Image-forming machine

Abstract: An image-forming machine including a process unit (6) to be mounted detachably. The process unit (6) has a rotating drum (16) having an electrostatographic material disposed on it peripheral surface, a corona discharger (22) for uniformly charging the electrostatographic material, a developing device (10) and a cleaning device (18). The corona discharger (22) has a grid electrode (204) formed of a piece of a conductive thin metallic plate. The developing device (10) include a development housing (50) for holding a developer (60), a developer applicator means (72) for applying the developer (60) in the development housing (50) to the electrostatographic material, and an agitating means (74; 128; 138) for stirring the developer (60) in the development housing (50). The agitating member (88; 130; 150) employs means for preventing damage of the agitating member even when an excessively large resistance is exerted by the developer (60). The developer applicator means (72) has a sleeve member (76) holding a developer (60) on its surface and a developer regulating blade (84) which can adjust the layer of the developer (60) held on the surface of the sleeve member (76) to an uniform thickness all the way in the width direction. The cleaning device (18) includes a toner removing means (30) for removing a residual toner from the electrostatographic material, a toner collecting chamber (34) and as toner conveying passage (36) extending from a toner recovery housing (32) to the toner collecting chamber (34). The toner removing means (30) is constructed of a cleaning blade which when the process unit (6) is mounted at a predetermined position in the image-forming machine, is moved from a non-operative position at which it is away from the electrostatographic material to an operative position at which it is brought elastically into contact with the electrostatographic material. A toner conveying means (44) comprised of a coil is disposed in the toner conveying passage (36).

Description: Field of the Invention This invention relates to an image-forming machine, such as a printer or a copying machine, of the electrostatic type which forms a latent electrostatic image on an electrostatographic material, developing it to a toner image, and thereafter, transferring the toner image to a receptor material. Description of the Prior Art Image-forming machines such as printers or copying machines of the above-described electrostatic type have been widely used. Such an image-forming machine usually comprises an electrostatographic material disposed on the surface of a rotating drum or an endless belt, a latent electrostatic image-forming means for forming a latent electrostatic image on the electrostatographic material, a developing device for developing the latent electrostatic image to a toner image, a transfer means for transferring the toner image on the electrostatographic material to a receptor material which may usually be a sheet of paper, and a cleaning device for removing the residual toner from the electrostatographic material after the toner image is transferred therefrom. The latent electrostatic image-forming means includes a charging corona discharger for uniformly charging the electrostatographic material and an optical system for selectively exposing the electrostatographic material corresponding to an image to be formed. A typical example of the developing device includes a development housing holding a developer, a developer applicator means for applying the developer in the development housing to the electrostatographic material, and an agitating means for agitating the developer within the development housing. The agitating means includes a rotating shaft to be rotated in a predetermined direction and an agitating member fixed to the rotating shaft. The developer applicator means usually has a sleeve member which holds the developer on its surface and conveys it, and in this case, there is provided a developer restricting blade which restricts the thickness of the developer layer conveyed while being held on the surface of the sleeve member. The developer may be a one-component developer composed of toner particles only or a two-component developer composed of toner particles and carrier particles. In a relatively small-sized image forming machine, it is convenient to construct a replaceable process unit by combining the electrostatographic material with the developing device and/or the cleaning device, and mount it detachably on a desired site. In this case, a cover member adapted to be selectively held at a covering position at which it covers part of the electrostatographic material is also provided. The cover member may be detachably mounted on the process unit in a mode in which it is held at the covering position; or in a mode in which it is free to move between the covering position and a non-covering position at which it exposes part of the electrostatographic material to view. In some cases, the charging corona discharger in the latent electrostatic image-forming means is also included in the process unit. The publication Patent Abstracts of Japan, Vol. 8, No. 153 (P-287) [1590], dated July 17, 1984 discloses a stirring device of a developer. A first stirring member is formed by bending a wire to form a bracket shape, which is attached to a rotatable shaft. A second stirring member formed by a coil of thin wire material is suspended on the first stirring member to extend over its entire length. When the first member is rotated, the second member moves freely about the first bar-type bracket member and is displaced by rotation of the first member. The conventional image-forming machines described above, however, have problems to be solved. At the time of starting the operation of the image-forming machine, the rotation resisting force exerted on the agitating member by the developer becomes excessively large, and is likely to damage the agitating member itself or a drive linking mechanism for rotating the rotating shaft. This problem is especially pronounced when the developer is a one-component developer of a relatively high bulk density and a relatively large amount of the developer is present in the developer housing. This problem could be solved by sufficiently increasing the strength of the agitating member and the drive coupling mechanism. However, it would necessarily increase the cost of production and the size of the machine. Summary of the Invention An object of this invention is to prevent the agitating member and its related drive connecting mechanism exactly from undergoing damage even when the developer exerts an excessively large rotation resisting force on the agitating member of the developer agitating means in the latent electrostatic image developing device without giving rise to other problems such as an increase in the cost of production and size. According to the present invention, an image-forming machine is provided having agitating means as defined in claims 1 and 6. In an image developing device, an agitating member is mounted on the rotating shaft of developer agitating means so that when a rotation resisting force of a magnitude above a predetermined value is exerted on the agitating member, the agitating member can slip with respect to the rotating shaft. Alternatively in an image developing device, an agitation member having an inside diameter larger than the outside diameter of the rotating shaft of the developer agitating means is formed, and idly fitted over the rotating shaft. The inside surface of the agitating member is provided with a protrusion. Brief Description of the Drawings Figure 1 is a simplified view showing a laser beam printer as one specific embodiment of the image-forming machine constructed in accordance with this invention; Figure 2 is an exploded view showing a process unit for use in the laser beam printer of Figure 1; Figure 3 is a sectional view showing a process unit for use in the laser beam printer of Figure 1; Figure 4 is a perspective view showing a developer agitating means used in a developing device in the process units of Figures 2 and 3; Figure 5 is a partial perspective view showing a portion of the developer agitating means of Figure 4; Figure 6 is a perspective view showing a modified example of the developer agitating means of Figures 4 and 5; Figure 7 is a perspective view showing another embodiment of the developer agitating means; Figures 8-A, 8-B, 8-C and 8-D are partial sectional view for illustrating the action of the developer agitating means of Figure 7; Figures 9, 10 and 11 are perspective views showing modified examples of the developer agitating means of Figure 7; Detailed Description of Preferred Embodiments With reference to the accompanying drawings, preferred embodiments of the image-forming machines of this invention improved in various respects will be described below in detail. Figure 1 shows a laser beam printer shown generally at 2. The printer is comprised of a printer body 4 shown by a two-dot chain line in a simplified manner and a process unit 6 to be mounted detachably on the printer body 4. The structure of the printer 2 excepting the structure of the process unit 6 and the method of mounting and detaching the process unit 6 on and from the printer body 4 may be substantially the same as in the laser beam printer described and shown in detail in the specifications and drawings of Japanese Patent Applications Nos. 290740/1987 (filed on November 19, 1987 and entitled "Image-Forming Machine") and 301775/1987 (filed on November 30, 1987 and entitled "Image-Forming Machine"). Accordingly, these applications are cited herein by way of reference, and a detailed description of the structure of the printer 2 and the method of mounting and detaching the process unit 6 is omitted herein. With reference to Figure 2, the process unit in the illustrated embodiment is constructed by assembling four components each formed and assembled independently, namely a first component 8, a second component 10, a third component 12 and a fourth component 14. With reference to Figures 2 and 3, the first component 8 has a rotating drum 16 and a cleaning device 18. The second component 10 is a developing device. The third component constitutes an upper fixed cover member covering a greater portion of the upper surfaces and both side surfaces of the first and second components 8 and 10 and at the same time, includes a charging corona discharger 22. The fourth component 14 is a cover member for covering the lower portion of the rotating drum 16 and detachably mounted on the covering position shown in Figure 3. Further, with reference to Figures 2 and 3, the first component 8 has a pair of supporting side walls 24 and 26 dispersed with a predetermined distance therebetween, and the rotating drum 16 is rotatably mounted between these supporting walls 24 and 26. An electrostatographic material which may be formed of a suitable material such as an organic photosemiconductor is disposed on the peripheral surface of the rotating drum 16. The rotating drum 16 has an input shaft (not shown) projecting through the supporting side wall 26. When the process unit 6 is mounted in position on the printer body 4 (Figure 1), the input shaft is drivingly coupled to a driving source (not shown) which may be an electric motor via a suitable drive coupling means (not shown), and at the time of performing the image-forming process, the rotating drum 16 is rotated in the direction shown by an arrow 28. The cleaning device 18 includes a cleaning blade 30 adapted to make contact with the peripheral surface of the rotating drum 16 by being biased elastically. The cleaning blade 30 constitutes a toner removing means for removing the residual toner from the peripheral surface of the rotating drum 16 after a toner image formed on the peripheral surface is transferred to a receptor material. Again with reference to Figures 2 and 3, the second component or developing device 10 includes a development housing 50 comprised of a main development housing member 46 and a developer cartridge member 48. An opening is formed in the left side surface of the main development housing member 46 in Figure 3, and an opening is also formed in its inclined upper surface located at the right top in Figure 3. Guiding channels 52 and 54 extending in the width direction (the direction perpendicular to the sheet surface in Figure 3) are formed in both end edge portions of the inclined upper surface of the main development housing member 46. The developer cartridge member 48 has an inclined lower surface located at the left bottom in Figure 3, and guide protrusions 56 and 58 extending in the width direction are formed in both end edge portions of the inclined lower surface. The developer cartridge member 48 is combined with the main development housing member 46 by sliding it and insert its guide protrusions 56 and 58 into the guiding channels 52 and 54 of the main development housing 46. A developer 60 which may be a one-component developer composed only of a magnetic toner is filled in the developer cartridge member 48 through a filling port (not shown) formed at its one side wall. The filling port is closed by bonding a closing member 62 (Figure 2) to it after the developer 60 is filled. The inclined lower surface of the developer cartridge member 48 is sealed up by an openable sealing member 64 which may be of any known form. When the components 8, 10, 12 and 14 constituting the process unit 6 are combined properly, an opening protruding end portion 66 of the sealing member 64 is projected outwardly through a slit 68 formed in the front side wall 106 of the third component 12, and bonded to the surface of the front side wall 106 by means of a bonding piece 70, as indicated by a two-dot chain line in Figure 2. Until the process unit 6 is actually put to use, the sealing member 64 is kept unopened, and therefore the developer 60 is held only in the developer cartridge member 48 and therefore no developer 60 exists in the developer housing member 46. When the process unit is to be mounted in position on the printer body 4 (Figure 1), the sealing member 64 is removed from the inclined lower surface of the developer cartridge member 48 by pulling the protruding end portion 66 (Figure 2), and the inclined lower surface is opened. As a result, the developer 60 is permitted to flow from the cartridge member 48 into the main development housing member 46. A developer applicator means 72 and a developer agitating means 74 are disposed in the main development housing member 46. The developer agitating means 74 has a rotating shaft 86 extending in the width direction (the direction perpendicular to the sheet surface in Figure 3) and an agitating member 88 mounted on the rotating shaft 86. The rotating shaft 86 is drivingly coupled to the sleeve member 76 via a suitable drive coupling means (not shown) such as a gear train, and is rotated in the direction shown by an arrow 90 when the rotating drum 16 is rotated in the direction of arrow 28 and the sleeve member 76, in the direction of arrow 80. Thus, the developer agitating means 74 agitates the developer 60 in the main development housing member 46, and permits it to flow toward the sleeve member 76 of the developer applicator means 72. The developer agitating means 74 will be described in more detail hereinafter. As already described with reference to Figure 3, the developer agitating means 74 is disposed in the main development housing member 46 of the developing device 10. The developer agitating means 74 is comprised of a rotating shaft 86 extending in the width direction (the direction perpendicular to the sheet surface in Figure 3) within the main development housing member 46 and a agitating member 88 mounted on the rotating shaft 86. In this invention, it is important that the agitating member 88 should be mounted on the rotating shaft 86 in such a manner that when a rotation resistance force of a magnitude above a certain limit is exerted on the agitating member 88 while the rotation shaft is in rotation in the direction of arrow 90, the agitating member 88 can slip with respect to the rotating shaft 86. With reference to Figure 4 in conjunction with Figure 3, the agitating member 88 in the illustrated embodiment is formed by properly deforming a single continuous metal wire which may be a stainless steel wire for a coil spring having a diameter of, for example, about 1.2 mm. The agitating member 88 has mounting portions 116 at both ends spaced from each other in the axial direction of the rotating shaft 86, an arm portion 118 extending substantially perpendicularly to the rotating shaft 86 and radially outwardly from the mounting portions 116 respectively, and a main agitating portion 120 extending between the arm portions 118 substantially in parallel to the rotating shaft 86. The mounting portion 116 at both ends are located at sites near both ends of the main development housing member 46 in the width direction, and therefore, the main agitating portion 120 conveniently extends within the main development housing member 46 nearly over its entire length of the development housing member 46 in the width direction. The radial length of each of the arm portions 118 is conveniently set such that as shown in Figure 3 while the agitating member 88 is rotated in the direction of arrow 90 incident to the rotation of the rotating shaft 86, the main agitating portion 120 moves in proximity to the inside surface 122 of the arcuate bottom wall of the main development housing member 46. With reference to Figures 4 and 5, the mounting portion 116 at both ends of the agitating member 98 is formed in a coil spring shape, and fitted over a receiving portion 124 (Figure 5). The inside diameter of the mounting portion 116 in a free condition is set slightly smaller than the outside diameter of the receiving portion 124 of the rotating shaft 86. The mounting portion 116 is elastically put over the receiving portion 124 of the rotating shaft 86 by elastically increasing its inside diameter. As clearly shown in Figure 5, the receiving portion 124 of the rotating shaft 86 is preferably made slightly smaller in diameter than the rest of the shaft 86, and annular shoulder surfaces 126 are formed on both sides of the receiving portion 124. The annular shoulder surfaces 126 prevent the mounting portion 116 of the agitating member 88 from moving axially with respect to the rotating shaft 86. Preferably, the winding direction of the agitating member 88 at the mounting portion 116 is such that it is loosened when the agitating member 88 is relatively revolved in a direction shown by an arrow 127 (the direction opposite to the rotating direction 90 of the rotating shaft 86). As stated hereinabove with regard to the prior art, when the developer 60 is a one-component developer having a relatively high density and a relatively large amount of the developer 60 exists in the developer housing 50, it is not rare that at the time of starting the initial operation of the process unit 6 or at the time of starting the operation after stoppage for a relatively long period of time (for example, at the time of starting the operation every morning), an excessively large rotation resisting force acts on the agitating member 88 of the agitating means 74 owing to the pressing and aggregation of the developer 60 around the developer agitating means 74. In contrast, in the developer agitating means 74 improved in accordance with this invention, the mounting portion 116 of the agitating member 88 is elastically fitted over the rotating shaft 86, and when an excessive rotation resisting force acts on the agitating member 88, the agitating member 88 can slip with respect to the rotating shaft 86. Accordingly, when the rotating shaft 86 of the developer agitating means 74 begins rotation in the direction of arrow 90 incident to the starting the use of the process unit 6 and the rotation resisting force on the agitating member 88 is excessively large, the agitating member 88 slips with respect to the rotating shaft 86 and an excessively large rotation resisting force is cushioned. As a result, the damage of the agitating member 88 or a drive coupling mechanism (not shown) relating to the rotating shaft 86 is accurately prevented. The degree of drive coupling of the rotating shaft 86 and the agitating member 88, or in other words, the rotation resisting force which causes the agitating member 88 to slip with respect to the rotating shaft 86, can be properly set based on experiment, etc. When the developer applicator means 72 of the developing device 10 applies the developer 60 to the latent electrostatic image, the developer 60 is consumed and some space is created near the developer applicator means 72. Consequently, the developer 60 flows and the rotation resisting force on the agitating member 88 abrubtly decreases. Then, the agitating member 88 is rotated in the direction of arrow 90 incident to the rotation of the rotating shaft 86. Figure 6 shows a modified example of the developer agitating means. In this developer agitating means 128, an agitating member 88 substantially the same as the agitating member 88 shown in Figure 5 and an additional agitating member 130 are secured to the rotating shaft 86 to be rotated in the direction of arrow 90. The additional agitating member 130 differs from the agitating member 88 in that both end mounting portions 132 are arranged inwardly of the two end mounting portion 116 of the agitating member 88 and therefore the axial length of a main agitation operative portion 134 is relatively short, and that the radial length of an arm portion 136 is shorter than the arm portion 118 of the agitating member 88 and therefore the distance between the rotating shaft 86 and the main agitation operative portion 134 is relatively small. The method of mounting on the rotating shaft 86 is substantially the same as the agitating member 88. Since in the developer agitating means 128 depicted in Figure 6, the main agitation operative portion 134 of the agitating member 130 is smaller than the main agitation operative portion 120 of the agitating member 88, the rotation resisting force acting on the agitating member 130 is usually smaller than that acting on the agitating member 88. Accordingly, when the degree of drive coupling of the agitating member 88 with respect to the rotating shaft 86 is substantially the same as that of the agitating member 130 with respect to the rotating shaft 86, and the rotation resisting force acting on the agitating members 88 and 130 is excessively large, the agitating member 130 begins rotation incident to the rotating shaft 86 after the lapse of some time from the starting the operation of the developing device 10, and then with some delay in time, the agitating member 88 begins rotation incident to the rotating shaft 86. If desired, it is possible to mount a plurality of agitating members having a relatively short axial length on the rotating shaft 86 at suitable axial intervals. Figure 7 shows another embodiment of the developer agitating means improved in accordance with this invention. The developer agitating means shown generally at 138 is comprised of a rotating shaft 140 to be rotated in the direction of arrow 90 and an agitating member 142 mounted on the rotating shaft 140. The rotating shaft 140 has formed therein a so-called crank-like deformed portion 144 which constitutes an eccentric portion made eccentric by a predetermined amount with respect to the central axis 146 of the rotating shaft 140. The agitating member 142 is formed of a coil having a relatively large inside diameter and is simply fitted idly over the rotating shaft 140. It will be understood by reference to Figures 8-A, 8-B, 8-C and 8-D that when the rotating shaft 140 is rotated in the direction of arrow 90, the agitating member 142 is properly vibrated in the radial direction by the action of the crank-like deformed portion 144. Furthermore, owing to the friction between the agitating member 142 and the crank-like deformed portion 144 of the rotating shaft 140, the agitating member 142 is rotated in the direction of arrow 90 to some extent incident to the rotation of the rotating shaft 140. If desired, it is possible to provide at the inside surface of the agitating member 142 a protrusion with which the crank-like deformed portion 144 can engage intermittently, and accurately rotate the agitating member 142 intermittently by a predetermined angle according to the rotation of the rotating shaft 140. As stated above, the agitating member 142 is simply fitted idly over the rotating shaft 140. Thus, when the excessively large rotation resisting force acts on the agitating member 142, the agitating member 142 slips with respect to the rotating shaft 140 and the excessively large rotation resisting force is cushioned. If desired, instead of forming the crank-like deformed portion 144 in the rotating shaft 140, it is possible to form a plurality of axially spaced eccentric cylindrical portions 146′ in the rotating shaft 140 as shown in Figure 9, or one relatively long eccentric cylindrical portion 148 extending continuously in the axial direction in the rotating shaft 140 as shown in Figure 10. It is also possible if desired to use an agitating member 150 shown in Figure 11 instead of the coil-like agitating member 142. The agitating member 150 is of a hollow cylindrical shape, and a plurality of pores 152 are formed in its cylindrical wall. This agitating member 150, too, is mounted on the rotating shaft 140 by merely fitting it idly over the shaft 140. Instead of providing one axially extending relatively long agitating member 150, a plurality of relatively short axially extending agitating members may be mounted on the rotating shaft 140.

Claims: An image-forming machine comprising a latent electrostatic image developing device (10) for developing a latent electrostatic image formed on an electrostatographic material, said developing device (10) including a development housing (50) for holding a developer (60), a developer applicator means (72) for applying the developer (60) in the development housing (50) to the electrostatographic material and a developer agitating means (74) for agitating the developer (60) in the development housing (50), said developer agitating means (74) including a rotating shaft (86) and an agitating member (88) having a mounting portion (116) for mounting the agitating member (88) to the rotating shaft (86), characterized in that an inside diameter of said mounting portion (116) in free unmounted condition is slightly smaller than the outside diameter of a receiving portion (124) on the rotating shaft (86), such that when a rotation resisting force above a certain limit acts on the agitating member, the agitating member (88) can slip with respect to the rotating shaft (86). The image-forming machine of claim 1, wherein the mounting portion (116) has a coil spring shape and is mounted on said receiving portion (124) by resiliently expanding the inside diameter of the coil spring shape mounting portion (116) and fitting it over the receiving portion (124) of the rotating shaft (86). The image-forming machine of claim 2, wherein the agitating member (88) is formed of one continuous metallic wire, and has two end mounting portions (116) axially spaced from each other and mounted on the rotating shaft (86), arm portions (118) extending radially from the both end mounting portions (116) respectively, and a main agitation operative portion (120) extending between the arm portions. The image-forming machine of claim 3, wherein the main agitation operative portion (120) of the agitating member extends substantially parallel to the rotating shaft (86). The image-forming machine of claim 1, wherein at least two agitating members (88, 130) are mounted on the rotating shaft (86), and the main agitation operative portion (120) of one agitating member (88) is larger in a radial distance from the rotating shaft (86) than the main agitation operative portion (134) of the other agitating member (130). An image-forming machine comprising a latent electrostatic image developing device for developing a latent electrostatic image formed on an electrostatographic material, said developing device (10) including a development housing (50) holding a developer (60), a developer applicator means (72) for applying the developer (60) in the development housing (50) to the electrostatographic material, and a developer agitating means (138) for agitating the developer (60) in the development housing (50), said developer agitating means (138) having a rotating shaft (140) and an agitating member (142) mounted on the rotating shaft (140); wherein the agitating member (142) has an inside diameter larger than the outside diameter of the rotating shaft (140), and is idly fitted over the rotating shaft (140), characterized in that an inside surface of the agitating member (142) is provided with a protrusion. The image-forming machine of claim 6, wherein the agitating member (142) is formed of a coil. The image-forming machine of claim 6, wherein the agitating member is formed of a hollow cylindrical body (150) having a plurality of spaced holes (152) formed thereon. The image-forming machine of claim 6, wherein the rotating shaft (140) has an eccentric portion (144) and when the rotating shaft is rotated, the agitating member (142) is vibrated in the radial direction by the action of the eccentric portion (144). The image-forming machine of claim 9, wherein the eccentric portion (144) is constructed of a crank-like deformed portion. The image-forming machine of claim 10 wherein the eccentric portion is constructed of an eccentric cylindrical portion (146′, 148).

Inventors: KOYAMA SHIGEO, MAEDE HIROYUKI, MAESHIMA MASANOBU, OTSUKA MASAO, SATO TOSHIHIRO, TSUCHIYA HIROAKI, TSUTSUI EIJI, KOYAMA, SHIGEO, MAEDE, HIROYUKI, MAESHIMA, MASANOBU, OTSUKA, MASAO, SATO, TOSHIHIRO, TSUCHIYA, HIROAKI, TSUTSUI, EIJI
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO., LTD.
Application year: 1989
Main classification: G03G15
IPC codes: G03G15, G03G21