Coordinate Positioning Metrology Split From Drive for Fast Accuracy
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Solution Overview
Problem
Existing coordinate positioning machines face challenges in achieving high accuracy and speed due to the integration of drive and metrology arrangements, which often require conflicting design considerations, leading to inefficiencies in positional accuracy and increased costs.
Innovation Solution
A coordinate positioning machine design that separates the metrology arrangement from the drive arrangement, allowing for a lightweight, fast drive system with high accelerations and rapid changes of direction, while the metrology arrangement focuses on positional accuracy using a hexapod-based metrology arrangement with direct measurements in six degrees of freedom, decoupled from the drive arrangement to minimize distortion and heat generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If drive and metrology arrangements are integrated in a single hexapod structure, then structural simplicity is maintained, but measurement accuracy deteriorates due to distortion and heat generation from the drive system
Solution Approach 1:
The system is divided into two separate hexapod structures: a drive hexapod for positioning and a metrology hexapod for measurement. Each structure independently performs its specific function, eliminating the interference between drive and measurement systems while maintaining the structural simplicity of hexapod configurations.
Solution Approach 2:
The metrology arrangement is extracted from the drive arrangement to form a separate, independent measurement system. This extraction removes the source of distortion and heat generation from the measurement path, thereby preserving measurement accuracy while the drive system continues to provide positioning functionality.
2Productivity
If a hexapod drive arrangement is used to achieve high speed and acceleration, then productivity is improved, but measurement accuracy deteriorates due to dynamic distortions
Solution Approach 1:
The system separates the dynamic drive function from the static measurement function into two independent hexapod structures. The drive hexapod can operate at high speeds and accelerations without affecting the metrology hexapod, which remains stable and undisturbed for accurate measurements.
Solution Approach 2:
The controller acts as an intermediary that coordinates between the drive hexapod and metrology hexapod. It uses measurements from the metrology system to compensate for and correct any dynamic distortions in the drive system, thereby maintaining measurement accuracy during high-speed operation.
3Device complexity
If drive mechanisms are integrated with the measurement system, then device complexity is reduced, but hysteresis effects increase leading to reduced accuracy
Solution Approach 1:
The system is segmented into two independent hexapod structures with separate drive and measurement functions. This segmentation eliminates hysteresis effects in the measurement system since the metrology hexapod operates independently without integrated drive mechanisms that would cause mechanical hysteresis.
Solution Approach 2:
The drive mechanisms are extracted from the measurement system and placed in a separate drive hexapod. This extraction removes the source of hysteresis from the measurement path, allowing the metrology hexapod to provide accurate measurements without being affected by mechanical hysteresis from integrated actuators.
4Speed
If a lightweight drive system is used to achieve rapid movement, then speed is improved, but structural rigidity decreases affecting measurement stability
Solution Approach 1:
The system segments the lightweight drive function from the stability-critical measurement function. The drive hexapod can be optimized for speed with lighter components, while the metrology hexapod maintains the structural rigidity needed for stable, accurate measurements during rapid movements.
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 enables quick movement of the structure around the working volume with retained accuracy, reducing production costs and minimizing hysteresis effects, while achieving higher dynamic bandwidth and finer motion control through direct sampling of measurement transducers.
Implementation Method 1
Each length-measuring transducer 10 may comprise an encoder scale paired with a readhead, with the encoder scale being mounted suitably to one of the pair of telescopic tubes and the readhead mounted suitably on the other. Extension of the leg 6 thus causes the encoder scale to move past the readhead thereby allowing the length of the extendible leg 6 to be measured.
Implementation Method 2
The extendable legs 6 are typically mounted on the structures 2, 4 via ball joints 8, with each leg 6 either having its own ball joint 8 at one or both ends thereof
Data Source
Figure 1
Figure 2~3
Figure 4~11
AI summary
A coordinate positioning machine is disclosed that comprises a structure (22) moveable within a working volume (34) of the machine, a hexapod metrology arrangement (26) for measuring the position of the structure (22) within the working volume (34), and a non-hexapod drive arrangement (28) for moving the structure (22) around the working volume (34). Also disclosed is a coordinate positioning machine comprising 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).