Control Lets Scientists See the Sun with New Eyes

The Advanced Technology Solar Telescope (ATST) project is expected to provide the sharpest views ever taken of the solar surface. Scientists expect toA learn how cosmic magnetic fields are generated and destroyed, as well as the mechanisms responsible for solar variability that eventually affects the Earth.

The Telescope’s optic support structure, which includes the mirror assemblies, is expected to weigh nearly 75 tons, the mount base nearly 90 tons, and the Coude rotator 160 tons. The 84-foot diameter enclosure will be thermally controlled, highly ventilated, and will be a co-rotating hybrid that has independent rotation when the telescope is positioned at zenith. The enclosure is where the controllers and much of the instrumentation will be located.

The instrumentation will incorporate more than 100 motion actuators at the beginning—that number will grow as instruments are added to the system. While each individual actuator will have minimal impact on the ATST Coudé environment by itself, all of the motion control hardware taken together will be a dominant factor in the generation of heat and EMI inside the telescope enclosure.

One critical area is maintaining multiple systems. If each area of control chose to use a different vendor for their motion controller, a tremendous burden would be placed on both the hardware and software maintenance personnel with respect to documentation, spare parts, periodic upgrades, maintenance of software code, and expertise in each of the systems.

The design solution had to use simple components and ensure the lowest cost and highest reliability without sacrificing performance. Other specs included an ease of removal, installation, servicing, alignment, and adjustment for the full 40-year life expectancy of the telescope. The controllers had to comply with NEC, minimize and offer immunity to EMI, comply with FCC reg Part 15 class B (class A for computer room), provide ESD immunity IEC 1000-4-2, and RFI immunity IEC 1000-4-3, IEC 1000-4-6, as well as provide power-line disturbance immunity per IEC 1000-4-9, IEC 1000-4-13.

Delta Tau was chosen because it offered a single controller capable of controlling many axes, unlike other vendors that were limited to 8-axis systems. The company’s Power PMAC Motion Controller provided the ATST team with a device that featured a real-time operating system, which allowed for the highest level of peripheral integration on the market, while maintaining the lower power consumption needed for the application.

The Power PMAC is equipped with a dedicated controller to make executing basic motion tasks easy, plus it incorporates a sophisticated general-purpose computer that permits the use of popular programming languages. In fact, the controller can be programmed in several languages simultaneously, including the Power PMAC’s built-in Script Language; general machine and I/O logic; industry standard graphical programming in any of five formats specified in IEC-61131 including ladder logic and sequential function charts; and in C for advanced programmers who wish to write servo, phase, PLC and general-purpose applications. Other languages accepted include G-Code, MatLabTM/Simulink, LabVIEWTM and EPICS.

Additional features of the Power PMAC include an 800 MHz and 1 GHz Risc processor with hardware floating-point engine; up to 4 Gbytes of error-correcting RAM; 100-Base-T and 1000-Base T Ethernet TCP/IP communications; standard interfaces to support keyboards, video cameras, disk drives, and other peripherals; built-in web server to support direct browser access for development and maintenance; the ability to control up to 256 motors or 128 coordinate systems simultaneously; and the ability to accept RS-274 G-code programs.

All in all, the chosen system was price competitive, capable, and offered the simplest Linux interface solution.