In mechatronics applications control is most often paired with motion. The following motion control system works with other components to deliver the required movement precision to research the Universe.
Photo by: Laura Hatch lauriehatch.com
Astronomers working for University of California Observatories (UCO) are creating the first comprehensive survey and map of the distant universe. Called the Deep Extragalactic Evolutionary Probe (DEEP), the team uses twin 10-m W.M. Keck Telescopes located in Hawaii, the Lick Observatory on Mount Hamilton in California, and the orbiting Hubble Space Telescope (HST).
The telescopes collect the light that stars and faint galaxies emitted more than 14 billion years ago. Detecting and analyzing this light requires an approach that includes a complex compliment of mechanical, electronic and optical instruments, along with sensors and software.
One of the key components of the Keck II telescope is the Deep Imaging Multi-Object Spectrograph (DEIMOS). Able to magnify the telescope’s capacity by a factor of seven for faint-galaxy optical spectroscopy, DEIMOS features:
• An optical beam camera with advanced optics and three 13-in. diameter calcium fluoride crystals lenses
• A “slitmask” system that allows observation of 140 galaxies simultaneously
• The largest spectroscopic charge-coupled device (CCD) detector of its type ever made (5-in.2, contains 67 million pixels)
• Sophisticated software for rapid setup and flexure compensation to keep the mirrors stable and aligned to prevent images from moving about on the detector. Conventional spectrographs that suffer from severe flexure make calibration and data reduction difficult.
The multiple detectors on each Keck telescope, the DEIMOS spectrograph, and other related instruments require precise motion control of a number of elements, including filter wheels, focusing, apertures and positioning stages. Barry Alcott, development engineer at UCO, has been specifying Galil motion controllers for more than 15 years to handle the motion control tasks.
Alcott used Galil’s RIO Pocket PLC to automate portions of the Hamilton Spectrograph system, the first cross-dispersed spectrograph installed at the Lick Observatory. It operates by having light fed to a grating that sends it in one direction and then immediately feeds it to a prism that disperses it at a 90° angle for very high-resolution spectra.
Alcott configured the multiple I/O points of the controller to automatically control four pneumatic stages used for moving an iodine cell into a beam, opening a light port, moving a mirror into a beam, and opening a mirror cover. The controller’s logic control ensured proper event sequencing. Communication between the controller, the motion system and the I/O points is handled through the built-in Ethernet port.
“I was able to put together this control system in under two weeks. By automating the control of these functions, our astronomers can remotely control the telescope instruments from a home base,” said Alcott. “They no longer need to come to the Mount Hamilton Observatory to adjust the instrumentation.”
Multiple Galil Motion Controllers enable astronomers to precisely control the movement of giant telescopes from a home base.
In addition to the RIO upgrade, the Hamilton Spectrograph was fitted with Galil’s DMC-4080 Accelera Series motion controller. The dual-loop position mode is used specifically for sub-micron, precise positioning and guidance of the correct light wavelength onto detectors. The dual-loop position data come from a 0.01-m resolution encoder that is placed on the stage and an
auxiliary encoder placed on the motor.
Additional upgrades using Galil controllers are in process at the Mt. Hamilton location. The 68000 MPU based system of the Kast spectrograph is being replaced with a pair of DMC-4080 controllers. Additionally, a spectrograph is being built for a new remotely operated 2.4 m Automatic Planet Finder (APF) telescope that will be used to search for extraterrestrial planets. Keck I’s flagship optical spectrograph, the High Resolution Spectrograph (HIRES), uses Galil controllers for precise velocity work in its search for extraterrestrial planets.
PEERING INTO THE DARKNESS
While the Lick Observatory sits atop the summit of 4200-ft Mt. Hamilton in the Diablo Range east of San Jose, CA, the W.M. Keck Observatory is positioned at the 14,000-ft summit of Mauna Kea, a dormant volcano on the Big Island of Hawaii. Its Keck I and Keck II are considered to be the world’s largest optical and near-infrared telescopes, each capable of collecting four times more light than the world-renowned Palomar 200-in. (5-m) telescope located in San Diego, CA.
Astronomers use multiple telescopes from several locations, including the Hubble Telescope, to survey and map the distant universe.
Photo courtesy of University of California Observatory.
Each of the Keck telescopes is equipped with a mirror 33 ft in diameter and composed of 36 hexagonal segments pieced together in a mosaic pattern. Keck I has been in operation since 1993 while the Keck II was commissioned in 1996.
According to a UCO data report, the beginnings of 8- to 10-m astronomical telescope development began at UCO/Lick, with the genesis of what eventually became the Keck telescopes. UCO/Lick faculty member Jerry Nelson designed the unique Keck mirrors, while UC Santa Cruz Professor Steve Vogt is credited for designing and building Keck I’s flagship optical spectrograph, the High Resolution Spectrograph (HIRES).
A second spectrograph at the Keck Observatory, the Eshelette Spectrograph and Imager (ESI), features Galil’s DMC-1500 motion controllers and was recently shipped and commissioned by the UCO/Lick team. DEIMOS, which also features the DMC-1500, represents the third and most advanced optical spectrograph built by UCO/Lick.
In addition to the three spectrographs, Alcott said that the UCO’s Atmospheric Dispersion Corrector (ADC) was built using a Galil DMC-2200 controller for the Keck I telescope. “This essentially helps to improve the differential refraction of the telescope as seen by the existing cassegrain instrument.”
A CLOSER LOOK AT HISTORY
Sandra Faber, a UCO astronomer, UOC professor and a founder of the Keck Observatory, said, “A great telescope like the Keck allows us to explore the River of Time back toward its source. Keck will allow us, like no other telescope in history, to view the evolving universe that gave us birth.”
In fact, UC Irvine scientists recently announced that with the aid of data obtained from the Keck telescope, they have discovered the minimum mass for galaxies in the universe: 10 million times the mass of the sun. “By knowing this minimum galaxy mass, we can better understand how dark matter behaves, which is essential to one day learning how our universe and life as we know it came to be,” said Louis Strigari, lead author of this study and a McCue Postdoctoral Fellow in the Department of Physics and Astronomy at UCI.