JP2006240831A - Sheet size detector and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of automatically detecting a sheet size more accurately without needing to be set by a user. <P>SOLUTION: A sensor arm 51 for rotating by contact with a conveyed sheet, a sensor arm 52 positioned on a further downstream side in the sheet conveying direction than the sensor arm 51, and a photo interrupter 21 for detecting movements of the sensor arm 52 are provided. The sensor arm 52 moves interlockingly with the sensor arm 51, and after the sensor arm 51 rotates, the sensor arm 52 is switched to a moving state. The sheet size is determined based on detection results of a plurality of detections made of the conveyed sheet at predetermined timings by the photo interrupter 21. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus having a function of forming an image on a recording medium such as a sheet, such as a copying machine, a printer, or a facsimile machine, and more particularly, a sheet for detecting the size of a conveyed sheet. The present invention relates to a size detection device.

  Conventionally, many image forming apparatuses including a fixing unit having a heat roller method or a film heating method have been used.

  In the image forming apparatus, sheets of various sizes (sheets) are used for passing, but the size in the width direction perpendicular to the conveying direction is the maximum sheet passing width of the heat fixing means (= heat roller of the heat roller type heat fixing means) When the sheet of small size is smaller than the effective maximum heating length of the film heating method, the effective maximum heating length of the heater of the heat fixing means is used, especially when the small size sheet is continuously used. When the sheet is used, a non-sheet passing portion which is a difference area between the maximum sheet passing width and the sheet width dimension of the heat fixing unit is generated. The temperature of the heat roller portion or heater portion corresponding to the non-sheet passing portion is higher than the temperature of the heat roller portion or heater portion corresponding to the sheet passing portion because the heat of the portion is not consumed for heating the sheet. A so-called “non-sheet passing portion temperature rise phenomenon” that becomes significantly large occurs. As a result, in the state where the heat roller and the heater are thermally damaged or the temperature rise of the non-sheet passing portion occurs, the image is fixed by passing the next wide sheet of a large size. In some cases, a so-called “high temperature offset” of the toner image may occur in a portion corresponding to the non-sheet passing portion temperature increasing portion.

  As means for avoiding this, a means for detecting the size type of the sheet used to pass through the apparatus (a plurality of size types having different sizes in the width direction perpendicular to the conveyance direction) is provided, and the detection result Based on the above, measures such as changing the heat fixing condition or changing the throughput have been taken.

  FIG. 23 shows a conventional example of a means for detecting the size type of a sheet used to pass through the apparatus.

  A0 is a sheet conveyance path including the sheet conveyance roller pair 4a, 4b. In this example, two types of size sheets, a small size sheet S1 and a large size sheet S2, are conveyed along the central conveyance reference O- in this conveyance path A0. O is selectively conveyed.

  A1 is a conveyance width area of the small size sheet S1 in the sheet conveyance path A0, A2 is a conveyance width area of the large size sheet S2, and B1 is a difference area between the conveyance width areas A1 and A2 of the small size sheet S1 and the large size sheet S2. It is.

  101 and 102 are first and second sets of sheet size type detection means, respectively. The first means 101 is located at a position in the conveyance width area A1 of the small size sheet S1, and the second means 102 is They are arranged corresponding to the positions in the difference area B1 between the transport width areas A1 and A2.

Each of the first and second sheet size type detection means 101 and 102 includes displacement means 101a and 102a that are displaced by contact with the conveyance sheet, and detection means 101b and 102b that detect the displacement of the displacement means. In the case of the example, the displacing means 101a and 102a are oscillators having an upper arm portion and a lower arm portion that are freely rotatable around the support shafts 101c and 102c, respectively, and the detecting means 101b and 102b are a light emitting portion and a light receiving portion. A photo interrupter having a portion. Both the oscillators 101a and 102a are maintained in a substantially vertical vertical posture by gravity in a free state.

  Thus, when the sheet passed through the conveyance path A0 is the small size sheet S1, the upper arm portion of the oscillator 101a of the first sheet size type detection unit 101 interferes with the front side of the conveyance sheet S1. Then, it is kicked and comes into contact with the lower surface of the conveying sheet, and the swinging element 101a is rotated and displaced in the counterclockwise direction around the support shaft 101c. The rotational displacement posture of the swinging element 101a causes the sheet S1 to swing. It is held until it passes through the position of the moving element 101a. This rotational displacement of the oscillator 101a is detected by closing the optical path of the photoelectric unit of the photo interrupter 101b by the rotation of the lower arm of the oscillator 101a, and the output signal of the photo interrupter 101b is changed from open to closed. Change.

  On the other hand, since the position of the oscillator 102a of the second sheet size type detecting means 102 is outside the conveyance width area A1 of the small size sheet S1, there is no kick by the conveyance sheet S1, and the output signal of the photo interrupter 101b is It remains open.

  The change of the output signal of the photo interrupter 101b of the first sheet size type detection unit 101 from the open state to the closed state after the sheet is passed, and the photo interrupter 102b of the second sheet size type detection unit 102 The control circuit (not shown) detects and determines that the passed sheet is the small-size sheet S1 from the continuous open state of the output signal.

  When the sheet passed through the transport path A0 is a large size sheet S2, the positions of the swingers 101a and 102a of the first and second sheet size type detecting means 101 and 102 are both large size sheet S2. Therefore, both the oscillators 101a and 102a are kicked by the conveying sheet S2, and the output signals of the photo interrupters 101b and 102b of the first and second sheet size type detecting means 101 and 102 are, respectively. Are changed from the open state to the closed state. Accordingly, a control circuit (not shown) detects and determines that the fed sheet is the large-size sheet S2.

  Even when there are three or more sheet size types to be used in the apparatus, the first and second sheet size type detecting units 101 and 102 are included in the difference area between the conveyance width areas of the respective sheet sizes. By adding a set of the same oscillator and photointerrupter, each type of sheet can be detected in the same manner. In the case of an image forming apparatus that controls the width of a sheet based on a central reference, it is common to determine the width of a sheet to be passed by providing a sheet width sensor for only one of them.

  Further, as a means for changing the heat fixing condition based on the detection result described above, the resistance heating element of the heating body of the fixing device can freely generate heat for each predetermined area with respect to the longitudinal direction, and each heat generation area is separately provided. There has also been proposed a means for preventing temperature rise of the non-sheet passing portion by controlling the temperature detection element independently to control the optimum set temperature regardless of the sheet passing region and the non-sheet passing region.

Note that there are Patent Documents 1 to 4 as documents in which related conventional examples are disclosed.
JP-A-06-274068 Japanese Patent Laid-Open No. 11-116097 Japanese Patent Laid-Open No. 10-181891 JP-A-8-119534

However, in the configuration described in the conventional example, for example, in an image forming apparatus in which sheet width regulation is performed based on a central reference, what should be detected as a small size sheet is detected as a large size sheet. There was a problem of sheet size misdetection.

  Specifically, as shown in FIG. 21, for example, in a configuration in which sheet width regulation is performed based on a central reference and a sheet size detection unit is provided only on one side in the longitudinal direction, a small size sheet is passed. Normally, the sheet width regulation guide 112 should be set in the center as a sheet support and then the sheet should be passed, but the sheet width regulation guide 112 is widened and the sheet size detecting means side passes the sheet as shown in FIG. As a result, the image forming apparatus has a problem that the sheet is detected as a large size sheet by passing through the sheet size detecting unit.

  Due to this erroneous detection, for example, in the case of fixing control, if a small-size sheet is originally passed, it is necessary to perform control as a small size, such as lowering the fixing temperature slightly or widening the gap between papers to reduce throughput. However, by controlling the fixing temperature to a higher size as a large size, or increasing the throughput by narrowing the gap between papers, the problems such as the “non-paper passing part temperature rise phenomenon” and “high temperature offset” described above Will cause.

  Furthermore, the fixing device is damaged due to excessive temperature rise of the non-sheet passing portion, and the main body is also broken.

  In order to accurately detect the sheet size, it is necessary to provide sheet width size detection means on both the left and right sides with respect to the center in the sheet conveyance direction. The increase in the number of photo interrupters as sensor means has led to an increase in cost.

  SUMMARY An advantage of some aspects of the invention is that it provides a technique capable of automatically detecting a more accurate sheet size regardless of user settings.

  It is another object of the present invention to provide a technique that can more suitably control the image forming process by more accurately detecting the sheet size.

In order to achieve the above object, in the sheet size detection apparatus according to the present invention,
A first sheet contactor that is movably provided in a sheet conveyance path for conveying a sheet and moves to a first position while the conveyed sheet is in contact;
A first predetermined interval is set in the sheet width direction substantially perpendicular to the sheet conveying direction with respect to the first sheet contact, and a second predetermined interval is set downstream of the first sheet contact in the sheet conveying direction. While the first sheet contactor assumes the first position, the sheet conveyed through the sheet conveyance path is moved to a second position where the sheet can be contacted, and the sheet contacts A second sheet contact that deviates from the second position while
Detecting means for detecting whether or not the second sheet contact is in the second position;
With
The size of the conveyed sheet is detected based on a detection result obtained by detecting the conveyed sheet a plurality of times at a predetermined timing by the detection unit.

  The image forming apparatus according to the present invention includes the sheet size detecting device described above and a transfer unit that transfers the toner image formed on the image carrier onto the sheet, and the image is formed on the sheet. It is characterized by forming.

  According to the present invention, a more accurate sheet size can be automatically detected regardless of user settings.

  Furthermore, the image forming process can be more suitably controlled by more accurately detecting the sheet size.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

  The present invention relates to a size type of a sheet that is conveyed on a sheet conveyance path for selectively conveying a plurality of size types of sheets (conveyed bodies) having different sizes in the sheet width direction substantially orthogonal to the sheet conveyance direction. The present invention relates to a detection device and an image forming apparatus including a sheet size detection device as a conveyance sheet size type detection device.

  FIG. 2 is a schematic configuration diagram of an example of an image forming apparatus provided with the sheet size detection apparatus according to the first exemplary embodiment of the present invention as a conveyance sheet size type detection apparatus. The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process.

  Reference numeral 3 denotes a feeding table as a sheet placement portion of the sheet S, and 2 denotes a movable sheet width regulating member (hereinafter referred to as a sheet width regulating guide) provided on the feeding table 3. The sheet S inserted into the apparatus main body is moved toward the center with respect to the sheet width direction and is regulated to the central conveyance reference.

  After the insertion of the sheet S inserted into the apparatus main body from the feeding table 3 is detected by a detection means (not shown), the feeding roller 1 is rotationally driven at a predetermined control time to be pulled into the apparatus main body. Further, the sheet is nipped and conveyed by a pair of conveying rollers 4a and 4b as a sheet conveying unit, and at a predetermined timing, at a pressure nip portion between a rotating photosensitive drum 7 as an image carrier and a transfer roller 8 as a transfer unit. The toner image is introduced into a certain transfer portion N and receives a toner image corresponding to target image information formed and supported on the outer peripheral surface of the rotary photosensitive drum 7.

  Reference numeral 20 denotes a sheet width size detection unit as a sheet size detection apparatus according to the present embodiment, which is disposed in a sheet conveyance path between the conveyance roller pairs 4a and 4b and the transfer unit N. Details will be described later.

  The sheet to which the toner image has been transferred at the transfer portion N is separated from the surface of the rotating photosensitive drum 7 and introduced into a fixing means (hereinafter referred to as a heat fixing means) 15 to undergo a heat fixing process for an unfixed toner image and discharged. In this example, the paper is discharged from the roller pair 17a / 17b onto the discharge tray 18 in the face-down mode with the image surface facing downward.

  A laser scanner 12 outputs a modulated laser beam corresponding to a time-series electric digital pixel signal of target image information input from a host device such as a computer / image reading device (not shown), and the laser beam is not shown. The surface of the rotary drum 7 is scanned and exposed through the folding mirror.

  Reference numeral 11 denotes a charging roller as charging means for uniformly charging the surface of the rotating photosensitive drum 7 to a predetermined polarity and potential. The laser is applied to the surface of the rotating photosensitive drum 7 uniformly charged by the charging roller 11. By performing optical scanning exposure, an electrostatic latent image corresponding to target image information is formed on the surface of the rotary photosensitive drum 7.

The electrostatic latent image is visualized as a toner image by the developing device 10 as a developing unit, and the toner image is transferred to the sheet S by the transfer unit N described above.

  The surface of the rotating photoconductor 7 after the transfer of the toner image to the sheet is cleaned by removing residual contaminants such as transfer residual toner by a cleaning device 14 as a cleaning means, and is repeatedly used for image formation.

  In the image forming apparatus of this embodiment, four process devices, that is, the photosensitive drum 7, the charging roller 11, the developing device 10, and the cleaning device 14, are formed as process cartridges, and the opening / closing cover plate of the device is opened so that it can be attached and detached collectively. is there.

  The heat fixing means 15 in this example is of the film heating type, 15a is a heater frame, 15b is a heater held on the lower surface of the heater frame, 15c is loosely attached to the heater frame 15a including the heater 15b. The fitted cylindrical heat resistant film 16 is a pressure roller that is pressed against the lower surface of the heater 15b with the film 15c interposed therebetween.

  When the pressure roller 16 is rotationally driven in the sheet conveying direction, the cylindrical heat-resistant film 15c is driven to rotate around the outer periphery of the heater frame 15a while the inner surface thereof is in close contact with the lower surface of the heater 15b.

  The sheet S that has received the transfer of the toner image is introduced between the film 15c at the pressure contact portion and the pressure roller 16 so that the heat of the heater 15b is applied to the sheet via the film 15c. The toner image is thermally fixed.

  Reference numeral 13 denotes a CPU that controls the entire printer body. Here, based on the sheet size recognized by the sheet width size detecting means 20, the temperature control temperature of the fixing device and the process speed of the apparatus body are controlled. The normal (default) temperature control temperature of the laser beam printer in this embodiment is controlled to 180 ° C. Further, the sheet is conveyed at a speed of 115 mm / sec, and the gap between the sheets is adjusted so that the process speed is 18 ppm. Here, the CPU 13 constitutes a control unit, a determination unit, a conveyance control unit, an image forming condition control unit, and a heat generation control unit according to the present invention.

  Next, details of the sheet width size detection unit 20 will be described.

  FIG. 18 is a schematic view of the sheet conveyance path including the sheet width size detection means 20 portion. It is assumed that two types of size sheets, a small size sheet S1 and a large size sheet S2, are selectively conveyed by the central conveyance reference OO in this conveyance path.

  Reference numerals 51 and 52 denote first and second sheet contactors (hereinafter referred to as sensor arms) that are rotationally displaced by contact with the conveyed sheet. In the figure, when the large size sheet S2 is passed, the large size sheet S2 passes through and contacts both the sensor arms 51 and 52 during conveyance, and when the small size sheet S1 is passed, the sensor arm 51 is passed. , 52 do not pass through and do not contact each other. Reference numeral 21 denotes a photo interrupter as detection means, which will be described in detail later.

  The sensor arms 51 and 52 are respectively disposed at a location of about 95 mm on the left and right from the central conveyance reference OO. This is arranged for the purpose of discriminating, as a general market sheet size, a sheet larger than A4 (210 mm width) size as a large size sheet and a sheet smaller than EXE (184.2 mm width) size as a small size sheet. .

Accordingly, the arrangement location of the sensor arms 51 and 52 can be changed according to the use of the image forming apparatus main body. However, in general, when the large size sheet and the small size sheet are discriminated, the central conveyance reference O is used. It is desirable to arrange between -O and 80-105 mm (first predetermined interval). Further, the sensor arms 51 and 52 are arranged at a position separated by about 60 mm in the transport direction. This is for the CPU 13 to detect the width size of the conveyed sheet at the timing when the sensor arms 51 and 52 are tilted, and details will be described later.

  Next, details of the sheet width size detecting means 20 including the sensor arms 51 and 52 will be described with reference to FIG.

  The sensor arms 51 and 52 are arranged so as to be rotatable (movable) by the stopper 22 and prevented from moving in the thrust direction, respectively, and are rotated by springs 61 and 62 and the stopper 22 as shown in FIG. It is kept in an angular posture.

  That is, in the initial state, the sensor arm 51 exerts a force in the direction a shown in FIG. Then, following this, the sensor arm 53 also exerts a force in the direction of FIG.

  On the other hand, force is applied to the sensor arm 52 by the spring 62 in the direction of FIG. D and the sensor arm 54 in the direction of FIG. However, since the force of the spring 61 is slightly stronger than that of the spring 62 due to the force of the springs 61 and 62, the sensor arm 53 pushes the sensor arm 54 in the opposite direction of FIG. It is positioned so that the initial state is fixed at a certain angle.

  Normally, when the large size sheet S2 is set for feeding, the state is as shown in FIG. When the large-size sheet S2 is conveyed to the area of the sensor arms 51 and 52, as shown in FIG. 4, the sheet tilts the sensor arm 51 and rotates it in the direction of FIG. While in contact, the first position will be taken. Then, the sensor arm 54 is released from the pressure from the sensor arm 53, and the sensor arm 52 is rotationally displaced in the direction of g in FIG.

  When the sheet passing is completed, the sensor arm 51 is returned to the fixed position by the spring 61, whereby the sensor arms 51 and 52 are each returned to the state shown in FIG. Here, the sensor arm 53, the sensor arm 54, and the spring 62 constitute the first interlocking means according to the present invention.

  Reference numeral 19 denotes a sensor flag that rotates and displaces together with the sensor arm 52. 21 is a position for detecting the displacement of the sensor flag 19, and the sensor arm 52 is rotationally displaced in the direction h shown in FIG. It is a photo interrupter as a detecting means for detecting whether or not the second position is present.

  Here, when the sensor flag 19 does not block the optical path of the photo interrupter 21, as shown in FIG. 3, the photo interrupter 21 is detected to be OFF. Further, as shown in FIG. 4, when the sensor flag 19 blocks the optical path of the photo interrupter 21, the photo interrupter 21 is detected to be ON.

  The feature of this embodiment is that the sheet size of the conveyed sheet is accurately detected by the ON / OFF signal of the photo interrupter 21 during sheet conveyance in this configuration, and fed back to process control.

The details of the detection of the photo interrupter and the determination of the sheet width executed by the CPU 13 when a sheet having various size widths is passed, and the process control change at this time will be described in detail.

  Table 1 is a table showing the sheet size determined by the CPU 13 in the first embodiment.

(1. Large size paper)
A series of flow of sheet conveyance will be described with reference to FIGS. 3 to 7 and Table 1-1.

  FIG. 3 shows an initial state when the large size sheet S2 is set on the feeding table 3. FIG. This time is defined as a sheet position A (third timing). The detection of the photo interrupter 21 at this time is OFF.

  Next, in FIG. 4, in the case of a large size sheet, the sensor arm 51 is tilted in the direction of FIG. This time is defined as a sheet position B (first timing). At this time, when the sensor arm 51 is tilted, the sensor arm 53 also follows this and rotates in the direction of FIG. 5f to release the pressure on the sensor arm 54. As a result, the sensor arm 52 and the sensor flag 19 rotate in the direction h in the figure, and the sensor flag 19 closes the optical path of the photo interrupter 21. At this time, detection of the photo interrupter 21 is turned ON.

  A position where the large-size sheet S2 is conveyed to the front of the sensor arm 52 is defined as a sheet position C (first timing) (FIG. 5). At this time, the detection of the photo interrupter 21 is still ON.

  Subsequently, the sheet position D (second timing) is defined as the time when the large-size sheet S2 has reached the position where the sensor arm 52 is tilted (FIG. 6). At this time, the detection of the photo interrupter 21 is turned off by causing the large size sheet S2 to tilt the sensor arm 52 and passing the optical path of the photo interrupter 21 blocked by the sensor flag 19 again.

  When the sheet position E in FIG. 7 is reached, that is, when the rear end of the sheet passes the sensor arm 51, the sensor arm 51 rotates in the direction of FIG. Thus, pressure is applied in the direction of FIG. The detection of the photo interrupter 21 at this time remains OFF.

  Thereafter, even after the trailing edge of the sheet passes through the sensor arm 54, the sensor arms 51 and 52 are in the same state as in FIG. 7, that is, the original state in FIG. 3, and the detection of the photo interrupter 21 is turned off. .

  When the CPU 13 reads the timing and time of a series of ON / OFF signals from the photo interrupter 21 as described above, the CPU 13 can accurately determine the sheet size width during conveyance.

That is, with reference to the time when the sheet is at the feeding position (sheet position A), the sheet position B to
The size of the sheet being conveyed is determined based on Table 1 based on the time until E and the ON / OFF signal at that time. FIG. 19 shows the distance between the sheet positions B to E and the distance between the sensor arms 51 and 52 when the sheet position A is set to 0 mm as a reference.

  When the large-size sheet S2 is passed like this time, the detection of the photo interrupter 21 is OFF at the time of the feeding position (sheet position A), that is, at the start of feeding at 0 second. The detection of the photo interrupter 21 is ON at the time when the sheet surely passes through the area of the sensor arm 51 (sheet position B) and at the time when the conveying speed of the laser beam printer is about 0.3 seconds.

  Furthermore, the detection of the photo interrupter 21 remains ON even at the time of 70 mm before the sensor arm 52 (sheet position C) and at the time of about 0.6 seconds at the conveyance speed of the laser beam printer. The detection of the photo interrupter 21 is turned off at the point of 100 mm (sheet position D) that reliably passes through the area of the sensor arm 52 and at the point of about 0.9 seconds at the conveyance speed of the laser beam printer.

  By detecting the sheet positions A to D described above, the size of the sheet being conveyed can be determined. The sheet position E is the time when the trailing edge of the sheet has passed a discharge sensor (not shown) of the image forming apparatus main body, that is, the sheet has passed through the areas of the sensor arms 51 and 52 at this time. . Accordingly, the sheet position E is in the same detection state as the sheet position A before being conveyed.

  Based on Table 1-1, if a signal of A: OFF → B: ON → C: ON → D: OFF → E: OFF is received, the CPU 13 determines that the size is large.

(2. Small paper size)
Next, a series of flows when the small-size sheet S1 is passed will be described based on FIGS. 8 to 10 and Tables 1-2 to 4. FIG.

  FIG. 8 shows an initial state when the small-size sheet S <b> 1 is set at the center of the center of the feeding table 3. As shown in the figure, the sheet width regulation guide 2 is usually fed in accordance with the small size position. This is the sheet position A. The detection of the photo interrupter 21 at this time is OFF.

  Next, at the sheet position B, in the case of a small size sheet, since it does not contact the sensor arm 51 as shown in FIG. For this reason, the pressure to the sensor arm 54 remains applied, the sensor flag 19 does not move, and the optical path of the photo interrupter 21 is not blocked, so that the detection of the photo interrupter 21 remains OFF.

  Even after that, the small-size sheet S <b> 1 is not passed through the sensor arm 52 and finishes passing. Accordingly, the detection of the photo interrupter 21 in this paper passing is always OFF.

  Here, the CPU 13 reads the signal from the photo interrupter 21 in the same way as the above-described large-size sheet passing, that is, A: OFF → B: OFF → C: OFF → D: OFF → based on Table 1-2. E: When a signal of OFF is received, it is determined that the size is small.

  Further, as shown in FIG. 10, a case where the small-size sheet S1 is passed left-justified while the sheet width regulation guide 2 is in the large size position will be described.

  Normally, such a sheet passing is not normally performed because it is a central reference main body. However, due to an erroneous operation by the user, it is possible that a small size sheet is passed left-justified or right-justified as shown in FIG. However, by using the sheet width size detection method according to this embodiment, the sheet size can be automatically determined as a small size during conveyance.

  Even in the case of passing the paper left-justified as in this case, the small size sheet S1 passes through without contacting the sensor arm 51, as in FIG. For this reason, as in Table 1-2, the photo interrupter 21 always detects OFF, so the CPU 13 can determine that the size is small.

  Next, as shown in FIG. 11, a case where the small-size sheet S1 is passed right-justified while the sheet width regulation guide 2 is in the large size position will be described.

  At the sheet position B, the small size sheet S1 tilts the sensor arm 51 as shown in FIG. As a result, the sensor arm 53 also follows this and rotates in the direction of f in the same figure to release the pressure on the sensor arm 54. As a result, the sensor arm 52 and the sensor flag 19 rotate in the direction h in the figure, and the sensor flag 19 closes the optical path of the photo interrupter 21. At this time, detection of the photo interrupter 21 is turned ON.

  However, at the sheet position D, the small size sheet S1 does not contact the sensor arm 52 (FIG. 13). Accordingly, the detection of the photo interrupter 21 remains ON. The sheet is conveyed as it is, and at the sheet position E shown in FIG. 14, that is, when the trailing edge of the sheet passes the sensor arm 51, the sensor arm 51 rotates in the direction of FIG. The pressure is applied to 54 in the direction of FIG. Here, the sensor arm 54 finally returns to the initial state, and the detection of the photo interrupter 21 is turned off.

  Here, in the CPU 13, when the signal from the photo interrupter 21 receives a signal of A: OFF → B: ON → C: ON → D: ON → E: OFF, the small size is obtained based on Table 1-4. It is judged that.

  As described above, according to the configuration of the present embodiment, even when a small size sheet is passed by a single shift while the central reference sheet width restriction guide is set to a large size due to an erroneous operation by the user, the photo interrupter being conveyed The accurate sheet width size can always be determined from the 21 signals.

  Next, the process control change according to the sheet width size determined as described above will be described below.

  In this laser beam printer, when the user does not set the sheet size in advance, the temperature control temperature for the first print is set to a normal (default) 180 ° C., and the process speed is controlled to 18 ppm.

  If the CPU 13 recognizes a large size sheet when the first sheet is passed, the second and subsequent sheets are set to the “large size mode”, and the temperature control temperature of the fixing device is set to the normal 180 ° C. as it is. Control is performed so that the speed becomes 18 ppm.

If the CPU 13 recognizes that the sheet is a small size sheet, the second and subsequent sheets are set to the “small size mode”, the temperature adjustment temperature of the fixing device is changed to 165 ° C., and the process speed of the main body is set to 10 ppm. Control to widen. This is because the non-sheet passing portion area that is excessively warmed (heated up) while the small size sheet passes through the fixing device 15 is suppressed by the space between the sheets.

  Here, using the laser beam printer having the above-described configuration of the present embodiment and the conventional laser beam printer having a sensor arm only on one side with a central reference, a small-size sheet S1 is placed on one side as shown in FIG. Table 2 shows the results of a comparative study of the pressure roller temperature when the paper is passed on the edge basis and the output image.

  When the small-size sheet S1 is continuously passed on the one-side end portion basis (FIG. 22), in the case of the conventional configuration, it is determined that the sheet being conveyed is a large-size sheet by passing the sheet width sensor. End up. As a result, the second and subsequent sheets are also controlled in the normal (default) “large size mode” so that the temperature adjustment temperature is 180 ° C. and the process speed is 18 ppm. As a result, the temperature rise in the non-sheet passing portion region of the fixing device 15 increased during continuous sheet passing, and exceeded 230 ° C. for the 20th consecutive sheet. Further, after passing a large-size sheet after that, an offset (high temperature offset) due to a temperature rise occurred in the non-sheet passing portion region.

  On the other hand, in the case of the configuration of the present embodiment, the CPU 13 determines that the first sheet is a small size sheet, so that the second and subsequent sheets are set to the “small size mode” and the temperature adjustment temperature is changed to 165 ° C. The space between the papers was widened so that the process speed of the main body was 10 ppm. As a result, even when continuous 200 sheets were passed, the temperature did not reach 220 ° C. or higher, and the result was stable at around 217 ° C. Further, even when a large-size sheet was passed through thereafter, no high temperature offset occurred.

  In this way, by performing optimal control along the sheet width size, for example, a rare sheet such that the small-size sheet S1 is passed on the basis of the one-side end portion while the sheet width regulation guide is positioned at the large size width. Even in such a case, the CPU 13 automatically determines the small-size sheet S1 while the first sheet is being passed, so that it is optimal for the temperature control temperature of the second and subsequent fixing devices and the process speed of the main body. Control can be performed reliably. As a result, image problems such as “non-sheet passing portion temperature rise phenomenon” and “high temperature offset”, which have been a problem in the past, as well as damage to the fixing device and failure of the main body can be prevented.

  As described above, according to the present embodiment, the first sheet contactor (sensor arm 51) that rotates by contact with the conveyed sheet and the downstream side in the conveying direction from the first sheet contactor. In the sheet size detection apparatus having a second sheet contactor (sensor arm 52) positioned and an optical sensor detection means (photointerrupter 21) for detecting the operation of the second sheet contactor, the second sheet contact The child can always detect an accurate sheet size regardless of the user's paper feeding method by taking a means for switching to the operation state after the first sheet contactor is rotated.

  Therefore, for example, even when the user passes the paper with a different sheet size setting, the accurate sheet size is automatically set without passing the paper while the image forming apparatus main body determines a different sheet size as in the past. Can be judged.

Further, by controlling the optimum fixing temperature adjustment temperature and process speed based on the detected sheet size, it is possible to always provide stable sheet conveyance and images.

  In addition, this causes image problems such as the “non-sheet passing portion temperature rise phenomenon” and “high temperature offset” of the fixing device, which has been a problem in the past, as well as breakage of the fixing device due to excessive non-sheet passing portion temperature rise. Failure of the main body can be prevented, and the life of the main body can be extended.

  Further, since only one photo interrupter serving as a photosensor detection unit is required and the configuration of the sensor arm is simple, the cost can be reduced and the main body can be downsized.

  In this embodiment, the control of the fixing temperature adjustment temperature and the throughput is changed after determining the width size of the conveyed sheet. However, it is changed in general process control relating to image formation such as transfer and development control. It shall be possible.

  In this embodiment, the position interval in the transport direction of the sensor arms 51 and 52 is set to 60 mm. However, this has an interval that allows the CPU 13 to read accurately including the error of reading the ON / OFF timing of the photo interrupter 21, and This is in order to deal with a sheet having a short length, and it is desirable that the sheet is arranged at 20 mm to 100 mm (second predetermined interval).

  As described above, by using the configuration as in the first embodiment, it is possible to accurately determine the sheet size by the CPU 13 during conveyance and perform optimum process control according to the sheet size.

  However, in the configuration of the first embodiment, although the width size of the conveyed sheet can be accurately determined, it is not possible to determine the details of where the sheet is passed, and there is room for further improvement. Also, when passing a small size sheet, if the user does not set a small size in advance with a host computer (not shown), the first sheet is controlled to the same temperature control temperature as in the normal “large size mode”. There is concern.

  Therefore, in this embodiment, as shown in FIGS. 15 and 16, the interlock wire 9 that links the sheet width regulation guide 2 and the sensor arm 51 is provided to determine the width size of the conveyed sheet. In addition, the position (the area where the sheet is conveyed in the sheet width direction of the sheet conveyance path) is accurately determined and optimal process control is performed according to the position. Is. Here, the interlocking wire 9, the sensor arm 53, the sensor arm 54, and the spring 62 constitute the second interlocking means according to the present invention.

  Furthermore, only by setting the sheet width regulation guide 2, a large size sheet larger than the reference width and a small size sheet less than the reference width are discriminated, and process control corresponding to the sheet size is performed from the first sheet passing, It also features added value, such as increasing speed. In addition, the distance between the sensor arms 51 and 52 and the intervals such as the sheet positions A to E are the same as those in the first embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be given. Omitted.

  Table 3 shows the sheet size and position determined by the CPU 13 in the second embodiment.

  Specifically, when the sheet width size is designated as a large size in the initial state, the initial state is the same as that of the first embodiment as shown in FIG. Accordingly, the detection of the photo interrupter 21 at this time is similarly OFF. When the large-size sheet S2 is passed in this state, the detection timing of the photo interrupter 21 is the same as that in the first embodiment, and the CPU 13 determines that the size is large (Table 3-1).

  However, in this configuration, when the sheet width regulating guide 2 is installed in a small size as shown in FIG. 16, the interlocking wire 9 rotates the sensor arm 51 in the direction i in FIG. Thus, the photo interrupter 21 is detected to be ON. That is, the photo interrupter 21 is detected to be ON in the initial sheet passing state (sheet position A).

  When the small-size sheet S1 is passed in this state, the small-size sheet S1 does not pass through the sensor arm 52 even during the passing as shown in FIG. 17, so that the photo interrupter 21 always detects ON. Here, in the CPU 13, when the signal from the photo interrupter 21 receives a signal of A: ON → B: ON → C: ON → D: ON → E: ON, the transport is performed based on Table 3-2. It is possible to determine that the width size of the sheet being conveyed is a small size and being conveyed on the basis of the center.

  Further, when the small-size sheet S1 is passed right-justified or left-justified while the sheet width regulation guide 2 is kept at the large size position, the same ON / OFF signal as in the first embodiment is received. However, it should be noted here that, as shown in Tables 3-2 to 4-4, even when the same small size sheet S1 is passed, the ON / OFF position differs depending on the center reference center, left justification, and right justification. The point is that it is an OFF signal.

  As described above, when the signal from the photo interrupter 21 receives a signal of A: ON → B: ON → C: ON → D: ON → E: ON, the width size of the conveyed sheet Can be determined to be transported in a small size and with a central reference. Further, when the signal from the photo interrupter 21 receives a signal of A: OFF → B: OFF → C: OFF → D: OFF → E: OFF, the width of the conveyed sheet is small. In addition, it can be determined that the sheet is conveyed left-justified. Further, when the signal from the photo interrupter 21 receives a signal of A: OFF → B: ON → C: ON → D: ON → E: OFF, the width size of the conveyed sheet is small, In addition, it can be determined that the sheet is conveyed right-justified.

  As described above, according to the configuration of the present embodiment, even when a small size sheet is passed by a single shift while the central reference sheet width restriction guide is set to a large size due to an erroneous operation by the user, the photo interrupter being conveyed From the signal 21, it is possible not only to always determine an accurate sheet width size, but also to accurately grasp the position of the sheet being conveyed.

Next, the process control change according to the sheet width size determined as described above will be described below. The laser beam printer in this embodiment has the same function as that of the first embodiment described above.

  In this laser beam printer, when the user does not set the sheet size in advance, the temperature control temperature for the first print is set to a normal (default) 180 ° C., and the process speed is controlled to 18 ppm.

  If the CPU 13 recognizes that the first sheet is a large size sheet, the second and subsequent sheets are also set to the “large size mode”, and the temperature control temperature of the fixing device is controlled to 180 ° C., and the process speed is increased. Control is carried out to 18 ppm.

  Further, when the CPU 13 recognizes that the conveyed sheet size is a small size and recognizes that the sheet is passed left-justified (FIG. 10), the CPU 13 switches to the “small size mode” and the second and subsequent fixing devices. The temperature adjustment temperature is changed to 165 ° C., and control is performed to widen the paper so that the process speed of the main body becomes 10 ppm. Further, when the CPU 13 recognizes that the conveyed sheet size is a small size and recognizes that the sheet is passed right-justified (FIG. 11), the CPU 13 switches to the “small size mode” and the second and subsequent fixing devices. The temperature control temperature is set to 165 ° C., and control is performed to widen the paper so that the process speed of the main body becomes 10 ppm.

  Further, when the user places the sheet width regulation guide 2 at the small size position and passes the small size sheet S1 (FIG. 16), the photo interrupter 21 is detected at the time of the initial sheet passing state (sheet position A). At this time, the CPU 13 can determine that the sheet size is a small size and can determine that the sheet is conveyed in the center of the center reference, so that the process control can be performed as the “small size mode” from the first sheet passing. I can do it.

  At this time, the CPU 13 can set the temperature adjustment temperature of the fixing device to 165 ° C. from the first sheet, and can control between the sheets so that the process speed becomes 12 ppm. Here, the process speed could be increased to 12 ppm instead of 10 ppm for single-sided paper. Even if the same small size sheet was passed at the center, the non-sheet-passing part at both ends was better than when the single-sided paper was passed. This is because the temperature rise in the region is small, so that the sheet conveyance can be performed with a slight gap between the sheets. As described above, it is possible to increase the process speed of the small-sized sheet by accurately determining the position where the sheet is conveyed.

  Further, for example, by changing the shape of the fixing device, further specs can be improved.

  For example, by setting the heating element pattern of the heater 15b as shown in FIG. 20, it is possible to add the following added value. Details will be described below.

  The heater 15b as the heat generating means shown in FIG. 20 is provided so as to be able to generate heat for each predetermined region in the sheet width direction, so that three independent heating element patterns (AA ′, BB ′, C−) are provided. C ′) is feasible. For example, A-A ′ has a pattern so that heat is generated in the a portion, and the b and c portions have a smaller resistance and a smaller amount of heat generation than the a portion. B-B 'has a pattern so that heat is generated in the portion b, and the a and c portions have a smaller resistance and a smaller amount of heat generation than the portion b. Further, C-C 'has a pattern so that heat is generated in the portion c, and the a and b portions have a smaller resistance and a smaller amount of heat generation than the portion c.

  And a temperature detection means (temperature detection element, thermistor) (not shown) is disposed at the center of each of the a, b, and c portions, and is controlled independently. Each main heat generating portion is in the nip range.

  In the heater 15b of this example, a silver-palladium resistance material is arranged as a pattern on an alumina substrate, and silver is installed at each end as an electrode at portions A, B, C, A ′, B ′, and C ′. Finally, a glass protective layer (not shown) is provided. Also, b = 180 mm (for EXE size vertical feed) and a, c = 20 mm (for A4 size vertical feed or more). Specific control when the above-described heating element pattern is inserted will be described below.

  If the user has not set the sheet size in advance, the temperature control temperature for the first print is similarly set to the normal (default) 180 ° C., and the process speed is controlled to 18 ppm.

  If the CPU 13 recognizes a large size sheet when the first sheet is passed, the second and subsequent sheets are also set to the “large size mode”, and the temperature control temperature of the fixing device is controlled to 180 ° C., and the process speed is set to 18 ppm. Control is performed as follows. At this time, the heat generation patterns A-A ′, B-B ′, and C-C ′ are all energized.

  Further, when the CPU 13 recognizes that the conveyed sheet size is a small size and recognizes that the sheet is passed left-justified (FIG. 20a side), it switches to the “small size mode” and the second and subsequent fixing devices. The temperature control temperature is changed to 165 ° C., and control is performed to widen the paper so that the process speed of the main body becomes 12 ppm. At this time, only the heat generation patterns A-A 'and B-B' are energized.

  When the CPU 13 recognizes the conveyed sheet size as a small size and recognizes that the sheet is passed right-justified (FIG. 20c side), it switches to the “small size mode” and the second and subsequent fixing devices. The temperature control temperature is set to 165 ° C., and control is performed to widen the paper so that the process speed of the main body becomes 12 ppm. At this time, only the heat generation patterns B-B 'and C-C' are energized.

  With the above-described configuration, the process speed at the time of small-size sheet feeding can be set to 12 ppm, and the specification can be increased.

  Further, when the user installs the sheet width restriction guide 2 at the small size position and passes the small size sheet S1, the detection of the photo interrupter 21 is turned ON at the time of the initial sheet passing state (sheet position A), At this point, the CPU 13 can determine that the sheet size is small, and can determine that the sheet is conveyed at the center of the center reference, so that the same process control as described above can be performed as the “small size mode” from the first sheet passing. . Further, at this time, only the heat generation pattern B-B ′ is energized to further reduce the temperature of the non-sheet passing area on both sides.

  Here, using the laser beam printer having the configuration of the present embodiment described above and the laser beam printer having the configuration of Embodiment 1, the pressure roller temperature when the small-size sheet S1 is passed on the basis of one side end portion. Table 4 shows the results of comparative studies on the output images.

  In the case of Example 1 as well, the second and subsequent sheets are set to the “small size mode”, the temperature adjustment temperature is set to 165 ° C., and the gap between the sheets is widened so that the process speed is 10 ppm. The temperature was suppressed to 220 ° C. or lower, and high temperature offset could be prevented. However, in this embodiment, not only the process speed was increased from 10 ppm to 12 ppm, but also the non-sheet passing portion temperature was further increased by 10 ° C. by efficiently applying heat to the sheet according to the sheet passing area. I was able to lower it. This not only increases the margin for high temperature offset, but also extends the life of the main body.

  In this way, by performing optimal control along the sheet width size, for example, a rare sheet such that the small-size sheet S1 is passed on the basis of the one-side end portion while the sheet width regulation guide is positioned at the large size width. Even in such a case, the CPU 13 can surely grasp the sheet width size and the position where the sheet is conveyed, and can control the optimum temperature control temperature, energization method, or optimum process speed for the fixing device. As a result, it is possible to prevent image problems such as “non-sheet-passing portion temperature rise phenomenon” and “high temperature offset”, which have been a problem in the past, as well as damage to the fixing device and failure of the main body with a margin. .

  As described above, according to the present embodiment, the sheet width regulating member (sheet width regulating guide 2) and the first sheet contact (sensor arm 51) are further coupled by the coupling means from the configuration of the first embodiment. Thus, it is possible not only to always determine the correct sheet size regardless of the user's paper passing method, but also to accurately determine the position of the sheet being conveyed.

  Therefore, even when the user performs sheet passing at a different sheet size setting and a non-standard position, the accurate sheet size and position can be automatically determined.

  Further, by controlling the optimum fixing temperature control temperature and process speed based on the determined sheet size and the transported position, it is possible to provide more stable sheet transport and images.

  In addition, this causes image problems such as the “non-sheet passing portion temperature rise phenomenon” and “high temperature offset” of the fixing device, which has been a problem in the past, as well as breakage of the fixing device due to excessive non-sheet passing portion temperature rise. A failure of the main body can be prevented, and the life of the main body can be further extended.

  Furthermore, by performing optimal process control according to the sheet passing, it is possible to increase specifications such as increasing the process speed when passing a small-size sheet.

  In addition, when the user previously installs the sheet width restriction guide at a small size position, it can be automatically recognized as a small size in the initial state of sheet passing. As a result, the optimum control can be performed as the “small size mode” from the first sheet passing, which is more effective for image problems such as “non-sheet passing portion temperature rise phenomenon” and “high temperature offset”. Become.

  Further, the conventional sheet contactor, the optical sensor means, and the sheet width regulation guide can be used for detection with a simple configuration and accurately, and the size can be reduced without taking up space at a low cost.

  In this embodiment, after determining the width size of the sheet being conveyed, and accurately recognizing the position being conveyed, control of the fixing temperature control temperature and throughput, and further change the energization to the heating element pattern. However, it can be changed in general process control related to image formation such as transfer and development control.

FIG. 3 is a schematic configuration diagram of a sheet width detection unit in Embodiment 1. 1 is a schematic configuration diagram of an image forming apparatus in Embodiment 1. FIG. In Example 1, it is the schematic which shows the state of the sheet | seat position A when passing a large sized sheet. In Example 1, it is the schematic which shows the state of the sheet | seat position B when passing a large sized sheet. In Example 1, it is the schematic which shows the state of the sheet | seat position C when passing a large sized sheet. In Example 1, it is the schematic which shows the state of the sheet | seat position D when passing a large size sheet. In Example 1, it is the schematic which shows the state of the sheet | seat position E when passing a large sized sheet. In Example 1, it is the schematic which shows the state of the sheet | seat position A when passing a small size sheet | seat in the center of a center reference | standard. In Example 1, it is the schematic which shows the state of the sheet | seat position B when a small size sheet passes in the center of a center reference | standard. In Example 1, it is the schematic which shows the state of the sheet | seat position A when passing a small size sheet | seat by left alignment. In Example 1, it is the schematic which shows the state of the sheet | seat position A when passing a small size sheet | seat right-justified. In Example 1, it is the schematic which shows the state of the sheet | seat position B when passing a small size sheet | seat by left alignment. In Example 1, it is the schematic which shows the state of the sheet | seat position D when a small size sheet is passed by left alignment. In Example 1, it is the schematic which shows the state of the sheet | seat position E when passing a small size sheet | seat by left alignment. FIG. 6 is a schematic configuration diagram of a sheet width detection unit in Embodiment 2. In Example 2, it is the schematic which shows the state of the sheet | seat position A when passing a small size sheet | seat in the center of a center reference | standard. In Example 2, it is the schematic which shows the state of the sheet | seat position D when a small size sheet passes in the center of a center reference | standard. 6 is a schematic diagram of a sheet conveyance path including a sheet width size detection unit 20 in Embodiments 1 and 2. FIG. 6 is a schematic diagram illustrating a distance of a sheet conveying path including a sheet width size detecting unit 20 in Examples 1 and 2. FIG. FIG. 6 is a schematic diagram showing a heat generation pattern of a heater in Example 2. It is the schematic which shows the prior art example which installed the sheet | seat width regulation guide in the position of small size. It is the schematic which shows the prior art example which installed the sheet | seat width regulation guide in the position of a large size, and performed one-sided paper passing. It is the schematic which shows the prior art example which detects the size type of a sheet | seat.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Feed roller 2 Sheet width regulation guide 3 Feed stand 4 Conveyance roller 5 Sensor arm 6 Pressure spring 7 Photosensitive drum 8 Transfer roller 9 Linking wire 10 Developer 11 Charge roller 12 Laser scanner 13 CPU
DESCRIPTION OF SYMBOLS 14 Cleaning device 15a Heater frame 15b Heater 15c Heat resistant film 16 Pressure roller 17 Discharge roller 18 Discharge tray 19 Sensor flag 20 Sheet width detection means 21 Photo interrupter 22 Stopper

Claims (23)

A first sheet contactor that is movably provided in a sheet conveyance path for conveying a sheet and moves to a first position while the conveyed sheet is in contact;
A first predetermined interval is set in the sheet width direction substantially perpendicular to the sheet conveying direction with respect to the first sheet contact, and a second predetermined interval is set downstream of the first sheet contact in the sheet conveying direction. While the first sheet contactor assumes the first position, the sheet conveyed through the sheet conveyance path is moved to a second position where the sheet can be contacted, and the sheet contacts A second sheet contact that deviates from the second position while
Detecting means for detecting whether or not the second sheet contact is in the second position;
With
A sheet size detection apparatus that detects a size of a sheet to be conveyed based on a detection result obtained by detecting the conveyed sheet a plurality of times at a predetermined timing by the detection unit.   The sheet size detection apparatus according to claim 1, further comprising a first interlocking unit that moves the second sheet contactor in conjunction with the movement of the first sheet contactor.   The center part in the sheet width direction of the sheet transport path and the center part in the sheet width direction of the sheet transported through the sheet transport path are provided so as to substantially coincide with each other. The sheet size detection apparatus described.   The sheet size according to any one of claims 1 to 3, wherein the first sheet contactor and the second sheet contactor are provided so that the second predetermined interval is 20 mm to 100 mm. Detection device.   The first sheet contact and the second sheet contact are set such that the first predetermined interval is set to 160 mm to 210 mm, and the center of the first predetermined interval is the center of the sheet conveying path in the sheet width direction. The sheet size detection device according to claim 3, wherein the sheet size detection device is provided so as to substantially coincide with the portion. A sheet placement section for placing a sheet conveyed along the sheet conveyance path;
Depending on the size of the sheet placed on the sheet placement section, the sheet width direction of the sheet transport path moves in the sheet width direction as a reference to regulate the sheet width direction of the sheet. A sheet width regulating member;
Second interlocking means for moving the second sheet contactor in conjunction with the movement of the sheet width regulating member;
The sheet size detection device according to claim 1, further comprising:   The said 2nd interlocking | linkage means moves the said 2nd sheet | seat contactor to the said 2nd position, when the said sheet | seat width control member is set to a reference width or less. Sheet size detection device.   The predetermined timing at which detection is performed a plurality of times by the detection means is a first timing at which a leading edge of a conveyed sheet is positioned between the first sheet contactor and the second sheet contactor, The sheet size detection device according to claim 1, further comprising a second timing beyond the second sheet contact. Control means for controlling the detection means such that detection is performed a plurality of times at a predetermined timing for the conveyed sheet;
Determination means for determining the size of the conveyed sheet based on the detection result of the detection means;
The sheet size detection device according to claim 1, comprising: When both the first sheet contact and the second sheet contact are in contact with the sheet,
The detecting means detects that the second sheet contactor is at the second position at the first timing, and detects that the second sheet contactor is not at the second position at the second timing.
The sheet size detection apparatus according to claim 9, wherein the determination unit determines that the sheet is a large size. When both the first sheet contact and the second sheet contact do not contact the sheet,
The detecting means detects that the second sheet contact is not in the second position at the first and second timings,
The sheet size detection apparatus according to claim 9 or 10, wherein the determination unit determines that the sheet is a small size. When the first sheet contact is in contact with the sheet and the second sheet contact is not in contact with the sheet,
The detecting means detects that the second sheet contactor is in the second position at the first and second timings,
The sheet size detection apparatus according to claim 9, wherein the determination unit determines that the sheet is a small size. The control means further controls the detection means to perform detection at a third timing before conveyance of the sheet or at a third timing where the leading edge of the conveyed sheet is upstream of the first sheet contact,
The determination unit determines, based on a detection result of the detection unit, a size of a sheet to be conveyed and a region in which the sheet is conveyed in a sheet width direction of the sheet conveyance path. The sheet size detection apparatus according to any one of claims 9 to 12. When the sheet width regulating member is set to be equal to or less than the reference width,
The detecting means detects that the second sheet contactor is in the second position at the third timing,
The sheet size detection apparatus according to claim 13, wherein the determination unit determines that the sheet is a small size and is conveyed in a substantially central portion of the sheet conveyance path in a sheet width direction. When the sheet width regulating member is set larger than the reference width, and when both the first sheet contactor and the second sheet contactor are in contact with the sheet,
The detecting means detects that the second sheet contactor is not in the second position at the third timing, and the second sheet contactor is in the second position at the first timing. By detecting and not being in the second position at the second timing,
The sheet size detection apparatus according to claim 13 or 14, wherein the determination unit determines that the sheet is a large size. When the sheet width regulating member is set to be larger than the reference width, and when the first sheet contact is in contact with the sheet and the second sheet contact is not in contact with the sheet. Is
The detection means detects that the second sheet contactor is not in the second position at the third timing, and the second sheet contactor detects the second sheet contact at the first and second timings. By detecting the position,
The determination unit determines that the sheet is small in size and is conveyed in an area where the first sheet contact is provided in a sheet width direction of the sheet conveyance path. Item 16. The sheet size detection device according to any one of Items 13 to 15. When the sheet width regulating member is set larger than the reference width, and the first sheet contactor does not contact the sheet,
The detecting means detects that the second sheet contactor is not in the second position at the third, first and second timings,
The determination unit determines that the sheet is a small size and is transported in an area where the second sheet contact is provided in a sheet width direction of the sheet transport path. Item 17. The sheet size detection device according to any one of Items 13 to 16. The sheet size detection device according to any one of claims 1 to 17,
Transfer means for transferring a toner image formed on the image carrier onto a sheet;
And forming an image on a sheet. Sheet conveying means for conveying the sheet to the transfer means;
A conveyance control means for controlling the sheet conveyance means according to the sheet size detected by the sheet size detection device;
The image forming apparatus according to claim 18, further comprising:   20. The image according to claim 18, further comprising an image forming condition control unit that controls a condition of an image forming operation performed by the transfer unit in accordance with a sheet size detected by the sheet size detecting device. Forming equipment. A fixing means for fixing an unfixed toner image on the sheet to the sheet;
21. The image forming apparatus according to claim 18, further comprising an image forming condition control unit that controls a condition of an image forming operation performed by the fixing unit in accordance with a sheet size detected by the sheet size detecting device. The image forming apparatus described.   The image forming condition control unit corresponds to a condition of an image forming operation performed by the fixing unit in a small size when the sheet width regulating member is set to the reference width or less before the sheet is conveyed. The image forming apparatus according to claim 21, wherein the image forming apparatus is controlled according to the adjusted conditions. The fixing means is
Heat generating means capable of generating heat for each predetermined region in the sheet width direction;
Temperature detecting means for detecting the temperature of each of the predetermined areas;
Heat generation control means for controlling the heat generation means based on the detection result of the temperature detection means;
The image forming apparatus according to claim 21, further comprising: