Design and development of a high-precision, high-payload telescope dual-drive system

Abstract

A high precision, dual drive system has been designed and developed for the Wide Field Upgrade to the Hobby-Eberly Telescope * at McDonald Observatory in support of the Hobby-Eberly Telescope Dark Energy Experiment ‡ . Analysis, design and controls details will be of interest to designers of large scale, high precision robotic motion devices. The drive system positions the 19,000 kg star tracker to a precision of less than 5 microns along its 4-meter travel. While positioning requirements remain essentially equal to the existing HET, tracker mass increases by a factor greater than 5. The 10.5-meter long tracker is driven at each end by planetary roller screws, each having two distinct drive sources dictated by the desired operation: one slowly rotates the screw when tracking celestial objects and the second rotates the nut for rapid displacements. Key results of the roller screw rotordynamics analysis are presented. A description of the complex bearing arrangement providing required degrees of freedom as well as the impact of a detailed Failure Modes and Effects Analysis addressing necessary safety systems is also presented. Finite element analysis results demonstrate how mechanical springs increase the telescope's natural frequency response by 22 percent. The critical analysis and resulting design is provided.

VIRUS: a massively replicated 33k fiber integral field spectrograph for the upgraded Hobby-Eberly Telescope

“…It will be a third generation evolution of the trackers for HET and SALT, and is in essence a precision six-axis stage. The tracker is being developed by the Center for Electro-Mechanics (CEM) at the University of Texas at Austin [18][19][20][21][22][23][24][25][26][27] , with integration at the CEM facility scheduled for Fall 2010.…”

Design of the fiber optic support system and fiber bundle accelerated life test for VIRUS

“…The operational limits for HETDEX occur at tracker X/Y positions of +/-1870.08 mm from the center of the primary mirror 12,13 . At this position the focal surface and collector mirror are tilted at +/-9 degrees from the tracker plane.…”

Design and analysis of the tracker bridge for the Hobby-Eberly Telescope wide-field upgrade

“…The tracker translates along two beams of the upper hex along the X-axis via a drive system consisting of a pair of planetary roller screws and linear bearings 11 shown in Figure 2. A second pair of linear bearings mounts on top of the two main bridge beams allowing the payload to translate in the Y-axis via a third roller screw 12 .…”

“…• The four anti-skew blocks 11 (165 kg each), four Y-axis hard stops 11 (50 kg each), two FMS carriages (305 kg each), Y-drive slew housing 12 (178 kg) and CFD (584 kg) are all modeled as simple beams in their respective locations. The density and CG locations of each component are manipulated within the beam's properties to match the actual hardware.…”

“…Due to the mass and geometry changes, the entire tracker, drive systems 11,12 , and control architecture 13 are being replaced, including the bridge which serves as the backbone of the tracker. Experience with the HET tracker created new requirements for the WFU system which influences the bridge design, such as required frequency response, obscuration limits, and hexapod location.…”