System and method for determining suspension member elongation

Abstract

The invention relates to a system and method for determining suspension member elongation. Specifically, an apparatus and method for determining the elongation of a suspension member in an elevator system including an elevator car supported by at least one suspension member for movement within a hoistway and a counterweight coupled to the elevator car with the at least one suspension member. A first sensor detects the presence of one of the counterweight and the elevator car, and a second sensor determines a position of the other of the elevator car and the counterweight within the hoistway in response to a detection signal generated by the first sensor. The elongation of the at least one suspension member is determined based on a change over time in the position of the elevator car or counterweight in the hoistway as determined in response to the detection signal.

Description

BACKGROUND OF THE INVENTION

[0001] For example, elevator systems are widely used to transport passengers between various floors in a building. Some elevator systems are traction-based, where a suspension assembly (sometimes referred to as ropes) suspends an elevator car and a counterweight. The suspension assembly also facilitates movement of the elevator car when needed. Traditional suspension assemblies include round steel ropes. Some elevator systems have included other types of suspension components, such as flat belts or other types of ropes, which have a tension member wrapped in a compressible polymer sheath. Elongation of the suspension component (especially a coated suspension component) is an indication of life / retained breaking strength. Since elongation occurs on a very small scale, it can be challenging to measure repeatedly and accurately. SUMMARY OF THE INVENTION

[0002] An exemplary elevator system includes: at least one suspension component that supports an elevator car and facilitates movement of the elevator car in a hoistway; a counterweight that is coupled to the elevator car using at least one suspension component; a first sensor that detects the presence of one of the counterweight and the elevator car; a second sensor that determines the position of the other of the counterweight and the elevator car within the hoistway in response to a detection signal generated by the first sensor; and a control system that determines elongation of at least one suspension component based on a change over time of the position of the elevator car or the counterweight in the hoistway as determined in response to the detection signal.

[0003] In addition to one or more of the above features, or as an alternative, the first sensor includes a counterweight sensor that is positioned at a fixed location in the hoistway and detects the presence of the counterweight.

[0004] In addition to one or more of the above features, or as an alternative, the second sensor includes a car sensor for an absolute position reference system that determines the position of the elevator car.

[0005] In addition to one or more of the above features, or as an alternative, the absolute position reference system includes a code strip that extends along a wall of the hoistway located beside the elevator car, and the car sensor includes an absolute position sensor that moves with the elevator car and interacts with the code strip to determine the precise position of the elevator car within the hoistway.

[0006] In addition to one or more of the above features, or as an alternative, the absolute position reference system records the precise position of the elevator car within the hoistway in response to each detection of the counterweight.

[0007] In addition to, or as an alternative to, one or more of the above features, the control system will compare the exact position of the elevator car in response to a detection signal generated by a counterweight sensor when the elevator car is in an initial installation state with the exact position of the elevator car in response to a detection signal generated by the counterweight sensor when the elevator car is in a subsequent operating state to determine elongation.

[0008] In addition to, or as an alternative to, one or more of the above features, the first sensor includes a car sensor that is positioned at a fixed location in the hoistway and detects the presence of the elevator car.

[0009] In addition to, or as an alternative to, one or more of the above features, the second sensor includes a counterweight sensor to determine the position of the counterweight.

[0010] In addition to, or as an alternative to, one or more of the above features, the counterweight sensor includes a reference tape associated with one of the counterweight and the hoistway wall, and a camera associated with the other of the counterweight and the hoistway wall.

[0011] In addition to, or as an alternative to, one or more of the above features, the fixed location includes the lowest landing zone, and a detection signal is generated to activate the camera once the elevator car stops at the lowest landing zone.

[0012] An exemplary elevator system includes: at least one suspension member that supports the elevator car and facilitates movement of the elevator car in the hoistway; a counterweight that is coupled to the elevator car by at least one suspension member; a first sensor assembly that detects the presence of one of the counterweight and the elevator car, wherein the first sensor assembly includes at least one first sensor mounted to a fixed location in the hoistway or to a first movable object; a second sensor assembly that determines the position of the other of the elevator car and the counterweight within the hoistway in response to a detection signal generated by the at least one first sensor, and wherein the second sensor assembly includes a reference tape mounted to one of a fixed structure or a second movable object, and at least one second sensor mounted to the other of the fixed structure or the second movable object; and a control system that determines elongation of the at least one suspension member based on the change over time of the position of the elevator car or the counterweight in the hoistway as determined in response to the detection signal.

[0013] In addition to, or as an alternative to, one or more of the above features, the first sensor includes a counterweight sensor that is positioned at a fixed location in the hoistway and detects the presence of the counterweight; and the reference tape is mounted along the wall of the hoistway including the fixed structure or to the outer surface of a second movable object including the elevator car, and the at least one second sensor is mounted to the other of the wall of the hoistway or the outer surface of the second movable object including the elevator car.

[0014] In addition to, or as an alternative to, one or more of the above features, the detection signal causes at least one second sensor to determine the car position, and then this car position is used to determine the change in car position over time, and wherein, during generation of the detection signal, the counterweight and the elevator car are in motion.

[0015] In addition to, or as an alternative to, one or more of the above features, at least one first sensor includes a car sensor that is mounted to a first movable object including the elevator car or to a fixed position on a wall including the hoistway, and detects the presence of the elevator car; and a reference tape is mounted to a fixed structure including the wall of the hoistway or to a second movable object including the counterweight, and at least one second sensor includes a camera mounted to the other of the counterweight or the wall of the hoistway.

[0016] In addition to, or as an alternative to, one or more of the above features, the car sensor triggers activation of the camera to determine the change in counterweight position over time, and wherein, during generation of the detection signal, the elevator car is stationary at a specific position.

[0017] An exemplary method includes, wherein an elevator car is supported by at least one suspension member for movement within a hoistway, and a counterweight is coupled to the elevator car by at least one suspension member, the method includes: detecting the presence of one of the counterweight and the elevator car using a first sensor; determining the position within the hoistway of the other of the elevator car and the counterweight in response to a detection signal generated by the first sensor; and determining the elongation of at least one suspension member based on the change in position over time of the elevator car or the counterweight within the hoistway as determined in response to the detection signal.

[0018] In addition to, or as an alternative to, one or more of the above features, the method includes moving the counterweight and the elevator car during generation of the detection signal.

[0019] In addition to, or as an alternative to, one or more of the above features, the method includes stationary the counterweight and the elevator during generation of the detection signal.

[0020] In addition to, or as an alternative to, one or more of the above features, the first sensor includes a counterweight sensor, and the second sensor includes a car sensor for an absolute position reference system that determines the position of the elevator car, and the method includes: positioning the first sensor at a fixed position within the hoistway to detect the presence of the counterweight; extending a code tape of the absolute position reference system along a wall of the hoistway adjacent to the elevator car; and mounting the car sensor to move with the elevator car and interact with the code tape to determine the precise position of the elevator car within the hoistway.

[0021] In addition to, or alternatively to, one or more of the above features, the first sensor includes a car sensor and the second sensor includes a counterweight sensor to determine the position of the counterweight, and includes: positioning the first sensor at a fixed position in the hoistway to detect the presence of the elevator car; providing the counterweight sensor as a reference tape associated with one of the counterweight and the hoistway wall and a camera associated with the other of the counterweight and the hoistway wall; and generating a detection signal to activate the camera to read the reference tape once the elevator stops at the fixed position.

[0022] From the following detailed description, various features and advantages of the exemplary embodiments will become apparent to those skilled in the art. The figures accompanying the detailed description can be briefly described as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Selected portions of an elevator system incorporating a system for determining elongation of a suspension member are schematically shown, wherein the system is in an initial state.

[0024] Figure 2 Similar to Figure 1 but shows the system in an elongated state.

[0025] Figure 3 A portion of an exemplary suspension member is schematically shown.

[0026] Figure 4 Is a flow chart depicting a method of determining elongation of a suspension member in an elevator system.

[0027] Figure 5 Selected portions of an elevator system incorporating another system for determining elongation of a suspension member are schematically shown, wherein the system is in an initial state.

[0028] Figure 6A Shows the Figure 5 system in an initial state.

[0029] Figure 6B Similar to Figure 6A but shows the system in an elongated state. DETAILED DESCRIPTION

[0030] Embodiments of the present disclosure provide a simple and cost-effective system and method for determining elongation of a suspension member.

[0031] Figure 1-2 Selected portions of an elevator system 20 are schematically shown. The elevator car 22 is supported by a rope arrangement or suspension assembly 24 including one or more suspension members 26. The elevator car 22 is coupled to the counterweight 28 by the suspension member 26. In one example, as Figure 3As shown, the suspension member 26 includes a coated rope or a coated steel strip, wherein the tension member 38 is wrapped in a compressible polymer sheath 40.

[0032] The machine sheave 30 is associated with the machine encoder 32. The machine sheave 30 facilitates the movement of the elevator car 22 within the hoistway 34. When the suspension member 26 moves in response to the rotation of the machine sheave 30, the elevator car 22 and the counterweight 28 move vertically. When the elevator car 22 moves between landings or floors, the suspension member 26 can move around an additional sheave 36.

[0033] In one example, the machine sheave 30 supports the suspension member 26 at a location between the counterweight 28 and the elevator car 22. The elongation determination system includes at least a first sensor 42 (e.g., a counterweight sensor) that detects the presence of the counterweight 28, and a second sensor 44 (e.g., a car sensor) that detects the presence of the elevator car 22. The control system includes a drive / controller 46 that interacts with the first sensor 42 and the second sensor 44 to determine the elongation or change in length of the suspension member 26 over time.

[0034] In one example, the first sensor 42 includes a single discrete sensor positioned at a fixed location 48 within the hoistway 34. In one example, the first sensor 42 is positioned on the hoistway wall 50 on the counterweight side of the hoistway 34. In one example, the single discrete sensor includes a limit switch, a photoelectric sensor, a proximity sensor, or a similar sensing device; however, other types of detection sensors may also be used.

[0035] In one example, the first sensor 42 may include an existing sensor that is already used in the elevator system 20. In one embodiment, the existing sensor may include a sensor for determining the overtravel of the counterweight 28 when the counterweight 28 contacts a buffer located in the hoistway pit.

[0036] In one example, the second sensor 44 includes an absolute position reference system (APRS). Any type of APRS can be used, and those skilled in the art having the benefit of this specification will be able to determine which type of APRS will be most suitable for these purposes. In one example, the APRS includes a code strip 52 mounted to the wall 54 on the car side of the hoistway 34, and an APRS sensor 56 that moves with the elevator car 22. The code strip 52 extends along the entire length of the hoistway 34. The APRS sensor 56 moves with the elevator car 22 and interacts with the code strip 52 to determine the absolute or precise position of the elevator car 22 within the hoistway 34. The APRS may include other components that can be used to mount the code strip and the APRS sensor as needed, such as guide clips and position indicator clips (not shown).

[0037] By reading a fixed-mounted code strip 52 in the hoistway 34, the APRS can be used to determine the absolute position and speed of the elevator car 22. The APRS transmits this information to the controller 46 using a specified communication interface. As is well known, the information of the absolute position is encoded on the code strip. In one example, the APRS sensor 56 is based on a dual-camera system that scans the code strip 52 via infrared illumination to determine the position.

[0038] In one example, the APRS has a resolution of 1 mm or less. In another example, the APRS has a resolution of 0.5 mm.

[0039] As discussed above, the counterweight sensor 42 detects the presence of the counterweight 28 within the hoistway 34, and the car sensor 44 determines the position of the elevator car 22 within the hoistway 34 in response to the detection signal generated by the counterweight sensor 42. The controller 46 of the control system can then determine the elongation of the suspension member 26 based on the change in the position of the elevator car 22 in the hoistway 34 over time as determined in response to the detection signal. Thus, position information is generated each time the counterweight 28 is detected, and this position information is stored / recorded in the control system to determine the elongation.

[0040] The suspension member 26 will stretch or elongate over time. During the initial installation of the elevator car 22, the system will determine the initial position of the elevator car 22 in the hoistway in response to the detection signal generated by the counterweight sensor 42, as Figure 1-2 indicated at p in 0 . As the suspension member 26 elongates over time, when the position of the counterweight 28 is detected by the sensor 42, the position of the elevator car 22 in the hoistway will change due to the increase in the length of the suspension member. In Figure 2 , this position change is exemplified as p > p 0 , specifically Δp = p 1 – p 0 .

[0041] Thus, the APRS records the exact position of the elevator car 22 within the hoistway 34 in response to each detection of the counterweight 28 by the sensor 42, and then uses this information for comparison purposes. For example, the control system will compare the exact position of the elevator car 22 in response to the detection signal generated by the counterweight sensor 42 when the elevator car 22 is in the initial installation state with the exact position of the elevator car 22 in response to the detection signal generated by the counterweight sensor 42 when the elevator car is in a subsequent operating state to determine the elongation. When the elongation reaches a predetermined limit over time, the control system can generate an indicator signal. In one example, the predetermined limit includes retirement criteria based on the elevator type and / or elevator operating application. Those skilled in the art with the benefit of this specification will be able to determine the appropriate retirement criteria for each system.

[0042] The drive / controller 46 is part of the control system and includes one or more processors that receive / record input data from sensors 42, 44 and determine the elongation of the suspension member 26. In one example, the processor includes one or more computing devices and associated memory. The processor is programmed or otherwise configured to use different types of information to quantify the proportional relationship of the car position over time.

[0043] As discussed above, the suspension member 26 tends to elongate during use. This characteristic can be used for health monitoring of the suspension member 26 to determine the remaining life based on the amount of elongation. As Figure 4 shown, the present disclosure presents a method for determining elongation. In one example, the method includes detecting the presence of the counterweight or the elevator car (as indicated at 100) using a first sensor, and determining the precise position of one of the elevator car or the counterweight within the hoistway (as indicated at 200) in response to a detection signal generated by detecting the other of the counterweight and the elevator car. Next, the method includes determining the elongation of at least one suspension member based on the change over time of the position of the elevator car or the counterweight in the hoistway as determined in response to the detection signal, as indicated at 300.

[0044] The method may also include any of the following steps, either alone or in any combination thereof. For example, the method may include positioning the counterweight sensor 42 at any fixed position within the hoistway 34.

[0045] The method may include using an APRS to determine the precise position of the elevator car 22 within the hoistway 34, where the APRS includes a code strip 52 extending along the wall 54 of the hoistway 34 located beside the elevator car 22, and an APRS sensor that moves with the elevator car 22 and interacts with the code strip 52 to determine the precise position of the elevator car 22 within the hoistway 34.

[0046] The method may include recording the precise position of the elevator car 22 within the hoistway 34 in response to each detection of the counterweight 28.

[0047] The method may include comparing the precise position of the elevator car 22 in response to a detection signal generated by the counterweight sensor 42 when the elevator car 22 is in an initial installed state with the precise position of the elevator car 22 in response to a detection signal generated by the counterweight sensor 42 when the elevator car is in a subsequent operating state to determine elongation.

[0048] The method may include generating an indicator signal when the elongation reaches a predetermined limit over time.

[0049] In Figure 5 and Figure 6AIn another example shown in -B, a reference tape 410 (e.g., a scale tape) and a reference line 416 are used in combination with a sensor 418 including, for example, at least one camera. In one example, the reference tape 410 or the scale tape includes lines 412 having a fixed interval 414 (e.g., ΔH), and the fixed interval 414 includes a fixed distance between two adjacent lines 412. As Figure 5 shown, the reference tape 410 can be mounted on the outer surface of the counterweight 28. In Figure 5 the example shown, the sensor 418 (e.g., a camera) is mounted at the top of the hoistway and is positioned in front of the reference tape 410 when the counterweight 28 is at the top of the hoistway. Optionally, the positions of the camera and the reference tape can be switched.

[0050] At initial installation, the elevator car 22 is moved to the lowest landing or floor, and the camera is positioned to be aligned with the reference line 416. The camera is capable of determining the number N1 of lines above the reference line 416 at this position ( Figure 6A ). As additional measurements are made, the number of lines above the reference line 416 will increase over time. Each time the car 22 is moved to the lowest landing, the camera will record the number of lines above the reference line 416, and this will result in an increased number of lines N2 ( Figure 6B ), which can be equivalent to elongation.

[0051] In this example, the elevator car 22 includes a sensor assembly that includes a first component 420 that moves with the car 22 and a second component 422 that is fixed to the hoistway wall at a fixed position. In one example, the first component 420 includes a door zone (DZ) switch and the second component 422 includes a DZ magnet. However, other types of sensors can also be used. In one example, the first component 420 and the second component 422 are located at the lowest possible DZ position, e.g., the lowest landing or floor, and the camera 418 and the reference tape 410 are located at the top of the hoistway.

[0052] To ensure that the elevator car 22 is always in the same position during each measurement, the elevator car 22 will move at a low speed until the available DZ switch is positioned in front of the edge of the lowest DZ magnet. The car 22 will stop at this position, and then the camera will be triggered. In other words, once the presence of the car is detected at this position, the camera will be activated. When the camera is triggered, an image of the reference tape 410 falls on the pixel grid 424 of the camera. In one example, image analysis software tallies the lines 412 above or below the reference line 416. The amount of elongation is determined by: ΔH multiplied by the number of lines between the initial position and the actual position of the reference line 416, e.g., elongation = ΔH * (N1 - N2). Figure 6A The initial position is shown, and Figure 6BShows subsequent positions after a period of time. Measurements are taken regularly, for example several times during a month. This makes it possible to accurately track the overall elongation as well as the elongation rate, while also estimating the actual state of health of the suspension components to predict before reaching a specified threshold.

[0053] This exemplary configuration is applicable to both rope-type and belt-type units and has a high accuracy compared to other solutions using switches on the counterweight side. The system is non-contact and maintenance-free and provides continuous monitoring of elongation and the associated rate of change during normal elevator operation.

[0054] In one example, a method includes: detecting the presence of one of a counterweight and an elevator car using a first sensor; determining the position of the other of the elevator car and the counterweight within a hoistway in response to a detection signal generated by the first sensor; and determining the elongation of at least one suspension component based on a change over time of the position of the elevator car within the hoistway as determined in response to the detection signal.

[0055] The method may include any of the following steps individually or in any combination. For example, the method may include moving the counterweight and the elevator car during generation of the detection signal.

[0056] For example, the method may include stationary the counterweight and the elevator during generation of the detection signal.

[0057] For example, the method may include, where the first sensor includes a counterweight sensor and the second sensor includes a car sensor for an absolute position reference system that determines the position of the elevator car, and the method further includes: positioning the first sensor at a fixed position in the hoistway to detect the presence of the counterweight; extending a code strip of the absolute position reference system along a wall of the hoistway located beside the elevator car; and mounting the car sensor to move with the elevator car and interact with the code strip to determine the precise position of the elevator car within the hoistway.

[0058] For example, the method may include where the first sensor includes a car sensor and the second sensor includes a counterweight sensor to determine the position of the counterweight, and the method further includes: positioning the first sensor at a fixed position in the hoistway to detect the presence of the elevator car; providing the counterweight sensor as a reference strip associated with one of the counterweight and the hoistway wall and a camera associated with the other of the counterweight and the hoistway wall; and generating a detection signal to activate the camera to read the reference strip once the elevator stops at the fixed position.

[0059] The foregoing description is exemplary in nature and not restrictive. Variations and modifications of the disclosed examples may become apparent to those skilled in the art, and these variations and modifications do not necessarily depart from the essence of the invention. The scope of legal protection given to the present invention can be determined only by studying the following claims.

Claims

1. An elevator system, comprising: at least one suspension member that supports the elevator car and facilitates movement of the elevator car in the hoistway; a counterweight coupled to the elevator car using the at least one suspension member; a first sensor that detects the presence of one of the counterweight and the elevator car; a second sensor that determines a position of the other of the counterweight and the elevator car within the hoistway in response to a detection signal generated by the first sensor; as well as A control system determines an extension of the at least one suspension member based on a change in position of the elevator car or the counterweight in the hoistway over time as determined in response to the detection signal.

2. The elevator system according to claim 1, wherein: The first sensor includes a counterweight sensor that is positioned at a fixed location in the hoistway and detects the presence of the counterweight.

3. The elevator system according to claim 2, wherein: The second sensor comprises a car sensor for an absolute position reference system that determines the position of the elevator car.

4. The elevator system according to claim 3, wherein: The absolute position reference system includes a code tape extending along a wall of the hoistway beside the elevator car, and the car sensor includes an absolute position sensor that moves with the elevator car and interacts with the code tape to determine the precise position of the elevator car within the hoistway.

5. The elevator system according to claim 4, wherein: The absolute position reference system records the precise position of the elevator car within the hoistway in response to each detection of the counterweight.

6. The elevator system according to claim 5, wherein: The control system compares the precise position of the elevator car in response to the detection signal generated by the counterweight sensor when the elevator car is in an initial installation state with the precise position of the elevator car in response to the detection signal generated by the counterweight sensor when the elevator car is in a subsequent operating state to determine the elongation.

7. The elevator system according to claim 1, wherein: The first sensor includes a car sensor that is positioned at a fixed location in the hoistway and detects the presence of the elevator car.

8. The elevator system according to claim 7, wherein: The second sensor includes a counterweight sensor to determine the position of the counterweight.

9. The elevator system according to claim 8, wherein: The counterweight sensor includes a reference tape associated with one of the counterweight and a hoistway wall, and a camera associated with the other of the counterweight and the hoistway wall.

10. The elevator system according to claim 9, wherein: The fixed position includes a lowermost door zone, and wherein the detection signal is generated to activate the camera once the elevator car stops at the lowermost door zone.

11. An elevator system, comprising: at least one suspension member that supports the elevator car and facilitates movement of the elevator car in the hoistway; a counterweight coupled to the elevator car using the at least one suspension member; a first sensor assembly that detects the presence of one of the counterweight and the elevator car, wherein the first sensor assembly includes at least one first sensor mounted to a fixed location in the hoistway or mounted to a first movable object; a second sensor assembly that determines a position of the other of the elevator car and the counterweight within the hoistway in response to a detection signal generated by the at least one first sensor, and wherein the second sensor assembly includes a reference tape mounted to one of a fixed structure or a second movable object, and at least one second sensor mounted to the other of the fixed structure or the second movable object; as well as A control system determines an extension of the at least one suspension member based on a change in position of the elevator car or the counterweight in the hoistway over time as determined in response to the detection signal.

12. The elevator system of claim 11, wherein: The first sensor comprises a counterweight sensor positioned at a fixed position in the hoistway and detecting the presence of the counterweight; and The reference tape is mounted along a wall of the hoistway including the fixed structure or to an outer surface of the second movable object including the elevator car, and the at least one second sensor is mounted to the other of the wall of the hoistway or the outer surface of the second movable object including the elevator car.

13. The elevator system according to claim 12, wherein: The detection signal causes the at least one second sensor to determine a car position, which is then used to determine a change in car position over time, and wherein the counterweight and the elevator car are in motion during generation of the detection signal.

14. The elevator system of claim 11, wherein: The at least one first sensor comprises a car sensor mounted to a first movable object comprising the elevator car or to a fixed location comprising a wall of the hoistway and detecting the presence of the elevator car; and The reference tape is mounted to the fixed structure comprising a wall of the hoistway or to the second movable object comprising the counterweight, and the at least one second sensor comprises a camera mounted to the other of the counterweight or the wall of the hoistway.

15. The elevator system according to claim 14, wherein: The car sensor triggers activation of the camera to determine a change in counterweight position over time, and wherein the elevator car is stationary at a particular position during generation of the detection signal.

16. A method wherein an elevator car is supported by at least one suspension member for movement within a hoistway and a counterweight is coupled to the elevator car using the at least one suspension member, the method comprising: detecting the presence of one of the counterweight and the elevator car with a first sensor; determining a position of the other of the elevator car and the counterweight within the hoistway in response to a detection signal generated by the first sensor; as well as An elongation of the at least one suspension member is determined based on a change in position of the elevator car or counterweight in the hoistway over time as determined in response to the detection signal.

17. The method of claim 16, comprising placing the counterweight and the elevator car in motion during generation of the detection signal.

18. The method of claim 16, comprising bringing the counterweight and the elevator to a standstill during the generation of the detection signal.

19. The method according to claim 16, wherein: The first sensor comprises a counterweight sensor, and the second sensor comprises a car sensor for an absolute position reference system for determining the position of the elevator car, and comprises: positioning the first sensor at a fixed position in the hoistway to detect the presence of the counterweight; extending a code strip of the absolute position reference system along a wall of the hoistway beside the elevator car; and The car sensor is mounted to move with the elevator car and interact with the code tape to determine the precise position of the elevator car within the hoistway.

20. The method according to claim 16, wherein: The first sensor comprises a car sensor, and the second sensor comprises a counterweight sensor to determine the position of the counterweight, and comprises: positioning the first sensor at a fixed position in the hoistway to detect the presence of the elevator car; providing the counterweight sensor as a reference tape associated with one of the counterweight and a hoistway wall and a camera associated with the other of the counterweight and the hoistway wall; and Once the elevator stops at the fixed position, the detection signal is generated to activate the camera to read the reference tape.

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