JP3524528B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer type image forming apparatus having a transfer means for transferring a transferable image formed and carried on an image carrier to a transfer material. More specifically, the present invention relates to an improvement in an image forming apparatus in which a transfer unit is a transfer unit of a contact transfer system. 2. Description of the Related Art A transferable image of image information, which is generally a toner image, is formed on a surface of an image carrier by an appropriate image forming process, and the transferable image is transferred onto paper or the like. 2. Description of the Related Art A transfer-type image forming apparatus in which an image carrier is transferred to a material, fixed on the image, output as an image formed product (copy, print), and the image carrier is repeatedly used for image formation has been widely used. FIG. 4 is a schematic structural diagram of a typical example of such a transfer type image forming apparatus. The image forming apparatus of this embodiment is a copying machine or a printer using a transfer type electrophotographic process. [0005] Reference numeral 10 denotes a drum-type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image bearing member.
Is rotated clockwise at a predetermined peripheral speed (process speed), and an image forming process of charging, image exposure, development, transfer, and cleaning is applied to the rotating photosensitive drum. That is, the surface of the photoreceptor drum 10 that is rotationally driven is uniformly charged to a predetermined polarity and potential by the primary charger 11. Next, image exposure 12 is performed on the charged surface by image exposure means (not shown) (projection exposure apparatus for an original image, scanning exposure apparatus for an image-modulated laser beam, etc.) as image information writing means. Then, the charged potential of the exposed light portion is attenuated, and an electrostatic latent image corresponding to the exposed image information is formed on the surface of the photosensitive drum. The electrostatic latent image is sequentially visualized as a transferable toner image (developed image) by the developing device 13 at the developing site A. The toner image is transferred to a transfer material 18 at a transfer portion T by a transfer means. The transfer means in this embodiment is a contact transfer type transfer means using a roller-shaped contact transfer charger 16 (hereinafter referred to as a transfer roller). The transfer roller 16 comprises, for example, a core metal and a medium-resistance elastic layer formed around the core metal.
The transfer portion T (transfer nip portion) is formed by pressing the photosensitive drum 10 with a predetermined pressing force against the elasticity of the elastic layer, and the photosensitive drum 10 is rotated in the forward direction with the rotation of the photosensitive drum 10. It rotates at a peripheral speed substantially the same as the rotational peripheral speed of. The transfer material 18 is fed from a feeding unit (not shown), and is fed to the transfer portion T at a timing adjusted by a registration roller 15 disposed in front of the transfer portion T. That is, when the leading end of the toner image formed on the surface of the rotating photoreceptor drum 10 reaches the transfer site T, the registration roller 15 also reaches the end of the transfer material 18 just at the transfer site T. Transfer material 18
To the transfer site T. The transfer material 18 fed to the transfer site T has its surface in close contact with the rotating photosensitive drum 10 and is conveyed while nipping the transfer site T. Further, during the period from when the leading end of the transfer material 18 arrives at the transfer site T to when the trailing end of the transfer material 18 exits the transfer site T, the core of the transfer roller 16 has a transfer bias power source 2.
From 0, a predetermined transfer bias is applied. In the process in which the transfer material 18 is conveyed while nipping the transfer portion T, the toner image on the rotating photosensitive drum 10 is formed on the transfer material 18 by the transfer roller 16 as a contact transfer charger. The image is sequentially transferred by the action of the electric field and the pressing force at the transfer portion T. When the transfer material 18 leaves the transfer portion T, it is separated from the surface of the rotating photosensitive drum 10 and transported to an image fixing device (not shown), and the transferred toner image is fixed as a permanently fixed image on the transfer material surface. The sheet is processed and discharged as an image forming product (copy, print). After the transfer material is separated, the surface of the photoreceptor drum 10 is cleaned by removing contaminants such as residual toner and paper dust by a cleaner 17, and is repeatedly used for image formation. As the image forming method, for example, a normal developing method in which a charged photosensitive member surface is exposed corresponding to a background portion of image information (background exposure method) and a portion other than the background portion is developed, There is a reversal development method in which exposure is performed corresponding to the image information section (image exposure method), and a non-exposed portion is developed. As a transfer means for transferring a toner image as a transferable image on the photosensitive drum 10 side as an image carrier to a transfer material 18 such as paper, the transfer roller 16 is used as described above.
The transfer means of the contact transfer method using the contact transfer charger represented by the above is widely used, and compared with the transfer means using the corona charger and the like, the power supply capacity is reduced and the discharge product represented by ozone is reduced. There are advantages such as a small amount of generation. In the case of such a contact transfer type transfer means, the following transfer defects are generally likely to occur. That is, when the transfer means is controlled by "constant current control", for example, when a small-size transfer material such as a postcard is passed, a paper passing area and a non-paper passing area at the time of paper passing are determined. The transfer current easily flows to the non-sheet passing area due to the difference in the resistance of the transfer material, the amount of transfer charge applied to the back surface of the transfer material is reduced, and transfer failure such as transfer omission is likely to occur. This phenomenon is more remarkable as the volume resistance of the transfer roller 16 as a contact transfer charger is smaller. Therefore, the phenomenon can be improved by increasing the volume resistance of the transfer roller. Problems arise. Therefore, there is a "constant voltage control" system in which a relatively large amount of transfer charge can be applied to a small-size sheet passing as compared to a large-size sheet passing. This is generally output with a voltage value determined according to the volume resistance of the transfer roller, and it is possible to apply a relatively similar amount of transfer charge to large and small size transfer materials. Has been adopted. However, problems at the time of transfer often occur due to an excessive or small amount of transfer charge applied to the back surface of the transfer material. For example, the "drum memory" by transfer, in which transfer charge passes through the transfer material during paper passing due to excess and creates a memory on a photosensitive drum as an image carrier, and creates a grayscale image when forming an image later. On the contrary, when the amount is small, there is "transfer missing" which occurs because the toner is not sufficiently attracted to the transfer material. In particular, in a method of forming a toner image on the surface of a photoconductor holding the same polarity as the toner, as represented by the reversal development system, the transfer polarity at the time of transfer is opposite to that of the photoconductor surface, and the normal development is performed. Drum memory is more likely to occur than in the system. These depend on the amount of transfer charge, that is, roughly on the value of the transfer current at the time of transfer. On the other hand, in the case of the constant voltage control, since the constant voltage value is usually set so as not to cause transfer omission even in a small size, the transfer charge amount of the transfer material tends to be excessive when the transfer material is large. . Therefore, in an environment and a configuration in which a transfer failure is more likely to occur, good transfer cannot be performed on transfer materials of various sizes. Accordingly, the present invention has been made to cope with such a situation. In a transfer type image forming apparatus in which the transfer unit is a contact transfer type transfer unit, the present invention is applicable to various paper passing sizes of a transfer material. It is another object of the present invention to provide an image forming apparatus capable of performing transfer with higher accuracy and constantly obtaining a high-quality image stably. According to the present invention, there is provided an image forming apparatus having a transfer means for transferring a transferable image formed and carried on an image carrier to a transfer material, wherein the transfer means comprises an image carrier. A transfer portion formed in contact with the transfer portion, and a transfer transfer device having a contact transfer charger for transferring a transferable image on the image carrier side to the transfer material side by applying a transfer charge to the transfer material passed through the transfer portion. Transfer means, comprising: a constant current control means for outputting a predetermined current value to the contact transfer charger; and a constant voltage control means for outputting a predetermined voltage value to the contact transfer charger. It is possible to switch between current control and constant voltage control. When the volume resistance value of the contact transfer charger is equal to or more than a predetermined value, constant current control is performed, and when the volume resistance value is less than a predetermined value, paper feeding is performed. The switching is performed according to the size of the transfer material to be performed. An image forming apparatus is characterized in that: That is,
In a transfer control device that uses constant current control and constant voltage control according to the size of the transfer material, when the volume resistance value of the contact transfer charger is less than a predetermined value, the constant value is set according to the size of the transfer material that is passed. By adopting a configuration for switching between the current control and the constant voltage control, the switching control may be performed only when the switching between the constant current control and the constant voltage control is necessary, thereby simplifying the control. Calculation (detection) of the optimal voltage value for constant voltage control
Is performed, the total number of rotations of the image carrier can be reduced by reducing the calculation (detection) time, and the life can be prolonged. <Operation> a) The transfer means is switched to either constant current control or constant voltage control in accordance with the size of the transferred transfer material. More specifically, By switching the transfer unit to the constant current control when the size is equal to or larger than the predetermined size, it is possible to perform more accurate control for a transfer failure that often depends on the transfer current value, and When the size of the transfer material is smaller than the predetermined size, by switching to the constant voltage control, it is possible to provide a constant transfer charge amount even in a small-size transfer material,
High quality images can be obtained constantly and stably. B) In an image forming apparatus having a plurality of feeding means for transporting a transfer material to a transfer site, the transfer means is selected according to the selection of the feeding means to be used among the plurality of feeding means. By switching between the constant current control and the constant voltage control, control corresponding to the sheet passing size of the transfer material can be relatively easily performed. This is particularly effective for an image forming apparatus that forms a visualized image by reversal development, in which image defects due to transfer drum memory are relatively conspicuous. C) By making the switching possible at a predetermined volume resistance value based on the volume resistance of the contact transfer charger, for example, the calculation time for executing constant voltage control can be reduced by the volume resistance value. As a result, the total number of rotations of the image carrier can be reduced, and as a result, the life of the image carrier can be extended. D) The control values controlled by the constant current control and the constant voltage control can be switched and controlled in accordance with the information on the transfer material.
By using at least one of the thickness, the rigidity, the moisture absorption, the material, the processing, the surface treatment, and the size, it is possible to perform a transfer corresponding to the characteristics of the transfer material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment (FIG. 1) FIG. 1 is a schematic structural diagram of an image forming apparatus according to the present embodiment. Since the configuration of the image forming apparatus of this embodiment is substantially the same as that of the image forming apparatus of FIG. 4, the same reference numerals are given to the same components and parts, and the description will not be repeated. In the image forming apparatus of this embodiment, the polarity of the charging process by the primary charger 11 of the photosensitive drum 10 as the image carrier is negative. The toner development of the electrostatic latent image formed on the surface of the photosensitive drum 10 by the developing unit 13 is a reversal development system using negative polarity toner (negative toner). The polarity of the transfer bias is positive. The transfer material passing speed is 105 mm / s. The maximum paper passing size is A4 horizontal paper width (297 m).
m), and the minimum paper passing size is a vertical postcard (equivalent to 105 mm). Transfer Roller 16 as Contact Transfer Charger
Was 315 mm in length. Reference numerals 21, 22, and 23 denote constant current power supply, constant voltage power supply, and transfer switching control means for the transfer roller 16. Either constant current control or constant voltage control of the transfer means is selected by the transfer switching control means 23, and the constant current power supply 21 (constant current control) is supplied to the transfer roller 16 during the transfer of the transfer material at the transfer portion T. A transfer bias is applied from a current control (in the case of current control) or a constant voltage power supply 22 (in the case of constant voltage control). In this embodiment, the transfer switching control means 2
Selection switching between the constant current control and the constant voltage control of the transfer unit 3 is performed according to the size of the transfer material 18 passed through the apparatus. The input of the paper passing size of the transfer material 18 is a user input, and the transfer switching control unit 23 outputs the output of the transfer bias to the transfer roller 16 based on the input. The paper passing size of the transfer material 18 is B5 horizontal paper width (257 m).
m), the constant current control output by the constant current power supply 21. When the paper passing size of the transfer material 18 is smaller than the B5 horizontal paper passing width, the output is switched to the constant voltage control output from the constant voltage power supply 22. During constant current control, output control was performed with a control value of 9 μA. The constant voltage control is performed when the transfer roller 1
6, the voltage applied at the time of the constant current of 9 μA was measured, the constant voltage value at the time of paper feeding was determined based on the detected voltage value, and output control was performed (this constant voltage control was performed by ATVC control (Au
to Transfer Voltage Contr
ol)). By adopting the structure of this embodiment, good transfer is obtained in both cases of large-size paper passing of B5 horizontal paper or more and small-size paper less than B5 horizontal paper. Sex was obtained. In this embodiment, the paper passing size of the transfer material is input by the user. However, the present invention is not limited to this. For example, the size detection result of the paper passing transfer material from the transfer material size detecting means such as a sensor may be used. At the same time, the switching of the constant current control or the constant voltage control of the transfer unit by the transfer switching control unit 23 may be performed. Of course, the maximum sheet passing size, the minimum sheet passing size, the length of the transfer roller, the transfer material reference width for selecting and switching between the constant current control and the constant voltage control of the image forming apparatus are not limited to the present embodiment. It is. For example, the transfer material reference width of the selection switching between the constant current control and the constant voltage control may be changed based on the volume resistance value of the transfer roller 16 to be used, and for example, the identification of typical postcards and envelopes of small size paper. The control may be switched according to the size of the transfer material. In this embodiment, the transfer material passing speed of the image forming apparatus is 105 mm / s, the constant current control value is 9 μA, and the constant voltage control is ATVC control. However, the present invention is not limited to this. , Of course. As described above, in the transfer roller system,
By executing constant current control for a large-size transfer material and constant-voltage control for a small-size transfer material, in the case of a large-size transfer material, generally in the case of a transfer defect that depends on current (transfer charge amount), Optimum control is performed. In the case of a small-size transfer material, almost optimal transfer charge can be applied by constant voltage control, and satisfactory transfer can be performed for both large and small-size transfer materials. That is, it is possible to improve the accuracy of the transfer control in the transfer roller system, and to perform optimal control corresponding to a transfer material having a large size and a small size. The corresponding width of the small-size transfer material can be reduced, and the constant voltage control value is
By being able to adapt to smaller size transfer materials,
In general, prevention and reduction of current-dependent transfer defects can be achieved. <Second Embodiment> (FIG. 2) FIG. 2 is a schematic structural diagram of an image forming apparatus according to the present embodiment. The image forming apparatus of this embodiment is different from the image forming apparatus of the first embodiment in that a humidity sensor 24
To switch between constant current control values during constant current control and / or constant voltage control values during constant voltage control based on the detected humidity data of the humidity sensor 24, Thus, it is possible to obtain a better transfer property corresponding to. The other configuration, specifications, control conditions, and the like of the image forming apparatus are the same as those of the image forming apparatus of the first embodiment, so that the description will not be repeated. The switching control means 23 includes a humidity sensor 24
Based on the detected humidity data, the switching of the constant current control value during the constant current control and / or the switching of the constant voltage control value during the constant voltage control are performed. In this embodiment, the humidity is less than 45%, 70%
The constant current control value at the time of constant current control was switched to 11 μA, 8 μA, and 6 μA, respectively, in three stages of less than and more than three stages. Also, at the time of constant voltage control, the constant voltage control value was switched according to three equations for the output conversion of the ATVC control. By adopting the structure of this embodiment, even when the transfer material 18 having a low resistance by absorbing moisture is used, and when the transfer material 18 is dried to have a high resistance, the transfer material 18 generally has a high resistance. As the transfer material tends to require more transfer charge, and when the resistance is low, the transfer voltage increases, so that the transfer material penetrates the transfer material from the back surface of the transfer material and affects the charge polarity of the toner. From the tendency, an optimal transfer charge amount can be given to the transfer material. By doing so, it is more environmentally friendly,
Stable and favorable image formation can be performed. In the present embodiment, the result of detection by the humidity sensor 24 is used as a basis, but the result of moisture absorption and the resistance value of the transfer material 18 are measured, and the constant current control value and the constant voltage control You can switch the value. In the present embodiment, switching is performed in three stages according to the detection result of the humidity sensor, but it may be performed in two stages or in multiple stages. Further, it is needless to say that the present invention is not limited to the constant current value and the like used in the present embodiment. In this embodiment, the control value is switched by detecting the degree of moisture absorption as a characteristic of the transfer material. However, other characteristics that contribute to the transfer characteristics, such as thickness, rigidity, material, processing, The control value may be switched based on one or more pieces of information such as surface treatment and size. Generally, in the case of a thick transfer material, a relatively large transfer current (transfer charge) tends to be required, and a higher transfer voltage tends to be required in order to uniformly apply the transfer charge. . Also, the higher the rigidity, the more likely it is that a hollow phenomenon, which often occurs in a character image, for example, is likely to occur. Similarly, for the material of the transfer material and the processing, the optimum transfer charge and voltage are different due to the difference in volume resistance and the like. Also, for example, if the releasability is good, missing in the character is likely to occur due to the surface treatment. Transfer charge and voltage are different. By performing transfer control in consideration of such characteristics, it is possible to cope with a wider range of transfer materials. <Third Embodiment> The main structure of the image forming apparatus of this embodiment is the same as that of the image forming apparatus of the first embodiment. In this embodiment, when the volume resistance value of the transfer roller 16 as a contact transfer charger is less than a predetermined resistance, the switching of the transfer bias depending on the paper passing size of the transfer material is controlled. This is performed only when a transfer roller having resistance is used. In this embodiment, the transfer roller 1
6, the voltage applied at the time of the constant current of 9 μA was measured, and based on the detected voltage value, the constant voltage output control was performed at the time of paper passing when the voltage was lower than the predetermined detection voltage. Generally, the volume resistance of the transfer roller changes depending on the durability and the environment. Accordingly, by enabling the constant voltage control based on the transfer material passing size when the volume resistance is less than a certain volume resistance, for example, the calculation time for calculating the constant current value for the constant voltage control is reduced, and as a result, the photosensitive member Drum 10
, The total number of rotations of the photosensitive drum can be reduced, and the damage to the photosensitive drum can be reduced, so that the durability of the photosensitive drum can be improved. With such a configuration, good transfer can be easily performed, and the life of the image forming apparatus, particularly, the photosensitive drum can be extended. <Fourth Embodiment> (FIG. 3) FIG. 3 is a schematic structural diagram of an image forming apparatus according to this embodiment. In the image forming apparatus of this embodiment, a multi-stage cassette paper feeding unit 25 is used as a transfer material feeding unit to the transfer site T.
And a manual paper feed unit 25a. The other configuration, specifications, control conditions, and the like of the image forming apparatus are the same as those of the image forming apparatus of the first embodiment, and thus the description will not be repeated. In the present embodiment, the constant current control of the transfer bias and the constant voltage control of the transfer bias are performed based on information on whether paper is supplied from the cassette paper supply unit 25 or paper is supplied from the manual paper supply unit 25a. Perform a switch. In the case of the apparatus according to the present embodiment, the control is switched to the constant voltage control by designating the manual paper feeding means 25a, which often feeds transfer materials of relatively various sizes and materials, to feed. By adopting the configuration of this embodiment, it is possible to effectively cope with large and small size transfer materials with a relatively simple configuration, and to form a good image. In this embodiment, the manual paper feeder 25a
Is designated by specifying the sheet feeding, but it is needless to say that any sheet feeding means may be supported. As described above, in the transfer roller system,
Executing constant voltage control during transfer material feeding from a specific sheet feeding means (feeding means) makes it suitable for large-size transfer materials, in general, in the case of a transfer failure depending on current (transfer charge amount dependency). In the case of a small-sized transfer material, almost optimal transfer charge can be applied by constant voltage control, and satisfactory transfer can be performed for both large and small-sized transfer materials. That is, it is possible to improve the accuracy of the transfer control in the transfer roller system, and to perform optimal control corresponding to a transfer material having a large size and a small size. Since the corresponding width of the small-size transfer material can be reduced, and the constant voltage control value can be adapted to the small-size transfer material as compared with the related art, it is possible to generally prevent and reduce the current-dependent transfer failure. Also in this embodiment, as in the second embodiment, one or more of the transfer material characteristics that contribute to the transfer characteristics, such as moisture absorption, thickness, rigidity, material, processing, surface treatment, etc. Of the constant current control value at the time of the constant current control, or the switching of the constant voltage control value at the time of the constant voltage control. By adopting such a configuration, it is a matter of course that good transfer can be performed corresponding to transfer materials having various characteristics. Also, in this embodiment, as in the third embodiment, it is possible to switch over at a predetermined volume resistance value based on the volume resistance of the transfer roller 16. <Others> 1) The image carrier 10 is not limited to an electrophotographic photosensitive member, but may be an electrostatic recording dielectric, a magnetic recording magnetic material, or the like, and forms a transferable image on the image carrier. The principle and process are arbitrary. The present invention is not limited to the drum type, but may be any type such as a belt type, a web type, and a sheet type. 2) The contact transfer charger 16 is not limited to the roller type, but may be of a belt type or a combination of a belt and an electrode blade. 3) The transfer material may be an intermediate transfer member such as an intermediate transfer drum or the same belt. As described above, according to the present invention,
Regarding the transfer type image forming apparatus in which the transfer unit is a contact transfer type transfer unit, it is possible to perform more accurate transfer even in various paper passing sizes of the transfer material and always obtain a stable and high quality image. An image forming apparatus can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration model diagram of an image forming apparatus according to a first embodiment. FIG. 2 is a schematic configuration model diagram of an image forming device according to a second embodiment. FIG. 4 is a schematic diagram of an image forming apparatus in an embodiment. FIG. 4 is a schematic diagram of an example of a conventional image forming apparatus. [Description of References] 10 Image carrier (photosensitive drum) 11 Primary charger 12 Image exposure 13 Development Unit 15 registration roller 16 contact transfer charger (transfer roller) 17 cleaner 18 transfer material 20 transfer bias power supply 21 constant current power supply 22 constant voltage power supply 23 switching control means 24 humidity sensor

Claims (1)

(57) An image forming apparatus having a transfer means for transferring a transferable image formed and carried on an image carrier to a transfer material, wherein the transfer means is in contact with the image carrier. To form a transcription site,
A contact transfer type transfer unit having a contact transfer charger for applying a transfer charge to a transfer material passed through the transfer portion and transferring a transferable image on the image carrier side to the transfer material side; A constant-current control unit that outputs a predetermined current value to the device, and a constant-voltage control unit that outputs a predetermined voltage value. The transfer unit is one of a constant-current control and a constant-voltage control. When the volume resistance value of the contact transfer charger is equal to or more than a predetermined value, constant current control is performed.When the volume resistance value is less than a predetermined value, according to the size of the transfer material to be passed. An image forming apparatus, wherein the switching is performed.