Abstract: A method for serial data transmission between a position measuring system and a processing unit that includes transmitting a digital data word of defined length between the processing unit and the position measuring system and having a position data request signal arrive during the transmitting of the digital data word. Determining a position signal regarding a relative chronological position of the position data request signal with respect to the transmitted digital data word and transmitting the determined position signal to the position measuring system.

Abstract: A position measuring device for measuring the relative positions of two objects. A scanning unit for scanning a graduation carrier is mounted on a bed of a processing machine through a coupling which is stiff in measuring direction. The coupling includes a first coupling part in the form of a plate fastened to the scanning unit and a second coupling part in the form of a pin having a spherical end face. The pin is fastened to an engagement member mounted on the bed of the processing machine. A sliding layer is provided between the two coupling parts in order to eliminate wear between the two coupling parts and to eliminate measuring inaccuracies.

Abstract: A phase grating is provided in this length or angle measuring apparatus, which operates by interference. A beam striking the phase grating from a laser is diffracted into .+-.1st order beams at the phase grating. The diffracted .+-.1st order beams are reflected at retroreflecting elements and, diffracted once again at the phase grating, and made to interfere in pairs. The modulations in intensity of the two-beam interferences are converted by detectors into electrical signals that are phase-displaced from one another. The diffraction grating is configured such that at least one partial beam cluster of the zero order of diffraction is involved in the formation of at least one of the two-beam interferences.