1. Oct 17, 2001SALT PFIS Preliminary Design Review Control System 1 Southern African Large Telescope Prime Focus Imaging Spectrograph Preliminary Control System Design Jeffrey W Percival University of Wisconsin - Madison

2. Oct 17, 2001SALT PFIS Preliminary Design Review Control System 2 PFIS Block Diagram

3. Oct 17, 2001SALT PFIS Preliminary Design Review Control System 3 Mechanical Requirements 9 unique mechanisms Collimator (shared by both beams) –Slit masks –Wave plates Cameras (Visible & IR) –Focus –Shutter (Visible beam only) –Etalons (2) –Gratings –Polarizing Beam Splitter –Filters –Camera Articulation

4. Oct 17, 2001SALT PFIS Preliminary Design Review Control System 4 Mechanical Requirements No servoed axes No “real time” needs Shutter is operated by detector subsystem Simple motions: In/Out Rotate Linear Single-axis Steppers & Pneumatics Low duty cycles COTS controllers and drivers

5. Oct 17, 2001SALT PFIS Preliminary Design Review Control System 5 Mechanical Requirements Actuators –Stepper motors: 4 + 7 (Visible) + 7 (IR) = 18 –Pneumatic Cylinders: 3 + 6 (Visible) + 5 (IR) = 14 Encoders –Position: 2 + 4 (Visible) + 4 (IR) = 10 –Angle: 2 + 3 (Visible) + 3 (IR) = 8 Index Marks: 4 + 7 (Visible) + 7 (IR) = 18 Limit Switches: 2 * (5 + 13 (Visible) + 12(IR)) = 60

6. Oct 17, 2001SALT PFIS Preliminary Design Review Control System 6 Mechanism Interlocks Mechanisms have interdependencies and restrictions. Interlock Manager will enforce correct control Hardware interlocks will backstop software

7. Oct 17, 2001SALT PFIS Preliminary Design Review Control System 7 Control System Implementation Control System Experience Hubble Space Telescope High Speed Photometer flight software WIYN 3.5m Control System: GUI, Astrometric kernel, PID loops Sounding Rocket Star Tracker control program HPOL Spectropolarimeter: motors, wave plates, WIYN TCS interface Guiding Principles Commercial-Off-The-Shelf (COTS) SALT-compatible (OS, Language, hardware, documentation) Buy, not build: PCs: high performance, low cost Linux or Windows LabVIEW Software environment National Instruments PCI-based products

8. Oct 17, 2001SALT PFIS Preliminary Design Review Control System 8 Control System Block Diagram Modular Low-level modules control actuators Mid-level modules combine actuators into mechanisms High-level modules apply constraints and manage configuration Simulation built in at lowest level; allows higher levels to be prototyped and used early High degree of common functionality will speed development

9. Oct 17, 2001SALT PFIS Preliminary Design Review Control System 9 Control System Software Modular, use LabVIEW Virtual Instrument (VI) modules in a hierarchical model Simulation modes built in at actuator level LabVIEW interface to Telescope Control System LabVIEW interface to Detector Control System LabVIEW VI for Etalon controllers delivered as part of Rutgers Etalon subsystem Emphasize parallelism: Drive down reconfiguration time by operating mechanisms in parallel wherever possible

10. Oct 17, 2001SALT PFIS Preliminary Design Review Control System 10 Failure Modes Overall strategy: No single-point failure modes Software is 1st line of defense –Check for inconsistent state of sensors –Monitor encoders during motion, check for expected direction and speed Hardware interlocks are next –Soft limits for software –Hard limits remove power, enforce direction Hard stops for critical components –Sacrifice gears and motors to protect optical elements

11. Oct 17, 2001SALT PFIS Preliminary Design Review Control System 11 Control System Interfaces PFIS interfaces –Etalons: this interface will disappear as the etalon assemblies are integrated into PFIS. –Detector and controller: mechanical, electrical, cryogenic, control, and data interfaces –Telescope: operations interface, bi-directional flow of commands and data

12. Oct 17, 2001SALT PFIS Preliminary Design Review Control System 12 Observatory-level Control Queue-efficient observing requires careful design –Automated observing, driven by scripts –Operator can not be expected to micromanage PFIS –Instrument-centered: PFIS is not hanging off the telescope; rather, the telescope is hanging off PFIS –The top-level interface in SALT is the silicon surface of the CCD; everything else is a subsystem –PFIS reaches out for services, which are provided quickly, deterministically, and in a closed loop –Telescope and Detector interfaces are critical: during slit mask peakup, the move/expose/centroid loop must be fast and dependable