1. Field of the Invention
The present invention relates to a fitting structure for fastening a doctor blade provided in a developing device to regulate the amount of developer, a cleaning blade provided in a cleaning device, or the like in an image forming apparatus such as a facsimile machine, a printer, a copier, or the like, to the body of the apparatus.
2. Description of Related Art
In recent years, there have been very strong demands for higher image quality in image forming apparatuses. On the other hand, demands for lower costs have also been increasing. Thus, methods for reducing initial costs while maintaining high image quality have been sought. As one solution, attention has been paid to techniques for easy and accurate gap/contact width adjustment and fitting of a doctor blade in a developing device and of a cleaning blade in a cleaning device.
Ideally, such adjustment should best be dispensed with (adjustment-free); however, in adjustment of a dimension directly related to improvement of image quality, higher dimensional accuracy is demanded than common dimensional tolerances. For example, the gap of a doctor blade in a developing device has to be within a tolerance range as small as about ±0.05 mm to ±0.1 mm; otherwise, uneven density, fogginess, or carrier deposition may result.
The dimensions of, and the fitting accuracy of, a plate-form member such as a doctor blade or a cleaning blade have variations, and suppressing these variations further within common dimensional tolerances requires corresponding costs. Accordingly, when the plate-form member is fitted to the body of an apparatus, positioning adjustment is performed as one conceivable way of achieving tighter dimensional tolerances while suppressing increases in costs.
For example, Patent Document 1 (Japanese Patent Publication No. H07-181802) discloses a doctor gap adjustment mechanism which allows accurate automatic adjustment of the gap (doctor gap) between a developing roller and a doctor blade. Here, after temporary positioning is performed by use of temporary positioning pins, the doctor blade is offset by a predetermined amount by use of adjustment pins, and is thereby positioned.
On the other hand, according to Patent Document 2 (Japanese Patent Publication No. 2001-100517), a support portion is provided in a developing container, and when a doctor blade is fastened to the developing container, a backup member is brought into contact with the support portion to prevent deformation of the developing container. Patent Document 2 thus discloses a method of accurately positioning and fastening a doctor blade even when the doctor blade or another component has a manufacturing variation. Moreover, according to Patent Document 2, the edge position of the doctor blade is detected with a camera. Thus, even when the doctor blade sags in its thickness direction and thus has a variation, it is possible to suppress a variation due to screw tightening and achieve easy and accurate positioning. It is also possible to simplify the inspection process.
However, with the technology disclosed in Patent Document 1, the actual value of the doctor gap after adjustment is unknown, and therefore it needs to be checked in an inspection process as conventionally practiced. With the technology disclosed in Patent Document 2, consideration is given to the pressing force of a screw driver during screw tightening, but no consideration is given to the tightening torque that acts upon the doctor blade during screw tightening. Moreover, during screw tightening, the doctor blade is fastened with contact pins pressed against it; when the contact pins are pressed against it, the doctor blade may be displaced, or may yield to the screw tightening torque and slide.
According to one aspect of the present invention, a fitting structure for fitting a plate-form member to a fitting destination member such that the position of the plate-form member relative to a target member is adjustable includes: an adjustment pin that is inserted, in a fashion movable in a position adjustment direction, in an adjustment hole formed in the plate-form member; and a screw member for fastening the plate-form member to the fitting destination member. Here, the direction of the force of the screw member that acts upon the plate-form member when the screw member is in the position where it fastens the plate-form member points from the side where a gap formed between the adjustment pin and the adjustment hole is smaller to the side where the gap is larger.
Preferably, the adjustment hole in the plate-form member has at least one of a circular shape, an elliptic shape, an oval shape, and an elongate shape.
Preferably, the side edge of the plate-form member opposite the target member has a curved shape. Further preferably, the side edge of the plate-form member opposite the target member has a curved shape protruding, in a central part in the longer-side direction, toward the target member.
Preferably, the adjustment hole in the plate-form member comprises three or more adjustment holes formed spaced from one another in the longer-side direction of the plate-form member.
Of the adjustment holes in the plate-form member, the adjustment hole arranged in a central part of the plate-form member in the longer-side direction thereof may have a circular shape and the adjustment holes arranged in both end parts of the plate-form member may have an elongate shape in the longer-side direction.
Preferably, cuts are formed in the plate-form member, in the side edge thereof facing away from the side edge opposite the target member, between every two adjacent ones of the adjustment holes in the longer-side direction of the plate-form member.
Preferably, the cut depth of the cuts is adjusted such that the strength of the fitting destination member (F1), the force that moves the adjustment pin (F2), the internal stress produced in the plate-form member during positioning (F3), and the force that acts in the fitting direction of the plate-form member during fastening (F4) fulfill expression (1) below
F1, F2>F3>F4 (1)
Preferably, the dimension of the cuts in the shorter-side direction of the plate-form member is equal to or less than half the dimension of the plate-form member in the shorter-side direction thereof.
Hereinafter, a structure for fitting a plate-form member according to the present invention will be described with reference to the accompanying drawings. It should however be understood that the present invention is in no way limited by any embodiment described below.
As an example of a plate-form member fitting structure according to the present invention, an automatic adjustment structure for a doctor blade (plate-shape member) 13 as shown in
(Outline of a Developing Device)
The developing device 1 shown in
The doctor blade 13 is a plate-form member in the shape of a strip, and is arranged such that one side edge (regulating surface) 13a thereof stays opposite the surface of the developing roller 10 with a predetermined gap in between. Adjusting the gap (doctor gap) between the doctor blade 13 and the developing roller 10 allows adjustment of the amount of developer transported to the developing position.
(Outline of the Doctor Blade Automatic Adjustment Device)
With reference to
The doctor blade 13 has through holes 131 formed in it at three places, namely in both end parts and a central part in the longer-side direction thereof. Near the three through holes 131, adjustment holes 134F, 134C, and 134R are respectively formed (in the following description, these are also collectively referred to as “adjustment holes 134”).
Above the developing device 1 fastened to the base 71, at positions corresponding to the adjustment holes 134F, 134C, and 134R, three adjustment pins 73F, 73C, and 73R are arranged respectively (in the following description, these are also collectively referred to as “adjustment pins 73”) which are fixed to a movable member 72 so as to point downward. The adjustment pins 73F, 73C, and 73R are freely movable, by the action of unillustrated actuators respectively, in the up/down direction and in the adjustment direction (horizontal direction) of the doctor blade 13. The adjustment direction of the doctor blade 13 is a direction in which the regulating surface 13a of the doctor blade 13 approaches or recedes from the developing roller 10. Adjusting the doctor blade 13 means positioning the doctor blade 13 such that the doctor gap equals a predetermined value.
Three screws 20 are put through the three through holes 131 in the doctor blade 13, and are screw-engaged with threaded holes (not shown) formed in the blade fitting surface 15a so as to be temporarily tightened into the blade fitting surface 15a such that the doctor blade 13 is barely movable. In this way, even when the doctor blade 13 has a distortion in the thickness direction thereof, the distortion is corrected by the pressure of the three screws 20. The three through holes 131 are formed in a shape elongate in the shorter-side direction of the doctor blade 13.
Next, with an unillustrated actuator, the movable member 72 is moved, so that the three adjustment pins 73 fit in the corresponding adjustment holes 134 respectively. The adjustment pins 73 have an outer diameter of 2.5 mm, and their tip ends are formed into a tapered shape so as to fit easily into the adjustment holes 134. The adjustment hole 134C at the center is formed in a circular shape, and is given a clearance of about ±15 μm to ±25 μm around the adjustment pins 73. The adjustment holes 134F and 134R in both end parts are given a shape elongate in the longer-side direction of the doctor blade 13, and are given, like the adjustment hole 134C at the center, a clearance of about ±15 μm in the shorter-side direction (the up/down direction in
Next, while the gap (doctor gap) between the doctor blade 13 and the developing roller 10 is illuminated with a light 75, the gap is monitored with a camera 76 so that, while the doctor gap is measured through image analysis, the position of the doctor blade 13 is adjusted by moving the three adjustment pins 73F, 73C, and 73R with actuators respectively.
After completion of adjustment of the doctor blade 13, the screws 20 at three places are fully tightened with an unillustrated screw driver, so that the doctor blade 13 is fastened to the developing device 1. Lastly, the doctor gap is measured at three spots, and if the results are within a tolerated range, the adjustment is complete. By contrast, if the doctor gap falls outside the tolerated range, the screws 20 are loosened, and the position adjustment is performed once again.
The moving and fastening of the doctor blade 13 during doctor gap adjustment may be achieved other than by use of adjustment pins as described above, for example by pushing the back edge of the doctor blade 13, inserting a member in the gap, or chucking the doctor blade 13. Moving and fastening them by use of adjustment pins, however, is preferable because that is simple and accurate.
(Problems in Automatic Adjustment)
Variations in the doctor gap after adjustment and after screw tightening as observed on about 100 units of developing devices adjusted through the above-described procedure by use of the above-described automatic adjustment device 7 are shown in the faun of a histogram in
However, tightening screws after position adjustment of the doctor blade posed the problem of the doctor blade being displaced, resulting in tenfold variations in the doctor gap. Moreover, the process of position adjustment of the doctor blade by use of the automatic adjustment device scored a yield of about 95%, resulting in defective adjustment in about 5% of the cases. This rate of defects is high compared with the variations in the doctor gap after screw tightening shown in
Through research on these problems, the following two causes have been found out. As for a deviation (unevenness) in the doctor gap during screw tightening, a cause is considered to be the positional relationship between the directions of the torques applied to tighten the screws 20 and the gaps S between the adjustment pins 73 and the adjustment holes 134. That is, as shown in
In the automatic adjustment device 7, control is performed in the direction in which the doctor gap becomes narrower. Thus, in a case where, as shown in
In the case shown in
As a second cause, through a close review of data, it has been found that, while the tolerance for the straightness of the regulating surface 13a of the doctor blade 13 is ±30 μm, such doctor blades 13 as have straightness close to the limits of the tolerance are liable to end in defective adjustment of the doctor gap.
When a doctor blade 13 with a curved regulating surface 13a as shown in
Moreover, even when no deviation is produced in the doctor gap during screw tightening, when the adjustment pins 73F, 73C, and 73R are removed out of the adjustment holes 134 after screw tightening, the internal stress in the doctor blade 13 may act as residual stress to produce strain in the housing 15 of the developing device 1, the strain causing a defective doctor gap.
In summary, as shown in
Accordingly, in the fitting structure according to the present invention, the positions of the adjustment holes 134 in the doctor blade 13 and the positions at which it is fastened with the screw member 20 are located at predetermined positions, and thereby deviations in the doctor gap during screw tightening are suppressed. Embodiments will be presented below.
Like
With the so shaped doctor blade 13, the adjustment holes 134F and 134R corresponding to the adjustment pins 73F and 73R are arranged on the left side of the screws 20 in
The regulating surface 13a of the doctor blade 13 may instead be given a curved shape protruding away from the developing roller 10 (upward in
Stress concentrates at the cuts 135, and therefore the cuts 135 are preferably given a shape having a substantially straight base with rounded corners at both ends of the base so that stress is distributed substantially evenly within the cuts 135 to suppress destruction resulting from concentration of stress.
Moreover, it is preferable to adjust the cut depth such that expression (1) noted earlier is fulfilled with respect to the housing strength (F1), the force that moves the adjustment pins (F2), the internal stress (F3), and the force that acts upon the doctor blade during fastening (screw tightening). The reason is as follows: if the internal stress in the doctor blade 13 is greater than the force of the actuators that move the adjustment pins 73F, 73C, and 73R, then doctor gap adjustment itself is impossible, posing a problem; to prevent a slight deviation resulting from an error factor such as vibration during screw tightening, however, it is preferable that moderate internal stress be acting upon the three adjustment pins 73.
The internal stress in the doctor blade 13 can be adjusted by adjusting the cut depth of the cuts 135, and the larger the cut depth, the smaller the internal stress. However, if the cut depth exceeds half the dimension of the doctor blade 13 in its shorter-side direction, it may affect the magnetism restricting ability of the doctor blade 13. Thus, it is preferable that the cut depth be equal to or less than half the dimension of the doctor blade 13 in its shorter-side direction. The internal stress in the doctor blade 13 may be adjusted by adjusting the width or number of cuts 135. Typically, the doctor blade 13 is given a thickness of about 1.6 mm and a width of about 14 mm, the cut depth is about 7 mm, and the cuts 135 are given a width of about 5 mm.
By use of the automatic adjustment device 7 shown in
As will be clear from
In the embodiments described above, the positioning of the doctor blade 13 on the developing device 1 is achieved through automatic adjustment; needless to say, it may instead be achieved through manual adjustment. Although the above description takes a doctor blade as a plate-form member, the present invention is also applicable to the fitting of, for example, cleaning blades used in cleaning devices to remove developer.
According to the present invention, a screw member is arranged such that the force that the screw member exerts on a plate-form member in a position adjustment direction points from the side where the gap formed between an adjustment pin and an adjustment hole is smaller to the side where the gap is larger. It is thus possible to suppress displacement of the plate-form member caused by the screw member, to reduce adjustment variations of the plate-form member, and to reduce manufacturing cost.
Number | Date | Country | Kind |
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2012-237360 | Oct 2012 | JP | national |