GB1420241A - Scanning device - Google Patents

Abstract

1420241 Automatic control of speed EASTMAN KODAK CO 3 May 1973 [3 May 1972] 21093/73 Heading G3R The deflection of a beam is linearized with respect to a beam deflection drive signal by varying the drive of a deflecting means according to a signal whose frequency is proportional to the measured beam scan velocity. As shown, light from source 16 e.g. a laser or projector bulb is deflected by an oscillating mirror 13 in a galvonometer and by a fixed mirror 19, through an optical grating 22 to a photo-cell 28. The cell receives light modulated by the grating at a frequency proportional to the spacing of opaque lines on the grating and to the beam scan velocity. The photo-cell output passes via a frequency discriminator 32 e.g. a bank of narrow pass filters, and an amplifier 34 to a comparator 36. The comparator 36, which may be a differential integrator, compares the signal from discriminator 32 with a speed reference, from source 38, that is related to the slope of the mirror drive signal from source 40. Any difference is used to supplement, via phase shifter 39, the mirror drive signal to linearize the beam deflection with respect to this drive signal and thus to regulate the beam scan velocity. The drive signal may be sawtooth or parabolic making the speed reference constant or time varying respectively. The apparatus may be used with radiation other than light in scanning systems with a rotating polygon or lens, or in a CRT display.