CLIC main beam quadrupole alignment using cam movers alignment using cam movers Juha Kemppinen...

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Transcript of CLIC main beam quadrupole alignment using cam movers alignment using cam movers Juha Kemppinen...

  • CLIC main beam quadrupole alignment using cam movers

    Juha Kemppinen

    23.01.2018

  • CLIC CDR (2012)

    MBQ pre-alignment requirement

    • Magnetic centres of MBQs situated on any 200 m section of the linacs shall be within a cylinder with a radius of 17 µm in 1 σ

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    • Tolerance for a single MBQ misalignment is: • x- and y-offsets at both ends of the MBQ: +/- 1 µm • Roll: 100 µrad (table 2.13 of CLIC CDR)

    http://cds.cern.ch/record/1500095?ln=en

  • MBQ stabilisation and adjustment

    • 5 DOF adjustment system takes care of the alignment

    • To reach CLIC luminosity requirement, the MBQ needs to be stabilised to within • 1.5 nm in vertical and 5 nm in horizontal

    • The piezo stabilisation stage imposes a stiffness requirement to the alignment stage • First eigenfrequency > 100 Hz

    • In CDR and this presentation, a system based on eccentric cam movers is proposed for the 5 DOF adjustment system

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    5 DOF adjustment system

    Stabilisation and nano- positioning

    MBQ

  • Cam mover

    Single cam and follower 5 DOF system

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    6 DOF possible with an additional cam and re- organisation of interfaces

  • Test setup

    • Wire Positioning Sensors (WPS) are mounted on ceramic balls through kinematic couplings (conical – flat – conical chamfer) • Sub-micron repeatability

    • 8 offsets (WPS 1 – 4) are used to calculate relative orientation in 5 DOF

    • 16 offsets and a laser tracker are used to calculate module absolute position

    Performance

    Resolution 0.1 µm

    Linearity 1 µm/mm (1 σ)

    5 DOF relative 3 µm (1 σ)

    5 DOF absolute 5 µm (1 σ)

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    See presentation of Anna Zemanek! (case two wires with cWPS)

  • Positioning performance

    • Type 4 cam movers were able to position the mock-up chassis within 1 µm (in relative) with iterative process already in 2012

    • Z. Kostka created a positioning algorithm with which the MBQ can be positioned within 1 µm in absolute (assuming the feedback is ideal) in one movement

    • The positioning algorithm calculates part of the whole trajectory before movement and updates the trajectory during motion • The trajectory points are calculated using

    a kinematic model and corrected based on WPS feedback

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  • Stiffness • Previous prototypes concentrated on the positioning accuracy (movement resolution)

    • Especially type 1 cam movers are difficult to make stiff (lack of space)

    • New prototype is being manufactured to tackle the problem

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  • Stiffness

    • Bearing around the eccentric part removed

    • Shaft is thicker

    • Back-to-back configuration of tapered roller bearings (radial and axial stiffness) on one side of the eccenter and radial roller bearing (radial stiffness) on the other.

    • Rotational stiffness from a worm gear through a belt drive

    • Crowned eccenter in order to ensure Hertzian contact with relatively large contact area

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  • Stiffness

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    • The eigenfrequencies and corresponding modes of the MBQ depend on:

    1. Structure of the MBQ and the stabilisation system 2. Structure of the cam movers 3. Interface between ground and cam movers 4. 5 Hertzian contacts between the cam movers and the followers

    • The Hertzian contact stiffness depends on: • Geometries • Materials • Contact force • Coefficient of friction (tangential stiffness)

    • Adding contact force increases the stiffness…

    • … but increases the friction force, which deteriorates movement resolution • Especially “stick-slip”

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  • Stiffness – resolution trade-off

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    • It is very hard if not impossible to formulate the stiffness – resolution trade-off only theoretically

    • The new type 1 prototype will serve as an experimental setup • Possibility to adjust the pre-load between 1 and 4 times

    the weight of the MBQ and the stabilisation system by adding or removing springs (mid-travel)

    • The test plan is: • To perform experimental modal analysis with 3 different

    pre-load configurations • Test movement resolution and positioning accuracy with

    the same configurations

    • It would be interesting to compare the EMA results to PACMAN results where there is no alignment stage

  • Expectations and threats

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    • Movement resolution gets lower as pre-load gets higher, but • As long as there is enough torque, accurate

    positioning can still be possible with longer movements (static vs. kinetic friction)

    • The 100 Hz goal seems impossible to achieve with type 1 • But maybe it’s possible to adapt to it if the first

    eigenfrequency is sufficiently close to 100 Hz and its mode is known

    • By combining the tests and FEM, it should be possible to estimate how the 100 Hz goal could be achieved

  • Thank you!