Torque Sensor Zero Point Adjustment for Robotic Manipulators
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Solution Overview
Problem
Existing methods for zeroing torque sensors on manipulators are complex and prone to inaccuracies due to installation-related inherent stresses, requiring frequent recalibration and relying on precise torque-free states that are difficult to achieve.
Innovation Solution
A method involving storing links in a locally stable condition, deactivating the drive to the joint with the torque sensor, and opening any present brake to ensure a torque-free state, allowing for the recording of a reference torque-dependent measured value, which improves accuracy and reproducibility by eliminating directional interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional zeroing methods are used with drives and brakes engaged, then the manipulator can maintain operational readiness, but the torque sensor readings are contaminated by installation stresses and drive torques reducing measurement precision
Solution Approach 1:
The calibration procedure is segmented into distinct phases: driving the manipulator to reference poses, deactivating the drive, opening the brake, and recording torque values. This segmentation allows each phase to be optimized independently, achieving high measurement precision without requiring overly complex simultaneous control of all systems.
Solution Approach 2:
The drive is deactivated and the brake is opened before recording the torque sensor values. This preliminary action eliminates drive torques and friction from the measurement, ensuring that only the torque from installation stresses and gravity act on the joint, thereby improving zero point determination accuracy.
2Measurement precision
If the drive and brake are deactivated during zeroing, then torque-free state is achieved improving measurement accuracy, but the manipulator loses operational readiness increasing loss of time
Solution Approach 1:
The drive is periodically deactivated only during the brief moment when torque sensor values are recorded, then reactivated for normal operation. This periodic deactivation minimizes the time the manipulator is non-operational while ensuring accurate zero point calibration is achieved during these brief calibration intervals.
Solution Approach 2:
The calibration procedure rushes through the drive deactivation and brake opening phases as quickly as possible, recording the necessary torque values in a brief window, then immediately restoring operational readiness. This minimizes the time loss while achieving the required measurement precision.
3Reliability
If multiple torque sensors are used for redundant detection, then reliability is improved, but the device complexity and cost increase
Solution Approach 1:
Multiple torque sensors are merged into a single torque sensor assembly that detects torque at the joint. This combining approach maintains the redundancy and reliability benefits of multiple sensors while reducing the overall system complexity compared to having separate sensor systems.
Solution Approach 2:
The torque sensor assembly serves multiple functions: it provides redundant torque detection, enables zero point calibration, and monitors joint status. This multi-functionality reduces the need for separate systems, thereby improving reliability without proportionally increasing device complexity.
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 method enhances the accuracy and reproducibility of zero point determination for torque sensors, allowing for more flexible reference poses and reducing the need for frequent recalibrations, even when loads are present on the manipulator arm.
Implementation Method 1
at least one strain gauge (DMS) is rigidly connected to the web section in such a way that bending of the web section causes deformation of the strain gauge, as a result of which an electrical resistance of a wire section of the strain gauge changes proportionally
Implementation Method 2
an electrical resistance of a wire section of the strain gauge changes proportionally, in particular linearly, to the elongation of the web section
Implementation Method 3
Up to four strain gauges are usually connected to an electrical voltage source in what is known as a Wheatstone bridge, so that an electrical voltage can be applied to such a torque sensor that is proportional, in particular linearly proportional, to the expansion of the web section
Implementation Method 4
DONGHAI MA ET AL 'Gravity Based Autonomous Calibration for Robot Manipulators' describes a method for finding the direction of gravity. In order to be able to obtain the sought-after direction of gravity, the torque sensor must be calibrated
Data Source
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AI summary
The invention relates to a method for adjusting the zero point of a torque sensor (4) relative to a manipulator (1, 1a), which has multiple elements (2) connected via joints (3). At least one joint (3) which can be moved by means of a drive rotatably connects a first element (9, 2.4) of the manipulator (1, 1a) to a second element (10, 2.5) of the manipulator (1, 1a), and at least one torque sensor (4) is coupled to said joint (3), said torque sensor supplying at least one torque-dependent measured value. The method has the following steps: - mounting the first element (9, 2.4) and the second element (10, 2.5) in a locally stable state; - connecting at least the drive of the joint (3) to which the torque sensor (4) to be adjusted is coupled without being driven; - opening an optionally provided closed brake of the joint (3) to which the torque sensor (4) to be adjusted is coupled; and - subsequently receiving the torque-dependant measured value of the torque sensor (4) to be adjusted as a reference value of a torqueless state of the joint.