JP2006058742A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of reducing the occurrence of "rear side staining" on the non-image forming side of the following recording material outputted after images are continuously formed, and also, capable of reducing the deterioration of image quality on the image forming side of the following recording material. <P>SOLUTION: The image forming apparatus is provided with one driving source M for driving an image forming means 49 and a fixing means 13, and a control means 55 for controlling the driving source, and the control means is provided with a control sequence of driving the driving source again after stopping the driving source for a prescribed time irrespective of the detection result by a temperature detecting means 63, and then, controlling the image forming means and the fixing means to start the operations in the case the number of continuously formed images reaches the prescribed number of images. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an image forming apparatus such as a laser beam printer (LBP), a fax machine, and a copying machine.

  In an image forming apparatus such as an LBP or a copying machine, an unfixed toner image is formed and supported on a recording material by an image forming unit as an image forming unit, and the recording material is nipped and conveyed by a fixing nip unit in a fixing device as a fixing unit. Thus, the unfixed toner image is fixed on the recording material as a permanently fixed image.

  As the above-mentioned fixing device, there is a heat roller fixing type device, a fixing roller containing a halogen heater (heating source) inside as a heat fixing member, and a pressure roller as a pressure member brought into pressure contact therewith Is the basic configuration. A recording material (transfer material sheet, electrostatic recording material, electrofax paper, printing paper on which an unfixed toner image is formed and supported on a fixing nip portion that is a pressure nip portion of the pair of rollers by rotating the pair of rollers. The toner image is fixed to the recording material surface as a permanently fixed image by heat and pressure by heat from the fixing roller and pressure applied to the fixing nip portion.

  In such a heat roller fixing type fixing device, as disclosed in Patent Document 1, unfixed toner on the recording material offset to the surface of the fixing roller is removed by a cleaning member to clean the surface of the fixing roller. Things have been done.

  In recent years, as a means for solving the offset problem in the fixing device, a bias is applied to a heat fixing member such as a fixing roller or a pressure roller having elasticity to prevent the offset electrostatically, An apparatus that performs potential control so that a stable potential can be obtained by performing static elimination so that the potential on the surface of the pressure member does not fluctuate due to the sheet passing through and feeding the recording material to the nip is widely used (Patent Document 2). .

As a result, the conventionally required cleaning member is no longer necessary, the fixing device can be reduced in size and cost, and the user can save the trouble of periodically replacing the cleaning member.
JP-A-9-171316 JP-A-3-231785

  However, the fixing device does not include a cleaning member, and a temperature detecting element (temperature detecting means) such as a separation claw for separating a recording material, a thermistor, or a thermo switch in a paper passing area (recording material conveying area) in the longitudinal direction of the fixing roller In the case of an image forming apparatus provided with a safety element such as abutment against the surface of the fixing roller, there are the following problems.

  In recent years, with the progress of networking, as the processing performance of host computers and image forming devices has improved, it is possible to easily perform continuous printing (long jobs) that allow multiple users to perform image formation continuously. Became. For this reason, when halftone images made up of halftone dots and fine lines are frequently used, these images are difficult to be fixed on the recording material, and the offset toner to the fixing device increases. The amount of offset toner per recording material is very small, and there is no problem with normal intermittent printing. However, as described above, it is now possible to easily output long jobs, so a separation claw, temperature detection element, safety element, etc. The amount of offset toner accumulated on the contact member increases.

  As a result, when the next job of the long job is executed, when the fixing device is driven, the offset toner accumulated in the contact member is ejected as a lump to the surface of the fixing roller, and the temperature of the toner is discharged via the nip portion. There is a problem that “back stain” occurs in the next recording material due to the transfer to the low pressure roller side.

  In particular, when the number of continuous prints (job length) is long, a toner lump appears on the print surface side (image forming surface side) of the next recording material, and the print quality (image quality) may be lowered. This tendency is prominent when a relatively long print job including a halftone image as an image image is performed. Therefore, the inconvenience of forcing the user to reprint has occurred.

  As a method for solving such a problem, a simple cleaning member is provided at a position corresponding to the contact member, or the contact member is separated while the recording material is passing through the nip portion of the fixing device. However, in both cases, the configuration becomes complicated, leading to an increase in the size and cost of the fixing device.

  The present invention has been made in view of the above points, and “back stains” or image forming surface generated on the non-image forming surface side of the recording material to be output next after continuous image formation is performed. An object of the present invention is to provide an image forming apparatus capable of reducing the deterioration in image quality on the side.

  In addition, it is possible to reduce “back stains” that occur on the non-image forming surface side of the recording material that is output next after the image forming operation is continuously performed, and to reduce the image quality on the image forming surface side. It is an object of the present invention to provide an image forming apparatus capable of minimizing a decrease in throughput of the recording material output to the printer.

  In order to achieve the above object, a typical image forming apparatus according to the present invention comprises an image forming means for forming and supporting an unfixed toner image on a recording material, and a recording material from the image forming means at a fixing nip portion. And a fixing unit that fixes the unfixed toner image on the recording material by nipping and conveying the fixing unit. The fixing unit includes a thermal fixing unit, a heating source that heats the thermal fixing unit, and a thermal fixing unit. Pressurizing means for forming a fixing nip portion by pressure contact, a temperature detecting means for detecting the temperature of the thermal fixing means, an abutting member in contact with the surface of the thermal fixing means or the pressing means, and a detection result of the temperature detecting means And a temperature control unit that controls energization to the heating source, and includes: one drive source that drives the image forming unit and the fixing unit; and a control unit that controls the drive source. The control means is capable of continuous image formation. Provided with a control sequence for stopping the drive source for a predetermined time and then driving it again to start the image forming means and the fixing means regardless of the detection result of the temperature detecting means when the fixed number of images is reached. An image forming apparatus characterized by the above.

  In order to achieve the above object, a typical image forming apparatus according to the present invention comprises an image forming means for forming and supporting an unfixed toner image on a recording material, and a recording material from the image forming means for fixing the fixing nip. A fixing unit that fixes the unfixed toner image on the recording material by being nipped and conveyed by the unit. The fixing unit includes a thermal fixing unit, a heating source that heats the thermal fixing unit, and a heat source. A pressure unit that forms a fixing nip portion in contact with the fixing unit, a temperature detection unit that detects the temperature of the thermal fixing unit, a contact member that contacts the surface of the thermal fixing unit or the pressure unit, and a detection by the temperature detection unit And a temperature control unit that controls energization to the heating source based on the result, a first drive source that drives the fixing unit, a second drive source that drives the image forming unit, Control means for controlling the first and second drive sources. The control means controls the driving of the second drive source to delay the image formation timing of the image forming means and to set the first drive source to a predetermined value when the continuous image formation reaches a predetermined number of images. An image forming apparatus comprising a control sequence for driving the first and second drive sources again after the time is stopped to start the operations of the image forming unit and the fixing unit.

  According to the present invention, when the continuous image formation reaches a predetermined number of images according to the control sequence, the driving source is stopped again for a predetermined time and then driven again to start the operations of the image forming unit and the fixing unit, respectively. Therefore, before the amount of toner mass accumulated on the contact member increases, the toner mass is moved to the contact surface side of the heat fixing means or pressure means by an impact when the fixing means is periodically stopped. Can be transferred. As a result, it is possible to reduce the “back stain” generated on the non-image forming surface side of the recording material to be output next after continuous image formation, and to improve the image quality on the image forming surface side. Reduction can be reduced.

  Further, when the continuous image formation reaches a predetermined number of images by the control sequence, only the first drive source is stopped for a predetermined time and then driven again to start the operation of the fixing unit. Before the amount of toner mass accumulated on the contact member increases, the toner mass can be transferred to the contact surface side of the heat fixing means or pressure means by an impact when the fixing means is periodically stopped. . As a result, it is possible to reduce the “back stain” generated on the non-image forming surface side of the recording material to be output next after continuous image formation, and to improve the image quality on the image forming surface side. Reduction can be reduced. Also, since the first drive source is stopped for a predetermined time, only the operation of the fixing unit is stopped for a predetermined time, so that the time required for a predetermined process required for the next image formation is shortened, and the recording material to be output next Throughput degradation can be minimized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a sectional view showing a schematic configuration of an example of an image forming apparatus according to the present invention. This image forming apparatus is an LBP (laser beam printer) using a transfer type electrophotographic process.

(1) Overall Schematic Configuration of LBP 1 is a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. The photosensitive drum 1 is driven to rotate at a predetermined speed in the clockwise direction of an arrow when a main motor (not shown) of the LBP is turned on. The surface of the rotationally driven photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the primary charger 29. Next, image exposure corresponding to image information to be printed is performed on the uniformly charged surface by a laser beam scanner 28 as an exposure device. As a result, an electrostatic latent image corresponding to image exposure is formed on the surface of the photosensitive drum 1. This electrostatic latent image is visualized as a toner image by the developing device 30.

  On the other hand, in synchronization with the image formation on the photosensitive drum 1, the recording material 19 such as transfer paper is taken out from the paper cassette 36 by the paper feed roller 25, separated one by one, and the conveyance guide 34, the conveyance roller 33, It is conveyed to the registration roller pair 31 through the conveyance guide 32. The registration roller pair 31 is stopped until the recording material 19 arrives, and the skew of the recording material 19 is corrected by the front end of the recording material 19 coming into contact therewith. A sensor flag (not shown) disposed in the recording material conveyance path is in front of the registration roller pair 31 and detects that the recording material has arrived by shielding a photocoupler (not shown) from light. Thereafter, the registration roller pair 31 starts to rotate in accordance with a writing signal for starting to form an image on the photosensitive drum 1. The recording material 19 is conveyed through a transfer guide 14 to a transfer nip formed by the photosensitive drum 1 and the transfer roller 4. The toner image formed on the photosensitive drum 1 is transferred onto the recording material 19 at the transfer nip.

  After the transfer, the recording material 19 is separated from the photosensitive drum 1 by the curvature separation by the small-diameter photosensitive drum 1 and the action of the static elimination needle 8. Reference numeral 12 denotes a photosensitive drum cleaner. The photosensitive drum surface after separation of the recording material is cleaned by removing the transfer residual toner by this cleaner, and is repeatedly used for image formation. The recording material 19 separated from the photosensitive drum 1 is conveyed to a fixing device (fixing device) 13 through a conveyance guide 10 where an unfixed toner image is fixed and becomes a fixed image. Thereafter, the paper 19 is guided by the flapper 37 toward the conveyance guide 38 toward the upper side and conveyed, and is discharged to the discharge tray 46 by the discharge roller 45. An apparatus upstream of the fixing device 13 in the recording material conveyance direction is an image forming unit 49 that forms and supports an unfixed toner image on the recording material.

  In the double-sided printing mode, the recording material 19 that has been printed on the first side and has exited the fixing device 13 is guided by the flapper 37 toward the conveyance guide 39 toward the lower side, and is conveyed to the conveyance roller (switchback roller). ) 40 once transported in the direction of the transport guide (switchback transport path) 41, and then the recording material 19 is transported in the direction of the transport guide 42 by the reverse rotation of the transport roller 40. In this process, the front and back of the recording material 19 are reversed.

The recording material 19 whose front and back are reversed is conveyed again to the transfer nip through the conveyance roller 43 and the conveyance guide 44, and is subjected to a toner image transfer process on the second surface side. The recording material 19 on which the toner image transfer and fixing process to the second surface side has been completed is guided by the flapper 37 toward the conveyance guide 38 toward the upper side, conveyed, and discharged as a duplex print through the discharge roller 45 and the discharge tray 46. To be discharged. Reference numeral 47 denotes an exterior for protecting and soundproofing the inside of the machine.
(2) Schematic Configuration of Fixing Device Next, the fixing device 13 of this embodiment will be described with reference to FIG. FIG. 2 is an enlarged schematic cross-sectional view of the main part of the fixing device 13. The fixing device 13 is a heat roller type fixing device including a heat source in a heat fixing unit.

  The fixing device 13 includes an aluminum (thickness 1 mm) pipe cored bar (outer diameter φ40) 60a and a fixing roller 60 serving as a heat fixing unit in which a fluororesin 10 to 50 μm is coated as a release layer 60b. A pressure roller 61 (outer diameter φ30) serving as a pressing means having a conductive silicone sponge rubber as an elastic layer 61b on an outer diameter φ14) 61a and a conductive fluorine resin 10 to 50 μm as a release layer 61c thereon. ). The pressure roller 61 is urged against and pressed against the fixing roller 60 with a predetermined pressure by a pressure unit (not shown), thereby forming a nip width of 7 mm as the fixing nip portion N. The fixing roller 60 includes a halogen heater 62 as a heating source inside, and a thermistor that is a temperature detecting means at the end of the non-sheet passing area corresponding to the recording material non-conveying area of the fixing nip N on the surface. 63 is abutted. Based on the detection voltage of the thermistor 63, the temperature control unit (temperature control means) 69 is rotationally driven by a main motor M as a drive source while the temperature of the roller surface is adjusted to be substantially constant.

  In this embodiment, the fixing roller 60 receives a driving force from a main motor M that drives the photosensitive drum 1, and the pressure roller 61 is driven to rotate as the fixing roller rotates.

  Note that no cleaning member is in contact with the fixing device 13 of this embodiment, and as shown in FIG. 2, a diode 68 is placed on the pressure roller core 61a in a direction in which the core potential is opposite to that of the toner. A configuration that can be connected and electrically reduced offset is adopted.

  Reference numeral 64 designates six separation claws arranged and brought into contact with each other in the sheet passing area in the longitudinal direction of the fixing roller 60 corresponding to the recording material conveyance area of the fixing nip N, and a shaft 65 for supporting each separation claw. By holding one end of the separation claw by a spring 66 while being held on a holder (not shown), the tip of the claw part is in contact with the surface of the fixing roller with a contact pressure of about 0.098 N / mm. The separation claw 64 has a base material molded with a PI resin and a fluororesin coated on the base material via a primer to minimize toner adhesion. The tip of the claw portion is sharply processed with a curvature radius of 30 to 50 μm, and the recording material 19 conveyed on the fixing roller can be reliably separated. A guide member 67 accurately conveys the recording material 19 to the fixing nip N.

  At the time of LBP image formation (printing), the surface temperature of the fixing roller 60 is adjusted to a predetermined fixing temperature, and the recording material 19 carrying the unfixed toner image t is introduced into the fixing nip portion N, and the fixing nip portion. Is being nipped and conveyed. The recording material 19 is heated from the fixing roller 60 in the process of being nipped and conveyed through the fixing nip portion N, and receives pressure from the fixing nip portion N, whereby the unfixed toner image t is fixed to the surface of the recording material 19 by heat and pressure. Is done.

(3) Sequence Control of Image Forming Unit FIG. 3 is an enlarged cross-sectional view of a main part that transfers the toner image on the photosensitive drum to the recording material. As shown in FIG. 3, a high voltage power supply 50 is connected to the cored bar 4 a of the transfer roller 4, and the high voltage power supply 50 is configured such that a constant current power supply unit 52 and a DC voltage variable circuit 51 can be switched by a changeover switch 53. Is done. In addition, a voltmeter 54 for voltage monitoring is connected to the constant current power supply unit 52.

  The high voltage power supply 50 applies a predetermined current between the photosensitive drum 1 and the transfer roller 4 by the constant current power supply unit 52, thereby monitoring the voltage corresponding to the transfer roller resistance value with the voltmeter 54 and entering the transfer nip T. Immediately before the recording material 19 arrives, the connection is switched to the DC voltage variable circuit 51, and an appropriate transfer bias is applied to the transfer roller 4 during the transfer nip sheet passing. This is a mechanism in which these are controlled by a control unit 55 as a control means constituted by a CPU, a ROM, and a RAM. Further, the control unit 55 executes a control sequence described later in accordance with the long job.

  The transfer roller 4 is generally known to be an electronic conductive material in which carbon is dispersed in a nonpolar rubber and an ionic conductive material in which several types of rubbers for resistance adjustment are blended with polar rubbers such as NBR and urethane. ing. The electronically conductive roller has a characteristic that resistance variation in the circumferential direction of the roller is large instead of being less dependent on the environment, and the resistance partially increases when a local pressure is applied. On the other hand, the ion conductive roller has a characteristic that the resistance variation in the circumferential direction of the roller is small and the resistance variation due to the pressure hardly occurs, but the environmental dependence is extremely large.

  However, recently, due to the improvement of the rubber formulation, there is a tendency that the environmental dependency is also kept small, and the number of cases using an ion conductive roller is increasing. In this embodiment, an ion conductive roller is also used. Therefore, it is necessary to keep track of the resistance characteristics of the transfer roller 4 before transfer to the recording material 19 and prepare for image formation instructions.

  Next, the high-pressure sequence control in the transfer portion T after the print instruction is given will be described with reference to FIG. FIG. 4 is a timing chart showing a transfer bias sequence in the case of continuous printing.

  First, when the LBP receives a print instruction, the photosensitive drum 1 starts driving, and at the same time, the primary charger 29 performs uniform charging.

  Next, before the recording material 19 arrives at the transfer nip T, a constant current bias of 8 μA is applied to the transfer roller 4 by the constant current power source 52, and the voltage at that time is monitored by the voltmeter 54. The monitor voltage at this time is set to Vto, and the DC voltage variable circuit 51 is selected by the changeover switch 53 to output Vto. The voltage Vto is applied to the transfer roller 4 until the other preparation operations of the image forming unit are completed (pre-rotation in FIG. 4).

When the preparation operation is completed, the recording material 19 is passed through the transfer nip T in accordance with the exposure timing, and the transfer bias is switched to the print bias (printing in FIG. 4). When the print bias is Vt, Vt is
Vt = Vt0 × a + b [kV]
(However, a = 1.0, b = 1.1)
Calculate with the following formula. Note that a and b are values that are appropriately adjusted according to the apparatus configuration and process speed so as to obtain an appropriate control expression.

  Thereafter, the bias of the transfer roller 4 is returned to Vto in accordance with the timing at which the trailing edge of the recording material comes in the transfer nip (between sheets in FIG. 4).

  As a result, the current flowing between the photosensitive drum 1 and the transfer roller 4 in the non-sheet-passing portion and the sheet-passing portion can be made substantially constant, and the drum potential can be kept substantially constant. Stable image quality can be maintained even for images. Thereafter, while continuous printing is performed, a print bias and a paper gap bias are repeatedly applied.

(4) Control Sequence of Control Unit A control sequence of the control unit 55 will be described with reference to FIGS. 5 and 6. FIG. 5 is a block diagram illustrating an example of a circuit configuration for controlling the image forming unit and the fixing device. FIG. 6 illustrates a print signal and a high-voltage control state when a long job (job length = 90 sheets) is printed from the standby state. 6 is a chart showing main motor drive and fixing roller temperature.

  In FIG. 6, the upper part of the upper half shows the print signal, the middle part shows the high-pressure control state in the above-described image forming unit, and the lower part shows the drive of the main body main motor. The lower half shows the transition of the fixing roller temperature.

  First, in the image forming unit, when the control unit 55 receives the first print signal from the operation panel 76 provided in the image forming apparatus, the control unit 55 starts driving (ON) the main motor M and the high voltage. The power supply 50 is subjected to high-voltage sequence control to perform a pre-rotation operation (A in FIG. 6) to prepare for image formation.

  On the other hand, in the fixing device 13, the temperature controller 69 is activated almost simultaneously with the driving of the main motor M in response to a command from the controller 55, and the fixing heater 63 is heated. As a result, the fixing roller 60 is heated toward the printing temperature (fixing temperature). Thereafter, image formation (B in FIG. 6) and paper feeding are repeated in accordance with a continuous print signal.

  When the print signal reaches a preset number of print images (30 sheets in the illustrated example), the image forming operation is interrupted and a post-rotation operation (D in FIG. 6) is performed to drive the main motor M to a predetermined value. Time is stopped (OFF (3 seconds in the illustrated example)). Here, the post-rotation operation is a period during which a predetermined post-operation is executed by continuing to drive the main motor M for a while after the image forming operation is completed to rotationally drive the photosensitive drum 1.

  During this time, the temperature of the fixing device 13 is controlled by the printing temperature. In other words, the temperature controller 69 turns the fixing heater 62 on and off so that the surface temperature of the fixing roller becomes substantially constant based on the detection voltage of the thermistor 63.

  When the predetermined time has elapsed, the remaining printing is resumed according to the above-described order, and the above operation is repeated up to the desired number of print images. Note that C in FIG. 6 is a sheet interval operation.

  In addition, the fixing roller temperature during continuous printing is stable at the printing temperature, maintains a sufficiently good fixing performance, and has a preset number of print images regardless of the detection result of the thermistor 63 as temperature detection means. The fixing device can be stopped.

《Experimental example》
The result of actually comparing the effect with the conventional image forming apparatus is shown.

  Conventionally, when a print job having a relatively long job length (10 to 100 images) including a halftone image is performed, “back stain” may occur on the first sheet of the next print. In other words, isolated dot images and halftone images formed with fine lines are not sufficiently fixed to the recording material because of the weak bonding force between adjacent toners, and a part of the image from the recording material to the fixing roller side. It will be transferred (offset). With a single recording material, the amount of offset toner is very small and has little effect on the printed image. However, if the job length is long, the amount of offset toner that accumulates on the separation claw located downstream of the fixing nip increases. . As a result, when the fixing roller rotates in the next print job, the toner lump accumulated on the separation claw is discharged and transferred to the pressure roller side, causing “back stain”.

Outputs print samples containing halftone images consisting of halftone dots on A4 size paper (basis weight 80 g / m ² ) in 23 ° C / 50% environment, and outputs the main body main motor. After M was stopped for 5 minutes in the standby state, the next printing was performed (this was evaluated as a sample image), and the presence and level of back stain was evaluated. The evaluation results are shown in Table 1.

  In Table 1, (I) shows a case where the main motor M is stopped in a standby state for 5 minutes after printing 200 continuous images as in the prior art, and the back side of the first sample output next. In other words, separation nail marks (hereinafter referred to as “back stains”) having a bad degree and a relatively bad level of “back stains” also occurred on the surface side.

  On the other hand, in Table 1, (II) to (IV) are examples in which the present embodiment is applied. In (II), the main body operation is stopped for 3 seconds every 30 images until the total number of images reaches 200. This is a case where the main motor M is output and stopped in a standby state for 5 minutes, and the first output sample indicates that a slight “back stain” has occurred only on the back surface. Here, the main body operation stop for 3 seconds is a time elapsed after the recording material 16 is output to the paper discharge tray 19 and the main body main motor M for driving the photosensitive drum 1 is stopped.

  Similarly, (III) is a case where the main body main motor M is stopped only for 3 seconds every 50 images, and as a result of an increase in the interval for stopping the main body main motor M compared to (II), as compared with (II). As a result, a slight “back stain” occurred on the surface side of the sample.

  Similarly, (IV) is a case where the main body main motor M is stopped for 10 seconds every 30 images. In the next sample after outputting 200 images, almost no “back stain” occurred.

  Thus, it can be seen that the shorter the interval at which the main body main motor M is stopped and the longer the stop time, the better the level of “back stain” appearing in the sample image.

  The longer the stop time of the main body main motor M, the better the level of “back dirt” is because the toner mass accumulated between the surface of the fixing roller 60 and the separation claw 64 increases in viscosity while the fixing roller 60 is stopped. This is because the toner is easily discharged. In addition, even when the stop time is as short as 3 seconds, the effect compared to the conventional example (I) is that the toner lump accumulated between the surface of the fixing roller and the separation claw due to the impact force when the fixing roller 60 stops. This is because the transfer to the fixing roller side. For this reason, for example, in (II), a very small toner lump is discharged onto the recording material every 30 images, but this is not enough to reduce the print quality.

  As described above, in the laser beam printer, the main body operation is stopped for about 3 to 20 seconds for every 20 to 40 images continuously, thereby reducing the reduction in print quality as in the prior art. Accordingly, it is possible to eliminate the inconvenience and the waste of the recording material that the next user performs the first printing again after performing the long job.

  In this embodiment, while the driving of the main motor M is stopped for a predetermined time, the heater 62 is controlled to be turned on / off to control the fixing roller 60 at the print temperature. If 62 is turned off, the discharge effect for each predetermined number of images is increased, so that the same effect can be exhibited even if the stop interval (stop interval between the predetermined number of images) is increased.

  Although the separation claw 64 has been described as an example of the contact member on the fixing roller 60, other contact members such as a thermistor 63 and a thermo switch (not shown) disposed in the sheet passing area of the fixing roller 60. However, it goes without saying that the same effect can be obtained.

(Second embodiment)
Next, a second embodiment of the image forming apparatus according to the present invention will be described. In the present embodiment, the same components as those in the image forming apparatus of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The image forming apparatus according to the present exemplary embodiment includes a fixing motor M1 as a first driving source for driving the fixing device 13 and a drum motor M2 as a second driving source for driving the image forming unit as driving sources.

  Since the two motors of the fixing motor M1 and the drum motor M2 are provided in this way, torque fluctuations generated in the fixing device 13 are not transmitted to the image forming unit, and therefore on the photosensitive drum 1 that is rotationally driven by the drum motor M2. In addition to reducing the pitch unevenness, the torque required for each motor can be reduced. Therefore, a small motor may be used, and the image forming apparatus can be downsized.

  A control sequence of the control unit 55 will be described with reference to FIGS. 7 and 8. FIG. 7 is a block diagram illustrating an example of a circuit configuration for controlling the image forming unit and the fixing device. FIG. 8 illustrates a print signal and a high-pressure control state when a long job (job length = 90 sheets) is printed from the standby state. 4 is a chart showing driving of each motor and fixing roller temperature. The description of the chart is the same as in FIG.

  In the present embodiment, only the fixing motor M1 that drives the fixing device 13 is temporarily stopped when the controller 55 reaches a predetermined number of images.

  As shown in FIG. 8, the drum motor M2 that drives the image forming unit continues to drive until the instructed number of long jobs is completed, and a predetermined print image number (FIG. When the number of print images reaches 30), the driving of the fixing motor M1 is stopped for a predetermined time for each number of print images to delay the image formation timing. While the image forming timing is delayed, the fixing motor M1 that drives the fixing device 13 is stopped for a predetermined time, thereby reducing the occurrence of “back stain” of the recording material 19 and reducing the print quality. Can be reduced.

  As can be seen from a comparison with FIG. 6, in this embodiment, the post-rotation operation and the next pre-rotation operation are not required in the image forming unit before and after the fixing device 13 is stopped for a predetermined time in a long job. Compared to 1, it is possible to suppress a decrease in throughput.

(Third embodiment)
Next, other embodiments of the image forming apparatus according to the present invention will be described. This embodiment can be applied to an image forming apparatus in which the photosensitive drum 1 is driven by the main motor 72, or an image forming apparatus in which the fixing device 13 is driven by the fixing motor M1 and the image forming unit is driven by the drum motor M2.

  FIG. 9 is a block diagram illustrating an example of a circuit configuration for controlling the image forming unit and the fixing device in the image forming apparatus according to the present exemplary embodiment.

  The DC controller 70 as a control unit receives power supply from the low voltage power source 71 and controls the main motor 72, the high voltage power source 73, and the AC driver 74. The fixing heater 75 is energized and controlled via an AC driver 74. Note that the DC controller 70 controls other laser lighting and the like but is omitted. An operation panel 76 and an external host computer 80 are connected to the DC controller 70, and the operation status of the printer can be confirmed by a display (not shown) provided in the operation panel 76 or the host computer 80.

  The operation panel 76 is provided with an input device (not shown) such as a numeric keypad.

  In this embodiment, a selection unit (selecting means) 77 having a function for selecting whether to stop driving of the fixing device 13 during continuous printing, a predetermined number of images for stopping driving of the fixing device during continuous printing, In addition, an input unit (input means) 78 is provided that can be input by the user as a set value for the time during which the drive is stopped.

  In this embodiment, the selection unit 77 and the input unit 78 can be set from the operation panel 76 mounted on the printer. The setting may be performed on the host computer 80 connected to the DC controller 70.

  If the selection unit 77 and the input unit 78 are provided, the user can select a stop interval and a stop time during continuous printing according to the usage situation, so that a user who uses only a character image decreases throughput. On the contrary, a user who frequently uses halftone images can reduce the printing quality and wasteful use of the recording paper, thereby increasing the convenience for the user.

(Fourth embodiment)
Further, other embodiments of the image forming apparatus according to the present invention will be described. This embodiment can be applied to an image forming apparatus in which the fixing device 13 is driven by the fixing motor M1 and the image forming unit is driven by the drum motor M2.

  In the third embodiment, an example has been described in which the convenience of the user is improved by selecting the stop interval and stop time of the fixing device during continuous printing according to the use situation. An example will be described in which it is possible to determine whether the image forming apparatus needs to automatically stop the fixing device, and to further improve the usability of the image forming apparatus.

  For example, in the case of an A4 size or an LTR size, a text image used in a laser beam printer has a standard printing rate of 4 to 6%. Therefore, in the A4 size and the LTR size, when the printing rate exceeds 8%, it is expected that the image includes a halftone image such as a graphic image or a halftone dot.

  Therefore, in this embodiment, the printing rate in one page in a long job is obtained from the laser lighting time, and the driving of the fixing device 13 is stopped at a predetermined interval only when an image with a printing rate exceeding 8% is included. Was controlled as follows.

  As a method for calculating the printing rate in the page (image pattern discrimination means), for example, the total number of pixels in the page is turned on, which is the value obtained by integrating the laser lighting time in one page, that is, the solid black image is turned on. It can be calculated by a simple logical expression as a value divided by time.

  FIG. 10 shows an example of a block diagram showing a circuit configuration for controlling the image forming unit and the fixing device in the image forming apparatus according to the present embodiment. An image pattern discriminating unit 80 as an image pattern discriminating unit takes in and integrates a laser lighting time signal in one page corresponding to image information to be printed from the laser beam scanner 28 shown in FIG. The printing rate in the page is obtained by dividing by the laser lighting time, and a signal corresponding to the printing rate is output to the control unit 55.

  The control unit 55 performs control so that the driving of the fixing device 13 is stopped at a predetermined interval only when an image in which the printing rate exceeds a predetermined value (8%) is included.

  In this way, by predicting the presence of a halftone image from the printing rate in the page, it is possible to achieve both print quality and throughput without making the user aware of it, which further increases convenience for the user. Become.

In addition, in the long job, the interval at which the fixing device 13 is stopped or the stop time may be automatically changed depending on the ratio of pages having a high printing rate.

For example, when all the pages in the long job are determined as halftone images by the image pattern determination unit 80 , the fixing device 13 is stopped for 15 seconds after 30 images, and pages of 3/4 or less in the long job are determined as halftone images. If it is determined, the fixing device 13 is stopped for 10 seconds after 30 images. Similarly, when it is determined that half or less pages in the long job are halftone images, the fixing device 13 is stopped for 3 seconds after 30 images. If the stop time of the fixing device is made variable according to the ratio of the number of pages including the tone image, the useless stop time can be further reduced.

Sectional drawing which shows schematic structure of an example of the image forming apparatus which concerns on 1st Example. Expanded cross-sectional model view of the main part of the fixing device Sectional view enlarging the main part that transfers the toner image on the photosensitive drum to the recording material Chart illustrating the high-pressure sequence operation of the transfer section in continuous printing Block diagram showing an example of a circuit configuration for controlling the image forming unit and the fixing device FIG. 3 is a chart illustrating a sequence operation during a long job of the image forming apparatus according to the first embodiment. FIG. 3 is a block diagram illustrating an example of a circuit configuration for controlling an image forming unit and a fixing device of an image forming apparatus according to a second embodiment. FIG. 7 is a chart for explaining a sequence operation during a long job of the image forming apparatus according to the second embodiment. 4 is a block diagram illustrating an example of a circuit configuration for controlling an image forming unit and a fixing device of an image forming apparatus according to a third embodiment. FIG. 4 is a block diagram illustrating an example of a circuit configuration for controlling an image forming unit and a fixing device of an image forming apparatus according to a fourth embodiment. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 4 ... Transfer roller 13 ... Fixing device 19 ... Recording material 49 ... Image forming means 55, 70 ... Control part 60 ... Fixing roller 61 ... Pressure roller 62 ... Heater 63 ... Thermistor 64 Separation claw 69 Temperature controller

Claims (9)

Image forming means for forming and supporting an unfixed toner image on the recording material; and fixing means for fixing the unfixed toner image on the recording material by sandwiching and conveying the recording material from the image forming means at the fixing nip portion. The fixing unit includes a thermal fixing unit, a heating source that heats the thermal fixing unit, a pressure unit that presses against the thermal fixing unit to form a fixing nip portion, and a temperature of the thermal fixing unit. An image forming apparatus comprising: a temperature detecting unit for detecting; a contact member that contacts the surface of the thermal fixing unit or the pressing unit; and a temperature control unit that controls energization to the heating source based on a detection result of the temperature detecting unit. In
One driving source for driving the image forming unit and the fixing unit and a control unit for controlling the driving source are provided, and the control unit detects the temperature when the number of consecutive image formations reaches a predetermined number of images. An image forming apparatus comprising: a control sequence for stopping the drive source for a predetermined period of time and driving the image forming unit and the fixing unit again, regardless of the detection result of the unit.   The image forming apparatus according to claim 1, wherein the control unit controls the temperature control unit to stop energization of the heating source while the drive source is stopped for a predetermined time. Image forming means for forming and supporting an unfixed toner image on the recording material; and fixing means for fixing the unfixed toner image on the recording material by sandwiching and conveying the recording material from the image forming means at the fixing nip portion. The fixing unit is a thermal fixing unit, a heating source for heating the thermal fixing unit, a pressurizing unit in contact with the thermal fixing unit to form a fixing nip portion, and a temperature of the thermal fixing unit. An image forming apparatus comprising: a temperature detecting means that performs contact; a contact member that contacts the surface of the heat fixing means or the pressure means; and a temperature control means that controls energization to the heating source based on a detection result of the temperature detecting means. ,
A first drive source for driving the fixing means; a second drive source for driving the image forming means; and a control means for controlling the first and second drive sources. When the number of formed images reaches the predetermined number of images, the driving of the second drive source is controlled to delay the image forming timing of the image forming means, and after the first drive source is stopped for a predetermined time, the first drive again And an image forming apparatus comprising: a control sequence for driving the second drive source to start the operations of the image forming unit and the fixing unit.   A selection means for selecting whether or not to execute the control sequence of the control means; an input means for inputting a predetermined number of images in a continuous image forming operation of the image forming means; and a predetermined time for stopping the first drive source; The image forming apparatus according to claim 1, further comprising:   4. The image according to claim 3, further comprising an image pattern discrimination unit for discriminating an image pattern, wherein the control unit executes a control sequence when it is determined that the image pattern discrimination unit includes a halftone image. Forming equipment.   4. The image forming apparatus according to claim 3, wherein the control sequence of the control unit controls the temperature control unit to stop energization of the heating source while the first drive source is stopped for a predetermined time. . 4. The image forming apparatus according to claim 1, wherein the contact member that contacts the surface of the heat fixing unit or the pressure unit is a separation claw that separates the recording material from the fixing unit. 4. The image forming apparatus according to claim 1, wherein the contact member that contacts the surface of the heat fixing unit or the pressure unit is a temperature detection unit. The image forming apparatus according to claim 1, wherein the contact member that contacts the surface of the heat fixing unit or the pressure unit is a thermo switch.

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