Robot Arm Torque Sensor Calibration for Offset Compensation
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Solution Overview
Problem
Torque sensors in robot arms often exhibit offset torque, leading to inaccurate measurements of external loads due to friction and other factors, necessitating calibration to correct for these offsets.
Innovation Solution
A method for adjusting torque sensors in robot arms involves measuring torques in specific positions, rotating links by 180° about different axes, and calculating the arithmetic mean of these measurements to determine and correct for offset torques, thereby improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If torque sensors are used to measure torques in robot arm joints, then torque measurement capability is provided, but offset torque causes measurement inaccuracy
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements before actual torque measurement operations. The method pre-determines offset torque values through measurements in specific positions (including 180° rotation about roll axes) and stores these calibration data for subsequent correction during normal operation, ensuring accurate measurements from the start.
Solution Approach 2:
The patent changes the positional parameters of the robot arm during calibration by rotating links 180° about roll axes to create different measurement conditions. This parameter change allows the system to capture offset torque under varied configurations, improving the robustness of the calibration process.
2Measurement precision
If calibration procedures are implemented to correct offset torque, then measurement accuracy is improved, but calibration complexity increases
Solution Approach 1:
The patent implements self-service calibration where the robot arm calibrates its own torque sensors using its own motion capabilities. The system performs 180° rotations about roll axes and automatically processes the measurement data to determine offset torque values, eliminating the need for external calibration equipment or complex manual procedures.
Solution Approach 2:
The patent creates equipotential measurement conditions by positioning the robot arm in specific configurations (including 180° rotated positions about roll axes) where gravitational and frictional effects are minimized or balanced. This allows offset torque to be measured and corrected under controlled, equivalent conditions.
3Measurement precision
If multiple measurement positions including 180° rotation are used for calibration, then offset torque determination accuracy is improved, but calibration time increases
Solution Approach 1:
The patent uses periodic action by rotating links 180° about roll axes to create alternating measurement positions. This periodic motion between calibrated positions allows the system to efficiently capture offset torque characteristics through repeated, systematic measurements that can be processed using arithmetic mean calculations.
Solution Approach 2:
The patent applies partial action by selecting specific critical positions (including 180° rotation about roll axes) for calibration rather than measuring all possible positions. This targeted approach captures the essential offset torque information needed for accurate correction while minimizing the total number of measurements required.
Data Source
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AI summary
The invention relates to a method for adjusting a torque sensor (D2, D3) of a robot arm (1). The robot arm (1) is configured as an open kinematic chain and comprises an attachment device (3) for attaching an end effector (4), a plurality of joints (J1-J7) and a plurality of members (G1-G8) arranged one after the other and connected by means of the joints (J1-J7). One of the members (G1-G8) is a start member (G1) forming a start of the robot arm (1), and another of the members is an end member (G8) forming an end of the robot arm (1). The end member (G8) comprises the attachment device (3), an axis of rotation (A1-A7) is assigned to each of the joints (J1-J7) and the members (G1-G8) can move relative to one another in relation to the axes of rotation (A1-A7). One portion of the axes of rotation (A1, A3, A5, A7) are configured as roll axes and another portion of the axes of rotation (A2, A4, A6) are configured as tilt axes. At least the axis of rotation (A7) assigned to the joint between the end member (G8) and the member (G7) mounted upstream of the end member (G8), and the axis of rotation (A1) assigned to the joint between the start member (G1) and the member (G1) mounted directly downstream of the start member (g1) are formed as roll axes. The torque sensor (D2, D3) is provided to measure a torque which is assigned to one of the axes of rotation (A1-A7).