NASA CHALLENGE - HANDRAIL CLAMP ASSEMBLY

Last crawled date: 1 year, 10 months ago

HANDRAIL CLAMP ASSEMBLY (HCA) DESCRIPTION
In the design of the handrail clamp, the following points were taken into consideration in their order of importance.
1. Safety
a. Sharp edge human factors were carefully adhered to as per CHAMP requirements with all edges rounded to appropriate radii
b. Pinch areas between moving parts were avoided wherever possible, otherwise anti-pinch shields were built-in.
c. A rigid connection between the clamp and rail was vital as described under point 2 below.
2. Function & strength
a. It was deemed of paramount importance that the assembly has a positive grip on the rail. This point is interleaved with Safety as sudden slippage or opening of the bracket is considered unsafe for the astronaut. This would be quite easily achieved with a 3 or 4 piece assembly by using cams, as is the case with the ISS current clamp assembly for example.
This design has two parts (see point 3) and this was achieved by a design with special arrangement of the clamp elements as described under OPERATION below. The object was to achieve rigidity of the clamp-rail connection at least to the level of the rail interface strength achievable with the ABS printed part.
3. Mass and form
It was decided to limit the assembly to two printed parts for simplicity of assembly for minimum astronaut time.
The shape envelope of 1” around the rail has been adhered to.
The volume of the HCA assembly is 5.42 in³, and the weight is 0.2 lb.
4. Both parts comply with the maximum print size of 2.36” x 2.36” x 4.72”.
OPERATION
The HCA is shown in Figure 1 with depicted names of various parts. Figure 1(a) is an isometric view while Figure 1(b) shows the assembly end-view as positioned on the rail in the locked position.
The part with the seat track interface is named ‘L-Track, while the bottom part is named ‘Clamp’.
After the two parts have been printed they are assembled as per Figure 2(a). The Clamp is hand-pressed into the L-Track until it snaps into position as per Figure 3(a). This is only done once, thereafter the assembly may be manipulated as an integral unit. This obviates mislaying or loosing parts.
The assembled unit may now be placed over the handrail as shown in Figure 2(c) and positioned axially on the rail as required – Figure 2(d).




Attaching the HCA assembly to the rail
The clamp is closed by pushing the Clamp on the Lock Serrations into the locked position, see Figure 1(b).
In the closing of the clamp around the rail, there are several clamping and wedging factors taking place. As the clamp ‘cam follower’ (Figure 3(c)) enters the space between the Latch and the cam surface several processes take place:
1. The Latch springs open driven by the cam follower larger radius.
2. The Clamp cam-following element, due to offset ‘e’ (Figure 3(a)), forces the cam surface element to flex and wedge its Rail Grip under the rail.
3. The lower Rail Grips (Figure 2(b)) wedge themselves at a shallow 35° (Arrows B), this in turn causes the assembly to float and wedge its tow Rail Grips on the rail at even shallower 25° (Arrows C).
The angles were more or less determined intuitively and proved satisfactory in tests on actual printed assemblies.
Similarly, the Latch spring thickness was determined during tests. These tests were done with an average female (at the risk of my wife being labeled 'average').
4. The Clamp is pushed further until the Latch snaps into the Locked position.
Figure 3(b) shows the relative position of the Latch landing to the Clamp pivot and it can be clearly seen that it would be quite difficult to force the latch open by pushing on the unlock serrations (Figure 1(b)) short of causing breakage.
5. It was found during testing that a very strong and stable attachment to the rail is achieved with normal hand pressure.

Detaching the HCA assembly
To dismount the HCA assembly from the rail it is necessary to pull the Latch while pressing down on the Unlock Serrations of the Clamp.
One easy way, it was found, is to use the thumb on the latch and the fore and middle finger, thereby unlocking the assembly with on hand.

General
It was found during tests that the snapping close of the Latch would not cause an injury of concern, however to prevent any possible discomfort, an anti-pinch shield was built in, see Figure 1(a).
Serrations were added on the Clamp to prevent finger slippage during mounting and dismounting the assembly.
There is a mid-groove on each side of the Clamp (Figure 1(a)) introduced to prevent finger slippage. This also helped in the attainment of the correct radii as required in the competition rules.