Patent Description:
Conventionally, in a developing device installed in an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction peripheral thereof, there has been known a developing device using a toner concentration sensor such as a magnetic sensor in order to detect the toner concentration of a two-component developer stored in the developing device (a ratio of a toner in a developer including the toner and a carrier) (see, for example, <CIT>).

There has been widely known a developing device in which a toner concentration sensor is held in a developing case.

In the conventional developing device, every time the toner concentration sensor is installed in the developing case during producing or maintenance or the like, the position of the toner concentration sensor with respect to the developing case is shifted from a target position.

Therefore, the toner concentration detected by the toner concentration sensor and the control of toner supply performed based on the detection result vary.

<CIT> discloses a developing device and image forming apparatus wherein a toner concentration detection unit is positioned and fixed by being penetrated by a projection formed on the housing.

The present disclosure has been made to solve the above-described problems, and an object of the present disclosure is to provide a developing device, a process cartridge, and an image forming apparatus in which the position of a toner concentration sensor with respect to a developing case is accurately determined at a target position.

A developing device according to the invention is defined in the appended claims.

According to another embodiment of the present disclosure, a process cartridge includes the developing device and the image bearer integrated with the developing device as a single unit. The process cartridge is installable to and detachable from a main body of an image forming apparatus.

According to still another embodiment of the present disclosure, an image forming apparatus includes the developing device and the image bearer.

According to the present disclosure, a developing device, a process cartridge, and an image forming apparatus can be provided in which the position of a toner concentration sensor with respect to a developing case is accurately determined at a target position.

With reference to drawings, embodiments of the present disclosure are described in detail below. Note that identical reference numerals are assigned to identical components or equivalents and a redundant description of those components is appropriately simplified or omitted.

First, with reference to <FIG>, the overall configuration and operation of an image forming apparatus <NUM> are described.

<FIG> illustrates a tandem color copying machine as the image forming apparatus <NUM>, a document conveying unit <NUM> that conveys a document to a document scanner, a document scanner <NUM> that scans image data of a document, and a sheet ejection tray <NUM> on which an output image is stacked.

<FIG> also illustrates a sheet feeding unit <NUM> that stores a sheet P such as a form, a registration roller <NUM> that adjusts the conveyance timing of the sheet P, and photoconductor drums 11Y, <NUM>, 11C, and 11BK as image bearers on which toner images of respective colors (Yellow, Magenta, Cyan, and Black) are formed.

Furthermore, <FIG> illustrates a developing device <NUM> that develops electrostatic latent images formed on the surfaces of the photoconductor drums 11Y, <NUM>, 11C, and 11BK, and a primary transfer bias roller <NUM> that transfers toner images formed on the photoconductor drums 11Y, <NUM>, 11C, and 11BK on the sheet P in an overlapping manner.

In addition, <FIG> illustrates an intermediate transfer belt <NUM> to which toner images of multiple colors are transferred in an overlapping manner, a secondary transfer bias roller <NUM> for transferring the multicolor toner images on the intermediate transfer belt <NUM> onto the sheet P, a fixing device <NUM> for fixing an unfixed image on the sheet P, and a toner container <NUM> of each color for supplying a toner (toner particles) of each color (Yellow, Cyan, Magenta, Black) to the developing device <NUM>.

A description is provided below of the operation of the image forming apparatus when forming a normal color image.

An image forming process performed on the surfaces of the photoconductor drums 11Y, <NUM>, 11C, and 11BK can also be described with reference to <FIG>.

First, a conveyance roller of the document conveying unit <NUM> conveys a document on a document table onto an exposure glass of the document scanner <NUM>. The document scanner <NUM> optically scans image data from the document on the exposure glass.

More specifically, the document scanner <NUM> scans an image of the document on the exposure glass with light emitted from an illumination lamp. The light reflected from the surface of the document is directed onto a color sensor via mirrors and lenses to form multicolor image data. The multicolor image data for the document, which is decomposed into red, green, and blue (RGB) data, is read by the color sensor and converted into electrical image signals. Furthermore, an image processor performs image processing (e.g., color conversion, color calibration, and spatial frequency adjustment) according to the image signals of the decomposed RGB data, and thus image data for yellow, magenta, cyan, and black toner images are obtained.

The image data for yellow, magenta, cyan, and black toner images are transmitted to a writing unit. The writing unit directs a laser beam L (see <FIG>) onto the surface of the corresponding one of the photoconductor drums 11Y, <NUM>, 11C, and 11BK according to the image data for each color.

Meanwhile, each of the four photoconductor drums 11Y, <NUM>, 11C, and 11BK rotates clockwise in <FIG>. Initially, the surface of each of the photoconductor drums 11Y, <NUM>, 11C, and 11BK is uniformly charged by a charging unit <NUM> (see <FIG>) at a position facing the charging unit <NUM> (charging process). Thus, a charging potential is formed on each of the photoconductor drums 11Y, <NUM>, 11C, and 11BK. Thereafter, the charged surface of each of the photoconductor drums 11Y, <NUM>, 11C, and 11BK reaches a position where the surface is irradiated with the laser beam L.

The writing unit emits the laser beam L from each of four light sources according to the image signals so as to correspond to each color. The respective laser beams L pass through different optical paths for the different components of yellow, magenta, cyan, and black (exposure process).

The laser beam corresponding to the yellow component irradiates the surface of the first photoconductor drum 11Y from the left in <FIG>. A polygon mirror that rotates at high velocity deflects the laser beam for yellow along the axis of rotation of the photoconductor drum <NUM> (i.e., the main-scanning direction) so that the laser beam L scans the surface of the photoconductor drum 11Y. Thus, an electrostatic latent image corresponding to the image data of yellow is formed on the photoconductor drum 11Y charged by the charging unit <NUM>.

Similarly, the laser beam corresponding to the magenta component irradiates the surface of the second photoconductor drum <NUM> from the left in <FIG>, forming an electrostatic latent image corresponding to the magenta component. The laser beam corresponding to the cyan component irradiates the surface of the third photoconductor drum 11C from the left in <FIG>, forming an electrostatic latent image corresponding to the cyan component. The laser beam corresponding to the black component irradiates the surface of the fourth photoconductor drum 11BK from the left in <FIG>, forming an electrostatic latent image corresponding to the black component.

Then, the surface of each of the photoconductor drums 11Y, <NUM>, 11C, and 11BK having the electrostatic latent image reaches a position facing the developing device <NUM>. Then, toners of the respective colors are supplied from the developing device <NUM> onto the photoconductor drums 11Y, <NUM>, 11C, and 11BK, and latent images on the photoconductor drums 11Y, <NUM>, 11C, and 11BK are developed (developing process).

After the developing process, the surfaces of the photoconductor drums 11Y, <NUM>, 11C, and 11BK reach positions facing the intermediate transfer belt <NUM>. Here, a primary transfer bias roller <NUM> is installed on each facing portion so as to abut against the inner peripheral surface of the intermediate transfer belt <NUM>. At the position of the primary transfer bias roller <NUM>, the toner images of the respective colors formed on the photoconductor drums 11Y, <NUM>, 11C, and 11BK are sequentially transferred onto the intermediate transfer belt <NUM> in an overlapping manner (primary transfer process).

After the primary transfer process, the surface of each of the photoconductor drums 11Y, <NUM>, 11C, and 11BK reaches a position facing a cleaning unit <NUM>. An untransferred toner remaining on each of the photoconductor drums 11Y, <NUM>, 11C, and 11BK is collected by the cleaning unit <NUM> (cleaning process).

Thereafter, the surface of each of the photoconductor drums 11Y, <NUM>, 11C, and 11BK passes through a discharger to complete a series of image forming processes performed on the photoconductor drums 11Y, <NUM>, 11C, and 11BK.

Meanwhile, the intermediate transfer belt <NUM> on which the toners of the respective colors on the photoconductor drums 11Y, <NUM>, 11C, and 11BK are transferred (carried) in an overlapping manner travels counterclockwise in <FIG> to reach a position facing the secondary transfer bias roller <NUM>. The multicolor toner image carried on the intermediate transfer belt <NUM> is transferred onto the sheet P at a position facing the secondary transfer bias roller <NUM> (secondary transfer process).

After the secondary transfer process, the surface of the intermediate transfer belt <NUM> reaches the position of an intermediate transfer belt cleaning unit. The intermediate transfer belt cleaning unit collects an untransferred toner adhering to the intermediate transfer belt <NUM> to complete a sequence of transfer processes performed on the intermediate transfer belt <NUM>.

Here, the sheet P conveyed between the intermediate transfer belt <NUM> and the secondary transfer bias roller <NUM> (to a secondary transfer nip) is conveyed from the sheet feeding unit <NUM> via the registration roller <NUM> and the like.

More specifically, a sheet feeding roller <NUM> feeds the sheet P from the sheet feeding unit <NUM> that contains multiple sheets P, and the sheet P is then guided by a sheet guide to the registration roller <NUM>. The sheet P that has reached the registration roller <NUM> is conveyed toward the secondary transfer nip, timed to coincide with the arrival of the multicolor toner image on the intermediate transfer belt <NUM>.

Then, the sheet P carrying the multicolor toner image is conveyed to the fixing device <NUM>. The fixing device <NUM> includes a fixing roller and a pressure roller pressing against each other. In a nip between the fixing roller and the pressure roller, the multicolor toner image is fixed on the sheet P.

After the fixing process, a sheet ejection roller ejects the sheet P as an output image outside the image forming apparatus <NUM>, and the ejected sheet P is stacked on the sheet ejection tray <NUM>. Thus, a series of the image forming processes is completed.

Next, a process cartridge <NUM> (image forming unit) in the image forming apparatus is described in detail with reference to <FIG> and the like.

<FIG> is a configuration diagram illustrating the process cartridge <NUM> (image forming unit), and is a diagram viewed in a cross section orthogonal to the rotation axis of the photoconductor drum <NUM>. <FIG> is a schematic cross-sectional view (vertical cross-sectional view) of the developing device <NUM> as viewed in the longitudinal direction.

Note that the alphabets of reference numerals (Y, M, C, and BK) of the process cartridge and the developing device are omitted in <FIG> and the like for simplicity because the image forming units have a similar configuration.

As illustrated in <FIG>, the process cartridge is a unit in which the photoconductor drum <NUM> as the image bearer, the charging unit <NUM> (and a cleaning roller <NUM>), the developing device <NUM>, and the cleaning unit <NUM> are integrated, and is detachably installed with respect to a main body <NUM> of the image forming apparatus. When the process cartridge <NUM> reaches its end of life, the process cartridge <NUM> is detached from the main body <NUM> of the image forming apparatus, and replaced with a new one.

The photoconductor drum <NUM> as the image bearer is a negatively charged organic photoconductor, and is rotationally driven clockwise by a rotation drive mechanism.

The charging unit <NUM> is an elastic charging roller and can be formed by coating a cored bar with an elastic layer of moderate resistivity, such as foamed urethane, that includes carbon black as conductive particles, a sulfuration agent, a foaming agent, and the like. The material of the elastic layer of moderate resistivity of the charging unit <NUM> includes, but is not limited to, rubber such as urethane, ethylene-propylene-diene-polyethylene (EPDM), acrylonitrile butadiene rubber (NBR), silicone rubber, and isoprene rubber to which a conductive material such as carbon black or metal oxide is added to adjust the resistivity. Alternatively, foamed rubber including these materials may be used.

The cleaning roller <NUM> is disposed so as to abut on the charging unit <NUM> (charging roller), and cleans foreign matter adhering to the surface of the charging unit <NUM>.

The cleaning unit <NUM> includes a cleaning blade that slidingly contacts the surface of the photoconductor drum <NUM> and mechanically removes an untransferred toner on the photoconductor drum <NUM>.

The developing device <NUM> (developing unit) is disposed such that a developing roller 13a as a developer bearer faces the photoconductor drum <NUM> with a slight gap therebetween via an opening (formed in a developing case <NUM>), and a developing region where the photoconductor drum <NUM> and a magnetic brush (a developer G standing on end) are in contact is formed in a portion where the developing roller 13a faces the photoconductor drum <NUM>. The developing device <NUM> contains a developer G (two-component developer) including a toner T and a carrier C. The developing device <NUM> develops the electrostatic latent image formed on the surface of the photoconductor drum <NUM> (forms a toner image). The configuration and operation of the developing device <NUM> are described in further detail later.

With reference to <FIG>, the toner containers <NUM> contain the toner T to be supplied to the developing devices <NUM>.

Specifically, the toner T is appropriately supplied from a supply port 13d (see <FIG>) from the toner container <NUM> into the developing device <NUM> through a toner conveying pipe on the basis of the data of a toner concentration (the ratio of the toner in the developer G) detected by a toner concentration sensor <NUM> (see <FIG>) such as a magnetic sensor installed in the developing device <NUM>.

Next, the developing device <NUM> of the image forming apparatus is described in further detail below.

With reference to <FIG>, the developing device <NUM> includes the developing roller 13a as the developer bearer, a supply screw 13b1 as a first conveying member, a conveying screw 13b2 as a second conveying member, a doctor blade 13c as a developer regulating member, a partition member 13e as a wall portion, a developing case <NUM> covering the developing device <NUM>, and the toner concentration sensor <NUM> and the like. The members such as the developing roller 13a, the supply screw 13b1, the conveying screw 13b2, the doctor blade 13c, and the partition member 13e are included in the developing case <NUM> (housing). The developing case <NUM> can also be said to be a case member that forms at least a part of the conveying path (first and second conveyance paths B1 and B2) of the developer.

The developing roller 13a as the developer bearer is configured such that a sleeve 13a2 formed by forming a nonmagnetic material such as aluminum, brass, stainless steel, or conductive resin into a cylindrical shape is rotated in an arrow direction illustrated in <FIG> together with the supply screw 13b1 and the conveying screw 13b2 by a rotation drive mechanism. With reference to <FIG>, a magnet 13a1 forming multiple magnetic poles on the peripheral surface of the sleeve 13a2 is fixed in the sleeve 13a2 of the developing roller 13a. The developer G carried on the developing roller 13a is conveyed along with the rotation of the developing roller 13a in a predetermined rotation direction (counterclockwise direction in <FIG>), and reaches the position of the doctor blade 13c (developer regulating member). The amount of the developer G on the developing roller 13a is adjusted to a suitable amount by the doctor blade 13c, after which the developer G is conveyed to a position facing the photoconductor drum <NUM> (the developing region). Then, the toner is attracted to the latent image formed on the photoconductor drum <NUM> due to the effect of an electric field (electric field for development) generated in the developing region.

With reference to <FIG> and the like, the doctor blade 13c as the developer regulating member is a plate-like member disposed so as to face the upper side of the developing roller 13a. Then, the developing roller 13a rotates clockwise in <FIG>, and the photoconductor drum <NUM> rotates clockwise in <FIG>.

In the present embodiment, a counter developing method is used in which the developing roller 13a rotates counter with respect to the rotation direction of the photoconductor drum <NUM> in the developing region. Meanwhile, it is also possible to use a developing method in which the developing roller 13a rotates in a trading direction with respect to the rotation direction of the photoconductor drum <NUM> in the developing region.

The two conveying members (the supply screw 13b1 and the conveying screw 13b2) stir and mix the developer G stored in the developing device <NUM> while circulating the developer G in the longitudinal direction (is a direction perpendicular to the surface of the paper of <FIG>, and is a left-right direction of <FIG>). Each of the supply screw 13b1 and the conveying screw 13b2 is a screw member in which a screw is spirally wound around a shaft portion.

The supply screw 13b1 as the first conveying member is disposed so as to face the lower side of the developing roller 13a. The supply screw 13b1 supplies the developer to the developing roller 13a while conveying the developer G from one end side in the longitudinal direction toward the other end side in the longitudinal direction, and collects the developer separated from the developing roller 13a.

Specifically, the supply screw 13b1 (first conveying member) is disposed below the developing roller 13a at a position facing the developing roller 13a. The developer G is conveyed horizontally in the longitudinal direction (rotation axis direction) (conveyance from right to left indicated by a dashed arrow in <FIG>). The developer G is supplied onto the developing roller 13a at the position of a scooping magnetic pole, and the developer G separated from the developing roller 13a and dropped at the position of a developer release magnetic pole is conveyed toward the downstream side in the axial direction. The supply screw 13b1 rotates clockwise in <FIG>.

The conveying screw 13b2 as the second conveying member is disposed so as to face the lower side of the supply screw 13b1 (first conveying member), and conveys the developer G from the other end side in the longitudinal direction toward one end side in the longitudinal direction to form a circulation path of the developer G together with the supply screw 13b1.

Specifically, the conveying screw 13b2 (second conveying member) is disposed obliquely below the supply screw 13b1 at a position facing the developing roller 13a via the supply screw 13b1. The developer G is conveyed horizontally in the longitudinal direction in the second conveyance path B2 (conveyance from left to right indicated by the dashed arrow in <FIG>). In the present embodiment, the rotation direction of the conveying screw 13b2 is set to be opposite to the rotation direction of the supply screw 13b1 (counterclockwise in <FIG>).

In the conveying screw 13b2, the developer is circulated from the axially downstream side of the first conveyance path B1 by the supply screw 13b1 through a second communication portion <NUM> (second relay portion). The conveying screw 13b2 conveys the developer G to the upstream side in the axial direction of the first conveyance path B1 by the supply screw 13b1 via a first communication portion 13f (first relay portion) (conveyance indicated by the dashed arrow in <FIG>).

Similarly to the developing roller 13a and the photoconductor drum <NUM>, the supply screw 13b1 and the conveyance screw 13b2 are disposed such that rotation axes thereof are substantially horizontal. In each of the supply screw 13b1 and the conveying screw 13b2, a screw portion (one thread is formed at a predetermined screw pitch) is spirally wound around a shaft portion. In order to stabilize the conveyance of the developer, the screw portion may have multiple threads, and in particular, the screw portion of the supply screw 13b1 may have multiple threads.

Note that the first conveyance path B1 by the supply screw 13b1 and the second conveyance path B2 by the conveyance screw 13b2 are isolated from each other by the partition member 13e (wall portion).

With reference to <FIG>, the upstream side of the first conveyance path B1 by the supply screw 13b1 and the downstream side of the second conveyance path B2 by the conveyance screw 13b2 communicate with each other via the first communication portion 13f. The developer G having reached the downstream side of the second conveyance path by the conveying screw 13b2 stays in the vicinity of the first communication portion 13f and rises. The developer G is conveyed (supplied) to the upstream side of the first conveyance path B1 by the supply screw 13b1 via the first communication portion 13f.

With reference to <FIG>, the downstream side of the first conveyance path B1 by the supply screw 13b1 and the upstream side of the second conveyance path B2 by the conveyance screw 13b2 communicate with each other via the second communication portion <NUM>. The developer G (the developer G that has not been supplied onto the developing roller 13a in the first conveyance path B1 and the developer G that has been separated from and dropped from the developing roller 13a at the position of a fourth magnetic pole) having reached the downstream side of the first conveyance path B1 by the supply screw 13b1 falls by its own weight at the second communication portion <NUM> and reaches the upstream side of the second conveyance path B2.

The toner concentration sensor <NUM> such as a magnetic sensor that detects the toner concentration of the developer G circulating in the developing device <NUM> is installed in the developing case <NUM> (a portion corresponding to the second conveyance path B2). Based on the data of the toner concentration detected by the toner concentration sensor <NUM>, a new toner T is supplied from the toner container <NUM> into the developing device <NUM> via the supply port 13d (disposed on the outer side in the longitudinal direction with respect to the second communication portion <NUM>) so that the toner concentration falls within a target range.

With reference to <FIG>, the supply port 13d (toner supply port) is disposed above the upstream side of the second conveyance path B2 by the conveying screw 13b2 at a position away from the developing region (outside the range in the longitudinal direction of the developing roller 13a). The new toner T discharged from the toner container <NUM> is appropriately supplied from the supply port 13d into the developing device <NUM> (supply in the direction of a white arrow in <FIG>). By disposing the supply port 13d in the vicinity of the second communication portion <NUM> in this manner, it is possible to sufficiently disperse and mix the supply toner over a relatively long time with respect to the developer G dropped by its own weight from the second communication portion <NUM> toward the downstream side in the second conveyance path B2.

In the present embodiment, the supply port 13d is disposed in the second conveyance path B2, but the position of the supply port 13d is not limited thereto, and for example, the first conveyance path B1 may be extended in the longitudinal direction and disposed above the downstream side.

As the developer G used in the present embodiment, a known developer can be used.

For example, as the toner T (the toner in the developer G, the toner in the toner container <NUM>), a small-diameter toner that is a polymerization toner and has a volume average particle diameter of about <NUM> can be used.

As the carrier C in the developer G, a small-diameter carrier formed to have a weight average particle diameter of <NUM> to <NUM> can be used.

Hereinafter, the characteristic configuration and operation of the developing device <NUM> according to the present embodiment are described.

As described above with reference to <FIG> and the like, the developing device <NUM> according to the present embodiment includes the developing case <NUM> that forms at least a part of the conveying path (first and second conveyance paths B1 and B2) of the developer, and the toner concentration sensor <NUM> that detects the toner concentration of the developer G stored in the developing device <NUM>.

In the present embodiment, a magnetic sensor that magnetically detects the toner concentration of the developer G is used as the toner concentration sensor <NUM>. The developing case <NUM> is made of a nonmagnetic resin material or the like.

Here, as illustrated in <FIG>, <FIG>, in the developing device <NUM> according to the present embodiment, a sensor holder 13r that holds the toner concentration sensor <NUM> is held by the developing case <NUM>.

The sensor holder 13r is a substantially rectangular parallelepiped box-shaped member formed of a nonmagnetic resin material or the like, and is detachably installed on the developing case <NUM> by fastening a screw <NUM> so as to cover the toner concentration sensor <NUM>.

In the sensor holder 13r, the toner concentration sensor <NUM> is fixed and held by fastening a screw or the like, and is attached to or detached from the developing device <NUM> together with the toner concentration sensor <NUM> during producing or maintenance or the like.

Furthermore, a connector to which the harness of the toner concentration sensor <NUM> is connected is exposed to the sensor holder 13r. When the sensor holder 13r is attached to and detached from the developing case <NUM>, the connector is connected to and detached from the case-side connector of the developing case <NUM>.

Furthermore, as illustrated in <FIG>, the developing device <NUM> includes a projection 13s1 as a positioning unit that engages with (fit into) a hole 13n1 as an engaging portion formed at the center of a sensor main section 13n (a sensing surface is formed, is responsible for the central function of the sensor, and is a portion directly affecting sensor accuracy) of the toner concentration sensor <NUM> to determine the position of the sensor main section 13n in the developing case <NUM>.

The projection 13s1 as the positioner is formed on an installation surface <NUM> of the developing case <NUM> so as to be fittable into the hole 13n1 (in the present embodiment, a through hole having a circular cross section) of the sensor main section 13n. In other words, in addition to the projection 13s1, the hole 13n1 of the sensor main section 13n functions as the positioner.

The installation surface <NUM> of the developing case <NUM> is a rectangular flat surface facing the toner concentration sensor <NUM> having a substantially rectangular outer shape, and the boss-shaped projection 13s1 protrudes in the vertical direction on the side away from the developing case <NUM>. As described above, in the present embodiment, the toner concentration sensor <NUM> (sensor main section 13n) detects the toner concentration of the developer G in the developing device <NUM> via the developing case <NUM> (installation surface <NUM>).

In the present embodiment, the sensor main section 13n is formed in a coil shape or an annular shape. That is, the sensor main section 13n is a substantially cylindrical member, and the hole 13n1 as the engaging portion is formed at the center of the sensor main section 13n.

As described above, in the developing device <NUM> according to the present embodiment, the projection 13s1 fitted into the hole 13n1 (engaging portion) at the center of the sensor main section 13n of the toner concentration sensor <NUM> is provided in the developing case <NUM> (installation surface <NUM>), whereby the position of the toner concentration sensor <NUM> (sensor main section 13n) with respect to the developing case <NUM> (installation surface <NUM>) is accurately determined at a target position. Therefore, every time the toner concentration sensor <NUM> is installed in the developing case <NUM> together with the sensor holder 13r during producing or maintenance or the like, a defect that the position of the toner concentration sensor <NUM> (sensor main section 13n) with respect to the developing case <NUM> deviates from a target position is reduced. Therefore, the toner concentration detected by the toner concentration sensor <NUM> and the control of toner supply performed based on the detection result are less likely to vary.

In particular, in the present embodiment, the toner concentration sensor <NUM> is fixed to the developing case <NUM> together with the sensor holder 13r in a state where the projection 13s1 of the developing case <NUM> is fitted into the hole 13n1 at the center of the sensor main section 13n. Therefore, even when the toner concentration sensor <NUM> (sensor holder 13r) is installed in the developing case <NUM> in a state of rotating around the projection 13s1, the sensor main section 13n is accurately positioned at a target position.

Since a direction in which the hole 13n1 and the projection 13s1 are fitted coincides with a direction in which the toner concentration sensor <NUM> (sensor holder 13r) is attached to and detached from the developing case <NUM>, the detachability thereof is also enhanced.

In the present embodiment, the hole 13n1 of the sensor main section 13n is a through hole, but the hole 13n1 may be a non-through hole (recessed hole).

Here, with reference to <FIG>, the developing device <NUM> according to the present embodiment includes first and second bosses 13k1 and 13k2 as a second positioner that determine the position of the sensor holder 13r in the longitudinal direction in the developing case <NUM>.

Specifically, the developing case <NUM> includes the two first bosses 13k1 (a female screw portion is formed at the central portion) so as to sandwich the installation surface <NUM>. Furthermore, the developing case <NUM> includes the second boss 13k2 so as to be adjacent to one first boss 13k1.

Meanwhile, the sensor holder 13r includes first through holes 13r1 (screw holes) at positions corresponding to the two first bosses 13k1, respectively. Furthermore, the sensor holder 13r includes a second through hole 13r2 (fitting hole) at a position corresponding to the second boss 13k2.

As illustrated in <FIG>, in a state where the projection 13s1 is fitted into the hole 13n1 and the second boss 13k2 is fitted into the second through hole 13r2, the screw <NUM> is screwed into the female screw portion of the first boss 13k1 through the first through hole 13r1, whereby the position of the sensor holder 13r in the longitudinal direction with respect to the developing case <NUM> is determined. In other words, the sensor holder 13r (toner concentration sensor <NUM>) is fixed and held on the developing case <NUM> so as not to rotate about the projection 13s1 (hole 13n1).

In the present embodiment, the fitting between the projection 13s1 and the hole 13n1 is main positioning, whereby the positioning between the first and second bosses 13k1 and 13k2 and the first and second through holes 13r1 and 13r2 described above is preferably performed in a sub-manner so as not to affect the fitting between the projection 13s1 and the hole 13n1. Specifically, it is preferable that the hole diameters of the first and second through holes 13r1 and 13r2 are relatively loose with respect to the female screw diameter and the boss diameter of the first and second bosses 13k1 and 13k2.

As illustrated in <FIG>, in a developing device <NUM> according to a first embodiment, a sensor holder 13r includes a protrusion 13r3 to fit into a hole 13n1 (engaging portion) of a sensor main section 13n from a side facing a projection 13s1 of a developing case <NUM> that fits in the hole 13n1.

Specifically, the protrusion 13r3 is a boss-shaped member having a circular cross section, and is formed so as to protrude in a direction perpendicular to the sensor main section 13n side on the inner wall surface of the sensor holder 13r. In a state where the protrusion 13r3 is inserted into the hole 13n1 of the sensor main section 13n, a toner concentration sensor <NUM> (sensor main section 13n) is positioned with respect to the sensor holder 13r.

With this configuration, the positional accuracy of the toner concentration sensor <NUM> (sensor main section 13n) with respect to the developing case <NUM> is enhanced in a state where the positional accuracy of the toner concentration sensor <NUM> (sensor main section 13n) with respect to the sensor holder 13r is enhanced. Therefore, the positional accuracy of the sensor holder 13r with respect to the developing case <NUM> can also be enhanced.

In the first embodiment, as illustrated in <FIG>, the projection 13s1 and the protrusion 13r3 fit in the hole 13n1 in non-contact with each other. That is, in the hole 13n1, a gap is provided between the leading end of the projection 13s1 and the leading end of the protrusion 13r3. With this configuration, the projection 13s1 and the protrusion 13r3 contact each other in the hole 13n1, to suppress a defect that the toner concentration sensor <NUM> and the sensor holder 13r are deformed.

Also in the first embodiment, the position of the toner concentration sensor <NUM> (sensor main section 13n) with respect to the developing case <NUM> is accurately determined at a target position.

As illustrated in <FIG>, also in a developing device <NUM> according to a second embodiment, similarly to the first embodiment, a sensor holder 13r includes a protrusion 13r3 fitted into a hole 13n1 (engaging portion).

Here, in the second embodiment, a projection 13s1 of a developing case <NUM> and the protrusion 13r3 of the sensor holder 13r are configured to be fitted into each other in the hole 13n1 of a sensor main section 13n.

Specifically, a shaft-shaped fitting portion 13s10 is formed at the end of the projection 13s1, and a recessed fitted portion 13r30 into which the fitting portion 13s10 is fitted is formed at the end of the protrusion 13r3.

With this configuration, the positional accuracy of the sensor holder 13r with respect to the developing case <NUM> can be directly enhanced.

Also in the second embodiment, the position of a toner concentration sensor <NUM> (sensor main section 13n) with respect to the developing case <NUM> is accurately determined at a target position.

As illustrated in <FIG>, in a developing device <NUM> according to a third embodiment, in a sensor holder 13r, an insertion portion 13r4 (through hole) into which the end of a projection 13s1 that is fitted into and penetrates a hole 13n1 (engaging portion) of a sensor main section 13n is inserted is formed.

Specifically, the projection 13s1 of a developing case <NUM> is formed to be sufficiently longer than the depth of the hole 13n1 (through hole), and the end thereof penetrates the insertion portion 13r4 of the sensor holder 13r and is exposed to the outside (a portion surrounded by a dashed line).

As illustrated in <FIG>, the insertion portion 13r4 of the sensor holder 13r may be formed as a non-through hole (recessed hole) so that the end of the projection 13s1 is not exposed to the outside.

With the configuration as illustrated in <FIG>, the positional accuracy of the sensor holder 13r with respect to the developing case <NUM> can be directly enhanced.

Also in the third embodiment, the position of a toner concentration sensor <NUM> (sensor main section 13n) with respect to the developing case <NUM> is accurately determined at a target position.

As illustrated in <FIG>, a developing device <NUM> according to a fourth embodimentis different from those of the above-described embodiments in the configuration of a positioner that determines the position of a toner concentration sensor <NUM> (sensor main section 13n) with respect to a developing case <NUM>.

As illustrated in <FIG>, the positioner in the fourth embodiment includes a shaft portion 13r5 (a boss-shaped member having a circular cross section) formed in a sensor holder 13r so as to be fittable into a hole 13n1 of the sensor main section 13n, and an insertion and fitting portion 13k5 (a non-through hole (recessed hole) having a circular cross section) formed in the developing case <NUM> so that the end of the shaft portion 13r5 that is fitted into and penetrates through the hole 13n1 can be inserted and fitted.

Even in such a configuration, the position of the toner concentration sensor <NUM> (sensor main section 13n) with respect to the developing case <NUM> is accurately determined at a target position. Furthermore, the positional accuracy of the sensor holder 13r with respect to the developing case <NUM> can be directly enhanced.

As described above, the developing device <NUM> according to the present embodiment is the developing device that stores the developer G including the toner T and the carrier C and develops the latent image formed on the surface of the photoconductor drum <NUM> (image bearer), and includes the developing case <NUM> that forms at least a part of the conveyance paths B1 and B2 of the developer G, and the toner concentration sensor <NUM> that detects the toner concentration of the developer G stored in the developing device <NUM>. Furthermore, a projection 13s1 (positioner) is provided, which is fitted into (engaged with) the hole 13n1 (engaging portion) formed at the center of the sensor main section 13n of the toner concentration sensor <NUM> to determine the position of the sensor main section 13n in the developing case <NUM>.

As a result, the position of the toner concentration sensor <NUM> (sensor main section 13n) with respect to the developing case <NUM> can be accurately determined at a target position.

In the present embodiment, the developing device <NUM> is one of the constituent members of the process cartridge <NUM>. However, a developing device according to an embodiment of the present disclosure is not limited to the configuration of the developing device <NUM>. For example, a developing device according to an embodiment of the present disclosure is configured as a unit to be alone attached to and detached from the main body of the image forming apparatus.

Here, in the present specification, the "process cartridge" is defined as a unit in which at least one of a charging unit (charging device) that charges an image bearer, a developing device (developing unit) that develops a latent image formed on the image bearer, and a cleaning unit (cleaning device) that cleans the image bearer and the image bearer are integrated and detachably installed with respect to a main body of an image forming apparatus.

In the present embodiment, the positioner (engaged portion) such as the projection 13s1 and the shaft portion 13r5 of the developing case <NUM> is fitted into (engaged with) the hole 13n1 as the engaging portion formed at the center of the sensor main section 13n of the toner concentration sensor <NUM>, but the relationship between the "engaging portion" and the" engaged portion" is not limited thereto, and for example, the "engaging portion" may be a recess (alternatively, a protrusion), and the "engaged portion" may be a protrusion (alternatively, a recess).

Even in such a case, it is possible to obtain substantially the same effects as those of the present embodiment.

Claim 1:
A developing device (<NUM>), comprising:
a developing case (<NUM>) to store a developer containing toner and carrier to develop a latent image on a surface of an image bearer, the developing case (<NUM>) including at least a part of a conveyance path of the developer;
a toner concentration sensor (<NUM>) to detect a toner concentration of the developer in the developing case (<NUM>); and
a positioner (13s1) to engage with an engaging portion (13n1) at a center of a sensor main section (13n) of the toner concentration sensor (<NUM>) to determine a position of the sensor main section in the developing case (<NUM>),
wherein the engaging portion (13n1) of the sensor main section is a hole, and the positioner (13s1) includes a projection (13s1) on the developing case (<NUM>) to fit into the hole,
characterized in that the developing device (<NUM>) further comprises a sensor holder (13r) holding the toner concentration sensor (<NUM>), the sensor holder (13r) held by the developing case (<NUM>),
wherein the sensor holder (13r) includes a protrusion (13r3) to fit into the hole from a side facing the projection (13s1) that fits in the hole.