U.S. patent application number 17/270958 was filed with the patent office on 2021-10-21 for blade control device for work machinery.
This patent application is currently assigned to KABUSHIKI KAISHA KOBE SEIKO SHO (Kobe Steel, Ltd.). The applicant listed for this patent is KABUSHIKI KAISHA KOBE SEIKO SHO (Kobe Steel, Ltd.), KOBELCO CONSTRUCTION MACHINERY CO., LTD.. Invention is credited to Yusuke KAMIMURA, Satoshi MAEKAWA, Daisuke NODA, Toshiaki SAWAMURA, Naoki SUGANO.
Application Number | 20210324604 17/270958 |
Document ID | / |
Family ID | 1000005735330 |
Filed Date | 2021-10-21 |
United States Patent
Application |
20210324604 |
Kind Code |
A1 |
SAWAMURA; Toshiaki ; et
al. |
October 21, 2021 |
BLADE CONTROL DEVICE FOR WORK MACHINERY
Abstract
In a blade control device, a blade operation control part
outputs a command for raising and lowering a blade such that a
position deviation between a blade position calculated by a blade
position calculating part and a blade target position approaches
zero in a case where a blade load is equal to or less than a second
load threshold value, and outputs a command for raising the blade
in a case where the blade load is greater than the second load
threshold value. In a case where an update condition is satisfied,
the update condition being set in advance so as to associate the
blade load and a first load threshold value with each other, a
target position setting part updates the blade target position
using the blade position obtained when the update condition is
satisfied as a reference.
Inventors: |
SAWAMURA; Toshiaki;
(Kobe-shi, JP) ; MAEKAWA; Satoshi; (Kobe-shi,
JP) ; SUGANO; Naoki; (Kobe-shi, JP) ; NODA;
Daisuke; (Hiroshima, JP) ; KAMIMURA; Yusuke;
(Hiroshima, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA KOBE SEIKO SHO (Kobe Steel, Ltd.)
KOBELCO CONSTRUCTION MACHINERY CO., LTD. |
Kobe-shi
Hiroshima-shi |
|
JP
JP |
|
|
Assignee: |
KABUSHIKI KAISHA KOBE SEIKO SHO
(Kobe Steel, Ltd.)
Kobe-shi
JP
KOBELCO CONSTRUCTION MACHINERY CO., LTD.
Hiroshima-shi
JP
|
Family ID: |
1000005735330 |
Appl. No.: |
17/270958 |
Filed: |
August 7, 2019 |
PCT Filed: |
August 7, 2019 |
PCT NO: |
PCT/JP2019/031265 |
371 Date: |
February 24, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E02F 3/964 20130101;
E02F 3/844 20130101; E02F 9/262 20130101 |
International
Class: |
E02F 3/84 20060101
E02F003/84; E02F 9/26 20060101 E02F009/26 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2018 |
JP |
2018-162283 |
Claims
1. A blade control device which is provided in a work machine
including a machine body and a blade attached to the machine body
so as to be raised and lowered and which controls raising and
lowering operation of the blade, the blade control device
comprising: a target design surface setting part which sets a
target design surface that specifies a target shape of an object to
be dug by the blade; a position information acquiring part which
acquires position information related to the work machine; a blade
position calculating part which calculates a blade position as a
position of the blade on the basis of the position information
acquired by the position information acquiring part; a blade load
acquiring part which acquires a blade load as a load applied on the
blade; a storage part which stores a first load threshold value as
a threshold value of the blade load and a second load threshold
value which is a threshold value of the blade load and is greater
than the first load threshold value; a target position setting part
which sets a blade target position that is a position as a target
of the blade position and that is a position above the target
design surface; and a blade operation control part which outputs a
command for raising and lowering the blade such that a position
deviation as a deviation between the blade position calculated by
the blade position calculating part and the blade target position
approaches zero in a case where the blade load acquired by the
blade load acquiring part is equal to or less than the second load
threshold value, and outputs a command for raising the blade in a
case where the blade load acquired by the blade load acquiring part
is greater than the second load threshold value, wherein in a case
where an update condition is satisfied, the update condition being
set in advance so as to associate the blade load and the first load
threshold value with each other, the target position setting part
updates the blade target position using the blade position obtained
when the update condition is satisfied as a reference.
2. The blade control device according to claim 1, wherein the
update condition includes a condition that the blade load reaches
the first load threshold value, or a condition that the blade load
reaches a determination value for determining whether the blade
load has neared the first load threshold value or not, the
determination value being set on the basis of the first load
threshold value.
3. The blade control device according to claim 1, wherein the
storage part is configured to store a first state indicating
allowance of update of the blade target position when the blade
load becomes greater than a flag threshold value as a threshold
value set in advance, and also store a second state indicating
non-allowance of update of the blade target position in place of
the first state when the blade target position is updated, and the
update condition includes a condition that the blade load reaches
the first load threshold value when the first state is stored in
the storage part, or a condition that the blade load reaches a
determination value when the first state is stored in the storage
part, the determination value being set on the basis of the first
load threshold value for determining whether the blade load has
neared the first load threshold value or not.
4. The blade control device according to claim 1, wherein the blade
target position to be updated by the target position setting part
is set at a position which passes the blade position when the
update condition is satisfied and is on a plane parallel to the
target design surface.
5. The blade control device according to claim 1, wherein the
storage part stores a target track as a target for an increase
process of the blade load when the blade load approaches the first
load threshold value while being increased, and the blade operation
control part outputs a command for raising and lowering the blade
such that the blade load approaches the first load threshold value
while following an increase process close to the target track
before the blade target position is set by the target position
setting part.
6. The blade control device according to claim 1, further
comprising: a load threshold value setting part which sets the
first load threshold value, wherein the position information
acquiring part includes a vehicle body position acquiring part
which acquires a vehicle body position as a position of the machine
body, and the load threshold value setting part updates the first
load threshold value such that the first load threshold value
becomes smaller when a body distance is a second distance than when
the body distance is a first distance, the body distance being a
distance between the vehicle body position acquired by the vehicle
body position acquiring part and the target design surface, the
second distance being smaller than the first distance.
7. The blade control device according to claim 1, wherein the blade
operation control part outputs the command on the basis of a
function having a term including, as a variable, a position
deviation which is an elevation difference between the blade
position and the blade target position and including a position
gain by which the position deviation is multiplied, the blade
control device further comprising: a position gain setting part
which sets the position gain, in a case where the blade position is
below the blade target position, the position gain setting part
updates the position gain such that a raising speed of the blade is
increased on the basis of the position deviation.
8. The blade control device according to claim 7, wherein the
function further has a term including, as a variable, a load
deviation which is a deviation obtained by subtracting the second
load threshold value from the blade load and including a load gain
by which the load deviation is multiplied, the blade control device
further comprising: a load gain setting part which sets the load
gain, in a case where the blade load is greater than the second
load threshold value, the load gain setting part updates the load
gain such that the raising speed of the blade is increased on the
basis of the load deviation.
Description
TECHNICAL FIELD
[0001] The present invention relates to a blade control device
provided in a work machine including a blade.
BACKGROUND ART
[0002] Conventionally, a work machine including a blade for use in
digging of the ground, land grading, transport of sediments, and
the like has been used widely. Patent Literature 1 discloses a load
control device for a bulldozer, the load control device
automatically controlling raising and lowering operation of a blade
such that a blade load applied on the blade becomes substantially
constant. The load control device recited in Patent Literature 1,
however, has a problem of waviness of an execution surface
generated due to raising and lowering operation of a blade.
[0003] Patent Literature 2 discloses a blade control device
intended to cope with the above-described problem of Patent
Literature 1. Patent Literature 2 discloses that the blade is
controlled so as not to be closer to the designed surface than the
virtual designed surface is, and can be inhibited from being
greatly lowered, and discloses that continuous undulations can be
thereby inhibited from being formed on the digging surface. In the
blade control device recited in Patent Literature 2, in a case
where a blade load is smaller than a first set load value, the
blade is lowered and in a case where the blade load is greater than
a second set load value which is greater than the first set load
value, the blade is raised. In other words, in the blade control
device recited in Patent Literature 2, raising and lowering
operation of the blade is controlled on the basis of comparison
between the blade load and the first set load value and the second
set load value.
[0004] Since in such blade control device recited in Patent
Literature 2 as described above, when the blade is above the
virtual design surface, raising and lowering operation of the blade
is controlled on the basis of a blade load but not on the basis of
a blade position, waviness of an execution surface greatly depends
on an increase and a decrease of the blade load. In the blade
control device of Patent Literature 2, therefore, an effect of
suppressing waviness of the execution surface is limitative and
cannot be always considered sufficient.
CITATION LIST
Patent Literature
[0005] Patent Literature 1: JP 3537182 B
[0006] Patent Literature 2: JP 5285805 B
SUMMARY OF INVENTION
[0007] An object of the present invention is to provide a blade
control device which is provided in a work machine including a
blade and controls raising and lowering operation of the blade, the
blade control device being capable of effectively suppressing
waviness of an execution surface.
[0008] There is provided a blade control device which is provided
in a work machine including a machine body and a blade attached to
the machine body so as to be raised and lowered and which controls
raising and lowering operation of the blade. The blade control
device includes a target design surface setting part which sets a
target design surface that specifies a target shape of an object to
be dug by the blade; a position information acquiring part which
acquires position information related to the work machine; a blade
position calculating part which calculates a blade position as a
position of the blade in a global coordinate system on the basis of
the position information acquired by the position information
acquiring part; a blade load acquiring part which acquires a blade
load as a load applied on the blade; a storage part which stores a
first load threshold value as a threshold value of the blade load
and a second load threshold value which is a threshold value of the
blade load and is greater than the first load threshold value; a
target position setting part which sets a blade target position
that is a position as a target of the blade position and that is a
position above the target design surface; and a blade operation
control part which outputs a command for raising and lowering the
blade such that a position deviation as a deviation between the
blade position calculated by the blade position calculating part
and the blade target position approaches zero in a case where the
blade load acquired by the blade load acquiring part is equal to or
less than the second load threshold value, and outputs a command
for raising the blade in a case where the blade load acquired by
the blade load acquiring part is greater than the second load
threshold value, in which in a case where an update condition is
satisfied, the update condition being set in advance so as to
associate the blade load and the first load threshold value with
each other, the target position setting part updates the blade
target position using the blade position obtained when the update
condition is satisfied as a reference.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a side view showing a hydraulic excavator as an
example of a work machine in which a blade control device according
to an embodiment of the present invention is provided.
[0010] FIG. 2 is a block diagram showing a main function of the
blade control device.
[0011] FIG. 3 is a graph showing a relationship among a blade
position, a blade target position, and raising and lowering
operation of the blade in the blade control device.
[0012] FIG. 4 is a graph showing a relationship among a blade load,
a first load threshold value, a second load threshold value, and
the raising and lowering operation of the blade in the blade
control device.
[0013] FIG. 5 is a flowchart showing one example of control
operation to be executed by a controller included in the blade
control device.
[0014] FIG. 6 is a graph showing a target track (target path) of a
blade load and a change of an actual blade load in the blade
control device.
[0015] FIG. 7 is one example of a time chart for explaining the
blade target position to be updated on the basis of a blade load in
the blade control device.
[0016] FIG. 8 is another example of a time chart for explaining the
blade target position to be updated on the basis of a blade load in
the blade control device.
[0017] FIG. 9 is a schematic view for explaining updating of the
first load threshold value on the basis of a distance between a
vehicle body position of a machine body and a target design surface
in the blade control device.
[0018] FIG. 10 is a graph for explaining updating of the first load
threshold value on the basis of a distance between the vehicle body
position of the machine body and the target design surface in the
blade control device.
[0019] FIG. 11 is a graph for explaining updating of a position
gain on the basis of a deviation between the blade position and the
blade target position in the blade control device.
[0020] FIG. 12 is a graph for explaining updating of a load gain on
the basis of a deviation between a blade load and a second load
threshold value in the blade control device.
[0021] FIG. 13 is a schematic view in which an execution surface
executed by the work machine provided with the blade control device
and an execution surface executed by a conventional work machine
are compared.
DESCRIPTION OF EMBODIMENTS
[0022] A preferred embodiment of the present invention will be
described with reference to the drawings.
[0023] [Overall Structure of Work Machine]
[0024] FIG. 1 is a side view showing a hydraulic excavator 1 as an
example of a work machine in which a blade control device according
to an embodiment of the present invention is provided. The
hydraulic excavator 1 includes a travelling device 2 (lower
travelling body) capable of travelling on the ground G, a vehicle
body 3 (upper slewing body) mounted on the travelling device 2, a
work device mounted on the vehicle body 3, and a blade 4 mounted on
the travelling device 2 or the vehicle body 3. The travelling
device 2 and the vehicle body 3 constitute a machine body of the
work machine. The vehicle body 3 has a slewing frame, an engine, a
driver's room, and the like.
[0025] The work device mounted on the vehicle body 3 includes a
boom 5, an arm 6, and a bucket 7. The boom 5 has a base end portion
supported at a front end of the slewing frame so as to go up and
down, i.e., to be turnable around a horizontal axis, and a distal
end portion on the opposite side. The arm 6 has a base end portion
attached to the distal end portion of the boom 5 so as to be
turnable around the horizontal axis, and a distal end portion on
the opposite side. The bucket 7 is turnably attached to the distal
end portion of the arm 6.
[0026] The hydraulic excavator 1 has a boom cylinder, an arm
cylinder, and a bucket cylinder provided for the boom 5, the arm 6,
and the bucket 7, respectively. The boom cylinder is interposed
between the vehicle body 3 and the boom 5 and extends and contracts
so as to cause the boom 5 to conduct up-down operation. The arm
cylinder is interposed between the boom 5 and the arm 6 and extends
and contracts so as to cause the arm 6 to conduct turning
operation. The bucket cylinder is interposed between the arm 6 and
the bucket 7 and extends and contracts so as to cause the bucket 7
to conduct turning operation.
[0027] The blade 4 mounted on the travelling device 2 or the
vehicle body 3 is provided for conducting digging of the ground,
land grading, transport of sediments, and the like. Specifically,
the blade 4 is supported by a lift frame 4a, and the lift frame 4a
is supported to be turnable around a horizontal axis 4b with
respect to the travelling device 2. Accordingly, the blade 4 can be
displaced in an up-down direction with respect to the travelling
device 2.
[0028] The hydraulic excavator 1 has a lift cylinder 8 provided for
the blade 4. The lift cylinder 8 has a head chamber 8h and a rod
chamber 8r (see FIG. 1), and extends to thereby cause the blade 4
to move in a down direction when a hydraulic oil is supplied to the
head chamber 8h, as well as discharging the hydraulic oil in the
rod chamber 8r, and also contracts to thereby cause the blade 4 to
move in an up direction when the hydraulic oil is supplied to the
rod chamber 8r, as well as discharging the hydraulic oil in the
head chamber 8h.
[0029] The hydraulic excavator 1 has a hydraulic circuit not shown.
The hydraulic circuit includes the boom cylinder, the arm cylinder,
the bucket cylinder, and the lift cylinder 8. The hydraulic circuit
further includes a hydraulic pump 9 (see FIG. 1), a lift cylinder
control proportional valve 41 (see FIG. 2), and a lift cylinder
flow rate control valve not shown.
[0030] [Blade Control Device]
[0031] FIG. 2 is a block diagram showing a main function of a blade
control device 100. The blade control device 100 is provided for
controlling raising and lowering operation of the blade 4. The
blade control device 100 includes a controller 10 (mechatronic
controller), a position information acquiring part, a blade load
acquiring part 34, an automatic control switch 35, and a travelling
lever 36 for manipulating the travelling device 2. The controller
10, which is configured with, for example, a microcomputer,
controls operation of each element included in the hydraulic
circuit.
[0032] The position information acquiring part is configured to
acquire position information about the hydraulic excavator 1.
Specifically, in the present embodiment, the position information
acquiring part includes a vehicle body position acquiring part 31,
a vehicle body angle acquiring part 32, and a blade angle acquiring
part 33. The vehicle body position acquiring part 31 is configured
to acquire a vehicle body position as a position of the machine
body. The vehicle body position acquiring part 31 is configured
with, for example, a receiver, such as a GNSS receiver (GNSS
sensor), capable of receiving satellite data (positioning signal)
from a satellite measurement system, such as GNSS (Global
Navigation Satellite System), and receives GNSS data indicative of
a position of the machine body in a global coordinate system. The
global coordinate system is a three-dimensional coordinate system
using an origin point defined on the earth as a reference, which is
a coordinate system indicating an absolute position defined by the
satellite measurement system.
[0033] The vehicle body angle acquiring part 32 is configured to
acquire an angle of the machine body. The vehicle body angle
acquiring part 32 is configured with, for example, a vehicle body
angle sensor which detects an angle of the machine body (an angle
of the vehicle body 3 in the present embodiment) in a global
coordinate system. Specifically, the vehicle body angle sensor may
be configured with, for example, one or a plurality of receivers
provided in the machine body and capable of receiving satellite
data (positioning signal) from a satellite measurement system.
[0034] The blade angle acquiring part 33 is configured to acquire
an angle of the blade 4. The blade angle acquiring part 33 is
configured with, for example, a blade angle sensor which detects
the angle of the blade 4 in a global coordinate system.
Specifically, the blade angle sensor may be configured with, for
example, one or a plurality of receivers provided in the machine
body and capable of receiving satellite data (positioning signal)
from a satellite measurement system.
[0035] A local coordinate system may be used in place of the global
coordinate system. Both the global coordinate system and the local
coordinate system may be used together. Examples of the local
coordinate system include a three-dimensional coordinate system
using the vehicle body position as a reference and a
three-dimensional coordinate system using a specific position at a
work site as a reference. In the above case, the vehicle body angle
sensor may be configured with, for example, an inertia measurement
device, or may be configured with, for example, the inertia
measurement device and the receiver capable of receiving the
satellite data. The inertia measurement device may be configured to
be capable of, for example, measuring an acceleration and an
angular velocity of the vehicle body 3, and detecting an
inclination (e.g., a pitch indicative of rotation with respect to
an X-axis, a yaw indicative of rotation with respect to a Y-axis,
and a roll indicative of rotation with respect to a Z-axis) of the
vehicle body 3 on the basis of a measurement result. The blade
angle sensor may be configured with, for example, a stroke sensor
which detects a cylinder stroke of the blade cylinder 8, or may be
configured with the stroke sensor and the receiver capable of
receiving the satellite data.
[0036] Although, in the present embodiment, the vehicle body
position acquiring part 31 and the vehicle body angle acquiring
part 32 are attached to an upper portion of the vehicle body 3 and
the blade angle acquiring part 33 is attached to an upper portion
of the blade 4 as shown in FIG. 1, the attachment positions are not
limited to the specific example shown in FIG. 1. Detection signals
as electrical signals generated by these acquiring parts 31, 32,
and 33 are input to the controller 10.
[0037] In the present embodiment, the blade load acquiring part 34
is configured to acquire a blade load as a load applied on the
blade 4 during digging work. The blade load corresponds to, for
example, a pump pressure of the hydraulic pump 9 which drives the
blade 4. Accordingly, the blade load acquiring part 34 is capable
of detecting the blade load by detecting the pump pressure. In the
present embodiment, the blade load acquiring part 34 includes a
head pressure sensor 3411 which detects a head pressure P1 as a
pressure of a hydraulic oil in the head chamber 8h of the lift
cylinder 8, and a rod pressure sensor 34R which detects a rod
pressure P2 as a pressure of a hydraulic oil in the rod chamber 8r
of the lift cylinder 8. The sensors 34H and 34R respectively
convert their detected physical quantities into detection signals
as electrical signals corresponding to the physical quantities and
input the detection signals to the controller 10.
[0038] The automatic control switch 35 is arranged in the driver's
room and is electrically connected to the controller 10. Upon
receiving manipulation for switching a control mode of the
controller 10 from a manual manipulation mode to an automatic
control mode, the automatic control switch 35 inputs a mode command
signal related to the manipulation to the controller 10. The
controller 10 switches setting of the control mode from the manual
manipulation mode to the automatic control mode by the mode command
signal input from the automatic control switch 35.
[0039] In the automatic control mode, the controller 10 is
configured to automatically control operation of the lift cylinder
8 such that an execution surface to be executed by the blade 4
approaches a target design surface set in advance. When a command
value (command current) to the lift cylinder control proportional
valve 41 for controlling operation of the lift cylinder 8 is output
from the controller 10, a secondary pressure of the proportional
valve 41 changes according to the command value and opening of the
lift cylinder flow rate control valve changes according to the
secondary pressure. As a result, a supply flow and a supply
direction of a hydraulic oil to be supplied from the hydraulic pump
9 to the lift cylinder 8 via the lift cylinder flow rate control
valve change to control an operation speed and a driving direction
of the lift cylinder 8. On the other hand, in the manual
manipulation mode, when a worker manipulates the travelling lever
36, a manipulation signal of the manipulation is input to the
controller 10, and the command value to the lift cylinder control
proportional valve 41 or a command value to the lift cylinder flow
rate control valve is output from the controller 10 according to an
amount of manipulation of a manipulation lever not shown for
manipulating raising and lowering of the blade 4.
[0040] The controller 10 has a target design surface setting part
11, a blade position calculating part 12, a storage part 13, a
target position setting part 14, a blade operation control part 15,
a load threshold value setting part 16, a position gain setting
part 17, a load gain setting part 18, and a distance calculating
part 19 as a function for executing the automatic control.
[0041] The target design surface setting part 11 sets a target
design surface (see FIG. 9) which specifies a target shape of an
object to be dug by the blade 4. The target design surface setting
part 11 may store a design surface input by a target design surface
input part provided in the driver's room and set the design surface
as a target design surface. The target design surface setting part
11 may also store data of a design surface acquired via various
kinds of storage media, a communication network, or the like and
set the design surface as a target design surface. The target
design surface setting part 11 inputs the set target design surface
to the target position setting part 14. The target design surface
is a surface which specifies a three-dimensional design topography
as a target shape of the ground which is an object to be dug. The
target design surface may be specified by external data such as BIM
or CIM (Building/Construction Information Modeling, Management).
The target design surface may be set using a position of the work
machine as a reference.
[0042] The blade position calculating part 12 calculates a blade
position x as a position of the blade 4 in the global coordinate
system on the basis of the position information acquired by the
position information acquiring part. In the present embodiment, the
blade position calculating part 12 calculates the blade position x
on the basis of the vehicle body position acquired by the vehicle
body position acquiring part 31, the angle of the machine body
acquired by the vehicle body angle acquiring part 32, and the angle
of the blade 4 acquired by the blade angle acquiring part 33. In
other words, the blade position x is calculated from a sum of a
vector from a reference point to the vehicle body position and a
vector from the vehicle body position to the blade position.
Although in the present embodiment, a blade position x is thus
calculated from a relative angle between the angle of the machine
body and the angle of the blade 4 in the global coordinate system,
a calculation method for the blade position x is not limited
thereto. The blade position x may be calculated on the basis of,
for example, a length of the lift cylinder 8, or may be calculated
on the basis of GNSS data received by a GNSS receiver (GNSS sensor)
attached to the blade 4.
[0043] Although in the present embodiment, the blade position x is
set at a blade edge position (a position of a lower edge of a
distal end of the blade 4) as the distal end of the blade 4, the
blade position may be set at other part of the blade 4.
[0044] The storage part 13 stores a first load threshold value f1
as a threshold value of the blade load f and a second load
threshold value 12 which is a threshold value of the blade load f
and is greater than the first load threshold value f1. The first
load threshold value f1 is set to be a value corresponding to a
proper blade load f with which the hydraulic excavator 1 can stably
travel. The second load threshold value 12 is a value set to
prevent occurrence of such a situation that the blade load f
becomes excessively large to cause a stuck state. In other words,
the second load threshold value 12 is a value set to realize stable
and efficient digging operation. These load threshold values f1 and
12 may be manually input to the controller 10 by a worker before
the digging work or appropriately calculated by the controller 10
and stored during the digging work.
[0045] The storage part 13 also stores an update condition set in
advance. The update condition is a condition set in advance in
which the blade load f and the first load threshold value are
associated with each other and which is used as a reference for
determining whether the target position setting part 14 should
update the blade target position xref or not. The update condition
includes a condition that the blade load f approaches the first
load threshold value f1 and a deviation therebetween becomes
sufficiently small. In the present embodiment, the update condition
includes a condition that the blade load f reaches the first load
threshold value f1, or a condition that the blade load f reaches a
determination value which is set on the basis of the first load
threshold value f1 for determining whether the blade load f has
neared the first load threshold value f1. The determination value
is a value by which determination is possible that a deviation
(f-f1) obtained by subtracting the first load threshold value f1
from the blade load f becomes sufficiently small. The determination
value is a threshold value set in advance through simulation,
experiment, or the like.
[0046] The storage part 13 also stores a target track (see FIG. 6
to be described later). The target track is a target for an
increase process of the blade load f when the blade load f
approaches the first load threshold value 11 while being increased.
The target track is set in advance for controlling the raising and
lowering operation of the blade 4 such that in a case where the
blade target position xref is not set at the start of the digging
work when the automatic control mode is selected, the blade load f
is increased up to the first load threshold value f1 while
following a preferable increase process.
[0047] The target position setting part 14 sets the blade target
position xref which is a position as a target for the blade
position x and is a position above the target design surface. The
target position setting part 14 sets the blade target position xref
on the basis of, for example, the blade load f and the blade
position x.
[0048] The load threshold value setting part 16 sets the first load
threshold value f1. The position gain setting part 17 sets the
position gain kx. The load gain setting part 18 sets the load gain
kf. These load threshold value setting part 16, position gain
setting part 17, and load gain setting part 18 will be detailed
later.
[0049] The blade operation control part 15 calculates and outputs a
command value to the lift cylinder control proportional valve 41
for controlling operation of the lift cylinder 8. Specifically, the
operation is conducted in the following manner.
[0050] FIG. 3 is a graph showing a relationship among the blade
position x, the blade target position xref, and the raising and
lowering operation of the blade 4 in the blade control device 100.
The blade operation control part 15 calculates and outputs a
command (command value) for raising and lowering the blade 4 such
that a position deviation .DELTA.x approaches zero, the position
deviation .DELTA.x being a deviation between the blade position x
calculated by the blade position calculating part 12 and the blade
target position xref.
[0051] Control of the blade position x is feedback control in which
an amount of control is changed according to an amount of the
position deviation .DELTA.x which is a deviation between the blade
position x and the blade target position xref. Specifically, the
blade operation control part 15 calculates and outputs the command
on the basis of a function having a term including, as a variable,
the position deviation .DELTA.x which is an elevation difference
between the blade position x and the blade target position xref and
including the position gain kx by which the position deviation
.DELTA.x is multiplied. In FIG. 3, the blade target position xref
is at a position corresponding to an origin point on a lateral axis
in the graph and is given a hysteresis for suppressing hunting. In
other words, in a case where the blade position x is included in a
predetermined range (e.g. a range of the blade target position
xref.+-.a as shown in FIG. 3) with respect to the blade target
position xref as a reference, the blade operation control part 15
refrains from controlling the blade position x.
[0052] FIG. 4 is a graph showing a relationship among the blade
load f, the first load threshold value f1, the second load
threshold value f2, and the raising and lowering operation of the
blade 4 in the blade control device 100. As shown in FIG. 4, in a
case where the blade load f acquired by the blade load acquiring
part 34 is greater than the second load threshold value 12, the
blade operation control part 15 calculates and outputs a command
(command value) for raising the blade 4. Specifically, the blade
operation control part 15 calculates and outputs the command on the
basis of, for example, a function having a term including, as a
variable, a load deviation .DELTA.f which is a deviation (f-f2)
obtained by subtracting the second load threshold value f2 from the
blade load f and including the load gain kf by which the load
deviation .DELTA.f is multiplied.
[0053] In the present embodiment, such position control of the
blade 4 as shown in FIG. 3 is given priority. Meanwhile, in a case
where the blade load f is greater than the second load threshold
value 12, the blade position is controlled so as to quickly raise
the blade 4. Such control as gives priority to the position control
enables stable and efficient digging operation while suppressing
waviness of an execution surface.
[0054] Next, description will be made of control operation
conducted by the controller 10 for the driving of the blade 4 in
the automatic control mode with reference to the flowchart of FIG.
5.
[0055] The controller 10 determines whether the automatic control
switch 35 is on or not, i.e., the automatic control mode is
selected or not (Step S1). In a case where the automatic control
mode is not selected (NO in Step S1), the controller 10 finishes
the processing without conducting control of the automatic control
mode.
[0056] In a case where the automatic control mode is selected (YES
in Step S1), the controller 10 takes in a signal to be input to the
controller 10, to be specific, a detection signal of each sensor
and designation signals (Step S2). The designation signals include
a signal for a target design surface designated by manipulation of
the target design surface input part by an operator, a signal for a
blade load f acquired by the blade load acquiring part 34, a signal
for the vehicle body position acquired by the vehicle body position
acquiring part 31, a signal for an angle of the machine body
acquired by the vehicle body angle acquiring part 32, a signal for
an angle of the blade 4 acquired by the blade angle acquiring part
33, a signal for a travelling speed corresponding to manipulation
received by the travelling lever 36, and the like. The controller
10 acquires an initial state of the hydraulic excavator 1 on the
basis of these designation signals. The target design surface
setting part 11 of the controller 10 sets a target design surface
on the basis of the signal for the target design surface.
[0057] Next, the controller 10 determines whether the blade target
position xref is set or not (Step S3). In a case where the blade
target position xref is not set (NO in Step S3), the blade
operation control part 15 outputs a command for raising and
lowering the blade 4 such that the blade load f approaches the
first load threshold value f1 while following an increase process
close to the target track (Step S4). Although setting of the target
track is not essential in the blade control device of the present
invention, setting the target track and controlling the blade
position x on the basis of the target track as in the present
embodiment has the following merits. Specifically, the merits are
as follows.
[0058] FIG. 6 is a graph showing a target track (target path) of
the blade load f and a change of an actual blade load f in the
blade control device 100. In FIG. 6, a curved line indicated by a
chain line represents the target track (target path) and a curved
line indicated by a solid line represents a change of an actual
blade load f.
[0059] In a case where such a target track as shown in FIG. 6 is
not set, when the digging work is started at a stage prior to
setting of the blade target position xref, the blade 4 enters into
the ground at a high lowering speed in some cases, so that a depth
of entering of the blade 4 into the ground when the blade load f
reaches the first load threshold value f1 is likely to be
increased. In such a case, an amount of soil on the blade 4 might
change greatly with respect to a travel distance of the hydraulic
excavator 1 and the blade load f might also change greatly in some
cases.
[0060] On the other hand, in a case where the target track shown in
FIG. 6 is set as in the present embodiment, since at a stage prior
to setting of the blade target position xref, the blade load f
approaches the first load threshold value f1 while following an
increase process close to the target track, the blade 4 enters the
ground at a moderate lowering speed, resulting in suppressing an
increase in a depth of entering of the blade 4 into the ground when
the blade load f reaches the first load threshold value f1. This
causes an amount of soil on the blade 4 to change little with
respect to a travel distance of the hydraulic excavator 1 and
causes the blade load f to also change little. As a result, an
effect of suppressing waviness of an execution surface can be
further enhanced. Any target track (target path) can be used that
enables the blade load f to be controlled such that the blade load
f gradually approaches the first load threshold value f1 as
described above, and a target track is not specifically limited.
The target track (target path) may be provided by a function
representing, for example, a curved line path which is indicated by
a chain line in FIG. 6 and in which the blade load f gradually
approaches the first load threshold value f1. The target track
(target path) may be also provided by a function representing a
straight path (linear function), and may be further provided by a
function representing a combination of a curved line path and a
straight path.
[0061] Then, in the present embodiment, when the condition is
satisfied, the condition being that the blade load f approaches the
first load threshold value f1 while following the increase process
close to the target track and the load deviation as a deviation
therebetween becomes sufficiently small, the target position
setting part 14 sets the blade target position xref. In the present
embodiment, the condition is that the blade load f reaches the
first load threshold value f1, more specifically, that the load
deviation which is the deviation (f-f1) of these loads becomes a
positive value from a negative value. In the present embodiment,
the blade target position xref set by the target position setting
part 14 is set at a position passing the blade position x when the
condition is satisfied, the position being on a plane parallel to
the target design surface. After the blade target position xref is
set, the blade operation control part 15 controls the raising and
lowering operation of the blade 4 such that the position deviation
.DELTA.x between the blade position x and the blade target position
xref approaches zero.
[0062] Next, the controller 10 compares the blade load f acquired
by the blade load acquiring part 34 and a flag threshold value as a
threshold value set in advance (Step S5). In the present
embodiment, although the flag threshold value is the same as the
second load threshold value 12, the flag threshold value is not
limited thereto and may be different from the second load threshold
value f2. The flag threshold value, however, should be set to be
any value greater than the first load threshold value f1.
[0063] In a case where the blade load f is greater than the second
load threshold value f2 (flag threshold value) (f>12, NO in Step
S5), the storage part 13 stores a first state (an update flag=1)
indicating allowance of update of the blade target position xref
(Step S6). On the other hand, in a case where the blade load f is
equal to or less than the second load threshold value f2 (flag
threshold value) (f.ltoreq.f2, YES in Step S5), storage of the
update flag is not changed.
[0064] Next, the controller 10 determines whether a condition
(update condition) is satisfied or not, the condition including
that the first state is stored in the storage part 13 (the update
flag=1) and that the blade load f reaches the first load threshold
value f1 (Step S7). Specifically, in the present embodiment, the
controller 10 determines whether an update condition is satisfied
or not, the update condition including a first condition that the
first state is stored in the storage part 13 (the update flag=1), a
second condition that the blade load f acquired this time by the
blade load acquiring part 34 is greater than the first load
threshold value f1 (f>f1), and a third condition that the blade
load f acquired last time by the blade load acquiring part 34 is
smaller than the first load threshold value f1 (f<f1) (Step
S7).
[0065] In a case where the update condition is satisfied (YES in
Step S7), the target position setting part 14 updates the blade
target position xref (Step S8). In the present embodiment, the
blade target position xref to be updated by the target position
setting part 14 is set at a position passing the blade position x
when the update condition is satisfied, the position being on the
plane parallel to the target design surface. When the blade target
position xref is updated, the storage part 13 stores a second state
(the update flag=0) indicating non-allowance of update of the blade
target position xref in place of the first state (Step S8).
[0066] The processing of Steps S5 to S8 will be specifically
described with reference to FIG. 7. FIG. 7 is one example of a time
chart for explaining the blade target position xref to be updated
on the basis of the blade load f in the blade control device
100.
[0067] At times t1 and t2 shown in FIG. 7, the second condition and
the third condition included in the update condition are satisfied.
However, since at times t1 and t2, the storage part 13 stores the
second state (the update flag=0) indicating non-allowance of update
of the blade target position xref, the first condition included in
the update condition is not satisfied. Accordingly, since at the
times t1 and t2, the update condition is not satisfied (NO in Step
S7), the target position setting part 14 refrains from updating the
blade target position xref.
[0068] On the other hand, since at time t3 shown in FIG. 7, the
blade load f becomes greater than the second load threshold value
12 (flag threshold value) and the storage part 13 stores the first
state (the update flag=1) (Step S6), all conditions included in the
update condition are satisfied (YES in Step S7) at time t4.
Accordingly, at time t4, the target position setting part 14
updates the blade target position xref.
[0069] Update of the blade target position xref is not limited to
the mode shown in FIG. 7. FIG. 8 is another example of a time chart
for explaining the blade target position xref to be updated on the
basis of the blade load f. In the mode shown in FIG. 8, the update
condition does not include the first condition and includes the
second condition and the third condition among the first condition,
the second condition, and the third condition. In the mode shown in
FIG. 8, at time when the update condition is satisfied, i.e., at
times t1, t2, and t4 when the second condition and the third
condition are satisfied, the target position setting part 14
updates the blade target position xref.
[0070] In the mode shown in FIG. 7, since while when the update
flag for the blade target position xref is in the first state (the
update flag=1), update of the blade target position xref is
allowed, when the update flag is in the second state (the update
flag=0), update of the blade target position xref is not allowed,
frequent update of the blade target position xref can be
suppressed.
[0071] Next, the blade operation control part 15 calculates a
command value to the lift cylinder control proportional valve 41
for controlling operation of the lift cylinder 8 (Step S9). The
blade operation control part 15 determines whether the command
value is equal to or less than an upper limit value set in advance
or not (Step S10). In a case where the command value is equal to or
less than the upper limit value set in advance (YES in Step S10),
the blade operation control part 15 outputs the command value and
the output command value is input to the proportional valve 41 (see
FIG. 2), so that the control is applied (Step S12). On the other
hand, in a case where the command value is greater than the upper
limit value set in advance (NO in Step S10), using a command value
cut off to the upper limit value as a command value (Step S11), the
blade operation control part 15 outputs the cut off command value
and the output command value is input to the proportional valve 41
(see FIG. 2), so that the control is applied (Step S12).
[0072] In the present embodiment, the command value to be
calculated by the blade operation control part 15 in Step S9 is
calculated on the basis of, for example, a function represented by
Formula (1) below.
Command
value=k.times.(.DELTA.x).times..DELTA.x+kf(.DELTA.f).times..DELT-
A.f (1)
[0073] The function represented by the above Formula (1) has a term
including, as a variable, a position deviation .DELTA.x as an
elevation difference between the blade position x and the blade
target position xref and also including a position gain kx by which
the position deviation .DELTA.x is multiplied, and a term
including, as a variable, a load deviation .DELTA.f which is a
deviation (f-f2) obtained by subtracting the second load threshold
value f2 from the blade load f and also including a load gain kf by
which the load deviation is multiplied.
[0074] FIG. 9 is a schematic view for explaining updating of the
first load threshold value f1 on the basis of a distance between a
vehicle body position of the machine body and a target design
surface in the blade control device 100, and FIG. 10 is a graph for
explaining the updating.
[0075] As shown in FIG. 9 and FIG. 10, the load threshold value
setting part 16 is configured to update the first load threshold
value f1 such that the first load threshold value f1 becomes
smaller when a body distance Z is a second distance Z2 than when
the body distance Z is a first distance Z1, the body distance Z
being a distance between the vehicle body position acquired by the
vehicle body position acquiring part 31 and the target design
surface, the second distance Z2 being smaller than the first
distance Z1. The distance calculating part 19 calculates the body
distance Z on the basis of the target design surface and the
vehicle body position.
[0076] In such present embodiment as described above, the blade
load f is more liable to reach the first load threshold value f1 in
a case where the body distance Z is the second distance Z2 (i.e.,
in a case where the machine body is close to the target design
surface) as compared with a case where the body distance Z is the
first distance Z1 (i.e., in a case where the machine body is away
from the target design surface). In the specific example of FIG. 9,
since the second distance Z2 is smaller than the first distance Z1,
a distance .DELTA.Z2 between the vehicle body position and the
blade target position xref in the former case is smaller than a
distance .DELTA.71 between the vehicle body position and the blade
target position xref in the latter case. This mode increases the
update frequency of the blade target position xref and increases a
possibility that the blade target position xref is set at a more
proper position corresponding to a state of the ground as a digging
target.
[0077] Specific examples of the present mode include the following.
For example, the first load threshold value f1 at the time of
execution of grading operation at a final stage of work by the
hydraulic excavator 1 is set to be a value smaller than the first
load threshold value f1 at the time of execution of digging
operation at an initial stage or an intermediate stage of the work.
In such a case, it is possible to execute, by using the same
control algorithm, both the digging operation in which more
importance is applied to quick digging work than in grading
operation, and the grading operation in which much importance is
applied to precision in causing an execution surface to approach a
target design surface.
[0078] In the present embodiment, the load threshold value setting
part 16 updates the first load threshold value f1 such that the
first load threshold value f1 becomes smaller as the body distance
Z becomes smaller in a part of the entire range of the body
distance Z, the part including the first distance Z1 and the second
distance Z2 as shown in FIG. 10. Then, the load threshold value
setting part 16 refrains from updating the first load threshold
value f1 in a range where the body distance Z is greater than the
part of the range and in a range where the body distance Z is
smaller than the part of the range. Update of the first load
threshold value f1 is, however, not limited to the specific example
shown in FIG. 10.
[0079] FIG. 11 is a graph for explaining updating of the position
gain kx on the basis of the position deviation .DELTA.x as a
deviation (x-xref) between the blade position x and the blade
target position xref in the blade control device 100.
[0080] As shown in FIG. 11, in a case where the blade position x is
below the blade target position xref, the position gain setting
part 17 updates the position gain kx such that a raising speed of
the blade 4 is increased on the basis of the position deviation
.DELTA.x. In this mode, since in a case where the blade position x
is below the blade target position xref, the raising speed of the
blade 4 is increased, an effect of suppressing digging of the
ground as a digging target to a position below the blade target
position xref is further enhanced, resulting in further enhancing
an effect of suppressing digging of the ground to a position below
a target design surface.
[0081] Additionally, in a case where the blade load f is greater
than the second load threshold value f2 (YES in Step S5), the blade
operation control part 15 outputs a command value for raising the
blade 4. FIG. 12 is a graph for explaining updating of the load
gain kf on the basis of the deviation .DELTA.f between the blade
load f and the second load threshold value f2 in the blade control
device 100.
[0082] As shown in FIG. 12, in a case where the blade load f is
greater than the second load threshold value f2, the load gain
setting part 18 updates the load gain kf such that the raising
speed of the blade 4 is increased on the basis of the load
deviation .DELTA.f. Since this increases the raising speed of the
blade 4 in a case where the blade load f is greater than the second
load threshold value f2, it is possible to further enhance an
effect of more quickly reducing the blade load f to prevent a stuck
state and the like caused by an excessive load, thereby enabling
stable travel of the hydraulic excavator 1.
[0083] According to the foregoing-described device, it is possible
to more effectively suppress waviness of an execution surface
executed by the hydraulic excavator 1 provided with the blade
control device 100 according to the present embodiment than
waviness of an execution surface executed by a conventional
hydraulic excavator 1, as shown, for example, in FIG. 13.
[0084] The present invention is not limited to the above-described
embodiment. The present invention may include the following modes,
for example.
[0085] A work machine to which the blade control device according
to the present invention is applied is not limited to a hydraulic
excavator. The present invention is widely applicable to other work
machines each provided with a blade, such as a wheel loader, a
bulldozer, and a grader.
[0086] As described in the foregoing, there is provided a blade
control device capable of effectively suppressing waviness of an
execution surface.
[0087] There is provided a blade control device which is provided
in a work machine including a machine body and a blade attached to
the machine body so as to be raised and lowered and which controls
raising and lowering operation of the blade. The blade control
device includes a target design surface setting part which sets a
target design surface that specifies a target shape of an object to
be dug by the blade; a position information acquiring part which
acquires position information related to the work machine; a blade
position calculating part which calculates a blade position as a
position of the blade in a global coordinate system on the basis of
the position information acquired by the position information
acquiring part; a blade load acquiring part which acquires a blade
load as a load applied on the blade; a storage part which stores a
first load threshold value as a threshold value of the blade load
and a second load threshold value which is a threshold value of the
blade load and is greater than the first load threshold value; a
target position setting part which sets a blade target position
that is a position as a target of the blade position and that is a
position above the target design surface; and a blade operation
control part which outputs a command for raising and lowering the
blade such that a position deviation as a deviation between the
blade position calculated by the blade position calculating part
and the blade target position approaches zero in a case where the
blade load acquired by the blade load acquiring part is equal to or
less than the second load threshold value, and outputs a command
for raising the blade in a case where the blade load acquired by
the blade load acquiring part is greater than the second load
threshold value, in which in a case where an update condition is
satisfied, the update condition being set in advance so as to
associate the blade load and the first load threshold value with
each other, the target position setting part updates the blade
target position using the blade position obtained when the update
condition is satisfied as a reference.
[0088] In a case where a blade load is greater than the second load
threshold value, the blade control device conducts control to raise
the blade, thereby preventing a stuck state and the like caused by
an excessive load and enabling stable travel of the work machine.
On the other hand, in a case where a blade load is equal to or less
than the second load threshold value, the blade control device
controls raising and lowering operation of the blade such that the
position deviation between the blade position and the blade target
position approaches zero. Also in a case where a blade load is
equal to or less than the second load threshold value, conducting
position control of the blade such that the position deviation
approaches zero enables waviness of an execution surface to be
suppressed more effectively than in such a device as recited in the
above Patent Literature 2, in which raising and lowering operation
of a blade is controlled on the basis of a blade load also in a
case where a blade load is equal to or less than the second set
load value. Then, such effective suppression of waviness of an
execution surface improves efficiency of digging work.
[0089] Additionally, in the blade control device, the first load
threshold value is set to a value corresponding to a proper blade
load with which the work machine can stably travel. Then, the
update condition is set in advance in which the actual blade load
varying during digging work and the first load threshold value
corresponding to a proper blade load are associated with each
other. Then, since the blade target position is updated using, as a
reference, a blade position when the update condition is satisfied,
the blade target position will be associated with a blade position
at which a blade load is proper. Accordingly, repeated update of
the blade target position during the digging work allows a blade
load during the digging work to be stable irrespective of a state
(e.g. hardness of sediments, a kind of sediments, etc.) of the
ground as a digging target.
[0090] Additionally, in the blade control device, the second load
threshold value is a value set for preventing occurrence of a stuck
situation caused by an excessive blade load and is a value greater
than the first load threshold value. In the blade control device,
in a case where a blade load becomes greater than the second load
threshold value, control to raise the blade is conducted. This
causes reduction in a blade load to prevent a stuck state and the
like caused by an excessive load, thereby enabling stable travel of
the work machine as described above.
[0091] From the foregoing, the blade control device enables
waviness of an execution surface to be effectively suppressed, and
besides, enables stable and efficient digging operation of a work
machine.
[0092] In the blade control device, the update condition preferably
includes a condition that the blade load reaches the first load
threshold value, or a condition that the blade load reaches a
determination value for determining whether the blade load has
neared the first load threshold value or not, the determination
value being set on the basis of the first load threshold value. In
this mode, since the blade target position is updated using, as a
reference, a blade position obtained when the blade load reaches or
nears the first load threshold value, the blade target position is
substantially matched with a blade position when the blade load is
proper. Accordingly, a blade load during the digging work is more
liable to be stabilized.
[0093] In the blade control device, the storage part may be
configured to store a first state indicating allowance of update of
the blade target position when the blade load becomes greater than
a flag threshold value as a threshold value set in advance, and
also store a second state indicating non-allowance of update of the
blade target position in place of the first state when the blade
target position is updated, and the update condition may include a
condition that the blade load reaches the first load threshold
value when the first state is stored in the storage part, or a
condition that the blade load reaches a determination value when
the first state is stored in the storage part, the determination
value being set on the basis of the first load threshold value for
determining whether the blade load has neared the first load
threshold value or not. In this mode, since while update of a blade
target position is allowed when the update flag for the blade
target position is in the first state, update of the blade target
position is not allowed when the update flag is in the second
state, frequent update of the blade target position can be
suppressed.
[0094] In the blade control device, the blade target position to be
updated by the target position setting part is preferably set at a
position which passes the blade position when the update condition
is satisfied and is on a plane parallel to the target design
surface. In this mode, since raising and lowering operation of the
blade is controlled such that the position deviation between a
blade target position set at a position on a plane parallel to the
target design surface and the blade position approaches zero,
efficiency of digging work for causing an execution surface to
approach a target design surface is further improved.
[0095] The blade control device may be configured such that the
storage part stores a target track as a target for an increase
process of the blade load when the blade load approaches the first
load threshold value while being increased, and the blade operation
control part outputs a command for raising and lowering the blade
such that the blade load approaches the first load threshold value
while following an increase process close to the target track
before the blade target position is set by the target position
setting part. In a case where the target track is set as in the
this mode, since at a stage prior to setting of the blade target
position, the blade load approaches the first load threshold value
while following an increase process close to the target track, the
blade enters the ground at a moderate lowering speed, resulting in
suppressing an increase in a depth of entering of the blade into
the ground when the blade load reaches the first load threshold
value. This causes an amount of soil on the blade to change little
with respect to a travel distance of the work machine and also
causes the blade load to change little. As a result, an effect of
suppressing waviness of an execution surface can be further
enhanced. Then, in the present mode, when the update condition is
satisfied, the condition being that the blade load reaches or nears
the first load threshold value while following the increase process
close to the target track, the target position setting part sets
the blade target position. Then, after the blade target position is
set, the blade operation control part controls the raising and
lowering operation of the blade such that the position deviation
between the blade position and the blade target position approaches
zero.
[0096] The blade control device may be configured to further
include a load threshold value setting part which sets the first
load threshold value, and such that the position information
acquiring part includes a vehicle body position acquiring part
which acquires a vehicle body position as a position of the machine
body, and the load threshold value setting part updates the first
load threshold value such that the first load threshold value
becomes smaller when a body distance is a second distance than when
the body distance is a first distance, the body distance being a
distance between the vehicle body position acquired by the vehicle
body position acquiring part and the target design surface, the
second distance being smaller than the first distance. In this
mode, the blade load is more liable to reach the first load
threshold value in a case where the body distance is the second
distance (i.e., in a case where the machine body is close to the
target design surface) as compared with a case where the body
distance is the first distance (i.e., in a case where the machine
body is away from the target design surface). This increases the
update frequency of the blade target position and increases a
possibility that the blade target position is set at a more proper
position corresponding to a state of the ground as a digging
target. Specific examples of the present mode include the
following. For example, the first load threshold value at the time
of execution of grading operation at a final stage of work by the
work machine is set to be a value smaller than the first load
threshold value at the time of execution of digging operation at an
initial stage or an intermediate stage of the work. In such a case,
it is possible to execute, by using the same control algorithm,
both the digging operation in which more importance is applied to
quick digging work than in grading operation, and the grading
operation in which much importance is applied to precision in
causing an execution surface to approach a target design
surface.
[0097] It is preferable that in the blade control device, the blade
operation control part outputs the command on the basis of a
function having a term including, as a variable, a position
deviation which is an elevation difference between the blade
position and the blade target position and including a position
gain by which the position deviation is multiplied, the blade
control device further including a position gain setting part which
sets the position gain, in which in a case where the blade position
is below the blade target position, the position gain setting part
updates the position gain such that a raising speed of the blade is
increased on the basis of the position deviation. In this mode,
since in a case where the blade position is below the blade target
position, the raising speed of the blade is increased, the effect
of suppressing digging of the ground as a digging target to a
position below the blade target position is further enhanced,
resulting in further enhancing the effect of suppressing digging of
the ground to a position below a target design surface.
[0098] It is preferable that in the blade control device, the
function further has a term including, as a variable, a load
deviation which is a deviation obtained by subtracting the second
load threshold value from the blade load and including a load gain
by which the load deviation is multiplied, the blade control device
further including a load gain setting part which sets the load
gain, in which in a case where the blade load is greater than the
second load threshold value, the load gain setting part updates the
load gain such that the raising speed of the blade is increased on
the basis of the load deviation. In this mode, since the raising
speed of the blade is increased in a case where the blade load is
greater than the second load threshold value, it is possible to
further enhance the effect of more quickly reducing the blade load
to prevent a stuck state and the like caused by an excessive load,
thereby enabling stable travel of the work machine.
* * * * *