Elevator Safety Switch Holding Unit for Control Resets
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Solution Overview
Problem
Conventional safety switches in electrical systems, particularly in safety-sensitive environments like elevator systems, often fail to guarantee reliable switching operations due to complexity and high demands on reliability, necessitating the need for a cost-effective and simple solution that ensures high reliability and safety.
Innovation Solution
A safety switch design featuring at least two switches connected in series with a holding unit, where the control unit generates a closing signal for a predetermined period, allowing the holding unit to maintain the switches in a closed state independently, ensuring reliability even during control unit resets or self-tests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional safety switches are used with simple design, then manufacturing cost is reduced, but switching reliability cannot be guaranteed
Solution Approach 1:
The safety switch is divided into multiple independent semiconductor switches connected in series, each controlled by separate control circuits. This segmentation allows individual failure analysis and maintains overall system reliability while using standard, cost-effective components rather than requiring a single complex high-reliability switch.
Solution Approach 2:
The system implements beforehand cushioning through redundant control circuits and a bridging mechanism that can compensate for control unit failures. The bridging circuit is prepared in advance to maintain switch closure during control unit resets or failures, preventing unintended switch openings and ensuring continuous safety monitoring without requiring expensive ultra-reliable components.
2Reliability
If control unit performs reset or self-test operations, then control reliability is improved, but switching operation may be interrupted
Solution Approach 1:
The control unit performs reset and self-test operations at predetermined time intervals before actual safety-critical switching is needed. The bridging circuit is activated in advance during these maintenance operations to maintain switch closure, ensuring that control reliability is improved through regular testing without interrupting the continuity of safety switching operations.
3Reliability
If multiple semiconductor switches are used in series, then switching reliability is improved, but device complexity increases
Solution Approach 1:
The control unit is designed with multi-functionality to perform both normal safety switching control and self-diagnostic functions (reset, self-test). The bridging circuit also serves multiple purposes: maintaining switch closure during control unit maintenance operations and providing fail-safe operation during control unit failures. This multi-functionality reduces the need for separate dedicated circuits, thereby reducing overall device complexity while maintaining high reliability through the series-connected semiconductor switches.
Data Source
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AI summary
A safety switch (1) for an electrical installation, in particular for a safety chain of an elevator installation, is proposed, comprising two switches (3, 5), at least one control unit (7), and at least one holding unit (17). The two switches (3, 5) are connected in series with each other and with a load element (21) to be switched. Each of the switches (3, 5) is configured to be held in a closed state by receiving a closing signal and to move to an open state when the closing signal is absent. The control unit (7) is equipped to generate the closing signal and transmit it to at least one of the switches (3, 5) when a desired state is present, and to not transmit a closing signal to the at least one switch (3, 5) when a non-desired state is present.As long as the desired state is maintained, the control unit (7) can, as a rule, keep the switches (3, 5), and thus the entire safety switch (1), closed. However, it may be necessary to occasionally subject the control unit (7) to a reset or self-test, so that it is temporarily unable to generate a closing signal. For this specific case, the safety switch (1) additionally features the holding unit (17, 19), which can be instructed by the control unit (7) to generate the closing signal independently of the control unit (7) for a maximum predetermined holding duration and to transmit it to at least one of the switches (3, 5).