1. Field of the Invention
The invention relates to an image forming apparatus such as a copying machine or a printer using a recording technique of the electrophotographic type, the electrostatic recording type or the like, and a developer replenishing apparatus for use in such apparatus.
2. Description of Related Art
FIG. 10 of the accompanying drawings is a general construction view of a color image forming apparatus, which will be helpful in understanding the present invention. In the color image forming apparatus, four process cartridges 1 as image forming portions are detachably mounted on the main body A. These four process cartridges 1 are four yellow, magenta, cyan and black, respectively. A photosensitive drum 2 as an image bearing member is rotatably mounted in each process cartridge 1, and a primary charger 3, a developing portion 4, etc. are arranged along the outer periphery of the photosensitive drum, and further a cleaning portion (not shown) etc. are provided. Image exposing light of each color is applied to each photosensitive drum 2. In order to replenish the developing portion 4 of each process cartridge 1 with a developer, a developer replenishing portion 6 is detachably mounted on the main body A of the apparatus in the upper portion thereof.
A transferring portion 5 is provided in such a manner as to contact with each photosensitive drum 2. The transferring portion 5 is comprised of a primary transferring portion 8 and a secondary transferring portion 9, and the primary transferring portion 8 has an intermediate transfer belt 10, a driving roller 11 for driving the intermediate transfer belt 10 and an intermediate roller 12, and a primary transfer roller 13 disposed on the back side of the intermediate transfer belt 10 in opposed relationship with each photosensitive drum 2. Also, the secondary transferring portion 9 has a secondary transfer roller 14 and a pressure roller 15.
The main body A of the apparatus is further provided with a plurality of feed cassettes 16 containing recording materials S of respective sizes therein, and a feed portion 18 for conveying the recording materials S to a pair of registration rollers 17, and the feed portion 18 in turn is provided with a pickup roller 19 and pairs of feed rollers 20-23, and is further provided with a pair of feed rollers 24 for feeding the recording material S from an insertion port provided in the main body A of the apparatus to the pair of registration rollers 17. The main body A of the apparatus is further provided with a fixing portion 25 for fixing the recording material S conveyed from the secondary transferring portion 9, and a delivery portion 26 for delivering the fixed recording material S to a delivery tray.
Description will now be made of the process of forming a color image by the above-described image forming apparatus. Each photosensitive drum 2 rotated at a constant speed in the direction indicated by the arrows is first uniformly charged by the primary charger 3, and then image exposing light of each color is applied to the surface thereof by the whole or a part of each exposing portion 7. A latent image is formed on each image-exposed photosensitive drum 2, and those latent images are then developed in the developing portions 4 by color toners as developers. These developed images are color developed images, but in the case of monochromatic image formation, a black developed image is formed only on the photosensitive drum 2 mounted in the process cartridge 1 for black.
Next, the developed image formed on each photosensitive drum 2 is primary-transferred in the primary transferring portion 8. That is, the developed image is transferred (multilayer-transferred) onto the intermediate transfer belt 10 running at a constant speed in the direction indicated by the arrow by a primary transfer bias voltage applied to each primary transfer roller 13. The developed images transferred to the intermediate transfer belt 10 are then transferred onto the recording material S in the secondary transferring portion 9 while the recording material S passes between the secondary transfer roller 14 and the pressure roller 15. The recording material S is stopped and stands by in advance at the pair of registration rollers 17 portion, and is fed to the secondary transferring portion 9 in accordance with the transfer timing.
The recording material S to which the developed image has been transferred in the secondary transferring portion 9 is then conveyed to the fixing portion 25, where the developers thereon are fused and fixed by heat and pressure, and the recording material S is further delivered from the delivery portion 26 onto the delivery tray.
The developing portion 4 provided in each process cartridge 1 has a developer container for containing the developer therein, agitating means for agitating the contained developer and supplying it to a developing sleeve, and a developing blade for regulating the layer thickness of the developer supplied onto the developing sleeve, and the developer on the developing sleeve is supplied onto the photosensitive drum 2 opposed to the developing sleeve with a minute gap therebetween. The developer necessary for image formation fills each developer container in advance, and as the amount of developer (filling level) in the developer container is reduced by development, the developing portion 4 may be automatically replenished with the developer from the developer replenishing portion 6.
FIG. 11 of the accompanying drawings is a detailed cross-sectional view of the developer replenishing portion 6 shown in FIG. 10, and FIG. 12 of the accompanying drawings is a right side view thereof. The developer replenishing portion 6 has an elongate main body 30 serving also as a container for containing the developer T therein, and agitating means 31 having a plurality of agitating vanes is rotatably supported in the substantially central portion of the main body 30, and a replenishing screw 32 is rotatably supported in the lower portion of the main body 30. Further, a developer discharge port 33 is provided in the bottom of the main body 30 so that when the developer replenishing portion 6 is mounted on the main body A of the apparatus, the developer discharge port 33 may communicate with a supply port opening to the upper portion of the developing portion 4 which is indicated by the double-dotted line.
The replenishing screw 32 is opposite in the helix direction of the screw on the left side and right side of FIG. 11, and when the replenishing screw 32 is clockwisely rotated, the developer T is moved from left to right toward the developer discharge port 33 and is discharged therethrough.
When the developer replenishing portion 6 is mounted on the main body A of the apparatus, the end portions of the rotary shaft 34 of the agitating means 31 and the rotary shaft 35 of the replenishing screw 32 are detachably connected to driving shafts 41 and 42, respectively, in a driving portion 40 provided on the main body A side of the apparatus through couplings. In the case of connection, two guide pins 43 and 44 protruding from the driving portion 40 side are inserted into two guide cylinders protruding in parallel to each other from the end portion of the main body 30, whereby accurate positioning is accomplished.
The driving portion 40 has a driving motor 45 as a drive source, and a gear mechanism 46 connected to the output shaft of the driving motor 45. The gear mechanism 46, as shown in FIG. 12 of the accompanying drawings, comprises a plurality of gears, and the detecting shaft 48 of rotation amount detecting means 47 is connected to a second gear G2 meshing with a first gear G1 coaxially coupled to the output shaft of the driving motor 45. A fifth gear G5 having the driving shaft 42 coupled thereto meshes with the second gear G2 via a third gear G3 and a fourth gear G4, and an eighth gear G8 having the driving shaft 43 coupled thereto meshes with the fifth gear G5 via a sixth gear G6 and a seventh gear G7.
The rotation amount (phase) detecting means 47 comprises a light emitting element and a light receiving element disposed in opposed relationship with each other with a slit portion interposed therebetween, and the output signal of the light receiving element is transmitted as a detection pulse to control means 50. That is, four flags 49 are provided on the tip end portion of the detecting shaft 48 at intervals of 90xc2x0, and these flags 49 shield the slit portion of the rotation amount detecting means 47 by the rotation of the detecting shaft 48, whereby light from the light emitting element is intercepted and a pulse-like flag detection signal (detection pulse) is transmitted from the light receiving element to the control means 50. On the other hand, the fill amount of the developer in the developing portion 4 is detected by level detecting means 51, and the detection signal thereof is likewise transmitted to the control means 50.
Description will now be made of the developer replenishment control from the developer replenishing portion 6 to the developing portion 4 by the control means 50. The fill level of the developer in the developing portion 4 is always monitored by the level detecting means 51, and the detection signal thereof is transmitted to the control means 50. The control means 50 compares the detected value with a preset level, and when for example, the detected value has dropped by a predetermined amount from the set value, the control means drives the driving motor 45 so that an amount of developer corresponding to the amount of drop (deficient amount) may be supplied from the developer replenishing portion 6 to the developing portion 4.
Here, when the rotation ratio between the driving shaft 42 for rotating the replenishing screw 32 and the detecting shaft 48 of the rotation amount detecting means 47 is defined as K, if the amount of developer corresponding to the aforementioned amount of drop corresponds to the amount supplied by the replenishing screw 32 of the developer replenishing portion 6 being caused to make five revolutions, the control means 50 drive-controls the driving motor 45 until the integrated value of the number of revolutions detected by the rotation amount detecting means 47 becomes 5K.
However, in the design of a popular gear mechanism 46, the gear ratio is set to non-integral multiple in order to prevent particular gears from always meshing with each other and therefore, the rotation ratio between the detecting shaft 48 of the rotation amount detecting means 47 and the replenishing screw 32 does not become an integer. Therefore, the stop angle (phase) of the replenishing screw 32 does not become a desired angle. The amount of opening xcex4 (see FIG. 11) formed between the screw of the replenishing screw 32 and the developer discharge port 33 is varied by the rotation phase of the screw when the replenishing screw 32 is stopped and therefore, in conformity therewith, the amount of developer supplied to the developing portion 4 becomes uneven.
Therefore, even if an attempt is made to supply the developer T in a slight amount in such a manner as to effect the rotation control of the replenishing screw 32 by one revolution (one-pitch feed: Pt in FIG. 11) or several revolutions each, the amount of one-pitch feed of the replenishing screw 32 and the phase detected by the rotation amount detecting means 47 do not coincide with each other, and this has led to the problem that when the driving and stop control of the driving motor 45 is repeated, the above-mentioned amount of error is integrated and the deviation of the amount of replenishment also becomes great.
FIG. 13 of the accompanying drawings shows the relation between the phase of one revolution (360xc2x0) of the replenishing screw 32 and the detection pulse (flag count) by the rotation amount detecting means 47. It is apparent from FIG. 13 that the detection pulse by the rotation amount detecting means 47 and the phase of one revolution of the replenishing screw 32 do not coincide with each other. Particularly, in the color image forming apparatus, the unevenness of the fill amount of developer in each developing portion 4 becomes a factor, which will cause the problem of deteriorated quality of image such as the unevenness of the hue of color of an output image or the instability of image density.
The present invention has been made in view of the above-noted problem and an object thereof is to provide a developer replenishing apparatus, which can effect highly accurate replenishment, and an image forming apparatus provided with the same.
A further object of the present invention is to provide a developer replenishing apparatus comprising:
a developer container having a discharge port for discharging a developer therethrough;
a screw for carrying the developer to the discharge port;
a drive source for driving the screw;
motive power transmitting means for transmitting motive power from the drive source to the screw; and
rotation amount detecting means for detecting the amount of rotation of a predetermined rotary shaft in the motive power transmitting means,
wherein the rotation period of the screw is an integral multiple of the rotation period of the predetermined rotary shaft.
Still a further object of the present invention is to provide an image forming apparatus comprising:
an image bearing member;
developing means for developing a latent image formed on the image bearing member;
a container for containing therein a developer to be supplied to the developing means;
a screw for carrying the developer to the discharge port of the container;
a drive source for driving the screw;
motive power transmitting means for transmitting motive power from the drive source to the screw; and
rotation amount detecting means for detecting the amount of rotation of a predetermined rotary shaft in the motive power transmitting means,
wherein the rotation period of the screw is an integral multiple of the rotation period of the predetermined rotary shaft.
Further objects of the present invention will become apparent from the following detailed description when read with reference to the accompanying drawings.