The Ohio State University College of Mathematical & Physical Sciences Department of Astronomy

Attendees: Bruce Atwood, Ross Zhelem, Dan Pappalardo, Mark Derwent, Phil Covington, Jason Eastman, Ed Teiga, Ray Gonzalez, Jerry Mason, & Rick Pogge

Optics

Ross presented his re-analysis of the SOML Coordinate Measuring Machine (CMM) profilometry of the red corrector lens parent aspheric surface. To recap from last week, the raw data consists of 7 runs with the CMM, clocking the parent in azimuth 1/7th of a circle between runs to cover the 800+mm diameter surface. Each run includes measurements of 4 reference balls to set the rotation/translation reference for each run. The reference ball data are used to stitch together the 7 runs into a map of the complete surface of the parent. The total data set is comprised of about 3300 data points.

Ross's analysis found that, except for the 200mm-diameter ding in the surface, the main range of the surface error in the CMM data is +/-7um. He resampled the data onto a regular grid using linear interpolation (the data are densely enough sampled to permit this compared to the scale of features in the map). This new map has none of the stitching artifacts we saw before, and clearly shows the kinds of zonal errors that are typical of this type of figuring process. One of the plausible sections for cutting out a corrector lens from the parent, away from the 200mm-diameter depression, looks pretty good, but the other zone still needs work.

Ross has sent his analysis to SOML and discussed it with them. They have adopted our analysis and are using it to generate a hit map. We have requested a videoconference with them next week to discuss the state of the part before the next iteration proceeds.

Jerry Mason presented his transmission scans of the dichroic test pieces sent by CSIRO, and is rigging up for the reflectance scans (due Wed or Thursdays). The scans were done at the 35-degree operating angle of the optic. The scans look very good. It is likely we will accept these coatings and ask them to proceed to coat the two dichroic substrates (CSIRO already has these). We can expect to take delivery of the final dichroics in mid-July to early-August, well in advance of when we need them for MODS1 assembly.

MODS Thermal Control

Bruce has been reviewing the glycol cooling needs for MODS. Bottom line is that a lot of stuff needs glycol (IE boxes, detector HE boxes, the Leach controllers for the AGW cameras, etc.), and working out the plumbing is a challenge. Bruce has been designated the plumber for the project and tasked with coming up with a connection design that minimizes the number of connections needed.

He also had a look at the connectors on the AGW camera bodies, and is not happy with them for use inside the instrument. He is going to explore another connector type.

MODS Electronics

Dan reported on testing of power relays for the MicroLYNX controllers (see the report for April 17 - last week). So far his second DIN-rail and automotive relay test pieces have been through about 1000 cycles and are still going without problems. We are going to adopt the automotive relay and mount it on the Rev2 motor board.

Dan spoke with an engineer at IMS, the maker of the MicroLYNX controllers, and learned two things:

1. In-rush current on startup is big, and why we were blowing the earlier relays. They provided us with sketches of components to mitigate this, and confirmed that using a heftier relay is a good thing.
2. They also provided us with suggestions for components for voltage suppresion for the controllers in the event that one of the controllers fails in a bad way producing significant back-EMF.

Dan also reported on testing of the pass-through harnesses for the grating tilt mechanisms on the grating-select turret. Two concepts are being tested, looking for problems with rubbing or twisting of the wires as the turret rotates. The harnesses are fed through the central axis of the turret, and provide power and sensor I/O to the grating tilt mechanisms. They're rigging up for more intensive life-testing later this week with assistance form Mark. Bruce suggested that Dan consider a third design using fine-strand wire used for test leads as a more supple alternative to the standard wire we use. Dan will setup one of these for testing.w

MODS Software

Ray has finished his work testing the power-relays for the MicroLYNX controller (see above). He has also finished testing each of the 16 motion axes of the Rev1 IEB for I/O and communications, and has exercised the WAGO for reading RTDs successfully. He is now working with Mark Derwent's filter wheel microcode, making modifications to include it in the motion control suite.

At this point, Ray is ready to move the Rev1 IEB into the Solarium for use with the MODS1 mechanisms being readied for installation on MODS1.

MODS Enclosure

Mark reported on progress with the MODS enclosure design. The prototype miniMODS testbed in the basement lab is working great. He is currently updating the design work and CAD model, and preparing a parts list. Dave Steinbrecher is working on parts for the fixed rings, which will probably require the next 1-2 weeks. The plan is to do the order for the hexagonal sections in stages.

The main work with the prototype now is on the light-tightness tests. Mark and Dave have verified that the neoprene gasket idea doesn't work, and instead they have had good success using heavy-duty hook-and-loop velcro. This work well for securing most of the side panels of the hexagonal section, requiring many fewer screws for the fixed portions, making them much easier to handle in the field. Overall it looks like an excellent solution.

Light leak tests are currently being done in a darkened room with a flashlight to find the most obvious leaks. This has already led to the introduction of corner shelds for the main hexagon-section panels. Much darker tests, with dark-adapted observers, will proceed soon. One problem is finding a room dark enough to use when we get the full-size enclosures built.

Parts will start arriving end of May to early-June, and we will start the assembly of the main hexagonal structure and one of the 2-panel removable sections in the McPherson high-bay shop where we have ready access to our machine tools, and then shift most of the work over to the west Campus "birdhouse" facility where we have more room to work.