JP4932327B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a digital multifunction machine.

  In recent years, toner images for each color component of yellow, magenta, cyan, and black are sequentially formed on a photosensitive drum, and these toner images are sequentially superimposed on the intermediate transfer belt and transferred to form a color toner image on the intermediate transfer belt. Then, this color toner image is transferred to a sheet. A rotary type image forming apparatus is known that forms a color image by fixing a color toner image onto a sheet with a fixing roller.

  In such a rotary image forming apparatus, it takes a certain time to form a four-color toner image on the intermediate transfer belt. Therefore, the sheet is conveyed to a registration roller disposed in front of the transfer position. After the primary paper feeding is completed, the paper is kept on standby until a predetermined transport standby time elapses.

  By the way, the fixing roller includes a heating roller having a heater and a pressure roller driven by the heating roller, and the color toner image transferred onto the paper is fixed by sandwiching the paper with both rollers. .

  Therefore, if the heater is always controlled to a constant temperature during the transport standby time, the heat from the heater moves to the pressure roller, and the pressure roller releases the heat, so the energy consumption of the heater increases, There is a problem that the temperature inside the image forming apparatus rises due to the heat released by the pressure roller.

  Therefore, a conventional image forming apparatus employs a method of turning off the heater during the conveyance waiting time and turning on the heater at the time of fixing, or a method of reducing the heater temperature and suppressing the amount of heat generated by the heater.

In Patent Document 1, when the temperature of the fixing roller is relatively low, the rotation speed of the fixing roller is set to low speed rotation. When the temperature of the fixing roller is relatively high, the rotation speed of the fixing roller is set to high speed rotation to form an image. Has been disclosed (Patent Document 1 paragraph [0055]).
JP 2003-255735 A

  However, in the method in which the heater is turned off during the conveyance standby time, it is necessary to quickly raise the temperature of the fixing roller to a predetermined fixing temperature. For this purpose, a high-performance heater must be used, which increases costs. There's a problem.

  In the method of lowering the heater temperature during the conveyance standby time, since the fixing roller is rotated at the paper conveyance speed, the heating roller has a larger total area in contact with the pressure roller, and more heat is applied to the pressure roller. Even if the heater temperature is increased after the paper standby time has elapsed, the temperature of the pressure roller cannot be set to a desired fixing temperature, and it becomes difficult to fix the toner image on the paper.

  Further, in the method of Patent Document 1, although description is made regarding the temperature control of the fixing roller, in the rotary image forming apparatus, the waiting time for conveyance until the color toner image is transferred to the intermediate transfer belt is taken into consideration. It is not described.

  An object of the present invention is to provide an image forming apparatus capable of fixing a good toner image on a sheet while suppressing energy consumption without using a high-performance heater.

An image forming apparatus according to the present invention is an image forming apparatus that forms a color image by a rotary development method, and includes conveying means for conveying a sheet at a predetermined first speed, and image data for each color component constituting the color image. In accordance with the image forming unit, a toner image for each color component is sequentially formed on the photosensitive drum and is sequentially transferred to an intermediate transfer belt to form a color toner image, a heating roller having a heater, and the heating roller. A color toner image is fixed to the sheet by conveying a sheet having a pressure roller and having the color toner image transferred by the intermediate transfer belt sandwiched between the heating roller and the pressure roller. And a fixing unit that causes the sheet to be conveyed to the intermediate transfer belt until a predetermined conveyance standby time for forming a color toner image on the intermediate transfer belt has elapsed. Conveying control means for controlling the rotation speed of the heating roller, and heater control means for controlling the heater so that the surface temperature of the heating roller maintains a predetermined fixing temperature at which a toner image can be fixed on paper. The transport control means rotates the heating roller at a predetermined second speed lower than the first speed during the transport standby time, and when the transport standby time has elapsed, The conveyance control unit is further rotated by a first speed, and the conveyance control unit further includes a sheet detection unit provided on a downstream side of the fixing unit to increase the second velocity as the conveyance standby time elapses. The conveyance control means is at least from when the paper detection means detects the trailing edge of the first paper, and the conveyance control means is at least from when the paper detection means detects the trailing edge of the first paper. Defined serial intermediate transfer belt to advance to the image writing signal for starting the exposure of the toner image of a color component of the second sheet conveyed next to the first sheet to be transferred to the last is output the time, characterized in that said conveyance waiting time for the previous SL second sheet.

  According to this configuration, the heater control means controls the heater so as to maintain a predetermined fixing temperature. The conveyance control unit rotates the heating roller at a second speed lower than the sheet conveyance speed during a conveyance standby time for waiting for conveyance of the sheet to the intermediate transfer belt until a color toner image is formed on the intermediate transfer belt. .

  As a result, the total area of contact between the heating roller and the pressure roller is reduced, and the heat taken away by the pressure roller is reduced. As a result, the energy consumption of the heater is reduced and energy saving can be achieved. The temperature rise in the machine can be suppressed. That is, when the heating roller is rotated at the first speed that is the sheet conveyance speed during the conveyance standby time, the total area of contact of the heating roller with the pressure roller increases. Increases, and the energy consumption of the heater increases. However, in the present invention, since the heating roller is rotated at the second speed lower than the sheet conveyance speed during the conveyance standby time, the energy consumption by the heater can be reduced.

Further, since the heating roller is rotated at the second speed during the conveyance standby time, the pressure roller is prevented from becoming low temperature, and when the conveyance standby time has elapsed, the heating roller is rotated at the first speed. Therefore, the temperature of the pressure roller can be raised to the fixing temperature at the time of image fixing, the toner image can be reliably fixed on the paper, and a good color image can be formed.
In addition, according to this configuration, as the conveyance waiting time elapses, the total area of contact between the heating roller and the pressure roller increases, and the amount of heat transferred to the pressure roller increases. The temperature of the heating roller can be raised to the fixing temperature more reliably.
Further, according to this configuration, the toner image of the color component that is finally transferred to the intermediate transfer belt after the trailing edge of the first sheet conveyed in front of the second sheet is detected by the sheet detecting unit is formed. Since the time until the start of printing is the conveyance standby time, the temperature of the pressure roller can be more reliably raised to the fixing temperature when the second sheet is fixed.

  According to this configuration, after the trailing edge of the first sheet conveyed before the second sheet is detected by the sheet detection unit, the formation of the toner image of the color component that is finally transferred to the intermediate transfer belt is started. Since the time until this is set as the conveyance standby time, the temperature of the pressure roller can be more reliably raised to the fixing temperature when the second sheet is fixed.

  According to the present invention, the heating roller is rotated at a second speed lower than the first speed, which is the paper conveyance speed, during the conveyance standby time, and when the conveyance standby time has elapsed, the heating roller is rotated at the first speed. Therefore, it is possible to fix a good toner image on the paper while saving energy without using a high-performance heater with a short start-up time.

  Embodiments of an image forming apparatus according to the present invention will be described below. FIG. 1 is a side view showing the internal structure of the image forming apparatus according to the present embodiment. In the direction indication by Y in FIG. 1, -Y indicates the front and + Y indicates the rear. The image forming apparatus shown in FIG. 1 is a printer. As shown in FIG. 1, the image forming apparatus feeds a sheet P stored as a bundle of sheets to an image forming unit 13 described later, and conveys the sheet P fed from the sheet feeding unit 12. An image forming unit 13 that transfers a toner image to the paper P, a fixing unit 14 that performs a fixing process on the toner image transferred to the paper P by the image forming unit 13, and a paper that has been subjected to a fixing process by the fixing unit 14 A discharge destination switching unit 15 that switches the discharge destination of P and a discharge unit 16 that discharges the paper P for which printing processing has been completed are mounted on the main body 11.

  The paper feeding unit 12 includes a paper cassette 121 that can store a plurality of paper P that is detachably attached to the lower part of the main body 11, and a manual feed tray 122 that is used when manually feeding the paper P. I have.

  Two pickup rollers 123 arranged side by side are provided at an upper position on the front side of the sheet cassette 121, and by driving these pickup rollers 123, the sheets P stored in the sheet cassette 121 are fed out one by one. A shaft center provided on the downstream side of 123 is sent out toward the image forming unit 13 via a large-diameter sheet feeding roller 124 extending in the left-right direction (a direction orthogonal to the sheet conveying direction).

  On the other hand, at the rear position of the manual feed tray 122, a manual feed roller 126 having an axial center extending in the left-right direction (a direction orthogonal to the paper transport direction) is provided, and the paper fed manually through the manual feed tray 122 is The manual feed roller 126 is driven to feed the image forming unit 13.

  The image forming unit 13 includes a photosensitive drum 131, a charging roller 132, an exposure device 133, a rotary developing device 20, a toner container 30, an intermediate transfer belt 134, a primary transfer roller 135, and a secondary transfer roller. 136, a roller cleaning device 137, and a belt cleaning device 138.

  The photosensitive drum 131 is for forming an electrostatic latent image on the peripheral surface and a toner image along the electrostatic latent image. In the central portion of the main body 11, the photosensitive drum 131 is formed in the left-right direction (a direction perpendicular to the paper surface of FIG. 1). ) Can be rotated around the axis extending to the center.

  The charging roller 132 is used to form a uniform charge on the peripheral surface of the photosensitive drum 131 by performing a charging process. The charging roller 132 is charged with a predetermined polarity on the peripheral surface by a high voltage applied from a power source (not shown). Since the peripheral surface of the charging roller 132 is in contact with the peripheral surface of the photosensitive drum 131, uniform charges are formed on the peripheral surface of the photosensitive drum 131.

  The exposure device 133 forms an electrostatic latent image on the circumferential surface of the photosensitive drum 131 to which a uniform charge is applied by the charging roller 132 by irradiating the circumferential surface of the photosensitive drum 131 with laser light based on image data.

  The exposure apparatus 133 irradiates a laser beam based on image data input from a computer (not shown), and forms an electrostatic latent image on the peripheral surface of the photosensitive drum 131 by the irradiation of the laser beam. To do. Toner from the rotary developing device 20 is supplied to the electrostatic latent image, a toner image is formed on the peripheral surface of the photosensitive drum 131, and the toner image is transferred to the intermediate transfer belt 134 that circulates.

  The rotary developing device 20 supplies toner to the peripheral surface of the photosensitive drum 131 on which the electrostatic latent image is formed by irradiation of laser light from the exposure device 133, thereby forming a toner image on the peripheral surface. The rotary developing device 20 is supplied with toner of each color from a plurality of toner containers 30 (black to yellow containers 30K, 30C, 30M, and 30Y).

  A toner image formed on the peripheral surface of the photosensitive drum 131 is transferred to the intermediate transfer belt 134, and a primary transfer roller 135 electrostatically peels off the toner image on the photosensitive drum 131 to remove the toner image from the intermediate transfer belt 134. Transfer to the surface.

  The secondary transfer roller 136 electrostatically peels off the toner image on the intermediate transfer belt 134 and transfers the toner image onto the paper P fed from the paper feeding unit 12.

  The roller cleaning device 137 cleans the peripheral surface of the photosensitive drum 131 after the transfer process to the intermediate transfer belt 134. The belt cleaning device 138 performs a cleaning process on the surface of the intermediate transfer belt 134 after the transfer process on the paper P.

  The rotary developing device 20 has a rotating frame body 21 formed in a circular shape in a side view (viewed from a direction orthogonal to the paper surface of FIG. 1), and 4 mounted on the rotating frame body 21 at an equal pitch in the circumferential direction. And two developing units 22 (22K, 22C, 22M, 22Y). The rotary frame 21 is pivotally supported at a position behind the photoconductive drum 131 so as to be rotatable around a frame shaft 211 arranged in parallel with the axis of the photoconductive drum 131 and at substantially the same height level. Yes. The rotating frame body 21 is equally divided into four sections in the circumferential direction by four partition plates 212 projecting in the radial direction from the frame body shaft 211, and a developing device 22 is mounted in each section. .

  The developing unit 22 includes a black developing unit 22K filled with black toner, a cyan developing unit 22C filled with cyan toner, a magenta developing unit 22M filled with magenta toner, and a yellow toner. There are four types of yellow developing device 22Y. When forming a toner image with yellow toner on the peripheral surface of the photosensitive drum 131, the yellow developing unit 22 </ b> Y is set to a position facing the photosensitive drum 131 by the rotation of the rotary frame 21 around the frame axis 211. In this state, the photosensitive drum 131 makes one turn, thereby forming a yellow toner image on the peripheral surface. This yellow toner image is immediately transferred to the rotating intermediate transfer belt 134.

  The magenta, cyan and black toner images are formed on the peripheral surface of the photosensitive drum 131 in the same manner as in yellow. The developing unit 22 filled with the target color toner is connected to the peripheral surface of the photosensitive drum 131. The toner images of the next color are sequentially transferred onto the peripheral surface of the photosensitive drum 131 from which the toner image has disappeared by the transfer process to the intermediate transfer belt 134. A color image is formed on the surface of the intermediate transfer belt 134 by appropriately synchronizing the rotation of the intermediate transfer belt 134 and the toner image forming operation of the photosensitive drum 131. This color image is transferred to the paper P fed from the paper supply unit 12 by the action of the secondary transfer roller 136, and color printing is performed on the paper P.

  A registration roller pair 125 is provided at a position immediately upstream of the secondary transfer roller 136, and the conveyance timing of the paper P sent from the paper supply unit 12 to the image forming unit 13 is adjusted by the registration roller pair 125. Is done. The color image on the intermediate transfer belt 134 is transferred to an appropriate position on the paper P by adjusting the conveyance timing by the registration roller pair 125. Further, a registration switch 700 for detecting whether or not the paper P is conveyed to the registration roller pair 125 is disposed on the upstream side in the vicinity of the registration roller pair 125. As the registration switch 700, a micro switch can be employed, which is turned on when the contact portion that contacts the paper P is in contact with the paper P, and is turned off when the contact portion does not contact the paper P. To do.

  The intermediate transfer belt 134 includes a primary transfer roller 135, an idle roller 134 c provided slightly behind the primary transfer roller 135, a drive roller 134 a provided slightly below the photosensitive drum 131, and a photosensitive roller. It is wound around a driving roller 134a and a driven roller 134b arranged opposite to the front position below the body drum 131.

  The driven roller 134b is urged in a direction away from the driving roller 134a by an urging force of an urging member 134d such as a coil spring, whereby the tension state of the intermediate transfer belt 134 is maintained. The secondary transfer roller 136 is disposed opposite to the drive roller 134a via the intermediate transfer belt 134 at a position directly below the drive roller 134a.

  A bias voltage for electrostatically peeling off the toner image on the intermediate transfer belt 134 is applied to the secondary transfer roller 136 from a power source (not shown). Accordingly, the toner image on the intermediate transfer belt 134 is transferred onto the paper P passing between the intermediate transfer belt 134 and the secondary transfer roller 136.

  A belt cleaning device 138 for cleaning the surface of the intermediate transfer belt 134 after the transfer process for the paper P is provided between the driving roller 134a and the idle roller 134c, and the belt cleaning device 138 performs a cleaning process. The intermediate transfer belt 134 that has been subjected to is directed to the photosensitive drum 131 in order to receive the next transfer process.

  The fixing unit 14 performs a fixing process on the transfer image transferred to the paper P by the image forming unit 13. The fixing unit 14 is disposed to face the heating roller 141 and the heating roller 141, and the peripheral surface thereof is the peripheral surface of the heating roller 141. And a pressure roller 142 to be pressed against. Then, the paper P that has been subjected to the transfer process by the intermediate transfer belt 134 in the image forming unit 13 is guided and fixed to the circumference of the intermediate transfer belt 134 while being sandwiched between the intermediate transfer belt 134 and the secondary transfer roller 136. The toner image is fixed on the paper P by being introduced into the section 14 and heated when passing between the heating roller 141 and the pressure roller 142.

  A discharge switch 800 for detecting the passage of the paper P is disposed on the downstream side in the vicinity of the fixing unit 14. As the discharge switch 800 (paper detection means), for example, a micro switch is adopted, which is turned on when the contact portion that contacts the paper P is in contact with the paper P, and the contact portion does not contact the paper P. Sometimes off.

  The paper P after the fixing process is led to the paper discharge conveyance path 101 by driving the first discharge roller pair 143, and is lifted to the paper discharge conveyance path 101 by the forward drive of the second discharge roller pair 102, and the paper discharge port 162 is discharged. The paper is discharged to a paper discharge tray 161 provided at the top of the main body 11.

  The discharge destination switching unit 15 is used when double-sided printing is performed on the paper P. The paper P once sent from the fixing unit 14 to the paper discharge conveyance path 101 after the one-side fixing process is completed. The image is returned again to the image forming unit 13 with the front and back reversed. The discharge destination switching unit 15 includes a return roller 151 disposed opposite to a lower end portion of the paper discharge conveyance path 101 so that a peripheral surface of the lower portion of the first discharge roller pair 143 comes into contact with each other, and the return roller 151. And a return conveyance path 152 extending from the lower part of the sheet to the upstream side (right side in FIG. 1) of the registration roller pair 125 through the fixing unit 14.

  When performing double-sided printing on the paper P, the paper P after the fixing process for which single-sided printing has been completed is led out to the paper discharge conveyance path 101 until the trailing edge passes through the first discharge roller pair 143, and the second printing is continued. The discharge roller pair 102 is reversely driven. In this way, the sheet P on which single-sided printing has been completed is guided by the drive of the return roller 151 and is sent back to the return conveyance path 152, and the reverse side is reversed through the return conveyance path 152 to the registration roller pair 125. Therefore, after that, the image forming unit 13 performs a printing process on the back side of the paper P.

  A return roller pair 153 is provided in front of the lower part of the registration roller pair 125 in the return conveyance path 152, and the sheet P moving on the return conveyance path 152 is driven to the registration roller pair 125 by driving the return roller pair 153. It is sure to be returned to the destination.

  FIG. 2 is a functional block diagram of the image forming apparatus shown in FIG. The image forming apparatus includes a conveying unit 200 (conveying unit), a fixing unit 300 (fixing unit), an intermediate transfer unit 400 (image forming unit), a toner image forming unit 500 (image forming unit), a control unit 600, a registration switch 700, And a discharge switch 800.

  The transport unit 200 includes a pickup roller 123, a paper feed roller 124, a registration roller pair 125, a second discharge roller pair 102, and the like shown in FIG. 1, and includes a paper feed clutch 201 that drives the pickup roller 123, and a paper feed roller 124. And a registration clutch 203 that drives the registration roller pair 125.

  The fixing unit 300 includes the fixing unit 14 shown in FIG. 1, and includes a fixing motor 301 that drives the heating roller 141, a temperature sensor 302 that is disposed in the vicinity of the heating roller 141, and measures the temperature of the surface of the heating roller 141. And a heater 303 for heating the heating roller 141. The fixing unit 300 fixes the color toner image onto the paper P by sandwiching and transporting the paper P onto which the color toner image has been transferred by the intermediate transfer unit 400 between the heating roller 141 and the pressure roller 142. Let Here, a stepping motor can be adopted as the fixing motor 301. Moreover, as the heater 303, an inexpensive heater having a relatively slow start-up time can be employed.

  The intermediate transfer unit 400 includes a drive roller 134a, a driven roller 134b, an intermediate transfer belt 134, and the like shown in FIG. 1, and includes an intermediate transfer clutch 401 that drives the drive roller 134a. The intermediate transfer unit 400 then sequentially transfers the magenta, cyan, black, and yellow toner images formed by the toner image forming unit 500 onto the intermediate transfer belt 134 under the control of the conveyance control unit 601. Then, the formed color toner image is transferred onto the paper P.

  The toner image forming unit 500 includes the exposure device 133, the photosensitive drum 131, the rotary developing device 20 and the like shown in FIG. 1, and generates a toner image for each color component according to image data for each color component constituting the color image. Sequentially formed on the photosensitive drum 131 and sequentially transferred to the intermediate transfer belt 134.

  The control unit 600 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and controls the entire image forming apparatus. In the present embodiment, the control unit 600 particularly includes the functions of a transport control unit 601, an exposure control unit 602, and a heater control unit 603. These functions are realized by the CPU executing a control program stored in the ROM.

  The conveyance control unit 601 performs on / off control of the paper feed clutch 201, the feed clutch 202, the registration clutch 203, the fixing motor 301, the intermediate transfer clutch 401, and the like based on detection results by the registration switch 700 and the discharge switch 800. The paper P is conveyed from the paper supply unit 12 to the paper discharge unit 16 at a predetermined paper conveyance speed (first speed). Here, after the conveyance control unit 601 starts conveyance of the paper P from the paper supply unit 12, the conveyance control unit 601 starts until the leading edge of the paper P reaches the leading edge of the registration roller pair 125 after the registration switch 700 detects the paper P. When a predetermined time has elapsed, the paper feed clutch 201 and the feed clutch 202 are turned off, and the conveyance of the paper P is stopped. The conveyance of the paper P to the registration roller pair 125 is called primary paper feeding.

  In addition, the conveyance control unit 601 detects a predetermined speed (second speed) at which the rotation speed of the heating roller 141 is lower than the paper conveyance speed from when the discharge switch 800 detects the trailing edge of the paper P until a predetermined conveyance standby time elapses. The fixing motor 301 is controlled such that The second speed is preferably a speed at which the temperature of the pressure roller 142 can return to the fixing temperature when the toner image is fixed. On the other hand, the conveyance control unit 601 controls the fixing motor 301 so that the rotation speed of the heating roller 141 becomes the sheet conveyance speed except during the conveyance standby time. Here, the conveyance standby time is determined in advance from when the discharge switch 800 detects the trailing edge of the first sheet P until the exposure control unit 602 outputs a yellow image writing signal for at least the second sheet. It is a fixed time.

  In addition, when the conveyance standby time has elapsed, the conveyance control unit 601 turns on the registration clutch 203 and starts feeding the paper P waiting on the registration roller pair 125. The conveyance of the paper P waiting on the registration roller pair 125 to the paper discharge unit 16 is called secondary paper feeding.

  The exposure control unit 602 controls the toner image forming unit 500 so that a toner image for each color component based on image data for each color component constituting one color image data is sequentially formed on the photosensitive drum 131. . Specifically, the exposure control unit 602 forms a toner image in the order of magenta, cyan, black, and yellow, and starts exposure of the magenta image data to the exposure device 133 when starting the formation of the magenta toner image. When starting the image writing signal for starting and forming the cyan toner image, the image writing signal for starting the exposure with the cyan image data is output to the exposure device 133, and the black toner image When the formation is started, an image writing signal for starting exposure with black image data is output to the exposure device 133, and when the formation of a yellow toner image is started, the exposure device 133 is supplied with yellow image data. An image writing signal for starting exposure is output.

  The exposure control unit 602 outputs a magenta image writing signal to the exposure device 133 when the primary paper feeding of the paper P is completed. By the time when the secondary paper feeding is started, the intermediate transfer unit 400 and the toner image forming unit 500 are controlled such that magenta, cyan, and black toner images are formed on the intermediate transfer belt 134.

  The heater control unit 603 feedback-controls the heater 303 so that the surface temperature of the heating roller 141 maintains a predetermined fixing temperature based on the detection result of the surface temperature of the heating roller 141 by the temperature sensor 302. . Here, the fixing temperature is a temperature at which the toner can be melted and the toner image can be fixed on the paper P.

  Next, the operation of the image forming apparatus will be described. FIG. 3 is a timing chart showing the operation of the image forming apparatus. FIG. 3A shows the timing at which the exposure control unit 602 outputs image write signals for magenta (M), cyan (C), black (BK), and yellow (Y) to the exposure device 133. FIG. 3B shows the on / off timing of the paper feed clutch 201 that drives the pickup roller 123, where the high level indicates off and the low level indicates on. FIG. 3C shows the on / off timing of the feed clutch 202 that drives the paper feed roller 124. The high level indicates off and the low level indicates on.

  FIG. 3D shows the on / off timing of the registration switch 700, where the high level indicates OFF and the low level indicates ON. FIG. 3E shows the on / off timing of the registration clutch 203 that drives the registration roller pair 125, where the high level indicates OFF and the low level indicates ON. FIG. 3F shows the on / off timing of the discharge switch 800, where the high level indicates off and the low level indicates on.

  FIG. 3G shows the rotation speed of the fixing motor 301. A high level indicates a predetermined speed (second speed: for example, 70% of the paper transport speed) lower than the paper transport speed, and a low level indicates the paper transport. Showing speed.

  First, at time T1, the conveyance control unit 601 turns on the registration clutch 203 and starts secondary feeding of the first sheet P. Here, the conveyance control unit 601 turns on the paper feed clutch 201 and the feed clutch 202, picks up the second paper P from the paper feed unit 12, and starts primary paper feeding of the second paper P. To do. At time T2, the conveyance control unit 601 passes the registration switch 700 at the rear end of the first sheet P, and the registration switch 700 is turned off. Therefore, at time T3 when a predetermined time has elapsed from time T2, the registration clutch 203 Turn off.

  At time T4, since the registration switch 700 detects the leading edge of the second sheet P and is turned on, the conveyance control unit 601 starts from time T4 until the leading edge of the second sheet P reaches the registration roller pair 125. At a time T5 when a predetermined time has elapsed, the paper feed clutch 201 and the feed clutch 202 are turned off, and the primary paper feed for the second paper P is ended. At this time, it is understood that the discharge switch 800 is on and the first sheet P is positioned on the discharge switch 800.

  When the time T4 elapses, the exposure control unit 602 outputs a magenta image writing signal to the exposure device 133 to start forming a magenta toner image on the photosensitive drum 131.

  At time T6, the trailing edge of the first sheet P passes through the discharge switch 800, and the discharge switch 800 is turned off. Therefore, the conveyance control unit 601 changes the rotation speed of the fixing motor 301 from the sheet conveyance speed to the sheet conveyance speed of 70. % Speed down. At this time, since the registration clutch 203 is turned off, it can be seen that the conveyance of the second sheet P is stopped at the position of the registration roller pair 125.

  At time T <b> 7, the exposure control unit 602 outputs a cyan toner image image writing signal to the exposure device 133 and causes the photosensitive drum 131 to start forming a cyan toner image. The conveyance control unit 601 forms a magenta toner image on the photosensitive drum 131 during a period from time T5 to time T7, and the magenta toner image is transferred to the intermediate transfer belt 134 and is transferred from the photosensitive drum 131. The intermediate transfer unit 400 and the toner image forming unit 500 are controlled so that the magenta toner image is erased.

  At time T <b> 8, the exposure control unit 602 outputs a black toner image image writing signal to the exposure device 133, and causes the photosensitive drum 131 to start forming a black toner image. The conveyance control unit 601 forms a cyan toner image on the photosensitive drum 131 during a period from time T7 to time T8, and the cyan toner image is transferred to the intermediate transfer belt 134 and is transferred from the photosensitive drum 131. The intermediate transfer unit 400 and the toner image forming unit 500 are controlled so that the cyan toner image is erased.

  At time T9 when the conveyance standby time I1 has elapsed from time T6, the conveyance control unit 601 turns on the registration clutch 203, starts secondary feeding of the second sheet P, and changes the rotation speed of the fixing motor 301. Increase the paper transport speed. At this time, the conveyance control unit 601 turns on the paper feed clutch 201 and the feed clutch 202 and starts primary feeding of the third paper P. Actually, the second sheet P waits from the time T5 when the primary paper feeding ends to the time T9 when the secondary paper feeding starts, but in this embodiment, from the time T6. The time until time T9 will be referred to as a transport standby time.

  At time T <b> 10, the exposure control unit 602 outputs a yellow toner image image writing signal to the exposure device 133, and starts forming a yellow toner image on the photosensitive drum 131. The conveyance control unit 601 forms a black toner image on the photosensitive drum 131 during the period from time T8 to time T10, and the black toner image is transferred to the intermediate transfer belt 134 and is transferred from the photosensitive drum 131. The intermediate transfer unit 400 and the toner image forming unit 500 are controlled so that the black toner image is erased.

  Accordingly, while the sheet P is waiting on the registration roller pair 125 in order to form magenta, cyan, and black toner images on the intermediate transfer belt 134, the heating roller 141 has a speed that is 70% of the sheet conveyance speed. Rotate with. Then, after the conveyance waiting time I1 has elapsed and the secondary paper feeding of the paper P has been started, the heating roller 141 moves the paper conveyance speed while the paper P to which the color toner image has been transferred reaches the heating roller 141. Will rotate.

  Therefore, the total area of contact between the heating roller 141 and the pressure roller 142 is reduced, and the amount of heat taken away by the pressure roller 142 is reduced. As a result, the energy consumption of the heater 303 is reduced, and energy saving can be achieved. At the same time, the temperature rise in the machine can be suppressed.

  4A and 4B are diagrams for explaining the effect of the image forming apparatus. FIG. 4A shows the temperature distribution of the heating roller 141 and the pressure roller 142 when the heating roller 141 is rotated at the sheet conveyance speed. ) Shows the temperature distribution of the heating roller 141 and the pressure roller 142 when the heating roller 141 is rotated at a speed lower than the paper conveyance speed. The circles radially indicated in the heating roller 141 and the pressure roller 142 indicate the temperature, and the darker the color, the higher the temperature.

  As shown in FIG. 4A, when the heating roller 141 is rotated at the paper conveyance speed, the total area of contact between the heating roller 141 and the pressure roller 142 increases. As a result, the heating roller 141 changes to the pressure roller 142. The amount of heat transferred increases. Here, the heater control unit 603 controls the heater 303 so that the surface temperature of the heating roller 141 becomes a constant temperature. As a result, energy consumption by the heater 303 increases. Further, since the amount of heat released from the pressure roller 142 increases, the temperature inside the machine also increases.

  On the other hand, as shown in FIG. 4B, when the heating roller 141 is rotated at a speed lower than the sheet conveyance speed, the total area of contact between the heating roller 141 and the pressure roller 142 decreases. The amount of heat transferred to the pressure roller 142 is reduced. As a result, even if the heater control unit 603 controls the heater 303 so that the temperature of the surface of the heating roller 141 is maintained at a constant temperature, the amount of heat consumed by the heater 303 is reduced, so that energy saving can be achieved. Become.

  Here, in order to reduce the movement of the amount of heat from the heating roller 141 to the pressure roller 142, it is conceivable to stop the rotation of the heating roller 141. In this case, the pressure roller 142 contacts the heating roller 141. Only the portions where the toner is applied become high temperature, and the other portions become low temperature, and the temperature of the pressure roller 142 becomes low as a whole, and it becomes difficult to melt the toner and fix the toner image on the paper P.

  In this image forming apparatus, the heating roller 141 is rotated at a speed that is 70% of the paper conveyance speed during the conveyance standby time I1, and when the conveyance standby time I1 has elapsed, the heating roller 141 is rotated at the paper conveyance speed, Since the temperature of the pressure roller 142 is prevented from becoming low, when the heating roller 141 fixes the color toner image on the paper P, the temperature of the entire surface of the pressure roller 142 is increased to the fixing temperature. The toner image can be fixed on the paper P.

  In other words, in this image forming apparatus, energy saving is achieved when the registration roller pair 125 waits for the paper P that has been primarily conveyed in order to form magenta, cyan, and black toner images on the intermediate transfer belt 134. Therefore, when the conveyance speed of the heating roller 141 is rotated at a speed lower than the paper conveyance speed (second speed) and the secondary conveyance of the paper P is started, heating is performed to increase the temperature of the pressure roller 142. The roller 141 is rotated at the paper transport speed (first speed). Therefore, it is possible to form a good image on the paper P while saving energy without using an expensive heater.

  The present invention can adopt the following aspects.

  (1) In the above embodiment, the toner images are formed in the order of magenta, cyan, black, and yellow. However, the present invention is not limited to this, and the toner images may be formed in other orders.

  (2) In the above embodiment, the heating roller 141 is rotated at 70% of the sheet conveyance speed during the conveyance standby time I1, but the present invention is not limited to this, and the sheet conveyance speed is 40% to 80%, 50% to It may be rotated at other speeds such as 60%. Further, as the time elapses in the conveyance waiting time I1, the speed of the heating roller 141 may be increased stepwise or continuously, and the heating roller 141 may be rotated to finally reach the sheet conveyance speed. When the speed of the heating roller 141 is increased stepwise, the conveyance standby time I1 is divided into two or three equal parts and divided into a plurality of periods, and in the first period, 50% of the sheet conveyance speed. In the next period, the heating roller 141 may be controlled so as to be 70% of the sheet conveyance speed.

  (3) Although the printer has been described in the above embodiment, the present invention is not limited to this, and the present image forming apparatus may be applied to a digital multifunction peripheral, a copying machine, a facsimile, or the like.

1 is a side view showing an internal structure of an image forming apparatus according to the present embodiment. FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus illustrated in FIG. 1. 3 is a timing chart showing the operation of the image forming apparatus. 4A and 4B are diagrams for explaining the effect of the image forming apparatus, in which FIG. 4A shows the temperature distribution of the heating roller and the pressure roller when the heating roller is rotated at the paper conveyance speed, and FIG. The temperature distribution of the heating roller and the pressure roller when rotated at a speed is shown.

Explanation of symbols

20 Rotating developing device 131 Photosensitive drum 133 Exposure device 134 Intermediate transfer belt 141 Heating roller 142 Pressure roller 200 Conveying unit 201 Feeding clutch 202 Feed clutch 203 Registration clutch 300 Fixing unit 301 Fixing motor 302 Temperature sensor 303 Heater 400 Intermediate transfer Unit 401 intermediate transfer clutch 500 toner image forming unit 600 control unit 601 transport control unit 602 exposure control unit 603 heater control unit 700 registration switch 800 discharge switch I1 transport standby time P paper

Claims (1)

An image forming apparatus for forming a color image by a rotary development method,
Conveying means for conveying the sheet at a predetermined first speed;
In accordance with image data for each color component constituting the color image, an image forming unit that sequentially forms a toner image for each color component on a photosensitive drum and sequentially transfers the image to an intermediate transfer belt to form a color toner image;
A heating roller having a heater and a pressure roller driven by the heating roller are provided, and a sheet on which a color toner image is transferred by the intermediate transfer belt is nipped between the heating roller and the pressure roller to be conveyed. Fixing means for fixing a color toner image to the paper;
A conveyance control unit that waits for conveyance of the sheet to the intermediate transfer belt and controls the rotation speed of the heating roller until a predetermined conveyance standby time for forming a color toner image on the intermediate transfer belt elapses;
Heater control means for controlling the heater so that the surface temperature of the heating roller maintains a predetermined fixing temperature at which a toner image can be fixed on a sheet;
The transport control means rotates the heating roller at a predetermined second speed lower than the first speed during the transport standby time, and when the transport standby time has elapsed, Rotate at speed,
The transport control means increases the second speed as the transport standby time elapses,
A paper detection unit provided on the downstream side of the fixing unit;
The conveyance control means is a second sheet conveyed next to the first sheet that is finally transferred to at least the intermediate transfer belt from when the sheet detection means detects the trailing edge of the first sheet. an image forming apparatus comprising an image writing signal for starting the exposure of the toner images of color components a predetermined time to output, and the transfer waiting time for the previous SL second sheet .

Images