The horizontal motion got "stuck" when the operator tried to move the target HOME = Out-of-Beam position at 8:20 am (the time stamp when the horizontal motion brake was released). This was in preparation for a Moller measurement.
The horizontal motion status screen showed a "power stage error". This error code usually means an internal error in the phytron motor controller. The target did move vertically to the out of beam position (Yenc = 0; Ypot ~ 1930), but did not appear to have moved at all on the horizontal axis, Xenc = 0.25 and Xpot was ~ 48.1 (the values for the LH2 in beam position). I told the TO that for all means and purposes for the HOME position the target only has to move vertically to be out of the beam axis, it does not have to move horizontally. Anyway, the MCC was not able to mask this FSD.
When I got into the counting house I tried resetting the power stage error from the software reset button for it. It did not clear the error code. The target did not move "manually" on the horizontal axis afterwards. I tried power-cycling the phytron motor controller from its power switch on the horizontal motion box in the Qweak Target crate (next to the target control computer screens in the counting house). The switch is labeled "Kill GSP". This did reset the horizontal motion encoder read-back to zero (which means that it most probably did power-cycle the motor controller). But the target still would not move horizontally with manual commands. Next I power-cycled the target ioc from its crate in the counting house electronics room. When the ioc came back to life all (persistent) error codes from the horizontal motion status screen got magically cleared. I was able to move the target with manual commands.
I reset the motor step counter to what it was before its controller was power-cycled, 400 steps for the LH2 position. I moved the target to the HOME switch, step 29000, the HOME switch light came ON. Next I moved the target to LS-, which got hit at step -66744. For the month of April the average LS- position was -66626 out of nine hits. So we are off some 74 microns, which means that no adjustments are needed, the motor step counter is set properly. Moved it to HOME one more time and handed over to the Moller gang. The whole thing lasted 45 min. In the end it seems that the problem may have been a combination of motor controller fault and target ioc fault. The target motion sequencer did not work properly even as the controller fault got cleared.
When the horizontal motion got stuck both the brake was released and the phytron stepper motor was stuck on the running current (2 Amps). They heat up by some 7 K in 40 minutes, which is in the warning region. Twice this would not be good for the motor. They both look fine now, their temperatures have bent down, once everything started working properly.
The target motion FSD only looks at the vertical axis brake. The target motion sequencer releases the vertical axis brake at the beginning of a motion sequence, moves the target vertically, releases the horizontal axis brake, moves the target horizontally, engages the horizontal axis brake, and, only then engages the vertical axis brake and the target motion FSD gets cleared. Since the target motion sequencer faulted, the vertical axis brake did not re-engage in this instance, as it was waiting for the horizontal axis brake to re-engage. In future, if the target motion sequencer were to fault again but the target would be in its correct position, like it was this time around, to clear the target position FSD the brakes need to be re-engaged manually.
Figure 1
