Abstract: To provide a measuring method on an electric motor with a rotor and a stator for determining the fly height and/or axial play, the rotor being mounted, and in particular fluid-mounted, on the stator, with which method the axial position of the rotor in relation to the stator can be determined with high levels of accuracy and reproducibility, it is provided that the electric motor is operated at a defined measuring speed, at which the rotor is in a specific axial position in relation to the stator, with this relative axial position being determined in that the rotor is brought in a defined manner, with the motor at a standstill, into a first stop position in relation to the stator, in that the rotor is brought in a defined manner, with the motor at a standstill, into a second stop position in relation to the stator, lying opposite the first stop position, and in that the relative axial position between the rotor and the stator is respectively measured in the two stop positions.

Abstract: A fluid dynamic bearing assembly including a shaft and a bearing sleeve. A bearing gap is formed between the shaft and the bearing sleeve and is filled with a lubricating fluid. A capillary seal is formed at one end of the bearing sleeve, and a recess is formed in the shaft immediately above the capillary seal. The surface of the recess forms an acute angle with an axis of the shaft.

Abstract: The method and a device to measure the repeatable and non-repeatable runouts of a rotating component of a spindle motor with the aid of at least one probe measuring changes in the distance between the probe and the rotating component depending on the angle of rotation. The probe records a first test signal in a first test cycle from which a signal defining the RRO is determined and stored. In a second test cycle, a command signal proportional to the amplitude and phase of the RRO signal is generated and fed to an electromechanical actuator supporting the probe. Depending on the command signal derived from the first test signal, the actuator changes the distance between the probe and the outer perimeter of the rotating component, thus compensating the runout defined by the RRO signal, while the probe records a second test signal defining the NRRO.