JP2007108505A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of accurately detecting the temperature rise of a paper non-passage area between the maximum passage width and the minimum passage width for a recording paper in a fixing nip area. <P>SOLUTION: In the image forming apparatus, if a distance between a transfer area T and the fixing nip area N is denoted by XL, and the maximum passage width and minimum passage width of the transfer area and fixing nip area through which a recording material is passed are denoted by Xmas and Xmin respectively, relations between the positions of temperature detecting means 11, 12-1, and 12-2 and a distance from a conveyance reference for the one edge of the recording material satisfy the following expression: the first temperature detecting means 11<Xmin/2≤XL/2<the second temperature detecting means 12-2<Xmax/2-Xmin/2<the third temperature detecting means 12-1<Xmax/2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a recording material.

  In an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, an electrostatic latent image is formed on a photosensitive drum, and the electrostatic latent image is developed as a toner image by a developing device. The toner image on the photosensitive drum is transferred onto a recording material by a transfer device, and the recording material is passed through an image heating and fixing device (hereinafter referred to as paper passing) to apply heat and pressure to the recording material. The toner image is heat-fixed.

  As an image heating fixing device (hereinafter referred to as a fixing device), a film heating type fixing device that heats a toner image using a heat-resistant and thin flexible film (fixing film) has been put into practical use. This film heating type fixing device is effective as an energy-saving on-demand fixing device capable of suppressing power consumption as much as possible without supplying power during standby.

  The fixing device includes a heating body such as a ceramic heater, a support member that supports the heating body, a flexible film that is loosely fitted to the support member, and a support member that supports the flexible film. And a pressure member that forms a fixing nip portion in pressure contact with the heating body. The heating body has an elongated substrate in the width direction orthogonal to the recording material conveyance direction, and a heating zone (hereinafter referred to as a fixing nip) for heating the recording material by providing a resistance heating element on the substrate along the longitudinal direction of the substrate. Part longitudinal heating zone).

  In this fixing device, a recording material carrying a toner image is nipped and conveyed between a flexible film and a pressure member, and heat and nip pressure are applied to the toner image in the conveying process to thereby transfer the toner image onto the recording material. Fix to heat.

  In the above fixing device, when a recording material having a relatively narrow width with respect to the longitudinal heating area of the fixing nip portion is continuously passed, such as an envelope or a postcard, a portion through which the recording material passes (paper passing portion) and a portion that does not pass through The amount of heat taken away from the heating body is significantly different from that of the non-sheet passing portion. Hereinafter, a recording material having a relatively narrow width with respect to the longitudinal heating region of the fixing nip is referred to as a narrow paper. Therefore, the temperature of the non-sheet passing portion where the heat quantity is not deprived of the narrow width sheet causes a so-called non-sheet passing portion temperature rising phenomenon that gradually increases as the number of sheets to be passed increases. Excessive temperature rise of the non-sheet passing portion causes problems such as heat-damaging the components of the fixing device and shortening the device life (durability life).

  In order to solve such an adverse effect, in the fixing device, a plurality of thermistors are provided on the substrate of the heating body, and control is performed to change the feeding interval of the recording material based on the temperature information of the thermistors. (Patent Document 1). In addition, control for temporarily stopping power supply to the heating element is performed based on temperature information of the thermistor (Patent Document 2). Further, control is performed to reduce the conveyance speed of the recording material based on the temperature information of the thermistor (Patent Document 3).

  FIG. 14 shows a schematic transmission plane model diagram of a conventional image forming apparatus. This image forming apparatus is configured to control the throughput of the recording material (the number of sheets of recording material passed per unit time) based on the temperature information of two thermistors provided on the heating body of the fixing device.

  In the image forming apparatus, reference numeral 21 denotes a manual paper feed unit, which feeds a recording material (not shown) on the manual paper feed tray 213 toward the transfer nip T by a manual paper feed roller 211. Reference numeral 212 denotes a recording material guide side plate. Reference numeral 22 denotes a registration unit, which feeds the recording material to the transfer unit 23 by a registration roller 222 at a predetermined timing. In the transfer unit 23, the toner image on the photosensitive drum is transferred onto the recording material by the transfer roller at a transfer nip T between the photosensitive drum 1 and a transfer roller (not shown). Reference numeral 24 denotes a fixing unit, which applies heat and nip pressure of the heating member 10 to the toner image on the recording material at the fixing nip N to heat and fix the toner image on the recording material. A paper discharge unit 25 discharges the recording material from the fixing unit 24 to the outside of the apparatus by a paper discharge roller (not shown). A conveyance reference (also referred to as a sheet passing reference) when the recording material is conveyed to the transfer nip T and the fixing nip N is the center between the recording material ends in the width direction perpendicular to the conveyance direction of the recording material (the length of the fixing nip). Center) A.

  The maximum sheet passing width of the recording material in the manual sheet feeder 21 is LETTER size (215.9 mm), and the guaranteed minimum sheet passing width is 3 (inch) × 5 (inch) (76.2 mm). As a recording material sensor that always detects a recording material for a series of printing operations for forming an image on the recording material, a recording material presence sensor Sf1 that controls the presence or absence of the recording material in the manual paper feed tray 213 is provided in the manual paper feeding unit 21. Has been placed. In addition, a top sensor St that controls detection of the leading end timing of the recording material being transported and the recording material transport length is disposed in the resist unit 22. A paper discharge sensor Sd that controls detection of the recording material discharge timing from the fixing unit 24 is disposed in the paper discharge unit 25.

  When the recording material sensors Sf1, St, Sd do not detect the passage of the recording material at a predetermined timing during printing, control is performed to stop the printing operation. Therefore, in order to complete a series of printing operations, the recording material needs to pass through all the recording material sensors Sf1, St, Sd.

  Further, the positions of the recording material sensors Sf1, St, and Sd with respect to the recording material being conveyed are, as viewed from the sheet passing reference line A, the recording material presence / absence sensor Sf1 at the 33 mm position on the right side in FIG. They are placed at 33mm points. The paper discharge sensor Sd is arranged on the paper passing reference line A.

  On the other hand, the main thermistor 11 that controls temperature detection for fixing temperature control during sheet passing is a sub that controls temperature rise detection at the end of the heated body when passing narrow paper on the sheet passing reference line A (0 mm point). The thermistor 12 is arranged at a point of 95 mm on the right side.

  With the thermistor arrangement as described above, the temperature rise at the end of the heating element can be detected by the output of the sub-thermistor 12 for a recording material having a B5 size width (182 mm) or less. As a result, when a predetermined high temperature state is reached, it is possible to control such as reducing the feeding interval of the recording material or pausing printing for a certain time, so that damage to the fixing device can be reduced.

  Next, control switching according to the conventional sub-thermistor detection temperature will be described with reference to the throughput control flowchart of FIG.

  First, when a series of print jobs is started, a feeding interval initial value F = F0 (2.4 sec, 25 ppm), a sub-thermistor threshold temperature Tth are set, and heating element energization and paper feeding are performed at a predetermined timing (S41). ~ S44). Here, the sub-thermistor threshold temperature Tth is set to a temperature at which the respective members do not melt or be damaged in consideration of the heat resistance temperature of the respective members constituting the fixing device.

  In S45, the recording material transport direction length Lp is calculated from the recording material top sensor St passage time.

  In S46, based on the result of S45, it is determined whether the recording medium has a length in the conveyance direction of less than 260 mm or a long medium of 260 mm or longer, and the process proceeds to printing control in S47 or S50, respectively.

  In the case of S47, that is, during short media printing control, the detected temperature Ts of the sub-thermistor 12 is monitored. When the detection temperature Ts of the sub-thermistor 12 exceeds the threshold temperature Tth, the control is switched to delay the feeding interval after the next recording material, and the temperature rise at the non-sheet passing portion during narrow sheet passing is alleviated. ing. In the above control, the initial feeding interval F is F0 = 2.4 sec (25 ppm), and every time the threshold temperature Tth is exceeded, F0 → F1 = 4 sec (15 ppm) → F2 = 6 sec (10 ppm) → F3 = 10 sec (5 ppm) ) Is set so as to sequentially switch the recording material feeding interval (S49).

In the case of S50, that is, during the printing control of long media, if the non-standard size paper such as a vertically long paper, the non-sheet passing portion temperature rise per sheet is large, and it is necessary to quickly reduce the throughput. Here, the vertically long paper refers to an atypical recording material in which the width in the width direction of the recording material is as narrow as an envelope and the length in the conveyance direction exceeds 260 mm. Therefore, the temperature increase ΔTs of the sub-thermistor detection temperature while one sheet of recording material passes through the fixing device is monitored, and when this increase ΔTs exceeds +80 deg, it is immediately extended from F0 to F4 = 20 sec (3 ppm). It is set (S52). As a result, the temperature rise of the non-sheet passing portion during the passage of the vertically long paper is reduced.
JP-A-5-080604 Japanese Patent Laid-Open No. 5-080605 JP-A-5-080665

  In an image forming apparatus, the higher the speed, the greater the difference in the amount of heat applied to the pressure roller between the paper passing part and the non-paper passing part. Therefore, the temperature difference between the paper passing part and the non-paper passing part increases. It becomes difficult to increase the throughput of narrow paper.

  FIG. 16 shows the relationship between the throughput and the longitudinal temperature distribution (longitudinal temperature distribution) on the pressure roller when Com-10 envelopes having a width of 104.7 mm and a length of 241.3 mm are continuously printed using the above image forming apparatus. Is shown. The temperature distribution in FIG. 16 shows the equilibrium temperature of the pressure roller surface when continuous printing is performed.

  In FIG. 16, the non-sheet passing portion temperature on the pressure roller reaches the highest temperature at a position several mm outside the paper edge, and the temperature gradually decreases from the peak position of the non-sheet passing portion temperature to the outside. . Therefore, for narrow paper, it is difficult to predict the peak temperature at the conventional sub-thermistor position, so it was necessary to control the throughput with a margin so that the pressure roller did not cause heat loss. .

  In addition, the temperature of the non-sheet-passing portion is a constraint on the throughput due to the difference in the size of regular paper (A4, A3, B5, LETTER, LEGAL, LEDGER, EXECECTIVE, etc.) that is frequently used. In particular, when printing smaller standard paper, the restriction is increased.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that can accurately detect a temperature increase in a non-sheet passing portion between a maximum passing width and a minimum passing width of a recording material in a fixing nip portion.

  A typical configuration of an image forming apparatus according to the present invention includes an image carrier that carries a toner image, a transfer unit that forms a transfer portion facing the image carrier, a heating rotator, and the heating rotator. A heating body that heats the heating body, a pressure rotator that presses against the heating rotator to form a fixing nip, and at least three temperature detection means that detect the temperature of the heating body or the heating rotator. The recording material conveyance reference to the transfer portion and the fixing nip portion is the center between the recording material ends in the width direction orthogonal to the recording material conveyance direction, and the heating is performed based on the temperature detected by the temperature detection means. An image in which a toner image on the image carrier is transferred to a recording material by the transfer means, and the toner image is heated and fixed to the recording material while the recording material is nipped and conveyed by the fixing nip portion. In the forming apparatus, the transfer unit and the fixing unit When the distance between the nip portions is XL, the maximum passage width of the transfer portion and the fixing nip portion through which the recording material passes is Xmax, and the minimum passage width is Xmin, the position of the temperature detection means and the end of the recording material The relationship with the distance from the conveyance reference is as follows: first temperature detection means <Xmin / 2 ≦ XL / 2 <second temperature detection means <Xmax / 2−Xmin / 2 <third temperature detection means <Xmax / 2 An image forming apparatus characterized by satisfying

  According to the present invention, it is possible to accurately detect the temperature increase in the non-sheet passing portion between the maximum passage width and the minimum passage width of the recording material in the fixing nip portion.

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

  FIG. 1 is a side model view of an example of an image forming apparatus according to the present invention. The image forming apparatus shown in this embodiment is a laser beam printer (hereinafter referred to as a printer) using an electrophotographic process method. In this embodiment, for the sake of simplification of explanation, members common to the conventional image forming apparatus are denoted by the same reference numerals.

  In the printer of this embodiment, the control unit (control means) 300 receives the print signal, and the drum-shaped electrophotographic photosensitive member 1 as an image carrier is rotationally driven in the direction of the arrow by a rotation driving system (not shown). The control unit 300 includes a CPU and a memory such as a ROM and a RAM, and various kinds of control data and control programs necessary for the printer are stored in the memory.

  An electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 is uniformly charged to a predetermined polarity and potential by a charging roller (charging means) 6 during rotation of the outer peripheral surface (surface). An electrostatic latent image is formed on the surface of the photosensitive drum by irradiating the charged surface of the photosensitive drum 1 with the laser beam L corresponding to the target image information from the exposure device 2 by turning it on / off. . Then, the electrostatic latent image is developed by the developing device 3. The developing device 3 supplies the toner contained in the developing container 32 to the surface of the photosensitive drum by the developing sleeve 31 and develops the electrostatic latent image as a toner image.

  On the other hand, the recording material P is sent out from either the cassette paper feeding unit 205 or the manual paper feeding unit 21. In the cassette paper supply unit 205, a recording material P of a certain size is stacked and stored on a paper supply tray 203 that is pushed upward by a spring 204 in the paper supply cassette 200. Then, the recording material P is sent out one by one from the paper supply tray 203 by one rotation of the paper supply roller 201 with a part of the circumference cut away. The recording material P is conveyed to the registration unit 22 by the conveyance roller 220. In the manual paper feed unit 21, a recording material of a desired size is placed on the intermediate bottom plate 213 pushed upward by the spring 214 on the manual paper feed tray 210. Then, the sheet feeding roller 211 with a part of the circumference cut off once makes the recording material P sent out from the sheet feeding tray 203 to the registration unit 22 one by one.

  Recording material presence / absence sensors (first recording material sensors) Sf1 and Sf2 are arranged in the cassette paper feeding unit 205 and the manual paper feeding unit 21, respectively. When the recording material presence / absence sensors Sf1 and Sf2 do not detect the recording material P, the control unit 300 notifies the user of “no recording material” when receiving the print signal, and stops the printing operation and control.

  The recording material P sent to the registration unit 22 is conveyed to the transfer unit 23 by the registration roller 221. Then, the recording material P passes through the top sensor (second recording material sensor) St during the conveyance and reaches the transfer unit 23. The top sensor St detects the leading edge arrival timing of the recording material P and the conveyance length Lp.

  The transfer portion 23 is formed by disposing a transfer roller (transfer means) 4 so as to face the photosensitive drum 1. The transfer roller 4 is in pressure contact with the photosensitive drum 1 to form a transfer nip T through which the recording material P passes. In the transfer portion 23, when the recording material P passes through the transfer nip portion T, a transfer electric field having a polarity opposite to that of the toner image is applied to the non-printing surface of the recording material by the transfer roller 4. The image is transferred onto the recording material.

  After the transfer of the toner image, the recording material P is separated from the photosensitive drum 1 and sent to the fixing unit 24 having the fixing device 7. The recording material P passes through the fixing nip portion N of the fixing device 7, whereby an unfixed toner image is heated and fixed on the recording material. The configuration of the fixing device 7 will be described later.

  The recording material P that has exited the fixing nip N passes through a paper discharge sensor (third recording material sensor) Sd of the paper discharge unit 25 and is then carried out onto the paper discharge tray 8 by the discharge rollers 222 and 223 as printed matter. .

  In the series of printing operations described above, the control unit 300 detects the leading edge arrival timing and the conveyance length Lp detected by the top sensor St for the recording material P, the leading edge arrival timing to the discharge sensor Sd, the passing time of the discharge sensor Sd, and the like. Ask for. When the obtained leading edge arrival timing or passage time is out of the predetermined time range, the user is notified of “recording material jam”, and the printing operation and control are stopped.

  Toner and paper dust remaining on the photosensitive drum 1 at the time of transfer are removed by the cleaning device 5, and the photosensitive drum is used for the next image formation.

  FIG. 2 is a cross-sectional side view of an example of the fixing device 7. The fixing device 7 of this embodiment is a film heating type fixing device.

  Reference numeral 10 denotes a ceramic heater (hereinafter referred to as a heater) as a heating body. The heater 10 is supported by a support stay 9 having a semi-circular cross section having heat resistance and heat insulation as a support member. A heat-resistant and thin flexible film 15 as a heating rotator is rotatably fitted on the support stay 9. Both ends of a flexible film (hereinafter referred to as a film) 15 are held by a film guide (not shown). The film guide is fixed to a device side plate pair (not shown) while holding both ends of the support stay 9. The film 15 supported by the support stay 9 is fixed between the film 15 by pressing a pressure roller 17 as a pressure rotating body at a position facing the surface of the heater 10 (surface on the film 15 side). A nip portion N is formed. The pressure roller 17 has an elastic layer 17b such as silicone rubber or silicone sponge on a metal core 17a such as iron or aluminum, and the surface layer is composed of a release layer 17c such as PFA or PTFE having excellent release properties. Is done. Both ends of the pressure roller 17 on the metal core 17a are rotatably supported by a pair of device side plates (not shown).

  FIG. 3 is an enlarged view of the fixing nip portion N and the vicinity thereof.

The heater 10 includes, for example, a ceramic substrate (heating body substrate) 10a having electrical insulation, good thermal conductivity, and low heat capacity such as alumina (Al ₂ O ₃ ) and aluminum nitride (AlN). This ceramic substrate (hereinafter referred to as a substrate) 10a is a member that is elongated in the width direction orthogonal to the conveying direction X of the recording material P, and a conductive heating resistance layer such as silver palladium (Ag / Pd) / Ta ₂ N is formed on the surface thereof. 10b is formed by screen printing or the like. Further, the energization heating resistor layer forming surface is covered with a thin glass protective layer 10c for protection.

  Three temperature detection elements (temperature detection means) 11, 12-1, and 12-2 are provided on the back surface (surface opposite to the film 15) of the substrate 10a of the heater 10 (FIG. 4). As the temperature detection elements 11, 12-1, and 12-2, NTC thermistor elements and the like are generally used. Hereinafter, the temperature detection element is referred to as a thermistor. The thermistors 11, 12-1, and 12-2 have the same configuration. As represented by the thermistor 11, a thermistor support 11a supports a thermistor element 11c disposed between one surface of a ceramic fiber layer 11b having heat resistance, heat insulation and elasticity and a polyimide thin film 11d. Let it be a thermistor unit. The thermistors 11, 12-1, and 12-2 have a structure that presses moderately against the back surface of the heater 10, a conductive pattern is formed on the back surface of the heater, and the thermistor is conductively bonded via a heat conductive adhesive. It is attached to the back of the heater using a configuration (not shown) or the like.

  In the fixing device 7, the pressure roller 17 is rotationally driven in the direction of the arrow by the rotation control system. As the pressure roller 17 is driven to rotate, the film 15 receives a rotational force from the pressure roller via the fixing nip N and rotates in the direction of the arrow.

  In the rotating state of the pressure roller 17 and the film 15, the heater 10 is energized to the energization heating resistance layer 10 b from an energization control unit (not shown). As a result, the heater 15 is heated by the energized heat generating resistance layer 10b, and the entire heater including the substrate 10a and the glass protective layer 10c is rapidly heated. The temperature rise of the heater 10 is detected by three temperature detection elements (temperature detection means) 11, 12-1, 12-2 arranged on the back surface of the heater and fed back to the energization control unit. The energization control unit energizes the heating resistor layer 10b so that the heater temperature detected by each temperature detection element (hereinafter referred to as the thermistor) 11, 12-1, 12-2 is maintained at a substantially constant temperature (fixing temperature). To control the energization. That is, the heater 10 is controlled to be heated to a predetermined fixing temperature.

  The recording material P carrying the unfixed toner image t in a state where the heater 10 is heated to the fixing temperature is guided to the fixing nip portion N by the entrance guide 105. The recording material P is nipped and conveyed at the fixing nip portion N, and is heated and pressed during the conveyance process, whereby the unfixed toner image t is heated and fixed on the recording material. Then, the recording material P that has exited the fixing nip N is sent to the discharge roller 222 by the discharge roller 109. Separating claws 106 and 107 are provided on the fixing nip portion N on the paper discharge roller 109 side. The separation claw 106 prevents the recording material P from being wrapped around the film 15, and the separation claw 107 prevents the recording material from being wrapped around the pressure roller 17.

  FIG. 4 is a schematic transmission plane model diagram of the image forming apparatus in the present embodiment. The conveyance reference (sheet passing reference) when the recording material is conveyed to the transfer nip T and the fixing nip N is the center between the recording material ends in the width direction perpendicular to the recording material conveyance direction (the longitudinal center of the fixing nip N). ) A. Hereinafter, A is referred to as a center paper passing reference line.

  In the image forming apparatus shown in the present embodiment, the maximum sheet passing width (maximum passing width) Xmax of the recording material P to the transfer nip portion Y and the fixing nip portion N in manual sheet feeding is a LETTER-P size (215.9 mm). The guaranteed minimum sheet passing width (minimum passing width) Xmin is 3 (inch) × 5 (inch) −P (76.2 mm).

  Here, regarding the recording material P, when the long side is vertical (parallel to the central sheet passing reference line A) and the transfer nip portion Y and the fixing nip portion N are passed (passed), they are described as P (direction). A case where the transfer nip portion Y and the fixing nip portion N are passed (passed) with the long side side set to be horizontal (perpendicular to the central paper passing reference line A) is described as L (direction).

  In the longitudinal direction of the heater 10, the recording material presence / absence sensor Sf1 is disposed at the right 33 mm point and the top sensor St is disposed at the right 33 mm point as viewed from the center sheet passing reference line A. The paper discharge sensor Sd is arranged on the center paper passing reference line A.

  Of the thermistors 11, 12-1, and 12-2, the main thermistor (first temperature detecting means) 11 is disposed on the center paper passing reference line A (0 mm point). The sub-thermistor 12-1 (third temperature detecting means) is disposed at a position of 95 mm on the right side when viewed from the center paper passing reference line A. The arrangement of the main thermistor 11 is not necessarily on the center sheet passing reference line A (center) as long as it is inside the minimum sheet passing width that can be printed by the image forming apparatus.

  With the thermistor arrangement described above, the end temperature of the heater 10 is controlled by the sub-thermistor 12-1 for a recording material print having a B5-P size width (182 mm) or less along the center paper passing reference line A (see FIG. 5). It can be detected.

  On the other hand, the sub-thermistor (second temperature detecting means) 12-2 is disposed at a position of 65 mm on the right side when viewed from the center paper passing reference line A. This is because the distance between the transfer nip portion Y and the fixing nip portion N is XL = 123 mm, so the maximum width of the recording material in which the paper passing direction is limited is 123 mm. , 61.5mm from the center paper passing reference line A. This was set to 65.0 mm in consideration of the distance capable of detecting the temperature rise at the non-sheet passing portion.

  The minimum sheet passing width that can pass through the transfer nip Y and the fixing nip N is 76.2 mm (3 (inch) x 5 (inch)-P). It is 38.1 mm from the paper reference line A. Therefore, the sub-thermistor 12-2 detects the non-sheet passing portion temperature rise at a position 26.9 mm from the end of the recording material of 3 (inch) × 5 (inch) -P.

  FIG. 5 shows the relationship between the thermistor position and paper, cards, envelopes, which are generally used as standard paper. Here, the paper that does not need to consider the temperature rise of the non-sheet passing portion of the pressure roller 17 is Gr.A. The paper that needs to control the non-sheet passing portion temperature of the pressure roller 17 by the sub-thermistor 12-1 is designated as Gr.B. Further, Gr.C is a paper for which the sub-thermistor 12-2 needs to control the non-sheet passing portion temperature of the pressure roller 17.

In particular, for narrow paper corresponding to Gr. C, the maximum throughput can be secured by installing the sub-thermistor 12-2 based on the concept of this embodiment. Assuming that the installation location of the sub-thermistor 12-2 is Xs1 from the central paper-feeding reference line as the installation location of the sub-thermistor closest to the central paper-feeding reference line A, excluding the main thermistor 11.
XL / 2 <Xs1 ≦ XL / 2 + 30mm.

Preferably,
XL / 2 <Xs1 ≦ XL / 2 + 15mm
It is good to install in the position.

  Conversely, if the paper size satisfies the above conditions, the non-sheet passing portion temperature can be controlled with high accuracy and the throughput can be made as fast as possible.

  That is, when the distance between the transfer nip portion T and the fixing nip portion N is XL, it is not possible to print a paper whose two sides are shorter than XL. On the other hand, even if the length of one side is less than XL, printing is possible if the other is XL or more. In this case, the paper passing direction is limited to the long side, and the paper width does not exceed XL. When the length of the two sides is longer than XL, printing the long side horizontally is advantageous for increasing the temperature of the non-sheet passing portion of the pressure roller 17 and can increase the throughput.

  Therefore, it is necessary to determine the optimal installation location as the second temperature detecting means capable of detecting the non-sheet passing portion temperature with respect to the narrow paper when the paper feeding direction is limited by the distance XL.

  That is, when the temperature control of the heater 10 and the temperature control of the non-sheet passing portion are accurately performed using at least three thermistors 11, 12-1 and 12-2, the following conditions are satisfied. One thermistor is arranged. In this embodiment, for the following three types of paper size groups, the relationship between the positions of the three thermistors 11, 12-1, and 12-2 and the distance from the central sheet passing reference line A at the end of the recording material is constant. Three thermistors are installed at a position that satisfies the above conditions.

Paper size group,
1) Maximum paper size that can be passed (Xmax / 2),
2) Intermediate paper size between the maximum paper size and the minimum paper size (Xmax / 2−Xmin / 2),
3) Paper size that allows only vertical paper feeding from the distance between the transfer nip and fixing nip (Xmin / 2 ≦ XL / 2)
These are the three types.

The thermistor
A) Main thermistor 11 for temperature control
B) Sub-thermistor 12-2 for detecting the temperature of a small non-sheet passing portion,
C) Sub-thermistor 12-1 for detecting the temperature of the intermediate size non-sheet passing portion,
It is.

  For the above three types of paper size groups, three thermistors are installed at positions that satisfy the following conditions.

A) <3) <B) <2) <C) <1)
Here, when the maximum printable paper size (the maximum paper size that can be passed) is LETTER-P (see FIG. 5), the standard paper sizes include LETTER-P, LGL-P, A4-P, and the like. . Examples of intermediate paper sizes include EXECECTIVE-P, B5-P, and A5-P.

  Next, throughput control in the present embodiment will be described with reference to the flowchart of FIG.

  First, when a series of print jobs is started, a feed interval initial value F = F (0) (2.4 sec, 25 ppm), sub-thermistor threshold temperatures Tth−1 and Tth−2 are set, and heating is performed at a predetermined timing. Body energization and paper feeding are performed (S1 to S4).

  In S5, the recording material transport direction length Lp is calculated from the top sensor St passage time of the recording material P.

  In S6, based on the result of S5, it is determined whether the short medium is less than Lp 260 mm or long medium that is 260 mm or longer, and the process shifts to S7 or S12, respectively. Then, it is determined whether the detected temperature of the sub-thermistor 12-1 is higher than the threshold temperature Tth-1, and whether the detected temperature of the sub-thermistor 12-2 is higher than the threshold temperature Tth-2 (S8, S9, S13, S14).

  When either the sub-thermistor 12-1 or 12-2 exceeds the threshold temperatures Tth-1 and Tth-2, the feeding interval is controlled in S10 and S15 to change the throughput. Here, the feeding interval in S10 and S15 is changed along the table in Table 1. If it is determined in S6 that the medium is short, the feeding interval is changed by one step. If it is determined that the medium is long, the feeding interval is changed by two steps.

  In this embodiment, the increase width of the sheet interval (feed interval) in S15 is set to twice that of the short media, but the non-sheet passing portion temperature depends on the thickness of the medium (recording material), the throughput, and the main thermistor. It differs from the relationship with the temperature control temperature. For this reason, the increase width between sheets can be arbitrarily set based on these conditions, and is not limited to the double setting. In addition, a feeding interval setting table may be created independently for short media and long media.

  In S8 and S9 and S13 and S14, the sub-thermistors 12-1 and 12-2 are compared with the threshold temperature, so that the non-sheet passing portion temperature can be accurately detected regardless of the paper width even in the long media. be able to. For this reason, the non-sheet passing portion temperature of the pressure roller 17 can be controlled within a safe temperature range.

  As described above, by applying the above-described throughput control to the image forming apparatus, the maximum throughput corresponding to each recording material size can be secured, and the job can be completed without reducing the heat-resistant temperature margin of the film 15. .

  FIG. 7 is a schematic transmission plane model diagram of another example of the image forming apparatus according to the present invention. In the present embodiment, members and portions that are common to the image forming apparatus of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The same applies to Examples 3 and 4.

  In the image forming apparatus of the present embodiment, the sheet passing standard is the same as that of the first embodiment, the maximum sheet passing width in the manual sheet feeding unit 21 is A3 full bleed (312 mm), and the guaranteed minimum sheet passing width is 3 (inch) × 5 ( inch) -P (76.2 mm). The arrangement of the thermistors, sensors, and rollers other than the sub-thermistor 12-1A as the third temperature detecting means is the same as that in the first embodiment.

  The main thermistor 11 is disposed on the center sheet passing reference line A (0 mm point), and the sub thermistor 12-1A is disposed at a position 145 mm on the right side from the center sheet passing reference line. The arrangement of the main thermistor 11 is not necessarily on the center sheet passing reference line A (center) as long as it is inside the minimum sheet passing width that can be printed by the image forming apparatus. With the above thermistor arrangement configuration, the end temperature of the heater 10 is set to the temperature of the sub-thermistor 12-1A with respect to the recording material print of the LETTER-L / LEDGER-P size width (279.4 mm) or less along the center paper passing reference line A. It can be detected by the output temperature Ts1.

  On the other hand, the sub-thermistor 12-2 as the second temperature detecting means is arranged at a position of 65 mm on the right side as in the first embodiment. This is because the distance between the transfer nip portion T and the fixing nip portion N is XL = 123 mm, so that the maximum width of the recording material P in which the paper passing direction is limited is 123 mm. Is 61.5 mm from the center paper feed reference line. This was set to 65.0 mm in consideration of the distance capable of detecting the temperature rise at the non-sheet passing portion.

FIG. 8 shows the relationship between the thermistor position and a paper called a standard paper, a card, an envelope, etc. that are generally used in an image forming apparatus capable of printing A3-P.
Here, paper that does not need to consider the temperature rise of the non-sheet passing portion of the pressure roller 17 is Gr. A. A paper whose sub-thermistor 12-1A needs to control the non-sheet passing portion temperature is Gr.B. The paper that needs to control the non-sheet passing portion temperature by the sub-thermistor 12-2 is designated as Gr.C.

  In particular, the narrow paper corresponding to Gr. C is based on the concept of Example 1, and the maximum throughput can be secured by installing the sub-thermistor 12-2.

  In this embodiment, the installation location of the sub-thermistor 12-2 closest to the center paper passing reference line A is the same as that in the first embodiment. Further, for the three types of paper size groups, the relationship between the positions of the three thermistors 11, 12-1A, 12-2 and the distance from the central sheet passing reference line A at the end of the recording material is the same as in the first embodiment. . The throughput control method is also the same as in the first embodiment.

  Here, when the maximum printable paper size is A3 full bleed paper (312 × 440 mm), A3-P / A4-L or the like corresponds to the standard paper size. Intermediate paper sizes include LEDGER-P, LETTER-L, EXECECTIVE-L, B4-P, B5-L, LETTER-P, LGL-P, A4-P, A5-L, EXECUTEIVE-P, B5-P , A5-P, etc. If the printing speed is slow, LEDGER-P and LETTER-L may be added to standard paper types.

  As described above, by applying the throughput control (FIG. 6) in the first embodiment to an image forming apparatus capable of printing full bleed paper, the same operations and effects as in the first embodiment can be obtained.

  FIG. 9 is a side model view of another example of the image forming apparatus according to the present invention.

  The image forming apparatus of this embodiment is the same as the image forming apparatus of Embodiment 1 except for the fixing device 7A. The distance between the transfer nip portion T and the fixing nip portion N is also XL = 123 mm. The paper passing standard is the same as that in the first embodiment.

  FIG. 10 is a cross-sectional side view of an example of the fixing device 7A. The fixing device 7A of this embodiment is a heat roller type fixing device.

  Reference numeral 100 denotes a fixing roller as a heating rotator. Reference numeral 130 denotes a halogen heater (hereinafter referred to as a heater) as a heating body, which is disposed at the center inside the fixing roller 100. Both ends of the fixing roller 100 are rotatably supported by a pair of apparatus side plates (not shown). Both ends of the heater 100 are held by the apparatus side plate pair. A fixing nip portion N is formed between the fixing roller 100 and a pressure roller by bringing a pressure roller 120 as a pressure rotating body into pressure contact therewith.

  As the heater 130, a heater that outputs 850 W at 100 V input is used, and the heater light distribution is symmetric with respect to the sheet passing reference. The fixing roller 100 is a roller having a diameter of 30 mm and a thickness of 1.0 mm using aluminum as a metal core 101, and a PFA release layer 102 is coated on the surface layer. The pressure roller 120 has an elastic layer 122 made of silicone rubber on an aluminum cored bar 121 having a thickness of 2.0 mm, a PFA release layer 123 on the surface layer, a diameter of 25 mm, and a product hardness of 42 ° (Asker-C / 500 g load). The thing of is used. By applying a pressure of 200 N, a nip width of 5.0 mm can be formed between the fixing roller 100 and the roller.

  On the outer peripheral surface of the fixing roller 100, a main thermistor (first temperature detecting means) 140, a sub thermistor (second temperature detecting means) 141-1, and a sub thermistor (third temperature detecting means) 141-2. Are in contact with each other. The thermistors 140, 141-1 and 141-2 are supported by a support member (not shown) provided on the apparatus side plate pair.

  In the fixing device 7, the pressure roller 120 is rotationally driven in the direction of the arrow by the rotation control system. As the pressure roller 120 is driven to rotate, the fixing roller 100 receives a rotational force from the pressure roller via the fixing nip portion N and rotates in the direction of the arrow.

  In the rotating state of the pressure roller 120 and the fixing roller 100, the heater 130 is intermittently turned on by a heater drive control unit (not shown). As a result, the heater 130 generates heat and the fixing roller 100 is heated. The temperature of the heater 130 is detected by the thermistors 140, 141-1 and 141-2 and fed back to the heater drive control unit. The heater drive controller controls ON / OFF of the heater 130 so that the heater temperatures detected by the thermistors 140, 141-1, and 141-2 are maintained at a substantially constant temperature (fixing temperature). That is, the heater 130 is controlled to be heated to a predetermined fixing temperature.

  The recording material P carrying the unfixed toner image t with the heater 130 heated to the fixing temperature is guided to the fixing nip portion N by the entrance guide 105. The recording material P is nipped and conveyed at the fixing nip portion N, and is heated and pressed during the conveyance process, whereby the unfixed toner image t is heated and fixed on the recording material.

  When the thin fixing roller 100 (low heat capacity) is used as in the present embodiment, the non-sheet passing portion temperature rise when printing narrow paper is similar to the on-demand fixing device 7 shown in the first embodiment. Will be the behavior. For this reason, also in the present embodiment, it is possible to take measures against temperature rise of the non-sheet passing portion by throughput control based on the same concept.

  FIG. 11 is a schematic transmission plane model diagram of the image forming apparatus in the present embodiment.

  In the image forming apparatus of the present embodiment, the maximum sheet passing width in the manual sheet feeder 21 is A3 (297 mm), and the guaranteed minimum sheet passing width is 3 (inch) × 5 (inch) −P (76.2 mm). The arrangement of the three thermistors 140, 141-1 and 141-2 is the same as in the first embodiment.

  By applying the throughput control in the first embodiment to the image forming apparatus of the present embodiment including the heating roller type fixing device 7A, the same operation and effect as in the first embodiment can be obtained.

  FIG. 12 is a schematic transmission plan view of another example of the image forming apparatus according to the present invention.

  The image forming apparatus according to the present embodiment is configured such that the sheet passing reference is the recording material end in the width direction orthogonal to the conveyance direction X of the recording material P in the image forming apparatus according to the first embodiment. The paper passing standard is referred to as the edge paper passing standard. This edge passing sheet reference line is denoted by B. Further, the maximum sheet passing width in the manual sheet feeder 21 is LETTER-P size (215.9 mm), and the guaranteed minimum sheet passing width is 3 (inch) × 5 (inch) −P (76.2 mm).

  When viewed from the sheet passing reference line B, the recording material presence / absence sensor Sf1, the top sensor St, and the paper discharge sensor Sd are all arranged at a position of 70 mm on the right side. The main thermistor 11 is disposed at a position 40 mm on the right side from the sheet passing reference line B. The sub thermistor 12-1 is arranged at a position 200 mm on the right side from the end sheet passing reference line B.

  On the other hand, the sub-thermistor 12-2 is arranged at a position of 126 mm on the right side from the end sheet passing reference line B. This is because the distance between the transfer nip portion T and the fixing nip portion N is set to XL = 123 mm, so the maximum width of the recording material P in which the sheet passing direction is limited is 123 mm. From the end paper passing reference line B, it becomes the paper width dimension. In consideration of this, the distance at which the non-sheet passing portion temperature can be detected is arranged at 126 mm.

  In this embodiment, the minimum sheet passing width which can be passed is 3 (inch) × 5 (inch) −P, which is 76.2 mm. For this reason, the distance between the recording material edge and the sub-thermistor 12-2 when printing on the left edge basis is 49.8 mm, which is a distance that slightly lowers the detection accuracy. However, since the distance to the sub thermistor 12-1 is less than half, an improvement effect can be obtained over the case where the sub thermistor 12-1 is constituted by one sub thermistor.

  FIG. 13 shows the relationship between the main paper type size and the thermistor position. Here, the paper that does not need to consider the temperature rise of the non-sheet passing portion of the pressure roller 17 is Gr.A. The paper that needs to control the non-sheet passing portion temperature of the pressure roller 17 by the sub-thermistor 12-1 is designated as Gr.B. Further, Gr.C is a paper for which the sub-thermistor 12-2 needs to control the non-sheet passing portion temperature of the pressure roller 17.

  As in this embodiment, when printing paper on the basis of edge passing, the influence of the paper width is twice that of printing on the basis of central paper feeding. In the present embodiment in which three thermistors are used, the sub-thermistor 12-2 can be set in a balanced position by setting the distance XL based on the distance XL as in the first and second embodiments. .

That is, as the installation location of the sub thermistor closest to the end paper passing reference line B, the installation location of the sub thermistor 12-2 is Xs1 from the end paper passing reference line.
XL <Xs1 ≦ XL + 30mm.

Preferably,
XL <Xs1 ≦ XL + 15mm
It is good to install in the position.

  Conversely, if the paper size satisfies the above conditions, the non-sheet passing portion temperature can be controlled with high accuracy and the throughput can be made as fast as possible.

  That is, when the temperature control of the heater 10 and the temperature control of the non-sheet passing portion are accurately performed using at least three thermistors 11, 12-1 and 12-2, the following conditions are satisfied. One thermistor is arranged. In this embodiment, for the following three types of paper size groups, the relationship between the positions of the three thermistors 11, 12-1, and 12-2 and the distance from the end sheet passing reference line B at the end of the recording material. Three thermistors are installed at positions that satisfy certain conditions.

Paper size group,
1) Maximum paper size that can be passed (Xmax),
2) Intermediate paper size between the maximum paper size and the minimum paper size (Xmax-Xmin),
3) Paper size (Xmin ≦ XL) that allows only vertical paper feeding from the distance between the transfer nip and fixing nip
These are the three types.

The thermistor
A) Main thermistor 11 for temperature control
B) Sub-thermistor 12-2 for detecting the temperature of a small non-sheet passing portion,
C) Sub-thermistor 12-1 for detecting the temperature of the intermediate size non-sheet passing portion,
It is.

  For the above three types of paper size groups, three thermistors are installed at positions that satisfy the following conditions.

A) <3) <B) <2) <C) <1)
By applying the throughput control (FIG. 6) in the first embodiment to the image forming apparatus of the present embodiment that employs the edge sheet passing standard as the paper passing reference, the same operations and effects as in the first embodiment can be obtained. it can.

[Others]
1) In the image forming apparatuses of Examples 1 to 3, the fixing device is not limited to a film heating type fixing device, and a heat roller type fixing device as shown in Example 4 may be used.

  2) In the image forming apparatus of the fourth embodiment, the fixing device is not limited to the heat roller type fixing device, and a film heating type fixing device as shown in the first to third embodiments may be used.

Side surface model diagram of an example of the image forming apparatus of Embodiment 1 Cross-sectional side view of an example of a fixing device Enlarged view of the fixing nip and its vicinity Schematic transmission plane model of image forming apparatus Illustration of the relationship between main paper type size and thermistor position Throughput control flowchart Schematic transmission plane model diagram of image forming apparatus of embodiment 2 Illustration of the relationship between main paper type size and thermistor position Side model diagram of image forming apparatus according to Embodiment 3 Cross-sectional side view of an example of a fixing device Schematic transmission plane model of image forming apparatus Side model diagram of image forming apparatus according to Embodiment 4 Illustration of the relationship between main paper type size and thermistor position Schematic transmission plane model diagram of a conventional image forming apparatus Flow chart of throughput control of conventional image forming apparatus Explanatory diagram showing the relationship between throughput and pressure roller longitudinal surface temperature when narrow paper is continuously printed

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 4 ... Transfer roller, 7, 7A ... Fixing device,
10 ... Ceramic heater, 15 ... Fixing film, 17 ... Pressure roller,
11. Main thermistor,
12-1, 12-1A, 12-2... Thermistor,
100 ... fixing roller, 120 ... pressure roller, P ... recording material 140 ... main thermistor,
141-1, 141-2... Thermistor

Claims (8)

An image carrier that carries a toner image; transfer means that forms a transfer portion opposite to the image carrier; a heating rotator; a heating body that heats the heating rotator; and the heating rotator. A pressure rotator for forming a fixing nip portion, and at least three temperature detecting means for detecting the temperature of the heating body or the heating rotator, and a recording material to the transfer portion and the fixing nip portion. Is the center between the recording material ends in the width direction perpendicular to the recording material conveyance direction, and the heating body is controlled to a predetermined temperature based on the temperature detected by the temperature detection means, In an image forming apparatus for transferring a toner image to a recording material by the transfer unit and heating and fixing the toner image to the recording material while nipping and conveying the recording material at the fixing nip portion,
When the distance between the transfer portion and the fixing nip portion is XL, the maximum passage width of the transfer portion and the fixing nip portion through which the recording material passes is Xmax, and the minimum passage width is Xmin, the position of the temperature detecting means The relationship with the distance from the conveyance reference of the recording material edge,
First temperature detection means <Xmin / 2 ≦ XL / 2 <second temperature detection means <Xmax / 2−Xmin / 2 <third temperature detection means <Xmax / 2
An image forming apparatus satisfying the requirements. When the distance from the conveyance reference of the recording material is Xs1, the second temperature detecting means is
XL / 2 <Xs1 ≦ XL / 2 + 30mm
The image forming apparatus according to claim 1, wherein the image forming apparatus is installed at a position. When the distance from the conveyance reference of the recording material is Xs1, the second temperature detecting means is
XL / 2 <Xs1 ≦ XL / 2 + 15mm
The image forming apparatus according to claim 1, wherein the image forming apparatus is installed at a position. An image carrier that carries a toner image; transfer means that forms a transfer portion opposite to the image carrier; a heating rotator; a heating body that heats the heating rotator; and the heating rotator. A pressure rotator for forming a fixing nip portion, and at least three temperature detecting means for detecting the temperature of the heating body or the heating rotator, and a recording material to the transfer portion and the fixing nip portion. Is the recording material end in the width direction orthogonal to the recording material conveyance direction, and the heating body is controlled to a predetermined temperature based on the temperature detected by the temperature detection means, and the toner image on the image carrier is In the image forming apparatus which transfers the toner image to the recording material while transferring the recording material to the recording material by the transfer unit and nipping and conveying the recording material at the fixing nip portion.
When the distance between the transfer portion and the fixing nip portion is XL, the maximum passage width of the transfer portion and the fixing nip portion through which the recording material passes is Xmax, and the minimum passage width is Xmin, the position of the temperature detecting means The relationship with the distance from the conveyance reference of the recording material edge,
First temperature detection means <Xmin ≦ XL <second temperature detection means <Xmax−Xmin <third temperature detection means <Xmax
An image forming apparatus satisfying the requirements. When the distance from the conveyance reference of the recording material is Xs1, the second temperature detecting means is
XL <Xs1 ≦ XL + 30mm
The image forming apparatus according to claim 4, wherein the image forming apparatus is installed at a position. When the distance from the conveyance reference of the recording material is Xs1, the second temperature detecting means is
XL <Xs1 ≦ XL + 15mm
The image forming apparatus according to claim 4, wherein the image forming apparatus is installed at a position. When the maximum passage width of the transfer portion and the fixing nip portion through which the recording material passes is set to a width that allows a recording material of LETTER (215.9 mm × 279.4 mm) size to pass from the short side, the maximum passage width The recording material end and the third temperature from the conveyance reference when the recording material of the EXECCTIVE (184.15 mm × 266.7 mm) size having the short side smaller than the width passes through the transfer portion and the fixing nip portion from the short side. The positional relationship of the detection means is
5. The image forming apparatus according to claim 1, wherein the third temperature detection unit is installed at a position satisfying EXECTIVE end <third temperature detection unit <LETTER end. 6. When the maximum passage width of the transfer portion and the fixing nip portion through which the recording material passes is set to a width that allows passage of a recording material of A3 (297 mm × 420 mm) size from the short side, the maximum passage width 3rd temperature detection means and the edge of the recording material from the conveyance reference when the LEDGER (279.4mm × 431.8mm) size recording material having a smaller short side passes through the transfer portion and the fixing nip portion from the short side. The positional relationship of
5. The image forming apparatus according to claim 1, wherein the third temperature detection unit is installed at a position satisfying LEDGER end <third temperature detection unit <A 3 end. 6.