The calibration of the Z1-3 and X motor is the process of determining a step size for each of the motors. The calibration is performed optically.
Procedure
For each motor, separately drive the motor alone for 2000, 4000, 6000, 8000, 10000 steps in both -(approach) and +(retract) direction. While doing so, ensure, that there is ample space to perform the movement and that the initial position of the stage is straight. After each of the 2000 etc. steps, the distance the motor has travelled is measured using the camera.
For this a distinguishable point on the motor or near it, that moves with the motor, has to be chosen as a point of reference. This point should be temporally stable and stable when moving the motor (i.e. it does not disappear when driving up for x steps). At best a set of multiple points along a line is chosen, as then you can draw a line through the points and measure the distance to the previous line.
Afterwards, a linear fit is performed on the data to obtain the step sizes of the motors.
When done outside UHV the motors themselves (any distinguishable point on the prism) can be chosen as the measurement points and the camera should be repositioned.
When done inside UHV the Z1 motor itself (any distinguishable point on the prism) can be chosen, but Z2 and Z3 are not visible. So instead the camera has to be refocussed on the screws near the Z2, Z3 motors and these are chosen as measuring points. They can also be used as camera calibrations, as their diameter is known (3 mm).
A python script that can perform this is found in the Folder "PythonScripts" it is called "CalibrationAfterRepair". It expects data in the format:
Voltage | Steps | Z3- | Z3+ | Z2- | Z2+ | Z1- | Z1+ | Z3- error | Z3+ error | Z2- error | Z2+ error | Z1- error | Z1+ error |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
80 | 2000 | x | x | x | x | x | x | x | x | x | x | x | x |
- | 4000 | x | x | x | x | x | x | x | x | x | x | x | x |
- | 6000 | x | x | x | x | x | x | x | x | x | x | x | x |
- | 8000 | x | x | x | x | x | x | x | x | x | x | x | x |
- | 10000 | x | x | x | x | x | x | x | x | x | x | x | x |
"-" stands for empty entries
"x" stands for a data point given in mm
The output will look like:
Tricks
If the calibration is performed outside UHV it is a good idea to look at the motors head on while driving to get better accuracy. When doing so, the Bresser software has to be recalibrated for the distances to fit properly. A simple trick to do this quickly is to use the circle tool and use the Neodym magnets as a calibration aid, as their diameter is known to be 5mm.
Additionally, the calibration of Z2 and Z3 can be performed from the same camera angle, reducing the amount of camera switching.
For a quick check of the motors speed drive the motor by hand (remote) for the distance of a solder ceramic as these are approximately 2 mm in size you can obtain a very rough estimate of step size very quickly like this and can check if the motors are still in sync when it comes to step sizes.