JP4154292B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus that forms an image by electrophotography.
[0002]
[Prior art]
Conventionally, a laser beam printer as shown in FIG. 9 is known. In this laser beam printer, a recording material is passed between an image carrier and a transfer means in contact with the image carrier, and a transfer material is transferred. A transfer bias is applied to the means, and the toner image formed on the surface of the image carrier is transferred to the recording material.
[0003]
The surface of the photoreceptor 1 rotating in the direction indicated by the arrow X in FIG. 9 is uniformly charged by the charging roller 2 connected to the high-voltage power supply 11, and the laser beam modulated based on the image signal on the charging surface. 3 is scanned to form an electrostatic latent image on the charged surface. The electrostatic latent image on the photoreceptor 1 is developed by the toner 5 of the developing device 4 and becomes a toner image and arrives at the transfer portion N. The charging roller 2 is pressed against the outer peripheral surface of the photosensitive member 1 with a predetermined pressing force, and is rotated by the rotation of the photosensitive member 1. A superposed voltage of an AC component and a DC component having a peak-to-peak voltage Vpp more than twice the charging start voltage is applied to the charging roller 2 from the high-voltage power source 11 through a cored bar, and is rotated and driven. The outer peripheral surface of the photosensitive member 1 is uniformly contact-charged by the AC application method.
[0004]
The transfer portion N is composed of a nip portion between the photosensitive member 1 and the conductive transfer roller 10 in contact with the photosensitive member 1, and the recording material is aligned with the timing when the toner image portion on the photosensitive member 1 arrives at the transfer portion N. 7 passes through the nip. At this time, a transfer bias is applied to the transfer roller 10 by the power supply 13, and the toner image on the photoreceptor 1 side is transferred to the recording material 7. Thereafter, the recording material 7 carrying the toner image leaves the transfer portion N and is conveyed to a fixing portion (not shown).
[0005]
In such a laser beam printer, for the purpose of simplifying replacement maintenance of consumables such as a photoconductor and toner, a toner storage unit, a developing unit, a photoconductor, a charging unit, a cleaning unit including a waste toner container, etc. Many are integrated as a process cartridge and configured to be detachable from the laser beam printer.
[0006]
There are also cartridges that manage cartridge information by mounting storage means (memory) on these cartridges. As described in Japanese Patent Application Laid-Open No. H10-228707, there are some that store the amount of cartridge used in a memory and change various process conditions. For example, the charging current value is switched or the exposure amount is adjusted. These are controlled in the same way as long as the amount used is the same despite the different cartridges.
[0007]
As for the transfer bias control of this type of laser beam printer, an ATVC (Active Transfer Voltage Control) method has been proposed previously. This method is a means for optimizing the transfer bias applied to the transfer roller 10 at the time of transfer. A desired constant current bias is applied from the transfer roller 10 to the photosensitive drum 1 during the pre-rotation of the laser beam printer, and the initial value at that time is applied. The transfer bias is optimized by detecting the resistance value of the transfer roller 10 from the detection voltage Vo and selecting a constant voltage bias according to the resistance value at the time of transfer. In this case, the transfer application constant voltage Vt is expressed by the following equation (ATVC equation) when A and B are constant.
Vt = AVo + B
[0008]
Further, the resistance value of the transfer roller 10 made of a semiconductive rubber material or the like greatly varies depending on the environment in which the device is placed (hereinafter, “the environment in which the device is placed” is also referred to as “environment”). It is easy to do, and the low humidity environment is larger than the high humidity environment. The characteristic is particularly remarkable in ion conductive solid rubber that is widely used in recent years, and this ion conductive solid rubber can be used as a kind of environmental sensor. For example, it is possible to control the constant current of the transfer roller 10 before printing and determine the environment in which the apparatus is located from the initial detection voltage Vo generated on the transfer roller 10 through the photosensitive member 1.
[0009]
[Patent Document 1]
US Pat. No. 5,272,503 specification
[Problems to be solved by the invention]
However, when determining the environment based on the resistance value of the conductive transfer roller 10, there is a problem that detection accuracy deteriorates due to durability or a transfer defect occurs due to the influence of factors other than the conductive transfer roller 10.
[0011]
In the transfer constant current control performed before printing, a bias is applied to a portion charged by the charging roller of the photoreceptor. Charging uses an AC application method, and positive and negative voltages are alternately applied as the applied voltage, and discharge and reverse discharge are repeated. Therefore, the surface of the photoreceptor to be charged is greatly deteriorated by this discharge, and the surface of the deteriorated photoreceptor The portion is scraped off by friction with a contact portion such as a cleaning blade, whereby the photosensitive layer of the photoreceptor is gradually thinned.
[0012]
As the photosensitive layer of the photosensitive member becomes thinner in this manner, the voltage Vo detected by the ATVC control decreases, and the environment determined based on this voltage Vo becomes different from the environment at the initial stage of use.
[0013]
In addition, a problem such as a transfer failure occurs due to a decrease in the voltage Vo.
[0014]
Therefore, an object of the present invention is to provide a laser beam printer that can solve the above-described problems and can stably form a high-quality image from the initial use to the end of its life.
[0015]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a photoconductor for carrying a toner image, a transfer unit for forming a transfer nip with the photoconductor, and a transfer bias for transferring the toner image on the photoconductor to a transfer material. Bias applying means for applying to the transfer means, and voltage detecting means for detecting the voltage value of the bias output from the transfer bias applying means to the transfer means, and when the transfer material is not present in the transfer nip, in the image forming apparatus biasing means detects said voltage detecting means detects a voltage value when the constant current control bias applied to the transfer means, for setting the bias on the basis of the detected voltage value, the photosensitive member having a cartridge having, by replacing the cartridge, it is possible to exchange the photoreceptor leaving the transfer means, the integrated use of the photosensitive member The corrected voltage value that increases with increases, and sets the transfer bias is added to the detected voltage value.
[0016]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the cartridge includes a storage unit, the storage unit stores an accumulated usage amount of the photosensitive member, and the storage unit stores the storage unit. The correction voltage value is set based on the accumulated usage amount of the photoreceptor .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0019]
<First Embodiment>
FIG. 1 shows a first embodiment of the present invention. This is an example of a laser beam printer. This laser beam printer has a photosensitive drum 1 as an image carrier, and has a charging roller 2, a developing device 4, and a transfer roller 10 around the photosensitive drum 1. A scanner unit 3 and a cleaning container 8 are provided above the photosensitive drum 1.
[0020]
The photosensitive drum 1, the charging roller 2, the developing device 4, and the cleaning container 8 are integrated into a process cartridge 12 that is detachable from the laser beam printer main body.
[0021]
The photosensitive drum 1 is formed by coating a photoconductive organic photoreceptor on a hollow aluminum base. The charging roller 2 is a semiconductive rubber roller. The developing device 4 is integrated as a developing unit in the cartridge 12 and includes a developing blade 4 a, a developing sleeve 4 b, and a toner 5 facing the photosensitive drum 1.
[0022]
The transfer roller 10 is made of an ion conductive solid rubber, and an elastic layer is formed on an iron cored bar of φ6 by an ion conductive NBR (nitrile butadiene rubber), φ14.5, hardness 45 degrees (Asker- C when weighting 500 g). The resistance value of the transfer roller 10 is about 700 MΩ in an N / N (room temperature and humidity) environment. The ion conductive solid rubber has a remarkable characteristic that its resistance value changes greatly according to the environment. FIG. 5 is a table showing the resistance values of the transfer roller 10 in each environment.
[0023]
After the surface of the photosensitive drum 1 is uniformly negatively charged by the charging roller 2, the photosensitive drum 1 is exposed by a laser beam from the scanner unit 3, and only the exposed area is neutralized to form a latent image. . Then, the toner 5 of the developing device 4 is frictionally charged between the developing blade 4a and the developing sleeve 4b with the same polarity as the charged surface of the photosensitive drum 1, and an electric field is generated in the developing gap portion where the photosensitive drum 2 and the developing sleeve 4b face each other. The toner 5 is selectively attached to the latent image on the photosensitive drum 1 while floating and vibrating by the action, and the latent image is used as a toner image. Thereafter, the photosensitive drum 1 is transferred by the transfer roller 10 and the photosensitive drum 1. Rotate to nip.
[0024]
In the transfer nip portion, the toner image on the photosensitive drum 1 is electrostatically attracted and moved to the recording material 7 side, so that a high voltage having a polarity opposite to that of the toner image is not applied to the transfer roller 10 in contact with the back surface of the recording material 7. Applied by the means shown in the figure, the back surface of the recording material 7 is charged with a polarity opposite to that of the toner 5 to give a transfer charge. As a result, the toner image is transferred and held on the recording material 7. In the present embodiment, the ATVC method described in the section of the prior art is used for the control of the transfer bias.
[0025]
Then, the recording material 7 onto which the toner image has been transferred is conveyed to a heat fixing device (not shown), and the toner image is permanently fixed by the heat fixing device. On the other hand, on the surface of the photosensitive drum 1 after the transfer, a slight amount of deposits such as toner having different polarities remain on the surface, but these deposits remain in the cleaning container 8 after the photosensitive drum 1 passes through the transfer nip portion. The cleaning blade 9 abutted at the position is scraped off and cleaned. Thereafter, the photosensitive drum 1 stands by for the next printing.
[0026]
Reference numeral 6 denotes a storage unit included in the developing device 4, which is detected by passing a predetermined constant current bias from the transfer roller 10 to the photosensitive drum 1 during the pre-rotation in the initial use stage before the surface film of the photosensitive drum 1 starts to deteriorate. The initial detection voltage Vo is stored, and the number of prints after the initial use stage is counted. The storage means 6 is not particularly limited as long as it can store and hold signal information in a rewritable manner. For example, an electrical storage means such as a RAM or a rewritable ROM, a magnetic storage medium, a magnetic bubble memory, an optical Magnetic storage means such as a magnetic memory is used. In the present embodiment, an NV (Non Volatile) RAM is used as the storage means 6 from the viewpoint of ease of handling and cost.
[0027]
An engine control unit 16 includes a high voltage power supply 13, a CPU (central processing unit) 14, a memory 15, and an NVRAM 19. The high voltage power supply 13 applies a bias voltage to the charging roller 2 and the transfer roller 10. The CPU 14 controls each part of the laser beam printer including the high voltage power supply 13. The memory 15 is used as a work area for the CPU 14. The NVRAM 19 stores the initial detection voltage Vo ≦ 500 and Vo ′ = Cn / 10 (where Cn is the number of counters) in association with each other, and 500 <initial detection voltage Vo ≦ 1200 and Vo ′ = Cn / 15 (where Cn is the number of counters) and 1200 <initial detection voltage Vo and Vo ′ = Cn / 60 (where Cn is the number of counters) are stored in association with each other. The relationship between the number of printers and the correction voltage Vo ′ is shown in FIGS. 2 (a), (b), and (c).
[0028]
Next, an example of a control procedure from the pre-rotation to the bias voltage determination will be described. First, after the initial stage of use, a predetermined constant current bias is passed from the transfer roller 10 to the photosensitive drum 1 during the pre-rotation of the photosensitive drum 1 to detect the initial detection voltage Vo, and the detected initial detection voltage Vo is stored in the storage means. Store in 6.
[0029]
When it is determined that the initial detection voltage Vo is in the range of Vo ≦ 500, Vo ′ = Cn / 10 (where Cn is the number of counters) is extracted from the NVRAM 19 as a calculation formula for the correction voltage Vo ′. .
[0030]
When it is determined that the initial detection voltage Vo is in the range of 500 <Vo ≦ 1200, Vo ′ = Cn / 15 (where Cn is the number of counters) is extracted from the NVRAM 19 as a calculation formula for the correction voltage Vo ′. .
[0031]
When it is determined that the detection voltage Vo is in the range of 1200 <Vo, Vo ′ = Cn / 60 (where Cn is the number of counters) is extracted from the NVRAM 19 as a calculation formula for the correction voltage Vo ′.
[0032]
Assume that the initial detection voltage Vo taken out from the storage means 6 is 550 V, for example, and the expression Vo ′ = Cn / 10 (where Cn is the number of counters) is taken out from the NVRAM 19. Then, during the pre-rotation after the initial stage of use, a predetermined constant current bias is applied from the transfer roller 10 to the photosensitive drum 1, for example, 350V is detected, and for example, 3000 sheets are taken out from the storage means 6 as the counter number Cn. .
[0033]
When the number of printed sheets reaches the drum life of 3000 sheets, the surface film thickness of the photosensitive drum 1 is about 3 μm / 1000 in proportion to the number of printed sheets in light of FIG. It will decrease by about 9 μm.
[0034]
In this example, 350 V is detected as the detection voltage Va. For example, in the case of a transfer roller having a resistance value of 0.2 GΩ in an N / N (room temperature and humidity) environment, the detection voltage Vo at the initial use stage is used. Is 550V, the detected voltage after printing 3000 sheets is about 350V in light of FIG. 4 which shows an example of the relationship between the detected voltage and the resistance value of the transfer roller.
[0035]
After 3000 sheets are taken out as the counter number Cn, this number is substituted into Vo ′ = Cn / 10 (where Cn is the number of counters) as a calculation formula of the correction voltage Vo ′, and correction is made from this calculation formula. 200V is obtained as the voltage Vo ′. Next, 200 V (correction voltage Vo ′) is added to 350 V (detected voltage), and 550 V is obtained as the corrected voltage Vm. Referring to FIG. 6, the environment where the laser beam printer is placed is shown. N / N (room temperature and humidity) environment).
[0036]
Incidentally, in the environmental judgment in the conventional example, 350 V (<500 V) is detected as the detection voltage in the present embodiment. Therefore, referring to FIG. 6, the environment where the laser beam printer is placed is H / H ( High temperature and high humidity) environment).
[0037]
Therefore, from the detection voltage Vo detected by the ATVC control and the deterioration state of the surface film thickness of the photosensitive drum 1 according to the number of printed sheets (counter number), the environment where the laser beam printer is placed is accurately determined regardless of the durability. Can be determined.
[0038]
This also makes it possible to optimally control transfer application constant voltage, charging bias, developing bias, fixing, and the like during printing.
[0039]
<Second Embodiment>
FIG. 7 shows a second embodiment of the present invention. This is an example of a laser beam printer. In FIG. 7, the same parts as those in FIG. An engine control unit 76 includes a high voltage power source 73, a CPU 74, a memory 75, and an NVRAM 79. The high voltage power source 73 applies a transfer bias voltage to the transfer roller 10. The CPU 74 controls each part of the laser beam printer including the high voltage power source 73. The memory 75 is used as a work area for the CPU 74. The NVRAM 79 stores the initial detection voltage Vo ≦ 500 and Vo ′ = Cn / 10 (where Cn is the number of counters) in association with each other, and 500 <initial detection voltage Vo ≦ 1200 and Vo ′ = Cn / 15 (where Cn is the number of counters) and 1200 <initial detection voltage Vo and Vo ′ = Cn / 60 (where Cn is the number of counters) are stored in association with each other. The relationship between the number of printers and the correction voltage Vo ′ is shown in FIGS. 2 (a), (b), and (c).
[0040]
Reference numeral 17 denotes a controller that converts image data from the PC 18 into video data and transfers the video data to the engine control unit 76 and the CPU 74.
[0041]
In the present embodiment, the constant current value for ATVC control is set to 4 μA, and the constant current value of 4 μA is set as a value that does not cause the transfer memory to be generated on the photosensitive drum 1 due to transfer charging. When the transfer current is small, the image is scattered in the solid black part. When the transfer current is large, the transfer current penetrates the recording material, and white spots and black spots appear in the solid black portion and the halftone image.
[0042]
FIG. 8 is a flowchart showing an example of a transfer bias control procedure. When the CPU 74 in the engine control unit 76 receives a print command from the PC 18 in step S1, a predetermined constant current bias is applied during the pre-rotation of the photosensitive drum 1 in step S2, as in the first embodiment. Is transferred from the transfer roller 10 to the photosensitive drum 1 to detect the initial detection voltage Vo, and the detected initial detection voltage Vo is stored in the storage means 6. Then, a calculation formula preliminarily related to the initial detection voltage Vo is extracted from the NVRAM 19, and the correction voltage Vo ′ is calculated by substituting the initial detection voltage Vo of the storage means 6 into this calculation formula.
[0043]
In step S3, the initial detection voltage Vo and the correction voltage Vo ′ are converted into an ATVC equation, that is,
Vt = 1.2 (Vo + Vo ′) + 1.1
Then, the transfer application constant voltage Vt is obtained, and then printing is started in step S4.
[0044]
Now, the initial detection voltage Vo taken out from the storage means 6 is, for example, 350 V, and the expression Vo ′ = Cn / 10 (where Cn is the number of counters) is taken out from the NVRAM 19 and the number of counters Cn is taken out from the storage means 6. For example, assume that 3000 sheets are taken out.
[0045]
Then, this counter sheet number is substituted for Vo ′ = Cn / 10 (where Cn is the counter sheet number), 300 V is calculated as the correction voltage Vo ′, and the initial detection voltage Vo and the correction voltage Vo ′ are calculated as described above. Substituted into the ATVC equation, 781.1 (V) is calculated as the transfer application constant voltage Vt.
[0046]
The obtained transfer application constant voltage Vt is an optimum transfer application voltage. When this transfer application voltage is applied, the transfer current can be controlled in a region where the transfer failure phenomenon does not occur, and a good image can be obtained.
[0047]
【The invention's effect】
As described above, according to the first invention, since the structure described above, it is possible to detect the exact environment regardless of the durability.
[0048]
Further, according to the second invention, it is possible to apply a proper transfer voltage after endurance, it is possible to suppress the transfer failure caused by photoreceptor deterioration, provides stable the images be able to.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of the present invention.
FIG. 2 is a diagram illustrating an example of a relationship between the number of printed sheets and a correction voltage Vo ′ in the first embodiment.
FIG. 3 is a diagram illustrating an example of a relationship between the number of printed sheets and a film thickness reduction amount in the first embodiment.
FIG. 4 is a diagram illustrating an example of a relationship between a transfer roller resistance value and a Vo down amount in the first embodiment.
FIG. 5 is a table showing an example of a relationship between an environment and a transfer roller resistance value in the first embodiment.
FIG. 6 is a table showing an example of a relationship between a detection voltage Vo and the environment in the first embodiment.
FIG. 7 is a block diagram showing a second embodiment of the present invention.
FIG. 8 is a flowchart illustrating an example of a transfer bias control procedure according to the second embodiment.
FIG. 9 is a cross-sectional view showing a conventional example of the structure of a laser beam printer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 4 Developing device 6 Storage means 10 Transfer roller 12 Process cartridge 13 High voltage power supply 14 CPU
15 Memory 17 Controller 18 PC
19 NVRAM

Claims (2)

A photoconductor that carries a toner image; a transfer unit that forms a transfer nip with the photoconductor; and a bias applying unit that applies a transfer bias to the transfer unit to transfer the toner image on the photoconductor to a transfer material; Voltage detecting means for detecting a voltage value of a bias output from the transfer bias applying means to the transfer means, and the bias applying means controls constant current when no transfer material is present in the transfer nip. an image forming apparatus for setting the bias on the basis has been a bias to detect the voltage detecting means detects a voltage value when applied to the transfer means, the detected voltage value,
A correction voltage that includes a cartridge having the photoconductor, and that can be replaced by replacing the cartridge, leaving the transfer means, and increases as the accumulated usage of the photoconductor increases. image forming apparatus characterized by value, and sets the transfer bias is added to the detected voltage value. The cartridge includes a storage unit, the storage unit stores an accumulated usage amount of the photoconductor, and sets the correction voltage value based on the accumulated usage amount of the photoconductor stored by the storage unit. The image forming apparatus according to claim 1, wherein:

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