Calibration and Characterization of Exposed Linear Incremental Encoders at DR. JOHANNES HEIDENHAIN GmbH - Selected Examples

摘要

Examples of encoder calibrations and characterizations are presented applying the two exposed linear encoders LIP 382 and LIP 401. Hereby, different error contributions, which include noise, interpolation error, graduation deviations and influences due to imperfect mounting, are evaluated. By simple means, error related to noise can be determined to be significantly less than 0.1% of the signal period when using the HEIDENHAIN IK 320 counter card. The other sources of error are quantified by applying a 100 mm comparator that is designed according to the Abbe principle. We use an LIP 382 with a resolution of 31.25 pm (interpolation factor: 4096) as a reference system, which is calibrated with a laser interferometer. The comparator's short-range deviations amount to some 1 nm. For the presented encoder types, the interpolation error is shown to be less than 1% of the signal period (more sophisticated investigations than applied here even prove the LIP 382's interpolation error to be less than 0.1 nm). Examples of calibration curves are shown in which the non-linear components of graduation error are 7 nm over 70 mm length (LIP 382) or 8 nm over 40 mm length (LIP 481). Using averaging techniques, the long-range repeatability of the measurements, which includes contributions from the encoder (influences due to mounting) and the 100 mm comparator, is within ±1 nm/70 mm over a period of one month (LIP 382). With respect to the short-range repeatability, our. evaluations show an agreement of the measurements within ±1 nm - even without averaging of the recorded values (LIP 481). These results are among others a consequence from a signal generation that depends not only on a single grating line, but on a single grating field of a size in the order of 10 mm~(2).