IFU Accelerated Life Test (Overview)

Ian Soukup

Center for Electromechanics

Hobby Eberly Telescope

One of the World’s largest optical telescopes• 9.2 meter Effective Aperture• 78 square meter Primary Mirror

Tracking is achieved by moving the tracker instrument package instead of moving the entire telescope

HET Upgrade for VIRUS (HETDEX)

The immense light-gathering capability of HET will allow HETDEX to build the largest map of the universe ever produced.

• Up to 192 spectrographs (VIRUS)

• As many as 43,008 optical fibers with a 21 meter average length

VIRUS

IFU Bundle

Strain Relief 2 (SR2)

Strain Relief 1 (SR1)

Focal Surface

Strain Relief 3 (SR3)

Fiber Segment MCP Beginning MCP End Behavior Length (m)1 Focal Surface Strain Relief 1 Static < 12 Strain Relief 1 Strain Relief 2 Dynamic 73 Strain Relief 2 Strain Relief 3 Dynamic 94 Strain Relief 3 VIRUS Cabinets Static 4

Fiber System Layout and Mechanical Coupling

Design Concerns

• Optical performance of the fibers is unknown after repeated cycles of extending, contracting and flexing

• Fiber quality and optical performance are dictated by:

– Transmission• Ratio of light exiting to light entering

– Focal Ratio Degradation (FRD) • Gradual decline in the F-ratio as light

passes from input end to output end (scattering of light at exit)

• Factors that lead to FRD– Specific to User Control

• Mechanical Deformation (Macro / Micro Bending)

• Localized stresses or stress points– Specific to Manufacture Control

• Random Irregularities• Fiber End Preparation• Materials

Figure: Far field images of the input and output spots. FRD has scattered the light both outwards and into the central obscuration (output spot -right)

• Size and complexity of the fiber system for HETDEX is much greater than previous fiber systems deployed

Accelerated Life Test

• Test Objective:– Provide a life cycle test simulating the HETDEX fiber system behavior, while continuously measuring relative

changes in the output focal ratio of individual fibers over the duration of the test

• Design Constraints:

• Design Concepts – (1) Rotary Fiber Tester (2) Cart / Cable Fiber Tester (3) Hexapod Fiber Test Apparatus

Item Constraint Driver Constraint Description

1 Deploy HETDEX strain reliefs at their proposed relative spatial orientation Defines Routing (Volume)

2 Operate Test within Task B Defines Volume

3 Replicate full range of telescope fiber movement between Strain Relief 1 & 2 Defines Motion (Volume)

4 Restrain 48 IFU Conduits Defines Force

5 Perform 5 year projected life cycle test within 2 to 3 months Defines Rate

6 Provide space for optical testing instruments 200 mm X 200 mm X 700 mm optical test bench at input and exit

7 Provide test bed for hexapod control system Defines Parallel Kinematics

Concept 1

Concept 2

Concept 3

Design Parameters

• Hexapod Travel: – Calculated using geometric constraints imposed by HETDEX Tracker Design– Explicitly replicates the fiber system movement of segment 2 throughout its operational limits

• Z = Max: 116.33 mm Min: 0 mm• X/Y = Max: 391.99 mm Min: -391.99 mm

• Actuator Travel:– Determined by positioning the SolidWorks model at over 1500 discrete locations within its

travel range and measuring the displacement of individual components• Actuator Travel: 496.08 mm• Upper U-Joint Misalignment: 44 degrees

ρ

Z

X

Yθy

θx

• θx/θy = Max: 9 deg Min: -9 deg• ρ = Max: 21 deg Min: -21 deg

• Upper U-Joint Rotation: 11 degrees• Lower U-Joint Misalignment: 31 degrees

Design Parameters

• Actuator Speed:– 21.9 mm/s Calculated at Tracker Slew Speed w/ Rho– Test Duration for 5 year life cycle representation at 21.9

mm/s • 360 hrs (15 – 24 hr days)

• Actuator Force: (worse case travel condition with fully weighted IFUs)

– 10.4 kN – Calculated using SolidWorks Simulation

• End Joint Design– 2 DOF and 3 DOF joints are required between the actuators and end plates – Custom designed end joints were needed to handle the large misalignment and axial loads

Optical Bench Axis

• Designed to move the fiber test bundle so that it approximates the dynamic behavior exhibited by fiber segment 3 of the HETDEX fiber system.

• Optical Bench Components:– Custom Wire Rope Drum– AKM-53G servo drive motor w/ Nema True Gear Box– Drum Mount Platform (Stationary)– Linear Bearing Platform (Stationary)– Optics Platform

1.2 m

IFU Hexapod

Conduit Routing to Strain Relief 2

IFU Test Strain Relief 2

Lower Axis

Fig. 9

IFU Test Strain Relief 1

Fig. 2