Image forming apparatus

Abstract

To provide a method that can reliably determine cancellation of a separation state without providing a special detection circuit, and to provide a method that can reduce unnecessary toner consumption and dirt due to failure in cancellation of the separation state.SOLUTION: An image forming apparatus comprises: an electrification device that is in contact with a photoreceptor to electrify the photoreceptor; a separation mechanism that holds the photoreceptor and the electrifying device in a separation state that can be cancelled; an exposure device that exposes the photoreceptor; a developing device that forms a toner image on a surface of the photoreceptor; a toner adhesion amount sensor that detects the toner image formed on the surface of the photoreceptor and the density of the toner image for image quality adjustment; an image quality adjustment unit that controls the voltage applied to the electrifying device, the voltage applied to the developing device, the amount of light emission when the exposure device perform exposure, and the detection of the toner image and the density of the toner image by the toner adhesion amount sensor; and a separation cancellation checking unit that detects, with the toner adhesion amount sensor, whether the toner image is formed even through the photoreceptor is not exposed in an initialization operation in an image forming process, and thereby performs separation cancellation checking as to whether the separation state held by the separation mechanism is cancelled.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This invention relates to an image forming apparatus including a charging roller and a toner adhesion amount sensor.

Background Art

[0002] In an image forming apparatus that charges a photoreceptor, which is an image carrier, with a charging roller, there is a mechanism (hereinafter referred to as a separation mechanism) that detachably separates the photoreceptor and the charging roller so that they do not physically contact each other when the image forming apparatus is shipped from the factory. Further, in an image forming apparatus configured as a unit (hereinafter referred to as a process unit) in which the photoreceptor and the charging roller are replaceable, a detachable separation mechanism is provided at the time of factory shipment of the replacement process unit so that the photoreceptor and the charging roller do not physically contact each other. This is to avoid the portion of the photoreceptor being physically or chemically damaged when the charging roller is in continuous pressure contact with the photoreceptor, which would affect the image quality. However, when forming an image, it is necessary to bring the charging roller into contact with the photoreceptor in order to charge the surface of the photoreceptor. Therefore, the separation mechanism is provided with a release mechanism that releases the separation and brings the charging roller into contact with the photoreceptor.

[0003] If a malfunction occurs in the release mechanism, the charging roller and the photoreceptor will remain separated. Then, the photoreceptor will not be charged during the image forming operation. Currently, in an image forming apparatus that forms a toner image (also referred to as development) on a photoreceptor by an electrophotographic method, it is common for toner to selectively adhere to areas where the photoreceptor is not charged (originally, exposed areas). Therefore, if the release mechanism does not operate and the charging roller remains separated, and the photoreceptor is not charged, instead of the toner image that should be formed by toner adhering only to the originally exposed areas, a toner image will be formed over the entire surface of the photoreceptor (solid image), resulting in wasteful consumption of toner. As a result, the surrounding area of the photoreceptor may be soiled by the scattered toner.

[0004] Therefore, a device has been proposed that includes a determination means for determining the separation state between the charging roller and the photoreceptor drum after use has begun (see, for example, Patent Document 1). Patent Document 1 describes a device comprising an image carrier (photoreceptor), a charging means (charging roller), a separation means for separating the two before use and bringing them into contact after use, and a determination means. The determination means applies a first bias to the charging means that is lower than the bias applied when charging the image carrier, and determines the separation state of the process cartridge (whether it is a new or uninstalled cartridge in a separated state, or an old cartridge after separation has been released) from the value of the current that flows at that time. If it is determined that the process cartridge is new or uninstalled, a second bias greater than the first bias is applied, and it is determined whether it is new or an uninstalled process cartridge from the value of the current that flows through the charging means at that time. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-008094 [Overview of the project] [Problems that the invention aims to solve]

[0006] The method described in Patent Document 1 determines whether a process cartridge is old, new, or not installed based on the magnitude of the current that flows when a voltage is applied to the charging means. To do this, it is necessary to provide a current detection circuit that detects the magnitude of the current that flows through the charging means. This invention was made in consideration of the above circumstances, and provides a method for reliably determining the release of the separated state without providing a dedicated detection circuit, thereby reducing wasted toner consumption and soiling due to poor release of separated states. [Means for solving the problem]

[0007] This invention provides an image forming apparatus comprising: a charging device that charges a photoreceptor involved in an image forming process by contacting it while a voltage is applied; a separation mechanism that holds the photoreceptor and the charging device in a releaseably separated state; an exposure device that exposes the photoreceptor; a developing device that forms a toner image on the surface of the photoreceptor while a voltage is applied; a toner adhesion amount sensor that detects the toner image formed on the surface of the photoreceptor for image quality adjustment; an image quality adjustment unit that controls the voltage applied to the charging device, the voltage applied to the developing device, the amount of light emitted when the exposure device exposes the photoreceptor, and the detection of the toner image and its density by the toner adhesion amount sensor; and a separation release confirmation unit that confirms whether the separated state by the separation mechanism has been released by detecting whether a toner image is formed even though the charging device and the developing device are not exposed while a voltage is applied during the initialization operation of the image forming process at the start of use, using the toner adhesion amount sensor. [Effects of the Invention]

[0008] In the image forming apparatus according to this invention, the separation release confirmation unit detects whether or not a toner image is formed despite the lack of exposure while voltage is applied to the charging device and developing device during the initialization operation of the image forming process at the start of use, using a toner adhesion amount sensor for image quality adjustment. This confirms whether or not the separation state caused by the separation mechanism has been released, thus providing a method that can reliably determine whether the separation state has been released without providing a dedicated detection circuit, thereby reducing wasted toner consumption and contamination due to faulty separation release. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view showing the external appearance of a digital multifunction device, which is one embodiment of the image forming apparatus of this invention. [Figure 2] Figure 1 is an explanatory diagram showing the internal configuration related to image formation in the multifunction printer. [Figure 3] Figure 1 is a block diagram showing the elements related to the control of the multifunction printer. [Figure 4] This is an explanatory diagram showing the internal configuration of a monochrome image forming machine, which is a different embodiment of the image forming apparatus of this invention. [Figure 5] Figure 2 is an assembly diagram showing an example of a separation cam, which is one of the main components of the separation mechanism of the multifunction printer shown in Figure 2 and is mounted on the front side of the charging roller. [Figure 6] Figure 2 is an assembly diagram showing an example of a separation cam, which is one of the main components of the separation mechanism of the multifunction printer shown in Figure 2 and is mounted on the rear side of the charging roller. [Figure 7] Figure 5 is an explanatory diagram showing the position of the front-side separation cam in its separated state. [Figure 8] Figure 6 is an explanatory diagram showing the position of the rear-side separation cam in the separated state. [Figure 9] Figure 5 is an explanatory diagram showing the position of the front-side separation cam in the released state. [Figure 10] Figure 6 is an explanatory diagram showing the position of the rear-side separation cam in the released state. [Figure 11] Figure 3 shows a first flowchart illustrating an example of the initialization process of the image forming process, including separation release confirmation, which is performed by the control unit. [Figure 12] Figure 3 shows a second flowchart illustrating an example of the initialization process of the image forming process, including separation release confirmation, which is performed by the control unit. [Figure 13] Figure 3 shows a third flowchart illustrating an example of the initialization process of the image forming process, including separation release confirmation, which is performed by the control unit. [Figure 14] Figure 3 shows a fourth flowchart illustrating an example of the initialization process of the image forming process, including separation release confirmation, which is performed by the control unit. [Figure 15] Figure 3 shows a fifth flowchart illustrating an example of the initialization process of the image forming process, including separation release confirmation, which is performed by the control unit. [Modes for carrying out the invention]

[0010] Hereinafter, this invention will be described in further detail with reference to the drawings. Note that the following description is illustrative in all aspects and should not be construed as limiting this invention. (Embodiment 1) ≪Configuration Example of Image Forming Apparatus≫ FIG. 1 is a perspective view showing the appearance of a digital multifunction peripheral which is an embodiment of the image forming apparatus of this invention. FIG. 2 is an explanatory view showing the internal configuration related to image formation of the multifunction peripheral 100 shown in FIG. 1. FIG. 3 is a block diagram showing elements related to the control by the control unit 110 shown in FIG. 1.

[0011] As shown in FIG. 1, the multifunction peripheral 100 has an image reading unit 111 for reading a document, an operation unit 105 for receiving user operations, and a printing unit 115 for performing image formation in the main body. Further, a paper feed tray 18a is provided below the printing unit 115. A discharge tray 39a is provided above the printing unit 115 and below the image reading unit 111, and a discharge tray 39b is provided on the right side surface. Also, a front door 31 which is an openable and closable main body cover is provided on the front side. FIG. 1 shows a state where the front door is closed. A document conveyance unit 103 for conveying a document to the reading unit is provided on the main body. A paper feed desk including three paper feed trays 18b, 18c, and 18d for storing printing sheets is provided below the main body.

[0012] Here, the internal configuration related to image formation of the multifunction peripheral 100 shown in FIG. 2 will be described. The multifunction peripheral 100 forms toner images of four colors, yellow (Y), magenta (M), cyan (C), and black (K), by an electrophotographic process, overlaps them on an intermediate transfer belt 21, and prints a color image on a printing sheet. Alternatively, a monochrome image using a single color (for example, black) is printed on a printing sheet. For this reason, four process units 30 each including a developing unit 12, a photosensitive drum 13, a charging roller 14, a drum cleaner 15, etc. are provided inside the printing unit 115. The process unit includes a photosensitive drum 13 and a charging roller 14. Also, an optical scanning unit 11 for exposing and scanning the photosensitive drum 13 corresponding to each color with a laser beam is arranged.

[0013] The multifunction device 100 has process units 30y, 30m, 30c, and 30k for each color. In FIG. 2, only the components of the yellow process unit 30y are labeled, and the other colors are omitted. For the process units, they may also be denoted as process unit 30 using representative symbols. The explanations using representative symbols should be understood to apply to each of the colors Y, M, C, and K.

[0014] In this embodiment, the process unit 30 is configured as an integrally replaceable consumable unit. This is to enable easy replacement of consumables such as the photosensitive drum 13 included in the process unit 30.

[0015] The multifunction device 100 further includes an image processing circuit 41 that generates an input signal to the optical scanning unit 11 (see FIG. 3). The image processing circuit 41 processes the image data of the document read by the image reading unit 111 and generates exposure data related to the exposure pattern of the photosensitive drum 13. The exposure data corresponds to the pattern of the electrostatic latent image formed on the surface of the photosensitive drum 13. Under the control of the image formation control unit 133 shown in FIG. 3, through the electrophotographic process of cleaning by the drum cleaner 15, charging by the charging roller 14, exposure by the optical scanning unit 11, and development by the developing unit 12, toner images of any one of Y, M, C, and K are formed on the photosensitive drum 13.

[0016] A primary transfer roller 16 is disposed at a position where it contacts the photosensitive drum 13 of the process unit 30 via the intermediate transfer belt 21. The image formation control unit 133 applies a voltage to the primary transfer roller 16 to transfer the toner images of Y, M, C, and K formed on the photosensitive drum 13 onto the intermediate transfer belt 21 in an overlapping manner and send them to a position where they contact the secondary transfer unit 23. The image formation control unit 133 drives the secondary transfer unit 23 and applies a voltage to transfer the toner image onto the printing sheet fed from the paper feed tray 18a or the like. A toner adhesion amount sensor 43 is positioned in front of the secondary transfer unit 23, facing the intermediate transfer belt 21 that moves from the primary transfer roller 16 to the secondary transfer unit 23. In this embodiment, the toner adhesion amount sensor 43 is a reflective optical sensor that detects the amount of toner that adheres to the toner image transferred to the intermediate transfer belt 21.

[0017] The image forming control unit 133 controls the printing unit 115 to form adjustment toner patches for each of the Y, M, C, and K colors, and detects the density of the formed toner patches with the toner adhesion amount sensor 43. Then, it adjusts at least one of the following: the voltage applied to the charging roller 14 corresponding to each color, the voltage applied to the developing unit 12, and the intensity of the laser beam irradiated from the optical scanning unit 11 onto the photoreceptor drum 13. Through this adjustment, image quality adjustment is performed to obtain a suitable image.

[0018] Furthermore, the image forming control unit 133 feeds and transports printed sheets from the main unit's paper feed tray 18a, the paper feed trays 18b, 18c, and 18d of the paper feed desk (not shown in Figure 2), and the manual feed tray 19. The manual feed tray 19 can also be folded and stored in the main unit when not in use, as shown in Figure 1.

[0019] The image forming control unit 133 transports the printed sheet, onto which the toner image has been transferred by the secondary transfer unit 23, to the fixing unit 17. The heating roller 24 and pressure roller 25 of the fixing unit 17 heat and pressurize the printed sheet as it passes between them, fixing the toner image transferred to the printed sheet. The image forming control unit 133 drives the fixing unit 17 and controls the heating temperature of the heating roller 24.

[0020] The image forming control unit 133 discharges the printed sheet that has passed through the fuser unit 17 to the discharge tray 39a. Alternatively, it switches the sheet back at the discharge roller 36 and discharges it to the discharge tray 39b on the right side. Or, it guides the switched-back printed sheet to the double-sided transport path 37 and returns it to the secondary transfer unit 23. There, it transfers the toner image to the back side of the printed sheet and discharges the printed sheet to the discharge tray 39a or 39b via the fuser unit 17.

[0021] As shown in Figure 3, the control unit 110 includes hardware resources such as a processor 121, RAM 122, and non-volatile memory 123. The processor 121 executes a control program pre-stored in the non-volatile memory 123 and works in cooperation with the hardware resources to realize the functions of the control unit 110. The control unit 110 also includes an image quality adjustment unit 131, an image formation control unit 133, and a separation release confirmation unit 135.

[0022] Figure 2 shows an example of the configuration of a color multifunction printer that forms a color image by superimposing four toner images. In contrast, Figure 4 shows an example of the printing unit of a monochrome multifunction printer that forms a monochrome image. The multifunction printer 101 shown in Figure 4 prints a monochrome image using black toner onto printing paper. The units corresponding to the multifunction printer 100 shown in Figure 2 are denoted by the same reference numerals as in Figure 2. The printing unit includes a light scanning unit 11, a developing unit 12, a photoreceptor drum 13, a charging roller 14, a drum cleaner 15, a fuser unit 17, and a toner adhesion amount sensor 43. Although the block diagram corresponding to Figure 3 is omitted for the multifunction printer 101 shown in Figure 4, the primary transfer roller 16, intermediate transfer belt 21, and secondary transfer unit 23 shown in Figure 3 are absent. Instead, there is a transfer unit 23 that transfers the toner image from the photoreceptor drum 13 to the printing sheet. Also, there is only one toner storage unit 27, one developer unit 12, and one process unit 30 for black toner. The other configurations are the same as in Figure 3. Note that the transfer unit 23 includes a transfer roller 22.

[0023] The image forming control unit 133 shown in Figure 3 controls the printing unit 115 to form an adjustment toner patch. The density of the formed toner patch is detected by the toner adhesion amount sensor 43, and image quality adjustment is performed by adjusting at least one of the following: the voltage applied to the charging roller 14, the voltage applied to the developing unit 12, or the intensity of the laser beam irradiated from the optical scanning unit 11 onto the photoreceptor drum 13, in order to obtain a suitable image.

[0024] The image forming control unit 133 shown in Figure 3 forms a toner image of black toner on the photoreceptor drum 13. Then, a voltage is applied to the secondary transfer roller 22 of the transfer unit 23 to transfer the black toner image formed on the photoreceptor drum 13 to the printing sheet fed from the paper tray 18a or the like. A toner adhesion amount sensor 43 is positioned in front of the transfer unit 23 so as to face the photoreceptor drum 13 as it moves from the developing unit 12, which is positioned opposite the photoreceptor drum 13, to the transfer unit 23. The toner adhesion amount sensor 43 detects the amount of toner that adheres to the toner image formed on the photoreceptor drum 13.

[0025] The image quality adjustment unit 131 controls the printing unit 115 to form an adjustment toner patch and detects the density of the formed toner patch with the toner adhesion amount sensor 43. It then adjusts at least one of the following: the voltage applied to the charging roller 14, the voltage applied to the developing unit 12, and the intensity of the laser beam irradiated from the optical scanning unit 11 onto the photoreceptor drum 13. Through this adjustment, the image quality is adjusted so that a suitable image is obtained when the image formation control unit 133 forms the image. Then, the separation release confirmation unit 135 performs processing related to confirming the separation state, as will be described later.

[0026] ≪Mechanism for separating and releasing the charging roller and photoreceptor≫ Before describing the process for confirming the separated state, we will first describe specific examples of the separated mechanism and release mechanism in the multifunction printer in this embodiment. The following explanation will use the color multifunction printer shown in Figure 2 as an example, but the same mechanism applies to the monochrome multifunction printer shown in Figure 4. Figure 5 is an assembly diagram showing an example of a separation cam, which is one of the main components of the separation mechanism of the multifunction printer shown in Figure 2, and is mounted on the front side of the charging roller 14 (the side in Figure 1 where the handles of the operating unit 105 and the paper feed trays 18a to 18d are located, the front side). Correspondingly, Figure 6 is an assembly diagram showing an example of a separation cam mounted on the rear side of the charging roller 14 (the back side opposite to the front side in Figure 1).

[0027] As shown in Figures 5 and 6, approximately spiral-shaped separation cams 50 and 54 are rotatably inserted into the front shaft portion 14a and the rear shaft portion 14b of the charging roller 14, respectively. The front separation cam 50 has a rib portion 51 at its spiral inner end, and its outer end functions as a spacer to maintain the separated state. The rear separation cam 54 also has a rib portion 55 at its spiral inner end, and its outer end functions as a spacer to maintain the separated state.

[0028] Figures 7 to 10 are explanatory diagrams showing the positions of the separation cam in the separated and released states. Figure 7 shows the separated position of the front separation cam 50. (a) is a perspective view, and (b) is a cross-sectional view showing a plane perpendicular to the axis of the charging roller 14. Figure 8 shows the separated position of the rear separation cam 54. Figures 8(a) and 8(b) are the same as Figures 7(a) and 7(b). Figure 9 shows the position of the front-side separation cam 50 in the released state. Figures 9(a) and 9(b) correspond to Figures 7(a) and 7(b). Figure 10 shows the position of the rear-side separation cam 54 in the released state. Figures 10(a) and (b) correspond to Figures 8(a) and (b).

[0029] As shown in the cross-sectional views of Figures 7 to 10, the charging roller 14 is biased in a direction that presses it toward the photoreceptor drum 13 by a spring 53 on the front side and a spring 57 on the rear side. This is to ensure that the charging roller 14 makes reliable contact with the photoreceptor drum 13 during image formation. As shown in Figure 7, in the initial separated state, the outer end of the separating cam 50 is located between the front ends of the photoreceptor drum 13 and the charging roller 14, functioning as a spacer to maintain the separated state. Also, as shown in Figure 8, the outer end of the separating cam 54 is located between the rear ends of the photoreceptor drum 13 and the charging roller 14, functioning as a spacer to maintain the separated state.

[0030] As shown in Figures 9 and 10, the photoreceptor drum 13 is driven in the direction of arrow R during the operation of the image forming process. When the photoreceptor drum 13 is driven in the direction of arrow R, the frictional force between the photoreceptor drum 13 and the outer ends of the separation cams 50 and 54 that are in contact with it causes the separation cams 50 and 54 to rotate along with it. As a result, the outer ends of the separation cams 50 and 54 move out of their position between the photoreceptor drum 13 and the charging roller 14, and the charging roller 14 is pushed by the springs 53 and 57 into contact with the photoreceptor drum 13. In other words, when a new process unit 30 in a separated state is mounted on the main body of the image forming apparatus and the photoreceptor drum 13 rotates for the first time, the separated state is released.

[0031] When the front-side separation cam 50 rotates along with the photoreceptor drum 13, the rib portion 51 slips under the anti-reverse stopper 52, which is fixed to the process unit 30 by elasticity. Having slipped under the anti-reverse stopper 52, the rib portion 51 expands outward by elasticity. Therefore, even if the separation cam 50 is subsequently subjected to a force that rotates it in the opposite direction to the rotation, the tip of the rib portion 51 will hit the anti-reverse stopper 52 and will not be able to rotate it any further in the opposite direction. Consequently, once the separation state is released, the separation cam 50 will not return to the separated position again. Similarly, when the rear separation cam 54 rotates with the photoreceptor drum 13, the rib portion 55 slips under the anti-reverse stopper 56, which is elastically fixed to the process unit 30. Having slipped under the anti-reverse stopper 56, the rib portion 55 expands outward elastically. Therefore, even if the separation cam 54 is subsequently subjected to a force that rotates it in the opposite direction of rotation, the tip of the rib portion 55 hits the anti-reverse stopper 56 and cannot rotate any further in the opposite direction. Consequently, once the separation state is released, the separation cam 54 will not return to the separated position again.

[0032] ≪Processing of the separation release confirmation section≫ Next, we will describe an example of the processing performed by the separation release confirmation unit with reference to the flowchart. Figures 11 to 15 are flowcharts showing an example of the initialization operation of the image forming process, including separation release confirmation, performed by the control unit shown in Figure 3. Figures 11 to 13 show the overall flow of the initialization operation of the image process, and Figures 14 and 15 show the process of checking whether the photoreceptor is charged, i.e., the separation release confirmation process. As shown in Figure 11, after power-on, after recovery from power-saving mode, or after replacement of the process unit 30, the control unit 110 performs the following series of processes as initialization operations for the image formation process. First, the control unit 110 performs basic initialization processing before starting the initialization operation of the image formation process, before driving the devices related to the image formation process (step S11). For example, it confirms that no error signal is output from either the high-voltage power supply that applies bias voltage to the charging roller 14 or the developing unit 12 (i.e., it is functioning normally). It also confirms that no error signal is output from the motor or drive circuit that drives the process unit 30 (i.e., it is functioning normally).

[0033] After the basic initialization process is completed and the conditions for starting the initialization operation of the image formation process are met (a loop returning to step S13 via No in step S13 and No in step S15, followed by Yes in step S13), the control unit 110 checks whether the process unit 30 is installed (step S17). In this embodiment, the process unit 30 is equipped with a non-volatile memory that stores data such as the usage history of the photoreceptor contained in the process unit 30 and the status of whether the separation mechanism is released or not. The control unit 110 can communicate with the non-volatile memory installed in the process unit 30, but communication is not possible if the process unit 30 is not installed, and the control unit 110 detects whether the process unit 30 is installed or not based on this. However, it is not limited to this, and a signal indicating whether it is installed or not may be provided, and the control unit 110 may determine whether the process unit 30 is installed or not based on that signal.

[0034] On the other hand, even if the determination in step S13 determines whether the conditions for starting the initialization operation of the image forming process are met (No in step S13), and a self-diagnosis execution instruction is received (Yes in step S15), the presence or absence of the process unit 30 is detected. This occurs when an instruction is received via the operation unit 105 or a communication circuit (not shown in Figure 3) to perform a self-diagnosis that confirms the release of the separated charging roller 14. If the process unit 30 is not installed (No. in step S19), the control unit 110 cancels the initialization operation of the image forming process, and informs the user that the initialization operation cannot be started by displaying it on, for example, the operation unit 105, prompting them to take action (step S21), and then terminates the process.

[0035] On the other hand, once the control unit 110 determines that the process unit 30 is installed and ready to start driving (step S19), the control unit 110 then determines whether or not the separation release confirmation has already been performed for the process unit 30 (step S23). If the separation release confirmation has already been performed, that is, if the process unit 30 is not new (No. in step S23), the control unit 110 skips the separation release confirmation process by the separation release confirmation unit 135 and executes the image quality adjustment process by the image quality adjustment unit 131. In other words, the control unit 110 proceeds to the process in step S57 shown in Figure 13.

[0036] On the other hand, in the case of a new process unit 30 for which separation release confirmation has not yet been performed (Yes in step S23), the control unit 110, as the separation release confirmation unit 135, executes the following separation release confirmation process. First, unlike the normal image formation process, a bias voltage (hereinafter also called a reverse bias voltage) selected to prevent toner images from forming in uncharged and unexposed areas of the photoreceptor drum 13 is applied to the developing unit 12 (step S31 shown in Figure 12). In the normal image formation process, the charged photoreceptor drum 13 is selectively exposed, and toner images are formed in the exposed areas.

[0037] Then, the control unit 110 drives the photoreceptor drum 13 to rotate and operates the toner deposition amount sensor 43 (step S33). The control unit 110 then adjusts at least one of the irradiation light amount emitted by the toner deposition amount sensor 43 or the sensitivity of the toner deposition amount sensor 43 in detecting reflected light so that the amount of reflected light reflected from the surface of the photoreceptor drum 13 where no toner image is formed is within a predetermined range (step S35).

[0038] The control unit 110 then determines whether the amount of light detected by the toner deposition amount sensor 43 has been adjusted to the predetermined range (i.e., whether it is normal) (step S37). If the amount of light detected could not be adjusted to the predetermined range (No. in step S37), the control unit 110 stops the drive of the process unit 30. The control unit 110 then notifies the user of the abnormality of the toner deposition amount sensor 43 by displaying it on, for example, the operation unit 105, and prompts them to take action (step S39), and terminates the process.

[0039] On the other hand, if the amount of light detected by the toner deposition sensor 43 can be adjusted to the predetermined range (Yes in step S37), the control unit 110 applies a bias voltage to the charging roller 14 and the developing unit 12 to a predetermined level at which an image can be formed (step S41). An example of a bias voltage in a normal image forming process is -600V for the charging roller 14 and -450V for the developing unit 12. However, in the case of step S41 described above, a lower voltage than in a normal image forming process may be used so that the density of the solid toner image (which can also be simply called a toner layer, as it is a solid image) formed in the event of a separation release failure is lower than in a normal image forming process. Furthermore, the control unit 110 applies a transfer bias voltage to the primary transfer roller 16.

[0040] Then, the control unit 110 waits for a predetermined period of time to elapse after raising the bias voltage (step S43), and then lowers the voltage applied to the charging roller 14 and the developing unit 12 (step S45). The period in step S43 is sufficient for the toner adhesion amount sensor 43 to detect the toner layer formed in the event of a separation release failure. An example of a suitable period is any period in the range of 50 milliseconds to 3 seconds. However, this is just an example, and the suitable period will vary depending on the process speed and the performance of the toner adhesion amount sensor.

[0041] After the power is turned down, the bias voltage is preferably such that the bias voltage of the charging roller 14 is zero, and the bias voltage applied to the developing unit 12 is the same reverse bias voltage as in step S31 (step S47). The control unit 110, acting as a separation release confirmation unit 135, waits for the toner layer formed in the event of a separation release failure to reach the detection point of the toner adhesion amount sensor 43, and then uses the toner adhesion amount sensor 43 to detect whether or not a toner layer has formed at that position (step S51 shown in Figure 13). Details of the process shown in step S51 will be described later.

[0042] Since the photoreceptor drum 13 is driven in step S33, the separation state should have already been released when the bias voltage is raised in step S41. Therefore, the charging roller 14 should be in contact with the photoreceptor drum 13 and in a state where it can charge the photoreceptor drum 13. The photoreceptor drum 13 is charged by the charging roller 14 and no toner image is formed in the unexposed areas. On the other hand, if a separation release failure occurs and the separation state is not released, the photoreceptor drum 13 is not charged. Therefore, a solid toner image (toner layer) is formed even in unexposed areas.

[0043] The control unit 110 determines whether the separation release was performed correctly as a result of the processing in step S51 (step S53). If it determines that there was a separation release failure (No. in step S53), the control unit stops the drive of the process unit. Then, it displays the state that the separation state has not been released (separation release failure) on, for example, the operation unit 105 to inform the user and prompt them to take action (step S55), and terminates the process. On the other hand, if it is determined that the separation release has been performed normally (Yes in step S53), the control unit 110 then performs image quality adjustment as the image quality adjustment unit 131.

[0044] As the image quality adjustment unit 131, the control unit 110 applies bias voltages to the charging roller 14 and the developing unit 12 at predetermined levels for image quality adjustment (step S57). An example of bias voltages is -600V for the charging roller 14 and -450V for the developing unit 12. Then, similar to step S35 described above, the light intensity of the toner deposition amount sensor 43 is adjusted (step S59). Next, the photoreceptor drum 13 is partially exposed using the light scanning unit 11 to form multiple patch images (toner patches) for image quality adjustment, and the amount of toner deposited (density) of the formed toner patches is detected by the toner deposition amount sensor 43. Based on the results, the bias voltage to be applied to the charging roller 14 and the developing unit 12 in the subsequent image formation process is determined, as well as the exposure intensity by the light scanning unit 11 and the gradation pattern to be applied (step S61).

[0045] Furthermore, the control unit 110 determines whether each step of the image quality adjustment has been completed successfully (step S63). This determination includes determining whether the light intensity adjustment in step S59 has been completed successfully, and whether an error signal was output from either the charging roller 14 or the high-voltage power supply that applies the respective bias voltages to the developing unit 12 during the execution of the image quality adjustment. It also includes determining whether the density of each toner patch detected using the toner adhesion amount sensor 43 is within a predetermined range. If the control unit 110 determines that there is an abnormality in the image quality adjustment (No. in step S63), it stops the process unit from running. The control unit 110 then displays the status of the detected abnormality in the image quality adjustment on the operation unit 105, for example, to inform the user and prompt them to take action (step S65), and then terminates the process.

[0046] On the other hand, if the image quality adjustment is completed successfully (step S63), the control unit 110 writes data indicating that the separation release confirmation has been performed to the non-volatile memory of the process unit 30 that performed the separation release confirmation (step S67). Then, it lowers the bias voltage applied to the charging roller 14 and the developing unit 12 (step S69) and stops the drive. The above is an example of the processing involved in the initialization of the image formation process.

[0047] Next, we will describe the details of the process in step S51 mentioned above. As a separation release confirmation unit 135, the control unit 110 waits for the area of ​​the toner layer to reach the detection area of ​​the toner adhesion amount sensor 43 when a toner layer is formed in the area where separation release is not successful, i.e., the area that was charged in steps S41 to S45 (loop of No in step S81). When the area reaches the detection area of ​​the toner adhesion amount sensor 43 (Yes in step S81), the control unit 110 initializes the sampling timer and error counter used to perform sampling using the toner adhesion amount sensor 43 to zero (step S83). Then, after setting a predetermined time corresponding to the sampling interval in the sampling timer, the sampling timer is started (step S85).

[0048] Here, the sampling timer is a timer used to ensure the sampling interval. The error counter is a counter that is incremented when the sampled data indicates a separation release failure, that is, when each level of consecutive sampled data corresponds to the amount of toner deposited when a toner layer is formed.

[0049] The control unit 110 waits for the sampling timer to time out (loop of No in step S87). When the sampling timer time out (Yes in step S87), the control unit 110 sets a predetermined time corresponding to the sampling interval in the sampling timer and then starts the sampling timer (step S89). Then, it determines whether or not it is within a predetermined period since the start of sampling (step S91). The period related to the determination in step S91 corresponds to the period related to the processing in step S43 described above. That is, it is the period during which the toner layer formed in the case of a separation release failure is detected by the toner adhesion amount sensor 43. However, considering the expansion of the detection area of ​​the toner adhesion amount sensor and errors in the mounting position of the charging roller 14, it is not necessary for this period to be exactly the same as the period in step S43.

[0050] If the determination in step S91 is within the predetermined period (Yes in step S91), the control unit 110 performs sampling of the toner adhesion amount using the toner adhesion amount sensor 43 (step S101). Then, it determines whether the sampling result indicates that a toner layer has been formed (step S111 in Figure 15). That is, it determines whether or not the toner is at a level where it has adhered. The formation of a toner layer indicates that the photoreceptor drum 13 is not charged, which indicates a separation release failure. In that case, the control unit 110 increments the value of the error counter by one (step S115). Then, it determines whether or not the value of the error counter has reached a predetermined threshold N (where N is a natural number) (step S117).

[0051] If the error counter reaches the threshold N (Yes in step S117), that is, if all N consecutive sampled data indicate a separation release failure, the system returns an error (separation release failure) as the result of the separation release confirmation (step S119). On the other hand, in the determination in step S111, if the sampling result indicates a level where no toner is attached (No. in step S111), the control unit 110 resets the value of the error counter to zero (step S113). By doing so, if the sampling data indicating a separation release failure is not continuous, errors up to that point will not be accumulated.

[0052] Then, the control unit 110 returns the process to the determination step S87 shown in Figure 14 and waits for the time to take the next sample. Similarly, if the error counter value does not reach a predetermined threshold N in the determination in step S117 (No. in step S117), the control unit 110 returns to the determination in step S87 shown in Figure 14 and waits for the next sampling to occur. The above is a detailed explanation of the process in step S51 shown in Figure 13, that is, the process for determining whether or not there is a problem with releasing the separation.

[0053] (Embodiment 2) In Embodiment 1, the flowcharts shown in Figures 11 to 15 show the processing for one process unit 30. However, in the case of the color multifunction printer shown in Figures 1 to 3, there are four process units 30, one for each of the colors Y, M, C, and K. In that case, the control unit 110 performs a separation release confirmation for each of the colors Y, M, C, and K.

[0054] As stated above, (i) The image forming apparatus according to this invention is characterized by comprising: a charging device that charges a photoreceptor involved in an image forming process by contacting it while a voltage is applied; a separation mechanism that holds the photoreceptor and the charging device in a releasely separated state; an exposure device that exposes the photoreceptor; a developing device that forms a toner image on the surface of the photoreceptor while a voltage is applied; a toner adhesion amount sensor that detects the toner image formed on the surface of the photoreceptor for image quality adjustment; an image quality adjustment unit that controls the voltage applied to the charging device, the voltage applied to the developing device, the amount of light emitted when the exposure device exposes the photoreceptor, and the detection and density of the toner image by the toner adhesion amount sensor; and a separation release confirmation unit that confirms whether the separated state by the separation mechanism has been released by detecting with the toner adhesion amount sensor whether a toner image is formed even though the charging device and the developing device are not exposed while a voltage is applied during the initialization operation of the image forming process at the start of use.

[0055] In this invention, the charging device contacts the photoreceptor to charge it. A specific embodiment of this device is, for example, the transfer roller described in the above-described embodiment. Furthermore, the photoreceptor is used in image formation using an electrophotographic method. A specific example of this is the photoreceptor drum described in the above-mentioned embodiment. The photoreceptor drum has a photoreceptor formed on the circumferential surface of a cylinder. However, the photoreceptor is not limited to being cylindrical. For example, it may be belt-shaped. A toner deposition amount sensor is a sensor for detecting toner patches formed on an image carrier. The toner deposition amount sensor is a reflective optical sensor that uses a pair of light-emitting and light-receiving elements to detect the amount of toner deposited on the toner image on the image carrier. As a specific embodiment of the image quality adjustment unit and the separation release confirmation unit, for example, one can consider an embodiment in which a processor and memory are centrally configured, as in the embodiment described above, and the processor executes a processing program stored in the memory.

[0056] Furthermore, preferred embodiments of this invention will be described. (ii) The separation release confirmation unit performs the separation release confirmation during the initialization operation of the image forming process at the start of use, and if it determines that the separation state has been released, it omits the separation release confirmation until at least one of the photoreceptor or the charging device is replaced. The image quality adjustment unit determines whether the devices related to the image forming process are normal and continues the initialization operation of the image forming process. If it determines that the separation state has not been released, or if the image quality adjustment unit determines that any of the devices related to the image forming process are not normal, the separation release confirmation unit may perform the separation release confirmation again during the initialization operation of the next image forming process. According to this embodiment, if the separation release confirmation unit confirms separation release and determines that the device involved in the image formation process is normal, it will omit further separation release confirmation until the device involved in the determination is replaced. However, if separation release or device abnormality is determined, it will not omit further separation confirmation. Therefore, compared to the case where separation release confirmation and device abnormality are not associated, misjudgment of separation release confirmation can be avoided more reliably.

[0057] (iii) The initialization operation of the continuing image forming process may be an image quality adjustment that forms a toner image for image quality adjustment, detects the toner image and its density with the toner adhesion amount sensor, and adjusts at least one of the voltage applied to the charging device, the voltage applied to the developing device, or the amount of light emitted when exposed by the exposure device. In this embodiment, after confirmation of separation release, image quality adjustment is performed to charge the photoreceptor.

[0058] (iv) The toner deposition amount sensor may be located at one or more different locations in the main scanning direction in which the exposure device exposes the photoreceptor, and the toner image may be detected on the surface of the photoreceptor or along the path through which the formed toner image is transported.

[0059] (v) The image quality adjustment unit may determine whether at least one of the toner deposition amount sensor, the charging device, the developing device, the photoreceptor, the path through which the formed toner image is transported, the toner storage unit that contains the toner supplied to the developing device, and the drive source involved in image formation is functioning normally.

[0060] (vi) The system may be equipped with multiple photoreceptors, charging devices, and separation mechanisms corresponding to different colors, and the separation release confirmation unit may perform the separation release confirmation for each color. According to this embodiment, when there are multiple separation mechanisms corresponding to different colors, it is possible to confirm the release of separation for each separation mechanism.

[0061] (vii) The photoreceptor and the charging device are provided as a single, mountable and replaceable process unit, the process unit may have a mechanism that allows the mounting body to detect whether it is a new, unmounted unit or a used, older unit, or the mounting body may have a non-volatile memory that can read and write data indicating whether it is a new or old unit. According to this configuration, the main unit can reliably distinguish between a brand-new, uninstalled process unit and a used, previously installed process unit.

[0062] (viii) If the process unit is equipped with the non-volatile memory, the separation release confirmation unit may write data to the non-volatile memory of the process unit indicating that the separation release confirmation has been performed if the separation release confirmation has been completed successfully. According to this embodiment, by writing data indicating that the separation release confirmation has been performed to the non-volatile memory of the process unit, the status of each process unit can be reliably recognized on the main unit side.

[0063] The embodiments of this invention also include combinations of any of the embodiments described above. In addition to the embodiments described above, various modifications of this invention are possible. These modifications should not be considered outside the scope of this invention. This invention should include the meaning of equivalence to the claims and all variations within that scope. [Explanation of symbols]

[0064] 11: Optical scanning unit, 12: Developing unit, 13: Photoconductor drum, 14: Charging roller, 14a, 14b: Shaft section, 15: Drum cleaner, 16: Primary transfer roller, 17: Fixing unit, 18a, 18b, 18c, 18d: Paper feed tray, 19: Manual feed tray, 21: Intermediate transfer belt, 22: Secondary transfer roller, Transfer roller, 23: Secondary transfer unit, Transfer unit, 24: Heating roller, 25: Pressure roller, 27: Toner storage unit, 30, 30y, 30m, 30c, 30k: Process unit, 31: Front door, 36: Discharge roller, 37: Double-sided transport path, 39a, 39b: Discharge tray, 41: Image processing circuit, 43: Toner adhesion amount sensor, 50, 54: Separation cam, 51, 55: Rib section, 52, 56: Anti-reverse stopper, 53, 57: Spring 100, 101: Multifunction printer, 103: Document transport unit, 105: Operation unit, 110: Control unit, 111: Image reading unit, 115: Printing unit, 121: Processor, 123: Non-volatile memory, 131: Image quality adjustment unit, 133: Image formation control unit, 135: Separation release confirmation unit

Claims

1. A charging device that, while a voltage is applied, contacts a photoreceptor involved in an image forming process to charge the photoreceptor, A separation mechanism for holding the photoreceptor and the charging device in a release-removable separated state, An exposure device for exposing the photosensitive material, A developing device that forms a toner image on the surface of the photoreceptor while a voltage is applied, A toner deposition amount sensor for detecting a toner image formed on the surface of the photoreceptor for image quality adjustment, An image quality adjustment unit that controls the voltage applied to the charging device, the voltage applied to the developing device, the amount of light emitted when exposed by the exposure device, and the detection of a toner image and its density by the toner adhesion sensor, The system includes a separation release confirmation unit that, during the initialization operation of the image forming process at the start of use, detects with the toner adhesion amount sensor whether or not a toner image is formed despite no exposure while voltage is applied to the charging device and the developing device, thereby confirming whether or not the separation state by the separation mechanism has been released. The separation release confirmation unit performs the separation release confirmation during the initialization operation of the image forming process at the start of use. If it is determined that the separation state has been released, the confirmation of separation release is omitted until at least one of the photoreceptor or the charging device is replaced, and the image quality adjustment unit determines whether the device related to the image forming process is normal and continues the initialization operation of the image forming process. If the separation state is determined not to have been released, or if the image quality adjustment unit determines that any device related to the image forming process is not functioning correctly, the separation release confirmation unit performs the separation release confirmation again during the initialization operation of the next image forming process.

2. The image forming apparatus according to claim 1, wherein the initialization operation of the continuing image forming process is to form a toner image for image quality adjustment, and the toner image and its density are detected by the toner deposition amount sensor, and image quality adjustment is performed by adjusting at least one of the voltage applied to the charging device, the voltage applied to the developing device, and the amount of light emitted when exposed by the exposure device.

3. The image forming apparatus according to claim 1, wherein the toner deposition amount sensor is arranged at one or more different locations in the main scanning direction in which the exposure device exposes the photoreceptor, and detects the toner image on the surface of the photoreceptor or along the path through which the formed toner image is transported.

4. The image forming apparatus according to claim 1, wherein the image quality adjustment unit determines whether at least one of the toner deposition amount sensor, the voltage applied to the charging device, the voltage applied to the developing device, the photoreceptor, the path through which the formed toner image is transported, the toner storage unit that contains the toner supplied to the developing device, and the drive source involved in image formation is normal.

5. It is equipped with multiple photoreceptors, charging devices, and separation mechanisms that correspond to different colors. The image forming apparatus according to claim 1, wherein the separation release confirmation unit performs the separation release confirmation for each color.

6. The photoreceptor and the charging device are provided as a process unit that can be mounted and replaced as a single unit. The image forming apparatus according to claim 1, wherein the process unit is equipped with a mechanism that allows the main unit to detect whether it is a new, uninstalled unit or a used, old unit, or the main unit is equipped with a non-volatile memory that can read and write data indicating whether it is a new or old unit.

7. The process unit includes the non-volatile memory, The image forming apparatus according to claim 6, wherein, if the separation release confirmation unit has successfully completed the separation release confirmation, it writes data indicating that the separation release confirmation has been performed to the non-volatile memory of the process unit.

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