Toshiba 453, 452, 350, 353 service manual Devaton

(3)fθ lenses-1 and -2

These two lenses perform the following adjustment on the laser beam reflected by the polygonal mirror.

a.Uniform-velocity scanning

Since the polygonal mirror is rotating at a uniform velocity, the laser beam reflected from the mirror scans over the drum surface at a uniform angular velocity; namely, the pitch between the dots on the drum is wider at both ends than at the center of the scanning range. The fθ lenses help to correct this difference, making all the dot-to-dot pitches equal on the drum surface.

b.Face tilt correction

The reflecting face of the polygonal mir- ror is tilted slightly to one side against the perfect vertical. Horizontal deviation of the laser beam which is caused by the tilt is corrected.

c.Sectional shape of laser beam

The shape of the laser beam spotted on the drum is adjusted.

Wder

Narrower

Drum

fØ Lens-

fØ Lens-2

Same ntervals

Fig. 8-203

Mrror plane s tlted. Devaton

Fig. 8-204

8

(4)H-Sync signal detection PC board

The laser beam which is started to be scanned from one of the reflected plane of the polygonal mirror is reflected by the H-Sync detection mirror and enters the PIN diode on the H-Sync signal detection PC board. The primary scanning synchronizing signal is generated based on this reflec- tion.

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