| 摘要 |
PURPOSE:To set absolute original points quickly and automatically, by comparing the number of slits between a plurality of reference marks, which are arranged on a length measuring slit line, with a preset value, and detecting the positions of the marks based on the coincidence signal and the detected mark signal immediately after the coincidence signal. CONSTITUTION:A plurality of reference marks 22A... are arranged on a main scale 10 in parallel with a length measuring slit line 12. The parts of the line 12 between the marks 22A... are sequentially made to be length measuring slits 12A.... A slit counting means 26, which reads the slit number, is operated by a mark detecting means 24 provided on an index scale. The slit number, which is read by the means 26, is compared with the preset slit number, which is determined by a reference-mark setting device 28, by a length-measuring slit-number confirming means 30. The positions of the detected marks 22A... are made to be length measuring original points on conditions of the coincidence signal from the means 30 and the detected mark signal from the means 24 immediately after the coincidence signal. |
