JP4072357B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile.
[0002]
[Prior art]
Conventionally, as a color image forming apparatus that forms a color image at a high speed, a photosensitive drum is arranged for each of yellow (Y), magenta (M), cyan (C), and black (Bk) along a conveying belt. The transfer material is sequentially conveyed by the conveyance belt to sequentially transfer the images of the respective colors, or the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt so as to overlap each other, and then the toner images on the transfer belt are collectively collected. There is what is called an in-line method of transferring to a transfer material.
[0003]
One of the main problems in this in-line color image forming apparatus is a color shift between colors of a color image. As components of color misregistration, there are misalignment in the scanning direction (main scanning direction) by a laser or LED, misalignment in the belt conveyance direction (sub scanning direction), expansion / contraction of an image in the main scanning direction, angular misalignment in the main scanning direction, and the like. Each color shift is adjusted so as to be equal to or less than an allowable value at the time of shipment of the apparatus. However, due to changes in environmental and device temperatures during adjustment and use, device distortion due to differences in floor surface, and color misregistration factors that the photosensitive drum has due to cartridge replacement, etc., color misregistration exceeding the allowable value may occur. May end up.
[0004]
Therefore, as a means for correcting the color misregistration timely, a color misregistration measurement pattern is formed at a predetermined interval on the conveyance belt or the intermediate transfer belt, and this measurement pattern is detected by the toner image detection sensor, and the detection result Therefore, it is necessary to calculate the color misregistration amount based on the above and correct the image forming position based on the calculation result. In order to accurately detect the color misregistration amount, the belt surface needs to be sufficiently stable with respect to the sensor.
[0005]
[Problems to be solved by the invention]
However, in the conventional toner image detection sensor, when the belt tension (hereinafter referred to as “belt tension”) is weakened with respect to the belt (conveyance belt or intermediate transfer belt), the belt is loosened, and the belt with respect to the toner image detection sensor becomes loose. There is a problem in that it becomes difficult to distinguish between the toner surface and the belt surface because the distance and angle change. When this problem occurs, the belt surface is erroneously determined to be toner, and incorrect correction may cause color misregistration, or correction itself cannot be performed. In addition, the belt that has been left for a long period of time is wrinkled along the roller at the portion that has been in contact with the roller, and problems similar to those described above occur after a long period of time. The same applies when the belt has deep dents and scratches.
[0006]
As far as the above-mentioned problems are concerned, it can be easily solved by increasing the belt tension. However, if the belt tension is increased, the offset force generated when the rollers are out of alignment, that is, the belt is There arises a problem that the force to move in the circumferential direction and the vertical direction becomes large. If this shifting force becomes too large, the belt or the belt unit itself may be damaged.
[0007]
The present invention has been made in view of the above circumstances, and provides an image forming apparatus capable of obtaining an optimum image quality by improving the detection accuracy of an image pattern by a sensor without increasing belt tension. It is for the purpose.
[0008]
[Means for Solving the Problems]
The invention according to claim 1, a sensor for detecting the endless belt image pattern is formed, a plurality of rollers before Symbol endless belt is passed over, the image pattern formed on the endless belt, the sensor anda support means for supporting the front Symbol sensor includes a line connecting the approximate center between said sensor of one roller of the plurality of rollers, the point at which the surface of the endless belt intersect In the image forming apparatus to be detected , the support means is supported so as to be swingable about a shaft of a roller around which the point portion of the endless belt is stretched .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in each drawing, what attached | subjected the same code | symbol has the same structure or effect | action, The duplication description about these shall be abbreviate | omitted suitably.
[0012]
<Embodiment 1>
FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in the figure is an electrophotographic four-color full-color image forming apparatus having image forming units at four locations, and the figure is a longitudinal sectional view showing a schematic configuration thereof.
[0013]
The entire image forming unit has image forming units A, B, C, and D in order from the bottom to the top. In this order, the image forming units form toner images of black, cyan, magenta, and yellow, respectively.
[0014]
The image forming apparatus shown in FIG. 1 includes four photosensitive drums 1a, 1b, 1c, and 1d as image carriers, and around each photosensitive drum 1a, 1b, 1c, and 1d according to the rotation direction. Almost sequentially, charging rollers (charging means) 2a, 2b, 2c, and 2d for uniformly charging the surfaces of the photosensitive drums 1a, 1b, 1c, and 1d, and laser beams are irradiated based on the image information to expose the photosensitive drums 1a, 1b, 1c, and Exposure devices (exposure means) 3a, 3b, 3c, 3d for forming an electrostatic latent image on 1d, development devices (development means) for developing toner images by attaching toner to the electrostatic latent images, and photosensitive drums Transfer members (transfer means) 5a, 5b, 5c, 5d for transferring toner images on 1a, 1b, 1c, 1d onto a transfer material (for example, paper, transparent film), photosensitive drums 1a, 1b, 1c after transfer, 1d surface Cleaner for removing post-transcriptional toner Tsu (cleaning means) 6a, 6b, 6c, 6d etc. is disposed to the image forming unit is constituted.
[0015]
Here, each of the photosensitive drums 1a, 1b, 1c, and 1d, the charging rollers 2a, 2b, 2c, and 2d, the developing device, and the cleaners 6a, 6b, 6c, and 6d are integrally formed into a cartridge and processed into a process cartridge. 7a, 7b, 7c, 7d are configured. These process cartridges 7a, 7b, 7c and 7d are individually detachable from the main body of the image forming apparatus.
[0016]
Further, the transfer material fed from the feeding unit 8 is conveyed to the image forming units A, B, C, and D by the conveying unit 9 having the electrostatic conveying belt 9a, and each color toner image is transferred to the first surface (front surface). ) Are sequentially transferred to form a color image, and then fixed by a fixing device (fixing means) 10 and discharged to a discharge tray (discharge portion) 13 by discharge roller pairs 11 and 12.
[0017]
When image formation (printing) is performed on both the front surface (first surface) and the back surface (second surface) of the transfer material, the transfer material is fixed by the fixing device 10 and the discharge roller 11, When the sensor 18 detects the rear end before the paper is completely discharged by 12, the paper discharge rollers 11 and 12 are reversed to be conveyed to the double-sided conveyance path 15 (in the direction of arrow A). The transfer material conveyed to the double-sided conveyance path 15 passes through the oblique feeding roller 16a on the front surface of the image forming apparatus main body and is conveyed vertically downward to the U-turn roller 17, and again by the U-turn roller 17 and the registration roller 8d. It is conveyed to the image forming unit A. Thereafter, a color image is formed on the second surface in the same manner as for the first surface, and then discharged onto the discharge tray 13. Thereby, the image formation on both surfaces of the transfer material is completed.
[0018]
Next, the configuration of each unit (each device) will be described sequentially.
[0019]
(Feeding department)
The feeding unit 8 includes a sheet feeding cassette 8a, a multi feeding tray 8b which is a multi feeding device, a multi feeding unit 8c, and a registration roller 8d.
[0020]
The paper feed cassette 8a stores a plurality of transfer materials and is inserted into the inner bottom portion of the image forming apparatus main body. At the time of image formation, the transfer material is separated and conveyed one by one from the sheet feeding cassette 8a by the cassette pickup roller 8a1, and conveyed to the image forming unit A by the cassette conveying roller 8a2 and the registration roller 8d.
[0021]
Next, the multi paper feed tray 8b is normally stored in front of the main body of the image forming apparatus, but when used, the multi paper feed tray 8b is rotated and opened from the main body of the image forming apparatus to set a plurality of transfer materials. To do. When forming an image from the multi-feed tray 8b, the transfer material is separated and conveyed one by one by the multi-pickup roller 8c1, and is conveyed to the image forming unit A by the multi-conveying roller 8c2 and the registration roller 8d. At this time, the feeding material from the multi-feed device, which uses a transfer material such as cardboard, envelope, special paper, etc., which is relatively difficult to electrostatically adsorb on the belt surface or has a strong stiffness, When it reaches the surface of the belt, it is composed only of Rs such that the leading and trailing ends are along the surface of the belt and the center part is curved. As shown in FIG. 1, the paper feed path from the paper feed cassette 8a has a curve that warps against the surface of the electrostatic conveyance belt 9a, but the transfer materials fed from the paper feed cassette 8a are compared. Since a transfer material is used which is weak and is easily attracted electrostatically to the belt surface, it has been found that there is no problem even if the cassette paper feed path as shown in FIG. 1 is taken.
[0022]
Separation and conveyance of the transfer material in the paper feed cassette 8a and the multi-feed unit 8c are performed by a paper feed motor (not shown) in the feed unit 8 via a gear drive train.
[0023]
(Image formation configuration)
The photosensitive drums 1a, 1b, 1c, and 1d as image carriers are configured by applying OPC (organic optical semiconductor) to the outer peripheral surface of an aluminum cylinder. Both ends of the photosensitive drums 1a, 1b, 1c, and 1d are rotatably supported by flanges, and a driving force is transmitted to one end from a driving motor (not shown). It is driven to rotate counterclockwise (arrow direction).
[0024]
Each of the charging rollers 2a, 2b, 2c, and 2d is a conductive roller formed in a roller shape. The roller is brought into contact with the surface of the photosensitive drums 1a, 1b, 1c, and 1d, and a charging bias application power source is applied to the rollers. By applying a charging bias (not shown), the surfaces of the photosensitive drums 1a, 1b, 1c, and 1d are uniformly charged to a predetermined polarity and potential.
[0025]
The exposure devices 3a, 3b, 3c, 3d have a polygon mirror, and the polygon mirror is irradiated with image light corresponding to an image signal from a laser diode (not shown). The light reflected by the polygon mirror passes through a lens or the like and is applied to the charged photosensitive drums 1a, 1b, 1c, and 1d. Thereby, electrostatic latent images corresponding to the image information are formed on the photosensitive drums 1a, 1b, 1c, and 1d.
[0026]
The developing device includes toner storage portions 4a1, 4b1, 4c1, and 4d1 that store toners of black, cyan, magenta, and yellow, and developing rollers 4a2, 4b2, 4c2, and 4d2, respectively. Among these, the developing rollers 4a2, 4b2, 4c2, and 4d2 are adjacent to the surface of the photosensitive drum, are rotationally driven by a driving unit (not shown), and are applied with a developing bias by a developing bias application power source (not shown). As a result, the toner is attached to the toner images on the photosensitive drums 1a, 1b, 1c, and 1d to be developed as toner images.
[0027]
Also, transfer members 5a, 5b, 5c, and 5d that are in contact with the electrostatic conveyance belt 9a facing the four photosensitive drums 1a, 1b, 1c, and 1d are provided inside the electrostatic conveyance belt 9a, which will be described later. Has been. These transfer members 5a, 5b, 5c and 5d are connected by a transfer bias application power source (not shown), and positive charges are transferred from the transfer members 5a, 5b, 5c and 5d via the electrostatic conveyance belt 9a. By applying this electric field to the material, the negative color toner images on the photosensitive drums 1a, 1b, 1c, and 1d are sequentially transferred onto the transfer material that is in contact with the photosensitive drums 1a, 1b, 1c, and 1d. Is formed.
[0028]
(Transfer material transfer configuration)
The transfer material is conveyed from the feeding unit 8 to the image forming area by the conveying unit 9.
[0029]
An electrostatic conveyance belt 9a as a transfer material carrier constituting the conveyance unit 9 is stretched and supported by four rollers of a driving roller 9b and driven rollers 9c, 9d, and 9e, and all the photosensitive drums 1a, 1b, and 1c are supported. , 1d. Since the driving roller 9b needs to be driven stably without slipping the electrostatic conveying belt 9a, a thin rubber having a thickness of about 1 mm is applied to the metal roller in consideration of driving grip performance and durability with respect to the electrostatic conveying belt 9a. Etc. are used.
[0030]
However, elastic members such as rubber have a larger coefficient of linear expansion than metal materials, so they are driven by expansion and contraction due to temperature rises in the machine (temperature rises in the image forming apparatus body) and changes in the usage environment. The diameter of the roller 9b changes. For this reason, even if the driving roller 9b drives the electrostatic conveyance belt 9a at the same rotation speed, the belt driving speed changes, and the printing position accuracy is deteriorated and the image quality is deteriorated.
[0031]
Therefore, it is necessary to control the speed of the electrostatic conveyance belt 9a. As a means for this, by generating one pulse signal every time the roller driven by the electrostatic conveyance belt 9a makes one rotation, The speed is detected and fed back to a drive motor that is a drive source of the drive roller 9b to control the rotation speed of the drive motor. In this way, the electrostatic conveyance belt 9a is driven stably, and the transfer material is electrostatically attracted to the outer peripheral surface facing the photosensitive drum 1 so that the transfer material comes into contact with the photosensitive drums 1a, 1b, 1c, and 1d. It is circularly moved by the drive roller 9b. As a result, the transfer material is conveyed to the transfer position by the electrostatic conveyance belt 9a, and the toner images of the respective colors on the photosensitive drums 1a, 1b, 1c, and 1d are sequentially transferred.
[0032]
Further, at the most upstream position of the electrostatic conveyance belt 9a, an attracting roller 9f that holds the transfer material together with the electrostatic conveyance belt 9a and attracts the transfer material to the electrostatic conveyance belt 9a is disposed. When transporting the transfer material, a voltage is applied to the attracting roller 9f to form an electric field between the opposing grounded roller 9c and dielectric polarization between the electrostatic transport belt 9a and the transfer material. To generate an electrostatic adsorption force between the two.
[0033]
(Fixing part)
The fixing device 10 applies heat and pressure to the toner image formed on the transfer material to fix it on the surface of the transfer material.
[0034]
The fixing device 10 includes a fixing belt 10a, an elastic pressure roller 10b, and a belt guide member 10c.
[0035]
Among them, the fixing belt 10a is a cylindrical belt having an electromagnetic induction heat generating layer, and is guided by a belt guide member 10c having a built-in magnetic field generating means including an exciting coil and a T-shaped magnetic core.
[0036]
The elastic pressure roller 10b sandwiches the fixing belt 10a with the belt guide member 10c, and forms a fixing nip portion N having a predetermined width with the fixing belt 10a.
[0037]
The pressure roller 10b is rotationally driven by a driving means (not shown), and the cylindrical fixing belt 10a is rotated accordingly, and the fixing belt 10a is supplied with power from an excitation circuit (not shown) to an excitation coil (not shown). Electromagnetic induction heat is generated.
[0038]
In a state where the fixing nip N rises to a predetermined temperature and is temperature-controlled, the transfer material on which the unfixed toner image conveyed from the image forming unit is formed is the fixing belt 10a and the pressure roller 10b of the fixing nip N. The image surface is introduced upward, that is, facing the fixing belt 10a, and the image surface is brought into close contact with the outer surface of the fixing belt 10a in the fixing nip portion N, and is nipped and conveyed together with the fixing belt 10a. To go.
[0039]
In the process in which the transfer material is nipped and conveyed together with the fixing belt 10a through the fixing nip portion N, the unfixed toner image on the transfer material is heated and fixed by being heated by electromagnetic induction heat generated by the fixing belt 10a.
[0040]
(Toner image detection sensor)
The toner image detection sensor 20 is disposed in the vicinity of the drive roller 9b. The toner image detection sensor 20 detects a toner pattern formed on the electrostatic conveyance belt 9a for measuring the color misregistration amount, calculates the color misregistration amount based on the detection result, and based on the calculation result, the image is detected. The formation position is corrected. At this time, in order to accurately detect the color misregistration amount, as shown in FIGS. 2A and 2B, the toner image detection sensor 20 is set in a swingable state and the belt unit is placed at the use position. The point P on the electrostatic conveyance belt 9a is seen on a line connecting the toner image detection sensor 20 and the approximate center of the driving roller 9b. This point P corresponds to the boundary between the contact portion and the non-contact portion of the electrostatic conveyance belt 9a with respect to the drive roller 9b.
[0041]
Further details will be described with reference to FIGS.
[0042]
The transport means 9 is unitized to form a transport unit. The transport unit includes a plate-like frame 22 disposed on the front side and the back side of the main body of the image forming apparatus (however, only one frame 22 is shown in FIG. 2A). A driving roller 9b whose parts are rotatably supported, driven rollers 9c, 9d, and 9e, and an electrostatic conveyance belt 9a stretched over these rollers are provided. The transport unit can be attached to and detached from the image forming apparatus main body as a whole unit.
[0043]
The toner image detection sensor 20 is supported by an L-shaped support member (support means) 23. The support member 23 is supported by a member (not shown) coaxial with the shaft of the drive roller 9b so that the base end side is swingable, and the toner image detection sensor 20 is attached to the front end side. An intermediate portion of the support member 23 is supported from below by a support portion 22 a protruding from the frame 22. Therefore, the support member 23 can rotate around the support portion 22a when the shaft of the drive roller 9b moves relative to the frame 22.
[0044]
Positioning means 24 is provided at the tip of the support member 23, and the toner image detection sensor 20 is attached via the positioning means 24. The positioning means 24 includes concave locking portions 24a and 24a formed on the support member 23 side, and positioning pins 24b and 24b protruding from the toner image detection sensor 20 side. The toner image detection sensor 20 is accurately positioned when the positioning pins 24b and 24b are engaged with the locking portions 24a and 24a described above, and is directed to the point P described above.
[0045]
With the configuration described above, the toner image detection sensor 20 moves following the entire transport unit when it moves unnecessarily, and the drive roller 9b moves unnecessarily with respect to the frame 22. In this case, the support member 23 follows the movement of the drive roller 9b by rotating around the support portion 22a. Thus, even when the distance between the toner image detection sensor 20 and the electrostatic conveyance belt 9a (hereinafter referred to as “belt distance”) varies, the toner image detection sensor itself follows the vibration of the driving roller 9b, and the belt distance. Becomes substantially constant (FIG. 2B).
[0046]
Further, the presence of the driving roller 9b on the back surface of the electrostatic transport belt 9a, that is, the presence of a member that abuts against the back surface of the electrostatic transport belt 9a, can correct deep dents in the electrostatic transport belt 9a. The belt distance and the belt angle (the angle of the toner image detection sensor 20 with respect to the electrostatic conveyance belt 9a: normally horizontal) are stable, and the toner surface and the belt surface can be easily distinguished.
[0047]
Even when the belt unit is detachable from the image forming apparatus main body or movable within the image forming apparatus main body, the belt distance and the belt angle are stable, and the toner surface and the belt surface can be easily distinguished.
[0048]
In addition to this, as shown in FIG. 1, image correction amount detection points by the toner image detection sensor 20 are points P on the electrostatic conveyance belt 9a that connect the drive roller 9b and the toner image detection sensor 20 positioned immediately after image formation. By making the roller stretched, the toner image formed on the electrostatic conveyance belt 9a can be made less susceptible to errors caused by the disturbance of the toner image caused by passing over the driving roller 9b. The disturbance of the toner image is caused by the fact that the electrostatic conveyance belt 9a passes over the driving roller 9b, whereby the voltage of the belt itself attenuates, and the toner on the electrostatic conveyance belt 9a is easily scattered. There is a belt expansion / contraction caused by refraction of 9a.
[0049]
This time, the toner image detection sensor 20 is limited to seeing a point P on the electrostatic conveyance belt 9a that connects the toner image detection sensor 20 and the substantially center of the drive roller 9a with the belt unit in the use position. However, as shown in FIG. 3, an abutting member 21 is provided on the back surface of the electrostatic conveying belt 9a, and a point P on the electrostatic conveying belt 9a connecting the abutting member 21 and the toner image detection sensor 20 is defined. A similar effect can be obtained by viewing.
[0050]
The toner image detection sensor 20 includes a light emitting unit that irradiates light to the electrostatic transport belt 9a and a member that receives light from the electrostatic transport belt 9a, and the light emitting unit and the light receiving unit are connected to the electrostatic transport belt 9a. It is a light reflection type sensor located in the same direction.
[0051]
With this configuration, the toner image detection sensor 20 is attached to the main body of the image forming apparatus when the belt unit reaches the end of its life or is damaged and is replaced, so that the toner image detection sensor 20 There is no need to replace the belt unit at the same time. Even when the belt unit is replaced, the positional relationship between the light emitting side and the light receiving side does not change.
[0052]
In the above embodiment, the case where the endless belt on which the toner image to be detected by the toner image detection sensor 20 is formed is an electrostatic conveyance belt that conveys a transfer material on the surface is described as an example. The present invention is not limited to this, and the basic configuration can be applied as it is even when the endless belt is an intermediate transfer belt.
[0053]
【The invention's effect】
As described above, according to the present invention, the distance and angle of the sensor with respect to the endless belt can be stabilized, and the image surface can be easily distinguished from other surfaces, so that the belt tension of the endless belt is increased. Therefore, it is possible to improve the detection accuracy of the image pattern by the sensor and obtain an optimum image quality.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to the present invention.
FIGS. 2A and 2B are diagrams illustrating a sensor that follows the movement of a driving roller. FIG.
FIG. 3 is a diagram illustrating an example in which an abutting member is disposed on the back surface of the electrostatic conveyance belt.
[Explanation of symbols]
9a Endless belt (electrostatic transfer belt)
9b Roller (drive roller)
20 sensor (toner image detection sensor)
23 Support means (support member)
24 Positioning means P Point

Claims (1)

An endless belt on which an image pattern is formed, a plurality of rollers before Symbol endless belt is stretched, a sensor for detecting the image pattern formed on the endless belt, support means for supporting said sensor, a has, before Symbol sensor, in the image forming apparatus one and the line connecting the approximate center between said sensor roller, and the surface of the endless belt to detect the point of intersection of the plurality of rollers,
The image forming apparatus , wherein the support means is supported so as to be swingable about a roller shaft around which the portion of the endless belt is stretched .

Images