Quarter-Bridge Force Torque Sensor Thermal Drift Compensation
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Solution Overview
Problem
Robotic force/torque sensors experience inaccuracies due to thermal drift caused by temperature changes, which are not fully compensated by existing methods, leading to errors in force and torque measurements.
Innovation Solution
A hardware temperature compensation procedure using trimming resistors is implemented in a quarter-bridge configuration to eliminate the effective temperature coefficient of load-sensing strain gages relative to an unstressed strain gage, ensuring accurate measurements over a predefined temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If strain gages are connected in a quarter-bridge circuit configuration, then the sensor achieves compact size and ease of manufacturing, but thermal drift causes measurement inaccuracies
Solution Approach 1:
The patent applies parameter changes by introducing trimming resistors with specific resistance values to adjust the temperature coefficients of the strain gages. By changing the electrical parameters (resistance values) of the compensation branch, the system achieves temperature compensation while maintaining the quarter-bridge configuration, thus resolving the contradiction between circuit simplicity and measurement accuracy.
Solution Approach 2:
The patent uses an unstressed strain gage as an intermediary element that experiences the same temperature changes as the load-sensing gages but is not subjected to mechanical stress. This intermediary gage, when connected in parallel with trimming resistors, provides a compensation signal that cancels out thermal drift effects, thereby improving measurement accuracy without increasing overall system complexity.
2Measurement precision
If trimming resistors are added to compensate for temperature effects, then measurement accuracy improves, but circuit complexity increases
Solution Approach 1:
The patent optimizes the resistance values of trimming resistors to achieve effective temperature compensation. By carefully selecting parameter values (resistance values), the system achieves accurate compensation with minimal additional components, balancing the trade-off between measurement precision and device complexity.
3Measurement precision
If half-bridge topology is used for temperature compensation, then thermal drift is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies local quality by making the compensation branch distinct from the measurement branch. The unstressed strain gage and trimming resistors form a dedicated compensation circuit with different properties (no mechanical stress) compared to the load-sensing gages. This localized differentiation allows temperature compensation without requiring precise matching and placement across the entire bridge structure, thus reducing manufacturing precision requirements.
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 approach significantly reduces thermal drift errors, enhancing the accuracy of force and torque measurements in robotic force/torque sensors by matching the temperature responses of load-sensing and unstressed strain gages, thereby improving sensor reliability.
Implementation Method 1
Resistive strain gages rigidly mounted to the sides of such a beam experience a corresponding elongation or abridgement, respectively, and the resistance of the strain gage is proportional to its length.
Implementation Method 2
the change in resistance of strain gages may be detected and quantified, such as by some configuration of a Wheatstone bridge circuit
Implementation Method 3
For silicon strain gages, changes in output voltage of the gage circuit due to temperature change can be several times the magnitude of output voltage changes due to induced stresses.
Data Source
AI summary
In a Force/Torque sensor employing strain gages, a hardware temperature compensation procedure substantially eliminates thermal drift of a plurality of load-sensing strain gages with changes in temperature, using trimming resistors and a single, unstressed strain gage. The strain gages are connected in a quarter-bridge configuration, in multiple parallel stages. An unstressed strain gage in quarter-bridge configuration is connected in parallel. Trimming resistors are added across one or more of the unstressed and load-sensing strain gages in a compensation procedure that substantially eliminates thermal drift of the load-sensing strain gages over a predefined temperature range.