JPH04335671A - Device and method for forming image - Google Patents

Abstract

PURPOSE:To reduce a packaging area by dividing fundamental frequency at frequency-dividing ratio corresponding to write density commanded from a host machine and obtaining picture element frequency required for each write density. CONSTITUTION:When a write density selection signal S showing write density 400dpi is transmitted to a laser printer 1 from the host machine 5, a signal corresponding to the write density 40Odpi is transmitted to a frequency-dividing ratio setting circuit 7 by a selection circuit 6. The circuit 7 transmits the frequency-dividing ratio N=1/16 corresponding to the wirte density 400dpi to a programable frequency division circuit 4 based on the transmitted signal. In such a case, a signal whose fundamental frequency is 25MHz is transmitted to the circuit 4 from the fundamental frequency generation circuit 2. The frequency divider 4 divides the fundamental frequency 25MHz at the frequency- dividing ratio N to obtain the picture element frequency 1.388MHz for the write density 4O0dpi. Then, the image is formed by the picture element frequency. Therefore, the picture element frequency is obtained just by setting the frequency-dividing ratio N to the circuit 4 according to a command from the host machine 5.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser printer or a digital copying machine, and an image forming method, and particularly to simplifying the switching of a plurality of writing densities.

0002

2. Description of the Related Art In an image forming apparatus such as a laser printer, the writing density is set to 240/240 by instructions from a host machine.
It may be necessary to switch between 300/400/600 dpi. In such cases, conventionally,
Either the crystal oscillator in the printer can be replaced according to the pixel frequency of the writing density, or the
Using the laser printer 52 for pi, the host machine 5
The laser printers 51 and 52 were switched and connected based on instructions from the printer. However, recently there has been a demand for a single laser printer to automatically switch between different writing densities without switching between different laser printers. are also appearing. As shown in FIG. 6, this laser printer has 240/240/
A switching circuit 65 switches a plurality of oscillators 61 to 64 to obtain pixel frequencies corresponding to writing densities of 300/400/600 dpi.
A switching circuit 65 is switched in response to a writing density selection signal S from the host machine 5 to select a predetermined pixel frequency, and an image is formed based on the selected pixel frequency.

0003

[Problems to be Solved by the Invention] As described above, in a laser printer that automatically switches between multiple writing densities to form an image, it is necessary to use multiple oscillators that send out pixel frequencies corresponding to each writing density. However, the mounting area of the multiple oscillators becomes large, and the efficiency is very low. Furthermore, the use of a plurality of oscillators increases the cost, and the reliability of the device itself decreases in proportion to the number of oscillators.

The present invention has been made in order to solve these shortcomings, and provides an image forming apparatus and an image forming apparatus that can automatically form images according to a plurality of writing densities using one oscillator. The purpose of this invention is to obtain a method for forming the method.

[0005]

[Means for Solving the Problems] An image forming apparatus according to the present invention automatically selects a predetermined writing density from a plurality of types of writing densities according to a command from an external host machine, and performs writing. An image forming apparatus that forms an image while scanning a photoreceptor with a light beam corresponding to the image includes a fundamental frequency generating means that outputs a fundamental frequency that is the least common multiple of the plurality of writing densities, and a fundamental frequency that is inputted. The present invention is characterized in that it includes pixel frequency generation means for generating a pixel frequency according to the writing density commanded by the host machine. Preferably, this pixel frequency generating means is constructed from a programmable frequency dividing circuit in which a frequency division ratio is set for each writing density. And multiple writing densities are 240dpi and 300dpi.
, 400dpi, 600dpi, the least common multiple of these multiple writing densities is 1200dpi, and from the host machine 240dpi, 300dpi, 400dpi, 6
When each writing density of 00dpi is commanded, 1200
The fundamental frequency corresponding to the dpi is set to 1/25 and 1/25, respectively.
It is preferable to divide the frequency at a frequency division ratio of 16, 1/9, or 1/4 to obtain the pixel frequency required for each writing density.

[0006] Furthermore, the image forming method according to the present invention automatically selects a predetermined writing density from among a plurality of types of writing densities according to a command from an external host machine, and performs processing according to the written image. In an image forming method in which an image is formed while scanning a photoreceptor with a light beam, a pixel frequency corresponding to the writing density commanded by the host machine is generated from the fundamental frequency of the least common multiple of the above-mentioned plurality of writing densities. It is characterized in that an image is formed based on the generated pixel frequency.

[0007]

[Operation] In this invention, one fundamental frequency generating means is provided that outputs a fundamental frequency that is the least common multiple of a plurality of writing densities, and this fundamental frequency is divided by a frequency division ratio according to the writing density commanded from the host machine. to obtain the pixel frequency required for each writing density.

[0008]The plurality of writing densities are 240 dpi, 3
At 00dpi, 400dpi, 600dpi,
The fundamental frequencies corresponding to the least common multiple of these multiple writing densities, 1200 dpi, are 1/25, 1/16, and 1/9, respectively.
, or by dividing the frequency at a frequency division ratio of 1/4, each writing density is 240 dpi, 300 dpi, 400 dpi, 6
The pixel frequency required for 00 dpi can be obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is an actual circuit diagram. As shown in the figure, a laser printer 1 has a fundamental frequency generation circuit 2 and a pixel frequency generation circuit 3. The basic frequency generation circuit 2 has a writing density of 24
0dpi, 300dpi, 400dpi, 600dpi
A fundamental frequency corresponding to the least common multiple of 1200 dpi is generated. The pixel frequency generation circuit 3 includes a programmable frequency dividing circuit 4 that generates a pixel frequency using a frequency division ratio N corresponding to each writing density, and a writing density selection signal S from the host machine 5.
The frequency division ratio setting circuit 7 includes a selection circuit 6 that switches and selects a frequency division ratio, and a frequency division ratio setting circuit 7 that sends a frequency division ratio N to the programmable frequency division circuit 4 based on a signal from the selection circuit 6.

Laser printer 1 configured as described above
In explaining the operation of this laser printer 1, first
Explain the principle of The pixel frequency of the writing density is the fundamental frequency corresponding to 1200 dpi generated by the fundamental frequency generation circuit 2 at the writing density of 240 dpi, 300 dpi, 400 dpi.
This can be obtained by dividing the frequency by a frequency division ratio N corresponding to 600 dpi. This pixel frequency is proportional to the square of the writing density ratio. Therefore, each writing density is 240 dpi,
Taking the ratio of 300dpi, 400dpi, 600dpi and the least common multiple of 1200dpi, the writing density is 240dp.
When the writing density is i, it is 1/5, when the writing density is 300 dpi, it is 1/4, when the writing density is 400 dpi, it is 1/3, and when the writing density is 600 dpi, it is 1/2. Here, the pixel frequency WCLK when the writing density is 240 dpi is 0.
If 5MHz, each writing density is 240dpi, 300d
The pixel frequencies WCLK corresponding to pi, 400 dpi, and 600 dpi and the fundamental frequency corresponding to the least common multiple of 1200 dpi are as shown in FIG. That is, 1200
The basic frequency corresponding to dpi is 12.5 MHz, and the pixel frequency WCLK corresponding to writing density 300 dpi, 400 dpi, and 600 dpi is 0.78125 MHz, respectively.
and 1.388MHz and 3.125MHz. The basic frequency corresponding to this 1200dpi is 12.5MHz
and each writing density 240dpi, 300dpi, 400dp
From the pixel frequency WCLK corresponding to i, 600 dpi,
Each writing density 240dpi, 300dpi, 400dpi
, 600dpi are respectively 1/2.
5, 1/16, 1/9, 1/4. Therefore, the frequency division ratio setting circuit 7 sets each writing density to 240 dpi, 300 dpi, and 4.
Obtain the frequency division ratio N corresponding to 00 dpi and 600 dpi. Note that the pixel frequency WCLK0. with a writing density of 240 dpi.
5 MHz is an example, and is actually calculated according to factors such as the maximum print paper width (laser beam main scanning speed) and print speed (laser beam sub-scanning speed).

Furthermore, laser printers with a writing density of 1200 dpi are not currently in use, and the writing density is approximately 600 dpi at most. Therefore, 240dpi and 300dpi, which are rarely used and are frequently used,
The standard was 1200 dpi, which is the least common multiple of dpi, 400 dpi, and 600 dpi.

Furthermore, in an actual circuit, the pixel frequency for each writing density requires a duty of 50% for the high level and low level, so the fundamental frequency of 12.5 MHz at 1200 dpi is
25MHz is used.

Laser printer 1 configured as described above
When a writing density selection signal S with a writing density of 400 dpi, for example, is sent from the host machine 2, the selection circuit 6 sends a signal corresponding to the writing density of 400 dpi to the frequency division ratio setting circuit 7. The frequency division ratio setting circuit 7 determines the writing density of 40 from the sent signal.
A frequency division ratio N=1/16 corresponding to 0 dpi is sent to the programmable frequency division circuit 4. A signal having a fundamental frequency of 25 MHz is sent to the programmable frequency dividing circuit 4 from the fundamental frequency generating circuit 2, as shown in the time chart of FIG. Therefore, the programmable frequency divider 4 has a basic frequency of 25MHz.
is divided by a frequency division ratio N to obtain a pixel frequency of 1.388 MHZ with a writing density of 400 dpi. Then, an image is formed using this pixel frequency. In this way, the pixel frequency for each writing density can be obtained simply by setting the frequency dividing ratio N in the programmable frequency dividing circuit 4 according to a command from the host machine 1. Note that the value of the frequency division ratio N remains constant and does not change even if the maximum print paper width, print speed, etc. change.
There is no need to change the circuit, and the basic frequency can be set by changing it depending on the specifications such as the printing speed of the laser printer.

[0014]

Effects of the Invention As explained above, the present invention provides one fundamental frequency generating means that outputs a fundamental frequency that is the least common multiple of a plurality of writing densities, and converts this fundamental frequency to the writing density specified by the host machine. Since the pixel frequency required for each writing density is obtained by dividing the frequency using a frequency division ratio corresponding to can also be reduced.

Furthermore, since it is possible to select a plurality of pixel frequencies by dividing the fundamental frequency with a frequency division ratio corresponding to each writing density, one image forming apparatus can automatically select a plurality of pixel densities. can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a circuit diagram of the above embodiment.

FIG. 3 is an explanatory diagram showing pixel frequencies and frequency division ratios in the above embodiment.

FIG. 4 is a time chart showing the operation of the above embodiment.

FIG. 5 is an explanatory diagram showing a conventional laser printer.

FIG. 6 is a block diagram of a conventional laser printer that switches writing density.

[Explanation of symbols]

1 Laser printer 2 Basic frequency generation circuit 3 Pixel frequency generation circuit 4 Programmable frequency division circuit 5
Host machine 6 Selection circuit 7 Division ratio setting circuit

Claims (5)

[Claims] Claim 1: A predetermined writing density is automatically selected from among multiple types of writing densities according to a command from an external host machine, and a light beam corresponding to the written image is applied onto the photoreceptor. In an image forming apparatus that forms an image while scanning,
A fundamental frequency generating means that outputs a fundamental frequency that is the least common multiple of the plurality of writing densities, and a pixel frequency generating means that receives the fundamental frequency and generates a pixel frequency according to the writing density commanded from the host machine. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein said pixel frequency generating means comprises a programmable frequency dividing circuit in which a frequency division ratio is set for each writing density. [Claim 3] The plurality of writing densities are 240 dpi and 30 dpi.
It consists of 0dpi, 400dpi, and 600dpi, and the least common multiple of the above plurality of writing densities is 1200dpi,
240dpi, 300dpi, 400 from host machine
When each writing density of dpi and 600dpi is commanded, the fundamental frequency corresponding to 1200dpi is set to 1/1.
3. The image forming apparatus according to claim 2, wherein the pixel frequency required for each writing density is obtained by dividing the frequency at a frequency division ratio of 25, 1/16, 1/9, or 1/4. 4. A predetermined writing density is automatically selected from among a plurality of writing densities according to a command from an external host machine, and a light beam corresponding to the written image is applied onto the photoreceptor. In an image forming method that forms an image while scanning,
An image forming method characterized by generating a pixel frequency according to a writing density commanded by a host machine from a fundamental frequency that is the least common multiple of the plurality of writing densities, and forming an image based on the generated pixel frequency. . [Claim 5] 240dpi, 300dpi, 400dpi
dpi, set the least common multiple of writing density consisting of 600 dpi to 1200 dpi, and write 240 dpi from the host machine.
When writing densities of i, 300dpi, 400dpi, and 600dpi are commanded, the fundamental frequency corresponding to 1200dpi is divided by a division ratio of 1/25, 1/16, 1/9, or 1/4, respectively. 5. The image forming method according to claim 4, wherein the pixel frequency required for each writing density is obtained.