Compact Robotic Force Torque Sensor with Single-Surface Strain Gages
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Solution Overview
Problem
Conventional force/torque sensors require precise and costly manual labor for instrumentation, necessitate significant physical space for strain gage placement, and suffer from complex bond wire routing, leading to design constraints and increased risk of device failure, especially at small sizes.
Innovation Solution
A compact force/torque sensor design featuring strain gages affixed to only one surface of each beam, allowing for automated manufacturing and reduced mechanical complexity, with a quarter or half-bridge topology configuration to cancel common-mode signals and facilitate temperature calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain gages are affixed to all four surfaces of each beam, then measurement precision is improved, but device complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent extracts the strain gage instrumentation from three of the four beam surfaces, retaining only top-surface mounting. This reduces the complexity of manual installation and inspection while maintaining adequate measurement capability through strategic gage placement on the accessible surface.
Solution Approach 2:
Instead of fully instrumenting all four surfaces of each beam, the patent uses a partial instrumentation approach with strain gages on only the top surface. This partial action reduces manufacturing complexity and cost while still providing sufficient measurement data when combined with finite element analysis for force/torque resolution.
2Measurement precision
If strain gages are placed on all four surfaces of beams, then measurement accuracy is improved, but physical space requirements increase
Solution Approach 1:
The patent removes strain gage instrumentation from bottom and side surfaces, keeping only top-surface mounting. This extraction reduces the physical space required for gage placement and eliminates the need for clearance around obscured surfaces, enabling more compact sensor designs.
3Measurement precision
If strain gages are mounted on all surfaces of beams, then measurement completeness is improved, but ease of manufacture deteriorates
Solution Approach 1:
The patent extracts the complex multi-surface gage mounting process and replaces it with simplified top-surface-only instrumentation. This enables automated manufacturing processes such as pick-and-place machines to mount gages, and automated wire bonding or surface-mount technology to connect them, dramatically improving ease of manufacture.
Solution Approach 2:
The patent replaces manual mechanical gage installation and wire routing with automated processes including pick-and-place mounting, automated wire bonding, or surface-mount technology. This substitution of manual mechanical operations with automated systems improves manufacturing efficiency and consistency.
4Measurement precision
If complex bond wire routing is used to connect strain gages on all surfaces, then signal completeness is improved, but reliability decreases
Solution Approach 1:
The patent removes the need for complex wire routing through beam interiors by restricting gage mounting to the top surface. This extraction of wires from the beam structure eliminates a major source of potential failure points while maintaining adequate signal coverage for force/torque measurement.
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 enables a more compact, cost-effective, and reliable force/torque sensor with reduced assembly steps, improved stiffness, and automated manufacturing options, while effectively eliminating common-mode signals and temperature drift, enhancing the sensor's accuracy and durability.
Implementation Method 1
The gages translate tensile and compressive strains at the beams' surfaces into electrical signals
Data Source
AI summary
A force/torque sensor comprising a Tool Adapter Plate (TAP) connected to a Mounting Adapter Plate (TAP) by one or more radially-spaced, deformable beams features a pair of strain gages affixed to only one surface of each beam. The two strain gages are affixed to, e.g., the top surface on either side of, and spaced away from, a neutral axis of the beam. This enables a very compact sensor design, in one embodiment, machined from a single piece of metal stock. The two sensors may be connected in a quarter bridge topology. In one embodiment, another pair of strain gages is affixed to the same side of the beam, and the four gages are wired in a half-bridge topology. In another embodiment, a second pair of strain gages is affixed to the opposite side of the beam, and the four gages are wired in a half-bridge topology—although this embodiment gives up some of the space and ease of manufacture advantages, it allows for electrical elimination of common-mode signal components, such as those induced by temperature drift. In one embodiment, a strain gage is connected to a non-stressed member of the sensor 10 to provide a signal for temperature calibration.