JPH04249182A - Laser beam printer - Google Patents

Abstract

PURPOSE:To provide a laser beam printer wherein printing function can be shifted in accordance with required image quality and printing time. CONSTITUTION:A main motor drive circuit 208 changes rotational speed of a main motor 216 so as to control conveying speed of a recording paper and a laser drive circuit 209 is controlled to select scanning face of a polygon mirror 102, so that printing speed and scanning line density are changed. Such a control, for example, can be realized easily by writing previously in a ROM 203 in a device as a control data.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam printer, and more particularly to a laser beam printer that can change printing speed and quality.

With the spread of workstations and Japanese word processors, various printers have been commercialized. Among such printers, laser beam printers are attracting attention as a printer that prints quietly and can print at high speed on plain paper.

FIG. 6 shows an outline of the configuration of a conventionally used laser beam printer. The main body 12 of the laser beam printer 11 is provided with a laser scanning device 13 on its upper part, and a photosensitive drum 15 is irradiated with a laser beam modulated according to an image signal. Parts such as a charge corotron 16, a developing device 17, a transfer corotron 18, and a cleaning device 19 are arranged around the photosensitive drum 15.

The charge corotron 15 has the role of uniformly charging the photosensitive drum 15. The charged photoreceptor drum 15 is scanned with a laser beam to selectively eliminate the charge, thereby forming an electrostatic latent image. The electrostatic latent image is developed by a developing device 17, and a toner image appears on the drum surface. This toner image is transferred from the cassette tray 21 to a sheet 23 fed out by a half-moon roller 22. The paper onto which the toner image has been transferred is fixed by the fixing device 24, and then discharged from the device. In FIG. 6, the broken line represents the conveyance path 26 of the paper 23 sent out from the cassette tray 21.

[0005]

[Problems to be Solved by the Invention] Incidentally, in a laser beam printer, since it is necessary to control the photosensitive drum 15 at a constant speed, it is necessary to control the printing speed and the density of scanning lines per unit time similarly to a normal electrostatic copying machine. The scanning line density is constant. However, the scanning line density ranged from 240 dots per inch (DPI) to 300 dots per inch (DPI) for early laser beam printers.
DPI was common, but recently laser beam printers with 400 DPI to 600 DPI have become mainstream. This is due to the fact that conventionally text information was mainly printed, but recently, input/output devices that handle image information have become widespread, and so-called desk-top electronic publishing has become commonplace. There is also a demand for smoothing fonts for text information, and there is a trend toward favoring outline fonts.

At present, as the quality of images continues to improve, the image processing of laser beam printers becomes more complex and the number of scanning lines increases. At present, the printing speed of printers has not improved much. Therefore, when the workload of an office in which a laser beam printer is installed increases, it becomes necessary to install another laser beam printer, which poses a problem of a heavy economic burden.

[0007] Furthermore, as the quality of images increases, a large capacity page memory is required to store one page's worth of images, which poses a problem in that it greatly affects the cost of laser beam printers.

Furthermore, in laser beam printers that process image information in addition to text information, it takes much more time to process image information than to process text information.
There has been a problem in that the time required from the start of information processing to the end of printing varies greatly depending on the content of the information to be printed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser beam printer that can further increase the printing speed when image quality is not so important.

Another object of the present invention is to provide a laser beam printer that can keep the time until printing substantially constant regardless of the content of the image to be printed.

Still another object of the present invention is to provide a laser beam printer that can perform image processing for printing using a plurality of line memories without using a page memory.

0012

[Means for Solving the Problems] The invention according to claim 1 has a speed decoding means for decoding the designation of the printing speed, and a speed for setting the conveying speed of the paper to be recorded according to the content of the decoding of the printing speed. The laser beam printer is provided with a setting means.

That is, in the invention as claimed in claim 1, a speed decoding means is provided for decoding the data for specifying the printing speed supplied from the host computer or the operation panel of this laser beam printer, and the paper is processed at the decoded printing speed. , so that printing can be performed by selecting one of a plurality of printing speeds.

In the invention according to claim 2, there is provided a density decoding means for decoding the designation of the scanning line density, a polygon mirror for scanning the laser beam, and a scanning surface of the polygon mirror according to the content of the decoding of the scanning line density. The laser beam printer is provided with scanning plane selection means for selecting the scanning plane.

That is, in the invention as claimed in claim 2, a density decoding means is provided for decoding data for specifying the scanning line density supplied from the host computer or the operation panel of this laser beam printer, and the decoded scanning line density is The number of scanning planes of the polygon mirror is selected to correspond to .

[0016] In the invention as set forth in claim 3, there is provided a printing speed control means for controlling the printing speed in two stages, high speed and low speed; and print content discriminating means for determining whether the print content is text information or other image information. The laser beam printer is equipped with a printing speed control means that selects the printing speed to the high speed side when the print content is text information, and to the low speed side when the print content is image information.

In other words, in the invention described in claim 3, it is determined whether the printed content is text information or image information on a page-by-page or line-by-line basis, and in the case of image information, it takes a relatively long time to process until printing. Therefore, printing is performed at low speed, and in the case of text information, the processing up to printing is relatively short, so printing is performed at high speed to adjust the overall processing time.

[0018]

EXAMPLES The present invention will be explained in detail with reference to Examples below. Outline of Structure of Laser Beam Printer FIG. 2 shows an outline of the laser beam printer used in this embodiment. Note that FIG. 2 shows this laser beam printer viewed from the side, and the left side of the figure is the front of the laser beam printer.

This laser beam printer 100 is equipped with a laser scanning device 101. Laser scanning device 101
A semiconductor laser (not shown) that modulates and outputs laser light according to an image signal is arranged. The laser beam emitted from this semiconductor laser is transmitted to a polygon mirror 102.
and is deflected according to this rotation. After passing through the fθ lens 103, the deflected laser beam passes through the mirror 1
The traveling direction is changed by 04 and 105, and the laser beam is outputted from this laser scanning device.

A photosensitive drum 106 is arranged on the extension of the laser beam output from the laser scanning device 101 and rotates at a constant speed in the direction of the arrow. Laser scanning device 10
The laser beam output from the photosensitive drum 1
A predetermined exposure position 107 of 06 is repeatedly scanned in its axial direction, that is, in the main scanning direction. A charge corotron 108 is arranged slightly in front of this exposure position 107 facing the photoreceptor drum 106, and the photoreceptor drum 1
The surface of 06 is uniformly charged. By irradiating the charged photoreceptor drum 106 with a laser beam, an electrostatic latent image corresponding to image information is formed on the drum surface. This electrostatic latent image is developed by a developing device 109 on the drum surface downstream of the exposure position. Inside the developing device 109, there is a developing roll 110 for developing an electrostatic latent image by magnetically making the toner stand up, a toner supply mechanism 111 for supplying the toner in the cartridge to the developing roll 110, etc. parts are arranged. A predetermined developing bias is applied to the developing roll 110.

The toner image formed by the developing device 109 is moved to a position facing the transfer corotron 112 by the rotation of the photosensitive drum 106, where it is electrostatically transferred onto recording paper (plain paper). That will happen. Note that the charge corotron 1 used in this example
08 and transfer corotron 112, a single corotron wire is stretched in a space covered with a shielding member.
It has a structure in which a voltage application terminal is provided at one end.

Next, a brief description will be given of the conveyance path of the recording paper. Recording paper (not shown) is stored in a cassette tray 114 that is inserted from the front into a paper feeder 113 that is removably disposed at the bottom of the laser beam printer 100.
It is designed to be layered. Cassette tray 114
The recording paper placed in the uppermost layer is sent out of the tray 114 by a half-moon roll 115 having a half-moon shape. Note that other means such as a retard roll may be used instead of the half-moon roll 115.

The fed recording paper travels along a path indicated by a broken line by a transport roll 128, and is stably transported at a constant speed in synchronization with the rotational position of the photosensitive drum 106. In this way, the recording paper passes between the photosensitive drum 106 and the transfer corotron 112 at a desired timing. Only at this point in time,
The transfer corotron 112 discharges, thereby electrostatically attracting the toner image on the photosensitive drum 106 in the direction of the transfer corotron 112, thereby transferring the toner image onto the recording paper. The recording paper on which the transfer has been performed is charged from its back surface by a charge eliminating needle (not shown) disposed on the downstream side of the transfer corotron 112, and is peeled off from the drum surface. After the peeled recording paper is conveyed along a conveyance path of a predetermined length to release the tension,
The toner is transported to a fixing device 118 consisting of a pair of heat roll 116 and pressure roll 117. In the fixing device 118, the recording paper is nipped by a heat roll 116 with a predetermined width.
and the pressure roll 117. At this time, the side of the recording paper onto which the toner image has been transferred becomes the heat roll 116 side, and the pressure roll 117 presses the recording paper against the heat roll 116 to enable efficient heat transfer. The heat roll 116 is controlled to a constant high temperature. In this state, the toner image on the recording paper is thermally fixed to the paper surface.

An exit roll 1 is provided on the exit side of the fixing device 118.
19 is prepared, and the recording paper conveyed to this exit roll 119 is discharged to the upper part of the laser beam printer 100. The recording paper is ejected through the above-mentioned path so that the recording surface is facing down, and the sheets can be printed one page at a time and then closed with a stapler in the order in which they were ejected.

On the other hand, the toner image that has not been transferred to the recording paper is removed from the drum surface by a cleaning device 120 located further downstream of the transfer corotron 112. The cleaning device 120 includes a blade 120b for scraping toner from the drum surface;
A film 120a is arranged to prevent toner leakage.

By the way, the laser beam printer 100 of this embodiment has a photosensitive drum 106, a cleaning device 120, a charge corotron 108, and a developing device 10.
9 are integrally constructed as an EP (Electric Printing) cartridge 121. Further, the laser beam printer 106 of this embodiment has a front cover 123 shown by a dotted line that opens and closes around a hinge 122. By opening the front cover 123, the user can remove paper jams and replace the EP cartridge 121 and transfer corotron 112 very easily. Furthermore, the laser beam printer 100 of this embodiment is configured so that the user can easily attach and detach the fixing device 118.

A power supply section 124 consisting of a low voltage power source and a high voltage power source is arranged at the rear of the laser scanning device 101.
It supplies the necessary power to each component. Power supply section 124
A control device 125 is arranged behind the laser beam printer 100 and electrically controls the laser beam printer 100. An image information processing device 1 is provided above the power supply section 124 and the control device 125.
26 is arranged to translate image information sent from a computer or the like into the language of the laser beam printer 100 and send it to the control device 125.

As described above, in the laser beam printer 100 of this embodiment, so-called mechanical components are arranged at the front of the device, and so-called electrical components 127 are arranged at the rear. Device circuit configuration

FIG. 1 shows the main part of the circuit configuration of a laser beam printer. Laser beam printer 10
0 is the first one for performing general operations as a printer.
A CPU (central processing unit) 201 is provided. The first CPU 201 connects to the ROM 203 through the internal bus 202.
, RAM 204, operation panel 205, internal interface (I/F) circuit 206, scanner motor drive circuit 20
7. Main motor drive circuit 209, laser drive circuit 20
It is connected to circuits or elements such as 9.

Here, a ROM (read only memory) 203 stores a program for general control of this laser beam printer. A RAM (Random Access Memory) 204 stores temporary data required to control the laser beam printer. The operation panel 205 is connected via an I/O port (not shown), and is configured to input necessary data using keys and to display data to be notified to the operator on a liquid crystal display board (not shown). The internal interface circuit 206 is connected via another internal bus 212 to a dedicated CPU 211 provided for image processing.

The scanner motor drive circuit 207 is a circuit that drives the scanner motor 215 provided to drive the polygon mirror 102 shown in FIG. In this embodiment, the polygon mirror 102 is always controlled to rotate at a constant speed regardless of the conveying speed of the recording paper. A main motor drive circuit 208 is configured to control the drive of the main motor 206. Here main motor 2
16 is used not only for rotating the photosensitive drum 106 shown in FIG. 2 but also for conveying recording paper. The laser drive circuit 209 is connected to a laser oscillator 217 for irradiating the polygon mirror 102 with a laser beam. The laser oscillator 217 is capable of controlling the laser oscillation output in two stages in order to change the diameter of the laser beam.

On the other hand, a CPU provided for image processing
211 is connected to the internal interface circuit 206, ROM 221, RAM 222, line memory group 223, and external interface circuit 224 via an internal bus 212. Here, the ROM 221 stores a control program for image processing. The RAM 222 temporarily stores data necessary to control this image processing. The line memory group 223 is composed of, for example, 12 line memories. The external interface circuit 224 is connected to a host computer 231 that supplies image signals and gives instructions regarding printing.

By the way, this laser beam printer operates according to the instructions of the host computer 231 or the operation panel 205.
By the operation of (a), the scanning line density during printing can be set to high or low.
(b) It is also possible to automatically change the transport speed of the recording paper according to the content of the image information. Note that in the laser beam printer of this embodiment, printing is performed at 600 DPI when the scanning line density is set to "high", and printing is performed at 300 DPI when the scanning line density is set to "low".

FIG. 3 shows an outline of the control of the laser beam printer when a change in scanning line density is instructed from the host computer side. In this case, when the CPU 211 of the laser beam printer receives a print command from the host computer 231 through the external interface circuit 224 (step S101; Y), it receives the resolution instruction command therein (step S102; Y).
, it is determined whether or not this is 300 DPI (step S103). Resolution or scanning line density is 300DP
If it is I (Y), the polygon mirror 102 is scanned across the surface (step S104). That is, as will be explained in detail later, scanning is performed by skipping over the surfaces of the polygon mirror 102 one by one.

On the other hand, the resolution instruction is 300DP.
When it is other than I, that is, when it is 600 DPI (step S103; N), normal control is performed to scan the entire surface of the polygon mirror 102 (step S105).

The control shown in FIG. 3 assumes that the recording paper is transported at a constant speed, and after a print command is issued, the scanning line density remains unchanged until the printing operation is completed. It is assumed that.

On the other hand, when the resolution is specified in units of lines or in units of blocks each consisting of a certain number of lines, the conveyance speed of the recording paper is fixed at a constant value, and the It is only necessary to change the number of scanning lines. In this case, the control flow may be such that the change in the resolution instruction command is grasped and the switching between the partition scan (step S104) and the full surface scan (step S105) is performed.

FIG. 4 shows an example of control when the laser beam printer side automatically controls printing according to the type of image information sent from the host computer. In this example, when a print command is received from the host computer 231 (step S
201; Y), the laser beam printer determines whether the image information sent is text information or image information (step S202). In the case of text information composed of code information such as characters, processing within the laser beam printer can be performed relatively quickly, so the printing speed of 2V (V represents a predetermined speed) is used to print the recording paper. Conveyance control is started (step S203). Further, in this case, the entire surface of the polygon mirror 102 becomes a target of laser beam scanning (step S204).

On the other hand, if the image information received from the host computer 231 is image information (step S
202;N), since the information is processed bit by bit, the processing time is relatively long. Therefore, in this case, the recording paper is conveyed at a printing speed V that is half of the text information (step S205). At this time, there is no change in the rotational speed of the polygon mirror 102. Therefore, when interplane scanning is performed (step S206), the scanning line density is the same as in the case of text information.

Incidentally, it is assumed that the number of surfaces of the polygon mirror 102 of the laser beam printer of this embodiment is 2N. Furthermore, as already explained, the conveyance speed of the recording paper, that is, the printing speed in the sub-scanning direction, is Vmm/sec and 2.
Vmm/sec can be selected.

In the laser beam printer of this embodiment, the number of revolutions of the scanner motor 215 is set in accordance with the printing speed of 2V. Therefore, if the scanning line density per 1 mm of recording paper is f, the rotation speed n of the scanner motor 215 can be expressed by the following equation (1).

[0042]

[Math 1]

Therefore, the video frequency used for pixel-by-pixel signal processing in a laser beam printer is F [Hz].
This can be expressed by the following equation (2).

[0044]

[Math. 2] F= 2V×f2×W
...(2) Here, the code W is
It represents the total scanning width (mm).

Assume that the laser beam printer 100 is given a command to select the printing speed V from the host computer 231, typically a personal computer. CPU 201 shown in FIG. 1 receives this command via internal interface circuit 206. Then, data for realizing the printing speed V in the ROM 203 is selected.

Such data includes: (1) scanning the polygon mirror 102; (2) scanning the main motor 216;
(2) Adjust other control timings such as conveyance of the recording paper so that they are simply double those in the case of a 2V printing speed. However, when the laser beam performs main scanning, the time from the time when the sensor that determines the start position of the image signal detects the laser beam until the start of the image signal is 2V at the printing speed.
The settings are exactly the same as in the case of . This is because the rotation speed itself of the polygon mirror 102 does not change, and if this time is set to twice that in the case of a printing speed of 2V, the starting position of the image signal on each line will be different from that in the case of a printing speed of 2V. This is because inconveniences may occur.

When the CPU 201 reads out data suitable for the printing speed V from the ROM 203, it controls each section accordingly. Further, when image information is sent from the host computer 231, the CPU 211 divides the line memory group 223 into two groups, writes image information one line at a time to a plurality of line memories belonging to one group, and writes the image information one line at a time to the line memories belonging to one group. Image information is read line by line from a plurality of line memories belonging to the same group. C.P.
The line memory group 223 is controlled by the U223 in this way on a group-by-group basis, and when writing in one group is completed, reading out of that group starts, and at the same time, writing of image information into the other group starts. The same applies below.

By the way, when control is performed at the printing speed V, the polygon mirror 102 rotates at the same rotational speed as when the printing speed is 2V, and the video frequency is also set to the same frequency as when the printing speed is 2V. . Therefore, in order to set the scanning line density when the printing speed is V to be the same as that when the printing speed is 2V, the partition scanning is performed as described above.

Now, assume that the number of sheets printed per minute by the laser beam printer at printing speed V is A1. If the length of the recording paper is L (mm) and the interval in the conveyance path between continuously conveyed recording sheets is ΔL, then the number of sheets printed per minute A1 can be calculated using the following equation (3). .

[0050]

[Math 3]

On the other hand, if an instruction is given to print at a printing speed of 2V, the laser beam printer will print at a printing speed of 2V.
V will be controlled in a predetermined manner. That is, the laser beam is modulated for each surface of the polygon mirror 102, and the number of sheets printed per minute A2 expressed by the following equation (4) is realized.

[0052]

[Math 4]

FIG. 5 shows the relationship between the video clock for controlling the scanning surface of the polygon mirror and the printing speed. Figure (a) shows the case where the printing speed is V, and the video clock 251 is set at time t1, which corresponds to each scanning plane.
Starting at t2, t3, . . . , the scanning time for each line is generated.

In contrast, FIG. 2B shows a print speed of 2V.
This represents the case of In this case, the video clock 252 is clocked at times t1, t3, . . . on the first, third, fifth, and so on of the polygon mirror 102 (FIG. 1).
The scanning time for each line is generated in a continuous manner with the start time being . . . . That is, in the example shown in FIG. 5, the video clock 252 is not generated on the line starting from time t2 because it is suppressed by a gate circuit (not shown).
No image is formed on this line.

Therefore, in the case of the printing speed V shown in FIG. 5(a), if the first line is scanned at time t1, the second line is scanned at time t2; In the case of printing speed 2V shown in figure (b), time t
When the first line is scanned at time t3, the second line is scanned at time t3.

Next, a supplementary explanation will be given regarding the control for switching the scanning line density. When a command for the scanning line density f is given from the host computer 231, the scanner motor 2
15 is given by the above-mentioned equation (1). In this example, the scanning line density f is "300". At this time, the laser beam printer scans the polygon mirror 102 across the surface. Therefore, the scanning line density f is given by the following equation (5).

[0057]

[Math 5]

On the other hand, when a command for a scanning line density of 2f is given from the host computer 231, the laser beam printer scans the entire surface of the polygon mirror 102. The scanning line density 2f at this time is given by the following equation (6).

[0059]

[Math 6]

[0060] In this way, twice the scanning line density in the sub-scanning direction of the recording paper is realized.

In this example of switching the scanning line density,
As explained above, it is assumed that the conveyance speed of the recording paper does not change before and after switching. For this reason, depending on the device, when the scanning line density is f, the line spacing may be too wide. In such a case, the scanning line density 2
The power of the laser beam may be increased when the scanning line density is f compared to when the scanning line density is f, and the spot diameter of the laser beam on the photoreceptor drum 106 may be made substantially thicker.

As explained above, in the laser beam printer of this embodiment, if the printing speed is switched in accordance with the method shown in FIG. 4 in consideration of the data processing speed in printing, text information that is processed quickly can be The printing speed becomes faster, and the printing speed becomes faster for image information that is processed slowly, so the capacity of the buffer memory that stores image information during printing can be significantly reduced. That is, it is no longer necessary to prepare a page memory and process images page by page as in the past, and images can be printed simply by using a plurality of line memories as described in the embodiment.

Furthermore, in this embodiment, control data is written in the ROM 203 to control switching of printing speed and scanning line density, so not only can control be performed easily, but even when changing the control contents, This can be easily realized by rewriting the contents or replacing the ROM 203.

Note that in consideration of the print quality required for text information and image information, text information is scanned at a scanning line density f, and image information is scanned at a finer scanning line density. Of course, scanning may be performed at 2f. In this case, the image information can be reproduced with high quality, and the expressiveness of the printed matter can be further enhanced.

[0065]

As explained above, according to the invention as set forth in claim 1, since the printing speed can be specified in the laser beam printer, the printing speed can be switched depending on the printing content. It is possible to improve administrative efficiency.

According to the second aspect of the invention, since the scanning line density can be switched without changing the rotation speed of the polygon mirror in the laser beam printer,
Speed control is not complicated, cost increases are avoided, and printing work can be performed efficiently according to the content of image information.

Furthermore, according to the third aspect of the invention, since the printing speed is switched depending on whether the image information to be processed is text information or not, memory can be used efficiently while keeping the scanning line density constant. This has the effect of providing an inexpensive printer.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main parts of the circuit configuration of a laser beam printer according to an embodiment.

FIG. 2 is a schematic configuration diagram of this laser beam printer.

FIG. 3 is a flowchart showing the flow of control when switching the scanning line density.

FIG. 4 is a flowchart showing the flow of processing when switching print control according to the content of image information.

FIG. 5 is a waveform diagram comparing the generation states of video clocks at two types of printing speeds.

FIG. 6 is a schematic configuration diagram showing an example of a conventional laser beam printer.

[Explanation of symbols]

100 Laser beam printer 102 Polygon mirror 201, 211 CPU 203, 221 ROM 207 Scanner motor drive circuit 208 Main motor drive circuit 209 Laser drive circuit 216 Main motor 223 Line memory group 231 Host computer 251, 252 Video clock

Claims (3)

[Claims] 1. A laser characterized by comprising speed decoding means for decoding a designation of a printing speed, and speed setting means for setting a conveying speed of paper to be recorded in accordance with the decoding of the printing speed. beam printer. 2. Density decoding means for decoding designation of a scanning line density, a polygon mirror for scanning a laser beam, and a scanning device for selecting a scanning surface of the polygon mirror according to the content of the decoding of the scanning line density. 1. A laser beam printer, comprising surface selection means. 3. Printing speed control means for controlling the printing speed in two stages, high speed and low speed; printing content determining means for determining whether the printed content is text information or other image information; 1. A laser beam printer comprising a printing speed control means for selecting a printing speed on a high speed side in the case of image information, and selecting a printing speed on a low speed side in the case of image information.