PISCO Atmospheric Dispersion Compensator

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PISCO Atmospheric Dispersion Compensator

• Will High
• Harvard University
• December 2006

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An ADC for PISCO

• ADC placeholder in blue below
• After shutter (green below)
• Before collimator
• Mounted on PISCOs optical bench

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An ADC for PISCO
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i
D3
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z
D1
D2
ADC placeholder
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An ADC for PISCO
r
i
D3
g
z
D1
D2
ADC placeholder
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Our ADC from the Ground Up
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2 Prisms

• 18 mm apart
• 130 mm diam
• 18 mm thick

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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

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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

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Stepper-Driven Non-slip Timing Belts
180 groove (zero-pointing)
Teeth 360 groove (timing belt)
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2 Microswitches to Mark Zero-point
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2 Microswitches to Mark Zeropoint
180 groove (zero-pointing)
Teeth 360 groove (timing belt)
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3 V-groove Track Rollers per Prism
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3 V-groove Track Rollers per Prism
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Aluminum Case
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Aluminum Case
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Purely Rectangular Profile
Beam toward you
Beam away from you
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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

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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

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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

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Steppers

• Oriental Motor 5-Phase Microsteppers (CRK513PAP)
• 2 x 367, in stock
• 0.72 Basic Step
• 24 Volts, 1/4 Amp
• lt 80 C operating temperature... BUT
• We dont 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
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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
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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)