Image forming apparatus

Abstract

To provide an image forming apparatus capable of improving both developability and productivity. [Solution] In the image forming apparatus 100, the cooling control unit 55 performs a pre-cooling operation to cool the inside of the image forming apparatus 10 based on the detected current detected by the current detection processing unit 54 and the detected temperature detected by the temperature sensor 8. Specifically, the cooling control unit 55 performs the cooling operation when the absolute value of the current difference ΔI between the target current (developing current or non-developing current) and a predetermined reference current value exceeds a first threshold, and the detected temperature exceeds a second threshold.

Description

Technical Field

[0001] The present invention relates to an electrophotographic image forming apparatus.

Background Art

[0002] An electrophotographic image forming apparatus that forms an image using a two-component developer containing toner and carrier is known. As a prior art, when the temperature inside the apparatus becomes high, the image quality deteriorates. Therefore, when the detected temperature by a temperature sensor becomes higher than a predetermined temperature, the image forming operation is stopped and a cooling operation for lowering the temperature inside the apparatus is performed. An image recording apparatus is disclosed (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in an electrophotographic image forming apparatus, the developability of toner may deteriorate as the temperature inside the apparatus rises. Specifically, as the temperature inside the apparatus rises, the surface of the toner softens, and external additives used as fluidizing agents are buried inside the toner, resulting in a decrease in the fluidity of the toner. At the same time, the adhesion of the toner to the carrier increases, making it difficult for the toner to separate from the carrier, and the amount of toner transferred to the photosensitive drum decreases, thereby reducing the developability. In order to prevent the deterioration of developability, when the temperature inside the apparatus is detected and the image forming operation is stopped and a cooling operation is performed when the temperature exceeds a predetermined temperature, in some cases, the image forming operation may be frequently stopped, which will impair the convenience of the user. Also, even if the temperature inside the apparatus exceeds the predetermined temperature, toner softening due to the temperature effect does not necessarily occur. In that case, the image forming operation will be stopped even though the developability has not deteriorated, resulting in a decrease in the productivity of the image forming apparatus.

[0005] The object of the present invention is to provide an image forming apparatus capable of improving both developability and productivity. [Means for solving the problem]

[0006] An image forming apparatus according to one aspect of the present invention includes: an image forming unit that applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the developing region of the first carrier and developing the developing region of the first carrier; a current detection unit that detects the target current flowing between the first carrier and the second carrier during development; and a temperature detection unit that detects the temperature inside the apparatus. The system includes a cooling control unit that performs a predetermined cooling operation based on the current detected by the current detection unit and the temperature detected by the temperature detection unit.

[0007] An image forming apparatus according to another aspect of the present invention comprises: an image forming unit that applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the developing region of the first carrier and developing the developing region of the first carrier; a calibration processing unit that performs a calibration process to set a set voltage value for the bias voltage; a temperature detection unit that detects the temperature inside the apparatus; and a cooling control unit that performs a predetermined cooling operation based on the set voltage value determined by the calibration processing unit and the temperature detected by the temperature detection unit. [Effects of the Invention]

[0008] According to the present invention, it is possible to improve both developability and productivity. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a block diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] Figure 2 shows the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 3] Figure 3 shows the configuration of the image forming section of an image forming apparatus according to an embodiment of the present invention. [Figure 4] Figure 4 is an explanatory diagram showing an example of the waveform of the development bias of an image forming apparatus according to an embodiment of the present invention. [Figure 5] Figure 5 is a flowchart showing the procedure of a first example of a cooling process performed by the control unit of an image forming apparatus according to an embodiment of the present invention. [Figure 6] Figure 6 is a flowchart showing the procedure for a second example of a cooling process performed by the control unit of an image forming apparatus according to an embodiment of the present invention. [Modes for carrying out the invention]

[0010] The embodiments of the present invention will be described below with reference to the attached drawings. The following embodiments are examples that embody the present invention and are not intended to limit the technical scope of the present invention.

[0011] [1] Overall configuration of the image forming apparatus First, the configuration of the image forming apparatus 10 according to this embodiment will be described with reference to Figures 1 and 2.

[0012] For the sake of explanation, the vertical direction is defined as the up-down direction D1 when the image forming apparatus 10 is in a usable installation state (as shown in Figure 2). The front-to-back direction D2 is defined with the left side of the image forming apparatus 10 shown in Figure 2 as the front. The left-to-right direction D3 is defined with the front of the image forming apparatus 10 in its installed state as the reference point.

[0013] The image forming apparatus 10 according to this embodiment is, for example, a multifunction device having multiple functions such as a scanning function for reading image data from a document, a printing function for forming an image based on the image data, a facsimile function, and a copying function. The image forming apparatus 10 only needs to have the function of forming an image, and may be a printer, a facsimile machine, a copier, etc.

[0014] As shown in Figure 1, the image forming apparatus 10 comprises an automatic document transport device 1, an image reading unit 2, an image forming unit 3, a paper feeding unit 4, a control unit 5, a storage unit 6, an operation display unit 7, a temperature sensor 8 (an example of the temperature detection unit of the present invention), and a cooling fan 9 (an example of the cooling fan of the present invention). The automatic document transport device 1 is an ADF (Auto Document Feeder), so it is labeled "ADF" in Figure 1 and will be referred to as "ADF1" in the following description.

[0015] The ADF1 transports the document whose image is read by the image reading unit 2. The ADF1 includes a document setting unit, multiple transport rollers, a document holder, and a paper discharge unit.

[0016] The image reading unit 2 reads an image from the original document and outputs image data corresponding to the read image. The image reading unit 2 includes a document glass, a light source, multiple mirrors, an optical lens, and a CCD (Charge Coupled Device), etc.

[0017] The image forming unit 3 realizes the printing function by forming a color or monochrome image on a sheet based on an electrophotographic method using a two-component developer. The image forming unit 3 forms an image on the sheet based on image data output from the image reading unit 2. In addition, the image forming unit 3 forms an image on the sheet based on image data input from an external information processing device of the image forming apparatus 10, such as a personal computer.

[0018] The paper feeding unit 4 supplies sheets to the image forming unit 3. The paper feeding unit 4 includes a paper feed cassette, a manual feed tray, a sheet conveyance path, a plurality of conveyance rollers, and the like. The image forming unit 3 forms an image on the sheet supplied from the paper feeding unit 4.

[0019] The control unit 5 comprehensively controls the image forming apparatus 10. The control unit 5 is mainly composed of a computer system having one or more processors and one or more memories. In the image forming apparatus 10, the functions of the control unit 5 are realized by one or more processors executing a program. The program may be recorded in advance in a memory (storage unit 6), may be provided through an electric communication line such as the Internet, or may be provided by being recorded in a computer-readable non-temporary recording medium such as a memory card or an optical disk. The one or more processors are composed of one or more electronic circuits including a semiconductor integrated circuit. Further, the computer system mentioned here includes a microcontroller having one or more processors and one or more memories. The control unit 5 may be a control unit provided separately from the main control unit that comprehensively controls the image forming apparatus 10.

[0020] The storage unit 6 is one or more non-volatile storage devices. The storage unit 6 is, for example, a non-volatile memory such as a flash memory and an EEPROM (registered trademark), an SSD (Solid State Drive), or an HDD (Hard Disk Drive). Information such as a control program for causing the control unit 5 to execute various processes is stored in the storage unit 6 in advance. Further, the storage unit 6 is used as a temporary storage memory (working area) for various processes executed by the control unit 5.

[0021] The operation display unit 7 is a user interface in the image forming apparatus 10. The operation display unit 7 has a display unit such as a liquid crystal display that displays various information according to a control instruction from the control unit 5, and an operation unit such as a switch or a touch panel that inputs various information to the control unit 5 according to a user's operation.

[0022] The temperature sensor 8 (see Figure 3) detects the ambient temperature inside the image forming apparatus 10 and is, for example, a thermistor. The temperature sensor 8 is located, for example, near the image forming unit 3. In this embodiment, the temperature sensor 8 is located near the image forming unit 34 that forms the K (black) toner image, and more specifically, near the case 343B of the developing device 343 of the image forming unit 34. In other words, the temperature sensor 8 is located near the developing device 343 in the image forming unit 3, which holds the toner that is most susceptible to the heating effects of the fixing device 38 and also contains the toner with the highest consumption. The temperature sensor 8 outputs a detection signal to the control unit 5 corresponding to the magnitude of the detected temperature.

[0023] The temperature sensor 8 may be provided in a location corresponding to each of the four image forming units 31 to 34 of the image forming unit 3.

[0024] The cooling fan 9 (see Figure 3) is a fan that blows air into the image forming apparatus 10 to lower the internal temperature. The cooling fan 9 is driven and controlled by the control unit 5. The cooling fan 9 is located, for example, near the image forming unit 34, and for example, near the case 343B of the developing apparatus 343 of the image forming unit 34.

[0025] [2] Configuration of the image forming unit Next, the configuration of the image forming unit 3 will be described in more detail with reference to Figures 1 to 4.

[0026] As shown in Figure 2, the image forming unit 3 includes four image forming units 31-34, an optical scanning device 35, an intermediate transfer device 36, a secondary transfer roller 37, a fixing device 38, and a paper output tray 39. In Figure 3, an enlarged schematic diagram of one of the four image forming units 31-34, image forming unit 34, is shown within the speech bubble.

[0027] Each of the four image forming units 31 to 34 is an example of an image forming unit of the present invention. Each of the image forming units 31 to 34 applies a development bias VB between a photoreceptor drum whose surface is charged and a developing roller that holds toner to be attached to the photoreceptor drum, thereby moving toner from the developing roller to the developing region of the photoreceptor drum and forming a toner image on the photoreceptor drum based on image data.

[0028] The image forming unit 31 forms a yellow (Y) toner image. As shown in Figure 3, the image forming unit 31 includes a photoreceptor drum 311 (an example of the first carrier of the present invention), a developing device 313 including a charging roller 312 and a developing roller 313A (an example of the second carrier of the present invention), a primary transfer roller 314, and a drum cleaning unit 315. The image forming unit 31 also further includes a toner container 316 (see Figure 2).

[0029] The image forming unit 32 forms a cyan (C) toner image. As shown in Figure 3, the image forming unit 32 includes a photoreceptor drum 321 (an example of the first carrier of the present invention), a developing device 323 including a charging roller 322 and a developing roller 323A (an example of the second carrier of the present invention), a primary transfer roller 324, and a drum cleaning unit 325. The image forming unit 32 also further includes a toner container 326 (see Figure 2).

[0030] The image forming unit 33 forms a magenta (M) toner image. As shown in Figure 3, the image forming unit 33 includes a photoreceptor drum 331 (an example of the first carrier of the present invention), a developing device 333 including a charging roller 332 and a developing roller 333A (an example of the second carrier of the present invention), a primary transfer roller 334, and a drum cleaning unit 335. The image forming unit 33 also further includes a toner container 336 (see Figure 2).

[0031] The image forming unit 34 forms a K (black) toner image. As shown in Figure 3, the image forming unit 34 includes a photoreceptor drum 341 (an example of the first carrier of the present invention), a developing device 343 including a charging roller 342 and a developing roller 343A (an example of the second carrier of the present invention), a primary transfer roller 344, and a drum cleaning unit 345. The image forming unit 34 also further includes a toner container 346 (see Figure 2).

[0032] Furthermore, each of the multiple image forming units 31 to 34, in addition to the above configuration, further includes a power supply circuit 301 and a current detection circuit 302 (an example of the current detection unit of the present invention), as shown in Figure 1. In other words, the power supply circuit 301 and the current detection circuit 302 are provided in each of the multiple image forming units 31 to 34. Each power supply circuit 301 includes a developing power supply circuit 301A and a charging power supply circuit 301B.

[0033] Thus, the multiple (in this case, four) image forming units 31-34 each correspond to the four colors Y (yellow), C (cyan), M (magenta), and K (black), and basically employ a common configuration. Therefore, unless otherwise specified, the configuration described for image forming unit 34 is the same for the other image forming units 31-33. In the callouts in Figure 3, only the parts of image forming unit 34, such as the photoreceptor drum 341, developing roller 343A, power supply circuit 301, and current detection circuit 302, are shown.

[0034] An electrostatic latent image is formed on the photoreceptor drum 341. The photoreceptor drum 341 is rotatably supported by a unit housing that houses the photoreceptor drum 341, the charging roller 342, and the drum cleaning unit 345, around a rotation axis extending in the left-right direction D3. The photoreceptor drum 341 rotates in the rotation direction D5 shown in Figure 3, for example, by receiving a driving force supplied from a motor.

[0035] Generally, photoconductor drums are classified into organic photoconductors (OPC), selenium photoconductors, amorphous silicon photoconductors, etc., depending on the type of thin film layer on the charged surface. In recent years, amorphous silicon photoconductors have become the mainstream for photoconductor drums due to their high durability, high hardness, and long lifespan. In this embodiment, the photoconductor drum 341 is an amorphous silicon photoconductor drum having an amorphous silicon layer on its surface.

[0036] In this embodiment, the charging roller 342 charges the surface (outer surface) of the photoreceptor drum 341 with positive polarity. Specifically, the charging roller 342 is electrically connected to the charging power supply circuit 301B of the power supply circuit 301, and charges the surface of the photoreceptor drum 341 by receiving high voltage from the charging power supply circuit 301B. However, the charging roller 342 is not limited to charging the surface of the photoreceptor drum 341 with positive polarity, but may also charge it with negative polarity.

[0037] Light based on image data is shone from the optical scanning device 35 onto the surface of the photoreceptor drum 341, which has been charged by the charging roller 342. As a result, an electrostatic latent image is formed on the surface of the photoreceptor drum 341. In other words, the potential of the exposed area on the surface of the photoreceptor drum 341, which is shone with light from the optical scanning device 35, drops below the charging potential of the surrounding area (unexposed area), and the electrostatic latent image is formed. In this embodiment, this exposed area is an example of the development area of ​​the present invention and is the image portion on which the toner image is formed. The unexposed area is an example of the undeveloped area of ​​the present invention and is the portion on which the toner image is not formed.

[0038] The developing device 343 performs a developing process to develop the electrostatic latent image formed on the surface of the photoreceptor drum 341. In this embodiment, the developing device 343 specifically uses a two-component developer containing toner and a carrier for development. For example, the developing device 343 includes a case 343B, a pair of stirring members, a magnetic roller, and a developing roller 343A, etc.

[0039] Case 343B contains a two-component developer containing a K (black) toner and a carrier. In addition to the toner and carrier, the two-component developer contains one or more types of external additives as fluidizers to improve the fluidity of the toner. These external additives, such as titanium dioxide particles, are fine particles that are sufficiently smaller than the toner and adhere to the surface of the toner particles.

[0040] Case 343B supports a pair of stirring members, a magnetic roller, and a developing roller 343A so as to be rotatable around a rotation axis extending in the left-right direction D3. The pair of stirring members stir the toner and carrier housed in case 343B, thereby charging the toner. In this embodiment, the toner is positively charged. However, the charge polarity of the toner is not limited to positive polarity; it may also be negative polarity. The magnetic roller draws up the toner and carrier stirred by the pair of stirring members and supplies the toner to the surface (outer circumferential surface) of the developing roller 343A.

[0041] The developing roller 343A develops the electrostatic latent image formed on the exposure area of ​​the photoreceptor drum 341 using charged toner. Specifically, the developing roller 343A is electrically connected to the developing power supply circuit 301A of the power supply circuit 301, and receives a developing bias VB (see Figure 4) from the developing power supply circuit 301A to supply toner to the surface of the photoreceptor drum 341. In other words, when a high-voltage developing bias VB is applied between the developing roller 343A and the photoreceptor drum 341 by the developing power supply circuit 301A, a developing electric field is formed between the developing roller 343A and the exposure area, and the charged toner moves from the developing roller 343A to the exposure area of ​​the photoreceptor drum 341. As a result, a toner image corresponding to the electrostatic latent image is formed on the surface of the photoreceptor drum 341.

[0042] In this embodiment, the photoreceptor drum 341 is an example of a "first carrier," and the developing roller 343A is an example of a "second carrier." That is, the image forming unit 3 moves charged toner from the developing roller 343A to the photoreceptor drum 341 using a developing electric field, developing the electrostatic latent image on the photoreceptor drum 341 with the toner, and forming a toner image (image) on the photoreceptor drum 341 that corresponds to the electrostatic latent image. In other words, in the development process, the image forming unit 3 moves charged toner from the second carrier to the first carrier and forms a toner image on the first carrier. Here, since the photoreceptor drum 341 rotates in the rotation direction D5 (see Figure 3), the portion of the surface of the photoreceptor drum 341 facing the developing roller 343A changes over time. In other words, the portion of the surface of the photoreceptor drum 341 facing the developing roller 343A moves in the rotation direction D5 of the photoreceptor drum 341.

[0043] Here, the developing bias VB applied between the developing roller 343A and the photoreceptor drum 341 is a voltage in which an AC component Vac is superimposed on a DC component Vdc, as shown in Figure 4. In other words, the developing power supply circuit 301A generates a developing bias VB in which an AC component Vac is superimposed on a DC voltage by superimposing an AC voltage on a DC voltage. Therefore, the developing bias VB has a fluctuating component due to the pulsation (ripple) of the AC component Vac superimposed on the value of its DC component Vdc, and periodically repeats between a value higher and a value lower than the value of the DC component Vdc. In the example in Figure 4, the AC component Vac of the developing bias VB is a square wave with a duty cycle of 50%, but it is not limited to this, and the AC component Vac may be a sine wave or a triangular wave, for example.

[0044] In this embodiment, the value (magnitude) of the DC component Vdc in the development bias VB can be changed. For example, if the surface potential of the charged photoreceptor drum 341 is "Vs", and the potential (exposure potential) of the exposed area on the surface of the photoreceptor drum 341 irradiated with light from the light scanning device 35 is "VL", then the DC component Vdc is set to a value between the surface potential Vs and the exposure potential VL. In other words, the value of the DC component Vdc is set to a voltage lower than the surface potential Vs and higher than the exposure potential VL of the exposed area.

[0045] In this embodiment, the developing bias VB is an example of a "bias voltage" applied between the developing roller 343A and the photoreceptor drum 341, and more specifically, the DC component Vdc in the developing bias VB is an example of the bias voltage of the present invention.

[0046] The primary transfer roller 344 transfers the toner image formed on the surface of the photoreceptor drum 341 by the developing device 343 to the outer surface of the intermediate transfer belt 361 (see Figure 3). Specifically, the primary transfer roller 344 is electrically connected to the power supply circuit 301, and by receiving high voltage from the power supply circuit 301, it transfers the toner image formed on the surface of the photoreceptor drum 341 to the outer surface of the intermediate transfer belt 361. In other words, a high-voltage transfer bias is applied between the photoreceptor drum 341 and the primary transfer roller 344 by the power supply circuit 301, creating a transfer electric field, and the charged toner moves from the photoreceptor drum 341 to the intermediate transfer belt 361. As a result, a toner image is formed (transferred) to the outer surface of the intermediate transfer belt 361.

[0047] The drum cleaning unit 345 cleans the surface of the photoreceptor drum 341 after the toner image has been transferred by the primary transfer roller 344. For example, the drum cleaning unit 345 has a blade-shaped cleaning member and a transport member. The cleaning member contacts the surface of the photoreceptor drum 341 and removes the toner adhering to the surface. The transport member transports the toner removed by the cleaning member to the toner container.

[0048] The toner container 346 supplies toner to the case 343B of the developing device 343. In the image forming unit 34, which forms a K (black) toner image, the toner container 346 supplies K (black) toner.

[0049] In this embodiment, when a development bias VB is applied between the developing roller 343A and the photoreceptor drum 341, a developing current and a non-developing current with a DC component Vdc flow between the developing roller 343A and the photoreceptor drum 341.

[0050] As described above, an electrostatic latent image is formed on the surface of the photoreceptor drum 341 when light based on image data is irradiated from the optical scanning device 35. The surface of the photoreceptor drum 341 includes an exposure area where the electrostatic latent image is formed and a non-exposure area where the electrostatic latent image is not formed. The exposure area is a light-irradiated area where light is irradiated and is a development area where a toner image is formed. The non-exposure area is a non-irradiated area where light is not irradiated and is a non-development area where a toner image is not formed.

[0051] A magnet is positioned inside the developing roller 343A, and the developing roller 343A rotates around the stationary magnet. One of the magnetic poles of the magnet faces the opposing region (developing gap) where the developing roller 343A and the photoreceptor drum 341 face each other with a predetermined gap between them. The two-component developer carried on the developing roller 343A forms a magnetic brush in the opposing region.

[0052] When a development bias VB is applied between the developing roller 343A and the photoreceptor drum 341, a first electric field is formed in the opposing region between the developing roller 343A and the exposure area, causing the toner to move from the developing roller 343A to the exposure area of ​​the photoreceptor drum 341 via the magnetic brush. Furthermore, when a development bias VB is applied between the developing roller 343A and the photoreceptor drum 341, a second electric field is formed in the opposing region between the developing roller 343A and the non-exposed area, causing the toner to move from the exposure area to the developing roller 343A via the magnetic brush. The toner contained in the magnetic brush in the opposing region moves to the exposure area on the surface of the photoreceptor drum 341, but does not move to the non-exposed area, due to the action of the first and second electric fields formed in the opposing region. As a result, the electrostatic latent image formed on the surface of the photoreceptor drum 341 is developed (visualized).

[0053] Furthermore, the developing area developed in the photoreceptor drum 341 does not have to be the exposed area, but may be the unexposed area. In this case, the undeveloped area that is not developed may be the exposed area, or it may be an uncharged area that is not charged by the charging roller 342. If the developing area where the toner image is developed is an unexposed area, the toner is charged with a polarity opposite to that of the charged area.

[0054] The development current includes a toner current that flows as toner moves from the development roller 343A to the exposure unit through the magnetic brush, and a magnetic brush current that flows from the development roller 343A to the exposure unit through the magnetic brush due to the potential difference between the development roller 343A and the exposure unit. In this embodiment, the current that flows from the development roller 343A to the exposure unit of the photoreceptor drum 341 is defined as "positive".

[0055] The non-developing current consists of a reverse toner current that flows as toner moves from the non-exposed area to the developing roller 343A through the magnetic brush, and a reverse magnetic brush current that flows from the non-exposed area to the developing roller 343A through the magnetic brush due to the potential difference between the developing roller 343A and the non-exposed area. In this embodiment, the current flowing from the non-exposed area of ​​the photoreceptor drum 341 to the developing roller 343A is defined as "negative".

[0056] The current detection circuit 302 detects the developing current and the non-developing current flowing between the photoreceptor drum 341 and the developing roller 343A. The current detection circuit 302 is, for example, a circuit including a current sensor such as a shunt resistor or a current transformer, and is provided on the power supply path from the power supply circuit 301 to the developing roller 343A. The current detection circuit 302 outputs a detection signal to the control unit 5 corresponding to the magnitude of the developing current flowing from the developing roller 343A to the exposure part of the photoreceptor drum 341. The current detection circuit 302 also outputs a detection signal to the control unit 5 corresponding to the magnitude of the non-developing current flowing from the non-exposure part of the photoreceptor drum 341 to the developing roller 343A.

[0057] Furthermore, in this embodiment, the current detection circuit 302 includes a filter circuit 302A. The filter circuit 302A is, for example, a low-pass filter, or integral filter, that attenuates frequency components of the developed current or the undeveloped current that are above the cutoff frequency. By including the filter circuit 302A, only DC current is detected by the current detection circuit 302.

[0058] The optical scanning device 35 irradiates light onto each of the photoreceptor drums 311, 321, 331, and 341 of the four image forming units 31 to 34, thereby lowering the potential of the irradiated exposed area to a level lower than the surrounding charging potential, and forming an electrostatic latent image on the surface. In this embodiment, the optical scanning device 35 includes two optical scanning units 351 and 352. Optical scanning unit 351 irradiates light based on image data onto the photoreceptor drum 311 in response to the input of Y (yellow) image data, forming an electrostatic latent image. Optical scanning unit 351 irradiates light based on image data onto the photoreceptor drum 321 in response to the input of C (cyan) image data, forming an electrostatic latent image. Optical scanning unit 352 irradiates light based on image data onto the photoreceptor drum 331 in response to the input of M (magenta) image data, forming an electrostatic latent image. Furthermore, optical scanning unit 352 irradiates light based on image data onto the photoreceptor drum 341 in response to the input of K (black) image data, forming an electrostatic latent image.

[0059] The toner images of each color formed by each of the multiple (in this case, four) image forming units 31 to 34 are transferred onto the outer surface of the intermediate transfer belt 361. As a result, a color image (toner image) is formed on the outer surface of the intermediate transfer belt 361.

[0060] As shown in Figure 3, the intermediate transfer device 36 includes an intermediate transfer belt 361, a drive roller 362, a tension roller 363, a belt cleaning unit 364, and a density detection unit 365. The intermediate transfer device 36 uses the intermediate transfer belt 361 to transport the toner image formed by the image forming units 31-34 to the transfer position P1 (see Figure 3) by the secondary transfer roller 37.

[0061] The intermediate transfer belt 361 is an endless belt on which toner images of each color are transferred from each of the photoreceptor drums 311, 321, 331, and 341. The intermediate transfer belt 361 is wrapped around drive rollers 362 and tension rollers 363 which are spaced apart from each other in the front-to-back direction D2 of the image forming apparatus 10. The drive rollers 362 rotate by receiving driving force supplied from a motor. As a result, the intermediate transfer belt 361 rotates in the rotation direction D4 shown in Figure 3. The toner image transferred to the outer surface of the intermediate transfer belt 361 is conveyed to the transfer position P1 by the secondary transfer rollers 37 as the intermediate transfer belt 361 rotates. The belt cleaning unit 364 cleans the outer surface of the intermediate transfer belt 361 after the toner image has been transferred at the transfer position P1.

[0062] The density detection unit 365 detects the density of the image (toner image) transferred to the outer surface of the intermediate transfer belt 361. For example, the density detection unit 365 includes a reflective optical sensor having a light-emitting unit that emits light directed toward the outer surface of the intermediate transfer belt 361, and a light-receiving unit that receives the light emitted from the light-emitting unit and reflected from the outer surface of the intermediate transfer belt 361. As shown in Figure 3, the density detection unit 365 is positioned downstream of the image forming unit 34 in the rotation direction D4 of the intermediate transfer belt 361 and upstream of the secondary transfer roller 37. The density detection unit 365 is also positioned opposite one end of the intermediate transfer belt 361 in the width direction (left-right direction D3) on the outer surface of the intermediate transfer belt 361. The density detection unit 365 may also be positioned opposite both ends of the intermediate transfer belt 361 in the width direction on the outer surface of the intermediate transfer belt 361. The density detection unit 365 may also detect the density of the toner image developed on the outer surface of the photoreceptor drum 341.

[0063] The secondary transfer roller 37 transfers the toner image formed on the outer surface of the intermediate transfer belt 361 to the sheet supplied by the paper feeding unit 4. As shown in Figure 3, the secondary transfer roller 37 is positioned opposite the tension roller 363, with the intermediate transfer belt 361 in between, so as to be in contact with the outer surface of the intermediate transfer belt 361. The secondary transfer roller 37 is pressed towards the tension roller 363 by a biasing member. The secondary transfer roller 37 is electrically connected to the power supply circuit, and by receiving a high voltage from the power supply circuit, it transfers the toner image formed on the outer surface of the intermediate transfer belt 361 to the sheet passing through the transfer position P1 (see Figure 3) where the secondary transfer roller 37 and the intermediate transfer belt 361 are in contact.

[0064] The secondary transfer roller 37 has a length in its axial direction (left-right direction D3) that is shorter than the width of the intermediate transfer belt 361. As a result, the outer surface of the intermediate transfer belt 361 has a contact area that contacts the secondary transfer roller 37 and a non-contact area (blank area) that does not contact the secondary transfer roller 37. The non-contact area is the area on both sides of the contact area on the outer surface of the intermediate transfer belt 361. The density detection unit 365 is positioned opposite one of the non-contact areas. The secondary transfer roller 37 transfers the image formed in the contact area to the sheet, but does not transfer the image formed in the non-contact area to the sheet. The secondary transfer roller 37 may have a length in its axial direction that is the same as the width of the intermediate transfer belt 361.

[0065] The fixing device 38 melts and fixes the toner image transferred to the sheet by the secondary transfer roller 37 to the sheet. For example, the fixing device 38 includes a fixing roller and a pressure roller. The fixing roller is positioned in contact with the pressure roller and heats the toner image transferred to the sheet to fix it to the sheet. The pressure roller presses the sheet as it passes through the contact area formed between it and the fixing roller.

[0066] The image-formed sheet is ejected into the output tray 39.

[0067] Incidentally, in electrophotographic image forming apparatuses, the developability of toner may deteriorate as the temperature inside the apparatus rises. Specifically, as the temperature inside the apparatus rises, the surface of the toner softens, and external additives used as fluidizers become embedded in the toner, reducing the toner's fluidity. At the same time, the adhesion of the toner to the carrier increases, making it difficult for the toner to separate from the carrier, and reducing the amount of toner that moves to the photoreceptor drum, thereby reducing the development performance. If the temperature inside the apparatus is detected and the image forming operation is stopped and a cooling operation is performed when the temperature exceeds a predetermined level in order to prevent the deterioration of developability, the image forming operation may stop frequently in some cases, which would impair the convenience of the user. Furthermore, even if the temperature inside the apparatus exceeds a predetermined level, toner softening due to the effect of temperature does not necessarily occur, and in that case, the image forming operation will stop even though the developability has not deteriorated, reducing the productivity of the image forming apparatus.

[0068] In contrast, the image forming apparatus 10 according to this embodiment, with the configuration described below, makes it possible to improve both the developability and productivity of the image forming apparatus 10 without reducing the developability or the productivity of the image forming apparatus 10, compared to conventional methods.

[0069] In other words, as shown in Figure 1, the image forming apparatus 10 according to this embodiment comprises image forming units 31 to 34, current detection circuits 302 provided in each of the image forming units 31 to 34, a temperature sensor 8, a calibration processing unit 51, a bias upper limit determination unit 53, a current detection processing unit 54, and a cooling control unit 55.

[0070] In this embodiment, as an example, a calibration processing unit 51, a bias upper limit determination unit 53, a current detection processing unit 54, and a cooling control unit 55 are provided in the control unit 5 as functions of the control unit 5, as will be described later.

[0071] [3] Configuration of the control unit Next, with reference to Figure 1, each functional unit included in the control unit 5 will be described in more detail. The control unit 5 includes various processing units such as a calibration processing unit 51, a bias upper limit determination unit 53, a current detection processing unit 54, and a cooling control unit 55. In other words, the image forming apparatus 10 is equipped with each of these processing units as a function of the control unit 5.

[0072] The calibration processing unit 51 performs a DC calibration process to adjust the voltage value of the DC component Vdc of the development bias VB. The calibration processing unit 51 performs the DC calibration process when predetermined adjustment execution conditions are met. These adjustment execution conditions include, for example, that the initial operation performed after the main power of the image forming apparatus 10 is turned on has been executed, or that a predetermined number of print cycles (for example, 1000) has been counted.

[0073] In this embodiment, the calibration processing unit 51 determines the set value (set voltage value) of the DC component Vdc when the image forming process is performed at a reference process speed which is initially set as the standard speed for multiple process speeds that the image forming unit 3 can take.

[0074] The DC calibration process involves causing the image forming unit 3 to perform a process to create a predetermined test toner image (an example of a measurement toner image of the present invention), and determining and setting the voltage value (set voltage value) of the DC component Vdc of the development bias VB in the image forming unit 3 according to the density of the test toner image.

[0075] For example, the calibration processing unit 51 causes the test toner image to be formed on each of the image forming units 31 to 34. As a result, the four color test toner images are developed on the surface of each photoreceptor drum and then transferred to the intermediate transfer belt 361. For example, the test toner image includes a toner patch. The test toner image is formed, for example, on the non-contact area on the outer circumferential surface of the intermediate transfer belt 361. Alternatively, the test toner image may be formed on the contact area of ​​the intermediate transfer belt 361.

[0076] Furthermore, the calibration processing unit 51 acquires the density detection results of the four test toner images by the density detection unit 365. Furthermore, the calibration processing unit 51 corrects the current set value (current set value) as the DC component Vdc according to the difference between the density detection results of the four test toner images and a predetermined target density. Specifically, if the density of the test toner image is lower than the target density, the calibration processing unit 51 determines the set value of the DC component Vdc to be a voltage value (set voltage value) that is larger than the current set value by a value corresponding to the density difference. Also, if the density of the test toner image is higher than the target density, the calibration processing unit 51 determines the set value of the DC component Vdc to be a voltage value (set voltage value) that is smaller than the current set value by a value corresponding to the density difference.

[0077] If the image forming apparatus 10 is a monochrome printer, the test toner image is formed on the photoreceptor drum 341, and the density detection unit 365 detects the density of the test toner image on the photoreceptor drum 341.

[0078] The bias upper limit determination unit 53 performs a process (bias upper limit determination process) to determine the upper limit voltage value (allowable upper limit) of the acceptable range that can be taken as the set value of the DC component Vdc of the development bias VB. The bias upper limit determination unit 53 determines the allowable upper limit based on the set value of the DC component Vdc determined by the calibration processing unit 51, for example. For example, the bias upper limit determination unit 53 determines and sets the allowable upper limit to a value obtained by adding a predetermined addition value to the set value of the DC component Vdc determined by the calibration processing unit 51.

[0079] Here, the bias upper limit determination unit 53 may calculate the first allowable upper limit by further taking into account the environmental conditions of the location where the image forming apparatus 10 is installed. In this case, the environmental conditions are, for example, absolute humidity. Specifically, the bias upper limit determination unit 53 calculates the allowable upper limit on the condition that the absolute humidity exceeds a predetermined threshold (for example, 80%). Alternatively, the bias upper limit determination unit 53 calculates the allowable upper limit when the absolute humidity changes significantly, for example, when the difference between the absolute humidity calculated last time and the absolute humidity calculated this time exceeds a predetermined threshold (for example, 30 degrees). The ambient temperature around the image forming apparatus 10 may be used as the environmental condition.

[0080] The current detection processing unit 54 may, for example, detect the developing current (an example of the target current of the present invention) that flows when the first electric field is formed in the opposing region where the two-component developer is present, causing the toner to move from the developing roller to the exposure section of the photoreceptor drum.

[0081] The current detection processing unit 54 acquires the current value detected by the current detection circuit 302 as the value of the development current when the first electric field is formed. Specifically, the current detection processing unit 54 detects the development current that flows when the first electric field is applied and the test toner image is developed when the DC calibration processing is performed by the calibration processing unit 51.

[0082] As described above, the developing current includes a current that flows from the developing roller to the exposure section side through the magnetic brush in the opposing region due to the action of the first electric field formed in the opposing region. For example, when toner softens due to heat and the external additive contained in the two-component developer becomes embedded in the toner, the fluidity of the toner decreases, making it difficult for the toner to move away from the carrier. In other words, the developing current decreases.

[0083] On the other hand, if the toner contained in the magnetic brush in the opposing region is not softened by heat, the external additive contained in the two-component developer will not be embedded in the toner, and the fluidity of the toner will not decrease, making it easier for the toner to move away from the carrier. In other words, the developing current will increase.

[0084] Another specific example of the current detection processing unit 54 is the detection of the non-developing current (an example of the target current of the present invention) that flows when the second electric field is formed in the opposing region where the two-component developer is present, causing the toner to move from the non-exposed part of the photoreceptor drum towards the developing roller. In this case, when the second electric field is formed, the current detection processing unit 54 acquires the current value detected by the current detection circuit 302 as the value of the non-developing current.

[0085] As described above, the non-developing current includes a current that flows through the magnetic brush in the opposing region from the non-exposed area to the developing roller side due to the action of the second electric field formed in the opposing region. For example, when toner softens due to heat and the external additive contained in the two-component developer becomes embedded in the toner, the fluidity of the toner decreases, making it difficult for the toner to move away from the carrier. In other words, the non-developing current decreases.

[0086] On the other hand, if the toner contained in the magnetic brush in the opposing region is not softened by heat, the external additive contained in the two-component developer will not be embedded in the toner, and the fluidity of the toner will not decrease, making it easier for the toner to move away from the carrier. In other words, the non-developing current will increase.

[0087] In this embodiment, when a continuous printing process is performed in which an image is formed on each of the sheets being transported in succession, the current detection processing unit 54 detects the non-developing current each time the inter-paper region corresponding to two sheets in a continuous transport order in the photoreceptor drum comes into contact with the developing roller. The current detection processing unit 54 detects the non-developing current for each of the image forming units 31 to 34.

[0088] The current detection processing unit 54 may also detect the non-developing current at any timing at which the second electric field is formed in the opposing region during the execution of the continuous printing process. For example, the current detection processing unit 54 may detect the non-developing current at the timing when the developing roller faces the non-developing region corresponding to a non-printing region, such as a margin region, included in the image data to be printed.

[0089] Furthermore, the current detection processing unit 54 may detect the non-developing current at any timing when the second electric field is formed in the opposing region during the execution of a discontinuous printing process that forms an image on a single sheet.

[0090] Furthermore, the current detection processing unit 54 may detect the non-developing current at any timing during the image forming operation of the image forming apparatus 10 when the second electric field is formed in the opposing region where the two-component developer is present.

[0091] The cooling control unit 55 performs a predetermined cooling operation based on the detected current detected by the current detection processing unit 54 and the detected temperature detected by the temperature sensor 8.

[0092] The cooling operation may include, for example, driving the cooling fan 9, reducing the process speed of the image forming unit 3, or stopping the image forming operation of the image forming unit 3, or one or more of these. Any of these operations can lower the internal temperature of the image forming apparatus 10.

[0093] In this embodiment, the cooling control unit 55 executes the cooling operation when, for example, the absolute value of the current difference ΔI between the detected current and a predetermined reference current value exceeds a predetermined first threshold, and the detected temperature exceeds a predetermined second threshold. The reference current value, the first threshold, and the second threshold are design elements that can be set to arbitrary values ​​for the developing current or the non-developing current, respectively.

[0094] In another embodiment of the cooling control unit 55, for example, the cooling operation may be performed based on the set voltage value set by the calibration processing unit 51 and the detected temperature detected by the temperature sensor 8.

[0095] Specifically, the cooling control unit 55 may, for example, execute the cooling operation when the absolute value of the voltage difference ΔV between the set voltage value set by the calibration processing unit 51 and a predetermined reference voltage value exceeds a predetermined third threshold, and the detected temperature exceeds a predetermined second threshold.

[0096] In another embodiment of the cooling control unit 55, for example, the cooling operation may be performed when the set voltage value set by the calibration processing unit 51 exceeds the allowable upper limit value determined by the bias upper limit determination unit 53, and the detected temperature exceeds a predetermined second threshold.

[0097] [4] Cooling process in an image forming apparatus (first example of processing) The following describes a cooling method performed in the image forming apparatus 10, along with an example of the procedure for the cooling process (first processing example) performed by the control unit 5 in the image forming apparatus 10, with reference to the flowchart in Figure 5. Here, steps S1, S2, etc. represent the processing procedure (step) numbers performed by the control unit 5.

[0098] <Step S1> First, in step S1, the control unit 5 determines whether or not the timing for detecting the developing current or the non-developing current (hereinafter referred to as the target current) has arrived.

[0099] Specifically, the control unit 5 determines that the detection timing for detecting the development current has arrived when the process of developing the test toner image is performed while the DC calibration process is being executed.

[0100] Furthermore, during the execution of the continuous printing process, the control unit 5 determines that the detection timing for detecting the non-developing current has arrived when the inter-paper region of the photoreceptor drum, which corresponds to two sheets in a continuous transport order, faces the developing roller.

[0101] If the control unit 5 determines that the detection timing has arrived (Yes side of S1), it proceeds to step S2. If the detection timing has not arrived (No side of S1), the control unit 5 waits for the detection timing to arrive in step S1.

[0102] <Step S2> In step S2, the control unit 5 detects the target current. Here, the processing in step S2 is performed by the current detection processing unit 54 of the control unit 5.

[0103] <Step S3> When the target current is detected in step S2, the control unit 5 calculates the absolute value of the current difference ΔI between the target current and a predetermined reference current value in the next step S3, and determines whether the absolute value of the current difference ΔI exceeds the predetermined first threshold. If the control unit 5 determines that the current difference ΔI exceeds the first threshold, it proceeds to step S4. On the other hand, if the current difference ΔI does not exceed the first threshold, the control unit 5 proceeds to step S1.

[0104] <Step S4> In step S4, the control unit 5 determines whether the temperature detected by the temperature sensor 8 exceeds a predetermined second threshold. If the control unit 5 determines that the detected temperature exceeds the second threshold, it proceeds to step S5. On the other hand, if the detected temperature does not exceed the second threshold, the control unit 5 proceeds to step S1.

[0105] <Step S5> In step S5, the control unit 5 stops the operation of the image forming apparatus 10 so that it cannot perform image forming operations, and then performs the cooling operation. While the cooling operation is running, even if a print command is input to the image forming apparatus 10, the image forming process will not be executed.

[0106] <Step S6> Subsequently, in step S6, the control unit 5 determines whether or not the stop conditions for stopping the cooling operation have been met. These stop conditions include, for example, that the temperature detected by the temperature sensor 8 has fallen to a predetermined temperature lower than the second threshold, or that a predetermined time has elapsed.

[0107] <Step S7> When it is determined that the aforementioned stopping conditions have been met, the control unit 5 stops the cooling operation and makes the image forming apparatus 10 ready to perform the image forming operation.

[0108] In this way, the image forming apparatus 100 performs the cooling operation to cool the inside of the image forming apparatus 10 based on the detected current detected by the current detection processing unit 54 and the detected temperature detected by the temperature sensor 8. More specifically, the cooling operation is performed when the absolute value of the current difference ΔI between the target current (the developing current or the non-developing current) and a predetermined reference current value exceeds the first threshold, and the detected temperature exceeds the second threshold. As a result, for example, even if the detected temperature exceeds the second threshold, if the absolute value of the current difference ΔI does not exceed the first threshold, the cooling operation is not performed, and the image forming apparatus 10 maintains a state in which image forming processing is possible. As a result, a decrease in developability can be prevented in the image forming apparatus 10. Furthermore, since the cooling operation is performed when the absolute value of the current difference ΔI exceeds the first threshold and the detected temperature exceeds the second threshold, it is possible to improve both developability and productivity compared to conventional methods without reducing developability or decreasing the productivity of the image forming apparatus 10.

[0109] [5] Cooling process in an image forming apparatus (second example of processing) The following describes a cooling method performed in the image forming apparatus 10, along with an example of the procedure for the cooling process (first processing example) performed by the control unit 5 in the image forming apparatus 10, with reference to the flowchart in Figure 6. In the following description, only steps that differ from the first processing example shown in Figure 5 will be described, and common steps will be denoted by the same reference numerals, thus omitting detailed explanations.

[0110] <Step S11> First, in step S11, the control unit 5 determines whether or not the adjustment execution conditions have been met.

[0111] <Step S12> If it is determined in step S11 that the adjustment execution conditions have been met, the control unit 5 executes the DC calibration process in step S12. The process in step S12 is performed by the calibration processing unit 51.

[0112] <Step S13> When the processing in step S12 is completed, the control unit 5 executes the bias upper limit determination process in step S13, which determines the upper limit voltage value (allowable upper limit) of the allowable range that can be set as the DC component Vdc of the development bias VB. The processing in step S13 is performed by the bias upper limit determination unit 53. The allowable upper limit determined in step S13 is stored in the storage unit 6.

[0113] <Step S14> In the next step S14, the control unit 5 calculates the absolute value of the voltage difference ΔV between the set voltage value set in the DC calibration process and the reference voltage value, and determines whether the absolute value of the voltage difference ΔV exceeds the predetermined third threshold. If the control unit 5 determines that the voltage difference ΔV exceeds the third threshold, it proceeds to step S4. On the other hand, if the voltage difference ΔV does not exceed the third threshold, the control unit 5 proceeds to step S15.

[0114] <Step S15> In step S15, the control unit 5 determines whether the set voltage value set in the DC calibration process exceeds the allowable upper limit. If the control unit 5 determines that the set voltage value exceeds the allowable upper limit, it proceeds to step S4. On the other hand, if the set voltage value does not exceed the allowable upper limit, the control unit 5 proceeds to step S11.

[0115] In this manner, the image forming apparatus 100 performs the cooling operation to cool the inside of the image forming apparatus 10 based on the set voltage value set by the calibration processing unit 51 and the detected temperature detected by the temperature sensor 8. More specifically, the cooling operation is performed when the absolute value of the voltage difference ΔV between the set voltage value and a predetermined reference voltage value exceeds the third threshold, and the detected temperature exceeds the second threshold. Even when such a cooling process is performed, it is possible to improve both the developability and productivity of the image forming apparatus 10 without reducing the developability or productivity of the image forming apparatus 10.

[0116] Furthermore, the cooling operation is performed when the set voltage value exceeds the allowable upper limit and the detected temperature exceeds the second threshold. Even when such a cooling process is performed, it is possible to improve both the developability and productivity compared to conventional methods without reducing the developability or the productivity of the image forming apparatus 10.

[0117] In the second example of the cooling process shown in Figure 6, it is not necessary for both the determination processes in step S14 and step S15 to be executed; at least one of the determination processes may be performed. Of course, by executing both the determination processes in step S14 and step S15, the developability and productivity of the image forming apparatus 10 can be further improved.

[0118] [Notes on the invention] The following is an overview of the invention extracted from the above-described embodiments. Note that each configuration and processing function described below can be selected and combined as desired.

[0119] <Note 1> An image forming unit that applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the developing region of the first carrier and developing the developing region of the first carrier, A current detection unit that detects the target current flowing between the first and second support bodies during development, A temperature detection unit that detects the temperature inside the device, An image forming apparatus comprising: a cooling control unit that performs a predetermined cooling operation based on the current detected by the current detection unit and the temperature detected by the temperature detection unit.

[0120] <Note 2> The image forming apparatus according to Appendix 1, wherein the cooling control unit performs the cooling operation when the current difference between the detected current and a predetermined reference current value exceeds a predetermined first threshold and the detected temperature exceeds a predetermined second threshold.

[0121] <Note 3> The target current is the developing current that flows from the second support to the developing region of the first support during development. The image forming apparatus according to Appendix 1 or 2, wherein the current detection unit detects the developing current flowing from the second carrier to the developing region of the first carrier when a calibration process is performed to set a bias voltage value, and a predetermined measuring toner image formed on the first carrier is developed.

[0122] <Note 4> The target current is the non-developing current that flows from the non-developing region of the first carrier to the second carrier when the bias voltage is applied. The image forming apparatus according to any one of the appendices 1 to 3, wherein the current detection unit detects the non-developing current at the timing when the second carrier faces the inter-paper region corresponding to the transport order between two consecutive sheets in the first carrier when a continuous printing process is performed to form an image on each of the sheets that are transported in succession.

[0123] <Note 5> An image forming unit that applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the developing region of the first carrier and developing the developing region of the first carrier, A calibration processing unit that performs a calibration process to set the bias voltage value, A temperature detection unit that detects the temperature inside the device, An image forming apparatus comprising: a cooling control unit that performs a predetermined cooling operation based on the set voltage value determined by the calibration processing unit and the temperature detected by the temperature detection unit.

[0124] <Note 6> The image forming apparatus according to Appendix 5, wherein the cooling control unit performs the cooling operation when the voltage difference between the set voltage value and a predetermined reference voltage value exceeds a predetermined third threshold and the detected temperature exceeds a predetermined second threshold.

[0125] <Note 7> The image forming apparatus according to Appendix 5 or 6, wherein the cooling control unit performs the cooling operation when the set voltage value exceeds a predetermined upper voltage value with respect to the bias voltage and the detected temperature exceeds a predetermined second threshold.

[0126] <Note 8> The image forming apparatus according to any one of the appendices 1 to 7, wherein the cooling control unit performs one or more of the following as the cooling operation: driving a cooling fan, reducing the process speed of the image forming unit, or stopping the image forming operation of the image forming unit. [Explanation of Symbols]

[0127] 1: Automatic document transport device 2: Image reading unit 3: Image forming unit 4:Paper feed section 5: Control Unit 6: Storage section 7: Operation display section 8: Temperature sensor 9: Cooling fan 10: Image forming apparatus 31-34: Image forming unit 35: Optical scanning device 36: Intermediate Transfer Apparatus 37: Secondary transfer roller 38: Fixing device 39: Paper output tray 51: Calibration Processing Unit 53: Bias Upper Limit Determination Unit 54: Current detection processing unit 55: Cooling Control Unit 100: Image forming apparatus 301: Power supply circuit 301A:Development power supply circuit 301B: Power supply circuit for static electricity 302: Current detection circuit 302A: Filter circuit 351: Optical scanning unit 352: Optical scanning unit 361: Intermediate transfer belt 362: Drive roller 363: Tension Roller 364: Belt Cleaning Department 365: Concentration detection unit

Claims

1. An image forming unit that applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the developing region of the first carrier and developing the developing region of the first carrier, A current detection unit that detects the target current flowing between the first and second support bodies during development, A temperature detection unit that detects the temperature inside the device, An image forming apparatus comprising: a cooling control unit that performs a predetermined cooling operation based on the current detected by the current detection unit and the temperature detected by the temperature detection unit.

2. The image forming apparatus according to claim 1, wherein the cooling control unit performs the cooling operation when the current difference between the detected current and a predetermined reference current value exceeds a predetermined first threshold and the detected temperature exceeds a predetermined second threshold.

3. The target current is the developing current that flows from the second carrier to the developing region of the first carrier during development. The image forming apparatus according to claim 1, wherein the current detection unit detects the developing current flowing from the second carrier to the developing region of the first carrier when a calibration process is performed to set a bias voltage value, and a predetermined measuring toner image formed on the first carrier is developed.

4. The target current is the non-developing current that flows from the non-developing region of the first carrier to the second carrier when the bias voltage is applied. The image forming apparatus according to claim 1, wherein the current detection unit detects the non-developing current at the timing when the second carrier faces the inter-paper region corresponding to the transport order between two consecutive sheets in the first carrier when a continuous printing process is performed to form an image on each of the sheets that are transported in succession.

5. An image forming unit that applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the developing region of the first carrier and developing the developing region of the first carrier, A calibration processing unit that performs a calibration process to set the bias voltage value, A temperature detection unit that detects the temperature inside the device, An image forming apparatus comprising: a cooling control unit that performs a predetermined cooling operation based on the set voltage value determined by the calibration processing unit and the temperature detected by the temperature detection unit.

6. The image forming apparatus according to claim 5, wherein the cooling control unit performs the cooling operation when the voltage difference between the set voltage value and a predetermined reference voltage value exceeds a predetermined third threshold and the detected temperature exceeds a predetermined second threshold.

7. The image forming apparatus according to claim 5 or 6, wherein the cooling control unit performs the cooling operation when the set voltage value exceeds a predetermined upper voltage value with respect to the bias voltage and the detected temperature exceeds a predetermined second threshold.

8. The image forming apparatus according to claim 1, wherein the cooling control unit performs one or more of the following as the cooling operation: driving a cooling fan, reducing the process speed of the image forming unit, or stopping the image forming operation of the image forming unit.

Images