JPH09304979A - Picture image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve picture quality by memorizing characteristics such as thickness of paper, surface property, electrical resistance, color of texture, etc., per type of paper and changing picture image formation condition in accordance with paper used. SOLUTION: CPU 20 in a control substrate refers to a data table written in ROM in advance in accordance with type of selected paper. Developing solution film thickness on a photosensitive body which is the optimum for the selected paper or a condition which realizes the film thickness is written in the data table to operate a machine in accordance with the condition. In addition, items such as proper toner adhesion amount (photosensitive body potential, developing bias), SR bias value, transfer current value, etc., which require changes depending on type of paper are written in the data table.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that changes image forming conditions according to the characteristics of a transfer sheet used.

[0002]

2. Description of the Related Art Conventionally, plain paper is mainly used in an electrophotographic image forming apparatus. The reason for this is that, in addition to being easily priced, the image to be handled was a black and white document, so that readability and editability were important. Also,
In the case of a character, it is a black and white binary (no halftone),
Subtle changes in image quality caused by differences in paper properties did not pose a problem.

As a conventional technique, a key for selecting a plain paper or an OHP sheet is provided on the operation unit, and the image forming condition is changed depending on whether the plain paper or the OHP sheet is selected. One reason is that the amount of toner adhered differs depending on whether the image is viewed with reflected light or the image viewed with transmitted light.
This is because the surface properties of the sheets are different.

[0004]

Thus, the above-mentioned prior art deals with sheets having different physical properties rather than high image quality, but in the image forming apparatus targeting full color high image quality, Even a subtle difference in
This subtle difference in image quality is caused by the characteristics of the paper such as the thickness of the paper, surface properties, electric resistance, and background color.

The present invention has been made in view of the above-mentioned circumstances, and has the following characteristics: paper thickness, surface property, electric resistance, background color,
It is an object of the present invention to provide an image forming apparatus that stores characteristics such as the above for each paper type and subtly changes the image forming conditions according to the paper used to further improve the image quality.

[0006]

According to a first aspect of the present invention, there is provided a photoconductor, an electrostatic latent image is formed on the surface of the photoconductor by an electrophotographic method, and the electrostatic latent image is developed. An image forming apparatus for transferring an image onto a transfer paper, characterized in that an image forming condition is changed according to the characteristics of the paper for transferring the image. The invention according to claim 2 is used in the invention according to claim 1. A number is determined in advance for each type of transfer paper to be used, and the operator inputs the number of the transfer paper from a ten-key pad or the like at the time of use. The invention of claim 3 is the invention of claim 1. The number of condition is set for each setting item of the image forming condition for each transfer sheet to be used, and the operator inputs the number of the transfer sheet from a ten-key etc. at the time of use.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a main part configuration diagram for explaining the outline of an electrophotographic image forming apparatus to which the present invention is applied. Photoconductor 10
As is well known, a main charging device 1, a surface potential sensor 2, a developing roller 3, a reverse roller 4, a set roller 5, a transfer charger 6, a cleaning roller 7, a blade 8, a quenching lamp 9 and the like are arranged around the area. Is installed, the surface of the photoconductor 10 is uniformly charged by the charger 1, and then,
A writing laser diode (LD) 11 forms a latent image on the photoconductor 10 that is uniformly charged, the developing roller 3 develops the latent image, and the transfer charger 6 transfers the development to the recording paper 12. It is a thing.

FIG. 2 is a block diagram of a main part for explaining the operation of the image forming apparatus shown in FIG. 1. The charging device 1 uses a corotron, and the power pack for supplying a current to the corona charge wire is fixed. In the current type, the photoconductor potential can be changed by changing the current, and the change of the current is controlled by the CPU 20 by, for example, a PWM (Pulse Width Modulation) signal. In addition, it may be a scorotron. In this case, the charging potential of the photoconductor can be controlled by changing the grid potential. Furthermore, charging rollers are also conceivable.

In the writing device, writing is performed by the laser beam 11, PM (power modulation) and PWM (pulse width control) are performed to express the gradation of one dot of the image, and the total lighting power is APC (Auto Power Control). ), The target value can be changed by setting. The surface potential sensor 2 generates a voltage signal proportional to the photosensitive body potential, and this signal is converted into a digital signal by the AD converter 21 and input to the control board of the CPU 20. The developing roller 3 supplies the developing solution to the photoconductor 10.
For example, it is possible to change the toner supply amount by supplying a developing solution between the scrubber and the roller to rotate the roller and changing the number of rotations.

The developing bias 22 controls the voltage applied to the developing roller 3 and is applied in a polarity opposite to that of the toner. When the voltage is increased, the amount of toner adhering to the photoconductor 10 decreases, and when the voltage is decreased, the background stain occurs. Larger (for positive-positive process). The reverse roller 4 has a function of scraping off the excess developer film on the photoconductor, and the film pressure of the liquid after passing through the reverse roller 4 can be changed by changing the number of rotations. There is an appropriate range, but when it is fast, it becomes thick when it is thin, and when it is electrically, it may be floated or GND. The set roller 5 is for stabilizing the toner adhesion state on the photoconductor. The voltage applied by the set roller bias 23 has the same polarity as that of the toner, and the adhesion state can be changed depending on the magnitude of this voltage. The power pack of this power supply is considered to be a constant voltage type or a constant current type. Is configured to be output by PWM.

When the transfer charging unit 6 uses a corotron or a roller and has a structure of bp-3 (a plurality of photoconductors 10 are arranged side by side to transfer the transfer paper on the transfer belt), the first transfer unit and the second transfer unit 2 The transfer conditions differ at the second transfer portion. This is because electric charges are accumulated on the transfer belt and the transfer paper due to the influence of the previous transfer, which affects the next transfer. This is also affected by the material of the transfer paper. The cleaning unit removes residual toner on the photoconductor, and includes a foam roller 7 and a blade 8. While supplying the cleaning liquid to the foam roller 7, the foam roller 7 is rotated to wipe the toner on the surface of the photoconductor 10 to collect the cleaning liquid containing the toner. The photoconductor 7 after the foam roller is wiped off with a blade 9. The collected cleaning liquid is sent to a cleaning liquid purifying unit (not shown) to remove the toner. Quenching lamp (hereinafter Q
L) 9 is composed of an LED and erases the potential pattern on the photoconductor 10 to make the potential uniform.

The cleaning liquid purifying unit is constructed so that a voltage is applied to the facing electrode plates to fill the cleaning liquid between the electrodes. The toner adheres to the electrode side to which a voltage having a characteristic opposite to that of the toner is applied. The developer concentration sensor 24 is
Measure the concentration of the developer. For example, it is a light transmissive sensor including a light emitting body such as an LED or a light bulb and a light receiving element such as a photodiode or a phototransistor. The transmitted light is converted into a voltage, the AD converter 25 converts it into a digital signal, the CPU 20 judges the developer concentration, and if it is judged to be thin, the solenoid 26 for supplying the toner from the contact toner bottle is turned on to replenish the toner. . Note that the process control itself is not limited to the positive-positive and negative-positive relations related to the writing and developing, but in order to simplify the description in the text, the following description will be given in the positive-positive process.

The purpose of controlling the process conditions is to deal with environmental changes, and to deal with changes over time. In addition to this, for example, it is also possible to deal with differences in sheets, developing solutions, etc. It also includes keeping the in-flight conditions constant.

One of the environmental change factors is temperature. The effect of temperature appears in the characteristics of the photoconductor. Photoconductor 10
Causes a change in the dark decay rate and sensitivity of the surface potential, and as a result, the amount of toner adhered differs. Since the developer changes its viscosity, it affects the film thickness on the photoconductor after passing through the reverse roller. Changes over time include long-term changes such as months to years, and short-term changes such as one-day changes and repeats. Long-term ones include deterioration of the photoconductor 10 and stains of the charging charger 1 and transfer charger 6, and short-term ones include light fatigue of the photoconductor 10.

To cope with the difference in the paper, it is necessary to change the proper toner amount and transfer charge current depending on the difference in the thickness and surface property of the paper. Further, the concentration of the developer is measured by the concentration sensor 2
4, the toner is added at a proper time to maintain a constant density. Further, the temperature sensor 27 detects the liquid temperature, and when it is below a certain temperature, it is heated by the heater 28. Process control is to control items such as these.

On the other hand, when viewed as an image on paper,
In order to maintain a constant image quality, it is important to keep the toner adhesion amount on the photoconductor 10 constant and the transfer conditions constant. To keep the toner on the photoconductor constant, the surface potential of the photoconductor at the time of development is made constant, the toner concentration of the developer is made constant, the replenishment of the liquid to the developing section 3 is made constant, and the developing bias 22 is used. Is required to be constant. As described above, the surface potential on the photoconductor is affected by the environment and changes with time, so that some measure is required to keep it constant. Although various methods can be considered for this device, the following method can be considered as an example.

The surface potential sensor 2 is arranged immediately before the developing section 3 to measure the surface potential of the photoconductor 10 and compare it with a target potential. The output current value of the charging power pack 29 is increased, and when it is high, the current value is decreased. By this operation, the surface potential on the photoconductor can be kept constant.

When the surface potential sensor 2 is arranged between the writing position and the developing section 3, the potential after exposure by the LD can be measured in addition to the unexposed light potential. When the potential after exposure is high, an abnormality occurs in the image, and therefore control is performed such that the power of the LD is increased or the developing bias 22 is increased. In this arrangement, since the photoconductor 10 moves in the order of charging, exposure, potential sensor, and development, the potential cannot be erased by writing after measuring the potential of the unexposed portion, so that toner adheres to the photoconductor 10. Occurs. FIG.
FIG. 4 is a diagram showing how the surface potential of the photoconductor 10 changes when the surface potential sensor 2 is arranged between the writing position 11 and the developing section 3.

The adhered toner adheres to the transfer belt or is collected by the cleaning unit, but if adhered to the belt, it may stain the paper. This can be prevented by providing an eraser between the potential sensor 2 and the developing section 3 to erase the charge before development, but in the present embodiment, the eraser is not provided for space reasons.

Since the potential pattern read by the surface potential sensor 2 must be formed outside the transfer paper image area, it must be provided outside the transfer paper area on the photoconductor shaft or at a portion corresponding between the transfer papers. . When it is provided outside the transfer paper area on the photoconductor axis, there are no timing restrictions for measuring the potential, but there are disadvantages in cost and size, such as widening the writing width of the optical system and lengthening the photoconductor. Therefore, in the case of measuring the potential between the transfer sheets, it is necessary to secure a sufficient distance between the transfer sheets to form a pattern.

As a method of controlling the surface potential by controlling the power pack from the read value of the surface potential sensor 2, there are a method of controlling the charging current of the corotron and a method of controlling the grid voltage of the scorotron. Compared to the corotron, the scorotron can make the electric potential on the photoconductor uniform, but requires a large amount of charge current to make the surface potential the same. In general, a scorotron is used because the discharge tends to be unstable with one charge. In this embodiment, a corotron is used to control the charge current. The charging power pack 29 (high-voltage power supply) in this embodiment uses PWM from the control board.
The current value can be determined by the signal.

As described above, the relationship between the charge current and the photoconductor potential varies due to various factors, and therefore it is necessary to frequently adjust this current (detect the potential and change the PWM signal). is there. When adjustment is performed without performing image formation such as when the power of the machine is turned on, replenishment of the developing roller 3 and the developing solution is stopped and the photoconductor 10, QL9, and main charging charger 1 are operated to change the current value. While adjusting the surface potential.

Although the potential at that time can be known by measuring the potential between the transfer papers by the pattern, it cannot be adjusted to match the target value (since the adjustment enters the next image area). Therefore, the current value is changed (to the extent that it does not go too far) outside the image area until the next measurement. The control between the transfer papers cannot be performed very often because the belt is soiled and the toner is consumed as described above. Usually, the potential fluctuation during repeat printing is considered to be caused by the light fatigue and temperature of the photoconductor, so there is no problem in controlling every several tens of sheets. If the gap between the measured potential and the target potential is large, the interval between the number of sheets to be controlled can be shortened, and in some cases, it is possible to achieve both dirt and responsiveness by carefully controlling the control method such as continuous control. .

When the potential pattern passes through the developing section, the voltage of the developing bias 22 can be made higher than that in the image section to reduce the amount of toner adhering to the pattern and reduce the toner consumption. When the potential pattern passes through the developing section (even if the developing bias is changed), toner adheres. On the other hand, in this method, a transfer belt is used, and the belt is in contact with the photoconductor 10 even outside the image area (the portion where the transfer paper is absent). Therefore, toner adheres to the transfer belt. As a measure for preventing the toner from adhering to the belt, the transfer current may be changed to reduce the transfer amount. However, the potential on the surface of the belt causes a difference between the image area and the paper, and if this trace remains even after the belt is discharged, next, when the transfer paper comes to the trace portion, uneven transfer occurs in the image portion. For this reason, the transfer current is often not changed even at the sheet interval. Toner stains on the belt are automatically cleaned by the belt cleaner. The transfer residual toner on the photoconductor is collected by the cleaning unit. The above is the black solid potential control.

The control of the exposed portion potential will be described below. When the charging current is set and the photoconductor potential is determined, L
It is necessary to set the potential after D exposure. In this case as well, as in the case of black solid potential control, the potential is measured when the machine is turned on or in the non-image area between transfer sheets. The adjustment at power-on is performed in the same way as the measurement of the solid black potential. In the case of carrying out between transfer papers, in this example, since the process is a positive-positive process, the space between papers is irradiated with an LD to erase the surface potential, so that the exposed portion potential can be measured as it is. In this case, unlike the solid black potential, it is not necessary to consider the toner adhesion at the developing portion, so that it is possible to measure each sheet interval.

When the exposed portion potential is higher than the set value, the LD power is increased. When the power is turned on, continue to make adjustments until the allowable value is reached. Since it is not possible to make adjustments while looking at the results between sheets, make adjustments each time and end when the tolerance is reached.
The LD power is gradually changed so that there is no difference in the density of the continuously printed paper. If the exposed area potential is low, LD
When it is not possible to increase the strength, the voltage of the developing bias 22 can be changed to prevent the background stain that secures the gradation of the highlight portion.

(Measurement of Gradation) It is possible to adjust the potential in the gradation portion as well as the adjustment in the solid black portion and the exposure portion. This is performed when rotating the photoconductor without developing, such as when the power is turned on (it is difficult in time between paper sheets). First, the unexposed portion potential is set (by the method described above), and then the potential after exposure (by the method described above) is set. Writing is performed for each gradation, and it is checked whether the potentials are at the set values. If there is a deviation, the gradation data is corrected so that it is controlled to the set value.

(Temperature Control, Transfer, Reverse Roller) The viscosity of the developer containing isopar and toner changes with temperature. When the viscosity changes, the film thickness of the developing solution on the photoconductor after passing through the reverse roller changes, and in the transfer in the next step, the thickness of the liquid film has an important influence on the quality. If the film is thick and the liquid amount is large, an abnormality such as an image flow is caused, and if the film is small, the toner is in a finely scattered state. Therefore, the film thickness must be kept constant. Also, the proper film thickness at the time of transfer differs depending on the type of transfer paper. For oil-absorbent paper (plain paper with a rough surface), it is better to have a thick film (more liquid), and for paper with poor oil absorption (coated paper), a thinner film (less liquid) is better. .

From the viewpoint of the film thickness after the reverse roller, two controls are required: 1: maintain a constant film thickness, 2: adjust the film thickness according to the characteristics of the transfer paper.

In the first control, the first thing that can be considered is the control of the liquid temperature. The liquid film is stabilized by keeping the temperature of the developer constant. A liquid temperature sensor (thermistor, thermocouple, etc.) 27 is submerged in a tank in which the developer is stored to measure the liquid temperature. Based on the result, the temperature of the liquid is kept constant by heating the liquid by the heater 28 provided in the lower portion or the side surface of the tank or in the tank.

As another control method, the film thickness on the photoconductor 10 is controlled. Factors that change the film thickness on the photoconductor include the gap between the reverse roller 4 and the photoconductor 10 and the peripheral speed ratio between the reverse roller 4 and the photoconductor 10. Photoconductor 10
The gap between and is difficult to control as a control item, but the peripheral speed ratio can be easily realized by using a variable speed motor as the reverse roller drive motor 4a. Therefore, based on the detected liquid temperature, the rotation speed of the reverse roller 4 is controlled so that the peripheral speed ratio is the target film thickness. By doing so, a constant film thickness can always be maintained even if the liquid temperature changes.

A method of controlling the film thickness by the number of revolutions of the reverse roller 4 and measuring the film thickness on the photoconductor after passing through the reverse roller and controlling it to a target film thickness, instead of changing it by temperature. There is also. As a detection method,
Reflected light type, transmitted light type, etc. are conceivable, but it is difficult to be precise because it measures a very small thickness.

(Paper Type Setting Method) FIG. 4 is a diagram for explaining the paper type setting method, and FIG. 4 (A) is a diagram for explaining an example of the related art, which corresponds to the characteristics of the transfer paper 31. When setting the thickness, the input of the paper type (the control side recognizing the paper type) is the first issue. As it is, in the example of the copying machine, regarding the paper size, the sensor 34 reads the code 33 provided on the paper cassette 32 to inform the machine of the paper size. Since it is virtually impossible to set the paper in the cassettes 32 having different sizes, if the machine recognizes the code 33, the paper size will not be wrong. On the contrary,
In the case of paper types, even if a dedicated cassette is prepared, different types of paper can be set if they have the same size.
When using the cassette 32, conventionally, the paper has been taken out of the package and set in the cassette 32. This can prevent mistakes in size, but cannot prevent mistakes in setting paper types.

FIG. 4B is a diagram for explaining one embodiment of the present invention, in which the paper 31 stored in the cassette 32 is not taken out from the package 35 and is necessary for the paper feed mechanism (indicated by diagonal lines). Remove only the part shown. In this state, the cassette 32 is set. There is a window in part of the cassette 32,
A paper type detection sensor provided in the machine body checks the packaging through this window. A symbol 37 indicating the paper type is written on the package corresponding to the window, and the machine body detects the type of the paper 31. This paper type mark 3
7 is written on both sides so that the paper packaging 35 may be set upside down. The paper type mark 37 includes paper size information in addition to the paper type information, and the conventional paper size detection is unnecessary. For the paper type detection means 36, there is a method of reading a black and white pattern printed on the package 37 by combining a general bar code reader and a plurality of photo reflectors.

It is also possible to symbolize the characteristics of the paper or the image forming conditions without symbolizing the type of the paper 31. In this case, even if the number of papers other than the paper type assumed in advance is newly increased, it is possible to cope with the change without changing the machine body side. In the case of characteristics, characteristics such as paper thickness, surface property, and electrical resistivity are coded. In the case of image forming conditions, parameters necessary for image formation such as an appropriate toner adhesion amount, transfer current value and SR bias value are coded. Even with a new paper type, the main machine can set optimal process conditions by coding the characteristics of that paper type.

When the paper feeding device is not the cassette 32 but a large amount of paper is stocked like a paper feeding tray, such a method (marking a package) cannot be used. It is conceivable to provide a symbol on one sheet as a mount and lay it at the bottom and place the sheet on it. It is also possible to print on the wrapping paper 35 by converting the paper type and characteristic information into numbers like a G code for video reservation and inputting to the machine by key operation of the operation unit when the user supplies paper. . This makes it possible to easily realize proper process conditions.

(Setting of process conditions for each transfer sheet) Table 1
Is a table in which a charging condition and a number for the charging condition are given in advance for each paper type, and a charging voltage value and a number are determined for each charging condition for each paper type. Therefore, it is possible to input the condition suitable for the property (paper quality) of the paper to the machine by determining, for example, 0508 (from Table 1, charging 800 V and transfer 850 μA). With this method, even if the types of paper increase,
You can tell the machine by coding the condition.

[0038]

[Table 1]

(Film thickness control according to paper type) The film thickness control by temperature is a control for keeping the film thickness constant against the disturbance, but the paper type correspondence control is for controlling the target film thickness depending on the paper. To change.

[0040]

[Table 2]

Table 2 is a data table showing the appropriate film thickness, photoconductor current, developing bias, SR bias, transfer current, etc. for each paper type, and the CPU in the control board preliminarily responds to the selected paper type. A data table such as Table 2 written in the ROM is referred to. In the data table, the optimum film thickness of the developing solution on the photoconductor for the selected paper or the condition for achieving the film thickness is written, and the machine is operated under the conditions. In the data table, other items such as an appropriate toner adhesion amount (photoconductor potential, development bias), SR bias value, transfer current value, etc., which need to be changed, are written.

FIG. 5 is a diagram showing the relationship between the reverse roller (hereinafter referred to as RR) and the film thickness on the photoconductor after passing through the RR. As shown in FIG. After taking the value, the thickness increases. In addition, the lower the viscosity (solid line A), the higher the viscosity (dotted line B) compared to the test results with liquids having different viscosities.
The thickness becomes thinner. This difference indicates that the film thickness varies depending on the temperature even if the same liquid is used. When the temperature changes and the film thickness changes, the film thickness can be controlled by changing the rotation speed of the RR.

One of the controls as a method for making the thickness of the liquid film on the photosensitive member constant is to measure the temperature of the liquid from the above data, the temperature of the liquid, and the relationship of the viscosity to the temperature of the liquid. The film thickness is made appropriate by selecting the RR rotation speed at which the temperature liquid achieves the desired film thickness. This method is, so to speak, open loop control, and it is not possible to achieve the desired film thickness depending on the machine conditions (for example, the gap between the photoconductor and RR is as specified, or the difference in viscosity depending on the liquid concentration). There is a nature.
On the other hand, there is also a method of detecting the film thickness on the photoconductor and feeding back the rotation speed of the RR. What is difficult with this method is the method of detecting the film thickness.

FIG. 6 is a diagram for explaining an example of a method of detecting the film thickness on the photoconductor, in which the light emitted from the light source 40 is the photoconductor 1.
The light is received by the light-receiving element 41 by grazing over 0. The arrival position of this light varies depending on the film thickness of the liquid, and the film thickness can be detected. In this way, the value detected by the film thickness detecting means is compared with the target, and the rotational speed of the RR is changed according to the difference to control the target film thickness.

(Other Control Items Depending on Paper Type) Depending on the paper, there are a developing bias, an SR bias, a charging current, a transfer current, and a fixing temperature, which are controlled by PWM or the like to values set for each paper type. .

[0046]

As is apparent from the above description, according to the present invention, characteristics such as the thickness, surface property, electric resistance, background color, etc. of the transfer paper for transferring the image are stored for each paper type. Since the process conditions can be delicately changed according to the paper used, the image quality can be further improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part for explaining an overall process control.

FIG. 2 is a control circuit diagram for explaining the overall process control.

FIG. 3 is a diagram showing how the surface potential of the photoconductor 10 changes.

FIG. 4 is a diagram for explaining a paper type setting method.

FIG. 5 is a diagram showing a relationship between a rotation number of a reverse roller and a film thickness on a photoconductor.

FIG. 6 is a diagram for explaining an example of a method for detecting the film thickness on the photoconductor.

[Explanation of symbols]

1 ... Main charging charger, 2 ... Surface potential sensor, 3 ... Developing roller, 4 ... Reverse roller, 5 ... Set roller, 6
... Transfer charger, 7 ... Foam roller, 8 ... Blade, 9 ... Quenching lamp, 10 ... Photoconductor, 11 ... Exposure light, 20 ... CPU, 21, 25 ... A / D converter,
22 ... Development bias power supply, 23 ... Set roller bias power supply, 24 ... Development liquid concentration sensor, 26 ... Toner supply solenoid, 27 ... Development liquid temperature sensor, 28 ... Development liquid heater, 29 ... Main charging power pack, 31 ... Paper, 32 ... Paper cassette, 33 ... Cassette size code, 34, 36 ...
Reading sensor, 35 ... Packaging, 36 ... Paper type code on packaging, 40 ... Light source, 41 ... Light receiving element.

Claims (3)

[Claims] 1. A photosensitive member, an electrostatic latent image is formed on the surface of the photosensitive member by an electrophotographic method, and the electrostatic latent image is developed,
An image forming apparatus for transferring the image onto a transfer sheet, wherein the image forming condition is changed according to the characteristics of the transfer sheet for transferring the image. 2. The image forming apparatus according to claim 1, wherein a number is determined in advance for each type of transfer paper to be used, and the number of the transfer paper is input from a ten-key pad or the like when used. 3. The condition number is set for each of the setting items of the image forming conditions for each transfer sheet to be used, and the number of the transfer sheet is input from a ten-key pad or the like at the time of use. Image forming device.