Robotic Arm Cable Routing via Non-Aligned Passages
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Solution Overview
Problem
Existing robotic arms used in convoluted paths, such as inside engines or human bodies, face instability and imprecision due to loose-fitting control cables, leading to uncontrolled link movement and hysteresis errors, as the cables must be slightly larger than apertures to accommodate manufacturing tolerances and load changes.
Innovation Solution
The robotic arm features passages in adjacent links with non-aligned axes, allowing cables to bear against specific portions, providing accurate positioning and constraining link movement, combined with low-friction materials and oscillating movements to reduce friction and improve geometric modeling for precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the cables are made to fit closely within the apertures to restrict link movement and improve positioning accuracy, then the arm positioning accuracy and stiffness are improved, but the manufacturing complexity and assembly difficulty increase due to the need for precise tolerances and cable installation
Solution Approach 1:
The passage through which the cable passes is divided into two non-aligned segments in adjacent links. This segmentation allows the cable to be slightly smaller than the passage while still achieving accurate positioning through the non-aligned configuration, resolving the contradiction between positioning accuracy and ease of manufacture.
Solution Approach 2:
The passage axes in adjacent links are intentionally made non-aligned, creating an asymmetric cable path. This asymmetry ensures the cable bears against predetermined portions of the passages, providing accurate positioning without requiring the cable to be a tight fit, thus improving ease of manufacture while maintaining positioning accuracy.
2Ease of manufacture
If the cables are made slightly smaller than the apertures to accommodate manufacturing tolerances and load changes, then the ease of manufacture and cable installation are improved, but the link movement control and arm stiffness deteriorate
Solution Approach 1:
The non-aligned passage axes create an asymmetric cable routing that ensures the cable contacts predetermined portions of the passages. This asymmetric configuration provides stable link movement control even when the cable is slightly smaller than the passage, resolving the contradiction between ease of manufacture and link movement control.
Solution Approach 2:
The non-aligned passage configuration acts as an intermediary mechanism that translates the slightly loose cable fit into effective link movement control. The geometric relationship between the non-aligned passages provides the necessary constraint without requiring a tight cable fit, resolving the contradiction between cable installation ease and link movement control.
3Ease of operation
If the cables are made smaller in diameter to reduce friction and improve movement, then the ease of operation and reduced hysteresis errors are improved, but the ability to constrain link movement and maintain positioning accuracy deteriorates
Solution Approach 1:
The non-aligned passage axes create an asymmetric cable path that ensures cables of smaller diameter still bear against predetermined portions of the passages. This asymmetric configuration maintains link position determination accuracy while allowing smaller diameter cables that experience reduced friction, resolving the contradiction between ease of operation and measurement precision.
4Ease of manufacture
If the passages are made larger than the cable diameter to allow cable movement and accommodate tolerances, then the ease of manufacture and cable installation are improved, but the positioning accuracy and arm stiffness deteriorate due to uncontrolled link movement
Solution Approach 1:
The non-aligned passage configuration creates an asymmetric cable routing that provides effective link movement control even when passages are larger than the cable diameter. The geometric relationship between non-aligned passages ensures cables bear against predetermined portions, maintaining arm stiffness while allowing for manufacturing tolerances and ease of assembly.
Data Source
Figure 1a~2
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AI summary
In a "tip following" robotic arm, the apertures through which control cables pass are arranged to ensure that the cables are in contact with a known part of the aperture. This leads to a more stable and controllable arrangement.