Robot Arm Wrist Gear Layout for Compact High-Torque Sensing
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Solution Overview
Problem
Designing a robot arm wrist that balances compactness, high torque transfer, stiffness, and accurate sensor integration is challenging due to the need for compact motor and gearing arrangements, as well as precise torque and position sensor placement without compromising these criteria.
Innovation Solution
The robot arm incorporates a joint mechanism with sector gears and bevel gears, along with a torque sensor arrangement featuring a deflectable torsion member and strain gauges, and a rotary position sensor system using magnetic rings and Hall effect sensors, allowing for compact and accurate torque and position measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional full-circle gears are used in the wrist, then torque transfer capability is improved, but the size and weight of the distal portion increases
Solution Approach 1:
The patent divides the gear system into multiple sector gears, each covering only a portion of the rotational range (e.g., 90-120 degrees per sector). Multiple sector gears are arranged sequentially to cover the full rotation, but each individual gear element is much smaller than a complete circle gear, reducing the volume and mass of each component while maintaining full rotational capability through the segmented arrangement.
Solution Approach 2:
The patent nests multiple sector gears and gear trains within the compact wrist structure. The sector gears are arranged in a nested configuration where smaller gears are positioned within the spatial envelope of larger components, allowing multiple gear stages to be contained in a minimal volume. This nesting enables high gear reduction ratios without proportionally increasing the overall wrist size.
2Measurement precision
If multiple sensors and motors are integrated into the wrist, then measurement accuracy and control capability are improved, but the complexity of the arrangement increases
Solution Approach 1:
The patent combines multiple sensor functions into integrated sensor assemblies. Torque sensors and position sensors are merged into compact units that measure multiple parameters simultaneously. The sensor assemblies are integrated directly with the gear and motor components, eliminating separate mounting structures and reducing the overall complexity of the arrangement while maintaining high measurement accuracy.
Solution Approach 2:
The patent employs universal sensor platforms that can measure both torque and position, and potentially other parameters, using the same physical component. This multi-functionality reduces the number of separate sensors needed and simplifies the integration process. The sensors are designed to work across multiple measurement functions, reducing system complexity while enhancing measurement capabilities.
3Weight of moving object
If the distal portion is made compact and light, then the force required from proximal joints is reduced, but the structural strength and stiffness may be compromised
Solution Approach 1:
The patent employs composite materials in the construction of the distal portion components. High-strength, low-density materials such as carbon fiber composites or aluminum alloys are used to create structural elements that provide the necessary strength and stiffness while minimizing weight. The composite materials allow the distal portion to be both lightweight and structurally robust, resolving the contradiction between weight reduction and strength maintenance.
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 configuration enables a compact, stiff, and highly accurate robot arm wrist capable of high torque transfer and precise sensor measurements, addressing the challenges of integrating motors, gearing, and sensors within a small, circularly symmetrical profile.
Implementation Method 1
a torsion member comprising a deflectable body attached at one end thereof to the interface member and comprising, at the other end of the deflectable body, an engagement configuration for rotationally engaging the second part
Implementation Method 2
with a bushing located between and in contact with both the sleeve and the deflectable body
Implementation Method 3
a first ring defining a plurality of magnetic poles, the first ring being attached to the first part; a second ring defining a plurality of magnetic poles, the second ring being attached to the first part
Implementation Method 4
a first sensor attached to the second part for sensing motion of the magnetic poles of the first ring past that sensor; and a second sensor attached to the second part for sensing motion of the magnetic poles of the second ring past that sensor
Implementation Method 5
a first drive gear disposed about the first rotation axis and fast with the carrier, whereby rotation of the carrier relative to the first limb about the first rotation axis can be driven; a second drive gear disposed about the second rotation axis and fast with the second one of the limbs
Data Source
AI summary
A robot arm comprising a joint mechanism for articulating one limb (310) of the arm relative to another limb (311) of the arm about two non-parallel rotation axes (20, 21), the mechanism comprising: an intermediate carrier (28) attached to a first one of the limbs by a first revolute joint having a first rotation axis and to a second one of the limbs by a second revolute joint having a second rotation axis; a first drive gear (33) disposed about the first rotation axis and fast with the carrier, whereby rotation of the carrier relative to the first limb about the first rotation axis can be driven; a second drive gear (37) disposed about the second rotation axis and fast with the second one of the limbs, whereby rotation of the second one of the limbs about the second rotation axis relative to the carrier can be driven; at least one of the first and second drive gears being a sector gear.