JP2005062858A - Fog development method and fog development device for image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fog development method and a fog development device for an image forming apparatus, whereby fog can be detected by a simple inexpensive method, and toner deterioration, a range of image density adjustment, etc. can be checked. <P>SOLUTION: A development bias in a developing means and/or a transfer bias in a transfer means is controlled. A fringe pattern is developed onto the recording medium and thereby a fog can be detected. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fog revealing method and a fog revealing device in an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and in particular, the occurrence of fog is a simple and inexpensive method. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fog revealing method and a fog revealing apparatus in an image forming apparatus that can be detected and can check a deterioration state of a toner, a deviation from an appropriate range of image forming conditions, an adjustment range at the time of image density adjustment, and the like. is there.

  In image forming apparatuses such as copiers, printers, facsimiles, and multi-function printers that use electrophotography, a background portion that is a portion other than the formed image on the paper that you do not want the toner to adhere to for various reasons A fogging phenomenon occurs in which toner adheres to the surface. In other words, the toner in the developing device generally has a reverse polarity toner having a charge polarity opposite to the charge polarity of the regular toner at a certain ratio, but the ratio of the reverse polarity toner is large due to the deterioration of the developer. Then, as described above, reverse polarity toner adheres to the background portion and the like, and the contrast of the image decreases. Further, fog may occur due to an increase in the residual potential of the photoconductor due to a change in environmental conditions such as high temperature and high humidity or deterioration of the photoconductor. In addition, even when the charge of the toner becomes extremely low, particularly in an image forming apparatus using a two-component developer, the toner holding force by the carrier is weakened, and the toner is not applied to the background portion where the toner is not originally desired to be attached. Fly away.

  However, when fogging occurs in this way, the problem is not limited to simple image problems. For example, if printing is continued with fogging, the amount of toner consumption increases and the specified number of prints cannot be printed. In addition, there is a problem that the amount of waste toner increases when fog occurs between papers. If the fog level can be easily recognized, it is recognized as a defect on the image, so there is no problem. However, if the fog level cannot be easily recognized visually, there is a risk that it will be overlooked until the problem occurs. is there.

  Furthermore, since the fog density is usually extremely low compared to the density of the image portion (image forming portion), it is difficult to detect the fog density. As a result, it is difficult to determine the fog level. If there is a uniform fog on the image, it is extremely difficult to determine the level.

  As a prior art for detecting such fog, for example, in Patent Document 1, the surface of the photoreceptor is negatively charged by a reversal development method using a one-component developer, and negatively charged toner is attached to a portion where the potential is lowered by exposure. In the image forming apparatus, the photosensitive member is damaged when a positive transfer bias is applied at the transfer portion. Therefore, the transfer bias is turned off at a portion where there is no latent image. Since the (charged) toner is transferred to the recording paper and fogged, when the transfer bias is turned off in the non-image area, the development bias is changed until the amount of the reversely charged toner adhering to the surface of the photoconductor decreases below the allowable value. There has been proposed an image forming apparatus including a control unit.

  In Patent Document 2, development is carried out while changing the developing bias from -40 V to -100 V in steps of 5 V before copying in order to prevent deterioration of the photoconductor and increase in fog caused by high temperature and high humidity. Each toner density is read by a toner sensor using infrared rays, and the relationship between the developing bias and the toner density is obtained by the least square method to obtain the fog level A. If the A is equal to or lower than a preset reference value, the normal developing bias is obtained. An image forming apparatus is shown in which the developing bias is increased by 40 V when the developing bias is equal to or greater than the reference value.

  In Patent Document 3, a toner density sensor provided in the developing device regulates the toner density in the developing device to a predetermined value, and a thin black and white mark (OD mark) or the like is printed on the photosensitive member to be printed on the photosensitive drum. Reading with the optical sensor arranged oppositely, the development bias is changed as a result, the surface potential of the photosensitive drum is lowered, the exposure energy of the exposure part is controlled, the control of the printing light, the back part 1 shows an image forming apparatus that performs control of dirt, control of deterioration of cleaning performance, control of transfer efficiency of a transfer portion, and control of white background fog.

  Further, Patent Document 4 discloses that when the toner concentration in the developing device (the ratio of toner to the carrier) exceeds a predetermined value, the toner is charged on the photosensitive drum charged with the same polarity to reduce the toner charge amount. Fog is likely to adhere and fog is generated, but a fog pattern detection and analysis means is provided, for example, on an image forming body such as a photosensitive drum or the like due to abnormal vibration caused by deterioration of a drive motor or a gear. When the development system, exposure system, etc. vibrate and the mutual positional relationship fluctuates to produce shades according to the amplitude of the vibration on the image forming body or recording medium, this shaded fog pattern and each An image forming apparatus is shown in which abnormalities in the mechanism are associated in advance and an abnormal part of the image forming apparatus can be identified by a fog pattern.

  In Patent Document 5, for example, if fogging occurs when the photoreceptor surface potential is +400 V, the charge charger ability can be controlled so that a surface potential of +500 V can be secured by adding a margin of +100 V. The grid voltage Vg and the developing bias Vb of the charging device for the photosensitive member are set to predetermined values in advance, and the grid voltage Vg is changed by a predetermined amount, so that the toner adhesion amount to the test pattern formed on the photosensitive drum with a small amount of light is determined. An image forming apparatus in which a grid voltage Vg detected at the time of image formation by an optical sensor is set is shown.

  Further, in Patent Document 6, conventionally, a toner mark is printed with a laser beam in a non-image area independently of a print signal, and the toner density is controlled by detecting a density of a white paper portion adjacent to the toner mark density by a toner density sensor. However, since the degree of deterioration of the photoconductor is different in the non-image area compared to the image area, it is difficult to detect the true deterioration state, and a toner mark remains on the printed recording medium, When reading an original and compressing data because it has the problem of reducing the quality, a line with a high white pixel compression ratio is specified to determine the fog detection position, and the print that reads the image at the fog detection position in the print image An image reading means is provided so that the amount of fog can be calculated by comparing the white / black contrast in the original image with the white / black contrast in the printed image. Image forming apparatus is shown with.

JP-A-3-153262 (FIGS. 4 and 5) JP-A-5-224512 (FIG. 3) JP-A-5-307328 (FIG. 1) Japanese Patent Laid-Open No. 9-50212 (FIG. 1) JP-A-11-160930 (FIG. 2) JP 2002-82498 A (FIG. 1)

  However, the image forming apparatus disclosed in Patent Document 1 is controlled only for reverse polarity toner, and the image forming apparatuses disclosed in Patent Documents 2 and 3 are applied to a toner sensor or a photosensitive drum using infrared rays. A photoconductor drum that requires a photosensor arranged oppositely and that changes the developing bias from −40 V to −100 V in increments of 5 V (Patent Document 2), and changes the developing bias. Therefore, complicated control (Patent Document 3) such as lowering the surface potential and increasing the exposure energy of the exposed portion is necessary, which is expensive.

  Another object of the image forming apparatus disclosed in Patent Document 4 is to make it possible to identify an abnormal part of the image forming apparatus by a fog pattern. It is adjusted and does not deal with fog caused by other causes. The image forming apparatus disclosed in Patent Document 5 is mainly intended to deal with dirt and image noise caused by a test pattern formed on a photoconductor, and is used for setting the grid voltage Vg by detecting the test pattern. A sensor is required and is expensive as described above. Further, the image forming apparatus disclosed in Patent Document 6 can calculate the amount of fog by comparing the white / black contrast of the print image, not the toner density on the photoconductor. Necessary and expensive.

  For this reason, in the present invention, it is possible to detect fog by a simple and inexpensive method, and at the same time, it is possible to check the deterioration state of the toner and the adjustment range at the time of adjusting the image density, and the like. It is a problem to provide a manifestation device.

  In order to solve the above problems, in the present invention, a latent image is formed on an image carrier by electrophotography, developed by a developing means to form a toner image, and then the toner image is directly or indirectly transferred by a transferring means. Used in an image forming apparatus which is designed to be transferred to a recording medium, and controls the developing bias in the developing means and / or the transfer bias in the transferring means to make fog appear on the recording medium. And

  It is desirable to use a method of turning on / off the developing bias in the developing unit, a method of alternately switching the DC developing bias in the developing unit between at least two voltages having different absolute values, etc. Furthermore, the developing bias in the developing unit may be changed stepwise.

  Also, a method for turning on / off the transfer bias in the transfer unit for fog detection, a positive transfer bias applied at the time of image formation as the transfer bias in the transfer unit, and a reverse transfer bias having a reverse polarity to the normal transfer bias Alternatively, a method of alternately switching between and may be used.

  Then, the developing bias in the developing unit is turned on / off while being changed stepwise, and the transfer bias in the transfer unit is applied when the developing bias is turned on and off, and the positive transfer bias applied during image formation and the transfer bias. The fog may be manifested on the recording medium by alternately switching the reverse transfer bias having the reverse polarity to the normal transfer bias.

  Further, in the present invention, a toner collecting unit is disposed between the developing unit and the transfer unit, and the developing unit is charged with the image carrier for a predetermined time and is not exposed. While developing the image carrier, the toner on the image carrier is collected by the collecting unit, and when the predetermined time has elapsed, the toner is discharged from the collecting unit to the image carrier, A fog revealing method in an image forming apparatus is obtained, wherein the toner on the image carrier is transferred to a recording medium by a transfer means to make the fog appear on the recording medium. At this time, the collecting unit is separated from the image carrier in the image forming mode in which image formation is performed, and is brought into contact with the image carrier in the deterioration measurement mode for measuring the degree of toner deterioration, and the bias voltage is turned on / off. By controlling, the transfer bias voltage applied to the transfer means is switched alternately between a forward transfer bias applied at the time of image formation and a reverse transfer bias having a polarity opposite to the forward transfer bias.

  In the present invention, each color image forming unit has an image forming unit for each color, and each color toner image is sequentially transferred to the intermediate transfer member to form a color toner image on the intermediate transfer member. Used in an image forming apparatus in which a toner image is transferred to a recording medium by a transfer unit, and is developed by a developing unit in a state where the image bearing member is charged and not exposed in at least one of the color image forming units. After developing the image carrier to form fog toner on the image carrier and transferring the fog toner to the intermediate transfer body a plurality of times, the fog toner on the intermediate transfer body is transferred to the transfer body The fog revealing method in the image forming apparatus is characterized in that the fog is made visible on the recording medium by being transferred to the recording medium by the means.

  Further, the number of the steps is N, and the result obtained by dividing the toner density value when the fog toner transferred onto the recording medium is detected by the image density sensor by the N is defined as a unit fog level. The surface density of the recording medium itself may be measured in advance by the image density sensor, and the result obtained by subtracting the surface density from the toner density value may be set as the fog level. In addition, a fog adjustment mode is performed in which the fog accumulation level is obtained by changing the fog accumulation count, with the number of times the process is executed as the fog accumulation count, and the fog level is stored in the memory as a reference fog curve, and the fog adjustment is performed. Then, the surface potential of the image carrier and the developing bias are changed, and the fog accumulation level is changed to obtain the fog level to obtain a plurality of measurement fog curves. The measurement fog curve and the reference The surface potential and development bias of the measured fog curve closest to the reference fog curve may be set by comparing with the fog curve.

  According to the present invention, an image forming unit for each color is provided, and each color toner image is sequentially transferred to the intermediate transfer member by each color image forming unit to form a color toner image on the intermediate transfer member. The image carrier is used in an image forming apparatus in which a toner image is transferred to a recording medium by a transfer unit, and the image carrier is charged by the developing unit in a state where the image carrier is charged and not exposed in each color image forming unit. And the fog toner is formed on the image carrier at different timings so that the fog toner of each color is transferred onto the intermediate transfer member at a different position in the transport direction of the intermediate transfer member. After the toner is transferred to the intermediate transfer member for each color, the fog toner on the intermediate transfer member is transferred to the recording medium by the transfer means to make the fog appear on the recording medium. It fogging obvious method is obtained in an image forming apparatus according to claim. At this time, the fog toner is preferably transferred onto the intermediate transfer member so as to overlap each other in the order of black, yellow, cyan, and magenta.

  In addition, according to the present invention, an image carrier that forms a latent image by electrophotography, a developing unit that develops the latent image on the image carrier to form a toner image, and a toner image on the image carrier. In a fog revealing apparatus in an image forming apparatus having a transfer unit that directly or indirectly transfers a toner to a recording medium, a development bias power source that supplies a development bias to the development unit, and a transfer bias to the transfer unit The transfer bias power supply, the development bias power supply and the transfer bias power supply are controlled to turn on / off while changing the development bias stepwise, and the transfer bias is imaged when the development bias is on and off. A control means for performing a control for alternately switching a forward transfer bias applied at the time of formation and a reverse transfer bias having a reverse polarity to the forward transfer bias. And fog actualized device is obtained, characterized in that to elicit a fog on the recording medium.

  As described above, according to the present invention, the development bias and / or the transfer bias is controlled, and the fog is made clear by using the recording medium. Although it is not easy to determine the level, it is possible to compare and form the fog stripes and the white background without fog, and the fog state can be easily confirmed.

  In order to realize fog, it is simple and inexpensive by using a method for turning on / off the developing bias in the developing unit, a method for alternately switching the DC developing bias in the developing unit between at least two voltages having different absolute values, and the like. With such a structure, it is possible to easily create a white background without fog stripes and fog.

  Further, by gradually changing the developing bias in the developing means, it is possible to check when the potential of the developing bias is generated, and to easily know the toner deterioration state, the density adjustment range, and the like. be able to.

  Also, a method for turning on / off the transfer bias in the transfer unit for detecting fog, a transfer bias in the transfer unit as a positive transfer bias applied at the time of image formation, and a reverse transfer bias having a reverse polarity to the normal transfer bias By using a method of alternately switching between, when there is fog with a simple and inexpensive configuration, a white background without fog stripes and fog can be easily created.

  Then, the developing bias in the developing unit is turned on / off while being changed stepwise, and the transfer bias in the transfer unit is changed between the positive transfer bias applied during image formation and the positive bias when the developing bias is turned on and off, respectively. It is possible to check when the development bias and the transfer bias occur when the transfer bias and the reverse transfer bias having the opposite polarity are alternately switched and the fog appears on the recording medium. Thus, it is possible to easily know the deterioration state of the toner, the density adjustment range, and the like.

  In the present invention, a toner collecting unit is disposed between the developing unit and the transfer unit, the image carrier is developed by the developing unit for a predetermined time, and fog toner is formed on the image carrier, and the collecting unit When the toner on the image carrier is collected and a predetermined time elapses, the toner on the image carrier is transferred to the recording medium by the transfer means while discharging the toner from the collecting means to the image carrier. Therefore, even if the amount of fog toner is extremely small when printing a single blank sheet, if a plurality of blank sheets are printed (that is, if blank sheets are printed for a predetermined time), the amount of fog toner collected by the collecting means Inevitably increases and fogging determination can be easily performed.

  In the present invention, at least one of the color image forming units develops the image carrier by the developing means in a state where the image carrier is charged and is not exposed to form fog toner on the image carrier. Then, after the process of transferring the fog toner to the intermediate transfer member is executed a plurality of times, the fog toner on the intermediate transfer member is transferred to the recording medium by the transfer means, so that the fog is accumulated. Then, if the fog toner is transferred from the intermediate transfer belt to the recording medium, the fog becomes obvious and the fog can be easily detected.

  Further, in the present invention, when the fog adjustment mode is executed, the surface potential of the image carrier and the development bias are changed, and the fog accumulation level is changed to obtain the fog level to obtain a plurality of measurement fog curves. The measurement fog curve and the reference fog curve are compared, and the surface potential and the development bias of the measurement fog curve closest to the reference fog curve are set. Therefore, it is possible to always reduce the fog and perform good image formation. There is an effect that can be done.

  In the present invention, the fog toner is formed on the image carrier at different timings, the fog toner is transferred to the intermediate transfer member for each color, and then the fog toner on the intermediate transfer member is transferred to the recording medium by the transfer means. As a result, the boundary line for each color appears clearly, and the degree of fog can be clearly determined according to the position of the boundary line.

  Further, a developing bias power source for supplying a developing bias to the developing means, a transfer bias power source for supplying a transfer bias to the transferring means, the developing bias power source and the transfer bias power source are controlled, and the developing bias is changed stepwise. In each of the on / off control and the on / off state of the developing bias, the forward transfer bias applied at the time of image formation and the reverse transfer bias having the opposite polarity to the forward transfer bias are alternately switched. Control means for performing control, and by revealing the fog on the recording medium, it is possible to confirm when the development bias and the transfer bias occur, and the deterioration state of the toner And a fog detection device in an image forming apparatus that can easily know the density adjustment range and the like with a simple and inexpensive configuration. It can be.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention only to the description unless otherwise specified. It is just an example.

  FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus that implements the fog revealing method according to the present invention, and FIG. 2 shows a toner charge amount and a toner amount distribution during normal operation and toner deterioration in a general developing device. FIG. 3 is a diagram for explaining the relationship between the photosensitive member potential, the developing bias, and the fog. FIG. 4 is a diagram for explaining a situation in which plus fog and minus fog are transferred to the recording medium by forward and reverse transfer bias. FIG. 5 is a diagram for explaining the basic concept of the fog revealing method according to the present invention, and FIG. 6 is a diagram for explaining the fog revealing method according to the present invention for judging the deterioration state of the toner. FIG.

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus that performs a fog revealing method according to the present invention. 1 is a developing device in the image forming apparatus, and 2 is a surface subjected to blasting treatment with regular or irregular particles. The developing sleeve 3 that rotates and has a magnetic pole adjacent to the photosensitive drum (image carrier) 12 is an N1 pole, a magnetic pole that faces the magnetic blade 5 is an S2 pole, and a magnetic pole that conveys toner to the developing sleeve 3 is S1. A developer carrying member 5 including a fixed magnet assembly 4 having a plurality of magnetic poles, ie, poles N2 and poles, is attached with a magnet 6 on the upstream side of the developing position of the developing sleeve 3, and is mounted on the developing sleeve 3. Magnetic blade for regulating the thickness of the magnetic one-component toner layer to be formed, 7 is a developer container, 8 is a stirring rod for stirring the toner in the developer container 7, and 9 is for replenishing the toner The toner container 10 is a toner sensor for detecting that the amount of toner in the developer container 7 is low and supplying the toner from the toner container 9, and 12 is a positively charged single layer type organic photoreceptor (for example, A photosensitive drum (image carrier) composed of OPC), 13 is a charger, 14 is an exposure unit, 15 is a transfer roller, 16 is a cleaner for cleaning residual toner on the photosensitive drum 12, and 17 is a charger 13. high pressure use power, 18 transfer bias power source configured to allow on / off or shaking the transfer bias V _T in forward and reverse, 19 stepwise changes the developing bias V _b by a command from the control circuit 20 A developing bias power source 20 configured to be capable of controlling the entire image forming apparatus, and charging high voltage power source 17, transfer bias power source 18, developing via This is a control circuit for controlling the power supply 19 and the like.

  The developer carrying member 2 has been described as being composed of the developing sleeve 3 and the fixed magnet assembly 4, but in addition to this, the sleeve 3 is fixed and the magnet assembly 4 is rotated. 3 and the magnet assembly 4 are rotated, and the present invention can be used in any configuration. Further, in the following description, an image forming apparatus using a developing device that performs jumping development using a positively charged magnetic one-component developer will be described as an example. However, the present invention is not limited to this type of developing device, but two-component development. It is apparent that the present invention can be applied to a contact-type developing device, a hybrid-type developing device and the like using an agent, and also to a color image forming apparatus.

First, the normal image forming operation of the image forming apparatus that implements the fog revealing method according to the present invention will be described. The toner in the developer container 7 is agitated by the agitating rod 8, and a thin layer of toner is formed on the developing sleeve 3 while being positively charged with the layer thickness being regulated by the magnetic blade 5. In the image formation, the control circuit 20 first applies a high voltage to the charger 13 from the charging high-voltage power supply 17 to the photosensitive drum 12 composed of, for example, a positively charged single-layer organic photoreceptor (OPC) that rotates in the direction of the arrow. Then, it is uniformly charged so that the charging potential V ₀ becomes about 475 (V), and the exposure unit 14 is driven and exposed by the image data sent to form a latent image. At this time, the surface potential _VL of the photosensitive drum 12 after exposure is about 10 (V). Then, between the developing sleeve 3 and the photosensitive drum 12, for example, a direct current of about 350 (V) and a rectangular wave (Vpp = 1.6 (kV), f = 2.4 (kHz), duty cycle, and the like by a developing bias power source 19. A developing bias _{Vb on} which an alternating electric field with a ratio of 50% is applied is applied to cause a thin layer of toner on the developing sleeve 3 to fly between the photosensitive drum 12 and an exposed portion on the photosensitive drum 12. Develop to make a toner image.

And this toner image on the recording medium coming fed between the transfer roller 15 and the photosensitive drum 12 is transferred by the negative polarity of the transfer bias V _T applied by the transfer bias power source 18 to the transfer roller 15, FIG. It is fixed and discharged by a fixing device not shown. The remaining toner remaining on the photosensitive drum 12 is scraped off by the cleaner 16 to prepare for the next image formation. The values of the charging voltage, surface potential, DC bias, and alternating electric field are examples, and it is obvious that the values are not limited to these values.

Next, the fog revealing method according to the present invention will be described. As described above, when the fog level can be easily recognized, it is recognized as a defect on the image, so there is no problem, but the fog density is usually extremely low as the image density. It is not easy to judge the level visually, and there is a risk that it will be overlooked until a problem occurs. In the present invention therefore, to control to apply the developing sleeve 3 is turned on / off a developing bias V _b applied between the photosensitive drum 12, a voltage which does not occur with the voltage generated by the fog alternately, the transfer roller the transfer bias V _T applied to 15 are turned on / off, to reverse the forward and reverse transfer bias V _T, the method etc., if the fog occurs, the parts and free from fogging portion of the fog on the recording medium Alternatingly provided, stripes are formed to make fog appear and fog can be detected. Depending on the development bias V _b and transfer bias V _T at that time, the developer deterioration state and development bias V _b The adjustment range can be determined. In other words, if a stripe pattern is formed by alternately providing a fogged portion and a non-fogged portion on the recording medium, the difference can be discriminated even with a slight fog.

  The toner normally used in the image forming apparatus is the friction between the toner and the carrier in the case of the two-component developer, the friction between the toner and the toner in the case of the magnetic one-component developer, and in the image forming apparatus as shown in FIG. When the spike standing on the blasted developing sleeve 3 by the layer thickness regulating member 5 formed of a magnetic blade is moved by the conveying force of the developing sleeve 3, it is rubbed by the layer thickness regulating member 5. For example, in the case of positively charged toner, the toner is charged so as to have a charge amount distribution as indicated by 30 in FIG. In FIG. 2, the horizontal axis represents the toner charge amount, and the vertical axis represents the toner amount of the same charge amount. In the case of a positively charged toner, a charge control agent is inserted so that the toner is charged to the plus side. However, there is a distribution by looking at each toner particle, and there is a negative polarity as indicated by 31. In other words, a reversely charged toner having a charged electric charge of approximately 10% is produced. The distribution of the charge amount of the toner is caused by various causes, such as peeling of the charge control agent or deterioration by selective development, as shown by 32 and 33 in FIG. Polar toner increases, tends to be positive or negative, and deteriorates with long-term use (toner with charging characteristics that are not suitable for development increases). It becomes broad.

Further, as described above, in the image formation, as shown in FIG. 3, the photosensitive drum 12 is charged to + V ₀ (V) by the charger 13, and the exposure of the photosensitive drum 12 by the exposure unit 14 is performed. Charging decreases to + V _L (V). Then, a positively charged toner is applied between the developer carrier 2 and the photosensitive drum 12 by applying a developing bias + V _b (V) (only a DC component is shown in FIG. 3) in which an alternating current is superimposed on a direct current. Flies to the photosensitive drum 12 by the developing bias + V _b (V), and is developed by being attached to the exposed portion of the photosensitive drum 12 where the potential is reduced to + V _L (V). That is, the difference between the developing bias + V _b (V) and the exposed and lowered potential + V _L (V) on the photosensitive drum 12 is the developing potential. When this difference increases, the toner density increases, and this difference increases. When it becomes smaller, the toner density decreases.

Then, as indicated by 32 and 33 in FIG. 2, if the toner charge amount distribution is biased to the plus side or the minus side due to various causes, the potential at which the + fogging region indicated as + V _{+ b in} FIG. The potential at which the -fogging region indicated by + V _-b starts approaches the developing bias potential + V _b (V), and overcharged toner (plus charged toner) or undercharged and reversely charged toner (minus charged toner) is on the photosensitive drum 12. It adheres to the unexposed part (V ₀ ) and becomes fogged. That is, when the amount of overcharged toner increases, the amount of flying to the photosensitive drum 12 increases even with the same developing bias potential + V _b (V), and fog increases. In addition, when insufficiently charged toner and reversely charged toner (negatively charged toner) increase, the insufficiently charged toner has a weak force of adhering to the developer carrier 2 due to the charged charge and is less susceptible to the repulsive force due to the charged charge of the photosensitive drum 12. Along with the reversely charged toner, it will fly to the background that you do not want to fog. In the case of contact development, if the carrier and toner holding force is weak (if the toner is not sufficiently charged), it adheres to the photosensitive drum 12 by the Coulomb force. Also, as shown by 34 in FIG. 2, when the toner charge amount distribution becomes broad as a whole and both the overcharged toner, the undercharged toner, and the reverse polarity toner increase, this + V _{+ b} is described as + Both the potential at the beginning of the fog area and the potential at which −V _−b is started approach the developing bias potential + V _b (V), and the range in which the fog does not occur becomes very narrow. In some cases, fogging of both toners may occur.

In the present invention therefore, the control circuit 20 as in the case of non-contact development was the controls the developing bias power source 19, the developing bias V _b ON / OFF to be applied between the developing sleeve 3 and the photosensitive drum 12 In addition, including non-contact development and contact development, the voltage at which fogging occurs, for example, the voltage entering the “+ fogging region” exceeding the voltage marked + V _{+ b in} FIG. 3, or marked + V− _{b in} FIG. By alternately applying a voltage that falls below the applied voltage and enters the “−fogging region” and a developing bias voltage + _Vb that deviates from these regions, the region where the fog toner adheres to the photosensitive drum 12 is adhered. A non-overlapping area is formed, and the resulting stripe pattern is transferred to a recording medium so that it becomes obvious, so that even a slight fog can be distinguished.

In the present invention, more than has been described developing bias V _b on / off and, not only controls to apply alternating developing bias voltage V _b does not occur and the developing bias voltage V _b to fogging, FIG the control circuit 20 as shown in 4 controls the transfer bias power source 18 to turn on / off the transfer bias V _T applied to the transfer roller 15, reversing the forward and reverse transfer bias V _T, by methods like, The fog toner adhering to the photosensitive drum 12 is transferred to the recording medium or not transferred alternately to make the fog stripe pattern appear on the recording medium so that the fog can be discriminated.

That is, when the positively charged photosensitive drum 12 described above and the positively charged toner are used and the latent image formed on the photosensitive drum 12 is developed, the transfer is performed to transfer the toner image to the recording medium. The roller 15 is supplied with a transfer bias of −V _T (V) from a transfer bias power source 18. Therefore, when the photosensitive drum 12 has fog of positively charged toner, the toner is transferred to the recording medium by turning on the transfer bias −V _T (V), and is not transferred by turning it off. A fog stripe pattern can be formed on the medium. However, when the photosensitive drum 12 is fogged with reversely charged toner (negatively charged toner), the toner is transferred to the recording medium even when the transfer bias is applied with -V _T (V) or the transfer bias is turned off. Therefore, the image is transferred for the first time by applying + V _T (V) with the polarity reversed, and is not transferred when the bias is turned off, so that a fogging stripe pattern is formed on the recording medium.

However, as indicated by 34 in FIG. 2, when the toner deteriorates and becomes broad as a whole and both the overcharged toner and the reverse polarity toner increase, if the transfer bias is switched between forward and reverse in this way, it is negative. When the transfer bias −V _T (V) is applied, the positively charged toner is transferred to the recording medium. When the transfer bias + V _T (V) is applied, the reversely charged toner (negatively charged toner) is transferred. As a result, the entire surface is covered with no striped pattern. Therefore, when the transfer bias is switched between the minus side and the plus side in this way, if the striped pattern does not appear over the entire surface, it indicates that the toner has deteriorated, and is either on the minus side or the plus side. When the striped pattern appears, it indicates that the toner charge is biased to the plus side or the minus side as indicated by 32 or 33 in FIG.

5, 6, turns on / off the developing bias V _b applied between the developing sleeve 3 which has been described above with the photosensitive drum 12, the developing bias V _b stepwise changed, occurrence of fog to controls to apply a voltage which does not occur with the voltage alternately turns on / off transfer bias V _T applied to the transfer roller 15, reversing the forward and reverse transfer bias V _T, in combination with the method of equal, toner It is a figure for demonstrating the fog manifestation method which enabled it to also distinguish a deterioration state and the bias | inclination of the amount of charge.

(A) in FIG. 5 First shows a state where the control circuit 20 instructs the high voltage charging power supply 17 to operate the charging device 13, and charges the photosensitive drum 12 on the + V ₀ in FIG. 1, FIG. 5 (B) also control circuit 20 controls the developing bias power supply 19, the development bias _{V b} applied between the developing sleeve 3 and the photosensitive drum 12 at time _{t 1, t 3, t 5} ...... indicates that the turning on / off, FIG. 5 (C) the control circuit 20 controls the transfer bias power source 18 in FIG. 1, the transfer bias V _t is applied between the photosensitive drum 12 and the transfer roller 15, a developing a bias _{V b} is turned on to become the time _{t 1} and _{t 1} at + _{V t} between _{t 3,} the -V _t at _{t 2,} also developing bias _{V b} is turned off _{t 3} and _{t t 3} of between ₅ in the + _{V t,} intended to -V _t at _{t 4} That. By thus developing bias V _b and changing a combination of the transfer bias V _t, in d from each interval a between time t ₁ ~t _5, as shown in the following Table 1, the toner The transfer state of the fog generated on the recording medium differs depending on the charged state. In other words, the charged state of the toner can be determined by observing the formation state of the fog stripe pattern transferred onto the recording medium.

In Table 1, to d represents a d from each interval a between time t ₁ ~t ₅ shown in FIG. 5, ○ indicates that fogging toner appears in fog is transfer recording medium by the respective X indicates that fog is not transferred and fog toner does not appear on the recording medium, and Δ indicates that fog toner is not developed and fog toner does not appear on the recording medium.

That is, first, “1. Overcharge, fog due to (+) charge” shows that the charging potential + V ₀ of the photosensitive drum 12 is on (for example, +475 V) at time t ₁ and development bias + V _b (here, only the DC component is shown). For example, when the transfer bias is + V _T (for example, +500 V) and the transfer bias is + V _T (for example, +500 V), the transfer bias is “x”, and at the time t ₂ the transfer bias is −V _T (for example, −1500 V), the recording medium is The result is a circle and a striped pattern is formed. And when the developing bias V _b is off at time t _3, the transfer from bias is + V _T c and the -V _T both in fogging toner of d does not appear on the recording medium without being developed △, and this case There will be no fog on both sides and no stripes. For this reason, when the toner is overcharged, the fog toner is transferred to the recording medium only by b, and is not transferred by a, c, d, and a stripe pattern is formed between a, b, c.

The next "2 insufficiently charged, (-) fog due to the charge" becomes reversed at a and b, a ○ Because developing bias + V _b is the transfer bias ON is transferred to a the recording medium + V _T, In b where the transfer bias is −V _T , the image is not transferred and becomes a cross and a striped pattern is formed. And even when the developing bias V _b is off, the photosensitive drum 12 charged potential + V ₀ is for on insufficiently charged or - charge of the toner flies to the photoreceptor drum 12, a ○ the c transfer bias + V _T Become. In the portion c, the potential difference between the charging potential + V ₀ and the developing bias _Vb is larger than that in the portion a. Therefore, a larger amount of −charge toner is developed than the portion a, and the fog density on the image is also increased. The transfer bias becomes × is not transferred in d becomes -V _T, even stripes here are formed.

“3. Poor charging, fogging due to (+, −) charging” indicates that the toner is in a broad charged state as shown by 34 in FIG. toner by a the + charge bias + V _b is the transfer bias oN + V _T is, b in the transfer bias is -V _T - toner is transferred to the recording medium not generated is streaks due to the charge, the developing bias + V _b is the c transfer bias + V _T off - the charge of the toner becomes ○ are transferred to the recording medium. In the portion c, the potential difference between the charging potential + V ₀ and the developing bias _Vb is larger than that in the portion a. Therefore, a larger amount of −charge toner is developed than the portion a, and the fog density on the image is also increased. Then, a transfer bias is the d of -V _T this - also not transferred charge toner, also + charge toner fogging toner does not appear on the recording medium from not developed, c, stripes are formed only between the d The

  The last “4. Insufficient toner holding power of developing roll, mechanical fogging” does not depend on the electric field, and thus fogging may occur in all of a to d. The presence / absence and level of fog on the image vary depending on the amount of toner scattered.

Next, in FIG. 6A, as in FIG. 5A, the control circuit 20 in FIG. 1 instructs the charging high-voltage power supply 17 to operate the charger 13 to charge the photosensitive drum 12 to + V ₀ . shows a state of being, a development bias V _b is applied from the developing bias power source 19 between in FIG. 6 (B) and the developing sleeve 3 shown in FIG. 1 and the photosensitive drum 12, the while oN / oFF In FIG. 3, the voltage is changed stepwise n times from the voltage of + V _−b or less shown as “−fogging region” to the voltage of + V _{+ b} or more shown as “+ fogging region”, while the photosensitive drum 12 and the transfer roller 15 are changed. the transfer bias V _t is applied from a transfer bias power source 18 between, as shown in FIG. 6 (C), the to vary alternately + V _t and -V _t in each section of the development bias V _b is oN / oFF It is a thing.

In this way, in each cycle 1, 2,... (N-1), n of the developing bias _Vb shown at the bottom of FIG. Depending on the presence or absence of fog toner transfer, a stripe pattern is generated. That is, when the developing bias _Vb1 in the cycle 1 of FIG. 6B is the potential in the “-fogging region” shown in FIG. 3 (that is, a potential lower than + V− _b ), it is indicated by 31 in FIG. When there is a reversely charged toner or there is a large amount of undercharged toner indicated by 33, fogging due to these toners occurs. Therefore, as described in “2. Insufficient charge, fogging due to (−) charge” in Table 1, the transfer is performed because + V _T is applied to the transfer roller 15 in the section a in the cycle 1. since the transfer is not performed when the -V _T is applied in the section b, the section a, stripes are formed Te b. Then, as the next developing bias V _b1 is the even c, d to be turned off, since the charge potential + V ₀ of the photoconductor drum 12 is on insufficiently charged or - charge of the toner flies to the photoreceptor drum 12 Since transfer is performed at c where the transfer bias is + V _T and transfer is not performed at d where −V _T is −V _T , a stripe pattern is formed in the sections a to d.

Then the next cycle 2, the developing bias _{V b} to _{V b2,} when its _{V b3} in the next cycle 3, go stepwise increasing the developing bias _{V b} so on, for example, a developing bias _{V b3} "- If the “fogging region” is left, no stripe pattern is formed. If this striped pattern is due to insufficiently charged toner indicated by 33 in FIG. 2, + V− _b (V _b3 ) in FIG. 3 is higher than that indicated by 30 in FIG. Since the voltage is close to the developing bias _Vb , an image without fogging can be obtained by adjusting the density with a voltage higher than + V− _b ( _Vb3 ).

If there is a large amount of excessively charged toner as indicated by 32 in FIG. 2, the developing bias _Vb is further increased stepwise. For example, the developing bias _Vb in the cycle (n-1) in FIG. When the potential in the “+ fogging region” shown in FIG. 3 (that is, a potential higher than + V _{+ b} ) _{Vb (n−1)} is reached, fogging due to the excessively charged toner occurs. As described in “1. Overcharge and fog due to (+) charge”, in section a in cycle (n−1), transfer is not performed because + _VT is applied to the transfer roller 15. when -V _T is applied at b the transfer takes place. Therefore, a striped pattern is formed. However, in c and d where the next development bias _{Vb (n-1)} is turned off, the fog toner is not developed and does not appear on the recording medium. Therefore, when the toner is overcharged, the fog toner is transferred to the recording medium only at the portion b, and a stripe pattern is formed between a, b, and c without being transferred at a, c, and d.

For this reason, the developing bias V _{b (n-2)} in the cycle (n-2) (not shown) immediately before the cycle (n-1) in which the stripe pattern is generated has an upper limit potential at which fog due to excessively charged toner does not occur. However, when the above-described stripe pattern is due to the overcharged toner indicated by 32 in FIG. 2, + V _{+ b} (V _{b (n−2)} ) in FIG. Since the voltage is lower than that shown in FIG. 30 and approaches the developing bias _Vb , an image without fogging can be obtained by adjusting the density at a voltage equal to or lower than this + V _{+ b} ( _{Vb (n-2)} ). It is done.

Further, when the toner is deteriorated and the charge amount distribution is broad as indicated by 34 in FIG. 2, both the insufficiently charged toner and the excessively charged toner described above increase, so that the developing bias _Vb is turned on. / Off cycles 1, 2,... (N−1), where n is a striped pattern as described above for both a small number cycle and a large number cycle, as shown in FIG. and + in the middle with between V _-b and + V + _b is narrowed, charging excessive toner when transfer bias of -V _T is, + in the case of V _T as entirely fogged insufficiently charged toner is transferred may occur Become.

That is, when fogging that does not become a striped pattern occurs when the transfer bias is switched between forward and reverse in this way, this indicates that the toner has deteriorated and is in the replacement period, and the development bias _Vb is turned on / off. In each cycle 1, 2,... (N-1), n, when fogging occurs at a shown in FIG. If fogging occurs at b shown in FIG. 6 but does not come out at a when the number is a large number, it can be determined that the toner is in a state as shown in 32 in FIG.

Therefore, according to the fog detection method of the present invention described above, toner deterioration can be determined, and at any cycle in each cycle 1, 2,... (N-1), n of developing bias _Vb on / off. The distribution of the charge amount of the toner can be determined by checking whether the fog has disappeared or in which cycle the fog has occurred. Therefore, for example, when adjusting the toner concentration, the development bias + V _b in these fog lost cycle or began cycles of fog, showed in + V _-b and + V + _b 3 - a "fog region"" Since the voltage starts with “+ fogging region”, it is possible to provide an image forming apparatus in which a good image can always be obtained by adjusting the density so that the developing bias + _Vb is not applied to + V− _b and + V _{+ b.} it can.

Specific experimental examples are shown below. First, regarding the configuration of the image forming apparatus used, a positively charged single layer type organic photoreceptor (OPC) having a linear velocity of 93 mm / sec and a diameter of 30 mm was used as the photoreceptor drum 12. Then, magnetic jumping development was performed by the corotron charging 13, and after the transfer by the transfer roller 15, cleaning was performed by the counter blade type cleaner 16 to perform the neutralization of the LED. In the developing device 1, the linear speed ratio between the photosensitive drum 12 and the developing sleeve 3 is 1.4, the developing gap with the photosensitive drum 12 is 0.32 mm, and the gap between the blade 5 and the developing sleeve 3 is 0.3 mm. . The toner composition includes 40% magnetic powder as an internal additive, 2% wax, 1.1% silica as an external additive, and 1.4% abrasive (titanium oxide), and the toner particle size is 25%. Was 6.3 μm, the 50% value was 7.5 μm, and the 75% value was 8.5 μm. As the set values, the drum charging potential is 475 V, the wavelength of the exposure laser is 780 nm, the laser exposure amount is 0.9 μJ / cm ² , the development bias is DC (DC) 350 V, the duty ratio is 50%, the frequency is 2.4 kHz, and the AC voltage is A rectangular wave alternating current (AC) with an amplitude of 1.6 kV was used. The forward transfer bias was controlled by 10 μA constant current control, and the reverse transfer bias was controlled by 550 V constant voltage control. Cleaning was performed using a linear pressure of 15 g / cm, neutralization using an LED wavelength of 630 nm, and an exposure amount of 4.0 μJ / cm ² .

  During normal printing, the development bias is applied in accordance with the recording paper transport timing, and the transfer bias is applied while the recording paper passes through the transfer section. When the fog detection method described above is performed, The development bias is repeatedly turned on / off, for example, with an on time of 400 msec and an off time of 400 msec. Further, the transfer bias is turned on / off with, for example, an on time of 200 msec and an off time of 200 msec while the recording paper passes through the transfer portion. It was. The fog was generated by changing the developing bias in the positive direction so that a desired fog was generated.

Under such conditions, an experiment was conducted to determine whether fog can be recognized when the fog revealing method according to the present invention is implemented or not. As a result, the fog density was defined as (background density−recording paper density), the density was measured with a reflection densitometer (MACBETH RD918), and the fog was visually recognized (a stripe pattern can be confirmed). ) And x, when the fog cannot be recognized visually, the results shown in Table 2 were obtained.

  That is, as apparent from Table 2, fog was recognized when the fog concentration was 0.020, but when the fog concentration was 0.015 and 0.010, it was not recognized by the fog revealing method of the present invention. However, it was not recognized when not used, and neither was recognized at a fogging concentration of 0.005. It should be noted that the fog clarification method of the present invention is performed in response to a serviceman when there is a complaint that the amount of toner consumption is abnormally large, that is, only a specified number of sheets can be printed with one toner container, This should be done when such an event is noticed.

  Referring to FIG. 7, in FIG. 7, the same components as those shown in FIG. As illustrated, a collection roller 41 is disposed between the transfer roller 15 and the developer carrier (development roller) 2, and the collection roller 41 is formed of an elastic body. In the image forming mode in which image formation is performed, the collection roller 41 is in a state of being separated from the photosensitive drum 12 (positioned at the standby position).

Now, in the toner deterioration measurement mode, the control circuit 42 moves the collection roller 41 from the standby position by a drive mechanism (not shown) to bring the collection roller 41 into contact with the photosensitive drum 12 (the collection roller 41 is set to the contact position). To do). Thereafter, the control circuit 42 charges the photosensitive drum 12 by the charger 13, rotates the photosensitive drum 12 in a state where the operation of the exposure unit 14 is stopped (that is, without performing exposure), and develops the developing device 1. Is operated for a preset time (for example, three sheets of A4 size paper) (hereinafter referred to as blank printing). That is, the fog toner described above is adhered from the developing device 1 to the photosensitive drum 12.
It should be noted that a bias having a polarity opposite to the developing bias (for example, −300 V) is first applied to the collecting roller 41 to attach only the overcharged toner, and then a developing bias and a transfer bias are applied. A bias having the same polarity as that of the developing bias (for example, +300 V) is applied to cause only undercharged toner or reversely charged toner to adhere, and then the developing bias and transfer bias shown in FIG. 8 are applied.

  At this time, the collecting roller 41 is rotated in the same direction as that of the photosensitive drum 12 by giving a linear velocity difference thereof (may be rotated in the opposite direction to the photosensitive drum 12), and thus the fog on the photosensitive drum 12 may be rotated. The toner is collected by the collection roller 41. When the preset time elapses, the control circuit 42 ends the developing operation, and when all the fog toner on the photosensitive drum 12 is collected by the collection roller 41, the control circuit 42 sends the collection roller 41 to FIG. A transfer bias is applied to the transfer roller 15 in addition to the development bias shown.

  That is, the control circuit 42 controls the switch device 43 to apply the developing bias from the developing bias power source 19 to the collecting roller 41. Further, the control circuit 42 controls the transfer bias power source 18 to apply the transfer bias to the transfer roller 15. As shown in FIG. 8, the developing bias applied between the collecting roller 41 and the photosensitive drum 12 is turned on / off to form a region where fog toner is attached and a region where the toner is not attached on the photosensitive drum 12. However, if the toner is deteriorated and the transfer bias is switched between forward and reverse, the positively charged toner is transferred to the recording medium when a negative transfer bias is applied, and the reverse when a positive transfer bias is applied. The charged toner (negatively charged toner) is transferred, and the entire surface is covered, and no stripe pattern appears.

  As described above, when the stripe pattern does not appear on the entire surface, it indicates that the fog toner is deteriorated. When it is determined that the fog toner is deteriorated, the control circuit 42 controls the switch device 43 to Then, the developing roller 2 and the developing bias power source 19 are connected, and the toner is discharged from the developing device 1 onto the photosensitive drum 12 by the developing roller 2 (at this time, the photosensitive drum 12 is charged and exposed). No), the photosensitive drum 12 is cleaned by the cleaner 16. At this time, the collection roller 41 is separated from the photosensitive drum 12 and no transfer bias is applied to the transfer roller 15. First, a bias (for example, −300 V) having a polarity opposite to the developing bias is applied to the collecting roller 41 to attach only the overcharged toner, and then the developing bias and the transfer bias are applied to transfer to the recording medium. Next, a bias having the same polarity as the developing bias (for example, +300 V) is applied to the collecting roller 41 to attach only an undercharged toner or a reversely charged toner, and then the developing bias and the transfer bias shown in FIG. 8 are applied. Transfer to recording medium. Based on Table 1 shown in Example 1, it is possible to determine the cause of fogging.

  After discharging the deteriorated toner from the developing device 1 as described above, the control circuit 42 replenishes the developing device 1 with toner from a toner container (not shown). In this way, the developing operation is performed for a preset time (for example, a plurality of blank paper prints), and the toner is collected by the collecting roller 41 while supplying the fog toner to the photosensitive drum 12, and then the collecting roller 41 is moved to FIG. When the developing bias shown in FIG. 2 is applied and the fog toner is discharged from the collection roller 41 to the photosensitive drum 12, even if the amount of fog toner is extremely small in the case of printing one blank sheet, a plurality of blank sheets can be printed. The amount of fog toner collected by the collection roller 41 inevitably increases, and the fog determination can be easily performed.

  The determination as to whether or not fogging has occurred may be made visually using a density comparison sheet prepared in advance, and the control circuit 42 detects the toner on the recording medium with a toner density sensor. The fog determination may be performed by comparing the detection result with the density comparison sheet.

  In the second embodiment described above, fog toner is collected for a plurality of sheets by the collecting roller so as to make fog appear. In an image forming apparatus having an intermediate transfer member (for example, an intermediate transfer belt), In this way, fog may be revealed. FIG. 9 is a diagram schematically showing an example of an image forming apparatus using the intermediate transfer belt 51. In the illustrated example, a magenta (M) image forming unit 52, cyan are arranged along the rotation direction of the intermediate transfer belt 51. (C) An image forming unit 53, a yellow (Y) image forming unit 54, and a black (BK) image forming unit 55 are arranged. Then, each color toner image is sequentially transferred from each color image forming unit to the intermediate transfer belt 51 to perform color superposition, and a color toner image is formed on the intermediate transfer belt 51. The color toner image on the intermediate transfer belt 51 is transferred onto a recording medium (not shown) by the transfer roller 56.

  In the illustrated image forming apparatus, the transfer roller 56 is detachable from the intermediate transfer belt 51. In the image forming mode, the transfer roller 56 is in contact with the intermediate transfer belt 51. On the other hand, in the fog determination mode in which the fog level is determined, after the transfer roller 56 is separated from the intermediate transfer belt 51, only the black image forming unit is operated, and as described with reference to FIG. The fog toner is transferred to. At this time, the black image forming unit performs blank paper printing as shown in FIGS. 5 and 6 described in the first embodiment.

  Then, when the intermediate transfer belt 51 makes one round, the fog toner is transferred onto the intermediate transfer belt 51 again by the black image forming unit. In this way, the fog toner is transferred to the same position on the intermediate transfer belt 51 by the black image forming unit a plurality of times (N times). Incidentally, when fog toner is formed on a photosensitive drum (not shown) in the black image forming unit, as described in the first embodiment, for example, the development bias is controlled to be turned on / off (first embodiment). The developing bias may be controlled by the other method described in the above, and the drive control of the intermediate transfer belt is performed by a control device (not shown).

  As described above, after the fog toner is transferred a plurality of times on the same location of the intermediate transfer belt 51 while the intermediate transfer belt 51 is rotated a plurality of times, the control device causes the transfer roller 56 to contact the intermediate transfer belt 51. Then, the fog toner on the intermediate transfer belt 51 is transferred onto the recording medium. The fog toner on the recording medium is detected by an image density sensor (not shown). As described above, since the fog toner is transferred to the same position on the intermediate transfer belt 51 a plurality of times, the fog toner has been manifested in the fog toner transferred to the recording medium. Thus, the fog can be easily detected. It is also possible to determine whether or not the fog is a problem level by comparing the fog density with a sheet printed with the standard fog density.

  By the way, before transferring the fog toner from the intermediate transfer belt 51 to the recording medium, the recording medium is passed through an image density sensor to detect the surface density of the recording medium and stored in the memory as the recording medium density. Subsequently, if the recording medium on which the fog toner is transferred is passed through the image density sensor to detect the fog density, and the control device subtracts the recording medium density from the fog density, the degree of fog accurately. (Fog level) can be detected, and the fog level can be detected stably regardless of the type of recording medium.

  Further, after the fog toner is transferred to the intermediate transfer belt 51 times, the fog toner on the intermediate transfer belt 51 is transferred to a recording medium, and the fog level is detected by an image density sensor. Dividing “level”) by N makes it possible to obtain the fog level per unit (unit fog level).

  Referring to FIG. 10, when the fog level is detected by changing the fog accumulation count with the fog level (fogging density after subtraction of the recording medium) as the vertical axis and the fog toner transfer count (fogging accumulation count) as the horizontal axis, FIG. Suppose that the result shown by the curve L1 is obtained. The fog curve L1 is stored in the memory as a reference fog curve (this fog curve L1 is stored in the memory when the image forming apparatus is installed). For example, when a predetermined number of sheets are printed, the control device displays on the front panel (operation panel: not shown) that the fog adjustment is necessary, and executes the fog adjustment. Now, assuming that the fog curve when performing the fog adjustment is L2, for example, in the fog adjustment, the surface potential of the photosensitive drum is changed by 10V and the development bias is changed every 10V, that is, the surface potential and the development. The fog level is examined by changing the relationship with the bias and changing the fog accumulation frequency. Then, the control device compares the obtained fog curve and the reference fog curve in this way, and determines the surface potential and development bias of the fog curve closest to the reference fog curve to obtain the surface potential and development bias after fog adjustment. Will be set as.

  In this way, in the image forming apparatus including the intermediate transfer belt, the fog toner is transferred to the intermediate transfer belt a plurality of times during blank paper printing, that is, the fog is accumulated, and then the fog toner is transferred from the intermediate transfer belt to the recording medium. Therefore, there is an effect that the fog is revealed and the fog can be easily detected.

  Furthermore, since the surface potential and the development bias are set by comparing the predetermined reference fog curve with the fog curve obtained by changing the surface potential and the development bias of the photosensitive drum, the fog is always set. It is possible to obtain a good image with less image quality.

  In the above example, the fog adjustment is performed every predetermined number of printed sheets. However, the fog adjustment may be performed when the driving time of the developing device reaches a predetermined time. The fog adjustment may be performed when an environmental condition such as the above changes beyond a predetermined range. Further, fog detection may be performed for magenta, cyan, and yellow as described above.

  Incidentally, in the color image forming apparatus shown in FIG. 9, when performing fog detection on a color image, fog toner for each color is sequentially transferred to the intermediate transfer belt 51. However, the color image is multicolor. For some reason, the fog is determined by the color. However, since the amount of fog toner is originally very small (that is, the density is very low), it is extremely difficult to know the degree of fog from a color image.

  Therefore, the image forming unit for each color is shifted in the image forming unit for each color by shifting the developing bias application timing so that the tip of the fog toner for each color is transferred to a different position in the transport direction of the intermediate transfer member for each color. Toner is formed on the photoreceptor drum. That is, the photosensitive drum is developed by the developing device in a state in which the photosensitive drum is charged in each color image forming unit and exposure is not performed. At this time, the application timing of the developing bias is shifted, and fog toner is formed on the photosensitive drum for each color as described in the first embodiment. Then, after each color fog toner is transferred to the intermediate transfer belt 51, each color fog toner on the intermediate transfer belt 51 is transferred to a recording medium by the transfer roller 51.

  FIG. 11A is a diagram showing each color fog toner transferred to the recording medium. In this way, when the application timing of the developing bias is shifted for each color, the signs “G1” to “G” in FIG. As indicated by G4 ″, the boundary line for each color clearly appears, and the degree of fog can be clearly determined according to the position of the boundary line. As shown in FIG. 11B, it is preferable that the respective color fog toners are arranged on the intermediate transfer belt 51 in the order of black (BK), yellow (Y), cyan (C), and magenta (M). In this way, the boundary line of each color looks good, and the degree of fog can be determined well.

  Since the fog is revealed using the recording medium by controlling the development bias and / or the transfer bias, the fog can be formed by comparing the fog stripes with the white background without the fog, and the fog state can be easily confirmed. As a result, it can be applied to fog confirmation in an image forming apparatus such as a copying machine or a printer using an electrophotographic system.

It is a schematic block diagram of an example of the image forming apparatus which implements the fog revealing method according to the present invention. 6 is a graph showing a toner charge amount and a toner amount distribution during normal operation and toner deterioration in a general developing device. It is a figure for demonstrating the relationship between a photoreceptor potential, a developing bias, and fog. FIG. 10 is a diagram for explaining a situation where + fogging and −fogging are transferred to a recording medium by forward and reverse transfer bias. It is a figure for demonstrating the fundamental view of the fog realization method which becomes this invention. FIG. 6 is a diagram for explaining a fog revealing method according to the present invention for judging a deterioration state of toner. It is a figure which shows roughly the other example of the image forming apparatus which enforces the fog | texture manifestation method by this invention. FIG. 8 is a diagram illustrating a bias (development bias) and a transfer bias applied to the collection roller in FIG. 7. FIG. 2 is a diagram schematically illustrating an example of an image forming apparatus using an intermediate transfer belt. It is a figure which shows the fog curve which shows the relationship between a fog level and the frequency | count of fog accumulation. FIG. 3 is a diagram illustrating fog toners of respective colors transferred to a recording medium.

Explanation of symbols

+ V _b Development bias -V _T Transfer bias during image formation + V _T Reverse transfer bias

Claims (16)

An image in which a latent image is formed on an image carrier by an electrophotographic method, developed by a developing unit to form a toner image, and then the toner image is transferred directly or indirectly to a recording medium by a transfer unit. Used in forming equipment,
A fog revealing method in an image forming apparatus, characterized by controlling a development bias in the developing means and / or a transfer bias in the transfer means to make fog appear on the recording medium.   2. The fog revealing method according to claim 1, wherein the developing bias in the developing unit is turned on / off.   2. The fog revealing method according to claim 1, wherein the DC developing bias in the developing unit is alternately switched between at least two voltages having different absolute values.   4. The fog revealing method according to claim 2, wherein the developing bias in the developing unit is changed in a stepwise manner.   2. The fog revealing method according to claim 1, wherein the transfer bias in the transfer unit is turned on / off.   2. The fog revealing method according to claim 1, wherein a transfer bias in the transfer unit is alternately switched between a normal transfer bias applied at the time of image formation and a reverse transfer bias having a polarity opposite to the normal transfer bias. A method of revealing fog in an image forming apparatus as a feature.   2. The fog revealing method according to claim 1, wherein the developing bias in the developing unit is turned on / off while being changed stepwise, and the transfer bias in the transfer unit is changed at each time the developing bias is turned on and off. A method of revealing fog in an image forming apparatus, wherein a forward transfer bias applied at the time of image formation and a reverse transfer bias having a polarity opposite to that of the forward transfer bias are alternately switched to be manifested on the recording medium . An image in which a latent image is formed on an image carrier by an electrophotographic method, developed by a developing unit to form a toner image, and then the toner image is transferred directly or indirectly to a recording medium by a transfer unit. Used in forming equipment,
A toner recovery means is disposed between the developing means and the transfer means,
The toner on the image carrier is collected by the collecting means while developing the image carrier by the developing means in a state where the image carrier is charged and not exposed for a predetermined time. When the predetermined time elapses, the toner on the image carrier is transferred to the recording medium by the transfer means while the toner is discharged from the collecting means to the image carrier, and the fog appears on the recording medium. A method of revealing fog in an image forming apparatus, comprising:   9. The fog revealing method according to claim 8, wherein the collecting unit is separated from the image carrier in an image forming mode in which image formation is performed, and is brought into contact with the image carrier in a deterioration measurement mode for measuring a degree of toner deterioration. Thus, the bias voltage is turned on / off, and the forward transfer bias applied to the transfer means at the time of image formation and the reverse transfer bias having the opposite polarity to the forward transfer bias are alternately switched. A method for revealing fog in an image forming apparatus characterized by the above. Each color image forming unit has an image forming unit for each color, and sequentially transfers each color toner image to the intermediate transfer member by each color image forming unit to form a color toner image on the intermediate transfer member. Used in image forming devices that are designed to be transferred to recording media,
The image carrier is developed by a developing means in a state where the image carrier is charged in at least one of the color image forming units and is not exposed to form fog toner on the image carrier, After the step of transferring the fog toner to the intermediate transfer member is executed a plurality of times, the fog toner on the intermediate transfer member is transferred to a recording medium by the transfer means to make fog appear on the recording medium. And a fog revealing method in the image forming apparatus.   11. The fog revealing method according to claim 10, wherein the number of steps is N, and the toner density value when the fog toner transferred onto the recording medium is detected by an image density sensor is divided by N. A method for revealing fog in an image forming apparatus, wherein the obtained result is set to a unit fog level.   12. The fog revealing method according to claim 11, wherein the surface density of the recording medium itself is previously measured by the image density sensor, and a result obtained by subtracting the surface density from the toner density value is set as a fog level. A fog revealing method in an image forming apparatus.   13. The fog revealing method according to claim 12, wherein the fog level is obtained and the fog level is stored in a memory as a reference fog curve while the fog accumulation count is changed with the number of times the step is executed as the fog accumulation count. When the fog adjustment mode for performing the fog adjustment is executed, the surface potential of the image carrier and the developing bias are changed, and the fog accumulation level is changed by changing the fog accumulation number to obtain a plurality of measurement fog curves. The image forming apparatus is characterized in that the measured fog curve and the reference fog curve are compared to set the surface potential and developing bias of the measured fog curve closest to the reference fog curve. Method. Each color image forming unit has an image forming unit for each color, and sequentially transfers each color toner image to the intermediate transfer member by each color image forming unit to form a color toner image on the intermediate transfer member. Used in image forming devices that are designed to be transferred to recording media,
The image carrier is developed by the developing means in a state where the image carrier is charged in each color image forming unit and is not exposed, and fog toner is applied to the image carrier on the intermediate transfer member for each color. The fog toner is formed at different timings so as to be transferred to different positions in the transport direction of the intermediate transfer member, and the fog toner is transferred to the intermediate transfer member for each color, and then the fog on the intermediate transfer member is transferred. A fog revealing method in an image forming apparatus, wherein toner is transferred onto a recording medium by the transfer means to make fog appear on the recording medium.   15. The image forming apparatus according to claim 14, wherein the fog toner is transferred to the intermediate transfer member so as to overlap each other in the order of black, yellow, cyan, and magenta. Fog revealing method. An image carrier that forms a latent image by electrophotography, a developing unit that develops the latent image on the image carrier into a toner image, and a toner image on the image carrier is recorded directly or indirectly. In a fog revealing device in an image forming apparatus having a transfer means for transferring to a medium,
A developing bias power source that supplies a developing bias to the developing unit, a transfer bias power source that supplies a transfer bias to the transfer unit, and a developing bias power source and a transfer bias power source that are controlled to change the developing bias stepwise. / Off control, and control for alternately switching between a forward transfer bias applied at the time of image formation and a reverse transfer bias having a reverse polarity to the forward transfer bias when the developing bias is turned on and off. A fog revealing device in an image forming apparatus, characterized by comprising: a control means for performing the above: and causing fog on the recording medium.

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