Developer supply system

Abstract: A developer supply system (1) wherein a spiral (4) and the like provided at a supply opening (6) positioned above a developing unit is rotated in response to a signal from a developer sensor (3) disposed in a place corresponding to a determined position on the way to the supply side from the center of said supply opening on the side of the developing unit so as to transport a developer contained within a developer supply tank (2) from the supply side of said supply opening to the ter­ minal side until the developer falls into the developer unit (10).

Description: The present invention relates to a developer supply system or particularly to an improvement of the developer supply system employing a process for feeding in a horizontal direction a developer by the rotations of a spiral, screw roller, etc. from the developer supply side of a supply opening to the terminal side until the developer falls down into a developing unit. A developer supply system 11 which does not constitute prior art will be described by way of comparison with reference of Figs. 3 - 5 in order to facilitate an easier understanding of the subject invention. Fig. 3 uses two reference numbers 1 and 11 to identify the developer supply system because it is in common with the developer supply system 1 in accordance with the present invention. The developer supply stystem 11 is mounted on a developing unit 10. Said developing unit 10 has associated thereto a developer sensor 3 for detecting the concentration of developer (concentration of toner in case of use of a developer of two-component system). If the concentration of developer is lowered, a spiral 4 is rotated by means of a drive mechanism 7. When the spiral 4 is put in motion, a developer contained within a developer supply tank 2 is transported in a horizontal direction in a pipe 5 and falls from a supply slit 6 (supply opening) into the developing unit 10. For attaining a uniform distribution of the developer drop rate, a portion of the supply slit 6 near the supply side for the developer is formed at so a high level that developer when piled up considerably high within the pipe 5, will fall down, while another portion of the supply slit 6 near the terminal side (opposite to the supply side) is formed at a low level so that the developer may fall down even if the developer within the pipe 5 has become low due to supply of the developer to the developing unit. The developer sensor 3 is provided in a position corresponding to the center of the supply slit 6. This arrangement makes it possible to detect decreasing of the developer at the center because the developer tends to be consumed to the greatest degree at this point when small-sized objects to be copied are subjected to repeated copying operations. Figs. 5(a) - (d) are views showing the change of the comparative developer supply system 11 in the operational phase with time. Fig. 5(a) shows an initial state of operation wherein the developer T has started to be supplied from the developer supply tank 2 to the supply slit 6. Dropping of developer T into the developer unit 10 is limited to a portion where the developer T has reached the supply slit 6. Further continuous rotation of the spiral 4 allows the developer T to arrive at the other side of the supply slit 6, which state is shown by Fig. 5(b). In the state of Fig. 5(b), the developer T has been distributed substantially uniformly in the range between the end at one side (supply) and the end at the other side (terminal) of the supply slit 6. The driving of the spiral 4 is controlled in response to a signal from the developer sensor 3. If the concentration of developer decreases, the spiral 4 is activated to supply the developer from the developer supply tank 2 until the developer falls from the supply slit 6. If the concentration of developer is sufficiently increased, the spiral 4 is stopped and the supply of the developer is discontinued. This will establish a balance between the drop of developer from the supply slit 6 and the supply of developer from the developer supply tank 2, and the height of the developer within the pipe 5 may be maintained at a determined level. As shown by Fig. 5(c), however, when the developer supply tank 2 is exhausted, thereby resulting in a discontinuation of supply of the developer T to the pipe 5, the developer T is too reduced in quantity to continue to drop at the area near the end of the supply side of the supply slit 6, and then, the dropping of the developer will take place only at the area near the end of the terminal side. When the area where an insufficient amount of developer remains, spreads over to a position corresponding to the center of the supply slit 6, the developer sensor 3 acts to detect it, and the spiral 4 is actuated to deliver fresh developer. However, since a rotation of the spiral 4 fails to overcome the deterioration of the developer concentration, it will be determined that the developer supply tank 2 has been exhausted. Consequently, it is impossible to detect the developer supply tank 2 being emptied until the area with insufficient developer left spreads from the end of the supply side of the supply slit 6 over to the center. Accordingly, in the comparative developer supply system 11, there is the problem that a time delay exists in determining that the developer supply tank 2 no longer contains developer. A further problem is that there may be created a non-uniformity in concentration of developer such that the specified concentration of developer fails to remain, rather being inclined downward at the area of the developing unit 10 close to the supply side of the supply slit 6, whereas at the other area of the developing unit 10 close to the terminal side there is an increase of the concentration of developer. There is another problem that even though the developer T₂ is added to the empty developer supply tank 2 after the detection of its emptiness, as shown by Fig. 5(d), a portion through which no developer drops may occur between the portion from which the old developer T₁ drops upon being delivered to the terminal side of the supply slit 6 and the portion through which the developer T₂ drops after having reached the end of the supply side of the supply slit 6, whereby some time is required until a uniform distribution in the drop rate of the developer is obtained again. A developing unit known from US-A-4 431 298 comprises a toner bath having a pair of side plates. Magnetic toner is supplied from a toner container to the bottom part of the toner bath via a chute through an opening in one of this side plates. A sensor is placed in the toner bath for detecting the presence or absence of toner therein. A signal from the sensor controls a toner supply controller having a magnetic shutter member. The magnetic shutter member has a movable piece surrounding the chute and a pair of permanent magnets fixed to the movable piece. The permanent magnets are disposed to establish, upon being moved into an operative position, a magnetic field within the chute, which field magnetically shuts off the chute when a predetermined amount of toner exists in the toner bath. When the amount of toner within the toner bath is reduced below the predetermined value, the permanent magnets are moved away from the chute thereby releasing the chute from the magnetically shut-off condition and allowing toner to be fed to the toner bath. In this prior developing unit a sensor likewise may be provided for detecting the amount of toner within the chute and for automatically stopping the operation of the developing unit when the toner container is emptied. In view of the fact that toner is supplied at one of the longitudinal ends of the developing unit only, there can be no uniform distribution of the developer along the developing unit irrespective of the positioning of the toner sensors. In an other prior toner dispenser (US-A-4 682 874) toner is supplied from a hopper to the entrance port of a first auger having a rotatingly driven helical member for metering and advancing to an exit port precise quantities of toner particles from the hopper. A second auger likewise comprising a rotatingly driven helical member is disposed beneath the first auger and has an entrance port coupled to the exit port of the first auger, so that toner particles are metered by the first auger to the second auger. The entrance port of the second auger in addition receives unused developer material and denuded carrier granules from a magnetic brush used to advance developer material into contact with an electrostatic latent image. This mixture of material is intermingled and advanced by the second auger so as to be dispensed substantially uniformly therefrom over a downward sloped edge of a trough associated to the second auger. A detector is disposed at the top of the enclosure of the first auger. The detector includes a switch having an elongated actuator arm which is periodically engaged and supported by the outer diameter of the first auger when the helical member thereof rotates. When particles are being transported by the first auger, the actuator arm resting on the advancing particles is raised to an upward position closing the switch. When the particles being transported are beneath a preselected quantity, the actuator arm moves downwardly and opens the switch, wherein a visual light display is energized to indicate to the machine operator that toner particles are to be replenished in the hopper. In normal operation a motor driving the helical members of the two augers is continuously energized. An object of the subject invention is to provide for a developer supply system adapted to maintain a predetermined developer level within the pipe of the developer supply system, to rapidly detect exhaustion of the developer supply tank and to reduce the time during which the developer drop rate from the supply opening of the system is non-uniform upon recharging of the developer supply tank. The subject of the invention consists in a developer supply system to be mounted on a developing unit, said developer supply comprising a developer supply tank, a developer sensor and a spiral or the like which is provided in a pipe having in its surface a supply opening positioned above and extending along said developing unit, characterized in that said developer sensor is located in the upper side of the developing unit down the developer stream side of said supply opening to detect the existence of developer stored in the developing unit faced toward said supply opening, and that said spiral or the like is rotated in response to a signal from said developer sensor to transport developer contained within said developer supply tank from a supply side of said supply opening to a terminal side thereof until the developer falls into the developing unit, and that said developer sensor is situated closer to the supply side than to the center of said supply opening. In the developer supply system of the present invention, when the developer supply tank is exhausted, the presence of such an emptiness can be detected more rapidly than in the conventional system. This allows to reduce to a minimum the time during which the concentration of developer within the developing unit and the distribution of the developer drop rate from the supply opening remain non-uniform. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a constructive conceptual view of a developer supply system embodying the present invention, including a partially cut-away view thereof, Fig. 2(a) is a typical conceptual view showing an initial state of operation of the system of Fig. 1. Fig. 2(b) is a typical conceptual view showing a normal state of operation of said system, Fig. 2(c) is a typical conceptual view showing the developer supply tank of said system being detected empty of developer, Fig. 2(d) is a typical conceptual view showing said system being additionally supplied with new developer after the detection, Fig. 3 is a typical side view of said system, including a partially cut-away view thereof, Fig. 4 is a view corresponding to Fig. 1, showing a comparative developer supply system, and Figs. 5(a), (b), (c), and (d) are views corresponding to Figs. 2(a), (b), (c), and (d) in the comparative system shown by Fig. 4. A developer supply system 1 as shown in Fig. 1 comprises a developer supply tank 2, a developer sensor 3, a spiral 4, a pipe 5, a supply slit 6 (supply opening), and a spiral driving mechanism 7. Those respective components are identical to the components of the comparative system, having the like reference numbers. The developing supply system 1 is different from the comparative developing supply system 11 shown in Fig. 4 in that the position where the developer sensor 3 is placed corresponds to a position closer to the supply side rather than to the center of the supply slit 6. It is to be noted that the distance by which the developer sensor 3 is brought to a position near the supply side corresponds, for example, to about a half the width of the typical smallest one of the sheets of various sizes to be copied, directed transversely of the supply slit. For example, if the developing unit 10 has a width of 326 mm and the supply slit 6 has a width of 250 mm so that the both members are in agreement with each other in their center points, the developer sensor 3 may be disposed in a position corresponding to the position on the supply side which is remote by 71 mm from the center. In short, any position between the center of supply slit 6 and the end of the supply side thereof can simply be used which enables both a decrease of the concentration of developer within the developcrease unit 10 and emptiness of the developer supply tank 2 to be detected rapidly. The system of the present invention is identical to the comparative developer supply system 11 in the structure except for the fact that the developer sensor 3 is situated closer to the supply side than to the center of the supply slit 6, and thus the arrangement of the present invention is the same as that of the comparative system as far as the side view shown in Fig. 3 is concerned. Various states of the developer supply system 1 will be described with reference to Figs. 2(a) - (d). Fig. 2(a) illustrates an initial operation state of the system 1. The spiral 4 is kept rotating continuously until the concentration of the developer within the developing unit 10 reaches a determined level. At this time, the developer T contained in the developer supply tank 2 is transported in a horizontal direction in the pipe 5. The developer T starts falling down from the end of the supply side of the supply slit 6, the falling portion of the developer T spreading as far as to the end of the terminal side. As shown in Fig. 2(b), when the developer T arrives at the terminal side of the supply slit 6, the developer T will drop in a uniform manner in any place of the supply slit 6. The concentration of the developer within the developing unit 10 will be increased, and when it is detected by the developer sensor 3 that the determined level has been reached, the rotation of the spiral 4 is stopped, with the consequential stop of dropping of the developer T. When the concentration of developer within the developing unit 10 is decreased by the consumption of the developer T for copying operation, the developer sensor 3 acts to detect the decrease. Then, since the spiral 4 is driven to restart, the developer T is delivered from the developer supply tank 2 to the pipe 5. Thus, only a supplied amount of the developer T falls down from the supply slit 6 to the developing unit 10. This helps to keep the balance between the amount of the developer T supplied from the developer supply tank 2 and the amount of the developer T falling from the supply slit 6, so as to maintain the developer T at the determined level inside the pipe 5, while the concentration of developer within the developing unit 10 is also maintained within a determined range. However, as shown in Fig. 2(c), if the developer supply tank 2 is exhausted, the supply of the developer T to the pipe 5 will be discontinued. On the other hand, if the spiral 4 is driven to rotate, the developer T remaining within the pipe 5 is fed toward the terminal side of the supply slit 6 to fall down, so that the level of the developer T at the supply side within the pipe 5 will be lowered. This will prevent the developer T from falling down in sequence from the end of the supply side of the supply slit 6. Then, a detection is made by the developer sensor 3 of the reduction of the concentration of developer within the developing unit 10, and if the spiral 4 is rotated accordingly, the concentration of developer will no longer be increased, whereby it can be detected that the developer supply tank 2 is void. In accordance with the developer supply system 1 of the present invention, since the developer sensor 3 is located on the way to the supply side from the center of the supply slit 6, as shown in Fig. 2(c), a quicker detection may be made of the developer supply tank 2 being empty of developer than in the comparative system. This makes it possible to limit the decreasing of the concentration of developer to only a small amount of the developer. Now, as shown in Fig. 2(d), after the detection of the emptiness of the developer supply tank 2, a fresh developer T₂ is added to the developer supply tank 2. At this time, the level of the old developer T₁ remaining within the pipe 5 is still not too low, so that the developer T₁ is instantly connected with the new developer T₂, thus resulting in a prompt and uniform distribution of the drop rate of the developer. Accordingly, the state of Fig. 2(b) is returned in a quick manner. As described above, in accordance with the developer supply system 1, the emptiness of the developer supply tank 2 may be detected without delay. Also, the time of the concentration of developer within the developing unit 10 remaining non-uniform as well as the time of the developer being distributed non-uniformly in its drop rate from the supply slit 6 may be reduced to a minimum. In the above-mentioned embodiment, instead of said supply slit 6, the opening for the supply of developer may be constituted by a plurality of apertures having different inner diameters consecutively arranged to extend from the supply side of the developer to the terminal side.

Claims: A developer supply system (1) to be mounted on a developing unit (10), said developer supply (1) comprising a developer supply tank (2), a developer sensor (3) and a spiral (4) or the like which is provided in a pipe (5) having in its surface a supply opening (6) positioned above and extending along said developing unit (10), characterized in that said developer sensor (3) is located in the upper side of the developing unit (10) down the developer stream side of said supply opening (6) to detect the existence of developer (T) stored in the developing unit faced toward said supply opening (6), and that said spiral (4) or the like is rotated in response to a signal from said developer sensor (3) to transport developer (T) contained within said developer supply tank (2) from a supply side of said supply opening (6) to a terminal side thereof until the developer (7) falls into the developing unit (10), and that said developer sensor (3) is situated closer to the supply side than to the center of said supply opening (6). A developer supply system as defined in claim 1, designed for processing sheets of various formats, wherein said developer sensor (3) is situated at a position on the supply opening (6), near the supply side and distant from the center of the supply opening by about half the width of the smallest one of formats in a direction transversely of the supply opening. The developer supply system of claim 1 or 2, wherein said supply opening (6) is a slit disposed in said pipe (5) at a level decreasing from the supply side to the terminal side thereof. The developer supply system of claim 1 or 2, wherein said supply opening (6) is comprised of a plurality of apertures having different diameters consecutively arranged from the supply side to the terminal side of the supply opening.

Inventors: FUJISAWA SHUJI, FUJISAWA, SHUJI
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO. LTD.
Application year: 1988
Main classification: G03G15
IPC codes: G03G15