JP2004252377A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus constituted so that a transfer paper with an image printed on the back surface is prevented from being wound around a pressure roller. <P>SOLUTION: The apparatus is constituted so that it has a fixing device 4 for fixing toner on the transfer paper 1 by a pressure roller 4b for bringing the transfer paper 1 in press contact with a heat roller 4a, and an image density detecting means 3 for detecting whether or not the image is already printed on the back surface of the transfer paper 1 is arranged on the upstream position of the fixing device 4 in the transfer paper 1 carrying path, and a 1st separation pawl 4c abutting on the outer peripheral surface of the heating roller 4a and a 2nd separation pawl 4d capable of abutting on the outer peripheral surface of the pressure roller 4b are arranged, and when it is discriminated by the image density detecting means 3 that the image is already printed on the back surface of the transfer paper 1, the 2nd separation pawl 4d is made to abut on the pressure roller 4b. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus for an electrophotographic machine such as a copying machine, a printer, a facsimile, and a printing machine.
[0002]
[Prior art]
Conventionally, it has a heating roller heated by a heater and a pressure roller for pressing the transfer paper against the heating roller. The toner image is transferred by pressing the transfer paper with both rollers and sending out while heating. In an image forming apparatus provided with a fixing device for fixing to paper, a first separation claw is brought into contact with an outer peripheral surface of a heating roller to prevent the transfer paper from being wound around the heating roller, and to perform transfer in a double-sided printing mode. When printing an image on the back surface of the paper, a second separation claw is brought into contact with the outer peripheral surface of the pressure roller to prevent the transfer paper from winding around the pressure roller (for example, see Patent Document 1).
Further, a paper thickness detecting device is provided in the transfer paper transport path, and when the transfer paper is thin paper, the second separation claw is brought into contact with the outer peripheral surface of the pressure roller.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2002-214956
[Problems to be solved by the invention]
However, in a conventional image forming apparatus, if an image has already been printed on the back side of a transfer sheet on which an image is to be formed in the single-sided printing mode, the transfer sheet may be wound around the pressure roller.
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an image forming apparatus in which a transfer sheet having an image printed on a back surface does not wind around a pressure roller.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a heating roller heated by a heater, and a pressure roller for pressing a transfer sheet against the heating roller, and holding the transfer sheet between the rollers. In addition, in an image forming apparatus provided with a fixing device for fixing a toner image to transfer paper by sending it out while heating, the image forming device is disposed at a position upstream of the fixing device on the transfer paper transport path, and the image has been printed on the back surface of the transfer paper. Image density detecting means for detecting whether or not there is, a first separating claw abutting on the outer peripheral surface of the heating roller constituting the fixing device, a second separating claw capable of abutting on and separating from the outer peripheral surface of the pressure roller, And a control unit for operating the contact / separation mechanism based on detection information from the image density detection unit, wherein the control unit operates the contact / separation mechanism based on detection information from the image density detection unit. Detection information from detection means The control section when it is determined that the image on the transfer sheet back surface is printed, characterized in that constitute the second separation claw so as to abut against the pressure roller by.
According to a second aspect of the present invention, in the first aspect, the control unit is configured to control the second separation claw only when the leading end of the transfer paper having an image printed on the back surface detected by the image density detection unit passes through the fixing device. The contact / separation mechanism is controlled so that the contact member comes into contact with the outer peripheral surface of the pressure roller.
According to a third aspect of the present invention, in the first aspect, the control unit measures a time during which an image printed portion on the back surface of the transfer paper is detected by the image density detecting unit, and satisfies the set condition. In some cases, the contact / separation mechanism is controlled so that the second separation claw contacts the outer peripheral surface of the pressure roller.
According to a fourth aspect of the present invention, in the first aspect, the control unit measures a time during which the image-printed portion on the back surface of the transfer paper is detected by the image density detection means and an image density on the back surface of the transfer paper. When the image density satisfies the set condition, the contact / separation mechanism is controlled such that the second separation claw contacts the outer peripheral surface of the pressure roller.
[0005]
According to the first aspect of the present invention, when it is detected by the image density detecting means that the image has already been printed on the back surface of the transfer paper, the second separation claw is brought into contact with the outer peripheral surface of the pressure roller to apply the pressure. The transfer paper is prevented from winding around the pressure roller, and the transfer paper is separated.
In the invention according to claim 2, when the image density detecting unit detects that the image has already been printed on the back surface of the transfer paper, the image forming apparatus performs the second process only when the leading end of the transfer paper passes through the fixing device. The wear of the pressure roller is suppressed by bringing the two separation claws into contact with the outer peripheral surface of the pressure roller.
According to the third aspect of the present invention, the area of the image printed portion is estimated from the detection time of the image printed portion on the back surface of the transfer paper measured by the image density detecting means, and when the set condition is satisfied, the second separation is performed. The claw is brought into contact with the outer peripheral surface of the pressure roller to suppress the wear of the pressure roller.
In the invention described in claim 4, the detection time of the image-printed portion on the back surface of the transfer paper measured by the image density detecting means, and when the image density satisfies the set conditions, the second separation claw is pressed by the pressing roller. The abrasion of the pressure roller is suppressed by contacting the outer peripheral surface.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The structure of a printer incorporating an example of the image forming apparatus of the present invention will be described with reference to FIG.
The transfer paper 1 stored in the printer is sent out one sheet at a time, and the toner is placed on the transfer paper 1 by the toner transfer unit 2 of the in-apparatus image forming process. Will be established. The arrow in FIG. 1 indicates the transfer path of the transfer paper 1.
The image forming apparatus includes an image density detecting unit 3 such as a photo sensor for checking whether or not an image has been printed on the back surface of the transfer sheet 1. The position of the image density detecting means 3 may be anywhere on the transport path of the transfer paper 1 as long as it is upstream of the fixing device 4. In addition, a control unit (not shown) operates a second separation claw contact / separation mechanism described later based on the detection information from the image density detection unit 3.
As shown in FIG. 2, the fixing device 4 includes a heating roller 4a heated by a heater, and a pressure roller 4b for pressing the transfer paper 1 on which the toner is loaded against the heating roller 4a and fixing the toner to the transfer paper 1. Have. The heating roller 4a and the pressure roller 4b may be any rotating body that can send out the transfer paper 1, and for example, a belt or the like may be used.
The fixing device 4 includes a first separating claw 4c whose tip always contacts the outer peripheral surface of the heating roller 4a by an urging mechanism formed of a spring, and a second separating claw that can selectively contact the outer peripheral surface of the pressure roller 4b. A claw 4d is provided. The second separating claw 4d is brought into contact with the outer peripheral surface of the pressure roller 4b by a contact / separation mechanism formed of a spring or a cam, or in a state in which the distal end is separated from the outer peripheral surface of the pressure roller 4b. The position is set alternatively. The contact / separation mechanism uses, for example, a driving force from a solenoid or a motor as a drive source, and the control unit controls the drive source, the clutch, and the like to operate the contact / separation mechanism.
Further, when the image density detecting unit 3 detects that the image has been printed on the back surface of the transfer paper 1, the contact / separation mechanism operates under the control of the control unit to move the position of the second separation claw 4 d. The pressure roller 4b is configured to be switched so that the leading end thereof contacts the outer peripheral surface of the pressure roller 4b.
Thereby, mutual adhesion between the toner placed on the transfer paper 1 and the outer peripheral surface of the heating roller 4a is prevented by the first separation claw 4c, and the transfer paper 1 is prevented from being wound around the heating roller 4a.
[0007]
When an image is not detected on the back surface of the transfer paper 1 by the image density detecting means 3, the contact / separation mechanism moves the position of the second separation claw 4d so as to separate the leading end of the second separation claw 4d from the outer peripheral surface of the pressure roller 4b. Switching is performed, and a gap D is formed between the tip of the second separation claw 4d and the outer peripheral surface of the pressure roller 4b (see FIG. 3A).
That is, when the transfer paper 1 on which the image is not printed on the back surface is sent out, the second separation claw 4d does not abut on the pressure roller 4b, and wear (surface deterioration) of the pressure roller 4b can be prevented.
When the image density detecting means 3 detects that the image has been printed on the back surface of the transfer paper 1, the contact is made so that the tip of the second separation claw 4 d comes into contact with the outer peripheral surface of the pressure roller 4 b. The separation mechanism switches the position of the second separation claw 4d (see FIG. 3 (2)).
Thereby, mutual adhesion between toner forming an image on the back surface of the transfer sheet 1 and the outer peripheral surface of the pressure roller 4b is prevented by the second separation claw 4d, and the transfer sheet 1 can be prevented from winding around the pressure roller 4b. .
The above operation is performed according to steps S1 to S8 shown in the flowchart of FIG. That is, from the print standby state, printing is started after designating the number of sheets to be passed (S1, 2), and if the control unit determines from the detection information from the image density detecting means 3 that the back side image is present, The two separation claws are brought into contact with the surface of the pressure roller (S3, 4). When the transfer paper passes through the fixing unit, it is prevented from adhering to the pressure roller (S5). After the printing is completed or reset, the second separation claw is separated from the pressure roller, and the printing is completed (S6, 7, 8).
[0008]
Further, when the leading end of the transfer paper 1 passes through the fixing device 4, the leading end of the second separation claw 4d is quickly separated from the outer peripheral surface of the pressure roller 4b, so that the second separation claw 4d and the outer periphery of the pressure roller 4b are separated. If the function of the contact / separation mechanism is set such that a gap D is formed between the pressure roller and the surface, wear of the pressure roller 4b can be more effectively prevented (see FIG. 3 (3)).
The phenomenon that the transfer paper 1 on which the image is printed on the back surface winds around the pressure roller 4b occurs as the area of the image portion increases.
Therefore, the time during which the image printed portion on the back surface of the transfer paper 1 is detected by the image density detecting means 3 is measured, and when the measured time satisfies the set condition, the second separating claw 4d is pressed by the pressing roller 4b. If it is configured to contact the outer peripheral surface, it is possible to more effectively prevent the abrasion of the pressure roller 4b while preventing the transfer paper 1 from winding.
When the transfer paper 1 on which the image is printed on the back surface is used, if the area of the image portion on the back surface is small or the image density is low, the transfer paper 1 hardly wraps around the pressure roller 4b.
Then, the time during which the image printed portion of the back side of the transfer paper 1 is detected by the image density detection means 3 and the image density of the back side of the transfer paper 1 are measured, and when the measurement time and the image density satisfy the set conditions, If the second separation claw 4d is configured to contact the outer peripheral surface of the pressure roller 4b, the user can freely set the contact and separation of the second separation claw 4d.
It should be noted that the image forming apparatus of the present invention is not limited to the above-described embodiment, and it goes without saying that changes can be made without departing from the spirit of the present invention.
[0009]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, the following excellent effects can be obtained.
(1) According to the first aspect of the invention, when the image density detecting unit detects that the image has already been printed on the back surface of the transfer paper, the second separation claw contacts the outer peripheral surface of the pressure roller. Therefore, it is possible to prevent the transfer paper from being wound around the pressure roller.
(2) In the invention according to the second aspect, when the image density detecting means detects that an image has already been printed on the back surface of the transfer sheet, only when the leading end of the transfer sheet passes through the fixing device. In addition, since the second separation claw is brought into contact with the outer peripheral surface of the pressure roller, wear of the pressure roller can be suppressed.
(3) In the invention according to claim 3, the area of the image printed portion is estimated from the detection time of the image printed portion on the back surface of the transfer paper measured by the image density detecting means, and when the set condition is satisfied, Since the second separation claw is brought into contact with the outer peripheral surface of the pressure roller, wear of the pressure roller can be effectively suppressed.
(4) In the invention according to claim 4, when the detection time of the image printed portion on the back surface of the transfer paper measured by the image density detection means and the image density satisfy the set conditions, the second separation claw is released. Since the pressure roller is brought into contact with the outer peripheral surface, the wear of the pressure roller can be effectively suppressed, and the user can freely set the contact / separation of the second separation claw.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing a printer in which an example of an image forming apparatus of the present invention is incorporated.
FIG. 2 is a conceptual diagram showing a structure of a fixing device and a position of an image density detecting unit in FIG.
FIG. 3 is a conceptual diagram showing an operation of a second separation claw in FIG. 2;
FIG. 4 is a flowchart showing operation steps of a second separation claw in FIGS. 2 and 3;
[Explanation of symbols]
REFERENCE SIGNS LIST 1 transfer paper 3 image density detecting means 4 fixing device 4a heating roller 4b pressure roller 4c first separation claw 4d second separation claw

Claims (4)

It has a heating roller that is heated by a heater and a pressure roller that presses the transfer paper against the heating roller. The transfer paper is fixed between the two rollers, and the toner image is fixed on the transfer paper by being sent out while heating. An image forming apparatus having a fixing device for causing
An image density detecting unit that is disposed at a position upstream of the fixing device on the transfer paper transport path and detects whether an image has been printed on the back surface of the transfer paper,
A first separating claw that contacts the outer peripheral surface of the heating roller that constitutes the fixing device, a second separating claw that can contact and detachably contact the outer peripheral surface of the pressure roller, and the second separating claw that contacts the outer peripheral surface of the pressing roller. A contact / separation mechanism for contacting / separating,
A control unit that operates the contact / separation mechanism based on detection information from the image density detection unit,
The control unit activates the contact / separation unit to apply the second separation claw when the control unit determines from the detection information from the image density detection unit that the image has been printed on the back surface of the transfer paper. An image forming apparatus which is brought into contact with a pressure roller. The control unit controls the contact so that the second separation claw contacts the outer peripheral surface of the pressure roller only when the leading end of the transfer paper having the image printed on the back surface detected by the image density detecting unit passes through the fixing device. The image forming apparatus according to claim 1, wherein the image forming apparatus controls a separation mechanism. The control unit measures the time during which the image printed portion on the back side of the transfer paper is detected by the image density detecting unit, and when the measured time satisfies the set condition, the second separation claw causes the outer periphery of the pressure roller to The image forming apparatus according to claim 1, wherein the contact / separation mechanism is controlled so as to contact the surface. The control unit measures the time during which the image printed portion on the back side of the transfer paper is detected by the image density detection unit and the image density on the back side of the transfer paper, and when the measurement time and the image density satisfy the set conditions. The image forming apparatus according to claim 1, wherein the contact / separation mechanism is controlled such that the second separation claw contacts the outer peripheral surface of the pressure roller.

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