The KM3NeT CLB Calibrator is a mechanism that automatically calibrates the magnetic compass of the central logic boards (CLBs) used in the digital optical modules (DOMs) of the KM3NeT neutrino telescope. I designed and implemented the system during my internship at N.C.S.R. “DEMOKRITOS” - Institute of Nuclear & Particle Physics between July and September 2020.
Every DOM of the KM3NeT telescope is submerged near the bottom of the Mediterranean Sea and continually reports its orientation based on data from the magnetic compass located on its CLB. For the magnetic compass to work properly, a calibration routine must be carried out for every CLB before its DOM integration. Conventionally, this is done manually using a gyroscope-like tool, seen below.
This process is monotonous, tedious and provides inconsistent calibration accuracy. For these reasons, an automated system needed to be developed.
The design constraints that the automated system needed to satisfy were the following.
- No metal parts should exist near the CLB. This was to ensure that no interference occured with the earth's magnetic field during calibration.
- The mechanism must perform a series of eight full 360° rotations about the vertical axis each one with the CLB placed in a different orientation.
- Each rotation must be smooth and last approximately 20s to ensure good data acquisition.
The mechanism is composed of two sub-assemblies.
- A: a gyroscope-like mechanism that rotates the CLB. It is made entirely out of plastic parts to satisfy design constraint #1. Most parts are 3D printed, some are machined in a lathe, while some are standard plastic bolts, nuts and timing belts.
- B: a base for the stepper motors and other electronics located ~1 meter away from the CLB. Actuation between the stepper motors and the gyroscope-like mechanism is achieved using 3 long non-metalic timing belts.
Both sub-assemblies are secured on a wooden base with plastic bolts and nuts. The two sub-assemblies are seen below.
The folder Assembly Files contains the CAD files (SolidWorks) of the automatic calibration system. Download the whole folder and open file "Calibrator Assembly v5.SLDASM".
Motion is achieved using three stepper motors each one controlling a rotational axis. Each motor is connected to a stepper driver on a CNC shield. Arduino UNO is used as the microcontroller and a small fan keeps the electronics cool.
Stepper motors are controled via stepperControl.ino. To run it, the AccelStepper library must be included.
Short video (<25MB) of the calibration system performing part of the calibration routine. An old version of the mechanism in shown in the video. It has a short base, the electronics are near the CLB, and the mechanism is held in place using zip-ties.
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Public License.
