Multiple axis robot arm

A robot assembly includes a support for mounting at least two arm portions and a wrist portion about an upright axis. The wrist has three axes of movement that are mutually perpendicular, and they are controlled by a single motor through an arrangement of electromagnetic clutches and gears so that one motor controls movement about all three axes of movement of the wrist. Additionally, gear drives are used for other movements on the robot arm to provide movement about seven independent axes in the arrangement shown with only two drive motors.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to robot arms and wrist assemblies therefor. 
2. Description of the Prior Art 
In the prior art there have been various robots designed for use. For 
example, in Machine Design Magazine, of Aug. 12, 1982, on Page 55, there 
is an illustration of a robot sold by the Bendix Corporation, Robotics 
Division of Southfield, Mich. utilizing bevel gear drives for a wrist. The 
details shown are not extensive, but it does show bevel gears in an 
arrangement that moves the tool holder shaft through a differential 
action. 
Likewise, U.S. Pat. No. 4,068,536 shows a type of a manipulator hand that 
provides for three axis movements in a wrist, as well as drives for 
mounting a robot arm on which the wrist is mounted. 
U.S. Pat. No. 4,047,448 shows a robot head that provides for movement of a 
wrist member about three mutually perpendicular axes, utilizing three 
separate hydraulic motors for drive and gear trains for accomplishing such 
drive. 
U.S. Pat. No. 4,332,147 shows an adjustable power transmitting device 
having an input and output shaft which are coupled together by drive 
gears, and which includes a housing that is rotatably mounted and is 
adjustable to a plurality of different positions. 
A drive is shown in U.S. Pat. No. 3,922,930, requires few drive motors but 
substantial gear and shafting, and typical manipulator hand operators are 
shown in U.S. Pat. Nos. 4,188,166; 2,861,701; and 3,817,403. 
U.S. Pat. Nos. 4,360,886, and 4,367,532 show devices for providing a 
program sequence of motions with a robot, and include controller systems 
for controlling the mechanical construction of the robot. 
In addition, another type of manipulator hand is shown in U.S. Pat. No. 
3,247,978, but which has its drive motors up near the end of the arm. The 
hand is driven through various gear drives. This hand, however, does show 
the use of electromagnetic clutches, which also form part of the present 
device. The grip operating motor is located down near the hand in this 
device. 
Another type of arm used in manipulators for handling workpieces is shown 
in U.S. Pat. No. 4,064,656. 
An industrial robot utilizing complex gear and shaft drives for obtaining 
the required motion is further described in U.S. Pat. No. 3,985,238. 
None of these, however, have very simple drives for providing a plurality 
of joint motions in a wrist, shoulder or elbow assembly with gear drives 
and selectively operable brakes for controlling motions about a plurality 
of axes for a robot arm and wrist using a minimum number of motors and 
very simple controls. 
SUMMARY OF THE INVENTION 
The present invention relates to industrial robots, and more particularly 
to robot controls utilizing brakes and gear drives that reduce the number 
of motors that are necessary for operating the robot about its operational 
axes. 
In particular, as illustrated, a robot arm is mounted on a base and has a 
shoulder joint supporting an upper arm and a forearm connected to the 
upper arm at an "elbow" joint. A wrist is connected to the forearm. The 
wrist is operable about three independent axes. The upper arm is connected 
to the base at the shoulder through an axis parallel to the "elbow" axis, 
and is also connected to the base about a vertical axis. The upper arm can 
be rotated about an axis mutually perpendicular to the elbow and shoulder 
axes to provide seven axes of operation for the robot. 
In the form shown, only two motors are necessary, and in particular the 
operation of the movable joints is through a unique arrangement to provide 
a compact, easily operated assembly that can easily be controlled through 
the use of drive motors and clutches that in turn control the operation 
about the various axes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An industrial robot illustrated generally at 10 made according to the 
present invention includes a support base 11 that is mounted onto a 
support floor 12, or on an overhead bridge, a trolley or the like which 
comprises the main support. The base 11 has a support sleeve 13 fixed to 
the top wall of the base. The axis of sleeve or housing 13 is vertical as 
shown and mounts a motor which is shown schematically at 20 in FIG. 1. The 
motor 20 is mounted on the base and powered through suitable controls. 
The motor 20 has an output shaft that drives through a suitable speed 
reducing drive 20A to drive an elongated coupling 22 coupled to a drive 
shaft 23 having an axis 21 called a neck axis which is rotatably mounted 
through a center bore of the hub 30 of an electric brake 24 having a 
housing 25 fixedly mounted on the interior of the sleeve 13 and rotably 
mounted on hub 30 through a large bearing 29. The hub 30 has a flange 30A 
that carries a brake armature 30B through an annular, flat spring 30C. The 
spring 30C is a ring fastened at three annularly spaced locations to the 
flange 30A and to the armature 30B at three different annular locations so 
the armature will rotate with the flange 30A but can move axially toward 
housing 25 under spring load. The spring acts as an axially flexible, 
rotationally driving member. The structure is a conventional flexible 
coupling and the coupling springs used for driving the armatures of each 
brake assembly herein are supplied with the brakes when purchased from a 
supplier. 
The housing 25 houses a coil 25A, which, when energized, magnetically locks 
the housing 25 and armature together to prevent rotation of hub 30 
relative to the brake housing 25. The armature is magnetically clamped 
against a matching steel plate. 
The hub 30 has a gear housing 32 fixed thereto on the end opposite from 
flange 30A. The shaft 23 passes into the interior of the gear housing 32 
and has a gear 65 driveably mounted thereon, as will be explained. 
A thrust bearing 26 is positioned between the end of the brake housing 25 
and a drive sprocket 27 which is drivably mounted on shaft 23. Sprocket 27 
comprises a typical rotating encoder drive means to provide signals 
indicating position of the shaft 23. A nut 28 threads onto the shaft 23 to 
permit adjustment. The hub 30 and the gear housing 32 are prevented from 
rotating relative to the sleeve 23 when the brake 24 is energized. The 
brake housing 25 is fixed to the sleeve 13 with a flange 25B that fastens 
to the end of the sleeve. 
The brake assembly shown at 24 is a conventional commercially available 
unit. The KEB-E brake, Model 02.320 made by Karl E. Brinkmann GmbH, 
Forsterweg, West Germany, is satisfactory. Other types of brakes or locks 
may be used as well. 
At the top of the sleeve 13 a main shoulder pivot assembly illustrated 
generally at 36 is rotatably supported on the hub 30 and through the 
bearing of the brake assembly to sleeve 13. The shoulder assembly 36 is 
used for supporting and driving an upper arm tube 37 about the axis 40A of 
a generally horizontal pivot shaft 40 that is perpendicular to the axis 
21. Upper arm 37 is a tube which has a support assembly at its lower 
(outer) end for supporting a forearm assembly 38, with a wrist assembly 39 
at the outer end of the forearm. 
The shoulder assembly 36 includes drive gearing for controlling rotation of 
the upper arm tube 37 about its longitudinal axis 37A, which is 
perpendicular to the axis 40A and for driving the gear housing 32 about 
the neck and axis 21. The vertical axis 21 or neck axis and axis 40A are 
perpendicular to each other and intersect to form a reference plane. The 
axis of upper arm tube 37 and the axis 40A also intersect. 
A drive motor 43 is mounted on a support which moves about axis 40A with 
the upper arm tube 37. Motor 43 provides power to drive the forearm 
assembly 38 about the elbow pivot axis indicated generally at 44 as well 
as powering the motions of the wrist assembly. The elbow pivot axis is 
perpendicular to the longitudinal axis of the upper arm tube 37 and 
parallel to the axis 40A. 
The gear housing 32 includes a pair of parallel plates 45 and 46 which are 
fixed to a base wall 47 of the gear housing 32. Base wall 47 is securely 
mounted on hub 30. The wall 47 and the gear housing 32 are free to rotate 
about the neck axis 21 when the brake 24 is released. The base wall 47 
supports the gear housing 32 for rotation about neck axis 21. Shaft 40 is 
mounted on and extends between the plates 45 and 46 and does not rotate 
relative to the plates 45 and 46. 
The upper arm tube 37 is carried on a support assembly 48, which includes a 
main mounting plate 49 that is positioned along one side of the gear 
housing 32, and specifically adjacent to the outer side of the plate 46. 
An annular thrust bearing 49A spaces plate 49 and plate 46. The plate 49 
is connected to an L shaped yoke 50 that has a yoke base 51, and a support 
leg 52. The support leg 52 has a suitable bushing 53 and bushing 53 is 
mounted onto an outer end of the shaft 40, as can be seen in FIG. 2. The 
yoke base 51, which is at right angles to the support leg 52, spans across 
the ends of the plates 45 and 46. The plates 45 and 46 have rounded end 
surfaces, so that the yoke 50 can rotate around the axis 40A of the shaft 
40. 
A shaft 54 is rotatably mounted in suitable bearings 55 in the yoke base 
51, and the shaft 54 has an axis that lies along the axis 21 when the yoke 
is in its position as shown in FIG. 2, and the axis of shaft 54 is 
coplanar with the axis 21 and the axis of shaft 54 intersects the axis 40A 
at the same point as where axis 21 intersects axis 40A. As the shaft 54 is 
moved with the yoke 50 around the axis 40A of the shaft 40 it moves in a 
plane with the axis 21. The plate 49 also will rotate about the axis of 
the shaft 40, and is mounted on the shaft with a suitable bushing 56. The 
shaft 40 has a retaining ring 57 at the end adjacent the bearing 56, and 
this retains a thrust bearing assembly 59 to hold the plate 49 on the 
shaft 40, and permits the plate 49 to rotate relative to the shaft 40. 
At the other end of the shaft 40 there is an adjustment nut 60 threaded 
onto the end of the shaft and bearing against a suitable thrust bearing 
assembly 61 to provide for adjustment and for retaining the yoke 50 in 
position on the shaft, and also holding the support assembly 48 on the 
shaft. 
It should be noted that the yoke base 51 is fixed to the plate 49 with 
suitable cap screws, and the plate 49 will rotate relative to an outer 
housing or cover 62 (removed in FIG. 1) that is positioned around the 
sleeve 13, the gear housing 32, and yoke 50. The shafts and bearings can 
be sealed in a suitable manner if desired. A thrust bearing 64 may be 
provided between the leg 52 of the yoke 50 and the plate 45. 
Plate 47, which is the base of the gear housing 32, is mounted on the hub 
30, and is fixed from rotation relative to the hub 30. The input shaft 23 
is also rotatable relative to plate 47 on suitable bearings, and the end 
of the input shaft 23 on the interior of the plate 47 has the bevel pinion 
gear 65 drivably mounted thereon, and held in place with a suitable nut 
65A. The bevel gear 65 drives a bevel gear 66 that in turn is rotatably 
mounted on the shaft 40. Bevel gear 66 is mounted with suitable bushings 
on the shaft 40, and a thrust bearing 67 is mounted between the base or 
hub of the gear 66 and the inner surface of the plate 45. For adjustment 
purposes, there are a plurality of threaded openings 70 into which set 
screws can be adjustably threaded to bear against the thrust bearing 67 
and provide for gear backlash adjustment. There are access openings in the 
yoke leg 52 so that set screws in threaded opening ,70 can be accessed for 
adjustment. 
The shaft 54 has a bevel gear 71 drivably mounted thereon, and a nut 72 is 
used for adjusting this gear. Likewise, a suitable thrust bearing 73 is 
used between the back side of the hub of gear 71 and the inner surface of 
the yoke base 51. 
A second electric brake assembly 75 is mounted in a recess on the outer 
surface of the plate 46 forming part of the gear housing 32, and this 
brake 75 has a housing 76 fixed to the plate 46 with an annular metal ring 
76B bearing against a snap ring 76C in a bore in housing 76. The ring 76B 
is held with cap screws which thread into the gear housing plate 46. The 
housing 76 may also be pinned to plate 46 to prevent rotation. An armature 
77 is coaxially mounted with the housing 76. The armature 77 is coupled to 
the mounting plate 49 for the support assembly 48 with an annular spring 
77A forming a flexible coupling so the armature and plate 49 will be in 
annular driving relationship to each other, but the armature can move 
axially relative to plate 49. When the brake 75 is energized in a 
conventional manner, a coil 76A in housing 76 will form a magnetic field 
to clamp the armature 77 tightly to the housing 76 and prevent rotation of 
the plate 49 relative to the housing 76 and gear housing 32 and therefore 
relative to shaft 40. A KEB brake model 02.130 made by Karl E. Brinkmann, 
GmbH of Forsterweg, West Germany, is satisfactory for use. 
The shaft 40 provides support for the entire arm assembly including the 
upper arm tube 37, and the rest of the components attached to it. 
The plate 49 has a motor mounting plate 48A attached thereto and extending 
alongside the sleeve 13, and this is for mounting the motor 43, and 
includes a support 49B as shown. Additionally, the arm support has an 
annular hub 78 adjacent to the end of the plate 49, and extending at right 
angles thereto. The hub 78 has a central opening for supporting the upper 
arm tube 37, as shown, and a plurality of rollers 79 are mounted in 
provided pockets on the hub 78, and these rollers in turn then roll 
against a inner bearing race 80 that surrounds and is fixed to the upper 
arm tube 37 with suitable screws. The race 80 will rotate on the rollers 
79, which comprise a bearing support, that gives adequate support for 
permitting the tube to rotate. A large circular roller bearing could also 
be used. 
At the inner or back end of the upper arm tube 37, a support ring 81 is 
fixed to the plate 49. The ring 81 supports an electromagnetic brake 
assembly 82 which includes a hub 82A, a housing 82C and an armature 82B 
mounted with an annular spring member 82D to a radial flange formed on hub 
82A. The armature rotates with the hub 82A but can move axially a short 
distance. When the brake 82 is energized, a coil 82E acts to clamp the 
armature to the housing 82C and the hub 82A will be held from rotation 
relative to housing 82C. 
Bearings 83 are provided on the interior of the hub 82A for rotatably 
mounting a shaft 84 which extends through a bore in the hub 82A. An end 
closure plate 85 is positioned on the interior of the upper arm tube 37 
forming the upper arm and is fixed to the tube 37. This end plate 85 is 
also fixed to the end of hub 82A, and thus the end of the upper arm tube 
37 is supported on the hub 82A and through a large bearing to the brake 
housing 82C. The upper arm tube is thus supported for rotation relative to 
the ring 81 and the plate 49. 
When the brake 82 is energized the upper arm tube 37 is prevented from 
rotation about its axis, but when the brake 82 is deenergized, the upper 
arm tube 37 can rotate on the rollers 79 and on the bearing forming part 
of the brake assembly 82. The brake 82 is the same construction as brake 
24. 
It can thus be seen that rotation of the support assembly 48 and the upper 
arm tube 37 about the shoulder pivot axis 40A, which is the axis of the 
shaft 40, will depend upon the condition of the brake 75, which, when 
energized, will prevent such rotation. The ability to rotate the upper arm 
tube 37 about its longitudinal axis will depend upon the state of the 
brake assembly 82. When the brake 82 is energized the upper arm tube 37 
cannot rotate about its axis. 
The upper arm tube 37 may be driven rotationally about its axis while 
supported on the rollers 79 and the hub 82A through the use of a chain and 
sprocket drive assembly 88. This includes a sprocket 89 which is drivably 
mounted onto the shaft 54, which is on the yoke base plate 51. Suitable 
thrust bearings can be used behind the sprocket 89. A sprocket 90 is 
drivably mounted onto the upper arm tube 37 between the plate 78 and the 
brake 82. This sprocket 90 has a large center bore so that it slips over 
the upper arm tube 37 and it is fixed with respect to the upper arm tube 
37. Then, a chain 91 drives between these two sprockets, through provided 
openings in the plate 49 (shown in dotted lines) so that when the shaft 54 
is driven and brake 82 is released, the upper arm tube 37 can be rotated, 
which will in turn also rotate the forearm 38 and wrist 39. 
Thus, in summary, brake 24, when energized, will prevent rotation of the 
hub 30 and plate 47 and thus the gear housing 32 relative to the main 
support sleeve 13, and when released will permit such rotation; when brake 
75 is energized it will prevent rotation of the plate 49, and thus the 
housing 48 which supports the upper arm, about the axis 40A of shaft 40, 
and when released will permit such rotation; and brake 82, when energized, 
will prevent rotation of the upper arm tube 37 about its longitudinal 
axis, and when released will permit such rotation. 
A suitable slip ring indicated generally at 92 is provided on the underside 
of the plate 47 of the gear housing 32, to carry control signals for the 
various brake members, including those which are provided in the arm 
assembly. The slip ring 92 of course will have suitable contacts acting 
against it, which contacts will be mounted on the sleeve 13 in a 
conventional manner. 
The shaft 84, which is driven from the motor 43 has its inner end, on the 
interior of the upper arm tube 37, drivably coupled to a drive shaft 95. A 
suitable coupling shown at 96 can be used for making this drive 
connection, and it is made so that it is adjustable and will telescope in 
longitudinal length if there is a slight shift in position. The drive 
coupling can be any conventional design, so that whenever the motor 43 is 
powered the shaft 95 will rotate. It can be seen that the tube 37 can be 
rotated independently of the shaft 95, and that the shaft 95 does not 
power any components in the shoulder assembly. Shaft 84 is hollow, so that 
suitable air lines can be provided through the center of the shaft and 
through the center of the drive shaft 95, which is tubular to other parts 
of the robot arm assembly. 
The motor 20 provides for control of motion of the complete arm assembly 
about the axis 21 and drives through the gears 65, 66 and 71 as controlled 
by the brakes 24 and 75. The motor 20 drives bevel gear 65, which in turn 
drives the ring gear 66 that is rotatably mounted onto shaft 40 and which 
gear meshes with gear 71. 
Encoders are utilized for determining the rotational position of the shaft 
23, as well as the rotational position of assembly 48 about shaft 40 and 
the rotational position of shaft 84. The amount of rotation of the upper 
arm tube 37 also can be determined by sensing the rotation of shaft 23 
through resolver drive sprocket 27 by simultaneously sensing which 
electric brake or brakes are energized. 
When the magnetic brake 82 is energized it will hold the hub 82A from 
rotation relative to ring 81 and prevent rotation of the upper arm tube 
37. When this rotation is prevented, and the electromagnetic brake 75 is 
released with brake 24 energized, the shaft 54 and gear 71 can rotate 
relative to the gear housing 32, and the gear 65 will cause the gear 66 to 
rotate and this will drive the plates 46 and 47, and all the connected 
parts, including the arm 37 and connected parts about the axis 40A for 
forming the shoulder pivot or rotation of the arm. 
When the tube 37 is to be rotated, brake 82 is released, so that the tube 
37 and hub 82B can rotate and the brakes 24 and 75 are also energized. 
Then the gear 66 will be rotated by the drive gear 65, which in turn will 
rotate the gear 71, driving the shaft 54 and sprockets 89 and 90, thereby 
rotating the upper arm tube 37 about its axis. 
When both brakes 75 and 82 are energized and brake 24 is released, driving 
the motor 20 will cause the entire arm assembly to rotate about the 
vertical axis 21 because as gear 65 is rotated, gears 71 and 66 are 
prevented from rotating. The gear housing 32 will be driven around the 
axis of gear 65. 
Table I is a summary of action occurring when the operable combinations are 
in effect. 
TABLE I 
______________________________________ 
Result when motor 20 
Brakes 24 75 82 is powered 
______________________________________ 
X O X Arm rotates about 40A 
O X X Arm rotates about 21 
X X O Rotates 37 about its axis 
______________________________________ 
X = locked 
O = Open 
ELBOW ASSEMBLY 
The elbow assembly controlled at elbow axis is driven operated from the 
motor 43 and operated by the shaft 95, and is shown in FIGS. 1 and 3. 
The elbow assembly 119 has a pair of side plates 120,120 which carry 
counterweights 121 at the outer ends of the plates. The side plates are 
used for supporting the forearm assembly 38 in a suitable holding bracket, 
and as can be seen in FIG. 3, the lower or outer end of the upper arm tube 
37 has a block 122 therein which is fixed to a housing 123. The housing 
123 has a first side plate 124, and a second side plate 125 which are 
fixed to a base 126 of the housing. The walls 124 and 125 mount the elbow 
axis shaft 130. The mounting plates 120 are mounted in suitable bearings 
at 131 on the shaft 130. 
The plates 124 and 125 of the housing 123 are spaced apart at the outer end 
portion shown at to provide for pivotal movement of the forearm 38 
relative to the housing. 
The wall 124 is made to mount an electromagnetic brake 135, with the brake 
housing 135A attached to the wall plate 124 in a provided recess. Cap 
screws pass through openings in a collar 135C and are threaded into wall 
124 and bears against a snap ring in the housing 135A to hold the housing 
135A clamped in position. The housing 135A is also pinned to the wall 124 
to prevent rotation. A brake armature 135B is drivably mounted in a 
suitable recess in the one side plate 120 through an annular flexible 
coupling spring 135D that permits axial movement, so that when the 
magnetic brake assembly is energized, the brake holds that side plate 120 
from rotation relative to the housing 123. When the brake 135 is released, 
the side plates 120 can rotate relative to housing 123 about elbow axis 
44, which is the axis of shaft 130. 
The lower or outer ends of the side plates 120 are bolted to a mounting 
block 136 that has an annular hub 137 fixed thereto on which a tube 138 is 
fixedly mounted. The tube 138 is the tube forming the forearm 38. 
The block 136 is spaced from the outer ends 140 of the housing walls 124 
and 125, so that the side plates 120 are able to move about the elbow axis 
44, which is the axis of the shaft 130. As the block 136 moves around the 
axis 44 the tube 138 will also move about this axis. 
An input bevel drive gear 145 is drivably mounted on the shaft 95. A thrust 
bearing 146 is used between gear 145 and wall 126. The shaft 130 has a 
bevel gear 147 rotatably mounted thereon. Gear 147 engages the gear 145. 
The shaft 95 is tubular, so that air conduits can be passed through the 
shaft 95. The base wall 126 of housing 123 and the mounting block 122 have 
bearings for supporting the shaft 95. 
Block 136 has suitable bearings or bushings 150 therein which in turn 
rotatably mount a shaft 151, which has an end positioned between the side 
wall plates 124 and 125 of the housing 123. A suitable thrust bearing 152 
is mounted over the shaft to back up and position a bevel gear 153 that is 
drivably mounted onto the shaft 151 and engages the bevel gear 145. The 
thrust bearing 152 reacts thrust loads from the bevel gear 153 onto the 
block 136. Because the block 136 is held with the side plates 120 through 
the use of suitable bolts such as that shown at 155, and the shaft 130 
holds the side plates 120 in place, the gear 153 will be driven by bevel 
gear 147 whenever the bevel gear is rotating, and the shaft 151 is free to 
rotate. 
The brake 135 when energized will hold the forearm assembly 38 from 
pivoting, and thus hold the side plates 120 in a fixed rotational 
position. Holding shaft 151 from rotation (with brakes in wrist assembly 
39) while releasing the brake 135 so that plates 120 can rotate, will 
permit changing the angular position of the forearm assembly about the 
elbow axis 44. 
The shaft 151 does not have to be hollow, because air lines and the like 
can come out from the shaft 95 in the elbow assembly and then pass through 
provided openings in the block 136 into the interior of the tube 138, and 
then carried on down to the wrist assembly 39. 
WRIST ASSEMBLY 
The wrist assembly 39 is shown in FIG. 4 in detail, and it can be seen that 
the forearm tube 138 is fixed to an outer sleeve housing 170, and housing 
170 in turn has an electromagnetic brake 171 mounted at the interior end 
thereof and fixed relative thereto. This is a conventional electromagnetic 
brake similar to brake 24 having an annular coil housing 172 for housing 
the energization coil 172A. Housing 172 is held in place on the housing 
170 with a flange 172B attached to the end surface of sleeve housing 170, 
and a hub 173 of the brake 171 is mounted through a suitable bearing 174 
relative to the housing 171. The hub 173 has an annular flange plate 175, 
which, when the brake is energized, will be held relative to the housing 
171 through an armature ring 175A which is attached to the flange 175 
through an annular spring 175B that provides a rotational drive between 
the flange 175 and the armature 175A but permits the armature 175A to move 
axially to be magnetically held on the housing 172 when coil 172A is 
energized and thus lock the brake. 
When the brake 171 is not energized the hub 173 will be free to rotate on 
the bearing 174 relative to housing 172. 
The shaft 151, which extends through the interior of the tube 138, has a 
drive coupling end indicated generally at 176 thereon which in turn drives 
a first or input wrist drive shaft 177. Drive shaft 177 is rotatably 
mounted on the interior hub 173 of the brake 171 on suitable bearings 180. 
A mounting flange 181 is drivably mounted on the inner end of brake hub 
173. The drive shaft 177 passes through an opening in flange 181. The 
flange 181 forms a base for a gear housing 182 that includes a pair of 
generally parallel plates 183 and 184 mounted on the flange 181 to form a 
space therebetween. Housing 182 is the wrist drive and support housing and 
on the interior of the housing there is a drive bevel gear 190 drivably 
mounted onto the shaft 177. 
A thrust bearing 187 is used between a nut 187A on shaft 177 and flange 175 
and thrust bearing 188 is between gear 190 and plate 181. A nut 188A holds 
the gear 190 on shaft 177 and permits adjustment of the bearing loads. The 
plates 183 and 184 in turn retain a cross shaft 191 that is at right 
angles to the axis of the shaft 177, and is nonrotatably mounted in the 
plates 183 and 184. Shaft 191 has a bevel gear 192 rotatably mounted 
thereon, which meshes with the gear 190 as shown to form a right angle 
drive. Bevel gear 192 is backed with a thrust bearing 193 which is backed 
up on the backside of the gear 192 through the use of adjustable set 
screws 194 threadably mounted in the plate 193. On the opposite plate 184, 
a coil housing portion 195 of an electromagnetic brake assembly 189 is 
mounted in place on the plate 184 through the use of cap screws 196 acting 
through a collar and threaded into plate 184 to bear against a snap ring. 
The brake 189 is the same construction as brakes 135 and 75. 
The shaft 191 has a wrist joint yoke 200 rotatably mounted thereon. This 
wrist joint yoke 200 includes a side plate 201 rotatably mounted on one 
end of the shaft 191 through the use of a bearing 202, and a plate 203 
that is rotatably mounted on the opposite end of the shaft 191 through the 
use of a bearing 204. Plate 203 is held spaced from the plate 183, and 
parallel thereto, and a suitable thrust bearing 205 can be utilized in 
wall 203 for taking any thrust loads. The plates 201 and 203 are supported 
on a base plate 206 shown at the right end in FIG. 4. 
A brake armature ring 210 of the electromagnetic brake member 189 is 
mounted with an axially movable, rotationally driving, flexible coupling 
spring ring 211 to the plate 201. When the coil 195A of brake 189 is 
energized, the plate 201 is held from rotation through the brake armature 
210 which is clamped against the housing 195 under magnetic force. The 
plate 201 is also held from rotation about the shaft 191. Brake 189 and 
brake 171 will provide for control of movement of the wrist as will be 
explained. 
The end or base plate 206 of wrist joint assembly 200 has hub section 216 
fixed thereon which extend outwardly from the plate and which rotatably 
mount a shaft 217 in suitable bearings 218. The shaft 217 has a bevel gear 
220 drivably mounted thereon and positioned between plates 183 and 184. A 
suitable thrust bearing 221 is used to back the gear 220. The gear 220 
drivably engages the gear 192. 
The opposite end of the shaft 217 extends outwardly from the hub portion 
216, and has a flange 223 drivably mounted to its end surface. A brake 
plate 222 is in turn mounted on the flange 223. The plate 223 carries the 
armature 228 of an electromagnetic brake 225. The armature 228 is 
driveably coupled to plate 222 through an annular flexible coupling spring 
229 which permits axial movement of the armature but which drives 
rotationally. A brake housing 230 is fixed to the plate 206 with suitable 
cap screws 231. A thrust bearing 224 is provided between plate 223 and the 
outer hub portion 216. When coil 230A of brake 225 is energized the plate 
222 will be held from rotation because the armature 228 will be pulled 
against the housing portion 230 by magnetic force and held clamped 
together. Brake 225 is the same as brake 189 except the housing has a 
mounting flange 230B for attaching the housing to the plate 206. 
A suitable slip ring assembly illustrated generally at 240 near the plate 
181 is provided carrying electrical connections that are necessary for 
operation of the electromagnetic coils that are in the brake portions 195 
and 230, so the control for such brakes is back at a central controller. 
A suitable tool or grip can be mounted onto the plate 222, and perform the 
functions necessary for robots. These grips can be conventional, and 
include automatic tools or the like. 
When the brakes 171, 189 and 225 are energized, the shaft 151 will be held 
from rotation, and this will provide the braking action necessary so that 
when the input shaft 95 is rotated, and the brake 135 (in the elbow, see 
FIG. 3) is released, the forearm assembly 38, including the wrist assembly 
39 will be forced to rotate, through the driving of gear 145 and 147, 
about the axis 44 of shaft 130 in the elbow. 
When the elbow brake 135 is energized, and shaft 95 is rotating, with the 
brake members 171 and 189 energized and the brake member 225 deenergized, 
the shaft 151 will be driven by rotation of the gear 145, 147 and gear 
153. This in turn will drive the shaft 177, gear 190, gear 192 and gear 
220 to rotate the shaft 217 and rotate the tool held on the plate 222. 
If the brake members 171 and 225 are energized, and the brake member 189 
deenergized, with the brake 135 energized to hold the plates 120 in 
position, gear 190 again will be driven as shown, and this will rotate the 
gear 192, but because gear 220 is held from rotation by brake 225, the 
gear 192 will rotate and drive the gear 220 and the robot wrist yoke 200 
about the axis shaft 191 and control movement about this axis. 
With the brake member 171 deenergized, and the three brake members 135, 189 
and 225 energized, rotation of the shaft 151 will cause the driving of 
gear 192 about the axis of the shaft 177, because there cannot be any 
other movement in the wrist and this will give full rotation of the wrist. 
Again, the slip rings 240 will accommodate this movement and still carry 
power to the brakes and also position signals from the movable parts. 
The axes of movement of the wrist all intersect at a common point on the 
axis of shaft 191 so the actions are easily controlled. The gear drive and 
brakes operate reliably with a minimum of power sources. 
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.