JP2023125003A - Image forming apparatus - Google Patents

Abstract

To solve a problem in which an image forming apparatus is not configured to include a heating element with a length corresponding to the widths of all sheets, and depending on the relationship between the length of the heating element and the width of the sheet, the image forming apparatus executes throughput down control to prevent an increase in temperature of a non-paper feeding part, which may reduce productivity.SOLUTION: When image formation is performed on a preceding first sheet and a subsequent second sheet, control means determines whether the image formation on the second sheet can be completed. When determining that the image formation on the second sheet cannot be completed, the control means determines whether the image formation by image forming means is performed on the second sheet. When the image formation is performed on the second sheet, the control means defines the interval between the first sheet and the second sheet to be a first interval, and when the image formation is not performed on the second sheet, it defines the interval between the first sheet and the second sheet to be a second interval smaller than the first interval and ejects the second sheet to an ejection tray.SELECTED DRAWING: Figure 7

Description

The present invention relates to an image forming apparatus employing an electrophotographic method, an electrostatic recording method, or the like, such as a copying machine, a printer, or a facsimile machine.

2. Description of the Related Art Conventionally, a heating device in an image forming apparatus fixes an unfixed image (toner image) formed on a sheet by an image forming means such as an electrophotographic process onto the sheet. For example, a heat roller type heating device using a halogen heater as a heat source, a film heating type heating device using a ceramic heater as a heat source, and the like are known.

In an image forming apparatus having a heating device using such a heater as a heat source, the heating element of the heater has a length corresponding to the width of the maximum sheet that can be fixed in the image forming apparatus, or a length corresponding to the width of a certain sheet. The structure may have a length. A certain sheet is, for example, a standard size sheet such as A4 or B4. In such a configuration, when performing the fixing process on a sheet whose width is shorter than the length of the heating element, the non-paper passing area within the heating area of the heating element where the sheet does not pass is within the heating area of the heating element. Therefore, there is a possibility that the temperature may become higher than that of the paper passing area through which the sheet passes. In other words, there is a possibility that the temperature of the non-paper-passing area may increase.

If the temperature in the non-sheet passing area increases and the temperature in the non-sheet passing area becomes too high, there is a risk that, for example, the support member that supports the heater may be damaged due to the high temperature. Conventionally, in order to suppress this situation, throughput reduction control that increases the sheet spacing is performed by detecting or predicting the temperature of the non-paper passing area, or based on the width of the sheet to be fixed. Although productivity decreased, temperature rise in non-paper passing areas was suppressed.

On the other hand, in order to suppress the temperature rise in the non-sheet passing area, Patent Document 1 discloses that a plurality of heating elements of different lengths are provided, and by exclusively switching the heating element to be supplied with power by a switching relay, the width of the sheet to be fixed is adjusted. Power is selectively supplied to heating elements of corresponding length. By selectively using a heating element whose length corresponds to the width of the sheet, when fixing a sheet whose width corresponds to the length of the heating element, it is possible to suppress temperature rise in the non-sheet passing area.

JP2001-100558

However, the structure is not equipped with a heating element whose length corresponds to the width of all sheets, and depending on the relationship between the length of the heating element and the width of the sheet, it may be necessary to suppress the temperature rise in the non-paper passing area. There were cases where throughput down control was implemented and productivity decreased.

The invention according to the present application has been made in view of the above-mentioned situation, and aims to suppress a decrease in productivity while suppressing temperature rise in the non-sheet passing area.

In order to achieve the above object, an image forming means for forming a toner image on a sheet, a fixing means for fixing an unfixed toner image formed on the sheet by the image forming means, and a fixing means for fixing an unfixed toner image formed on the sheet by the image forming means; The control means includes an ejection tray to be ejected and a control means for controlling conveyance of the sheet, and the control means is configured to perform image formation on a preceding first sheet and a subsequent second sheet. , it is determined whether the image formation on the second sheet can be completed, and if it is determined that the image formation on the second sheet cannot be completed, the image forming means is applied to the second sheet. If image formation is being performed on the second sheet, the distance between the first sheet and the second sheet is determined as a first distance. , when image formation is not performed on the second sheet, the interval between the first sheet and the second sheet is set to a second interval narrower than the first interval, and the second sheet is discharged onto the discharge tray.

According to the configuration of the present invention, it is possible to suppress a rise in temperature of the non-paper-passing portion and also to suppress a decrease in productivity.

Schematic configuration diagram of image forming apparatus Control block diagram of image forming apparatus Schematic diagram of fixing device Schematic diagram and cross-sectional diagram of heater Diagram showing heater and paper width sensor Conventional printing operation timing chart Timing chart of printing operation in the first embodiment Flowchart of printing operation in the first embodiment Schematic diagram and cross-sectional diagram of heater Power supply circuit for powering the heater Diagram showing heater and paper width sensor Timing chart of printing operation in second embodiment Flowchart of printing operation in second embodiment

Embodiments of the present invention will be described below with reference to the drawings. Note that the following embodiments do not limit the claimed invention, and not all combinations of features described in the embodiments are essential to the solution of the invention.

(First embodiment)
[Image forming device]
FIG. 1 is a schematic configuration diagram showing an in-line type color image forming apparatus as an example. The operation of an electrophotographic image forming apparatus will be described with reference to FIG. Note that the first station is a station for forming a yellow (Y) color toner image, and the second station is a station for forming a magenta (M) color toner image. Further, the third station is a station for forming a cyan (C) color toner image, and the fourth station is a station for forming a black (K) color toner image. In the following description, the alphabetic characters a, b, c, and d at the end of the reference numerals indicate that the member is a yellow (Y), magenta (M), cyan (C), or black (K) toner image, respectively. This indicates that it is a member related to formation. In the following description, if there is no need to distinguish between colors, reference numerals may be used without the suffix letters a, b, c, and d.

The photosensitive drum 1 as a photosensitive member is formed by laminating multiple layers of functional organic materials, including a carrier generation layer that generates charges by exposure to light on a metal cylinder, a charge transport layer that transports the generated charges, etc. The outermost layer has low electrical conductivity and is almost insulating. A charging roller 2 serving as a charging unit is brought into contact with the photosensitive drum 1, and uniformly charges the surface of the photosensitive drum 1 while being rotated as the photosensitive drum 1 rotates. A charging bias in which a DC voltage or an AC voltage is superimposed is applied to the charging roller 2, and discharge occurs from the nip between the charging roller 2 and the surface of the photosensitive drum 1 in minute air gaps on the upstream and downstream sides in the rotation direction. As a result, the photosensitive drum 1 is charged.

The cleaning unit 3 cleans toner remaining on the photosensitive drum 1 after primary transfer, which will be described later. A developing unit 8 as a developing means includes a developing roller 4, a non-magnetic one-component toner 5, and a developer application blade 7. The photosensitive drum 1, the charging roller 2, the cleaning unit 3, and the developing unit 8 form an integrated process cartridge 9 that is detachable from the image forming apparatus.

The exposure device 11 serving as an exposure unit is a scanner unit that scans and exposes the photosensitive drum 1 by reflecting laser light emitted from a light source by a polygon mirror. Alternatively, it is composed of an LED (light emitting diode) array and exposes the photosensitive drum 1 to light. The exposure device 11 irradiates the photosensitive drum 1 with a scanning beam 12 modulated based on an image signal. Furthermore, the charging roller 2 is connected to a charging high-voltage power source 20 that serves as a voltage supply means to the charging roller 2 . The developing roller 4 is connected to a developing high-voltage power source 21 that serves as a means for supplying voltage to the developing roller 4 . The primary transfer roller 10 is connected to a primary transfer high voltage power source 22 that serves as a voltage supply means for the primary transfer roller 10 .

The intermediate transfer belt 13 is supported by three rollers, a secondary transfer opposing roller 15, a tension roller 14, and an auxiliary roller 19, which serve as tension members. Only the tension roller 14 is applied with a spring force in the direction of tensioning the intermediate transfer belt 13, so that an appropriate tension force is maintained on the intermediate transfer belt 13. The secondary transfer opposing roller 15 rotates under rotational drive from a main motor (not shown), and the intermediate transfer belt 13 wound around its outer circumference rotates. The intermediate transfer belt 13 moves in a forward direction (clockwise in FIG. 1) at substantially the same speed as the photosensitive drum 1 (rotates counterclockwise in FIG. 1). Further, the primary transfer roller 10 is arranged on the opposite side of the photosensitive drum 1 with the intermediate transfer belt 13 in between. The primary transfer roller 10 rotates in accordance with the rotation of the intermediate transfer belt 13 as the intermediate transfer belt 13 rotates clockwise. Note that the nip portion formed by the photosensitive drum 1 and the primary transfer roller 10 with the intermediate transfer belt 13 in between is also referred to as a primary transfer position. The auxiliary roller 19, the tension roller 14, and the secondary transfer opposing roller 15 are electrically grounded.

Next, the image forming operation of the image forming apparatus will be explained. When the image forming apparatus receives a print command in a standby state, it starts an image forming operation. The photosensitive drum 1, intermediate transfer belt 13, and the like are rotated in the direction of the arrow at a predetermined process speed by a main motor (not shown). The photosensitive drum 1 is uniformly charged by a charging roller 2 to which a charging bias is applied by a charging high-voltage power source 20 . Subsequently, an electrostatic latent image is formed according to image information (also referred to as image data) by a scanning beam 12 irradiated from an exposure device 11.

The toner 5 in the developing unit 8 is negatively charged by the developer applying blade 7 and applied to the developing roller 4 . A predetermined developing bias is applied to the developing roller 4 from the developing high-voltage power supply 21 . When the photosensitive drum 1 rotates and the electrostatic latent image formed on the photosensitive drum 1 reaches the developing roller 4, the electrostatic latent image is made visible by the adhesion of negative polarity toner, and the electrostatic latent image is made visible on the photosensitive drum 1. A toner image of a first color (for example, yellow) is formed. Toner images are similarly formed at each of the other magenta, cyan, and black stations.

Electrostatic latent images are formed on each of the photosensitive drums 1a to 1d while delaying a write signal from a controller (not shown) at a constant timing depending on the distance between the primary transfer positions of each color. A DC high voltage having a polarity opposite to that of the toner image is applied to each of the primary transfer rollers 10a to 10d. Through the above steps, toner images are primarily transferred to the intermediate transfer belt 13 in order, and a toner image (hereinafter also referred to as an image) in which the toner images of each color are superimposed is formed on the intermediate transfer belt 13.

In accordance with the formation of the toner image, the sheets P, which are, for example, paper, loaded in the cassette 16 are conveyed along the conveyance path Y. Specifically, the sheet P is fed (picked up) by a paper feed roller 17 that is rotationally driven by a paper feed solenoid (not shown). The fed sheet P is conveyed to the registration roller 18. The sheet P then passes through a paper width sensor 102 serving as a detection means for detecting the length (hereinafter also referred to as width) in a direction perpendicular to the conveyance direction. A registration sensor 103 is arranged downstream of the registration roller 18. The registration sensor 103 can detect the leading and trailing ends of the sheet P and output an on/off signal depending on the presence or absence of the sheet.

The sheet P is conveyed by the registration roller 18 to a nip portion (also referred to as a secondary transfer position) formed by the intermediate transfer belt 13 and the secondary transfer roller 25 in synchronization with the toner image on the intermediate transfer belt 13. be done. A secondary transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 25 by a secondary transfer high voltage power supply 26, and the toner image formed on the intermediate transfer belt 13 is secondarily transferred onto the sheet P. Toner that is not secondarily transferred onto the sheet P and remains on the intermediate transfer belt 13 is cleaned by the cleaning unit 27 . The sheet P on which the toner image has been secondarily transferred is conveyed to a fixing device 50 as a fixing means, and the toner image is fixed onto the sheet P by heat and pressure. The sheet P with the toner image fixed thereon is discharged to the discharge tray 30. The specific configuration of the fixing device 50, including the film 51, nip forming member 52, pressure roller 53, heater 54, etc., will be described later.

Hereinafter, the mode in which images are successively printed on a plurality of sheets P will also be referred to as continuous printing. In continuous printing, the trailing edge of the sheet P (hereinafter also referred to as the preceding sheet) on which an image is formed in advance, and the leading edge of the sheet P (hereinafter also referred to as the following sheet) on which the image is formed following the preceding sheet. The space between is the paper space. The image forming apparatus in FIG. 1 is a center-based printer that performs a printing operation by aligning the center positions of each member related to image formation and the sheet P in a direction perpendicular to the conveying direction (also referred to as the longitudinal direction). . Therefore, whether the printing operation is for a sheet P having a large width in the longitudinal direction or the printing operation for a sheet P having a small width in the longitudinal direction, each sheet P is conveyed so that the center position thereof coincides.

[Control block diagram of image forming apparatus]
FIG. 2 is a control block diagram illustrating the operation of the image forming apparatus. The printing operation of the image forming apparatus will be described with reference to FIG. The PC 110, which is a host computer, outputs a print command to a video controller 91 inside the image forming apparatus, and transmits image data to be printed to the video controller 91. The print command may also include information regarding the width, which is the length of the sheet P to be printed in the direction (main scanning direction) orthogonal to the conveyance direction. Note that the width of the sheet P may be specified from the PC 110 as described above, or may be specified by user input from an operation panel (not shown) included in the image forming apparatus.

Video controller 91 converts image data input from PC 110 into exposure data that can be exposed by exposure device 11 of the image forming apparatus, and transmits it to exposure control device 93 in engine controller 92 . The exposure control device 93 is controlled by the CPU 94 and controls the exposure device 11 based on exposure data. The size of exposure data is determined by the image size. The CPU 94 serving as a control unit starts an image forming sequence upon receiving the print command. The CPU 94 also functions as a receiving unit that receives information regarding the width of the specified sheet P.

The engine controller 92 is equipped with a CPU 94, a memory 95, etc., and performs preprogrammed operations. The high-voltage power supply 96 is comprised of the above-described charging high-voltage power supply 20, development high-voltage power supply 21, primary transfer high-voltage power supply 22, and secondary transfer high-voltage power supply 26. Further, the power control section 97 includes a bidirectional thyristor 56 (hereinafter also referred to as a triac). The power control unit 97 also includes a heating element switching device 57 as a switching means for switching a plurality of heating elements 54b1 and 54b2, which will be described later, by switching the power supply route for supplying electric power. The power control unit 97 selects a heat generating element that generates heat in the fixing device 50 and determines the amount of power to be supplied. The heating element switch 57 is, for example, a relay.

The drive device 98 includes a main motor 99, a fixing motor 100, and the like. Further, the sensor 101 includes a fixing temperature sensor 59 that detects the temperature of the fixing device 50, a paper width sensor 102 that detects the width of the sheet P, and the like, and the detection results of the sensor 101 are transmitted to the CPU 94. Note that the registration sensor 103 is also included in the sensor 101. The CPU 94 acquires the detection results of the sensor 101 in the image forming apparatus, and controls the exposure device 11 , high voltage power supply 96 , power control section 97 , and drive device 98 . Thereby, the CPU 94 controls image forming processes such as forming an electrostatic latent image, developing the electrostatic latent image, transferring the developed toner image, and fixing the toner image onto the sheet P. Note that the image forming apparatus is not limited to the image forming apparatus having the configuration described in FIG. Any forming device may be used.

[Fusing device]
FIG. 3 is a diagram showing the configuration of the fixing device 50. The conveyance direction of the sheet P in FIG. 3 is the lateral direction of the heater 54. This is the left and right direction in the figure. Further, the direction perpendicular to the lateral direction is the longitudinal direction of the heater 5. This is the front and back direction in the figure. Further, the direction perpendicular to the lateral direction and the longitudinal direction is the thickness direction of the heater 5. This is the vertical direction in the figure. The length of the sheet P and the length of the heating element in the longitudinal direction are also referred to as width. Further, FIG. 4(a) is a schematic diagram of the heater 54, and FIG. 4(b) is a schematic cross-sectional diagram of the heater 54. FIG. 4(b) shows the center line in the longitudinal direction of the heating elements 54b1 and 54b2, and shows the center line in the longitudinal direction of the sheet P conveyed to the fixing device 50 (dotted chain line a in FIG. 4(a)). 54 is a diagram showing a cross section of FIG. Hereinafter, line a will also be referred to as reference line a.

The sheet P holding the unfixed toner image Tn is conveyed from the right side in FIG. is fixed on the sheet P. The fixing device 50 includes a cylindrical film 51, a nip forming member 52 that holds the film 51, a pressure roller 53 that forms a fixing nip portion N together with the film 51, and an elongated heater 54 that heats the sheet P. It is made up of.

The film 51 as the first rotating body uses, for example, polyimide as a base layer. An elastic layer made of silicone rubber and a release layer made of PFA are formed on the base layer. The inner diameter of the film 51 is, for example, 18 mm, and the outer circumferential length of the film 51 is approximately 58 mm. Grease is applied to the inner surface of the film 51 in order to reduce the frictional force generated between the nip forming member 52 and the heater 54 and the film 51 due to the rotation of the film 51.

The nip forming member 52 serves to guide the film 51 from inside and to form a fixing nip N with the pressure roller 53 via the film 51. That is, the film 51 is held between the heater 54 and the pressure roller 53. The nip forming member 52 is a member having rigidity, heat resistance, and heat insulation properties, and is made of liquid crystal polymer or the like. The film 51 is fitted onto the nip forming member 52 . The pressure roller 53, which serves as the second rotating body, includes a core metal 53a, an elastic layer 53b, and a release layer 53c. The pressure roller 53 is rotatably held at both ends and is rotationally driven by the fixing motor 100. Furthermore, the film 51 is driven to rotate by the rotation of the pressure roller 53. A heater 54 as a heating member is held by the nip forming member 52 and arranged in the internal space of the film 51. The substrate 54a, heating elements 54b1 and 54b2, protective glass layer 54e, and fixing temperature sensor 59 will be described later.

[heater]
The heater 54 will be explained in detail using FIG. 4(a). The heater 54 includes a substrate 54a, heating elements 54b1 and 54b2, contacts 54d1 and 54d2, a conductive path 54d3, and a protective glass layer 54e. Hereinafter, the heating elements 54b1 and 54b4 are also collectively referred to as the heating element 54b. The substrate 54a is made of ceramic alumina (Al ₂ O ₃ ). Alumina (Al ₂ O ₃ ), aluminum nitride (AlN), zirconia (ZrO ₂ ), silicon carbide (SiC), and the like are widely known as ceramic substrates. Among them, alumina (Al ₂ O ₃ ) is inexpensive and easily available industrially.

Further, the substrate 54a may be made of a metal having excellent strength. Stainless steel (SUS) is preferably used as the metal substrate because it is excellent in both cost and strength. Regardless of whether a ceramic substrate or a metal substrate is used as the substrate 54a, if it has conductivity, an insulating layer may be provided. Heat generating elements 54b1 and 54b2, contacts 54d1 and 54d2, and a conductive path 54d3 are formed on the substrate 54a. A protective glass layer 54e is formed thereon to ensure insulation between the heating elements 54b1, 54b2 and the film 51.

The heating elements 54b1 and 54b2 have the same length in the longitudinal direction (hereinafter also referred to as size), and have the following dimensions: thickness t=10 μm, width W=0.7 mm, and length L=222 mm. Note that the width W is the length in the transverse direction. The heating elements 54b1 and 54b2 correspond to the width of an A4 (210 mm) sheet P. The electrical resistance values of the heating elements 54b1 and 54b2 are both 20Ω. Further, a contact 54d1 is electrically connected to one end of the heating element 54b1, a contact 54d2 is electrically connected to one end of the heating element 54b2, and a conduction path 54d3 is electrically connected to the other end of the heating element 54b1, 54b2. The combined electrical resistance value of 54b1 and 54b2 is 10Ω.

The distance between the heating elements 54b1 and 54b2 is 2.6 mm. Note that in the first embodiment, the width W of the heating element 54b is the same as 0.7 mm. However, depending on the performance required of the fixing device 50, it may be difficult to select a conductive material in order to form the heating elements 54b of the same width. In that case, the width W of the heating element 54b may be varied depending on the performance required of the fixing device 50.

The fixing temperature sensor 59 in FIG. 3 is a thermistor. A fixing temperature sensor 59 serving as a temperature detection means is located on the opposite side of the substrate 54a from the protective glass layer 54e, and is in contact with the substrate 54a. The output value of the fixing temperature sensor 59 changes depending on the temperature of the heater 54. The fixing temperature sensor 59 is connected to the CPU 94, detects the temperature of the heater 54, and outputs the detection result to the CPU 94.

[Width of sheet P, heating element and throughput]
Next, the relationship between the width of the sheet P to be printed and the throughput will be described using FIG. 5. FIG. 5 shows the positional relationship of the paper width sensor 102 in the longitudinal direction in comparison with a schematic diagram of the heater 54. There is a pair of paper width sensors 102, and paper width sensors 102a1 and 102a2 are installed symmetrically. For example, it is assumed that the distance SL between the paper width sensors 102a1 and 102a2 is 187 mm (SL=187 mm). Although the paper width sensors 102 are arranged symmetrically in this embodiment, they do not have to be symmetrical. Further, when the sheet P is conveyed on the conveyance path Y, the sheet P is conveyed so that the center of the width direction of the sheet P is aligned with the center of the width direction of the conveyance path Y. In other words, the transport reference is the central reference.

FIG. 5 shows two ranges ([1], [2]) determined by the position of the end of the heating element 54b and the position of the paper width sensor 102 in the longitudinal direction. The CPU 94 controls the number of prints per unit time (hereinafter also referred to as throughput) depending on where in this range the end of the sheet P corresponds. The relationship between the two ranges and throughput will be explained below. Note that the full throughput used in the following description refers to the highest throughput (the highest number of sheets printed per unit time) that can be achieved by the image forming apparatus.

・Microwave [1]
A case where the end of the sheet P corresponds to range [1] will be described. In this case, the temperature of the non-paper-passing region within the heat-generating region of the heat-generating body through which the sheet P does not pass increases compared to the paper-passing region within the heat-generating region of the heat-generating body through which the sheet P passes. However, since the end of the sheet P corresponds to range [1], the non-sheet passing area is relatively small, and the temperature increase in the non-sheet passing area is also relatively small. Therefore, even when printing is performed at full throughput, the temperature does not rise to the extent that the pressure roller 53 and the film 51 melt. Therefore, printing is performed at full throughput. In this way, when the end of the sheet P corresponds to range [1], the CPU 94 controls the printing operation by setting the throughput to full throughput.

・Microwave [2]
A case where the end of the sheet P corresponds to range [2] will be described. In this case as well, the temperature of the non-paper passing area increases compared to the paper passing area. Also, since the difference in length in the longitudinal direction of the sheet P and the heating elements 54b1 and 54b2 is larger than in range [1], the non-sheet passing area is larger than in range [1], and the non-sheet passing area is elevated. The temperature will also be higher compared to microwave [1]. Therefore, there is a possibility that the pressure roller 53 and the film 51 will melt. In order to suppress the possibility of melting, the distance between the preceding paper and the following paper is made wider than in the case of full throughput to reduce the temperature rise in the non-paper passing area. Therefore, since printing is performed at a lower throughput than in range [1], productivity is lower than in range [1].

Next, the printing operation of this embodiment will be explained using FIGS. 6 and 7. 6 and 7 are timing charts showing printing operations for the preceding paper and the following paper when the end of the sheet P corresponds to range [2]. Note that here, the preceding paper is referred to as sheet P1, and the subsequent paper is referred to as sheet P2. FIG. 6 shows the printing operation of the conventional image forming apparatus, and FIG. 7 shows the printing operation of the image forming apparatus of this embodiment.

[Conventional control]
First, the printing operation of a conventional image forming apparatus will be explained using FIG. When the CPU 94 receives a print instruction from the video controller 91, it starts a print operation and drives the paper feed solenoid and the registration roller 18 (t601). The fixing device 50 starts temperature adjustment control to reach the target temperature TE2. After that, when the preparation for image formation is completed, the completion of the preparation is notified to the video controller 91, and reception of image information from the video controller 91 is started (t602).

The first sheet P1 fed by driving the paper feed solenoid is temporarily stopped at the timing when it reaches the registration sensor 103 (t603). Then, the paper is re-fed by the registration roller 18 toward the secondary transfer position in synchronization with the toner image formed on the intermediate transfer belt 13 (t604). By the time the sheet P1 reaches the fixing device 50, the temperature of the fixing device 50 reaches the target temperature TE2. The sheet P1 is subjected to a fixing process at a target temperature TE2 by the fixing device 50 (t605). At this time, the temperature of the thermistor 59 corresponding to the longitudinal center of the fixing device 50 through which the sheet P1 passes is controlled to converge to the target temperature TE2.

On the other hand, at the longitudinal end of the fixing device 50 through which the sheet P1 does not pass, the temperature increases because heat is not removed by the sheet P1, and the limit temperature TE3 is at which there is a possibility of damage to the fixing device 50. approaches. In order to avoid damage to the fixing device 50, the CPU 94 performs throughput down control. Specifically, the process waits for a time Tdown from the timing (t608) when the trailing edge of the sheet P1 passes through the fixing device 50 until the temperature at the end of the fixing device 50 falls below the target temperature TE2. After the time Tdown has elapsed, the subsequent sheet P2 is re-fed (t610). Note that the sheet P2 is fed at a timing that does not overlap with the sheet P1 before the refeeding timing (t606). Then, the sheet P2 is temporarily stopped at the timing when it reaches the registration sensor 103 (t609). The re-fed sheet P2 is subjected to printing processing in the same manner as the sheet P1. The details of the printing process for the sheet P2 are the same as for the sheet P1, so a description thereof will be omitted here.

In such a series of printing operations, image formation on the sheet P2 may be stopped due to some error occurring. In this embodiment, as an example, a case is shown in which an exposure error occurs in which the scanning beam 12 from the exposure means 11 is not irradiated (t607). In such a case, the sheet P2 is ejected from the image forming apparatus without forming an image on the sheet P2. In this case as well, a waiting time is required until the time Tdown elapses before the sheet P2 is conveyed again, and throughput reduction control is performed, resulting in a decrease in productivity. Note that the case where an exposure error occurs is just one example, and if a situation occurs in which image formation cannot be performed normally on sheet P2, image formation is stopped as an error.

[Control of this embodiment]
Next, the printing operation of the image forming apparatus in this embodiment will be explained using FIG. 7. In this embodiment, if any error occurs in the series of printing operations described above, the subsequent processing is changed depending on whether or not the image forming operation for sheet P2 has been started.

When the image forming operation on sheet P2 has been started, the temperature of the fixing device 50 is set to the target temperature in order to fix the formed toner image on the sheet P2, similar to the conventional control described above with reference to FIG. Fixing is performed in a state where the temperature is TE2. Therefore, in order to suppress the temperature rise of the non-sheet passing portion at the longitudinal end of the fixing device 50, throughput down control is performed to wait for the time Tdown.

On the other hand, if the image forming operation on the sheet P2 has not been started, there is no unfixed toner image on the sheet P2. Therefore, if the temperature of the fixing device 50 exceeds the target temperature TE4 at which the pressure roller 53 can rotate, the sheet P2 can be passed through the fixing device 50. Therefore, it is no longer necessary to maintain the temperature of the fixing device 50 at the target temperature TE2, and the target temperature can be lowered to TE4. As a result, since the target temperature has been lowered, the temperature increase in the non-sheet passing portions at the ends of the fixing device 50 in the longitudinal direction is also moderated, so there is no need to provide a standby period of time Tdown. Therefore, a decrease in productivity due to throughput down control can be suppressed.

Hereinafter, a specific printing operation will be explained using the timing chart of FIG. 7. Note that the description of the same parts as the printing operation described using FIG. 6 will be omitted here. Further, the occurrence of any error in this embodiment will be described assuming that an exposure error occurs, as in FIG. 6 above.

After feeding the sheet P2, an exposure error occurs in which the scanning beam 12 from the exposure means 11 is not irradiated (t701).At this time, no image formation is performed on the sheet P2. Therefore, the CPU 94 changes the target temperature at the timing (t702) when the rear end of the sheet P1 passes through the fixing device 50 and there is no need to perform temperature control at the target temperature TE2 necessary for fixing the toner. That is, the target temperature TE2 is changed to the target temperature TE4, which is a temperature that does not cause any problem in conveying the sheet P2 to the fixing device 50.

In this case, since the temperature at the longitudinal center of the fixing device 50 where the thermistor 59 is located is higher than the target temperature TE4, the triac 56 is not driven, and both the longitudinal center and end portions of the fixing device 50 are heated. The temperature is dropping. When the sheet P2 reaches the registration sensor 103 (t703), the CPU 94 continues to drive the registration roller 18 to convey the sheet P2. As a result, the sheet P2 passes through the fixing device 50 without providing a standby period of time Tdown (t704). As described above, according to the printing operation of this embodiment, the sheet P2 can be discharged from the image forming apparatus faster than the conventional printing operation described using FIG. 6, and a decrease in productivity can be suppressed. can do. Further, it is also possible to prevent the temperature of the fixing device 50 from reaching the limit temperature TE3.

[flowchart]
The printing operation when an error occurs will be described using the flowchart in FIG. 8. FIG. 8A shows a process for determining whether to stop conveying the sheet P2. Further, FIG. 8(b) shows a process of starting the conveyance again after stopping the conveyance of the sheet P2. First, the process of determining whether to stop conveying the sheet P2 will be described using FIG. 8(a).

In S801, the CPU 94 determines whether an error has occurred in the exposure means 11. If no error has occurred, conveyance of sheet P2 is continued. If an error has occurred, in step S802, the CPU 94 proceeds to processing for stopping the conveyance of the sheet P2.

Next, the process for stopping the conveyance of the sheet P2 will be described using FIG. 8(b).

In S811, the CPU 94 determines whether there is a sheet P2 (hereinafter also referred to as residual paper) that can be ejected into the image forming apparatus. If there is no remaining paper, perform the normal recovery process and perform the printing process again. If there is any remaining paper, the CPU 94 determines in S812 whether image formation on the remaining paper has started. If image formation has started, the process advances to S813; if image formation has not started, the process advances to S818.

If image formation on the remaining paper has started, the CPU 94 stops driving the registration roller 18 in S813. In S814, the CPU 94 continuously controls the temperature of the fixing device 50 at the target temperature TE2. In S815, the CPU 94 determines whether to end throughput down control. In other words, it is determined whether or not the temperature increase in the non-sheet passing portion of the fixing device 50 has been alleviated. If it is determined that the temperature increase in the non-paper passing area has not been alleviated, the process of S815 is repeated. If it is determined that the temperature increase in the non-paper passing area has been alleviated, the process advances to S816.

In S816, the CPU 94 resumes driving the registration roller 18. In S817, the CPU 94 discharges the remaining paper out of the image forming apparatus.

On the other hand, if image formation on the remaining paper has not started, in S818 the CPU 94 lowers the target temperature of the fixing device 50 from TE2 to TE4. Then, the remaining paper is transported and discharged to the outside of the image forming apparatus. Thereby, it is possible to suppress a decrease in productivity without performing throughput down control.

In this way, if a sheet remains inside the image forming apparatus when an error occurs, it is determined whether an image has been formed on the sheet or not, and the processing until the sheet is ejected from the image forming apparatus is changed. When no image is formed on the sheet, the target temperature of the fixing device 50 can be lowered and the sheet can be ejected from the image forming apparatus, thereby suppressing a decrease in productivity without performing throughput down control. be able to.

(Second embodiment)
In this embodiment, control in a configuration in which the number of heating elements and the number of paper width sensors is different from that in the first embodiment will be described. Note that the same components as in the first embodiment, such as the image forming apparatus, are given the same reference numerals, and detailed explanations are omitted in this embodiment.

9(a) is a schematic diagram of the heater 154, FIG. 9(b) is a schematic cross-sectional diagram of the heater 154, and FIG. 10 is a schematic circuit diagram of the power control unit 197 of the heater 154 of the fixing device 50.

[heater]
The heater 154 will be explained in detail using FIG. 9(a). The heater 154 includes a substrate 154a, a heating element 154b1 as a first heating element, a heating element 154b2 as a second heating element, a heating element 154b3 as a third heating element, and a heating element as a fourth heating element. 154b4. Furthermore, the heater 154 has contacts 154d1 to 154d4 and a protective glass layer 154e. Hereinafter, the heating elements 154b1, 154b2, 154b3, and 154b4 are also collectively referred to as the heating element 154b. The substrate 154a is made of ceramic alumina (Al ₂ O ₃ ). Alumina (Al ₂ O ₃ ), aluminum nitride (AlN), zirconia (ZrO ₂ ), silicon carbide (SiC), and the like are widely known as ceramic substrates. Among them, alumina (Al ₂ O ₃ ) is inexpensive and easily available industrially.

Further, the substrate 154a may be made of a metal having excellent strength, and stainless steel (SUS) is preferably used as the metal substrate since it is superior in terms of cost and strength. Regardless of whether a ceramic substrate or a metal substrate is used as the substrate 154a, if it has conductivity, an insulating layer may be provided. Heat generating elements 154b1, 154b2, 154b3, 154b4 and contacts 154d1 to 154d4 are formed on the substrate 154a. A protective glass layer 154e is formed thereon to ensure insulation between the heating elements 154b1, 154b2, 154b3, and 154b4 and the film 51.

The heating elements 154b have different lengths in the longitudinal direction (hereinafter also referred to as sizes). Hereinafter, the length in the longitudinal direction is also simply referred to as length. The heating element 154b has the longest heating element 154b1, 154b4, the second length heating element 154b2, and the third length heating element 154b3. The dimensions of each heating element 154b will be explained. The heating elements 154b1 and 154b4 have a thickness t=10 μm, a width W1=0.7 mm, and a length L1=222 mm. The heating element 154b2 has a thickness t=10 μm, a width W2=0.7 mm, and a length L2=188 mm. The heating element 154b3 has a thickness t=10 μm, a width W3=0.7 mm, and a length L3=154 mm.

The length L1 that is the first width of the heating elements 154b1 and 154b4, the length L2 that is the second width of the heating element 154b2, and the length L3 that is the third width of the heating element 154b3 are such that L1>L2>L3 The relationship is Note that the widths W1 to W3 are lengths in the lateral direction. The heating elements 154b1 and 154b4 correspond to the width of an A4 (210 mm) sheet P. The heating element 154b2 corresponds to the width of the sheet P of B5 (182 mm). The heating element 154b3 corresponds to the width of the A5 (148.5 mm) sheet P.

A conductive material is selected according to the target electrical resistance value for each of the heating elements 154b having different lengths, and the electrical resistance value of the longest heating elements 154b1 and 154b4 is both 20Ω. Further, the electric resistance value of the second length heating element 154b2 is 20Ω. The electrical resistance value of the third length heating element 154b3 is also 20Ω. Further, a common contact 154d1 is electrically connected to one end of the longest heating elements 154b1 and 154b4, and a common contact 154d2 is electrically connected to the other end of the longest heating element 154b1 between the contact 154d1 and the contact 154d2. , 154b4 has a combined electrical resistance value of 10Ω.

The heating elements 154b1 and 154b4 are electrically connected to a first contact 154d1 and a second contact 154d2, and the heating element 154b2 is electrically connected to a contact 154d2 and a third contact 154d3. has been done. The heating element 154b3 is electrically connected to a contact 154d3 and a fourth contact 154d4. Here, the heating element 154b1 and the heating element 154b4 have the same length, and are supplied with power substantially at the same time. The heating element 154b1 is provided at one end of the substrate 154a in the lateral direction, and the heating element 154b4 is provided at the other end of the substrate 154a in the lateral direction. The heating elements 154b2 and 154b3 are provided symmetrically about the center in the lateral direction between the heating element 154b1 and the heating element 154b4 in the lateral direction of the substrate 154a.

The distance between each heating element 154b is 0.7 mm. Note that in the first embodiment, the widths W1 to W3 of the heating elements 154b are all 0.7 mm, but depending on the performance required of the fixing device 50, the heating elements 154b may have the same width. Therefore, there are cases where it is difficult to select a conductive material. In that case, the widths W1 to W3 of the heating element 154b may be varied depending on the performance required of the fixing device 50.

[Aim of configuration of heating element 154b]
The longest heating elements 154b1 and 154b4 have the largest amount of heat generation among the plurality of heating elements 154b, and it is common to use the heating elements 154b1 and 154b4 to heat the fixing device 50 to the target temperature in a short time. This configuration is also adopted in this embodiment. On the other hand, the fact that the amount of heat generated is large may lead to a situation where the device is susceptible to excessive power supply due to malfunction of the device. If excessive power is supplied, the temperature will rise excessively, and there is a possibility that the substrate 154a may be deformed.

In this embodiment, the configuration of the heater 154 is such that it achieves both a high power supply capacity and a reduction in the possibility that the substrate 154a will be deformed. Specifically, the longest heating element is configured as two heating elements 154b1 and 154b4, thereby distributing power, that is, reducing power density. Further, one heating element 154b1 is arranged at one end of the substrate 154a in the transverse direction, and the other heating element 154b4 is arranged at the other end (opposite end) of the substrate 154a. The two heating elements 154b1 and 154b4 are electrically connected through common contacts 154d1 and 154d2, and power is supplied to the two longest heating elements 154b1 and 154b4 at the same time. This suppresses a situation in which only the heating element disposed at one end in the lateral direction of the substrate 154a generates heat, and the heat generation distribution in the lateral direction of the substrate 154a is uneven. When the heating elements 154b1 and 154b4 are generating heat, the distribution of heat generation in the transverse direction of the substrate 154a can be made substantially uniform, and the risk of deformation of the substrate 154a can be reduced.

Further, in this embodiment, one heating element 154b2 and one heating element 154b3 are each provided as heating elements that are not the longest. As a result, even when fixing a sheet P that is narrower than the maximum size sheet P corresponding to the heating elements 154b1 and 154b4, the heating elements can be made to generate heat according to the width of the sheet P. You can increase your sexuality. Note that the heating elements 154b2 and 154b3 which are not the longest generate less heat than the longest heating elements 154b1 and 154b4. Further, in the lateral direction of the substrate 154a, the two longest heating elements 154b1 and 154b4 are arranged so as to be substantially symmetrical in the lateral direction. As a result, the substrate 154a can be uniformly heated and the temperature distribution of the substrate 154a can be made gentle, compared to the case where the heating element is biased toward one end of the substrate 154a in the transverse direction. , the risk of deformation of the substrate 154a can be reduced. The longest heating elements 154b1 and 154b4, which require a high power supply capacity, are configured to have two pieces, and the heating elements 154b2 and 154b3, which are not the longest, are configured to have a minimum of one piece per length level of the heating element. This suppresses deformation of the substrate 154a, increases productivity when printing on a plurality of small-sized papers, and minimizes the dimensions of the substrate 154a.

[Power supply circuit]
FIG. 10 shows a power supply circuit for supplying power to the heater 154. In FIG. 10, contacts 154d1 to 154d4 are connected to a heating element switch 57 for switching the power supply path. In addition, since the heating element 154b that generates heat is switched by switching the power supply path using the heating element switch 57, switching the power supply path is also referred to as switching the heating element 154b. In this embodiment, the heating element switch 57 is an electromagnetic relay 57a, 57b having a C contact configuration.

The electromagnetic relay 57a has a contact 57a1 connected to the first pole of the AC power supply 55 via the triac 56, a contact 57a2 connected to the contact 154d1, and a contact 57a3 connected to the contact 154d3. The electromagnetic relay 57a is switched by the engine controller 92 to either a state where the contacts 57a1 and 57a2 are connected, or a state where the contacts 57a1 and 57a3 are connected. The electromagnetic relay 57b has a contact 57b1 connected to the second pole of the AC power source 55, a contact 57b2 connected to the contact 154d2, and a contact 57b3 connected to the contact 154d4. The electromagnetic relay 57b is switched by the engine controller 92 to either a state in which the contacts 57b1 and 57b2 are connected, or a state in which the contacts 57b1 and 57b3 are connected. The triac 56 can switch between supplying power to or cutting off power to a predetermined heating element 154b among the plurality of heating elements 154b.

FIG. 10 shows the electromagnetic relays 57a and 57b when they are not operating, with the electromagnetic relay 57a having its contacts 57a1 and 57a2 connected, and the electromagnetic relay 57b having its contacts 57b1 and 57b2 connected. When the electromagnetic relays 57a and 57b are not operating, power is supplied between the contacts 154d1 and 154d2, so the longest heating elements 154b1 and 154b4 generate heat. The CPU 94 performs PI control based on the detection result detected by the thermistor 59 and the target temperature so that the fixing nip portion N has a predetermined temperature. Specifically, the ratio of conduction/non-conduction (hereinafter also referred to as duty) of the triac 56 is calculated, and the triac 56 is controlled based on this.

When the electromagnetic relays 57a and 57b are operated, the contacts 57a1 and 57a3 of the electromagnetic relay 57a are connected, and the contacts 57b1 and 57b3 of the electromagnetic relay 57b are connected. When the electromagnetic relays 57a and 57b operate, power is supplied between the contacts 154d3 and 154d4, so only the heating element 154b3 generates heat. When only the electromagnetic relay 57a is operated, the contacts 57a1 and 57a3 of the electromagnetic relay 57a are connected, and the contacts 57b1 and 57b2 of the electromagnetic relay 57b are connected. When only the electromagnetic relay 57a is in operation, power is supplied between the contacts 154d3 and 154d2, so only the heating element 154b2 generates heat. For the electromagnetic relays 57a and 57b, a contact switch such as an electromagnetic relay with an a contact configuration or an electromagnetic relay with a b contact configuration may be used, or a non-contact switch such as a solid state relay (SSR), a photomos relay, or a triac may be used. I don't mind.

[Width of sheet P, heating element and throughput]
Next, the relationship between the width of the sheet P to be printed, the heating element 154b used, and the throughput will be described using FIG. 11. FIG. 11 shows the longitudinal positional relationship of the paper width sensor 102 and the thermistor 59 in contrast to the schematic diagram of the heater 154 described in FIG. There are two pairs of paper width sensors 102, and four paper width sensors are installed symmetrically. Note that when the sheet P is transported on the transport path Y, the sheet P is transported so that the center of the width direction of the sheet P is aligned with the center of the transport path Y in the width direction. In other words, the transport reference is the central reference.

The paper width sensor 102 includes large paper width sensors 102a1 and 102a2, and medium paper width sensors 102b1 and 102b2, which are arranged from the outside (both end sides) in the longitudinal direction. For example, the distance SLa between the large paper width sensor 102a1 and the large paper width sensor 102a2 is set to 198 mm (SLa=198 mm). Furthermore, the distance SLb between the paper width middle sensor 102b1 and the paper width middle sensor 102b2 is set to 170 mm (SLb=170 mm).

On the other hand, there are three thermistors 59, a fixing temperature sensor 59a is arranged at the center in the longitudinal direction, and fixing temperature sensors 59b1 and 59b2 are arranged symmetrically in the longitudinal direction. The fixing temperature sensor 59a is disposed at a position where the sheet P passes through the fixing device 50 no matter what size the sheet P is, and is used to control the temperature of the heater 154. On the other hand, the fixing temperature sensors 59b1 and 59b2 are arranged at positions where the sheet P does not pass depending on the size of the sheet P to be printed. The fixing temperature sensors 59b1 and 59b2 are used more than the fixing temperature sensors 59b1 and 59b2 to determine the temperature increase in the non-sheet passing area on the outside in the longitudinal direction and to control the temperature of the non-sheet passing area. Here, as an example, the distance SLt between the fixing temperature sensors 59b1 and 59b2 is 142 mm (SLt=142 mm).

The large paper width sensors 102a1 and 102a2, which serve as a pair of first detection means, are located in a region inside in the longitudinal direction from both ends of the heat generating elements 154b1 and 154b4, and a region outside in the longitudinal direction from both ends of the heat generating body 154b2. It is located in The paper width sensors 102b1 and 102b2, which serve as a pair of second detection means, are arranged in a region inside in the longitudinal direction from both ends of the heating element 154b2, and outside in a region in the longitudinal direction from both ends of the heating element 154b3. has been done. The fixing temperature sensors 59b1 and 59b2 as a pair of third detection means are arranged in a region inside in the longitudinal direction from both ends of the heat generating body 154b3 and near both ends of the heat generating body 154b3. From the above, the length relationship of L1>SLa>L2>SLb>L3>SLt holds for the heating elements 154b1 to 154b4, each paper width sensor 102, and the fixing temperature sensor 59b.

FIG. 11 shows six ranges ([1] to [6]) determined from the position of the end of each heating element 154b in the longitudinal direction, the position of the paper width sensor 102, and the fixing temperature sensor 59b. The CPU 94 controls the heating element 154b that supplies power and the throughput per unit time depending on which of these ranges the end of the sheet P corresponds to. For example, the CPU 94 controls the throughput per unit time by controlling the conveyance speed of the sheet P, the paper interval between the preceding paper and the following paper, the heat generation rate of the heating element 154b, and the like. The relationship between the six ranges, the heating element 154b that supplies power, and throughput will be described below. Note that the full throughput used in the following description refers to the highest throughput (the highest number of sheets printed per unit time) that can be achieved by the image forming apparatus. Furthermore, in the following description, when the CPU 94 selects and uses a predetermined heating element 154b, it is assumed that the CPU 94 controls the electromagnetic relays 57a and 57b described in FIG. 10 to switch the power supply path. .

・Microwave [1]
A case where the end of the sheet P corresponds to range [1] will be described. In this case, in order to perform the fixing process on the sheet P that is wider than the length L2 of the heating element 154b2, power is supplied to the heating elements 154b1 and 154b4, which are the longest heating elements 154b. The temperature of the non-sheet passing area through which the sheet P does not pass increases compared to the sheet passing area through which the sheet P passes. However, since the end of the sheet P corresponds to range [1], the non-sheet passing area is relatively small, and the temperature increase in the non-sheet passing area is also relatively small. Therefore, even if printing is performed at full throughput as the first throughput, the temperature does not rise to the extent that the pressure roller 53 and the film 51 melt. Therefore, printing is performed at full throughput. In this way, when the end of the sheet P corresponds to range [1], the CPU 94 supplies power to the heating elements 154b1 and 154b4, and controls the printing operation by setting the throughput to full.

・Microwave [2]
A case where the end of the sheet P corresponds to range [2] will be described. As in the case of range [1], printing is performed using the heating elements 154b1 and 154b4 in order to perform the fixing process on the sheet P whose width is larger than the length L2 of the heating element 154b2. Since the difference between the width of the sheet P and the length in the longitudinal direction of the heating elements 154b1 and 154b4 is larger than that in range [1], the non-sheet passing area is larger than in range [1], and the non-sheet passing area rises. The temperature will also be higher compared to microwave [1]. Therefore, there is a possibility that the pressure roller 53 and the film 51 will melt. In order to suppress the possibility of melting, the paper gap between the preceding paper and the following paper is made wider than in the case of full throughput to reduce the temperature rise in the non-paper passing area. Therefore, since printing is performed at a lower throughput (second throughput) than in range [1], productivity is lower than in range [1]. In this way, when the end of the sheet P corresponds to range [2], the CPU 94 supplies power to the heating elements 154b1 and 154b4, and controls the printing operation by setting the throughput to be lower than the full throughput.

・Microwave [3]
A case where the end of the sheet P corresponds to range [3] will be described. In order to perform the fixing process on the sheet P having a width larger than the length L3 of the heat generating element 154b3 and smaller than the length L2 of the heat generating element 154b2, power is supplied to the heat generating element 154b2. However, if printing is continued using only the heating element 154b2, heat will not be supplied to the area outside the heating element 154b2 and the temperature will drop, causing the pressure roller 53 corresponding to the non-paper passing area to be lowered compared to the paper passing area. The degree of expansion of the area becomes smaller. If the fixing device 50 is continued to be driven in this state, the difference in the degree of expansion in the longitudinal direction of the pressure roller 53 will cause a difference in the transport distance in the longitudinal direction, which may cause the film 51 to twist and break. . In order to avoid this phenomenon, while supplying power primarily to the heating element 154b2, power is also supplied to the heating elements 154b1 and 154b4 at a predetermined ratio to reduce the temperature difference between the paper passing area and the non-paper passing area. controlled to do so.

Further, since the end portion of the sheet P corresponds to range [3], the non-sheet passing area is relatively small, and the temperature increase in the non-sheet passing area is also relatively small. Therefore, even when printing is performed at full throughput, the temperature does not rise to the extent that the pressure roller 53 and the film 51 melt. Therefore, printing is performed at full throughput. In this way, when the end of the sheet P corresponds to range [3], the CPU 94 mainly supplies power to the heating element 154b2 and controls the printing operation with the throughput set to full throughput.

・Microwave [4]
A case where the end of the sheet P corresponds to range [4] will be described. As in the case of range [3], the fixing process is performed on a sheet P having a width larger than the length L3 of the heat generating element 154b3 and smaller than the length L2 of the heat generating element 154b2. Therefore, power is mainly supplied to the heating element 154b2, and power is also supplied to the heating elements 154b1 and 154b4 at a predetermined ratio. Since the difference between the width of the sheet P and the length of the heating element 154b2 in the longitudinal direction is larger than in range [3], the non-sheet passing area is larger than in range [3], and the temperature of the non-sheet passing area is also increased. It is larger than range [3]. Therefore, there is a possibility that the pressure roller 53 and the film 51 will melt. In order to suppress the possibility of melting, the paper interval is made wider than in the case of full throughput to reduce the temperature rise in the non-paper passing area. Therefore, since printing is performed at a lower throughput than in range [3], productivity is lower than in range [3]. In this way, when the end of the sheet P corresponds to range [4], the CPU 94 mainly supplies power to the heating element 154b2 and controls the printing operation by setting the throughput to be lower than the full throughput.

・Microwave [5]
A case where the end of the sheet P corresponds to range [5] will be described. In order to perform the fixing process on the sheet P having a width smaller than the length L3 of the heating element 154b3, power is supplied to the heating element 154b3. However, if printing is continued using only the heating element 154b3, heat will not be supplied to the area outside the heating element 154b3 and the temperature will drop, causing the pressure roller 53 corresponding to the non-paper passing area to be lowered compared to the paper passing area. The degree of expansion of the area becomes smaller. If the fixing device 50 is continued to be driven in this state, the difference in the degree of expansion in the longitudinal direction of the pressure roller 53 will cause a difference in the transport distance in the longitudinal direction, which may cause the film 51 to twist and break. . In order to avoid this phenomenon, power is mainly supplied to the heating element 154b3, and power is also supplied to the heating elements 154b1 and 154b4 at a predetermined ratio to reduce the temperature difference between the paper passing area and the non-paper passing area. controlled to do so.

Since the end of the sheet P corresponds to range [5], the non-sheet passing area is relatively small, and the temperature increase in the non-sheet passing area is also relatively small. Therefore, even when printing is performed at full throughput, the temperature does not rise to the extent that the pressure roller 53 and the film 51 melt. Therefore, printing is performed at full throughput.

However, in range [5], unlike ranges [1] and [2] and ranges [3] and [4], the sensors at the boundaries are temperature detection sensors 59b1 and 59b2. Therefore, range [5] and range [6] are not determined uniquely like ranges [1] and [2] or ranges [3] and [4], but are determined based on the width of the specified sheet P. This is performed based on the temperature detected by the temperature detection sensors 59b1 and 59b2. If the width of the sheet P is smaller than 148 mm, it is determined to be in range [6], and if it is 148 mm or more, it is determined to be in range [5]. However, even if it is determined that the range is [5] based on the width of the designated sheet P, the following determination is further made. If either of the temperature detection sensors 59b1 and 59b2 detects a temperature that is, for example, 10° C. higher than the temperature of the temperature detection sensor 59a, the sheet P is smaller in width than the sheet P corresponding to range [5]. Therefore, it is determined that it corresponds to range [6].

In this way, when the end of the sheet P corresponds to range [5], the CPU 94 mainly supplies power to the heating element 154b3 and controls the printing operation with the throughput set to full throughput.

・Microwave [6]
A case where the end of the sheet P corresponds to range [6] will be described. Similar to range [5], the fixing process is performed on the sheet P having a width smaller than the length L3 of the heating element 154b3. Therefore, while power is mainly supplied to the heating element 154b3, power is also supplied to the heating elements 154b1 and 154b4 at a predetermined ratio. Since the difference between the width of the sheet P and the length of the heating element 154b3 in the longitudinal direction is larger than in range [5], the non-sheet passing area is larger than in range [5], and the temperature of the non-sheet passing area is also increased. It is larger than range [5]. Therefore, there is a possibility that the pressure roller 53 and the film 51 will melt. In order to suppress the possibility of melting, the paper interval is made wider than in the case of full throughput to reduce the temperature rise in the non-paper passing area. Therefore, since printing is performed at a lower throughput than in range [5], productivity is lower than in range [5]. In this way, when the end of the sheet P corresponds to range [6], the CPU 94 mainly supplies power to the heating element 154b3 and controls the printing operation by setting the throughput to be lower than the full throughput.

[Control of this embodiment]
Next, the printing operation of the image forming apparatus in this embodiment will be explained using FIG. 12. As in the first embodiment, the preceding paper is assumed to be sheet P1, and the subsequent paper is assumed to be sheet P2. Further, as in the first embodiment, there is a case where image formation on the sheet P2 is stopped due to the occurrence of some kind of error in the printing operation as an example. In this embodiment, as an example, when it is determined that the width of the sheet P detected by any one of the large paper width sensor 102a, the medium width sensor 102b, and the temperature detection sensor 59b is narrower than the prespecified width of the sheet P. It is determined that an error has occurred. If the detected width of the sheet P is narrower than the prespecified width of the sheet P, the image formed outside the width of the sheet P is not secondarily transferred to the sheet P. Therefore, a large amount of residual toner is generated on the intermediate transfer belt 13, and a large amount of the residual toner is collected by the cleaning unit 27. However, since there is a limit to the amount of toner that the cleaning unit 27 can collect, if the detected width of the sheet P is narrower than the pre-specified width of the sheet P, the printing operation is interrupted (hereinafter, this interruption is referred to as (Also called interruption due to narrow error).

In a series of printing operations, if any error as described above occurs, subsequent processing is changed depending on whether or not the image forming operation for sheet P2 has been started. If the image forming operation on the sheet P2 has been started, the temperature of the fixing device 50 is at the target temperature TE2 in order to fix the formed toner image on the sheet P2, similar to conventional control. Perform fixation. Therefore, in order to suppress the temperature rise of the non-sheet passing portion at the longitudinal end of the fixing device 50, throughput down control is performed to wait for the time Tdown.

On the other hand, if the image forming operation on the sheet P2 has not been started, there is no unfixed toner image on the sheet P2. Therefore, if the temperature of the fixing device 50 exceeds the target temperature TE4 at which the pressure roller 53 can rotate, the sheet P2 can be passed through the fixing device 50. Therefore, it is no longer necessary to maintain the temperature of the fixing device 50 at the target temperature TE2, and the target temperature can be lowered to TE4. As a result, since the target temperature has been lowered, the temperature increase in the non-sheet passing portions at the ends of the fixing device 50 in the longitudinal direction is also moderated, so there is no need to provide a standby period of time Tdown. Therefore, a decrease in productivity due to throughput down control can be suppressed.

Hereinafter, a specific printing operation will be explained using the timing chart of FIG. 12. Note that the description of the same parts as the printing operation described using FIG. 7 in the first embodiment will be omitted here.

Furthermore, the occurrence of some kind of error in this embodiment will be explained as a case where a narrow sheet width error occurs as described above. Specifically, when a print instruction for sheets P1 and P2 is input as the width corresponding to range [2], sheet P1 is set to have a width corresponding to range [2], and sheet P2 is set to range [4]. A case where the narrow sheet width error occurs in sheet P2 will be described.

At the timing when the sheet P2 reaches the registration sensor 103, the CPU 94 determines the width of the sheet P2 based on the detection result of the paper width sensor 102 (t1201). Specifically, since the medium width sensors 102b1 and 102b2 are not turned on, it is determined that the sheet P2 is narrower than the specified width, and a narrow sheet width error is notified. The control after notifying the narrow sheet width error is the same as the printing operation described with reference to FIG. 7 in the first embodiment, so a detailed explanation will be omitted here. As described above, according to the printing operation of this embodiment, the sheet P2 can be discharged from the image forming apparatus faster than the conventional printing operation described using FIG. 6, and a decrease in productivity can be suppressed. can do. Further, it is also possible to prevent the temperature of the fixing device 50 from reaching the limit temperature TE3.

[flowchart]
The printing operation when an error occurs will be described using the flowchart in FIG. 13. FIG. 13 shows a process for determining whether to stop transporting sheet P2. Note that the process of restarting the conveyance of the sheet P2 after stopping the conveyance is the same as the explanation using FIG. 8(b) in the first embodiment, so the explanation here will be omitted. .

In S1301, the CPU 94 determines whether the width of the sheet P2 specified in advance by the controller 91 corresponds to range [1]. If the width corresponds to range [1], the process advances to S1302; if the width does not correspond to range [1], the process advances to S1305.

In S1302, the CPU 94 determines whether the sheet P2 is detected by the large paper width sensor 102a. If the sheet P2 is detected by the large paper width sensor 102a, the specified width of the sheet P2 and the detected width of the sheet P2 match, so the process ends. If the sheet P2 is not detected by the large paper width sensor 102a, the detected width of the sheet P2 is narrower than the specified width of the sheet P2, so the process advances to S1303. The process for stopping the conveyance in S1303 is the same as that shown in FIG. 8(b), so the explanation here will be omitted.

If it is determined in S1301 that the width of the specified sheet P2 does not correspond to range [1], then in S1304 the CPU 94 determines whether the width of the specified sheet P2 corresponds to range [2] or range [3]. Decide whether or not. If it does not correspond to range [2] or range [3], the width of sheet P2 corresponds to any one of ranges [4], [5], and [6]. Ranges [4], [5], and [6] are ranges in which the medium width sensor 102b cannot detect the sheet P2, so the conveyance of the sheet P2 is not stopped and the process ends.

On the other hand, if the specified width of the sheet P2 corresponds to range [2] or range [3], in S1305, the CPU 94 determines whether the sheet P2 is detected by the medium width sensor 102b. If the sheet P2 is detected by the paper width sensor 102b, the specified width of the sheet P2 and the detected width of the sheet P2 match, so the process ends. If the sheet P2 is not detected by the medium width sensor 102b, the detected width of the sheet P2 is narrower than the specified width of the sheet P2, so the process advances to S1303. The process for stopping the conveyance in S1303 is the same as that shown in FIG. 8(b), so the explanation here will be omitted.

In this way, if a sheet remains inside the image forming apparatus when an error occurs, it is determined whether an image has been formed on the sheet or not, and the processing until the sheet is ejected from the image forming apparatus is changed. When no image is formed on the sheet, the target temperature of the fixing device 50 can be lowered and the sheet can be ejected from the image forming apparatus, thereby suppressing a decrease in productivity without performing throughput down control. be able to.

30 Paper output tray 50 Fixing device 54 Heater 94 CPU

Claims (13)

an image forming means for forming a toner image on a sheet;
a fixing unit including an elongated heater and fixing an unfixed toner image formed on the sheet by the image forming unit;
an ejection tray from which sheets are ejected;
A control means for controlling conveyance of the sheet,
When performing image formation on a preceding first sheet and a subsequent second sheet, the control means determines whether or not image formation on the second sheet can be completed. judge,
If it is determined that image formation on the second sheet cannot be completed, determining whether or not image formation is being performed on the second sheet by the image forming means;
If image formation is performed on the second sheet, the interval between the first sheet and the second sheet is a first interval, and the image formation is not performed on the second sheet. In the case of image formation, the interval between the first sheet and the second sheet is set to a second interval narrower than the first interval, and the second sheet is discharged to the discharge tray. Device. When image formation is being performed on the second sheet, the control means discharges the second sheet to the ejection tray with a target temperature of the fixing means as a first temperature, and 2. If no image is formed on the sheet, the target temperature of the fixing means is set to a second temperature lower than the first temperature, and the second sheet is discharged to the discharge tray. 1. The image forming apparatus according to 1. If the control means determines that image formation on the second sheet cannot be completed, the control means stops the conveyance of the second sheet, and then adjusts the temperature of the second sheet according to the temperature of the fixing means. The image forming apparatus according to claim 1 or 2, wherein the image forming apparatus restarts conveyance. The image forming means further includes a photoreceptor and an exposure means for irradiating the photoreceptor with laser light to form an electrostatic latent image,
4. The control means determines that image formation on the second sheet cannot be completed when the laser light cannot be irradiated from the exposure means. Image forming device. Receiving means for receiving the length of the second sheet in a direction perpendicular to the conveying direction of the second sheet;
a detection means for detecting the length of the second sheet in the orthogonal direction,
The control means may determine that image formation on the second sheet cannot be completed if the detected length of the second sheet is shorter than the received length of the second sheet. The image forming apparatus according to any one of claims 1 to 3. 6. The image forming apparatus according to claim 5, wherein the detection means is arranged inside a region of the heater in the orthogonal direction. The heater includes a substrate, a first heating element, a second heating element shorter in length in the longitudinal direction of the substrate than the first heating element, and a second heating element shorter in length than the second heating element in the longitudinal direction. a third heating element having a short length, and a fourth heating element;
7. Any one of claims 1 to 6, wherein the first heating element, the second heating element, the third heating element, and the fourth heating element are arranged on the substrate. The image forming apparatus described in . Claim 7, wherein the first heating element, the second heating element, the third heating element, and the fourth heating element are arranged in this order in the lateral direction of the substrate. The image forming apparatus described above. a first contact to which one end of the first heating element and the fourth heating element are electrically connected;
a second contact to which the other ends of the first heating element, the second heating element, and the fourth heating element are electrically connected;
a third contact to which one end of the second heating element and the third heating element are electrically connected;
a fourth contact to which the other end of the third heating element is electrically connected;
The image forming apparatus according to claim 7 or 8, characterized by comprising:. The length in the longitudinal direction of the first heating element and the fourth heating element is a length corresponding to the width of a sheet having the maximum width among the sheets that can be printed in the image forming apparatus. The image forming apparatus according to any one of claims 7 to 9. a first rotating body heated by the heater;
a second rotating body forming a nip portion together with the first rotating body;
The image forming apparatus according to any one of claims 1 to 10, characterized by comprising: The image forming apparatus according to claim 11, wherein the first rotating body is a film. The heater is disposed in the internal space of the film, the film is sandwiched between the heater and the second rotating body, and the image on the sheet is displayed between the film and the second rotating body. The image forming apparatus according to claim 12, wherein the image forming apparatus is heated through the film at a formed nip portion.

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