Patent Application
20120230708
This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2011-054197, filed on Mar. 11, 2011, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.
The present invention generally relates to an image forming apparatus, such as a copier, a printer, a plotter, or a multifunction machine including at least two of these functions.
There are electrophotographic image forming apparatuses in which the amount of developer contained in a development device decreases as it is consumed in image development, and fresh developer is supplied from a developer container to the development device when the amount of developer therein falls to or below a predetermined amount. Thus, the amount of developer therein is kept in a given range. Additionally, the developer container and the development device may be housed in a common unit casing, forming a single development unit removably installed in the image forming apparatus. When the amount of developer contained in the development unit falls to or below the predetermined amount, the development unit is replaced as a whole.
Such configurations require a detector to detect the amount of developer inside the development device or development unit. Therefore, various types of detectors have been proposed to detect the amount of developer. For example, light transmission-type detectors including optical elements are used to detect the amount of developer.
Light transmission-type developer amount detectors determine the amount of developer in the developer container based on the amount of light transmission therein.
In this method, light emitted from a light-emitting element can be guided to a light-receiving element using first and second light guides provided inside the developer container across a clearance. The first and second light guide are constructed of, for example, prisms or mirrors. When the amount of developer in the developer container is sufficient, a light path formed between the first and second light guides is blocked by the developer, and the light-receiving element does not receive the light. However, when the amount of developer in the developer container is reduced to or below a reference amount, the developer does not block the light path, and the light can reach the light-receiving element. It can be determined whether the amount of developer has decreased below the reference amount by measuring the output from the light-receiving element (as disclosed in JP-2007-219269-A, JP-4358038-B, and JP-4398421-B).
The development unit, an image bearer such as a photoreceptor, and the like may be housed in a common unit casing, forming a modular unit (i.e., a process unit), which is typically longer in the axial direction of the photoreceptor. In such process units, the amount of developer tends to be uneven in an end portion in its longitudinal direction. Accordingly, it is preferred to detect the amount of developer in a center portion in the longitudinal direction, in which the amount of developer is relatively uniform.
Depending on the layout of the development unit, the photoreceptor, and the like, however, it is difficult to dispose the light-emitting element and the light-receiving element in the center portion in the longitudinal direction. For example, in an arrangement in which the development unit is above the photoreceptor, it is difficult to provide a separate positioning member around the development unit for fixing the light-emitting element and the light-receiving element in position. Therefore, the light-emitting element and the light-receiving element are disposed on a side wall of the image forming apparatus adjacent to an end of the development unit in the longitudinal direction.
Although the amount of developer in the center portion of the development unit can be detected using a light guide extending from the end portion to the center portion of the development unit to guide the light from the light-emitting element, it is possible that the light is attenuated while passing through the long light guide. Accordingly, light-emitting elements of higher output power are required, thus increasing the cost.
In view of the foregoing, in one embodiment of the present invention, an image forming apparatus includes an image bearer, an optical writing unit to writing an electrostatic latent image on the image bearer, a development device to develop the electrostatic latent image on the image bearer with developer, a developer container for containing the developer supplied to the development device, and a developer amount detector including a light-emitting element and a light-receiving element. The optical writing unit includes multiple optical writing elements arranged in a longitudinal direction of the image bearer and a frame to hold the multiple optical writing elements. The developer amount detector detects an amount of developer contained in the developer container based on a light transmission amount between the light-emitting element and the light-receiving element, and at least one of the light-emitting element and the light-receiving element of the developer amount detector is attached to the optical writing unit.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof, and particularly to
It is to be noted that the suffixes Y, M, C, and K attached to each reference numeral indicate only that components indicated thereby are used for forming yellow, magenta, cyan, and black images, respectively, and hereinafter may be omitted when color discrimination is not necessary.
Referring to
An image forming apparatus 100 shown in
More specifically, each process unit 1 includes a drum-shaped photoreceptor 2 serving as a latent image bearer, a changer 3 to charge the surface of the photoreceptor 2, a development device 4 to supply toner to the surface of the photoreceptor 2, and a cleaning unit 5 to clean the surface of the photoreceptor 2. It is to be noted that, in
An optical writing head 6 (optical writing unit) to optically write electrostatic latent images on the photoreceptor 2 is provided above the photoreceptor 2 in each process unit 1 in
Additionally, the optical writing head 6 is disposed at a predetermined or given position accurately using spacers provided to a housing of the photoreceptor 2 and those provided between the photoreceptor 2 and the optical writing head 6 to keep the focal distance of the optical writing head 6 relative to the photoreceptor 2 within a reference focal distance ±about 60 μm.
Additionally, a transfer device 7 is provided beneath the respective photoreceptors 2. The transfer device 7 includes an intermediate transfer belt 8 that can be, for example, an endless belt onto and from which an image is transferred. The intermediate transfer belt 8 is stretched around support rollers, namely, a driving roller 9 and a driven roller 10. As the driving roller 9 rotates counterclockwise in
The image forming apparatus 100 further includes four primary-transfer rollers 11 positioned facing the respective photoreceptors 2 via the intermediate transfer belt 8. Each primary-transfer roller 11 is pressed against an inner circumferential surface of the intermediate transfer belt 8, thus forming a primary-transfer nip between the intermediate transfer belt 8 and the corresponding photoreceptor 2. Each primary-transfer roller 11 is electrically connected to a power source and receives a predetermined amount of voltage including at least one of direct-current (DC) voltage and alternating current (AC) voltage. It is to be noted that, instead of the primary-transfer rollers 11, transfer chargers or transfer brushes may be used.
Additionally, a secondary-transfer roller 12 is provided at a position facing the driving roller 9 via the intermediate transfer belt 8. The secondary-transfer roller 12 is pressed against an outer circumferential surface of the intermediate transfer belt 8, and thus a secondary-transfer nip is formed between the secondary-transfer roller 12 and the intermediate transfer belt 8. Similarly to the primary-transfer rollers 11, the secondary-transfer roller 12 is electrically connected to a power source and receives a predetermined amount of voltage including at least one of DC voltage and AC voltage.
The image forming apparatus 100 further includes a sheet cassette 14 for containing sheets P of recording media such as paper or overhead projector (OHP) films, provided beneath the apparatus body, a pair of discharge rollers 16, and a discharge tray 17. The sheet cassette 14 is provided with a feed roller 15 to pick up and transport the sheets P from the sheet cassette 14. The pair of discharge rollers 16 is positioned in an upper portion of the apparatus body to discharge the sheets P outside the image forming apparatus 100, and the sheets P thus discharged are stacked on the discharge tray 17 formed on an upper surface of the apparatus body. A fixing device 18 is provided above the secondary-transfer nip in
A conveyance path is formed inside the apparatus body so that the sheet P is conveyed from the sheet cassette 14 to the secondary-transfer nip and further to the discharge tray 17. The conveyance path includes a post-feeding path 19 leading from the sheet cassette 14 to the secondary-transfer roller 12, a post-transfer path 20 leading from the secondary-transfer roller 12 to the fixing device 18, a post-fixing path 21 leading from the fixing device 18 to the discharge rollers 16, and a discharge path 22. A pair of registration rollers 23 is provided adjacent to a downstream end of the post-feeding path 19 in the direction in which the sheet P is conveyed (hereinafter “sheet conveyance direction”).
The image forming apparatus 100 configured as described above operates as follows.
When image formation is started, the photoreceptors 2 in the respective process units 1 are rotated clockwise in
Meanwhile, the driving roller 9 rotates, and accordingly the intermediate transfer belt 8 rotates in the direction indicated by arrow Y1 shown in
Additionally, when image formation is started, the feed roller 15 rotates, thereby transporting the sheet P from the sheet cassette 14 to the post-feeding path 19. Then, the registration rollers 23 forward the sheet P to the secondary-transfer nip formed between the secondary-transfer roller 12 and the intermediate transfer belt 8, timed to coincide with the multicolor toner image (superimposed single-color toner images) formed on the intermediate transfer belt 8. At that time, the transfer bias voltage whose polarity is opposite that of the toner image on the intermediate transfer belt 8 is applied to the secondary-transfer roller 12, and thus the transfer electrical field is formed in the secondary-transfer nip. The transfer electrical field generated in the secondary-transfer nip transfers the superimposed toner images from the intermediate transfer belt 8 onto the sheet P at a time. The belt cleaning unit 13 removes any toner remaining on the intermediate transfer belt 8 after image transfer.
Subsequently, the sheet P is transported through the post-transfer path 20 to the fixing device 18. In the fixing device 18, while the sheet P is transported by the fixing roller 18a and the pressure roller 18b pressing against each other via the sheet P, the toner thereon is fused and fixed with heat and pressure. After being discharged from the fixing device 18, the sheet P is transported through the post-fixing path 21 as well as the discharge path 22 and discharged by the discharge rollers 16 outside the apparatus to the discharge tray 17.
It is to be noted that, although the description above concerns multicolor image formation, alternatively, the image forming apparatus 100 can form single-color images, bicolor images, or three-color images using one, two, or three of the four process units 1.
As shown in
Operation of the development unit 4 is described below.
As the agitator 30 and the agitation paddle 29 rotate, the developer inside the developer container 25 moves down under its own weight toward the supply roller 27 while being agitated. The supply roller 27 includes a metal core and a roller portion constructed of, for example, foam resin, that covers the surface of the metal core. The supply roller 27 rotates while adsorbing developer to an outer surface of the roller portion. The developer adhering to the surface of the supply roller 27 is supplied to the development roller 26 at a position where the supply roller 27 contacts the development roller 26. As the development roller 26 rotates, the developer carried on the surface of the development roller 26 passes through a regulation gap, where a tip of the doctor blade 28 is adjacent to or in contact with the surface of the development roller 26. Thus, the layer thickness of the developer on the development roller 26 is adjusted, forming a thin developer layer thereon. Subsequently, the developer is transported to a development range, where the development roller 26 is adjacent to or in contact with the photoreceptor 2, and adheres to the electrostatic latent image on the photoreceptor 2, thereby developing it into a toner image.
Additionally, as shown in
Configurations of the light guide 32 and the developer amount detector 31 are described in further detail below.
As shown in
As shown in
The light emitted from the light-emitting element 33 enters the first light guide member 35 from the exposed first edge face 35a, is reflected, and exits from the second edge face 35b. The light then enters the second light guide member 36 from the second edge face 36b facing the second edge face 35b of the first light guide member 35. The light is reflected inside the second light guide member 36, exits from the first edge face 36a, and then reaches the light-receiving element 34.
When the amount of developer in the developer container 25 is sufficient, the light is blocked by the developer present in the gap (clearance) between the second edge face 35b of the first light guide member 35 and the second edge face 36b of the second light guide 36 facing each other. Thus, the light-receiving element 34 does not receive the light. However, as the developer is consumed in printing, the level of the developer in the developer container 25 descends below the first and second light guide members 35 and 36, that is, no developer is present in the gap between the second edge faces 35b and 36b of the first and second light guide members 35 and 36. Accordingly, the light reaches the light-receiving element 34. The controller can recognize that the level of the developer in the developer container 25 is below the first and second light guide members 35 and 36 with the value output from the light-receiving element 34 at that time.
As shown in
It is to be noted that, in
As shown in
Further, as shown in
In view of the foregoing, in the present embodiment, deformation of the frame 39 in attachment of the developer amount detector 31 (light-emitting element 33 and light-receiving element 34) to the optical writing head 6 can be prevented as follows.
As shown in
Additionally, the legs 41a engage the respective arms 39a in clearance fit, and a clearance D3 (shown in
In the present embodiment, the distance D2 between the inner faces 390 of the respective arms 39a is thus made greater than the distance D1 between the outer faces 410 of the respective legs 41a to secure the clearance D3 between the engagement faces 390 and 410. Thus, the legs 41a can engage the respective arms 39a in clearance fit. Accordingly, even when the legs 41a are fitted inside the respective arms 39a, the distance D2 between the arms 39a is not expanded by the legs 41a.
It is to be noted that, although both the light-emitting element 33 and the light-receiving element 34 are provided to an identical optical writing head 6 in the description above, alternatively, only one of the light-emitting element 33 and light-receiving element 34 may be provided to the optical writing head 6. Yet alternatively, the light-emitting element 33 and the light-receiving element 34 may be provided to separate optical writing heads 6.
Thus, when the pair of arms 39a of the frame 39 engages the detector holder 41 for holding at least one of the light-emitting element 33 and light-receiving element 34 in clearance fit, deformation of the frame 39 can be prevented in attachment of the detector holder 41 to the frame 39.
Additionally, when the clearance D3 between the inner face 390 of the arm 39a and the outer face 410 of the leg 41a is within a range of from 0.1 mm to 0.5 mm (0.1 mm≦D3≦0.5 mm), easiness in attachment of the detector holder 41 as well as a higher accuracy in the detection of the amount of developer can be attained. More specifically, if the clearance D3 is less than 0.1 mm, the clearance D3 is too small and makes it difficult to attach the detector holder 41 to the frame 39. By contrast, if the clearance D3 is greater than 0.5 mm, it is possible that the backlash between the engagement faces 390 and 410 can exceed a tolerable range for the developer amount detector 31.
Additionally, as shown in
As shown in
To insert the projections 41b into the first cutouts 39b1 and the second cutouts 39b2, initially the projections 41b are aligned with upper openings of the first cutouts 39b1. In this state, the detector holder 41 is lowered relative to the frame 39 as indicated by chain double-dashed lines shown in
Subsequently, the detector holder 41 is moved to the right in
As described above, with the first and second cutouts 39b1 and 39b2 engaging the respective projections 41b, the detector holder 41 can be prevented from moving in the two directions, namely, upward direction and the longitudinal direction, relative to the frame 39. In other words, in
This configuration can prevent unintended disengagement of the detector holder 41 from the frame 39. Additionally, accuracy in positioning the light-emitting element 33 and the light-receiving element 34 can increase because the attachment position of the detector holder 41 relative to the frame 39 can become more reliable. Accordingly, detection accuracy of the developer amount detector 31 can be secured. It is to be noted that, differently from the configuration shown in
As described above, although deformation of the frame 39 of the optical writing head 6 can result in deviation of the focal distance of the optical writing head 6 to the photoreceptor 2, the configuration according to the first embodiment can keep the focal distance of the optical writing head 6 constant with a higher degree of accuracy, preventing degradation of image quality.
Additionally, the detector holder 41 includes engagement portions (projections 41a) to engage engagement portions (cutouts 39b) of the frame 39. The engagement portions of one of the detector holder 41 and the frame 39 are projections, and the engagement portions of the other are cutouts. The engagement between the engagement portions of the detector holder 41 and those of the frame 39 can prevent relative movements between the detector holder 41 and the frame 39 in the Y-axis direction and the Z-axis direction as well as unintended disengagement of the detector holder 41 from the frame 39.
Additionally, at least one of the projections 41b is designed to engage the cutout 39b due to elastic deformation to facilitate the engagement.
It is to be noted that, in the third, fourth, and fifth embodiment, subscripts “−1”, “−2”, or “−3” are given to reference characters of components having configurations different from those in the first embodiment.
As shown in
Additionally, when the clearance D3′ between the outer face 391 of the arm 39a and the inner face 411 of the leg 41a-1 is within a range of from 0.1 mm to 0.5 mm (0.1 mm≦D3′≦0.5 mm), easiness in attachment of the detector holder 41-1 as well as a higher accuracy in the detection of the amount of developer can be attained.
Additionally, in the second embodiment, the legs 41a-1 include projections 41b-1 projecting inward in
In the third embodiment, a detector holder 41-2 includes a pair of legs 41a-2 and 41a-2′ disposed at distance from each other, and a frame 39-2 includes a pair of arms 39a and 39a′. The arm 39a is clamped between the legs 41a-2 and 41a-2′. In this configuration, because the detector holder 41-2 is fixed to a single arm 39a only, the frame 39-2 is neither expanded nor deformed when the detector holder 41-2 is attached thereto.
Clamping the arm 39a between the legs 41a-2 and 41a-2′ can prevent relative movement between the detector holder 41-2 and the frame 39-2 in the direction X in which the legs 41a-2 and 41a-2′ are disposed at a distance. Additionally, the engagement between the respective projections 41b-1 and the respective cutouts 39b restricts relative movements between the detector holder 41-2 and the frame 39-2 in the Y-axis direction and the Z-axis direction, both perpendicular to the direction X. Specifically, similarly to the above-described first and second embodiments, the projections 41b-1 are inserted into the two types of cutouts 39b (first cutouts 39b1 and second cutouts 39b2), respectively, and the engagement therebetween can prevent relative movements between the detector holder 41-2 and the frame 39-2 in the Y-axis direction and the Z-axis direction.
In the fourth embodiment, a frame 39-3 includes a pair of arms 39a′ and 39a-3. The arm 39a-3 is extended upward and includes a mounting portion 39c to which the circuit board 40 for supporting the light-emitting element 33 and the light-receiving element 34 is fixed. The circuit board 40 may be bonded to the mounting portion 39c with an adhesive member 42 such as double-sided adhesive tape as shown in
The configurations according to the variation shown in
In the fourth embodiment shown in
Thus, according to the above-described embodiments, the developer amount detector 31 including the light-emitting element 33 and the light-receiving element 34 is fixed to the optical writing head 6, and the position thereof can be set with a high degree of accuracy. Accordingly, the positioning accuracy and design flexibility of the developer amount detector 31 can be enhanced. Specifically, this configuration can eliminate the necessity of a separate positioning member provided around the developer container 25 for setting in position the developer amount detector 31. Thus, limitations on component layout can be reduced. Additionally, the optical writing head 6 is longer in the direction in which the optical writing elements are aligned, and the developer amount detector 31 can be disposed at any given position in the range where the optical writing elements are arranged. Thus, flexibility in layout of the developer amount detector 31 can be enhanced.
For example, in an arrangement in which the development unit 4 is disposed above the photoreceptor 2 as shown in
By contrast, according to the above-described features of this specification, at least one of the components of the developer amount detector 31 is provided to the optical writing head 6. That is, the developer amount detector 31 can be disposed at any position in the area where the optical writing head 6 extends. Thus, the developer amount detector 31 can be disposed at a desired position, for example, a position facing the center portion of the developer container 25 in the longitudinal direction, suitable for detecting the amount of developer. Detection accuracy in developer amount detection can be enhanced when at least one of the light-emitting element 33 and the light-receiving element 34 are disposed in the center portion of the developer container 25 in the longitudinal direction, in which the amount of developer is relatively uniform. Accordingly, the detection accuracy can be enhanced.
Additionally, the above-described features of this specification can eliminate the need for longer light guide to detect the amount of developer at a desired position, thus attaining a higher accuracy in developer amount detection at a relatively low cost.
Further, the mounting structure according to the above-described embodiments can prevent deformation of the frame 39 of the optical writing head 6 in attachment of the developer amount detector 31 to the optical writing head 6. Accordingly, the focal distance of the optical writing head 6 relative to the photoreceptor 2 can be kept constant at a higher degree of accuracy, and thus degradation in image quality can be prevented or alleviated.
Additionally, the features of the above-described embodiments can adapt to other image forming apparatuses than tandem-type electrophotographic image forming apparatuses in which four process units are arranged laterally. For example, the features of the above-described embodiments can be adapted for single-color image forming apparatuses, or image forming apparatuses capable of image formation of five or more different colors. The image forming apparatus may be a copier, a printer, a facsimile machine, or a multifunction machine having at least two of those capabilities. Moreover, the process units 1 may be arranged vertically, and layout of other components such as the intermediate transfer belt 8 and the fixing device 18 can be changed.
It is not necessary to unit all of image forming components, such as the developer container 25, the development device 24, and the photoreceptor 2, into a single modular unit as the process unit 1. Alternatively, only the developer container 25 and the development device 24 may be united into a single unit removably installable in the apparatus, or the developer container 25 may be independently installed or removed from the apparatus.
Although the description above concerns configurations using two-component developer consisting essentially of carrier and toner, the above-described features of this specification can adapt to image forming apparatuses using one-component developer.
Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-054197 | Mar 2011 | JP | national |
