Toner replenishing device with timing control of toner replenishing device

A toner replenishing device having a stable performance without causing variation of the toner suction pressure, even if the toner characteristics vary in a toner vessel in a volume-reducing type toner carrying device. In the toner replenishing device comprising a flexible toner storing vessel, a sucking means for arrying the toner in the toner storing vessel to a prescribed place by a negative pressure, and a substantially airtight toner carrying passage, the toner storing vessel being reduced in volume by sucking the toner, the sucking means is a single-shaft eccentric screw pump, whose operation time is longer than the time for generating a maximum pressure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a toner replenishing device of a developing device used for an image forming device of an electro-photographic system, in particular, for a printer, a facsimile device, or a copier using a binary or a mono-component developer.

2. Description of the Background Art

Hard bottles have been conventionally used as storing vessels for dry toner, a carrier, or a mixture of the toner and carrier (hereafter referred to as toner) used for electrophotography in general. As the conventional toner replenishing devices, one in which a toner agitator-cum-discharge device is provided in the vessel, one which moves the toner in the vessel by rotating the vessel by providing a spiral groove on the vessel wall to discharge the toner, or one which has no discharge mechanism and is manually replenished with the toner, are known. In recent years, however, recovery or recyclability of the toner storing vessel is requested by attaching greater importance to the environmental problem.

Therefore, volume-reducible soft vessels made of flexible materials are proposed, as disclosed in the Japanese Patent Laid-Open Publication, for example, No. 2001-324863 or No. 2002-072649. The dry toner for electrophotograpy is, however, considered very difficult to be discharged from the soft vessel, since it has poor fluidity in general, and is liable to coagulate. This is because an agitator or a discharge mechanism is difficult to be added to the soft vessel, or addition of the discharge mechanism prevents volume reduction, or handleability is poor for manual replenishing.

The toner in the flexible vessel may be sucked and discharged by a sucking type powder pump, or a single-shaft eccentric screw pump, and the volume of the toner vessel may be reduced following toner discharge. Since an automatic volume-reduction type toner carrying apparatus carries the toner by a suction pressure (negative pressure) of the powder pump, carrying volume of the toner varies unless the suction pressure is constant, and the volume of the vessel cannot be gradually reduced. With a constant one-operation time of the powder pump, the pressure generated is constant, however, according to the state of the toner, for example, fluctuation of the toner characteristics due to the environment, or due to storing for a long period, a problem of variation of the suction pressure necessary for carrying the toner occurs.

SUMMERY OF THE INVENTION

An object of the present invention is to provide a toner replenishing device having a stable performance without causing variation in the toner suction pressure, even if the toner characteristics vary in the toner vessel of the volume-reduction type toner carrying apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

One embodiment of the present invention is explained in details as below, on the basis of the drawings.

FIG. 1shows the contour of the image forming device which uses the toner replenishing device related to the present invention. As the toner is consumed according to the forming amount of the images, the toner vessel is replaced when it is empty. The replacement is conducted, as shown in the drawing, by opening a toner vessel attaching/detaching door100by drawing it to one side, taking out an empty vessel, setting a new toner storing vessel, and closing the door.

FIG. 2shows a constitution of a toner feeding means from the toner vessel to the developing device. As shown in the drawing, an electrostatic latent image is formed on the surface of a photoreceptor drum2by a charging device and a photo-writing device (not shown in the figure). A casing14composing the developing device contains therein screws15and16rotating in the arrow directions C, D, having spiral fins called carrying augers, and contains a developer of a mixture of the toner and carrier. In the screw15, for example, the developer is carried from this side to the deep side in the drawing, and in the screw16, the developer is carried from the deep side to this side. Parts with no central partition plate17are provided in the deep side and this side to form a constitution for agitating the developer while circulating it. A part of the circulating developer is sucked up and attracted to a developing roller19by magnetic force, unifomized in thickness by a doctor blade18, and brought into contact with a photoreceptor, to form a toner image by developing the electrostatic latent image on the photoreceptor by the toner. In this stage, only the toner adheres to the photoreceptor. The development is carried out by replenishing the toner little by little from a toner replenishing port67, in order to keep a quantity of the toner constant in the circulating developer in the developing device.

A toner replenishing part has the toner storing vessel20for storing new toner and the toner in the toner storing vessel20is sucked and discharged by the powder pumping means60(the single-shaft eccentric screw pump in the present embodiment) to be fed to the toner replenishing port67of the developing device.

The toner storing vessel20is composed of a bag-like soft vessel21for storing the toner and a connector part30connected to the lowest part of the toner vessel21. A suction nozzle110is inserted into the connector part. A shutter50is provided for stopping flowing out of the toner when the nozzle110is not inserted. A sealing material42is disposed on both sides of the nozzle110or the shutter50to keep airtightness.

The powder pumping means60is connected to the nozzle110via a tube65. In the present embodiment, the powder pumping means60is composed of the single-shaft eccentric screw pump, comprising two main parts of a rotor61and a stator62. The rotor61has a spirally twisted circular cross section, and is made of a hard material, while the stator62is made of a rubber-like soft material, with an ellipsoidal cross section having a spirally twisted hole. The spiral pitch of the stator62is formed in a length of two times of the spiral pitch of the of the rotor61. By fitting these two parts and rotating the rotor61, the toner entering the space formed between the rotor61and the stator62is transferred. A motor66drives the rotor61via a universal joint64.

The toner is sucked and carried from the left of the drawing to the right and drops downward from the toner discharging port67to be fed to the developing device14. The part from the nozzle110to the developing device14is fixed to the main device, and the toner storing vessel20is replaced with a new toner storing vessel20every time the toner contained therein is used up. The airtightness between the connector part30and the nozzle110is quite important for preventing contamination or air leakage at detachment and attachment, since the nozzle110is detached and attached in every replacement.

FIG. 3andFIG. 4show a state of the toner vessel21filled with the toner, and a state of the toner vessel21volume-reduced or shriveled by discharging the toner in the toner vessel21, respectively.

A sheet forming the toner vessel21is a double-layered sheet with an inner side composed of polyethylene for depositing, and an outer side composed of nylon. Aluminum or PET (polyethylene terephthalate) can be provided on the outer side in order to enhance strength of the sheet. The thickness of the sheet is 50–210 □m.

FIG. 5shows an exploded view of the connector part30of the toner storing vessel20. The connector part30is composed of a connector40thermally melt-stuck to the sheet, a cap43engaged with the connector40, the shutter50, and the sealing material42for keeping close contact with the shutter50. The bottom face of the cap43is provided with a circular recessed part41, to which a filter is stuck to communicate the inside of the vessel with the atmosphere through it.

The characteristics of the connector system are that the shutter50does not hinder the passage of the toner as the shutter50is extruded to the outside from the connector inside, that the connector40can be formed very compact since no retracting space is necessary for retracting the shutter50to the outside of the connector40, and that the shutter50is kept stable without being pushed out by the vessel pressure, as the shutter50is disposed orthogonal to the passage (or pressure) of the toner.

The connector part30is divided into the connector main body40and a cap43in order to easily fill the toner into the vessel. An integrated constitution narrows the filling path and forms a bent state, while the divided constitution allows straight filling of the toner from a comparatively large opening. The cap is attached after filling the toner, then the shutter50is inserted to facilitate filling of the toner. A defect such as contamination of the sealing material by the filling work can be resolved.

The sealing material42is formed of a rubber material or the like lightly press-contacting on the shutter50.

The shutter50can be moved by pushing with the finger. In order to prevent the defect of leakage of the toner due to the movement of the shutter50during operation, the shutter is preferably sized to 8 mm square at the maximum, desirably 6 mm square or less to avoid accidental pushing with the finger.

When replenishing the toner, the motor is energized by a power source N by a signal indicating the shortage of the toner in the developing device14, to turn on the single-shaft eccentric screw pump60, and the toner in the bag-like soft toner vessel21is sucked and fed (dropped) to the developer part of the developing device14. After replenishing a prescribed amount of the toner, the pump60is turned off.

It is supposed that the single-shaft eccentric pump60is operated in a driving time in a region A (less than a driving time T1) shown inFIG. 6in the toner replenishing device of the present embodiment. “A” indicates a case where the pressure of the screw pump60has not yet sufficiently risen. A required pressure for sucking the toner at this time is assumed as Pa. The screw pump60cannot suck the toner, unless the driving time of the pump60is set to T0or more. The required pressure Pa for sucking the toner is, however, not constant. According to the variation of the toner characteristics due to the surroundings, Pa also varies. In a high temperature and humidity condition, for example, the fluidity of the toner is lowered, and Pa becomes higher than that in a normal temperature. When the toner becomes tight (reduction of air volume included) due to a long-time settling or vibration, Pa becomes high.

FIG. 6shows a relation between the driving time of the single-shaft eccentric screw pump and the suction pressure. By using the screw pump60in a region B (the maximum pressure of the pump) ofFIG. 6, therefore, the generated pressure becomes always constant, and the toner can be surely sucked without being affected by the variation of the toner characteristics. The maximum pressure is set to Pa or higher.

The maximum generated pressure can be freely set by the size of the screw pump60, the rotation speed of the rotor61, biting amount of the rotor61with the stator62, and is preferably set with a margin of about three times of the required suction pressure of the toner at the normal temperature.

FIG. 7shows a relation between the driving time of the single-shaft eccentric screw pump60and suction pressure based on secular change. The maximum pressure of the screw pump60is sometimes lowered due to abrasion of the stator62made of a rubber material after a long period of use. As shown inFIG. 7, the time required for saturation becomes longer compared to that in the initial stage, together with the lowering of the maximum pressure. The driving time, therefore, is to be set longer than that for generating the maximum pressure for the single-shaft eccentric pump60having a service life equivalent to that of the electrophotographic device main body.

In the automatic volume-reducing type toner carrying device of the present embodiment, securing of airtightness of the replenishing passage including the vessel is important. In order to surely transmit the pressure generated in the single-shaft eccentric screw pump60to the toner for carrying, a stable amount of replenishing volume cannot be obtained, unless the airtightness is kept high enough in relation to the pressure generated in the screw pump60, for preventing sucking air from outside of the replenishing passage (idle sucking). In the case of the maximum pressure of 20 kPa of the screw pump60, for example, the airtightness of the replenishing passage may be secured higher than that for the pressure. As seen above, even if the condition of the toner varies, a stable amount of replenishing can be secured to surely reduce the volume of the toner vessel21.

As explained above, the present invention can supply a toner replenishing device having a stable performance without causing variation of the sucking pressure of the toner, even if the toner characteristics vary in the toner vessel of the volume-reducing type toner carrying device.