Image forming apparatus and image forming method

Abstract

To improve image quality.SOLUTION: An image forming apparatus 1 performs image formation on a roll paper P by using an image formation unit 10, and the image forming apparatus 1 is provided with a print control unit 50 that performs image formation by using the image formation unit 10, with the image density of the image formation unit 10 after the image formation unit 10 is replaced as low density that is lower than image density after density correction to be performed subsequently.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus and an image forming method, and is suitably applied to, for example, an electrophotographic image forming apparatus. [Background technology]

[0002] Conventionally, in image forming devices, when an image forming unit, including a developer unit that contains developer and a developing device that forms an image using developer, is replaced, a density correction is performed thereafter, so that images are formed at an appropriate density even after the image forming unit has been replaced (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-300615 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, if it is desired to resume image formation immediately after replacing an image forming unit, unless density correction is performed, an image with a higher density than expected may be formed, which may result in degradation of image quality, such as blurring.

[0005] The present invention has been made in consideration of the above points, and aims to propose an image forming apparatus and an image forming method capable of improving image quality. [Means for solving the problem]

[0006] In order to solve such problems, in the image forming apparatus of the present invention, in an image forming apparatus that forms an image on a medium using an image forming unit, a control unit is provided that sets the image density of the image forming unit after the image forming unit has been replaced to a low density that is lower than the image density after density correction is subsequently performed, and forms an image using the image forming unit.

[0007] Furthermore, in the image forming method of the present invention, in the image forming method for forming an image on a medium using an image forming unit, a detection step for detecting that the image forming unit has been replaced, a post-unit replacement image forming step for forming an image on the medium with the image density of the image forming unit at the post-unit replacement density when it is detected in the detection step that the image forming unit has been replaced, a density correction step for correcting the density of the image forming unit after starting to form an image on the medium with the image forming unit at the post-unit replacement density, and a post-density correction image formation step for forming an image on the medium with the image density of the image forming unit at a density higher than the post-unit replacement density after the density correction.

[0008] As a result, the present invention can prevent a decrease in image quality caused by high image density by keeping the image density low, even if image formation is resumed before density correction is performed after replacing the image forming unit. Effect of the Invention

[0009] According to the present invention, even if image formation is resumed before density correction is performed after replacing an image forming unit, by keeping the image density low, it is possible to prevent a decrease in image quality caused by high image density, thereby realizing an image forming apparatus and an image forming method that can improve image quality. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a left side view showing the internal configuration of the image forming apparatus. [Diagram 2]FIG. 2 is a left side view showing the internal configuration of the image forming unit. [Diagram 3] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus. [Figure 4] The graph shows the change in the development bias, where (A) is the case where the image forming unit is replaced when there is no roll paper remaining in the image forming device, and (B) is the case where the image forming unit is replaced when there is roll paper remaining in the image forming device. [Diagram 5] 10 is a flowchart showing a printing operation process procedure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0012] [1. Internal structure of image forming device] 1, the image forming apparatus 1 is a so-called intermediate transfer type color electrophotographic printer, and prints a desired color image on roll paper P. The image forming apparatus 1 has a housing 2 that is substantially box-shaped.

[0013] The roll paper feeder 3 is provided in front of the image forming device 1, and holds roll paper P, which is a long sheet of paper, wound into a roll shape and feeds the roll paper P to the image forming device 1. The rewinder 4 is provided at the rear of the image forming device 1, and holds the roll paper P printed by the image forming device 1 wound into a roll shape. The cutter 5 is located near the front inside the housing 2, and cuts a predetermined portion of the roll paper P. In this embodiment, the roll paper P has a width in the main scanning direction of, for example, 105 mm.

[0014] The intermediate transport section 6 is composed of multiple roller pairs that guide the roll paper P. The intermediate transport section 6 forms a transport path for the roll paper P in a straight line that crosses the inside of the housing 2 in the front-to-rear direction, and transports the roll paper P in the longitudinal direction. A toner transfer section 8 is provided approximately in the center of the intermediate transport section 6 from front to rear.

[0015] An image forming section 9 is provided above the intermediate conveying section 6. In the image forming section 9, five image forming units 10Y, 10M, 10C, 10K, and 10W (hereinafter collectively referred to as image forming units 10) that form toner images of yellow (Y), magenta (M), cyan (C), black (K), and white (W) are arranged in this order from rear to front. The image forming units 10Y, 10M, 10C, 10K, and 10W are configured similarly to one another. The image forming units 10 are configured to be detachable from the image forming apparatus 1.

[0016] Between the image forming unit 9 and the intermediate conveying unit 6, there is provided a belt running unit 13 that runs the intermediate transfer belt 12, which is a wide endless belt. The belt running unit 13 has a belt cleaning member 24, and the intermediate transfer belt 12 is stretched around a plurality of rollers, such as a first backup roller 14, a reverse bending roller 15, and a second backup roller 16. The belt running unit 13 also brings the intermediate transfer belt 12 into contact with the photosensitive drums 37 (FIG. 2) of the image forming units 10 at its upper portion, and brings the intermediate transfer belt 12 into contact with the conveying path of the roll paper P at the toner transfer unit 8 at its lower portion. The intermediate transfer belt 12 rotates clockwise when viewed from the left side. Therefore, the image forming units 10Y, 10M, 10C, 10K, and 10W are arranged in order from upstream to downstream with respect to the belt advance direction, which is the advance direction of the intermediate transfer belt 12.

[0017] Each image forming unit 10 (10Y, 10M, 10C, 10K, and 10W) ​​is provided with primary transfer rollers 18Y, 18M, 18C, 18K, and 18W (hereinafter, these are also collectively referred to as primary transfer rollers 18) at five positions directly below the image forming units 10. That is, each image forming unit 10 sandwiches the upper portion of the intermediate transfer belt 12 between itself and each primary transfer roller 18. A primary transfer bias, which is a predetermined amount of DC voltage, is applied to the primary transfer roller 18 by a transfer roller power source 64 (FIG. 3). In this embodiment, the primary transfer bias is set to +1000 [V].

[0018] When image data is supplied to each image forming unit 10, the image forming unit 10 forms a toner image according to the image data. The belt running unit 13 runs the intermediate transfer belt 12, thereby sequentially transferring the toner images of each color formed by each image forming unit 10 onto the intermediate transfer belt 12, and advances the transferred toner images to the toner transfer unit 8. The toner transfer unit 8 presses the roll paper P against the intermediate transfer belt 12 with the secondary transfer roller 19, and applies a secondary transfer bias, which is a predetermined amount of DC voltage, to the secondary transfer roller 19 by the transfer roller power supply 64 (FIG. 3), thereby transferring the toner image from the intermediate transfer belt 12 to the roll paper P. In this embodiment, the secondary transfer bias is set to +1000 [V].

[0019] The intermediate transport unit 6 transports the roll paper P onto which the toner image has been transferred to the downstream side, toward the rear, toward the fixing unit 20, and causes it to proceed into the fixing unit 20. The fixing unit 20 applies heat and pressure to the roll paper P and toner while rotating a heating roller 21 and a pressure roller 22, which are arranged above and below the transport path, in a predetermined direction, thereby fixing the toner to the roll paper P, and causes the roll paper P to proceed further backward. As a result, an image based on the print data is formed on the roll paper P.

[0020] In this way, the image forming apparatus 1 transfers and fixes a toner image while sequentially transporting the roll paper P fed from the roll paper feeder 3, thereby forming an image on the roll paper P, and cuts the roll paper P as appropriate.

[0021] The belt cleaning member 24 is a blade made of urethane rubber, and removes toner remaining on the surface of the intermediate transfer belt 12 by contacting the intermediate transfer belt 12 downstream of the toner transfer unit 8 in the belt transport direction. The belt waste toner storage unit 25 stores the toner (hereinafter also referred to as belt residual toner after secondary transfer) that has been scraped off from the intermediate transfer belt 12 by the belt cleaning member 24 and transported by a waste toner transport member (not shown).

[0022] In this way, the image forming apparatus 1 removes the toner adhering to the surface of the intermediate transfer belt 12 using the belt cleaning member 24 and stores it in the belt waste toner storage section 25, thereby enabling the intermediate transfer belt 12 to be repeatedly used to transfer a toner image onto the roll paper P.

[0023] On the transport path of the roll paper P, sensors 27a, 27b, 27c, 27d, and 27e (hereinafter, these are also collectively referred to as sensors 27) that detect the presence or absence of the roll paper P are provided. The sensor 27a is installed on the upstream side of the cutter 5, and detects the roll paper P that arrives from the roll paper feeder 3. The sensor 27b is installed near the upstream side of the contact portion between the intermediate transfer belt 12 and the secondary transfer roller 19 in the toner transfer unit 8, and detects the roll paper P that arrives at the toner transfer unit 8. The sensor 27c is installed near the upstream side of the fixing unit 20, and detects the roll paper P that arrives at the fixing unit 20. The sensor 27d is installed near the downstream side of the fixing unit 20, and detects the roll paper P discharged from the fixing unit 20. The sensor 27e is installed upstream of the discharge port through which the roll paper P is discharged from the image forming device 1, and detects the roll paper P discharged from the image forming device 1.

[0024] When the sensor 27 detects the roll paper P, it notifies the print control unit 50 (FIG. 3) of the detection result. The print control unit 50 recognizes various timings such as the timing of exposure and the timing of applying high voltage based on the detection results obtained from the sensor 27, and determines whether or not the roll paper P remains inside the image forming device 1. Specifically, when the print control unit 50 obtains a detection result from at least one of the sensors 27a, 27b, 27c, 27d, or 27e that the roll paper P has been detected, it determines that the roll paper P remains inside the image forming device 1.

[0025] [2. Internal structure of the image forming unit] 2, the image forming unit 10 is composed of a developing device 28 and a toner cartridge 29. In the image forming unit 10 according to the present embodiment, the developing device 28 and the toner cartridge 29 are not separate, but are integrated with each other.

[0026] [2-1. Configuration of the developing device] The developing device 28 uses a contact reversal development method and a contact roller charging method, and is mainly provided with a supply roller 34, a developing roller 35, a developing blade 36, a photosensitive drum 37, a charging roller 38, and a cleaning member 41.

[0027] The developing device 28 is provided with a supply port 30 connected to an unused toner chamber 47 of the toner cartridge 29, and unused toner is collected from the unused toner chamber 47 into a toner hopper 31 via the supply port 30. The toner hopper 31 is provided with a stirring bar 32 adjacent to a supply roller 34 for stirring the toner in the toner hopper 31.

[0028] The supply roller 34 is in contact with and opposed to the developing roller 35 and is rotatably supported. The supply roller 34 comes into contact with the developing roller 35 at a contact position upstream of the pressing position of the developing blade 36 in the rotation direction of the developing roller 35, scrapes off and collects undeveloped toner adhering to the developing roller 35, and frictionally charges the toner, while supplying the toner supplied from the supply port 30 to the developing roller 35. The toner in this embodiment is a non-magnetic one-component pulverized toner that is negatively charged (i.e., a non-magnetic one-component negatively charged toner).

[0029] The developing roller 35 is made of a charging member to which a predetermined voltage can be applied, and is supported rotatably. The developing roller 35 comes into contact with the photosensitive drum 37, and develops the electrostatic latent image formed on the photosensitive drum 37 by attaching toner to the image. A developing bias and a supply bias, which are DC voltages of predetermined amounts, are applied to the developing roller 35 and the supply roller 34 at predetermined timings by a developing roller power supply 68 and a supply roller power supply 70 (FIG. 3). In this embodiment, the developing bias is set to -200 [V], and the supply bias is set to -320 [V].

[0030] The developing blade 36 is fixed so that one end of the developing blade 36 is pressed against the developing roller 35 upstream of the contact position between the developing roller 35 and the photosensitive drum 37 in the rotational direction of the developing roller 35. A supply bias, which is a predetermined amount of DC voltage, is applied to the developing blade 36 by the supply roller power source 70 (FIG. 3), and the developing blade 36 is charged to a predetermined polarity, thereby regulating the toner layer thickness (toner amount) on the developing roller 35 and forming a thin toner layer on the developing roller 35.

[0031] The photoconductor drum 37 is supported so as to be rotatable at a predetermined speed in a counterclockwise direction by a motor driving force supplied from a drive motor control unit 80 (FIG. 3). The photoconductor drum 37 is uniformly charged by a charging roller 38, and then exposed to LED light corresponding to light emission data from an exposure head 39, which is a 1200 dpi LED (Light Emitting Diode), so that an electrostatic latent image is formed in the exposed area. The electrostatic latent image is then developed by attaching toner to the photoconductor drum 37, and a visible image is formed on the surface of the photoconductor drum 37.

[0032] The exposure head 39 has a plurality of light-emitting elements, LEDs, arranged in the main scanning direction (the direction of the rotational axis of the photosensitive drum 37) and a rod lens array, and exposes the charged surface of the photosensitive drum 37 by focusing the light of the light-emitting elements, which emit light in accordance with the light emission data, onto the photosensitive drum 37 using the rod lens array, thereby forming an electrostatic latent image.

[0033] The charge removing light unit 40 is provided downstream of the cleaning member 41 in the rotation direction of the photosensitive drum 37, and is composed of, for example, an LED, and removes unexposed charges remaining on the photosensitive drum 37 after transfer by irradiating it with light.

[0034] The charging roller 38 is made of a metal shaft and semiconductive epichlorohydrin rubber, and is provided in contact with the peripheral surface of the photosensitive drum 37. It rotates in accordance with the rotation of the photosensitive drum 37, and uniformly charges the surface of the photosensitive drum 37. A charging bias, which is a predetermined amount of DC voltage, is applied to the charging roller 38 by a charging roller power source 66 (FIG. 3). In this embodiment, the charging bias is set to −1000 [V]. The charging cleaning roller 42 is a sponge roller that comes into contact with the charging roller 38, rotates in accordance with the rotation of the charging roller 38, or rotates at a different peripheral speed, and cleans the charging roller 38 by scraping off the toner and external additives of the toner that adhere to the charging roller 38.

[0035] The cleaning member 41 is a urethane rubber blade that comes into contact with the photoconductor drum 37 downstream of the contact position with the primary transfer roller 18 in the rotation direction of the photoconductor drum 37, thereby removing toner remaining on the surface of the photoconductor drum 37 after transfer. A developing device plate (not shown) is attached to the left end of the developing device 28. The first waste toner transport member 44 has a spiral shape and transports the toner scraped off by the cleaning member 41 (hereinafter also referred to as drum residual toner after primary transfer) to the developing device plate.

[0036] In this configuration, the image forming unit 10 exposes the surface of the photosensitive drum 37, which has been uniformly charged by the charging roller 38, with the exposure head 39 based on light emission data to form an electrostatic latent image. Next, the image forming unit 10 electrostatically attaches toner supplied by the supply roller 34 to the electrostatic latent image formed on the photosensitive drum 37 with the development roller 35 to form a toner image. The image forming unit 10 then transfers the toner image on the surface of the photosensitive drum 37 to the surface of the intermediate transfer belt 12 between the primary transfer roller 18 and the photosensitive drum 37.

[0037] [2-2. Toner cartridge configuration] The toner cartridge 29 has an outer cartridge 46 made of resin and formed into a thin, approximately rectangular parallelepiped shape. Inside the outer cartridge 46, an unused toner chamber 47 for accommodating unused toner, a waste toner chamber 48 for accommodating waste toner, and a partition member 43 are provided. The partition member 43 is an LDPE (low density polyethylene) film having a thickness of 0.1 to 0.4 mm. The partition member 43 is installed between the unused toner chamber 47 and the waste toner chamber 48, and an end portion of the partition member 43 is fixed to the outer cartridge 46, so that the unused toner and the waste toner are not mixed. The second waste toner transport member 49 has a spiral shape and transports the toner transported to the developing device plate to the waste toner chamber 48. Therefore, the toner scraped off by the cleaning member 41 is transported by the first waste toner transport member 44 and the second waste toner transport member 49 and is stored in the waste toner chamber 48.

[0038] [3. Control configuration of image forming device] As shown in FIG. 3, the print control unit 50 is composed of a CPU (Central Processing Unit), and by reading and executing a predetermined program from a storage unit 62 consisting of a ROM (Read Only Memory), a RAM (Random Access Memory), a hard disk drive, a flash memory, etc., it controls the print data monitoring unit 52, the image data conversion unit 54, the drum rotation count measurement unit 56, the head light emission count measurement unit 58, the calculation unit 60, the transfer roller power supply 64, the charging roller power supply 66, the developing roller power supply 68, the supply roller power supply 70, the head drive control unit 72, the static elimination light unit power supply 74, the fixing control unit 76, the conveying motor control unit 78, the drive motor control unit 80 and the cutter operation control unit 82, and generally controls the image forming apparatus 1.

[0039] The print data monitoring unit 52 receives print data from an external PC (Personal Computer) or the like of the image forming apparatus 1, and inputs the print data to the image data conversion unit 54. The print data monitoring unit 52 also monitors page changes of the print data. The image data conversion unit 54 converts the input print data into light emission data for the exposure heads 39 of each color.

[0040] Drum rotation count measurement unit 56 measures the drum count for each image forming unit 10. The drum count is a measurement value of the number of rotations (printing distance) of the photoconductor drum 37. Head light emission count measurement unit 58 measures the dot count for each image forming unit 10. The dot count is the number of dots that are lit when dots are formed by the exposure head 39.

[0041] The calculation unit 60 calculates the drum usage rate, the toner consumption rate, and the waste toner storage rate (described later) for each image forming unit 10. The storage unit 62 stores the drum usage rate, the toner consumption rate, and the waste toner storage rate (described later) for each image forming unit 10 calculated by the calculation unit 60.

[0042] The transfer roller power supply 64 applies a voltage to the primary transfer roller 18, the secondary transfer roller 19, and the reverse bending roller 15. The charging roller power supply 66 applies a voltage to the charging roller 38. The developing roller power supply 68 applies a voltage to the developing roller 35. The supply roller power supply 70 applies a voltage to the supply roller 34 and the developing blade 36.

[0043] The head drive control unit 72 controls ON / OFF of the light emission of the exposure head 39 based on the light emission data. The static electricity removal light unit power supply 74 controls ON / OFF of the light emission of the static electricity removal light unit 40. The fixing control unit 76 controls the heating roller 21 and the pressure roller 22. The transport motor control unit 78 controls the roll paper feeder 3 and the rewinder 4. The drive motor control unit 80 controls the intermediate transfer belt 12, the secondary transfer roller 19, the photoconductor drum 37 and the reverse bending roller 15. The cutter operation control unit 82 controls the cutter 5.

[0044] [4. Operation of image forming device] Next, a description will be given of the operation of the image forming apparatus 1. The print control unit 50 of the image forming apparatus 1 starts the printing process when the image data conversion unit 54 starts receiving print data from a higher-level device such as a personal computer (not shown).

[0045] The print control unit 50 drives the photosensitive drum 37 via the drive motor control unit 80, causing the photosensitive drum 37 to rotate at a constant peripheral speed in the direction of the arrow in FIG. 2. The driving force generated by the rotation of the photosensitive drum 37 is transmitted by a gear train (not shown), causing the development roller 35 and the supply roller 34 to rotate in the direction of the arrow in FIG. 2, and the first waste toner transport member 44 and the second waste toner transport member 49 to transport the waste toner. The charging roller 38 is not connected to these gears, and rotates together with the photosensitive drum 37 in the direction of the arrow in FIG. 2. At this time, a charging bias is applied from the charging roller power source 66 to the charging roller 38 provided in contact or pressure contact with the surface of the photosensitive drum 37, and the surface of the photosensitive drum 37 is uniformly or evenly charged. In this embodiment, the aluminum tube of the photosensitive drum 37 is grounded, and a charging bias of −1000 V is applied to the charging roller 38, so that the surface of the photosensitive drum 37 is charged to approximately −500 V.

[0046] Next, in the exposure process, light corresponding to the light emission data is irradiated from the exposure head 39 onto the charged surface of the photoconductor drum 37, and an electrostatic latent image is formed on the photoconductor drum 37. In this embodiment, the potential on the photoconductor drum 37 in the exposed portion becomes approximately -50 [V].

[0047] Furthermore, the electrostatic latent image on the photosensitive drum 37 is developed with toner by the operation of the developing device 28, and a toner image is formed on the photosensitive drum 37. In this embodiment, a developing bias of −200 [V] is applied to the developing roller 35 by the developing roller power supply 68. The potential of the thin toner layer on the thinned developing roller 35 is about −50 [V]. Since the sum of the potential of the thin toner layer and the voltage applied to the developing roller 35 exceeds the potential of the exposed portion on the photosensitive drum 37, the exposed portion on the photosensitive drum 37 is developed with toner. On the other hand, since the sum of the potential of the thin toner layer and the voltage applied to the developing roller 35 does not exceed the potential of the unexposed portion of the photosensitive drum 37, the unexposed portion on the photosensitive drum 37 is not developed with toner.

[0048] Further, the intermediate transfer belt 12 is rotated in the direction of the arrow in FIG. 1 by the drive motor control unit 80. A primary transfer bias of +1000 [V] is applied to the primary transfer roller 18 provided opposite the photosensitive drum 37 by the transfer roller power supply 64. The toner image formed on the photosensitive drum 37 is primarily transferred onto the intermediate transfer belt 12 by an electric field generated between the primary transfer roller 18 and the grounded aluminum tube of the photosensitive drum 37. As the intermediate transfer belt 12 rotates, toner images of up to five colors, Y, M, C, K, and W, are superimposed on the intermediate transfer belt 12 after it has passed through the image forming unit 10W.

[0049] Meanwhile, the roll paper P is subjected to secondary transfer by driving the roll paper feeder 3 connected to the conveying motor control unit 78, that is, sent between the intermediate transfer belt 12 and the secondary transfer roller 19. At this time, the secondary transfer roller 19 is in contact with the intermediate transfer belt 12. The first backup roller 14 is grounded. A secondary transfer bias of +1000 [V] is applied to the secondary transfer roller 19 provided opposite the first backup roller 14 by the transfer roller power supply 64. The toner image formed on the intermediate transfer belt 12 is transferred to the roll paper P by the electric field generated between the secondary transfer roller 19 and the grounded first backup roller 14.

[0050] The roll paper P then passes between the heating roller 21 and pressure roller 22 that make up the fixing unit 20, where the toner on the roll paper P melts due to the heat and pressure and penetrates between the fibers of the roll paper P, fixing the toner image to the roll paper P. The roll paper P with the fixed toner image is taken up by the rewinder 4.

[0051] The print data monitoring unit 52 recognizes the change of pages by detecting that the light emission of the exposure head 39 based on the light emission data converted by the image data conversion unit 54 has ended, and then the cutter 5 is operated by the cutter operation control unit 82 to cut the roll paper P at a location upstream of the end of printing on the roll paper P by the margin.

[0052] Furthermore, a small amount of toner may remain on the photoconductor drum 37 after the primary transfer, but this residual toner (i.e., transfer residual toner) is removed by the cleaning member 41. Here, some of the transfer residual toner and external additives may slip through the cleaning member 41 and wind around the charging roller 38, but these are removed by the charging cleaning roller 42.

[0053] Furthermore, the charge removing light unit 40 emits light and irradiates the photoconductor drum 37, thereby removing unexposed charges on the photoconductor drum 37. The surface of the photoconductor drum 37 from which the charges have been removed is charged again by the charging roller 38. In this manner, the photoconductor drum 37 is repeatedly used for image formation. Furthermore, a small amount of toner may remain on the intermediate transfer belt 12 after the secondary transfer, but this remaining toner is removed by the belt cleaning member 24. The toner removed by the belt cleaning member 24 is transported by the first waste toner transport member 44 and the second waste toner transport member 49, and is collected in the waste toner chamber 48. In this manner, the intermediate transfer belt 12 is repeatedly used for image formation.

[0054] In the image forming unit 10Y at the most upstream position, when a toner image primarily transferred from an image forming unit 10 upstream of each image forming unit 10 passes through the photoconductor drum 37 of the image forming unit 10, a phenomenon called reverse transfer occurs in which a part of the toner image is transferred from the intermediate transfer belt 12 onto the photoconductor drum 37. For example, in the case of the image forming unit 10C, when the toner images of the upstream colors Y and M pass through the photoconductor drum 37 of the image forming unit 10C, a part of the toner of the toner image is reverse-transferred and transferred to the photoconductor drum 37. The toner thus reverse-transferred is removed from the photoconductor drum 37 by the cleaning member 41 as the photoconductor drum 37 rotates, similar to the transfer residual toner.

[0055] Here, the operation of the developing device in the printing process will be described. As described above, the developing roller 35 and the supply roller 34 rotate in the direction of the arrow in FIG. 2 by obtaining the rotational driving force of the photosensitive drum 37. The toner stored in the toner hopper 31 is sent to the developing roller 35 by the rotation of the supply roller 34. Since the supply roller 34 and the developing roller 35 rotate in the opposite directions at their contact portion, the toner is negatively charged by friction. When the toner sent to the developing roller 35 passes through the contact portion with the developing blade 36 due to the rotation of the developing roller 35, the toner is frictionally charged by the developing roller 35 and the developing blade 36 and thinned. In this embodiment, a supply bias of −320 [V] is applied to the supply roller 34 and the developing blade 36 by the supply roller power source 70. Thereafter, the thinned toner on the developing roller 35 is developed in correspondence with the electrostatic latent image formed on the photosensitive drum 37, and the electrostatic latent image becomes a toner image.

[0056] [5. Life control of image forming unit] Next, a description will be given of lifespan control of the image forming unit 10. Whether or not the image forming unit 10 has reached the end of its lifespan is determined based on the drum usage rate, toner consumption rate, and waste toner storage rate, which will be described later. If any one of the drum usage rate, toner consumption rate, and waste toner storage rate of the image forming unit 10 exceeds 100[%], the print control unit 50 determines that the image forming unit 10 has reached the end of its lifespan and needs to be replaced.

[0057] The calculation unit 60 calculates the drum usage rate [%], which is the usage rate of the photoconductor drum 37 relative to its lifespan, using the following formula. Here, the drum usage amount is the drum count of the image forming unit 10 after the image forming unit 10 is replaced. The drum lifespan is a preset upper limit value of the drum usage amount. When the drum usage amount reaches the drum lifespan, the drum usage rate becomes 100 [%].

[0058] Drum usage rate = (drum usage amount / drum life amount) x 100

[0059] Furthermore, calculation unit 60 calculates the toner consumption rate [%], which is the usage rate of toner in toner cartridge 29 and toner hopper 31, using the following formula. Here, the toner consumption amount is the amount of toner consumed after toner cartridge 29 is replaced, and is calculated based on the dot count. The toner filling amount is the amount of toner filled in a new toner cartridge 29 and toner hopper 31, which is set in advance. When the toner consumption amount reaches the toner filling amount, the toner consumption rate becomes 100 [%].

[0060] Toner consumption rate = (toner consumption amount / toner filling amount) x 100

[0061] Furthermore, calculation unit 60 calculates waste toner storage rate [%], which is the storage rate of waste toner in waste toner chamber 48, using the following formula. Here, the waste toner occupied volume is the volume of waste toner stored in waste toner chamber 48 after image forming unit 10 is replaced, and is calculated based on the drum count and dot count. The waste toner storage capacity volume is a preset upper limit value for the amount of waste toner that can be stored in a new waste toner chamber 48. When the waste toner occupied volume reaches the waste toner storage capacity volume, the waste toner storage rate becomes 100 [%].

[0062] Waste toner storage rate = (volume occupied by waste toner / volume available for waste toner storage) x 100

[0063] Here, the calculation unit 60 calculates the amount of toner consumed by printing from the dot count, and calculates the amount of toner consumed by fogging from the drum count. At this time, the calculation unit 60 calculates the amount of toner consumed by printing from the dot count, assuming that the target density (also called the target density) is achieved. Therefore, if the density of the actual printed matter varies from the target density, the calculated (i.e., calculated) amount of toner consumption will deviate from the actual amount of toner consumption. For example, if the density of the printed matter becomes higher than the target density, the actual amount of toner consumption will be greater than the calculated amount of toner consumption (i.e., actual amount of toner consumption > calculated amount of toner consumption).

[0064] For this reason, if the calculation unit 60 calculates the toner consumption rate based on such a calculated toner consumption amount that is deviated from the actual toner consumption amount, the print control unit 50 cannot determine that the image forming unit 10 has reached the end of its life even if there is no toner remaining in the image forming unit 10, and continues to use the image forming unit 10. In that case, image defects such as fading may occur, and in some cases the image forming unit 10 may be damaged.

[0065] [6. Procedure when the image forming unit reaches the end of its life] Next, a procedure to be followed when the image forming unit 10 reaches the end of its life will be described.

[0066] [6-1. Procedure for Comparative Example] First, the procedure of the comparative example will be described. In the procedure of the comparative example, when the image forming unit 10 reaches the end of its life while printing on the roll paper P, the image forming device 1 operates the cutter 5 by the cutter operation control unit 82 to cut the roll paper P, and winds up the cut roll paper P on the rewinder 4 so that it does not remain in the image forming device 1, and the image forming unit 10 that has reached the end of its life is replaced with a new image forming unit 10.

[0067] If the roll paper P remains in the image forming device 1, the image forming device 1 cannot perform density correction or color shift correction on the newly replaced image forming unit 10. In response to this, when performing density correction or color shift correction, the image forming device 1 transfers a correction pattern from the replaced image forming unit 10 to the intermediate transfer belt 12. At this time, as the image forming device 1 drives the fixing unit 20 to warm it up, the intermediate transfer belt 12 also rotates and the roll paper P is also transported. Therefore, the correction pattern is transferred from the intermediate transfer belt 12 to the roll paper P at the toner transfer unit 8. Although the correction pattern reaches the fixing unit 20 as the roll paper P is transported, the fixing unit 20 is not sufficiently warmed up at this time. Therefore, the image forming device 1 ejects the roll paper P onto which the correction pattern has been transferred and is not sufficiently fixed.

[0068] On the other hand, if the image forming apparatus 1 had a mechanism for moving the first backup roller 14 upward so as to separate it from the secondary transfer roller 19, the correction pattern would not normally be transferred from the intermediate transfer belt 12 to the roll paper P when the first backup roller 14 is separated from the secondary transfer roller 19, but if the roll paper P floats, the correction pattern may be transferred from the intermediate transfer belt 12 to the roll paper P. Even if the correction pattern is not transferred from the intermediate transfer belt 12 to the roll paper P, blank portions will be generated on the roll paper P that are not printed and are transported in vain.

[0069] For this reason, if the roll paper P remains in the image forming apparatus 1, it is not possible to perform density correction or color shift correction on the newly replaced image forming unit 10. For this reason, in the image forming apparatus 1 of the comparative example, the roll paper P is not left in the image forming apparatus 1 when replacing the image forming unit 10. When the image forming unit 10 is replaced, the image forming apparatus 1 of the comparative example applies a first developing bias (described later), which is a fixed value stored in advance in the storage section 62, to the new image forming unit 10 to perform density correction. However, in the case of such a procedure of the comparative example, because the roll paper P has been cut, the operator has to take the time to set the leading end of the roll paper P in the rewinder 4 every time he replaces the image forming unit 10 and resumes printing.

[0070] [6-2. Procedure according to this embodiment] In contrast, the procedure of the image forming apparatus 1 according to this embodiment will be described. In the procedure of the image forming apparatus 1, if the image forming unit 10 reaches the end of its life while printing on the roll paper P, the image forming apparatus 1 does not cut the roll paper P, but replaces the image forming unit 10 that has reached the end of its life with a new image forming unit 10 while the roll paper P remains inside the image forming apparatus 1. Therefore, compared to the comparative example, the image forming apparatus 1 can omit the step of setting the leading end of the roll paper P in the rewinder 4 when the operator replaces the image forming unit 10 and resumes printing.

[0071] In this case, however, the image forming apparatus 1 cannot perform density correction or color shift correction on the newly replaced image forming unit 10 because the roll paper P remains inside the image forming apparatus 1. In particular, if density correction cannot be performed, the image forming apparatus 1 may not be able to apply an appropriate developing bias to the new image forming unit 10. In this case, the image forming apparatus 1 does not perform density correction, and therefore applies a second developing bias, which has an absolute value smaller than that of the first developing bias, to the new image forming unit 10 instead of the first developing bias, and continues printing.

[0072] Here, for example, if the density of the actual printout becomes higher than the target density when the first developing bias is applied, the actual toner consumption becomes larger than the calculated toner consumption as described above, and the toner in the image forming unit 10 runs low before the image forming unit 10 reaches the end of its life. In this case, problems occur such as image defects such as fading, even though the image forming unit 10 has not reached the end of its life, and in some cases the image forming unit 10 may be damaged.

[0073] Thus, in the procedure when image forming unit 10 in image forming apparatus 1 according to this embodiment reaches the end of its life, the process of resetting roll paper P into rewinder 4 after replacing image forming unit 10 can be omitted compared to the comparative example, but there is a risk of poor printing or damage to image forming unit 10 after replacement.

[0074] Here, the first developing bias is a value (developing bias value) that results in a target density (OD value is 1.50 in this embodiment) when the design values ​​of the components of the image forming unit 10 are median values, and is a reference developing bias value. On the other hand, the second developing bias is a developing bias value at which the target density (OD value is 1.50) is achieved when the components of the image forming unit 10, such as the roughness of the developing roller 35 and the curvature of the portion of the developing blade 36 that curves to contact the developing roller 35, are at their maximum in the direction of increasing density relative to the design value. For this reason, when the absolute value of the first developing bias is compared to the absolute value of the second developing bias, the absolute value of the second developing bias is smaller.

[0075] [7. Changes in developing bias] The transition of the developing bias will be described with reference to FIG.

[0076] [7-1. Change in developing bias when an image forming unit is replaced when there is no roll paper remaining in the image forming device] 4A shows an example of the transition of the developing bias when the image forming unit 10 is replaced when there is no roll paper P remaining in the image forming apparatus 1, as in the comparative example. This is the case where the printing operation processing procedure RT1 (FIG. 5) transitions in the order of steps SP1, SP2, SP5, and SP6.

[0077] From time Ta0 to time Ta1, printing is performed on the roll paper P. At time Ta1, when the image forming unit 10 reaches the end of its life, printing is stopped, the roll paper P is cut, and the cut roll paper P is wound up by the rewinder 4 so that no more roll paper P remains in the image forming device 1. After that, the image forming unit 10 that has reached the end of its life is replaced with a new image forming unit 10. The image forming unit 10 before replacement that has reached the end of its life has a density of OD value 1.50 and a development bias of -120 [V].

[0078] In section Ta2, a first developing bias of -140 [V] is applied to the new image forming unit 10 after the replacement as a reference, and density correction is performed. The density during the density correction is, for example, 1.60 in OD value. When printing is resumed, in section Ta3, an appropriate developing bias of -135 [V] reflecting the density correction value is applied to the replaced image forming unit 10, and printing is performed. The density after the density correction is the target density, and is 1.50 in OD value.

[0079] [7-2. Change in developing bias when an image forming unit is replaced while roll paper remains in the image forming device] 4(B) shows an example of the transition of the developing bias when, as in this embodiment, the image forming unit 10 is replaced while roll paper P remains in the image forming apparatus 1. This is the case where the printing operation processing procedure RT1 (FIG. 5) transitions in the order of steps SP1, SP2, SP3, SP4, SP5, and SP6.

[0080] Printing is performed on the roll paper P from time Tb0 to time Tb1. When the image forming unit 10 reaches the end of its life at time Tb1, printing stops and the image forming unit 10 that has reached the end of its life is replaced with a new image forming unit 10 with the roll paper P remaining in the image forming device 1. The image forming unit 10 before replacement that has reached the end of its life has a density of OD value 1.50 and a development bias of -120 [V].

[0081] In section Tb2, a second developing bias of -110 [V], which is a smaller absolute value than the reference first developing bias of -140 [V], is applied to the new image forming unit 10 after replacement, and printing is resumed on the roll paper P remaining in the image forming apparatus 1. At this time, the image forming unit 10 to which the second developing bias has been applied has a density of OD value 1.30.

[0082] When the remaining roll paper P in the image forming apparatus 1 runs out, in section Tb3, a reference first developing bias (-140 [V]) higher than the current second developing bias (-110 [V]) is applied to the replaced image forming unit 10, and density correction is performed. The density during density correction is, for example, 1.60 in OD value. When a new roll paper P is set in the roll paper feeder 3 and rewinder 4 and printing is resumed, in section Tb4, an appropriate developing bias of -135 [V] reflecting the density correction value is applied to the replaced image forming unit 10, and printing is performed. The density after density correction is the target density, and is 1.50 in OD value.

[0083] Incidentally, if the first developing bias (-140 [V]) were set to the same value as the second developing bias (-110 [V]), the second developing bias (-110 [V]) would be applied to the new image forming unit 10 after replacement in section Ta2 instead of the first developing bias (-140 [V]), and density correction would be performed. In this case, density correction would be performed with the second developing bias (-110 [V]) instead of the reference first developing bias (-140 [V]), so the accuracy of the density correction would decrease.

[0084] In this way, when the image forming unit 10 reaches the end of its life and is replaced, if there is no roll paper P remaining in the image forming device 1, the image forming device 1 applies a first developing bias (-140 [V]) to the replaced image forming unit 10 to perform density correction and then resumes printing. On the other hand, when the image forming unit 10 reaches the end of its life and is replaced, if there is still roll paper P remaining in the image forming device 1, the image forming device 1 applies a second developing bias (-110 [V]) to the replaced image forming unit 10 and continues printing until no roll paper P remains in the image forming device 1.

[0085] [8. Printing Operation Processing] A specific procedure for the printing operation process by the image forming apparatus 1 will be described with reference to the flowchart in Fig. 5. When the print data monitoring unit 52 receives the print data and the image data conversion unit 54 converts the print data into light emission data, the print control unit 50 reads out and executes a printing operation processing program from the storage unit 62, thereby starting a printing operation processing procedure RT1, and proceeds to step SP1.

[0086] In step SP1 (detection step), the print control unit 50 determines whether or not the image forming unit 10 has been replaced. If a negative result is obtained here, the print control unit 50 returns to step SP1 and waits until the image forming unit 10 is replaced. On the other hand, if the image forming unit 10 is replaced, the print control unit 50 obtains a positive result in step SP1 and proceeds to step SP2.

[0087] In step SP2, the print control unit 50 determines whether or not roll paper P remains inside the housing 2 of the image forming device 1. If a positive result is obtained here, this indicates that the image forming unit 10 has been replaced during printing on the roll paper P, and the print control unit 50 then proceeds to step SP3.

[0088] In step SP3 (image forming step after unit replacement), the print control unit 50 applies a second development bias (-110 [V]) to the development roller 35 of the replaced image forming unit 10 by the development roller power supply 68 (Figure 3) to resume printing, and then proceeds to step SP4.

[0089] In step SP4, the print control unit 50 waits until printing has been completed to the end of the roll paper P, and when printing has been completed to the end of the roll paper P, a positive result is obtained and the process proceeds to step SP5. At this time, printing has been completed to the end of the roll paper P and there is no roll paper P remaining inside the housing 2 of the image forming device 1, so density correction can be performed.

[0090] In step SP5 (density correction step and image formation step after density correction), the print control unit 50 applies a first development bias (-140 [V]) to the development roller 35 of the replaced image forming unit 10 using the development roller power supply 68 (Figure 3) to perform density correction, then starts printing, and proceeds to step SP6, ending the printing operation processing procedure RT1.

[0091] On the other hand, if a negative result is obtained in step SP2, this indicates that the image forming unit 10 was replaced when not printing on the roll paper P, and in this case the print control unit 50 skips steps SP3 and SP4 and moves to step SP5. At this time, there is no roll paper P remaining inside the housing 2 of the image forming device 1, so density correction can be performed.

[0092] In step SP5, the printing control unit 50 applies a first developing bias (-140 [V]) to the developing roller 35 of the replaced image forming unit 10 using the developing roller power supply 68 (Figure 3) to perform density correction, then starts printing, proceeds to step SP5, and ends the printing operation processing procedure RT1.

[0093] [9. Effects, etc.] In the above configuration, when the image forming unit 10 reaches the end of its life and is replaced, if there is no roll paper P remaining in the image forming device 1, the image forming device 1 suspends printing and applies the reference first developing bias (-140 [V]) to the replaced image forming unit 10 to perform density correction before resuming printing.

[0094] On the other hand, when the image forming unit 10 reaches the end of its life and is replaced, if the roll paper P remains within the image forming device 1, the image forming device 1 does not immediately perform density correction, but applies a second developing bias (-110 [V]) that has an absolute value smaller than the first developing bias (-140 [V]) to the replaced image forming unit 10 as a density after unit replacement, and continues printing until no roll paper P remains within the image forming device 1. Furthermore, if the image forming device 1 continues printing and no roll paper P remains within the image forming device 1, it interrupts printing and applies the first developing bias (-140 [V]) as a reference to the replaced image forming unit 10 to perform density correction, and then resumes printing on new roll paper P.

[0095] In this way, when the image forming unit 10 reaches the end of its life and is replaced, if the roll paper P remains in the image forming device 1, the image forming device 1 applies the second developing bias (-110 [V]) with a smaller absolute value than the first developing bias (-140 [V]) to the replaced image forming unit 10 to continue printing. Therefore, if the roll paper P remains in the image forming device 1 when the image forming unit 10 is replaced (time point Tb1 in FIG. 4B), the image forming device 1 can reduce the image density of the replaced image forming unit 10. This allows the image forming device 1 to reduce the image density (e.g., OD value 1.30) (section Tb2 in FIG. 4B) after the replacement of the image forming unit 10 and restarting printing to a level lower than the image density (e.g., OD value 1.50) (section Tb4 in FIG. 4B) after the density correction (section Tb3 in FIG. 4B) that is performed thereafter.

[0096] Therefore, even if the image forming unit 10 is replaced in the middle of printing on the roll paper P while the roll paper P remains in the image forming device 1, and printing is resumed without performing density correction, the image forming device 1 can suppress an increase in density after replacement of the image forming unit 10, and prevent image defects such as smearing and, in some cases, damage to the image forming unit 10.

[0097] This allows the image forming apparatus 1 to replace the image forming unit 10 while the roll paper P remains in the image forming apparatus 1 during printing on the roll paper P, and therefore eliminates the need to reset the roll paper P in the rewinder 4 after replacing the image forming unit 10. In particular, when printing is performed on the roll paper P, when replacing the image forming unit 10, the worker must remove the roll paper P from inside the image forming apparatus 1, replace the image forming unit 10, perform density correction, and then reset the roll paper P, which is very time-consuming. In particular, when a post-processing machine is used downstream of the image forming apparatus 1 at the same time as the image forming apparatus 1, resetting the roll paper P in both the image forming apparatus 1 and the post-processing machine is very time-consuming. In contrast, the image forming apparatus 1 can eliminate the need for the worker to perform such complicated work.

[0098] Incidentally, roll paper P, which is continuous paper, is usually longer in the transport direction than cut paper, such as A4 size paper, which is pre-cut and each sheet is separate. For this reason, the amount of toner required to complete printing on one piece of roll paper P is greater than the amount of toner required to complete printing on one piece of cut paper. As a result, printing on roll paper P is more likely to result in smearing than on cut paper. Also, it takes more effort to reset roll paper P than on cut paper. For this reason, the present invention is more effective when applied to printing on roll paper P than when printing on cut paper.

[0099] According to the above configuration, the image forming apparatus 1 forms an image on roll paper P as a medium using the image forming unit 10, and is provided with a print control unit 50 that performs image formation using the image forming unit 10 by setting the image density of the image forming unit 10 after the image forming unit 10 has been replaced to a low density that is lower than the image density after density correction is subsequently performed.

[0100] As a result, even if the image forming device 1 resumes image formation before performing density correction after replacing the image forming unit 10, the image density can be kept low, thereby preventing a deterioration in image quality caused by high image density.

[0101] [10. Other embodiments] In the above embodiment, the image forming apparatus 1 increases the image density of the image forming unit 10 by increasing the absolute value of the developing bias applied to the image forming unit 10, and decreases the image density of the image forming unit 10 by decreasing the absolute value of the developing bias applied to the image forming unit 10, i.e., adjusts the image density of the image forming unit 10 by changing the absolute value of the developing bias applied to the image forming unit 10. The present invention is not limited to this, and the image forming apparatus 1 may increase the image density of the image forming unit 10 by decreasing the absolute value of the charging bias applied to the image forming unit 10, and decrease the image density of the image forming unit 10 by increasing the absolute value of the charging bias applied to the image forming unit 10, i.e., adjusts the image density of the image forming unit 10 by changing the absolute value of the charging bias applied to the image forming unit 10. The image forming apparatus 1 may also adjust the image density of the image forming unit 10 by changing the value of a predetermined coefficient multiplied by a print duty, which is the ratio of dots per unit area in image data.

[0102] In the above-described embodiment, the present invention is applied to the case where the image forming unit 10 in which the developing device 28 and the toner cartridge 29 are integrated is replaced. However, the present invention is not limited to this, and the present invention may be applied to the case where the image forming unit 10 in the image forming apparatus 1 is separable into the developing device 28 and the toner cartridge 29, or where the developing device 28 alone is replaced, or where the toner cartridge 29 alone is replaced. That is, the image forming unit in the present invention includes the case where the developing device 28 and the toner cartridge 29 are integrated as in the present embodiment, the developing device 28 alone, and the toner cartridge 29 alone. In the above-described embodiment, the image forming apparatus 1 is described as being the toner filling amount of a new toner cartridge 29 and the amount of toner filled in the toner hopper 31. However, the present invention is not limited to this, and the image forming apparatus 1 may be described as being the toner filling amount of a new toner cartridge 29 in the case where the toner cartridge 29 is detachably attached to the developing device 28 in the image forming unit 10.

[0103] Furthermore, in the above-described embodiment, when the image forming unit 10 reaches the end of its life while printing on the roll paper P, the image forming device 1 cuts the roll paper P and winds the cut roll paper P onto the rewinder 4 so that it no longer remains in the image forming device 1, and the image forming unit 10 that has reached its end of its life is replaced with a new image forming unit 10, density correction is performed, and printing is resumed; alternatively, the roll paper P is left uncut and remains in the image forming device 1, and the image forming unit 10 that has reached its end of its life is replaced with a new image forming unit 10, and printing is resumed without density correction.The operator can choose between this.

[0104] Furthermore, in the above-described embodiment, the present invention has been described as being applied to an image forming apparatus 1 that prints on roll paper P. The present invention is not limited to this, and the present invention may also be applied to an image forming apparatus 1 that prints on cut paper that has been cut in advance and separated into individual sheets.

[0105] Furthermore, in the above-described embodiment, the image forming apparatus 1 has been described as having five image forming units 10 of different colors. However, the present invention is not limited to this, and the image forming apparatus 1 may be equipped with a plurality of image forming units 10 of the same color, such as, for example, two black image forming units 10K, two magenta image forming units 10M, and one white image forming unit 10W.

[0106] Furthermore, in the above-described embodiment, the present invention has been described as being applied to an image forming apparatus 1 that has five image forming units 10 corresponding to the colors of yellow, magenta, cyan, black, and white and forms a color image using five colors of toner. However, the present invention is not limited to this, and the present invention may be applied to an image forming apparatus that has four or less image forming units 10 or six or more image forming units 10 depending on the number of colors of toner used in the image forming apparatus, or an image forming apparatus that has one image forming unit and performs monochrome printing.

[0107] Furthermore, in the above-described embodiment, the present invention has been described as being applied to a tandem type image forming apparatus 1 having image forming units 10 of each color arranged in series along the front-rear direction. However, the present invention is not limited to this, and the present invention may be applied to various other types of image forming apparatuses, such as a four-cycle type.

[0108] Furthermore, in the above-described embodiment, a description has been given of a case in which the present invention is applied to an intermediate transfer type image forming apparatus 1 in which a toner image that has been primarily transferred from the image forming unit 10 to the intermediate transfer belt 12 is secondarily transferred to the roll paper P. However, the present invention is not limited to this, and the present invention may also be applied to a direct transfer type image forming apparatus in which a toner image is directly transferred from the image forming unit to the roll paper P.

[0109] Furthermore, in the above-described embodiment, the image forming apparatus 1 is provided with five sensors 27, namely, sensors 27a, 27b, 27c, 27d, and 27e, and when a detection result indicating that the roll paper P has been detected is obtained from at least one of the sensors 27a, 27b, 27c, 27d, or 27e, the image forming apparatus 1 may determine that the roll paper P remains inside the image forming apparatus 1. The present invention is not limited to this, and the image forming apparatus 1 may be provided with at least sensor 27b, and when a detection result indicating that the roll paper P has been detected is obtained from sensor 27b, the image forming apparatus 1 may recognize that the roll paper P is located between the first backup roller 14 and the secondary transfer roller 19, and determine that the roll paper P remains inside the image forming apparatus 1. Also, when the image forming apparatus is of the direct transfer type, it may be determined that the roll paper P remains inside the image forming apparatus 1 when a detection result indicating that the roll paper P is located at least between the transfer roller corresponding to the primary transfer roller 18 and the photosensitive drum 37 is obtained from the sensor.

[0110] Furthermore, in the above-described embodiment, the present invention has been described as being applied to an image forming apparatus 1 having a developing device 28 of a one-component development type in which the developer is made of toner. However, the present invention is not limited to this, and the present invention may be applied to an image forming apparatus having a developing device of a two-component development type in which a carrier and a toner are mixed together and friction between the carrier and the toner is used to impart an appropriate amount of charge to the toner.

[0111] Furthermore, in the above-described embodiment, the present invention has been described as being applied to the image forming apparatus 1 which is a single-function printer. However, the present invention is not limited to this, and the present invention may be applied to image forming apparatuses having various other functions, such as an MFP (Multi Function Peripheral) having the functions of a copier or facsimile machine.

[0112] Furthermore, in the above-described embodiment, the image forming apparatus 1 is configured as an image forming apparatus by the print control unit 50 as a control unit. However, the present invention is not limited to this, and the image forming apparatus may be configured by a control unit having various other configurations. [Industrial Applicability]

[0113] The present invention can also be used in electrophotographic printers, fax machines, copiers, and image forming apparatuses that incorporate a combination of these. [Explanation of symbols]

[0114] 1...image forming apparatus, 2...casing, 3...roll paper feeder, 4...rewinder, 5...cutter, 6...intermediate transport section, 8...toner transfer section, 9...image forming section, 10...image forming unit, 12...intermediate transfer belt, 13...belt running section, 14...first backup roller, 15...reverse bending roller, 16...second backup roller, 18...primary transfer roller, 19...secondary transfer roller, 20...fixing section, 21...heating roller, 22...pressure roller, 24...belt cleaning member, 25...belt waste toner storage section, 27...sensor, 28...developing device, 29...toner cartridge, 30...supply port, 31...toner hopper, 32...agitating bar, 34...supply roller, 35...developing roller, 36...developing blade, 37...photoconductor drum, 38...charging roller, 39...exposure head, 40...static charge removal light unit, 41...cleaning member, 42...charged cleaning roller, 43...partition member, 44...first waste toner transport member, 46...outer cartridge, 47...unused toner chamber, 48...waste toner chamber, 49...second waste toner transport member, 50...print control unit, 52...print data monitoring unit, 54...image data conversion unit, 56...drum rotation speed measurement unit, 58...head light emission number measurement unit, 60...calculation unit, 62...memory unit, 64...transfer roller power supply, 66...charge roller power supply, 68...developing roller power supply, 70...supply roller power supply, 72...head drive control unit, 74...static charge removal light unit power supply, 76...fixing control unit, 78...transport motor control unit, 80...drive motor control unit, 82...cutter operation control unit, P...roll paper.

Claims

1. In an image forming apparatus which forms an image on a medium using an image forming unit, a control unit for performing image formation by the image forming unit after the image forming unit is replaced, the control unit setting the image density of the image forming unit after the image forming unit is replaced to a low density that is lower than the image density after the density correction that is performed thereafter; An image forming apparatus comprising:

2. The control unit is With the medium remaining in the image forming apparatus, after the image forming unit is replaced, the image density of the image forming unit is set to the low density and an image is formed by the image forming unit. The image forming apparatus according to claim 1 .

3. The control unit is The absolute value of the developing bias of the image forming unit after the image forming unit is replaced while the medium remains in the image forming apparatus is set to a value smaller than the absolute value of the developing bias after density correction is performed thereafter, and image formation is performed by the image forming unit. The image forming apparatus according to claim 2 .

4. The control unit is When the image forming unit is replaced while the medium remains in the image forming apparatus, the image density of the image forming unit is set to the low density and an image is formed by the image forming unit. When the image forming unit is replaced with the medium no longer remaining in the image forming apparatus, a density correction is performed on the image forming unit by setting the image density of the image forming unit to a density higher than the low density, and then an image is formed by the image forming unit with an image density according to the density correction. The image forming apparatus according to claim 1 .

5. The control unit is With the medium remaining in the image forming apparatus, the image forming unit after the image forming unit is replaced is set to the low density, and an image is formed by the image forming unit. When the medium is no longer remaining in the image forming apparatus, the image forming unit is set to a density higher than the low density, and a density correction is performed for the image forming unit. Then, the image forming unit is formed to an image density according to the density correction. The image forming apparatus according to claim 1 .

6. The control unit is If the medium is in a state where an image can be formed on it, it is determined that the medium is in a state where it remains in the image forming device.

6. The image forming apparatus according to claim 1,

7. The image forming apparatus forms an image on a long sheet of paper, which is the medium.

6. The image forming apparatus according to claim 1,

8. An image forming method for forming an image on a medium using an image forming unit, a detection step of detecting that the image forming unit has been replaced; a post-unit replacement image forming step of forming an image on a medium using an image density of the image forming unit as a post-unit replacement density when the detection step detects that the image forming unit has been replaced; a density correcting step of correcting the density of the image forming unit after starting image formation on the medium with the image forming unit set to the density after unit replacement; a post-density-correction image forming step of forming an image on a medium with an image density of the image forming unit set to a density higher than the density after the unit replacement after the density correction; The image forming method according to claim 1,

Images