JPH04321071A - Image forming device - Google Patents

Abstract

PURPOSE:To enhance the image quality of a formed image or increase recording speed, without making a device large and expensive, in an image forming device having a laser writing device or an optical writing element array. CONSTITUTION:This image forming device has an optical system deflecting optical beams projected from a laser light source, which are modulated in response to a picture signal, by a polygon mirror 13a, and composed of mirrors 151-153 for folding the optical beams deflected for scanning via a ftheta lens 14 converging them on a focus, and a laser beam scanning position P on the photosensitive belt 20 in a sub-scanning direction is travelled at constant speed slower than the linear velocity of a photosensitive belt 20, and desirably, at the constant speed that the ratio of travelling speed in the sub-scanning direction of the laser beam scanning position P and the moving linear velocity of the photosensitive belt 20 is >=1/5 and >=1/2, in synchronization with an image forming action, while the optical path length of the optical beams is kept constant.

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 digital copying machine equipped with a recording device that records an image by repeatedly scanning a light beam emitted from a light emitting element such as a laser light emitting element or an LED array.

0002

[Background Art] In recent years, with the spread of digital copying machines,
2. Description of the Related Art Laser recording devices have come into widespread use, which record images on recording paper using an electrostatic photographic process by irradiating a photoreceptor with a laser beam in accordance with image information. FIG. 5 shows a document reading device I that scans a document image and converts the image information into electrical signals, an optical recording device II equipped with an image forming device (photosensitive drum, developing device, etc.), and an automatic document feeder (ADF) III. FIG. 6 is a configuration diagram of a conventional digital copying machine configured with
FIG. 2 is a plan view of the laser scanning device of the optical recording device II. In the figure, 1 is a semiconductor laser light emitting device (LD
); 2 is an image forming device that visualizes the electrostatic latent image formed on the photoreceptor by the optical writing device 1 and reproduces the original image on transfer paper; 30 is the original surface; 31 is an illumination lamp that illuminates the original; 32 is a plurality of mirrors that refract and guide light reflected from the original so that the optical path length thereof is constant; 33 is a scanner that directs the original image onto a photoreceptor; 34 is a one-dimensional solid-state imaging device that converts an optical signal into an electrical signal, and 35 is a contact glass. After inputting copy data such as the number of copies by operating the numeric keypad (not shown) on the operation display board 3, and then pressing the copy start button, the originals placed on the ADF III are sequentially transferred to the original reading device I one by one. It is supplied onto the contact glass 35. The original image is optically scanned by the scanner 30 and then read by the original reading device I, converted into multi-tone image data by the image processing section, further converted into binary image data, and stored in the image memory. The image data is then read out and output to the optical recording device II. In the optical recording device II, a recording signal of binary image data is input to the laser driving section of the optical writing device 1, and a laser driver modulated and controlled according to the image recording signal drives the LD 10 to blink or emit strong and weak light. In this way, the LD 10 emits the optically modulated laser beam BM. The laser beam BM passes through the collimator lens 11 and the cylindrical lens 12, enters the polygon mirror 13a surface driven by the polygon motor 13b of the deflector 13, is deflected by constant speed rotation of the polygon mirror 13a, and is deflected by the fθ lens 1.
4, passes through a mirror 15 and a dust-proof glass 16, and is guided onto the photoreceptor drum 20, and scans the surface of the photoreceptor drum 20 in parallel to the rotation axis of the photoreceptor drum 20. A portion of the laser beam BM deflected by the rotation of the polygon mirror 13a is projected onto the optical sensor 17, which detects the incident light and outputs a detection signal. Each photosensitive drum 20
Electrostatic photographic process units such as a charger 21, a developing device 22, and a transfer charger 23 are attached around the image forming apparatus. A latent image of a recorded image is formed on the photosensitive drum 20 uniformly charged by the charger 21 by exposure to the laser beam BM, and the formed latent image is developed by the developing device 22 to become a developed image. The transfer paper taken out from the paper feed cassette 50 by the paper feed roller 51 is sent to the transfer section by the registration roller 52 with its leading edge aligned in synchronization with the movement of the starting end of the developed image formed on the photoreceptor drum 20. The developed image formed on the photosensitive drum 20 is transferred to the registration roller 5 under the charging action of the transfer charger 23.
The image is transferred onto a transfer paper conveyed by 2. The transfer paper on which the developed image has been transferred is further transported by a transport belt 53,
The fixing process is performed by the fixing roller 54, and the paper ejection roller 5
5, the paper is ejected onto the paper ejection tray 56. After the transfer is completed in the transfer section, the surface of the photoreceptor drum 20 is cleaned by the cleaning unit 24.

On the other hand, there is an image forming apparatus that uses an optical writing device that does not have a scanning drive mechanism and is equipped with an optical writing element array such as an LED array, a liquid crystal shutter array, or a fluorescent tube dot array, and a Selfoc lens. The simplicity of its mechanism has attracted attention, and its development has been actively progressing, with many applications already filed. FIGS. 7 and 8 show a schematic configuration of a digital copying machine as an example of such a conventional example, and a main part of an optical writing system of the digital copying machine, respectively. The basic mechanism of this digital copying machine is not much different from that of the digital copying machine equipped with the laser recording device described above, but as mentioned above, it does not have a scanning mechanism that optically scans the surface of the photoreceptor in the main scanning direction. The mechanism has been simplified and downsized accordingly. The same reference numerals are given to parts that are the same as those of the conventional example described above or can be considered to be the same, and redundant explanation will be omitted. The same applies to the following description. In the figure, 61 is an optical writing device, 62 is an LED (light emitting diode) array, and 63 is a SELFOC lens, which reads the original image placed on the contact glass of the original reading device I and generates a multi-gradation image. Obtain data, binarize it, and write it into image memory. The binary image data read from the image memory is supplied to the drive circuit of the LED array 62 as many times as the number of times the scanner of the original reading device I reads in the sub-scanning direction, and the data is output from the LED array 62 according to the supplied drive current. Strong and weak light or intermittent light is emitted, is focused by the SELFOC lens 63, and is imaged on the photoreceptor drum 20. A latent image corresponding to the original image formed on the photosensitive drum 20 is fixed as a recorded image on a transfer paper fed and conveyed from a paper feed cassette 50 by an image forming device 2 that executes a known electrostatic photographic process. , a copy of the original is sent out to a paper ejection roller 55 and ejected onto a paper ejection tray 56.

0004

[Problem to be solved by the invention] By the way, high functionality,
In response to the demand for higher quality, there is an urgent need to develop copying machines that can produce high-speed, high-quality copies. Therefore, in order to increase the copying speed of the copying machine and improve the recording density, for example, in a digital copying machine equipped with the optical recording device II using the above-mentioned laser emitting element, the rotational linear velocity of the photoreceptor drum 20 is If the speed is increased, the rotational speed of the polygon motor 13b must also be increased. However, the rotational speed RP of the polygon motor 13b has a certain limit value determined by the type of bearing, and when a ball bearing is used, the limit value is 15,000 to 20,000 (rpm). When higher rotational speed is required, an expensive polygon motor 13 using dynamic pressure bearings or static pressure bearings is required.
b must be used, and even in that case, it will vary depending on the inscribed circle diameter and the number of surfaces n of the polygon mirror 13a, but approximately 4
0,000 (rpm) is the limit rotation speed. If it is desired to use a polygon motor 13b with a rotation speed higher than that, the motor becomes large and extremely expensive. On the other hand, the current mainstream image recording density is a sub-scanning line density of approximately 16 lines/mm;
(lines/mm) or 32 (lines/mm), etc., is required. For example, the image recording density is 2
The recording density is as high as 4 (lines/mm), and the photoreceptor drum 2
0 linear velocity to 240 (mm/s) (copying speed = 45 to 5
0 cpm [A4]), when a polygon mirror 13a with 8 surfaces is used, the rotation speed of the polygon motor 13b is 43,200 (rpm), and a special motor must be used as described above. , the recording device becomes very expensive. When the linear velocity of the photosensitive drum 20 is vk (mm/s), the recording density is l (lines/mm), and the number of surfaces of the polygon mirror 13a is n, the rotation speed RP (rpm) of the polygon motor 13b is RP =(60・vk・l)/n

...(1) becomes. (1) From the formula, if the number of surfaces n of the polygon mirror 13a is increased, the rotation speed RP of the polygon motor 13b is
can be lowered, but then the angle that can be deflected during the main scanning period becomes smaller, so fθ with a long focal length
The lens 14 must be used, and accordingly the optical path length of the laser beam BM becomes longer. Furthermore, in an image forming apparatus equipped with an optical writing device using an LED array,
As mentioned above, since the optical system does not have a mechanical drive part, it has advantages such as a simplified mechanism, improved reliability, and miniaturization. Although it is not limited by the number, the limit driving frequency is about an order of magnitude lower than that of a laser light emitting element, for example, about several MHz, and the rotational speed of the photoreceptor drum cannot be increased significantly. The present invention has been made based on the above circumstances, and is equipped with a laser writing device using a drive motor that rotates a deflection device such as a polygon mirror at high speed, or an optical writing device with a low limit drive frequency such as an LED array. An object of the present invention is to provide an image forming apparatus that can improve the quality of formed images or the image forming speed without making the apparatus larger or more expensive.

[0005]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention includes a photoreceptor that moves at a constant speed in the sub-scanning direction, and a photoreceptor that is modulated according to an image signal and that scans the photoreceptor in the main scanning direction for exposure. a light emitting source that emits a light beam that emits a light beam, and a plurality of electrophotographic processing means that visualizes a latent image formed on the photoreceptor by exposure according to an electrophotographic process, the imaging position of the light beam to be moved in the same direction as the moving direction of the photoreceptor in synchronization with the image forming operation, at a speed slower than the moving speed of the photoreceptor, preferably at a ratio of 1/5 or more; It also has a moving means for moving at a constant speed of 1/2 or less. Specifically, the moving means includes a plurality of mirrors set in the sub-scanning direction to bend the deflected and scanned light beam by a deflector that deflects the light beam emitted from the laser emission source, and to keep the optical path length constant. It is composed of a mirror moving means for moving at a high speed and a transport means for moving the optical writing element array at a constant speed in the sub-scanning direction.

[0006]

[Operation] The moving means moves the imaging position of the light beam on the photoreceptor in the same direction at a constant speed slower than the moving speed of the photoreceptor, which moves at a constant speed in the sub-scanning direction, in synchronization with the image forming operation. This reduces the apparent sub-scanning speed of the light beam on the photoreceptor.

[0007]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, a first embodiment of the present invention will be described which includes an optical recording device using a laser diode as a light emitting element. This embodiment uses a photoreceptor belt in place of the photoreceptor drum in the conventional example, and is equipped with a two-dimensional scanning mechanism that can also scan the laser beam emitted from the LD in the sub-scanning direction. By synchronizing the scanning of the laser beam and the rotational movement of the photoreceptor belt, the scanning speed of the laser beam in the sub-scanning direction on the photoreceptor belt is apparently reduced. Therefore, a first embodiment of the optical recording apparatus II, which has a different configuration and operation from the optical recording apparatus using a laser light emitting element of a conventional digital copying machine, will be described below. FIG. 1 is a block diagram showing the internal structure of the optical recording device II according to the first embodiment as seen from the front, and FIG. 2 shows the structure of the mirror optical system inside the optical writing device 1 and its drive system. FIG. In the figure, 151, 152, and 153 are first to third mirrors that move horizontally in synchronization with the rotation of the polygon mirror 13a, 17 is a first bracket that supports the first and second mirrors 151, 152, and 18 is a first bracket that supports the first and second mirrors 151, 152; Third
A second bracket that supports the mirror 153 and the dust-proof glass 16; 41 is a drive pulley that is attached to the rotating shaft of the drive motor 40 and driven to rotate; 42 is the first bracket 1;
A movable pulley rotatably fixed to the side surface of 7, 43 a fixed pulley fixed to the housing of the laser scanning device 1, 44
is stretched between the drive pulley 41 and the fixed pulley 43
These are wires fixed to the side surfaces of the bracket 18, and these wires are arranged at symmetrical positions on the front and rear sides of the laser scanning device 1, respectively. In this embodiment, unlike the conventional example, the laser beam scanning position P on the photoreceptor belt 20 changes as the first to third mirrors 151 to 153 move.
It moves at a constant speed in the moving direction of the photoreceptor belt 20 in synchronization with the image forming timing. That is, the second bracket 18
Since the wire 44 is fixed to the drive motor 4
0 rotates forward and backward, the wire 44 is passed through the drive pulley 41.
The driving force is transmitted to the first and second mirrors 151, 152.
The third mirror 153 and the dustproof glass 16 are supported by the first bracket 17 and the second bracket 18, respectively, and reciprocate in the direction of the arrow h. Due to the above operation of the drive mechanism of the mirror optical system, the distance from the LD 10 to the laser beam scanning position P on the photoreceptor belt 20 is always kept constant, and the moving speed of the moving body driven by the drive mechanism is The speed of the first and second mirrors 151 and 152 is the third
It becomes 1/2 of that of the mirror 153 and the dustproof glass 16. The laser beam scanning position P starts moving in synchronization with the image forming operation, and returns to the initial position (home position) after the image forming is completed.

Movement speed vB of laser beam scanning position P
The rotation speed RP (rpm) of the polygon motor 13b when is set to 1/m of the moving speed vK of the photoreceptor belt 20
is, RP = (vK - vB)・l・6
0/n = (m-1)/m×(60
・vK ・l)/n = (m-1)
/m×RP0
...(2) (However, the number of rotations of the polygon motor 13b when RP0; vB = 0), compared to the case where the laser beam scanning position P is not moved, is (m-1)/m
It will be doubled. For example, the image recording density is 24 (lines/m
m) Considerable high recording density, linear velocity vK of photoreceptor belt 20
240 (mm/s), laser beam scanning position P
When the moving speed vB of is set to 1/3·vK (m=3) and a polygon mirror 13a with 8 faces is used,
The rotation speed of the polygon motor 13b is 28,800 (rp
m) becomes. (2) From formula, reduce the value of m (
1), the rotational speed RP becomes smaller, which is convenient for using an inexpensive polygon motor. However, since the moving distance of the laser beam scanning position P becomes longer, it takes time to return the mirror optical system to its initial position. It takes. Furthermore, since the actual image forming speed is reduced, the image forming speed of the optical recording device II is also reduced. On the other hand, if the value of m is increased, the rotational speed RP of the polygon motor will not decrease much, and the effects of this embodiment cannot be expected. Therefore, the optimum value of m may be determined in consideration of the interval between transfer sheets during continuous recording, the time required for the scanner 30 to return to the initial position after reading the original by the original reading device, and the like. According to the experimental results of the inventor of the present application, a suitable value for m is 2 to 5.

Next, LEDs are used as light emitting elements of optical recording devices.
A second embodiment including an array will be described. This embodiment also includes a transport mechanism for transporting the optical writing device in the sub-scanning direction, and the scanning speed of the light beam in the sub-scanning direction on the photoreceptor belt is different from the circumferential movement speed of the photoreceptor belt. It's tight. FIG. 3 is a block diagram showing the internal structure of the optical recording apparatus II as seen from the front, and FIG. 4 is a perspective view showing the conveyance drive system of the optical writing device 61 of the optical recording apparatus II. In the figure, reference numeral 45 denotes a construction pulley which is rotatably attached to the other end of a spring 46 whose one end is fixed to a frame (not shown) of the optical recording device II, and which stretches the wire 44 between the drive pulleys 41. A portion is fixed to the front and rear sides of the optical writing device 61, and is rotated by the drive motor 40.
The wire 44 moves around and the optical writing device 61 can be moved horizontally in the direction of the arrow h along a guide rail (not shown). It is controlled to move in the same direction at a slower speed. If the moving speed of the optical writing device 61 during image forming operation is vA, and the circumferential moving speed of the photoreceptor belt 20 is vK (vA < vK), the LED
The driving frequency H of the array 62 is: H=[(vK - vA)/vK]×H0
...(3)
(However, when H0 ; vA = 0, the LED array 6
2 driving frequency), and if vA > 0, then (vK
-vA)/vK <1, so in this case H<H
0, the optical writing device 61 is moved at a slower speed in the circumferential movement direction of the photoreceptor belt 20, and the LED array 6
By slowing down the apparent moving speed of the light beam BM emitted from the photosensitive belt 20 on the photoreceptor belt 20, that is, the sub-scanning speed, the driving frequency H of the LED array 62 can be lowered. Conversely, when the driving frequency H of the LED array 62 is fixed, the rotational movement speed vK of the photoreceptor belt 20
Since the recording speed or recording density of the optical recording device II can also be increased. The scanning movement distance LA between the scanning start point PS and the scanning end point PE of the optical writing device 61 shown in FIG. 3 is LA = [vA / (vK - vA)] x L
0...(4) (where L0 is the document scanning distance of the scanner), and when the value of vA approaches the value of vK, the driving frequency H of the LED array 62 decreases from equation (3), but (
4) According to the formula, the scanning movement distance LA of the optical writing device 61 increases, and as a result, the optical writing device 61 finishes writing in the sub-scanning direction and returns to the scanning starting point PS (home position) position. The time required for copying a plurality of original documents also increases. Therefore, the moving speed vA of the optical writing device 61
is set to the optimum value, taking into account the paper interval during continuous copying, the time it takes for the scanner to return to its home position, etc.

0010

As described above, according to the invention as set forth in claims 1 to 3, the image formation position of the light beam on the photoreceptor can be synchronized with the image forming operation and in the same direction as the moving direction of the photoreceptor. Since the device has a moving means for moving the light beam at a constant speed in the direction, the apparent sub-scanning speed of the light beam on the photoreceptor decreases during image forming operation, which makes it difficult to increase the size of the device.
The quality of the formed image or the speed of image formation can be improved without making it expensive. According to the invention as set forth in claim 4, since the moving means includes mirror moving means for bending the laser beam and moving the plurality of mirrors at a constant speed in the sub-scanning direction to keep the optical path length constant. The above effects can be obtained with an inexpensive device without increasing the size of the laser recording device. Further, according to the invention as set forth in claim 5, since the optical writing element array is provided with a transport means for moving the optical writing element array at a constant speed in the sub-scanning direction, it is possible to increase the image forming speed or the image forming density with an inexpensive device. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an optical recording apparatus according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a mirror optical system and a drive system thereof of the optical writing device.

FIG. 3 is a schematic configuration diagram showing the internal configuration of an optical recording device according to a second embodiment.

FIG. 4 is a perspective view showing a conveyance drive system of the optical writing device.

FIG. 5 is a configuration diagram of a conventional digital copying machine.

FIG. 6 is a plan view of the same laser scanning device.

FIG. 7 is a schematic configuration diagram of another conventional digital copying machine.

FIG. 8 is a perspective view showing the main parts of the optical writing system.

[Explanation of symbols]

1, 61 Optical writing device 13a Polygon mirror 13b Polygon motor 14 fθ lens 15, 151, 152, 153 Mirror 20 Photoreceptor belt (drum) 22 Developing device 40 Drive motor 62 LED array 63 Selfoc lens

Claims (5)

[Claims] 1. A photoconductor that moves at a constant speed in the sub-scanning direction; a light emitting source that emits a light beam that is modulated according to an image signal and scans the photoconductor in the main scanning direction; In an image forming apparatus equipped with a plurality of electrostatographic processing means for visualizing a latent image formed thereon according to an electrostatic photographic process, an image formation method is employed to determine the imaging position of a light beam exposed and scanned on the photoreceptor. An image forming apparatus comprising a moving means for moving the photosensitive member at a constant speed in the same direction as the moving direction of the photoreceptor in synchronization with the operation. 2. The image forming apparatus according to claim 1, wherein the moving speed of the imaging position of the light beam is set to a slower speed than the moving speed of the photoreceptor. 3. The method according to claim 2, wherein the ratio of the moving speed of the imaging position of the light beam to the moving speed of the photoreceptor is 1/5 or more and 1/2 or less. Image forming device. 4. A deflector for deflecting the light beam emitted from the light emitting source; a lens group for converging the light beam deflected and scanned by the deflector; The optical system includes a plurality of mirrors that bend the beam and keep the optical path length constant, the light emitting source is a laser light emitting source that emits laser light, and the moving means moves at least some of the plurality of mirrors. An image forming apparatus characterized in that the image forming apparatus is a mirror moving means for moving a mirror at a constant speed in a sub-scanning direction. 5. The light emitting source according to claim 1, wherein the light emitting source is an optical writing element array consisting of a large number of light emitting element rows arranged in the main scanning direction, and the moving means moves the optical writing element array in the sub scanning direction. An image forming apparatus characterized in that the image forming apparatus is a transport means for moving at a constant speed in a direction.