Image forming apparatus

An image forming apparatus includes an image forming unit configured to form an image; a holding portion configured to hold the image forming unit; a supporting portion configured to support the holding portion; a fastening portion configured to fasten the holding portion and the supporting portion to each other; and an arcuate slit portion provided in at least one of the holding portion and the supporting portion and extending substantially about the fastening portion in a range at least not less than 180° and less than 360° around the fastening portion.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an image forming apparatus such as a copying machine, a printing machine, a facsimile machine, a multifunction machine having two ore more functions of the preceding machines, and so on.

An electrophotographic image forming apparatus forms an electrostatic latent image on an image bearing component such as a photosensitive drum, with the use of an image forming section having an exposing device or the like, and turns the electrostatic latent image into a visible image with the use of toner. An exposing device and a photosensitive drum (component on which an image is formed), such as those mentioned above, are attached to the main frame of the image forming apparatus with the use of stays or the like. To the main frame, a motor for driving the photosensitive drum, developing device, a fixing device, etc., and a driving force transmitting device such as gears, are attached. Thus, if the vibrations from the driving force transmitting device travel to the exposing device and/or photosensitive drum, it is possible that image defects such as pitch anomaly will occur.

Therefore, there has been proposed an image forming apparatus structured so that its exposing device is supported with the main frame of the apparatus, with the placement of a shock absorbing component between the exposing device and main frame (Japanese Laid-open Patent Application No. H09-146324). There has also been proposed an image forming apparatus structured so that its exposing device is supported by a stay or the like, with the placement of an elastic component between one of the four points of the exposing device, by which the exposing device is held to the stay, and the stay (Japanese Laid-open Patent Application No. H08-278670).

However, in the case of the image forming apparatus structured as disclosed in Japanese Laid-open Patent Application No. H09-146324, the exposing device is supported by the main frame of the apparatus, with the placement of a shock absorbing component between the exposing device and the main frame. Thus, it is impossible to ensure that the exposing device is precisely positioned relative to the photosensitive drum. Therefore, an additional structural arrangement is necessary to keep the exposing device precisely positioned relative to the photosensitive drum. Thus, the image forming apparatus increases in component count, and also, the main assembly of the apparatus becomes complicated in structure.

Further, in the case of the image forming apparatus structured as disclosed in Japanese Laid-open Patent Application No. H08-278670, it is only one of the four points at which the exposing device is held by the main frame of the apparatus, that is provided with elasticity. Thus, as long as vibrations are transmitted to the exposing device through a specific path, that is, only when the vibrations are transmitted through this point having elasticity, it can be expected that the amount by which vibrations are transmitted to the exposing device will reduce. That is, in a case where vibrations are transmitted to an exposing device through multiple paths, it is difficult to reduce the amount by which vibrations are transmitted to an exposing device.

SUMMARY OF THE INVENTION

Thus, the primary object of the present invention is to provide an image forming apparatus, the main frame of which supports the image forming components, and is significantly smaller in the amount by which vibrations are transmitted to its image forming components, than any conventional image forming apparatus.

According to an aspect of the present invention, there is provided an image forming apparatus comprising an image forming unit configured to form an image; a holding portion configured to hold said image forming unit; a supporting portion configured to support said holding portion; a fastening portion configured to fasten said holding portion and said supporting portion to each other; and an arcuate slit portion provided in at least one of said holding portion and said supporting portion and extending substantially about said fastening portion in a range at least not less than 180° and less than 360° around said fastening portion.

DESCRIPTION OF THE EMBODIMENTS

Next, referring toFIGS. 1-9, the first embodiment of the present invention is described. To begin with, referring toFIG. 1, the overall structure of the image forming apparatus in this embodiment is described.

The image forming apparatus100in this embodiment is a full-color printer which uses an electrophotographic image forming method. An image forming apparatus such as the image forming apparatus100has: an image forming section101which forms a toner image; and a recording medium conveying section102which conveys recording medium (sheet of paper, OHP film, etc.), onto which a toner image formed by the image forming sections101are transferred. The image forming section101has the so-called tandem type structure. That is, it is structured so that multiple process cartridges2are aligned in tandem in the direction parallel to the direction in which the intermediary transfer belt6of the apparatus100is moved. In the multiple image forming stations of the image forming sections, yellow, magenta, cyan and black toner images are formed, one for one.

An image forming apparatus such as the one in this embodiment is structured so that multiple (four in this embodiment) process cartridges2can be removably installed in the main assembly1of the apparatus100. Here, the four process cartridges2are the same in structure. Hereafter, therefore, only the leftmost process cartridge2is described as the one which represents all the process cartridges2(referential suffixes which indicate color of toner they form, and their position in terms of moving direction of intermediary transfer belt, are not shown).

The process cartridge2has a photosensitive drum3, a charge roller3a, a developing device3b, and a drum cleaner3c. The photosensitive drum3is an image bearing component (image forming component). It is an electrophotographic photosensitive component, and is in the form of a drum. It is rotationally driven by an unshown drum motor, at a preset process speed. The peripheral surface of the photosensitive drum3is uniformly charged by the charge roller3aas a charging means. As the uniformly charged peripheral surface of the photosensitive drum3is scanned by the beam of laser light projected by a pair of scanner units4aand4b, which are image forming components (image forming sections (exposing means), while being modulated according to the information about the image to be formed, an electrostatic image is effected on the peripheral surface of the photosensitive drum3. The electrostatic latent image on the photosensitive drum3is developed into a developer image T (toner image), that is, an image formed of developer (toner), through a process of adhering toner to the electrostatic image with the use of the developing device3b. Then, the toner image on the photosensitive drum3is transferred (primary transfer) onto the intermediary transfer belt6by the application of the primary transfer bias between a primary transfer roller5, as the primary transferring means, and the photosensitive drum3. The transfer residual toner, which is the toner remaining on the peripheral surface of the photosensitive drum3after the primary transfer, is removed by the drum cleaner3c.

As a process such as the above-described one is carried out by each process cartridge2, four toner images, different in color, are formed on the four photosensitive drums3in the four process cartridges2, one for one, and are transferred in layers onto the intermediary transfer belt6. Consequently, a full-color image is effected on the intermediary transfer belt6. Then, the toner images on the intermediary transfer belt6are transferred (secondary transfer) onto a sheet of recording medium conveyed to the secondary transferring section formed by the intermediary transfer belt6and a secondary transfer roller as the secondary transferring means, by a recording medium conveying section102, which will be described later. The toner remaining on the intermediary transfer belt6after the secondary transfer is removed by a belt cleaner6a.

The recording medium conveying section102is made up of multiple conveyance rollers. It picks up sheets of recording medium stored in a cassette102a, and conveys the sheets to the secondary transferring section of the image forming section101. Regarding the conveyance of a sheet of recording medium to the secondary transferring section, each sheet of recording medium is delivered to the secondary transferring section by a pair of registration rollers102bso that the sheet arrives at the secondary transferring section with the same timing as the toner images on the intermediary transfer belt6. In the case of the image forming apparatus100shown inFIG. 1, a sheet of recording medium is conveyed upward of the main assembly of the image forming apparatus100from the cassette102adisposed in the bottom portion of the main assembly. That is, the recording medium conveying section102is disposed so that it extends upward in the roughly vertical direction, on one side (right side as seen from front side of apparatus) of the main assembly.

After the transfer of the toner images onto a sheet of recording medium in the secondary transferring section, the sheet and the toner images thereon are heated and pressed by a fixing device8. Consequently, the toner images are fixed to the sheet. After the fixation of the toner images to the sheet, the sheet is discharged into a delivery tray9.

[Structure of Main Frame]

Next, referring toFIG. 2, the main frame50of the main assembly1of the image forming apparatus100is described. The main frame50is made up of a rear plate10, a front plate unit14, connective stays18,19,20,21,22,23, etc., which connect the rear plate10and front plate unit14to each other. The front plate unit14is made up of a front stay14a, a top-front stay14b, a right supporting column15, a left supporting column18, which are connected to each other. Each of the connective stays18-23are connected to the left or right ends of the rear plate10and front plate unit14, with the use of small screws or like components.

A main driving unit11and a fixing device driving unit12are driving force transmitting devices, and are vibration sources. They are supported by the rear plate10, by being held to the rear plate10with the use of small screws. As described above, the rear plate10makes up a part of the main frame55by being connected to the front plate unit14with the use of connective stays18-23. Thus, the main frame50, which includes the rear plate10, makes up the section of the image forming apparatus100, by which the driving force transmitting devices are supported. The main driving unit11has a combination of a motor, a gear train, etc., which are for driving the photosensitive drum3and developing device3bin each of the above-described process cartridges2, a combination of a motor, a gear train, etc., which are for driving the driver roller for the intermediary transfer belt6, etc. The fixing device driving unit12has a combination of a motor, a gear train, etc., which are for driving the above-described fixing device8.

Referring to part (a) ofFIG. 2, a pair of scanner stays13aand13bare supporting sections for supporting the scanner units4aand4b, each of which is an optical exposing device, and are connected in parallel to multiple points (three points in this embodiment) of the rear plate10with the use of small screws. Further, the pair of scanner stays13aand13bare connected to multiple points (two points in this embodiment) of the front stays14, with the use of small screws. In other words, the scanner stays13aand13bare fixing components for fixing the scanner units4aand4b, as image forming sections, to the main frame50.

Referring to part (b) ofFIG. 2, four shells2aof four process cartridges2, one for one, each of which holds the photosensitive drum3which is an image bearing component, are supported in parallel by the main frame50. The front side (−Y side) of the shell2ais held by the cartridge holding sub-frame24, which is held to the front stay14a, shown in part (b) ofFIG. 2, with the use of small screws. By the way, the cartridge holding sub-frame24is made up of multiple structural components connected to each other with the use of small screws. Further, the toner recovery device driving unit25, as a driving force transmitting device, which is a vibration source, is held to the top surface of the cartridge holding sub-frame24. The toner recovery device driving unit25has a combination of a motor, a gear trains, etc., for driving a conveyance screw for sending to an unshown recovery container, the toner discharged from each process cartridge2.

Next, referring toFIG. 3, the positioning of the optical system of each of the pair of scanner units4aand4bfixed to the main frame50as described above is described. Since the scanner units4aand4bare the same in structure,FIG. 3shows only the scanner unit4a. The scanner unit4abears a role of exposing two photosensitive drums1. More specifically, in this embodiment, it bears the role of exposing the photosensitive drum3which corresponds to the yellow (Y), and the photosensitive drum3which corresponds to the magenta (M) components of the image to be formed, whereas the scanner unit4bbears the role of exposing the photosensitive drums3which correspond to the cyan (C) and black (Bk) components of the image to be formed. Thus, the scanner unit4ahas the first scanning path which leads to the photosensitive drum3for the Y component, and the second scanning path which leads to the photosensitive drum3for the M component. It is provided with the first mirror opening202a, which is between a pair of fθ lenses201aand203a, which are in the first scanning path. It is also provided with the second mirror204awhich is on the downstream side of the fθ lens203a, in terms of the direction in which the beam of laser light in projected, in the first scanning path. Thus, the beam of laser light is guided to the photosensitive drum3for the Y component, by being deflected twice. Further, the scanner unit4ais provided with the first mirror202bwhich is positioned between a pair of fθ lenses201band203b, in the laser beam path in the second scanning path. It is also provided with the second mirror204b, which is positioned on the downstream side of the fθ lens203bin terms of the direction in which the beam of laser light is projected. Thus, the beam of laser light for the M component is guided to the photosensitive drum3by being deflected twice.

As described above, the main driving unit11for operating the photosensitive drum3and developing device3b, etc., and the fixing device driving unit12for driving the fixing device8, are made up of a motor and a gear train. They are attached to the rear plate10. When an image is formed by an image forming apparatus structured as described above, vibrations occur in the main driving unit11and fixing device driving unit12. The occurrence of these vibrations is primarily attributable to the meshing between the gears of the gear trains of the driving units, and the rotational imbalance of the motors.

Thus, as the vibrations which occurred in the driving units transmit through the main frame50and reach the scanner units4aand4b, the scanner unit4aand4bthemselves, and/or the optical components such as mirrors and lenses in the scanner units4aand4b, are made to vibrate by the vibrations from the driving units. If the frequency of the vibrations from the motors and gear trains is the same as the natural frequency of the scanner units4aand4b, and/or the optical components of the units4aand4b, the vibrations are amplified in amplitude. Consequently, the beams of laser light projected from the scanner units4aand4bare caused to periodically deviate from the intended point on the peripheral surface of the photosensitive drum3, causing thereby the image forming apparatus to output an image which suffers from periodic illusional strips, that is, an image defect which is referred to as “pitch anomaly”. In this embodiment, therefore, the amount by which the vibrations generated in the driving units are transmitted to the scanner units4aand4bis minimized with a structural arrangement, which will be described later.

Next, the method, in this embodiment, for reducing the amount by which vibrations are transmitted from the driving units to the scanner units4aand4b, is described in terms of principle. There is the following relationship among amplitude X [mm] of vibration at a point of evaluation of a structural component, an amount F [N] of load inputted into the structural component, and the transfer function H [mm/N] (vibration, per unit load, of given point):
X=F·H(1)

Adaptation of X, F and H in Equation (1) to the problems related to the above-described image defect which attributable to the vibrations of the scanner units4aand4b, and those of the internal components of the scanner units4aand4bleads to the following deduction.

To begin with, the vibration X of a point of evaluation is that of the second mirror204a, which is the point of final beam deflection in the scanner unit4a, and which is closely correlated to pitch anomaly. Assuming here that the structures, the characteristics of which are definable by the equation (1), are the scanner unit4aand scanner stay13a, the amount of the inputted load F is the amount of load injected into these structures. Thus, the amount of input load F may be thought to be the amount of load which transmits through the rear plate10and front plate unit14, and causes the scanner stay13ato vibrate. Further, the transfer function H of each of these structures can be expressed as the transfer characteristics of the portion of each structure, which is from the point of connection between the lateral plate of the scanner stay13a, to the second mirror204a, or the point of beam deflection.

Here, one of possible methods for reducing vibration X at the point of evaluation (vibration of optical component) is to reduce the transfer function H. For example, it is possible to increase the scanner stay13in thickness, and/or the number of times it is bent in the direction perpendicular to its lengthwise direction, or provide the scanner unit4awith internal ribs, in order to increase the rigidity of scanner stay13. It is also possible to attach an elastic component to the optical components (second deflection mirror204a, for example) to reduce the amount by which the optical components resonate with the vibrations transmitted thereto, in a specific mode. Both methods require additional measures, which results in cost increase. In the present invention, therefore, as the method for reducing vibration X at the point of evaluation in attention was paid to the amount of input load F, that is, the amount by which input load is transmitted to the scanner13athrough the lateral plate, instead of the transfer function H.

Next, the method for reducing the input load F is described. Generally speaking in terms of static rigidity, it has been known that if force is transmitted through a component that is made up two sections, which are different in rigidity, the component transmits more force through the section which is higher in rigidity than the section which is lower in rigidity. For example, referring toFIG. 4, it is assumed here that a load f is transmitted through a component made of multiple sections (vibration transmission paths) which are different in rigidity; the rigidity K of the top and bottom paths is greater than the rigidity k of the middle path. In this case, the amount f2by which the load is transmitted through the center path is smaller than the amounts f1and f3by which the load f is transmitted through the top and bottom paths, respectively. Thus, it is evident that if it is wanted to reduce the amount of load transmission in a specific path of a structural component having multiple load transmission paths, all that is necessary is to make the specific path less rigid than the other paths.

If it possible to apply concept such as the above-described one to an issue related to vibration, all that is necessary is to make the load path from each of the driving units which are the vibration sources, to the scanner stay13a, smaller in rigidity than other load paths. With the load path from each of the driving units to the scanner stay13abeing smaller in rigidity than the other load paths, the amount by which the input load F, which causes the scanner stay13ato vibrate, is transmitted to the scanner stay13a, becomes smaller, and therefore, it becomes possible to reduce the amount of vibration X in the second deflection mirror204a.

In the present invention, the lateral plate is not considered to be related to transfer function H. Instead, it is thought as a structural component (that is, input load F) which transmits load, for the following reason. That is, it is based on conventional knowledge that the specific mode of the lateral plate by which the driving units are held has virtually no effect upon the vibration X of an evaluation point (vibration of optical component).

[Concrete Structural Arrangement as Countermeasure to Vibrations]

Next, referring toFIGS. 5-8, the concrete structural arrangement as countermeasure to the vibrations, in this embodiment, is described.FIG. 5is a portion of the main structure, shown inFIG. 2, to which the scanner units4aand4bare fixed. By the way, hereinafter, only the scanner unit4aand scanner stay13aare described in detail. The description of the scanner unit4band scanner stay13bare the same as those of the scanner unit4aand scanner stay13a.

The scanner unit4ais held to the scanner stay13aat three points of the scanner stay13a. It remains pressed by three leaf springs in the direction indicated by an arrow mark Z (vertical direction in this embodiment). The scanner stay13ais fixed to the rear plate10of the main frame50. Thus, the scanner stay13ais equivalent to a component for fixing the scanner unit4a, which is an image forming section, to the main frame50, by which the scanner unit4ais supported.

The scanner stay13ahas: a bottom section33c, to which the scanner unit4ais attached, and a pair of bent sections33aand33b, which are formed by bending in the direction Z the lengthwise ends (in terms of the direction Y) of the bottom section33cand by which the scanner stay13ais attached to the front stay14a, and rear plate10, respectively. Thus, the scanner unit4ais held to the bottom section33cof the scanner stay13aby being pressed by the leaf springs, as described above. The reason why the scanner unit4ais held to the bottom section13aby the leaf springs as described above is that, even if the scanner stay13ais deformed by heat, the deformation can be absorbed by the leaf springs to prevent the scanner unit4afrom deforming.

The scanner stay13ais attached to the rear plate10(first supporting component) and front stay14a(second supporting component), by the bent sections33aand33bso that the bent sections33aand33bbecome parallel to each other. The rear plate10and front stay14a, as a pair of the first supporting components, oppose each other across the space in which the scanner unit4ais disposed, being thereby positioned in parallel in the direction Z. The rear plate10, and the front plate unit14which includes the front stay14a, are connected to each other by the connective stays18-23as connective sections.

The bent section33ais fixed to the rear plate10by its three sections26,27and28. As for the bent section33b, it is fixed to the front stay14aby its two connective sections29and30. In this embodiment, each connective section includes a small screw. Further, the rear plate10which is one of the plates to which the scanner stay13ais fixed, is provided with a slit126(first slit), a slit127(first slit), and a slit128(first slit), whereas the front stay14a, which is the other plate to which the scanner stay13ais fixed, is provided with a slit129(second slit) and a slit130(second slit). These slits are configured and positioned so that they are concentric with the connective sections (26,27,28,29and30, respectively), and concentrically extend by no less than 180° about corresponding connective sections, respectively. That is, each of the slits126-130is configured and positioned so that it concentrically extends, in the shape of a letter C, about the corresponding connective section (hole) by no less than 180°. In this embodiment, the slits126-130are through holes in terms of the thickness direction of the bent sections33aand33b.

Here, the connective sections26-28are the sections of the bent sections33a, by which the bent section33ais fixed to the rear plate10. The connective section26is on one side of the center (line B-B′ inFIG. 5) of the scanner unit4a, and the connective sections27and28are on the other side. More concretely, the left side of the bent section33a, in terms of the direction X of the scanner unit4a, is fixed to the rear plate10by the connective section26, whereas the right side of the bent section33ais fixed to the rear plate10by the connective sections27and28. Further, the slits126-128are positioned on the center side of the bent section33a, in terms of the direction X, relative to the connective sections26and28. That is, the slit126is configured and positioned so that it encircles at least the right side of the connective section26, inFIG. 5, whereas the slits127and128are positioned so that they encircle at least the left side of the connective sections27and28, respectively, inFIG. 5.

Similarly, the connective section29, which is one of the sections of the bent section33bby which the scanner stay13ais attached to the front stay14a, is on one side of the centerline (line B-B′ inFIG. 5) of the bent section33b, whereas the connective section30is on the other side of the centerline (line B-B′ inFIG. 5) of the bent section33b. More concretely, the left side of the bent section33binFIG. 5, in terms of the direction X of the scanner unit4a, is fixed to the front stay14aby the connective section29, whereas the right side of the bent section33binFIG. 5, is fixed to the front stay14aby the connective section30. Further, the slits129and130which concentrically surround the connective sections29and30, respectively, are positioned on the center side of the bent section33bin terms of the direction X, relative to the connective section29and30. That is, the slit129which concentrically surrounds the left connective section29inFIG. 5is configured so that it encircles at least the right side of the connective section29. As for the slit130which is formed in the adjacencies of the right connective section30is positioned so that it encircles the left side of the connective section30. These five slits126-130are the same in configuration, although they are different in the side of the corresponding connective section they encircle.

In this embodiment, as described above, the scanner stay13a, by which the scanner unit4ais held, is provided with the connective sections26-28, by which the scanner stay13ais attached to the rear plate10, which is a part of the main frame50. It is also provided with the slits126-128which concentrically surround the connective sections26-28. Further, the scanner stay13ais provided with the connective sections29and30, by which the scanner stay13ais attached to the front stay14a, which also is a part of the main frame50. It is also provided with the slits129and130which concentrically surround the connective sections29and30. Thus, the load paths from the driving units supported by the main frame50to the scanner stay13a, which go through the connective sections26-30, are less in rigidity than the other load paths. In other words, the input load F in the above-described equation (1) is smaller, and therefore, the point of evaluation of the scanner stay13a, and that of the scanner unit4aare smaller in the amplitude X.

Here, it is the bent sections33aand33bof the scanner stay13athat are provided with the slits126-130. Therefore, there is an effect that the transfer characteristics H in equation (1), which is related to the transfer characteristic of a structure, is not increased for the following reason. That is, the slits, with which the bent sections33aand33bare provided, has little effect upon the transfer characteristic (characteristic frequency) of a “structural component” in terms of essential specific modes. As for the specific modes, there are a mode in which bottom section33cof the scanner stay13avibrates, a mode in which the scanner unit4arigidly vibrates in the direction Z, and a mode in which the scanner unit4avibrates in a manner of being twisted. Therefore, if a slit is formed around the point of connection between the bottom section33cand scanner unit4a, for example, it is possible that a “structural component” will change in the above-described specific modes, and therefore, the “structural component” will increase the transfer characteristic H. Thus, even if the input load F can be reduced by the formation of the slit, the structural component increases in the transfer characteristics H. Therefore, it is possible that the amplitude X at the point of evaluation will not be reduced. In this embodiment, therefore, the bent sections33aand33b, which are unlikely to be affected by the vibrations in the above-described specific modes and also are unlikely to be changed in the specific modes by the formation of the slits, are provided with the slits.

Next, referring toFIGS. 6 and 7, the configuration of each of the slits126-130formed as described above is described. By the way, the slits126-130are the same in configuration. Therefore, only the configuration of the slit126is described, as the one which represents all the slits. The slit126is formed so that it continuously encircles the connective section26by no less than 180°. In this embodiment, the scanner stay13ais 1 mm in thickness, and the slit126, which is positioned in a manner to encircle the connective section26, is 15 mm in external diameter, 11 mm in internal diameter, and 270° in the angle θ of encirclement. That is, the slit126is in the form of an arc. The center of the slit126and the center of the connective section26(center of small screw) roughly coincide with each other.

The dimension of the slit126is optional, as long as the bent sections33aand33bremains sufficiently rigid (in other words, a part (connective section26) does not break away). Regarding the dimension of the slit126in terms of the diameter direction, for example, the slit126may be formed so that its internal diameter becomes 11 mm, and its external diameter falls within a range of 15 mm-19.6 mm. Incidentally, the reason why the slit126was made to be 11 mm in internal diameter is to ensure that the connective section26is provided with an area (seat) for the head of a small screw. Regarding the angle θ of encirclement of the connective section26by the slit126, as long as it is no more than 300°, the bent section33ais provided with a sufficient amount of rigidity. Therefore, the angle θ is desired to be no more than 300°. However, in consideration of the fact that it is possible that the image forming apparatus100will fall during its shipment, and also, in consideration of the resultant vibrations and impact, the angle θ is desired to be no more than 270°, to afford some latitude in terms of rigidity. As for the smallest value for the angle θ, it is desired to be 180°, for the following reason.

FIGS. 7 and 6are graphs which are related to the angle θ by which the slit126encircles the connective section26. More specifically, they show the relationship between the angle θ of encirclement of the connective section26by the slit126, and the ratio of change in the rigidity of the scanner stay13a. The graphs show how much a structural component (formed of plate) changes in rigidity, compared to a structural component having no slit (that is, when θ=0), as the slit126is increased in the angle θ of encirclement. These results were obtained with the use of a finite element method (FEM). More concretely, referring toFIG. 6, the connective section26is restrained, and the reciprocal of the amount of positional deviation which occurred to the point (connective section26) to which a unit amount of static load is applied from two directions, that is, horizontal direction Fx and vertical direction Fz in the drawing, is used as the amount of rigidity. Further, the slit126was formed so that it becomes symmetrical with reference the horizontal line C-C′ to prevent the model from being rotated by the load.

Referring toFIG. 7, regarding the horizontal load Fx, as the slits126was increased in the angle θ of encirclement, the connective section26roughly linearly reduced in rigidity. It is evident fromFIG. 7that when the angle θ of encirclement of the slit126is 180°, the connective section26was roughly 28% less in rigidity. On the other hand, regarding the vertical load Fz, when the slit126is small in the angle θ of encirclement, it is not effective to reduce the connective section26in rigidity. However, as the slit126was increased in the angle θ of encirclement to no less than 180°, its effectiveness in reducing the connective section26in rigidity increased by the square of the amount by which the slit126was increased in the angle θ of encirclement. For example, when the angle θ of encirclement of the slit126was no more than 120°, the amount by which the connective section26was reduced in rigidity was no more than 5%. However, as the slit126was increased in the angle θ of encirclement to 180°, 240° and 300°, the connective section26was reduced in rigidity by 13%, 30% and 50%, respectively. Thus, it is evident that it is wanted to reduce the connective section26in rigidity with regard to all the directions from which load is inputted (loads Fx and Fz from driving units), the angle θ of encirclement of the slit126, is desired to be no less than 180° (half of circumference). In this embodiment, the angle θ was set to 270° as described above. This configuration of the connective section26and its adjacencies is effective to reduce the connective section26in rigidity by roughly 40% with regard to both the horizontal and vertical input load Fx and Fz.

Next, the slit126having the above-described angle θ of encirclement is described about its positioning relative to the connective section26of the scanner stay13ais described. By the way, the positional relationship between the slits129and130of the scanner stay13a, shown inFIG. 5, and the connective sections29and30of the scanner stay13ais the same in concept as the positional relationship between the slit126and connective section26. Hereinafter, therefore, only the positioning of the slits129and130relative to the connective section29and30of the front stay14ais described in detail. That is, the positioning of the slits126-128relative to the connective section26-28of the rear plate10is not described.

Part (a) ofFIG. 8is a sectional view of the connective sections29and30of the front stay14a, and the scanner stay13a, respectively (at plane which coincides with center of connective section29, and center of connective section30, inFIG. 5). Referring to part (b) ofFIGS. 8 and 8(c), the slits129and130are opposite in positioning (attitude) in terms of the direction X, as described above. The slits with which the scanner stay13ais provided are intended to reduce the connective sections in rigidity in terms of all directions (input loads Fx and Fz from driving units). Therefore, they are formed in the above-described position and attitude. To elaborate this point, referring to part (a) ofFIG. 8, because the bent section33bof the scanner stay13ais provided with the slits129and130, the bent section33bis compressed in the direction X by the load which comes from the direction Fx in the drawing. Therefore, the slits129and130are positioned on the scanner unit4aside of the connective sections29and30, in order to reduce in rigidity the load path of the bent section33b, which is to be compressed in the direction X.

The slits with which the scanner unit4ais provided are effective in a case where the load Fx is dominant. Thus, in a case where the load Fx is dominant, the slits may reversed in attitude. In essence, all that is necessary is that the slits are present in the path through which a load transmits to the scanner unit4a, so that the presence of the slits reduces the path in rigidity. However, it is desired that the slits are placed in the dominant load transmission path between the connective section29and scanner unit4a, and that between the connective section30and scanner unit4a, for example.

In this embodiment, the bent section33ais provided with the slits126-128, which encircle the connective sections26-28, respectively, by no less than 180°. Thus, it is possible to reduce the amount by which vibrations are transmitted to the scanner unit4afrom the driving units, in any of multiple transmission modes, even thought the means for preventing the vibration transmission is simple in structure. That is, the slits126-128are provided in the adjacencies of the connective sections26-28, respectively, of the bent section33a, by which the scanner stay13ais attached to the rear plate10of the main frame50which supports various driving units. Further, the slits129and130are provided in the adjacencies of the connective sections29and30, respectively, of the bent section33b, by which the scanner stay13ais attached to the front stay14aof the main structure50. Thus, the adjacencies of the connective sections26-30by which the scanner stay13is attached to the main frame50are smaller in rigidity than the other sections of the apparatus main assembly. Therefore, the amount by which load is inputted into the scanner stay13athrough the connective sections26-30is smaller. In other words, the load attributable to the vibrations from the driving units is transmitted by a greater amount to the other sections of the image forming apparatus, which are higher in rigidity than to the scanner stay13athrough the connective sections26-30, from the main frame50. Therefore, the scanner stay13ais smaller in the amount by which it receives the vibrations attributable to the driving units. Therefore, the scanner unit4ais smaller in the amount by which it receives the vibrations from the driving units. Therefore, the image forming apparatus is less likely to suffer from image defects such as pitch anomaly.

Further, a shock absorbing component, for example, formed of rubber or the like substance is not placed between the scanner stay13aand main frame50. Therefore, it is ensured that the scanner unit4aand photosensitive drum3remain precisely positioned relative to each other. In particular, in this embodiment, no shock absorbing component is provided even between the scanner unit4aand scanner stay13a. Therefore, the scanner unit4aand photosensitive drum3remain precisely positioned to each other at a higher level accuracy. By the way, if an elastic component formed of rubber or the like substance is used to reduce the amount by which vibrations are transmitted to the scanner unit4a, it is possible that the elastic component will be made to deteriorate by environmental causes and/or elapse of time, and therefore, will fail to continuously reduce the amount by the vibrations are transmitted to the scanner unit4a. In comparison, in this embodiment, such an elastic component is not employed, and therefore, it is possible to continuously reduce the amount by which vibrations are transmitted to the scanner unit4afor a long period of time.

Embodiment

Next, referring toFIG. 9, the tests conducted to confirm the effectiveness of this embodiment are described.FIG. 9shows the results of the comparison, in terms of vibration amplitude, between an image forming apparatus, the bent sections33aand33bof the scanner stay13a, which are provided with the slits126-130in the shape of a letter C as described above, and an image forming apparatus which is not provided with the slits126-130. In the tests, vibrations are applied to the main frame50under two conditions, that is, the first and second conditions, and the vibrations were measured in amplitude at various frequencies. In the first condition (vibration1), it is assumed that the fixing device driving unit12is the driving force source. The fixing device driving unit12is attached to the rear plate10(vibration is transmitted in direction Z). Thus, a vibration generator was positioned in the adjacencies of the fixing device driving unit12. As for the second condition (vibration2), it is assumed that the vibration source is the toner recovering device driving unit25attached to the rear plate10(vibration is transmitted in direction Z). Thus, the driving force source of which is attached to the front plate unit14. Thus, the vibration generator was positioned in the adjacencies of the toner recovering device driving unit25.

In the tests, the main frame50shown inFIG. 2was used. As the point of evaluation, the second mirror204of the scanner unit4bfor black component was selected for both tests. Regarding vibration generation, if the driving units are operated as the vibration sources, that is, if the gear trains and motor are operated, the evaluation is done for only the specific frequency. In this embodiment, therefore, vibration generators were placed in the adjacencies of the driving force source as described above. Further, the point of evaluation was evaluated in the amplitude of the vibration, under the same condition in terms of vibration, across the entire spectrum of vibration in terms of frequency. That is, the vibration generators were kept stable in the amount (amplitude) of vibration, and were gradually varied in frequency in a manner to sweep the entire frequency range. The vibrations were measured in amplitude at the points of evaluation. In these tests, the vibrations were changed in frequency within a range of 0-1280 Hz. Further, the vibrations were generated for a length of 1.6 seconds at each frequency.

“No vibration” (dotted line) inFIG. 9indicates the vibration level (amplitude) of the connective sections having no slit. A solid line stands for the vibration level (amplitude) of the connective section having the slits126-130. Numbers1,2and3(models1,2and3) surrounded by circles stand for the range of each of specific modes extracted and separated with the use of the modal tests carried out independently from the vibration tests. By the way, “modal test” is a vibration test to be carried out to identify the dynamic characteristics (mode characteristic) of an object. In the vibration test, vibrations are applied to a given point of the main frame50as an object to vibrated. Then, both the vibration input and acceleration are measured to extract the characteristics of the second mirror204as the object to be tested. As the items in the above-described equation (1) are substituted with the thus obtained values (characteristics), the acceleration is X; characteristics of the object to be tested, H; and vibration input is F. In these tests, the vibrations peaked in amplitude across three specific mode ranges, under both the first and second conditions (vibrations1and2).

As is evident from part (a) ofFIGS. 9 and 9(b), providing the slits reduces the point of evaluation in the amplitude of vibration in each specific mode, regardless of the condition. Part (c) ofFIG. 9is a graph that shows the relationship between the amount by vibrations wee reduced in amplitude and three specific modes. It shows the ratio of the average amplitude value in each of three mode (modes1,2and3) in part (a) ofFIGS. 9 and 9(b), relative to that when no slit was provided. Therefore, if the vibrations are reduced in amplitude, the ratio of change in amplitude becomes negative. As is evident from part (c) ofFIG. 9, by forming a slit in the immediate adjacencies of the connective section as in this embodiment, it is possible to reduce the connective section in the amplitude of the vibration, regardless of the direction (vibrations1and2) in which vibrations are transmitted to the connective section, in all the specific modes (modes1,2and3).

Next, referring toFIG. 10, the second embodiment of the present invention is described. In the case of this embodiment, the front stay14ais provided with positioning sections for precisely positioning the scanner stay13aand front stay14arelative to each other, in addition to the structural arrangements provided in the first embodiment. Otherwise, the structural components in this embodiment, and their functions, are the same as the counterparts in the first embodiment. Hereafter, therefore, description is focused upon the difference of this embodiment from the first embodiment.

The front stay14ais provided with a pair of positioning pins31aand31b, which are integrally formed with the front stay14aor formed independently from the front stay14aand then attached to the front stay14a. On the other hand, the bent portion33bof the scanner stay13ais provided with a pair of holes32aand32b, as positioning holes, into which the positioning pins31aand31bcan be fitted. Thus, the scanner stay13acan be precisely positioned relative to the front stay14awhen the scanner stay13ais attached to the main frame50. Further, it is possible to prevent the problem that, with the elapse of time, the front stay14aand scanner stay13adeviate in position from each other due to the slippage or the like of small screws.

More specifically, one of the two positioning pins31aand31bis used to precisely position the front stay14aand scanner stay13arelative to each other in terms of both the directions X and Y, and the other pin31is used to precisely position the front stay14aand scanner stay13ain terms of the direction Z. In this embodiment, therefore, one of the holes32aand32bwas made round, whereas the other was elongated in the direction Z so that the front stay14aand scanner stay13aare precisely positioned relative to each other in terms of the direction parallel to the short axis of the elongated hole32. For example, the hole32awas made perfectly round, whereas the hole32bwas given an elongated round shape. Thus, the positioning pins31aand31bare fitted into the holes32aand32b, respectively, to precisely position the scanner stay13arelative to the front stay14a. Then, the scanner stay13awas fixed to the front stay14awith the use of small screws.

These positioning sections which are in the adjacencies of the connective sections29and30do not have strength like a small screw. Therefore, it hardly occurs that this positioning structure negatively affects the effectiveness of the slits. This invention is based on the idea of diverting the load F inputted into a structural component, to a specific path by reducing the specific path in rigidity relative to other paths. In other words, it is not intended to absorb (attenuate) the vibrations. Therefore, it is possible to reduce the amount by which vibrations are transmitted to each scanner unit4, while ensuring that each scanner unit4and corresponding photosensitive drum3remain precisely positioned relative to each other. By the way, in this embodiment, the positioning protrusions were in the form of a pin. However, they may be in the form of a structural component formed by embossing, or by cutting-and-bending (perpendicularly erecting) parts of the front stay14a. Further, it may be the scanner stay13athat is provided with the positioning protrusions, whereas it may be the front stay14athat is provided with the positioning holes. Moreover, it is not mandatory that the rear plate10and scanner stay13aare provided with positioning components such as the above-described ones.

Next, referring toFIG. 11, the third embodiment of the present invention is described. In each of the above-described embodiments, it was the scanner stay13athat was provided with the slits. In comparison, in this embodiment, it is the main frame50(FIG. 2) that is provided with the slits. By the way, the concept of providing a slit in the adjacencies of the connective sections by which the scanner stay13aare fixed to the rear plate10is the same in principle as the concept of providing the adjacencies of the connective sections by which the scanner stay13ais connected to the front stay14a. Therefore, only the slits229and230with which the connective sections29and30by which the scanner stay13ais connected to the front stay14aare described in detail. That is, the connection between the scanner stay13aand rear plate10is not described.

Referring toFIG. 11, the adjacencies of the connective sections29and30of the front stay14aare provided with slits229and230, respectively. The slits with which the main frame50for holding the scanner stay13ais provided are different in the phase (direction) from the slits with which the scanner stay13ais provided in each of the preceding embodiments. More concretely, the slits229and230are on the opposite side of the connective sections29and30, respectively, from the centerline B-B′ of the scanner unit4a.

More concretely, the connective sections29and30are the sections by which the bent section33band front stay14aare connected to each other on one side of the scanner unit4aand the other, respectively, relative to the center line B-B′ of the scanner unit4a. That is, the slit229, which is in the adjacencies of the left connective section29(shown in part (a) ofFIG. 11) extends in a manner of encircling at least the right side of the connective section29, as shown in part (c) ofFIG. 11. As for the slit230, which is in the adjacencies of the left connective section30shown in part (a) ofFIG. 11, the slit230extends in a manner to encircle at least the left side of the connective section30, as shown in part (b) ofFIG. 11. In other words, the slits are reversed in position, depending on which component is provided with the slits.

In this embodiment, in order to deal with the load which comes from the direction Fx in the drawing, the path from the connective sections29and30to the scanner stay13ais reduced in rigidity on the front stay14aside. Thus, the slits are positioned on the opposite side of the connective sections29and30from the center line B-B′ of the scanner unit4a. By the way, it is when the Fx load is dominant that positioning the slits as described above is effective to reduce the amount by which vibrations are transmitted to the connective sections29and30. Therefore, in a case where the Fx load is dominant, even if it is the front stay14a, or the like, of the main frame50that is provided with the slits, the slits may be positioned as in the first embodiment. Further, this embodiment is especially effective in a case where the load Fx is transmitted from the outward side of the connective sections29and30(opposite side from center of the scanner unit4a). That is, in a case where the front stay14aor the like of the main frame50is provided with the slits, the slits are desired to be on the upstream side of the connective sections29and30, in terms of the direction in which the load is transmitted from the vibration source to the scanner unit4a. As described above, this embodiment can reduce the amount by which load is inputted into the scanner stay13aby way of the connective sections29and30. Except for the above-described structural components and the functions thereof, this embodiment is the same as each of the above-described embodiments.

Next, referring toFIG. 12, the fourth embodiment of the present invention is described. In this embodiment, both the main frame50(FIG. 2) and scanner stay13awere provided with the slits, which were placed in the adjacencies of the connective sections. That is, the scanner stay13ais provided with the slits129and130as in the first embodiment, as shown inFIG. 8, and also, the front stay14aof the main frame50is provided with connective section return screw229and230as in the third embodiment, as shown inFIG. 11. With the provision of the four slits129,130,229and230in the adjacencies of the connective sections29and30, the load path to the scanner stay13ais further reduced in rigidity, and therefore, the amount by which vibrations are transmitted through the load path is further reduced. By the way, the concept of placing the slits in the adjacencies of the connective sections by which the scanner stay13ais connected to the rear plate10, is the same in principle as the concept of placing the slits in the connective sections by which the scanner stay13ais connected to the front stay14a. Further, except for the above-described structural arrangements and their effects, this embodiment is the same as each of the above-described embodiments.

Next, referring toFIG. 13, the fifth embodiment of the present invention is described. In each of the above-described embodiments, the slits were formed so that they extend in a manner to encircle the corresponding connective sections by no less than 180°. In comparison, in this embodiment, two or more slits are provided in the adjacencies of each connective section so that the combination of the slits encircles the connective sections by no less than 180°. Although this embodiment is described with reference to only the slits in the adjacencies of the connective section26, the slits in the adjacencies of the other connective sections are the same as those in the adjacencies of the connective section26.

Referring toFIG. 13, there are provided multiple slits in the adjacencies of the connective section26. These slits are different in position in terms of the radius direction of the connective section26. The center of curvature of each slit coincides with the center of the connective section26. More concretely, in this embodiment, the multiple slits326a,326b,426aand426bare provided in the adjacencies of the connective section26. It may be either the main frame50or scanner stay13athat is provided with the slits326a,326b,426aand426b. In this embodiment, it is the bent section33aof the scanner stay13athat is provided with the slits326a,326b,426aand426b. Further, the multiple slits326a,326b,426aand426bare configured and positioned so that the connective section26are entirely encircled by the combination of the slits326a,326b,426aand426b.

To describe more concretely, the slits326aand326bare positioned so that they coincide with a circle, the center of which coincides with the center of the connective section26(axial line of small screw), whereas the slits426aand426bare positioned so that they coincide with another circle, which are greater in radius than the first circle, and the center of which coincides with the center of the connective section26. That is, the pair of slits326aand326bare configured and positioned so that they coincide with the inner of the two circles which are different in radius, and the center of which coincides with that of the connective section26, whereas the pair of slits426aand426bare configured and positioned so that they coincide with the outer of the two circles. Further, in terms of the vertical direction (direction Z) inFIG. 13, the slits326aand326bare positioned so that the former is on the bottom side of the connective section26, whereas the latter is on the top side of the connective section26. As for the slits426aand426b, they are positioned on the left and right sides, respectively, of the connective section26in terms of the left-right direction (direction X) inFIG. 13. Further, they are symmetrically positioned with reference to the center of the connective section26. Moreover, the slits326aand326bextend in a manner to encircle the connective section26by 120°. Further, they are positioned so that their one half extends leftward of a line which is parallel to the direction Z and coincides with the center of the connective section26, by a distance equivalent to 60° and the other half extends rightward of the line which is parallel to the direction Z. As for the slits426aand426b, they extend in the direction parallel to the circumferential direction of the connective section26by a distance equivalent to 120°. More specifically, they are positioned so that their top half, with reference to the horizontal line which coincides with the center of the connective section26, extends upward by a distance equivalent to 60°, and the bottom half extend downward by a distance equivalent to 60°. Thus, the combination of the multiple slits326a,326b,426aand426bentirely encircles the connective section26while overlapping with each other in terms of the circumferential direction of the connective section26. In a case where multiple slits are configured and positioned so that they overlap with each other in terms of the circumferential direction of the connective section26, it is desired, from the standpoint of reducing the amount by which vibrations are transmitted through the connective sections, that the combination of the adjacent two slits continuously encircles the connective section26by no less than 180°.

More concretely, the scanner stay13awas made to be 1.0 mm in thickness. Further, the inward slits326aand326bwere made to be 8 mm in internal diameter, 11 mm in external, and 120° in the angle θ of encirclement, whereas the outward slits426aand426bwere made to be 15 mm in internal diameter, 18 mm in external diameter, and 120° in the angle θ of encirclement.

In this embodiment, the connective section26is entirely encircled by the combination of multiple slits. Therefore, the amount by which vibrations are transmitted to the connective section26are satisfactorily reduced whether the vibrations come from the direction X (load Fx) or Z (load Fz). By the way, the configuration, numbers, and angle θ of encirclement can be properly set by a static rigidity test which uses the above-described finite element method (FEM). Sections, in this embodiment, other than the above-described ones are the same in structure and function as the counterparts in each of the above-described preceding embodiments.

Next, referring toFIG. 14, the sixth embodiment of the present invention is described. In the description of each of the above-described embodiments, focus was on the sections of the scanner stay13a(including their adjacencies) by which the scanner stay13a, which holds the scanner unit4a, is connected to the main assembly50. However, the pitch anomaly attributable to the vibrations of the driving units attached to the main frame is a problem attributable to the positional deviation between the beam of laser light projected from the scanner unit4a, and the photosensitive drum. Therefore, the pitch anomaly also occurs for the following reason. That is, the vibrations having occurred within the driving units reach the photosensitive drum3through the main frame and cause photosensitive drum3to vibrate. As a result, the positional relationship between the beam of laser light and photosensitive drum3periodically changes. Consequently, the pitch anomaly occurs. In this embodiment, therefore, the present invention was applied to the point of connection between the cartridge holding frame51, which is the portion of the process cartridge, by which the photosensitive drum3, which is an image bearing component, is held, and the main frame50. By the way, the slits formed in the adjacencies of the connective sections in this embodiment are basically the same as those formed in the adjacencies of the point of connection between the scanner unit4aand main assembly50. Therefore, the sections of the point of connection between the cartridge supporting frame51and main frame51, in this embodiment, which are similar to the counterparts in each of the above-described embodiments, are not described at all, or is described only briefly. Further, they are not illustrated at all, or is described only schematically. That is, the description of this embodiment is focused on the sections of this embodiment, that characterize this embodiment.

FIG. 14is a sectional view of the structural components by which the process cartridge2, which includes the photosensitive drum3, is held to the main frame50. The process cartridge2which contains the photosensitive drum3is held by the cartridge supporting frame51as a section by which the photosensitive drum3is fixed to the main frame50. The cartridge supporting frame51is made up of four components, more specifically, stays34,35,36and37, which are attached to each other with the use of small screws44-47. The cartridge supporting frame51is connected to the rear plate10and front stay14aof the main frame50. That is, a pair of stays34and35are connected to the front stay14aand rear plate10, respectively. The front stay14aand rear plate10are a pair of supporting sections which are positioned on one side of the space, in which the photosensitive drum3is placed, and the other.

Concretely, the front stay14a, which is a supporting plate for supporting the cartridge supporting frame51and stay34, by one side of the cartridge supporting frame51and stay34, and are connected to each other at connective sections38and39(with use of small screws). Further, the rear plate10, which is the supporting plate on the other side, and the cartridge stay35, which is the fixing plate on the other side, are positioned relative to each other at positioning sections40and41. The positioning section40is a combination of a positioning pin42a, and a positioning hole43ain which the positioning pin42afits. The positioning section41is a combination of a positioning pin42b, and a positioning hole43bin which the positioning pint42bfits.

The positioning pin42aand42bare formed as integral parts of the stay35, or separately formed from the stay35and attached to the stay35. On the other hand, the rear plate10is provided with the positioning holes43aand43b, into which the positioning pins34cand34dcan be fitted. In this embodiment, one of the positioning holes43aand43bis formed round, and the other is given an elongated round shape, the long axis of which is parallel to the direction Z. That is, the positioning holes43aand43bare configured so that the stay35and rear plate10align in the direction parallel to the short axis of the elongated hole. For example, the positioning hole43ais made to be round, whereas the positioning hole43bmay be elongated.

Further, in this embodiment, the cartridge stay34of the cartridge supporting frame51is provided with a pair of slits138and139, which are formed in the adjacencies of the connective sections38and39, respectively, and positioned as shown in part (b) ofFIGS. 14 and 14(c). The details of the configuration and positioning of the slits138and139are the same as those of the slits shown inFIG. 6. The positioning of the slits138and139in terms of attitude relative to the connective section is the same as the slits shown inFIG. 8. That is, the connective section38is on one side of the rotational axis of the photosensitive drum3, whereas the connective section39is on the other side. The connective sections38and39connect the cartridge stay34to the front stay14a. The cartridge stay34is provided with the slits138and139, which are configured and positioned so that they are on the photosensitive drum side of the connective sections38and39, respectively.

The cartridge stay35of the cartridge supporting frame51is provided with a pair of slits140and141, which are positioned in the adjacencies of the positioning sections40and41, respectively, as shown in part (d) ofFIGS. 14 and 14(e). The details of the configuration and positioning of the slits140and141are the same as those of the above-described slits138and139, and therefore, they are not described here.

In this embodiment, the cartridge stay35of the cartridge supporting frame51, and the rear plate10are not connected to each other with the use of small screws. They are positioned relative to each other, and held to each other, only by the engagement between the positioning pins34cand34d, and positioning holes. Therefore, unlike the second embodiment shown inFIG. 10, the rear end portion of the cartridge supporting frame51is supported by the rear plate10, and is positioned by the engagement between the positioning pins42aand42b, and positioning holes43aand43b, respectively. In this embodiment, therefore, the points of engagement between the positioning pin42aand42b, and positioning holes43aand43bhave a sufficient amount of retention force. Therefore, these points may be deemed connective sections (elements). These points of engagement function as positioning sections40and41.

Also in this embodiment, the slits138and139are provided in the adjacencies of the connective sections38and39, respectively, and the slits140and141are provided in the adjacencies of the positioning sections40and41. Therefore, it is possible to reduce in rigidity the path through which vibrations (load) is inputted into the cartridge supporting frame51, no matter from which direction the load is inputted. Therefore, it is possible to reduce the amount by which the photosensitive drum3is made to vibrate by the vibrations from the driving units. Therefore, it is possible to prevent the occurrence of image defects such as pitch anomaly.

The above-described slit configuration and slit positioning are not intended to limit this embodiment in terms of slit configuration and slit positioning. That is, this embodiment is compatible with all of the slit configurations and slit positioning in each of the preceding embodiments.

In the first to fifth embodiments, the bent sections33aand33b, rear plate10, and front stay14aare formed of a piece of metallic plate or the like, and at least one of them is provided with slits. However, a component which is not provided with slits does not need to be flat. For example, in a case where the bent sections33aand33b, by which the scanner stay13ais attached to the main frame50, are provided slits, the supporting sections of the main frame50, to which the bent sections33aand33bare attached, do not need to be formed of a piece of metallic plate or the like. For example, they may be columnar. Similarly, in a case where the rear plate10and front stay14a, which are formed of a piece of metallic plate or the like, and by which the scanner stay13ais supported, are provided with slits, the sections of the scanner stay13a, by which the scanner stay13ais attached to the rear plate10and front stay14ado not need to be flat. For example, they may be columnar. Similarly, also in the case of the sixth embodiment, at least one of the cartridge stays34and35which are formed of a piece of metallic plate or the like, and at least one of the rear plate10and front stay14a, are provided with slits. However, the component which is not provided with slits does not need to be flat.

Further, in the first to fifth embodiments, the slits were provided in the adjacencies of the connective sections, by which the scanner stay13awhich holds the scanner unit4a, is connected to the main frame50. However, these embodiments are not intended limit the present invention in scope in terms of the configuration and positioning of the slits. For example, the slits may be provided in the adjacencies of the points of connection between the scanner unit4aand scanner stay13a. Here, in a case where the slits are provided in the adjacencies of the points of connection between the bottom plate33cof the scanner stay13a, and the scanner unit4a, it is possible that the main frame will change in specific mode, and therefore, will increase in transmission characteristics H. However, in certain cases, the main structure does not increase in transmission characteristics H, even if the slits are provided in the abovementioned connective section, although it depends on the transmission characteristics of the main structure (structural component). Even in a case where the structural component increases in transmission characteristics H, as long as the amount by which the slits reduces the amount by which the inputted load is transmitted is greater than the increase in the transmission characteristics H of the structural component, the slits may be provided in this area.

Further, the connecting means does not need to be limited to a small screw. That is, means other than a small screw may be employed as long as it can keep connected, the holding section and the section to be held. For example, the holding section and the section to be held, may be connected to each other with the use of a combination of a nut and a bolt, crimping, welding, or engagement between a protrusion, and a recess or hole.

Further, the present invention is applicable to such an image forming apparatus as a copying machine, a printing machine, a facsimile machine, a multifunction machine capable of performing two or more functions of the preceding machines, etc. Moreover, the present invention is also applicable to a monochromatic image forming apparatus, in addition to a full-color image forming apparatus. Further, the present invention is applicable to an image forming apparatus of the so-called direct transfer type, in addition to an image forming apparatus of the so-called intermediary transfer type, such as the one described above. That is, the present invention is applicable to various conventional image forming apparatuses which are different in structure.

This application claims the benefit of Japanese Patent Application No. 2015-057876 filed on Mar. 20, 2015, which is hereby incorporated by reference herein in its entirety.