Device for indicating a certain proximity between movable units

A device for indicating a certain proximity between movable units emitting to the units a synchronizing signal with a very high transmission speed. A transmitter device is situated at least on certain of the units. The transmitter device is activated by the synchronizing pulse to emit an information signal in the form of a wave propagation movement in the medium in which the units are located. The wave propagation movement has in comparison with the synchronizing signal a considerably lower transmission speed. In at least certain others of the units the information signal is received by and related to the difference in time between the synchronizing signal and the received information signal to a predetermined time value corresponding to a certain proximity between the units. Thereafter the difference in time is evaluated in relation to the predetermined time value.

The present invention relates to a device for indicating a certain 
proximity between movable units. 
In order to avoid a mutual collosion between movable units or between 
movable and fixed units, which can come into inadmissible proximity to one 
another, automatic safety devices have been developed in certain fields, 
which indicate a certain proximity between the movable units. There are 
several different solutions, for example, for loop-controlled vehicles 
which are intended to follow a path predetermined by a control loop. 
Common to these is the fact that the vehicle in a certain path is given 
priority over a vehicle in another adjacent path, as a result of the fact 
that the last-mentioned vehicle is automatically stopped. This has 
previously been solved, for example, by the fact that sensing loops are 
placed out in the two paths in front of each point of conflict and when 
two vehicles approach this point, each on its own path, it is decided 
locally at the actual point of conflict or centrally, which vehicle shall 
be given priority, whereupon the other vehicle is stopped. Another known 
solution utilizes radio communication between a fixed, locally situated 
installation and the vehicles, to stop the one vehicle when a conflict 
situation arises. Common to all the previously known solutions is the fact 
that these require both a fixed and a movable installation, which makes 
these solutions expensive. 
The main object of the present invention is to develop a simple device with 
which the installation work and associated costs can be kept low, while at 
the same time a reliable and unambiguous indication of inadmissible 
proximity is obtained between different units. 
Said object is achieved by means of a device according to the present 
invention which is characterized in that included in the device is a 
device to emit to said units a synchronizing signal with a very high 
transmission speed, a transmitter device situated at least at certain of 
said units to be activated by the synchronizing signal to emit an 
information signal in the form of a wave propagation movement in the 
medium in which the units are located, with a considerably lower 
transmission speed in comparison with the synchronizing signal, devices 
situated at least at certain others of said units, to receive the 
information signal, to relate the difference in time between the 
synchronizing signal and the information signal received to a 
predetermined time value corresponding to a certain proxmity between the 
units and to evaluate said difference in time in relation to the 
predetermined time value.

The example illustrated in the drawings relates primarily to an 
installation fo loop-controlled vehicles where at least two movable units 
in the form of vehicles 1, 2 are adapted to travel along tracks 4, 5, the 
extent of which is determined by magnetic loops which are generally placed 
in the support on which the vehicles travel. A prerequisite for the 
present invention in the actual example is that the tracks 4, 5 comprise 
two parts which come into conflict with one another at a conflict point 6. 
Furthermore, the one track portion 4 is of such a character that the 
vhicle 1 which is travelling along this track portion is given priority 
over the vehicle 2 which is travelling along the other track portion 5. 
Hereinafter, the one track portion 4 is called the main track and the 
other track portion 5 the side track which is intended to join the main 
track at the conflict point 6. 
In the example shown, the vehicles 1, 2 are driverless and comprise, in 
conventional manner, a drive device and a control device by means of which 
the trucks automatically following the associated magnetic loop. In the 
present example, this loop is divided into separate component loops which 
are electrically insulated from one another, one for each track portion, 
and they are fed individually from a current generator 7 which comprises 
two outputs 8, 9. At each of these, an alternating current is delivered 
with a frequency in the range of 1.2 kHz for example. The two component 
loops are fed with alternating current at mutually different frequencies 
to render it possible to detect, in each vehicle, whether it is on the 
track with priority or not. Different frequencies are also required to 
avoid extinction of the magnetic field between the two loop portions at 
the conflict point 6, which would result in a faulty control of the 
vehicles. 
The object of the device according to the present invention is to prevent a 
collision between two vehicles 1, 2 which are approaching the conflict 
point 6 on the main track 4 and the side track 5 respectively. For this 
purpose, a decision must be reached as to which vehicle on which track it 
is to be given priority over the other vehicle on the other track. In the 
present case, priority has been given to the vehicle 1 on the main track 
4. Further required is detection of a certain proximity between the two 
vehicles 1, 2 and action on the one vehicle 2, in this case the vehicle on 
the side track 5, that is to say without priority, so that the vehicle 
stops or is braked when such proximity occurs, as a result of which a 
collision is avoided. 
For this purpose, the device according to the invention comprises a 
synchronizing pulse generator 10 which is connected to the current 
generator 7 to emit a synchronizing signal to the two component loops. The 
synchronizing signal consists of synchronizing pulses which are emitted, 
for example, at a pulse repetition frequency of 0.5-1 Hz. The 
synchronizing signal may, for example, be superimposed on the alternating 
current in the magnetic loop or be emitted in series in time with this 
alternating current so that the alternating current is interrupted briefly 
at certain intervals during the transmission of the synchronising signal. 
In the example shown, the synchronizing pulse generator 10 consists of a 
simple fixed installation which may appropriately be integrated with the 
rest of the central installation, which is necessary for the operation of 
the installation as a whole. 
Included as a main part in the device according to the invention is an 
equipment which is related to each vehicle 1, 2 and which thus accompanies 
the vehicle. This equipment is provided with a receiver device 11 with an 
input 12 for wireless reception via an aerial 26 of the synchronizing 
signal transmitted via the magnetic loops. Also included is a transmitter 
device 13 with an input 14 to receive the synchronizing signal from the 
output 15 of the receiver device 11. In the example shown, the transmitter 
device 13 consists of an ultrasonic transmitter and is thus adapted to 
emit an information signal, in this example hereinafter called the warning 
signal, which has a considerably lower speed of propagation in comparison 
with the speed of propagation of the synchronizing signal. Also included 
in said equipment accompanying each vehicle is a receiver device 16 for 
the warning signal. Thus, in the example shown, the receiver device 
consists of an ultrasonic receiver which comprises an output 17 which is 
connected to the stop input 19 of a counter 18. Connected to the start 
input 20 of the counter is the output 15 from the receiver 11 of the 
synchronizing signal. The counter 18 is further connected, at its output 
side 21, to the input side 22 of a comparator 23. A preset comparative 
value is fed into a further input 24 of the comparator. Under certain 
conditions, an indicating signal to indicate a certain proximity between 
the vehicles appears at an output 25 from the comparator 23. The output 25 
can be coupled to a circuit, not shown, to stop the vehicle or reduce its 
speed. 
When the installation is in operation, synchronizing signals are 
transmitted continuously via the magnetic loops in the form of 
synchronizing pulses with a certain pulse repetition frequency. These are 
received by the receiver devices 11 of all the vehicles 1, 2, at their 
inputs 12. The synchronizing signal is transmitted from the magnetic loop 
via the magnetic field extending around this loop, which is sensed by the 
aerial 26 of the receiver device 11. In the diagram shown in FIGS. 3 and 
4, a synchronizing pulse 27 is shown which is received in each vehicle 1, 
2. Each synchronizing pulse is detected in the receiver device 11 and 
emitted at its output 5, and is fed on the one hand to the input 14 of the 
ultrasonic transmitter 13 and on the other hand to the start input 20 of 
the counter 18. At this, the counter 18 is started and for each 
synchronizing pulse 27, a warning signal 28 is emitted from the ultrasonic 
transmitter 13 in the form of an ultrasonic pulse, which is indicated by a 
full line in FIG. 3, which represents the warning signal emitted from the 
one vehicle 1 and is indicated by a broken line in FIG. 4 which represents 
the warning signal emitted from the other vehicle 2. 
During the travel of the vehicles along the tracks of the installation, 
warning signals are thus transmitted continuously with intervals of time 
which are determined by the pulse repetition frequency of the 
synchronizing signal 27. For example, the interval of time in the present 
application may be in the range 200-500 ms. With the use of ultrasonics, 
the warning signal is in the range of 40-100 kHz. Thus the warning signal 
is emitted from all the vehicles using the air as a transmission medium, 
that is to say with a speed of propagations of about 340 m/s. With a 
vehicle speed of 1 m/s a warning signal is emitted about every 0.5 m. The 
speed of propagation or speed of travel of the synchronizing signal is of 
the order of magnitude of the speed of light, that is to say 
3.times.10.sup.8 m/s, and is thus practically "infinitely great" in 
comparison with the speed of propagation of the warning signal. Each 
synchronizing pulse 27, in relation to the interval of time between the 
pulses and the speed of propagation of the warning signals, can be 
regarded as reaching all the trucks 1, 2 practically simultaneously. The 
theoretical difference in time which occurs can thus be ignored in this 
connection. 
The transmitted warning signals from each vehicle 1, 2 are received by the 
other vehicles in the ultrasonic receivers 16 a certain time after the 
warning signal has been transmitted from another vehicle. The delay in 
time can easily be measured because of the relatively low speed of 
propagation and is proportional to the distance between the transmitting 
and the receiving vehicle. By measuring this difference in time, it is 
therefore possible to find out whether two vehicles are in inadmissible 
proximity to one another, which information is particularly important in 
front of a conflict point 6 where two vehicles may appear simultaneously 
with the risk of a collision. When each ultrasonic pulse 29 is received in 
the ultrasonic receiver 16, a signal is therefore emitted at its output 17 
to the stop input 19 of the counter 18. A received ultrasonic pulse is 
shown by a broken line in FIG. 3 and is designated here by 29 representing 
the warning signal received in the one vehicle 1, while the corresponding 
pulse 29 is designated by a full line in FIG. 4 representing the warning 
signal received in the other vehicle. When the counter 18 is stopped, a 
counted value appears at its output side 21 and is fed to the comparator 
23 at its one input side 22. This counted value is compared with the 
preset comparative value, whereupon said indicating signal is emitted at 
the output 25 of the comparator and indicates whether the counted value 
exceeds or is below the preset value. The preset value actually represents 
a certain preset interval of time from the moment t.sub.1 to the moment 
t.sub.2, which corresponds to a previously selected distance between two 
vehicles 1, 2. If said counted value is below the preset value, this means 
that the ultrasonic pulse 29 received appeared within the predetermined 
interval of time t.sub.1 -t.sub.2 and that the two vehicles 1, 2 are 
within a predetermined distance from one another, for example 3 meters. If 
the ultrasonic pulse received is received after the moment t.sub.2, that 
is to say outside the predetermined interval of time t.sub.1 -t.sub.2, 
which is illustrated by an ultrasonic pulse in chain lines in FIGS. 3 and 
4, which is designated by 30, there is a counted value at the output side 
21 of the counter 18 which exceeds the preset counted value, in which case 
the indicating signal at the output 25 of the comparator 23 is zero, for 
example, indicating that the vehicles are outside the monitored proximity 
zone, so that there is no risk of collision, so that the travel of the 
vehicles should not be interrupted. 
Since a collision at the conflict point 6 is avoided by the one vehicle 2 
being braked or stopped, while the other vehicle 1 continues up to and 
past the conflict point, the indicating signal at the output 25 from the 
comparator 23 is thus used only for vehicles on the one track. Since it 
has been predetermined, in the example shown, that the vehicle 1 on the 
main track 4 should be given priority, this vehicle is not acted upon by 
the indicating signal. This is brought about in a manner not shown as a 
result of the fact that each vehicle 1, 2 detects whether it is on a track 
with priority or not at a conflict point. This is brought about, as 
mentioned above, by detecting the different frequencies on the main track 
and side track respectively. The vehicle 2, which detected presence on a 
track without priority at a conflict point 6 and detected a certain 
nearness to another vehicle, thus receives an indicating signal at the 
output 25. The signal thus indicates this proximity to another vehicle and 
activates a circuit to reduce the speed of the vehicle or stop it. This 
state of the vehicle is maintained until there is no risk of a conflict. 
This is brought about, for example, as a result of the fact that the 
activation of the circuit for stopping or reducing the speed of the 
vehicle ceases, whereupon the vehicle is started again as a result of the 
fact that feed voltage is supplied to the drive motor of the vehicle, or 
this takes place after a certain predetermined delay in time which is 
determined by a timing circuit belonging to said circuit. 
According to the present invention, the device is based on the fundamental 
idea that use is made on the one hand of a synchronizing signal with a 
very high speed of propagation and on the other hand of a warning signal 
which is activated by the synchronizing signal and transmitted from at 
least certain units, and which is transmitted via the medium in which the 
units are, with a speed of propagation which is so low in comparison with 
the speed of propagation of the synchronizing signal that at least certain 
other units, on receiving the warning signal, with reference to the time 
which elapses for the warning signal to travel between the units, can 
decide whether these are in a certain proximity and if this exists between 
the units, an indicating signal indicates this and can be used for 
indication or to stop one of the units or to reduce the speed of this one 
unit. 
The invention is not restricted to the example of embodiment described 
above and shown in the drawings but can be varied within the scope of the 
following patent claims. For example, the synchronizing signal can be 
transmitted in another way, for example via radio in the form of an 
electromagnetic wave movement which, like the example described, has a 
very high speed of propagation. In this case, it is not necessary for the 
synchronizing signal to be transmitted from a fixed installation but it 
can be transmitted from certain of the vehicles. The device according to 
the invention is not restricted to loop-controlled or railbound vehicles 
but can be used, in principle, as a warning system or information system 
mutually between other kinds of movable units. Nor is it necessary to have 
an automatic stop or reduction of speed, which is normally the case with 
driverless vehicles, but in manned vehicles, the indicating signal can be 
used to activate an optical or acoustic signal member. Various 
applications are conceivable for people with defective vision to warn them 
of various obstacles and dangers. In the example shown, there is no 
problem in discriminating between received warning signals because of the 
low signal strength of the preceding signal. In principle, however, a 
level detection should be effected so that the strongest signal is always 
detected. 
Above, it has been presupposed that all the vehicles transmit and receive 
warning signals. Nevertheless, the above-mentioned detection of presence 
on the main track or side track can be used to inhibit the transmission of 
warning signals from vehicles on the side track and possibly to give 
vehicles on the main track only a transmitting function. The device can 
also detect nearness of two vehicles on the same path within a distance 
determined by the present time interval described above. In this way the 
detection will exclude vehicles passing along another path beyond said 
distance.