cern wp… · web viewweplate. wp8 6dof alignment platform. m. lino dos santos, s. evrard, j....

CERN-ACC-NOTE-2019- 1566898630_258012019-08-20

[email protected]

WEPLATEWP8 6DOF ALIGNMENT PLATFORM

M. Lino dos Santos, S. Evrard, J. Fuchs, J. Labarthe-Vacquier, F. Sanchez Galan, A. VieilleCERN, Genève, Switzerland

Keywords: CERN LHC-LS2, FP7 HiLumi LHC

Abstract

In the context of the LHC (Large Hadron Collider) upgrade at CERN (European Organization for Nuclear Research) known as HL-LHC (High Luminosity LHC) which will increase the LHC luminosity (rate of collisions) by a factor of five beyond the original design value and the integrated luminosity (total collisions created) by a factor ten, WP8 (Work Package 8) proposed a new alignment platform concept for the alignment of TANB (Target Absorber Neutrals) being installed in LS2 (Long Shutdown 2) at Point 8. The increase of luminosity expected at Point 8 will create a shower of secondary forward particles, namely of neutrals (mostly neutrons and photons) and charged particles (mostly pions and protons), that will leave the interaction point 8 in both directions towards the machine creating a non-negligible energy deposition in the region. TANB main function will be as a protective absorber for the dipole D2. This continuous deposition during HL-LHC Run 3 and Run 4 will activate the TANB rendering any human activity in the region conditioned to very strict and short timed periods. Among this activities alignment is placed as one of the most time consuming and one that obliges a closer proximity with the TANB absorber mainly due to the current design of the “standard” CERN alignment platforms. Inserted in the ALARA (As Low As Reasonably Achievable) approach the new alignment platform presented takes the design of the “standard” CERN alignment platform and through simple modifications moves the actuators for each degree of freedom to the foreseen intervention side facilitating its access, improving the ergonomics of the alignment operations and principally decreasing the alignment operation time for the equipment mitigating the exposure of the professionals to the activated area.

This is an internal CERN publication and does not necessarily reflect the views of the CERN management.

Contents

1 INTRODUCTION............................................................................................................................1

2 ALIGNMENT REQUIREMENTS..................................................................................................1

3 DEVELOPMENT.............................................................................................................................2

3.1 Kinematics................................................................................................................................3

3.2 Mechanical Design...................................................................................................................6

3.2.1 Actuators design...............................................................................................................6

3.2.2 Main plates.....................................................................................................................12

3.2.3 Locking mechanism design............................................................................................13

3.3 Stability Analysis....................................................................................................................14

3.4 Operation................................................................................................................................15

4 TESTS............................................................................................................................................18

4.1 Set Up.....................................................................................................................................18

4.2 Mechanical Reliability............................................................................................................19

4.3 Stability...................................................................................................................................20

4.4 Range......................................................................................................................................21

4.5 Precision.................................................................................................................................21

5 FUTURE DEVELOPMENTS........................................................................................................21

6 CONCLUSION..............................................................................................................................23

7 REFERENCES...............................................................................................................................23

Internal Note CERN-ACC-NOTE-2019-xxx

1 INTRODUCTIONThe High Luminosity LHC [1] project is a major upgrade being undertaken to the LHC in the 2020’s at CERN being in line with the highest priority of the European Strategy for Particle Physics: the full capacity exploitation of the LHC particle accelerator. This upgrade will increase the LHC luminosity or collision rate by a factor of five and integrated luminosity by a factor of ten beyond its design values after 2026. It will require remarkable technological advancements to be successfully achieved, bringing together the efforts and R&D from all over the world. Among the challenges foreseen, the protection of the many delicate components of the machine and even more important, of the people operating and maintaining the machine from the induced background is placed as one of the main priorities. This will be evaluated by Radio Protection (RP) experts and experts from the experiments and, when required, mitigation solutions are to be developed like the correct choice of materials, special tooling and optimized procedures for maintenance and repair actions.

Inserted in WP8 scope the TANB neutral absorber [2] is one equipment developed for the protection of the D2 dipoles on either side of the Interaction Point 8 (IP8) [3] [4]. This point hosts the LHCb experiment which is one of the four major physics detectors installed in the LHC. For the HL-LHC this experiment will see an increase of peak luminosity to 2×10³³ [cmˉ²sˉ¹], meaning that the number of collisions will increase by almost a factor of 10 and as consequence the number of secondary particles resulting from the increased interactions. This particles can potentially damage the sensitive components on the forward regions of the interaction point (like the D2) and, for this reason, an added level of protection is needed. The TANB is the response that will prevent the D2 dipoles from quenching by absorbing this secondary particles before they can be deposited in the D2 superconductive coils.

Using the ALARA approach a new alignment plate was proposed and developed for aligning the TANB. As one of the mitigating solutions of exposure during operations, being actively reinforced during the conception, design and operation of the HL-LHC, the CERN ALARA (As Low As Reasonably Achievable) approach has as main objective to minimize the exposure of CERN personnel and contractors to ionizing radiation. The approach concerns with all aspects and phases of the project, from conception to operation, ensuring that a safer operation and maintenance is carried thorough the full HL-LHC era. The named WEPLATE was developed for minimizing the intervention time and proximity with the activated TANB during the survey and alignment operations. By modifying the current “standard” solution used at CERN the WEPLATE places all the actuators for all the 6DOF on the same side improving the access and the ergonomics of the operation. This note aims to describe the R&D process, tests and results that ultimately lead to the successful validation and implementation of the WEPLATE.

2 ALIGNMENT REQUIREMENTSThe WEPLATE was developed for the TANB absorber, however as it is installed in the HL-LHC and no particular requirements are needed to align it (the TANB), the WEPLATE was designed for the HL-LHC baseline requirements for survey and alignment, defined and based on each HL-LHC working groups (vacuum, collimators, beam monitors, etc.) requirements. The service load of the WEPLATE on the other hand was specifically defined for the TANB, which amounts to 600kg. The baseline requirement for the alignment of manual/semi manual platforms in the HL-LHC are listed in the Tab. 1 [5]. Additional requirements from the ones listed on the Tab. 1 were requested by the WEPLATE users justified with the improvement of the ergonomics for the alignment making it more user friendly, maintenance and reliability in the activated regions (Table 2).

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Internal Note CERN-ACC-NOTE-year-xxx

Table 1: HL-LHC Baseline requirements for manual/semi-manual alignment platform

MANUAL/SEMI-MANUAL ALIGNMENT PLATFORMS REQUIREMENTSAccess to Actuators From the transport sideKinematics Simple and intuitive (independent axis moments)Plug in Motors yes, if the doses are importantDegrees of Freedom (DOF) 6Stroke ± 10 mmResolution < 20 µmBacklash < 50 µm

Table 2: WEPLATE Additional requirements

WEPLATE ADDITIONAL REQUIREMENTSLocking mechanism For each degree of freedomRadiation Compliant Yes (careful choice of materials)Lubrication NoUser friendly characteristics Same size for actuators (one key for all operations) Identification of the movement direction Identification of actuators to the respective DOF

3 DEVELOPMENTThe development of the WEPLATE started at the end of 2016 and 2 years were necessary to bring its design to conclusion. The conceptual idea of the WEPLATE was not to recreate the alignment plate but instead to modify the proven “standard” alignment plate used at CERN for almost every alignment operation. This approach preserved the successful alignment methodology used at CERN now for decades, guaranteeing that the basic kinematics would stay the same, facilitating the transition to the new alignment equipment and avoiding the need for dedicated training or formation to operate the equipment. In fact the ergonomics and the focus on the user friendly characteristics was one of the priorities of the WEPLATE development. The modifications, after development, allowed to move all the actuators that control the 6DOF to one of the sides but it did so without changing their actuating interfaces on the equipment to be aligned, Figure1.

Fig. 1: Actuator position and function, coloured and legended. “Standard” CERN Alignment Plate, on the left, compared with the WEPLATE, on the right.

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3.1 Kinematics

The WEPLATE kinematics were developed based on the kinematics of the “standard” CERN alignment plate and the HL-LHC baseline requirements both converging in the following base points:

All actuators are on one side of the alignment platform The alignment platform allows 6 degrees of freedom Each degree of freedom operates independently from the next Each degree of freedom must be fully locked after the alignment operation Simple and intuitive mechanics No lubrication is allowed No backlash <50μm

All this points are verified in the “standard” CERN alignment plate except the one fundamental for the ALARA approach, the 1st point. And this point was the development focus for the WEPLATE. To achieve it successfully, without compromising any of the following, once they are strongly correlated, no modifications were made to the basic kinematic structure of the “standard” CERN alignment plate. Instead 3 different actuators were developed with the objective of converting the rotation of each bolt into a translation using the least number of components possible and without using any lubrication. These actuators allow the movement to be propagated in 90 or 180 degrees angles, from one of the sides of the plate to the actuating interface Fig. 2.

Fig. 2: Actuators basic kinematics. Each one of the actuators schematized on the right is installed in the WEPLATE as indicated in Fig. 1.

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Each of the 3 actuators represented in Fig. 2 is composed of 3 or less components (bearings not represented). This simple structure is the result of several iterations with the aim of improving the reliability of the WEPLATE and the mitigation of parasitic movements and backlash due to the interplay of each component and manufacturing tolerances.

For the Z and Y movements the actuators are based on a wedge mechanism to convert the rotation of the bolt into a translation of the actuator. The wedge mechanism was chosen due to its simplicity, compact size and for the application, it can be engineered to be lubricant free if the relevant parameters are well balanced (forces, materials, geometry, etc.). Also it comes with two main advantages: the possibility of adapting the actuator to several loads and displacement ranges by changing the wedge angle and the inherent movement reduction factor which improves the precision that can be achieved in the alignment operation Fig. 3.

The X axis actuator is composed of 2 parts: one bolt, and one L shaped bar, the actuator. The bolt rotates inside the threaded L bar converting the rotation into translation which is redirected to the tip of the L profile and in its turn to the object to be aligned. Its sturdy construction avoids any deformation of the L bar or bolt on contact and ensures its smooth and reliable operation Fig. 4.

Fig. 3: WEPLATE Z and Y on left and right actuators kinematics based on the wedge mechanism.

Fig. 4: WEPLATE X actuator kinematics based on a bolted connection.

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Fig. 5: WEPLATE kinematics examples. a) Radial; b) Beam; c) Vertical; d) Roll. The actuators responsible for each set of movements are indicated with red arrows.

Fig. 6: WEPLATE Full displacement range volumes for a given Centre of Mass (CM) belonging to the equipment to be aligned (all measurement in mm).

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The actuators basic structures represented in Figs. 2, 3 and 4 are repeated in the WEPLATE: 2 x Z actuator for the positioning respect to the beam, 3 x Y actuator for the vertical and tilt angles, and 2 x X actuator with 2 extra bolts (also actuators) allowing the full radial and roll displacements. Together these actuators fully control each one of the 6 degrees of freedom. Using each one of these actuator sets the equipment can be aligned on all 6 DOF independently and without parasitic movements once each movement it’s isolated from the next. Several examples of these movements can be identified in the Fig. 5 with the respective responsible actuators for the movement identified by red arrows. Each DOF (Figure 5) can be combined to allow a full displacement range for the equipment, represented and limited, by the volumes given in the Fig. 6.

3.2 Mechanical Design

After the basic kinematics of the WEPLATE defined, the full mechanical design followed with the optimization of the actuators encasing plates considering the expected operational loads. Also a careful choice of materials was carried to eliminate the need for lubrication. The mechanical design was developed founded in the following three points:

Compact design - Often the envelope available for the equipments to be installed in the beam-lines is very limited rendering the compactness of each one of the parts composing the equipment fundamental. Currently the available solution for the alignment used at CERN has a fairly small footprint in the overall assembly of each equipment. This is especially true in thickness. The proposed WEPLATE must thus not be thicker than the aforementioned plate and possess roughly the same footprint.

Reliability - Simple design and no lubrication. Less components used to move each DOF, less is the chance of system fail. Also the less components used the less are the tolerance errors from manufacturing avoiding among other issues backlash. On this basis the design of the WEPLATE has to be as simple as possible. Also and no less important simplicity brings to the project economic benefices.The region on which the WEPLATE is to be deployed is notably activated due to the ionising radiation from the secondary particles deriving from the collisions in P8, and a lubricated mechanism is then not an option for the WEPLATE once lubricants tend to degrade over time when exposed to radiation to a point where they are actually more prejudicial to the movement than beneficial. On this fact the reliability of the WEPLATE depends on the development of non-lubricated kinematics.

Service Load - The service load was defined by the equipment to which the WEPLATE was in the first place developed for, the TANB. In this sense an initial design load of 500kg (+safety factor) was used. The service load will define the thickness of each plate and geometry of each actuator.

3.2.1 Actuators design

The mechanical dimensioning of the actuators according to the expected operational load was evaluated. For the purpose a set of FEA and analysis by formula was performed. The optimization of each actuator was an extensive process and thus will not be presented in detail. Only the final results are presented:

The force to be applied to the tool (wrench, refer to Figs. 7, 8 and 9) for moving the object to be aligned was determined according to the following equations:

The equation that describes the Lifting Force (FLift) for the Y and Z actuators is the following:

6


FLift=(dm

2 ) ( F0 )

LTool(1)

With:dm - Average Ø of the boltF0 - Force generated by the boltLTool - Length of the tool arm

The force generated by the bolt can be calculated as following:

F0=F × ¿

With:

N1=P

cos α−μe1

μe 1 - Static coef. of friction 1μe 2 - Static coef. of friction 2P - Weight of the equipment to be aligned (design load) for the Z actuator P z=μe 1 Pα - Angle of the wedge

When we replace the respective terms in the equation 1 by the equation 2 and 3 we have the basic equation for the Lift Force for the Y and Z actuators which is dependent mainly of the weight of the equipment to be lifted the angle of the wedge slope the diameter of the actuator bolt and the coefficients of friction:

FLift (YorZ )=(dm2 )(μe1 P+μe2

Pcosα−μe 1

cosα +P

cosα−μe 1sin α)¿¿

For the X actuator the equation is deduced in the same way as equation (4) but without considering the wedge mechanism given by the equation (3):

In the X actuator F is simply calculated by:

F=μe 1 P(5)

And thus:

FLiftX=( dm2 )( μe1 P )¿¿

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Applying the equations (4) and (6) to the WEPLATE actuators for the operational load we have:

For the Y actuator:Y ACTUATOR

PARAMETER UNITS VALUEμe N/A 0.50μe1 N/A 0.45μe2 N/A 0.50 dm [mm] 18 P [N] 6000Py [N] 2000 LTool [mm] 400 α [°] 11.00β [°] 1.70 N1 [N] 3762F [N] 3464F0 [N] 1863FLift [N] 42

Fig. 7: Y actuator Lifting Force calculation for the design service load

For the Z actuator:

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Z ACTUATORPARAMETER UNITS VALUEμe N/A 0.50μe1 N/A 0.45μe2 N/A 0.50 dm [mm] 12 P [N] 6000Pz [N] 2700 LTool [mm] 400 α [°] 16.00β [°] 1.70 N1 [N] 5281F [N] 5209F0 [N] 2801FLift [N] 42


Fig. 8: Z actuator Lifting Force calculation for the design service load

For the X actuator:X ACTUATOR

PARAMETER UNITS VALUEμe N/A 0.50μe1 N/A 0.45 dm [mm] 18 P [N] 6000Px [N] 6000 LTool [mm] 400 β [°] 1.70 N1 [N] 6000F [N] 2700F0 [N] 1452FLift [N] 33

Fig. 9: X actuator Lifting Force calculation for the design service load

The Figs. 7, 8 and 9 summarize the calculations done to determine FLift for each one of the actuators used in the WEPLATE. The design load P was defined as being the initial weight of the TANB, 500 kg, plus 100 kg of safety margin. The LTool, lengt of the tool arm, was considered to be 400 mm as this is the approx. length of the standard wrench used by surveyors while performing the alignment operations. According to the materials chosen the coefficient of friction, considered the static coefficient of friction for the presented calculations, was defined as such:

μe is the static coef. of friction between the threading’s of the actuator bolt and the movable part of the actuator, for all the actuators the bolt is manufactured in stainless steel and the movable part (wedge) is manufactured in a brass alloy. The highest static coefficient of friction found in the literature for a non-lubricated surface between this two materials is 0.5.

μe 1 static coef. of friction. For each actuator μe 1 is defined as the highes static coeficien of friction found in the literature for a non lubricated surface between aluminum and brass alloy corresponding to 0.45.

μe 2 static coef. of friction for the X and Y actuators only is defined as the highest static coefficient of friction found in the literature for a non-lubricated surface between steel and brass alloy corresponding to 0.5.

The coefficients of friction are the most preponderant factors in the equations presented for calculating the FLift. In this was a very careful choice of materials was made to allow the lowest possible FLift for

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each actuator without using lubricated surfaces. The highest static friction coefficient values were considered for the interaction between each one of the materials chosen, in this way assuming a pessimistic approach, considering the manufacturing imperfections and material properties tolerances. The graph presented in the Fig. 10 gives the FLift with the variation of friction coefficients from the lowest values to approx. 20% above the max values used in the calculations.

The impact of the increase of the design load P for the actuators FLift was also assessed. Fig. 11 displays such results with a design load comprehended between 100 kg and 1100 kg.

Fig. 10: WEPLATE actuators Lift force for different static friction coeficients, for the same 600 kg load (P) and 400 mm tool length (L¿¿Tool)¿

Fig. 11: WEPLATE actuators Lift force for different operational loads, for the same static friction coefficient conditions ( μe=0.5 μe 1=0.45 μe 2=0.5 ) and 400 mm tool length(L¿¿Tool)¿

It is considered that above 5 kg of applied force in a wrench tool (with a length of 400 mm) is the limit for a comfortable operation of the WEPLATE. The actuators were all dimensioned to be below this threshold in a pessimistic scenario, with the X and Z actuators needing a max. 4.2 kg of force and the X actuator a max. 3.3 kg of force to move the expected operational load of 600 kg (TANB).

The determination and optimization of the FLift inherently enabled to define the geometric characteristics of the actuators like the size of the bolts, threading and angle of the wedge mechanisms.

10

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 1150.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

FLift[N]

Coef

. Fric

tion

[mm

]

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 800

100020003000400050006000700080009000

100001100012000

FLift[N]

Load

[N]


For mechanical validation of each actuator FEA was used to assess the mechanical deformations and max displacements generated by the foreseen operational loads (Figure 12). Design by analysis was used for mechanical validation of the actuator bolts, respective tapped holes and threads, Tab. 3 and 4.

Fig. 12: FEA Plots for max. displacement and von-Mises stress for X, Y and Z actuators and WEPLATE main plate for the expected operational load (600kg). For stress analysis the material considered in the actuators is brass (R0.2 335 MPa) and SS (R0.2 280 MPa); for the main plate aluminium (R0.2 280 MPa). The boundary

conditions in the actuators were defined according to the Fig. 7, 8 and 9.

Table 3: Y and X Actuators threads and bolt tension analysis

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Table 4: Z Actuator thread and bolt tension analysis

3.2.2 Main plates

The WEPLATE was conceptualized in 3 main modules Figure 13. This modularity adds flexibility to the aligned equipment integration providing two simple designed, and thus easily adaptable, intermediate plates and a main alignment module with all the moving parts responsible for controlling the 6 degrees of freedom. These modules are semi permanently attached to each other by means of a locking system preventing the relative movement of the modules after alignment. The plates were designed and dimensioned for the expected loads of the TANB (Figure 12 main plate plots).

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Fig. 13: WEPLATE exploded view with main modules description

3.2.3 Locking mechanism design

The locking interfaces of the WEPLATE are based on the “standard” alignment plate. These simply rely on locking nuts for each actuator preventing the rotation of the bolt Figure 14. Once locked the actuators will prevent the movement of the Intermediate Plate 1.1 in the Z, X, and Yaw directions. However the WEPLATE is composed of 3 main modules and the Intermediate Plate 1.1 together with the Alignment Module can move in the Y, roll and pitch direction if not properly locked, due to vacuum forces generated in the equipment attached to the Intermediate Plate 1.1 pulling the plates upwards. In this sense a mechanism was developed to lock the 3 plates together preventing any vertical movement. This locking mechanism was designed to allow its operation from the same side as the alignment actuators and to allow locking even if the Alignment Module together with the Intermediate Plate 1.1 is tilted in relation to the Intermediate Plate 1.2. Figure 15.

Fig. 14: WEPLATE actuators locking washers

Fig. 15: WEPLATE Vertical locking mechanism. Left: layout in the WEPLATE; Right: Mechanism description

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A study was also conducted to evaluate if the Y actuator would automatically retain the slide/unbolting due to the operational load (Table 5). Equation (7) was used, correlating the friction angle with the Y actuator bolt angle using the same parameters for the analysis performed in Fig. 7. This evaluation is especially important to safety during alignment operations.

For auto retaining the operational load without unbolting the Y actuator has to comply with the following equation:

tan(tan−1(μ¿¿e)−β)>0(7)¿

Table 5: Y Actuator auto retention analysisY ACTUATOR AUTO RETENTION

PARAMETER UNITS VALUEμe N/A 0.50β [°] 1.70Tan (tan^ ¹ ˉ (μe)-β) N/A 0.46

3.3 Stability Analysis

A stability analysis of the WEPLATE was conducted with the aim of determining the safe positioning of the equipment centre of mass to be fixed on top of the Interface Plate 1.1. The Alignment Module and Interface Plate 1.1 are supported by the Interface Plate 1.2 by means of three spheres. This 3 spheres provide a precise and quick (if necessary) positioning of the Alignment Module, and avoid the isostaticity of the WEPLATE once a degree of freedom is needed to cope with the roll and pitch movements, however it means that there is no permanent connection between these elements (Alignment Module and Interface Plate 1.2). From the moment the WEPLATE is unlocked, to allow the alignment operations, the stability of the WEPLATE and therefore of the equipment attached rely on these 3 spherical supports. The compacity of the WEPLATE gives a small distance between each one of the spheres and thus a compromise had to be made on the area available for the positioning of the centre of mass of the equipment. This centre of mass should stay within the triangular area given by the three spherical supports (Figure 16). Also the tilt angle allowed by the WEPLATE decreases slightly this area as the centre of mass of the equipment gets further away from the three spherical supports plane (Figure 17).

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Fig. 16: WEPLATE (Top view) Allowed centre of mass region for the supported equipment accounting with the full displacement ranges given by the actuators in all 6DOF. In green the area with an added safety factor, in

yellow the calculated area.

Fig. 17: Allowed centre of mass volume with the variation of the centre of mass distance to the Intermediate Plate 1.2 support spheres for a tilt angle of 3° (52mrad) on every direction. The triangle area is calculated for a

triangle with the geometric characteristics in Figure 16.

3.4 Operation

The operation of the WEPLATE is fully manual. The working principle is based on the “standard alignment plate”, made this way in view of its simplicity and to promote an easy transition to the WEPLATE mechanics for the operators. Still all the actuators are on the same side and an engraved plate was designed and placed on the WEPLATE to allow the easy correlation of each one of them with the respective DOF. Other information’s like the direction of movement, displacement p/turn and max displacement, for each DOF, were also added Figure 18.

Fig. 18: WEPLATE Engraved plate with the operational info.

The info. in Fig. 18 plate was made in accordance with the usual needs and jargon used by the alignment operators. In this sense the identification of each axis was made as follow:

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0 50 100 150 200 250 300 350 400 450 5000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Distance [mm]

Area

[mm

²]


Y, Roll and Pitch - ALT X, Yaw - RADIAL Z - BEAM

With the positive directions given by Fig. 19 (reference axis for the HL-LHC).

The alignment process starts with the WEPLATE unlocking procedure were the vertical locking mechanism (described in the paragraph 3.2.3) is unlocked (with the lower safety bolt) and then depending on the alignment operation to be performed i.e. which actuator is to be moved the unlocking procedure is (ref. to Fig. 18):

For a Y or Tilt alignment only the ALT actuators are unlocked. For an X and YAW, Z or both all RADIAL and BEAM actuators are unlocked. For a combination of the two points above always unlock all actuators before the

alignment procedures

Fig. 19: HL-LHC Alignment operations reference axis

After the unlocking procedure the alignment operation can be performed:

The alignment procedure for the Y direction or Tilt angles doesn’t require any special remark, still as the tilt range offered by the WEPLATE is very high consideration should be taken to not over tilt the equipment in order to not compromise its stability (refer to previous chapter).

For the X and Z directions and YAW angle special consideration should be taken to always unlock two of the sides (perpendicular sides) of the movable plate (Intermediate Plate 1.1 ref. Fig. 13) before the alignment operations to avoid marking (mechanically deform) by the other actuators the Intermediate Plate 1.1 due to isostaticity.

The displacement range and displacement p/turn given by each actuator is resumed in the Tab. 6.

Table 6: Actuators design range and displacement p/turnY ACTUATOR (VERTICAL) Z ACTUATOR (BEAM) X ACTUATOR (RADIAL)

PARAMETER UNITS VALUE PARAMETER UNITS VALUE PARAMETER UNITS VALUE

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Range [mm] +/- 6 Range [mm] +/- 10 Range [mm] +/- 15Disp. P/Turn [mm] 0.28 Disp. P/Turn [mm] 0.40 Disp. P/Turn [mm] 0.9

After the alignment procedure the table should be locked in the reverse order it was unlocked.

A graphic resume of the needed steps for the alignment set up using the WEPLATE can be seen in Fig. 20.

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Fig. 20: WEPLATE alignment set up: 1 - Safety washer unbolting; 2 - Vertical lock unlocking; 3 – Actuators unlocking; 4 - Unlocking 2 sides of the Intermediate Plate 1.1(If alignment operation comprises X, Z or YAW movements); 5 – Alignment. At the end of the alignment reverse the order for safely locking the WEPLATE.

The points 1 to 4 take on average less than 1 min. to perform.

4 TESTSA WEPLATE prototype was tested under the operational load for evaluating its mechanical reliability, stability, range and precision. Overall the test objective was to validate the WEPLATE for installation in the HL-LHC as a functional and reliable component of the accelerator complex. The first aspect assessed was its mechanical reliability under the operational load. Being the TANB the heaviest object to be aligned by the WEPLATE it was considered as the max service load (being the BPM’s the other equipment aligned by the WEPLATE with a load of approx. 100kg). Under the TANB load each actuator was tested multiple times in their full range guaranteeing that each part moved smoothly and continuously. Also the mechanical functionality of the locking mechanisms was tested.

After mechanical validation of the WEPLATE an alignment test was conducted with the WEPLATE under the operational load. This test was supervised by SU (survey) group simulating real alignment conditions and using the same measurement equipment’s employed for the LHC equipments, objectively measuring with the same range of precision one could expect in the LHC. Both range and precision were evaluated having into consideration the independency of each degree of freedom. The measurements were conducted for each DOF for their full range were data was taken before and after each continuous movement. Measurements in real time were taken during the alignment process assessing the accuracy of the alignment in progress until the target was reached. For the stability test a period of 11 days was defined for three WEPLATE specimens with operational loads, where measurement were taken before and after this period comparing the positions for any possible movement.

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Fig. 21: WEPLATE test bench set up. Left: The WEPLATE in the TANB support. Right: Stability test set up with the laser tracker in first plan for measurement and the WEPLATE(s) with the test loads equipped with the

fiducial targets (in blue) in the foreground.

4.1 Set Up

The test bench was assembled in a way that would best resemble to the operational conditions of the equipments TANB and BPM’s (Beam Positioning Monitor) as the WEPLATES will be installed for both this equipments. The WEPLATE was placed on top the support to be used in the LHC, the same support that the TANB and BPM assemblies will be using, anchored to the concrete floor by means of 4 M12 Bolts and 4 HILTI HKD anchors. For simulating the load of the TANB 2 x 250 kg steel blocks were stacked on top of the WEPLATE with the approximate dimensions of the TANB and with the centre of gravity approximately in the same location.

For the survey measurements an array of targets was scattered across the test bench room for reference, 1 target was placed in the WEPLATE support and 4 targets placed on top of the test load allowing the measurement of its 6DOF, simulating the fiducials and roll surface of a real LHC equipment. The placement of one target in the WEPLATE support isolates the ground movement displacements during the stability tests to the WEPLATE and its test load. A laser tracker, Leica absolute tracker AT960-MR, with a precision of 0.01mm was used together with a customized software for data acquisition and treatment. The test bench room did not have temperature control and the measurements presented do not have into account temperature changes.

4.2 Mechanical Reliability

The first tests conducted on the WEPLATE prototype, 3 of the 9 actuators (2 vertical and 1 radial) under the 500kg, revealed fretting markings between the actuator shafts and their respective bearing surfaces. It was identified to be the result of the first material selection, in which two parts made of the same material were in contact under the high pressures of the operational load. The issue was corrected and measures were adopted for the series production. During the following mechanical and alignment tests the WEPLATE actuators mechanical reliability was continuously tested and no other issue appeared.

Fig. 22: WEPLATE prototype fretting markings. Left and centre: Actuator bearing surfaces; Right: Surface between Interface Plate 1.1 and Alignment Module

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A similar issue was identified in the prototype between the Interface Plate 1.1 and the Alignment Module (Figure 22). A thin brass (2mm) plate was introduced between this two assemblies to promote the correct friction coefficients between these two aluminium parts avoiding fretting. The zinc plated washers (see Figure 19 bottom left figure) used for the bearing surfaces of the actuator bolts particulated (the zinc plating) during the mechanical tests, which didn’t reveal to be an issue for the functioning of the actuators, whoever for future productions it is advisable to change these washer for another material such as brass or copper to promote a smother feeling and functioning of the actuators kinematics.

Another future modification is the vertical locking system currently using a commercial component bounded to the mass production manufacture tolerances. This component needs always to be finely adjusted in order to operate according with the WEPLATE requirements. A redesign of the system is therefore recommended.

After the WEPLATE prototype inherent adjustments have been made the series to be installed in the LHC was produced accordingly. All the WEPLATES in the series were once again mechanically tested without any of the former described issues reappearing. The series were successfully tested fully unlubricated and with the expected operational load.

4.3 Stability

The stability tests of the WEPLATE were performed over a period of 11 days for 3 different subjects (Figure 20 Right). Making a stability test on 3 subjects allowed to account with statistics giving to the obtained results a higher significance. The results obtained are presented in Fig. 23.

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Fig. 23: WEPLATE Stability test results (11 days). Top graph: Absolute values of 3D displacement. Bottom 3 Graphs: Displacement in X, Y and Z axis. Left picture: Fiducials and axis identification in the WEPLATE test set up. Each graph shows the results for the same 3 WEPLATES and fiducial positions

The max absolute displacement obtained after 11 days of test was 0.055 mm for the tested table N°2 with a max vertical (Z) displacement of 0.029 mm for the tested table N°3. The measurements were taken with a difference of temperature of about 2° which can justify in part the displacement obtained, along with the measurements precision.

For the HL-LHC equipments alignment baseline for manual alignment plates the WEPLATE measured stability is within the specifications and despite the small displacements verified the WEPLATE is considered to be stable enough under the operational loads of the TANB and BPM’s for installation in HL-LHC.

4.4 Range

The verification of the design range compared with the true range of the prototype was made for each actuator. The design range is given in Tab. 6. For the prototype the tested range is given in Tab.7.

Table 7: Actuators design range and displacement p/turnY ACTUATOR (VERTICAL) Z ACTUATOR (BEAM) X ACTUATOR (RADIAL)

PARAMETER UNITS VALUE PARAMETER UNITS VALUE PARAMETER UNITS VALUE

MEASURED [mm] 12.268 MEASURED [mm] 18.966 MEASURED [mm] 30.244RANGE [mm] +/- 6.134 RANGE [mm] +/- 9.483 RANGE [mm] +/-15.122

The Z actuators revealed a slightly smaller displacement range that the one designed due to project changes during manufacture. Still the displacement range is close enough from the functional specifications to validate the actuator. The other two actuators have the expected range.

4.5 Precision

The precision tests conducted revealed a calculated precision inferior to 0.03 mm placing the WEPLATE resolution very close to the 0.02 mm required by the functional specifications. The WEPLATE can thus guarantee an alignment precision below 0.03 mm around the point defined on every direction.

The precision achieved in the WEPLATE however is not only bounded to the mechanical functioning and kinematics of the table it also depends strongly on the sensibility of the operator performing the alignment once the movement of each actuator is made by rotating each actuator bolt, analogously with what is done currently with the “standard“ CERN alignment plates. Still the WEPLATE has the benefit of the movement reduction offered by the mechanical characteristics of the actuators allowing a much finer resolution, facilitating the alignment operation and relaxing the sensibility needed.

5 FUTURE DEVELOPMENTSMultiple options could be developed for future applications in different contexts. The flexibility of the WEPLATE allowed by its modular design means that other equipments can be aligned in the same way as the TANB or the BPM’s. Other sizes for the WEPLATE can be predicted enabling heavier or

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lighter equipments to be installed guaranteeing the stability and alignment precision with simple optimization steps to the WEPLATE baseline if required.

Also a further modularization can be done facilitating the adaptation of the design to other equipments while reducing production costs. Each actuator in itself can work as its own module moving its respective DOF. To the purpose encasing the actuators independently and then attach them to a bespoke simple plate (equipment or set of equipments compliant, in size, weight, services, etc.) could be an interesting option for adapting the WEPLATE actuators to the numerous equipment configurations existing at CERN (Figure 24).

In the context of ALARA to further limit the exposure time remote alignment can be envisaged. The WEPLATE interfaces are designed to accept motorization that operated with a dedicated software can render the alignment procedure fully automatic. Semi-permanent or permanent motors can be installed for this instance, dependent on the region criticality, and equipments functional specifications. More economic, and as effective, solution to the exposure limitation, can also pass by the development of extensions to the WEPLATE actuators, maintaining the manual alignment but imposing a safer distance between the equipment and the alignment operator (Figure 25).

Fig. 24: WEPLATE Actuators Modularity Concept

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Fig. 25: WEPLATE Remote alignment module (Left); Removable manual alignment concept at distance (right). The WEPLATE (in light grey) in both figures is integrated with the TANB (in dark grey).

6 CONCLUSIONA new alignment plate, WEPLATE, was successfully conceptualised, developed, tested and manufactured responding to the ALARA requirements for the HL-LHC era aiming to lower the accumulated doses for the alignment operations of the equipments TANB and BPM’s installed in the P8 Long Straight Sections Left and Right of the LHC.

The WEPLATE offers a more ergonomic and a quicker alignment procedure, while maintaining or improving all the functionalities of the “standard” CERN alignment plate, with 6DOF independent kinematics, allowing an intuitive alignment with a range for each DOF superior to +/- 5 mm. The WEPLATE was purposely designed for the TANB weight (500 kg) and the TANB operational conditions. Its actuators in SS and Brass do not require lubrication, meaning that they are radiation compliant. Also the same actuators were dimensioned so that they can be actuated with an applied load inferior to 5 kg (for a 400 mm arm wrench) with an operational load up to 700 kg.

A prototype was produced and successfully tested validating the several mechanical systems, stability, range and precision for the envisaged application. A small series stability test was also successfully performed giving an important repeated confirmation.

The mechanical reliability of the WEPLATE was confirmed for the TANB operational load with minor adjustments to the prototype, guaranteeing a smooth functioning of all the actuators without lubrication.

A stability study was conducted to the WEPLATE revealing that the centre of mass of the equipment to be aligned has to be installed in a determined virtual pyramidal volume above the Intermediate plate 1.2. This volume guarantees that the full range of the WEPLATE can be used to align the equipment safely. For either the TANB or BPM’s their centres of mass are well within this defined volume.

The new alignment table described in this paper with its mechanical system, is a successful ALARA proposal for the TANB and BPM’s alignment in the LSS8 for the HL-LHC era. Still the concept can be extended to numerous other equipments. The modularity of the WEPLATE, and the possibility of the actuators mechanisms modularization in themselves allows an easy and low cost adaptability and extension of the concept to any equipment. Other possibilities such as the addition of motors for remote alignment or even simple extensions of the actuator bolts for handling in activated regions are upgrades that can be explored and implemented in the future to the WEPLATE.

7 REFERENCES[1] http://hilumilhc.web.cern.ch/

[2] High-Luminosity Large Hadron Collider (HL-LHC) : Technical Design Report V. 0.1 - Apollinari G. (ed.) (FERMILAB) ; Béjar Alonso I. (ed.) (CERN) ; Brüning O. (ed.) (CERN) ; Fessia P. (ed.) (CERN) ; Lamont M. (ed.) (CERN) ; Rossi L. (ed.) (CERN) ; Tavian L. (ed.) (CERN) - Geneva : CERN, 2017.

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http://hilumilhc.web.cern.ch/


[3] TANB_Functional_Specification.v1.0. - F. Sanchez Galan - (CERN) - Geneva: CERN, 2018. https://edms.cern.ch/document/1960537/1.0

[4] TANB - Engineering Specification - H. Garcia Gavela, F. Sanchez Galan, M. Santos - (CERN) - Geneva: CERN, 2019. https://edms.cern.ch/document/1961576/0.9

[5] Platforms for Full Remote Alignment Context and requirements - Hélène Mainaud Durand - https://indico.cern.ch/event/815064/contributions/3401629/attachments/1838839/3013757/Platform_meeting_context_requirements.pdf

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https://indico.cern.ch/event/815064/contributions/3401629/attachments/1838839/3013757/Platform_meeting_context_requirements.pdf

https://indico.cern.ch/event/815064/contributions/3401629/attachments/1838839/3013757/Platform_meeting_context_requirements.pdf

https://edms.cern.ch/document/1961576/0.9

https://edms.cern.ch/document/1960537/1.0

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