DENSITY UNEVENNESS REDUCTION METHOD AND SHEET TRANSPORT MECHANISM

Abstract

A density unevenness reduction method of a printing apparatus having a sheet transport mechanism which transmits a driving force of a driving device to a roller via a plurality of gears to drive the roller for transporting a sheet, the method includes: assuming one tooth and one turn of each of the gears each to be a simple harmonic oscillation of a single sine wave, and generating a synthesized wave of the sine waves of the gears; and adjusting the module and the number of teeth of each of the gears, thereby dispersing a frequency at which the oscillations of the gears overlap and are amplified in the synthesized wave.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention contains subject matter related to and claims priority to Japanese Patent Application No. 2009-021269 filed in the Japanese Patent Office on Feb. 2, 2009, the entire contents of which is incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

1. Technical Field

The present disclosure relates to a density unevenness reduction method of a printing apparatus including a sheet transport mechanism which transmits a driving force of a driving device to a roller for transporting a sheet via a plurality of gears, and the sheet transport mechanism.

2. Related Art

In the past, in a printing apparatus, a sheet transport mechanism which transmits a driving force of a drive motor as a driving device to a roller used for transporting a sheet such as a platen roller or a paper feed roller via a plurality of gears so as to rotate the roller has been used.

In the sheet transport mechanism of the printing apparatus, there is a concern that errors in gear mesh occur for each tooth and for each turn of the gears for transmitting the driving force of the drive motor to the platen roller or the paper feed roller, resulting in a change in paper feed speed. When a change in the paper feed speed occurs in the sheet transport mechanism, there is a concern that density unevenness, which is called jitter, may occur in an image that can be obtained by the printing apparatus.

Therefore, in order to obtain an image with high quality by reducing the generation of jitter, in Japanese Unexamined Patent Application No. 11-295949, a drive transmission mechanism in which gear mesh frequencies are different from each other is disclosed. In addition, in Japanese Unexamined Patent Application No. 2002-189325, a driving device including a rotor in which the module and the number of teeth of a large gear are different from those of a small gear in a multiple-gear is disclosed.

However, in the case where the gear mesh frequencies are different from each other in the drive transmission mechanism disclosed in Japanese Unexamined Patent Application No. 11-295949, over a short period, it is possible to reduce the amplitude of the mesh frequencies. However, over a long period, there may be a case where the gear mesh frequencies overlap and the amplitude of the frequencies increases, so that there is a problem in that whizzing may occur in the drive transmission mechanism over a long period and jitter may be generated.

In addition, even in the case where the module and the number of teeth of the large gear are set to be different from those of the small gear in the multiple-gear of the rotor of the driving device disclosed in Japanese Unexamined Patent Application No. 2002-189325, as in the drive transmission mechanism of Japanese Unexamined Patent Application No. 11-295949, there is a concern that over a long period, the gear mesh frequencies overlap and the amplitude of the frequencies increases, whizzing occurs, and jitter may be generated.

Moreover, improving precision in tooth shapes and engagement of gears to reduce errors in gear mesh and prevent the generation of jitter may be considered. However, with the improvement of the precision of the gears, production costs are increased.

These and other drawbacks exits.

SUMMARY OF THE DISCLOSURE

It is desirable to provide a density unevenness reduction method and a sheet transport mechanism capable of reducing errors in gear mesh over a long period to suppress a change in paper feed speed so as to reduce the generation of density unevenness such as jitter without an increase in production costs, thereby obtaining an image with high quality.

According to an embodiment, there is provided a density unevenness reduction method of a printing apparatus having a sheet transport mechanism which transmits a driving force of a driving device to a roller via a plurality of gears to drive the roller for transporting a sheet. The method includes: assuming one tooth and one turn of each of the gears each to be a simple harmonic oscillation of a single sine wave, and generating a synthesized wave of the sine waves of the gears; and adjusting the module and the number of teeth of each of the gears so as not to allow the amplitude of the frequencies of the synthesized wave to be significant over a long period, thereby dispersing a frequency at which the oscillations of the gears overlap and are amplified in the synthesized wave.

Here, the long period in this aspect is not a period for each tooth or each turn of an individual gear but indicates a period of whizzing that occurs when the synthesized wave of the gears is generated.

In addition, the statement that the amplitude of the frequency of the synthesized wave is not significant means that sharp peaks and regular peaks do not exist in the synthesized sine wave.

According to this embodiment, errors in engagement of gears can be reduced when the printing apparatus prints on a sheet while the sheet transport mechanism transports the sheet, thereby suppressing a change in paper feed speed.

According to vairous embodiments, there is provided a sheet transport mechanism including: a roller used for transporting a sheet; a driving device for driving the roller; and a plurality of gears for transmitting a driving force of the driving device to the roller, wherein, assuming one tooth and one turn of each of the gears each to be a simple harmonic oscillation of a single sine wave, a synthesized wave of the sine waves of the gears is generated; and the module and the number of teeth of each of the gears are adjusted so as to disperse a frequency at which the oscillations of the gears overlap and are amplified in the synthesized wave and shortens the amplitude of the frequency of the synthesized wave over a long period.

Here, the long period in this aspect is not a period for each tooth or each turn of an individual gear but indicates a period of whizzing that occurs when the synthesized wave of the gears is generated.

In addition, the statement that the amplitude of the frequency of the synthesized wave is not significant means that sharp peaks and regular peaks do not exist in the synthesized sine wave.

According to this embodiment, errors in engagement of gears can be reduced when the printing apparatus prints on a sheet while the sheet transport mechanism transports the sheet, thereby suppressing a change in paper feed speed.

Also, the roller is a paper feed roller disposed on at least one of the upstream side and the downstream side of a platen roller in a transport direction of the sheet.

Accordingly, the sheet transport mechanism can reduce errors in engagement of gears when the printing apparatus prints on a sheet while the sheet transport mechanism transports the sheet, thereby suppressing a change in paper feed speed.

In this embodiment, the paper feed roller is configured as a projection roller of which a plurality of projection teeth engaged with the teeth of one of the gears are arranged in parallel with the circumferential direction of the paper feed roller, assuming one projection tooth and one turn of the paper feed roller each to be a simple harmonic oscillation of a single sine wave, a synthesized wave of the sine waves of the gears and the paper feed roller is generated, and the size of the paper feed roller and the number of projection teeth are set so as to disperse a frequency at which the oscillations of the gears and the paper feed roller overlap and are amplified in the synthesized wave so as to shorten the amplitude of the frequency of the synthesized wave over a long period.

Accordingly, the sheet transport mechanism can reduce errors in engagement of gears when the printing apparatus prints on a sheet while the sheet transport mechanism transports the sheet, thereby suppressing a change in paper feed speed.

In this embodiment, the roller is a platen roller.

Accordingly, the sheet transport mechanism can reduce errors in engagement of gears when the printing apparatus prints on a sheet while the sheet transport mechanism transports the sheet, thereby suppressing a change in paper feed speed.

As described above, according to the density unevenness reduction method and the sheet transport mechanism in the aspects, errors in engagement of the gears over a long period can be reduced without significantly improving the precision of the gears, thereby suppressing a change in paper feed speed. Accordingly, the printing apparatus including the sheet transport mechanism can reduce the generation of density unevenness such as jitter without an increase in production costs, thereby obtaining an image with high quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating the main part of a sheet transport mechanism according to an embodiment of the disclosure.

FIG. 2 is a flowchart of a process of setting the module and the number of teeth of each gear on the basis of a density unevenness reduction method according to the embodiment of the disclosure.

FIGS. 3A to 3c are graphs showing oscillation components in the case where one tooth and one turn of each gear in the sheet transport mechanism illustrated in FIG. 1 are represented as a single sine wave.

FIG. 4 is a graph showing a synthesized wave of the sine waves of the gears illustrated in FIGS. 3A to 3C.

FIG. 5 is a graph showing a synthesized wave of the sine waves of gears in an example of the sheet transport mechanism.

FIG. 6 is a graph showing a synthesized wave of the sine waves of gears of a sheet transport mechanism.

FIG. 7 is a graph showing a synthesized wave of the sine waves of gears of a sheet transport mechanism.

FIG. 8 is a graph showing a synthesized wave of the sine waves of gears of a sheet transport mechanism.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description is intended to convey a thorough understanding of the embodiments described by providing a number of specific embodiments and details involving density unevenness reduction method and sheet transport. It should be appreciated, however, that the present invention is not limited to these specific embodiments and details, which are exemplary only. It is further understood that one possessing ordinary skill in the art, in light of known systems and methods, would appreciate the use of the invention for its intended purposes and benefits in any number of alternative embodiments, depending on specific design and other needs.

Hereinafter, a density unevenness reduction method according to an embodiment of the invention will be described with reference to FIGS. 1 to 8.

FIG. 1 is a perspective view illustrating a sheet transport mechanism 1 of a printing apparatus 1 using a density unevenness reduction method according to an embodiment. As illustrated in FIG. 1, the sheet transport mechanism 1 may include, as a roller for transporting a sheet in a predetermined transport direction with rotation, a paper feed roller 2 having a cylindrical shape disposed on the upstream side in the transport direction from a platen roller (not shown). The paper feed roller 2 may be rotated by the driving of a drive motor as a driving device via a plurality of gears having different gear ratios.

A paper feed gear 3a of gears 3 may be fixed to an end portion of the paper feed roller 2, and the paper feed gear 3a may be engaged with a small gear (pinion) of a first gear 3b which may be a double gear. In addition, a large gear of the first gear 3b may be engaged with a small gear of a second gear 3c which may be a double gear such that a large gear of the second gear 3c may be connected to the drive motor as the driving device (not shown) with a small gear 3d.

FIG. 2 is a flowchart of a process of setting the module and the number of teeth of each of the gears 3 on the basis of the density unevenness reduction method. In order to set the module and the number of teeth of each of the gears 3, first, a drive motor may be selected, and a torque needed for transporting a sheet and the gear ratio of the gears 3 may be set (ST1). Thereafter, the number of stages, the module, and the intermediate gear ratio of each of the gears 3 may be set (ST2), and assuming one tooth and one turn of each gear 3 each to be the simple harmonic oscillation of a single sine wave, a synthesized wave of the sine waves of the gear 3 may be generated (ST3).

For example, according to this embodiment, in the case where a gear having an oscillation period of 0.6 mm pitch is used as the paper feed gear 3a, a gear having an oscillation period of 0.15 mm pitch is used as the first gear 3b, and a gear having an oscillation period of 0.07 mm pitch is used as the second gear 3c, when one tooth and one turn of each of the gears 3 are each assumed to be a simple harmonic oscillation of a single sine wave, sine waves as illustrated in FIG. 3A to 3C may be obtained in a graph in which a vertical axis represents an amplitude and a horizontal axis represents a pitch (mm). In addition, when a synthesized wave of the sine waves of the gears 3 is generated, parts in which the oscillations of the gears 3 overlap and are amplified occur, and at the same time, parts in which they are attenuated occur, thereby obtaining a synthesized wave having oscillation components as illustrated in FIG. 4.

In addition, it may be determined whether or not the amplitude of the frequency of the synthesized wave is significant over a long period, and on the basis of the synthesized wave, a density unevenness during printing when a sheet may be transported via the gears is predicted (ST4). Whether or not the amplitude of the frequency of the synthesized wave is significant over a long period may be determined by, for example, the existence of sharp peaks or regular peaks.

FIGS. 5 to 8 are graphs showing the synthesized waves of the sine waves of the selected gear 3. As a first example, in the case where a gear having an oscillation period of 0.61 mm pitch and a gear having an oscillation period of 0.64 mm pitch are used for the sheet transport mechanism 1, as shown in FIG. 5, the amplitude of the synthesized wave is about ±2, however, the regular oscillation frequency is about 12 mm, so that whizzing for a long period may be predicted. As a second example, in the case where the gears 3 having oscillation periods of 0.26 mm, 0.46 mm, 0.52 mm, and 0.61 mm pitches are used for the sheet transport mechanism 1, as shown in FIG. 6, the oscillation period of the synthesized wave is about 1.5 mm, however, the amplitude thereof is about ±2, and particularly, the amplitude is high in a part indicated by an arrow A, so that frequency dispersion may not be suitable. As a third example, in the case where the gears 3 having oscillation periods of 0.23 mm, 0.25 mm, 0.48 mm, and 1.28 mm pitches are used for the sheet transport mechanism 1, as shown in FIG. 7, the amplitude of the synthesized wave is about ±2, however, the oscillation frequency is about 3.5 mm, so that frequency dispersion may not be suitable. As a fourth example, in the case where the gears 3 having oscillation periods of 0.058 mm, 0.103 mm, 0.184 mm, and 0.61 mm pitches are used for the sheet transport mechanism 1, as shown in FIG. 8, the amplitude of the synthesized wave is about ±2, and the oscillation frequency is about 0.5 mm, so that sharp peaks or regular peaks do not exist and frequency dispersion may be suitable.

When it is determined that the amplitude of the frequency of the synthesized wave is significant over a long period (in the case of No in ST4), the number of stages, the module, and the intermediate gear ratio may be re-set (ST2), assuming one tooth and one turn of each gear 3 each to be the simple harmonic oscillation of a single sine wave, a synthesized wave of the sine waves of the gear 3 is generated (ST3), and it is determined whether the amplitude of the frequency of the synthesized wave is significant over a long period (ST4). When it is determined that the amplitude of the frequency of the synthesized wave is not significant over a long period (in the case of Yes in ST4), with regard to the gears 3, whether or not the sheet transport mechanism 1 including the gears 3 can be accommodated in a space set in the printing apparatus (ST5), and when it is determined that the accommodation is not possible (No in ST5), ST2 to ST4 are repeated. In addition, when it is determined that the accommodation is possible in ST5, the module and the number of teeth of each gear 3 are set (ST6). As described above, with regard to the sheet transport mechanism 1, on the basis of the synthesized wave, the module and the number of teeth of each gear 3 are set so that a frequency at which the oscillations of the gears 3 overlap and are amplified is dispersed in the synthesized wave so as not to allow the amplitude of the frequencies of the synthesized wave to be significant over a long period.

In addition, when the module and the number of teeth of each gear 3 are set, the gear disposed on the upstream side in the transport direction of a sheet among the gears 3 in the sheet transport mechanism 1 may be a gear having a period smaller than the period of the sine wave of the gear disposed on the downstream side in the transport direction from the gear. Accordingly, the rotations of the paper feed roller 2 which enable a suitable paper feed speed using the small drive motor having a small driving force and fast driving speed via the gears 3 can be obtained.

The sheet transport mechanism 1 may transmit the driving force of the drive motor to the paper feed roller 2 via the gear 3 to rotate the paper feed roller 2 for transporting a sheet in a predetermined transport direction. The printing apparatus may print on the sheet while transporting the sheet using the sheet transport mechanism 1.

According to this embodiment, when the module and the number of teeth of each gear 3 of the sheet transport mechanism 1 are set, one tooth and one turn of each gear 3 are each assumed to be a simple harmonic oscillation of a single sine wave, and the synthesized wave of the sine waves of the gears 3 may be generated. Then, the module and the number of teeth of each gear 3 may be adjusted so that the frequency at which the oscillations of the gears 3 overlap and are amplified may be dispersed in the synthesized wave so as not to allow the amplitude of the frequencies of the synthesized wave to be significant over a long period. Accordingly, when the printing apparatus prints on the sheet while the sheet transport mechanism 1 transports the sheet, errors in engagement of the gears 3 are reduced over a long period, so that a change in paper feed speed can be suppressed.

Therefore, the sheet transport mechanism 1 in which the module and the number of teeth of each gear are set by using the density unevenness reduction method according to this embodiment, can reduce errors in engagement of the gears 3 over a long period without significantly improving the precision of the gears 3, thereby suppressing a change in paper feed speed. Accordingly, the printing apparatus including the sheet transport mechanism 1 can reduce the generation of density unevenness such as jitter without an increase in production costs, thereby obtaining an image with high quality.

In addition, the invention is not limited to the embodiment described above, and various modifications can be made as needed.

For example, the embodiment is described by using as the roller used for transporting a sheet, the paper feed roller 2 which is disposed on the upstream side in the transport direction of the sheet from the platen roller. However, the invention is not limited thereto, and for example, a paper feed roller 2 disposed on the downstream side in the transport direction from the platen roller, or the platen roller for transporting a sheet may also be applied.

In addition, according to various embodiments, the paper feed gear 3a may be fixed to the end portion of the paper feed roller 2, however, the invention is not limited thereto. For example, the paper feed roller 2 may be a projection roller on which a plurality of projection teeth engaged with the teeth of one of the gears 3 are arranged in parallel with the circumferential direction of the paper feed roller 2. In this case, one tooth and one turn of the paper feed roller 2 are each assumed to be a simple harmonic oscillation of a single sine wave, and the synthesized wave of the sine waves of the gears 3 and the paper feed roller 2 is generated. Then, the size of the paper feed roller 2 and the number of projection teeth may be set so that the frequency at which the oscillation of the gears 3 and the paper feed roller 2 overlap and are amplified is dispersed in the synthesized wave so as to shorten the amplitude of the frequency of the synthesized wave over a long period. Accordingly, errors in engagement of the paper feed roller 2 and the gears 3 are reduced to suppress a change in paper feed speed, so that it is possible to reduce the generation of density unevenness such as jitter in the printing apparatus having the sheet transport mechanism 1.

Accordingly, the embodiments of the present inventions are not to be limited in scope by the specific embodiments described herein. Further, although some of the embodiments of the present invention have been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art should recognize that its usefulness is not limited thereto and that the embodiments of the present inventions can be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the embodiments of the present inventions as disclosed herein. While the foregoing description includes many details and specificities, it is to be understood that these have been included for purposes of explanation only, and are not to be interpreted as limitations of the invention. Many modifications to the embodiments described above can be made without departing from the spirit and scope of the invention.

Claims

1. A density unevenness reduction method of a printing apparatus having a sheet transport mechanism which transmits a driving force of a driving device to a roller via a plurality of gears to drive the roller for transporting a sheet, the method comprising:

assuming one tooth and one turn of each of the gears each to be a simple harmonic oscillation of a single sine wave, and generating a synthesized wave of the sine waves of the gears; and

adjusting the module and the number of teeth of each of the gears, thereby dispersing a frequency at which the oscillations of the gears overlap and are amplified in the synthesized wave.

2. A sheet transport mechanism comprising:

a roller used for transporting a sheet;

a driving device for driving the roller; and

a plurality of gears for transmitting a driving force of the driving device to the roller,

wherein, assuming one tooth and one turn of each of the gears each to be a simple harmonic oscillation of a single sine wave, a synthesized wave of the sine waves of the gears is generated; and

the module and the number of teeth of each of the gears are adjusted so as to disperse a frequency at which the oscillations of the gears overlap and are amplified in the synthesized wave and shorten the amplitude of the frequency of the synthesized wave over a long period.

3. The sheet transport mechanism according to claim 2, wherein the roller is a paper feed roller disposed on at least one of the upstream side and the downstream side of a platen roller in a transport direction of the sheet.

4. The sheet transport mechanism according to claim 3,

wherein the paper feed roller is configured as a projection roller of which a plurality of projection teeth engaged with the teeth of one of the gears are arranged in parallel with the circumferential direction of the paper feed roller,

assuming one projection tooth and one turn of the paper feed roller each to be a simple harmonic oscillation of a single sine wave, a synthesized wave of the sine waves of the gears and the paper feed roller is generated, and

the size of the paper feed roller and the number of projection teeth are set so as to disperse a frequency at which the oscillations of the gears and the paper feed roller overlap and are amplified in the synthesized wave so as to shorten the amplitude of the frequency of the synthesized wave over a long period.

5. The sheet transport mechanism according to claim 2, wherein the roller is a platen roller.