Split spline screw

A split spline screw type payload fastener assembly including three identical male and female type split spline sections. The male spline sections are formed on the head of a male type spline driver. Each of the split male type spline sections have an outwardly projecting load baring segment including a convex upper surface which is adapted to engage a complementary concave surface of a female spline receptor in the form of a hollow bolt head. Additionally, the male spline section also includes a horizontal spline releasing segment and a spline tightening segment below each load bearing segment. The spline tightening segment consists of a vertical web of constant thickness, having at least one flat vertical wall surface which is designed to contact a generally flat vertically extending wall surface tab of the bolt head. Mutual interlocking and unlocking of the male and female splines result upon clockwise and counter clockwise turning of the driver element.

CROSS REFERENCE TO RELATED APPLICATIONS 
This invention is related to an invention shown and described in U.S. Pat. 
No. 5,174,772 dated Dec. 29, 1992, entitled "Work Attachment 
Mechanism/Work Attachment Fixture", filed in the name of John M. Vranish 
on Jan. 22, 1992. This invention is assigned to the assignee of the 
present invention. Moreover, the teachings of this related invention is 
herein meant to be incorporated by reference. 
BACKGROUND OF THE INVENTION 
This invention relates generally to attachment means for joining two bodies 
together, and more particularly to a spline type fastener for joining two 
bodies together, for example, in outer space. 
DESCRIPTION OF THE PRIOR ART 
Fasteners utilized to attach and release structural elements by means of a 
robot are generally known. In an environment where payloads are required 
to be attached to and released from a spacecraft, for example, payload 
fasteners have special requirements, irrespective of whether the 
attachment is made by way of a robot or an astronaut. The fastener should 
be designed, for example, so that it cannot be cross threaded, it cannot 
be loosened by launch vibrations, and must be able to be preloaded with 
modest torque against multiple "G" launch loads. 
One such fastener is comprised of a spring-loaded male spline nut located 
at the tip of a threaded male positioning member that is affixed to a body 
being fastened. A complementary female type spline fitting or bolt adapted 
to engage the spline nut is located at the lower end of a female conical 
receiving member which is affixed to a structure or receiving body to 
which the payload body is being fastened. During a fastening guidance and 
mating procedure, the male nut and female bolt are aligned in a soft 
docking phase which is followed by a forward movement of the spline nut 
against and into the female spline member. This is then followed by a 
rotation of the male spline nut into a locking arrangement with the female 
spline fitting. To release the fastener, the process is simply reversed. 
While this system operates as intended, undesired stresses can build up and 
accumulate in the locking splines. Accordingly the present invention is 
directed to a technique to reduce these stresses, thus significantly 
improving the performance and safety of the system without a significant 
increase in size. 
SUMMARY 
Accordingly, it is an object of the present invention to provide an 
improved fastener device which may be repeatedly applied and removed by a 
machine. 
It is a further object of the invention to provide an improved fastener 
device which can be automated for use in connection with a robot. 
It is still another object of the invention to provide a relatively simple, 
compact and lightweight fastener device for spacecraft payloads which can 
be attached and released by a robot as well as an astronaut. 
And still a further object of the invention is to provide an improved 
spline type fastener for payload fastener which can be attached and 
released by both a robot and an astronaut. 
The foregoing and other objects of the invention are realized by a split 
spline screw type payload fastener assembly comprised of three identical 
male type split spline sections formed on the head of a male type spline 
driver and wherein each of the split spline sections include an outwardly 
projecting load bearing segment having a convex upper surface which is 
adapted to engage a complementary concave surface of a female spline 
receptor in the form of a bolt head. The male spline section also includes 
a horizontal spline releasing segment below each load bearing segment and 
having flat upper and lower surfaces and a curved outer surface and spline 
tightening segment consisting of a vertical web of constant thickness 
toward one side of the load bearing segment and having at least one flat 
vertical wall surface which is designed to contact a generally flat 
vertically extending wall surface tab of the bolt head. Mutual 
interlocking and unlocking of the male and female splines result upon 
clockwise and counter clockwise turning of the driver element.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings wherein like reference numerals refer to like 
parts throughout, reference will be first made to FIG. 1 where there is 
disclosed two generally cylindrical bodies, a work attachment mechanism 
(WAM) 10 which is attached to the arm of a robot, not shown, and the other 
a work attachment fixture (WAF) 12 which is attached to a work site, for 
example, in outer space also not shown. In a berthing and attachment 
sequence between the bodies, the work attachment mechanism 10 is first 
positioned in the vicinity of the work attachment fixture 12 for docking 
by means of a remote manipulator system which may be located, for example, 
on a space station. 
As an adjunct in the docking process, an automatic alignment system for the 
two bodies 10 and 12 includes three equally spaced round roller type 
members 14, 16 and 18 which are rotatably mounted on the cylindrical outer 
surface 20 of the work attachment mechanism 10 adjacent respective leading 
chamfered surfaces 22, 24 and 26. The work attachment fixture 12 below 
includes a complementary mating structure comprised of three mounting 
blocks 28, 30 and 32 having upwardly directed V-shaped grooves 34, 36 and 
38 which are coextensive with adjacent chamfered surfaces 40, 42 and 44. 
As shown, the mating blocks 28, 30 and 32 are equidistantly arranged on 
the outer surface 46 of the work attachment fixture 12 to match the 
separation of the roller members 14, 16 and 18. 
In a docking maneuver, one or more of the roller members 14, 16 and 18 of 
the work attachment mechanism 10 first contact a respective outwardly 
radiating V-shaped mating groove 34, 36, 38 of the work attachment fixture 
12. This provides an automatic alignment capability for a spline screw 
coupling and locking mechanism for the two bodies 10 and 12 and consisting 
of a male type split spline driver element 48, and a female spline type 
receptor element 50, which comprises the subject matter of this invention. 
Surrounding the spline connector elements 48 and 50 are three sets of fold 
back door type dust covers 52, 54 and 56, which are located on the 
underside 58 of the work attachment mechanism 10 and three mutually 
opposite sets of dust covers 60, 62 and 64 located on the upper surface 61 
of the work attachment fixture 12. The dust covers 52, 54, 56 and 60, 62, 
64 automatically open and close to protect complementary sets of 
electrical connectors, not shown, in order to provide an electrical 
interface between the bodies 10 and 12 for the transfer of power and 
electrical signals therebetween. 
Referring now collectively to FIGS. 2 through 5, FIG. 2 is illustrative of 
a vertical cross section of the preferred embodiment of the invention 
including, among other things, the male split spline driver 48 and the 
female spline receptor element 50. As further shown in FIG. 3, the driver 
element 48 includes an alignment cone 66 behind which are located three 
identical male spline sections 68.sub.1 . . . 68.sub.3, two of which, 
68.sub.1 and 68.sub.2, are shown. These spline sections are formed on the 
outer surface of a hollow shank 70 which includes a shoulder 72 (FIG. 2) 
that abuts a thrust bearing 74 and a compliance spring 76. The shank 70 
includes an axial bore 78 which is adapted to receive a splined shaft 80 
of a drive motor, not shown. 
As shown in FIGS. 2 and 3, the alignment cone 66 is adapted to seat in a 
conical recess 82 located in inner cavity 84 of a female spline bolt head 
86 which forms part of the receptor element 50 and includes three spline 
elements 88.sub.1, 88.sub.2 and 88.sub.3 at the top thereof. Each of the 
male spline sections 68.sub.1 . . . 68.sub.3 is comprised of an upper 
outwardly projecting spline segment 90.sub.1 . . . 90.sub.3 having a 
convex upper load bearing surface 92.sub.1 . . . 92.sub.3 which matches 
the undersurfaces 94.sub.1 . . . 94.sub.3 of the female spline sections 
88.sub.1, 88.sub.2 and 88.sub.3. At the bottom of each load bearing spline 
segment 90.sub.1 . . . 90.sub.3, there is located a horizontally oriented 
flat spline releasing segment 96.sub.1 . . . 96.sub.3 which are adapted to 
contact an annular depth and tilt alignment surface 97 within the cavity 
84 of the spline bolt head 86. Each male spline section 68.sub.1 . . . 
68.sub.3 includes a third spline segment 100.sub.1 . . . 100.sub.3 used 
for tightening the male and female splines and comprises a vertical web 
separated from the respective releasing spline segment 96.sub.1 . . . 
96.sub.3 and having at least one flat vertical wall surface which is 
designed to contact a generally flat wall surface of one of three like 
inwardly projecting bolt torque tabs 102.sub.1 . . . 102.sub.3, two of 
which 102.sub.1 and 102.sub.2, are depicted in FIG. 3 formed on the inner 
surface 104 of the female spline bolt 86. 
Before describing the operation of the male and female spline elements 
68.sub.1 . . . 68.sub.3 and 88.sub.1 . . . 88.sub.3, the remaining 
structure illustrated in FIG. 2 will first be considered. As shown in FIG. 
2, the female spline bolt head 86 is joined to a threaded shank 106 which 
narrows at its lower end 108 where it passes through a recess 110 and hole 
112 in the bottom of the work attachment fixture 12 where it is surrounded 
by preload spring 114 and is held in place by an enlarged butt end portion 
116. 
A captured nut body member 118 is located on the threaded shank 106. The 
nut member 118 is permitted to move axially up and down the bolt shank 
106, but is constrained from rotation by one or more spline guides 120 
which ride up and down in respective vertical channels 122 between top and 
bottom shoulder stops 124 and 126. The nut body 118 is shown comprised of 
an angulated member having an upper surface 128 on which is located a set 
of, for example, male type electrical connectors 130, shown in phantom 
view, around the periphery thereof and which are adapted to engage a 
respective set of female type electrical connectors 132, also shown in 
phantom view, located directly above in the work attachment mechanism 10. 
Associated with both sets of electrical connectors 130 and 132 are 
respective sets of dust covers 52, 54, 56 and 60, 62, 64, as shown in FIG. 
1. The dust covers are adapted to open and close automatically when the 
electrical connectors are brought together upon docking of the two bodies 
10 and 12. 
In operation, as soon as the two bodies 10 and 12 have seated as shown in 
FIG. 2, the spring loaded male spline driver 48 drops down into the cavity 
84 of the female spline bolt head 86, thereby creating a soft dock 
condition. 
When the male spline driver 48 is rotated clockwise, the flat vertical wall 
surfaces 100.sub.1 . . . 100.sub.3 of the three male spline sections 
68.sub.1, 68.sub.2 and 68.sub.3 hit the flat wall surfaces of the 
respective torque tabs 102.sub.1, 102.sub.2 and 102.sub.3 inside of the 
spline bolt head 86. The bolt shank 106, however, is spring loaded against 
the body 12 by the spring 114. Since the threaded nut member 118 cannot 
rotate, the structural arrangement depicted causes the nut member 118 to 
remain in place while the bolt shank 106 and the bolt head 86 translate 
downward until the gap 93.sub.2 (FIG. 4) is closed and the spline surfaces 
92.sub.1 . . . 92.sub.3 and 94.sub.1 . . . 94.sub.3 lock. When this 
occurs, the spring load shifts from the bottom of the nut 118 to the 
convex surfaces 92.sub.1 . . . 92.sub.3. At that point the bolt 50 can no 
longer translate downwardly. Accordingly, the nut 118 begins to travel 
upwardly as indicated in FIG. 2. 
The spline structure disclosed herein results in a significant difference 
in the load bearing and safety capabilities of this type of system. The 
top male and female spline segments 90.sub.1 . . . 90.sub.3 and 88.sub.1 . 
. . 88.sub.3, respectively, attend to the main tensile forces, while the 
bottom segments thereof, i.e. segments 100.sub.1 . . . 100.sub.3, 96.sub.1 
. . . 96.sub.3 and 102.sub.1 . . . 102.sub.3 attend to torquing and 
detorquing forces. 
The spherical bearing surfaces 92.sub.1 . . . 92.sub.3 and 94.sub.1 . . . 
94.sub.3 yield relatively larger shear plane lengths and greater shear 
plane area which further strengthen the system. The bottom segments also 
provide a desired positioning sequence to permit soft docking between the 
bodies 10 and 12 throughout a fastening and unfastening process. 
In the arrangement as shown, the spline segments 90.sub.1 . . . 90.sub.3, 
which are load bearing members, are optimized for the load bearing 
function and act to reduce contact stresses by virtue of their respective 
upper spherical surfaces 92.sub.1 . . . 92.sub.3. This permits tiny 
seating adjustments between the driver 48 and the receptor 50 such that 
when one of the three lower spline segments 96.sub.1 . . . 96.sub.3 make 
contact with the alignment surface 98 during the tightening or preload 
process, the top spline segments 90.sub.1 . . . 90.sub.3 are free to pivot 
in the manner of a ball and a socket. This then permits force equilibrium 
to occur in which simultaneously each of the lower spline segments 
100.sub.1 . . . 100.sub.3 bears one third of the tightening forces, while 
each of the upper spline segments 90.sub.1 . . . 90.sub.3 bear one third 
of the actual load forces. 
When the split spline fastening system of the subject invention encounters 
large stresses in usage, the male and female type spline elements 68.sub.1 
. . . 68.sub.3 and 88.sub.1 . . . 88.sub.3 have already been optimally 
positioned with respect to each other during the tightening process so 
these large usage forces are evenly distributed, even though the splines 
cannot pivot under the large loads. During the loosening process, the 
locking splines are initially held together with friction between the load 
bearing spline surfaces 92.sub.1 . . . 92.sub.3 and 94.sub.1 and 94.sub.3 
so the initial loosening forces are evenly distributed, even though the 
splines cannot pivot with respect to each other. As the female spline 
member 50 loosens, the friction forces recede and the spline member 50 
slips slightly in rotation with respect to the driver member 48 until the 
back side of the three bolt torque tabs 102.sub.1 . . . 102.sub.3 
encounter the spline releasing segments 96.sub.1 . . . 96.sub.3 and the 
two members 48 and 50 once again rotate in unison with the loosening 
process continuing. But now pivoting can occur between the upper and lower 
spline surfaces 92.sub.1 and 92.sub.3 and 94.sub.1 and 94.sub.3 so that 
the forces on the spline members go into force equilibrium, with each 
sharing one third of the force induced by the loosening torque. This 
condition continues until the two members 48 and 50 are ready for 
separation. 
The torquing and position control splines 96.sub.1 . . . 96.sub.3, and 
100.sub.1 . . . 100.sub.3 are optimized solely for the functions described 
below. First, they must transmit torque from the driver 48. Second, they 
must position the load bearing splines 90.sub.1 . . . 90.sub.3 and 
88.sub.1 . . . 88.sub.3 of both the driver 48 and receptor 50 so that they 
line up with each other during tightening so as to produce maximum holding 
and preload forces and thereafter disengage the load bearing splines and 
permit easy separation of driver 48 and receptor 50 after the loosening 
process is complete. Third, they must provide a means of maintaining a 
soft or hard dock fastening status throughout both tightening and 
loosening to provide a hedge against inadvertent release It can be seen, 
particularly from FIG. 3, that the lower splines 88.sub.1 . . . 88.sub.3 
in the coupling process are directly below the upper load bearing spline 
segments 90.sub.1 . . . 90.sub.3 so the end of the driver 48 will fit into 
the spline bolt head 86 through the bolt head's three minimum passage ways 
between the splines 88.sub.1 . . . 88.sub.3. Once the driver 48 enters the 
bolt head 86, the bottom spline segments 96.sub.1 . . . 96.sub.3 and 
100.sub.1 . . . 100.sub.3 seat on the annular tilt and alignment surface 
97 (FIG. 3) by spring loading, leaving a slight clearance (0.010 to 0.030 
in.) between the lower spline segments 88.sub.1 . . . 88.sub.3 and the 
bolt torque tabs 102.sub.1 . . . 102.sub.3. Thus, when the driver 48 is 
turned clockwise (CW) to tighten, it will turn within the female spline 
bolt head 86 until one spline segment, e.g. 100.sub.1 contacts its 
corresponding bolt torque tab 102.sub.1. Shortly thereafter the adjustment 
process between the driver 48 and bolt head 86 will continue until all 
three spline tightening segments 100.sub.1 . . . 100.sub.3 and bolt torque 
tabs 102.sub.1 . . . 102.sub.3 are engaged with equal forces. As the 
driver 48 and the bolt head 86 continue to turn clockwise together, the 
spring-loaded bolt shank 106 and bolt head 86 translate downwards relative 
to the driver 48 and each of the three bolt torque tabs 102.sub.1 . . . 
102.sub.3 is captured in a slot 98.sub.1 . . . 98.sub.3 (FIG. 3) between 
the spline releasing segment 96.sub.1 . . . 96.sub.3 and spline tightening 
segments 100.sub.1 . . . 100.sub.3. And, as the clockwise rotation and 
relative translation continue, each of the three bolt torque tabs 
102.sub.1 . . . 102.sub.3 continue to ride up its corresponding slot 
98.sub.1 . . . 98.sub.3 until the load bearing splines 90.sub.1 . . . 
90.sub.3 and 88.sub.1 . . . 88.sub.3 of driver and bolt lock. 
When a counterclockwise rotation is initiated to loosen a previously 
fastened spline driver 48 and receptor 50, the contact between each bolt 
torque tab 102.sub.1 . . . 102.sub.3 and its corresponding lower spline 
releasing segment 96.sub.1 . . . 96.sub.3 couple these two mating parts 
together, both for transmitting torque and for maintaining hard/soft dock 
throughout the loosening process. When the loosening process is complete, 
the respective elements of both of the driver 48 and the female receptor 
50 are aligned so that as the counterclockwise motion continues, the 
driver 48 rotates within the bolt cavity 84 until the back side of the 
vertically oriented spine segments 100.sub.1 . . . 100.sub.3 hits an 
adjacent bolt torque tab 102.sub.1 . . . 102.sub.3. In the process, the 
female spline bolt 86 and driver 48 are positioned for easy disengagement 
and it is impossible for the two to get entangled or jammed together. 
Having thus shown and described what is considered to be the preferred 
method and embodiment for implementing the subject invention, it is to be 
noted that the same has been made by way of illustration and not 
limitation. Accordingly, all modifications, alterations and changes coming 
within the spirit and scope of the invention are herein meant to be 
included.