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Resin double helical gear and gear train using same

Resin double helical gear and gear train using same description/claims

1. Field of the Invention

The present invention generally relates to a double helical gear (or a herringbone gear) of a resin, and a gear train using the same. More specifically, the invention relates to a resin double helical gear which is widely used for various image forming systems, such as copying machines, facsimile terminal equipments and printers, various automotive parts, such as wiper driving units, power window driving units and auto slide door driving units, various electronic equipments, and precision instruments, and a gear train using the same.

2. Description of the Prior Art

A typical ink jet printer serving as an image forming system is often connected to a personal computer to be used, and is arranged on or near a desk, on which the personal computer is operated, to be operated near an operator, so that it is desired to suppress operation noises and vibrations of the ink jet printer.

Therefore, in conventional ink jet printers, a helical gear is used as each of an output gear of a motor and an idle gear meshing with the output gear, and the contact ratio of the output gear to the idle gear is increased to decrease noises (see, e.g., “Handbook of Molded Plastic Gears”, p 22 and p 477, edited by Ad Hoc Committee for Molded Plastic Gear Research of Precision Engineering Institution, published by Sigma Publisher on Apr. 20, 1995). In addition, a spur gear is used as each of a driven gear of a paper feeding roller shaft and an idle gear meshing therewith to prevent thrust force from being applied to the paper feeding roller shaft. Furthermore, if thrust force is applied to the paper feeding roller shaft, a paper feeding transport roller moves so as to be dislocated in the axial directions of the roller shaft. Then, a sheet (a sheet-like recording material, such as a copy paper or a post card) transported by the paper feeding transport roller is transported so as to be dislocated in the axial directions of the paper feeding roller shaft, so that the printing starting position and so forth are deviated to deteriorate the precision of printing.

However, if the helical gears are used as the output gear and the idle gear meshing therewith as conventional ink jet printers, thrust force is applied to both of the gears, so that there are some cases where vibrations are caused by the backlash of the gears and the mounting portion of the rotational shaft rotatably supporting thereon the gears.

Moreover, in the above described ink jet printers, a plurality of idle gears must be arranged between the output gear of the motor and the driven gear of the paper feeding roller shaft, and the number of parts of a gear train is large. Therefore, it is required to reduce the number of the parts in order to reduce the price of the ink jet printers.

It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a resin double helical gear capable of reducing operation noises and vibrations of an image forming system, such as an ink jet printer, which is arranged in the vicinity of an operator, and a gear train using the same.

It is another object of the present invention to reduce the number of parts of the gear train to reduce the price of the image forming system.

In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, there is provided a resin double helical gear which is mounted on one of a driving shaft and a driven shaft so as to rotatable therewith and which is capable of meshing with another double helical gear mounted on the other shaft, the resin double helical gear comprising: a first gear portion arranged on one side in face width directions from a substantially central portion in the face width directions, the first gear portion having teeth which are helical in a direction; and a second gear portion arranged on the other side in the face width directions from the substantially central portion in the face width directions, the second gear portion having teeth which are helical in a direction opposite to that of the first gear portion, wherein the first gear portion and the second gear portion are molded so as to be integrated with each other in such a shape that a pair of helical gear halves being helical in opposite directions to each other are stuck together.

In this resin double helical gear, a stepped portion of each of teeth between the first and second gear portions may be elastically or plastically deformed to collapse to allow an excess thickness due to deformation of the stepped portion to be received in a space between the resin double helical gear and a companion double helical gear when the resin double helical gear meshes with the companion double helical gear. Each of teeth of the resin double helical gear may have a different helix angle from that of a companion double helical gear meshing therewith. Each of the first and second gear portions may be curved so as to be convex toward a companion double helical gear meshing with the resin double helical gear.

According to another aspect of the present invention, a gear train comprises a first resin double helical gear which is mounted on a driving shaft so as to be rotatable therewith, and a second resin double helical gear which is mounted on a driven shaft so as to be rotatable therewith and which meshes with the first resin double helical gear, each of the first and second resin double helical gears comprising: a first gear portion arranged on one side in face width directions from a substantially central portion in the face width directions, the first gear portion having teeth which are helical in a direction; and a second gear portion arranged on the other side in the face width directions from the substantially central portion in the face width directions, the second gear portion having teeth which are helical in a direction opposite to that of the first gear portion, wherein the first gear portion and the second gear portion are molded so as to be integrated with each other in such a shape that a pair of helical gear halves being helical in opposite directions to each other are stuck together.

In this gear train, a stepped portion of each of teeth of the first resin double helical gear between the first and second gear portions may be elastically or plastically deformed to collapse to allow an excess thickness due to deformation of the stepped portion to be received in a space between the first resin double helical gear and the second resin double helical gear when the first resin double helical gear meshes with the second resin double helical gear. Each of teeth of the first resin double helical gear may have a different helix angle from that of the second resin double helical gear. Each of the first and second gear portions of the second resin double helical gear may be curved so as to be convex toward the first resin double helical gear. The first resin double helical gear may have a greater face width than that of the second resin double helical gear.

The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiments of the invention. However, the drawings are not intended to imply limitation of the invention to a specific embodiment, but are for explanation and understanding only.

In the drawings:

FIG. 1 is a schematic diagram showing the preferred embodiment of a gear train of an ink jet printer according to the present invention;

FIG. 2 is a schematic diagram of an example of a gear train to be compared with the gear train of FIG. 1;

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• Utility Patent

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