JP2005195635A - Power unit and image forming apparatus provided with same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect an excessive discharge caused in a discharging area near a transfer area by a simple method. <P>SOLUTION: The power unit 100 applies a DC transfer bias to a primary transfer roller 62 configured so as to cause the excessive discharge between a photoreceptor drum 20 and the roller itself when the transfer bias becomes large. In the power unit 100, an AC feedback signal of an output terminal HV is input to a control device 101. On the basis of the AC feedback signal, the value of the specific frequency band area of a current flowing through the transfer area is detected. The specific frequency band area refers to a frequency band area where the current increases according to an amount of discharge caused in a pre-transfer area or a post-transfer area. Thus, it is possible to grasp whether the excessive discharge has occurred or not in the pre-transfer area or the post-transfer area on the basis of the detected value, thereby correcting the transfer bias to the optimum value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power supply apparatus that applies a DC bias or a bias obtained by superimposing an AC bias on a DC bias to a bias application target member, and an image forming apparatus including the power supply apparatus.

  As this type of image forming apparatus, there is an apparatus that forms an image by electrostatically transferring a toner image on an image carrier such as a photoreceptor to a transfer target such as transfer paper. In such an image forming apparatus, it is generally arranged at a position facing the image carrier so as to form a transfer electric field for moving the toner on the image carrier to the transfer member side between the image carrier and the transfer member. A transfer bias is applied to a transfer bias applying member such as a transfer roller. In such an image forming apparatus, the main causes of deterioration of image quality in the transfer process include a decrease in transfer rate, generation of so-called transfer dust, transfer failure, and the like.

  FIG. 12 is a graph schematically showing a general relationship between the transfer bias and the transfer rate. Generally, when the transfer bias is increased, the transfer rate starts to increase, and the transfer rate is saturated within a certain bias range. When the transfer bias is further increased beyond the bias range, an excessive bias state occurs, and the transfer rate decreases. When transfer is performed using a transfer roller, in an excessive bias state, the transfer electric field becomes unstable in a region immediately before entering the transfer region (pre-transfer region) or a region immediately after exiting the transfer region (post-transfer region). Cheap. For this reason, transfer failure occurs or transfer dust occurs in the pre-transfer area and the post-transfer area. Therefore, if the transfer bias is optimized to a value immediately before the state of excessive bias, the transfer rate is high and the occurrence of transfer failure and transfer dust can be sufficiently suppressed, so that high image quality can be obtained.

However, the optimum value of such a transfer bias varies depending on the use of the image forming apparatus over time.
For example, when the transfer target is an intermediate transfer belt, a polymer belt containing carbon is often used as the intermediate transfer belt. In this type of belt, the resistance value is lowered by applying a transfer bias for a long time. For this reason, even when the correlation between the transfer rate and the transfer bias in the initial state is as shown by the solid line in FIG. 12, the resistance value of the intermediate transfer belt decreases as it is used over time, and in FIG. It becomes like the graph shown with a dashed-dotted line. Therefore, the optimum value of the transfer bias after being used over time shifts in a lower direction than in the initial state, as shown in the figure. As a result, if the transfer bias is maintained at the optimum value in the initial state, the bias becomes excessive due to use over time, and transfer defects and transfer dust occur.
Further, for example, when the toner deteriorates due to use over time, the toner charge amount (Q / M) may increase, or the surface state of the toner may change and the adhesion may increase. In such a case, the correlation between the transfer rate and the transfer bias is as shown by a two-dot chain line in FIG. 12 even after the initial use, as indicated by the solid line in FIG. . Therefore, the optimum value of the transfer bias after being used over time shifts in a higher direction than in the initial state as shown in the figure due to toner deterioration. As a result, if the transfer bias is maintained at the optimum value in the initial state, the bias becomes insufficient due to use over time, and the transfer rate is lowered.
There are various other conditions (optimum value changing conditions) that change the optimum value of the transfer bias with use over time in addition to those exemplified here.

As described above, since the optimum value of the transfer bias changes depending on the use over time, in order to obtain high image quality over time, the transfer bias set value is appropriately adjusted according to the fluctuation of the optimum value change condition, that is, It is desirable to optimize the transfer bias.
For this reason, conventionally, in a state where paper is not passed in advance, a transfer bias that has been subjected to constant voltage control or constant current control is applied to detect the current or voltage in the transfer region, and the detection result is obtained by performing predetermined calculation processing. An image forming apparatus is known in which a transfer bias is set to a predetermined value. However, since there are various optimum value changing conditions for changing the optimum value of the transfer bias with use over time, as described above, it is extremely difficult to perform arithmetic processing in consideration of all such conditions. Therefore, in this image forming apparatus, the transfer bias cannot be optimized appropriately.

  On the other hand, for example, Patent Document 1 discloses an image forming apparatus that allows a user to confirm the degree of occurrence of a discharge pattern generated on an image due to discharge that occurs in a pre-transfer area or a post-transfer area, and allows the user to manually input the occurrence degree. It is disclosed. In this image forming apparatus, the transfer bias is optimized based on the degree of occurrence of the discharge pattern input by the user. Specifically, a gradation of the surface potential that continuously changes from the dark part potential (non-image part) to the bright part potential (image part potential) in the direction of surface movement on the photosensitive drum is created and developed. Then, a gradation pattern chart is output. Then, the user visually recognizes where the discharge pattern appears on the gradation pattern, and the user forms the numerical value (density level value) written beside the pattern portion where the discharge pattern appears in the image formation. Enter manually using the control panel of the device. According to Patent Document 1, since the potential difference corresponding to the density level value of the portion where the discharge pattern is generated represents the surplus potential with respect to the appropriate value of the transfer bias, the transfer bias can be reduced by lowering the transfer bias by the surplus. Has been optimized to prevent the occurrence of discharge patterns. In this image forming apparatus, the optimum transfer bias value is not judged from the various optimum value changing conditions that exist, but the optimum transfer bias value is judged from the transfer defect itself called a discharge pattern. Can be performed appropriately.

JP-A-10-221922

However, in the image forming apparatus disclosed in Patent Document 1, it is necessary to output a gradation pattern chart each time an attempt is made to optimize the transfer bias. It will be tough. Therefore, there is a demand for a method for optimizing the transfer bias by a simpler method that does not output an image and does not impose a complicated operation on the user.
For example, a method of measuring transfer dust, transfer failure, etc. appearing in the output image with a microscope installed in the image forming apparatus and automatically optimizing the transfer bias based on the measurement result is also conceivable. . In this case, confirmation work and manual input work by the user are not necessary, but image output is necessary. In addition, in this case, since it is necessary to provide an image forming apparatus with a large measuring unit for measuring transfer dust or transfer failure of the output image, it is not practical.

  As a result of extensive research conducted by the present inventors, transfer dust and transfer defects due to a transfer bias being smaller than the optimum value have a higher image quality than a decrease in transfer rate due to the transfer bias being smaller than the optimum value. It turned out to have a big impact. Therefore, how to detect the occurrence of transfer dust and transfer failure by a simple method is important for easily optimizing the transfer bias. However, conventionally, there has been no method for easily detecting transfer dust or transfer failure without outputting an image.

Here, according to the study by the present inventors, it is considered that the transfer dust and transfer failure are caused by excessive discharge generated in the pre-transfer area and the post-transfer area when the bias is excessive. Therefore, if the occurrence of this excessive discharge can be easily detected, the occurrence of transfer dust or transfer failure can be easily detected.
In the above description, a case has been described in which the transfer bias is optimized in order to suppress transfer dust and transfer failure caused by excessive discharge generated in the pre-transfer area and the post-transfer area in the image forming apparatus. However, it is an important issue to detect the occurrence of excessive discharge in a general method in which the apparatus is defective due to excessive discharge and to detect the occurrence of the defect by a simple method.

The present invention has been made in view of the above background, and a first object is to provide a power supply device capable of detecting the occurrence of excessive discharge by a simple method.
A second object is to provide an image forming apparatus capable of appropriately optimizing the transfer bias using the result of detecting the occurrence of excessive discharge by a simple method.

In order to achieve the above object, the invention of claim 1 is directed to a bias application target member arranged and configured so that a discharge exceeding a specified range is generated between the opposing member when the applied bias increases. Or, in a power supply device that applies a bias in which an AC bias is superimposed on a DC bias, a current or voltage in or near the discharge generating region between the bias application target member and the opposing member is generated in the discharge generating region. It has a detection means which detects the value of the specific frequency band which increases according to the amount of discharge.
The power supply apparatus according to claim 2 is characterized in that, in the power supply device according to claim 1, the detection means passes a filter circuit that passes only the current or voltage in the discharge generation region or the vicinity thereof in the specific frequency band, and And a rectifier circuit that rectifies the current or voltage that has passed through the filter circuit, and detects the value of the current or voltage output from the rectifier circuit.
According to a third aspect of the present invention, in the power supply device of the second aspect, the frequency band detected by the detecting means is a band of 1 MHz to 100 MHz.
Further, the invention according to claim 4 is the power supply device according to claim 1, 2 or 3, so that the detection value of the detection means falls within a range in which the discharge exceeding the specified range does not occur in the discharge generation region. It has an application bias correction means for correcting the bias applied to the bias application target member.
According to a fifth aspect of the present invention, in the power supply device of the first, second, third or fourth aspect, the first output means for outputting the detection result of the detection means to the outside and the bias application target member are applied. And a second output means for outputting a DC component of the applied bias to the outside.
According to a sixth aspect of the present invention, there is provided a transfer bias application object that is arranged so as to face the image carrier and that discharge exceeding the specified range occurs between the image carrier and the transfer bias when the transfer bias increases. The member is provided with a transfer bias applying means for applying a DC transfer bias or a transfer bias in which an AC bias is superimposed on the DC bias to the member, and a toner image on the image carrier is covered by a transfer electric field formed by the transfer bias. In an image forming apparatus that forms an image by transferring to a transfer body, the current or voltage in the transfer area between the transfer bias application target member and the image carrier is a discharge amount generated in or near the transfer area. Detecting means for detecting a value of a specific frequency band that increases correspondingly, and discharge that exceeds the specified range at or near the transfer region. To be within a range that does not, is characterized in that it has a transfer bias correction means for correcting a transfer bias applied to the transfer bias application target member.
The image forming apparatus according to claim 7 is the image forming apparatus according to claim 6, wherein the detection unit extracts only the current or voltage of the input transfer region from the specific frequency band, and the extracted current It is characterized by comprising an arithmetic unit that executes a detection program for calculating a value or a voltage value as the detection value.
According to an eighth aspect of the present invention, in the image forming apparatus of the sixth or seventh aspect, the detection value storage means for cumulatively storing the detection values of the detection means, and the cumulative value stored in the detection value storage means And an informing means for informing for urging maintenance when a predetermined value or more is reached.
According to a ninth aspect of the present invention, in the image forming apparatus according to the sixth, seventh, or eighth aspect, the high potential portion is formed on the surface of the image carrier along the moving direction of the image carrier during the non-image formation period. Pattern forming means for forming a surface potential pattern in which a low potential portion exists, the value detected by the detection means when the high potential portion exists in the transfer region, and the low potential portion A difference from a value detected by the detecting means when present in the region is used as the detected value.

As a result of intensive studies by the inventors, when a discharge occurs in the discharge generation region between the bias application target member and the opposing member, the current flowing in or near the discharge generation region according to the amount of discharge generation It has been found that the specific frequency band of the voltage increases. This can be inferred from the fact that noise having a specific frequency band is generated by the discharge of the corotron charger or the like.
In the power supply device according to any one of claims 1 to 5, a value in a specific frequency band of a current flowing in or near the discharge generation region and a voltage generated there is detected. Thereby, it can be determined from the detected value whether or not a discharge is generated in the discharge generation region. Since this detected value increases in accordance with the amount of discharge generated, it can be determined whether or not a discharge exceeding a specified range has occurred in the discharge generating region based on the detected value.
In the image forming apparatus according to any one of claims 6 to 9, similarly, the value of a specific frequency band of the current flowing through the transfer region and the voltage generated there is detected, and a discharge is generated in or near the transfer region from the detected value. It can be determined whether or not. Since this detected value increases in accordance with the amount of discharge generated, it can be determined whether or not a discharge exceeding the specified range has occurred in the transfer region or in the vicinity thereof based on the detected value. Therefore, in this apparatus, the transfer bias can be corrected to the optimum value so that the detected value is within a range where discharge exceeding the specified range does not occur in or near the transfer region.

As described above, according to the first to fifth aspects of the present invention, it is possible to grasp whether or not a discharge exceeding a specified range has occurred in the discharge generation region without performing image output and without complicating the user. Therefore, an excellent effect is obtained that the occurrence of excessive discharge can be detected by a simple method.
In addition, according to the sixth to ninth aspects of the present invention, there is an excellent effect that the transfer bias can be appropriately optimized using the result of detecting the occurrence of excessive discharge by a simple method. The

Hereinafter, an embodiment in which the present invention is applied to an electrophotographic color copier as an image forming apparatus will be described.
In recent years, in electrophotographic image forming apparatuses, color image forming apparatuses such as color copiers and color printers have increased in response to demands from the market. The color image forming apparatus includes a plurality of color developing devices around one latent image carrier, forms toner images by these developing devices, and superimposes these toners to obtain a color image. A drum-type image forming apparatus is known. Some of these image forming apparatuses use a so-called revolver type developing apparatus that performs development by sequentially rotating a plurality of developing units to a developing position. On the other hand, a plurality of latent image carriers are provided, and a developing device is provided for each latent image carrier, and toner images of each color are formed on each latent image carrier, and these toner images are sequentially stacked. A so-called tandem type image forming apparatus is also known that obtains a color image by transferring the images together. Comparing the one-drum type and the tandem type, the former has one latent image carrier, and therefore has the advantage of being relatively easy to downsize and easy to reduce costs. Since it is necessary to obtain a color image by repeating image formation a plurality of times (usually 4 times) using a body, there is a drawback that it is difficult to speed up image formation. On the other hand, the latter has the advantage that it is easy to increase the speed of image formation, although it is difficult to reduce the size and cost. Recently, since a speed similar to that of monochrome is desired for a color image, a tandem type image forming apparatus has attracted attention. In particular, after the toner images on each latent image carrier are transferred onto the intermediate transfer member so as to overlap each other by the primary transfer device, the toner images on the intermediate transfer member are collectively transferred to the sheet S by the secondary transfer device. Attention has been paid to those employing an intermediate transfer system for transferring. This is because the secondary transfer position can be set relatively freely, so that the degree of freedom of arrangement of the paper feeding device and the fixing device is increased, and the miniaturization is facilitated. In addition, since the degree of freedom in the arrangement of the fixing device is increased, a sufficient margin can be given to allow the sheet portion between the fixing device and the transfer portion to bend, so that the fixing device has almost no influence on image formation. It can be prevented from reaching. For these reasons, recently, among the tandem type image forming apparatuses, particularly those of the intermediate transfer type have been attracting attention.
Therefore, in this embodiment, a tandem type image forming apparatus that employs an intermediate transfer method will be described as an example. Needless to say, the present invention is not limited to the image forming apparatus shown in the present embodiment.

First, the configuration of the entire copying machine according to the present embodiment will be described.
FIG. 2 is a schematic configuration diagram of the entire copying machine according to the present embodiment. The copying machine includes a copying machine main body 500, a paper feed table 200 on which the copying machine main body is placed, a scanner 300 mounted on the copying machine main body, and an automatic document feeder (ADF) mounted on the upper portion of the scanner. 400.

  FIG. 3 is an enlarged view showing the configuration of the copying machine main body 500. The copying machine main body 500 is provided with an intermediate transfer belt 10 that is an endless belt-like intermediate transfer member. The intermediate transfer belt 10 is rotationally driven in the clockwise direction in FIG. 3 while being stretched around the three support rollers 14, 15, and 16. Among the supporting rollers, four image forming units 18Y, 18C, 18M, and 18K of yellow, cyan, magenta, and black are arranged in a belt stretch portion between the first supporting roller 14 and the second supporting roller 15. Has been placed. Above these image forming units 18Y, 18C, 18M, and 18K, an exposure device 21 is provided as shown in FIG. The exposure device 21 is formed on the photosensitive drums 20Y, 20C, 20M, and 20K, which are latent image carriers as image carriers provided in the respective image forming units, based on the image information of the original read by the scanner 300. This is for forming an electrostatic latent image. A secondary transfer device 22 is provided at a position facing the third support roller 16 among the support rollers. This secondary transfer device 22 has a configuration in which an endless belt-like secondary transfer belt 24 is stretched between two rollers 23a and 23b. When the toner image on the intermediate transfer belt 10 is secondarily transferred onto the transfer paper, the secondary transfer belt 24 is pressed against the portion of the intermediate transfer belt 10 wound around the third support roller 16 to perform the secondary transfer. I do. The secondary transfer device 22 may not be configured using the secondary transfer belt 24 but may be configured using, for example, a transfer roller or a non-contact transfer charger. A fixing device 25 for fixing the toner image transferred onto the transfer paper is provided on the downstream side of the secondary transfer device 22 in the conveyance direction of the transfer paper by the secondary transfer belt 24. The fixing device 25 has a configuration in which a pressure roller 27 is pressed against a heating roller 26.

Further, a belt cleaning device 17 is provided at a position facing the second support roller 15 among the support rollers of the intermediate transfer belt 10. The belt cleaning device 17 is for removing residual toner remaining on the intermediate transfer belt 10 after the toner image on the intermediate transfer belt 10 is transferred to transfer paper as a recording material. The belt cleaning device 17 includes two fur brushes as cleaning members. These fur brushes have a diameter of 20 mm, are brush rollers made of acrylic carbon of 100,000 / inch ² at 6.25 D / F, and have a resistance value of 10 ⁷ Ω. These fur brushes are driven to rotate in the counter direction with respect to the intermediate transfer belt 10. Each fur brush is in contact with a metal roller, and biases of different polarities are applied from a power supply device (not shown) through the metal roller. In the present embodiment, a minus voltage is applied to the fur brush located on the upstream side in the surface movement direction of the intermediate transfer belt 10, and a plus voltage is applied to the fur brush located on the downstream side. Further, the tip of the blade is pressed against each metal roller. With such a configuration, first, the surface of the intermediate transfer belt is cleaned using the fur brush on the upstream side in the surface movement direction of the intermediate transfer belt 10. Specifically, when −700 V is applied to the metal roller, −400 V is applied to the fur brush in contact with the metal roller, and the positively charged toner on the intermediate transfer belt 10 adheres to the fur brush 90. The attached positively charged toner is transferred from the fur brush to the metal roller due to the potential difference, and is scraped off and collected by the blade. Similarly, the negative polarity toner on the intermediate transfer belt 10 is also cleaned using a fur brush on the downstream side of the surface movement direction of the intermediate transfer belt 10. The toner scraped off by each blade is collected in a tank (not shown). You may make it return in a developing device using a toner recycling apparatus. As described above, most of the toner is removed by cleaning using the fur brush, but a small amount of toner may still remain on the intermediate transfer belt 10. Since this toner is positively charged during cleaning by the fur brush on the downstream side, it is reversely transferred to the photosensitive drum 20K side at the black primary transfer position and collected by the photosensitive member cleaning device 63K.

Next, the configuration of the image forming units 18Y, 18C, 18M, and 18K will be described. In the following description, the image forming unit 18K that forms a black toner image will be described as an example, but the other image forming units 18Y, 18C, and 18M have the same configuration.
FIG. 4 is an enlarged view showing the configuration of two adjacent image forming units 18M and 18K. In addition, in the code | symbol in a figure, the symbol of "M" and "K" which shows distinction of a color is abbreviate | omitted, and a symbol is abbreviate | omitted suitably also in the following description.
In the image forming unit 18, a charging device 60, a developing device 80, and a photoconductor cleaning device 63 are provided around the photoconductor drum 20. A bias application target member and a primary transfer roller 62 that is a transfer bias application target member are provided at a position facing the photosensitive drum 20 via the intermediate transfer belt 10.

  The charging device 60 is of a contact charging type employing a charging roller, and uniformly charges the surface of the photosensitive drum 20 by applying a voltage while contacting the photosensitive drum 20. As the charging device 60, a non-contact charging type using a non-contact scorotron charger or the like can be used.

  The developing device 80 may use a one-component developer, but in the present embodiment, a two-component developer composed of a magnetic carrier and a nonmagnetic toner is used. The developing device 80 includes a casing 84 provided with an opening for allowing a part of the surface of the developing sleeve 81 as a developer carrying member to face the photosensitive drum 20. In this embodiment, the diameter of the developing sleeve 81 is φ18, and the surface thereof is subjected to a sandblasting process or a process of forming a plurality of grooves extending in the axial direction having a depth of 1 to several mm to obtain a rough surface. The thickness Rz falls within the range of 10 to 30 μm. Inside the developing sleeve 81, magnets having five magnetic poles N1, S1, N2, S2, and S3 are fixedly arranged along the developing sleeve surface moving direction from a position facing the doctor blade 83. Further, an internal space A as a developer accommodating space for accommodating a two-component developer (hereinafter simply referred to as “developer”) is formed in the casing 84. The developing sleeve 81 is driven to rotate in the following direction with respect to the rotation of the photosensitive drum 20 with the developer carried on the surface. In the internal space A, two conveying screws 82 a and 82 b are provided as conveying members that convey the developer in the direction of the rotation axis of the developing sleeve 81. The two conveying screws 82a and 82b rotate the fins fixed to the rotating shaft to convey the developer in a direction parallel to the rotating shaft direction of the developing sleeve 81 while stirring the developer. Each of the conveying screws 82a and 82b is configured to convey the developer in opposite directions. A partition member 84 a that partitions the two conveying screws 82 a and 82 b so as to communicate with each other at both ends in the developing sleeve rotation axis direction is formed integrally with the casing 84. As a result, the developer conveyed to the end of conveyance of one of the conveyance screws 82a and 82b reaches to the conveyance start end of the other conveyance screws 82b and 82a in both end regions of the two conveyance screws 82a and 82b. A movement path for movement is formed. Therefore, when the developer is transported to the end of transport by each transport screw 82a, 82b, the developer moves to the other transport screw 82b, 82a side through the moving path, and this time transports in the opposite direction. Then, the developer circulates in the internal space A. Details of the configuration and operation of the developing device 80 will be described later.

The primary transfer roller 62 is disposed so as to be pressed against the photosensitive drum 20 with the intermediate transfer belt 10 interposed therebetween. Instead of the primary transfer roller 62, a member having a shape other than the roller shape may be used. The primary transfer roller 62 is provided with a power supply device (not shown) that applies a DC transfer bias. Note that a transfer bias in which an AC bias is superimposed on a DC bias may be used. Details of the power supply device will be described later. A member denoted by reference numeral 74 in FIG. 3 is a conductive roller provided between the primary transfer rollers 62. The conductive roller 74 is provided in contact with the base layer side (inner peripheral surface side) of the intermediate transfer belt 10, and the transfer bias applied to each primary transfer roller 62 at the time of primary transfer is a base having a medium resistance. This is to prevent the liquid from flowing into the adjacent primary transfer portion via the layer or the surface.
The photoconductor cleaning device 63 includes a cleaning blade 75 made of, for example, polyurethane rubber, which is disposed so that the front end is pressed against the photoconductor drum 20. In this embodiment, in order to improve the cleaning performance, a conductive fur brush 76 that contacts the photosensitive drum 20 is also used. A bias is applied to the fur brush 76 from a metal electric field roller 77, and the tip of a scraper 78 is pressed against the electric field roller 77. The toner removed from the photoconductor drum 20 by the cleaning blade 75 and the fur brush 76 is accommodated in the photoconductor cleaning device 63. Thereafter, the toner is brought to one side of the photoconductor cleaning device 63 by the recovery screw 79, returned to the developing device 80 through a toner recycling device (not shown), and reused.
Further, the static elimination device 64 is constituted by a static elimination lamp, and irradiates light to initialize the surface potential of the photosensitive drum 20.

  In the image forming unit 18 having the above configuration, first, the surface of the photosensitive drum 20 is uniformly charged by the charging device 60 as the photosensitive drum 20 rotates. Next, based on the image information read by the scanner 300, the exposure device 21 irradiates writing light L such as a laser or LED to form an electrostatic latent image on the photosensitive drum 20. Thereafter, the electrostatic latent image is visualized by the developing device 80 to form a toner image. This toner image is primarily transferred onto the intermediate transfer belt 10 by the primary transfer roller 62. The transfer residual toner remaining on the surface of the photosensitive drum 20 after the primary transfer is removed by the photosensitive member cleaning device 63, and thereafter, the surface of the photosensitive drum 20 is discharged by the static eliminating device 64, and the next image formation is performed. Provided.

Next, the operation of the copying machine in this embodiment will be described.
When copying a document using the copying machine having the above configuration, first, the document is set on the document table 30 of the automatic document feeder 400 shown in FIG. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it. Thereafter, when the user presses a start switch (not shown), when the document is set on the automatic document feeder 400, the document is conveyed onto the contact glass 32. Then, the scanner 300 is driven and the first traveling body 33 and the second traveling body 33 start traveling. Thereby, the light from the first traveling body 33 is reflected by the document on the contact glass 32, and the reflected light is reflected by the mirror of the second traveling body 33 and guided to the reading sensor 36 through the imaging lens 35. . In this way, the image information of the original is read.

  When the start switch is pressed by the user, a drive motor (not shown) is driven, and one of the support rollers 14, 15, 16 is rotationally driven to rotate the intermediate transfer belt 10. At the same time, the photosensitive drums 20Y, 20C, 20M, and 20K of the image forming units 18Y, 18C, 18M, and 18K are also rotationally driven. The details of the drive mechanism for the photosensitive drums 20Y, 20C, 20M, and 20K will be described later. Thereafter, based on the image information read by the reading sensor 36 of the scanner 300, the writing light L is transferred from the exposure device 21 onto the photosensitive drums 20Y, 20C, 20M, 20K of the image forming units 18Y, 18C, 18M, 18K. Are each irradiated. Thereby, electrostatic latent images are formed on the photosensitive drums 20Y, 20C, 20M, and 20K, respectively, and are visualized by the developing devices 80Y, 80C, 80M, and 80K. Then, yellow, cyan, magenta, and black toner images are formed on the photosensitive drums 20Y, 20C, 20M, and 20K, respectively. Each color toner image formed in this way is primarily transferred by the primary transfer rollers 62Y, 62C, 62M, and 62K so as to sequentially overlap the intermediate transfer belt 10. As a result, a composite toner image in which the toner images of the respective colors overlap is formed on the intermediate transfer belt 10. The transfer residual toner remaining on the intermediate transfer belt 10 after the secondary transfer is removed by the belt cleaning device 17.

  When the user presses the start switch, the paper feed roller 42 of the paper feed table 200 according to the transfer paper selected by the user rotates, and the transfer paper is sent out from one of the paper feed cassettes 44. The transferred transfer paper is separated into one sheet by the separation roller 45 and enters the paper feed path 46, and is transported by the transport roller 47 to the paper feed path 48 in the copying machine main body 500. The transfer paper conveyed in this way is stopped when it hits the registration roller 49. When using transfer paper that is not set in the paper feed cassette 44, the transfer paper set on the manual feed tray 51 is fed by the paper feed roller 50 and conveyed through the manual paper feed path 53. Then, it stops when it hits the registration roller 49.

The registration roller 49 rotates in accordance with the timing at which the composite toner image formed on the intermediate transfer belt 10 as described above is conveyed to the secondary transfer unit facing the secondary transfer belt 24 of the secondary transfer device 22. To start. In this embodiment, a conductive rubber roller is used as the registration roller 49, and a bias is applied. Specifically, the surface of the core rod having a diameter of φ18 is coated with a conductive NBR rubber having a thickness of 1 mm, and the electrical resistance value of this rubber is about 10 ⁹ Ω · cm in terms of volume resistivity. A voltage of about −850 V is applied to the roller facing the transfer paper surface (front surface) on the toner transfer side, and a voltage of about +200 V is applied to the roller facing the back surface. In particular, when there is little need to consider the transfer of paper dust on the back surface, the registration roller 49 may be grounded without applying a voltage. In this embodiment, a DC bias is used as the voltage applied to the registration roller 49, but an AC bias on which a DC bias is superimposed may be used. The use of an AC bias on which a DC bias is superimposed is suitable for uniformly charging the surface of the transfer paper. In this embodiment, the surface of the transfer paper portion after passing through the registration roller 49 is slightly charged to the negative side. Therefore, care must be taken during the secondary transfer from the intermediate transfer belt 10 to the transfer paper, since the transfer condition may change from when the voltage is not applied to the registration roller 49.

  The transfer paper sent out by the registration roller 49 is sent between the intermediate transfer belt 10 and the secondary transfer belt 24, and the secondary transfer device 22 transfers the composite toner image on the intermediate transfer belt 10 onto the transfer paper. Next transferred. Thereafter, the transfer paper is conveyed to the fixing device 25 while being attracted to the secondary transfer belt 24, and heat and pressure are applied by the fixing device 25 to perform a toner image fixing process. The transfer paper that has passed through the fixing device 25 is discharged and stacked on a discharge tray 57 by a discharge roller 56. When image formation is also performed on the back surface of the surface on which the toner image is fixed, the transfer paper transport path that has passed through the fixing device 25 is switched by the switching claw 55. Then, the transfer paper is fed to a sheet reversing device 28 located below the secondary transfer device 22 where it is reversed and guided again to the secondary transfer unit.

  In the present embodiment, components such as the photosensitive drums 20Y, 20C, 20M, and 20K and the developing device 80 arranged around the photosensitive drums 20Y, 20C, 20M, and 20K are configured as an integrated process cartridge. This process cartridge is detachable from the printer body. Therefore, when the life of a component housed in the process cartridge comes to an end or maintenance is necessary, the process cartridge may be replaced, and the convenience is improved.

Supplementing the specific configuration of this embodiment, in this embodiment, a photosensitive layer is formed by applying a photosensitive organic photosensitive material to an element tube such as aluminum as the photosensitive drums 20Y, 20C, 20M, and 20K. However, it may be an endless belt. In this embodiment, the photosensitive drums 20Y, 20C, 20M, and 20K have a diameter of 50 mm, and the photosensitive layer has a thickness of 30 μm. In the present embodiment, the linear speed of each of the photosensitive drums 20Y, 20C, 20M, and 20K is 200 mm / s, and the toner charge amount is in the range of −10 to −30 μC / g. Further, the beam spot diameter of the exposure device 21 is 50 × 60 μm, and the amount of light is 0.47 mW. Further, the charging potential V0 before exposure of the photosensitive drums 20Y, 20C, 20M, and 20K is −700V, and the exposed portion potential VL after exposure is −120V. Since the developing bias is −470V, the developing potential is 350V.
In the toner used in this embodiment, a charge control agent (CCA) and a colorant are mixed in a resin such as polyester, polyol, and styrene acrylic, and a substance such as silica and titanium oxide is externally added to the mixture. Therefore, the charging characteristics and fluidity are improved. The particle size of the additive is usually in the range of 0.1 to 1.5 μm. Examples of the colorant include carbon black, phthalocyanine blue, quinacridone, and carmine. The charging polarity is a negative polarity in this embodiment. As the toner, a toner obtained by externally adding the above-mentioned types of additives to a base toner in which wax or the like is dispersed and mixed can be used. In addition to the toner prepared by the pulverization method, toner prepared by the polymerization method or the like can be used. In general, a toner prepared by a polymerization method, a heating method, or the like can be formed to have a shape factor of 90% or more, is nearly spherical, and has a very high additive coverage. Here, the shape factor is originally sphericity, and is defined as “the surface area of a sphere having the same volume as the particle / the surface area of the actual particle * 100%”. It may be calculated in degrees. The definition of the average circularity is an average value of “the circumference of a circle having the same projected area as a particle / the projected contour length of an actual particle * 100%”. Therefore, the closer the projected circle is to a perfect circle, the closer to the average circularity is 100%. The range of the volume average particle diameter of the toner is preferably 3 to 12 μm. In the present embodiment, the toner has a volume average particle diameter of 6 μm, and can sufficiently cope with a high-resolution image of 1200 dpi or more.
The magnetic carrier used in this embodiment contains a magnetic material such as ferrite with a metal or resin as a core, and the surface layer is coated with a silicon resin or the like. The particle size is preferably in the range of 20-50 μm. The electric resistance value is optimally a dynamic resistance in the range of 10 ⁴ to 10 ⁶ Ω. This dynamic resistance is achieved by supporting a magnetic carrier on a roller (φ20; 600 rpm) containing a magnet and bringing an electrode having a width of 65 mm and a length of 1 mm into contact with a gap of 0.9 mm to obtain a high withstand voltage level (high resistance This is a measured value when an applied voltage of 400 V is applied for a silicon-coated carrier and several volts for an iron powder carrier.

Next, a problem caused by excessive discharge when the transfer bias is in an excessive bias state will be described.
It has been confirmed that when the transfer bias becomes excessively biased, so-called reverse transfer in which the toner moves to the photosensitive drum 20 side occurs in the pre-transfer area and the post-transfer area. When this reverse transfer occurs, from the measured values of the surface potential of the photosensitive drum 20 and the charge amount (Q / M) of the residual toner after the primary transfer when this reverse transfer occurs, the primary transfer area It was confirmed that excessive discharge occurred in Therefore, when the transfer bias is in an excessive bias state, excessive discharge occurs in the pre-transfer area and the post-transfer area, and it can be assumed that reverse transfer occurs due to this excessive discharge. When this reverse transfer occurs, the transfer rate decreases. This can be seen from the graph shown in FIG. 12 that the transfer rate decreases when the transfer bias is increased too much. In addition, when reverse transfer occurs, other color toners adhere to the photosensitive drum 20, resulting in a problem that other color toners are mixed during toner recycling.
In addition, when excessive discharge occurs in the pre-transfer area and the post-transfer area, the toner image on the photosensitive drum 20 before transfer or the toner image on the intermediate transfer belt 10 after transfer is destroyed, resulting in a problem of transfer dust. To do. In addition, the toner on the photosensitive drum 20 is not transferred to an appropriate position on the intermediate transfer belt 10, which causes a problem of transfer failure.

In order to suppress the above-described problems, it is necessary to optimize the transfer bias so as not to cause an excessive bias state. However, as shown in FIG. 12, the optimum value of the transfer bias changes with the passage of time, and the optimum value change condition includes various changes such as the change of resistance value of the intermediate transfer belt 10 and the like and the deterioration of toner with time. Varies depending on the factors. Therefore, even if the transfer bias is optimized in the initial state, the above-described problems occur over time. Therefore, in order to suppress problems that occur over time, it is necessary to periodically optimize the transfer bias.
Here, as a result of intensive studies by the inventors, the graph shown in FIG. 5 was obtained. This graph shows the relationship between the transfer bias and the value of the specific frequency band of the current flowing through the transfer region. This graph corresponds to the graph shown in FIG. 12, where the solid line is the initial one, the alternate long and short dash line is the one when the resistance value of the intermediate transfer belt 10 decreases with time, and the two-dot chain line is The cases where the toner deteriorates due to use over time and the toner charge amount (Q / M) increases or the adhesion of the toner increases are shown. In this graph, symbols P1, P2, and P3 indicate transfer bias values that provide the highest transfer rate when the resistance value of the intermediate transfer belt 10 is lowered at the initial stage and when the toner is deteriorated. As can be seen from the graph shown in FIG. 5, when a transfer bias exceeding the transfer bias value at which the maximum transfer rate is achieved is applied, the value of the specific frequency band of the current flowing through the transfer region increases. When a transfer bias exceeding the transfer bias value that provides the maximum transfer rate is applied, the amount of discharge also increases, so if the value of a specific frequency band of the current flowing through the transfer region is detected, It can be understood that excessive discharge is generated in the post-transfer area.
If the charge amount (Q / M) of the untransferred toner can be measured in the copying machine, it is possible to confirm whether or not a discharge has occurred. However, such a measurement is practically difficult. This is because, for example, when measuring by the sack-in method, an electronic balance / electrometer is required, and the measurement result must be constantly monitored, which not only increases the size of the apparatus but also increases the cost.

  In this embodiment, since the transfer bias is controlled at a constant voltage as will be described later, the value of a specific frequency band of the current flowing through the transfer region is detected to grasp the occurrence of discharge. When the transfer bias is controlled at a constant voltage, the occurrence of discharge can be similarly grasped by detecting the value of the specific frequency band of the voltage generated in the transfer region.

Next, features of the present invention will be described in detail.
In the present embodiment, the features of the present invention are concentrated in the power supply device connected to the primary transfer rollers 62Y, 62C, 62M, and 62K. Since the image forming units 18Y, 18C, 18M, and 18K have the same configuration and operation as their power supply units, symbols that indicate color distinction will be omitted below.

FIG. 1 is a circuit block diagram showing a schematic configuration of the power supply device 100 connected to the primary transfer roller 62.
The power supply device 100 applies a DC transfer bias, and performs constant voltage control for changing the current so that the voltage applied to the primary transfer roller 62 is constant. In this power supply apparatus 100, the control apparatus 101 performs ON / OFF control of the power transistor 103 from the trigger ON / OFF terminal via the constant voltage control unit 102 based on the DC feedback signal of the output voltage. The transformer drive circuit 104 generates a high-frequency transformer drive signal based on the output from the CLK terminal or the PWM terminal of the control device 101. In the following description, the PWM terminal will be described as an example. As the transformer driving circuit 104, a circuit that outputs an analog signal by a low-pass filter or the like and controls the secondary current value of the transformer 105 according to the magnitude of the signal can be used. Further, the output from the PWM terminal of the control device 101 may be directly fV converted. The transformer 105 is composed of a high-voltage excitation transformer that can output a high voltage. A rectifier circuit unit 106 is connected to the secondary side of the transformer 105. Since this rectifier circuit unit 106 needs to reduce the noise of the transformer 105 as much as possible, it is full-wave rectification in this embodiment. Of course, half-wave rectification may be used in order to select an inductance. With such a configuration, the output voltage (DC voltage) appearing at the output terminal HV of the power supply apparatus 100 is obtained by multiplying the secondary current value of the transformer 105 by R1 / (R1 + R2).

  Further, the power supply apparatus 100 is provided with a voltage buffer 107 on the path of a DC feedback signal of the output voltage input to the control apparatus 101. The voltage buffer 107 supplies the end potential of the detection resistor R1 to the integration circuit 108 stably. The integrating circuit 108 also operates as a low frequency filter having a time constant of 1 kHz or less. With such a configuration, even if there is a load fluctuation on the output side, it can be dealt with moderately to some extent.

Also, an AC signal (high frequency signal) appearing at the output terminal HV is input to the control device 101 of the power supply device 100 as an AC feedback signal. A high-frequency circuit 109, a voltage buffer 110, a band-pass filter 111, and a detection circuit 112 are provided on the AC feedback signal path. RF circuit 109 operates as a high pass filter comprising series-connected two capacitors C1, C2 from the resistor R _AC. The band pass filter 111 and the detection circuit 112 extract a specific frequency band that increases in accordance with the amount of discharge generated in the pre-transfer area and the post-transfer area from the high-frequency signal output from the high-frequency circuit 109. Then, a DC signal indicating the band value is input to the control device 101. The cut-off frequency of the band-pass filter 111 is preferably higher than the image frequency to avoid a series of frequency bands during image formation. In this embodiment, the filter is performed in a high-frequency region of 1 MHz to 100 MHz. Since the surface moving speed (process speed) of the photosensitive drum 20 and the intermediate transfer belt 10 is usually 1 m / s or less, it is possible to prevent noise from appearing on the image in this band. Moreover, as a filter means which passes the band of 1 MHz-100 MHz, since a commercially available cheap thing can be utilized, it is desirable also in terms of cost reduction. With the above configuration, an AC signal (high frequency signal) appearing at the output terminal HV can be detected.

Next, the operation of the power supply apparatus 100 configured as described above will be described.
The power supply apparatus 100 has three operation modes: an operation stop mode, a SCAN mode, and a HOLD mode. In the operation stop mode, an OFF signal is output from the trigger ON / OFF terminal of the control device 101, the power transistor 103 is turned off, and no transfer bias is output from the output terminal HV. The power supply apparatus 100 is in an operation stop mode before the image forming operation is started under the control of the control unit 90 provided on the copier body side. Further, the SCAN mode is set from the start of image formation until just before the leading edge of the toner image on the photosensitive drum 20 reaches the transfer region. Further, the HOLD mode is set from immediately before the leading edge of the toner image on the photosensitive drum 20 reaches the transfer region until the transfer is completed.

FIG. 6 is a flowchart showing the operation in the SCAN mode.
When image formation is started, a signal to that effect is output from the control unit 90 on the copier body side to the input terminal 114 of the control device 101, and the control device 101 outputs an ON signal from the trigger ON / OFF terminal. The predetermined PWM value is output from the PWM terminal (S1). Then, after the PWM value is incremented (S2), the control device 101 detects an AC signal (high frequency signal) appearing at the output terminal HV based on the input AC feedback signal (S3). Then, it is determined whether or not the detected value is equal to or less than a certain value (S4). This constant value is set to a threshold value in a range where excessive discharge does not occur in the pre-transfer area and the post-transfer area. This value varies depending on the circuit constants of the power supply apparatus 100, but can be selected as appropriate through experiments or the like. If it is determined that it is not below a certain value, the PWM value is changed so that the transfer bias output from the output terminal HV is lowered (S5). In this way, S2 to S5 are repeated until it is determined that the detected value is equal to or less than a certain value. When it is determined that the detected value is equal to or less than a certain value (S4), the mode shifts to the HOLD mode.

FIG. 7 is a flowchart showing the operation in the HOLD mode.
When the above-described SCAN mode ends and the mode shifts to the HOLD mode, the PWM value output from the control device 101 is fixed to the PWM value last set in the SCAN mode (S11). Thereafter, when the transfer process is actually performed and the transfer process is completed or the transfer process is forcibly interrupted, for example, the mode shift is required (S12), the control unit of the copying machine main body In step S13, it is determined whether or not images are continuously formed. If the image is not continuously formed, a command for shifting to the operation stop mode is sent to the control device 101, and the operation shifts to the operation stop mode (S14). On the other hand, when images are continuously formed, a command for shifting to the above-described SCAN mode is sent to the control apparatus 101, and the mode shifts to the SCAN mode (S15).

As described above, according to the present embodiment, by executing the SCAN mode before the actual transfer process, the optimum transfer bias is set so that excessive discharge does not occur in the pre-transfer area and the post-transfer area. Then, a transfer process can be performed. As a result, defects such as transfer dust and transfer defects caused by the excessive discharge can be effectively suppressed by a simple method without performing image output and without complicating the user. be able to.
If the output capacity of the power supply device 100 in this embodiment is large, the voltage value of the transfer bias output from the output terminal HV can be constant even if the PWM value is constant during the transfer process as in the HOLD mode. it can. However, when the output capacity is small, the voltage value of the transfer bias may fluctuate depending on the load condition on the output side only by keeping the PWM value constant. Therefore, when the output capacity is small, the HOLD mode as shown in FIG. 8 is adopted. This HOLD mode initially uses the PWM value set in the SCAN mode (S21), but based on the DC feedback signal input to the control device 101 (S22), the voltage value of the transfer bias becomes the target voltage value. Feedback control is performed to increase / decrease the PWM value so as to match (S23). Thereby, the voltage value of the transfer bias output from the output terminal HV can be made constant. If the HOLD mode shown in FIG. 7 can be adopted, the DC feedback signal transmission circuit portion shown in FIG. 1 can be omitted.

  In the present embodiment, the power supply device for applying the primary transfer bias has been described as an example, but the same effect can be obtained with a power supply device for applying the secondary transfer bias. However, in the secondary transfer process, there is a possibility that paper peeling, a bias at the time of charge removal, and the like may enter the secondary transfer area. Therefore, since it is necessary to optimize the transfer bias in consideration of the influence of this wraparound, the optimization is difficult as compared with the case of the primary transfer bias.

  Further, the control device 101 of the present embodiment employs a configuration similar to that of a lock-in amplifier, and is configured to detect a difference with an input SN ratio of about 40 dB of a reasonable lock-in amplifier. Q is about 100. It is desirable to set it to 1/100 of the value when everything except the transfer process is driven. In order to enhance the ability to detect the occurrence of excessive discharge, it is desirable to increase the SN ratio. Therefore, instead of the circuit configuration shown in FIG. 1, a circuit configuration as shown in FIG. 9 may be adopted. In this circuit, an adder 113 adds the AC signal (high frequency signal) appearing at the output terminal HV of the power supply device 100 shown in FIG. 1 and the high frequency component of the transfer current flowing into the substrate of the photosensitive drum 20, The output of the adder 113 is input to the bandpass filter 111. There are many noise sources around the photosensitive drum 20. For example, the bias used for the charging device 60, the developing device 80, or the like often uses an AC component superimposed, and in that case, the AC component becomes noise and is mixed into the AC feedback signal. There is. In this case, a signal in a specific frequency band that increases due to excessive discharge cannot be detected appropriately, and there is a risk of causing false detection. However, with the circuit configuration shown in FIG. 9, noise components other than the signal in the specific frequency band increased due to excessive discharge are canceled. Therefore, it is possible to obtain an AC feedback signal in which a signal in a specific frequency band that is increased due to an excessive discharge is strongly reflected and the S / N ratio is strongly reflected.

Further, as a method for appropriately detecting a signal in a specific frequency band increased by discharge, there is the following method.
First, in the SCAN mode, a primary transfer electric field that varies periodically is formed. Specifically, an electrostatic latent image pattern in which the surface potential is periodically changed along the surface movement direction is formed on the photosensitive drum 20. Such an electrostatic latent image pattern may be formed by the exposure device 21, for example, but can also be formed by periodically turning on / off the charging process of the charging device 60. At this time, the development bias is sufficiently low so that unnecessary development is not performed. A small amount of reversely charged toner may adhere to the surface of the photosensitive drum, but this does not cause a problem. The electrostatic latent image pattern thus formed periodically varies the primary transfer electric field in the primary transfer region. The output waveform of the bandpass filter 111 at this time is a waveform in which a large signal portion and a small signal portion are repeated corresponding to the electrostatic latent image pattern, as shown in FIG. The signal input to the control device 101 as an AC feedback signal has a waveform as shown in FIG. Since the value AC2 corresponding to a large signal portion of the AC feedback signal is in a state where the primary transfer electric field is high, discharge occurs in the pre-transfer area and the post-transfer area. Therefore, this signal portion includes a signal due to discharge in the pre-transfer area and the post-transfer area. However, this signal portion includes noise due to discharge or the like generated in other places. On the other hand, since the value AC2 corresponding to a small signal portion of the AC feedback signal is in a state where the primary transfer electric field is low, no discharge occurs in the pre-transfer area and the post-transfer area. Therefore, this signal portion is composed only of noise due to discharge or the like generated in other places, which does not include signals due to discharge in the pre-transfer area and post-transfer area. Therefore, if the difference between the value AC2 corresponding to the small signal portion and the value AC1 corresponding to the large signal portion is taken, the pre-transfer area and the post-transfer area in which noise due to discharge or the like generated in other places is removed. An appropriate signal including only the signal due to the discharge of the region can be obtained. As a result, it is possible to appropriately grasp whether or not excessive discharge occurs in the pre-transfer area and the post-transfer area.

  In this embodiment, the power supply apparatus 100 performs not only the detection of the value of the AC feedback signal in the specific frequency band that increases due to the discharge, but also the transfer bias correction processing based on the detection result. Therefore, when the present invention is applied to an apparatus such as an existing image forming apparatus, there is an advantage that if the existing power supply is replaced with the power supply apparatus 100, the other existing portions need not be significantly changed. In addition, the cable connecting the control unit 90 on the copier body side and the control device 101 of the power supply device 100 only needs to be able to transmit a signal for changing the operation mode of the power supply device from the control unit 90 to the control device 101. Therefore, there are advantages in reducing the cost of the cable and routing the cable inside the copying machine. In particular, the present embodiment is a tandem type copying machine having four photosensitive drums, and this advantage is obtained considering that four power supply devices for applying the primary transfer bias are required. It is beneficial. Note that, when a pulse is given several times in a short time, it is easy to improve the function such as stopping the control device 101.

  In this embodiment, an AC output terminal 115 and a second output unit serving as a first output unit that outputs an AC feedback signal and a DC feedback signal to the control unit 90 on the copier body side are sent to the control device 101 of the power supply device 100. And a DC output terminal 116 as an output means. Therefore, the control unit 90 can grasp the units around the transfer process and the toner life. Specifically, as shown in FIG. 11A, it is possible to grasp a change in the resistance value of the intermediate transfer belt 10 or the like, a conduction failure due to toner scattering, and the like by the fluctuation of the DC feedback signal. Further, as shown in FIG. 11B, it is possible to grasp that the above-described excessive discharge occurs due to the fluctuation of the AC feedback signal. Therefore, in the present embodiment, the control unit 90 is provided with a memory as detection value storage means for storing the value of the AC feedback signal. When the value stored in the memory becomes equal to or greater than a predetermined value, the control unit 90 outputs a sound, a warning sound, a warning display, or the like to notify the user or the like for maintenance. Do.

  In this embodiment, the specific frequency band is extracted by hardware using the bandpass filter 111 in order to detect the value of the AC feedback signal. However, this can also be performed by software. In this case, for example, in the circuit configuration shown in FIG. 1, the bandpass filter 111 and the detection circuit 112 are removed, and the output of the voltage buffer 110 is directly input to the control device 101. In this case, the basic software blocks in the control apparatus 101 are only averaging (DC conversion) processing and FFT / inverse FFT processing for extracting a specific frequency band. Therefore, it is easy to implement such software in the control apparatus 101. In this way, the configuration in which the specific frequency band is extracted by software has an advantage that the frequency band to be extracted can be easily changed.

As described above, the power supply apparatus 100 according to the present embodiment is a bias application target member 1 that is arranged and configured such that when the applied bias increases, a discharge exceeding the specified range is generated between the photosensitive drum 20 that is the opposing member. A DC bias or a bias in which an AC bias is superimposed on a DC bias is applied to the next transfer roller 62. The power supply device 100 generates a discharge of current or voltage in a pre-transfer area or a post-transfer area (transfer area) that is a discharge generation area between the primary transfer roller 62 and the photosensitive drum 20. It has components 109, 110, 111, 112 on the path of the AC feedback signal as detection means for detecting a value in a specific frequency band that increases according to the amount of discharge generated in the region. Thereby, it can be determined from the detected value whether or not an excessive discharge exceeding the specified range has occurred in the pre-transfer area and the post-transfer area. Therefore, according to the power supply apparatus 100, it is possible to correct the transfer bias to an optimum value so that the detected value is within a range where discharge exceeding a specified range does not occur in the pre-transfer area and the post-transfer area.
In addition, the power supply device 100 according to the present embodiment includes a bandpass filter 111 that is a filter circuit that passes only the current in the transfer region or the voltage in the specific frequency band, and the current or voltage that has passed through the bandpass filter 111. And a detection circuit 112 that is a rectification circuit that rectifies the voltage, and detects a current value or a voltage value output from the detection circuit 112. Thereby, the current or voltage in the specific frequency band can be extracted with simple hardware.
Moreover, the power supply apparatus 100 of this embodiment makes the frequency band to detect into 1 MHz or more and 100 MHz or less. Thereby, as the band pass filter 111, an inexpensive product for a specific frequency band television or radio can be adopted, and the cost can be reduced.
In addition, the power supply apparatus 100 according to the present embodiment is configured so that the detection value of the detection unit is applied to the primary transfer roller 62 so that excessive discharge does not occur in the pre-transfer area and the post-transfer area. A control device 101 as applied bias correction means for correcting the above. As described above, since the transfer bias can be appropriately corrected only by the power supply device 100, the present invention can be easily applied to an existing device as described above.
Further, the power supply apparatus 100 according to the present embodiment includes an AC output terminal 115 as a first output means for outputting an AC feedback signal, which is a detection result of the detection means, to the control apparatus 101, and a primary A DC output terminal 116 is provided as second output means for outputting to the outside a DC feedback signal that is a DC component of the bias applied to the transfer roller 62. Thereby, as described above, various problems can be grasped in the control unit 90 which is a device provided outside the power supply device.
The color copying machine of the present embodiment is disposed so as to face the photosensitive drum 20 as an image carrier, and excessive discharge exceeding the specified range occurs between the photosensitive drum 20 and the transfer bias when the transfer bias increases. A transfer bias applying means for applying a DC transfer bias or a transfer bias in which an AC bias is superimposed on the DC bias to a primary transfer roller 62 as a transfer bias application target member configured to be An image is formed by transferring the toner image on the photosensitive drum 20 to the intermediate transfer belt 10 as a transfer target by the transfer electric field formed. The color copying machine has a specific frequency band in which the current or voltage in the transfer area between the primary transfer roller 62 and the photosensitive drum 20 increases according to the amount of discharge generated in the pre-transfer area and the post-transfer area. Detection means for detecting the value of the transfer, and transfer for correcting the transfer bias applied to the primary transfer roller 62 so that the detection value of the detection means falls within a range in which excessive discharge does not occur in the pre-transfer area and the post-transfer area. The power supply apparatus 100 described above including a control apparatus 101 as bias correction means is provided. Accordingly, it is possible to set an appropriate transfer bias so that excessive discharge does not occur in the pre-transfer area and the post-transfer area, and it is possible to suppress problems such as transfer dust and transfer defects caused by the excessive discharge.
Further, as described above, the control device 101 extracts only the current or voltage of the input transfer region in the specific frequency band, and calculates the extracted current value or voltage value as the detected value. It can also be comprised with the arithmetic unit which performs a detection program. In this case, as described above, there is an advantage that the frequency band to be extracted can be easily changed.
Further, the color copying machine of this embodiment has a memory as a detection value storage means for storing the value of the AC feedback signal as the detection value in the control unit 90, and the value stored in this memory is equal to or greater than a certain value. When it becomes, it has the control part 90 as an alerting | reporting means which alerts | reports to urge maintenance. As a result, it is possible to notify the user of deterioration of members around the transfer process, toner deterioration, and the like.
In addition, the color copying machine of this embodiment generates a surface potential pattern in which a high potential portion and a low potential portion exist along the surface movement direction of the photosensitive drum 20 on the surface of the photosensitive drum 20 during the non-image forming period. As the pattern forming means to be formed, the exposure device 21 or the charging device 60 is used. Then, the difference between the value detected by the detection means when the high potential portion exists in the transfer area and the value detected by the detection means when the low potential portion exists in the transfer area is calculated as the detection value. Used as As a result, as described above, noise other than signals due to discharge in the pre-transfer area and post-transfer area can be reduced, and it is possible to appropriately grasp whether or not excessive discharge occurs in the pre-transfer area and post-transfer area. it can.

1 is a circuit block diagram showing a schematic configuration of a power supply device connected to a primary transfer roller of a copying machine according to an embodiment. 1 is a schematic configuration diagram of the entire copier. FIG. 3 is an enlarged view showing the configuration of the main body of the copier. FIG. 2 is an enlarged view showing a configuration of two adjacent image forming units in the copier. The graph which shows the relationship between a transfer bias and the value of the specific frequency band of the electric current which flows through a transfer area | region. The flowchart which shows operation | movement of the SCAN mode which is one of the operation modes of the power supply device. The flowchart which shows the operation | movement of the HOLD mode which is one of the operation modes of the power supply device. The flowchart which shows the operation | movement of the HOLD mode of another example. The circuit block diagram which shows schematic structure of the power supply device of another example. . (A) is explanatory drawing which shows the output waveform of a band pass filter at the time of forming the electrostatic latent image pattern in which the surface potential changed periodically. (B) is explanatory drawing which similarly shows the signal input into a control apparatus. (A) is explanatory drawing which shows the time-dependent change of the DC feedback signal output from the control apparatus of the power supply device. (B) is explanatory drawing which shows the time-dependent change of the AC feedback signal output from the control apparatus of the power supply device. A graph schematically showing a general relationship between a transfer bias and a transfer rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Intermediate transfer belt 18Y, 18C, 18M, 18K Image forming unit 20Y, 20C, 20M, 20K Photosensitive drum 21 Exposure device 22 Secondary transfer device 60 Charging device 62Y, 62C, 62M, 62K Primary transfer roller 80 Developing device 100 Power supply device 101 Control device 109 High frequency circuit 111 Bandpass filter 112 Detection circuit 113 Adder 114 Input terminal 115 DC output terminal 116 AC output terminal

Claims (9)

A power supply that applies a direct current bias or a bias in which an alternating current bias is superimposed on a direct current bias to a bias application target member that is arranged and configured so that a discharge exceeding the specified range occurs between the opposing members when the applied bias increases. In the device
Detection means for detecting a value of a specific frequency band that increases in accordance with the amount of discharge generated in the discharge generation region of a current or voltage in or near the discharge generation region between the bias application target member and the opposing member; A power supply device comprising: The power supply device according to claim 1, wherein
The detection means includes a filter circuit that passes only the current or voltage in the discharge generation region or the vicinity thereof in the specific frequency band, and a rectifier circuit that rectifies the current or voltage that has passed through the filter circuit. A power supply apparatus for detecting a current value or a voltage value output from the rectifier circuit. The power supply device according to claim 2, wherein
A power supply apparatus characterized in that a frequency band detected by the detecting means is a band of 1 MHz to 100 MHz. In the power supply device of Claim 1, 2, or 3,
And an application bias correction unit that corrects a bias applied to the bias application target member so that a detection value of the detection unit falls within a range in which discharge exceeding the specified range does not occur in the discharge generation region. Power supply. The power supply device according to claim 1, 2, 3 or 4,
First output means for outputting the detection result of the detection means to the outside;
And a second output means for outputting a DC component of an applied bias applied to the bias application target member to the outside. With respect to a transfer bias application target member that is arranged so as to face the image carrier and is configured to generate a discharge exceeding a specified range between the image carrier and the transfer bias, a direct current transfer bias or A transfer bias applying means for applying a transfer bias in which an AC bias is superimposed on a DC bias;
In an image forming apparatus that forms an image by transferring a toner image on the image carrier to a transfer target by a transfer electric field formed by the transfer bias.
Detecting means for detecting a value of a specific frequency band that increases in accordance with a discharge amount generated in or near the transfer region of a current or voltage in a transfer region between the transfer bias application target member and the image carrier; ,
A transfer bias correction means for correcting a transfer bias applied to the transfer bias application target member so that a detection value of the detection means falls within a range in which discharge exceeding the specified range does not occur in or near the transfer region; An image forming apparatus comprising: The image forming apparatus according to claim 6.
An operation for executing a detection program for extracting only the one in the specific frequency band from the input current or voltage in the transfer region, and calculating the extracted current value or voltage value as the detected value. An image forming apparatus comprising the apparatus. The image forming apparatus according to claim 6 or 7,
Detection value storage means for storing the detection value of the detection means;
An image forming apparatus comprising: an informing unit that performs an informing for urging maintenance when a detected value stored in the detected value storing unit becomes a predetermined value or more. The image forming apparatus according to claim 6, 7 or 8.
Pattern forming means for forming a surface potential pattern in which a high-potential portion and a low-potential portion exist on the surface of the image carrier along the moving direction of the image carrier during the non-image formation period;
The difference between the value detected by the detection means when the high potential portion exists in the transfer area and the value detected by the detection means when the low potential portion exists in the transfer area An image forming apparatus that is used as a detection value.

Images