JPH10142862A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grasp the states of toner and recording paper and to attain excellent transfer by controlling a transfer condition according to the secular change of two environmental data on environment near a developing means and near a paper supply means. SOLUTION: The transfer condition is controlled cosidering a difference between the environment near paper supply cassettes 31 to 33 and the environment near developing devices 27 to 30 and the difference of the secular change of the characteristic of the recording paper and the toner. A CPU 14 controls output from a transfer charger HV power source 212 and a pretransfer charger HV power source 131 in accordance with the values of absolute humidity detected by an environment sensor 15 detecting the absolute humidity near the developing devices 27 to 30 and the absolute humidity detected by an environment sensor 18 detecting the absolute humidity near the cassettes 31 to 33. A current is always supplied to the sensors 15 and 18 separately from a main power source supplying power to the driving part, such as a motor, of a copying machine main body. Thus, the image with stable density is formed on the recording paper regardless of the states of the recording paper and the toner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine employing an electrophotographic system.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine employing an electrophotographic system, it is desired that an image having a constant density for the same image data be reproduced on a recording paper. However, the state of factors that affect the transfer efficiency, such as the charge amount of the toner and the resistance value of the recording paper, changes depending on the surrounding environment. For example, when the humidity changes, the resistance value of the recording sheet as the transfer object changes. In particular, in a high-humidity environment, the resistance value of the recording paper decreases, and even if the toner is properly charged, the toner may be reversely charged, so that optimum transfer efficiency cannot be obtained. To cope with this, there has been proposed an image forming apparatus which includes a sensor for detecting an environment inside the copying machine and controls a transfer condition based on the environment detected by the sensor.

[0003]

As described above, as described above, the amount of toner charge, the resistance value of recording paper, etc.
The state of the factors affecting the transfer efficiency changes. By the way, the time required for responding to environmental changes differs between the toner charge amount and the resistance value of the recording paper. Therefore, even under the same environment, appropriate transfer conditions change with time. In a conventional image forming apparatus, transfer conditions are controlled in accordance with an environment detected by a sensor. For this reason, in order to maintain the transfer efficiency in an optimum state, a series of control processes of forming a reference pattern, detecting the transfer efficiency, comparing with a reference value, and switching the transfer output based on the comparison result must be frequently performed. Instead, it often takes time for adjustment before starting the image forming process.

It is an object of the present invention to provide an image forming apparatus for forming an image having a stable density on a recording sheet regardless of the state of the recording sheet and toner.

[0005]

According to an image forming apparatus of the present invention, in an image forming apparatus employing an electrophotographic system, a first detecting means for detecting an environment near a developing means for forming a toner image on a photoreceptor is provided. Transfer means for transferring the toner image formed on the photoreceptor onto recording paper, second detecting means for detecting an environment near a paper feeding means for feeding recording paper to the transfer means, first detecting means, The recording device includes a recording unit that records a temporal change of each environment detected by the second detection unit, and a control unit that controls a transfer condition of the transfer unit based on the recording by the recording unit. Further, in the image forming apparatus having the above-described configuration, the image forming apparatus further includes a charging unit configured to charge the toner image formed on the photoconductor just before the transfer by the transfer unit is performed. It is preferable to control the transfer condition of the transfer unit and the charge amount of the toner image by the charging unit.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A copying machine which is an embodiment of the image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. The copying machine is characterized in that the transfer conditions are controlled based on the aging of environmental data in the vicinity of the developing device and the paper cassette. FIG. 1 is a sectional view of a digital full-color copying machine according to an embodiment. This copier is
An image reader unit 100 reads an image of a document, and a printer unit 200 forms an image on a recording sheet based on image data of the read document. In the image reader unit 100, a document placed on the platen glass 1 is irradiated by a lamp 3 provided in the scanner 2. Light reflected from the document surface forms an image on a CCD line sensor 8 via mirrors 4, 5, 6 and an imaging lens 7. The scanner 2 is moved by the scanner motor 10 in the direction of the arrow (sub-scanning direction) at a speed V according to the set magnification. Thus, the original placed on the original platen glass 1 is scanned over the entire surface. Also, mirrors 5 and 6
Move in the direction of the arrow (sub-scanning direction) at the speed V / 2 with the movement of the scanner 2. CCD line sensor 8
Are converted into 8-bit gradation data by the read signal processing unit 9 and then output to the printer unit 200. Printer section 200
, The print head unit 20 includes the read signal processing unit 9
A laser diode drive signal is generated based on the input grayscale data, and the semiconductor laser is caused to emit light by the drive signal. The laser beam emitted from the print head unit 20 exposes and scans the surface of the photosensitive drum 23 via mirrors 21 and 22. The surface of the photoconductor drum 23 is irradiated with an eraser lamp 24 before being exposed for each copy, and is uniformly charged by a charging charger 25. When exposure is performed in this state, an electrostatic latent image of the document is formed on the photosensitive drum 23. First, among the cyan, magenta, yellow, and black toner developing devices 27 to 30 each using a two-component developer, the cyan toner developing device 27 is selected, and the electrostatic latent image on the photosensitive drum 23 is developed. . Recording paper of an appropriate size is transported from the paper feed cassettes 31 to 33 to the timing roller pair 34. The timing roller pair 34 conveys the recording paper to the transfer drum 40 at a timing when the front end of the toner image developed on the photosensitive drum 23 and the front end of the recording paper coincide. The transported recording paper is electrostatically attracted to the transfer drum 40 by the suction charger 35 and the suction roller 37. The pressing member 36 presses the transfer drum 40 in the direction of the suction roller 37 in order to bring the recording paper into close contact with the transfer drum 40 and more strongly attract the recording paper. The cyan toner image developed on the photoconductor drum 23 is transferred to a recording paper wound around the transfer drum 40 by the transfer charger 38. The pressing member 39 presses the transfer drum 40 in the direction of the photosensitive drum 23 in order to increase the degree of adhesion between the recording paper and the photosensitive drum 23 and enhance transferability. The toner remaining on the photosensitive drum 23 after the transfer of the toner image is removed by the cleaner 26. Subsequent to cyan, magenta, yellow, and black toner developing units are sequentially selected, and charging, exposure, and toner development of the photosensitive drum 23 are performed. The toner images of each color developed on the photosensitive drum 23 are sequentially transferred onto the recording paper wound on the transfer drum 40 in a superimposed manner. The recording paper on which the toner images of the four colors have been transferred is destaticized on the surface of the transfer drum 40 by the separation static elimination charger 41, and then pushed up by the push-up member 42. The transfer drum 4
Separated from surface 0. The recording paper separated from the transfer drum 40 passes through a fixing device 44 and is fixed to a tray 4.
It is discharged to 5.

The resistance value of the paper and the charge amount of the toner affect the transfer efficiency when the toner image visualized on the photosensitive drum 23 is transferred onto the recording paper. For this reason, in order to transfer an image having a stable density onto recording paper, it is necessary to control the output of the transfer based on the change over time of these two characteristics.
Before describing the transfer condition control, the characteristics of the recording paper and the toner charge amount will be described. If the recording paper absorbs moisture or dries due to the surrounding environment, its electrical characteristics change. FIG. 2 shows the volume resistance (Ω · c) of the recording paper.
³ is a graph showing the relationship between m) and absolute humidity (g / m ³ ). As can be seen from this graph, the volume resistance of the recording paper decreases as the absolute humidity increases. Further, the charge amount of the toner before being transferred to the recording paper also changes depending on the humidity. FIG. 3 shows the toner charge amount (μc / g) before transfer.
4 is a graph showing a relationship between the absolute humidity and g / m ³ . As can be seen from the graph, as the absolute humidity increases, the toner charge amount before transfer decreases. FIG.
7 is a graph showing a change in toner density when an image is output by changing the transfer output after leaving the apparatus for 7 to 8 hours to adjust to the environment under each of the three environments. The solid line graph shows a temperature of 23 ° C and a humidity of 50% R.
3 shows a characteristic curve in an environment of H. When the transfer output is within the range of L _1, the transfer efficiency becomes the best, the toner density on a recording sheet becomes maximum. The toner density gradually decreases when the transfer output exceeds about 400 μA. The graph represented by the dotted line shows a characteristic curve under an environment of a temperature of 18 ° C. and a humidity of 20% RH. The increase rate of the toner density with the increase of the transfer output is lower than the case of the humidity of 50% RH.
The value of the transfer output at which the transfer efficiency is the best, that is, the toner density is maximized, is large. Toner density on the recording sheet, the transfer current becomes maximum in the range of L _2. The toner density is
Humidity 50% R from the area where the transfer output exceeds 550 μA
It decreases more slowly than in the case of H. The graph represented by the dashed line indicates a characteristic curve under an environment of a temperature of 28 ° C. and a humidity of 80% RH. As can be understood from the graph, the humidity 50
As compared with the case of% RH, the increase rate of the toner density with the increase of the transfer output is high, and the toner density increases rapidly. Toner density, the transfer current becomes maximum in the range of L _3, a humidity of 50 from around the transfer current exceeds 200μA
It drops more rapidly than in the case of% RH. As understood from the above three graphs, when the humidity is high, the rate of increase of the toner density with the increase of the transfer output increases, and the rate of decrease after reaching the maximum density also increases. When the humidity is low, the rate of increase of the toner density with the increase of the transfer output decreases, and the rate of decrease after reaching the maximum density also decreases. In addition, the range of the transfer output in which the maximum toner density can be obtained is wider when the humidity is lower. The proper transfer output area at the time of high humidity will be described with reference to FIG. As shown in FIG. 4, when the humidity is high, for example, at 80% RH, the range of the transfer output at which the toner density is maximum on the paper becomes very narrow as compared with the case where the humidity is low. This is because the timing at which the toner density starts to decrease particularly on the high output side is early. This decrease in toner density on the high output side is shown in FIG.
As shown in (2), the amount of toner charge decreases in a high-humidity environment, and the toner is charged to the opposite polarity by the transfer output of the transfer charger 38. As a result, the toner remains on the photosensitive drum 23 without being transferred onto the recording paper. That is a major cause. For this reason, it is expected that when the toner charge amount before transfer is higher, the timing at which the toner density starts to decrease on the high output side is later, and the rate of decrease in the density is expected to be smaller. This has been confirmed by experiments.
Further, as shown in FIG. 2, the resistance value of the recording paper also decreases with an increase in humidity, but when the resistance value is sufficiently high,
The transfer output can be kept low, and the reverse charging of the toner can be suppressed. That is, even when the charge amount of the toner is very low, the timing at which the toner density starts to decrease on the high output side is delayed if the resistance value of the paper is sufficiently high, and
The rate of decrease in the concentration is small.

FIG. 5 is a graph showing an example of changes in the absolute humidity near the paper feed cassettes 31 to 33 and the absolute humidity near the developing units 27 to 30 from 6:00 in the morning to 22:00 at night. This graph shows the case where the power of the apparatus is turned on at the time A and the power of the apparatus is turned off at the time B. The graph represented by the solid line indicates a change in the absolute humidity in the vicinity of the sheet cassettes 31 to 33. The graph shown by the dotted line shows the change in the absolute temperature in the vicinity of the developing devices 27 to 30. As can be seen from the figure, the manner of changing the absolute humidity is different between the vicinity of the sheet cassette and the vicinity of the developing device. This is because, in general, the confidentiality is poor near the paper feed cassette and is strongly affected by changes in the external environment. This is because it is hard to receive.

FIGS. 6 and 7 show a copying machine at 28 ° C. and 80%
After leaving for 8 hours or more in the environment of RH,
5 is a graph showing a change over time in a volume resistance value of a recording sheet in a sheet cassette and a charge amount of a toner formed on a photoconductor in a% RH environment. As can be seen from FIGS. 6 and 7, the speed at which the volume resistance value and the toner charge amount correspond to changes in the environment is different. Change in paper resistance value is 4
After being stabilized after about 5 hours, the toner charge amount is
Stabilizes in 1-2 hours. As described above, when the toner image on the photoconductor is transferred to the recording paper, the charge amount of the toner formed on the photoconductor and the resistance value of the recording paper affect the transfer efficiency. Therefore, in this copying machine, in order to transfer an image having a stable density onto recording paper, the output of the transfer is controlled based on the change over time of these two characteristics.

In this copying machine, the transfer conditions are controlled in consideration of the difference between the environment near the paper feed cassettes 31 to 33 and the environment near the developing units 27 to 30 and the difference between the characteristics of the recording paper and the toner over time. I do. FIG. 8 is a diagram illustrating a more detailed configuration around the photoconductor drum 23 and the transfer drum 40. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will not be repeated. Central processing unit (hereinafter referred to as CPU) 1
The data of each control table described below is stored in the ROM 16 connected to the
Data necessary for the execution of the control process is temporarily stored.
A transfer charger HV power supply 212 that supplies a charge wire current (hereinafter, referred to as a transfer output) is connected to the transfer charger 38. Further, a pre-transfer charger 130 for raising the toner charge amount immediately before the transfer is provided at a position immediately before the transfer portion. Charger 130 before transfer
Is controlled by the pre-transfer charger HV power supply 131. The CPU 14 controls the transfer charger HV power supply 212 and the transfer charger HV in accordance with the absolute humidity value detected by the environment sensor 15 detecting the absolute humidity near the developing device and the environment sensor 18 detecting the absolute humidity near the sheet cassette. The output of the front charger HV power supply 131 is controlled. An electric current is always supplied to the environment sensors 15 and 18 separately from a main power supply for supplying electric power to a driving unit such as a motor of the copying machine body. The CPU 14 controls the environmental sensors 15 and 18
The absolute humidity value detected by the RAM 1
Write to 3. As described above with reference to FIG. 7, when the environment changes, the toner charge amount stabilizes after a lapse of one to two hours. The CPU 14 stores the absolute humidity near the developing device for three hours in the RAM 13. As will be described later, the stability of the charge amount of the toner is checked based on whether or not the detected values for the three hours are stable. Also, as described above with reference to FIG. 6, when the environment changes, the resistance value of the recording paper becomes stable after a lapse of 4 to 5 hours with respect to the change in the environment. The CPU 14 stores the absolute humidity in the vicinity of the sheet cassette for 5 hours in the RAM 13. As described later, the stability of the resistance value of the recording paper is checked based on whether or not the detected values for the five hours are stable. Note that old data stored in the RAM 13 is deleted in order, and new data is stored instead.

FIG. 9 is a flowchart of a transfer output control process executed by the CPU 14. When the power of the copying machine is turned on, an average value of the absolute humidity for the past three hours detected by the environment sensor 15 at that time is obtained (step S1). Referring to the control table shown in Table 1 stored in the ROM 16, the transfer output of the transfer charger 38 is specified based on the section to which the average value obtained in step S1 belongs (step S2).

[Table 1] Here, Table 1 will be described. Table 1 is a control table for specifying a transfer output corresponding to the detected absolute humidity. This control table is a table used when forming a full-color image.
It is stored in the OM16. As shown, the transfer output is set to be higher as the absolute humidity is lower based on the experimental data. The transfer output in each humidity section is set so as to increase in order from the first color to the second color, from the second color to the third color, and so on. This takes into account the effect of charge-up of the transfer film due to the output of the previous color. The CPU 14 controls and outputs the transfer output of the pre-transfer charger separately from the control of the transfer output of the transfer charger. Normally, the charge wire current of the pre-transfer charger 130 is 300 μA, and the grid voltage is 450
V is set. Here, if the average value of the absolute humidity of the environment sensor 15 near the developing device for three hours and the value of the absolute humidity at the present time are 26 g / m ³ or more (YES in step S3), after the development, It is determined that the toner charge amount (before transfer) is lower than the appropriate value, and the grid voltage of the charger 130 before transfer is increased to 700 V (step S4). Thereby, the charge amount of the toner before transfer is increased. Note that the above average value and the absolute humidity at the current time are 2
If less than 6 g / m ³ (N in step S3)
O), output control of the pre-transfer charger 130 is not performed.
The change in the resistance value of the recording paper is more gradual than the change in the charge amount of the toner due to the change in the environment. Therefore, the history up to that point has a greater effect on the control of the transfer condition than the environment when the power of the copying machine is turned on. Therefore, an average value of the absolute humidity for 5 hours near the sheet cassette detected by the environment sensor 18 is obtained (step S5). According to Table 3 shown below, the transfer output is corrected by the shift amount specified based on the difference between the absolute humidity value currently detected by the environment sensor 18 and the average value obtained in the above step S5 ( Step S6).

[Table 2] As described above, by controlling the transfer output in consideration of the temporal change of the environment, it is possible to maintain appropriate transfer efficiency for a longer time. Although the transfer charger 38 is used in the copying machine of the present embodiment, a transfer brush or a transfer roller may be used. Further, a transfer belt may be used instead of the transfer drum 40.

[0012]

According to the image forming apparatus of the present invention, the transfer conditions are controlled by the change over time of two environmental data near the developing means and near the paper feeding means. Therefore, good transfer can be performed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a digital full-color copying machine according to an embodiment.

FIG. 2 is a graph showing a relationship between a volume resistance value (Ω · cm) of recording paper and an absolute humidity (g / m ³ ).

FIG. 3 Amount of toner charge before transfer (μc / g)
4 is a graph showing a relationship between the absolute humidity and g / m ³ .

[FIG. 4] Under three environments, the devices are respectively 7 to
6 is a graph illustrating a change in toner density when an image is output by changing a transfer output after being left for 8 hours to adjust to an environment.

FIG. 5 is a graph showing an example of a change with time of the absolute humidity near the sheet feeding cassette and the absolute humidity near the developing device.

FIG. 6 is a graph showing a change over time of a volume resistance value of a recording sheet in a sheet feeding cassette when a copying machine is placed under different environments.

FIG. 7 is a graph showing a change over time of the charge amount of the toner formed on the photoconductor when the copying machine is placed under different environments.

FIG. 8 is a diagram showing a more detailed configuration around a photosensitive drum and a transfer drum.

FIG. 9 is a flowchart of a transfer output control process executed by a CPU.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 13 ... RAM 14 ... CPU 16 ... ROM 15, 18 ... Environmental sensor 23 ... Photoconductor drum 31-33 ... Paper cassette 38 ... Transfer charger 40 ... Transfer drum 130 ... Pre-transfer charger 131 ... Pre-transfer charger HV power supply 212 ... Transfer Charger H power supply

Claims (2)

[Claims] 1. An image forming apparatus employing an electrophotographic method, wherein: first detecting means for detecting an environment near a developing means for forming a toner image on a photoreceptor; and a toner image formed on the photoreceptor. Transfer means for transferring onto a recording sheet; second detecting means for detecting an environment in the vicinity of a paper feeding means for feeding recording paper to the transferring means; and aging of each environment detected by the first detecting means and the second detecting means An image forming apparatus comprising: a recording unit that records a change; and a control unit that controls a transfer condition by a transfer unit based on recording by the recording unit. 2. The image forming apparatus according to claim 1, further comprising: charging means for charging a toner image formed on the photoconductor immediately before transfer by the transfer means is performed. An image forming apparatus which controls a transfer condition of a transfer unit and a charge amount of a toner image by a charging unit based on recording by a recording unit.