The Connector Space Reduction Mechanism (CSRM) is a simple device that can reduce the number of electromechanical devices on the Payload Interface Adapter/Station Interface Adapter (PIA/SIA) from 4 to 1. The device uses simplicity to attack the heart of the connector mating problem for large interfaces. The CSRM allows blind mate connector mating with minimal alignment required over short distances. This eliminates potential interface binding problems and connector damage. The CSRM is compatible with G and H connectors and Moog Rotary Shutoff fluid couplings. The CSRM can be used also with less forgiving connectors, as was demonstrated in the lab. The CSRM is NASA-Goddard exclusive design with patent applied for. The CSRM is the correct mechanism for the PIA/SIA interface as well as other similar berthing interfaces

Milam, M. Bruce

English

NASA Technical Reports Server

A _ N90-2Z092
The Connector Space Reduction Mechanism
by M. Bruce Milam
NASA/GSFC
Code 716
INTRODUCTION:
In the summer of 1987 the Telerobotic Engineering office
initiated an effort to review the current Space Station Work
Package 3 hardware concepts and fabricate mockups for the
Robotics laboratory (NASA/GSFC Building Ii). The particular
hardware selected for the mockup effort was the Station
Interface Adapter (SIA), Payload Interface Adapter (PIA),
Deck Carrier (DC) and the box-type Orbital Replacement Unit
(ORU) (see figure i). At that time only a rough design
concept existed for the hardware, allowing the opportunity
to fill in vague areas in the design as necessary to allow
the mockups to function. A decision was made to generate
and select concepts that were reasonable for upgrade to
space flight.
One vague area was the utility connection at the PIA/SIA
interface. The PIA/SIA interface consists of two devices
with three legs. Each leg includes provision for coarse
alignment, fine alignment and a utility connection (see
figure 2). The utility connection consists of electrical
data, electrical power, fibre optics and fluid couplings.
The interface is held together with a single mechanism. The
mechanism has the capability to pull the interface together,
preload the interface and eject the interface halves. Only
one electromechanical device is required to mate the system.
BACKGROUND:
A review of current NASA and industry concepts was
initiated. The concepts fell into two general categories,
connector mating orthogonal to the PIA/SIA interface and
connector mating parallel to the PIA/SIA interface (see
figure 3). In each category some concepts use the
mechanical power of the single structural attachment
mechanism while others have independent motors. A decision
was made to use a concept that did not require a dedicated
electrical motor. This would reduce the interface total
number of electromechanical devices from four to one. This
is a tremendous reduction in system complexity, providing
schedule and cost savings with no affect on the function of
the utility connections.
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The next choice was the direction of connector motion with
respect to the PIA/SIA interface desired to mate connectors.
The connectors can be mated parallel or orthogonal to the
PIA/SIA interface (see figure 3). The motorless parallel
concepts require provisions to ensure that the interface is
structurally together prior to connector mating. This adds
complexity to the system levers, pivots, etc. This also
introduces the possibility of the utility connection
mechanism preventing structural attachment of the payload.
The motorless orthogonal concepts are the simplest. A
decision was made to pursue the motorless orthogonal concept
where the connectors are mated as the structural mating of
the PIA/SIA occurs. This is the simplest possible approach
using only the mechanical power of the structural mating
mechanism for the utility connection.
The next step was to plot the mating trajectory of the
PIA/SIA alignment system and select suitable connectors.
The mating trajectory is determined by the fine and coarse
alignment provisions in the system. The system has
trajectory plots for each degree of freedom but only the
most critical translation plots are shown. To make a
trajectory plot of the PIA/SIA system, one must plot the
worst-case misalignment vs. the interface height.
Misalignment is the linear or angular measure from perfect
alignment at the location in the system where the connectors
are located (see figure 4). Then one simply compares these
plots with connector-required trajectory plots from the
manufacturer's drawings and specifications.
THE PROBLEM:
The connector evaluated for our application was the G & H
Technologies shell #i type connector. These have many
desirable features and have flight history on the Modular
Multimission Spacecraft ORUs. The housings are tough and
have forgiving geometry; it is unlikely pins will be bent
during operation. The connector-required trajectory plot
was compared with the system plot and it was found that in
the worst case connectors could not be mated (see figure 5).
THE SOLUTION :
To resolve this problem two avenues exist. The interface
alignment system can be changed or the connectors can be
modified. Improving the alignment system must be done with
care since fine alignment over long interface heights will
cause system binding (see figure 6). This is a problem on
the PIA/SIA interface with its central attachment mechanism.
When mating or demating the interface, the alignment pins
and cones will not separate or mate in unison. This problem
forced modifications to the mockup hardware to eliminate
172
binding. With this in mind a decision was made to leave the
mating system as it is and modify the connector trajectories
instead.
The connector translational and rotational requirements can
be relieved with the addition of guides and gimbals, but
these do not change the travel required. The guides must be
long and protrude above the interface. This could be a
safety hazard. The problem could be eliminated with the
addition of an alignment cusp with a feature that when
depressed an amount the connector halves move together twice
that amount. This device eliminates the requirement for
tight tolerances over large distances for the connectors.
If the device is designed carefully, blind mate connectors
of all types could be used. The only problem with the
system is with the l-to-2 motion ratio, the force to mate
connectors doubles. The structural mating mechanism has
ample force margins to overcome this problem. G & H
Technologies has been working on connectors that require
significantly lower mating force. Other companies have
successfully accomplished this with different styles of
connectors. This imminent marriage of connector technology
will eliminate the mating force problem. Several design
concepts were generated, ranging from a mechanism using
levers and cams to one with racks and gears. The latter was
chosen for the first cut since it appeared more robust.
The device has some design features that are essential and
others that are arbitrary. The device has two halves an
active half and a passive half (see figure 7). The active
half contains the mechanism that provides the mating motion.
Both halves can rotate about an axis and translate along
that axis. When mounted into position, these axis are
orthogonal to one another. This allows for misalignment of
mating interfaces in rotation and translation about two
axis. The halves can gimbal about only one axis each or
binding and pin bending will occur upon demating of
connectors.
The sequence of operation is as follows(see figure 8):
i. and 2. The PIA and SIA are brought into close
proximity in the worst-case alignment situation.
3. The interface height is reduced until the cusp
makes contact. Each half of the mechanism is
gimbaled until each half is parallel.
4. and 5. As the interface height is reduced, the
connector moves twice as fast, cutting the distance
or space with the fine alignment requirement by 50%.
For this reason the device is called the Connector
Space Reduction Mechanism (CSRM).
173
The amounts of translation and rotation can be chosen to
match the application. For our application and geometry,
+/- 0.635 cm (0.25") translation and +/- 6 degrees rotation
were allowed on the passive half and +/- 0.635 cm (0.25")
translation and +/- 1.5 degrees rotation for the active
half. These values allow ample margins for our specific
application. Translational and rotational misalignments
about the axis orthogonal to the PIA/SIA interface are
handled by the proven means of giving one connector half a
compliant mounting.
A requirement is that malfunctioning or damaged connectors
must not interfere with structural attachment. This is
simply achieved by mounting one connector half on springs
with a preload exceeding the normal connector force by 50%.
If the connector is damaged, the connectors will simply push
out of the way, allowing structural mating (see figure 9).
THE HARDWARE:
The prototype CSRM was designed for G & H Technologies shell
#i blind-mate connector. An adapter plate was fabricated
for operation with 3 AMP, blind-mate connectors. The CSRM
was designed for a 3109-N (700-pound) worst-case mating
force. The mounting includes material that encloses the PIA
and SIA 5.08-cm (4") square tube with through bolts. The
motion of the device is provided by dual racks and pinion.
These require good alignment and this is provided with four
IKO linear roller bearings. The bearings provide smooth,
precise motion between the cusp and the connector mounting
plate. The device is made predominantly of aluminum with an
anodized coating. The device has brass gimbal bushings that
provide translation as well as rotation. The CSRM halves
are held in neutral position in translation and rotation by
compression and tension springs. The device consists
primarily of milled-out pieces. This provided the strongest
final product (see figure i0).
ASSEMBLY AND TEST:
The device was assembled and installed on the PIA/SIA mockup
in the GSFC Telerobotics laboratory. The device halves were
placed loosely on the PIA/SIA structure. Both halves were
adjusted until, when perfectly aligned, both halves were in
the neutral position with respect to translation and
rotation. Then matching holes were drilled through the SIA
and PIA square tube for permanent mounting.
The device was tested several cycles with the PIA/SIA mating
normally. No problems were encountered. Then several
mating cycles were accomplished with the PIA imbalanced to
174
force the worst-case misalignments to the system. The CSRM
performed flawlessly. The CSRM has operated several cycles
weekly since 3-24-89 without a single malfunction. The
prototype CSRM has exceeded the number of life cycles for a
flight unit by a factor of ten. The testing was
accomplished with G & H connector shells and repeated with
AMP blind-mate connectors on an adapter plate. The AMP
connectors are excellent for the laboratory since they are
low cost and readily available. AMP connectors are much
more fragile than G & H connectors, and the CSRM has yet to
damage a shell or bend a pin.
IMPROVEMENTS AND FUTURE WORK:
Since this was a prototype device, two areas for potential
improvement came up. The first area is that one of the
telescoping shells on the active half of the device can be
eliminated (see figure ii). This would offer decreased
weight and complexity. The second improvement would be to
reduce the weight of the device. The prototype passive half
weighs 14.5 kg (32 pound) and the active half weighs 25.8 kg
(57 pounds). The weights are to high due to limited stress
analysis and compound factors of safety. The device could
be reduced in weight by 30% and possibly 50%.
CONCLUSION:
The CSRM is a simple device that can reduce the number of
electromechanical devices on the PIA/SIA from 4 to I. The
device uses simplicity to attack the heart of the connector
mating problem for large interfaces. The CSRM allows blind-
mate connector mating with minimal alignment required over
short distances. This eliminates potential interface
binding problems and connector damage. The CSRM is
compatible with G & H connectors and Moog Rotary Shutoff
fluid couplings. The CSRM can be used also with less
forgiving connectors, and this has been demonstrated in the
laboratory. The CSRM is a NASA/GSFC exclusive design with
patent applied for. The CSRM is the correct mechanism for
the PIA/SIA interface as well as other similar berthing
interfaces.
175
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The connector space reduction mechanism

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