Hand gear train with three degrees of freedom

A remotely operated hand gear train for the orientation of an end effector has an external housing mounted onto a robot arm and defines a first axis A.sub.1. A first housing is rotatably mounted within the external housing for movement about the first axis A.sub.1 and defines therein a second axis A.sub.2 which is substantially perpendicular to the first axis A.sub.1. A second housing is rotatably mounted in the first housing for rotation about the second axis A.sub.2 and defines therein an axis A.sub.3 which is normal to axis A.sub.2 and radially spaced from axis A.sub.1. A third housing is rotatably mounted in the second housing for rotation about axis A.sub.3 and has a gear rack circumferentially disposed about the end thereof.

BACKGROUND OF THE INVENTION 
The invention is directed to industrial manipulators. More particularly, 
the invention is directed to a wrist for use in industrial manipulators. 
The improved wrist of this invention provides three degrees of freedom. 
The introduction of robotics into the manufacturing facility has resulted 
in a demand for a variety of robotic components, such as end effectors 
which are gripper like devices which manipulate tools or components in the 
manufacturing process and wrists which can offer any number of degrees of 
freedom or levels of compliance. The specific application of the end 
effector to a given manufacturing process can require a multi-jointed, 
complex wrist design which provides several degrees of freedom. The 
dexterity of the end effector and the industrial manipulator is reflected 
in directional movement capabilities which are indicated as degrees of 
freedom. 
It is an objective in the design and construction of industrial 
manipulators to mimic limited aspects of various human capabilities in 
order to improve the positional accuracy of industrial manipulators in a 
variety of tasks. A robot must be able to reach workpieces and tools. This 
requires a combination of an arm and a wrist subassembly, plus an end 
effector. The robot's sphere of influence is based upon the volume into 
which the robot's arm can deliver the wrist subassembly. A variety of 
geometric configurations have been studied and tried and their relative 
kinematic capabilities appraised. Such configurations include cartesian 
coordinates, cylindrical coordinates, polar coordinates and revolute 
coordinates. Evidently each of these configurations offers a different 
shape to its sphere of influence, the total volume of which depends upon 
arm link lengths. For different applications, different configurations may 
be appropriate. For example, a revolute arm might be best for reaching 
into a tub, while a cylindrical arm might be best suited to a straight 
thrust between the dies of a punch press. 
In every case however, the arm carries a wrist assembly to orient its end 
effector as demanded by workpiece placement. Commonly, the wrist provides 
three articulations that offer motions labeled pitch, yaw and roll. 
It should be noted that any of the arm coordinate systems requires three 
articulations to deliver the wrist assembly anywhere in this sphere of 
influence. It then requires three more articulations in the wrist for 
universal orientation of the end effector. 
Quite often, robots are able to cope with job assignments without employing 
a full set of six articulations. This arises out of some symmetry in 
either the workpiece or the workpiece layout. For example, to move a 
bowling ball around in the sphere of influence requires only three 
articulations, because a ball is always oriented, irrespective of a 
gripper's orientation. More frequently, parts have one axis of symmetry, 
i.e. cylindrical, and this allows the robot arm to degenerate to five 
articulations. 
Actually, five articulations are quite often adequate when the workpiece is 
arranged to reduce part manipulation needs. This happens, for example, 
when the beds of machine tools are all located parallel to one axis of a 
cartesian coordinate robot or on a radius of base rotation for 
cylindrical, polar or revolute robot arms. It may be argued that this 
compromising of the number of articulations is begging the question of 
robots versus special purpose automation. The rotor should be the 
universal solution, readily transferred to other applications. In this 
vein, reference should be made to the elegance of computer control of 
robot arms. Given a six articulation arm of any configuration, software 
can permit a program to be generated in cartesian coordinates irrespective 
of the choice of articulations. Indeed, the software can be powerful 
enough to think only in tool coordinates. That is, the programmer concerns 
himself with the tool on the end of the robot arm. He can think in terms 
of the tool's frame of reference and computer subroutines automatically 
make the various articulations move so as to accomplish the desired tool 
manipulation. 
It is therefore an object of this invention to provide a hand gear train 
for use with an industrial manipulator. It is a further object of this 
invention to provide a hand gear train that provides more accurate 
positioning with three degrees of freedom. 
It is yet another object of this invention to provide a hand gear train 
with three degrees of freedom which is readily adaptable to existing 
robots and robotic systems. It is still another object of this invention 
to provide a hand gear train which utilizes unique bearing placement and 
simplified bearing construction to provide a dimensionally smaller hand 
gear train which can be both easily upscaled and downscaled. 
SUMMARY OF THE INVENTION 
The invention provides a remotely operated hand gear train for the 
orientation of an end effector mounted at one end of a hand gear train. 
The invention comprises an external housing adapted to be mounted onto a 
robot arm. The housing defines a first axis A.sub.1. A first housing is 
rotatably mounted within the external housing for movement about the first 
axis A.sub.1. The first housing defines therein a second axis A.sub.2 
which is substantially perpendicular to the first axis A.sub.1. A second 
housing is rotatably mounted in the first housing for rotation about the 
second axis A.sub.2. The second housing defines therein an axis A.sub.3 
which is normal to axis A.sub.2 and radially spaced from axis A.sub.1. A 
third housing is rotatably mounted in the second housing for rotation 
about axis A.sub.3. The third housing has a gear rack circumferentially 
disposed about the end thereof. A first drive system for effecting the 
rotation of the first housing about the first axis A.sub.1 comprises gear 
means disposed about the first housing and gear drive means operatively 
associated therewith. A second drive system for effecting rotational 
movement of the second housing about the second axis A.sub.2 comprises a 
first gear means with a first gear rack and a second gear rack 
concentrically disposed about one end of the first axis A.sub.1 within the 
housing. Gear drive means are operatively associated with the first gear 
rack. The second housing includes gear means disposed thereabout and the 
second rack is operatively associated therewith such that rotation of the 
gear drive means is effected thereby. A third drive system for effecting 
rotational movement of the third housing about the third axis A.sub.3 
comprises gear means rotatably mounted about the other end of the first 
axis A.sub.1. The third drive system includes a first gear rack and a 
second gear rack. A third gear drive means is operatively associated with 
the first gear rack and a drive shaft having a first gear rack at one end 
and a second gear rack at the other end is rotatably mounted within the 
second housing about the second axis A.sub.2. The gear means second rack 
is operatively associated with the gear rack and the second gear rack is 
operatively associated with the third housing gear rack.

DETAILED DESCRIPTION OF THE INVENTION 
A hand gear train generally indicated by the reference character 11, is 
shown in FIG. 1 mounted at the end of an arm of a Unimate Series 2000 
industrial robot generally indicated by the reference character 13. The 
hand gear train 11 provides three degrees of freedom as indicated by the 
axes designated A.sub.1, A.sub.2 and A.sub.3. The Unimate Series 2000 
robot 13 is but a single example of any one of a variety of robots onto 
which the hand gear train of this invention can be mounted. The robot 13 
is designated for welding, adhesive or sealant deposition, machine 
loading, inspection and a variety of other material handling applications. 
The robot 13 is secured to a work area by means of base member 15 and 
includes an arm 17 mounted onto the base member 15. As can be seen from 
FIG. 1, the hand gear train 11 is operably mounted on the free end of the 
arm 17 as at 19. 
Considering now FIGS. 2, 3, 4 and 5 the construction and operational 
capabilites of the hand gear train 11 are described with respect to the 
axes of motion incorporated therewith. More specifically, FIGS. 3, 4 and 5 
are individually dedicated to axes A.sub.1, A.sub.2 and A.sub.3, 
respectively while FIG. 2 illustrates a sectional view of the hand gear 
train in which the cooperation of the various subsystems is shown in 
detail. As can be seen axes A.sub.1 and A.sub.3 are perpendicular to axis 
A.sub.2 and are in a spaced relationship with respect to each other. The 
hand gear train housing which defines the several axes of motion and 
encloses the various drive means associated with the hand gear train 
includes a housing right half and a housing left half 31 and 33, 
respectively. A further portion of the housing provides a robot arm 
interface as at 35. A housing cover 37 is fixedly secured to the housing 
right half 31 in order to enclose the A.sub.3 axis drive pinion which will 
be described in detail hereinafter. The several housing components 31, 33, 
35 and 37 generally comprise an external housing collectively indicated by 
the reference character 39 and defining therein a first axis A.sub.1 which 
is substantially perpendicular to the arm 19 of the robot to which the 
housing is attached. 
A first housing generally indicated by the reference character 41 is 
rotatably mounted within the external housing 39 for rotation about the 
first axis A.sub.1. The housing 41 is mounted by means of bearing sets for 
rotation within the housing 39. The housing 41 includes a geared portion 
47 which cooperates with the geared portion 49 of the drive pinion 51. 
Rotational movement is imparted to the drive pinion 51 by a conventional 
drive take off from the robot schematically indicated at the reference 
character 53. The drive pinion 51 is supported within the housing 39 by 
several bearing sets indicated at 55. The first housing 41 defines therein 
the second axis A.sub.2 which is substantially perpendicular to axis 
A.sub.1. Thus, as the drive pinion rotates and drives the through gears 49 
and 47 the first housing 41, the hand gear train rotates about axis 
A.sub.1. Rotation can be effected in either direction and is typically 
limited to approximately 270.degree. in order to avoid interference with 
the robot arm 19 by the hand gear train. The housing 41 includes a center 
shaft member 47 which extends through the right and left housing portions 
31 and 33 of the external housing 39. In addition to providing rigidity to 
the first housing 41 the center shaft 57 also serves to prevent the 
spreading of the right and left housing halves 31 and 33 during gear train 
operation. As can be seen, each end of shaft 57 includes a cap portion 59 
between which cap portion 59 and the housing portion 61 adjacent thereto 
are disposed thrust bearings 63. This configuration in which the shaft 
extends beyond the housing portions and includes bearings disposed between 
the external portion of the housing and the ends of each shaft tends to 
eliminate any problems previously encountered due to the spreading of the 
external housing 39. 
A second housing 71 is rotatably mounted within the first housing 41 for 
rotation about the second axis A.sub.2 defined by the first housing 41. 
The second housing 71 defines therein a third axis A.sub.3 which is normal 
to axis A.sub.2 and in a spaced relationship with axis A.sub.1. The second 
housing 71 has a hollow inner portion which is adapted to receive the 
drive means and third housing for rotation about axis A.sub.3 which will 
be described hereinafter. The first housing portion 41 supports the second 
housing 71 therewithin by means of bearing sets 73 and 75. The portion of 
the housing 71 furthest from the center shaft 57 includes an extended 
housing portion as at 77 which is adapted to receive therein the third 
housing 101. The portion 77 of the second housing 71 is capable of 
360.degree. of rotation about axis A.sub.2 due to drive motion imparted to 
the housing portion 71 by means of the gear 79 mounted for rotation about 
shaft 57 and the drive pinion 81. The drive pinion 81 is mounted in the 
external housing 39 by means of bearing sets 83. A geared face 85 of the 
drive pinion 81 is in communication with a first geared section 87 of the 
gear means 79. The gear 79 also has a second toothed portion at 87 which 
is in mechanical communication with the geared portion 89 of the second 
housing 71. Here again, proper bearing support is provided as at 91 for 
the gear member 79 to permit rotational movement with respect to the shaft 
57 of the first housing 41. 
The third housing 101 is rotatably mounted within the second housing 
portion 77 for rotation about axis A.sub.3 defined by the third housing 
portion 77. Typically, the third housing 101 would be adapted to receive 
at the outside face 103 thereof, an end effector or appropriate tool for 
use in a desired application. Such a tool could be fixedly attached to the 
face portion 103 of the third housing 101 or removably mounted thereon for 
tool selection in a robotic system. The third housing 101 is mounted for 
rotation within the second housing member 77 by means of bearings 105. A 
geared face 107 is disposed on the inside face 110 of the third housing 
101. Rotational movement of the third housing 101 about the axis A.sub.3 
is effected by means of a drive system. The drive system consists of drive 
pinion 105 mounted in the external housing 41 of the gear hand train. The 
drive pinion 105 which is supported within the external housing 41 by 
means of bearings 107 includes a gear portion 109 which is in direct 
mechanical communication with geared shaft 111. The geared shaft 111 
includes a first geared portion as at 113 which is in communication with 
the drive pinion 105 gear set 109 and a second geared portion at the other 
end thereof 118. The shaft 111 is rotatably mounted about the center shaft 
57 of the first housing 41 and supported thereon by means of bearings 115. 
Additional bearings as at 116 are disposed between the outside portion of 
the geared shaft 111 and the inner portion of the external housing 41. The 
gear portion 118 of the shaft 111 is in communication with a center drive 
shaft 117 by means of geared portion 119 of the shaft 117. The shaft 117 
is disposed along the second axis A.sub.2. At the end of the shaft 117 
which extends away from the central shaft 57 is a gear portion 121 which 
is in communication with the gear portion 107 of the third housing 101. 
Accordingly as the drive pinion 105 rotates, shaft 111 concentrically 
mounted with the shaft 57 along axis A.sub.1 is rotated. The rotation of 
shaft 111 effects the rotation of pinion 117 which is coaxial with axis 
A.sub.2. The rotation of pinion 117 effects the rotation of the third 
housing portion 101 about axis A.sub.3. 
What has been described is a remotely operated hand gear train which 
orients an end effector mounted at one end of three interconnected drive 
means and housings. The hand gear train has two sets of concentric shafts 
with individual shafts that engage at an angle of 90.degree.. The third 
connected drive shaft is not a set of concentric shafts. The preferred 
embodiment has the axis of the two sets intersecting at a single point and 
permits the rotation of two axes relative to each other by the combined 
movement of the connected drive shafts.