JP4872977B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus and a developing device used therefor. More specifically, the present invention relates to a developing device and an image forming apparatus that use a two-component developer and can determine the toner concentration of the developer stored therein.

  Conventionally, some electrophotographic image forming apparatuses use a two-component developer. The two-component developer is a mixture of a carrier that is magnetic particles and a non-magnetic toner, and only the toner is consumed by the development process. Therefore, in order to keep the toner density of the developer within an appropriate range, the toner is appropriately replenished. Alternatively, a new carrier is added together with the toner, and the carrier in the apparatus is replaced little by little.

In order to keep the toner concentration of the developer contained in the developing device within an appropriate range, it is required to detect the toner concentration as accurately as possible. As a method for detecting the toner density of the developer, there is a method by measuring a resonance frequency using an LC resonance circuit. In particular, a toner concentration detection device using a planar coil as its inductance has been proposed (for example, see Patent Document 1). In the apparatus described in this document, the copper foil of the printed board is etched to form a spiral coil. In order to obtain as much inductance as possible in a limited plane of the printed circuit board, the coils are formed substantially uniformly from the center to the outer periphery within a square range.
Japanese Utility Model Publication No. 6-76961

  However, in the case of a coil shaped like the above-described conventional planar coil, the detection sensitivity is highest at the center of the coil, and has a mountain shape that descends outward. For this reason, the degree of the influence on the detection result due to the change in the amount of carriers in the detection area varies considerably depending on the location in the area. For this reason, there is a problem that the reliability of the detection result of the toner density is not so high. In particular, when a method of increasing or decreasing the total amount of the developer in the developing device according to the conditions is adopted as the developing device control method, this problem may become remarkable.

  Further, in the conventional planar coil, since the coil is formed up to the center, the positioning of the coil can be performed only at a place other than the coil. On the other hand, it is inevitable that the printed circuit board of the toner concentration detection device and the developer tank to which the printed circuit board is attached expand and contract slightly due to the influence of the operating environment and external force. In that case, since the expansion and contraction is performed with the positioning portion fixed, the position of the coil with respect to the developer tank may be slightly shifted. However, the positional relationship of the detection coil with respect to the developer tank to be detected for the toner density is very important, and there is a possibility that accurate detection cannot be performed even by a slight deviation. This positional relationship is particularly important in the case where a screw or the like is provided in the developer tank and the developer is stirred and conveyed in the axial direction thereof.

  The present invention has been made to solve the above-described problems of the prior art. That is, an object of the present invention is to provide a developing device and an image forming apparatus having a toner concentration detecting device capable of accurately detecting the toner concentration regardless of the amount of developer.

  In order to solve this problem, the developing device of the present invention is a developing device having a developer carrying member for carrying a developer and a developer containing tank for containing the developer, and has an LC oscillation circuit. And a toner concentration detecting device arranged at a position where the inductance of the coil constituting the LC oscillation circuit is influenced by the toner concentration of the developer in the developer storage tank, and the coil of the LC oscillation circuit is formed on a flat plate This is due to the wound printed pattern, and has a hollow area without the printed pattern at the center of the wound.

  The developing device of the present invention has a toner concentration detection device using an LC oscillation circuit. Since the coil of this LC oscillation circuit is based on a printed pattern having a hollow area in the center, the distribution of detection sensitivity is approximately flat in the center. Therefore, the influence on the detection result due to the change in the amount of the developer in the detection area is small. The hollow area here is an area without a print pattern and does not mean that there is nothing.

Furthermore, in the present invention, the first positioning shape is formed in the hollow region, the second positioning shape is formed in the developer storage tank, and the first positioning shape and the second positioning shape are fitted. Therefore, it is desirable that the toner concentration detection device is positioned in the developer storage tank.
If it is such, the hollow area | region of a coil will be positioned in the positioning location of a developer storage tank. Therefore, even if the flat plate on which the coil is formed and the developer storage tank expand and contract to some extent, the position of the coil with respect to the positioning position of the developer storage tank hardly changes.

Furthermore, in the present invention, a screw is disposed in the developer storage tank, and the axial length of the screw in the coil is not less than 1/2 and not more than 3/2 of the screw pitch of the screw. desirable.
In such a case, there is at least one developer peak due to the screw in the range of the coil, and there is no possibility that the coil becomes excessive.

  The present invention also relates to an image forming apparatus having an image carrier and a developing device for developing an electrostatic latent image formed on the image carrier, wherein the developing device carries a developer carrier. And a developer storage tank for storing the developer and an LC oscillation circuit, and the inductance of the coil constituting the LC oscillation circuit is arranged at a position affected by the toner concentration of the developer in the developer storage tank. The coil of the LC oscillation circuit is based on a wound print pattern formed on a flat plate, and the image forming apparatus has a hollow area without a print pattern at the center of the winding. It also extends.

  According to the developing device and the image forming apparatus of the present invention, the toner concentration detecting device capable of accurately detecting the toner concentration regardless of the amount of the developer is provided.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In the present embodiment, the present invention is applied to an image forming apparatus that forms an image using a two-component developer.

  The image forming apparatus 1 according to the present embodiment is a so-called tandem type image forming apparatus in which image forming units 10Y, 10M, 10C, and 10K of respective colors are arranged along the intermediate transfer belt 20, as shown in FIG. . Each image forming unit includes a photoreceptor 11, a charging unit 12, an exposure unit 13, a developing unit 14, a primary transfer unit 15, and a cleaner unit 16. Further, a paper feeding unit 21 is disposed at the lower part of each image forming unit in the figure. In addition, the image forming apparatus 1 of this embodiment further includes a secondary transfer unit 22, a belt cleaner unit 23, a fixing unit 24, a toner hopper 25 for each color, and the like.

  At the time of image formation by the image forming apparatus 1 of the present embodiment, toner images of each color are formed on the respective photoreceptors 11 in the image forming units 10Y, 10M, 10C, and 10K for each color. The toner images of the respective colors are transferred to the intermediate transfer belt 20 by the primary transfer unit 15 and superimposed. The superimposed toner images are transferred to the sheet fed from the sheet feeding unit 21 by the secondary transfer unit 22 and fixed to the sheet by the fixing unit 24.

  In this embodiment, the developing unit 14 is a detachable cartridge type. The developer housed in the developing unit 14 is a two-component developer including a carrier that is magnetic particles and a non-magnetic toner. Only the toner is consumed by image formation. Therefore, the toner density in the developer is controlled to be kept within an appropriate range by appropriately supplying toner from the toner hopper 25.

  As shown in FIGS. 2 and 3, the developing unit 14 of this embodiment includes a developing sleeve 41 and two conveying screws 42 and 43. These are arranged substantially parallel to each other inside the housing 45. The developer is accommodated in the housing 45, stirred by the conveying screws 42 and 43, and conveyed in the axial direction (the depth direction in the figure). A partition wall 46 is formed inside the housing 45. As a result, the inside of the developing unit 14 is divided into a first chamber 48 in which the conveying screw 42 is disposed and a second chamber 49 in which the conveying screw 43 is disposed.

  As shown in FIG. 2, the first chamber 48 is adjacent to the developing sleeve 41, but the second chamber 49 is not adjacent. In a state where the developing unit 14 is mounted on the image forming apparatus 1, the second chamber 49 is disposed below the first chamber 48 and the developing sleeve 41. For this reason, in the state where the conveying screws 42, 43, etc. are stopped, the developer in the developing unit 14 mainly accumulates in the lower portion of the second chamber 49. In addition, toner newly supplied from the toner hopper 25 is first supplied into the second chamber 49. The replenished toner is mixed with the developer already stored, and is supplied to the developing sleeve 41 by the conveying screws 42 and 43 through the second chamber 49 and the first chamber 48 in this order.

  As shown in FIG. 2, the toner concentration detector 51 is attached to the developing unit 14 of the present embodiment on the outer surface of the housing 45 in the lower part of the second chamber 49. This position is outside the location where the developer accumulates. The toner concentration detection unit 51 is positioned and fixed by penetrating a protrusion 52 formed in the housing 45.

  The toner concentration detector 51 of this embodiment is based on detecting a change in the resonance frequency of the LC resonance circuit. Therefore, for example, a resonance circuit such as a Colpitts oscillation circuit shown in FIG. 4 is provided. This resonance circuit has an inductance coil L, a transistor Q, a resistor R, two capacitors C1, C2, and the like.

  As shown in FIG. 5, the toner concentration detection unit 51 has a planar coil 54 formed on one surface of a rectangular printed board 53. The planar coil 54 corresponds to the inductance coil L in FIG. The planar coil 54 has a substantially rectangular outer shape and is formed by a print pattern. In the present embodiment, the toner concentration detection unit 51 is arranged so that the surface on which the planar coil 54 is formed is on the side (the upper side in FIG. 2) in contact with the housing 45 of the development unit 14.

  In this embodiment, as shown in FIG. 5, the planar coil 54 is not formed up to the central portion 54a, but is a substantially ring-shaped coil as a whole. The central portion 54a is a region where a coil by a printed pattern is not formed, and this corresponds to a hollow region. The hollow region here means that no coil is formed, and the printed circuit board 53 itself exists. In the present embodiment, the central portion 54a is not provided with a member such as a core. The planar coil 54 has an air core. Therefore, the sensitivity distribution is substantially flat inside the central portion 54a.

  On the other surface of the printed circuit board 53 (the back surface of the surface on which the planar coil 54 is formed), other components (transistor Q, resistor R, capacitors C1, C2) of the resonance circuit are mounted. As shown in FIG. 5, a connector 55 is attached to the other end of the printed circuit board 53 at the end in the longitudinal direction on the side where the planar coil 54 is not formed. Further, a positioning through hole 57 is formed in the central portion 54 a of the printed circuit board 53. Further, an elongated through hole 58 is formed outside the planar coil 54 and at a substantially central portion of the printed circuit board 53.

  Two positioning projections 52 (see FIG. 2) are formed on the outer surface of the housing 45 of the developing unit 14 so as to be fitted into the through holes 57 and 58. As a result, the toner concentration detection unit 51 is positioned in the housing 45. In particular, the positional relationship between the housing 45 and the planar coil 54 is correctly held by the through hole 57 and the projection 52 which are round holes. Therefore, for example, even if the environmental temperature changes, the position of the central portion 54a of the planar coil 54 with respect to the housing 45 does not change. Here, the projection is formed in the housing 45 and the through hole is formed in the toner concentration detection unit 51, but the reverse may be possible. Further, these protrusions and through holes correspond to a first positioning shape and a second positioning shape.

  The toner density detector 51 is arranged so that the longitudinal direction of the planar coil 54 is parallel to the longitudinal direction of the developing sleeve 41 and the conveying screws 42 and 43. In addition, the toner density detection unit 51 is disposed at the lowest position in the developing unit 14 when mounted on the image forming apparatus 1 so that the planar coil 54 is substantially horizontal. Alternatively, it may be arranged in the tangential direction of the outer surface of the housing 45.

  Next, the size of the planar coil 54 will be described. As shown in FIG. 6, the planar coil 54 has a substantially rectangular shape (A <B), and is arranged so that the long side B is parallel to the axial direction of the developing unit 14. Here, the detection target of the toner concentration detection unit 51 is the developer in the second chamber 49, and the conveying screw 43 is disposed in the second chamber 49. The amount of developer present above the planar coil 54 is periodically changed by the rotation of the conveying screw 43. As a result, the detection result by the toner density detector 51 also periodically varies.

  The fluctuation width of this periodic fluctuation differs depending on the relationship between the long side B of the planar coil 54 and the screw pitch P of the conveying screw 43 (see FIG. 3). It is also related to the inner diameter of the planar coil 54. In this embodiment, it is preferable to select B from a range larger than P / 2 and smaller than 3P / 2. If B is greater than P / 2, there is usually more than one developer pile on the coil. Moreover, if B is smaller than 3P / 2, the size of the planar coil 54 will not be excessive.

  In this embodiment, it is further preferable that the long side B of the planar coil 54 is set so that the fluctuation range is relatively small within this range. In this case, within the above-mentioned range, a plurality of toner density detecting parts 51 having different lengths of the long side B of the planar coil 54 are formed, and the toner density of the same developer is measured, respectively. Side B can be selected. For example, the toner density is detected using three types of toner density detectors 51 with P: B of 1: 0.5, 1: 0.7, and 1: 1.2. The result is shown in FIG. In the figure, S1 is a result of 1: 0.5, S2 is a result of 1: 0.7, and S3 is a result of 1: 1.2. The fluctuation range of the detection signal intensity was S2 <S1 <S3. In other words, in this example, there is a long side B having a minimum fluctuation width within a range larger than 0.5 × P and smaller than 1.2 × P.

  That is, in this embodiment, for each model, a plurality of types of planar coils 54 having different long sides B are created within a range of P / 2 <B <3P / 2, and toner density is detected by each. In this way, the long side B where the fluctuation range of the detection result of the toner concentration detection unit 51 becomes the smallest can be found by actual measurement. Even if it is larger than 3P / 2, there is a long side B that makes the fluctuation range small, but it is not preferable because the planar coil 54 becomes large and the toner density detection unit 51 becomes large.

  In the image forming apparatus 1 of the present embodiment, after the image formation is executed and the toner is consumed, the toner concentration detection unit 51 detects the toner concentration. When it is determined that the toner density is lower than a predetermined density, the toner is replenished to increase the toner density. Thereby, the toner density in the developing unit 14 can be maintained within an appropriate range.

  Further, according to the developing unit 14 of the present embodiment, since the hollow area where no coil is formed is provided in the central part 54a of the planar coil 54, the distribution of toner density detection sensitivity is flat within the range. . Therefore, an accurate toner density can be obtained regardless of the amount of developer. Therefore, even in an image forming apparatus that employs a control system that increases or decreases the amount of developer according to the total count of development, the toner density can be managed appropriately.

  Further, since the long side B is selected so as not to be affected by the periodic fluctuation of the developer amount by the conveying screw 43, the developer concentration can be detected while the conveying screw 43 is rotated. Further, the toner density detecting portion 51 is positioned in the housing 45 by a through hole 57 formed in the central portion 54 a of the planar coil 54. Therefore, even if an external force is applied to the toner concentration detection unit 51, the positional relationship between the toner layer and the planar coil 54 can be prevented from shifting. Further, since a positioning space is not required at a position different from that of the planar coil 54, the toner concentration detection unit 51 can be made small.

  As described in detail above, according to the image forming apparatus of the present embodiment, the toner concentration detection unit 51 is provided outside the second chamber 49, so that the developer toner accommodated in the second chamber 49 is provided. The concentration can be detected. In particular, since the positioning is performed at the central portion 54a of the planar coil 54 of the toner concentration detection unit 51, the position does not shift even when an external force is applied. The length of one side of the planar coil 54 is set in consideration of the screw pitch of the conveying screw 43 in the second chamber 49. Therefore, the toner density is not easily affected by the rotation of the conveying screw, and the toner density can be accurately detected regardless of the amount of the developer.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, the shape of the planar coil is not limited to a rectangle, and may be a rounded rectangle, a square, an octagon, an ellipse, a circle, or the like. In any case, it is sufficient that the coil is not formed up to the center. Further, for example, the present invention can be applied not only to a tandem image forming apparatus but also to a monochrome image forming apparatus or a FAX.

1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment. It is sectional drawing which shows a image development part. It is a perspective view which shows the image development part. It is a circuit diagram which shows the example of LC circuit. FIG. 6 is a plan view showing a toner concentration detection unit. FIG. 4 is an explanatory diagram showing a planar coil of a toner concentration detection unit. It is a graph which shows the example of the change of the signal fluctuation width by the long diameter of a planar coil.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Photoconductor 14 Developing part 41 Developing sleeve 45 Housing 51 Toner density detecting part 52 Projection 54 Planar coil 54a Center part 57,58 Through hole

Claims (4)

In a developing device having a developer carrying member carrying a developer and a developer containing tank containing a developer,
Having a LC oscillation circuit, and having a toner concentration detection device disposed at a position where the inductance of the coil constituting the LC oscillation circuit is influenced by the toner concentration of the developer in the developer storage tank,
The coil of the LC oscillation circuit is:
This is due to the wound print pattern formed on the flat plate,
A developing device having a hollow area without a print pattern in a central portion of a winding. The developing device according to claim 1,
A first positioning shape is formed in the hollow region;
A second positioning shape is formed in the developer storage tank;
The developing device according to claim 1, wherein the toner density detecting device is positioned in the developer containing tank by fitting the first positioning shape and the second positioning shape. The developing device according to claim 1 or 2,
A screw is disposed in the developer storage tank;
The developing device characterized in that the length of the screw in the axial direction of the coil is not less than 1/2 and not more than half of the screw pitch of the screw. In an image forming apparatus having an image carrier and a developing device for developing an electrostatic latent image formed on the image carrier,
The developing device is
A developer carrier for carrying the developer;
A developer storage tank for storing the developer;
A toner concentration detection device that has an LC oscillation circuit and is arranged at a position where the inductance of the coil constituting the LC oscillation circuit is influenced by the toner concentration of the developer in the developer accommodating tank;
The coil of the LC oscillation circuit is:
This is due to the wound print pattern formed on the flat plate,
An image forming apparatus comprising a hollow area having no print pattern in a central portion of a winding.

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