Abstract:
A system for monitoring elevator car travel includes a plurality of bi-stable sensors ( 12 ) traveling with an elevator car ( 10 ); a plurality of sense elements ( 20 ) positioned along a path of the sensors ( 12 ); the sense elements ( 20 ) causing the sensors ( 12 ) to assume one of a first state and a second state; wherein states of the sensors ( 12 ) define a zone code ( 30 ) identifying a zone corresponding to the elevator car ( 10 ) position, the zone code ( 30 ) being a gray code.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to determining elevator car position. More particularly, the subject matter disclosed herein relates to determining elevator car position using bi-stable sensors. 
         [0002]    It is known in the elevator art to define terminal zones at both ends of the elevator hoistway. The top landing of the building will normally be located within the top terminal zone as will the lower landing be located within the bottom terminal zone. It is desired that the elevator car stop normally at a top or bottom landing of the hoistway in such a terminal zone. As a safety measure, it is necessary to provide a number of backup means to ensure the elevator car does not collide with the mechanical hard-limits. Three levels of protection are usually provided when the elevator enters a terminal zone: the Normal Stopping Device, the Normal Terminal Stopping Device (or NTSD), and the Emergency Terminal Speed Limiting Device (or ETSLD). Embodiments of the invention may be used with NTSD which will take over from the Normal Stopping Device should the normal speed control signals fail to stop the car at the designated positions at the upper and lower ends of the hoistway. Two similar NTSDs are usually provided in the two terminal zones. One NTSD is installed at the bottom of the hoistway and one NTSD at the top of the hoistway. The NTSD system is designed to override the normal speed command signals and bring the car to stop at the terminal. It is also designed such that the NTSD terminal speed profile causes the slowdown pattern to be relatively smooth. 
         [0003]    In order to implement the NTSDs, the position of the elevator car needs to be known by a control system. One existing method of determining elevator car position employs three sensors for detecting car position and a fourth sensor as a latching or clock input. The clock input indicates when the three sensors should be read to determine car position. As system noise can cause false clocking signals, improvements to such systems would be well received in the art. In addition, positions identified through the use of a simple binary code is sub-optimal in the required number of sense elements. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one aspect of the invention, a system for monitoring elevator car travel includes a plurality of bi-stable sensors traveling with an elevator car; a plurality of sense elements positioned along a path of the sensors; the sense elements causing the sensors to assume one of a first state and a second state; wherein states of the sensors define a zone code identifying a zone corresponding to the elevator car position, the zone code being a gray code. 
         [0005]    According to one aspect of the invention a method for monitoring elevator car travel includes positioning a plurality of bi-stable sensors to travel with an elevator car; positioning a plurality of sense elements along a path of the sensors; the sense elements causing the sensors to assume one of a first state and a second state; obtaining states of the sensors, wherein the states of the sensors define a zone code identifying a zone corresponding to the elevator car position, the zone code being a gray code. 
         [0006]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0007]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  depicts an elevator car and top and bottom NTSD zones; 
           [0009]      FIG. 2  depicts the top NTSD zone; 
           [0010]      FIG. 3  depicts the bottom NTSD zone; and 
           [0011]      FIG. 4  depicts a control system. 
       
    
    
       [0012]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  depicts an elevator car and top and bottom NTSD zones. As known in the art, certain safety systems need to know the elevator car zone in order to apply the appropriate safety measure (e.g., reduce car speed). The exemplary embodiment of  FIG. 1  includes a car  10  having a plurality of sensors  12  mounted to the car  10 . In the embodiment of  FIG. 1 , three sensors  12  are employed, but it is understood that any number of sensors may be used. 
         [0014]    Sensors  12  travel with car  10 , and may be mounted directly to the car  10  or on a support  14  extending from the car  10 . Sensors  12  are positioned and spaced to correspond to sense elements  20 . As described in further detail herein, sensors  12  are bi-stable sensors, meaning sensors  12  maintain a first state until being toggled to a second state, and vice versa. To change state, the sensors  12  need to be exposed to energy initiating the change in state; mere absence of a sensed element  20  will not cause the state of sensor  12  to change. In an exemplary embodiment, sensors  12  are bi-stable reed switches sensitive to magnetic energy. It is understood that other types of bi-stable sensors may be used (e.g., optical). 
         [0015]    Sense elements  20  are positioned along a path of travel of the sensors  12 . The sense elements  20  are positioned and spaced to correspond to the positions and spacing of the sensors  12 . Sense elements  20  may be mounted in the hoistway, if sensors  12  travel within the hoistway. As long as the sensors  12  pass close enough to the sense elements  20  to detect the sense elements  20 , the exact mounting location in the elevator system is not critical. 
         [0016]    The sense elements  20  are mounted on vanes  22 , with each vane positioned at a transition between zones. As described in further detail herein, as the group of sensors  12  passes each zone boundary, one of the sensors  12  changes states in response to a sense element  20  positioned at the boundary between the zones. As only one sensor  12  changes state at each zone transition, the zone code  30  generated by the sensors  12  follows a gray code. As known in the art, a gray code is a series of binary numbers in which only a single bit changes from one element in the series to the next. 
         [0017]      FIG. 2  depicts the top NTSD zone, the on and off states of the sensors  12  and the zone code  30  generated by the three sensors  12  as the car travels along the top zones. The sense elements  20  include two types of sense elements having different characteristics. Sense elements  20   1  have a first characteristic and sense elements  20   2  have a second characteristic, different from the first characteristic. In an exemplary embodiment, the first sense element  20   1  is a north polarity magnet and the second sense element  20   2  is a south polarity magnet. It is understood that other characteristics (e.g., wavelength of light) may be used to provide the two different sense elements  20   1  and  20   2 . The different characteristics of the sense elements  20   1  and  20   2  cause the sensors  12  to assume different states. 
         [0018]    The direction of travel of the car  10  also affects the state of the sensor  12 . For example, when the car  10  (and sensors  12 ) is traveling upwards, the first sense element  20   1  causes the sensor  12  to assume a first value (e.g., a logic  1 ) and the second sense element  20   2  causes the sensor  12  to assume a second value (e.g., logic  0 ). Alternatively, when the car  10  (and sensors  12 ) is traveling downwards, the first sense element  20   1  causes the sensor  12  to assume the second value (e.g., a logic 0) and the second sense element  20   2  causes the sensor  12  to assume a first value (e.g., logic 1). 
         [0019]      FIG. 2  illustrates the on (e.g., logic 1) and off (e.g., logic 0) states of the three sensor  12   1 ,  12   2 ,  12   3 .  FIG. 2  also depicts the zone code  30  as the sensors travel through each zone. The zone code corresponds to the state of sensors  12   1 ,  12   2 , and  12   3 . The state of sensors  12   1 ,  12   2  and  12   3  is altered when the sensor passes proximate to a sensed element  20 . The sensors  12  and sense elements  20  are positioned and spaced so that a sensor  12  will not change state if it is not the closest sensor  12  to a sensed element  20 . Each vane  22  includes a single sense element  20  so that only a single bit is changed upon the transition from one zone to the next. Accordingly, the zone code  30  is a gray code. 
         [0020]    In the example of an upwardly moving car  10 , the zone code is initially  000  when the car  10  is between the top zones and the bottom zones (shown in  FIG. 1 ). As the car moves upwards through the zones (approaching terminal zone  1 ), the zone code  30  changes by one bit as the car  10  passes through each zone. Eventually the zone code  30  becomes  000  again as the car enters the terminal zone  1 . A controller, described in further detail herein, monitors the zone code  30  to determine what zone the car  10  is in and the appropriate safety measures, in any, for that zone. 
         [0021]    As the car moves downward through the top zone, the states of sensor  12   1 ,  12   2 ,  12   3  are altered by the sensors  12  passing the sense elements  20 . When the car  10  is moving downwards, the sense elements  20  have the opposite effect on the states of sensors  12  (as compared to an upwardly moving car) and the zone code  30  is the same for each zone, regardless of whether the car is moving up or down. 
         [0022]      FIG. 3  depicts the bottom NTSD zone, the on and off states of the sensors  12  and the zone code  30  generated by the three sensors  12  as the car travels along the bottom zones. Operation is similar to that described above with reference to  FIG. 2 . The zone code  30  is initially 000 as the car enters the bottom zones and the zone code  30  follows the same pattern as when the car  10  is traveling upwards through the top zones. As noted above with reference to  FIG. 2 , the direction of travel of car  10  and the characteristic of the sense element  20  controls the state of the sensors  12 . As only one sense element  20  is mounted at each transition between zones, the zone code  30  is a gray code with a single bit changing with each transition. 
         [0023]      FIG. 4  is a block diagram of an exemplary control system  100 . Control system  100  includes a sampling unit  102  for receiving the zone code  30  from the sensors  12   1 ,  12   2  and  12   3 . The sampling unit  102  may sample the value of sensors  12  periodically (e.g., once per millisecond) to effectively continuously monitor the zone code. The signals from sensors  12   1 ,  12   2  and  12   3  are provided to a debounce unit  104 , which serves to debounce the signals. Debouncing may involve detecting a transition in the state of the signal from a sensor  12  and then pausing until the signal stabilizes before accepting the signal value. 
         [0024]    A controller  106  receives the zone code  30  and issues control signals, as needed. The controller  106  may be implemented with one or more processors executing computer program code, memory adapted to store software programs and data structures, input-output devices, etc. The controller  106  may also receive other inputs, such as elevator car speed. In an exemplary embodiment, the controller determines when the car  10  is entering a terminal zone (e.g., top or bottom) and determines if the car speed is acceptable. If not, a control signal is generated to initiate the NTSD to reduce car speed in the terminal zones. As the zone code  30  for the top zone and bottom zone follows the same pattern (from entry to the terminal zone), controller  106  can be simplified to detect when the terminal zone is approaching. 
         [0025]    In alternate embodiments, the top zone codes  30  and the bottom zone codes  30  are different and follow a different pattern. This can be useful in determining whether the car is in the top zone or bottom zone. Processor  106  can determine which zone the car is in by analyzing the zone code  30 . 
         [0026]    Technical effects of exemplary embodiments include providing a mechanism for accurately determining the zone of an elevator car. The determination of the zone of the elevator car may then be used to determine whether certain safety initiatives are warranted. 
         [0027]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.