| 摘要 |
PURPOSE:To prevent printing errors and quality degradation from occurring due to an irregularity in a linear scale, by providing a circuit means for correcting the DC level of a read signal to be constant when optically reading a linear scale. CONSTITUTION:Light emitted from a light-emitting diode 11 is received by a photo-transistor 31 through the linear scale 10 such as a steel scale provided with a slit pattern. The read signal (a) containing an increment or decrement is amplified by an amplifier 32 such as a differential amplifier. An output signal from the amplifier 32 is rectified and smoothed by a rectifying circuit 33, which sets a time constant for a C-R combination so as to leave only the increment or decrement (b) of the read signal (a). When the increment or decrement (b) is inputted to a page-side input terminal of the amplifier 32, an output (c) from the amplifier 32 is corrected so that the DC level becomes constant. The output (c) from the amplifier 32 is converted into a pulse by a comparator 34, which pulse is used as a printing timing pulse. |
