Patent Application
20140147141
This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2012-259178 filed Nov. 27, 2012.
1. Technical Field
The present invention relates to a developing device and an image forming apparatus including the developing device.
2. Summary
According to an aspect of the invention, there is provided a developing device includes a transporting unit that rotates while facing an image carrier that rotates while carrying an electrostatic latent image, the transporting unit transporting developer toward the image carrier so that the electrostatic latent image on the image carrier is developed; a feeding unit having a peripheral surface that rotates and to which the developer is attached, the feeding unit contacting the transporting unit to feed the developer to the transporting unit; a transport path that connects a containing chamber that contains the developer to a feeding chamber that houses the feeding unit; a supplying unit that retains the developer to be supplied to the feeding unit in the transport path and supplies the developer to the feeding unit in a supply region that is separated from a contact region in which the feeding unit contacts the transporting unit; and an attaching unit that is disposed downstream of the contact region and upstream of the supply region in a rotation direction of the feeding unit, the attaching unit attaching the developer to the feeding unit with an elastic force at a location below the contact region.
Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:
Referring to
Referring to
In the above-described technical configuration, the toner carrier 1 is not particularly limited as long as the toner carrier 1 is configured to carry the toner to the developing region M between the toner carrier 1 and the image carrier 10.
The rotation direction of the feeding member 2 may either be such that opposing portions of the feeding member 2 and the toner carrier 1 move in opposite directions or in the same direction. In the case where the opposing portions of the feeding member 2 and the toner carrier 1 move in the same direction, the opposing portions need to move at different speeds to allow the toner to be fed from the feeding member 2 to the toner carrier 1. The feeding member 2 is not particularly limited as long as the feeding member 2 has a rough (irregular) peripheral surface capable of capturing the toner. A typical example of the feeding member 2 is made of a foamed material. However, an elastic rubber member, for example, having recesses such as grooves in the peripheral surface thereof may instead be used. The foamed material may either be an open-cell foam or a closed-cell form. The open-cell foam may be used from the viewpoint of softness and cost.
The toner supplying unit 3 is not particularly limited as long as the toner supplying unit 3 is capable of supplying new toner Tn to the predetermined supply region X of the feeding member 2. A containing chamber (not shown) that contains the new toner Tn may be provided near the feeding member 2, and the new toner Tn contained in the containing chamber may be supplied to the supply region X of the feeding member 2 through a toner transport path 3a.
The supply region X to which the new toner Tn is supplied by the toner supplying unit 3 is separated from the contact region N between the feeding member 2 and the toner carrier 1. The reason for this is because if the toner supplying unit 3 supplies the new toner Tn directly to the contact region N between the feeding member 2 and the toner carrier 1, the new toner will be positively mixed with the old toner on the feeding member 2.
The regulating member 4 is not particularly limited as long as the regulating member 4 is configured to triboelectrically charge the toner carried by the toner carrier 1 and regulate the amount of the toner to a predetermined amount. Although a typical example of the regulating member 4 is a plate-shaped member that extends against the rotation direction of the toner carrier 1 and elastically contacts the toner carrier 1, a rotating member, for example, may instead be used. The regulating member 4 triboelectrically charges the toner fed from the feeding member 2 to the toner carrier 1. Therefore, if the new toner and the old toner having different electrification characteristics are mixed, the amount of charge differs between the new toner and the old toner by a large amount and the width of the charge distribution increases. When most of the toner captured by the feeding member 2 is old toner Tc, the amount of charge does not vary and the width of the charge distribution does not increase because the electrification characteristics of the old toner Tc are substantially uniform.
The attaching unit 5 is not particularly limited as long as the guide member 6 is included. The guide member 6 is not particularly limited as long as the guide member 6 is configured to receive the released toner Td that has been released upon passing through the contact region N as shown by arrow A in
The above-described guide member 6 may be a plate-shaped member, a rotatable member, etc., as appropriate.
Next, a typical example of a developing device will be described.
A typical example of the attaching unit 5 includes an elastically deformable plate-shaped member as the guide member 6, the plate-shaped member being inclined so that the pressed portion 6a thereof that is pressed against the feeding member 2 is below a portion thereof that receives the released toner Td.
In this example, the plate-shaped member that serves as the guide member 6 may have a smooth surface that allows particles of the released toner Td to roll toward the feeding member 2. Here, the “smooth surface” is a surface having an arithmetical mean roughness of, for example, Rz≦0.6 μm.
The toner carrier 1 and the feeding member 2 may be configured to rotate such that opposing portions thereof move in different directions. In this against-type configuration, the toner that has been captured by the feeding member 2 is released from the feeding member 2 by applying a shear force. Some of the released toner is fed to the toner carrier 1, and the remaining released toner falls. The surface of the feeding member 2 elastically returns to its original shape after passing through the contact region N. Accordingly, the toner that has remained on the surface of the feeding member 2 also falls when the surface of the feeding member 2 elastically returns to its original shape.
As illustrated in
The guide member 6 may be configured such that a contact force applied to the feeding member 2 by the guide member 6 is smaller than a contact force applied between the feeding member 2 and the toner carrier 1 in the contact region N. If the contact force applied between the feeding member 2 and the guide member 6 is too large, the feeding member 2 will be deformed by a large amount by the guide member 6 and there is a risk that the toner attached to the feeding member 2 will be released again when the feeding member 2 elastically returns to its original shape after passing the pressed portion 6a of the guide member 6.
The toner supplying unit 3 may be configured to connect the containing chamber (not shown) to a developing chamber 8 with the toner transport path 3a. The containing chamber contains the new toner Tn such that the new toner Tn is capable of being supplied. The developing chamber 8 houses the feeding member 2 and the toner carrier 1. The toner transport path 3a has a containing-chamber-side opening and a developing-chamber-side opening that faces the feeding member 2 and that is located below the containing-chamber-side opening.
In this example, the new toner Tn is retained in the toner transport path 3a so as to fill the toner transport path 3a, and the new toner Tn retained in the toner transport path 3a is arranged so as to face the feeding member 2 owing to its own weight. Therefore, it may be assumed that an interface is formed between the new toner Tn retained in the toner transport path 3a and the peripheral surface of the feeding member 2, so that the new toner Tn is not supplied to the feeding member 2 in regions where the old toner Tc is captured on the peripheral surface of the feeding member 2 and is supplied to the feeding member 2 only in regions where the old toner Tc is not captured on the peripheral surface of the feeding member 2. The old toner Tc captured by the feeding member 2 is pressed by the new toner Tn retained in the toner transport path 3a, and is therefore prevented from being mixed into the new toner Tn retained in the toner transport path 3a.
An example of an image forming apparatus including the above-described developing device 11 includes a control device 12 capable of controlling the toner consumption, as illustrated in
The control device 12 of this type may include a calculating unit that calculates an amount of toner consumption when, for example, an amount of image formation reaches a predetermined amount; a determining unit that determines whether or not the amount of toner consumption calculated by the calculating unit is greater than or equal to a predetermined threshold; an ejecting unit that ejects a predetermined amount of toner from the developing device 11 toward the image carrier 10 when it is determined by the determining unit that the amount of toner consumption is less than the threshold; and a cleaning process unit that cleans the image carrier 10 by removing the toner that has been ejected to the image carrier 10 by the ejecting unit.
In the case where the amount of toner consumption is small, the state in which the old toner Tc is not consumed and remains on the feeding member 2 continues, and therefore the toner is easily degraded. Accordingly, in this example, the toner is removed before it is degraded to stabilize the developing quality.
A typical example of the calculating unit that calculates the amount of toner consumption performs the calculation on the basis of an image density. The amount of image formation may be determined by, for example, counting the number of sheets in terms of the number of sheets having a standard size, or measuring the operating time of the developing device 11. The threshold used for the determination may, for example, be experimentally determined as a limit (lower allowable limit) of a range in which developing failure does not occur. The ejecting unit is not particularly limited as long as the ejecting unit is configured to forcedly eject the toner from the developing device 11 when the developing failure is likely to occur and it is assumed that the toner captured by the feeding member 2 is degraded. Typically, the toner ejection operation is performed by forming a toner-ejecting electrostatic latent image on the image carrier 10 and developing the toner-ejecting electrostatic latent image. The image formed in the toner ejection operation is not particularly limited, and may be a solid image or other images. Different types of images may be formed depending on the amount of toner consumption. The amount of toner to be ejected needs to be increased as the amount of toner consumption decreases. The cleaning process unit generally uses a cleaning unit for the image carrier 10. However, the cleaning process unit is not limited to this, and may instead clean the image carrier 10 by causing the toner to be transferred onto a recording medium or by using another cleaning member.
Exemplary embodiments of the present invention illustrated in the accompanying drawings will now be described in detail.
Referring to
In this example, the recording medium 28 is ejected after the image that has been transferred onto the recording medium 28 is fixed by a fixing device 30. A control device 100 controls the components of the image forming apparatus 20. Although the recording medium 28 is described as an example of the transfer medium, the transfer medium is not limited to this, and may instead be an intermediate transfer body that temporarily carries the toner image before the toner image is transferred onto the recording medium 28.
The photoconductor 21 includes a drum-shaped metal frame body and a photosensitive layer formed on the metal frame body.
The charging device 22 may include, for example, a charging container and a discharge wire that is disposed in the charging container as a charging member. However, the charging device 22 is not limited to this, and may instead include, for example, a roll-shaped charging member as appropriate.
The exposure device 23 may be a laser scanning device or a light-emitting-diode (LED) array.
The developing device 24 is a one-component developer type developing device that uses non-magnetic toner. The developing device 24 will be described in detail below.
The transfer device 25 is not particularly limited as long as the transfer device 25 is configured to generate a transfer electric field that causes the toner image on the photoconductor 21 to be electrostatically transferred onto the recording medium 28. The transfer device 25 may include, for example, a roll-shaped transfer member to which a transfer voltage is applied. However, the transfer device 25 is not limited to this, and a transfer corotron including a discharge wire, for example, may instead be used as appropriate.
The cleaning device 26 illustrated in
All or some of the photoconductor 21, the charging device 22, the developing device 24, and the cleaning device 26 may be assembled together in advance as a process cartridge, which is an image forming assembly, and be detachably attached to a receiving section provided in a housing of the image forming apparatus.
In this example, as illustrated in
A sealing member (not shown) composed of an elastic member is fixed at one end to the bottom edge of the opening in the developing container 40, and a free end of the sealing member is in elastic contact with the developing roller 41. Thus, the gap between the developing roller 41 and the developing container 40 is covered.
In this example, the developing roller 41 rotates so that opposing portions of the developing roller 41 and the photoconductor 21 move in the same direction. The developing roller 41 includes a metal shaft 41a and a roller body layer 41b that is formed around the metal shaft 41a and made of a resin or a rubber having a predetermined volume resistivity. The surface of the roller body layer 41b has a certain surface roughness so as to be capable of carrying the toner.
The feeding roller 42 rotates so that opposing portions of the feeding roller 42 and the developing roller 41 move in opposite directions. The feeding roller 42 includes a metal shaft 42a and an elastically deformable elastic layer 42b that is formed around the metal shaft 42a and has a predetermined volume resistivity. The elastic layer 42b is made of, for example, a foamed material, such as urethane foam sponge rubber, and has a rough surface 42c (see
In this example, the elastic layer 42b of the feeding roller 42 is sufficiently softer than the roller body layer 41b of the developing roller 41. Therefore, the developing roller 41 and the feeding roller 42 are arranged such that the developing roller 41 intrudes into the elastic layer 42b of the feeding roller 42 by a predetermined amount. With this arrangement, a contact region N (nip region) is formed between the developing roller 41 and the feeding roller 42. In this example, the feeding roller 42 is rotated so as to move downward and the developing roller 41 is rotated so as to move upward in the contact region N between the developing roller 41 and the feeding roller 42.
Accordingly, the feeding roller 42 serves functions of removing the toner that has been transported by the developing roller 41 from the developing roller 41 and feeding the toner on the feeding roller 42 to the developing roller 41 in the contact region N between the developing roller 41 and the feeding roller 42. The developing roller 41 transports the non-magnetic toner fed from the feeding roller 42 to a developing region M in which the developing roller 41 faces the photoconductor 21, so that the non-magnetic toner is used in a developing process in the developing region M.
The charging blade 45 is composed of, for example, a metal plate made of phosphor bronze or the like, and is fixed at one end to an edge of the opening in the developing container 40. The charging blade 45 extends so as to project in a direction opposite to a rotation direction of the developing roller 41, and is pressed against the surface of the developing roller 41 at a predetermined pressing force. Therefore, the toner T held by the developing roller 41 is triboelectrically charged when the toner T passes through the region in which the charging blade 45 is pressed against the developing roller 41, and the amount of transported toner T is regulated to a predetermined amount. The charging blade 45 is fixed to the edge of the opening in the developing container 40 by a bracket 46.
The developing container 40 includes a developing chamber 51 that houses the developing roller 41 and the feeding roller 42 and a containing chamber 52 that is adjacent to the developing chamber 51 and that contains the new toner Tn that may be supplied to the developing chamber 51.
In this example, a block-shaped partition member 53 that separates the developing chamber 51 and the containing chamber 52 from each other is disposed in the developing container 40 separately from the bottom wall of the developing container 40. The bottom wall of the developing container 40 includes two curved portions 40a and 40b that are curved so as to protrude downward and formed integrally with each other, and a ridge-shaped separating portion 54 is formed at the boundary between the curved portions 40a and 40b.
In this example, the toner supplying mechanism 60 is configured such that the new toner Tn is contained in the containing chamber 52 of the developing container 40 and the containing chamber 52 is connected to the developing chamber 51 with a toner transport path 61. An agitator 62, which functions as a stirring-and-transporting member, is disposed in the containing chamber 52. The agitator 62 transports the new toner Tn to the developing chamber 51 through the toner transport path 61 while stirring the new toner Tn.
The curved portion 40b, which is a portion of the bottom wall of the developing container 40 that corresponds to the containing chamber 52, has a curvature corresponding to that of the trajectory of free ends of the agitator 62.
In this example, the toner transport path 61 is formed between the partition member 53 and the curved portion 40a, which is a portion of the bottom wall of the developing container 40.
As illustrated in
The developing-chamber-side opening 66 of the toner transport path 61 is arranged so as to face the feeding roller 42, and defines a supply region X in which the new toner Tn is supplied to the developing chamber 51.
In particular, in this example, the developing-chamber-side opening 66 of the toner transport path 61 is separated from the contact region N between the developing roller 41 and the feeding roller 42 (substantially halfway around the feeding roller 42 in this example), and is positioned below the center C of the feeding roller 42. The width w of the developing-chamber-side opening 66 along a rotation direction of the feeding roller 42 is smaller than the outer diameter d of the feeding roller 42 in a plane of projection in a direction from the feeding roller 42.
In this example, the new toner Tn in the containing chamber 52 is transported to the toner transport path 61 by the agitator 62. Therefore, as shown by one-dot chain lines in
The containing-chamber-side opening 65 of the toner transport path 61 is at a position ys corresponding to the top of the ridge-shaped separating portion 54 that is formed integrally with a portion of the bottom wall of the developing container 40. The containing-chamber-side opening 65 may be positioned at least below a contact position yb at which the charging blade 45 contacts the developing roller 41. According to the above-described dimensional relationship, even when the new toner Tn is retained in the toner transport path 61 so as to fill the toner transport path 61, the toner in the developing chamber 51 is prevented from being pushed up to the contact position yb at which the charging blade 45 contacts the developing roller 41 by the pressure applied by the new toner Tn retained in the toner transport path 61. As a result, the risk that a region around the charging blade 45 in the developing chamber 51 will be filled with the toner and the state in which the charging blade 45 is pressed against the developing roller 41 will be changed may be effectively reduced.
In this example, the partition member 53 has a curved regulating surface 70 in a region adjacent to the developing-chamber-side opening 66 of the toner transport path 61. The regulating surface 70 faces the feeding roller 42 and extends along the peripheral surface of the feeding roller 42 with a gap g therebetween. The gap g is not particularly limited as long as the toner layer to be formed on the feeding roller 42 may be regulated, but is set so that an amount of toner that satisfies the maximum toner consumption per unit time of the developing device 24 may be supplied. In this example, the gap g is set in the range of 0.5 mm to 1.0 mm. Here, the lower limit (0.5 mm) is set in consideration of mounting tolerance so as to allow the partition member 53 to be mounted in the developing container 40 without causing the partition member 53 to contact the feeding roller 42, and the upper limit (1.0 mm) is set so that the toner layer to be formed on the feeding roller 42 may be regulated.
In this example, the developing roller 41 is provided with a developing power supply 81 for generating a developing electric field between the developing roller 41 and the photoconductor 21, and the feeding roller 42 is provided with a feeding power supply 82 for generating a feeing electric field for feeding the non-magnetic toner T to the developing roller 41.
The developing power supply 81 applies a developing voltage obtained by superimposing an alternating-current component on a predetermined direct-current component to the developing roller 41. The feeding power supply 82 applies a feeding voltage obtained by superimposing an alternating-current component having the same period as that of the alternating-current component of the voltage applied by the developing power supply 81 on a direct-current component having a predetermined potential difference (including ‘0’) relative to the direct-current component of the voltage applied by the developing power supply 81.
In the case where the toner may be reliably fed from the feeding roller 42 to the developing roller 41 in the contact region N even when the feeding electric field is not generated between the developing roller 41 and the feeding roller 42, the developing power supply 81 may, of course, be used also as the feeding power supply 82 so that the potential difference between the developing roller 41 and the feeding roller 42 is set to substantially 0.
In the present exemplary embodiment, an attaching mechanism 90 is provided below the contact region N between the developing roller 41 and the feeding roller 42 in the developing chamber 51 of the developing container 40. The attaching mechanism 90 attaches the toner released from the developing roller 41 and the feeding roller 42 to the feeding roller 42.
As illustrated in
In this example, the guide member 91 is composed of an elastically deformable elastic sheet 92, one end of which is fixed to an attachment member 95 provided on a portion of the bottom wall of the developing container 40. The elastic sheet 92 is inclined by an angle of θ with respect to a horizontal direction so that a pressed portion S of the elastic sheet 92 that is pressed against the feeding roller 42 is below a portion of the elastic sheet 92 that receives the released toner Td.
The elastic sheet 92 of this type may be, for example, a thermoplastic polyurethane sheet, a polyimide sheet, a polyester sheet, or a PET sheet. A lower limit of the inclination angle θ of the elastic sheet 92 is set to a value (for example, 10°) in a range in which particles of the released toner Td may roll along the elastic sheet 92. When the inclination angle θ is excessively large, the volume of a toner-receiving region that receives the released toner Td decreases. Therefore, an upper limit of the inclination angle θ is set to a value (for example, 45°) in a range in which releasing failure due to an increase in the pressure of the toner in the toner-receiving region does not occur at the feeding roller 42.
In this example, the elastic sheet 92 may have a smooth surface 93 at a front side thereof (side at which the elastic sheet 92 receives the released toner Td), the smooth surface 93 allowing the particles of the released toner Td to roll toward the feeding roller 42. Here, the smooth surface 93 is a surface having an arithmetical mean roughness Rz of, for example, Rz≦0.6 μm.
In this example, the pressed portion S of the elastic sheet 92 is near an end of the elastic sheet 92, and a contact force applied to the feeding roller 42 by the elastic sheet 92 is smaller than a contact force applied between the developing roller 41 and the feeding roller 42 in the contact region N. More specifically, when an amount of deformation of the elastic sheet 92 is defined as an amount by which the elastic sheet 92 is elastically deformed by being pressed against the feeding roller 42 from the state in which the elastic sheet 92 is straight and not elastically deformed, the contact force may be calculated from the modulus of elasticity of the elastic sheet 92 and the amount of deformation. Accordingly, the contact force of the elastic sheet 92 may be appropriately set.
In this example, the pressed portion S of the elastic sheet 92 is closer to the contact region N than the bottom portion of the feeding roller 42. Therefore, in the pressed portion S of the elastic sheet 92, the contact force gradually increases toward the end of the elastic sheet 92.
In the developing device 24 according to the present exemplary embodiment, as illustrated in
In this example, the opposing portions of the developing roller 41 and the feeding roller 42 move in opposite directions in the contact region N. Therefore, when the toner T captured by the feeding roller 42 reaches the contact region N, some of the toner T is fed to the developing roller 41, and the remaining toner T remains on the feeding roller 42 or is released and falls.
The toner T fed to the developing roller 41 is transported by the rotation of the developing roller 41, and passes the charging blade 45. When the toner T passes the charging blade 45, the toner T is triboelectrically charged and the amount thereof is regulated to a predetermined amount. Then, the toner T is transported to the developing region M between the developing roller 41 and the photoconductor 21, and is used to develop the electrostatic latent image formed on the photoconductor 21.
Remaining unused toner Te that has passed through the developing region M of the developing roller 41 is transported to the contact region N between the developing roller 41 and the feeding roller 42 by the rotation of the developing roller 41. Most of the remaining unused toner Te is scraped off from the developing roller 41 in the contact region N and is released (see
The released toner Td (see
When the amount of toner captured on the peripheral surface of the feeding roller 42 becomes insufficient, the toner supplying mechanism 60 supplies the new toner Tn to the peripheral surface of the feeding roller 42 as appropriate (see
The developing device 24 performs the developing process in the above-described manner.
Behavior of the toner around the attaching mechanism 90 in the developing process performed by the developing device 24 will now be described.
As illustrated in
The remaining unused toner Te that has not been used in the developing region M of the developing roller 41 is transported to the contact region N by the rotation of the developing roller 41. The remaining unused toner Te held by the developing roller 41 is scraped off and falls at an upstream position of the contact region N in the rotation direction of the developing roller 41 (downstream position in the rotation direction of the feeding roller 42).
The released toner Td that falls from the contact region N as described above travels as shown by arrow A in
In this state, the elastic sheet 92 has the smooth surface 93 at the front side and is inclined so that the pressed portion S that is pressed against the feeding roller 42 is below the portion that receives the released toner Td. Therefore, as shown by arrow B in
A contact force P applied to the pressed portion S of the elastic sheet 92 gradually increases toward the end of the elastic sheet 92 in accordance with the curvature of the peripheral surface of the feeding roller 42. Therefore, the released toner Td that has moved along the surface of the elastic sheet 92 and reached the pressed portion S of the elastic sheet 92 is gradually pressed and triboelectrically charged between the elastic sheet 92 and the feeding roller 42. Then, the released toner Td is captured by the feeding roller 42 together with the remaining toner Ta that has remained on the rough surface 42c at the periphery of the feeding roller 42.
The contact force P applied to the elastic sheet 92 is substantially uniformly distributed over the pressed portion S in the axial direction of the feeding roller 42. Therefore, the amount of transportation of the toner at the peripheral surface of the feeding roller 42 is reliably determined by the elastic sheet 92, and is uniform in the axial direction. Therefore, the released toner Td is pressed against the feeding roller 42 together with the remaining toner Ta by the contact force P applied by the elastic sheet 92, and is attached to the peripheral surface of the feeding roller 42 by the image force of the toner. As a result, old toner Tc, which include the remaining toner Ta and the released toner Td, is captured on the peripheral surface of the feeding roller 42 when it passes the pressed portion S of the elastic sheet 92, and is re-transported by the rotation of the feeding roller 42.
Most of the released toner Td is attached to the peripheral surface of the feeding roller 42. Therefore, the released toner Td is prevented from collecting in a region below the contact region N in the developing chamber 51.
In the above-described manner, the old toner Tc, which is not the new toner Tn, is re-transported by the feeding roller 42 and reaches the supply region X of the toner supplying mechanism 60, as illustrated in
In this example, the toner supplying mechanism 60 includes the curve-shaped toner transport path 61 that connects the containing chamber 52 to the developing chamber 51. The developing-chamber-side opening 66 of the toner transport path 61 is arranged so as to face the feeding roller 42, and is positioned below the containing-chamber-side opening 65 of the toner transport path 61.
Therefore, a substantially constant amount of new toner Tn is retained in the toner transport path 61 so as to fill the toner transport path 61, and the developing-chamber-side opening 66 receives a pressing force generated by the weight of the new toner Tn retained in the toner transport path 61 (shown by one-dot chain lines in
Although the new toner Tn contained in the containing chamber 52 is transported to the toner transport path 61 by the agitator 62, the toner transport path 61 is already filled with the new toner Tn. Therefore, the amount of new toner Tn retained in the toner transport path 61 is substantially constant.
In this example, the developing-chamber-side opening 66 of the toner transport path 61 is positioned below the center C of the feeding roller 42. In addition, the toner transport path 61 has a curved shape and a portion thereof near the developing-chamber-side opening 66 extends laterally and slightly downward toward the developing-chamber-side opening 66.
The layer of the old toner Tc captured by the feeding roller 42 is formed around the feeding roller 42, and is moved along the developing-chamber-side opening 66 of the toner transport path 61 by the rotation of the feeding roller 42.
In the region in which the feeding roller 42 faces the developing-chamber-side opening 66, the feeding roller 42 rotates so as to move upward and approach the toner transport path 61. Therefore, the direction in which the feeding roller 42 is pressed by the new toner Tn through the developing-chamber-side opening 66 of the toner transport path 61 is opposite to the rotation direction of the feeding roller 42. In addition, the old toner Tc that has been attached to the feeding roller 42 in a smooth state by the attaching mechanism 90 is re-transported by the feeding roller 42. Therefore, in the developing-chamber-side opening 66, the old toner To on the feeding roller 42 is moved along the interface of the new toner Tn retained in the toner transport path 61 while the old toner To is suppressed from being mixed with the new toner Tn.
In the present exemplary embodiment, if, for example, the developing-chamber-side opening 66 of the toner transport path 61 extends to a region above the center C of the feeding roller 42, the feeding roller 42 rotates so as to move away from the toner transport path 61 in the region above the center C of the feeding roller 42. Therefore, the new toner Tn that is positioned at the interface of the new toner Tn retained in the toner transport path 61 is easily extracted by the rotation of the feeding roller 42, and is easily mixed into the toner on the feeding roller 42. To avoid such a situation, the above-described configuration of the present exemplary embodiment may be applied.
Also when the feeding roller 42 is rotated in the opposite direction (direction in which a portion of the feeding roller 42 that faces the developing-chamber-side opening 66 moves downward), the above-described configuration of the present exemplary embodiment may be applied to avoid a situation in which the new toner Tn at the interface of the new toner Tn retained in the toner transport path 61 is easily extracted by the rotation of the feeding roller 42 and mixed into the toner on the feeding roller 42.
As illustrated in
In addition, since the new toner Tn retained in the toner transport path 61 presses the peripheral surface of the feeding roller 42, the old toner Tc captured by the feeding roller 42 is blocked by the interface of the new toner Tn retained in the toner transport path 61, and is prevented from being mixed into the new toner Tn in the toner transport path 61.
As illustrated in
As described above, the new toner Tn is not supplied to the feeding roller 42 when a sufficient amount of old toner Tc is captured, and is supplied when the amount of old toner Tc becomes insufficient. Therefore, the old toner Tc and the new toner Tn are prevented from being unnecessarily mixed at the peripheral surface of the feeding roller 42, and the old toner Tc is preferentially used.
In the present exemplary embodiment, there is a risk that the toner surrounding the old toner Tc captured on the peripheral surface of the feeding roller 42 will move together with the old toner Tc owing to viscosity or the like when the feeding roller 42 rotates.
However, in the present exemplary embodiment, the regulating surface 70, which has a curved shape and extends along the peripheral surface of the feeding roller 42 with the predetermined gap g therebetween, is formed on the partition member 53 in a region adjacent to the developing-chamber-side opening 66 of the toner transport path 61. Therefore, even when, for example, excess toner tries to move together with the toner captured at the periphery of the feeding roller 42 in the developing-chamber-side opening 66 of the toner transport path 61 or in the region where the feeding roller 42 faces the bottom wall of the developing container 40, the excess part of the toner captured on the peripheral surface of the feeding roller 42 is scraped off when the toner passes the regulating surface 70 of the partition member 53. Thus, the amount of toner captured by the feeding roller 42 is regulated to a desired amount.
To evaluate the performance of the developing device according to the first exemplary embodiment, the performance of a developing device according to comparative exemplary embodiment 1 will be described.
Referring to
The operation of the present comparative exemplary embodiment will now be described.
When the agitator 62′ starts a toner supplying operation, the new toner Tn contained in the containing chamber 52′ is supplied to the developing chamber 51′ through the toner transporting hole 56′. When the amount of toner in the developing chamber 51′ increases and the height of the toner exceeds the height of the toner transporting hole 56′, old toner Tc flows backward into the containing chamber 52′ from the developing chamber 51′.
In addition, released toner that has been released at a contact region N′ between the developing roller 41′ and the feeding roller 42′ is collected in the developing chamber 51′. The collected toner receives frictional stress from the feeding roller 42′ without being consumed, and becomes mixed with the new toner Tn.
When the new toner Tn and the old toner Tc are mixed in the developing chamber 51′, the new toner Tn and the old toner Tc have very different coating levels because an external additive added to the old toner Tc becomes separated from or embedded into particle bases of the toner. Therefore, when the new toner Tn and the old toner Tc are mixed, mutual charging is caused by the charging blade 45′ and the charge distribution significantly differs between the new toner Tn and the old toner Tc. As a result, improperly charged toner particles are easily generated, and a fogging phenomenon easily occurs in which the improperly charged toner particles unnecessarily adhere to the recording medium in, for example, a background area.
As described above, in comparative exemplary embodiment 1, the new toner and the old toner are unavoidably mixed on the feeding roller 42′. In contrast, in the first exemplary embodiment, the toner supplying mechanism 60 that retains the new toner and the attaching mechanism 90 are used so that the disadvantage of the developing device according to comparative exemplary embodiment 1 may be reduced.
In the present exemplary embodiment, the control device 100 performs a toner ejection control process in which the toner contained in the developing device 24 is forcedly ejected when the amount of toner consumption is smaller than a predetermined amount.
In the developing device 24 of the present example (see
Accordingly, in the present exemplary embodiment, a toner ejection control process illustrated in
In the toner ejection control process, as illustrated in
Next, it is determined whether or not the calculated average print percentage is smaller than a predetermined threshold. If it is determined that the calculated average print percentage is greater than or equal to the threshold, it is determined that the toner has been fairly consumed and there is no risk that degradation of the toner will occur. Then, the toner ejection control process is ended.
If it is determined that the average print percentage is not greater than or equal to the threshold, that is, if it is determined that the average print percentage is smaller than the threshold, it is determined that the toner is being degraded and a toner ejection amount corresponding to the average print percentage is calculated. The method for calculating the toner ejection amount is not particularly limited as long as the toner ejection amount for when the average print percentage is small is larger than that for when the average print percentage is large. For example, a computational expression showing the relationship between the average print percentage and the toner ejection amount may be prepared in advance, and the toner ejection amount may be determined by using this expression. Alternatively, several ranges may be set for the average print percentage, and toner ejection amounts corresponding to the respective ranges may be determined in advance.
After the toner ejection amount is calculated, a toner ejection operation is performed by controlling the charging device 22, the exposure device 23, the developing device 24, and the transfer device 25. More specifically, a toner-ejecting electrostatic latent image corresponding to the calculated toner ejection amount is formed on the photoconductor 21, and is then developed by the developing device 24. When the toner is ejected as described above, not only the toner on the developing roller 41 but also the toner attached to the feeding roller 42 is consumed. As a result, the old toner that may have been degraded is removed from the developing device 24.
The toner that has been ejected onto the photoconductor 21 is removed by the cleaning device 26.
The toner ejection operation is performed at a time different from the time at which a normal image forming operation is performed. The toner ejection operation is appropriately performed when a normal image forming operation is not performed, for example, in a pause period in the image forming operation or when the image forming apparatus is activated or stopped. In the case where the toner on the photoconductor 21 is removed by the cleaning device 26 in the toner ejection operation, the operation of the transfer device 25 is stopped to prevent the toner on the photoconductor 21 from being transferred onto the transfer device 25. Alternatively, the transfer device 25 may be separated from the photoconductor 21 if the transfer device 25 is a contact-type transfer device, or an electric field that prevents the toner from adhering to the transfer device 25 may be applied between the transfer device 25 and the photoconductor 21. Although the toner that has been ejected onto the photoconductor 21 in the toner ejection operation is removed by the cleaning device 26 in this example, the toner may instead be transferred onto the recording medium 28 or be removed by another cleaning device.
In the present exemplary embodiment, the level of degradation of the toner is determined by calculating the average print percentage per each sheet from the accumulated amount of consumption of the toner when the number of sheets that have been output has reached the predetermined number. However, the method for determining the level of degradation of the toner is not limited to this, and the following method may instead be used.
That is, an amount of toner consumption per unit time may be calculated from the amount of toner consumption within a predetermined operation time of the developing device 24, and the level of degradation of the toner may be determined on the basis of whether or not the amount of toner consumption per unit time is greater than or equal to a predetermined threshold. In this case, the toner ejection operation may be performed when the amount of toner consumption per unit time is small.
Alternatively, the level of degradation of the toner may be determined on the basis of how long an output operation in which the amount of toner consumption per sheet is smaller than a predetermined threshold has continued. In general, when an image in which photographic images and character images are mixed is output, the average print percentage is high owing to the influence of the photographic images. In the case where the output image mainly includes character images and the area occupied by photographic images is small, an output operation with a small print percentage may be continuously performed. Accordingly, it may be recognized whether or not the state in which the amount of toner consumption per sheet is small continues, and when such a state continues for a long time, it may be determined that the toner may have been degraded and the toner ejection operation may be performed.
The level of degradation of the toner may also be determined in consideration of environmental conditions.
In the present exemplary embodiment, the attaching mechanism 90 includes the elastic sheet 92 as the guide member 91. One end of the elastic sheet 92 is fixed and the other end of the elastic sheet 92 is pressed against the peripheral surface of the feeding roller 42. However, the attaching mechanism 90 is not limited to this, and may be designed as in modifications 1-1 to 1-3 illustrated in
The attaching mechanism 90 illustrated in
When the urging member 97 is used, the pressing conditions under which the sheet member 96 is pressed against the feeding roller 42 are maintained substantially constant. Accordingly, the released toner that has reached the pressed portion S of the sheet member 96 is attached to the feeding roller 42 at a stable contact force.
In modification 1-1, the elastic sheet 92 according to the first exemplary embodiment may be used as the sheet member 96. However, unlike the elastic sheet 92, it is not necessary that the sheet member 96 itself be pressed against the feeding roller 42. The sheet member 96 is not particularly limited as long as the sheet member 96 has a surface that allows particles of the released toner to roll therealong and is capable of being bent when pressed against the urging member 97, and may be formed of, for example, a leaf spring made of a metal (for example, SUS).
The attaching mechanism 90 illustrated in
In this modification, the sheet member 96 extends beyond the bottom portion of the feeding roller 42, and therefore the area of the pressed portion S of the sheet member 96 that is pressed against the feeding roller 42 is relatively large. In this modification, a portion of the sheet member 96 that is upstream of the bottom portion of the feeding roller 42 in the rotation direction of the feeding roller 42 needs to be inclined downward from the portion that is positioned below the contact region N between the developing roller 41 and the feeding roller 42 and that receives the released toner toward the bottom portion of the feeding roller 42. Accordingly, the released toner received by the sheet member 96 is reliably pressed by the pressed portion S that is pressed against the feeding roller 42 when the released toner is attached to the feeding roller 42.
The attaching mechanism 90 illustrated in
In this example, a portion of the peripheral surface of the roller 98 that is closer to the feeding roller 42 than the top portion of the roller 98 is positioned so as to be able to receive the released toner that falls from the contact region N between the developing roller 41 and the feeding roller 42.
In this example, the roller 98 is rotated by the rotation of the feeding roller 42. Therefore, the released toner that has fallen from the contact region N and landed on the peripheral surface of the roller 98 is guided to a pressed portion S between the roller 98 and the feeding roller 42 and attached to the feeding roller 42.
Referring to
Similar to the first exemplary embodiment, the attaching mechanism 90 of this example includes an elastic sheet 92 having a cantilever structure as a guide member 91. The elastic sheet 92 is conductive, and is connected to an attracting power supply 83 capable of applying an attracting voltage for generating an attractive electric field in which toner T interposed between the elastic sheet 92 and a feeding roller 42 is attracted to the feeding roller 42.
In this example, an elastic sheet whose volume resistivity is adjusted to a predetermined value by, for example, dispersing a conductive filler may be used as the elastic sheet 92. The attractive electric field may be appropriately set so as to accelerate the adhesion of the toner within a range in which unnecessary discharge does not occur between the feeding roller 42 and the elastic sheet 92 in consideration of the feeding voltage applied to the feeding roller 42.
In the present exemplary embodiment, as illustrated in
According to the present exemplary embodiment, the entire body of the elastic sheet 92 is conductive. However, the elastic sheet 92 is not limited to this, and may instead have a multilayer structure including a high-resistance layer having a volume resistivity of, for example, 109 Ω·cm or more on the side facing the feeding roller 42 and a conductive layer on the opposite side. In this case, since the high-resistance layer is provided, the attracting voltage applied by the attracting power supply 83 may be higher than that in the case where the entire body of the elastic sheet 92 is conductive. In addition, dielectric polarization of the high-resistance layer easily occurs owing to the attracting power supply 83, and it may be expected that a force that attracts the elastic sheet 92 to the feeding roller 42 is also generated. In the present exemplary embodiment, the attaching mechanism 90 includes the elastic sheet 92 having a cantilever structure as the guide member 91. However, the guide member 91 is not limited to this, and may, of course, instead be structured as in the above-described modifications 1-1 to 1-3.
Referring to
As illustrated in
In this example, the pressure applied to the peripheral surface of the feeding roller 42 at the interface (a type of a wall) of the new toner Tn retained in the toner transport path 61 increases as the height of the vertical passage 611 increases. When the vertical passage 611 is formed such that the cross sectional width thereof increases toward the top, the volume of the new toner Tn that fills the vertical passage 611 increases. Also in this case, the pressure applied at the interface of the new toner Tn retained in the toner transport path 61 increases.
The lateral passage 612 is bent from the vertical passage 611 in a desired direction and extends so that the interface is formed by the new toner Tn retained in the toner transport path 61 at a position where the lateral passage 612 faces the peripheral surface of the feeding roller 42.
The toner transport path 61 is defined between a partition member 53 and a curved portion 40a, which is a portion of a bottom wall of a developing container 40. A wall of the partition member 53 that defines the top surface of the lateral passage 612 is inclined downward from the vertical passage 611 toward the feeding roller 42. The inclination angle η of the wall with respect to the horizontal direction is smaller than or equal to an angle of repose of the toner that is used.
The angle of repose of the toner is an index of fluidity of the toner. In the present exemplary embodiment, the inclination angle η of the top wall of the lateral passage 612 with respect to the horizontal direction is smaller than or equal to the angle of repose of the toner that is used. Therefore, the new toner Tn that fills the lateral passage 612 does not easily flow and serves to reduce the excessive pressure applied by the new toner Tn in the vertical passage 611. The supply pressure of the new toner Tn applied to the feeding roller 42 may be adjusted by adjusting the combination of the height of the vertical passage 611, the length of the lateral passage 612, and the inclination angle η.
In the present exemplary embodiment, a corner portion 613 of the partition member 53 at which the lateral passage 612 is bent from the vertical passage 611 has an angular shape. However, to reduce the resistance against the movement of the new toner Tn from the vertical passage 611 to the lateral passage 612, the corner portion 613 may instead have a curved shape.
Referring to
In this example, similar to the first exemplary embodiment, the toner transport path 61 is formed between a partition member 53 and a curved portion 40a, which is a portion of the bottom wall of the developing container 40. The toner transport path 61 has a containing-chamber-side opening 65 that is positioned above a developing-chamber-side opening 66, and is curved from a containing chamber 52 toward a developing chamber 51 along the curved portion 40a.
The width w1 of the developing-chamber-side opening 66 of the toner transport path 61 along a rotation direction of a feeding roller 42 is smaller than the outer diameter d (see
In the present exemplary embodiment, similar to the first exemplary embodiment, the new toner Tn retained in the toner transport path 61 is pressed in a slightly downwardly inclined direction at the developing-chamber-side opening 66. In the region in which the feeding roller 42 faces the developing-chamber-side opening 66, the old toner Tc captured by the feeding roller 42 moves upward and comes into contact with the new toner.
When the new toner and the old toner repeatedly come into contact with each other over time, a location at which the old toner Tc captured by the feeding roller 42 joins the new toner Tn retained in the toner transport path 61 is generated near the bottom edge of the developing-chamber-side opening 66 of the toner transport path 61. In this case, since the pressing force based on the weight of the new toner Tn retained in the toner transport path 61 is applied to the peripheral surface of the feeding roller 42 and the new toner Tn retained in the toner transport path 61 is pressed by the rotational force of the old toner Tc captured by the feeding roller 42, the new toner and the old toner gradually collect at the location where they join and solidify in a soft-blocking fashion. As a result, a substantially triangular toner wall 110 made of toner that has collected (so-called dead toner) is formed.
When the toner wall 110 is formed near the bottom edge of the developing-chamber-side opening 66 of the toner transport path 61 over time, the old toner Tc captured by the feeding roller 42 comes into contact with the toner wall 110 immediately after reaching the developing-chamber-side opening 66. Therefore, the old toner Tc is reliably prevented from flowing backward into the toner transport path 61.
When the toner wall 110 is formed as described above, the width of the developing-chamber-side opening 66 is substantially reduced from W1 to w2 (w2<w1). Therefore, the developing-chamber-side opening 66 may be designed in consideration of the formation of the toner wall 110.
Although the toner wall 110 is formed over time in the above-described example, a partition member corresponding to the toner wall 110 formed of the new toner Tn may, of course, instead be formed in the developing container 40.
In the present exemplary embodiment, the developing-chamber-side opening 66 of the toner transport path 61 extends to a position above the center C of the feeding roller 42. However, when the width w1 (or w2) of the developing-chamber-side opening 66 along the rotation of the feeding roller 42 is smaller than the outer diameter d of the feeding roller 42 in a plane of projection in a direction from the feeding roller 42, the new toner Tn retained in the toner transport path 61 comes into contact with the peripheral surface of the feeding roller 42 through the developing-chamber-side opening 66. Therefore, compared to the case in which the width of the developing-chamber-side opening 66 is greater than or equal to the outer diameter d of the feeding roller 42, the risk that the new toner Tn in the toner transport path 61 will be directly mixed into the developing chamber 51 may be reduced.
In particular, in this example, the partition member 53 has the predetermined regulating surface 70. Therefore, even when excess toner tries to move together with the toner captured on the peripheral surface of the feeding roller 42, the excess toner is removed by the regulating surface 70 of the partition member 53. Thus, the amount of toner that is captured on the peripheral surface of the feeding roller 42 is regulated by the regulating surface 70.
Referring to
In this example, a developing container 40 includes a separating wall 55 that separates a developing chamber 51 from a containing chamber 52 of new toner Tn, and an opening 55a is formed in the separating wall 55.
A downstream partition member 53a and an upstream partition member 53b are arranged near the opening 55a in the separating wall 55 in the developing chamber 51 of the developing container 40 at a downstream position and an upstream position, respectively, in a rotation direction of a feeding roller 42.
The upstream partition member 53b is attached to a portion of the separating wall 55 above the opening 55a, and is arranged so as to face the opening 55a and project toward the feeding roller 42.
The downstream partition member 53a is attached to a portion of the separating wall 55 below the opening 55a, and is arranged so as to face the feeding roller 42 and project into the opening 55a.
In this example, the toner supplying mechanism 60 includes a toner transport path 61 that is connected to the containing chamber 52, and an agitator 62 is disposed in the containing chamber 52. The toner transport path 61 is formed between the upstream partition member 53b and the downstream partition member 53a, and includes a lateral passage 615 that faces the containing chamber 52 and extends laterally in a substantially horizontal direction and a vertical passage 616 that is bent from the lateral passage 615 and extends in a substantially vertical direction toward the feeding roller 42. A developing-chamber-side opening 66, which corresponds to an outlet of the vertical passage 616, is disposed below a containing-chamber-side opening 65, which corresponds to an inlet of the lateral passage 615.
The width of the developing-chamber-side opening 66 along a rotation direction of the feeding roller 42 is at least smaller than the outer diameter of the feeding roller 42 in a plane of projection in a direction from the feeding roller 42. The position at which the developing-chamber-side opening 66 is formed may be set as appropriate. In this example, the developing-chamber-side opening 66 is formed at a position slightly above the center of the feeding roller 42.
In this example, each of the downstream partition member 53a and the upstream partition member 53b has a curved regulating surface 70 in a region adjacent to the developing-chamber-side opening 66 of the toner transport path 61. Each regulating surface 70 faces the feeding roller 42 and extends along the peripheral surface of the feeding roller 42 with a gap g therebetween. The gap g is not particularly limited as long as the toner layer to be formed on the feeding roller 42 may be regulated, and is in the range of 0.5 mm to 1.0 mm in this example. The meanings of the lower and upper limits are similar to those in the first exemplary embodiment.
The regions in which the regulating surfaces 70 are formed on the partition members 53a and 53b are not particularly limited. In this example, the regulating surface 70 of the downstream partition member 53a extends from the developing-chamber-side opening 66 of the toner transport path 61 to near the top portion of the feeding roller 42, and the regulating surface 70 of the upstream partition member 53b extends from the developing-chamber-side opening 66 of the toner transport path 61 to a location downstream of the bottom portion of the feeding roller 42 in the rotation direction of the feeding roller 42.
In the toner supplying mechanism 60 according to the present exemplary embodiment, the agitator 62 transports the new toner Tn in the containing chamber 52 to the toner transport path 61, so that the new toner Tn is retained in the toner transport path 61 so as to fill the toner transport path 61 (see
Also in the present exemplary embodiment, the released toner is attached to the peripheral surface of the feeding roller 42 by an attaching mechanism 90, and the feeding roller 42 captures and re-transports the old toner Tc, which is not the new toner Tn. In this state, when the old toner Tc captured by the feeding roller 42 reaches the region in which the feeding roller 42 faces the developing-chamber-side opening 66 of the toner transport path 61, similar to the first exemplary embodiment, the peripheral surface of the feeding roller 42 is pressed by the weight of the new toner Tn retained in the toner transport path 61. Therefore, the interface of the new toner Tn retained in the toner transport path 61 serves as a type of a wall, and the old toner Tc captured by the feeding roller 42 is prevented from being mixed with the new toner Tn in the toner transport path 61 and is transported along the peripheral surface of the feeding roller 42. When a sufficient amount of old toner Tc is captured on the peripheral surface of the feeding roller 42, the new toner Tn is not supplied from the toner transport path 61. When the amount of old toner Tc captured on the peripheral surface of the feeding roller 42 is insufficient, the new toner Tn retained in the toner transport path 61 is supplied to the peripheral surface of the feeding roller 42 in regions where the old toner Tc is not captured.
In the present exemplary embodiment, as illustrated in
Therefore, in this example, the amount of old toner Tc that has been attached to the feeding roller 42 by the attaching mechanism 90 and re-transported is regulated by the regulating surface 70 of the upstream partition member 53b. The regulated amount of old toner Tc is moved along the developing-chamber-side opening 66 of the toner transport path 61 by the rotation of the feeding roller 42, and the amount of toner that passes the regulating surface 70 of the downstream partition member 53a is regulated by the regulating surface 70 of the downstream partition member 53a. Even when excessive new toner Tn tries to follow the peripheral surface of the feeding roller 42 in the region where the feeding roller 42 faces the developing-chamber-side opening 66, the excess toner is removed by the regulating surface 70.
As described above, in the present exemplary embodiment, the toner containing space in the developing chamber 51 is limited by the partition members 53a and 53b. When the toner containing space is limited substantially in correspondence with the amount of toner that may be transported by the feeding roller 42, there will be no space for toner that has received stress to scatter or collect in the developing chamber 51. The new toner Tn is not supplied as long as a sufficient amount of old toner Tc is captured on the peripheral surface of the feeding roller 42. Therefore, the old toner Tc and the new toner Tn are prevented from being unnecessarily mixed at the periphery of the feeding roller 42. As a result, broadening of the charge distribution obtained by the charging blade 45 due to unnecessary mixing of the new toner and the old toner may be avoided.
Referring to
In the present exemplary embodiment, the developing container 40 includes a developing chamber 51 and a containing chamber 52 that contains new toner. Unlike the fifth exemplary embodiment, the new toner is supplied in a substantially vertical direction.
The toner supplying mechanism 60 includes a toner transport path 61 that connects the containing chamber 52 to the developing chamber 51, and an agitator 62 is disposed in the containing chamber 52.
In this example, the toner transport path 61 includes a first passage 617 that extends obliquely downward from a containing-chamber-side opening 65 and a second passage 618 that is bent from the first passage 617 and extends substantially vertically downward. A transport member 620, which includes a rotating shaft and helical blade members provided on the periphery of the rotating shaft in this example, is provided at a bent portion between the first passage 617 and the second passage 618. The transport member 620 transports the new toner that has been transported through the first passage 617 toward the second passage 618. A stirring agitator 621 is disposed at an intermediate position of the second passage 618, and a developing-chamber-side opening 66 is formed at the bottom of the second passage 618.
The toner transport path 61 is defined by passage-forming portions 40d and 40e, which are portions of peripheral walls of the developing container 40, and a passage-forming member 622 disposed in the developing container 40.
In this example, the passage-forming member 622 is arranged so as to face the passage-forming portion 40d and form the developing-chamber-side opening 66 between the passage-forming member 622 and the passage-forming portion 40d. In this example, the developing-chamber-side opening 66 is formed so as to face the feeding roller 42 at a location upstream of the top portion of the feeding roller 42 in a rotation direction of the feeding roller 42. The width of the developing-chamber-side opening 66 along the rotation direction of the feeding roller 42 is smaller than the outer diameter of the feeding roller 42 in a plane of projection in a direction from the feeding roller 42.
A facing wall 623 that faces the peripheral surface of the feeding roller 42 is formed integrally with the passage-forming member 622 in a region downstream of the developing-chamber-side opening 66 in the rotation direction of the feeding roller 42. The facing wall 623 has a curved regulating surface 70 that faces the feeding roller 42 and extends along the peripheral surface of the feeding roller 42 with a gap g therebetween.
In this example, a portion of a peripheral wall of the developing container 40 that faces the peripheral surface of the feeding roller 42 in a region upstream of the developing-chamber-side opening 66 in the rotation direction of the feeding roller 42 serves as a facing wall 40f. The facing wall 40f has a curved regulating surface 70 that faces the feeding roller 42 and extends along the peripheral surface of the feeding roller 42 with a gap g therebetween.
The gap g is not particularly limited as long as the toner layer to be formed on the feeding roller 42 may be regulated, and is in the range of 0.5 mm to 1.0 mm in this example. The meanings of the lower and upper limits are similar to those in the first exemplary embodiment.
In the toner supplying mechanism 60 according to the present exemplary embodiment, the agitator 62 transports the new toner in the containing chamber 52 to the toner transport path 61, and the transport member 620 transports the new toner that has been transported through the first passage 617 of the toner transport path 61 to the second passage 618. The stirring agitator 621 transports the new toner that has been transported to the second passage 618 toward the developing-chamber-side opening 66. Also in this example, the new toner is retained in the toner transport path 61 so as to fill the toner transport path 61.
In the present exemplary embodiment, similar to the fifth exemplary embodiment, the peripheral surface of the feeding roller 42 is pressed by the weight of the new toner retained in the toner transport path 61. Therefore, the interface of the new toner retained in the toner transport path 61 serves as a type of a wall, and the old toner captured by the feeding roller 42 is prevented from being mixed with the new toner in the toner transport path 61 and is transported along the peripheral surface of the feeding roller 42. When a sufficient amount of old toner is captured on the peripheral surface of the feeding roller 42, the new toner is not supplied from the toner transport path 61. When the amount of old toner captured on the peripheral surface of the feeding roller 42 is insufficient, the new toner retained in the toner transport path 61 is supplied to the peripheral surface of the feeding roller 42 in regions where the old toner is not captured.
In the present exemplary embodiment, the facing wall 623 of the passage-forming member 622 and the facing wall 40f that is a portion of the peripheral wall of the developing container 40 are provided on both sides of the developing-chamber-side opening 66 of the toner transport path 61, and are provided with the respective regulating surfaces 70 that regulate the amount of toner captured by the feeding roller 42. Therefore, only a part of the toner captured by the feeding roller 42 that is within a range determined by each regulating surface 70 is transported, and excess toner is removed by each regulating surface 70.
Therefore, in this example, the amount of old toner that has been attached to the feeding roller 42 by an attaching mechanism 90 and re-transported is regulated by the regulating surface 70 of the facing wall 40f that is a portion of the peripheral wall of the developing container 40. The regulated amount of old toner is moved along the developing-chamber-side opening 66 of the toner transport path 61 by the rotation of the feeding roller 42, and the amount of toner that passes the regulating surface 70 of the passage-forming member 622 is regulated by the regulating surface 70 of the passage-forming member 622. Even when excessive new toner tries to follow the peripheral surface of the feeding roller 42 in the region where the feeding roller 42 faces the developing-chamber-side opening 66, the excess toner is removed by the regulating surface 70.
Therefore, also in the present exemplary embodiment, similar to the fifth exemplary embodiment, the toner containing space in the developing chamber 51 is limited by the facing walls 40f and 623. When the toner containing space is limited substantially in correspondence with the amount of toner that may be transported by the feeding roller 42, there will be no space for toner that has received stress to scatter or collect in the developing chamber 51.
Referring to
Referring to
In this example, the developing-chamber-side opening 66 is arranged so as to face a portion of the feeding roller 42 above the center of the feeding roller 42 in a region from a location near the top portion of the feeding roller 42 to a location upstream of the top portion in a rotation direction of the feeding roller 42. The width of the developing-chamber-side opening 66 along the rotation direction of the feeding roller 42 is smaller than the outer diameter of the feeding roller 42 in a plane of projection in a direction from the feeding roller 42.
The toner transport path 61 is defined by a pair of partition members 531 and 532 which are disposed in the developing container 40. One partition member 531 has a curved regulating surface 70 that faces the feeding roller 42 and extends along the peripheral surface of the feeding roller 42 with a gap g therebetween. The gap g is not particularly limited as long as the toner layer to be formed on the feeding roller 42 may be regulated, and is in the range of 0.5 mm to 1.0 mm in this example. The meanings of the lower and upper limits are similar to those in the first exemplary embodiment.
In the present exemplary embodiment, first and second sealing members 171 and 172, which are made of elastic materials, are provided on the edges of the developing-chamber-side opening 66 of the toner transport path 61 along an axial direction of the feeding roller 42. The sealing members 171 and 172 are in elastic contact with the peripheral surface of the feeding roller 42. In this example, the first sealing member 171, which is on the upstream side in the rotation direction of the feeding roller 42, is a block of elastic rubber or the like that is pressed against the feeding roller 42. The second sealing member 172, which is on the downstream side in the rotation direction of the feeding roller 42, is made of, for example, an elastic sheet. The second sealing member 172 has an end fixed to the partition member 532 and a free end pressed against the feeding roller 42 along the movement direction. The contact forces applied to the sealing members 171 and 172 need to be set so that the toner to be captured by the feeding roller 42 is prevented from being scraped off.
To evaluate the performance of the developing device according to the present exemplary embodiment, a developing device of comparative exemplary embodiment 7-1 (see
In a developing device 24′ according to comparative exemplary embodiment 7-1, when the new toner is supplied through the toner transport path 61 of the toner supplying mechanism 60, there is a risk that the new toner will be directly supplied from the developing-chamber-side opening 66 to a contact region N between the developing roller 41 and the feeding roller 42 and a contact region J between the developing roller 41 and the charging blade 45, as illustrated in
The contact regions N and J are regions in which toner exchange occurs and the toner fluidity is high. Therefore, according to comparative exemplary embodiment 7-1, mixing of the new toner and old toner is accelerated and a fogging phenomenon due to mixing of the new toner and old toner that have different electrification characteristics easily occurs.
Although the gap g is provided between the partition member 531 and the feeding roller 42, when the new toner is supplied in the direction of gravity, the new toner easily enters the gap g. Accordingly, the new toner is easily mixed with the old toner captured by the feeding roller 42.
In contrast, according to the present exemplary embodiment, the gap g between the partition member 531 and the feeding roller 42 is covered by the sealing member 171. Therefore, even when the new toner is supplied in the direction of gravity, the new toner is prevented from directly entering the gap g.
The sealing member 172 covers the gap between the feeding roller 42 and the partition member 532 located downstream of the developing-chamber-side opening 66 in the rotation direction of the feeding roller 42. Therefore, the new toner is prevented from being directly supplied from the developing-chamber-side opening 66 to the contact region N between the developing roller 41 and the feeding roller 42 and the contact region J between the developing roller 41 and the charging blade 45. Thus, the new toner and the old toner are prevented from being unnecessarily mixed.
A developing device according to Example 1 is obtained by simplifying the structure of the toner supplying mechanism 60 (which includes the toner transport path 61 that retains new toner) in the developing device 24 according to the first exemplary embodiment.
More specifically, referring to
The manner in which new toner and old toner are captured on the peripheral surface of the feeding roller 42 in the developing device of Example 1 is evaluated while changing an amount of deformation of the elastic sheet 92 into the feeding roller 42.
Conditions of components of Example 1 are as follows.
Developing roller: φ12-mm roller which includes a φ5-mm shaft (shaft portion) and a silicone rubber layer provided around the shaft and which has a surface roughness Ra of 1.2 μm.
Feeding Roller: φ11-mm roller which includes a φ5-mm shaft and a urethane foam sponge rubber layer provided around the shaft and which has an average cell diameter of 300 μm and an Asker C hardness of 20.
Applied Voltages (Developing Voltage and Feeding Voltage): DC-160V for each of the developing roller and the feeding roller.
Charging Blade: Stainless steel blade having a thickness of 0.08 mm and a linear load of 40 mN/mm (≈4 gf/mm).
Elastic Sheet: Thermoplastic polyurethane sheet having a thickness of 180 μm.
Toner: Negatively-charged toner having an average particle diameter of 6.5 μm formed by emulsion polymerization.
Toners of two colors are successively used and variation in color mixture ratio caused by variation in the amount of deformation of the elastic sheet is evaluated. The color mixture ratio is determined as follows. That is, first, the developing chamber of the developing container is filled with magenta (M) toner and an idle operation is performed until a steady state is established. Then, the containing chamber is filled with cyan (C) toner. Assuming that the cyan toner does not mix into the magenta toner unless the magenta toner in the developing chamber is consumed, 20 sheets of paper are continuously subjected to a blank printing operation, and an average mixture ratio of 18th to 20th sheets is calculated. A color phase based on the L*a*b* color system or the Munsell color system is measured for each output image. The color phase obtained when the color mixture ratio of magenta and cyan is varied is measured in advance, so that the relationship between the color mixture ratio of magenta and cyan and the color phase is determined. The color mixture ratio is determined from the color phase of each of the actually output images. Values of brightness and color saturation may, of course, also be taken into consideration in addition to the color phase.
The relationship between the amount of deformation of the elastic sheet and the color mixture ratio is obtained by repeating the above-described measurement while varying the amount of deformation.
Referring to
When the amount of deformation of the elastic sheet into the feeding roller is increased, the elastic sheet of the attaching mechanism attaches a sufficient amount of magenta toner, which corresponds to the old toner, to the feeding roller and appropriately levels the magenta toner. In this case, the amount of cyan toner, which corresponds to the new toner, supplied to the surface of the feeding roller in the new-toner supply region is smaller than that in the case where the amount of deformation of the elastic sheet is small. As a result, the amount of cyan toner, which corresponds to the new toner, used to form the output image is reduced, and the color mixture ratio is reduced accordingly. The point shown by β in
It is clear from the above-described result that the old-toner attaching operation may be effectively performed by the attaching mechanism when the amount of deformation of the elastic sheet into the feeding roller is greater than or equal to a certain value. In this case, the old toner may be preferentially consumed and the amount of supply of the new toner may be reduced. As a result, excessive consumption of the new toner is suppressed.
A developing device according to Example 2 is similar to the developing device according to Example 1 illustrated in
Conditions of components of Example 2 are as follows.
Developing roller: φ12-mm roller which includes a φ5-mm shaft (shaft portion) and a silicone rubber layer provided around the shaft and which has a surface roughness Ra of 1.2 μm.
Feeding Roller: φ11-mm roller which includes a φ5-mm shaft and a urethane foam sponge rubber layer provided around the shaft and which has an average cell diameter of 300 μm and an Asker C hardness of 20.
Applied Voltages (Developing Voltage and Feeding Voltage): DC-160V for each of the developing roller and the feeding roller.
Charging Blade: Stainless steel blade having a thickness of 0.08 mm and a linear load of 40 mN/mm (≈4 gf/mm).
Elastic Sheet: Polyimide sheet having a thickness of 200 μm and a volume resistivity of 1.6×106 Ω·cm.
Amount of deformation of Elastic Sheet into Feeding Roller: 1 mm.
Bias Voltage Applied to Elastic Sheet: Voltage with the positive side at the feeding roller.
Toner: Negatively-charged toner having an average particle diameter of 6.5 μm formed by emulsion polymerization.
Similar to Example 1, toners of two colors are successively used and variation in the color mixture ratio caused by variation in the potential difference between the elastic sheet and the feeding roller is evaluated.
Referring to the measurement result shown in
When the potential difference is applied between the elastic sheet and the feeding roller such that the feeding roller is at the positive side, the magenta toner, which corresponds to the old toner, on the elastic sheet receives a force that electrostatically attracts the magenta toner to the feeding roller. Accordingly, the magenta toner on the elastic sheet may be easily attached to the feeding roller. In addition, the elastic sheet levels the magenta toner, so that the amount of cyan toner, which corresponds to the new toner, supplied in the new-toner supply region is reduced and the color mixture ratio is reduced accordingly. The color mixture ratio is also small when the potential difference is zero (point shown by γ in
In Example 2, toner aggregation occurs when the potential difference between the elastic sheet and the feeding roller is excessively increased (for example, to 600 V or more). This is because electric discharge occurs between the elastic sheet and the feeding roller when the potential difference is too large. When a potential difference is provided between the elastic sheet and the feeding roller, it is necessary to prevent an excessive potential difference from being applied between the elastic sheet and the feeding roller in consideration of a resistance between the elastic sheet and the feeding roller and the amount of deformation of the elastic sheet into the feeding roller.
The influence of the potential difference is further evaluated by the present inventors by using elastic sheets having different volume resistivities. As a result, the potential difference may be set to about 300 V (point shown by δ in
The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-259178 | Nov 2012 | JP | national |
