Elevator Sub-Safety Chain for Pit Access Fault Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Elevator systems with shallow pits and low overheads, also known as machine room-less systems, require periodic access for maintenance and repair, necessitating the stopping of the elevator car and ensuring safety through deactivation of the motor and brake, but existing safety arrangements lack comprehensive fault detection and prevention mechanisms to prevent unintended movement during maintenance.
Innovation Solution
The elevator system incorporates a sub-safety chain with bi-stable landing key switch contacts and door contacts connected to relays that deenergize the drive system upon detecting faults, and a remote station to detect additional control system faults, ensuring the elevator car remains stationary during maintenance by preventing movement through a secondary safety measure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the motor and brake are deactivated to stop the elevator car for maintenance access, then maintenance personnel can safely access the hoistway, but the elevator car may become unintentionally moved due to lack of comprehensive fault detection mechanisms
Solution Approach 1:
The system performs preliminary actions by deactivating the motor and brake before maintenance personnel access the hoistway. The sub-safety chain is activated in advance to ensure the elevator car remains stationary, preventing unintended movement during the maintenance period.
Solution Approach 2:
The sub-safety chain acts as an intermediary safety mechanism between the maintenance personnel and the elevator car. It includes intermediate components such as the first and second pairs of relays, door contacts, and key switch contacts that mediate the safety control, ensuring that the car cannot move unless all safety conditions are met.
2Reliability
If a sub-safety chain with multiple relays and contacts is implemented to prevent unintended movement, then safety is enhanced, but the device complexity increases
Solution Approach 1:
The safety system is segmented into distinct functional modules: door contacts for landing door status, key switch contacts for authorized operation, relay pairs for control logic, and a remote station for additional fault detection. This segmentation allows each component to perform a specific safety function independently, making the overall complex system manageable and maintainable.
Solution Approach 2:
The sub-safety chain merges multiple safety functions into a single integrated control circuit. The door contacts, key switch contacts, and relay pairs are combined in series to create a unified safety interlock system that controls the motor and brake deactivation, ensuring that all safety conditions must be satisfied simultaneously for maintenance access to be permitted.
3Reliability
If the drive system is deenergized upon fault detection to prevent movement, then safety is improved, but the productivity of the elevator system decreases due to more frequent stoppages
Solution Approach 1:
The sub-safety chain implements continuous feedback monitoring of door contacts, key switch contacts, and system faults. The relays continuously detect the status of safety conditions and provide feedback control to the motor and brake. When faults are detected, the system automatically deenergizes the drive system, and the remote station provides additional feedback for comprehensive fault detection and reporting.
Data Source
Figure 1
Figure 2
AI summary
An elevator system includes a hoistway and an elevator car moveable along the hoistway. A drive system is located in the hoistway and is operably connected to the elevator car to urge movement of the elevator car along the hoistway. A safety system to establish a protected volume in the hoistway includes a prop installable in the hoistway to prevent downward movement of the elevator car and a plurality of relays configured to detect faults in the elevator control system to prevent movement of the elevator car prior to installation of the prop.