JP6834365B2 - Image forming device - Google Patents

Description

This disclosure relates to an image forming apparatus, for example, an image forming apparatus capable of forming an image on both sides of a recording medium.

The ease with which the transfer current flows when the toner image on the photoconductor drum is directly transferred to the recording medium or when the toner image on the intermediate transfer belt is secondarily transferred to the recording medium depends on the moisture absorption state of the recording medium. .. For example, in the case of a recording medium having a relatively large amount of water, the electric resistance value becomes low, so that a transfer current easily flows. On the contrary, in the case of a recording medium having a relatively small amount of water, the electric resistance value becomes high, so that the transfer current becomes difficult to flow. Therefore, it is necessary to adjust the transfer conditions according to the moisture absorption state of the paper.

For example, in the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2013-137364 (Patent Document 1), at the time of the first image formation after the power of the image forming apparatus is turned on, or when paper is replenished in the paper feed cassette, etc. The moisture absorption state of the paper is detected. Specifically, the moisture absorption state of the paper is estimated from the difference between the electric resistance value at the time of transfer on the first side of the paper and the electric resistance value at the time of transfer on the second side of the paper.

Japanese Unexamined Patent Publication No. 2010-54813 (Patent Document 2) discloses a technique for forming a good image on the second side of a paper in an image forming apparatus capable of double-sided image formation. Specifically, in the image forming apparatus of this document, the estimated resistance value of the paper is estimated between the time when the image transferred to the first side of the paper is heat-fixed and the time when the image is transferred to the second side of the paper. The paper is cooled by the fan accordingly.

Also in JP-A-11-272902 (Patent Document 3), JP-A-10-293433 (Patent Document 4), and JP-A-10-213975 (Patent Document 5), an image forming apparatus capable of double-sided image formation. Discloses a technique for forming a good image on the second surface of the paper. Specifically, in the image forming apparatus of these documents, the image transferred to the first surface of the paper is heat-fixed, and then the image is transferred to the second surface of the paper according to the elapsed time. The transfer voltage for the two surfaces is determined.

Japanese Unexamined Patent Publication No. 2013-137364 JP-A-2010-54813 Japanese Unexamined Patent Publication No. 11-2722092 Japanese Unexamined Patent Publication No. 10-293433 Japanese Unexamined Patent Publication No. 10-23975

In recent years, in consideration of energy saving, an image forming apparatus that switches to the minimum required fixing temperature for each printed page has appeared. When images are formed on both sides of the paper in such an image forming apparatus, the amount of water evaporation of the paper may differ depending on the set value of the fixing temperature for the first side of the paper. Therefore, it is necessary to adjust the transfer conditions for the second side of the paper according to the fixing temperature for the first side of the paper, but this point is not taken into consideration in the prior art.

This disclosure takes into consideration the above situation, and the purpose of the disclosure is to use an image forming apparatus capable of double-sided image formation on the second surface of the recording medium even when the fixing temperature for the first surface of the recording medium is changed. The purpose of the present invention is to provide an image forming apparatus capable of suppressing image quality deterioration.

The image forming apparatus in one embodiment is capable of forming an image on both sides of a recording medium, and includes an image carrier, a primary transfer unit, a secondary transfer unit, a fixing unit, and a control unit. The image carrier carries a toner image formed based on the image information. The primary transfer unit transfers the toner image supported on the image carrier to the intermediate. The secondary transfer unit transfers the toner image transferred to the intermediate to a recording medium. The fixing unit fixes the toner image transferred to the recording medium set by the target fixing temperature. The control unit sets the secondary transfer voltage and the target fixing temperature of the secondary transfer unit. Target fixing temperature may be set even without least to a first temperature and a second temperature lower than the first temperature. When the target fixing temperature for the first surface of the recording medium is set to the first temperature, the control unit sets the secondary transfer voltage for the second surface of the recording medium to the first voltage and sets the secondary transfer voltage for the first surface. When the target fixing temperature of is set to the second temperature, the secondary transfer voltage for the second surface is set to the second voltage lower than the first voltage.

When the image information imaged on the second surface represents a color image, the control unit determines that the target fixing temperature for the first surface is the first temperature or the second temperature. The secondary transfer voltage for the two surfaces may be set to the first voltage or the second voltage, respectively. In this case, the control unit determines whether the target fixing temperature for the first surface is the first temperature or the second temperature when the image information imaged on the second surface represents a monochrome image. Instead, the secondary transfer voltage for both the first surface and the second surface may be set to either the first voltage or the second voltage.

When the amount of toner adhered to the second surface estimated based on the image information is equal to or greater than the first threshold value, the control unit determines whether the target fixing temperature for the first surface is the first temperature or the second temperature. Depending on the situation, the secondary transfer voltage for the second surface may be set to the first voltage or the second voltage, respectively. In this case, when the amount of toner adhered to the second surface is less than the first threshold value, the control unit has a second surface regardless of whether the target fixing temperature for the first surface is the first temperature or the second temperature. The secondary transfer voltage for both the first surface and the second surface may be set to either the first voltage or the second voltage.

The control unit may set a target fixing temperature according to the paper type. The control unit may set the target fixing temperature for the first surface to the first temperature or the second temperature based on the image information imaged on the first surface.

More specifically, the control unit may set the target fixing temperature for the first surface to the first temperature when the image information imaged on the first surface represents a color image. In this case, the control unit may set the target fixing temperature for the first surface to the second temperature when the image information imaged on the first surface represents a monochrome image.

When the image information imaged on the first surface includes only character information, the control unit may set the target fixing temperature for the first surface to the second temperature. In this case, the control unit may set the target fixing temperature for the first surface to the first temperature when the image information imaged on the first surface includes information other than the character information.

When the maximum value of the toner adhesion amount per unit area of the first surface estimated based on the image information is equal to or more than the second threshold value, the control unit sets the target fixing temperature for the first surface to the first temperature. You may. In this case, the control unit may set the target fixing temperature for the first surface to the second temperature when the maximum value of the toner adhesion amount per unit area of the first surface is less than the second threshold value.

According to the above embodiment, in the image forming apparatus capable of double-sided image formation, deterioration of the image quality of the second surface of the recording medium can be suppressed even when the fixing temperature for the first surface of the recording medium is changed.

It is sectional drawing which shows typically the main composition of the part related to image formation in a full-color tandem type image formation apparatus. It is a block diagram which shows the whole structure of an image forming apparatus. It is a figure which shows an example of the relationship between a secondary transfer current and transfer efficiency. It is a figure which shows the relationship between the fixing temperature of the 1st surface, and the secondary transfer current of the 2nd surface in the case of performing double-sided image formation. It is a figure which shows the relationship between the secondary transfer current and transfer efficiency, and the relationship between a secondary transfer current and a secondary transfer voltage. It is a flowchart which shows an example of the control procedure of the secondary transfer voltage for the 2nd surface at the time of performing automatic double-sided image formation. It is a flowchart which shows the control procedure of the secondary transfer voltage at the time of image formation of the 2nd surface in the image forming apparatus of Embodiment 2.

Hereinafter, each embodiment will be described in detail with reference to the drawings. The same or corresponding parts may be designated by the same reference numerals and the description may not be repeated.

<Embodiment 1>
[Structure of image forming part and conveying part of image forming apparatus]
FIG. 1 is a cross-sectional view schematically showing a main configuration of a part related to image formation in a full-color tandem type image forming apparatus. With reference to FIG. 1, the image forming apparatus 1 is based on an electrophotographic image forming process, transfers a toner image formed on the surface of a photoconductor to a recording medium, and transfers the transferred toner image to a recording medium. The image is formed by fixing the image. As shown in FIG. 1, the image forming apparatus 1 includes an image forming unit 2 for forming an image and a conveying unit 3 for conveying the paper 31 as a recording medium T.

The image forming unit 2 includes cartridges 10Y, 10M, 10C, 10K, an intermediate transfer belt 20 as an intermediate, support rollers 21 and 22, and primary transfer rollers 15Y, 15M, 15C, 15K as a primary transfer unit. A secondary transfer roller 24 as a secondary transfer unit, a heating roller 25a and a pressure roller 25b as a fixing unit 25, and an intermediate transfer belt cleaning unit 23 are provided.

The cartridges 10Y, 10M, 10C, and 10K are provided corresponding to the toner colors of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Cartridge 10Y, 10M, 10C, 10K is referred to as cartridge 10 when it is generically referred to or when it indicates an unspecified one. The primary transfer rollers 15Y, 15M, 15C, and 15K are arranged so as to face the cartridges 10Y, 10M, 10C, and 10K, respectively. The primary transfer roller 15Y, 15M, 15C, 15K is referred to as the primary transfer roller 15 when it is generically referred to or when it indicates an unspecified one.

Each cartridge 10 includes a photoconductor drum 11 as an image carrier, a charging unit 12, an exposure unit 13, a developing unit 14, and a photoconductor cleaning unit 16. The photoconductor drum 11 is for supporting an electrostatic latent image formed on the surface of the photosensitive layer on the surface layer thereof. The charging unit 12, the exposure unit 13, the developing unit 14, the primary transfer roller 15, and the photoconductor cleaning unit 16 are provided around the photoconductor drum 11 in this order along the rotation direction of the photoconductor drum 11. .. Therefore, the process proceeds in the order of charging, exposure, development, primary transfer, and photoconductor cleaning.

The charging unit 12 uniformly charges the surface of the photoconductor drum 11. The exposure unit 13 generates an electrostatic latent image on the surface of the photoconductor by exposing a portion corresponding to the image on the surface of the photoconductor drum 11. The developing unit 14 attaches the charged toner to the electrostatic latent image on the surface of the photoconductor by the action of the electric field force generated by the counter electrode. In the case of the present embodiment, it is reverse development in which an image is formed by adhering toner to an exposed portion. The primary transfer roller 15 transfers the toner image formed on the surface of the photoconductor onto the intermediate transfer belt 20 by the action of an electric field force. The photoconductor cleaning unit 16 scrapes the surface of the photoconductor with a cleaning blade to remove the residual transfer toner on the surface of the photoconductor without being transferred to the intermediate transfer belt 20.

In each cartridge 10, a static elimination unit (also referred to as an eraser) (also referred to as an eraser) (not shown) may be provided between the photoconductor cleaning unit 16 and the charging unit 12. The static elimination unit initializes the charged state of the surface of the photoconductor by, for example, irradiating light or bringing a member to which a bias voltage is applied into contact with the surface of the photoconductor.

The intermediate transfer belt 20 constitutes an intermediate transfer unit together with the support rollers 21 and 22. The intermediate transfer belt 20 is supported in a state where a constant tension is applied by support rollers 21 and 22 arranged in parallel. One of the support rollers 21 and 22 is connected to a machine body (not shown) and is driven by the machine body. The intermediate transfer belt 20 is sandwiched between the photoconductor drums 11 of the cartridges 10Y, 10M, 10C, 10K and the corresponding primary transfer rollers 15Y, 15M, 15C, 15K, and the cartridges 10Y, 10M, 10C, respectively. It rotates along the arrangement direction of 10K. The toner images formed on the surface of the photoconductor drum 11 of each cartridge 10Y, 10M, 10C, 10K are transferred onto the intermediate transfer belt 20 in a state of being superposed on each other.

The secondary transfer roller 24 is arranged at a position downstream of the primary transfer rollers 15Y, 15M, 15C, and 15K in the moving direction of the intermediate transfer belt 20. The secondary transfer roller 24 transfers the toner images of a plurality of colors transferred on the intermediate transfer belt 20 onto the paper 31 as the recording medium T. The fixing unit 25 fixes the toner image transferred on the recording medium T to the recording medium T by heating and pressurizing the toner image. The intermediate transfer belt cleaning unit 23 cleans the intermediate transfer belt 20 by removing the transfer residual toner remaining on the intermediate transfer belt 20 without being transferred to the recording medium T.

Photoreceptor drum 11, charging unit 12, exposure unit 13, developing unit 14, photoconductor cleaning unit 16, primary transfer roller 15, intermediate transfer belt 20, secondary transfer roller 24, fixing unit 25, intermediate transfer belt cleaning For the unit 23 and the like, a well-known technique of the electrophotographic method may be arbitrarily selected and used.

Next, the transport unit 3 will be described. The transport unit 3 includes a recording medium storage unit 30, a paper feed roller 32, a timing roller 33, a paper passage sensor 34, a paper discharge roller 36, and double-sided paper transport rollers 35a and 35b.

The paper feed roller 32 feeds the recording medium T such as the paper 31 from the recording medium storage unit 30 into the transport path 40. The timing roller 33 temporarily stops the recording medium T conveyed on the transfer path 40 in order to adjust the timing at which the toner image is transferred onto the recording medium T by the secondary transfer roller 24. The paper ejection roller 36 ejects the recording medium T after being fixed by the fixing portion 25, or conveys the recording medium T to the double-sided conveying path 41. The double-sided transfer rollers 17a and 17b convey the recording medium T to the timing roller 33 via the double-sided transfer path 41.

[Overall configuration of image forming apparatus]
FIG. 2 is a block diagram showing the overall configuration of the image forming apparatus. With reference to FIG. 2, the image forming apparatus 1 includes a scanner unit 50, an ADF (Auto Document Feeder) unit 51, a control unit 100, a storage device 105, and an operation in addition to the image forming unit 2 and the conveying unit 3 already described. It includes a panel 106, a communication interface (I / F: Interface) 107, and an image processing unit 108. The configuration of the image forming apparatus in FIG. 2 is based on the assumption of a copying machine, but when the image forming apparatus is a dedicated printer, the scanner unit 50 and the ADF unit 51 in FIG. 2 may not be provided.

The scanner unit 50 reads the document placed on the platen by the image sensor and converts it into image data. The ADF unit 51 conveys a plurality of documents placed on the document tray one by one, and ejects the documents that have been scanned at the scanning position of the platen to the paper output tray.

The control unit 100 includes a CPU (Central Processing Unit) 101, a RAM (Random Access Memory) 102, a ROM (Read Only Memory) 103, and an interface (I / F: Interface) 104.

The CPU 101 realizes the processing of the entire image forming apparatus 1 by reading and executing the program stored in the ROM 103.

The RAM 102 is typically a DRAM (Dynamic Random Access Memory) or the like, and temporarily stores data and image data necessary for the CPU 101 to operate the program. Therefore, the RAM 102 functions as a so-called working memory.

The ROM 103 is typically a flash memory or the like, and stores a program executed by the CPU 101 and various setting information related to the operation of the image forming apparatus.

The interface 104 exchanges various signals with an external device. Specifically, the control unit 100 is electrically connected to the storage device 105, the operation panel 106, the communication interface 107, the image processing unit 108, the image processing unit 2, the transport unit 3, the scanner unit 50, and the ADF unit 51 via the interface 104. Is connected.

The storage device 105 stores various control values, data and image data input via the communication interface 107, and the like.

The operation panel 106 is for the user to input various setting values such as the number of copies to be printed, the printing method, the type and size of paper, and the like. The operation panel 106 is further provided with a start button for the image forming apparatus to start reading and printing the original.

The communication interface 107 is a device for communicating with an external device. The communication interface 107 is, for example, a wireless LAN (Local Area Network) card. The image forming apparatus 1 is configured to be communicable with an external device connected to a LAN or WAN (Wide Area Network) via a communication interface 107. The communication interface 107 receives data such as image data and various setting values from an external device.

The image processing unit 108 is composed of, for example, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The image processing unit 108 converts the R (red), G (green), and B (blue) image data read by the scanner unit 50 into Y, M, C, and K image data and outputs the data.

[About the image quality of the second side during double-sided image formation]
In the following, the relationship between the secondary transfer current and the transfer efficiency will be described first. Further, in the case of performing double-sided image formation, the relationship between the fixing temperature during the first surface image formation and the secondary transfer current during the second surface image formation will be described. Based on these findings, a method for improving the image quality of the second surface when the fixing temperature at the time of image formation on the first surface is changed will be described.

FIG. 3 is a diagram showing an example of the relationship between the secondary transfer current and the transfer efficiency. In the graph of FIG. 3, the horizontal axis shows the secondary transfer current, and the vertical axis shows the transfer efficiency.

The transfer efficiency refers to the ratio of the weight of the toner image actually transferred on the recording medium to the weight of the toner image formed for image formation on the recording medium. Therefore, the higher the numerical value, the better the transfer device, and when the transfer efficiency is equal to 1, it means that all the imaged toner images have been transferred onto the recording medium.

If the secondary transfer current is less than the optimum value, the transfer of toner onto the recording medium is incomplete, and the transfer efficiency is lowered. On the other hand, if the secondary transfer current is too large, the current that effectively acts as the secondary transfer is reduced due to the discharge generated in the secondary transfer portion, and the transfer efficiency is lowered. Therefore, as shown in the graph of FIG. 3, the relationship between the secondary transfer current and the transfer efficiency is an upper convex curve, and the secondary transfer current has an optimum value that maximizes the transfer efficiency. A high-quality image is obtained at the optimum value of this secondary transfer current.

FIG. 4 is a diagram showing the relationship between the fixing temperature of the first surface and the secondary transfer current of the second surface when performing double-sided image formation. The graph in FIG. 4 shows the results of data collection using the bizhub C368 manufactured by Konica Minolta Co., Ltd. as an experimental machine. The experiment was carried out as follows.

First, a blank image is passed by setting the fixing temperature to a standard temperature. Then, the paper after passing through the fixing is re-fed, and the secondary transfer current when the blank image is passed again is measured. Here, the blank image passing is a process of performing a series of electrophotographic processes without forming a toner image. Next, the setting of the fixing temperature is changed from the standard temperature, a blank image is passed through in the same manner, and the secondary transfer current when the paper after passing through the fixing is re-fed is measured in the same manner as described above. In FIG. 4, the vertical axis represents the difference between the secondary transfer current when the fixing temperature is set as standard and the secondary transfer current when the fixing temperature is changed from the standard fixing temperature. The horizontal axis represents the difference between the standard setting fixing temperature and the fixing temperature when changed from the standard setting.

As shown in FIG. 4, the higher the setting of the fixing temperature at the time of passing the paper on the first side, the more difficult the secondary transfer current on the second side on both sides flows. This means that if the fixing temperature during image formation on the first surface is raised, the evaporation of water when the paper passes through the fixing portion increases and the electrical resistance of the paper increases, making it difficult for the secondary transfer current on the second surface to flow. It is shown that.

FIG. 5 is a diagram showing the relationship between the secondary transfer current and the transfer efficiency and the relationship between the secondary transfer current and the secondary transfer voltage. Hereinafter, the relationship between the fixing temperature at the time of the first surface image formation and the secondary transfer efficiency at the time of the second surface image formation in the case of performing double-sided image formation will be described with reference to the graph of FIG.

The value of the secondary transfer current at which the maximum transfer efficiency is obtained varies depending on the paper type used. Therefore, in advance at the product development stage, the secondary transfer voltage value at which the optimum secondary transfer current will flow for the paper type to be used is experimentally obtained. The relationship between the paper type to be used and the set value of the secondary transfer voltage is preliminarily incorporated in the product body by a table or a relational expression. During actual use of the product, the set value of the secondary transfer voltage is controlled according to the paper type used by the user on the operation panel or the like. This makes it possible to image with the optimum secondary transfer current.

For example, when the straight line shown by VI1 is obtained as the secondary transfer current-voltage characteristic in the graph of FIG. 5, the maximum transfer efficiency can be obtained when the secondary transfer voltage is 1500 V.

However, when the setting of the fixing temperature for the first side can be changed in the case of automatic double-sided image formation, the amount of moisture absorbed by the paper changes depending on the fixing temperature at the time of the first side image formation, so that the electrical resistance of the paper increases. It will change. Therefore, at the initially set secondary transfer voltage, a deviation occurs from the optimum secondary transfer current.

For example, in the graph of FIG. 5, the secondary transfer current-voltage characteristic when the fixing temperature at the time of image formation on the first surface is raised above the standard temperature is shown by VI2. Since the fixing temperature is raised above the standard fixing temperature, the electrical resistance of the paper is higher than that at the standard fixing temperature. Therefore, when the secondary transfer voltage is set to 1500 V, which is the standard voltage value, the secondary transfer current is reduced, so that the transfer efficiency deviates from the peak value.

Therefore, if the secondary transfer voltage is corrected by an amount corresponding to the deviation of the secondary transfer current from the optimum value, it becomes possible to return to the optimum secondary transfer current value. Specifically, in the example of FIG. 5, it is possible to return to the optimum secondary transfer current value by increasing the secondary transfer voltage.

[Control method of transfer voltage on the second surface during double-sided image formation]
FIG. 6 is a flowchart showing an example of a secondary transfer voltage control procedure for the second surface when automatic double-sided image formation is performed. Hereinafter, an example of the secondary transfer voltage control procedure will be described in detail by summarizing the explanations so far. The following control procedure is executed by the control unit 100 of FIG.

First, in the case of the first surface of the automatic double-sided image formation (NO in step S100), the secondary transfer voltage is executed at the voltage for the first surface (step S150). The set value of the secondary transfer voltage in this case differs depending on the paper type input by the user depending on the operation panel.

The process in the case of the second surface of the automatic double-sided image formation (YES in step S100) differs depending on the fixing temperature at the time of fixing the first surface. In the example shown in FIG. 6, the fixing temperature of the first surface is set to the standard temperature T1, the case where the fixing temperature is set to T2 which is lower than the standard temperature T1, and the case where the fixing temperature is higher than the standard temperature T1. The process is divided into the case where it is set to T3.

Here, the control unit 100 may determine the fixing temperature of the first surface based on the image information imaged on the first surface. For example, the control unit 100 sets the fixing temperature of the first surface to the low temperature T2 when the first surface is a monochrome image, and sets the fixing temperature of the first surface to the standard temperature T1 when the first surface is a color image. .. Alternatively, the control unit 100 sets the fixing temperature of the first surface to the standard temperature T1 when the first surface is a monochrome image, and sets the fixing temperature of the first surface to a high temperature T3 when the first surface is a color image.

Similarly, the control unit 100 sets the fixing temperature of the first surface to a relatively low temperature when the first surface contains only characters, and when the first surface contains photographs or charts other than characters, the fixing temperature of the first surface is set. May be set to a relatively high temperature. Further, when the maximum value of the amount of toner adhered per unit area calculated based on the image information of the first surface is less than the threshold Th1, the control unit 100 sets the fixing temperature of the first surface to a relatively low temperature. When the maximum value of the amount of toner adhered per unit area of the first surface is the threshold Th1 or more, the fixing temperature of the first surface may be set to a relatively high temperature.

As described above, when the image information on the first surface is a color image, contains information other than text information, or the maximum value of the toner amount per unit area is the threshold Th1 or more, the amount of toner to be fixed on the recording medium is Since the amount is relatively large, it is desirable to set the fixing temperature to a relatively high temperature. On the other hand, in any of the above cases, the fixing temperature may be set to a lower value from the viewpoint of energy saving.

Next, the control unit 100 determines the secondary transfer voltage for the second surface according to the set value of the fixing temperature for the first surface (steps S120, S130, S140). Then, the control unit 100 starts the secondary transfer operation at the set secondary transfer voltage (step S160).

Specifically, in the example of FIG. 6, when the fixing temperature for the first surface is set to the standard temperature T1, the control unit 100 determines the secondary transfer voltage for the second surface according to the paper type, which is the standard voltage value V1. (Step S120). When the fixing temperature for the first surface is set to the low temperature T2, the control unit 100 sets the secondary transfer voltage for the second surface to a voltage value V2 lower than the standard voltage V1 (step S130). When the fixing temperature for the first surface is set to the high temperature T3, the control unit 100 sets the secondary transfer voltage for the second surface to a voltage value V3 higher than the standard voltage V1 (step S140).

According to the control procedure described above, even when the fixing temperature of the first surface is changed, the secondary transfer of the second surface can be performed with a more appropriate secondary transfer current value and therefore higher transfer efficiency. It is possible to prevent deterioration of the image quality of the surface.

<Embodiment 2>
Deterioration of image quality is noticeable because the secondary transfer efficiency deviates from the maximum value when a color image is formed or when the amount of toner adhered is large. Therefore, the secondary transfer voltage of the second surface may be changed according to the fixing temperature of the first surface only when applicable. In the image forming apparatus of the second embodiment, the secondary transfer voltage is changed only when the image information on the second surface corresponds to a predetermined condition in this way. Hereinafter, a specific description will be given with reference to the drawings.

FIG. 7 is a flowchart showing a control procedure of the secondary transfer voltage at the time of image formation on the second surface in the image forming apparatus of the second embodiment. The flowchart of FIG. 7 differs from the flowchart of FIG. 6 in that steps S200 and S210 are added. Since the other points of FIG. 7 are the same as those of FIG. 6, the same or corresponding steps are designated by the same reference numerals and the description is not repeated.

When the fixing temperature for the first surface is set to the low temperature T2 with reference to FIG. 7, the control unit 100 determines whether or not the image information for the second surface matches the predetermined condition (step S200). In this case, the predetermined condition is at least one of the fact that the image information represents a color image and that the amount of toner adhering to the recording medium estimated based on the image information is the threshold Th2 or more. Is. When this predetermined condition is satisfied (YES in step S200), the control unit 100 changes the secondary transfer voltage of the second surface to V2, which is a voltage lower than the standard value V1 (step S130). On the other hand, when the above predetermined conditions are not satisfied, for example, when the image information represents a monochrome image and the estimated toner adhesion amount to be fixed is less than the threshold Th2, the control unit 100 is on the second surface. The secondary transfer voltage is left at the standard voltage value V1 and is not changed (step S120).

When the fixing temperature for the first surface is set to the high temperature T3, the control unit 100 determines whether or not the image information on the second surface matches the above-mentioned predetermined conditions (step S210). When the above predetermined condition is satisfied (YES in step S210), the control unit 100 changes the secondary transfer voltage of the second surface to V3, which is a voltage higher than the standard value V1 (step S140). On the other hand, when the above predetermined conditions are not satisfied, for example, when the image information represents a monochrome image, or when the estimated toner adhesion amount to be fixed is less than the threshold Th2, the control unit 100 is on the second surface. The secondary transfer voltage is left at the standard voltage value V1 and is not changed (step S120).

When the image information represents a monochrome image as described above, or when the estimated toner adhesion amount to be fixed is less than the threshold Th2, the secondary transfer voltage of the second surface is changed according to the fixing temperature of the first surface. Even with the simplified process of not doing so, the degradation in image quality is not noticeable.

The embodiments disclosed this time should be considered as exemplary in all respects and not restrictive. The scope of the present invention is shown by the claims rather than the above description, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

1 Image forming device, 2 Image forming part, 3 Transfer part, 10 Cartridge, 11 Photoreceptor drum, 12 Charge part, 13 Exposure part, 14 Development part, 15 Primary transfer roller, 17a, 17b, 35a, 35b Double-sided transfer roller , 20 Intermediate transfer belt, 24 Secondary transfer roller, 25 Fixing unit, 31 Paper, 40 Transfer path, 41 Double-sided transfer path, 100 Control unit, T Recording medium.

Claims (7)

An image forming apparatus capable of producing images on both sides of a recording medium.
An image carrier that supports a toner image formed based on image information,
A primary transfer unit that transfers a toner image supported on the image carrier to an intermediate, and a primary transfer unit.
A secondary transfer unit that transfers the toner image transferred to the intermediate to the recording medium, and
A fixing unit for fixing the toner image transferred to the recording medium set by the target fixing temperature,
A control unit that controls the secondary transfer voltage of the secondary transfer unit and the target fixing temperature is provided.
The target fixing temperature, can be set even without least to the lower than the first temperature first temperature second temperature,
When the target fixing temperature for the first surface of the recording medium is set to the first temperature, the control unit sets the secondary transfer voltage for the second surface of the recording medium to the first voltage. When the target fixing temperature for the first surface is set to the second temperature, the secondary transfer voltage for the second surface is set to a second voltage lower than the first voltage.
When the image information imaged on the second surface represents a color image, the control unit determines whether the target fixing temperature for the first surface is the first temperature or the second temperature. Depending on the presence, the secondary transfer voltage for the second surface is set to the first voltage or the second voltage, respectively.
When the image information imaged on the second surface represents a monochrome image, the control unit determines whether the target fixing temperature for the first surface is the first temperature or the second temperature. An image forming apparatus that sets the secondary transfer voltage for both the first surface and the second surface to either the first voltage or the second voltage regardless of the presence or absence. An image forming apparatus capable of producing images on both sides of a recording medium.
An image carrier that supports a toner image formed based on image information,
A primary transfer unit that transfers a toner image supported on the image carrier to an intermediate, and a primary transfer unit.
A secondary transfer unit that transfers the toner image transferred to the intermediate to the recording medium, and
A fixing unit for fixing the toner image transferred to the recording medium set by the target fixing temperature,
A control unit that controls the secondary transfer voltage of the secondary transfer unit and the target fixing temperature is provided.
The target fixing temperature, can be set even without least to the lower than the first temperature first temperature second temperature,
When the target fixing temperature for the first surface of the recording medium is set to the first temperature, the control unit sets the secondary transfer voltage for the second surface of the recording medium to the first voltage. When the target fixing temperature for the first surface is set to the second temperature, the secondary transfer voltage for the second surface is set to a second voltage lower than the first voltage.
When the amount of toner adhered to the second surface estimated based on the image information is equal to or greater than the first threshold value, the control unit determines whether the target fixing temperature for the first surface is the first temperature. The secondary transfer voltage for the second surface is set to the first voltage or the second voltage, respectively, depending on whether the temperature is the second temperature.
When the amount of toner adhered to the second surface is less than the first threshold value, the control unit determines whether the target fixing temperature for the first surface is the first temperature or the second temperature. An image forming apparatus that sets the secondary transfer voltage for both the first surface and the second surface to either the first voltage or the second voltage. The image forming apparatus according to claim 1 or 2, wherein the control unit sets the target fixing temperature according to the paper type. The control unit sets the target fixing temperature for the first surface to the first temperature or the second temperature based on the image information imaged on the first surface, according to claims 1 to 3. The image forming apparatus according to any one item. When the image information imaged on the first surface represents a color image, the control unit sets the target fixing temperature for the first surface to the first temperature.
According to claim 4, the control unit sets the target fixing temperature for the first surface to the second temperature when the image information imaged on the first surface represents a monochrome image. The image forming apparatus described. When the image information imaged on the first surface includes only character information, the control unit sets the target fixing temperature for the first surface to the second temperature.
The fourth aspect of the present invention, wherein the control unit sets the target fixing temperature for the first surface to the first temperature when the image information imaged on the first surface includes information other than character information. Image forming device. When the maximum value of the toner adhesion amount per unit area of the first surface estimated based on the image information is equal to or more than the second threshold value, the control unit sets the target fixing temperature for the first surface. Set to the first temperature,
When the maximum value of the toner adhesion amount per unit area of the first surface is less than the second threshold value, the control unit sets the target fixing temperature for the first surface to the second temperature. The image forming apparatus according to claim 4.

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