Abstract: A breather filter for a hard disk drive is attached to a hole provided in the cover of the disk drive. The breather filter has a first sheet that forms a diffusing tube at a position corresponding to the hole provided in the cover of the disk drive. The filter also has a second sheet forming an opening at a position corresponding to the diffusing tube of the first sheet. A third sheet of the filter has an adsorbent layer at a position corresponding to the opening in the second sheet. Finally, a fourth sheet, including a filter layer, covers the adsorbent layer of the third sheet and is stacked with each of the sheets.

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.

Abstract: An apparatus for correcting a scranning beam produced by a polygonal mirror tilting in small surface segments in each mirror surface segment caused by uneven mirror surfaces of the polygonal mirror. Data indicative of the amount of tilting in each of the surface segments is stored in a memory, which is addressed by a data signal indicative of the present scanning position of the polygonal mirror. Output data from the memory is applied to an acousto-optical modulator disposed in the beam path between the light source and the polygonal mirror.

Abstract: A monitor mechanism for use with a scanning optical apparatus in which the direction of polarization is utilized to separate a source laser light beam into a pattern drawing and a monitor beamlet and to synthesize them again into a single after passing through a scanning lens and beam deflector. The two beamlets can thus be controlled so as to project towards the deflector and scanning lens in the same direction, which is effective in reducing the offset between the pattern drawing and monitor beams that may occur on account of such factors as variations in lens performance.

Abstract: A drawing surface adjusting mechanism for use with a scanning pattern drawing apparatus capable of not only moving a drawing board in a vertical direction but also tilting it, whereby the chance of bringing the drawing surface within the depth of focus of a scanning lens is increased even if the drawing surface has waviness or other flaws within the width of a single storke of scanning.

Abstract: A table assembly that is simple in construction and which yet resists yawing in an effective way and is adapted for use with a scanning pattern drawing apparatus which involves continuous movements of the table. The inventive table assembly includes a master table that is slidable in one direction with respect to a fixed portion of the overall assembly and to which a drive force for causing the table to slide in the one direction is transmitted directly, and a working table that is slidable in the one direction with respect to the fixed portion and which is linked to the master table by connecting means having rigidity in the one direction and elasticity in a direction perpendicular to the one direction.