Back-EMF Motor Stop Detection Eliminates Duplicate Contactors
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Solution Overview
Problem
Existing safety systems for detecting the stop of three-phase motors, particularly those using star-delta starting methods, require duplication of main magnetic contactors for power supply interruption, leading to potential malfunctions and false disconnection alarms during connection state changes.
Innovation Solution
A safety system that employs back electromotive force detection parts connected to both ends of multiple phases of the three-phase motor wiring, allowing stop detection without needing two main switching devices for duplication, and electrically insulated detection parts to prevent short-circuiting and incorrect disconnection states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two main magnetic contactors are duplicated for power supply interruption in star-delta starting, then safety is improved, but device complexity increases and potential for malfunction during connection changes occurs
Solution Approach 1:
The patent extracts the stop detection function from the main magnetic contactor system by connecting the stop detection unit directly to the motor terminals. This allows detection of motor stop through back electromotive force without requiring two main magnetic contactors for duplication, thereby reducing device complexity while maintaining safety.
Solution Approach 2:
The patent introduces an intermediary detection mechanism (stop detection unit measuring back electromotive force) that mediates between the motor and the control system. This intermediary approach enables reliable stop detection without duplicating the main magnetic contactor, resolving the contradiction between safety and complexity.
2Reliability
If main magnetic contactors are duplicated for safety, then reliability is improved, but the risk of false disconnection alarms increases
Solution Approach 1:
The patent replaces the mechanical/electrical switching system (main magnetic contactors) with an electromagnetic field-based detection system (back electromotive force measurement). This substitution eliminates the false disconnection alarms associated with contactor duplication while maintaining reliable stop detection.
3Use of energy by moving object
If star-delta starting is used to suppress starting current, then energy consumption is reduced, but the complexity of control increases
Solution Approach 1:
The stop detection unit serves multiple functions: it detects motor stop through back electromotive force and simultaneously provides safety control signals. This multi-functionality allows the system to handle star-delta starting complexity while maintaining simple stop detection and safety control integration.
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 reliable detection of motor stop without malfunctions during connection changes, ensuring safety by eliminating the need for duplicate main switching devices and preventing false alarms, thus securing worker safety in production environments.
Implementation Method 1
a plurality of back electromotive force detection parts connected to both ends of the wiring of at least two phases or more of each phase of the three-phase motor respectively, for detecting each back electromotive force
Data Source
AI summary
To provide the safety system and safety equipment that can be constituted by only one main magnetic contactor, although two main magnetic contactors have been required for duplication to interrupt the power supply to the three-phase motor started by star-delta starting. Two back electromotive force detection parts of a stop detection unit 3 are respectively connected to both ends of wiring of U-phase and W-phase of a three-phase motor 2. Therefore, a stop of the three-phase motor 2 can be detected, based on a back electromotive force generated in the wiring of the three-phase motor 2, in a state of turning off both of a star connecting switching device 8 and a delta connecting switching device 9, at the time of interrupting power supply in which a main switching device 7 is turned off. That is, there is no necessity for turning on either the star connecting switching device 8 or the delta connecting switching device 9 for detecting a back electromotive force, and therefore it is not necessary to provide two main switching devices 7 for duplication.