Escalator Safety Chain Encoding for Noise-Resistant Switch Detection
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Solution Overview
Problem
The long signal transmission cable connecting the controller and the safety chain box in escalators introduces noise into the transmission signal, leading to misoperation and difficulty in accurately locating the protective switch with a changed state due to non-linear equivalent resistance of the passive resistive network.
Innovation Solution
A safety chain device with a resistive network encoder and controlled current sources is employed to suppress noise, using a processor to analyze the encoder output values and control unit to perform safety protection operations based on current signals, enhancing the accuracy of protective switch state detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a long signal transmission cable is used to connect the controller and the safety chain box, then the detection range is extended, but noise is introduced into the transmission signal causing misoperation
Solution Approach 1:
The patent replaces the traditional passive resistive network with an active encoder circuit that outputs digital signals. This substitution transforms the analog resistance-based detection system into a digital encoding system, which is inherently more resistant to noise interference during transmission over long cables.
Solution Approach 2:
The patent changes the signal transmission parameter from analog voltage/resistance to digital encoded signals. The encoder converts the state of multiple protective switches into a digital code that can be transmitted reliably over long distances without degradation from noise.
2Device complexity
If a passive resistive network is used to detect protective switch states, then the circuit structure is simple, but the non-linear equivalent resistance makes it difficult to locate the changed switch
Solution Approach 1:
The patent replaces the passive resistive network with an active encoder circuit that provides linear, deterministic output values. The encoder circuit actively generates digital codes based on switch states, eliminating the non-linear resistance characteristics that made precise measurement difficult.
Solution Approach 2:
The encoder circuit acts as an intermediary between the protective switches and the controller. It translates the physical switch states into a standardized digital encoding format that is easy for the controller to interpret, improving measurement precision while maintaining reasonable circuit complexity.
3Reliability
If multiple protective switches are connected in series, then the safety coverage is increased, but the number of possible state combinations increases making location difficult
Solution Approach 1:
The patent applies binary encoding to transform the exponential growth of state combinations into a manageable digital representation. Each protective switch corresponds to a bit in the encoded output, allowing the controller to efficiently decode the state of individual switches from the composite signal regardless of how many switches are in series.
Data Source
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AI summary
The present application relates to elevator technology, in particular to a safety chain device and a safety protection system for an escalator. The safety chain device according to an aspect of the application comprises: a safety chain including a plurality of protective switches connected in series, each of the protective switches is configured to switch from a first state to a second state in the event of abnormal operation of a respective corresponding drive chain; a resistive network encoder coupled with the safety chain and having a plurality of encoder output values, each of the encoder output values corresponds to one of combinations of states of the plurality of protective switches; a processor coupled with the resistive network encoder and configured to output a level signal corresponding to the encoder output values; a first controlled current source coupled with the safety chain and configured to output a first current corresponding to a current flowing through the safety chain; and a second controlled current source coupled with the processor and configured to output a second current corresponding to the level signal.