JP2746925B2 - Image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming apparatus such as a laser printer and a laser copying machine.

[Conventional technology]

A laser beam printer or the like that irradiates a recording medium (image carrier) with a light beam modulated by an image signal, forms a toner image by an electrophotographic process, and transfers and fixes the toner image on recording paper to form an image. In an image forming apparatus, factors that determine image quality are in each process.
The fixing step related to the final image quality is particularly important.

In recent years, there has been an increasing demand for forming color images with printers and copiers. However, in the case of color images, if the transparency and gloss of the toner image cannot be obtained, the image quality will be poor. In particular, when creating an overhead projector (OHP) sheet, the requirement for transparency is much more severe than that of a normal print or copy output. Conventionally, when using OHP sheets or when high image quality (surface gloss) is desired,
The linear velocity of the heat roll of the fixing device is lowered, and the fusing time of the toner image is lengthened. Therefore, the linear velocities of the latent image forming and transferring processes are synchronized with the linear velocities.

In a general image forming apparatus using one light beam scanning device as an optical writing device, the scanning cycle of the light beam has to be changed in accordance with the change in the linear velocity.

As a means for changing the scanning cycle of this light beam, in a device using a rotating polygon mirror as an optical deflector, the rotating speed of the rotating polygon mirror is changed to change the pixel clock, the rotating speed of the rotating polygon mirror is not changed, and the rotating polygon is not changed. There is known a method in which a mirror having a different surface is prepared and switched (JP-A-57-104102).

[Problems to be solved by the invention]

However, in this method, it is generally necessary to stably control the polygon mirror driving motor which requires extremely strict constant speed rotation at a plurality of speeds having different speed ranges, and the driving motor and the control device become expensive. Alternatively,
Providing a plurality of rotary polygon mirrors that require high precision also results in expensive ones. In addition, a mechanical means for switching a plurality of rotating polygon mirrors is required.

On the other hand, a device that has a plurality of light beam light sources as light beam light sources and achieves luminous flux recording by simultaneously deflecting and scanning the light beam light sources is known. There is no known device that lowers the linear velocity of the roller and changes the linear velocity in the latent image forming and transferring steps in synchronization with the linear velocity.

The present invention has been made based on such a background, and an image forming apparatus that obtains an image by multi-beam optical recording has a simple configuration capable of reducing the printing speed. Aim.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a plurality of light emitting sources which are modulated and driven in accordance with an information signal, light beam scanning means for imaging and scanning a light beam of the light emitting source into a spot light beam, and scanning of the light beam. Means for forming an electrostatic latent image on an image carrier moving at a constant speed, developing means for developing the electrostatic latent image, and transfer for moving a visible image developed by the developing means at a constant speed. In an image forming apparatus having a transfer unit for transferring to a transfer material and a fixing unit for fixing an image transferred to the transfer material to the transfer material, the image carrier, the moving speed of the transfer material, and the fixing heat roll of the fixing unit. Rotation speed is 1 / integer of constant speed
Switching means for switching to the light beam scanning means, and a control means for selectively modulating and driving the plurality of light emitting sources in accordance with the speed switching by the switching means so as not to change the scanning speed of the light beam by the light beam scanning means, At constant speed,
When an electrostatic latent image is formed on the image carrier by all the lines of the plurality of light emitting sources per one scan of the light beam, and when the switching means is switched to a constant speed of an integral number, one scan of the light beam is performed. The electrostatic latent image is formed on the image carrier by a line from a light emitting source selectively modulated among the plurality of light emitting sources, and all lines formed at the constant speed by the line from the light emitting source. Is formed on the image carrier.

[Action]

According to the present invention, in an image forming apparatus having a plurality of light beam light sources and performing deflection scanning at the same time to form a latent image, a predetermined light beam is turned off in response to a change in linear velocity. , The scanning synchronization of the light beam can be changed to a fraction of an integer.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The image forming apparatus of the present invention may be either a copying machine or a printer, but the description will be made by taking a printer as an example.

FIG. 1 and FIG. 4 show examples of the apparatus of the present invention, which are monochromatic and multicolor laser printers, respectively. FIG. 2 shows a light beam scanning device commonly used for each.

 The operation of each section will be briefly described with reference to FIG.

The photoconductor 8 is a photoconductive semiconductor using an OPC (organic light guide) or the like, and is uniformly charged by a charging charger 9. When exposed by a spot-like light beam 16 modulated by an information signal, an electrostatic latent image is formed on the photoreceptor 8. When the photosensitive member 8 reaches the developing position by the rotational movement, the charged toner corresponding to the potential distribution adheres by the operation of the developing device 10, and the latent image is visualized. On the other hand, the transfer paper 7 fed by the feed roller 6 at a predetermined timing is
When the leading end of the visible image reaches the transfer point with the timing by the registration roller 5, it moves to the transfer point almost simultaneously and moves at the same speed as the linear velocity v of the photoconductor 8. During this time, the transfer charger 11 operates to transfer the toner for forming a visible image onto the transfer paper 7. After the transfer, the photoreceptor 8 moves at a constant speed as it is, and when the photoreceptor 8 meets the cleaner 12, the residual toner is removed, and the process of recharging and re-exposure is started. On the other hand, the transfer paper 7 keeps moving and the toner image is fixed by the fixing device 13 using a heat roller or the like, and is discharged.

In the drawing, 14 is a rotating polygon mirror, 15 is an fθ lens,
17 is a mirror, 18 is an optical unit, and 19 is dustproof glass.

The optical system is a multiple beam batch scanning system as shown in FIG. The light source 1 is a semiconductor laser array element,
A combination of a plurality of laser light sources (three-beam method in the figure) may be used. 2 is a collimator lens, 3 is a mirror for a light detector, and 26 is a light detector.

Next, a circuit configuration for controlling the beam output of the laser printer shown in FIG. 3 and its operation will be described. It should be noted that the laser printer of FIG. 1 shows a configuration for controlling the output of the single-beam semiconductor laser for convenience of explanation.

In the laser printer of FIG. 1, a laser (light) beam output from a semiconductor laser (light source) 1 is collimated by a collimator lens 2 and deflected by an optical deflector 14 composed of a rotating polygon mirror. 15 forms an image on the charged surface of the photoconductor 8. The image spot is repeatedly moved in the direction of arrow X by the rotation of the rotary polygon mirror 14, and at the same time, the photosensitive member 8 is rotated. The photodetector 26 is provided outside the information writing area, and detects a laser beam deflected by the rotary polygon mirror 14 to generate a synchronization signal. The signal processing circuit 27 applies an information signal (video data) to the semiconductor laser drive circuit 28, and controls the timing of the information signal with a synchronization signal from the photodetector 26.

The semiconductor laser drive circuit 28 drives the semiconductor laser 21 in response to the information signal from the signal processing circuit 27, and irradiates the photoconductor 8 with a laser beam modulated by the information signal, thereby forming an electrostatic latent image. .

This electrostatic latent image is developed by a developing device, and further transferred to a transfer paper such as paper by a transfer device.

A laser beam emitted backward from the semiconductor laser 1 is incident on a photodetector 29 and high intensity is detected, and a control circuit 30 controls a semiconductor laser drive circuit 28 according to an output signal of the photodetector 29. Thus, the output light amount of the semiconductor laser 1 is controlled to be constant. Here, the case where the laser beam emitted backward is incident on the photodetector 29 to detect the light intensity has been described, but with this method, a part of the laser beam emitted forward is This is advantageous because the light intensity of the laser beam that can be actually used is not reduced unlike the method of leading to the light detector 29.

Although the above description based on FIG. 3 relates to the case of a single beam instead of the case of a plurality of beams, the control processing circuit of the semiconductor laser output shown in FIG. 3 can be easily extended and applied to a plurality of beams. It is. However, in the case of a plurality of beams, it is necessary to perform synchronous control individually for each beam. Therefore, in FIG. 3, the same number of circuits A enclosed by dotted lines may be provided.

The operation of the apparatus shown in FIG. 4 is basically the same as that of the apparatus shown in FIG. In the case of the apparatus shown in FIG. 4, the image forming, developing, and transferring steps include yellow (Y), magenta (M), cyan (C),
There is a black (Bk) for each color, and the transfer paper 48 has Bk, C,
The toners of the respective colors M and Y are sequentially transferred, and finally fixed by the fixing device 52. Needless to say, the light source generates a plurality of light beams for each color and performs deflection scanning collectively.

The configuration of the multicolor laser printer shown in FIG. 4 is well known and will not be described in detail. However, if only the reference numerals are described, 40 is a printer unit, 41 is a scanning optical system, and 42 is an optical unit. Beam, 43: developing unit, 44: photoreceptor, 45: separation charger, 46: charging unit, 47: calling roller, 49: feeding roller, 50: transfer belt cleaner, 51: transfer belt drive roller, 53: paper discharge Rollers, 54 are cleaners, 55 is a transfer belt, and 56 is an electrical system.

In the present invention, when a color image is formed on an OHP sheet or when an image having a high surface gloss is to be obtained, the rotation speed of the fixing heat roll is set to 1/2, 1/3 or the like (an integral number of minutes). 1) can be switched. Then, the moving linear velocity of the photosensitive member and the transfer paper is switched to v / 2, v / 3, and the like, and the light beam light source is selectively switched. The linear speed can be changed by the drive motor (reference numeral 20 in FIG. 1).
It can be easily realized by switching the speed indicated by reference numeral 57) in FIG. For example, a DC motor changes the drive voltage, and a pulse motor changes the number of drive pulses. In general, changing the conditions of the developing unit is not as simple as the motor speed. However, if the set values of the developing sleeve linear speed, the developing bias potential, and the like are appropriately determined for the predetermined linear moving speed of the photosensitive member, the setting can be performed. Changing the value itself is easy.

Next, the reason why the optical system can respond to the switching of the linear velocity in the present invention will be described.

The case of two-beam writing will be described. Normally, as shown in FIG. 5, the light beam L1 and the light beam L2 form an image on the photosensitive member 8 so as to form a pitch P (see FIG. 6), and form two lines per scan.

That is, the rotation speed N of the rotating polygon mirror 14 and the linear velocity v of the photoconductor 8 are as follows: v = N · f · (2P) (1) Becomes

When the OHP sheet is used, and in the high image quality mode, the linear speed of the fixing heat roller is halved, and the linear speed v of the photoconductor is also v / 2. At this time, the light beam writing uses only the light beam L1. That is,
One line of latent image is formed per one scan. Then, v / 2 = N · f · P (2) holds, and it can be seen that the number of revolutions N and the number of faces f of the rotating polygon mirror do not need to be changed from the normal time.

Similarly, in the case of n-beam writing (n is an integer of 2 or more), it is easy to see that the linear velocity can be changed to a fraction of an integer.

 Next, switching of the light beam will be described.

FIG. 7 is a block diagram of a main part of the present invention. An information signal and an external synchronizing signal indicating one line are sent from an external controller (in the case of a printer) or an image scanner (in the case of a copying machine).
The minute is stored in the line buffer 40. The external synchronization signal is counted by the distributor 41, and is distributed for each number set in advance by the distribution signal. That is, distribution is usually performed every (n-1) lines (one line). Each information signal becomes a drive signal for each of the semiconductor lasers 1a and 1b at a timing at which an internal synchronization signal generated from a light beam detection signal is applied. The linear velocity is, for example, 1 / n (1/2)
Is switched, the distribution signal is reset, and the information signal is distributed so as to drive only the light beam L1.

The above is the case where there is no change in the information signal when the linear speed is switched, that is, the case where the transmission speed of the information signal also becomes slow. Otherwise, line buffer 40 will overflow.

On the other hand, in a digital copying machine or the like, if the information transmission speed of the image scanner is changed, the drive clock of the photoelectric conversion element that converts an image into an information signal must be changed, and the optical conditions (light amount, etc.) must be greatly changed. If the transmission speed is not changed, a problem arises that a large amount of memory is required. For this reason, the scanning speed of the original is adjusted to n
In some cases, the driving is switched to one-half and the driving of the photoelectric conversion element is not changed. By doing so, the information signal becomes n times,
In practice, 1 / n is used. In this case, the line buffer 40 may overflow. Therefore, the configuration shown in FIG. 7 can be used.

In addition, the line buffer 40, the distributor 41, the signal processing circuit 27a,
27b, control means for selectively modulating and driving a plurality of light sources by the laser drive circuits 28a and 28b.

〔The invention's effect〕

As described above, according to the present invention, at a constant speed,
When an electrostatic latent image is formed on the image carrier by all the lines of the plurality of light emitting sources per scan of the light beam, and when the switching speed is switched to an integer fraction of a constant speed, a plurality of light beams are scanned per scan. An electrostatic latent image is formed on the image carrier by the lines of the light emitting sources selectively modulated and driven among the light emitting sources, and all the lines formed at a constant speed by the lines by the light emitting sources are formed on the image carrier. Therefore, when it is necessary to reduce the rotation speed of the fixing heat roll of the fixing unit, in a multi-beam optical recording, by not changing the scanning speed of the light beam by the light beam scanning unit, simple control can be performed. You can change the print speed to 1 / integer,
In addition, the image quality does not deteriorate.

[Brief description of the drawings]

FIG. 1 is a mechanical diagram of a monochromatic laser printer according to one embodiment of the present invention, FIG. 2 is a diagram showing an optical system, FIG. 3 is a light beam output control circuit diagram, and FIG. 4 is another embodiment of the present invention. FIG. 5 is a schematic diagram of a two-beam writing system, FIG. 6 is a diagram showing the diameter of a light beam, and FIG. 7 is a switching circuit diagram of the light beam. 1 ... light source (semiconductor laser), 14 ... rotating polygon mirror, 16 ...
… Light beam, 20,57… drive motor, 27 …… signal processing circuit, 28 …… laser drive circuit, 40 …… line buffer, 41
……Distributor.

Claims (1)

(57) [Claims] A plurality of light-emitting sources which are modulated and driven in accordance with an information signal; light beam scanning means for forming a light beam of the light-emitting source into a spot-shaped light beam and scanning the light beam; A means for forming an electrostatic latent image on an image carrier moving at a constant speed, a developing means for developing the electrostatic latent image, and transferring a visual image developed by the developing means to a transfer material moving at a constant speed; In an image forming apparatus having a transfer unit and a fixing unit for fixing an image transferred to the transfer material to the transfer material, a moving speed of the image carrier, the transfer material, and a rotation speed of a fixing heat roll of the fixing unit are determined. Switching means for switching the speed to an integer fraction of a speed; and selectively modulating the plurality of light emitting sources in accordance with the speed switching by the switching means so as not to change the scanning speed of the light beam by the light beam scanning means. Control means At a constant speed, an electrostatic latent image is formed on the image carrier by all the lines of the plurality of light emitting sources per one scan of the light beam; Forming an electrostatic latent image on the image carrier by a line of a light emitting source selectively modulated and driven among the plurality of light emitting sources per scan of the light beam, and at the constant speed by a line of the light emitting source. An image forming apparatus, wherein all lines to be formed are formed on the image carrier.