When the motor is homed the step counter starts to decrease until but never stops. The full stroke of the motor is about 1500 steps; so no matter what the starting point is, if you see a value of -2000 steps or less it means that the homing is not having success.

Possible cause

The Newport NSA12 linear actuator has a stroke of 10mm and a single negative limit switch (corresponding to the fully-retracted position) that is used for homing.

When the motor is fully-elongated the actuator may detach from the rotor. In this case the motor is not able to retract unless manually "helped". With the motor rotating in the retracting direction one has to push the actuator toward the motor to let the the actuator hook again up to the rotor.

It is to be noted that similar symptoms could be experienced when the motor is actually completely retracted but the limit switch is broken (not very likely in our statistics). The 2 cases can be discriminated by checking the actual elongation of the actuator: if it is fully retracted (only the spheric tip is visible) then the limit switch is broken. If instead the actuator is fully elongated the procedure below can be attempted.

The image shows a detail of the actuator spherical tip touching the stage. In this example the actuator is almost completely retracted: 20140328_123142.jpg

Procedure to recover from a motor stuck in the fully elongated position.

1. Access the LGSW from the side of the connectors and the cooling pipes (opposite to M1). The operator can stand on the inclined beam of the instrument gallery, very close to the RFBG/LFBG cable chain.

2. Remove the front upper panel of the LGSW. See photo. A 2.5mm Allen key is needed.


3. Identify the motor. The one circled in the photo is the yellow Y.


4. Using the software start the motor homing procedure. Startup the system using the ARGOS ENG GUI for the devices.Once the power up is started, the process connects to the motors that shows the green dot that it is connected and that point it can be perform the home of the individual motor and axe. "It doesn't require to wait to have the PnCCd coold down".

The step counter starts to decrease, the operator can feel the motor that is rotating, but the stage does not translate.

5. Separate the stage from the actuator (move against the spring) and then let the stage come back and press against the actuator. See photo and movie (also here). Please, don't touch the lens, use your finger on the corner of the mount as shown in the picture.


6. When the actuator is pushed against the motor rotor it should hook up again to it. The actuator should start to retract and the homing should succeed.

From the GUI the encoder reading change and decreasing (approaching to zero)

7. Put back in place the upper cover, tight the screws.

Image of the SX configuration at the telescope.

looking at from the top of the WFS platform.


I Attachment Action Size Date Who Comment
20140328_122723.jpgjpg 20140328_122723.jpg manage 2 MB 28 Mar 2014 - 14:37 LorenzoBusoni How to recover from a stuck full-extended motor
20140328_122812.jpgjpg 20140328_122812.jpg manage 2 MB 28 Mar 2014 - 14:31 LorenzoBusoni How to recover from a stuck full-extended motor
20140328_122942.jpgjpg 20140328_122942.jpg manage 3 MB 28 Mar 2014 - 14:31 LorenzoBusoni How to recover from a stuck full-extended motor
20140328_123036.mp4mp4 20140328_123036.mp4 manage 7 MB 28 Mar 2014 - 14:31 LorenzoBusoni How to recover from a stuck full-extended motor
20140328_123142.jpgjpg 20140328_123142.jpg manage 2 MB 28 Mar 2014 - 14:31 LorenzoBusoni How to recover from a stuck full-extended motor
IMG_2213.jpgjpg IMG_2213.jpg manage 689 K 14 Jun 2023 - 03:45 JuanCarlosGuerra  
IMG_2214.jpgjpg IMG_2214.jpg manage 726 K 14 Jun 2023 - 03:45 JuanCarlosGuerra  
Topic revision: r4 - 14 Jun 2023, JuanCarlosGuerra
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