Force Torque Transducer Drift Elimination via Load Cell Matrix
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Solution Overview
Problem
Conventional force/torque transducers are prone to drift, particularly in measuring Z-axis forces and torques, due to thermal expansion and strain gauge errors, leading to unreliable measurements in robotic surgical applications.
Innovation Solution
A force/torque transducer design featuring a plurality of load cells with sensors that utilize a transformation matrix to cancel systematic noise and offset, ensuring that forces of opposite algebraic signs cancel each other out, thereby eliminating drift and thermal effects, and providing reliable measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional force/torque transducer with strain gauges is used, then force measurement capability is provided, but drift and thermal expansion cause measurement reliability to deteriorate
Solution Approach 1:
The transducer divides the measurement function into multiple independent load cells (at least three) arranged in different orientations. Each load cell measures force components independently, and the results are combined through a transformation matrix to produce the final force/torque measurements. This segmentation allows systematic errors in individual cells to be distributed and cancelled out in the aggregate measurement.
Solution Approach 2:
The invention changes the measurement parameters by using multiple load cells oriented at different angles (e.g., 0°, 60°, 120°) rather than a single strain gauge configuration. By measuring the same physical quantity through multiple parameter configurations and combining them mathematically, the system achieves cancellation of systematic drift and thermal expansion effects that affect all measurements equally.
2Stability of the object's composition
If multiple load cells are used to cancel systematic noise, then measurement stability improves, but device complexity increases
Solution Approach 1:
The invention merges the output signals from multiple load cells through a transformation matrix to produce the final force and torque measurements. By combining the measurements from at least three load cells in a coordinated manner, the system achieves stability through error cancellation while maintaining a relatively compact transducer structure that integrates all components within a unified mechanical assembly.
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 effectively eliminates start-up and thermal drift, ensuring stable and accurate measurements of forces and torques across all axes, enhancing the reliability of robotic surgical procedures.
Implementation Method 1
The load cells include strain gauges or other sensors for measuring the physical deformations of the load cells
Implementation Method 2
drift may occur during initialization of the conventional force/torque transducer 10. A strain gauge 18 is a resistor having a value that changes due to strain. As a resistor, the strain gauge 18 consumes power. The consumed power is transformed into heat. The heat of the strain gauge 18 is conducted locally to the material of the spoke 16 upon which the strain gauge 18 rests. An internal stress develops on the spokes 16 because the material of the spokes 16 expands, but is constrained.
Data Source
AI summary
A force/torque transducer comprises a first member, a second member for receiving a load, and load cells connecting the first and second members. The load cells include sensors for measuring physical deformation of the load cells. Sensor measurements are convertible into force/torque measurements using a transformation matrix configured with M rows and N columns. M and N are respectively defined by a number of degrees of freedom monitored by the transducer and a number of load cells employed by the transducer, or vice-versa. Each row or column that corresponds to each load cell has values relating to that one load cell. Each row or column that corresponds to each degree of freedom has values relating to that one degree of freedom. A sum of the values in each row or column corresponding to each degree of freedom is substantially equal to zero.