Drawing surface adjusting mechanism for scanning pattern drawing

Abstract

A drawing surface adjusting mechanism suitable for use with a large scanning pattern drawing apparatus in which a scanning optical system scans drawing rays of light along scanning lines on a workpiece on a drawing board. A plurality of light-emitting units project rays of light in a wavelength region outside a sensitivity range of the workpiece onto a drawing surface of the workpiece in such a way that the rays substantially converge at more than one point along a scanning line of the drawing rays of light, preferably at center and end points along the scanning line. A plurality of condenser lenses are provided for focusing beams of light from the plural light-emitting units after the beams have been reflected by the drawing surface. A plurality of light-detecting elements are disposed at points of condensation by respective ones of the condenser lenses to produce output signals representing differences in condensation points that occur as the lenses depart from or approach the drawing surface. A drive unit effects relative displacement between the scanning optical system and the drawing board in response to the outputs from the light-detecting elements.