U.S. patent number 3,554,291 [Application Number 04/681,522] was granted by the patent office on 1971-01-12 for level and slope control for surfacing machines.
This patent grant is currently assigned to Baldwin-Lima-Hamilton Corporation. Invention is credited to Rex C. Knapp, Richard E. Rogers.
United States Patent |
3,554,291 |
Rogers , et al. |
January 12, 1971 |
LEVEL AND SLOPE CONTROL FOR SURFACING MACHINES
Abstract
A level and slope control for road graders and similar surfacing
machines is described in which one or more very narrow
electromagnetic beams are projected along the path to be graded,
and photoelectric sensors on the grading machine are utilized to
receive and detect positional information from the light beams and
to generate correction signals which both adjust the position of
the surfacing blade and steer the machine in the desired
direction.
Inventors: |
Rogers; Richard E. (Oswego,
IL), Knapp; Rex C. (Aurora, IL) |
Assignee: |
Baldwin-Lima-Hamilton
Corporation (Chicago, IL)
|
Family
ID: |
24735624 |
Appl.
No.: |
04/681,522 |
Filed: |
November 8, 1967 |
Current U.S.
Class: |
172/4.5;
404/84.5 |
Current CPC
Class: |
E02F
3/847 (20130101) |
Current International
Class: |
E02F
3/84 (20060101); E02F 3/76 (20060101); E02f
003/85 () |
Field of
Search: |
;172/4.5
;37/A.C.,A.L.,S.A.L. ;250/202,203 ;299/1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pulfrey; Robert E.
Assistant Examiner: Kopecki; Alan E.
Claims
We claim:
1. In a self-propelled surfacing machine having a chassis, ground
engaging support means for said chassis, steering means for said
support means, a ground engaging leveling element carried by said
chassis, and power means connected between said chassis and said
leveling element for adjusting the vertical position of said
leveling element relative to said chassis; an automatic control
system for steering said machine along a predetermined path while
maintaining said leveling element along a predetermined grade by
following a collimated electromagnetic beam projected along said
path and parallel to said grade by a remotely stationed
transmitter; said control system comprising the combination of:
a beam target mounted on said leveling element and having a target
area that is large relative to the cross-sectional area of said
beam, said target area including a central null region positioned
to intercept said beam under nominal operating conditions,
vertically spaced sensing regions responsive to impingement of said
beam thereon for supplying a first control signal, and horizontally
spaced sensing regions responsive to impingement of said beam
thereon for generating a second control signal; said vertically and
horizontally spaced sensing regions having sensitivities which vary
outwardly from said central null region so that said first and
second control signals have magnitudes that are respectively
proportional to the vertical and horizontal deviation of said beam
from said central null region;
first control means coupled between said target and said power
means and proportionally responsive to the magnitude of said first
control signal for correctively actuating said power means to
maintain said leveling element along said grade; and
second control means coupled between said target and said steering
means and proportionally responsive to the magnitude of said second
control signal for correctively actuating said steering means to
steer said machine along said path.
2. In a self-propelled surfacing machine having a chassis, ground
engaging support means for said chassis, steering means for said
support means, a support structure pivotably mounted on said
chassis for rotational movement about its own longitudinal axis and
vertical movement relative to said chassis, a ground engaging
leveling element pivotably mounted on said support structure for
rotation about an axis perpendicular to the longitudinal axis of
said support structure, first power means connected between said
chassis and said leveling element for varying the vertical position
of said leveling element relative to said chassis, and second power
means connected between said chassis and said leveling element for
varying the angle of said leveling element transversely of said
chassis; an automatic control system for maintaining said leveling
element along a predetermined grade with a predetermined slope by
following a collimated electromagnetic beam projected along a
predetermined path of travel for said machine and parallel to said
grade by a remotely stationed transmitter; said control system
comprising the combination of:
a beam target mounted on said leveling element and having a target
area which is large relative to the cross-sectional area of said
beam, said target area including a null region positioned to
intercept said beam under nominal operating conditions and
vertically spaced sensing regions which are responsive to
impingement of said beam thereon for supplying a first control
signal;
first control means coupled between said target and said first
power means for correctively actuating said first power means in
response to said first control signal to thereby return said
leveling element to said grade;
reference means mounted on said machine for providing a reference
signal indicative of the predetermined slope for said leveling
element;
detector means for supplying a second control signal indicative of
the actual slope of said leveling element, said detector means
including the series connected combination of a first
gravity-operated potentiometer mounted on said support structure
for providing a signal representative of the angle between said
grade and true horizontal transversely of the machine, a second
potentiometer coupled between said support structure and said
chassis for operation in response to vertical movement of said
support structure relative to said chassis for providing a signal
representative of the angle between said leveling element and true
horizontal longitudinally of said machine, and a third
potentiometer coupled between said leveling element and said
support structure for operation in response to rotation of said
leveling element about said perpendicular axis for providing a
signal representative of the rotational position of said leveling
element; and
second control means coupled to said reference means, said detector
means and said second power means for correctively actuating said
second power means in response to an imbalance between said
reference signal and said second control signal to thereby return
said leveling element to said predetermined slope.
3. In a self-propelled surfacing machine having a chassis, ground
engaging support means for said chassis, steering means for said
support means, a ground engaging leveling element pivotably mounted
on said chassis, first power means connected between said chassis
and said leveling element for varying the vertical position of said
leveling element relative to said chassis, and second power means
connected between said chassis and said leveling element for
varying the angle of said leveling element transversely of said
chassis; an automatic control system for maintaining said leveling
element along a predetermined grade with a predetermined slope by
following a collimated electromagnetic beam projected along a
predetermined path of travel for said machine and parallel to said
grade by a remotely stationed transmitter; said control system
comprising the combination of:
a beam target mounted on said leveling element and having a target
area which is large relative to the cross-sectional area of said
beam, said target area including a null region positioned to
intercept said beam under nominal operating conditions, vertically
spaced sensing regions which are responsive to impingement of said
beam thereon for supplying a first control signal and a pair of
horizontally spaced sensing regions one on either side of said null
region for supplying a second control signal in response to the
impingement of said beam on either of them;
first control means coupled between said target and said first
power means for correctively actuating said first power means in
response to said first control signal to thereby return said
leveling element to said grade;
a second control means coupled between said target means and said
steering means for correctively actuating said steering means in
response to said second control signal to maintain said machine
along said predetermined path of travel;
reference means mounted on said machine for providing a reference
signal indicative of the predetermined slope for said leveling
element;
detector means coupled to said leveling element for supplying a
third control signal indicative of the actual slope of said
leveling element; and
third control means coupled to said reference means, said detector
means and said second power means for correctively actuating said
second power means in response to an imbalance between said
reference signal and said third control signal to thereby return
said leveling element to said predetermined slope.
4. The combination of claim 3 wherein said leveling element is
mounted on a support structure for rotation about an axis
perpendicular to the longitudinal axis of said support structure,
said support structure is pivotably mounted on said chassis for
vertical movement relative to said chassis and for rotational
movement about the longitudinal axis of said support structure; and
said detector means includes the series-connected combination of a
first gravity-operated potentiometer mounted on said support
structure for providing a signal representative of the angle
between said leveling element and true horizontal transversely of
the machine, a second potentiometer coupled between said support
structure and said chassis for operation in response to vertical
movement of said support structure relative to said chassis for
providing a signal representative of the angle between said
leveling element and true horizontal longitudinally of the machine,
and a third potentiometer coupled between said leveling element and
said support structure for operation in response to rotation of
said leveling element about said perpendicular axis for providing a
signal representative of the rotational position of said leveling
element.
Description
DESCRIPTION OF THE INVENTION
The present invention relates to surfacing machines and equipment,
and more particularly concerns an automatic control apparatus for
regulating the grade and cross slope of a road grader or similar
earthmoving machine. In surfacing machines having ground engaging
blades for earth moving and road grading it is often important to
achieve very accurate control over the angle and height of the
blade as the machine passes over the surface to be graded. This is
especially true in the final cuts of the grading operation where
the finished grade must be accurate to within a fraction of an inch
in order to provide the proper crown of a road, for example, or to
create a desired drainage pattern.
A number of attempts have been made in the past to provide
automatic control apparatus for achieving the necessary accuracy in
grading operations. The design of modern grading and surfacing
machines lends itself to automatic operation in that the
earthmoving blade element which engages the ground is generally
carried by hydraulic cylinders which allow the ends of the blade to
be raised or lowered either independently or simultaneously to
control both the depth of the cut and the cross slope. In the
language of the earthmoving art the angle to be cut along a
fore-and-aft path with respect to the grading vehicle is known as
the grade, while the angle along a lateral transverse axis to the
machine is known as the cross slope, or simply as the slope. In
addition, on most machines the angle of the blade with respect to
the direction of travel can also be adjusted, and a like adjustment
can be made to change the vertical angle of the blade with respect
to the ground. The latter adjustments change the angle of attack of
the cutting edge of the blade with respect to the ground to suit
various operating conditions.
In the past, control over the operation of grading machines has
been achieved by locating a large number of grade stakes along the
path of machine travel by the use of surveying equipment. The
stakes would be driven into place and the desired grade would be
marked on them in a manner visible to the machine operator. The
operator would then adjust the blade of his machine by reference to
the line of stakes in order to achieve the desired cut as he moved
along the grade. It is easily appreciated that this procedure
requires considerable skill and close attention on the part of the
operator, and even then some trial and error operation is often
necessary due to soil conditions and other variables that might be
encountered. The grade stakes used in such an operation must be
placed very closely together so that the machine operator may
easily observe them and thereby work to the desired level or grade
between the stakes. Such procedures generally result in the grading
operation proceeding at a very slow rate in comparison to the rate
at which the machine itself was capable of operating, principally
because of the operator's need to carefully and slowly adjust the
operation of his machine to conform to the level and slope set by
the grade stakes.
Various attempts at automatic operation have also been made. In one
such system, a long wire is stretched taut along one or both sides
of the path to be graded in order to establish a reference level
for the equipment. Although this system furnishes a continuous
reference line for the operator instead of the spaced reference
points afforded by the stakes, the presence of a stretched wire
across the working area caused considerable disadvantages. Such a
wire must be supported at intermediate points if over a long grade
because the weight of the wire will cause considerable sagging and
thus create a deviation from the desired grade. The locating and
installation of the guide wire also requires almost as much time
and effort as the previous grade stakes. Finally, the presence of
the wire is a considerable nuisance, considering that it is easily
tripped over or run over by equipment and vehicles.
Other systems have used light beams in one fashion or another in
order to establish grade reference lines, but none are known which
ever achieved any practical utility. Ordinary light beam apparatus
suffers from lack of adequate collimation of the beam, and the
grade line thus established becomes inaccurate at long distances.
An operator using a machine controlled by such a light beam is
generally unable to determine whether his machine is on the beam or
off, and he may easily lose the beam entirely without being aware
of it. In addition, such beams are useful only for setting up the
primary grade to be cut by the earthmoving machine, and do not have
the capability of allowing control over cross slope as well.
Accordingly, it is a principal object of the present invention to
provide an improved system for controlling the ground engaging
element of an earthmoving or leveling machine which allows the
machine to cut a predetermined grade and follow a predetermined
linear path without the necessity of placing grade stakes,
stringing wires, or setting up any permanent grade reference
indications whatever. It is intended that the system make use of a
linear beam of electromagnetic energy, preferably a light beam,
which can be quickly and easily set up or shifted from place to
place on the job site.
It is also intended that the system of the present invention be
suitable for multiple use in which both ends of the ground engaging
blade of the leveling apparatus may be independently controlled.
Alternatively, it is intended that the system be useful in
conjunction with other forms of control apparatus, including
pendulum-operated cross slope detection means. In order to make the
system wholly automatic, automatic, it is contemplated that the
system include steering correction means which enable the machine
to follow the electromagnetic beam automatically without
intervention by the operator.
A more detailed object is to provide such a system in which the
leveling and steering operations are carried out sequentially, so
that the ground engaging element is first adjusted vertically to
the desired position, and then the direction of the vehicle is
adjusted by steering correction so that the more important grade
and cross slope adjustments are always accomplished first. A
proportioned response is contemplated in which the corrective
control reaction is proportioned to the relative degree of
deviation of the blade from the desired path as determined by the
beam.
A further refinement in this respect is the provision of a
compensating system which takes into account the widely varying
positions of the ground engaging element in its mounting structure
so that the control system will operate accurately without regard
to changes in the mounting position of the blade in the
machine.
Other objects and advantages of the present invention will become
apparent upon reading the following detailed description in
conjunction with the attached drawings, in which:
FIG. 1 is a perspective view of a self-propelled surfacing machine,
specifically a grader, which embodies the present invention for
automatic steering and grader blade attitude control;
FIG. 2 is an enlarged, fragmentary perspective view to better
illustrate the support means for the grader blade shown in FIG.
1;
FIG. 3 is an enlarged, fragmentary view, partly in elevation and
partly in vertical section, showing the grader blade with its
associated lift cylinders and illustrating the mounting of sensing
units provided in accordance with the present invention; and
FIG. 4 is a simplified schematic diagram of a representative form
of the automatic control system.
While the invention is described in connection with certain
preferred embodiments and procedures, it will be understood that it
is not intended to so limit the invention. Instead, it is intended
to cover all alternative and equivalent constructions as may be
included within the spirit and scope of the invention as defined by
the appended claims.
Turning to the drawings, there is shown in FIG. 1 a grading machine
employing a blade level control system constructed according to the
present invention. In this instance, the machine is a road grader
having a chassis 10 which carries a scraper blade or moldboard 11.
The grader is equipped with a cab 12 for the operator, a rear
mounted engine 13, and a pair of powered rear driving wheels 15
which exert tractive effort to propel the machine along its
intended path of travel. At the front, a pair of steerable wheels
16 is provided. The rear wheels 15 may also be made steerable in
order to give the machine greater versatility of operation. The
grader is generally of conventional design in most respects, save
for the novel control system of the present invention.
The scraper blade 11 is suspended from the chassis 10 in a manner
which allows it to be moved over a wide range of adjustment.
Adjustment during operation is achieved by a pair of hydraulic
cylinders consisting of a right cylinder 17 and a left cylinder 18,
as seen from the operator's compartment, each of which is pivoted
to the chassis 10 directly above the blade 11. The cylinders 17, 18
each terminate in a ball joint 20 on a blade mounting ring 21
carried beneath the arched central portion of the chassis 10.
The blade 11 is suspended from the chassis 10 in a manner which
allows a wide degree of freedom in positioning the blade with
respect to the ground. To start with, the operating plane of the
blade 11 is determined by a mounting ring 21 to which the blade is
attached. Although the blade 11 may be made pivotable or shiftable
with respect to the mounting ring 21, the ring is always
determinative of the plane in which the cutting surface will lie.
For example, the cutting angle of the blade 11 with respect to the
ground may be varied by a hydraulic blade circle reverse cylinder
(not shown) linking the drawbar yoke 22 and the mounting ring 21.
Another possible adjustment is accomplished by making the blade 11
shiftable longitudinally with respect to the mounting ring 21 so
that the blade may be extended beyond the track of the vehicle for
certain grading operation. This is accomplished by another
hydraulic cylinder (not shown) located behind the blade 11.
The mounting ring 21 to which the blade 11 is secured is in turn
carried by the chassis 10 by means of a yoke or drawbar 22. The
latter is a triangular structure having a ball joint 23 at one end
which connects to the forward portion of the chassis 10. The ball
joint 23 allows complete freedom of articulation of the yoke 22
with respect to the chassis, allowing the mounting ring 21 to swing
from side to side, to move up and down, and to rotate about a
longitudinal axis extending through the ball joint 23. The entire
tractive effort of the machine is thus exerted through the ball
joint 23 and in turn through the yoke 22 and blade mounting ring 21
to the blade 11.
In order to locate the mounting ring 21 and its attached blade 11
for performing a particular grading operation, a locating link 25
is provided at the rear of the yoke 22. The link 25 has another
ball joint 26 at one end which may be attached to one or the other
of two mounting points 27 located on each side of the yoke 22. The
locating link 25 is selectively positioned by a locating hydraulic
cylinder 28 which operates in conjunction with the two hydraulic
cylinders 17, 18 previously mentioned to locate the blade 11 in a
desired position. The locating link is articulated about a pivot 29
in order to allow a range of adjustment in the new position. For
instance, if it is desired to swing the blade over to one side in
order to perform a certain operation, the locating link 25 is
attached to the particular locating ball joint 26 opposite the side
on which the grading operation is to be performed. The locating
hydraulic cylinder 28 is then actuated to shift the locating link
25 toward the desired side, thereby bringing the yoke 22 with it.
This establishes the final position of the mounting ring 21 with
respect to the chassis 10, with the mounting ring then being
rotatable about an axis determined by a line extending between the
forward ball joint 23 and the locating link pivot 29. The hydraulic
cylinders 17, 18 are actuated in unison if it is desired to raise
or lower the mounting ring 21 through a path of travel determined
by the yoke 22 and locating link ball joint 26, or to rotate the
mounting ring 21 about an axis determined by the ball joint 23 and
the locating link pivot 29 as previously mentioned.
As a principal feature of the invention, a means is provided
whereby the position of the blade 11 with respect to the chassis 10
is adjusted by an automatic control system which uses as its
reference a collimated beam of light projected along the path of
desired blade travel. Such a beam is preferably generated by a
laser unit, this term being an acronym for Light Amplification by
Stimulated Emission of Radiation. Such a beam is characterized by
its very great intensity and almost total lack of dispersion or
diffusion from a straight line path. Within the distances
contemplated in the present application the dispersion or widening
of the light beam from such a source is negligible and the beam
approximates a straight line over its entire useful path of travel.
Because the beam does not diverge, its energy per unit area is
substantially undiminished except for losses which may result from
haze, smoke, dust or the like on the job site. In the present
application, a laser beam generating unit 30 is set up on a tripod
mount 30a or similar support, and located with respect to the grade
line by ordinary surveying means, such as a plumb line 30b. The
laser unit 30 is supplied by a source of electrical energy (not
shown) which may comprise a field generating unit or the like.
While the present embodiment is described with a beam generation
unit 30 which consists of a laser it will be appreciated that any
similarly intense, highly collimated electromagnetic beam would
also be satisfactory in carrying out the invention. However, the
properties of the laser unit described make it preferable for use
in the present application.
In the illustrated embodiment, the beam from the laser unit 30 is
received by a sensing unit 31 carried by one end of the blade 11.
The sensing unit 31 consists generally of a broad plate having a
plurality of sensitive areas which respond to the impingement of
the laser beam by generating an electrical output voltage. This
voltage is then used to control the various hydraulic cylinders
which effect positional changes in the blade 11. In addition,
directional changes in the vehicle itself are accomplished by means
of a control circuit which effects steering changes in the vehicle
through a steering hydraulic control cylinder 32 which is
operatively connected to the front wheels 16 of the grader.
Referring to FIG. 4 it may be seen that the sensing unit 31 is
provided with photovoltaic surface areas, each of which is
responsive to a particular direction of deviation of the blade 11
from the desired path of travel as determined by a shift in the
impingement of the laser beam. Deviation in a vertical direction is
indicated by an upper sensing surface 35 and a lower sensing
surface 36. Lateral deviation is detected by a left sensing surface
37 and a right sensing surface 38, while the correct path of travel
is indicated by the impingement of the laser beam on a central or
null surface 40. In keeping with the invention, the cross-sectional
area of the laser beam is relatively small as compared with the
surface area of the various sensitive photovoltaic elements 35, 36,
37, 38. This allows provision for a proportional control system in
which the various photovoltaic sensing elements are made
progressively move responsive as the distance away from the null
surface 40 increases. This may be achieved either by graded
deposition of the photovoltaic material on the photosensitive
surfaces 35, 36, 37, 38, or may alternatively be accomplished by
the application of a graded shading material over the
photosensitive surfaces, such as smoked glass. The shading is
arranged so that the areas nearest the null area 40 generate a
proportionately lower error signal than do the areas further
away.
The error signal generated by the sensing unit 31 is translated
into movement of the blade 11 by a system of electrically actuated
control valves which govern the movement of the various hydraulic
cylinders. The control cylinders 17, 18 may be controlled
simultaneously in order to effect an overall raising or lowering of
the blade 11, but in the illustrated embodiment an additional
feature is included by which the cross slope of the blade is kept
constant relative to the true vertical. More specifically, in one
form of the present invention the position of the blade 11 relative
to true horizontal transversely of the machine is detected by a
pendulum sensor 41 which in the illustrative embodiment is mounted
on the yoke 22. This sensor 41, illustrated schematically in FIG.
4, is of a known pendulum type in which a pendulum element is
operatively connected to a potentiometer 42 so that the resistance
value of the potentiometer is a function of the pendulum position.
With the blade 11 at a given transverse angle relative to true
horizontal, the resistance value of the potentiometer 42 will be at
a predetermined value and any variation from this angle will cause
a corresponding deviation in the resistance value.
It will be observed that changes in the rotational position of the
blade 11 with respect to the yoke 22 will cause a change in the
true cross slope which is cut as the vehicle moves along. This is
especially true when the blade 11 is cocked over at a steep angle
by suitable positioning of the locating link 25. In such instances,
the yoke 22 will be swung about its axis between the ball joint 23
and the locating link pivot 29, thereby introducing further
variation into the system. The net effect of such shifts of the
blade 11 with respect to the chassis 10 is to cause an error to
appear between the position indicated by the pendulum sensor 41 and
the actual cross slope grading position of the blade 11.
To eliminate this difficulty, and according to a further aspect of
the invention, the error resulting from shifting the position of
the blade 11 with respect to the chassis 10 is compensated by the
provision of a blade circle potentiometer 43 and a yoke position
potentiometer 45. As shown in FIG. 4, these two potentiometers are
connected in series with the output of the pendulum potentiometer
42 so that the net output of the three potentiometers 42, 43, 45 is
used for positional information of the blade 11 rather than the
output of the pendulum sensor potentiometer 42 alone. In the case
of the yoke position potentiometer 45, this instrument is arranged
with a suitable actuating means to indicate vertical angularity
change of the yoke 22 and its attached blade mounting ring 21 with
respect to the chassis 10. In other words, the potentiometer 45
supplies a signal that is representative of the position of the
blade 11 relative to true horizontal longitudinally of the machine.
This signal is simply added to or reduced from the output of the
pendulum sensor potentiometer 42 in order to generate a corrective
signal corresponding to the angular position of the blade 11 with
respect to the true horizontal transversely of the machine. The
blade circle potentiometer 43 is used to generate a further
correction signal which is dependent on the rotation position of
the blade 11 and mounting ring 21 in respect to the yoke 22. This
is done because rotation of the blade 11 will effect a change in
the true cross slope cut by the grader, making compensation
necessary in the control system.
Of course, it will be appreciated that the specific mechanical
mounting (not shown) of the potentiometers 43 and 45 may be
affected in a variety of ways. For example, since the potentiometer
43 is to provide a signal representative of the rotational position
of the blade 11 and mounting ring 21 with respect to the yoke 22,
it may suitably be driven by the rotational motion relative to the
yoke 22 of the mounting ring 21. On the other hand, since the
potentiometer 45 is to provide a signal representative of the
vertical angularity of the blade 11, it may suitably be driven by
the vertical movement of the neck of the ball joint 23 as indicated
in FIG. 2.
Up to this point, the blade position compensation system has been
described as comprising a pair of additional potentiometers 43, 45
connected in series with the pendulum potentiometer 42. It will be
appreciated that the pendulum sensor 41 could be mounted on either
the blade mounting ring 21 or the yoke 22 without departing from
the invention. The electrical output from the cross slope sensing
system is directed to an electrically actuated blade slope
hydraulic control valve 46. As indicated schematically in FIG. 4,
the valve 46 has an electric actuator which is responsive to the
output of the slope position sensor potentiometers, and also to the
output of a slope selector potentiometer 47. In a typical
installation, the slope selector potentiometer 47 would be located
in the cab of the grader so that the operator could simply dial in
the desired cross slope to be graded. This would cause a signal to
actuate the blade slope control valve 46. As long as an electrical
bias exists between the slope selector potentiometer 47 and the
output of the pendulum sensor potentiometer 42 as corrected by
potentiometers 43, 45, the unbalance will cause actuation of the
control valve 46 and admit pressure fluid to one of the blade
control hydraulic cylinders 17, 18. One end or the other of the
blade 11 is thereby moved to a new position in which the cross
slope actually cut by the grader (as indicated through the
corrected output signal of the pendulum sensor potentiometer 42) is
corrected, whereupon the signals fed to the electrically actuated
blade slope control valve 46 are equalized and the system is
brought back to neutral.
The foregoing description has been based on the blade slope control
valve 46 being connected to one or the other of the blade control
cylinders 17, 18. Thus it has been assumed that the opposite
cylinder remained stationary during the correction process which
brings the actual cross slope as cut by the machine into agreement
with the desired cross slope as indicated by the position of the
slope selector potentiometer 47. If one of the blade control
cylinders, say cylinder 17, is thus connected to the blade slope
control valve 46, the other cylinder 18 would then be used in
connection with the blade height control system. As the blade 11 is
shifted vertically by one hydraulic cylinder 18, it will be seen
that the proper cross slope position is maintained by the cross
slope control system previously described. As one edge of the blade
is shifted vertically by the cylinder 18, the balance of the blade
slope hydraulic control valve 46 is shifted and the other blade
cylinder 17 is operated until the balance is again restored and the
blade 11 is returned to the proper cross slope. Stated another way,
the cylinder 18 moves one end of the blade to the proper vertical
position, and the cylinder 17 then follows automatically to
maintain the proper cross slope.
The operation of the blade height control system is governed by
another electrically actuated control valve 48 which supplies
pressure fluid to the blade control cylinder 18 as previously
described. The blade height control valve 48 operates in a manner
similar to that of the slope control valve 46, except that the
electric actuators are connected to the electrical output of a
corresponding portion of the sensing unit 31. For instance, the
upper sensing surface 35 of the sensing unit 31 would be energized
by the laser beam when the blade 11 is too low, and therefore this
surface is connected through an amplifier 50 to that portion of the
blade height control valve 48 which will admit fluid into the
cylinder 18 which will raise the blade 11. Similarly, the lower
surface 36 is connected through an amplifier 51 to the opposite
side of the blade height control valve 48 to effect a lowering of
the blade 11 when the laser beam falls too low on the sensing unit
31.
According to yet another aspect of the invention, the correction of
the blade height and cross slope is accomplished prior to any
steering correction, whereby the more important blade positioning
function is always carried out prior to the steering correction.
This result is achieved by positioning the steering correction
control surfaces 37, 38 in the relatively narrow horizontal band
containing the null surface 40. The horizontal band including the
steering correction surfaces 37, 38 and null surface 40 functions
as a null band for vertical corrections of the blade 11, and
steering corrections are not initiated until the laser beam is in
this region.
Once in this region, the steering control sections 37, 38 of the
sensing unit 31 act through their associated amplifiers 52, 53
which in turn supply actuating signals to an electrically actuated
steering control valve 44 similar to the control valves 46, 48
previously described. When the beam falls on the left steering
control surface 37, an electrical signal is supplied through the
amplifier 52 to that portion of the steering control valve 44 which
turns the wheel 16 of the vehicle to the left, thereby bringing the
path of travel back to the desired line. When the beam again falls
on the null surface 40, the correction is removed and the vehicle
continues to travel in a straight path. Preferably, the steering
control surfaces 37, 38 are also provided with a graded surface
which increases the relative output signal as the beam falls
further from the null surface 40. In this way a proportional
control is achieved which provides large corrections for large
deviations from the desired path and smaller corrections for
deviations requiring a smaller corrective action.
It will be appreciated that the blade positioning means of the
present invention need not be restricted to the embodiment
disclosed, but may be used in other ways. For instance, to replace
the slope control potentiometers 42, 43, 45 and 47, an additional
laser unit 60 can be used to project a beam generally parallel to
the beam of the first laser unit 30. The blade 11 is then equipped
with an additional sensing unit 61 to correctively control the
cylinder 18 in a manner similar to the previously described manner
in which the sensing unit 31 is used in conjunction with the first
laser beam to correctively control the cylinder 17. In this manner
both ends of the blade 11 are independently controlled to achieve
the desired blade position along the entire path of vehicle travel.
Only one laser sensing unit 31 is used to control steering when the
second beam is used. If desired, a varying cross slope may be
achieved with this apparatus by shifting one or the other of the
laser beams so that they no longer lie in the same plane, but are
still substantially equally spaced from each other at all points
along their effective range. This distance will be dictated by the
distance between the respective null points 40 of the two sensing
units 31, 61.
An important advantage of the laser beam in the present invention
is the fact that its impingement on the sensing unit 31 is visible
to the machine operator. In this way he can maintain a constant
check on the operation of his machine, and can even "find" the beam
again in the event that the sensing unit 31 should shift out of the
beam entirely. If desired, the operator can even use the beam as a
visual guide for manual control of the machine.
* * * * *