JP2007101823A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the degradation of image quality without increase of cost by performing a cleaning with a cleaning roller even in a condition being liable to cause toner contamination. <P>SOLUTION: In order to prevent the toner pollution in an image forming apparatus, a toner stuck to a claw tip of a separating member 75 during printing is solidified by stopping a heat fixing device 22 with a heat source 23 on for a certain time (a) after the end of printing though the toner being gradually accumulated. Next, the heat dicing device 22 is driven for a certain time b. The solidified toner is fused out by this cleaning operation and is moved from a heat roller 30 to a pressure roller 32 and is recovered to a cleaning roller 74. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  Conventionally, in a heat fixing device provided in an electrophotographic image forming apparatus, a heating member such as a heating roller and a heating belt that is heated to a fixing temperature by a heat source, and a pressure member such as a pressure roller and a pressure belt that are pressed against the heating member In the meantime, by rotating the heating member and the pressure member through the recording medium on which the unfixed toner image is placed, the toner image is fixed on the recording medium by applying heat and pressure while conveying the recording medium. The Lord.

  In this type of thermal fixing device, the surface of the heating member and the pressure member is coated with fluorine to prevent toner adhesion, but the offset phenomenon that the toner on the recording medium adheres to the heating member during fixing. The offset toner further adheres to the pressure member, and the toner on the heating member and the pressure member is reversely transferred to the recording medium that passes through the toner, and the recording medium is contaminated.

  For this reason, in a conventional thermal fixing device, a roller-shaped cleaning member is contacted so as to be driven and rotated by a heating member or a pressure member, and the offset toner on the heating member or pressure member is removed by the cleaning member. There is something to do. For example, the surface of the heating member or pressure member prevents the toner from adhering with a fluorine coat or the like as described above. Therefore, the surface of the cleaning member is made of solid metal, so that the heating member or the pressure member is different depending on the release performance difference. The offset toner on the member adhered to the cleaning member.

  Similarly, due to the recent demand for energy saving, the toner used in an image forming apparatus or the like has been lowered in melting point. As the melting point is lowered, the fixing temperature can surely be set lower than in the past, but on the other hand, it becomes more sensitive to the temperature distribution of the heating member, and offset is more likely to occur than in the past.

  In recent years, with the demand for higher image quality, the toner has been made smaller in particle size and polymerized toner. It goes without saying that as the toner particle size is reduced, offset is more likely to occur as the toner becomes smaller. As the polymerization toner progresses, as described above, the toner having a low storage elastic modulus adheres to the heating member, and an offset is likely to occur. In addition, a part of the offset toner gradually adheres to the separation claw of the heating member and the thermistor for detecting the temperature, and this adheres to the recording medium and degrades the image quality.

  For this reason, the thermal fixing device is driven for a certain period of time after the printing is completed, and the toner adhering to the cleaning roller is removed. However, there is a limit to the cleaning ability of the cleaning roller, which may decrease depending on printing conditions and time.

Therefore, as in the technique disclosed in Patent Document 1, a method for controlling the fixing temperature and the fixing roller rotation speed by providing a means for detecting toner adhering to the cleaning roller has been proposed.
JP 2005-70602 A

  However, in the technique of Patent Document 1 described above, since a change in the outer diameter where toner is attached to the cleaning roller is detected, a complicated detection mechanism is required. For this reason, it leads to an increase in the number of parts, leading to an increase in cost.

  Further, since the outer diameter of the toner adhering to the cleaning roller is detected and controlled, a certain number of sheets must be passed before the detection is performed. For this reason, there is a problem that control cannot be performed until a change in the outer diameter is detected, even if image quality is degraded.

  Accordingly, an object of the present invention is to propose a method for preventing a reduction in image quality without increasing the cost.

  An image forming apparatus according to claim 1 of the present invention includes a developing device for attaching a toner image to an electrostatic latent image formed on an image carrier, a transfer device for transferring the toner image onto a recording medium, and a fixing temperature. A heating member that heats the pressure member, a pressure member that presses against the heating member, and a cleaning member that contacts the pressure member and removes toner on the pressure member, the gap between the heating member and the pressure member In an image forming apparatus including a thermal fixing device that fixes a toner image on a recording medium through the recording medium and a control device that controls the operation of each of the devices, the control device is configured to perform a predetermined time at the end of the printing operation. The thermal fixing device is driven, the cleaning member performs a cleaning operation on the toner attached to the heating member, and the cleaning operation time is variable.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the control device makes the cleaning operation time variable in accordance with the number of printed sheets for each job.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus includes a mechanism that detects an average image area ratio for each job, and the control device performs the cleaning operation according to the average image area ratio. The time is variable.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the control device makes the cleaning operation time variable in accordance with the number of printed sheets for each job and the average image area ratio. .

  According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the developing device includes a two-component developer obtained by mixing a toner and a carrier at a constant ratio and a detection sensor for detecting a mixing ratio, and the control. The apparatus is characterized in that the cleaning operation time is variable according to the detection value of the sensor.

  According to the sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, when the output of the detection sensor before the end of printing is Vt1, and the output value of the detection sensor after resuming the printing is Vt2, Vt1-Vt2 is constant. The control device makes the cleaning operation time variable when the value exceeds the value.

  In the image forming apparatus of the present invention, cleaning with a cleaning roller can be performed even under conditions where toner contamination is likely to occur, and deterioration in image quality can be prevented without increasing costs.

  The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus which is an example of an object of the present invention. The photoreceptor 1 can be made of an amorphous compound having photoconductivity, an amorphous metal such as amorphous selenium, or an organic compound such as a bisazo pigment or a phthalocyanine pigment. In consideration of the environment and post-treatment after use, it is preferable to use a photoreceptor made of an organic compound.

  The charging device may be any one of a corona method, a roller method, a brush method, and a blade method, and here, a roller-type charging device is shown. The charging roller 2 applies a predetermined high voltage to generate corona discharge with the photoreceptor 1 to uniformly charge the surface of the photoreceptor 1. The exposure device 3 converts data read by the scanner in the reading device and an image signal sent from the outside such as a PC (not shown), scans the laser beam 3a with a polygon motor, and based on the image signal read through the mirror. An electrostatic latent image is formed on the photoreceptor 1.

  The developing device 4 is for attaching toner to the electrostatic latent image, and the visualized toner image reaches the transfer device 6.

  The transfer device 6 includes a transfer belt 6a, a transfer bias roller 6b, and a tension roller 6c. The transfer bias roller 6b is configured by providing an elastic layer on the surface of a core metal such as iron, aluminum, and stainless steel. The transfer bias roller 6 b is applied with a necessary pressure on the photosensitive member 1 side in order to bring the recording paper into close contact with the photosensitive member 1. The transfer belt 6a can obtain an effect by selecting various heat-resistant materials as a base material, and can be composed of, for example, a seamless polyimide film. A configuration in which a fluororesin layer is provided on the outside can be employed. Further, if necessary, a silicone rubber layer may be provided on the polyimide film, and a fluororesin layer may be provided thereon. A tension roller is provided inside the transfer belt 6a to drive and stretch the transfer belt 6a.

  The fixing device 7 includes a fixing roller having a heater that is a heating unit such as a halogen lamp, and a pressure roller that is in pressure contact. This will be described in detail later.

  The control device 10 controls devices constituting the image forming apparatus. A known microcomputer or the like may be used. Of course, other control means may be used.

  FIG. 2 shows an enlarged view around the thermal fixing device 22 corresponding to the fixing device 7 of the apparatus of FIG. Reference numeral 70 in the drawing is a fixing case of the thermal fixing device 22. The fixing case 70 has an elongated box shape and is provided with a sheet inlet 71 on the lower surface and a sheet outlet 72 on the upper surface along the sheet conveyance path R.

  In the fixing case 70, in the illustrated example, the heating roller 30 as the heating member and the pressure roller 32 as the pressure member are rotatably provided as described above.

  For example, the heating roller 30 may be a roller having a wall thickness of 1 mm or less to improve temperature responsiveness, and the temperature raising time to the fixing temperature may be shortened to about 10 seconds. The surface is subjected to fluorine coating treatment. And the heat source 23 is provided inside. In the illustrated example, the number of the heat sources 23 is two, but may be one, or may be three or more.

  A sheet separating member 75 is provided around the heating roller 30. The sheet separating member 75 is rotatably supported around a fulcrum, and is urged by a spring 76 to press the claw tip against the peripheral surface of the heating roller 30. Then, the sheet S that passes through the nip position between the heating roller 30 and the pressure roller 32 and adheres closely to the heating roller 30 is peeled off from the heating roller 30 and guided to the sheet outlet 72.

  Further, a thermistor (heating member temperature detecting means) 28 and a thermostat 29 are provided around the heating roller 30 so as to be in contact with the peripheral surface thereof. Then, the thermistor 28 detects the temperature of the heating roller 30, and based on the detection result, the heat source 23 is turned on and off to keep the heating roller 30 at a predetermined fixing temperature.

  On the other hand, around the pressure roller 32, a pressure spring 25 urges the pressure arm 26 to rotate counterclockwise about the fulcrum 27. Then, the pressure arm 32 pushes the pressure roller 32 against the heating roller 30 to form a nip between the heating roller 30 and the pressure roller 32.

Further, the cleaning member is brought into contact with the peripheral surface of the pressure roller 32. The cleaning member may be a belt, a pad or a blade, and may be made of metal or rubber. In the illustrated example, a solid metal cleaning roller 74 is used. Then, the toner attached to the pressure roller 32 is removed by the cleaning roller 74.
Note that reference numeral 77 in FIG. 2 denotes a sheet detection sensor that is provided in plural along the sheet conveyance path R and detects the passage of the sheet S. Reference numeral 78 denotes a cleaning member temperature detecting means for detecting the temperature of the cleaning roller 74.

  Next, details of the present embodiment will be described. As described above, a part of the toner having the offset adheres to the tip of the nail of the separating member 75 and the surface of the heating roller 30. The toner adhering to the surface of the heating roller 30 is transferred to the pressure roller 32 and collected by the cleaning roller 74. The toner adhering to the tip of the nail is heated by the heat source 23 of the heat fixing device 22 being cut off at the end of printing. Decreases, so that it solidifies. Next, in preparation for printing again, when the temperature of the heating roller 30 rises, it melts and adheres to the surface of the heating roller 30. Since the toner adhering to the heating roller 30 in this manner adheres to the image surface of the recording paper, it becomes toner stains and the image quality is significantly impaired.

  Therefore, an operation as shown in FIG. 3A is performed in order to prevent toner contamination. The toner adhering to the nail tip during printing gradually accumulates, but at the end of printing, for example, for a second, the heat fixing device 22 is stopped while the heat source 23 is turned on to solidify the toner adhering to the nail tip. . Next, the thermal fixing device 22 is driven for b seconds. By this cleaning operation, the solidified toner is melted, moved from the heating roller 30 to the pressure roller 32, and collected by the cleaning roller 74.

  However, such a cleaning operation is not performed until the end of printing in a method in which continuous printing is frequently used. Accordingly, when used in a state where there is a lot of continuous printing, the amount of toner that accumulates at the tip of the nail is large. Therefore, in a normal cleaning operation, toner that could not be cleaned becomes print stains when printing is resumed. For this reason, when the continuous printing is frequently used, setting the cleaning operation time b longer than usual is effective in preventing toner contamination. In the case where there are many continuous prints, it is also effective to repeat the cleaning operation several times as shown in FIG.

  This setting change can be changed by a maintenance person inputting from the operator panel of the image forming apparatus main body, but in this embodiment, this state is automatically detected on the apparatus side to change the setting. I have to. The control device 10 of the image forming apparatus such as a copying machine is preliminarily input with the number of prints for each job and the optimum cleaning operation time in addition to the image forming and various settings of the paper travel unit. From these data, an optimum cleaning time is selected according to the number of printed sheets for each job. As a result, when there is a lot of toner stains on the tip of the nail, cleaning is performed longer than usual to prevent toner stains. Conversely, when the number of prints per job is small, the tip stains are small. , Shorten the cleaning time. The heating roller 30 of the heat fixing device 22 is worn by contact with paper, but besides that, scratching occurs due to sliding with the nail and temperature detection as in the cleaning operation, and the life is shortened early. It may become. Accordingly, when the number of prints per job is small, that is, when the toner contamination at the front end is small and the cleaning time is unnecessary, the cleaning operation is shortened, so that the service life is not shortened early.

  Further, as a matter of course, the cleaning roller 74 is likely to become dirty as the printing area ratio increases. For this reason, in this embodiment, the cleaning operation time is made variable in accordance with the print area ratio. When the printing area ratio increases and the amount of toner stains attached to the tip of the nail increases, the thermal fixing device 22 is rotated longer than usual, for example, (a + 5) seconds after the end of printing. As a result, even when there is a lot of toner on the heating roller 30, the heat fixing device 22 rotates longer than usual, so that the toner on the tip of the nail can be cleaned.

  The print area ratio can be detected by the ratio of turning on / off the laser. Like the average number of printed sheets, the print area ratio is automatically detected by the control device 10 and can be changed according to a predetermined control table. To do. In addition, if the control table for the optimum cleaning operation time is input based on the average number of prints per job and the print area ratio, the optimum cleaning operation time can be selected according to the printing status, which is effective in preventing toner contamination. Is.

  Incidentally, the offset greatly depends on the toner density of the developer. The developing device 4 as shown in FIG. 4 includes a developing sleeve 80 that is a developer carrying member at a position close to the photoconductor 1, and carries the developer on the photoconductor 1. A doctor blade 81 for restricting the amount of developer on the developing sleeve 80 is provided around the developing sleeve 80.

  A storage portion 82 for storing the developer is provided at a lower position of the developing device 4, and a paddle 83 for stirring and transporting the developer and a T sensor 84 for measuring the toner concentration are provided in the storage portion 82. Although not shown, the toner from the toner replenishing device enters. The toner density is detected by detecting the magnetic permeability of the developer passing on the detection surface 85 of the T sensor 84 and converting it into a voltage. The toner density and the output voltage have a relationship as shown in FIG. The control device 10 controls the toner density so that the detected value falls within a certain range. However, a slight time difference occurs between the toner replenishment and the followability of the T sensor 84. It may end up. As described above, when the toner density exceeds the target, the toner becomes excessively attached, so that the amount of toner attached to the tip of the nail increases.

  In this embodiment, when the toner density exceeds a certain range due to the output value of the T sensor 84, the cleaning operation time is made variable. Since the detected value of the T sensor 84 may vary depending on the developer carrier production lot, it is determined not by an absolute value but by a relative difference. Specifically, when a new developer formulated at a constant density is introduced, the detected value Vt0 of the T sensor 84 is previously input as a reference value to the control device, and exceeds a certain range in comparison with the reference value. Sometimes, for example, when the detected value of the T sensor is Vt, if Vt−Vt0> 0.2, it is determined that the toner density is high.

  Further, the offset greatly affects the toner charge amount in addition to the toner concentration. During normal printing, large fluctuations do not occur, but when left for a long time, the amount of charge is remarkably reduced, especially under high temperature and high humidity. When the charge amount is reduced in this way, the amount of toner that is developed increases even under the same development conditions, so that the amount of adhesion becomes excessive, and offset and dirt on the tip of the nail are likely to occur.

  When the charge amount of the developer decreases, the fluidity of the developer changes, so that the detection value of the T sensor also varies. For this reason, in this embodiment, when the detection sensor output before the end of printing is Vt1, and the detection sensor output value after resuming printing is Vt2, if Vt1-Vt2 exceeds a certain value, it is considered that the charge amount is reduced, and the cleaning time To control. This constant value depends on the physical property value of the carrier, but may be set to about 0.2 to 0.3 V, for example.

  As a method for detecting the toner density, there is a method of creating a solid image of a certain area on the photosensitive member 1 and detecting the reflectance of the toner adhering thereto. It is also effective to use a reflectance detection value as an alternative to the T sensor.

  Further, the time for turning off the heater of the fixing device and the drive time after the heater is turned on are shown as examples only in this embodiment, but are not limited to the times in this example, and the fixing temperature and the number of rotations are not limited. Since it varies depending on the thermal characteristics of the toner, optimization may be performed according to the conditions.

  That is, in the image forming apparatus of the present invention, the thermal fixing device is driven for a predetermined time at the end of the printing operation, the cleaning member performs the cleaning operation of the toner adhering to the heating member, and the cleaning operation time is variable. Even under conditions where toner contamination is likely to occur, cleaning with the cleaning roller can be performed. Further, since the cleaning operation time is made variable according to the number of printed sheets for each printing operation, the cleaning roller can perform cleaning even under conditions where the number of printed sheets is large and toner contamination is likely to occur.

  In addition, a mechanism for detecting the average image area ratio for each printing operation is provided, and the cleaning operation time is made variable according to the average image area ratio, so that the cleaning roller can be used even under conditions where the image area ratio is high and toner contamination is likely to occur. Can be cleaned. Further, a mechanism for detecting the number of printed sheets and the average image area ratio for each printing operation is provided, and the cleaning operation time is made variable according to the detected value. Therefore, the number of printed sheets and the image area ratio are high, and toner contamination is likely to occur. Even under the conditions, cleaning by the cleaning roller can be performed.

  Furthermore, a two-component developer in which toner and carrier are mixed at a constant ratio and a detection sensor for detecting the mixing ratio are provided, and the cleaning operation time is variable according to the sensor detection value. In this case, cleaning with the cleaning roller can be performed. If the output value of the detection sensor before the end of printing and after resuming printing exceeds a certain level, the cleaning operation time is variable, so cleaning with the cleaning roller is possible even under conditions where toner contamination is likely to occur as the charge amount decreases. It can be carried out.

1 is a schematic configuration diagram of an image forming apparatus that is an example of an implementation target of the present invention. Enlarged view around the thermal fixing device FIG. 2 shows an example of operation control of the thermal fixing apparatus of FIG. Enlarged view around the developing device Diagram showing the relationship between toner density and output voltage

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging roller 3 Exposure apparatus 3a Laser beam 4 Developing apparatus 6 Transfer apparatus 6a Transfer belt 6b Transfer bias roller 6c Tension roller 7 Fixing apparatus 10 Control apparatus 22 Thermal fixing apparatus 23 Heat source 25 Pressure spring 26 Pressure arm 28 Thermistor 29 Thermostat 30 Heating roller 32 Pressure roller 70 Fixing case 71 Sheet inlet 72 Sheet outlet 74 Cleaning roller 75 Sheet separation member 76 Spring 77 Sheet detection sensor 78 Cleaning member temperature detection means 80 Developing sleeve 81 Doctor blade 82 Housing portion 83 Paddle 84 T Sensor R Sheet transport path S Sheet

Claims (6)

  A developing device that attaches a toner image to an electrostatic latent image formed on an image carrier, a transfer device that transfers the toner image onto a recording medium, a heating member that heats to a fixing temperature, and a pressure member that presses against the heating member A pressure member and a cleaning member that contacts the pressure member and removes the toner on the pressure member; passes the recording medium between the heating member and the pressure member; In the image forming apparatus including the heat fixing device for fixing and the control device for controlling the operation of each of the devices, the control device drives the heat fixing device for a predetermined time at the end of the printing operation, and the cleaning member An image forming apparatus, wherein a cleaning operation of toner adhering to the heating member is performed and the cleaning operation time is variable.   2. The image forming apparatus according to claim 1, wherein the control device varies a cleaning operation time according to the number of printed sheets for each job.   2. The image forming apparatus according to claim 1, further comprising a mechanism for detecting an average image area ratio for each job, wherein the control apparatus makes the cleaning operation time variable according to the average image area ratio. Image forming apparatus.   4. The image forming apparatus according to claim 3, wherein the control device varies the cleaning operation time in accordance with the number of printed sheets for each job and the average image area ratio.   2. The image forming apparatus according to claim 1, wherein the developing device includes a two-component developer in which toner and a carrier are mixed at a constant ratio and a detection sensor that detects a mixing ratio, and the control device detects a detection value of the sensor. Accordingly, the image forming apparatus is characterized in that the cleaning operation time is variable. 6. The image forming apparatus according to claim 5, wherein when the detection sensor output before the end of printing is Vt1, and the detection sensor output value after resuming printing is Vt2, the control is performed when Vt1-Vt2 becomes a predetermined value or more. The image forming apparatus is characterized in that the cleaning operation time is variable.