U.S. patent number RE32,414 [Application Number 06/827,109] was granted by the patent office on 1987-05-12 for robot and control system.
This patent grant is currently assigned to Zymark Corporation. Invention is credited to Louis Abrahams, Raymond R. Dunlap, Burleigh M. Hutchins.
United States Patent |
RE32,414 |
Hutchins , et al. |
May 12, 1987 |
Robot and control system
Abstract
A compact robot of the 3-axis type comprising a base-mounted
motor control system with means to sense the position of a robot
arm through a servo-system comprising position-sensing
potentiometers mounted in the motor control system and a feed-back
control system to co-ordinate the vertical and horizontal movement
of a robot arm.
Inventors: |
Hutchins; Burleigh M.
(Hopkinton, MA), Dunlap; Raymond R. (Uxbridge, MA),
Abrahams; Louis (Worcester, MA) |
Assignee: |
Zymark Corporation (Hopkinton,
MA)
|
Family
ID: |
26986482 |
Appl.
No.: |
06/827,109 |
Filed: |
February 7, 1986 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
328726 |
Dec 8, 1981 |
04507044 |
Mar 26, 1985 |
|
|
Current U.S.
Class: |
414/744.6;
318/568.11; 318/67; 414/749.1; 74/89.22; 901/14; 901/21 |
Current CPC
Class: |
B25J
9/041 (20130101); B25J 18/02 (20130101); B25J
9/104 (20130101); Y10T 74/18848 (20150115) |
Current International
Class: |
B25J
9/10 (20060101); B25J 9/04 (20060101); B25J
18/02 (20060101); B25J 18/00 (20060101); B25J
9/02 (20060101); B66C 023/16 () |
Field of
Search: |
;414/7,589,744R,744A,590,591,749,751,753 ;254/283,286,334,338
;187/27,20 ;74/89.2,89.22,469 ;318/568,67 ;901/17,21 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Spar; Robert J.
Assistant Examiner: Underwood; Donald W.
Attorney, Agent or Firm: Kehoe; Andrew F.
Claims
What is claimed is:
1. In a robot apparatus of the type comprising means to move a
robot arm in a vertical direction, and in a horizontal direction
substantially co-axial with said arm, and means to rotate said arm
through a plane co-planar with said horizontal direction, the
improvement wherein the means to move comprises motor means mounted
on a horizontal turntable with winch means for operating horizontal
cable means and vertical cable means, respectively, and the means
to rotate comprises a turntable-rotating motor; means with winch
means for operating said turntable and said vertical cable means
comprising a first cable means for moving said robot arm
vertically, and first cable means being fastened at each end to an
arm-holding bracket adapted to slide on vertical tracks and said
first cable means being looped around a winch which is part of said
winch means for operating the vertical cable means proximate the
bottom of said track and around a pulley proximate the top of said
track, and said horizontal cable means comprising a second cable
means to move said arm horizontally through said bracket, said
second cable means having ends of which are attached to said arm
near the ends of said arm on opposite sides of said bracket; and
wherein the second cable means runs from one said cable end to a
pulley in said bracket downwardly .Iadd.around a winch means and
thence upwardly .Iaddend.to a pulley mounted proximate the top of
said vertical track, downwardly around a second pulley attached to
said bracket and thence to the other of said cable ends.
2. A robot apparatus as defined in claim 1 wherein said motor means
are direct current servo motors and wherein said cable means are
steel cables.
3. A robot apparatus as defined in claim 1 wherein said motor means
for moving said arm in vertical or horizontal directions is
controlled by a motor control system including means to sense the
vertical and horizontal position of said robot arm and sensing
means comprising a potentiometer mounted on said turntable and
forming means to measure the rotational position of each said winch
means and connect said rotational position into an electrical
signal which resulting signals are co-ordinated through a
servo-system with one another to achieve a smooth movement of said
robot arm.
4. A robot as defined in claim 1 wherein said arm is adapted to
slide back-and-forth within said support bracket in a horizontal
direction in response to a first motor and is adapted to move in
vertical direction in response to a second motor which forms means
to move said bracket, the improvement comprising motor control
means whereby said first motor is operated at a speed of at least
four times the maximum gear-speed ratio of said second motor.
5. A robot as defined in claim 4 wherein the motor control system
of said first motor comprises a signal inversion means allowing its
operating speed to be determined, at least in part, by the control
system for said second motor.
6. Apparatus as defined in claim 1 wherein each of said first cable
means and said second cable means comprise two segments, each said
segment having one end terminating on the winch about which each
said cable is looped.
Description
BACKGROUND OF THE INVENTION
This invention relates to robots and control mechanisms for robots
which provide a light, relatively compact, highly versatile, robot
system.
A substantial amount of work has been done in robots over the
years. An example of a typical robot operable in a three
dimensional plane is disclosed in U.S. Pat. No. 4,229,136 to
Panissidi and, also, in U.S. Pat. No. 3,661,276 to Wiesener. These
patents are particularly illustrative of problems faced by the
prior art in providing counterbalancing of such apparatus against
gravity. The parent invention relates to the solution of both of
these problems.
SUMMARY OF THE INVENTION
It is a principal object of the present invention to provide an
improved robot system, one that is versatile with respect to the
number and energy requirements of permissable robot tasks, and one
which has a highly stable structure.
Another object of the invention is to provide a novel,
base-mounted, motor control system for such a robot.
A further object of the invention is to provide a robot which can
perform operations in a three dimensional zone, relative to its
central structure, which zone comprises an exceptionally large
percentage of the total space occupied by the robot.
Another object of the invention is to provide a robot, the arm of
which can move smoothly from position to position by a unique
positioning of, and control of, its cables.
Another object of the invention is to utilize a unique
position-feedback information from said cable-operating motors.
Another object of the invention is to provide an improved process
for generating and processing input signals into individual robot
motors.
A further object of the invention is to provide means to
co-ordinate the vertical and horizontal motor means for said robot
arm to achieve a smooth movement and to most efficiently use the
energy of the robot.
Another object of the invention is to provide improved means to
generate and transmit digital signals through a cable in the time
domain, that is in a relatively independent voltage form.
Other objects of the invention will be obvious to those skilled in
the art on their reading of this description.
The above objects have been substantially accomplished by the
construction of a robot apparatus of the type comprising means to
move a robot arm in a vertical direction, in a horizontal direction
substantially coaxial with said arm, and in a plane of rotation
coplanar with said horizontal direction, wherein motor means for
moving said robot arms in said vertical and horizontal directions
are mounted on a horizontal turntable with winch means for
operating horizontal cable means and vertical cable means,
respectively, and wherein, mounted beneath, said turntable is a
turntable-rotating motor, and winch and cable means for driving the
turntable.
The motor means for moving said vertical or horizontal directions
is controlled by a motor control system including means to sense
the vertical and horizontal position of said robot arm. Preferably
the sensing means comprises a potentiometer mounted on said
turntable and forming means to measure the rotational position of
each winch means and convert the rotional position into an
electrical signal which resulting signals are coordinated through a
servo-system with one another to achieve a smooth movement of said
robot arm.
These motor means and winch means are the sole means for providing
motive power for moving said robot arm. Consequently, very
substantial forces can be applied to the robot arm by merely
providing large motors in the base. The provision of these motors
in the base position only further stabilizes the apparatus.
It should also be understood that the apparatus described herein
may be substantially modified, e.g., with respect to the movement
and reach of its arm, with no fundamental change in components of
the apparatus. For example, were one to wish to provide more travel
one could merely increase the length of the cable and, if
necessary, the arms. (Moreover, as will be seen below, if one is to
utilize a preferred motor control system, one would have to select
a winch/potentiometer combination that allows the potentiometer to
sense the number of turns and thereby sense the rotary position of
the winch.)
In order to provide smooth movement of the arm, it is desirable to
co-ordinate the relative speed of cable movement of the vertical
cable with the horizontal cable. In the sense used herein the
"vertical cable" is conventionally used to describe that cable
system which operates the robot arm to move it up and down.
Moreover, the term "down" is used to refer to the base position as
shown in the drawings. Despite the use of such conventions for the
purpose of illustration, and despite the fact that the motor
position lends substantial stability in this conventional position,
it is to be emphasized that the design of the present system is
such that it can be advantageously attached to vertical surfaces
and, when desired, to ceilings. Thus it may be conceived as a
relatively gravity-independent apparatus although as will be seen
from considerations discussed below, it may be more desirable to
use different motor systems to maintain desirable gearing ratios
when the arm becomes the vertical axis.
It is preferred that direct current, servo motors geared down to
the desired operating speed, usually from about 2 to 20 inches per
second, be used to drive the cables.
Each of the position-indicating potentiometers is used to send a
signal which is indicative of where each winch (and thus each cable
and the arm) is at any given time. This signal is fed back and
summed with a input signal of different polarity, in the
illustrated case a negative signal, which is indicative of where
the winch wants to be. Then the winch is driven by an amplified
"difference signal". When the difference is zero the winch is where
it is supposed to be.
What is achieved by controlling the horizontal motor with reference
to the vertical motor is that, were this not done, it would be
necessary to have each of the winches for vertical and horizontal
movement driven at a precisely determined value when, say, a
vertical movement is required. However when the horizontal movement
is controlled by, i.e., servoed to, the vertical motor, the desired
result is achieved without any need to feed a precise independent
input to the horizontal motor to have it respond with proper
relationship to the vertical movement.
The illustrated circuit is one way in which the
vertical-motor-driving circuit can be utilized to control the
activity of the horizontal-motor-driving circuit by a signal
inversion means; however numerous other such
signal-investing-control means can also be employed.
It would be entirely practical to operate and control the apparatus
with stepping motors and, for example, chains or flat straps as
cables. However, it has been found particularly advantageous to
utilize wire cable with geared-down direct current motors. This
allows one to avoid having to deal with resonance- or
vibration-imparting problems (which are associated with the use of
such cables and stepping motors) with each change in system
size.
The placement of the motors on the base reduces bulk, puts the
weight near the center of gravity of the robot where it contributes
to stability.
Typical travel specifications of the apparatus comprise a 13-inch
travel in each of the horizontal and vertical distances. However,
it is important to note that there is nothing in the design to
preclude the arm from travelling over a much larger range, e.g.,
three or four feet. The turntable is advantageously adapted to turn
more than 360 angular degrees. Additional, e.g., an additional
90-degree, turning capacity allows the apparatus to proceed
directly to a nearby work assignment, say the 80 degrees from a
290-degree position to a 360.degree. plus 10.degree. position
without the need to go 280.degree. in the other direction.
The position of the motors and associated winches and
potentiometers, the centers of gravity of which are positioned
substantially within the cylinder out of which the end of the robot
arm must remain, is a substantial benefit in stabilizing the robot
apparatus.
As is seen from FIGS. 1 and 5, each cable is divided into two
segments such that each segment of each cable terminates on the
pulley as well as with the robot arm-moving apparatus with which it
is associated.
ILLUSTRATIVE EMBODIMENT OF THE INVENTION
In the application and accompanying drawings there is shown and
described a preferred embodiment of the invention and suggested
various alternatives and modifications thereof, but it is to be
understood that these are not intended to be exhaustive and that
other changes and modifications can be made within the scope of the
invention. These suggestions herein are selected and included for
purposes of illustration in order that others skilled in the art
will more fully understand the invention and the principles thereof
and will be able to modify it and embody it in a variety of forms,
each as may be best suited in the condition of a particular
case.
FIG. 1 is perspective view of a robot constructed according to the
invention.
FIG. 2 illustrates a cable diagram indicating the relative position
of cables, winches and pulleys in the apparatus.
FIG. 3 is a somewhat schematic elevation of the apparatus of the
invention indicating the relative position of the motors and
principal robot member.
FIG. 4 is a schematic diagram indicating a preferred way of
generating pulses for the motor circuits.
FIG. 5 is a circuit diagram disclosing a preferred way of
controlling vertical and horizontal motors.
FIG. 6 illustrates schematically the nature of input signals to the
three axis of motion.
Referring to FIGS. 1 and 2, it is seen that robot 20 comprises a
vertical track 22 formed of hollow vertical track rods 24, and a
turntable 26 which provides means to rotate vertical track 22 about
a 360 degree arc.
Mounted for movement up and down along track 22 is an arm-bearing
bracket 28 which, in addition to apertures for rods 24 comprises a
diamond-shaped aperture for passage of arm 30. Arm 30 rests on four
sets of roller bearings mounted on the lower surfaces of the
passage and which are not shown but are conventionally used in the
mechanical arts and is adapted to be moved back and forth through
bracket 28 on the roller bearings.
Motion is impacted by three motor-driven cable systems, each of
which comprises a length of cable, pulleys or sheaves for
facilitating the movement of said cable, biasing means for
maintaining desired tension on said cables and a winding means for
the cable operation. (See FIG. 2) In each case, the winch is
mounted between the ends of the cable which it is moving so that
movement of the winch (about which are wound several windings of
cable) pulls one end of the cable while feeding out the cable
demanded by the integrated movement being imparted to the robot arm
by the sum of the action of all three cable/winch systems.
Upper pulleys 32 and 33 for the cable system are housed in an upper
housing bracket 36. Pulleys 42 and 43 for horizontal arm movement
are housed within cavities of the central bracket 28.
Cable 50 is the operating cable for moving arm 30 in and out of
bracket 28. One end of the cable is attached to the arm 30 near
each end thereof. Cable 50 feeds from an initial anchoring position
48 back over pulley 43 downwardly around the horizontal, or
arm-operating winch 52, around the winch for several turns thence
upwardly to pulley 33, downwardly to pulley 42 and back to its
terminal anchoring position at 54. The anchoring positions are
selected to assure they will not engage the pulley or
pulley-holding bracket during the desired travel path.
Similarly, bracket 28 is itself carried in a vertical direction in
response to the movement of a cable 60 which is attached to the
bracket at anchor positions 62 and 64. Rotation of winch 66 will
cause the cable to carry the up and down tracking rods 24.
Each combination of motor, gear box, winch, and potentiometer is
assembled so that the individual parts rotate together. Thus,
referring to FIG. 3, it is seen that the turntable motor 80 is
aligned on a common shaft with gear box 82, winch 84 and
potentiometer 86 below turntable 90 which comprises a rotary
mounting plate 92 and a grooved circumference for receiving
turntable cable 62.
Also seen in FIG. 3 and numbered to correspond with FIG. 5, are the
horizontal, or arm, motor 360, its gear box 358, its winch 52
(hidden), and its potentiometer 332. Also seen on FIG. 3 are the
vertical control motor system comprising vertical motor 260, its
gear box 258, its winch 66, and its potentiometer 232.
Winch 66 is connected, on a common shaft, to turn with a multiturn
potentiometer 232 (described below) and gear box 258 of motor
260.
Likewise winch 358 is connected on a common shaft to turn with a
multiturn potentiometer 332 and gear box 358 of motor 360.
The illustrated cable arrangement is of particular value in tying
in the horizontal and vertical movement of the arm by having each
anchored to the bracket 28. In this arrangement, for example, the
arm will move horizontally when the block moves downwardly unless,
of course, horizontal movement counteracts the effect. This
interacting cable arrangement facilitates a smooth control of the
robot as will be described below.
FIG. 5 describes the operation of the motors. Specific detail is
set forth only for the horizontal and vertical motors which can
interact to assure desirable tracking characteristics for the robot
arm. It will be understood that the turntable motor can be driven
by a similar circuit.
The circuit described as FIG. 4 has as its object the generation of
three modulated, pulse-width signals for vertical, horizontal and
rotary motion of the robotic arm.
Any appropriate controlling computer 200 is connected through a
standard buss interface 202 to a series of three digitally
programmable one-shot multivibrators. An example of a device
readily utilized for this function is a programmable interval timer
203 sold by Intel Corporation under the trade designation
Intel8523. This device is well known in the art and its use is
described, among other places, in Intel Corporation's publications
entitled "The 8086 Family User's Manual" (October, 1979) and
"Component Data Catalog" (January, 1981). (However, it is not
believed that the precise use described herein is disclosed
anywhere in the prior art.)
An oscillator 204 is connected to the clock inputs of the one-shots
has a frequency of about 1 megacycle. (However it should be
realized that the frequency could be up to the maximum count rate
of the particular one-shot. Lower frequencies could be used but
this is generally undesirable. Such lower frequencies will cause
reduction in resolution or a reduction in the frequency of the
pulse rate modulated signal outputs.)
The one-shots generate a pulse which is proportional to their
digital inputs up to maximum value permitted by the frequency
divider counter 205 which is suitably of thirteen binary bits or a
count of 8192 decimal.
The percentage of "on" time (as opposed to "off" time) of the
output pulses from the one shots of timer 203 is proportional to
the input digital data and the frequency of the output is equal to
the oscillator frequency divided by the frequency of the divider
counter. These signals are sent over a transmission line from the
computer to the robotic arm-operating mechanisms as shown
schematically at 206, 207 and 208. This has the advantage that the
information component of the signal is in the time domain and is
not directly dependent upon the voltage levels or voltage drop in
the cable. Typical useful pulse width inputs profiles are shown in
FIG. 6. These inputs cause a change-of-state of a C-MOS switch 210,
typically a National Semiconductor Model No. 4053, which switches
the output from voltage reference to ground through a pair of
resistors 212 and 214. This switching is smoothed by capacitor 216
followed by an integrating amplifier 220 whose time constants,
together, filter the AC component out of the
pulse-width-signal.
It is well to note that the reference voltage (at 230) to the C-MOS
switch 210 is the same as the reference voltage (at 230a) to the
feedback potentiometer 232. This is the potentiometer associated
directly with motor and winch. Thus the input signal becomes
independent of voltages generated other than the reference voltage.
Moreover, because the input switch (210) and feedback potentiometer
(232) both ratio the reference voltage, that voltage is not itself
critical except that there be no substantial difference between the
reference tied to the input switch 210 and the feedback
potentiometer. Tracing the signal from potentiometer 232, the wiper
234 of potentiometer 232 is connected to a feedback repeater
amplifier 240 which forms means to minimize or reduce the effect of
loading on the potentiometer 232. (A load resistor connected across
the potentiometer would normally cause a non-linearity of the
feedback signal, i.e., a undesirable difference between the
feedback signal and the actual position of the potentiometer.) The
feedback voltage is then summed together with the input voltage
which is of opposite polarity. The difference in feedback and input
voltages is suitably amplified in difference amplifier 250. The
amplified signal is sent to powerdriver 252 which generates the
necessary voltage to drive the permament magnet direct current
motor that moves the "vertical" servo drive mechanism 260. The
stabilizing network 256 which is connected from the motor input
back to the summing junction prevents oscillation of the total
system. Use and design of such stabilizing networks is well known
in the art.
The vertical drive gear box 258 has a relatively high gear ratio
which increases the lifting force yet, at the same time, limits the
vertical speed of the motor which causes the vertical lift and,
thus, limits the speed of the robot arm lift motion. This has the
advantage of allowing the horizontal servo 334-360 system to track
the position of the vertical motion with minimum error and provides
for the force necessary for the verticle servo to lift a large
mass.
The direct current motor 260, the gear box 258, the cable pulley
66, or sheave, and the multiturn feedback potentiometer 232 are
connected to a common shaft. Thus the position of the vertical
motion is locked directly to the motor 260 and the feedback
potentiometer 232.
Referring to FIG. 6, showing the processing of the pulses width
input to the horizontal drive control system (300) goes through the
same process of being switched from reference voltage to ground
through the resistances that are in series with those leads and is
smoothed by the integrating inverting amplifier 220 as in the
vertical motion circuitry. The resulting D.C. voltage is summed
together with the feedback from the horizontal feedback
potentiometer 334 along with a signal that is inversely
proportional to the feedback signal from the vertical feedback
potentiometer 232 through a signal inverting potentiometer 400.
This signal causes the horizontal servo 360 to closely track the
position of the vertical servo 260 allowing the cable system
controlling the arm to be of simple construction. When the arm is
raised, the horizontal cable 60 must be moved exactly synchronously
with it to provide that a tool mounted on arm 30 to move directly
upward. The inverse is true when arm 30 is to be moved in: a
downward direction. To accomplish this, the horizontal gear box 358
has a lower gear ratio allowing higher speeds in the horizontal
direction and, hence a faster response than is provided by the
vertical gear box 258. This is permissible and convenient because
horizontal arm 30 does not need to lift mass.
Thus forces generated on the cable and sheave will be suitably low
despite the relatively rapid movement of the arm in a horizontal
direction. The horizontal stabilizing circuitry, of course, will be
optimized forthe different speed. This stabilizing is within the
ordinary skill of the art.
It is also to be understood that the following claims are intended
to cover all of the generic and specific features of the invention
herein described and all statements of the scope of the invention
which might be said to fall therebetween.
* * * * *