Final Design

Component list:

    The final design includes a linear pneumatic actuator, a cam pulley, eight pucks to accommodate the DUTs, spring steel compliance rollers between each of the eight pucks as well as a tensioner roller, hard stop plates and a timing belt to tie it all together! Of course, these components would be like an airplane with no dials if they didn't have the kit plate, since the kit plate provides each component with its location and orientation to allow each to work properly together.

Pneumatic actuator v.2:

    One of the design ideas inherited from the original prototype plate Quartus created was the use of an Airpot pneumatic cylinder with Airpel 2K95 components (the pyrex cylinder, the piston and rod, and all the many seals) and a custom-machined aluminum housing. Keeping this design was preferred because the MATRiX handler is already equipped with pneumatic hoses and choosing a different actuation method may have required changing the size of the e-chain that houses the cables underneath the shuttle. It also allowed the team to focus on other key components with the knowledge that this design had already proven its worth. This component went mostly unmodified through this design process with the exception that it is now secured to the kit plate via a pivoting bearing. The actuator is dual-acting, meaning that pressure can be applied to both sides of the piston to move it. Every motion starts with a little air pressure.

Cam timing belt pulley:

    The purpose of this pulley is to transform the otherwise linear motion provided by the pneumatic actuator into rotational motion that will drive the timing belt system. The center bearings and pin fix the cam to the kit plate at the right height, and the off-center bearing and pin attach to the shaft of the pneumatic actuator. Using bearings for both the actuator and cam as well as for their connecting pin effectively eliminates sliding friction in this portion of the design to extend the life of the kit plate. Pulley stock which has been machined into a hollow ring is press fit onto the cam pulley between two steel flanges which will together grip and guide the timing belt as it shuffles its way around the underside of the plate.

Pucks holding DUT:

Spring steel compliance rollers:

Hard stops:

    The hard stop blocks combine with the hard stop rings on the pucks to form the hard stop mechanism. The collision of hard stop ring and hard stop block forces each puck to stop at 90 degrees. Each of the hard stop collisions is spaced two degrees apart--this makes sure that they hit in sequence, and that each puck turns 90 degrees on a single pull of belt.

Final Performance:

After assembling the prototype, it became apparent that with the current set-up, compliance wasn’t working as designed. Because the real-life belt tension was considerably higher than anticipated in the analyses, pretensioning bent the spring steel tensioners more than expected. As a result, the tensioners couldn’t bend as much to give compliance as designed, and many pucks could not hit their hard stops.

In addition, assembly proved to be particularly difficult in this iteration of the design, as the belt wound very tightly in the grooves of the plate. This, combined with the lack of room for the tensioners to give compliance, made it difficult to properly align the belt with the puck pulley stock. Many of the pucks weren’t in good alignment and couldn’t be corrected easily.

Thirdly, the lack of a moving tensioner between the cam and the first puck made it such that spare belt would “pile up” during the cam’s counter-clockwise rotation.

Finally, imperfections in the timing belt’s advertised width led to it binding between some of the puck flanges.

Long-term cycling and thermal performance has yet to be tested, but will be investigated in the near future.