1. Towards a common mechanical interface
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface *
* *
Thomas Touzé
CERN BE-ABP
Université de Paris-Est

2. Introduction Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
Several measurement systems are developed for the CLIC pre-alignment. Inter-comparison tests are planned. A common mechanical interface for all the sensors would simplify the metrology and fiducialization aspects and increase the possibilities of the setups.
Objectives of this presentation :
Definition of a sensor mechanical interface for the CLIC pre-alignment,
Uncertainties constraints of such an interface,
Overview of different solutions,
How to tight the sensor ?
I do not want to dictate a particular design but propose ideas to help the convergence of our researches.
Introduction
Thomas Touzé

3. The mechanical interface
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
What are we looking for ?
We want to align the girders (MB+DB) and the main beam quadrupoles with respect to a reference (stretched wire, laser beam) with a 3 μm budget error (RMS).
The mechanical interface
The mechanical interface is the link between the pre-alignment sensor and the component we want to align.
Thomas Touzé

4. The mechanical interface
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
(some personal thoughts about the CLIC pre-alignment)
The propagation network deals with the definition of a pre-alignment reference along the whole CLIC linacs by overlapping stretched wires or laser beam.
The mechanical interface
The proximity network measures the positions of the mechanical interfaces with respect to the pre-alignment reference, directly (WPS) or indirectly (RasNik).
The fiducialization consists of the measurement of the component axis with respect to the mechanical interface.
Thomas Touzé

5. The mechanical interface
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
Hence, any device used in the proximity network has to do the link between the pre-alignment reference and the mechanical interface with a budget error of 3 μm (RMS). It has to be a high precision and high accuracy measurement system.
The mechanical interface
The accuracy can be defined as the uncertainty of the definition of the sensor measurement on its centering system, i.-e. on the mechanical interface.
Thomas Touzé

6. 6 balls centering system
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
The position is given by 6 balls on 3 different plans. The three balls A, B and C give the plan on which the sensor is mounted. The balls D and E give the orientation and F give the position.
6 balls centering system
A, B and C give the plan :
D and E give the orientation :
F gives the position :
Thomas Touzé

7. 6 balls centering system
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
The WPS centering system of the LHC low-beta quadrupoles is quite close to this design. Pins are used instead of balls. Two critical issues on the repeatability and reproducibility have been detected from our feedback on this design.
6 balls centering system
If the sensor is not tight, it is free to move. The tightening system must block the sensor on the 3 plans of the balls.
The position and orientation of the sensor depend on the surfaces in contact with the balls. To ensure a good repeatability, these surfaces must not change.
Thomas Touzé

8. 3 balls centering system
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
It is the design chosen for the BCAM, the OPI-WPS and the Fogale WPS at CERN.
3 balls centering system
One ball gives the position (3 degrees of freedom),
One ball gives the orientation of the sensor (2 degrees of freedom),
The last one gives the plan (1 degree of freedom).
Thomas Touzé

9. 3 balls centering system
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
The calculations, in order to build a coordinates system, are close to the 6 balls case (here is the OPI-WPS definition). The sensor tightening is easier (along k-axis).
3 balls centering system
The repeatability depends on the surface in contact with the ball. This surface is more protected.
Thomas Touzé

10. 3 balls centering system
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
Repeatability of the Fogale WPS given by the calibration of the sensors zeros. 17 sensors have been calibrated. A RMS value of 36 centerings per sensor has been computed (9 times on 4 centering systems, including upside-down position).
3 balls centering system
 RMS values
Transversal
Vertical
Minimum (μm)
0.6
0.5
Maximum (μm)
1.8
1.0
Average (μm)
1.1
0.7
Median (μm)
Thomas Touzé

11. Improvements to be done ???
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
According to my personal experience, I would slightly modify my existing 3 balls centering system.
The longitudinal axis “i” would be directly given by the direction between 2 balls. The machining would be easier without this angle.
Improvements to be done ???
Thomas Touzé

12. Improvements to be done ???
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
The 3 balls centering system seems to ensure a better repeatability than the 6 balls one. But improvements can probably be done, especially regarding the tightening.
We could manage to have the 3 balls center of gravity H, the zero of the sensor, the sensor’s center of gravity and the tightening axis on the same line.
Improvements to be done ???
The sensor would be much more stable, especially if it is mounted upside-down.
Thomas Touzé

13. Improvements to be done ???
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
Some last requirements…
Because of the capacitive technology, the balls must be non-conductive. The one we use are made of ceramic.
On the centering system, we have the possibility to install a 1½” survey prism. Thanks to the metrology measurements, the center of this prism is known with respect to the balls.
Improvements to be done ???
It would be convenient to keep this idea. But actually, to install such a prism, we have to remove the WPS.
It would be more practical to have it accessible without touching the sensor.
Thomas Touzé

14. Improvements to be done ???
Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
Improvements to be done ???
The interface could also support two 3-balls centering system.
By rotating the sensor, systematic effects could be studied.
If a ball is broken, the interface could still be used without losing the metrology… just by rotating the center.
(Thanks for the idea, Andreas Herty and Michel Rousseau !)
Thomas Touzé

15. Conclusion Brainstorming on CLIC pre-alignment studies
Towards a common mechanical interface
Interchangeability tests are planned. A common centering system would be more efficient. Measurement systems could be replaced without any change on the metrology !
And the design costs could be divided by 3 !
Conclusion
We could use the same centering system for WPS, RasClic, inclinometers and – why not – HLS systems…
Thomas Touzé