Cyrostat Design -Camera Section Justin Holwell

Transcription

1 Cyrostat Design -Camera Section Justin Holwell July 6 th, 2004 JLH 1

2 Camera Dewar 3D Layout JLH 2

3 Camera Dewar X-Section JLH 3

4 Camera Components Lens Mounts 12 Lens Cells and 2 Mounts Grism Assembly 2 Filter Wheels Fixed Lyot Stop Grim Wheel Detector Assembly Thermal System LN2 Reservoir,Fill and Vent Lines Measurement System Vacuum System Components Vessel with Blanked-off Pumping Port Isolation Valve Pressure Sensor Cold Finger JLH 4

5 Camera Section General Specifications Must operate at pressures between 1 Atm and 10-8 Torr Must operate at temperatures between 300K and 80K Use vacuum compatible materials and with consideration given to temperature effects JLH 5

6 Grism Assembly Specifications Common mounting plane for optics within ± 250 microns along the focal direction; perpendicular to optical beam within 1 arc-min Wheel repeatability: TBD arc-sec Wheel stability: TBD arc-sec (one full instrument rotation) Motor torque margin: 2.5 times worst case Move time (180 ): 10 seconds with a goal of 5 seconds Detent Offset: < 1 arc-min optic centerline to detent centerline JLH 6

7 Grism Assembly Two Filter Wheels six positions each (one open) Grism Wheel six positions (one open) Fixed Lyot Stop 303 SST shaft fixed to support plate SST angular contact ball bearings Shaft preload set by belleville washer All Wheels worm driven on outside edge and positioned using detents JLH 7

8 Filter Mounts Heritage from FLAMINGOS-2 Filter mount larger than filter to accommodate thermal contraction Teflon washers instead of lead due to vacuum environment Spring loaded clamp Wheel next to primary stop accepts additional stops mounted at each filter location for the K and H + K bands JLH 8

9 Grism Mounts 3-Point spring loaded radial mount Teflon washers Spring loaded clamp Spring fingers provide conductive cooling Flat on grism for angular orientation Empty slot will have balancing weight added JLH 9

10 Lyot Stop Fixed stop mounted to wheel support plate Position is adjusted during setup and then fixed JLH 10

11 Grism/Filter Wheel Worm Drives Cryo/Vacuum rated Phytron VSS 52 stepper motor w/ 8:1 planetary gearhead Worm ratio: 63:1 (252 Teeth / 4 starts) Max motor speed: 3000 rpm Max wheel speed: 5.95 rpm Min move time (180 ): 5.8 sec Torque required: 4.7 in-oz Torque available: 15.9 in-oz JLH 11

12 Detent Mechanism Wheel position set by detent; not held by drive Spring loaded arms w/ cam follower Detent provides registration Detent detected by microswitch JLH 12

13 Wheel Index Index Home position coincides with open aperture Ramp on wheel detected by microswitch JLH 13

14 Vacuum Isolation Valve Isolates MOS & Camera sections Custom gate valve designed by VAT Entirely internal to vacuum tank to reduce penetrations Stepper motor driven with 6:1 gear-head 3/8 Ball screw Worm gear reduction 20:1; nonbackdrivable Includes position and interlock switches Move time: 2 minutes Low emissivity coating on surface facing lens 3 JLH 14

15 IR Array Assembly Specifications IR Array must be centered on optical axis within 0.1 mm; perpendicular to entrance slit within 5 arc-sec Temperature change rate: < 0.5 K/min Focus Travel: ± 2.5 mm Focus position resolution: 5 microns JLH 15

16 IR Array Drive Array Mounted on translation stage similar to FLAMINGOS-2 design Stage driven by linear cam Stage uses sapphire balls for thermal connection to optical bench LVDT sensor used for position sensing, resolution approx 10 µm Resolution: 3.4µm/step; ~10 steps within depth of focus JLH 16

17 Array Mount Uses mounting and thermal attachment from FLAMINGOS-2 Gusseted L-bracket Baffling surrounds detector Pinned in position on optical bench JLH 17

18 Thermal Design Optical Bench Welded aluminum dewar clamps to aluminum support plate Capacity: 109 liters max. Top plate forms bench to mount optics Bench forward mount provides stiffness JLH 18

19 Thermal Design - Radiation Shields Two aluminum shields surround lens #3 Two aluminum shields w/ rear access covers surround optical bench Shields have low emissivity JLH 19

20 Camera Support Mount Tube assembly mounts between bulkhead and camera support plate Composite tube provides thermal isolation Assembly is light-tight Heritage design from FLAMINGOS-2 JLH 20

21 Vacuum Housing 304L SST vacuum housing and bulkhead Bulkhead is main support for entire Cryostat Housing and bulkhead seal with Viton o-ring Preamps mount to rear of vacuum vessel JLH 21