JPH08278723A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device capable of preventing hot offset which tends to occur in a fixing device when longitudinal sheet insertion and lateral sheet insertion are alternately changed for each copy, in the copying machine with a so-called electronic sort function. CONSTITUTION: When a number of copies are taken from each of originals, digital image information stored in a storage means, and each time a part of image is formed, the image is turned 90 degrees and another part of image is formed on a recording sheet. This image forming device is equipped with the electronic sort function which feeds a recording sheet for each copy in such a manner that the sheets are fed alternately in the longitudinal direction and the lateral direction and ejects the recording sheets with images formed on them onto a sheet ejection tray in such manner that they are ejected alternately in the longitudinal direction and lateral direction. A specific length of standby time is provided between the finish of the formation of the part of the image and the start of the another part of the image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device for an electrophotographic image forming apparatus, in which a heating roller end portion is used when a wide recording paper is passed after a narrow recording paper is continuously passed. The present invention relates to an image forming apparatus capable of preventing hot offset caused by being in an overheated state.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic process such as a copying machine, a printer and a facsimile machine, image information such as reflected light of a document is irradiated onto a photosensitive body which is uniformly charged in advance. The electrostatic latent image obtained by the above is visualized by the toner from the developing device, the toner image is transferred onto the recording paper, and then the image is formed by fixing while heating and pressurizing by the thermal fixing device. . In a digital copying machine, after image information obtained by reading an image of an original is converted into digital data, the digital image information is subjected to required processing in an image processing unit, and then written from a writing unit onto a photoconductor. Image information is emitted to form an image. In such a digital copying machine, it is possible to equip a so-called electronic sort function that sorts a plurality of copies on a single tray and discharges them without using a sorter.
This function temporarily stores the image information of the original in the storage means,
Each time a partial image is formed, the image is rotated 90 degrees, and the paper feed direction of the recording paper is alternately switched from longitudinal paper to horizontal paper for each set, so that the sheets are stacked on one tray. This is a sorting function in which the direction of the recording paper is changed by 90 degrees for each copy.

By the way, as the warm-up time of the copying machine has been shortened, the heating roller constituting the fixing device has been made thinner. However, as the heating roller becomes thinner, heat in the axial direction of the heating roller is reduced. Since the conduction is deteriorated, the temperature of the non-sheet passing portion during continuous copying rises, and the state of overheating tends to occur. In particular, when the number of continuous copies is large and when a small-sized recording sheet is fixed, the temperature of the non-sheet passing portion (both ends in the axial direction) becomes remarkable.

Further, when the electronic sort mode is used in the digital copying machine, since the horizontal paper feed is performed immediately after the vertical paper feed is continuously performed, both end portions of the horizontal paper feed sheet are overheated. Since both ends of the heating roller in the above are subjected to fixing, hot offset occurs in that portion, which causes defective fixing and the like. In other words, in the state where the temperature of the heating roller non-sheet passing portion during vertical sheet passing has reached a high temperature sufficient to cause hot offset, horizontal sheet passing is performed immediately after that,
A hot offset will occur at a position corresponding to that portion. That is, FIG. 7 is a diagram showing a hot offset generation area of the heating roller. The left and right end portions that exceed the paper passing range when vertically passing A4 size recording paper are hot offset generation areas. When the size recording paper is passed horizontally, the A4 that touches this hot offset area
The toner on both ends of the horizontal recording paper adheres to the heating roller side,
Poor fixing.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and in a copying machine having a so-called electronic sort function, a fixing device is provided in the case where the longitudinal paper and the lateral paper are alternately switched for each copy. It is an object of the present invention to provide an image forming apparatus capable of preventing hot offset that tends to occur in the image forming apparatus.

[0006]

To achieve the above object, the invention according to claim 1 provides an image processing section for performing image processing on digital image information obtained by digitally converting image information of an original read by a scanner section, and an image on a recording paper. An image forming apparatus comprising: an image forming unit for forming a sheet; and a paper feeding unit for feeding and conveying recording paper to the image forming unit, wherein the digital image information is used when copying a plurality of originals. Is stored in the storage means, the image is rotated by 90 degrees each time part of the image formation is completed, and the next part of the image is formed on the recording paper. Alternate between passing paper and horizontal paper,
In an image forming apparatus having an electronic sort function that discharges recording paper on which images have been formed on a discharge tray alternately in the vertical and horizontal directions, from the time when one image formation is completed until the next one image formation is started. It is characterized in that a predetermined waiting time is inserted into. The invention according to claim 2 is characterized in that the predetermined waiting time is inserted when the longitudinal paper is switched to the horizontal paper. According to a third aspect of the present invention, the image forming unit has a heat fixing device and temperature detecting means for detecting a temperature of an axial end portion of the heating roller forming the heat fixing device. When the direction edge temperature is equal to or higher than the predetermined temperature, the start of image formation of the next portion is delayed until the edge temperature decreases to the predetermined temperature or lower. According to a fourth aspect of the invention, the detection position of the end temperature of the heating roller is a position corresponding to the passage position of the end of the maximum size recording paper. The invention according to claim 5 is characterized in that the length of the waiting time provided at the time of switching from the vertical paper to the horizontal paper is changed according to the number of documents.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic structural explanatory view of a digital copying machine as an image forming apparatus to which the present invention is applied, and reference numeral 1
Is an original reading unit (image scanner), which includes a light source 5, mirrors 6, 7, and 8, an imaging lens 9, an image reading device 10 including an image sensor such as a CCD, and the like. Reading, digital conversion (2
The binarized signal is sent to the writing unit or stored in the image memory (storage means). Reference numeral 11 is a cooling fan.
Further, a known automatic document feeder (ADF) 4 is mounted on the document table (contact glass) 1a of the document reading unit 1.
Also, a platen cover is installed. Reference numeral 2 denotes a writing unit, which includes a light source such as a laser diode, a rotary polygon mirror 13 for scanning, a polygon motor 12, a scanning optical system 14 such as an fθ lens, and the like, and is read by the document reading unit 1. The laser beam is scanned according to the image information, and the image is written on the photoconductor 16 via the mirror 15. Reference numeral 3 is an image forming portion, which is a photoconductive photosensitive drum 1
6, charging charger 17, developing device 18, transfer charger 20, separation charger 21, cleaning device 22,
It is composed of a fixing device 24, paper feed units 27, 28, etc., and forms an image by an electrophotographic method, and together with the writing unit 2 constitutes a so-called laser printer. Reference numeral 19 is a developing roller (developing sleeve), 23 is a conveyor belt, 25 is a heating roller having a built-in heater, and 26 is a heating roller.
Is a pressure roller, 29 is a manual feed table, 30 and 31 are paper feed rollers, 32 and 33 are paper discharge rollers, 34 is a paper discharge tray, and 35 is a registration roller.

The image forming operation by the image forming apparatus having the above structure is as follows. In FIG. 1, an automatic document feeder (ADF) 4 feeds a document on a document table 4a onto a document table 1a, or a document is directly placed on the document table 1a by a manual operation. Start key is O
Then, the light source 5 of the document reading unit 1 is turned on, the document surface is scanned, the document image is read by the image reading device 10 on a pixel-by-pixel basis, and a digitally converted (binarized) signal is written into the writing unit 2. Sent to or stored in the image memory. In synchronization with this, in the image forming section 3, the photosensitive drum 1
6 is uniformly charged by the charging charger 17, and the writing unit 2 scans a laser beam in accordance with the image information read by the document reading unit 1 to perform optical writing on the photoconductor drum 16, and according to the image information. To form an electrostatic latent image. The electrostatic latent image formed on the photoconductor drum 16 is transferred to the developing device 18
The toner carried on the developing roller 19 is developed to form a visible image (toner image). Then, the toner image on the photoconductor drum 16 is fed from the paper feed units 27 and 28,
The image is transferred by the transfer charger 20 onto the transfer paper conveyed through the registration rollers 35. Then, the transfer paper after the toner image transfer is separated from the photoconductor drum 16 by the separation charger 21 and the separation claw, and the transfer belt 23
Is sent to the fixing device 24, and the toner image is fixed on the transfer paper by the fixing roller 25 and the pressure roller 26. Then, the transfer sheet after fixing is discharged onto the discharge tray 34 by the discharge rollers 32 and 33. On the other hand, the photoconductor drum 16 after the transfer is cleaned by the cleaning device 22 and discharged by a discharge lamp (not shown) or the like, and is in a standby state for the next image forming process.

By the way, in the above-mentioned digital copying machine, it is possible to rotate the digital image information taken in by a desired angle and output it by the image processing section.
By rotating by 90 degrees for each set and writing, and switching the recording paper on which each image is recorded between vertical and horizontal paper feeding, it is possible to sort the recording paper on a single discharge tray. It has a so-called electronic sort function. In a digital copying machine equipped with such an electronic sort function, a fixing device using a thin heating roller tends to be used in order to shorten the warm-up time when the power is turned on. In the roller, there is a problem that the image quality is deteriorated by the hot offset as described in the conventional example.

In order to solve such a problem, according to the present invention, when a plurality of copies are made from a plurality of originals, the end portion of the heating roller is sufficiently moved after the preceding one copy is completed. The feature is that the next copy operation of one copy is not started until it is cooled. Hereinafter, as an example of the operation of the electronic sort mode according to the present invention, 20 A4 sheets are displayed.
A procedure for copying 10 copies of a Y (horizontal) document will be described. First, (1) Sequentially read the image information of 20 originals one by one,
All the image information is stored in a memory (storage means). (2) Based on the stored image information of the 20 sheets, the first image is formed, and the recording paper is discharged onto the paper discharge tray as A4 horizontal paper. (3) The stored image information is rotated 90 degrees to form the second copy image. At this time, the recording paper is ejected onto the ejection tray as A4 vertical paper. (4) By repeating the steps of (2) and (3), five sets of the horizontal and vertical sheets of recording paper are alternately discharged to the discharge tray (10 copies in total).

In the image forming apparatus of the present invention, in order to solve the above-mentioned problems, in order to delay the timing of starting the next image formation for a predetermined time every time a part of the image formation is completed, I try to set aside time. This waiting time is a cooling time for lowering the temperature of the non-sheet passing portion of the heating roller, which has been excessively heated by the preceding first copy, to a normal temperature. As shown in FIG. 2, the temperature of the non-sheet passing portion at the end of the heating roller in the axial direction becomes overheated when the A4 portrait sheet is continuously passed, but by setting (inserting) the standby time as in the present invention. As shown in the figure, the temperature is lowered to such an extent that hot offset may not occur, and a good transfer state can be obtained at the time of the next part of image formation. In addition, in order to improve the productivity, the waiting time may be provided only after the vertical paper feed is completed. This is because the non-sheet passing portion (both axial end portions, see FIG. 7) is formed only during vertical sheet passing, and an overheated portion is generated at that portion. This is because it is possible to shorten the image forming time.

Next, FIG. 3 is an explanatory view of the essential parts of a fixing device according to another embodiment of the present invention. In addition to the thermistor 50 for controlling the temperature of the roller provided in the central portion in the axial direction of the heating roller, the shaft is also provided. A thermistor 51 as a roller end temperature detecting means is arranged in contact with the end portion in the direction (non-sheet-passing portion during vertical sheet passage). In the present embodiment, the waiting time is not uniformly set after the vertical sheet is passed, but the standby time is provided only when the non-sheet passing portion is overheated beyond the allowable limit during the vertical sheet feeding. The start of paper passing is delayed. The thermistor 51 detects the presence or absence of this overheating.

According to this embodiment, only when the temperature of the non-sheet passing portion is higher than the predetermined temperature, the start of image formation is waited until the temperature of the non-sheet passing portion becomes equal to or lower than the predetermined temperature. When the temperature of the non-sheet passing portion immediately after the image formation of the preceding one copy is equal to or lower than the predetermined temperature, the image formation is continuously performed, so that the operation rate of the device can be increased and the productivity can be increased. For example, if the number of originals is small, the vertical paper feed may end before the temperature of the end of the heating roller exceeds the specified temperature during vertical paper feed. However, hot offset does not occur. Therefore, when the number of originals is small, by controlling as described above, the productivity can be improved without causing hot offset.

FIG. 4 is a diagram showing changes in the temperature of the end portion of the heating roller in image formation when the number of originals is small, and FIG.
FIG. 6 is a diagram showing a change in end temperature of the heating roller during image formation when the number of originals is large. As shown in FIG. 5, when the number of originals is large, the end temperature of the heating roller rises sharply after the vertical paper passage and reaches the hot offset generation temperature (or a predetermined temperature immediately below it), so it is necessary to provide a waiting time. However, as shown in FIG. 4, when the number of originals is small, the end temperature of the heating roller does not reach the above-mentioned predetermined temperature even immediately after the vertical paper passage. Therefore, the productivity can be improved by continuously performing the horizontal sheet feeding on the condition that the edge temperature does not reach the predetermined temperature immediately after the vertical sheet feeding is completed.

In the above-mentioned embodiment, even when the number of originals is small and the end temperature of the heating roller is not expected to be overheated, the end time is detected and the waiting time is inserted. Although the control method that determines whether or not the number of originals is clearly not expected to be overheated when the number of originals is exceeded, a judgment is made based on the number of originals, and when switching from portrait to landscape. It is also possible to determine whether or not to insert the waiting time, or to determine the length of the waiting time, respectively. By doing so, the same effect can be obtained while omitting the end temperature detecting means such as the thermistor. For example, when the number N of originals is simply N ₁ or less, continuous paper feeding is performed without a waiting time between sets, and when the number of originals N is more than N ₁ , when switching from vertical to horizontal paper feeding. Insert a waiting time of T ₃ seconds.

Alternatively, as shown in Table 1 of FIG. 6, it is judged whether the number N of originals is larger or smaller than some reference numbers N ₁ , N ₂ and N ₃ so that the number of originals is gradually increased. The classification may be performed, and the waiting time may be controlled to increase as the number of sheets increases. By configuring in this way,
It is possible to further increase productivity.

[0017]

As described above, according to the invention of claim 1,
An image processing unit for performing image processing on digital image information obtained by digitally converting image information of a document read by a scanner unit,
An image forming apparatus comprising: an image forming unit for forming an image on a recording sheet; and a paper feeding unit for feeding and conveying the recording sheet to the image forming unit, wherein when a plurality of originals are copied, The digital image information is stored in the storage means, and the image is rotated by 90 degrees each time a part of the image formation is completed to form the next part of the image on the recording paper, and the recording paper is fed for each set. Some image formation is completed in an image forming device with an electronic sort function that alternates vertical and horizontal paper as the paper direction and discharges image-formed recording paper to the paper discharge tray alternately vertically and horizontally. After that, a predetermined waiting time is inserted between the start of the next part of image formation, so that the temperature rise at the end portion of the heating roller can be suppressed and the occurrence of hot offset can be prevented.

According to the second aspect of the present invention, the predetermined waiting time is inserted when switching from vertical paper to horizontal paper, so that the end temperature of the heating roller rises without lowering productivity. It is possible to prevent hot offset from occurring. According to a third aspect of the invention, there is provided temperature detecting means for detecting the temperature of the end portion in the axial direction of the heating roller constituting the heat fixing device,
When the temperature of the end portion of the heating roller in the axial direction is equal to or higher than the predetermined temperature, the start of image formation of the subsequent portion is delayed until the temperature of the end portion falls below the predetermined temperature. Therefore, the hot offset due to the temperature rise of the end portion of the heating roller can be prevented.

According to the fourth aspect of the present invention, since the detection position of the end temperature of the heating roller is a position corresponding to the passing position of the end of the maximum size recording paper, the temperature at the position where it is most likely to overheat is ensured. Therefore, hot offset can be accurately prevented. According to the fifth aspect of the invention, the length of the waiting time provided at the time of switching from the vertical paper to the horizontal paper is configured to be changed according to the number of originals, so that the temperature detecting means, etc. It is possible to suppress the edge temperature below the hot offset generation temperature without providing
It is possible to prevent deterioration in image quality due to hot offset without impairing productivity.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a temperature change state of a heating roller.

FIG. 3 is a diagram showing a main part configuration of another embodiment of the present invention.

FIG. 4 is a diagram showing a change in edge temperature when the number of originals is small.

FIG. 5 is a diagram showing changes in edge temperature when the number of originals is large.

FIG. 6 is a diagram showing the relationship between the number of documents and the standby time.

FIG. 7 is a diagram for explaining a defect of a conventional example.

[Explanation of symbols]

1 original reading unit, 2 writing unit, 3 rotary polygon mirror, 4
Automatic document feeder, 6, 7, 8 mirror, 9 imaging lens, 10 image reader, 16 photoconductor drum, 17
Charging charger, 18 developing device, 20 transfer charger, 21 separation charger, 22 cleaning device, 24 fixing device, 27, 28 paper feeding section, 50, 51
Thermistor (temperature detection means).

Claims (5)

[Claims] 1. An image processing unit for performing image processing on digital image information obtained by digitally converting image information of an original read by a scanner unit, an image forming unit for forming an image on recording paper, and the image forming. An image forming apparatus having a sheet feeding unit for feeding and conveying recording paper to a set, wherein the digital image information is stored in a storage unit when a plurality of copies of a plurality of originals are made, and a part of the image is stored. Each time the formation is completed, the image is rotated 90 degrees to form the next part of the image on the recording paper, and the longitudinal and lateral papers are alternately carried out as the paper feeding direction of each recording paper. In an image forming apparatus with an electronic sort function that discharges recording paper that has undergone image formation to the discharge tray alternately vertically and horizontally, from the time when one image formation is completed until the next image formation is started. To insert a predetermined waiting time into An image forming apparatus symptoms. 2. The image forming apparatus according to claim 1, wherein the predetermined waiting time is inserted when switching from the vertical paper to the horizontal paper. 3. The image forming unit has a thermal fixing device, and temperature detecting means for detecting the temperature of the axial end of the heating roller constituting the thermal fixing device, and the axial end of the heating roller. 2. The image forming apparatus according to claim 1, wherein when the temperature is equal to or higher than a predetermined temperature, the start of image formation of the next portion is delayed until the end temperature decreases to the predetermined temperature or lower. 4. The image forming apparatus according to claim 3, wherein the detection position of the end temperature of the heating roller is a position corresponding to the passage position of the end of the maximum size recording paper. 5. The image according to claim 2, wherein the length of the waiting time provided at the time of switching from the vertical paper to the horizontal paper is changed according to the number of originals. Forming equipment.