JP3994043B2 - Image forming apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer, and more particularly to a technology for conveying stability from when an image is transferred to a recording medium until it is fixed.
[0002]
[Prior art]
FIG. 8 is a diagram illustrating an example of an image forming apparatus.
In the figure, reference numeral 1 denotes a photosensitive drum, 2 denotes a charging roller, 3 denotes an exposure device, 4 denotes a developing device, 5 denotes a paper feed tray, 6 denotes a registration roller, 7 denotes a transfer roller, 8 denotes a conveyance guide plate, and 9 denotes fixing. Reference numerals 10 and 10 denote discharge trays.
The photosensitive drum 1 whose surface is uniformly charged by the charging roller 2 is subjected to exposure modulated by image information from the exposure device 3, and an electrostatic latent image corresponding to the image is formed on the surface of the photosensitive drum 1. Formed. The electrostatic latent image is visualized by the developing device 4 and becomes a toner image. A recording medium S such as paper or an OHP sheet is sent out from the paper feed tray 5, temporarily stopped by the registration roller 6, and further sent out in time with the photosensitive drum-like toner image.
[0003]
A transfer roller 7 to which a predetermined transfer bias is applied is pressed against the photosensitive drum 1 in a timely manner to form a transfer nip. The recording medium S sent from the registration roller 6 passes through the transfer nip, whereby the toner image is transferred from the photosensitive drum 1 to the recording medium S, and sent to the fixing device 9 along the conveyance guide plate 8. The toner image on the recording medium S is fixed as a permanent image on the recording medium S by heat or other means.
[0004]
Normally, when transferring the toner image, control is performed so that a predetermined current flows through the transfer roller 7, and this current flows from the transfer roller shaft to the transfer roller portion, passes through the recording medium S, and passes through the photosensitive drum 1. It is flowing. The resistance value of the transfer roller portion changes significantly due to environmental fluctuations such as temperature. In particular, at low temperatures, the resistance of the transfer roller portion is several tens of times higher than that at normal temperature. For this reason, a high potential may be applied to the recording medium S.
[0005]
Further, the current flowing through the transfer roller 7 can be more stably transferred depending on the type of the recording medium S, and the toner image on the photosensitive drum 1 can be transferred. This is because when the thickness of the recording medium S increases, the toner image on the photosensitive drum 1 is not easily transferred to the recording medium S unless the transfer current is increased, and a transfer material such as OHP needs to be applied with a higher potential. . Further, when the width of the recording medium S is reduced, a portion where the transfer roller 7 is in direct contact with the photosensitive drum 1 is increased. In order to transfer the image to the medium S, it is necessary to increase the value of the current flowing through the transfer roller 7, so that the charge amount of the recording medium S increases.
[0006]
Originally, since the recording medium S is transported along the transport guide plate 8, when the recording medium S is transported in a charged state from a low potential to a high potential in this way, the recording medium S is transferred to the transport guide plate 8. In some cases, the recording medium S may be transported without being touched, and the upper surface of the recording medium S may come into contact with a guide or the like. Therefore, a grounded conductive member is arranged as an electrostatic suction member in the vicinity of the conveyance path of the recording medium S, and the recording medium S is attracted to the conveyance guide plate 8 and conveyed (for example, , See Patent Document 1).
[0007]
When the recording medium S is charged at a low potential, the recording medium S cannot be moved along the transport guide plate 8 unless the suction member is brought close to the recording medium S. In the case of a high potential, if the suction member is too close, the charge charged on the transfer paper is discharged to the conductive member all at once, and the toner on the recording medium S is scattered by this discharge, which may disturb the image. is there. As a configuration that eliminates such problems and improves the conveyance stability of the recording medium, a method is known in which the suction force of the suction member varies depending on the location along the conveyance direction of the recording medium S (for example, patents). Reference 2).
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-199592 (Claim 1, FIG. 3)
[Patent Document 1]
JP-A-8-96325 (Claim 1, FIG. 1)
[0009]
[Problems to be solved by the invention]
The present invention provides a new configuration that ensures conveyance stability that does not cause image distortion when a recording medium is conveyed along the conveyance guide plate side even if environmental conditions and conditions of the recording medium to be used change. The purpose is to do.
[0010]
[Means for Solving the Problems]
According to the first aspect of the present invention, in the image forming apparatus having a transfer unit, a fixing unit, and a guide member that guides the recording medium onto which the toner image has been transferred by the transfer unit to the fixing unit, A conductive suction member that is grounded and electrostatically attracts the recording medium is disposed in the vicinity of the passage surface of the recording medium, and the upper surface of the suction member is lowered below the passage surface as the charge amount of the recording medium increases. A movable member is provided that changes the distance so that the distance in the direction of separation increases .
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the distance is changed so as to increase as the environmental temperature decreases .
[0011]
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, a bimetal is used as the movable member .
According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect, a shape memory alloy is used as the movable member .
According to a fifth aspect of the present invention, in the image forming apparatus according to the first or second aspect , a stepping motor is used as the movable member .
[0012]
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the distance is changed so as to increase as the thickness of the recording medium increases .
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the distance is changed so as to increase as the width of the recording medium decreases .
[0013]
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the distance is changed so as to increase as the environmental humidity decreases .
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the upper surface of the suction member is parallel to the passage surface.
According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the upper surface of the suction member is closer to the transfer unit side on the fixing device side than the passage surface. It is characterized by being farther away.
[0014]
【Example】
The present invention will be described below with reference to examples.
FIG. 1 is a perspective view of a unit including a conveyance guide portion of the present invention.
In the figure, reference numeral 11 denotes a suction member. Other reference numerals are the same as FIG.
In this unit, the lower registration roller 6, the transfer roller 7, and the conveyance guide plate 8 are integrated, but the registration roller 6 is not necessarily integrated.
The conveyance guide plate 8 includes a plurality of elongated plates that are connected to each other and are spaced from each other at substantially equal intervals, and the suction member 11 that is formed into a plurality of elongated plates does not contact the gaps. It is integrally supported by the movable member so that it can be moved up and down with a margin.
[0015]
FIG. 2 is a cross-sectional view of the substrate portion including the conveyance guide plate of the unit shown in FIG.
In the figure, reference numeral 12 denotes a bimetal as a movable member, and a denotes a distance from the upper surface of the conveyance guide plate 8 to the upper surface of the suction member 11. In addition, since there is no possibility of confusion, hatching of the cross section is omitted. The same applies to the following drawings.
Both ends of the suction member 11 are fixed to the conveyance guide plate 8 via bimetals 12 respectively. The suction member is made of a conductive material and is grounded to the image forming apparatus main body.
[0016]
FIG. 3 is a diagram showing a case where the environmental temperature is low in the configuration of FIG.
The upper surface of the suction member 11 is formed in parallel with the upper surface of the transport guide plate 8, and the distance a between the upper surfaces changes depending on the degree of bending corresponding to the environmental temperature of the two bimetals 12. When the environmental temperature is high, the value of a is set to approximately 0, and the upper surface of the suction member 11 and the upper surface of the transport guide plate 8 are set to be substantially flush with each other. When the environmental temperature is low, the value of a increases, and the upper surface of the suction member 11 becomes lower as shown in FIG.
[0017]
Therefore, when the environmental temperature is high and the charge amount of the recording medium S is not so large, the suction member 11 approaches the path of the recording medium S to increase the suction force, and conversely, the environmental temperature is low and the recording medium S When the charge amount is large, the suction member 11 is moved away from the path of the recording medium S, the suction force is appropriately reduced, and discharge from the recording medium S to the suction member 11 does not occur.
[0018]
2 and 3, a shape memory alloy can be used instead of the bimetal. Even if the shape memory alloy is deformed to some extent, it has a property of returning to a previously memorized shape when the temperature is raised and a specific transition temperature is reached. There are alloys whose shape no longer changes even when the temperature is lowered, and alloys that return to the shape before raising the temperature again when the temperature is lowered. If it is in the range of about the temperature change inside the image forming apparatus, it is possible to make a change similar to bimetal if the alloy transition temperature is properly selected.
[0019]
As described above, since the charge amount of the recording medium S varies depending on the type and size of the recording medium S, the distance between the suction member 11 and the recording medium S can be varied in accordance with this, thereby providing a better guide for the recording medium S. A method of carrying is shown below.
FIG. 4 is a block diagram showing the relationship of controlling the stepping motor according to environmental conditions and recording medium conditions.
In the figure, reference numeral 13 is a stepping motor, 14 is motor drive control means, ST is a temperature sensor, SH is a humidity sensor, and OP is an operation panel.
[0020]
The charge amount of the recording medium S is affected not only by the environmental temperature but also by the humidity. If the humidity is high, depending on the type of recording medium, the resistance value may decrease and the charge amount may decrease. Therefore, in addition to the temperature sensor ST, a sensor SH that detects humidity is also provided as an environmental condition. As the condition of the recording medium S, as described above, the width and size of the recording medium S are important. Means for the operator to specify and input these are provided on the operation panel OP, and the CPU that obtains the respective conditions issues necessary instructions to the motor drive control means 14 to drive the stepping motor 13. Even in the case of the above-described apparatus that only supports the environmental temperature, it is possible to use the stepping motor. In that case, only the temperature sensor ST may be used as a condition detection means.
[0021]
FIG. 5 is a diagram showing a configuration in which the value of the distance a is changed in consideration of environmental conditions and recording medium conditions.
FIG. 6 is a diagram showing a state when the value of the distance a is increased in the configuration shown in FIG.
In both figures, the code | symbol 15 shows a supporting member.
[0022]
The suction member 11 is supported by support members 15 at both ends, and is regulated so as to be movable in parallel up and down by a known mechanism (not shown). The stepping motor 13 has an eccentric shaft 13a at a position slightly away from the rotation shaft, and is slidably attached to an elongated hole 15a provided in a substantially central portion of the support member 15. The amount of eccentricity of the eccentric shaft 13a is set to one half or more of the maximum size required as the distance a.
[0023]
The motor drive control means 14 instructed by the CPU for the control amount rotates the stepping motor 13 and moves the suction member 11 up and down to the target position.
Thus, the suction member 11 can be moved closer to or away from the path of the recording medium S with respect to changes in environmental conditions and recording medium conditions, so that stable conveyance of the recording medium can be ensured. Become.
The configuration is substantially the same even when an eccentric cam is used instead of the eccentric shaft 13a and the elongated hole 15a and the support member 15 is brought into contact with the eccentric cam with a pressing force.
[0024]
The force for sucking the recording medium S of the suction member 11 does not need to be constant at all positions in the transport direction. As the recording medium S leaves the transfer nip, the resistance that the recording medium S receives from the conveyance guide plate 8 increases. In the case of a so-called low-waist recording medium, a phenomenon in which the vicinity of the leading end sticks to the conveyance guide plate 8 and does not move easily occurs. Therefore, the upper surface of the suction member may not be parallel to the passing surface of the recording medium S but may be inclined so that the distance on the fixing device side is larger than that on the transfer unit side. However, the vertical movement of the suction member is in principle a parallel movement.
FIG. 7 is a diagram showing a configuration in which the upper surface of the suction member is not parallel to the passage surface of the recording medium.
In the case of this configuration, the distance a between the upper surface of the suction member and the passage surface is the average value of the distances, in other words, the distance at the center of the upper surface of the suction member 11 in the length direction.
[0025]
【The invention's effect】
According to the present invention, in response to changes in environmental conditions, changes in the recording medium to be used, etc., the transferred recording medium can be fed into the fixing device while being transported with an appropriate suction force. Abnormalities such as toner image rubbing and toner scattering during conveyance can be eliminated. .
[Brief description of the drawings]
FIG. 1 is a perspective view of a unit including a conveyance guide unit according to the present invention.
2 is a cross-sectional view of a substrate portion including a conveyance guide plate of the unit shown in FIG.
FIG. 3 is a diagram showing a case where the environmental temperature is low in the configuration of FIG. 2;
FIG. 4 is a block diagram showing a relationship of controlling a stepping motor according to environmental conditions and recording medium conditions.
FIG. 5 is a diagram illustrating a configuration in which the value of distance a is changed in consideration of environmental conditions and recording medium conditions.
6 is a diagram showing a state when the value of distance a is increased in the configuration shown in FIG.
FIG. 7 is a diagram illustrating a configuration in which the upper surface of the suction member is not parallel to the passage surface of the recording medium.
FIG. 8 illustrates an example of an image forming apparatus.
[Explanation of symbols]
8 Transport guide plate 11 Suction member 12 Bimetal 13 Stepping motor 14 Motor drive control means

Claims (10)

In an image forming apparatus having a transfer unit, a fixing unit, and a guide member that guides a recording medium onto which a toner image has been transferred by the transfer unit to the fixing unit, the guide member in the vicinity of a passage surface of the recording medium In addition, a conductive suction member that is grounded and electrostatically attracts the recording medium is disposed, and as the charge amount of the recording medium increases, the distance in the direction in which the upper surface of the suction member separates downward from the passage surface increases. An image forming apparatus comprising a movable member that changes the distance as described above . 2. The image forming apparatus according to claim 1, wherein the distance is changed so as to increase as the environmental temperature decreases . The image forming apparatus according to claim 2, wherein a bimetal is used as the movable member . The image forming apparatus according to claim 2, wherein a shape memory alloy is used as the movable member . 3. The image forming apparatus according to claim 1, wherein a stepping motor is used as the movable member . 6. The image forming apparatus according to claim 1, wherein the distance is changed so as to increase as the thickness of the recording medium increases . 7. The image forming apparatus according to claim 1, wherein the distance is changed so as to increase as the width of the recording medium decreases . 8. The image forming apparatus according to claim 1 , wherein the distance is changed so as to increase as the environmental humidity decreases .   9. The image forming apparatus according to claim 1, wherein the upper surface of the suction member is parallel to the passage surface.   9. The image forming apparatus according to claim 1, wherein the upper surface of the suction member is separated from the passage surface on the fixing device side than on the transfer unit side. A featured image forming apparatus.

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