yalinerkaya / hall_probe

Python scripts to read from NI cDAQ and Zeiss Accura CMM

Hall Probe / CMM Integration

Intro

This project is designed to integrate a Senis 3-axis hall sensor with a Zeiss Accura CMM. Instead of using a start-and-stop method of mapping a magnetic field, this system will map on-the-fly along a given path. The advantages to this method is a major time savings for large mapping areas while only sacrificing a relatively small amount of positional accuracy.

Equipment and Hardware

Zeiss Accura CMM

The CMM used here is a Zeiss Accura model with a VAST Gold measurement sensor. The controller box is C99. The commands python sends to the controller are relatively basic compared to its native communication with Calypso, however, it tends to do the job nicely.
This setup will work with other Zeiss CMMs so long as a C99 controller box is used, which is most likely the case unless it is a very old machine. The CMM used here is about 15 years old.

National Instruments cDAQ

• cDAQ-9185 CompactDAQ Chassis, 4-slot
• NI-9212 C Series Temperature Input Module
• NI-9229 C Series Voltage Input Module
• NI-9263 C Series Voltage Output Module

The two main modules of the NI cDAQ are the voltage input and output. The voltage input module is used to read the ± 12 V analog signal and convert it to digital values. It also reads the on-board temperature sensor of the hall probe.
The voltage output module sends a 1.3 V signal to turn on the electronic control box and 5 V signals to turn on the current for the FSV tool and select the sensitivity range of the hall sensor.

Senis Electronic Control Box

This electronic control box performs the following tasks:

• Takes in the signals generated from the hall sensor and outputs a ± 12 V analog signal.
• Supplies current to the FSV tool.
• Takes input in the form of 5 V to switch on/off the box itself, current for the FSV tool, and select sensitivity range of the hall sensor.

Field Sensitive Volume (FSV) Tool

The FSV tool is used to determine the x, y, and z spatial offset relative to the master probe. Since all travel commands sent to the CMM are with respect to the master probe, those coordinates need to take the different position of the hallprobe into consideration. A Calypso CMM program is used to establish a local coordinate system of the FSV tool. The FSV tool does not need to be aligned with the machine coordinate system (MCS) for qualification to take place. A Calypso PCM script is used to generate rotation and translation values between the local part coordinate system (PCS) and the MCS.

Orthogonal Cube

The orthogonal cube helps correct any non-orthogonality due to sensor placement within the ceramic probe. This, alongside an additional Calypso program helps establish rotational correction with respect to the MCS.

Software

The entire project is written in Python. So far this is still a work in progress and code may break or change in the meantime. GUI started out as an empty proof of concept and is slowly being modified to contain actual functionality. Currently only the probe qualification routines are integrated and working within the graphical interface.

Prerequisites

National Instruments NI-DAQmx drivers must be installed. Software version 20.0 is used here. Newer versions have not been tested with this system.
Driver software can be found from NI's website here.
Device names in the python scripts are static and must be renamed in NI MAX to the following:

• cDAQ-9185 "MagnetcDAQ"
• NI-9212 "MagnetTemp"
• NI-9229 "FieldSensor"
• NI-9263 "AnalogOut"

Third party python libraries utilized are:

• numpy
• matplotlib
• Pillow
• nidaqmx

All libraries are installable via pip. For example:

pip install nidaqmx

Graphical Interface

The graphical interface was built with python's included library, tkinter. The main purpose of the GUI is to simplify the magnet measurement process. The interface is broken down into the following sections:

• Magnet Information
  • Enter in part and serial number information as well as any relevant notes that pertain to the part in question.
• Probe Qualification
  • Contains a step-by-step guide for qualifying a newly setup hall probe.
• Measurement Controls
  • Input parameters to perform magnet measurements
  • Only point and line measurements are complete and functional. Area mapping is still a work in progress.
• Program Controls
  • Buttons for creating a new measurement plan, saving, or opening an existing one.
  • No functional controls yet. This section is still a work in progress.
• Visualization Controls
  • Create various plots from the measurement results
  • This section is still a work in progress
• TBD - Alignment Analysis
  • Still TBD, but possibly output data useful for alignment purposes.

Zeiss Calypso CMM Software

The main use of the Calypso CMM software is to physically measure the part in order to determine the relationship between the PCS and MCS so that the hall probe can accurately travel to known points in space in relation to the aligned part system. PCM (an optional add-on to the standard Calypso package) is used in order to generate a text file containing the transformation matrix needed for hallprobe scanning.
The PCM script is entered into Calypso's measurement plan post-settings PCM window.

if fileExists("alignment.txt"):
	deleteFile("alignment.txt")
endif
writeDiffCoordSysToFile("MCS", "PCS", "alignment.txt")

If PCM is not installed, one can manually execute the writeDiffCoordSysToFile function using a Result Element characteristic and executing a formula.