Patent Application
20190018363
The present invention relates to an image forming apparatus including an electrophotographic photosensitive member and a roller actable on the photosensitive member, and a cartridge detachably mountable to an apparatus main assembly of the image forming apparatus.
Here, the image forming apparatus forms an image on a recording material by using an electrophotographic image formation type. Examples of an electrophotographic image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (such as a laser beam printer, an LED printer or the like), a facsimile machine, and a word processor.
Further, a process cartridge is a cartridge prepared by integrally assembling the photosensitive member and a process means actable on the photosensitive member into a cartridge (unit) detachably mountable to the apparatus main assembly of the image forming apparatus. The apparatus main assembly is a portion of the image forming apparatus from which the process cartridge is removed.
The recording material is a material on which the image is to be formed by the image forming apparatus and includes paper, an OHP sheet, a cloth, for example. Further, the recording material includes an image display member for the image forming apparatus, such as an electronic white board (blackboard).
Conventionally, in the electrophotographic image forming apparatus, a process cartridge type in which the photosensitive member and the process means actable on the photosensitive member are integrally assembled into a cartridge detachably mountable to the apparatus main assembly of the image forming apparatus has been employed. According to this process cartridge type, maintenance of the image forming apparatus can be carried out by an operator himself (herself) without relying on a service person, so that operativity can be remarkably improved. Therefore, this process cartridge type has been widely used in the image forming apparatus. The process cartridge includes a photosensitive drum (electrophotographic photosensitive drum) which is an image bearing member, a voltage applying device for imparting electric charges to the photosensitive drum, and other process means actable on the photosensitive drum. The process means generally include a developing means for supplying a developer (hereinafter referred to as “toner”) to the photosensitive drum, and a cleaning means for removing the toner remaining on a photosensitive drum surface without being transferred.
As a charging means in the voltage applying device, a roller charging means (type) using a charging roller has been widely used in recent years. In the roller charging type, the charging roller which is an electroconductive elastic roller is urged against and contacted to the photosensitive drum, and a voltage is applied to the charging roller, so that a surface of the photosensitive drum is electrically charged. The charging roller is in general in the form in which an entire longitudinal region of a core metal shaft except for both end portions is coated with an elastic layer, and as a supporting constitution, a method of rotatably supporting the core metal shaft end portions by supporting members as disclosed in Japanese Laid-Open Patent Application 2013-109209 is employed in general. Further, the supporting members are supported movably in a radial direction of the photosensitive drum by a frame of the process cartridge, and are urged toward the photosensitive drum by compression coil springs with a predetermined urging force (pressure), so that the charging roller is rotated by rotation of the photosensitive drum.
However, with speed-up and downsizing of the image forming apparatus in recent years, slip is liable to generate between the photosensitive drum and the charging roller. When the slip generates, a charge potential of the photosensitive drum causes a difference between a slip portion and a non-slip portion of the charging roller, so that stripe non-uniformity generates in an electrophotographic image in some cases.
As a countermeasure against the stripe non-uniformity, a sliding torque between the supporting member and the core metal shaft is lowered by reducing a diameter of the core metal shaft of the charging roller, whereby followability to the photosensitive drum can be enhanced. However, with a decreasing core metal shaft diameter, flexural rigidity of the charging roller lowers, with the result that there arises a problem such that the charging roller is not readily uniformly contacted to the photosensitive drum in an entire longitudinal region.
A principal object of the present invention is to provide a constitution in which followability to a photosensitive drum is improved.
According to an aspect of the present invention, there is provided a cartridge comprising: a photosensitive member; a roller actable on the photosensitive member and including a core metal shaft and a coating layer for coating the core metal shaft; roller supporting portions for rotatably supporting the roller; and a regulating portion for regulating a position of the roller with respect to a longitudinal direction of the roller, wherein the roller supporting portions are provided so as to support one end portion and the other end potion of the core metal shaft, respectively, with respect to a direction of a rotational axis of the roller, wherein the roller is further provided with cylindrical holes disposed at respective ends of the core metal shaft with respect to the direction of the rotational axis and extending in the direction of the rotational axis with the rotational axis as a center, and wherein the roller is supported by the roller supporting portions at inner peripheral surfaces of the holes.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
In
In
In
In
In
In
Embodiments of the present invention will be specifically described with reference to the drawings. Dimensions, materials, shapes and relative arrangements of constituent elements described in the following embodiments should be appropriately be changed depending on structures and various conditions of devices (apparatuses) to which the present invention is applied. Accordingly, the scope of the present invention is not intended to be limited to the following embodiments unless otherwise specified.
The charging roller 2 as a charging means is contacted to the surface of the photosensitive drum 1 with a predetermined urging force and is rotationally driven, and a predetermined charging bias is applied from a charging bias voltage source (not shown) to the charging roller 2, so that the photosensitive drum 1 is electrically charged to a predetermined potential and a predetermined polarity. The developing roller 5 as a developing means carries toner accommodated in a toner accommodating portion 31c to a developing position which is a contact position with the photosensitive drum 1. Then, the toner is deposited on an electrostatic latent image formed on the photosensitive drum 1, so that the electrostatic latent image is developed (visualized) as a toner image. To the developing roller 5, a predetermined developing bias is applied from a developing bias voltage source (not shown). The transfer roller 104 as a transfer means is contacted to the surface of the photosensitive drum 1 with a predetermined urging force and is rotationally driven, and a predetermined transfer bias is applied from a transfer bias voltage source (not shown) to the transfer roller 104. Then, the toner image is transferred from the surface of the photosensitive drum 1 onto the transfer (-receiving) material P as a transfer-receiving member to be fed to a transfer nip between the transfer roller 104 and the photosensitive drum 1. The transfer material P on which the toner image is transferred is fed to the fixing device 106, where predetermined pressure and heat are applied to the toner image, so that the toner image is fixed on the transfer material P. Thereafter, the transfer material P is discharged from the apparatus main assembly 100 to an outside by a discharging roller pair 107. The cleaning blade 6 as a cleaning means removes transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer and collects the transfer residual toner in a residual toner accommodating portion 21c. Thereafter, the above-described process is repeated in a similar manner.
A structure of the process cartridge 7 will be described based on
The process cartridge 7 is roughly consisting of a cleaning unit 9 and a developing unit 4. The cleaning unit 9 is prepared by integrally holding the photosensitive drum 1, the cleaning blade 6 and the charging roller 2 by a cleaning (unit) frame 21 in the form of a unit. In the cleaning frame 21, the residual toner accommodating portion 21c is formed. On the other hand, the developing unit 4 is prepared by integrally holding the developing roller 5 and a developing blade 12 by a developing (unit) frame 31 in the form of a unit. Further, in the developing frame 31, a toner accommodating portion 31c is formed. The developing unit 4 is swingably supported relative to the cleaning unit 9 by unshown supporting portions provided at longitudinal end portions thereof. The developing unit 4 is urged rotationally about an unshown supporting portion in a direction in which the developing roller 5 contacts the photosensitive drum 1 by an unshown pressing spring.
The process cartridge 7 is provided at one longitudinal end thereof with a drive inputting portion engaging with an unshown drive imparting portion provided in the apparatus main assembly 100, so that a rotational driving force is transmitted to the photosensitive drum 1 and the developing roller 5.
A structure of the cleaning unit 9 will be described with reference to
The cleaning frame 21 rotatably supports longitudinal end portions of the photosensitive drum 1 as shown in (a) of
The charging roller 2 includes a hollow core metal shaft 2b, an electroconductive elastic layer 2a as a coating layer for coating an entire longitudinal region of the core metal shaft 2b except for longitudinal end portions, and end portion members (hereinafter referred to as caps) 2c, formed of a resin material, mounted at the longitudinal end portions of the core metal shaft 2b. The core metal shaft 2b is prepared by molding a stainless steel plate in a cylindrical shape by press work. Of the two caps 2c and 2c at the end portions of the core metal shaft, the cap 2c in the side where the energization member 43 is provided (the left-hand side in (a) of
A supporting constitution of the charging roller 2 will be described with reference to (b) of
The cap 2c has a hollow cylindrical shape as shown in (b) of
As described above, an urging means 41 for urging the charging roller 2 in a direction toward the photosensitive drum 1 is constituted by the pressing spring 44 which is an elastic portion and the roller supporting member 42 (the swingable arm portion 42a and the roller supporting portion 42b). By thus constituting the urging means 41, the charging roller 2 is urged at the portion-to-be-supported 3e thereof toward an axial center of the photosensitive drum 1 by the pressing spring 44, and is rotatably supported.
An urging force of the pressing spring 44 is set so that the pressing spring 44 generates an urging force of 500 gf in a state in which the charging roller 2 contacts the photosensitive drum 1. In this embodiment, the compression coil spring is illustrated as an example of the elastic portion, but the elastic portion is not limited to the compression coil spring. The elastic portion may have any constitution when the elastic portion can generate a desired urging force.
Further, the urging means 41, the boss 21f said and the bearing surface 21g in the drive inputting portion 1a side are disposed at positions where these portions are rotated relative to the urging means 41, the boss 21f and the bearing surface 21g in the opposite side (the energization member 43 side) by a predetermined angle (1.2° in this embodiment) toward an upstream side with respect to a rotational direction of the photosensitive drum 1 with the axial center of the photosensitive drum 1 as a rotation center. That is, a rotation shape (axis) of the charging roller 2 is inclined relative to a rotation shape (axis) of the photosensitive drum 1 so as to be positioned so that a shape end in the drive inputting portion la side is positioned in a side upstream of a shape end in the energization member 43 side with respect to the rotational direction of the photosensitive drum 1. As a result, when the photosensitive drum 1 starts rotation thereof, the charging roller 2 is obliquely moved toward the drive inputting portion 1a side (the right side of (a) of
Further, one end of the energization member 43 is provided between the pressing spring 44 and the bearing surface 21g in the energization member 43 side (the left side of (a) of
A rotational operation of the charging roller 2 will be described with reference to
In the comparison example, as shown in (b) of
The charging roller 2 (102) is required to be rotated by the photosensitive drum 1 without slipping with the photosensitive drum 1. Force acting on the charging roller 2 (102) in the arrow u direction include an urging force F for urging the charging roller 2 (102) in the direction toward the photosensitive drum 1 by the pressing spring 44 (141) and drag F′ for supporting the charging roller 2 (102) by the photosensitive drum 1 against the urging force F. These forces are balanced with each other, and therefore the following formula 1 is satisfied.
F=F′ (formula 1)
Further, as regards forces acting in the arrow v direction, a frictional force T1 in which the photosensitive drum 1 is pulled in the rotational direction of the photosensitive drum 1 at a surface of the elastic layer 2a (102a) of the charging roller 2 (102) and a frictional force T2 for preventing rotation of the charging roller 2 (102) at the portion-to-be-supported 2e (102e) exist with associated constitutions. In the case of the comparison example, the portion-to-be-supported 102e is an outer peripheral portion of the core metal shaft 102b, and the portion-to-be-supported 2e in this embodiment is the inner peripheral surface of the cap 2c. The frictional forces T1 and T2 are proportional to normal reaction, and therefore are represented by the following formulas 2 and 3, respectively.
T1=μ1×F (formula 2)
T2=μ2×F (formula 3)
Here, μ1 is a frictional coefficient between the surface of the photosensitive drum 1 and the surface of the elastic layer 2a (102a) of the charging roller 2 (102). Further, μ2 is a frictional coefficient between the roller supporting member 142 and the outer peripheral surface of the core metal shaft 102b which is a portion-to-be-supported in the comparison example, and is a frictional coefficient between the roller supporting portion 42b and the portion-to-be-supported 2e in this embodiment. However, the frictional coefficients in the constitutions of this embodiment and the comparison example can be made equal to each other by appropriately selecting the materials used, and therefore in this case, it is assumed that the frictional coefficients in the respective constitutions are equal to each other. In order to cause the charging roller 2 (102) to follow the photosensitive drum 1, with respect to a balance of moment of the charging roller 2 (102) about the axial center of the charging roller 2 (102), there is a need that moment in a direction (the counterclockwise direction in
R×T1>r×T2 (formula 4)
Here, R is a radius of the elastic layer 2a (102a) of the charging roller 2 (102), and r is radius of the portion-to-be-supported 2e (102e). When the formulas 1 to 3 are substituted into the formula 4, the following formula 5 is obtained.
μ1×R>μ2×r (formula 5)
From the formula 5, it is understood that in order to improve rotation followability to the photosensitive drum 1, an increase in the radius R of the elastic layer 2a (102a) of the charging roller 2 (102) or a decrease in the radius r of the portion-to-be-supported is effective. The increase in the radius R of the elastic layer 2a of the charging roller 2, i.e., an increase in outermost diameter leads to upsizing of the process cartridge and an increase in cost of the charging roller 2, and therefore is not desirable. In order to improve followability, it is desirable that the radius r of the portion-to-be-supported is made small. In order to ensure flexural rigidity of the charging roller 2, there is a need that the outer diameter of the core metal shaft 2b ensures a thickness to some extent, but by employing the constitution of this embodiment, the radius r of the portion-to-be-supported 2e can be set at a small value. For that reason, rotation followability to the photosensitive drum 1 can be improved compared with the comparison example.
By employing the constitution of this embodiment, translational followability to the photosensitive drum 1 in the arrow u direction can also be improved. This will be described below. In the comparison example, as shown in (b) of
T4=T1+T2 (formula 6)
Accordingly, the supporting portion 121b of the cleaning frame supports the roller supporting member 142 with the force T4. Then, on the roller supporting member 142, a frictional force W1 proportional to the normal reaction T4 generates in the arrow u direction or a direction opposite to the arrow u direction. When a frictional coefficient is represented by μ3, the frictional force W1 is represented by the following formula 7 (into which the formula 6 is substituted).
W1=±μ3×T4=±μ3(T1+T2) (formula 7)
On the other hand, in this embodiment, as shown in (a) of
T3=T1−T2 (formula 8)
On the boss 21f, a force T3′ equal in magnitude to the force T3 acts in the opposite direction to the direction of the force T3. When a frictional coefficient between the boss 21f and the hole 42c is represented by μ4 and when the charging roller 2 swings in the arrow u direction, at a supporting portion s of the roller supporting member 42 by the boss 21f, a frictional force W2 generates in the arrow u direction. That is, the frictional force W2 is represented by the following formula 9 (into which the formula 8 is substituted).
A frictional force W3 exerting in the arrow u direction against the urging force F at the charging roller 2 is represented, on the basis of a lever ratio of the roller supporting member 42, by the following formula 10 (into which the formula 9 is substituted) when a distance from the center of the hole 42c to the center of the roller supporting portion 42b is L1 and a distance from the center of the hole 42c to the supporting portion s is L2.
Compared with the distance L2, the distance L1 is sufficiently large, and therefore by the leverage effect, the frictional force W3 is remarkably smaller than the frictional force W2. The frictional forces of the charging roller 2 in the arrow u direction are compared with each other. The frictional coefficients μ3 and μ4 can be made equal to each other by appropriately selecting the materials, and therefore in this case, it is assumed that μ3=μ4 holds. Then, it is clear from a comparison between the formulas 7 and 10 that the frictional force W3 in this embodiment is remarkably smaller than the frictional force W1 in the comparison example. In other words, in the comparison example, the frictional force W1 is proportional to the sum of the frictional forces T1 and T2, whereas in this embodiment, the frictional force W3 is proportional to the difference between the frictional forces T1 and T2 and is also remarkably suppressed by the leverage effect. The low frictional force in the arrow u direction means nothing other than improvement in translational followability to the photosensitive drum 1 in the arrow u direction. With speed-up of the image forming apparatus in recent years, it is desired that the charging roller 2 translates and follows a minute change in radius of the photosensitive drum 1 with reliability, but by employing the constitution of this embodiment, it is move easy to meet the speed-up.
In order to always uniformly charge the photosensitive drum 1 by the charging roller 2 with no non-uniformity, there is a need that not only the charging roller 2 is always rotated by the photosensitive drum 1 without slipping with the photosensitive drum 1, i.e., the charging roller 2 is excellent in rotational followability, but also the nip between the charging roller 2 and the photosensitive drum 1 is kept at a constant value without separation of the charging roller 2 from the photosensitive drum 1, i.e., the charging roller 2 is excellent in translational followability. When at least one of the rotational followability and the translational followability is impaired, the charging roller 2 cannot always uniformly charge the photosensitive drum 1, and therefore, there is a great significance in that both of the rotational followability and the translational followability are kept simultaneously at a certain level or more.
As described above, according to this embodiment, it is possible to simultaneously improve the rotational followability and the translational followability of the charging roller 2 to the photosensitive drum 1 while maintaining desired flexural rigidity of the charging roller 2. As a result, a high-quality electrophotographic image can be stably provided. Further, at the same time, a sliding speed between the cap 2c and the roller supporting portion 42b in the energization member 43 side lowers, so that a change in electric resistance at the sliding portion can be suppressed. Also this effect contributes to stable provision of the high-quality electrophotographic image.
A position of the portion-to-be-supported 2e with respect to the rotational axis direction of the charging roller 2 will be described. As shown in (b) of
An effect of a constitution in which the portion-to-be-supported 2e is disposed at the position overlapping with the elastic layer 2a with respect to the rotational axis direction of the charging roller 2 will be described with reference to
Incidentally, the roller supporting member 42 contacts the portion-to-be-supported 2e and urges the charging roller 2 against the photosensitive drum 1 at the portion-to-be-supported 2e. In the following, a position where the roller supporting portion 42b of the roller supporting member 42 urges the portion-to-be-supported 2e is an urging position.
In
Further, in
As shown in (b) of
In the case of the constitution in which the outer peripheral surface of the core metal shaft 2b is supported, in order to minimize the distortion at the center of the elastic layer 2a with respect to the rotational axis direction, it is only required that a constitution in which the charging roller 2 is urged at a just extreme end position of the elastic layer 2a is employed. However, the core metal shaft 2b has to be rotatably supported, and therefore, a bearing member for rotatably supporting the core metal shaft 2b is needed, so that a width, with respect to the axial direction, for permitting the sectional view of the core metal shaft 2b by the bearing member is required to some extent. Accordingly, even when the urging position of the core metal shaft 2b is the center of the width of the bearing member with respect to the rotational axis direction, the bearing member has to urge the outside of the extreme end (end portion position) of the elastic layer 2a by half of the width. However, in this embodiment, the constitution in which the inner peripheral surface of the core metal shaft 2b is supported is employed, and therefore there is no such constraint, so that it is possible to urge the extreme end (end portion position) shown by the arrow B in (c) of
With reference to (d) of
At this time, at a central portion between the two arrows C with respect to the rotational axis direction, the charging roller 2 is flexed in the direction in which the charging roller 2 is spaced from the photosensitive drum 1, and at the same time, is flexed toward the photosensitive drum 1 in the outsides of the arrows C. Further, with respect to the rotational axis direction, in the outsides of the arrows C, the charging roller 2 is flexed in the direction in which the charging roller 2 is spaced from the photosensitive drum 1, and at the same time, in the inside of the arrows C, the charging roller 2 is flexed toward the photosensitive drum 1. By interaction of these, with respect to the rotational axis direction, in both sides (central side and outside) sandwiching the urging position (position of the arrow C), the flexure in the direction in which the charging roller 2 is spaced from the photosensitive drum 1 is cancelled.
As shown in (b) of
Therefore, the maximum distortion can be more suppressed in the case where the elastic layer 2a is urged at the positions of the arrows C ((d) of
In the case where the urging position is caused to approach the center as shown in (a) and (e) of
As described above, if the portion-to-be-supported 2e is positioned inside the elastic layer 2a of the core metal shaft 2b, even when the elastic layer 2a is urged at any position, the degree of the distortion of the core metal shaft 2b can be made smaller compared with the constitution (comparison example) in which the charging roller 2 is urged outside the elastic layer 2a while being supported at the outer peripheral surface of the core metal shaft 2b.
When a full length of the elastic layer 2a with respect to the axial direction is L, the maximum distortion of the core metal shaft 2b can be minimized in the case where the charging roller 2 is urged inside each of the extreme end positions in both sides of the elastic layer 2a by about 0.2 L. Thus, it is preferable that the charging roller 2 is urged at the position inside each of the extreme end positions in both sides of the elastic layer 2a by about 0.2 L.
As described above, as in this embodiment, by disposing the portion-to-be-supported 2e at the position overlapping with the elastic layer 2a with respect to the rotational axis direction of the charging roller 2, it is possible to decrease the difference in pressure between the end portion and the central portion with respect to the rotational axis direction of the charging roller 2. For this reason, a phenomenon that the central portion of the charging roller 2 with respect to the rotational axis direction does not readily contact the opposing photosensitive drum 1 does not readily generate. That is, according to this embodiment, with an inexpensive constitution, the difference in pressure between the end portion and the central portion with respect to the rotational axis direction of the charging roller 2, and therefore, it is possible to improve contact uniformity of the charging roller with the photosensitive drum while maintaining the flexural rigidity of the roller with the inexpensive constitution.
A constitution according to Embodiment 2 will be described based on
In Embodiment 1, the urging means 41 is constituted by the pressing spring 44 and the roller supporting member 42, but in this embodiment, an urging means 41 is constituted by a single part having elasticity. The urging means 41 is constituted by a spring wire material, and one end 41d thereof is fixed in a fixing hole 21h provided in a side surface of a cleaning frame 21. The one end 41b of the urging means 41 is fixed in the fixing hole 21h with respect to both of a rotational direction and a pulling-out direction (axial direction). The other end 41b, in the opposite side, of the urging means 41 which is a roller supporting portion is bent from an arm portion 41a toward a longitudinal center by 90 degrees. The one end 41b engages with a portion-to-be-supported 2e which is an inner peripheral surface of a hole 2g of the charging roller 2. An inner diameter of the portion-to-be-supported 2e is set so as to be slightly larger than a wire diameter of the urging means 41. Further, in a state in which the charging roller 2 contacts the photosensitive drum 1, the urging means 41 is disposed so that the arm portion 41a is flexed and generates a desired urging force (500 gf in this embodiment).
Thus, the urging means 41 is constituted by the single part including the arm portion 41a which is an elastic portion and which is swingable and including the one end 41b which is the roller supporting portion, so that it is possible to reduce the number of parts compared with the constitution in Embodiment 1 while achieving the effects obtained in Embodiment 1.
A constitution according to Embodiment 3 will be described based on
In Embodiment 2, the urging means 41 is constituted by the spring wire material as the single member having the elasticity, but in this embodiment, an urging means 41 is constituted particularly by a torsion coil spring.
The urging means 41 includes a wire-wound portion 41e engaged with and locked by a spring-engaging boss 21a provided on a side surface of the cleaning frame 21. One end 41b of the urging means 41 which is a roller supporting portion is bent from an arm portion 41a in a direction parallel to a wire-wound shaft by 90 degrees and extends toward a longitudinal center. The spring engaging boss 21a is provided at a position where the arm portion 41a urges the charging roller 2 toward an axial center of the photosensitive drum 1. The one end 41b of the urging means 41 which is the roller supporting portion engages with a portion-to-be-supported 2e which is an inner peripheral surface of a hole 2g of the charging roller 2. An inner diameter of the portion-to-be-supported 2e is set so as to be slightly larger than a wire diameter of the urging means 41. Further, in a state in which the charging roller 2 contacts the photosensitive drum 1, the urging means 41 is disposed so that the wire-wound portion 41e is elastically deformed and generates a desired urging force (500 gf in this embodiment). Further, the other end 41c of the urging means 41 in a side opposite from the one end 41b is locked by a locking portion 21e provided in the cleaning frame 21.
Thus, the urging means 41 is constituted by the torsion coil spring, so that it is possible to reduce spring constant by providing the wire-wound portion compared with the constitution in Embodiment 2 while achieving the effects obtained in Embodiment 1. For that reason, it is possible to considerably suppress a manufacturing variation in spring force generating during use. The urging force can be further stabilized.
A constitution according to Embodiment 4 will be described based on
In Embodiment 3, as the urging means 41, the torsion coil spring is used, but particularly in the case where the wire diameter is small, a size can be reduced, but on the other hand, a degree of flexure of the one end 41b which is a supporting portion for the charging roller 2 increases, so that there is a liability that a circumferential position of the charging roller 2 relative to the photosensitive drum 1 becomes unstable. In this embodiment, in view of the above liability, a constitution capable of alleviating the flexure of the one end 41b will be described. Particularly, as regards portions omitted from description, the portions are in accordance with the constitution in Embodiment 3.
As shown in (b) of
Further, a portion in the neighborhood of a free end of the arm portion 41a engages with the portion-to-be-supported 2e which is the inner peripheral surface of the hole 2g of the charging roller 2 described above. The elongated hole 21b is, as shown in
By thus employing the constitution, the elongated hole 21b supports a bending base portion between the arm portion 41a and the one end 41b, so that it is possible to stabilize the position of the charging roller 2 while limiting a fluctuation of the charging roller 2 with respect to a circumferential direction of the photosensitive drum 1.
In the constitution of this embodiment, a mechanism of translational followability of the charging roller 2 to the photosensitive drum 1 is different from that in Embodiments 1-3, and therefore, will be described below. Incidentally, the rotational followability of the charging roller 2 to the photosensitive drum 1 is the same in the constitutions of Embodiments 1-4 and will be omitted from description. In the following, description will be made by comparing constitutions of the comparison example (conventional constitution) and this embodiment with reference to (b) of
In this embodiment, as shown in
T3=T1−T2 (formula 11)
When the one end 41b of the urging means 41 which is the roller supporting portion is flexed by receiving the force in the arrow v direction, the one end 41b contacts the elongated hole 21b. The elongated hole 21b supports the one end 41b with the force T3.
Then, between the one end 41b and the elongated hole 21b, a frictional force W4 proportional to the normal reaction T3 generates in the arrow u direction or a direction opposite to the arrow u direction. When a frictional coefficient is represented by μ5, the frictional force W4 is represented by the following formula 12 (into which the formula 11 is substituted).
The frictional forces of the charging roller 2 in the arrow u direction are compared with each other. The frictional force W1 in the comparison example is proportional to the sum of the forces T1 and T2 as shown in the formula 7, whereas the frictional force W4 in this embodiment is proportional to the difference between the forces T1 and T2 as shown in the formula 12. The frictional coefficients μ3 and μ5 can be made equal to each other by appropriately selecting the materials, and therefore in this case, it is assumed that μ3=μ5 holds. Then, it is clear that the frictional force W4 in this embodiment is remarkably smaller than the frictional force W1 in the comparison example. The low frictional force in the arrow u direction means nothing other than improvement in translational followability to the photosensitive drum 1 in the arrow u direction.
As described above, the elongated hole 21b for supporting the one end 41b which is the roller supporting portion is provided in the cleaning frame 21, whereby stability of the position of the charging roller 2 is further improved while achieving the effects obtained in Embodiment 1. As a result, charging non-uniformity of the photosensitive drum can be suppressed, so that formation of a higher-quality image can be realized.
A constitution according to Embodiment 5 will be described based on
In this embodiment, as shown in
In this embodiment, the core metal shaft 2b of the charging roller 2 is a solid metal shaft and is provided with a recessed portion (hole) 2m recessed from each of end portions in both sides toward a central side with respect to the axial direction. In a rear side of the recessed portion 2m, a small hole 2g having an inner diameter smaller than that of the recessed portion 2m is provided, and a portion-to-be-supported 2e is provided at an inner peripheral surface of the small hole 2g. An inner diameter of the portion-to-be-supported 2e is set so as to be slightly larger than a wire diameter of the urging means 41 formed with the torsion coil spring. The inner peripheral surface of the portion-to-be-supported 2e is finished finely in terms of surface roughness so that the inner peripheral surface of the portion-to-be-supported 2e is not abraded by being slid with the urging means 41. Mounting of the urging means 41 to the cleaning frame 21 is performed, similarly as in Embodiment 4, by engaging a wire-wound portion 41e with a spring-engaging boss 21a and by penetrating the one end 41b, which is the roller supporting portion, through the elongated hole 21b.
As described above, by forming the portion-to-be-supported 2e with the core metal shaft 21b of the charging roller 2, a manufacturing cost can be reduced by the absence of the member corresponding to the cap 2c while achieving the effects obtained in Embodiment 1.
In the above-described embodiments, the example in which the voltage applying device in the present invention is incorporated in the process cartridge was described, but the present invention is not limited thereto. For example, the voltage applying device in the present invention may also be incorporated in an image forming apparatus in which a cartridge type is not employed. Further, a minimum unit consisting only of the charging roller and the frame provided with the urging member may also be constituted so as to be detachably mountable to the process cartridge or the apparatus main assembly of the image forming apparatus.
In the above-described embodiments, as the roller for charging the member-to-be-charged, the charging roller 2 was described but the roller is not limited thereto. For example, even when the present invention is applied to the transfer roller 104 or the developing roller 5, a similar effect is achieved.
In the above-described embodiments, an example of the case where the transfer(-receiving) material P as the transfer receiving member onto which the toner image is transferred from the photosensitive drum 1 is the recording material such as paper or a sheet was described. However, the transfer receiving member may also be an endless belt such as the intermediary transfer belt onto which the toner image is transferred from the photosensitive drum 1.
In the above-described embodiments, a single process cartridge is used, but the number of the process cartridges used is not limited and may also be appropriately set as desired.
In the above-described embodiments, as the process cartridge detachably mountable to the apparatus main assembly of the image forming apparatus, the process cartridge integrally including the photosensitive drum and, as the process means actable on the photosensitive drum, the charging means, the developing means and the cleaning means was described. However, the process cartridge is not limited thereto. For example, the process cartridge may also be a process cartridge including not only the photosensitive drum but also either one of the charging means, the developing means and the cleaning means.
In the above-described embodiments, as the image forming apparatus, the printer is described, but the present invention is not limited thereto. For example, the image forming apparatus may also be other image forming apparatuses such as a copying machine, a facsimile machine and a multi-function machine having a combination of functions of these machines. By applying the present invention to voltage applying devices in these image forming apparatuses, similar effects can be obtained.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
According to the present invention, it is possible to improve followability of a roller to a photosensitive member while ensuring flexural rigidity of the roller with an inexpensive constitution.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-028494 | Feb 2016 | JP | national |
| 2016-028495 | Feb 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/006692 | 2/16/2017 | WO | 00 |
