This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The improvement and optimization of the Vibrationally Cooled MALDI-FTMS continues. This year we carried out further testing and evaluation of the XY stage that was designed and constructed in collaboration with the Fraunhofer Institute. This stage is a critical component for full automation of the MALDI-FTMS. The design parameters for this stage were defined to handle the typical proteomic type sample. Many proteomic experiments use robots that are designed to work with microtiter plates which are ~76 x 89 mm in size. Therefore, the stage was required to have full travel of at least 100 x 100 mm. For the MALDI Fourier transform mass spectrometer used, the travel time from spot to spot is not the limiting factor in the experiment speed, so a travel of 2 mm/sec was defined as it would allow the stage to position to the next spot 1 mm away in 0.5 seconds. The positioning accuracy was defined to be 1 um, which is much more accurate than is needed for the standard MALDI experiment in which the laser beam spot is often 50 um diameter, but will allow the stage to be used in a MALDI imaging mode. Aside from this, the stage had to be truly vacuum compatible, had to be mounted vertically, and to generate no detectable RF interference noise, and had to take up minimal space so that the vacuum chamber could be made as small as possible for improved pumping performance. The two-dimensional stage is a single block design with the two axis motors, linear encoders, and position switches all integrated into the central block. The system uses ballscrews and crossed roller bearings which will require minimal lubrication in vacuum;what little lubrication is needed is provided by low vapor pressure diffusion pump oil. In order to build the motors into this block, they are mounted on copper brackets (to dump their heat into the block which acts as a heat sink) and pulleys are used to transfer their torque to the ballscrew. The belts for these pulleys are actually small electrowelded stainless steel bands, and in order to keep them centered on the pulleys, the pulley wheels are ground to be slightly concave. Tensioning set screws are mounted into the block to allow the pulleys to be tightened properly during testing. In order to prevent over determination of the position of the ballscrew, it is mounted in two places only: the pulley bearing assembly and the plate. The stage itself is designed in three pieces, an upper and lower plate, and the central block. The motors, limit switches, and linear encoder electronics are all mounted (and heat sinked) to the central block. The linear encoder slides are mounted to the upper and lower plates. The three pieces are black anodized to improve surface hardness, but even more importantly, to improve radiative cooling of the blocks. All wire routes are also contained within the block. The motors and electronics dump their heat loads into the central block, which is only able to dissipate that heat through conductive cooling at the bearings and radiative cooling. The conductive cooling is very inefficient since the bearings are stainless steel (very low heat transfer capacity) and the contact area is very low. A copper band or braid was considered for improving the conductive heat transfer rate, but a quick calculation of the heat transfer of such a band compared to the radiative cooling rate showed that the heat transfer through the copper band was negligible. There are several positioning screws for the crossed roller bearings, wire traces, and bolt holes for mounting the motors, bearings, and electronics. All of these holes are vented to minimize virtual leaks. The system uses four position encoders, two linear encoders for determining position, and two rotary encoders mounted on the back of the motors for determining velocity. The system uses optical limit switches. The switch is a photodiode/phototransistor pair mounted on the central stage body which is interrupted by an aluminum flag mounted on the upper and lower stage plates. Two such switches are mounted for each axis. When the stage moves to the end of its range of motion, this flag blocks the photodiode's signal to the phototransistor, and the electronics signal the stage to stop. Such a system, while similar to a rocker switch or magnetic switch involves fewer parts and greater positioning accuracy. The sample translation stage requires a large number of vacuum electrical feedthroughs (46) to control 2 motors, 4 encoders, 4 limit switches, and a thermocouple. Furthermore, because this is being mounted on an FTMS which has high sensitivity to RF interference noise, it was critical that the feedthrough and cables be well shielded. The vacuum chamber for this sample translation stage was designed to be as small as possible (for efficient pumpdown) but large enough to allow the full range of motion for the stage. The sample translation stage control was developed as a set of commands that can be called from a dynamically linked library (dll) in any Microsoft window's based programming language. The language used here was C++ as implemented in Microsoft Visual C++, version 6. A copy of the stage was constructed for use with the cryogenic FTMS being assembled within the BUSM Cardiovascular Proteomics Center and the Resource instrument has been used for its testing and evaluation prior to installation in the cryoFTMS. Additional copies have been shipped to R. Heeren, FOM Amsterdam and A. G. Marshall, NHMFL, Gainesville, FL. K. Aizikov visited FOM for the installation, testing and initial experiments.
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