Patent Publication Number: US-6337957-B1

Title: Image forming apparatus and developing device with improved self toner density control

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to image forming apparatuses such as copying machines, printers, facsimiles, etc. and a developing device for use in such image forming apparatuses. The present invention more particularly relates to a developing device and an image forming apparatus using the developing device that uses a two component developer including a toner and a magnetic carrier and that includes a self toner density control device to control the toner density of the developer on a developer bearing member so as to be within a fixed range without using a complex toner replenishing device. 
     2. Discussion of the Background 
     An example of a developing device that controls the density of toner in the developer on a developer bearing member without using a complex toner replenishing device is one in which the quantity of developer carried on and conveyed by a developer bearing member, that has an internally disposed magnetic field generating device, is regulated by a developer regulating member. The developer scraped off by the developer regulating member is put in a developer accommodating unit, and toner accommodated in a toner accommodating unit is supplied to the developer carried on the developer bearing member through a toner supplying opening, which is adjacent to the developer accommodating unit upstream in a developer conveying direction and which opposes a surface of the developer bearing member (see e.g. Japanese Laid-open Patent publication No. 9-22178). In this developing device, the toner contacting the developer carried on and conveyed by the developer bearing member at the toner supplying opening is taken into the conveyed developer at the interface between the conveyed developer and the developer in the developer accommodating unit. Once the toner density of the developer on the developer bearing member reaches a certain level, the volume of the developer accommodated in the developer accommodating unit starts to swell and thereby the developer in the developer accommodating unit extends so as to cover the toner supplying opening. As a result, the toner is stopped from being taken into the developer on the developer bearing member from the toner accommodating unit at the toner supplying opening. Thus, the toner density of the developer on the developer bearing member is controlled to be within a fixed range. 
     Also, a developing device is known in which a second developer regulating member is provided between the developer accommodating unit and the toner supplying opening of the toner accommodating unit so as to have a predetermined gap relative to a surface of a developer bearing member (see e.g. Japanese Laid-open Patent No. 9-197833). In this developing device, as the toner density of the developer on the developer bearing member increases, the thickness of a developer layer on the developer bearing member increases, and the increased portion of the developer layer is regulated by the second developer regulating member to pass the second developer regulating member. The developer thus regulated by the second developer regulating member covers the toner supplying opening located adjacent to and upstream of the second developer regulating member in the developer conveying direction, and thereby the toner is stopped from being taken into the developer being carried and conveyed by the developer bearing member. As a result, the toner density of the developer on the developer bearing member is controlled to be within a fixed range. 
     Such developing devices as noted above that control the toner density of the developer on a developer bearing member to be within a certain range (such a control is hereinafter referred to as a self toner density control) have an advantage in that a toner supplying unit can be simplified, because a toner density sensor is not required, and further a stirring device such as a paddle screw for stirring the developer can be eliminated. In addition, compared to a two component developing method, less magnetic carrier is required. Therefore, torque of the apparatus can be greatly reduced. From these points, the apparatus can be made compact and the cost of the apparatus reduced. Furthermore, because the toner in the toner accommodating unit can be directly supplied to the developer on the developer bearing member passing a developing area, the toner is promptly supplied to a part of the developer on the developer bearing member, where the toner density has been reduced by passing through the developing area. Accordingly, the developing devices can develop a solid image without decreasing the image density. 
     However, in such developing devices with a self toner density control capability, background soiling and decrease of image density occasionally occur with the lapse of time. Also, uneven image density sometimes occurs in a widthwise direction of an image, which direction is perpendicular to the direction in which the developer on the developer bearing member is conveyed (hereinafter referred to as the image width direction). The inventors of the present invention have analyzed the causes of the decrease in the image quality, and have found that the followings are some of the possible causes. 
     First, background soiling and decrease of image density with the lapse of time might be caused by an early deterioration of developer due to insufficient replacement of the developer on a developer bearing member with the developer in a developer accommodating unit. That is, if the developer carried on the developer bearing member is conveyed without being peeled off the developer bearing member at all, the developer on the developer bearing member is hardly replaced with the developer in the developer accommodating unit. If such replacement of the developer is not made, stress to the magnetic carrier in the developer carried on the developer bearing member is increased, which may lead to a deterioration of the magnetic carrier earlier than the magnetic carrier in the developer accommodated in the developer accommodating unit. If the magnetic carrier on the developer bearing member deteriorates earlier than the magnetic carrier in the developer in the developer accommodating unit, even when the developer as a whole in the developing device is not deteriorated so much, the charging capability of the magnetic carrier on the developer bearing member, that acts on a formation of a toner image, might be decreased. The decrease of the charging capability of the developer on the developer bearing member causes background soiling or decrease in the image density, thereby decreasing the image quality. Accordingly, the developer is forced to be replaced earlier than desired. 
     If a replacement of the developer on a developer bearing member with the developer in a developer accommodating unit is not sufficiently performed, inferior toner charging may also result. Namely, when such a replacement of the developer is not made, the toner in an amount corresponding to a consumed amount of the toner on the developer bearing member, which has been supplied onto the developer bearing member, must be mixed thereupon with the developer so as to be charged. However, when the surface moving speed of the developer bearing member is relatively fast (e.g., several hundred rpm when the developer bearing member is a roller), the toner can not be sufficiently charged in time for development, thereby causing an inferior charging of the toner. In particular, when much toner has been consumed at some parts of the developer bearing member, decrease of image density remarkably appears in such parts compared to other parts, thereby leading to a decrease of the image quality. 
     Secondly, uneven image density in the width direction of the developer bearing member (i.e., in the image width direction) might be caused by uneven toner charging in the width direction of the developer bearing member. When new toner is supplied to a part of the developer where toner has been consumed, supplying of the new toner might be delayed or the supplying quantity of the new toner might be varied. Such a delay in supplying new toner or an uneven new toner supplying amount causes a decrease in the toner density of the developer at the corresponding parts of the developer, and as a result the toner charging amount increases. In particular, when an image consuming a large amount of toner, such as one having a solid part, is formed, supplying of a sufficient amount of toner to a part of the developer, where the large amount of toner has been consumed, can not be made in time for a next development, and the next development might be performed with developer with decreased toner density at that part of the developer. Also, because toner is rather rapidly taken into a part of the developer where a large amount of toner has been consumed, extra toner may be unnecessarily taken into the part of the developer, leading to a development of a subsequent image with unnecessarily high toner density at that part of the developer. 
     Further, because toner is not consumed at non-image parts of an image, toner should not be taken into such parts of the developer corresponding to the non-image parts of the image. However, a small amount of the toner might be also taken into such parts of the developer corresponding to the non-image parts of the image, thereby causing an increase of the toner density and resulting in a decrease of the toner charging. 
     Thus, if uneven toner density or uneven toner charging occurs in the developer on the developer bearing member in the width direction of the developer bearing member, uneven image density is caused in the width direction of the developer bearing member such that a part of the image corresponding to a part of the developer where the toner density is low and the toner charging is high is relatively faint, forming a white strip, and a non-image part corresponding to a part of the developer where the toner density is high and the toner charging is low is relatively dark. 
     In addition, uneven image density in the width direction of the developer bearing member might be also caused by a variation in the dimension or position of a toner supplying opening of a toner accommodating unit in the width direction of the developer bearing member or by a variation of a magnetic force of a magnetic roller, that is provided inside of the developer bearing member as a magnetic force generating device, in the width direction of the developer bearing member. 
     Furthermore, the inventors of the present invention have also found that uneven image density in the width direction of a developer bearing member might be also caused by surface roughness of a part of a second developer regulating member opposing the developer bearing member or by an insufficient pressing force of an agitator provided in a toner accommodating unit for pressing the toner to be conveyed. Specifically, the surface roughness of the part of the second developer regulating member opposing the developer bearing member affects the quantity of toner to be taken into the developer. If the surface roughness is uneven in the width direction of the developer bearing member, the quantity of toner to be taken into the developer becomes uneven in the width direction of the developer bearing member, and thereby uneven image density is caused in the width direction of the developer bearing member. The toner pressing force of the agitator in the toner accommodating unit also affects the quantity of toner to be taken into the developer. If the toner pressing force of the agitator is uneven in the width direction of the developer bearing member, and when the toner pressing force is not sufficient to convey toner to a part of the developer where a large amount of toner is necessary for forming, for example, a solid image, the toner cannot be sufficiently taken into such a part of the developer, thereby causing uneven image density in the width direction of the developer bearing member. 
     The inventor of the present invention has proposed a developing device having a second developer regulating member, in which a developer peeling off member for peeling off the developer on a developer bearing member and a developer stirring member for stirring the developer are provided in a developer accommodating unit for preventing the above-discussed uneven image density from occurring (see e.g. Japanese Laid-open Patent Publication No. 10-232540). In that developing device, all of the developer carried and conveyed by the developer bearing member inside the developer accommodating unit is once peeled off by the developer peeling off member and the peeled off developer is stirred by the stirring member. According to a result of an experiment recently made by the inventors of the present invention with the above developing device, it has been found that the self toner density control is not stable enough and that in the worst case the self toner density control does not appropriately function. Specifically, because all of the developer on the developer bearing member is peeled off in the developer accommodating unit, the peeled off developer is accommodated in the developer accommodating unit one after another until the space in the developer accommodating unit is filled with the peeled off developer. Therefore, when the toner density is increased, it is hard to suppress a movement of the developer on the developer bearing member at the upstream side of the developer peeling off member in the developer conveying direction, such that a developer accumulated portion is not formed as desired upstream of the second developer regulating member in the developer conveying direction. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-discussed and other problems and addresses the above-discussed and other problems. 
     Preferred embodiments of the present invention provide a novel developing device and image forming device using the developing device, which prevent background soiling and decrease of image density due to a lapse of time while maintaining a stable self toner density control, and which at the same time perform a satisfactory development without causing uneven image density in the width direction of a developer bearing member, which is perpendicular to a direction in which the developer on the developer bearing member is conveyed. 
     Preferred embodiments of the present invention also provide a novel developing device and image forming apparatus using the developing device, which performs a satisfactory development without causing uneven image density in the width direction of the developer bearing member while keeping a stable self toner density control. 
     According to a preferred embodiment of the present invention, a developing device includes a developer bearing member which includes an internal magnetic field generating device and which is configured such that a surface thereof moves so as to carry and convey a developer including toner and carrier. A developer regulating member is configured to regulate a quantity of the developer carried and conveyed by the developer bearing member toward a developing area, and a developer accommodating unit is configured to accommodate the developer regulated to be conveyed toward the developing area by the developer regulating member. A toner accommodating unit is configured to have a toner supplying opening opposing a surface of the developer bearing member at a position adjacent to and upstream of the developer accommodating unit in a developer conveying direction. The toner in the toner accommodating unit is taken into the developer on the developer bearing member based on a toner density of the developer on the developer bearing member by a movement of the developer with a conveyance of the developer on the developer bearing member. According to the preferred embodiment, the developing device further includes a peeling off member that opposes, without contacting, a surface of the developer bearing member in the developer accommodating unit so as to peel off an upper layer part of the developer carried and conveyed by the developer bearing member. 
     In the developing device of the above preferred embodiment, an upper layer part of the developer on the developer bearing member, which is conveyed to a position opposing the developer accommodating unit, is peeled off by the peeling off member in the developer accommodating unit. The developer thus peeled off by the peeling off member is mixed with the developer accommodated in the developer accommodating part. By this mixing of the developer, the toner taken in the developer is stirred and distributed, and at the same time the charging of the toner is accelerated, and thereby the distribution and the charging amount of the toner in the developer on the developer bearing member are made uniform. A part of the developer thus mixed in the developer accommodating unit is carried by the developing sleeve at the downstream side of the peeling off member in the developer conveying direction together with the developer carried by the developer bearing member without having been peeled off by the peeling off member. The developer on the developer bearing member is regulated by the developer regulating member so as to have a predetermined layer thickness and is then used for development. Because only the upper layer part of the developer on the developer bearing member is peeled off, the effect of peeling off the developer relative to the conveyance of the developer on the developer bearing member is suppressed and thereby the self toner density control is stably performed without being deteriorated. 
     According to another preferred embodiment of the present invention, the developing device includes a developer stirring member which opposes, without contacting, a surface of the developer bearing member in the developer accommodating unit at a position adjacent to the toner accommodating unit so as to stir a part of the developer carried and conveyed by the developer bearing member, where the toner has been taken into the developer from the toner accommodating unit. 
     In the developing device of the above another preferred embodiment of the present invention, the upper layer part of the developer on the developer bearing member entered into the developer accommodating part is peeled off by the developer stirring member which opposes, without contacting, a surface of the developer bearing member in the developer accommodating unit at the position adjacent to the toner accommodating part. By this stirring of the developer, the mixing of the developer on the developer bearing member and that accommodated in the developer accommodating unit is performed. Further, by this stirring of the developer, the toner which has been taken in the upper layer part of the developer on the developer bearing member is stirred and mixed with the developer such that the toner density of the developer is made uniform. Thus, the developer in which the toner density is made uniform is carried by the developer bearing member and conveyed to a developing area so as to be used for development. 
     According to still another preferred embodiment of the present invention, the developing device includes a flexible plate-like member which opposes, without contacting, a surface of the developer bearing member in the developer accommodating unit at a position adjacent to the toner accommodating unit so as to contact a part of the developer carried and conveyed by the developer bearing member, where the toner has been taken into the developer from the toner accommodating unit. 
     In the developing device according to the above another still preferred embodiment, a flexible plate-like member opposing a surface of the developer bearing member at a position adjacent to the toner accommodating part in the developer accommodating unit contacts the supplied toner existing on the upper layer part of the developer on the developer bearing member entered into the developer accommodating part. When the supplied toner contacts the flexible plate-like member, the flexible plate-like member is bent or restored by a pressure force of the toner attempting to pass the flexible plate-like member, thereby preventing the excessive toner existing on the upper layer part of the developer on the developer bearing member from being conveyed to an area at the downstream side of the flexible plate-like member in the developer conveying direction together with the developer on the developer bearing member. Further, because of the flexible plate-like member, the supplied toner existing on the upper layer part of the developer on the developer bearing member is uniformly distributed in a width direction of the developer bearing member, which is perpendicular to the developer conveying direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in conjunction with accompanying drawings, wherein: 
     FIG. 1 is a schematic drawing illustrating a laser printer as an example of an electrophotographic image forming apparatus to which a developing device according to an embodiment of the present invention is applied; 
     FIG. 2 is a schematic drawing illustrating an exemplary overall construction of the developing device; 
     FIG. 3 is an enlarged view of a main part of the developing device; 
     FIG. 4 is a schematic drawing for explaining a positional relationship among a developing sleeve, a peeling off roller, and a pre-doctor of the developing device; 
     FIG. 5 is a side view of the peeling off roller; 
     FIGS.  6 ( a ) and  6 ( b ) are schematic drawings for explaining a self toner density control mechanism in the developing device; 
     FIG. 7 is an exemplary block diagram of a control part of the laser printer; 
     FIG. 8 is a graph explaining a relation between temperature and a coagulation degree of toner; 
     FIG. 9 is a graph explaining a relation between humidity and a coagulation degree of toner; 
     FIG. 10 is an enlarged view of a main part of the developing device including a peeling off member having a scooping surface for scooping the developer on the developing sleeve so as to be peeled off the developing sleeve; 
     FIG. 11 is a diagram illustrating a test chart used for an experiment, in which black stripes are formed at intervals in a width direction of the chart; 
     FIG. 12 is a front view illustrating an exemplary construction of a printer according to another embodiment of the present invention; 
     FIG. 13 is a cross-section of a developing device of the printer; 
     FIG. 14 is a cross-section of the developing device in which a magnetic roller is used for the peeling off roller; 
     FIG. 15 is another cross-section of the developing device in which another exemplary magnetic roller is used for the peeling off roller; 
     FIG. 16 is a perspective view of the another exemplary magnetic roller; 
     FIGS.  17 ( a )- 17 ( c ) are diagrams illustrating peeling off rollers in which N and S poles are alternately magnetized in the axial direction of the peeling off rollers; 
     FIGS.  18 ( a )- 18 ( e ) are diagrams illustrating half-tone images formed on sheets, respectively having residual black stripes of different density; 
     FIG. 19 is a schematic drawing illustrating a developing device according to still another embodiment of the present invention; 
     FIG. 20 is a perspective view of a peeling off member used in the developing device of FIG. 19; 
     FIG. 21 is a perspective view of another peeling off member of the developing device; 
     FIG. 22 is a schematic drawing indicating intervals of relevant parts of the developing device; 
     FIG. 23 is a schematic drawing illustrating a developing device according to still another embodiment of the present invention; 
     FIG. 24 is a schematic drawing indicating an arrangement position of a stirring comb member in the developing device; 
     FIG. 25 is a perspective view of the stirring comb member; 
     FIG. 26 is a schematic drawing illustrating a developing device according to still another embodiment of the present invention; 
     FIG. 27 is a partly enlarged schematic drawing illustrating a developer accommodating part and a toner take-in part of the developing device of FIG. 26, including a sheet member; 
     FIG. 28 is an enlarged schematic drawing illustrating the developer accommodating part and the toner take-in part of the developing device, in which another example of the sheet member is included; 
     FIG. 29 is an enlarged schematic drawing illustrating the developer accommodating part and the toner take-in part of the developing device, in which another example of the sheet member is included; 
     FIG. 30 is an enlarged schematic drawing illustrating the developer accommodating part and the toner take-in part of the developing device, in which another example of the sheet member is included; and 
     FIG. 31 is an enlarged schematic drawing illustrating the developer accommodating part and the toner take-in part of the developing device, in which another example of the sheet member is included. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, preferred embodiments of the present invention are described. 
     FIG. 1 illustrates a laser printer (hereinafter referred to as a printer) as an example of an electrophotographic image forming apparatus in which a developing device according to an embodiment of the present invention can be applied. 
     A photoconductive drum  1  as a latent image bearing member is rotated in the direction indicated by arrow A in FIG. 1, and is uniformly charged, while being rotated, by a charging roller  50  contacting a surface of the photoconductive drum  1 . The surface of the photoconductive drum  1  is scanned and exposed by a light according to image information with an optical writing unit  51 , thereby forming a latent image thereupon. In this embodiment, a charging roller  50  and the optical writing unit  51  are used for a latent image forming device. However, any other types of charging devices and writing units can be used for the latent image forming device. The latent image formed on the photoconductive drum  1  is developed by a later described developing device  2  so as to form a toner image on the photoconductive drum  1 . The toner image formed on the photoconductive drum  1  is transferred to a sheet  52  as a transfer member by a transfer device having a transfer roller  53 . The sheet  52  is conveyed from a sheet feeding cassette  54  via a feeding roller  55  and a registration roller pair  56 . The sheet  52  after completion of the transfer passes a fixing unit  57 , where the toner image is fixed to the sheet  52 , and the sheet  52  is then discharged out of the apparatus. Residual toner on the photoconductive drum  1  is removed from the drum  1  by a cleaning unit  58 , and further, residual charge on the photoconductive drum i is removed by a discharging lamp  59 . 
     FIG. 2 illustrates an exemplary overall construction of the developing device  2 , and FIG. 3 illustrates a main part of the developing device  2 . 
     The developing device  2  is arranged beside the photoconductive drum  1 , and includes a developing sleeve  4  of non-magnetic material as a developer bearing member to carry on its surface a two-component developer  3  (hereinafter referred to as a developer) including a toner  3 a and a magnetic carrier (hereinafter simply referred to as a carrier). The developing sleeve  4  is disposed so as to be partly exposed through an opening of a casing  2   a , that is formed at the side of the photoconductive drum  1 . The developing sleeve  4  is configured so as to be driven to be rotated by a driving device (not shown) in a direction indicated by arrow B to convey the developer  3  downward in a developing area opposing the photoconductive drum  1 . A magnetic roller  5  including a series of fixed magnets is provided inside the developing sleeve  4  as a magnetic field generating device. 
     The developing device further includes a doctor  6  as a developer regulating member for regulating the quantity of the developer carried and conveyed by the developing sleeve  4  toward the developing area, a developer accommodating case  7  configured so as to form a developer accommodating part S to accommodate the developer  3  between a surface of the developing sleeve  4  and the doctor blade  6  upstream of the doctor blade  6  in a direction in which the developer  3  is conveyed, and a toner hopper  8  as a toner accommodating part. The toner hopper  8  includes a toner supplying opening  8   a  opposing a surface of the developing sleeve  4  at a position adjacent to and upstream of the developer accommodating part S in the direction in which the developer  3  on the developer sleeve  4  is conveyed. Inside the toner hopper  8 , a toner agitator  9  as a toner stirring member is arranged so as to be driven in a clockwise direction indicated by arrow C to stir and convey the toner  3   a  toward the toner supplying opening  8   a.    
     An end part (eaves part) of the developer accommodating case  7  in close proximity to the developing sleeve  4  is used as a pre-doctor blade  7   a  as a second developer regulating member that regulates the quantity of the developer, to which the toner  3   a  has been supplied from the toner hopper  8  and which attempts to move toward the developer accommodating part S. The developer regulated by the doctor  6  to move to the developing area is also accommodated in the developer accommodating part S. 
     A plurality of magnetic poles are formed at a surface part of the magnetic roller  5  so as to extend in an axial direction of the magnetic roller  5 . Specifically, a primary pole N 1  is disposed in a position opposing the developing area, and a secondary pole S 2  is disposed between a position opposing the pre-doctor  7   a  and a position reaching the developing area so that a magnetic force of the magnetic field reaches the developer accommodating part S. Further, as generally practiced in developing devices for an image forming apparatus, magnetic poles (S and N poles) for carrying the developer on the developing sleeve  4  to convey the developer are arranged on a surface of the magnetic roller  5  in an appropriate manner. 
     In this embodiment, a fixed magnet member in which a magnet piece is engaged with and fixed to a substrate member, a so-called block type magnetic roller, is used for the magnetic roller  5 , but any other type of the magnetic roller  5  can be used. For example, a so-called integrated plastic magnetic roller of ferrite system, which is made by magnetizing a plastic magnetic member molded in a certain shape at the same time the magnetic poles are arranged, can be used. 
     The developing device further includes a peeling off roller  11  as a peeling off member, that opposes, without contacting, a surface of the developing sleeve  4  in the developer accommodating part S so as to peel off a part (a surface layer part) of the developer carried and conveyed by the developing sleeve  4 . In this embodiment, a roller-like rotating member formed by a magnetic member is used for the peeling off roller  11 , but the peeling off roller  11  can be formed in a cylinder-like shape. 
     For the peeling off roller  11 , a magnetic member such as a SUM member (sulfur and sulfur-mixed finely-ground steel member), a SUS member having magnetism, steel, nickel, and so forth, can be used. Also, a steel core plated with nickel and a stainless member coated with magnetic material can be used. 
     The surface of the peeling off roller  11  is preferably roughened by a sand blasting process and so forth so as to securely carry and convey the developer peeled off the developing sleeve  4 . The surface roughness of the peeling off roller  11  may be set, for example, to about 30 μm as defined by JIS (Japan Industrial Standard). The surface roughness of the peeling off roller  11  may be appropriately set so that the developer can be conveyed according to conditions such as the kind of toner and material of the peeling off roller  11 . 
     The peeling off roller  11  is driven to rotate in the same direction as the developing sleeve  4  (in the direction indicated by arrow E) by a driving device (not shown). Because of this rotation, at a part where the developing sleeve  4  and the peeling off roller  14  oppose each other, the surface of the peeling off roller  14  moves in an opposite direction relative to a surface moving direction of the developing sleeve  4 . Thereby, the upper layer part of the developer on the developing sleeve  4  is blocked by the peeling off roller  11  to be securely peeled off the developing sleeve  4 . The developer thus peeled off is conveyed with the surface movement of the peeling off roller  11  to separate from the surface of the developing sleeve  4 , and is then mixed with the developer in the developer accommodating part S. 
     The magnetic pole S 2  of the magnetic roller  5  opposing the developer accommodating part S is disposed so as not to be located between the position opposing the peeling off roller  11  and the position opposing the pre-doctor  7   a . In this embodiment, as illustrated in FIG. 4, the position of the magnetic pole S 2  is set so that the angle θ between a line passing through the center of the magnetic roller  5  and that of the peeling off roller  11  and a line passing through the center of the magnetic roller  5  and the magnetic pole S 2  is 2-10 degrees. 
     By thus avoiding the magnetic pole to be disposed between the position opposing the peeling off roller  11  and the position opposing the doctor blade  7   a , an abnormal flow of the developer in the developer accommodating part S, such as the one attracted toward a gap between the pre-doctor blade  7   a  and the surface of the developing sleeve  4 , is avoided regardless of the toner density of the developer. 
     Further, it is preferable to set a gap Gh between the peeling off roller  11  and the surface of the developing sleeve  4  and a gap Gd2 between the pre-doctor  7   a  and the surface of the developing sleeve  4  so as to satisfy the relation: 0&lt;Gh&lt;Gd2. By thus setting the gaps Gh and Gd2, the upper layer part of the developer conveyed by the developing sleeve  4 , into which the toner has been taken from the toner hopper  8  and which has passed the regulating position by the pre-doctor blade  7   a , securely contacts the peeling off roller  11  to be peeled off. 
     When the peeling off roller  11  made of a magnetic member is used, a magnetic pole is generated at a surface of the peeling off roller  11  by a magnetic force action of the magnetic roller  5  in the developing sleeve  4 , and thereby the developer  3  on the developing sleeve  4  can be efficiently peeled off. However, because of the magnetic force acting on the peeling off roller  11 , the center part of the peeling off roller  11  in the axial direction of the peeling off roller  11  is bent so as to come closer to the developing sleeve  4 , and thereby the gap relative to the developing sleeve  4  may become smaller than desired. 
     Therefore, when the peeling off roller  11  is configured to be bent as above, as illustrated in FIG. 5, a diameter D2 at the center part of the peeling off roller  11  is preferably made smaller than a diameter D1 of both end parts of the peeling off roller  11 . With the use of the peeling off roller  11  configured as above, the gap between the peeling off roller  11  and the developing sleeve  4  can be made substantially uniform over the entire length of the peeling off roller  11  in the axial direction thereof Accordingly, a uniform peeling off operation can be performed over the entire part of the peeling off roller  11  from the center part to the both end parts thereof. 
     When the peeling off roller  11  is configured not to be bent, the peeling off roller  11  can be formed in a straight rod-like shape having a circular cross-section with a constant diameter over the entire length thereof in the axial direction. 
     Now, an exemplary developing operation of the above-described developing device is described with reference to FIGS. 2 and 3. 
     The developer  3  on the developing sleeve  4  is conveyed with a rotation of the developing sleeve  4  in the direction of the arrow B, and is regulated by the doctor  6  so as to be thinly layered. The thinly layered developer  3  is conveyed to the developing area opposing the photoconductive drum  1  rotating in the direction of the arrow A. In this developing area, toner is supplied to a latent image formed on the photoconductive drum  1  to visualize the latent image. The developer on the developing sleeve  4  which has passed the developing area is further conveyed with the rotation of the developing sleeve  4  to reach the position opposing the toner supplying opening  8   a . At the toner supplying opening  8   a , the toner  3   a  conveyed thereto by the agitator  9  from the toner hopper  8  halts there so as to contact the developer on the developing sleeve  4 . The developer on the developing sleeve  4  returns, after taking the new toner  3   a  therein to at the toner supplying opening  8   a , to the developer accommodating part S. The developer containing the new toner  3   a  is regulated by the doctor  6  and thereby the internal pressure of the developer increases. The toner is charged by friction with the carrier in the developer having thus increased internal pressure. A part of the developer  3  regulated by the doctor  6  so as not to be conveyed to the developing area is moved so as to be circulated in the developer accommodating part S. 
     Next, an exemplary self toner density control operation of the developing device is described with reference to FIGS.  6 ( a ) and  6 ( b ). In FIGS.  6 ( a ) and  6 ( b ), a two-dot chain line indicates an interface between developers having different behaviors from each other. 
     First, a developer having a predetermined toner density and a predetermined weight is set in the developing device as an initial developer, and by driving the developing sleeve  4  and the peeling off roller  11  so as to rotate, the developer  3  is divided into three parts, a conveyed developer  3   b , an accommodated developer  3   c , and a peeled off developer  3   d . The conveyed developer  3   b  is the developer that is carried on a surface of the developer sleeve  4  by a magnetic force and conveyed by being brought around by the surface of the developing sleeve  4 . The accommodated developer  3   c  is the developer that is accommodated in the developer accommodating part S and that moves in the developer accommodating part S to circulate therein with a movement of the conveyed developer  3   b . The peeled off developer  3   d  is the developer that is peeled off the conveyed developer  3   b  on the developing sleeve  4  and that moves along a surface of the peeling off roller  11  with a rotation of the peeling off roller  11 . 
     In the developer accommodating part S, as illustrated in FIG.  6 ( a ), four developer flows F 1 , F 2 , F 3 , and F 4  are generated. The first developer flow F 1  is the flow of the conveyed developer  3   b  passing between the developing sleeve  4  and the peeling off roller  11 . The second developer flow F 2  is the circulating flow of a part of the peeled off developer  3   d  that is peeled off the developing sleeve  4  and that moves along the peeling off roller  11  so as to circulate in a space between the peeling off roller  11  and the pre-doctor  7   a . The third developer flow F 3  is the flow of a part of the peeled off developer  3   d  that flows along a surface of the peeling off roller  11  above the peeling off roller  11 . The fourth developer flow F 4  is the circulating flow of the accommodated developer  3   c  that rises along a back surface of the doctor  6  due to the regulation by the doctor  6  to circulate in a space between the doctor  6  and the peeling off roller  11 . 
     Under conditions that the above four developer flows F 1 -F 4  are generated in the developer accommodating part S, if the toner  3   a  is put in the toner hopper  8 , the toner  3   a  is supplied from the toner supplying opening  8   a  to the conveyed developer  3   b  carried by the developing sleeve  4 . The conveyed developer  3   b  to which the toner  3   a  has been supplied is conveyed to the developer accommodating part S together with the supplied toner  3   a . While the conveyed developer  3   a  is being thus conveyed, the toner  3   a  which has been supplied to the conveyed developer  3   b  slightly shifts toward the axial center of the developing sleeve  4 . After the conveyed developer  3   b  to which the toner  3   a  has been supplied passes the regulation position of the pre-doctor  7   a , the upper layer part thereof is peeled off by the peeling off roller  11  to become the peeled off developer  3   d . The peeled off developer  3   d  is conveyed while being mixed with the accommodated developer  3   c , and a part thereof merges with the above circulating developer flow F 2  generated in a vicinity of the pre-doctor  7   a . The peeled off developer  3   d  being carried and conveyed by the peeling off roller  11  is further conveyed while being mixed with the accommodated developer  3   c , and is then carried again by the developing sleeve  4  downstream of the peeling off roller  11  in the developer conveying direction to become the conveyed developer  3   b . By this mixing of the peeled off developer  3   d  with the accommodated developer  3   c , replacement of a part of the peeled off developer  3   d  with the accommodated developer  3   c , uniform distribution of the toner  3   a  in the developer, and toner charging by a frictional charging between the toner and the carrier are realized. 
     As the toner density of the developer  3  gradually rises with the above supply of the toner  3   a  to the developer  3 , the volume of the developer  3  increases and thereby the layer of t he conveyed developer  3   b  on the developing sleeve  4  becomes thick in the area from the position opposing the toner supplying opening  8   a  to the regulation position by the doctor  6 . 
     Because the ratio of the carrier in the conveyed developer  3   b  on the developing sleeve  4  decreases as the layer thickness of the conveyed developer  3   b  increases, the magnetic force acting on the conveyed developer  3   b  decreases, and thereby the moving speed of the conveyed developer  3   b  decreases, resulting in further increasing the layer thickness of the conveyed developer  3   b  on the developing sleeve  4  in the above area. This conveyed developer  3   b  on the developing sleeve  4  with the increased layer thickness receives a rather strong braking force in a direction of stopping the conveyance of the conveyed developer  3   b  from the peeling off roller  11 , and thereby the moving speed of the conveyed developer  3   b  being conveyed toward the peeling off position by the peeling off roller  11  decreases even more. 
     The upper layer part of the conveyed developer  3   b  with the layer thickness having been increased at the position opposing the toner supplying opening  8   a  is peeled off by the pre-doctor  7   a , and the peeled off developer starts to halt, as illustrated in FIG.  6 ( a ), at an upstream side of the pre-doctor  7   a  in the developer conveying direction. Hereinafter, the halting developer is referred to as halting developer  3   e . The halting developer  3   e  circulates along with a movement of the conveyed developer  3   b  contacting the halting developer  3   e . The toner  3   a  supplied to the toner supplying opening  8   a  is attracted to an exposed part of the conveyed developer  3   b , and is taken into the conveyed developer  3   b  at a merging point P where the conveyed developer  3   b  and the halting developer  3   e  merge with each other. 
     As the toner density of the developer  3  further increases, as illustrated in FIG.  6 ( b ), the quantity of the halting developer  3   e  at the toner supplying opening  8   a  increases so that the exposed surface of the conveyed developer  3   b  contacting the toner  3   a  is closed by the halting developer  3   e  and the merging point P moves up to an upstream end of the toner supplying opening  8   a  in the developer conveying direction, and at the same time, the circulating and moving speed of the halting developer  3   d  at the toner supplying opening  8   a  decreases, and finally the take-in of the toner  3   a  into the developer is completed and the toner density stops increasing. 
     The upper layer part of the conveyed developer  3   b , into which the toner  3   a  has been taken and which has passed the gap between the pre-doctor  7   a  and the developing sleeve  4 , is peeled off by the peeling off roller  11 . The peeled off developer  3   d  is conveyed along a surface of the peeling off roller  11  while being mixed with the accommodated developer  3   c , and a part thereof is again carried on the developer sleeve  4 . The conveyed developer  3   b  which has passed the gap between the developer sleeve  4  and the doctor  6  is conveyed to the developing area opposing the photoconductive drum  1 . In the developing area the toner is supplied to a latent image formed on the photoconductive drum  1  so as to be used for development of the latent image. 
     As the toner  3   a  on the developing sleeve  4  is consumed as a result of the development of the latent image on the photoconductive drum  1 , the toner density of the corresponding part of the conveyed developer  3   b  decreases, the conveying force by the developing sleeve  4  acting on that part of the conveyed developer  3   b  increases, and further, the volume of that part of the conveyed developer  3   b  decreases. Then, the layer thickness of the conveyed developer  3   b  regulated by a tip end of the pre-doctor  7   a  decreases, the quantity of the halting developer  3   e  halting in the vicinity of the toner supplying opening  8   a  decreases, and the circulating and moving speed of the halting developer  3   e  increases. Thereby, the conveyed developer  3   b  conveyed by the developing sleeve  4  is caused to contact the toner  3   a  from the toner hopper  8 , such that the toner  3   a  is again taken into the conveyed developer  3   b  and the toner density of the developer  3  is increased as described above. 
     As described above, according to a change of the toner density on the developing sleeve  4 , the regulating condition with the pre-doctor  7   a  for the conveyed developer  3   b  on the developing sleeve  4  changes, and thereby the toner density of a part of the developer where the toner has been consumed is self controlled so as to be within a predetermined range. With this self control, the toner density of the conveyed developer  3   b  on the developing sleeve  4  is maintained to be constantly in a fixed range. Therefore, a complicated toner density control mechanism including, for example, a toner sensor and a toner supplying member, is not necessary. 
     According to the above-described embodiment of the present invention, by peeling off a part of the conveyed developer  3   b  on the developing sleeve  4  so as to be mixed with the accommodated developer  3   c  in the developer accommodating part S, replacement of the conveyed developer  3   b  with the accommodated developer  3   c  is accelerated, so that early deterioration of the developer  3  due to a decrease of the charging capability of the carrier in the developer  3  is prevented. In addition, by mixing the conveyed developer  3   b  with the accommodated developer  3   c , the toner in the developer  3  is stirred and distributed such that the toner density of the developer  3  is made uniform with respect to an image width direction perpendicular to the developer conveying direction, making it possible to perform a satisfactory development without having uneven image density. 
     Further, according to the above-described embodiment of the present invention, because the peeling off roller  11  having a circular shape in its cross-section is used, the gap between the circumferential surface of the peeling off roller  11  and that of the developing sleeve  4  does not change even when the peeling roller  11  rotates. Therefore, an uneven peeling off does not occur. Accordingly, variation of the toner density and toner charging is suppressed with respect to the conveyed developer  3   b  on the developing sleeve  4  in the developer conveying direction, and thereby uneven image density in the developer conveying direction can be avoided. According to an experiment made by the inventors of the present invention, when a peeling off member having other shapes than a circular cross-section, for example a crank-like shape, is used, an uneven peeling off occurs, resulting in having uneven image density at a pitch corresponding to a rotation pitch of the crank-like shaped peeling off roller. 
     According to the above-described embodiment of the present invention, because the peeling off roller  1  made of a magnetic member is used, by magnetizing the peeling off roller  11  by the magnetic roller  5  in the developing sleeve  4 , a part of the conveyed developer  3   b  carried on and conveyed by the developing sleeve  4  can be attracted to the peeling off roller  11  by a magnetic force. Accordingly, peeling the developer off the developing sleeve  4  and generating the developer flow to force the peeled off developer to move along a surface of the peeling off roller  11  as indicated by F 3  in FIG.  6 ( a ) can be made rather remarkably, and thereby mixing and stirring of the peeled off developer with the developer in the developer accommodating part S is further efficiently made. 
     In the above-described embodiment, the peeling off roller  11  may be configured such that the rotation speed thereof is controlled according to the ratio of an image part and a non-image part of an original document for printing or the result of detecting a temperature and humidity condition in the apparatus. 
     FIG. 7 is a block diagram of an exemplary control part of the printer according to the above-described embodiment of the present invention. Image data received from an outside apparatus  200  such as a personal computer is processed by an image data processing part  110 . In this image data processing by the image data processing part  110 , data for forming a latent image, that is used at the latent image forming part, is generated and the image ratio data of an image for printing is calculated. An engine control part  100  controls each part of the apparatus according to the data sent from the image data processing part  110 . The engine control part  100  includes an engine control CPU  101 , a ROM  102 , a RAM  103 , and an I/O interface  104 . To the engine control part  100 , a photoconductive drum driving part  105 , a driving part  106  for the latent image forming part, a developing device driving part  107 , and a temperature and humidity sensor  108  are connected. The engine control CPU  101  outputs various instructions to each part of the apparatus so as to be operated according to a control program read out from the ROM  102  and in response to an input signal from the image data processing part  110 , while performing various recognition and determination operations such as ones relating to operating timings of respective driving parts. The engine control CPU  101  also controls each part of the apparatus according to temperature and humidity data obtained by the temperature and humidity sensor  108 . 
     The engine control part  100  controls the rotation of the peeling off roller  11  of the developing device  2 , for example, according to the image ratio data of an image for printing. More specifically, the circumferential moving speed of the peeling off roller  11  is changed according to a toner consumption, which changes according to the image ratio, so as to appropriately charge the toner and to avoid unnecessary mixing of the developer, thereby preventing a deterioration of the developer. 
     Further, it has been found in an experiment performed by the inventors of the present invention that the quantity of the taken-in toner  3   a , the conveying speed of the developer  3 , and the volume of the developer  3  change according to the coagulation degree of the toner  3   a , which changes based on environmental conditions. The coagulation degree of the toner  3   a  changes based on the temperature and humidity, and as illustrated in FIGS. 8 and 9, the coagulation degree rises under a high temperature condition and under a high humidity condition as well. A higher coagulation degree indicates that the toner  3   a  has become hard. 
     Accordingly, an ambient temperature near the photoconductive drum  1  is measured by the temperature and humidity sensor  108  provided inside the apparatus, and when the temperature rises, the linear speed of the peeling off roller  11  is increased by increasing the number of rotations of the peeling off roller  11 . Thereby, the developer  3  is sufficiently mixed and stirred, and by which replacement of the developer  3  with each other and frictionally charging of the developer  3  are sufficiently accelerated. Also, the humidity inside the apparatus is measured by the temperature and humidity sensor  108 , and when the humidity rises, by controlling the driving of the peeling off roller  11  in substantially the same manner as when the temperature rises, the developer  3  is sufficiently mixed and stirred, such that replacement of the developer  3  with each other and frictionally charging of the developer  3  are sufficiently accelerated. 
     Further, in this embodiment, as illustrated in FIG. 4, the magnetic pole S 2  in the position opposing the developer accommodating part S is slightly deviated to the side of the doctor  6 ; however, the magnetic pole S 2  may be arranged such that the peak position of a density distribution of a magnetic flux generated by the magnetic pole S 2  in a normal line direction substantially coincides with a direction leading to the center of the peeling off roller  11 . By this arrangement, the peeling off roller  11  can be most strongly magnetized and thereby the peeling off and conveying force of the peeling off roller  11  is most greatly exerted. As a result, in the developer accommodating part S, the frictional charging of the developer  3  is effectively made at the gap between the developing sleeve  4  and the peeling off roller  11 . 
     Further, for effectively circulating the developer  3  along the circumferential surface of the peeling off roller  11  in the developer accommodating part S, the magnetic flux distribution in the normal line direction at a circumferential surface of the peeling off roller  11  at the side opposite the surface thereof opposing the developing sleeve  4  may be preferably made to be greater than 5 mT. 
     Furthermore, for effectively circulating the developer  3  along the circumferential surface of the peeling off roller  11  in the developer accommodating part S, a certain space must be maintained in the developer accommodating part S so that the developer  3  can circulate. For maintaining such a space in the developer accommodating part S, the take-in of the toner  3   a  must be stopped while the space remains in the developer accommodating part S. In this respect, the inventors of the present invention found out through various experiments that the space can be maintained in the developer accommodating part S if the following condition (1): MF2&lt;(⅔)MF1 is satisfied, wherein a magnetic force which is received by the developer  3  on the developing sleeve  4  at the position opposing the peeling off roller  11  is MF1 and a magnetic force which is received by the developer  3  on the developing sleeve  4  at the position opposing the pre-doctor  7   a  is MF2. 
     If the above force MF2 becomes relatively large on the developing sleeve  4 , an effect of the breaking force by the peeling off roller  11  does not reach a vicinity of the toner supplying opening  8   a . As a result, the conveying speed of the developer  3  does not decrease even when the toner density of the developer  3  increases, making it difficult to increase the thickness of the layer of the developer  3 . Accordingly, the taking-in of the toner  3   a  can not be stopped until the developer accommodating part S is filled with the developer  3 . Therefore, in this embodiment, as indicated by the condition (1), the magnetic force MF2 which is received by the developer  3  at the position opposing the pre-doctor  7   a  is made weaker relative to the magnetic force MF1 received by the developer  3  at the position opposing the peeling off roller  11 , such that the effect of the breaking force by the peeling roller  11  reaches the vicinity of the toner supplying opening  8   a . The control of a waveform of the magnetic force may be appropriately made according to the position, the magnetism, the shape, and the magnetic force of a magnet piece arranged at each pole. 
     Further, in this embodiment, as the peeling off member, the peeling off roller  11  formed in a rotatable roller-like shape is used; however, the peeling off member can be differently shaped. For example, as illustrated in FIG. 10, a peeling off member  10  having a scooping surface  10   a  may be provided so as to extend substantially over the entire longitudinal area of the developer accommodating space S (the area along an axial direction of the developing sleeve  4 ) for scooping the developer  3  on the developing sleeve  4  so as to be peeled off the developing sleeve  4 . The scooping angle θ of the scooping surface  10   a  of the peeling off member  10  relative to a tangent line to a surface of the developing sleeve  4  is preferably greater than 90 degrees so that the developer  3  is efficiently peeled off without being halted. Because of this scooping surface  10   a  of the peeling off member  10 , the upper layer of the conveyed developer  3   b  being carried and conveyed by the developing sleeve  4  rotating in a counterclockwise direction is peeled off and a developer flow indicated by the arrow D is generated. Due to this flow of the peeled off developer, mixing and stirring of the developer peeled off the developing sleeve  4  and the developer in the developer accommodating part S is accelerated. A part of the developer thus mixed and stirred is carried on the developing sleeve  4  between the peeling off member  10  and the doctor  6  by a magnetic force. 
     Now, a result of an experiment made using a concrete example of the developing device according to the above-described embodiment of the present invention is described. In the experiment, the developing device as illustrated in FIG. 2 was used, and  20  prints were made using a test chart  60  illustrated in FIG.  1 . As illustrated, the test chart  60  includes black stripes which are formed at intervals so that the toner consumption varies in a direction perpendicular to a surface moving direction (indicated by the arrow G in FIG. 11) of the developing sleeve  4 , i.e., an image width direction of the test chart  60 . After making 20 prints of the test chart  60 , another 20 prints were made using another test chart having an even half-tone over the entire surface thereof. The experiment was made under the conditions of Table 1. 
     Table 1 
     Linear speed of the photoconductive drum: 120 mm/sec; 
     Gap Gp between the developing sleeve and the photoconductive drum: 0.3-0.5 mm; 
     Gap Gd 1 between the developing sleeve and the doctor: 0.3-0.5 mm; 
     Gap Gd2 between the developing sleeve and the pre-doctor: 0.5-1.5 mm; 
     Gap Gh between the developing sleeve and the peeling off roller: 0.2-0.4 mm; 
     Diameter of the developing sleeve: 16-20 mm; 
     Linear speed ratio of the developing sleeve and the photoconductive drum: 1.5-3.0; 
     Magnetic flux density (in the normal line direction) on the developing sleeve N 1 : 93 mT; 
     Magnetic flux density (in the normal line direction) on the developing sleeve S 1 : 75 mT; 
     Magnetic flux density (in the normal line direction) on the developing sleeve N 2 : 60 mT; 
     Magnetic flux density (in the normal line direction) on the developing sleeve S 2 : 53 mT; 
     Material of the carrier: magnetite or steel; 
     Particle diameter of the carrier: 40-50 μm; 
     Volume of the magnetic member in the toner: 15-40 wt %; 
     Volume of silica in the toner: 0.5-1.0 wt %; 
     Covered ratio of the toner relative to the carrier: 50-120%; 
     Q/M: 10-30 μc/g. 
     For example, using the peeling off roller  11  having the diameter of 7 mm, the gap Gp was set to 0.35 mm, the gap Gd1 to 0.4 mm, the gap Gd2 to 0.65 mm, and the gap Gh to 0.35 mm. In the experiment made under the conditions as above, the developer peeled off by the peeling roller  11  was well mixed and stirred, such that the developer was made uniform, and thereby a good image without having uneven image density was obtained. In the above example of the developing device, the gap Gh between the developing sleeve  4  and the peeling off roller  11  and the gap Gd2 between the developing sleeve  4  and the pre-doctor  7   a  satisfied the relation: 0&lt;Gh&lt;Gd2, and thereby a good stirring capability was obtained with the peeling off roller  11 . 
     Further, the peeling off roller  11  may be a magnetic member such as a SUM member, and the center part of the peeling off roller  11  may be slightly bent so as to come close to the developing sleeve  4  by 0.1 mm under the condition that the magnetic flux density in the normal line direction on the developing sleeve  4  opposing the peeling off roller  11  is 56 mT. Therefore, the shape of the peeling off roller  11  was made, as illustrated in FIG. 5, such that the center diameter D2 is smaller (6.8 mm) than the diameter D1 at both ends thereof (7 mm). By thus shaping the peeling off roller  11 , the gap between the peeling off roller  11  and the developing sleeve  4  was kept at about 0.35 mm over the entire axial direction of the peeling off roller  11 , and thereby peeling off of the developer  3  and mixing and stirring of the developer  3  thereafter were uniformly made over the entire area of the peeling off roller  11  from the center part to the both ends thereof. 
     On the other hand, when the above test chart having a half-tone image was printed using a conventional developing device in which the peeling off member  12  was not used, uneven image density was observed in the half-tone image. Thus, it has been confirmed that if the peeling off roller  12  is not provided, when printing a test chart having black stripes such that the toner consumption changes in the longitudinal direction of the developing sleeve  4 , the toner density becomes uneven in the longitudinal direction of the developing sleeve  4 , thereby resulting in deteriorating the produced image. 
     FIG. 12 is a front view illustrating an exemplary construction of a printer according to another embodiment of the present invention, and FIG. 13 is a cross-section illustrating an exemplary construction of a developing device of the printer. In FIGS. 12 and 13, the parts similar to those of the printer according to the previous embodiment, illustrated in FIGS. 1 and 2, are denoted by like references, and the description thereof is omitted because the function is substantially the same. One-dot-and-dash lines in FIG. 12 and 13 around the developing sleeve  4  respectively denote the components of a magnetic flux in the normal line direction at a surface of the developing sleeve  4 . 
     In this embodiment, in contrast to the previous embodiment in which the peeling off roller  11  made of a magnetic member is used, a peeling off roller  13  including a magnetic roller, in which the magnetic pole has been magnetized in advance so as to have a magnetic force by itself, is used for the peeling off member. Further, in the developing device, at a bottom part of a casing  2  in a vicinity of a toner supplying opening  8   a , a protruded part  2   b  having an opposing surface  2   c  is formed. The opposing surface  2   c  is formed so as to have a predetermined length and to be inclined downward toward the developing sleeve  4 . The construction of the toner hopper  8  is different from that of the previous embodiment, however, because its relevancy to the invention is very little, the description thereof is omitted. 
     FIG. 14 is a cross-section illustrating the developing device in a more simplified manner than FIG. 13 for highlighting the peeling off roller  13  including a magnetic roller. In this developing device, the peeling off roller  13 , in which a pair of magnetic poles (S and N poles) are arranged at a surface thereof so as to extend along the axial direction thereof, is used, and the peeling off roller  13  is rotated at a position opposing a magnetic pole  5   a  of the developing sleeve  4  as in the previous embodiment. This peeling off roller  13  can more strongly attract the developer  3 , which is carried and conveyed by the developing sleeve  4 , by a magnetic force. Accordingly, a peeling off of the developer  3  from the developing sleeve  4  and an enforced flow of the peeled off developer  3  are more securely performed, and thereby mixing and stirring of the peeled off developer with the developer in the developer accommodating part S is more effectively performed. 
     FIG. 15 is a section view of the developing device including a peeling off roller  14  having another exemplary magnetic roller. The peeling off roller  14  includes a plurality of N and S poles alternately arranged at the circumferential surface thereof. In the example of the peeling off roller  14  illustrated in FIG. 15, four pairs of N and S poles are arranged. The peeling off roller  14  is disposed so as to be rotatable and in a position opposing an S pole  5   a  of the magnet roller  5  arranged in the developing sleeve  4 . When the peeling off roller  14  rotates and one of the S poles arranged at its surface thereof comes close to the S pole  5   a  of the magnet roller  5 , the developer  3  between the peeling off roller  14  and the developing sleeve  4  receives a force to be expelled therefrom. When one of the N poles of the peeling off roller  14  comes close to the S pole  5   a , the developer  3  between the peeling off roller  14  and the developing sleeve  4  receives an attracting force. Thus, expelling and attracting forces are alternately exerted in a small space between the developer sleeve  4  and the peeling off roller  14 , and thereby mixing and stirring of the developer in the space is actively performed so that the toner density is made uniform. Further, because of the magnetic force of the magnetic poles alternately magnetized on the peeling off roller  14 , a part of the developer  3  is attracted to the peeling off roller  14  at other parts than the vicinity of the developing sleeve  4 , and thereby the stirring force is further enhanced. Accordingly, the toner distribution is more effectively made uniform, and thereby an abnormal image such as an image having uneven image density is prevented. 
     Further, as illustrated in FIG. 16, a plurality of poles  14   a ,  14   b  having substantially the same length as that of the peeling off roller  14  in the axial direction thereof may be arranged such that S and N poles are alternately disposed in the circumferential direction. In this case, when the developer  3  adheres to the surface of the peeling off roller  14  to form a layer of the developer  3  threupon, the surface of the layer of the developer  3  is unevenly formed, by which a stirring effect similar to the one obtained when a member having a uneven surface is used for the peeling off roller  14  can be obtained. 
     FIG.  17 ( a ) is a perspective view of another example of the peeling off roller. A peeling off roller  15  is configured such that a magnetic pole having a predetermined length in the axial direction of the peeling off roller  15  is alternately magnetized with a S pole  15   a  and a N pole  15   b  in the axial direction thereof. If the developer  3  adheres to this peeling off roller  15 , in addition to the stirring effect described with respect to the peeling off roller  14  illustrated in FIG. 16, a stirring mechanism is also generated between the poles alternately arranged in the axial direction of the peeling off roller  15 , thus more effectively mixing and stirring the developer  3 . 
     Further, in a peeling off roller  16  illustrated in FIG.  17 ( b ), the N and S poles may be slightly separated from each other in the axial direction thereof, or in a peeling off roller  17  illustrated in FIG.  17 ( c ), the N and S poles may be separated from each other such that the poles of the same polarity overlap with each other in the circumferential direction thereof. 
     Now, a result of an experiment made using a concrete example of the developing device  2  according to the above-described embodiment is described. Using the developing device  2  of FIG. 15,  20  prints were made for the test chart  60  in which black stripes are repeatedly formed as illustrated in FIG. 11 so that the toner  3   a  is consumed in particular places of the developing sleeve  4  in the width direction thereof, i.e., correspondingly to the black stripes. Thereafter, an image having a half-tone of about ID 0.2-0.5 (measured by a reflecting density measuring device) over the entire surface thereof was printed for  20  prints, and the image density unevenness was evaluated for ranking the degree of the image density unevenness. The developing conditions were set as specified in the following Table 2. 
     Table 2 
     Diameter of the photoconductive drum: 30 mm; 
     Linear speed of the photoconductive drum: 100 mm/sec; 
     Gap Gp between the developing sleeve and the photoconductive drum: 0.4 mm; 
     Gap Gd1 between the developing sleeve and the doctor: 0.4 mm; 
     Gap Gd2 between the developing sleeve and the pre-doctor: 0.6 mm; 
     Gap Gh between the developing sleeve and the peeling off roller: 0.4 mm; 
     Diameter of the developing sleeve: 16 mm; 
     Linear speed ratio of the developing sleeve relative to the photoconductive drum: 2.5; 
     Linear speed ratio of the peeling off roller relative to the developing sleeve: 0.8; 
     Material of the carrier: magnetite; 
     Particle diameter of the carrier: about 50 μm; 
     Material of the toner: resin in which a magnetic member is mixed; 
     Particle diameter of the toner: 6.5-9.5 μm. 
     FIGS.  18 ( a )- 18 ( e ) are diagrams for explaining the degree of the image density unevenness, each illustrating a half-tone image having residual black stripes  52   a  of different density, which was formed on a sheet  52 . The image density unevenness of FIG.  18 ( a ) is given a rank 2, that of FIG.  18 ( b ) a rank 3, that of FIG.  18 ( c ) a rank 3.5, that of FIG.  18 ( d ) a rank 4, and that of FIG.  18 ( e ) a rank 5. The higher the rank, the image density unevenness is less. The image density unevenness of rank 3 is the one obtained by conventional apparatuses. 
     In the experiments made under the conditions as above, it was confirmed that the image density unevenness has been improved. Specifically, with the peeling off roller  14  illustrated in FIG. 16, images of rank 3 or 3.5 were obtained, and with the peeling off rollers  15 ,  16 , and  17  illustrated in FIGS.  17 ( a ),  17 ( b ) and  17 ( c ), images of rank 3.5 or 4 were obtained. 
     Further, with respect to the developing device according to the above-described embodiment, the inventors of the present invention have found that the ratio between the linear speed of the developing sleeve  4  and that of the peeling off roller  14  plays an important role in generating a circulating movement of the developer  3  around the peeling off roller  14  and in sufficiently accelerating the frictional charging of the developer  3  with each other. Therefore, an independent variable speed driving device (not shown) that rotates the peeling off roller  14  with the linear speed thereof made variable may be provided inside a driving part of the developing device, such that the variable speed driving device is controlled by the engine control part  100  illustrated in FIG.  7 . The variable speed driving device may include a stepping motor for a driving source. An AC motor or a servo motor may also be used for the driving source of the variable speed driving device. 
     In order to confirm an effect of the ratio between the linear speed of the developing sleeve  4  and that of the peeling off roller  14 , an experiment to form images while changing the above ratio was performed under the following conditions of Table 4. 
     Table 4 
     Linear speed of the photoconductive drum: 120 mm/sec; 
     Gap Gp between the developing sleeve and the photoconductive drum: 0.3-0.5 mm; 
     Gap Gd1 between the developing sleeve and the doctor: 0.3-0.5 mm; 
     Gap Gd2 between the developing sleeve and the pre-doctor: 0.5-1.5 mm; 
     Gap Gh between the developing sleeve and the peeling off roller: 0.3-1.2 mm; 
     Diameter of the developing sleeve: 16 mm; 
     Diameter of the peeling off roller: 7 mm; 
     Linear speed ratio of the developing sleeve relative to the photoconductive drum: 1.5-3.0. 
     As a result of the above experiments, it was found that under the condition of the linear speed of the developing sleeve  4  at S(mm/sec) and the linear speed of the peeling off roller  14  at T(mm/sec), by setting the ratio ε of T/S so as to satisfy a condition: 5&lt;ε&lt;1.5, the frictional charging of the developer  3  with each other is effectively made in the developer accommodating part S at the gap between the developing sleeve  4  and the peeling off roller  14 . This is because, the quantity of the carrier which is set in the apparatus being fixed, if at least the linear speed ratio between the developing sleeve  4  and the peeling off roller  14  is within the above range of Table 4, an appropriate quantity of the toner is taken into the developer, and thereby the conveying speed and the volume of the toner on the developing sleeve  4  change such that the frictional charging of the developer  3  is effectively made. 
     Also, it was found that in the developing device of the above-described embodiment, the quantity of the toner  3   a  to be taken into changes according to a change of the coagulation degree of the toner  3   a  due to the environmental conditions, thereby causing a change in the conveying speed and the volume of the toner  3   a . The coagulation degree of the toner  3   a  changes according to a change of the temperature and humidity, and as indicated in FIGS. 8 and 9, the coagulation degree rises under a high temperature condition and a high humidity condition as well. A higher coagulation degree indicates that the toner  3   a  tends to be easily hardened. 
     Accordingly, by providing a temperature sensor (not shown) for measuring an ambient temperature in the vicinity of the photoconductive drum  1  and by increasing the rotation number of the peeling off roller  14  with the above variable speed driving device when the temperature rises so as to increase the linear speed of the peeling off roller  14 , the developer  3  can be sufficiently mixed and stirred and the frictional charging of the developer  3  with each other can be sufficiently accelerated. 
     Furthermore, in the digital image forming apparatuses such as the printer according to the above-described embodiment, it is also possible to change the linear speed of the peeling off roller  14  by obtaining information of the quantity of the toner  3   a  to be consumed in the development based upon the ratio of an image portion of an original for printing, which is obtained from an image signal for the original, and by changing the linear speed of the peeling off roller  14  according to the quantity of the toner  3   a  to be consumed. Specifically, when the toner density is decreased as a result of forming an image having a high image portion ratio, because a relatively large amount of the toner  3   a  is supplied and thereby the frictional charging of the developer  3  must be aggressively made, the peeling off roller  14  is controlled such that the linear speed thereof is increased. On the other hand, when the toner density is kept constant as a result of forming an image having a relatively low image portion ratio, because the frictional charging of the developer  3  needs not be aggressively made for avoiding earlier deterioration of the developer  3 , the peeling off roller  14  is controlled such that the linear speed thereof is kept the same or decreased. 
     Also, it was found that if the above ratio ε becomes greater than 1.5 by increasing the linear speed of the peeling off roller  14 , not only is the deterioration of the developer  3  accelerated, but also the developer  3  is regulated to be taken into the developer accommodating part S, thereby decreasing the toner density to be less than a desired level. In contrast, if the ratio ε becomes smaller than 0.5 by decreasing the linear speed of the peeling off roller  14 , the mixing and stirring effect was not obtained and uneven supplying of the toner  3   a  was confirmed on the image. The above-described control applied to the peeling off roller  14  can be also applied to the peeling off rollers  15 ,  16 , and  17  to obtain substantially the same effect. 
     FIG. 19 is a schematic drawing illustrating a developing device according to another embodiment of the present invention. In FIG. 19, the parts similar to those of the previous embodiment illustrated in FIGS. 2 and 3 are denoted by like references, and because the function thereof is substantially the same, the description thereof is omitted. Also, an image forming apparatus using the developing device of this embodiment can be controlled by the control part illustrated in FIG.  7 . 
     In the developing device of this embodiment, a peeling off member  12  formed in a grid-like flat plate is arranged in the developer accommodating part S downstream of the pre-doctor  7   a  in the rotating direction of the developing sleeve  4 . The peeling off member  12  is uniformly flat in the longitudinal direction thereof and a gap Gh relative to the developing sleeve  4  and an interval L2 relative to the pre-doctor  7   a  are kept constant (see FIG.  22 ). 
     In the developing device of FIG. 19, the toner  3   a  supplied from the toner hopper  8  formed upstream of the pre-doctor  7   a  passes the pre-doctor  7   a  to reach the peeling off member  12 . The developer attempting to move toward the doctor  6  caused by the conveying force of the developing sleeve  4  is once peeled off the developing sleeve  4  by the peeling off member  12 . The developer peeled off by the peeling off member  12  is replaced and mixed with the developer accommodated in the developer accommodating part S and is then carried again by the developing sleeve  4  by a magnetic force. With this replacement and mixture of the developer, the developer is stirred such that the toner density becomes uniform and also the toner charging is accelerated. 
     As described above, according to the above-described embodiment, by accelerating the replacement and mixture of the developer on the developing sleeve  4  with the one in the developer accommodating part S, earlier deterioration of the developer due to a decrease of a charging capability of the carrier in the developer is prevented. Furthermore, even when the toner is unevenly supplied to the developing sleeve  4  in the longitudinal direction thereof, the developer in which the toner is uniformly distributed can be conveyed to the developing area, thereby enabling development of an image without causing uneven image density. 
     The peeling off plate  12  formed in a grid-like flat plate is disposed so as to be in close proximity to and to have the gap Gh relative to a surface of the developing sleeve  4 . 
     Therefore, a space for enabling the developer to freely move therein can be realized in the developer accommodating part S at a position separated from a surface of the developing sleeve  4 . Accordingly, the developer blocked by the doctor  6  freely moves in the developer accommodating part S to the side of the toner supplying opening  8   a  without being obstructed. Therefore, the toner density control function of the developer, which is realized by changing the condition of taking the toner into the developer by changing the contact condition of the developer thus moved to the side of the toner supplying opening  8   a  with the toner supplied from the toner hopper  8 , can be securely maintained. 
     Now, a concrete example of the developing device of the above-described embodiment and a result of an experiment made using the developing device according to the example are described. Using the developing device illustrated in FIGS. 19 and 20 prints were made with a test chart having an image in which black stripes are formed at intervals such that the toner consumption varies in the longitudinal direction of the developing sleeve  4 . Thereafter, another 20 prints were made using a test chart having an image with an even half tone over the entire surface thereof. The developing conditions were substantially the same as the ones indicated in Table 1. 
     For the peeling off member, flat plates  12   a  and  12   b  of a non-magnetic member formed in a grid-like shape as illustrated in FIGS. 20 and 21 were used. The developer on the developing sleeve  4  is peeled off the developing sleeve  4  by the peeling off members  12   a  and  12   b  through the grid holes thereof. The gap Gh between the peeling off member  12  and the developing sleeve  4  was set to 0.3 mm and the interval L2 between the peeling off member  12  and the pre-doctor  7   a  was set to 10 mm (see FIG.  22 ). 
     According to the result of the experiment made under the above conditions, the developer on the developing sleeve  4  was peeled off the developing sleeve  4  to be replaced and mixed with the one in the developer accommodating part S, such that the toner density of the developer was made uniform, and thereby a good image having a uniform image density was obtained. 
     In the experiment with the developing device of the above-described embodiment, by configuring the developing device such that the gap Gh between the peeling off member  12  and the developing sleeve  4  and the gap Gd2 between the developing sleeve  4  and the pre-doctor  7   a  satisfy the relation: 0&lt;&lt;Gh&lt;Gd2, a good mixing and stirring capability was realized. 
     Further, because only an upper part layer of the developer  3  on the developing sleeve  4  was peeled off by the peeling off member  12  of a grid-like flat plate, the self toner density control mechanism to change the condition of taking the toner  3   a  into the developer  3  by changing the contact condition of the conveyed developer  3   b  with the toner  3   a  from the toner hopper  8  at the toner supplying opening  8   a  was stably maintained. 
     FIG. 23 is a schematic drawing illustrating a developing device according to still another embodiment of the present invention. In FIG. 23, the parts similar to those of the previous embodiment illustrated in FIGS. 2 and 3 are denoted by like references, and because the function thereof is substantially the same, the description thereof is omitted. Also, an image forming apparatus using the developing device of this embodiment can be controlled by the control part illustrated in FIG.  7 . 
     In the developing device of this embodiment, a stirring comb member  20  is provided in the developer accommodating part S as a developer stirring member downstream of the pre-doctor  7   a  and upstream of the doctor  6  in the developer conveying direction of the developing sleeve  4 . The stirring comb member  20  is shaped so as to have a uniform width and thickness in the longitudinal direction thereof, and the stirring comb member  20  is fixed in the developer accommodating part S so as to keep constant a distance L2 from the pre-doctor  7   a  and an interval Gk between a tip end of the stirring comb member  20  and a surface of the developing sleeve  4  (see FIG.  24 ). 
     In the developing device according to the above-described embodiment, an upper layer part of the conveyed developer on the developing sleeve  4  conveyed into the developer accommodating part S is stirred by the stirring comb member  20  opposing the developing sleeve  4  in a non-contacting manner at a position adjacent to the toner hopper  8  in the developer accommodating part S. Due to this stirring of the developer, the conveyed developer on the developing sleeve  4  and the accommodated developer in the developer accommodating part S are mixed and stirred with each other. Also, due to the above stirring of the developer, the toner  3   a  taken from the toner hopper  8  into the upper layer part of the developer on the developing sleeve  4  is stirred and mixed with the developer such that the toner density of the developer is made uniform. Thereby, the developer having a uniform toner density is carried on the developing sleeve  4  and conveyed to the developing area so as to be used for a development of a latent image on the photoconductive drum  1 . 
     According to the above-described embodiment, because the stirring comb member  20  stirs a part (the upper layer part) of the developer on the developing sleeve  4 , the conveying state of the developer on the developing sleeve  4  is not disturbed and a stable self toner density control mechanism is maintained. Further, because of the mixing and stirring of the developer with the stirring comb member  20 , background soiling and decrease in the image density due to deterioration of the developer with a lapse of time are prevented, and at the same time a good development having no uneven image density in the axial direction of the developing sleeve  4  can be realized. 
     Now, a concrete example of the developing device according to the above-described embodiment and a result of an experiment made with the developing device according to the example are described. The developing device illustrated in FIG. 24 was used in the experiment and the experiment conditions were set as indicated in the following Table 5. 
     Table 5 
     Diameter of the photoconductive drum: 30 mm; 
     Linear speed of the photoconductive drum: 120 mm/sec; 
     Gap Gp between the developing sleeve and the photoconductive drum: 0.3-0.5 mm; 
     Gap Gd1 between the developing sleeve and the doctor: 0.3-0.5 mm; 
     Gap Gd2 between the developing sleeve and the pre-doctor: 0.5-1.5 mm; 
     Diameter of the developing sleeve: 16 mm; 
     Linear speed ratio of the developing sleeve relative to the photoconductive drum: 1.5-3.0; 
     Material of the toner: magnetite or steel; 
     Particle diameter of the toner: 40-50 μm; 
     Volume of a magnetic member in the toner: 15-40 wt %; 
     Volume of silica in the toner: 0.5-1.0 wt %; 
     Covered ratio of the toner with the carrier: 50-120%; 
     Q/M: 10-30 μc/g. 
     FIG. 24 is a schematic drawing indicating an arrangement position of the stirring comb member  20 . The gap Gk between the stirring comb member  20  and the developing sleeve  4  was set to 0.3 mm and the distance L2 between the stirring comb member  20  and the pre-doctor  7   a  to 1 mm. 
     FIG. 25 is a perspective view of the stirring comb member  20  used in this embodiment. The stirring comb member  20  includes a series of comb tooth  20   a  at the side opposing the developing sleeve  4 . The interval Pk between the tips of neighboring two comb tooth  20   a  was set to 2 mm. 
     Using the developing device configured as described above, first,  20  prints were made for the test chart  60  illustrated in FIG. 11, in which black stripes are formed at intervals such that the toner consumption varies in a direction perpendicular to a surface moving direction of the developing sleeve  4  (indicated by the arrow G in FIG.  11 ), i.e., the image width direction of the chart  60 . Thereafter, another  20  prints were made using another test chart of an image having an even half-tone over the entire surface thereof. According to a result of the experiment, the toner density of the developer  3  was made uniform with respect to the image width direction because of the stirring comb member  20 , and thereby good half-tone images having no image density unevenness were obtained. In contrast, with the developing device in which the stirring comb member  20  was not provided, uneven image density was observed in the half-tone images. 
     From the above experiment, it was found that when developing a test chart in which black stripes are formed such that the toner consumption varies in the longitudinal direction of the developing sleeve  4 , if the chart is developed without using the stirring comb member  20 , a good image cannot be obtained because of uneven toner density in the image width direction, and that on the other hand, with the provision of the stirring comb member  20 , the uneven toner density in the image width direction can be avoided. 
     More specifically, the toner  3   a  supplied from the upstream of the pre-doctor  7   a  in the developer conveying direction passes the gap between the developing sleeve  4  and the pre-doctor  7   a  together with the conveyed developer on the developing sleeve  4  to reach the stirring comb member  20 . The conveyed developer containing the toner  3   a  thus supplied is stirred by a resisting force generated by the stirring comb member  20  when the developer is conveyed by the developing sleeve  4 , and at the same time, when passing the stirring comb member  20 , the developer hits the series of comb tooth  20   a  to be separated to both sides of each comb tooth  20   a  sandwiching the comb tooth  20   a , so that each separated developer is mixed with another developer separated by the neighboring comb tooth  20   a  in each space between the neighboring comb teeth  20   a . Because of this mixing of the developer in the lateral direction, the toner density in the developer is made uniform in the axial direction of the developing sleeve  4  and charging of the toner  3   a  is accelerated. As a result, even when the toner  3   a  is unevenly supplied in the longitudinal direction of the developing sleeve  4 , the toner density of the developer is made uniform in the longitudinal direction of the developing sleeve  4  and thereby a good image can be obtained. 
     Further, because the stirring comb member  20  is arranged with the gap Gk relative to the developing sleeve  4  so as to stir a part (the upper layer part) of the conveyed developer on the developing sleeve  4 , the movement of the conveyed developer on the developing sleeve  4  in the developer accommodating part S is not obstructed. Accordingly, there is no possibility that the self toner density control mechanism fails. In particular, because the developer stirring member is shaped to have comb teeth, the movement of the developer obstructed by the doctor  6  in the developer accommodating part S is hardly obstructed. Therefore, the toner  3   a  taken into the developer can be stirred while securely maintaining the mechanism of the self toner density control. 
     It was also found that a good stirring capability can be realized by using a nonmagnetic member for the stirring comb member  20  and by setting the gap Gk so as to satisfy the condition: 0&lt;Gk&lt;Gd2. By thus setting the gap Gk, at least a part of the toner  3   a  supplied from the regulating position of the pre-doctor  7   a  securely passes the spaces between the comb tooth  20   a  and comb tooth  20   a  of the stirring comb member  20 . Therefore, the supplied toner  3   a  can be securely stirred in the lateral direction. 
     It was also found that a good stirring capability can be realized by setting the interval Pk between the tip ends of neighboring two comb tooth  20  to satisfy the condition. 0&lt;Pk&lt;5 mm. In this embodiment, the interval Pk is set to be smaller than 5 mm, and with this setting, uneven toner density in the image width direction was satisfactorily avoided. 
     FIG. 26 is a schematic drawing illustrating a developing device according to still another embodiment of the present invention. The developing device is configured in substantially the same manner as the one of the previous embodiment illustrated in FIG. 23 except for the following differences. In the developing device of this embodiment, in place of the stirring comb member  20 , a sheet member  21  as an example of a flexible plate member is provided at a position adjacent to the toner hopper  8  in the developer accommodating part S so as to oppose a surface of the developing sleeve  4  and to contact a part of the developer carried on the developing sleeve  4 , that contains the toner  3   a  taken from the toner hopper  8 . In the developing device of FIG. 23, the base plate surface of the toner supplying opening  8   a  is slightly curved like a saucer. In contrast, in the developing device of this embodiment, the base plate surface of the toner supplying opening  8   a  is shaped so as to straightly decline toward the developing sleeve  4  from the toner hopper  8 . Further, at a horizontal cross-section of the toner hopper  8 , the area of the toner hopper  8  is smaller than that of the developing device of FIG.  23 . Furthermore, in the developing device of FIG. 23, the developer accommodating case  7  is made such that the border parts of the upper wall, the side wall, and the bottom wall (the pre-doctor  7   a ) surrounding the developer accommodating part S are respectively curved. In contrast, in the developing device of FIG. 26 according to this embodiment, the developer accommodating case  7  is made such that the border part of the side wall and the bottom wall (the pre-doctor  7   a ) are sharply bent. The construction and the operation of the developing device except for the above-described differences are substantially the same as those of the developing device of FIG. 23, and therefore the description thereof is omitted. 
     More concrete examples of the developing device of this embodiment are now described. FIG. 27 is a partly enlarged schematic drawing illustrating the developer accommodating part S and a toner take-in part of the developing device. In the developing device, the sheet member  21  is provided to a side surface of the pre-doctor  7   a  at the side of the developer accommodating part S. The sheet member  21  in this embodiment includes a polyurethane seal. However, any sheet-like or plate-like member having flexibility can be used for the sheet member  21 . 
     The sheet member  21  is pasted to an internal surface of the pre-doctor  7   a  such that an end part thereof at the side of the developing sleeve  4  is formed into a free end part  21   a  and the free end part  21   a  is bent toward the downstream side of the developer conveying direction by being pulled by the developer carried and conveyed by the developing sleeve  4 . The position of the tip end of the free end part  21   a  when the free end part  21   a  is thus bent defines a third regulating position. The sheet member  21  is bent or restored due to its flexibility according to a pressing force exerted by the toner  3   a  which has been taken into the developer accommodating part S through the second regulating position with the pre-doctor  7   a . The toner  3   a  which has been excessively taken into the developer is prevented from being conveyed toward an area at the downstream side in the developer conveying direction with the developing sleeve  4 . At the same time, at the third regulating position, the toner density in the developer is made uniform in the image width direction which is perpendicular to the developer conveying direction by the developing sleeve  4 . Thus, the excessive toner  3   a  is removed and the toner  3   a  which has been uniformly distributed in the image width direction is taken into the conveyed developer on the developing sleeve  4 , and the toner density in the conveyed developer on the developing sleeve  4  is further made uniform at the regulating position by the doctor  6  so as to be used for development. 
     Good images were obtained without having uneven image density in the image width direction in an experiment made using a developing device provided with the sheet member  21  as described above. 
     FIG. 28 is an enlarged schematic drawing illustrating the developer accommodating part S and a toner take-in part of the developing device, that includes another example of the sheet member. According to this example of the sheet member, a free end part  22   a  of a sheet member  22  is longer than a shortest length to reach a surface of the developing sleeve  4 . Because of this length of the free end part  22   a , a tip end of the free end part  22   a  contacts a surface of the developing sleeve  4 , and with a movement of the developing sleeve  4 , the free end part  22   a  is bent toward the downstream side in the developer moving direction by being pulled by the developer carried and conveyed by the developing sleeve  4 . The position of the tip end of the free end part  22   a  when the free end part  22   a  is thus bent defines the third regulating position. The toner  3   a  carried and conveyed by the developing sleeve  4  is moved relative to the sheet contacting member  22  while contacting the sheet member  22 . The excessive toner  3   a  is thus regulated at the third regulating position and at the same time the toner density in the developer is made uniform in the image width direction perpendicular to the developer conveying direction by the developing sleeve  4 . 
     Thus, the excessive toner  3   a  is removed and the toner  3   a  which has been uniformly distributed in the image width direction is taken into the developer on the developing sleeve  4 , and the developer containing the uniformly distributed toner  3   a  passes the regulating position by the doctor  6  to be used for development. 
     Good images were obtained without having uneven image density in the image width direction in an experiment made using the developing device provided with the sheet member  22  as described above. 
     FIG. 29 is an enlarged schematic drawing illustrating the developer accommodating part S and a toner take-in part of the developing device, in which another example of the sheet member is included. According to this example, a free end part  23   a  of a sheet member  23  is made longer than a shortest length to reach a surface of the developing sleeve  4  as in the immediately above example. In addition, the thickness of the sheet member  23  is made such that the free end part  23   a  is bent by a pressure caused by the conveyed developer on the developing sleeve  4 , and thereby a surface of the free end part  23   a  contacts the conveyed developer on the developing sleeve  4  uniformly in the image width direction and for a relatively long distance in the developer conveying direction. The position of this surface contacting part of the free end part  23   a  of the sheet member  23  defines the third regulating position. With this configuration, the excessive toner  3   a  is removed and the toner  3   a  uniformly distributed in the image width direction is taken into the developer on the developing sleeve  4 , and the developer containing thus uniformly distributed toner  3   a  passes the regulating position by the doctor  6  so as to be used for development. 
     Good images were obtained without having uneven image density in the image width direction in an experiment made using the developing device provided with the sheet member  23  as described above. 
     FIG. 30 is an enlarged schematic drawing illustrating the developer accommodating part S and a toner take-in part of the developing device, in which another example of the sheet member is included. According to this example, a free end part  24   a  of a sheet member  24  is made longer than a shortest length to reach a surface of the developing sleeve  4  as in the immediately above example. In addition, the length of the free end part  24   a  of the sheet member  24  is made such that the free end part  24   a  is bent by a pressure caused by the conveyed developer on the developing sleeve  4  and such that the free end part  24   a  contacts the conveyed developer on the developing sleeve  4  uniformly in the image width direction and for a relatively long distance in the developer conveying direction. This surface contacting part of the free end part  24   a  of the sheet member  24  forms the third regulating position. With this configuration, the excessive toner  3   a  is removed and the toner  3   a  uniformly distributed in the image width direction is taken into the developer on the developing sleeve  4 , and the developer containing thus uniformly distributed toner  3   a  passes the regulating position by the doctor  6  so as to be used for development. 
     Good images were obtained without having uneven image density in the image width direction in an experiment made using a developing device provided with the sheet member  24  as described above. 
     In the developing device of FIG. 30, the end part of the sheet member  24  opposite the free end part  24   a  is made longer than a length necessary for fixing this end part to the side of the pre-doctor  7   a  at the side of the developer accommodating part S. Specifically, this end part is made to extend over the internal surface of the pre-doctor  7   a  in a perpendicular direction relative to a surface of the developing sleeve  4  and that of a part of the side wall of the developer accommodating part S, which extends from the pre-doctor  7   a  upward by being bent. The sheet member  24  is pasted to the internal surface of the pre-doctor  7   a  to be bent such that the sheet member  24  is separated from the position of the internal surface of the pre-doctor  7   a  where the pre-doctor  7   a  is bent. With this configuration, the developer can be more smoothly circulated in the developer accommodating part S. Thus, even if the shape of the internal surface of the developer accommodating part S is made to include such a bending portion and is not smooth enough to circulate the developer, such a bending portion can be covered by the sheet member  24  so that the developer can be smoothly circulated in the developer accommodating space S. 
     FIG. 31 is an enlarged schematic drawing illustrating the developer accommodating part S and a toner take-in part of the developing device, in which another example of the sheet member is included. According to this example, a free end part  25   a  of a sheet member  25  is made sufficiently longer than a shortest length to reach a surface of the developing sleeve  4 , such that the free end part  25   a  is rolled up and an outer circumferential part  25   b  at a curved part of the rolled up free end part  25   a  contacts the conveyed developer on the developing sleeve  4 . With this rolling up configuration, the sheet member  25  is strengthened, and the position of the contacting part of the free end part  25   a  of the sheet member  25  defines the third regulating position. With this configuration, the excessive toner  3   a  is removed and the toner  3   a  uniformly distributed in the image width direction is taken into the developer on the developing sleeve  4 , and the developer containing thus uniformly distributed toner  3   a  passes the regulating position by the doctor  6  so as to be used for development. 
     Good images were obtained without having uneven image density in the image width direction in an experiment made using the developing device provided with the sheet member  25  as described above. 
     As described above, in the developing device according to the above embodiment, the sheet members  21 - 25  regulate the take-in of the toner  3   a  into the developer and make the toner density in the developer uniform in the image width direction such that uneven image density is prevented. 
     Further, with respect to the stirring comb member  20  and the sheet members  21 - 25 , the toner density is made uniform in the longitudinal direction of the developing sleeve  4  only by fixing these members in the developer accommodating part S. Therefore, it is not necessary to provide and drive by a motor a member for stirring the developer in the developer accommodating part S. Accordingly, an effect of avoiding uneven image density in the image width direction can be obtained at relatively low cost. 
     Numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein. 
     The present application claims priority and contains subject matter related to Japanese Patent Applications No. 11-174693, No. 11-187727, No. 11-188219, No. 11-269348, No. 11-272551, and No. xx-xxxxxx, respectively filed in the Japanese Patent Office on Jun. 21, 1999, Jul. 1, 1999, Jul. 1, 1999, Sep. 22, 1999, Sep. 27, 1999, and May xx, 2000, and the entire contents of which are hereby incorporated herein by reference.