JP2000335421A - Monitoring method and monitoring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform monitoring without a dead angle capable of monitoring an area to be monitored by a monitoring device by 100% by a simple constitution in monitoring method and monitoring device for a railroad crossing. SOLUTION: A transmitter 1 emitting beam for monitoring 4 and a receiver 8 receiving reflection beam from an obstacle 5 of beam for monitoring 4 are provided so that reflection beam may be received, even if the direction of beam for monitoring 4 is revolved or rotated. Rotating the direction θ of beam for monitoring 4 and repeating scanning that a monitoring area is changed by monitoring beam, the presence or absence, the size and/or the distance of the obstacle 5 within the above range are detected from an output of the receiver 8. To pick up data components by return beam by reflection of a stationary existence 25 existing stationarily, data to be used for the picking is preliminarily stored in a memory 19, is properly read and is picked up.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monitoring method for monitoring the intrusion of obstacles such as people and vehicles in a certain area such as a railroad crossing, and a monitoring apparatus used for the method.

[0002]

2. Description of the Related Art There is a monitoring device for detecting when a person or a vehicle enters a certain area, for example, a railroad crossing. Regarding railroad crossings, even after a train or the like approaches and an alarm starts sounding, or after a circuit breaker begins to fall, a person, for example, a disabled person in a wheelchair or a car enters the railroad crossing and gets out of the wheelchair. There is a case where the vehicle keeps stopping due to an engine trouble such as a so-called stall of a wheel or a car and cannot escape. In such a case, an accident may occur, possibly causing a catastrophic event. Therefore, the inside of the railroad crossing is monitored, and after the train starts approaching and the alarm starts to sound, or even after the circuit breaker starts getting off, if there is an obstacle in the railroad crossing, an alarm is issued to the train driver, A system that operates a stop mechanism to stop automatically is being introduced,
Improvements in such systems are being actively pursued.

It is essential for the system to monitor whether a person or a car has entered the railroad crossing. Conventionally, the monitoring is generally performed by arranging a transmitter and a receiver at a corner of a railroad crossing, and detecting a change in the output of the receiver caused by a failure between the transmitter and the receiver. It was done in a way that made sure that there was a fault. FIG. 3 is a plan view showing a typical conventional example.

In FIG. 3, reference numerals 31 and 31 denote rails,
Reference numerals 2 and 32 denote blocking bars, and 33, 33, 33, and 3 denote four corners of a railroad crossing area. A transmitter that generates a light beam and the light beam are emitted to the corners 33, 33, 33, and 33, for example. A receiver for receiving is arranged, and when an obstacle such as a person or a car enters the place indicated by a broken line arrow, the obstacle prevents the monitoring beam from being transmitted from the transmitter to the receiver. He came to recognize the existence of things. Monitoring lines were usually provided slightly inside the crossing barriers 32, 32 and at one diagonal of the crossing. Such a monitoring method is commonly called a Z-shaped arrangement monitoring method. This is because the monitoring line draws a Z-shape.

[0005]

The conventional Z-shaped arrangement monitoring method as shown in FIG. 3 has a problem that a blind spot exists in a railroad crossing. That is, even within the railroad crossing area, there is a position where the obstacle does not block the monitoring line that draws the Z-shape, which means that there is a blind spot.
An obstacle located in the blind spot cannot be detected. This is the biggest problem of the conventional example. Although the wheelchair of a physically handicapped person was derailed at an unmanned railroad crossing and was unable to get out of the derailed state, the derailed position hit the blind spot and the train could not be detected because the obstacle was not detected. Can not be stopped, and accidental death occurs.

A more accurate analysis of the blind spot problem of such a Z-shaped arrangement monitoring method can be said as follows. The area of the region between the blocking rods 32 in FIG. 3 is the area to be monitored,
Assuming that the area of the area that can be monitored by the Z-shaped arrangement monitoring method is the monitorable area, the ratio of the monitorable area to the area to be monitored (hereinafter, referred to as “monitoring area ratio” in this specification) is several. % Or less, and 90% is blind spot. Therefore, according to the Z-shaped arrangement monitoring method described above, when a large truck or the like becomes an obstacle or the obstacle is not a blind spot,
There is a fatal flaw that failure can not be detected unless it is lucky to be on the monitoring line.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to make it possible to perform monitoring without blind spots in which a region to be monitored can be monitored 100% with a simple configuration. I do.

[0008]

SUMMARY OF THE INVENTION A first aspect of the present invention is as follows.
The return beam can be received even if the direction of the monitor beam is rotated or rotated by the transmitter that emits the monitor beam and the receiver that receives the return beam due to reflection of the monitor beam from an obstacle or the like. And detecting the presence / absence, size, and / or distance of the obstacle in the range from the output of the receiver while repeating the scanning in which the direction of the monitoring beam is rotated to change the monitoring area with the monitoring beam. Or do so.

Therefore, according to the first aspect of the present invention, the direction of the monitoring beam emitted from the transmitter and detected by the receiver is rotated or rotated, so that the monitoring beam is used on the monitoring area by the monitoring beam. Can be scanned. Therefore,
When a fault enters the area, when the fault is scanned, the monitoring beam is reflected by the fault and the reflected beam is detected by the receiver. Therefore, it is necessary to monitor the occurrence and approach of the fault in the monitoring area. Can be.

Then, since the direction of the monitoring beam is rotated and the inside of the monitoring area is scanned by the beam, the monitoring area can be monitored without blind spots. That is, the monitoring area ratio can be set to 100%. In addition, this can be realized by placing at least the sensing part of one monitoring device including a transmitter and a receiver in a part of or near the monitoring area, and does not require a plurality of monitoring devices.

According to a second aspect of the present invention, in the first aspect, output data of the receiver, that is, steady data, is obtained when scanning of the monitoring area by the monitoring beam is performed without any obstacle. In addition, the presence / absence, size and / or distance of the obstacle within the range is detected or compared by comparing the output data of the receiver with the steady-state data while repeatedly scanning the monitoring area with the monitoring beam. It becomes like this.

Therefore, according to the second aspect of the present invention, the steady data of the receiver by the return beam due to the reflection from the object steadily existing near and around the monitoring area is stored and stored in the receiver. Is compared with the output data of the receiver, the data by the reflected beam from the object other than the obstacle can be omitted from the output data of the receiver, and only the data indicating the obstacle can be extracted.

According to a third aspect of the present invention, a transmitter for emitting a monitoring beam and a receiver for receiving a monitoring beam are arranged opposite to each other, and between the transmitter and the receiver, a signal is transmitted from the transmitter. The right-angle reflector that reflects the monitoring beam to the monitoring target side and reflects the return beam of the monitoring beam from the monitoring target side to the receiver is rotatable about the axis connecting the transmitter and the receiver. It is a monitoring device provided.

Therefore, according to the third aspect of the present invention, the transmitter and the receiver are fixed, and the right-angle reflector positioned therebetween is rotated or rotated about the axis connecting the transmitter and the receiver. The direction of the monitoring beam can be changed by turning the right angle reflector so that the direction of the monitoring beam can be changed. Can be maintained, and the rotation or rotation of the direction of the monitoring beam can be performed by driving the right-angle reflector, so that the size and power consumption of the monitoring device can be reduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention basically comprises a transmitter for emitting a monitoring beam and a receiver for receiving a return beam due to reflection of the monitoring beam from an obstacle. The monitoring beam is provided so as to be rotatable or rotatable so as not to be damaged, and the receiver is configured to repeat the scanning of the monitoring beam on the visual field by the rotation or rotation of the monitoring beam. The presence or absence, size and / or distance of the obstacle in the above range is detected or made from the output of the electromagnetic wave, and the monitoring beam is an electromagnetic beam such as an ultrasonic beam or a laser beam or an infrared beam. Is preferred.

In order to scan the monitoring area with the monitoring beam, the direction of the monitoring beam is rotated (for example, 360 ° is rotated clockwise or counterclockwise repeatedly) or rotated (predetermined). It is necessary to repeat the reciprocating change of the direction within the angle of), but the range in which the direction of the beam is changed is naturally determined by the relationship between the monitoring area and the installation position of the monitoring device. For example,
In the case of a railroad crossing, generally, the monitoring device may be placed at one corner of a rectangular crossing region, and the monitoring beam may be rotated within a range of approximately 90 °. However, the monitoring target according to the present invention is not necessarily limited to a railroad crossing, and there may be other monitoring targets.
Then, a monitoring device is installed, for example, near the center of the region to be monitored, and the monitoring beam is continuously rotated in a fixed direction (for example, clockwise or counterclockwise) to 360 °
It is also possible to monitor the range.

Rotating or rotating the monitoring beam so that reception by the receiver is not impaired can be achieved by integrally providing a transmitter and a receiver that are provided close to each other so that their axes are substantially parallel to each other. This can be performed by rotating or rotating, but by fixing the transmitter and the receiver and rotating or rotating the right-angle reflector positioned between them about the axis connecting the transmitter and the receiver. The direction of the reflected beam may be changed.

In addition, stationary data, which is output data of the receiver when the scanning of the monitoring area by the monitoring beam is performed without any obstacle, is obtained, and the scanning of the monitoring area by the monitoring beam is repeated. While detecting the presence / absence, size, and / or distance of the obstacle within the above range by comparing the output data of the receiver with the steady-state data, the data output from the receiver is reflected by the reflected beam from an object other than the obstacle. And only the data indicating the failure can be extracted.

The presence or absence of a fault in the monitoring area, its size,
The shape and the like can be determined based on output data for one frame (scan for sweeping the monitoring area by one) of the receiver.
The distance from the obstruction monitoring device shall be such that the monitoring beam is emitted from the transmitter in a pulsed manner, and the time at which the pulsed beam hit the obstacle is emitted from the transmitter and the time at which the pulsed beam is incident It can be determined from the time difference.
Specifically, the propagation speed of the monitoring beam × the time difference / 2
The distance can be calculated by the following equation. The propagation speed of the monitoring beam is 3 × 10 ⁸ m / sec for electromagnetic waves (light) and 331 m / sec for ultrasonic waves. The moving direction and moving speed of the obstacle can be determined from data for a plurality of frames. Therefore, it is also possible to determine from the data for a plurality of frames whether the failure is a failure that immediately escapes from outside the monitoring area or a failure that cannot escape, and issue an alarm based on the determination result.

As a monitoring beam, it can be said that it is better to use an ultrasonic beam when the monitoring area is relatively narrow, and to use a light beam such as a laser beam when the monitoring area is wide. However, techniques are being established that allow for relatively accurate measurement of relatively short distances using light beams, so that light beams can be used satisfactorily for monitoring narrow areas, such as railroad crossings. When using an ultrasonic beam as monitoring data, use an ultrasonic transceiver with a transmitter and a receiver,
This may be rotated or rotated by a motor. The prism mirror used when the light beam is used as the monitoring beam is not necessary in the case of using the ultrasonic beam.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIGS. 1A to 1C show an embodiment of the monitoring apparatus according to the present invention, and FIG.
1, (B) is a circuit block diagram of a monitoring device,
(C) is a schematic diagram of one-frame scanning when the monitoring device is applied to the detection of a failure in a railroad crossing.

First, the configuration of the sensing unit 11 which is a main part of the monitoring apparatus will be described with reference to FIG. 1 is an infrared laser diode for generating an infrared laser beam,
Form a transmitter. Reference numeral 2 denotes a collimator lens for collimating the laser beam emitted from the laser diode 1, and reference numeral 3 denotes a prism mirror which is rotated about an axis o by a motor (12) described later. The return beam 6 is reflected at right angles to the monitoring area side and further reflected by the laser beam 4 at the obstacle 5.
At right angles to the photodiode 8 side. Reference numeral 7 denotes a condensing lens provided between the prism mirror 3 and a photodiode 8 forming a receiver. The return beam 6 is reflected by the prism mirror 3 and condensed by the condensing lens 7, and is condensed on the photodiode 8. The light is incident, and is converted into an electric signal by the photodiode 8.

Next, the overall configuration of a monitoring device that drives the sensing section 11 and further processes the output signal of the sensing section 11 (the output signal of the photodiode 8) will be described with reference to FIG. Note that the sensing unit 11 of the monitoring device shown in FIG. 1A is represented as one block 11 in FIG. The prism mirror 3 of the sensing unit 11 is rotated by a motor (for example, a pulse motor) 12. In the present embodiment, since the monitoring device is used for monitoring the level crossing, the rotation axis is set to be substantially perpendicular to the ground at one corner of the level crossing. And FIG.
As shown in (C), the rotation of the prism mirror 3 is repeated within a range of 90 °. Thereby, the monitoring beam 4
Thus, the railroad crossing area can be used as a monitoring area to scan over the area.

Reference numeral 13 denotes a rotary encoder for detecting the rotation angle of the motor 12 (and, consequently, the rotation angle θ of the prism mirror 3). Reference numeral 14 denotes a pulse for causing the laser diode 1 forming the transmitter of the sensing unit 11 to emit light. The transmission pulse generator is controlled by a pulse controller 17. The pulse controller 17 controls the transmission pulse generator 14 to generate a pulse for causing the laser diode 1 to emit light, and controls the motor driver 16 that drives the motor 12. The pulse controller 17 is controlled by the monitoring controller 23. The monitoring controller 23 starts controlling the pulse controller 17 when receiving a monitoring command signal indicating that monitoring is necessary, for example, from a terminal device or the like of a computer system (not shown). To stop.

For example, in the case of a railroad crossing, a monitoring command signal is issued when the crossing barrier at the railroad crossing gets down and the alarm starts sounding, the monitoring state is entered, the train passes safely, the crossing barrier at the railroad crossing rises, and the alarm is issued. When the sound stops, the monitoring command signal disappears and the device enters the non-monitoring state. In the case of a warehouse, for example,
When entering the unmanned state at night, the monitoring control unit 23 forms a monitoring state according to the monitoring command signal.
3 sets the monitoring device to a non-monitoring state.

Reference numeral 15 denotes a receiving amplifier for amplifying an output signal of the photodiode 8 forming a receiver of the sensing unit 11. Reference numeral 18 denotes a distance calculator, which controls a control signal sent from the pulse controller 17 to the transmission pulse generator 14. A distance calculator for measuring a distance of a fault in response to a reception signal obtained by photoelectrically converting a return beam due to reflection of a monitoring beam from the reception amplifier 15, specifically, a signal from the pulse controller 17. And a calculation of multiplying the time difference between the signals from the reception amplifier 15 by a predetermined constant (specifically, the beam propagation speed / 2), and outputs the calculation result.

An address data memory 19 receives an address signal indicating the rotation angle θ from the rotary encoder 13 via the pulse controller 17 and outputs steady data corresponding to the address. Reference numeral 21 denotes a writing circuit for writing the steady data to the address data memory 19, and performs an operation necessary for writing the steady data when the monitoring device is installed or whenever the state of the monitoring area is changed. During normal monitoring, no particular operation is performed.

Here, the steady data will be described. When a monitoring device is installed in a monitoring area, even if there is no obstacle in the monitoring area, the monitoring beam is reflected, and a return beam enters and enters a receiver [Fig.
Reference numeral 25 in (C) indicates the stationary entity. ]
Is usually the case. It may be inside the monitoring area or outside the monitoring area. In any case, since it is not the obstruction to be monitored, data from the beam returning to the monitoring device due to such a reflection from stationary entity 25 must be discarded.

Therefore, when the monitoring device is installed, or when there is a change or change in the condition of the monitoring area, the data for each θ (the distance in the case where there is a return beam due to reflection) under no fault condition. The calculation result is taken and stored in the memory as data for each address.
At the time of monitoring, steady data at an address corresponding to the rotation angle θ of the monitoring beam is output in synchronization with the change of the rotation angle θ of the monitoring beam, and a distance calculation obtained from this and the reception signal from the photodiode 8 forming the receiver is performed. By comparing with the result,
The stationary data is discarded from the received signal, and only the data component by the return beam due to the failure of the monitoring beam is extracted.

Numeral 20 denotes a comparator for comparing the signal, that is, for comparing the received signal from the distance calculator 18 with the stationary data.
2 is controlled, and if it is determined that there is a fault, the alarm output device 2
2 generates an alarm signal. This warning signal is sent to a driver's seat of a train heading for a control room or a railroad crossing, for example, through a terminal device or further through a host computer, and further sent to an emergency automatic stop system as an emergency stop signal.

Next, the operation of the monitoring device will be described. Upon receiving the monitoring command signal, the monitoring controller 23 receives the pulse controller 17
, The pulse controller 17 causes the motor drive 16 to start driving the motor 12 based on the control, and causes the transmission pulse generator 14 to start outputting transmission pulses. The rotation angle θ of the motor 12 is detected by the rotation encoder 13, and the detection result is fed back to the pulse controller 17.

The direction θ of the monitoring beam is
As shown in (C), the angle is changed by θ0, θ1,... At a predetermined angle (in FIG.
Only possible θs are shown, but usually more. )
However, the following operation is performed for each θ.

As an operation for each θ, the transmission pulse generator 1
7, a pulse is generated from the laser diode 7, a laser beam 4 is generated in the laser diode 1, the return beam 5 is received by the photodiode 8, and the reception signal and the transmission pulse generator 1 are received.
The distance calculation is performed by the distance calculator 38 based on the signal from. The comparator 20 compares the output signal of the distance calculator 38 with the steady data of the address (corresponding to the monitoring beam direction θ) read from the address memory 19. Then, if they do not match, it is determined that there is a failure, and an alarm signal is issued from the alarm output device 22.

The operation will be described in more detail with reference to FIG. 1 (C). Since there is no beam reflecting at θ0, there is no return beam of the monitoring beam and the photodiode 8 as a receiver is No beam is incident. In this case, it is determined that there is no obstacle. At θ1, since the monitoring beam is reflected by the stationary entity 25 and the return beam is received, the distance is calculated by the distance calculator 18 from the time difference between the received signal and the signal from the pulse controller 17, and The data at the address θ0 is read from the steady data previously stored in the address memory 19, and the output of the distance calculator 18 and the address θ0
Are compared, and in this case, they are the same, and it is determined that there is no failure.

In the case of θ2 to θ5, as in the case of θ0, since there is no object that reflects the beam, it is determined that there is no obstacle. At θ6, the obstacle 5 exists, the reflected beam is reflected there, and the return beam is received by the photodiode 8, the distance of the obstacle 5 to the monitoring device is calculated by the distance calculator 18, and the calculated value and the steady data are calculated. However, since there is no stationary entity at the address θ6, there is a large difference between the stationary data to be compared with each other and the output value of the distance calculator 18. Yes, it is determined that there is a failure 5. As a result, an alarm is issued from the alarm output device 22. Note that θ7, θ
8 is the same as θ0, θ2 to θ5.

The scanning in the range of 90 ° from θ0 to θ8 is a scanning of one frame, and the scanning of one frame is repeatedly performed at a predetermined cycle. Such an operation is performed while the monitoring control unit 23 receives the monitoring command signal, but when the monitoring command signal disappears, the monitoring operation is stopped.

In the above embodiment, the laser beam is used as the monitoring beam. However, it is not essential that the laser beam be used as the monitoring beam, and an ultrasonic beam may be used as the monitoring beam. In this case, as shown in FIG. 2, it is preferable that the sensing unit is constituted by an ultrasonic transceiver 26, which is rotated or rotated by the motor 12.

In the above embodiment, an alarm is issued immediately when a failure is detected based on the monitoring data at a certain address θ. However, instead, an alarm is issued based on the comparison result for one frame. In addition, the shape and size of the obstacle are also determined, and if the failure is not considerably small or a problem is not caused according to the determination result, an alarm generation command is not issued even if it is determined that there is a failure. You may do it.

It is determined from the monitoring data for a plurality of frames, not the monitoring data for one frame, whether the fault is stationary or moving. If the fault is moving, the moving direction and the moving speed are further determined. It is also possible to make a determination, determine whether the failure will be lost soon or not based on the determination result, and determine whether to issue an alarm based on the determination result.

[0040]

According to the first aspect of the present invention, the direction of the monitoring beam emitted from the transmitter and detected by the receiver is rotated to scan the monitoring area with the monitoring beam. Can be. Therefore, when a fault enters the area, when the fault is scanned, the monitoring beam is reflected by the fault, and a return beam due to the reflection is detected by the receiver. , Can monitor the approach.

Since the direction of the monitoring beam is rotated to scan the monitoring area with the beam, the monitoring area can be monitored without blind spots. That is, the monitoring area ratio can be set to 100%. In addition, this can be realized by placing at least the sensing part of one monitoring device including a transmitter and a receiver in a part of or near the monitoring area, and does not require a plurality of monitoring devices.

According to the second aspect of the present invention, stationary data of a receiver is stored by a reflected beam from an object (stationary object) which is constantly present in the vicinity of and around the monitoring area, and is received. Since the data is compared with the output data of the receiver, the data by the reflected beam from the object other than the obstacle can be discarded from the output data of the receiver, and only the data indicating the obstacle can be extracted.

According to the third aspect of the present invention, the transmitter and the receiver are fixed, and the right-angle reflector positioned therebetween is rotated or rotated about the axis connecting the transmitter and the receiver. The direction of the reflected beam can be changed by turning or rotating the right-angle reflector, but the state of receiving the reflected beam due to obstacles or the like can be maintained. The rotation or rotation of the direction can be performed by driving the right-angle reflector,
The size and power consumption of the monitoring device can be reduced.

[Brief description of the drawings]

FIGS. 1A to 1C show one embodiment of a monitoring device according to the present invention, wherein FIG. 1A is a configuration diagram of a sensing portion as a main part, and FIG. 1B is a circuit block diagram of the monitoring device; (C) is a schematic diagram of one-frame scanning in a case where the monitoring device is applied to detection of a failure in a railroad crossing.

FIG. 2 is a diagram showing an ultrasonic transceiver of a monitoring device of a type using an ultrasonic beam as a monitoring beam.

FIG. 3 is an explanatory diagram of a conventional example.

[Explanation of symbols]

11 sense part, 1 transmitter, 3 right-angle reflector, 4 monitoring beam, 5 obstacle, 6 ...
Return beam due to reflection at the obstacle, 8 ... receiver, 25
... Stationary entity, 26 ... Ultrasonic transceiver, θ
・ Rotation angle.

Claims (5)

[Claims] 1. A transmitter for emitting a monitoring beam and a receiver for receiving a return beam due to reflection of the monitoring beam from an obstacle, the orientation of the monitoring beam so that reception by the receiver is not impaired. Is provided so as to be rotatable or rotatable, and the presence or absence of a fault in the monitoring area is obtained from the output of the receiver while repeatedly scanning the monitoring area with the monitoring beam by rotating or rotating the direction of the monitoring beam. , Size, shape and / or distance are detected. 2. A transmitter for emitting a monitoring beam and a receiver for receiving a reflected beam from an obstacle of the monitoring beam.
The direction of the monitoring beam is rotatably or rotatably provided so that reception by the receiver is not impaired, and the monitoring beam is scanned over the monitoring area by the rotation or rotation of the direction of the monitoring beam. A monitoring device for detecting presence, absence, size, shape and / or distance in the monitoring area from the output of the receiver while repeating 3. A transmitter for emitting a monitoring beam and a receiver for receiving a reflected beam of the monitoring beam are rotated or rotated so that the reception by the receiver is not impaired. It is possible to obtain stationary data that is output data of the receiver when scanning for changing the direction of the monitoring beam in an arbitrary range is performed without any obstacle in the range. Detecting the presence / absence, size, and / or distance of an obstacle in the range by comparing output data of the receiver with the steady-state data while repeating scanning for changing a beam direction in the range. How to monitor. 4. A transmitter for emitting a monitoring beam and a receiver for receiving a reflected beam of the monitoring beam are rotated or rotated so that the reception by the receiver is not impaired. It is possible to obtain steady data which is output data of the receiver when scanning for changing the direction of the monitoring beam in a monitoring area is performed without any obstacle in the monitoring area. By comparing the output data of the receiver with the steady-state data while repeating the scanning for changing the beam direction in the area, the presence or absence, the size, and / or the distance of the obstacle in the area are detected. A monitoring device, characterized in that: 5. A transmitter that emits a monitoring beam and a receiver that receives a monitoring beam are arranged opposite to each other, and a monitoring beam from the transmitter is monitored between the transmitter and the receiver. A right-angle reflector that reflects to the side and reflects the return beam of the monitoring beam from the monitoring target side to the receiver, is provided so as to be rotatable about an axis connecting the transmitter and the receiver. Monitoring equipment