JPH07129027A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device capable of surely detecting the size of a paper sheet even when it is fed from a place other than a paper housing means and preventing an image from being made defective because of that the fixing temperature of a paper passing region is not raised and a temperature in a paper nonpassing region from being made high, even when a small- sized paper is consecutively printed. CONSTITUTION:A lever 52 provided in the vicinity of the center of a carrying path is disposed so that the upper part of the lever 52 crosses a photosensor 51 when the paper is absent and does not cross the photosensor 51 when the paper is present, and a lever 53 provided in the vicinity of the end part of the carrying path is disposed so that the upper part of the lever 53 crosses the photosensor 51 only when the leading edge of the paper reaches the position of the lever 53. Then, the length and width of the paper in its carrying direction are detected by timing when the levers 52 and 53 cross the photosensor 51 or the presence of a crossing action and in the small-sized paper, the paper nonpassing region of a fixing roller is cooled by a fan and a fixing roller passing position for the paper is changed in accordance with the surface temp. of the fixing roller.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium size detecting means and a heat fixing means of an image forming apparatus using an electrophotographic process such as a copying machine and a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, a recording medium size detecting means provided in an apparatus of this type is provided in a recording medium accommodating means or the like independently of a conveying state detecting means for detecting the position of the recording medium being conveyed. It was being done.

Further, in the heat fixing means, controls such as cooling the heat roller and changing the heat roller passage position of the recording medium according to the size of the recording medium have not been performed.

[0004]

However, in the above-mentioned conventional example, since the recording medium size detecting means and the transport state detecting means are provided independently of each other, the cost is high, and the storage is performed as in the case of manual paper feeding. In some cases, the size of the recording medium cannot be detected when the recording medium is supplied from other means.

Further, in the heat fixing means, controls such as cooling the heat roller and changing the heat roller passing position of the recording medium according to the size of the recording medium are not performed, so that the recording medium of a small size is continuously connected. When the heat roller is passed through the heat roller, the surface temperature of the heat roller in the passing area does not rise, resulting in poor image fixing and high temperature in the non-passing area.

The present invention solves the above-mentioned problems and can reliably detect the size of a recording medium even when the recording medium is supplied from a means other than the storage means for the recording medium, and the recording medium of a small size can be continuously connected. It is an object of the present invention to provide an image forming apparatus that does not cause a fixing failure and a temperature rise in a non-passage area even when supplied as a sheet.

[0007]

According to the first invention of the present application,
In the image forming apparatus having the recording medium conveying means and the conveying state detecting means for detecting the position of the recording medium by interfering with the recording medium being conveyed, the length and width of the recording medium in the conveying direction are defined as above. This is achieved by detecting by the conveyance state detecting means.

Further, according to the second invention of the present application, the above object is to provide a heat fixing device using a heat roller for fixing the developer transferred onto the recording medium by applying heat and pressure, and a predetermined portion of the heat roller. This is achieved by cooling the heat roller according to the size of the recording medium, which has a cooling unit for cooling the recording medium and a size detecting unit for detecting the width of the recording medium.

Further, according to the third invention of the present application, a plurality of heat roller surface temperature detecting means provided in the heat roller axial direction, and moving means for moving the recording medium conveyed to the fixing device in the heat roller axial direction, This is achieved by having a detecting means for detecting the length of the recording medium in the heat roller axial direction, and changing the heat roller passing position of the recording medium according to the length of the recording medium in the heat roller axial direction and the surface temperature of the heat roller.

[0010]

According to the first aspect of the present invention, the length and width of the recording medium in the conveying direction are detected based on the detection timing of the conveying state detecting means, the presence or absence of interference with the recording medium, and the like. Even when supplied from other means, the detection operation is surely performed.

Further, according to the second aspect of the present invention, the heat roller is cooled according to the size of the recording medium, so that the temperature rise in the non-passage area when a small size recording medium is continuously supplied is suppressed.

Further, according to the third invention of the present application, the heat roller passing position of the recording medium is changed according to the length of the recording medium in the axial direction of the heat roller and the surface temperature of the heat roller, so that the recording medium of a small size is continuously supplied. In this case, the non-passage area is not fixed in one place, and the temperature rise in the non-passage area is suppressed.
Further, since the passage area is not fixed, the fixing failure due to the decrease of the heat roller surface temperature is prevented.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1> First, Embodiment 1 of the present invention will be described with reference to FIGS. 1 is a diagram showing a laser beam printer according to a first embodiment of the present invention. In the figure, 1 is a laser beam printer main body, 2 is a photosensitive drum, 3
In the optical unit, the laser light is modulated by the video data transmitted via the video interface 18, and the photosensitive drum is scanned by the rotating polygon mirror. Reference numeral 4 is a folding mirror for the laser beam, and 5 is a charger, which uniformly charges the photosensitive drum 2. A developing device 6 develops the electrostatic latent image on the photosensitive drum 2 into a toner image. A transfer device 7 transfers the toner image on the photosensitive drum 2 onto a sheet. A cleaner 8 collects the toner remaining on the photosensitive drum 2 after the transfer. A paper feed roller 10 stops and conveys the paper stored in the cassette 9. A paper feed sensor 12 has a function of detecting the size of the width of the paper, and detects the presence or absence of the paper conveyed by the registration rollers 11 and also detects whether the conveyed paper is larger or smaller than a certain width. A fixing device 13 includes a heat roller 13a, a pressure roller 13b, a halogen heater 13c provided inside the heat roller 13a,
It is composed of a thermistor 13d for detecting the surface temperature of the heat roller 13a, and fixes the toner image transferred onto the paper by applying heat. A paper discharge sensor 14 detects the presence or absence of paper discharged from the fixing device 13. 15
Is a paper ejection tray.

In the apparatus of this embodiment as described above, when the print data for one page is prepared in the controller section 16,
By turning on the charging device 5 and the transfer device 7 and rotating the photosensitive drum 2, the surface potential of the photosensitive drum 2 is initialized.
The pre-rotation operation is started to start the rotation of the scanner motor in the optical unit. When the pre-rotation is completed, the photosensitive drum 2 is initialized, and the rotation of the scanner motor is stabilized, the paper feed roller 10 and the registration roller 11 are rotated to feed the paper loaded in the cassette 9, Paper feed sensor 1
At the timing when the leading edge of the paper is detected by 2, the paper conveyance by the registration rollers 11 is stopped, and a synchronization signal request signal (VSREQ signal) in the width scanning direction is sent to the controller unit 16 via the video interface 18. 16 to the sync signal in the width scanning direction (VSYNC
Signal) is sent. Controller unit 16
When receiving the VSREQ signal, the engine control unit 1 sends the VSYNC signal through the video interface 18.
7 and at the same time, in synchronization with a synchronization signal (BD signal) in the main scanning direction sent from the engine control unit 17 via the video interface 18, one page of video data (image data) is line by line. Send out. The BD signal is outside the photosensitive drum 2 and the photosensitive drum 2
It is configured to detect and obtain the laser light by an optical sensor arranged at an equal distance. Engine control unit 1
When receiving the VSYNC signal, the registration roller 11 restarts the sheet conveyance, the developing unit 6 is turned on, and the optical unit 3 receives the VSYNC signal.
The laser light is modulated by the video data transmitted via the video interface 18 and the photosensitive drum 2 is scanned by the polygon mirror to form an electrostatic latent image. The electrostatic latent image is transformed into a toner image by the developing device, the toner image is transferred to the sheet conveyed by the transfer device 7 in synchronization, the toner image is fixed on the sheet by the fixing device 13, and the paper output tray 15
Is discharged to.

Next, the structure of the paper feed sensor 12 having a function of detecting the width of the paper will be described with reference to FIG. In the figure, 51 is a photo sensor, and 52 is a lever for detecting the presence / absence of paper near the center of the conveyance path. The upper part of the lever crosses the photo sensor 51 when there is no paper, and does not cross when there is paper. Reference numeral 53 is a lever for detecting the presence or absence of a sheet near the end of the transport path, and is arranged so that the upper portion of the lever crosses the photo sensor 51 only when the leading edge of the sheet reaches the lever 53 position.

Next, the operation of the paper feed sensor 12 will be described in detail. As shown in FIG. 3, when the paper is not pushing the levers of the paper feed sensor, the lever 52 is across the photo sensor 51, and the lever 53 is the photo sensor 51.
It is in a position outside of. However, when the paper reaches the position shown in FIG. 4, the lever 52 is pushed and the lever that crosses the photo sensor 51 is in a state where nothing exists. Then, when the width of the paper is wide as the paper further advances, as shown in FIG. 5, the lever 53 located near the end of the transport path is started to be pushed. In this state, the lever 53 crosses the photo sensor 51. When the paper further advances, the state shown in FIG.
There is no lever crossing 1. Therefore, in the case of a small sheet that does not cover the position of the lever 53, even if the sheet arrives at the same position as in FIG. 5, the lever 53 is not pushed as in FIG. 7 and the photosensor is not crossed by the lever 53. Absent. By performing such an operation, a double pulse is obtained when a wide paper is passed as shown in FIG. 8, and a single pulse is obtained when a narrow paper is passed.

As described above, cost can be reduced by detecting the paper size by the paper feed sensor 12, and it is possible to detect whether the paper size is small even if the paper size is not known before paper feed. Therefore, when printing small size paper continuously, the paper interval should be longer than usual, so that the heat roller surface temperature in the paper passing area does not rise and image fixing failure or high temperature in the non-paper passing area occurs. It becomes possible to prevent such problems as

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIGS. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

FIG. 9 is a diagram showing the configuration of this embodiment. Reference numeral 100 in the figure denotes an electric fan, which is arranged so as to be blown to a non-sheet passing area (hatched portion A in the figure) on the heat roller 13a during printing on small size paper. Heat roller 13a
After the heat is removed, the air is sent by the housing 101 toward the paper passing area of the heat roller 13a.

FIG. 10 is a diagram showing the control unit of the present embodiment, in which 102 is a one-chip microcomputer (MPU) which is the main control unit of the present control, and a timer 1 is provided inside it.
03, ROM104, RAM105, arithmetic unit (AL
U) 106, an input / output port 107, etc. are provided.
109 is a driver transistor for driving the electric fan 100, 110 is a base resistance of the driver transistor 109, and 108 is a diode for absorbing the counter electromotive force of the electric fan 100.

In such a control unit, when the output port of the MPU becomes High output and the transistor 109 is turned on, a current flows through the electric fan 100 to rotate and the output port becomes Low output, and when the transistor 109 is turned off, the electric fan 100 becomes Stop. A paper size sensor 111 detects whether or not the paper is a small size paper.

FIG. 11 is a flowchart of this control.
First, it is determined whether or not printing is in progress (S1). If printing is not in progress, the electric fan 100 is turned off (S4). If printing is in progress, it is determined whether the printing paper is a small size paper (S2). If it is not small size paper, the electric fan 100 is turned off (S4), and if it is small size paper, the electric fan 100 is turned on (S3).

As described above, at the time of printing on small size paper, the non-paper passing area on the heat roller 13a is cooled by the electric fan 100 to heat the heat roller 1 in the paper passing area.
3a Prevents problems such as poor image fixing and high temperature in the non-paper passing area that occur when the surface temperature does not rise, and is expected by blowing air again after the heat of the heat roller 13a is taken in toward the paper passing area. Prevents temperature rise inside the body.

<Third Embodiment> Next, a third embodiment of the present invention will be described with reference to FIGS. In addition, Example 1
The same parts as in FIG.

FIG. 12 is a diagram showing the configuration of this embodiment.
In the figure, reference numeral 200 denotes a pair of conveying rollers which constitutes a moving means for moving the recording sheet P in the axial direction of the heat roller 13a, 201 denotes a DC motor for giving a driving force for conveying the sheet to the roller pair 200, and 202 denotes A gear for meshing with a worm gear 204 provided on one roller shaft of the roller pair 200 to move the roller pair 200 in the axial direction, 20
3 is a stepping motor for giving a driving force to the gear 202, 205 is a photo interrupter for detecting that the roller pair 200 is at the initial position, and is attached to the housing 207 holding the roller pair 200. It is detected by whether the flag 206 crosses the photo interrupter 205. 208 and 209 are heat rollers 13
These are thermistors for detecting the surface temperature of a and are arranged near both ends of the heat roller 13a.

Next, the control unit of this embodiment will be described with reference to FIG. In the figure, 17 is an engine control unit, 102
Is a one-chip microcomputer that is the main control unit of this control, and has a timer 103, ROM 104, RA
M105, arithmetic unit (ALU) 106, input / output port 1
07, an analog / digital conversion input port (A / D input port) 208 and the like are provided. 209 to 212 are transistors for driving the stepping motor 203, 2
17 to 220 are base resistances of transistors, and 213 to 2
Reference numeral 16 is a diode for absorbing back electromotive force. When the output ports (P1 and P2) are set to High output, the transistors (209 to 212) are turned on and the stepping motor 203
An electric current flows through the coil of each phase, and the coil is excited. By changing the output pattern of the output ports (P1 and P2), the stepping motor rotates normally or reversely. 221 is a transistor for driving the DC motor 201, 222 is a base resistance of the transistor 221, 223 is a DC motor 2
01 is a diode for absorbing back electromotive force. When the output port (P5) becomes High output and the transistor 221 is turned on, current flows through the DC motor 201 to rotate, and the output port (P5) becomes Low output, so that the transistor 22
When 1 is turned off, the DC motor 201 is stopped. 224 and 225 are current limiting resistors connected to the anode of the photodiode 205a of the photointerrupter 205 and the collector of the phototransistor 205b for detecting that the roller pair 200 is in the initial position. The collector of the phototransistor 205b is further connected to the MPU 102. When the photodiode 205a and the phototransistor 205b are connected to the input port (P6) and are shielded from each other, the phototransistor 205b is turned off and a high level is input to the input port (P6). A paper size sensor 111 detects whether or not the paper is a small size paper. One of the thermistors 208 and 209 is grounded, and the other of the thermistors 208 and 209 has one end connected to a DC power source (+ 5V), which is a resistor 226.
227 and A / D input ports of MPU 102 (P9, P1
0). The MPU 102 is the thermistor 2
The surface temperature of the heat roller is detected by an analog voltage determined by the resistance values of 08 and 209 and resistors 226 and 227. A gate array 228 generates and sends a synchronization signal (BD signal) in the main scanning direction to the controller 16 via the video interface 18 based on the laser light detected by the optical sensor 229. The gate array 228 changes the BD signal transmission timing based on the image shift signal (initial position at Low, shift at High) output from the output port (P8) of the MPU 102.
Even if the image writing position on the photosensitive drum 2 is changed and the position of the recording paper passing through the photosensitive drum 2 is changed by the roller pair 200, the image can be formed at a predetermined position on the recording paper.

FIG. 14 is a timing chart showing the BD signal transmission timing of the gate array 228. When an image is printed at the initial position of the photosensitive drum 2 (when the image shift signal is Low), immediately after the gate array 228 receives the laser light detection signal (C1) from the photosensor 229 (T0), the clock of the gate array 228 is clocked. (Or a clock after frequency division thereof) (C3) sends a BD signal in synchronization with (C2), and the controller 16 sends a video signal (C5) a predetermined time (T1) after receiving the BD signal. When the image is printed at the shift position (when the image shift signal is High), when the gate array similarly receives the laser light detection signal from the photosensor 229, the time corresponding to the image shift distance (L) is spent. By delaying (T2) and then transmitting the BD signal in synchronization with the clock of the gate array 228 (or the clock obtained by dividing the frequency). Cormorant.

Here, the delay time T2 is obtained by L / V (L: image shift distance, V: main scanning speed of laser beam on photosensitive drum surface).

Next, this control will be explained based on the flowchart of FIG. First, determine whether printing is in progress (S1
1) If the printing is not in progress, turn off the DC motor 201 that gives the roller pair 200 a driving force for sheet conveyance (S1).
2) The image shift signal to the gate array 228 is turned off (S13). If printing is in progress, it is determined that the roller pair 200 is in the initial position (whether P6 is High) (S14), and if it is not in the initial position, the stepping motor 203 is reversely rotated by one step (roller pair 20).
For 0, one step is performed in the initial position direction (left) (S15), and it is determined again whether the initial position is reached. The roller pair 200 is returned to the initial position by repeating S14 and S15. When the roller pair 200 reaches the initial position, the DC motor 01 is turned on (S16), and the roller pair 200 is given a driving force for sheet conveyance. Next, it is determined whether the printing paper is a small size paper and the right end (shift position) of the surface temperature of the heat roller 13a is higher than the left end (initial position) (S17, S).
18) Under the above conditions, the image shift signal to the gate array 228 is turned on (S19), and it is confirmed that the paper is caught in the roller pair 200 from the paper feeding timing (S19).
20) Then, the stepping motor 203 is rotated forward by a predetermined step (the roller pair 200 is moved in the shift direction (right) by a predetermined step) (S21). In cases other than the above conditions, the image shift signal is simply turned off (S22), the writing of the image on the photosensitive drum is completed (S23), and the process stands by until the paper comes out of the roller pair 200 (S24).

As described above, a plurality of heat roller surface temperature detecting means are provided in the heat roller axial direction, and a means for moving the recording medium conveyed to the fixing device in the heat roller axial direction is provided. By changing the heat roller passing position of the recording medium according to the heat roller surface temperature, it is possible to prevent problems such as image fixing failure and high non-sheet passing area that occur without the heat roller surface temperature rising.

[0032]

As described above, according to the first invention of the present application, the cost can be reduced by detecting the length and width of the recording medium in the conveying direction by the conveying state detecting means for detecting the position of the recording medium being conveyed. In addition, the size of the recording medium can be detected even when the recording medium is supplied from a means other than the storage means, such as when manually feeding.

Further, according to the second invention of the present application, a means for cooling a predetermined portion of the heat roller is provided to cool the heat roller according to the size of the recording medium. A plurality of heat roller surface temperature detecting means in the axial direction and a moving means for moving the recording medium conveyed to the fixing device in the heat roller axial direction are provided, and according to the heat roller axial length of the recording medium and the heat roller surface temperature. By changing the heat roller passage position of the recording medium, it is possible to prevent image fixing failure and high temperature in the non-passage area of the heat roller even in a portion where a small-sized recording medium is continuously passed through the heat roller.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a printer according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a paper feed sensor according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a state of a paper feed sensor according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a state of a paper feed sensor according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a state of a paper feed sensor according to the first embodiment of the present invention.

FIG. 6 is a diagram showing a state of a paper feed sensor according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a paper feed sensor state according to the first embodiment of the present invention.

FIG. 8 is a diagram showing a paper feed sensor output according to the first embodiment of the present invention.

FIG. 9 is a configuration diagram of a printer according to a second embodiment of the present invention.

FIG. 10 is a control circuit diagram according to the second embodiment of the present invention.

FIG. 11 is a flowchart showing control in Embodiment 2 of the present invention.

FIG. 12 is a configuration diagram of a third embodiment of the present invention.

FIG. 13 is a control circuit diagram according to the third embodiment of the present invention.

FIG. 14 is a BD signal timing chart according to the third embodiment of the present invention.

FIG. 15 is a flowchart showing control in Embodiment 3 of the present invention.

[Explanation of symbols]

10 Paper Feed Roller (Means for Conveying Recording Medium) 13a Heat Roller 51 Photo Sensor (Means for Conveying State Detection) 52, 53 Lever (Means for Conveying State Detection) 54 Paper with Large Width (Recording Medium) 55 Paper with Small Width (Recording Medium) ) 100 electric fan (cooling means) 111 paper size sensor (size detecting means) 200 roller pair (conveying means for recording medium) 203 stepping motor (moving means) 208, 209 thermistor (heat roller surface temperature detecting means)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03G 15/00 510 210 7-2H 21/00 370 2107-2H

Claims (5)

[Claims] 1. An image forming apparatus comprising: a recording medium conveying unit; and a conveyance state detecting unit that detects the position of the recording medium by interfering with the recording medium being conveyed, and determining the length and width of the recording medium in the conveying direction. An image forming apparatus characterized by being detected by the conveyance state detecting means. 2. A thermal fixing device using a heat roller for fixing the developer transferred to the recording medium by applying heat and pressure, a cooling means for cooling a predetermined portion of the heat roller, and a width of the recording medium. An image forming apparatus comprising: a size detecting unit for detecting the size of the heat roller; and cooling the heat roller according to the size of the recording medium. 3. The image forming apparatus according to claim 2, wherein the conveyance state detecting means according to claim 1 is used as the size detecting means of the recording medium. 4. A plurality of heat roller surface temperature detecting means provided in the heat roller axial direction, a moving means for moving the recording medium conveyed to the fixing device in the heat roller axial direction, and a length of the recording medium in the heat roller axial direction. An image forming apparatus, comprising: a detection unit for detecting the temperature of the recording medium, and changing the heat roller passing position of the recording medium according to the length of the recording medium in the heat roller axial direction and the surface temperature of the heat roller. 5. The image forming apparatus according to claim 4, wherein the conveyance state detecting unit according to claim 1 is used as a heat roller axial length detecting unit of the recording medium.