Developing device

Abstract: A developing device suitable for in an electrophotographic recording apparatus includes either a toner stirring portion (23) arranged in a toner hopper portion, the toner stirring portion being provided with a portion for varying toner conveying speed, or in the toner a toner stirring and moving means (42) provided in a toner cartridge. Printing irregularity tends not to occur on printing paper even if the printing is performed when the amount of toner, which is collected in the toner hopper portion is so reduced as not to cover the toner hopper stirring portion sufficiently.

Description: The present invention relates to a developing device for xerographic (otherwise known as electrophotographic) recording apparatus such as a printer or a copier. A developing device of this type is disclosed in EP-A-0435259 filed by the present applicant. In this developing device, a toner is supplied from a toner cartridge to a developing portion to be collected in a toner hopper portion, and is stirred by a stirring means provided in the toner hopper portion. Thereafter the toner is supplied to a photoconductor drum via a supply roller and developing roller. In some electrophotographic recording apparatus, an indicator for positioning a printing paper is set at the central portion of the printing paper in the width direction thereof. Such an electrophotographic recording apparatus has typically a stirring means for the developing device as illustrated in Fig. 20. This device comprises: a developing portion for supplying toner to an electrostatic latent image on a photoconductor drum and developing said latent image, a toner hopper portion for storing toner and supplying the toner to the developing portion, a stirring portion disposed in the toner hopper portion and composed of a shaft, and first and second helical members which are wound around the shaft in opposite directions, wherein the first and second helical members are rotated to thereby stir a part of the toner and convey the same toward the central portion of the toner hopper portion; the first and second helical members comprising respective coil shaped members. US-A-4 566 776 discloses a stirring means having first and second helical members comprising respective coil shaped members. The device of Fig. 20 will now be described in more detail. A toner hopper stirring means 80 comprises a shaft 19 and helical members 81a and 81b respectively formed of springs. The helical members 81s and 81b have the same coil diameters and the same winding pitches. The helical members 81a and 81b are wound around a shaft in the directions opposite to each other. When the shaft 19 of the toner hopper opposite to each other. When the shaft 19 of the toner hopper stirring means 80 is turned in the direction of the arrow C, the toner positioned at both ends of the shaft 19 is stirred and moved toward the central portion of the shaft 19. If the feeding standard of the electrophotographic recording apparatus is set at the central portion of the printing papers, a printing frequency is increased at the central portion of the photoconductor drum when printing is performed on the printing papers having different sizes, so that toner is much consumed at the central portion of the toner hopper portion in the developing device but is supplemented with the toner which is moved toward the central portion of the toner hopper portion by the toner hopper stirring means 80. However, in the conventional developing apparatus, the toner collected in the toner hopper portion is always conveyed by the toner hopper stirring means toward the central portion of the toner hopper portion at a constant speed and supplied to the supply roller of the developing portion. Accordingly, there is no problem when the amount of toner collected in 15 the toner hopper portion is much enough to sufficiently cover the toner hopper portion but there arises the problem that the toner is locally positioned at the central portion of the toner hopper portion and is reduced at the both ends of the toner hopper portion when the amount of the toner reduced to the extent not to sufficiently cover the toner hopper stirring portion. If the printing is performed in the latter case, there is a problem that a printing irregularity occurs on the printing paper, which deteriorates the printing quality. Especially, if printing few characters on a printing paper continues, the printing quality is remarkably deteriorated. It is an object of the present invention to provide a developing device capable of preventing printing irregularity on a printing paper even if the printing is performed at the state where the amount of the toner is reduced in a toner hopper portion and the toner cannot sufficiently cover a toner hopper stirring portion. According to the present invention, there is provided a developing device of the type defined above, characterized by the first and second helical members being arranged such that the speed at which toner is conveyed is not uniform along their respective axes. Preferred features of the present invention are set out in claims 2 to 6, appended hereto. The present invention also extends to a xerographic apparatus incorporating a developing device according to the present invention. Embodiments of the present invention will now be described, by way of example, with reference to Figs. 1 to 19 of the accompanying drawings, in which: Fig. 1 is a perspective view showing an external appearance of a developing device according to a first embodiment of the present invention; Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1; Fig. 3 is a perspective view showing an external appearance of a toner hopper stirring portion of the developing device in Fig. 1; Fig. 4 is a view showing a circulating state of toner in the toner hopper stirring portion in Fig. 3; Fig. 5 is a perspective view showing an external appearance of a toner hopper stirring portion of a developing device according to a second embodiment of the present invention; Fig. 6 is a view showing a circulating state of toner in the toner hopper stirring portion in Fig. 5; Fig. 7 is a perspective view showing an external appearance of a toner hopper stirring portion of a developing device according to a third embodiment of the present invention; Fig. 8 is a view showing a circulating state of toner in the toner hopper stirring portion in Fig. 7; Fig. 9 is a perspective view showing an external appearance of a toner hopper stirring portion of a developing device according to a fourth embodiment of the present invention; Fig. 10 is a view showing a circulating state of toner in the toner hopper stirring portion in Fig. 9; Fig. 11 is a cross-sectional view of a developing device according to a fifth embodiment of the present invention; Fig. 12 is a view showing a connecting state of rollers which are driven when a toner cartridge is mounted on the developing device in Fig. 11; Fig. 13 is a perspective view showing an external appearance of the toner cartridge which is employed in the sixth embodiment in Fig. 11; Fig. 14 is a cross-sectional view taken along line XIV-XIV in Fig. 13; Fig. 15 is a perspective view showing a cartridge stirring portion in Fig. 11; Fig. 16 is a perspective view showing an external appearance of an electrophotographic recording apparatus employing the developing device according to the first to fifth embodiments of the present invention; Fig. 17 is a view showing a printing process in the electrophotographic recording apparatus; Fig. 18 is a view showing the state where a printing paper is fed to the developing device; Fig. 19 is a view showing a conveying state of collected toner; and Fig. 20 is a perspective view showing an external appearance of the toner hopper portion of a conventional developing device. First Embodiment (Figs 1 to 4): A developing device according to a first embodiment will be described with reference to Figs 1 to 4 in which elements which are common to these figures are denoted at the same numerals. In Fig. 1 showing an external appearance of the developing device, a toner cartridge 4 for storing toner as one component developer extends in the width direction of a printing paper and is mounted on a mounting portion 3a of a frame 3 of a developing device 1. The printing paper is fed toward the developing device 1 in the direction of the arrow A. In Fig. 2 showing a cross-sectional view taken along the line II-II in Fig. 1, the developing device 1 comprises a toner hopper portion 8 for collecting toner 5 therein, a photoconductor drum 17, and a developing portion 9 for supplying toner 5 on an electrostatic latent image on the photoconductor drum 17 to thereby develop the same. The developing portion 9 comprises a supply roller 10, a developing roller 13, and a developing blade 16. The toner hopper portion 8 is positioned under the toner cartridge 4 and has a toner hopper stirring portion 21 which is positioned adjacent to the developing portion 9 for stirring the collected toner 5. Fig. 3 shows a perspective view of an external appearance of the toner hopper stirring portion in the developing device 1. The toner hopper stirring portion 21 comprises a shaft 19 and first and second helical members 22 and 23 respectively fixed to the shaft 19 by welding, etc. The first and second helical members 22 and 23 are formed of coil springs by machining a wire such as piano wire. The first helical member 22 has a toner conveying speed varying portion 22a at the central portion thereof and has coils of same winding pitches and same outer diameters at the other portions thereof. At the toner conveying speed varying portion 22a the coil is closely wound around the shaft 19 being in close contact with the shaft 19 at the inner diameter thereof. The toner conveying speed at the toner conveying speed varying portion 22a can be reduced remarkably compared with those at other portions of the first helical member 22. The second helical member 23 is wound on the shaft 19 in the direction opposite to that of the first helical member 22 and is formed by the coil with the same outer diameter, A toner conveying speed varying portion 23a is provided at the central portion of the second helical member 23 in the same way as the first helical member 22. When the toner hopper stirring portion 21 rotates of the shaft 9 in the direction of the arrow C while stirring the toner, the first helicl member 22 conveys toner in the direction of the arrow G and the second helical member 23 conveys toner in the direction of the arrow H. The operation of the developing device 1 will be described with reference to Fig. 2. The toner cartridge 4 mounted on the developing device 1 turns a shutter 7 disposed thereunder in the direction of the arrow B to open an opening 6, thereby dropping the toner 5 downward from the opening 6. The dropped toner 5 is collected in the toner hopper portion 8 disposed under the toner cartridge 2. Toner 5 collected in the toner hopper portion 8 is stirred by the rotation of the toner hopper stirring portion 21, The toner hopper stirring portion 21, the supply roller 10, the developing roller 13 and the photoconductor drum 17 have respectively their shafts 19, 11, 15 and 18 which are respectively turnably supported by the frame 3, Each of the shafts 19, 11, 15 and 18 has one end to which a gear, not shown, is fixed, and these gears mesh with one another to constitute a chain of gears. When the chain of gears are driven, the toner hopper stirring portion 21, the supply roller 10, the developing roller 13 and the photoconductor drum 17 are synchronously rotated in the directions of the arrows C, D, E and F. The toner 5 supplied from the toner hopper portion 8 to the supply roller 10 is supplied to the developing roller 13 by turning of the supply roller 10 in the direction of the arrow D. The toner 5 thus supplied to the developing roller 13 is brought into close contact with the developing blade 16 by the turning of the developing roller 13 in the direction of the arrow E, whereby a thin toner layer is formed on the surface of the developing roller 13. The thin layered toner 5 is supplied to the electrostatic latent image on the surface of the photoconductor drum 17 to develop the latent image. The stirring operation of the toner hopper stirring portion 21 will be described hereinafter with reference to Fig. 4 which shows the state where toner is circulated in the toner hopper stirring portion 21. In Fig. 4 the toner 5 is denoted at two dot chain line and the first and second helical members 22 and 23 are disposed at a given interval from the frame 3. Assume that the end side of the first helical member 22 and the side opposite to the end side of the first helical member 22 at the central side of the toner hopper stirring portion 21 are respectively called as an S portion and a T portion bordering on each other at the toner conveying speed varying portion 22a. When the amount of toner 5 in the toner hopper portion is too reduced to sufficiently cover the toner hopper stirring portion 21, the toner 5 conveyed from the end side of the first helical member 22 by the S portion forms a heap portion 5a at the portion adjacent to the toner conveying speed varying portion 22a. The heap portion 5a is formed because of the fact that the toner conveying speed varying portion 22a has a small conveying ability and the toner 5 conveyed from the end side of the toner hopper stirring portion 21 is successively supplied to the toner conveying speed varying portion 22a. When the toner 5 is further conveyed by the S portion, the toner 5 on the heap portion 5a starts to collapse toward the central side of the toner hopper stirring portion 21. The toner 5 thus collapsed from the heap portion 5a toward the central side of the toner hopper stirring portion 21 is conveyed by the T portion toward the central side of the toner hopper stirring portion 21 to thereby form a heap portion 5b. The toner 5 conveyed by the second helical member 23 is conveyed in the same way as by the first helical member 22. At the state where the amount of toner 5 is too small to sufficiently cover the toner hopper stirring portion 21, a part of the toner 5 to be conveyed from the end side of the toner hopper stirring portion 21 toward the central side thereof is blocked by the toner conveying speed varying portion 22a and forms a heap portion at the blocked portion. Accordingly, the toner 5 is not concentrated at the central portion of the toner hopper portion 8 but distributed therein so that the height of the toner 5 is uniformed. According to the first embodiment, one toner conveying speed varying portion is provided for one helical member but a plurality of toner conveying speed varying portions may be provided for each helical member if the hopper stirring portion is long. Second Embodiment (Fig. 5): A developing device according to a second embodiment will be described with reference to Fig. 5 which shows an external appearance of a toner hopper stirring portion 24. The developing device of the second embodiment is the same as that of the first embodiment except the toner hopper stirring portion 24, hence elements except the toner hopper stirring portion 24 are omitted to be explained. The toner hopper stirring portion 24 comprises a shaft 19 and first and second helical members 25 and 26 which are fixed to the shaft 19 by welding, etc. The first and second helical members 25 and 26 are formed of coils by machining a wire such as a piano wire. The first helical member 25 has a toner conveying speed varying portion 25a at the central portion thereof. The toner conveying speed varying portion 25a is closely wound around the shaft 19 being in close contact with the shaft 19 at the inner diameter thereof. The first helical member 25 is formed of a coil outer diameter of which is the same but winding pitches of which at the central side is smaller than those at the end side of the toner hopper stirring portion 24 while both sides border on each other at the toner conveying speed varying portion 25a. The toner conveying speed at the toner conveying speed varying portion 25a can be reduced remarkably compared with those at other sides of the first helical member 25 and the toner conveying speed at the central side of the toner hopper stirring portion 24 is reduced compared with that at the end side thereof. The second helical member 26 is wound around the shaft 19 in the direction opposite to that of the first helical member 25 and is formed of a coil outer diameter of which is the same as that at the first helical member and is provided with a toner conveying speed varying portion 26a at the central portion thereof. Winding pitches of the coil at the central side of the toner hopper stirring portion 24 is smaller than winding pitches of the coil at the end side thereof while both sides border on each other at the toner conveying speed varying portion 25a. The toner hopper stirring portion 24 stirs toner by the rotation of the shaft 19 in the direction of the arrow C while the first helical member 25 conveys toner in the direction of the arrow G and the second helical member 26 conveys toner in the direction of the arrow H. The stirring operation of the toner hopper stirring portion 24 will be described with reference to Fig.6 which shows the state where toner is circulated in the toner hopper stirring portion 24 according to the second embodiment. In Fig. 6, denoted at a two dot chain line is toner 5 and the first and second helical members 25 and 26 are disposed in a given interval relative to the frame 3, Assume that an end side portion of the first helical member 25 is a U portion and a central side portion is a V portion while the U portion and the V portion are bordered on each other at the toner conveying speed varying portion 25a. When the amount of toner 5 in the toner hopper portion is reduced to the extent that the toner hopper stirring portion 24 is not sufficiently covered , the toner 5 conveyed from the end to the U portion of the first helical member 25 forms a heap portion 5c at the portion adjacent to the toner conveying speed varying portion 25a, The heap portion 5c is formed because of the fact that the toner conveying speed varying portion 25a has a small conveying ability and the toner 5 conveyed from the end side of the toner hopper stirring portion 24 is successively supplied to the toner conveying speed varying portion 25a, When the toner 5 is further conveyed by the U portion, toner 5 on the heap portion 5c starts to collapse toward the central portion of the toner hopper stirring portion 24. The toner 5 thus collapsed from the heap portion 5c toward the central portion of the toner hopper stirring portion 24 is conveyed by the V portion toward the central portion of the toner hopper stirring portion 24 to thereby form a heap portion 5d. Toner 5 conveyed by the second helical member 26 is conveyed in the same way as the first helical member 25. At the state where the amount of toner 5 is too reduced to sufficiently cover the toner hopper stirring portion 24, the toner 5 to be conveyed from the end portion of the toner hopper stirring portion 24 toward the central portion thereof is blocked by the toner conveying speed varying portion 25a and forms a heap portion at the blocked portion. According to the second embodiment, since the conveying speed at the V portion is set to be smaller than that at the U portion, the amount of toner to be conveyed from the V portion to the central portion of the toner hopper stirring portion 24 is less than the amount of toner to be successively conveyed from the U portion to the toner conveying speed varying portion 25a. Accordingly, much toner heaps on the heap portion 5c compared with that of the first embodiment and the amount of toner heaps on the V portion is greater than that of the first embodiment. Furthermore, since the amount of toner to be conveyed from the V portion to the central portion of the toner hopper stirring portion 24 is reduced, the amount of toner to heap at the heap portion 5d in the central portion is reduced so that the height of the heap portion 5d is low and the slope in the heap portion 5d is gentle. According to the second embodiment, since the amount of toner which heaps on the toner conveying speed varying portion 25a is increased and the amount of toner which heaps at the central portion is reduced, the toner is distributed in the toner hopper portion so that the height of the toner 5 is uniformed. Third Embodiment (Fig. 7): A developing device according to a third embodiment will be described with reference to Fig. 7 which shows an external appearance of a toner hopper stirring portion 27. The developing device of the second embodiment is the same as that of the first embodiment except the toner hopper stirring portion 27, hence elements except the toner hopper stirring portion 27 are omitted to be explained. The toner hopper stirring portion 27 comprises a shaft 19 and first and second helical members 28 and 29 which are fixed to the shaft 19 by welding, etc. The first and second helical members 28 and 29 are formed of coil springs by machining a wire such as a piano wire. The first helical member 28 is formed of a coil of which the outer diameter is constant along its length but winding pitches are different in its two portions bordering on each other at the central portion 28a thereof. Winding pitches of the central side portion 28b is smaller than those of an end side portion of the first helical member, i.e., at the end side of the shaft 19. As a result, the toner conveying speed at the side of the central side portion 28b is slower than that at the end side portion while both side portions are bordered on each other at the central portion 28a. The second helical member 29 is formed of a coil outer diameter of which is same but wound in the direction opposite to the first helical member 28. In the second helical member winding pitches of the central side portion 29b is smaller than those of the end side portion, both side portions being bordered on each other at the middle portion 29a. The toner hopper stirring portion 27 stirs toner by the rotation of the shaft 19 in the direction of the arrow C so that the first helical member 28 conveys toner in the direction of the arrow G and the second helical member 29 conveys toner in the direction of the arrow H. The stirring operation of the toner hopper stirring portion 27 will be described with reference to Fig.8 which shows the state where toner is circulated in the toner hopper stirring portion 27 according to the third embodiment. In Fig. 8, denoted at a two dot chain line is toner 5 and the first and second helical members 28 and 29 are disposed at a given interval relative to the frame 3. Assume that an end portion of the first helical member 28 is a W portion and a central side portion thereof is an X portion while the W portion and the X portion are bordered on each other at the central portion 28a. When the amount of toner in the toner hopper portion is too reduced to sufficiently cover the toner hopper stirring portion 27, the toner 5 conveyed from the end side of the toner hopper stirring portion 27 forms a heap portion 5e at the portion adjacent to the middle portion 28a because the conveying speed in the W portion is set to be greater than that in the X portion, so that the amount of toner successively fed to the W portion exceeds that conveyed to the central portion of the toner hopper stirring portion 27 by the X portion. The toner 5 conveyed to the central portion by the X portion forms a heap portion 5f. The second helical member 29 conveys toner in the same way as the first helical member 28. When the amount of toner in the toner hopper portion is too reduced to sufficiently cover the toner hopper stirring portion 27, the toner 5 conveyed from the end side to the central portion of the toner hopper stirring portion 27 forms a heap portion 5e at the portion adjacent to the middle portion 28a because of the difference in conveying speeds between the W portion and the X portion. According to the third embodiment, the toner conveying speed is slowed from the middle portion 28a, but the third embodiments has not toner conveying speed varying portions which are formed in the second embodiment. Accordingly, the amount of toner which heaps on the heap portion 5e is less than that in the second embodiment in which the toner conveying power is not applied to the toner at the toner conveying speed varying portion. Since the amount of toner which heaps on the X portion is large but amount of toner which heaps on the heap portion 5f is small in the same way as the second embodiment, the toner 5 in the toner hopper portion is distributed more uniformly. Fourth Embodiment (Figs. 9(a) and 9(b)) A developing device according to a fourth embodiment will be described with reference to Fig. 9(a) which shows an external appearance of a toner hopper stirring portion 30 thereof. The developing device of the fourth embodiment is the same as that of the first embodiment except the toner hopper stirring portion 30, hence elements except the toner hopper stirring portion 30 are omitted to be explained. The toner hopper stirring portion 30 comprises a shaft 19 and first and second helical members 31 and 32 which are fixed to the shaft 19 by welding, etc. The first and second helical members 31 and 32 are formed of coils respectively by machining a wire such as a piano wire. The first helical member 31 is formed of a coil which has constant winding pitches. The outer diameter of the coil between one end side of the shaft 19 to a changing point 31a is gradually decreased from the changing point 31a to the other side thereof in the direction of the central portion of the shaft 19. The second helical member 32 is formed of a coil which is wound in the direction of contrary to that of the first helical member 31 and has constant winding pitches. The outer diameter of the coil between one end side thereof to a changing point 32a is gradually decreased from the changing point 32a to the other side thereof in the direction of the central portion of the shaft 19. The toner hopper stirring portion 30 stirs toner by the rotation of the shaft 19 in the direction of the arrow C so that the first helical member 31 conveys toner in the direction of the arrow G and the second helical member 32 conveys toner in the direction of the arrow H while stirring the same. The stirring operation of the toner hopper stirring portion 30 will be described with reference to Fig.10 which shows the state where toner is circulated in the toner hopper stirring portion 30 according to the fourth embodiment. In Fig. 10, denoted at a tow dot chain line is toner 5 and the first and second helical members 31 and 32 are disposed at a given interval relative to the frame 3. As set forth above, the first helical member 31 is such structured that the toner conveying speed is gradually slowed from the end side portion to the central side portion thereof. Accordingly, the amount of toner to be conveyed by the first helical member 31 is gradually increased from the central portion to the end side. If the amount of toner is too reduced to sufficiently cover the toner hopper stirring portion 27, a heap portion 5g is formed at the central portion of the toner hopper stirring portion 30. The toner to be conveyed by the second helical member 32 is conveyed in the same manner as the first helical member 31. According to the fourth embodiment, the toner conveying speed is gradually slowed from the end side portion to the central side portion of each of the first and second helical members 31 and 32, the toner is prevented from heaping locally, which entails more uniform supply of the toner. The toner conveying speed is changed by varying the diameter of the coil as set forth above but can be changed by varying winding pitches of the coil as illustrated in Fig. 9 (b). That is, the winding pitches of the coil of a helical member 31′ of a toner hopper stirring portion 30′ are varied to be gradually reduced from a changing point 31′a in the toner conveying direction to thereby vary the toner conveying speed so as to uniformly supply the toner. Fifth Embodiment (Fig. 11): A developing device according to a fifth embodiment will be described with reference to Fig. 11 which is a cross-sectional view of the developing device 40. The developing device 40 has a toner cartridge 41 which contains toner therein and extends in the width direction of a printing paper to be fed and is mounted on the mounting portion 3a of the frame 3 of the developing device 40. As illustrated in Fig. 11, the toner cartridge 41 mounted on the developing device 40 has a cartridge stirring portion 42 which conveys the toner 5 in the cartridge 41 while stirring the same, The cartridge stirring portion 42 conveys the toner 5 in the direction opposite to the direction in which the toner stirring portion 9 in the toner hopper portion 8 conveys the toner 5. The cartridge stirring portion 42 is connected to a driving means for driving a supply roller 10, etc. when the toner cartridge 41 is mounted on the developing device 40. Fig. 12 shows a connecting state of the driving means when the toner cartridge 41 is mounted on the developing device. As illustrated in Fig. 12, shafts 19, 11 and 15 are driven by driving gears 33, 34 and 35 and the cartridge stirring portion 42 is driven by a driving gear 48. The driving gears 33 and 34, 34 and 35, and 35 and 48 are connected with one another via idle gears 36. Each gear is roughly illustrated by a (one dot chain line) pitch circle. Solid lines in Fig. 12 shows the state where the toner cartridge 41 is mounted on the developing device and two dot chain lines in Fig. 12 show the state where the toner cartridge 41 is dismounted from the developing device, When the toner cartridge 41 is mounted on the developing device, the driving gear 48 is connected to the idle gears 36 to thereby transmit the driving force to the cartridge stirring portion 42. Other arrangements of the developing device are the same as those in the first embodiment, hence the explanation thereof is omitted. Sixth Embodiment (Figs. 13 to 15) Fig. 13 shows an external appearance of a toner cartridge as employed in a developing device according to a sixth embodiment. In Fig. 13, the toner cartridge comprises an outer cylinder 43 and an inner cylinder 44. The outer and inner cylinders 43 and 44 are substantially same in length and the inner cylinder 44 is brought into contact with the inner periphery of the outer cylinder 43 at the entire length thereof. End plates 45a and 45b are fixed to both ends of the inner cylinder so as to close the inner cylinder 44 thereby. Outer diameters of the end plates 45a and 45b are substantially the same as the outer diameter of the outer cylinder 43. With such an arrangement, the outer cylinder 43 does not get out of position and can turn relative to the inner cylinder 44. Both the outer and inner cylinders 43 and 44 have openings 46 and 47 at their side surfaces, When both the outer and inner cylinders 43 and 44 are turned relative to each other, the toner cartridge 41 can be opened, whereby the toner in the toner cartridge 41 can drop in the toner hopper portion 8 through the openings 46 and 47. The toner cartridge 41 has inside thereof a cartridge stirring portion 43 which is supported integrally with a gear 48 by the toner cartridge 41. In Fig. 14 which is a cross-sectional view taken along arrows XIV-XIV in Fig. 13, the gear 48 has a shaft portion 48a and a pawl 48b which are integrally formed with the gear 48. The shaft portion 48a has a central axis, not shown, which is common to the gear 48 and a first helical portion 50. The central axis penetrates a round hole 44b provided at the center of the end surface 44a of the inner cylinder 44 and is turnably supported by the inner cylinder 44. The pawl 48b penetrates an angular hole 49a provided in an end surface member 49 and engages with a projecting portion 49b. A root of the pawl 48b which penetrates the angular hole 49a has a cross-sectional shape which is brought into contact with an inner surface of the angular hole 49a, whereby the end surface member 49 is turned while driven by the rotation of the gear 48. The end surface member 49 is a rectangular metallic plate to which the first helical portion 50, which is formed by machining a wire such as a piano wire, etc., is fixed by silver brazing, soldering or (projection) welding. The gear 48 is connected to a driving means for driving the supply roller 10 (refer to Fig. 4), etc., when the toner cartridge 41 is mounted on the developing device 40. Fig. 15 is a perspective view of an external appearance of the cartridge stirring portion 42. As illustrated in Fig. 15, the cartridge stirring portion 42 comprises the gear 48, the end surface member 49, the first helical member 50, a central portion 51 and a second helical portion 52. The first and second helical portions are formed of coils by machining a wire such as a piano wire,etc. The first helical portion 50, the central portion 51 and the second helical portion 52 are fixed to one another by silver brazing, soldering or (projection) welding, etc. The first helical portion 50 and the second helical portion 52 are wound in the directions opposite to each other. Accordingly, when the gear 48 is driven to turn the cartridge stirring portion 42 in the direction of an arrow I, toner, not shown, is stirred and conveyed in the toner cartridge 41 from the central portion 51 to the end side portions of the first and second helical portions 50 and 52 in the directions of arrows J and K. An operation of the developing device is described with reference to Fig.s 11 and 13. The toner cartridge 41 mounted on the developing device 40 opens the openings 46 and 47 to thereby drop the toner 5 to the toner hopper portion which is disposed under the toner cartridge 41. The toner 5 dropped and heaped on the toner hopper portion 8 is stirred in the toner hopper portion 8 by the rotation of the toner hopper stirring portion 9 in the direction of the arrow C and is conveyed toward the central portion of the toner hopper portion 8 while stirred and a part of the toner 5 is supplied to the supply roller 10 of the developing portion 9. The toner supplied from the toner hopper portion 8 to the supply roller 10 is supplied to the electrostatic latent image on the surface of the photoconductor drum 17 and develops the electrostatic latent image in the same manner as the conventional manner. When the amount of toner in the toner cartridge 41 begins to reduce, the toner 5 tends to be distributed locally at both ends of the toner cartridge 41 since it is conveyed by the turning of the toner cartridge stirring portion 42 in the direction of the arrow I. Accordingly, the toner 5 is supplied concentrically to the both ends of the toner hopper portion 8. In the toner hopper portion 8, although the toner 5 on both ends of the toner hopper portion 8 is conveyed toward the central portion thereof by the stirring operation of the toner hopper stirring portion 9, the toner is prevented from distributing locally in the central portion thereof since the toner 5 supplied from the toner cartridge 41 is concentrically supplied to both ends thereof. In the fifth embodiment, in the toner hopper portion 8, the toner is stirred and conveyed from both ends thereof toward the central portion thereof while the toner is concentrically supplied to both ends thereof from the toner cartridge 41, whereby the toner is prevented from heaping locally and is supplied uniformly to the developing roller, Although the toner is stirred and conveyed toward both ends of the toner cartridge 41, the toner conveying direction in the toner cartridge 41 is not limited to both ends thereof but it may be opposite to the toner conveying direction by the toner hopper stirring portion in the toner hopper portion. It is possible to prevent the reduction of toner at both ends of the toner hopper portion to thereby facilitate the uniform supply of the toner if the arrangement of fifth embodiment is combined with the toner hopper stirring portions as set forth in the first to fourth embodiments. Fig. 16 is a perspective view of an external appearance of the electrophotographic recording apparatus employing the developing device of the present invention. In Fig. 16, the electrophotographic recording apparatus 60 includes a power source switch 61 for actuating the electrophotographic recording apparatus 60, an operation panel for indicating setting of a printing condition and an error state of the electrophotographic recording apparatus 60 and a stacker on which the printed paper is let out. The electrophotographic recording apparatus 60 has printing paper cassettes 64 and 65 at one side thereof. The printing paper casettes 64 and 65 are detachable from the electrophotographic recording apparatus 60 and stack the printing papers thereon. Fig. 17 is a view explaining a printing process of the electrophotographic recording apparatus 60. In Fig. 17, the electrophotographic recording apparatus 60 includes therein feed rollers 66 and 67 for feeding the printing papers which are stacked on the printing paper cassettes 64 and 65, pairs of rollers 68, 69 and 70 for conveying the printing papers fed from the printing paper casettes 64 and 65 in the electrophotographic recording apparatus 60, an electrostatic charger 76 for uniformly applying electrostatic charge to the surface of the photoconductor drum 17, an LED array 71 for emitting light on the photoconductor drum 17 to thereby form an electrostatic latent image on the surface of the photoconductor drum 17, a transfer electrifier 72 for transferring the toner attached to the photoconductor drum to the printing paper and a pair of heat rollers 73 for fixing the toner, transferred on the printing paper, to the printing paper by heat and pressure. The printing process will be described with reference to Fig. 17. The printing paper fed from the printing cassette 64 or 65 through the feed roller 66 or 67 is conveyed to the photoconductor drum 17 through the pair of rollers 68. The feed of a printing paper 81 to the developing device 1 provided with the photoconductor drum 17 will be described with reference to Fig. 18. In Fig. 18, a center line 82 represents a center of a printing paper conveying path 80 in the width direction W thereof and a center line 83 represents a center of the printing paper 81 in the width direction w thereof. The printing paper 81 is fed toward the developing device in the direction of arrow A. At this time, the printing paper is fed by aligning its center line 83 with the center line 82 of the printing paper conveying path. Referring back to Fig. 17, the photoconductor drum 17 is turned by the driving source, not shown, and is uniformly charged with electricity by the electrifier 76 and the electrostatic latent image is formed on its surface by the LED array 71 while the printing paper 81 is conveyed to the photoconductor drum 17, The electrostatic latent image charged with electricity on the surface of the photoconductor drum 17 is visualized by the toner supply roller 13 for supplying the toner 5. The visualized toner image is transferred on the printing paper 81 by the transfer electrifier 72. The toner which has not been transferred on the printing paper 81 but remains on the surface of the photoconductor drum 17 is scraped by a cleaning blade 74 which contact closely to the surface of the photoconductor drum 17, whereby the photoconductor drum 17 is cleaned and next image forming process starts. The toner thus scraped by the cleaning blade 74 is collected and conveyed to the toner hopper portion 8 and is recycled. The recycle of the collected toner will be described with reference to Fig. 19 showing the conveying of the collected toner. In Fig. 19 showing the developing device from the side thereof, the toner collected from the photoconductor drum 17 by the cleaning blade 74 is conveyed to a recycling route 77, which is provided at the side of the developing device, by a collected toner conveying spiral 75. The toner conveyed to the recycling route 77 is conveyed by a recycling spiral 78 to a portion adjacent to the end of the toner hopper stirring portion 21 in the toner hopper portion 8. Both the collected toner conveying spiral 75 and the recycling spiral 78 are means for conveying the toner 5 and are formed of spiral members (the recycling spiral 78 alone is illustrated as a spiral member in Fig. 19) which are turned to thereby convey the toner. Referring back to Fig. 17, the toner image is transferred by the transfer electrifier 72 on the printing paper 81 and the thus transferred toner image is fixed on the printing paper by the heat roller 73. The printing paper having the toner image fixed thereto is discharged toward the stacker portion 63 and the printing process ends. Although the invention has been described in its preferred form with a certain degree of particularity, it is to be understood that many variations and changes are possible in the invention without departing from the scope thereof.

Claims: A developing device (1) comprising: a developing portion (9) for supplying toner to an electrostatic latent image on a photoconductor drum (17) and developing said latent image, a toner hopper portion (8) for storing toner and supplying the toner to the developing portion, a stirring portion (21) disposed in the toner hopper portion (8) and composed of a shaft (19), and first and second helical members (22,23) which are wound around the shaft in opposite directions, wherein the first and second helical members are rotated to thereby stir a part of the toner and convey the same toward the central portion of the toner hopper portion; the first and second helical members comprising respective coil shaped members, characterized by the first and second helical members (22,23) being arranged such that the speed at which toner is conveyed is not uniform along their respective axes. A developing device according to Claim 1, wherein the first and second helical members are formed with portions (22a,23a) of reduced winding diameter. A developing device according to Claim 1, wherein the first and second helical members comprise, arranged in the direction of toner travel, a portion (U) having a first diameter and a first pitch, a portion (25a,26a) having a second reduced diameter and a portion (V) having a second reduced pitch. A developing device according to Claim 1, wherein the first and second helical members comprise, arranged in the direction of toner travel, a first portion (W) having a first pitch and a second portion (X) having a second reduced pitch. A developing device according to Claim 1, wherein the first and second helical members taper in the direction of toner travel. A developing device according to claim 1, wherein the pitch of the first and second helical members progressively reduces in the direction of toner travel. A developing device according to any preceding claim, further comprising: a toner cartridge (41) for storing toner and supplying it to the toner hopper portion (8), a toner cartridge mounting portion (3a) and drive means for driving the first and second helical members, wherein the toner cartridge includes a toner cartridge stirring portion (42) composed of third and fourth helical members (50,52) which are wound oppositely to each other and the driving means is arranged for rotating the third and fourth helical members to stir and convey toner in the toner cartridge in a manner opposite to the concurrent conveying of toner in the toner hopper portion. A xerographic image recording device including a developing device according to any preceding claim.

Inventors: MOMIYAMA YOSHIHARA C O OKI ELE, NAKAJIMA SHIGEKI C O OKI ELECT, MOMIYAMA, YOSHIHARA, C/O OKI ELECTR.IND.CO.,LTD., NAKAJIMA, SHIGEKI, C/O OKI ELECTR.IND.CO.,LTD., YUKIO OTA, C/O OKI ELECTRONIC INDUSTRY CO., LTD.
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY CO., LTD.
Application year: 1992
Main classification: G03G15
IPC codes: G03G15