JP2009115953A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of recovering the fixability of a toner image transferred to a paper surface by increasing the temperature of a fixing section which heats paper, when the fixability of the toner image transferred to the paper surface decreases. <P>SOLUTION: The image forming apparatus 1 includes a transfer roller 25, a fixing unit 30, a control section 60, and measuring sections including a slide-contact conveying roller pair 40, a second density measuring section 43 and a first density measuring section 44. The transfer roller 25 transfers a toner image to paper P. The fixing unit 30 heats paper P passed through the transfer roller 25. The measuring sections measure the fixability of a toner image transferred to the surface of paper P conveyed from the fixing unit 30. The control section 60 controls the temperature of the fixing unit 30 based on the measurement results of the measuring sections. When the measurement value is lower than a given measurement value, the temperature of the fixing unit 30 is increased to a predetermined temperature. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that performs electrophotographic image formation.

  An electrophotographic image forming apparatus includes a fixing unit designed to reliably fix a toner image transferred onto the surface of a sheet under normal use conditions. However, when it is used in an ambient temperature lower than that assumed in advance as the design specification of the image forming apparatus, or when it is used in a state where the supplied voltage is insufficient and a predetermined voltage is not supplied There is also. In such a case, there is a problem that the temperature of the fixing unit is lowered and the fixability of the toner image transferred to the paper surface is lowered.

Therefore, some conventional image forming apparatuses rub the toner image transferred on the surface of the paper with a constant pressure, and stop printing when the density value of the printed portion after the friction is below a certain value. There is also a thing (refer patent document 1).
Japanese Patent Laid-Open No. 5-323807

  However, the image forming apparatus disclosed in Patent Document 1 has a problem in that it takes time to restore because the printing is stopped when the fixability of the toner image transferred to the paper surface is reduced.

  Therefore, in the present invention, when the fixability of the toner image transferred to the paper surface is lowered, the fixability of the toner image transferred to the paper surface can be recovered by increasing the temperature of the fixing unit that heats the paper. It is an object of the present invention to provide an image forming apparatus that can be used.

  The image forming apparatus according to the present invention includes a transfer unit, a fixing unit, a measurement unit, and a control unit. The transfer unit transfers the toner image to the surface of the paper. The fixing unit heats the sheet that has passed through the transfer unit. The measurement unit measures the fixability of the toner image transferred to the surface of the paper conveyed from the fixing unit. The control unit controls the temperature of the fixing unit based on the measurement result in the measurement unit. The control unit raises the temperature of the fixing unit to a predetermined temperature when the measurement value measured by the measurement unit is lower than the predetermined measurement value.

  In this configuration, when the measurement value measured by the measurement unit is lower than the predetermined measurement value, the temperature of the fixing unit is increased to the predetermined temperature. Therefore, when the fixability of the toner image transferred to the surface of the paper is low, the fixing temperature of the toner image transferred to the paper surface can be improved by increasing the temperature at which the paper is heated in the fixing unit. .

  In this configuration, the measuring unit measures the density of the slidable conveying roller pair that conveys the sheet conveyed from the fixing unit while rubbing the toner image transferred to the surface of the sheet that has passed through the slidable conveying roller pair. The control unit may include one density measurement unit, and when the density measured by the first density measurement unit is lower than a predetermined density, the temperature of the fixing unit may be increased to a predetermined temperature.

  In this configuration, when the density of the surface of the paper rubbed by the sliding contact conveyance roller pair is lower than a predetermined density, the temperature of the fixing unit is raised to a predetermined temperature. Therefore, when the density of the toner image transferred to the surface of the paper is lower than a predetermined density, the fixing temperature of the toner image transferred to the paper surface is improved by increasing the temperature at which the paper is heated in the fixing unit. Can be made.

  In this configuration, the control unit also controls the sheet conveyance in the conveyance direction passing through the transfer unit, the fixing unit, and the sliding contact conveyance roller pair in this order, and the transfer is performed on the surface of the sheet measured by the first density measurement unit. When the density of the toner image is lower than the predetermined density, the conveyance of the paper may be stopped, and the conveyance of the paper may be resumed after the temperature of the fixing unit rises to a predetermined temperature. As a result, when the density on the surface of the sheet is lower than the predetermined density, the conveyance of the sheet can be stopped and the conveyance of the sheet can be resumed after the temperature of the fixing unit rises to a predetermined temperature.

  The measurement unit may further include a second density measurement unit that is disposed between the fixing unit and the sliding contact conveyance roller pair and measures the density of the toner image transferred to the surface of the paper. The control unit may control the temperature of the fixing unit based on a difference in density of the toner image transferred to the surface of the paper measured by the first density measuring unit and the second density measuring unit. As a result, the fixability of the toner image transferred to the paper surface can be determined based on the difference in density on the paper surface before and after passing through the sliding contact conveyance roller pair.

  The sliding contact roller pair includes a transport roller that rotates in the direction of transporting along the paper transport direction, and a slide roller that rotates in the same direction as the transport roller and rubs the paper. You may further provide the spring member urged | biased toward a roller. As a result, the surface of the paper can be rubbed by rotating in the direction opposite to the paper transport direction while urging the sliding contact roller toward the transport roller.

  Further, the fixing unit may include a transport roller that transports the paper and a heater that heats the transport roller. The control unit performs on / off control of the power supplied to the heater at a predetermined duty ratio, and when the density of the toner image transferred to the surface of the paper measured by the first density measurement unit is lower than the predetermined density The duty ratio may be changed so that the ON time becomes longer. Thereby, the temperature of the conveyance roller can be raised by increasing the power to be supplied and raising the temperature of the heater.

  The density measuring unit may measure the density of the test pattern formed on the surface of the paper. Accordingly, it is possible to determine whether or not the fixing property of the toner image transferred to the surface of the sheet is deteriorated with reference to the density of the test pattern.

  According to the present invention, when the fixability of the toner image transferred to the paper surface decreases, the fixing temperature of the toner image transferred to the paper surface can be recovered by increasing the heating temperature of the paper in the fixing unit. it can.

  An image forming apparatus 1 according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram schematically illustrating an overall configuration of the image forming apparatus 1 in a side view.

  The image forming apparatus 1 includes an image reading unit 10, a printing unit 20, a fixing unit (fixing unit) 30, a sliding contact roller pair (measurement unit) 40, a second density measurement unit (measurement unit) 43, and a first density measurement unit. A (measurement unit) 44, a sheet feeding unit 50, and a control unit 60 are provided, and a toner image is transferred to the sheet P to perform a printing process. The image forming apparatus 1 also includes an image memory M (see FIG. 2) formed by a storage device such as a RAM (not shown).

  The image reading unit 10 is disposed above the printing unit 20 and includes a document table 11 having an upper surface formed of a transparent glass body and a plurality of documents set on a document set tray one by one. And an exposure unit 13.

  The exposure unit 13 includes a scanning unit, a light source lamp, an optical lens, a CCD line sensor, and the like, and scans and reads a document placed on the document table 11.

  The sheet feeding unit 50 includes sheet feeding trays 51 to 53 disposed below the developing unit 24, a conveying roller that feeds the sheet P from the sheet feeding trays 51 to 53, and each conveying path corresponding to the sheet feeding trays 51 to 53. Are provided with a plurality of conveying roller pairs, and the like.

  The control unit 60 controls the document reading device 10, the printing unit 20, the fixing unit 30, the sliding contact conveyance roller pair 40, the second density measuring unit 43, the first density measuring unit 44, and the paper feeding unit 50.

  Here, a transport method for transporting the paper P from the paper feed tray 51 to the photosensitive drum 22 along the transport path A will be specifically described.

  The paper P is set in a predetermined position on the paper feed tray 51 in a stacked state, and is fed downstream one by one by a feed roller mechanism 51A disposed in the vicinity of the paper feed tray 51. Then, after finely adjusting the conveying position by the registration roller pair 55, the toner image is placed on the printing surface of the paper P facing the photosensitive drum 22 by being sandwiched in the gap between the downstream photosensitive drum 22 and the transfer roller 25. Is transcribed.

  The printing unit 20 includes a photosensitive drum 22, a charger 23, a laser scan unit LSU, a developing unit 24, a transfer roller 25, and a cleaner 26.

  The photosensitive drum 22 and the transfer roller 25 rotate in a direction along the conveyance direction of the sheet P, and the sheet P conveyed from the sheet feeding unit 50 located on the upstream side of the conveyance path of the sheet P on the downstream side. It is nipped and conveyed to the fixing unit 30.

  The cleaner 26 is disposed immediately downstream of the transfer roller 25 in the rotation direction of the photosensitive drum 22 and collects toner and the like remaining on the surface of the photosensitive drum 22.

  The charger 23 is located on the downstream side of the cleaner 26 in the rotation direction of the photosensitive drum 22 and charges the photosensitive drum 22 to a predetermined potential.

  The laser scanning unit LSU is disposed in the vicinity of the photosensitive drum 22, and a photosensitive member positioned downstream of the charger 23 in the rotational direction in accordance with image data transferred from the image reading unit 10 or the like. Irradiate the surface of the drum 22 to form an electrostatic latent image.

  The developing device 24 is disposed immediately below the laser scanning unit LSU, and supplies toner to the electrostatic latent image formed on the photosensitive drum 22 via a developing roller so that the toner image is transferred to the surface of the photosensitive drum 22. To visualize.

  The transfer roller 25 transfers the toner image formed on the surface of the photosensitive drum 22 onto the paper P.

  The fixing unit 30 is disposed directly above the photosensitive drum 22 on the downstream side of the transfer roller 25, and heats and presses the paper P on which the toner image is transferred, thereby fixing the toner image on the surface of the paper. The fixing unit 30 detects a temperature of the surface of the heating roller 31 that is located near the heating roller 31 and a pair of rollers including a heating roller 31 and a pressure roller 32 that sandwich the paper P, a heater 33 built in the heating roller 31, and the like. A temperature sensor 34;

  The heating roller 31 heats the paper P and fixes the toner image transferred to the surface of the paper P. The pressure roller 32 is urged toward the heating roller 31 and presses the paper P when the paper P passes and fixes the toner image when it is transferred to the surface of the paper P.

  The sheet P on which the toner image is fixed on the printing surface in the fixing unit 30 is conveyed to the post-processing device 54 along the conveyance path A by the sliding contact conveyance roller pair 40 and the plurality of conveyance roller pairs 46. The post-processing device 54 performs post-processing such as stapling or punching, and then discharges the paper to the paper discharge tray 9.

  The sliding contact conveyance roller pair 40 is disposed on the downstream side of the fixing unit 30 and conveys the paper P along the conveyance path A. The pair of sliding conveyance rollers 40 includes a paper discharge roller 41 that rotates in a direction along the conveyance path A, and a friction roller 42 that rotates in a direction opposite to the direction along the conveyance path A and rubs the surface of the paper P. ,have.

  Here, the configuration around the sliding contact conveyance roller pair 40 will be described with reference to FIG.

  The friction roller 42 is disposed so as to be orthogonal to the conveyance direction of the paper P, and includes a rotary shaft 42A attached to the side surface of the conveyance path A so as to be movable in a direction contacting the paper discharge roller 41, and a spring 42B. ,have. The spring 42 </ b> B is disposed so as to connect the rotation shaft 42 </ b> A and the bottom surface of the conveyance path A located directly below the rotation shaft 42 </ b> A, and biases the friction roller 42 toward the paper discharge roller 41. Thereby, when the paper P passes through the gap between the paper discharge roller 41 and the friction roller 42, the test pattern TP can be rubbed by the friction roller 42 while pressing the paper P with a constant pressing force.

  The second density measuring unit 43 is located immediately upstream of the sliding contact conveyance roller pair 40, and a light emitting unit 43A that irradiates the paper P with a predetermined amount of light, a light receiving unit 43B that receives reflected light from the paper P, have. The first density measuring unit 44 is located immediately downstream of the sliding contact conveyance roller pair 40, and a light emitting unit 44A that irradiates the paper P with a predetermined amount of light, a light receiving unit 44B that receives reflected light from the paper P, have.

  In the present embodiment, an example in which the friction roller 42 rotates in the opposite direction is described. However, the present invention is not limited to this. For example, when the effect of sufficiently rubbing the test pattern TP can be obtained, the friction roller 42 may be rotated in the direction along the transport path A at a lower rotational speed than the paper discharge roller 41.

  Further, for example, the control unit 60 may rotate the friction roller 42 in the direction along the conveyance path A at the same rotational speed as that of the paper discharge roller 41 during printing processing other than when rubbing the test pattern TP. In this case, the friction roller 42 can be used as a transport roller for transporting the paper P in the direction along the transport path A except when rubbing the test pattern TP. It is also possible to prevent the friction roller 42 from rubbing the printing surface of the paper P.

  FIG. 2 is a block diagram illustrating a main configuration of the image forming apparatus 1.

  The control unit 60 includes a heating roller 31, a pressure roller 32, a transfer roller (transfer unit) 25, a friction roller (sliding contact roller) 42, and a paper discharge roller (conveyance roller) 41 arranged along the conveyance path of the paper P. , Etc. are controlled. Further, the control unit 60 controls the heater 33 and the temperature sensor 34 that measures the surface temperature of the heating roller 31 via the sub-control unit 80. Further, the control unit 60 controls the concentration measurement in the second concentration measurement unit 43 and the first concentration measurement unit 44 via the concentration determination control unit 70. The control unit 60 includes a CPU, a ROM, a RAM, an HDD, and the like, and various control programs recorded in the ROM, the RAM, and the HDD are arithmetically processed by the CPU and the like to execute various control processes.

  Similar to the control unit 60, the sub control unit 80 includes a CPU, a ROM, a RAM, and the like, and controls the heater 33 and the temperature sensor 34 based on control signals from the control unit 60. As shown in FIG. 4, the sub-control unit 80 performs on / off control of power supplied to the heater 33 via the driver 33 </ b> A, and constantly monitors the temperature of the surface of the heating roller 31 by the temperature sensor 34. Temperature control.

  The sub control unit 90 includes a CPU, a ROM, a RAM, and the like, and controls the image reading unit 10 and the automatic document feeder 12 based on various control signals from the control unit 60.

  The image memory M is formed by a storage device such as a RAM, and temporarily stores image data of a document that is transported and scanned by the automatic document feeder 12 or the like to the document table 11 (see FIG. 11). Note that the image memory M may be provided in a storage device such as a RAM mounted on the control unit 60 or the sub-control unit 90 according to the specifications of the image forming apparatus 1.

  A NIC (Network Interface Card) 61 is a communication means for the control unit 60 to communicate with a PC via a communication line.

  FIG. 7 is a flowchart showing a flow of conveyance control of the paper P in the control unit 60.

  When the control unit 60 receives a control signal for notifying the fixing abnormality of the test pattern TP from the density determination control unit 70, the heating roller 31, the pressure roller 32, the transfer roller 25, and the friction disposed along the conveyance path. The rotation driving of the conveying roller such as the roller 42 and the paper discharge roller 41 and the photosensitive drum 22 is stopped (S1, S2). Then, a control signal (hereinafter referred to as a warm-up command) for raising the heater 33 to a predetermined temperature and raising the surface temperature of the heating roller 31 to a set temperature is transmitted to the sub-control unit 80 (S3). Further, when the control unit 60 receives from the sub control unit 80 a control signal notifying that the temperature sensor 34 has detected that the surface temperature of the heating roller 31 has risen to the set temperature, the control unit 60 is disposed along the conveyance path. The driving of each conveying roller is resumed to execute the printing process. Thereby, the surface temperature of the heating roller 31 is raised to the set temperature, and the conveyance of the paper P can be stopped until the surface temperature of the heating roller 31 detected by the temperature sensor 34 reaches the set temperature. When the surface temperature of the heating roller 31 reaches the set temperature, the conveyance of the paper P can be resumed. For this reason, when the fixability of the toner image transferred to the paper P is lowered, the temperature of the surface of the heating roller 31 is raised to recover the fixability of the toner image, and then the printing process can be resumed promptly. (S4, S5).

  In the image forming apparatus 1 according to the present embodiment, the control unit 60 restarts the printing process after the temperature of the surface of the heating roller 31 is raised by the heater 33. However, the present invention is not limited to this. For example, when there is little decrease in the fixability of the toner image transferred onto the paper P, the controller 60 may increase the surface temperature of the heating roller 31 to the set temperature by the heater 33 while continuing the printing process. good.

  FIG. 8 is a flowchart showing the flow of document reading control in the sub control unit 90.

  The sub-control unit 90 operates the automatic document feeder 12 to feed and read the documents on the document tray one by one and store them in the image memory M (S6). Further, the image of the test pattern TP is synthesized with the document image data stored in the image memory M (see FIG. 6) (S7). This is continued until there are no more documents on the document tray (S8).

  FIG. 9 is a flowchart showing a flow of temperature control of the heater 33 in the sub-control unit 80.

  As shown in FIG. 5A, the sub control unit 80 supplies power to the heater 33 so that the duty ratio of the heater control signal becomes the initial value (70%). Here, the duty ratio is a ratio indicating the ratio of the on time to the on / off control signal per predetermined time (S11). Then, the document image data in the image memory M is confirmed, and it is confirmed that image data corresponding to one page has been accumulated (S12). Then, it is confirmed that the warm-up command is not received from the control unit 60. If the command is not received, the control unit 60 is caused to transmit image data for one page from the image memory M to the control unit 60. (S13, S14). When the warm-up command is received, the sub-control unit 80 changes the duty ratio of the heater control signal to 100% after the document reading on the document table 11 is completed (see FIG. 5B). Thereby, the electric power supplied to the heater 33 can be increased and the heating roller 31 can be heated (S13, S15). As described above, the duty ratio is switched to 100% after the document reading is completed, so that the maximum power consumption of the entire image forming apparatus 1 does not exceed a predetermined power (for example, 1.5 kW). it can.

  Then, the original image data stored in the image memory M is transmitted to the control unit 60 one page at a time, and when all the image data in the image memory M is transmitted, a series of processing is terminated (S17, S18).

  FIG. 10 is a flowchart showing the flow of density determination control in the density determination control unit 70.

  The density determination control unit 70 measures the density of the test pattern TP formed on the printing surface of the paper P with the second density measurement unit 43 and the first density measurement unit 44. More specifically, as shown in FIG. 3B, the second density measurement is performed when the sheet P passes immediately above the second density measuring unit 43 located on the upstream side of the sliding contact conveyance roller pair 40. The unit 43 measures the density of the test pattern TP transferred to the surface of the paper P. Then, as shown in FIG. 3C, the paper P is transported along the transport path A, and the paper P is guided by the paper discharge roller 41 into the gap between the paper discharge roller 41 and the friction roller 42 located immediately below. The At this time, the printing surface of the paper P is rubbed by the friction roller 42. Further, as shown in FIG. 3D, when the paper P passes immediately above the first density measuring unit 44 located downstream of the sliding contact roller pair 40, the first density measuring unit 44 is The density of the test pattern TP transferred to the surface of P is measured (S21, S22). Then, the density values measured in the second density measuring unit 43 and the first density measuring unit 44 are compared (S23). If the density difference is larger than the predetermined value, a control signal for notifying the controller 60 that an abnormality has occurred in the fixing property is transmitted (S24, S25).

  As a result, the second density measuring unit 43 and the first density measuring unit 44 measure the density value of the test pattern TP before and after passing through the sliding contact conveyance roller pair 40 and fix the toner image transferred onto the paper P. It can be determined whether there is any abnormality.

  Note that, as shown in FIG. 6, the test pattern TP is formed in a gray color at the tip portion located on the downstream side of the printing surface of the paper P. Further, the test pattern TP may be formed at the corner of the paper P. Thereby, the test pattern TP can be formed at a position that is not easily noticeable by the user.

  For example, in the case of single-sided printing, the test pattern TP may be formed on the surface opposite to the surface on which the document image is printed. The conveyance control of the control unit 60 in this case will be specifically described as follows.

  The control unit 60 rotates the sliding contact conveyance roller pair 40 in the direction along the conveyance path A to convey the paper P to a predetermined position, and the rear end on the upstream side of the paper P is directly above the second density measurement unit 43. Is detected from the measurement result of the second concentration measurement unit 43. Then, the guide 48 is rotated from the position indicated by the solid line in FIG. 1 to the position indicated by the broken line. Further, the sliding contact conveyance roller pair 40 is rotated in the direction opposite to the direction along the conveyance path A, and the sheet P is conveyed to the registration roller pair 55 via the reverse path B indicated by a two-dot chain line in FIG. As a result, the test pattern TP can be transferred to the surface opposite to the surface on which the original image has been subjected to printing processing, thereby making the test pattern TP less noticeable. As described above, instead of causing the second density measurement unit 43 to detect that the rear end on the upstream side of the sheet P passes, a sensor that detects the passage of the rear end on the upstream side of the sheet P is provided with a pair of sliding conveyance rollers. You may arrange | position separately in the immediately upstream side of 40.

  In the present embodiment, an example in which the fixability of the toner image is determined by rubbing the test pattern TP transferred to the printing surface of the paper P is described. However, the present invention is not limited to this. For example, when printing on the paper P is single-sided printing, the test pattern TP may be transferred to the surface of the paper P opposite to the printing surface. Further, for example, if the second density measuring unit 43 and the first density measuring unit 44 can measure the density, the toner image transferred to a predetermined place on the paper P may be rubbed without using the test pattern TP. Conceivable.

  In the present embodiment, an example in which the second concentration measuring unit 43 and the first concentration measuring unit 44 are provided is described. However, the present invention is not limited to this. For example, the image forming apparatus 1 may include only the first density measurement unit 44 and set a threshold value in the density determination control unit 70 in advance. In this case, the fixability of the toner image can be determined by comparing the density value of the test pattern TP measured by the first density measuring unit 44 with the threshold value.

  In the image forming apparatus 1 according to the above embodiment, the control unit 60 restarts the printing process after the temperature of the surface of the heating roller 31 is raised by the heater 33. However, the present invention is not limited to this. For example, when there is little decrease in the fixability of the toner image transferred onto the paper P, the controller 60 may increase the surface temperature of the heating roller 31 to the set temperature by the heater 33 while continuing the printing process. good.

  In the image forming apparatus 1 according to the embodiment, the control unit 60 controls the second density measurement unit 43 and the first density measurement unit 44 via the density determination control unit 70 and the heater 33 via the sub-control unit 80. An example of controlling the temperature sensor 34 has been described. However, the present invention is not limited to this. For example, the functions of the concentration determination control unit 70 and the sub control unit 80 are integrated into the control unit 60, and the control unit 60 directly connects the second concentration measurement unit 43, the first concentration measurement unit 44, the heater 33, and the temperature sensor 34. You may make it control.

  In the above embodiment, the example in which the test pattern TP is synthesized with the document image data in the image memory M has been described. However, the present invention is not limited to this.

  For example, in the image memory M, instead of synthesizing the test pattern TP with the original image data, only the test pattern TP is printed on the paper P every time a predetermined number of print processes (for example, 10 sheets) are executed. Also good. Furthermore, the paper P on which the test pattern TP is printed may be discharged to a paper discharge tray 8 provided above the laser scan unit LSU. In this case, the control unit 60 rotates the guide 47 from the position indicated by the solid line in FIG. As a result, the paper P on which the normal printing process has been performed can be transported to the paper discharge tray 9, and the paper P on which the test pattern TP has been printed can be transported to the paper discharge tray 8. For this reason, it is possible to prevent the sheet P on which the test pattern TP has been printed from being mixed with the sheet P on which the normal printing process has been performed.

  The processing flow of each control unit in this case will be described below. Note that the flow of processing in the density determination control unit 70 is the same as that in the above embodiment, and is therefore omitted.

  FIG. 12 is a flowchart showing a flow of document reading control in the sub control unit 90.

  The sub-control unit 90 operates the automatic document feeder 12 to send the documents on the document tray one by one to the document table 11 and read the documents. Then, as shown in FIG. 14, it is stored in the image memory M (S31). This is continued until there are no more documents on the document tray (S32).

  FIG. 13 is a flowchart showing a flow of temperature control of the heater 33 in the sub-control unit 80. Here, since S42 and S43 perform the same process as S11 and 12, description is abbreviate | omitted. Also, since S49 to S52 perform the same processing as S15 to S18, description thereof is omitted. In the following, parts different from the above embodiment will be described.

  In S41, the sub control unit 80 substitutes 0 for a variable C for counting the number of printed pages.

  In S44, the sub-control unit 80 determines whether or not the warm-up command has been received from the control unit 60. If not received, 1 is added to the variable C to determine whether or not the variable C is a multiple of 10 (S45, S46). When the variable C is a multiple of 10, the test pattern TP data (see FIG. 14) stored in the image memory M is transmitted to the control unit 60, and only the test pattern TP is placed on the paper P. Printing is performed (S48). If the variable C is not a multiple of 10, the document data is transmitted to the control unit 60 (S46, S47).

  The image forming apparatus 1 according to the above embodiment includes the sliding contact roller pair 40, the second density measuring unit 43, and the first density measuring unit 44 as the measurement unit, and the density of the toner image transferred to the paper P. An example of determining the fixability of a toner image by measuring the value has been described. However, the present invention is not limited to this. For example, when the fixability of the toner image can be sufficiently determined by the temperature of the toner image transferred to the surface of the paper P passing through the fixing unit 30, the toner image is transferred to the surface of the paper P immediately downstream of the fixing unit 30. You may provide the measurement part which measures the temperature of a toner image. In this case, the fixability can be determined based on the temperature of the toner image transferred to the surface of the paper P.

  In addition, it should be thought that description of the above-mentioned embodiment is an illustration in all the points, Comprising: It is not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a configuration of an image forming apparatus. (A) shows the configuration around the sliding contact conveyance roller pair. (B)-(D) are figures which show typically operation of a pair of sliding contact conveyance rollers at the time of paper conveyance. It is a circuit diagram of the driver which performs temperature control of a heater based on the control signal from a sub control part. It is a figure which shows typically the control signal which a sub control part controls on / off of a heater via a driver, (A) shows the case where a duty ratio is 70%, (B) shows a duty ratio of 100%. Shows the case. It is a figure which shows the paper in which the test pattern was formed in the front-end | tip part. It is a flowchart which shows the flow of the printing process in a control part. 6 is a flowchart illustrating a flow of document reading control in a sub-control unit. It is a flowchart which shows the flow of the temperature control of the heater in a sub control part. It is a flowchart which shows the flow of the density determination control in a density determination control part. It is a figure which shows typically the image data accumulate | stored in an image memory. It is a flowchart which shows the flow of document reading control in the sub-control part which concerns on other embodiment. It is a flowchart which shows the flow of the temperature control of the heater in the sub control part which concerns on other embodiment. It is a figure which shows typically the image data accumulate | stored in the image memory which concerns on other embodiment.

Explanation of symbols

1 Image forming device 25 Transfer roller (transfer section)
30 Fixing unit (fixing part)
40 Sliding contact roller pair (measurement unit)
43 Second concentration measurement unit (measurement unit)
44 First concentration measurement unit (measurement unit)
60 control unit P paper

Claims (7)

A transfer section for transferring a toner image to the surface of the paper;
A fixing unit for heating the sheet that has passed through the transfer unit;
A measuring unit for measuring the fixability of the toner image transferred to the surface of the paper conveyed from the fixing unit;
A control unit for controlling the temperature of the fixing unit based on a measurement result in the measurement unit;
With
The control unit raises the temperature of the fixing unit to a predetermined temperature when the measurement value measured by the measurement unit is lower than a predetermined measurement value.
Image forming apparatus. The measuring unit measures a density of a slidable conveying roller pair that rubs and conveys a sheet conveyed from the fixing unit, and a density of a toner image transferred to the surface of the sheet that has passed through the slidable conveying roller pair. A concentration measuring unit;
The controller raises the temperature of the fixing unit to a predetermined temperature when the density measured by the first density measuring unit is lower than a predetermined density;
The image forming apparatus according to claim 1. The control unit also controls paper conveyance in a conveyance direction that passes through the transfer unit, the fixing unit, and the sliding contact conveyance roller pair in this order, and controls the surface of the paper measured by the first density measurement unit. When the density of the transferred toner image is lower than a predetermined density, the conveyance of the paper is stopped, and the conveyance of the paper is resumed after the temperature of the fixing unit rises to the predetermined temperature.
The image forming apparatus according to claim 2. The measurement unit further includes a second density measurement unit which is disposed between the fixing unit and the sliding contact conveyance roller pair and measures the density of the toner image transferred to the surface of the paper,
The control unit controls the temperature of the fixing unit based on a difference in density of the toner image transferred to the surface of the paper measured by the first density measurement unit and the second density measurement unit.
The image forming apparatus according to claim 2. The sliding contact conveyance roller pair includes a conveyance roller that rotates in a direction in which the sheet is conveyed along the conveyance direction, and a sliding contact roller that rotates in the same direction as the conveyance roller and rubs the sheet.
A spring member that urges the sliding roller toward the conveying roller;
The image forming apparatus according to claim 2. The fixing unit includes a conveyance roller that conveys a sheet, and a heater that heats the conveyance roller.
The control unit performs on / off control of the power supplied to the heater at a predetermined duty ratio, and the density of the toner image transferred to the surface of the paper measured by the first density measurement unit is lower than the predetermined density. When the duty ratio is low, the duty ratio is changed to increase the on-time.
The image forming apparatus according to claim 2. The density measuring unit measures the density of the test pattern transferred to the surface of the paper by the transfer unit;
The image forming apparatus according to claim 2.

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