Coordinate Positioning Machine With Decoupled Drive and Metrology
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Solution Overview
Problem
Existing coordinate positioning machines face challenges in achieving high-speed movement with accurate positioning due to conflicting design considerations between drive and metrology arrangements, leading to issues such as increased weight, heat generation, friction, and distortion.
Innovation Solution
The separation of the metrology and drive arrangements allows for a lightweight, fast drive mechanism and a robust, accurate metrology system, using a hexapod metrology arrangement with independent measurement transducers and a non-hexapod drive arrangement like tri-glide, decoupled via kinematic couplings to minimize distortion and maintain precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a combined drive and metrology arrangement is used (e.g., hexapod with motors on each leg), then the machine can achieve positioning capability, but the moving mass increases, leading to reduced speed and increased thermal and inertial distortions
Solution Approach 1:
The patent divides the combined drive-metrology system into two separate arrangements: a drive arrangement (e.g., tri-glide with three mechanical linkages) and a metrology arrangement (e.g., hexapod with six measurement transducers). This segmentation allows the drive system to be lightweight and fast while the metrology system remains robust and accurate, eliminating the need to move motors and heavy components with the moving structure.
Solution Approach 2:
The patent extracts the measurement function from the drive system by providing a separate metrology arrangement that is not attached to the moving structure. The measurement transducers are fixed to the base and measure the position of the moving structure directly, without being carried by it. This extraction eliminates the problems of moving mass, thermal distortion, and friction associated with mounted motors and transducers.
2Measurement precision
If a combined drive and metrology arrangement with motors on each leg is used, then positioning can be achieved, but thermal distortion from motors affects measurement accuracy
Solution Approach 1:
The patent extracts the measurement function from the thermally active drive system. The metrology arrangement uses separate measurement transducers that are not heated by motors, eliminating thermal distortion at the measurement points. The drive arrangement generates thermal energy, but this does not affect the metrology system since they are physically separated.
Solution Approach 2:
The patent introduces an intermediary measurement system that indirectly measures the position of the moving structure without being mechanically coupled to it. The measurement transducers measure the position of the moving structure relative to the base through a different mechanical path than the drive system, avoiding thermal interference from the drive motors.
3Measurement precision
If a combined drive and metrology arrangement is used, then positioning capability is achieved, but friction in the drive mechanism reduces positioning accuracy
Solution Approach 1:
The patent introduces an intermediary measurement system that measures position independently of the friction-prone drive mechanism. The measurement transducers provide a direct geometric measurement of the moving structure's position without being affected by friction, backlash, or other harmful factors generated by the drive mechanism.
Solution Approach 2:
The patent replaces the mechanical coupling between drive and measurement functions with a geometric measurement system. Instead of using the drive mechanism's mechanical position (which is affected by friction), the system uses measurement transducers to directly determine position through geometric relationships, substituting mechanical position transmission with optical or electromagnetic measurement.
4Adaptability or versatility
If a hexapod drive arrangement with six actuators is used, then six degrees of freedom can be controlled, but the device complexity and cost increase
Solution Approach 1:
The patent segments the control functions by using a tri-glide drive arrangement with three actuators to control three translational degrees of freedom, while a separate hexapod metrology arrangement with six measurement transducers measures all six degrees of freedom (three translational and three rotational). This segmentation allows versatile 6-DOF measurement capability without requiring six expensive and complex actuators for driving.
Solution Approach 2:
The patent makes the metrology arrangement universal by using a hexapod configuration that can measure all six degrees of freedom of the moving structure, regardless of which three translational degrees are actively controlled by the drive system. This multi-functional measurement capability provides adaptability without increasing drive complexity.
Data Source
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AI summary
A coordinate positioning machine is disclosed that comprises a structure (22) moveable within a working volume (34) of the machine, a drive arrangement (28) for moving the structure (22) around the working volume (34) in fewer than six degrees of freedom, and a metrology arrangement (26) for measuring the position of the structure (22) within the working volume (34) in more degrees of freedom than the drive arrangement (28).