DOOR MECHANISM DESIGN

Devising a way to open the doors in the COLLIDE dust boxes has been our most formidable challenge (so far). Due to the arrangement of the boxes and the characteristics of the dust in zero gravity, it became necessary to incorporate sliding doors. The primary difficulty introduced in the design was the need to open the door slowly. If the doors are opened too fast, the dust will be disturbed, creating problems in acquiring accurate data. We wanted to keep the design as simple as possible, so we explored using basic stepper motors, muscle wire, and even parafin actuators. After several frustrating weeks, we discovered a device called a digital linear actuator.

This device has an integrated stepper-motor which can be digitally controlled with electric pulses. Each electrical pulse sent to the actuator triggers the motor and a pre-loaded bearing, which extends the actuator shaft a pre-determined amount (as small as .001"). After the proper modifications were made to assure functioning in a vacuum-environment, this actuator opened the doors slowly and accurately. We have used a pin and track method of sliding open the door. Below are two of the initial CAD drawings of the door system:

The door system design changed slightly for the first prototype and a second door track was added to the side of the box. Two additional pins mounted to the door linkage run horizontally to remove all degrees of freedom other than the desired direction. Below is an older CAD schematic of the box and door system. A picture of the completed prototype is also shown for comparison:

After thorough testing and experimentation with the prototype box, a flight model design was finalized. Six flight boxes have been machined and were first integrated with the primary structure in July of 1997. Below is a picture of three boxes attached to the COLLIDE structure:

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