Image forming apparatus

Abstract

To reduce the gloss unevenness of an image.SOLUTION: An image forming apparatus includes: a transfer portion that transfers a toner image onto a sheet; a fixing device that heats the toner image transferred onto the sheet to fix the toner image to the sheet; a conveyance belt that conveys the sheet from the transfer portion toward the fixing device; driving means that drives the conveyance belt; and control means that controls the driving means. In a case of switching the image forming apparatus to a standby state in which the image forming apparatus is ready to start image forming operation and stands by for input of an image forming job, the control means executes preheating in which the fixing device is preliminarily heated, and causes the driving means to rotate the conveyance belt while the preheating is executed.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that forms an image on a recording material.

Background Art

[0002] Patent Document 1 describes a conveyance belt that conveys a recording material on which a toner image has been transferred in a transfer unit to a fixing device in an electrophotographic image forming apparatus.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to shorten the waiting time (First Print - out Time: FPOT) from when an image forming job is input until the first product is discharged, it is known to pre - heat a fixing device. However, when the surface temperature of the conveyance belt in the above - mentioned document locally rises due to radiant heat from the heated fixing device, there is a possibility that gloss unevenness of an image occurs due to a temperature difference in the circumferential direction of the conveyance belt during the execution of an image forming job.

[0005] Therefore, an object of the present invention is to provide an image forming apparatus capable of reducing gloss unevenness of an image.

Means for Solving the Problems

[0006] One aspect of the present invention is an image forming apparatus comprising: a transfer unit for transferring a toner image onto a sheet; a fixing device for heating and fixing the toner image transferred onto the sheet; a transport belt for transporting the sheet from the transfer unit to the fixing device; a driving means for driving the transport belt; and a control means for controlling the driving means, wherein the control means is In a state where the image formation operation can be started. Waiting for image formation jobs to be submitted. In some cases The fixing device Preheating control is performed to preheat the water to the preheating temperature and maintain that temperature. death, When the image forming job is received, the fixing device is heated to a fixing temperature higher than the preheating temperature, and the control means, during the execution of the preheating control, The image forming apparatus is characterized by rotating the conveyor belt using the aforementioned driving means. [Effects of the Invention]

[0009] According to the present invention, it is possible to reduce uneven gloss in images. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic diagram of the image forming apparatus according to Example 1. [Figure 2] A cross-sectional view showing the configuration between transfer and fixation in Example 1. [Figure 3] A block diagram showing the system configuration of the image forming apparatus according to Example 1. [Figure 4] A graph showing the measurement results of the surface temperature of the conveyor belt. [Figure 5] An example of gloss unevenness appearing in the deliverable (a) and a perspective view of the pre-fixing transport section according to Example 1 (b). [Figure 6] A graph showing the change in surface temperature of a conveyor belt when it is running idle. [Figure 7] A flowchart illustrating the control method according to Example 1. [Figure 8] An example of gloss unevenness appearing in the deliverable (a) and a perspective view of the pre-fixing transport section according to Example 2 (b). [Figure 9] A flowchart illustrating the control method according to Example 2. [Figure 10] A flowchart showing the control method for modified examples. [Modes for carrying out the invention]

[0011] The embodiments relating to this disclosure will be described below with reference to the drawings. [Examples]

[0012] (Image forming apparatus) Figure 1 is a schematic diagram showing an image forming apparatus 100 according to one embodiment (Example 1). First, the overall configuration of the image forming apparatus 100 will be described with reference to Figure 1. The image forming apparatus 100 is an electrophotographic printer that forms an image on a sheet S by an electrophotographic process based on image information received from an external device. As the recording material, the sheet S can be a variety of sheet materials of different sizes and materials, such as plain paper and cardboard, plastic film, cloth, sheet materials with surface treatments such as coated paper, and sheet materials with special shapes such as envelopes and index paper. Furthermore, the "image forming apparatus" is not limited to a printer (single-function printer), but may also be a copier, a facsimile, or a multifunction device equipped with multiple functions of these.

[0013] The image forming apparatus 100 includes a feeding unit 110 for feeding a sheet S, an image forming unit 920 for forming a toner image on the sheet S fed by the feeding unit 110, and a pre-fixing transport unit 904 for transporting the sheet to the fixing unit 50. Furthermore, the image forming apparatus 100 includes a fixing unit 50 for fixing a toner image to the sheet S received from the pre-fixing transport unit 904, a post-transport unit 903 for transporting the sheet on which the toner image has been fixed by the fixing unit 50, and a control unit 170.

[0014] The feeding unit 110 includes a cassette 111 for storing sheets, a pickup roller 112 for picking up a sheet from the cassette 111, and a separating device 113 for separating and feeding the sheet picked up by the pickup roller 112. That is, the feeding unit 110 has a function of feeding the sheets S set in the cassette 111 as a storage unit one by one while separating them. Further, the feeding unit 110 includes a feeding path 901 through which the sheet S separated and fed by the separating device 113 is conveyed, and a delivery roller 114 and a registration roller 115 for conveying the sheet S through the feeding path 901.

[0015] The image forming unit 920 is a so-called tandem type image forming means in which electrophotographic stations 200Y, 200M, 200C, and 200K for forming yellow, magenta, cyan, and black toner images are arranged in series. Further, the image forming unit 920 is an intermediate transfer type image forming means for transferring the toner images formed by these stations 200Y to 200K to the sheet S via an intermediate transfer belt 125 as an intermediate transfer member.

[0016] The configurations of the stations 200Y to 200K are common except that the colors of the developers (toners) used for development are different. Each of the stations 200Y to 200K has a photosensitive drum 120 as an image carrier, a charging device 121, an exposure device 122, and a developing device 123. The photosensitive drum 120 is formed by forming an organic photoreceptor (OPC) layer as an electrophotographic photoreceptor on the outer periphery of an aluminum substrate formed in a drum shape (cylindrical shape), for example.

[0017] The intermediate transfer belt 125 is supported in a state of being stretched over a driving roller 126, a tension roller 127, and a transfer inner roller 128, and rotates in the direction of arrow R2 in FIG. 1 by the driving of the driving roller 126. The cleaning device 129 has a cleaning member such as a web that contacts the outer surface of the intermediate transfer belt 125. Further, in the space on the inner peripheral side of the intermediate transfer belt 125, primary transfer rollers 124 are arranged at positions facing the photosensitive drum 120 with the intermediate transfer belt 125 interposed therebetween.

[0018] The secondary transfer roller 131 is disposed at a position facing the inner transfer roller 128 with the intermediate transfer belt 125 interposed therebetween. A secondary transfer nip (hereinafter simply referred to as transfer nip N2) is formed between the secondary transfer roller 131 and the intermediate transfer belt 125. The secondary transfer roller 131, the intermediate transfer belt 125, and the inner transfer roller 128 constitute a secondary transfer unit 130 as the transfer unit of this embodiment.

[0019] The pre-fixing conveyance unit 904 is disposed between the secondary transfer unit 130 and the fixing device 50 in the sheet conveyance direction FD. The sheet conveyance direction FD is the direction along the conveyance path of the sheet S when an image is formed on the sheet S in an image forming operation described later. The pre-fixing conveyance unit 904 of this embodiment includes a first conveyance unit 10 and a second conveyance unit 20. The configuration of the pre-fixing conveyance unit 904 will be described later.

[0020] The fixing device 50 is a heat fixing type fixing device (fixing means) that heats the toner image transferred to the sheet S and fixes it to the sheet S. The fixing device 50 includes a heating roller 52 as a first rotating body, a pressure roller 53 as a second rotating body disposed so as to be able to contact the heating roller 52, and a heater 51 as a heating means. When the heating roller 52 and the pressure roller 53 are pressed against each other with a predetermined pressing force, a fixing nip Nf is formed between the heating roller 52 and the pressure roller 53. The heater 51 is, for example, a halogen lamp disposed inside the heating roller 52 and heating the heating roller 52 by radiant heat.

[0021] The fixing device 50 has a cooling unit for cooling the pressure roller 53. The cooling unit includes a cooling fan and a cooling duct for uniformly applying the air from the cooling fan to the pressure roller 53 in the longitudinal direction. Here, the longitudinal direction is the sheet width direction orthogonal to the sheet conveyance direction FD, that is, the main scanning direction during image formation. In order to maintain high image quality and high productivity, a cooling fan with a large air volume is used. Also, in order to suppress the change in image quality (for example, glossiness) depending on the position in the main scanning direction, the cooling duct also has a sufficient size.

[0022] The fixing device 50 also includes a first temperature sensor 70 for detecting the surface temperature of the heating roller 52 and a second temperature sensor 71 for detecting the surface temperature of the pressure roller 53. The control unit 170, described later, controls the heating roller 52 and the pressure roller 53 to maintain the surface temperatures at appropriate levels based on the detection signals from the first temperature sensor 70 and the second temperature sensor 71. The control unit 170 also adjusts the airflow of the cooling fan in response to the detection signal from the second temperature sensor 71 to control the pressure roller 53 so that its temperature remains constant.

[0023] The rear transport section 903 includes a discharge roller 911 as a discharge section, a reversing roller 912 as a reversing transport section, and a double-sided transport section 913. The discharge roller 911 discharges the sheet S discharged from the fixing device 50 to the outside of the image forming apparatus 100. The reversing roller 912 reverses and transports the sheet S discharged from the fixing device 50 during double-sided image forming. The double-sided transport section 913 is the reversing roller 912 The sheet S, which has been inverted and transported, is then transported again towards the image forming unit 920.

[0024] In addition, the image forming apparatus 100 is equipped with at least one door (opening / closing door) as an opening / closing member for jamming or maintenance. The door is provided to be openable relative to the image forming apparatus body so as to expose the sheet transport path inside the apparatus. If a sheet transport abnormality (paper jam) occurs, the user can open the door and remove the jammed sheet S from inside the apparatus by following the instructions displayed on the operation unit 210 (Figure 3).

[0025] In this embodiment, an intermediate transfer type and tandem type image forming unit 920 is exemplified as the image forming means. However, for example, a direct transfer type image forming means that directly transfers the toner image formed on the photosensitive drum (image carrier) to the sheet without going through an intermediate transfer unit may also be used. In that case, the transfer unit is composed of a photosensitive drum and a transfer roller or the like facing it.

[0026] Furthermore, the configuration of the fixing device 50 shown in the figure is just one example, and for example, a belt member stretched over multiple rollers may be used instead of the heating roller 52. Also, as a heating means, a heating mechanism including a coil and core for generating heat in the heating roller 52 (first rotating body) by induction heating, or a heater substrate on which a pattern of resistance heating elements that generate Joule heat is formed may be used.

[0027] (Image formation process) Next, the flow of a series of operations (image formation operation) by the image forming apparatus 100 in which an image is formed on the sheet S will be explained. When a job (image formation job) instructing the image forming apparatus 100 to perform the image formation operation is fed in, the image formation operation starts. Then, at each station 200Y to 200K, the photosensitive drum 120 is rotated, and the charging device 121 uniformly charges the surface of the photosensitive drum 120. The exposure device 122 exposes the photosensitive drum 120 based on the image information contained in the image formation job, and forms an electrostatic latent image on the surface of the photosensitive drum 120. The developing device 123 develops the material with a developer containing charged toner, and visualizes the electrostatic latent image on the photosensitive drum 120 as a monochrome toner image.

[0028] The monochrome toner images supported on the surface of each photosensitive drum 120 are first transferred to the intermediate transfer belt 125 by the primary transfer roller 124. At this time, the monochrome toner images formed on the surfaces of the multiple photosensitive drums 120 are transferred (superimposed transfer) so that they overlap each other on the intermediate transfer belt 125, thereby forming a full-color toner image (hereinafter simply referred to as the toner image) on the intermediate transfer belt 125. The intermediate transfer belt 125 is rotated by a drive roller 126 that rotates at a constant speed, so that its peripheral speed is maintained at a constant speed. The toner images supported on the intermediate transfer belt 125 are conveyed toward the transfer nip N2 by the rotation of the intermediate transfer belt 125.

[0029] In parallel with the formation of the toner image described above, sheets S are fed one by one from the feeding unit 110. The sheets S are fed out from the cassette 111 by the pickup roller 112 and separated into individual sheets by the separation device 113, and then transported to the registration roller 115 by the feed roller 114. The registration roller 115 corrects the skew of the sheets S and then transports the sheets S to the transfer nip N2. At this time, the transport timing of the sheets S is adjusted so that the entry of the sheets S into the transfer nip N2 and the arrival of the toner image carried on the intermediate transfer belt 125 at the transfer nip N2 are synchronized. Then, while the sheets S are passing through the transfer nip N2, the toner image is transferred from the intermediate transfer belt 125 to the sheets S (secondary transfer) by the electric field formed in the transfer nip N2 by the secondary transfer roller 131.

[0030] The sheet S, having passed through the transfer nip N2, is transported to the fixing device 50 by the pre-fixing transport unit 904. The fixing device 50 holds the sheet S between the fixing nip Nf and transports it while heating and pressurizing the toner image on the sheet S to fix it to the sheet S. During the execution of the image forming operation, the control unit 170 controls the heater 51 based on the detection signal from the first temperature sensor 70 so that the surface temperature of the heating roller 52 is maintained at a target temperature (fixing temperature) suitable for fixing the toner image.

[0031] When forming an image on one side of the sheet, the sheet S sent from the fixing device 50 is discharged to the outside of the image forming apparatus 100 by the discharge roller 911. When forming an image on both sides of the sheet, the sheet sent from the fixing device 50 is reversed and transported by the reversing roller 912, and transported again to the feeding path 901 via the double-sided transport section 913. Then, by passing through the transfer nip N2 and fixing nip Nf again, the sheet S has an image formed on the second side opposite to the first side on which the image has already been formed, and is then discharged to the outside of the image forming apparatus 100 by the discharge roller 911.

[0032] (Pre-fixing transport section) Next, the pre-fixing transport section 904 will be described. Figure 2 is a cross-sectional view showing the secondary transfer section 130, the pre-fixing transport section 904, and the fixing device 50. The pre-fixing transport section 904 is the transport means (sheet transport mechanism) of this embodiment that transports the sheet from the transfer section to the fixing device.

[0033] As shown in Figure 2, the pre-fixing transport section 904 includes a first transport unit 10 and a second transport unit 20. The first transport unit 10 and the second transport unit 20 are transport units that can transport the sheet S independently. In this embodiment, the first transport unit 10, which is located upstream of the sheet transport direction FD, and the second transport unit 20, which is located downstream of the sheet transport direction FD, are arranged in series. That is, the first transport unit 10 is located downstream of the transfer nip N2 and upstream of the second transport unit 20 in the sheet transport direction FD. 2 0 is the first transport unit in the sheet transport direction FD. 1 It is positioned downstream of 0 and upstream of the anchoring nip Nf.

[0034] The first conveying unit 10 includes a first conveying belt 11 as a conveying belt, and a plurality of rollers that rotatably tension the first conveying belt 11. In this embodiment, the first conveying belt 11 is tensioned on a first drive roller 12 and three driven rollers 12a, 12b, and 12c. The first conveying unit 10 also includes a first drive motor 14 as a driving means for driving the first conveying belt 11. The first drive motor 14 rotates the first conveying belt 11 in a rotational direction (counterclockwise in the figure) along the sheet conveying direction FD by rotationally driving the first drive roller 12.

[0035] The first conveyor belt 11 is an endless belt member with a number of holes (Figure 5(b)) that penetrate from the outer surface to the inner surface arranged in a regular pattern. That is, the first conveyor belt 11 has permeability, allowing air to pass between the outer and inner surfaces through the multiple holes. The first conveying unit 10 of this embodiment has four first conveyor belts 11 arranged side by side in the sheet width direction (Figure 5(b)).

[0036] A first suction fan 15 is positioned in the space on the inner circumference side of the first conveyor belt 11 as a suction means. The first suction fan 15 draws air from the outer circumference side (outside) to the inner circumference side (inside) of the first conveyor belt 11 through a number of holes formed in the first conveyor belt 11, thereby generating a suction force (negative pressure) to hold the sheet S on the outer surface of the first conveyor belt 11.

[0037] The second conveying unit 20 has substantially the same configuration as the first conveying unit 10. That is, the second conveying unit 20 includes a second conveying belt 21 as a conveying belt, and a plurality of rollers that rotatably tension the second conveying belt 21. In this embodiment, the second conveying belt 21 is tensioned on a second drive roller 22 and three driven rollers 22a, 22b, and 22c. The second conveying unit 20 also includes a second drive motor 24 as a driving means for driving the second conveying belt 21. The second drive motor 24 rotates the second conveying belt 21 in a rotational direction (counterclockwise in the figure) along the sheet conveying direction FD by rotationally driving the second drive roller 22.

[0038] The second conveyor belt 21 is an endless belt member with a number of holes 21a (Figure 5(b)) that penetrate from the outer surface to the inner surface arranged in a regular pattern. That is, the second conveyor belt 21 has permeability, allowing air to pass between the outer and inner surfaces through the multiple holes. The second conveyor unit 20 in this embodiment has four second conveyor belts 21 arranged side by side in the sheet width direction (Figure 5(b)).

[0039] Furthermore, a second suction fan 25 is positioned in the space on the inner circumference side of the second conveyor belt 21 as a suction means. The second suction fan 25 draws air from the outer circumference side (outside) to the inner circumference side (inside) of the second conveyor belt 21 through a number of holes formed in the second conveyor belt 21, thereby generating a suction force (negative pressure) to hold the sheet S on the outer surface of the second conveyor belt 21.

[0040] The pre-fixing transport unit 904 transfers the sheet S between the first transport unit 10 and the second transport unit 20, moving the sheet S from the transfer nip N2 to the fixer nip Nf. of The sheets are transported. More specifically, the first transport belt 11 of the first transport unit 10 carries the sheet S sent from the transfer nip N2 on its transport surface and transports it in the sheet transport direction FD. The second transport belt 21 of the second transport unit 20 carries the sheet S received from the first transport belt 11 on its transport surface and transports it in the sheet transport direction FD, sending it towards the fixing nip Nf.

[0041] Furthermore, the central position of the second suction fan 25 in the sheet conveying direction FD may be positioned downstream of the central position of the second conveyor belt 21 in the sheet conveying direction FD. In this way, the sheet S can be conveyed to the fixing nip Nf while being closer to the outer surface of the second conveyor belt 21.

[0042] A sheet detection sensor 116 is positioned between the registration roller 115 and the transfer nip N2 in the sheet transport direction FD. The sheet detection sensor 116 detects the presence or absence of a sheet at the detection position P1 between the registration roller 115 and the transfer nip N2 in the sheet transport direction FD. The signal output by the sheet detection sensor 116 is transmitted to the control unit 170 (Figure 3).

[0043] In the sheet transport direction FD, a post-transfer guide 951 is positioned between the transfer nip N2 and the first transport unit 10. The post-transfer guide 951 guides the sheet S, which is fed out from the transfer nip N2, to the transport surface of the first transport belt 11 (the outer surface that constitutes the transport path of the sheet S; the upper surface of the first transport belt 11 in Figure 2).

[0044] In the sheet transport direction FD, a pre-fixing guide 952 is positioned between the second transport unit 20 and the pre-fixing transport section 904. The pre-fixing guide 952 guides the sheet S, which is separated by curvature from the transport surface of the second transport belt 21 (the outer surface that constitutes the transport path of the sheet S; the upper surface of the second transport belt 21 in Figure 2), to the fixing nip Nf. Here, separation by curvature refers to the separation of the sheet S from the transport surface due to the rigidity of the sheet S at the curved portion (the portion wrapped around the second drive roller 22) at the downstream end of the transport surface of the transport belt.

[0045] Also, the pre-fixing transport section 90 4 A loop detection sensor 16 is positioned. The loop detection sensor 16 detects the height of the conveyed sheet S (position in a direction perpendicular to the sheet conveying direction FD and the sheet width direction, the vertical position in the figure). The loop detection sensor 16 in this embodiment has a detection flag 161 that swings according to the height of the sheet S, and a sensor unit 162 that detects the angle of the detection flag 161. The detection flag 161 protrudes upward from the conveying surface of the first conveying belt 11 and swings when it comes into contact with the sheet S. The sensor unit 162 is a photointerrupter that switches between a light-shielding state and a light-transmitting state according to the angle of the detection flag 161, for example, and outputs an ON signal or an OFF signal.

[0046] The control unit 170 (Figure 3) adjusts the transport speed of the sheet S in the fixing device 50 based on the detection result of the loop detection sensor 16, and controls the degree of deflection (loop amount) of the sheet S between the transfer nip N2 and the fixing nip Nf. Specifically, if the height of the sheet S detected by the detection flag 161 is above a predetermined height, i.e., if the loop amount is below a predetermined amount, the driving speed of the fixing device 50 by the fixing motor 54 (Figure 3) is slowed down to increase the loop amount. Conversely, if the height of the sheet S detected by the detection flag 161 is below a predetermined height, i.e., if the loop amount is above a predetermined amount, the driving speed of the fixing device 50 by the fixing motor 54 is increased to decrease the loop amount. By performing this loop control, the posture of the sheet S between the transfer nip N2 and the fixing nip Nf can be kept constant.

[0047] (System Configuration) Figure 3 is a block diagram showing the system configuration of the image forming apparatus 100. The control unit 170, which acts as a control means (controller) for controlling the operation of the image forming apparatus 100, has an arithmetic processing unit including a CPU 171, memory 172, and timer 175. The control unit 170 also has circuits for exchanging data with the outside, such as I / O ports 173 and a communication interface 174.

[0048] The CPU 171 controls the operation of the image forming apparatus 100 by reading and executing programs stored in the memory 172. The memory 172 stores programs and data necessary for program execution, and also provides a workspace for the CPU 171 when executing programs. The memory 172 is a non-transient storage medium that can be read by a computer. The CPU 171 also manages time based on signals from the timer 175.

[0049] Control unit 17 0 The control unit 17 determines the status of the device based on the detection results of various sensors, such as the door open / close sensor 151, the loop detection sensor 16, the seat detection sensor 116, the first temperature sensor 70, and the second temperature sensor 71. 0 The system controls the operation of each part by sending commands to the controlled objects of the feeding unit 110, the image forming unit 920, the pre-fixing transport unit 904, and the fixing device 50.

[0050] For example, control unit 17 0 Based on the detection signal from the door opening / closing sensor 151 (opening / closing sensor), it is possible to detect when a door for jam processing, etc., has been opened or closed. Also, the control unit 17 0 The control unit 17 controls the start / stop rotation and rotation speed of the first conveyor belt 11 and the second conveyor belt 21 by issuing commands to the first drive motor 14 and the second drive motor 24 of the pre-fixing conveyor unit 904. 0 The control unit 17 controls the start / stop rotation and suction amount of the first suction fan 15 and the second suction fan 25 of the pre-fixing transport unit 904 by issuing commands to them. 0The fixing device 50 controls the rotational speed (peripheral speed) of the heating roller 52 and the pressure roller 53 by a command to the fixing motor 54, and controls the amount of heat generated by the heater 51 by a command to the temperature control unit 55.

[0051] Furthermore, the control unit 170 is communicatively connected to the operation unit 210, which serves as the user interface for the image forming apparatus 100. The operation unit 210 includes a display device such as a liquid crystal panel, a touch panel function for the liquid crystal panel, and an input device such as a numeric keypad. The control unit 170 can notify the user of paper jams and receive instructions from the user (for example, instructions for mode selection or input of sheet material, etc.) via the operation unit 210.

[0052] The control unit 170 controls the feeding unit 110, the image forming unit 920, the pre-fixing transport unit 904, and the fixing device 50 to perform image forming operations according to the image forming job sent from an external device. In addition, when no image forming job is fed, the control unit 170 controls the preheating and idle rotation of the pre-fixing transport unit 904, which will be described later.

[0053] (Uneven gloss after preheating) Next, we will explain, using Figures 4 and 5, the case in which uneven gloss occurs when an image forming job is submitted after the image forming apparatus 100 has entered standby mode.

[0054] First, using Figure 4, we will explain the preheating of the fixing device 50 and the local temperature rise of the second conveyor belt 21 (hereinafter simply referred to as conveyor belt 21) that occurs after preheating. "Preheating" refers to the preliminary heating of the fixing device to a predetermined temperature before the image forming apparatus accepts an image forming job. Preheating is performed as part of a series of preliminary operations (also called an initial sequence or pre-multi-turns) to put the image forming apparatus into a standby state, such as when the power to the image forming apparatus is turned on or after the door is opened and closed for jamming.

[0055] The standby state refers to the state of the image forming apparatus 100 (and the corresponding state of the control unit 170) that is ready to start image forming operations and is waiting for the input of an image forming job. In addition to preheating the fixing unit 50, the initial sequence also involves forming patch images at each station 200Y~200K of the image forming unit 920 to adjust the density, and rotating the photosensitive drum 120 to clean the surface.

[0056] In contrast to the preheating performed during the initial sequence, during the preparation operation (pre-rotation) from the input of the image forming job until the actual fixing of the toner image begins, the control unit 170 raises the fixing device 50 to a target temperature (fixing temperature) suitable for fixing the toner image. The target temperature (preheating temperature) of the fixing device 50 during preheating may be lower than the target temperature (fixing temperature) when the fixing device 50 is heated to fix the toner image to the sheet during the execution of the image forming job.

[0057] After the initial sequence is completed, the control unit 170 enters a standby state, ready to start image forming operations and waiting for the input of an image forming job. The control unit 170 also enters a standby state if no next image forming job has been input when the previous image forming job has finished. While in standby state, the control unit 170 can control the heat generation of the heater 51 to maintain the fixing device 50 at the preheat temperature based on the detection signal from the first temperature sensor 70.

[0058] In standby mode, the fixing device 50 is preheated. As a result, the portion of the conveyor belt 21 closest to the fixing device 50 is heated by radiant heat from the fixing device 50, while the rest of the conveyor belt approaches the ambient temperature of the environment in which the image forming apparatus 100 is installed. If the standby state continues for a long time, the difference between the surface temperature of the conveyor belt 21 near the fixing device 50 and the surface temperature of the rest of the conveyor belt 21 widens. For example, the surface temperature of the conveyor belt 21 near the fixing device 50 may exceed 60°C, while the surface temperature of a portion far from the fixing device 50 may be around 30°C.

[0059] Figure 4 shows the results of measuring the surface temperature of the conveyor belt 21 at a predetermined detection position St (Figure 2) using a surface thermometer when an image forming job is started after the image forming apparatus 100 has entered standby mode and the drive of the conveyor belt 21 has begun. In Figure 4, the horizontal axis t [s] indicates the elapsed time after the job has started, and the vertical axis T [°C] indicates the measured surface temperature of the conveyor belt 21.

[0060] Figure 4 shows the measurement results when the drive of the conveyor belt 21 was stopped in standby mode. As described above, when the conveyor belt 21 was driven while a surface temperature difference occurred in the circumferential direction of the conveyor belt 21 during standby, periodic peaks appeared in the surface temperature change measured at detection position St. Here, T0 is the surface temperature of the conveyor belt 21 at job start, T1 is the first peak temperature, and Ti (i=2~5) is the 2nd to 5th peak temperature. ts indicates the section in which the sheet S passes through detection position St, and ΔT represents the difference between the highest (peak temperature) and lowest values ​​of the surface temperature while the first sheet S passes through detection position St.

[0061] In this situation, the sheet S being transported in each section ts is transported with a portion of the sheet in contact with the high-temperature portion of the transport belt 21. The toner image in the area where the sheet S was in contact with the high-temperature portion of the transport belt 21 is preheated by the heat transmitted from the transport belt 21 before entering the fixing nip Nf. As a result, the glossiness of the toner image after fixing is higher compared to the toner image in other areas. Consequently, uneven gloss occurs in the part of the finished product corresponding to the high-temperature portion of the transport belt 21. In other words, when ΔTs is large, uneven gloss is more likely to occur. Also, the higher the peak temperature Ti, the more likely uneven gloss is to occur.

[0062] Figure 5(a) illustrates the gloss unevenness that appears in the finished product. Figure 5(b) is a perspective view of the pre-fixing transport section 904. Here, we illustrate a case where gloss unevenness is more likely to become apparent when a halftone image is formed on the entire surface of the sheet S.

[0063] In Figure 5(b), the high-temperature portion 21H of the conveyor belt 21, heated by radiant heat from the fixing device 50, is shown by a dashed line. In Figure 5(a), the area of ​​the sheet S that was in contact with the high-temperature portion 21H of the conveyor belt 21 is shown by a dashed line. In Figure 5(a), visible unevenness in gloss, resembling a belt mark, is present in the portion that was in contact with the high-temperature portion 21H of the conveyor belt 21.

[0064] As shown in Figure 4, the peak temperatures T2 to T5 decrease over time after the start of the image formation job, and the difference ΔTs between the highest and lowest surface temperatures in the section ts where the sheet S is transported also decreases. Therefore, gloss unevenness is more likely to occur in the product immediately after the start of the image formation job, but it gradually becomes less noticeable.

[0065] (Idle rotation of the conveyor belt) To reduce the possibility of the aforementioned uneven gloss occurring, it is effective to allow the conveyor belt that receives radiant heat from the fixing device 50 to rotate idle during at least one of the following: (1) during the preheating of the fixing device 50, and (2) in the standby state of the image forming apparatus 100 after preheating. In this embodiment, during both the preheating of the fixing device 50 and in the standby state, the conveyor belt (second conveyor belt 21) of the two conveyor belts 11 and 21 that is closer to the fixing device 50 is allowed to rotate idle.

[0066] Here, "idle rotation of the conveyor belt" means rotating the conveyor belt when not image forming. Non-image forming time refers to any period other than the period during which an image forming job is performed on the sheet (image forming time). An image forming job generally includes a pre-rotation process (preparation operation before image forming), an image forming process, and a post-rotation process (cleaning operation after image forming). In the pre-rotation process, various voltages used for image forming are started up. In the image forming process, as described above, the sheet is transported while the image is transferred and fixed onto the sheet. Non-image forming time includes not only the pre-rotation and post-rotation processes, but also periods when no image forming job is performed, such as standby or sleep states, and the execution period of the initial sequence after power-on.

[0067] Fig. 6 shows the change in the surface temperature of the conveyance belt 21 when the conveyance belt 21 is idled after preheating. The method for measuring the surface temperature is the same as that described using Fig. 4.

[0068] As shown in Fig. 6, even when the standby state of the image forming apparatus 100 continues with the fixing device 50 preheated, by idling the conveyance belt 21, its surface temperature converges to a constant temperature, and the temperature distribution in the circumferential direction approaches uniformity. That is, the fluctuation width ΔT of the surface temperature for each period in which the conveyance belt 21 makes one rotation is maximum (ΔT0) in the first period, and then decreases with the passage of time (ΔT0 > ΔTa > ΔTb. However, 0 < ta < tb). Here, ΔT is the difference between the highest value and the lowest value of the surface temperature of the conveyance belt 21 measured at the detection position St (Fig. 2) during the period in which the conveyance belt 21 makes one rotation. Also, the peak temperature of the surface temperature also decreases with the passage of time stomach <(Tamx > Tbmx).

[0069] If the fluctuation width ΔT of the surface temperature becomes sufficiently small (for example, ΔT ≤ 6°C) by the time the first sheet S reaches the conveyance belt 21 during the execution of an image forming job, as shown in Fig. 5, the occurrence of gloss unevenness due to the temperature difference in the circumferential direction of the conveyance belt 21 can be reduced. Also, the lower the peak temperature after the first sheet S reaches the conveyance belt 21, the less likely gloss unevenness is to occur. Therefore, it is preferable to continuously idle the conveyance belt 21 (rotation of the conveyance belt 21 performed during non-image formation) for a predetermined time or longer (for example, 60 seconds or longer).

[0070] (Flowchart) In this embodiment, the conveyance belt 21 is idled according to the flowchart shown in Fig. 7. Each of the following control steps is implemented by the CPU 171 (Fig. 3) of the control unit 170 executing a program while the power of the image forming apparatus 100 is ON.

[0071] When the power to the image forming apparatus 100 is turned on (S101:Y), the initial sequence is started and preheating of the fixing device 50 is performed (S102). If an event indicating that the door of the image forming apparatus 100 has been closed from an open state is detected (door close) (S101:Y), the initial sequence is also started and preheating of the fixing device 50 is performed (S102). In this embodiment, the conveyor belt 21 is rotated idle while preheating is being performed. That is, during the execution of the initial sequence, the control unit 170 rotates the conveyor belt 21 with the second drive motor 24 (driving means) in parallel with the supply of power to the heater 51 in the fixing device 50.

[0072] In this way, by rotating the conveyor belt 21 (idling) while the fixing device 50 is being preheated, it is possible to reduce the localized heating of the conveyor belt 21 due to radiant heat from the fixing device 50.

[0073] Here, the conveying speed (peripheral speed) of the conveyor belt 21 when it is idle does not need to be the same as the conveying speed (process speed) of the conveyor belt 21 when it is forming an image. In this embodiment, the conveying speed of the conveyor belt 21 when it is forming an image is 300 mm / s, while the conveying speed of the conveyor belt 21 when it is idle is set to 200 mm / s. That is, when the conveyor belt 21 is rotated during preheating, the peripheral speed of the conveyor belt 21 is slower than the peripheral speed of the conveyor belt 21 when it is performing the image forming operation. This reduces the generation of noise due to the idle rotation of the conveyor belt 21 and the decrease in durability of the drive system (second drive motor 24 and the drive transmission path from the motor to the conveyor belt 21).

[0074] Furthermore, setting the transport speed to slower than 200 mm / s sometimes resulted in the second drive motor 24 entering its resonance range, which actually increased noise and vibration. Therefore, to avoid this resonance range, the transport speed during idle rotation was set to 200 mm / s.

[0075] Furthermore, when the conveyor belt 21 is rotated idle, the upstream conveyor belt, the first conveyor belt 11, is not rotated idle. This reduces noise generation and deterioration of the drive system's durability caused by the idle rotation of the first conveyor belt 11.

[0076] When the fixing device 50 reaches the target temperature for preheating and the other processes of the initial sequence are completed (S103:Y), the control unit 170 enters a standby state (S104). Even in the standby state, the conveyor belt 21 continues to rotate idle. However, the first conveyor belt 11, which is the upstream conveyor belt, is not allowed to rotate idle.

[0077] In this way, by rotating the conveyor belt 21 (idle rotation) in the standby state, it is possible to reduce the localized heating of the conveyor belt 21 due to radiant heat from the fixing device 50.

[0078] When an image forming job is submitted in the standby state (S105:Y), the control unit 170 starts executing the image forming operation. If an image forming job is submitted before the end of the initial sequence, the control unit 170 starts executing the image forming job as soon as the initial sequence is completed. During the execution of the image forming job, the transport speed of the transport belt 21 is increased to the process speed (S106) and the drive of the first transport belt 11 is also started until the first sheet S in the job reaches the pre-fixing transport unit 904.

[0079] When the image forming job is completed (S107), the control unit 170 returns to standby mode (S104) and waits for the next job to be fed in while the conveyor belt 21 rotates idle.

[0080] Thus, according to this embodiment, the conveyor belt 21 is allowed to rotate idle during preheating and standby of the fixing device 50. This reduces the occurrence of uneven gloss caused by temperature differences in the circumferential direction of the conveyor belt 21.

[0081] In a specific case, when the initial sequence is executed after the power is turned on to the image forming apparatus 100, in this embodiment, the conveyor belt 21 is rotated idle in parallel with preheating, thus preventing a localized temperature rise in the conveyor belt 21. This reduces the occurrence of uneven gloss in the first job after power-on.

[0082] In another case, if the previous job was interrupted due to a conveying malfunction, a localized temperature rise in the conveyor belt 21 may occur due to radiant heat from the fixing device 50 during the period until jamming is performed. Even in this case, according to this embodiment, the conveyor belt 21 rotates idle during the initial sequence, thereby reducing the temperature difference in the circumferential direction of the conveyor belt 21 and reducing the occurrence of uneven gloss in the first job after power-on. Since the initial sequence usually takes more than one minute, the conveyor belt 21 will rotate idle for more than one minute after the door is closed. Therefore, the temperature difference in the circumferential direction of the conveyor belt 21 can be sufficiently reduced (for example, ΔT to 6°C or less).

[0083] In another case, if the conveyor belt 21 is stopped during the standby period between the completion of the previous job and the input of the next job, a localized temperature rise in the conveyor belt 21 may occur due to radiant heat from the fixing device 50. According to this embodiment, since the conveyor belt 21 is continuously rotated idle in the standby state, the occurrence of gloss unevenness in the next job can be reduced.

[0084] Furthermore, in the case of recording materials with a higher fixing temperature compared to general recording materials, gloss unevenness caused by temperature differences in the circumferential direction of the conveyor belt 21 may become more apparent. For example, in the case of coated paper or OHT (projector sheet), gloss unevenness caused by temperature differences in the circumferential direction of the conveyor belt 21 is more easily visible. According to this embodiment, even when using such recording materials, the occurrence of gloss unevenness can be reduced. [Examples]

[0085] An image forming apparatus according to another embodiment (Embodiment 2) will now be described. In this embodiment, it is possible to select a mode to prioritize either productivity or image quality, and the time (predetermined time) for the conveyor belt to rotate idle differs from that of Embodiment 1 depending on the mode. In addition, the configuration of the pre-fixing conveyor unit 904 in this embodiment differs from that of Embodiment 1. Hereinafter, elements denoted by the same reference numerals as in Embodiment 1 will have substantially the same configuration and operation as those described in Embodiment 1, and the parts that differ from Embodiment 1 will be described.

[0086] Figure 8(a) shows an example of gloss unevenness that appears in the finished product when using the pre-fixing transport unit 904 of this embodiment, and Figure 8(b) is a perspective view of the pre-fixing transport unit 904 according to this embodiment.

[0087] As shown in Figure 8(b), the pre-fixing transport section 904 of this embodiment is composed of a single transport unit 30. The transport unit 30 has a single transport belt 31 located in the center in the sheet width direction. Multiple holes are formed in the transport belt 31, and the sheet S is carried and transported by the suction force generated by an internal suction fan.

[0088] Even when using a transport unit 30 with such a configuration, if the image forming operation is performed while there is a temperature difference in the circumferential direction of the transport belt 31, uneven gloss may occur in a part of the sheet S that was in contact with the high-temperature region 31H of the transport belt 31 (Figure 8(a)).

[0089] Figure 9 is a flowchart showing the control method of the image forming apparatus according to this embodiment. The control unit 170 of this embodiment is configured to allow selection between a productivity priority mode (first mode) that prioritizes productivity when executing an image forming job, and an image quality priority mode (second mode) that prioritizes image quality compared to the productivity priority mode. The mode can be switched, for example, by the user operating the operation unit 210 or by operating the settings screen of a host computer connected to the image forming apparatus 100.

[0090] In image quality priority mode, the output of images with high gloss is required. Image quality priority mode is applied when forming images that are close to solid color across the entire surface, such as photographs, or when forming images on coated paper, etc. In productivity priority mode, the output is mainly required for text, and productivity is prioritized over gloss. The difference between image quality priority mode and productivity priority mode lies in which of the two modes is prioritized when forming images continuously on multiple types of sheets with different basis weights in mixed-load jobs.

[0091] As shown in Figure 9, in this embodiment, the lower limit of idle rotation time in productivity priority mode (30 seconds) is set shorter than the lower limit of idle rotation time in image quality priority mode (60 seconds) (S111~S113). That is, in productivity priority mode, the conveyor belt 21 is idled for at least 30 seconds during the initial sequence, so that gloss unevenness can be reduced and the increase in FPOT can be suppressed compared to when the conveyor belt 21 is not idled. On the other hand, in image quality priority mode, the conveyor belt 21 is idled for at least 60 seconds during the initial sequence, so that the temperature difference in the circumferential direction of the conveyor belt 21 can be further reduced, and gloss unevenness can be reduced more than in productivity priority mode.

[0092] In Figure 9, processes other than S111 to S113 are the same as in Example 1 (Figure 7).

[0093] Please note that the initial sequence may take more than 60 seconds. Therefore, regardless of whether productivity priority mode or image quality priority mode is selected, the initial sequence may end (S103:Y) after more than 60 seconds of idle rotation.

[0094] (modified version) As a variation, as shown in Figure 10, the conveyor belt 21 may be idled during the preparation operation after the image forming job is fed in (during the pre-rotation) (S110). In this case, the idle rotation of the conveyor belt 21 is started at least before the start of the image forming operation (start of feeding the first sheet), and productivity priority mode is enabled. mosquitoIt is preferable to ensure an idle rotation time (S111~S113) for the conveyor belt 21 depending on whether it is in image quality priority mode. In this modified example, the conveyor belt 21 may not be allowed to idle during preheating of the fixing device 50 and in standby mode.

[0095] According to this modified version, even if there is a temperature difference in the circumferential direction of the conveyor belt 21 at the time of job input, the temperature distribution gradually becomes uniform due to idle rotation during the previous rotation, thus reducing gloss unevenness as in the embodiment described above. Furthermore, by changing the idle rotation time (predetermined time) according to the mode, it is possible to achieve both productivity and image quality.

[0096] (Other examples) In the embodiments described above, a configuration was shown in which the sheet S is transported by being sucked onto a conveyor belt with numerous holes using the suction force of a suction fan, and in this case, the shape of the holes in the conveyor belt was reflected in the uneven gloss. However, even when using a conveyor belt without holes, uneven gloss may occur if a temperature difference occurs in the circumferential direction of the conveyor belt due to radiant heat from the fixing device. Therefore, this technology can also be applied to image forming apparatuses equipped with a conveyor belt that electrostatically attracts and transports the sheet S. Furthermore, it is not necessary for the entire conveyor belt to be positioned between the transfer unit and the fixing device; this technology can also be applied to image forming apparatuses equipped with a conveyor belt (transfer belt) that extends from the upstream side of the transfer unit beyond the transfer unit to the fixing device side.

[0097] In each of the embodiments described above, the airflow of the suction fan may be changed according to the material of the sheet S. For example, when using recording materials such as OHT film, coated paper, or synthetic paper (recording materials whose surface is formed of a synthetic resin material at least), gloss unevenness is more likely to occur compared to plain paper. Therefore, when using such recording materials, the airflow of the suction fan may be reduced compared to when using plain paper to suppress the temperature drop of the holes in the conveyor belt. This suppresses the temperature difference between the periphery of the holes and the rest of the surface of the conveyor belt, further reducing the occurrence of gloss unevenness.

[0098] In each of the embodiments described above, the fixing device 50 was preheated and the conveyor belt was allowed to rotate idle when entering the standby state. In the case of an image forming apparatus equipped with an energy-saving mode that consumes less power than the normal mode, the conveyor belt may not be allowed to rotate idle in the energy-saving mode. In the energy-saving mode, the fixing device 50 is not preheated, or at least the target temperature for preheating is set lower than that of the standby state in the normal mode. Therefore, by not allowing the conveyor belt to rotate idle, power consumption can be reduced and noise levels can be improved.

[0099] In the embodiments described above, a configuration was shown in which the conveyor belt continuously rotates idle during the initial sequence and in the standby state. The method of idle rotation of the conveyor belt is not limited to this, and for example, idle rotation and pauses may be repeated intermittently.

[0100] Furthermore, even if the conveyor belt is described as being allowed to rotate idle in each of the embodiments described above, the conveyor belt may not be allowed to rotate idle while, for example, the temperature detected by the temperature sensors (70, 71) of the fixing device 50 is below a predetermined threshold. This is because if the temperature of the fixing device 50 is not high, a localized temperature rise of the conveyor belt due to radiant heat is less likely to occur.

[0101] (Other embodiments) The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions. [Explanation of symbols]

[0102] 11…Upstream conveyor belt (first conveyor belt) / 21,31…Conveyor belts / 24…Driving means / 50…Fixing device / 130…Transfer unit (secondary transfer unit) / 170…Control means (control unit)

Claims

1. A transfer unit that transfers the toner image onto the sheet, A fixing device that heats the toner image transferred to the sheet to fix it to the sheet, A conveyor belt that transports the sheet from the transfer unit toward the fixing device, A driving means for driving the aforementioned conveyor belt, Control means for controlling the drive means, An image forming apparatus comprising, The control means, when waiting for an image forming job to be submitted in a state where the image forming operation can be started, performs preheating control to preheat the fixing device to a preheating temperature and maintain it at that preheating temperature, and when an image forming job is accepted, heats the fixing device to a fixing temperature higher than the preheating temperature. The control means rotates the conveyor belt by the drive means during the execution of the preheating control. An image forming apparatus characterized by the following:

2. The control means rotates the conveyor belt by the drive means during the period from when the preheating of the fixing device is started until the fixing device reaches the preheating temperature. The image forming apparatus according to feature 1.

3. The control means rotates the conveyor belt by the drive means during the period from when the fixing device reaches the preheating temperature until it accepts the image forming job. The image forming apparatus according to feature 1.

4. The control means rotates the conveyor belt by the drive means during the period from receiving the image forming job to starting the image forming operation. The image forming apparatus according to feature 1.

5. The control means is capable of selectively executing a plurality of image forming modes, and changes the length of time the conveyor belt is rotated during the period according to the image forming mode to be executed. The image forming apparatus according to feature 3 or 4.

6. The plurality of image forming modes include a productivity priority mode and an image quality priority mode, When the control means is executing the productivity priority mode, it shortens the time the conveyor belt is rotated during the period compared to when the image quality priority mode is executing. The image forming apparatus according to feature 5.

7. The control means is capable of selectively executing a plurality of image forming modes, including a normal mode and an energy-saving mode. When the energy-saving mode is executed, the control means (a) does not perform preheating of the fixing device, or sets the preheating temperature lower than when the normal mode is executed, and (b) further does not rotate the conveyor belt until the image forming job is accepted. The image forming apparatus according to feature 1.

8. The control means rotates the conveyor belt for at least 30 seconds while the preheating control is being performed. The image forming apparatus according to any one of claims 1 to 7.

9. Further comprising an upstream conveyor belt positioned upstream of the conveyor belt in the sheet conveying direction, which conveys the sheet from the transfer unit to the conveyor belt, The control means rotates the conveyor belt and does not rotate the upstream conveyor belt during the execution of the preheating control. The image forming apparatus according to any one of claims 1 to 8.

10. When the conveyor belt is rotated during the execution of the preheating control, the peripheral speed of the conveyor belt is slower than the peripheral speed of the conveyor belt during the execution of the image forming operation. The image forming apparatus according to any one of claims 1 to 9.

11. The control means starts the preheating control when the power to the image forming apparatus is turned on. The image forming apparatus according to any one of claims 1 to 10.

12. An opening / closing member that can be opened to expose a sheet transport path provided inside the image forming apparatus, The system further includes an opening / closing sensor for detecting the opening and closing of the opening / closing member, The control means starts the preheating control when it detects that the opening / closing member has been closed from an open state based on the detection signal of the opening / closing sensor. The image forming apparatus according to any one of claims 1 to 11.

13. The control means performs the preheating control during the period between the completion of the previous image forming job and the input of the next image forming job, and rotates the conveyor belt using the drive means. The image forming apparatus according to any one of claims 1 to 9.

14. When the rotation of the conveyor belt is started during non-image formation, the control means continues the rotation of the conveyor belt until the rotation time of the conveyor belt exceeds a predetermined time. The image forming apparatus according to any one of claims 1 to 13.

15. The conveyor belt has a plurality of holes, The system further includes a suction means for drawing air from the outside to the inside of the conveyor belt through the plurality of holes, so as to hold the sheet on the surface of the conveyor belt. The image forming apparatus according to any one of claims 1 to 14.

Images