Robot Wrist Torque Sensor with Bushing-Isolated Torsion
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Solution Overview
Problem
Designing a robot arm wrist that balances compactness, high torque transfer, stiffness, and accurate torque and position sensing is challenging due to the need for efficient motor and gearing integration and compact sensor arrangements.
Innovation Solution
A torque sensor arrangement featuring a deflectable body with a strain gauge and a bushing that isolates torsion from the sleeve, allowing for compact and accurate torque measurement, combined with a position sensing system using Hall effect sensors and magnetic rings, enables efficient data transmission and precise joint control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If motors and gearing are integrated into the wrist to deliver high torque, then torque capability is improved, but device complexity and size increase
Solution Approach 1:
The torque sensor arrangement integrates the deflectable body, strain gauges, and bushing into a single compact unit that combines torque sensing and transmission functions. The interface member with engagement configurations merges coupling and sensing capabilities into one component, reducing overall drive arrangement complexity while maintaining high torque capability.
Solution Approach 2:
The bushing is located between and in contact with both the rigid sleeve and the deflectable body, creating a nested structure where the deflectable body is surrounded by the rigid sleeve. This nesting allows compact packaging of multiple functional elements within the wrist assembly, achieving high torque transfer in a limited space.
2Measurement precision
If torque sensors are added to the wrist for accurate sensing, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The torque sensing function is merged with the torque transmission path by using the deflectable body that is naturally deformed by applied torque. The strain gauges are attached directly to this deflectable body, combining the load path and sensing function into a single integrated arrangement, thereby improving torque measurement accuracy without proportionally increasing complexity.
3Volume of moving object
If the wrist is made compact to accommodate multiple joints, then volume is reduced, but stiffness and torque transfer capability deteriorate
Solution Approach 1:
The rigid sleeve provides localized stiffness and structural support in specific regions where torque transmission is critical, while the deflectable body provides controlled flexibility for torque sensing. This local differentiation of mechanical properties allows the wrist to maintain compact size while preserving necessary stiffness and torque transfer capability through strategic placement of rigid and flexible elements.
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 solution provides a compact, stiff, and accurate drive arrangement for robot arm wrists, enabling high torque transfer and precise position sensing, enhancing the robot's ability to perform complex surgical procedures with reduced maintenance needs.
Implementation Method 1
a deflection sensor attached to the deflectable body
Implementation Method 2
a position sensing system using Hall effect sensors and magnetic rings
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A torque sensor arrangement (150) for attachment between a first part (108) and a second part (101) to sense torque therebetween, the torque sensor arrangement comprising: an interface member (155) having on its exterior an engagement configuration for rotationally engaging the first part (108); a torsion member comprising a deflectable body (156) attached at one end thereof to the interface member (155) and comprising, at the other end of the deflectable body, an engagement configuration (163) for rotationally engaging the second part; a deflection sensor (160) attached to the deflectable body (156); wherein the torque sensor (150) arrangement further comprises a bushing (161) located around and in contact with the deflectable body (156).