Don Bilderback, Tom Szebenyi
and Sterling Cornaby
are seen
standing beside CHESS' next generation capillary glass puller.
The
first capillary was pulled on Friday, February 18, 2005 under LabView
program control. This is a very great achievement as we have set up
lots of new equipment over the course of the last year around an ABTech
air bearing slide with on-board metrology through a dual Keyence High
Speed LED/CCD Optical Micrometer. With this equipment, we hope to make
better capillaries and to make them more quickly.
January, 2006. The hope in the long run is to make higher quality capillaries with slope errors below 60 microradians (the best result from the prior puller). The puller mechanics are undergoing some performance testing at present. The good news is that we pulled our first fully drawn capillary with a profile similar to that of the old one, so control of figure has been demonstrated. We do have some "teething" problems, however. Periodic vibrations of the tiny stepping motors that rotate the glass in the middle of the furnace during drawing are rather strong and produce a 10 gram oscillation (peak to peak) in the nominal 100 gram tensioner system, keeping us from having a better result at the moment (170 microradians slope errors). When this problem is resolved, we hope to resume further pulling tests again.
August, 2006. We have produced capillaries that exceeded most of our design parameters of the new puller (design parameters in parenthesis). The best capillary to date was drawn on July 26, 2006 with profile slope errors of 10 microradians (<60μrad) and the centerline straightness slope errors of 160 microradians. Temperature and tension control is maintained using PID feedback loops, attaining ±0.2șC (±0.1șC) and ±0.5 grams (±1.0 grams) respectively. We solved some of the vibration problems by shielding the capillary from the air pushed out by the air bearing. Thanks to Robert Santavicca, an RET from the Detroit public schools, for building the baffle.
Some of the challenges left to solve are:
a) Alignment of capillary in puller so that rotation does not produce 2 gram variations in tension. We have reduced the problem by meticulous alignment - manually. This will require designing a new glass tubing holder.
b) Work with glass tubing manufacturer to improve centerline straightness from ±150 μm profile error in 20 cm to <50 μm and outer profile errors from 2 μm to < 0.5 μm on all different sized ID/OD capillaries we use. Surface imperfections before the pull imprint on the capillary during the pull.
c) Understanding of the limitations in measurement and its effect on slop errors.
d) And others that may come up in the future.
Rong Huang (not shown), who has moved to the Advanced Photon Source is still helping us draw capillaries on the earlier puller (on occasions when he is back periodically in Ithaca), is teaching our new staff how to best draw quality capillaries and also helping to further develop the Matlab design tools for capillary optics development.
