JP3595667B2 - Image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, an LBP, and a facsimile, and more particularly, to an image forming apparatus in which a scattered developer collecting unit provided near a developing unit is improved.
[0002]
[Prior art]
One example of a conventional image forming apparatus such as a copying machine or LBP is to uniformly charge the surface of a photosensitive drum, which is an image bearing member, with a primary charger and expose the photosensitive drum, which is an electrophotographic photosensitive member, with a laser beam. An electrostatic latent image is formed, the latent image is developed by a developing unit using a toner as a dry developer to form a toner image, and the toner image is transferred to a transfer sheet such as paper by a transfer unit. The image is fixed on the transfer paper by heating and pressing.
[0003]
In recent years, in such an image forming apparatus using a dry developer such as a copying machine and LBP, the particle size of the toner as a developer for forming an image has been increased from about 12 μm to 5 to 6 μm in order to improve image quality. The diameter is getting smaller.
[0004]
Conventionally, in an apparatus using such a toner, that is, a developer powder, as a countermeasure against scattering of the toner which causes contamination inside the apparatus such as a transfer paper or a transfer paper transport guide, a downstream side of the developing means (with respect to a moving direction of the image carrier) is used. On the downstream side, an air suction method and a bias roller for collecting scattered toner disposed near the photosensitive drum are known.
[0005]
[Problems to be solved by the invention]
In the above-mentioned conventional technology, the air suction method requires a duct, which may cause a space problem or a noise caused by a fan. On the other hand, the collecting bias roller system has relatively lower developer collecting performance than the air suction method.
[0006]
Conventionally, a bias of a fixed polarity, that is, either one of positive and negative polarities has been applied to the collecting bias roller. However, it has been found that as the toner particle diameter becomes smaller, many of the scattered toner particles are also charged to both polarities.
[0007]
Immediately below the developing means, when the image ratio is high, the amount of toner to be developed is large, so that the amount of scattered normally charged toner increases. , The scattering amount of the toner whose polarity is reversed is increased.
[0008]
An object of the present invention is to improve scattering toner collection by a collecting bias roller system, particularly to improving toner collection at a downstream side of a developing unit. An object of the present invention is to cope with a reduction in toner particle diameter and a change in image ratio. It is another object of the present invention to provide an image forming apparatus capable of satisfactorily recovering toner.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a representative means of the present invention includes an image carrier, an exposure unit for forming an electrostatic latent image on the image carrier, and a visualization of the latent image using a dry developer. a developing unit that of, disposed on the downstream vicinity of the developing means relates to a mobile direction of the image bearing member, an image forming apparatus having a developer collecting unit having a collecting roller for collecting the scattered developer, the formation Control means for changing the bias applied to the collection roller in accordance with the image ratio to be applied, wherein the control means adjusts the bias applied to the collection roller to an alternating voltage when the image ratio is less than 5%. Is a bias in which a DC voltage having the same polarity as the normal charging polarity is superimposed. In the case of 5 to 15%, only the alternating bias is applied, and when it exceeds 15%, the alternating voltage is opposite to the normal charging polarity of the developer. Bias with superimposed DC voltage of polarity Characterized in that that.
[0010]
According to the present invention, with such a configuration, the bias applied to the collection roller is changed according to the image ratio to be formed , and the scattered developer is collected satisfactorily.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
(Reference Example 1)
Reference Example 1 of the image forming apparatus according to the present invention will be described with reference to FIG. In FIG. 5, reference numeral 1 denotes a photosensitive drum as an image carrier, 2 denotes a primary charger for uniformly charging the surface of the photosensitive drum, and 3 denotes an image exposure emitted from an optical unit. By irradiating the drum 1, an electrostatic latent image is formed on the surface of the drum.
[0012]
Reference numeral 4 denotes a developing means, which is a developer container 4a for storing a toner as a dry developer, a developing sleeve 4b as a developer carrier for transporting the developer to the photosensitive drum, and a doctor for regulating the toner layer thickness on the developing sleeve. It has a blade 4c. The latent image on the photosensitive drum is developed by the toner carried and transported by the developing sleeve to form a toner image. The toner image is transferred to a transfer sheet such as paper in the next transfer step.
[0013]
Reference numeral 7 denotes a transfer sheet transport guide for guiding the transfer sheet, 8 denotes a transfer unit that transfers the toner image on the photosensitive drum to the transfer sheet, and 9 denotes a separation unit that separates the transfer sheet from the photosensitive drum. The transfer sheet on which the toner image has been transferred is conveyed to a fixing unit, where it is heated and fixed, and is discharged to a discharge tray.
[0014]
In Reference Example 1 , the scattered developer collecting means is provided near the downstream of the developing means (the term "downstream" means the positional relationship in the moving direction of the photosensitive drum in this specification). The collecting means 5 has a collecting roller 5a for collecting the developer, a developer collecting container 5b for storing the collected developer, and a blade 5c for scraping the developer on the collecting roller, and scatters near the developing means 4. The developer is sucked and collected by a collecting roller.
[0015]
Reference numeral 6 denotes a voltage control unit for the collection roller, which includes a control unit 6a having a CPU and a storage unit 6b such as a ROM for storing a bias voltage sequence and the like for the collection roller and the developing sleeve. The control unit 6 controls a bias power supply 5d. As a result, a predetermined voltage is applied to the collection roller.
[0016]
FIG. 1 shows a reference example 1 of the bias during the pre-rotation, the image formation (copy), and the post-rotation of the photosensitive drum 1 before the image formation in the image forming apparatus.
[0017]
In Reference Example 1 , the DC components of the bias applied to the developing unit 4 are Vdc = + 600 V during pre-rotation, Vdc = + 200 V during image formation, and Vdc = + 600 V during post-rotation.
[0018]
Usually, an original having an image ratio of about 6% is often used, and FIG. 2 shows the scattering amount of the developer with respect to the developing bias when this original is used.
[0019]
The normal development method was carried out, and the light portion potential of the photoconductor was Vl = + 70 V. When the developing bias is +200 V or less, the normally charged (minus) developer is large, and when the developing bias exceeds +200 V, the polarity is inverted and the positively charged developer is scattered.
[0020]
Therefore, the bias (DC component) applied to the collection roller of the scattered developer immediately below the developing means is:
During photoconductor pre-rotation: Vdc = -1000V
During image formation: Vdc = + 1000 V
During rotation after photoconductor: Vdc = -1000V
And
[0021]
On the basis of the above result, a bias voltage of +1000 V or more is applied to the collection roller 5 a with respect to a bias of the developing unit that changes the polarity of the charged voltage of the scattered developer, for example, 200 V or less. The developer scattered on the collecting roller could be satisfactorily attracted to the collecting roller and collected.
[0022]
(Reference Example 2)
In Reference Example 1 , a bias of +1000 V was applied to the collection roller during image formation. However, the scattered developer when the application voltage of the developing bias is +200 V may include a lot of those charged to the opposite polarity (plus) in addition to those charged to the normal (minus). In this case, the voltage applied to the collection roller is preferably not an AC DC component but an AC AC component.
[0023]
In Reference Example 2 , for example, a bias voltage of an alternating rectangular wave or a sine wave Vpp = 2000 V was applied during image formation. As a result, the developer charged to the opposite polarity (plus) could be collected by the collection roller when the alternating bias voltage was negative.
[0024]
(Embodiment 1)
In Reference Example 2 , a sine wave was applied to the collection roller. However, as the image ratio of the document increases, the amount of the scattered developer increases in a normal (negative) charge. Therefore, the collection efficiency can be improved by controlling the bias applied to the collection roller according to the image ratio.
[0025]
When the image ratio is 5 to 15%, the scattered developer is charged to both polarities. Therefore, only the AC component Vpp = 2000 V is applied to the collection roller, and no DC component is applied. If the image ratio is less than 5%, the scattering of the developer whose polarity has been reversed (plus) increases, so that an alternating current of Vpp = 1000V is weighted by a direct current Vdc = −500V.
[0026]
When the image ratio exceeds 15%, a large amount of normally charged particles are scattered, so that the DC component of Vdc = + 500V is added to the AC of Vpp = 1000V.
[0027]
The image ratio is calculated and determined by the control unit 6a by detecting the potential of the photosensitive drum by the potential sensor 10. The bias power is controlled by the control means 6 in accordance with the image ratio, and a predetermined bias voltage is applied to the collection roller.
[0028]
【The invention's effect】
As described above, according to the present invention, the bias applied to the collecting roller scattered developer disposed in the vicinity of the developing unit, by changing in accordance with the size of the image ratio at the time of image formation, scatter developer Can be improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of Reference Example 1 of a bias voltage in an image forming apparatus according to the present invention.
FIG. 2 is a diagram illustrating a voltage applied to a developing unit and an amount of scattered developer.
FIG. 3 is a view for explaining a scattered amount of a developer according to an image ratio.
FIG. 4 is an explanatory diagram of Embodiment 1 of a bias voltage in the image forming apparatus according to the present invention.
FIG. 5 is an overall schematic diagram of Reference Example 1 of the image forming apparatus according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum 2 ... Charging means 3 ... Image exposure 4 ... Developing means 5 ... Developer collecting means 5a ... Collecting roller 5b ... Developer collecting container 5c ... Blade 5d ... Power supply 6 ... Voltage control means 6a ... Control part 6b ... Storage means 7 Transfer sheet transport guide 8 Transfer separation means 9 Separation means
10 ... potential sensor

Claims (3)

An image carrier, an exposure unit that forms an electrostatic latent image on the image carrier, a developing unit that visualizes the latent image using a dry developer, and the developing unit with respect to a moving direction of the image carrier. A developer collecting means provided near the downstream of the means and having a collecting roller for collecting the scattered developer, wherein the bias applied to the collecting roller is adjusted in accordance with an image ratio to be formed. have a control means for changing, the control means, the bias applied to the collecting roller, the image ratio is less than 5%, the regular charging polarity of the same polarity as the DC voltage of the developer and superimposed bias to the alternating voltage , 5 to 15%, only the alternating bias is applied, and when it exceeds 15%, a bias is obtained by superimposing a DC voltage having a polarity opposite to the normal charging polarity of the developer on the alternating voltage. Forming equipment. 2. The image forming apparatus according to claim 1 , wherein the developer collecting unit includes a scraping unit that scrapes off the developer adhering to the collecting roller, and a container that stores the developer collected by the collecting roller. . 3. The image forming apparatus according to claim 1 , further comprising a detection unit configured to detect a potential of the surface of the image carrier, wherein the control unit determines a bias to the collection roller based on a detection result of the detection unit. apparatus.

Images