Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1226433
Description
Apparatus For Controlling An Earthmovinq Implement
Technical Field
This invention relates generally to apparatus
for controlling an implement and, more particularly, to
apparatus for controlling, in response to working
conditions, an earth moving implement supported on an
earth moving machine.
Background Art
Implements supported on machines, and the
machines carrying the implements, should normally be
operated to achieve maximum productivity. Earth moving
machines, and implements on these machines, are prime
I examples of such devices. The productivity or
production rate for these machines can be defined as
the volume of soil moved per unit time multiplied by
the distance over which the soil is moved for a given
working or soil condition environment. This, and other
definitions of productivity, are known and used in the
art. In machines and implements that are manipulated
by a human operator, the skill of the operator is a
practical limitation to attaining maximum
productivity. Productivity usually is lower with
unskilled operators than with skilled operators. For
example, an unskilled operator may achieve as little as
65% of the productivity obtained by a highly skilled
operator using the same machine.
Maximum productivity can be achieved by
maximizing the "draft power" of the earth moving
machine. Draft power is the rate of actual useful work
being done in moving the soil and is defined as the
product of the draft force of the earth moving implement
and the ground speed of the earth moving machine. A
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track/wheel bulldozer and a bulldozer blade constitute
one type of earth moving machine and implement that
moves or pushes soil. For these devices, draft force
is the force on the blade and ground speed is the
bulldozer ground speed.
A simple example of a working condition is the
operation of the bulldozer to level an area. As the
bulldozer starts forward with the blade elevated, draft
power is zero since draft force is zero. As the blade
lo is lowered and cuts into the soil, draft force
increases and, hence, draft power increases. As the
blade cuts deeper, draft force may continue to rise,
but ground speed may decrease. Maximum draft power is
reached when the bulldozer is moving at maximum ground
speed commensurate with draft force.
Control systems have been developed that
provide information for controlling the blade during
various working conditions. These include control
systems disclosed in (1) US. Patent No. 4,194,574 by
Benson et at., issued March 25, 1980; 12) US. Patent
No. 4,166,506 by Tusk et at., issued September 4,
1979; and, (3) US. Patent No. 4,157,118 by Suganami
et at., issued June 5, 1979. A common problem with
these control systems is the inability to adequately
maintain stable blade control over the entire working
area of the bulldozer. While stable blade control may
be maintained when the bulldozer and blade are being
operated over a substantially level or horizontal area,
the problem arises when the bulldozer pitches forward
into a cut and then pitches aft on ascending the other
side of the cut. Upon pitching forward into the cut,
the blade can quickly cut more deeply into the isle and
become overloaded, and upon pitching aft the blade can
move totally out of the soil and become unloaded or
leave underneath a substantial amount of soil that had
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been carried during the cut. At the time of pitching,
either forward or aft, the earth moving machine ha a
substantial longitudinal angular velocity.
Whereas the information provided by the prior
control systems may be useful for controlling the blade
during the level portion of the cut, this information
is not satisfactory for controlling the blade during
the pitching conditions. For example, in US. Patent
No. 4,194,574, the information is an audible or visual
representation of the blade power. The operator must
respond to this data by manually moving a control lever
to hydraulically raise the blade upon the forward
pitching to compensate for the downward blade movement
or to lower the blade upon aft pitching to compensate
for the upward blade movement. Not only is the
operator response to this information slow when a
quicker response time is needed during the pitching
conditions, but the operator can overshoot or
undershoot the proper blade position, causing blade
oscillation. Moreover, productivity is reduced during
these pitching conditions because maximum blade power
is not achieved.
Other disadvantages occur with the prior blade
control systems, whether the bulldozer and blade are
being controlled over a level area or during the
pitching conditions. In US. Patent No. 4,194,574, the
control system senses blade force and bulldozer ground
speed, and then calculates blade power. This
information controls, for example, a variable rate
audible signal generator whose audible tone rate varies
as the calculated power changes. The operator must
then manually move a control lever that controls a
hydraulic actuator which, in turn, controls a lift
cylinder that moves the blade. This manual control is
performed in an attempt to achieve maximum blade power,
which is indicated when a predetermined tone is
produced by the signal generator.
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One problem with the system of the '574 patent
is the relatively quick onset of operator fatigue, both
mental and physical, in responding to the alarm signal
generator and moving the control lever to control the
hydraulic actuator. For example, a percentage of
operator lever control movement does not result in lift
cylinder movement to reposition the blade. This is
because the operator has not moved the control lever
far enough to overcome cylinder pressure due to blade
load. Also, a percentage of the control lever
movements overshoot or undershoot the lever position
corresponding to maximum blade power. Furthermore, the
undercarriage life of the bulldozer is reduced owing to
the occurrence of excessive and repeated track/wheel
slippage, resulting in reduced ground speed, until the
operator can manipulate the lever to again achieve
maximum blade power.
In US. Patent No. 4,166,506, the control
system is designed to maintain a constant,
predetermined load or force on the blade and not to
control blade power. This is not sufficient to
optimize productivity. This system senses the actual
variable load, compares the sensed load to a
predetermined fixed load, and produces control
information to automatically raise or lower the blade
in response to the comparison until the actual and
predetermined loads are equal. The use of the
predetermined fixed load also has the disadvantage of
not allowing the operator to vary the setting of this
important parameter which is directly related to blade
power. The option to select a parameter directly
related to blade power is beneficial when dictated by
changing soil conditions and terrain irregularities.
For example, for harder soil, it is beneficial lo
operate the blade under higher loads than the
predetermined load.
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The us. Patent No. 4 ,157 ,118 has a control
system in which the operator selects a desired or
command blade height relative to the soil or depth of
cut, which is then compared to the actual blade height
according to sensed height data. The blade is then
raised or lowered automatically until the command blade
height and actual blade height are the same. Actual
blade load is not sensed directly, but is calculated in
response to engine speed and throttle opening and
compared with a maximum preset load which is dictated
by the particular working conditions. Should the load
of the blade exceed the preset maximum load when the
blade is at the commanded height, the control system
overrides the height control and automatically causes
the blade to rise until the actual load falls below the
maximum load. As with the '506 patent, the control
system of the '118 patent is not designed to control
blade power, but rather blade height and maximum blade
force or load. The latter, for example, may be preset
too low if blade power were taken into consideration.
furthermore, the blade load control feature can
function only to raise the blade and not to lower the
blade.
The present invention is directed to
overcoming one or more of the problems as set forth
above.
Disclosure of the Invention
In one aspect of the present invention, an
apparatus controls an earth moving implement of an
earth moving machine, wherein the earth moving implement
is movable to a plurality of positions and the
earth moving machine is movable at a longitudinal
angular velocity, and includes means for sensing the
angular velocity and moving the earth moving implement
in response to the sensed angular velocity.
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Control systems producing implement control
information do not provide stable control during
critical working conditions when the earth moving
machine is pitching forward or aft into or out of a
cut. Also, the control systems either are not designed
to maximize blade power and, hence, productivity, or
require manual implement control resulting in operator
mental and physical fatigue. The present invention
detects the longitudinal angular velocity of the
lo earth moving machine to compensate the position of the
implement during pitching conditions, increasing blade
stability and optimizing implement power and
productivity by sensing at least one variable
responsive to the power and automatically controlling
the blade position in response to this variable.
Brief Description of the Drawings
Fig. l is a side elevation of an earth moving
machine including an embodiment of the present
invention;
Fig. 2 is a view of the earth moving machine
pitching forward into a cut;
Fig. 3 is a view of the earth moving machine
pitching aft during exiting of the cut;
Fig. 4 is a flow chart used to explain one
embodiment of the present invention;
Fig. 5 is a flow chart used to explain a
second embodiment of the present invention;
fig. 6 is a flow chart used to explain a third
embodiment of the present invention; and,
Fig. 7 is a graphic representation of a
typical ground speed v. implement power curve.
Best Mode For Carrying Out the Invention
Fig. l illustrates an earth moving machine lo
having an earth moving implement 12 used to move earth
or soil. For example, the earth moving machine lo is a
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wheel or track-type bulldozer 14 and the earth moving
implement 12 is a bulldozer blade 16. The bulldozer 14
is shown as being a track-type machine having tracks
18, and includes a draft arm 20 connected to push the
blade 16 and a lift cylinder 22 connected to raise and
lower the blade 16. While the invention is described
using the example of the bulldozer 14 and bulldozer
blade 16, it is intended that the invention also be
used on other types of earth moving machines 10 and
earth moving implements 12.
Power applied to the blade 16 during
earth moving operations of the bulldozer 14 causes the
blade 16 to push and carry the soil, occasionally slips
the tracks 18, and overcomes friction and other losses,
etc. A parameter known as draft or blade power "P" is
a measure of the rate of actual useful work being done
in moving the soil, and can be expressed by a
simplified equation, as follows:
P = F x V where "F" is the draft or blade
force of the blade 16, and "V" is the true ground speed
or machine velocity of the bulldozer 14 relative to the
ground. Maximum productivity is achieved by
maintaining maximum power "P" on the blade 16 during
earth moving operations. For example, if the blade 16
is above the soil and blade force "F" is zero, or if
the bulldozer 14 is stationary and ground speed "V" is
zero, the draft power is zero. Between the extremes of
zero blade force "F" and zero ground speed "V", a
maximum value of draft power "P" exists, resulting in
maximum productivity. For example, as the blade 16 is
lowered by the cylinder 22 and cuts deeper into the
soil, or as the blade 16 is raised towards the soil
surface by the cylinder 22 and reduces the depth of the
cut, the blade force "F" is higher or lower,
respectively, for a given soil condition and ground
speed "V".
.,
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The relationship between ground speed "V" and
draft or blade power "P" is shown in Fig. 7, where "P"
is seen to peak between states "A" and "B ". Operation
on the curve between states "A" and "B" is desirable
for maximum productivity. Raising the blade 16 while
at state "B" or lowering the blade 16 while at state
"A" causes the blade power "P" to approach the peak.
Because the blade 16 usually is raised and
lowered by the cylinder 22 during the earth moving
operation in order to optimize blade power "P", blade
stability is important. That is, in being moved by the
cylinder 22 to a position corresponding to the position
of maximum blade power "P", oscillation by the blade 16
about this optimum position should be minimized. Blade
stability is highly important during the working
conditions illustrated in Figs. 2 and 3, to achieve
both the general advantages of stable control and
optimum blade power "P". These figures show the
profile of a cut 26 into soil 28.
In Fig. 2, the bulldozer 14 and blade 16 are
shown pitching forward into the cut 26 from the top
I As this forward pitch occurs, the blade 16 quickly
cuts deeper into the soil 28, increasing blade force
"F" beyond a value appropriate for optimal blade power
"P" at a given ground speed "V". As the bulldozer 14
rotates or pitches into the cut 26 in the direction
shown by the arrow, the optimum blade force "F" changes
quickly, and compensation should be made by raising the
blade 16. A parameter identifying this forward
pitching is the pitch rate or longitudinal angular
velocity of the bulldozer 14. Stable positioning of
the blade 16 is difficult when the bulldozer 14 has a
high longitudinal angular velocity, as is present
during this working condition.
,
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Similarly, in Fig. 3, the bulldozer 14 is
shown as moving upwardly or ascending from a bottom 32
of the cut 26. As the bulldozer 14 pitches aft or in
the rotational direction shown by the arrow, the blade
16 tends to move out of the soil 28, resulting in a
decreasing blade force "F" and a reduced blade power
"P" at a given ground speed "V". Moreover, as the
blade 16 quickly raises, spillage of accumulated soil
28 beneath the cutting edge of the blade 16 occurs.
Again, stable positioning of the blade 16 is difficult
when the bulldozer 14 has a high longitudinal angular
velocity during this working condition.
Adverting back to Fig. 1, an apparatus 34 is
shown for controlling the earth moving implement 12 of
the machine 10, for example, the blade 16. The
apparatus 34 provides stable blade control to
compensate for the effects of pitching shown in Figs. 2
and 3, and performs three distinct modes of operation
or control, respectively called Underspend Control,
Ground Speed Control, and lade Power Control, for
optimizing blade power. The stable blade control
feature is incorporated in all three modes.
The apparatus 34 includes means 36 for moving
the blade 16 to a plurality of positions. The means 36
includes means 38 for automatically generating a blade
position control signal and delivering the signal to a
line 40. An actuatable means 42 of the means 36
responds to the position control signal received from
the line 40 by producing and delivering a signal to an
output line 44 which leads to the lift cylinder 22 and
functions to raise or lower the blade 16.
The generating means 38 includes means 46 for
sensing a variable directly related to at least one
parameter of blade power "P", i.e., bulldozer ground
speed "V" or blade force "F". The means 46 includes,
for example, a ground speed sensor means 48 and draft
or_.
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or blade force sensor means Ahab. The ground speed
sensor means 48 senses the true ground speed "V" of the
bulldozer 14 and produces and delivers a speed signal
to a line 52 in response to the sensed ground speed
"V". Roy draft or blade force sensor means Ahab sense
the force on the blade 16 and produce and delivers
force signals to lines Ahab in response to the sensed
blade force "F".
The ground speed sensing means 48 is suitably
positioned on the bulldozer 14 and includes, for
example, a non-contacting ultrasonic or radar type
sensor 49. The draft or blade force sensor means 50
includes, for example, strain gauges or load cells
Ahab suitably fixed to the lift cylinder 22 and the
draft arm 20- As an alternative, and to estimate blade
force "F", the sensor means 50 can, for example, be a
driveling torque sensor which measures driveling torque
and is located on a universal joint or other element in
the driveling (not shown) for driving the tracks 18.
In this alternative, torque measurements are combined
with transmission gear ratios and the effective
sprocket radius to convert the torque measurement to a
tangential sprocket force which is an estimation of
blade force "F". The sprocket force is modified to
eliminate the gravitational component that appears when
the bulldozer 14 traverses non-level terrain.
A pitch angle sensor means 56 of the means 38
is suitably supported on the bulldozer 14 to sense the
nominal longitudinal pitch angle of the bulldozer 14
with respect to horizontal, for example, the ground
line indicated in figs. 2 and 3. The sensor means 56
produces and delivers a pitch signal to an output line
58 in response to the pitch angle.
The means 38 also includes data processor
means 60 for producing and delivering the position
control signal to the line 40 in response to data
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signals received from the lines 52, 54 and 58. The
data processor means 60 includes, for example, a
Motorola MCKEE microprocessor 61 which is under
software control.
S The actuatable means 42 includes, for example,
an electro-hydraulic actuator 62 that controls a
hydraulic valve 64 in response to the control signal
received from the line 40. The valve 64, in turn,
controls the supply of hydraulic fluid delivered
lo through the line 44 and utilized to raise and lower the
cylinder 22.
The apparatus 34 also includes means 66 for
sensing the longitudinal angular velocity of the
bulldozer 14 and for producing and delivering an
angular velocity signal to a line 68 in response to the
sensed angular velocity. The means 66 is, for example,
an accelerometer or pitch rate sensor 69. The data
processor means 60 responds to receiving the signal
from line 68 by modifying or compensating the moving
means 38 to adjust any one position of the blade 16.
In particular, in response to receiving the angular
velocity signal from the line 68, the means 60 modifies
the control signal of the line 40 that otherwise is
produced in response to receiving the signals on the
lines 52, 54, and 58.
A means 70 is connected to a transmission 71
of the bulldozer 14 and delivers forward and reverse
direction signals to a line 72 in response to the
transmission 71 being in a forward or reverse gear,
respectively. In response to receiving the reverse
direction signal, the data processor means 60 inhibits
the delivery of control signals to the actuatable means
42.
To maintain an operator's control over the
bulldozer 14, the apparatus 34 preferably includes, for
example, means 74 for controllable modifying desired or
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command ground speed "V" or desired or command blade
power "P". The means 74 includes a manual control
member or lever 76. An encoder 78 senses the position
of the lever 76 and produces and delivers a command
signal to an output line 80 in response to either the
selected command ground speed "V" or the selected
command blade power "P". Alternatively, if operator
control of these parameters is not desired, a command
ground speed "V" or command blade power "P" can be
lo preset at a predetermined level, for example by a
thimble or other wettable control, or automatically
calculated by the means 60 according to working
conditions and apparatus 34 specifications. The
command ground speed "V" or command blade power "P" is
calculated, for example, by continuously monitoring the
actual ground speed and actual blade force delivered to
the means 60 from the sensing means 48,56 during an
initial procedure wherein the operator drives the
bulldozer 14 at a ground speed represented by the
rightmost portion of the power curve depicted in Figure
7. In response to the operator slowly lowering the
blade 16 into the soil 28, blade power increases along
the curve of Figure 7 toward the peak power point and
then decreases until the leftmost portion of the curve
is reached, at which time the bulldozer 14 is stopped
and the tracks 18 are in a full slip condition. The
means 60 repeatedly calculates the actual blade power
from the blade force/ground speed relationship and the
location of the peak power point on the curve of Figure
7 is determined. This point establishes the command
blade power "P" or command ground speed "V" according
to actual working conditions.
The apparatus 34 also includes a means 82 that
is coupled to the hydraulic valve 64 by a line 84 and
manually controls the raising and lowering of the blade
, . .
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16. The data processor means 60 is normally activated
by a signal received over a line 86 in response to the
lever 82 being in a neutral position.
In addition to storing and executing software
instructions for carrying out the longitudinal angular
velocity compensation feature mentioned above, the data
processor means 60 stores and executes, for example,
any one of three software programs "A", "B", and "C".
Each program "A", "B", and "C" is used to support one
distinct control or operational mode. Although the
longitudinal angular velocity compensation feature is
described as being used in conjunction with any one of
the three modes, this feature can also be utilized
independent of these three modes, for example, if only
manual control via lever 82 is used but compensation is
needed for the pitching conditions. The three modes
described are designated as ~nderspeed Control -
Program "A", Ground Speed Control - Program "B", and
Blade Power Control - Program "C".
The functional flow charts depicted in Figures
4-6 are useful in developing a complete understanding
of an implementation of the present invention. It will
be appreciated that the actual coding of the software
can vary according to the microprocessor 61 and other
hardware selected, without deviating from the appended
claims.
Industrial Applicability
~nderspeed Control - Program "A" - Fig. 4:
Assume first that the bulldozer 14 is moving
along a horizontal ground line without any track
slippage. The bulldozer operator lowers the blade 16
to cut into the soil 28, using the manual control lever
82. The lever 82 is then placed in neutral to activate
Jo
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the data processor means 60, with the blade 16
remaining lowered. The ground speed sensor means 48
delivers the speed signal to line 52 in response to the
ground speed "V", and the pitch angle sensor means 56
delivers the pitch signal to line 58 in response to the
pitch angle.
If excessive slippage of the track 18 occurs,
the ground speed sensor means 48 senses the reduced
ground speed "V" and delivers a resultant speed signal
to line 52 in response to the reduced speed. Excessive
track slippage is a working condition resulting in loss
of maximum blade power "P". Under control by program
"A", and in response to the magnitude of the speed
signal being less than a predetermined value, the data
processor means 60 automatically generates and delivers
a position control signal to line 40 which causes the
actuatable means 42 to raise the blade 16. The blade
16 is raised until the data signal from line 52
identifies an increased ground speed "V" in response to
substantially reduced track slippage.
Program "A" does not allow the blade 16 to be
automatically lowered via any control signal on the
line 40. Program "A" only generates and delivers a
position control signal to line 40 that frees the blade
16 to be automatically raised. The bulldozer operator
retains the option of raising or lowering the blade 16
in response to his moving the lever 82 from the neutral
position. If the operator determines that the blade 16
can be lowered more deeply into the soil 28 without
causing excessively reduced ground speed "V", the lever
82 is manipulated to lower the blade 16. Returning the
lever 82 to its neutral position after lowering the
blade 16 reactivates the data processor means 60.
Now assume that the bulldozer 14 is moving at
a ground speed "V" without excessive track slippage,
that the blade 16 has been partially lowered into the
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soil 28, and that the bulldozer 14 starts to pitch
forward into the cut 26 created by the blade 6, as
shown by numeral 30 in Fig. 2. During the initial
portion of this forward pitching, failure to raise the
blade 16 to compensate for this motion drives the blade
16 more deeply into the soil 28, resulting in a
substantial, rapid and undesirable increase in blade
force "F". The longitudinal angular velocity sensor
means 66 senses this forward pitching and delivers an
angular velocity signal to line 68 in response to the
rate of pitching. The data processor means 60, in
response to receiving the data signal from line 68,
modifies the position control signal that is delivered
to line 40 in response to the data signals from lines
52, 58 and causes the actuatable means 42 to raise the
blade 16 to a position to compensate for this angular
velocity, and reduces blade force "F". When the
angular velocity has substantially ceased and the
bulldozer 14 is moving towards the bottom 32 of the cut
26, the blade 16 position is again governed primarily
in response to the ground speed data.
AS the bulldozer 14 moves away from the bottom
32 and ascends the cut 26, as shown in Fig. 3, it
pitches aft with reduced ground speed "V" and causes
the blade 16 to be raised out of the soil 28. Under
this condition, the blade 16 should be lowered relative
to the bulldozer 14 to prevent spillage of accumulated
soil beneath the blade 16. Although program "A" does
not automatically lower the blade 16, the means 60
responds to the longitudinal angular velocity signal
from line 68 by modifying the control signal to line 40
to reduce the tendency of the blade 16 to be raised in
response to the reduced ground speed signal from line
52.
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The Underspend Control Process of Fig. 4,
executed by the data processor means 60, may be
characterized by the mathematical algorithm or feedback
error relationship given by the following equation:
E = clue (VREF(o) VTGS) 2
(VTGs) + K3 I
where:
Ells is the total Underspend Control error signal
VREF(~) is the ground speed reference threshold
which is a function of
the longitudinal pitch angle
VTGs is the actual ground speed
VTGS is the actual time rate of change of ground
speed
is the longitudinal angular velocity
K1, lK2, & K3 are adjustable, positive gain
parameters
= {1 if the quantity in square brackets is 0
Note that and are defined to have positive
values when the tractor is forwardly pitched on a
downgrade and forwardly pitching toward a lesser grade,
respectively.
In all three control modes, the magnitude of
the error determines the rate at which the blade
position is adjusted. The sign of the error determines
the direction. Positive errors result in a raise
correction while negative errors produce a lowering
correction. A null or zero value for the error causes
the blade 16 to be held in its current position.
The Underspend Control is designed to only
raise or hold the blade. Corrections to lower the
blade are precluded by the presence of the delta (~)
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parameter. A control mode based purely upon the
longitudinal angular velocity is obtained by setting
the gain parameters K1 & K2 to zero.
Ground Speed Control - Program "B" - Fig. 5:
In this mode, the lever 82 is in neutral and
activates the data processor means 60. The operator
rotates the lever 76 over a predetermined range and
selects a desired or command ground speed "V" for the
bulldozer 14. The encoder 78 senses the position of
the lever 76 and delivers to line 80 a predetermined
command signal responsive to the command ground speed
"V". As discussed previously, the predetermined
command signal can likewise be a preset value or can be
automatically calculated by the means 60.
With the bulldozer 14 in motion, the data
processor means 60 receives the speed signal from line
52, the pitch angle signal from line 58, and the
command signal from line 80. In response to these
signals, and under control of program "B", the data
processor means 60 generates and delivers position
control signals to line 40, which cause the actuatable
means 42 to automatically raise and lower the blade 16
in the soil 28. The blade 16 is automatically raised
in response to the magnitude of the speed signal being
less than the predetermined command signal value, just
as in the Underspend Control, but the blade 16 is also
automatically lowered in response to the magnitude of
the speed signal being greater than the predetermined
command signal value. This frees the bulldozer 14 to
continue to move at the desired or command ground speed
"V" .
In the embodiment including the lever 76, the
operator modifies the ground speed command at any time
by repositioning the lever 76 in response to changes in
:
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the working conditions, such as terrain profile and
soil properties. In response to selection of a
different command ground speed "V", a different command
signal is produced and delivered to line 80. The data
processor means 60 responds, under control of program
"B", to the new command signal from line 80 and the
speed signal from line 52, by producing and delivering
a different position control signal to line 40 which in
turn causes the actuatable means 42 to raise or lower
lo the blade 16. In response to the actual ground speed
and the command ground speed being substantially the
same, i.e., the error is substantially zero, the data
processor means 60 delivers a control signal to line 40
which controls the actuatable means 42 and maintains
the blade 16 at the current position.
As described in the Underspend Control mode,
the longitudinal angular velocity sensor means 66 and
the data processor means 60 compensate or modify the
position of the blade 16 in response to changes in
pitch of the bulldozer 14. This compensation is
performed independent of operator control or
manipulation of the lever 76. The operator maintains
the option of manually controlling the blade 16 by
manipulating the lever 82 from its neutral position.
The Ground Speed Control process of Fig. 5,
executed by the data processor means 60, may be
characterized by the following algorithm or feedback
error relationship:
ERGS Al (VOYEUR) VTGs) K2 (VOW
VTGS) + K3 (~)
where:
ERGS is the total Ground Speed Control error
Signal
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Vow is the command ground speed which is a
function of the longitudinal pitch angle
Vow is the command time rate of change of
ground speed
VTGS is the actual ground speed
VTGs is the actual time rate of change of ground
speed
is the longitudinal angular velocity
I, K2, & K3 are adjustable, positive gain
lo parameters
The Ground Speed Control algorithm permits
positive, zero, and negative values of ERGS.
Blade Power Control - Program "C" - Fig. 6:
In this mode, the lever 82 is in neutral to
activate the data processor means 60. The operator
rotates the lever 76 over a predetermined range and
selects a desired or command blade power "P". The
encoder 78 senses the position of the lever 76 and
delivers to line 80 a predetermined command signal in
response to the command blade power "P". The range of
positioning of the lever 76 for selecting command blade
power "P" is different than the range of positioning of
the lever 76 for selecting command ground speed "V".
As discussed previously, the predetermined command
signal can likewise be a preset value or can be
automatically calculated by the means 60.
With the bulldozer 14 in motion, the data
processor means 60 receives the speed signal from line
52, the pitch angle signal from line 58, the blade
force signal from line 54, and the command signal from
line 80.
In response to the signals from lines 52, 58,
and 54, and under control of program "C", the data
processor means 60 determines actual blade power and
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compares this with the predetermined command signal
value. The data processor means 60 then produces and
delivers position control signals to line 40 and causes
the actuatable means 42 to raise or lower the blade 16
until the determined blade power and the command blade
power are substantially the same.
In the embodiment including the lever 76, the
operator modifies the blade power selection at any time
by repositioning the lever 76 in response to changes in
lo the working conditions, such as terrain profile and
soil properties. In response to selection of a
different command blade power, a different
predetermined command signal is delivered to line 80.
The data processor means 60 responds, under control of
program "C", by producing and delivering a different
position control signal to line 40, and causes the
actuatable means 40 to raise or lower the blade 16. In
response to the actual blade power and the command
blade power being substantially the same, i.e., the
error is substantially zero, the data processor means
60 delivers a control signal to line 40 for controlling
the actuatable means 42 and maintaining the blade 16 at
the current position.
As described in the Underspend Control and the
Ground Speed Control, the longitudinal angular velocity
sensor means 66 and the means 60 compensate or modify
the position of the blade 16 in response to changes in
pitch of the bulldozer 14. This compensation is
performed independent of operator control or
manipulation of the lever 76. The operator maintains
the option of manually controlling the blade 16 by
manipulating the lever 82 from its neutral position.
The Blade Power Control process of Fig. 6,
executed by the data processor means 60, may be
characterized by the following algorithm or feedback
error relationship:
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Ebb - Viol Al (BRACT BPREQ) 2
(BRACT J3PREQ)3 + K3 (bias) K4 (I )
where:
BRACT is the actual blade power (or estimated
from driveling torque x ground speed)
BP~CT is the time rate of change of blade power
BPREQ is the command blade power
BPREQ is the time rate of change of command
blade power
Al if VTGs VREF(~) + TV
VIOL 0 if ¦VTGs - VREF(e)l < a
-1 if VTGS < VREF ( )
where:
VTGS is the true ground speed
VR~F(~ is the ground speed at peak power, and
a is a headband velocity around VREF(~)
O if VTGS VREF ( )
BIAS
, VREF(~) VTGS if VTGS< VREF(~)
is the longitudinal pitch rate of the tractor. Al,
K2, K3, & K4 are positive gain parameters.
The factor, Vp~L, which multiplies the first
two terms in Equation 3 inverts the polarity of the
error signal Ebb when the ground speed falls below
that speed associated with the peak in the power vs.
ground speed relationship (shown in Fig. 7). For a
typical reference power, the machine 10 can exist in
two distinct states, "A" and "B". The direction of
blade correction required for a given blade power error
is opposite for the two states. The term Bias
biases the system toward state "A" of Fig. 7, the more
stable of the two system states.
lZZ6433
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In summary, stable implement control is
maintained over all working conditions of the
earth moving machine 10, and in particular during
pitching conditions, by compensating or modifying the
blade position in response to the longitudinal angular
velocity of the machine. Productivity is substantially
enhanced by controlling the implement 12 in response to
sensed variables directly related to implement power,
including at least machine round speed for the
Underspend Control and Ground Speed Control modes, and
machine ground speed and implement force for the
Implement Power Control mode. Operator mental and
physical fatigue are reduced since the apparatus 34
automatically moves the implement 12, yet the operator
retains control of the machine 10 by manipulating the
lever 76 and/or the lever 82. Furthermore, the
apparatus 34, being automatic, shortens the time
required to react to changing working conditions.
Additionally, by sensing machine ground speed, the
apparatus 34 enhances the life of the machine
undercarriage by controlling the implement 12 and
effectively preventing excess track or wheel slippage
in response to high implement loads.
Other aspects, objects and advantages of this
invention can be obtained from a study of the drawings,
the disclosure and the appended claims.
