A remotely operable manipulator orients an end-effector mounted to one end of a plurality of serially connected drive shafts. The manipulator has two sets of concentric shafts with individual shafts within each set independently rotatable about an axis common to the set. The common axes of the two sets are obliquely oriented with respect to each other; and a third shaft, rotatable about a third axis, is angularly oriented and connected to the most remote set of shafts. The preferred embodiment has the axes of the two sets and the third shaft intersecting at a single point and permits orientation of the third axis normal to any point upon the spherical surface of a spherical sector generated by the combined movement of the plurality of shafts.

BACKGROUND 
This invention relates to mechanical manipulators and will be disclosed in 
connection with an improved remotely operable articulated cantilevered 
wrist manipulator. Mechanical manipulators are of ancient origin and have 
been utilized in a wide variety of applications including handling of 
explosives or other dangerous materials and performing work tasks in 
unsafe or undesirable working areas, as for example radioactive or 
underwater environments. More recently, and particularly since the 
embarkment of computer controlled industrial equipment, manipulators have 
been increasingly used to perform unsafe and undesirable tasks previously 
performed by humans with resultant cost savings and increased production 
efficiency. This increased use may be partially explained by dramatic 
improvements in control systems within recent years. These improved 
controls enhance the exploitation of the manipulator's potential as a 
general purpose machine and give the manipulator the ability and 
flexibility to perform a wide range of work tasks. Present day controls 
permit "pre-programmed input" information, usually coded in numerical 
form, on punched tape or magnetic storage, to instruct the machine through 
a series of complex movements needed to perform a particular task. The 
tapes for these control systems can then be easily stored and reinserted 
into the machine when it becomes necessary to perform the particular task 
again. The expensive and time-consuming set up time for the controlled 
machine is then eliminated once the tape is generated; and the machine may 
be designated as a general purpose machine capable of performing a wide 
variety of work tasks. The growing interest in general purpose automated 
manufacturing equipment suggests that the trend for the future is toward 
even further proliferation of the computer controlled industrialized 
manipulators or industrial robots. 
The prior art robots are generally variations of three different type 
designs. One of these designs is the link and pivot design. This design 
employs a series of pivotally supported segments with an end-effector, as 
for example a grasping device or a welding gun, attached to one end. A 
second type has extending links in combination with pivots wherein the end 
points of the links translate along the axes of the links relative to each 
other. A third type of robot design is that employed by U.S. Pat. Nos. 
3,922,930 and 3,739,923 which utilize a plurality of serially connected 
rotatable drive shafts to provide two or more axes of pivotal motion at a 
common point capable of being remotely operated. It is this latter type of 
design to which the present invention is directed. 
Implicit in the concept of general purpose automated manufacturing 
equipment is a requirement of flexability. Indeed, as applied to 
industrial robots and particularly to those robots which are designed to 
be controlled by programmable computers, the requirement of flexability is 
of central importance. It is this characteristic, more than any other, 
which distinguishes the programmable robot from a dedicated machine 
capable of performing only a limited predetermined repetitive function. 
The flexibility offered by a programmable industrial robot is dependent 
upon both programming for the computers and the orientational and 
positional capability of the robot arm. More particularly, it is dependent 
upon the positioning and orientation of the end-effector attached to the 
end of that robot arm. This flexibility is enhanced by improving either 
the orientational capabilities of the robot arm or increasing the range of 
movement of the end-effector. 
The instant invention utilizes a wrist section of the robot arm generally 
of the type disclosed in the above-mentioned patents, but makes important 
improvements, over these prior art devices which retain virtually all of 
the previous advantages while increasing both the orientational and 
positional capabilities. It increases the robot's flexibility and makes it 
more suitable as a general purpose automated apparatus. 
The invention's unique organizational and positional arrangement of drive 
members permits three serially connected rotary shafts with axes 
intersecting at a single point to undergo continuous "rolls". The 
continuous "rolls", rotation about axes parallel to the shaft members, is 
possible as the arrangement voids the mechanical interference inherent in 
prior art devices. This advantageous situation is coupled with the 
capability of orientating the third, or most remote shaft, about a single 
point, achieved by making all of three shafts intersect at a single point. 
The present invention, like most prior art manipulators, generates an 
imaginery spherical sector as it is rotated through space. It is capable 
of orientating a part normal to any point on the generated spherical 
sector. This capability thus eliminates "holes" or "voids" in the spacial 
orientation of the end-effector and increases the manipulator's 
flexibility. 
SUMMARY OF THE INVENTION 
The invention relates to manipulators of the type having a plurality of 
serially connected drive shafts with a mounting surface affixed to one 
end. A first shaft rotatable about a first axis coincident with one 
ordinate of a mutually perpendicular triordinate system is drivingly 
engaged to transmit rotary motion to a second shaft obliquely orientated 
with respect to the first shaft. A mounting surface having a centerline 
angularly orientated with respect to the second shaft is affixed thereto. 
This mounting surface is rotatable about the axis of the second shaft and 
has a directional component of movement in each of the directions defined 
by the mutually perpendicular triordinate system as it is rotated about 
this second shaft.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings and to FIG. 1 in particular, an industrial robot 
1 is shown with control apparatus typically accompanying the robot 1 in an 
environmental setting. The robot 1 has a base 2 secured to the floor. A 
shoulder 3 is rotatably mounted upon the base 2 and has an upper arm 
section 4 extending therefrom. A pivoted elbow joint 5 connects the upper 
arm section 4 with a forearm section 6. Relative movement between the arm 
sections 4 and 6 is controlled by a hydraulic cylinder 7 extending from 
the shoulder 3 to a clevis bracket 8 offset from the elbow joint 5. The 
forearm section 6 is actually a set of three concentric shafts 
independently rotatable by individual hydraulic motors 9a, 9b and 9c 
supported in motor housing 9d. A wrist joint 10 adjoins the forearm 
section 6 on the end opposite the elbow joint 5. The wrist 10, which 
embodies the subject matter of the present invention supports an 
end-effector or grasping device 11 upon its most remote end. Associated 
control apparatus including a computer console 12 and a hydraulic power 
unit 13 are shown adjacent to the robot 1 and connected in a conventional 
fashion. 
Referring now to FIGS. 2 and 3, the wrist portion 10 is shown in 
cross-section and in greater detail. The wrist 10 has a split outer 
housing 14 having housing portions 14a and 14b mounted upon a forearm 
section 6 of the robot arm. Housing portions 14a and 14b are both mounted 
upon an outer forearm shaft 15, the former portion 14a being rotatably 
mounted with respect to both an outer forearm shaft 15 and its 
complementary housing portion 14b and rotatable about an axis B-B'. Both 
housing portions 14a and 14b are attached to the outer forearm shaft 15 
and movable therewith as all three members rotate about a second axis 
A-A', the attachment of shaft 15 and housing portion 14b being rigid. 
Rotational movement of the housing portion 14a about axis B-B' is imparted 
by an intermediate forearm shaft 16 concentrically disposed and contained 
within outer forearm shaft 15. Like forearm shaft 15, intermediate shaft 
16 is rotatable about axis A-A'. This second axis A-A' is obliquely 
orientated with respect to the first axis B-B', i.e., the axes or their 
projections intersect at an oblique angle. Rotation of shaft 16 about the 
axis A-A' drives a bevel gear 17 mounted upon shaft 16 and also rotatable 
about axis A-A'. Gear teeth on the bevel gear 17 are in mesh with the 
complementary bevel teeth 18 on the housing portion 14a and drive this 
rotatable housing portion 14a, translating rotary movement of the shaft 16 
about the axis A-A' into rotary movement of housing portion 14a about 
obliquely oriented axis B-B'. The housing portion 14a has a rotatable 
planer mounting surface 14c having a centerline C-C' obliquely oriented 
with respect to the axis B-B'. The end-effector 11 is rotatably affixed 
upon mounting surface 14c. It is thus seen that housing portion 14a is 
multi-functional in that it serves as a drive shaft in addition to its 
housing function. 
A third forearm shaft 19, in the set of concentric shafts 15, 16 and 19 
rotatable about axis A-A', is disposed within shaft 16 and is rigidly 
attached to still another drive shaft 20. The drive shaft 20, also 
rotatable about axis A-A', extends into the housing 14. It should be 
apparent that the shafts 19 and 20 may be combined into a single shaft. 
The preferred embodiment of the present description utilizes a solid shaft 
20 for extension into the housing 14 and a hollow shaft or tube 19 
integrally attached to the shaft 20. Like forearm shaft 16, drive shaft 20 
has a bevel gear 21 attached proximate to the extremity extending into the 
housing 14. This bevel gear 21 is drivingly engaged with a matched bevel 
gear 22 attached to an internal shaft 23 completely constrained with the 
housing 14. Both the bevel gear 22 and the shaft 23 are rotatable about 
axis B-B' and concentric with housing portion or shaft 14a, the two latter 
mentioned shafts forming a second set of concentric shafts obliquely 
oriented with respect to the first set of forearm shafts 15, 16 and 19. 
Opposite ends of the shaft 23 are rotatably supported in housing shaft 14a 
and housing portion 14b respectively by a suitable bearing system. 
Proximate to the end of shaft 23, opposite the bevel gear 22, is another 
bevel gear 24. The gear 24 is rotatable about axis B-B' and drivingly 
engaged with still another bevel gear 25. The bevel gear 25 is attached to 
a shaft 26, integral with mounting surface 14c, which is supported by 
suitable bearings within the housing shaft 14a. The shaft 26, as well as 
the bevel gear 25 is rotated about, and shown coincident with, centerline 
C-C' of the mounting surface 14c. Since the housing shaft 14a is itself 
rotated about axis B-B' and shaft 23 is supported in that housing portion, 
it follows that the shaft 26 as well as its axis of rotation C-C' rotates 
about axis B-B' with rotation of the housing shaft 14a. This rotation of 
the axis C-C' about axis B-B' is readily apparent from a comparison with 
the phantom position of mounting surface 14c in FIG. 2, obtained by 
rotating housing shaft 14a through an angle of 180.degree. about axis 
B-B'. An even broader appreciation of the orientational capabilities of 
the instant invention might be realized from a comparison of FIGS. 2 and 
3. FIG. 3 shows the wrist of FIG. 2 with shafts 15 and 14a both rotated 
180.degree.. 
As should be apparent from the above description, each individual shaft of 
the set of concentric forearm shafts 15, 16 and 19 moves the end-effector 
11 affixed to mounting surface 14c, about different axes of rotation. 
Rotation of the forearm drive shaft 15 rotates the entire housing 14 about 
the axis A-A'. This rotation also imparts rotational movement to shaft 14a 
about axis B-B' due to the coupling of bevel gears 17 and 18 and the 
motion of shaft 14a in turn imparts rotation of mounting surface 14c about 
axis C-C' through bevel gears 24 and 25. The forearm drive shaft 16 
translates rotary motion about the axis A-A' into rotary motion about the 
obliquely oriented axis B-B' through the bevel gear 17 and housing portion 
14a. This motion similarly imparts rotational movement of mounting surface 
14c about axis C-C' due to the coupling of bevel gears 24 and 25. Rotation 
of forearm shaft 19 converts rotary motion of drive shafts 19 and 20 into 
rotary motion of obliquely oriented shaft 23, which in turn converts this 
imparted motion into rotary motion of shaft 26 about axis C-C'. 
Additionally, and again as should be apparent from a comparison of FIGS. 2 
and 3, drive shaft 15 rotates axis B-B' about axis A-A' and rotation of 
inner forearm shaft 16 rotates shaft 26 about axis B-B'. Rotation of one 
or more of the individual shafts 15 or 16 of the set of concentric forearm 
shafts provides for planetary motion of the end-effector 11. 
The illustration of FIG. 2 shows the axis C-C' coincident with the axis 
A-A'. As readily apparent from FIG. 3, this condition is unique to the 
position of FIG. 2. In all positions of the illustrated embodiment, 
however, the axes A-A', B-B' and C-C' intersect at a single point, P. This 
means, inter alia, that the axis C-C' and shaft 26 as well as the attached 
end-effector 11 may be oriented normal to the spherical surface at any 
point on the spherical sector generated by the combined movement of the 
aforementioned shafts. In the illustrated embodiments, the angle, A'PB', 
between axis A-A' and B-B' as well as the angle, B' PC', between axes B-B' 
and C-C' is fixed at an angle greater than 45.degree.. Consequently, the 
spherical sector generated by the movement of the end-effector is greater 
than a hemisphere and the axis C-C' may be oriented normal to the 
spherical surface at any point on the sector. It should be apparent that 
the orientation of the axis C-C' about a single point P is vital for the 
normal orientation of the axis C-C' to any location on the generated 
spherical sector without any "holes", i.e. locations in which normal 
orientation of the axis C-C' is not possible. The oblique orientation of 
axis B-B' with respect to the axis A-A' facilitates the mechanical 
implementation and construction of these mutually intersecting axes. 
Deviations from the single point of axes coincidence may be made very 
small with correspondingly small "holes" in the spherical surface 
generated by positioning the end-effector 11 in all of its potential 
locations. Again, a small deviation of the single point of axes 
intersection is facilitated in its mechanical implementation by the 
oblique orientation of the axes. It should also be apparent that small 
deviations from this point of coincidence are possible and may even be 
preferable for some applications. These deviations, however, inherently 
fail to provide the full range of orientation capabilities made possible 
by arranging the three axes to intersect at a single point. 
The oblique orientation of the three axes, A-A', B-B' and C-C' permit the 
end-effector 11, attached to the mounting surface 14c of drive shaft 26, 
to move with directional components in each direction defined by a 
mutually perpendicular triordinate system which has the axis P-A' as one 
ordinant. In other words, with regards to a reference system (X, Y, Z) 
having one ordinate X, coincident with axis P-A', a perpendicular ordinate 
Y, (which like X is in the plane of the illustration sheet) and a mutually 
perpendicular ordinate Z, (normal to the sheet of the illustration), the 
rotation of the end-effector about axis B-B' provides for components of 
motion in each of the directions (X, Y and Z) defined by the mutually 
perpendicular triordinate system. In a similar manner, when axis C-C' has 
been rotated about axis B-B' and is not coincident with axis A-A', the 
equal rotation of the concentric shafts 15 and 16 about axis A-A' provides 
for components of motion at the end-effector 11 in the Y and Z directions 
defined by the triordinate system. 
Each of the three concentric forearm 15, 16 and 19 shafts is rotated by a 
separate hydraulic motor 9a, 9b and 9c mounted upon the robot elbow 5 as 
shown in FIG. 1. The diagrammatic illustration of FIG. 4 depicts the drive 
mechanism employed to rotate the drive shafts 15, 16 and 19 about the axis 
A-A'. Hydraulic motor 9a has a shaft 30 extending into motor housing 9d. 
The shaft 30 drives a spur gear 31 which is in mesh with a spur gear 32 
fixed to forearm shaft 15, the hydraulic motor 9c has a shaft 33 and a 
spur gear 34 which is drivingly engaged with a meshed spur gear 35. The 
spur gear 35 is axially spaced from gear 32 and affixed to forearm shaft 
16 which extends through the gear 32 and beyond the terminus of forearm 
shaft 15. The intermost forearm shaft 19 is driven in a similar manner by 
a spur gear 26 driven by spur gear 37 from shaft 38 extending from 
hydraulic motor 9b. The gear 36 is axially spaced from the gear 35 and 
affixed to forearm shaft 19 beyond the terminus of forearm shaft 16. 
It should be apparent to those skilled in the art from the above 
description that the instant invention transmits power through a 
selectively variable angled joint and that the invention or subsets 
thereof has potential utility in a variety of applications requiring such 
capability. 
Although the present invention has been described in conjunction with the 
preferred embodiments it is to be understood that modifications and 
variations may be resorted to without departing from the spirit of the 
invention as those skilled in the art will readily understand. Such 
modifications and variations are considered to be within the view and 
scope of the present invention as defined by the appended claims.