Force feedback control for backhoe

A force feedback control system for a backhoe includes a single grip articulated control arm having members and joints therebetween analogous to the members and joints of an articulated backhoe arm connecting an excavation bucket to a backhoe frame. A bilateral closed loop control circuit compares slave position signals from output joint position sensors associated with the backhoe arm joints with corresponding master position signals from input joint sensors associated with the control arm joints and provides command signals to actuators associated with the backhoe joints to move them so that differences in corresponding master and slave position signals are minimized. Backhoe joint load sensors provide load signals indicating resistance to movement of the associated backhoe joints, and the control circuit generates force feedback signals to drive feedback motors associated with the control arm joints to apply toruqes thereto to reflect the resistance to movement of the associated backhoe joints.

FIELD OF THE INVENTION 
The present invention relates to earthworking implements and, more 
particularly, to a force feedback control system for a backhoe. 
BACKGROUND OF THE INVENTION 
In conventional earthworking implements, such as backhoes, excavators, 
loaders, and the like, an earthworking tool is mounted on one or more arms 
connected to a vehicle, and the tool and arm are moved by the extension 
and retraction of hydraulic cylinders. An operator controls the functions 
of the tool by the operation of levers associated with hydraulic valves. 
High pressure hydraulic systems are employed, in which pressures may range 
to 2000 pounds per square inch and more. Thus, depending on the diameter 
of the hydraulic cylinders employed and the leverage involved, great 
amounts of force can be brought to bear by the implement tool. 
Hydraulic valves for such equipment are generally of the reversible on/off 
type wherein, for example, pressing a control lever in one direction opens 
a valve to cause a cylinder to extend; releasing the lever allows it to 
center thereby closing the valve; and pressing the lever in the opposite 
direction reverses the valve to cause retraction of the cylinder. The only 
input force required of the operator is that which is required to overcome 
a lever centering spring. Because the input force of the system is very 
low and the output force resulting therefrom is relatively high, the force 
or power gain of the system is very high. 
The type of control systems used on conventional earthworking implements, 
absent the operator, is of the open loop type. That is, the output 
parameter of the system, displacement of the tool or arm, is not fed back 
to the system for comparison with the input parameter to derive an error 
signal, which then causes correction of the displacement until the error 
signal is zeroed. The only feedback available is visual feedback to the 
operator who makes a judgement about the displacement "error" and manually 
controls a corrective displacement. The lack of displacement or force 
feedback in conventional implement control systems results in a lack of 
"feel" in the control levers. 
In general, each available function of the tool is controlled by a 
corresponding single axis control lever, although the combination of two 
functions on a dual axis lever, or joystick, is sometimes provided. In a 
conventional backhoe, four tool functions are controlled including boom 
swing, boom elevation, crowd or elbow angle, and bucket curl or pitch. 
Thus, a minimum of two dual axis levers or, more conventionally, four 
single axis levers are required to control the bucket of a backhoe. The 
two or four control levers do not resemble the configuration of the bucket 
arm such that learning to control a given backhoe by its levers is not 
intuitive. An operator must associate the labeled name of a lever or its 
position in relation to the other levers with the backhoe function it 
controls. An additional problem, particularly with four levers, is that 
efficiency of operation of the backhoe suffers form the need for the 
operator to switch hands from lever to lever to coordinate the movements 
of the bucket. As a result of these and other factors, considerable 
expense and practice time is often required to train a profficient and 
safe backhoe operator. 
Because of the lack of feel in the hydraulic control levers, problems can 
arise even for an experienced operator. For example, if it is necessary to 
excavate near a pipeline or other existing structure using a backhoe, 
great car must be exercised to avoid damage to the existing structure, 
since resistance to movement of the bucket caused by contact of the bucket 
with the structure is not fed back to the control levers. In order to 
avoid such damage when working at close quarters, it is sometimes 
necessary to station an additional worker to observe the operation and 
signal movements to the backhoe operator. 
It is foreseen that the use of a unilateral closed loop control system to 
control a backhoe might result in the creation of problems and hazards not 
present in conventional backhoe control systems. In a unilateral 
master-slave position control system, a position input at a control lever 
is compared with a sensed position of the corresponding function, and the 
function actuator, such as a hydraulic cylinder, is activated to reduce 
the position error sensed. Because it takes a finite amount of time to 
fill a hydraulic cylinder, it would be possible for the master lever to 
get considerably ahead of the cylinder controlled resulting in a 
desynchronization of the master and slave. The same result could occur, 
for example, if the bucket encounters an obstacle. The situation is 
further complicated by multiple control axes such that an operator can 
become, in effect, "disoriented" with respect to the positions of the 
control levers relative to the position of the bucket. Attempts by the 
operator and the control system to recover from such a situation could 
result in unpredictable movements of the backhoe arm. With a large heavy 
implement capable of applying tens of thousands of pounds of force in the 
vicinity of other workers, equipment, and structures, such a situation is 
of necessity to be avoided. 
In conventional backhoes the bucket is movable through four degrees of 
freedom: extension and retraction, raising and lowering, swinging from 
side to side, and curl of the bucket about a horizontal axis. To some 
extent, this limits the utility of such a backhoe. In some situations, it 
would be desirable for the bucket to be able to yaw with respect to the 
dipper arm to which it is connected and to rotate about a wrist type of 
axis. This would provide the bucket with six degrees of freedom and would 
facilitate the use of a backhoe in trenching types of excavation in planes 
other than vertical. Such a capability might be desirable in excavating 
beneath an elongated horizontal structure, such as an existing pipe. One 
obstacle to developing such a six degree backhoe is that two additional 
single axis control levers or an additional dual axis control lever would 
be required which would exacerbate the problem of coordinating the control 
levers. 
SUMMARY OF THE INVENTION 
The present invention provides a bilateral closed loop force feedback 
backhoe control system in which command inputs are made through a single 
grip control arm which is mechanically analogous to a backhoe bucket 
manipulator arm. In essence, a forward control loop of the bilateral 
control system causes the backhoe arm to mimic or articulate in 
correspondence to articulation of the operator control arm. A reflected or 
reverse control loop causes feedback forces to be applied to the control 
arm in correspondence to resistances to articulation of the backhoe arm. 
A desired articulation of the backhoe arm or bucket is effected by 
inputting a geometrically or mechanically analogous articulation through 
the control arm. The force feedback feature provides a tactile sense 
through the control arm when the backhoe arm or bucket has encountered an 
obstacle. Control of all the backhoe functions by one hand or arm using a 
single grip control arm greatly improves the coordination of control 
functions as compared to multiple lever controls. The combination of these 
features greatly accelerates training an operator for a backhoe so 
equipped and improves the efficiency and safety of operation thereof by an 
experienced operator. 
A preferred embodiment of the control system is adapted for controlling the 
operation of a four axis backhoe having a boom connected by a swing joint 
and a boom elevation joint to a backhoe frame, a dipper arm connected by a 
crowd joint to the boom, and a bucket connected by a bucket rotation joint 
to the dipper arm. Each backhoe arm joint has a hydraulic actuator, a 
backhoe arm joint position sensor, and a backhoe joint load sensor 
associated with it. All of the backhoe joints allow pivoting about 
horizontal axes except the swing joint which is about a vertical axis. 
The control arm is a four axis control arm adapted for operation by one 
hand and includes an upper arm connected by a shoulder swing joint and a 
shoulder elevation joint to a control arm base, a forearm connected by an 
elbow joint to the upper arm, and a handle connected by a handle rotation 
joint to the forearm. A control arm joint position sensor and feedback 
motor is associated with each of the control arm joints. The master joints 
including shoulder swing and elevation joints, elbow joint, and handle 
joint of the control arm correspond respectively to the slave joints 
including the swing joint, boom elevation joint, crowd joint, and bucket 
curl or pitch joint of the backhoe arm. 
The bilateral closed loop control circuit compares a slave joint position 
signal caused by an articulation of a master joint with a corresponding 
master joint position signal and activates the associated hydraulic 
actuator to articulate the slave joint to zero a difference between the 
slave and master joint position signal. The backhoe joint load sensors 
generate slave joint load signals indicating resistance to articulation of 
the associated slave joints which causes the control circuit to activate 
the corresponding feedback motors to apply torques or counter articulation 
forces to the corresponding master joints. 
The control circuit may be separated into a master controller associated 
with the control arm and a slave controller associated with the backhoe, 
with the master and slave controllers communicating over a wired or 
wireless data communication link. Such an arrangement allows remote 
control of the backhoe functions by the control arm, as for use in 
hazardous environments or to handle hazardous materials. 
A modified embodiment of the control system includes a control arm having 
six degrees of freedom for controlling the functions of a backhoe arm 
having six degrees of freedom. The six axis control arm adds a handle yaw 
joint and a wrist rotation joint to the four axis control arm described 
above. The six axis backhoe adds a bucket yaw joint and a bucket wrist 
rotation joint to the four axis backhoe arm. A control circuit for a six 
axis arrangement is substantially similar to the four axis control circuit 
except that two control channels are added. 
OBJECTS OF THE INVENTION 
The principal objects of the present invention are: to provide an improved 
system for controlling earthworking implements, particularly implements 
with implement tools movable through multiple degrees of freedom; to 
provide such a control system which greatly facilitates the manipulation 
of such an implement tool; to provide such a system which is a closed loop 
control system, particularly a bilateral closed loop control system; to 
provide such a system which feeds back to a control input device forces 
proportional to those acting on the implement tool and means articulating 
it to the implement; to provide such a system particularly for controlling 
a backhoe; to provide such a system including a control input arm having 
members and joints which correspond to members and joints of a backhoe 
bucket articulation arm; to provide such a system in which all the 
functions of a backhoe arm can be controlled by one handed manipulation of 
the control input arm; to provide such a system for controlling a 
conventionally configured backhoe including a swing joint, a boom 
elevation joint, a crowd joint, and a bucket curl or pitch joint along 
with corresponding hydraulic actuators for movement of the bucket via such 
joints; to provide such a system in combination with a backhoe which 
additionally incorporates a bucket yaw joint and a bucket curl or pitch 
joint; to provide such a system including a backhoe joint position sensor 
for each backhoe joint and a control arm joint position sensor for each 
control arm joint, the position sensors being connected to a controller 
whereby upon movement of a control arm joint the controller compares a 
control joint position signal with a corresponding backhoe joint position 
signal and activates the associated actuator to move the backhoe joint to 
zero differences between the respective position signals; to provide such 
a system including a backhoe joint load sensor for each backhoe joint and 
a feedback motor for each control arm joint whereby the controller 
activates a feedback motor to reflect a resistance to movement of a 
backhoe joint back to the corresponding control arm joint; to provide such 
a system wherein the controller is capable of selectively scaling the 
ratio of motion of the control arm to the that of the backhoe arm; to 
provide such a system wherein the controller is capable of selectively 
offsetting the position of the control arm to that of the backhoe arm, as 
for operator comfort; to provide such a system wherein the controller is 
capable of establishing boundaries to motion of the backhoe arm in 
selected axes or the lockout of any motion in selected axes particularly 
for working in close quarters; to provide such a system wherein the 
controller is capable of recording a sequence of motions of the backhoe 
arm for subsequent recall and execution; to provide such a system in which 
the operator may freeze the backhoe arm in any position; to provide such a 
system including a communication or telemetry link between a master 
controller connected to the control arm and a slave controller connected 
to the actuators, position sensors, and load sensors of the backhoe for 
use of the backhoe in hazardous environments or to handle hazardous 
materials; to provide such a system which provides intuitive control of a 
backhoe thereby facilitating training of a backhoe operator; to provide 
such a system which increases the utility and safety of a backhoe; to 
provide such a system which is applicable to a wide variety of 
earthworking implements other than backhoes such as excavators, loaders, 
and the like; to provide such a system retrofittable to a variety of 
existing backhoes; and to provide such a force feedback control system for 
a backhoe which is economical to manufacture, positive and precise in 
operation, and which is particularly well adapted for its intended 
purpose. 
Other objects and advantages of this invention will become apparent from 
the following description taken in conjunction with the accompanying 
drawings wherein are set forth, by way of illustration and example, 
certain embodiments of this invention. 
The drawings constitute a part of this specification and include exemplary 
embodiments of the present invention and illustrate various objects and 
features thereof.

DETAILED DESCRIPTION OF THE INVENTION 
As required, detailed embodiments of the present invention are disclosed 
herein; however, it is to be understood that the disclosed embodiments are 
merely exemplary of the invention, which may be embodied in various forms. 
Therefore, specific structural and functional details disclosed herein are 
not to be interpreted as limiting, but merely as a basis for the claims 
and as a representative basis for teaching one skilled in the art to 
variously employ the present invention in virtually any appropriately 
detailed structure. 
Referring to the drawings in more detail: 
The reference numeral 1 (FIG. 3) generally designates a bilateral force 
feedback control system for a backhoe embodying the present invention. The 
system 1 generally includes an operator input device or control arm 2 
(FIG. 1) positioned in the cab of an earthworking implement or backhoe 3 
and coupled through controller circuitry 4 (FIG. 4) to an implement or 
backhoe arm 5 connecting an implement tool or backhoe bucket 6 to a 
backhoe frame 7. As will be detailed below, the control arm 2 is 
mechanically analogous to the backhoe arm 5, and the controller circuitry 
4 causes movements of the backhoe arm 5 which correspond to similar 
movements of the control arm 2 by an operator of the backhoe 3. 
Additionally, the controller circuitry 4 causes resistance to movement of 
the backhoe arm 5 to be reflected proportionately to the control arm 2 as 
resistance to motion of the control arm 2. 
As used herein, the term "articulate" and derivations thereof such as 
"articulation" and the like are intended to indicate joints or connections 
between members and, additionally, relative movement of such members 
through such joints. The term "articulation" is broadly intended to 
encompass pivotal and rotary joints as well as other types of connections 
of members, such as sliding or telescoping joints. 
The backhoe 3 illustrated in FIG. 1 is substantially conventional in most 
respects and includes the backhoe vehicle frame 7. An operator cab 10 has 
an operator seat 11 therein which may be rotated to a rearward facing 
position, as shown, to facilitate operation of the backhoe arm 5. The 
control arm 2 is mounted within the cab 10 in proximity to the seat 11 for 
convenient reach by an operator. The backhoe 3 includes a backhoe motor 
(not shown) which drives a hydraulic pump 12 (FIG. 4) for powering the 
backhoe arm 5 and a hydraulic reservoir 14 (FIG. 5) which supplies 
hydraulic fluid therefor. Additional earthworking implement tools may be 
provided on the backhoe 3, such as a front end loader bucket 15 which is 
articulated to the backhoe frame 7 by a front end loader arm assembly 16. 
In order to provide stability to the backhoe 3 during manipulation of the 
backhoe bucket 6, a pair of laterally extending outrigger feet 17 are 
provided. 
The backhoe bucket 6 is articulated to the backhoe frame 7 by the backhoe 
arm 5. The arm 5 includes a swing frame 20, a boom 21, and a dipper stick 
or arm 22. The swing frame 20 is connected to the backhoe frame 7 through 
a swing joint 23 to allow pivoting of the arm 5 from side to side about a 
vertical swing axis. The boom 21 is connected to the swing frame 20 
through a boom elevation joint 24 which allows pivoting of the boom 21 up 
and down about a horizontal boom elevation axis. The dipper arm 22 is 
connected to the boom 21 through a crowd joint 25 which allows pivoting 
the dipper arm 22 relative to the boom 21 about a horizontal crowd axis. 
The bucket 6 is connected to the dipper arm 22 through a bucket curl or 
pitch joint 26 which allows pivoting the bucket 6 relative to the dipper 
arm 22 about a horizontal bucket curl axis. 
The swing frame 20 is pivoted relative to the backhoe frame 7 by a pair of 
opposed hydraulic swing cylinders 29 pivotally connected therebetween. The 
boom 21 is pivoted relative to the swing frame 20 by a hydraulic boom 
cylinder 30 pivotally connected therebetween. The dipper arm 22 is pivoted 
relative to the boom 21 by a hydraulic crowd cylinder 31 pivotally 
connected therebetween. Finally, the bucket 6 is pivoted relative to the 
dipper arm 22 by a hydraulic bucket curl cylinder 32 connected between the 
dipper arm 22 and a bucket frame assembly 33 including a bell crank which 
is pivotally connected to the bucket 6. Each of the hydraulic actuators or 
cylinders 29, 30, 31, and 32 is double acting and, thus, reversible. The 
swing cylinders 29 act in a complementary manner such that as one is 
extending, the other is retracting. 
Referring to FIGS. 2 and 3, the illustrated single grip control arm 2 is 
mechanically analogous to the backhoe arm 5 and, to a limited degree, to 
the human arm. The control arm 2 includes a base 35 which is attached to a 
frame member 36 within the backhoe cab 10. A shoulder swing frame 37 is 
pivotally connected to the base 35 through a shoulder swing or azimuth 
joint 38, symbolized in FIG. 3 by cross hairs locating the vertical pivot 
axis of the swing joint 38. An upper arm assembly 39 is pivotally 
connected to the shoulder frame 37 through a shoulder elevation joint 40, 
symbolized by cross hairs locating the horizontal shoulder elevation pivot 
axis of the joint 40. A forearm 41 is pivotally connected to the upper arm 
39 through an elbow joint 42 for articulation about a horizontal elbow 
axis. The illustrated forearm 41 is an L-shaped member. A handle or grip 
43 is pivotally connected through an L-shaped handle bracket 44 to the 
forearm 41 by means of a wrist curl or pitch joint 45 for pivoting 
relative to the forearm 41 about a horizontal curl axis. The control arm 2 
is adapted for controlling all the functions of the backhoe arm 5 with one 
hand. This leaves the other hand free for controlling other functions, 
such as mobility functions of the backhoe 3. The various pivot joints of 
the backhoe arm 5 and the control arm 2 are interchangeably referred to 
hereinbelow by either their designations as joints or as axes. 
FIG. 4 is simplified block diagram of the control system 1. In FIG. 4, 
solid lines between blocks represent electrical signals, lines with single 
dots therein represent hydraulic signals, lines with double dots represent 
mechanical signals, and lines with triple dots are repetition lines, 
representing connections of components of additional control channels. 
FIG. 4 illustrates a single control channel related to a set of 
corresponding joints on the control arm 2 and the backhoe arm 5. It should 
be understood that the remaining sets of articulation joints of the 
control arm 2 and the backhoe arm 5 are related by parallel channels of 
the system 1 which are omitted from FIG. 4 for graphic simplification. 
In FIG. 4, an operator input joint 48, representing one of the control arm 
joints 38, 40, 42, or 45, is illustrated along with a slave output 
articulation or joint 49, representing one of the backhoe arm joints 23, 
24, 25, or 26. A control arm or input joint position sensor 50 is 
associated with each of the input joints 48. The input joint position 
sensor 50 may be any of several types of rotary position sensors such as a 
rotary potentiometer, a rotary digital position sensor, or the like. The 
sensor 50 is mechanically connected between the control arm members 
forming the input joint 48 and provides an input joint or master position 
signal having a parameter indicative of the relative positions of the 
control arm members forming the joint 48 to the controller circuitry 4. 
Each slave or backhoe joint 49 has a hydraulic actuator 51 associated 
therewith, representing one of the cylinders 30-31 or the cylinder set 29. 
Each actuator 51 has an actuator position sensor 52 coupled thereto to 
provide an actuator or slave position signal having a parameter indicating 
the relative extension or retraction thereof to the controller circuitry 
4. The actuator position sensor 52 may be resistive, digital, or the like. 
Alternatively, the actuator position sensor 52 could be coupled between 
the backhoe members forming the output joint 49, wherein it would be 
equivalently be referred to as an output joint position sensor. The flow 
of hydraulic fluid from the hydraulic pump 12 to each actuator 51 is 
controlled by a corresponding hydraulic servo valve 53, or valve set in 
the case of the swing cylinder set 29. The valve 53 receives operating 
signals from the controller circuitry 4. 
The controller circuitry 4 is a closed loop control system. A displacement 
of the input joint 48 is sensed by the controller 4 by way of the master 
position signal provided by the input joint position sensor 50. The 
current position of the corresponding actuator 51 is indicated by the 
slave position signal provided by the actuator position sensor 52. The 
controller 4 compares the master and slave position signals and generates 
an error signal indicating the difference therebetween and applies it to 
the actuator 51 through the valve 53 to move the slave joint 49 in such a 
direction or sense as to diminish the error signal. The time response of 
the system 1 is preferably fast enough that the slave joints 49 of backhoe 
arm 5 appear to move in synchronism with the input joints 48 of the 
control arm 2. 
The system 1 is a bilateral control system in that command signals are sent 
from the input joints 48 to the slave joints 49, and force feedback 
signals are sent from the slave joints 49 back to the input joints 48 to 
provide the operator with a tactile sense or feel of resistance to 
articulation of the slave joints 49. Each input joint 48 is provided with 
a feedback motor 56 connected between the control arm members connected by 
the input joint 48. Each feedback motor 56 includes feedback motor driver 
circuitry 57 which is connected to the controller circuitry 4. Each 
hydraulic actuator 51 has a differential hydraulic pressure transducer or 
sensor 58 connected in the hydraulic lines thereto. The pressure 
transducer 58 provides a slave joint load signal to the controller 
circuitry 4 proportional to the difference in pressure in the hydraulic 
fluid being pumped into the double acting actuator 51 and the fluid being 
forced out. 
The difference in pressure is a measure of resistance to articulation of 
the slave joint 49 arising from inertia in the backhoe arm members 
connected by the slave joint 49, from contact by members of the backhoe 
arm 5 with the ground being excavated or structures in proximity to the 
backhoe 3 (including members of the backhoe 3 itself), or from the limit 
of extension or retraction of one of the actuators 51. The controller 
circuitry 4 processes the slave joint load signals and generates force 
feedback signals proportional to the load signals which cause the 
application of forces or torques proportional to the resistance forces to 
the corresponding input joints 48. The scaling or proportionality between 
the slave joint resistances and the input joint torques can be adjusted 
through the controller circuitry 4 according to the size and leverage of 
the backhoe arm members and the force capacities of the actuators 51. 
The control system 1 may be a single integrated unit mounted in the cab 10 
of the backhoe 3 along with the control arm 2, and this is a preferred 
configuration in most installations. Alternatively, the functions of the 
backhoe arm 5 can be controlled remotely. Such a configuration might be 
desirable if the backhoe 3 were to be used in a hazardous environment or 
to handle hazardous materials. For such a remote operation, the controller 
circuitry 4 is separated into a master controller 61 and a slave 
controller 62 coupled or interfaced by a communication link 63. The 
communication link 63 may be any appropriate conventional type of wired or 
wireless serial or parallel data communication link, such as a direct 
wired link, a fiber optic link, a radio link, a microwave link, or the 
like. 
A master unit 64 including the master controller 61 and the control arm 2 
with input position sensors 50 and feedback motors 56 may be stationed in 
a fixed installation, a mobile installation such as another vehicle, or a 
portable installation which is conveniently deployed and stowed. In some 
situations, it might even be desirable to mount the control arm 2 on the 
body of the operator thereof. A slave unit 65 including the slave 
controller 62 is mounted on the backhoe 3 along with the transducers 58 
and the actuator position sensors 52 and other components connected 
thereto. Such an arrangement may also include a video link (not shown) to 
facilitate remote operation of the backhoe 3. In general, the 
communication link 63 communicates command signals from the master unit 64 
to the slave unit 65 to cause articulation of the backhoe arm 5. Load 
signals from the pressure transducers 58 and actuator position signals 
from the actuator position sensors 52 are communicated by the link 63 from 
the slave unit 65 back to the master unit 64. 
FIG. 5 illustrates further details of a typical hydraulic channel of the 
system 1. The hydraulic pump 12 which supplies hydraulic fluid under 
pressure to the actuators 51 is activated by the controller circuitry 4 in 
response to the operation of a hydraulic system enable switch 68 (FIG. 2) 
located on the base 35 of the control arm 2 and connected to the circuitry 
4. The switch 68 also controls a hydraulic on/off valve 69 which enables 
the flow of hydraulic fluid throughout the hydraulic components of the 
system 1. The hydraulic servo valve 53 channels hydraulic fluid to the 
actuator 51 to actuate in one direction by filling one side thereof and 
channels fluid out of the other side and back to the reservoir 14. 
In FIG. 5, between the valve 53 and actuator 51, hydraulic flow to cause 
the actuator 51 to move in one direction, e.g. to extend, is represented 
by black arrow heads while flow to cause the actuator 51 to move in the 
opposite direction, e.g. to retract, is represented by white arrow heads. 
The pressure transducer 58 is connected to hydraulic lines 71 and 72 
handling hydraulic flow to and from both sides of the actuator 51, and 
arrows representing the connection of the transducer 58 to these lines are 
black and white to indicate that the transducer 58 senses pressure 
differentials between the lines in either direction of flow therein. 
The system 1 is adapted to allow the backhoe arm 5 to be halted an any 
desired position. For this, controllable hydrostatic hold valves 73 and 74 
are positioned respectively in the actuator supply lines 71 and 72. The 
hold valves 73 and 74 are controlled by the on/off valve 69 such that 
whenever the valve 69 is opened, the hold valves 73 and 74 also open. 
Conversely, when the valve 69 is closed, the hold valves 73 and 74 are 
also closed to trap hydraulic fluid within the actuator 51 to thereby 
freeze its current position. The on/off valve 69 is controlled by a hold 
switch 75 (FIGS. 2 and 3) which is illustrated as positioned on the handle 
43 of the control arm 2. 
The controller circuitry 4 incorporates a digital computer along with 
interfacing circuitry to the input and output circuitry within the system 
1. The controller circuitry 4 includes computer storage or memory 78 which 
may include read only memory , read/write memory, or any appropriate 
combination of non-volatile and/or volatile memory. The memory 78 stores 
an operating program for the system 1. A remote terminal 79, including a 
read out device, may be removably connected to the controller 4 for 
inputting certain data thereto and for selecting special routines for 
execution. Such special routines may include programs for scaling the 
motion ratio of the backhoe arm 5 to the control arm 2, for offsetting the 
position of the control arm 2 to the backhoe arm 5 for operator comfort, 
for constraining the motion of the backhoe arm 5 about certain joint axes 
or preventing any motion about a selected axis or axes, or for selection a 
teach/playback mode in which a sequence of commands representing backhoe 
arm articulations is stored in the memory 78 for later recall and 
execution. The memory 78 may also store standard sequences of commands for 
the backhoe arm 5, such as automatic deployment and stowing. 
Referring to FIGS. 2 and 3, in the illustrated control arm 2, the feedback 
motors 56 for the shoulder elevation joint 40 and the wrist curl joint 45 
are mounted coaxial to the respective axes of these joints and include 
respective heat exchangers or sinks 80 and 81 (FIG. 3). The feedback motor 
56 for the shoulder swing joint 38 is mounted in the shoulder swing frame 
37 and includes a heat sink 82. The feedback motor 56 for the elbow joint 
42 is not mounted at the joint 42, but within the shoulder swing frame 37. 
Torque from the elbow joint motor is transferred to the elbow joint 42 
through a parallelogram arrangement including an elbow motor arm 84 
parallel to the upper arm 39. The elbow joint feedback motor and heat sink 
therefor are mounted below corresponding components of the shoulder 
elevation joint 38 and are not visible in the drawings. The control arm 
joint position sensors 50 are preferably mounted coaxial with the 
respective joint feedback motors 56. 
FIGS. 6-8 illustrate a modified operator control arm 90 having six degrees 
of freedom between a handle 91 and a base 92 of the arm 90. The arm 90 is 
substantially similar to the arm 2 and includes a shoulder swing frame 93 
articulated to the base 92, an upper arm 94 articulated to the swing frame 
93, and a forearm 95 to provide a shoulder swing joint 96, a shoulder 
elevation joint 97, and an elbow joint 98, all similar to corresponding 
components of the arm 2. In addition, the arm 90 is provided with a handle 
wrist or yaw frame 99 pivotally connected to the forearm 95 and providing 
a handle wrist or yaw joint 100 with a horizontal axis between the elbow 
joint 98 and a handle or wrist curl joint 101 similar to the joint 45 of 
the arm 2. A handle bracket 102 is connected to the yaw frame 99 through 
the handle curl joint 101 and has the handle 91 articulated thereto for 
pivoting about a wrist rotation or roll joint 103 having an axis 
positionable in a plane perpendicular to the axis of the handle curl joint 
101. The illustrated wrist rotation joint 104 is formed by a D-shaped 
segment attached to the handle 91 and slidably engaging a guide 105 
positioned at an end of the handle bracket 102. Each of the joints of the 
control arm 90 is provided with a joint position sensor and a feedback 
motor (not shown) in a manner similar to the control arm 2. In the case of 
the wrist rotation axis 103, the position sensor and feedback motor are 
quasi-linear in nature. 
The six axis control arm 90 is particularly useful in controlling the 
operation of a six axis backhoe arm 110. The backhoe arm 110 is similar in 
many respects to the four axis backhoe area 5 but includes a bucket yaw 
joint 111 and a bucket wrist rotation or roll joint 112. The arm 90 
includes a boom 113 and a dipper arm 114 articulated with a backhoe frame 
115 and mutually in a manner similar to corresponding components of the 
backhoe arm 5. 
A bucket curl frame 116 is connected to the dipper arm 114 through a bucket 
curl joint 117 for pivoting about a horizontal axis. A bucket yaw frame 
118 is connected to the bucket curl frame 116 through the bucket yaw joint 
111 for yawing side to side about an axis positionable in a plane 
perpendicular to the bucket curl axis 117. An opposed set of hydraulic 
bucket yaw actuators 119 are connected between the curl frame 116 and the 
yaw frame 118 for articulation of the yaw frame 118 relative to the curl 
frame 116. A backhoe bucket 120 is connected by a rotary hydraulic wrist 
rotation or roll actuator 121 to the yaw frame 118 for rotation of the 
bucket 120 about the bucket wrist rotation joint 112. The addition of the 
yaw joint 111 and the bucket wrist rotation joint 112 increases the 
utility of the backhoe arm 90 by increasing the flexibility of 
articulation of the bucket 120 relative to the backhoe frame 115. For 
example, the bucket 120 can be rotated to a side about the joint 112 and 
yawed to excavate beneath a horizontally extending structure, such as a 
pipe. Excavation in this manner with a conventional four axis backhoe, 
such as the backhoe 3, is not possible. 
While the control system 1 has been described and illustrated in 
conjunction with the operation of the backhoe arms 5 of the backhoe 3, 
other uses of the control system 1 are contemplated and are considered 
equivalent uses of the present invention. For example, the front end 
loader arm 16 (FIG. 1) could be controlled by the system 1 using a two 
axis control arm not shown) similar in many respects to the control arm 2. 
An excavator implement (not shown) could be controlled using the system 1 
with the control arm 2. In controlling such an excavator, the shoulder 
swing joint 38 would be analogous to a cab turret joint of an excavator. 
Additionally, other types of articulation joints besides pivoting and 
rotary joints are intended to be covered by the present invention. For 
example, some backhoes are provided with telescoping dipper arms. The 
forearm 41 of the control arm 2 could similarly be provided with an 
analogous telescoping joint for controlling such a telescoping backhoe 
joint. 
It is to be understood that while certain forms of the present invention 
have been illustrated and described herein it is not to be limited to the 
specific forms or arrangement of parts described and shown.