Robot Axis Torque Estimation for Spot Welding Contact Position
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Solution Overview
Problem
Existing spot welding systems face challenges in accurately detecting the contact position between the welding electrode and the workpiece due to delays in referencing torque information from the robot controller, leading to reduced accuracy in position compensation and potential deformation of the workpiece.
Innovation Solution
A robot system that utilizes torque information from robot axes to detect contact positions by estimating changes in torque characteristics, incorporating a torque restriction unit and control method switching based on S/N ratios to enhance contact detection accuracy and reduce workpiece deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If torque information from the robot controller is referenced to detect contact position, then contact detection can be performed, but a delay occurs due to individual controllers for robot axis and gun axis
Solution Approach 1:
The patent merges the robot controller and gun controller into a single integrated controller. This consolidation eliminates the communication delay between separate controllers when referencing torque information, allowing real-time detection of contact position based on robot axis torque characteristics without the time loss inherent in distributed control architectures.
Solution Approach 2:
The patent introduces a dedicated torque information acquisition unit within the integrated controller that directly accesses robot axis torque data. This intermediary mechanism enables efficient retrieval of torque information without the communication overhead and delays associated with inter-controller data exchange, facilitating timely contact position detection.
2Measurement precision
If the movable electrode and workpiece are brought into contact to detect contact position, then contact detection is possible, but it is impossible to detect contact when the opposite electrode and workpiece make contact
Solution Approach 1:
The patent replaces mechanical contact-based detection with torque-based detection using the robot axis motor. By monitoring changes in torque characteristics during the closing operation, the system can detect contact positions without requiring physical contact between electrodes and workpiece, thereby enabling detection in all contact scenarios including when the opposite electrode contacts the workpiece.
Solution Approach 2:
The patent uses torque information from the robot axis motor as an intermediary indicator of contact. Instead of directly observing electrode-workpiece contact, the system detects changes in the torque required to move the robot arm, which indirectly but reliably indicates when contact occurs, regardless of which electrode contacts the workpiece.
3Productivity
If torque threshold monitoring is used for contact detection, then contact can be detected, but the accuracy of contact position detection is lowered compared to torque characteristic variation monitoring
Solution Approach 1:
The patent implements feedback monitoring of torque characteristic variations throughout the closing operation. By continuously tracking how torque changes evolve during the process and comparing these variations against expected patterns, the system achieves high-precision contact position detection while maintaining real-time operation, overcoming the accuracy limitations of simple threshold-based methods.
Solution Approach 2:
The patent transitions from static torque threshold checking to dynamic analysis of torque characteristic variations. By examining how torque changes over time and comparing the rate of change during closing versus idle periods, the system achieves both rapid detection and high precision in contact position determination, adapting the detection criteria to the actual operational state.
Data Source
AI summary
A robot system includes: an articulated type robot which retains a processing tool at an arm tip end portion and which includes a plurality of drive units that drive a plurality of drive axes; and a robot controller which controls the drive units so as to control a relative position of the processing target and the processing tool and the robot controller includes: a torque information detection unit which detects torque information on the torques of the drive units; a contact position estimation unit which estimates, based on the change of tendency of a variation in the detected torque information of at least one of the drive units, a contact position in which the processing target and the processing tool make contact with each other; and a position compensation unit which compensates the target position of the robot based on the estimated contact position.