Image forming apparatus

Abstract

To easily confirm a conduction state between an image formation unit and an FG although a configuration is simple.SOLUTION: An image formation unit is attachable to / detachable from a body section and conducts to a frame ground of the body section when mounted in the body section. A control section executes both of processing for transferring a first developer image to a medium or a transfer belt by executing an image formation process by setting transfer voltage to be applied to a transfer section from exposure to development to first voltage and processing for transferring a second developer image to the medium or the transfer belt by executing the image formation process by setting transfer voltage to be applied to the transfer section from the exposure to the development to second voltage different from the first voltage.SELECTED DRAWING: Figure 6

Description

[Technical field]

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

[0002] An electrophotographic image forming device comprises an image forming unit having a photosensitive drum as an image carrier, an exposure unit, and a transfer unit. The exposure unit forms an electrostatic latent image on the surface of the photosensitive drum by exposing the surface of the photosensitive drum, the image forming unit forms a toner image as a developer image by developing the electrostatic latent image with toner as a developer, and the transfer unit transfers the toner image formed on the surface of the photosensitive drum to a medium such as paper.

[0003] In such an image forming apparatus, the drive elements of each section are operated by supplying a drive voltage from a voltage application section to the drive elements, but if a conduction failure occurs between the drive elements and the voltage application section, the drive elements will not operate normally. Therefore, in the past, an image forming apparatus has been proposed that includes a current detection section that detects the current that flows when a voltage is applied to the drive elements, and that determines the conduction state between the drive elements and the voltage application section based on the detection result by the current detection section (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-175291 A Summary of the Invention [Problem to be solved by the invention]

[0005] By the way, there is an image forming apparatus in which the image forming section is an image forming unit that is detachable from the main body. In this type of image forming apparatus, when the image forming unit is attached to the main body, the image forming unit and the FG (frame ground) of the main body are electrically connected.

[0006] However, in this type of image forming device, if the image forming unit is not properly installed, poor conductivity may occur between the image forming unit and the FG, and this poor conductivity may cause poor image formation in the image forming unit.

[0007] For this reason, in this type of image forming device, if a poor electrical continuity occurs between the image forming unit and FG, it is necessary to inform the user of this and have the image forming unit reattached. However, in a method of detecting the electrical continuity using a current detection unit, as in the prior art, for example, this current detection unit must be added separately, resulting in increased costs.

[0008] The present invention has been made in consideration of the above points, and aims to propose an image forming apparatus that has a simple configuration yet allows the electrical continuity between the image forming unit and FG to be easily confirmed. [Means for solving the problem]

[0009] The image forming apparatus of the present invention comprises a main body, an image forming unit having an image carrier and forming a developer image by developing an electrostatic latent image formed on the image carrier with a developer, an exposure unit forming an electrostatic latent image on the image carrier by exposing the image carrier, a transfer unit transferring the developer image formed on the image carrier to a medium or a transfer belt, a voltage application unit applying a voltage to the transfer unit, and a control unit controlling the image formation process from exposure to transfer, wherein the image forming unit is detachable from the main body and is conductive to the frame ground of the main body when attached to the main body, and the control unit performs both a process of transferring a first developer image to the medium or the transfer belt by setting a transfer voltage applied to the transfer unit to a first voltage between exposure and development and executing the image formation process, and a process of transferring a second developer image to the medium or the transfer belt by setting a transfer voltage applied to the transfer unit to a second voltage different from the first voltage between exposure and development and executing the image formation process.

[0010] In this way, if a conduction failure occurs between the image forming unit and the frame ground of the main body, a difference occurs in density between the transferred first developer image and the second developer image. Therefore, if a difference occurs in density between the first developer image and the second developer image transferred to a medium, for example, the user can confirm that a conduction failure has occurred between the image forming unit and the frame ground of the main body, and can eliminate the conduction failure by reattaching the image forming unit to the main body, etc. Effect of the Invention

[0011] According to the present invention, it is possible to realize an image forming apparatus that has a simple configuration and allows easy confirmation of the electrical continuity state between an image forming unit and FG. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a diagram showing a configuration of a printing mechanism of the image forming apparatus according to the first embodiment. [Diagram 2] 2 is a block diagram showing a configuration of a control system of the image forming apparatus according to the first embodiment; FIG. [Diagram 3] FIG. 2 is a cross-sectional view of the photosensitive drum according to the first embodiment. [Figure 4] 1A is a plan view of a photosensitive drum according to a first embodiment, as viewed from a direction perpendicular to an axial direction, and FIG. [Diagram 5] 6 is a graph showing a measurement result of a drum shaft potential when there is poor contact between the drum shaft and the shaft support portion according to the first embodiment. [Figure 6] FIG. 4 is an operation sequence diagram of a print test mode according to the first embodiment. [Figure 7] 5 is a table showing an example of a surface potential of the photosensitive drum in each process according to the first embodiment. [Figure 8] FIG. 11 is a diagram showing a configuration of a printing mechanism of an image forming apparatus according to a second embodiment. [Figure 9]FIG. 11 is a block diagram showing a configuration of a control system of an image forming apparatus according to a second embodiment. [Figure 10] FIG. 11 is an operation sequence diagram of a continuity failure determination operation according to the second embodiment. [Figure 11] 10 is a table showing an example of a surface potential of a photosensitive drum in each process according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings.

[0014] 1. First embodiment [1-1. Configuration of image forming device] 1 and 2 show the configuration of an image forming apparatus 1 according to a first embodiment. This image forming apparatus 1 is an electrophotographic color printer, with Fig. 1 showing the configuration of a printing mechanism of the image forming apparatus 1 and Fig. 2 showing the configuration of a control system that controls the image forming apparatus 1.

[0015] First, the printing mechanism of the image forming apparatus 1 will be described with reference to Fig. 1. As shown in Fig. 1, the image forming apparatus 1 has a substantially box-shaped main body 2. Here, the right side of the main body 2 in the figure is the front side of the image forming apparatus 1, the left side of the main body 2 in the figure is the rear side of the image forming apparatus 1, the right side of the main body 2 in the figure is the front side of the image forming apparatus 1, the front side of the main body 2 in the figure is the left side of the image forming apparatus 1, the back side of the main body 2 in the figure is the right side of the image forming apparatus 1, the upper side of the main body 2 in the figure is the upper side of the image forming apparatus 1, and the lower side of the main body 2 in the figure is the lower side of the image forming apparatus 1.

[0016] Although not shown in the figure, the upper part of the main body 2 is an openable and closable main body cover, and opening the main body cover allows access to the inside of the main body 2. Furthermore, although not shown in Fig. 1, an operation panel (operation panel 51 in Fig. 2) is provided on the front side of the main body 2.

[0017] Inside the main body 2, a transport path R for transporting a print medium P such as printing paper is provided, and various parts are arranged along this transport path R. Specifically, the transport path R extends from a paper feed unit 3 provided at the bottom of the main body 2 to a stacker 12 provided on the top surface of the main body 2. Inside the main body 2, along this transport path R, a first registration roller pair 5, a second registration roller pair 6, a writing position sensor 7, an image forming unit 8, a transfer unit 9, a fixing unit 10, and a discharge roller pair 11 are provided in this order from the upstream side of the transport path R in the medium transport direction (i.e., the side closer to the paper feed unit 3).

[0018] The paper feed section 3 is a section that stores a stack of print media P. The paper feed section 3 is provided with a paper feed roller 4 that sends out (i.e., feeds) the stored print media P to the transport path R.

[0019] The first registration roller pair 5 and the second registration roller pair 6 convey the printing medium P along the conveying path R while correcting any skew of the printing medium P. The writing start position sensor 7 detects the printing medium P conveyed along the conveying path R.

[0020] The image forming section 8 is provided above a straight portion extending in the front-rear direction of the transport path R. The image forming section 8 has four image forming units 20 (20K, 20Y, 20M, 20C) and four LED (Light Emitting Diode) heads 21 (21K, 21Y, 21M, 21C).

[0021] The four image forming units 20K, 20Y, 20M, and 20C are arranged in this order from the upstream side in the medium transport direction, and each is detachable from the main body 2. The four image forming units 20K, 20Y, 20M, and 20C have the same configuration except for the different colors of toner they handle. Image forming unit 20K forms a toner image using a black developer (e.g., toner), image forming unit 20Y uses a yellow developer, image forming unit 20M uses a magenta developer, and image forming unit 20C uses a cyan developer (e.g., toner).

[0022] Each of these four image forming units 20 (20K, 20Y, 20M, 20C) has a photosensitive drum 22 (22K, 22Y, 22M, 22C), a charger 23 (23K, 23Y, 23M, 23C), and a developer 24 (24K, 24Y, 24M, 24C).

[0023] 3, the photosensitive drums 22 (22K, 22Y, 22M, 22C) serving as image carriers are composed of a metallic drum shaft 25 and a cylindrical aluminum tube 26 fixed to the drum shaft 25 and rotating about the drum shaft 25 as a rotation axis. A photosensitive film 27 of about 18 μm is formed on the surface (outer periphery) of the aluminum tube 26.

[0024] Returning to FIG. 1, chargers 23 (23K, 23Y, 23M, 23C), LED heads 21 (21K, 21Y, 21M, 21C), and developers 24 (24K, 24Y, 24M, 24C) are provided around the upper periphery of the photosensitive drums 22 (22K, 22Y, 22M, 22C).

[0025] The chargers 23 (23K, 23Y, 23M, 23C) negatively charge the surfaces of the photosensitive drums 22 (22K, 22Y, 22M, 22C). The LED heads 21 (21K, 21Y, 21M, 21C) expose the surfaces of the photosensitive drums 22 (22K, 22Y, 22M, 22C) charged by the chargers 23 (23K, 23Y, 23M, 23C) to light, thereby forming electrostatic latent images on the surfaces. The developers 24 (24K, 24Y, 24M, 24C) develop the electrostatic latent images formed on the surfaces of the photosensitive drums 22 (22K, 22Y, 22M, 22C) with toner, thereby forming toner images on the surfaces.

[0026] As described above, each of the four image forming units 20 (20K, 20Y, 20M, 20C) is detachable from the main body 2, and when attached to the main body 2, the photosensitive drums 22 (22K, 22Y, 22M, 22C) are configured to be conductive to the FG (frame ground) of the main body 2.

[0027] Specifically, when each of the image forming units 20 (20K, 20Y, 20M, 20C) is attached to the main body 2, both ends of the drum shaft 25 are fitted into grooves 40h provided in the shaft support portion 40 of the main body 2, as shown in Figures 4(A) and (B), which are plan views of the photosensitive drums 22 (22K, 22Y, 22M, 22C) viewed from a direction perpendicular to the axial direction and a plan view of the photosensitive drums 22 (22K, 22Y, 22M, 22C) viewed from the axial direction.

[0028] The shaft support portion 40 is made of a metal member and serves as the FG (frame ground) of the main body portion 2. Thus, when both ends of the drum shaft 25 are fitted into the groove 40h and come into contact with the shaft support portion 40, the drum shaft 25 is electrically connected to the FG of the main body portion 2. When the drum shaft 25 is electrically connected to the FG of the main body portion 2 in this manner, the potential of the drum shaft 25 (hereinafter referred to as the drum shaft potential) becomes constant in accordance with the FG, and similarly, the potential of the aluminum tube 26 in contact with the drum shaft 25 (hereinafter referred to as the aluminum tube potential) also becomes constant. In this manner, the photosensitive drums 22 (22K, 22Y, 22M, 22C) are electrically connected to the FG of the main body portion 2.

[0029] On the other hand, if the image forming unit 20 (20K, 20Y, 20M, 20C) is not completely attached to the main body 2, poor contact may occur between the drum shaft 25 and the shaft support portion 40, resulting in poor conductivity between the photosensitive drum 22 (22K, 22Y, 22M, 22C) and the FG.

[0030] Returning to FIG. 1, a transfer unit 9 is disposed below the image forming unit 8 across a conveying path R. The transfer unit 9 includes a transfer belt 30, belt rollers 31a and 31b, and transfer rollers 32 (32K, 32Y, 32M, and 32C).

[0031] The transfer belt 30 is a circular belt that is stretched around belt rollers 31a and 31b spaced apart in the front-rear direction and has an upper running portion and a lower running portion that extend in the front-rear direction. One of the belt rollers 31a and 31b (for example, the rear belt roller 31b) is a drive roller and the other is a driven roller.

[0032] The upper running portion of the transfer belt 30 extends along the transport path R and travels below each of the photosensitive drums 22 (22K, 22Y, 22M, 22C). The upper running portion of the transfer belt 30 travels backward, thereby transporting the print medium P along the transport path R.

[0033] The transfer rollers 32 (32K, 32Y, 32M, 32C) are disposed below the photosensitive drums 22 (22K, 22Y, 22M, 22C) facing each other across an upper running portion of the transfer belt 30. In other words, the transfer belt 30 is sandwiched between the photosensitive drums 22 (22K, 22Y, 22M, 22C) and the transfer rollers 32 (32K, 32Y, 32M, 32C).

[0034] When a predetermined transfer voltage is applied to the transfer rollers 32 (32K, 32Y, 32M, 32C), the transfer rollers 32 (32K, 32Y, 32M, 32C) transfer the toner image formed on the photosensitive drum 22 (22K, 22Y, 22M, 22C) to the printing medium P transported by the transfer belt 30.

[0035] The fixing unit 10 fixes the toner image transferred to the printing medium P to the printing medium P by heat and pressure while transporting the printing medium P. The printing medium P with the toner image fixed by the fixing unit 10 is transported by a pair of discharge rollers 11 and discharged onto a stacker 12. The configuration of the printing mechanism of the image forming apparatus 1 is as described above.

[0036] Next, the configuration of a control system that controls the image forming apparatus 1 will be described with reference to Fig. 2. As shown in Fig. 2, the control system of the image forming apparatus 1 is configured around a mechanism control unit 50, and includes an operation panel 51, a motor control unit 52, a high voltage control unit 53, a high voltage power supply 54, an image processing unit 55, and an LED head control unit 56 in addition to the mechanism control unit 50.

[0037] The mechanism control unit 50 controls the entire print mechanism of the image forming apparatus 1. The mechanism control unit 50 has a CPU 50a, a storage device 50b, a timer 50c, and a counter 50d. The CPU 50a controls the print mechanism by executing a control program read from the storage device 50b. The storage device 50b is, for example, a non-volatile memory, and stores programs, correction values, print data, patch data (hereinafter referred to as patch data) described later, and the like. The timer 50c measures time. The counter 50d counts various numbers of times.

[0038] The operation panel 51 is composed of an operation unit such as buttons and a display unit such as a display, and notifies the mechanism control unit 50 of operation input received via the operation unit, and displays various information on the display unit according to instructions from the mechanism control unit 50.

[0039] In accordance with instructions from the mechanism control unit 50, the motor control unit 52 drives and rotates motors 57, such as a belt motor that drives the drive roller of the transfer unit 9, a drum motor that drives the photosensitive drums 22 (22K, 22Y, 22M, 22C), and a feed motor that drives various rollers that transport the printing medium P.

[0040] The high voltage control unit 53 controls the high voltage power supply 54 according to instructions from the mechanism control unit 50, thereby applying a voltage to each unit of the image forming unit 8 and the transfer unit 9. Specifically, a predetermined charging voltage is applied from the high voltage power supply 54 to the chargers 23 (23K, 23Y, 23M, 23C) of the image forming unit 8. A predetermined developing voltage is applied from the high voltage power supply 54 to the developers 24 (24K, 24Y, 24M, 24C) of the image forming unit 8. A predetermined transfer voltage is applied from the high voltage power supply 54 to the transfer rollers 32 (32K, 32Y, 32M, 32C) of the transfer unit 9.

[0041] The image processing unit 55 executes image processing to convert print data received from a higher-level device (not shown) and patch data read from the storage device 50b into bitmap image data of each color in accordance with instructions from the mechanism control unit 50. The bitmap image data converted by the image processing unit 55 is sent to the LED head control unit 56.

[0042] The LED head control unit 56 transfers a print pattern based on bitmap image data sent from the image processing unit 55 to the LED heads 21 (21K, 21Y, 21M, 21C) in accordance with instructions from the mechanism control unit 50, and controls exposure by the LED heads 21 (21K, 21Y, 21M, 21C). At this time, the LED head control unit 56 synchronizes with the feed motor and the belt motor in accordance with instructions from the mechanism control unit 50, and controls the exposure timing in the sub-scanning direction (rotation direction of the photosensitive drum 22) and the main scanning direction (axial direction of the photosensitive drum 22). The configuration of the control system that controls the image forming apparatus 1 is as described above.

[0043] [1-2. Operation of image forming device] Next, the operation of the image forming apparatus 1 will be described. First, as the operation of the image forming apparatus 1, the normal printing operation will be briefly described. In the image forming apparatus 1, the mechanism control unit 50 controls each unit to execute the normal printing operation. In the normal printing operation, in the case of color printing, the four image forming units 20K, 20Y, 20M, and 20C operate at their own operation timings, but since the basic operations of these four image forming units 20K, 20Y, 20M, and 20C are the same, the operation of the image forming unit 20K will be described here as an example, and the operations of the image forming units 20Y, 20M, and 20C will be omitted.

[0044] Specifically, during normal printing operation, the mechanism control unit 50 of the image forming apparatus 1 conveys the printing medium P fed from the paper feed unit 3 by the first registration roller pair 5 and the second registration roller pair 6. Then, after the mechanism control unit 50 detects the passage of the leading edge of the printing medium P by the writing position sensor 7, after a predetermined timing, as an exposure process, the LED head control unit 56 starts transferring the printing pattern to the LED head 21K, and the LED head 21K exposes the surface of the photosensitive drum 22K. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 22K. Note that the surface of the photosensitive drum 22K is negatively charged by the charger 23K before the exposure process, and then, when exposed in the exposure process, the charge of the exposed portion is attenuated to about -50V toward the aluminum tube potential by electron transfer, forming an electrostatic latent image.

[0045] Next, the mechanism control unit 50 develops the electrostatic latent image formed on the surface of the photosensitive drum 22K with toner by the developer 24K to form a toner image on the surface of the photosensitive drum 22K, and then proceeds to the transfer process. In this developing process, the toner adheres to the electrostatic latent image, which is the exposed portion of the surface of the photosensitive drum 22K, that is, the portion where the charge has attenuated to about -50V toward the potential of the aluminum tube 26, thereby developing the electrostatic latent image to form a toner image.

[0046] Meanwhile, the print medium P that has passed the writing position sensor 7 is transported by the transfer belt 30 and passes between the photosensitive drum 22K and the transfer roller 32K. At this time, the mechanism control unit 50 applies a predetermined transfer voltage VP to the transfer roller 32K as a transfer process, thereby transferring the toner image formed on the surface of the photosensitive drum 22K to the print medium P. Note that the transfer voltage VP applied to the transfer roller 32K at this time is a transfer voltage for normal printing that is optimally set in advance according to the printing environment.

[0047] In this manner, the image forming apparatus 1 prints an image (transfers a toner image) onto the print medium P through an image forming process that includes three steps: an exposure step, a development step, and a transfer step.

[0048] Then, the mechanism control unit 50 fixes the toner image transferred to the print medium P to the print medium P using the fixing unit 10, and then discharges the print medium P onto the stacker 12 using the discharge roller pair 11. The normal printing operation of the image forming apparatus 1 is as described above.

[0049] As described above, in the image forming apparatus 1, if the image forming units 20 (20K, 20Y, 20M, 20C) are not completely attached to the main body 2, poor contact may occur between the drum shaft 25 and the shaft support portion 40, resulting in poor conductivity between the photosensitive drums 22 (22K, 22Y, 22M, 22C) and the FG.

[0050] 5 shows the measurement result of the drum shaft potential when, for example, there is poor contact between the drum shaft 25 of the image forming unit 20K and the shaft support part 40. In FIG. 5, the horizontal axis is seconds and the vertical axis is V (volts), with one division on the horizontal axis representing 2 seconds and one division on the vertical axis representing 100V, and the measurement result of the drum shaft potential is shown on a graph.

[0051] In the image forming apparatus 1, if the drum shaft 25 and the shaft support portion 40 are in normal contact, the drum shaft potential is always 0V, which is equal to FG. In contrast, if there is poor contact between the drum shaft 25 and the shaft support portion 40, the drum shaft potential falls below -100V during printing, as shown in Fig. 5. If the drum shaft potential at this time is -150V, for example, the aluminum tube potential is also -150V, which is equal to the drum shaft potential. That is, in this case, the surface potential of the photosensitive drum 22K is also -150V.

[0052] In this state, even if the surface of the photosensitive drum 22K is charged and then exposed to light, the charge in the exposed portion will only decay to about -200 V. As described above, in normal printing operations, the charge in the exposed portion of the surface of the photosensitive drum 22K is designed to decay to about -50 V, so if the charge only decays to -200 V, the image will not be developed with sufficient toner density, resulting in poor image formation.

[0053] In this way, in the image forming apparatus 1, if a printing operation is performed while there is poor electrical conductivity between the photosensitive drum 22 (22K, 22Y, 22M, 22C) and the FG, poor image formation will occur in the image forming unit 20 with the poor electrical conductivity, resulting in poor printing.

[0054] In many cases, poor conductivity between the photosensitive drum 22 (22K, 22Y, 22M, 22C) and the FG can be resolved by removing the image forming unit 20 having the poor conductivity and then reinstalling it, but in order to perform this procedure, the user needs to check whether or not poor conductivity has occurred between the photosensitive drum 22 (22K, 22Y, 22M, 22C) and the FG.

[0055] Therefore, the image forming apparatus 1 has a print test mode for allowing the user to check whether or not a continuity failure has occurred between the image forming units 20 (20K, 20Y, 20M, 20C) and the FG. This print test mode can be executed by the user via the operation panel 51, for example.

[0056] The operation of this print test mode will be described using the operation sequence shown in Fig. 6. This print test mode is also executed by controlling each section under the control of the mechanism control section 50. In this print test mode, patches of each color, black, yellow, magenta, and cyan, are printed in order on the print medium P. The operation during patch printing is the same for each color, and for the sake of simplicity, the operation when printing a black patch Pk by the image forming unit 20K will be described here.

[0057] The operation sequence shown in Fig. 6 is the operation sequence from the start (left side in the figure) to the end (right side in the figure) of the printing operation when printing a black patch Pk in the print test mode, and the horizontal axis indicates time. As shown in Fig. 6, in this print test mode, the black patch Pk is printed twice under different conditions. The first patch Pk printed is called the first patch Pk1, and the second patch Pk printed is called the second patch Pk2. The first patch Pk1 and the second patch Pk2 are the same patch.

[0058] This operation sequence shows, from the top, the changes over time of "CH (channel)," "exposure," "development," "transfer voltage," and "drum shaft potential."

[0059] "CH" indicates the start and end of the printing operation of the black patch Pk (Pk1, Pk2). "Exposure" indicates the exposure timing. "Development" indicates the change over time in the development voltage. "Transfer voltage" indicates the change over time in the transfer voltage applied to the transfer roller 32K. "Drum shaft potential" indicates the change over time in the potential of the drum shaft 25 of the photosensitive drum 22K.

[0060] The charging voltage and developing voltage when printing patch Pk (Pk1, Pk2) are set to the same values ​​as in normal printing operations, i.e., -900 V and -150 V. In contrast, the transfer voltage, which will be described in detail later, is set to three values: 0 V, which is lower than in normal printing operations, a voltage VP (e.g., 1 kV) equal to that in normal printing operations, and a voltage V1 (e.g., 1.5 kV) higher than voltage VP.

[0061] As shown in Fig. 6, when the print test mode is started, the mechanism control unit 50 sets the transfer voltage applied to the transfer roller 32K to 0V in step SP1. At this time, if the drum shaft 25 of the photosensitive drum 22K and the shaft support unit 40 are in normal contact (i.e., normal conduction with FG), the drum shaft potential is constant at 0V, which is equal to FG, regardless of the transfer voltage at this time, as shown by the dotted line in Fig. 6. On the other hand, if there is poor contact between the drum shaft 25 of the photosensitive drum 22K and the shaft support unit 40 (i.e., poor conduction with FG occurs), the drum shaft potential changes significantly negatively, as shown by the solid line in Fig. 6.

[0062] In the next step SP2, the mechanism control unit 50 exposes the surface of the photosensitive drum 22K based on the patch data of the first patch Pk1 using the LED head 21K as an exposure step. As a result, an electrostatic latent image of the first patch Pk1 is formed on the surface of the photosensitive drum 22K.

[0063] In the next step SP3, the mechanism control unit 50 develops the electrostatic latent image formed on the surface of the photosensitive drum 22K with black toner as a developing process. As a result, a toner image of the first patch Pk1 is formed on the surface of the photosensitive drum 22K. In this way, the mechanism control unit 50 performs the exposure process to the development process of the first patch Pk1 with the transfer voltage set to 0V.

[0064] In the following step SP4, as a transfer process, the mechanism control unit 50 changes the transfer voltage to a voltage VP equal to that used during normal printing before the area on the surface of the photosensitive drum 22K on which the toner image (i.e., the first patch Pk1) is formed reaches the transfer roller 32K located at the lower end side of the photosensitive drum 22K, and then transfers the toner image (i.e., the first patch Pk1) to the printing medium P.

[0065] After the first patch Pk1 is transferred to the printing medium P, in the following step SP5, the mechanism control unit 50 changes the transfer voltage to a voltage V1 that is higher than the voltage VP.

[0066] In the next step SP6, the mechanism control unit 50 exposes the surface of the photosensitive drum 22K based on the patch data of the second patch Pk2 using the LED head 21K as an exposure step. As a result, an electrostatic latent image of the second patch Pk2 is formed on the surface of the photosensitive drum 22K.

[0067] In the next step SP7, the mechanism control unit 50 develops the electrostatic latent image formed on the surface of the photosensitive drum 22K with black toner as a developing process. As a result, a toner image of the second patch Pk2 is formed on the surface of the photosensitive drum 22K. In this way, the mechanism control unit 50 performs the exposure process to the development process of the second patch Pk2 in a state where the transfer voltage is set to a voltage V1 (1.5 kV) higher than the voltage (i.e., 0 V) ​​when the first patch Pk1 is exposed and developed.

[0068] In the following step SP8, as a transfer process, the mechanism control unit 50 changes the transfer voltage to the same voltage VP as that during normal printing before the area on the surface of the photosensitive drum 22K where the toner image is formed (i.e., the second patch Pk2) reaches the transfer roller 32K located on the lower end side of the photosensitive drum 22K, and then transfers the toner image (i.e., the second patch Pk2) to the printing medium P.

[0069] Through the operational sequence up to this point, the first patch Pk1 and the second patch Pk2 are transferred onto the printing medium P. After that, although not shown in Fig. 6, the mechanism control unit 50 fixes the first patch Pk1 and the second patch Pk2 transferred onto the printing medium P to the printing medium P using the fixing unit 10, and ejects the printing medium P onto the stacker 12. The operation of the print test mode is as described above.

[0070] Although not described here, the mechanism control unit 50 prints patches of each color, yellow, magenta, and cyan, in sequence on the printing medium P in the same manner as the black patch Pk (Pk1, Pk2). Therefore, the printing medium P discharged onto the stacker 12 has a first patch and a second patch printed for each of the colors black, yellow, magenta, and cyan.

[0071] Next, the reason for providing a difference between the transfer voltage applied to the transfer roller 32K between the first patch Pk1 and the second patch Pk2 from the exposure step to the development step will be described.

[0072] As described above, for the first patch Pk1, the mechanism control unit 50 performs the exposure process through the development process by setting the transfer voltage applied to the transfer roller 32K to 0 V, and for the second patch Pk2, the mechanism control unit 50 performs the exposure process through the development process by setting the transfer voltage to a voltage V1 that is greater than 0 V (see the area surrounded by a solid ellipse in Figure 6).

[0073] Here, if the drum shaft 25 of the photosensitive drum 22K and the shaft support portion 40 are in normal contact and the photosensitive drum 22K is normally conductive to the FG, the drum shaft potential is constant at 0 V regardless of the transfer voltage. For this reason, if the photosensitive drum 22K is normally conductive to the FG, even if a difference is provided in the transfer voltage applied from the exposure process to the development process between the first patch Pk1 and the second patch Pk2, the charge of the exposed portion of the surface of the photosensitive drum 22 will attenuate to about -50 V toward the aluminum tube potential, which is equal to the drum shaft potential, due to electron transfer, and the photosensitive drum 22 will be developed with a sufficient toner concentration in the subsequent development process.

[0074] In other words, if the photosensitive drum 22K is normally conductive to the FG, even if there is a difference in the transfer voltage applied between the first patch Pk1 and the second patch Pk2 from the exposure process to the development process, the first patch Pk1 and the second patch Pk2 will each be developed with sufficient toner concentration.

[0075] 6, the density of the first patch Pk1 printed on the printing medium P becomes equal to the density of the second patch Pk2 printed on the printing medium P. In other words, the density of the first patch Pk1=the density of the second patch Pk2.

[0076] Therefore, the user can compare the density of the first patch Pk1 printed on the printing medium P with the density of the second patch Pk2, and if there is no difference between them, determine that the image forming unit 20K is properly installed in the main body 2.

[0077] On the other hand, when the drum shaft 25 of the photosensitive drum 22K and the shaft support portion 40 have poor contact and poor conduction occurs between the photosensitive drum 22K and the FG, the drum shaft potential changes according to the change in the transfer voltage. That is, as shown in the part surrounded by the solid ellipse in Fig. 6, when the transfer voltage (V1 = 1.5 kV) applied from the exposure process to the development process of the second patch Pk2 is higher than the transfer voltage (0 V) applied from the exposure process to the development process of the first patch Pk1, the drum shaft potential from the exposure process to the development process of the second patch Pk2 becomes higher than the drum shaft potential from the exposure process to the development process of the first patch Pk1, as shown in the part surrounded by the dotted ellipse in Fig. 6. That is, the drum shaft potential from the exposure process to the development process of the first patch Pk1 is smaller than the drum shaft potential from the exposure process to the development process of the second patch Pk2.

[0078] In this way, when the drum shaft potential changes from the exposure process to the development process, the aluminum tube potential also changes accordingly. Since the charge of the exposed portion of the surface of the photosensitive drum 22K attenuates toward the aluminum tube potential due to electron transfer, when the aluminum tube potential changes from the exposure process to the development process between the first patch Pk1 and the second patch Pk2, the surface potential of the photosensitive drum 22K also changes accordingly. In other words, the surface potential of the photosensitive drum 22K from the exposure process to the development process of the first patch Pk1 is less than the surface potential of the photosensitive drum 22K from the exposure process to the development process of the second patch Pk2.

[0079] In this way, when the surface potential of the photosensitive drum 22K changes from the exposure process to the development process, the amount of toner used to develop the electrostatic latent image in the development process also changes accordingly. In other words, the amount of toner used to develop the electrostatic latent image of the first patch Pk1 is less than the amount of toner used to develop the electrostatic latent image of the first patch Pk1.

[0080] In this way, when a difference occurs in the amount of toner used to develop the electrostatic latent image, a difference occurs between the density of the first patch Pk1 and the density of the second patch Pk2 transferred with the same transfer voltage VP. In other words, the density of the first patch Pk1 is less than the density of the second patch Pk2.

[0081] As a result, as shown in FIG. 6 as density on paper (with continuity failure), the density of the first patch Pk1 printed on the printing medium P becomes lighter than the density of the second patch Pk2.

[0082] Therefore, the user can compare the density of the first patch Pk1 printed on the printing medium P with the density of the second patch Pk2, and if there is a difference between them, determine that the image forming unit 20K is not properly attached to the main body 2 (i.e., the attachment is incomplete).

[0083] Similarly, the user can compare the density of the first patch and the density of the second patch of each of the colors yellow, magenta, and cyan printed on the printing medium P, and if there is a difference between them, he or she can determine that the image forming unit 20 of the color with the difference is not properly installed in the main body 2 (i.e., is incompletely installed).

[0084] Furthermore, in addition to the first and second patches for each color, for example, when comparing the patch densities of the first and second patches for each color, the mechanism control unit 50 prints (i.e., transfers) an image on the printing medium P that urges the user to re-install the image forming unit 20 of that color and execute the print test mode again if there is a color whose patch density differs. In this way, the user can identify and re-install an image forming unit 20 that is not properly installed simply by looking at the printing medium P, and the conduction failure between the image forming unit 20 and the FG can be easily and quickly eliminated.

[0085] Here, an example of the surface potential of the photosensitive drum 22K at each step of the image formation process is shown in Fig. 7. Fig. 7 shows the surface potential of the photosensitive drum 22K when the charging voltage is set to -900V, the developing voltage is set to -150V, and the image forming unit 20K is normally installed in the main body 2 (normal), and the surface potential of the photosensitive drum 22K when the image forming unit 20K is not normally installed in the main body 2 (conductivity failure).

[0086] The surface potential of the photosensitive drum 22K is shown when it is charged, before exposure, during exposure, and during development. Furthermore, for the case of poor electrical continuity, three patterns are shown: when the transfer voltage applied to the transfer roller 32K from the exposure process to the development process is 0V, 1kV, and 1.5kV. Note that although the surface potential of the photosensitive drum 22K changes depending on the resistance and charging characteristics of each roller, the magnitude relationship between the normal state and when there is poor electrical continuity remains the same.

[0087] 7, under normal circumstances, the surface potential of the photosensitive drum 22K is attenuated by electron transfer to about -50V toward the aluminum tube potential, forming an electrostatic latent image, which is then developed to form a toner image. In this way, if the surface potential of the photosensitive drum 22K is attenuated to about -50V by exposure, development will be achieved with sufficient toner density.

[0088] In contrast, when there is a conduction failure and the transfer voltage applied to the transfer roller 32K from the exposure process to the development process is 0 V, the surface potential of the exposed portion of the photosensitive drum 22K attenuates only to about -400 V. As a result, the toner density of the developed toner image becomes significantly lower than under normal conditions.

[0089] Also, when there is a conduction failure, if the transfer voltage applied to the transfer roller 32K from the exposure process to the development process is 1 kV, the surface potential of the exposed portion of the photosensitive drum 22K attenuates only to about -200 V. For this reason, the toner density of the developed toner image is darker than when the transfer voltage is 0 V, but is lighter than under normal conditions.

[0090] Furthermore, when the transfer voltage applied to the transfer roller 32K from the exposure process to the development process is 1.5 kV during the conduction failure, the surface potential of the exposed portion of the photosensitive drum 22K attenuates to about -50 V. As a result, the toner density of the developed toner image becomes almost the same as in the normal state.

[0091] Therefore, the toner concentration of the developed toner image is darkest under normal conditions and when there is poor conductivity and the transfer voltage from the exposure process to the development process is 1.5 kV (i.e., when the second patch Pk2 is printed), next when there is poor conductivity and the transfer voltage from the exposure process to the development process is 1 kV, and finally when there is poor conductivity and the transfer voltage from the exposure process to the development process is 0 V (i.e., when the first patch Pk1 is printed).

[0092] [1-3. Summary and Effects] As described above, in the first embodiment, the image forming apparatus 1 is provided with a main body 2, an image forming unit 20 having a photosensitive drum 22 which is an example of an image carrier and which forms a toner image which is an example of a developer image by developing an electrostatic latent image formed on the photosensitive drum 22 with toner which is an example of a developer, an LED head 21 which is an example of an exposure unit which forms an electrostatic latent image on the photosensitive drum 22 by exposing the photosensitive drum 22, a transfer unit 9 which transfers the toner image formed on the photosensitive drum 22 to a printing medium P which is an example of a medium, a high-voltage control unit 53 and a high-voltage power supply 54 which are examples of a voltage application unit which applies a transfer voltage to the transfer unit 9, and a mechanism control unit 50 which is an example of a control unit which executes the image formation process from exposure to transfer.

[0093] Furthermore, the image forming unit 20 provided in the image forming apparatus 1 is detachable from the main body 2, and is electrically connected to an FG (frame ground) of the main body 2 when attached to the main body 2.

[0094] The mechanism control unit 50 sets the transfer voltage applied to the transfer unit 9 between exposure and development to 0 V, which is an example of a first voltage, and sets the transfer voltage applied to the transfer unit 9 during transfer to voltage VP (1 kV), which is an example of a third voltage, and executes an image formation process to transfer a first toner image (first patch Pk1), which is an example of a first developer image, to the printing medium P; and sets the transfer voltage applied to the transfer unit 9 between exposure and development to voltage V1 (1.5 kV), which is an example of a second voltage different from the first voltage, and sets the transfer voltage applied to the transfer unit 9 to voltage VP (1 kV), which is an example of a third voltage, and executes an image formation process to transfer a second toner image (second patch Pk2), which is an example of a second developer image, to the printing medium P.

[0095] In this way, in the image forming apparatus 1, when a conduction failure occurs between the image forming unit 20 and the FG of the main body 2, a difference in density occurs between the first toner image and the second toner image (i.e., the first patch Pk1 and the second patch Pk2) transferred to the print medium P. Therefore, if a difference in density occurs between the first toner image and the second toner image transferred to the print medium P, the user can confirm that a conduction failure has occurred between the image forming unit 20 and the FG of the main body 2, and in this case, the conduction failure can be eliminated by, for example, reattaching the image forming unit 20 to the main body 2.

[0096] Thus, according to the image forming apparatus 1 of the present embodiment, there is no need for a separate current detection unit or the like for detecting the electrical continuity state between the image forming unit 20 and FG, and a simple configuration that only changes the transfer voltage applied to the transfer section 9 between exposure and development allows the user to easily check the electrical continuity state between the image forming unit 20 and FG without increasing costs.

[0097] Furthermore, the mechanism control unit 50 of the image forming apparatus 1 prints (i.e., transfers) on the printing medium P not only the first toner image (first patch Pk1) and the second toner image (second patch Pk2), but also compares the densities of the first toner image (first patch Pk1) and the second toner image (second patch Pk2), and if there is a difference in the densities, prints (i.e., transfers) a toner image containing instructions to the user to reinstall the image forming unit 20.

[0098] As a result, by simply looking at the printing medium P, if there is a poor electrical connection between the image forming unit 20 and FG, the user can recognize that the problem is with the installation of the image forming unit 20 and can immediately perform maintenance work such as re-installing the image forming unit 20 in the main body 2, thereby shortening the time it takes to restore the image forming device 1.

[0099] 2. Second embodiment Next, a second embodiment will be described. In the first embodiment, the user checks whether or not a continuity failure has occurred between the image forming unit 20 and FG by comparing the density difference between two patches (a first patch Pk1 and a second patch Pk2). In contrast, in the second embodiment, the image forming apparatus 1 detects the density difference between the two patches and determines whether or not a continuity failure has occurred between the image forming unit 20 and FG based on the detection result.

[0100] Hereinafter, the second embodiment will be described, but the description of the same parts as those in the first embodiment will be omitted as appropriate. In the second embodiment, the image forming apparatus 1 will be referred to as the image forming apparatus 1x in order to distinguish it from the first embodiment.

[0101] [2-1. Configuration of image forming device] 8 and 9 show the configuration of an image forming apparatus 1x according to the second embodiment. This image forming apparatus 1x has a configuration in which a density detection sensor 100 is added to the image forming apparatus 1 of the first embodiment.

[0102] As shown in Fig. 8, the concentration detection sensor 100 is provided downstream in the belt running direction of the rear belt roller (drive roller) 31b that runs the transfer belt 30. In the image forming device 1x, a patch for detecting the toner concentration is transferred onto the transfer belt 30 by an image forming unit 8 and a transfer unit 9. Then, a mechanism control unit 50 shown in Fig. 9 is configured to detect the concentration of the patch transferred onto the transfer belt 30 using the concentration detection sensor 100. The concentration detection sensor 100 is configured to output the detected concentration as an OD (Optical Density) value.

[0103] Specifically, the mechanism control unit 50 transfers a density detection patch onto the transfer belt 30 using the image forming unit 8 and the transfer unit 9, and detects the density of the density detection patch using the density detection sensor 100. Then, based on the detected density, density correction is performed so that each color of toner has a constant density. This density correction is an existing technology, so a detailed description is omitted. The patch transferred onto the transfer belt 30 is removed from the transfer belt 30 by a toner removal unit (not shown).

[0104] Furthermore, the mechanism control unit 50, which will be described in detail later, transfers two patches for each color onto the transfer belt 30 by the image forming unit 8 and the transfer unit 9. At this time, the two patches are transferred under different conditions. The mechanism control unit 50 then detects the densities of these two patches using the density detection sensor 100, and determines whether or not a conduction failure has occurred between the image forming unit 20 and the FG based on the detected density difference between the two patches. The mechanism control unit 50 then displays the determination result on the operation panel 51. The image forming apparatus 1x is configured as described above.

[0105] [2-2. Operation of image forming device] Next, the operation of the image forming apparatus 1x will be described. Note that the normal printing operation is the same as that of the first embodiment, and therefore the description will be omitted. Also, the density correction operation is an existing technique, and therefore the description will be omitted.

[0106] In the image forming apparatus 1x, during the initialization operation performed after the image forming unit 20 is installed, a continuity failure determination operation is performed to determine whether or not a continuity failure occurs between the image forming unit 20 and the FG. This continuity failure determination operation is described below. This continuity failure determination operation is also performed by the mechanism control unit 50 controlling each unit. In this continuity failure determination operation, patches of each color, black, yellow, magenta, and cyan, are transferred to the transfer belt 30 in order. The operation during patch transfer is the same for each color, and for the sake of simplicity, the operation when the black patch Pk is transferred by the image forming unit 20K will be described here.

[0107] An operation sequence of the continuity failure determination operation is shown in Fig. 10. Note that this operation sequence is similar to the operation sequence shown in Fig. 6 except for some parts, so the description of the similar parts will be omitted or simplified as appropriate.

[0108] As shown in Fig. 10, in the continuity failure judgment operation, the black patch Pk is transferred twice with different conditions. The patch Pk transferred first is called the third patch Pk3, and the patch Pk transferred next is called the fourth patch Pk4. The third patch Pk3 and the fourth patch Pk4 are the same patch.

[0109] The charging voltage and developing voltage when transferring the patch Pk (Pk3, Pk4) are set to -900V and -150V, respectively, as in normal printing operations. In contrast, the transfer voltage, which will be described in detail later, is set to three values: 0V, which is lower than that during density correction, a voltage VB (e.g., 0.7kV) equal to that during density correction, and a voltage V2 (e.g., 1.5kV) higher than the voltage VB. Incidentally, in density correction, the patch is transferred directly to the transfer belt 30 without passing through the printing medium P, so the transfer voltage is set to a value (0.7kV) lower than that during normal printing operations (1kV).

[0110] As shown in Fig. 10, when the mechanism control unit 50 starts the conduction failure determination operation, in step SP11, the transfer voltage applied to the transfer roller 32K is set to 0V. At this time, if the drum shaft 25 of the photosensitive drum 22K and the shaft support unit 40 are in normal contact (i.e., normal conduction with FG), the drum shaft potential is constant at 0V, which is equal to FG, regardless of the transfer voltage at this time, as shown by the dotted line in Fig. 10. On the other hand, if there is a contact failure between the drum shaft 25 of the photosensitive drum 22K and the shaft support unit 40 (i.e., if there is a conduction failure with FG), the drum shaft potential changes significantly negatively, as shown by the solid line in Fig. 10.

[0111] In the next step SP12, the mechanism control unit 50 exposes the surface of the photosensitive drum 22K based on the patch data of the third patch Pk3 using the LED head 21K as an exposure step, thereby forming an electrostatic latent image of the third patch Pk3 on the surface of the photosensitive drum 22K.

[0112] In the next step SP13, the mechanism control unit 50 develops the electrostatic latent image formed on the surface of the photosensitive drum 22K with black toner as a developing process. As a result, a toner image of the third patch Pk3 is formed on the surface of the photosensitive drum 22K. In this way, the mechanism control unit 50 performs the exposure process to the development process of the third patch Pk3 with the transfer voltage set to 0V.

[0113] In the following step SP14, as a transfer process, the mechanism control unit 50 changes the transfer voltage to the voltage VB equal to that during concentration correction before the area on the surface of the photosensitive drum 22K on which the toner image (i.e., the third patch Pk3) is formed reaches the transfer roller 32K located on the lower end side of the photosensitive drum 22K, and then transfers the toner image (i.e., the third patch Pk3) to the transfer belt 30.

[0114] After the third patch Pk3 is transferred onto the transfer belt 30, in the following step SP15, the mechanism control unit 50 changes the transfer voltage to a voltage V2 higher than the voltage VB.

[0115] In the next step SP16, the mechanism control unit 50 exposes the surface of the photosensitive drum 22K based on the patch data of the fourth patch Pk4 using the LED head 21K as an exposure step, thereby forming an electrostatic latent image of the fourth patch Pk4 on the surface of the photosensitive drum 22K.

[0116] In the next step SP17, the mechanism control unit 50 develops the electrostatic latent image formed on the surface of the photosensitive drum 22K with black toner as a developing process. As a result, a toner image of the fourth patch Pk4 is formed on the surface of the photosensitive drum 22K. In this way, the mechanism control unit 50 performs the exposure process to the development process of the fourth patch Pk4 in a state where the transfer voltage is set to a voltage V2 (1.5 kV) higher than the voltage (i.e., 0 V) ​​when the third patch Pk3 is exposed and developed.

[0117] In the following step SP18, as a transfer process, the mechanism control unit 50 changes the transfer voltage to the voltage VB equal to that during concentration correction before the area on the surface of the photosensitive drum 22K where the toner image is formed (i.e., the fourth patch Pk4) reaches the transfer roller 32K located on the lower end side of the photosensitive drum 22K, and then transfers the toner image (i.e., the fourth patch Pk4) to the transfer belt 30.

[0118] Through the operation sequence up to this point, the third patch Pk3 and the fourth patch Pk4 are transferred onto the transfer belt 30. Thereafter, in step SP19, the mechanism control unit 50 uses the density detection sensor 100 to detect the density of the third patch Pk3 transferred onto the transfer belt 30. In the following step SP20, the mechanism control unit 50 uses the density detection sensor 100 to detect the density of the fourth patch Pk4 transferred onto the transfer belt 30. Note that, here, after the fourth patch Pk4 is transferred onto the transfer belt 30 in step SP18, the density of the third patch Pk3 is detected in the following step SP19. However, depending on the diameter of the photosensitive drum 22K and the sizes of the third patch Pk3 and the fourth patch Pk4, the density of the third patch Pk3 may be detected before the fourth patch Pk4 is transferred onto the transfer belt 30.

[0119] In the next step SP21, the mechanism control unit 50 calculates the difference between the density of the third patch Pk3 and the density of the fourth patch Pk4, and if the difference is equal to or less than a predetermined threshold, it determines that there is normal electrical continuity between the image forming unit 20K and FG. On the other hand, if the difference between the density of the third patch Pk3 and the density of the fourth patch Pk4 exceeds a predetermined threshold, it determines that there is an electrical continuity failure between the image forming unit 20K and FG. The threshold at this time is set to, for example, 0.1 in OD value.

[0120] In the next step SP22, mechanism control unit 50 displays the determination result in step SP21 on operation panel 51. Specifically, when mechanism control unit 50 determines that there is normal continuity between image forming unit 20K and FG, it displays, for example, the determination result and a message that image forming unit 20K is normally installed on operation panel 51. On the other hand, when it determines that there is a continuity failure between image forming unit 20K and FG, it displays, for example, the determination result and a message instructing the user to re-install image forming unit 20K because image forming unit 20K is not properly installed on operation panel 51. The continuity failure determination operation is as described above.

[0121] Although not explained here, the mechanism control unit 50 transfers patches of yellow, magenta, and cyan onto the transfer belt 30 in the same manner as the black patch Pk (Pk3, Pk4), and detects the density using the density detection sensor 100.

[0122] As described above, for the third patch Pk3, the mechanism control unit 50 performs the exposure process through the development process by setting the transfer voltage applied to the transfer roller 32K to 0V, and for the fourth patch Pk4, the mechanism control unit 50 performs the exposure process through the development process by setting the transfer voltage to a voltage V2 that is greater than 0V (see the area surrounded by a solid ellipse in FIG. 10).

[0123] Here, if the drum shaft 25 of the photosensitive drum 22K and the shaft support portion 40 are in normal contact and the photosensitive drum 22K is normally connected to the FG, the drum shaft potential is constant at 0 V regardless of the transfer voltage. For this reason, if the photosensitive drum 22K is normally connected to the FG, the third patch Pk3 and the fourth patch Pk4 are each developed with sufficient toner concentration even if a difference is provided in the transfer voltage applied from the exposure process to the development process between the third patch Pk3 and the fourth patch Pk4.

[0124] 10, the density of the third patch Pk3 transferred to the transfer belt 30 is equal to the density of the fourth patch Pk4. In other words, the density of the third patch Pk3 is equal to the density of the fourth patch Pk4.

[0125] At this time, since the density difference between the third patch Pk3 and the fourth patch Pk4 is 0.1 or less in OD value, the mechanism control unit 50 can determine that there is normal conductivity between the image forming unit 20K and FG.

[0126] In contrast, when there is poor contact between the drum shaft 25 of the photosensitive drum 22K and the shaft support portion 40, causing poor conductivity between the photosensitive drum 22K and FG, the drum shaft potential changes in accordance with changes in the transfer voltage, as shown in the area surrounded by the dotted ellipse in Figure 10.

[0127] In this way, when the drum shaft potential changes from the exposure process to the development process, the aluminum tube potential also changes accordingly. Since the charge of the exposed portion of the surface of the photosensitive drum 22K attenuates toward the aluminum tube potential due to electron transfer, when the aluminum tube potential changes from the exposure process to the development process between the third patch Pk3 and the fourth patch Pk4, the surface potential of the photosensitive drum 22K also changes accordingly. In other words, the surface potential of the photosensitive drum 22K from the exposure process to the development process of the third patch Pk3 is less than the surface potential of the photosensitive drum 22K from the exposure process to the development process of the fourth patch Pk4.

[0128] In this way, when the surface potential of the photosensitive drum 22K changes from the exposure process to the development process, the amount of toner used to develop the electrostatic latent image in the development process also changes accordingly. That is, the amount of toner used to develop the electrostatic latent image of the third patch Pk3 is less than the amount of toner used to develop the electrostatic latent image of the fourth patch Pk4.

[0129] In this way, when a difference occurs in the amount of toner used to develop the electrostatic latent image, a difference occurs between the density of the third patch Pk3 and the density of the fourth patch Pk4 transferred with the same transfer voltage VB, as shown as the density on the belt (with poor conductivity) in Figure 10.

[0130] At this time, since the density difference between the third patch Pk3 and the fourth patch Pk4 exceeds 0.1 in terms of OD value, the mechanism control unit 50 can determine that a conduction failure has occurred between the image forming unit 20K and FG.

[0131] Similarly, the mechanism control unit 50 can determine whether a poor electrical conductivity has occurred between the image forming units 20Y, 20M, 20C and FG based on the difference between the density of the third patch and the density of the fourth patch of each of the colors yellow, magenta, and cyan transferred to the transfer belt 30.

[0132] Furthermore, if the mechanism control unit 50 determines that a poor electrical conductivity has occurred between at least one of the image forming units 20 (20K, 20Y, 20M, 20C) and FG, it may not allow normal printing operations to be performed until the poor electrical conductivity is resolved (i.e., after the image forming unit 20 with the poor electrical conductivity is reinstalled, until the density difference between the third patch and the fourth patch for all colors becomes 0.1 or less in OD value).

[0133] Here, an example of the surface potential of the photosensitive drum 22K at each step of the image formation process is shown in Fig. 11. Fig. 11 shows the surface potential of the photosensitive drum 22K when the image forming unit 20K is normally installed in the main body 2 (normal state) with the charging voltage set to -900V and the developing voltage set to -150V, and the surface potential of the photosensitive drum 22K when the image forming unit 20K is not normally installed in the main body 2 (conductivity failure).

[0134] The surface potential of the photosensitive drum 22K is shown when it is charged, before exposure, during exposure, and during development. Furthermore, for the conduction failure, three patterns are shown, where the transfer voltage applied to the transfer roller 32K from the exposure process to the development process is 0 V, 0.7 kV, and 1.5 kV.

[0135] 11, under normal circumstances, the surface potential of the photosensitive drum 22K is attenuated by electron transfer to about -50V toward the aluminum tube potential, forming an electrostatic latent image, which is then developed to form a toner image. In this way, if the surface potential of the photosensitive drum 22K is attenuated to about -50V by exposure, development will be achieved with sufficient toner density.

[0136] In contrast, when there is a conduction failure and the transfer voltage applied to the transfer roller 32K from the exposure process to the development process is 0 V, the surface potential of the exposed portion of the photosensitive drum 22K attenuates only to about -400 V. As a result, the toner density of the developed toner image becomes significantly lower than under normal conditions.

[0137] Also, when there is a conduction failure, if the transfer voltage applied to the transfer roller 32K from the exposure process to the development process is 0.7 kV, the surface potential of the exposed portion of the photosensitive drum 22K attenuates only to about -100 V. For this reason, the toner density of the developed toner image is darker than when the transfer voltage is 0 V, but is lighter than under normal conditions.

[0138] Furthermore, when the transfer voltage applied to the transfer roller 32K from the exposure process to the development process is 1.5 kV during the conduction failure, the surface potential of the exposed portion of the photosensitive drum 22K attenuates to about -50 V. As a result, the toner density of the developed toner image becomes almost the same as in the normal state.

[0139] Therefore, the toner concentration of the developed toner image is densest when there is normal conductivity and when the transfer voltage from the exposure process to the development process is 1.5 kV (i.e., when the fourth patch Pk4 is transferred) and is next densest when there is poor conductivity and the transfer voltage from the exposure process to the development process is 0.7 kV, and is thinnest when there is poor conductivity and the transfer voltage from the exposure process to the development process is 0V (i.e., when the third patch Pk3 is transferred).

[0140] [2-3. Summary and Effects] As described above, in the second embodiment, in addition to the configuration of the image forming apparatus 1, the image forming apparatus 1x is provided with a concentration detection sensor 100, which is an example of a concentration detection unit that detects the concentration of the toner image transferred to the transfer belt 30 of the transfer unit 9.

[0141] Furthermore, the mechanism control unit 50 of the image forming apparatus 1x sets the transfer voltage applied to the transfer unit 9 between exposure and development to 0 V, which is an example of the first voltage, and sets the transfer voltage applied to the transfer unit 9 during transfer to voltage VB (0.7 kV), which is an example of the fourth voltage, and executes an image formation process to transfer a first toner image (third patch Pk3), which is an example of a first developer image, to the transfer belt 30, and then sets the transfer voltage applied to the transfer unit 9 between exposure and development to voltage V2 (1.5 kV), which is an example of a second voltage different from the first voltage, and sets the transfer voltage applied to the transfer unit 9 during transfer to voltage VB (0.7 kV), which is an example of the fourth voltage, and executes an image formation process to transfer a second toner image (fourth patch Pk4), which is an example of a second developer image, to the transfer belt 30.

[0142] Furthermore, the mechanism control unit 50 detects the density of the first toner image (third patch Pk3) and the density of the second toner image (fourth patch Pk4) using the density detection sensor 100, and based on the difference between these densities, determines whether or not a poor electrical connection has occurred between the image forming unit 20 and the FG of the main body 2, and displays the result of the determination on the operation panel 51.

[0143] In this way, in the image forming device 1x, when a conduction failure occurs between the image forming unit 20 and the FG of the main body part 2, the user can be notified of this fact. Therefore, upon receiving this notification, the user can eliminate the conduction failure by, for example, reattaching the image forming unit 20 to the main body part 2.

[0144] Thus, according to the image forming apparatus 1x of the present embodiment, there is no need for a separate current detection unit or the like for detecting the electrical continuity state between the image forming unit 20 and FG, and the image forming apparatus 1x has a simple configuration in which the transfer voltage applied to the transfer section 9 is changed between exposure and development, yet the user can easily check the electrical continuity state between the image forming unit 20 and FG.

[0145] Furthermore, when the mechanism control unit 50 of the image forming device 1x determines that a poor electrical continuity has occurred between the image forming unit 20 and the FG, the mechanism control unit 50 displays on the operation panel 51 the result of the determination and a message instructing the user to re-install the image forming unit 20 because the image forming unit 20 is not installed properly.

[0146] This allows the user to recognize, by simply looking at the operation panel 51, that when a continuity defect occurs between the image forming unit 20 and the FG, that the defect is due to the mounting condition of the image forming unit 20, and immediately perform maintenance work such as remounting the image forming unit 20 to the main body 2, thereby shortening the time required to restore the image forming apparatus 1. Furthermore, in this second embodiment, whether or not a continuity defect occurs between the image forming unit 20 and the FG is determined on the image forming apparatus 1x side, which has the advantage of imposing less of a burden on the user compared to the first embodiment in which the determination is made on the user side.

[0147] 3. Other embodiments [3-1. Another embodiment 1] In the above-mentioned first and second embodiments, the surface of the photosensitive drum 22K is charged negatively from the aluminum tube potential (i.e., FG), and the surface is exposed to light to attenuate the surface potential of the photosensitive drum 22K toward the aluminum tube potential. However, the surface of the photosensitive drum 22K may be charged positively from the aluminum tube potential (i.e., FG), and the surface may be exposed to light to attenuate the surface potential of the photosensitive drum 22K toward the aluminum tube potential. In this case, too, a difference may be provided in the transfer voltage applied from the exposure process to the development process between the first patch and the second patch (or the third patch and the fourth patch).

[0148] [3-2. Other embodiment 2] Furthermore, in the first embodiment described above, the print test mode is executed when instructed by the user, but this is not limited to the above. For example, as in the second embodiment, an operation similar to the print test mode may be executed during the initialization operation performed after the image forming unit 20 is installed.

[0149] On the other hand, in the second embodiment, the continuity fault determination operation is executed during the initialization operation performed after the image forming unit 20 is attached, but this is not limited to the above, and the continuity fault determination operation may be executed when instructed by the user.

[0150] [3-3. Other embodiment 3] Furthermore, in the first embodiment described above, for the first patch Pk1, the transfer voltage applied to the transfer roller 32K from exposure to development is set to 0V, and for the second patch Pk2, the transfer voltage applied to the transfer roller 32K from exposure to development is set to 1.5 kV, which is higher than 0V. This is not limited to the above, and it is sufficient that there is a difference in the transfer voltage applied to the transfer roller 32K from exposure to development between the first patch Pk1 and the second patch Pk2. For example, the transfer voltage applied to the transfer roller 32K from exposure to development for the first patch Pk1 may be higher than that for the second patch Pk2. The same applies to the second embodiment.

[0151] [3-4. Other embodiment 4] Furthermore, in the above-described first embodiment, the process of printing the first patch Pk1 (the process of steps SP1 to SP4 in FIG. 6) is executed, followed by the process of printing the second patch Pk2 (the process of steps SP5 to SP8), but this is not limiting, and the process of printing the second patch Pk2 may be executed first, followed by the process of printing the first patch Pk1. Similarly, in the second embodiment, the process of transferring the fourth patch Pk4 may be executed first, followed by the process of transferring the third patch Pk3.

[0152] [3-5. Other embodiment 5] Furthermore, in the first and second embodiments described above, the present invention is applied to a direct transfer type image forming apparatus 1 in which a toner image formed on a photosensitive drum 22 (22K, 22Y, 22M, 22C) is directly transferred to a print medium P. However, the present invention may also be applied to a secondary transfer type image forming apparatus in which a toner image formed on a photosensitive drum is transferred to a transfer belt and then transferred from the transfer belt to a print medium. The configurations of the image forming apparatus 1 shown in FIGS. 1 and 2 and the image forming apparatus 1x shown in FIGS. 8 and 9 are merely examples, and configurations different from those shown in FIGS. 1 and 2 or 8 and 9 may be used as long as they have equivalent functions.

[0153] Furthermore, in the first and second embodiments described above, the present invention is applied to an image forming apparatus 1 that is a color printer employing an electrophotographic system and has a detachable image forming unit 20, but the present invention is not limited to this and can be applied to various image forming apparatuses, such as monochrome printers and multifunction devices, as long as they employ an electrophotographic system and have a configuration in which the image forming unit is detachable.

[0154] [3-6. Other embodiment 6] Furthermore, the present invention is not limited to the above-described embodiments, and the scope of application of the present invention extends to embodiments in which some or all of the above-described embodiments are combined in any manner, or in which some of the embodiments are extracted. [Industrial Applicability]

[0155] The present invention can be widely used in, for example, electrophotographic printers. [Explanation of symbols]

[0156] 1...image forming apparatus, 2...main body, 8...image forming section, 9...transfer section, 20...image forming unit, 21...LED head, 22...photosensitive drum, 23...charger, 24...developer, 25...drum shaft, 26...aluminum tube, 27...photosensitive film, 30...transfer belt, 32...transfer roller, 40...shaft support section, 50...mechanism control section, 51...operation panel, 53...high voltage control section, 54...high voltage power supply, 55...image processing section, 56...LED head control section, P...printing medium, Pk1...first patch, Pk2...second patch, Pk3...third patch, Pk4...fourth patch.

Claims

1. A main body portion, an image forming unit having an image carrier and forming a developer image by developing an electrostatic latent image formed on the image carrier with a developer; an exposure section for forming an electrostatic latent image on the image carrier by exposing the image carrier to light; a transfer section that transfers the developer image formed on the image carrier onto a medium or a transfer belt; A voltage application unit that applies a voltage to the transfer unit; A control unit that controls the image formation process from exposure to transfer. Equipped with The image forming unit includes: The sensor is detachably attached to the main body, and when attached to the main body, is electrically connected to a frame ground of the main body; The control unit is A process of transferring a first developer image to the medium or the transfer belt by setting a transfer voltage applied to the transfer unit during the period from exposure to development to a first voltage and executing the image forming process, and a process of transferring a second developer image to the medium or the transfer belt by setting a transfer voltage applied to the transfer unit during the period from exposure to development to a second voltage different from the first voltage and executing the image forming process.

1. An image forming apparatus comprising:

2. The control unit is a transfer voltage applied to the transfer section during the period from exposure to development is set to the first voltage, and a transfer voltage applied to the transfer section during transfer is set to a third voltage, and the image forming process is executed to transfer the first developer image to the medium; and subsequently, a transfer voltage applied to the transfer section during the period from exposure to development is set to the second voltage, and a transfer voltage applied to the transfer section during transfer is set to the third voltage, and the image forming process is executed to transfer the second developer image to the medium.

2. The image forming apparatus according to claim 1,

3. The control unit is In addition to the first developer image and the second developer image, a developer image with a content instructing a user to reattach the image forming unit when a difference in density is detected by comparing the density of the first developer image with that of the second developer image is transferred onto the medium.

3. The image forming apparatus according to claim 2,

4. the first voltage is set to a value lower than the third voltage; The second voltage is set to a value higher than the third voltage.

4. The image forming apparatus according to claim 2, wherein the image forming apparatus is a multi-color image forming apparatus.

5. Display and a density detection unit for detecting a density of the developer image transferred onto the transfer belt, The control unit is a transfer voltage applied to the transfer section during the period from exposure to development is set to the first voltage, and a transfer voltage applied to the transfer section during transfer is set to a fourth voltage, and the image forming process is executed to transfer the first developer image to the transfer belt, and subsequently, a transfer voltage applied to the transfer section during the period from exposure to development is set to the second voltage, and a transfer voltage applied to the transfer section during transfer is set to the fourth voltage, and the image forming process is executed to transfer the second developer image to the transfer belt; Furthermore, the control unit a density detection unit detects a density of the first developer image transferred to the transfer belt and a density of the second developer image transferred to the transfer belt, and determines whether or not the image forming unit is electrically connected to a frame ground of the main body unit based on a difference between the detected densities of the first developer image and the second developer image, and displays a result of the determination on the display unit.

2. The image forming apparatus according to claim 1,

6. The control unit is When it is determined that the image forming unit is not electrically connected to the frame ground of the main body, the display unit displays the result of the determination and a message instructing the user to reattach the image forming unit.

6. The image forming apparatus according to claim 5,

7. the first voltage is set to a value lower than the fourth voltage; The second voltage is set to a value higher than the fourth voltage.

7. The image forming apparatus according to claim 5, wherein the image forming apparatus is a multi-color image forming apparatus.

Images