JP3542408B2 - Image forming device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an image forming apparatus using an electrophotographic method, such as a printer and a digital copying machine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic method, such as a digital copying machine or a laser beam printer, is uniformly charged in advance by a charging device using a known charging roller to which an AC or DC superimposed bias is applied, for example. An electrostatic latent image is formed on an electrophotographic photosensitive member or an electrostatic recording dielectric by an exposure unit such as an optical system that scans a semiconductor laser or the like modulated by image information. As a developing device that develops the electrostatic latent image, for example, a developer is transferred from the developer carrier on a developing area opposed to the electrostatic latent image carrier at a predetermined minute gap to the electrostatic latent image carrier. A method of developing an electrostatic latent image by transferring the image to an electrostatic latent image and applying the transferred image is known.
[0003]
In the developed image, a transfer material such as paper, which is fed and conveyed in a timely manner by a paper supply device, is conveyed to a transfer portion, and is transferred onto the transfer material by a transfer unit using a transfer roller or the like. The transfer material onto which the toner image has been transferred is separated from the electrostatic latent image carrier and sent to a fixing unit such as a known heat fixing device, where the toner image is fixed on the transfer material.
[0004]
As a fixing method for fixing an unfixed image on a recording material, a contact heating type fixing device having good thermal efficiency and safety is widely used. Above all, from the viewpoint of energy saving, a heat fixing device of a film heating type, which heats a film having a very small heat capacity from the inside with high energy efficiency and a rapid rise in surface temperature from the viewpoint of energy saving, is disclosed in JP-A-63-313182 and JP-A-2-157788. These have been proposed in Japanese Unexamined Patent Publication Nos. Hei 4-44075-44083 and Japanese Patent Application Laid-Open No. Hei 4-204980-204984.
[0005]
Specifically, a thin heat-resistant film (or sheet), a means for driving the movement of the film, and a heating element which is fixedly supported and arranged on one side of the film with the film in the middle ( Heater) and a pressure member which is disposed on a multi-faceted side so as to face the heating element, and which brings the developer image carrying surface of a transfer material to be image-fixed to the heating element via the film into close contact with the heating element. The film is moved at substantially the same speed in the forward direction as the transfer material conveyed and introduced between the film and the pressure member at least at the time of performing image fixing, and is pressed against the heating body with the running film interposed therebetween. By passing through a fixing nip formed by pressure contact with the member, the developer image carrying surface of the transfer material is heated by a heating body through the film, and is pressed to soften and melt the developer image to be transferred. It is to be fixed as a permanent image on a material.
[0006]
The transfer material having passed through the fixing means is discharged out of the image forming apparatus. The toner remaining on the electrostatic latent image carrier after the transfer is removed by a known cleaning means using a cleaning blade, and the next image is formed.
[0007]
In the case of performing double-sided printing, the transfer material after fixing is not discharged to a paper discharge port, but is sent to a reversing unit. The transfer material inverted by the reversing unit is conveyed through the conveyance path, and performs the printing operation on the second side from the position of the re-feed roller.
[0008]
[Problems to be solved by the invention]
As a problem of the present invention, conventionally, when primary charging is performed by a contact charging device such as a charging roller, the surface potential of the photoconductor at the start of charging cannot be completely charged to a predetermined potential by one charging, and at least Image exposure is performed after two or more charges.
[0009]
However, recently, the first print time has become very important in the performance of a printer, and it has become necessary to shorten the pre-rotation as much as possible. Usually, it takes about 1 to 5 seconds for one rotation of the photosensitive drum. For example, in a constant-speed machine capable of printing four sheets per minute, it takes about four seconds for one rotation of the photosensitive drum. Therefore, even if the charging is started simultaneously with the start of the pre-rotation, the portion charged at that time is the second time. Since it takes about 4 seconds just to receive the charge, it is necessary to wait for the writing of the image (image exposure) during that time, which prevents shortening of the pre-rotation.
[0010]
Accordingly, it is an object of the present invention to shorten the pre-rotation time and shorten the first print time.
[0011]
[Means for Solving the Problems]
The present invention provides a charging unit for uniformly charging a photoconductor by applying a bias in which DC and AC are superimposed on a contact charging member, and an exposure unit for exposing the charged photoconductor to form a latent image. Developing means for developing the electrostatic latent image formed by the exposure means with toner, transfer means for transferring the toner image developed by the developing means to a transfer material using a contact transfer member, and the toner image And a fixing unit for heating and fixing the transfer material onto which the image is transferred, and applying a bias in which DC and AC are superimposed on the contact charging member during the pre-rotation of the photoconductor, and By applying a bias in which DC and AC are superimposed on the member, not only the contact charging member but also the contact transfer member is used for uniform charging of the photoconductor before exposure.
[0012]
The charging by the transfer member is performed as a supplement to the charging by a charging member such as a charging roller, and is performed from the start of the pre-rotation until the photosensitive member, which was at the charged portion at the start, rotates and reaches the transfer portion. .
[0013]
As described above, the portion that can be completely charged to the predetermined potential is the portion after the second charging. The image exposure can be started only by the charging roller when the charged portion of the photoconductor passes the second charging and reaches the exposure position, so that it takes more than one rotation of the photosensitive drum. On the other hand, by charging the transfer roller from the start of the pre-rotation, if the portion charged by the transfer roller is charged by the charging roller, a predetermined surface potential can be obtained, and the drum surface can be moved about half a circle earlier. Image exposure can begin.
[0014]
【Example】
Next, embodiments of the present invention will be described with reference to the drawings.
[0015]
(Example 1)
FIG. 1 is a schematic diagram of an image forming apparatus according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a photosensitive drum on which a photosensitive material such as OPC is formed on a cylindrical base such as aluminum or nickel. The photosensitive drum 1 is driven to rotate, and its surface is first uniformly charged by a charging roller 2 as a charging device. Next, scanning exposure is performed by a laser beam 3 that is ON / OFF controlled according to image information, and an electrostatic latent image is formed. This electrostatic latent image is developed and visualized by the developing device 4. As a development method, a jumping development method, a two-component development method, an FEED development method, or the like is used, and a combination of image exposure and reversal development is often used.
[0016]
The visualized toner image is transferred from the photosensitive drum 1 onto the transfer material P conveyed at a predetermined timing by a transfer roller 5 as a transfer device. At this time, the transfer material P is nipped and conveyed between the photosensitive drum 1 and the transfer roller 5 with a constant pressing force. The transfer material P to which the toner image has been transferred is conveyed to the fixing device 6 and fixed as a permanent image. On the other hand, the transfer residual toner remaining on the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the cleaning device 7.
[0017]
The transfer material on which the image has been transferred to the first side and fixed by the fixing device 6 is directly conveyed to the paper discharge unit 14 in the case of single-sided printing, but is sent to the reversing device 10 to perform the double-sided printing. The sheet is sent to the second sheet re-feeding unit 11 with the rear end changed, and the next print operation is awaited at the position of the sheet re-feeding unit 11. Further, reference numeral 12 in the drawing denotes a paper feed cassette, and reference numeral 13 denotes an MP tray (multi-purpose tray). That is, in the apparatus of the present embodiment, there are three paper feeding units including the re-feeding unit 11.
[0018]
Describing the charging portion, the charging bias is obtained by superimposing a sine wave of DC-670V, AC2000V (peak-to-peak value), and frequency of 700Hz, thereby uniformly charging the photosensitive member to about -650V. The superposition of AC is for improving the uniformity of charging.
[0019]
Regarding the heat fixing device 6, a fixing film 61 having a small heat capacity has a heat resistance of 100 μm or less, a thermoplastic polyimide, a polyamideimide, a PEEK, a PES, a PPS, and a thickness of 100 μm or less in order to enable quick start. Films such as PFA, PTFE, and FEP. Reference numeral 62 denotes a heating member provided inside the fixing film 11, which heats a nip portion where the toner image on the transfer material is melted and fixed.
[0020]
The pressure member is made of an elastic layer formed by foaming heat-resistant rubber such as silicon rubber or fluorine rubber or silicon rubber on the outside of the cored bar, and a release layer such as PFA, PTFE, FEP is formed thereon. You may have. The pressing member is sufficiently pressed from both ends in the longitudinal direction to form a nip portion necessary for heat fixing by a pressing member (not shown) in the direction of the fixing member, and a core metal is formed from the longitudinal end. , And is rotationally driven by a rotational drive (not shown).
[0021]
FIG. 2 shows a sequence diagram of the present embodiment, and the timing of charging, fixing, image exposure (VIDEO signal), and the like will be described. 2 in FIG. 2 is a sequence diagram according to the present invention. It is necessary to uniformly charge the photoreceptor before starting image exposure. As described above, in order to charge the photoreceptor to a predetermined potential, two or more charges must be passed. , As soon as the pre-rotation starts. Since the fixing is an on-demand fixing device using a film and having a rapid rise, it can be started from room temperature in about 10 seconds, and is turned on at the same time as the start of the pre-rotation.
[0022]
When the preparation for printing is completed in the pre-rotation, image exposure on the first side is started, and printing on the first side is performed. When the image writing on the first surface is completed, the operation proceeds to post-rotation, and the charging is turned off after the DC is turned off, the AC is applied, and the potential on the photoconductor becomes zero. On the other hand, the fixing temperature is turned off when the transfer material passes through the fixing device and the rear end passes through the fixing device.
[0023]
The transfer material is turned over and sent to the re-feed unit 11. During this time, according to the present invention, both charging and fixing are OFF. When the processing of the image data of the second surface is completed, a print signal of the second surface is sent to the engine. An example of this timing is indicated by an arrow in the figure. At this point, since the preparation for printing the second side of the engine has not been completed, according to the present invention, even if a print signal is received until the transfer material reaches the refeeding position, the pre-rotation does not start, and Start rotation before reaching.
[0024]
On the other hand, in the conventional example shown in (2), up to the printing of the first side is the same as that of .sup., But when a print signal comes during the subsequent paper conveyance, the pre-rotation starts from that point, so that charging and It can be seen that the fixing is ON.
[0025]
Comparing (1) and (2) above, it can be seen that the invention of (1) has a shorter charging bias application time and a temperature adjustment time during the paper conveyance from the first surface to the second surface.
[0026]
In the example of FIG. 2, the print signal comes in the latter half of the paper conveyance from the first side to the second side. However, when the image data processing of the second side is completed earlier, during the post-rotation of the first side or immediately thereafter. Therefore, the time from the post-rotation of the first surface to the pre-rotation of the second surface is all the difference between the charging bias application time and the fixing temperature adjustment time. This is, for example, about 10 seconds from the post-rotation of the first surface to the pre-rotation of the second surface in the printer having a process speed of 48 mm / sec of the present embodiment, and thus the difference is only this time. Since the time required for printing one sheet on one side is less than 20 seconds, if one sheet is printed intermittently on both sides twice, drum shaving for one sheet on one side can be prevented and power can be saved.
[0027]
Note that the above is an intermittent double-sided printing of one sheet, so that even if a print signal for the second side is received, the paper is rotated backward, and the paper is rotated forward after the paper reaches the paper re-feeding position. Although an example has been described, the present invention is not limited to this. In other words, when a print signal is received during or immediately after an arbitrary print is being performed, if the print signal is the print signal for the second side of the print, it takes time to invert and transport the paper. Enters the post-rotation mode. If no time is required from the feeding of the MP tray or the like, there is not enough time to perform the post-rotation and the pre-rotation, so that the apparatus enters the sheet interval mode. In addition, it takes time to feed a sheet such as a feeder externally attached to the main body, and there is time to perform post-rotation and pre-rotation.
[0028]
As described above, it is possible to reduce the charging time and the fixing temperature adjustment time by changing the mode according to the paper feed port specified by the print signal.
[0029]
(Example 2)
The second embodiment is an embodiment including not only the case of double-sided printing but also the case of single-sided printing. FIG. 3 shows a schematic diagram of the apparatus. Recently, even in a laser printer, several sizes and types of paper have been simultaneously placed in a cassette, and there has been a tendency to provide several stages of paper cassettes so that the host computer can select them. The apparatus shown in FIG. 3 also has a total of six paper feeding ports, that is, four paper feeding cassettes, an MP tray, and a second paper re-feeding port for printing.
[0030]
When four paper feed cassettes are provided, the paper transport path from the paper feed cassette 16 located farthest from the main body printing section becomes considerably long. When the first sheet is printed from an arbitrary sheet feeding port and a print signal is received from the sheet feeding cassette 16 during or immediately after the printing, the sheet is fed from the cassette 16 until the sheet reaches the pre-feed position 17. After that, the post-rotation is performed once, the high-pressure bypass and the fixing temperature control are turned off, and the pre-rotation is started when the paper reaches the pre-feed position. This has the effect of preventing drum abrasion and saving power as compared with keeping the high pressure and the temperature control ON in the sheet interval mode during this time.
[0031]
Here, the pre-feed position 17 means that the paper is fed at the same time as the print signal, but when the paper reaches the pre-feed position, the pre-rotation is started, and the preparation for printing such as the scanner, the fixing device, and the charging is completed. This is the position where the paper is stopped until the preparation is completed.
[0032]
FIG. 4 shows a sequence diagram of the second embodiment. When a print signal from the next cassette 16 comes in the latter half of the first sheet printing, in the present invention of (1), after the first sheet is printed, post-rotation is started, and then both high pressure and temperature control are turned off. In the conventional example of 2), it can be seen that even if a print signal comes in, the mode is switched to the sheet interval mode and remains ON.
[0033]
(Example 3)
The apparatus used in the third embodiment is the same as the apparatus shown in FIG. FIG. 5 is an enlarged view of the vicinity of the photosensitive drum. As shown in FIG. 5, a charging roller and a transfer roller are arranged at substantially opposite positions around the photosensitive drum.
[0034]
The portion on the drum that was at the charging roller position at the time when the pre-rotation started is A, and the portion that was at the transfer roller position is B. Simultaneously with the pre-rotation, the charging roller is applied with a DC-670V, AC2000V (peak-to-peak value), a sine wave superimposed bias having a frequency of 700Hz, and a DC bias of -2000V is applied to the transfer roller. If it is charged two or more times, it can be charged to a predetermined potential. Therefore, the portion B, which is first charged by the transfer roller, is charged by the charging roller, and the image exposure by the laser is started from the time when it reaches the image exposure position. Is done.
[0035]
FIG. 6 is a graph showing a change in potential on the photosensitive drum at the laser exposure position. The horizontal axis of the graph is time. B. A indicates the timing when the drum rotates and the portion A, the portion B, and the portion A on the drum come to the exposure position at the exposure position.
[0036]
According to the graph shown in (1) of FIG. 6, according to the present invention, the potential which was 0 at the start time becomes about -620 V after the portion of A once charged by the charging roller, and then the first transfer is performed. When the portion B charged by the roller and charged by the charging roller for the second time comes, it completely rises to a predetermined potential of -650V. The time during this period was about 1 second because it was about half a rotation of the photosensitive drum.
[0037]
FIG. 6B shows a comparison of the case of the conventional example. In the conventional example, since the charging is performed only by the charging roller, the potential that was 0 at the start of rotation becomes approximately −620 V after the portion A charged once by the charging roller, and then the drum rotates another round. Then, when the portion A charged by the charging roller twice came, it was charged to a predetermined -650V. Compared with the present invention, more time is required for about half the circumference of the drum.
[0038]
In the case of the present embodiment, the transfer roller was charged only with a DC bias of -2000 V at the start of the pre-rotation. However, since the second charging was performed by the charging roller, the charging uniformity at the image writing portion was not improved. There was no particular problem and no problem on the image. The experiment by the present inventors has revealed that the transfer roller is charged to about 90% of a predetermined charging potential. The transfer roller used had a resistance value of about 10 ⁸ Ω, and had a higher resistance than the charging roller, so a bias of −3 KV was applied. The transfer roller is charged only for half a rotation start, and thereafter used as a normal transfer roller.
[0039]
As described above, in the present embodiment, the image exposure on the drum during the pre-rotation can be accelerated by about one half of the drum, and the first print time can be shortened.
[0040]
(Example 4)
In the fourth embodiment, the charging by the transfer roller at the start of the pre-rotation is not DC-2000V but the DC-670V, AC2000V (peak-to-peak value) frequency of 700 Hz is the same as the bias for the charging roller. The feature is that a bias in which waves are superimposed is used, and the other points are the same as those in the above-described embodiment.
[0041]
In this embodiment, by applying a superimposed bias of DC + AC to the transfer roller, it is possible to obtain a more uniform charging property as shown in the graph of FIG. 6 and the same effect to shorten the first print time. was gotten.
[0042]
The use of a superimposed bias on the transfer roller complicates the bias power supply. However, if a switching circuit that applies the bias output for the charging roller to the transfer roller is also provided only when the superimposed bias is applied, the complexity becomes much more complicated. It is possible to implement without becoming.
[0043]
(Example 5)
Embodiment 5 is characterized in that a member similar to the charging roller is used for the transfer roller. Specifically, the charging roller is provided with an isoelectric layer made of EPDM rubber or the like in which carbon or the like is dispersed around a cored bar, and a high-resistance layer or a surface release layer having a thickness of about 100 to 200 μm is provided outside thereof. However, a roller having a similar configuration is used for the transfer roller. However, as the resistance, the charging roller has a resistance value of about 10 ⁶ Ω at the nip area with the photoreceptor, and the transfer roller has a resistance of about 10 ⁶ Ω. use.
[0044]
In the fourth embodiment, the same effect as in the third embodiment is obtained, as shown in FIG. 6 (1). In this embodiment, since the charging roller and the transfer roller use the same member, there is an advantage that the cost can be reduced.
[0045]
【The invention's effect】
As described above, according to the present invention, the potential of the photoconductor can be increased to a predetermined charging potential, the start of image exposure can be accelerated, and the first print time can be shortened.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an image forming apparatus according to the present invention.
FIG. 2 is a sequence diagram according to the present invention, together with a sequence diagram of a conventional example.
FIG. 3 is a configuration diagram of an image forming apparatus according to the present invention.
FIG. 4 is a sequence diagram according to the present invention shown together with a sequence diagram of a conventional example.
FIG. 5 is a configuration diagram around a photosensitive drum according to the present invention.
FIG. 6 is a diagram of a potential of a photoconductor according to the present invention, which is shown together with a sequence diagram of a conventional example.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 photosensitive drum 2 charging roller 3 laser exposure 4 developing unit 5 transfer roller 6 fixing unit 7 cleaner

Claims (1)

Charging means for uniformly charging the photoreceptor by applying a bias in which DC and AC are superimposed on the contact charging member,
Exposure means for exposing the charged photoconductor to form a latent image,
Developing means for developing the electrostatic latent image formed by the exposure means with toner,
Transfer means for transferring the toner image developed by the developing means to a transfer material using a contact transfer member,
Fixing means for heating and fixing the transfer material to which the toner image has been transferred, and outputting the fixed image.
During the pre-rotation of the photoreceptor, a bias in which DC and AC are superimposed is applied to the contact charging member, and a bias in which DC and AC are superimposed is applied to the contact transfer member. An image forming apparatus, wherein not only the contact transfer member but also the contact transfer member is used for uniform charging of the photosensitive member before exposure.

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