Operation Procedures for the SPS Rotatable
Collimator Prototype
The most important thing to keep in mind when operating the jaw is that the software really only knows three
things, 1) the number of steps the motor takes, 2) the LVDT readings and 3) the limit switches. Motion is
typically only stopped if one of the limit switches is activated. So, if one of the limit switches is not operational
or there is an obstruction, the software will continue to tell the motors to move resulting in the drive table
hitting a hard stop. The motor shaft will then skip on its thread.
It is therefore good on first motion of the day to stand near the computer to be ready to hit the red STOP
button in case of a problem.
Steps for moving the jaws:
1) Make sure no obstructions will interfere with the motion of the jaw
2) Open the Collimator Interface Labview software and press the play button to run the VI
a. The default settings for the software will correctly operate the jaw so no settings need to be
set.
3) Select the jaw to move (or the individual motor A, B, C or D)
4) Enter the desired distance to travel or select which limit switch to hit
a. Positive values are toward the center beam position, negative values are toward the outer
chamber wall (so, positive is “in” and negative is “out.”).
5) Press the START or SWITCH button
a. START moves the jaw the desired distance
i. If moving a jaw (versus a motor) then both motors will move in parallel and will stop
once the distance is reached or either limit switch is activated
b. SWITCH button moves the jaw to the desired limit switch
i. The jaw will continue to move until both limit switches are activated. If one end of the
jaw hits a limit switch first then that end will stop but the other end will continue to
move until its limit switch is activated.
There is anti-skew logic in the software that will inhibit the jaw from skewing more than the entered value
(default is 3 mm).
Occasionally, the stepper controllers will get into a fault state where the Labview software detects no
problems but the stepper motor motion will be very choppy. If this occurs, pressing the Reset UMI button
usually rectifies the problem. If pressing it once doesn’t work try again. If still to no avail try closing and
reopening the LabView software.
Steps for Ratcheting:
Keep in mind the ratcheting logic is only aware of the inner limit switch and the ratchet limit switch. If either
limit switch is not working properly then the stepper will continue to move resulting in the drive table hitting a
hard stop. The motor shaft will then skip on its thread.
1) The jaw to be ratcheted should be at the inner limit switches. The opposing jaw should be at the outer
limit switches.
a. If one attempts to ratchet and the jaws are not in the correct starting position the LabView
software will display an error dialog window informing the user of the error.
2) Press the Rotate Jaw button
3) A new ratchet window will be displayed and a dialog box will ask to select which jaw to rotate. Another
dialog box will then be displayed to enter the number of times to ratchet. Once one clicks OK on this
second dialog box the jaw will begin to ratchet.
4) The window will display the total number of ratchets to do and the number performed so far.
5) Once the desired number of ratchets is performed the ratchet window will close and the standard
window for jaw motion will be displayed.
Once ratcheting is finished the jaw may not be in the exact same position as when ratcheting began. So, if one
wishes to immediately perform a second set of ratchets then it is a good idea to first move the jaw away from
the inner limit switch a little (say 2 mm) and then move it back to the inner limit switch. This guarantees the
jaw is in the appropriate starting position.
The LVDT’s gain and offset can be adjusted. The default gain values are calibrated for the LVDTs that are
connected. The offset is arbitrary and simply to set the zero point, so if one wants to use to the LVDTs to
measure the motion of the jaws away from some position, the LVDT offset can be adjusted to zero their
readings at that position. In principle the LVDT readings should be repeatable, however, experience has
suggested they will drift by tens of microns. This should be confirmed with the CERN motion control experts.