Note: Descriptions are shown in the official language in which they were submitted.
131~'7j22
P~OBOT ~1RIST
BACK~P~OUND OF THE INVENTION
1. Field of the Invention.
The present invention relates to mechanical
05 joints and robot wrists, and in particular, it relates
to robot wris~s capable of compound pitch/yaw motion
with continuous roll rotation.
2. Description of the Prior Art.
A number of robot wrist designs and drive
mechanisms have b~en developed in trying to achieve a
wrist having dexterity equal to the human wrist. An
ideal wrist should have 180 of singularity-free
- pitch/yaw motion with continuous roll rotation. A
brief summary of some of the prior art wrists is
given below.
A rotary actuator mechanism is described in
the Higuchi et al U.S. Patent 4,009,644. The rotary
actuator of the Higuchi et al Patent is not very
useful for the transmission of pitch, yaw and roll
motion to a tool or implement rnember.
A number of robot joints are illustrated in
the Vykukal U.S. Patent 3,405~406 and the Vykukal et
al U.S. Patent 4,046,262. The Vykukal Patents
describe hard-type space suits that permit the users
inside the space suits to ~ove around somewha~
unrestricted.
~he Bolner U.S. Patent 3,912,172 describes a
back-dxivable, direct-drive hydraulically-actuated
pitch and roll actuator.
The Rosheim U.S. Patents 4,194,437 and
4,296,681, which were issued to the applicant of the
present application, describe hydraulic servo
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mechanisms which impart rotary movements to a device
to be driven.
The Stackhouse U.SO Patent 4,068,536
describes a remotely-driven, mechanical manipulator.
05 The manipulator is controlled by three concentric
drive shafts which terminate in a spherically-shaped
wrist mechanism.
The Totsuka U.S. Patent 3,739,9~3 and the
Niitu et al U.S. Patent 3,784,031 describe a
manipulator arm having two parallel rotating drive
shafts in a beveled gear system which translates the
drive shaft's rotating motion to a bending pitch
motion and rotary roll motion in a tool member.
A mechanical wrist is described in German
Patent 2,752,236 that includes three electric motors
providing pitch, yaw and roll, which axe mounted on
the outside of a housing with the inside of the
housing being hollow. The wrist is used for holding
welding tongs and the hollow inside housing permits
electrical power lines to be fed through the wrist.
The Molaug U.S. Patent 4,107,948 describes a
flexible robot arm that is composed of a number of
mutually connected rigid links being connected at one
end to a drive means and at the other end to a tool
member.
Another robot arm is illustrated in th~
Wells U~S. Patent 3,631,737. The robot arm of the
Wells Patent includes a plurality of rigid tubular
sections joined end-to-end by flexible joints to form
an articulated arm. The rigid sections are
manipulated by slender control cables which are
1 3 ~ 53'2
attached to the respective sections and selectively
extend and retract.
In addition, a number of well known universal
joints are illustrated and described on pages 16 and
05 17 of the Pictorial Handbook_of Technica _Devices by
Pete Grafstein and O. Schwarz, puhlished by the
Chemical Publishing Company, Inc. of New York, 1971.
Although rotational motion can be transmitted through
the universal joints illustrated on pages 16 and 17,
the universal joints cannot be used in operations for
transmitting pitch, yaw and roll motion to an
implement or a tool member.
The development of robot arms and wrists is
discussed in an article entitled, "Robot Wrist
Actuators," Robotics A~e, ~ovember/December 1982,
pages 15-22 written by the applicant of the present
invention. In this article, several characteristics
are described which make robot wrists attractive.
Disadvantages of prior art wrists are also discussed
in the axticle.
SUMMARY OF THE INVENTION
The present invention includes an improved
drive train for a robot wrist. The wrist includes a
first and second gimbal assembly rotatably mounted
within an interior of a support means. ~ach gimbal
assembly has means for transferring motion to the
other gimbal assembly to effect yaw and pitch
motion. The wrist further includes decoupling means
in slidable engagement with the support means for
effecting movement of the wrist in a compound
yaw/pitch motion. The improved drive train includes
a yaw drive means having a gear =urface and which i-
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pivotally connected to the decoupling means. A drive
shaft with a beveled gear end portion is arranged to
engaye the gear surface of the yaw drive means to
impart yaw motion to the wrist. The drive train
05 further includes a pitch drive means having a pitch
gear surface and which is pivotally connected to the
decoupling means. A drive shaft with a beveled gear
end portion is arranged to engage the gear suxface of
the pitch drive means to impart pitch motion to the
wrist. Means is also provided for rotational motion,
said means for providing rotational motion being
attached to the first gimbal assembly.
In another aspect of the present invention,
the wrist includes a conduit useful for passing
optical fibers or wirings therethrough, extending
through each gimbal assembly. Each gimbal assembly
includes an inner gimbal member rotatably mounted to
the support means and includes means for transmitting
motion to another inner gimbal member of the other
gimbal assembly. Each gimbal assembly also includes
an outer gimbal member rotatably mounted to the
support means and having means for transmitting
motion to the other outer gimbal member of the second
gimbal assembly. The conduit means extends from the
inner gi~bal member through a slot of the outer
gimbal me~ber. The slot has oppositely facing first
and second surfaces, each surface having first and
second ~racks. A first bearing means i5 disposed
about the conduit and engages a first track of a
first surace of the slot. A second bearing is also
disposed about the conduit and engages a second track
of a second surface of the slot.
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-- 5
In another aspect of the present invention,
the robot wrist includes first and second gimbal
assemblies rotatably mounted within a support means,
with each gimbal assembly having means for
05 transferring motion to the other gimbal assembly.
Drive means are operatively connected to the support
means for effecting selective movement of the first
and second gimbal assemblies. Means are also
included for transmitting rotational movement to the
joint and includes a drive shaft extending from a
base and attached to the first gimbal assembly.
~leans for stabilizing the wrist engages the drive
shaft, said means including an arm member that is
preloaded against the drive shaft and slidably
engages the drive shaft and is pivotally attached to
the support means.
In still a further aspect of the present
invention, a linkage means is provided for
stabili~ing a wrist having first and second gimbal
assemblies. The linkage mPans has a first end that
is pivotally attached to a support means that
supports the first and second gimbal assemblies and a
second end that is pivotally attached to a base from
which the drive ~eans that eff'ects selective movement5 of the first and second gimbal assemblies extends.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of the wrist
and drive train of the present invention.
Figure 2 is a sectional view of with some
portion~ shown whole for purposes of clarity.
.
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Flgure 3 is a perspective view of an alterna-
tive embodiment and alternative drive mechanism of
the present invention.
Figures ~ and 5 are sectional views of the
05 wrist of Figure 3.
Figure 6 is a perspective view of another
embodiment showing the mechanism to stabilize the
wrist using the central rotational drive shaft.
Figure 7 i9 a sectional view perpendicular
to the axis of the wrist of Figure 6.
Figure 8 is a perspective view of another
embodiment of a mechanism to stabilize the wrist
using a scissors linkage.
DETAILED DESCRIPTION OF THE_PREFERRED EMBODIMENTS
The wrist of the present invention is
generally indicated at 10 in Figure 1. The wrist 10
is similar in general concept to the wrist described
in the Rosheim U.S. Patent 4,686,866, issued to the
applicant of the present application. The present
application is directed to improvements in the wrist
and the drive train.
The wrist 10 includes an upper gimbal
assembly 12 and a lower gimbal assembly 14. The
reference to upper and lower gimbal assemblies is or
purposes of convenience with respect to drawings and
is not intended to limit the present invention in any
way.
The upper gimbal assembly 12 includes an
outer upper gimbal 16 rotatably attached to a housing
18 along a pivot axis 20, a4 best illustrated in
Figure 2. The lower gimbal a~sembly includes an
outer lower gimbal 22 pivotally attached to the
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housing 18 about a pivot axis 24. The gimbal 16
includes a pair of spur gears 25. Similarly, the
gimbal 22 includes a pair of spur gears 28 that are
in cooperative engagement with the spur gears 26 such
05 that motion is transmitted between the gimbals 16 and
22 through the spur gears 26 and 28. Movement of the
outer gimbals causes "pitch" motion in the wrist 10.
The gimbals 16 and 14 are pivotally attached to the
housing structure 18.
To accomplish movement of the wrist in a
direction essentially perpendicular to the axis 20
and 24 ("yaw" motion), the wrist includes upper and
lower drive shafts 30 and 32 attached to inner
gimbals 31 and 33, respectively. The upper inner
gimbal 31 includes gears 34. Similarly, the lower
inner gimbal 33 includes gears 36 that mate and
cooperate with the geaxs 34 permitting pivoting of
the wrist about axis 38 and the upper drive shaft
about axis 40, as best illuqtrated in Figure 2.
The outer ~imbals 16 and 14 include slots 42
and 44 through which the drive shafts 30 and 32,
respectively, extend. To facilitate movement within
the slots 42 and 44, the slots each include first
tracks 46 and 50, and second tracks 48 and 52.
; 25 Although only one side surfac~ of the gimbals is
illustrated, it will be understood that a second
oppo itely-facing surface with like tracks exists.
The tracks 46 and 48 are offset and the tracks 50 and
52 are offset. By offset is meant that one track
extends towaxd the center of the slot more than the
other. For example, as illustrated in Figure 1,
track 46 extends inwardly more than track 48. The
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1 3 1 5~22
-- 8 --
tracks 50 and 52 are also offset in a manner similar
to the tracks 46 and 48.
Bearings 54 and 56 are disposed about the
shaft 30 to engage the tracks 46 and 48, respectively.
05 The bearings 46 and 48 permit movement of the upper
drive shaft 30 within the slot 42 with minimal
backlash. Similarly, bearings 58 and 60 are disposed
about the shaft 32 and engage the tracks 50 and 52,
respectively, such that the drive shaft 32 travels
through the slot 44 with minimal backlash~
As can best be seen in Figure 2, the
cooperation between the lower drive shaft 32 and the
upper drive shaft 30 through the respective gear
portions 34 and 36 provides movement (pitch movement)
of the drive shaft 30 from a position that is coaxial
to the drive shaft 32 to a position that is
essentially perpendicular to the drive shaft 32 (or
90). It will be understood that ~he drive shaft 30
is movable in exactly an opposite direction for 90
or a total of 180. Movement in a direction
perpendicular to the pitch movement (yaw movement) is
caused by outer gimbals 16 and 14 through their
respective spur gear portions. Yaw movement extends
for a total of 180. If both the inner and outer
gimbals are actuated, a compound yaw/pitch motion
results.
Motive force to the wrist 10 is provided by
a drive mechanism generally indicated at 62 in Figure
1. The drive mechanism 62 transfers motive force
from a plurality of drive motors disposed within the
housing 64 to the wrist 10. The driving mechanism 62
; includes a yaw drive gimbal 66, a pitch drive gimbal
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68 and the previously mentioned lower drive shaft
32. The gimbal 66 is pivotally attached along the
axis 24 to a first decoupling member 70 in
circumferential ~lidable engagement with the housing
05 structure 18. In a similar fashion, the drive gimbal
68 is pivotally attached to a second decoupling
member 72 about an axis 73 which is aIso in
circumferential slidable engagement with the hou~ing
structure 18. ~t will be appreciated, that the
decoupling member 70 and 72 also rotate
circumferentially around the housing structure 18
with respect to each other such that decoupling of
: the wrist during compound yaw/pitch motion occurs.
Both decoupling members 70 and 72 are in slidable
engagement with the housing structure 18 through
bearings.
Motive force is imparted to the dxive gimbal
68 through rotating shaft 74 whose uppex end portion
includes gears 76 that engage a gear surface 78 of
the gimbal 68 in an arcuate arrangement so that
pivoting can occur about axis 73. The gear surface
78 extends along one side of the gi~bal 68.
5imilarly, the drive gimbal 66 includes a gear
surface 80 disposed along one side of the gimbal that
is cooperatively engaged by sears 82 which comprise
the end portion of a rotating drive shaft 84. The
gimbal 66 i5 arcuately shaped with the gear surface
arcuately arranged so that pivotal movement of the
drive gimbal about axis 24 occurs.
To minimize backlash and facilitate
precision movement, both drive gimbals 62 and 68 are
preloaded. For example, the drive gimbal 66 is
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-- 10 --
preloaded against idler rollers 86 and 88 which are
mounted on the housing 64 through mounting bracket
90, as best illustrated in Figure 1. As best
illustrated in Fig~re 2, a bearing 88 is positioned
05 between the lower drive shaft 32 and the gimbal 66 in
a 510t of the gimbal 66.
5imilarly, the drive gimbal 68 is preloaded
against an idler roller 89 (illustrated in Figure l)
that is mounted on the bracket 90 on a side of the
gimbal 68 opposite from the gear surface 78. The
gimbal 68 is preloaded against the idler roller 89
and a bearing 91 is disposed in a slot of the gimbal
68 between the drive shaft 30 and the gimbal 68.
An electric motor 92 is disposed within the
housing 64 and provides motive force to the drive
shaft 32 through a gear reduction assembly 94 to
provide rotational motion to the wrist lO. The drive
shaft of the motor 92 is held in aligned rotation
through engagement of bearings 96 disposad on a side
of the gear reduction assembly 96 opposite from the
motor 92~
The shaft 84 is rotated by electric motor 98
which is directly connected to the shaft 84 through
coupling lO0. Similarly, rotational movement to the
shaft 74 (which is illustrated in Figure 1 ) is
supplied by electric motor 102 (which is depicted in
Figure 2 as extending outwardly from the figure).
The motor 102 is directly connected to the shaft 74
through coupling 104.
It will be appreciatPd that rotational
movement of the shaft 84 is translated into yaw
motion through the gimbal 66. Rotational movement of
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11
the shaft 74 is translated into pitch motion through
the gimbal 68. Rotation of both shafts 74 and 84
will provide a compound pitch-yaw movement of the
wrist of the present invention through decoupling
05 action o the ~embers 70 and 72 as described
previously. Rotational movement is imparted to the
wrist through rotation of the drive qhaft 32 by motor
92.
The lower drive shaft 32 includes an inne.r
10 passage 106 and the upper drive shaft 30 also
includes an inner pas~age 108~ The passages 106 and
108 are open at their gear end portions 36 and 34 and
permit placement of wires, fiber optic lines, fluid
or pneumatic lines for use at the distal end of the
lS drive shaft 32.
An alternative embodiment of the present
invention is generally indicated at 120 in Figure 3.
The wrist 120 includes a housing 122 and a first
gimbal assemhly 124 and a second gimbal assembly
126. The irst gimbal assembly includes an outer
gimbal 128 that is pivotally attached to the housing
122 about axis 130. Similarly, the gimbal assembly
126 includes an outer gimbal 132 pivotally attached
to the housins 123 about an axis 134 that extends
substantially parallel to the axis 130. Thè gimbals
; 128 and 126 include spur gear sections 136 and 138,
respectively, that cooperatively engage each other to
transmit movement between the gimbals 1~8 and 134, as
best illustrated in Figure 5. The gimbal assembly
124 further includes an inner gimbal 140 having spur
gear sectlons 132 disposed on opposite ends thereof,
as best illustrateù in Figure 4. ~he inner gi~b~l
.
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- 12 -
140 is pivotally attached to the housing 122 about
axis 144. Similarly, the gimbal assembly 126
includes an inner gimbal 146 having spur gear
portions 138 positioned on oppo ite encls of the
05 gimbal 146~ and pivotally attached to the housing 122
along axis 150. The axis 150 is substantially
parallel to the axis 144.
Each of the gimbals, 140, 128, 146 and 132
includes slots or openings through which conduits 152
and 154 extend. As best illustrated in Figures 4 and
5, the conduit 152 extends through ~he gimbals 128
and 140 and is pivotally attached to the gi~bal 140.
Similarly, the conduit 154 exte~ds through the
gimbals 132 and 146 and is pivotally attached to the
gimbal 146, as best illustrated in Figure 5. The
conduits 152 and 154 are used to facilitate
electrical wiring, fiber optic cables, fluid or
pneumatic lines, to a distal end of the conduit 152.
To facilitate movement o~ the conduit 152
with respect to the gimbal 128, bearings 156 and 158
are provided around the conduit 152. As best
illustrated in Figure 4, the bearing 156 is preloaded
against one surface of the slot of the gimbal 12R
while the bearing 158 is preloaded on an oppositely
facing surface of the slot of the gimbal 128.
To provide motive force to the wrist 120, a
coaxially disposed unique drive train 160 is
provided. The drive train 160 includes rotational
drive shaft 162, pitch drive shaft 164 and yaw drive
shaft 166. The drlve shafts 162, 164 and 166 are
disposed coaxially with reYpect to each other. The
pitch drive shaft is disposed within the yaw drive
1 3 1 5322
shaft 166 and extends outwardly therefrom through a
distal end. Similarly, the rotational drive shaft
162 is disposed within the pitch drive shaft and is
preferably the same member as the conduit 154. The
05 drive shaft 162 (conduit 154) extends out of a distal
end of the pitch drive shaft 164. Each of the drive
shafts are suitably connected to an electric motor
(not shown) in a manner that is well known.
To impart rotational movement to the wrist
of the present invention, the drive shaft 162
(conduit 154) is rotated about the axis 161 and the
entire wrist is rotated.
To impart pitch movement, the pitch drive
shaft 164 includes bevel gear portion lG8. The
gimbal 132 includes a cooperating bevel gear 170 that
cooperates with the year portion 168. An idler
roller 172 preloads the gear 170 against the gear
portion 168. Rotational movement of the shaft 164 is
translated into pivotal movement of the gimbal 146
about the axis 150~
The yaw drive shaft 166 also includes a
bevel gear portion 174. A bevel gear yaw drive
member 176 is pivotally attached to the housing 122
along the axis 150. The drive member 176 includes a
bevel gear portion 178 that cooperatively engages the
bevel gear 174 of the shaft 166. An idler roller 180
provides a force to preload the sear portion 178 in
cooperative engagement with the gear portion 174. It
will be appreciated that rotational movement of the
shaft 166 is transmitted into pivotal movement of the
housing along the axis lS0.
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14 -
An alternative embodiment of the wrist of
Figures 3-5 is generally indicated at 200 in Figures
6-7. In most respects, the embodiment 200 is similar
to the wrist illustrated in Figures 3-5 except for
05 the drive train, and a mechanism for minimizing
backlash during movement of the wrist.
The wrist 200 includes a housing 202, a
first gimbal asse~bly 204 and a second gimbal
assembly 206. The hou~ing 202 is rota~ably secured
10 within a collar 208 through bearings 210 that are
circumferentially disposed betwe~n the collar 208 and
the housing 202. The gimbal assambly 204 includes an
outer gi~bal 212 having spur gear end portions 214
and pivotally attached to the housing 202 along an
15 axis 216.
5imilarly, the gimbal asse~bly 206 has an
outer gimbal 218 having spur gear end portions 220
and pivotally attached to the housing 202 along axis
222. The axis 222 is substantially parallel to the
20 axis 216.
The gimbal assembly 204 also has inner
gimbal 224 with spur gear end portions 226 and is
pivotally attached to the housing 202 along axis
228. Similarly, the gimbal assembly 206 has inner
2S glmbal 230 with spur gear portion 232 in cooperative
engagement with the ~pur gear portion 226 and is
pivotally attached to the housing 202 along an axis
233.
A drive shaft 234 for providing rotational
motive force to the wrist 200 extends through the
gimhal 218 and is attached to the gimbal 230 in a
manner similar to th~ one described with reference to
1 3 1 5322
- 15 -
the embodiment of Figures 3 5. A conduit 236 is
attached to the gimbal 224 and extends therethrough
and threugh the gimbal 212 in a manner also si~ilar
to the embodiment of Figures 3-5. Electrical wires,
05 fiber optic cables, fluid or pneumatic lines may be
disposed within the passage of the drive shaft 234
and the passage of the conduit 236 to a tool member
(not shown) located at a distal end of the conduit
236.
Push-pull rod 238 extending from a housing
240 provides motive force for yaw rotation of the
wrist 200 through link 242. The link 242 is
pivotally attached at one end to the push-pull rod
238 and at another end to the collar 208.
A push-pull rod 244 extends through the
housing 240 and travels along the general direction
indicated by arrow 246 and is connected to the collar
208 by link 248. The link 24~ is pivotally attached
to the rod 244 at one end and pivotally attached to
the collar at another end.
~o stabilize the wrist: and decrease possible
backlash, the wrist is provided with a guidance
gimbal 250 having a pair of arms 261 and 262 defining
a slot 263. The gimbal 250 is pivotally attached to
the collar 208 by pivot pins 252 and 254. As best
illustrated in Figure 7, the guidance gi~bal 250 is
preloaded against the drive shaft 234 by idler
rollers 256 and 258. A bearing 260 is interposed
between the drive shaft 234 and the arm 262 of the
gimbal 250. It will be appreciated, as the wrist 200
is actuated, that the arm 262 of the gimbal 262 will
1 31 5322
travel between the idler rollers 256 and 258 and the
bearing 260.
An alternative method of stabilizing the
wrist 300 is illustrated in Figure 8. Since many of
05 the elements of the wrist of Figure 8 are the same as
the elements of the wrist of Figures 6 and 7, like
reference characters will be used to indicate like
elements.
A scissors 1inkage 302 includes a lower link
304 pivotally attached through a pin 306 to an upper
link 308. The upper link 308 is pivotally attached
to the collar 208 by pivot pin 310 engaging a tab
member 312 that is fixedly attached to the collar
208. The bottom link 304 is pivotally attached to
the housing 240 through pivot pin 314 pivotally
attaching the link 304 to tab 316, which is fixedly
attached to the housing.
Although the present invention has been
described with reference to preferred embodiments,
workers skilled in the art will recognize that
changes may be made in form and detail without
departing from the spirit and scope of the invention.
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