Elevator Drive Safety Circuit for Brake Failure Backup Braking
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Solution Overview
Problem
Redundant brake systems in elevator systems are prone to simultaneous failure due to shared environmental influences, compromising safety even when one brake is impaired.
Innovation Solution
A drive system for elevators incorporating an electric machine, converter, drive controller, and drive safety circuit unit that allows for delayed emergency stop commands and verification of mechanical brake functionality, enabling the converter to continue operating as a backup brake.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a redundant brake system with two identical mechanical brakes is used, then the safety of the elevator system is improved, but the reliability deteriorates because both brakes are exposed to the same environmental influences and may fail simultaneously
Solution Approach 1:
The patent segments the brake system into two functionally independent parts: the mechanical brake system and the electrical drive system with converter. This segmentation allows the electrical drive to serve as a backup braking mechanism that is not subject to the same environmental influences as the mechanical brakes, thereby resolving the reliability issue while maintaining safety redundancy
Solution Approach 2:
The electrical drive system with the converter is given a dual function: it serves both as the primary drive for the elevator and as a backup braking system. This multi-functionality eliminates the need for additional dedicated backup components while ensuring that a functional backup braking mechanism is available when mechanical brakes fail
2Speed
If the converter is immediately switched off upon receiving an emergency stop command, then the response time is improved, but the ability to use the converter as a backup brake deteriorates
Solution Approach 1:
The patent implements preliminary action by maintaining the converter in an operational state for a predetermined time period after an emergency stop command is received. This allows the converter to immediately provide backup braking capability if needed, while still achieving emergency stop functionality. The delay is carefully calibrated to balance rapid response with backup brake availability
Solution Approach 2:
The system dynamically adjusts the converter's operational state based on the timing of the emergency stop command. The converter transitions from full operation to a delayed shutdown state, providing dynamic braking capability during the transition period. This dynamic behavior allows the system to adapt to different emergency scenarios while maintaining backup brake availability
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
Enhances elevator safety by ensuring reliable braking even if mechanical brakes fail, increasing availability and reliability of the braking system without additional mechanical brakes.
Implementation Method 1
an electric machine (5), in particular an induction machine
Implementation Method 2
a first converter (7), in particular a bidirectional converter, which can be electrically connected to an alternating current source (9) and to the electric machine (5)
Implementation Method 3
at least one first mechanical brake (19), in particular a shod brake, which can be closed by a brake closing command
Data Source
AI summary
An elevator system drive includes: an electric machine: a first converter electrically connected to an alternating current source and the electric machine: a drive controller controlling the drive: a drive safety circuit unit electrically connected to a safety circuit of the elevator system, to a controller of the elevator system, and to the drive controller; and at least one mechanical brake that is closed by a brake closing command from the elevator system controller. The drive safety circuit unit operates in a first operating state wherein it transmits an emergency stop command coming from the elevator system safety circuit directly and without delay to the first converter, and operates in a second operating state wherein it relays a modified emergency stop command coming from the elevator system safety circuit, with a delay, to the first converter to ensure safe braking of the elevator system even if the mechanical brakes fail.