Robot Torque Feedback Control for Precise Tool Contact Detection
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Solution Overview
Problem
Conventional spot welding systems face challenges in accurately detecting contact between electrodes and workpieces, leading to potential damage due to excessive pressure, as existing methods have low detection accuracy and can cause deformation and stress increases during the welding process.
Innovation Solution
A robot control device that monitors torque from internal and external drive axes to accurately detect contact and compensate for the target position, incorporating a torque limiting unit to prevent excessive pressure, allowing for precise control of the processing tool's contact with the workpiece.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If torque monitoring is used to detect contact between electrode and workpiece, then contact detection capability is improved, but detection accuracy deteriorates due to delayed reference and low precision in determining contact instant
Solution Approach 1:
The system continuously monitors torque values from drive axes and uses this feedback to detect contact between the electrode and workpiece. The control device receives torque information from multiple sources (robot drive axis, tool drive axis, and external drive axis) and processes this feedback in real-time to determine contact timing and position, thereby improving both detection accuracy and reliability.
Solution Approach 2:
The invention expands detection from a single torque source to multiple dimensions by monitoring torque from three different drive axes simultaneously. This multi-dimensional approach allows the system to cross-validate torque changes and more accurately determine the instant of contact, resolving the limitation of single-source torque monitoring.
2Measurement precision
If mobile electrode and workpiece contact is required for detection, then contact position can be estimated, but counter electrode and workpiece contact cannot be detected
Solution Approach 1:
The torque monitoring system is designed to detect contact for both mobile electrode and counter electrode with the workpiece. By monitoring torque from multiple drive axes including the external drive axis that positions the entire robot, the system can detect contact regardless of which electrode makes contact first, providing universal detection capability for both electrode types.
Solution Approach 2:
The detection system is segmented into multiple independent torque monitoring channels, each monitoring a different drive axis. This segmentation allows the system to independently detect contact events from different electrodes and combine the information, enabling comprehensive detection coverage for both mobile and counter electrodes.
3Device complexity
If threshold-based torque monitoring is used, then contact detection is simplified, but detection occurs after workpiece deformation and stress increase
Solution Approach 1:
The system performs preliminary detection by monitoring torque trends and changes from multiple drive axes before the workpiece undergoes significant deformation. By analyzing torque variations across multiple axes simultaneously, the system can detect contact at an earlier stage, allowing compliance control to prevent excessive pressing and workpiece damage before deformation occurs.
Solution Approach 2:
The detection system dynamically adjusts its monitoring approach by continuously tracking torque changes from multiple drive axes rather than using a fixed threshold. This dynamic monitoring allows the system to adapt to different contact scenarios and detect contact at the optimal moment, preventing workpiece deformation while maintaining detection sensitivity.
4Adaptability or versatility
If separate controllers are used for internal drive axes and tool drive axis, then control flexibility is improved, but communication delay increases
Solution Approach 1:
The control system merges torque monitoring from multiple separate controllers (robot controller and tool controller) into a unified detection framework. By integrating torque information from the robot drive axis, tool drive axis, and external drive axis in the control device, the system reduces communication delays and achieves more synchronized contact detection while maintaining the flexibility of separate control architectures.
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 enables more reliable prevention of damage to both the processing tool and workpiece by accurately detecting contact and controlling the pressure, thereby improving weld quality and reducing the risk of deformation.
Implementation Method 1
a torque limiting unit that limits output torque of at least one torque limiting axis among the internal drive axis and the external drive axis
Data Source
AI summary
A robot control device for a robot system including: a robot having a plurality of internal drive axes; a processing head retained to a leading end of the robot and having a processing tool and a tool drive axis to move the processing tool; and an external driving mechanism having one or more external drive axes and positions the robot. The robot system causes the processing tool to make contact with a processing target and conducts predetermined processing on the processing target. The control device controls the internal and external drive axes to position the processing head at a target position and controls the tool drive axis to make the processing tool make contact with the processing target, and the robot control device detects contact between the processing tool and the processing target by monitoring torque of the internal drive axis, the tool drive axis and the external drive axis.