JP3832128B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine, and more particularly to an improvement of an image forming apparatus that prevents an image transferred from an image carrier such as a photoconductor to a sheet.
[0002]
[Prior art]
In general, in an image forming apparatus such as a printer, a facsimile, or a copying machine using an electrophotographic method, a toner is attached to and visualized on an electrostatic latent image formed on a photoconductor as an image carrier, and then the visualized toner is displayed. The image is transferred onto a sheet by transfer means.
[0003]
When the toner image is transferred from the photoconductor to the paper by the transfer means described above, the image (particularly character) portion formed in particular with fine lines is not transferred to the paper but remains on the photoconductor, resulting in a void phenomenon in the image. There is.
[0004]
FIG. 9 shows a state in which fine lines are formed on the photoreceptor 1. Since the toner image 2 is formed with a narrow width S, the area in contact with the paper is reduced. For this reason, when the paper 3 is pressed against the toner image by the force F through the transfer means, the pressure received by the fine toner image 2 increases. Since the central portion of the toner image 2 is formed with few flat portions, the pressure is much higher and the toner image 2 is not transferred to the paper 3 side while being pressed against the photoconductor 1 side. The above process is considered to be a cause of image dropout.
[0005]
On the other hand, FIG. 10 shows a state in which a thick line is formed on the photoreceptor 1. Since the toner image 4 is formed with a large width S, the area in contact with the paper is increased. For this reason, even if the sheet 3 is pressed by the force F through the transfer means, the force F is dispersed and the hollow toner image 4 is less likely to be lost.
[0006]
In order to reduce the occurrence of the above-described thin line image void as much as possible, slip transfer is conventionally performed by providing a speed difference between the peripheral speed of the photoreceptor and the conveyance speed of the conveyed paper. .
[0007]
In order to realize this, for example, the following method is taken. Referring to FIG. 11, when the VP transport speed is given to the paper 3 by the peripheral speed VR of the pair of registration rollers 10 which are paper transport rollers for transporting the paper (VP and VR are substantially the same), the circumference of the photoreceptor 1 is shown. The speed VD is set several percent slower than the peripheral speed VR of the registration roller 10. Further, the peripheral speed VB of the transfer means 11 that contacts the peripheral surface of the photosensitive member 1 is set to be faster (VB> VR) than the peripheral speed VR of the registration roller 10.
[0008]
As described above, when VB> VR, VP (VP and VR are substantially the same)> VD and transfer processing is performed, a shearing force is applied to the toner image 2 shown in FIG. It will be. As a result, the occurrence of voids in the image is reduced as much as possible.
[0009]
As a recent trend, in order to reduce the installation space, it is desired to reduce the size of the apparatus, and there are many attempts to achieve this by forming a curved sheet conveyance path.
[0010]
FIG. 12 is an enlarged conceptual view of a main part of the image forming apparatus in which the paper conveyance path 12 is formed in a curved shape.
[0011]
In FIG. 12, reference numeral 13 denotes a charging roller, 14 denotes a developing roller, P denotes a point where the photosensitive member 1 and the transfer roller 11 serving as transfer means come into contact, that is, a nip point, and 15 denotes a nip point P. Nip tangent.
[0012]
As shown in FIG. 12, when a curved sheet conveyance path 12 including a registration roller 10 that is a sheet conveyance roller that conveys a sheet to the nip point P and sheet guides 12a and 12b is formed, the sheet that conveys the sheet to the nip point P is formed. The registration roller 10 serving as a conveyance roller is positioned on the transfer roller 11 side with the nip tangent line 15 as a boundary.
[0013]
In this case, the sheet 3 that has passed through the registration roller 10 is conveyed while being in sliding contact with one of the pair of sheet guides 12 a and 12 b that constitute the curved sheet conveying path 12.
[0014]
Therefore, the sheet conveyance speed VP ′ is smaller than the sheet conveyance speed VP shown in FIG. 11 (VP ′ <VP). However, when thin paper is used as the sheet 2, the decrease in the speed is negligible, so that the void is worsened. Never do. However, when a thick paper such as a postcard is used as the paper 3, this speed reduction cannot be ignored, and becomes remarkable especially after the paper passes through the registration roller. For this reason, there is no difference in speed between the peripheral speed VD of the photosensitive member 1 and the transport speed VP ′ of the transported paper, and the probability of occurrence of a void in the image is further increased when thick paper such as a postcard is used.
[0015]
As described above, a speed difference is provided between the peripheral speed VD of the photosensitive member 1 and the transport speed VP of the paper 3 in order to prevent the occurrence of a void in the image. Therefore, it is considered that the speed difference between the peripheral speed VD of the photosensitive member 1 and the transport speed VP of the paper 3 should be set larger. However, if the speed difference between VD and VP is set larger, toner scattering at the nip point P where the transfer roller 11 abuts on the photoreceptor 1 will increase. When the amount of toner scattering increases, a so-called rough feeling is produced in the halftone of the transferred image, which causes a significant deterioration in the quality of the transferred image. Therefore, it is not desirable to set a large speed difference between VD and VP.
[0016]
Also, as shown in FIG. 12, when thin paper is used as the paper 3, in order to prevent so-called gap transfer at the nip point P, the front end of the paper 3 starts from the nip tangent 15 and the nip point P from the photoreceptor side 1 side. In order to enter, the leading end 12b 'of one paper guide 12b, that is, the portion adjacent to the image carrier 1 and the transfer roller 11 is protruded toward the photoconductor side 1 with the nip tangent line 15 as a boundary.
[0017]
When such a paper guide 12b is used, particularly when a thick thick paper is used as the paper 3, if the paper 3 enters the nip point P from the front end 12b 'of the paper guide 12b, the strength of the paper 3 Thus, the repulsive force acts strongly on the photosensitive member 1 side, whereby the force F shown in FIG.
[0018]
In order to prevent image dropout when using thick paper, the tip 12b 'of one paper guide 12b constituting the paper transport path 12 described above is set on the transfer roller 11 side with the nip tangent line 15 as a boundary. Although it is good, image disturbance due to gap transfer occurs when thin paper is used as described above.
[0019]
Therefore, in order to prevent gap transfer when thin paper is used as paper and to prevent occurrence of image hollowing when using thick paper, conventionally, as disclosed in JP-A-9-240880, There is a type in which a guide for guiding a sheet to a transfer unit before transfer is movable, and the shape of the sheet conveyance path is changed depending on whether a thick sheet is guided as a sheet or a thin sheet is guided. Further, as disclosed in Japanese Patent Application Laid-Open No. 6-118803, a static eliminating member is disposed in a notch-corresponding portion of the pre-transfer guide, thereby preventing gap transfer as much as possible when using thin paper. There is something.
[0020]
[Problems to be solved by the invention]
However, in the above-mentioned Japanese Patent Application Laid-Open No. 9-240880, the guide for guiding the paper to the transfer unit before transfer, that is, the pre-transfer guide is made movable so that the number of parts is large, and its movement control is performed. However, even if it is disclosed in Japanese Patent Application Laid-Open No. 6-118803, a static eliminating member is provided in a portion corresponding to a notch in the pre-transfer guide. This also has a problem that causes a cost increase such as an increase in the number of parts.
[0021]
In view of the above-described circumstances, the present invention is capable of generating a void in an image when using thick paper as a paper with a simple structure without increasing the number of parts, and generating gap transfer as much as possible when using thin paper. It is an object of the present invention to provide an image forming apparatus that prevents the above-mentioned problems.
[0022]
[Means for Solving the Problems]
In order to solve the above-described problems, according to the present invention, an image carrier that holds a toner image, a transfer unit that forms a nip point in contact with the image carrier, and a paper conveyance that conveys the paper to the nip point. In an image forming apparatus having at least a roller and a sheet guide for guiding a sheet from the sheet conveying roller to the nip point, VR is a peripheral speed of the sheet conveying roller and VD is a peripheral speed of the image carrier. > VD is set so as to satisfy the relationship of VD, and the sheet conveying roller is positioned on the transfer unit side with a nip tangent passing through the nip point as a boundary, and the image carrier and the transfer unit of the sheet guide A notch portion located on the transfer means side is formed at a part of a portion adjacent to the nip tangent passing through the nip point, and located on the transfer means side with the nip tangent as a boundary. Except Riketsu portion, a portion adjacent to the transfer means and the image bearing member of said paper guide is located on the image bearing member to the boundary of the nip tangent, located on the image bearing member to the boundary of the nip tangent The sheet passing through the sheet guide portion is caused to enter the nip point from the image carrier side with the nip tangent as a boundary, and the transfer means with the sheet passing through the notch portion of the sheet guide as the boundary. is characterized in Rukoto made to enter from the side to the nip point.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described in detail.
[0024]
FIG. 1 is a conceptual diagram of a main part of an image forming apparatus 20 according to the present invention, and the same parts as those in FIG.
[0025]
Also in this image forming apparatus 20, slip transfer is performed by providing a speed difference between the peripheral speed VD of the photosensitive member 1 and the transport speed VP of the transported paper, thereby preventing the occurrence of image void as much as possible. Therefore, the peripheral speed of the registration roller 10 which is a paper transport roller for transporting the paper to the nip point P is VR, the paper transport speed (not shown) is VP, the peripheral speed of the photosensitive member 1 is VD, and the peripheral speed of the transfer roller 11 is VB. In this case, VB> VR, VP (VP and VR are substantially the same when running on thin paper)> VD.
[0026]
On the other hand, in the image forming apparatus 20 of the present invention, of the pair of sheet guides 12a and 12b constituting the sheet conveyance path 12 that guides the sheet from the registration roller 10 to the nip point P, the photosensitive member 1 that is an image carrier and the transfer roller. 11, a sheet guide 12 b adjacent to the nip tangent line 15 passing through the nip point P, and a notch recess 30, which is a notch, is provided on the transfer roller 11 side. Forming. Further, a portion 12b ′ adjacent to the photosensitive member 1 and the transfer roller 11 in the sheet guide 12b except for a portion (notch recess 30) positioned on the transfer roller 11 side with the nip tangent line 15 as a boundary. It is located on the image carrier 1 side with the nip line 15 as a boundary. A part of the guide surface (surface for guiding paper) 30a of the notch recess 30 described above passes through the nip point P, and the photosensitive member 1 is bounded by a straight line 40 that intersects the nip tangent line 15 at an angle θ = 5 degrees. It is formed to be on the side.
[0027]
Further, the width of the cutout recess 30, that is, the width along the axial center direction of the photoreceptor 1 is set slightly larger than the width of the standard postcard.
[0028]
2 is a conceptual perspective view of a principal portion of the paper conveying path 12 showing the above-described cutout recess 30 in detail, and the same parts as those in FIG.
[0029]
Next, the operation of the image forming apparatus 20 described above will be described.
[0030]
First, when a sheet 3 having a width wider than the postcard width is used as the sheet 3 to be used, the sheet 3 conveyed from the registration roller 10 is a pair of sheet guides 12a constituting the sheet conveying path 12 as shown in FIG. , 12b, and finally enters the nip point P from the leading end 12b 'of the sheet guide 12b protruding beyond the notch recess 30 and projecting toward the photoreceptor side 1 with the nip tangent line 15 as a boundary.
[0031]
For this reason, when thin paper is used as the paper 3, the so-called gap transfer is prevented since the nip tangent line 15 enters the nip point P from the photoconductor side 1 side over the entire length of the paper 3. Become.
[0032]
On the other hand, when a postcard which is a thick paper is used as the paper 3, the paper 3 is nipped along the guide surface 30a of the notch recess 30 formed in one paper guide 12b as shown in FIG. It enters the nip point P from the transfer roller 11 side with the tangent line 15 as a boundary.
[0033]
In this case, the sheet 3 does not enter the nip point P from the photosensitive member 1 side at the nip tangent line 15 due to the notch recess 30, and the nip point from the transfer roller 11 side at the nip tangent line 15 as described above. Since it penetrates P, the curved deformation of the paper 3 which is a thick paper is less than the case where it penetrates from the photosensitive member 1 side with the nip tangent line 15 as a boundary, and therefore the repulsive force of the paper 3 due to the curved deformation is reduced. Since the force with which the sheet 3 presses the photoreceptor 1 is also reduced, the occurrence of image voids is reduced as much as possible.
[0034]
When the angle θ of the straight line 40 intersecting with the nip tangent line 15 shown in FIG. 1 is changed, the experimental results shown in the graph of FIG. 5 were obtained with respect to the image dropout generated on the thick paper and the image disturbance generated on the thin paper.
[0035]
In this graph, the vertical axis on the left indicates the degree of occurrence of image dropout due to the thick paper 3. G0 indicates a level at which no omission occurs in the image, G1 indicates a level where there is an omission in the image but no problem in practical use, and G4 indicates a level at which only the outline is transferred because most of the center of the character is lost. The right vertical axis indicates the degree of occurrence of image disturbance when thin paper is used as the paper 3. G0 is not generated, G1 is a level at which there is no practical problem, and G4 is a level at which general users feel uncomfortable. In the graph of FIG. 5, the horizontal axis represents the angle θ at which the nip tangent line 15 and the straight line 40 shown in FIG. 1 intersect.
[0036]
As is apparent from the experimental results shown in the graph of FIG. 5, the range in which the occurrence of image hollowing and the occurrence of image disturbance are compatible with each other without any practical problem is the hatched portion, that is, the angle at which the nip tangent 15 and the straight line 40 intersect. It was verified that θ should be within about 6 degrees.
[0037]
Further, in the image forming apparatus 20 of the present invention, the downstream end 30b of the guide surface 30a of the notch recess 30 is connected to the nip tangent 15 as in the other embodiment of FIG. May be moved closer to the transfer roller 11 side by d along a straight line 40 that intersects at an angle θ (in this case, angle θ = 5 degrees).
[0038]
FIG. 7 is a conceptual perspective view of a principal part fracture of the sheet conveying path 12 showing in detail the notch recess 30 in which the downstream end 30b of the guide surface 30a is made closer to the transfer roller 11 side by d. The same parts as those in FIG. 6 are denoted by the same reference numerals.
[0039]
As described above, when the downstream end 30b of the guide surface 30a of the notch recess 30 is formed so as to approach the transfer roller 11 side along the straight line 40 by d, the d is changed to change between thin paper and thick paper. When the relationship between the void in the image generated on each sheet 3 and the image disturbance was verified by experiments, the experimental results shown in the graph of FIG. 7 were obtained.
[0040]
In the graph, the vertical axis on the left indicates the degree of occurrence of image dropout due to the thick paper 3 as in FIG. G0 indicates a level at which no omission occurs in the image, G1 indicates a level where there is an omission in the image but no problem in practical use, and G4 indicates a level at which only the outline is transferred because most of the center of the character is lost. The right vertical axis shows the degree of image disturbance when thin paper is used as the paper 3. G0 is not generated, G1 is a level at which there is no practical problem, and G4 is a level at which general users feel uncomfortable.
[0041]
In the graph of FIG. 7, the horizontal axis represents a distance d (millimeter) that causes the downstream end 30 b of the guide surface 30 a of the notch recess 30 to approach the transfer roller 11.
[0042]
As is apparent from the graph shown in FIG. 7, when d is within about 1.4 mm, the void in the image generated on the thick paper is not deteriorated, and the image disturbance generated on the thin paper is further reduced.
[0043]
The reason why such a phenomenon occurs is that when a thin paper sheet is conveyed, the amount of slack that occurs in the center of the thin paper is regulated to the vicinity of the nip point P by the guide surface downstream end 30b that is extended by the distance d. This is probably because it is difficult to enter the gap transfer region.
[0044]
【The invention's effect】
According to the present invention, an image carrier that holds a toner image, a transfer unit that abuts on the image carrier to form a nip point, a paper conveyance roller that conveys paper to the nip point, and a paper conveyance roller In an image forming apparatus having at least a paper guide for guiding paper to the nip point, the relationship VR> VD is satisfied, where VR is the peripheral speed of the paper transport roller and VD is the peripheral speed of the image carrier. And the paper transport roller is positioned on the transfer means side with a nip tangent passing through the nip point as a boundary, and a part of the paper guide adjacent to the image carrier and the transfer means. Forming a notch portion positioned on the transfer means side with a nip tangent passing through the nip point as a boundary, and excluding the notch portion positioned on the transfer means side with the nip tangent as a boundary. A portion adjacent to the transfer means and the image bearing member is positioned on the image bearing member to the boundary of the nip tangent of de, passes through portions of the paper guide positioned in the image bearing member to the boundary of the nip tangent The sheet to be moved enters the nip point from the image carrier side with the nip tangent as a boundary, and the sheet passing through the notch portion of the sheet guide enters the nip point from the transfer means side with the nip tangent as a boundary. because the the, when the sheet waist strong cardboard is transported, cardboard reduces the bending deformation of the cardboard can be reduced as much as possible the pressure acting on the image bearing member, thereby nipping tangential sheet conveyance roller Even if it is positioned on the transfer means side with respect to the boundary, it is possible to reduce the void in the image generated on the cardboard as much as possible.
As described above, a simple shape change prevents as much as possible image gaps when using thick paper and gap transfer when using thin paper, and provides a small image forming device with high image quality at a very low cost. can do.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a main part of an image forming apparatus according to the present invention.
FIG. 2 is a conceptual fragmentary perspective view showing a notch portion.
FIG. 3 is a conceptual diagram showing the main part of the operation of the image forming apparatus according to the present invention.
FIG. 4 is a conceptual diagram showing the main part of the operation of the image forming apparatus according to the present invention.
FIG. 5 is an experimental graph that verifies the extent of gap transfer and image void when the angle of a straight line intersecting the nip tangent is changed.
FIG. 6 is a conceptual diagram showing the main part of another embodiment of the image forming apparatus according to the present invention.
FIG. 7 is a conceptual fragmentary perspective view showing a notch portion.
FIG. 8 is an experimental graph that verifies the extent of gap transfer and the occurrence of image dropout when the distance at which the downstream end of the notch recess approaches the transfer means side is changed.
FIG. 9 is a view showing the principle of occurrence of a void in an image.
FIG. 10 is a view showing the principle of occurrence of a void in an image.
FIG. 11 is a conceptual diagram showing slip transfer.
FIG. 12 is a conceptual diagram of a main part of an image forming apparatus in which a horizontal distance between a registration roller and a photoconductor is set short.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image carrier 3 ... Paper 10 ... Paper conveyance roller (registration roller)
11. Transfer means (transfer roller)
12a, 12b ... paper guide 12b '... a part adjacent to the image carrier and the transfer means excluding a part located on the transfer means side with the nip tangent as a boundary 15 ... a nip tangent 20 ... an image forming apparatus 30 ... a notch (notch) Notch)
30b ... downstream end 40 ... straight line P passing through the nip point and intersecting the nip tangent line ... the nip point

Claims (6)

An image carrier for holding a toner image;
Transfer means for forming a nip point in contact with the image carrier;
A paper transport roller for transporting the paper to the nip point;
In an image forming apparatus having at least a paper guide for guiding paper from the paper transport roller to the nip point,
When the peripheral speed of the paper conveying roller is VR and the peripheral speed of the image carrier is VD, the relation VR> VD is satisfied.
The paper conveying roller is positioned on the transfer means side with a nip tangent passing through the nip point as a boundary,
Forming a notch portion on the transfer means side of a part of the paper guide adjacent to the image carrier and the transfer means, with a nip tangent passing through the nip point as a boundary;
Except for the notch portion located on the transfer means side with the nip tangent as a boundary, the portion of the paper guide adjacent to the image carrier and the transfer means is located on the image carrier side with the nip tangent as a boundary. ,
A sheet passing through the portion of the sheet guide located on the image carrier side with the nip tangent as a boundary, and entering the nip point from the image carrier side with the nip tangent as a boundary;
The image forming apparatus , wherein a sheet passing through the notch portion of the sheet guide is caused to enter the nip point from the transfer unit side with the nip tangent as a boundary . The transfer means is rotationally driven,
If the peripheral speed of the transfer means is VB,
The image forming apparatus according to claim 1, wherein a relationship of VB>VR> VD is satisfied. In the notch portion located on the transfer means side with a nip tangent passing through the nip point in the paper guide as a boundary, the image passing through the nip point and intersecting the nip tangent has an angle of about 5 degrees as a boundary. The image forming apparatus according to claim 1, further comprising a portion positioned on the carrier side.   A notch portion positioned on the transfer unit side with a nip tangent passing through the nip point in the paper guide has a width slightly larger than a postcard width along the axial direction of the image carrier. The image forming apparatus according to claim 1.   The downstream end of the cutout portion positioned on the transfer unit side with a nip tangent passing through the nip point in the paper guide as a boundary has a portion that is closer to the transfer unit side than other portions. The image forming apparatus according to claim 1.   A downstream end of a notch portion located on the transfer means side with a nip tangent passing through the nip point in the paper guide as a boundary, has a portion that is closer to the transfer means side than other portions; and The image forming apparatus according to claim 1, wherein the portion approaching the transfer unit has a width slightly larger than a postcard width along the axial direction of the image carrier.

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