Homing

The motors have home switches (ZOSA and ZSTG use limit switches; see Tab. 11.2). In general you should not touch them unless you are absolutely certain of what you are doing. The locations of the home positions are shown in Tab. 11.2. If you do Home the motors, wait for the operation to be completed. The position is set to zero automatically. You can issue the Home command either from the Advanced menu in SM_GUI or over the XPS' web interface or remote control. But be aware, that for the latter two, ``position compare'' (11.4) will not be set up like it is done when homing via SM_GUI. This means, the XPS will not put out the trigger pulses, that we need for timing scans.

You can set the home position to be at either end of the travel range or in the middle (see the little holes marked ``ZM''), but please don't adjust it or you may have microscope components banging into each other! (unless you know exactly, what you are doing and how to adjust the alignment file.)

The XPS has an advance feature called "Referencing", that allows you to set a motor to any desired position, instead of homing it. Homing of ZOSA is quite cumbersome, so we use referencing, to avoid homing if possible. After each motion of ZOSA it's new position is written to a file. If the XPS then looses power, the last known position is restored from this file. This happens, when the program sm_server is (re-)started and a warning is issued at startup. It is important not to move motors, before their position is restored by sm_server. Otherwise, the restore will be faulty and might have fatal consequences. The restore feature can be turned on for any motor in the source code, but since it is not entirely safe - especially for motors, that we scan often - we chose to use it only for the OSA motor and issue a warning.