Electromagnetic Contactor Contact Fusion Detection Without Auxiliary Contacts

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Solution Overview

Problem

Existing motor drive devices require an auxiliary contact and additional circuits to detect contact fusion in electromagnetic contactors, leading to increased costs and complexity.

Innovation Solution

A motor drive device with an AC/DC converter and integrated detection circuits, including a three-phase bridge circuit and current detector, allows for contact fusion detection without an auxiliary contact or additional circuit, utilizing the existing AC/DC converter's functionality to turn the electromagnetic contactor on/off and detect current flow.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an auxiliary contact and additional monitoring circuit are added to detect contact fusion, then contact fusion detection capability is improved, but device complexity and cost increase

Engineering Contradiction:

Improvecontact fusion detection capabilityVSAvoiddevice complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent makes the existing current detector serve dual functions: its original function of detecting motor operating current and an additional function of detecting contact fusion. By controlling the electromagnetic contactor to be in a specific state (turned off) during motor stopping, the current detector can distinguish between motor current and contactor leakage current, enabling contact fusion detection without adding hardware

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system uses its own existing components (electromagnetic contactor, current detector, control circuit) to perform the detection function. The control circuit leverages the motor stopping state and contactor switching state to enable the current detector to self-diagnose contact fusion, eliminating the need for external monitoring equipment

Inventive Principle:

Principle #25Self-service

2Reliability

If an auxiliary contact and additional monitoring circuit are added to detect contact fusion, then contact fusion detection capability is improved, but cost increases

Engineering Contradiction:

Improvecontact fusion detection capabilityVSAvoidcost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent uses inexpensive control logic and existing components rather than expensive dedicated detection hardware. The solution relies on software/control circuit logic that evaluates current measurements under different operating conditions, which is much cheaper than adding physical auxiliary contacts and dedicated monitoring circuits

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Ease of operation

If the electromagnetic contactor is turned off to stop motor operation, then motor operation is stopped, but contact fusion cannot be detected during normal operation

Engineering Contradiction:

Improvemotor stoppingVSAvoidcontact fusion detection

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent performs contact fusion detection during the motor stopping period, which is a natural idle time in the motor operation cycle. By utilizing this otherwise unused time window, the system can conduct detection without extending the overall operation cycle or affecting productivity

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements periodic detection at motor stopping intervals. The control circuit periodically evaluates the current detector output during each motor stop to check for contact fusion, transforming the detection into a rhythmic process that aligns with the motor's operational cycle rather than requiring continuous monitoring that would interfere with operation

Inventive Principle:

Principle #19Periodic action

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

Enables contact fusion detection in electromagnetic contactors without the need for additional components or circuits, reducing costs and simplifying the detection process.

Implementation Method 1

an AC/DC converter which converts an alternating current voltage which is supplied from a three-phase alternating current power supply to a direct current voltage

Methodology Applied

Scientific EffectElectrical energy conversion:

Implementation Method 2

a current detector for detecting if current is flowing or not flowing

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS9306487B2Motor drive device having function of detecting contact fusion in electromagnetic contactor

Publication Date: 2016.04.05 FANUC LTD

AI summary

A motor drive device driven by a three-phase AC, which drives a motor by an AC/DC converter and DC/AC converter controlled by a controller, and which has an electromagnetic contractor without an auxiliary contact in an input power circuit, which motor control device is provided at the controller with an off circuit of the electromagnetic contactor and a partial controller of the three-phase bridge circuit at the AC/DC converter, turns on an upper arm of a predetermined phase of the three-phase bridge circuit and turns on the lower arms of other phases in the state where the electromagnetic contactor is turned off, judges the presence of current in this state by the current detector, and, when the current detector detects current, uses a contact fusion detector to detecte contact fusion in the electromagnetic contactor and thereby can detect fusion of a contact in the electromagnetic contactor without an additional circuit.