Embodiments described herein relate generally to an image forming apparatus and a voltage applying method.
In the related art, in an image forming apparatus such as a Multi Function Peripheral (MFP), a developing bias is applied to a developing roller and the like to develop an image when generating the image.
In an image forming apparatus for performing two-component development with a reversal developing system, a carrier is prevented from adhering to a photoconductive member in the following manner. For example, the image forming apparatus applies the developing bias to a developing roller at a timing earlier than a timing when a charged photoconductive element faces the developing roller. However, in this case, the developing roller to which the developing bias is applied faces a photoconductive element region in which charging is insufficient. Therefore, toner adheres to a region in which charging of the photoconductive element is insufficient. Then, it is necessary to perform processing so that the toner adhered to the region does not appear in an output image.
An image forming apparatus of an embodiment includes a charger, a charging bias voltage application section, an exposing device, a toner carrier, and a developing bias voltage application section. The charger charges a surface of an image carrier in a wide-angle by discharge. The charging bias voltage application section applies a charging bias voltage to the charger. The exposing device forms an electrostatic latent image in a charged image carrier. The toner carrier causes toner to adhere to the electrostatic latent image formed in the image carrier. The developing bias voltage application section applies the developing bias voltage to the toner carrier. In addition, the charging bias voltage application section changes the charging bias voltage in one step. The developing bias voltage application section changes the charging bias voltage in one step and changes the developing bias voltage applied to the toner carrier in multiple steps.
Hereinafter, an image forming apparatus and a voltage applying method of the embodiment will be described with reference to the drawings.
The charger 10 charges a surface (photoconductive element layer) of the photoconductive element 20 in a wide-angle by corona discharge. For example, the charger 10 charges the surface of the photoconductive element 20 to be a negative polarity. Therefore, an electrostatic latent image is formed on the surface of the photoconductive element 20 by the exposing device 13.
Here, a structure of the charger 10 will be described with reference to
The charger 10 performs discharge by applying a high voltage to the charging electrode 11 and charges the photoconductive element 20. If a high voltage is applied to the charging electrode 11, air around needle electrode is charged and the surface of the photoconductive element 20 facing the charging electrode 11 is charged. This phenomenon is called corona discharge, a grid bias voltage as a control bias is applied to the grid 32, and thereby a charging amount is controlled.
Returning to
The charging voltage application section 12 applies a charging bias voltage to the charger 10.
The exposing device 13 forms the electrostatic latent image by applying laser beams to the charged image carrier.
The photoconductive element 20 has the photoconductive element layer on the surface. The photoconductive element 20 is rotated in the clockwise direction by driving of a developing motor.
The developing device 30 includes a developing roller 31 as a developer carrier (toner carrier) and develops the electrostatic latent image formed on the surface of the photoconductive element 20 by the developer. The developer is composed of a carrier and toner. The developer carrier carries the carrier in addition to the toner. The developing device 30 is rotated in the counterclockwise direction by driving of the developing motor. The developing roller 31 is connected to the developing bias voltage application section 40.
The developing bias voltage application section 40 applies a developing bias voltage to the developing roller 31. The voltage applied to the developing roller 31 is, for example, a negative DC voltage. In the embodiment, a charging potential of the photoconductive element 20 is set at −600 V and a developing bias potential is set at −400 V. The developing bias voltage application section 40 applies voltages different in multiple steps to the developing roller 31 until a voltage is set up in a developing bias of a target.
The charging potential of the photoconductive element 20 when the charging bias voltage applied to the charger 10 is changed will be described with reference to
The photoconductive element 20 is charged at a moment when a voltage after a change required for charging the photoconductive element 20 to −650 V is applied from the charging voltage application section 12 to the charging electrode 11 within the charger 10, but the charging potential is not uniform. The reason is that discharge is started by the charger 10 at a moment when a voltage is applied to the charging electrode 11, but a reaching amount of a discharge charge, that is, a charging amount is different between a point d1 and a point d2.
Here, the point d1 indicates a point of the photoconductive element 20 closest to the charging electrode 11 (or the grid 32) and, in the embodiment, indicates a region of the photoconductive element 20 which is positioned beneath the charging electrode 11. The charging electrode 11 configures a center of discharge. The point d2 indicates a point of which a distance is farthest away from the charging electrode 11 in a reaching range of the discharge from the charging electrode (or the grid 32). However, the reaching amount of the discharge charge is reduced as the distance from the charging electrode 11 is increased (separated). Therefore, the discharge charge after the change does not reach portions based on the point d2 as a border. Therefore, the point d2 is also a border point where the discharge charge does not substantially reach.
The point d1 is charged to a value substantially close to −650 V of the charging potential at the point in time when the charging bias voltage after changed is applied. On the other hand, the point d2 is charged to a potential, for example, −600 V that is charged by the charging bias voltage before changed. That is, a difference occurs in the charging potential between the point d1 and the point d2. The potentials of the point d1 and the point d2 are substantially linearly changed. Then, regions having such a potential difference sequentially face the developing roller 31 due to a rotation of the photoconductive element 20.
Here, a position facing the photoconductive element 20 and the developing roller 31, more specifically, a contact point between a line 11 connecting a rotary shaft S1 of the photoconductive element 20 and a rotary shaft S2 of the developing roller 31, and the photoconductive element 20 is d3. In this case, a size (per unit time) of a change of the charging potential of the photoconductive element 20 passing through the contact point d3 is represented as the following Expression 1. The line 11 indicates a line connecting a rotation center of the photoconductive element 20 and a rotation center of the developing roller 31.
(Vg1−Vg2)/(L1/Vp) (V/sec) (Expression 1)
In Expression 1, Vg1 indicates the charging potential that is charged at the point d1 when the charging bias voltage after changed is applied to the charger 10. Vg2 indicates the charging potential that is charged at the point d2 when the charging bias voltage after changed is applied to the charger 10. In the embodiment, |Vg1|>|Vg2| is satisfied. L1 is a distance (mm) of an arc of the photoconductive element 20 from the point d1 to the point d2 and Vp (mm/sec) is a process speed, that is, a peripheral speed of the photoconductive element 20.
In the embodiment, the developing bias voltage is applied from the developing bias voltage application section 40 to the developing roller 31 facing a region of the photoconductive element 20 having such a potential difference in multiple steps.
As described above, the charging potential of the photoconductive element 20 facing the point d3 is changed from Vg2 to Vg1. The timing when the region of the photoconductive element 20 charged to the potential Vg2 faces the point d3 is indicated as a time t1 in
In the embodiment, −400 V is applied to the developing roller 31 before the time t1. However, a predetermined developing bias Vb=−450 V is applied to the developing roller 31 at the time t2. This is because it is necessary to maintain a potential difference between a potential after exposure of the photoconductive element 20 and the potential of the developing roller 31, and a potential difference between the charging potential of the photoconductive element 20 and the potential of the developing roller 31 constant (for example, 200 V) to prevent carrier adhesion even if the charging voltage is changed.
The developing bias voltage applied to the developing roller 31 is applied in multiple steps so as to substantially match to a slope |Vg1−Vg2|/(L1/Vp) between t1 and t2 of the graph 52.
The slope between t1 and t2 is uniquely determined by the size of the photoconductive element 20 and the process speed. Therefore, the developing bias voltage may be changed in multiple steps in a permissible range in consideration of a time required to switch the developing bias voltage. That is, since transition of the developing bias voltage is linearly changed as the number of switching occurrences of the developing bias voltage is increased, the transition can be performed with a predetermined potential difference in the change of the potential of the photoconductive element 20.
The timing when the developing bias voltage is applied in multiple steps is the timing after (L2-L1)/Vp (sec) has elapsed from the start of charging. Here, L2 indicates an arc length of the photoconductive element 20 from the point d1 to the point d3. Thereafter, the developing bias voltage application section 40 starts application of the developing bias voltage to the developing roller 31. Then, the developing bias voltage application section 40 sets up the developing bias in multiple steps so that the developing bias sets up to a predetermined developing bias value until a predetermined time L1/Vp (sec) has elapsed.
Here, for comparison,
In addition, as illustrated in
Then, in the image forming apparatus 100 of the embodiment, different voltages are applied to the developing roller 31 at a predetermined timing by changing the developing bias in multiple steps in accordance with Expression 1 described above.
As described above, the image forming apparatus 100 of the embodiment changes the developing bias voltage in multiple steps due to the charging bias voltage while changing the charging bias voltage in one step. The number of switching occurrences of the developing bias voltage is equal to or greater than three times and more preferably equal to or greater than five times. If the number of changes of the developing bias voltage is increased, the developing bias voltage may be applied in accordance with the change of the charging potential.
Moreover, in the embodiment described above, the charging bias voltage is changed so that an absolute value of the charging potential is increased, but may be changed so that the absolute value of the charging potential is decreased. For example, the charging bias voltage is changed from −600 V to −550 V and the developing bias voltage is changed from −400 V to −3500 V.
In this case, the changing amount of the charging potential is (Vg1−Vg2)/(L1/Vp). An absolute value of the changing amount is |Vg1−Vg2|/(L1/Vp).
Here, if the charger 10 has contrasting right and left shapes, the charging bias voltage is changed from −600 V to −550 V due to the charging bias voltage change from the point d1 to a position of a point d4 that is in a right and left symmetry position with the point d2. A point that the developing bias voltage is also changed in multiple steps in accordance with the change is the same as the embodiment described above. However, the timing when the developing bias voltage is changed becomes timing when L2/Vp (sec) has elapsed after the charging voltage is changed. After the developing bias voltage application section 40 applies the developing bias voltage after changed to the developing roller 31, a size (absolute value) of the developing bias voltage is decreased during (L2−L1)/Vp (sec).
The developing bias voltage set-up control according to another embodiment will be described with reference to
A slope of the graph 52 of
It is possible to prevent carrier adhesion and unnecessary toner from adhering to the photoconductive element 20 by setting up the developing bias voltage in multiple steps while setting up the charging bias voltage in one step.
The timing when the application of the developing bias voltage is started is timing when (L2−L1)/Vp (sec) has elapsed from the start of charging. Thereafter, the application of the developing bias voltage is started. Then, the developing bias voltage application section 40 sets up the developing bias stepwise so that the developing bias is set up to a predetermined developing bias value before a predetermined time L1/Vp (sec) elapses.
Moreover, even when charging is completed, that is, the charging bias voltage is turned off, it goes without saying that control is performed so as to be the same as the charge set-up. The developing bias voltage is decreased in multiple steps so as to be 0 V. Thus, toner adhesion does not occur in an uncharged region after the charge is turned off.
According to the image forming apparatus 100 having such a configuration described above, it is possible to suppress occurrence of image failure such as stain and carrier adhesion. Hereinafter, the effects will be described in detail. In the image forming apparatus 100 of the embodiment, different voltages are applied by changing the developing bias in multiple steps in accordance with the change of Expression 1 described above. Therefore, the potential difference between the developing bias and the surface potential is kept substantially constant. Therefore, it is possible to suppress occurrence of image failure such as stain and carrier adhesion.
In addition, according to the image forming apparatus 100 having such a configuration described above, the number of switching occurrences of the voltage is performed multiple times (for example, five times). Therefore, it is easy to match the potential of the developing bias to the change of the charging bias. Therefore, it is possible to suppress occurrence of image failure.
Hereinafter, modification examples will be described.
The charger 10 may be a roller charger disposed to come into contact with or come close to the photoconductive element 20. In addition, the charger 10 may be other devices as long as the surface of the photoconductive element is charged in a wide-angle.
According to at least one embodiment described above, the image forming apparatus 100 includes the charger 10, the charging voltage application section 12, the exposing device 13, the developing device 30, and the developing bias voltage application section 40. The charger 10 charges the surface of the photoconductive element 20 by discharging in a wide-angle. The charging voltage application section 12 applies the charging bias voltage to the charger 10. The exposing device 13 forms the electrostatic latent image on the charged photoconductive element 20. The developing device 30 causes toner to adhere to the electrostatic latent image formed on the photoconductive element 20. The developing bias voltage application section 40 applies the developing bias voltage to the developing device 30. In addition, the charging voltage application section 12 changes the charging bias voltage in one step. The developing bias voltage application section 40 changes the developing bias voltage applied to the developing device 30 in multiple steps besides changing the charging bias voltage in one step. Therefore, it is possible to suppress occurrence of image failure.
A part of functions of the charger 10 in the embodiment described above may be realized by a computer. In this case, a program for realizing the function is stored in a computer readable recording medium. Then, programs stored in the recording medium, in which the program described above is stored, are read by a computer system and may be realized by executing the programs. Moreover, the “computer system” described here includes hardware such as an operating system and a peripheral device. In addition, the “computer readable recording medium” refers to a portable medium, a storage device, and the like. The portable medium is a flexible disc, a magneto-optical disk, a ROM, a CD-ROM, and the like. In addition, the storage device is a hard disk which is built into the computer system and the like. Furthermore, the “computer readable recording medium” holds dynamically programs in a short period of time as a communication line if the programs are transmitted via the communication line. The communication line is a network such as the Internet, a telephone line, and the like. In addition, the “computer readable recording medium” may be a volatile memory within the computer system serving as a server or a client. The volatile memory holds programs for a fixed period of time. In addition, the programs described above may realize a part of the functions described above. In addition, the programs described above may be realized in combination with a program in which the functions described above are already recorded in the computer system.
While certain embodiments have been described these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms: furthermore various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.
This application is a Continuation of application Ser. No. 15/157,524 filed on May 18, 2016, the entire contents of which are incorporated herein by reference.
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Number | Date | Country | |
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Number | Date | Country | |
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Parent | 15157524 | May 2016 | US |
Child | 15688976 | US |