Spot Welding Robot Electrode Positioning via Servo Current Monitoring
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Solution Overview
Problem
Existing spot welding robot positioning methods face challenges in accurately positioning the opposition electrode tip due to dynamic friction, leading to potential gaps between electrode tips and work pieces, which degrades welding quality and increases operation time.
Innovation Solution
A method involving a movable electrode tip and an opposition electrode tip, where the opposition electrode tip is temporarily positioned on one side of the work piece, and the movable electrode tip is moved towards it while monitoring the servo motor current, allowing for accurate positioning by measuring the open separation and adjusting the opposition electrode tip's position based on the work piece's thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the robot moves the electrode tip to detect the work piece position by monitoring reaction force, then the work piece position can be detected, but dynamic friction in the robot mechanism causes inaccurate detection especially when reaction force is small
Solution Approach 1:
The patent introduces a force sensor as an intermediary device between the electrode tip and the work piece. The force sensor directly measures the reaction force when the electrode tip contacts the work piece, providing accurate position detection without being affected by dynamic friction in the robot mechanism. This mediator isolates the measurement system from the frictional effects in the mechanical transmission chain.
2Measurement precision
If the robot suppresses detection speed to reduce dynamic friction influence, then detection accuracy improves, but the time required for positioning increases
Solution Approach 1:
The patent replaces the mechanical friction-based detection method with an electrical sensing method using a force sensor. Instead of relying on slow, friction-reduced mechanical movement to detect position, the system uses the force sensor to instantly measure reaction force and calculate position, substituting mechanical detection with electrical measurement to eliminate the speed-accuracy trade-off.
3Manufacturing precision
If the electrode tips are positioned to sandwich the work piece without gap, then welding quality is maintained, but position variation of the work piece held by the jig makes accurate positioning difficult
Solution Approach 1:
The patent implements a feedback mechanism where the force sensor continuously monitors the reaction force during electrode tip movement. When the electrode tip contacts the work piece, the sudden change in reaction force provides feedback about the actual position, allowing the system to adjust and accurately position the electrode tip regardless of initial work piece position variations caused by jig tolerances.
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 reliability of welding by ensuring the opposition electrode tip is precisely positioned at the spot welding point without impairing the workability of the welding robot, allowing for improved quality and reduced operation time.
Implementation Method 1
a movable electrode tip capable of being moved forward and backward by means of a servo motor
Implementation Method 2
a reaction force exerted to a robot due to elastic deformation of a work piece when a pair of electrode tips of a spot welding gun is brought into contact with the work piece
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
A positioning method of spot welding robot (1) having: (A) moving a welding gun (6) with a separation between an opposition electrode tip (10) and a movable electrode tip (11) kept open and larger than a preset plate thickness (t1) of a work piece (12) so as to position the opposition electrode tip and the movable electrode tip on both sides of the work piece in a plate-thickness direction of the work piece, respectively, and temporarily positioning the opposition electrode tip at a stand-by position; (B) moving the movable electrode tip in a direction approaching toward the opposition electrode tip, monitoring the current value of the servo motor driving the movable electrode tip, and when the current value exceeds a prescribed value, determining that a distal end of the movable electrode tip has been brought into contact with the work piece, stopping a movement of the movable electrode tip and measuring an open separation (γ1) of two opposing tips between the movable electrode tip and the opposition electrode tip that has been temporarily positioned at the stand-by position; and (C) determining the difference value by subtracting the preset value for the work piece from the open separation of two opposing tips, and moving the opposition electrode tip in the direction approaching toward the movable electrode tip from the stand-by position to the position of a spot welding point to finally position the opposition electrode tip, by using the difference value as the amount of movement of the opposition electrode tip.