JP2006078879A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the impedance detection precision of a transfer area, to improve the setting precision of a transfer bias, and to make image quality stable at high level, in an image forming apparatus which preliminarily measures the impedance of the transfer area and sets an optimum transfer bias according to the measurement result of the impedance. <P>SOLUTION: In an image forming process of forming toner images at a plurality of stations by receiving toner transferred from a photosensitive drum, the impedance of the transfer area is detected where the contact area between a transfer roller and a transfer belt is the largest. The impedance detection result is used even to set transfer biases of other stations. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that forms an image by electrophotographic technology.

  There is an image carrier on which a toner image is formed, and transfer means for transferring the toner image of the image carrier to a transfer material or a transfer belt, and the bias of the transfer means is detected as a result of detecting the impedance of the transfer means. There is an image forming apparatus controlled based on this (for example, Patent Document 1). Hereinafter, a method for controlling the transfer bias will be described using the portion of the conventional example described in Patent Document 1.

  The full-color image forming apparatus disclosed in Patent Document 1 is shown in FIG. This is an example of an image forming apparatus using a four-color full-color conventional electrophotographic system in which four process stations 2a, 2b, 2c, and 2d, which are image forming units, are arranged side by side, and has a so-called inline image forming apparatus configuration. .

  The process stations 2a to 2d have photosensitive drums 21a to 21d as image carriers, and the surfaces of the photosensitive drums 21a to 21d are uniformly charged by a primary charger and then exposed to, for example, LEDs or lasers. An electrostatic latent image is formed by exposure based on image information by the apparatus. The electrostatic latent image is developed as a toner image by attaching toner of each color by a developing device.

  Referring to FIG. 14, the transfer material P is fed from the paper feed cassette 18 into the image forming apparatus by the paper feed roller 14, conveyed to the registration roller 13 and the resist facing roller 10, and then positively charged from the suction bias power source 12. The suction roller 15 to which the suction bias is applied is electrostatically attracted and transported by the transport belt 1 of the transfer material carrier. In the image forming apparatus, the conveyance belt 1 is stretched around four rollers, that is, a driving roller 7, a suction counter roller 6, and tension rollers 8 and 9. Process stations 2a, 2b, 2c, and 2d for black, magenta, cyan, and yellow are arranged in series in this order from the upstream along the moving direction of the conveyor belt 1 (the direction of arrow R1).

  The transfer material P adsorbed on the conveying belt 1 sequentially passes in the vicinity of the process stations 2a to 2d of the respective colors, and the toner images of the respective colors on the photosensitive drums 21a to 21d 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. The conveyor belt 1 that has completed a series of operations is neutralized by the static eliminator 11 to prepare for the next image forming process.

  In the adsorption portion, an adsorption roller 15 as an adsorption means is disposed opposite to the adsorption counter roller 6 via the conveyance belt 1 so that the conveyance belt 1 and the transfer material P are sandwiched between the adsorption roller 15 and the opposite roller 6. It has become. By applying a voltage (adsorption bias) from the adsorption bias power supply 12 (high voltage power supply) to the adsorption roller 15, an adsorption charge is applied to the transfer material P, and the transfer material P to which the charge is applied polarizes the conveyance belt 1. As a result, the transfer material P is electrostatically attracted to the transport belt 1.

  Next, a method for determining the transfer bias for transferring the toner image to the transfer material P will be briefly described. As a conventional technology, the recording material is detected with constant current control before the recording material reaches the transfer area, and based on the detection result, the recording material enters the transfer portion and transfers the developer. There is a method of controlling the roller bias at a constant voltage. This is a method called ATVC (Active Transfer Voltage Control) method.

In this transfer voltage control method, that is, when the transfer material P does not exist in the transfer area in the transfer bias, a constant current is applied to the transfer portion for a predetermined time by constant current control, and the transfer bias is preset from the generated voltage at that time. The voltage value calculated and determined by the control equation is applied when the transfer material is present, and is a control method as disclosed in Patent Document 2.
Japanese Patent Laid-Open No. 2002-23512 Japanese Patent Laid-Open No. 02-123385

  Here, it is desirable that the measurement accuracy of the impedance of the transfer portion be within the requirement generated from the range of the transfer bias setting latitude. In recent years, the transfer bias setting latitude has been narrowed in response to the improvement in image quality demanded by the market, and there is a demand for improving the impedance accuracy of the transfer portion. SUMMARY OF THE INVENTION The present invention is to meet the above-mentioned demands, and an object of the present invention is to improve the accuracy of the impedance of the transfer part as compared with the conventional one.

  In order to solve the above-described problems, an image forming apparatus according to a first aspect of the present application includes a plurality of image carriers that carry toner, and a transfer unit that forms the plurality of image carriers and a plurality of transfer regions. A first bias supply member and a second bias supply member for supplying a bias to the transfer area for transferring the toner on the image carrier, and a bias applying means for applying a bias to the first bias supply member; The first bias supply member is in contact with the transfer means with a first contact area, the second bias supply member is in contact with the transfer means with a second contact area, and the bias application The means outputs a first bias determined in advance with constant current control or constant voltage control before transferring the toner, and when transferring the toner, a second bias different from the first bias is output. In the image forming apparatus that outputs the bias and the second bias value is set according to the output value of the first bias, the area of the first contact region is the area of the second contact region It is characterized by being larger than.

  An image forming apparatus according to a second aspect of the present application includes a plurality of image carriers that carry toner, a transfer unit that forms a plurality of transfer regions with the plurality of image carriers, and an image on the image carrier. A first bias supply member and a second bias supply member for supplying a bias to the transfer region to which toner is transferred; and bias applying means for applying a bias to the first bias supply member. The first bias supply member is in contact with the transfer means with a first contact area, the second bias supply member is in contact with the transfer means with a second contact area, and the bias application means performs constant current control. One or both of a portion for outputting a bias and a portion for outputting a bias under constant voltage control and a detection portion for detecting an output value of the bias. The controlled bias output portion or the constant voltage controlled bias output portion is operated to output a predetermined first bias, and the detection portion corresponds to the first bias. A step of applying a second bias and a step of outputting a third bias when transferring the toner, and when the second bias value is different from the previous image formation, In the image forming apparatus having a different bias value, the area of the first contact region is larger than the area of the second contact region.

  An image forming apparatus according to a third aspect of the present application includes a plurality of image carriers that carry toner, transfer means that receives transfer of toner on the image carrier in a transfer region, and biases the transfer region. First bias supply member and second bias supply member to be supplied; bias application means for applying a bias to the first bias supply member and the second bias supply member; and heating the toner on the transfer material P The bias applying means applies a predetermined first bias subjected to constant current control or constant voltage control to the first bias supply member before transferring the toner, and transfers the toner. A second bias different from the first bias is applied to the first bias supply member and a third bias is applied to the second bias supply member. And the second bias value and the third bias value are set according to the output value of the first bias, wherein the first bias supply member is the second bias supply member. It is arrange | positioned far from the said heating means rather than.

  According to a fourth aspect of the present invention, there is provided an image forming apparatus comprising: a plurality of image carriers that carry toner; transfer means that receives transfer of toner on the image carrier in a transfer region; and biasing the transfer region. First bias supply member and second bias supply member to be supplied; bias application means for applying a bias to the first bias supply member and the second bias supply member; and heating the toner on the transfer material P The bias applying means has one or both of a part for outputting a bias with constant current control and a part for outputting a bias with constant voltage control, and a detection part for detecting the output value of the bias. Then, before transferring the toner, the part that outputs the bias with the constant current control or the part that outputs the bias with the constant voltage control is operated and predetermined. And outputting a first bias to the first bias supply member, applying a second bias corresponding to the first bias to the detection portion, and transferring the toner. And outputting a third bias to the first bias supply member, and outputting a fourth bias to the second bias supply member at the time of transferring the toner. In the case where the second bias value is different from the time, the first bias supply member in the image forming apparatus in which the third bias value and the fourth bias value are different from the values at the previous image formation, respectively. The second bias supply member is disposed farther from the heating means than the second bias supply member.

  According to the first invention and the second invention according to the present application, it is possible to accurately detect the impedance of the transfer portion.

  According to the third and fourth aspects of the present application, it is possible to accurately detect the impedance of the transfer portion, and in particular, it is possible to prevent a decrease in detection accuracy due to heat.

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

  The image forming apparatus includes a conveyance belt 1 (transfer belt) that is a transfer unit. The steps from the time when the transfer material P is fed to the time when the transfer, fixing, and discharge are substantially the same as the example of the image forming apparatus described in the conventional example of FIG. A method for determining the transfer bias from the detection result (so-called ATVC or a similar technique) will be described.

  The method employed in the present embodiment applies a bias for performing (virtual) constant current control before the paper enters the transfer area, detects the voltage at that time, and based on the result, A control method is used for determining a transfer voltage when the transfer is made while entering the transfer region. This is a method similar to the ATVC method as disclosed in JP-A-2-123385.

  A bias power source 4a (bias applying unit) as a bias applying unit and a control method will be described with reference to FIG. FIG. 2 is a conceptual diagram of bias applying means for transfer. Before the transfer material P reaches the transfer area (before transferring the toner), the bias of the transfer roller 3a, which is a bias supply member, is applied to measure the impedance of the transfer area formed by the transfer roller 3a. A voltage value to be applied when transferring the toner is determined according to the measurement result of the impedance, and the constant voltage output unit outputs the determined voltage value.

  At the time of impedance measurement, a virtual constant current is output from the constant voltage output unit (portion for outputting a bias) in FIG.

  As a method of outputting a virtual constant current, first, a predetermined signal is input from the CPU to the comparison operational amplifier in order to output a predetermined voltage. The comparison operational amplifier outputs an output corresponding to the difference between the detection result of the voltage value output from the bias output unit and the signal from the CPU. Since a desired voltage is output from the bias output unit in accordance with the output of the comparison operational amplifier, the output from the bias output unit is an output that matches the signal from the CPU. On the other hand, the output from the bias output unit is applied to the transfer roller 3a via the protective resistor R. The current value flowing into the transfer roller 3a is detected by the current detection unit of the bias power source 4a, and the detection result is input to the CPU. In the CPU, the target current value applied at the time of impedance measurement is compared with the detection result in the current detection unit, and if the target current value is smaller, the signal value input from the CPU to the comparison operational amplifier is decreased. If the target current value is larger, the signal value input from the CPU to the comparison operational amplifier is increased. This is repeated, and control is performed so that the target current value and the detection result of the current detection unit coincide. By these controls, a virtual constant current output is performed.

  Next, regarding impedance measurement, the impedance is calculated based on the target current value when this virtual constant current is output and the CPU signal value of the voltage value output from the bias output unit. do.

  Furthermore, the transfer voltage value when applied to the transfer roller 3a at the time of transfer is determined by taking into consideration the result of this impedance and the impedance of the assumed transfer material, and a transfer voltage value at which a current suitable for transfer can be obtained. The calculation is executed by the CPU and outputting it from the signal CPU for outputting the transfer voltage value.

  If the impedance of the transfer roller 3a changes depending on temperature and humidity, the detection result of the current detection unit when a predetermined voltage is applied to the transfer roller 3a when the transfer voltage value is determined. This is different from the detection result of the current detection unit at the previous image formation, and the transfer voltage value applied to the transfer roller 3a at the time of impedance measurement and transfer may also change. On the other hand, a current suitable for transfer flows into the transfer roller 3a.

  The output process by this transfer voltage control method is shown in FIG. The transfer bias is set in advance from a voltage generated at that time by applying a constant current from the power source 4a to the transfer roller 3a for a predetermined time α by a constant current control when there is no transfer material in the transfer area of the first station in FIG. The voltage value calculated and determined by the control equation is applied when the transfer material P exists.

  The reason why the above control is performed is as follows. A transfer roller or the like, which is a bias supply member that supplies a transfer bias to the conveyance belt 1 (transfer belt), has a resistance value appropriately adjusted by dispersing conductive particles or the like in rubber, sponge, or the like. Yes. However, the resistance value of the transfer roller may change by an order of magnitude or more due to the effects of variations in manufacturing, temperature and humidity of the use environment, and durability fluctuations. Therefore, if the transfer bias is a fixed value, the current value and voltage value of the transfer bias will fluctuate, making it difficult to ensure stable transfer performance at all times.

  In order to always obtain good transferability, it is ideal to control the amount of charge applied to the back of the transfer material P. If the transfer material P to be used is of the same type, for example, a transfer roller is used. A constant current control can also be considered. However, in actuality, when using various transfer materials, the amount of charge applied to the back of the transfer material changes depending on the size, thickness, etc. of the transfer material. This is because a region where the transfer material is sandwiched and a region where the transfer material is not sandwiched in the transfer region change due to a change in the size of the transfer material used in the apparatus. This is because when the impedance of the transfer material is high, the load impedance becomes small in the region where there is no transfer material, a large amount of current flows in a concentrated manner, and transfer failure occurs in the region where the transfer material is present.

  As a transfer method for improving the above-mentioned problems, the recording material is subjected to impedance detection using a constant current controlled bias before the recording material reaches the transfer region, and based on the detection result, the recording material is detected. Rushes into the transfer portion and performs transfer control of a system in which the bias of the transfer roller for transferring the developer is controlled at a constant voltage. ("Constant voltage control" here is not limited to the one that can obtain a voltage value that is completely fixed with respect to the load fluctuation. As shown in FIG. Includes a voltage value that fluctuates due to the presence of a protective resistor R between the members, etc. Similarly, the “constant current control” also includes a protective resistor R, etc. If the voltage value during constant voltage control is set on the premise of the impedance of the transfer roller and the transfer material, the current value varies between the transfer roller and the image carrier. This is because even if there are many regions where there is no transfer material, it is possible to allow a desired current density to flow into the region where the transfer material is present, and the charge necessary for transfer is applied to the back surface of the transfer material. . This is because when the area of the transfer material is small, even if a large amount of current flows into the area where there is no transfer material, the total amount of current flowing into the entire transfer roller only increases. The necessary charge density is formed on the back surface of the transfer material.

  When measuring impedance, a bias by constant voltage control may be used. This is because the impedance can be measured if the reference bias for measuring the impedance of the transfer portion is substantially constant.

  A contact area between the transfer roller and the conveyance belt 1 which is a characteristic part of the present invention will be described. In this embodiment, the impedance of the transfer area is detected at the first station, and the transfer bias of each of the first to fourth stations is determined based on the result. In the first station that performs the impedance detection, the contact area between the conveyance belt 1 and the transfer roller 3 is made wider than the contact areas of other stations in order to improve detection accuracy. That is, the impedance is measured at the station with the highest detection system, and the bias value at the time of transfer is set at other stations based on the information.

Specifically, the area of the contact area between the transfer belt 1 (transfer belt) that is the transfer means of the first station and the transfer roller 3a that is the charge supply member is 570 mm ² , whereas the contact area of other stations The area is set to 228 mm ² . In the contact area of the first station, the width of the transport belt 1 in the moving direction is 2.5 mm, and the other stations are 1.0 mm. The reason why the area of the contact area of the first station is increased in this way is to improve detection accuracy based on the following experimental results. An experiment for obtaining the relationship between the area of the contact region and the detection accuracy using the image forming apparatus of this embodiment is as shown in FIG. This is a comparison of the standard deviation, which is the variation in sampling of 40 points for impedance detection, with the area of the contact area of the first station being variable. The unit of impedance detection is a unit (bit) on software that controls the apparatus body, and 1 bit is a value corresponding to about 10 V of the body high voltage.

  As shown in FIG. 4, it can be recognized that stable impedance detection with little variation can be performed by securing the area of the contact area of the first station of the present embodiment. The material and shape of the transfer roller 3a used will be described. An ion conductive roller having a diameter of 12 mm in which a foam rubber based on NBR is formed as a single layer in a thickness of 3 mm on a core metal having a diameter of 6 mm was used. . Its hardness is a 35 ° roller with Asker C (500 g load). The area of the contact area is measured when the toner is applied to the back surface of the conveyance belt 1 and the transfer roller 3a is pushed toward the conveyance belt 1 with the image forming apparatus main body stopped. The area from which the toner was peeled was measured to determine the area of the contact area.

  The area of the contact area of the image forming apparatus of FIG. 1 of the present embodiment is set by changing the spring pressure for pressing the transfer roller toward the conveying belt 1 at each station. A spring that applies a load of 500 g to the bearings of the core metal on both sides is used for pressing the transfer roller in the first station. A spring that applies a load of 150 g is used for the core metal bearing of the transfer roller in the second to fourth stations.

FIG. 11 shows a flow for determining the transfer bias of the present embodiment based on the impedance detection result.
S1 starts control.
In S2, the bias output unit of the power supply 4a is operated, and the current value flowing into the transfer roller 3a is controlled to match the target current value.
In S3, the impedance of the first station is measured (calculated).
Based on the result of S3 in S4 to S7, the bias of each station is calculated.
A transfer bias is applied in S8 to S11.
Control ends in S12.
It is like this.

  If the area of the contact area is increased, a reaction force acts on the unit having the transfer roller support member, so it is inappropriate to increase the area of the contact area of all stations. This is because if a strong reaction force acts on the unit having the support member for the transfer roller, the contact area between the transfer roller and the transport belt 1 will not be stable, resulting in impedance variation.

  Next, the effect resulting from the positional relationship with the fixing device 16 that is a heating means will be described. As shown in FIG. 1, in the image forming apparatus of the present embodiment, the first station for measuring impedance is arranged farthest from the fixing device 16 that is a heating unit. For this reason, the transfer roller 3a is in a state where it is least affected by heat as compared with other stations, and resistance fluctuation due to heat does not occur. On the other hand, the transfer roller 3d disposed in the vicinity of the heating unit is heated in the region on the fixing device 16 side, and therefore, when impedance is measured here, resistance unevenness occurs in the rotation cycle of the transfer roller 3d. It will be. For this reason, if impedance is measured at the fourth station, the detection accuracy is lowered. Therefore, by performing the measurement at the first station farthest from the fixing device 16, it is possible to perform the measurement with the highest accuracy from the viewpoint of heat. Further, in this embodiment, a so-called vertical path arrangement is adopted, and the first station is located at the lowest position in the direction of gravity. This has the advantage that it is difficult for the transfer roller of the first station to receive the heat of the fixing device 16 from the viewpoint of heat convection, and the impedance detection accuracy is also improved.

  Next, deterioration of a member that detects impedance, which is another effect of the present embodiment, will be described. In the image forming apparatus of the present embodiment, it will be described that the transfer roller, which is one of the components that perform impedance detection, can be prevented from deteriorating (resistance increase and destruction), and a highly accurate impedance detection system can be maintained over a long period. It should be noted that preventing the transfer roller from degrading eventually leads to ensuring the stability of electrical transfer conditions such as the mechanical and transfer electric field of the transfer area during transfer.

  The transfer roller 3a of the station that performs impedance detection is applied with a bias for a longer time than the detection process. The resistance of the transfer roller of this embodiment increases as a bias is applied, and the surface of the transfer roller may be destroyed by applying the bias for a long time.

FIG. 6 is a view showing the fluctuation range of the area of the contact region and the resistance value of the transfer roller. A transfer roller having an initial resistance of 1.0E + 08 (Ω / 1 kv applied) was used and evaluated by passing 50,000 (50K) sheets. Compared with FIG. 6, in the image forming apparatus of the present embodiment, the area of the contact area of the first station where impedance detection is performed is 570 mm ² , which suppresses the increase in resistance of the transfer roller. I can understand.

  On the other hand, FIG. 7 shows an observation of the degree of breakage of the transfer roller using the transfer roller 3b of the second station of the same apparatus as in the first embodiment. The transfer roller when the output of the transfer bias is 3.5 kv which is the maximum value of the internal power supply of the main body and when the paper is endured while intentionally forcibly applying 7.0 KV, which is not normally used, using an external power supply It is the figure which showed observation of the destruction condition of. The circles in FIG. 7 are unchanged. Δ is slightly cracked on the surface, and × indicates a level at which cracks clearly appear and cracks can be confirmed. From this, it can be seen that if the bias is continuously applied to the transfer roller under a certain condition, the transfer roller is broken after a certain application time has elapsed.

  Since it has been found that the increase in the resistance value of the transfer roller and the destruction of the surface are related to the size of the area of the contact area between the transfer roller and the transfer belt 1, the estimation mechanism will be described.

  FIG. 5A is a diagram for explaining that a portion that discharges toward the belt and the drum is generated by the bias applied to the core of the transfer roller 3a, and shows a state where the area of the contact region is small. Show. On the other hand, FIG. 5B is a diagram showing a state where the area of the contact region is large. When the transfer portion transfer bias is applied, a discharge occurs between the transfer roller, the transfer belt, and the photosensitive drum as shown in FIG. When the amount of discharge, that is, the discharge current amount Id increases, the oxidation of the transfer roller is promoted and the resistance increases. The discharge current amount Id of the transfer portion increases as the nip becomes narrower. This can also be understood from the fact that the narrower the nip, the smaller the contact portion between the roller surface and the belt, the less the transfer current In flowing through the nip, and the easier the discharge. If the amount of discharge current Id is large, the amount of ozone generated increases accordingly, and the generated ozone promotes oxidative degradation and hydrolysis of the transfer roller. Furthermore, the resistance value of the transfer roller increases due to the formation of an oxide film. This problem is likely to occur when the transfer roller is made of a material that is vulnerable to electric discharge. In a low-humidity environment, electric discharge is likely to occur, and this deterioration phenomenon is promoted. In some cases, the rubber surface of the transfer roller may be cracked.

  Therefore, a configuration that increases the area of the contact region and suppresses the discharge current as in the first station of the present embodiment is suitable for the deterioration of the transfer roller. In particular, by reducing the value of the discharge current Id of the transfer roller 3a for which the accumulated time during which the bias is applied is larger than that of the transfer rollers 3b, 3c, 3d of other stations, the transfer roller 3a is faster than the other transfer rollers. It is intended to prevent deterioration. Since the impedance is measured using the transfer roller 3a, the transfer bias setting of other stations is also affected. Therefore, preventing the transfer roller 3a from deteriorating is effective in maintaining the image quality at a high level. A derivative effect by preventing an increase in the resistance value of the transfer roller is that the output capacity of the transfer bias power source can be suppressed to a low level.

  In the present embodiment, as described above, the transfer roller 3a is the lowest position in the vertical direction among the plurality of transfer rollers, and is separated from the fixing device 16 that is the most heat source in the apparatus. In the position. Since it is not easily affected by heat, the progress of oxidation of the transfer roller, which is an impedance detection member, can be suppressed, and an increase in resistance can also be suppressed.

  Next, the effect of having a station with a wide contact area as an upstream station in the image forming process will be described. While the transfer material and the transfer belt 1 pass through a plurality of transfer regions, the transfer material and the transfer belt 1 may be charged up. This is an effect of minimizing the adverse effects of the charge-up.

  FIG. 8 is a diagram showing the relationship between the area of the contact region and the necessary transfer voltage. The environment is a normal temperature and humidity environment of 23 ° C. and 50% RH. It is the figure which showed the optimal transfer bias about 2 types of XEROX brand paper of the basis weight of 176g, and XEROX brand paper of the basis weight of 176g. From FIG. 8, it can be seen that if the area of the contact region is large, the required transfer voltage value may be low. The optimum transfer bias shown here is the transfer bias of the first station, and its value is larger than the value at which a transfer failure occurs when the bias is insufficient, and the transfer electric field is increased when the bias is excessive. This bias is suitable for transfer and is lower than the bias that reversely charges the drum potential.

In the setting of the image forming apparatus of FIG. 1 of the present embodiment, the area of the contact area of the first station is 570 (mm ² ), and the area of the contact area of the second to fourth stations is 228 (mm ² ). The transfer bias setting example of XX75g for plain paper and XX176g for cardboard was 23 ° C, 50% RH environment, and the transfer bias setting for each station was as follows.

  This is because a wider nip can obtain a sufficient current for transfer with a lower transfer bias, and the transfer bias value of the first station can be kept low. As a result, the bias value of the subsequent station is also lowered. It has been set. If the station that increases the area of the contact area is only the fourth station, the transfer bias for the XX176g paper of the first station is 2700 V, and the transfer bias of the second station downstream thereof is 3100 V, the transfer of the third station. The bias will reach 3200V, and the bias of the fourth station will reach 3300V. If the set value of the transfer bias is increased, for example, a phenomenon occurs in which the toner image formed on the transfer material P at the first station is retransferred at the second station. Retransfer is a phenomenon in which when the transfer bias is high, the toner on the transfer material P is charged by discharge, and the charged toner returns to the photosensitive drum of the second station. FIG. 9 shows a conceptual diagram thereof. T1 is a toner image formed at the first station, T2 is a toner image formed at the second station, and (a) a state in which the toner is transferred from the photosensitive drum of the second station to the transfer material P. It was shown in the order of (b) and (c). Since these settings are set under an environment of 23 ° C. and 50% RH, naturally, this phenomenon is remarkable in a low temperature and low humidity environment where the impedance of the transfer material P, the transfer belt, and the transfer roller is high. Needless to say.

  According to the setting of the present embodiment, since a relatively low voltage is used in the first station, it is possible to suppress the charge-up of the transfer material P and the transfer belt, thereby preventing retransfer at the second to fourth stations. The effect that occurs. Furthermore, from the viewpoint of suppressing retransfer, it is also effective that the area of the contact area is smaller in the second to fourth stations than in the first station.

  Further, as an additional effect of the present embodiment, an improvement in the conveyance force of the transfer material can be given. This will be described below. In the present embodiment, the process of adsorbing the transfer material P onto the transport belt is performed at the first transfer station on the most upstream side. Furthermore, in this embodiment, since the area of the contact area of the first station is wide, the transfer belt can be pressed in a wide range, and the medium can be stably and reliably adsorbed to the transfer belt. This is useful for suppressing color misregistration between stations.

  The apparatus according to the present embodiment has been described on the assumption that the transfer body moving on the belt is opposed to the image carrier. However, the same effect can be obtained even when the transfer body is a drum-shaped transfer drum 22 as shown in FIG. It goes without saying that can be obtained. Further, although the power supply is shown in FIG. 2 as the power supply for the transfer bias, the power supply described in Japanese Patent Laid-Open No. 2001-25249 can also be used.

  In the above embodiment, the impedance measurement for setting the transfer voltage value is described. However, the impedance measurement is performed in order to obtain the target current value with the transfer bias power source having a constant current output portion as the transfer bias. The above embodiment can also be applied to the case where

  In addition, as described in the above embodiment, the fact that the impedance measurement accuracy is high at a location where the area of the contact region is wide can be applied to the following configuration. In other words, impedance is measured for each station, and the result is reflected in the transfer bias setting of each station, but the area of the contact area is widened only for stations where the transfer bias setting latitude is narrow, and the measurement accuracy is increased. It is a form of improving.

(Embodiment 2)
The schematic diagram of the image forming apparatus of the second 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 is the same as that of the first embodiment. Omitted.

In the present invention, when the medium passes through the impedance detection means, the impedance component combined with the medium is detected, and the transfer bias is determined based on the result. This series of control will be described with reference to the flowchart of FIG.
S1 starts control.
In S2, a 10 μA constant current of I0 is applied to the transfer roller of the first station.
The average voltage at S2 is calculated at S3.
In S4, a voltage to be applied to the paper leading edge of the first station is calculated.
In S5, the voltage determined in S4 is applied.
In S6, I0 is calculated as the average current at S5.
In S7, it is determined whether or not the average current I0 calculated in S6 is equal to or greater than the current Ix.
If the determination result in S7 is YES, the process proceeds to S8. If NO, the control in S17 is executed.
In the case of S8, it is determined that the medium is a normal resistance medium, the transfer bias to be applied to each station is calculated in S9 to S12, and the bias is applied in S13 to S16.
In the case of S17, it is determined that the medium is a high resistance medium, the transfer bias to be applied to each station is calculated in S18 to S21, and the bias is applied in S22 to S25.
Control ends in S26.
It is like this.

  In the second embodiment, the impedance is detected at the paper tip of the first station, and the first station also feeds back immediately from the middle of the paper. However, as another application example, the first station is in the paper. A control method is also conceivable in which the impedance is detected and fed back to the transfer bias of the downstream second to fourth stations.

  As described above, according to the second embodiment, since the resistance of the medium can be detected by widening the nip width, it is possible to detect the medium resistance with high accuracy and to determine the transfer bias according to the detection. An image device that obtains image quality can be obtained.

(Embodiment 3)
The third embodiment will be described with reference to a schematic diagram 13 of an image forming apparatus. The third embodiment is different from the first embodiment in that the transfer means 1 in this embodiment is an intermediate transfer member, and the toner image transferred to the intermediate transfer member is transferred to the transfer material P. It is a point.

  The operation of the image forming apparatus according to the third embodiment will be briefly described. The image forming apparatus shown in the schematic configuration diagram of FIG. 13 is a so-called in-line four-color full-color image forming apparatus having process stations 2a to 2d which are four image forming units that form toner images of different colors. It is.

  The image forming apparatus of this embodiment includes an intermediate transfer transfer belt. The process from when the transfer material P is fed to when it is transferred, fixed, and discharged is substantially the same as the example of the image forming apparatus described in the embodiment of FIG.

  The impedance of the transfer area is detected in the same manner as in the first embodiment, but at the transfer section of the first station having a wide transfer area. The method for determining the transfer bias of each station from the detection result is the same as in the first embodiment.

  According to the third embodiment, impedance detection can be performed stably, and the first to fourth optimum transfer biases can be determined with high accuracy. Further, it is possible to prevent deterioration (resistance increase and destruction) of the transfer roller, which is one of the components that perform impedance detection. Therefore, an image forming apparatus that can obtain a good image can be obtained.

It is a figure explaining the apparatus section concerning a 1st embodiment of the present invention. It is a figure explaining the bias power supply concerning the 1st Embodiment of this invention. It is a figure explaining the impedance detection which concerns on the 1st Embodiment of this invention. It is a figure explaining the effect of the 1st Embodiment of this invention. It is a figure explaining the effect of the 1st Embodiment of this invention. It is a figure explaining the effect of the 1st Embodiment of this invention. It is a figure explaining the effect of the 1st Embodiment of this invention. It is a figure explaining the effect of the 1st Embodiment of this invention. It is a figure explaining the effect of the 1st Embodiment of this invention. It is apparatus sectional drawing explaining the application example of the 1st Embodiment of this invention. It is a figure explaining the control flow of the 1st Embodiment of this invention. It is a figure explaining the control flow of the 2nd Embodiment of this invention. It is apparatus sectional drawing explaining the 3rd Embodiment of this invention. It is a figure explaining the apparatus section concerning background art

Explanation of symbols

1 Conveyor belt (transfer means)
2a, 2b, 2c, 2d Process station 3a, 3b, 3c, 3d Transfer roller (bias supply member)
4a, 4b, 4b'4c, 4d, 4d 'Transfer bias power supply (bias applying means)
6 Driving roller 7 Adsorption roller 10 Registration roller 13 Registration roller 14 Paper feed roller 16 Fixing device 18 Paper feed cassette 21a, 21b, 21c, 21d Photosensitive drum (image carrier)
26a, 26b, 26c, 26d Waste toner container 22 Transfer drum P Transfer material

Claims (13)

A plurality of image carriers that carry toner; transfer means that forms a plurality of transfer regions with the plurality of image carriers; and a first that supplies a bias to the transfer region that transfers toner on the image carrier. A bias supply member, a second bias supply member, and a bias application unit that applies a bias to the first bias supply member, wherein the first bias supply member is in contact with the transfer unit and a first contact region; The second bias supply member is in contact with the transfer means with a second contact area, and the bias applying means is subjected to constant current control or constant voltage control before transferring the toner. When the toner is transferred, a second bias different from the first bias is output, and the second bias value is set to the output value of the first bias. In the image forming apparatus is set Flip,
The image forming apparatus according to claim 1, wherein an area of the first contact region is larger than an area of the second contact region.   The third bias is applied to the second bias supply member when transferring toner, and the third bias value is set according to an output value of the first bias. The image forming apparatus according to 1. A plurality of image carriers that carry toner; transfer means that forms a plurality of transfer regions with the plurality of image carriers; and a first that supplies a bias to the transfer region that transfers toner on the image carrier. A bias supply member, a second bias supply member, and a bias application unit that applies a bias to the first bias supply member, wherein the first bias supply member is in contact with the transfer unit and a first contact region; The second bias supply member is in contact with the transfer means with a second contact area, and the bias applying means outputs a bias output with constant current control and a bias with constant voltage control. One or both of the first and second detection parts and a detection part for detecting the bias output value, and before transferring the toner, the part for outputting the bias under the constant current control or the constant current A step of operating a controlled bias output portion and outputting a predetermined first bias, and a second bias corresponding to the first bias is applied to the detection portion; and toner An output of a third bias when transferring the image, and when the second bias value is different from the previous image formation, the image forming apparatus having a different third bias value,
The image forming apparatus according to claim 1, wherein an area of the first contact region is larger than an area of the second contact region.   A fourth bias is applied to the second bias supply member when transferring toner, and the fourth bias value is different when the second bias value is different from the previous image formation. The image forming apparatus according to claim 3.   2. A heating unit for heating toner on a transfer material, wherein the first bias supply member is disposed farther from the heating unit than the second bias supply member. 5. The image forming apparatus according to claim 4.   The image forming apparatus according to claim 1, wherein the transfer unit carries a transfer material.   The image forming apparatus according to claim 1, wherein the transfer unit receives the transfer of toner from the image carrier. A plurality of image carriers that carry toner; transfer means that receives transfer of toner on the image carrier in a transfer region; and a first bias supply member and a second bias supply member that supply a bias to the transfer region A bias applying means for applying a bias to the first bias supplying member and the second bias supplying member, and a heating means for heating the toner on the transfer material. The bias applying means transfers the toner. Before the toner is transferred, a predetermined first bias subjected to constant current control or constant voltage control is applied to the first bias supply member, and when transferring toner, a second bias different from the first bias is applied. Is applied to the first bias supply member, a third bias is applied to the second bias supply member, and the second bias value and the third bias are applied. In the image forming apparatus is set in accordance with the output value of the first bias,
The image forming apparatus according to claim 1, wherein the first bias supply member is disposed farther from the heating unit than the second bias supply member. A plurality of image carriers that carry toner; transfer means that receives transfer of toner on the image carrier in a transfer region; and a first bias supply member and a second bias supply member that supply a bias to the transfer region Bias applying means for applying a bias to the first bias supplying member and the second bias supplying member, and a heating means for heating the toner on the transfer material. The bias applying means is controlled by constant current control. One or both of a bias output portion and a constant voltage controlled bias output portion and a detection portion for detecting the bias output value, and the constant current controlled bias before toner transfer Or a portion outputting a bias subjected to the constant voltage control is operated, and a predetermined first bias is applied to the first bias supply member. A second bias corresponding to the first bias is applied to the detection portion, and a third bias is applied to the first bias supply member when transferring toner. And a step of outputting a fourth bias to the second bias supply member when transferring the toner, and when the second bias value is different from the previous image formation, In the image forming apparatus in which the third bias value and the fourth bias value are different from the values at the previous image formation,
The image forming apparatus according to claim 1, wherein the first bias supply member is disposed farther from the heating unit than the second bias supply member.   10. The image forming apparatus according to claim 5, wherein the first bias supply member is located below the second bias supply member in a gravitational direction. 11.   7. The image forming apparatus according to claim 6, wherein when the bias applying unit outputs the first bias, there is a transfer material between the transfer unit and the image carrier.   The transfer means receives a plurality of times of toner transfer from the plurality of image carriers to form one toner image on the transfer means, and the first toner transfer of the plurality of times of toner transfer. The image forming apparatus according to claim 1, wherein a bias for supplying the bias is supplied from the first bias supply member. . On the transfer material carried by the transfer means, the toner is transferred a plurality of times from the plurality of image carriers to form one toner image on the transfer material, and the first of the plurality of toner transfers 12. The bias according to claim 1, wherein a bias for transferring the toner is supplied from the first bias supply member. 13. Image forming apparatus.

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