JP2015043032A - Sheet peeling device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce costs and prevent reduction in quality of images.SOLUTION: A sheet peeling device peels, in fixing a toner image formed on a sheet by applying heat and pressure to the sheet conveyed at a nip part, which is formed by a heating roller 202 including a heater 201 and a pressure roller 203 brought into pressure contact with the heating roller 202, the sheet from the heating roller 202; and includes an air pump 301 that generates compressed air, a regulator 302 that adjusts the air pressure of the compressed air, a solenoid valve 304 that opens and closes a valve included therein to spray the compressed air transferred in a compressed state from the regulator 302 through a duct 320 to the heating roller 202, an air nozzle 305, and a control unit 300, where the control unit 300 stops the generation of the compressed air by the air pump 301, and subsequently exhausts, a plurality of times, the compressed air in the duct 320 through the solenoid valve 304 for a predetermined time, so as to reduce the air pressure in the duct 320.

Description

  The present invention relates to a sheet peeling apparatus that peels a sheet when a toner image is fixed at a fixing nip portion by heat and pressure, and an image forming apparatus including the sheet peeling apparatus.

  An image forming apparatus that forms an image using an electrophotographic system includes a fixing device that fixes a toner image transferred onto a sheet. The fixing device sandwiches a sheet on which an unfixed toner image is transferred at a fixing nip formed by contact between a heated roller and a pressure roller whose surface is heated, and the fixing nip is applied while applying heat and pressure. By passing the toner, unfixed toner is melted and fixed on the paper.

  Conventionally, in the above-described fixing device, a separation claw that is in contact with the heating roller is used in order to peel off the paper wound around the heating roller. The separation claw easily peels off the paper from the heating roller when the image density is low or when the distance between the edge of the paper and the image formed on the paper (hereinafter referred to as a margin) is large. However, for example, in the case of a paper having a small basis weight (particularly coated paper) or a color image having a high image density, the adhesive force of the molten toner to the heating roller is increased. For this reason, the separation claw is difficult to enter between the paper and the heating roller, and the end of the paper may be damaged. Further, in the case of an image with little margin, there is a problem that the toner image on the paper is easily damaged by the separation claw coming into contact with the melted toner image. Further, since the separation claw is in contact with the heating roller, the heating roller is scratched, and the scratch is transferred to the melted toner image, which may deteriorate the image quality.

  For this reason, as a separation method that does not damage the toner image on the paper and the heating roller, for example, in Patent Document 1, compressed air is supplied from a nozzle provided at the tip of a peeling guide plate disposed near the paper discharge port of the fixing device. There has been proposed a method of injecting water. That is, by ejecting compressed air from the nozzle of the peeling guide plate provided in the vicinity of the heating roller so as not to contact the heating roller, the leading edge of the paper stuck to the heating roller is separated (peeled) from the heating roller, The entire paper is peeled off from the heating roller by the peeling guide plate.

Japanese Utility Model Publication No. 05-071865

  When the compressed air is jetted to peel off the paper, an air pump is used to generate the compressed air. When driving the air pump, if the air pressure in the duct from which compressed air is output from the air pump is high, a large load (air pressure) is applied to the air pump, and the air pump may not be driven. Therefore, an electromagnetic valve for discharging the compressed air in the duct is provided separately from the electromagnetic valve for injecting the compressed air to the fixing device, and when the print job is finished, this electromagnetic valve is operated to operate the duct from the exhaust port. The compressed air inside was discharged and the air pressure was lowered. Therefore, it is necessary to provide two solenoid valves for controlling the injection of compressed air, that is, an electromagnetic valve for injection to the fixing device and an electromagnetic valve for discharging the compressed air in the duct, which increases costs. It was. Even when the solenoid valve is only used for injection to the fixing device, if the compressed air is discharged in a short time, the surface temperature of the heating roller is locally and rapidly decreased by the injection of the compressed air. . Then, temperature unevenness generated on the surface of the heating roller appears as gloss unevenness of the toner image on the paper, leading to deterioration of the quality of the image formed on the paper.

  The present invention has been made under such circumstances, and an object thereof is to reduce costs and prevent deterioration in image quality.

  In order to solve the above-described problems, the present invention is configured as follows.

  (1) The toner image formed on the sheet is fixed by heating and pressing the conveyed sheet at a nip formed by a heating rotator including a heat source and a pressure rotator that is in pressure contact with the heating rotator. A sheet peeling device for peeling the sheet from the heating rotator by opening and closing a generating means for generating compressed air, an adjusting means for adjusting the air pressure of the compressed air, and a valve included therein, Injecting means for injecting the compressed air pressure-fed through the duct from the adjusting means, an exhaust port for discharging the compressed air injected by the injecting means to the heating rotator, and for discharging the compressed air The generating means, the adjusting means, and a control means for controlling the injection means, and the control means, after stopping the generation of compressed air by the generation means, by the injection means Multiple times a predetermined time discharge of the compressed air in the duct having the same air pressure as the air pressure at the time of image formation performed, sheet peeling apparatus characterized by lowering the air pressure within the duct.

  (2) The toner image formed on the sheet is fixed by heating and pressing the conveyed sheet at a nip formed by a heating rotator including a heat source and a pressure rotator that is in pressure contact with the heating rotator. A sheet peeling device for peeling the sheet from the heating rotator by opening and closing a generating means for generating compressed air, an adjusting means for adjusting the air pressure of the compressed air, and a valve included therein, Injecting means for injecting the compressed air pressure-fed through the duct from the adjusting means, an exhaust port for discharging the compressed air injected by the injecting means to the heating rotator, and for discharging the compressed air The generating means, the adjusting means, and a control means for controlling the injection means, the control means, after stopping the generation of compressed air by the generating means, by the adjusting means The air pressure of the compressed air in the duct is adjusted to an air pressure lower than the air pressure at the time of image formation, the compressed air in the duct is discharged at once by the ejecting means, and the air pressure in the duct is lowered. Sheet peeling device.

  (3) An image forming apparatus having an image forming means for forming an image on a sheet, comprising the sheet peeling device according to (1) or (2), which peels off a sheet conveyed from a fixing device. An image forming apparatus.

  According to the present invention, it is possible to reduce costs and prevent deterioration in image quality.

Schematic diagram showing the configuration of the image forming apparatus of Examples 1 and 2, and schematic diagram showing the configuration of the fixing device The control block diagram of the conventional sheet peeling apparatus for the comparison with an Example, and the schematic diagram which shows the structure of a sheet peeling apparatus Control block diagram of sheet peeling apparatus of Examples 1 and 2 and schematic diagram showing configuration of sheet peeling apparatus 7 is a flowchart illustrating control during image formation of the image forming apparatus according to the first exemplary embodiment. Time chart at the time of image formation of the image forming apparatus of Embodiment 1 7 is a flowchart illustrating control during image formation of the image forming apparatus according to the second exemplary embodiment. Time chart at the time of image formation of the image forming apparatus of Example 2

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

[Outline of image forming apparatus]
FIG. 1A is a schematic configuration diagram illustrating a configuration of an image forming apparatus using an electrophotographic system, and illustrates a schematic configuration of a laser beam printer as an example of the image forming apparatus. The laser beam printer of this embodiment will be described as a single color (for example, black and white) printer. A photosensitive drum 101 shown in FIG. 1A is formed of an optical semiconductor layer whose electrical characteristics change when irradiated with laser light, and is driven at a constant speed during an image forming operation.

  An image forming operation will be described with reference to FIG. The optical semiconductor layer of the photosensitive drum 101 is uniformly charged by the charger (charging roller) 102. The photosensitive drum 101 is irradiated with laser light from the scanning optical system 103, and an electrostatic latent image that is an image pattern is formed on the photosensitive drum 101. Subsequently, the developing device 104 develops the toner by adhering to the electrostatic latent image on the photosensitive drum 101 to form a toner image. Then, the toner image on the photosensitive drum 101 is transferred to the paper by the transfer roller 105. The sheet on which the toner image is transferred is conveyed to the fixing device 106. The fixing device 106 heats the toner image and pressurizes the toner image on the paper to fix the toner image on the paper, and the paper on which the toner image is fixed is discharged onto the paper discharge tray 107. Toner remaining on the photosensitive drum 101 without being transferred to the paper is scraped off by the blade 108, whereby the photosensitive drum 101 is cleaned. A sheet (also referred to as a sheet, a transfer material, or a recording material) accommodated in the paper feed cassette 110 in accordance with the transfer timing of the transfer roller 105 is indicated by a broken line in FIG. Transported on the transport path. The operation unit panel 113 is used to notify the user of the state of the apparatus and to specify an operation mode by the user.

[Outline of fixing device]
Next, the fixing device 106 will be described with reference to FIG. FIG. 1B is a schematic configuration diagram illustrating the configuration of the fixing device 106. The fixing device 106 in FIG. 1B is heated by a heater 201 that is a heat source and is in pressure contact with a heating roller 202 that is a heating rotator that heats a toner image, while pressing the heating roller 202. The pressure roller 203 is a pressure rotator to be rotated. In order to control the temperature of the heater 201, a thermistor 208 that detects the temperature of the heating roller 202 is provided near the surface of the heating roller 202. A control device (not shown) controls on / off of the heater 201 based on the temperature detection result of the thermistor 208. The sheet S on which the unfixed toner image T is transferred is conveyed on the conveyance path 206 in the direction of arrow A (the sheet conveyance direction), and a fixing nip portion formed by contacting the heating roller 202 and the pressure roller 203. Heated and pressurized at N, the unfixed toner is fused and fixed on the paper S.

  A peeling guide plate 204 included in a sheet peeling apparatus for peeling the paper S from the heating roller 202 is installed in the vicinity of the discharge port of the heating roller 202. In order to peel the paper S, an air nozzle 305 for injecting compressed air into the gap between the peeling guide plate 204 and the heating roller 202 is provided in the peeling guide plate 204. A paper detection sensor 207 is disposed on the conveyance path 206 that guides the paper S to the fixing device 106. The paper detection sensor 207 is used to detect the timing at which the air nozzle 305 ejects compressed air toward the leading edge of the paper S discharged from the fixing nip N. For example, the control device (not shown) determines the air based on the detection result of the paper detection sensor 207, the distance along the transport path 206 between the paper detection sensor 207 and the fixing nip N, and the transport speed of the paper S. The timing for injecting compressed air from the nozzle 305 is determined.

[Outline of sheet peeling device]
(Configuration of conventional sheet peeling device)
FIG. 2 shows a conventional example of a sheet peeling apparatus for comparison with the present embodiment, and FIG. 2 (a) is a control block diagram showing control functions related to the sheet peeling apparatus, and FIG. These are the schematic diagrams which show the structure of a sheet peeling apparatus.

2A, the sheet peeling apparatus includes an air pump 301, a regulator 302, electromagnetic valves 304 and 306, an air nozzle 305, connection pipes (also referred to as ducts) 320, 321, and 322, and an exhaust port 307. . The air pump 301 generates compressed air that is pumped to the electromagnetic valves 304 and 306. For example, in the case of paper that is easily peeled off from the heating roller 202, such as thick paper with strong rigidity, it is not necessary to inject compressed air in order to peel off the paper from the heating roller 202. Is not driven. On the other hand, in the case of paper that is difficult to peel off from the heating roller 202, such as thin paper with a low rigidity, it is necessary to assist the peeling of the paper from the heating roller 202. The air pump 301 is driven. The paper type is set by a user input from the operation unit panel 113 or a detection result of a paper type detection sensor (not shown). Further, the paper type can be expressed not only by the thickness of the paper but also by, for example, the basis weight (g / m ² ) indicating the weight per unit volume of the paper, the strength and weakness of the paper. The regulator 302 adjusts the air pressure of the compressed air generated by the air pump 301. The electromagnetic valve 304 opens or closes a valve provided therein, thereby sending or stopping sending compressed air from the regulator 302 to the air nozzle 305 via the connecting pipe 321. The air nozzle 305 is composed of a plurality of holes provided at predetermined intervals in the width direction orthogonal to the sheet conveying direction of the fixing device 106 at the tip portion of the peeling guide plate 204 facing the fixing device 106. Yes. The air nozzle 305 injects compressed air from the regulator 302 to the vicinity of the heating roller 202 of the fixing device 106 in order to peel off the paper that is a sheet discharged from the fixing nip portion N. The compressed air generated by the air pump 301 is sent through connecting pipes 320 and 321 connected from the regulator 302 to the air nozzle 305. Further, the electromagnetic valve 306 opens the valve provided inside to discharge the compressed air in the connection pipe 320 (in the duct) from the exhaust port 307 and reduce the air pressure in the connection pipe 320 to the normal air pressure. .

  The control unit 300 controls the entire image forming apparatus, including the above-described control of the image forming unit and control related to image formation such as paper conveyance control. The control unit 300 also has a timer function for measuring time. Further, the control unit 300 includes a ROM and a RAM (not shown). The ROM stores a program and data for controlling the image forming apparatus. The RAM temporarily stores a control program executed by the control unit 300. Memory used to store information. Further, the control unit 300 includes a compressed air control unit 315 that controls the compressed air, a temperature control unit 313 that calculates the temperature of the heating roller 202 based on the temperature detection signal 339 of the thermistor 208, and a paper transport control that controls the paper transport. Part 314 is provided.

  The compressed air control unit 315 controls driving / stopping of the air pump 301 by a control signal 330 in order to drive the air pump 301 and generate compressed air. The compressed air control unit 315 controls the regulator 302 with a control signal 331 in order to adjust the air pressure of the compressed air generated by the air pump 301. Further, the compressed air control unit 315 opens and closes the electromagnetic valve 304 by a control signal 332 and controls the injection of compressed air from the air nozzle 305. The compressed air control unit 315 opens and closes the electromagnetic valve 306 according to the control signal 333 to control the discharge of the compressed air in the connection pipe 320 from the exhaust port 307. Thereby, the air pressure of the compressed air in the connection pipe 320 can be lowered to a normal air pressure.

  The temperature control unit 313 calculates the temperature of the heating roller 202 based on the temperature detection signal 339 from the thermistor 208 and stores the detection result of the thermistor 208 in the RAM 316. And the temperature control part 313 controls on / off of the heater 201 in order to control the temperature of the heating roller 202 as needed from the temperature calculation result. The sheet conveyance control unit 314 transmits a control signal 334 to the sheet conveyance drive unit 309 based on a control signal 336 that notifies a detection result of the sheet detection sensor 207 that detects the position of the sheet, and performs drive control of the motor 310. . The operation unit 318 is a control unit that controls the operation unit panel 113 illustrated in FIG. 1A, and displays an apparatus state on the operation unit panel 113 based on an instruction from the control unit 300, or from the operation unit panel 113. The user input is transmitted to the control unit 300.

  FIG. 2B is a schematic diagram illustrating a configuration of a conventional sheet peeling apparatus. As shown in FIG. 2B, the sheet peeling apparatus includes an air pump 301, a regulator 302, electromagnetic valves 304 and 306, an air nozzle 305, an exhaust port 307, and connecting pipes 320, 321, and 322.

(Configuration of sheet peeling apparatus of this embodiment)
FIG. 3 shows the sheet peeling apparatus of the present embodiment, FIG. 3 (a) is a control block diagram showing control functions related to the sheet peeling apparatus, and FIG. 3 (b) shows the configuration of the sheet peeling apparatus. It is a schematic diagram shown. 3 (a) and 3 (b), the same components as those in FIGS. 2 (a) and 2 (b) are denoted by the same reference numerals.

  The difference between FIG. 3A showing the present embodiment and FIG. 2A of the conventional example is that the electromagnetic valve 306, the connecting pipe 322, and the exhaust port 307 provided in FIG. In a), it has been removed. That is, in the conventional example, after the print job is finished, the control unit 300 opens the electromagnetic valve 306 via the compressed air control unit 315 and discharges the compressed air from the exhaust port 307 in order to lower the air pressure in the connection pipe 320. It was. On the other hand, in this embodiment, after the print job is finished, the solenoid valve 304 is controlled to discharge the compressed air in the connection pipe 320 from the air nozzle 305 and to lower the air pressure in the connection pipe 320. 3A and 3B are the same as those in FIGS. 2A and 2B except for the solenoid valve 306, the connecting pipe 322, and the exhaust port 307, and thus the description thereof is omitted. To do.

[Control sequence during image formation of image forming apparatus]
Next, the operation at the time of image formation of the image forming apparatus of the present embodiment will be described using a flowchart. FIG. 4 is a flowchart illustrating a control sequence when a print job is input to the image forming apparatus according to the present exemplary embodiment. Note that the control sequence shown in FIG. 4 is a control sequence for forming an image on a sheet that is difficult to peel off from the heating roller 202, such as a thin sheet having low rigidity. On the other hand, it is not necessary to inject compressed air to a sheet that is easily peeled off from the heating roller 202, such as a thick paper having high rigidity, in order to peel off the sheet. Therefore, since the air pump 301 that generates compressed air is not driven, it is not necessary to discharge the compressed air in the connection pipe 320.

  In step 501 (hereinafter referred to as S501), the control unit 300 sets the operation mode to the print mode in order to perform image formation. In step S <b> 502, the control unit 300 starts temperature control for setting the temperature of the heating roller 202 of the fixing device 106 to an optimum temperature for image formation. That is, the controller 300 controls the temperature of the heater 201 via the temperature controller 313 based on the temperature detection signal 339 from the thermistor 208. In step S <b> 503, the control unit 300 transmits a control signal 330 to the air pump 301 via the compressed air control unit 315 in order to generate compressed air for peeling the sheet from the heating roller 202, thereby driving the air pump 301. Let it begin. In S504, the control unit 300 transmits a control signal 331 to the regulator 302 via the compressed air control unit 315, and instructs the air pressure of the compressed air generated by the air pump 301 to be adjusted to a predetermined air pressure. Note that the optimum air pressure of the compressed air to be ejected corresponding to the thickness of the paper is stored in a ROM (not shown) of the control unit 300 and adjusted to the air pressure corresponding to the thickness of the paper to be used. Good. In step S <b> 505, the control unit 300 controls the above-described image forming operation, and performs image formation (printing) on the paper conveyed from the paper feed cassette 110. Since the sheet on which the image is formed is thin, the control unit 300 transmits a control signal 332 to the electromagnetic valve 304 via the compressed air control unit 315 at the timing when the leading end of the sheet is discharged from the fixing nip N. Then, the solenoid valve 304 is opened. As a result, the compressed air in the connection pipe 320 is ejected from the air nozzle 305 through the connection pipe 321, and the sheet on which the toner image is fixed is peeled off from the heating roller 202.

  In step S506, the control unit 300 determines whether the print job has been completed. If the print job has not ended, the control unit 300 returns to step S505, and if it has ended, the process proceeds to step S507. In step S507, the control unit 300 determines whether there is a print job to be printed next. If there is a print job, the process returns to step S505, and if there is no print job, the process proceeds to step S508. In step S <b> 508, the control unit 300 stops driving the air pump 301 with the control signal 330 via the compressed air control unit 315.

  In S509, the control unit 300 starts a post-rotation process. In S510, in order to discharge the compressed air in the connection pipe 320, the control unit 300 opens the electromagnetic valve 304 and measures the opening time by the control signal 332 via the compressed air control unit 315. Start the timer. In S511, the control unit 300 reads the timer value from the timer, determines whether t1 time has elapsed after opening the solenoid valve 304, proceeds to S512 if it has elapsed, and proceeds to S511 if it has not elapsed. repeat. The time t1 is a time during which the temperature drop of the heating roller 202 due to the compressed air is blown is within a predetermined temperature range.

  In S512, the control unit 300 closes the solenoid valve 304 by the control signal 332 via the compressed air control unit 315 in order to stop the discharge of the compressed air in the connection pipe 320. Then, the control unit 300 resets the timer and then starts again in order to measure the closing time. In S513, the control unit 300 reads the timer value from the timer, determines whether t2 time has elapsed since the solenoid valve 304 was closed, proceeds to S514 if it has elapsed, and if not, proceeds to the processing of S513. repeat. The time t2 is a time required for the temperature of the heating roller 202, which has been lowered by the jet of compressed air, to rise to a predetermined temperature, for example, a temperature within an error range of the fixing temperature that is optimal for fixing.

  In S514, the control unit 300 determines whether the opening / closing of the electromagnetic valve 304 has been performed a predetermined number of times. If not, the control unit 300 returns to S510, and if it has been performed, the process proceeds to S515. Note that the predetermined number of times is determined by the number of times compressed air is discharged until the air pressure in the connection pipe 320 drops to the normal air pressure, and the control unit 300 counts the number of times discharged with a counter (not shown) and It is determined whether the discharge has been performed a predetermined number of times.

  In S515, the control unit 300 determines whether or not other known post-rotation processing has ended. If it has ended, the control unit 300 proceeds to S516, and if not, repeats the processing in S515. In step S516, the control unit 300 sets the operation mode to a standby mode that waits for input of a print job, and ends the process. The predetermined times of t1 and t2 and S514 described above may be a predetermined time interval or number of times, or may be variable according to the temperature of the heating roller 202 or the air pressure set by the regulator 302, for example.

  The above-described flowchart shows a control sequence in the case of a print job for forming an image on thin paper. For example, for image formation in the case where not only thin paper but also print jobs for printing on thick paper are mixed, the following control sequence may be changed. That is, before starting the driving of the air pump 301, it is determined whether the print job is image formation on thin paper. In the case of image formation on thin paper, the air pump 301 is driven and the air pressure of the regulator 302 is adjusted. After that, image formation is performed. Then, when the print job is finished, the driving of the air pump is stopped. On the other hand, in the case of cardboard image formation, compressed air does not have to be jetted to peel off the sheet, so image formation (printing) is performed without driving the air pump 301 and adjusting the air pressure of the regulator 302. To do. When the print job is completed, it is determined whether or not there is a next print job. If there is a print job, the process returns to the determination of whether or not to form an image on the thin paper. If there is no print job, the compression in the connection pipe 320 is performed. Discharge air.

[Time chart during image formation by image forming apparatus]
FIG. 5 is a time chart showing the states of the air pump 301 and the electromagnetic valve 304 and the temperature state of the heating roller 202 when the image forming apparatus executes a print job. In FIG. 5, the graph shown in FIG. 5A is a time chart when the compressed air is discharged once after the print job is finished, and the graph shown in FIG. 5B is a discharge of compressed air after the print job is finished. It is a time chart of a present Example performed by dividing into multiple times. 5A and 5B, the compressed air is discharged by opening the solenoid valve 304. The graphs in FIGS. 5A and 5B show, in order from the top in the vertical axis direction, the fixing temperature, which is the target temperature set by the heating roller 202, in the driving (ON) and stopping (OFF) states of the air pump 301. Indicates an open (open) / closed (closed) state of the electromagnetic valve 304. Further, the actual fixing temperature indicates the temperature of the heating roller 202 detected by the thermistor 208. The horizontal axis direction indicates time.

  In FIG. 5A, when the power supply of the image forming apparatus is turned on, the heater 201 is turned on and the temperature of the heating roller 202 is increased so as to become the fixing temperature. When the temperature of the heating roller 202 reaches the fixing temperature, the image forming apparatus is set to a standby mode that is a standby mode in which an image forming operation is possible. When the print job is started, the air pump 301 is driven (ON) to generate compressed air. Then, at the timing when the sheet is discharged from the fixing device 106, the electromagnetic valve 304 is opened (pulse interval in the figure), and the compressed air is discharged. While the compressed air is being discharged, the surface of the heating roller 202 temporarily decreases due to the jet of compressed air, but since the control unit 300 is controlled to achieve the target fixing temperature, the heating roller 202 is kept constant. Be drunk. In FIG. 5A, after the electromagnetic valve 304 is opened five times, the print job is finished and the driving of the air pump 301 is stopped (OFF). The operation up to this point is the same in both the case of the conventional example of FIG. 5A and the case of the present example of FIG.

  Regarding the operation after the driving of the air pump 301 is stopped, in the conventional example of FIG. 5A, the compressed air in the connection pipe 320 is discharged, so that the electromagnetic valve 304 is longer than that in FIG. Open for a while and exhaust the compressed air at once. As a result, the surface temperature of the heating roller 202 decreases locally and rapidly as shown in part A of FIG. 5A, and it is necessary for the surface temperature of the heating roller 202 to rise to the target fixing temperature. It can be seen that the time is longer than that in FIG.

  On the other hand, in the present embodiment shown in FIG. 5B, the amount of compressed air discharged at one time is limited by intermittently discharging the compressed air in the connecting pipe 320. Furthermore, since the heating roller 202 is driven to rotate, the places where the jetted compressed air is sprayed onto the surface of the heating roller 202 can be dispersed. As a result, as shown in part B of FIG. A local temperature drop of the heating roller 202 can be prevented. As a result, in the case of FIG. 5B of this embodiment, even if the next print job starts immediately after the discharge of compressed air, the surface temperature of the heating roller 202 is immediately stabilized at the target fixing temperature. The next print job can be executed without downtime.

  Note that the intermittent operation of the solenoid valve 304 is not performed in a situation where the next print job is not immediately executed, for example, when an abnormality occurs in the image forming apparatus or in the case of paper jam processing, and FIG. Thus, the compressed air may be discharged by opening the solenoid valve 304 for a long time by one discharge.

  The image forming apparatus shown in FIG. 1 according to the present embodiment has been described as a single-color (for example, black and white) laser beam printer, but is not limited to the one illustrated in FIG. 1, and for example, an image forming apparatus including a plurality of image forming units. It may be a device. Further, the image forming apparatus may include a primary transfer unit that transfers a toner image on the photosensitive drum 101 to an intermediate transfer belt, and a secondary transfer unit that transfers the toner image on the intermediate transfer belt to a recording material.

  As described above, according to the present embodiment, it is possible to reduce the cost and prevent the image quality from being lowered. As described above, the cost can be reduced by eliminating the dedicated solenoid valve for discharging the compressed air in the connecting pipe after the print job is completed. Further, when the compressed air is discharged, the discharge is performed in a plurality of times, so that the temperature of the surface of the heating roller does not decrease locally and rapidly. Therefore, it is possible to prevent the image quality from being deteriorated due to the temperature unevenness of the heating roller.

  In Example 1, the example which discharges | emits compressed air in multiple times was demonstrated. In the second embodiment, a description will be given of an embodiment in which the compressed air is discharged at once by reducing the air pressure. The image forming apparatus in the present embodiment is the laser beam printer shown in FIG. 1 described in the first embodiment, and detailed description thereof is omitted. Moreover, since the structure of the sheet peeling apparatus in a present Example is also as having demonstrated in FIG. 3 of Example 1, description is abbreviate | omitted.

[Control sequence during image formation of image forming apparatus]
An operation at the time of image formation of the image forming apparatus according to the present exemplary embodiment will be described with reference to a flowchart. FIG. 6 is a flowchart illustrating a control sequence when a print job is input to the image forming apparatus according to the present exemplary embodiment. Note that the control sequence shown in FIG. 6 is a control sequence in the case of forming an image on a sheet that is difficult to peel off from the heating roller 202, such as a thin sheet with low rigidity, as in the first embodiment. On the other hand, it is not necessary to spray compressed air to peel off the paper that is easily peeled off from the heating roller 202, such as thick paper with high rigidity. Therefore, the air pump 301 that generates compressed air is not driven, and there is no need to discharge the compressed air in the connection pipe 320.

  In FIG. 6, the processing from S601 to S609 is the same as the processing from S501 to S509 in FIG. In step S610, the control unit 300 transmits a control signal 331 to the regulator 302 via the compressed air control unit 315, and adjusts the air pressure of the compressed air generated by the air pump 301 to a lower air pressure than the air pressure during image formation. To instruct. Note that the air pressure in this case is adjusted to such an air pressure that the temperature drop of the heating roller 202 by the injected compressed air falls within a predetermined temperature range.

  In step S611, the control unit 300 transmits a control signal 332 to the electromagnetic valve 304 via the compressed air control unit 315 to release the compressed air in the connection pipe 320, and opens the electromagnetic valve 304 as well as the opening time. Start a timer to measure In S612, the control unit 300 reads the timer value from the timer, determines whether t3 time has elapsed after opening the solenoid valve 304, proceeds to S613 if it has elapsed, and proceeds to S612 if it has not elapsed. repeat. The time t3 is the time required for the air pressure in the connection pipe 320 to drop to the normal air pressure by opening the electromagnetic valve 304 and discharging the compressed air.

  In S613, the control unit 300 closes the solenoid valve 304 by the control signal 332 via the compressed air control unit 315 in order to stop the discharge of the compressed air in the connection pipe 320. In S614, the control unit 300 determines whether or not the post-rotation mode has ended. If it has ended, the control unit 300 proceeds to S615, and if not, repeats the processing in S614. In step S615, the control unit 300 sets the operation mode to a standby mode that waits for input of a print job, and ends the process. The time t3 described above may be a predetermined time interval, or may be variable according to the air pressure set by the regulator 302, for example.

  The above-described flowchart shows a control sequence in the case of a print job for forming an image on thin paper. For example, image formation in the case where print jobs for printing on not only thin paper but also thick paper are mixed can be dealt with by changing to the control sequence described in the first embodiment.

[Time chart during image formation by image forming apparatus]
FIG. 7 is a time chart showing the state of the air pump 301 and the electromagnetic valve 304 and the temperature state of the heating roller 202 when the image forming apparatus executes a print job. In FIG. 7, the graph shown in FIG. 7A is a time chart when compressed air is discharged once after the end of the print job, as in FIG. 5A of the first embodiment. On the other hand, the graph shown in FIG. 7B is a time chart of this embodiment in which discharge is performed by lowering the air pressure of the compressed air after the end of the print job. Note that the compressed air is discharged in the case of FIGS. 7A and 7B by opening the solenoid valve 304. 7A and 7B, in the graphs displayed, the fixing temperature, which is the target temperature set for the heating roller 202, is driven (ON) and stopped in order from the top in the vertical axis direction. The (OFF) state indicates the control state of the compressed air pressure in the regulator 302. Further, the graph of FIG. 7 shows the actual fixing temperature, which is the temperature of the heating roller 202 detected by the thermistor 208, in the open (open) / closed (closed) state of the electromagnetic valve 304. The horizontal axis direction indicates time.

  In FIG. 7, compared to FIG. 5, a graph showing the control state of the compressed air pressure in the regulator 302 is added. In FIG. 7A showing a conventional example, the control of the air pressure by the regulator 302 is only one stage of a predetermined air pressure. On the other hand, in FIG. 7B showing the present embodiment, the control of the air pressure by the regulator 302 is performed in two stages of “high” that is a predetermined air pressure and “low” that is lower than the predetermined air pressure. In FIG. 7B, the air pressure at the time of image formation is the same as that in FIG. 7A (“high”), but when the compressed air is discharged, the air pressure is controlled to be “low”. This is different from FIG.

  In FIG. 7, the operation from when the image forming apparatus is turned on until the print job is completed is the same as that in FIG. As for the operation after the print job is completed, in the conventional example of FIG. 7A, the compressed air in the connection pipe 320 is discharged after the print job is completed. , And the compressed air is discharged at a stretch while maintaining the same high air pressure as during image formation. As a result, as shown in part C of FIG. 7A, the surface temperature of the heating roller 202 is locally and rapidly decreased, and the time required for the surface temperature of the heating roller 202 to return to the fixing temperature. However, it turns out that it becomes long compared with FIG.7 (b).

  On the other hand, in this embodiment of FIG. 7B, the discharge amount per unit time is smaller than that in FIG. 7A by discharging the compressed air in the connecting pipe 320 after lowering the air pressure of the compressed air. Less. Therefore, the time required for discharging the compressed air in the connection pipe 320 is longer than that in FIG. However, since the heating roller 202 is rotationally driven during that time, the place where the jetted compressed air is blown onto the surface of the heating roller 202 is uniform, and the air pressure is low. As shown, a local temperature drop of the heating roller 202 can be prevented. Therefore, in the case of FIG. 7B of this embodiment, even if the next print job starts immediately after the discharge of compressed air, the surface temperature of the heating roller 202 is immediately stabilized at the target fixing temperature. Therefore, the next print job can be executed without downtime.

  Note that, for example, when an abnormality occurs in the image forming apparatus or when a paper jam process is performed, a subsequent print job is not immediately executed. The valve 304 may be opened to discharge the compressed air.

  As described above, according to the present embodiment, it is possible to reduce the cost and prevent the image quality from being lowered. As described above, the cost can be reduced by eliminating the dedicated solenoid valve for discharging the compressed air in the connecting pipe after the print job is completed. Furthermore, when the compressed air is discharged, the air pressure is lowered and discharged, so that the temperature on the surface of the heating roller does not decrease locally and rapidly. Therefore, it is possible to prevent the image quality from being deteriorated due to the temperature unevenness of the heating roller.

300 Control Unit 301 Air Pump 302 Regulator 304 Solenoid Valve 305 Air Nozzle 320 Duct

Claims (9)

When fixing the toner image formed on the sheet by heating and pressurizing the conveyed sheet at a nip formed by a heating rotator including a heat source and a pressure rotator that is in pressure contact with the heating rotator. A sheet peeling apparatus for peeling a sheet from the heating rotator,
Generating means for generating compressed air;
Adjusting means for adjusting the air pressure of the compressed air;
An injection means for injecting the compressed air pressure-fed from the adjusting means through a duct by opening and closing a valve included therein;
An exhaust port for discharging the compressed air injected by the injection means to the heating rotator;
Control means for controlling the generating means, the adjusting means, and the injection means for discharging the compressed air;
The control means, after stopping the generation of compressed air by the generating means, discharges the compressed air in the duct having the same air pressure as that at the time of image formation for a predetermined time by the ejecting means a plurality of times. A sheet peeling apparatus characterized by lowering the air pressure in the duct.   2. The sheet peeling apparatus according to claim 1, wherein when the next print job is not immediately executed, the control unit discharges compressed air having the same air pressure as that at the time of image formation at a time. . When fixing the toner image formed on the sheet by heating and pressurizing the conveyed sheet at a nip formed by a heating rotator including a heat source and a pressure rotator that is in pressure contact with the heating rotator. A sheet peeling apparatus for peeling a sheet from the heating rotator,
Generating means for generating compressed air;
Adjusting means for adjusting the air pressure of the compressed air;
An injection means for injecting the compressed air pressure-fed from the adjusting means through a duct by opening and closing a valve included therein;
An exhaust port for discharging the compressed air injected by the injection means to the heating rotator;
Control means for controlling the generating means, the adjusting means, and the injection means for discharging the compressed air;
The control means, after stopping the generation of compressed air by the generating means, adjusts the air pressure of the compressed air in the duct to an air pressure lower than the air pressure at the time of image formation by the adjusting means, and the jetting means controls the duct. A sheet peeling apparatus characterized in that the compressed air in the inside is discharged at a time to lower the air pressure in the duct.   When the next print job is not immediately executed, the control unit does not adjust the air pressure of the compressed air in the duct by the adjusting unit, and discharges the compressed air having the same air pressure as that during image formation. The sheet peeling apparatus according to claim 3, wherein the sheet peeling is performed at a time.   The sheet peeling apparatus according to any one of claims 1 to 4, wherein the sheet is a paper type that is difficult to peel off from the heating rotating body.   The sheet peeling apparatus according to claim 1, wherein the generation unit is an air pump.   The sheet peeling apparatus according to claim 1, wherein the adjusting unit is a regulator.   The sheet peeling apparatus according to claim 1, wherein the ejection unit is a solenoid valve. An image forming apparatus having image forming means for forming an image on a sheet,
An image forming apparatus comprising the sheet peeling device according to claim 1, which peels a sheet conveyed from a fixing device.

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