(2) Description of Related Art Many current elevator positioning systems use car position information which is derived from a machine mounted encoder, from car mounted vane reader assemblies, and from limit switches which are mounted in the hoistway to implement all functional and operational requirements related to the car position in the hoistway. In addition, many high-end systems also use a quasi-absolute position encoder for higher position accuracy and resolution. The installed cost of such positioning systems is generally high. What is therefore needed is an absolute positioning system for elevator car assemblies which combines low cost and high reliability.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method, and apparatus for so performing, for determining an absolute position of a moveable platform.

In accordance with the present invention, an apparatus for determining the position of an elevator car in a hoistway comprises an elevator car, a governor attached to the elevator car, at least one absolute multi-turn encoder in communication with the governor capable of communicating an absolute position of the elevator car, at least one sill sensor affixed to the elevator car capable of transmitting a position signal, a plurality of sensor activation means affixed to the hoistway at a predetermined position capable of indicating to said at least one sill sensor when an actual position of said elevator car is approximately equal to said predetermined position, and means for receiving the position signal and the absolute position and performing an update of the absolute position.

In accordance with the present invention, a method of determining the position of a moveable platform comprises the steps of affixing at least one absolute multi-turn encoder to a governor attached to the moveable platform, the multi-turn encoder in communication with a controller adapted to communicate an absolute position of the moveable platform, affixing at least one sill sensor to the moveable platform, the at least one sill sensor in communication with a controller, affixing at least one vane at a predetermined position, communicating an absolute position of the moveable platform to the controller, controlling the absolute position of the moveable platform with the controller, periodically determining when the at least one sill sensor is coincident with the at least one vane, communicating the coincidence to the controller, and updating the absolute position data via the controller based upon the communicated coincidence.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 A diagram of the absolute positioning system of the present invention.

FIG. 2 A diagram of a sill sensor known in the art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT (S) The present invention teaches a combination of absolute positioning encoders with sill sensors mounted on an elevator car to effectively facilitate all car position related requirements. While described with reference to elevator cars, the present invention extends broadly to encompass any and all movable platforms which travel over a predefined mode.

With reference to FIG. 1, there is illustrated the absolute positioning system 11 of the present invention. In a preferred embodiment, elevator car 17 is attached via cable 14 to a governor 13 and a tension element 18. Governor 18 functions to measure the rate of speed of elevator car 17 as it moves up and down through a hoistway so as to prevent elevator car 17 from traveling at excessive speeds. Tension element 18 functions to maintain tension in cable 14. As elevator car 17 moves up and down in the hoistway, governor 13 rotates in response to the movement of elevator car 17. Absolute multi-turn encoder 15 is mounted in communication with governor 13 so that multi-turn encoders 15 can measure the rotation of governor 15. In a preferred embodiment, there are mounted two absolute multi-turn encoders 15 in communication with governor 13. In a preferred embodiment, multi-turn encoders 15 are mounted to governor 13.

Mounting two or more absolute multi-turn encoders 15 in communication with governor 13 provides system redundancy in the event of a failure as required by existing codes and standards.

Absolute multi-turn encoders 15 may be any form of encoder capable of measuring a degree of rotation attributable to the movement of the elevator car 11 along a hoistway and converting the measured degree of rotation to an absolute position of the elevator car 11 along the hoistway. In a preferred embodiment, absolute multi-turn encoders 15 make use of two or more tracks to ascertain degree of rotation wherein such tracks are either optical or magnetic in nature.

At least one sill sensor 21 is attached to elevator car 17.

Sill sensors 21 function to detect when the elevator car 17 sill is level with the landing door sill. In a preferred embodiment, two sill sensors 21 are attached, preferably one located horizontally from the other. Sill sensors 21 interact with sensor activation means, preferably vanes 19, attached to the hoistway at the landing door sill as described more fully below.

Sill sensors 21 and vanes 19 interact to provide accurate information as to an elevator car 17 position with respect to a predetermined position of known location. The precise location of each vane is stored and is accessible to controller 12. Information indicating that sill sensor 21 and vane 19 are in exact correspondence, and hence that the elevator car 17 is at a precisely predefined position, preferably at a landing door sill, is forwarded to controller 12 via link 20. Link 20 may be any mode of communication which enables information about the position of elevator car 17 recorded by sill sensor 21 to be transmitted to controller 12. Similarly, information from the one or more absolute multi-turn encoders 15 in communication with the governor 13 is likewise communicated to controller 12.

The information communicated from sill sensor 21 and from the one or more absolute multi-turn encoders 15 to controller 12 is described more fully below.

With reference to FIG. 2, there is illustrated a preferred embodiment of sill sensor 21 of the present invention. Sill sensor 21 consists of a light emitting element 23 and a light detector element 25. In a preferred embodiment, light emitting element 23 is a light emitting diode, laser, or other light emitting device capable of emitting light of a wavelength able to be detected by light detector 25. Light detector 25 receives the preferably continuous emission of light from light emitting element 23. As the elevator car 17 moves up and down the hoistway, the continuous emission of light is interrupted by an interruption means, namely vanes 19, mounted at known positions along the hoistway. When a signal emitted from light emitting element 23 and detected by light detector 25 is interfered with in this manner, a signal is sent from sill sensor 21 to controller 12 to indicate the precise position of elevator car 17.

While described herein with reference to a vane system, the present invention is not so limited. In another preferred embodiment, the sill sensor 21 comprises retro-reflective sensor (light emitter and detector are part of the same device) mounted on a car sill, and the sensor activation means consists of a reflector mounted on (or integral to) the landing sill.

Alternative embodiment include the use of magnetic sensors.

The sill sensors 21, in conjunction with the absolute encoder, (1) establishes the landing positions in the hoistway, following an initial'learn'run, (2) provides updates/corrections of landing positions relative to each other in case of building settling, (3) provides updates/corrections of elevator car 17 position relative to landings in case of governor rope slippage. During the learn run, the controller records the absolute location data for each landing door sill for later access.

During normal operation, absolute multi-turn encoders 15 send continuously updated signals to controller 12 indicating the precise position of elevator car 17. As a result, absolute multi-turn encoders 15 provide controller 12 with continuously updated information regarding the absolute position of elevator car 17 in the hoistway. It is known that in normal operation, the cable 14 moving in conjunction with the governor 13 may slip. When this occurs, the absolute multi-turn encoders 15 will not give a precise and accurate reading on the location of elevator car 17. The slip between cable 14 and the sheave of the governor 13 is typically minimal, and is usually less than 2 mm for a full hoistway length run. When such slippage exceeds acceptable threshold limits, the present invention is able to correct the car position reading obtained from the absolute multi-turn encoders 15 by combining the information provided therefrom with the information collected from sill sensors 21.

Specifically, when an elevator is moved to a known precise location corresponding to the position of at least one sill sensor, such as a location exactly corresponding to a particular floor level, controller 12 makes use of the sill sensors 21 to correct the information being received from the absolute multi-turn encoder 15 as follows. Controller 12 controls the positioning of the elevator to a close tolerance based on the position information received from absolute multi-turn encoder 15. If, when the elevator car 11 is maneuvered to such a position, sill sensor 21 indicates that the elevator car 11 is in fact a short distance out of position, usually in the range of 1 to 3 mm, controller 12 proceeds to precisely position elevator car 17 based upon the information returned from the sill sensor 21. After precisely positioning the elevator car 17 at the precise known location coincident with sill sensor 21, the controller 12 communicates with the absolute multi-turn encoder 15 so as to update the recorded absolute location for each landing door sill In addition, the controller 12 performs position updates/corrections based on information received from sill sensors even when the elevator car 17 travels at full speed, every time the elevator car 17 passes by a sill sensor.

As a result, controller 12 continually updates the recorded absolute location of each landing door sill.

It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.