JP2005242178A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which implements a means of applying a cleaning bias having the polarity opposite to a developer to a transfer part as a cleaning means for a transfer body, the image forming apparatus being equipped with the transfer body cleaning means which displays excellent cleaning performance even when the electrostatic charge quantity of the developer is high, when the amount of a developer to be cleaned is large, or in low-temperature and low-humidity environment and damages neither an image carrier nor the transfer body. <P>SOLUTION: The image forming apparatus which has an image carrier which has a toner image formed on its surface, the transfer boy whose surface moves facing the image carrier, and a transfer means of applying a transfer bias between the image carrier and transfer body, and cleans the transfer body by applying a cleaning bias for reversely transferring a developer sticking on the transfer body to the image carrier to the transfer means is characterized in that the cleaning time is made variable depending upon specified conditions. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a developer in which a toner image is formed on an image carrier and the toner image is transferred to a transfer material, thereby forming an image on the transfer material and adhering to the intermediate transfer member or the transfer material carrier. The present invention relates to an image forming apparatus that performs cleaning by reversely transferring the toner to an image carrier.

  Conventionally, in an image forming apparatus such as a copying machine, a printer, or a facsimile that forms an image on a transfer material by an electrophotographic method or an electrostatic recording method, a developer image (toner image) is formed on an image carrier, An image is formed through a process of transferring it to a transfer material. In this transfer process, an intermediate transfer body as a second image carrier or a transfer material as a second image carrier is carried. As the transfer material carrier to be transferred, a transfer member such as a belt-shaped member is often used. In addition, there is an image forming apparatus that performs cleaning by electrostatically transferring the unnecessary toner remaining on the transfer body back onto the image carrier. In particular, a device that performs cleaning by applying a constant bias at the time of cleaning is disclosed (for example, see Patent Document 1).

  As a conventional example of such an image forming apparatus, an operation of the image forming apparatus that electrostatically cleans unnecessary toner remaining on the transfer member that is a belt-like member that carries a transfer material that is the second image carrier will be described. To do.

  FIG. 13 shows an example of an image forming apparatus using a four-color full-color electrophotographic system in which four process stations 2 (2a, 2b, 2c, 2d), which are image forming units each having an image carrier, are arranged side by side. A configuration of a so-called inline type image forming apparatus D is shown.

  Each of the process stations 2 (2a, 2b, 2c, 2d) has a photosensitive drum 21 (21a, 21b, 21c, 21d) as an image carrier. At each process station 2, the surface of the photosensitive drum 21 is After being uniformly charged by a primary charger (not shown), an electrostatic latent image is formed by exposure based on image information by an exposure device (not shown) such as an LED or a laser. The electrostatic latent image is developed as a developer image (toner image) by a developer (not shown) to which each color developer (toner) determined for each process station 2 is attached.

  Each process station 2 can be attached to and detached from the image forming apparatus D main body (not shown) as a process cartridge PC. Each process cartridge PC has a configuration in which a photosensitive drum 21, a primary charger, a developing device, and a cleaning unit (not shown) are integrated.

  Referring to FIG. 13, in the case of the image forming apparatus D, the transfer material P is fed into the image forming apparatus D from the sheet feeding cassette 18 by the sheet feeding roller 14, conveyed to the registration roller 13 and the registration counter roller 10, and then The transfer belt 1 of the transfer material carrier is electrostatically adsorbed and carried by the suction roller 15 to which a positive suction bias is applied from the suction bias power source 12.

  In the image forming apparatus D, the transfer belt 1 is wound around four rollers, that is, a driving roller 7, a suction counter roller 6, and tension rollers 8 and 9, along the moving direction of the transfer belt 1 (arrow R <b> 1 direction). The process stations 2a, 2b, 2c, and 2d for black, magenta, cyan, and yellow are arranged in series in this order from the upstream.

  The transfer material P adsorbed to the transfer belt 1 sequentially passes through the process stations 2a to 2d of the respective colors, and the toner images of the respective colors on the photosensitive drum 21 are electrostatically transferred sequentially. Thereafter, these toner images are heated and pressed by the fixing device 16 to be fixed on the transfer material P, thereby forming a permanent image.

  After completing a series of operations in this image forming process, the photosensitive drum 21 is cleaned by the cleaning means in the process station 2, and the transfer belt 1 is discharged by the charge removing charger 11 to prepare for the next image forming process.

  Since the above-described transfer belt 1 does not normally carry a toner image directly on the surface, it is rarely contaminated with toner. However, the transfer belt is used in the case of using a system in which a registration mark or a density detection pattern is formed directly on the transfer belt 1 and detected when a background fog toner adheres to a non-image portion or the like. The toner adheres directly to the surface 1.

  In order to remove this, a separate cleaning device 17 can be provided. Here, a method of applying a cleaning bias to the transfer blade 3 (3a, 3b, 3c, 3d) constituting the transfer means will be described.

  In the transfer process, the toner image is transferred from the photosensitive drum 21 to the transfer material P by a transfer blade 3 (3a, 3b, 3c, 3d) which is a transfer unit provided so as to sandwich the transfer belt 1 therebetween. Has been transcribed. The transfer blade 3 is generally made of a low-resistance resin film as a material and is in contact with the photosensitive drum 21 in each process station 2 via the transfer belt 1. When transferring a toner image to a transfer material, A transfer bias is applied from the transfer bias power supplies 4a, 4b, 4c, and 4d.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, for example, a developing device including a negative organic photoreceptor as the photosensitive drum 21 and a negative toner as a developer is used. Accordingly, the transfer blade 3 is applied with a positive transfer bias by the transfer bias power source 4 at the time of transfer.

  The transfer blade 3 functions as a part of the transfer unit as described above, but also functions as a cleaning unit for the transfer belt 1. In the case of the image forming apparatus D, when the transfer belt 1 is cleaned, the bias applied to the transfer blades 3a and 3c disposed first and third in the moving direction of the transfer belt 1 among the four transfer blades 3 is bias switching. Switches from positive to negative by the switches 5a and 5c. That is, the power source connected to the transfer blades 3a and 3c is switched from the power source 4a and 4c to which the positive polarity bias is applied to the power source 4A and 4C to which the negative polarity bias is applied by the bias changeover switches 5a and 5c. For each of the transfer blades 3a, 3b, 3c, and 3d, as a cleaning bias, for example, negative, positive, negative, and positive are applied in this order from the upstream station, and the toner adhered on the transfer belt 1 is applied to the photosensitive drum 21. Proposals have already been made to remove the residual toner on the transfer belt 1 by efficiently performing reverse transfer.

  More specifically, for example, a cleaning bias (main cleaning bias) that forms an electric field opposite to that at the time of transfer is applied to the transfer blades 3a and 3c of the transfer blade 3 from the power sources 4A and 4C, and normal polarity toner is applied to the photosensitive drum 21. In addition, a cleaning bias (sub-cleaning bias) having the same polarity as that at the time of transfer is applied to the transfer blades 3b and 3d from the same power source 4b and 4d as at the time of transfer, and toner having a reverse polarity is reversed to the photosensitive drum 21. The toner deposited on the transfer belt 1 is removed to the photosensitive drum of each station.

  However, in the case of the cleaning means as described above, an effective cleaning performance can be maintained with a toner having a relatively low charge amount (for example, −5 to −30 μC / g). If the charge amount of the toner to be used is high, a sufficient effect may not always be obtained. For this reason, it may be necessary to increase the cleaning time, and there is a concern that problems such as deterioration of the image forming member may occur.

  Another factor that is difficult to clean is the environmental factor of the atmosphere in which the apparatus is placed. For example, in a low-temperature and low-humidity environment, cleaning is difficult compared to a normal temperature and normal humidity or high-temperature and high-humidity environment. This is because, in the low temperature and low humidity environment, as described above, the charge amount of the toner tends to increase, and the resistance of the portion to which the cleaning bias is applied increases, so that the current necessary for cleaning becomes difficult to flow. is there.

  Further, by setting the peripheral speed of the transfer belt 1 faster than that of the photosensitive drum 21 with respect to toner having a high charge amount (for example, −40 to −80 μC / g) that cannot be removed only by applying the cleaning bias as described above. In addition, it has been proposed to more efficiently clean the transfer belt 1.

However, in this case, it is necessary to drive the transfer belt 1 by a drive source different from the photosensitive drums 21a to 21d, which leads to an increase in cost. In addition, wear deterioration due to rubbing due to increase in the speed of the transfer belt 1 and the photosensitive drum 21 may occur, and thus the life of the photosensitive drum 21 may be shortened.
JP 2002-23512 A JP-A-2-123385

  An object of the present invention is to develop a transfer unit as a cleaning unit for a second image carrier to which a developer image is transferred from an image carrier or a transfer material carrier that transports the second image carrier. In an image forming apparatus that implements means for applying a cleaning bias having a polarity opposite to that of the agent, good cleaning properties can be obtained even when the charge amount of the developer is high, the developer amount to be cleaned is large, or even in a low temperature and low humidity environment. An object of the present invention is to provide an image forming apparatus provided with a transfer body cleaning means that is low cost and does not damage the image carrier or transfer body.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to an image carrier on which a toner image is formed on the surface, a transfer body whose surface moves opposite to the image carrier, and a transfer between the image carrier and the transfer body. A transfer means for applying a bias, and cleaning the transfer body by applying a cleaning bias that reversely transfers the developer attached to the transfer body onto the image carrier. In the image forming apparatus,
An image forming apparatus is provided, wherein the cleaning time is variable based on a predetermined condition.

  According to an embodiment of the present invention, the apparatus further includes an environment detection unit that detects an environment in which the apparatus is installed, and the cleaning time is made variable based on a detection result of the environment detection unit. Is a temperature inside the apparatus, and the cleaning time is often set longer than when the temperature inside the apparatus is lower than the predetermined temperature, based on the temperature detection result of the environment detection means.

  According to another embodiment of the present invention, the apparatus further includes a use history storage unit for storing a use history of the apparatus, and the cleaning operation time is made variable based on information in the use history storage unit, and is executed at that time. When the number of image formations is greater than a predetermined number, the cleaning time is often set longer than when the number of image formations is less than the predetermined number.

  According to another embodiment of the present invention, there is further provided impedance detection means for detecting impedance in the transfer portion to which the transfer bias is applied, and the cleaning time is made variable based on the detection result of the impedance detection means. At that time, when the impedance of the transfer portion is larger than a predetermined value, the cleaning time is often set longer than when the impedance is smaller than the predetermined value.

  According to another embodiment of the present invention, the cleaning bias is variable based on the predetermined condition.

  According to another embodiment of the present invention, the transfer member is a transfer material carrier that conveys a transfer material to a portion facing the image carrier, and the toner is applied to the transfer material that is conveyed by the transfer agent carrier. An image is transferred, or the transfer body is an intermediate transfer body to which the toner image is transferred from the image carrier, and the toner image transferred to the intermediate transfer body is transferred to a transfer material. .

  The image forming apparatus of the present invention applies an image bearing member on which a toner image is formed on a surface, a transfer member whose surface moves opposite the image bearing member, and a transfer bias between the image bearing member and the transferring member. In an image forming apparatus that cleans a transfer body by applying a cleaning bias that reversely transfers the developer adhered to the transfer body onto the image carrier. Since the cleaning time is made variable based on the above, the cleaning time of the apparatus can be arbitrarily changed, the optimum cleaning time can be selected, and in a condition with good cleaning properties, the cleaning can be performed with a small cleaning time, and the image forming member It is also possible to prevent harmful effects such as deterioration of the product.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
The image forming apparatus A shown in the schematic configuration diagram of FIG. 1 is a so-called in-line four-color full-color image forming having process stations 2a to 2d which are four image forming units that form toner images of different colors. Device.

  The image forming apparatus A includes a conveyance belt 1 (transfer belt) that is a transfer material carrier. The steps from when the transfer material P is fed to when it is transferred, fixed and discharged are the same as those of the conventional image forming apparatus shown in FIG.

  As a method for collecting the toner adhering to the belt 1 described above, in this embodiment, among the transfer rollers 3 constituting the transfer means similar to the conventional example, for example, the transfer rollers 3b and 3d are biased by switches 5b and 5d. A power source for applying a bias to the transfer rollers 3b and 3d is changed from a power source (transfer bias power source) 4b, 4d for applying a positive bias at the time of transfer to a power source (main cleaning bias power source) 4B, 4D for applying a reverse polarity bias. By switching, for example, −2.5 kv is applied as a cleaning bias (main cleaning bias) that forms an electric field opposite to that at the time of transfer, and toner of normal polarity is reversely transferred to the photosensitive drums 21b and 21d.

  Further, for example, +1 kv is applied as a cleaning bias (sub-cleaning bias) having the same polarity from the power sources 4a and 4c at the time of transfer to the transfer rollers 3a and 3c, and reverse polarity toner is reversely transferred to the photosensitive drums 21a and 21c.

  The toner reversely transferred to the photosensitive drum 21 is collected as waste toner in a waste toner container 26 (26a, 26b, 26c, 26d) constituting an image carrier cleaning means in the process station 2 as an image forming unit. Like to do.

  The transfer belt 1 is cleaned by the operation as described above. When the cleaning mode is provided, the distance from the rotation of the transfer belt 1 to the position where the transfer rollers 3a to 3d are installed, that is, the most upstream in the moving direction of the belt 1. The main cleaning bias and the sub-cleaning bias can be applied to the entire surface transfer area of the transfer belt 1 by rotating more than the rotation distance obtained by adding the distance to the transfer roller 3 installed on the most downstream side. All the unnecessary toners on the transfer belt 1, that is, the normal polarity toner and the opposite polarity toner can be reversely transferred to the photosensitive drum 21 and collected by the cleaning means 26 in the process station 2.

  In the present invention, the transfer belt 1 can be sufficiently cleaned in a minimum time.

  In this embodiment, environment detection means (environment detection sensor) (not shown) for detecting the atmosphere in which the apparatus is installed is mounted in the image forming apparatus, and when executing the cleaning mode, the environment detection sensor Based on the detection result, the optimum cleaning time is obtained and the cleaning operation is executed.

  Here, in this image forming apparatus, the rotation speeds of the transfer belt 1 and the photosensitive drum 21 are the same and are always constant during cleaning. This is because, conventionally, a method of increasing the cleaning effect by making the rotation speeds of the two different from each other has been implemented, but problems such as damage due to friction between the two have occurred.

  Therefore, when the cleaning time is a time for applying a cleaning bias to a certain region of the belt 1, as a method for increasing the cleaning time, a method for increasing the cleaning time for one rotation of the belt 1 by slowing the rotation of the belt 1 is used. In this case, the belt 1 is rotated many times and the cleaning bias is continuously applied during that time, whereby the belt is cleaned a plurality of times to increase the total cleaning time.

  That is, the cleaning time is the belt rotation speed when the cleaning bias is applied.

  The time when the cleaning bias is rotated once is the time during which the belt 1 travels the distance between the transfer rollers 3a and 3d installed at the most upstream and the most downstream in one rotation and the belt rotation direction. Say. The cleaning time is set to be at least longer than the time for rotating the belt one rotation and the distance between the transfer rollers 3a and 3d (one rotation).

  In this way, the toner at all positions on the belt 1 can pass through the process stations 2a to 2d where cleaning is performed n times during the belt n rotation time. The cleaning effect can be obtained.

  In other words, the time for the belt n round is (time for one belt rotation and the distance traveled between the transfer rollers 3a to 3d) × n time.

  An outline of the cleaning operation in the cleaning mode in this embodiment in which the cleaning time is selected according to the environment will be described with reference to FIG.

  step 1: The cleaning control is started.

  Step 2: The environment where the apparatus is installed is detected by the environment detection sensor.

  Step 3: Determine whether the temperature T is 20 ° C. or higher as a result of detection by the environment detection sensor.

  Step 4: When T is 20 ° C. or more, the cleaning operation, that is, the application of the cleaning bias is started in Step 4, and then the belt is rotated once, and the cleaning bias is applied for that time.

  Step 5: If T is less than 20 ° C., the cleaning operation, that is, the application of the cleaning bias is started in Step 5, and then the belt is rotated twice, and the cleaning bias is applied for that time.

  Step 6: After performing Step 4 or Step 5, the cleaning control is terminated at Step 6.

  That is, in this embodiment, in Step 3, it is determined whether or not the installation environment of the apparatus is a low temperature and low humidity environment, and if it is a low temperature and low humidity environment, the cleaning time is longer than that in a normal temperature normal humidity environment or a high temperature high humidity environment. To make it longer.

  In the above process shown in FIG. 2, the effect of changing the circumferential rotation speed of the belt during the cleaning time, that is, the time during which the cleaning bias is applied, according to the environmental temperature will be described.

  First, the graph shown in FIG. 3 shows the cleaning property of the transfer belt 1 at each environmental temperature.

  That is, the graph line HH in FIG. 3 indicates an environment of 32.5 ° C., the graph line NN indicates an environment of 23 ° C., and the graph line LL indicates an environment of 15 ° C. This evaluation is based on the amount of toner remaining on the belt 1 when a single-color solid pattern is printed on the transfer belt 1 and the belt 1 is rotated and cleaned while applying a cleaning bias to the transfer roller 3. FIG. 6 is a graph plotting values obtained by measuring a density (residual density) (OD) of a residual image of a toner image with a densitometer RD918 manufactured by Macbeth. This value is indicated by the difference from the density detected for the belt in which no toner image is formed.

  Here, as the cleaning bias, a main cleaning bias of −2.5 KV is applied to the transfer rollers 3b and 3d of the second and fourth stations, and the transfer rollers 3a and 3c of the first and third stations are applied to the transfer rollers 3b and 3d. A sub-cleaning bias of +1.0 KV is applied.

  The toner reversely transferred onto the drum 21 is collected in a waste toner container 26 provided in the station 2 together with each drum 21. In this way, the toner on the belt 1 is cleaned.

  As shown in FIG. 3, the remaining density on the belt 1 decreases as the number of rotations of the belt 1 increases, that is, as the time for applying the cleaning bias increases. This is because a large amount of toner on the belt 1 is reversely transferred to the drum 21 of each station 2 by the cleaning bias.

  That is, it became clear that the cleaning effect is improved by increasing the cleaning time.

  Here, the cleaning on the belt 1 can be performed regardless of the environment, the toner loading amount, and the toner charge amount. The effect of this embodiment for each situation will be described.

  (1) Low temperature and low humidity environment: From the results shown in FIG. 3, it can be seen that the toner on the belt 1 is easy to clean in a high temperature environment and difficult to clean in a low temperature environment. This is because the toner is strongly attached to the belt 1 because the charge amount of the toner is high under the low temperature environment of LL. Further, under a low temperature environment, the resistance of the transfer belt 1 and the transfer roller 3 that are members to which the cleaning bias is applied becomes high, so that the current for reversely transferring the toner to the drum 21 is insufficient.

  As a countermeasure, if a high voltage is used as the cleaning bias, the effect of cleaning the toner on the belt 1 is increased, but the following problems occur.

  That is a problem of drum memory. This problem is that when a high cleaning bias is applied, a large amount of current flows through the drum 21, which affects the charge generation layer and the charge transport layer of the drum 21. If the current flows excessively in the drum 21, it becomes impossible to charge to a desired potential during image formation or to obtain an exposure potential obtained during exposure. Then, a defect that causes the image density to become non-uniform in a halftone image or the like occurs.

  Therefore, in this embodiment, a voltage in a range where no drum memory is generated is used. Specifically, the main cleaning bias is set to -2.5 KV, and the sub-cleaning bias is set to +1.0 KV. The cleaning performance is improved by increasing the number of rotations of the belt 1 and extending the cleaning time without increasing the voltage and preventing the occurrence of the above.

  (2) Toner loading amount: When the belt 1 cleaning time is lengthened, a large amount of toner can be removed without using a cleaning blade.

  That is, by performing a blade cleaning method in which the blade-like member is brought into contact with the belt 1 and the belt 1 is moved to scrape off the toner on the belt 1 by a transfer member cleaning method other than the above-described method. Thus, since the toner remaining on the belt 1 is mechanically scraped off, for example, even if there is a solid image with a large amount of load on the belt 1, it can be cleaned without any problem.

  However, since the belt 1 moves in contact with the fixed blade, there is a problem that the belt 1 and the blade are rubbed and the both members are easily damaged.

  Therefore, in the method of applying the bias of this embodiment and electrostatically cleaning, when the amount of toner loaded on the belt 1 is large, for example, in the case of a solid image, the cleaning time is lengthened. We decided to solve this problem.

  In the method of electrostatically returning the toner on the belt 1 to the drum side as in this embodiment, when the cleaning bias is applied, the toner is recovered from the toner on the surface layer side of the belt 1. In the electrostatic cleaning method as in the present embodiment, in the case of a solid image in which two to three layers of toner are formed on the belt 1, since it is gradually returned from the surface layer to the drum 21 side by an electric field, it takes a long time. Need to clean.

  (3) Toner charge amount: When the charge amount of the toner on the belt 1 is low, the toner on the belt 1 is discharged by applying a cleaning bias so that the toner is charged and then cleaned. become. In this case, the toner can be charged only on the surface layer side to be discharged. Therefore, when a solid image formed with two or three layers of toner is on the belt 1, first, the surface toner is firmly charged to clean the surface toner.

  That is, by supplying a cleaning bias while the belt 1 rotates a plurality of times, the toner in the lower layer appears on the surface, so that the toner in the lower layer can also be discharged and charged. it can. Since the lower layer toner can be charged as described above, it can be cleaned.

  As described above, in any situation, the toner on the belt 1 can be cleaned by lengthening the cleaning time. As a feature of this embodiment, the cleaning time is changed according to the environment. It is done.

  In a low temperature environment where cleaning is difficult, a longer cleaning time is required than in a normal temperature or high temperature environment. Therefore, in this embodiment, the cleaning time can be selected in Step 3 in the cleaning process shown in FIG. The cleaning time is set to one round of the belt under high temperature and high humidity and normal temperature and normal humidity, whereas the cleaning time is set to twice as the number of belt rotations under a low temperature environment.

  Assuming that the number of belt revolutions is 2, as is apparent from the graph of FIG. 3, the residual toner density on the belt 1 can be 0.05 or less even under low temperature and low humidity. If the residual density on the belt is 0.05 or less, even if the paper is carried during the actual printing operation, the back of the paper will not be stained and there is no problem.

  Here, if the cleaning bias is applied for the same amount of time regardless of the environment where the device is installed, that is, if the belt is cleaned for the same amount of time in a low temperature and low humidity environment in all environments, Below, cleaning will be wasted for a long time.

  According to the present embodiment, the optimum cleaning time can be selected depending on the environment. Therefore, the cleaning time at room temperature or high temperature can be shortened, and the cleaning time can be minimized.

Example 2
The schematic configuration of the image forming apparatus according to the present embodiment is the same as that of FIG. 1 described in the first embodiment, and the operation from when the transfer material P is fed to when it is fixed and the operation at the time of cleaning are the same. is there. Therefore, the description of the same parts as those in the first embodiment is omitted.

  In this embodiment, the ability to sufficiently clean the transfer belt 1 in a minimum time can be obtained.

  In this embodiment, a usage history storage unit (memory) 101 for storing the usage history of the apparatus is installed in a part of the control unit 100 of the image forming apparatus shown in the block diagram of FIG. Specifically, the memory 101 stores the accumulated number of prints (total number of prints), which is the number of times the image has been formed. When executing the cleaning mode, the CPU 102 determines the accumulated print number of the apparatus. Based on this, an optimum cleaning time is obtained and transmitted to the power supply driving circuit 103 that drives the power supply operation in the apparatus, the transfer bias power supply 4 is operated, and the cleaning operation is executed.

  The cleaning operation will be described with reference to the flowchart of FIG.

  Step 1: Cleaning control is started.

  Step 2: Read the total print number P stored in the apparatus memory 101.

  Step 3: It is determined whether or not the total print number P is less than 30K.

  Step 4: If P is less than 30K sheets, the cleaning bias is applied for the time that the belt rotates once after the cleaning operation, that is, the cleaning bias is applied in Step 4.

  Step 5: If P is 30K or more, the cleaning operation, that is, the cleaning bias is applied for the time that the belt rotates twice after starting the cleaning bias application in Step 5.

  Step 6: After performing Step 4 or Step 5, the cleaning control is terminated at Step 6.

  That is, in this embodiment, in Step 3, it is determined whether or not the total number of printed sheets P, that is, the number of image formations is equal to or greater than a predetermined number.

  The effect of changing the cleaning time according to the total number of printed sheets in the above-described process shown in FIG. 5 will be described.

  Here, the graph shown in FIG. 6 shows the total number of prints (durable number) that is the number of image formations of the apparatus and the cleaning property of the transfer belt 1. Similar to FIG. 3, this evaluation is performed by printing a solid pattern on the transfer belt 1, and when the belt 1 is cleaned while applying a cleaning bias to the transfer roller 3, the density in the toner image remaining on the belt 1. It is the figure which plotted the value which measured (residual density | concentration) (OD) with the densitometer RD918 by Macbeth.

  As can be seen from FIG. 6, the cleaning performance deteriorates as the number of printed sheets increases. This is because when the apparatus is used and printing is repeated, the surface of the belt 1 is damaged and becomes uneven, or paper dust adheres to it, so that the releasability of the belt 1 is reduced, and the toner on the belt 1 This is thought to be due to an increase in the adhesive strength of the slag. Accordingly, the cleaning performance is maintained by extending the cleaning time while the printing durability of the apparatus is advanced.

  In this embodiment, when the number of prints is less than 30K, the cleaning time is set to one rotation of the belt 1, and when the number of prints exceeds 30K, the number of belt rotations is set to two. Here, the definition of the rotation speed of the belt is the same as that described in the first embodiment.

  By setting the cleaning time to two rotations of the belt 1, as is apparent from the graph of FIG. 6, the residual toner density on the belt can be made 0.05 or less. If the remaining density on the belt 1 is 0.05 or less, even if the paper is carried during the actual printing operation, the back of the paper is not contaminated and there is no problem.

  That is, it became clear that the cleaning effect is improved by increasing the cleaning time.

  As described in the first embodiment, the cleaning time is reduced even in a situation where the cleaning property is deteriorated, for example, in a low-temperature and low-humidity environment, a large amount of toner loaded on the belt 1 or a low charge amount of toner. By increasing the length, the belt 1 can be cleaned satisfactorily by applying a cleaning bias to the transfer roller 3. However, in this embodiment, the cleaning time is changed according to the total number P of prints.

  Here, if the cleaning bias is applied for the same time regardless of the usage history of the apparatus, that is, even if the total number of printed sheets P is small, if the belt cleaning is performed for the same time as after the endurance, the apparatus will be much more durable. If not, cleaning is wasted for a long time.

  According to the present embodiment, since an optimal cleaning time can be selected according to the usage history of the apparatus main body, the cleaning time when the apparatus is not used and the durability is not advanced so much is shortened, and the execution time of the cleaning mode is shortened. It became possible.

Example 3
The schematic configuration of the image forming apparatus according to the present embodiment is almost the same as that of FIG. 1 described in the first embodiment, and the operation from when the transfer material P is fed to when it is fixed, and also the operation at the time of cleaning. It is the same. Therefore, the description of the same parts as those in the first embodiment is omitted.

  In this embodiment, the ability to sufficiently clean the transfer belt 1 in a minimum time can be obtained.

  In this embodiment, in each image forming apparatus, a photosensitive drum 21 on which a toner image is formed and a transfer unit when a transfer bias is applied between the photosensitive drum 21 and the transfer material P for each process station 2. The cleaning operation time described in the first embodiment is made variable based on the detection result of the impedance detection means. The impedance at the transfer portion is the impedance of the transfer bias applied from the transfer roller 3 between the photosensitive drum 21 and the transfer material P, and most is the total impedance of the transfer roller 3 and the belt 1.

  The cleaning operation will be described with reference to the flowchart of FIG.

  Step 1: Cleaning control is started.

  Step 2: Impedance is detected at the transfer part.

  Step 3: Determine whether the impedance is small from the detection result.

  Step 4: If the impedance is small, the cleaning bias is applied for the time that the belt rotates once after the cleaning operation, that is, the application of the cleaning bias is started in Step 4.

  Step 5: If the impedance is large, a cleaning bias is applied for the time that the belt rotates twice after starting the cleaning operation, that is, applying the cleaning bias in Step 5.

  Step 6: After performing Step 4 or Step 5, the cleaning control is terminated at Step 6.

  Here, the impedance detection method performed in Step 2 will be described.

  In this embodiment, impedance detection is performed by so-called ATVC control. In ATVC control, a voltage as shown in FIG. 8 is applied to the transfer roller 3 to determine the transfer bias. That is, the transfer bias is a voltage determined by applying a constant current for a predetermined time T1 by constant current control when the transfer material P is not present on the transfer roller 3, and calculating from a voltage generated at that time by a preset control equation. This is a method of applying a value when the transfer material P is present, and is a so-called control method disclosed in Patent Document 2. In the present embodiment, since each process station 2 uses the same transfer roller 3, impedance detection is performed at the first process station 2a, and the detected impedance is detected by the other process stations 2b, 2c, Consider the same impedance as in 2d.

  In this embodiment, the transfer bias at the time of cleaning is also determined using the result of the ATVC control used when determining the transfer bias at the time of printing.

  Specifically, the constant current control of 3.5 μA flowing through the transfer roller 3a of the first station 2a is performed for the time that the transfer roller 3a rotates once, and the average voltage at that time is obtained.

  When the average voltage is less than 1.5 KV, it is determined that the impedance in the transfer portion is small, and the time cleaning operation for one round of the belt 1 is executed.

  When the average voltage is 1.5 KV or more, it is determined that the impedance is large, and a time cleaning operation for two rounds of the belt 1 is executed.

  As described above, the effect of changing the cleaning time based on the impedance detection result will be described.

  The graph shown in FIG. 9 shows the impedance (Vto (V)) at the transfer portion and the cleaning performance of the belt 1. In this evaluation, a solid pattern was printed on the transfer belt 1 and the residual density (OD) on the belt 1 when the belt 1 was rotated while applying a cleaning bias to the transfer roller 3 was manufactured by Macbeth. It is the figure which plotted the value measured with densitometer RD918.

  As can be seen from FIG. 9, when the impedance Vto at the transfer portion increases, the cleaning performance deteriorates. This is because when the impedance of the belt 1 or the transfer roller 3 is increased, the transfer current necessary for cleaning is insufficient and cleaning becomes difficult. Therefore, when the impedance at the transfer portion is large, the cleaning property is maintained by setting the cleaning time longer.

  In this embodiment, when the impedance is detected to be small, the number of laps is one, and the number of belt laps where the impedance is detected is two.

  Accordingly, as can be seen from the graph of FIG. 9, the residual toner density (OD) on the belt can be made 0.05 or less. If the residual density on the belt is 0.05 or less, even if paper as a transfer material is carried during an actual printing operation, the back of the paper is not contaminated and there is no problem.

  As described in the first embodiment, the cleaning time is reduced even in a situation where the cleaning property is deteriorated, for example, in a low temperature and low humidity environment, a large amount of toner loaded on the belt 1 or a low amount of toner charge. The belt 1 can be satisfactorily cleaned by applying a cleaning bias to the transfer roller 3 by increasing the length, but this embodiment is characterized in that the cleaning time is changed according to the impedance in the transfer portion.

  Here, if the cleaning bias is applied for the same time regardless of the impedance at the transfer portion, that is, even when the impedance of the transfer roller 3 or the belt 1 is low, the belt is cleaned in a high impedance state with poor cleaning properties. If this is done, cleaning is wasted for a long time when the resistance of the belt 1 and the transfer roller 3 is low.

  The reasons why the resistances of the transfer roller 3 and the belt 1 are varied include manufacturing variations, resistance UP due to use, and influence of the use environment.

  As described above, according to the present embodiment, by performing impedance detection at the transfer portion, an optimum cleaning time can be selected in various cases, so that the cleaning time when the impedance is small can be shortened. Became.

  Note that this impedance detection is not necessarily performed immediately before cleaning, and the main body may store the final impedance detection result before cleaning and may be performed based on the detection result. By doing in this way, the time which performs the impedance detection at the time of cleaning can be shortened.

Example 4
The schematic configuration of the image forming apparatus according to the present embodiment is the same as that of FIG. 1 described in the first embodiment, and the operation from when the transfer material P is fed to when it is fixed and the operation at the time of cleaning are the same. is there. Therefore, the description of the same parts as those in the first embodiment is omitted.

  In this embodiment, the ability to sufficiently clean the transfer belt 1 in a minimum time can be obtained.

  In this embodiment, in the cleaning mode, the cleaning time is adjusted by the impedance at the transfer portion as described in the third embodiment, and further, a process for cleaning a large amount of toner remaining on the belt 1 is performed here. A cleaning bias applied at the stations 2b and 2d to reversely transfer the toner on the belt 1 to the photosensitive drum 2 is determined. In particular, a bias for reversely transferring a large amount of positive toner, that is, a main cleaning bias is determined. It is what.

  The impedance detection method is the same as the method described in the third embodiment, and a description thereof will be omitted.

  Next, FIG. 10 showing an outline of an operation flow for changing the cleaning bias based on the impedance detection result, which is a feature of the present embodiment, will be described.

  Step 1: Cleaning control is started.

  Step 2: Impedance detection between the transfer roller 3 and the transfer belt 1 is performed.

  Step 3: It is determined whether or not the impedance is small based on the detection result in Step 2.

  Step 4: When the impedance is small, the cleaning bias Vtc1 is applied for a predetermined time Ta at Step 4.

  Step 5: When the impedance is large, the cleaning bias Vtc2 is applied for a predetermined time Tb in Step 5.

  Step 6: After performing Step 4 or Step 5, the cleaning control is terminated at Step 6.

  Next, the effect of changing the cleaning bias based on the impedance detection result will be described.

  Here, the graph shown in FIG. 11 shows the main cleaning bias Vtc, the total impedance Vto of the transfer belt 1 and the transfer roller 3, and the cleaning performance of the belt 1.

  This evaluation is performed on the belt 1 when the belt is rotated while a cleaning bias is applied to the transfer roller 3 in a state where a 100% solid image of two colors is placed on the transfer belt 1 to form a 200% solid pattern. 6 is a graph plotting values obtained by measuring the density of an afterimage due to the toner remaining on the surface with a densitometer RD918 manufactured by Macbeth.

  As apparent from FIG. 11, when the total impedance Vto of the belt 1 and the transfer roller 3 is increased, the cleaning performance is deteriorated, and the cleaning performance is improved by increasing the cleaning bias Vtc. The remaining toner amount is low.

  This is because when the impedance of the belt 1 and the transfer roller 3 increases, the transfer current necessary for cleaning becomes insufficient and cleaning becomes difficult. However, by increasing the cleaning bias, the toner on the belt 1 is transferred to the drum 21. This is because a transfer current sufficient for reverse transfer can be obtained.

  Therefore, when the amount of toner on the belt 1 is large or the impedance of the transfer roller 3 is large, the cleaning performance is further improved by extending the cleaning time and applying a larger cleaning bias.

  In this embodiment, when it is detected that the impedance is small at Step 4, the cleaning time Ta is set to one rotation and the cleaning main bias is set to -2.5 KV.

  If the impedance is detected to be large at Step 5, the cleaning time Tb is set to twice as the belt rotation speed, and the cleaning main bias is set to -3.5 KV.

  As a result, even when there is a 200% solid pattern on the belt and the impedance between the photosensitive drum 21 and the transfer belt 3 is high, cleaning is performed for a long time using a high cleaning bias. Thus, the residual density on the belt 1 could be reduced to 0.05 or less (FIG. 11). If the residual density on the belt is 0.05 or less, even if the paper is carried during the actual printing operation, the back of the paper will not be stained and there is no problem.

  As a possibility that a 200% solid image is placed on the belt 1 and needs to be cleaned, a secondary color patch for adjusting the registration between the stations 2 is formed on the transfer belt 1 and the patch is formed. In the image forming apparatus using the intermediate transfer belt as described in the sixth embodiment, for example, when JAM occurs during printing of a secondary solid blue color formed with magenta solid and cyan solid, for example. Etc. are considered.

  As described above, according to the present embodiment, when there is a 200% solid image on the belt and the conditions for degrading cleaning properties such as low impedance are overlapped, the optimum cleaning time in various cases is obtained. Since it can be selected, the cleaning time can be shortened.

  Note that the method of increasing the main cleaning bias described in the present embodiment to improve the cleaning performance is the same as that described in the first and second embodiments in the configuration where the cleaning time is extended under the conditions of the low temperature and low humidity environment and the total number of prints. This can be applied by increasing the main cleaning bias when extending the cleaning time.

Example 5
The schematic configuration of the image forming apparatus according to the present embodiment is the same as that of FIG. 1 described in the first embodiment, and the operation from when the transfer material P is fed to when it is fixed and the operation at the time of cleaning are the same. is there. Therefore, the description of the same parts as those in the first embodiment is omitted.

  In this embodiment, the ability to sufficiently clean the transfer belt 1 in a minimum time can be obtained.

  In the present embodiment, in the cleaning mode, the cleaning time is adjusted by the impedance at the transfer portion as described in the third embodiment, and the toner on the belt 1 is transferred to the photosensitive drum 2 as in the fourth embodiment. In this embodiment, the main cleaning bias is determined, and further, the sub-cleaning bias applied at the process stations 2a and 2c for reverse transfer of the reversal toner is determined in this embodiment. It is a feature to change. The sub-cleaning bias is a + bias for reversely transferring the toner on the drum 1, that is, the toner charge is reversed on the belt 1.

  In this embodiment, the high voltage applied to the transfer rollers 3 of the first and third stations 2a and 2c to which + is applied during the cleaning operation has a constant current circuit. By doing so, a low voltage is applied when the impedance is high, and a high voltage is applied when the impedance is large.

  By making the + cleaning bias automatically change depending on the impedance, the following effects can be obtained.

  That is, the problem of drum memory and fog that occurs during image formation is solved. This problem occurs due to the influence of the charging ability of the drum 21 when a large amount of positive current flows through the drum when the impedance is low. That is, a large amount of positive transfer current flows to the drum 21, which affects the charge generation layer and charge transport of the drum 21, and makes it impossible to charge the drum 21 to a desired −potential during image formation. is there.

  If the drum 21 has a + memory, it cannot be charged to a desired −potential, so that the halftone density becomes high or fog occurs.

  In this embodiment, since the bias current value applied at the process stations 2a and 2c is made constant by the sub-cleaning bias, it is possible to prevent an excessive cleaning current from being applied when the impedance is small. The occurrence of defective images due to the drum memory can be prevented without depending on the impedance.

  In this embodiment, the sub-cleaning bias is not limited to the impedance and is kept constant at +2.5 μA.

  Table 1 shows the relationship between the impedance detection result Vto, the sub-cleaning bias (+), the drum memory, and the fog.

  In the comparative example, in the image forming apparatus having the same configuration as that of the present embodiment, the sub-cleaning bias is changed to +500 V, +1000 V, and +2000 V after the impedance of each transfer unit.

  In the evaluation of the drum memory and fog, the main cleaning bias is kept constant at −2.5 (KV), the voltage value of the sub cleaning bias (+) is changed, and the halftone image is printed immediately after executing the cleaning mode. This is an evaluation of drum memory and fogging.

  The drum memory measures the halftone density, and if it is measured darkly, the drum memory is generated. The normal density of the halftone used in this evaluation is 0.7, ◯ when the image density of 0.7 ± 0.2 is measured, and Δ when the density is 0.9 to 1.0 higher. The case where the density was 1.0 or higher was determined as x.

  On the actual paper, the level of fog was determined as ◯ (less than 2%), the level that was faintly determined as Δ (2-4%), and the level that was severely recognized as x (5% or more).

The paper used was XEROX 4024 with a basis weight of 75 g / m ² . The fog measurement is measured by DENSOMETER TC-6DS (manufactured by Tokyo Denshoku). As a reference, it is a difference value from the value obtained by measuring the non-image portion on the paper when the reflectance of the paper not to be printed is obtained.

  As can be seen from Table 1, in the comparative example, when the sub-cleaning bias (+) is excessively applied when the impedance is low, it can be seen that drum memory and fogging occur.

  In this embodiment, since the sub-cleaning bias is set to −2.5 μA, the toner on the belt can be satisfactorily cleaned without occurrence of drum memory or fog.

Example 6
In this embodiment, an example in which the belt-like member as a transfer body is an intermediate transfer body to which a toner image is directly transferred from the photosensitive drum 21 will be described. That is, the present invention can also be applied to an intermediate transfer type image forming apparatus as shown in FIG.

  Similarly to the image forming apparatus A shown in FIG. 1, the image forming apparatus B shown in the schematic configuration diagram of FIG. 12 is a process station 2a to 4 that is four image forming units that form toner images of different colors. 2d. That is, the image forming apparatus according to the present exemplary embodiment is a so-called inline intermediate transfer type four-color full-color image forming apparatus.

  The image forming apparatus B includes an intermediate transfer belt 1 a that is a belt-like intermediate transfer body instead of the transfer belt 1. Then, the toner images are directly transferred from each process station 2 and transferred, and the toner images are fed from the paper feed cassette 18 at the secondary transfer portion which is a nip portion between the intermediate transfer belt 1a and the secondary transfer means 30. The toner is fed into the image forming apparatus by the roller 14 and transferred onto the transfer material P conveyed to the registration roller 13 and the registration counter roller 10 at a time. A secondary transfer bias is applied to the secondary transfer unit 30 from a power source (not shown).

  Here, the configuration of the transfer roller 3, the toner image forming process in the process station 2, and the operation in the cleaning mode, which is a configuration other than those described above in the present embodiment, have been described in the first to fifth embodiments. Since it is the same, description is abbreviate | omitted.

  In the intermediate transfer type image forming apparatus as in this embodiment, the cleaning time of the belt 1a can be arbitrarily changed, and an optimum cleaning time is selected according to conditions such as the environment, the total number of prints, and impedance in the transfer portion. Thus, a good belt 1 cleaning property can be exhibited. Further, in a condition where the cleaning property is good, the cleaning time is shortened, and in a condition where the cleaning property is deteriorated, the cleaning time is lengthened, thereby providing a total cleaning time. Can also be prevented, and adverse effects such as deterioration of the image forming member due to wear or the like can be prevented.

  In the first to fifth embodiments, the present invention is applied to a full-color image forming apparatus having a plurality of image carriers as photosensitive drums. However, a single-color image forming apparatus having a single photosensitive drum or a photosensitive drum is used. The present invention can also be applied to an image forming apparatus having a single developing device and a plurality of developing devices.

  The dimensions, materials, shapes, and relative positions of the components of the image forming apparatus described above are not intended to limit the scope of the present invention only to those unless otherwise specified.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. 3 is a flowchart illustrating a transfer body cleaning operation in Embodiment 1. 6 is a graph showing a relationship between a cleaning time and a residual toner amount on a belt. It is a block diagram of the control means in Example 2. 6 is a flowchart illustrating a transfer body cleaning operation in Embodiment 2. 6 is a graph showing the relationship between the number of image formations per cleaning time and the amount of residual toner on a belt. 10 is a flowchart illustrating a transfer body cleaning operation in Embodiment 3. 6 is a timing chart showing how to apply a transfer bias in ATVC control. 6 is a graph showing a relationship between an impedance in a transfer portion and a residual toner amount on a belt for each cleaning time. 10 is a flowchart illustrating a transfer body cleaning operation in Embodiment 4. 6 is a graph showing the relationship between the impedance at the transfer portion for each main cleaning bias and the amount of residual toner on the belt. It is a schematic block diagram which shows the other example of the image forming apparatus which concerns on this invention. It is a schematic block diagram which shows an example of the conventional image forming apparatus.

Explanation of symbols

1 Transfer belt (transfer body)
1a Intermediate transfer belt (transfer body)
2 Process station 3 Transfer roller (transfer means)
4a, 4b, 4c, 4d Transfer bias power supply 4a, 4B, 4c, 4D Cleaning bias power supply 21 Photosensitive drum (image carrier)
26 Waste toner container (image carrier cleaning means 101 memory (use history storage means)

Claims (10)

An image carrier on which a toner image is formed on the surface; a transfer member whose surface moves opposite to the image carrier; and a transfer unit that applies a transfer bias between the image carrier and the transfer member; An image forming apparatus that cleans the transfer body by applying a cleaning bias that reversely transfers the developer attached to the transfer body onto the image carrier.
An image forming apparatus, wherein the cleaning time is variable based on a predetermined condition.   2. The image forming apparatus according to claim 1, further comprising environment detection means for detecting an environment in which the apparatus is installed, wherein the cleaning time is variable based on a detection result of the environment detection means.   The environment is a temperature inside the apparatus, and the temperature detection result of the environment detection means makes the cleaning time longer when the temperature inside the apparatus is lower than a predetermined temperature than when it is higher than the predetermined temperature. The image forming apparatus according to claim 2.   The image forming apparatus according to claim 1, further comprising a use history storage unit that stores a use history of the apparatus, wherein the cleaning operation time is variable based on information in the use history storage unit.   5. The image forming apparatus according to claim 4, wherein when the number of executed image formations is greater than a predetermined number in the information of the usage history storage unit, the cleaning time is made longer than when the number of image formations is less than the predetermined number.   2. The apparatus according to claim 1, further comprising impedance detection means for detecting an impedance in a transfer portion to which the transfer bias is applied, wherein the cleaning time is variable based on a detection result of the impedance detection means. Image forming apparatus.   7. The image forming apparatus according to claim 6, wherein in the detection result of the impedance detection means, when the impedance at the transfer portion is larger than a predetermined value, the cleaning time is made longer than when the impedance is smaller than the predetermined value.   The image forming apparatus according to claim 1, wherein the cleaning bias is variable based on the predetermined condition.   The transfer member is a transfer material carrier that conveys a transfer material to a portion facing the image carrier, and the toner image is transferred to the transfer material that is conveyed by the transfer agent carrier. The image forming apparatus according to claim 1.   The transfer body is an intermediate transfer body to which the toner image is transferred from the image carrier, and the toner image transferred to the intermediate transfer body is transferred to a transfer material. 9. The image forming apparatus according to any one of items 8.

Images