+/-10um shifts with anti-lag

[tgruene]

branch: main, date of testing: 12/5/2025
As far as I can tell, the buttons +/-10 um move the stage by 10um in the respective X-direction. In order to reduce lag, the +10um should move +12um and then -2um (2um just a guess, 1um might be sufficient). There should then be a 'back' button, that moves the stage -10um.
Respectively for the opposite direction.

[KiyofumiTakaba]

I do not understand what mechanisms behind could reduce the lag by the proposed two-step movement. If it means the lag by backlash, it has already been considered (#147). Otherwise there should be different reasons inducing the lag.

[tgruene]

If I understand correctly, the function 'move_with_backlash' moves the stage in one direction, but with a reduced value. This is not the idea of mechanical backlash reduction. The idea of the '+10um' button is to move the beam away from the crystal, then do some (beam) alignment or calibration, then move back to the crystal. At that stage, just before moving back to the crystal, the cogs of the drive (gear drive) that move the stage should already in position to return the drive. This is achieved by overdriving a small step, (e.g. 10+2 um), then going back 2um. This way, the cogs of the motor touch the cogs of the stage in the right direction of the desired movement. Is this already done by the code?

[KiyofumiTakaba]

I post this comment assuming the purpose of this issue is to correct the backlash. Then, the working of two-step movement is understandable.
The feature merged into the developer branch (two months ago) is also intended to correct the backlash. It accounts for stage movement if the cogs are contacting with the gear or not, by recording the last movement vector. The value for stage movement is corrected when backlash is present. This way should result in the almost equivalent to the two-step movement, by one-step.
Any other better way could replace the one-step correction as long as the assignee understands the idea.

[erikfrojdh]

Evaluate, quality of the shifting

[tgruene]

to be done: +10um button means: move crystal 11um in X-direction (plus backlash correction), followed immediately by a translation by -1um in X-direction (plus backlash correction).

[KiyofumiTakaba]

I (KT) do not understand the necessity of this test and reassigned this task to the original person (KF). Testing at TEM can be planned if the code is provided.