U.S. patent number 3,887,012 [Application Number 05/421,119] was granted by the patent office on 1975-06-03 for automatic levelling system for earth working blades and the like.
This patent grant is currently assigned to Caterpillar Tractor Co.. Invention is credited to Donald Frederick Coleman, Edward Lawrence Johnson, Rolland Dale Scholl, William Edward Streight.
United States Patent |
3,887,012 |
Scholl , et al. |
June 3, 1975 |
Automatic levelling system for earth working blades and the
like
Abstract
A laser beam or like radiant energy source is swept in a
reference plane in order to generate pulsating radiant energy
within the plane so a system can automatically adjust an earth
working blade or the like in reference thereto. A special receiver
is attached to the blade which has a plurality of vertically spaced
energy receiving regions formed by solar cells or the like,
arranged so each of the regions is isolated from the others so that
only one region is excited by the beam at a given time. A central
region in the receiver corresponds to a null point and circuitry in
the system employs digital gating elements to avoid ambiguities and
to effect relative fast blade movement when the null point of the
receiver is out of the plane by a relatively large amount and
relatively slow movement when the null point is only slightly off
the plane.
Inventors: |
Scholl; Rolland Dale (Peoria,
IL), Coleman; Donald Frederick (Dunlap, IL), Johnson;
Edward Lawrence (Peoria, IL), Streight; William Edward
(East Peoria, IL) |
Assignee: |
Caterpillar Tractor Co.
(Peoria, IL)
|
Family
ID: |
23669232 |
Appl.
No.: |
05/421,119 |
Filed: |
December 3, 1973 |
Current U.S.
Class: |
172/4.5; 356/138;
37/907; 250/239 |
Current CPC
Class: |
E02F
3/847 (20130101); G01C 15/006 (20130101); Y10S
37/907 (20130101) |
Current International
Class: |
E02F
3/84 (20060101); E02F 3/76 (20060101); G01C
15/00 (20060101); E02f 003/76 () |
Field of
Search: |
;172/4.5,779 ;37/DIG.20
;250/239 ;356/138,152,153 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
The Laserplane System, Agr. Eng., August, 1971 pp. 418 and 419 by
David C. Studebaker. .
Laser Beam Controls Ditch Digger, Farm Journal, Dec., 1969, p. 14
by Bob Coffman..
|
Primary Examiner: Burr; Edgar S.
Assistant Examiner: Sewell; Paul T.
Attorney, Agent or Firm: Phillips, Moore, Weissenberger
Lempio & Strabala
Claims
What is claimed is:
1. In an earthworking implement control system for maintaining an
implement in a fixed relationship to a plane comprising means for
producng a narrow beam of radiant energy of a fixed wave length,
means for sweeping said beam throughout the plane to produce
pulsating radiation at any site in the plane, a multidirectional
receiving control mounted on the implement for receiving the beam
comprising a receiving means including a plurality of sets of at
least two series connected angularly disposed light actuated cells
for producing an electric signal in response to impingement of said
beam thereon, spacer means for supporting said sets of cells in a
stacked vertical relationship so that there is at least a first set
of said cells and a second set of said cells spaced from said first
set across a null region, a plurality of mutually parallel opaque
planar members horizontally disposed on opposite sides of said sets
of cells and thereby defining said null region between said sets so
said planar members are operable to define at least three beam
defining channels, and circuit and power means responsive to an
electric signal from said cells for moving said implement in a
direction when one of said sets produces an electrical signal
whereby the null region of said receiving means is moved into the
plane of said beam.
2. The receiving control defined in claim 1 wherein the receiving
means includes filtering means for excluding radiant energy from
the cells at wave lengths below that of said beam producing
means.
3. The receiving control defined in claim 2 wherein said filtering
means includes a deformable tinted impervious plastic sheet
overlying the peripheral edges of the opaque planar members for
excluding deleterious matter from the channels.
4. The receiving control defined in claim 1 wherein the individual
cells of each said set are angularly displaced from one another by
an angle of about 60.degree. so that the receiving means has a
substantially flat response to beams impinging thereon from all
directions within .+-.90.degree. of a plane bisecting the
60.degree. angle.
5. The receiving control defined in claim 1 in combination with a
plurality of third cells one of which is associated with each said
set of cells, the individuall cells of each set being displaced
about 60.degree. from one another so that said receiving means has
a substantially flat response to beams impinging thereon from all
directions.
6. The receiving control defined in claim 1 including a third set
of cells adjacent said first set and opposite said null region and
a fourth set of cells adjacent said second set and opposite said
null region, whereby the circuit and power means responding to said
third and fourth sets of said cells moves the implement faster than
when responding to said first and second sets.
7. The receiving control defined in claim 1 wherein circuit and
power means comprises a source of pressurized fluid, a double
acting cylinder having a piston and rod in driving relation to said
implement, a valve for controllably delivering fluid to said
cylinder to selectively move said piston in said cylinder, and
electrical means for controlling said valve in response to the
signals from the cells.
8. The receiving control defined in claim 7 wherein the electrical
means comprises circuit means for producing a DC signal having a
first polarity when said receiving means is in a position such that
the beam impinges on said first set of cells and a second polarity
when said receiving means is in a position such that the beam
impinges on said second set of cells.
9. The receiving control defined in claim 8 wherein said DC signal
producing means including means for connecting the cells of said
first set in series opposition of the cells of said second set so
that the polarity of the output voltage is indicative of the
direction that the receiving means is displaced from said plane,
first and second comparators having input terminals connected to
the series connected cells, said first comparator producing an
output signal when said first set of cells receives said beam and
said second comparator producing an output signal when said second
set of cells receives said beam, logic means for generating an
inverse of the output of said first comparator, logic means for
generating an inverse of the output of said second comparator, a
first gate for producing a first control signal when there coexists
at the input thereof an output signal from said first comparator
and the inverse of said second comparator, a second gate for
producing a second control signal when there coexists at the input
thereof an output from said second comparator and the inverse of
said first comparator, means for inverting the output of said first
gate, and means for combining the outputs of said inverting means
and said second gate.
10. The receiving control defined in claim 6 wherein said circuit
and power means includes means for generating an A binary signal
responsive to impingement of said beam on said first set of light
activated cells, a B binary signal responsive to impingement of
said beam on said second set of light activated cells, a C binary
signal responsive to impingement of said beam on said third set of
light activated cells, and a D binary signal responsive to
impingement of said beam on said fourth set of light activated
cells, first logic means responsive to the signals A.sup.. B.sup..
C.sup.. D and B.sup.. A.sup.. C.sup.. D for transmitting to the
power means a signal of relative low magnitude of approprate
polarity to move the implement and sets of cells in a direction to
bring said null region of said receiving control into the plane,
and second logic means responsive to the signals C.sup.. B.sup.. D
and D.sup.. A.sup.. C for transmitting to said circuit and power
means a relatively high magnitude signal of appropriate polarity to
move the implement and sets of cells in a direction to bring said
null region of said receiving means into the plane.
11. The receiving control defined in claim 10 wherein the circuit
and power means includes a third logic means operable to indicate
the last polarity registered by the second logic means when the
receiving means completely leaves the plane.
Description
BACKGROUND OF THE INVENTION
This invention relates to a system for automatically maintaining an
earth working blade on a motor grader or the like in fixed relation
to a plane in order to achieve an earth surface that conforms to a
desired grade or plane. Because the system is totally independent
of the terrain engaging wheels or tracks on the motor grader,
employment of the system materially enhances the accuracy and speed
with which a rough surface can be graded to a smooth surface of
desired configuration.
The nature and advantages of the present invention can be more
fully appreciated in the context of the known prior art,
wherein:
U.S. Pat. No. 2,916,836, issued to Stewart, et al., discloses a
transit mounted light source which produces a steady flat beam of
non-coherent light in a plane used to activate two vertically
spaced photo-electric cells on the vehicle, so one or the other is
excited by the light beam when the structure supporting the photo
cells deviates from the plane of the light beam. The patented
structure is limited in its accuracy because the light beam is
non-coherent, and the sensing mechanism is not adapted to detect
the degree to which the vehicle deviates from the plane.
U.S. Pat. No. 3,009,271 issued to Kuehne et al employs an
incandescent light source which is modulated and sensed by two
horizontally spaced photo-electric devices mounted on an earth
working vehicle. For successful operation of the device, rather
precise alignment between the transit mounted light source and the
earth working vehicle are required, thereby detracting from the
utility and accuracy of the disclosed apparatus.
U.S. Pat. No. 3,046,681 issued to Kutzler discloses an earth
working vehicle which carries a light source that is projected to a
transit mounted reflector from which the light beam is returned to
sensors carried on the vehicle. The reflector has limited angular
effectiveness, thereby requiring rather precise positioning between
the reflector and the earth working vehicle. Moreover, the system
employs numerous moving parts on the vehicle which, in view of the
severe environment of operation, are of marginal accuracy and
longevity.
U.S. Pat. No. 2,796,685 issued to Bensinger discloses a transit
mounted electromagnetic energy source which cooperates with an
antenna mounted on an earth working vehicle to maintain the earth
working parts of the vehicle in fixed relation to the plane of the
radiation. The system disclosed employs very sensitive detectors
which are subject to noise. Moreover, the system utilizes the
output of the detectors in an analog system.
Lasers have been used in systems for controlling functions on
vehicles as illustrated in U.s. Pat. No. 3,494,426 to Studebaker,
No. 3,604,512 to Carter, et al., and No. 3,659,949 to Walsh and
Apostolico.
An object of the present invention is to provide a system of the
type referred to above wherein the location of the plane defining
radiant energy source is not critical. This object is achieved
according to the present invention by providing a receiver that has
an extremely broad reception angle. As will appear in more detail
hereinafter one form of receiver according to the present invention
is operative over 180.degree. and another form is operative over
360.degree..
Another object of the present invention is to provide a receiver in
which the response is substantially flat over all angles of
incidence of the light beam thereon. Achievement of this object
enhances the accuracy of the device and simplifies the circuitry
contained therein. This object is achieved by providing two or more
solar cells in each region of the receiver and orienting the solar
cells with respect to one another so as to achieve the flat
response.
Still another object of the present invention is to provide a
system that generates an error signal that is proportional to the
degree of displacement of the blade from the reference plane.
Because the receiver of the present invention has a plurality of
discrete spaced apart light sensitive regions, excitation of the
remote regions results in an error signal of greater magnitude than
is produced upon excitation of regions closer to the reference
plane.
Yet another object of the present invention is to provide a system
of the type referred to above, that is virtually immune to
ambiguities arising from spurious light signals and/or minor
misalignments of the apparatus. This object is achieved by
providing a digital system for processing the outputs of the
various radiant energy sensors. Appropriate gating of such signals
renders the system virtually immune to ambiguities or false
signals.
A feature and advantage of the present invention arising from
employment of a pulsating radiant energy source is that the digital
circuitry requires no internal clock, but relies on the repetitive
pulses for timing.
A further object of the present invention is to provide a system
that will restore the earth working blade to the correct position
even when the blade has been displaced by a large amount as occurs
at the outset of grading operations on extremely rough terrain. The
provision of a plurality of energy sensors in the receiver of the
present invention in cooperation with the digital circuitry
employed makes achievement of this object possible.
A still further object of the present invention is to provide
visual indicators to apprise the operator that the earth working
machine system is operating correctly. This object is achieved in a
simple straight-forward way because of the digital elements used in
the system.
The foregoing together with other objects, features and advantages
of the present invention will be more apparent after referring to
the following specification and accompanying drawings.
SUMMARY OF THE INVENTION
The present invention employs a transit mounted laser that includes
a motor driven reflector for sweeping the beam from the laser
throughout a reference plane so at any given location within the
place there is a pulsating radiant energy signal whereby a special
receiver mounted on the blade of an earth working vehicle having a
plurality of discrete active sensors, such as solar cells that are
optically isolated from one another can generate outputs for a
digital circuit that generates a corrective or error signal. The
corrective signal has a polarity and magnitude proportional to the
direction and amount that the receiver deviates from the plane,
which signal is employed to move the blade so that the receiver
resumes proper orientation with respect to the plane.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a motor grader provided with a
system according to the present invention.
FIG. 2 is a perspective view of one embodiment of a receiver
according to the present invention, with portions being broken away
to reveal internal details.
FIG. 3 is a perspective view of another embodiment of a receiver
according to the present invention, portions being broken away to
reveal internal details.
FIGS. 4A, 4B and 4C are schematic diagrams showing the circuitry
employed in the present invention.
FIG. 5 is a graph of energy sensor output versus angular
orientation for various configurations of light sensors employed in
the present invention.
FIG. 6 is a perspective view of a fragment of the motor grader of
FIG. 1, showing the general arrangement of the present invention in
more detail.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring more particularly to the drawing, FIG. 1 shows a motor
grader 12 which exemplifies an earth working vehicle with which the
present invention can be used to advantage. Motor grader 12 has an
earth working blade 14 that is carried on arms 16, the upper ends
of which are supported on a circle 18. As is conventional, circle
18 is driven through a gear box 20 to establish the angular
position of blade 14 and the circle is carried on a draw bar 22
which is pivotally mounted to the frame of grader 12 in bolster 24.
Hydraulic actuators 26 move the free ends of the draw bar
vertically so as to effect corresponding movement of blade 14. This
structure is conventional and does not, per se, constitute a part
of the present invention. As will appear in more detail, the system
of the present invention controls hydraulic actuators 26 to
maintain the position of blade 14 at a constant distance from a
reference plane.
Mounted on blade 14, and extending upward therefrom, is a mast 28
which supports on its upper end a receiver 30. Receiver 30 is
adapted to receive a pulsating radiant energy beam 31 from a source
32 which is supported on a tripod 34, which radiant energy beam is
confined to a reference plane, which is above the finished grade
which blade 14 is used to achieve. Mast 28 has a telescoping
adjustment 36 to effect appropriate spacing between the reference
plane and the plane of the finished grade. An angular adjustment,
including a hydraulic cylinder 38, allows adjustment of the angular
relationship between the reference plane and the mast when the
slope of the blade is changed.
For producing beam 31 in a reference plane, radiation source 32
includes a laser 40 supported in a housing 42 as shown in FIG. 4A.
Housing 42 is of hollow cylindric shape and has a cover 44 which is
supported for rotation by a bearing 46 so that the cover can rotate
with respect to the housing. Cover 44 has a depending ring gear 48
which meshes with a pinion 50 driven by a motor 52, so a reflecting
prism in alignment with laser 40 and mounted in cover 44 reflects
the energy from laser 40 through an opening 56 in the cover. Beam
31 is thus swept through a plane that is normal to the axis of
rotation of the cover on the housing. Because the laser 40 produces
a very narrow beam of coherent radiation and prism 54 is
continuously rotated, beam 31 is swept throughout the plane so that
there exists at any given site in the plane a pulsating field of
radiant energy. This radiant energy plane is monitored by receiver
30.
Referring now to FIG. 2, the receiver 30 includes a base 58 which
is secured to the upper end of mast 28, and the base is preferably
of hollow construction so electrical components can be mounted
therein as described in more detail hereinafter. On the top 60 of
the base three tiers of spacers 62, 64 and 66 are stacked at
uniform intervals around the circumference thereof. The spacers
support, parallel to top 60, a plurality of opaque circular members
68, shown in FIG. 2. These spaced apart opaque members preferably
are coated on both upper and lower surfaces with a dull black paint
to avoid energy reflection, and define therebetween energy channels
70, nine such channels being shown in FIG. 2. Located within each
of the energy channels is a prism shaped support member 72, the
upper and lower faces of which define equilateral triangles and
which are secured to the respective surfaces of opaque members 68.
On each of the three vertical faces of each prism shape support
member, solar cells 74 are supported. A solar cell such as that
distributed by Central Laboratories under the trade designation N
120 CGN/P is suitable. These cells produce an electrical voltage in
response to impingement thereon of radiant energy of appropriate
wave length and this voltage is carried by output conductors of the
solar cells (not shown) through a central opening 76 to the base 58
for connection to the circuitry therein. Although the solar cells
for only one channel 70 are shown in FIG. 2, it is to be understood
that each of the channels, with the exception of a central or null
channel 70', is provided with cells configured as shown in the
uppermost channel shown in FIG. 2. In order to immunize the cells
from spurious signals from sunlight and the like, it is desirable
to interpose a filter medium between the solar cells and the energy
entering channels 70. One form of filter medium shown at 78 is a
red plastic transparent sheet directly overlaying the active faces
of the solar cells when the laser 40 produces a beam of radiant
energy of a wave length of 6328 angstroms. An alternate form of
filter medium is a plastic sheet 80 of the same material as plastic
sheet 78. Plastic sheet 80 is wrapped entirely around the exterior
of the receiver and fastened by suitable means, such as rivets 82.
Plastic sheet 80 has the additional advantage that it excludes
deleterious substances from the interior of channels 70.
The solar cells 74 in each channel 70 are series connected and it
has been found that the output of the solar cells within one
channel when arranged at angles of 60.degree. with respect to one
another produces a substantially flat electrical output for most
angles of impingement of the beam from radiant energy source 32.
Referring to FIG. 5, the output for this configuration is depicted
by curve 84, while other configurations exhibit more directional
sensitivity. For example, curve 86 indicates the output response
when the solar cells are oriented at 90.degree.with respect to one
another and curve 88 indicated the response when the solar cells
are oriented at an angle of 120.degree. with respect to one
another. Thus FIG. 5 graphically illustrates the importance of a
60.degree. angle between the solar cells, since it affords an
optimally flat output response irrespective of the angle
impingement of the radiant energy source.
An alternate form of receiver is shown at 30' in FIG. 3. The
receiver has a response over a 180.degree. angle in contrast to the
360.degree. response angle of the receiver of FIG. 2. The details
of construction of receiver 30' are substantially identical as
those described hereinabove in respect to FIG. 2 except that the
receiver is of semi-cylindric configuration having an opaque
non-reflective vertical backing plate 90. Opaque non-reflective
semi-circular plates 92 define a plurality of radiant energy
channels 94 with prism shaped member 96 supporting solar cells 98
therein. The solar cells in each channel 94 are oriented at
60.degree. with respect to one another and are provided with an
overlying filter medium 100 and/or a filter medium 102 that
entirely circumscribes and encloses the structure.
As both the embodiments of the invention shown in FIGS. 2 and 3
have nine channels, further description will be made with reference
to FIG. 3, having its central channel identified by reference
character 94a. This channel is referred to as a null channel in
that there are no active solar cells in such channel. When the
channel 94b above channel 94a receives energy from source 32, the
blade on which the receiver is mounted is below the desired plane.
As will appear hereinafter, excitation of channel 94b causes the
blade to be raised at a slow rate in order to effect a relatively
fine adjustment of the blade position. Channel 94b is consequently
referred to as the raise-fine channel. When the channels 94c, above
channel 94b, are excited by the energy from source 32, it indicates
a situation wherein the blade 14 is well below the desired
location, rapid corrective movement of blade 14 is thus required.
Because the apparatus responds to excitation of channels 94c by
effecting rapid upward movement of the blade, channels 94c are
referred hereinafter as the raise-coarse channels.
When the channel 94d, immediately below null channel 94a, is
excited by radiant energy source 32, the blade 14 is slightly above
the desired location. Excitation of the solar cells in channel 94d
thus effects relatively slow lowering of the blade and for that
reason, channel 94d is referred to hereinafter as the lower-fine
channel. When the channels 94e, below channel 94d, are excited, the
blade is well above the desired location and rapid lowering
movement is required, in consequence of which channels 94e are
referred to hereinafter as lower-coarse channels. Channels 94b and
94d, because they are relatively close to null region 94a, are
referred to as proximal regions. Excitation of either of the
proximal regions effects relatively slow restorative movement of
the blade 14. Channels 94c and 94e, because they are relatively
remote from null region 94a, are referred to as distal regions, and
excitation of either of the distal regions effects relatively rapid
restorative movement of the blade 14.
In FIG. 4A solar cells 98 are shown schematically and are shown in
positions approximating the relative position shown in FIG. 3, and
in each channel there is a set of two solar cells that are series
connected. With respect to a common or ground connection 106, the
solar cells in channels 94b and 94c, located above null region 94a
are arranged to produce a positive going output signal whereas the
solar cells located below the null region in channels 94d and 94e
are arranged to produce a negative going output. In FIG. 4A only
one raise-coarse channel 94c and only one lower-coarse channel 94
is shown, because the other respective channels effect an
equivalent response, i.e., to restore the blade and receiver toward
a null position at a relatively rapid rate.
Because the radiant energy impinging on the solar cells is
pulsating, due to rotation of reflecting prism 54, the output of
the excited solar cells will be a pulse. The output of the solar
cells in channel 94c and AC coupled to the input of an operational
amplifier 117 through a capacitor 108 and an input resistor 109.
Similarly, the output of the solar cells in channel 94b is AC
coupled to the input of an operational amplifier 116 through a
capacitor 110 and input resistor 111, the output of the solar cells
in channel 94d is AC coupled to the input of amplifier 116 through
a capacitor 112 and input resistor 113 and the output of the solar
cells in channel 94e is AC coupled to the input of amplifier 117
through a capacitor 114 and input resistor 115. Thus, the signal
appearing at the input of amplifier 116 is a positive pulse when
there is an output from channel 94c and is a negative pulse where
there is an output from channel 94d. The signal at the input of
amplifier 117 is a posivite pulse when there is an output from
channel 94c and is a negative pulse when channel 94e has an
output.
The outputs of channels 94b and 94d, which correspond to relatively
small deviations from the desired location of blade 14, are
connected to the input of operational amplifier 116 which is
arranged to invert the signal supplied thereto and to produce at
the output thereof an amplified signal having a polarity depending
on whether the energy from source 32 impinges on channel 94b or
channel 94d. Likewise, the outputs of the solar cells in channel
94c and 94e are connected to operational amplifier 117 which
corresponds in structure and function to amplifier 116. The output
of amplifier 116 is connected to an input network to a pair of
operational amplifiers 118 and 119 that are connected as
comparators so that when the signal input to amplifier 118 is above
a reference signal, there will be at the output terminal of the
amplifier a signal; this occurs when the solar cells in channel 94b
are excited and accordingly the output of amplifier 118 is
designated as B. When the output signal from amplifier 116 is a
positive going signal, amplifier 119 produces an output signal;
this occurs when the solar cells in channel 94d are excited and the
output of amplifier 119 will therefore be referred to as D. In a
similar fashion, the output of amplifier 117 is connected to an
input network to amplifiers 120 and 121 which are identical in
structure and function to amplifiers 118 and 119. Thus when the
solar cells in channel 94c are excited, a positive pulse is
produced at the input of amplifier 117 and inverted by that
amplifier so as to produce an output at amplifier 120. The output
of amplifier 120 is accordingly designated C. Excitation of the
solar cells in channel 94e will produce an output signal at
amplifier 121, such output being designated hereinafter as E.
With reference to FIG. 4B, the output of each of the amplifiers
118, 119, 120 and 121 is fed to an AND gate. More specifically,
signal B from amplifier 118 is connected to one of two inputs of an
AND gate 122; the output D of amplifier 119 is connected to one of
two inputs of an AND gate 123; the output C of amplifier 120 is
connected to one of two inputs of an AND gate 124; the output E of
amplifier 121 is connected to one of two inputs of an AND gate 125.
The other input of each of the AND gates is the complement or
inverse of the output of the solar cells of the opposite channel.
This can be illustrated most concisely in Boolean notation as
follows:
122 = B .sup.. D
123 = D .sup.. B
124 = C .sup.. E
125 = E .sup.. C
The output of each gate 122-125 is fed to the input of a single
shot or monostable multi-vibrator. That is to say, the output of
AND gate 122 is connected to the input of a single shot
multi-vibrator 122s; the output of AND gate 123 is connected to the
input of the one shot multi-vibrator 123s; the output of AND gate
124 is connected to the input of a single shot multi-vibrator 124s;
the output of AND gate 125 is connected to the input of a single
shot multi-vibrator 125s. In order to provide the complement of
each of the signals there is an inverter in the output of each of
the multi-vibrators, such inverter circuits 122i being identified
with the reference characters corresponding to the AND gates. Thus
it will be seen that only one of the single shot multi-vibrators
will have a high output with the particular mutli-vibrator being
determined by the channel on which the radiation from source 32
impinges.
Although the outputs of the multi-vibrators are substantially
accurate and free of ambiguities, a further gating stage is
desirable to reduce further the possibility of erroneous control
signals. The gating stage includes AND gates 126 and 127 which have
four inputs and AND gates 128 and 129 which have three inputs. The
output of AND gate 126 will be referred to herein as B'; the output
of AND gate 127 will be referred to herein as D'; the output of AND
gate 128 will be referred to herein as C'; the output of AND gate
129 will be refereed to herein as E'. The following equations taken
in conjunction with FIG. 4B define the operations performed in the
gating stage:
B .sup.. D .sup.. C .sup.. E = B'
D .sup.. B .sup.. C .sup.. E = D'
C .sup.. D .sup.. E = C'
E .sup.. B .sup.. C = E'
It will be seen from the foregoing that in order to produce a
signal for moving the blade 14 slowly, it is necessary that there
be no signal in the other three active channels. For moving the
blade rapidly, however, AND gates 128 and 129 afford priority of a
coarse signal in a given direction over the fine signal in the same
direction. Stated otherwise, a signal C' (corresponding to
raise-coarse) is produced without regard to the presence or absence
of a signal in the raise-fine channel. Similarly, signal E'
(corresponding to lower-coarse) is produced without regard to the
presence or absence of a signal in the lower-fine channel.
The signals B', C', D' and E', because of the circuitry described
up to this point, are highly immune to ambiguities such as might
arise from noise and/or the entry of spurious radiation into one or
more of the channels in receiver 30'. Such signals are used to
derive an output that has a magnitude and polarity corresponding to
the direction and amount that is necessary to restore receiver 30'
so that null region 94a is within the reference plane produced by
source 32. Such output signal appears at 130.
Output signal 130 is constituted by the output signal from an
operational amplifier 132 which is arranged so that the output
corresponds in magnitude but is of opposite polarity relative to
the magnitude and polarity of the input signal. Signal D'
(corresponding to the lower-fine channel) is fed to the input
through a resistor RLF and the signal E' (corresponding to the
lower-coarse channel) is fed to the input through a resistor RLC.
Resistor RLF has a higher resistance (e.g., 5 times) than the
resistance of RLC so that amplifier 132 produces a greater output
in response to signal E' than the amplifier produces in response to
signal D'. The difference in magnitude is reflected at output
130.
Signal B' (corresponding to the raise-fine channel) is connected to
an inverting amplifier 134 through a resistor RRF. Signal C'
(corresponding to the raise-coarse channel) is connected to the
input of inverting amplifier 134 through a resistor RRC. Resistor
RRF is greater than (e.g., 5 times) the resistance of RRC so that
the magnitude of the output of amplifier 134 is proportional to the
speed at which it is desired to restore the blade toward the null
position. The output of inverting amplifier 134 is connected to
input 133 of amplifier 132 so that the signal at the output of
amplifier 132 has a polarity and magnitude that corresponds to the
desired direction and speed of movement of blade 14.
Referring to FIG. 4C the signal at output 130 is connected to a
power amplifier 135 which activates an electrohydraulic transducer
136. The transducer controls cylinder 26, the piston and rod of
which are attached to blade 14.
The transducer 136 includes a hydraulic valve 137 which controls
delivery of hydraulic fluid from a pump 138 and a reservoir 139 to
cylinder 26. Valve 137 includes a valve body having a center
section 140 ported to inhibit fluid communication between pump 138
and cylinder 26, a down section 142 which is ported to deliver
hydraulic fluid from pump 138 to the top of cylinder 26, and an up
section 144 which is ported to deliver hydraulic fluid to the lower
end of cylinder 26. The valve body is maintained in the position
shown in FIG. 4C by springs 145 and 146. Up section 144 is moved
into an active position in response to energization of the solenoid
147 and down section 142 is moved into active position by
energization of a solenoid 148. The inputs to the solenoids are
derived through oppositely polarized diodes 149 and 150 from power
amplifier 135 so that depending on the polarity of the output of
the power amplifier, hydraulic fluid will be delivered to the end
of cylinder 26 appropriate for the direction of desired movement.
When the magnitude of the signal at lead 130 is of relatively high
magnitude (corresponding to a relatively large deviation of
receiver 30 from the null position) the valve body is fully
displaced toward one extreme or the other. When the signal on
output lead 130 is of relatively low magnitude (corresponding to a
slight deviation of the receiver from the null position) the valve
body is only partially displaced, thereby affording a restricted
path for the hydraulic fluid and a corresponding slow movement of
the piston rod associated with cylinder 26. Accordingly, blade 14
is moved in a direction and at a speed appropriate for the
direction and degree of deviation from the null position.
In order to limit the size of receiver 30, the circuitry of the
present invention is arranged to produce an error signal of correct
magnitude and polarity even though blade 14 and receiver 30 deviate
from the null position to such a large degee that the radiant
energy from source 32 impinges on no part of the receiver. For
achieving this advantageous mode of operation, the invention
provides a receiver extender circuit 152 (see FIG. 4B). The
receiver extender circuit includes two substantially identical
sections, one for moving the blade in each direction, depending on
the direction from which receiver 30 leaves the plane of radiant
energy. The upper section of the receiver extender circuit, as
viewed in FIG. 4B acts to lower the receiver and blade 14 should
the entire receiver reach a position totally above the plane of
radiant energy from source 32. Such section includes a flip-flop
154 which is set by signal E' (corresponding to the lower-coarse
channels). The flip-flop 154 is reset by the output of an OR gate
155. As is clear from FIG. 4B, OR gate 155 functions according to
the following equation:
155 = D' + B' + C'.
Thus, flip-flop 154 is reset when the system has responded to
signal E' to return the receiver to a position at which beam 31
impinges on one of channels 94d, 94b or 94c. If receiver 30 is
totally above the plane of the radiant energy from source 32, OR
gate 155 will not produce a signal to reset flip-flop 154 whereupon
the output 156 of the flip-flop, which is connected to one input of
an AND gate 157, will remain high. The other input of AND gate 157
is suppled with a high input when the receiver is totally above the
plane of the radiant energy beam. Because signal E' (lower-coarse)
also triggers a single shot multi-vibrator 158, the output of which
is inverted by an inverter 159 before connection to the input of
AND gate 157. Single shot multi-vibrator 158 produces a high output
in response to signal E' that has a duration in excess of the rate
of pulsations of the energy in the reference plane, i.e., a period
in excess of the time required for one revolution of prism 54. By
virtue of inverter 159, there is a low input to gate 157 for such
extended duration. If on the succeeding pulse, however, no energy
is received by any of the channels in receiver 30, flip-flop 154 is
not reset and output lead 156 thereof remains high. When the period
of multi-vibrator 158 ends, the output of the multi-vibrator goes
down and the output of inverter 159 goes up, whereupon a signal is
produced at the output of AND gate 157. Such signal is connected
through a resistor 160 to the input of amplifier 132, whereby an
error signal of appropriate magnitude and polarity is produced at
output 130, thereby activating transducer 136 and cylinder 26 to
restore the receiver and blade to a position within the reference
plane. At such time as the receiver returns to the plane of the
beam, multi-vibrator 158 is triggered when beam 31 impinges on
channel 94e. This causes the output of inverter 159 to go down so
as to turn off gate 157. As the receiver approaches the null point,
OR gate 155 is activated so as to reset flip-flop 154, which also
turns off gate 157.
The lower section of receiver extender circuit 152 operates
identically except that it is arranged to raise the receiver and
blade 14 when those elements assume a position below the reference
beam. Accordingly, no description of the lower section is
considered necessary and each element of corresponding function has
the same reference character as used with the upper section with
the addition, however, of a prime.
The circuit of FIG. 4B includes means for affording to the operator
of earth working vehicle 12 a visual indication of the particular
mode at which the system is operating at any given time. For
indicating that the system is operating in the lower-fine mode, the
output D' of AND gate 127 is connected to an amplifier 162d which
actuates a lamp 164d which is visible to the operator. When lamp
164d is illuminated, it apprises the operator that the receiver is
in the lower-fine mode of operation, i.e., that beam 31 is
impinging upon channel 94d of receiver 30. A similar amplifier 162b
is activated by AND gate 126 to cause illumination of a lamp 164,
illumination of which apprises the operator that the system is
operating in the raise-fine mode. An amplifier 162e receives its
input from AND gate 129 and drives a lamp 164e to apprise the
operator that the system is operating in the lower-coarse mode. An
amplifier 162c is connected to the output of AND gate 128 and
drives a lamp 164c, illumination of which apprises the operator
that the system is operating in the raise-coarse mode. Adjacent
lamps 164 are indicia 166 so that the operator can understand the
significance of the lamps.
To afford an indication to the operator that the system is in the
null region or either the raise or lower fine region, a panel lamp
168 is provided. Lamp 168 is driven by an amplifier 170, the input
of which is controlled by an OR gate 172. As can be seen in FIG.
4B, OR gate 172 produces an output which energizes amplifier 170 to
illuminate lamp 168 if a flip-flop 174 is set or if an OR gate 176
is on. OR gate 176 also causes flip-flop 174 to reset. The
operation of OR gate 176 is most clearly described by the following
equation:
176 = C' + E'
Thus, when the system is correcting in either the raise-coarse mode
or the lower-coarse mode, a pulsating signal, corresponding to the
rotative speed of energy source 32 is applied to amplifier 170,
whereby lamp 168 is activated in an intermittent or blinking mode.
When the system is operating in either the raise-fine mode or the
lower-fine mode, flip-flop 174 is set by virtue of an OR gate 178.
The function of OR gate 178 is defined by the following
equation:
178 = B' + D'
When flip-flop 174 is set, a continuous signal appears at its
output 180 which is fed through OR gate 172 to amplifier 170.
Accordingly, lamp 168 will be illuminated continuously. Lamp 168 is
also illuminated continuously when the reference beam 31 is within
null region 94a, because the beam in reaching the null region goes
through either channel 94b or channel 94d so as to set flip-flop
174 through OR gate 178. The flip-flop is reset only when beam 31
impinges on channels 94c or 94e. Accordingly, even though none of
the lamps 164 are illuminated, the operator of the grader is
apprised of the mode of system operation by lamp 168.
The system of the present invention operates as follows: Usually
radiation source 32 is set up at the job site and is adjusted in
accordance with conventional surveying procedures to produce a
reference plane. Telescoping joint 36 assists in establishing
receiver 30 at the correct height. Radiation source 32 is then
activated, thereby producing a pulsing energy beam 31 in a
reference plane above the desired plane of the finished grade with
motor 52 adjusted to provide a suitable sweep frequency; in one
system designed according to the present invention, a sweep
frequency between 4.5 cycles per second and 10.5 cycles per second
was found satisfactory.
Although the invention is exemplified hereinabove in connection
with a horizontal reference plane, it will be obvious that the
system can be adapted for use with respect to a plane oriented in
any direction and that receiver 30, by use of the system of this
invention, can be restored in an appropriate direction so that null
region 94a intersects the beam produced by source 32.
While the receivers exemplified in FIGS. 2 and 3 employ nine
channels, this number is merely exemplary and in certain instance,
a greater or lesser number of channels can be employed. Thus, it
will be seen that the present invention provides a substantially
automatic system for maintaining a working member in a proper
relation to a plane. The employment of digital circuitry in
generating the error signal enhances the accuracy of the system and
avoids ambiguities such as might arise from the entrance of
spurious energy into receiver 32.
Although one embodiment of the invention has been shown and
described, it will be obvious that other adaptations and
modifications can be made without departing from the true spirit
and scope of the invention.
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