Note: Descriptions are shown in the official language in which they were submitted.
lza~s~72
- SPECIFICATION
BACKGROUND OF THE INVENTION
This invention relates generally to robotic apparatus,
and rnore particularly, to robotic manipulator arms which are oper-
ated to perform a desired series of movements.
Various robot arm systerns have been disclosed in the
paten-t literature and are con~nercially available. Such arsns
invariably include a tool at their free end for moving the tool to
desired spatial positions to effect some task. Prior art arms are
frequently jointed or articulated so that the tool can be moved to
any position in a three dimensional envelope. This envelope is
co~only referred to as the working volume of the arm.
Typical prior art arms which are formed of plural joints
with interconnecting sections (sometimes referred to as "links")
are those whose joints are arranged so that the links can be moved
to simulate movements of a human arm. pence, robot arms frequent-
ly include a "shoulder joint" for rotating the arln about a hori-
zontal axis, a "wrist joint" for rotating the tool holder about a
horizontal or pitch axis, a "wrist joint" for rotating the pitched
2U tool holder about an axis, etc. Motors or other actuators, e.g.,
solenoids, are used to effect the motion of the jointed ann sec-
tions. The operation of the motors is usually accomplished under
computer control. In this regard, in state of the art systems,
the robot arms are controlled by colnputer means which frequently
include microprocessors for effecting movement of the ann to
various positions within the workiny volume in accordance with the
predetermined teachable, repeatable program. To accomplish such
computer control, the joint rnotors frequently have associated with
them encoders to provide signals indicative of the joint position.
30 These signals are operated on by matheMatical computating means in
the system's microprocessors so that the exact position of the
tool within the working volume is deter~nined to insure accurate
~2~91'^~2
arm positioning when the joint motors are operated to rnove the arm
to another position within the workiny volume.
Heretofore, the geometry of the location of the various
joints of prior art robot arms has rendered the calculation of
tool position a relatively complicated matter, thereby necessi-
tating powerful processiny or computer capacity to effect such
calculations.
As will be appreciated by those skilled in the robotic
art, the working volume of the arm is a function of the degree of
mobility of the joints and the extension of links rnakiny up the
arm, less the actual volurne taken up by the arm itself. Needless
to say, it is desirable to maximize the working volume of a robot
arm since an arm with a large working volume permits the perfor-
mance of a wide range of tasks. Heretofore, prior art robot arms
have not provided a sufficiently large workiny volume for a given
size arm.
OBJECTS OF THE INVENTION
Accordingly, it is a general object of the instant inven-
tion to overcome the disadvantages of prior art robot arms.
It is another object of the instant invention to provide
a robot arm which is compact in size and which provides a hiyh
working volume.
It is a further object of the instant invention to pro-
vide a robot err havinc3 plural joints for effecting movement of a
tool mounted on the arrn throughout the working volume, with the
axes of said joints intersecting at points to facilitate the
colnputation of tool position within the working volume.
It is a further object of the instant invention to pro-
vide a robot arm having four rotary joints and one linear joint,
3U with the linear joint consisting of one stationary and two moving
links to result in an arm that is extremely co-mpact, when
retracted, yet exhibits a long reach.
-- 2 --
~2Q9~7;~
It is a furtner feature of the instant invention to
provide a robot arm which is light in weight, yet providing great
strengt'h.
It is still a further object of the instant invention to
provide a jointed robot arrn formed of a modular construction.
It is still a further object of the instant invention to
provide a robot arm including plural drives for its various joints
and which drives do not require adjustment while in operation.
SUMMARY OF THY INVENTION
These and other objects of the instant invention are
achieved by providing a robotic system includiny a manipulator arm
for moving a device to a predetermined point within a working
volume under the control of microprocessor based control means.
In accordance with one aspect of the invention, the manipulator
arm includes joint base means, a first section extending from the
joint base means, shoulder joint rneans, a second section extending
along an extension axis from the shoulder joint rneans and wrist
joint means mounted adjacent an end of the second section, said
wrist joint means for supporting the device thereon, with the
wrist joint means comprising pitch joint means and roll joint
means. The base joint rneans is arranged to pivot the first sec-
tion through a first predetermined arc about a first axis. The
shoulder joint means is arranged to pivot the second section
through a second predetermined arc about a second axis. The
second axis and the first axis intersect perpendicularly at a
first point. The pitch joint means is arranged to pivot the
device through a t'hird predetermined arc about a third axis. The
roll joint means is arranged to pivot the device through a fourth
predetermined arc about a fourth axis. The fourth axis intersects
the third axis perpendicularly at a second point. The third axis
and the second axis are parallel to each other. T'he first and
second points lie along the extension axis.
-- 3 --
12~9172
In accordance with another aspect of tile invention, the
manipulator awl includes first joint means, an arm section mounted
on the first joint means for rotation throuyh a predetermined arc
about a first axis and second joint means mounted on the arm sec-
tion at a space location from the -first joint means. The second
joint means is arranged to support a device thereon. The arm
section comprises first, second and third link means which are
telescopically interconnected, whereupon second joint means can be
positioned at various predetermined distances from the first joint
means.
Other objects and many of the attendant advantayes of the
instant invention will be readily appreciated as the same becoMes
better understood by reference to the following detailed descrip-
tion when considered in connection withs the accompanying drawing
wherein:
DESCRIPTION OF THE DRAWING
Fig. 1 is a schematic diagram of a robotic system with a
perspective view of the robot arm of the system;
Fig. 2 is a top plan view of the arm shown in Fig. 1,
~0 with portions broken away;
Fig. 3A is one portion of the enlarged sectional view
taken along lines 3A, 3B-3A, 3B of Fig. 2;
Fig. 3Bis the remaining portion of the sectional view
taken along line 3A, 3B-3A, 3B of Fig. 2;
Fig. 4 is an enlarged sectional view taken along line 4-4
of Fig. 3A;
Fig. 5 is an enlarged sectional view taken along line 5-
of Fig. 3A;
Fig. 6 is an enlarged sectional view taken along line 6-6
3U of Fig. 3A;
Fig. 7 is an enlarged sectional view taken along line 7-7
of Fig. 3B;
-- 4 --
12C~9~72
Fiy. is a sc`hematic perspective view of a portion of
the arrn shown in Fig. 1 showing the means for effecting linear
extension retraction of said arm;
Fig. 9 is an enlarged sectional view taken lone 9-9 of
Fig. l;
Fig. l is an enlarged sectional view taken along line
10-10 of Fig. l;
Fig. 11 is a sectional view taken alony lines 11-11 of
Fig. l
Fig. 12 is a side view waken along line 12-12 of Fig. 9;
and,
Fig. 13 is a sectional view taken along line 13-13 of
Fig. 10.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the various figures of the drawing
wherein like reference characters refer to like parts, there is
shown generally at 20 in Fig. 1 a robotic system of the instant
invention. The system comprises a robot arm 22, a controller 24
and a teach pendant 2~. The arm 22 includes plural joints, to be
20 described later, which are pivotable about respective axes, under
the control of associated actuators or motor rneans, to be des-
cribed later. Operation of the motors is controlled by separate
rnicroprocessors (not shown) in the controller 24.
The robot system 20 is arranged to be operated in what is
known as teach-repeat mode. In the teach mode, the arm is tauyht
to perform its desired tasks by leading it tnrough those tasks
under operator control. To that end, the teach pendant includes
plural switches or keys (not shown which are arranged to be
manually operated to cause the robot arm to move to a desired
3U position in space. This position is then recorded in memory in
the controller 24 by the manual operation of other switch means
(not shown) at the teach pendant. The arm can then be moved to
-- 5 --
~2~9~
another position by the suitable operation vf the switches of the
teach pendant, whereupon the next position is sirnilarly recorded
in rneMcry. Accordingly, an entire program of arm rnovements is
recorded in the controller lnemory for subsequent replay. In the
repeat mode, the arm automatically moves to the positions wnich
had been taught . Thus, in the repeat rnode, the control ler pro-
vides signals to the associated actuators in the various joints of
the arm to cause the arm to move to those sequential positions
previously prograimned.
In accordance with the comrnercial embodiment of the
robotic system 2() sold by the assignee of the instant invention,
United States Robots, Inc. under the trademark MAKER, the con-
troller includes a collection of electronic and computer devices,
such as microprocessors, which oversee and effect the rnotions of
the arm 22. The teach pendant 26 also contains a microprocessor
which interprets the teach pendant switches and which commurlicates
appropriate inforrnation to the controller :24, via an intercor~nuni-
cating cable 2~. Information frorn the controller is also sent
back to the teach pendant, via the sarne cable. Signals to and
;~ O from the arrn 20 are provided by cable 30 . The controller 24
includes various microprocessors to effect operation of the arrn
22. Such rnicroprocessors are not shown herein, but basically
comprise an I/O microprocessor for overall coordination of the
operation of the arm, five joint processors (not shown), one for
each of the joints forrning the arm 22, and a math processor for
forming the mathematical calculations and computations attendant
in effecting the moveMent of the arm through the predetermined
program. All of the processors art interconnected on a common
bus, as shown and claimed in our co-pending United States Patent
3() Application Serial No . 314, 914, filed on October 26, 1981,
entitled "Robot Arra Controller With Common Bus Memory" and
assigned to the same assignee as the instant invention. By virtue
-- 6 --
9~'72
of the colNnon bus memory, the system 20 has wide utility since
other processors or devices can be readily incorporated in the
system. The co~non rnernory enables ready col~nunication between the
processors on the common bus.
Also included in the system 20 are ,neans for enabling the
direct editing of any program taught to the robvt arm by the teach
pendant, without necessity of rewriting of the program. To that
end, any program can be edited by deleting steps, inserting addi-
tional steps or sub-routines in the program, etc.
Referring now generally to Fig. 1, the basic components
forsning the arm 22 are shown. As can be seen, the arm 22 basic-
ally comprises a base 32 which serves as the mount for the manipu-
lator, as well as its first joint. This first joint is referred
to as the base or sweep joint. The base 32 is arranged to be
mounted on a suitable support structure, such as a pier 34, adja-
cent a work station (not shown). The next portion of the arm
consists of a colul~n 36 which is mounted on the base and arranyed
to be pivoted through an arc of up to 350 about the vertical axis
38 shown by the broken line in Fig. 1. Thus, the column is
20 arranged to sweep through the arc of 350 by the operation of the
sweep joint 32. Mounted at the top of the column 36 is the second
joint of the arm, namely, the shoulder joint 40. Attached to the
shoulder joint is an extensible arm assembly 42. The shoulder
joint is arranged to pivot the anm assembly 42 through an arc of
up to 300 about a horizontal axis 44. The arm assembly 42 is in
the fonn of a linearly telescoping joint consisting of links 46,
48 and 50. The links 48 and 50 are arranyed to telescope within
the link 42 so that the ann can be either extended or retracted.
Hence, the third joint of the arm, which is formed of assembly 42,
30 is referred to as the extension joint. At the free end of the
extension joint 42 is the "wrist" of the arm. the wrist includes
a tool holder 52 at its free end. The tool holder is arranged to
-- 7 --
~Z09~72
support a tool, such as a pneurnatic gripper (not shown, for per-
forminy the task(s) desired of the robotic system. At the wrist,
there are two joints, narnely, the wris-t pitch joint 54 and wrist
roll joint 56. The wrist pitch joint is arranged to pivot the
tool holder through an arc of up to ~10 about a pitch axis 58.
The pitch axis 58 is parallel to the shoulder axis 44. The wrist
roll joint 5~ is arranged to pivot the tool holder through an arc
of up to 355 about a roll axis 60. The roll axis 6~ extends
perpendicular to tlle pitch axis 58. The wrist pitch joint 54
forrns the fourth joint of the arm, while the wrist roll joint 56
forms the fifth joint.
Each of the five joints has a closed loop servo system
associated with it. The servo system includes a O servo motor
and an associated power transmission. In particular, the first,
second and fifth joints use harmonic drive reducers, to be des-
cribed later, whereas the third joint uses a ball bearing screw to
generate linear motion and the fourth joint uses a gear set.
Feedback information is provided by an optical shaft
encoder, to be described later, associated with each motor. The
20 encoder provides signals through the cables of the arrn and inter-
connecting cable 30 back to the controller 24 so that the control-
ler knows the position of each motor shaft, and hence, the
position of the arm's joints.
In accordance with one aspect ox this invention and as
can be seen in Fig. 1, the base axis 38 and the shoulder axis 44
intersect at a point A, whereas the pitch axis S8 and the roll
axis 60 intersect at a point B. The points A and B are located
along a common axis 62, whose lenyth is the length of the exten-
sion of the link assembly 42, narnely, links 46, 48 and 50 makiny
3~ up the extension joint. The shoulder-base intersect point A is
referred to as the shoulder intersect point, while the wrist
intersect point B is referred to as the wrist intersect point.
~2Q9~'7;~
The axis ~2 is referred to as the extension axis.
By using the angles of the base and shoulder joint and
the length of the extension axis, as provided by the optical
encoders, the rnath processor in the controller 24 can readily
calculate the position of the wrist intersect point B. By using
the angles of the wrist pitch joint and the wrist roll joint, com-
pared to the base-shoulder intersect point, the math processor can
readily calculate the orientation of the tool holder 52. Thus,
for all intents and purposes, the arm 2~ effectively looks like a
vector in cartesion coordinate space so that the calculation of
the position of the tool holder can be accomplished simply throuyh
geometric calculations.
In accordance with another aspect of this invention, the
arm section 42 is extendable through the telescopeability of the
three compact links 46, 48 and 50. This results in an arm which
is extrernely compact when retracted, yet exhibits a long reach.
Thus, the arm takes up only a small volurne, while providing a
large working volume. This renders the arm particularly suited
for operations entailing the assembly of large or small parts or
for reaching into small spaces for loading and unloading machine
tools.
The details of the first joint, that is the base joint,
will now be considered with reference to Fig. 10. It rnust be
pointed out at this juncture that while the base joint is shown
mounted horizontally on a pier 34, it is clear that the arm can be
mounted in any orientation on any support structure. For example,
the awn can be mounted on a vertical wall, on a horizontal ceil-
ing, etc.
Basically the base joint comprises two components: A
base support 64 and a base housing 66. The base support 64
consists of an inverted cup-shaped me~nber having a flange 6~,
including mounting holes 70 for secureMent by bolts 72 (Fig. 13)
g _
î~9i~2
to the pier 34. Disposed over the upper end 74 of the base sup-
port is the base housing 66. The base housiny is also a cup-
shaped member. The base housing is rnounted on the base support by
a lower bearing assernbly 76 and an upper bearing assernbly 78
extending between the circular sidewalls forming the base support
and base housing. The bearing assemblies are preferably of the
angular contact ball bearing type. The lower beariny assernbly is
held in place about the periphery of the base support by a retain-
ing ring 80 and a retaining plate 8~. The retaining plate is
secured to the base housiny 66 by a plurality of bolts 84. The
upper bearing assembly 78 is held in place about the periphery of
the base support by a shoulder 86 extending about the periphery of
the top 74 of the base support and a spring washer located
within an annular recess 90 about the inner periphery of the base
housing adjacent the top 92.
The vase housing 66 is arranged to be rotated about the
vertical sweep axis 38 (Figs. 1 and 10) under control of the con-
troller 24, via signals provided through cable 30. The actual
means for effecting the rotation of the base housing 66 with
20 respect to the base support 64 comprises a DC servo motor 94
mounted within the base support and whose output shaft 96 extends
vertically, centered on axis 38. The motor g4 is mounted and held
within the base support by a plurality of screws 98 extending
through the top plate of the base support.
In accordance with the comrnercial embodiment of the
instant invention, the servo motor 94 for the sweep joint as well
as the servo motors for the other joints is a model T03SP sold by
PMI Motors.
The output shart of t-he servo rnotor, which is designated
by the reference numeral 96, is connected through rotational speed
reduction means, to be described in detail hereinafter, to the
base housing 66. The reduction means is coupled to the base
-- 10
~Z~172
housing to reduce the rotational speed of tlle output shaft of the
motor as is coupled to the base housing. Preferably the reduction
means eomprises a harmorlic drive unit 100.
A harmonic drive 100 is a conventional device for
reducing rotational speed and increasing torque and is sold by
United Shoe Machinery Company, a division of Bnhart Industries.
One particularly suitable harrLlonic drive is model EUF2~-160.
Since the harmonie drive 100 is a conventional,
commercially available product, all of its components will not be
specifically described herein. Suffice it to state that the drive
unit 100 basically comprises the following components which are
shown in Figs 10 and 11: A wave generator 102, which is fixedly
secured to tne motor output shaft 96, a flexible spline 104, which
fits tightly about the periphery of the wave generator 102 and two
rigid splines 106 and 108. The rigid spline 108 is stationarily
mounted and is secured in an annular recess 110 in the top 92 of
the base support by plural screws 112. The other rigid spline
106, serves as the output of the drive unit 100, and is connected
in an annular recess 114 in the inside of the top portion 74 of
the base housing by plural serews 116. The harmonic drive unit
100 is arranged so that upon rotation of the output shaft 96 of
the motor, the output spline 106 moves relative to the stationary
spline 108 in the direction opposite to the direction of rotation
of the motor shaft and at a small fraction, e.g., 1/160, of the
rotational speed thereof. Thus, the base housiny 66 is rotated
slowly, e.g., at 11~2 radians/second, about the vertical sweep axis
38 upon operation of motor 94.
Also connected to the output shaft of the motor is an
optieal shaft encode 118 whieh provides position signals to the
contoller 24, via an eleetrieal eable seetion 120 in the arm and
whieh is eonneeted to eable 30.
-- 11 --
~Z(~9~7Z
The base support also includes an air port 12~ for
providing air through pneUInatic lines 124 to a pneumatic gripper
(not snown) or other pneumatic tool mounted on the mounting plate
at the end of the arm. The air port 122 is in the form of a hose
fitting 12b. The air line or conduit 124 extends through a
sidewall in the base support and through an opening 128 in the
sidewall of the base housing into the column 36. The electrical
cable for the arm, which is denoted by the reference numeral 130,
is attached to an electrical connector 132 in the base support.
The cable 130 extends through the sidewall of the base support and
the opening 128 in the base housing into the column 36. The cable
terminates at its upper end in the column 3b in an electrical
connector portion 134. The connector portion 134 mates with a
second connector portion 136 to which another section of the cable
130 is connected. That latter section of cable extends down the
arm from the shoulder.
A pneumatic connector 13~ is provided at tne end of the
air conduit 124 at the top of the column 36 for connection to a
corresponding air line connector in the arm at the shoulder. my
20 providing the connectors 134 and 138 within the top of the column
36, the base and the column can be readily disconnected from the
remaining portion of the robot arm, thereby expediting servicing,
should such become necessary.
In Fig. 13, a top view of the base joint and column 36 is
shown. As can be seen, the column 36 consists of a hollow square
tube having four sidewalls, one of which is identified by the
reference numeral 140. The sidewall 140 is secured, via two
bosses 14~ to the base housing 66 by a plurality of screws 144
(Fig. 10).
The base joint is only permitted to rotate about axis 38
through an arc of 350 as shown in Fig. 1. In order to preclude
any overtravel, a pair of stops are provided at the base joint.
- 12 -
~2~7~
To that end, one cylindrical, rod-like stop 136 is mounted pro-
jecting upward frol~ the flange on the base support and another
similarly constructed stop 148 is mounted on the base housing.
The upper end of the arm's column 36 terminates in the
shoulder joint 40. The shoulder joint is shown in detail in Fig.
9, and is of the same basic construction as that of the base joint
except that in the latter, there is a shoulder support in lieu of
the base support of the former. The shoulder support is desiglla-
ted by the reference numeral 150 and is unctionally equivalent to
the base support but has a differently shaped flange to mount the
extensible arm joint 42 on the shoulder. In the interest of
simplicity, all of the details of the shoulder joint will not be
reiterated Suffice it to state that the shoulder joint comprises
a shoulder base 152, and a shoulder housing 66 mounted on the
base, via a pair of bearings 76 and 78. A DC servo motor 94 is
mounted within the shoulder support. A harmonic drive unit 100 of
the same construction, as described heretofore, is connected to
the output shaft of the O servo motor. The output spline 106 of
the drive unit is connected to the shoulder housing. Power to the
motor is provided through the electrical cable section 130. An
encoder 118 is also Inounted on the motor's output shaft.
The shoulder housing is mounted on the top of t-he column
36 by a pair of bosses 151. The flange 152 of the shoulder
support is secured to the sidewall 1~4 of the link 42 by plural
bolts 156 (Fig. 13). An opening 158 is provided in the sidewall
of the shoulder housing and an opening 160 is provided in the
sidewall of shoulder support for electrical cables and the
conduits of the arm to pass through.
The range of motion of the shoulder joint is 300 about
axis 44. In order to insure that there is no overtravel, plural
stops are also provided at the shoulder joint. Those stops are
shown in Fig. 12 and comprise a pair of rod-like stops 162 mounted
- 13 -
lZ~9~L7~2
on the bosses 151 of the shoulder housing 6~ and a similarlyshaped stop 164 mounted on the shoulder support flange. Thus,
when tne shoulder housing is rotated in a clockwise direction, the
leftmost boss mounted stop 162 contacts the support mounted stop
lb4~ whereas when the motor is rotated in -the opposite direction,
the rightmost boss Inounted stow contacts the support mounted stop,
thereby limitiny the travel of the arc or tile shoulder to 30~
max:Lmum .
Turning now to Figs. 2 and 8, the basic constructional
features of the extension joint, that is the telescoping arm 4~,
will be descri'bed. As noted 'heretofore, the extension joint
consist of three links. Namely, 46, 48 and 50, with lin'ks 48 and
50 being telescopeable wit-h respect to link 46. In particular,
the links 48 and 50 are arranged to be extended in unison into and
out of the link 46 to bring the tool holder to any desired radial
position with respect to the vertical sweep axis 38 within the
working volume.
In order to expedite the understanding of the telescopillg
nature and operation of the links 46, 48 and ~0, reference will be
made to the schematic view of Fig. 8. That view shows the inter-
connection of the three links making up the extensible arm, with
the means for moving the links also being s'hown. To that end,
each link is a tubular member having four elongated sidewalls, a
front bulkhead and a rear bulkhead. The front bulkhead is mounted
within the interior enclosed by the sidewalls adjacent the front
end thereof, while the rear bulkhead is rnounted within the in-
terior defined by the sidewalls adjacent the rear end thereof. In
Fig. 8, the sidewalls of each of t'he links are omitted for drawing
simplicity and only the bulkheads are shown. us can be seen in
Fig. 1, the sidewalls forrniny link 48 are of lesser width than the
sidewalls forming link 46 so that the link 48 can telescope within
link 46. In a similar manner, the sidewalls forming link 50 are
- 14 -
~2~9~%
of smaller widtll than the corresponding sidewalls of link 48 toenable link 50 to telescope within link 48.
As can be seen in Fig. 8, the link 42 includes a rear
bulkhead 16~ which is fixedly secured to the sidewalls forming the
link at the rear end thereof and a front bulkhead 168 which is
fixedly secured to the sidewalls at the front end thereof. An
elongated ball screw 170 is mounted within link 42. The rear end
of the ball screw is supported within a 'bearing 172 in the rear
bulkhead 166, while the front end of the screw is mounted within
the bearing 174 in the front bulkhead 168. The rear end of the
ball screw is connected, via a coupling 176, to the rotary output
shaft 178 of a DC servo motor (to be described later). A ball nut
180 is mounted on the rear bulkhead 182 of link 48. The front and
the rear bulkheads of link 48 are mounted within the sidewalls
forming link 48. The ball screw 170 extends throuyh the ball nut.
The motor shaft 178 of joint 46 rotates the ball screw in either
the clockwise or counter-clockwise direction upon receipt of
specific signals from the controller. The rotation of the ball
screw causes the ball nut 180 to travel along the screw.
Accordingly, since the ball nut 180 is fixedly secured on the rear
bul'k'head 182 of link 48, the link 48 moves relative to link 42
upon rotaton of the ball screw. Thus, when the ball screw is
rotated in one rotational direction, the link 48 is pulled within
the link 46, whereas when the ball screw is rotated in the
opposite direction, the link 48 is extended out of link 46.
As stated heretofore, link 50 is arranged to telescope
within link 48 in unison with the telescoping of link 48 with
respect to link 46. The means for effecting such unison motion
comprises a series of ropes which interconnect links 46, 48 and
50. Such ropes consist of a pair of extension ropes 184 and a
pair of retraction ropes 186.
~2~9~2
The extension ropes 184 are interconnected between link
46 and lir* 50. To that end, the rear end of each of the
extension ropes is fixedly secured to the rear bulkhead 166 of
link 46, while the opposite end of the extension ropes is fixedly
secured to the rear bulkhead 188 of link 50. Each of the
extension ropes 184 extends abou-t a respective pulley 190 rnounted
on the front bulkhead 192 of link 4~.
As will be appreciated by those skilled in the art, when
the ball nut 18~ moves alony the ball screw 17~ in the outward
direction, that is toward the tool joint holder, the link 48 is
moved outward. Since the rear end of the extension ropes 184 are
connected to the back bulkhead 166 of link 46, which link is
stationary, the forward movement of link 48 causes the pulleys 190
mounted on the front bulkhead thereof Jo rotate, thereby pulling
on the opposite end of the extension ropes. Since the opposite
end of the extension ropes is fixedly secured to the rear bulkhead
188 of link SO, and since that bulkhead is secured to the side-
walls of link 50, link 50 is pulled forward. Thus, it can be
appreciated that as link 48 is moved outward by the ball screw and
cooperating ball nut, there is a corresponding outward movement of
link SO.
The rneans for effecting the retraction of the links 48
and 50 into link 46 is accomplished, via the retraction ropes 186.
As can be seen, the retraction ropes 186 are connected at one end
thereof to the rear bulkhead 188 of link 50. The opposite end of
the retraction ropes 186 is connected to the front bulkhead 168 of
link 46, the stationary link. The retraction ropes extend about
respective pulleys 194 mounted on the rear bulkhead 182 of link
48. The extension ropes also extend about pins, to be described
in detail later, mounted on the front bulkhead 168 of the link 46.
These pins are provided to alter the direction of the retraction
ropes and hold the ropes out of the way of other cornponents
located within the arm section 42.
~9~
As will be appreciated by those skilled in the art, the
rotation of the ball screw in the opposite direction from that
occurring duriny the extension operation has the effect of pulling
the ball nut toward the rear of the arm, that is away from the
tool `holder. Since the retraction ropes are mounted at one end to
the stationary front bulkhead 168 of link 46, the rearward move-
ment of link 48 with respect thereto causes the pulleys 194 to
rotate the pull on the retraction ropes 186. This action pulls on
the opposite ends of the retraction ropes, that is the ends
connected to the rear bulkhead l of link 50, whereupon link 50
moves to the rear in unison with link 48.
Inasmuch as the extension-retraction operation of links
46, 48 and 50 has now been described, reference will be made to
the constructional details of the links 46, 48 and ~0.
Accordingly, referring now to Figs. 2 and 3A, it can be
seen that the link 46 consists of a hollow shell formed of plural
interconnected sidewalls 196 and an end wall 198. The rear bulk-
head 166 is mounted within the interior of the shell of link 46
adjacent the end wall 198. The motor for effectin4 rotation of
the ball screw comprises a VC servo motor 200. That motor is
mounted on the back of bulkhead 166 by a Inounting flange 202 and
associated screws 204. An optical shaft encoder 206 is mounted on
the rear of the servo motor housing and is coupled to the motor's
output shaft. The output shaft 178 of the motor is connected to
the ball screw 170 by the coupling 176.
The heretofore mentioned bearing 172, which is mounted in
the rear bulkhead 166 of link 48, actually comprises a pair of
ball bearings 208 (Fig. 3A) mounted within an opening in the
bulkhead.
The link 4~, like link 46, also cornprises a shell formed
of plural sidewalls 210. In the rear end of the shell, the rear
bulkhead 182 is Inounted- A pillow block 212 is n~ounted on the
- 17 -
9~'2
bottom sidewall of the link 4~ shell at t'he rear bulkhead. The
ball nut 180 is rnounted on the plllow block 212. The ball screw
170 extends through the ball nut 180 into the bearing 170 in the
forward bulkhead 168 of link 46 and located below the bottom
sidewall 210 of the shell of link 48.
In order to guide the extension and retraction of the
link 48 within link 46, a pair of guide rails 214 are provided in
the shell of link 46. A second pair of guide rails 215 are
provided in the shell of link 48 to guide the extension and
retraction of link 50 therein. The guide rails 214 are best seen
in Fiys. 2, 3A, 4 and 6. As can be seen, each guide rail is a
round, elongated steel rod. The rear end of each rod is fixedly
secured within a hole 216 in the rear bulkhead 166 by set screws
218 (Fig. 4). The forward end of each of the rails 214 is mounted
within a respective hole 220 (Fig. 5) in the forward bulkhead 168
of link 46. In order to stiffen the guide rails 214 along their
length, each guide rail 'has mounted thereunder an elongated
stiffening brace 222 (Fig. 6). Each brace is secured to its
associated guide rail, via threaded bolts 224 (Fig. 6).
The means for supporting the link 48 on the guide rails
214 comprises the heretofore mentioned pillow blocks 212 and
associated bushings 226. To that end, the guide rails 214 extend
t'hrough he bushing 226 in the pillow blocks 214. As can be seen
in Fig. 6, each bushing 226 includes a slot 228 in the underside
thereof to accomlnodate the rail brace 224.
The guide rails 215 for guiding the movernent of link 50
within link 48 are each elongated steel rods, with one rail 230
being of larger diaIneter than the other 232 (see Fig. 5). The
rear ends of the guide rails 215 are mounted within respective
openings 234 and 236 in the rear bulkhead 182 of link 48 (Fig. 6).
The forward ends of the rails 230 and 232 are secured in similar
openings, 234 and 236, respectively, in the front bulkhead of link
~9~72
48 (Fig. 7). The larger diameter guide rail 230 is mounted within
link 48 in a similar rnanner to the mounting of guide rails 214 in
link 46, narnely, by the use of an elongated stiffening brace. The
link 50 is mounted on the guide rails 230 and 232 in a similar
manner to the mounting of link 4~ on the guide rails 214, namely,
the use of pillow block rnounted bushings.
Referriny now to Figs. 3B and 7, the details of the
construction of link S0 will now be described. As can be seen,
link 50 comprises a shell forrned of plural, elonyated sidewall
238, which are connected together, and a bac`k wall and which forms
the rear bulk'head 18~. Mounted on the top wall 238 of link 5~
contiguous with the rear bulkhead 188 is a pillow block 240 (Fig.
3B) supporting the 'bushings t'hrough which the guide rails 230 and
232 extend. A mounting plate 242 is fixedly rnounted within the
sidewalls 23~ to the front of the rear bulkhead 188. A DC servo
motor 244 is mounted on plate 242 and serves as the rneans for
effecting the rotation of the wrist joint about the pitch axis 58
(Fiy. 1). An encoder 250 is mounted on the end of the motor
housing 244 and is coupled to its output shaft. The encoder and
motor are electrically connected to the remaining portions of t'he
system, via electrical cable sections 250.
The output shaft of the motor is denoted by reference
numeral 246 and is connected, via a coupling 252 to an elongated
drive shaft 254. The drive shaft 254 extends the length of the
link 3 shell for connection to means, to be described generally
later, for effecting the pitch rotation of the wrist joint.
A pair of terminal blocks 256 (Fig. 2) are mounted on the
rear bulkhead 166 of link 48 and serve as the means for effecting
the electrical interconnection between the shoulder and the remain-
der of the arm, that is links 46, 48 and 50 and the wrist pitchand roll mechanisms.
-- 19 --
~zo9~z
As can be seen in Fig. 3A, the extension ropes 184 are
secured to the rear bulkhead 166, via respective turnbuckles 258.
The extension ropes are connected at their opposite ends to the
rear bulkhead 188 of link 50 by swaged fittings (not shown). The
retraction ropes 186 are secured to the front bulkhead 168 of link
46, via respective anchor screws 260 (Fig. 5). The retraction
ropes extend about screw-type guide pins 2b2 to keep the retrac-
tion ropes out of the central portion of the link. The opposite
ends of the retraction ropes are connected to the rear bulkhead
10 188 of link 50 by swaged fittings 264 (Fig. 3B).
In order to insure that during the extension and retrac-
tion of the link components making up arm portion 42, the elec-
trical cables located therein are maintained relatively taut and
extend over guide means, as will be described hereinafter. To
that end, the electrical cable for carrying the electrical signals
and power to the remaining portions of the arm from the shoulder
are in the form of a cable section 266 secured to the rear bulk-
head and in electrical comrnunication with the connections at the
terminal blocks 2S6. The cable section 266 extends up to a "Y"
connection or joint 268. The pair of cable sections 250 form the
legs of the "Y" cormection, with cable section 266 forming the
base of the Y. The Y connection 268 is held in place with respect
to link 46 by a pair of hook wires swaged to the forward bulkhead
168 of link 46. The pair of cable section 250 extend about
respective guide pulleys 272 mounted on the rear bulkhead 182 of
link 48 at the pillow block 212. Each cable section 250 also
bends about a horizontally disposed guide roller 274 located in an
opening in the rear bulkhead 182 of link 48 to extend to the rear
bulkhead 188 of link 50. The cable sections are connected to
bulkhead 188, via anchors 276 (Fig. 3~). The cable sections 250
provide the electrical connections for the motor 244 and encoder
248, as well as the other electrical components mounted at the
wrist of the arrn.
- 20 -
lZ09~72
It should thus be appreciated since the cable section 50
is maintained relatively taut between the rear bulkhead 188 of
link 5~ and the fixed Y connection point adjacent the forward
bulkhead 168 of the link 46, no impediment to free extension or
retraction of the links is produced by the cables.
The wrist joint of the arrn, as noted heretofore, is
arranged to pivot about the pitch axis 58. The means for
effecting pivoting of the joint about the pitch axis will be
described hereinafter. To that end, as can be seen in Fig. 1, the
forward end of link 50 is in the forrn of a yoke having an opposed
pair of extending legs 280. The legs 280 forrn the stationary
portion of the wrist pitch joint 54. The movable portion of the
wrist's pitch joint comprises a housing box 282. The housing box
282 is mounted on the yoke legs by pivotiny means (not shown) and
is arranged to pivot about axis 58. The means for effecting
pivoting of the box 282 about axis 58 comprises a drive chain,
(not s`hown) and associated sprocket snot shown) Inounted within one
leg 280 of the yoke. The sprocket is mounted on a drive shaft
(not shown) fixedly secured to the housing box 282. The drive
chain is rotated, via a gear reducer train (not shown) and mounted
adjacent the yoke by the end of the elongated drive shaft 252
extending down link 50. Accordingly, upon rotation of the drive
shaft 252 under the control of motor 244, the housing box 282 is
pivoted about axis 58 through a maximum arc of 210~.
At the forward end of the 'housing box 282 is another
housing 284. The housing 284 serves as one portion of the fifth
joint, t'hat is the wrist roll joint. To that end, the housing 284
is stationarily secured to the front end of housing box 282.
Located within the housing 284 is a DC servo rnotor and harmonic
drive unit, constructed similarly to the motor's harmonic drives
forming t'he shoulder and base 40 and 32, respectively. The output
spline of the harmonic drive unit is fixedly secured to the tool
- 21 -
~Z~9~7;~
mounting plate ~2. rrhe tool mounting plate 52 is arranged toreceive a conventional gripper or any tool desired to be mani-
pulated by the arm ~0O The pneumatic power for the tool is
provided, via the heretofore identifed pneumatic lines. Respec-
tive encoders (not shown) are associated with the wrist roll joint
and the wrist pitch joint and are coupled, via the electrical
cables back to the controller. The electrical siynals provided to
the harrnonic drive within the housing 284 also provided, via the
electrical cables.
Upon operation of the DC servo .notor within housing 284,
the tool mounting plate 52 is enabled to be rotated through a
maximum arc of 3~5 about the roll axis 60.
As will be appreciated from the foregoing, the robot arm
of the instant invention, due to the arrangernent of its component
joints and their intersecting axes, enables the calculation of the
position of the tool to be readily calculated by the micropro-
cessor means in the controller. Moreover, the compactness and
light weight of the arrn coupled with its wide extensibility range
enables the arm to provide a large working volume in comparison to
arm volurne.
Furtherstill, various colnponents of the arm are modular,
e-g., DC servo motors are used in all joints and a co~non design
motor is used for the base, shoulder and extension drives. This
feature allows for rninimum spare part inventory and in addition
enables the arm to be readily assembled and disassembled in
sections to provide ready access to any portion of the arm for
servicing, should such become necessary.
Without further elaboration, the foregoing will so fully
illustrate our invention that others may, by applying current or
future knowledge, readily adapt the same for use under various
conditions of service.
- 22 -
