Image forming apparatus

Abstract

The present invention provides an image forming apparatus that prevents a decrease in image quality due to changes in transferability caused by environmental changes. [Solution] The image forming apparatus 100 includes an intermediate transfer belt 71, a conductive intermediate transfer drive roller 72, a conductive transfer roller 11a that transfers and transports the toner image intermediately transferred to the surface of the intermediate transfer belt 71 to a sheet P, a transfer power supply 184 that can switch between a first output state in which a first bias is output to the intermediate transfer drive roller 72, which is a voltage or current of the same polarity as the charge polarity of the toner image, and the transfer roller 11a is grounded, and a second output state in which a second bias is output to the transfer roller 11a, which is a voltage or current of the opposite polarity to the charge polarity of the toner image, and the intermediate transfer drive roller 72 is grounded, an environmental sensor 183, and a control unit 180 that performs the transfer of the toner image to the sheet P in either the first output state or the second output state based on the detection result of the environmental sensor 183.

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus that transfers toner onto a sheet to form an image.

Background Art

[0002] In image forming apparatuses such as copiers, facsimile machines, printers, and multifunction peripherals, for example, in a tandem type color image forming apparatus, toner images formed on a plurality of photosensitive drums arranged in a line in the running direction of a transfer belt are superimposed and transferred onto the transfer belt, and the toner image formed on the transfer belt is transferred onto a sheet (paper) to form an image on the sheet. Thus, an image is formed on the sheet by two transfers: transfer from the photosensitive drum to the transfer belt (intermediate transfer) and transfer from the transfer belt to the sheet (transfer).

[0003] Here, the toner is charged, and transfer is performed by applying a voltage or the like to a member related to transfer to apply a bias. For example, in the transfer from the photosensitive drum to the transfer belt, which is intermediate transfer, a voltage is applied to an intermediate transfer roller provided to face the photosensitive drum through the transfer belt, and an electric field is generated between this intermediate transfer roller and the photosensitive drum such that the side of the intermediate transfer roller has the opposite polarity to the charged toner. Also, in the transfer from the transfer belt to the sheet, which is transfer, a voltage is applied to a transfer roller, and an electric field is generated between this transfer roller and a counter roller (driving roller) that is disposed to face the transfer roller and grounded through the transfer roller and the transfer belt such that the side of the secondary transfer roller has the opposite polarity to the charged toner.

[0004] Although transfer is performed as described above, when the distance between the part where intermediate transfer is performed and the part where transfer is performed is too narrow, there may be a problem that, due to the influence of the potential difference between the intermediate transfer roller and the counter roller, the current that should originally flow from the intermediate transfer roller to the photosensitive drum flows to the counter roller through the inner peripheral surface of the transfer belt. As a result, there is a problem that transfer failure occurs and the image quality of the image formed on the sheet deteriorates.

[0005] To resolve these problems, for example, according to the image forming apparatus disclosed in Patent Document 1, a positive voltage of the same polarity as that applied to the intermediate transfer roller is applied to the opposing roller, which is positioned opposite the transfer roller via a transfer belt, to perform image formation. Furthermore, the magnitude of the voltage applied to the opposing roller is approximately equal to the magnitude of the voltage applied to the intermediate transfer roller. This suppresses transfer defects and prevents a decrease in image quality. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2000-275979 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] As mentioned above, the image forming apparatus disclosed in Patent Document 1 can suppress transfer defects caused by the gap between the intermediate transfer area and the transfer area being too narrow. However, there are other reasons for transfer defects. For example, when voltage is applied to the opposing roller during transfer, current escapes through the sheet via a metal guide provided in the sheet transport path, reducing the amount of current flowing to the transfer roller and potentially distorting the toner image. In particular, in high-humidity environments, the moisture content of the sheet increases, making it easier for current to escape through the sheet, and if current flows from the transfer roller, transfer defects may occur. When transfer defects occur, the image formed on the sheet becomes rough, resulting in a decrease in image quality. Such transfer defects are difficult to address even with the image forming apparatus disclosed in Patent Document 1.

[0008] This disclosure has been made in view of the circumstances described above, and its purpose is to provide an image forming apparatus that prevents a decrease in image quality due to changes in transferability caused by environmental changes. [Means for solving the problem]

[0009] An image forming apparatus according to one aspect of the present disclosure is characterized by comprising: an intermediate transfer belt onto which a toner image formed in an image forming unit is intermediately transferred to the surface; a conductive drive roller around which the intermediate transfer belt is wrapped and rotates to move the intermediate transfer belt in a predetermined direction; a conductive transfer member provided at a position opposite to the drive roller so as to contact the surface of the intermediate transfer belt, and transferring and conveying the toner image intermediately transferred to the surface of the intermediate transfer belt to a sheet at the contact portion with the intermediate transfer belt; a transfer power supply switchable between a first output state in which a first bias is output to the drive roller, which is a voltage or current of the same polarity as the charge polarity of the toner image, and the transfer member is grounded, and a second output state in which a second bias is output to the transfer member, which is a voltage or current of the opposite polarity to the charge polarity of the toner image, and the drive roller is grounded; and a control unit that performs the transfer of the toner image to the sheet in either the first output state or the second output state based on the detection result of the environmental sensor.

[0010] This allows for the output of appropriate bias to the transfer roller and drive roller according to humidity and temperature conditions. Therefore, it is possible to prevent image quality degradation caused by humidity and temperature changes. In other words, it is possible to prevent image quality degradation due to changes in transferability caused by environmental changes.

[0011] Furthermore, in the image forming apparatus described above, the transfer power supply may include a first power supply capable of generating a voltage or current of the same polarity as the charging polarity of the toner image, a second power supply capable of generating a voltage or current of the opposite polarity to the charging polarity of the toner image, and a switching device that switches the connection destination of the first power supply and the second power supply to the drive roller or the transfer member, and the first output state, the second output state, and the third output state may be switched by changing the connection destination by the switching means.

[0012] This eliminates the need for a dedicated power supply to clean the transfer material, preventing waste toner from remaining on the material. This reduces the number of parts, enabling miniaturization and cost reduction. [Effects of the Invention]

[0013] According to this disclosure, it is possible to provide a developing apparatus that is less susceptible to deterioration in image quality due to changes in transferability caused by environmental changes, and an image forming apparatus equipped therewith. [Brief explanation of the drawing]

[0014] [Figure 1] This is a perspective front view showing a schematic configuration of an image forming apparatus according to an embodiment of the present disclosure. [Figure 2] This diagram shows a schematic circuit diagram illustrating the transfer power supply according to the embodiment of this disclosure, the connection state of the transfer power supply to the intermediate transfer drive roller and the transfer roller, and the first output state. [Figure 3] This figure shows a second output state in which the second power supply is connected to the transfer roller and the intermediate transfer drive roller is grounded, according to the switching means for the transfer power supply according to the embodiment of this disclosure. [Figure 4] This is a block diagram showing the control configuration of a control unit according to an embodiment of the present disclosure. [Figure 5] This figure shows an example of a drive table in which the transfer output conditions, which are the output state of the transfer power supply when transferring a toner image to a sheet, are defined in an image forming apparatus according to an embodiment of the present disclosure. [Figure 6] This figure shows the output state of the transfer power supply during cleaning operation according to the embodiment of the present disclosure, and illustrates a third output state in which the first power supply is connected to the transfer roller by the switching means and the intermediate transfer drive roller is in a grounded state. [Figure 7] This flowchart shows an example of the operation of an image forming apparatus according to the present disclosure. [Modes for carrying out the invention]

[0015] Embodiments according to the present disclosure will be described with reference to the drawings.

[0016] An image forming apparatus according to an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a front view schematically showing a perspective view of the configuration of an image forming apparatus 100 according to an embodiment of the present disclosure.

[0017] The image forming apparatus 100 is a multifunction device having a copying function, a scanner function, a facsimile function, and a printer function, and includes an image reading device 102 and an image forming apparatus main body 101.

[0018] The image reading device 102 includes an image reading unit 130 and a document feeder 160 [automatic document feeder (ADF)]. The document feeder 160 is provided above the image reading unit 130 and is supported so as to be openable and closable with respect to the image reading unit 130.

[0019] The image reading unit 130 includes a document placement table 130a on which a document G is placed, a document reading unit 130b, a scanning optical system 130c that scans the document, and an imaging unit 130d.

[0020] When the document feeder 160 is opened, the document placement table 130a above the image reading unit 130 is opened, and the document G can be placed manually. The scanning optical system 130c is provided below the document placement table 130a so as to be movable in the direction of arrow D in FIG. 1. By moving in the direction of arrow D, the scanning optical system 130c scans the document placed on the document placement table 130a and converts it into electronic data by imaging with the imaging unit 130d. The document reading unit 130b is a part that reads the document sent by the document feeder 160 with the scanning optical system 130c.

[0021] The document feeder 160 includes a document tray 161 on which one or more documents G are placed, a document transport path W that guides the documents G placed on the document tray 161 to the document reading unit 130b, a document feeding unit 162 that sequentially feeds one or more documents G placed on the document tray 161 one by one along the document transport path W, and a paper output tray 163 on which the documents G read by the image reading unit 130b via the scanning optical system 130c are discharged. When the image reading unit 102 reads documents G using the document feeder 160, it moves the scanning optical system 130c below the image reading unit 130b. The image reading unit 130 generates image data by scanning the scanning optical system 130c to read documents placed on the document placement table 130a or by reading documents G being transported by the document feeder 160.

[0022] Next, the main body 101 of the image forming apparatus will be described. The image forming apparatus 100 of this disclosure is an intermediate transfer type electrophotographic image forming apparatus 100 capable of forming color images. Therefore, the image forming apparatus 100 handles image data corresponding to color images using black (K), cyan (C), magenta (M), and yellow (Y), or monochrome images using a single color (for example, black). The main body 101 of the image forming apparatus comprises an image forming unit 50, an intermediate transfer device 70, a transfer device 11, a fixing device 12, a sheet transport path S, a paper feed cassette 18, and a sheet discharge tray 141.

[0023] The image forming unit 50 of the image forming apparatus 100 has four image stations Pa, Pb, Pc, and Pd corresponding to black, cyan, magenta, and yellow, and an exposure device 3. Each of these image stations Pa, Pb, Pc, and Pd is equipped with a photoreceptor drum 1, a charger 2, a developer 4, and a drum cleaning device 5. Four types of toner images are formed on each of the photoreceptor drums 1-1 of these image stations Pa, Pb, Pc, and Pd. In other words, the image forming apparatus 100 is provided with four photoreceptor drums 1, four chargers 2, four developers 4, and four drum cleaning devices 5, each corresponding to form black, cyan, magenta, and yellow toner images.

[0024] The photoreceptor drum 2 has a photosensitive layer formed on the surface of a grounded metal tube. The photosensitive layer exhibits insulating properties when not exposed to light, and changes to conductive properties in areas exposed to light. The charger 2 charges the surface of the photoreceptor drum 2 to a predetermined potential (e.g., -500V). The light scanning device 4 exposes the surface of the photoreceptor drum 1, which has been charged to the predetermined potential, to form an electrostatic latent image. (The potential of the exposed area of ​​the photoreceptor drum 1 drops to about -80V, and an electrostatic latent image with a different surface potential distribution depending on the image is formed.) The developing device 4 comprises a developer containing toner, a stirring and conveying member, and a developing tank containing the developing roller 4. The developing device 4 conveys the developer to the developing roller while stirring it with the stirring and conveying member. The toner contained in the developer is frictionally charged to a predetermined polarity (e.g., -25μC / mg) as it is conveyed while being stirred by the stirring and conveying member. A portion of the developer conveyed by the stirring and conveying member is supplied to the surface of the developing roller. The developing roller 4 is positioned facing the photoreceptor drum 1. Toner charged to a predetermined polarity is supplied from the developing roller toward the exposed area of ​​the photoreceptor drum 1, thereby revealing (developing) the electrostatic latent image on the surface of the photoreceptor drum 1. As described above, the developing device 4 develops the electrostatic latent image on the surface of the photoreceptor drum 1 and forms a toner image on the surface of the photoreceptor drum 1. The drum cleaning device 5 removes and collects any residual toner remaining on the surface of the photoreceptor drum 1 after the toner image has been transferred to the intermediate transfer belt 71 (described later). The electrostatic latent image on the photoreceptor drum 1, which has been cleaned by the drum cleaning device 5, is erased by an anti-static device (not shown). The charger 2 uniformly recharges the surface of the photoreceptor drum 1, which has been de-staticized by the anti-static device, to a predetermined potential. Through the series of operations described above, toner images of each color are formed on the surface of each photoreceptor drum 1.

[0025] The intermediate transfer device 70 includes an intermediate transfer roller 6, an endless intermediate transfer belt 71, an intermediate transfer drive roller 72 (drive roller), an intermediate transfer driven roller 73, and a cleaning device 9. The intermediate transfer belt 71 is an endless belt that can move around and is wrapped around the intermediate transfer drive roller 72 and the intermediate transfer driven roller 73. In other words, the intermediate transfer drive roller 72 and the intermediate transfer driven roller 73 tension the intermediate transfer belt 71. The intermediate transfer drive roller 72 is conductive and rotates by a drive source (not shown) to rotate the intermediate transfer belt 71 in the direction of arrow F (predetermined direction F) in Figure 1. There are four intermediate transfer rollers 6, each positioned inside the intermediate transfer belt 71 and facing the corresponding photoreceptor drum 1. The intermediate transfer rollers 6 intermediate transfer the toner images of each color formed on the surface of the photoreceptor drum 1 to the surface of the intermediate transfer belt 71. In other words, the image forming apparatus 100 includes an intermediate transfer belt 71 on which the toner image formed in the image forming unit 50 is intermediately transferred to the surface, and a conductive intermediate transfer drive roller 72 on which the intermediate transfer belt 71 is wrapped around the surface and rotates to rotate the intermediate transfer belt 71 in a predetermined direction F.

[0026] The image forming apparatus 100 sequentially transfers the toner images of each color formed on the surface of each photoreceptor drum 1 to an intermediate transfer belt 73, and then transfers the resulting toner images to a sheet P using a transfer device 11, which will be described later. The cleaning device 9 removes and collects waste toner that remains on the surface of the intermediate transfer belt 71 without being transferred to the sheet P.

[0027] The transfer apparatus 11 forms a transfer nip region TN between a conductive transfer roller 11a (transfer member) and an intermediate transfer belt 71 wound around an intermediate transfer drive roller 72, and transports the sheet P that has been transported through the sheet transport path S by sandwiching it in the transfer nip region TN. The transfer roller 11a is positioned opposite the intermediate transfer drive roller 72, with the intermediate transfer belt 71 sandwiched between it and the intermediate transfer drive roller 72. As the sheet P passes through the transfer nip region TN, the toner image on the surface of the intermediate transfer belt 71 is transferred to the sheet P and it is transported to the fixing apparatus 12. In other words, the image forming apparatus 100 is provided with a conductive transfer roller 11a that is positioned opposite the intermediate transfer drive roller 72 and in contact with the surface of the intermediate transfer belt 71, and that transfers the toner image intermediately transferred to the surface of the intermediate transfer belt 71 to the sheet P at the contact point with the intermediate transfer belt 71 (transfer nip region TN) and transports it. As will be explained in more detail later, when transferring the toner image from the intermediate transfer belt 71 to the sheet P, the intermediate transfer drive roller 72 and the transfer roller 11a are grounded or electrically biased to facilitate the movement of negatively charged toner from the intermediate transfer belt 71 to the sheet P. For this purpose, a transfer power supply 184 (see Figure 2, etc.) is provided, which will be explained later.

[0028] The fixing device 12 is equipped with a fixing roller 31 and a pressure roller 32 that rotate with the sheet P in between. The fixing device 12 heats and pressurizes the sheet P, on which the toner image has been transferred, between the fixing roller 31 and the pressure roller 32, thereby fixing the toner image to the sheet P. The surface of the fixing roller 31 is heated to a predetermined temperature by a heater, which is a heat source provided inside, and the heat transmitted from the heated fixing roller 31 and the pressure from the pressure roller 32 melt the toner image transferred to the sheet P and fix it to the sheet P.

[0029] The paper feed cassette 18 is a cassette for storing sheets P used for image formation and is located on the lower side of the optical scanning device 3. The sheets P are pulled out of the paper feed cassette 18 by the pickup roller 16 and transported to the sheet transport path S. The sheets P transported to the sheet transport path S are transported via the transfer device 11 and the fixing device 12 to the discharge roller 17 and discharged to the sheet discharge tray 141 in the discharge section 140. The sheet transport path S is equipped with a transport roller 13, a registration roller 14, and a discharge roller 17. The transport roller 13 facilitates the transport of the sheets P. The registration roller 14 temporarily stops the sheets P and aligns the leading edge of the sheets P. Furthermore, the registration roller 14 transports the temporarily stopped sheets P in accordance with the timing of the color toner image on the intermediate transfer belt 71. As described above, the color toner image on the intermediate transfer belt 71 is transferred to the sheets P in the transfer nip region TN between the intermediate transfer belt 71 and the transfer roller 11a.

[0030] Although Figure 1 shows only one paper feed cassette 18, the system is not limited to this configuration. Multiple paper feed cassettes 18 may be provided, each loaded with a different type of sheet P.

[0031] Furthermore, if the image forming apparatus 100 is to perform image formation not only on the front surface but also on the back surface of the sheet P, it transports the sheet P in the reverse direction from the discharge roller 17 to the sheet reversal path Sr. The image forming apparatus 100 reverses the front and back surfaces of the sheet P that has been transported in the reverse direction and guides it back to the register roller 14. The image forming apparatus 100 then forms an image on the back surface of the sheet P guided to the register roller 14 in the same way as the front surface, and transports it to the sheet discharge tray 141.

[0032] Next, we will explain the transfer power supply 184 connected to the intermediate transfer drive roller 72 and the transfer roller 11a, and the transfer of the toner image to the sheet P by the transfer power supply 184 in the transfer nip region TN.

[0033] Figure 2 is a schematic circuit diagram showing the transfer power supply 184 according to the embodiment of this disclosure, and the connection state of the transfer power supply 184 to the intermediate transfer drive roller 72 and the transfer roller 11a, and is a diagram showing the first output state. Also in Figure 2, in order to make the transfer operation by the transfer power supply 184 easier to understand, the configuration around the transfer nip region TN, which is the contact point between the intermediate transfer belt 71 and the transfer roller 11a, the sheet transport guides 34 and 35 that transport the sheet P to the transfer nip region TN, and the transport path P1 of the sheet P formed by the sheet transport guides 34 and 35 are shown. The sheet transport guide 34 is made of metal and is grounded so that the sheet P does not stick to the guide even when it is charged by friction when it is transported by the register roller 14 in a low humidity environment. Note that the surface of the register roller 14 is coated with an elastic material to prevent the sheet P from slipping, so it is prone to frictional charging when the sheet P is passed through.

[0034] As shown in Figure 2, the transfer power supply 184 includes a first power supply 184a that outputs a first bias (e.g., -800V or -40μA) which is a negative polarity voltage or current, and a second power supply 184b that outputs a second bias (e.g., +800V or +40μA) which is a positive polarity voltage or current. Furthermore, the transfer power supply 184 includes a switching means 185 that switches the connection destination of the first power supply 184a and the second power supply 184b to either the intermediate transfer drive roller 72 or the transfer roller 11a, respectively.

[0035] The switching means 185 includes a first changeover switch 185a, one end of which is connected to the intermediate transfer drive roller 72 and the other end of which can be switched between being connected to the first power supply 184a or being grounded, and a second changeover switch 185b, one end of which is connected to the transfer roller 11a and the other end of which can be switched between being connected to the second power supply 184b or being grounded.

[0036] Figure 2 shows the first output state in which the first power supply 184a is connected to the intermediate transfer drive roller 72 by the switching means 185 of the transfer power supply 184, and the transfer roller 11a is in a grounded state. In other words, the first output state is the state in which a negative polarity first bias is supplied to the intermediate transfer drive roller 72. Since the toner according to the embodiment of this disclosure is negatively charged, the toner image formed by the toner is also negatively charged. Therefore, when the sheet P is conveyed to the transfer nip region TN in the first output state, the negative polarity toner image formed on the surface of the intermediate transfer belt 71 is repelled by the negative polarity first bias supplied to the intermediate transfer drive roller 72 and electrostatically moved (transferred) to the sheet P side.

[0037] On the other hand, Figure 3 shows the second output state in which the second power supply 184b is connected to the transfer roller 11a by the switching means 185 of the transfer power supply 184 according to the embodiment of this disclosure, and the intermediate transfer drive roller 72 is in a grounded state. In other words, the second output state is the state in which a positive polarity second bias is supplied to the transfer roller 11a. As described above, since the toner image according to the embodiment of this disclosure is negatively charged, when the sheet P is transported to the transfer nip region TN in the second output state, the negative polarity toner image formed on the surface of the intermediate transfer belt 71 is attracted to the positive polarity second bias supplied to the transfer roller 11a and electrostatically moves (transfers) to the sheet P side.

[0038] As described above, the transfer power supply 184 can realize the conditions for transferring the toner image formed on the surface of the intermediate transfer belt 71 to the sheet P in the transfer nip region TN, in other words, the transfer output conditions which are the output state of the transfer power supply 184 when the toner image intermediately transferred to the surface of the intermediate transfer belt 71 is transferred to the sheet P, by switching between a first output state and a second output state. Here, the transfer characteristics of the toner image in the first output state and the second output state will be explained.

[0039] In the first output state, the transfer operation to sheet P has the characteristic that even if a phenomenon called fouling occurs, where toner adheres to areas other than the toner image on the intermediate transfer belt 71, the so-called fouled toner adhering to areas other than the toner image is less likely to be transferred to sheet P. The problem when fouling occurs is that when transferring toner images to multiple sheets P consecutively, between sheets P (between the sheets of paper), the fouled toner is transferred to the surface of the transfer roller 11a in the transfer nip region TN, and then transferred to sheet P when it comes into contact with sheet P, resulting in back-side staining of the sheet. In the first output state, the toner image is transferred by repulsive force due to the first bias of the same polarity as the charge polarity of the toner, so fouled toner with a smaller charge than the toner image (because the area is smaller than the toner image, the overall charge is small) is less likely to move to sheet P. In other words, even if fouled toner is present, it is less likely to move to the transfer roller 11a. Therefore, it has the characteristic of being less likely to cause back-side staining of sheet P. However, because the toner image is transferred to the sheet P by electrostatic repulsion, when the resistance of the sheet P decreases in a high-humidity environment, in the transfer nip region TN, the amount of current flowing from the intermediate transfer drive roller 72 to the metal sheet transport guide 34 via the surface of the sheet P with reduced resistance becomes greater than the current flowing from the intermediate transfer drive roller 72 to the transfer roller 11a. As a result, the toner image is not sufficiently transferred to the sheet, and re-transfer is likely to occur where some of the toner that has been transferred to the sheet repels from the potential of the surrounding toner image and returns to the intermediate transfer belt 71. Consequently, the surface of the toner image transferred to the sheet P is prone to becoming rough, a characteristic known as "roughness."

[0040] On the other hand, in the second output state, the transfer operation to the sheet P is performed in the transfer nip region TN, where a second positive bias acts on the negatively charged toner image, pulling it towards the sheet P. Therefore, even if the resistance of the sheet P decreases in a high-humidity environment, it is difficult for current to flow from the transfer nip region TN to the metal sheet transport guide 34, and as a result, re-transfer is less likely to occur. This suppresses the occurrence of roughness and allows for stable transfer. However, the second output state more actively attracts the toner towards the transfer roller 11a, so the surface of the transfer roller 11a is more likely to become soiled with toner and the back of the sheet is more likely to be soiled in low-temperature, low-humidity environments where the charge amount of the fouled toner is high (this is relatively less noticeable in high-temperature, high-humidity environments).

[0041] Therefore, the image forming apparatus 100 of this disclosure includes an environmental sensor 183 that detects temperature and humidity and is provided around the transfer roller 11a (not shown), and a control unit 180 that transfers a toner image to the sheet P in either a first output state or a second output state based on the detection result of the environmental sensor 183.

[0042] Furthermore, after the toner image is transferred from the intermediate transfer belt 71 to the sheet P, that is, after the image formation operation on the sheet P is completed, the control unit 180 can perform a cleaning operation by supplying a third bias (for example, -100V or -8μA), which is a predetermined voltage or current with the same polarity as the charging polarity of the toner and a smaller absolute value than the first bias, to the transfer roller 11a. This electrostatically repels the toner adhering to the transfer roller 11a, returning it to the intermediate transfer belt 71, and allowing it to be collected by the cleaning device 9. Figure 6 shows the output state of the transfer power supply 184 during the cleaning operation according to the embodiment of this disclosure, and shows the third output state in which the first power supply 184a is connected to the transfer roller 11a by the switching means 185 and the intermediate transfer drive roller 72 is in a grounded state. The first power supply 184a is a variable power supply that can change the voltage or current. Therefore, it is possible to supply a third bias with a smaller absolute value than the first bias to the transfer roller 11a.

[0043] As described above, the image forming apparatus 100 of this disclosure is equipped with a cleaning device 9 (cleaning unit) for removing deposits adhering to the intermediate transfer belt 71. The transfer power supply 184 is further switchable to a third output state in which the intermediate transfer drive roller 72 is grounded and a third bias is output to the transfer roller 11a, which is a voltage or current of the same polarity as the toner image and whose absolute value is smaller than that of the first bias. The control unit 181 sets the transfer output state of the transfer power supply 184 to the third output state after the transfer of the toner image to the sheet P, and can perform a cleaning operation of the transfer roller 11a that drives the intermediate transfer drive roller 72 for a predetermined time. The reason why the absolute value of the third bias is made smaller than that of the first bias during the cleaning operation is that the amount of toner adhering to the transfer roller 11a is small compared to the toner image, so if the first bias is supplied instead of the third bias, a phenomenon similar to re-transfer occurs, and return toner is generated that returns to the transfer roller 11a without moving to the intermediate transfer belt 71. Therefore, by making the absolute value of the third bias smaller than the absolute value of the first bias, the generation of this return toner can be prevented, and the toner adhering to the transfer roller 11a can be efficiently moved to the intermediate transfer belt 71. In addition, the third output state, in which the third bias, which is the charging polarity of the toner, is output to the transfer roller 11a, can be achieved by switching the switching means 185. In other words, it is not necessary to provide a dedicated power supply for cleaning the transfer roller 11a, so costs can be reduced.

[0044] Next, the control unit 180 that controls the transfer power supply 184 will be explained using Figure 4.

[0045] Figure 4 is a block diagram showing the control configuration of the control unit 180 according to the embodiment of this disclosure. Figure 5 is a diagram showing an example of a drive table in which the transfer output conditions, which are the output state of the transfer power supply 184 when transferring a toner image to a sheet P in an image forming apparatus according to the embodiment of this disclosure, are defined.

[0046] As shown in Figure 4, the control unit 180 includes a processing unit 181 and a storage unit 182.

[0047] Furthermore, the control unit 180 is connected to the image forming unit 50 and the transfer power supply 184 via signal lines, and can control the image forming unit 50 and the transfer power supply 184. The control unit 180 is also connected to the environmental sensor 183 via signal lines, and can receive the output signals (temperature information and humidity information) from the environmental sensor 183.

[0048] The memory unit 182 consists of ROM (Read Only Memory), RAM (Random Access Memory), etc., and stores in advance control programs for the operation of the image forming apparatus 100. The memory unit 182 also stores conditions for image forming in the image forming unit 50, such as the drive table described later. In addition, it stores electronic data related to images and documents for image forming in the image forming unit 50.

[0049] The processing unit 181 is composed of a microcomputer such as a CPU (Central Processing Unit), and controls the entire image forming apparatus 100 by executing a predetermined program stored in the memory unit 182. The processing unit 181 includes a transfer output condition setting unit 187 that sets the output state of the transfer power supply 184 based on the detection results of the drive table and the environmental sensor 183, which will be described later.

[0050] The control unit 180 may be implemented by one or more control / arithmetic devices (CPU, SoC (System on a Chip)). Furthermore, the control unit 180 may be composed of one or more control circuits.

[0051] Next, the drive table stored in the memory unit 182 will be explained using Figure 5. The drive table defines the transfer output conditions, which are the output state of the transfer power supply 184, for each of the 25 environmental areas (5 × 5 = 25, from the 1st environmental area to the 25th environmental area) that are divided into environmental areas based on combinations of temperature and humidity.

[0052] In the drive table in Figure 6, "1" indicates the first output state, and "2" indicates the second output state. For example, in the first environmental area, which is an environmental area with low temperature and humidity, such as a temperature of 15°C or less and humidity of 30% or less, it is defined that the system will be driven in the first output state. In the 25th environmental area, which is an environmental area with high temperature and humidity, such as a temperature exceeding 30°C and humidity exceeding 75%, it is defined that the system will be driven in the second output state. Furthermore, for each environmental area from the second environmental area, where the temperature is 15°C or less and humidity is between 30% and 45%, to the 24th environmental area, where the temperature is above 30°C and humidity is between 60% and 75%, it is defined whether the system will be in the first output state or the second output state. More specifically, in environmental areas with more moisture in the air, where roughness, which causes surface disturbance of the toner image, is likely to occur, the system is defined to be driven in the second output state, which reduces the occurrence of roughness. These transfer output conditions have been determined in advance through experiments and are stored in the memory unit 182.

[0053] The transfer output condition setting unit 187 of the processing unit 181 sets the transfer output conditions, which are the output state of the transfer power supply 184, by comparing the detected temperature and humidity detected by the environmental sensor 183 with the drive table stored in the storage unit 182. In other words, the transfer condition output state setting unit 183 determines the transfer output conditions by referring to the drive table in relation to the temperature and humidity conditions detected by the environmental sensor.

[0054] As described above, by pre-storing the drive table in the storage unit 182, the control unit 180 can set the transfer output conditions of the transfer power supply 184 to appropriate output conditions according to the environment based on the detection results of the environmental sensor 183. This prevents a decrease in image quality when the toner image is transferred from the intermediate transfer belt 71 to the sheet P, and also prevents soiling of the back surface of the sheet P. Note that this drive table is just an example and is not limited to the one shown in Figure 6. Depending on the model and structure of the image forming apparatus 100, the drive table should be pre-created so that the transfer output conditions are in a desirable state according to the environment, and stored in the storage unit 182. In addition, in this embodiment, the output state is determined by humidity and temperature, but the output state may be determined by other factors.

[0055] Next, the specific control operations performed by the control unit 181 will be explained using Figure 7. Figure 7 is a flowchart showing an example of the operation of the image forming apparatus 100 according to the embodiment of this disclosure, performed by the control unit 181.

[0056] Figure 7 shows the operation of the image forming apparatus 100 after power-on. The processing unit 181 determines whether the image forming apparatus 100 has been instructed to perform image forming operations such as copying and printing. Specifically, it determines whether or not image forming processing has been instructed (step S1). If image forming processing has not been instructed in step S1, the process returns to step S1 (step S1: No). If image forming processing has been instructed, the process proceeds to step S2 (step S1: Yes).

[0057] In step S2, the processing unit 181 compares the detection data (detected temperature, detected humidity) sent from the environmental sensor 183 via the signal line with the drive table stored in the memory unit 182 to determine whether to select the first output state or the second output state (step S2), and proceeds to the next step 3. In step S3, the processing unit 181 sends an instruction signal to the transfer power supply 184 to set the output state of the transfer power supply 184 to the first output state or the second output state determined in step S2. Specifically, to set the first output state, the first changeover switch 185a is connected to contact a3 to connect the first power supply 184a to the intermediate transfer drive roller 72, and the second changeover switch 185b is connected to contact a5 to ground the transfer roller 11a. (See Figure 2) To switch to the second output state, the first changeover switch 185a is connected to contact a2 to ground the intermediate transfer drive roller 72, and the second changeover switch 185b is connected to contact a4 to connect the second power supply 184b to the transfer roller 11a. (See Figure 3) When the output state of the transfer power supply 184 is set to the first output state, the first bias is output to the first output power supply 184 to perform the image forming operation, and when the output state of the transfer power supply 184 is set to the second output state, the second bias is output to the second power supply 184a to perform the image forming operation (step S3). When the image forming operation is completed, the process proceeds to the next step S4.

[0058] In step S4, the processing unit 181 determines whether or not it is necessary to perform an image forming operation next. That is, it determines whether or not it is not necessary to perform an image forming operation again and whether the image forming operation has finished (step S4). If the image forming operation has not finished, it returns to step S2 (step S4: No), and if the image forming operation has finished, it proceeds to step S5 (step S4: Yes).

[0059] In step S5, the processing unit 181 sends an instruction signal to the transfer power supply 184, setting the transfer output state of the transfer power supply 184 to the third output state (step S5). Specifically, the first changeover switch 185a is connected to contact a1 to ground the intermediate transfer drive roller 72, the second changeover switch 185b is connected to contact a3 to connect the first power supply 184a to the transfer roller 11a, and the first power supply 184a outputs a third bias with an absolute value smaller than the first bias (see Figure 6). Then, the process proceeds to the next step S6. In step S6, a drive source (not shown) is driven to rotate the transfer drive roller 72 for a predetermined time (for example, about 20 seconds), and a cleaning operation is performed in which the toner adhering to the surface of the transfer roller 11a is moved to the intermediate transfer belt 71 by electrostatic force and collected by the cleaning device 9 (step S6). When the cleaning operation in step S6 is completed, the series of operations is finished.

[0060] As described above, the image forming apparatus 100 according to this embodiment determines the output state of the transfer power supply 184 to achieve a more favorable state based on environmental data such as humidity and temperature. This makes it possible to improve the image quality of the image formed on the sheet P and prevent soiling of the back surface of the sheet P.

[0061] Furthermore, the control unit 181 controls the output state of the transfer power supply 184 based on the detection results of the environmental sensor 183 and the drive table stored in the storage unit 182. Here, the drive table has predefined transfer output conditions, which are the output state of the transfer power supply when transferring the toner image to the sheet P, for each of several environmental areas defined by temperature and humidity. In environmental areas with more moisture in the air, where roughness, which causes the surface of the toner image to become uneven, is likely to occur, the system is defined to set to a second output state, which reduces the occurrence of roughness. Therefore, the occurrence of roughness under high humidity can be suppressed. Also, in environmental areas with less moisture in the air, where fouled toner is likely to move between sheets and stain the back side of the sheet P, the system is defined to set to a first output state, thus suppressing the occurrence of staining on the back side of the sheet P.

[0062] Furthermore, after the transfer operation in which the toner image is transferred from the intermediate transfer belt 71 to the sheet P is completed, the control unit 181 sets the output state of the transfer power supply 184 to the third output state and rotates the intermediate transfer belt 71 for a predetermined time by a drive source (not shown), thereby performing a cleaning operation to move the toner adhering to the transfer roller 11a to the intermediate transfer belt 71 and collect it with the cleaning device 9. In the embodiment of this disclosure, the transfer power supply 184 has a changeover switch 185, so during the cleaning operation, the third bias can be supplied from the first power supply 184a to the transfer roller 11a by operating the changeover means. In other words, by providing the changeover switch 185, the cleaning operation of the transfer roller 11a can be performed using the first power supply 184a, which is the power supply for transfer. This eliminates the need to provide a dedicated cleaning power supply for the transfer roller 11a, and as a result, costs can be reduced.

[0063] (Other embodiments) Other embodiments relating to this disclosure will now be described. Note that the same reference numerals will be used for components similar to those in the above embodiments, and similar descriptions will be omitted.

[0064] In the image forming apparatus 100 according to the above embodiment, the processing unit 181 controls the transfer power supply 184 so that when the cleaning operation is performed, the output state of the transfer power supply 184 is set to the third output state, and a third bias with a smaller absolute value than the first bias is output from the first power supply 184a.

[0065] In contrast, in the image forming apparatus 100 according to another embodiment, the transfer power supply 184 operates in the same manner as in the above embodiment during image formation, but when the cleaning operation is performed, the intermediate transfer drive roller 72 is grounded and an AC bias is output to the transfer roller 11a, switching to a fourth output state.

[0066] Here, the second power supply 184b is also a variable power supply, similar to the first power supply 184a, and is capable of outputting a fourth bias (e.g., +8μA or +100V), which is a positive voltage or current with a smaller absolute value than the second bias. Then, by operating the second changeover switch 185b to alternately connect contact a3 and contact a4, a negative third bias and a positive fourth bias can be alternately output to the transfer roller 11a. This makes it possible to output an AC bias to the transfer roller 11a.

[0067] In other words, in the image forming apparatus 100, when the intermediate transfer belt 71 is cleaned after the image forming operation is completed, the processing unit 181 sends an instruction signal to the transfer power supply 184 to set it to the fourth output state. As a result, the second changeover switch 185b is alternately connected to contacts a3 and a4, and the first changeover switch 185a is connected to contact a1, so that the transfer power supply 184 is set to the instructed fourth output state. In the fourth output state, output is provided to the transfer roller 11a from the first power supply 184a and the second power supply 184b. In this case, it is preferable that the first power supply 185a outputs a third bias, which is a negative voltage or current with a smaller absolute value than the first bias, and the second power supply 185b outputs a fourth bias, which is a positive voltage or current with a smaller absolute value than the second bias.

[0068] Most waste toner is negatively charged, but some is positively charged. By alternately outputting negative and positive toner to the transfer roller 11a, both negatively charged and positively charged toners can be reliably moved to the intermediate transfer belt 71 for cleaning, even if they are adhering to the transfer roller 11a.

[0069] Thus, according to another embodiment, in the cleaning operation, the second changeover switch 185b is alternately connected to contact a3 and contact a4, so that a third bias, which is a negative voltage or current from the first power supply 185a, and a fourth bias, which is a positive voltage or current from the second power supply 185b, are alternately output to the transfer roller 11a, and the first changeover switch 185a is connected to contact a1, resulting in a fourth output state in which the intermediate transfer drive roller 72 is grounded.

[0070] As a result, the image forming apparatus 100 according to other embodiments can more reliably clean the transfer roller 11a during the cleaning operation.

[0071] This disclosure is not limited to the embodiments described above and can be implemented in various other ways. Therefore, such embodiments are merely illustrative in all respects and should not be constrained. The scope of this disclosure is defined by the claims and is not restricted by the text of the specification. Furthermore, any variations or modifications falling within the equivalent scope of the claims are all within the scope of this disclosure. [Explanation of Symbols]

[0072] 1. Photoconductor drum 2. Charger 4. Developing device 5. Drum cleaning device 6. Intermediate transfer roller 9. Cleaning device (cleaning section) 11 Transfer device 11a Transfer roller (transfer member) 14 Registrola 34, 35 Sheet transport guide 50 Image forming unit 70 Intermediate Transfer Apparatus 71 Intermediate transfer belt 72 Intermediate transfer drive roller (drive roller) 73 Intermediate transfer driven roller 100 Image forming apparatus 101 Image forming apparatus main unit 180 Control Unit 181 Processing Unit 182 Memory section 183 Environmental Sensors 184 Transfer power supply 184a 1st power supply 184b 2nd power supply 185 Changeover switch 185a First changeover switch 185b Second changeover switch 187 Transfer Output Condition Setting Unit a1, a2, a3, a4, a5 contacts D, F arrows

Claims

1. An intermediate transfer belt onto which the toner image formed in the image forming unit is transferred to the surface, The intermediate transfer belt is wrapped around the surface and a conductive drive roller rotates to move the intermediate transfer belt in a predetermined direction, A conductive transfer member is provided at a position opposite to the drive roller so as to contact the surface of the intermediate transfer belt, and transfers and conveys the toner image intermediately transferred to the surface of the intermediate transfer belt to a sheet at the contact portion with the intermediate transfer belt. A transfer power supply that can switch between a first output state in which a first bias is output to the drive roller, which is a voltage or current of the same polarity as the charging polarity of the toner image, and the transfer member is grounded, and a second output state in which a second bias is output to the transfer member, which is a voltage or current of the opposite polarity to the charging polarity of the toner image, and the drive roller is grounded, An image forming apparatus comprising: a control unit that transfers the toner image onto the sheet in either the first output state or the second output state based on the detection result of the environmental sensor.

2. The control unit, A storage unit stores a drive table in which the transfer output conditions, which are the output state of the transfer power supply when the toner image is transferred to the sheet, are predetermined for each of a plurality of environmental areas defined by temperature and humidity. The image forming apparatus according to claim 1, further comprising: a transfer output condition setting unit that determines the transfer output conditions by referring to the drive table with respect to the temperature and humidity conditions detected by the environmental sensor.

3. The system includes a cleaning unit for removing deposits attached to the intermediate transfer belt, The transfer power supply is further switchable to a third output state in which the drive roller is grounded and a third bias is output to the transfer member, which is a voltage or current of the same polarity as the toner image and whose absolute value is smaller than the first bias. The image forming apparatus according to claim 1, characterized in that the control unit can set the output state of the transfer power supply to the third output state after the transfer of the toner image to the sheet, and perform a cleaning operation of the transfer member that drives the drive roller for a predetermined time.

4. The aforementioned power supply for transfer is A first power supply capable of generating a voltage or current of the same polarity as the charging polarity of the toner image, A second power supply capable of generating a voltage or current with the opposite polarity to the charging polarity of the toner image, The device includes a switching device that switches the connection destination of the first power supply and the second power supply to the drive roller or the transfer member, The image forming apparatus according to claim 3, characterized in that the first output state, the second output state, and the third output state are switched by changing the connection destination by the switching means.

Images