JPH09152758A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the carrying accuracy of a recording paper by making a transfer roller come close to an electrostatic latent image carrier together with a roller attaching frame so that a medium carrying level may come into contact with the carrier and guiding the attaching/detaching operation of the roller attaching frame to/from the carrier. SOLUTION: A horizontal link 35a for a link driving mechanism 35 is moved in a state where the paper carrying belt 1 is separated from the photoreceptor drum 3. Then, the roller attaching frame 32 is moved upward along a guide groove 33a cooperatively with the link driving mechanism 35, and when a guide projection 34 reaches the positioning end part 33C required at printing, the frame is not moved upward any more, and the roller attaching frame 32 is positioned. Thus, the paper carrying belt 1 comes into contact with the drum 3, then, a printing time state is obtained. And also, the shafts of the guide rollers 14 and 15 for the paper carrying belt 1 are fixed, and the transfer roller 9 is driven so as to bring the belt l into contact with the photoreceptor drum 3, then, the belt 1 is accurately brought into contact with the drum 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a laser printer, and more particularly to an image forming apparatus which conveys a transfer sheet by using a belt-like conveying means.

[0002]

2. Description of the Related Art As an image forming apparatus of this kind, for example, in a color laser printer, Japanese Patent Laid-Open No. 63-29607.
The one disclosed in Japanese Laid-Open Patent Publication No. 8-9 is known. In this color laser printer, as shown in FIG. 4, a sheet conveying belt 101, which is an endless belt-shaped medium conveying belt stretched inside the apparatus main body, has magenta (M), cyan (C),
A plurality of printing stations 1021 for yellow (Y), etc.
1023 are arranged continuously. Each of the printing stations 1021 to 1023 is an electrophotographic process mechanism including a photosensitive drum 103 as an electrostatic latent image holder, a charger 104 arranged around the photosensitive drum 103, an exposure device 105 having a laser diode, a developing device 106, and the like. Equipped with.

In such a color laser printer, the drive mechanism 107 of the paper transport belt 101 is conventionally divided into blocks, and the drive mechanism 10 of the paper transport belt 1 is used.
By moving the cam 7 up and down along the guide groove 109 by the cam 108, the respective printing stations 1021 to 102
It is structured so as to be brought into contact with and separated from the photosensitive drum 103 of No. 3.

Specifically, the drive mechanism 107 of the sheet conveying belt 101 has a pair of guide rollers 111 and 112 mounted on both ends of a support base 110, and the sheet conveying belts are attached to the guide rollers 111 and 112. It is configured by endlessly straddling 101, and a transfer device 113 is arranged at a position facing the photosensitive drum 103 of the printing stations 102 1 to 102 3 sandwiching the sheet conveying belt 101.

Below the support base 110, a pair of cams 108 are provided at both ends thereof, and the cam shaft 108a is formed by cutting out a guide groove 1 from the lower side of the support base 110.
It has been inserted in 09. The guide groove 109 includes a linear portion 109a that vertically guides the support base 110 that is formed upward from the lower opening, and a spacing position determination portion 109b that is formed at the upper end of the linear portion 109a.

Further, the outer shape of the cam 108 is formed into an oval shape, and in response to the cam 108, the sheet conveying belt 10 is moved.
The entire drive mechanism of No. 1 moves up and down along the guide groove 109.

This sheet conveying belt 101 is provided at each printing station 102 as shown in FIG.
1 to 102 3 are separated from the photosensitive drums 103, and the cam 10 is moved from the state shown in FIG.
8 is driven in the direction of the dotted line arrow in the figure to convey the sheet conveying belt 101.
(A) by raising the drive mechanism 107 together with
In this state, the paper transport belt 1 is attached to each photosensitive drum 103.
01 is abutted.

Subsequently, the photosensitive drum 103 and the conveyor belt 1
01 is rotated to enable printing, and the paper transport belt 1
By printing the recording paper conveyed in the direction of the arrow 01 in the figure in the direction of the solid line arrow at each of the printing stations 1021 to 1023, the respective colors are superimposed to form a color image.

At the end of printing, the photosensitive drum 103
By stopping the paper feeding belt 101 and the feeding belt 101, the cam 108 is driven in the direction of the dotted line arrow in the figure to lower the sheet feeding belt 101 together with the drive mechanism 107 from the state shown in FIG. Put in a state. At this time, the drive mechanism 107
Descends along the straight portion 109a of the guide groove 109,
When the cam shaft 108a reaches the separating position determining portion 109b, the cam shaft 108a is stopped and positioned.

[0010]

However, in such an image forming apparatus, since the lower side of the guide groove 109 is open, the sheet conveying belt 101 is connected to the photosensitive drum 103.
The position of the cam 108 is determined by the cam 108. Therefore, depending on the mounting accuracy of the left and right cams 108, the paper transport belt 101 may not be able to sufficiently contact the photosensitive drum 103. In addition, the guide roller 1 of the paper transport belt 101 that determines most of the transport accuracy of the recording paper.
Since the components 11 and 112 are movable, the sheet conveying belt 101 may not be sufficiently brought into contact with the photosensitive drum 103.

Further, in the image forming apparatus having the above-described structure, the paper transport belt 101 must be moved up and down together with the drive mechanism 107, and the cam 108 and the support base 110.
Since the frictional resistance with the motor becomes large, a motor etc. capable of obtaining a large driving force capable of moving these up and down is required, which requires large power consumption and does not meet the demand for downsizing of the entire printer device. There was also.

Therefore, the present invention is intended to provide an image forming apparatus capable of improving the conveyance accuracy of a recording sheet, reducing the power consumption, and meeting the demand for downsizing. .

[0013]

SUMMARY OF THE INVENTION The present invention is an endless printing station for charging the surface of an electrostatic latent image carrier, forming an electrostatic latent image by exposure, and visualizing the electrostatic latent image. An electrostatic latent image is held via the medium conveyance belt in an image forming apparatus in which a plurality of belt-shaped medium conveyance belts are arranged and a toner image visualized by a printing station is transferred onto a recording medium conveyed by the medium conveyance belt. A transfer roller that can be brought into and out of contact with the body, a roller mounting frame that rotatably supports all transfer rollers, and a transfer roller together with the roller mounting frame that are separated from the electrostatic latent image holder. The medium conveyance belt is placed in a standby state for printing, separated from the electrostatic latent image holder, and the transfer roller is brought close to the electrostatic latent image holder together with the roller mounting frame so that the medium conveyance belt holds the electrostatic latent image. Roller contacting / separating mechanism to bring the roller into contact with the printing device, a positioning protrusion fixed to the apparatus main body, and a contacting / separating operation of the roller mounting frame with respect to the electrostatic latent image holder by inserting the positioning protrusion. And a guide positioning notch having at least one positioning end at the time of printing, which is one end surface of the guide groove for stopping the positioning protrusion and determining the position at the time of printing of the roller mounting frame.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention applied to a color laser printer will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a color laser printer according to the present embodiment. Reference numerals 21 to 24 are continuous with a sheet conveying belt 1 which is an endless belt-shaped medium conveying belt stretched inside the main body of the apparatus. 4 printing stations arranged in parallel.

In each of the printing stations 21 to 24, a charging device 4, an exposure device 5, a developing device 6, a drum cleaner 7, and a discharge lamp 8 are provided around a photosensitive drum 3 as an electrostatic latent image holder.
Are opposed to each other. The developing devices 6 of the printing stations 21 to 23 store yellow (Y), magenta (M), and cyan (C) color toners, respectively.
The developing device 6 of the printing station 24 stores the black (K) toner, and the developing roller 1 is rotatably provided at the bottom.
When 0, toner is supplied to the photosensitive drum 3.

The sheet conveying belt 1 is made of a conductive material,
The surface is covered with an insulating layer. The conductive material is wound around the pair of guide rollers 14 and 15 so as to come into contact with each other. Guide roller 1 on the downstream side in the belt conveying direction
A driving roller 5 is connected to a driving device (not shown). The guide roller 14 on the upstream side in the belt conveying direction is a driven roller, and is suspended by a spring (not shown) to apply tension to the sheet conveying belt 1.

The shafts of the guide rollers 14 and 15 are rotatably attached to the housing of the printer main body in a state where the tangents to these shafts are separated from each other so as not to contact the photosensitive drum 3 of the printing station. The printing stations 21 to 24 are also fixed to this housing.

Inside the paper transport belt 1,
A transfer roller 9 is arranged so as to face each of the photosensitive drums 3 with the sheet conveying belt 1 sandwiched therebetween, and a tension roller 12 for slackening the sheet conveying belt 1 and maintaining a predetermined tension is arranged. The transfer roller 9 is composed of a conductive member and is supplied with a transfer voltage by a high voltage power source. Further, since the sheet conveying belt 1 is also made of a conductive member as described above, the transfer roller 9 as a whole constitutes a transfer device.

The transfer roller 9 and the tension roller 12 can be integrally brought into contact with and separated from the photosensitive drum 3 by a roller driving mechanism 31 shown in FIG. Specifically, the roller driving mechanism 31 includes a pair of roller mounting frames 32 that are provided along the stretching direction of the sheet conveying belt 1 and that are arranged to face each other while being spaced apart from each other in the width direction of the sheet conveying belt 1. . FIG. 2 shows one of the roller mounting frames 32 on one side, and the other side has the same structure, so that the other side is omitted for convenience of explanation.

The transfer roller 9 is axially supported by the roller mounting frame 32. That is, the transfer roller 9 has the roller mounting frame 32 as shown in FIG.
In the printing state in which the sheet conveying belt 1 is in contact with the photosensitive drums 3, the photosensitive drums 3 face each other. In addition, a predetermined tension is applied to the upper sheet corners of both ends of the roller mounting frame 32, which stretches upward, and the sheet conveyor belt 1 linearly moves between each transfer roller 9 and the photosensitive drum 3. The upper tension roller 12a is provided so as to draw

Further, at the lower corners of both ends of the roller mounting frame 32, there are provided lower tension rollers 12b which, together with the upper tension roller 12a, give a predetermined tension to the sheet conveying belt 1 stretched downward. .

The roller mounting frame 32 is provided with guide positioning elongated holes 33 as guide positioning notches at both ends in the vertical direction. The guide positioning elongated hole 33 guides the contact movement of the roller mounting frame 32 with respect to the photosensitive drum 3.
a, a print standby positioning end 33b which is formed at the upper end of the guide groove 33a and determines a separation position (print standby state position) with respect to the photosensitive drum 3, and a lower end of the guide groove 33a. Positioning end 33c at the time of printing for determining the belt contact position (position at the time of printing)
Consists of

Guide protrusions 34 formed on a supporting portion fixed to the casing of the printer body are inserted into the guide positioning elongated holes 33, respectively. The guide protrusion 34 moves the roller mounting frame 32 in the vertical direction along the guide positioning long hole 33, so that the transfer roller 9 comes into contact with and separates from the photosensitive drum 3 via the sheet conveying belt 1.

A link drive mechanism 35 as a roller contact / separation mechanism for vertically driving the roller mounting frame 32 is mounted on the roller mounting frame 32.
The link drive mechanism 35 is configured by arranging a pair of Scott Russell type linear motion mechanisms in the belt conveying direction.

That is, the link drive mechanism 35 is a lower horizontal link 35a slidably provided in the housing of the printer body.
Rotatably connect the lower end of the first oblique link 35b to
The skew link 35b is provided in the middle of the first skew link 35b.
A long hole in which the upper end of the second skew link 35c is rotatably connected to a position where the length is half the length of the above, and the lower end of the second skew link 35c is horizontally formed in the horizontal link 35a. 35d is rotatably and slidably inserted.

The link drive mechanism 35 thus constructed
Causes the upper end of the first oblique link 35b to move vertically by sliding the horizontal link 35a horizontally. Therefore, by connecting the upper end of the first oblique link 35b to the roller mounting frame 32, the roller mounting frame 32 is moved in the vertical direction together with the transfer roller 9 and the tension roller 12.

A drive unit (not shown) for sliding the horizontal link 35a in the horizontal direction is connected to one end 35e of the horizontal link 35a via a coil spring 36. This drive unit is composed of, for example, a crank mechanism that converts the rotational movement of a motor, which is a drive source, into a linear movement.

Specifically, the link driving mechanism 35 moves the horizontal link 35a from the print standby state shown in FIG.
The front end of b moves in the vertical direction shown by the dotted arrow, and the roller mounting frame 32 moves upward together with this, and the paper transport belt 1 is extended upward and abuts on the photosensitive drum 3.
As a result, the printing state shown in FIG. 3 is obtained.

At this time, the abutting portions of the photosensitive drum and the transfer roller of the sheet conveying belt 1 are connected to the upper tension roller 12a.
Also moves upward, so that it is kept horizontal and a predetermined tension is maintained, and the lower side of the sheet conveying belt 1 is prevented from being projected downward due to the lower tension roller 12b moving upward.

Further, when the link drive mechanism 35 moves the horizontal link 35a from the printing state shown in FIG. 3 in the horizontal direction indicated by the solid arrow, the tip of the first oblique link 35b is indicated by the dotted arrow. The roller mounting frame 32 moves in the vertical direction, and the roller mounting frame 32 moves downward together therewith so that the sheet conveying belt 1 is not extended upward and is separated from the photosensitive drum 3. As a result, the printing state shown in FIG. 3 is obtained.

At this time, the lower side of the sheet conveying belt 1 is extended downward by the lower tension roller 12b moving downward. As a result, the looseness of the paper transport belt 1 is eliminated.

Further, the rotating shaft of the transfer roller 9 is provided with an urging spring 37 for urging the transfer roller 9 upward so as to contact the photosensitive drum 3 with a predetermined pressure. Then, the guide roller 14 is applied so as to apply tension to the paper transport belt 1.
Also, a biasing spring 3 that biases the paper transport belt 1 in the tension direction.
8 are provided.

Further, describing the printer main body, a belt charger 11 is arranged at the carrying start position of the paper carrying belt 1 as shown in FIG. The belt charger 11 is for charging and adhering the recording paper to the paper conveyance belt 1. Further, below the paper transport belt 1, a paper feeding device 19 in which recording papers 18 as recording media are stacked and accommodated is detachably provided. A paper feed roller 23 for picking up the recording paper 18 and a conveying roller for guiding the recording paper 18 to the conveying path 13 are provided above the paper feeding device 19.

A conveyance path 13 for guiding the recording paper 18 from the paper feeding device 19 to the end of the paper conveyance belt 1 is provided near one guide roller 14. Further, the fixing device 20 is arranged close to the outside of the other guide roller 15.

In the embodiment of the present invention having such a configuration, at the start of printing, the link drive is performed in the print standby state as shown in FIG. 2, that is, in the state where the sheet conveying belt 1 is separated from the photosensitive drum 3. Horizontal link 35 of mechanism 35
Move a in the direction of the solid arrow. Then, the roller mounting frame 32 is interlocked with the link driving mechanism 35 and the roller mounting frame 32 is guided by the guide groove 3
When the guide protrusion 34 moves upward along 3a and reaches the positioning end portion 33c during printing, the guide protrusion 34 does not move further upward and the roller mounting frame 32 is positioned. As a result, the paper transport belt 1 contacts the photosensitive drum 3 and
The printing state is as shown in.

As described above, by providing the guide groove 33a in the roller mounting frame 32 and providing the positioning end portion 33c at the time of printing under the guide groove 33a, the transfer roller 9 is reliably positioned at the printing position, and the paper conveying belt. 1 can always be brought into contact with the photosensitive drum 3 with a predetermined tension. As a result, it is possible to improve the conveyance accuracy of the recording sheet.

Further, the shafts of the guide rollers 14 and 15 of the paper carrying belt 1 which determine most of the carrying accuracy of the recording paper are fixed, and the transfer roller 9 is driven to bring the paper carrying belt 1 into contact with the photosensitive belt 3. Therefore, the paper transport belt 1 can be accurately brought into contact with the photosensitive drum 3. This can also improve the conveyance accuracy of the recording paper.

Further, in the conventional structure in which the sheet conveying belt has to be moved up and down together with the drive mechanism, the frictional resistance between the cam 108 and the support base 110 becomes large, so that a motor capable of moving them up and down with a large driving force is obtained. However, in the mechanism according to the present invention, since the transfer roller 9 is driven, the transfer roller 9 can be driven with a small driving force.
A motor or the like for moving up and down can be downsized and power consumption can be saved.

Further, since the paper transport belt 1 can be moved up and down with a small driving force, the mechanism can be downsized.
Therefore, it is possible to reduce the size of the entire printer device. Further, since the load when the paper transport belt 1 is moved up and down is small, the load applied to the links and bearings used for the mechanism (roller drive mechanism) is small, and the durability is improved.

Further, since the upper tension roller 12a is provided at the upper corner of the roller mounting frame 32 so as to have the same height as that of the transfer roller 9, the paper transport belt 1
Draws a straight line between each transfer roller 9 and the photosensitive drum 3.
As a result, the recording sheet can be conveyed linearly to the contact point between the photosensitive drum 3 and the sheet conveying belt, so that stable transfer can be performed to the recording sheet, and high print quality can be maintained. it can.

At the end of printing, the horizontal link 35a of the link drive mechanism 35 is moved in the direction of the solid line arrow in the printing state as shown in FIG. 3, that is, in the state where the sheet conveying belt 1 is in contact with the photosensitive drum 3. . Then, the roller mounting frame 32 moves downward along with the guide groove 33a by linking with the link driving mechanism 35, and when the guide protrusion 34 reaches the positioning end 33b in the print standby state, the roller mounting frame 32 further moves downward. Without, roller mounting frame 32
Is positioned. As a result, the paper transport belt 1 is accurately positioned with a predetermined distance from the photosensitive drum 3 and returns to the print standby state as shown in FIG.

As described above, since the roller mounting frame 32 is provided with the guide groove 33a and the positioning standby end portion 33b for printing is also provided above the guide groove 33a, the transfer roller 9 is reliably positioned at the printing standby position. The paper transport belt 1 can be spaced apart from the photosensitive drum 3 at regular intervals. Thereby, for example, the recording paper jammed between the paper transport belt 1 and the photosensitive drum 3 can be easily removed.

In the embodiment of the present invention, the link drive mechanism 35 utilizing the Scott Russell type linear motion mechanism is used as the mechanism for moving the roller mounting frame 32 up and down, but this is not always the case. The mechanism is not limited, and any mechanism that moves the roller mounting frame 32 up and down may be used, for example, a Posrier type linear motion mechanism or the like.

In the present embodiment, the guide positioning positioning notch 33 is provided with the guide positioning positioning long hole 33. However, the guide positioning positioning notch 33 is not limited to this. Below the guide groove 33a of the long hole 33, at least the positioning end portion 3 for printing is provided.
As long as 3c is formed, the upper portion of the guide positioning long hole 33 may be further cut out.

[0046]

As described above in detail, according to the present invention, it is possible to improve the conveyance accuracy of the recording paper, reduce the power consumption, and meet the demand for downsizing. Can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a main configuration of an embodiment of the present invention.

FIG. 2 is a diagram for explaining a state of the roller driving mechanism shown in FIG. 1 during printing standby.

FIG. 3 is a diagram illustrating a state of the roller driving mechanism shown in FIG. 1 during printing.

FIG. 4 is a diagram illustrating an operation of a conventional color laser printer.

[Explanation of symbols]

1 ... Paper transport belt (medium transport belt) 21 to 24 ... Printing station 3 ... Photosensitive drum (electrostatic latent image carrier) 9 ... Transfer roller 18 ... Recording paper (recording medium) 31 ... Roller drive mechanism 32 ... Roller mounting frame 33 ... Guide positioning elongated hole (guide positioning notch) 33a ... Guide groove 33c ... Printing positioning end 35 ... Link drive mechanism (roller contact / separation mechanism)

Claims (1)

[Claims] 1. A plurality of printing stations are provided on an endless belt-shaped medium carrying belt for charging the surface of an electrostatic latent image carrier, forming an electrostatic latent image by exposure, and visualizing the electrostatic latent image. In the image forming apparatus, which is arranged and transfers the toner image visualized by the printing station to the recording medium conveyed by the medium conveying belt, the electrostatic latent image holding member is transferred to the electrostatic latent image holding body via the medium conveying belt. A transfer roller provided so as to be able to contact and separate, a roller mounting frame that rotatably supports all transfer rollers, and the transfer roller together with the roller mounting frame with respect to the electrostatic latent image holding member. The medium conveying belt is placed in a print standby state in which it is separated from the electrostatic latent image holding member, and the transfer roller is brought close to the electrostatic latent image holding member together with the roller mounting frame. A roller contact / separation mechanism for bringing the body conveying belt into contact with the electrostatic latent image holding member during printing.
A positioning protrusion fixed to the apparatus main body, a guide groove for inserting the positioning protrusion to guide the contact / separation operation of the roller mounting frame with respect to the electrostatic latent image holding member, and at least the positioning protrusion to stop the roller. An image forming apparatus, comprising: a guide positioning notch having a print positioning end that is one end surface of the guide groove that determines the print state position of the mounting frame.