Failure Detection in Electric Lifting Motor Contactors
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Solution Overview
Problem
Conventional techniques fail to directly monitor the state of contactors or semiconductor devices in driving circuits for electric lifting-lowering devices, such as welding or fusing, and lack a reverse-phase detecting function for three-phase alternating-current power supplies.
Innovation Solution
A failure detecting apparatus with a detecting circuit connected in parallel to each on/off mechanical contact or semiconductor device, outputting a pulse signal synchronized with the alternating current, and a signal processing means to detect normal or abnormal conditions, including reverse phases, using a photocoupler with a light-emitting diode and phototransistor to convert alternating current voltage into an electric pulse signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional phase-detecting circuits are used to detect interphase voltages, then reverse phase detection is possible, but direct monitoring of contactor or semiconductor device state (welding or fusing) is not achieved
Solution Approach 1:
The patent divides the detection function into separate detecting circuits for each phase (R, S, T phases), with each circuit independently monitoring its phase's voltage and current. This segmentation allows precise measurement of each phase's state while enabling comprehensive monitoring of contactor and semiconductor device conditions through the combination of individual phase detections.
2Reliability
If detecting circuits are connected in parallel to monitor contactor state, then welding or fusing detection is achieved, but device complexity increases
Solution Approach 1:
Each detecting circuit is designed to perform multiple functions: detecting voltage, detecting current, monitoring contactor state, and identifying welding or fusing conditions. By making each circuit multi-functional, the patent reduces the need for separate dedicated circuits for each detection task, thereby limiting the increase in device complexity while achieving comprehensive monitoring.
3Loss of information
If photocoupler is used to convert alternating current voltage into pulse signal, then electrical isolation and signal processing are achieved, but detection precision may be affected by signal synchronization requirements
Solution Approach 1:
The patent incorporates a feedback mechanism where the detecting circuit continuously monitors the pulse signal from the photocoupler and adjusts its detection timing and threshold based on the synchronized alternating current waveform. This feedback ensures that the electrical isolation provided by the photocoupler does not compromise detection precision, as the system adapts to maintain accurate synchronization.
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 fail-safe detection of normal or abnormal conditions of contactors or semiconductor devices before or after they turn on, and detects reverse phases before supplying power to the electric motor, ensuring reliable operation and preventing damage from welding or fusing.
Implementation Method 1
a photocoupler with a light-emitting diode and phototransistor to convert alternating current voltage into an electric pulse signal
Implementation Method 2
a photocoupler with a light-emitting diode and phototransistor to convert alternating current voltage into an electric pulse signal
Data Source
AI summary
Detecting circuits are connected in parallel to respective on/off mechanical contacts or on/off semiconductor devices of a motor contactor and/or a brake contactor of a driving circuit supplying driving electric power from a three-phase alternating-current power supply circuit to a three-phase alternating-current electric motor and a brake through the motor contactor and the brake contactor, respectively. The detecting circuits output pulse signals synchronized with the alternating current from the alternating-current power supply circuit. A signal processing circuit processes the pulse signals from the detecting circuits and detects a normal or abnormal condition of each on/off mechanical contact or on/off semiconductor device of the motor contactor and/or the brake contactor.