JP3815012B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming apparatus, such as a copying machine, a printer, and a FAX, which forms a toner image on an image carrying means, and transfers and fixes the toner image on the image carrying means to a transfer material. In particular, the present invention relates to an image forming apparatus capable of forming an image on both sides of a transfer material.
[0002]
[Prior art]
Conventionally, in double-sided image formation, a toner image formed on an image carrying unit is transferred and fixed on one side of a transfer material, and after the transfer material is once stored in a double-sided reversing paper feeder, it is again placed on the image carrying unit. The transfer material is fed from the double-sided reversing paper feeder in time with the formed toner image, and the toner image on the image carrier is transferred and fixed to the other surface of the transfer material to form an image on both sides of the transfer material. The way to do it is taken.
[0003]
[Problems to be solved by the invention]
As described above, this double-sided image forming apparatus transports a transfer material such as feeding to a double-sided reversing paper feeding device or passing through a fixing device twice. Causes wrinkling of the material. In addition, since the transfer distance of the transfer material becomes long, it takes a lot of processing time to form an image, and the transfer material is heat-treated twice for image fixing, so that the paper quality is damaged.
[0004]
Therefore, the present inventor previously provided an apparatus for transferring a toner image onto both sides of a transfer material and fixing a transfer material having the toner image on both sides simultaneously by providing two image forming means and two transfer means. Research has made it possible to realize a double-sided image forming apparatus that can significantly increase the processing speed of double-sided image formation.
[0005]
In this double-sided image forming apparatus, the transfer material on which the toner images are transferred to the front and back surfaces is fixed at the same time by a single heat treatment by the fixing device, so there is no risk of damaging the paper quality of the transfer material. The transfer path for the transfer material can be shortened to increase the processing speed of image formation.
[0006]
The present inventor has continued research on shortening of the copy processing time, and has made it an object to realize an image forming apparatus capable of remarkably increasing the image forming speed as compared with the previously proposed double-sided image forming apparatus. It is another object of the present invention to provide an image forming apparatus capable of performing good image formation in addition to the above functions and to improve the usability of the image forming unit.
[0007]
[Means for Solving the Problems]
The above problem can be solved by the following configuration.
[0008]
First image carrying means for carrying a toner image, second image carrying means, third image carrying means, first toner image forming means for forming a toner image on the first image carrying means, and the first toner image Forming means Includes lower γ correction than γ correction for image formation in With image forming conditions , Second toner image forming means for forming a toner image on the second image carrying means, and a toner image formed on the first image carrying means by the first toner image forming means on the first surface of the transfer material A first transfer means for transferring; a second transfer means for transferring the toner image formed on the second image carrying means by the second toner image forming means to the third image carrying means; and the second transfer means. The third transfer means for transferring the toner image transferred to the third image carrying means to the second surface opposite to the first surface of the transfer material, and the fixing for fixing the toner image transferred to the transfer material. And an image forming apparatus.
[0009]
That is, a toner image is formed on the first and second image carrying means by the first and second toner image forming means, respectively, and the toner image formed on the second image carrying means is temporarily transferred onto the third image carrying means. Thereafter, the toner images on the first and third image carrying means are transferred onto both surfaces of the transfer material and fixed simultaneously, so that the image forming speed can be remarkably increased. Further, in this case, the image formation on the first surface of the transfer material may be performed only once from the first image carrying means to the transfer material, whereas the image formation on the second surface of the transfer material is the second image. Since the transfer is performed twice from the carrying means to the third image carrying means and from the third image carrying means to the transfer material, the image density on the second surface is lower than the first surface (the transfer rate is not 100%). This is because the toner adhesion amount decreases. Further, the gradation is changed by the transfer of the toner image twice, and a good image cannot be formed. However, in the first invention, since the first toner image forming unit and the second toner image forming unit have different image forming conditions, in response to such a decrease in image density and a change in gradation, Good image formation can be performed.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. In the following description, the surface of the transfer material facing the first image carrying means in the transfer area is referred to as the front surface (first surface), and the other surface of the transfer material is referred to as the back surface (second surface). An image transferred onto the surface of the transfer material is referred to as a front image, and an image transferred onto the back surface of the transfer material is referred to as a back image.
[0017]
First, an image forming process and each mechanism according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus showing an embodiment of the image forming apparatus of the present invention.
[0018]
The intermediate transfer member 10 serving as a third image carrier is an endless belt capable of holding a toner image on its peripheral surface, and has a thickness of, for example, 0.5 to 2.0 mm and a volume resistivity of 10 ⁸ -10 ¹⁴ A two-layer structure is provided in which a semiconductive fluorine coating having a thickness of 5 to 50 μm is applied to the outside of a semiconductive rubber belt substrate made of Ω · cm silicon rubber or urethane rubber as a toner filming prevention layer. Instead of rubber belt substrate, thickness 0.1-0.5mm, volume resistivity 10 ⁸ -10 ¹⁴ Ω · cm semiconductive polyester, polystyrene, polyethylene, polyethylene terephthalate, polyimide, modified polyimide, ETFE (ethylene-tetrafluoroethylene copolymer), or the like can also be used.
[0019]
The intermediate transfer member 10 is transmitted to the driving roller 11A while being stretched horizontally by the driving roller 11A, the tension roller 13, the driven roller 11B, the guide roller 12B, the driven roller 11C, and the guide roller 12B. Circulates counterclockwise and is conveyed and rotated.
[0020]
First and second process units 20A and 20B are horizontally arranged on the upper surface of the rotating intermediate transfer body 10. Each of the first and second process units 20A and 20B is composed of a photosensitive drum 21 which is an image carrying means for carrying a toner image and a toner image forming means 26 for forming a toner image on the photosensitive drum 21. The process unit 20 forms a toner image on the photosensitive drum 21 by a known electrophotographic process, and has the same configuration except for control, as will be described in detail later. In the case where the first and second process units 20A and 20B have the same configuration, the reference numerals are used except for the suffixes A and B. The process unit 20 is mounted with its position regulated via a guide member (not shown) so that the peripheral surface of each photosensitive drum 21 comes into contact with the intermediate transfer body 10 with a predetermined contact pressure from above the apparatus main body. The toner image forming unit 26 includes a scorotron charger 22 as a charging unit, an exposure unit 25 as an exposure unit, a developing unit 23 as a developing unit, and a cleaning device 24 as a cleaning unit.
[0021]
The photosensitive drums 21A and 21B as the first and second image carrying means are formed by forming an organic photosensitive layer (OPC) on the outer periphery of a grounded cylindrical aluminum substrate having an outer diameter of 30 to 80 mm. Driven and rotated in the clockwise direction by the power at the same speed as the peripheral speed of the intermediate transfer member 10.
[0022]
The scorotron charger 22 includes a corona discharge electrode formed of a sawtooth electrode or a wire electrode, and a control grid held at a predetermined potential with respect to the above-described organic photoreceptor layer of the photoreceptor drum 10. The photosensitive drum 21 is mounted in close proximity to the photosensitive drum 21 in a direction perpendicular to the moving direction of the photosensitive drum. The scorotron charger 22 performs corona discharge having the same polarity as the toner (in this embodiment, negative charging) and applies a uniform potential to the photosensitive drum 21.
[0023]
The exposure unit 25 has the same magnification as a linear exposure element in which a plurality of LEDs (light emitting diodes) as image exposure light emitting elements arranged in the main scanning direction parallel to the axis of the photosensitive drum 21 are arranged in an array. It is composed of a SELFOC lens as an imaging element. As the exposure element, a linear element in which a plurality of light emitting elements such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array is used. The exposure unit performs image exposure on the photosensitive drum 21 based on image data read by a separate image reading device and stored in the memory, and forms a latent image on the photosensitive drum 21.
[0024]
The developing unit 23 includes a developing sleeve 230 formed of, for example, a cylindrical nonmagnetic stainless steel or aluminum material having a thickness of 0.5 to 1 mm and an outer diameter of 10 to 30 mm, and a one-component or two-component developer is contained therein. Contained. The developing sleeve 230 rotates in the forward direction with respect to the rotation direction of the photosensitive drum 21, and a developing bias in which a DC voltage having the same polarity as the toner (negative polarity in the present embodiment) or further AC is applied to the developing sleeve 230. Is applied to the exposed portion of the photosensitive drum 21 so that reversal development is performed in a contact or non-contact state.
[0025]
The transfer device 14A, which is the first transfer means, and the transfer device 14B, which is the second transfer means, apply a charge having a polarity opposite to that of the toner to the back surface of the intermediate transfer body 10 to form a toner image between the photosensitive drum 21. The transfer device 14A is arranged to face the peripheral surface of each photoconductive drum 21, and the transfer unit 14A is an upper surface of a recording paper P (transfer material to which the toner image of the photoconductive drum 21A is supplied ( On the other hand, the transfer unit 14B transfers the toner image on the photosensitive drum 21B onto the intermediate transfer member 10, respectively.
[0026]
The paper charger 14C, which is a transfer material charging means, is a brush-like charger, which is located between the first process unit 20A and the second process unit 20B and is disposed on the peripheral surface of the grounded driven roller 11C. The recording paper P, which is disposed oppositely, enables contact with and separation from the intermediate transfer body 10, and charges the recording paper P supplied in sliding contact with the same polarity as the toner when transporting the recording paper P to the intermediate transfer body 10, thereby charging the recording medium. The paper P is conveyed to the transfer area with the photosensitive drum 21A via the toner image transferred onto the intermediate transfer body 10 by the transfer device 14B or directly adsorbed. The paper charger 14C may be a corona charger.
[0027]
The transfer device 14D, which is a third transfer unit, applies a charge having a polarity opposite to that of the toner to the upper surface (front surface) of the recording paper P on the intermediate transfer member 10 to transfer the toner image on the intermediate transfer member 10 to the recording paper P. It is transferred to the lower surface (back surface), and is arranged to face the peripheral surface of the grounded driving roller 11A.
[0028]
The static eliminator 14E, which is a separation means, discharges the recording paper P, to which the toner image has been transferred on the upper and lower sides, that is, both the front and back surfaces, to separate it from the peripheral surface of the intermediate transfer body 10, and is adjacent to the transfer unit 14D. The drive roller 11A is provided so as to face the peripheral surface of the grounded drive roller 11A.
[0029]
The fixing device 18 serving as a fixing unit is a heat roller type fixing device that includes a first roller 18A and a second roller 18B both having a heater therein, and is a recording separated from the intermediate transfer member 10 by a static eliminator 14E. When the paper P is nipped and conveyed, the toner images transferred to both the front and back surfaces are simultaneously pressed and fixed.
[0030]
Next, the process of this image forming apparatus will be described. When image data is input from an image reading device or a personal computer (not shown), the image processing described in detail later is performed, and then the image data on the front and back surfaces is temporarily stored in a memory and corresponding to the image forming process. The images are processed in a mirror image relationship and sequentially output to the exposure units 25A and 25B (respectively selected).
[0031]
First, the back side image data is input to the exposure unit 25B of the second process unit 20B. In the second process unit 20B (the second toner image forming means 26B), the operations of the scorotron charger 22B, the exposure unit 25B, and the developing unit 23B. As a result, a toner image on the back surface based on the image data on the back surface is formed on the peripheral surface of the photosensitive drum 21B as the second image carrying means, and this toner image is transferred to the intermediate transfer body by the transfer device 14B as the second transfer means. The back surface of the battery 10 is charged and temporarily transferred onto the peripheral surface of the intermediate transfer member 10.
[0032]
In parallel with the formation and transfer of the toner image on the back side, the recording paper P is fed from the paper feeding cassette 15 by the operation of the carry-out roller 15A, and the recording paper P is fed to the timing roller 17 through the paper feeding path 16. Sent.
[0033]
On the other hand, the front side image data is input to the exposure unit 25A of the first process unit 20A with a predetermined time difference from the input of the back side image data, and the first process unit 20A (the first toner image forming unit 26A) By the action of the scorotron charger 22A, the exposure unit 25A, and the developing unit 23A, a toner image on the surface is formed on the peripheral surface of the photosensitive drum 21A as the first image carrying means.
[0034]
The operation of the timing roller 17 is started in synchronization with both the formation of the front toner image on the peripheral surface of the photosensitive drum 21A in the first process unit 20A and the position of the back toner image transferred onto the intermediate transfer member 10. Then, the toner image is fed onto the intermediate transfer member 10 via the toner image on the back surface of the intermediate transfer member 10 so that the leading edge position of the front and back toner images matches the leading edge position of the recording paper P.
[0035]
At this time, the recording paper P is attracted onto the intermediate transfer member 10 via the toner image on the intermediate transfer member 10 due to the charging of the paper charger 14C, and is conveyed integrally with the intermediate transfer member 10. Then, the back surface of the intermediate transfer member 10 is charged by the transfer device 14A as the first transfer means, and the toner image on the surface carried by the photosensitive drum 21A of the first process unit 20A is transferred to the recording paper P being conveyed. Transfer to the upper surface (first surface). Next, the surface of the recording paper P is charged by the transfer device 14D as the third transfer means, and the toner image on the back surface of the intermediate transfer body 10 transferred from the photosensitive drum 21B of the second process unit 20B is recorded on the recording paper. Retransfer to the lower surface (second surface) of P.
[0036]
Thus, the recording paper P on which the toner images are transferred on both the front and back surfaces is discharged by the discharge of the charge eliminator 14E, separated from the peripheral surface of the intermediate transfer body 10, and passed through a spur member 18C that guides the lower surface of the recording paper P. After the toner image is welded in the fixing device 18, it is discharged to the tray 19B through the discharge roller 19A. In addition, when using curvature separation, the static eliminator 14E can be omitted. On the other hand, the photosensitive drum 21 and the intermediate transfer body 10 that have finished transferring the toner image are removed and cleaned by the cleaning device 24 or 140 provided for the respective toner drums 21 and 140 to prepare for the subsequent formation and transfer of the toner image.
[0037]
As described above, in the image forming apparatus according to the present embodiment, toner images are formed on the photosensitive drums 21A and 21B by the toner image forming units 26A and 26B, respectively, and the toner images formed on the photosensitive drum 21B are temporarily stored. Since the toner image on the photosensitive drum 21A and the intermediate transfer body 10 is transferred onto both surfaces of the recording paper P and fixed at the same time, the image forming speed can be significantly increased. In particular, the front and back toner images are formed at a slight time interval, and the transfer of the recording paper P to the front and back is performed during one rotation of the intermediate transfer body 10, so that the time required for recording the double-sided image is remarkably large. It will be shortened.
[0038]
When images are formed on both sides of the recording paper P described above, the transfer conditions of the transfer units 14A, 14B, and 14D are different. This is because when a toner image is transferred by each of the transfer units 14A, 14B, and 14D, the recording paper and the toner image interposed between the transferred toner image and the transfer unit are different. Therefore, in the present embodiment, each transfer device 14A, 14B, 14 D When the image forming is performed on both sides of the recording paper P, the transfer units 14A, 14B, and 14 are stored in a storage means (described later). D These transfer conditions are read out from the storage means, and based on this, the power supplies 140A, 140B and 140D (see FIG. 3) for supplying a transfer current or applying a transfer voltage to each transfer device are controlled. Thereby, a good double-sided image can be formed.
[0039]
More specifically, in the transfer by the transfer device 14A, the transfer electric field is weakened by the recording paper P and the toner image on the back surface as compared with the transfer by the transfer device 14B. Alternatively, the absolute value of the transfer voltage is made larger than the absolute value of the transfer current or transfer voltage, which is the transfer condition of the transfer device 14B. Further, in the transfer by the transfer device 14D, it is necessary to cancel the charge on the back surface of the intermediate transfer body 10 (charges by the transfer devices 14A and 14B) and to change the polarity of the toner image on the surface of the recording paper P. The absolute value of the transfer current or transfer voltage, which is the transfer condition of the transfer device 14D, is made larger than the absolute value of the transfer current or transfer voltage, which is the transfer condition of the transfer device 14A.
[0040]
By the way, in the above-described double-sided image formation, when the first toner image forming unit 26A and the second toner image forming unit 26B perform image formation under the same control (process) conditions, the first process unit 20A (on the front side) The image formation may be performed only once from the photosensitive drum 21A to the front surface of the recording paper P, whereas the image formation on the (back side) by the second process unit 20B is performed from the photosensitive drum 21B to the intermediate transfer body 10, the intermediate transfer. Since the transfer is performed twice from the body 10 to the back side of the recording paper P, the image density of the back side image formed by the second process unit 20B becomes low. This is because the toner adhesion amount is reduced because the transfer rate is not 100% during the transfer.
[0041]
In order to solve this problem, in this embodiment, the first toner image forming unit 26A and the second toner image forming unit 26B have different process conditions. Here, the process conditions are charging, exposure, and development conditions, and more specifically, the charging potential of the photosensitive drum 21, the exposure amount (exposure intensity or exposure time), the development bias, or the rotation speed of the development sleeve 230. That is. In this way, the first and second process units 20A and 20B are configured as the same process unit to reduce the cost, and the process conditions that can be easily changed are made different so that optimum image formation on the front and back surfaces can be achieved. Make it possible. In particular, as described above, since the toner adhesion amount is reduced in the image formation on the back surface, the toner amount adhering to the photosensitive drum 21B is larger than the toner amount adhering to the photosensitive drum 21A (forms the same image). If so) different.
[0042]
For example, the absolute value of the current or voltage applied to the corona discharge electrode or control grid of the scorotron charger 22B is made larger than the absolute value of the current or voltage applied to the corona discharge electrode or control grid of the scorotron charger 22A. Change the charging conditions. The light emission intensity or pulse width of the exposure unit is changed so that the exposure amount from the exposure unit 25B corresponding to the maximum density of the image is larger than the exposure amount from the exposure unit 25A corresponding to the maximum density of the same image. The absolute value or AC voltage of the bias voltage applied to the developing sleeve 230B is made larger than the absolute value or AC voltage of the bias voltage applied to the developing sleeve 230A. The rotational speed of the developing sleeve 230B is made faster than the rotational speed of the developing sleeve 230A.
[0043]
By the way, in the image forming apparatus of the present embodiment, when copying an image of an original (image formation), as shown in FIG. 2 showing an example of a digital image processing system, the image of the original is read by a sensor such as a scanner ( S1) After the A / D conversion (S2) of the read image information and the shading correction (S3), the image signal is stored in the image memory (S5) after data compression (S4). When an image is formed by using a signal from a computer or the like, the signal is developed from font data or the like into bitmap data and rasterized, and then input to the image memory (S5). Next, the image data sequentially read from the image memory (S5) according to the output command is subjected to data restoration processing (S6), and then the image data to be formed by the second process unit 20B by the selector (S7). That is, the image data is sorted into the image data of the back image and the image data to be formed by the first process unit 20A, that is, the image data of the front image. The image data of the front image is stored in the frame memory (SA9) as it is, but the image data of the back image is stored in the frame memory (SB9) after mirror image processing for inverting the left and right of the image (S8). Each frame memory (SA9, SB9) has a memory for two screens. The memory for one screen is used for developing the image data, and the other one screen memory is used for outputting the image data alternately. used.
[0044]
The image data from the frame memory (SA9) is subjected to image processing corresponding to the surface image such as γ conversion (SA10), filtering (SA11) and multi-value (SA12), and then the first exposure unit 25A of the first process unit 20A. The image data from the frame memory SB9 is subjected to image processing according to the back image such as γ conversion (SB10), filtering such as MTF correction (SB11), and multi-valued (SB12), and the like. It is output to the second exposure unit 25B of the process unit 20B.
[0045]
In the image forming apparatus as in the present embodiment, when the front side image is formed and when the back side image is formed, that is, the image formation by the first process unit 20A and the image by the second process unit 20B. In the formation, it is preferable to change the image processing conditions. That is, as in the present embodiment, since the image formation (on the back surface) by the second process unit 20B performs the transfer twice, there is a tendency that the halftone is crushed (γ increases) and the line becomes thick. Therefore, in the present embodiment, the second process unit 20B (on the back surface) is related to the γ conversion, which is one of the image processes, as compared with the γ conversion (SA10) for image formation (front surface) by the first process unit 20A. ) Perform γ conversion (SB10) for image formation and perform low γ correction (using a distorted γ correction curve) (that is, make the γ correction curve different between the front side image formation and the back side image formation) . Further, regarding filtering which is one of the image processing, filtering for image formation of the second process unit 20B (back side) is compared with filtering for image formation (SA11) of the (front surface) by the first process unit 20A. (SB11) is processed so that the fine line processing becomes stronger (the MTF filter is strengthened, that is, the MTF filter is different between the front side image formation and the rear side image formation). The γ correction curve and the MTF filter in these image processes are determined in advance (different during front side image formation and back side image formation, and are set independently), and the front side image and the back side image on the recording paper P. It is preferable that the adjustment is made so that the
[0046]
The image forming conditions such as the process conditions and the image processing conditions described above are not limited to the case where image formation is performed on both sides of the recording paper P in the image forming apparatus of the present embodiment, but only on one side of the front or back side. The same applies to image formation.
[0047]
Here, image formation on only one side of the recording paper P in the image forming apparatus of the present embodiment will be described.
[0048]
First, when image formation is performed only on the surface of the recording paper P, when image data is input from an image reading device or a computer (not shown), the image processing is performed, and then stored in a memory and sequentially exposed. It is output to the unit 25A. In the first process unit 20A (first toner image forming means 26A), a toner image based on image data is formed on the peripheral surface of the photosensitive drum 21A by the action of the scorotron charger 22A, the exposure unit 25A, and the developing unit 23A. It is formed. On the other hand, in parallel with the formation of the toner image, the recording paper P is started to be fed from the paper feeding cassette 15 by the operation of the carry-out roller 15A, and the recording paper P is fed to the timing roller 17 via the paper feeding path 16. The operation of the timing roller 17 is started in synchronism with the formation of the toner image on the peripheral surface of the photosensitive drum 21A, so that the front end position of the toner image and the front end position of the recording paper P coincide with each other. Paper is fed to The recording paper P is conveyed integrally with the intermediate transfer member 10 by charging of the paper charger 14C, and a toner image carried on the photosensitive drum 21A of the first process unit 20A is transferred to the upper surface (first surface) by the transfer device 14A. Transcribed. The recording paper P on which the toner image is transferred only on the surface is discharged by the discharge of the charge eliminator 14E, separated from the peripheral surface of the intermediate transfer member 10, and conveyed to the fixing device 18 through the spur member 18C. After the toner image is welded, the toner image is discharged to a tray 19B through a discharge roller 19A.
[0049]
Next, when image formation is performed only on the back surface of the recording paper P, when image data is input from an image reading device or a computer (not shown), the above-described image processing (of course, as described above, low γ correction and fine line correction are performed. After processing, the data is once stored in the memory and sequentially output to the exposure unit 25B. In the second process unit 20B (second toner image forming means 26B), a toner image based on the image data is formed on the peripheral surface of the photosensitive drum 21B by the action of the scorotron charger 22B, the exposure unit 25B, and the developing unit 23B. The toner image is formed (of course, with different process conditions as described above), and this toner image is once transferred onto the peripheral surface of the intermediate transfer body 10 by the transfer device 14B. On the other hand, in parallel with the formation and transfer of the toner image, the recording paper P is started to be fed from the paper feeding cassette 15 by the operation of the carry-out roller 15A, and the recording paper P is fed to the timing roller 17 via the paper feeding path 16. The operation of the timing roller 17 is started in synchronization with the position of the toner image transferred to the intermediate transfer body 10 and the intermediate transfer body 10 so that the leading edge position of the toner image and the leading edge position of the recording paper P coincide with each other. The sheet is fed onto the intermediate transfer member 10 via the upper toner image. The recording paper P is transported integrally with the intermediate transfer member 10 by the charging of the paper charger 14C, passes directly under the first process unit 20A, and then the photosensitive member of the second process unit 20B on its lower surface (second surface). The toner image on the intermediate transfer body 10 transferred from the drum 21B is retransferred by the transfer device 14D. The recording paper P, to which the toner image is transferred only on the back side, is neutralized by the discharge of the static eliminator 14E, separated from the peripheral surface of the intermediate transfer member 10, and conveyed to the fixing device 18 via the spur member 18C. After the toner image is welded, the toner image is discharged to a tray 19B through a discharge roller 19A.
[0050]
As described above, in the image forming apparatus according to the present embodiment, image formation is performed on both sides of the recording paper P (also referred to as a double-sided image formation mode, but this double-sided image formation mode has two modes as described in detail later. In addition, image formation can be performed only on one side of the front surface or the back surface of the recording paper P (also referred to as a front surface image formation mode and a back surface image formation mode, respectively).
[0051]
By the way, in this image forming apparatus, the transfer for transferring the toner image onto the recording paper P when the image is formed on both sides of the recording paper P and when the image is formed on one side (the first side or the second side). If the transfer conditions of the transfer device 14A and / or the transfer device 14D are the same, the transfer of the toner image to be transferred is affected by the presence of the toner image that is not transferred due to the presence or absence of the toner image. Problems such as poor toner quality and toner image distortion occur. More specifically, at the position of the transfer device 14A, the back side toner image exists between the recording paper P and the intermediate transfer body 10 in the double-sided image forming mode, but the back side toner image does not exist in the front side image forming mode. Further, at the position of the transfer unit 14D, the front toner image exists on the surface of the recording paper P in the double-sided image forming mode, but the front toner image does not exist in the back-side image forming mode. In the double-sided image forming mode, since there is a toner image that is not transferred by each transfer device, the transfer electric field is weakened compared to the single-sided image forming mode (front surface image forming mode or back surface image forming mode). If the transfer conditions are the same and the transfer conditions are the same, transfer defects occur.
[0052]
In order to solve this problem, in the present embodiment, the transfer conditions of the transfer device 14A and / or the transfer device 14D are set such that an image is formed on only one side of the recording paper P, and an image is formed on both sides of the recording paper P. It differs depending on when the formation is performed. This will be described in detail with reference to FIG. 3 which is a conceptual diagram of the control block. A double-sided image forming mode is provided by an image forming mode selection button 41 provided on an operation panel (not shown) (although this will be described in detail later, this double-sided image forming mode has two modes, but will be described as one mode here). Any one of the front surface image forming mode and the back surface image forming mode is selected. This selection can also be performed from an external device such as a computer. When the mode is selected, the control unit (CPU) 42 controls the image forming apparatus based on the sequence (the above-described process) stored in the ROM or RAM as the storage unit according to the selected mode. Then, image formation is performed. At this time, the optimum transfer conditions of the transfer units 14A and 14D obtained in advance by experiments or the like are stored in the storage means. Based on the transfer conditions, the control unit 42 supplies or transfers the transfer current to the transfer unit 14A. A power source 140A for applying a voltage and a power source 140D for supplying a transfer current to the transfer device 14D or applying a transfer voltage are controlled.
[0053]
As described above, in order to make the transfer conditions of the transfer units 14A and 14D different between the double-sided image forming mode and the single-sided image forming mode, in this embodiment, the transfer conditions stored in the storage means are set to the double-sided image forming mode. At least two images for the image forming mode and one-sided image forming mode are stored, and the transfer conditions corresponding to the selection of the image forming mode selection button 41 are read from the storage means, and the power supplies 140A and 140D are controlled based on this. To. Thereby, in both the double-sided image forming mode and the single-sided image forming mode, good transfer can be performed and good image formation can be performed.
[0054]
More specifically, in the front surface image formation mode (when image formation is performed only on the surface of the recording paper P), the absolute value of the transfer current or transfer voltage, which is the transfer condition of the transfer device 14A, is set in the double-side image formation mode. It may be smaller than (when image formation is performed on both sides of the recording paper P). In the back side image formation mode (when image formation is performed only on the back side of the recording paper P), the absolute value of the transfer current or transfer voltage, which is the transfer condition of the transfer unit 14D, may be smaller than that in double side image formation. In other words, the absolute value of the transfer current or transfer voltage in the double-sided image formation mode may be larger than that in the single-sided image formation mode.
[0055]
The same thing can be said for the static eliminator 14E as the transfer conditions of the transfer units 14A and 14D described above are different between the double-sided image forming mode and the single-sided image forming mode. That is, in this case, if the image forming is performed on both sides or the back surface of the recording paper P and the image forming is performed on the front surface, the discharge or recording by the transfer device 14D is performed under the same separation conditions. Depending on the presence or absence of a toner image on the front or back surface of the paper P, the charge staying on the recording paper P is different, and the adhesion between the recording paper P and the intermediate transfer member 10 is different. , Separation is not done well.
[0056]
Therefore, in the present embodiment, the separation condition of the static eliminator 14E is different between when the image is formed only on the front surface of the recording paper P and when the image is formed only on both sides or the back surface of the recording paper P. ing. Therefore, in the present embodiment, the separation condition stored in the storage unit is read according to the selection of the image forming mode selection button 41, and based on this, the charge removal current is supplied to the separator 14E or the charge removal voltage is applied. The power supply 140E to be controlled is controlled. Thereby, in any mode, good separation is performed and good image formation can be performed.
[0057]
More specifically, in the front surface image formation mode, the value of the neutralization current or the neutralization voltage, which is the separation condition of the static eliminator 14E, may be made smaller than that in the back surface image formation mode. In addition, in the back surface image formation mode, the neutralization current or the neutralization voltage, which is the separation condition of the static eliminator 14E, may be equal to or smaller than that in the double-side image formation mode.
[0058]
The same can be said for the paper charger 14C in that the transfer conditions of the transfer units 14A and 14D and the separation condition of the static eliminator 14E are different between the double-sided image forming mode and the single-sided image forming mode. In other words, in this case, if the charging condition of the paper charger 14C is the same in both the case where the image is formed on both sides or the back side of the recording paper P and the case where the image is formed on the front side, the image is formed on the intermediate transfer member 10. Depending on whether or not there is a toner image, the adhesiveness between the recording paper P and the intermediate transfer member 10 becomes poor, and the toner image on the intermediate transfer member 10 is disturbed, making it impossible to form a good image.
[0059]
Therefore, in the present embodiment, the charging condition of the paper charger 14C is different between when the image is formed only on the front surface of the recording paper P and when the image is formed only on both sides or the back surface of the recording paper P. It is Therefore, in the present embodiment, the charging condition stored in the storage unit is read according to the selection of the image forming mode selection button 41, and based on this, the charging current is supplied to the paper charger 14C or the charging voltage is set. The power supply 140C to be applied is controlled. Thereby, in any mode, good adhesion can be obtained, and good image formation can be performed.
[0060]
More specifically, in the surface image forming mode, the absolute value of the charging current or charging voltage, which is the charging condition of the paper charger 14C, may be made smaller than that in the double-sided image forming mode. In addition, in the double-sided image forming mode, the absolute value of the charging current or charging voltage, which is the charging condition of the paper charger 14C, may be equal to or smaller than that in the back-side image forming mode.
[0061]
By the way, the above-described transfer devices 14A, 14D, static eliminator 14E, paper charger 14C, and transfer device 14B are charged, transferred, and separated according to changes in the type of recording paper P and environmental conditions (in addition, intermediate characteristics due to repeated use). In the present exemplary embodiment, the transfer body 10 is adapted to the above and is configured so that good image formation is always possible. This will be described below with reference to FIG.
[0062]
A humidity detection sensor 43 (not shown in FIG. 1) for detecting the humidity in the image forming apparatus as environmental condition detection means is provided between the process units 20A and 20B and close to the intermediate transfer member 10. The humidity detection signal is input to the control unit 42. In order to detect the environmental conditions, the humidity detection sensor 43 is provided in the present embodiment, but in addition to this, a temperature detection sensor for measuring the temperature in the image forming apparatus is provided, and the temperature detected by this is adjusted. And environmental conditions may be detected.
[0063]
The type of the recording paper P is a switch for selecting the type of the recording paper P provided on an operation panel (not shown) (for example, a thick paper switch that is pressed when the recording paper P is a thick paper or a switch that is pressed when the recording paper P is an OHP. A signal from an OHP switch or the like is input to the control unit 42 as a transfer material detection signal. The detection of the type of the recording paper P is not limited to this, and the type of the recording paper P may be detected by detecting the resistance or capacity of the recording paper P. For example, the resistance and capacity of the recording paper P can be detected by detecting the energization current value at the leading end portion of the recording paper P using the paper charger 14C. In this case, when the width of the recording paper P changes, the energization current value changes. Therefore, it is preferable to detect the resistance and capacity of the recording paper P while referring to the width information of the recording paper P.
[0064]
Further, in order to detect a change or deterioration of the intermediate transfer member 10 due to repeated use, in the present embodiment, detection is performed using a paper charger 14C. That is, since the change or deterioration of the intermediate transfer member 10 can be detected by the resistance or capacity of the intermediate transfer member 10, when the recording paper P does not pass over the intermediate transfer member 10, the paper charger 14 </ b> C is transferred to the intermediate transfer member 10. A voltage is applied in contact with the body 10 to detect an energization current value. Then, this signal is input to the control unit 42 as an intermediate transfer body resistance / capacitance detection signal.
[0065]
In the control unit 42, according to the input humidity detection signal, transfer material detection signal, and intermediate transfer body resistance / capacitance detection signal, the transfer conditions of the transfer units 14A, 14B, and 14D, the separation conditions of the static eliminator 14E, the paper The charging condition of the charger 14C is read or calculated from the storage means, and each is controlled based on this condition. This eliminates the occurrence of charging, transfer, and separation defects, and enables good image formation. That is, when the humidity increases, the charging characteristics of the recording paper P deteriorate, the charging characteristics of the intermediate transfer member 10 deteriorate, etc., by increasing the absolute value of the current or voltage of each condition, The impact can be covered. In this embodiment, the transfer conditions of the transfer units 14A, 14B, and 14D, the separation conditions of the static eliminator 14E, and the charging conditions of the paper charger 14C are controlled by the type of recording paper P, environmental conditions, and the intermediate transfer member. However, the present invention is not limited to this, and may be performed according to at least one of the three deteriorations.
[0066]
Furthermore, in the present embodiment, at least two of the transfer conditions of the transfer units 14A, 14B, and 14D, the separation condition of the static eliminator 14E, and the charging condition of the paper charger 14C are changed in conjunction with each other. As described above, in the image forming apparatus according to the present embodiment, the means for driving (controlling) differs depending on each mode of the double-sided image forming mode, the front-side image forming mode, and the back-side image forming mode. By changing at least two of the complicatedly intertwined controls in conjunction with each other, the optimum conditions can be easily set. For example, when each control is performed independently, each control is not independent but complicatedly related, and the optimum setting range of each control has a maximum value. In some cases, the current value increases too much or the current value increases too little, and not only the optimum condition cannot be set, but also this control becomes very complicated.
[0067]
This control will be described in more detail. At least one of the following a) to i) is preferably performed.
[0068]
a) In the double-sided image forming mode, when the absolute value of the transfer current or transfer voltage that is the transfer condition of the transfer device 14B is increased, the absolute value of the transfer current or transfer voltage that is the transfer condition of the transfer device 14A is increased, or The absolute value of the transfer current or transfer voltage, which is the transfer condition of the transfer device 14D, is increased. Thereby, a good double-sided image can be formed.
[0069]
b) In the double-sided image forming mode, when the absolute value of the transfer current or transfer voltage, which is the transfer condition of the transfer device 14A, is increased, the transfer current or transfer voltage, which is the transfer condition of the transfer device 14D, is increased, or The value of the static elimination current or the static elimination voltage, which is the separation condition of the static eliminator 14E, is increased. Thereby, a good double-sided image can be formed.
[0070]
c) In the double-sided image forming mode, when the absolute value of the transfer current or transfer voltage, which is the transfer condition of the transfer device 14D, is increased, the value of the discharge current or discharge voltage, which is the separation condition of the charge remover 14E, is increased. Thereby, a good double-sided image can be formed.
[0071]
d) In the double-sided image forming mode, when the absolute value of the charging current or charging voltage that is the charging condition of the paper charger 14C is increased, the absolute value of the transfer current or transfer voltage that is the transfer condition of the transfer device 14A is increased. Alternatively, the absolute value of the transfer current or transfer voltage that is the transfer condition of the transfer device 14D is increased, or the value of the charge removal current or charge removal voltage that is the separation condition of the charge remover 14E is increased. Thereby, a good double-sided image can be formed.
[0072]
e) In the surface image forming mode, when the absolute value of the transfer current or transfer voltage, which is the transfer condition of the transfer device 14A, is increased, the value of the charge removal current or charge removal voltage, which is the separation condition of the charge remover 14E, is increased. Thereby, a favorable surface image can be formed.
[0073]
f) In the surface image forming mode, when the absolute value of the charging current or charging voltage as the charging condition of the paper charger 14C is increased, the absolute value of the transfer current or transfer voltage as the transfer condition of the transfer device 14A is increased. Alternatively, the value of the static elimination current or static elimination voltage, which is the separation condition of the static eliminator 14E, is increased. Thereby, a favorable surface image can be formed.
[0074]
g) When the absolute value of the transfer current or transfer voltage that is the transfer condition of the transfer device 14B is increased in the back surface image forming mode, the absolute value of the transfer current or transfer voltage that is the transfer condition of the transfer device 14D is increased. Thereby, a favorable back image can be formed.
[0075]
h) When the absolute value of the transfer current or transfer voltage, which is the transfer condition of the transfer device 14D, is increased in the back surface image forming mode, the value of the charge removal current or the discharge voltage, which is the separation condition of the charge remover 14E, is increased. Thereby, a favorable back image can be formed.
[0076]
i) When the absolute value of the charging current or charging voltage that is the charging condition of the paper charger 14C is increased in the back surface image forming mode, the absolute value of the transfer current or transfer voltage that is the transfer condition of the transfer device 14D is increased. Alternatively, the value of the static elimination current or static elimination voltage, which is the separation condition of the static eliminator 14E, is increased. Thereby, a favorable back image can be formed.
[0077]
By the way, in the double-sided image forming mode (hereinafter also referred to as the first double-sided image forming mode), an odd-numbered page image is formed on the first photosensitive drum 21A (the surface of the recording paper P), and an even-numbered page image is formed by the second photosensitive material. When formed on the body drum 21B (the back surface of the recording paper P), the recording paper P discharged on the tray 19B has the image on the first page facing downward as shown in FIG. When the paper is discharged in a so-called face-down state and image formation on all pages is completed, image formation with the pages aligned becomes possible. However, as a request from the user side, there is a case where an image is formed in a so-called face-up state in which the image on the first page faces upward. The image forming apparatus according to the present embodiment can cope with such user requests and can improve usability. This will be described below with reference to FIG. 4 schematically showing the discharge state of the recording paper P on which an image has been formed.
[0078]
As described above, when image formation is performed in the first double-sided image formation mode, images with pages aligned in a face-down state. On the other hand, when the user requests face-up as a form of paper discharge, in this embodiment, image formation is performed in the second double-sided image formation mode in which the output destination and output order of image signals are changed. That is, an image of even pages is formed on the first photosensitive drum 21A (the front surface of the recording paper P), and an image of odd pages is formed on the second photosensitive drum 21B (the back surface of the recording paper P) (in other words, The output destination of the image signal is opposite to that in the first double-sided image formation mode). Further, for the n-page image, the n, n-1 page is not formed from the first and second pages. The output order of image signals is changed so as to form an image. As a result, as shown in FIG. 4B, it is possible to form a page-aligned image in a face-up state.
[0079]
The same can be said for single-sided image formation. That is, since the recording paper P discharged on the tray 19B is in a face-down state, in the surface image forming mode already described, image formation is performed by performing image formation from the first page. Can be formed (FIG. 4C). On the other hand, in the back side image forming mode, the recording paper P discharged onto the tray 19B is in a face-up state, so that image formation is not performed from the first page, but the nth page. The output order of image signals is changed so as to form an image. As a result, as shown in FIG. 4D, it is possible to form a page-aligned image in a face-up state.
[0080]
As described above, in the present embodiment, the output destination or / and the output order of the image signal for forming the toner image are changed according to the discharge form (face-up or face-down) of the recording paper P. Since the image forming apparatus is configured, it is possible to form an image with uniform pages and to improve usability.
[0081]
In the present embodiment, since the recording paper P is discharged onto the tray 19B (second paper discharge means) provided at the top of the image forming apparatus, the recording paper P on the tray 19B is the second paper. The paper is discharged with its surface facing up, but is separate from the tray 19B so that the recording paper P discharged from the fixing device 18 can be discharged to the side of the image forming apparatus (left side in FIG. 1). A tray (first paper discharge means) (not shown) may be provided so that paper is discharged with the first surface of the recording paper P facing upward. In this case, in the first double-sided image forming mode, odd-numbered pages are formed on the first photosensitive drum 21A, and even-numbered pages are formed on the second photosensitive drum 21B, and images are formed from the nth and (n-1) th pages. By changing the output order of the image signals so as to perform the above, it is possible to form a page-aligned image in the face-up state. In this case, in the second double-sided image formation mode, even-numbered pages are imaged on the first photosensitive drum 21A, and odd-numbered pages are imaged on the second photosensitive drum 21B, and image formation is performed from the first and second pages. By changing the output order of the image signals so as to perform the above, it is possible to form an image in which pages are aligned in the face-down state. Further, in this case, in the surface image forming mode, by forming an image from the nth page, it is possible to form an image with pages aligned in the face-up state. Further, in this case, in the back side image forming mode, by forming an image from the first page, it is possible to form an image with pages aligned in a face-down state.
[0082]
Further, a tray 19B that discharges with the first side of the recording paper P facing upward, a tray that discharges with the second side of the recording paper P facing upward, and either of these trays after the fixing device 18 Switching means for switching to discharge the recording paper P is provided, and according to the switching of the switching means, as described above, the output destination or / and output of the image signal so that the pages are aligned. The order may be changed.
[0083]
The toner image forming units 26A and 26B of the present embodiment described above are units for forming a monochrome toner image on the photosensitive drums 21A and 21B. However, the present invention is not limited to this, and a unit for forming a color toner image. It may be. In this case, in order to form toner images of at least yellow, magenta, and cyan (preferably further black), a scorotron charger 22, an exposure unit 25, and a developer 23 may be provided for each color. Further, instead of superimposing the color toner images on the photosensitive drums 21A and 21B, process units 20A and 20B are provided for the respective colors, and the toner images formed by the respective process units are transferred to the intermediate transfer body. 10 or an image forming apparatus that forms a color toner image by superimposing on the recording paper P.
[0084]
【The invention's effect】
As described above in detail, according to the invention, the image forming speed can be remarkably increased.
[0085]
further , Departure According to Akira, satisfactory image formation can be performed in response to a decrease in image density and a change in gradation due to a difference in the number of transfers on the front and back surfaces.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus showing an embodiment of an image forming apparatus of the present invention.
FIG. 2 is a diagram illustrating an example of a digital image processing system.
FIG. 3 is a conceptual diagram of a control block.
FIG. 4 is a diagram schematically illustrating a discharge state of an image-formed transfer material.
[Explanation of symbols]
10 Intermediate transfer member (third image carrier)
14A transfer device (first transfer means)
14B Transfer device (second transfer means)
14C paper charger (transfer material charging means)
14D transfer device (third transfer means)
14E Static eliminator (separation means)
20A, 20B process unit
21A, 21B Photosensitive drum (first and second image carrying means)
26A, 26B Toner image forming means

Claims (2)

A first image carrying means for carrying a toner image, a second image carrying means, a third image carrying means,
First toner image forming means for forming a toner image on the first image carrying means;
Second toner image forming means for forming a toner image on the second image carrying means under image forming conditions including low γ correction rather than γ correction for image formation in the first toner image forming means;
First transfer means for transferring a toner image formed on the first image carrying means by the first toner image forming means to a first surface of a transfer material;
Second transfer means for transferring the toner image formed on the second image carrying means by the second toner image forming means to the third image carrying means;
Third transfer means for transferring the toner image transferred to the third image carrying means by the second transfer means to a second surface opposite to the first surface of the transfer material;
Fixing means for fixing the toner image transferred to the transfer material;
An image forming apparatus. The image forming condition varied by the first toner image forming means and the second toner image forming means, the image forming apparatus according to claim 1, characterized in that it comprises a process condition.

Images