Developer circulator unit of the images forming apparatus

Abstract: A developer circular unit is detachably set in a copier or a copier type printer (9) which print on images on a paper sheet with toner (56). The unit includes at least a developing device (16), a cleaner (20), and a developer conveying device having a pipe (62) communicated with both the cleaner and the developing device and a toner flowing-back preventing mechanism (66, 68). The action of the mechanism is automatically released by the first set of the unit in the copier or printer and/or the first use of the copier or printer after that first set.

Description: The present invention relates to a developer circulator unit freely detachable to the image forming apparatus such as electrophotographic copying machines and various printers, the image forming apparatus comprising an image carrier, means for forming latent image corresponding to image information on the surface of the image carrier, means for developing the latent image on the surface of the image carrier by developer, means for transferring the developed image onto recording means, a cleaner for removing the developer left on the surface of the image carrier after the developed image transferring process, and means for conveying the developer from the cleaner to the developing means, wherein at least the developing means, cleaner and means for conveying the developer from the cleaner to the developing means are combined with one another to form the developer circulator unit. More particularly, the present invention relates to a developer circulator unit in which the developer conveyor means is provided with a means for preventing the developer from flowing backward from the developing means to the cleaner before the unit is installed in the image forming apparatus. Such developer circulator unit sometimes includes photosensitive drum which serves as the image carrier. Image forming apparatuses, which have the above described construction but in which developer-backflow preventing is not mounted in the developer circulator unit, have been well known from USP 3,752,576 and USP 4,323,306. The developer circulator unit is shipped from its factory and put on the market, independently of the other various components of the image forming apparatus. A predetermined amount of developer has already been contained in the developing means of the developer circulator unit at the time when the unit is to be shipped from the factory. In a case where the unit includes no developer-backflow preventing means, therefore, the developer flows backward from the developing means to the developer conveying means and even to the cleaner when the unit is roughly treated on the way of its shipment or circulation in the market. When it flows backward like this, the developer becomes insufficient in the developing means and this causes the image forming apparatus to sound alarm, telling that the developer is insufficient, when the developer circular unit is installed in the image forming apparatus. When developer is supplied responsive to the alarm, however, the amount of developer becomes excessive in the whole of the developer circulator unit, thereby causing the unit not to be operated as requested and making it difficult to control the density of images transferred on the recording means. In a case where the developer consists of various elements, the ratio of these elements in the developer circulator unit changes to make it impossible to well transfer image on the recording means. When the images forming apparatus is operated, even if no alarm is sounded, under such a condition that the developer in the developing means is insufficient, image cannot be well transferred on the recording means. In a case where the developer circulator unit includes the developer-backflow preventing means, the above-mentioned drawbacks are not caused even if the unit is roughly treated on the way of its shipment or circulation in the market. Image forming apparatuses in which the developer circulator unit includes the developer-backflow preventing means have been well known from the published and unexamined Japanese Patent Application Nos. 63-71864 and 63-29776, for example. An adhesive seal disclosed in the former and serving as the developer-backflow preventing means, however, the manually seal peeling work is troublesome and likely to be forgotten just before the developer circulator unit is set in the image forming apparatus. A developer-backflow preventing means disclosed in the latter must be manually operated just after the developer circulator unit is installed in the image forming apparatus, but its manual operation is troublesome. In addition, the mechanism for manually operating the developer-backflow preventing means is so large-sized as to need large space. The present invention is contrived from the above described circumstances, and the main object of the present invention is to provide a developer circulator unit including a developer-backflow preventing means easier in operation, smaller in size and also smaller in the space for operating the developer-backflow preventing means. A developer circulator unit for achieving the first object of the present invention is comprises at least developing means, a cleaner and developer conveying means, which includes a communicating pipe communicating with the cleaner and the developing means and a developer conveying member arranged in the communicating pipe and conveying developer from the cleaner to the developing means. And, means for preventing developer from flowing backward through the communicating pipe from the developing means to the cleaner before the developer circulator unit which is freely detachable as a whole to a common image forming apparatus is installed in the images forming apparatus is provided in the developer conveying means, and the developer circulator unit further includes means for making the developer-backflow preventing means inoperative when the developer circulator unit is firstly installed in the image forming apparatus and/or when the unit is firstly used. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a side view schematically showing the construction of an image forming apparatus in which a developer circulator unit of a first embodiment according to the present invention is set; Fig. 2 is a schematical longitudinal sectional view of the developer circulator unit of the first embodiment; Fig. 3 is an enlarged schematical longitudinal sectional view taken along line III - III in Fig. 2 and showing an end portion of developer conveying means of the developer circulator unit, which is located in developing means, wherein a developer discharge opening at the developing-means-side end portion on the outer peripheral surface of a communicating pipe of the developer conveying means is shielded by a shield member; Fig. 4 is a cross sectional view taken along a line IV - IV in Fig. 3; Fig. 5 is an enlarged schematical longitudinal sectional view similar to Fig. 3, but wherein the developer discharge opening of the communicating pipe is opened; Fig. 6 is an enlarged schematical longitudinal sectional view similar to Fig. 3, but wherein the developer circulator unit upside down while the developer discharge opening of the communicating pipe is closed by the shield member; Fig. 7 is an enlarged schematical longitudinal sectional view of an end portion of developer conveying means of a developer circulator unit according to a second embodiment of the present invention, which is located in developing means, wherein a developer discharge opening at an open end on a developing-means-side end portion of a communicating pipe of the developer conveying means is shielded by a shielding member; Fig. 8 is an enlarged schematical perspective view showing both of the developing-means-side end portion of the communicating pipe and the shield member in a condition that they are separated from each other; Fig. 9 is an enlarged schematical longitudinal sectional view similar to Fig. 7, wherein the shield member is separated from the developer discharge opening of the communicating pipe to open the latter; Fig. 10 is a side view schematically showing how a developer circulator unit according to a third embodiment of the present invention is set in an image forming apparatus; Fig. 11 is an enlarged schematical longitudinal sectional view of an end portion of developer conveying means of a developer circulator unit according to a third embodiment of the present invention, which is located in developing means, wherein a developer discharge opening at a developing-means-side end portion on the outer peripheral surface of a communicating pipe of the developer conveying means is shielded by a shield member, and means for detecting the predetermined moving distance of the shield member is shown; Fig. 12 is an enlarged schematical longitudinal sectional view similar to Fig. 10, wherein the shield member is separated by a predetermined distance from the developer discharge opening of the communicating pipe shown in Fig. 11 to open the latter; Fig. 13 is an enlarged schematical longitudinal sectional view of an end portion of developer conveying means of a developer circulator unit according to a fourth embodiment of the present invention, which is located in a developing means, wherein a developer discharge opening at a developing-means-side end portion on the outer peripheral surface of a communicating pipe of the developer conveying means is shielded by a shield member; Fig. 14 is a side view schematically showing a mechanism for driving the shield member of the developer circulator unit according to the fourth embodiment shown in Fig. 13; Fig. 15 is an enlarged schematical perspective view showing both the shield member and the developing-means-side end portion of the communicating pipe of Fig. 13 in a condition that they are separated from each other; Fig. 16 is an enlarged schematical longitudinal sectional view of a developing-means-side end portion of a communicating pipe and a shield member both of which are a variation of the developer circulator unit shown in Fig. 13 and according to the fourth embodiment, wherein a developer discharge opening at the developing-means-side end portion on the outer peripheral surface of the communicating pipe is shielded by the shield member; Fig. 17 is an enlarged schematical longitudinal sectional view of an end portion of developer conveying means of a developer circulator unit according to a fifth embodiment of the present invention, which is located in developing means, wherein a developer discharge opening at a developing-means-side end portion on an outer peripheral surface of a communicating pipe of the developer conveying means is shielded by magnetic powder in developer attracted by a magnet which is arranged around the developer discharge opening of the pipe; Fig. 18 is a schematical cross sectional view taken along a line XVIII - XVIII in Fig. 17; Fig. 19 is an enlarged bottom view schematically showing the developing-means-side end portion of the developer conveying means in Fig. 17; Fig. 20 is an enlarged schematical longitudinal sectional view of an end portion of developer conveying means of a developer circulator unit according to a sixth embodiment of the present invention, which is located in developing means, wherein a developer discharge opening at an opening end of a developing-means-side end portion of a communicating pipe of the developer conveying means is shielded by a thin seal; Fig. 21 is an enlarged schematical perspective view showing both the developing-means-side end portion of the communicating pipe, the thin seal, and a thin-seal breaking member in a condition that they are separated from each another; Fig. 22 is a schematical longitudinal sectional view similar to Fig. 20, wherein the thin seal for shielding the developer discharge opening at the open end of the developing-means-side end portion of the communicating pipe is broken by the thin-seal breaking member; Fig. 23 is an enlarged schematical longitudinal sectional view of an end portion of developer conveying means of a developer circulator unit according to a seventh embodiment of the present invention, which is located in developing means, wherein a developer discharge opening of a developing-means-side end portion of a communicating pipe of the developer conveying means is shielded by a thin seal; Fig. 24 is a schematical longitudinal sectional view similar to Fig. 23, wherein the thin seal film for shielding the developer discharge opening at the open end of the developing-means-side end portion of the communicating pipe is broken by the thin-seal breaking member; Fig. 25 is an enlarged schematical longitudinal sectional view of an end portion of developer conveying means of a developer circulator unit according to an eighth embodiment of the present invention, which is located in developing means, wherein a developer discharge opening at a developing-means-side end portion on the outer peripheral surface of a communicating pipe of the developer conveying means is shielded by a shield member; Fig. 26 is an enlarged schematical perspective view showing a mechanism for moving the shield member shown in Fig. 25, wherein the shield-member-moving mechanism is exploded; Fig. 27 is an enlarged schematical longitudinal sectional view similar to Fig. 25, but wherein the developer circulator unit shown in Fig. 25 is set in an image forming apparatus so that the shield-member-moving mechanism operates to move the shield member to open the developer discharge opening of the communicating pipe; Fig. 28 is an enlarged schematical longitudinal sectional view of an end portion of developer conveying means of a developer circulator unit according to a ninth embodiment of the present invention, which is located in developing means, wherein a developer discharge opening at a developing-means-side end portion on the outer peripheral surface of a communicating pipe of the developer conveying means is shielded by a shield member; Fig. 29 is an enlarged schematical perspective view showing a mechanism for moving the shield member shown in Fig. 28, wherein the shield-member-moving mechanism is exploded; Fig. 30 is an enlarged schematical longitudinal sectional view similar to Fig. 28, but wherein the developer circulator unit shown in Fig. 28 is set in the image forming apparatus so that the shield-member-moving mechanism operates to move the shield member to open the developer discharge opening of the communicating pipe; Fig. 31 is an enlarged schematical longitudinal sectional view of an end portion of developer conveying means of a variation of the developer circulator unit according to the eighth embodiment shown in Fig. 25, which is located in developing means, wherein a developing-means-side end portion of a communicating pipe of the developer conveyor means is shielded by a thin seal; Fig. 32 is an enlarged schematical longitudinal sectional view similar to Fig. 31, but wherein the developer circulator unit shown in Fig. 31 is set in an image forming apparatus, so that a thin-seal-breaking member breaks the thin seal for a developer discharge opening of the communicating pipe; Fig. 33 is an enlarged schematical longitudinal sectional view of an end portion of developer conveying means of a variation of the developer circulator unit according the ninth embodiment shown in Fig. 28, which is located in a developing means, wherein a developer discharge opening at an opening end of a developing-means-side end portion of a communicating pipe of developer conveyor means is shielded by a thin seal; Fig. 34 is an enlarged schematical longitudinal sectional view similar to Fig. 33, but wherein the developer circulator unit in Fig. 33 is set in an image forming apparatus, so that a thin-seal-breaking member breaks the thin seal for the developer discharge opening of the communicating pipe; Various embodiments of the present invention and various variations thereof will be described in detail with reference to the accompanying drawings. [First Embodiment] Fig. 1 schematically shows an arrangement of a printer as an image forming apparatus into which a developer circulator unit according to a first embodiment of the present invention is incorporated. Printer 9 comprises photosensitive drum 10 which serves as an image carrier, electrifier 12, printing head 14 (a liquid crystal shutter device in this embodiment), developing device 16, transferring device 18, cleaner 20, and a paper-sheet conveying mechanism. Electrifier 12, printing head 14, developing device 16, transferring device 18, and cleaner 20 are arranged near to and around photosensitive drum 10 in this order. The paper-sheet conveying mechanism includes paired slip rolls 26 and paired waiting rolls 28, both pair of which are for conveying paper sheets as the recording means supplied from automatic paper-sheet supply cassette 22 or paper-sheet manual supply tray 24, to image transferring device 18, and paired image-fixing rolls 32 and paired sheet-discharging rolls 34, both pair of which are for conveying the image-transferred paper-sheets from image-transferring device 18 to sheet-discharging tray 30 located at the upper portion of the printer. Electrifier 12 electrify the photosensitive surface of photosensitive drum 10 which rotates in direction R, printing head 14 exposes the photosensitive surface of drum 10 in response to printing data, developing device 16 develops static latent images, which have been formed on the photosensitive surface of drum 10 by printing head 14, by toner, transferring device 18 transfers the toner images on the photosensitive surface of drum 10 to paper sheets which are supplied from manual supply tray 24 or automatic supply cassette 22 and conveyed in direction L, and cleaner 20 removes toner still left on the photosensitive surface of drum 10 after the image transferring process. Paired image-fixing rolls 32 heat the paper sheets, on which the toner images have been transferred, to fix the toner images on the paper sheets while the rolls 32 convey these paper sheets. In this embodiment, photosensitive drum 10, cleaner 20, electrifier 12 and developing device 16 are combined with one another to form image forming unit 40, which is larger than a developer circulator unit constructed by combining cleaner 20 and developing device 16. Image forming unit 40 can be freely detachable to the printer by moving unit 40 in the horizontal direction. Developing means 16 includes developing chamber 42 located adjacent to photosensitive drum 10 and toner supply chamber 44 located above and adjacent to developing chamber 42. In developing chamber 42, developing sleeve 46 is housed to be located adjacent to the photosensitive drum 10, and also stirring roll 48 is housed to be located below toner supply opening 47 which is formed in a partition wall between developing chamber 42 and toner supply chamber 44. In toner supply chamber 44, toner supply roll 50 is mounted to close toner supply opening 47. Toner supply roll 50 is covered on the outer surface of rotating shaft 50a with porous elastic matter 50b. Toner supply roll 50 is driven to be rotated in response to a toner supply signal generated from toner sensor 52 which is mounted in developing chamber 42. In this embodiment, developing chamber 42 is filled with developer 54 which consists of two components of toner and carrier, while toner supply chamber 44 is filled with toner 46 to be supplied. Cleaner 20 includes cleaning blade 58 for scraping off residual toner from the surface of photosensitive drum 10, and cleaning hopper 60 for storing the scraped toner. Communicating pipe 62 of toner conveying means extends between cleaning hopper 60 and developing chamber 42 to use again toner scraped off from the surface of drum 10. In communicating pipe 62, coil member 64 which serves as the toner conveying member is coaxially arranged. End portion 62a of communicating pipe 62 which is located in cleaner 20 is arranged on the bottom of hopper 60 and opened into hopper 60. Communicating pipe 62 is projected outside from image forming unit 40 between hopper 60 and developing chamber 42 to form a half-ring shape. End portion 62b of communicating pipe 62 which is located in developing means 16 is arranged in the upper portion of developing chamber 42. Toner conveying member 64 extends in communicating pipe 62 over the whole length of communicating pipe 62, and the cleaner-side end portion of toner conveying member 64 is selectively rotated by a rotation mechanism (not shown) when image forming unit 40 is set in the printer. As shown in Fig. 3, shutter member 66 is mounted on developing-means-side end portion 62b of pipe 62, and the opening end of end portion 62b of pipe 62 is closed by pipe end 68. In this embodiment, shutter member 66 is shaped like a stepped cylinder. First cylinder portion 66a of shutter member 66 having smaller diameter is loosely fitted into the opening of developing-means-side end 62b of pipe 62 while second cylinder portion 66b thereof having larger diameter also loosely fitted into the internal bore of pipe end 68. As shown in Figs. 3 and 4, engaging projection 66c is formed in the inner surface of shutter member 66 to loosely enter into a gap between two neighboring turns of toner conveying member 64, so that shutter member 66 is rightwardly pushed out of the opening of developing-means-side end 62b of pipe 62 when toner conveying member 64 rotates in clockwise direction shown by an arrow in Fig. 2 to convey toner from cleaner 20 to developing means 16. Toner discharge opening 68a is formed in the peripheral wall of pipe end 68, and closed by second cylinder portion 66b of shutter member 66 which is fitted into the opening of end portion 62b of communicating pipe 62. Then, the opening action of shutter member 66 will be explained in the following. When the printer shown in Fig. 1 starts printing process after setting image forming unit 40 shown in Fig. 2 in the printer, toner conveying member 64 is rotated in communicating pipe 62 by the rotating mechanism (not shown). Shutter member 66 whose projection 66c is engaged with the developing-means-side end portion of toner conveying member 64 is thus moved rightwardly in Fig. 3 until projection 66c of shutter member 66 is released from end 64a of the developing-means-side end portion of toner conveying member 64, as shown in Fig. 5. When shutter member 66 is separated rightwardly from the opening of end portion 62b of communicating pipe 62, developer discharge opening 66b is opened. Residual toner conveyed from cleaner 20 to developing means 16 through pipe 62 due to the rotation of toner conveying member 64 is dropped into developing chamber 42 through toner discharge opening 68a of pipe end 68. Developer 54 in developing chamber 42 of Figs. 3 and 5 is omitted to more clarify these figures. The opening of end portion 62b of communicating pipe 62 and toner discharge opening 68a of pipe end 68 both of which is located in developing chamber 42 are kept closed by shutter member 66 until image forming unit 40 is set in the printer and then the printer 40 starts printing process. Even when image forming unit 40 is turned upside down as shown in Fig. 6, therefore, developer 54 filled in developing chamber 42 can be prevented from entering into pipe end 68 and communicating pipe 62 through toner discharge opening 68a of pipe end 68 and the opening of end 62b of pipe 62. This first embodiment of the present invention can be variously changed and modified. For example, pipe end 68 may be omitted. In this case, end portion 62b of pipe 62 is extended to a position corresponding to the closed end of pipe end 68, and the opening of end portion 62b of pipe 62 is closed by a cap. The toner discharge opening is formed in the peripheral wall of end portion 62b of pipe 62. The outer peripheral surface of shutter member 66 is shaped to have no stepped portion so as to be slidable in communicating pipe 62. Shutter member 66 may be so constructed that it is not rotated while it is moved in end portion 62b of pipe 62 by the rotation of toner conveying member 64. Further, the shutter member 66 may be omitted. In this case, pipe end 68 is freely slidably fitted on end portion 62b of communicating pipe 62, and the projection which enters into a gap between two neighboring turns of toner conveying member 64 is formed on the inner peripheral surface of pipe end 68. In this case, the toner discharge opening is formed in the peripheral wall of one or both of communicating pipe 62 and slidable pipe end 68. In addition, a mechanism for preventing pipe end 68 from falling out of end portion 62b of pipe 62 is needed. [Second Embodiment] An image forming unit, which includes a developer circulator unit according to a second embodiment of the present invention, will be described in detail with reference to Figs. 7 through 9. The same reference numerals in the second embodiment as those in the first embodiment denote the same components as in the first embodiment, and a description thereof will be omitted. In the case of the second embodiment, the opening of developing-means-side end 62b of communicating pipe 62 is sealed by seal member 70 which is fitted into the opening, as shown in Fig. 7. Seal member 70 is formed to have a columnar shape, and engaging protrusion 70a is formed at a proper position on the outer peripheral surface thereof. Knob 70b is formed on the outer end surface of seal member 70. Seal member 70 formed as described above is fixed to toner conveying member 64 in such a way that the developing-means-side end of toner conveying member 64 is embedded in the inner end surface of seal member 70. Inner diameter d1 of developing-means-side end portion 62b of communicating pipe 62 is larger than that of the other portion thereof and substantially the same as outer diameter D of seal member 70 (see Fig. 8). As shown in Fig. 8, substantially L-shaped engaging groove 72 is formed in the peripheral wall of developing-means-side end portion 62b to extend from the opening of end portion 62b of pipe 62 in the axial direction of pipe 62 and then in the circumferential direction thereof. The circumferentially extending portion of engaging groove 72 extends within about 90 degrees around the center axis of pipe 62. This portion of engaging groove 72 is not limited to have a length within 90 degrees but it is preferably in a range of about 45 to 135 degrees. As shown in Fig. 9, seal member 70, which has been separated from developing-means-side end 62b of connecting pipe 62, is pushed into end portion 62b of pipe 62 against the urging force of toner conveyor member 64, which has been expanded to its limit, while gripping knob 70b of seal member 70 by fingers. At this time, engaging protrusion 70a of seal member 70 is inserted in an axially extending portion of engaged groove 72 of pipe 62. When protrusion 70a strikes against the inner end of the axially extending portion of engaged groove 72 and it is stopped from entering into end portion 62b of pipe 62, seal member 70 is then rotated in anti-clockwise direction (when viewed from outside) until protrusion 70 strikes against the inner end of the circumferentially extending portion of engaged groove 72. Seal member 70 is thus held in end portion 62b of pipe 62 against the urging force of toner conveying member 64, as shown in Fig. 7. Even when the image forming unit is turned upside down, therefore, developer 54 in developing chamber 42 can be prevented from flowing backward into communicating pipe 62. When the image forming unit, which includes the developer circulator unit according to the present invention and constructed as described above, is set in the printer and then the printer starts printing process, the above described rotation mechanism (not shown) rotates toner conveying member 64 in pipe 62 in such a direction that toner conveying member 64 conveys toner from cleaner 20 to developing means 16 (clockwise direction when viewed from outside of end portion 62b of pipe 62). When seal member 70 is rotated together with toner conveying member 64 by about 90 degrees, the engagement of engaging protrusion 70a with the circumferentially extending portion of engaged groove 72 is released. Disengaged seal member 70 is then separated from end portion 62b of pipe 62 by the urging force of toner conveying member 64. The opening of end portion 62b of communicating pipe 62 is thus completely opened, thereby allowing scraped toner conveyed from cleaner 20 to developing means 16 through pipe 62 by toner conveying member 64 to drop into developing chamber 42 through the opening. According to the present invention, the mechanism for engaging and disengaging seal member 70 with and from end portion 62b of communicating pipe 62 may be constructed by forming a female screw groove on the inner peripheral surface of end portion 62b of pipe 62 and a male screw thread on the outer peripheral surface of seal member 70. The seal member may be shaped like a cap which can be fitted on the outer peripheral surface of end portion 62b of pipe 62. [Third Embodiment] An image forming unit, which includes a developer circulator unit according to a third embodiment of the present invention, will be described in detail with reference to Figs. 10 through 12. The same reference numerals in the third embodiments as those in the first embodiment denote the same components as in the first embodiment, and a description thereof will be omitted. Fig. 10 schematically shows an appearance of printer 82 as an image forming apparatus, in which image forming unit 80 including a developer circulator unit according to the third embodiment is freely detachably set. Printer 82 is constructed by lower body 84 and roof 86 connected to lower body 84 to be freely swingable. Image forming unit 80 can be freely mounted in and dismounted from lower body 84 of printer 82 in the vertical direction, while roof 86 is opened. Fig. 11 shows developing-means-side end portion 62b of communicating pipe 62 which is located in developing means 16. A plurality of longitudinally extending ribs are arranged on the inner surface of communicating pipe 62, so that contacting areas between the inner surface of pipe 62 and toner conveying member 64 are reduced. Therefor, friction between pipe 62 and toner conveying member 64 is reduced, and contact noise caused by this friction can be prevented. End portion 62b of pipe 62 extends to a position located above the center of stirring roll 48 in developing chamber 42, and toner discharge opening 88 is formed in the lower portion of the peripheral wall of end portion 62b. Shutter member 90 whose one end is closed is slidably fitted on the outer peripheral surface of end portion 62b of pipe 62. In Fig. 11, toner discharge opening 88 at end portion 62b of pipe 62 is closed by shutter member 90. A shield member may be mounted on the inner surface of shutter member 90 to more tightly seal toner discharge opening 88. Shutter driving shaft 92 is fixed to the closed end of shutter member 90 so as to be coaxial with communicating pipe 62. Shutter driving shaft 92 is screwed into casing 16a of developing means 16, and shutter gear 94 is fixed to the outwardly projected end of shutter driving shaft 92 which is projected outside from casing 16a. Shutter gear 94 engages with idler gear 96 mounted on casing 16a. When image forming unit 80 is set in printer 82 as shown in Fig. 10, idler gear 96 engages with a drive gear of a drive means (not shown) mounted in lower body 84 of printer 82. When image forming unit 80 is set in printer 82 and then printer 82 starts for the first printing process, therefore, shutter driving shaft 92 driven and rotated by the drive means of printer 82 through idler and shutter gears 96 and 94 is moved rightwardly in Fig. 11 to cause shutter member 90 to open toner discharge opening 88 at end portion 62b of pipe 62, as shown in Fig. 12. Shutter member 90 can also be moved by mounting shutter member 90 on the outer peripheral surface of end portion 62b of pipe 62 to be slidable only in the axial direction and screwing shutter driving shaft 92 into shutter member 90. The third embodiment includes a means for detecting that shutter member 90 reaches at its open position. In this embodiment, the detecting means is constructed as follows. Detection lever 98 is rockably mounted in lower body 84 of printer 82 to be located adjacent to shutter gear 94 of image forming unit 80. Center of detection lever 98 is swingably pivoted on rotational center shaft 100, one end 98a thereof contacts the outer peripheral surface of flange 102 of shutter gear 94, flange 102 being formed adjacent to shutter gear 94, and spring 104 is stretched between the other end 98b thereof and lower body 84 of printer 82. Micro-switch 106 is mounted adjacent to other end 98b of detection lever 98. With such construction, when shutter gear 94 is rotated and moved together with shutter driving shaft 92 and shutter member 90 in the axial direction, and thus shutter member 90 reaches at its open position, sliding contact of one end 98a of detection lever 98 to flange 102 of shutter gear 94 is released. Detection lever 98 is thus rotated by the urging force of spring 104, and its other end 98b pushes micro-switch 106 to caused micro-switch 106 to generate detection signal. Even in the case of the third embodiment, toner discharge opening 88 at end portion 62b of pipe 62 is closed by shutter member 90 until image forming unit 80 is set in printer 82 and then printer starts for a first printing process. This prevents developer 54 in developing chamber 42 from flowing backward into communicating pipe 62 even when image forming unit 80 is turned upside down. The above-described detector means works at only one time for every image forming unit 80. Therefore, the detection signal generated by the detector means can be used, for example, to reset the counter of developing means 16. End portion 62b of communicating pipe 62 is supported by shutter member 90 at the inner end of shutter driving shaft 92, which is supported by casing 16a of developing means 16. This prevent end portion 62b of pipe 62 from being vibrated by the rotation of toner conveyor member 64, thereby preventing pipe 62 from becoming loose at fixing portion 16b of casing 16a where pipe 62 is fixed to casing 16a. Further, shutter member 90 is rotated directly by the rotation means of printer 82 through idler gear 96, shutter gear 94 and shutter driving shaft 92, so that shutter member 90 can surely operate. [Fourth Embodiment] An image forming unit, which includes a developer circulator unit according to a fourth embodiment of the present invention, will be described in detail with reference to Figs. 13 through 15. The same reference numerals in the fourth embodiment as those in the first embodiment denote the same components as in the first embodiment, and a description thereof will be omitted. As shown in Fig. 13, end portion 62b of communicating pipe 62 extends to a position located above the center of stirring roll 48 in developing chamber 42 of developing means 16. Toner discharge opening 110 is formed at the lower portion of the peripheral wall of end portion 62b of pipe 62. A plurality of longitudinally extending ribs (not shown) are arranged on the inner surface of communicating pipe 62. These ribs can reduce contacting areas between the inner surface of pipe 62 and toner conveying member 64. Therefor, frictional resistance caused by these contact can be reduced, and contact noise caused by this frictional resistance can be prevented. As shown in Figs. 13 and 15, cylindrical shutter member 111 whose one end is closed is freely rotatably fitted on the outer peripheral surface of end portion 62b of pipe 62. Toner discharge opening 112 is formed at the peripheral wall of shutter member 111. Shutter driving shaft 114 is coaxially fixed to the closed end of shutter member 111, and supported by casing 16a of developing means 16 through bearing 116. The circumferential surface of the outwardly projected end of shutter driving shaft 114, which is projected outside the casing 16a, is horizontally cut away at part 114a thereof, and shutter gear 118 having a center hole whose inner surface is also horizontally cut away at part 118a is fixed to shutter driving shaft 114, with horizontally cut part 118a of shutter gear 118 fitting on horizontally cut part 114a of driving shaft 114. End portion 62b of pipe 62 is supported by shutter member 111 on shutter driving shaft 114 which is supported by casing 16a. When toner conveying member 64 is rotated in pipe 62, therefore, end portion 62b of pipe 62 is not vibrated. As shown in Fig. 14, shutter gear 118 is engaged with gear train 120 arranged on casing 16a of developing means 16. In the case of this embodiment, image forming unit 80 is freely detachable to printer 82 by moving unit 80 in a vertical direction, as shown in Fig. 10. When image forming unit 80 is set in printer 82, output gear 122 driven by a rotation source (not shown) in lower body 84 of printer 82 is engaged with gear train 120. As shown in Figs. 13 and 14, mark 124a is formed on the outer side surface of shutter gear 118, and mark 124b is formed at a position on casing 16a of developing means 16, locating adjacent to shutter gear 118. When both marks 124a and 124b are on a same line, toner discharge opening 110 at end portion 62b of pipe 62 is closed by the circumferential wall of shutter member 111, as shown in Fig. 13. In this case, developer 54 in developing chamber 42 of developing means 16 cannot flow backward into communicating pipe 62 even when image forming unit 80 is turned upside down before unit 80 is set in printer 82. When image forming unit 80 is set in printer 82 and then printer starts printing process, shutter member 111 is rotated by rotation force transmitted from output gear 122 in Fig. 14 through gear train 120, shutter gear 118 and shutter driving shaft 114. When toner discharge opening 112 of shutter member 111 coincides with toner discharge opening 110 at end portion 62b of pipe 62 while shutter member 110 being rotated, toner 56 conveyed from cleaner 20 to developing means 16 through communicating pipe 62 is discharged into developer 54 in developing chamber 42 to be used again. Since toner discharge opening 112 of shutter member 111 is cyclically matched with toner discharge opening 110 of pipe 62 as shutter member 110 is rotated, toner discharge opening 110 of pipe 62 is intermittently opened and closed. In the case of this embodiment, the time period during which toner discharge opening 110 of pipe 62 is closed is longer than the time period during which toner discharge opening 110 is opened. However, the amount of toner 56 conveyed from cleaner 20 to developing means 16 through communicating pipe 62 occupies only several or several tens percents of toner which is used for one developing process. Therefor, toner 56 in end portion 62b of pipe 62 can be discharged into developing chamber 42 through toner discharge opening 110 of end portion 62b without clogging in end portion 62b of pipe 62. Fig. 16 shows a variation of the above-described fourth embodiment. In this variation, shutter driving shaft 114, shutter gear 118 and gear train 120 are omitted and shutter member 111 is rotated by toner conveying member 64 in communicating pipe 62. As shown in Fig. 16, boss 126 is coaxially formed on the inner surface of the closed end of shutter member 111, and forcibly fitted into the central bore of the terminal end of toner conveying member 64. Shutter member 110 is set at a circumferential position on end portion 62b of pipe 62 at which its toner discharge opening 112 does not overlap toner discharge opening 110 of pipe 62, thereby preventing developer 54 in developing chamber 42 from flowing backward into communicating pipe 62 until image forming unit 80 is set in printer 82. When image forming unit 80 is set in printer 82 and then printer 82 start printing process, shutter member 111 is rotated by the rotation of toner conveying member 64, so that toner discharge opening 110 at end portion 62b of pipe 62 can be intermittently opened and closed as seen in the case of the fourth embodiment. [Fifth Embodiment] An image forming unit, which includes a developer circulator unit according to a fifth embodiment of the present invention, will be described in detail with reference to Figs. 17 through 19. The same reference numerals in the fifth embodiment as those in the first embodiment denote the same components as in the first embodiment, and a description thereof be omitted. The image forming unit of this embodiment is freely detachable to the printer by moving the unit in a horizontal direction to the side surface of the printer. As shown in Fig. 17, terminal end 64a of toner conveying member 64 extends straight forwardly in end 62b portion of communicating pipe 62, and support shaft 130 is coaxially fixed to this straight end 64a of toner conveying member 64. As shown in Figs. 17 through 19, distal end of end portion 62b of pipe 62 is closed, and toner discharge opening 131 is formed at the lower end of end portion 62b of pipe 62. One end portion of beating sheet 132 made by non-magnetic flexible sheet material such as Mylar (trade name) is wound around and fixed on support shaft 130. The size of beating sheet 132 in the axial direction is substantially the same as length L of toner discharge opening 131, and the circumferential length of sheet 132 is made longer than the radius of the inner peripheral surface of pipe 62 so as to enable the free end portion of beating sheet 132 to slide on the inner peripheral surface of pipe 62. Magnet 134 is embedded around toner discharge opening 131 at end portion 62b of communicating pipe 62. A curtain of magnetic field is thus formed at toner discharge opening 131, and magnetic carriers belonging to one of the two components which form developer 54 in developing chamber 42 collect in toner discharge opening 131 along the curtain of magnetic field to form curtain 136 of magnetic carriers in toner discharge opening 131. This curtain 136 of magnetic carriers in toner discharge opening 131 can prevent developer 54 in developing chamber 42 from flowing backward into communicating pipe 62 through toner discharge opening 131 when the image forming unit 40 is turned upside down before it is set in the printer. When the image forming unit is set in the printer and the printer starts printing process, beating sheet 132 is rotated together with toner conveying member 64 and to cyclically beat toner discharge opening 131. Toner 56 (shown only in Fig. 18) conveyed from cleaner 20 to end portion 62b of pipe 62 is thus forcedly beaten down into developing chamber 42 through toner discharge opening 131. Since the toner is not influenced by the magnetic field, it can relatively quickly pass through curtain 136 of magnetic carriers. According to the present invention, the means for conveying toner from cleaner 20 to developing means 16 may use pressurized air instead of coil-spring-like toner conveying member 64. Further, the means for forcing toner in end portion 62b of pipe 62 into developing chamber 42 through curtain 136 of magnetic carriers may be constructed by a plate spring located in end portion 62b of pipe 62 and an electromagnet mounted on end portion 62b to vibrate the plate spring. [Sixth Embodiment] An image forming unit, which includes a developer circulator unit according to a sixth embodiment of the present invention, will be described in detail with reference to Figs. 20 through 22. The same reference numerals in the sixth embodiment as those in the first embodiment denote the same components as in the first embodiment, and a description thereof will be omitted. As shown in Figs. 20 and 21, open end of end portion 62b of communicating pipe 62 serves as toner discharge opening 62c, and seal sheet 140 made by thin film covers the open end of end portion 62b. Seal sheet 140 is made by a circular aluminum foil in this embodiment, and it is fixed to end portion 62b of pipe 62 by fitting fixing cap 142, which has opening 142a in the center thereof, on the outer circumferential surface of end portion 62b of pipe 62. Namely, the rim portion of seal sheet 140 is sandwiched between the outer circumferential surface of end portion 62b of pipe 62 and fixing cap 142 fitted on the outer circumferential surface of end portion 62b of pipe 62. Breaking member 144 is attached to the end of toner conveying member 64 in end portion 62b of pipe 62. As shown in detail particularly in Fig. 21, breaking member 144 has cylindrical body 144b whose one end is closed by conical tip portion 144a, and flange 144c is formed on the outer circumferential surface of body 144b to circumferentially extend along the border of body 144b with conical tip 144a. The diameter of the outer peripheral surface of body 144b is substantially the same as the inner diameter of toner conveying member 64, and flange 144c is projected outside from the outer circumferential surface of body 144b by a distance substantially the same as the diameter of the wire rod constructing toner conveying member 64. Engaging protrusion 144d is formed on a part of flange 144c to outwardly project in the radial direction. Breaking member 144 is connected to the end portion of toner conveying member 64 by forcibly fitting body 144b into the end portion of toner conveying member 64. Engaged protrusion 62d is formed on the inner peripheral surface of end portion 62b of pipe 62 to project inwardly in the radial direction. Protrusion 62d extends in the circumferential direction of pipe 62 on the inner peripheral surface thereof. The height of engaged protrusion 62d from the inner peripheral surface of pipe 62 is set in such a manner that a value obtained by subtracting the height of engaged protrusion 62d from the inner diameter of pipe 62 becomes larger than the outer diameter of flange 144c of breaking member 144 but smaller than a value obtained by adding the outer diameter of flange 144c to the height of engaging protrusion 144d. Engaged protrusion 62d can be engaged with engaging protrusion 144d of breaking member 144 by pushing breaking member 144 into end portion 62b of pipe 62 against the urging force of toner conveyor member 64. When engaged protrusion 62d is engaged with engaging protrusion 144d of breaking member 144 in this manner, breaking member 144 is urged toward toner discharge opening 62c of end portion 62b of pipe 62 by the urging force of toner conveying member 64. Even when the image forming unit having the above-described arrangement is turned upside down before it is set in the printer, developer 54 in developing chamber 42 cannot flow backward into communicating pipe 62 because toner discharge opening 62c of end portion 62b of pipe 62 is closed by seal sheet 140, as shown in Fig. 20. Next, the seal-sheet breaking action of breaking member 144 will be explained in the following. When the image forming unit arranged as described above according to the sixth embodiment of the present invention is set in the printer and the printer starts for first printing process, toner conveying member 64 is rotated in communicating pipe 62 by the rotation system (not shown) described in the first embodiment. Breaking member 144 is rotated together with toner conveying member 64, thereby releasing engaging protrusion 144d of breaking member 144 from engaged protrusion 62d in end portion 62b of pipe 62. Breaking member 144 is thus moved outwardly in communicating pipe 62 by the urging force of toner conveying member 64, breaks seal sheet 140 and passes through center opening 142a of fixing cap 142 to project outside of pipe 62. Toner discharge opening 62c of end portion 62b of pipe 62 is thus opened, so that toner 56 conveyed from cleaner 20 to developing means 16 through pipe 62 by the rotation of toner conveying member 64 can be dropped into developing chamber 42 through toner discharge opening 62c at end portion 62b of communicating pipe 62. According to the invention, a rubber cover made of thin rubber film may be used as the seal member for sealing toner discharge opening 62c of end portion 62b of pipe 62. In this case, the rubber cover is shaped like a cap and its rim portion is formed thick like a rib, while its other portion is made so thin as to be easily breakable by breaking member 144. The outer diameter of the rib-formed rubber cover is set a little smaller than the outer diameter of the outer circumferential surface of end portion 62b of pipe 62. An engaged rib is formed on the outer circumferential surface of end portion 62b of pipe 62 to be located adjacent to toner discharge opening 62c. The rubber cover can be held on end portion 62b with closing toner discharge opening 62c only by engaging the rib-formed rim portion of the rubber cover with the engaged rib on the outer circumferential surface of end portion 62b of pipe 62. The attaching of the rubber cover to end portion 62b of pipe 62 need not the independent fixing members such as fixing cap 142 used in the above-described sixth embodiment. [Seventh Embodiment] An image forming unit, which includes a developer circulator unit according to a seventh embodiment of the present invention, will be described in detail with reference to Figs. 23 and 24. This seventh embodiment has the same fundamental construction as the image forming unit of the third embodiment shown in Figs. 11 and 12, and the same reference numerals in the seventh embodiment as those in the third embodiment denote the same components as in the third embodiment, and a description thereof will be omitted. In the seventh embodiment, as shown in Fig. 23, seal sheet 150 of thin film is used instead of cylindrical shutter member 90 used in the third embodiment. In addition, a toner discharge opening of end portion 62b of communicating pipe 62 is constructed by opening end 62c of end portion 62b. Seal sheet 150 closes toner discharge opening 62c of end portion 62b of pipe 62, and its rim portion is fixed to the outer circumferential surface of end portion 62b of pipe 62 by adhesive. The center portion of seal sheet 150 which closes toner discharge opening 62c is fixed by adhesive to the inner end of shutter driving shaft 92 screwed into casing 16a of developing means 16. When the image forming unit according to the seventh embodiment and constructed as described above is set in the printer and the printer starts first printing process, shutter driving shaft 92 is moved away from end portion 62b of pipe 62 in the axial direction of pipe 62 and seal sheet 150 is thus peeled off from end portion 62b of pipe 62, as shown in Fig. 24. Toner discharge opening 62c of end portion of pipe 62 is thus opened, thereby allowing toner 56 conveyed from cleaner 20 to developing means 16 through pipe 62 by rotating toner conveying member 64 to fall into developing chamber 42 through toner discharge opening 62c. [Eighth Embodiment] An image forming unit, which includes a developer circulator unit according to an eighth embodiment of the present invention, will be described in detail with reference to Figs. 25 through 27. The same reference numerals in the eighth embodiment as those in the first embodiment denote the same components as in the first embodiment, and the description thereof will be omitted. The image forming unit of the eighth embodiment is freely detachable to printer 82 as shown in Fig. 10 by moving the unit in the vertical direction. Fig. 25 shows end portion 62b of communicating pipe 62 which is located in developing chamber 42 defined in casing 16a of developing means 16. A plurality of longitudinally extending ribs are arranged on the inner surface of pipe 62, so that contacting areas between the inner surface of pipe 62 and toner conveying member 64 are reduced. Therefor, frictional resistance generated at the contacting area can be reduced, thereby preventing contact noise from being caused by the frictional resistance. End portion 62b of pipe 62 extends to a position located above the center of stirring roll 48 in developing chamber 42, and toner discharge opening 160 is formed, at the lower portion of the peripheral wall of end portion 62b of pipe 62. Cylindrical shutter member 162 is fitted on the outer peripheral surface of end portion 62b of pipe 62 so as to close and open toner discharge opening 160. Shutter member 162 is closed at its one end and seal member 164 is mounted on the inner surface of shutter member 162 to more tightly seal toner discharge opening 160. One end of shutter driving shaft 166 is fixed to the closed end of shutter member 162, while the other end thereof is axially slidably supported by support member 168 such as a thrust bearing on casing 16a of developing means 16. Communicating pipe 62 whose end portion 62b is supported by shutter member 162 on the one end of shutter driving shaft 166 held by casing 16a is not vibrated even when toner conveying member 64 is rotated in pipe 62. The outwardly projected end portion of shutter driving shaft 166 which is projected outside casing 16a of developing means 16 is fixed to pin 176. Pin 76 is inserted into vertically-extending slit 174 in downwardly extending portion 172a of reversed L-shape shutter driving lever 172, the lever being pivoted on shaft 170 supported on the outside surface of the casing 16a of developing means 16, as shown in Fig. 25. Sidewardly extending portion 172b of lever 172 extends away from the outer side surface of casing 16a, and lever 172 is urged by tension coil spring 178 stretched between hook 172c on downwardly extending portion 172a and the outside surface of casing 16a to bring its downwardly extending portion 172a nearer to casing 16a or in a direction in which shutter driving shaft 166 is moved into developing chamber 42. Shutter driving shaft 166 provided with shutter member 162, shutter driving lever 172, pin 176, tension coil spring 178 and support member 168 construct a mechanism for moving shutter member 162 to open and close toner discharge opening 160 of end portion 62b of pipe 62. Fig. 26 shows these components for the shutter member driving mechanism in a large size. In the above described condition, shutter member 162 closes toner discharge opening 160 of end portion 62b of pipe 62, as shown in Fig. 25. Therefor, developer 54 in developing chamber 42 cannot flow backward into communicating pipe 62 even when the image forming unit is turned upside down before it is set in the printer. When the image forming unit according to the eighth embodiment and constructed as described above is set in lower body 84 of printer 82 (Fig. 10), the lower edge of sidewardly extending portion 172a of lever 172 is engaged with a part of lower body 84, and lever 172 is thus swung round shaft 170 against the urging force of tension coil spring 178, as shown in Fig. 27. When lever 172 is swung as described above, shutter driving shaft 166 pin 176 of which is inserted in vertical slit 174 of downwardly extending portion 172a of lever 172 is moved away from end portion 62b of communicating pipe 62. The horizontal movement of shutter driving shaft 166 causes shutter member 162 to open toner discharge opening 160 of end portion 62b of pipe 62. Toner 56 conveyed from cleaner 20 to developing means 16 through pipe 62 by rotating toner conveying member 64 is thus dropped into developing chamber 42 through toner discharge opening 160 and mixed with developer 54 in developing chamber 42 so as to be used again. When the image forming unit is detached from lower body 84 of printer 82, shutter driving shaft 166 is moved into developing chamber 42 by the urging force of tension coil spring 178, thereby causing shutter member 162 to close toner discharge opening 160 of end portion 62b of pipe 62. [Ninth Embodiment] An image forming unit, which includes a developer circulator unit according to a ninth embodiment of the present invention, will be described in detail with reference to Figs. 28 through 30. This image forming unit of this embodiment is freely detachable to lower body 84 of printer 82 by moving the unit in the vertical direction as seen in the eighth embodiment. In this embodiment, shutter member 162, shutter driving shaft 166, and support member 168 for shutter driving shaft 166 are so arranged as the same as those in the eighth embodiment. Shutter member 162 is moved on end portion 62b of pipe 62 to close and open toner discharge opening 160 by the action of roof 86 of printer 82 toward its closing position. Next, a shutter member opening/closing mechanism for causing shutter member 162 to move between open and closure positions by the opening/closing action of roof 86 will be explained, with reference to Figs. 28 and 29. Guide member 182 having vertically-extending guide hole 180 is attached to the outer side surface of casing 16a of developing means 16 at a position below the outwardly projected end of shutter driving shaft 166. Vertically movable opening/closing member 186 in which cam groove 184 extending obliquely is located above guide member 182, and pin 176 fixed on the outwardly projected end of shutter driving shaft 166 is inserted into oblique cam groove 184 of member 186. Guide pin 186a which is inserted into guide hole 180 of guide member 182 is fixed to the undersurface of member 186, and compression coil spring 188 is wound around guide pin 186a between vertically movable member 186 and guide member 182. Spring 188 urges vertically movable member 186 upward so that pin 176 of shutter driving shaft 166 is positioned at the lower end of cam groove 184. In this condition, shutter driving shaft 166 is moved toward end portion 62b of pipe 62 in developing chamber 42, and thus shutter member 162 on one end of shutter driving shaft 166 closes toner discharge opening 160 of end portion 62b of pipe 62. When the image forming unit according to the ninth embodiment is set in lower body 84 (Fig. 10) of printer 82 and then roof 86 is swung onto the top of lower body 84, a part of roof 86 strikes against the upper surface of member 186 to move member 186 downward against the urging force of compression coil spring 188, as shown in Fig. 30. Pin 176 on the shutter driving shaft 166 is thus moved along cam groove 184, causing shutter driving shaft 166 and shutter member 162 to move apart from end portion 62b of pipe 62 in the axial direction of shaft 166. As the result, toner discharge opening 160 at end portion 62b of pipe 62 is opened, and toner 56 conveyed from cleaner 20 to developing means 16 through communicating pipe 62 by rotating toner conveying member 64 is discharged into developing chamber 42 through toner discharge opening 160 and mixed with developer 54 in developing chamber 42 so as to be used again. [Variation of Eighth Embodiment] A variation of the eighth embodiment shown in Figs. 25 through 27 will be described with reference to Figs. 31 and 32. The same reference numerals in this variation as those in the eighth embodiment denote the same components as in the eighth embodiment, and the description thereof will be omitted. In this variation, as shown in Fig. 31, seal sheet 190 of thin film is used instead of cylindrical shutter member 162 used in the eighth embodiment. In addition, end opening 62c at end portion 62b of pipe 62 is used as the toner discharge opening. Seal sheet 190 covers toner discharge opening 62c of end portion 62b of communicating pipe 62, and its rim portion is fixed to the outer circumferential surface of end portion 62b of pipe 62 by adhesive. The center portion of seal sheet 190 is fixed to the inner end of shutter driving shaft 166 by adhesive, and shutter driving shaft 166 is freely slidably supported by casing 16a of developing means 16. When the image forming unit according to the variation and constructed as described above is set in lower body 84 of printer 82 (Fig. 10), shutter driving lever 172 is struck against a part of lower body 84 of printer 82 as shown in Fig. 32 and swung around pin 170 against the urging force of tension coil spring 178, thereby causing shutter driving shaft 166 to move away from end portion 62b of pipe 62 in the axial direction of shaft 166. Seal sheet 190 is thus peeled off from end portion 62b of pipe 62 to open toner discharge opening 62c. Toner 56 conveyed from cleaner 20 (Fig. 10) to developing means 16 (Fig. 10) through pipe 62 by rotating toner conveying member 64 is discharged into developing chamber 42 through toner discharge opening 62c. [Variation of Ninth Embodiment] A variation of the ninth embodiment shown in Figs. 28 through 30 will be described with reference to Figs. 33 and 34. The same reference numerals in this variation as those in the ninth embodiment denote the same components as in the ninth embodiment, and the description thereof will be omitted. In this variation, as shown in Fig. 33, seal sheet 200 of thin film is used instead of cylindrical shutter member 162 used in the ninth embodiment. In addition, end opening 62c at end portion 62b of pipe 62 is used as the toner discharge opening. Seal sheet 200 covers toner discharge opening 62c of end portion 62b of pipe 62, and its rim portion is fixed to the outer circumferential surface of end portion 62b of pipe 62 by adhesive. The center portion of seal sheet 200 is fixed to the inner end of shutter driving shaft 166 by adhesive, and shutter driving shaft 166 is freely slidably by casing 16a of developing means 16. When the image forming unit according to the variation and constructed as described above is set in lower body 84 of printer 82 (Fig. 10) and roof 86 is swung onto lower body 84, member 186 is pushed by a part of roof 86 and moved downward against the urging force of compression coil spring 188 as shown in Fig. 34, causing shutter driving shaft 166 to be moved away from end portion 62b of communicating pipe 62 in the axial direction of pipe 62. Seal sheet 200 is thus peeled off from end portion 62b of pipe 62 to open toner discharge opening 62c. Toner 56 conveyed from cleaner 20 (Fig. 10) to developing means 16 (Fig. 10) through pipe 62 by rotating toner conveying member 64 is allowed to fall into developing chamber 42 through toner discharge opening 62c.

Claims: A developer circulator unit (40, 80), comprising at least developing means (16), a cleaner (20), and developer conveying means including a communicating pipe (62) communicating with the cleaner (20) and the developing means (16) and a developer conveying member (64) located in the communicating pipe (62) to convey developer (56) from the cleaner (20) to the developing means (16), the developer conveying means being provided with means (60, 70, 90, 111, 136, 140, 150, 162, 190, 200) for preventing developer from flowing backward from the developing means (16) to the cleaner (20) through the communicating pipe (62) before the developer circulator unit (40, 80), which is freely detachable as a whole to a common image forming apparatus, is firstly used, characterized in that the developer circulator unit (40, 80) further comprises means (66c, 70a, 72, 92, 94, 96, 114, 118, 120, 124, 132, 144, 166, 172, 186) for automatically releasing the action of the developer-backflow-preventing means by the first installation of the developer circulator unit (40, 80) in the image forming apparatus and/or the first use of the image forming apparatus after the first installation of the developer circulator unit (40, 80) in the image forming apparatus. The developer circulator unit according to claim 1, characterized in that the developer-backflow preventing means (66, 70, 90, 111, 136, 140, 150, 162, 190, 200) is located at the developing-means-side end portion (62b) of the communicating pipe (62). The developer circulator unit according to claim 2, characterized in that the developer-backflow preventing means includes a shield mechanism (60, 70, 90, 111, 136, 140, 150, 162, 190, 200) for opening a developer discharge opening (68a, 88, 110, 131, 62b, 160) formed at the developing-means-side end portion (62b) of the communicating pipe (62), by the first installation of the developer circulator unit (40, 80) in the image forming apparatus (9, 82) and/or the first use of the apparatus after the first installation of the unit in the apparatus. The developer circulator unit according to claim 3, characterized in that the shield mechanism (60, 70, 90, 111, 136, 140, 150, 162, 190, 200) for the developer-backflow preventing means is arranged to open the developer discharge opening (68a, 88, 110, 131, 62c, 160) formed at the developing-means-side end portion (62b) of the communicating pipe (62) by the first installation of the developer circulator unit (40, 80) in the image forming apparatus (9, 82) and/or the first use of the apparatus after the first installation of the unit in the apparatus. The developer circulator unit according to claim 4, characterized in that the shield mechanism for the developer-backflow preventing means includes a shield member (66, 70, 90, 111, 132, 162) freely movably mounted on the developing-means-side open end portion (62b) of the communicating pipe (62), and opening means (64, 66c, 92, 94, 96, 114, 118, 120, 166, 172, 186) for moving the shield member to open the developer discharge opening (68a, 88, 110, 131, 160) formed at the developing-means-side end portion (62b) of the communicating pipe (62) by the first installation of the developer circulator unit (40, 80) in the images forming apparatus (9, 82) and/or the first use of the apparatus after the first installation of the unit in the apparatus. The developer circulator unit according to claim 5, characterized in that the opening means (64, 66c, 92, 94, 96, 166, 172, 186) is arranged to cause the shield member (66, 70, 90, 162) to move on the developing-means-side open end portion (62b) of the communicating pipe (62) in the axial direction of the pipe to open the developer discharge opening (68a, 88, 160) at the developing-means-side end portion of the communicating pipe. The developer circulator unit according to claim 6, characterized in that the opening means is constructed by the developer conveying member (64), and the opening means is arranged to cause the shield member (66, 70) to move on the developing-means-side end portion (62b) of the communicating pipe (62) in the axial direction of the pipe to open the developer discharge opening (68a) at the developing-means-side end portion of the communicating pipe by the first installation of the developer circulator unit (40) in the image forming apparatus (9) and/or the first use of the apparatus after the first installation of the unit in the apparatus. The developer circulator unit according to claim 7, characterized in that the developer conveying member is a coil spring, the developer discharge opening is constructed by the open end at the developing-means-side end portion of the communicating pipe, the shield member is attached to the developer discharge opening against the urging force of the coil spring, and the shield member is released from the developer discharge opening by the rotating coil spring and then separated from it by the urging force of the coil spring. The developer circulator unit according to claim 7, characterized in that the developer conveying member (64) is a spiral member. The developer circulator unit according to claim 9, characterized in that the spiral member (64) is a coil spring. The developer circulator unit according to claim 6, characterized in that the opening means is constructed by means (96) for driving the developing means (16), the opening means (92, 94) is projected outside the developing means and connected to the developing-means driving means, and the shield member (90) is movable on the developing-means-side open end portion (62b) of the communicating pipe (62) in the axial direction of the pipe to open the developer discharge opening (88) at the developing-means-side end portion of the communicating pipe when the developing-means driving means starts its action. The developer circulator unit according to claim 11, characterized in that the shield member (90) is movable by a predetermined distance in the axial direction of the communicating pipe (62) to open the developer discharge opening (88) at the developing-means-side end portion (62b) of the pipe (62), and the connection of the shield member (90) to the opening means (96) is then releasable and the axial movement thereof, when in use, is stopped. The developer circulator unit according to claim 11, characterized in that means (98, 106) for detecting whether or not the shield member (90) has been moved by the opening means (92, 94, 96) over the predetermined distance so enough in the axial direction of the communicating pipe (62) as to open the developer discharge opening (88) at the developing-means-side end portion (62b) of the pipe (62). The developer circulator unit according to claim 5, characterized in that the developer discharge opening (110) is formed in the circumferential wall of the developing-means-side end portion (62b) of the communicating pipe (62), the shield member (111) also has the developer discharge opening (112) in its circumferential wall, and the opening means (114, 118, 120, 64) is arranged to rotate the shield member on the developing-means-side end portion of the pipe in the circumferential direction so that the developer discharge opening (112) of the shield member (111) match with that (110) of the developing-means-side end portion (62b) at the pipe to open the developer discharge opening at the developing-means-side end portion of the pipe. The developer circulator unit according to claim 14, characterized in that the opening means is constructed by the developer conveying member (64), and the shield member (111) is rotatable on the developing-means-side end portion (62b) of the communicating pipe (62) in the circumferential direction, by the rotating developer conveying member so that the developer discharge opening (112) of the shield member (111) match with that (110) of the developing-means-side end portion (62b) of the pipe (62) to open the developer discharge opening (110) at the developing-means-side end portion of the pipe. The developer circulator unit according to claim 14, characterized in that the opening means is constructed by the developing-means driving means (114, 118, 120), the shield member (114) is projected outside the developing means (16) and connected to the developing-means driving means (118, 120), and the shield member is rotatable on the developing-means-side open end portion of the communicating pipe in the circumferential direction when the developing means driving means starts to its action so that the developer discharge opening of the shield member match with that of the developing-means-side end portion of pipe to open the developer discharge opening at the developing-means-side end portion of the pipe. The developer circulator unit according to claim 4, characterized in that the developer discharge opening (131) is formed in the circumferential wall of the developing-means-side end portion (62b) of the communicating pipe (62), and the shield mechanism includes a magnet (134) arranged around the developer discharge opening (131) at the developing-means-side end portion of the pipe and a developer-pushing-out member (132) driven by the developer conveying member (64) to push out developer from the developing-means-side end portion of the pipe into the developing means (16) through the developer discharge opening. The developer circulator unit according to claim 17, characterized in that the developer-pushing-out member (132) is a sheet member fixed to the terminal end of the developer conveying member (64) located in the developing-means-side end portion (62b) of the communicating pipe (62). The developer circulator unit according to claim 4, characterized in that the open end (62c) of the developing-means-side end portion (62b) of the communicating pipe (62) serves as the developer discharge opening, and the shield mechanism includes a thin seal (140, 150, 190, 200) for shielding the developer discharge opening (62c) and breaking means (144, 92, 94, 96, 166, 172, 186) driven to break the thin seal by the first installation of the developer circulator unit (40, 80) to the image forming apparatus (9, 82) and the first use of the apparatus after the first installation of the unit to the apparatus. The developer circulator unit according to claim 19, characterized in that the breaking means (144) is mounted on the terminal end portion of the developer conveying member (64) in the developing-means-side end portion (62b) of the communicating pipe (62), and it is drivable by the action of the developer conveying member (64) to break the thin seal (140). The developer circulator unit according to claim 19, characterized in that the breaking means (92, 94) is projected outside the developing means (16) and connected to the developing-means driving means (96), and the breaking means is movable at the developing-means-side open end portion (62b) of the communicating pipe (62) in the axial direction of the pipe to break the thin seal (150) when the developing means (16) starts its action. The developer circulator unit according to claim 3, characterized in that the shield mechanism (166, 172, 186) of the developer-backflow preventing means serves to open the developer discharge opening (160, 62c) formed at the developing-means-side end portion (62b) of the communicating pipe (62) when the developer circulator unit (80) is firstly set in the image forming apparatus (82). The developer circulator unit according to claim 22, characterized in that the shield mechanism includes a shield member (162) freely movably mounted at the developing-means-side open end portion (62b) of the communicating pipe (62), and opening means (166, 172, 186) arranged to strike against the body (84) of the image forming apparatus (82) when the developer circulator unit (80) is firstly installed in the apparatus and to move the shield member to open the developer discharge opening, formed at the developing-means-side end portion of the pipe, due to the collision of the opening means to the body. The developer circulator unit according to claim 23, characterized in that the opening means (166, 172, 186) of the shield mechanism is arranged to move the shield member (162) to close the developer discharge opening (160), formed at the developing-means-side end portion (62b) of the communicating pipe (62), due to the detachment of the developer circulator unit (80) from the image forming apparatus (82). The developer circulator unit according to claim 22, characterized in that the open end (62c) at the developing-means-side end portion (62b) of the communicating pipe (62) serves as the developer discharge opening, and the shield mechanism includes a thin seal (190, 200) for shielding the developer discharge opening (62c) and breaking means (166, 172, 186) arranged to strike against the body (84) of the image forming apparatus (82) when the developer circulator unit (80) is firstly set in the apparatus and to break the thin seal due to the collision of the breaking means to the body. The developer circulator unit according to claim 3, characterized in that the image forming apparatus (82) comprises a lower body (84) and an upper body (86) connected to the lower body to be swingable between open and closure positions, the developer circulator unit (80) is set in the lower body after swinging up the upper body from the lower body toward the open position, and the shield mechanism (162, 166, 186, 200) is arranged to open the developer discharge opening (62c, 160) formed at the developing-means-side end portion of the communicating pipe (62) due to the swing down of the upper body to the lower body toward the closure position. The developer circulator unit according to claim 26, characterized in that the shield mechanism includes a shield member (162) freely movably mounted on the developing-means-side open end portion (62b) of the communicating pipe (62) and opening means (166, 186) arranged to strike against the upper body (86) of the image forming apparatus (82) when the developer circulator unit (80) is set in the lower body (84) after swinging up the upper body of the apparatus from the lower body thereof toward the open position, and the upper body is then swung down onto the lower body toward the closure position, and to move the shield member to open the developer discharge opening, formed at the developing-means-side end portion of the pipe, due to the swing-down action of the upper body. The developer circulator unit according to claim 27, characterized in that the opening means (166, 186) of the shield mechanism moves the shield member (162) to close the developer discharge opening (160) formed at the developing-means-side end portion (62b) of the communicating pipe (62) by releasing its contact with the upper body (86) of the image forming apparatus (82) when the upper body swing upward from the lower body (84) toward the open position. The developer circulator unit according to claim 26, characterized in that the open end (62c) at the developing-means-side end portion (62b) of the communicating pipe (62) serves as the developer discharge opening, and the shield mechanism includes a thin seal (200) for shielding the developer discharge opening (62c) and breaking means (166, 186) arranged to strike against the upper body (86) of the image forming apparatus (82) when the developer circulator unit (80) is set in the lower body (84) of the apparatus after swing up the upper body (86) from the lower body (84) toward the open position and then the upper body is swung downward onto the lower body toward the closure position, and to break the thin seal (200) due to the swing-down action of the upper body.

Inventors: HAYASHI MITSUO PATENT DPT DEV, MARUYAMA MASATOSHI PATENT DPT, ONO NORIKI PATENT DPT DEV DIV, YORIFUJI TAKAO PATENT DPT DEV, HAYASHI, MITSUO PATENT DPT. DEV. DIV. HAMURA, MARUYAMA, MASATOSHI PATENT DPT. DEV. DIV. HAMURA, ONO, NORIKI PATENT DPT. DEV. DIV. HAMURA, YORIFUJI, TAKAO PATENT DPT. DEV. DIV. HAMURA
Applicants: CASIO COMPUTER CO LTD, CASIO ELECTRONICS MFG CO, CASIO COMPUTER COMPANY LIMITED, CASIO ELECTRONICS MANUFACTURING CO., LTD.
Application year: 1989
Main classification: G03G15
IPC codes: G03G21, G03G15