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Claims  |
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We claim:
1. A robot which can be manually programmed to repetitively execute a
series of programmed motions, comprising:
a base engageable with a supporting structure for supporting the robot,
a first relatively massive elongated link having first and second
extremities,
first means interconnecting said base and said first extremity of said
first link for facilitating selective movement of said first link in a
first direction relative to said base to provide a first degree of freedom
for said robot,
a second relatively lightweight elongated link having an outer end to which
a device is connectable for programmed movement in a path having at least
two degrees of freedom, said second link also having an inner end,
second means interconnecting said inner end of said second link to said
second extremity of said first link for facilitating selective movement of
said second link in a second direction relative to said first link to
provide said robot with a second degree of freedom,
a first actuator associated with said first link for moving, when actuated,
said first link in said first direction relative to said base,
a second actuator associated with said second link for moving, when
actuated, said second link in said second direction,
a first position transducer associated with said first link for providing a
signal corrlated to the position of said first link,
a second position transducer associated with said second link for providing
a signal corrleated to the position of said second link,
a force transducer mounted in series with said first and second links for
sensing the force to which said first link is subjected in said first
direction by the application of a manual programming force to said outer
end of said second link during manual programming of said robot, said
manual programming force being applied in an arbitrary direction and
having force components simultaneously in both said first and second
directions to induce movement of said first and second links
simultaneously in both said first and second directions, respectively,
said force transducer providing an output signal having a component
correlated to the manual force component applied to said outer end of said
lightweight link in said first direction,
said lightweight second link being movable relative to said massive link in
said second direction without power assistance when a manual force is
applied to said outer end of said lightweight link during manual
programming of said robot, said massive link being relatively immovable in
said first direction without power assistance in response to application
of manual force to said outer end of said lightweight link during manual
programming,
means to apply said force transducer output signal to said first actuator
during manual programming to produce power-assisted movement of said first
link in said first direction while said second link moves without power
assistance in said second direction, said power-assisted motion of said
first link and unpowered motion of said second link combining to move said
outer end of said second link in said arbitrary direction in which said
manual force is applied,
means to record the output of said position transducers during manual
programming, and
means to reproduce said recorded position transducer outputs and apply them
to their respectively associated actuators to execute said programmed
motions without manual assistance.
2. The apparatus of claim 1 wherein said force transducer is mounted
inboard of said second link to render the output thereof independent of
the orientation of said second link.
3. The apparatus of claim 1 wherein said force transducer has an output
component correlated to the vertical force due to acceleration of said
second link in said first direction, said apparatus further including
inertial force compensation circuit means for cancelling at least a
portion of said force transducer output signal component correlated to the
inertial force of said second link in said first direction to provide an
inertial force compensated signal to said first actuator which is
correlated to the component of said manual force applied in said first
direction.
4. The apparatus of claim 1 wherein said first link moves substantially
only in a vertical plane; said force transducer has a first output
component correlated to the inertial force due to acceleration of said
second link in said first direction and a second component correlated to
the gravitational force acting on said second link; said apparatus further
including inertial and gravitational force compensation circuit means for
cancelling at least a portion of said first and second force transducer
output components to provide an inertial and gravitational force
compensated signal to said first actuator which is correlated to the
component of said manual force applied in said first direction.
5. The robot of claim 1 wherein said first actuator includes a linear
proportional servo valve and an electrical intergrator for producing
power-assisted acceleration of said first link in said first direction
when a manual force is applied to said outer end of said second link
having a force component in said first direction of constant magnitude.
6. The robot of claim 1 wherein said first and second interconnecting means
provide for pivotal movement in said first and second directions,
respectively, about first and second axes, respectively, which are
substantially orthogonal, and wherein said force transducer senses shear
force in said first link in a direction perpendicular to (a) an imaginary
radial line extending between said first and second axes and (b) a plane
containing said first axis.
7. The robot of claim 1 further including means responsive to said force
transducer during execution of said programmed motions for detecting
abnormal forces existing in said robot.
8. The robot of claim 1 wherein said output signal of said force transducer
is at least partially compensated for nonuniform acceleration of said
second link, said robot including compensation means for modifying said
output of said force transducer in dependence upon the third derivative
with respect to time of the displacement of said lightweight link in said
first direction.
9. A support assembly for a tool which can be manually controlled to
position the tool in different locations by the application of manual
force to the tool in the direction in which it is desired to move the
tool, comprising:
a base,
at least one relatively massive elongated link, said link having first and
second extremities,
first means interconnecting said base and said first extremity of said
massive link for facilitating selective movement of said massive link in a
first direction relative to said base to provide a first degree of freedom
for said tool,
at least one other relatively lightweight elongated link having an outer
end to which said tool is connectable for movement in a path having at
least two degrees of freedom, said other link also having an inner end,
second means interconnecting said inner end of said other link to said
second extremity of said massive link for facilitating selective movement
of said other link in a second direction relative to said massive link,
said second direction being different from said first direction to provide
said tool with a second degree of freedom and facilitate motion thereof in
two different directions,
said massive link being relatively immovable in said first direction
without power assistance in response to application of manual force to
said outer end of said other link during manual control of said tool
support assembly, said lightweight second link being movable relative to
said massive link in said second direction without power assistance when a
manual force is applied to said outer end of said lightweight link during
manual programming of said robot,
an actuator associated with said massive link for moving, when actuated,
said massive link in said first direction relative to said base,
a force transducer mounted in series with said massive and other links
between said base and said outer end of said other link for sensing the
force to which said massive link is subjected in said first direction by
the application of a manual force to said outer end of said other link
during manual control of said tool support assembly, said manual force
being applied in an arbitrary direction noncoincident with either of said
first or second directions, but having force components simultaneously in
both said first and second directions to induce movement of said massive
and other links simultaneously in both said first and second directions,
respectively, said force transducer providing an output signal having a
component correlated to said manual force component applied to said outer
end of said other link in said first direction, and
means to apply to said first actuator the output of said force transducer
which is correlated to the component of said manual force applied in said
first direction for producing, during manual control of said tool support
assembly, power-assisted movement of said massive link in said first
direction while said other link moves in said second direction without
power assistance, said power-assisted motion of said first link and
unpowered motion of said other link combining to move said outer end of
said other link in said arbitrary direction in which said manual force is
applied. |
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Claims |
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Description |
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This invention relates to programmable robots, and more particularly to
programmable robots having power-assisted motion during manual
programming.
Programmable robots have been used for many years to execute, on a
repetitive basis, relatively complex motions which the robot has been
"trained," or "programmed," to do. Typically, the robot consists of a
plurality of interconnected links or members. At each interconnection
point, or joint, an actuator and associated position transducer is
located. By applying a series of suitable electrical motion control
signals to the actuators, which have been prerecorded during the
programming or training phase, the links can be moved relative to each
other to accomplish the desired series of motions.
The position transducers continuously provide signals indicating the
relative positions of the respective robot links. During program
execution, the position transducer outputs are incorporated in closed loop
servo controls for assuring that the various links execute the desired, or
programmed, motion dictated by the stored motion control signals. During
programming, the outputs of the position transducers associated with the
various robot links are recorded such that they can later be reproduced
and applied to their respectively associated servo position loops to
execute the previously taught motion.
In the past, movement of the robot links during programming, or teaching,
was typically accomplished in one of several ways. With one approach, a
joystick is used to control the actuators during programming such that the
robot links move to position the robot output element in accordance with
manual manipulation of the joystick. A disadvantage of this approach is
that training of the robot is not accomplished by manually moving the
robot output element, which might have mounted to it a spray gun or the
like, but rather is accomplished by moving a joystick. While a skilled
spray painter can move a spray gun in the desired pattern to accomplish
spray coating an object, that same spray painter is not likely to be able
to effectively control the motion of a spray gun mounted at the end of a
robot utilizing a joystick. Hence, the robot cannot readily be programmed
to spray paint by a spray painter, but rather can only be programmed by
one possessing relatively specialized skills not typically possessed by a
spray painter.
A second approach to robot programming, or training, involves utilization
of an additional, lightweight "training robot" which, except for the mass
of the "training robot" and the absence of actuators for the links, is
identical in all respects to the considerably more massive "working robot"
being programmed. To program the "working robot", the output element of
the "training robot" is grasped manually by the individual doing the
programming and moved through a sequence of motions which it is desired to
have the "working robot" subsequently execute. Since the "training robot"
is lightweight, it can be moved manually by the operator with little
difficulty. As the "training robot" is being moved through the desired
sequence of motions, position transducers at the joints of its links
provide electrical signals which are recorded for subsequent reproduction
and input to the actuator servo loops of the "working robot". Thus, during
programming, the "working robot" is at rest. Similarly, during execution
of the programmed steps by the "working robot", the "training robot" is at
rest. The obvious disadvantage of utilizing a "training robot" is that a
separate robot structure, albeit one which is lightweight and has no
actuators, is required which serves no useful purpose except during
programming. This unnecessarily adds to the cost of the system, and
involves either a position offset or a mechanical changeover at the
location of the robot; removing one and replacing it with the other.
A third approach to training a robot involves the provision of
actuator-controlling electrical switches at the robot joints. The switches
are responsive to slight movement of the robot links when the operator
physically grips the output element of the robot during programming and
attempts to move it through the desired sequence of motions. As the
programmer attempts to manually move the robot output element during
programming, there is some slight motion of the robot links which is
sensed at the joints by the electrical switches thereat. The switches
respond to energize their respectively associated actuators, moving the
links in the direction of the manual force transmitted to the joints by
robot links as an incident to programming. In accordance with this scheme,
the switch-operated actuators are either energized or de-energized during
robot programming, with the result that the robot responds in a very jerky
fashion. While this approach has been described in the patent literature
for many years, it has never been sufficiently satisfactory to be
commercialized to any significant extent.
A fourth method involves bypassing or decoupling of the actuators and
counterbalancing the robot so that the operator may more easily move it
through the desired path. The inertia of the robot remains and even in a
lightweight machine is a substantial quantity and restricts free motion
greatly.
Accordingly, it has been an objective of this invention to provide a
trainable robot which responds to manual forces applied to the robot
output element during training to produce smooth robot motions and do so
without the need for a joystick control, a specially designed lightweight
auxiliary training robot, or means to decouple the actuators and
counterbalance the robot links. This objective has been accomplished in
accordance with certain of the principles of this invention by providing,
in combination with a robot having plural series connected links
interconnected at joints having associated actuators and position
transducers, some of which links are relatively lightweight such as those
making up the wrist and others of which are relatively massive such as
those interconnecting the wrist and the stationary base, plural force
transducers which are responsive to the forces transmitted to the massive
links via the wrist as the output element of the robot is manually urged
along the desired path, and applying the outputs of the force transducers
to their respectively associated actuators to provide power-assisted
motion of the massive links in the direction of the manual force
components transmitted thereto. The power-assisted motion of the massive
links, coupled with the unpowered motions of the lightweight links
comprising the wrist, are due solely to the manual force applied to the
robot output element by the programmer, collectively move the output
element of the robot along the path it is urged by the manual force
applied thereto by the programmer. The output signals of these force
transducers responding to nonvertical manual programming force components
are compensated for inertial force effects of the lightweight arms located
outboard of the force transducers. The output signals of force transducers
which respond to vertical programming force components are compensated for
gravitational force effects of the outboard wrist, as well as for inertial
force effects.
An important advantage of this invention, particularly attributable to
locating the force transducers between the lightweight links of the wrist
and the massive links inboard of the wrist is that the force transducer
output need not be adjusted for varying orientation of the wrist which
would otherwise be necessary were the force transducers located at the
robot output element, that is, outboard of the wrist.
A still further advantage of the robot of this invention is that the force
transducers are in series with the robot links. As such, the force
transducers respond to the net force applied to the output element of the
robot. Since the force transducers do respond to the net force applied to
the output end of the robot, if the programmer were to stumble and fall
and in doing so pull the robot output against his body, the force applied
to the programmer's body by the power-assisted links could not exceed the
force which the programmer himself applies to the output of the robot.
A further advantage of placement of the force transducers in series with
the robot links is that during execution of the programmed steps the
forces in the robot links can be monitored, and if they exceed a
predetermined safety threshold level, the robot can be shut down and/or a
suitable alarm provided.
If desired the "feel" of the robot during manual programming, that is, its
response to manual programming forces as subjectively determined by the
programmer, can be enhanced by further compensation of the force
transducer outputs. Specifically, the force transducer outputs can be
modified in accordance with the third derivative with respect to time of
the displacement of the wrist.
These and other features, advantages, and objectives of the invention will
become more readily apparent from a detailed description of the robot
taken in conjunction with the drawings in which:
FIG. 1 is a perspective view in schematic form of the robot of this
invention showing the general relationship of the robot links, actuators,
and position transducers.
FIG. 2 is a perspective view in schematic form of the force transducers.
FIGS. 3a, 3b, and 3c are circuit diagrams of the electrical bridges in
which the force transducers are connected for the X', Y', and Z'
directions, respectively.
FIGS. 4a and 4b are schematic circuit diagrams of a preferred embodiment of
the control circuit of this invention illustrating the circuitry utilized
in both the programming mode and the execution mode.
With reference to FIG. 1, a preferred form of the robot of this invention
is seen to include a base 10 which rests on the floor or other appropriate
surface for supporting the robot. Extending from the base 10 are plural
series-connected elongated articulated members 12 of relatively large mass
which provide the robot with several degrees of freedom, and plural
series-connected elongated articulated members 14 of relatively small mass
which provide the robot with several additional degrees of freedom. In the
preferred embodiment the series of articulated members 12 and 14
collectively provide the robot with a total of six degrees of freedom.
The series of articulated members 12 include a pedestal 16, an upper arm or
link 18, and forearm or link 20, all of which are relatively massive
structural members fabricated of steel or some other suitable material
exhibiting high strength. Typically, the pedestal 16 and the links 18 and
20 each approximate 1-3 feet in length and weigh in the range of 50-400
lbs. The pedestal 16 is vertically disposed and mounted to the base 10 by
a suitable joint which permits the pedestal to rotate about its
longitudinal axis which is coincident with the X axis. An actuator 22 is
associated with the pedestal 16, and is responsive to a position command
signal to facilitate selective bidirectional angular motion of the
pedestal 16 in an azimuthal direction about its longitudinal axis. Also
associated with the pedestal 16 is a position transducer 24 which provides
an electrical signal correlated to the angular, or azimuthal, position of
the pedestal 16 relative to the base 10.
The link 18 at its inner end is connected to the upper end of the pedestal
16 by a suitable joint for permitting pivotal, elevational movement of the
link in a vertical plane about a horizontal axis 26 which is perpendicular
to the X axis and parallel to the Y-Z plane. Associated with the link 18
is an actuator 28 which is responsive to a position command signal and
facilitates selective bidirectional elevational pivotal movement of the
link about horizontal axis 26. Also associated with the link 18 is a
position transducer 30 which provides an electrical signal correlated to
the elevational position of the link relative to the pedestal 16.
The link 20 at its inner end is connected to the outer end of the link 18
by a suitable joint for permitting the link 20 to move in a vertical plane
about horizontal axis 32 which is parallel to axis 26. A suitable
transducer 34 is associated with the link 20 for providing an electrical
output signal correlated to the angular elevational position of the link
20 with respect to the link 18. An actuator 33 is associated with the link
20 which is responsive to a position command signal and facilitates
selective bidirectional elevational pivotal movement of the link 18 about
horizontal axis 32.
The actuator 24 which bidirectionally drives the pedestal 16 about the X
axis provides the robot with one degree of freedom, namely, azimuthal
positioning motion, while the actuators 28 and 33 which bidirectionally
drive the link 18 and link 20, respectively, provide the robot with two
degrees of freedom, each in an elevational direction.
The articulated members 14, which collectively constitute a wrist, include
series-connected arms, links, or members 38, 40 and 42. Link 38 at its
inner end is connected via a suitable joint to the outer end 20a of the
link 20. An actuator 44 is associated with the wrist member 38 for
bidirectionally rotating the wrist member 38 about its longitudinal axis
which is coincident with the longitudinal axis of the link 20. A suitable
position transducer 46 is associated with the wrist member 38 for
providing an electrical signal correlated to the relative rotational
position of the wrist member 38 with respect to the link 20.
The wrist member 40 is connected at its inner end via a suitable joint to
the outer end of the wrist member 38 for providing rotational movement of
member 40 about its longitudinal axis which is perpendicular to the
longitudinal axis of member 28. An actuator 48 is associated with wrist
member 40 for bidirectionally rotating wrist member 40 about its
longitudinal axis perpendicular to the longitudinal axis of wrist member
38. A suitable position transducer 50 is also associated with wrist member
40 for providing an electrical output correlated to the rotational
position of wrist member 40 relative to wrist member 38.
Wrist member 42 is connected via a suitable joint to the outer end of wrist
member 40 to facilitate rotation of member 42 about its longitudinal axis
which is disposed perpendicularly to the longitudinal axis of wrist member
40. An actuator 52 associated with wrist member 42 facilitates
bidirectional motion of the member 42 about its longitudinal axis. A
transducer 54, also associated with wrist member 42, provides an
electrical signal output correlated to the relative rotational position of
wrist member 42 relative to wrist member 40.
Wrist member 42 constitutes the mechanical output element of the robot.
While the mechanical output of the robot can be utilized for positioning a
wide variety of devices, in the preferred form of the invention the robot
is utilized to position a spray coating gun 58. The barrel 58a of the
spray coating gun, which has a nozzle 58b which emits coating particles,
is connected at its rearward end to the upper end of the wrist member 42.
The lower end of the wrist member 42 has secured to it a handle member 58c
which can be grasped by an operator during manual programming of the robot
in a manner to be described hereafter. The handle 58c together with the
barrel 58a closely approximate the structure of a conventional manually
operated spray gun. The handle 58c mounts a suitable trigger mechanism 58d
which, when actuated during manual programming, functions to control and
program the emission of coating particles from the nozzle 58b of the spray
gun 58.
The longitudinal rotational axis of wrist members 38, 40 and 42 are
mutually perpendicular, and accordingly constitute three degrees of
freedom for the robot. The three degrees of freedom of the wrist 14,
coupled with the three degrees of freedom on the pedestal 16 and links 18
and 20, provide a total of six degrees of freedom for the robot.
The wrist members 38, 40 and 42, as well as their associated actuators 44,
48 and 52 and transducers 46, 50 and 54, are relatively lightweight, for
example, in practice not weighing more than approximately 15-25 lbs.,
exclusive of the gun 58 which weighs approximately 2 lbs. As a
consequence, when the handle 58c of the gun 58 is grasped by the user
during manual programming for the purpose of moving the gun through the
desired sequence of motions it is desired to have the robot repetitively
execute thereafter under program control, the wrist members 38, 40 and 42
will move without power assistance under the action of the manual force
applied by the operator to the handle of the spray gun. However, due to
the substantial mass of the pedestal 16, link 18, and link 20, these
series-connected articulated members will not move without power
assistance in response to forces transmitted to the outer end 20a of link
20 via the wrist 14 pursuant to the application of manual force to the
handle 58c by the operator during programming.
With respect to the output of the robot constituted by wrist member 42 to
which the gun 58 is connected, the pedestal 16, link 18, and link 20 and
their associated actuators 22, 28 and 33 can be considered to effectively
provide linear motion in three mutually perpendicular directions parallel
to the Y, Z, and X axes, respectively. Specifically, with respect to gun
58 rotational motion imparted to pedestal 16 about the X axis provided by
the actuator 22 effectively imparts lateral motion to the gun 58 parallel
to the Y axis. Elevational movement of the link 18 about axis 26 provided
by actuator 28 effectively imparts in/out, or horizontal, motion to the
gun 58 parallel to the Z axis. Finally, elevational motion of link 20
provided by actuator 33 effectively imparts up/down, or vertical, movement
to the gun 58 parallel to the X axis. Thus, as viewed by the gun 58,
rotary actuators 22, 28, and 33 effectively impart linear motion to the
gun 58 in three mutually perpendicular directions parallel to the mutually
perpendicular Y, Z, and X axes, respectively.
Similarly, when the operator grasps handle 58c and applies a manual force
to it in some arbitrary direction to move the gun along a prescribed path,
the force applied by the operator to the gun can be resolved into force
components parallel to the X, Y, and Z a | | |
