JP2006038920A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, which has a device for heating and fixing an unfixed toner image formed on a recording material, ability to steadily convey a recording material, by applying optimum amount of heat to the recording material according to the type of the recording material. <P>SOLUTION: The image forming apparatus includes a temperature-detecting means, disposed downstream of the fixing nip of a heat fixing device so as to be in contact with a recording material with a predetermined pressure. The apparatus identifies the type of the recording material by the temperature detected by the temperature detecting means, and by altering the interval between the recording materials to be supplied, the amount of heat supplied to each recording material is optimized. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a recording material (transfer material, printing paper, photosensitive paper, electrostatic recording paper, etc.) in an image forming process section in an image forming apparatus that employs an image forming process such as an electrophotographic method or an electrostatic recording method. The present invention relates to a heat fixing device that performs heat fixing processing using an unfixed toner image of target image information formed and supported by a transfer method or a direct method as a fixed image, and an image forming apparatus having the heat fixing device.

  2. Description of the Related Art Conventionally, in a fixing device provided in an image forming apparatus that employs an electrophotographic system, an electrostatic recording system, etc., a fixing roller and a pressure roller that rotate a recording material carrying an unfixed toner image in pressure contact with each other. A so-called heat roller type heat fixing device is widely used in which a toner image is fixed as a permanent image on a recording material by passing through a nip portion formed by the above method. In this heat roller type heat fixing device, as a means for preventing the recording material after heat fixing from being wound around the fixing roller, the recording material is disposed in contact with the surface of the fixing roller, and the recording material after fixing is forcibly separated from the fixing roller. Separating nails are known. However, since the separation claw easily damages the surface of the fixing roller due to its mechanism, the scar on the fixing roller by the separation claw is transferred to the image at the time of fixing, and there is a problem that the image quality is deteriorated.

  On the other hand, from the standpoint of promoting energy conservation in recent years, a method that suppresses power consumption as much as possible without supplying power to the fixing device during standby, more specifically, through a thin film with a small heat capacity between the heater unit and the pressure roller. Patent Document 1, Patent Document 2, and Patent Document 3 propose a heat fixing method by a film heating method for fixing a toner image on a recording material. This film heating type fixing device is attracting attention as a method that has higher heat transfer efficiency than the conventional heat roller method and quick start-up of the device, and has been applied to higher-speed models. In this method, it is necessary to reduce the heat capacity of the heating surface of the fixing unit in order to emphasize the rate of temperature increase. As a result, it is difficult to form an elastic layer on the heating surface, and a hard heating surface is used. For this reason, this type of fixing method has a configuration in which a difference in heating efficiency is likely to occur due to the unevenness of the recording material surface. In this film heating type heat fixing device, it is difficult to use the separation claw itself.

Therefore, Patent Document 4 proposes a configuration in which the recording material after fixing is separated from the fixing roller and the fixing film by using the curvature of the fixing roller and the fixing film without using a separation claw.
JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44074 JP-A-6-75505

  However, the fixing device that does not use the separation claw as described above has the following problems.

  The recording material is supported at one point of the fixing nip portion until the leading end in the conveyance direction of the recording material passes through the fixing nip portion and reaches the paper discharge roller. For this reason, the conveyance behavior of the tip side region in this state is in an unstable state. In particular, in the case of recording paper made of resin such as OHT film, etc., where the stiffness becomes weak when heat is applied, it is easy to wrap around the fixing member due to the influence of the adhesive force between the toner and the fixing member. , Jam caused by winding will occur.

  Further, in order to reduce the adhesive force between the toner and the fixing member, by increasing the amount of heat supplied from the fixing member to the recording material, it is possible to completely melt the toner and prevent the recording material from being wound around the fixing member. it can. However, if the amount of heat supplied from the heating member is increased for thin paper with a small heat capacity, the temperature of the thin paper discharged increases, so that when the thin paper is continuously stacked on the paper discharge tray, A phenomenon occurs in which the recording materials stick to each other as an adhesive. Further, when the attached recording material is peeled off, the toner is also peeled off, and an image defect occurs.

  The invention according to the present application has been made to solve the above-described problems of the prior art, and an object of the invention is to provide a heat fixing device that realizes stable paper conveyance.

In order to solve the above-described problems, the present invention provides a non-printing surface side after passing through a heat fixing device in a heat fixing device that forms a permanent image by passing an unfixed image formed on a recording material through the heat fixing device. And a means for measuring the temperature of the recording material by contacting the non-printing surface side of the recording material with a predetermined pressure, and when the preceding recording material passes through the fixing device, the subsequent recording material forms an image. When the state in which the image forming operation has already been started continues continuously, the temperature of the preceding recording material is detected, and the subsequent recording material supply interval is made variable according to the temperature. And
When the detected temperature of the preceding recording material is higher than a predetermined threshold temperature, the subsequent recording material supply interval is widened.

(Function)
An optimal amount of heat can be applied to the recording material according to the type of the recording material to prevent the recording material from being wound around the heating member and sticking on the paper discharge tray when the paper is continuously fed.

  Means for detecting a temperature or humidity depending on at least one of an environmental temperature and a humidity in which the image forming apparatus is installed, and the predetermined threshold temperature is determined according to the detected temperature or the humidity; Control is performed to vary the recording material supply interval in accordance with the humidity.

(Function)
By optimizing the amount of heat applied to the recording material regardless of the temperature and humidity of the environment in which the image forming apparatus is installed, the recording material is wrapped around the heating member or continuously on the discharge tray when the paper is passed. Sticking can be prevented.

  In a heating and fixing apparatus that forms a permanent image by passing an unfixed image formed on a recording material through a nip formed by a heating rotator and a pressing rotator, a non-fixed image after passing through the heating and fixing apparatus. A preceding recording, comprising means for measuring a temperature of the recording material and a means for measuring the surface temperature of the pressurizing rotating body, arranged on the printing surface side, contacting the non-printing surface side of the recording material with a predetermined pressure. When the material passes through the fixing device, the temperature of the preceding recording material and the pressurizing rotation are continued when the subsequent recording material continues in a state where the image forming operation has already started in the image forming unit. The surface temperature of the body is detected, and the subsequent recording material supply interval is made variable according to the temperature.

(Function)
By detecting the temperature of the recording material and the temperature of the pressure rotator and optimizing the amount of heat applied to the recording material regardless of the type of recording material and the paper passing mode, the recording material can be wound around the heating member and continuously passed. It is possible to prevent sticking on the paper discharge tray when paper is printed.

  According to the present invention, the temperature detection means formed of a low heat capacity member is disposed on the non-printing surface side immediately after passing through the heat fixing unit, and is brought into contact with the non-printing surface of the recording material with a predetermined pressurizing force. By detecting the temperature depending on the temperature of the recording material discharged from the printing section, the type of the recording material is automatically determined, and when the recording material is easy to wind around the fixing member, the recording material is changed by changing the recording material supply interval. It is possible to optimize the amount of heat applied to the recording material and to stably convey the recording material regardless of the type of the recording material.

  In addition, when the recording material supply interval is changed, slip jamming is likely to occur. By detecting the temperature of the pressure roller, the recording material is further prevented from being wound and slip jamming. By changing the supply interval of the recording medium, it becomes possible to perform stable recording material conveyance.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  Embodiments according to the present invention will be described below. First, FIG. 2 is a configuration diagram of an image forming apparatus according to the present invention.

  In FIG. 2, reference numeral 50 denotes a photosensitive drum, and a photosensitive material such as OPC, amorphous Se, or amorphous Si is formed on a cylindrical substrate such as aluminum or nickel. The photosensitive drum 50 is rotationally driven in the direction of the arrow. First, the surface is uniformly charged by a charging roller 51 as a charging device. Next, scanning exposure is performed by the laser beam 52 that is ON / OFF controlled according to the image information, and an electrostatic latent image is formed. This electrostatic latent image is developed and visualized by the developing device 53. As a developing method, a jumping developing method, a two-component developing method, an FEED developing method, or the like is used, and image exposure and reversal development are often used in combination.

  The visualized toner image is transferred from the photosensitive drum 50 onto a recording material conveyed at a predetermined timing by a transfer roller 54 as a transfer device. The recording material conveyed at a predetermined timing is nipped and conveyed to the photosensitive drum 50 and the transfer roller 54 with a constant pressure. The recording material onto which the toner image has been transferred is conveyed to the heat fixing device 56 and fixed as a permanent image. On the other hand, the transfer residual toner remaining on the photosensitive drum 50 is removed from the surface of the photosensitive drum 50 by the cleaning device 55.

  FIG. 1 shows a configuration of a heat fixing apparatus according to the present invention. In the present embodiment, a case where the present invention is applied to a film fixing heating apparatus (on-demand fixing apparatus) that heats a sheet through a thin film will be described. However, the present invention is not limited to an on-demand fixing apparatus, The present invention can also be applied to an image fixing method such as a heat roller method in which a sheet is nipped and conveyed by a heating roller maintained at a temperature and a pressure roller pressed against the heating roller via an elastic layer.

  The recording material is developed and transferred by an image forming unit composed of a photosensitive drum, a transfer roller, and the like, and then sent to a heat fixing unit. The leading edge of the recording material is guided by a fixing inlet guide 21 to a pressure nip N formed by a heating body 23 and a pressure roller 24 with a fixing film 22 interposed therebetween.

  Reference numeral 22 denotes a thin flexible endless belt-shaped fixing film as a rotating body for heating, and a release layer is formed on the surface layer. The endless belt-like fixing film is externally fitted to the semicircular arc-shaped film guide member 25 with a margin in the circumference.

  The fixing film 22 has a total thickness of 100 μm or less, preferably 60 μm or less and 20 μm or more in order to reduce the heat capacity and improve the quick start property, and heat resistant resin film such as polyimide, PEEK, Ni electroformed film, stainless seamless film Use a metal film. In the case of a metal film, since the thermal conductivity is good, its thickness is 150 μm or less, and it can be practically used.

  Reference numeral 24 denotes a pressure roller as a pressure rotating body, which has a silicone rubber layer on a core metal such as iron or aluminum, and further has a PFA tube layer as a release layer thereon.

  The fixing film 22 is driven by the rotation of the pressure roller 24 so that at least when the image is fixed, the fixing film 22 is in close contact with the surface of the heating body (heating heater) in the clockwise direction indicated by an arrow while sliding on the surface of the heating body. That is, it is rotationally driven without wrinkles at substantially the same peripheral speed as the conveying speed of the recording material carrying the unfixed toner image T conveyed from the image forming unit side (not shown).

  The heating element 23 is, for example, a ceramic heater, and includes an energization heating element (resistance heating element) as a heat source that generates heat by supplying power, and the temperature is raised by the heat generated by the energization heating element. As the heating element, alumina (Al2O3) or aluminum nitride (AlN) is used as a substrate, and a resistor made of silver / palladium is printed on the substrate in a thick film to form a heating element pattern having a desired resistance value. Further, a glass layer is formed on the heating element as a sliding layer with the protective layer / fixing film. A thermistor, which is a temperature detection element, is bonded and fixed to the back side of the heating element forming surface, the heater temperature is monitored, and the monitor temperature information is input to the control circuit unit. The control circuit unit controls an AC driver to maintain the heater temperature (fixing nip portion temperature) at a predetermined temperature, thereby controlling the amount of power supplied from the AC power source to the heating element of the heating element.

  A pressure nip formed between the heating member and the heating member by the elastic force generated by the deformation of the elastic layer of the pressure roller when the heating member is heated by the power supply to the energizing heating element and the fixing film is rotationally driven. When the recording material is introduced into the portion N (fixing nip portion), the recording material passes through the fixing nip portion N in a state of being in close contact with the fixing film and overlapping with the fixing film.

  In the process of passing through the fixing nip portion of the recording material, thermal energy is applied from the heating body to the recording material through the fixing film, and the unfixed toner image on the recording material is heated and melted and fixed. Thereafter, the recording material passes through the fixing nip portion N, is separated and discharged from the fixing film, and is sent to the paper discharge portion by the FU paper discharge roller 26 and the FU paper discharge roller 27.

  In the image forming apparatus according to the present embodiment, a temperature detection unit including a heat collecting plate and a temperature detection sensor is provided on a paper discharge sensor installed on a recording material conveyance path from the heat fixing device to the paper discharge unit. ing. The temperature detecting means detects the temperature of the non-printing surface of the recording material after image fixing discharged from the heat fixing device. Here, there are two advantages of detecting the temperature on the non-printing surface side of the recording material. First, during normal single-sided printing, the recording material comes into contact with the heat collecting plate on the surface opposite to the surface on which the toner is fixed, so that it is affected by the adhesion of toner to the heat collecting plate. There is no. That is, the toner does not adhere to the heat collecting plate, and the temperature detection accuracy is not lowered. Secondly, since heat energy is applied from the heating element to the printing surface side of the recording material via the fixing film, the temperature is detected on the non-printing surface, so that the recording material printing surface side is changed to the non-printing surface side. It is possible to predict the characteristics of the recording material from the detected temperature by utilizing the difference in temperature gradient characteristics due to heat conduction to the recording medium. For example, the temperature on the non-printing surface side of the thin recording material is higher than the temperature on the non-printing surface side of the thick recording material.

(Temperature detection means configuration)
Between the fixing nip portion N and the paper discharge roller nip portion, a fixing paper discharge guide 28 that forms a recording material conveyance path is provided. The fixing paper discharge guide is made of a material having high heat resistance such as PBT or PET. The conveyance surface of the fixing paper discharge guide 28 is set below a line A (see FIG. 3) connecting the fixing nip portion N and the paper discharge roller nip portion, and the recording material conveyance speed of the paper discharge roller 26 is set at the fixing nip. The speed is set faster than the recording material conveyance speed in the portion N, so that the recording material and the conveyance surface of the fixing paper discharge guide 28 do not directly touch when the recording material passes.

  The fixing paper discharge guide 28 is provided with a paper discharge sensor that detects the presence or absence of a recording material passing through the heat fixing device. The paper discharge sensor includes a paper discharge sensor lever 29 and a photo interrupter 30. The paper discharge sensor lever 29 is mainly made of a highly slidable plastic member such as polyacetal, and is installed at a position where the recording material passing portion at the front end blocks a line A connecting the fixing nip portion N and the paper discharge roller nip portion. The The paper discharge sensor lever 29 is tilted in the paper transport direction when the recording material passes (FIG. 4), and the shielding portion blocks the infrared light of the photo interrupter. When there is no recording material, the paper discharge sensor lever returns to the home position, and the shielding portion comes to a position where the infrared light of the photo interrupter is not blocked (FIG. 1). As described above, the infrared light of the photo interrupter is turned on and off by the movement of the paper discharge sensor lever to detect the presence or absence of the recording material.

  FIG. 5 is a detailed view of the vicinity of the paper discharge sensor lever 29. A heat collecting plate 31 made of a thin plate having a thickness of about 0.1 mm such as aluminum or stainless steel having a small heat capacity is integrated with the paper discharge sensor lever 29 by outsert molding or the like at the recording material passage portion at the tip of the paper discharge sensor lever. It is configured to come into contact with the non-printing surface side of the recording material discharged from the heat fixing device by an urging means (not shown) such as a spring.

  The heat collecting plate is disposed above line A connecting the fixing nip portion and the discharge roller nip portion. The leading end of the recording material that has passed through the fixing nip first contacts the plastic portion of the paper discharge sensor lever 29. Further, when the recording material is sent to the downstream side, the paper discharge sensor lever rotates, and the heat collecting plate contacts the non-printing surface side of the recording material. Thus, by reducing the heat capacity of the heat collecting plate and positively contacting the recording material, the temperature of the heat collecting plate can be made substantially the same as the temperature of the recording material in a short time. Here, in order to reduce the heat capacity of the heat collecting plate, it is desirable that the heat collecting plate be as small as possible in the recording material conveyance direction and in the direction perpendicular to the recording material conveyance direction and in the direction substantially parallel to the width of the recording material. .

  When performing double-sided printing, the heat collecting plate on the paper discharge sensor lever comes into contact with the first printing surface of the recording material when the second side passes, so there is a concern that toner adheres to the surface of the heat collecting plate. Is done. As a countermeasure, the surface of the heat collecting plate may be coated with Teflon (registered trademark) or a surface treatment such as UV coating as long as it does not affect the heat conduction of the heat collecting plate. Further, the surface of the heat collecting plate may be coated with PI (polyimide) or the like.

  A highly sensitive temperature detection sensor 32 such as a thermistor is attached to the back surface of the heat collecting plate 31 at the tip of the paper discharge sensor lever 29 by a method such as adhesion. When the recording material after image fixing is conveyed from the heat fixing device, the paper discharge sensor lever 29 is rotated, and the heat collecting plate 31 comes into contact with the non-printing surface of the recording material, deprives the recording material of heat, and on the back surface. Heat is conducted to the installed temperature detection sensor 32 to detect the temperature of the recording material. At this time, the temperature detection sensor is attached directly below the position where the recording material and the heat collecting plate 31 are in contact with each other when the paper ejection sensor lever 29 rotates, that is, when the paper ejection sensor lever 29 detects the presence of the recording material. The accuracy of temperature detection of the recording material is improved by minimizing the influence of the temperature gradient in the heat collecting plate. Further, by using a metal member for the sliding portion with the recording material, wear of the sliding portion can be prevented, and the durability of the paper discharge sensor lever 29 can be improved.

  As described above, by providing the heat collecting plate 31 and the temperature detection sensor 32 such as the thermistor on the paper discharge sensor lever 29 that detects the presence or absence of the recording material, the positional information and temperature information of the recording material can be accurately synchronized. Thus, it is possible to accurately detect at which position of the recording material the temperature information output from the thermistor. For example, the temperature information of the thermistor tends to rise at the trailing edge compared to the leading edge of the recording material, so it is possible to detect the recording material temperature more reliably by synchronizing with the recording material position information. become.

  It has been confirmed that the temperature detected by the temperature detection sensor 32 (hereinafter referred to as “paper discharge temperature detection means”) disposed on the paper discharge sensor lever 29 is affected by the type of recording material conveyed to the fixing nip portion. By automatically changing the fixing conditions according to the detected temperature, it is possible to obtain stable fixing performance regardless of the type of recording material.

  Next, details of the present embodiment will be described.

  FIG. 6 is a graph showing a heater control temperature table for this embodiment. The laser beam printer to which this control is applied has a printing speed of 50 sheets of letter-size paper per minute (throughput of 50 ppm) and a recording material feed speed (process speed) of 300 mm / sec. In the present embodiment, an algorithm for lowering the heater control temperature according to the number of continuous prints is employed. This is because the fixing roller temperature required for obtaining sufficient fixing performance can be lowered by increasing the pressure roller temperature during continuous printing.

  Further, at the time of initial printing, the temperature of the heater is monitored at the start of printing, and the number of sheets at the start is determined according to the temperature.

  Specifically, when the heater temperature at the time of printing the first sheet is 85 ° C. or less, the temperature starts from the set temperature of the first sheet. On the other hand, when the heater temperature at the time of the first printing is higher than 85 ° C., the temperature starts from the set temperature of the 21st sheet, and thereafter the number counter is increased to 22 sheets and 23 sheets at the time of continuous printing. .

  Further, when the heater temperature at the time of printing the first sheet is 100 ° C. or higher, it starts from the set temperature of the 41st sheet, and thereafter the sheet number counter is incremented to 42 sheets and 43 sheets at the time of continuous printing.

  Consider printing 500 sheets of recording material continuously. The heating heater is controlled at a temperature indicated by a solid line A in FIG. When thin paper with weak stiffness was used as the recording material, when the heater target temperature reached 205 ° C. after 150 continuous prints, the recording material was jammed around the fixing film. This is because the amount of heat supplied from the heater to the recording material has decreased, the toner is not completely melted and the adhesiveness to the fixing film is increased, and the fixing film and the recording material are wound without being separated. Is due to. This is because thin paper with weak stiffness is used as a recording material, and with thick paper with strong stiffness, winding does not occur even when the heater target temperature is 205 ° C.

  On the other hand, as shown by the broken line B in FIG. 6, when the heater target temperature for continuous printing of 150 sheets or more is set to 210 ° C. and thin paper is continuously printed, printing can be performed without generation of winding even after 150 sheets. However, since an excessive amount of heat is supplied to thin paper with a small heat capacity, the temperature of the recording material on the paper discharge tray rises, and when 500 sheets are stacked, the recording materials adhere to each other.

  Therefore, when it is determined that the thin paper has been printed by using the discharge temperature detecting means, the control is performed for the continuous printing of 150 sheets or more by setting the target temperature to 205 ° C. and widening the recording material supply interval to the throughput of 40 ppm. . As the recording material supply interval increases, the temperature rise of the pressure roller between the papers increases, so the amount of heat supplied to the paper leading edge of the subsequent recording material increases, so that the toner at the paper leading edge can be melted in particular. In addition, the recording material and the fixing film can be easily separated, and the occurrence of winding jam can be prevented. Further, when the throughput is lowered, the interval at which the recording material is discharged to the paper discharge tray is widened, and the temperature of the recording material is easily lowered, so that sticking can be prevented from occurring.

Next, a method for discriminating the type of recording material using the discharge temperature detecting means will be described. Shows the detection result of the paper discharge temperature detecting means when the cardboard having a basis weight of 60 g / m ² of thin paper and basis weight 100 g / m ² was continuously printed in FIG. The horizontal axis represents the detected temperature (initial temperature T0) of the paper discharge temperature detecting means immediately before the start of printing, and the vertical axis represents the detected temperature (detected temperature T1) when the 30th sheet during continuous printing is passed. . When the standby state of the printer continues for a long time and the temperature in the fixing device becomes room temperature, the initial temperature T0 also becomes a value close to room temperature. On the other hand, when the printing operation is continued and the temperature in the fixing device is increased and the next printing operation is performed, the initial temperature T0 also becomes a high value. Further, the detection temperature T1 of the 30th sheet discharge temperature detection means during continuous printing also changes in accordance with each initial temperature T0. However, since there is a difference in the detection temperature T1 of the 30th sheet between thin paper and thick paper, it is possible to determine the paper type using the solid line control equation shown in FIG. 7 as a threshold value.

  FIG. 8 shows a flowchart for preventing the winding jam and sticking by discriminating the type of the recording material by using the discharge temperature detecting means and supplying the optimum amount of heat. When the laser beam printer receives the signal, it measures the initial temperature T0 by the paper discharge temperature detecting means before starting the printing operation. Next, the initial temperature T0 is substituted into the control equation shown in FIG. 7 based on the initial temperature T0 to determine the threshold temperature Ta. Thereafter, the sheet feeding operation of the recording material from the sheet feeding device, the image forming operation in the image forming unit, and the energization of the heater of the heat fixing device are started, and the detected temperature T1 by the sheet discharge temperature detecting means (in this embodiment, continuous printing) Measure the temperature of the 30th sheet). Next, when the number of continuous prints exceeds 150, the magnitude of T1 and Ta measured previously are compared. When T1 is smaller, the printing operation is performed with the throughput kept at 50 ppm. When T1 is larger Performs a printing operation with a recording material supply interval widened and a throughput of 40 ppm. As described above, the printing operation is continued by automatically controlling the amount of heat applied to the recording material according to the type of the recording material conveyed based on the temperature detected by the paper discharge temperature detecting means, and the printing operation is finished after the last page is heated and fixed. To do.

  As described above, in this embodiment, the discharge temperature detecting means having a low heat capacity is arranged on the non-printing surface side immediately after the fixing nip, the type of the recording material is automatically determined, and the optimum amount of heat corresponding to the type of the recording material is supplied. Thus, it is possible to prevent the occurrence of a thin paper winding jam and to perform a printing operation without reducing the throughput on a thick paper or the like that does not generate a winding jam.

  The second embodiment of the present invention will be described below. Since the overall configuration of the image forming apparatus according to the present embodiment is the same as that shown in the first embodiment, description thereof is omitted. In this embodiment, temperature detection means such as a thermistor for detecting the environment (room temperature) in which the image forming apparatus is installed is used in the first embodiment according to the environment in which the image forming apparatus is used. A method for performing optimum heat fixing of the recording material by the indicated sheet discharge detecting means is proposed.

  A control method using the paper discharge temperature detecting means according to this embodiment will be described below. The laser beam printer to which this control is applied has a printing speed of 50 sheets of letter-size paper per minute (throughput is 50 ppm) and a recording material feed speed (process speed) of 300 mm / sec as in the first embodiment. Usually, the temperature of the recording material stacked in the sheet feeding toilet is kept close to the temperature of the environment depending on the environment where the image forming apparatus is arranged. In addition, even if the heating condition of the heat fixing device is the same depending on the environment in which the image forming apparatus is installed, the temperature around the heat fixing device varies due to the influence of convection and the like. In addition, since the film heating type heat fixing apparatus uses a low heat capacity film, the temperature of the heater is finely adjusted according to the number of continuous prints according to the environment where the image forming apparatus is installed. The control method is taken, and the specific temperature control is shown in FIG. In FIG. 9, the horizontal axis represents the number of continuous prints, and the vertical axis represents the target temperature of the heater.

  As shown in FIG. 9, for example, when the image forming apparatus is installed in a high temperature environment (room temperature of 30 ° C. or more), the temperature of the recording material in the paper feed tray is close to the environmental temperature. Since sufficient fixing performance can be obtained even if the amount of heat applied to the recording material is kept low, the control temperature of the heater is set low. On the other hand, in the normal temperature environment (room temperature 20 ° C. to 30 ° C.) and the low temperature environment (20 ° C. or less), the control temperature of the heater is determined in consideration of the temperature of the recording material in the paper feed tray. By setting the control temperature of the heater high, the same fixing performance can be obtained regardless of the environment. In addition, since the fixing roller temperature is increased during continuous printing and the fixing temperature required to obtain sufficient fixing performance is low, an algorithm that lowers the heater control temperature according to the number of continuous prints is adopted. ing.

Consider printing 500 sheets of recording material continuously at each environmental temperature. When thin paper with a basis weight of 60 g / m ² is used as the recording material, the recording material jams around the fixing film after the 150th continuous printing in a high temperature environment, that is, when the heater temperature reaches 205 ° C. There has occurred. This is because the amount of heat supplied from the heater to the recording material is reduced, so that the toner is not completely melted and the adhesion of the fixing film is increased, and the fixing film and the recording material are wound without being separated. Is. In addition, since the temperature of the heater is set high in a normal temperature environment or a low temperature environment, the toner can be completely melted, so that the recording material does not wrap around the fixing film. Further, in a normal temperature environment or a low temperature environment, the temperature drop rate of the discharged recording material is faster than in a high temperature environment, so that even if 500 recording materials are stacked on the discharge tray, the recording materials stick to each other. There was no.

Next, when thick paper having a strong basis weight of 100 g / m ² is used as the recording material, no winding jam occurs in all environments, and even if 500 sheets are stacked on the paper discharge tray, the recording material They did not stick to each other. This is because the thick paper is strong in paper and overcomes the adhesive force between the toner and the fixing film and is separated from the fixing film. In addition, thick paper having a large heat capacity has a low temperature on the paper discharge tray after heat-fixing, so that the recording materials do not stick to each other.

  Therefore, when the image forming apparatus is installed in a high temperature environment, the type of the recording material is discriminated by the discharge temperature detecting means. When thin paper is passed, the supply of the recording material is performed after 150 continuous sheets. By increasing the interval and reducing the throughput, the occurrence of winding jam can be prevented.

  The above control flow is shown in FIG. When the laser beam printer receives the signal, it measures the environmental temperature Te and the initial temperature T0 by the paper discharge temperature detecting means before starting the printing operation. Next, the initial temperature T0 is substituted into the control equation shown in FIG. 7 based on the initial temperature T0 to determine the threshold temperature Ta. Thereafter, the sheet feeding operation of the recording material from the sheet feeding device, the image forming operation in the image forming unit, and the energization of the heater of the heat fixing device are started, and the detected temperature T1 by the sheet discharge temperature detecting means (in this embodiment, continuous printing) Measure the temperature of the 30th sheet). Here, if the environmental temperature is 30 ° C. or lower, printing is performed up to the number of prints completed while maintaining the throughput. When the environmental temperature is higher than 30 ° C and the continuous print exceeds 150 sheets, the T1 and Ta measured previously are compared. If T1 is smaller, the throughput remains at 50 ppm. When the print operation is performed and T1 is larger, the print material supply interval is widened and the print operation is performed with a throughput of 40 ppm. As described above, the printing operation is continued by automatically controlling the amount of heat applied to the recording material according to the type of the recording material conveyed based on the temperature detected by the environmental temperature and the discharge temperature detecting means, and the final page is printed after heat fixing. End the operation.

  As described above, in this embodiment, the environmental temperature in which the image forming apparatus is installed is measured, and the discharge temperature detecting means having a low heat capacity is arranged on the non-printing surface side immediately after the fixing nip, and the type of the recording material is automatically determined. Depending on the environmental temperature and the type of the recording material, it is possible to reduce the throughput by increasing the supply interval of the recording material and to prevent the occurrence of winding jam. In addition, it is possible to perform a printing operation without unnecessarily reducing throughput at an environmental temperature or a recording material in which winding jam is unlikely to occur.

  The third embodiment of the present invention will be described below. FIG. 11 shows the configuration of the heat fixing apparatus according to this embodiment. In this embodiment, the temperature detection element 33 that measures the surface temperature of the pressure roller is used, and the recording material supply interval is changed according to the surface temperature of the pressure roller and the type of the recording material, thereby optimizing the recording material. A method for carrying out heat fixing is proposed.

A control method using the paper discharge temperature detecting means and the pressure roller surface temperature detecting means according to this embodiment will be described below. The laser beam printer to which this control is applied has a printing speed of 50 sheets of letter-size paper per minute (throughput is 50 ppm) and a recording material feed speed (process speed) of 300 mm / sec as in the first embodiment. When continuous paper was passed using thin paper having a basis weight of 60 g / m ² as a recording material, when printing was performed with 50 ppm without changing the throughput, winding jam occurred on the 150th and subsequent sheets. The pressure roller surface temperature at this time was 90 ° C. On the other hand, when the throughput was set to 40 ppm after the 150th continuous paper feed, no wrap jam occurred, and the pressure roller temperature at this time was saturated at 100 ° C.

Next, when continuous thin paper with a surface weight of 60 g / m ² is passed, the smooth recording material has a large contact area with the fixing film, so that heat is efficiently transferred from the fixing film to the recording material. . Therefore, the target temperature cannot be maintained unless more electric power is supplied to the heater. For this reason, the amount of heat generated by the heater is increased, and the pressure roller temperature rise width between sheets is increased. When the thin paper with smooth surface properties is continuously fed and the throughput after the 150th sheet is 40 ppm, the surface temperature of the pressure roller further rises without being saturated at 100 ° C.

  Also, if the pressure roller temperature rises too much, the amount of moisture contained in the recording material increases during heat fixing in the heat fixing device, so the friction coefficient between the pressure roller and the recording material decreases, and slip jamming occurs. Will occur. Therefore, when the temperature of the pressure roller continues to rise, it is necessary to increase the throughput and maintain the pressure roller at a constant temperature to prevent the occurrence of slip jamming. In the heat fixing apparatus used in this embodiment, slip jam occurred when the pressure roller temperature exceeded 120 ° C.

  Therefore, when it is determined that the thin paper has been passed by the paper discharge temperature detecting means during continuous printing, and the throughput is changed to prevent winding around the fixing film, the temperature of the pressure roller is set to 100 ° C. to 115 ° C. By performing the throughput control so as to keep it within the range, the recording material can be stably conveyed. The above control flow is shown in FIG. Since the control flow shown in FIG. 8 in the first embodiment is the same as that in FIG. 8 until it is determined by the paper discharge temperature detection means whether thin paper is passed during continuous printing, the description is omitted. In FIG. 12, when it is determined by the paper discharge temperature detection means that thin paper has been passed during continuous printing, the recording material is prevented from being wound around the fixing film by setting the throughput to 40 ppm. Next, the pressure roller temperature detection element is used to measure the pressure roller temperature Tp. If Tp is 115 ° C. or less, slip jam does not occur, so the throughput is set to 40 ppm until the end of printing. Further, when Tp is higher than 115 ° C., slip jam may occur, so that the temperature of the pressure roller is prevented from being raised by setting the throughput to 50 ppm. At this time, since the temperature of the pressure roller is sufficiently high, the toner at the leading end of the recording material is melted, so that no winding jam occurs. Next, if Tp is 100 ° C. or higher, the printing operation is performed while maintaining 50 ppm. When Tp becomes smaller than 100 ° C., the throughput is set to 40 ppm.

  As described above, in this embodiment, the discharge temperature detecting means having a low heat capacity is arranged on the non-printing surface side immediately after the fixing nip, the type of the recording material is automatically determined, and the throughput is lowered when the thin paper is passed. Prevent wrap jams. Further, even when thin paper is passed, due to the difference in paper surface roughness, the pressure roller temperature rises and slip jam occurs. Therefore, the occurrence of slip jam is prevented by measuring the pressure roller temperature by means for detecting the surface temperature of the pressure roller and changing the throughput in accordance with the temperature. By controlling the throughput according to the type of the recording material and the pressure roller temperature, it becomes possible to carry the recording material stably.

Configuration diagram of heat fixing apparatus according to the present invention Configuration of an image forming apparatus according to the present invention Configuration of an image forming apparatus according to the present invention Configuration of an image forming apparatus according to the present invention Detailed view of the area around the paper ejection sensor lever The graph which shows the heater control temperature table for a heating of a present Example Shows the detection results of cardboard having a basis weight of 60 g / m ² of thin paper and basis weight 100 g / m ² at a sheet discharge temperature detecting means when the continuously printed Flowchart for preventing jamming and sticking by discriminating the type of recording material using the discharge temperature detection means and supplying the optimum amount of heat The horizontal axis is the number of continuous prints and the vertical axis is the target temperature of the heater Control flow of embodiment 2 FIG. 6 is a diagram illustrating a configuration of a heat fixing device according to a third embodiment. Control flow of embodiment 3

Explanation of symbols

21 Entrance guide 22 Fixing film 23 Heating body 24 Pressure roller 25 Film guide member 26 Paper discharge roller 27 Paper discharge roller 28 Paper discharge guide 29 Paper discharge sensor lever 30 Photo interrupter 31 Heat collecting plate 32 Temperature detection element 33 Pressure roller temperature Detection element 50 Photosensitive drum 51 Charging roller 52 Laser beam 53 Developing device 54 Transfer roller 55 Cleaning device 56 Fixing device

Claims (5)

In a heat fixing device that forms a permanent image by passing an unfixed image formed on a recording material through a heat fixing device,
It is arranged on the non-printing surface side after passing through the heat fixing device, has a means for contacting the non-printing surface side of the recording material with a predetermined pressure, and measures the temperature of the recording material, and the preceding recording material passes through the fixing device. At this point, when the subsequent recording material continues to be in a state where the image forming operation has already started in the image forming unit, the temperature of the preceding recording material is detected, and the subsequent recording material is detected according to the temperature. An image forming apparatus characterized in that a material supply interval is variable.   2. The image forming apparatus according to claim 1, wherein when the detected temperature of the preceding recording material is higher than a predetermined threshold temperature, the subsequent recording material supply interval is widened. A means for detecting temperature or humidity depending on at least one of environmental temperature and humidity in which the image forming apparatus is installed;
The image forming apparatus according to claim 1, wherein the predetermined threshold temperature is determined according to the detected temperature or humidity. A means for detecting temperature or humidity depending on at least one of environmental temperature and humidity in which the image forming apparatus is installed;
The image forming apparatus according to claim 1, wherein control is performed to vary the supply interval of the recording material in accordance with the detected temperature or humidity. In a heating and fixing apparatus for forming a permanent image by passing an unfixed image formed on a recording material through a nip formed by a heating rotator and a pressing rotator,
Means for measuring the temperature of the recording material, which is disposed on the non-printing surface side after passing through the heat fixing device, is in contact with the non-printing surface side of the recording material at a predetermined pressure;
Comprising means for measuring the surface temperature of the pressing rotor;
When the preceding recording material passes through the fixing device, when the succeeding recording material continues in a state where the image forming operation has already been started in the image forming unit, the temperature of the preceding recording material, An image forming apparatus characterized by detecting a surface temperature of a pressurizing rotating body and varying a subsequent recording material supply interval according to the temperature.

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