Elevator – industrial lift truck – or stationary lift for vehicle – Having specific means contacting or on load support for... – Includes movable contact component on support for engaging...
Reexamination Certificate
2000-06-21
2001-10-02
Brahan, Thomas J. (Department: 3652)
Elevator, industrial lift truck, or stationary lift for vehicle
Having specific means contacting or on load support for...
Includes movable contact component on support for engaging...
C187S373000, C188S188000
Reexamination Certificate
active
06296080
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to elevator safety braking systems, and in particular, to a variable traction mechanism for a rotary actuator that reduces the required preload on the actuator.
BACKGROUND OF THE INVENTION
Elevator systems generally include an elevator car suspended by a rope (as wire cables are called within the elevator industry) or coated steel belt system. The car is guided along guide rails within an elevator hoistway so that relatively little lateral motion is imparted to the car during use. Passenger elevators are required to have a braking system to halt the elevator car in an overspeed event. Such a braking system is commonly activated by an actuation device known as a governor. The governor detects excessive speed of the car and actuates an emergency stop device.
The governor system typically consists of sheaves at the top and bottom of the hoistway with a governor rope reeved in an endless loop over both sheaves. A part of the governor rope is connected to a safety link that is mounted on the elevator car frame. As the car ascends and descends, the governor rope travels with it, rotating the sheaves. One of the sheaves has a centrifugal governor mounted in it, so that when the sheaves rotate too fast, paired flyweights or flyballs rotating on a spindle are accelerated outward by centrifugal force, where they trip an overspeed switch, thus cutting power to the elevator drive motor. If further overspeed occurs, a clamping device is actuated that clamps onto the governor rope to activate the braking safeties, bringing the elevator car to a safe albeit abrupt stop.
More modern systems omit the stationary governor pulley and rope combination by fitting each elevator car with its own governor, such as that disclosed in U.S. Pat. No. 5,377,786 (Nakagawa) or in U.S. patent application Ser. No. 09/428,023 filed on Oct. 27, 1999 and entitled ROTARY ACTUATED OVERSPEED SAFETY DEVICE, incorporated herein by reference.
SUMMARY OF THE INVENTION
Briefly stated, in an elevator safety braking device, a variable traction mechanism in a rotary actuator allows the drive wheels of the rotary actuator to operate at a reduced preload during normal elevator operation. When engaging, a higher preload is necessary. In the event of safety braking, the variable traction mechanism increases the preload on the drive wheel to ensure timely and proper safety engagement. The variable traction mechanism therefore allows the drive wheels to be subjected to a reduced preload during normal operation, thus relaxing the design criteria for the drive wheels while maintaining reliability.
According to an embodiment of the invention, a variable traction mechanism includes a rotary actuator; first and second wheels pivotably connected to an elevator car via first and second linking members, respectively; the first and second wheels riding on opposing sides of a guide rail for the elevator car; the rotary actuator including means for sensing when the first wheel exceeds a predetermined speed of rotation and locking the first wheel to the rotary actuator; a first spring acting between the second wheel and a first pivot point on the rotary actuator; a second spring acting between a center of the second wheel and a second pivot point on the rotary actuator; and wherein the first and second pivot points are located such that a friction force between the first wheel and the guide rail times a length of a normal to a direction of the friction force passing through a center of the first wheel plus a second spring force of the second spring times a length of a normal to a direction of the second spring force passing through the center of the first wheel is greater than a first spring force times a length of a normal to a direction of the first spring force of the first spring passing through the center of the first wheel.
REFERENCES:
patent: 2931466 (1960-04-01), Allenbaugh
patent: 5065845 (1991-11-01), Pearson
patent: 5377786 (1995-01-01), Nakagawa
patent: 6082506 (2000-07-01), Huang et al.
patent: 5-262472 (1993-10-01), None
Draper James M.
Kulak Richard E.
Brahan Thomas J.
Otis Elevator Company
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