JP2004145211A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that prevents a fixing rotor such as a heat roll from being partially excessively heated even in a case where image formation is carried out forcibly feeding a recording sheet Px, as a recording sheet P, which has a feed width S smaller than a guaranteed minimum size Smin. <P>SOLUTION: A temperature detecting element 40 which detects the temperature of a heat roll 31 is disposed at least within a sheet passage area W3 through which a recording sheet Pmin of the guaranteed minimum size Smin in the direction of the rotation axis of the heat roll 31 is passed but within an area W4 through which a recording sheet Px of the feed width smaller than the feed width of the guaranteed minimum size Smin is not passed when conveyed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile, a multifunction machine, or the like using an electrophotographic system, an electrostatic recording system, or the like.
[0002]
[Prior art]
2. Description of the Related Art In an image forming apparatus such as a printer using an electrophotographic method, an image formed of toner is formed on an image carrier such as a photoconductor through an electrophotographic process, and the toner image is directly formed on a recording sheet or through an intermediate transfer body. After the indirect transfer, the recording sheet carrying the transferred unfixed image is conveyed to a fixing device and subjected to a fixing process to form an image.
[0003]
As the fixing device, for example, a recording sheet carrying an unfixed image is passed between a heating roll and a pressure roll (fixing nip portion) which are arranged opposite to each other while being pressed against each other, and the fixing process is performed by heating and pressing. The type that does it is used. In such a fixing device, a heating lamp is installed inside the heating roll along the rotation axis direction, and a temperature detecting element for detecting the surface temperature of the heating roll is installed, and the temperature information detected by the temperature detecting element is used. By controlling the heating operation of the heating lamp accordingly, the heating roll is heated and maintained at a predetermined temperature (mainly a fixing temperature).
[0004]
By the way, in such an image forming apparatus, in general, from the viewpoint of assuring stable transportability of a recording sheet and good fixability, a feed width at the time of transporting the recording sheet (a sheet along a direction orthogonal to the transport direction) is used. Guaranteed width is set as the width.
[0005]
The regulation on the setting of the guaranteed minimum size is performed, for example, by defining a slide area of a sheet-side end regulation guide provided on a sheet feed tray (cassette) that stores recording sheets. That is, the recording sheets (bundles) stacked and accommodated in the sheet feeding tray are aligned by a plate-shaped sheet side end regulating guide whose side end in the conveying (sheet feeding) direction slides in a direction orthogonal to the conveying direction. Although the position is restricted by the position, the movement end point on the small size side in the slide area is set to a position corresponding to the guaranteed minimum size. As a result, even if an attempt is made to use a recording sheet having a feed width smaller than the guaranteed minimum size, one end of the recording sheet is not regulated by the sheet-side end regulation guide, and the sheet can be fed and conveyed satisfactorily. It is becoming lost. In addition to this, the description is given in the instruction manual of the image forming apparatus for notifying the user that the guaranteed minimum size is specified as the feeding width of the recording sheet to be handled.
[0006]
On the other hand, in the fixing device, even if a recording sheet of any feed width usable in the image forming apparatus is conveyed for the fixing process, the heating roller is heated and maintained at a predetermined fixing temperature. A plurality of elements are provided so that the temperature of the heating roll is detected as accurately as possible, and the heating operation of the heating lamp is appropriately controlled.
[0007]
For example, when two temperature detecting elements are installed, as shown in FIG. 7, one of the temperature detecting elements 200 </ b> A has a recording sheet Pmin of the minimum size S guaranteed in the rotation axis direction (J) of the heating roll 100. It is known that the temperature detecting element 200B is installed in a range corresponding to the minimum passing area W2 that passes therethrough, and the other temperature detecting element 200B is installed in a range outside the minimum passing area W2 (Patent Document 1). The reference numeral W1 in the drawing is a maximum passage area through which the largest recording sheet permitted as the feed width passes.
[0008]
[Patent Document 1] Japanese Patent No. 2698494
[Problems to be solved by the invention]
However, such an image forming apparatus in which the guaranteed minimum size of the recording sheet is set has the following problems.
[0010]
That is, as illustrated in FIG. 7, there is a case where a recording sheet Px having a feeding width S smaller than the guaranteed minimum size is forcibly fed as a recording sheet and image formation is performed. When the image formation using Px is repeatedly performed, at least a part of the minimum passage area W2 in the heating roll 100 of the fixing device becomes overheated, and the release layer formed on the surface of the heating roll becomes excessive. Due to the high heat generated by the excessive heating, the material is thermally deformed and deformed or deformed, and the heating roll 100 is greatly damaged.
[0011]
The portion of the heating roll that is in the excessively heated state is an area of the minimum passing area W2 other than an area W3 through which the recording sheet Px having a feed width smaller than the guaranteed minimum size passes (an area through which the recording sheet Px does not pass). W4 (see FIG. 5). This is because even if the temperature detection element 200A is installed in the minimum passage area W2, as long as the installation position is the area W3 where the recording sheet Px passes, the surface temperature itself of the heating roll 100 in the area W3 will be lower. As the sheet Px passes, the temperature decreases (changes) almost in the same manner as in the normal fixing, so that the control content regarding the heating operation of the heating lamp based on the information on detecting such temperature is almost the same as in the normal fixing. Then, a heating operation for maintaining the fixing temperature is performed. As a result, even in the same minimum passage area W2, the area W4 through which the recording sheet Px does not pass is heated more than necessary.
[0012]
The problem of local overheating of the heating roll when the image formation is performed by forcibly feeding the recording sheet Px having a feed width smaller than the guaranteed minimum size is a problem in that the recording sheet is conveyed. The so-called center register type, in which the recording sheet is always conveyed based on the center position of the feed width without being limited to the image forming apparatus adopting the so-called side registration type conveyance method which always performs the conveyance with one side end as the conveyance reference. This can also occur in an image forming apparatus employing the above-described transport method.
[0013]
Incidentally, in order to solve such a problem, it is conceivable to install a larger number of temperature detecting elements in the rotation axis direction of the heating roll, but in this case, the temperature information from each of the temperature detecting elements is used. The content of control based on this becomes complicated, which leads to a complicated configuration and an increase in cost. Further, Patent Document 1 does not describe the problem when the unexpected recording sheet Px is used as described above and its countermeasures, and merely describes “the minimum paper passing area” in paragraph 0037 or FIG. Is provided with one temperature sensing element ".
[0014]
The present invention has been made to solve such a problem, and its main purpose is to forcibly feed a recording sheet having a feed width smaller than the guaranteed minimum size as a recording sheet. An object of the present invention is to provide an image forming apparatus capable of preventing local excessive heating of a fixing rotating body such as a heating roll even when image formation is performed.
[0015]
[Means for Solving the Problems]
An image forming apparatus according to the present invention includes an image forming apparatus that forms an unfixed image on a recording sheet, and a recording sheet on which the unfixed image is formed by the image forming apparatus is conveyed so as to be pressed to record the unfixed image. A fixing rotator for fixing to the sheet, heating means provided along the rotation axis direction of the fixing rotator to heat the fixing rotator, and a fixing rotator provided to face the fixing rotator to be heated. A temperature detecting element for detecting a temperature, and control means for controlling a heating operation of the heating means according to the temperature information detected by the temperature detecting element. Although the size is set, in the image forming apparatus in which even a recording sheet having a feed width smaller than the guaranteed minimum size can be conveyed, the temperature detecting element is disposed in the rotation axis direction of the fixing rotator. Within a sheet passing area through which a recording sheet having a guaranteed minimum size feed width passes, and within an area not passing when a recording sheet having a feed width smaller than the guaranteed minimum size is conveyed. It is characterized by being installed at least.
[0016]
In such an image forming apparatus, since the temperature detecting element is installed at least in the area of the fixing rotator through which a recording sheet having a feed width smaller than the guaranteed minimum size does not pass, the feed width is smaller than the guaranteed minimum size as a recording sheet. When the image formation is performed by forcibly feeding the recording sheet, the temperature of the area through which the recording sheet does not pass is detected, and the control regarding the heating operation of the heating means is performed based on the temperature information. . For this reason, the heating means is controlled in accordance with the temperature of the region through which the recording sheet does not pass, and there is no possibility that the region is excessively heated.
[0017]
Further, in such an image forming apparatus, from the viewpoint of more appropriately preventing an area of the fixing rotating body through which a recording sheet having a feed width smaller than the guaranteed minimum size does not pass from being excessively heated, the temperature is not higher than the temperature. It is desirable that the detection element is provided at a position corresponding to an end portion in a sheet passage area through which a recording sheet having a feed width of the guaranteed minimum size passes.
[0018]
The image forming apparatus refers to an image forming apparatus that forms an unfixed image (for example, a toner image) requiring a fixing process by a fixing rotator, and transfers the unfixed image directly to a recording sheet or indirectly via an intermediate transfer member. Anything that can be done is acceptable.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
<< Embodiment 1 >>
As shown in FIG. 1, the image forming apparatus according to Embodiment 1 of the present invention accommodates an image forming apparatus 10 that forms a toner image T based on image information and transfers the toner image T to a recording sheet P, and the recording sheet P. And a fixing device 30 that performs a fixing process on the recording sheet onto which the toner image has been transferred.
[0020]
The main part of the image forming apparatus 10 includes a photosensitive drum 11, a charging device 12, a laser exposure device 13, a developing device 14, a transfer device 15, a cleaner 16, and the like. Is formed.
[0021]
First, after the photosensitive drum 11 rotating in the direction of the arrow is uniformly charged by the charging device 12, a laser beam modulated based on image information is scanned and exposed from the laser exposure device 13 onto the charged drum 11. Thus, an electrostatic latent image is written. Subsequently, after the electrostatic latent image on the photosensitive drum 11 is developed by a toner (developer) supplied from the developing device 14 to be visualized as a toner image, the toner image is transferred to the photosensitive drum 11 and the transfer device. The image is transferred by the transfer device 15 to the recording sheet P supplied during the period 15. After the transfer, the surface of the photosensitive drum 11 is cleaned by the cleaner 16 to prepare for the next image forming process.
[0022]
The paper feeding device 20 includes a paper feeding tray 21 for stacking and storing a plurality of recording sheets P used for image formation, a feeding device 22 for feeding the stacked and stored recording sheets P one by one from the paper feeding tray 21, The main part thereof is constituted by a pair of registration rolls 23 for feeding the recording sheet P sent from the tray 21 between the photosensitive drum 11 and the transfer device 15 at a predetermined timing.
[0023]
In addition, in the entire image forming apparatus including the sheet feeding device 20, the recording sheet P is conveyed by using the above-described side registration type conveyance method. For this reason, as illustrated in FIG. 4, a transport reference guide 25 having a transport reference surface 25 a formed on a sheet storage surface is provided on the paper feed tray 21 of the paper feed device 20 in a protruding state. As a result, the recording sheets P accommodated in the paper feed tray 21 are accommodated in such a state that one side end thereof is brought into contact with the conveyance reference surface 25a of the conveyance reference guide 25 and aligned. It goes without saying that other sheet conveyance paths in the image forming apparatus are also configured to guide and convey various recording sheets along the conveyance reference surface 25a. Further, in order to regulate the recording sheets P accommodated in the paper feed tray 21 into a state in which the recording sheets P are pressed against the (conveyance reference surface 25a of) the conveyance reference guide 25, the conveyance reference P is positioned at a position opposed to the reference surface 25a. A sheet-side end regulating guide 26 slidable in a direction (arrow M in the drawing) approaching or separating from the guide 25 is provided. Reference numeral 27 in the drawing denotes a slide guide groove for regulating the sliding direction of the regulation guide 26 and its area.
[0024]
As shown in FIGS. 1 and 2, the fixing device 30 has a roll nip type in which a main part includes a heating roll 31 and a pressure roll 35 that presses against the heating roll 31 to form a fixing nip portion N. The fixing process is performed by introducing and passing the recording sheet P on which the toner image has been transferred by the image forming apparatus 10 into the fixing nip portion.
[0025]
The heating roll 31 includes a cylindrical roll base 32 made of a metal material or the like and a release layer 33 made of PFA or the like formed on the surface of the roll base 32, and is driven to rotate in the direction of the arrow. Are located in Further, an electric heating lamp 34 for heating the heating roll 31 is arranged in the internal space of the heating roll 31. On the other hand, the pressure roll 35 includes a cylindrical roll base 36 made of a metal material or the like, an elastic layer 37 formed on the surface of the base 36, and the like, and is pressed against the heating roll 31 at a predetermined pressure to be driven. It is arranged to rotate.
[0026]
In this fixing device, as shown in FIGS. 1 to 3, one temperature sensor element 40 for detecting the surface temperature of the heating roll 31 is brought into contact with or close to the surface of the heating roll 31. Is provided. The temperature sensor element 40 is connected to a control device 50 for controlling the overall operation of the fixing device 30, and transmits information on the detected surface temperature to the control device 50. The control device 50 is connected to a lamp drive control circuit 51 that performs on / off control of power supply to the electric heating lamp 34 and adjusts supply power, and is stored in a storage device or the like in advance of temperature information from the temperature sensor element 40. A control signal is transmitted to the lamp drive control circuit 51 in accordance with the fixing temperature control program. The control device 50 receives an input signal of a start signal of an image forming operation, a type of a recording sheet to be fed, and the like.
[0027]
Thus, in the fixing device 30, for example, when the main power supply of the image forming apparatus is turned on, power supply to the electric heating lamp 34 is started to heat the heating roll 31 to a predetermined fixing temperature. When the temperature detected by the temperature sensor element 40 exceeds a predetermined upper threshold (temperature), the power supply to the electric heating lamp 34 is stopped to stop the heating operation of the heating roll 31, while the heating roll 31 is stopped. When the temperature detected by the temperature sensor element 40 falls below a predetermined lower threshold value, the power supply to the electric heating lamp 34 is restarted and the heating operation of the heating roll 31 is restarted. By performing such control relating to the heating operation, the heating roll 31 is maintained at a predetermined fixing temperature or a temperature around the predetermined fixing temperature.
[0028]
In this image forming apparatus, the guaranteed minimum size Smin is set as the feed width S when the recording sheet P is conveyed.
[0029]
Due to this relationship, as shown in FIG. 4, the sliding limit position E1 (the position closest to the conveyance reference guide 25) E1 of the sheet side end regulating guide 26 in the sheet feeding tray 21 is the minimum guaranteed value. The recording sheet Pmin having a feed width of the size Smin is set to a position where the recording sheet Pmin is pressed toward the conveyance reference guide 25 and aligned. On the other hand, the slide limit position E2 on the large size side of the sheet side end regulating guide 26 is adjusted to a position where one side end of the recording sheet having the maximum size of the feeding width is pressed toward the conveyance reference guide 25 and aligned. Is set. W1 in the drawing is a maximum passage area through which a recording sheet having a maximum size of the feeding width passes.
[0030]
In this image forming apparatus, as described above, the slide limit position E1 on the small size side of the sheet side end regulating guide 26 in the sheet feed tray 26 is set in accordance with the recording sheet Pmin having a feed width of the guaranteed minimum size Smin. However, in practice, it is possible to forcibly feed a recording sheet Px having a feed width Sx smaller than the guaranteed minimum size Smin as the recording sheet P, and it is also possible to form an image on the recording sheet Px. It is permitted without being prohibited.
[0031]
Further, due to the relationship of setting the guaranteed minimum size Smin, the temperature sensor element 40 in the fixing device 30 also has a guaranteed minimum size in the rotation axis direction (J) of the heating roll 31, as shown in FIGS. Passes when a recording sheet Px having a feed width Sx (≦ Pmin) that is within the sheet passage area W2 through which the recording sheet Pmin having the feed width S of Smin passes and is smaller than the guaranteed minimum size Smin is conveyed. It is installed at a position that is within the area W4 that is not to be used.
[0032]
Accordingly, even if the image forming apparatus may forcibly feed a recording sheet Px having a feed width smaller than the guaranteed minimum size Smin as the recording sheet P to form an image, the fixing device 30 Is that the control regarding the heating operation of the heating lamp 34 according to the temperature of the region W4 through which the recording sheet Px having a feed width smaller than the guaranteed minimum size Smin does not pass is executed, and the region W4 is There is no possibility of excessive heating.
[0033]
That is, in the fixing device 30, since the temperature sensor element 40 is provided at least in the area W4 through which the recording sheet Px does not pass, the temperature of the heating roll 20 in the area W4 is surely detected by the temperature sensor element 40. The control regarding the heating operation of the heating lamp 34 based on the temperature information is performed. That is, when the temperature of the region W4 through which the recording sheet Px does not pass exceeds the upper limit threshold, the power supply operation to the heating lamp 34 is stopped and the heating of the heating roll 20 is also stopped as described above. As a result, the heating roll 30 is not heated more than necessary by the heating operation of the heating lamp 34.
[0034]
FIG. 5 shows the results of a test performed using this image forming apparatus.
[0035]
This test measures the surface temperature of each heating roll 20 when the temperature sensor element 40 is installed in the area W3 where the recording sheet Px does not pass and when the temperature sensor element 40 is installed in the area W4 where the recording sheet Px does not pass. It is. The guaranteed minimum size Smin was set to “147 mm” which is the length of the long side (LE) of a fixed postcard (100 mm × 147 mm). Further, the same postcard was used as the recording sheet Px having a feed width smaller than the guaranteed minimum size Smin, and was fed in a vertically fed state (a state in which the feed width S was 100 mm).
[0036]
Thus, the width of the passage area W2 of the recording sheet Pmin in the fixing device 10 becomes “147 mm”, the width of the passage area W3 of the recording sheet Px becomes “100 mm”, and the width of the area W4 through which the recording sheet Px does not pass becomes “47 mm”. Become. Then, the temperature sensor element 40 installed in the passage area W3 of the recording sheet Px is installed at a position 50 mm away from the transfer reference position of the side register on the heating roll 31 (the position "0 mm" on the horizontal axis of the graph in FIG. 5). . Further, the temperature sensor element 40 installed in the non-passage area W4 of the recording sheet Px was installed at a position 138 mm away from the reference conveyance position of the side register on the heating roll 31.
[0037]
At this time, the electric heating lamp 34 was controlled so that the surface temperature of the heating roll 31 became “215 ° C.”. In addition to the temperature sensor element 40 for detecting the surface temperature of the heating roll 31, nine temperature sensor elements were installed at different positions, and the temperature was detected at each position. In each case, the temperature was measured after 90 sheets of the blank recording sheet Px were continuously passed through the fixing nip.
[0038]
As is clear from the results shown in FIG. 5, when the temperature sensor element 40 is installed in the passage area W3 of the recording sheet Px (at a position 50 mm from the reference conveyance position), the heating roll in the non-passage area W4 of the recording sheet Px While the temperature reaches a high temperature of 280 ° C., which is much higher than the target heating temperature, when the temperature sensor element 40 is set in the non-passing area W4 of the recording sheet Px (at a position 138 mm from the conveyance reference position), recording is performed. It can be confirmed that the heating roll temperature in the non-passage area W4 of the sheet Px can be maintained at 230 ° C. or lower.
[0039]
When the recording sheet Px having a feed width Sx smaller than the guaranteed minimum size Smin is forcibly fed and the image formation is continuously performed, the temperature of the heating roll in the area W3 through which the recording sheet Px passes is determined by the fixing temperature. , The cold offset occurs, and there is a tendency that good fixing cannot be achieved gradually.
[0040]
In addition, the temperature sensor element 40 is installed at a position corresponding to the end of the passage area W2 of the recording sheet Px having the feeding width of the guaranteed minimum size among the non-passage areas W4 of the recording sheet Px as much as possible. The installation at a portion corresponding to the end of the passage area W2 means, for example, as shown in FIG. 4, the detection effective area (end) of the temperature sensor element (40) and the end of the passage area W2 (the area W2 and the end thereof). That is, the temperature sensor element is installed such that the distance β from the boundary line to the continuous area W1 is in the range of 0 to 10 mm.
[0041]
When installed in such a site, the temperature of the non-passage area W4 can be detected more appropriately. Further, since the temperature sensor element used in the fixing device 10 is installed at a position where the temperature of the area where various recording sheets of the normal guaranteed size always pass can be detected, one of the temperature sensor elements installed at the position is used. In some cases, it is only necessary to install the temperature sensor element 40, which is beneficial.
[0042]
<< Other embodiments >>
In the first embodiment, a case where a side registration type is used as a recording sheet conveyance method is described as an example, but the present invention is also applicable to an image forming apparatus employing a center registration type conveyance method as described above. .
[0043]
FIG. 6 is a diagram showing an installation position of the temperature sensor element 40 in the fixing device when a center-register-type conveyance method is employed. In the drawing, a one-dot broken line C is a transport reference line in the center register system. In this case, there are two non-passing areas W4 (W4a, W4b) on both sides of the passing area W3 through which the recording sheet Px having the feed width Sx smaller than the guaranteed minimum size Smin does not pass. For this reason, the temperature sensor element 40 may be installed in the two non-passage areas W4a and W4b, but may be installed in at least one of the areas.
[0044]
Further, in the fixing device 10, instead of the heating roll 31, a belt-shaped fixing rotator that stretches and rotates a fixing belt around a supporting roll such as a heating roll or a driving roll may be applied.
[0045]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, even if image formation is performed by forcibly feeding a recording sheet having a feeding width smaller than the guaranteed minimum size as a recording sheet, even if image formation is performed, Local overheating of the fixing rotating body such as a roll is prevented from occurring.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a main configuration of an image forming apparatus according to a first embodiment;
FIG. 2 is a schematic diagram illustrating a main configuration of a fixing device.
FIG. 3 is an explanatory view mainly showing an installation position of a temperature sensor element and the like.
FIG. 4 is an explanatory diagram showing a relationship between a feeding state of a recording sheet or the like having a guaranteed minimum size feeding width and an installation position of a temperature sensor element.
FIG. 5 is a graph showing a result of a test in which a relationship between an installation position of a temperature sensor element and a temperature state of a heating roll is examined.
FIG. 6 is an explanatory view mainly showing an installation position of a temperature sensor element and the like in a case where a center-register type transfer method is adopted.
FIG. 7 is an explanatory view mainly showing the installation position of a conventional temperature sensor element and the like.
[Explanation of symbols]
Reference Signs List 10 image forming device, 30 fixing device, 31 heating roll (fixing rotating body), 34 electric heating lamp (heating means), 40 temperature sensor element (temperature detecting element), 50 control device (one of control means) , 51: Heating control circuit (part of control means), W3: Passing area of recording sheet of guaranteed minimum size, W4: Non-passing area of recording sheet of guaranteed minimum size, P: Recording sheet, S: Feed width , Smin: a recording sheet having a guaranteed minimum size, Pmin: a recording sheet having a feeding width of the minimum guaranteed size, and Px: a recording sheet having a feeding width smaller than the minimum guaranteed size.

Claims (2)

An image forming apparatus for forming an unfixed image on a recording sheet;
A fixing rotator that conveys the recording sheet on which the unfixed image is formed by the image forming apparatus so as to be pressed and fixes the unfixed image on the recording sheet;
Heating means installed along the rotation axis direction of the fixing rotator to heat the fixing rotator;
A temperature detecting element installed opposite to the fixing rotator to detect the temperature of the fixing rotator;
Control means for controlling the heating operation of the heating means according to the temperature information detected by the temperature detection element,
Although the guaranteed minimum size is set as the feed width at the time of transporting the recording sheet, in an image forming apparatus in which a recording sheet having a feed width smaller than the guaranteed minimum size can be transported,
The temperature detecting element is located within a sheet passing area through which the recording sheet having the guaranteed minimum size feed width in the rotation axis direction of the fixing rotator passes, and has a feed width smaller than the guaranteed minimum size. An image forming apparatus is provided at least in a portion which is in an area that does not pass when conveyed. 2. The image forming apparatus according to claim 1, wherein the temperature detecting element is provided at a position corresponding to an end in a sheet passage area through which the recording sheet having the guaranteed minimum size of the feed width passes. 3.

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