JPH06202022A - Laser printer device - Google Patents

Abstract

PURPOSE:To form a longitudinally long spot suitable for gradational expression without changing an optical system and sacrificing the resolution by assigning plural laser elements as a light source, and composing the longitudinally long laser spot of laser lights obtained by driving the laser elements at the same time. CONSTITUTION:As a hexagonal mirror 8 rotates, the spot position shifts from a point A to a point B on a photosensitive drum 1, and consequently, one scanning line is drawn. Then, the photosensitive drum 11 is rotated in a specific direction to draw lines in order, thereby forming one image called an electrostatic latent image on the photosensitive drum 11. Here, a multi-beam laser element is utilized as a laser unit 4 to form the longitudinally long spot. Namely, the laser elements are assigned as the light source which emits the laser lights for scanning the photosensitive body 11, and the laser lights obtained by driving the laser elements at the same time are put together to form the longitudinally long spot.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser printer device, and in particular, it can be applied to a laser printer device in which gradation is expressed by laser light.

[0002]

2. Description of the Related Art Conventionally, as a laser printer, a laser beam emitted from a laser light source is bent and shaken in a predetermined direction by a reflection mirror such as a galvanometer mirror or a polygon mirror, and is shaken on a photosensitive drum through a condenser lens such as an fθ lens. There is one that is configured to perform scanning and imaging in the cylindrical direction.

[0003]

By the way, in such a laser printer, when outputting not only a binary image of black and white but also an image with gradation, it is necessary to continuously change the energy of laser light, For example, a so-called brightness modulation method in which the output of the laser is changed, or a so-called PWM modulation method in which the width of the drive pulse is changed while keeping the output of the laser constant is used.

Of these, the brightness modulation is likely to be unstable, so that the PWM modulation is usually used. P in fact
The WM modulation changes the driving time, and the time given to form one dot and the distance the laser spot moves during that time are fixed.

That is, as shown in FIG. 2, assuming that the spot of the laser is circular and the distance that the laser moves within the time for forming one dot of the image is L, the dot D0 _min formed with the minimum PWM pulse width. 2A, and the dot D0 _max formed with the maximum PWM pulse width is shown in FIG.
(B). This maximum dot D0 _max is the minimum dot D0 _min pulled by the distance L.

Since the expressiveness of gradation corresponds to the area ratio of the minimum dot D0 _min and the maximum dot D0 _max , it is desirable that the spot shape when driven by the minimum pulse is as small as possible in order to increase this ratio. . Therefore, as shown in FIG. 3, if the circular spot is left as it is, it is possible to increase the ratio between the minimum dot D1 _min and the maximum dot D1 _max .

However, in this case, the pitch in the sub-scanning direction, which is considered to be almost equal to the diameter of the spot circle, is reduced, so that it is necessary to increase the number of scanning lines, which eventually reduces the printer speed. become.
Therefore, in order to solve this problem, as shown in FIG. 4, the spots D2 _min and D2 _max of the laser light have an ellipse having a short axis in the main scanning direction and a long axis in the sub scanning direction as shown in FIG. It is possible to make it into a shape.

Such an elliptic spot D2 _min , D2
_{In order} to obtain _max , the lens system must be designed so that the magnification of the optical system differs in the vertical and horizontal directions, and even if it is designed in this way, there is a limit to the vertical and horizontal ratios, so the resolution must be increased. At the sacrifice, a method of performing gradation expression over two dots or more was used.

The present invention has been made in consideration of the above points, and proposes a laser printer device capable of forming a vertically long spot suitable for gradation expression without changing the optical system and without sacrificing the resolution. Is what you are trying to do.

[0010]

In order to solve such a problem, according to the present invention, in a laser printer device 1 for scanning a photosensitive member 11 with laser light to print predetermined information, a light source 4 for emitting laser light. A plurality of laser elements are assigned to the laser diode and laser beams obtained by simultaneously driving the plurality of laser elements are combined to form a vertically long laser spot D10.

Further, in the present invention, a laser for arranging a plurality of laser lights in a direction orthogonal to the scanning direction on the photoconductor 11 and scanning the plurality of laser lights on the photoconductor 11 to print predetermined information. In the printer device 1, as the light source 4, a plurality of laser elements are assigned to a plurality of groups each including a plurality of laser elements, and the laser beams obtained by driving the plurality of laser elements of each group at the same time are combined to form a photoconductor. A plurality of vertically long laser spots D10 arranged in a direction orthogonal to the scanning direction on 11 are formed.

[0012]

A plurality of laser elements are assigned to the light source 4 which emits a laser beam for scanning the photoconductor 11, and the laser beams obtained by driving the plurality of laser elements at the same time are combined so that an optical system is obtained. The vertically long spot D10 can be formed without changing the resolution and without sacrificing the resolution.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a laser printer according to the present invention as a whole, and a video controller 2 and a DC controller 3 are arranged between them and an external device, and the writing optical system 4 is controlled by the DC controller 3. The desired data can be printed.

The light emitted from the laser diode in the laser unit 5 under the control of the DC controller 3 passes through the collimator lens 6 and the cylindrical lens 7, and then rotates according to the scanner motor 7 to form a hexahedral mirror. A spot is formed on the photosensitive drum 11 by the image forming lens 9 and the reflecting mirror 10 after being reflected by 8.

With the rotation of the hexahedral mirror 8, the position of the spot moves from the point A to the point B on the photosensitive drum 11 so that one scanning line is drawn. Here, rotate the photosensitive drum 11 in the direction of arrow a in the figure,
By drawing lines one by one, one image called an electrostatic latent image is formed on the photosensitive drum 11. This latent image is visualized by a developing device (not shown) which is not shown, and is further transferred and fixed on paper and then output.

In this embodiment, a so-called multi-beam laser element in which laser elements are integrated on one chip is used as a laser unit to form a vertically long spot. Assuming that the divergence of the laser beam is actually isotropic and the vertical and horizontal magnifications of the optical system are equal, the spot D0 of one laser has an energy distribution as shown in FIG. The graph shows the energy level on the orthogonal axis passing through the center of spot D0.

Two spots D0 having such a spread are
As shown in FIG. 3, the combined energy EN expands only in the array direction and hardly expands in the direction orthogonal to the array as shown in FIG.
It becomes 0. In this embodiment, such a composite vertically long spot D10 is easily formed by simultaneously driving two adjacent dots of the multi-beam laser.

If this composite vertical spot D10 is used for writing, the same effect as that obtained by using the elliptical spot D2 described above can be obtained. Composite vertical spot D
The fact that the shape of 10 is not an ellipse is not a problem because it is the aspect ratio of the spot that is important as is apparent from the use of the elliptical spot D2.

The shape of the synthetic energy distribution in the long axis direction when the laser spots are combined changes depending on the pitch of each laser and the spot diameter. For example, as shown in FIG. 4, four beams are combined. As shown, it is monomodal or multimodal.

In electrophotography and the like, a portion having a predetermined threshold level or higher actually contributes to image formation. Therefore, even if multi-modality is exhibited, if the valley portion of the energy level exceeds the threshold. Although there is no problem, it is preferable to have a characteristic that the peak is as flat as possible in the case of gradation expression.

From this point of view, the shape of the composite energy distribution shown in FIG. 4 (B) is the best, so it is desirable to determine the relationship between the pitch interval and the spot diameter in such a manner as described above. Since the pitch interval is determined in the manufacturing process of the laser element, the spot diameter of each beam is actually controlled to obtain the synthetic vertically long spot of the synthetic energy distribution shown in FIG. 4 (B).

According to the above structure, a multi-laser element in which a plurality of laser elements are allocated on one chip is used as a laser unit for emitting a laser beam for scanning the photosensitive drum 11, and the plurality of laser elements are simultaneously driven. By combining the laser beams obtained in this way, it is possible to realize a laser printer capable of forming a vertically long spot suitable for gradation expression without changing the optical system and without sacrificing the resolution.

In the above embodiment, the two spots are arranged so as to obtain the composite vertically long spot. However, if the vertically long spot is required, the number of lasers is three or four. Even if the number is increased, the same effect as that of the above embodiment can be realized.

In the above-mentioned embodiment, the laser printer which draws one line by one scanning is described, but the invention is not limited to this, and it is also applied to a multi-beam printer which draws a plurality of lines by one scanning. it can. In practice, this multi-beam printer uses a multi-beam laser as an ordinary laser printer. Although the basic configuration is the same as that shown in FIG. 1, a multi-beam laser is used in the laser unit 4, and the photosensitive drum 1
A plurality of dots are formed at a time on the drum 1 along the drum rotation direction, and a plurality of lines are drawn at a time by scanning the plurality of dots at a time.

To apply writing by dot combination to such a multi-beam printer, the multi-beam laser elements may be divided into groups by a predetermined number of dots, and each group may be driven simultaneously. For example, as shown in FIG.
If you divide it into groups, you will be able to draw 25 lines at a time.

In the multi-beam laser, the laser elements are normally arranged at equal intervals, but if the desired line spacing cannot be obtained by grouping the laser elements at equal intervals in sequence, FIG.
Or leave some lasers without using (Fig. 6
(A)) or unequal intervals (FIG. 6 (B)) may be used.

When driving each laser element as shown in FIGS. 5 and 6, the driving circuit is basically the same as the conventional one. Although it is possible that each dot can be driven independently and the same write signal is applied to all the dots in each group, as shown in FIG. 7, the drive circuits in the same group are bundled into one signal. It is possible to reduce the number of write signal lines by controlling with. Although the same circuit can be used in both FIG. 5 and FIG. 6, the unused dot portion as shown in FIG. 6A is not wired from the beginning. Therefore, the number of write circuit groups is 25 in FIG. 5 and FIG.
Then it becomes 20 pieces.

[0029]

As described above, according to the present invention, there is provided a laser printer device capable of easily forming a vertically long spot suitable for gradation expression without changing the configuration of the optical system and without sacrificing the resolution. realizable. Further, if the number of dots used for synthesis is increased, a vertically elongated beam much thinner than that of the conventional one can be obtained, and thus sufficient gradation expression can be performed.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of a laser printer according to the present invention.

FIG. 2 is a schematic diagram showing the energy distribution of a circular dot.

FIG. 3 is a schematic diagram showing an energy distribution of a vertically long dot in which two circular dots are superposed.

FIG. 4 is a characteristic curve diagram for explaining a relationship between a pitch interval of a laser element and a beam shape and synthetic energy.

[Fig. 5] 100-beam laser as a multi-beam laser
FIG. 11 is a schematic diagram showing a case where 25 groups are formed.

[Fig. 6] 100-beam laser as a multi-beam laser
FIG. 11 is a schematic diagram showing a case where 25 lines are divided and the line spacing is expanded.

FIG. 7 is a connection diagram showing a drive circuit when 100-beam lasers are divided into 25 groups.

FIG. 8 is a schematic diagram for explaining a case where gradation is expressed by a circular spot.

FIG. 9 is a schematic diagram for explaining a case where gradation is expressed by reducing a circular spot.

FIG. 10 is a schematic diagram for explaining a case where the spot shape is elliptical and gradation is expressed.

[Explanation of symbols]

1 ... Laser printer, 2 ... Video controller, 3
...... DC controller, 4 ... Laser unit, 5 ...
Collimator lens, 6 ... Cylindrical lens, 7 ...
... Skiyan motor, 8 ... hexahedral mirror, 9 ... imaging lens, 10 ... reflection mirror, 11 ... photosensitive drum.

Claims (2)

[Claims] 1. A laser printer apparatus for scanning a photosensitive member with laser light to print predetermined information, wherein a plurality of laser elements are assigned to a light source for emitting the laser light, and the plurality of laser elements are simultaneously driven. A laser printer device characterized in that the laser beams obtained by the above are combined to form a vertically long laser spot. 2. A laser printer apparatus for arranging a plurality of laser beams in a direction orthogonal to a scanning direction on a photoconductor, and scanning the plurality of laser beams on the photoconductor to print predetermined information. As a plurality of laser elements are assigned to a plurality of groups each consisting of a plurality of laser elements, laser light obtained by simultaneously driving a plurality of laser elements of each group is combined, and orthogonal to the scanning direction on the photoconductor. A laser printer device, characterized in that a plurality of vertically long laser spots arranged in the same direction are formed.