JP3376199B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an electrostatic latent image on an image carrier by scanning and exposing, for example, spot light, and using the latent image with toner. And an image forming apparatus for visualizing by a non-contact developing method. 2. Description of the Related Art Conventionally, in an image forming apparatus, a method of obtaining an electrostatic latent image by exposing an optical image serving as a document to a photoconductor as an image carrier is roughly classified into a so-called analog exposure system. Two digital exposure methods are known. In the analog exposure method, reflected light obtained by irradiating an original with a light source such as a halogen lamp is directly guided to a photosensitive drum by an optical system such as a lens and a mirror to form an image, thereby exposing the photosensitive drum. . In the digital exposure method, the reflected light of an original is focused on photoelectric conversion means such as a CCD by an optical system such as a lens or a mirror, and the original image is converted into an electric signal.
The electric signal is converted into light by a light emitting element such as a laser or an LED to expose the photosensitive drum. [0004] In recent years, copiers and printers of the digital exposure system have begun to spread with the improvement of the processing capability of computers. As the exposure system, a laser scanning optical system that scans a laser beam with a polygon mirror called a polygon mirror is widely used. [0005] When this laser scanning optical system is applied, major problems are deviation and vibration of the laser scanning line, vibration of the photosensitive drum, and deviation of the moving speed of the outer peripheral surface. These shakes and vibrations during laser scanning cause unevenness in the formed latent image, and as a result, cause image unevenness called banding in an image obtained by development, and the quality of the image is significantly deteriorated. For this reason, when designing the image forming apparatus, the optical system unit is separated from the vibration source; the number of optical systems that return light is reduced; the vibration of the optical system is suppressed; We are taking measures to reduce vibration and unevenness. A developing device for visualizing an electrostatic latent image is, as typified by a two-component developing system, a system in which a developer is brought into contact with a photosensitive drum to obtain a toner image, and a developing device in which a developer is not brought into contact with a photosensitive drum. The method is broadly classified into a method of obtaining a toner image by applying an AC bias as a developing bias when the apparatus is positioned in a state. In particular, the latter non-contact development method is called a jumping development method, and a development method using a magnetic one-component toner as a developer and a development method using a non-magnetic one-component toner have been developed. In the case of using this non-contact developing method, the distance between the developing sleeve and the photosensitive drum,
That is, because the allowable amount of the interval (SD interval) is small, the developing sleeve is abutted against the photosensitive drum via a roller,
It is common to get an interval. However, when the developing sleeve is brought into contact with the photosensitive drum via a roller, rotation and vibration of the developing sleeve are directly transmitted to the photosensitive drum, which is one of the major causes of the vibration of the photosensitive drum. Further, if the rollers are soiled with toner or the like due to long-term use, the stains are fused between the photosensitive drum and the rollers, so that the SD interval cannot be accurately set or the vibration is deteriorated. [0010] In view of the above,
In order to suppress the vibration of the photosensitive drum due to the one-component non-contact developing device, the roller is stopped against the photosensitive drum, and the developing device is fixed to the main body of the image forming apparatus. A mechanism that guarantees the position of the sleeve from the rotation center of the photosensitive drum has been considered. However, the fitting accuracy of the flange of the photosensitive drum becomes larger than the allowable amount of the SD interval, and there is a problem that image unevenness occurs at the period of the outer peripheral surface of the photosensitive drum. An object of the present invention is to eliminate the need for abutting rollers against a photosensitive drum on a developing sleeve of a one-component non-contact developing device, and to improve developability even when the SD interval between the developing sleeve and the photosensitive drum fluctuates. An object of the present invention is to provide an image forming apparatus which can guarantee an image without a decrease in density. The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image carrier, and a developer carrier for non-contact development of an electrostatic latent image obtained by imagewise exposing the uniformly charged image carrier with a one-component developer. And a bias power supply for applying a developing bias in which an AC voltage is superimposed on a DC voltage to the developer carrier, a capacitor C1 connected in parallel to an output side of the bias power supply. And a resistor R is inserted in series to change the peak-to-peak voltage of the developing bias in accordance with the variation of the capacitance C2 between the image carrier and the developer carrier,
The image forming apparatus is characterized in that a variable capacitor C3 is inserted in parallel with the capacitance C2. Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic structural view showing an embodiment of the image forming apparatus of the present invention. In FIG. 1, reference numeral 1 denotes a photosensitive drum as an image carrier, and the photosensitive drum 1 has a photoconductive layer provided on a cylindrical conductive substrate. A photosensitive material such as an organic photoreceptor (OPC), an amorphous silicon photoreceptor (a-Si), or Se is used. The photosensitive drum 1 is rotatably supported by the image forming apparatus main body so as to be rotatable in the direction of the arrow in the figure. The surface of the photosensitive drum 1 is uniformly charged by the scotron charger 2 while being rotated. The uniformly charged photosensitive drum 1 is exposed to a laser beam driven by a signal proportional to the image density of the document from the laser scanner unit 10, and an electrostatic latent image corresponding to the document is formed on the surface of the photosensitive drum 1. Is done. The laser scanner unit 10 includes a platen glass 1
An illumination lamp 13 for optically scanning a document 12 placed on the document 1 is provided. The reflected light of the image information from the document 12 optically scanned by the illumination lamp 13 is reflected by mirrors 15a, 15b and 15c.
To form an image on the photoelectric conversion element 14 via the lens. The photoelectric conversion element 14 converts the image information on the reflected light into an analog image electric signal, and the A / D converter 16 converts the image signal into a digital image electric signal proportional to the image density. The digital image signal is sent to a laser driver 17, and the laser driver 17 drives a laser 18 with the image signal to generate a laser beam modulated in accordance with the image density. The image laser light is transmitted to the polygon mirror 19.
The electrostatic latent image is formed as described above by scanning the photosensitive drum 1 through. The electrostatic latent image on the photosensitive drum 1 is developed by a developing unit 3 and visualized as a toner image. The obtained toner image is conveyed to the transfer section facing the corona charger 4 as the photosensitive drum 1 rotates, and is transferred onto the transfer paper conveyed to the transfer section from a paper cassette (not shown) by the corona charger 4 from the corona charger 4. Is transcribed by the action of The transfer paper on which the toner image has been transferred is separated from the photosensitive drum 1 and sent to the fixing device 5, where the toner image is fixed on the paper. After the transfer, the photosensitive drum 1 is prepared for the next image formation by removing the transfer residual toner remaining on the surface of the photosensitive drum 1 with a blade of the cleaning unit 6 or the like. According to the present invention, the developing device 3 employs a magnetic jumping developing system. In general, in the jumping developing method, a toner is held in a thin layer on a developing sleeve 3a as a rotating developer carrier of a developing unit 3, and the toner layer is brought into non-contact with the photosensitive drum at a developing unit facing the photosensitive drum 1. And apply an AC bias or an AC bias obtained by superimposing a DC voltage between the photosensitive drum 1 and the developing sleeve 3a to cause the toner to fly on the photosensitive drum and develop the electrostatic latent image on the photosensitive drum. Things. When a non-magnetic toner is used, a non-magnetic jumping development system is used, and when a magnetic toner is used, a magnetic jumping development system is used. In the magnetic jumping developing method used in the present invention, a magnet is provided inside the developing sleeve 3a, and the magnetic toner adhered on the developing sleeve 3a by the magnet is regulated by the magnetic blade 3b. A thin layer of toner is formed on the surface of the toner, and uniform development faithful to the latent image can be performed. In this embodiment, an amorphous silicon photosensitive drum having an outer diameter of 80 mm is used as the photosensitive drum 1, and the latent image has a dark potential Vd = 400 to 450V and a bright potential Vl = 10 to 50V. The process speed of the image forming apparatus was 300 mm / sec. The developing sleeve 3a of the developing device 3 is a non-magnetic SUS sleeve having an outer diameter of 25 mm, the surface of which is coated with a resin. The distance between the magnetic blade 3b and the developing sleeve 3a is 300 to 400 μm, and the magnetic toner layer on the developing sleeve regulated by the magnetic blade is:
The layer thickness was about 100 μm, and the toner amount was 1 mg / cm ² . The magnetic toner used had an average particle size of 6 μm and a magnetic substance content of 90 parts. The interval (SD interval) between the developing sleeve 3a and the photosensitive drum 1 is 200 μm.
A rectangular wave bias having a frequency of 2 kHz and a peak-to-peak voltage of 1 kVpp was applied as a developing bias between the developing sleeve 3a and the photosensitive drum. According to the present invention, the developing device 3 is fixed to the main body side plate of the image forming apparatus with the above-mentioned SD interval between the developing sleeve 3a and the photosensitive drum 1. Thus, the position of the developing sleeve 3a from the rotation center of the photosensitive drum 1 is guaranteed, and the SD interval is guaranteed. According to such an SD interval guarantee method, S
The D interval is 150 to 250 μm depending on the rotation of the photosensitive drum 1.
m. The causes of this variation were mainly due to the fitting accuracy of the flange of the photosensitive drum 1 and the wobbling of the bearing. FIG. 2 shows the SD distance dependency of the image density when a normal AC bias without DC voltage superposition is applied and development is performed. As shown in FIG. 2, it can be seen that the image density is reduced because the developing electric field is weakened when the space between SDs is widened. As a result, the image density varies with the rotation cycle of the outer peripheral surface of the photosensitive drum 1. FIG. 3 shows the dependence of the capacitance formed in the gap between the developing sleeve and the photosensitive drum on the SD distance. As shown in FIG. 3, when the SD interval increases, the capacitance between the SDs decreases, and the capacitance between the SDs has an SD distance dependency that has almost the same tendency as the image density in FIG. I understand. FIG. 4 is a graph showing the relationship between the developing bias Vpp and the image density at a plurality of latent image potential levels. As can be seen from FIG. 4, the image density obtained by development varies depending on the applied development bias Vpp, and the developability increases as Vpp increases. From the above three factors, in the present invention, a change in the image density due to a change in the SD interval between the photosensitive drum 1 and the developing sleeve 3a is regarded as a change due to a change in the capacitance between the SDs. In the above, the change in the capacitance is guaranteed by the change in the developing bias by Vpp. FIG. 5 shows a circuit configuration of the bias power supply according to the present invention. As shown in FIG. 5, the bias power supply 7 has a capacitor C1 and a resistor R connected in parallel, which are connected in series, on the output side of an AC voltage source EAC and a DC voltage source EDC connected in series. The electrostatic capacity (load capacity) formed between the developing sleeve 3a and the photosensitive drum 1 is represented by C2.
Indicated by According to such a bias power supply 7, assuming that Vpp on the bias power supply 7 side is Vpp ₀ , the Vpp applied to the developing sleeve 3a can be obtained by writing the capacitance of the capacitor C1 as C1. Vpp ₀ × C1 / (C1 + C2) According to this, when the capacitance C2 between the SDs becomes small due to the widening of the SD interval, the capacitance term on the right side of the above equation becomes large, so that Vpp becomes large. Therefore, the developability due to the developing bias is enhanced, and the image density can be maintained so as not to decrease irrespective of the increase in the SD interval. Similarly, even if the SD interval is narrowed, the image density can be maintained so as not to increase. In order to obtain Vpp changed according to the change of the capacitance C2 between SDs, the capacitor C1 incorporated in the power supply 7 is almost the same as C2 or about 0.5 to 1.5 times C2. Preferably, the capacitance is used. If C1 is set so large that C2 can be ignored, V according to the change of C2
No change in pp is obtained, and the effect of the present invention is not exhibited. To give a specific example, the capacitance C2 between SD is 150-20.
When about 0 pF, the capacitor C1 is set to 50 to 150 pF.
There was an effect if it was a degree. In the above description, the capacitor C1 is incorporated in the bias power source 7. However, the capacitor C1 is arranged closer to the developing device 3 than used integrally with the power source 7, so that the variation of the capacitance inherent in the developing device 3 is absorbed. It is more preferable to configure them. Alternatively, as shown in FIG. 6, in addition to the capacitor C1 of the bias power source 7, a variable capacitor C3 that absorbs a variation in the capacitance inherent in the developing device 3 is provided. It can be placed in parallel with the capacitance C2 between the photosensitive drum 1 and the photosensitive drum 1. Vpp applied to the developing sleeve 3a is as follows: Vpp = Vpp ₀ × C1 / (C1 + C2 + C3) As described above, according to the present invention, the image bearing
Image exposure of the body and the uniformly charged image carrier
Development of non-contact development of the obtained electrostatic latent image with one-component developer
A developer with a developer carrier and an AC voltage superimposed on a DC voltage
Bias voltage applied to the developer carrier
And a bias power source.
The capacitor C1 and the resistor R connected in parallel to the output side
By inserting in series, the peak-to-peak
To the fluctuation of the capacitance C2 between the image carrier and the developer carrier
Variable capacitor in parallel with the capacitance C2.
The configuration is such that the capacitor C3 is inserted. In this way,
In this case, the peak-to-peak voltage of the developing bias is
Change according to the fluctuation of the capacitance between the agent carriers
, A capacitor C3 is inserted in parallel with the capacitance C2.
Capable of variably adjusting the capacitance of the capacitor C3
In this way, it is possible to absorb fluctuations in capacitance
Can, even if variations in the SD gap, by changing the amplitude of the AC component of the developing bias by a change in capacitance between SD due to variations in the SD gap, it is possible to increase the developability, SD
A decrease in developability due to a change in the interval can be guaranteed. Therefore, an image without a decrease in density can be obtained, and the allowable amount of fluctuation of the SD interval is wide. Further, since the abutting rollers are not used, the vibration due to the rotation of the developing sleeve is not transmitted to the photosensitive drum via the rollers, and there is no image unevenness due to the vibration.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram showing one embodiment of an image forming apparatus of the present invention. FIG. 2 is a diagram showing a relationship between an SD interval and an image density. FIG. 3 is a diagram illustrating a relationship between SD intervals and capacitance between SDs. FIG. 4 is a diagram illustrating a relationship between an amplitude of an AC component of a developing bias and an image density. FIG. 5 is a diagram illustrating a circuit configuration of a bias power supply installed in the image forming apparatus of FIG. 1; FIG. 6 is a diagram illustrating another example of the circuit configuration of the bias power supply. [Description of Signs] 1 Photosensitive drum 3 Developing device 3a Developing sleeve 7 Bias power supply C1, C3 Capacitor C2 Capacitance EAC AC source EDC DC source R Resistor

Claims (1)

(57) Claims 1. An image carrier and an electrostatic latent image obtained by imagewise exposing the uniformly charged image carrier are non-contacted with a one-component developer. A developing device having a developer carrier for developing;
And a bias power supply for applying a developing bias in which an AC voltage is superimposed on a DC voltage to the developer carrier, wherein a capacitor C1 and a resistor R connected in parallel to an output side of the bias power supply are connected in series. By inserting it, the peak-to-peak voltage of the developing bias is changed according to the fluctuation of the capacitance C2 between the image carrier and the developer carrier, and a variable capacitor C3 is inserted in parallel with the capacitance C2. An image forming apparatus.