JPS58132720A - Picture recording device - Google Patents

Abstract

PURPOSE:To improve a surface quality, by making a beam spot diameter on a surface to be scanned, larger than a scanning line interval, and making its shape elliptical, in an optical scanner. CONSTITUTION:A beam of a gas laser 1 is modulated by a modulating optical system 2 containing an acoustic optical element (AOM)3. When carrier frequency of the AOM3 is varied, as for incident light to a cylindrical lens 4, Wx in the sub-scanning direction remains constant, and a diameter Wy in the main scanning direction is varied, a spot diameter on a photosensitive drum 8 also remains constant in the sub-scanning direction, and a diameter in the main scanning direction is varied. For instance, in case of a portrait system in which the main scanning direction and the longitudinal direction of a character are vertical, the AOM3 is operated, the Wy is made small, and a spot on the photosensitive drum 8 is made an ellipse whose diameter in the main scanning direction is small. It is possible to obtain printing of a good quality, which has eliminated an uneven pitch, by preparing 2 kinds of oscillators, and switching the using oscillator in the main scanning direction and the direction of a character.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention attempts to improve image quality in an optical scanning device by selecting the shape of a beam spot on a scanned object tIfi.

(2) When using a mechanical deflector such as an inverter Ifi@Ii as a deflector for the original beam in an optical scanning table.

When the light deflection surface of a mirror or the like is not perpendicular to its axis of rotation (so-called surface tilt), pitch unevenness of scanning lines occurs on the surface to be scanned, which has an adverse effect of appearing as black or white stripes on a single page. In order to prevent this negative effect, in the so-called sub-scanning direction perpendicular to the scanning line, the lens system (in contrast, the deflection surface and the surface to be scanned are arranged in a military relationship). There are limits to the correction function, and it is not possible to eliminate all effects.

In such a case, as shown in FIG. 1, the beam width (f!) in the sub-scanning direction on the photoreceptor is WXt scanning line pitch d
It is possible to avoid the above-mentioned adverse effects by increasing the size of 7ζ so that the spots on adjacent scanning lines overlap each other. Even in this case, since it is desired that the beam spot size W in the main scanning direction be small, it is desirable that the spot shape be an ellipse with its long axis in the direction perpendicular to the scanning direction.

On the other hand, a place where characters are recorded by laser dating,
There are two methods: boat rate, where im is parallel to the line direction of the sentence, and land skating, where im is perpendicular to this.
As shown in the figure, even with the portrait method of r@), tb
) also, the printed product vt will be better if the spot for forming the character is an ellipse with the long axis in the vertical direction of the character.

The present invention is based on a1! that conventionally, in a light beam scanning device, the smaller the spot flti, the better, and the better the spot shape is circular. On the other hand, in addition to having a certain size, if the spot shape is such that the vertical direction of the character is perpendicular to the main scanning direction, the beam diameter in the main scanning direction versus the beam diameter in the sub scanning direction should be 0.7 or more.
If the vertical direction of one character below 0 is in the royal scanning direction and the f line, by setting this ratio to 10 or more and 13 or less, the pitch unevenness f
vI4 eraser and also made it possible to improve print quality.

Figure 3 shows an example of an implementation in which a gas laser is used as the vanguard and the emitted laser beam is fp4 using an AOMI. The beam of the gas laser is modulated by the AuM optical system 2. In this case, the direction in which the ultrasonic waves travel within the AuM is arranged perpendicular to the scanning direction by the beam deflector 5 such as a rotary multifunction txtts.A VC@-shaped spot is formed on the deflection surface by the cylindrical lens 4, The beam scanned by 650 rotations of deflection is directed to a photoreceptor drum 8 in the scanning direction by an imaging lens 6 having an fe% ratio.
At the same time as forming a spot on the top, since the deflection surface and the photoreceptor l are placed in a geometrically conjugate relationship in the copper travel direction by the fθ lenses 6 and 7, the lindrical lens 7 creates a spot. At the same time when forming the Vc leakage, the inward facing surface prevents the scanning position from being changed due to the Vc leakage.

The beam emitted from a gas laser is generally Iffff-shaped, but the variable beam modulated by AQM becomes an elliptical beam with its short axis in the direction of ultrasonic propagation, as shown in FIG.

The handling axis/minor axis ratio of this beam cross section varies depending on parameters such as the 4y tit laser wavelength, the beam diameter in A□M, the carrier MIl waveform, the refractive index and sound speed of the ultrasonic medium, but this change This is due to changes in the short axis Wy,
During this time, W remains constant. Figure 5 shows the change in x4a due to the change in carrier frequency.
Using a beam of 6v-the, as the ultrasonic medium dNjL=
14m+ PbMo04 (n=2.26 ν== 3.
63-,,,c), and the song @1 shows a beam radius of about 50 μm in AuM and the song 2 also shows a Vk meeting where the beam radius!P is about 60 μm.

Now, as shown in FIG. 6, which shows the optical path diagram in the sub-scanning direction, the imaginary 1! a
P' is formed at a position caused by the light source rather than the deflection surface at a rate β, and has a tilt correction function such that the palm of the cylindrical lens 7 of this virtual plate P' is formed on the photoreceptor drum at a magnification m. In the scanning optical system, the incidence on the cylindrical lens 4 is jt, the east diameter is WX in the sub-scanning direction, Wx in the main scanning direction, and the position of the spot on the photosensitive drum surface is Wc in the main scanning direction, and Wc in the sub-scanning direction. When Wd is the focal length of the first cylindrical lens 4, f4fθ lens 6
Focal length f6. It is known that the following relationship between the focal length f7 of the second cylindrical V lens 7 is sufficient.

Using this relationship, for example, when the carrier frequency of A (JM) is 86 MHz, the beam spot on the photosensitive drum is approximately circular (wc: ``d''), and the optical beam spot is adjusted so that the half peak thereof is slightly larger than the scanning line pitch. Set up the system.

With such an optical arrangement, when the carrier frequency of ALIM is set to 1 kHz, the diameter Wy of the incident light to the cylindrical lens 4 in the main scanning direction changes while the VkWx in the sub-scanning direction remains constant, and! 11. The photoconductor drum-like hot spot is also constant in the sub-scanning direction. For example, the main scanning direction and the vertical direction of the character are perpendicular.

In the case of the portrait method shown in Figure 2 (ra), 80MHz
If A□M is operated in the above manner, Wy becomes small, so the spot on the photosensitive drum has a diameter Wc in the main scanning direction.
becomes a small ellipse. Conversely, in the case of the landscape method shown in Fig. 2 (1b), if the %ALIM is operated at 8 uM) (s or less, an elliptical spot with a large diameter W (in the main scanning direction) can be obtained. By preparing an oscillator and switching the related oscillator between the main scanning direction and the text direction, high-quality printing without pitch unevenness can be obtained.

FIG. 7 shows another embodiment, in which a semiconductor laser 11 is used as a light source.

The divergence of the emitted light from a semiconductor laser is noticeably different in the direction f to the active layer and in the direction perpendicular to it, and even when the light beam travels through the coupling lens 12, the cross section of the light beam has an elongated elliptical shape. It is known that 6. However, in this case too,
The focal resistance 111fθ of the fθ lens 15 and the focal length f of the cylindrical lens 13 inserted as a tilt correction optical system
, , and the focal length f of the cylindrical lens 16
A desired spot size wc1wdf can be obtained on the photosensitive drum 17 by selecting 16 so as to maintain the relationships of equations -1) 2 and 12).

In this case, an external liquid device such as an acousto-optic device AOM is not required for optically variable sea bream, and the optical system can be made simple and compact. It is not possible to create a dual-purpose type by switching between portrait and land scoop use.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the relationship between scanning line pitch and spot size, Fig. 2 is a diagram showing θ of the fixed meal method of Vi211Il, and Fig. 3 is an optical system layout diagram of an embodiment of optical scanning LF production of the present invention. Fourth
The figure is an explanatory diagram of changes in beam surface due to A□M, Figure 5 is a graph showing the relationship between carrier frequency and beam cross-sectional shape, Figure 6 is an original schematic diagram of the optical scanning device in one scanning direction, and Figure 7 is the main @
FIG. 6 is an optical layout diagram of a bright optical scanning device. 1.11: Laser 2: Modulating optical system 3: At1M
4.13 Nijilintrical lens 5.14: Rotating polygon i
1i! 16% t5: fθ lens 7.16: Cylindrical lens 8.17: Photoconductor drum
Figure 5 Figure 6

Claims (1)

[Claims] In an optical scanning device that deflects and scans a light beam from a laser light source using a rotating deflector and forms a beam spot on a scanning surface using a condensing optical system, a light source is disposed in relation to the deflection device and is placed on the deflection surface. @ The optical system that forms the entire inward spot, the linking lens, and the scanning surface are arranged at the intersection, and in a plane perpendicular to the scanning line, the above-mentioned inward direction and the scanning surface are kept in a geometrically optical conjugate relationship, and on the scanning surface. An image recording device characterized in that the beam spot diameter is larger than the scanning line interval, and the shape is entirely elliptical.