JPS61209467A - Electrophotographic device having plural developing unit - Google Patents

Abstract

PURPOSE:To obtain a sufficient image density after leaving a developing unit for a long period of time by constituting such that all developing units can abut when the photosensitive body is inoperable (non-rotation). CONSTITUTION:The developing units 4 and 5 can move in a space covering the state where they abut on the surface of the photosensitive body 1 and the separate state several mm away from said state by means of eccentric cams 9 and 10 and other mechanisms. The photosensitive body has a heating source 11 in its inside, and is always conductive irrespective of turning on and off of a main switch and temperature-adjusted by a temperature adjusting element, for instance, a thermyster. The heating source 11 prevents the moisture absorption of the sensitizing material, and acts as preventing the drop in the resistance of the photosensitive body and the disturbance of an electrostatic latent image due to the drop. Thus each developing unit can obtain a stable image density after it is stopped for a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic apparatus having a plurality of developing units, and in particular, an electrophotographic apparatus having a plurality of developing units, in which an image bearing member (hereinafter simply referred to as a "photoreceptor") such as a photosensitive drum and an insulating drum is located inside. The present invention relates to an electrophotographic apparatus having a heating source and at least one developing device movable toward and away from a photoreceptor. In this specification, the term "electrophotographic apparatus" includes various color printing apparatuses other than color printers that constitute the output section of color copying apparatuses, computers, and facsimiles.

Recently, the demand for color copying has increased rapidly, not only in special fields but also in general office work, and with this demand there has been a desire to improve the quality of images.

The most commonly used color electrophotographic apparatus at present is an electrophotographic apparatus that employs a parallel multicolor developing apparatus in which a plurality of developing units each having a developer of each color are arranged around a photoreceptor.

In such an electrophotographic apparatus, toner generally has hygroscopic properties, and the amount of charge decreases due to a decrease in volume resistivity due to moisture absorption, especially in a high-temperature environment, and a sufficient amount of flight cannot be obtained even when a developing bias is applied.

This caused a decrease in image density.

To this end, as an existing technology to prevent the photoreceptor from absorbing moisture, reducing the resistance of the photoreceptor, and thereby preventing the electrostatic latent image from being disturbed, a heating source, such as a planar heater, has been placed on the inner surface of the photoreceptor. However, a method has been implemented in which the temperature is controlled by a temperature control element, such as a thermistor, by constantly supplying electricity regardless of whether the main switch of the main body of the machine is ON or OFF.

In general, a developing device arranged around a photoreceptor is constructed so that it can be moved toward and away from the photoreceptor in order to prevent color mixing and for other reasons. Therefore, the developing device that is in contact with the photoreceptor has less moisture absorption and adhesion due to the heat supplied from the photoreceptor, and the decrease in image density is small, but the developing device that is separated from the photoreceptor remains separated because a sufficient amount of heat is not supplied to it. When left for a long time, image density significantly decreased. Therefore, there is a problem in that a conventional developing device which is left in a separated state for a long time after the photoreceptor is stopped cannot obtain a sufficient image density immediately after being left.

In order to prevent this, it has been considered to provide the developing device with a heater, but this has the problem of making the device large, complicated and expensive.

Therefore, an object of the present invention is to eliminate the above-mentioned problems in the conventional technology, and to provide a simple and easy-to-use developing device that can provide stable image density even after being stopped for a long time. An object of the present invention is to provide an electrophotographic device.

The above-mentioned object of the invention is to have a plurality of developing devices for visualizing an electrostatic latent image on a photoconductor, and at least one of the developing devices is connected to the photoconductor by a spacing mechanism. In an electrophotographic apparatus movable between a contact state and a separation state, a heating source for controlling the temperature of the photoreceptor is disposed on the inner surface of the photoreceptor, and the separation mechanism This is achieved by an electrophotographic apparatus characterized in that the device is configured to abut against the photoreceptor when the photoreceptor is not in operation or at least when the main switch is off.

The electrophotographic apparatus of the present invention having the above configuration will be described in detail below with reference to the drawings.

As mentioned above, the principle of the present invention can be applied to an electrophotographic apparatus for printing two or more colors (multicolor), or even for printing in all colors (full color). For the sake of simplicity, an electrophotographic apparatus having two developing devices 4 and 5 as shown in FIG. 1 will be described as an example. An electrophotographic apparatus can use various image forming processes, but in this embodiment, a so-called Carlson process is used.

In this embodiment, a charger 2, an image exposure 3. Developing units 4 and 5, transfer/separation chargers 6 and 7, and a cleaner 8 are arranged, and image formation is performed by the so-called Carlson process.

The developing device 4.5 generally includes toner supply containers 4b and 5b with side openings, and a fixed magnet (
Developing rollers 4a and 5a are arranged, each of which includes a magnet (not shown) and a sleeve (not shown) that is rotatably attached to surround the magnet.

Furthermore, the developing devices 4 and 5 are separated from the state in which they are in contact with the surface of the photoreceptor 1 (hereinafter referred to as the "contact state") by a mechanism such as the eccentric cams 9 and 10, with an interval of several mm. (hereinafter referred to as the "separated state"). Each developer has a different type of toner. Therefore, for example, if developer 4 has red toner and developer 5 has black toner, when creating an image in red, the color selection switch (Fig. (not shown), the developing device 4 is brought into contact with one island,
The developing device 5 is placed in a separated state, and an image is formed using red toner. In addition, in the case of image formation using black toner, the opposite is performed.

On the other hand, the photoreceptor has a heating source 11 (for example, a planar heater) on its inner surface, and is constantly energized regardless of whether the main switch is ON or OFF to control the temperature using a temperature control element, such as a thermistor (not shown). be done.

This heating source 11 functions to prevent moisture absorption in the photoreceptor, and to prevent a decrease in the resistance of the photoreceptor and the accompanying disturbance of the electrostatic latent image.

Next, regarding the electrophotographic apparatus according to the present invention having the above-described configuration, each element including the photoreceptor 1, the charger 2. Exposure 3, developer 4
．． 5 and the operation of the drum heater 11 will be explained with reference to the sequence shown in FIG.

First, from OFF to ON of the main SW, both the developing devices 4.5 are in contact (in contact with the photoconductor). When the main SW is turned ON, preheating of the fixing device, etc. Waiting is in progress for this reason, and in synchronization with this, developing device 4.5
Both become separated.

Further, regulated rotation (e.g., erasing residual charges on the photoreceptor by irradiation such as pre-exposure) is performed, and the photoreceptor l rotates.

Simultaneously with the completion of this regulated rotation, the reproducing devices 4 and 5 enter a contact state.

Next, when a copy start signal is input, the developing device to be used is placed in the contact state, and the other developing device is placed in the separated state.For example, developing device 4 is set to be red.

When the developing device 5 is set to black and an image is to be formed in red, only the developing device 4 is brought into contact. Photoreceptor l receives a copy start signal,
The developing device 4.5 is rotated by receiving power from a drive source (not shown), but since the developing device 4.5 is directly driven by the photoreceptor l via a gear, the developing roller 4a of only the developing device 4 that is in contact with it is The developing roller 5a of the developing device 5, which rotates and is in a separated state, does not rotate.

Next, when the rotation of the photoreceptor 1 is stopped at the same time as copying is completed, the developing device (here, the developing device 5) which is in the separated state is brought into contact with the reproducing device 4.5.

After this, if the copy cycle is repeated, the above sequence is repeated. Further, even if the main SW is turned off, the reproducing devices 4 and 5 are maintained in the abutting state.

On the other hand, the temperature of the heater 11 built into the photoreceptor is constantly controlled as described above.

The sequence described above provides the following effects.

(I) When the photoreceptor is not driven, all the developing devices are in contact with the photoreceptor, so even if left for a long time, an appropriate amount of heat is supplied from the photoreceptor, the temperature of the toner increases, and the amount of moisture absorption decreases. Therefore, the volume resistance of the toner is small, and a decrease in image density is prevented.

(II) When the photoreceptor is driven, except during copying, the developing device is kept in a separated state, so that the developing device does not operate, and unnecessary scattering of toner caused by the rotation of the developing roller can be prevented.

In the above embodiment, the developing device is always in contact with the photoreceptor even after copying cycles are repeated. Therefore, after a large number of copies have been made, the temperature of the peripheral area including the photoreceptor becomes sufficiently high. Therefore, if a toner with a low melting point or low blocking temperature is used as a developer, if the developer is left in contact after copying, not only the drum heater but also the residual heat of the fuser will cause damage. The temperature of the developing device further increases and approaches the above-mentioned melting point or blocking temperature, and in the worst case, a suitable image cannot be obtained.

Therefore, in other embodiments, for example, the main SW is turned off.
The developing device is brought into contact only when . The sequence in this case is shown in FIG.

First, when the main SW is OFF, one developing device is 4.5
Both are in contact. When the main SW is turned ON, the reproducing device enters a separated state and waits until the copy SW is turned ON. When the copy SW is turned on, only the developing device used (for example, developing device 4 in this embodiment) comes into contact and contributes to image formation. After the copy cycle is completed, the developer is set apart again. A similar sequence is performed for the other developing device 5 as well. Finally, when the main SW is turned off, both the imager and the imager are brought into contact in synchronization, and this state is maintained until the next main 5WON. Incidentally, the temperature of the drum heater 11 is constantly regulated regardless of the above sequence. Implementation of such a sequence brings about the following effects.

CI) Under the main 5WOFF condition, both the reproducing devices are in the ≦contact state, and the amount of moisture absorbed by the developer is small due to residual heat from the drum heater. Sufficient density and image quality can also be achieved in images.

(II) After the copy cycle is completed, the developing device is separated, so an appropriate amount of residual heat is transferred not only from the drum heater but also from the entire device including the fixing device, suppressing moisture absorption and preventing blocking fusion. It becomes possible to maintain the developer at a certain temperature, and sufficient density and image quality are always maintained.

The presence or absence of regulated rotation in the above sequence is irrelevant to the present invention, and is not necessarily limited to apparatuses having a heat fixing device.

Furthermore, in the second embodiment, at least the main S
It is necessary to keep the developer in contact while W is OFF, and in addition to this requirement, after the main SW is turned on, the developer must be kept in contact until the first copy SW is turned ON. It is possible to add a sequence etc. that maintains the Similarly, in the first example described above, it is possible to add a sequence in which the developing device is placed in the contact state after the main SW is in contact and before the start of the regulated rotation.

In an electrophotographic apparatus that has a plurality of developing devices and has a mechanism for separating at least one of the developing devices from the photoreceptor, the photoreceptor is not in operation (not rotating). ) can obtain sufficient image density even after being left for a long period of time by configuring all the developing units to be in contact with each other. In addition, unnecessary scattering of toner can also be prevented by keeping the developing device having the # gap mechanism in a separated state except during image formation and when the photoreceptor is not in operation.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the area around a photoreceptor of an electrophotographic apparatus having a plurality of developing units. FIG. 2 illustrates a specific example of a sequence in an electrophotographic apparatus according to the present invention. FIG. 3 illustrates another specific example of a sequence in an electrophotographic apparatus according to the present invention. l: Photoreceptor 4.5: Developing devices 4a, 5a: Developing roller 9.10: Separation mechanism 11: Heat source Fig. 1

Claims (1)

[Claims] 1) It has a plurality of developing devices for visualizing the electrostatic latent image on the image carrier, and at least one of the developing devices is brought into contact with the image carrier by a spacing mechanism. In an electrophotographic apparatus that is movable between a contact state and a separated state, a heating source for controlling the temperature of the image carrier is disposed on the inner surface of the image carrier, and the separating mechanism is configured to connect a corresponding developing device. An electrophotographic apparatus, characterized in that: is configured to abut against the image carrier when the image carrier is not in operation or at least when the main switch is OFF.