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A design study of a Cryogenic High Accurate Derotator.

A design study of a Cryogenic High Accurate Derotator.

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A design study of a Cryogenic High Accurate Derotator.

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  1. A design study of a Cryogenic High Accurate Derotator.

  2. A design study of a Cryogenic High Accurate Derotator. Assignment Perform a design study a derotator to prevent the smearing of the image with such a precision that an object falling on one pixel does not shift more then 1/5th (6.2μm) in one hour of observation time.

  3. Introduction (E-ELT,METIS) Problem definition Concept design Feasibility test Conclusion and remarks A design study of a Cryogenic High Accurate Derotator.

  4. A design study of a Cryogenic High Accurate Derotator. Introduction (E-ELT,METIS)

  5. A design study of a Cryogenic High Accurate Derotator. Introduction (E-ELT,METIS) • Mid-infrared E-ELT Imager and spectrograph • Imaging/spectroscopy in the mid infrared range (wavelengths of 2.9-14 µm) • Environment cryogenic and vacuum

  6. A design study of a Cryogenic High Accurate Derotator. Introduction (E-ELT,METIS) • Mid-infrared E-ELT Imager and spectrograph • Imaging/spectroscopy in the mid infrared range (wavelengths of 2.9-14 µm) • Environment cryogenic and vacuum

  7. A design study of a Cryogenic High Accurate Derotator. Why is derotationnecessary • The detector of the metis instrument needs and integration time of at least 15 minutes to get an high enough signal to noise ratio. • When not derotating smearing on the detector will occur, due to the rotation of the earth. • Because of the altitude azimuth configuration of the E-ELT the rotation can not be compensated by the telescope

  8. A design study of a Cryogenic High Accurate Derotator. Optical configuration

  9. A design study of a Cryogenic High Accurate Derotator. Influence of DOF • Mirror influences • 6 degrees of freedom for each mirror • Only 3 influence the science beam • Derotator • 6 degrees of freedom for the derotator • 4 influence the science beam

  10. A design study of a Cryogenic High Accurate Derotator. Influence of DOF • Mirror influences • 6 degrees of freedom for each mirror • Only 3 influence the science beam • Derotator • 6 degrees of freedom for the derotator • 4 influence the science beam

  11. A design study of a Cryogenic High Accurate Derotator. Influence of DOF • Derotator • Specific property when rotating around the specific rotation point • Red (1 degree) • Blue (2 degrees)

  12. A design study of a Cryogenic High Accurate Derotator. Concluding optical analysis • When defining the rotation point as shown in the previous slide the problem will reduce to a 3 DOF problem. • In the x-z plane the axis of the derotator needs to be directed to the rotation point (β) • The angle of the axis of the derotator in the z-y plane needs to be zero (α). • The rotation around the axis needs to be controlled to control the rate of derotation (γ)

  13. A design study of a Cryogenic High Accurate Derotator. Problem definition The end goal for the derotator is to prevent the smearing of the image with such a precision that an object falling on one pixel does not shift more then 1/5th (6.2μm) in one hour of observation time.

  14. A design study of a Cryogenic High Accurate Derotator. Requirements mirrors • Requirementsmirrors • Rotation: 2,6 arcsecond • Translation: 5 micrometer • Environmental aspects • Working temperature: 25-90 K • Working pressure 10-7-1 bar

  15. A design study of a Cryogenic High Accurate Derotator. Requirements Derotator • Requirements derotator • rotation αandβ: 2,6 arcseconds • rotationγ: 2 arcseconds • Maximum rotation speed: 7,5 degrees/hour • Minimum rotation speed: 0 degrees/hour • Setup speed: 90 degrees/minute • Needs to rotate in both directions • MTBF: 36500 hours • Maximum allowed weight: 30 Kg • Environmental aspects • Working temperature: 25-90 K • Working pressure 10-7-1 bar

  16. A design study of a Cryogenic High Accurate Derotator. Concept design Derotator

  17. A design study of a Cryogenic High Accurate Derotator. Concept design Derotator

  18. A design study of a Cryogenic High Accurate Derotator. Concept design Derotator

  19. A design study of a Cryogenic High Accurate Derotator. Feasibility test • Purpose of test setup • Test the feasibility of the used principles • Test the accuracy of the capacitive sensors • Kept as simple as possible • Modelled as a pendulum

  20. A design study of a Cryogenic High Accurate Derotator. Feasibility test Calculating PID values

  21. A design study of a Cryogenic High Accurate Derotator. Feasibility test • Closed loop bode plot • Phase margin in zero degrees up to 1 hertz

  22. A design study of a Cryogenic High Accurate Derotator. Feasibility test

  23. A design study of a Cryogenic High Accurate Derotator. Feasibility test

  24. A design study of a Cryogenic High Accurate Derotator. Test results Required accuracy: 2,6 arcseconds = 12 micro radians Signal that needs to be followed is of very low frequency • Applying a sinusoidal reference signal with: • Amplitude 400 micro radians • Frequency 0,02 Hz

  25. A design study of a Cryogenic High Accurate Derotator. Test results • Proven that an accuracy of 2,6 arcsecond is feasibly with a low disturbing frequency (up to 0.02 Hz) • This was done with relative simple building block (capacitive sensor; Voice coil actuator)

  26. A design study of a Cryogenic High Accurate Derotator. Conclusion and remarks • With optical analyses the 4 DOF system is reduced to a 2 DOF system • This 2 DOF can steer the science beam on the detector • Errors in the mirrors position can be compensated with the derotator reducing the requirements on the mirror • Relative easy to build a system with a 2,6 arcsecond angular accuracy at low frequencies

  27. A design study of a Cryogenic High Accurate Derotator. Conclusion and remarks • There is still some work that needs to be done • The test setup can be improved with a discrete controller such that error at higher frequencies is reduced • A trade of has to be made between the amount of heat dissipation and the required force to reduce error at higher frequencies • A thermal analyses of the system needs to be done

  28. A design study of a Cryogenic High Accurate Derotator. Questions