JPH08174944A - Paper feed device for printer - Google Patents

Abstract

PURPOSE: To improve conveying precision of a record medium by forming a paper sending roller which conveys the record medium with rotation such that it has the same outer diameter at a part butting against a bearing means and a part butting against a pinch roller. CONSTITUTION: When a recording data is received, a paper feed roller 6 is operated by rotation of a paper feed motor and a record medium 8 housed in a paper feed tray 65 is sent toward a pressure fitting part of a paper sending roller 3 and a pinch roller 32. After paper feeding operation and head outing operation of the record medium 8 are completed, a carriage 2 moves in a horizontal scanning direction H. After a record head 1 reaches a recording area in the horizontal scanning direction H, it is energized so as to record characters within the recording area in the horizontal scanning direction of the record medium 8. In this case, a part of the paper sending roller 3 butting against a bearing 33 i.e., a part to be an axis of rotation of the paper sending roller 3 and a part butting against the pinch roller 32 are made to have the same outer diameter. Thus, generation of eccentricity between them is prevented so as to convey the recording paper with a high precision.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paper feeding device of a printer, and more particularly to a paper feeding device of a printer for recording characters, images and the like at high density.

[0002]

2. Description of the Related Art Conventionally, as a paper feeding device of a printer, a method whose cross section is shown in FIG. 11 is generally used. In FIG. 11, 3 is a paper feed roller. The outer peripheral portion 35 of the paper feed roller 3 is mainly made of a material such as rubber. 32
Reference numerals 8 and 329 denote pinch rollers, which are pressed against the outer peripheral portion 35 of the paper feed roller 3 with the recording medium 8 interposed therebetween. The recording medium 8 is wound around the outer peripheral portion 35 of the paper feed roller 3 by pinch rollers 328 and 329. The paper feed roller 3 has a shaft portion 34 mainly made of metal at the center in the circumferential direction, and is rotatably supported by a frame 41 via a bearing 33 that rotatably supports the shaft portion 34. A paper feed roller gear 31, which is the final stage of the driving force transmission means, is coupled to one end of the shaft portion 34 of the paper feed roller 3. The paper feed roller gear 31 is directly engaged with the paper feed motor gear 51 which is the starting stage of the driving force transmission means, or is an intermediate part which is engaged with the paper feed motor gear 51 and forms the driving force transmission means of multistage deceleration. It engages with a reduction gear (not shown). The paper feed motor gear 51 is coupled to the paper feed motor 5.

The operation of the paper feeding device of the printer having such a configuration is as follows. That is, the paper feed motor 5
Is rotated by a predetermined amount, the driving force of the paper feed motor 5 is transmitted to the paper feed roller gear 31 via the driving force transmission means, and the paper feed roller 3 coupled with the paper feed roller gear 31 is rotated by a predetermined amount, The recording medium 8 is conveyed by a predetermined amount.

[0004]

In recent years, the densities of printers have been increased, and particularly in printers for recording pictorial images with high density, high recording accuracy is required. Therefore, it is becoming more and more important to convey the recording medium with high accuracy even in the paper feeding device of the printer.

However, in the above-mentioned conventional example, it is very difficult to greatly increase the accuracy of transporting the recording medium due to its structure. More specifically, the main factors that affect the accuracy of conveyance of the recording medium are the paper feed roller that directly engages the recording medium and performs the conveying operation, and errors such as runout and diameter variation, and the paper feed roller. These are errors such as tooth profile error of gears, runout, pitch error, backlash error, motor stop position error, etc., which occur before the driving force transmitting means for driving. Of the former error factors of the paper feed roller, the runout of the paper feed roller is as shown in FIG.
The center P of the bearing portion 34 which is rotatably supported by the shaft 3 and serves as a shaft for rotational driving.
And the center O of the outer peripheral portion 35, that is, eccentricity, and the conveyance amount of the recording medium that is conveyed along the surface of the outer peripheral portion 35 with respect to the same rotation angle θ of the paper feed roller 3. For example, the difference between the indicated amounts a and b occurs. This error occurs periodically and is difficult to correct. The latter error factor that occurs before the driving force transmission means is finally accumulated on the pitch circumference of the paper feed roller gear 31, which is the final stage of the driving force transmission means, in terms of conveyance accuracy, and the paper feed roller. An error in the amount of movement of the gear 31 in the pitch circumferential direction, that is, an error in the rotation angle of the paper feed roller gear 31, and further,
The paper feed roller 3 coupled with the paper feed roller gear 31 appears as a deviation of the predetermined rotation angle θ itself. All of these greatly impaired the conveyance accuracy of the recording medium.

The present invention has been made to solve the above problems, and provides a paper feeding device for a printer in which the deviation of the amount of recording medium conveyed due to the eccentricity of the paper feeding roller does not occur or is minimized. The purpose is to provide. Another object of the present invention is to provide a paper feeding device for a printer, which can reduce the deviation of the amount of conveyance of a recording medium due to an error factor occurring before the driving force transmitting means.

[0007]

A paper feeding device for a printer according to the present invention comprises a paper feeding roller for carrying a recording medium by rotating, a bearing means for rotatably supporting the paper feeding roller, and a paper feeding roller. A pinch roller that holds the recording medium between the paper feeding roller and the paper feeding roller, and a driving force transmitting means for rotating the paper feeding roller by transmitting the driving force to the paper feeding roller; and a driving force transmitting means. In a paper feeding device of a printer, which comprises a motor for generating a driving force transmitted by the same, the paper feeding roller has the same contact portion with the bearing means and the contact portion with the pinch roller. It is characterized by having an outer diameter.

Further, the paper feed roller is characterized by having the same outer diameter over the entire area in the longitudinal direction.

Further, the bearing means is provided with an open portion in its side view shape, and the open end surface of the open portion does not intersect with at least one contact surface with respect to the outer periphery of the paper feed roller, and the bearing means is in the recording area of the printer. It is characterized in that a plurality of them are arranged in each.

In addition, the final stage of the driving force transmission means is composed of toothed transmission means such as gears coupled to the paper feed roller, and the pitch circle diameter D of the toothed transmission means such as gears and the outer diameter of the paper feed roller. A total error amount that a diameter ratio D / d with respect to d is generated before the final stage of the driving force transmission means and can be accumulated on the pitch circumference of the toothed transmission means such as a gear which is the final stage of the driving force transmission means. It is characterized in that it is configured to be larger than the ratio f / p between f and the minimum recording pitch p in the recording medium conveyance direction in the printer.

[0011]

According to the above-mentioned structure of the present invention,
A contact portion with the bearing means, that is, a portion pivotally supported by the bearing means and serving as a rotation axis of the paper feed roller;
Since the contact part with the pinch roller, that is, the part where the recording medium is conveyed along its surface is formed on the circumferential surface of the paper feed roller having the same outer diameter, eccentricity occurs between the two. None or the amount of eccentricity is extremely reduced. Further, by configuring the diameter ratio of the pitch circle diameter of the toothed transmission means such as a gear connected to the paper feed roller, which is the final stage of the driving force transmission means, and the outer diameter of the paper feed roller to be sufficiently large. The error amount that occurs before the final stage of the driving force transmission means and that can accumulate on the pitch circumference of the final stage gear or the like is sufficiently small because it decreases by the diameter ratio on the outer peripheral surface of the paper feed roller. Will be things. Therefore, it is possible to obtain the paper feeding device of the printer, which has high conveyance accuracy of the recording medium.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 is a perspective view showing an embodiment of the present invention, FIG. 2 is a side sectional view thereof, and FIG. 3 is a partial sectional view thereof.

In these drawings, reference numeral 1 denotes a recording head, which is # 1 to #n in the sub-scanning direction (recording medium conveying direction) V.
The plurality of recording elements 11 up to are arranged at a constant inter-element pitch. Regarding the arrangement of the recording elements 11, the elements may be arranged in one row to obtain the element pitch, or the elements may be arranged in a plurality of rows to obtain the element pitch.

Reference numeral 2 denotes a carriage, which carries the recording head 1 and is driven by a carriage motor 21 via, for example, a timing belt 24, and reciprocates in the main scanning direction (recording medium width direction) H along a guide shaft 22. To do.

A paper feed roller 3 is arranged upstream of the recording head 1 in the path of the recording medium 8. The paper feed roller 3 has the same outer diameter over the entire area in the longitudinal direction. Since the structure does not have a convex portion with respect to the outer diameter, it can be precisely finished by center lace polishing or the like. In particular, when a metal material is used, it is possible to easily obtain high precision in both roundness and outer diameter dimension. As the metal material, a metal that is resistant to corrosion, rust, etc. is preferable in order to avoid deterioration in accuracy due to post-treatment such as plating, and a metal having high wear resistance is used in order to avoid deterioration in accuracy over time. Are preferred, and stainless steel and the like are preferred. Even if the paper feed roller 3 is partially provided with a concave portion at an arbitrary position in the longitudinal direction, if the concave portion is processed and the above-described finishing is performed, a high accuracy is obtained for the entire outer diameter. It is possible to get.

The paper feed roller 3 is rotatably supported by a plurality of bearings 33 provided on a support plate 43.

A plurality of bearings 33 forming the bearing means are arranged in the recording region in the main scanning direction (recording medium width direction) H. As shown in the sectional view of FIG. 3, the bearing 33 is provided with an opening 331 in its side view shape.
The open end surface 332 of the open portion 331 has a shape that does not project with respect to the outer diameter of the paper feed roller 3, that is, the paper feed roller 3
Has a shape that does not intersect with at least one contact surface with respect to the outer periphery of the. Therefore, by arranging the recording medium 8 so that the contact surfaces do not intersect with each other, the recording medium 8 can pass between the paper feed roller 3 and the pinch roller 32 without being interfered by the bearing 33. Becomes That is, when the bearing 33 has the above structure, the bearing 33
It is possible to dispose a plurality of recording media in the recording area. A non-lubricated bearing material is suitable for the bearing 33, and a plastic material such as polyacetal can also be used as a paper feeding device of an ordinary printer.

A plurality of pinch rollers 32 are rotatably supported by pinch roller holders 36 at positions facing the bearing 33 with the paper feed roller 3 interposed therebetween, and a plurality of pinch rollers 32 are provided.
The paper feed rollers 3 are independently pressed by the springs 37 acting on the pinch roller holders 36. By rotating the paper feed rollers 3, the recording medium 8 sandwiched therebetween is moved in the sub-scanning direction (recording medium conveyance direction). ) Transport to V. The pinch roller 32 needs to follow the movement of the recording medium 8 due to the frictional force between the paper feeding roller 3 and the recording medium 8 that occurs when the paper feeding roller 3 is rotationally driven.
The diameter ratio between the outer peripheral portion 321 of the pinch roller 32 and the shaft portion 322 is made large, and further, the outer peripheral portion 321 is formed of rubber or the like having a high friction coefficient, and the shaft portion 322 is formed of metal or the like having a small friction coefficient. Of the torque generated on the outer peripheral portion 321 when the rotor rotates following the movement of the shaft 32
It is preferable that the configuration is such that the difference (shaft loss) from the above-mentioned stop torque is small.

With the above configuration of the paper feed roller 3, the bearing 33 and the pinch roller 32, the pressing force of the pinch roller 32 against the paper feed roller 3 by the spring 37 does not act as a force for bending and deforming the paper feed roller 3. Therefore, the outer diameter of the paper feed roller 3 can be set to an arbitrarily small value without considering the bending strength.

In this embodiment, a gear is used as the toothed transmission means forming the driving force transmission means.

A paper feed roller gear 31, which is the final stage of the driving force transmission means, is connected to one end of the paper feed roller 3 by means of press fitting or the like. Paper feed roller 3 and paper feed roller gear 31
The paper feed roller unit consisting of
It is carried out by putting in a plurality of bearings 33 provided on the upper part 3. At this time, the paper feed roller gear 31 is sandwiched between the frame 41 and the support plate 44 provided on the frame 41 together with the elastic member 38 such as a bending washer so that the paper feed roller 3 can be positioned in the longitudinal direction. At the same time, the elastic member 38 rotates against the rotation of the paper feed roller 3.
Gives a frictional load. Next, by setting the pinch roller holder 36, the paper feed roller 3 is pressed against the bearing 33 by the spring 37, and the paper feed roller 3
The circumferential position of is determined.

Reference numeral 5 is a paper feed motor, and its rotation shaft has a paper feed motor gear 51 which is the starting stage of the driving force transmission means.
Are connected by means such as press fitting.

The construction of the driving force transmission means is such that a paper feed motor gear 51 and a paper feed roller gear 31 are provided as shown in FIGS. 1 and 2 depending on how the total reduction ratio between the start stage and the final stage is selected. It is also possible to directly engage and reduce the speed by one step, as shown in FIG. 4, the paper feed motor gear 51 and the paper feed roller gear 31.
It is also possible to insert an intermediate reduction gear 39 between and to achieve two-stage deceleration or further multi-stage deceleration.

The paper feed motor 5 is preferably a general step motor having, for example, 48 poles, 96 poles or 200 poles per revolution. The carry amount (paper feed resolution) of the recording medium 8 per step of the paper feed motor 5 is
It is determined by a combination of the number of poles per revolution of the paper feed motor 5, the driving method of the paper feed motor 5, the total reduction ratio from the paper feed motor gear 51 to the paper feed roller gear 31, and the outer diameter of the paper feed roller 3. . Details will be described later.

Reference numeral 6 denotes a paper feed roller, which is a paper feed roller gear 6
3. The recording medium 8 that is rotationally driven by the paper feeding motor 61 and stored in the paper feeding tray 65 is fed to the paper feeding device of the printer through the power transmission means including the paper feeding motor gear 62 and the like. The power transmission means includes a planetary gear mechanism 64,
Alternatively, a clutch or the like (not shown) is provided, and after feeding the recording medium 8 to the paper feeding device of the printer, the paper feed roller 6 is configured to idle with respect to the movement of the recording medium 8. It is also possible to provide a power switching mechanism or the like to drive the paper feed roller 6 with the power of the paper feed motor 5, and in this case, the paper feed motor 61 can be omitted.

Reference numeral 81 denotes a paper edge sensor, which is provided along the path of the recording medium 8 between the paper feed roller 6 and the paper feed roller 3 and detects the position of the end surface of the recording medium 8 in the transport direction V. To do.

Denoted at 71 and 72 are a paper discharge roller and a paper discharge driven roller which are provided downstream of the recording head 1 in the path of the recording medium 8 for discharging the recording medium 8 after recording. . The paper discharge roller 71 is driven by the paper feed motor 5 like the paper feed roller 3. The drive amount of the outer circumference of the discharge roller 71 is the same as that of the recording medium 8 on the front surface of the recording head 1.
In order to prevent the occurrence of slack, the amount of rotation of the paper feed motor 5 is set to be several percent larger than the amount of drive of the outer circumference of the paper feed roller 3.

Reference numeral 9 is a protection device for protecting the ink ejection surface of the recording head 1 and sucking ink when an ink jet head is applied as the recording head 1.

Next, the operation of the printer and the paper feeding device of the printer having the above-mentioned configuration will be described.

When the print data is received, the paper feed motor 61 starts rotating for paper feed. The rotation of the paper feed motor 61 drives the paper feed roller 6, and one recording medium 8 stored in the paper feed tray 65 is selected and fed toward the pressing engagement portion between the paper feed roller 3 and the pinch roller 32. Be done. When the leading edge of the recording medium 8 is detected by the paper edge sensor 81 in the path between the paper feed roller 6 and the paper feed roller 3, the selected recording medium 8 moves from the position to the leading edge of the recording medium 8. The paper is fed by a predetermined amount that reaches the paper feed drive roller 3 sufficiently. The leading end of the recording medium 8 is sufficiently pressed against the tangent portion where the paper feed roller 3 and the pinch roller 32 are press-engaged with each other, and the feeding motor 61 stops rotating in a state where the skew is corrected and the feeding operation is performed. Ends.

Next, the paper feed motor 5 starts to rotate so as to locate the recording medium 8. The rotation of the paper feed motor 5 drives the paper feed roller 3. The recording medium 8 is fed while being sandwiched between the paper feed roller 3 and the pinch roller 32, and is fed by a predetermined amount to face the recording head 1 and the cueing operation is completed. At this time, the paper feed roller 6 idles in the drawing direction of the recording medium 8 as described above, and the recording medium 8 is drawn out from the paper feeding tray 65 with a small load.

After the recording medium 8 is fed and the cueing operation is completed as described above, the carriage motor 21 starts rotating. After the carriage 2 moves in the main scanning direction (recording medium width direction) H and the recording element 11 of the recording head 1 mounted on the carriage 2 reaches the recording area in the main scanning direction,
The recording element 11 is selectively energized according to the recording data, and an arbitrary character or image for one band is recorded in the recording area of the recording medium 8 in the main scanning direction.

For example, when recording a continuous pattern such as an image, after the recording of the first band is completed,
The drive of the carriage motor 2 is stopped, the paper feed motor 5 is driven, and the recording medium 8 is conveyed by the entire length of the recording element array 11 in the sub scanning direction (recording medium conveyance direction) V by the rotation of the paper feed roller 3. . After that, the carriage motor 21 is reversely driven to move the recording head 1 in the opposite direction, and the second band adjacent to the first band is recorded. Less than,
The movement operation of the carriage 2 and the conveyance operation of the recording medium 8 are repeated.

A recording pitch smaller than the element pitch of the recording elements 11 can be obtained by the following method, for example. The desired recording pitch is 1 / m of the element pitch. By one movement of the carriage 2 in the main scanning direction, the recording element 11 is selectively energized according to the recording data to record arbitrary characters or image elements for one time, and then a recording medium for a desired recording pitch. 8 is conveyed by a small amount. The carriage 2 is reversed to record an arbitrary character or image element for the second time. The above process is repeated m times to obtain the first band recorded at a pitch of 1 / m of the pitch between the recording elements 11. After that, the recording medium 8 is conveyed by the entire length of the recording element array 11 in the sub-scanning direction, and similarly, the second band adjacent to the first band is recorded. Hereinafter, the movement operation of the carriage 2 and the conveyance operation of the recording medium 8 are repeated.

When the recording approaches the end of the recording medium 8, the end of the recording medium 8 passes the paper edge sensor 81, and the paper edge sensor 8
1, the end of the recording medium 8 is detected. After that, the moving operation of the carriage 2 and the conveying operation of the recording medium 8 are repeated until the final band allocated by the end of the recording medium 8 is recorded, and the recording for one page is completed.

Here, the conveyance accuracy of the recording medium 8 by the rotation of the paper feed roller 3 will be described in more detail.

The recording medium 8 is conveyed along the outer peripheral surface of the paper feed roller 3. Therefore, the error in the transport amount of the recording medium 8 occurs as an error in the moving distance of the outer peripheral surface with respect to the rotation amount of the paper feed roller 3. Paper feed roller 3
The error of the movement distance of the outer peripheral surface with respect to the rotation amount of <1
> The error in the movement distance of the outer peripheral surface that occurs even though the rotation amount of the paper feed roller 3 is correct, and <2> The movement distance of the outer peripheral surface that occurs because the rotation amount of the paper feed roller 3 is incorrect. It can be considered as an error.

The error <1> is caused by the deviation of the paper feed roller 3 itself, and in particular, the friction force is applied to the drive center, which is the rotation axis when the paper feed roller 3 is rotationally driven, and the recording medium 8. Giving the deviation from the center of the outer shape (outer diameter center),
That is, it is caused by eccentricity.

The error <2> is caused by the deviation of the rotation amount of the paper feed roller gear 31 directly coupled to the paper feed roller 3. Further, as a cause thereof, on the pitch circumference of the paper feed roller gear 31 which is the final stage of the driving force transmission means (on the meshing circumference for receiving the driving force), all the errors that occurred before the final stage of the driving force transmission means. It can be considered that, as a result of the accumulation of, the deviation of the movement amount of the paper feed roller gear 31 in the pitch circumferential direction (the rotation amount of the paper feed roller gear 31) is incorrect. Examples of these accumulated errors include gear eccentricity error, pitch error, tooth profile error, backlash error, and paper feed motor stop position error.

Here, regarding the error amount caused by the eccentricity,
An outline will be given with reference to FIG.

The error due to the eccentricity is caused when the outer peripheral lengths corresponding to the respective angles θ are different when they are rotated by an arbitrary constant angle θ about a certain point deviated from the center of the outer diameter.

In FIG. 5, the drive center is P, the outer diameter center is O, and the eccentricity amount OP = e, and the outer diameter is a perfect circle.

The eccentricity is the difference between the circumferential length AB when rotated about the drive center P by an arbitrary angle θ and the circumferential length CD corresponding to the angle θ (centered on the outer diameter center O) of the perfect circle. Due to the circumference error.

The maximum circumference error occurs due to the positional relationship where OP divides the arbitrary angle θ (the position shown in the figure or the position shifted by π by the arc method).

Here, the true circle radius is r, an arbitrary angle is θ,
Let α be the center angle of the perfect circle ∠AOB corresponding to the arc AB.
The maximum circumference error ε is ε = AB-CD = rα-rθ.

From the positional relationship shown in FIG. 5, a relationship of e.sin (.theta. / 2) = r.sin ((. Alpha .-. Theta.) / 2) is obtained, and e is small and sin ( In the range where (α−θ) / 2) ≈ (α−θ) / 2 holds, ε = r (α−θ) = 2e · sin (θ / 2) is obtained as an approximate solution.

That is, the outer circumference length error ε caused by the eccentricity can be expressed in the form of ε = 2e · sin (θ / 2) (1).

Next, from a different point of view, the minimum required accuracy condition in the conveyance operation of the recording medium 8 by the paper feeding device of the printer will be outlined with reference to FIG.

In FIG. 6, Xn-2, Xn-1, and Xn indicate the lower several dots when a certain band is recorded by the recording head 1. Y1, Y2, and Y3 indicate the upper several dots when the recording medium 8 is conveyed by the rotation of the paper feed roller 3 after recording a certain band and recording the next band. δ is the diameter of each dot. p is the minimum recording pitch. p'is the pitch between the lowest dot Xn previously recorded and the highest dot Y1 recorded after the recording medium 8 is conveyed.

FIG. 6A shows a recording state when the recording medium 8 is correctly conveyed by the paper feeding device of the printer. In this case, p '= p.

FIGS. 6B and 6C show the recording state when the recording medium 8 is conveyed more than the correct value. In this case, p'is larger than p. When the lowest dot Xn and the highest dot Y1 shown in FIG. 6B are in contact with each other, p '= δ. When the carry amount further increases, the lowest dot Xn and the highest dot Y1 are separated, as shown in FIG. 6 (c). In the state of FIG. 6C, even when black recording is to be performed by the recording command, dots are not filled and white stripes occur, which is a serious defect in recording quality. To avoid this,
As a condition of p ', δ>p' is derived.

FIGS. 6D and 6E show the recording state when the recording medium 8 is conveyed smaller than the correct value. In this case, p'is smaller than p. When the carrying amount further decreases from the state shown in FIG. 6 (d), FIG. 6 (e)
As shown in FIG. 7, the lowest dot Xn previously recorded and the second highest dot Y2 recorded after the recording medium 8 is conveyed come into contact with each other. In this state, p '
+ P = δ. In the state of FIG. 6 (e), a dot Y as shown in FIG.
Even when the 1 is omitted and the white part is to be recorded, the dot Xn and the dot Y2 are in contact with each other, and a white defect cannot be recorded, which causes a serious defect in recording quality. In order to avoid this, as the condition of p ′, p ′ + p> δ, that is,
p ′> δ−p is derived.

From the above, the lowest dot Xn previously recorded and the highest dot Y recorded after the recording medium 8 is conveyed.
The precision condition required for the pitch of 1 and the pitch p'determined by the conveyance operation of the recording medium 8 by the paper feeding device of the printer is δ> p '> δ-p. This is p '
The range of possible values of δ is δ− (δ−p) = p. Therefore, the minimum required accuracy condition in the conveyance operation of the recording medium 8 by the paper feeding device is to keep the error range of the conveyance amount within the value of the minimum recording pitch p.

Now, the relationship between the outer diameter d of the paper feed roller 3 and the pitch circle diameter D of the paper feed roller gear 31 will be described with reference to FIG.

As shown in FIG. 7, the error amount 83 transmitted to the outer circumference of the paper feed roller 3 is a ratio of its diameter to the error amount 82 that can occur on the pitch circumference of the paper feed roller gear 31. Just smaller.

That is, the total error amount f which is generated before the final stage of the driving force transmission means and can be accumulated on the pitch circumference of the paper feed roller gear 31 which is the final stage of the drive force transmission means is the paper feed roller 3 On the outer circumference of the paper feed roller gear 3
The diameter ratio D of the pitch circle diameter D of 1 and the outer diameter d of the paper feed roller 3
It is reduced by / d to become f / (D / d).

As described above, the recording medium 8 by the paper feeding device
Since the minimum required accuracy condition in the conveyance operation is to keep the error range of the conveyance amount within the value of the minimum recording pitch p, in the case where the error due to the accuracy of the paper feed roller 3 itself does not matter so much. , F / (D / d)
By setting <p, that is, (D / d)> (f / p) (2), it is possible to obtain the paper feeding device that satisfies the desired accuracy.

This is obtained by increasing the pitch circle diameter D of the paper feed roller gear 31, and more desirably, by decreasing the outer diameter d of the paper feed roller 3.

Based on the above, a more specific embodiment of the present invention will be described. Embodiment 1: The first trial production of a paper feeding device of a printer was performed with the following specifications. The recording head 1 has a number n of recording elements 11 = 64 and an element pitch of 1/360 inch (about 70 μm).
m) inkjet head was used.

The minimum recording pitch p in the sub-scanning direction (recording medium conveyance direction) A is set to p = 1/720 inch (about 35 μm) by interpolating the element pitch once.

The paper feed roller 3 has the same outer diameter over the entire area in the longitudinal direction, and the outer diameter is 0.5 inch in perimeter, that is, the outer diameter d = 4.043 mm. The paper feed roller 3 is made of stainless steel, and its outer diameter is made by precision polishing.

The bearings 33 were made of polyacetal, and five bearings 33 were arranged on the support plate 43 along the longitudinal direction of the paper feed roller 3.

Further, a bearing 33 is provided with the paper feed roller 3 interposed therebetween.
Five pinch rollers 32 were arranged at positions that correctly face each other. With this configuration, the pinch roller 32 by the spring 37
Since the pressing force of the sheet feeding roller 3 does not act as a force for bending and deforming the sheet feeding roller 3, the outer diameter d of the sheet feeding roller 3 should be an arbitrarily small value without considering the bending strength. As described above, it was possible to realize the paper feed roller 3 having a small outer diameter of about 4 mm without any problem.

In the pinch roller 32, the outer peripheral portion 321 was made of styrene / butadiene rubber, and the shaft portion 322 was made of steel. The outer diameter was 4.5 mm for the outer peripheral portion 321 and 1.5 mm for the shaft portion 322, that is, the diameter ratio was 3. The pinch roller holder 36 is made of polyacetal. As a result, the torque on the outer peripheral portion 321 generated when the recording medium 8 rotates following the movement of the recording medium 8 and the shaft portion 3 that prevents the rotation thereof.
The difference from the stopping torque on 22 (axial loss) can be suppressed to 10% or less, and even if the paper feed roller 3 having a small friction coefficient with the recording medium 8 is used, only the pressing load by the spring 37 is selected. As a result, it was possible to obtain any appropriate transporting force.

The driving force transmitting means was composed of an involute gear of module 0.5. The precision of the gears was created in 3 grades defined by JIS, which enables economical mass production.

The paper feed roller gear 31 has 105 teeth. Therefore, the pitch circle diameter D is 52.5 mm
(= Module 0.5 × number of teeth 105). The paper feed roller gear 31 was made of polyacetal, and provided with a press-fitting margin of 35 μm to 70 μm, and was press-fitted and fixed to the paper feed roller 3.

The paper feed motor gear 51 has 28 teeth. The paper feed motor gear 51 is made of brass and is 10μ
A press-fitting margin of m to 22 μm was provided and press-fitted and fixed to the rotary shaft of the paper feed motor 5.

The driving force transmitting means is the paper feed motor gear 51.
Is the first stage, and the paper feed roller gear 31 is the last stage, and the gears are directly engaged to reduce the speed by one stage. Therefore, the total reduction ratio is 105 teeth / 28 teeth = 3.75.

As the paper feeding motor 5, a stepper motor having 96 poles per round was used.

With the above combination, the paper feed motor 5
With respect to the rotation of the step, that is, 1/96 rotation, the paper feed roller 3 (since the reduction ratio is 3.75) is 1 / (96
× 3.75) = 1/360 rotations. Here, since the circumference of the paper feed roller 3 is 0.5 inch, the outer circumference of the paper feed roller 3 is 0.5 inch × 1/360 = 1 / when the paper feed motor 5 is driven in one step. 7
Move 20 inches. That is, the conveyance of the recording medium 8 is 1
/ 720 inch resolution.

By utilizing the fact that the outer diameter of the paper feed roller 3 which is one of the features of this construction can be made small, the above-mentioned method can be used even if a step motor with a relatively low resolution of about 96 poles per turn is used. Feed motor 5 to paper feed roller 3
With a minimum transmission element of one-stage deceleration up to 1 /
This shows that a high transport resolution of 720 inch units can be obtained.

The carrying accuracy of the recording medium 8 according to this example will be described below.

In this structure, the contact portion of the paper feed roller 3 with the bearing 33, that is, the portion pivotally supported by the bearing 33 and serving as the axis of rotation of the paper feed roller 3, and the pinch roller 32 of the paper feed roller 3 are used. The contact portion of the paper feeding roller 3, that is, the portion where the recording medium 8 is sandwiched between the paper feeding roller 3 and the pinch roller 32 and conveyed along the surface of the paper feeding roller 3 is exactly the same as the paper feeding roller 3. Since it is a place, there is almost no eccentricity between them.

Further, since the paper feed roller 3 has the same outer diameter over the entire area in the longitudinal direction, and the outer diameter is made by precision polishing using stainless steel, both the roundness and the outer diameter accuracy of the paper feed roller 3 are increased. It became very expensive.

In the prototype example, the deviation of the outer diameter of the paper feed roller 3 near the bearing 33 was at most 0.5 μm order. The error ε in the conveyance amount of the recording medium due to the eccentricity of the paper feed roller 3 is expressed by the equation (1) ε = 2e · sin (θ /
From 2), the maximum value was about ± 1 μm, which was negligible.

Next, in this configuration, the outer diameter d of the paper feed roller 3 is
Since it can be made small, the diameter ratio D / d between the pitch circle diameter D of the paper feed roller gear 31, which is the final stage of the driving force transmission means, and the outer diameter d of the paper feed roller 3 is set reasonably large. We were able to. Therefore, on the outer circumference of the paper feed roller 3, the total error amount f that is generated before the final stage of the driving force transmission means and can be accumulated in the pitch circumferential direction of the paper feed roller gear 31 is large. It can be reduced by the amount, and without increasing the precision of parts such as driving force transmission means,
High transfer accuracy could be obtained.

The amount of error that can be accumulated in the pitch circumferential direction of the paper feed roller gear 31, which is the final stage of the driving force transmission means, in the prototype example is shown below.

In the 3rd class gear specified in JIS,
For the paper feed roller gear 31 with a pitch circle diameter of 52.5 mm,
An eccentricity error of 13.5 μm can occur. This allows
From the equation (1), a rotation amount error on the pitch circumference of up to ± 27 μm can occur. That is, the rotation amount of the paper feed roller gear 31 on the pitch circumference may vary over an error amount range of 54 μm. There is a possibility of producing an error of 10 μm as a single pitch error, and a possibility of producing a tooth profile error of 7 μm. By combining these, the rotation amount per tooth is over the range of error amount 17 μm. Variation can occur. Further, as the amount of backlash, for example, precise meshing may be performed to cause variations over a range of 40 μm.

Similarly, in the paper feed motor gear 51 having a pitch circle diameter of 14 mm, the paper feed motor gear 51 has an eccentricity error of 46 μm, a single pitch error and tooth profile error of 15 μm, and a backlash of 30 μm.
The amount of rotation on the pitch circle may vary. These error amounts on the pitch circumference of the paper feed motor gear 51 are
Paper feed roller gear 31 engaging with paper feed motor gear 51
Accumulate on the pitch circumference of.

Further, the paper feed motor 5 causes an error in the stop position of the step drive, and the error amount is 5 of the step angle.
%. This error amount also accumulates on the pitch circumference of the paper feed roller gear 31, and in this example,
The rotation amount of the paper feed roller gear 31 may vary over a range of 46 μm.

From the above, in this prototype example, the total error amount f that can be accumulated in the pitch circumferential direction of the roller gear 31 is
For example, f = 54 + 17 + 40 + 46 + 15 + 30 + 4
It can be estimated that 6 = 248 μm.

Therefore, in the present example in which the minimum recording pitch p in the sub-scanning direction (recording medium conveying direction) V is p = 1/720 inch (about 35 μm), the equation (2) (D / d)
> (F / p), the diameter ratio D / d between the pitch circle diameter D of the paper feed roller gear 31 and the outer diameter d of the paper feed roller 3 is calculated by the ratio f / of the total error amount f and the minimum recording pitch p. p = 248 μm / 3
By making it larger than 5 μm = 7.1, it becomes possible to obtain the minimum required transport accuracy for an arbitrary rotation amount of the paper feed roller 3. The method can be applied even when the components or the precision of the components is changed. For example, when the gear precision is set to the 4th grade specified in JIS, the diameter ratio D / d should be 8.5 or more. Therefore, the minimum required transfer accuracy can be obtained.

In this prototype, the paper feed roller gear 3
1 pitch circle diameter D is D = 52.5 mm, paper feed roller 3
Of the outer diameter d of d = 4.043 mm and the diameter ratio D / d of D / d
By setting a large value of d = 52.5 / 4.043≅13, it is possible to obtain higher conveyance accuracy for an arbitrary rotation amount of the paper feed roller 3.

FIG. 8 shows a paper feed roller 3 using this apparatus.
The following shows the conveyance accuracy when the recording medium 8 is conveyed by 64/360 inches by the entire length of the recording element array 11 in the sub-scanning direction. The error range of the carry amount is within 15 microns, and the minimum recording pitch is 1/720
The accuracy was sufficiently high even for high recording densities in the inch class. In addition, an image was recorded using this apparatus, and a good image output in which neither white stripes nor black stripes were noticeable could be obtained.

As a comparative example, a prototype was made with the structure shown in the conventional example. The outer diameter of the outer peripheral portion 35 of the paper feed roller 3 is d = 3.
The outer peripheral portion 35 was formed of rubber with a length of 2.34 mm (perimeter length 4 inches). Shaft 34 has a diameter of 12 mm to give strength
It was made from steel. The paper feed motor was the same 96-pole step motor, and the conveyance resolution was also 1/720 inch. Therefore, the total reduction ratio of the driving force transmission means was 30, which was obtained by the two-step reduction by gears. The gear precision is the same as the third grade, and the paper feed roller gear at the final stage of the driving force transmission means has a pitch circle diameter D = 60 mm.

With the above construction, the same 64/360 inch pitch conveyance was performed and the accuracy was compared. The error range of the carry amount is 60 microns, and the minimum recording pitch is 1/72
When it was set to about 0 inch, the minimum required accuracy requirement was not met. By this accuracy comparison, the paper feed roller of the comparative example having a structure having a step in the circumferential direction has an eccentricity of a little over 20 μm between the shaft portion and the outer peripheral portion, and the conveyance amount error due to the eccentricity factor of the paper feed roller itself is considerable. It turned out that a large amount was generated.

Since the diameter ratio D / d is as small as about 1.9, the amount of error generated before the final stage of the driving force transmission means and accumulated on the pitch circumference of the paper feed roller gear, which is the final stage of the driving force transmission means. It is transmitted to the outer periphery of the paper feed roller without being significantly reduced,
It has been found that even with a relatively small carry amount with respect to the outer circumference length of 4 inches, that is, 64/360 inches, a considerable carry amount error occurs. It was also confirmed that a larger transport amount error occurs at a larger arbitrary transport amount.

Since the outer diameter of the paper feed roller 3 in the first prototype is as small as about 4 mm, the moment of inertia for the rotation is about 1/500 of the moment of inertia of the paper feed roller of the comparative example, which is very small. Will be things. Therefore, by applying a frictional load to the paper feed roller gear 31 by a simple means such as the elastic member 38, the tooth surface on one side of the paper feed roller gear 31 is always made to be the tooth surface on the drive side of the paper feed motor gear 51. It is possible to make them. result,
It was found that variations in the amount of rotation of the paper feed roller gear 31 due to backlash between both tooth surfaces were reduced, and in the first prototype example, the carry amount error was smaller.

Embodiment 2 A second prototype of the paper feeding device of the printer was made with the following specifications.

The recording head 1 has the number of recording elements 11 n = 3.
2. An inkjet head having an element pitch of 1/180 inch (about 140 μm) was used.

As the paper feed roller 3, the bearing 33, and the pinch roller 32, the same ones as in the first trial were used with the same constitution.

The same paper feed motor 5 as that used in the first prototype was used.

The driving force transmitting means was composed of gears, and the tooth profile, module, precision and the like of the first prototype were used.

The driving force transmitting means further includes an intermediate reduction gear 3 having a large gear and a small gear coaxially arranged, as shown in FIG.
9 was used, and it comprised by two steps of deceleration. The total reduction ratio from the first stage to the last stage is 18.75, and the number of teeth thereof is 100 teeth for the paper feed roller gear 31, 20 small teeth for the intermediate reduction gear 39, and a large gear for the intermediate reduction gear 39. Has 75 teeth and the paper feed motor gear 51 has 20 teeth.

With the above combination, one of the paper feed motors 5 is
By driving the steps, the recording medium 8 is conveyed by 1/360
It can be performed with a very high resolution of 0 inch.

The above is also one of the features of the present configuration, and by utilizing the fact that the outer diameter of the paper feed roller 3 can be made small, it is not possible to use a step motor with a relatively low resolution of about 96 poles per round. However, it shows that a very high carrying resolution of, for example, 1/3600 inch unit can be obtained.

By obtaining a very high carrier resolution,
In a high recording density printer, it is possible to record with several different recording densities with one printer.

In this case, the reciprocal of the pitch between elements (resolution between elements) of the recording head 1 is set as the greatest common divisor of the reciprocal of each of several kinds of recording densities (recording resolutions) to be obtained. This is possible by setting the reciprocal of the least common multiple of the reciprocal of each of several types of recording densities.

For the sake of explanation, the resolution will be expressed in units of dpi (dots per inch), which is the same numerical value as the reciprocal number. That is, the resolution of 1/3600 inch is expressed as the resolution of 3600 dpi.

For example, when the desired recording densities are 720 dpi and 900 dpi, the element pitch of the recording head 1 is set to 180 dpi, which is the greatest common divisor, and the transport resolution is set to 3600 dpi, which is the least common multiple thereof. Both recording densities can be realized by interpolating the element pitch of the recording head 1 by an arbitrary number of times at equal pitches.

By the second trial manufacture realizing the above, recording with the recording densities of 720 dpi and 900 dpi was performed with one printer. The conveyance accuracy of the recording medium 8 is high due to the same effect as that of the first prototype example, and particularly 900
It was possible to obtain a high-quality image output at a recording density of dpi.

According to the configuration of the present invention, the outer diameter of the paper feed roller 3 which does not require bending strength can be further reduced, so that it is easy to obtain higher carrying resolution, and the above method is used. Thus, various recording densities can be obtained with one printer. Alternatively, there is a possibility of obtaining a high transport resolution by decelerating one step.

As described above, according to this embodiment of the present invention, the contact portion of the paper feed roller 3 with the bearing 33, that is, the axis of rotation of the paper feed roller 3 supported by the bearing 33. And a contact portion of the paper feed roller 3 with the pinch roller 32, that is, the recording medium 8 is nipped between the paper feed roller 3 and the pinch roller 32 and conveyed along the surface of the paper feed roller 3. By making the parts to be formed have the same outer diameter, it is possible to easily create the circularity and the outer diameter dimension with high accuracy.

Further, by making both the above-mentioned parts the same part in the longitudinal direction of the paper feed roller 3, eccentricity hardly occurs between the two parts, and an arbitrary rotation amount of the paper feed roller 3, that is, Therefore, it is possible to obtain the paper feeding device of the printer in which the feeding error due to the eccentricity factor of the paper feeding roller 3 is extremely small with respect to the arbitrary feeding amount of the recording medium 8.

Further, the diameter ratio D / d between the pitch circle diameter D of the paper feed roller gear 31 and the outer diameter d of the paper feed roller 3 which is the final stage of the driving force transmission means is set to the value before the final stage of the driving force transmission means. Is set to a value larger than the ratio f / p of the total error amount f that can be accumulated on the pitch circumference of the paper feed roller gear 31, which is the final stage of the driving force transmission means, and the minimum recording pitch p. A paper feeding device of a printer is obtained in which the conveyance error is small due to an error factor generated before the final stage of the driving force transmission means with respect to an arbitrary rotation amount of the paper feeding roller 3, that is, an arbitrary conveyance amount of the recording medium 8. be able to.

In addition, by arranging the bearing 33 and the pinch roller 32 at positions facing each other with the paper feed roller 3 in between, the outer diameter of the paper feed roller 3 which does not require bending strength is
Since it can be set to a small value, it has the following special effects.

By setting the outer diameter of the paper feed roller 3 to a small value, the moment of inertia with respect to the rotation of the paper feed roller 3 becomes extremely small, and a simple means such as the elastic member 38 against the rotation of the paper feed roller 3. It is possible to eliminate the unstable rotation operation of the paper feed roller 3 only by giving a frictional load, and it is possible to obtain a paper feed device of a printer with higher conveyance accuracy.

By making the outer diameter d of the paper feed roller 3 a small value, the paper feed roller 3 itself becomes small and lightweight, and the pitch circle diameter D of the paper feed roller gear 31 is not made large. Since the diameter ratio D / d can be made large, it is possible to make the paper feeding device having high carrying accuracy and the printer including the paper feeding device very small and lightweight.

By setting the outer diameter of the paper feed roller 3 to a small value, it is possible to obtain a high conveyance resolution with a small reduction ratio, that is, with a driving force transmission means having a simple structure.

By setting the outer diameter of the paper feed roller 3 to a small value, a very high conveyance resolution can be obtained as compared with the recording density of the printer. For example, one printer can have various recording densities. It is possible to obtain a paper feeding device of a printer capable of recording.

Further, all of the above can be realized at low cost because no additional mechanism is required.

Here, the diameter ratio D / d of the pitch circle diameter D of the paper feed roller gear 31, which is the final stage of the driving force transmission means, and the outer diameter d of the paper feed roller 3 and the rotation of the paper feed roller 3 The relationship with the transport error amount of the recording medium 8 will be briefly described.

FIG. 9 shows the result of calculation by simulation of the transport error amount with respect to various values of D / d when the recording medium 8 is transported at a pitch of 64/360 inches. The horizontal axis represents the D / d value, and the vertical axis represents the transport error amount.

[0114] When carrying out a constant desired amount of conveyance,
As shown in FIG. 9, when the value of D / d is increased, it can be seen that the conveyance error amount is significantly reduced until the value of D / d reaches around 10. This is mainly
When the value of D / d is further increased, for example, as the value of D is increased, the absolute value of the error amount that can occur for gears of the same accuracy class slightly increases. When the paper feed roller 3
And the amount of rotation of the gear increases and the amount of error due to rotation increases slightly, but these should make a relatively large contribution to the amount of conveyance error that has already decreased and the absolute value has decreased. This is because

Therefore, by setting the value of D / d to approximately 10 or more, it is possible to enjoy a great reduction in the amount of conveyance error, and it is possible to obtain a paper feeding device for a printer with high conveyance accuracy.

FIG. 10 shows another embodiment of the present invention.

In FIG. 10, the paper feed roller 3 uses a metal material such as stainless steel as a base material and has a number 3 in the drawing.
As shown in 0, a material partially different from the base material is arranged at a plurality of locations. The dissimilar material portion 30 is used for the paper feed roller 3
The paper feed roller 3, which is fixed to a concave portion provided in advance, has the same outer diameter over the entire region in the longitudinal direction including the different material portion 30. It is desirable that the dissimilar material has a high friction coefficient with the recording medium 8, and the dissimilar material portion 30 is preferably made by spraying ceramics.

In the paper feed roller 3, the base material portion near the dissimilar material portion 30 is rotatably supported by a plurality of bearings 33 provided on the support plate 43.

A plurality of pinch rollers 32 are rotatably supported by the pinch roller holders 36, and a plurality of pinch rollers 32 are provided at positions where they come into contact with the dissimilar material portion 30 of the paper feed roller 3.
The paper feed rollers 3 are independently pressed by the springs 37 acting on the pinch roller holders 36, and the recording media 8 sandwiched therebetween are conveyed by rotationally driving the paper feed rollers 3.

The structure of the bearing 33, the pinch roller 32, the driving force transmitting means and the like are the same as in the first embodiment.

According to this structure, the coefficient of friction between the dissimilar material portion 30 of the paper feed roller 3 and the recording medium 8 can be set to be sufficiently large, so that even with a smaller pressing load of the spring 37,
A larger carrying force can be obtained, and the applicable range can be further increased depending on the type of the recording medium 8 to be handled.

Due to the structure of the bearing 33 described above, also in this structure, the bearing 33 serving as the fulcrum of the load can be arranged in the immediate vicinity of the dissimilar material portion 30 where the load acts, and the paper feed roller 3 is In terms of strength, it is possible to reduce the outer diameter to about 4 mm. Further, the paper feed roller 3 is a contact portion between the base material portion pivotally supported by the bearing 33 and serving as an axis of rotation of the paper feed roller 3, and the pinch roller 32 of the paper feed roller, and is the recording medium 8
Since the different material portions 30 that are conveyed along the surface thereof are formed on the circumferential surface having the same outer diameter, the eccentricity between them is extremely small. Therefore, also in this example, it is possible to obtain a high conveyance accuracy according to the first embodiment.

In the description of the embodiments, specific numerical values or materials are shown for the purpose of explanation, but the application of the present invention is not limited to these.

Further, the arrangement position of the paper feed roller 3 in the path of the recording medium 8 and the like can be freely laid out regardless of the description in the embodiment.

[0125]

As is apparent from the above description, according to the present invention, the contact portion of the paper feed roller with the bearing means, that is, the portion pivotally supported by the bearing means and serving as the axis of rotation of the paper feed roller. And the contact portion of the paper feed roller with the pinch roller, that is, the portion where the recording medium is conveyed along its surface is constituted by a circumferential surface having the same outer diameter of the paper feed roller. The amount of eccentricity generated between the parts becomes extremely small. Therefore, due to the eccentricity factor of the paper feed roller, the conveyance error of the recording medium that occurs even when the rotation amount of the paper feed roller is correct is extremely small, and the conveyance accuracy is high.
The paper feeding device of the printer can be obtained.

Further, the diameter ratio between the pitch circle diameter of the toothed transmission means such as a gear connected to the paper feed roller, which is the final stage of the driving force transmission means, and the outer diameter of the paper feed roller is made sufficiently large. By doing so, the error amount that occurs before the final stage of the driving force transmission means and that can be accumulated on the pitch circumference of this final stage gear or the like is reduced by the diameter ratio on the outer peripheral surface of the paper feed roller, It will be small enough. Therefore, the conveyance error of the recording medium caused by the incorrect rotation amount of the paper feeding roller is sufficiently reduced, and the paper feeding device of the printer with high conveyance accuracy of the recording medium can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing the configuration of an embodiment of a paper feeding device device of a printer of the present invention.

FIG. 2 is a side sectional view of a paper feeding device of the printer shown in FIG.

FIG. 3 is a partial cross-sectional view of a paper feeding device of the printer shown in FIG.

FIG. 4 is a partial view showing another configuration of the embodiment of the present invention.

FIG. 5 is a diagram illustrating a transport error in the embodiment of the present invention.

FIG. 6 is a diagram illustrating a transport error according to an embodiment of the present invention.

FIG. 7 is an operation explanatory diagram of the embodiment of the present invention.

FIG. 8 is a diagram showing conveyance accuracy according to an embodiment of the present invention.

FIG. 9 is a diagram showing a calculation example of a transport error according to an embodiment of the present invention.

FIG. 10 is a partial view showing the configuration of another embodiment of the present invention.

FIG. 11 is a diagram showing a conventional example.

FIG. 12 is a diagram showing a conventional example.

[Explanation of symbols]

 1: Recording head 11: Recording element 2: Carriage 3: Paper feed roller 31: Paper feed roller gear 32: Pinch roller 33: Bearing 331: Bearing open part 332: Bearing open part end face 36: Pinch roller holder 37: Spring 38: Elastic member 39: Intermediate reduction gear 5: Paper feed motor 51: Paper feed motor gear 6: Paper feed roller 6: Paper ejection roller 6: Paper ejection driven roller 8: Recording medium 81: Paper edge sensor 9: Protective device

Claims (9)

[Claims] 1. A paper feed roller that conveys a recording medium by rotating it, bearing means that rotatably supports the paper feed roller, and the recording medium sandwiched between the paper feed roller. The pinch roller pressed by the paper feed roller, the drive force transmission means for rotating the paper feed roller by transmitting the drive force to the paper feed roller, and the drive force transmitted by the drive force transmission means In a paper feeding device of a printer including a motor for generating, the paper feeding roller has the same outer diameter in a contact portion with the bearing means and a contact portion with the pinch roller. A paper feeding device for a printer. 2. The paper feeding device for a printer according to claim 1, wherein the paper feeding roller has the same outer diameter over the entire area in the longitudinal direction. 3. The paper feeding device for a printer according to claim 1, wherein the paper feeding roller is formed of a single material. 4. The paper feeding device for a printer according to claim 1, wherein the paper feeding roller is formed of a single metal material. 5. The printer according to claim 1, wherein the paper feed roller is made of different materials in a contact portion with the bearing means and a contact portion with the pinch roller. Paper feeder. 6. The bearing means has an opening in a side view of the bearing means, and an opening end surface of the opening does not intersect with at least one contact surface with the outer circumference of the paper feed roller. 2. The paper feeding device for a printer according to claim 1, wherein a plurality of the paper feeding devices are arranged in a recording area of the printer. 7. The contact portion of the paper feed roller with the bearing means and the contact portion of the pinch roller are arranged at the same position in the longitudinal direction of the paper feed roller. A paper feeding device for a printer according to claim 1 or 6. 8. A paper feed roller that conveys a recording medium by rotating it, bearing means that rotatably supports the paper feed roller, and the paper feed roller sandwiching the recording medium. The pinch roller pressed by the paper feed roller, the drive force transmission means for rotating the paper feed roller by transmitting the drive force to the paper feed roller, and the drive force transmitted by the drive force transmission means In a paper feeding device of a printer including a generating motor, the final stage of the driving force transmitting means is a toothed transmission means such as a gear coupled to the paper feeding roller, and the toothing of the gear or the like is provided. The diameter ratio D / d between the pitch circle diameter D of the transmission means and the outer diameter d of the paper feed roller is generated before the final stage of the driving force transmission means, and the final stage of the driving force transmission means is a gear or the like. On the pitch circumference of the toothed transmission means of Characterized by being configured as larger than the ratio f / p of the minimum recording pitch p of the recording medium conveying direction in the total error amount f and a printer may be cumulative, the paper feeder of the printer. 9. A diameter ratio D / d between a pitch circle diameter D of a toothed transmission means such as a gear which is the final stage of the driving force transmission means and an outer diameter d of the paper feed roller is greater than 10. A paper feeding device for a printer according to claim 1 or claim 8, which is characterized in that.