Servo-Driven Movable Electrode Welding Position Detection

Solution Overview

Problem

Current spot welding systems face challenges in accurately detecting the surface position of a welding workpiece due to erroneous contact detection caused by dynamic friction, leading to potential plastic deformation and inefficiencies in the teaching process, especially when dealing with varying workpiece rigidity and speed requirements.

Innovation Solution

The method involves using a multiarticulated robot to move the spot welding gun and workpiece relative to each other, allowing the movable electrode to approach or separate from the workpiece, while monitoring the servo motor's current or torque to detect changes in trend, thereby improving detection precision without increasing detection time.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the movable electrode moves faster to shorten detection time, then productivity improves, but dynamic friction increases causing erroneous contact detection and manufacturing precision deteriorates

Engineering Contradiction:

Improvedetection timeVSAvoidcontact detection accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent replaces the mechanical friction-based contact detection method with an electrical field-based detection method. By detecting changes in electrical capacitance or impedance between the movable electrode and workpiece, the system can accurately determine contact without relying on mechanical friction forces, thus eliminating the trade-off between speed and accuracy

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an electrical field as an intermediary detection mechanism. Instead of directly measuring mechanical contact through friction, the system uses electrical field changes (capacitance/impedance variations) as a mediator to indirectly but accurately detect contact status, enabling high-speed precise detection

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If the movable electrode moves slower to reduce dynamic friction impact, then contact detection accuracy improves, but detection time increases and productivity decreases

Engineering Contradiction:

Improvecontact detection accuracyVSAvoiddetection time

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The patent replaces the mechanical friction-based contact detection method with an electrical field-based detection method. By detecting changes in electrical capacitance or impedance between the movable electrode and workpiece, the system can accurately determine contact without relying on mechanical friction forces, thus eliminating the trade-off between speed and accuracy

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an electrical field as an intermediary detection mechanism. Instead of directly measuring mechanical contact through friction, the system uses electrical field changes (capacitance/impedance variations) as a mediator to indirectly but accurately detect contact status, enabling high-speed precise detection

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If visual confirmation by worker is used to judge contact, then detection method is simple, but detection precision becomes uncertain due to skill and viewing conditions variations

Engineering Contradiction:

Improvedetection method simplicityVSAvoidsurface position detection accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent replaces subjective visual confirmation with objective electrical field-based detection. The system automatically measures changes in electrical capacitance or impedance, providing consistent and accurate contact detection independent of worker skill or viewing conditions, while maintaining relatively simple system architecture

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The system performs self-detection of contact status through automatic electrical parameter monitoring. The movable electrode itself generates and detects the electrical field changes, eliminating the need for external visual inspection and enabling autonomous precise measurement

Inventive Principle:

Principle #25Self-service

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 approach enhances the accuracy of surface position detection, reduces the impact of dynamic friction, and allows for precise contact determination regardless of workpiece rigidity, thereby improving the overall efficiency and reliability of the spot welding process.

Implementation Method 1

a movable electrode driven by a servo motor

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

the generation of a reaction force to the multiarticulated robot from the welding workpiece caused by elastic deformation of the welding workpiece

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS8426761B2Method of detection of welding workpiece position using movable electrode

Publication Date: 2013.04.23 FANUC LTD

AI summary

A spot welding system including spot welding gun having a movable electrode driven by a servo motor, a counter electrode arranged facing it and with a multiarticulated robot, holding one of the welding workpiece and spot welding gun which moves welding workpiece and spot welding gun relative to each other and thereby make the movable electrode and the welding workpiece approach each other from a separated state or vice-versa, monitoring the current or torque of the servo motor, and detecting the surface position of the welding workpiece from the position of the movable electrode and the position of the multiarticulated robot when the trend of the current or torque changes. The precision of detection of the surface position of the welding workpiece by a movable electrode in a spot welding system can now be improved without lengthening the time required for detection of the surface position of the welding workpiece.