Torque Sensor Spoke Design for Articulated Robot Joints
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Solution Overview
Problem
Existing torque measurement systems in articulated-arm robots are prone to measurement inaccuracies due to deformation caused by lateral forces, axial forces, and bending moments, leading to potential false emergency shutdowns.
Innovation Solution
A torque sensor design featuring multiple strain gauges arranged on measuring spokes, connected in Wheatstone bridge circuits, which compensates for deformations by using strain gauges that are both stretched and compressed, ensuring accurate torque detection through cross-comparison of bridge voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain gauges are used to measure torque in articulated robot joints, then torque measurement capability is provided, but measurement precision deteriorates due to deformation from lateral forces, axial forces, and bending moments
Solution Approach 1:
The torque sensor is divided into multiple measuring spokes (typically three or four) arranged radially around the joint axis. Each spoke contains strain gauges that measure local deformation. By segmenting the measurement into multiple independent spokes, the system can distinguish between torque-induced deformation and deformation from other forces, thereby improving measurement precision while compensating for harmful deformations.
Solution Approach 2:
Multiple strain gauge measurements from different spokes are combined through a signal evaluation unit that processes the measurements collectively. The evaluation unit merges the data from all spokes and applies compensation algorithms to eliminate the effects of lateral forces, axial forces, and bending moments, leaving only the pure torque measurement. This merging approach transforms individual imperfect measurements into a precise combined result.
2Reliability
If multiple strain gauges are arranged on measuring spokes to compensate for deformations, then measurement reliability improves, but device complexity increases
Solution Approach 1:
The measuring spokes are arranged asymmetrically at specific angular intervals (e.g., 120 degrees for three spokes, or 90 degrees for four spokes) rather than uniformly. This asymmetric arrangement optimizes the compensation of specific force components while maintaining structural simplicity. The asymmetric configuration allows the evaluation unit to mathematically eliminate unwanted force components while keeping the physical structure relatively simple.
Solution Approach 2:
The system changes the measurement parameters by using multiple strain gauges at different orientations and locations on each spoke. By varying the orientation angles and positions of the strain gauges, the system creates a set of measurements with different sensitivity to various force components. This parameter variation enables the evaluation unit to solve for pure torque while compensating for other forces, improving reliability without requiring overly complex hardware.
3Measurement precision
If strain gauges are arranged on multiple spokes to reduce measurement errors, then measurement precision improves, but the number of components increases
Solution Approach 1:
Each measuring spoke serves multiple functions: it measures torque, compensates for lateral forces, compensates for axial forces, and compensates for bending moments. By designing the spokes and strain gauges to fulfill multiple measurement functions simultaneously, the system achieves high measurement precision without needing to add separate dedicated sensors for each force component. The same physical structure performs multiple measurement tasks, reducing the overall quantity of components needed.
Solution Approach 2:
The system transitions from a single-plane measurement approach to a multi-dimensional measurement approach by distributing strain gauges at different angular positions and orientations around the joint. This dimensional expansion in the angular and spatial domains allows the system to capture information about multiple force components simultaneously. By adding angular dimensionality rather than simply adding more sensors in one direction, the system improves precision while minimizing component quantity.
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 provides reliable and precise torque measurement by minimizing interference from disturbing influences, reducing the likelihood of false shutdowns and enhancing the safety and accuracy of robot operation.
Implementation Method 1
A torque sensor can, for example, as shown in DE 36 05 964 A1, consist of a central hub section and an outer rim connected to each other by means of four measuring spokes offset by 90°... Two strain gauges are arranged on opposite sides of a measuring spoke in such a way that one side of the measuring spoke is stretched under the influence of the torque, while the opposite side is compressed.
Data Source
Figure 1~1c
Figure 2~2c
Figure 3~3c
AI summary
The invention relates to a torque sensor (10), in particular for detecting torques occurring on or in a joint of an articulated arm robot. The sensor comprises a number of measuring spikes (1, 2, 3, 4) that are designed to deform under the effects of torque, and a number of strain gauges (DR11, DR12, DR21, DR22, DR31, DR32, DR41, DR42), wherein two respective strain gauges are arranged on two opposing sides of the several measuring spikes (1, 2, 3, 4). In addition, a number of strain gauges are each connected in one of at least two bridge circuits.