Offset mobile probe to centre gripper

This section describes why and how the offset between the mobile probe and the centre off the gripper jaws should be measured and adjusted.

The mobile probe is located approximately -55000, 75000 microns away from the gripper centre axis. Therefore the current mobile probe co-ordinate is given by:

The exact value of the offset is kept as two variables in the control software and must be calibrated if major work has been done to the gripper or the probe has been knocked.

The simplest way to calibrate the offset between  gripper and mobile probe is to do on sky using a bright star (M10-12). Position a guide fibre at the centre of the fieldplate (0,0) and point the telescope at that star, acquire the star in the guide fibre and let the telescope track. Now use the mobile probe to look at the object which is going down the fibre (af_viewobject n, at the ICL prompt, where n is the fibre number being used). Start the autoguider grabbing images continuously in the mobile probe with a short integration time. Centre the image in the mobile probe by using the robot but not the telescope and check the robot gripper position. The gripper position will then be equal in size but opposite in sign to the offset between the gripper and the probe. For example if the above values were correct then to place the mobile probe at 0,0 the gripper would be moved to 55000, -75000.

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Last updated 12 january 2003 by Michiel van der Hoeven