JPH03212664A - Optical scanner - Google Patents

Abstract

PURPOSE:To form electrostatic latent images which vary in resolution with dots of several kinds of diameters on a surface to be scanned by changing the output of a laser beam with which a photosensitive member is irradiated by the operation of a dot diameter changing means thereby changing the diameter of the laser beam. CONSTITUTION:The resistance value between a power source circuit 1 and a laser diode 20 is changed by turning on a short switch 23 to vary the quantity of the current to be supplied to the diode 20 and to switch the light output of the scanning light with which the surface to be scanned is irradiated to two stages; Pa, Pb, when the dot diameter is changed by the need for changing the resolution of printed images or others with the optical scanner 19. Then, the diameters Da, Db of these laser beams vary in the part where the light intensity is higher than the threshold THL of the surface to be scanned and, therefore, the electrostatic latent images varying in the resolution are formed with the dots of two kinds of the diameters on the surface to be scanned.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical scanning device used in laser printers and the like.

2. Description of the Related Art In recent years, electrophotography has been developed as a simple and high-quality printing method, and optical scanning devices exist to realize this method. In this optical scanning device, a scanning mirror equipped with at least one reflective surface is attached to the rotating shaft of a driving device and placed on the output optical path of a laser light source, and a surface to be scanned is placed on the optical path of the reflection surface of the scanning mirror. A photosensitive member is positioned to move relatively in the sub-scanning direction, and there are post-objective type and pre-objective type optical scanning devices (both not shown) depending on the optical path and the arrangement of optical components. There is.

In such an optical scanning device, the light emitted from the laser light source is reflected on the reflective surface of a scanning mirror that rotates by the driving force of a driving device to form main scanning light, and this main scanning light is relatively moved in a sub-scanning direction. An electrostatic latent image is formed by irradiating the surface of the photosensitive member to be scanned.

Then, for example, the electrostatic latent image on the photosensitive member is developed with charged toner and transferred onto printing paper, thereby performing image formation by electrophotography.

Laser printers and the like exist as devices that utilize the above-mentioned optical scanning device, and there is a demand for such devices to have a function that allows the resolution to be varied according to the operator's wishes. In other words, if printing speed is more important than image quality, image formation is performed at high speed with normal dots, and if printing with higher image quality than printing speed is desired, the scanned surface of the photosensitive member is irradiated with a predetermined method. Small dots are arranged densely by reducing the beam diameter and lowering the scanning speed. As a means for changing the diameter of dots forming an electrostatic latent image on the scanned surface of a photosensitive member, Japanese Patent Laid-Open No. 60-2
There are devices disclosed in Japanese Patent Publication No. 20309 and Japanese Patent Application Laid-open No. 164759/1983.

Therefore, the device disclosed in Japanese Patent Application Laid-Open No. 60-220309 is used as the first conventional example of an optical scanning device as shown in FIGS. 5 and 6.
This will be explained based on the diagram. In this optical scanning device 1, a scanned surface 5, which is a reflective surface of a scanning mirror, is positioned on the optical axis of a laser light source 2 via a collimator lens 3 and an aperture 4, and the light reflected by the scanned surface 5 is A scanned surface 7 such as a photosensitive drum is placed on the scanning optical path of the laser beam via an fθ lens 6. Here, as illustrated in FIG. 6, the aperture 4 refers to two long plates 10 and 11 each having a slit 8.9 formed with a width different in the elongated direction, each of which is slidably supported and orthogonal to each other. The optical path is located in the aperture 12 formed by the two slits 8 and 9.

With such a configuration, in this optical scanning device 1, the size of the opening 12 consisting of the slits 8 and 9 is varied by sliding each of the long plates 10, 11, so that the laser beam irradiated onto the scanned surface 7 Corresponds to changes in resolution by changing the diameter of the light beam.

Next, the device disclosed in Japanese Patent Application Laid-Open No. 57-164759 is shown in FIGS. 7 and 8 as a second conventional example of an optical scanning device.
This will be explained based on the diagram. In this optical scanning device 13, the emitted light from two laser light sources 14 and 15 arranged in parallel are focused on the same point on the scanned surface 18 of the photosensitive drum 17, which is a photosensitive member, by the deflection of the imaging lens 16. It's like a statue. Note that, as illustrated in FIG. 8, the laser light source 14
．． 15 is an output characteristic A with different light intensity distribution on the beam plane;
B, and the photosensitive characteristics of the scanned surface 18 of the photosensitive drum 17 are determined by a threshold value THL (Threshold Level
l).

In such a configuration, in this optical scanning device 13, by driving one or both of the laser light sources 14 and 15, the output characteristics of the scanning light irradiated onto the surface to be scanned 18 are controlled by CA.
By changing to three types, L[B] and (A+B), the diameter of the portion where the light intensity of the laser beam is equal to or higher than the threshold value THL is changed to correspond to a change in resolution.

Problems to be Solved by the Invention The above-mentioned optical scanning devices 1 and 13 are capable of varying the diameter of the dots that form electrostatic latent images on the scanned surfaces 7 and 18 through predetermined operations, so that they are suitable for high-resolution printing and other applications. High-speed printing can be selectively performed.

However, the optical scanning device 1 illustrated in FIG. This complicates the structure, lowers productivity, and impedes miniaturization and weight reduction of equipment.

In addition, the optical scanning device 13 illustrated in FIG. It is also necessary to form parts, which increases the number of parts in the optical system, which reduces the productivity of the device, and requires extremely high precision in the optical system, making it less practical.

Means for solving the problem A laser light source in which the light intensity of the emitted light is larger toward the center of the beam,
A scanning mirror with a reflecting surface located on the emission optical path of the laser light source, a drive device that rotatably supports this scanning mirror, and a scanned surface having a photosensitive characteristic having a threshold value are arranged relative to each other on the reflection optical path of the scanning mirror. The dot diameter changing means variably sets the light output of the laser light source, and the dot diameter changing means is operated to irradiate the surface of the photosensitive member to be scanned. The optical output of the laser beam is changed, and the diameter of the portion of the laser beam with the light intensity that exposes the surface to be scanned is changed.

The light output of the laser beam irradiated onto the surface to be scanned of the photosensitive member is changed by operating the action dot diameter changing means, and the diameter of the portion of the light intensity that exposes the surface to be scanned by this laser beam is changed. This makes it possible to form electrostatic latent images with different resolutions on the scanned surface using dots of several diameters, contributing to the production of printers that can switch the print mode between high-resolution printing and high-speed printing. I can do it.

Embodiment A first embodiment of the present invention will be explained based on FIGS. 1 and 2. In the optical scanning device 19 of the present embodiment, a reflecting surface (not shown) of a rotatable scanning mirror is located on the optical axis of a laser diode 2o, which is a laser diode 2o, which is a laser light source in which the light intensity of the emitted light is greater toward the center of the beam. The scanned surface (
(not shown) is located so as to be movable in the sub-scanning direction.

In this optical scanning device 19, a first current limiting resistor 22 is connected between the laser diode 20 and the power supply circuit 21.
and a second current limiting resistor 24 connected in parallel with a short switch 23 serving as dot diameter changing means are inserted.

In this configuration, in this optical scanning device 19, when the dot diameter is changed because the resolution of the printed image needs to be changed, the short switch 23 is turned on and off to reduce the resistance between the power supply circuit 21 and the laser diode 20. By changing the value and varying the amount of current flowing through the laser diode 2O, the optical output of the scanning light irradiated onto the surface to be scanned can be changed to Pa and P.
Switch to step b.

Then, as illustrated in FIG.
, Db are different, it is possible to form electrostatic latent images with different resolutions on the scanned surface using dots having these two types of diameters.

In this optical scanning device 19, as illustrated in Table 1 below, when the short switch 23 is turned off, the amount of current Ia flowing into the laser diode 20 is equal to the resistance of the two current limiting resistors 22 and 24. Value [R, + R,]
The dot diameter Da is small because the optical output of the laser diode 20 is reduced.

Furthermore, when the short switch 23 is turned on, the amount of current Ib flowing into the laser diode 20 is regulated only by the resistance value [R1] of one current limiting resistor 22, so it becomes large, and the optical output of the laser diode 2o increases. Therefore, the dot diameter Db is large.

Table 1 Next, a second embodiment of the present invention will be described based on FIGS. 3 and 4. This optical scanning device 25 has a structure in which a third current limiting resistor 27 to which a second short switch 26 is connected in parallel is added to the circuit structure of the optical scanning device 19 described above.

In this configuration, in this optical scanning device 25, the diameter of the dot that forms the electrostatic latent image on the surface to be scanned can be adjusted from D1 to D by operating the two short switches 23 and 26, respectively.
4 types can be selected.

In other words, in this optical scanning device 25, the combination of the three current limiting resistors 22, 24° 27 can be changed by operating the short switches 23, 26, as illustrated in Table 2 below. The resistance value that regulates the amount of current I flowing into 20 is [R+R, 10Ryo], [
The optical output of the laser diode 20 can be switched in four stages by changing it to four types: [R, + R3], [R, + R,], and [R3], and the electrostatic latent image can be created by dots with diameters D to D4. can be formed in a variety of ways.

Table 2 Effects of the Invention As described above, the present invention comprises a laser light source in which the light intensity of the emitted light is larger toward the beam center, a scanning mirror provided with a reflecting surface located on the emission optical path of this laser light source, and this scanning mirror. A drive device that is rotatably supported, a photosensitive member whose scanned surface having a photosensitive characteristic having a threshold value is located on a reflection optical path of a scanning mirror so as to be movable in the sub-scanning direction, and a light output of a laser light source that is variably set. The dot diameter changing means changes the light output of the laser beam irradiated onto the scanned surface of the photosensitive member by operating the dot diameter changing means, and the part of the light intensity of the laser beam that exposes the scanned surface. By changing the diameter of the dots, it is possible to form electrostatic latent images with different resolutions on the scanned surface using dots with several different diameters, so the print mode can be switched between high-resolution printing and high-speed printing. In addition, there is no need to provide a mechanism to move a long plate with slits formed therein, or optical components to focus multiple optical paths onto a single point, and the structure of the optical system, etc. Since it is similar to existing optical scanning devices, it has advantages such as extremely simple structure and high productivity.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG.
The figure is a characteristic diagram showing the relationship between the output characteristics of the laser beam and the photosensitive characteristics of the surface to be scanned, FIG. 3 is a block diagram showing the second embodiment of the present invention, and FIG. 5 is a plan view showing the first conventional example, FIG. 6 is a front view of the main part, and FIG. 7 is a side view showing the second conventional example. FIG. 8 is a characteristic diagram showing the relationship between the output characteristics of the laser beam and the photosensitivity characteristics of the surface to be scanned. 19.25... Optical scanning device, 20... Laser light source,
24.26... Applicant for dot diameter changing means: Tokyo Electric Co., Ltd. Diagram

Claims (1)

[Claims] A laser light source in which the light intensity of emitted light is greater toward the center of the beam, a scanning mirror with a reflective surface located on the emission optical path of this laser light source, a drive device that rotatably supports this scanning mirror, and a photosensitive material having a threshold value. A photosensitive member whose characteristic scanned surface is relatively movable in sub-scanning on the reflection optical path of the scanning mirror, and dot diameter changing means for variably setting the light output of the laser light source, The optical output of the laser beam irradiated onto the surface to be scanned of the photosensitive member is changed by operating a diameter changing means, and the diameter of the portion of the laser beam with the light intensity that exposes the surface to be scanned is changed. An optical scanning device characterized by: