Brakes – Operators – Fluid pressure
Reexamination Certificate
1997-12-22
2001-02-27
Schwartz, Chris (Department: 3613)
Brakes
Operators
Fluid pressure
C187S288000, C187S351000
Reexamination Certificate
active
06193026
ABSTRACT:
TECHNICAL FIELD
The present invention relates to elevators, and more particularly to brakes for such elevators.
BACKGROUND OF THE INVENTION
A typical traction elevator includes a car, a counterweight, and a plurality of ropes interconnecting the car and counterweight. The ropes are engaged with a traction sheave that is rotated by a machine. Rotation of the traction sheave moves the car and counterweight through the hoistway.
In order to prevent the car from over-speeding in the downward direction, the car includes a safety device that is triggered by a governor. In a conventional configuration, if the car begins to travel faster than a predetermirned speed, the governor will cause a lift rod to be lifted relative to the car. As the lift rods are lifted, a pair of wedge shaped blocks are pulled into contact with the guide rail for the car. Friction between the guide rail and the wedge shaped blocks pulls the blocks into further engagement with the guide rails and thereby results in the application of a braking force to bring the car to a safe stop.
Such safety devices have proven reliable through use. A drawback to such devices, however, is that they work in only one direction, typically the down direction for the car. It is now desirable to prevent an over-speed condition from occurring in the up direction of the car as well. A simple solution to this problem is to install safety brakes on both the car and the counterweight. This solution may be expensive due to the doubling of the number of safety brakes.
Another possible solution is to place a spring-loaded brake on the car that stops the movement of the car in either the up or down direction. Due to the loads involved, this requires significant braking force between the braking surface and the guide rail and therefore the spring must be large enough to provide an adequate amount of force. A more significant problem is that during normal operation, the braking force of the safety brake must be removed to permit the car to travel through the hoistway. The removal of the braking force requires a device that applies an opposing force to overcome the force applied by the spring. In addition, the means to apply an opposing force should permit the spring to apply a braking force in the event of a loss of power. A possible solution is to provide an electromagnetic device, such as a solenoid, that counters the braking force when power is applied to the coil of the solenoid. Unfortunately, the forces required result in a large, heavy solenoid and a require a significant amount of power. Therefore, such a configuration is not practical.
The above art notwithstanding, scientists and engineers under the direction of Applicants' Assignee are working to develop improved braking systems for elevators.
DISCLOSURE OF THE INVENTION
According to the present invention, a brake for a passenger conveyor includes a fluid enclosure, wherein the fluid pressure within the enclosure counters the braking force generated by a biasing means. The use of the fluid enclosure provides a simple and effective means to remove the braking force, while permitting the braking force to be applied quickly if the need arises.
In a particular embodiment, the enclosure is a fluid pressure amplifier disposed between an actuator and a braking surface. The fluid pressure amplifier increases the force of the actuator that opposes the braking force.
As a result of the fluid pressure amplifier, the actuator may be smaller relative to the size of the means biasing the braking surface to brake the passenger conveyor. Smaller actuators provide a more compact brake system and require less power in order to be actuated. This is particularly advantageous for passenger conveyors, such as elevators, which need compact and lightweight devices. In addition, since less power is needed to overcome the braking force, greater braking force may be applied to the braking surface. This feature permits the brake to be used as a bidirectional safety brake for an elevator.
In a particular embodiment, the braking surface is disposed on a piston including a flange having a surface area A
1
. The fluid pressure amplifier is defined by a sealed enclosure containing a fluid, and wherein the sealed enclosure includes an inner wall defined in part by the flange. The enclosure also includes a branch that extends to the actuator. The actuator includes another flange with a surface area A
2
, wherein A
2
<A
1
. This surface defines a portion of the inner surface of the branch. Movement of the actuator applies a force on the fluid that urges the piston flange to move the braking surface and reduce the braking force.
In another particular embodiment, the fluid enclosure is in communication with an accumulator and a pressure relief valve. The accumulator provides a source of stored, pressurized fluid to the enclosure through an operation valve. The pressure relief valve provides means to release the pressure within the enclosure and thereby permit the brake to stop the elevator car.
According to a further embodiment of the present invention, a brake for a passenger conveyor includes a braking surface, biasing means that applies a braking force to the braking surface, a controllable actuator engaged with the braking surface to apply a second force opposing the force of the biasing means, and a controller that controls the position of the actuator. The controller receives inputs from the passenger conveyor that provide information on the position of the passenger conveyor car. The controller positions the actuator to permit movement of the car until the car reaches a desired location.
In a particular configuration of this embodiment, the controller further receives inputs that provide information on the car speed. The controller positions the actuator to limit the speed of the car to less than a predetermined speed.
As a result of the features of this embodiment, the brake may be used to permit movement of the passenger conveyor car in the event of a shut-down of the passenger conveyor. The controller, which may be powered by a back-up power source, provides variable power to the actuator such that the removal of braking force is controlled, and thereby the speed of the car is controlled. The controller monitors the position and speed of the car and maintains the power to the actuator until the car arrives at a landing. Once the car is at the desired landing, the controller removes power from the actuator and the biasing means applies sufficient force to stop the movement of the car At this point, passengers in the car may safely exit the car.
The foregoing and other objects, features and advantages of the present invention become more apparent in light of the following detailed description of the exemplary embodiments thereof, as illustrated in the accompanying drawings.
REFERENCES:
patent: 5014828 (1991-05-01), Baldassarre
patent: 5265701 (1993-11-01), Ogasawara et al.
patent: 5648644 (1997-07-01), Nagel
patent: 5739610 (1998-04-01), Nemoto et al.
patent: 0183616 (1986-06-01), None
Servia Armando
Sevilleja Jose
Otis Elevator Company
Schwartz Chris
LandOfFree
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