JP4123147B2 - Image forming apparatus - Google Patents

Description

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

    An electrophotographic image forming apparatus uses, for example, a photosensitive drum as an image carrier, forms an electrostatic latent image on the surface, develops the electrostatic latent image, transfers the image to a sheet, and then develops the sheet. An image forming apparatus that fixes a formed image is known. In such an image forming apparatus, a preparatory operation is performed in advance before performing an image forming operation or a fixing operation on the photosensitive drum, and then a steady operation is performed to perform image formation. However, performing the preparatory operation more than necessary has problems in terms of wear of the photosensitive drum, toner consumption, and power consumption, and it is required to perform the preparatory operation as much as necessary.

For example, when the rotation speed of the scanner motor is started, the photosensitive drum is not irradiated with laser until the rotation speed is equal to or higher than a predetermined speed, and after the initialization of the photosensitive drum is finished, the fixing temperature reaches a predetermined temperature. The point that the conveyance of the paper is started is described. Also, in Patent Document 2, the roller surface temperature is detected after a predetermined time has elapsed from the start of rotation of the fixing roller, and either the time or the roller surface temperature is selected as the end condition of the warm-up rotation based on the detection result. The point which was made to do is indicated.
Japanese Patent Laid-Open No. 10-133136 JP-A-11-133802

  In the above-mentioned prior documents, preparation operations in individual operations such as an exposure operation and a fixing operation are proposed. However, the image forming operation and the fixing operation of the image forming apparatus are a series of highly combined operations, and are performed as a whole. A series of preparatory actions to be performed has not been studied.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can more efficiently perform a series of preparation operations related to image formation.

The image forming apparatus according to the present invention, by using the photosensitive drum, and image forming means for transferring the sheet to form a visible image on the photosensitive drum, a fixing roller the visible image transferred to the sheet fixing A fixing unit for driving, a driving unit for rotating the photosensitive drum and the fixing roller using a main motor, and controlling the driving unit, the image forming unit, and the fixing unit to form an image on a sheet. A control means, a fixing temperature detecting means for detecting a fixing temperature in the fixing means, and an in-apparatus temperature detecting means for detecting a temperature in the apparatus, wherein the control means receives the warm-up start signal at the timing Means for determining a driving start temperature, which is a fixing temperature for starting driving of the driving means, based on a detection signal output from the internal temperature detecting means; and output from the fixing temperature detecting means. That means for determining whether reaches the operation starting temperature based on the detection signal, and means for driving start control of the drive means when it is determined to reach the operation starting temperature, driving of the driving means And a drive stop control unit after a predetermined time has elapsed from the start . Furthermore, the control means determines the drive start temperature so as to have a negative correlation with the temperature detected by the apparatus temperature detection means.

  By having the configuration as described above, the drive start temperature that is the fixing temperature at which the drive of the drive unit is started based on the detection signal output from the internal temperature detection unit at the timing of receiving the signal related to the drive start of the drive unit. Therefore, the driving start temperature can be determined in association with the fixing temperature, and if the driving means starts driving when the fixing temperature reaches the driving start temperature, a series of preparatory operations for image formation are performed. It becomes possible to carry out efficiently.

  In the preparatory operation of the image forming apparatus, image formation cannot be performed unless the temperature of the fixing surface of the fixing unit reaches a predetermined temperature state that can be fixed. Although necessary, this preparatory operation greatly depends on the temperature state in the apparatus. That is, when the fixing unit is heated when the temperature in the apparatus is low, the gradient of the temperature rise is small, so it takes time for the preparation operation to reach a predetermined temperature state. Since the rising gradient becomes large, the preparation operation does not take much time.

  Therefore, the temperature transition of the preparatory operation of the fixing unit is predicted from the temperature data detected by the internal temperature detecting unit, and when the fixing temperature is reached, the driving unit is started to prepare for the image forming operation and the like. It is possible to determine whether or not the operation should be performed, and it is possible to perform control so that the preparatory operation such as the image forming operation is completed when the preparatory operation is completed when the fixing unit reaches a fixable temperature state.

  Further, when a warm-up start signal is received as a signal related to the drive start of the drive means, if the drive stop control is performed after a lapse of a predetermined time from the drive start of the drive means, preparation for an image forming operation or the like by the drive means in the warm-up operation By setting the time required for the operation to a certain time, a preparatory operation such as an image forming operation can be reliably performed.

  Further, if the driving start temperature is determined so as to have a negative correlation with the temperature detected by the apparatus internal temperature detection means, the gradient of the temperature rise of the fixing temperature is small when the apparatus internal temperature is low as described above. Therefore, the drive start temperature is set high to delay the drive start timing of the drive means, and conversely, when the apparatus internal temperature is high, the gradient of the temperature rise of the fixing temperature is large, so the drive start temperature is set low and the drive start We just need to advance the timing. Here, the negative correlation has such a relationship that the correlation between the temperature in the apparatus and the driving start temperature is set to a low level in contrast to the change in the temperature in the apparatus. Means that.

  Hereinafter, embodiments according to the present invention will be described in detail. The embodiments described below are preferable specific examples for carrying out the present invention, and thus various technical limitations are made. However, the present invention is particularly limited in the following description. Unless otherwise specified, the present invention is not limited to these forms.

  FIG. 1 is a schematic sectional view of the entire image forming apparatus according to the present invention. A document reading unit 2 is disposed in the upper part of the image forming apparatus 1, and a sheet feeding unit 3 and a recording unit 4 are disposed in the lower part from the bottom.

  In the document reading section 2, a document placed on a document tray 11 provided with a document cover 10 is transported to a position facing the reading means 5 by a document transport device 12 and a document reading operation is performed, and a document discharge tray. 13 is discharged. When reading a book or the like, the document cover 10 is rotated upward, a portion to be read such as a book is placed on the flat bed platen 14, and a reading operation is performed by the reading means. The above-described configuration is the same as that of a conventional document reading apparatus called a so-called ADF or flat bed type.

  In the paper feed unit 3, a paper feed cassette 15 is disposed, and a plurality of sheets of a predetermined size are stacked on the flapper 16. A pickup roller 17 is disposed at the end of the paper feed cassette 15 (the right end in FIG. 1). The flapper 16 is urged upward so that the upper surface of the stacked paper is pressed against the pickup roller 17. When the pickup roller 17 is rotationally driven in this state, the sheets are fed one by one to the sheet conveyance path by the frictional force.

  The fed paper is first conveyed to the recording unit 4 by a feed roller 18 and a press roller 19. In the recording unit 4, a developer 20, a rotating brush 21, a charger 22, a photosensitive drum 23, a transfer roller 24, and a laser scan unit (hereinafter abbreviated as “LSU”) 25 are used for recording on the conveyed paper. In addition, a fixing roller 26 is provided.

  The photosensitive drum 23 has a cylindrical shape, and a photoconductive film having a predetermined thickness is provided on the outer peripheral surface as a photosensitive member. The photosensitive drum 23 is rotationally driven by a main motor, and an image is formed on the surface thereof by the charger 22, the LSU 25, and the developing unit 20. The charging device 22 uses a charging roller, and acts to uniformly charge the outer peripheral surface of the photosensitive drum 23 by applying a charging voltage in contact with the surface of the photosensitive drum 23. A known charging brush may be used instead of the charging roller. The charged state of the photosensitive drum 23 means a state where electric charges are held on the surface of the photosensitive drum 23.

  The LSU 25 performs exposure by irradiating the uniformly charged surface of the photosensitive drum 23 with laser light generated by a laser. When irradiating the laser beam, the surface of the photosensitive drum 23 is scanned by an optical system such as a polygon mirror to form an electrostatic latent image according to the image information. The developing device 20 stores toner therein, and transfers the toner to the surface of the photosensitive drum 23 by the supply roller 27 and the developing roller 28 to visualize the electrostatic latent image formed on the surface. A developing voltage is applied to the developing roller 28, and the toner adhering to the surface of the developing roller 28 is moved by a potential difference between the charged charge on the surface of the photosensitive drum 23 and the developing voltage to form a toner image. .

  As the transfer roller 24, an electronic conductive roller or an ion conductive roller is mainly used, and in any case, the toner developed on the surface of the photosensitive drum 23 by the electric field attractive force when a high transfer voltage is applied. Move. When a sheet exists between the photosensitive drum 23 and the transfer roller 24, the toner is transferred to the sheet. When there is no sheet, the transfer roller 24 is in contact with the surface of the photosensitive drum 23. The toner transferred to the paper is removed of electric charge by a neutralizing brush (not shown).

  The rotary brush 21 is disposed on the downstream side of the transfer roller 24, and removes paper dust adhering to the surface by contacting the surface of the photosensitive drum 23, or removing toner remaining on the surface without being transferred. It acts to disperse on the surface of the photosensitive drum 23. A constant voltage is applied to the rotating brush 21 so that the residual toner is efficiently dispersed.

  The transferred toner image is nipped by the fixing roller 26 and the press roller 29 and heated and pressed to be fixed on the paper. A heater lamp is provided in the fixing roller 26 and heats the heater lamp by generating heat. The fixed sheet is nipped between the sheet discharge roller 30 and the press roller 31 and is carried out to the sheet discharge tray 32.

  In FIG. 1, a sheet conveyance path is indicated by a one-dot chain line from the sheet feeding unit 3 to the sheet discharge tray 32. A reversal conveyance unit 40 is detachably mounted on the side surface of the apparatus main body 1, and a paper carry-out port 41 and a paper carry-in port 42 are formed on the mounting side surface. In the transport unit 40, two pairs of transport rollers, a feed roller 43 and a press roller 44, and a feed roller 45 and a press roller 46, are arranged up and down. Then, as shown by a two-dot chain line in FIG. 1, the reverse conveyance path branches off from the sheet conveyance path between the paper discharge roller 30 and the fixing roller 26, and the two pairs of conveyance rollers 43 and 44, 45 and 46 The sheet is formed so as to pass through the sheet and to join the sheet conveyance path between the roller pairs 18 and 19 and the pickup roller 17.

  In the paper conveyance path, a paper detection sensor 33 is disposed between the paper discharge roller 30 and the fixing roller 26 of the recording unit 4, and the paper detection sensor 34 is also provided between the roller pairs 18 and 19 and the pickup roller 17. Is arranged. When recording on only one side of the sheet, the sheet is conveyed to the sheet conveyance path indicated by the alternate long and short dash line, and image formation is performed by appropriately controlling the operation based on the detection signals of the sheet detection sensors 33 and 34. When recording on one side, the single-sided recording paper is once discharged to the paper discharge tray 32, and when the rear end of the paper is detected by the paper detection sensor 33, the paper discharge roller 30 is rotated reversely to reverse the paper. It is controlled so as to be carried into the conveyance path. The sheet carried into the reverse conveyance path is again carried into the conveyance rollers 18 and 19 and conveyed through the sheet conveyance path, and recording is performed on the other side.

  FIG. 2 is an overall block diagram of the image forming apparatus. In this embodiment, a facsimile function and a copying function are provided. Specifically, the MPU 100 as a control means, the NCU 101 that performs communication control with the network, the MODEM 102 that performs facsimile communication control, the ROM 103 that stores programs, data RAM 104 for storing image information, image memory 105 for storing received or read image information, CODEC 106 for encoding or decoding image information, operation unit 107 for transmitting and receiving notification information such as input information and warning from an operator, A scanner 108 for reading image information and a printer interface 109 for receiving a print command from an external computer or the like are provided. These functional blocks are connected to each other by a data bus and an address bus, and are controlled by the MPU 100 as a whole. The information received by the facsimile, the information read by the scanner, and the information received together with the print command are transmitted to the recording unit controller 110 to form an image on the paper.

  FIG. 3 is a schematic diagram illustrating a circuit configuration in the recording unit 4. As described above, around the photosensitive drum 23, the charger 22, the LSU 25, the developing device 20, the transfer roller 24, and the rotating brush 21 are arranged in this order along the rotation direction.

  A charging voltage application circuit 50 is connected to the charger 22, and a positive charging voltage HVC is applied thereto. When the charging voltage application circuit 50 applies the charging voltage HVC to the charger 22 based on the control signal from the recording unit controller 110, the surface of the photosensitive drum 23 is uniformly charged to about + 900V. A recording signal based on image information is transmitted from the recording unit controller 110 to the LSU 25, and laser light is irradiated on the surface of the photosensitive drum 23 while being irradiated based on the recording signal, and the photosensitive drum 23 is uniformly charged. The exposed surface is exposed to form an electrostatic latent image corresponding to the image information. By being exposed, the surface potential of the photosensitive drum 23 becomes an exposure potential of about + 100V.

  A developing voltage application circuit 51 is connected to the supply roller 27, the developing roller 28, and the blade 35 in the developing device 20, and the developing voltage application circuit 51 applies a voltage to each based on a control signal from the recording unit controller 110. To do. A predetermined supply voltage (+300 V to +700 V) is applied to the supply roller 27 to supply the toner in the developing device 20 to the developing roller 28 while being positively charged. A predetermined developing voltage HVB (+300 V to +700 V) is applied to the developing roller 28, and the toner is transferred using the potential difference from the exposed portion while contacting the surface of the photosensitive drum 23. In addition, a predetermined bias voltage (+300 V to +700 V) is applied to the blade 35, and the layer thickness of the toner layer attached to the surface of the developing roller 28 is made uniform by being pressed against the surface of the developing roller 28 by an elastic force.

  A transfer voltage application circuit 52 is connected to the transfer roller 24, and the transfer voltage application circuit 52 applies a transfer voltage HVT (1700 V) to the transfer roller 24 based on a control signal from the recording unit controller 110, and the photosensitive drum. The toner image formed on the surface 23 is transferred onto a sheet by electric field attraction.

  A heater driving circuit 53 is connected to the fixing roller 26, and the heater driving circuit 53 operates based on a control signal from the recording unit controller 110 to cause the heater lamp in the fixing roller 26 to generate heat. A thermistor 54 is arranged in contact with the surface to detect the surface temperature of the fixing roller 26, and the recording unit controller 110 controls the heater drive circuit 53 based on the detection signal of the thermistor 54, and the surface of the fixing roller 53. The temperature is maintained at a predetermined temperature.

  A distributed voltage application circuit 55 is connected to the rotary brush 21, and the distributed voltage application circuit 55 applies the distributed voltage HVCL to the rotary brush 21 based on a control signal from the recording unit controller 110, so that the surface of the photosensitive drum 23 is exposed. Residual toner is efficiently dispersed.

  The recording unit controller 110 transmits a control signal to the main motor 56 and the sub motor 57 to perform drive control. The main motor 56 controls the pickup roller 17, the feed roller 18, the rotating brush 21, the photosensitive drum 23, the supply roller 27, the developing roller 28, the fixing roller 26, and the press roller 29 based on a control signal from the recording unit controller 110. Drive to rotate. Further, the paper discharge roller 30 is rotated in the direction of discharging the paper via the clutch by the rotational driving force from the main motor 56. The sub motor 57 rotates the feed rollers 43 and 45 based on a control signal from the recording unit controller 110, and rotates the paper discharge roller 30 in the direction of reversing and conveying the paper via the clutch.

  The recording unit controller 110 transmits control signals to the exhaust fan 58 and the intake fan 59 disposed in the apparatus to perform intake / exhaust control in the apparatus. The exhaust fan 58 discharges the air in the apparatus to the outside, and the intake fan 59 acts to take outside air into the apparatus.

  The transfer roller 24 is connected to a current value detection circuit 60 for detecting a current value flowing between the photosensitive drum 23 and a temperature detection sensor 61 and a humidity detection sensor 62 are provided in the apparatus. Has been. The detection signals of the current value detection circuit 60, the temperature detection sensor 61, and the humidity detection sensor 62 are transmitted to the recording unit controller 110. Based on these detection signals, the recording unit controller 110 determines an abnormal state such as a pinhole on the surface of the photosensitive drum 23 that causes a reduction in image quality.

  FIG. 4 is a process flow diagram relating to a preparatory operation in the warm-up process from when the apparatus is turned on to entering the standby state in the above-described embodiment, and FIG. 5 is a time chart in the warm-up process.

When the apparatus is turned on at time t ₀ , initialization processing is first performed (S 100), and initial setting of the apparatus is performed. After the initialization process, the recording unit controller 110 receives a detection signal related to the temperature inside the apparatus from the temperature detection sensor 61 (S101a), and performs a process of determining Temp1 which is the driving start temperature of the main motor 56 (S101b). Temp1 with respect to the temperature in the apparatus is stored in advance in the recording unit controller 110 as a data table. For example, as illustrated in FIG. 7, the change in the fixing temperature Temp (vertical axis) with respect to the elapsed time (horizontal axis) changes the gradient of the temperature rise when the apparatus internal temperature is different. In this example, with respect to three temperatures A, B, and C (assuming A <B <C) as the apparatus internal temperature, the gradient of the temperature increase increases as the apparatus internal temperature increases. As will be described later, since the driving time of the main motor 56 during the warm-up process is set to a fixed time by the timer T11, the time of the timer T11 is calculated backward from the time when the fixing temperature reaches Temp2 at each internal temperature. If the temperature at the time is determined as Temp1, when the fixing temperature reaches Temp2, a predetermined preparation operation is completed and the main motor 56 stops driving. Therefore, there is no extra preparatory operation (idle rotation of the main motor 56 or extra heat treatment to the fixing roller) as a whole, and an efficient preparatory operation can be performed. Further, as can be seen from FIG. 7, the set temperature of Temp1 is determined to be lower as the apparatus internal temperature is higher. Therefore, Temp1 may be obtained by a mathematical formula based on such a negative correlation.

  Simultaneously with such processing, a driving signal is transmitted to the heater driving circuit 53 to start heating the fixing roller 26 (S101c). A detection signal from the thermistor 54 that detects the surface temperature of the fixing roller is input to the recording unit controller 110, and the fixing roller temperature is constantly monitored, and control is performed to increase the temperature to the fixing roller temperature Temp2 at which the warm-up process ends.

It is checked whether or not the heating of the fixing roller 26 is started and the temperature of the fixing roller has increased to Temp1 (S102). When the fixing roller temperature at time t ₁ is to have reached the Temp1, pre-rotation process from time t ₁ (S103) is performed.

  In the pre-rotation process, the polygon motor that rotates the polygon mirror of the LSU 25 starts to rotate (S103a), and at the same time, the main motor 56 starts to rotate (S103b). As the main motor 56 rotates, the photosensitive drum 23, the supply roller 27, the developing roller 28, the transfer roller 24, and the rotating brush 21 are driven to rotate. Also, the timer T11 starts counting from the start of rotation of the main motor 56.

  In the pre-rotation process, the sub motor 57 starts to rotate (S103c), and the presence / absence of paper remaining in the reverse conveyance unit 40 is detected. As shown in the time chart, the auxiliary motor 57 is driven so as to first rotate in the forward direction while the timer T101 is counting, and then rotate in the reverse direction while the timer 102 is counting. The remaining paper is discharged to the paper discharge tray 32 by the rotation processing in the forward and reverse directions, or is detected by the paper detection sensor 34.

  In the pre-rotation process, rotation control of the exhaust fan 58 and the intake fan 59 is started (S103d). The rotation of the exhaust fan 58 is started and the warm air in the vicinity of the fixing roller is exhausted outside the apparatus, and the rotation of the intake fan 59 is started and the outside air is introduced into the vicinity of the power supply unit.

In the pre-rotation process, voltage control for performing a cleaning process on the photosensitive drum 23 is performed (S103e). The driving of the charging voltage application circuit 50 is started from the time t ₁ when the main motor 56 starts to rotate, and the charging voltage HVC is applied to the charger 22, and the surface of the photosensitive drum 23 is uniformly charged by the application of the charging voltage HVC. To go. Next, the developing voltage HVB is applied to the developing roller 28 at a timing when the surface of the photosensitive drum 23 charged by the charger 22 comes to a position where it contacts the developing roller 28 by rotation.

  The applied developing voltage HVB is initially set to a voltage (for example, +10 V) smaller than the developing voltage (for example, +400 V) at the time of image formation. When such a small voltage is applied, a large potential difference is generated between the charged surface of the photosensitive drum 23 and the developing roller 28, so that the toner remaining on the surface of the photosensitive drum 23 is efficiently collected by the developing roller 28. can do.

  Next, the transfer voltage HVT is applied to the transfer roller 24 at a timing when the surface area of the photosensitive drum 23 charged by the charger 22 comes to a position where it contacts the transfer roller 24 by rotation. The applied transfer voltage HVT is set to a positive transfer voltage (for example, +1000 V) having a polarity opposite to the transfer voltage (negative polarity) applied at the time of image formation, and is attached to the entire circumferential surface of the transfer roller 24. Residual toner is transferred to the surface of the photosensitive drum 23 due to a potential difference between the transfer roller 24 and the surface of the photosensitive drum 23.

  Next, the distributed voltage HVCL is applied to the rotating brush 21 at the timing when the surface of the photosensitive drum 23 charged by the charger 22 comes to a position where it contacts the rotating brush 21 by rotation. By applying the dispersion voltage HVCL, the adhesive force of the residual toner attached to the surface of the photosensitive drum 23 is weakened.

  In S104, it is checked whether the timer T11 has expired and the fixing roller temperature has increased to Temp2. If both conditions are satisfied, the main motor 56 is stopped (S105), and standby state control is performed. Migrate to

  In the above processing flow, the warm-up process when the power is turned on has been described, but the same applies to the case where the warm-up process is performed when an instruction is given by a user operation, when the cover is opened or closed, or when the sleep state is released.

  FIG. 7 shows a processing flow of the image forming process in the above-described embodiment, and FIG. 8 shows a time chart in the image forming process.

When receiving the signal for instructing the image forming process on the sheet at time t ₃ , the recording unit controller 110 receives the detection signal related to the temperature inside the apparatus from the temperature detection sensor 61 (S 200 a), at the driving start temperature of the main motor 56. A process of determining a certain Temp4 is performed (S200b). The value of Temp4 with respect to the temperature in the apparatus is stored in advance in the recording unit controller 110 as a data table in the same manner as Temp1 described above. Temp4 may be determined in the same manner as Temp1, but in this example, Temp4 is determined by back-calculating Temp4 so as to reach Temp6 in accordance with the output timing of the Ready signal indicating the completion of the preparation operation of LSU 25. .

  Simultaneously with such processing, a driving signal is transmitted to the heater driving circuit 53 to start heating the fixing roller 26 (S200c). A detection signal from the thermistor 54 that detects the surface temperature of the fixing roller 26 is input to the recording unit controller 110, and the fixing roller temperature is constantly monitored, and control is performed to increase the temperature to the fixing roller temperature Temp6 at which paper feeding is started. Is called.

It is checked whether the heating of the fixing roller 26 is started and the temperature of the fixing roller has increased to Temp4 (S201). When the fixing roller temperature at time t ₄ is to have reached the Temp4, pre-rotation process from time t ₄ (S202) is performed.

  In the pre-rotation process, the polygon motor that rotates the polygon mirror of the LSU 25 starts to rotate (S202a), and at the same time, the main motor 56 starts to rotate (S202b). As the main motor 56 rotates, the photosensitive drum 23, the supply roller 27, the developing roller 28, the transfer roller 24, and the rotating brush 21 start to rotate. At the same time, control of the fans 58 and 59 is also started (S202c). Then, voltage control similar to the warm-up process is started (S202d).

Been advanced pre-rotation processing as described above, the time up of the timer T14 which has started counting from the time t _4, the three conditions of the output and the fixing roller temperature Ready signal from LSU25 reaches Temp6 satisfied It is checked whether or not (S203). Here, the timer T14 is set so that the paper feed clutch that connects and disconnects the drive transmission from the main motor 56 to the pickup roller 17 is maintained in the OFF state. When the paper feed operation starts when the Ready signal output from the LSU 25 and the fixing roller temperature reach Temp6, the sheet is transferred to the photosensitive drum 23 and the transfer roller during the cleaning of the transfer roller 24 while the timer 42 is counting. 24, the toner may adhere to the paper and become contaminated. Therefore, the timer 14 is timed out earlier than the timer 42, thereby preventing such a trouble. .

When the three conditions in step S203 are satisfied at time t _5, the image formation processing is performed (S204). First, a sheet is conveyed from the sheet feeding cassette 15 (S204a). The paper feed clutch is turned on, the paper is carried in from the paper feed cassette 15, and the paper detection sensor 34 detects the front edge of the paper. When the paper detection sensor 34 is turned on, the timers T2 and T16 start counting, and the LSU 25 starts exposing the surface of the photosensitive drum 23 at the timing when the timer T2 expires. At the time when the timer T16 expires, the registration clutch is turned on, the paper is nipped and conveyed by the feed roller 18 and the press roller 19, and is carried between the photosensitive drum 23 and the transfer roller 24. Since the paper feed clutch is turned on at an earlier timing than the registration clutch, the front end of the fed paper is in contact with the feed roller 18 and the press roller 19 and is correct when the paper is skewed. Will be corrected.

  The toner image is transferred to the paper as the paper passes between the photosensitive drum 23 and the transfer roller 24, and is transferred as the paper passes between the fixing roller 26 and the press roller 29. The toner image thus fixed is fixed on the paper. When the front end of the sheet conveyed between the fixing roller 26 and the press roller 29 is detected by the sheet detection sensor 33, the sub motor 57 starts to rotate and the sheet discharge roller 30 rotates, and the sheet is discharged from the sheet discharge roller 30. The paper is sandwiched between the press rollers 31 and carried out to the paper discharge tray 32.

  When the trailing edge of the paper passes the paper detection sensor 34, the detection output of the paper detection sensor 34 is turned off, and the timer T17 starts counting at that timing. The registration clutch is turned off when the timer T17 expires. The timer T17 is set longer than the time required for the trailing edge of the sheet to be conveyed from the position of the sheet detection sensor 34 to the position of the feed roller 18 and the press roller 19. Further, when the trailing edge of the paper passes the paper detection sensor 33, the detection output of the paper detection sensor 33 is turned off, the timer 105 starts counting at that timing, and the timer T105 reaches the time-up timing of the sub motor 57. The rotation stops and the paper discharge operation by the paper discharge roller 30 stops. The timer T105 is set to a sufficient time that is longer than the time necessary for the paper detection sensor 33 to pass through the rear end of the paper and eject it.

  In step 204, voltage control for image formation is started together with sheet conveyance control (S204b). The charging voltage HVC is applied to the charger 22 to uniformly charge the surface of the photosensitive drum 23, and the developing voltage HVB is applied to the developing roller 28 for the electrostatic latent image formed by the exposure control of the LSU 25. Thus, the electrostatic latent image is developed with toner. Then, a transfer voltage HVT is applied to the transfer roller 24 to transfer the toner image formed on the surface of the photosensitive drum 23 onto a sheet. The charging voltage HVC and the dispersion voltage HVCL are maintained at a constant voltage during image formation.

  When the image forming process is completed, a post-rotation process is performed (S205). In the post-rotation process, a small voltage is applied to the transfer roller as the transfer voltage HVT to reduce the load on the transfer roller 24 due to a rapid voltage change, and then the transfer voltage 24 is controlled by controlling the transfer voltage HVT and the development voltage HVB. The residual toner adhering to the toner is collected. The rotation of the main motor 56 is stopped at a predetermined timing after the post-rotation process (S206).

It is a schematic sectional drawing which shows the whole structure regarding embodiment which concerns on this invention. It is a whole block diagram regarding the embodiment concerning the present invention. It is a principal part circuit block diagram regarding embodiment which concerns on this invention. It is a warm-up process flowchart of embodiment which concerns on this invention. It is a time chart figure at the time of the warming-up process of embodiment which concerns on this invention. FIG. 6 is a diagram for explaining a change in fixing temperature with respect to an apparatus internal temperature. It is an image formation processing flowchart of embodiment which concerns on this invention. It is a time chart figure at the time of image formation processing of an embodiment concerning the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Apparatus main body 2 Original reading part 3 Paper feed part 4 Recording part 5 Reading means

Claims (2)

Using the photosensitive drum, and image forming means for transferring to form a visible image on the sheet on the photosensitive drum, a fixing unit for fixing with a fixing roller the visible image transferred to the sheet, the main motor Driving means for rotating the photosensitive drum and the fixing roller, control means for controlling the driving means, the image forming means and the fixing means to form an image on a sheet, and fixing in the fixing means A fixing temperature detecting means for detecting the temperature and an in-apparatus temperature detecting means for detecting the temperature in the apparatus;
The control means determines a driving start temperature, which is a fixing temperature at which driving of the driving means is started based on a detection signal output from the apparatus temperature detection means at a timing of receiving a warm-up start signal , and the fixing Means for determining whether or not the drive start temperature has been reached based on a detection signal output from the temperature detection means; and means for performing drive start control of the drive means when it is determined that the drive start temperature has been reached. An image forming apparatus comprising: a drive stop control unit after a predetermined time has elapsed from the start of driving of the drive unit. The image forming apparatus according to claim 1, wherein the control unit determines the drive start temperature so as to have a negative correlation with the temperature detected by the apparatus temperature detection unit.

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