Split Wheatstone Bridge Force Sensor for Off-Axis Noise Rejection
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Solution Overview
Problem
Force sensors on surgical instruments face challenges in accurately measuring orthogonal forces due to noise from off-axis moments, torsion, and temperature variations, with limited space and high manufacturing costs hindering the addition of redundant measurement circuits.
Innovation Solution
A force sensor design with interleaved or staggered split Wheatstone bridges at the proximal and distal ends of a beam, using tension and compression gauge resistors aligned along the neutral axis to cancel noise and temperature effects, allowing for redundant measurements to detect errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional full-bridges are provided to produce redundant force measurements for error detection, then measurement reliability is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The beam is divided into multiple segments along its longitudinal axis, with Wheatstone bridges positioned at different locations (proximal and distal ends). Each bridge measures strain in its local segment, and the segmented measurements are combined to cancel out common-mode errors while maintaining redundancy for error detection.
Solution Approach 2:
The Wheatstone bridge circuit configuration serves multiple functions simultaneously: it measures orthogonal forces, cancels temperature effects through gauge arrangement, rejects off-axis moments through differential measurement, and provides redundant measurements for error detection. This multi-functionality reduces the need for separate dedicated error detection circuits.
2Measurement precision
If full-bridges are formed on four side faces to improve measurement accuracy, then measurement precision is improved, but manufacturing cost increases significantly
Solution Approach 1:
Instead of uniformly distributing bridges on all four side faces, the invention places Wheatstone bridges strategically at specific locations (proximal and distal ends) on the beam. The bridge orientation and gauge placement are locally optimized to capture the strain patterns relevant to orthogonal force measurement while rejecting other stress components.
Solution Approach 2:
The Wheatstone bridge gauges are arranged in an asymmetric pattern relative to the beam geometry, with tension and compression gauges positioned at specific orientations. This asymmetric arrangement allows the bridge to selectively measure orthogonal forces while automatically rejecting symmetric stress components like off-axis moments and torsion through differential measurement.
3Measurement precision
If strain gauges are placed close to anatomical tissue interaction to improve haptic accuracy, then measurement precision is improved, but the sensor is more susceptible to noise from off-axis moments and torsion
Solution Approach 1:
The harmful effects of off-axis moments, torsion, and temperature variations are extracted and separated from the desired orthogonal force measurement through the Wheatstone bridge differential measurement technique. By measuring strain at multiple locations and combining the signals, the bridge configuration isolates the orthogonal force component while extracting and canceling the unwanted noise components.
Solution Approach 2:
The invention converts the harmful effects of complex stress states (off-axis moments, torsion, temperature gradients) into beneficial information. By strategically placing gauges that experience these harmful effects, the Wheatstone bridge configuration uses the differential strain patterns to automatically reject these components and isolate the desired orthogonal force measurement, turning potential noise sources into useful reference signals for error cancellation.
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 design effectively cancels noise and temperature variations, ensuring accurate force measurement and error detection, enhancing safety and reliability in surgical procedures.
Implementation Method 1
A first Wheatstone bridge is disposed on a first face of the beam and includes first and second tension gauge resistors and first and second compression gauge resistors
Implementation Method 2
the beam may be secured to a distal portion of a surgical instrument shaft to sense forces orthogonal to a longitudinal axis of the shaft
Data Source
AI summary
A force sensor comprising a beam having a longitudinal axis and a proximal end portion and a distal end portion; a first Wheatstone bridge disposed on a first face of the beam, including multiple tension gauge resistors and multiple compression gauge resistors; a second Wheatstone bridge disposed on the first face of the beam, including multiple tension gauge resistors and multiple compression gauge resistors; wherein at least one tension gauge resistor and at least one compression gauge resistor from each of the first and second Wheatstone bridges is disposed at a proximal end portion of the beam; wherein at least one tension gauge resistor and at least one compression gauge resistor from each of the first and second Wheatstone bridges is disposed at a distal end portion of the beam.