DRIVE SYSTEM IN A GEODETIC MEASUREMENT INSTRUMENT

The invention relates to a geodetic surveying instrument (1), configured to move a measurement light beam into a desired measurement direction (4) in space, comprising at least one movement axis (2,3) which is motorized for providing a positioning of the measurement direction (4) of the geodetic surveying instrument (1), and an instrument-encoder (5) at the movement axis (2,3) configured for deriving the measurement direction (4) as a measurement value of the geodetic surveying instrument (1). [0002] According to the invention, the geodetic surveying instrument (1) comprises a transmission link of the movement axis (2,3) of the geodetic surveying instrument (1) to a motor axis (7) of a stepper motor (8), which transmission link is configured with a gear reduction (1 ,14) and a slipping clutch arrangement (6), and wherein the stepper motor (8) comprises a rotational motor-encoder (9) on its motor-axis (7) and is driven by a motor controller (10) that provides a field oriented control of phase currents of the stepper motor (8), which field orientation is derived based on the rotational motor-encoder (9).