Machine Design

Scanning for Ideas: Encoder Takes on Drift

Edited by Stephen J. Mraz

Linear actuators can have 10-decimal accuracy when they leave the factory or right after calibration, but thermal and linear-guiding drift while the actuator is operating can make that accuracy figure meaningless. Engineers at Heidenhain Corp., Schaumburg, Ill. (, have eliminated this problem with the two-dimensional 1Dplus encoder. It detects and measures thermal and linear-guiding drift while a stage or machine is moving, letting linear actuators compensate for these factors on the fly.

The frictionless, interferential-type linear encoder has gratings set up in two dimensions and can use up to three scanners to continually check for drift. The measuring standard is DIADUR with a thermal expansion coefficient of 0 ppm⁄K°. Current measuring range is 300 × 2 mm, but the company plans to increase that significantly soon. The Xaxis measurement has 1- m accuracy and includes a reference mark. The grating period of the encoder is 8 m; the signal period is 4 m.

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