Developing device

Abstract

 A developing device is equipped with a toner detecting means capable of correctly detecting whether an adequate amount of a magnetic toner is present or not. The toner detecting means comprises a permeability detector (82) having a permeability detection surface (86) exposed to a predetermined region, a periodically flowing means (88) for periodically flowing the toner present in the predetermined region to the permeability detection surface (86) of the permeability detector, and a determination means (98) for analyzing an output signal from the permeability detector.

Description

[0001] This invention relates to a developing device for use in developing a latent electrostatic image to a toner image in an image forming machine such as an electrostatic copying apparatus or a laser printer. More specifically, it relates to a developing device equipped with a toner detector for detecting whether a magnetic toner to be consumed is present in an adequate amount or not.

[0002] As is well known, an image forming machine such as an electrostatic copying apparatus or a laser printer forms a latent electrostatic image on a photosensitive member, and develops this image to a toner image. A typical example of a developing device for developing the latent electrostatic image to the toner image comprises a development container, a developer applicator means and a toner feeding means. The development container accommodates a developer which may be a so-called two-component developer comprising carrier particles and a toner, or a so-called one-component developer consisting of a toner alone. The developer applicator means conveys the developer, contained in the development container, to a development zone, where it applies the developer to a latent electrostatic image to be developed, thereby converting the latent electrostatic image into a toner image by means of a toner. The toner feeding means feeds a toner into the development container in accordance with the consumption of the toner contained in the development container. The toner feeding means is usually provided with a toner detecting means for detecting whether an adequate amount of a toner is present or not. When the amount of the toner in the toner feeding means decreases, the toner detecting means detects the decrease, and warns the user that the necessity for replenishing a toner to the toner feeding means has occurred. The toner detecting means in customary use is a photointerrupter. Such a toner detecting means includes a light emitting element and a light receiving element. When an adequate amount of toner is present in the toner feeding means, an optical path between the light emitting element and the light receiving element is blocked by the toner. When the amount of the toner in the toner feeding means decreases, light from the light emitting element is received by the light receiving element, thereby detecting that the amount of the toner in the toner feeding means has decreased.

[0003] In the case that the toner detecting means uses a photointerrupter, a detection site defined by a transparent member needs to be additionally formed in the toner feeding means. The light emitting element and the light receiving element of the toner detecting means are disposed on both sides of the detection site. When an adequate amount of toner is present at the detection site, the optical path between the light emitting element and the light receiving element is blocked by the toner. When there is no adequate amount of toner at the detection site, the light receiving element receives light from the light emitting element. Furthermore, if the toner adheres to the inner surface of the transparent member defining the detection site, the optical path between the light emitting element and the light receiving element is blocked, although an adequate amount of toner is not present at the detection site. Thus, a cleaning means for cleaning the inner surface of the transparent member defining the detection site should also be provided.

[0004] If the developer contained in the development container is a two-component developer comprising carrier particles and a toner, the magnetic resistance of the developer generally increases when the proportion of the toner in the developer, namely, the toner concentration, decreases. In this case, the toner concentration in the developer can be detected using a permeability detector whose output voltage changes with magnetic resistance. If the toner used is a magnetic toner, one can use the permeability detector for the detection of the toner itself in place of the toner detecting means of the photointerrupter type. The use of the permeability detector for detecting the toner itself, however, poses the following problem to be solved: As is well known to those skilled in the art, the output voltage of a magnetism detector changes according to a change in temperature as well as a change in magnetic resistance. The magnetic strength of the toner is very low: compared with the magnetic strength of the developer containing carrier particles. Thus, an attempt to detect the toner based on the absolute value of the output voltage of the permeability detector is highly likely to cause wrong detection owing to a change in ambient temperature. To detect whether or not an adequate amount of toner is present in a predetermined region of the toner feeding means, moreover, it is necessary to expose the permeability detection surface of the permeability detector to the predetermined region of the toner feeding means. If the toner adheres to the permeability detection surface exposed, however, there may be a false detection that an adequate amount of toner is present, owing to the toner adhering to the permeability detection surface, even when such an adequate amount of toner is no longer present in the predetermined region.

[0005] As disclosed in Japanese Laid-Open Patent Publication No. 56384/95, a proposal has recently been made of a toner for a two-component developer which contains 0.1 to 5.0% by weight of a magnetic material such as magnetite instead of a relatively expensive CCA (charge control agent). Such a toner called CCA-less toner, is a so-called micromagnetic toner having slight magnetism. If the toner to be detected is a micromagnetic toner, the aforementioned problem posed when the permeability detector is used for toner detection shows up in a particularly enhanced manner.

[0006] A principal object of the present invention is to provide a novel and improved developing device in which whether or not an adequate amount of a magnetic toner is present in a predetermined region can be appropriately detected by a permeability detector with false detection being fully avoided.

[0007] We have extensively studied the relationship between a magnetic toner, especially, a micromagnetic toner, and the detection characteristics of a permeability detector. As a result, we have found that the above principal object can be attained by periodically flowing a toner toward that permeability detection surface of a permeability detector which detects whether an adequate amount of toner is present or not, and which is exposed to a predetermined region, and by analyzing an output signal from the permeability detector, where necessary, to discriminate it.

[0008] That is, the present invention provides, as a developing device for attaining the principal object, a developing device equipped with a toner detecting means for detecting whether or not an adequate amount of a magnetic toner is present in a predetermined region, wherein the toner detecting means comprises a permeability detector having a permeability detection surface exposed to the predetermined region; a periodically flowing means for periodically flowing the toner present in the predetermined region toward the permeability detection surface of the permeability detector; and a determination means for analyzing an output signal from the permeability detector to determine whether or not an adequate amount of the toner is present in the predetermined region.

[0009] A typical example of the toner is a micromagnetic toner containing 0.1 to 5.0% by weight of a magnetic material. Preferably, the permeability detector is of a type which changes in output voltage in response to magnetic resistance, and the determination means makes a determination based on the magnitude of a change in the output voltage. Alternatively, the determination means makes a determination based on the integral of the output voltage during a predetermined period of time. Preferably, the periodically flowing means is composed of a rotary flowing member which, when rotationally driven, has a front end portion periodically rubbing against the permeability detection surface of the permeability detector, and the central axis of rotation of the rotary flowing member extends substantially parallel to the permeability detection surface of the permeability detector. Advantageously, the rotary flowing member is formed of a plastic film such as a polyethylene terephthalate film. Preferably, the permeability detection surface of the permeability detector makes an angle of inclination, θ, to the horizontal, expressed as 0 degree < θ ≤ 90 degrees, especially, 30 degrees ≤ θ ≤ 60 degrees, and the front end portion of the rotary flowing member is rotated in a direction in which it rubs against the permeability detection surface of the permeability detector from below to above. It is possible to dispose a cleaning means acting on the rear surface, in the direction of rotation, of the rotary flowing member, thereby releasing the toner that has adhered. Preferably, the cleaning means comprises a rotary cleaning member to be rotationally driven. Preferably, the central axis of rotation of the rotary cleaning member extends substantially parallel to the central axis of rotation of the rotary flowing member, the direction of rotation of the rotary cleaning member is opposite to the direction of rotation of the rotary flowing member, and the front end portion of the rotary cleaning member acts on the rear surface, in the direction of rotation, of the rotary flowing member. Preferably, the rotary cleaning member is also formed of a plastic film such as a polyethylene terephthalate film. Preferably, the predetermined region lies in a magnetic toner conveyance path, and toner stagnation is caused in the predetermined region since at least one factor related to the conveyance of toner differs between the upstream side and the downstream side of the predetermined region. This toner stagnation can be generated because the conveying capacity of an upstream toner conveying means disposed upstream from the predetermined region is greater than the conveying capacity of a downstream toner conveying means disposed downstream from the predetermined region, or because the direction of toner conveyance is abruptly changed in the predetermined region. Preferably, a depression for forming a toner reservoir is formed in the predetermined region, and the periodically flowing means acts also on the toner present in the depression. In a preferred embodiment, the developing device comprises a development container, a developer applicator means for applying a developer present in the development container to a latent electrostatic image to be developed, and a toner feeding means for feeding a magnetic toner to the development container. The toner feeding means includes a hopper container having formed therein a toner conveyance path having a toner inlet and a toner outlet made to communicate with the development container, and a conveying means for conveying the magnetic toner through the toner conveyance path. The predetermined region lies in the toner conveyance path formed in the hopper container. The developer present in the development container is a two-component developer comprising carrier particles and a magnetic toner. The toner feeding means includes a toner cartridge which is mounted replaceably. The magnetic toner accommodated in the toner cartridge is fed to the hopper container through the toner inlet.

[0010] According to the developing device of the present invention, the toner is periodically flowed toward the permeability detection surface of the permeability detector to periodically change the output signal of the permeability detector. Furthermore, the absolute value per se of the output signal of the permeability detector is not relied on, but the output signal is analyzed where necessary. As a result, whether or not an adequate amount of toner is present is determined on the basis of the magnitude of a change in output voltage during a predetermined period of time, or on the basis of the integral of output voltage during a predetermined period of time. Thus, wrong detection does not occur even if the output signal of the permeability detector is changed because of a change in ambient temperature. Moreover, the toner is periodically flowed to the permeability detection surface of the permeability detector, so that the adhesion of the toner to the permeability detection surface of the permeability detector is effectively avoided. Thus, wrong detection due to toner adhesion to the permeability detection surface is also effectively avoided. In addition, if an off-specification (such as substantially non-magnetic or considerably high-magnetic) toner is replenished in the developing device of the present invention, the toner detecting means does not determine that an adequate toner is present. Thus, the user can be made to recognize that an off-specification toner has been replenished by mistake.

[0011] The invention is described further hereinafter, by way of example, only, with reference to the accompanying drawings, in which:-

Fig. 1 is a perspective view showing a part of a preferred embodiment of a developing device constructed in accordance with the present invention;

Fig. 2 is a sectional view showing a hopper container in the developing device of Fig. 1;

Fig. 3 is a schematic block diagram showing a toner detecting means in the developing device of Fig. 1;

Fig. 4 is a sectional view, similar to Fig. 2, showing the hopper container in the developing device of Fig. 1 when containing an adequate amount of toner;

Fig. 5 is a sectional view, similar to Fig. 2, showing the hopper container in the developing device of Fig. 1 when containing an inadequate amount of toner;

Fig. 6 is a chart showing an example of the data on the output voltage of a permeability detector measured in the developing device of Fig. 1; and

Fig. 7 is a sectional view, similar to Fig. 2, showing the action of a cleaning means in the developing device of Fig. 1.

[0012] With reference to Figs. 1 and 2, an illustrated developing device has a development container 2 and a toner feeding means 4 for feeding a toner to the development container 2. As illustrated schematically in Fig. 2, a developer applicator means 6 is disposed in the development container 2. The developer applicator means 6 includes a rotary sleeve member, and a stationary magnet member disposed in the rotary sleeve member. The developer applicator means 6 transports a developer present in the development container 2 to a development zone 8 while holding the developer on the peripheral surface of the rotary sleeve member, and applies the developer to a latent electrostatic image formed on the peripheral surface of a rotary drum 10 to develop the latent electrostatic image to a toner image. The developer may be a two-component developer comprising carrier particles and a toner. In the development container 2, there is disposed a developer agitating/conveying means (not shown) for agitating the developer to charge the toner, and for conveying the developer through a required conveyance path. There is also disposed a toner concentration detecting means (not shown) for detecting the toner concentration in the developer within the development container 2. When the toner concentration in the developer falls below a predetermined value, the toner feeding means 4 is actuated, whereupon the toner is fed by the toner feeding means 4 to the development container 2. The toner concentration detecting means may be composed of a permeability detector whose output voltage changes according to the magnetic resistance of the developer. The development container 2, and the developer applicator means 6, developer agitating means and toner concentration detecting means disposed in the development container 2 do not constitute the novel feature of the illustrated developing device constructed in accordance with the present invention. Their structures may be in well known forms, and thus details of their structures will be omitted in the present specification.

[0013] With reference to Figs. 1 and 2, the toner feeding means 4 is composed of a hopper container 12 and a toner cartridge 14. The hopper container 12 includes a box-like container body 16 in a nearly rectangular shape as a whole. The container 16 has four side walls 18, 20, 22 and 24, and a bottom wall 26. As will be understood by reference to Fig. 2, the upper surface of that main portion of the bottom wall 26 which excludes a depression to be described later has two arcuate portions 28 and 30 positioned adjacent to each other. On the bottom wall 26, an upright partition wall 32 extending between the two arcuate portions 28 and 30 is formed. The partition wall 32 extends longitudinally (perpendicularly to the sheet face of Fig. 2) on the bottom wall 26, but does not exist in the longitudinally opposite end portions of the container body 16. In this manner, toner conveyance paths 34 and 36 separated by the partition wall 32 and extending parallel to each other are defined in the container body 16. These toner conveyance paths 34 and 36 are made to communicate transversely at the opposite end portions of the container body 16, namely, those portions where the partition wall 32 is not present. In a middle portion of the toner conveyance path 36, a toner outlet 38 is formed in the bottom wall 26. This toner outlet 38 is made to communicate with the inside of the development container 2 disposed below the hopper container 12. As will be described in further detail, the toner is fed from the hopper container 12 into the development container 2 through the toner outlet 38. The upper surface of the hopper container 12 is covered with a substantially flat upper wall 40. At a site corresponding to one end portion of the toner conveyance path 34, the upper wall 40 has a toner inlet 42 disposed therein.

[0014] In the toner conveyance paths 34 and 36 formed in the hopper container 12, a conveying means 44 generally indicated at 44 is disposed. This conveying means 44 includes a rotating shaft 46 extending along the toner conveyance path 34, and a rotating shaft 48 extending along the toner conveyance path 36. The rotating shafts 46 and 48 are rotatably mounted between the side walls 18 and 20 of the hopper container 12. The rotating shafts 46 and 48 are drivingly connected to an electric motor (not shown) via suitable transmission mechanisms (not shown) such as transmission gears. When the electric motor is energized, the rotating shaft 46 is rotationally driven in a direction shown by an arrow 50, while the rotating shaft 48 is rotationally driven in a direction shown by an arrow 52. Discs 47 and 49 are formed at the opposite ends of the rotating shaft 46. On a main part of the rotating shaft 46, i.e., the portion excluding the opposite end portions, a continuously extending helical blade 54 is formed. At each of the opposite end portions of the rotating shaft 46, a single rectangular delivery piece 56 or 58 extending radially from the peripheral surface of the rotating shaft 46 is formed. The axially outward end of the delivery piece 56 or 58 is joined to the inner surface of the disc 47 or 49. At the opposite ends of the other rotating shaft 48 as well, discs 59 and 61 are formed. On a main part of the rotating shaft 48, i.e., the portion excluding the opposite end portions, two helical blades 60 and 62 are formed. Between the helical blade 60 and the helical blade 62, four delivery pieces 64 extending radially from the peripheral surface of the rotating shaft 48 are formed at a 90-degree angular distance from each other. The site where the four delivery pieces 64 are formed corresponds to the site where the toner outlet 38 is formed, and the four delivery pieces 64 are positioned above the toner outlet 38. At each of the opposite end portions of the rotating shaft 48, a single rectangular delivery piece 66 or 68 extending radially from the peripheral surface of the rotating shaft 48 is formed. The axially outward end of the delivery piece 66 or 68 is joined to the inner surface of the disc 59 or 61. At one end portion of the rotating shaft 48, two short helical blades 70 and 72 extending over a nearly 180-degree angular range are formed in addition to the delivery piece 66. These two short helical blades 70 and 72 are disposed on a diametrically opposite side relative to the delivery piece 66.

[0015] As shown clearly in Fig. 1, the toner cartridge 14 of the toner feeding means 4 is in the form of a hollow container, and mounted replaceably over the hopper container 12. In the bottom surface of the toner cartridge 14, a toner feed port (not shown) is formed. Such a toner feed port has been sealed with a suitable sealing member until the toner cartridge 14 is mounted at a required position. When the toner cartridge 14 is mounted at a required position, the toner feed port is unsealed, and made to communicate with the toner inlet 42 formed in the upper wall 40 of the hopper container 12. In the toner cartridge 14, there is also disposed a toner conveying means (not shown) for conveying the toner accommodated therein toward the toner feed port. Such a toner conveying means may be composed of a rotary helical blade or the like. The toner accommodated in the toner cartridge 14 is dropped into the hopper container 12 through the toner feed port formed in the toner cartridge 14 and the toner inlet 42 formed in the hopper container 12. In the hopper container 12, the rotating shafts 46 and 48 are rotationally driven in the directions shown by the arrows 50 and 52 upon energization of the electric motor (not shown). At this time, the toner dropped through the toner inlet 42 is urged into the toner conveyance path 34 by the action of the delivery piece 56 formed at the one end portion of the rotating shaft 46. Then, the toner is conveyed in a direction shown by an arrow 74 along the toner conveyance path 34 by the action of the helical blade 54 formed on the rotating shaft 46. At the other end portion of the hopper container 12, the toner is transferred from the toner conveyance path 34 to the toner conveyance path 36 as shown by an arrow 76 by the action of the delivery piece 58 formed on the rotating shaft 46. In the toner conveyance path 36, the toner is conveyed in a direction shown by an arrow 78 toward the toner outlet 38 by the action of the helical blades 70, 72 and 60 formed on the rotating shaft 48. Then, under the action of the delivery piece 64 formed on the rotating shaft 48, the toner is urged downward and dropped through the toner outlet 38 to be supplied to the development container 2. The toner that has failed to be dropped through the toner outlet 38 is further conveyed in the direction of arrow 78 by the action of the helical blade 62 formed on the rotating shaft 48. Then, this toner is transferred, at one end portion of the hopper container 12, from the toner conveyance path 36 to the toner conveyance path 34 by the action of the delivery piece 68 formed on the rotating shaft 48.

[0016] A preferred example of the toner accommodated in the toner cartridge 14, accordingly the toner discharged from the toner cartridge 14, conveyed through the toner conveyance paths 34 and 36 formed in the hopper container 12, and supplied to the development container 2, is a toner as disclosed in Japanese Laid-Open Patent Publication No. 56384/95. Such a toner contains 0.1 to 5.0% by weight of a magnetic material such as magnetite instead of a relatively expensive CCA (charge control agent). Such a toner is usually called "CCA-less" toner, and is a so-called micromagnetic toner having slight magnetism resulting from the magnetic material contained.

[0017] In the illustrated developing device constructed in accordance with the present invention, it is important that a toner detecting means 80 be disposed which detects whether or not an adequate amount of toner is present in the aforementioned predetermined region within the hopper container 12. With reference to Figs. 1 and 2, the toner detecting means 80 includes a permeability detector 82 disposed in relation to one end portion of the toner conveyance path 36. In greater detail, a circular opening 84 is formed in the bottom wall 26 to side wall 24 of the hopper container 12. A front end portion of the permeability detector 82 is situated in the opening 84, and a circular front end surface of the permeability detector 82, namely, a permeability detection surface 86, is exposed to the toner conveyance path 36 through the opening 84. Preferably, the exposed permeability detection surface 86 is inclined at an angle of inclination, θ, to the horizontal, expressed as 0 degree < θ ≤ 90 degrees, especially, 30 degrees ≤ θ ≤ 60 degrees. A preferred example of the permeability detector 82 is a differential transducer type permeability detector (TS0524LB, TDK), which can serve as a high-sensitivity permeability detector. This permeability detector 82 changes in output voltage in response to magnetic resistance in the vicinity of the permeability detection surface 86. That is, the permeability detector 82 generates a relatively high output voltage when a relatively large amount of a magnetic material is present near the permeability detection surface 86, resulting in low magnetic resistance, while the permeability detector 82 generates a relatively low output voltage when a relatively small amount of a magnetic material is present near the permeability detection surface 86, resulting in high magnetic resistance.

[0018] With reference to Figs. 1 and 2, a periodically flowing means 88 and a cleaning means 90 are disposed in the hopper container 12 in relation to the permeability detector 82. The periodically flowing means 88 in the illustrated embodiment is composed of a rotary flowing member 92 fixed to the delivery piece 66 formed at one end portion of the rotating shaft 48. This rotary flowing member 92 is preferably formed of a suitable plastics film such as a polyethylene terephthalate film. The rotary flowing member 92 is a rectangular piece extending radially of the rotating shaft 48 from a base portion fixed by a suitable method, such as bonding, to the front side surface of the delivery piece 66 as viewed in the direction of rotation shown by the arrow 52. The length of extension of the rotary flowing member 92 is set to be considerably larger than the length from the central axis of the rotating shaft 48 to the permeability detection surface 86 of the permeability detector 82. As will be described in more detail, when the rotating shaft 48 is rotationally driven in the direction of arrow 52, the rotary flowing member 92 is also rotationally driven accordingly, whereupon its front end portion rubs against the permeability detection surface 86 of the permeability detector 82 from below to above. The rotating shaft 48 and the permeability detection surface 86 of the permeability detector 82 are substantially parallel. Thus, the central axis of rotation of the rotary flowing member 92 constituting the periodically flowing means 88 and the permeability detection surface 86 of the permeability detector 82 are substantially parallel. The cleaning means 90 is composed of a rotary cleaning member 94 fixed to the delivery piece 58 formed at one end portion of the rotating shaft 46. This rotary cleaning member 94 is also preferably formed of a suitable plastics film such as a polyethylene terephthalate film. The rotary cleaning member 94 is a rectangular piece extending radially of the rotating shaft 46 from a base portion fixed by a suitable method, such as bonding, to the delivery piece 58. The length of extension of the rotary cleaning member 94 is set to be considerably larger than the length from the central axis of the rotating shaft 46 to a boundary region between the toner conveyance path 34 and the toner conveyance path 36. As will be described in more detail, when the rotating shaft 46 is rotationally driven in the direction of arrow 50, the rotary cleaning member 94 is also rotationally driven accordingly, whereupon its front end portion acts on the rear surface, in the direction of rotation, of the rotary flowing member 92 constituting the periodically flowing means 88. The rotating shaft 46 and the rotating shaft 48 are substantially parallel to each other. Thus, the central axis of rotation of the rotary flowing member 92 constituting the periodically flowing means 88 and the central axis of rotation of the rotary cleaning member 94 constituting the cleaning means 90 are substantially parallel to each other. The direction of rotation of the rotating shaft 46 and the direction of rotation of the rotating shaft 48 are opposite to each other. Thus, the direction of rotation of the rotary flowing member 92 constituting the periodically flowing means 88 and the direction of rotation of the rotary cleaning member 94 constituting the cleaning means 90 are opposite to each other.

[0019] As will be illustrated clearly in Fig. 2, no partition wall 32 is present at one end portion of the hopper container 12. In addition, a depression 96 depressed downward of other parts is formed in correspondence with the region where the permeability detector 82, periodically flowing means 88 and cleaning means 90 are disposed. Such a depression 96 is defined by forming the upper surface of the bottom wall 26 not into a shape having two arcuate portions, but into a single arcuate shape depressed downward of the lowermost parts of the two arcuate portions. The front end portion of the rotary flowing member 92 constituting the periodically flowing means 88 is set at such a length as to rub against the surface of the depression 96 as well.

[0020] As will be illustrated schematically in Fig. 3, an output signal from the permeability detector 82 is sent to a determination means 98 which may be composed of a microprocessor. The determination means 98 analyzes the output signal of the permeability detector 82 where necessary, and determines whether or not an adequate amount of toner is present in a predetermined region of the hopper container 12, i.e., at one end portion of the toner conveyance path 36. In more detail, the toner still remains in the toner cartridge 14, and when the toner is fed from the toner cartridge 14 into the hopper container 12 in accordance with toner supply from the hopper container 12 to the development container 2, an adequate amount of toner 100 is present in the toner conveyance paths 34 and 36 of the hopper container 12, as shown in Fig. 4. In this state, when the rotating shaft 48 is rotated in the direction of arrow 52, the periodically flowing means 88 constituted by the rotary flowing member 92 disposed on the rotating shaft 48 acts on the toner 100 present at one end portion of the toner conveyance path 36. Thus, the periodically flowing means 88 flows the toner 100 periodically, namely, by each rotation, while pressing it against the permeability detection surface 86 of the permeability detector 82 from below to above. When the front end portion of the rotary flowing member 92 rubs against the permeability detection surface 86 of the permeability detector 82, the toner 100 is pressed against the permeability detection surface 86. Since magnetic resistance detected by the permeability detector 82 is very low, the ouput voltage of the permeability detector 82 is very high. When the front end portion of the rotary flowing member 92 has passed the permeability detection surface 86 of the permeability detector 82, the pressure of the toner 100 on the permeability detection surface 86 vanishes, so that the output voltage of the permeability detector 82 lowers. As will be easily understood by reference to Fig. 4, however, when an adequate amount of toner 100 is present in the hopper container 12, a large amount of toner 100 still exists near the permeability detection surface 86, even after the front end portion of the rotary flowing member 92 has passed the permeability detection surface 86. Thus, the decrease in the output voltage of the permeability detector 82 after passage of the front end portion of the rotary flowing member 92 beside the permeability detection surface 86 is relatively small. On the other hand, when the toner 100 in the toner cartridge 14 is substantially used up, and even thereafter the toner 100 continues to be supplied from the hopper container 12 to the development container 2, the amount of the toner 100 in the hopper container 12 markedly decreases, as shown in Fig. 5. In this state, when the rotating shaft 48 is rotated in the direction of arrow 52, the front end portion of the rotary flowing member 92 disposed on the rotating shaft 48 flows the toner 100, pressing it against the permeability detection surface 86 of the permeability detector 82. At this time, the output voltage of the permeability detector 82 is relatively high because of the toner 100. As will easily be understood by reference to Fig. 5, however, immediately after the front end portion of the rotary flowing member 92 passes the permeability detection surface 86, there is only a little toner 100 near the permeability detection surface 86, so that the output voltage of the permeability detector 82 noticeably declines.

[0021] Fig. 6 shows an example of the output voltage data on the permeability detector 82 obtained by performing the following experiments: In experiments, the hopper container 12 of a shape as illustrated in Figs. 1 and 2 was used, and filled with a micromagnetic toner as aforementioned. Then, the rotating shafts 46 and 48 were continuously rotated to discharge the toner 100 from the hopper container 12 through the toner outlet 38. The toner 100 was not supplied to the hopper container 12 through the toner inlet 42. With the passage of time, therefore, the amount of the toner 100 in the hopper container 12 was gradually decreased. The actual data in Fig. 6 showed that a relatively large amount of the toner 100 was present in the hopper container 12 at the time point T1. During the period up to T1, the magnitude of change, L1, in the output voltage of the permeability detector 82 due to the periodical flow of the toner 100 by the rotary flowing member 92 was understood to be relatively small. During the period from T1 to the time point T2, the magnitude of change in the output voltage of the permeability detector 82 gradually increased. After passage of T2, the magnitude of change, L2, in the output voltage of the permeability detector 82 stabilized at a relatively high value. After passage of T2, the amount of the toner 100 present in the region where the permeability detector 82 was disposed markedly decreased, corresponding to a state as illustrated in Fig. 5.

[0022] With reference to Fig. 3 along with Figs. 4 to 6, the determination means 98 analyzes an output signal from the permeability detector 82, i.e., output voltage changing as in Fig. 6 according to the amount of the toner 100 in the hopper container 12, and makes a determination. As will be clearly seen from the example of the actual data in Fig. 6, when an adequate amount of the toner 100 is present in the hopper container 12, the magnitude of change L1 in the output voltage of the permeability detector 82 upon rotation of the rotating shaft 48 is relatively small. When the amount of the toner 100 in the hopper container 12 is markedly decreased, by contrast, the magnitude of change L2 in the output voltage of the permeability detector 82 upon rotation of the rotating shaft 48 is much larger. In view of these facts, the determination means 98 analyzes the magnitude of change in output voltage when the rotating shaft 48 is rotated and the periodically flowing means 88 periodically flows the toner, thereby making a determination. For instance, the determination means 98 calculates the difference L between the maximum value and the minimum value for each waveform of the output voltage. When this L has exceeded a predetermined threshold a predetermined number of times (e.g. three times) consecutively, the determination means 98 generates a toner replenishment signal showing that an adequate amount of the toner 100 is not present in the hopper container 12, in other words, that the amount of the toner 100 in the hopper container 12 has markedly decreased. If desired, it is possible that the determination means 98 calculates the difference L between the maximum value and the minimum value of the output voltage of the permeability detector 82 during a predetermined period of time, say, 10 seconds (according to the example of actual data in Fig. 6, the time interval expressed as D1 was 10 seconds); then, the determination means 98 determines whether or not this difference L is greater than the predetermined threshold; and when the difference L is greater than the predetermined threshold, the determination means 98 generates a toner replenishment signal showing that an adequate amount of the toner 100 is not present in the hopper container 12. Generation of the toner replenishment signal by the determination means 98 energizes a warning means 102, optionally a warning lamp, to warn the user that the necessity for toner replenishment has occurred, in other words, that the necessity for replacing the toner cartridge 14 by a fresh one has occurred.

[0023] According to our experiments, the output voltage of the aforesaid differential transducer type permeability detector 82 is affected by ambient temperature. When the ambient temperature rises, the output voltage of the permeability detector 82 is increased, and the entire output waveform in Fig. 6 tends to be moved upward. If the toner 100 is a micromagnetic toner and the magnetic resistance of the toner 100 is relatively high, the absolute value of the output voltage of the permeability detector 82 is relatively small. If a determination is made based on the absolute value of the output voltage of the permeability detector 82, a false determination is highly likely to occur because of the ambient temperature. Changes in the output voltage of the permeability detector 82 due to fluctuations in ambient temperature, however, are such that the entire output waveform in Fig. 6 tends to be moved upward or downward. Hence, changes in the magnitude of change in the output voltage (the difference between the maximum and minimum values) during a predetermined period of time are relatively slight, even if the ambient temperature changes. As stated earlier, therefore, the magnitude of change in the output voltage of the permeability detector 82 during a predetermined period of time is determined while the rotating shaft 48 is being rotated, and the periodically flowing means 88 is periodically flowing the toner. This procedure permits detection of whether or not an adequate amount of the toner 100 is present in the hopper container 12, with substantial freedom from mistakes.

[0024] In the foregoing embodiment, the determination means 98 makes a determination by analyzing the magnitude of change in the output voltage of the permeability detector 82. Alternatively, a determination of whether or not an adequate amount of the toner 100 is present may be made based on the integral, during a predetermined period of, say, 10 seconds, of the output voltage of the permeability detector 82. In this case as well, the risk of an error due to a change in ambient temperature is none or markedly low, as will be easily seen by reference to Fig. 6.

[0025] To reliably avoid the risk of an error in the detection of the toner 100 by the toner detecting means 80, it should be noticed that the following technical construction is adopted in the illustrated developing device constructed in accordance with the present invention:

[0026] As has been mentioned by reference to Fig. 2, the permeability detection surface 86 of the permeability detector 82 is inclined at an angle of inclination, θ, to the horizontal, expressed as 0 degree < θ ≤ 90 degrees, especially, 30 degrees ≤ θ ≤ 60 degrees. The rotary flowing member 92 is adapted to rub against the permeability detection surface 86 of the permeability detector 82 from below to above. Because of this construction, it can be avoided fully reliably that the toner 100 adheres to or stagnates on the permeability detection surface 86 of the permeability detector 82, adversely affecting the output voltage of the permeability detector 82. If the permeability detection surface 86 of the permeability detector 82 is inclined at an angle of inclination of more than 90 degrees to the horizontal; or if the rotary flowing member 92 rubs against the permeability detection surface 86 of the permeability detector 82 from above to below, then the toner 100 is excessively pressed against the permeability detection surface 86 of the permeability detector 82, and has a tendency, although slight, toward adhesion thereto or stagnation thereon.

[0027] As will be understood easily by reference to Fig. 2, while the rotary flowing member 92 is rubbing against the permeability detection surface 86 of the permeability detector 82, the rotary flowing member 92 is elastically deformed into a convex shape protruding forward in the direction of rotation. When the rotary flowing member 92 has passed the permeability detection surface 86 of the permeability detector 82, it is elastically restored at least partially toward a straightly extending shape. Our experience has shown that owing to the above-mentioned behavior of the rotary flowing member 92, the toner 100 adhering to the front surface, in the direction of rotation, of the rotary flowing member 92 is scattered from this front surface during elastic restoration of the rotary flowing member 92. Thus, there is little tendency for the toner 100 to adhere to the front surface of the rotary flowing member 92. On the rear surface, in the direction of rotation, of the rotary flowing member 92, however, it is likely, without provision of the cleaning means 90, that some toner 100 adheres to this surface, adversely affecting the output voltage of the permeability detector 82. In the illustrated embodiment, as will be evidently understood by reference to Fig. 7, when the rotating shaft 46 is rotated along with the rotating shaft 48, the front end portion of the rotary cleaning member 94 disposed on the rotating shaft 46 acts on the rear surface, in the direction of rotation, of the rotary flowing member 92. Thereby, this front end portion cleans the toner 100 about to adhere there, thus fully preventing toner adhesion to the rear surface, in the direction of rotation, of the rotary flowing member 92. If the toner 100 tends to adhere to the front surface, in the direction of rotation, of the rotary flowing member 92, a rotary cleaning member acting on the front surface, in the direction of rotation, of the rotary flowing member 92 may be provided on the rotating shaft 46 in addition to or in place of the rotary cleaning member 94.

[0028] With reference to Figs. 1 and 2, attention should also be paid to the position where the permeability detector 82 in the hopper container 12 is disposed. According to our experience, the permeability detection surface 86 of the permeability detector 82 is preferably located at that position in the toner conveyance paths 34 and 36 where the toner 100 tends to be stagnant. If the permeability detection surface 86 of the permeability detector 82 is disposed at that position in the toner conveyance paths 34 and 36 where the toner 100 is conveyed satisfactorily, considerable voids are produced accidentally in the toner 100 because of the satisfactory conveyance of the toner 100. Such voids result in a high apparent magnetic resistance of the toner 100, thus causing the risk of adversely affecting the output voltage of the permeability detector 82. At such a position that the toner is stagnant, by contrast, toner stagnation compresses the toner 100, fully suppressing the generation of voids. Thus, an adverse influence on the output voltage of the permeability detector 82 is fully suppressed. To cause the stagnation of the toner 100 at the site where the permeability detection surface 86 of the permeability detector 82 is situated, it is important that at least one of factors related to the conveyance of the toner 100 be different between the side upstream and the side downstream from this site. In the illustrated embodiment, at that upstream end portion of the toner conveyance path 36 where the permeability detection surface 86 of the permeability detector 82 is exposed, the toner 100 is transferred transversely from the downstream end portion of the toner conveyance path 34; and the helical blades formed on the rotating shaft 48 at the upstream end portion of the toner conveyance path 36 are short helical blades 70 and 72. Thus, the toner conveying capacity at the upstream end portion of the toner conveyance path 36 is somewhat lower than the toner conveying capacity on the upstream side thereof. Hence, the toner 100 is rendered stagnant at the upstream end portion of the toner conveyance path 36. Needless to say, a factor such as the direction of toner conveyance, the toner conveying capacity, or the cross sectional area of the toner conveyance path (the area of conveyance) may be suitably changed in a manner different from the illustrated embodiment to cause the stagnation of the toner 100 at a predetermined site, and the permeability detection surface 86 of the permeability detector 82 is exposed to this site. For instance, a somewhat excess toner 100 may be fed from the toner cartridge 14 to the hopper container 12 through the toner inlet 42 to cause the stagnation of the toner 100 at the upstream end portion of the toner conveyance path 34 in the hopper container 12, namely, below the toner inlet 42, and the permeability detection surface 86 of the permeability detector 82 may be exposed to this site.

[0029] In the illustrated embodiment, moreover, it should also be noticed that the depression 96 depressed downward of other parts is formed at that one end portion of the hopper container 12 where the permeability detector 82, periodically flowing means 88 and cleaning means 90 are disposed. As is well known to those skilled in the art, it is common practice with a copying machine that development is repeatedly performed even after an adequate toner is no longer present in the toner feeding means 4, and so the toner is no longer fed to the development container 2. Thus, when the toner concentration in the development container 2 has decreased below a predetermined value, a warning means (not shown), optionally a warning lamp, is energized to warn the user of this fact, and to incapacitate the user from performing copying operations continuously. As a stopgap, however, the user is allowed to perform a single copying operation at a time. For this single copying operation performed at a time, if the depression 96 is not formed in the hopper container 12, the following problem will arise: Since the toner concentration in the development container 2 is less than the predetermined value, when the rotating shafts 46 and 48 are rotated in the hopper 12 in accordance with the execution of the copying operation, the toner 100 in the hopper container 12 becomes extremely small in amount. Thus, even when the rotary flowing member 92 constituting the periodically flowing means 88 is rotationally driven, the toner 100 is not flowed to the permeability detection surface 86 of the permeability detector 82. Thus, the output voltage of the permeability detector is not high, but remains low. Hence, the magnitude of change in the output voltage during the predetermined period is a small value less than the predetermined value. In this condition, the determination means 98 of the toner detecting means 80 may determine that an adequate toner is present in the hopper container 12. When the aforementioned depression 96 is formed in the hopper container 12, on the other hand, the depression 96 constitutes a toner reservoir. That is, even when the amount of the toner in the hopper container 12 is extremely small, the toner 100 in the depression 96 cannot be conveyed downstream. Thus, some toner 100 always remains in the depression 96. When the rotating shaft 48 is rotated to turn the rotary flowing member 92, the rotary flowing member 92 acts on the toner 100 in the depression 96 to periodically flow it onto the permeability detection surface 86 of the permeability detector 82. Thus, the output voltage of the permeability detector 82 is fully fluctuated, whereupon the determination means 98 correctly determines that an adequate amount of the toner 100 is not present in the hopper container 12.

[0030] While some preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, it is to be understood that the invention is in no way limited thereto, but various changes and modifications may be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A developing device equipped with a toner detecting means for detecting whether or not an adequate amount of a magnetic toner is present in a predetermined region, characterised in that
   said toner detecting means comprises a permeability detector (82) having a permeability detection surface (86) exposed to said predetermined region; periodically flowing means (88) for periodically flowing the toner present in said predetermined region toward said permeability detection surface (86) of said permeability detector; and determination means (98) for analyzing an output signal from said permeability detector (82) to determine whether or not an adequate amount of the toner is present in said predetermined region.

2. A developing device as claimed in claim 1, wherein the toner is a micromagnetic toner containing 0.1 to 5.0% by weight of a magnetic material.

3. A developing device as claimed in claim 1 or 2, wherein said permeability detector (82) is of the type which changes in output voltage in response to magnetic resistance, and said determination means (98) makes a determination based on the magnitude of a change in the output voltage.

4. A developing device as claimed in claim 1 or 2, wherein said permeability detector (82) is of a type which changes in output voltage in response to magnetic resistance, and said determination means (98) makes a determination based on the integral of the output voltage during a predetermined period of time.

5. A developing device as claimed in claim 1, wherein said periodically flowing means (88) is composed of a rotary flowing member (92) which, when rotationally driven, has a front end portion periodically rubbing against said permeability detection surface (86) of said permeability detector.

6. A developing device as claimed in claim 5, wherein the central axis of rotation of said rotary flowing member (92) extends substantially parallel to said permeability detection surface (86) of said permeability detector.

7. A developing device as claimed in claim 5 or 6, wherein said rotary flowing member (92) is formed of a plastics film.

8. A developing device as claimed in claim 5, 6 or 7 wherein said permeability detection surface (86) of said permeability detector makes an angle of inclination, θ, to the horizontal, expressed as 0 degree < θ ≤ 90 degrees, and the front end portion of said rotary flowing member is rotated in a direction in which it rubs against said permeability detection surface of said permeability detector from below to above.

9. A developing device as claimed in claim 8, wherein said angle of inclination, θ, is 30 degrees ≤ θ ≤ 60 degrees.

10. A developing device as claimed in any of claims 5 to 9, wherein a cleaning means (90) is disposed which acts on the rear surface, in the direction of rotation, of said rotary flowing member (92) to release the toner that has adhered.

11. A developing device as claimed in claim 10, wherein said cleaning means (90) comprises a rotary cleaning member (94) to be rotationally driven, the central axis of rotation of said rotary cleaning member extends substantially parallel to the central axis of rotation of said rotary flowing member (92), the direction of rotation of said rotary cleaning member (94) is opposite to the direction of rotation of said rotary flowing member (92), and the front end portion of said rotary cleaning member acts on the rear surface, in the direction of rotation, of said rotary flowing member.

12. A developing device as claimed in claim 11, wherein said rotary cleaning member (94) is formed of a plastics film.

13. A developing device as claimed in any of claims 1 to 12, wherein said predetermined region lies in a magnetic toner conveyance path, and toner stagnation is caused in said predetermined region since at least one factor related to the conveyance of the toner differs between the upstream side and the downstream side of said predetermined region.

14. A developing device as claimed in claim 13, wherein said toner stagnation is caused since the conveying capacity of upstream toner conveying means disposed upstream from said predetermined region is greater than the conveying capacity of downstream toner conveying means disposed downstream from said predetermined region.

15. A developing device as claimed in claim 13, wherein said toner stagnation is caused since the direction of toner conveyance is abruptly changed in said predetermined region.

16. A developing device as claimed in any of claims 1 to 15, wherein a depression (96) for forming a toner reservoir is formed in said predetermined region, and said periodically flowing means (88) acts also on the toner present in said depression.

17. A developing device as claimed in any of claims 1 to 16, which comprises a development container, developer applicator means for applying a developer present in said development container to a latent electrostatic image to be developed, and toner feeding means for feeding a magnetic toner to said development container; and wherein said toner feeding means includes a hopper container having formed therein a toner conveyance path having a toner inlet and toner outlet made to communicate with said development container, and conveying means for conveying the magnetic toner through said toner conveyance path; and said predetermined region lies in said toner conveyance path formed in said hopper container.

18. A developing device as claimed in claim 17, wherein the developer present in said development container is a two-component developer comprising carrier particles and a magnetic toner.

19. A developing device as claimed in claim 17, wherein said toner feeding means includes a toner cartridge which is mounted replaceably, and the magnetic toner accommodated in said toner cartridge is fed to said hopper container through said toner inlet.

Drawing