JPH02238475A - Resolution switching device for electrophotographic printing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a resolution switching device for an electrophotographic printing device, and particularly to a resolution switching device for a two-color electrophotographic printing device that performs dot-by-dot exposure using a light beam. The aim is to be able to perform high-resolution single-color printing at a low cost, and to do so at a low cost. Beam diameter switching means is provided for switching the amount of energy applied from the light source driving means to the light source so as to reduce the beam diameters of the first and second light sources by about half each, and an image signal for monochrome printing is provided. An image signal distributing means is provided which inputs the signal, distributes the signal to the first and second light source driving means, and outputs the signal, and when printing in monochrome, the signal is input from the first and second light source. It is configured to alternately expose dots on the surface of the photoreceptor with a beam whose diameter is reduced to one-fold. [Field of Industrial Application] This invention relates to a resolution switching device for an electrophotographic printing device.
In particular, it relates to a resolution switching device for a two-color electrophotographic printing device that performs dot-by-dot exposure using a light beam. Two-color printing by two-color electrophotographic printing equipment is used for form overlays, charts, and highlighted text. However, two-color electrophotographic printing devices are generally capable of printing in a single color, and in the case of monochromatic black documents, such as official documents, minutes, and reports,
High quality printing is often required. Therefore, it would be very convenient for the user if the resolution could be higher when performing monochrome printing with a two-color electrophotographic printing device than when printing in two colors. [Prior Art] A two-color electrophotographic printing device using LEDs exposes a photosensitive drum to two types of images to be printed in different colors.
Two sets of exposure devices are placed around the photosensitive drum.
It has an exposure process of 2 times. In conventional two-color electrophotographic printing equipment, one exposure device performs one exposure for single-color printing, and the other exposure device does not operate. [Problems to be Solved by the Invention] However, as in the past, one exposure device simply performed one exposure during monochrome printing, but in the case of monochrome printing that requires high resolution, it is difficult to increase the resolution. Because we were unable to provide the necessary information, we were unable to meet the needs of our users. Furthermore, various attempts have been made to make the resolution switchable in general dot matrix printers, but these usually require a large amount of equipment cost. The present invention solves such conventional drawbacks and improves the resolution of an electrophotographic printing device that can perform high-resolution single-color printing in a two-color color photo printing device, and can achieve this at low cost. The purpose is to provide a switching device. [Means for Solving the Problems] In order to achieve the above object, the resolution switching device of the electrophotographic printing device of the present invention has two types of resolution switching devices for printing in different colors, as shown in FIG. first and second light sources 2.3 that expose dots of an image on the surface of the photoreceptor l, and first and second light sources that apply luminous energy to each of the light sources 2 and 3 in accordance with an input image signal. from each of the light source driving means 4.5 to the light source 2.3 so as to reduce the beam diameters of the first and second light sources 2.3 to about half each. By inputting the beam diameter switching step 6 for changing the applied energy amount and the image signal for monochrome printing,
It has an image signal distribution stage 7 for distributing and outputting the signal to the first and second light source driving means 4.5, and when printing in monochrome, the first and second light source driving means 4.5 are output. 3, single-color printing can be performed with twice the resolution of two-color printing by alternately exposing dots on the surface of the photoreceptor l with a beam whose diameter is reduced to about one-half of the normal diameter. It is characterized by the following. [Function] When performing two-color printing, the first and second light sources 2
, 3, with the normal beam diameter and normal resolution, the photoreceptor l
Dots of two types of images are each exposed on the surface of the image. When performing monochrome printing, image signals for monochrome printing are distributed to the first light source driving means 4 and the second light source driving means 5 in the image signal distribution means 7. From the first and second light source drive means 4.5, the light sources 2.
The applied energy that reduces the beam diameter of 3 to about half is the first
and applied to the second light source 2.3. And the first
The beams from the second light source 2.3 alternately expose dots on the surface of the photoreceptor l, and monochrome printing is performed at twice the resolution of two-color printing. [Example] An example will be explained with reference to the drawings. Figure 2 shows the part of the photosensitive drum that exposes and transfers images in a printer. In the figure, l is a photosensitive drum, which is a photosensitive member, and is rotationally driven in the direction of arrow R by a motor (not shown). A first charger 12 uniformly charges the surface of the photosensitive drum 1 passing through this charger. Reference numeral 13 denotes a first exposure section, in which a laser beam emitted from a first laser source (2 in FIG. 3) is scanned by a known polygon mirror (not shown) to expose the surface of the photosensitive drum l. The first developing device 14 exposes the dots of the image at this position, and the toner supplied from the replaceable toner case is
A toner image of the image that is attracted to the surface of the photosensitive drum 1 and exposed at the first exposure section l3 is formed on the surface of the photosensitive drum 1. In this way, the first charger l2, the first exposure part l3
First exposure and development are performed by the first developing device l4. In the case of normal two-color printing,
For example, red color toner is used to form a red toner image on the surface of the photosensitive drum 1. l6 is the second charger, and here again the photosensitive drum l
Charge the surface uniformly. 17 is a second exposure section,
A laser beam emitted from a second laser source (3 in FIG. 3) is scanned by a second polygon mirror (not shown) to expose image dots on the surface of the photosensitive drum l. 1B is a second developing device, which forms a toner image of the image exposed at the second exposure section 17 using black toner. In this way, the second charger l6, the second exposure part l7
A second developing device 18 performs second exposure and development, and a black toner image is formed on the surface of the photosensitive drum 1. A transfer device 19 transfers the toner image formed on the surface of the photosensitive drum 1 by the first and second development onto a sheet of paper (not shown). 20 and 2l are an AC static eliminator and an optical static eliminator that apply an electric field and light to the photosensitive drum l to remove static electricity from the surface of the photosensitive drum l. Reference numeral 22 denotes a cleaning section for cleaning waste toner etc. adhering to the surface of the photosensitive drum 1.
FIG. 3 shows a control circuit that controls the light emission of the first and second laser sources 2 and 3 that perform exposure. In the figure, 2.3 is a semiconductor laser, each of which emits light in response to a current value given by a drive circuit 4.5. Reference numeral 30 denotes a main control section of a so-called mechanical control section which inputs control signals and image signals from a controller (not shown) to control the mechanical section of the printer. 4.5 is each laser source consisting of a semiconductor laser diode (LD)? , 3 are the first and second drive circuits. Each drive circuit 4.5 has a first and second changeover switch 35.
．． 36 to the two-color image signal output terminals c1 and c2 of the main control section 3o. Therefore, 2
When printing in color, the first and second switches 35.3
6 to the two-color image signal output terminals c, , C2. Then, dots of an image to be printed in different colors are formed on the photosensitive drum l by the first and second laser sources 2.3.
is exposed to light on the surface of The main control unit 30 is provided with an output terminal M for outputting a monochromatic image signal and a delayed signal output terminal D, and each output terminal M
, D are connected to the input terminals of the first and second AND circuits 41 and 42, respectively, and a NOT circuit 43 is inserted between the delayed signal output terminal D and the input terminal of the second AND circuit 42. It is connected. The output end of each AND circuit 41.42 is connected to the first and second drive circuits 4.5 via the first and second changeover switches 35.36. When performing monochrome printing using the embodiment apparatus, first, black toner is put into both the first and second developing devices 14.18, and the first and second changeover switches 35.36 are set to As shown in Figure 3, both are connected to the AND circuits 41 and 42.
A monochrome image signal is output from the monochrome image signal output terminal M of the .
The subsequent operations will be explained with reference to the time chart in Figure 4. A pulse signal for displaying the brightness and darkness of each dot is output from the monochrome image signal output terminals MI and M2. Furthermore, M
+ outputs information on hatched dots in Fig. 6, and M2 outputs information on unhatched dots. t in FIG. 4 is the pulse length for displaying one normal dot. For example, a pulse with a length of t/2 is output from the delayed signal output terminal D. Then, the lth
The AND circuit 4 outputs a pulse that matches the first half of t and inputs it to the first drive circuit 4, and the second AND circuit 4 outputs a pulse that matches the first half of t.
A pulse matching the latter half of t is output from the circuit 42 and input to the second drive circuit 5. In addition, when using a laser scanning optical system, the monochromatic image signal is
It is output in synchronization with a clock created based on the beam detection output of the laser beam detection sensor installed at the laser scanning start position. In this way, pulses are distributed to the first and second drive circuits 4.5 in such a manner that one monochromatic image signal pulse is divided into halves. Figure 5 shows the relationship between laser power and beam diameter. For example, if the maximum value of the distribution of laser power A is 1, the beam spread at a power of 1/e 2 is generally used as the beam diameter. The beam diameter at this time is A'
Then, the beam diameter of laser power B at this level is B'. Therefore, if the original beam diameter is A' and the beam diameter during monochrome printing is B', then B'''iA'/
It is only necessary to control the energy B applied to each laser source 2.3 in each drive circuit 4, 5 so that .2. In this way, the beam diameter output from the first and second laser sources 2.3 is reduced to approximately half of the original beam diameter, and the beam diameter output from the first and second laser sources 2.3 is reduced to approximately half of the original beam diameter. By alternately exposing the surface of the photosensitive drum 1 with a beam so that dots do not overlap, a monochrome image can be printed at twice the resolution of two-color printing. The 1s6 diagram shows the dots (for example, 2
40 dpi) and dots of a single-color printed image at double resolution (for example, 480 dpi). In addition, in the process of printing at double resolution as described above,
The number of rotations of the scanning polygon mirror (not shown) is 2.
It can be the same as for color printing. Further, in the above embodiment, the output end for the two-color image signal and the output end for the monochrome image signal are provided separately, but the present invention is not limited to this. The signal and monochrome image signal may share any signal route. In this embodiment, a semiconductor laser is used as a light source that emits a light beam, but the present invention is not limited to this, and a light emitting diode (LED) may also be used. Furthermore, in this embodiment, the first. Second developer 14
．． We have explained the example of adding black toner to the 1st
Even if red toner is still in the developer L4,
The developing bias voltage of the first developing device l4 is set so that the first developing device 14 does not perform development. Or the first
The developing device 14 may be positioned at a position apart from the photosensitive drum, and only the second developing device may be operated. [Effects of the Invention] According to the resolution switching device for an electrophotographic printing device of the present invention,
By simply exposing the dots of a single-color image alternately using two light sources for two-color printing, it is possible to print twice as many dots, and the size of the dots at that time is , approximately 2 by controlling the energy applied to the light source.
As the size has been reduced to 1/2, it is possible to perform high-resolution single-color printing using only firmware control, without changing the basic structure of conventional two-color electrophotographic printing equipment, and at low cost. It has excellent effects that can meet the needs of users.

[Brief explanation of drawings]

Figure 1 is a diagram of the principle of the present invention. Figure 2 is a configuration diagram of an embodiment; Figure 3 is a circuit block diagram of the embodiment. FIG. 4 is a time chart diagram of the embodiment, Figure 5 is a diagram showing the relationship between laser power and beam diameter. FIG. 6 is a schematic illustration of image dots in the example. In the figure, l... photoreceptor, 2... light source, 3... light source, 4...Light source driving means, 5...Light source driving means, 6...beam diameter switching means, 7... Image signal distribution means.

Claims (1)

[Claims] First and second light sources (2,
3), and first and second light source driving means (4) that apply luminous energy to each of the light sources (2, 3) according to the input image signal.
, 5), and each of the light source driving means (4, 5) so as to reduce the beam diameter of the first and second light sources (2, 3) to approximately one-half, respectively.
) to the light sources (2, 3); and a beam diameter switching means (6) for switching the amount of energy applied to the light sources (2, 3) from the above; It has an image signal distributing means (7) for distributing and outputting image signals to the means (4, 5), and in the case of monochrome printing, from the first and second light sources (2, 3), the normal approximately 2 By alternately exposing dots on the surface of the photoreceptor (1) with a beam whose diameter is reduced to one-fold, monochrome printing can be performed at twice the resolution of two-color printing. Features: Resolution switching device for electrophotographic printing equipment.