Patent Application
20180039198
The present invention relates to an image forming apparatus using an electrophotographic system.
Conventionally, there has been known an image forming apparatus such as a copier and a laser beam printer configured to use an endless belt as an intermediate transfer member. In the image forming apparatus, a toner image formed on the surface of a photosensitive drum serving as an image bearing member is transferred onto a belt as a primary transfer step when a voltage is applied from a voltage power supply to a primary transfer member arranged at a part opposing the photosensitive drum. Then, the primary transfer step is repeatedly performed with respect to toner images of a plurality of colors to form the toner images of the plurality of colors on the surface of the belt. Subsequently, the toner images of the plurality of colors formed on the surface of the belt are collectively transferred onto the surface of a recording material such as a paper as a secondary transfer step when a voltage is applied to a secondary transfer member. After that, the collectively transferred toner images are permanently fixed onto the recording material by fixing unit. In the way described above, a color image is formed.
Japanese Patent Application Laid-open No. 2013-213990 discloses a configuration allowing a change in the surface potential of a belt while making it possible to perform the miniaturization and the cost reduction of an image forming apparatus. According to the configuration, circuits having a plurality of Zener diodes different in setting voltage are provided between the belt and ground, and the setting voltage is changed according to a use environment to change the surface potential of the belt and stabilize primary transfer efficiency.
Generally, a plurality of members such as a photosensitive drum, an intermediate transfer member, and a primary transfer member are interposed as the configuration of a primary transfer portion, and there is a case that the resistance of the primary transfer portion changes or a case that an optimum primary transfer current changes depending on a surrounding environment or the use situation of an image forming apparatus. In the configuration of Japanese Patent Application Laid-open No. 2013-213990, a surrounding environment is detected and the surface potential of a photosensitive drum is slightly adjusted with a change in voltage maintaining unit to ensure optimum transferability. However, in the slight adjustment of the surface potential of the photosensitive drum, each of a developing potential and a primary transfer potential has a potential difference necessary for properly moving toner. Therefore, when the surface potential of the photosensitive drum is largely changed to be adjusted, a reduction in image quality is caused. That is, in order to slightly adjust various fluctuations caused by a surrounding environment or the use situation of the body of the image forming apparatus, it is necessary to further increase the number of Zener diodes serving as voltage maintaining unit, which results in a difficulty in maintaining the miniaturization of the apparatus.
It is an object of the present invention to provide an image forming apparatus capable of making the surface of an intermediate transfer member have an optimum potential for primary transfer while maintaining the miniaturization of the image forming apparatus.
In order to achieve the above object, an embodiment of the present invention provides an image forming apparatus comprising:
According to an embodiment of the present invention, it is possible to make the surface of an intermediate transfer member have an optimum potential for primary transfer while maintaining miniaturization.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, a description will be given, with reference to the drawings, of embodiments (examples) of the present invention. However, the sizes, materials, shapes, their relative arrangements, or the like of constituents described in the embodiments may be appropriately changed according to the configurations, various conditions, or the like of apparatuses to which the invention is applied. Therefore, the sizes, materials, shapes, their relative arrangements, or the like of the constituents described in the embodiments do not intend to limit the scope of the invention to the following embodiments.
The first image forming station a has a drum-shaped electrophotographic photosensitive member (hereinafter called a photosensitive drum) 1a serving as an image bearing member, a charging roller 2a serving as a charging member, a developing device 4a, and a cleaning device 5a. The photosensitive drum 1a is an image bearing member that is rotationally driven in an arrow direction at a prescribed peripheral speed (process speed) and bears a toner image (developer image). In addition, the developing device 4a is a device that accommodates yellow toner serving as developer and develops an electrostatic latent image formed on the photosensitive drum 1a using the yellow toner. The cleaning device 5a is a member that collects the toner attached onto the photosensitive drum 1a. In the embodiment, the cleaning device 5a has a cleaning blade serving as a cleaning member that contacts the photosensitive drum 1a and a waste toner box that accommodates the toner collected by the cleaning blade.
When an image forming operation starts with an image signal, the photosensitive drum 1a is rotationally driven. In a rotation process, the photosensitive drum 1a is uniformly charged by the charging roller 2a to have a prescribed polarity (negative polarity in the embodiment) and a prescribed potential and then exposed by exposure unit 3a according to the image signal. Thus, an electrostatic latent image corresponding to a yellow component image of an objective color image is formed. Then, the electrostatic latent image is developed by the developing device (yellow developing device) 4a at a developing position and visualized as a yellow toner image. Here, the normal charging polarity of the toner accommodated in the developing device is negative.
An intermediate transfer belt 10 is an endless belt. The intermediate transfer belt 10 is extended between extending members 11, 12, and 13 serving as support members and rotationally driven at substantially the same peripheral speed while contacting the photosensitive drum 1a in the same movement direction as the photosensitive drum 1a at its opposing part contacting the photosensitive drum 1a. The yellow toner image formed on the photosensitive drum 1a is transferred onto the intermediate transfer belt 10 (primary transfer) when passing through the contact part (hereinafter called the primary transfer nip) between the photosensitive drum 1a and the intermediate transfer belt 10. The method of the primary transfer characterizing the embodiment will be described later. The untransferred toner of the primary transfer on the surface of the photosensitive drum 1a is cleaned and removed by the cleaning device 5a and then subjected to an image forming process following a charging process. In the same way as the above, a magenta toner image of a second color, a cyan toner image of a third color, and a black toner image of a fourth color are formed by the second, third, and fourth image forming stations b, c, and d, respectively, and successively transferred onto the intermediate transfer belt 10 in an overlapped state. Thus, a combined color image corresponding an objective color image is obtained.
The toner images of the four colors on the intermediate transfer belt 10 are collectively transferred onto the surface of a recording material P fed by paper feeding unit 50 (secondary transfer) when passing through a secondary transfer nip formed by the intermediate transfer belt 10 and a secondary transfer roller 20. The secondary transfer roller 20 serving as a secondary transfer member has an outer diameter of 18 mm in which a nickel-plated steel rod having an outer diameter of 8 mm is covered with a blowing sponge body mainly composed of NBR adjusted to have a volume resistance of 108 acm and a thickness of 5 mm and epichlorohydrin rubber. In addition, the secondary transfer roller 20 contacts the intermediate transfer belt 10 with an applied pressure of 50 N and forms a secondary transfer part (hereinafter called the secondary transfer nip). The secondary transfer roller 20 rotates following the intermediate transfer belt 10. When the toner on the intermediate transfer belt 10 is being secondarily transferred onto the recording material P such as a paper, a voltage of 1800 to 2300 V is applied to the secondary transfer roller 20. The recording material P bearing the toner images of the four colors is introduced into a fixation unit 30 to be heated and pressed. Thus, the toner of the four colors is melted and mixed together and fixed onto the recording material P. Untransferred toner on the intermediate transfer belt 10 after the secondary transfer is cleaned and removed by the cleaning device 16. By the above operations, a full-color print image is formed.
A description will be given, with reference to
Hereinafter, a description will be given of the configuration of the primary transfer portion characterizing the embodiment. The embodiment is characterized by a configuration in which a current is supplied in the peripheral direction of the intermediate transfer belt 10 to perform the primary transfer, i.e., a configuration in which a primary transfer current is supplied at a position different from the primary transfer nips of the photosensitive drums 1a, 1b, 1c, and 1d in the peripheral direction (rotating direction) of the intermediate transfer belt 10. The intermediate transfer belt 10 and the photosensitive drums 1a to 1d form the contact parts (primary transfer nips) with the extension of the intermediate transfer belt 10 by the extending rollers 11 and 13 and are connected to a voltage adjustment circuit 15 including a transistor serving as a voltage adjustment member connected to the extending roller 13. At its positions opposing the respective image forming stations a to d, the intermediate transfer belt 10 serving as an intermediate transfer member is arranged. The intermediate transfer belt 10 is an endless belt in which a conducting agent is added to a resin material to have conductivity. The intermediate transfer belt 10 is extended by the three shafts of the driving roller 11, the tension roller 12, and the secondary transfer opposing roller 13 and extended by the tension roller 12 at a total pressure of 60 N. The intermediate transfer belt 10 is rotationally driven at substantially the same peripheral speed as those of the photosensitive drums 1a to 1d in the same movement direction at its opposing parts contacting the photosensitive drums 1a to 1d.
In addition, the secondary transfer opposing roller 13 serving as a contact member is connected to the voltage adjustment circuit 15 including a transistor as voltage adjustment unit (voltage adjustment portion). The intermediate transfer belt 10 used in the embodiment has a peripheral length of 700 mm and a thickness of 90 μm. The intermediate transfer belt 10 is made of an endless polyethylene terephthalate (PET) resin molded by mixing an ion-based conducting agent as a conducting agent. As its electrical characteristics, the intermediate transfer belt 10 is characterized in that the unevenness or the like of a resistance value in the peripheral direction is fine although the resistance value fluctuates with respect to temperature and humidity in an atmosphere since the intermediate transfer belt 10 exhibits ion conducting characteristics and electrical conductivity is obtained when ion is transmitted between high polymer chains. In the embodiment, a current is supplied in the movement direction of the intermediate transfer belt to perform the transfer. Therefore, a voltage drop becomes large when the resistance of the intermediate transfer belt 10 is high. As a result, the intermediate transfer belt preferably has a low resistance layer since there is a likelihood of its primary transferability being impaired. In the embodiment, a base layer having a volume resistivity of 1×108 Ω·cm or less as a resistance was used to suppress a voltage drop in the intermediate transfer belt 10. For the measurement of the volume resistivity, the type UR (MCP-HTP12) of a ring probe is used in Hiresta-UP (MCP-HT450) manufactured by Mitsubishi Chemical Corporation. In the measurement of the volume resistivity, room temperature was set at 23° C. and room humidity was set at 50%. In addition, a voltage of 100 V was applied for 10 seconds. Further, in the embodiment, the intermediate transfer belt 10 is configured by two layers. By the arrangement of a high resistance layer on its surface, the intermediate transfer belt 10 suppresses a current flowing through a non-image part to further increase its transferability. However, the intermediate transfer belt 10 is not limited to this configuration but may be configured by a single layer or three or more layers.
In addition, the intermediate transfer belt 10 is made of a polyethylene terephthalate resin in the embodiment but may be made of other materials. Examples of the other materials include polyester, polycarbonate, polyarylate, and acrylonitrile-butadiene-styrene copolymer (ABS). Besides, examples of the other materials include polyphenylene sulfide (PPS), polyvinylidene difluoride (PVdF), and polyethylene naphthalate (PEN). These materials and the mixed resins of these materials may be used as the material of the belt 10.
In the embodiment, the voltage adjustment circuit 15 having a transistor is connected as the voltage adjustment portion between the secondary transfer opposing roller 13 and ground. The voltage adjustment circuit 15 adjusts a voltage to be applied from a secondary transfer power supply 21 to the intermediate transfer belt 10 via the secondary transfer roller 20 to generate a primary transfer voltage for performing the primary transfer to move the toner on the respective photosensitive drum 1a to 1d onto the intermediate transfer belt 10. By the application of the primary transfer voltage adjusted by the voltage adjustment circuit 15 to a desired size, the surface potential of the intermediate transfer belt 10 becomes a desired primary transfer potential. Based on the potential differences (transfer contrast) between the surface potential of the intermediate transfer belt 10 and the surface potentials of the respective photosensitive drums 1a to 1d, the primary transfer is performed. A description will be given, with reference to
The primary transfer voltage Vt1 indicating the potential difference between the point A and the ground in
The voltage input to the base terminal of the transistor Q1 to control the collector current is the output voltage of an operational amplifier IC1. The PWM signal output from the controller 100 is smoothened by a resistor R7 and a capacitor C1. A smoothened control voltage V− is input to the inversion input terminal (− terminal) of the operational amplifier IC1. A voltage output from the operational amplifier IC1 is divided by resistors R9 and R10 and input to the base terminal of the transistor Q1. As described above, the current generated by the secondary transfer voltage Vt2 flows through the transistor Q1 as the collector current when the voltage is applied to the base terminal of the transistor Q1, whereby a voltage is generated between the collector and the emitter of the transistor Q1 and used as be the primary transfer voltage Vt1. The generated primary transfer voltage Vt1 is divided by resistors R5 and R6, and a resulting voltage is input to the input terminal (+ terminal) of the operational amplifier IC1 as a monitor voltage V+. Accordingly, the size of the primary transfer voltage Vt1 is determined according to the size of the control voltage V− by the virtual short (V+=V−) of the operational amplifier IC1. The control voltage V− is controlled by the on-duty of the PWM signal. That is, when the on-duty of the PWM signal increases, both the control voltage V− and the primary transfer voltage Vt1 becomes large. Conversely, when the on-duty of the PWM signal reduces, both the control voltage V− and the primary transfer voltage Vt1 becomes small.
As described above, the embodiment employs the configuration in which the voltage of the transistor Q1 is controlled by the PWM signal from the controller to determine the primary transfer voltage. Note that a resistor R8 and a capacitor C2 in
As shown in
In view of the above circumstances, the present inventors have determined an optimum voltage for the primary transfer in the following way. First, in order to deal with the above fluctuations of the transfer efficiency, the transistor Q1 variable in the range of 0 V to 600 V was used as the voltage adjustment member. The resistance value fluctuations of the intermediate transfer belt 10 according to a surrounding environment are predicted and a bias setting table corresponding to the output value of the environmental sensor 106 is generated in advance to determine an optimum primary transfer voltage. In the configuration of the present invention, the primary transfer voltage is determined with reference to the bias setting table of the following table 1.
A description will be given, with reference to
As described above, the resistance fluctuations of the intermediate transfer belt 10 according to a surrounding environment are predicted with the use of the transistor Q1 as the voltage adjustment unit for the primary transfer in the embodiment, whereby an appropriate primary transfer voltage may be determined and excellent primary transferability may be ensured.
In the embodiment, the resistance fluctuations of the intermediate transfer belt according to a surrounding environment were predicted to determine the primary transfer voltage. However, as shown in
Vt1=Vt0+Vtb
That is, the controller 100 changes the size of the control signal output to the voltage adjustment circuit 15 to change the amount of the current supplied to the intermediate transfer belt 10 such that the size of the primary transfer potential becomes larger as the remaining service life of the belt becomes shorter. Note that in the embodiment, the above use situation of the intermediate transfer belt 10 is determined in such a way that the CPU 150 serving not only as the control portion but also as acquisition unit collects information on the number of printed sheets accumulated in the RAM 152 of the image forming apparatus. However, other information may be acquired as the information on the service life. For example, the same effect is obtained even with image information such as the number of the total pixels of an image obtained by an image forming operation, the time of the rotation of the intermediate transfer belt, and the number of the rotation times of the intermediate transfer belt.
As described above, in the embodiment, although a primary transfer voltage is generated from a secondary transfer voltage after a current necessary for secondary transfer is ensured from a secondary transfer power supply, it is possible to separately set the primary transfer voltage with the use of a transistor as the voltage adjustment unit for primary transfer. Further, regardless of a surrounding environment and the use situation of an intermediate transfer belt, an appropriate primary transfer voltage may be determined and excellent primary transferability may be ensured. In addition, it is possible to select optimum settings as secondary transfer voltage settings.
In the embodiment, a transistor is used as the voltage adjustment member to adjust the voltage of the primary transfer portion. However, an element such as a digital volume (digital variable resistor) may be used so long as the same effect is obtained by the element. That is, it may be possible to use an element capable of changing the size of a current supplied from the secondary transfer roller 20 to the intermediate transfer belt 10 according to the size of a control signal such as a PWM signal variable in size.
A description will be given, with reference to
As shown in
The primary transfer rollers 14a to 14d contact the photosensitive drums 1a to 1d, respectively, with a prescribed pressing force in a state of sandwiching the intermediate transfer belt 10 and rotate following the intermediate transfer belt 10. In the embodiment, the arrangement of the primary transfer rollers results in an increase in the number of components but allows a high degree of flexibility in selecting the intermediate transfer belt.
A yellow toner image formed on the photosensitive drum 1a is transferred onto the intermediate transfer belt 10 (primary transfer) when passing through the primary transfer nip between the photosensitive drum 1a and the intermediate transfer belt 10. A primary transfer roller serving as a primary transfer member has an outer diameter of 12 mm in which a nickel-plated steel rod having an outer diameter of 6 mm is covered with a blowing sponge body mainly composed of NBR adjusted to have a volume resistance of 107 Ω·cm and a thickness of 3 mm and epichlorohydrin rubber. In addition, the primary transfer roller 14a contacts the photosensitive drum 1a with an applied pressure of 10 N and forms the primary transfer nip.
A description will be given, with reference to
In the embodiment, the Zener diode ZD1 serving as the voltage maintaining unit for maintaining a potential of 500 V was used, and the transistor Q1 serving as the voltage adjustment unit variable in the range of 0 V to 600 V like the first embodiment was used. Therefore, in the configuration of the embodiment, it becomes possible to control the potential of the primary transfer portion in the range of 500 V to 1100 V. In the configuration of the embodiment, optimum primary transferability may be ensured using a reference voltage shown in the following table 3.
The control flow of the embodiment is the same as that of the first embodiment.
As described above, the embodiment is so configured that a transistor is used as voltage adjustment unit for primary transfer and a Zener diode is used as voltage maintaining unit, the transistor and the Zener diode being connected in series to each other. Thus, even with a primary transfer member having high resistance, an appropriate primary transfer voltage may be determined and excellent primary transferability may be ensured.
Note that in the embodiment as well, primary transferability may be further improved as a matter of course in such a way as to perform correction according to the use situation (the remaining service life) of the intermediate transfer belt 10 described in the first embodiment. In addition, the Zener diode is used as the voltage maintaining unit in the embodiment. However, the voltage maintaining unit is not limited to such an element, and an element such as a varistor may be used so long as the same effect is obtained by the element. In addition, the roller members are used as the primary transfer members in the embodiment. However, the same effect is obtained even with, for example, conductive brushes or conductive sheet members.
A description will be given, with reference to
A CPU 100 serving as a control portion outputs a voltage generation signal to the secondary transfer voltage source 21 and the cleaning voltage source 201. Based on the signal, the secondary transfer voltage source 21 applies a direct current having a positive polarity to the secondary transfer roller 601, and the cleaning voltage source 201 applies a direct voltage having a positive polarity to the cleaning brush 602. A secondary transfer current Itr2 flowing through the secondary transfer roller 601 and a cleaning current Iic1 flowing through the cleaning brush 602 merge with each other via the intermediate transfer belt 600 and the secondary transfer opposing roller 603a. Then, the current diverges into the primary transfer current Itr1 necessary for the primary transfer and a control current Icon flowing through a current control circuit 315. The primary transfer current Itr1 flows into the ground via resistors 702a, 702b, 702c, and 702d, primary transfer brushes 701a, 701b, 701c, and 701d, the intermediate transfer belt 600, and the photosensitive drums 700a, 700b, 700c, and 700d.
The image forming apparatus of
Vtr1=(V−)×((R500+R501)/R501) (1)
Note that R500 and R501 are the resistance values of the resistors 500 and 501, respectively, and a current flowing through the input terminal of the operational amplifier 302 is not taken into consideration since it is minute. The monitor voltage V+ is a direct current obtained by dividing the primary transfer voltage Vtr1 by the resistors 500 and 501. On the other hand, the control voltage V− is a direct current obtained by smoothening a PWM signal serving as a current adjustment signal (control signal variable in size) output from the CPU 100 by a resistor 300 and a capacitor 301. The control voltage V− changes with the on-duty (on-duty ratio) of the PWM signal. The control voltage V− becomes larger as the on-duty increases, and the primary transfer voltage Vtr1 becomes larger according to the above formula (1). A resistor 304 and a capacitor 303 are connected as elements to determine the response of the operational amplifier 302. The output voltage of the operational amplifier 302 is divided by resistors 305 and 306 and input to the base terminal of a transistor 307. Thus, the collector current of the transistor 307 is controlled. The primary transfer voltage Vtr1 is generated as the collector-emitter voltage of the transistor 307.
In the configuration, an endless polyethylene terephthalate (PET) resin obtained by mixing an ion conducting agent as a conducting agent or the like is used as the intermediate transfer belt. As electrical characteristics, a resistance value fluctuates with respect to temperature and humidity in an atmosphere since the intermediate transfer belt exhibits ion conducting characteristics and electrical conductivity is obtained when ion is transmitted between high polymer chains. In addition, the resistance value of the primary transfer brush used in the configuration increases with energization deterioration due to the endurance of the image forming apparatus. In order to ensure the primary transfer current necessary to deal with the fluctuations of the resistance value of a primary transfer load like this, it is necessary to change the primary transfer voltage.
When the resistance value of a primary transfer load is predicted from a surrounding environment and an endurance sheet number and a primary transfer voltage is determined according to the resistance value of the predicted primary transfer load in the configuration of the above comparative example, there is a case that the determined applied voltage does not become optimum depending on the fluctuations of a load resistance value.
The upstream electric load of the embodiment includes a resistance component from the secondary transfer roller 601 to the secondary transfer opposing roller 603a via the intermediate transfer belt 600 and a resistance component from the cleaning brush 602 to the secondary transfer opposing roller 603a via the intermediate transfer belt 600. In addition, the downstream electric load of the embodiment includes a resistance component from the secondary transfer opposing roller 603a to the ground via primary transfer brushes 701a, 701b, 701c, and 701d. In addition, like the comparative example, a current control circuit 315 is connected in parallel to the downstream electric load 70 and controls a primary transfer voltage Vtr1 by controlling a control current Icon flowing through itself.
The image forming apparatus of
The image forming apparatus has, as current detection portions, a secondary transfer current detection circuit 400 that detects a secondary transfer current Itr2 flowing through the secondary transfer roller 601 and a cleaning current detection circuit 401 that detects a cleaning current Iic1 flowing through the cleaning brush 602. Current detection results detected by the respective current detection circuits are output to the CPU 100. In general, the secondary transfer portion and the cleaning portion of an image forming apparatus often have respective current detection circuits, and these current detection circuits are applicable to the control of the embodiment. Here, the relationship between the secondary transfer current Itr2, the cleaning current Iic1, and the primary transfer current Itr1 is expressed by the following formula (2).
Itr2+Iic1=Itr1+Icon (2)
Icon is a control current flowing through the current control circuit 315. In calculating the resistance value of a primary transfer load, a state in which the control current Icon flowing through the current control circuit 315 is known is created. In the embodiment, a condition for turning off the transistor 307 is set and the control current Icon is set at 0 (zero) to create the state in which the control current is known. Specifically, the on-duty of the PWM signal output from the CPU 100 is set at 100%, and the control voltage V− is set at 3.3 V. In addition, a secondary transfer voltage Vtr2 or a cleaning voltage Vic1 at which the primary transfer voltage Vtr1 does not exceed 600 V regardless of the resistance values of the upstream electric load 60 and the downstream electric load 70. For example, when the secondary transfer voltage Vtr2 is set at 600 V and the cleaning voltage Vicl is set at 0 V, the primary transfer voltage Vtr1 does not exceed 600 V. At this time, the monitor voltage V+ becomes 3.0 V or less, the control voltage V− becomes 3.3 V, the output of the operational amplifier 302 is fixed to its lower limit, and the transistor 307 is reliably turned off. However, in this case, it is necessary to design the monitor voltage and the control voltage such that the differential input voltage range of the operational amplifier is satisfied. In this case, the following formula (3) is obtained from the above formula (2).
Itr1=Itr2+Iic1 (3)
Since the secondary transfer current Itr2 and the cleaning current Iic1 are detected by the current detection circuits, the primary transfer current Itr1 may be calculated and acquired. In addition, since the primary transfer voltage Vtr1 is detected by a voltage detection circuit 350 at this time, a resistance value Rtrl of the primary transfer load may be calculated and acquired by the following formula (4).
Rtr1=Vtr1/(Itr2+Iic1) (4)
Icon=(Vtr1−Vzd)/R308 (5)
Note that Vzd is the Zener voltage of the Zener diode 800, and R308 is the resistance value of the resistor 308. At this time, the primary transfer current Itr1 is calculated by the following formula (6) based on the above formula (2).
Itr1=Itr2+Iic1−((Vtr1−Vzd)/R308) (6)
In addition, a resistance value Rtrl of the primary transfer load may be calculated by the following formula (7).
Rtr1=Vtr1/(Itr2+Iic1−((Vtr1−Vzd)/R308)) (7)
The CPU 100 has the table of the optimum primary transfer voltage Vtr1 corresponding to the resistance value Rtrl of the calculated primary transfer load and performs the constant voltage control of the optimum primary transfer voltage Vtr1 corresponding to the resistance value Rtrl of a primary transfer load calculated in an image forming operation.
In
In the control method of the comparative example, the primary transfer voltage to be applied is determined according to the primary transfer load having the middle resistance value, and a voltage of 610 V is applied as such. Therefore, the applied voltage is smaller by about 160 V than the voltage applied with respect to the primary transfer load having the highest resistance value, and larger by about 160 V than the voltage applied with respect to the primary transfer load having the lowest resistance value. On the other hand, in the control method of the embodiment, the resistance value of the primary transfer load is calculated to determine the applied voltage. Therefore, even when the primary transfer load has the highest or the lowest resistance value, the optimum primary transfer voltage may be applied.
According to the embodiment, an optimum primary transfer voltage may be applied even when the resistance value of a primary transfer load fluctuates as described above. Thus, excellent primary transferability may be ensured.
In the third embodiment shown in
In the image forming apparatus in
Itr2+Iic1=(Itr1a+Icona)+(Itr1b+Iconb)+(Itr1c+Iconc)+(Itr1d+Icond) (8)
Icona, Iconb, Iconc, and Icond are control currents flowing through the current control circuits 315a, 315b, 315c, and 315d of the respective image forming stations.
In calculating the resistance value of a primary transfer load for each of the image forming stations, the control currents flowing through the current control circuits of all the image forming stations are set to be known, and photosensitive drums other than the photosensitive drum of an image forming station of which the resistance value of the primary transfer load is to be calculated are separated. This control is separately performed for all the four image forming stations with a time deviation for each of the image forming stations. Like the third embodiment, a condition for turning off a transistor is set in the embodiment as well. By setting the control currents Icona, Iconb, Iconc, and Icond at 0, a state in which the control currents are known is created.
In addition, the photosensitive drums of image forming stations other than an image forming station of which the resistance value is to be calculated are separated by the contacting/separating unit 900a, 900b, 900c, and 900d to set currents flowing through the image forming stations other than the image forming station of which the resistance value is to be calculated at 0. For example, when the resistance value of an image forming station 70a is calculated, the photosensitive drums of image forming stations 70b, 70c, and 70d are separated to set Iconb, Iconc, and Icond at 0. At this time, the following formula (9) is obtained from the above formula (8).
Itr1a=Itr2+Iic1 (9)
Thus, a resistance value Rtr1a of the primary transfer load of the image forming station 70a may be calculated by the following formula (10).
Rtr1a=Vtr1a/(Itr2+Iic1) (10)
The above control is performed for the image forming stations 70b, 70c, and 70d with a time deviation, whereby resistance values Rtr1a, Rtr1b, Rtr1c, and Rtr1d of all the image forming stations may be calculated.
A CPU 100 has a table for optimum primary transfer voltages corresponding to the resistance values of calculated primary transfer loads and performs the constant voltage control of optimum primary transfer voltages Vtr1a, Vtr1b, Vtr1c, and Vtr1d corresponding to the resistance values of the primary transfer loads calculated in an image forming operation.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Applications No. 2016-153769, filed on Aug. 4, 2016, and No. 2017-26151, filed on Feb. 15, 2017 which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-153769 | Aug 2016 | JP | national |
| 2017-026151 | Feb 2017 | JP | national |
