FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
FORWARD MONITORING DEVICE AND FORWARD MONITORING METHOD;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED
AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

2
DESCRIPTION
Field
[0001] The present disclosure relates to a forward
5 monitoring device and a forward monitoring method each for
monitoring an area in the travel direction of a train.
Background
[0002] In the past, there has been a conventional
10 practice in which a train monitors an upside of a railway
track in a travel direction to detect some obstacle. In
general, a monitoring device used on a train to detect an
obstacle is unable to monitor the entire area in the travel
direction of the train with the same accuracy, so that a
15 resolution of a detection result and the like can vary
depending on a distance. For this reason, the train is
adapted to set a target scope for monitoring in the travel
direction. Patent Literature 1 discloses a technique in
which a forward monitoring device sets a monitoring area
20 ahead of a train in accordance with a braking distance of
the train. The forward monitoring device described in
Patent Literature 1 detects a distant obstacle without
unnecessary increase of a monitoring range, and at the same
time, avoids an increase in size and rise in cost of the
25 device, by setting a monitoring area in accordance with the
braking distance of the train.
Citation List
Patent Literature
30 [0003] Patent Literature 1: Japanese Patent Application
Laid-open No. 2019-181996
Summary

3
Technical Problem
[0004] The forward monitoring device described in Patent
Literature 1 calculates a braking distance in consideration
of route information, a train speed, a brake performance,
5 and/or the like, but not taking into account a processing
time until a brake command is actually outputted from
determination that there is an obstacle in the monitoring
area, i.e., detection of an obstacle, based on an image
captured by an imaging device. The train is supposed to
10 run even during this processing time. This has presented a
problem in that the braking distance calculated by the
forward monitoring device described in Patent Literature 1
has low accuracy with respect to a braking distance from
actual capture of the image until the train is stopped.
15 Low accuracy of the braking distance calculated by the
forward monitoring device described in Patent Literature 1
causes, in turn, initially-desired accuracy in detection of
an obstacle in the monitoring area to be lowered.
[0005] The present disclosure has been made in view of
20 the foregoing, and it is an object of the present
disclosure to provide a forward monitoring device capable
of improving accuracy of detection of an obstacle in a
desired monitoring scope.
25 Solution to Problem
[0006] In order to solve the above-mentioned problems
and achieve the object, the present disclosure provides a
forward monitoring device to be installed on a train, the
forward monitoring device comprising: a storage unit to
30 store map information and brake performance information,
the map information representing location information and a
track geometry of a track on which the train is to run, the
brake performance information representing performance of a

4
brake system installed on the train; a train information
acquisition unit to acquire train location information and
train speed information of the train; a monitoring unit to
monitor an upside of the track in a travel direction of the
5 train; an obstacle determination unit to determine presence
or absence of an obstacle on the track based on a
monitoring result of the monitoring unit; a braking
distance calculation unit to calculate a braking distance
of the train using the map information, the brake
10 performance information, the train location information,
the train speed information, and a processing time from
when the monitoring unit performs monitoring until the
obstacle determination unit determines presence or absence
of an obstacle; and a monitoring distance determination
15 unit to determine a monitoring distance based on the
braking distance to set a monitoring range of the
monitoring unit.
Advantageous Effects of Invention
20 [0007] According to the present disclosure, an
advantageous effect is achieved in that a forward
monitoring device can improve accuracy of detection of an
obstacle in a desired monitoring range.
25 Brief Description of Drawings
[0008]
FIG. 1 is a diagram illustrating an example
configuration of a forward monitoring device according to a
first embodiment.
30 FIG. 2 is a first diagram illustrating an overview of
a braking distance calculated by the forward monitoring
device according to the first embodiment.
FIG. 3 is a second diagram illustrating an overview of

5
the braking distance calculated by the forward monitoring
device according to the first embodiment.
FIG. 4 is a flowchart illustrating an operation of the
forward monitoring device according to the first embodiment.
5 FIG. 5 is a diagram illustrating an example in which a
processing circuitry included in the forward monitoring
device according to the first embodiment is composed of a
processor and a memory.
FIG. 6 is a diagram illustrating an example in which
10 the processing circuitry included in the forward monitoring
device according to the first embodiment is composed of a
dedicated hardware set.
FIG. 7 is a diagram illustrating an example
configuration of a forward monitoring device according to a
15 second embodiment.
FIG. 8 is a diagram illustrating an example of an
operation of the forward monitoring device according to the
second embodiment.
FIG. 9 is a flowchart illustrating an operation of the
20 forward monitoring device according to the second
embodiment.
FIG. 10 is a diagram illustrating an example
configuration of a forward monitoring device according to a
third embodiment.
25 FIG. 11 is a diagram illustrating an example of an
operation of the forward monitoring device according to the
third embodiment.
FIG. 12 is a flowchart illustrating an operation of
the forward monitoring device according to the third
30 embodiment.
Description of Embodiments
[0009] A forward monitoring device and a forward

6
monitoring method according to embodiments of the present
disclosure will be described in detail below with reference
to the drawings.
[0010] First Embodiment.
5 FIG. 1 is a diagram illustrating an example
configuration of a forward monitoring device 12 according
to a first embodiment. The forward monitoring device 12 is
installed on a train 10. The train 10 monitors whether or
not there is an obstacle on a track 20 in the travel
10 direction using the forward monitoring device 12 while
running on the track 20. The train 10 includes a train
control device 11, the forward monitoring device 12, and an
output device 13. The forward monitoring device 12 is
connected to the train control device 11 and the output
15 device 13. The forward monitoring device 12 includes a
storage unit 121, a train information acquisition unit 122,
a braking distance calculation unit 123, a monitoring
distance determination unit 124, a monitoring unit 125, and
an obstacle determination unit 126.
20 [0011] The train control device 11 detects the location
and the speed of the train 10 using devices such as a
ground coil (not illustrated) installed on the ground, and
an on-board antenna and a tachogenerator (both not
illustrated) installed on the train 10. The train control
25 device 11 outputs train location information representing
the detected location of the train 10 and train speed
information representing the detected speed of the train 10
to the forward monitoring device 12. The method of
detecting the location of the train 10 in the train control
30 device 11 is a common method as is conventionally done.
[0012] The storage unit 121 stores map information
representing location information and a track geometry such
as the inclination and presence or absence of a curve, of

7
the track 20 on which the train 10 is to run. The map
information may be represented in kilometrage from the
point of origin, may be represented in latitude and
longitude, may be represented in a set of coordinates based
5 on a point cloud obtained by three-dimensional measurement,
or may be represented in their combinational manner. The
storage unit 121 also stores brake performance information
representing the performance of a brake system (not
illustrated) installed on the train 10. The brake
10 performance information is, for example, information that
represents the time from when the brake system of the train
10 receives a brake command until the brake system actually
applies brakes, that is, until the brake system provides
control to decelerate or stop the train, which includes
15 acceleration representing how fast the train decelerates at
the time of brake output, and the like.
[0013] The train information acquisition unit 122
acquires the train location information representing the
location of the train 10 and the train speed information
20 representing the speed of the train 10 from the train
control device 11. The train information acquisition unit
122 outputs the acquired train location information and
train speed information of the train 10 to the braking
distance calculation unit 123.
25 [0014] The braking distance calculation unit 123
acquires the map information and the brake performance
information from the storage unit 121. In addition, the
braking distance calculation unit 123 acquires the train
location information and the train speed information of the
30 train 10 from the train information acquisition unit 122.
The braking distance calculation unit 123 calculates the
braking distance of the train 10 using the map information,
the brake performance information, the train location

8
information, the train speed information, the processing
time required for the forward monitoring device 12 to
determine the presence or absence of an obstacle, and the
reaction time that elapses before the brakes are applied.
5 The processing time is, specifically, a time defined as the
time from when the monitoring unit 125 performs monitoring
until the obstacle determination unit 126 determines the
presence or absence of an obstacle in the forward
monitoring device 12. The reaction time is, specifically,
10 a time defined as the time from when information indicating
that an obstacle has been detected is outputted from the
output device 13 until a train operator actually applies
brakes in the train 10, that is, until the operator of the
train 10 outputs a brake command to the brake system. It
15 is assumed here that the brake system installed on the
train 10 is not an automatic brake system. The automatic
brake system said herein refers to a brake system that has
a function of automatically outputting a brake in
accordance with output results from the forward monitoring
20 device 12. The processing time and the reaction time may
be stored in advance in the braking distance calculation
unit 123 based on, for example, design values, measured
values, and/or the like, by a manufacturer of the forward
monitoring device 12, or may be stored in advance in the
25 braking distance calculation unit 123 based on measured
values by a railway company that operates the train 10.
Note that the processing time and the reaction time may be
stored in the storage unit 121, and read from the storage
unit 121 by the braking distance calculation unit 123. The
30 braking distance calculation unit 123 outputs the braking
distance obtained by the calculation to the monitoring
distance determination unit 124.
[0015] The monitoring distance determination unit 124

9
determines the monitoring distance based on the braking
distance acquired from the braking distance calculation
unit 123. The monitoring distance is a distance on the
track 20 from the train 10 in the travel direction of the
5 train 10. In the present embodiment, the monitoring
distance determination unit 124 uses the braking distance
calculated by the braking distance calculation unit 123 as
the monitoring distance. The monitoring distance
determination unit 124 sets a monitoring range in which the
10 monitoring unit 125 performs monitoring, on the basis of
the monitoring distance. The monitoring range is a range
represented in, for example, a distance defined in the
front-back direction from the monitoring distance on the
track 20, and a distance defined in the left-right
15 direction from the monitoring distance with respect to the
travel direction of the train 10. The monitoring distance
determination unit 124 outputs the monitoring range that
has been set, to the monitoring unit 125.
[0016] The monitoring unit 125 monitors an upside of the
20 track 20 in the travel direction of the train 10.
Specifically, the monitoring unit 125 monitors an obstacle
in the monitoring range that has been set by the monitoring
distance determination unit 124 and acquired from the
monitoring distance determination unit 124. The monitoring
25 unit 125 is a device capable of detecting an obstacle in
the monitoring range, and is, for example, a stereo camera
equipped with two or more cameras, a light detection and
ranging (LIDAR) apparatus, a radio detection and ranging
(RADAR) apparatus, or the like. The monitoring unit 125
30 may be configured to include two or more devices. Note
that the specific configuration of the monitoring unit 125
is not necessarily limited to these examples. The
monitoring unit 125 generates a distance image from data

10
obtained by monitoring the monitoring range, and outputs
the generated distance image to the obstacle determination
unit 126. The distance image is a monitoring result
obtained by the monitoring unit 125 monitoring an area
5 surrounding the train 10, and includes one or both of a
two-dimensional image and a three-dimensional image
including distance information. The monitoring unit 125 is
installed on a lead vehicle of the train 10. When the
train 10 has a formation of multiple vehicles, a lead
10 vehicle alternates depending on the travel direction, and
therefore, the monitoring unit 125 is installed on each of
the vehicles at both ends. For example, when the train 10
has a ten-car formation composed of vehicle No. 1 to
vehicle No. 10, either vehicle No. 1 or vehicle No. 10
15 becomes a lead vehicle depending on the travel direction.
In this case, the monitoring unit 125 is installed on each
of the vehicle No. 1 and the vehicle No. 10 of the train 10.
The forward monitoring device 12 uses the monitoring unit
125 installed on the lead vehicle in the travel direction
20 of the train 10.
[0017] The obstacle determination unit 126 determines
the presence or absence of an obstacle on the track 20
based on the monitoring result of the monitoring unit 125.
Specifically, the obstacle determination unit 126
25 determines the presence or absence of an obstacle in the
travel direction of the train 10 based on the distance
image acquired from the monitoring unit 125. When the
obstacle determination unit 126 determines that the
distance image includes an image of an obstacle, the
30 obstacle determination unit 126 generates obstacle
information that is information indicating that an obstacle
has been detected, and outputs the generated obstacle
information to the output device 13. The obstacle

11
information may be information only indicating that an
obstacle has been detected, or may include information such
as a location and/or an image where the obstacle has been
detected.
5 [0018] When the obstacle information is acquired from
the obstacle determination unit 126, the output device 13
outputs information indicating that an obstacle has been
detected, to the operator of the train 10 and the like.
The output device 13 may show that an obstacle has been
10 detected, to the operator of the train 10 and the like with
use of a monitor or the like, or may announce that an
obstacle has been detected, by voice through a loudspeaker
or the like. In addition, when the brake system installed
on the train 10 is an automatic brake system, the output
15 device 13 outputs a brake command to the automatic brake
system.
[0019] An operation of the forward monitoring device 12
will next be described. FIG. 2 is a first diagram
illustrating an overview of a braking distance A calculated
20 by the forward monitoring device 12 according to the first
embodiment. FIG. 2 illustrates a transition of the speed
of the train 10 running on the track 20. In FIG. 2, v is
the speed at the time when the train 10 calculated the
braking distance A. In addition, in FIG. 2, the travel
25 direction of the train 10 is a direction from left to right
of FIG. 2. As illustrated in FIG. 2, the braking distance
A is the sum of an idle running distance B, a decelerated
running distance C, and a marginal distance D.
[0020] The idle running distance B consists of a first
30 idle running distance Δt1·v, a second idle running distance
Δt2·v, and a third idle running distance Δt3·v. The first
idle running distance Δt1·v is a distance for which the
train 10 travels during the processing time that is a time

12
Δt1 from when the monitoring unit 125 performs monitoring
until the obstacle determination unit 126 determines the
presence or absence of an obstacle in the forward
monitoring device 12. The second idle running distance
5 Δt2·v is a distance for which the train 10 travels during
the reaction time that is a time Δt2 from when information
indicating that an obstacle has been detected is outputted
from the output device 13 in the forward monitoring device
12 until the operator of the train 10 actually applies
10 brakes. The third idle running distance Δt3·v is a
distance for which the train 10 travels during a time Δt3
from when the brake system of the train 10 acquires a brake
command until the brake system provides control to actually
apply brakes, that is, during a time Δt3 indicated by the
15 brake performance information.
[0021] The decelerated running distance C is a distance
for which the train 10 travels during a time from when the
train 10 starts deceleration by application of braking
until the train 10 actually stops. The decelerated running
20 distance C is calculated based on a factor or factors, for
example, deceleration at the time of braking, air
resistance, effect of inclination, and/or the like. These
factors may be precisely calculated or calculated while
adding an allowance to the factors on the safe side. The
25 marginal distance D is a distance obtained with taking into
account some measurement error of the monitoring unit 125,
idling and slipping, and/or the like. The marginal
distance D may be a fixed value or a variable value that
varies with the speed of the train 10. The braking
30 distance calculation unit 123 may store in advance
information on the marginal distance D, or may obtain the
information on the marginal distance D by calculation from
the speed v of the train 10 in the case where the distance

13
D is a variable value.
[0022] In the forward monitoring device 12, the braking
distance calculation unit 123 can improve accuracy in
calculation of the braking distance A by summing the idle
5 running distance B, the decelerated running distance C, and
the marginal distance D to obtain the braking distance A as
illustrated in FIG. 2. Note that when the brake system
provided on the train 10 is an automatic brake system and
the output device 13 outputs a brake command to the
10 automatic brake system, the reaction time that is the time
Δt2 can be considered as zero, and therefore the braking
distance calculation unit 123 may set the second idle
running distance Δt2·v to 0. That is, the braking distance
calculation unit 123 may calculate the braking distance A
15 without using the reaction time that elapses before the
brakes are applied. The braking distance A in the case
where the brake system provided on the train 10 is an
automatic brake system is equal to the sum of the first
idle running distance Δt1·v, the third idle running
20 distance Δt3·v, the decelerated running distance C, and the
marginal distance D. When the brake system provided on the
train 10 is an automatic brake system, the braking distance
calculation unit 123 calculates the braking distance A of
the train 10 using the map information, the brake
25 performance information, the train location information,
the train speed information, and the processing time that
elapses before the forward monitoring device 12 determines
the presence or absence of an obstacle.
[0023] Note that the speed v of the train 10 may be
30 assumed to be in an acceleration speed state as illustrated
in FIG. 3 rather than in a constant speed state as
illustrated in FIG. 2. FIG. 3 is a second diagram
illustrating an overview of the braking distance A

14
calculated by the forward monitoring device 12 according to
the first embodiment. FIG. 3 is similar to FIG. 2 except
that the speed of the train 10 increases from speed v1 to
speed v4 in a section corresponding to the idle running
5 distance B. Note that FIG. 3 gives the first idle running
distance as Δt1·(v1+v2)/2, the second idle running distance
as Δt2·(v2+v3)/2, and the third idle running distance as
Δt3·(v3+v4)/2. In this example, the train acceleration is
constant and has a value a, and there are expressed
10 v2=v1+aΔt1, v3=v2+aΔt2, and v4=v3+aΔt3. The forward
monitoring device 12 assumes an acceleration condition
regardless of the actual running state, thereby making it
possible to calculate a more safety-oriented braking
distance. Although the acceleration a is assumed to be
15 constant in this example, the forward monitoring device 12
may additionally take into account effects of the train
speed, the inclination, the air resistance, and/or the like.
In addition, the forward monitoring device 12 may calculate
the braking distance with additionally taking into account
20 the running state at the time of start of calculation of a
braking distance.
[0024] An operation of the forward monitoring device 12
will now be described using a flowchart. FIG. 4 is a
flowchart illustrating an operation of the forward
25 monitoring device 12 according to the first embodiment. In
the forward monitoring device 12, the braking distance
calculation unit 123 acquires the map information and the
brake performance information from the storage unit 121,
and acquires the train location information and the train
30 speed information of the train 10 from the train
information acquisition unit 122. The braking distance
calculation unit 123 calculates the braking distance A of
the train 10 using the map information, the brake

15
performance information, the train location information,
the train speed information, the processing time required
for the forward monitoring device 12 to determine the
presence or absence of an obstacle, and the reaction time
5 that elapses before the brakes are applied (step S11). The
braking distance calculation unit 123 outputs the braking
distance A obtained by the calculation to the monitoring
distance determination unit 124.
[0025] The monitoring distance determination unit 124
10 determines the monitoring distance based on the braking
distance A acquired from the braking distance calculation
unit 123 (step S12). The monitoring distance determination
unit 124 sets the monitoring range of the monitoring unit
125 based on the monitoring distance (step S13). The
15 monitoring distance determination unit 124 outputs the
monitoring range that has been set, to the monitoring unit
125.
[0026] The monitoring unit 125 monitors an obstacle in
the monitoring range acquired from the monitoring distance
20 determination unit 124 (step S14). The monitoring unit 125
generates a distance image from data obtained from the
monitoring, and outputs the generated distance image to the
obstacle determination unit 126 as the monitoring result.
[0027] The obstacle determination unit 126 acquires the
25 distance image from the monitoring unit 125, and determines
whether or not an obstacle has been detected (step S15).
When an obstacle has been detected (step S15: Yes), the
obstacle determination unit 126 outputs obstacle
information to the output device 13 (step S16). The
30 forward monitoring device 12 returns in process to step S11,
and repeats the foregoing operation. When no obstacle has
been detected (step S15: No), the forward monitoring device
12 returns in process to step S11, and repeats the

16
foregoing operation.
[0028] Note that for the forward monitoring device 12,
some cases are contemplated in which time needed for the
obstacle determination unit 126 to determine that a
5 detected object is an obstacle is wanted to be longer if
the object is an animal such as a bird that can quickly
move away in the determination about an obstacle, in order
to avoid any unnecessary braking operations. The case in
which the time needed is wanted to be longer is a case in
10 which accuracy of determination is desired to be improved
by the obstacle determination unit 126, for example, with
use of multiple distance images obtained through multiple
monitoring operations from the monitoring unit 125. An
unnecessary braking operation may impair ride comfort of
15 passengers of the train 10. In addition, an unnecessary
braking operation may delay arrival at the next station.
Meanwhile, the forward monitoring device 12 is preferably
configured to avoid a delayed braking operation if a
suspicious object is actually an obstacle. A delayed
20 braking operation may cause the train 10 to hit the
obstacle. For these reasons, when the obstacle
determination unit 126 detects an object that may be
regarded as a candidate for an obstacle in the monitoring
result of the monitoring unit 125 and determines that a
25 determination needs to be made regarding the presence or
absence of an obstacle based on multiple monitoring results,
the obstacle determination unit 126 may output obstacle
information to the output device 13 so that control is
performed on the brake system to apply an initial pressure
30 to the brake system, to inhibit power running, or to make
weakened braking in order to shorten the time Δt3 from the
time of issuance of a brake command for necessity to
actually output a brake thereafter until a brake is

17
actually outputted. This enables the forward monitoring
device 12 to avoid an unnecessary braking operation, and at
the same time to avoid an unsatisfactorily delayed braking
operation when a suspicious object is actually an obstacle.
5 That is, the forward monitoring device 12 can avoid
impairment of ride comfort of passengers of the train 10,
and can avoid a situation in which the train 10 comes in
contact with an obstacle while avoiding a situation of
delayed arrival at the next station.
10 [0029] A hardware configuration of the forward
monitoring device 12 will next be described. In the
forward monitoring device 12, the storage unit 121 is a
memory. The monitoring unit 125 is a sensor such as a
stereo camera or a LIDAR apparatus. The train information
15 acquisition unit 122, the braking distance calculation unit
123, the monitoring distance determination unit 124, and
the obstacle determination unit 126 are implemented by a
processing circuit. The processing circuit may be a
processor that executes a program stored in a memory, and
20 the memory, or may be a dedicated hardware set.
[0030] FIG. 5 is a diagram illustrating an example in
which the processing circuit included in the forward
monitoring device 12 according to the first embodiment is
composed of a processor and a memory. When the processing
25 circuit is composed of a processor 91 and a memory 92, the
functionalities of the processing circuit of the forward
monitoring device 12 are implemented in software, firmware,
or a combination of software and firmware. The software or
firmware is described as a program, and is stored in the
30 memory 92. In the processing circuit, each functionality
is implemented by an operation in which the processor 91
reads and executes a program stored in the memory 92. That
is, the processing circuit has the memory 92 for storing

18
programs by which processes for the forward monitoring
device 12 are resultantly curried out. It can also be said
that these programs cause a computer to perform a procedure
and a method of the forward monitoring device 12.
5 [0031] In this respect, the processor 91 may be a
central processing unit (CPU), a processing device, a
computing device, a microprocessor, a microcomputer, a
digital signal processor (DSP), or the like. In addition,
the memory 92 corresponds to:, for example, a non-volatile
10 or volatile semiconductor memory such as a random access
memory (RAM), a read-only memory (ROM), a flash memory, an
erasable programmable ROM (EPROM), or an electrically
erasable programmable ROM (EEPROM) (registered trademark);
a magnetic disk; a flexible disk; an optical disk; a
15 compact disc; a Mini Disc; a digital versatile disc (DVD);
or the like.
[0032] FIG. 6 is a diagram illustrating an example in
which the processing circuit included in the forward
monitoring device 12 according to the first embodiment is
20 composed of a dedicated hardware set. When the processing
circuit is composed of a dedicated hardware set, a
processing circuit 93 illustrated in FIG. 6 corresponds to,
for example, a single circuit, a composite circuit, a
programmed processor, a parallel programmed processor, an
25 application specific integrated circuit (ASIC), a field
programmable gate array (FPGA), or a combination thereof.
The functionalities of the forward monitoring device 12 may
be implemented by the processing circuit 93 on a functionby-function basis, or may be collectively implemented in
30 the processing circuit 93 as a whole.
[0033] Note that some of the functionalities of the
forward monitoring device 12 may be implemented by a
dedicated hardware set and the remainder thereof may be

19
implemented by software or firmware. As just described,
the processing circuit can realize the foregoing
functionalities in a dedicated hardware set, software,
firmware, or a combination thereof.
5 [0034] As described above, according to the present
embodiment, the braking distance calculation unit 123 of
the forward monitoring device 12 acquires the map
information and the brake performance information from the
storage unit 121, and acquires the train location
10 information and the train speed information of the train 10
from the train information acquisition unit 122. The
braking distance calculation unit 123 calculates the
braking distance A of the train 10 using the map
information, the brake performance information, the train
15 location information, the train speed information, the
processing time required for the forward monitoring device
12 to determine the presence or absence of an obstacle, and
the reaction time that elapses before the brakes are
applied. The monitoring distance determination unit 124
20 determines the monitoring distance on the basis of the
braking distance A calculated by the braking distance
calculation unit 123, and sets the monitoring range of the
monitoring unit 125. The braking distance calculation unit
123 can improve accuracy in calculation of the braking
25 distance A by taking into account the idle running distance
B. This enables the forward monitoring device 12 to
improve accuracy in detection of an obstacle on the
periphery of the braking distance A, i.e., in a desired
monitoring range. In addition, the forward monitoring
30 device 12 can avoid unnecessary monitoring and reduce the
amount of computation in monitoring by virtue of
eliminating monitoring of a distant area beyond the
monitoring range obtained based on the braking distance A.

20
[0035] Second Embodiment.
In a second embodiment, the forward monitoring device
determines the monitoring distance further with use of
information on a stop limit point of the train.
5 [0036] FIG. 7 is a diagram illustrating an example
configuration of a forward monitoring device 12a according
to the second embodiment. The forward monitoring device
12a is installed on a train 10a. The train 10a monitors
whether or not there is an obstacle on the track 20 in the
10 travel direction using the forward monitoring device 12a
while running on the track 20. The train 10a includes the
train control device 11, a forward monitoring device 12a,
the output device 13, an on-vehicle communication unit 14,
and an on-vehicle safety device 15. The forward monitoring
15 device 12a is connected to the train control device 11, the
output device 13, and the on-vehicle safety device 15. In
addition, the train 10a is connected to a ground safety
device 21 via a ground communication unit 22.
[0037] The ground safety device 21 collects, from the
20 train 10a and other trains (not illustrated), location
information of the trains to manage an interval between the
train 10a and another train. The ground safety device 21
calculates a stop limit point of each of the trains based
on the location information of the trains and the like.
25 The ground safety device 21 transmits the stop limit point
obtained by the calculation, to each train via the ground
communication unit 22. The ground communication unit 22
transmits the stop limit point acquired from the ground
safety device 21 to each train by wireless communication.
30 On the train 10a, the on-vehicle communication unit 14
receives the stop limit point from the ground safety device
21 via the ground communication unit 22. The on-vehicle
communication unit 14 outputs the stop limit point received,

21
to the on-vehicle safety device 15. The on-vehicle safety
device 15 outputs the stop limit point acquired from the
on-vehicle communication unit 14 to a train information
acquisition unit 122a of the forward monitoring device 12a.
5 [0038] In this operation, when the train 10a and the
ground safety device 21 constitute a communication based
train control (CBTC) system, the ground safety device 21
transmits the stop limit point from the ground
communication unit 22 that is a wireless communication
10 device. On the train 10a, the on-vehicle communication
unit 14 that is a wireless communication device receives
the stop limit point. Otherwise, when the train 10a and
the ground safety device 21 constitute an automatic train
control (ATC) system, the ground safety device 21 causes
15 the ground communication unit 22 to transmit the stop limit
point via the track 20. On the train 10a, the on-vehicle
communication unit 14 that is a power receiver receives the
stop limit point from the track 20. Still otherwise, when
the train 10a and the ground safety device 21 constitute a
20 pattern-controlled automatic train stop (ATS-P) system, the
ground safety device 21 causes the ground communication
unit 22 that is a ground coil to transmit the stop limit
point. On the train 10a, the on-vehicle communication unit
14 that is an on-board antenna, receives the stop limit
25 point.
[0039] A configuration of the forward monitoring device
12a will next be described. The forward monitoring device
12a includes the train information acquisition unit 122a
and a monitoring distance determination unit 124a in place
30 of the train information acquisition unit 122 and the
monitoring distance determination unit 124, respectively,
of the forward monitoring device 12 of the first embodiment
illustrated in FIG. 1.

22
[0040] The train information acquisition unit 122a has a
function of acquiring the stop limit point from the onvehicle safety device 15 installed on the train 10a in
addition to the function for the train information
5 acquisition unit 122 of the first embodiment. The train
information acquisition unit 122a outputs the stop limit
point acquired from the on-vehicle safety device 15 to the
monitoring distance determination unit 124a.
[0041] The monitoring distance determination unit 124a
10 determines the monitoring distance on the basis of the
braking distance A acquired from the braking distance
calculation unit 123 and the stop limit point acquired from
the train information acquisition unit 122a. For example,
when the location represented by the braking distance A is
15 nearer to the train 10a than the location represented by
the stop limit point, the monitoring distance determination
unit 124a determines that the braking distance A is the
monitoring distance. When the location represented by the
stop limit point is nearer to the train 10a than the
20 location represented by the braking distance A, the
monitoring distance determination unit 124a determines that
the distance from the train 10a to the location represented
by the stop limit point is the monitoring distance.
[0042] An operation of the forward monitoring device 12a
25 will next be described. FIG. 8 is a diagram illustrating
an example of an operation of the forward monitoring device
12a according to the second embodiment. In FIG. 8, X
represents the stop limit point. When the forward
monitoring device 12a calculates the braking distance A
30 with taking into account the idle running distance B as
illustrated in FIG. 2 of the first embodiment, it may be
contemplated that the location represented by the braking
distance A is more distant from the train 10a than the stop

23
limit point X. However, the train 10a needs to stop before
the stop limit point X calculated by the ground safety
device 21 based on the location relationship between the
train 10a and another train 30. In this case, the train
5 10a will not run in practice in a portion of the braking
distance A distant from the stop limit point X. Therefore,
when the stop limit point X is nearer to the train 10a than
the location represented by the braking distance A, the
monitoring distance determination unit 124a determines, as
10 described above, that the distance to the stop limit point
X is the monitoring distance.
[0043] An operation of the forward monitoring device 12a
will now be described using a flowchart. FIG. 9 is a
flowchart illustrating an operation of the forward
15 monitoring device 12a according to the second embodiment.
In the forward monitoring device 12a, the train information
acquisition unit 122a acquires the stop limit point X from
the on-vehicle safety device 15 (step S21). The train
information acquisition unit 122a outputs the stop limit
20 point X obtained, to the monitoring distance determination
unit 124a.
[0044] The braking distance calculation unit 123
acquires the map information and the brake performance
information from the storage unit 121, and acquires the
25 train location information and the train speed information
of the train 10a from the train information acquisition
unit 122a. The braking distance calculation unit 123
calculates the braking distance A of the train 10a using
the map information, the brake performance information, the
30 train location information, the train speed information,
the processing time required for the forward monitoring
device 12a to determine the presence or absence of an
obstacle, and the reaction time that elapses before the

24
brakes are applied (step S22). The braking distance
calculation unit 123 outputs the braking distance A
obtained by the calculation to the monitoring distance
determination unit 124a.
5 [0045] The monitoring distance determination unit 124a
acquires the braking distance A from the braking distance
calculation unit 123, and acquires the stop limit point X
from the train information acquisition unit 122a. The
monitoring distance determination unit 124a determines the
10 monitoring distance of the monitoring unit 125 based on the
braking distance A and the stop limit point X (step S23).
The monitoring distance determination unit 124a sets the
monitoring range of the monitoring unit 125 based on the
monitoring distance (step S24). The monitoring distance
15 determination unit 124a outputs the monitoring range that
has been set, to the monitoring unit 125.
[0046] The monitoring unit 125 monitors an obstacle in
the monitoring range acquired from the monitoring distance
determination unit 124a (step S25). The monitoring unit
20 125 generates a distance image from data obtained by the
monitoring, and outputs the distance image generated, to
the obstacle determination unit 126.
[0047] The obstacle determination unit 126 acquires the
distance image from the monitoring unit 125, and determines
25 whether or not an obstacle has been detected (step S26).
When an obstacle has been detected (step S26: Yes), the
obstacle determination unit 126 outputs obstacle
information to the output device 13 (step S27). Then, the
forward monitoring device 12a returns in process to step
30 S21, and repeats the foregoing operation. When no obstacle
has been detected (step S26: No), the forward monitoring
device 12a returns in process to step S21, and repeats the
foregoing operation.

25
[0048] As described above, according to the present
embodiment, the monitoring distance determination unit 124a
of the forward monitoring device 12a determines the
monitoring distance based on the braking distance A and the
5 stop limit point X to set the monitoring range. This
enables the forward monitoring device 12a to further
improve accuracy in detection of an obstacle on a periphery
of the braking distance A, i.e., in a desired monitoring
range, as compared to the first embodiment. In addition,
10 the forward monitoring device 12a can avoid unnecessary
monitoring and further reduce the amount of computation in
monitoring as compared to the first embodiment, by virtue
of eliminating monitoring of a more distant area beyond the
monitoring range based on the braking distance A and the
15 stop limit point X.
[0049] Third Embodiment.
In a third embodiment, the forward monitoring device
determines the monitoring distance additionally with use of
information of an in-station stop location of the train or
20 information of a remaining running distance to a stop
location such as a station.
[0050] FIG. 10 is a diagram illustrating an example
configuration of a forward monitoring device 12b according
to the third embodiment. The forward monitoring device 12b
25 is installed on a train 10b. The train 10b monitors
whether or not there is an obstacle on the track 20 in the
travel direction using the forward monitoring device 12b
while running on the track 20. The train 10b includes the
train control device 11, the forward monitoring device 12b,
30 the output device 13, an on-board antenna 16, and an
automatic train operation (ATO) device 17. The forward
monitoring device 12b is connected to the train control
device 11, the output device 13, and the ATO device 17. In

26
addition, the train 10b is connected to a ground coil 23.
[0051] The ground coil 23 transmits the in-station stop
location or the remaining running distance to a stop
location such as a station, to the train 10b by wireless
5 communication. The in-station stop location is a location
where the train 10b stops upon arrival at a station. The
remaining running distance is a remaining distance for
which the train 10b is to be run before the stop location
when the train 10b arrives at a station or the like. The
10 on-board antenna 16 receives the in-station stop location
or the remaining running distance from the ground coil 23
by wireless communication. The on-board antenna 16 outputs
the received in-station stop location or remaining running
distance to the ATO device 17. The ATO device 17 that is
15 an automatic train operation device outputs the in-station
stop location or remaining running distance acquired from
the on-board antenna 16 to a train information acquisition
unit 122b of the forward monitoring device 12b.
[0052] A configuration of the forward monitoring device
20 12b will next be described. The forward monitoring device
12b includes the train information acquisition unit 122b
and a monitoring distance determination unit 124b in place
of the train information acquisition unit 122 and the
monitoring distance determination unit 124, respectively,
25 of the forward monitoring device 12 of the first embodiment
illustrated in FIG. 1.
[0053] The train information acquisition unit 122b has a
function of acquiring the in-station stop location or the
remaining running distance from the ATO device 17 installed
30 on the train 10b in addition to the function for the train
information acquisition unit 122 of the first embodiment.
Note that the in-station stop location may be beforehand
stored in the storage unit 121, and the train information

27
acquisition unit 122b may read the in-station stop location
from the storage unit 121. The train information
acquisition unit 122b outputs the in-station stop location
or remaining running distance acquired from the ATO device
5 17, to the monitoring distance determination unit 124b.
[0054] The monitoring distance determination unit 124b
determines the monitoring distance on the basis of the
braking distance A acquired from the braking distance
calculation unit 123 and the in-station stop location or
10 remaining running distance acquired from the train
information acquisition unit 122b. For example, when a
location represented by the braking distance A is nearer to
the train 10b than a location represented by the in-station
stop location or remaining running distance, the monitoring
15 distance determination unit 124b determines that the
braking distance A is the monitoring distance. When a
location represented by the in-station stop location or
remaining running distance is nearer to the train 10b than
a location represented by the braking distance A, the
20 monitoring distance determination unit 124b determines that
a distance from the train 10b to the location represented
by the in-station stop location or remaining running
distance is the monitoring distance.
[0055] An operation of the forward monitoring device 12b
25 will next be described. FIG. 11 is a diagram illustrating
an example of an operation of the forward monitoring device
12b according to the third embodiment. In FIG. 11, Y
represents the in-station stop location, and Z represents
the remaining running distance. When the forward
30 monitoring device 12b calculates the braking distance A
with taking into account the idle running distance B as
illustrated in FIG. 2 of the first embodiment, it is
contemplated that the location represented by the braking

28
distance A is more distant from the train 10b than the
location represented by the in-station stop location Y or
the remaining running distance Z. However, the train 10b
needs to stop before the location represented by the in5 station stop location Y or the remaining running distance Z.
In this case, the train 10b is practically supposed not to
run in the portion of the braking distance A more distant
than the location represented by the in-station stop
location Y or the remaining running distance Z. For that
10 reason, as described above, when the location represented
by the in-station stop location Y or the remaining running
distance Z is nearer to the train 10b than the location
represented by the braking distance A, the monitoring
distance determination unit 124b determines that the
15 distance to the location represented by the in-station stop
location Y or the remaining running distance Z is the
monitoring distance.
[0056] An operation of the forward monitoring device 12b
will now be described using a flowchart. FIG. 12 is a
20 flowchart illustrating an operation of the forward
monitoring device 12b according to the third embodiment.
In the forward monitoring device 12b, the train information
acquisition unit 122b acquires the in-station stop location
Y or the remaining running distance Z from the ATO device
25 17 (step S31). The train information acquisition unit 122b
outputs the in-station stop location Y or remaining running
distance Z acquired, to the monitoring distance
determination unit 124b.
[0057] The braking distance calculation unit 123
30 acquires the map information and the brake performance
information from the storage unit 121, and acquires the
train location information and train speed information of
the train 10b from the train information acquisition unit

29
122b. The braking distance calculation unit 123 calculates
the braking distance A of the train 10b using the map
information, the brake performance information, the train
location information, the train speed information, the
5 processing time required for the forward monitoring device
12b to determine the presence or absence of an obstacle,
and the reaction time that elapses before the brakes are
applied (step S32). The braking distance calculation unit
123 outputs the braking distance A obtained by the
10 calculation to the monitoring distance determination unit
124b.
[0058] The monitoring distance determination unit 124b
acquires the braking distance A from the braking distance
calculation unit 123, and acquires the in-station stop
15 location Y or the remaining running distance Z from the
train information acquisition unit 122b. The monitoring
distance determination unit 124b determines the monitoring
distance of the monitoring unit 125 based on the braking
distance A and the in-station stop location Y or remaining
20 running distance Z (step S33). The monitoring distance
determination unit 124b sets the monitoring range of the
monitoring unit 125 based on the monitoring distance (step
S34). The monitoring distance determination unit 124b
outputs the monitoring range that has been set, to the
25 monitoring unit 125.
[0059] The monitoring unit 125 monitors an obstacle in
the monitoring range acquired from the monitoring distance
determination unit 124b (step S35). The monitoring unit
125 generates a distance image from data obtained by the
30 monitoring, and outputs the distance image generated, to
the obstacle determination unit 126.
[0060] The obstacle determination unit 126 acquires the
distance image from the monitoring unit 125, and determines

30
whether or not an obstacle has been detected (step S36).
When an obstacle has been detected (step S36: Yes), the
obstacle determination unit 126 outputs obstacle
information to the output device 13 (step S37). Then, the
5 forward monitoring device 12b returns in process to step
S31, and repeats the foregoing operation. When no obstacle
has been detected (step S36: No), the forward monitoring
device 12b returns in process to step S31, and repeats the
foregoing operation.
10 [0061] As described above, according to the present
embodiment, the monitoring distance determination unit 124b
of the forward monitoring device 12b is configured to
determine the monitoring distance based on the braking
distance A and the in-station stop location Y or remaining
15 running distance Z to set the monitoring range. By so
doing, the forward monitoring device 12b can further
improve accuracy in detection of an obstacle on the
periphery of the braking distance A, i.e., in a desired
monitoring range, as compared to the first embodiment. In
20 addition, the forward monitoring device 12b can avoid
unnecessary monitoring and further reduce the amount of
computation in monitoring as compared to the first
embodiment, by virtue of eliminating monitoring of a more
distant area beyond the monitoring range that is based on
25 the braking distance A and the in-station stop location Y
or remaining running distance Z.
[0062] The configurations described in the foregoing
embodiments are illustrated as just examples. These
configurations may be each combined with other publicly
30 known techniques, and the embodiments may be combined to
each other. Moreover, each of the configurations may be
partially omitted and/or modified without departing from
the scope of the present disclosure.

31
Reference Signs List
[0063] 10, 10a, 10b train; 11 train control device; 12,
12a, 12b forward monitoring device; 13 output device; 14
5 on-vehicle communication unit; 15 on-vehicle safety
device; 16 on-board antenna; 17 ATO device; 20 track; 21
ground safety device; 22 ground communication unit; 23
ground coil; 30 another train; 121 storage unit; 122,
122a, 122b train information acquisition unit; 123
10 braking distance calculation unit; 124, 124a, 124b
monitoring distance determination unit; 125 monitoring
unit; 126 obstacle determination unit; A braking
distance; B idle running distance; C decelerated running
distance; D marginal distance; X stop limit point; Y in15 station stop location; Z remaining running distance.

32
We Claim:
1. A forward monitoring device to be installed on a train,
the forward monitoring device comprising:
5 a storage unit to store map information and brake
performance information, the map information representing
location information and a track geometry of a track on
which the train is to run, the brake performance
information representing performance of a brake system
10 installed on the train;
a train information acquisition unit to acquire train
location information and train speed information of the
train;
a monitoring unit to monitor an upside of the track in
15 a travel direction of the train;
an obstacle determination unit to determine presence
or absence of an obstacle on the track based on a
monitoring result of the monitoring unit;
a braking distance calculation unit to calculate a
20 braking distance of the train using the map information,
the brake performance information, the train location
information, the train speed information, and a processing
time from when the monitoring unit performs monitoring
until the obstacle determination unit determines presence
25 or absence of an obstacle; and
a monitoring distance determination unit to determine
a monitoring distance based on the braking distance to set
a monitoring range of the monitoring unit.
30 2. The forward monitoring device according to claim 1,
wherein
the train information acquisition unit acquires a stop
limit point of the train from an on-vehicle safety device

33
installed on the train, and
the monitoring distance determination unit determines
the monitoring distance based on the braking distance and
on the stop limit point.
5
3. The forward monitoring device according to claim 2,
wherein
when a location represented by the stop limit point is
nearer to the train than a location represented by the
10 braking distance, the monitoring distance determination
unit determines that a distance from the train to the
location represented by the stop limit point is the
monitoring distance.
15 4. The forward monitoring device according to claim 1,
wherein
the train information acquisition unit acquires, from
an automatic train operation device installed on the train,
information of an in-station stop location of the train or
20 information of a remaining running distance representing a
distance to the in-station stop location, and
the monitoring distance determination unit determines
the monitoring distance of the monitoring unit based on the
braking distance and the in-station stop location or the
25 remaining running distance.
5. The forward monitoring device according to claim 4,
wherein
when a location represented by the in-station stop
30 location or the remaining running distance is nearer to the
train than a location represented by the braking distance,
the monitoring distance determination unit determines that
a distance from the train to the location represented by

34
the in-station stop location or the remaining running
distance is the monitoring distance.
6. The forward monitoring device according to any one of
5 claims 1 to 5, wherein
when the brake system is not an automatic brake system,
the braking distance calculation unit calculates the
braking distance with additional use of information of a
predetermined reaction time that elapses before an operator
10 of the train outputs a brake command to the brake system.
7. The forward monitoring device according to any one of
claims 1 to 6, wherein
the monitoring unit performs monitoring in the
15 monitoring range that has been set by the monitoring
distance determination unit.
8. The forward monitoring device according to any one of
claims 1 to 7, wherein
20 when the obstacle determination unit detects an object
that is regarded as a candidate for the obstacle in the
monitoring result and determines that a determination on
presence or absence of the obstacle based on multiple
monitoring results is required to be made, the obstacle
25 determination unit provides control to apply an initial
pressure to the brake system, or provides control to
inhibit power running.
9. The forward monitoring device according to any one of
30 claims 1 to 8, wherein
a speed of the train represented by the train speed
information is in a constant speed state or an accelerated
speed state at a time when the braking distance calculation

35
unit calculates the braking distance of the train.
10. A forward monitoring method in a forward monitoring
device to be installed on a train, the forward monitoring
5 method comprising:
a train information acquisition step of, by a train
information acquisition unit, acquiring train location
information and train speed information of the train;
a monitoring step of, by a monitoring unit, monitoring
10 an upside of a track in a travel direction of the train;
an obstacle determination step of, by an obstacle
determination unit, determining presence or absence of an
obstacle on the track based on a monitoring result of the
monitoring unit;
15 a braking distance calculation step of, by a braking
distance calculation unit, calculating a braking distance
of the train using map information, brake performance
information, the train location information, the train
speed information, and a processing time from when the
20 monitoring unit performs monitoring until the obstacle
determination unit determines presence or absence of an
obstacle, the map information representing location
information and a track geometry of the track on which the
train is to run, the brake performance information
25 representing performance of a brake system installed on the
train; and
a monitoring distance determination step of, by a
monitoring distance determination unit, determining a
monitoring distance based on the braking distance to set a
30 monitoring range of the monitoring unit.
11. The forward monitoring method according to claim 10,
wherein

36
in the train information acquisition step, the train
information acquisition unit acquires a stop limit point of
the train from an on-vehicle safety device installed on the
train, and
5 in the monitoring distance determination step, the
monitoring distance determination unit determines the
monitoring distance based on the braking distance and the
stop limit point.
10 12. The forward monitoring method according to claim 11,
wherein
in the monitoring distance determination step, when a
location represented by the stop limit point is nearer to
the train than a location represented by the braking
15 distance, the monitoring distance determination unit
determines that a distance from the train to the location
represented by the stop limit point is the monitoring
distance.
20 13. The forward monitoring method according to claim 10,
wherein
in the train information acquisition step, the train
information acquisition unit acquires, from an automatic
train operation device installed on the train, information
25 of an in-station stop location of the train, or information
of a remaining running distance representing a distance to
the in-station stop location, and
in the monitoring distance determination step, the
monitoring distance determination unit determines the
30 monitoring distance of the monitoring unit based on the
braking distance and the in-station stop location or the
remaining running distance.

37
14. The forward monitoring method according to claim 13,
wherein
in the monitoring distance determination step, when a
location represented by the in-station stop location or the
5 remaining running distance is nearer to the train than a
location represented by the braking distance, the
monitoring distance determination unit determines that a
distance from the train to the location represented by the
in-station stop location or the remaining running distance
10 is the monitoring distance.
15. The forward monitoring method according to any one of
claims 10 to 14, wherein
when the brake system is not an automatic brake system,
15 in the braking distance calculation step, the braking
distance calculation unit calculates the braking distance
with additional use of information of a predetermined
reaction time that elapses before an operator of the train
outputs a brake command to the brake system.
20
16. The forward monitoring method according to any one of
claims 10 to 15, wherein
in the monitoring step, the monitoring unit performs
monitoring in the monitoring range that has been set by the
25 monitoring distance determination unit.
17. The forward monitoring method according to any one of
claims 10 to 16, wherein
in the obstacle determination step, when the obstacle
30 determination unit detects an object that is regarded as a
candidate for the obstacle in the monitoring result and
determines that a determination on presence or absence of
the obstacle based on multiple monitoring results is

required to be made, the obstacle determination unit
provides control to apply an initial pressure to the brake
system, or provides control to inhibit power running.
18. The forward monitoring method according to any one of
claims 10 to 17, wherein
a speed of the train represented by the train speed
information is in a constant speed state or an accelerated
speed state at a time when the braking distance calculation
10 unit calculates the braking distance of the train in the
braking distance calculation step.