Elevator Brake Shoe Assembly for Fast Reset and Consistent Braking
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Solution Overview
Problem
Existing elevator braking systems face challenges in providing consistent and smooth braking, especially when brake pads are worn, and require time to reset, which can lead to unsafe conditions during mechanical failures or overspeed situations.
Innovation Solution
A braking apparatus comprising a pair of brake shoes, a cam follower, a compressible spring, and an actuation assembly that uses an electromagnetic clutch and ball screw assembly to control the movement of the brake shoes, allowing for quick transition between brake applied and release positions, ensuring consistent braking force and rapid reset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a known braking device is used that grips the car guide rails, then the emergency brake can arrest the descent of the elevator car, but the brake requires several seconds to reset to a fully open state during which the brake cannot be applied
Solution Approach 1:
The brake shoe is designed with a cam mechanism that enables dynamic transition between applied and released states. The cam follower moves along a cam surface that is adjustable in position, allowing the brake to quickly transition from the applied state to the released state, reducing reset time while maintaining reliable braking capability.
Solution Approach 2:
The spring is pre-compressed during normal operation, storing potential energy. When the brake needs to be applied, the cam mechanism simply releases the pre-compressed spring, which immediately pushes the brake shoe against the drum. This preliminary compression eliminates the delay of spring compression during braking activation.
2Force
If the brake is designed to provide substantial braking force, then the emergency brake can stop the elevator, but the braking force is not constant even with wear of brake shoe linings
Solution Approach 1:
The cam surface position is made adjustable to compensate for wear of the brake shoe linings. As the linings wear and the brake shoe thickness decreases, the cam surface position can be adjusted to maintain the correct geometric relationship between the cam follower and cam surface, ensuring constant braking force throughout the lining life.
Solution Approach 2:
The system includes wear indicators that provide feedback on the condition of the brake shoe linings. When wear reaches a threshold, the cam surface position is adjusted to compensate, ensuring the braking force remains constant. This feedback mechanism maintains stable braking performance over time.
3Speed
If the brake is designed to be responsive to overspeed, then the brake can activate in emergency situations, but the reset process takes too long to reach a fully open state
Solution Approach 1:
The cam mechanism provides dynamic control of the brake shoe position. During reset, the cam follower moves along the cam surface to quickly position the brake shoe in the fully open state. This dynamic geometric mechanism enables rapid state transition without requiring complex actuation systems.
Solution Approach 2:
The cam mechanism extracts the reset function from complex multi-stage actuation systems and implements it through a simple geometric relationship. The cam surface geometry itself performs the reset action, eliminating the need for additional motors, clutches, or control systems that would increase reset time.
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
The apparatus provides a consistent and smooth braking force even with worn brake pads and enables rapid resetting, enhancing safety by quickly engaging the brake in emergency situations, such as overspeed or door-open events, within a predetermined time of 0.1 to 0.2 seconds.
Implementation Method 1
a compressible spring connected to the cam follower for actuating the cam follower and thereby causing the face of the at least one of the shoes to move relative to the face of the other of the shoes
Implementation Method 2
an actuation assembly connected to the cam follower and acts through the cam follower for compressing the compressible spring
Data Source
AI summary
In one embodiment, a braking apparatus includes a pair of brake shoes, a cam follower connected to at least one of the shoes, a compressible spring connected to the cam follower, and an actuation assembly including a motor, a ball screw and an electromagnetic clutch. The braking apparatus is operative to transition from a brake applied position where the brake shoes are closed and a brake release position where the brake shoes are separated. When the braking apparatus is in the brake release position, a brake application may be commenced to close the shoes by power no longer being supplied to the electromagnetic clutch. Additionally, when the braking apparatus is undergoing a brake release cycle to separate the brake shoes, the brake application cycle may also be commenced prior to completion of the brake release cycle when power is no longer supplied to the electromagnetic clutch and the motor.