JPH10329987A - Paper conveying mechanism for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paper conveying mechanism, by which a load due to a paper feeding unit feeding a paper sheet toward a recording head is prevented from affecting positioning precision of a main roller positioning the paper sheet relative to the recording head, for an image forming device. SOLUTION: In the subject paper conveying mechanism 2, a paper sheet 30 fed out by means of a paper feeding roller 6 is advanced upward by means of a conveying roller 10 and a pinch roller 12 while being tilted at the predetermined angle to the straight advancing direction to a main roller 14. If the paper sheet is fed out further by means of the conveying roller 10, a warped part 30a is formed in the paper sheet 30 because of its self-weight, and then, the paper sheet 30 is advanced to the main roller 14. A conveying load due to a paper feeding collar 7 and a paper pressing part 8 is absorbed by means of the warped part 30a so as not to affect the main roller 14. Therefore, positioning precision for the paper sheet 30 by means of the main roller 14 can be maintained, so that a desired image can be precisely formed on the paper sheet 30.

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 constructed as a part of a printer or a facsimile machine, and transfers a sheet, which is a medium on which an image is to be formed, from the place where the sheet is stored. The present invention relates to a sheet transport mechanism that actually transports a sheet to a position of a recording head that forms an image on the sheet.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses such as a thermal transfer system and an ink jet system have been provided at low cost, and printers for forming a color image have been sold for general household use.

In such an image forming apparatus, it is important to accurately convey a sheet on which an image (including characters and graphics) is formed to a recording head. That is,
This is because the paper transport mechanism not only sends the paper to the recording head but also positions the formed image in the transport direction. For this reason, a roller (herein referred to as a main roller) driven to accurately feed the paper is provided in a portion immediately before the recording head in the transport direction.
Is arranged, and by controlling this rotation, the image is positioned in a direction parallel to the transport direction.

[0004]

The paper on which an image is formed in this way is continuous paper or pre-separated paper,
The sheet is stored in a predetermined portion (hereinafter, referred to as a sheet holding unit) of the image forming apparatus, and is fed from there to a main roller. Therefore, the image forming apparatus is provided with a mechanism for feeding paper (hereinafter, referred to as a paper feeding unit). However, the force related to the paper feeding may adversely affect the positioning of the paper by the main roller. . In other words, the paper feeding section must draw out the paper from the paper holding section and securely pass it to the main roller for its original purpose. On the other hand, if the force of the paper feed unit remains as a load when the paper reaches the main roller, slippage occurs between the main roller and the paper, and the paper cannot be sent to the recording head at an accurate speed. I will.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to prevent a load by a paper feeding unit from affecting a main roller. Further, the present invention described in claims 2 and 3 proposes specific embodiments of the invention of claim 1.

A fourth object of the present invention is to provide a method for supplying a sheet to a main roller steadily in addition to the objects of the first to third aspects of the present invention.

[0007]

According to a first aspect of the present invention, there is provided a sheet transport mechanism for an image forming apparatus which holds a sheet as a medium on which an image is formed. A paper holding unit, a paper feeding unit that feeds the paper from the paper holding unit toward the recording head, a main roller that supplies the paper fed by the paper feeding unit to the recording head at a predetermined speed, A paper transport mechanism of the image forming apparatus, comprising: a bending portion that bends the paper between the paper feeding portion and the main roller.

In the paper transport mechanism configured as described above,
Since the sheet is bent between the sheet feeding section and the main roller, the influence of the conveyance load by the sheet feeding section is unlikely to affect the main roller. Therefore, an image can be formed at a desired position with high accuracy. The present invention according to claim 2, wherein the bending portion, at a position between the paper feeding unit and the main roller, a first transport roller that abuts the paper and transports the paper,
A first pinch roller that indirectly abuts the first transport roller with the paper interposed therebetween, and further includes, among the first pinch roller and the first transport roller, the main roller with respect to the transported paper. A common tangent line between the roller on the same side and the main roller forms an obtuse angle with a straight line connecting the center of the first pinch roller and the center of the first transport roller, thereby bending the sheet. It is characterized by the following.

In this description, the paper transport mechanism is described according to the state of the paper viewed from the edge parallel to the transport direction. For example, as is the case with many printers, if the printer is of a type that forms an image by transporting paper placed substantially horizontally from the back to the front (there is no problem that the paper may meander in the middle). Expressed as seen from either the left or right direction.

There are four common tangents between the two rollers, and the "common tangent" here means that the paper conveyed by the first conveying roller and the main roller has no contact with each roller. The closest tangent to the point of contact with both rollers. In other words, it indicates the common tangent closest to the trajectory of the sheet being transported.

[0011] A straight line connecting the center of the first pinch roller and the center of the first transport roller forms an obtuse angle with the common tangent line. Since the sheet is conveyed by being sandwiched between the first pinch roller and the first conveying roller, at least immediately after being sent out from both rollers, the sheet is in a direction perpendicular to a straight line connecting the centers of both rollers (that is, the straight line). Conveyed. Since the straight line connecting the centers of the two rollers forms an obtuse angle with the common tangent, the sheet immediately after being sent out from both rollers does not go straight toward the main roller, but 90 deg from the obtuse angle. Is drawn at a predetermined angle.

The paper that advances in this way comes into contact with the main roller and is supplied to the recording head at a speed defined by the peripheral speed of the main roller. As described above, the sheet sent out by the first pinch roller and the first transport roller travels toward the recording head at a predetermined angle with respect to the main roller, so that the paper is transported between the main roller and the first transport roller (first pinch roller). There is no tension between them. That is, the sheet is bent at this point. Therefore, similarly to the first aspect of the invention, the transport load of the paper feeding unit is reduced.
This can be absorbed at the bent portion of the sheet, and does not affect the conveyance drive by the main roller.

Although the first pinch roller has been described as "indirectly abutting on the first transport roller with the paper interposed therebetween", it goes without saying that the first pinch roller directly abuts on the first transport roller when there is no paper. No. According to a third aspect of the present invention, the sheet holding section holds the sheets separated in advance to a predetermined size, and the sheet feeding section holds the sheets one by one from the sheet holding section. A second conveying roller for feeding the sheet in contact with the sheet at a position between the sheet feeding section and the main roller, wherein , The second
A second pinch roller indirectly abutting on a transport roller, and wherein the sheet is bent by making the peripheral speed of the second transport roller greater than the peripheral speed of the main roller. It is characterized by.

In this paper transport mechanism, the paper fed by the second pinch roller and the second transport roller is transported by the second pinch roller and the second transport roller.
Since the peripheral speed of the transport roller is also higher than the peripheral speed of the main roller, the transport roller is bent between the main roller and the second transport roller (second pinch roller).
Therefore, similarly to the first aspect of the invention, the transport load of the paper feed unit can be absorbed at the bent portion of the paper, and the transport drive of the main roller is not affected.

If there is a difference between the peripheral speeds of the main roller and the second transport roller as described above, the sheets are accumulated one after another by the difference in the peripheral speed between the main roller and the second transport roller. However, it is conceivable that the paper held by the paper holding unit is separated into a predetermined size (for example, A4 size or B5 size) in advance, and the paper feeding unit Since the sheets are sent one by one in the direction of the recording head, the accumulated amount is canceled each time one sheet is conveyed.

According to a fourth aspect of the present invention, there is provided a guide member for bending the sheet bent by the bending portion along a desired shape. By doing so, the shape of the deflection is uniquely determined, so that the paper can be steadily conveyed to the main roller.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 is a cross-sectional view showing the periphery of a paper transport mechanism 2 of an ink jet printer to which the present invention is applied.

The paper transport mechanism 2 feeds the paper (not shown) held at the upper left of the drawing one by one to the recording head 4 along the direction of arrow A. Paper feed roller 6, paper feed color 7, and paper holding unit 8 corresponding to the paper feed unit of the present invention, transport roller 10 corresponding to the first transport roller of the present invention, and pinch corresponding to the first pinch roller of the present invention A roller 12, a main roller 14, a pinch roller 16 for the main roller 14, a discharge roller 18 for discharging the paper on which printing has been completed, a coil spring 20 for urging the paper holding unit 8, and the present invention. A first chute 22 and a second chute 24 corresponding to the guide members of
It has. The paper holding unit of the present invention is denoted by reference numeral 26.
, Where sheets separated one by one are stacked.

The recording head 4 is driven by a moving mechanism (not shown) in a direction perpendicular to the drawing. Then, based on a command from a CPU (not shown) provided in the inkjet printer, the paper is moved by the moving mechanism to form an image at a desired position on a sheet, and ink is also ejected based on a command from the CPU. Thus, an image is formed on a sheet.

The paper feed roller 6 is a roller that abuts two places in the width direction of the paper, and has a shape in which the outer periphery is partially cut as shown in FIG. The paper feeding color 7 is formed to have a diameter slightly smaller than the maximum diameter of the paper feeding roller 6, and one paper feeding color 7 is provided on each side of the paper feeding roller 6. ), Contact paper.
The sheet held by the sheet holding unit 26 is conveyed by the paper feed roller 6 being rotated counterclockwise in the drawing, and the sheet holding unit 8 holding the sheet stacked below, so that only the top sheet is conveyed. It is sent out toward the roller 10.

The transport roller 10 is driven clockwise at a peripheral speed slightly higher than that of the main roller 14 in FIG. That is, the transport roller 10 also functions as the second transport roller of the present invention. The pinch roller 12 is urged toward the transport roller 10 by an unillustrated urging mechanism, and is driven by the rotation of the transport roller 10.

The main roller 14 finally determines the speed at which the paper is fed to the recording head 4. The paper is sent to the recording head 4 while being nipped between the main roller 14 and the pinch roller 16. The angle between the common tangent B between the main roller 14 and the transport roller 10 and a straight line C connecting the center of the pinch roller 12 and the center of the transport roller 10 is an obtuse angle. That is, when the normal D of the common tangent B is set at the intersection of the common tangent B and the straight line C, the normal D and the straight line C form an acute angle α.

FIG. 2 shows how the paper is transported by the paper transport mechanism 2. FIG. 2 shows a state in which the leading end of one sheet of paper 30 is discharged from the discharge roller 18.
The other end of the paper 30 still remains in the paper holding unit 26. As shown in the drawing, the paper 30 transported by the paper transport mechanism 2 has a shape in which a portion 30a between the transport roller 10 and the main roller 14 is bent obliquely upward.

This is because the straight line C shown in FIG. 1 forms an obtuse angle with respect to the common tangent line B, and the peripheral speed of the transport roller 10 is higher than the peripheral speed of the main roller 14. According to. That is, since the straight line C forms an obtuse angle with respect to the common tangent line B, the paper 30 driven by the transport roller 10 and sent out from between the transport roller 10 and the pinch roller 12 has a direction perpendicular to the straight line C. At an acute angle α with respect to the common tangent line B.
Proceed only in the upward direction. A first chute 22 is located above the advanced position, and the sheet 30 is guided by the first chute 22 to further advance. Further, when the paper 30 is sent out by the transport roller 10, the paper 30 abuts on the second chute 24, and is advanced toward the main roller 14 by being guided by the second chute 24 and by the weight of the paper 30. Moreover, since the peripheral speed of the transport roller 10 is higher than the peripheral speed of the main roller 14, the transport roller 10 and the paper 3
Even if a little slippage or uneven rotation of the transport roller 10 occurs between 0 and 0, the bent portion 30a is steadily formed.

At this time, the other end of the paper 30 is sandwiched between the paper feeding collar 7 and the paper holding portion 8, but the transport load caused by this is absorbed by the bending of the portion 30a and does not reach the main roller 14. Therefore, the main roller 14
The supply accuracy of the paper 30 to the recording head 4 is maintained,
A desired image can be formed accurately.

As described above, the paper transport mechanism 2 has been described as an embodiment of the present invention. However, the present invention is not limited to this embodiment, and can be implemented in various modes. For example, in the above-described embodiment, the present invention is applied to an ink-jet printer.However, a printer of another aspect requiring a paper transport mechanism, a word processor having a printing mechanism,
It may be applied to a facsimile machine.

In the above-described embodiment, the transport roller 10 and the pinch roller 12 are employed as equivalent to the bending portion of the present invention.
May be employed as long as they can form the roller (for example, a rubber belt).

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the periphery of a paper transport mechanism of an inkjet printer to which the present invention has been applied.

FIG. 2 is a cross-sectional view illustrating a state in which a sheet is transported by a sheet transport mechanism.

[Explanation of symbols]

2. Paper transport mechanism 4. Recording head 6. Paper feed roller 7. Paper feed color 8. Paper holding unit 10. Transport roller 12. Pinch roller 14. Main roller 16.
Pinch roller 18 Discharge roller 22 First chute 24
2nd shot

Claims (4)

[Claims] A sheet holding unit for holding a sheet as a medium on which an image is formed; a sheet feeding unit for sending the sheet from the sheet holding unit toward a recording head; and the sheet fed by the sheet feeding unit And a main roller for supplying the recording head to the recording head at a predetermined speed. A bending section for bending the sheet between the sheet feeding section and the main roller, comprising: A sheet transport mechanism for an image forming apparatus, comprising: 2. The sheet feeding device according to claim 1, wherein the bending portion includes a first conveyance roller that abuts on the paper and conveys the paper at a position between the paper feeding portion and the main roller, and that sandwiches the paper. A first pinch roller indirectly in contact with the first transport roller, and a roller of the first pinch roller and the first transport roller that is on the same side as the main roller with respect to the sheet to be transported. And the common tangent to the main roller is
2. The paper transport of the image forming apparatus according to claim 1, wherein the paper is bent by forming an obtuse angle with a straight line connecting the center of the first pinch roller and the center of the first transport roller. mechanism. 3. The sheet holding section holds the sheets separated in advance to a predetermined size, wherein the sheet feeding section feeds the sheets one by one from the sheet holding section toward a recording head. A second transporting roller that abuts on the paper and transports the paper at a position between the paper feeder and the main roller; and A second pinch roller that sandwiches and indirectly abuts on the second transport roller, and that the paper is bent by making the peripheral speed of the second transport roller greater than the peripheral speed of the main roller. 3. The sheet transport mechanism of an image forming apparatus according to claim 1, wherein 4. The paper transport of the image forming apparatus according to claim 1, further comprising a guide member for guiding the paper to be bent into a desired shape by the bending portion. mechanism.