Note: Descriptions are shown in the official language in which they were submitted.
This application is a division of Canadian Application
No. 432,678 filed July 18, 1983 for Servo Ampli~icafion System.
Background of the Invention
Modern construction equipment is generally hydraulically
operated. The controls used by the operator constitute hydraulic
valves which directly connect to the hydraulic cylinders at the
articulations, or other sites of relative motion between the
structural members which mount the operative elemen-t of the
equipment. It is common to have three, four, and more hydraulic
drive cylinders which operate the equipment, requiring the corres-
ponding number of hand operated valves.
A skilled operator of a backhoe or other piece of equipment
can operate it as though it were an extension of his own body
utilizing the hydraulic valves. However, it may take a couple
of years before an operator achieves this level of skill, and
in the meantime an extremely expensive piece of equipment is
being underutilized during the training process.
Additionally, during the learning period, when the operator
does not accurately move and stop the machine as he should, it
is difficult on the equipment and puts a strain on most of the
operating parts. This is especially evident in rental units.
A backhoe in a rental year will require quite frequent major
maintenance.
Many of these training problems are a result of the hydraulic
control system available to the operator. Like playing a musical
instrument, it takes a time before the operator can freely move
all of the controls concurrently in a smooth, synchronized
fashion which maximizes the productivity of the machine and
minimizes structural damage. A system which could integrate
all of this motion into a single analog control device, in which
the operator merely moves the operative element such as a back-
hoe on a miniature scale, causing the comparable movement of
the actual backhoe, would unquestionably speed the operator
learning process, save equipment, and enable nonprofessionals
such as those renting units from a rental yard to utilize
equipment more effectively.
Summary of the Invention
The present invention fulfills the above stated need by
replicating in miniature the operative parts which support the
operative element of the equipment. Although the system is
applicable to a wide range of construction equipment, earth
moving machines and virtually anything where an operator controls
a machine, and thus the system described and claimed herein is
intended to cover all applications, the description from this
point on will pertain to a backhoe to eliminate the need for
repetitive, broadening verbiage. It is clear the principles and
systemic elements of the backhoe device can be generalized to
any hydraulically operated machine having any number of
dimensions of motion.
The replica backhoe contains internal hydraulic lines to
avoid the need for loose external lines which would be subject
to breakage. Each articulation in the operative portion of the
backhoe arm is provided with a control cylinder which is
operated by motion about the articulation and transmits informa-
tion concerning the motion by way of hydraulic lines to a pilot
valve. The pilot valve, which in itself is a novel element
created by the inventor for this particular purpose, operates
a pilot piston which is incorporated in the same unit which
mechanically controls the valve for the drive cylinder for the
respective articulation on the actual boom structure.
Each of the analog drive mechanisms for each articulation
described above also has associated with it a feedback system
comprising a cylinder moun-ted on or adjacent the drive cylinder
of the respective articulation and mechanically driven by
motion at the articulation to deliver hydraulic fluid to the
pilot inlets of the respective pilot valves. The feedback
system delivers pilot fluid at what amounts to 180 out of phase
with the control system so that, for example, rotation o the
replica shovel causes rotation of the actual shovel which is
immediately cancelled by the negative feedback from the feedback
system, as soon as the replica control valve stops moving. In
this fashion, a direct analog movement occurs virtually
simultaneously in the actual operative members of the backhoe
with the replica backhoe.
Brief Description of the Drawings
Figure 1 is a somewhat diagrammatic illustration of the
replica backhoe;
Figure 2 is a front elevation view of the replica;
15Figure 3 is a top elevation vlew of the replica showing
the hand knobs in place;
Figure 4 is a schematic illustrating the hydraulics of
the system;
Figure 5 is a section through the pilot valve-pilot piston;
20Figure 6 is an elevation view from line 6-6 of Figure 5;
Figures 7 through 9 are sections taken along the lines
numerically indicated in Figure 5;
Figure 10 is a side elevation, partially cut away and
partially in phantom, of a fragment of the spindle which operates
the pilot piston;
Figure 11 is a projection of the perimeters of the relieved
sections of the piston of Figure 10 as projected into a planar
configuration;
Figures 12 through 15 are sections taken along the
indicated section line of Figure 10;
Figure 16 is a partially cut away, partially phantom
illustration of the hydraulic feedback mechanism;
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Figure 17 is a section taken along line 17-17 of Figure 16;
Figures 18 and 19 are sections taken through the indicated
lines of Figure 17;
Figure 20 is a section taken through the backhoe arm
structure to illustrate the operative control mechanism therein;
Figures 21 through 26 are sections taken along the respect-
ive section lines indicated in Figure 20;
Figure 27 is a section taken along line 27-27 of Figure 26;
and
Figure 28 is a section through -the portion of the backhoe
arm including the two outermost articulations.
Detailed Description of the Preferred Embodiment
The replica backhoe arm is shown at 10 in Figure 1. The
arm consists of a replica shovel 12, a dipper stick 14, a boom
16 mounted -to a swivel 18 which is articulated about a vertical
axis on a base member generally indicated at 20.
The replica 10 is mounted in its en-tirety in the cab of
the backhoe and ordinarily positioned such that the operator
straddles the base 20 in operation, and has a full view of the
actual backhoe. The actual backhoe arm is not shown in the
drawings, as it is not needed in order to clearly understand
the operation of the system.
Before turning to the mechanical details of the device, the
operation of the hydraulic system will be explained. This system
is fully set forth in Figure 4. Actually, it is more accurate
to say Figure 4 represents one subsystem, there being four
identical subsystems in the backhoe implementation which together
define the complete system.
Between each of the par-ts of the backhoe arm which define
relative movement a dimension of movement is defined. For example,
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the bucket 12 sweeps a circle about its axis to define an
angular progression about a horizontal axis as its dimension
of motion. This is a single dimension of motion in that it
may be defined by a single, non-vectorial coordinate. Thus,
each of the articulations 24, 26, 28 and 30 defines a separate
dimension of movement in which any and all positions may be
exactly located with a single number. It will become apparent
from the description of the hydraulic system that each dimension
of motion is separately treated by its own hydraulic subsystem
and, acting independently of the other dimensions, causes the
analog movement to occur on an amplified scale in the actual
articulation of the real backhoe arm.
Returning to Figure 4, the control cylinder 22 is a general-
ized control cylinder, as are all the other elements in Figure
4, which are, in fact, found four times in the actual physical
implementation. For simplicity, Figure 4 will be described as
though the control cylinder 22 was connected to and represented
the articulation 24 between the dipper stick and the bucket 12.
Assuming that the simulated bucket is dipped and this
causes the control piston 32 of the cylinder 22 to move to the
left, this in turn causes a pressure in the pilot inlet 34
of the pilot valve 36 from the control chamber 38 and simultan-
eously permits drainage from the pilot inlet 40 back into the
second pilot chamber 42. Action of the pilot inlets 34 and 40,
of course, causes the pilot valve 36 to shift, actuating the
pilot piston 46.
The pilot piston 46 is mechanically linked to the drive
cylinder valve 48 which operates the respective actual bucket
on the real backhoe arm. Assuming the valve 48 is moved to
the right, fluid will commence to flow into the drive cylinder
50, which actually powers the real bucket, and move the piston
52 to the left. This, in turn, moves the mechanical feedback
linkage 54 to the left, driving the feedback piston 56 in the
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feedback cylinder 5~ to the left, -Y~hich has the e.fect of fillir,~
pilot inlet 40 and draining pilot inlet 34, which cancels the
action of piston 32.
The feedback mechanism 54, 56 and 58 is mechanicall~
implemented by a spring loaded cable connected to the distal end
of the rod of piston 52 in an arrangement detailed below. An
analysis of the hydraulics of the system reveals that displace-
ment of the control cylinder 32, by rotating the bucket 12,
will cause valve 48 to open until this displacement is equaled
by piston 56 in the feedback cylinder, which neutralizes the
effect of control cylinder 22. In normal operation there is
also a restraint on the control piston 32 caused by the hydraulic
back pressure which will occur as the inlet 34 fills, and will
not be relieved until the feedback cylinder 58 supplies enough
feedback fluid. Therefore, there is a virtual simultaneous
analagous motion between the replica arm and the real arm.
Unless too much force is applied to the piston 32, it will not
anticipate the action of the drive cylinder 50 by more than a
few milliseconds. For all intents and purposes, the operator,
operating on the replica, is simultaneously operating on the
real world through the actual backhoe arm.
Reverse action of the bucket 12, of course, has exactly the
opposite action through the hydraulic system. This bi-directional
analog is duplicated at each of the articulations 24 through 30
and acts through a bank of four side-by-side pilot valves 36
which are mechanically linked directly to the usual operating
knobs of the conventional hydraulic controls, not shown. From
this bank of valves, hydraulic lines extend both the base 22
of the replica, and, in the other direction, out to the feedback
cylinders 58 which are mounted on the drive cylinders 50~
Turning now to the mechanical description, with a few
exceptions the details of construction of the dipper stick do
not form part of the novelty of the invention. The exact
combination of plates, panels, pivot pins, annular hydraulic
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fluid ducts and other hydraulic fluid passayes, are for tns
most part standard engineering design. For this reason the
arm of the backhoe will be described in somewhat summar~ fashion.
The base 20 defines a plurality of passage~7ays 60 in a ~.ind
of manifold which communicate from the arm to the pilot valves.
These passageways are defined in a block structure which includes
aS the same or separate piece) a portion having a bore 64 through
it with a plurality of annular fluid passageways 66 separated by
O-rings 68.
A drum 70 fits snugly within the bore 64 and defines a
plurality of generally radial bores 72, each of which communica,es
with one of the passageways 66, and extends in-ternally of the
drum and downwardly into the block portion 74 which, by virtue
OI the angular sliding ability of the drum 70 in the bore 64,
is freely articulated about a vertical axis.
Each articulation, including the articulation 30 between
the base member and the lower rotating block 74, operates a
control piston and cylinder combination such as the diagrammat-
ically illustrated piston 32 and cylinder 22. For the articula-
20 tion 30, a spur 76 extends above the drum 70 and rotates there-
with, operating a rack on a piston rod 78 which connects to
piston 80 sliding in cylinder 82. The piston has a rear piston
rod 84 so that displacement on both sides of the piston is
equal. The piston preferably has relief checkvalves such as
valves 86 shown in Figure 22 to prevent damage to the structure
should a jam occur. Once fluid passes through the checkvalves,
the control and actual cylinders will be out of synchronization.
To re-synchronize the pair, the actual bucket can be brought
against an immovable object~ and the control cylinder pushed
beyond the ability o~ the actual cylinder's ability to respond
until synchronization is achieved.
The pinion, rack, and piston-cylinder arrangement for all
four articulations are similar to that just described for
articulation 30, and will not be redescribed for eacil articula-
tion, but will be referred to in each instance as a "control
cylinder system", which will be understood to include the
above components, plus seals, plates, and other items that are
5 apparent from the drawings and necessary for the proper
operation of the machine.
In the block 74 another relief cylinder system 88 is
provided for articulation 28. This cylinder communicates through
passageways 90 to the drum 70. This is the boom control syst m,
10 and operation of the boom causes the pinion to operate the
rack and move the piston.
Figure 25 illustrates the pinion shaft 92 on which the
pinion 94 is pinned. Passageways 96 (shown in Figure 25)
communicate with two pairs of annular passageways 98 and 100
15 which interface with transmittal port pairs 102 and 104 which
communicate respectively wi-th the bucket control cylinder
system 106 and the dipper stick control system 108.
The port pairs 102 and 104 communicate with passageway
pairs 110 and 112, seen in phantom in Figure 20, which respect-
20 ively service the bucket control cylinder and dipper stickcontrol cylinder. These passageways are defined in boom side
plates 114, through which pins 116 pass to engage pinion
shafts 92 shown in Figure 25. Cover plates 118 cover the
boom side plates 114 to create a discrete set of channels
25 defined within the side plates 1140
Without going into more detail, it can be seen that at
each articulation a pinion drives a piston within the appropriate
control system as the articulation moves, and control fluid
from these cylinders is delivered through the drum 70 and
30 manifold blocks 62 to be distributed to the appropriate pilot
valve.
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Attention is now directed to the pilot valve, illustrated
in the Figure sequence from Figure 5 through Figure 15.
Generally speaking, all the body parts of the valve are
rectangular with the exception of the piston and cylinder. The
valve has a base plate 120, a cylinder wall 122, a cylinder cap
124 and an end wall 126, all being held together by the bolts
128. The cylinder wall defines cylinder 130 in which rides
the piston 132, which is prevented from axial motion by t~"o
parallel piston rods 134 which pass through suitable sealed
apertures in the cylinder cap 124 to terminate in a tie bracket
136. A pair of through bolt holes 138 pass through the
cylinder block and join four blocks together.
Drainage is provided to the cylinder through restricted
orifice nuts 140 linked with passageway 142, with consecutive
cylinder blocks being linked by pass-through bore 144.
Turning to the piston assembly, the piston 132 has end
seals 146 and a relieved annular area between the seals defining
a chamber 148. This chamber is continuous around the piston and
communicates with a bore 150 in the cylinder block, indicated
in phantom in Figure 8. This bore ordinarily would be the
hydraulic fluid supply line, and again would pass through all
cylinder blocks. A radial bore 152 in the piston communicates
between the chamber 148 and an axial bore through the piston
which seats spindle 154. The spindle is mounted on bearings
156 at either end and locked in place with nut 158.
The spindle has two relieved portions 160 and 162 shaped
somewhat like elongated lamb chops and illustrated as they would
appear if the perimeters were rolled into a flat plane in
~igure 11. Due to these relieved portions, which communicate
between opposite ends of the cylinder 130 and the central
portion of the piston bore, rotation of the spindle in one
direction or the other will cause the nearest portion of the
inclined surface 164 of the respective bore to index with the
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piston bore 152, permitting the fluid, which is under pressure
in the cylinder, to escape from the respecti~Je end of the
cylinder through the bore 152, and the bores 1~0 in the blocks,
to a hydraulic reservoir. Clearly, rotation of the spindle in
opposite directions causes the piston to move in opposite
directions. The tapered edges 164 of the relieved portions
causes the piston to smoothly slow down, coming to a stop as
the orifice 152 passes across the edge 164, out of the relieved
zone.
It can thus be seen that power control of the piston 132
can be effected by rotating the spindle 154 in a controlled
manner. This is accomplished with a rack 166, cut in a cylin-
drical rack bar 168 having O-ring seals 170 and end plugs 172
which are too small to seal the opening. The O-rings 170
provide the seal.
The inlet ports 34 and 36 shown in conjunction with tne
pilot portion of the system in the description of Figure 4 can
also be seen in the physical embodiment of the valve in Figure
5. Feedback ports are bored directly into the base plate 120
and indicated at 174 and 176. All ports communicate through
relief ball checkvalves 178 into the cylinder which drains
-through orifice 140, to permit thermal expansion~ It should
thus be clear from the above description that pilot pressures
and faedback pressures dslivered to the valve at the respective
inlet ports will cause the rack bar 168 to translate, thus
rotating the spindle and causing the piston to move one
direction or the other. ~s will be recalled from the discussion
of the entire hydraulic circuit and the feedback system, the
piston, through its coupling plate 136, drives the valve of
the actual equipment hydraulic cylinder which, through a
mechanical and hydraulic coupling, immediately feeds back
through the appropriate port 174 or 176, cancelling the initial
pilot action, unless the initial action is continued by the
continual operation of the control cylinder 132. In the latter
event, the pilot piston 132 will remain in a fixed, displaced
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position as lo~lg as the control cylinder moves at a Ci~ed
velocity. In other words, the static, offset position of the
piston 132 corresponds to the steady, proportional movement o~
the control piston and drive piston in their respective
cylinders.
Another feature of the pilot valve-piston system can be
seen in Figures 10, 13 and 14. A passageway 180 defined axiall~
inside the spindle communicates with the cylinder throllgh
opening 181 and an outlet 192, which indexes with port 152
when the system is in its neutral through position. This
passageway supplies fluid to the control system in the event of
contraction due to temperature.
The feedback structure is shown in Figure 16. This sub-
system, which ordinarily would be on the order of six to eight
inches long, would mount directly on the cylinder housing, or
near the cylinder housing, out on the arm of the actual equip-
ment. The mechanism has a housing 184 with mounting brackets
86 of the equivalent to permit mounting of the unit as a retro-
fit item. A cable 188 has a terminal 190 which is bolted into
the other side of the equipment articulation, ordinarily the
distal end of the piston rod or adjacent structure. The
extension of the cable 188 is thus exactly the same as the
extension of the drive piston.
I'he housing, which includes a pair of side plates 192 and
194 and a peripheral wall 196, also mounts a spool or reel
198 for the cable. Cable tension is maintained by a leaf
spring 200 inside the reel~
Mounted coaxially on the axle 202 is a sprocket 204 for
driving a chain or toothed belt 206 which passes around a
larger pulley or sprocket 210 at the other end of the housing.
The ratio between the two sprockets is such that several
revolutions of the small sprocket will cause only a partial
rotation of the large sprocket.
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A cam 212 is driven by -the larye sprocket, and is moun-ted
coaxially therewith on a post 214. A cam follower 216 is ileld
firmly against -the cam surface ~y exlension sprirlgs 2l8.
The feedback cylinder 58 occurs on -the other side of an
end wall 220 and is driven by a pis-ton rod 222 connec-ted to the
cam follower 216. As can be seen in Figure 16, hydraulic f:luid
passageways 224 and 226 terminate in ports into which return
lines connect, communicating with the feedback ports 174 and
176 of the pilot apparatus.
Although there are clearly more direct ways of converting
the extension of the drive cylinder into the operation of a feed-
back hydraulic cylinder, several advantages are inherent in the
use of the cam assembly illustrated. First, because tension on
the cable drives the cam in-to its lower profile positions, there
can be no forcing action on the feedback piston in case of
jambing. Since a cable cannot be pushed, force from the equip-
ment cannot cause damage to the feedback unit in case anything
is jammed. Undue pressure backing up into the passageway 226
would not occur because this passageway communicates with the
threshold relief valve 178.
Another, and more important advantage of the cam lies in
the fact that the rack and pinion control movement at the
articulations of the replica do not physically duplicate the
geometry of movement of most hydraulic cylinders. The presence
of the cam provides an ideal means of proportionating what
would otherwise be a non-linearity in the operation of the
drive cylinders by the control cylinders. Another control
feature lies in the spring-loaded nature of the drive cylinders
48 which will bring them back to the neutral posi-tion absent
a control force. This causes a bias toward the stopped mode
for the entire system.
While I have described the preferred embodiment of the
invention, other embodiments may be devised and different uses
may be achieved without departing fro~ the spirit and scope of
the appended claims.
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