NIIS Cryo-Mechanical Design

NIIS Filter Wheel

         filter wheel on optical bench

The NIIS filter wheel was constructed from a 14-inch aluminum worm gear manufactured by Edward Byers. It contains 7 openings for 100-mm circular filters and/or grisms. Each filter opening is machined with a 5-degree tilt in order to minimize filter ghosting witin the WFNIC optics. The filter wheel is postioned using a stepper motor attached to a matching stainless steel worm. The wheel is mounted on a vertical support plate using two sets of 1/4-inch saphire balls running in circular v-groves. This design should provide good thermal coupling between the vertical mounting plate (attached to the cold optical bench) and the filter wheel. Small button-head screws around the filter periphery are used to trigger micro switches for the filter and home positions. The vertical support includes a cold pupil mask (80 mm diameter pupil) for reducing thermal radiation from the telescope. The wheel is controlled and monitored using a labview interface described in the software section of this web page. The maximum time for filter change is just under 30 seconds. The filter wheel module is designed to enable a second wheel mounted on the opposite side of vertical support.

Cryo-Mechanical Components