Image forming apparatus

Abstract

To prevent the amount of waste developer from becoming too large even when the temperature of an image forming unit is high.SOLUTION: The image forming apparatus 1 includes the image forming unit 10 having the photosensitive drum 11 as the image carrier and configured to form the toner image as the developer image on the photosensitive drum 11, the temperature detector 70 configured to detect the unit temperature T correlated with the temperature of the image forming unit 10, and the controller 80 configured to control the image forming unit 10 and execute the printing operation and the developer discarding operation. When the unit temperature T is a first temperature, the controller 80 performs the discarding operation by forming a discarding pattern A as a first discarding pattern on the photoconductor drum 11, and when the unit temperature T is a second temperature higher than the first temperature, the controller 80 performs the discarding operation by forming a discarding pattern B as a second discarding pattern having a lower printing rate than the discarding pattern A on the photoconductor drum 11.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus using electrophotography. [Background technology]

[0002] In an electrophotographic image forming apparatus, repeated printing operations can cause degraded toner whose charging characteristics and fluidity have changed to accumulate in the image forming unit, potentially resulting in a decline in image quality. Therefore, a toner disposal operation is performed to discard the toner in the image forming unit depending on the number of prints, etc.

[0003] In the toner disposal operation, toner is attached to an image carrier (e.g., a photosensitive drum) to form a disposal pattern, the toner on the image carrier is scraped off with a cleaning member, and the scraped toner is transported by a waste toner transport member and removed from the image forming unit (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-45481 (see, for example, FIGS. 4 and 5) Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the temperature inside the image forming unit is high, the amount of toner adhering to the photosensitive drum increases, and the amount of toner waste increases, which increases the load on the waste toner transport member and may cause a malfunction.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to prevent the amount of developer discarded from becoming too large even when the temperature of the image forming unit is high. [Means for solving the problem]

[0007] The image forming apparatus of the present disclosure includes an image forming unit having an image carrier and forming a developer image on the image carrier, a temperature detection unit detecting a unit temperature that is correlated with the temperature of the image forming unit, and a control unit controlling the image forming unit to perform a printing operation and a developer disposal operation. When the unit temperature is a first temperature, the control unit forms a first disposal pattern on the image carrier and performs a disposal operation, and when the unit temperature is a second temperature higher than the first temperature, the control unit forms a second disposal pattern on the image carrier, the second disposal pattern having a lower printing rate than the first disposal pattern and performs a disposal operation. [Effects of the Invention]

[0008] According to the image forming apparatus of the present disclosure, when the unit temperature is at the second temperature, a second waste pattern with a low print rate is formed, thereby preventing the amount of waste developer from becoming too large. This reduces the load on the transport member that transports the waste developer and prevents breakdowns. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a basic configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing an image forming unit according to the embodiment. [Figure 3] FIG. 2 is a block diagram showing a control system of the image forming apparatus according to the embodiment; [Figure 4] 10 is a flowchart showing a toner disposal operation according to an embodiment. [Figure 5] 1A and 1B are diagrams showing a first discard pattern and a second discard pattern used in a toner discard operation according to an embodiment. [Figure 6] 10 is a table showing the results of a verification experiment conducted using image forming apparatuses according to an embodiment and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] <Image forming device> First, an image forming apparatus according to an embodiment will be described. Image forming apparatus 1 includes a medium supply unit 40 that supplies medium P such as printing paper, image forming units 10K, 10Y, 10M, and 10C that form toner images of black (K), yellow (Y), magenta (M), and cyan (C), a transfer unit 30 that transfers the toner images onto medium P, a fixing unit 50 that fixes the toner images onto medium P, a medium discharge unit 60 that discharges medium P, a housing 101 that houses these components, and an openable and closable top cover 102 that covers the top of housing 101.

[0011] The medium supply unit 40 has a medium tray 41, a pickup roller 42, a feed roller 43, a retard roller 44, and a pair of conveying rollers 45. The medium tray 41 stores a stack of media P. The media P may be, for example, printing paper, overhead projector sheets, envelopes, copy paper, special paper, etc.

[0012] Pickup roller 42 is positioned to contact the topmost medium P stored in medium tray 41, and sends the medium P one by one onto the transport path. Feed roller 43 transports medium P sent out from medium tray 41 along paper feed guide 46. Retard roller 44 applies resistance to medium P sent out from medium tray 41 to prevent double feeding.

[0013] The conveying roller pair 45 conveys the medium P toward the image forming units 10K, 10Y, 10M, and 10C. The conveying roller pair 45 starts rotating a predetermined time after the leading edge of the medium P contacts the nip portion between the two rollers, thereby correcting the skew of the medium P before conveying it.

[0014] Image forming units 10K, 10Y, 10M, and 10C serving as image forming sections are arranged from upstream to downstream, i.e., from right to left in FIG. 1, along the transport path of medium P. Print heads 8K, 8Y, 8M, and 8C serving as exposure heads are arranged to face photosensitive drums 11 (described below) of image forming units 10K, 10Y, 10M, and 10C, respectively.

[0015] Image forming units 10K, 10Y, 10M, and 10C will be referred to as "image forming units 10" unless there is a need to distinguish them. Similarly, print heads 8K, 8Y, 8M, and 8C will be referred to as "print heads 8" unless there is a need to distinguish them.

[0016] 2 is a cross-sectional view showing the image forming unit 10. The image forming unit 10 has a photosensitive drum 11 as an image carrier, a charging roller 12 as a charging member, a developing roller 13 as a developer carrier, a supply roller 14 as a supply member, a developing blade 15 as a layer regulating member, a cleaning member 16, a waste toner transport member 17, a static eliminator 18, and a unit housing 20.

[0017] The photoconductor drum 11 is a cylindrical conductive support body coated with a photoconductive layer. The conductive support body is, for example, an aluminum pipe. The photoconductive layer is, for example, a stack of charge generating layers and charge transport layers alternately laminated together. An electrostatic latent image is formed on the photoconductive layer by photo-attenuating the potential of the area irradiated with light. The photoconductor drum 11 rotates clockwise in FIG. 2.

[0018] The charging roller 12 has a conductive shaft on the surface of which a conductive elastic layer is formed. The shaft is made of, for example, stainless steel. The elastic layer is made of, for example, epichlorohydrin rubber. The charging roller 12 is disposed so as to come into contact with the surface of the photosensitive drum 11, and rotates in accordance with the rotation of the photosensitive drum 11. A charging voltage is applied to the charging roller 12, which uniformly charges the surface of the photosensitive drum 11.

[0019] The print head 8 (FIG. 1) is disposed opposite the surface of the photosensitive drum 11. The print head 8 is suspended, for example, from the top cover 102 and disposed opposite the surface of the photosensitive drum 11. The print head 8 has a light-emitting element array in which a plurality of LEDs (light-emitting diodes) are arranged as light-emitting elements in the axial direction of the photosensitive drum 11, and a lens array that focuses the light from each LED onto the surface of the photosensitive drum 11. The print head 8 exposes the surface of the photosensitive drum 11 to light to form an electrostatic latent image.

[0020] The developing roller 13 has an elastic layer formed on the surface of a conductive shaft. The shaft is made of, for example, stainless steel. The elastic layer is made of, for example, semiconductive silicone rubber, and is 6 mm thick with a rubber hardness of 58 degrees (Asker C hardness). The elastic layer may be subjected to a surface treatment. The developing roller 13 is disposed so as to contact the surface of the photosensitive drum 11, and rotates in the opposite direction to the photosensitive drum 11 (in the direction in which the surface moves at the contact point). A developing voltage is applied to the developing roller 13, and it deposits toner on the electrostatic latent image on the photosensitive drum 11 to form a toner image.

[0021] The supply roller 14 has an elastic layer formed on the surface of a conductive shaft. The shaft is made of, for example, stainless steel. The elastic layer is made of, for example, a foam such as silicone sponge, and is 5 mm thick with a rubber hardness of 43 degrees (Asker F hardness). The supply roller 14 is disposed so as to contact the surface of the developing roller 13, and rotates in the same direction as the developing roller 13 (the direction in which the surface moves at the contact point is opposite). A supply voltage is applied to the supply roller 14, and the supply roller 14 supplies toner to the developing roller 13.

[0022] The developing blade 15 is a thin metal plate that is long in the axial direction of the developing roller 13 and has spring properties. The developing blade 15 is made of, for example, stainless steel, and has a plate thickness of 0.08 mm. The developing blade 15 is provided so as to come into contact with the surface of the developing roller 13, and the contact portion with the developing roller 13 is bent. A blade voltage is applied to the developing blade 15, and the developing blade 15 regulates the thickness of the toner layer (developer layer) formed on the surface of the developing roller 13.

[0023] The cleaning member 16 is a blade that is arranged to come into contact with the surface of the photosensitive drum 11 and is made of rubber such as urethane rubber. The cleaning member 16 scrapes off toner remaining on the surface of the photosensitive drum 11.

[0024] A waste toner transport member 17 serving as a developer transport member is provided below the cleaning member 16. The waste toner transport member 17 is, for example, a wire made of a metal such as stainless steel, processed into a spiral shape. The axial direction of the waste toner transport member 17 is parallel to the axial direction of the photosensitive drum 11. The waste toner transport member 17 rotates as the photosensitive drum 11 rotates, with rotation transmitted by a gear (not shown).

[0025] Inside the unit housing 20 of the image forming unit 10, the portion surrounding the waste toner transport member 17 constitutes the waste toner transport path 26. The waste toner scraped off by the cleaning member 16 falls into and is collected in the waste toner transport path 26. The waste toner collected in the waste toner transport path 26 is transported in the axial direction by the waste toner transport member 17.

[0026] A static eliminator 18 is disposed between the cleaning member 16 and the charging roller 12 in the rotation direction of the photosensitive drum 11. The static eliminator 18 is formed by arranging LEDs in a row on a substrate (static eliminator plate) in the axial direction of the photosensitive drum 11. The static eliminator 18 reduces the surface potential of the photosensitive drum 11 to zero by irradiating it with static elimination light, thereby making the surface potential of the photosensitive drum 11 uniform in the axial direction.

[0027] Inside the unit housing 20 of the image forming unit 10, the portion including the developing roller 13, the supply roller 14, and the developing blade 15 forms a toner storage section 21 that stores toner. In addition to the developing roller 13, the supply roller 14, and the developing blade 15, the toner storage section 21 is also provided with stirring bars 23 and 24 that stir the toner.

[0028] The image forming unit 10 has a cartridge mounting section 22 at the top of the unit housing 20. A toner cartridge 25 serving as a developer cartridge is removably attached to the cartridge mounting section 22. The toner cartridge 25 has a toner storage section that stores unused toner, and supplies toner to the toner storage section 21 through a toner supply port 22a. The toner cartridge 25 also has a waste toner storage section (not shown) that stores waste toner transported by the waste toner transport member 17.

[0029] The toner is a non-magnetic, single-component, negatively charged toner. The toner contains, for example, a binder resin such as polyester and a colorant. In addition, an external additive such as silica or titanium oxide is added to control the fluidity and chargeability of the toner. Note that the toner is not limited to being negatively charged, and may also be positively charged.

[0030] As shown in FIG. 1, the transfer unit 30 has a transfer belt 32 as a transfer body (or contact member), a belt drive roller 33 and a driven roller 34 around which the transfer belt 32 is stretched, and four transfer rollers 31 as transfer members arranged between the belt drive roller 33 and the driven roller 34.

[0031] The transfer unit 30 also has a belt cleaning member 35 that removes residual toner from the transfer belt 32 , and a waste toner storage unit 36 ​​that stores the residual toner removed by the belt cleaning member 35 .

[0032] The transfer belt 32 is an endless belt made of a semi-conductive plastic film with high resistance. The transfer belt 32 has a glossy surface, and attracts and holds the medium P on the surface to transport it.

[0033] The belt drive roller 33 and the driven roller 34 are located downstream and upstream of the image forming units 10K, 10Y, 10M, and 10C, respectively, in the transport direction of the medium P. The belt drive roller 33 causes the transfer belt 32 to run in the direction indicated by the arrow F. The driven roller 34 applies a predetermined tension to the transfer belt 32.

[0034] The transfer roller 31 is disposed opposite the photosensitive drum 11 via the transfer belt 32. The transfer roller 31 is made of a metal shaft with a semiconductive elastic layer formed on the surface thereof. A transfer voltage is applied to the transfer roller 31, and the toner image on the photosensitive drum 11 is transferred to the medium P on the transfer belt 32.

[0035] The fixing unit 50 has a heat roller 51 and a pressure roller 52. The heat roller 51 has a built-in heater 53 (FIG. 3) such as a halogen lamp. The heat roller 51 rotates so as to transport the medium P transported from the transfer unit 30 further downstream.

[0036] The pressure roller 52 is pressed against the heat roller 51, forming a fixing nip between the heat roller 51 and the pressure roller 52. The heat roller 51 and the pressure roller 52 apply pressure and heat to the toner transferred onto the medium P, thereby fixing the toner to the medium P.

[0037] The medium discharge section 60 is disposed downstream of the fixing unit 50 in the transport direction of the medium P. The medium discharge section 60 has a discharge guide 62 that guides the medium P toward the paper discharge outlet, and a pair of discharge rollers 61. The pair of discharge rollers 61 discharge the medium P from the paper discharge outlet to the outside of the device. A stacker 63 that stacks the discharged medium P is provided on the top cover 102 of the image forming apparatus 1.

[0038] The image forming apparatus 1 includes a temperature detection unit 70 that detects a temperature (referred to as a unit temperature) that is correlated with the temperature of the image forming unit 10. The temperature detection unit 70 is disposed, for example, opposite the surface of the transfer belt 32, and detects the surface temperature of the transfer belt 32. Because the transfer belt 32 contacts the photosensitive drum 11, the temperature of the image forming unit 10 (particularly the temperature of the photosensitive drum 11) is likely to be reflected in the temperature detection unit 70.

[0039] 1, the temperature detection unit 70 is disposed in the vicinity of the belt drive roller 33 and facing the surface of the transfer belt 32. Therefore, it is possible to detect a temperature that reflects the temperature of the photosensitive drum 11 of the image forming unit 10C, which is closest to the fixing unit 50 (and therefore most likely to have a high temperature) among the image forming units 10K, 10Y, 10M, and 10C.

[0040] However, the location of the temperature detection unit 70 is not limited to the location shown in Fig. 1. The temperature detection unit 70 may be located in any location as long as it can detect a temperature correlated with the temperature of at least one image forming unit 10.

[0041] For example, the temperature detection unit 70 may be arranged to detect the surface temperature of the photosensitive drum 11, the developing roller 13, or the developing blade 15 of any one of the image forming units 10. Furthermore, the temperature detection unit 70 may be provided in multiple image forming units 10.

[0042] In Figure 1, the axial direction of the photosensitive drum 11 is the X direction. The direction of movement of the medium P as it passes through the image forming units 10K, 10Y, 10M, and 10C is the Y direction. The direction perpendicular to the X and Y directions is the Z direction. The X direction coincides with the arrangement direction of the LEDs in the print head 8, and is therefore also referred to as the main scanning direction.

[0043] A ventilation opening 103 is formed at a predetermined position in the housing 101 of the image forming apparatus 1. In the example shown in Fig. 1, the ventilation opening 103 is formed so as to face the fixing unit 50. However, the position of the ventilation opening 103 is arbitrary as long as it can dissipate heat inside the image forming apparatus 1.

[0044] The image forming apparatus 1 may also have a double-sided printing function. For example, the double-sided printing function can be realized by providing a re-conveyance mechanism that turns over the medium P discharged from the fixing unit 50 (i.e., the medium P with the toner image fixed on its surface) and re-conveys it to the pair of conveyance rollers 45.

[0045] The color of each image forming unit 10 is not limited to black, yellow, magenta, and cyan. In addition, the number of image forming units 10 may be one or more. For example, the image forming apparatus 1 may form a single-color image using a single image forming unit 10.

[0046] <Control system> Fig. 3 is a block diagram showing the control system of image forming apparatus 1. As shown in Fig. 3, image forming apparatus 1 has a print control unit 80, a memory unit 83, a high voltage control unit 85, an exposure control unit 86, a fixing control unit 87, and a motor control unit 88. Image forming apparatus 1 also has a receiving unit 71, an operation unit 72, a sensor group 73, and a temperature detection unit 70.

[0047] The receiving unit 71 receives print commands, print data, etc. from a higher-level device such as a personal computer. The operation unit 72 is, for example, an operation panel equipped with an input unit (keyboard, operation buttons, etc.) and a display unit, and accepts user input. The sensor group 73 is, for example, a medium sensor that detects the position of the medium P, or a density sensor that detects the density of the toner image.

[0048] As described above, the temperature detection unit 70 detects, for example, the surface temperature of the transfer belt 32 in the vicinity of the belt drive roller 33 as a temperature correlated with the temperature of the photosensitive drum 11 of the image forming unit 10 (that is, the unit temperature).

[0049] The print control unit 80 is a processor such as a CPU (Central Processing Unit), and controls the overall operation of the image forming apparatus 1. The print control unit 80 has a count measurement unit 81 and a discard pattern determination unit 82. The count measurement unit 81 has a print number measurement unit 81a and a dot count measurement unit 81b.

[0050] The print count measurement unit 81a measures the number of prints in a printing operation. The number of prints can be measured, for example, based on a drum count corresponding to the number of rotations of the photosensitive drum 11. The dot count measurement unit 81b measures the dot count during the printing operation. The dot count is calculated by multiplying the number of light-emitting dots of the print head 8 during the printing operation by 8192 (=2 13 ) is the value divided by

[0051] The print control unit 80 calculates the toner waste count based on the number of printed sheets and the dot count, and further determines whether to perform a toner waste operation based on the toner waste count. These will be described later.

[0052] The discard pattern determination unit 82 determines the discard pattern to be used in the toner discard operation. Specifically, the discard pattern to be used in the toner discard operation is determined to be discard pattern A or discard pattern B, which will be described later, based on the temperature detected by the temperature detection unit 70.

[0053] The storage unit 83 is configured to include, for example, a RAM (Random Access Memory) 41 and a ROM (Read Only Memory) 42. The storage unit 83 stores a control program as software executed by the print control unit 80.

[0054] The memory unit 83 also stores the number of printed sheets C and the dot count D measured by the count measurement unit 81, the toner waste count L calculated based on these, and the unit temperature T detected by the temperature detection unit 70.

[0055] High voltage control unit 85 as a voltage control unit controls the charging voltage applied to charging roller 12, the developing voltage applied to developing roller 13, the supply voltage applied to supply roller 14, the blade voltage applied to developing blade 15, the transfer voltage applied to transfer roller 31, and the neutralization voltage applied to neutralization device 18. These voltages are also collectively referred to as bias voltages.

[0056] The exposure control unit 86 controls the light emission of the print head 8. The fixing control unit 87 controls the heater 53 built into the heat roller 51 of the fixing unit 50. The motor control unit 88 controls the drive motor 74 that rotates the photosensitive drum 11, the conveyance motor 75 that rotates the pickup roller 42, the feed roller 43, and the conveyance roller pair 45, the belt motor 76 that rotates the belt drive roller 33, and the fixing motor 77 that rotates the heat roller 51.

[0057] 3, count measurement unit 81 (print number measurement unit 81a and dot count measurement unit 81b) of print control unit 80 measures the number of printed sheets and the dot count for each of image forming units 10K, 10Y, 10M, and 10C. Memory unit 83 stores the number of printed sheets C, the dot count D, and the toner waste count L for each of image forming units 10K, 10Y, 10M, and 10C.

[0058] In addition, high-voltage control unit 85 controls the bias voltage of each of image forming units 10K, 10Y, 10M, and 10C. Exposure control unit 86 controls the light emission of each of print heads 8K, 8Y, 8M, and 8C. Motor control unit 88 controls drive motor 74 that rotates photoconductor drum 11 of each of image forming units 10K, 10Y, 10M, and 10C.

[0059] <Printing operation> Next, a printing operation by the image forming apparatus 1 will be described with reference to Figures 1 to 3. When the print control unit 80 of the image forming apparatus 1 receives a print job from a host device via the receiving unit 71, the print control unit 80 starts the printing operation.

[0060] In response to instructions from the print control unit 80, the motor control unit 88 rotates the drive motors 74 corresponding to the image forming units 10. This causes the photosensitive drums 11, developing rollers 13, and supply rollers 14 to rotate in each image forming unit 10. Following the rotation of the photosensitive drums 11, the charging rollers 12 also rotate, uniformly charging the surfaces of the photosensitive drums 11.

[0061] In response to instructions from the print control unit 80, the high voltage control unit 85 applies a charging voltage to the charging roller 12, a developing voltage to the developing roller 13, a supply voltage to the supply roller 14, and a blade voltage to the developing blade 15.

[0062] The print control unit 80 also transmits image data for each page to the exposure control unit 86. Based on the image data, the exposure control unit 86 determines whether or not to emit light from each LED of the print head 8, and based on that determination, causes each LED to emit light and exposes the photosensitive drum 11. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 11.

[0063] In the toner storage section 21 of the image forming unit 10, toner (indicated by reference numeral 3 in FIG. 2) is rubbed between the supply roller 14 and the developing roller 13 and becomes negatively charged. The negatively charged toner adheres to the developing roller 13 due to a magnetic field generated by the potential difference between the supply voltage of the supply roller 14 and the developing voltage of the developing roller 13.

[0064] The toner adhering to the developing roller 13 is turned into a toner layer of a certain thickness by the developing blade 15, and is then frictionally charged by rubbing between the developing roller 13 and the developing blade 15. The toner on the developing roller 13 adheres to the latent image on the photosensitive drum 11 due to a magnetic field generated by a potential difference with the latent image (exposed portion) on the photosensitive drum 11. As a result, a toner image is formed on the surface of the photosensitive drum 11.

[0065] At approximately the same time as the formation of an electrostatic latent image begins in image forming unit 10, motor control unit 88 drives conveyance motor 75 in response to instructions from print control unit 80, causing pickup roller 42 and feed roller 43 shown in FIG. 1 to rotate. Pickup roller 42 pays out medium P stored in medium tray 41, and feed roller 43 transports the fed medium P along paper feed guide 46. In addition, conveyance motor 75 rotates conveyance roller pair 45, which transports medium P to transfer unit 30.

[0066] Furthermore, in response to instructions from the print control unit 80, the motor control unit 88 drives the belt motor 76, which rotates the belt drive roller 33 and moves the transfer belt 32. The transfer belt 32 attracts and holds the medium P and transports it. As a result, the medium P electrostatically attracted to the transfer belt 32 is sent to the transfer nip between the photosensitive drum 11 and the transfer roller 31 of each image forming unit 10.

[0067] When the leading edge of medium P reaches the transfer nip between photosensitive drum 11 and transfer roller 31, high voltage control unit 85 applies a transfer voltage to transfer roller 31. The toner image on photosensitive drum 11 is transferred to medium P on transfer belt 32 by the transfer voltage applied to transfer roller 31.

[0068] Residual toner remaining on the surface of photosensitive drum 11 after the toner image has been transferred is scraped off by cleaning member 16 and transported by waste toner transport member 17 to a waste toner storage section of toner cartridge 25. Furthermore, charge-removing device 18 irradiates photosensitive drum 11 with charge-removing light, so that the surface potential of photosensitive drum 11 becomes zero. This eliminates variations in the surface potential of photosensitive drum 11 in the X direction.

[0069] In this way, the toner images of each color formed on the photosensitive drums 11 of the image forming units 10K, 10Y, 10M, and 10C are sequentially transferred and superimposed onto the medium P. The medium P onto which the toner images of each color have been transferred is further transported by the transfer belt 32 toward the fixing unit 50. Note that the toner adhering to the surface of the transfer belt 32 is removed by the belt cleaning member 35 and collected in the waste toner collection section 36.

[0070] In the fixing unit 50, the heat roller 51 is heated to a fixing temperature and rotated by the fixing motor 77. The medium P that has reached the fixing unit 50 is heated and pressurized between the heat roller 51 and the pressure roller 52, and the toner image is fixed to the medium P.

[0071] The medium P on which the toner image has been fixed is discharged from the discharge port by the pair of discharge rollers 61 of the medium discharge section 60, and is stacked on the stacker 63. This completes the printing operation.

[0072] <Toner disposal operation> Next, the toner disposal operation will be described. During printing, the toner contained in the toner container 21 of the image forming unit 10 moves to the photosensitive drum 11 via the supply roller 14 and the developing roller 13, and is used to develop an electrostatic latent image. The toner not used for development returns to the toner container 21 via the developing roller 13.

[0073] When printing operations are repeated, toner with changed charging characteristics or fluidity is produced due to the loss of external additives, etc. Such toner is also called degraded toner. When degraded toner accumulates in the image forming unit 10 (more specifically, in the toner storage section 21), it adheres to the non-image areas (non-exposed areas) of the photosensitive drum 11, resulting in a decrease in print quality.

[0074] Therefore, after the printing operation is completed or when the number of printed sheets reaches a specified number during the printing operation, the print control unit 80 executes a toner disposal operation to discard the deteriorated toner in the image forming unit 10. The toner disposal operation is executed when the toner disposal count L, which is calculated based on the number of printed sheets and the dot count during the printing operation, is equal to or greater than a threshold value (here, 1).

[0075] In the toner disposal operation, a disposal pattern is formed on the surface of the photosensitive drum 11 to cause degraded toner to adhere thereto, and the toner is then scraped off by the cleaning member 16. The toner scraped off by the cleaning member 16 is transported by the waste toner transport member 17 and stored in the waste toner storage section of the toner cartridge 25.

[0076] 4 is a flowchart showing a series of operations including a printing operation and a toner disposal operation by the image forming apparatus 1. When the print control unit 80 (FIG. 3) of the image forming apparatus 1 receives a print job at the receiving unit 71 (step S11), it executes a printing operation (step S12). The details of the printing operation are as described above.

[0077] During the printing operation in step S12, the count measurement unit 81 (print number measurement unit 81a) of the print control unit 80 measures the number of rotations of the photosensitive drum 11 and counts the number of printed sheets based on this. The number of printed sheets can be measured, for example, based on a drum count corresponding to the number of rotations of the photosensitive drum 11.

[0078] During the printing operation in step S12, the count measurement unit 81 (dot count measurement unit 81b) of the print control unit 80 counts the number of light-emitting dots of the print head 8 and calculates the dot count based on this. One dot count is 8192 (=2 13 ) dots of an electrostatic latent image. In other words, the dot count is calculated by multiplying the number of light-emitting dots on the print head 8 by 8192 (=2 13 ) is the value divided by

[0079] When the printing operation of the print job is completed, the print control unit 80 acquires the number of printed sheets C and the dot count D measured by the count measurement unit 81, and further acquires the unit temperature T detected by the temperature detection unit 70 at the end of the printing operation (step S13). The print control unit 80 stores the acquired number of printed sheets C, dot count D, and unit temperature T in the memory unit 83.

[0080] Next, the print control unit 80 calculates the toner waste count L from the number of printed sheets C and the dot count D. The toner waste count L is calculated based on the following formula (1) (step S14). L = L + (S × CD) / Y … (1)

[0081] In equation (1), L on the right side is the value of the toner waste count L stored in the memory unit 83. S is the threshold dot count, and Y is a conversion coefficient for the toner waste count. Here, S is set to 792, and Y is set to 831.

[0082] The threshold dot count S of 792 is calculated by multiplying 6,488,064, the number of light-emitting dots when forming an electrostatic latent image at a print rate of 5% in an area equivalent to A4 size, by 8,192 (=2 13 ) is the value divided by

[0083] The value of 831 for the conversion coefficient Y is calculated by multiplying 4992, which is the number of dots in the main scanning direction, by 1364, which is the number of print lines in the sub-scanning direction, to obtain 6809088, which is the number of dots obtained by multiplying 4992, which is the number of dots in the main scanning direction, by 1364, which is the number of print lines in the sub-scan 13 ) is the value divided by

[0084] The print control unit 80 stores the value of the toner waste count L calculated by the above formula (1) in the storage unit 83. In other words, the value of the toner waste count L stored in the storage unit 83 is updated.

[0085] Next, the print control unit 80 determines whether the currently set discard pattern is discard pattern A (step S15). Discard patterns A and B are both patterns formed by toner on the surface of the photosensitive drum 11. The storage unit 83 stores information indicating whether the currently set discard pattern is A or B. Discard patterns A and B will now be described.

[0086] 5(A) is a schematic diagram showing a disposal pattern A. Disposal pattern A has a length W in the main scanning direction and a length H1 in the sub-scanning direction. The main scanning direction is the axial direction of photosensitive drum 11 (i.e., the arrangement direction of the LEDs in print head 8), which is the X direction mentioned above. The sub-scanning direction is a direction perpendicular to the main scanning direction, for example, the circumferential direction of photosensitive drum 11.

[0087] The length W of the discard pattern A in the main scanning direction corresponds to the distance from one end to the other end of the exposable area of ​​the photosensitive drum 11 (i.e., the area where the LEDs of the print head 8 are arranged), and is, for example, 210 mm. The length H1 of the discard pattern A in the sub-scanning direction is, for example, 28 mm.

[0088] The printing rate (density) of discard pattern A is 50%. The toner amount per unit area of ​​discard pattern A is 2.6 g / m 2 ].

[0089] 5B is a schematic diagram showing the discard pattern B. The discard pattern B has a length W in the main scanning direction and a length H2 in the sub-scanning direction.

[0090] The length W of discard pattern A in the main scanning direction is the same as the length W of discard pattern A in the main scanning direction. The length H2 of discard pattern B in the sub-scanning direction is longer than the length H1 of discard pattern A in the sub-scanning direction, for example, 56 mm. Therefore, the area of ​​discard pattern B is larger than the area of ​​discard pattern A.

[0091] The printing rate (density) of the discard pattern B is smaller than that of the discard pattern A, for example, 25%. The toner amount per unit area of ​​the discard pattern B is also smaller than that of the discard pattern A, for example, 1.3 g / m 2 ].

[0092] Thus, discarded pattern B has a lower printing rate, a longer length in the sub-scanning direction, and a larger area than discarded pattern A. Specifically, the printing rate of discarded pattern B is half that of discarded pattern A, and the length H2 of discarded pattern B in the sub-scanning direction is twice the length H1 of discarded pattern A in the sub-scanning direction. The area of ​​discarded pattern B (W × H2) is twice the area of ​​discarded pattern A (W × H1).

[0093] Therefore, the amount of toner discarded by discard pattern A is, by design, the same as the amount of toner discarded by discard pattern B. The reason we say "by design" is because discard pattern B is formed at a higher temperature than discard pattern A, and therefore more toner adheres to it than the design value.

[0094] The printing rate is defined as follows: If the printing rate is η, then the printing rate η is expressed as η = [Cm / (Cd × C0)] × 100. Cm is the number of dots emitted by the print head 8 while the photosensitive drum 11 rotates Cd times. C0 is the number of dots that can be emitted by the print head 8 while the photosensitive drum 11 rotates once. Cd × C0 is the number of dots that can be emitted by the print head 8 while the photosensitive drum 11 rotates Cd times.

[0095] If a solid image is printed over the entire printable area of ​​the medium P, the print rate will be 100%. If an image with an area of ​​1% of this 100% print rate is printed, the print rate will be 1%. The print rate is also called print image density or print duty.

[0096] If discard pattern A is set in step S15 (Y in step S15), the print control unit 80 determines whether the unit temperature T is 45°C or less (step S16). 45°C corresponds to the specified temperature (or the first specified temperature).

[0097] If the unit temperature T is 45°C or less (Y in step S16), discard pattern A is selected (step S17) and the process proceeds to step S22. If the unit temperature T is greater than 45°C (N in step S16), discard pattern B is selected (step S18) and the process proceeds to step S22. A temperature of 45°C or less is also referred to as the first temperature, and a temperature greater than 45°C is also referred to as the second temperature.

[0098] On the other hand, if discard pattern B is set in step S15 (N in step S15), it is determined whether unit temperature T is 40°C or less (step S19). 40°C corresponds to the specified temperature (or second specified temperature).

[0099] If the unit temperature T is 40°C or less (Y in step S19), discard pattern A is selected (step S20) and the process proceeds to step S22. If the unit temperature T is greater than 45°C (N in step S19), discard pattern B is selected (step S21) and the process proceeds to step S22. A temperature of 40°C or less is also referred to as the first temperature, and a temperature greater than 45°C is also referred to as the second temperature.

[0100] In step S22, it is determined whether the toner disposal count L is equal to or greater than 1. If the toner disposal count L is equal to or greater than 1 (Y in step S22), toner is disposed of using the disposal pattern (disposal pattern A or B) set in steps S16 to S21 (step S23).

[0101] Specifically, the high voltage control unit 85 applies a charging voltage to the charging roller 12, a developing voltage to the developing roller 13, a supply voltage to the supply roller 14, and a blade voltage to the developing blade 15. In addition, the motor control unit 88 drives the drive motor 94 to rotate the photosensitive drum 11.

[0102] Furthermore, the exposure control unit 86 causes each LED of the print head 8 to emit light, and an electrostatic latent image corresponding to the discard pattern is formed on the surface of the photosensitive drum 11. The toner in the toner storage unit 21 of the image forming unit 10 is transferred via the supply roller 14 and the developing roller 13 to adhere to the electrostatic latent image on the photosensitive drum 11, and the discard pattern is formed on the surface of the photosensitive drum 11.

[0103] As the photosensitive drum 11 rotates, the waste pattern on the photosensitive drum 11 reaches a contact position with the cleaning member 16. The toner forming the waste pattern on the photosensitive drum 11 is scraped off by the cleaning member 16 and falls into the waste toner transport path 26.

[0104] The toner (ie, waste toner) that has fallen into waste toner transport path 26 is transported in the X direction by waste toner transport member 17, and further transported toward the waste toner storage section of toner cartridge 25, and is stored in the waste toner storage section.

[0105] Thereafter, the print control unit 80 decrements the value of the toner waste count L stored in the storage unit 83 by 1 (step S24), and the operation of the image forming apparatus 1 shown in FIG. 4 ends.

[0106] Also, if the toner disposal count L is less than 1 in step S22 (N in step S22), the operation of the image forming apparatus 1 shown in FIG. 4 is terminated without toner disposal.

[0107] The processes of steps S13 and S14 and steps S22, S23, and S24 are executed for each of image forming units 10K, 10Y, 10M, and 10C. In contrast, the processes of steps S15 to S21 (setting of the discard pattern) are common to the multiple image forming units 10K, 10Y, 10M, and 10C.

[0108] That is, print control unit 80 determines whether to perform the toner disposal operation for each of image forming units 10K, 10Y, 10M, and 10C, but the disposal pattern is common to image forming units 10K, 10Y, 10M, and 10C.

[0109] <effect> Next, a description will be given of the operation of the image forming apparatus 1 according to the embodiment. When the temperature inside the image forming unit 10 rises, the amount of toner adhering to the electrostatic latent image on the photosensitive drum 11 increases. When the image forming apparatus 1 is in a normal operating state, heat is sufficiently dissipated from the ventilation openings 103 of the housing 101, so a large rise in the temperature inside the image forming unit 10 is unlikely to occur.

[0110] However, if the image forming apparatus 1 is placed near a wall or other location that prevents heat from radiating from the ventilation opening 103, the temperature inside the image forming unit 10 rises and the fluidity of the toner decreases. When the fluidity of the toner decreases, the toner tends to condense, and the amount of toner adhering to the photosensitive drum 11 per unit area may exceed a predetermined amount.

[0111] When the amount of toner per unit area increases, the amount of toner scraped off per unit time by the cleaning member 16 increases, and the amount of toner transported per unit length of the waste toner transport member 17 also increases. Furthermore, the fluidity of the toner decreases, which increases the resistance to toner transport.

[0112] As a result, the load on the waste toner transport member 17 increases, which may cause a breakdown of the waste toner transport member 17. As the melting point of the toner decreases, the increase in the load on the waste toner transport member 17 may become more significant.

[0113] In contrast, in the image forming apparatus 1 of the embodiment, as shown in FIG. 4, when the unit temperature T is equal to or lower than a first specified temperature (for example, 45°C), a discard pattern A with a high printing rate is formed, whereas when the unit temperature T is higher than the first specified temperature, a discard pattern B with a low printing rate is formed (steps S16 to S18, S23).

[0114] By using the waste pattern B with a low printing rate when the unit temperature T is high, the amount of toner per unit area can be prevented from exceeding a specified amount. This prevents an increase in the transport amount per unit length of the waste toner transport member 17, reduces the load on the waste toner transport member 17, and prevents breakdowns.

[0115] Furthermore, when the unit temperature T is low, the toner disposal operation can be completed in a short time by using the disposal pattern A with a high printing rate.

[0116] Furthermore, because the length H2 of the disposal pattern B in the sub-scanning direction is longer than the length H1 of the disposal pattern A in the sub-scanning direction, the total amount of toner to be discarded can be secured. Therefore, the toner disposal operation can be performed efficiently, and degradation of image quality can be suppressed.

[0117] If discard pattern B was used in the previous toner discard operation, the temperature of image forming unit 10 is high, making toner more likely to aggregate on photosensitive drum 11. In this case, even if unit temperature T drops to 45°C or below, the toner may still be in a state where it is more likely to aggregate.

[0118] Therefore, in the toner disposal operation of this embodiment, if disposal pattern B has already been set, disposal patterns A and B are selected based on a second specified temperature (for example, 40°C) that is lower than the first specified temperature (steps S15, S19 to S21). If there is a possibility that the toner will continue to be in a state where it is easy for the toner to aggregate, disposal pattern B is used, thereby making it possible to prevent the amount of toner per unit area from exceeding the specified amount.

[0119] Here, the first specified temperature is set to 45°C and the second specified temperature is set to 40°C, but these specified temperatures can be changed as appropriate if the first specified temperature is higher than the second specified temperature.

[0120] In addition, here, the printing rate of discarded pattern B is set to 1 / 2 of the printing rate of discarded pattern A, and the length H2 of discarded pattern B is set to twice the length H1 of discarded pattern A, but it is sufficient if the printing rate of discarded pattern B is lower than the printing rate of discarded pattern A, and the length H2 of discarded pattern B is longer than the length H1 of discarded pattern A.

[0121] Furthermore, if the printing rate of the discard pattern B is lower than that of the discard pattern A, the length H2 of the discard pattern B may be the same as the length H1 of the discard pattern A. In this case, the efficiency of the toner discarding operation decreases, but the effect of avoiding breakdown of the waste toner transport member 17 can be obtained.

[0122] Although the example in which the toner on the photosensitive drum 11 is scraped off by the cleaning member 16 and transported by the waste toner transport member 17 has been described, it is also possible to discard the toner by other methods. For example, the toner on the photosensitive drum 11 can be transferred to the transfer belt 32, scraped off by the belt cleaning member 35, and then discarded.

[0123] <Verification experiment> Next, a verification experiment for verifying the effects of the image forming apparatus 1 according to the embodiment and the results thereof will be described.

[0124] In the experiment, in order to evaluate the influence of temperature rise in the image forming unit 10, the second condition was a case where walls were provided close to both sides in the X direction (left and right sides), the +Z direction (above), and the +Y direction (behind) of the image forming device 1 shown in Figure 1, and the first condition was a case where these walls were not provided. Under the second condition, the distance between the image forming device 1 and each wall was 100 mm.

[0125] Continuous printing was performed under both the first and second conditions. A4-sized plain paper was used as the medium P, and double-sided printing was performed continuously on 3,000 sheets of the medium P. In the flowchart of FIG. 4, the toner disposal operation was performed after the printing operation (step S12) was completed, but in the verification test, the toner disposal operation was performed according to the toner disposal count L every 50 sheets printed during the continuous printing of 3,000 sheets.

[0126] In the toner disposal operation, as described with reference to Fig. 4, disposal pattern A or disposal pattern B was used depending on the unit temperature T detected by the temperature detection unit 70 (see Fig. 4). In addition, for comparison with the first embodiment, the image forming apparatus of the comparative example performed the toner disposal operation using disposal pattern A regardless of the unit temperature T.

[0127] 6 is a table showing the evaluation results for the embodiment and the comparative example. If no abnormal noise was generated from the image forming unit 10 (especially the waste toner conveying member 17 and its surroundings) during the continuous printing of 3,000 sheets, the evaluation result was rated as good (◯), and if abnormal noise was generated, the evaluation result was rated as bad (×).

[0128] 6, under the first condition (no wall), no abnormal noise was observed from image forming unit 10 in either the embodiment or the comparative example. This is because under the first condition, heat from image forming unit 10 was dissipated from ventilation opening 103 (FIG. 1) of housing 101, and unit temperature T did not rise.

[0129] On the other hand, under the second condition (with walls), no abnormal noise was observed from image forming unit 10 in the embodiment, but abnormal noise was observed from image forming unit 10 in the comparative example. This is because under the second condition, image forming apparatus 1 is surrounded by walls, which prevents heat from being dissipated from ventilation opening 103, causing a rise in unit temperature T of image forming unit 10.

[0130] When the unit temperature T of the image forming unit 10 rises, the image forming device 1 of the embodiment can suppress an increase in the amount of toner waste by using waste pattern B, whereas the image forming device of the comparative example uses waste pattern A, which increases the amount of toner waste and increases the load on the waste toner conveying member 17.

[0131] <Effects of the embodiment> As described above, the image forming apparatus 1 of the embodiment includes an image forming unit 10 having a photosensitive drum 11 as an image carrier and forming a developer image on the photosensitive drum 11, a temperature detection unit 70 detecting a unit temperature T that is correlated with the temperature of the image forming unit 10, and a print control unit 80 as a control unit that controls the image forming unit 10 to perform a printing operation and a toner disposal operation (developer disposal operation). When the unit temperature T is a first temperature (for example, a temperature below 45°C), the print control unit 80 performs a toner disposal operation using disposal pattern A as a first disposal pattern, and when the unit temperature T is a second temperature higher than the first temperature (for example, a temperature above 45°C), the print control unit 80 performs a toner disposal operation using disposal pattern B as a second disposal pattern with a lower printing rate than disposal pattern A.

[0132] In this way, by using the waste pattern B with a low printing rate when the unit temperature T is high, the amount of toner per unit area of ​​the waste pattern can be prevented from exceeding the specified amount, thereby reducing the load on the waste toner transport member 17 and preventing malfunctions.

[0133] Furthermore, since the area of ​​waste pattern B is larger than the area of ​​waste pattern A, the total amount of toner to be discarded using waste pattern B can be secured, improving the efficiency of the toner disposal operation and improving image quality.

[0134] Furthermore, by setting the printing rate of discard pattern B to 1 / α (α is a number greater than 1) of the printing rate of discard pattern A and setting the area of ​​discard pattern B to α times the area of ​​discard pattern A, the total amount of toner discarded by discard patterns A and B can be made roughly the same, thereby improving the efficiency of the toner disposal operation.

[0135] Furthermore, since the length H2 of the waste pattern B in the sub-scanning direction is longer than the length H1 of the waste pattern A in the sub-scanning direction, the total amount of toner discarded using the waste pattern B can be secured, improving the efficiency of the toner disposal operation and improving image quality.

[0136] Furthermore, by setting the printing rate of discard pattern B to 1 / α (α is a number greater than 1) of the printing rate of discard pattern A and setting the length H2 of discard pattern B in the sub-scanning direction to α times the length H1 of discard pattern A in the sub-scanning direction, the total amount of toner discarded by discard patterns A and B can be made roughly the same, thereby improving the efficiency of the toner disposal operation.

[0137] In addition, the print control unit 80 as a control unit compares the unit temperature T detected by the temperature detection unit 70 with a specified temperature and selects discard pattern A or discard pattern B depending on the comparison result, so that discard patterns A and B can be appropriately selected depending on the unit temperature T.

[0138] Furthermore, if discard pattern A was selected the previous time, the first specified temperature is used as the specified temperature, and if discard pattern B was selected the previous time, the second specified temperature, which is lower than the first specified temperature, is used as the specified temperature. This makes it possible to use discard pattern B when there is a possibility that a state in which toner is likely to aggregate continues, and to prevent the amount of toner per unit area of ​​the discard pattern from exceeding the specified amount.

[0139] Variant. Although the preferred embodiment has been specifically described above, various improvements and modifications can be made.

[0140] For example, in the above-described toner disposal operation (FIG. 4), the unit temperature T is compared with a first specified temperature (e.g., 45°C) in step S15, and the unit temperature T is compared with a second specified temperature (e.g., 40°C) in step S19. In addition to these, the specified temperature may be further increased. In this case, three or more types of disposal patterns with different printing rates may be selectively formed according to the unit temperature T.

[0141] Also, for example, in the above-described toner disposal operation (FIG. 4), the determination of whether to perform the toner disposal operation (step S22) may be performed before the setting of the disposal pattern based on the unit temperature T (steps S15 to S21).

[0142] However, regardless of whether toner is actually discarded or not, it is better to set the discard pattern based on the unit temperature T (steps S15 to S21). This is because by storing whether discard pattern A or B is selected, an increase in the amount of discarded toner can be effectively suppressed in subsequent toner discard operations.

[0143] Furthermore, the temperature detection unit 70 is positioned to detect the surface temperature of the transfer belt 32, but it is sufficient if it can detect a temperature that is correlated with the temperature of any of the image forming units 10 (including the components thereof, the photosensitive drum 11, the developing roller 13, and the developing blade 15).

[0144] Furthermore, each of the plurality of image forming units 10K, 10Y, 10M, and 10C may be provided with a temperature detection unit 70 that detects the unit temperature T. In this case, the discarding pattern A or B can be selected for each image forming unit 10.

[0145] For example, if the unit temperature T of image forming units 10K, 10Y, and 10M is below a reference value and the unit temperature T of image forming unit 10C is higher than the reference value, toner disposal operation can be performed using disposal pattern A in image forming units 10K, 10Y, and 10M, and toner disposal operation can be performed using disposal pattern B in image forming unit 10C.

[0146] The present disclosure can also be used in image forming apparatuses that form images using an electrophotographic system, such as copying machines, facsimiles, and multifunction machines.

[0147] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) an image carrier; an image forming unit that forms a developer image on the image carrier; a temperature detection unit that detects a unit temperature that is correlated with the temperature of the image forming unit; a control unit that controls the image forming unit to perform a printing operation and a developer disposal operation; Equipped with The control unit When the unit temperature is a first temperature, a first discard pattern is formed on the image carrier and the discard operation is performed; When the unit temperature is a second temperature higher than the first temperature, a second discard pattern having a lower printing rate than the first discard pattern is formed on the image carrier, and the discard operation is performed. An image forming apparatus characterized by: (Appendix 2) The area of ​​the second discard pattern is larger than the area of ​​the first discard pattern. 2. The image forming apparatus according to claim 1, (Appendix 3) the printing rate of the second discard pattern is 1 / α (α is a number greater than 1) of the printing rate of the first discard pattern; The area of ​​the second discard pattern is α times the area of ​​the first discard pattern. 3. The image forming apparatus according to claim 2, (Appendix 4) The main scanning direction and the sub-scanning direction on the surface of the image carrier are defined as follows: The length of the second discard pattern in the sub-scanning direction is longer than the length of the first discard pattern in the sub-scanning direction. 4. The image forming apparatus according to claim 1, wherein: (Appendix 5) the printing rate of the second discard pattern is 1 / α (α is a number greater than 1) of the printing rate of the first discard pattern; The length of the second discard pattern in the sub-scanning direction is α times the length of the first discard pattern in the sub-scanning direction. 5. The image forming apparatus according to claim 4, (Appendix 6) The control unit compares the unit temperature with a specified temperature, and selects the first discard pattern or the second discard pattern depending on the comparison result. 6. The image forming apparatus according to claim 1, wherein: (Appendix 7) The control unit If the first discard pattern was selected in the previous selection, the first specified temperature is used as the specified temperature; If the second discard pattern was selected in the previous selection, a second specified temperature higher than the first temperature is used as the specified temperature. 7. The image forming apparatus according to claim 6, (Appendix 8) The control unit selects the first discard pattern or the second discard pattern based on a comparison result between the unit temperature and the specified temperature, and then determines whether to perform the discard operation. 8. The image forming apparatus according to claim 6 or 7. (Appendix 9) an exposure head for exposing the surface of the image carrier to light to form an electrostatic latent image; The control unit performs a printing operation based on a print job, and then determines whether to perform the disposal operation based on the number of exposure dots of the exposure head and the number of rotations of the image carrier during the printing operation. 9. The image forming apparatus according to claim 8, (Appendix 10) The temperature detection unit detects the temperature of the surface of a contact member that contacts the image carrier. 10. The image forming apparatus according to any one of claims 1 to 9. (Appendix 11) a cleaning member that scrapes off the developer that forms the first waste pattern or the second waste pattern from the surface of the image carrier; a developer transport member that transports the developer scraped off from the surface of the image carrier; 11. The image forming apparatus according to claim 1, further comprising: [Explanation of symbols]

[0148] 1 image forming apparatus, 8, 8K, 8Y, 8M, 8C print head, 10, 10K, 10Y, 10M, 10C image forming section, 11 photosensitive drum (image carrier), 12 charging roller (charging member), 13 developing roller (developer carrier), 14 supply roller (supply member), 15 developing blade (layer regulating member), 16 cleaning member, 17 waste toner transport member (developer transport member), 18 charge removal device, 20 housing, 21 toner storage section, 25 toner cartridge (developer storage body), 26 waste toner transport path, 30 transfer unit, 31 transfer roller (transfer member), 32 transfer belt (transport section), 33 belt drive roller, 34 driven roller, 40 medium supply section, 50 fixing unit, 60 medium discharge section, 70 Temperature detection unit, 80 Print control unit (control unit), 81 Count measurement unit, 81a Printed sheet number measurement unit, 81b Dot count measurement unit, 82 Disposal pattern determination unit, 83 Memory unit, A Disposal pattern (first disposal pattern), B Disposal pattern (second disposal pattern), C Printed sheet number, D Dot count, L Toner disposal count, T Unit temperature.

Claims

1. an image carrier; an image forming unit that forms a developer image on the image carrier; a temperature detection unit that detects a unit temperature that is correlated with the temperature of the image forming unit; a control unit that controls the image forming unit and executes a printing operation and a developer disposal operation; Equipped with The control unit When the unit temperature is a first temperature, a first discard pattern is formed on the image carrier and the discard operation is performed; When the unit temperature is a second temperature higher than the first temperature, a second discard pattern having a lower printing rate than the first discard pattern is formed on the image carrier, and the discard operation is performed. An image forming apparatus characterized by:

2. The area of ​​the second discard pattern is larger than the area of ​​the first discard pattern.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. a printing rate of the second discard pattern is 1 / α (α is a number greater than 1) of a printing rate of the first discard pattern; The area of ​​the second discard pattern is α times the area of ​​the first discard pattern.

3. The image forming apparatus according to claim 2, wherein the image forming apparatus is a recording medium.

4. The main scanning direction and the sub-scanning direction on the surface of the image carrier are defined as follows: The length of the second discard pattern in the sub-scanning direction is longer than the length of the first discard pattern in the sub-scanning direction.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. a printing rate of the second discard pattern is 1 / α (α is a number greater than 1) of a printing rate of the first discard pattern; The length of the second discard pattern in the sub-scanning direction is α times the length of the first discard pattern in the sub-scanning direction.

5. The image forming apparatus according to claim 4.

6. The control unit compares the unit temperature with a specified temperature, and selects the first discard pattern or the second discard pattern depending on the comparison result.

6. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises: a first fixing member;

7. The control unit If the first discard pattern was selected in the previous selection, the first specified temperature is used as the specified temperature; If the second discard pattern was selected in the previous selection, a second specified temperature higher than the first temperature is used as the specified temperature.

7. The image forming apparatus according to claim 6, wherein the image forming apparatus is a recording medium.

8. The control unit selects the first discard pattern or the second discard pattern based on a comparison result between the unit temperature and the specified temperature, and then determines whether or not to perform the discard operation.

7. The image forming apparatus according to claim 6, wherein the image forming apparatus is a recording medium.

9. an exposure head for exposing the surface of the image carrier to light to form an electrostatic latent image; The control unit performs a printing operation based on a print job, and then determines whether to perform the disposal operation based on the number of exposure dots of the exposure head and the number of rotations of the image carrier during the printing operation.

9. The image forming apparatus according to claim 8,

10. The temperature detection unit detects the temperature of the surface of a contact member that contacts the image carrier.

6. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises: a first fixing member;

11. a cleaning member that scrapes off the developer forming the first waste pattern or the second waste pattern from the surface of the image carrier; a developer transport member that transports the developer scraped off from the surface of the image carrier; 6. The image forming apparatus according to claim 1, further comprising:

Images