Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2001-11-09
2004-08-17
Braun, Fred (Department: 2852)
Electrophotography
Image formation
Photoconductive member
C474S249000
Reexamination Certificate
active
06778795
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Filed of the Invention
The present invention generally relates to a driving force transmission apparatus used in an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite type machine made of these appliances. More specifically, the present invention relates to an improvement in such a driving force transmission apparatus for transmitting driving force by wearing, or tensioning an endless flat belt on a plurality of tension members, and also relates to an improvement in an image forming apparatus with employment of this driving force transmission apparatus.
2. Description of the Related Art
Driving force transmission apparatus which are utilized in image forming apparatus such as a printer and a copying machine own such specific characteristics that structural defects of these driving force transmission apparatus may directly induce image defects. Under such a circumstance, various sorts and higher requirements such as high engaging rates, high transmission rate, and suppression of rotation fluctuations.
In order to realize the high engaging rates and the high transmission rates, or in order to achieve the better low rotation fluctuation performance as driving force transmission apparatus of image forming apparatus according to the related art, there has been proposed a technique transmitting driving force to an image carrier by using helical gears (see, for instance, Japanese Laid-open Patent Applications No. Hei-9-80840, and No. Hei-5-72862).
Also, another technique using belts equipped with teeth has been proposed as driving force transmission member since employment of the belts equipped with teeth can realize lower rotation fluctuation performance than the employment of the helical gear.
Furthermore, in order to realize a lower rotation fluctuation than that realized by employing the belt equipped with teeth, another technique using a helical gear belt has been proposed (see, for example, Japanese Laid-open Patent Applications No. Hei-9-160332 and No. Hei-10-26903).
In general, in the case that a helical gear is employed as a driving force transmission member, the engaging rate is made large easily, as compared with such a case that a spur gear is employed as this driving force transmission member, and also, a meshing between a drive gear and a driven gear is carried out slowly. As a result, it can be found that meshing vibrations which are transferred to this driven gear can be considerably reduced. However, in such a case that a gear is employed as such a driving force transmission member, such a technical problem cannot be avoided. Namely, rotation fluctuations are produced by a back lash.
In other words, when the drive gear is meshed, or engaged with the driven gear so as to rotary-drive this driven gear, the teeth of the drive gear is mutually made in contact with the teeth of the driven gear only for a predetermined time duration. However, after this time duration elapses, the teeth of the drive gear and the teeth of the driven gear are brought into non-contact states until the next teethes are meshed with each other, which implies a back lash (play). As a result, a back lash produces vibrations when the next teethes of these drive/driven gears are engaged with each other, and the driven gear constitutes a factor by which periodic rotation fluctuations occur (namely, engagement between teethes of gears are repeated).
This back lash cannot be in principle avoided in the case that gears are used. In such a case that gears are employed as a driving force transmission member of an image forming apparatus, a driven gear is vibrated by such a gear engagement to be easily moved only by a movement corresponding to a back lash under non-constraint state. As a result, even such a small vibration force caused by the engagement vibration causes the periodic concentration (density) fluctuations to be produced in an output image.
Also, even when a helical gear is employed, a total number of meshed teeth cannot be largely increased, as compared with such a case that a spur gear is used. As a consequence, when a deformation problem as to teeth is considered, the helical gear is required to be manufactured by using such a material having a certain high hardness especially in a meshing contact portion thereof.
However, in such a case that a drive gear made of a material having a high hardness is engaged with a driven gear made of a material having a high hardness, since a portion capable of absorbing vibrations produced by this gear engagement is not present in a driving force transmission path (namely, within transmission path in case that several rotating members are driven by gear train), meshing vibrations which are produced by meshing the drive gear with the driven gear are not attenuated, but are directly transferred to the driven gear. As a result, there is another technical problem that periodic concentration fluctuations are produced in an output image.
On the other hand, in a driving force transmission apparatus with employment of a belt equipped with teeth, since the belt equipped with the teeth which is meshed with a pulley is made of such a material as a rubber material having superior flexibility, it is so expected that vibrations produced by engaging the pulley with the belt equipped with the teeth are smaller than those produced by the gears. However, as a result of the actual measurement, there is substantially no difference between the vibrations produced by the belt equipped with the teeth and the gears, as explained as follows:
That is to say,
FIG. 31
is a diagram for representing rotation fluctuations in case that both a spur gear belt and a spur gear are employed as a driving force transmission member.
As apparent from
FIG. 31
, even when the spur gear belt is employed, rotation fluctuation results thereof are obtained which are not different from those of the spur gear.
Apparently, a rotation fluctuation can be improved by narrowing a pitch of teeth. However, when this pitch of the teeth is excessively narrowed, a so-called “teeth skipping phenomenon” caused by an increased load occurs, so that gears cannot be actually driven. Therefore, a great improvement could not be expected. As a result, even when the spur gear belt is employed, it is impossible to avoid an occurrence of concentration fluctuations in an output image.
FIG. 32
represents a relationship between a concentration fluctuation allowable value and a rotation fluctuation of an image carrier drum in an image forming apparatus such as a printer.
In this drawing, such a rotation fluctuation level of the image carrier drum, at which a concentration fluctuation contained in an output image can be recognized, is equal to approximately 0.3% in a speed variation rate of &Dgr;V0−p (%) which constitutes an index of such a rotation fluctuation. When such a speed variation rate larger than, or equal to this fluctuation level occurs, there is a problem as to concentration fluctuations of the output image. As a consequence, the engaging vibration levels produced in the gears and the belt equipped with the teeth constitute a very serious problem in view of this concentration (density) fluctuation.
In other words, as to the rotation fluctuation requirement as the image forming apparatus, very high levels are required. Even when a helical gear belt is employed, a so-called “teeth skipping phenomenon” occurs in a similar manner to that of the spur gear belt. It is practically difficult to achieve such an improvement that the rotation fluctuation level of the spur gear belt shown in
FIG. 31
is reduced lower than, or equal to the allowable value.
As a consequence, as the techniques according to the related arts capable of solving such a technical problem, for instance, the following driving force transmission apparatus has already been proposed (see, for instance, Japanese Laid-open Patent Application No. Hei-7-319254). That is, as a driving force transmission apparatus for moving outer peripheral planes of a plurality of image carrier drums
Iijima Kiichiroh
Kido Mamoru
Braun Fred
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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