JP2012171763A - Elevator control device and sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an elevator control device and sensor capable of preventing a useless control operation by properly setting the threshold with respect to rope swing in accordance with a quake amount of a building and a duration time of quake.SOLUTION: The elevator control device 22 includes: an acceleration sensor 23 which detects the quake amount of the building; a rope swing detection unit 31 which monitors the duration time of quake every quake amount of the building detected by the acceleration sensor 23, sets the threshold with respect to the swing of a rope on the basis of a function expression derived from analytical result of the quake amount of the building and the duration time and outputs a rope swing detection signal when the product of the quake amount of the building and the duration time is the threshold or more; and a controlled operation control unit 33 which stops a car on the nearest floor or subjects the car to controlled operation to a siding floor on the basis of a rope swing detection signal output from the rope swing detection unit 31.

Description

  Embodiments described herein relate generally to an elevator control device that detects a rope shake accompanying a shake of a building due to an earthquake, a strong wind, or the like and switches to control operation, and a sensor having a rope shake detection function.

  Generally, an elevator built in a building is provided with a P-wave earthquake detection device for detecting a P wave (Primary Wave) of an earthquake at the bottom (pit part) in the hoistway, and the machine room at the top of the hoistway, etc. Is provided with an S-wave earthquake detection device for detecting an earthquake S-wave (Secondary Wave). And the acceleration by an earthquake is detected with these earthquake detection apparatuses.

  However, for long-period earthquakes that have become a problem in high-rise buildings in recent years, only a value of about 1 to 20 Gal, which is much lower than the set value of 150 to 200 Gal (gal) detected by the earthquake detection device, is generated. do not do. The period of shaking is 2 to 10 seconds, which is much longer than 0.05 to 0.5 seconds, which is a general earthquake period. Nevertheless, depending on the structure of the building, the maximum amplitude of shaking may reach 10 cm to 1 m.

  Here, if the natural frequency of the building matches the natural frequency of the elevator rope (main rope, governor rope, etc.) installed in the hoistway, the rope will shake greatly due to resonance, and the equipment in the hoistway and the elevator There is a risk of contact with the road wall and a so-called “confinement accident”.

  In order to prevent such an accident, recent elevators are equipped with a safety device called a “control operation device”. In this technique, when a building shakes, a rope shake accompanying the shake of the building is detected, and when the amount of shake is equal to or greater than a preset threshold, the car is moved to a retreat floor.

JP 2008-133105 A JP 2010-52924 A JP 2008-285335 A

“Explanation of technical standards for elevators, 2009 edition, separate volume Elevator seismic design and construction guidelines, 2009 edition”, supervised by Ministry of Land, Infrastructure, Transport and Tourism Housing Bureau, Building Guidance Division, Japan Building Equipment and Elevator Center, Japan Elevator Association, 2009, p, 147-166

  The threshold value for the rope swing associated with the shaking of the building (conditions for controlling operation) was fixedly set based on the relationship between the amount of shaking of the building and its duration. That is, the threshold value is set with one pattern in the combination of the amount of shaking of the building and its duration. For this reason, if a threshold value is set so that the equipment in the hoistway does not contact reliably when the rope swings (that is, the building shake is small and the duration is short), frequent control operations with a slight shake Could occur.

  The problem to be solved by the present invention is to provide an elevator control device and a sensor that appropriately set a threshold for rope swing according to the amount of shaking of a building and its duration to prevent useless control operation. It is in.

  An elevator control device according to an embodiment includes an elevator control device including a car that moves up and down via a rope installed in a hoistway of a building; The duration of each of the building shakes detected by the building shake detection means is monitored, and the rope runout is based on a functional expression derived from the analysis result of the building shake amount and the duration. A rope shake detection means for outputting a rope shake detection signal when the product of the amount of shaking of the building and the duration is equal to or greater than the threshold, and the rope shake output from the rope shake detection means. Control operation means for stopping the above-mentioned car at the nearest floor based on the detection signal or for controlling the car to the retreat floor is provided.

  The sensor according to the embodiment is a sensor connected to an elevator control device having a car that moves up and down via a rope installed in a hoistway of a building, and the amount of shaking of the building A function derived from the analysis result of the amount of shaking of the building and the duration of time, and monitoring the duration of each building shaking detected by the building shaking detecting means. Rope shake detection means for setting a threshold value for the rope shake based on an equation and outputting a rope shake detection signal to the elevator control device when the product of the amount of shaking of the building and the duration is equal to or greater than the threshold value It comprises.

FIG. 1 is a diagram illustrating a configuration of an elevator according to the first embodiment. FIG. 2 is a block diagram showing a functional configuration of the elevator control device according to the embodiment. FIG. 3 is a diagram showing the relationship between the amount of shaking of the building and the duration when the amount of rope shake in the embodiment is 300 mm. FIG. 4 is a view showing the analysis result of the rope runout in the same embodiment, and shows the result of analyzing the rope runout amount in three stages of “runout height”, “runout low”, and “runout low”. . FIG. 5 is a flowchart showing the processing operation of the elevator rope runout detection in the embodiment. FIG. 6 is a diagram showing a relationship between the amount of shaking of the building and the acceleration signal in the same embodiment. FIG. 7 is a block diagram showing a functional configuration of an elevator control device according to the second embodiment. FIG. 8 is a diagram for explaining the relationship between the rope length of the elevator and the resonance frequency in the same embodiment. FIG. 9 is a flowchart showing the processing operation of the elevator rope runout detection in the same embodiment. FIG. 10 is a block diagram illustrating a configuration of a sensor having a rope shake detection function according to the third embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration of an elevator according to the first embodiment. Assume that one elevator 11 is installed in a building 10.

  As shown in FIG. 1, a hoisting machine 12 that is a drive source of the elevator 11 is installed in the uppermost machine room 10 a of the building 10. In the machine roomless type elevator, the hoisting machine 12 is installed in the upper part of the hoistway 10b.

  A main rope 13 is wound around the hoisting machine 12. One end of the main rope 13 is attached to a car 14 and the other end is attached to a counterweight 15. A compensatory sheave 16 is disposed at the lowermost part of the hoistway 10 b, and the end of the compensatory rope 17 is attached to the lower part of the car 14 and the counterweight 15 via the compensatory sheave 16.

  Further, a car control device 18 is provided above the car 14, and controls the opening and closing of the car door 19 when the car 14 is landed on any one of the landings 21a, 21b, 21c. The car control device 18 is connected to a control device 22 (to be described later) through a transmission cable 20 called a tail cord.

  On the other hand, in the machine room 10a or the machine room-less type of the building 10, a control device 22 for controlling the operation of the elevator 11 is installed in the hoistway 10b.

  The control device 22 includes a computer equipped with a CPU, ROM, RAM, and the like, and executes a series of processes relating to operation control of the elevator 11 such as drive control of the hoisting machine 12. In addition, as will be described later, when the building 10 is shaken by an earthquake, strong wind, or the like, the control device 22 detects a rope swing associated with the shaking of the building 10 and the detection result. A function for controlling the car 14 is provided.

  The “rope swing” means that the rope swings in the horizontal direction when the building 10 swings. In addition, the “rope” referred to here is a rope related to the raising / lowering operation of the car 14, and includes a compen- sion rope 17 in addition to the main rope 13 in the example of FIG. 1.

  Here, an acceleration sensor 23 for detecting the shaking of the building 10 due to an earthquake or a strong wind is installed near the top of the building 10. The acceleration sensor 23 is a biaxial acceleration sensor that can detect the acceleration in the horizontal direction (x direction and y direction) of the building, and outputs a detection signal to the control device 22.

  The control device 22 is connected to a setting switch 24 composed of, for example, a rotary switch. This setting switch 24 is operated by maintenance personnel and sets various parameters (Δt, Δα, G, A1) necessary for the rope swing detection by the control device 22.

  FIG. 2 is a block diagram illustrating a functional configuration of the elevator control device 22 according to the first embodiment.

  As shown in FIG. 2, the control device 22 includes a rope shake detection unit 31, a timer 32, and a control operation control unit 33.

  The rope shake detection unit 31 monitors the duration of shaking for each shaking amount of the building 10 detected by the acceleration sensor 23, and is derived from the analysis result of the shaking amount and duration of the building 10 with respect to the rope shaking amount. Based on the function expression f (α, t), a threshold value for rope shake is set, and a rope shake detection signal is output when the product of the shaking amount of the building 10 and the duration is equal to or greater than the threshold value.

  The timer 32 is activated by the rope shake detection unit 31 and counts the duration time for each shaking amount of the building 10.

  Based on the rope runout detection signal output from the rope runout detection unit 31, the control operation control unit 33 stops the car 14 at the nearest floor or controls the car 14 at the retreat floor.

Here, a function formula used in rope runout detection will be described.
When the relationship between the amount of swing of the building 10 and the duration is analyzed with respect to the amount of swing of the rope, the following functional expression f (α, t) is established.

(Α−Δα) (t−Δt) ≧ G (1)
α is the amount of shaking of the building 10, and t is the duration of the building shaking. Δt, G, Δα are parameters for detecting rope runout.

  Δt is the minimum duration of building shaking. During the time Δt after the building shake occurs, the rope shake is not detected regardless of the magnitude of the shake.

  G is a rope shake detection threshold and is provided for the product of the amount of shaking α of the building 10 and its duration t. If the product of the shaking amount α of the building 10 and its duration t is equal to or greater than the threshold value G, a predetermined amount of rope shaking occurs when the car 14 is stopped at a position where the rope resonates with the building shaking.

  The threshold G is set according to the amount of rope runout. For example, when the amount of rope swing is 300 mm, if the relationship between the amount of swing α of the building 10 and the duration t is graphed, an inversely proportional graph as shown in FIG. 3 is obtained, and the product of α and t is a constant value.

  Δα is the minimum amount of shaking of the building. This is the magnitude of the shaking of the building in which the rope resonates due to the shaking of the building, and the force that grows the rope swing and the force that converges the rope swing balance. Even if the building shake of Δα or less continues for a long time, the rope swing does not grow from the predetermined amount.

  FIG. 4 is a diagram showing the analysis result of the rope runout, and shows the result of analyzing the runout amount of the rope in three stages of “runout height”, “runout low”, and “runout low”.

  The “runout height” refers to a shake state in which the rope may come into contact with equipment in the hoistway 10b. “Low runout” refers to a state in which the rope swings at about 50 to 70% of the “runout height”. “Running low” is the state at the beginning of the rope swing.

  By setting the threshold value G for each of these three stages, three types of rope runout = “runout height”, “runout low”, and “runout low” based on the above equation (1). A rope runout detection signal can be output.

Next, the operation of the first embodiment will be described.
FIG. 5 is a flowchart showing the processing operation of the elevator rope runout detection in the first embodiment.

  First, as an initial setting, a maintenance staff operates the setting switch 24 to set various parameters necessary for rope shake detection in the rope shake detection unit 31 of the control device 22 (step S11).

  The various parameters are the above-described minimum duration Δt, minimum shake amount Δα, and threshold G. In addition to these, the continuous monitoring time A1 is included. The values of the various parameters set here are stored in a storage unit (not shown) provided in the control device 22 and are appropriately read out by the rope shake detection unit 31.

  The continuous monitoring time A1 is a time for which it is considered that the building shake of the same size continues. That is, as shown in FIG. 6, since the building shaking signal is alternately repeated up and down like a sine wave, even if it temporarily becomes lower than α, the continuous monitoring time A1 is used in order to see the next cycle. Monitoring will continue until

  Here, it is assumed that the building 10 is shaken by an earthquake, strong wind, or the like, and an acceleration signal indicating the shake amount α of the building 10 is input from the acceleration sensor 23 to the rope shake detection unit 31 of the control device 22 (Yes in step S12).

  When the acceleration signal is input from the acceleration sensor 23, the rope shake detection unit 31 activates the timer 32 and monitors the duration t of the shake amount α indicated by the acceleration signal (step S13). At that time, the duration t is monitored in consideration of the duration monitoring time A1.

  In the example of FIG. 6, the duration of the shaking amount α of 1 Gal and 3 Gal is shown, but actually the duration is monitored for each acceleration input, that is, for each building shaking amount, and the above equation (1) An operation is performed.

  When the shaking amount α of the building 10 and the duration t thereof are obtained, the rope shake detecting unit 31 calculates the product of the shaking amount α and the duration t and detects the rope shake (step S14). Specifically, in consideration of the minimum duration Δt and the minimum fluctuation amount Δα set as the various parameters, (α−Δα) (t−Δt) according to the function formula f (α, t) expressed by the above formula (1). Perform the operation.

  If the value obtained as a result of this calculation is equal to or greater than a preset threshold G (Yes in step S15), the rope shake detection unit 31 is in a state where the rope is shaken more than a predetermined amount determined by the threshold G. It is determined that there is, and a rope shake detection signal is output to the control operation control unit 33 (step S16). As a result, the control operation control unit 33 controls the hoisting machine 12 to move the car 14 to the nearest floor or move it to the retreat floor, and for the sake of safety, the elevator operation is stopped until the building shake is settled. Is paused (step S17). Since the rope may further resonate depending on the position of the retreat floor at the destination, a position that does not resonate is determined as the retreat floor in advance.

  As described above, according to the first embodiment, it is possible to set a threshold value for rope shake using a functional expression indicating the relationship between the amount of shaking of the building and the duration, and by detecting the rope shake using the threshold value. , Can prevent useless control operation.

(Second Embodiment)
Next, a second embodiment will be described.

  In the second embodiment, the rope runout threshold is set in consideration of the car position.

  FIG. 7 is a block diagram illustrating a functional configuration of the elevator control device 22 according to the second embodiment. In addition, the same code | symbol is attached | subjected to the same part as the structure of FIG. 2 in the said 1st Embodiment, and the description shall be abbreviate | omitted.

  In the second embodiment, a car position detection unit 34 is added to the control device 22. The car position detector 34 detects the current position of the car 14 and outputs a detection signal to the rope shake detector 31. As a car position detection method, for example, a pulse encoder installed on the motor shaft of the hoisting machine 12 is used, and detection is performed by counting pulse signals output in synchronization with the rotation of the motor from the pulse encoder. There are methods.

  The rope shake detection unit 31 changes the rope shake threshold value according to the car position detected by the car position detection unit 34 and outputs a rope shake detection signal to the control operation control unit 33 according to the changed threshold value.

  That is, during a long-period earthquake or a strong wind, the building 10 easily shakes at the primary natural frequency, and in a high-rise building with a building height of 120 m or more, the primary natural frequency is generally in the range of 0.1 to 0.5 Hz. When it is a super high-rise building, the natural frequency range of the rope may be within 0.1 to 0.5 Hz, and there is a high possibility that the rope will resonate with the shaking of the building.

Here, as shown in FIG. 8, the rope length L 0 varies depending on the stop position of the car 14. As shown in the following equation (2), the primary frequency is obtained according to the rope length L0, and when the primary frequency of the rope matches the frequency of the building shake, resonance occurs and the rope swing grows. Conversely, if the primary frequency of the rope is different from the frequency of the building shake, the rope will not resonate and the rope swing will not grow.

Building height: H (m)
Natural period of the primary building: T (s) = 0.025 × H
Building primary frequency: f (Hz) = 1 / T
Amplitude at top of building: D (m)
Acceleration at the top of the building: α (m / s ² )
α = D × (2π / T) ²
Rope primary frequency: fi (Hz)
Rope length: L0 (m)
Average rope tension: T0 (N)
Mass per rope unit length: ρA (kg / m).

  Thus, since the amount of shake when the rope resonates differs according to the car position, it is preferable to switch the threshold value for the product of the amount of shake α and its duration t.

  FIG. 9 is a flowchart showing the processing operation of the elevator rope runout detection in the second embodiment.

  First, as an initial setting, a maintenance person operates the setting switch 24 to set various parameters necessary for rope shake detection in the rope shake detection unit 31 of the control device 22 (step S21).

  The various parameters are the above-described minimum duration Δt, minimum shake amount Δα, and threshold G. In addition to these, the continuous monitoring time A1 is included. Furthermore, for the threshold value G, the amount of swinging of the rope that resonates with the building shake is measured in advance according to the car position, and a threshold value corresponding to the amount of shaking is set for each car position. The values of the various parameters set here are stored in a storage unit (not shown) provided in the control device 22 and are appropriately read out by the rope shake detection unit 31.

  Here, it is assumed that the building 10 is shaken due to an earthquake, strong wind, or the like, and an acceleration signal indicating the shake amount α of the building 10 is input from the acceleration sensor 23 to the rope shake detection unit 31 of the control device 22 (Yes in step S22).

  When the acceleration signal is input from the acceleration sensor 23, the rope shake detection unit 31 starts the timer 32 and monitors the duration t of the shake amount α indicated by the acceleration signal (step S23). At that time, the duration t is monitored in consideration of the duration monitoring time A1.

  When the amount of shaking α of the building 10 and its duration t are obtained, the rope shake detecting unit 31 calculates the product of the amount of shaking α and its duration t to detect the rope shake (step S24). Specifically, in consideration of the minimum duration Δt and the minimum fluctuation amount Δα set as the various parameters, (α−Δα) (t−Δt) according to the function formula f (α, t) expressed by the above formula (1). Perform the operation.

  At this time, if it is assumed that the car 14 is stopped at an arbitrary floor, the rope shake detection unit 31 acquires information on the stop position (current car position) from the car position detection unit 34 (step S25). . Then, the rope runout detection unit 31 switches the threshold G according to the car position (step S26), and compares the threshold G after the switching with the value calculated in step S24 (step S27).

  As a result, if the calculated value is greater than or equal to the threshold value G (Yes in step S27), the rope shake detection unit 31 determines that the rope is in a state of greater than or equal to the predetermined amount determined by the threshold value G, and performs the control operation. A rope runout detection signal is output to the control unit 33 (step S28). As a result, the control operation control unit 33 controls the hoisting machine 12 to move the car 14 to the nearest floor or move it to the retreat floor, and for the sake of safety, the elevator operation is stopped until the building shake is settled. Is paused (step S29). Since the rope may further resonate depending on the position of the retreat floor at the destination, a position that does not resonate is determined as the retreat floor in advance.

  As described above, according to the second embodiment, by setting the threshold value in consideration of the car position, it is possible to more accurately detect the rope run-out associated with the building shake and switch to the control operation.

(Third embodiment)
In the first embodiment, the elevator control device 22 has been described as performing a series of processes related to rope shake detection. However, a sensor that detects building shake may have the same function.

  FIG. 10 is a block diagram showing a configuration of a sensor 50 having a rope shake detection function in the third embodiment.

  The sensor 50 is installed above the building 10 in place of the acceleration sensor 23 shown in FIG. The sensor 50 includes an acceleration sensor 51, a calculator 52, a timer 53, and a setting switch 54. The acceleration sensor 51 has the same function as the acceleration sensor 23, and detects shaking of the building 10 due to an earthquake, strong wind, or the like.

  The computing unit 52 corresponds to the rope shake detection unit 31 in FIG. That is, the computing unit 52 monitors the duration of shaking for each shaking amount of the building 10 detected by the acceleration sensor 51, and is derived from the analysis result of the shaking amount and duration of the building 10 with respect to the rope shaking amount. Based on the function formula f (α, t), a threshold value for the rope swing is set, and when the product of the swing amount and the duration of the building 10 is equal to or greater than the threshold value, a rope swing detection signal is output to the elevator controller 22. To do.

  The timer 53 is activated by the computing unit 52 and counts the duration for each shaking amount of the building 10.

  The calculator 52 is connected to a setting switch 54 composed of, for example, a rotary switch. The setting switch 54 is operated by maintenance personnel and sets various parameters (Δt, Δα, G, A1) necessary for detecting the rope runout by the computing unit 52.

  In such a configuration, when the building 10 shakes due to an earthquake, strong wind, or the like, the acceleration sensor 51 in the sensor 50 detects the amount of shaking α of the building 10 and gives it to the computing unit 52. The calculator 52 calculates the product of the swing amount α and its duration t to detect the rope swing. Specifically, in consideration of the minimum duration Δt and the minimum fluctuation amount Δα set as the various parameters, (α−Δα) (t−Δt) according to the function formula f (α, t) expressed by the above formula (1). Perform the operation.

  If the value obtained as a result of the calculation is equal to or greater than a preset threshold G, a rope shake detection signal is output from the calculator 52 to the control device 22.

  In this case, as shown in FIG. 4, if the threshold value G is set for each of the results of analysis of the swing amount of the rope in three stages of “runout height”, “runout low”, and “runout low”. Based on the above equation (1), three types of rope runout detection signals of rope runout = “runout height”, “runout low”, and “runout low” are output to the controller 22. . When the control signal is input to the control device 22, the operation mode is switched to the control operation, and the car 14 is stopped by moving to the nearest floor or moving to the waiting floor.

  As described above, according to the third embodiment, the sensor 50 has the same function as that of the first embodiment, so that the rope 50 according to the amount of shaking and the duration of the building can be detected by the sensor 50. It can be detected with high accuracy, and the detection signal can be output to the control device 22 to switch to the control operation.

  According to at least one embodiment described above, there is provided an elevator control device and a detector that appropriately set a threshold for rope swing according to the amount of shaking of a building and its duration to prevent useless control operation. can do.

  In addition, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 ... Building, 11 ... Elevator, 12 ... Hoisting machine, 13 ... Main rope, 14 ... Ride car, 15 ... Counterweight, 16 ... Compensation, 17 ... Compen rope, 18 ... Car control device, 19 ... Car door, DESCRIPTION OF SYMBOLS 20 ... Transmission cable, 21a, 21b, 21c ... Landing place, 22 ... Control apparatus, 23 ... Acceleration sensor, 24 ... Setting switch, 31 ... Rope shake detection part, 32 ... Timer, 33 ... Control operation control part, 34 ... Car position Detection unit, 50 ... sensor, 51 ... acceleration sensor, 52 ... calculator, 53 ... timer, 54 ... setting switch.

Claims (8)

In an elevator control device equipped with a car that moves up and down via a rope installed in a hoistway of a building,
Building shaking detection means for detecting the amount of shaking of the building,
The duration of each building shake detected by the building shake detecting means is monitored and the duration of the rope is detected based on a functional expression derived from the analysis result of the building shake and the duration. A rope shake detection means for setting a threshold and outputting a rope shake detection signal when the product of the amount of shaking of the building and the duration is equal to or greater than the threshold;
An elevator control device, comprising: control operation means for stopping the passenger car on the nearest floor or performing control operation on the retreat floor based on the rope shake detection signal output from the rope shake detection means. It has setting means for setting the minimum shaking amount and minimum duration of the building,
The rope runout detection means is
The product of both is calculated by adding the minimum shaking amount set by the setting means to the shaking amount of the building and adding the minimum duration set by the setting means to the duration time. The elevator control device according to claim 1. Comprising setting means for setting a threshold value for the amount of runout of the rope in stages;
The rope runout detection means is
The product of the amount of shaking of the building and the duration time is calculated, the calculation result is compared with each threshold value set by the setting means, and a rope shake detection signal corresponding to the rope shake amount is output. The elevator control device according to claim 1. A car position detecting means for detecting the position of the car,
The rope runout detection means is
2. The elevator control device according to claim 1, wherein the threshold value is switched in accordance with the position of the car detected by the car position detecting means. A sensor connected to an elevator control device having a car that moves up and down via a rope installed in a hoistway of a building,
Building shaking detection means for detecting the amount of shaking of the building,
The duration of each building shake detected by the building shake detecting means is monitored and the duration of the rope is detected based on a functional expression derived from the analysis result of the building shake and the duration. And a calculation means for setting a threshold value and outputting a rope shake detection signal to the elevator control device when the product of the amount of shaking of the building and the duration time is equal to or greater than the threshold value. . It has setting means for setting the minimum shaking amount and minimum duration of the building,
The rope runout detection means is
The product of both is calculated by adding the minimum shaking amount set by the setting means to the shaking amount of the building and adding the minimum duration set by the setting means to the duration time. The sensor according to claim 5. Comprising setting means for setting a threshold value for the amount of runout of the rope in stages;
The rope runout detection means is
The product of the amount of shaking of the building and the duration time is calculated, the calculation result is compared with each threshold value set by the setting means, and a rope shake detection signal corresponding to the rope shake amount is output. The sensor according to claim 5. A car position detecting means for detecting the position of the car,
The rope runout detection means is
6. The sensor according to claim 5, wherein a threshold value is switched in accordance with the position of the car detected by the car position detecting means.

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