PISCO Atmospheric Dispersion Compensator

1. PISCO Atmospheric Dispersion Compensator Will High Harvard University December 2006

2. An ADC for PISCO • ADC placeholder in blue below • After shutter (green below) • Before collimator • Mounted on PISCO’s optical bench

3. An ADC for PISCO r i D3 g z D1 D2 ADC placeholder

4. An ADC for PISCO r i D3 g z D1 D2 ADC placeholder

5. Our ADC from the Ground Up

6. 2 Prisms 18 mm apart 130 mm diam 18 mm thick

7. Stainless Steel Housings Gear teeth + 360˚ groove for timing belt Another 180˚ groove for zero-pointing with microswitches Lip: precision machined chamfer with semi-circular cross section

8. Stepper-Driven Non-slip Timing Belts • McMaster: • Non-slip, double sided timing belts (teeth + groove) • 2 specialty pulleys • Oriental Motor steppers • Custom axles and stepper mounting flanges

9. Stepper-Driven Non-slip Timing Belts 180˚ groove (zero-pointing) Teeth + 360˚ groove (timing belt)

10. 2 Microswitches to Mark Zero-point

11. 2 Microswitches to Mark Zeropoint 180˚ groove (zero-pointing) Teeth + 360˚ groove (timing belt)

12. 3 V-groove Track Rollers per Prism

13. 3 V-groove Track Rollers per Prism

14. Aluminum Case

15. Aluminum Case

16. Purely Rectangular Profile Beam toward you Beam away from you

17. Zero-pointing • McMaster-Carr Long Roller Lever Snap-Acting Switches • 2 x $8.50 • 0.95" x 1.94" x 0.69“ • Max ratings: • 15 Amps • 250 Volts AC/DC (Screw terminals) • 186 Watts • 3 terminals (SPDT) • “Rising edge” means zero, “falling edge” can mean anti-zero if machined precisely

18. Rollers • McMaster-Carr Adjustable-Height Perma-Lube V-Groove-Guided Track Rollers • 6 x $62.93 • 1/32" adjustable height play • Ball bearings • Permanently lubricated and sealed = maintenance free • 90˚ groove • Smallest available: • About 1 2/3” long • 1 ½” roller diameter

19. Timing Belts • McMaster-Carr Double-Sided Flexi-Timing Belts and Pulleys • 2 x $29.66 (belts) + 2 x $23.56 (pulleys) • Single stranded (one groove) • 0.20" wide • 24” outer circumfrence belts • 1 ½” diam pulleys • Anodized aluminum pulleys

20. Steppers • Oriental Motor 5-Phase Microsteppers (CRK513PAP) • 2 x $367, in stock • 0.72˚ Basic Step • 24 Volts, ~1/4 Amp • < 80˚ C operating temperature... BUT: • We don’t need high speeds nor long run times • Can turn off current if we install friction devices on prism housing • “High torque motor current is reduced to suppress heat generation. Eg, to avoid temperature rise in precision machinery.” I think this means a lower current gives the same torque as the standard model • We make the flanges • Want to use the same focus stepper drivers • 5 pins per stepper Stock Driver

21. Wiring • Goal: single cable • Wires 3 x 2 microswitches + 5 x 2 steppers = 16 wires • Run wires along inside case surfaces to single D connector • ADC cable runs to on-board PISCO driver rack (water cooled) • Drivers controlled downstairs Single D Connector

22. Summary • About 18 lbs • 4 ½” deep x 11” wide x 10” tall • Goals • Single cable from ADC to driver rack • Use focus stepper driver instead of stock • Minimize stepper heat dissipation by switching off current and using simple friction devices • Heat dissipation by ADC negligible • Assumed by drivers • Driver rack water cooled • To do • Mounting holes • Internal wire guides • Microswitch mounts • Alignment (tolerances)