Shoulderless Rotary Joints for Lightweight Accurate Portable CMMs
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Solution Overview
Problem
Conventional portable coordinate measuring machines face accuracy issues due to thermal and load-induced warping, and improvements in accuracy often result in increased weight and bulkiness, with existing construction processes limiting precision in long joints.
Innovation Solution
The development of a portable coordinate measurement machine with shoulderless rotary joints, controlled damping mechanisms, and structural elements made from materials with matching thermal expansion coefficients, combined with advanced manufacturing techniques like grinding and honing, to achieve precise and lightweight measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional portable coordinate measuring machines use traditional joint construction with shoulders and flanges, then manufacturing is easier, but measurement accuracy deteriorates due to cumulative errors and thermal expansion
Solution Approach 1:
The patent removes the traditional shoulder and flange features from joint construction, extracting only the essential bearing mounting functionality. This eliminates the cumulative errors associated with multiple machining operations and thermal expansion differences between dissimilar materials, thereby improving measurement accuracy while simplifying the manufacturing process through fewer critical dimensions
Solution Approach 2:
The patent changes the fundamental geometric parameters of joint construction by eliminating shoulders and flanges, transitioning to a shoulderless design where bearings are mounted directly on precision-ground journal surfaces. This parameter change reduces the number of critical dimensions and eliminates thermal expansion mismatches, improving both accuracy and manufacturability
2Measurement precision
If conventional portable coordinate measuring machines use improved accuracy components, then measurement accuracy improves, but weight and bulkiness increase significantly
Solution Approach 1:
The patent segments the joint construction into essential functional components only, eliminating non-essential mass-contributing features like large shoulders and flanges. Each joint is designed with minimal material while maintaining precision through careful selection of critical surfaces, reducing overall machine weight while preserving measurement accuracy
Solution Approach 2:
The patent changes the dimensional parameters of joint components by eliminating shoulders and flanges, resulting in more compact and lighter joints. The precision is maintained through focused machining of essential surfaces rather than relying on massive structural features, achieving weight reduction without sacrificing measurement accuracy
3Manufacturing precision
If conventional portable coordinate measuring machines use traditional joint design with shoulders and flanges, then assembly is simpler, but manufacturing precision deteriorates due to multiple critical dimensions
Solution Approach 1:
The patent extracts and removes the shoulder and flange features from joint construction, eliminating the multiple critical dimensions associated with these features. This leaves only the essential bearing mounting surfaces, thereby improving manufacturing precision by reducing the number of dimensions that must be controlled while simplifying the overall joint construction
Solution Approach 2:
Instead of adding shoulders and flanges to provide mounting surfaces, the patent inverts the approach by providing mounting surfaces directly on the journal surfaces without protruding features. This inversion eliminates the need for multiple critical dimensions and simplifies both construction and assembly
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
The machine achieves high accuracy and reduced weight by minimizing thermal expansion effects and improving joint precision, resulting in significantly better measurement accuracy compared to prior art machines.
Implementation Method 1
at least one of the rotary joints includes a rotary damper operably coupled to the shaft and the housing and configured to provide controlled damping of rotational movement of the shaft about the axis of rotation
Implementation Method 2
Particularly in portable coordinate measuring machines, warping of the arm caused by thermal changes or by changes in loads has a negative effect on the measurement's accuracy
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A portable coordinate measurement machine (CMM) includes an articulated arm including arm segments and rotary joints. At least one of the rotary joints includes a shaft configured to rotate about an axis of rotation of at least one of the rotary joints. The shaft includes a middle portion and first and second end portions fixedly attached to ends of the middle portion. At least one of the rotary joints includes first and second housing ends, the first housing end having an inner diameter that engages an outer diameter of the first bearing and the second housing end having an inner diameter that engages an outer diameter of the second bearing. The first and second bearings are preloaded to remove play.