanism
Solution Approach 2:
The moveable structure serves multiple functions: it supports both the drive mechanism components and the metrology system components. By integrating these functions into a single platform that can move in six degrees of freedom, the system achieves versatility while managing complexity through unified design
3Measurement precision
If the metrology frame is isolated from the drive frame, then thermal distortion is reduced and measurement accuracy improves, but the structural coupling between drive and metrology systems becomes more complex
Solution Approach 1:
A thermal barrier or isolation mechanism is introduced between the drive frame and metrology frame to prevent thermal distortion transfer. This intermediary element allows the two frames to be physically connected while thermally isolating them, resolving the contradiction between structural simplicity and measurement accuracy
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 design ensures higher accuracy and consistent metrology measurements by isolating the metrology frame from thermal effects, maintaining precise position determination despite temperature variations.
Implementation Method 1
the metrology frame has a coefficient of thermal expansion that is lower than that of the drive frame, thereby causing (in use) an extra thermal expansion and contraction of the drive frame compared to the metrology frame
Data Source
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AI summary
A coordinate positioning machine comprises a drive frame (37) and a metrology frame (36). The drive frame (37) comprises a drive arrangement (28) for moving a moveable structure (22) around a working volume (34) of the machine. The metrology frame (36) comprises a metrology arrangement (26) for measuring the position of the structure (22) within the working volume (34). In one aspect, the metrology arrangement (26) is a hexapod metrology arrangement and the drive arrangement (28) is a non-hexapod drive arrangement. The metrology frame (36) has a coefficient of thermal expansion that is lower than that of the drive frame (37). The drive frame (37) is coupled to the metrology frame (36) via a coupling arrangement (38) which prevents at least some distortion associated with any extra thermal expansion and contraction of the drive frame (37) from being transferred to the metrology frame (36). In another aspect, the drive arrangement (28) moves the structure (22) around the working volume (34) in fewer than six degrees of freedom, and the metrology arrangement (26) measures the position of the structure (22) within the working volume (34) in more degrees of freedom than the drive arrangement (28).