Elevator Eddy-Current Overspeed Brake with Nonlinear Force
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Solution Overview
Problem
Conventional overspeed detection and actuation mechanisms in elevators, such as the cable-loop system, are inefficient in power consumption and imprecise in triggering the emergency brake, especially in multi-car elevator systems, where they are impractical and costly to install and maintain.
Innovation Solution
An eddy-current overspeed emergency brake sensing and actuation system with a nonlinear velocity-force relationship, where the overspeed detector magnet only partially overlaps the reaction surface during normal operation, generating a low opposing force, and increases overlap as speed rises, triggering the brake with a sharply increasing force at the pre-set overspeed velocity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cable-loop system is used for overspeed detection, then the overspeed emergency brake can be triggered, but the system becomes difficult and expensive to install and maintain, especially for high-rise buildings
Solution Approach 1:
The patent extracts the overspeed detection function from the complex cable-loop system and implements it within the elevator car itself using a governor assembly that directly measures car speed through rotational speed sensing, eliminating the need for building-spanning cables and pulleys
Solution Approach 2:
The patent replaces the mechanical cable-loop system with an eddy current-based sensing system that uses electromagnetic principles to detect overspeed conditions, substituting complex mechanical linkages with a more compact electromagnetic sensor assembly
2Device complexity
If a conventional eddy current overspeed detector is used, then the moving components are contained within the elevator car, but the system generates excessive opposing force during normal operation, reducing power efficiency
Solution Approach 1:
The patent implements a dynamic gap adjustment mechanism where the gap between the detector magnet and reaction surface varies with elevator car speed: at normal speeds the gap is larger reducing opposing force, while at overspeed conditions the gap decreases to increase detection sensitivity and triggering force
Solution Approach 2:
The patent changes the magnetic field interaction parameters by adjusting the relative position and gap distance between magnetic components based on speed conditions, optimizing the balance between power efficiency during normal operation and detection sensitivity during overspeed events
3Ease of manufacture
If a linear velocity-force relationship is used in eddy current detection, then the system is simple to implement, but the overspeed trigger velocity cannot be precisely controlled due to manufacturing tolerances
Solution Approach 1:
The patent implements a feedback mechanism where the governor assembly continuously monitors the elevator car's rotational speed and provides real-time feedback to the eddy current detector, allowing precise control of the overspeed trigger point through adjustable mechanical linkages and magnetic field positioning
Solution Approach 2:
The patent incorporates preliminary calibration and adjustment mechanisms during system installation that allow the overspeed trigger velocity to be precisely set before operation, using adjustable mechanical components to compensate for manufacturing tolerances and ensure accurate trigger points
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
This system enhances power efficiency and precision in detecting overspeed conditions, reducing mechanical losses and ensuring accurate triggering of the emergency brake, making it more compact, reliable, and suitable for multi-car elevator systems.
Implementation Method 1
The idea of generating force from eddy currents, called eddy current brakes, are based on the magnetic principle of Faraday's law of induction and Lenz's law
Implementation Method 2
When a magnetic gradient moves over a conductive (metal) plate, the changing magnetic flux induces eddy currents in the plate
Implementation Method 3
The eddy currents in turn induce a magnetic flux, and due to the interaction with the original magnetic flux, a force appears in the opposite direction to the motion
Data Source
AI summary
An overspeed emergency brake system includes an overspeed detector magnet generating a brake actuation force and a kinematic constraint element guiding the movement of the magnet. The magnet and a kinematic constraint element in the brake system are arranged such that a linear brake actuation force is generated at a normal operating speed condition (i.e in a first position of the magnet with respect to the kinematic constraint element), due to the movement of the kinematic constraint element when guiding the magnet along a reaction surface and the kinematic constraint element converts the linear speed-force relationship into a nonlinear speed-force relationship in an overspeed condition (i.e a second position), while the magnet translates with respect to the kinematic constraint element generating a sharply increasing force for triggering the overspeed emergency brake.