A NOVEL BPM MECHANICAL CENTER CALIBRATIONMETHOD BASED ON LASER RANGING
Xuhui Tang1,2, Yanfeng Sui1,2, Jun He1, Yaoyao Du1, Jianshe Cao1, Junhui Yue1†
1Institute of High Energy Physics, Chinese Academy of Science, 2University of Chinese Academy of ScienceIntroduction

 Due to processing errors, the mechanical center and electrical center ofBPM do not coincide. Therefore, each BPM is demanded to calibrate
before use.
 About 600 BPMs are produced during the construction of High Energy
Photon Source (HEPS) project, the calibration task is heavy.
 Finding the mechanical center is extremely difficult, so it is hard todetermine and 𝑋offset and 𝑌offset .

A four button-type BPM of HEPSMethods
 Principle

System error evaluation

 System error𝑠∆𝑋offset = ∆𝐻𝑠 + ∆𝐻 ≤ 20μm𝑠∆𝑌offset= ∆𝐿 + ∆𝐹 ≤ 20μm

the processing errors
from BPM wing andantenna support leadto system errors

The tiny angle wobble produced by each
installation produces random errors, inwhich the error around the Z-axis is thelargest. Because the 𝑙4 is a larger value.

The HEPS project located in Beijing
BPM measurement formula

𝑉𝑎 + 𝑉𝑑 − 𝑉𝑏 − 𝑉𝑐
𝑥 = 𝐾𝑥+ 𝑋offset
𝑉𝑎 + 𝑉𝑏 + 𝑉𝑐 + 𝑉𝑑
𝑉𝑎 + 𝑉𝑏 − 𝑉𝑐 − 𝑉𝑑𝑦 = 𝐾𝑦+ 𝑌offset
𝑉𝑎 + 𝑉𝑏 + 𝑉𝑐 + 𝑉𝑑

Distance relationship when antenna islocated in the BPM mechanical center

𝐻𝑌𝑠 + 𝐻𝑠 = 𝑌𝑏𝑝𝑚 + + 𝑟
2
𝐿
𝑋𝑠 = 𝑋𝑏𝑝𝑚 + + 𝑟
2

Two key distances representing BPM
mechanical center

𝐻𝑌𝑏𝑝𝑚_𝑀 = 𝑌𝑠 + 𝐻𝑠 − − 𝑟2
𝐿𝑋𝑏𝑝𝑚_𝑀 = 𝑋𝑠 − − 𝑟2

The formula for calculating
electro-mechanical offset

𝑋offset = 𝑌𝑏𝑝𝑚_𝑀 − 𝑌𝑏𝑝𝑚_𝐸

 Hardware Implementation

Error analysis

𝑌offset = 𝑋𝑏𝑝𝑚_𝐸 − 𝑋𝑏𝑝𝑚_𝑀 Random error
Source of randomerror

symbol𝑟𝑥∆𝑋𝑏𝑝𝑚_𝐸

BPM tiny
installation angle𝑟𝑥∆𝑌𝑠around GCS X-axis𝑟𝑦∆𝑋𝑏𝑝𝑚_𝐸

BPM tiny
installation angle𝑟𝑦around GCS Y-axis ∆𝑋𝑠𝑟𝑧∆𝑋𝑏𝑝𝑚_𝐸

BPM tiny
installation angle∆𝑌𝑠𝑟𝑧around GCS Z-axis ∆𝑋 𝑟𝑧
𝑠

Evaluation
methodHardware
elimination

Softwareelimination\\𝑙1 𝜃𝑥

averaging themeasured 𝑌𝑠 atmultiple positions\𝑙2 𝜃𝑦Tighten the BPM
mounting screws
using a fixed
torque wrench\averaging themeasured 𝑋𝑠 atmultiple positions\𝑙3 𝜃𝑧 − 𝐻𝜃𝑧2 /2𝑙4 𝜃𝑧\Experiment and discussion

 Experiment platform
The BPM automatic
calibration system, whichuses Libera electronics toposition the antenna in theBPM electrical center.

 Experiment data
Base data(mm): 𝐻 = 210, 𝐿 = 12, 𝑟 = 0.105, 𝑋𝑠 = 5.820, 𝑌𝑠 = 1.780
Repeat the experiment 5 times in three different ways and observe the variance.

σx_offset / mm
Measurement operation
Repeat installation of BPM only
0.0033
Repeat installation of antenna only
0.0081
Repeat installation of the antenna
0.0154and BPM simultaneously

σy_offset / mm
0.01020.00240.0122

Change the BPM and antenna simultaneously, with a maximum variance of 15μm

Conclusion and prospect Conclusion
 In order to quickly, low-cost, and high-precision measure the BPM
electro-mechanical offset, a new method using precision antenna
support and laser ranging sensor is proposed.
 The measuring platform of the new method is built, and the automatic
testing program is designed.
 The experiment shows that the repetition accuracy of this method is lessthan 30μm, and the absolute system error is less than 20μm.
 Prospect Update the software and hardware of the calibration platform toaccommodate different sizes of BPM.
 Compare this method with Lambertson method.

Acknowledgements

This work was funded by the Foundation of Youth Innovation Promotion
Association, CAS (Y202005), the Major achievements cultivation project ofmajor scientific and technological infrastructure, CAS (NE01G74Y2), andthe National Natural Science Foundation of China (11805221).

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