JPS58179052A - Laser printer - Google Patents

Abstract

PURPOSE:To ensure a circular form for a spot which has a horizontal scan on a photosensitive drum, by controlling the glowing time of a laser light source within a range of time corresponding to a dot and in relation to the scanning position of a light spot. CONSTITUTION:A glowing time controlling circuit 7 supplies the signals related to scanning spot positions P3, P1, Pc, P2 and P4 from the glowing time controlling data which is previously stored in an RM, etc. and supplies a signal Salpha to a light source driving circuit 5. With the signal Salpha, the longest glowing time talpha is obtained in the vicinity of the positions P1 and P2, and the time talpha is decreased in the vicinity of the positions P3, Pc and P4, respectively. The circuit 5 supplies a writing signal given from a buffer memory 6 and a control signal S and drives a laser light source 1 in response to these two signals. At the same time, the circuit 5 controls the time talpha. The form of a light spot is set at (l+ omegao) with the signal Salpha to the horizontal spot diameter omegao in order to obtain the same diameter as a longer axis (h). Thus the spot becomes circular.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a laser printer that uses a laser as a light source and is constructed by combining four electronic technologies. More specifically, the present invention horizontally scans a laser beam spot on a photoreceptor using an optical scanning means such as a rotating mirror or a galvano mirror so that an image to be recorded is displayed as a set of dots (pixels). It is related to printers.

[Description of prior art]

FIG. 1 is a block diagram of the main parts of a conventionally known laser printer. This device projects a light beam from a laser light source 1 such as a semiconductor laser onto a polygon mirror 3 via a focusing lens 2, and projects the reflected light from there onto a photosensitive drum 4 to form a laser beam spot. Horizontal scanning (main scanning) is performed on the photosensitive drum 4. Here, the laser beam #IU is controlled on and off by the drive circuit 5 according to the image information to be recorded, and the photosensitive drum 4 is rotated in a direction perpendicular to the horizontal scanning direction of the laser beam spot. (referred to as sub-scanning), and an electrostatic latent image corresponding to image information is formed on the photosensitive drum 4 as a collection of dots. Although not shown, this electrostatic latent gI can be used to obtain a recording surface gI on recording paper through a development process, a transfer process, and a fixing process.

By the way, in a laser printer with such a configuration,
Focusing/Z2 focuses the laser beam spot so that it converges, for example, at the center point P of the photosensitive drum (so that the spot diameter is minimized), but in this case, the convergence point is at the same time as the laser beam scans. It moves as indicated by the broken line t, and the binding position shifts near both ends of the photosensitive drum 4, which has the disadvantage that the solution *i decreases.

In order to eliminate such drawbacks, an optical system such as a lens may be installed between the polygon mirror 2-3 and the photosensitive drum 4, but such an optical system such as a lens is expensive, and
The disadvantage is that the configuration is complicated.

[Object of the present invention]

The present invention aims to eliminate these drawbacks of conventional devices and provide a laser printer that has a simple configuration, has a high resolution gIf, and therefore can obtain clear ms.

[Summary of the present invention] The device according to the present invention makes the shape of the light spot from the light source entering the light scanning means into an elliptical shape, and directs this light spot onto the light body in a direction Km perpendicular to the long axis direction of the spot. The lighting time or light output of the light source is controlled within the time range corresponding to one dot in relation to the scanning position of the light spot, and the shape of the laser beam spot on the photoreceptor is determined. The scanning position is also almost the same and has a circular shape.

[Explanation of Examples]

FIG. 2 is a block diagram showing an example of a laser printer according to the present invention. In the figure, 1 is a laser light source, for example a semiconductor laser is used for this. 2 is a spot shape setting optical system, which is not necessarily required if the spot shape from the laser light source 1 is a predetermined shape. This optical system 2 includes, for example, a cylindrical lens 21.
It is composed of a focusing lens 22. Note that this spot shape setting optical system may be a light shielding plate having an elliptical through hole or the like. 3 optically deflects the light beam from optical system 2°
Then, a light deflecting means such as a polygon mirror for horizontally scanning the photosensitive trim 4, and a light source drive circuit for the 5F1 semiconductor laser 1 control the semiconductor laser 1 to turn on and off depending on, for example, the ms information to be recorded. Reference numeral 6 denotes a buffer memory, in which information to be recorded is sequentially stored in the form of a set of dots, for example, for one raster or one sheet. 6
゜ is a counter that specifies the read address of the buffer memory 6, and 61 is a clock generator whose output is applied to the counter 60. Reference numeral 7 denotes a lighting time control circuit that controls the lighting time or optical output of the laser light source 10, and the output from this circuit is applied to the light source drive circuit 5. Reference numeral 8 denotes a timing control NIO circuit, to which a timing signal from the light beam scanning position detection means 80 is applied, and controls the rotational operation of the optical deflection means 3 and the photosensitive drum 4 via the drive motor 30 and the drive motor 40'ft. ing.

FIG. 3 is an explanatory diagram for explaining the spot shape of the laser beam from the spot shape setting optical system 2 used in the apparatus shown in FIG. The shape of the light beam emitted from the spot shape setting optical system 2 is elliptical at its final position, as shown in FIG. 3(A). In addition, in this laser beam A, the depth of focus of the long axis diameter h (in the direction of arrow V) of the elliptical spot is the depth (
The minor axis diameter of the elliptical spot is ω. (arrow 2 directions)
The depth of focus is shallow as shown in FIG. 3(c). In the apparatus of the present invention, such a spot shape is used, and horizontal scanning is performed such that the long axis of this spot is perpendicular to the horizontal scanning direction (arrow X direction).

For example, if a double Peter junction structure semiconductor laser is used as the laser light source 1, the laser beam spot emitted from the laser beam spot itself has the shape and depth of focus as shown in FIG. 3, and in this case, The spot shape setting optical system 2Fi becomes unnecessary.

FIG. 4 is a plan view showing an example of the arrangement of the photosensitive drum 4, the optical deflection means 3, and the laser light source 1 in the apparatus shown in FIG. Here, the imaging position of the laser beam from the laser light source 1 (indicated by a solid line t) is two points p on the photosensitive drum 4,
, p2, each optical system is installed so that they match.

FIG. 5 shows the shape of a spot on the photosensitive drum 4 when the laser beam spot is simply scanned in the optical system shown in FIG. In this case, the image formation positions match at the two points P and I on the photosensitive drum 4, and the laser beam has an elliptical shape, near the center point PC, and near both ends P5. Near P45, the spot deviates from the imaging position and takes on a substantially circular spot shape due to the depth of focus relationship as shown in FIG.

Therefore, in the present invention, by controlling the lighting time ta of the laser light source 1 near the point P, + P2, P, r A circular spot shape is obtained at any scanning position on the photosensitive drum 1, including near the PH point.

FIG. 6 shows the shape of a scanning spot corresponding to one dot near Pl and P2 on the photosensitive drum 4 in the apparatus according to the present invention. In the present invention, the spot diameter (minor axis diameter) ω in the horizontal scanning direction (arrow X direction). , the lighting time (writing time) tα of the laser light source l is determined by the signal Sα from the lighting time control circuit 7.
By controlling according to , the shape of the scanning spot becomes t+ω as shown in FIG. It is controlled so that

However, t is the scanning length corresponding to one dot.

Here, if the long axis diameter of the spot diameter is ih, then preferably ω. By controlling the scanning spot so that +z=h, the shape of the scanning spot 'k, near P1+P2, can be equally circular.

FIG. 7 is an operational waveform diagram for explaining the operation of the apparatus shown in FIG.

FIG. 7(a) is a waveform diagram of the clock signal from the clock oscillator 61, and FIG. 7(b) is a waveform diagram of the clock signal from the clock oscillator 61.
FIG. 3 is a waveform diagram showing an example of a write signal output from the . Here, exposure Fi% t I, non-exposure is 10#
It is represented by the signal. FIG. 7(c) is a waveform diagram showing the control signal Sα from the lighting time control circuit 7. This control signal Sα corresponds to the period of the clock signal and uses a nine-pulse width signal, and this pulse width α changes in relation to the position of the scanning spot on the photosensitive drum. There is.

The light source drive circuit 5Fi inputs the write signal from the buffer memory 6 and the control signal Sα, and drives the laser light source 1 and controls its lighting time tα according to both signals.

FIG. 7) shows a signal waveform for driving the laser light source 1 from the light source drive circuit 5, and the lighting time ta t'' can be changed within the time range BT corresponding to one dot according to the pulse width α of the control signal Sα. I can do it.

FIG. 8 is a diagram showing the relationship between the scanning spot position on the photosensitive drum 4 and the lighting time tα of the laser light source 1.

In the device shown in FIG. 2, lighting time control circuit 7ti, ROM
A signal related to the scanning spot position is input from the lighting time control data stored in advance in the Pg, etc., so that the lighting time tα is the longest near the P , * P 2 point, as shown in Fig. 8. The lighting time tα is controlled to be short near the e Pcm P4 point.

By controlling the lighting time of the laser light source 10 in relation to the scanning position of the light spot within the time range corresponding to one dot, the shape of the spot horizontally scanned on the photosensitive drum can be controlled in which scanning direction. It can be made equally circular in position, and a laser printer with high resolution and good quality can be realized.

In the above embodiment, it is assumed that the optical system is arranged so as to form a spot at points p, , p2 on the photosensitive drum 4 as shown in FIG. 4, and the fC force ζP6. P
The optical system may be arranged so as to form images at around 4 or 20 points. Furthermore, although the lighting time of the laser light source is controlled here, the light output of the laser light source may be controlled in place of or in combination with the lighting time control.

In addition, in FIG. 2, a clock period correction circuit is coupled to the clock oscillator 61, and the period T of this clock signal is changed little by little according to the deflection angle of the laser beam (corresponding to the scanning position of the scanning spot). You can also do this.

This makes it possible to eliminate scanning distortion caused by circular arc scanning.

[Effects of the present invention]

As explained above, according to the present invention, the resolution is high with a simple configuration without using a complicated optical system such as an fθ lens,
A laser printer that can produce clear images can be realized.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the main parts of a conventionally known laser printer;
The figure is a block diagram showing the main parts of an example of a laser printer according to the present invention, Figure 11@3 is an explanatory diagram of the shape of the laser beam spot in the apparatus shown in Figure 2, and Figure 4 shows the arrangement of the optical system in the apparatus shown in Figure 2. FIG. 5 is an explanatory diagram showing the shape of the scanning spot on the photosensitive drum, FIG. 6 is an explanatory diagram of the shape of the scanning spot in the apparatus according to the present invention, and FIG. 7 is an illustration of the shape of the scanning spot on the photosensitive drum. The operating waveform diagram, FIG. 8, is a diagram showing the relationship between the lid with the scanning spot and the lighting time of the laser light source. DESCRIPTION OF SYMBOLS 1... Laser light source, 2... Spot shape setting optical system, 22... Focusing lens, 3... Light deflection means, 4...
・Photosensitive drum, 5...Light source drive circuit, 6...Buffer memory, 7...Lighting time control (b) Patent attorney Nobusuke Ozawa -) (a)
Atsushi 3 figure Leather 4 figure Seri figure 6

Claims (1)

[Claims] (11 In a laser printer in which a laser beam from a laser light source is horizontally scanned on a photoreceptor by an optical scanning means to display and record an image to be recorded as a set of dots, the laser beam spot entering the optical scanning means The laser beam spot is horizontally scanned on the photoreceptor in a direction perpendicular to the long axis direction of the spot, and the lighting time and/or light output of the laser light source is controlled by scanning the light spot. A laser printer characterized in that control is performed within a time range corresponding to one dot in relation to position.