JPH10142954A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a stable transfer regardlessly of the states of a recording paper and toner by detecting the electrostatic capacity between a member for applying a transfer charge to a transfer film and a photoreceptor and indirectly checking the resistance value of the recording paper and the deteriorated state of the toner based on the value of the detected electrostatic capacity. SOLUTION: When a key for executing transfer output adjustment processing provided on a control panel is depressed, a CPU 14 obtains the electrostatic capacities of the recording paper and the toner from the value of a current flowing through a transferring part and decides whether the electrostatic charge quantity of pretransfer toner and the resistance value of the recording paper are reduced or not, from the obtained values. As the result of the decision, when the electrostatic charge quantity of the pretransfer toner is at the optimal value or below, the grid voltage of a pretransfer charger is increased. Further, when the electrostatic capacity and resistance value of the recording paper are out of the optimal value, a voltage applied to a transfer roller 38 is decreased by a fixed level. Thus, the toner remaining on the photoreceptor 23 can be reduced by reverse electrification in the transferring part.

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. In response to this demand, in order to reproduce a stable density image on recording paper, a reference toner image is formed on a photoconductor before copying is performed or when a predetermined mode is set, and the formed toner is formed. 2. Description of the Related Art There has been known an apparatus which detects transfer efficiency of an image on a recording sheet and controls development conditions or transfer conditions based on the detected result.

[0003]

However, in the above-described conventional image forming apparatus, when the toner is deteriorated, or when the paper absorbs moisture and the resistance value is lower than expected, appropriate control is not performed. There was a problem that the transfer efficiency was reduced. For example, when the recording paper absorbs moisture, its resistance value decreases. For this reason, even if the toner is appropriately charged, reverse charging of the toner occurs in the transfer portion, and the amount of toner remaining on the photosensitive drum increases, resulting in a decrease in transfer efficiency. When the toner is deteriorated, the charge amount of the toner after development and before transfer is reduced. As a result, reverse charging of the toner occurs in the transfer portion, and the amount of toner remaining on the photosensitive drum increases, resulting in a decrease in transfer efficiency.

An object of the present invention is to provide an image forming apparatus which performs stable transfer regardless of the state of recording paper or toner.

[0005]

An image forming apparatus according to the present invention comprises, in an image forming apparatus employing an electrophotographic system, a developing means for forming a toner image on a photoreceptor, and a member for applying a transfer charge to a transfer film. A measuring unit for detecting a capacitance between the photoconductor and the photoconductor; and a control unit for controlling a transfer condition based on a value of the capacitance detected by the measuring unit at a predetermined timing.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a copying machine according to an embodiment of the image forming apparatus of the present invention will be described in order with reference to the accompanying drawings. (1) Embodiment FIG. 1 is a sectional view of a digital full-color copying machine according to an embodiment. The copying machine includes an image reader unit 100 that reads an image of a document, and a printer unit 20 that forms an image on a recording sheet based on image data of the read document.
It is roughly divided into 0. 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. Scanner 2
Is in the direction of the arrow (sub-scanning direction) by the scanner motor 10.
At the speed V according to the set magnification. Thus, the original placed on the original platen glass 1 is scanned over the entire surface. The mirrors 5 and 6 also move in the arrow direction (sub-scanning direction) at the speed V / 2 with the movement of the scanner 2. R, G, obtained by the CCD line sensor 8,
The B-valued electric signal is converted to 8-bit gradation data by the read signal processing unit 9 and then output to the printer unit 200. An operation panel 5 for setting the number of copies and executing the copy is provided above the image reader unit 100.
0 is provided. The operation panel 50 is provided with an execution key for performing a transfer output adjustment process (not shown). When the execution key of the transfer output adjustment process is pressed, the transfer output adjustment process is executed in a procedure described later. In the printer unit 200, the print head unit 20 is configured to perform the following based on the gradation data input from the read signal processing unit 9.
A laser diode drive signal is generated, 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. Cyan, magenta, yellow and black toner developing units 27 to 30
Among them, first, the cyan toner developing device 27 is selected,
The electrostatic latent image on the photosensitive drum 23 is developed. A suitable recording paper is fed from the paper feed cassettes 31 to 33 to the timing roller pair 3.
4 transported. The timing roller pair 34 transfers the recording paper to the transfer drum 40 at a timing when the leading end of the toner image developed on the photosensitive drum 23 coincides with the leading end of the recording paper.
Transport to The transported recording paper is supplied to the suction charger 35.
Then, the toner is electrostatically attracted to the transfer drum 40 by the attracting 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 photosensitive drum 23 is transferred to a recording paper wound around the transfer drum 40 by applying a predetermined voltage to a transfer roller 38 made of metal via a transfer film. You. The pressing member 39 is used to increase the degree of adhesion between the recording paper and the photosensitive drum 23 and to improve transferability.
0 is pressed toward the photosensitive drum 23. 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. Thus, the transfer drum 40 is separated from the surface. The recording paper separated from the transfer drum 40 is supplied to the fixing device 4
After passing through 4, the sheet is discharged onto a tray 45 after being fixed.

[0007] The resistance value of the paper and the amount of toner charge affect the transfer efficiency when the toner image visualized on the photosensitive drum 23 is transferred onto recording paper. The characteristics of the recording paper and the toner charge amount will be described below. If the recording paper absorbs moisture or dries due to the surrounding environment, its electrical characteristics change. FIG. 2 is a graph showing the relationship between the volume resistivity (Ω · cm) of the recording paper and the absolute humidity (g / m ³ ). As you can see from this graph, as the absolute humidity increases,
The volume resistance of the recording paper decreases. FIG. 3 is a graph showing the relationship between the relative dielectric constant ε of the paper and the absolute humidity (g / m ³ ). As can be seen from this graph, the relative dielectric constant ε of the paper increases as the absolute humidity increases and the volume resistivity of the paper decreases. Further, the charge amount of the toner before being transferred to the recording paper also changes depending on the humidity. FIG. 4 is a graph showing the relationship between the toner charge amount (μc / g) before transfer and the absolute humidity (g / m ³ ). As can be seen from the graph, as the absolute humidity increases, the toner charge amount before transfer decreases. FIG. 5 shows that the apparatus was left for 7 to 8 hours to adjust to the environment under the three environments.
6 is a graph illustrating a change in toner density when an image is output by changing a transfer output. The graph represented by the solid line shows a characteristic curve under an environment of a temperature of 23 ° C. and a humidity of 50% RH. When the transfer output is within the range of L1, the transfer efficiency becomes the best and the toner density on the recording paper becomes the 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. Humidity 5
Compared with the case of 0% RH, the increase rate of the toner density with the increase of the transfer output is low, and the transfer efficiency is the best, that is, the value of the transfer output at which the toner density is maximized is large. The toner density on the recording paper becomes maximum when the transfer output is within the range of L2. The toner density decreases more gradually than when the transfer output exceeds 550 μA and the humidity is 50% RH. The graph represented by the dashed line is a temperature of 28 ° C. and a humidity of 80%.
3 shows a characteristic curve in an environment of RH. As can be understood from the graph, the increase rate of the toner density with the increase in the transfer output is higher than that in the case of the humidity of 50% RH, and the toner density sharply increases. When the transfer output is 100 to
It is maximum in the range of 200 μA, and the transfer output is 2
When the humidity exceeds 50 μA, the temperature decreases more rapidly than when the humidity is 50% 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. 5, 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. As shown in FIG. 4, the decrease in toner density on the high output side causes the toner charge amount to decrease in a humid environment, and the transfer roller 38 causes the toner to have the opposite polarity due to the voltage applied through the transfer film. The main cause is that the toner is not transferred onto the recording paper and remains on the photosensitive drum 23 as a result of being charged. This reverse charging of the toner can be prevented by increasing the toner charging amount to some extent. 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 is suppressed to a low value.
Reverse charging of the toner can be suppressed.

FIG. 6 is a diagram showing a detailed configuration around the photosensitive drum 23 and the transfer drum 40 of the copying machine according to the embodiment. The same components as those in FIG. 1 are denoted by the same reference numerals,
The duplicate description here is omitted. A ROM 16 connected to a central processing unit (hereinafter referred to as a CPU) 14 includes:
The data of each control table described below is stored, and the RAM 13 temporarily stores data necessary for executing control processing. An HV power supply 212 for applying a predetermined voltage is connected to the transfer roller 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. The charge wire current flowing through the pre-transfer charger 130 is 30
The grid voltage is fixed to 0 μA, and the grid voltage is controlled by the HV power supply 131 as needed. During normal copying, the CPU 14 detects the absolute humidity (% RH) of the printer unit 200 by the environment sensor 15 and changes the voltage applied to the transfer roller 38 based on the result to keep the transfer efficiency constant. Table 1 shown below is a control table for specifying an applied voltage corresponding to the detected absolute humidity. This control table is used when forming a full-color image, and is stored in the ROM 16 together with various control data. 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.

[Table 1]

When an execution key for the transfer output adjustment process provided on the operation panel 50 is pressed, the CPU 14 calculates the capacitance of the recording paper and the toner from the value of the current flowing through the transfer section, and calculates the toner before transfer from the calculated values. It is determined whether or not the charge amount of the recording paper has decreased, and whether or not the resistance value of the recording paper has decreased. If the result of the determination is that the charge amount of the toner before transfer is equal to or less than the appropriate value, the grid voltage of the charger 130 before transfer is increased to increase the charge amount of the toner before transfer.
If the capacitance and the resistance of the recording paper are outside the appropriate values, the voltage applied to the transfer roller 38 is reduced by a predetermined amount. As a result, the amount of toner that is reversely charged in the transfer portion and remains on the photoconductor is reduced. FIG. 7 is a flowchart of a process executed by the CPU 14 when the execution key of the transfer output adjustment process provided on the operation panel 50 is pressed. Hereinafter, the contents of the processing will be described in detail according to the flow of this flowchart and with reference to the related drawings.
First, a reference toner pattern is formed at a position on the photosensitive drum 23 corresponding to the latter half position of the recording paper conveyed to the transfer drum 40 by a predetermined laser exposure amount, a grid voltage, and a developing bias (step S1). ). The transfer roller 38 starts applying a predetermined voltage immediately before the leading end of the recording paper wound around the transfer drum reaches the transfer portion, and stops applying the voltage after the end of the recording paper passes through the transfer portion. . FIG. 8A illustrates a state in which the recording paper 502 has not yet reached the transfer section, that is, a state in which only the transfer film 503 exists between the transfer roller 38 and the photosensitive drum 23, and FIG. , Transfer roller 38 and photosensitive drum 2
3 shows a state where the recording paper 502 and the transfer film 503 exist between the transfer roller 38 and the transfer roller 38 and the photosensitive drum 23. FIG. Indicates a state in which CPU14
Measures the capacitance based on the value of the current flowing through the current measuring unit 214 at the timings shown in FIGS. 8A, 8B, and 8C (step S2). FIG. 9 shows the photoconductor dielectric layer 500, the toner layer 501, the recording paper 502, the thickness d of the transfer film 503, the relative dielectric constant ε, and the capacitance C existing between the transfer roller 38 and the photoconductor drum 23. FIG. The value of the current flowing in the current measuring unit 214 depends on the capacitances C1 to C4 of the photoconductor dielectric layer 500, the toner layer 501, the recording paper 502, and the transfer film 503, respectively. The capacitance C per unit area is proportional to the relative dielectric constant ε / thickness d. That is, the current flowing through the current measuring unit 214 depends on the values of the thicknesses d1 to d4 and the relative dielectric constants ε1 to ε4. In this apparatus, the transfer film 503 has a volume resistance value of 1
An insulating film of 0 ¹⁴ to 10 ¹⁵ Ω · cm is used. For this reason, even if a voltage is applied for measuring a current, only a charge moves due to polarization of each phase, and almost no free charge flows. Therefore, the total capacitance when each layer is connected in series as a capacitor can be determined from the measured current value. In the state of FIG. 8A, the capacitance C _a of the photoconductor dielectric layer 500 and the transfer film 503 in series is set.
Is measured. In the state of (b) in FIG. 8, a photoreceptor dielectric layer 500, the recording sheet 502, the capacitance C _b of the time series of the transfer film 503 is measured. In the state (c) in FIG. 8, a photoreceptor dielectric layer 500, the toner layer 501, the recording sheet 502, the capacitance C _c of the time series of the transfer film 503 is measured. FIG.
, The capacity of the photoconductor dielectric layer 500 is C1, the capacity of the toner layer 501 is C2, and the capacity of the recording paper 502 is C3.
When the capacity of the transfer film 503 is represented by C4, the above C _a ,
C _b and C _c satisfy the following equations (1) to (3).

## EQU1 ## _Ca ^-1 = C1 ^-1 + C4 ^-1

## EQU2 ## C _b ^-1 = C1 ^-1 + C3 ^-1 + C4 ^-1

C _c ^-1 = C1 ^-1 + C2 ^-1 + C3 ^-1 + C4 ^{-1 The} reference toner pattern is created under the same exposure conditions and the same development conditions. The relative dielectric constant of the toner does not change much due to the absolute humidity. On the other hand, the charge amount of the toner before transfer is
As shown in FIG. 4, it decreases as the absolute humidity increases. Therefore, the amount of the developing toner on the photoconductor changes as shown in the graph of FIG. 10 due to the change of the absolute humidity. As a result, the thickness d2 of the toner layer 501 at the time of measuring the capacitance changes, and the capacitance changes. Therefore, by measuring the capacitance of the toner layer, the charge amount of the toner can be indirectly known. Therefore, based on the value of the capacitance in each state measured in step S2, the capacitance C2 of the toner layer 501 is obtained by the following equation (step S2).
3).

## EQU4 ## If the obtained capacitance C2 of the toner layer 501 is equal to or larger than the reference value C2 _ref (= 20 pf) stored in the ROM 16, C2 = (C _c ^-1 -C _b ^-1 ) ^-1 (YES in step S4), it is determined that the charge amount of the developed toner (before transfer) is low, the toner is reversely charged by the transfer output, and is likely to remain on the photosensitive drum 23, and the state before transfer is determined The grid voltage of the charger 130 is increased by a predetermined amount from a normally used value to increase the toner charge amount (step S5). Specifically, ROM
The grid voltage of the pre-transfer charger 130 is determined with reference to the control table shown in Table 2 stored in the pre-transfer charger 16. The obtained capacitance C2 of the toner layer 501 is equal to the reference value C2.
_ref (= 20 pf) (step S4
NO), the control of the grid voltage of the pre-transfer charger 130 is skipped.

[Table 2] By controlling the grid voltage as described above, the charge amount of the toner before transfer increases, and even when the transfer output is high, the toner is charged to the opposite polarity in the transfer portion,
It can be prevented from remaining on the photosensitive drum 23. As a result, as shown by the dashed line in FIG. 11, the relationship between the transfer output and the toner density is corrected.
A stable transfer efficiency can be obtained. On the other hand, as shown in FIG. 3, the capacitance C3 of the recording paper 502 is affected by a change in relative dielectric constant due to a change in absolute humidity.
Further, as described above, since the resistance value of the recording paper 502 also changes according to the absolute humidity, the change in the resistance value can be indirectly known by detecting the capacitance C3. Therefore, based on the values of the capacitances C _a , C _b , and C _c in the respective states measured in step S2, the capacitance C3 of the recording paper 502 is calculated by the following equation 5 (step S6).

Equation 5] C3 ₌ (YES at step ^{S7) (C b -1 + C} a -1) ^-1 If the capacitance C3 of the recording sheet 502 obtained is equal to or larger than the reference value C3 _ref, as indicated by an arrow in FIG. 12 Next, the HV power source 2 reduces the voltage applied to the transfer roller 38 by a predetermined amount from the currently set value.
12 is controlled (step S8). Specifically, the relationship between the absolute humidity and the transfer output in the transfer output control table shown in Table 1 is shifted to a value one step lower. For example, the transfer output value corresponding to the absolute humidity is reduced by 0.2 overall. When the capacitance C3 of the recording sheet 502 is less than the reference value C3 _ref (NO in step S7), and terminates the process.

(2) Modification Hereinafter, a modification of the transfer output adjustment processing executed by the CPU 14 when the execution key of the transfer output adjustment processing provided on the operation panel 50 is pressed will be described. In the modified example of the transfer output adjustment processing, the processing flow itself is the same as the flowchart shown in FIG. 7, but the formation contents of the reference toner pattern (the processing corresponding to step S1 in FIG. 7) are different. Accordingly, the timing for measuring the capacitance (the process corresponding to step S2 in FIG. 7), the equation used to determine the capacitance C2 of the toner layer 501 from the measured value of the capacitance, and the recording paper 502 Are different from each other when the capacitance C3 is obtained. The contents of the output control of the pre-transfer charger 130 and the transfer roller 38 based on the obtained capacitance C2 of the toner layer 501 and the capacitance C3 of the recording paper 502 are the same as those in the above-described transfer output adjustment processing. Hereinafter, this difference will be described. FIG. 13 is a flowchart executed by the CPU 14 in a modified example of the transfer output adjustment processing. In a modified example of the transfer output adjustment processing, the toner image formed on the photosensitive drum 23 is directly transferred onto the transfer film by a predetermined laser exposure amount, a grid voltage, and a developing bias (Step S10). The CPU 14 shown in FIG.
(A), when the recording paper 502 has not yet reached the transfer portion, that is, when the transfer roller 38 and the photosensitive drum 23
(B), the timing at which the toner layer 501 and the transfer film 503 exist between the transfer roller 38 and the photosensitive drum 23, and (c). As shown, at the timing when the recording paper 502 and the transfer film 503 exist between the transfer roller 38 and the photosensitive drum 23, the capacitance is measured from the value of the current flowing through the current measuring means 214 (step S11). Here, in the state of FIG. 14 (a), the photoreceptor dielectric layer 500, the capacitor C _'a when the series of the transfer film 503 is measured. In the state of (b) in FIG. 14, the photoreceptor dielectric layer 500, the toner layer 501, the capacitance C _'b when the series of the transfer film 503 is measured. FIG.
4 (c), the photoconductor dielectric layer 500 and the recording paper 5
02, the capacitance C _'c at the time series of the transfer film 503 is measured. As in the case of the transfer output adjustment process, the capacitance of the photoconductor dielectric layer 500 is C1, and the capacitance of the toner layer 501 is C4.
2, C3 a capacity of the recording sheet 502, to represent the capacity of the transfer film 503 in C4, the _{C 'a, C' b,} C 'c satisfy the relationship of the following numbers 6 to Equation 8.

## EQU6 ## C ′ _a ⁻¹ = C1 ⁻¹ + C4 ⁻¹ = C _a ⁻¹

C ′ _b ⁻¹ = C1 ⁻¹ + C2 ⁻¹ + C4 ⁻¹

C ' _c ^-1 = C1 ^-1 + C3 ^-1 + C4 ^-1 = C _b ^{-1 From the} above formulas 6 to 8, the toner layer 50 is obtained by using the following formula 9.
The first capacitance C2 is calculated (step S12).

Equation 9] ^{_{C2 = (C 'b -1 -C}} ' a -1) -1 . If the calculated value of the capacitance C2 of the toner layer 501 is not less than a predetermined reference value C2 _ref YE in (step S13
S), it is determined that the toner is deteriorated and the charge amount of the toner before transfer is reduced, and the grid voltage of the charger 130 before transfer is increased by a predetermined amount from a normally used value to increase the toner charge amount. (Step S14). If the calculated value of the capacitance C2 of the toner layer 501 is less than the predetermined reference value _C2ref (N in step S13)
O), the process proceeds to the next step S15 without performing the output control of the pre-transfer charger 130. Further, the capacitance C3 of the recording paper 502 is calculated using the following Expression 10 (Step S).
15).

C3 = (C ′ _c ⁻¹ −C ′ _a ⁻¹ ) ^{−1 When the} calculated value of the capacitance C3 of the recording paper 502 is equal to or _larger than the predetermined reference value C3 _ref (YE in step S16).
S), it is determined that the resistance value of the recording paper 502 has decreased and the toner is likely to be reversely charged in the transfer portion, and the voltage applied to the transfer roller 38 is reduced by a predetermined amount (step S17). . Calculated value of the capacitance C3 of the recording sheet 502 in the case of less than the predetermined reference value C3 _ref terminates the processing without (NO at step S16), and output control of the transfer roller 38. Although the copying machine of the present embodiment uses the transfer roller 38, the same effect can be obtained by using a transfer brush or the like. Also,
A transfer belt may be used instead of the transfer drum 40.

[0011]

According to the image forming apparatus of the present invention, the capacitance between the member for applying the transfer charge to the transfer film and the photosensitive member is detected by the measuring means at a predetermined timing. The resistance value of the recording paper and the deterioration state of the toner are indirectly examined. Thereby, the transfer conditions can be appropriately controlled. Further, since the resistance value of the recording paper and the state of deterioration of the toner are checked only by the measured values by the measuring means, the apparatus can be simplified.

[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 is a graph showing the relationship between the relative dielectric constant ε of paper and absolute humidity (g / m ³ ).

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

FIG. 5 shows that each of the devices is 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. 6 is a diagram illustrating a detailed configuration around a photosensitive drum and a transfer drum of the copying machine according to the embodiment.

FIG. 7 is a flowchart of a transfer output adjustment process executed by a CPU.

FIGS. 8A to 8C are diagrams showing three states between a transfer roller and a photosensitive drum.

FIG. 9 is a diagram showing the relationship between the thickness of each of a photoconductor dielectric layer, a toner layer, a recording paper, and a transfer film and capacitances C1 to C4.

FIG. 10 is a graph showing the amount of toner adhering to a photoconductor when the amount of toner charge changes due to a change in absolute humidity.

FIG. 11 is a graph showing a relationship between transfer output and toner density.

FIG. 12 is a graph showing a relationship between a transfer output and a toner density.

FIG. 13 is a flowchart of a modified example of the transfer output adjustment process executed by the CPU.

FIGS. 14A to 14C are diagrams illustrating three states between a transfer roller and a photosensitive drum.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 13 ... RAM 14 ... CPU 15 ... Environment sensor 16 ... ROM 23 ... Photoconductor drum 31-33 ... Paper cassette 38 ... Transfer roller 40 ... Transfer drum 130 ... Pre-transfer charger 131,212 ... HV power supply 214 ... Current measuring part

Claims (1)

[Claims] 1. An image forming apparatus employing an electrophotographic method, wherein a developing means for forming a toner image on a photoreceptor, and a measurement for detecting a capacitance between a member for applying a transfer charge to a transfer film and the photoreceptor. An image forming apparatus comprising: a control unit configured to control a transfer condition based on a capacitance value detected by a measurement unit at a predetermined timing.