JP2003150002A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a copying operation without switching the rotational speed of a polygon motor even when switching a process speed according to a transfer material type, in an image forming device having a plurality of laser beam emitting means and a plurality of process speeds. SOLUTION: (1) When thick paper, OHP, or the like is carried, the process speed is switched and the number of laser beams emitted to a photoreceptive medium is also switched. (2) In a method for switching the number of laser beams, a laser beam on the same side is always used or the laser beams are alternately switched.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a semiconductor laser for image exposure and irradiates a photosensitive medium with a laser beam emitted from the semiconductor laser to form an electrostatic latent image. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art In a conventional digital color image forming apparatus, as shown in FIG. 1, a semiconductor laser element 101, a cylindrical lens 102, a dihedral hexahedral polygon mirror 103 are usually provided in an electrostatic latent image forming section (hereinafter referred to as a printer section). A polygon motor 104, an imaging lens 105, a beam detect (BD) sensor 106, a photosensitive drum 107, and a laser control board 108 are provided.

The laser control board turns the laser on and off in accordance with the image signal from the image reading section, applies the emitted light to a polygon mirror which rotates at high speed, and reflects the reflected light from the polygon mirror through an imaging lens. The surface of the BD sensor, which is necessary to generate the write timing signal in the main scanning direction, is irradiated from almost the entire edge of the photosensitive drum.

On the other hand, as a material used as a recording medium when an electrostatic latent image formed on a photosensitive drum is developed with toner or the like and a visualized image is transferred to the recording medium, plain paper and special materials are used. As thick paper or OHP sheet,
There are many types of postcards, and recently glossy paper. Among them, when transferring a toner image to a thick paper such as thick paper, OHP sheet, glossy paper or a recording medium using a special material, generally, the speed of transporting the recording medium is approximately 1 / about the time when the toner image is formed. Transfer and fixing are performed after reducing the speed to about 2.

Because of the material and thickness of these media, the heat of the fixing device is less likely to be transferred than the plain paper, so the toner on the recording medium is not sufficiently melted at the normal fixing speed, and the toner to the fixing roller is not melted. Therefore, the fixing speed is decreased so that the heat can be sufficiently transmitted because the offset, the winding of the recording medium, and the tint abnormality occur.

In this case, since the number of revolutions of the polygon motor and the value of the image processing system clock are fixed values, it is necessary to switch the medium carrying speed at the time of transfer or fixing after forming the electrostatic latent image. If the speed is switched at any other timing, the magnification of the image will change. In this configuration, the speed is switched during operation, so that it takes time to stabilize at the switched speed and idle rotation is required to match the phase of the front end of the recording medium and the front end of the toner image, resulting in a great decrease in productivity.

To prevent this, a method of switching the process speed can be considered. This is to switch from the rotation speed of the polygon motor, the image forming system motor, and the conveyance system motor to the frequency of the image processing system clock.
In order to operate at a speed of / 2, it is necessary to manually set the type of recording medium in advance and the operability is poor.

In addition, even if automatic discrimination is performed, at the time of the first activation, each motor rotates at a normal speed to perform preparation.
After that, it is necessary to feed the recording medium to some extent, determine the type by a photo sensor, a paper thickness detection sensor, etc., and then take steps to switch the speed of each motor. In this case, the polygon motor has extremely high rotational speed and high accuracy such as uneven rotation and jitter, so it takes time to stabilize the rotation as compared with other motors, which reduces productivity.

[0009]

Therefore, when trying to switch the process speed with the above configuration, it becomes necessary to switch the rotation speed of the polygon motor, so it is necessary to wait until the speed stabilizes, and as a result, the productivity is reduced. There is a problem in that the usability is deteriorated due to a significant decrease.

[0010]

In order to solve the above problems, the present invention uses a twin-beam type laser as a semiconductor laser for image exposure, and the polygon motor rotation speed is not changed.
When the recording medium is plain paper, the process speed is standard speed and the image is formed by two laser beams, and when the recording material is special material, the process speed is 1/2 speed and the image is formed by one laser beam. By doing so, it is possible to handle a plurality of types of recording media without changing the rotational speed of the polygon motor, and the speed switching time is kept to a minimum.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) One embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a cross-sectional view (front view) showing the structure of the digital color copying machine according to the present invention. The image scanner unit and the printer unit may be independent or integrated.

Reference numeral 1 denotes an image scanner section for reading an original and outputting a digital color image signal, 2 denotes a printer section for performing an operation for recording the digital color image signal output from the image scanner section on a recording sheet, and 3 denotes a plurality of sections. The document feeder is a document feeder for feeding / discharging the document on the platen glass 207, and may not be equipped.

Reference numeral 5 is a CCD, 6 is a substrate on which the CCD 5 is mounted, and 7 is a printer control unit having a circuit for driving loads such as various motors of the printer unit. 8 is CCD 5
The analog image signal converted into an electric signal by the above is subjected to processing such as sample hold, amplification, A / D conversion, and the like.
An image processing unit that converts each GB digital signal into 8-bit digital signals, performs various processes such as masking and γ correction, and sends an image signal to the laser scanning unit, and a stepping motor 214.
Reader controller that controls the printer and communicates with the printer controller,
Reference numeral 9 is a fluorescent lamp that illuminates the original, 10 is a reflector that collects the light of the fluorescent lamp 9 onto the original, 11 to 13 are mirrors, 14 is a lens that collects reflected light or projection light from the original on the CCD 5.
209 is a carriage (hereinafter referred to as a first mirror stand) that houses the fluorescent lamp 9, the reflector 10 and the mirror 11, 210 is a mirror 12
A carriage for accommodating 13 (hereinafter, second mirror base).

Reference numeral 17 denotes a fluorescent lamp control circuit, which generates a PWM pulse signal of variable duty at a constant cycle in response to a lighting control signal from the image processing section 9 and supplies it to the fluorescent lamp drive circuit 18.

The fluorescent lamp drive circuit 18 turns on the fluorescent lamp based on the PWM pulse signal. The fluorescent lamp control circuit 17 observes the output of the light amount sensor 19 and controls the light amount by changing the duty of the PWM pulse signal so that the output value becomes a certain value.

The speed of the first mirror table is V, the speed of the second mirror table is V / 2, and the stepping motor 214 is rotated to mechanically move the CCD 5 in a direction perpendicular to the electric scanning (main scanning) direction. To scan (sub-scan) the entire surface of the document.

Reference numeral 20 denotes a photosensitive drum, which is driven in the clockwise direction indicated by an arrow at a predetermined peripheral speed ν (process speed). The peripheral surface of the photosensitive drum 20 is charged to a predetermined polarity and potential by a charging roller 21. Then, the charged surface is subjected to scanning exposure by the laser beam 23 output from the laser scanning unit 22 and pulse-width modulated in accordance with the digital image signal input from the image processing unit, so that the image information is statically exposed. A latent image is formed.

Reference numeral 24 denotes a laser beam reflecting mirror, which deflects the laser beam from the laser scanning section 22 with respect to the photosensitive drum 20. Reference numeral 25 is a developing device, which is a rotation-switching color developing device including a yellow toner developing device 25Y, a magenta toner developing device 25M, and a cyan toner developing device 25C.
The black toner developing device 25BK for black is used.

Reference numeral 26 is an intermediate transfer drum. It is arranged in contact with or close to the photoconductor drum 20, and is rotationally driven in the forward direction of rotation of the photoconductor drum 20 at substantially the same peripheral speed as the photoconductor drum 20. Then, formation of electrostatic latent images corresponding to the color separation images of the target full-color image and toner development of the electrostatic latent images are sequentially executed on the rotating photosensitive drum 20, and the toner images of the respective toner images are Overlapping transfer is sequentially performed on the intermediate transfer drum 26, and a full-color toner image corresponding to a mirror image of the target full-color image is synthetically formed on the surface of the intermediate transfer drum 26.

A cleaner 27 cleans the surface of the intermediate transfer drum 26 after the toner image is transferred onto the transfer material. A transfer material P as a recording material is fed from the paper feed cassette 27 to the intermediate transfer body drum 26 by a paper feed roller 29.
Sheets of paper are fed, and the intermediate transfer drum 2 is transferred onto the transfer material P.
The 6-sided mirror image full-color toner image is transferred by the transfer roller 31 to form a full-color toner image on the surface of the transfer material P.

The transfer roller 31 supplies an electric charge having a polarity opposite to that of the toner from the back surface of the transfer material P, so that the intermediate transfer drum 2
The toner image is transferred from 6 to the transfer material P. When transferring, when the type of transfer material P is plain paper, the rotational speeds of the intermediate transfer drum 26, the transfer roller 31, and the fixing device 32 are the same as those of the photosensitive drum 2.
It rotates at the same velocity ν as 0, and in the case of special materials, it rotates at ν / 2.

The transfer material P, to which the full-color toner image has been transferred, is separated from the intermediate transfer body drum 26 and introduced into a fixing device 32, where the toner image is heated and fixed, and a paper discharge tray 33 is provided.
Alternatively, it is discharged to 34. Numerals 35 and 36 are paper type discrimination sensors for discriminating the types of transfer materials placed in the upper cassette and lower cassette, respectively, and 37 is a paper type discrimination sensor for discriminating the types of transfer materials placed in the manual paper feed section 38. is there. These may be of a type in which light is applied to the transfer material to detect transmitted light, a type of reflected light is detected, a type of thickness is detected, or a combination thereof may be used.

Next, the laser driving process will be described with reference to the drawings.

FIG. 3 is a block diagram of a laser drive circuit, in which 301 is a semiconductor laser element and 302 is a laser control circuit. Inside the semiconductor laser element 301, a first laser diode 301a, a second laser diode 301b, and an output monitor diode 301 are provided.
c is built in.

Inside the laser control circuit 302, a power source section 3 for supplying a stable power source to the semiconductor laser element 301.
03, a first drive circuit 304 for driving the first laser diode 301a, a second laser diode 301
A second drive circuit 305 for driving b, a current detection circuit 306 for detecting a current flowing through the output monitoring diode 301c according to the light quantities of the laser diodes 301a and 301b, and converting a pulsed current waveform into a stable DC waveform. An integrating circuit 307, a BD sensor 307 for generating a horizontal synchronizing signal from a laser beam scanned by rotating a polygon motor, and a current detecting circuit 306.
From the BD sensor 307 and the image signal of the nth line from the printer control circuit 7 at a predetermined timing and a predetermined output.
01a ON / OFF control circuit 308, output from the current detection circuit 306, output from the BD sensor 307 and the image signal of the (n + 1) th line from the printer control circuit 7 based on predetermined timing and predetermined output. The control circuit 309 controls ON / OFF of the laser diode 301b.

FIG. 4 is a view as seen from the light emitting surface of the semiconductor laser device 301. Light emitting portion 401 of laser diode 301a and light emitting portion 402 of laser diode 301b
Since the pitch L is wider than the desired line pitch, the desired line pitch 1 is obtained by inclining it by θ degrees as shown in the figure.

Next, the actual operation will be described with reference to FIGS. 5, 6 and 7.
Will be explained.

When a copy start key (not shown) is pressed (S701), the CPU 50 of the printer control unit 7 is first operated.
1 outputs a rotation signal to the motor drive IC 502 to rotate the paper feed motor 40 and the polygon motor 104, and the paper feed roller 3 via an electromagnetic clutch (not shown).
Rotate any of 0, 31, 39 to cassette 28, 29
Alternatively, the transfer material is fed from the manual paper feed unit 38 to the nearest paper type discrimination sensor 35, 36 or 37 (S70).
2).

Here, the printer control board 7 discriminates what kind of transfer material is by reading the output value of the paper type discriminating sensor 37 (S703, S704). If it is determined that the paper is plain paper, the main motor 41 is rotated at the standard speed (S705). At the same time, an operation permission signal is sent to the reader controller 8.

Upon receiving the operation permission signal, the reader control unit 8 operates the document feeding device to feed one document onto the platen glass, starts the image reading operation, and then starts the first mirror table 2
09 and the second mirror base 210 are back-scanned and returned to their original positions. The image signal of the read document is input to the timing RAM 503 in the printer control unit 7 from the reader control unit 8 every two lines and frequency-converted to match the operation timing with the printer. The image data is sent to the laser control circuit 302.

During rotation of the polygon motor, the laser control board 302 outputs a forced lighting signal as shown in FIG. 6A to the semiconductor laser element 301 in order to keep the light quantity of the semiconductor laser element 301 at a constant value. As a result, the BD sensor 307 which receives the laser beam by the scanning of the polygon mirror outputs the horizontal synchronizing signal shown in (b) to the laser control board 302.

Since the laser control board 302 adjusts the write start timing, it takes time t from the rise of this signal.
The image signal of the n-th line and the image signal of the (n + 1) -th line sent from the control board 7 later are sent to the first drive circuit 304.
And to the second drive circuit 305 (FIG. 6 (c),
(D)).

As a result, the first laser diode 30
1a and the second laser diode 301b are shown in FIG.
A light emitting operation as shown in (e) and (f) is performed. The laser light is deflected by the laser light reflection mirror 24 and irradiates the photoconductor drum 20. The laser light emitted onto the photosensitive drum 20 is only the light in the range A of FIGS. 6 (e) and 6 (f).

Laser light is irradiated onto the photosensitive drum 20 to form an electrostatic latent image, which is developed to form a toner image.
The operation of transferring the toner image to the intermediate transfer drum 26 is performed for each color of Y, M, C, and BK, and then a full-color toner image in which four color toners are superimposed on the transfer material (plain paper in this case) is formed. The image is transferred, heated and fixed by the fixing device 32, and discharged, and a series of copying operations is completed (S706, S707).

Next, the operation when the paper type discrimination sensor 37 is assumed to be a reflection type sensor and the transfer material is an OHP film will be described. In sequence S702, the transfer material is sent to the paper type discrimination sensor 35, 36 or 37 to the nearest position, and in sequence S702.
When the type of the transfer material is discriminated at 703, since the OHP film is almost transparent, the LED light of the paper type discrimination sensor is transmitted as it is, and the light of the LED does not enter the light receiving surface of the paper type discrimination sensor.

Therefore, the CPU determines that this transfer material is OHP, and rotates the main motor 41 at 1/2 speed (S708). After that, the document reading operation is performed as described above.

Next, the image signal of the read original is transferred from the reader controller 8 to the timing RAM 50 in the printer controller 7.
3 is input, only the image signal of the nth line is output to the first drive circuit 304 this time. As a result, only the first laser diode 301a performs the light emitting operation as shown in FIG.

The rotation speed of the polygon motor is the same as that of plain paper, but the photosensitive drum 20 and the intermediate transfer drum 26
Since the rotational speed of and the transfer material transfer speed are ν / 2,
Even if only one laser beam is emitted from the semiconductor laser element 301, the recording density can be recorded at a resolution of 1 line / inch in both cases as shown in FIG.

(Second Embodiment) In the above embodiment, the image signal is output only to the drive circuit 304 and only the first laser diode 301a is turned on. In this case, all the points of the laser diode 301a are included. Since the isochronous time is longer than the total isochronous time of the laser diode 301b, the life of the laser diode on one side is shortened. In addition, the heat balance in the laser chip may be lost, and the amount of light emitted from each laser diode may be slightly different.

Therefore, as shown in FIG. 8C, these defects can be eliminated by alternately lighting the first laser diode 301a and the second laser diode 301b for each line.

(Third Embodiment) In the above-mentioned embodiment, the main material motor is rotated after the transfer material is first fed and the type of the transfer material is discriminated. Since the switching time is faster than that of the polygon motor, the main motor is also rotated at the same time as the paper feeding motor is rotated, and the rotation speed of the main motor is switched after the type of transfer material is discriminated. Does not affect much. A flow chart in this case is shown in FIG.

[0043]

As described above, according to the present invention,
When the recording medium is plain paper, the process speed is standard speed and the image is formed by two laser beams, and when the recording material is special material, the process speed is 1/2 speed and the image is formed by one laser beam. By doing so, it is possible to support a plurality of types of recording media without changing the rotation speed of the polygon motor, and the speed switching time can be minimized.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of a conventional laser scanning system.

FIG. 2 is a sectional view (front view) showing a configuration of a digital color copying machine according to the first embodiment.

FIG. 3 is a block diagram of a laser drive circuit in the first embodiment.

FIG. 4 is a diagram showing a light emitting surface of a semiconductor laser device according to a first embodiment.

FIG. 5 is a block diagram around a printer control circuit in the first embodiment.

FIG. 6 is a timing chart in the first embodiment.

FIG. 7 is a flowchart of the operation in the first embodiment.

FIG. 8 is a diagram showing laser scanning in the first and second embodiments.

FIG. 9 is a flowchart of the operation in the second embodiment.

[Explanation of symbols]

1 Reader section 2 Printer section 7 Printer control unit 8 Reader control unit 35,36,37 Paper type discrimination sensor 301 Semiconductor laser device 302 Laser control circuit

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2C362 AA03 AA12 AA16 BA56 BA66                       CB01 CB14 CB47 CB62 CB64                       CB66                 2H027 DC02 ED04 ED06 ED16 ED17                       ED24 EE03 EE04 EF06 EF13                       FB07 FB19                 2H076 AB05 AB06 AB12 AB68 EA01

Claims (5)

[Claims] 1. A semiconductor laser device for image exposure is provided, and an image forming system is provided for irradiating a photosensitive medium with two laser beams emitted from one semiconductor laser device to form an electrostatic latent image. An image forming apparatus characterized in that the type of transfer material is discriminated and the process speed and the number of laser beams of a semiconductor laser element used for image formation are switched according to the type. 2. The process speed is a reference speed and a half speed of the reference speed.
The image forming apparatus described. 3. The image forming apparatus according to claim 1, wherein the process speed switching timing is before or after the paper feeding operation. 4. The image forming apparatus according to claim 1, wherein the process speed switching timing is before or after rotation of the main motor. 5. When operating at half the reference speed,
2. The image forming apparatus according to claim 1, wherein only one of the two lasers is used for image formation, or the laser is alternately switched line by line.