Z axis as stepper motor PU/PD

[Marmadoc]

I try to understand how Z Axis Pen Up/Down works I have stepper 24 BYJ 48 12V. When I press Z jogging 10z motor moves a little next stops and start moves again and finally stops. Stops jogging on mouse is OFF on picture is my setup for Z axis My mechanical design is 10mm up and 10m down for pen holder. I calculated that 1mm it is 102 steps (#102 GRBL) How to use setup to get movement different than 2mm - I tried 20mm but not move that much. Thx in advance