EP0676678A1

EP0676678A1 - Image forming apparatus

Info

Publication number: EP0676678A1
Application number: EP95104830A
Authority: EP
Inventors: Koji C/O Mita Industrial Co. Ltd. Maeda; Junichi C/O Mita Industrial Co. Ltd. Oura
Original assignee: Mita Industrial Co Ltd
Current assignee: Kyocera Mita Industrial Co Ltd
Priority date: 1994-04-04
Filing date: 1995-03-31
Publication date: 1995-10-11
Also published as: JPH07281489A

Abstract

The improvement of precision of the surface temperature control of a photoreceptor drum is intended. A CPU (28) determines whether the copying machine is in a waiting state or in a copying state or in an initial calibration state and decides the amount of output to a drum heater (19) by a fuzzy reasoning according to the state of the copying machine. The fuzzy reasoning is performed based on information from a sheet size sensor (31), a drum surface temperature sensor (23) and a room temperature sensor (32). <IMAGE>

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an image forming apparatus such as an electrographic copying machine, a printer and a facsimile machine using a photoreceptor drum as an electrostatic latent image carrier, and more particularly, to an improvement of the control of power supply to a drum heater incorporated in the photoreceptor drum.

Description of the Prior Art

Typically, an electrographic copying machine provided with a photoreceptor drum is designed so that the surface of the photoreceptor drum rotating at a constant speed is electrically charged, the charged surface is exposed by using an optical system means, an electrostatic latent image obtained by the exposure is developed into a toner image, and the toner image is transferred to the surface of a sheet of paper supplied onto the drum surface.
The sensitivity of the photoreceptor drum of an electrographic copying machine designed as described above presents a high dependency on the atmospheric temperature. For example, even if the voltage applied to a charger is the same when the drum surface is charged, the charging potential largely differs according to the atmospheric temperature. This affects the density of the image transferred to the sheet. For this reason, a conventional photoreceptor drum incorporates a drum heater. By controlling power supply to the drum heater, the surface temperature of the photoreceptor drum is maintained at a predetermined temperature irrespective of the variation in atmospheric temperature.
In this case, conventionally, the surface temperature of the photoreceptor drum is detected by a thermistor incorporated in the drum. When the output value of a temperature detection signal of the thermistor is sensed to be higher than a set value, the power supply to the drum heater is cut off. When the output value is sensed to be lower, the power is continuously supplied to the drum heater to heat the drum. In either case, the power supply to the drum heater is cut off when the output value reaches the set value to maintain the drum surface temperature at a predetermined reference value.
In recent years, an amorphous silicon material has been widely used as a material for the photosensitive layer formed on the surface of the photoreceptor drum of the image forming apparatus of this type. Compared to a conventional photoreceptor drum using an arsenic selenium photosensitive material, the sensitivity of the photoreceptor drum using the amorphous silicon material is greatly influenced by the temperature. Therefore, in the case of the drum using the amorphous silicon material, the drum surface temperature is necessarily maintained constant.
However, when the above-described conventional drum surface temperature controlling means is employed for the amorphous silicon made drum, the variation in actual drum surface temperature from the set temperature is great, so that it is difficult to control the temperature so as to be maintained constant with a high precision.
Specifically, according to the conventional drum temperature control, since the drum surface temperature is detected only by the thermistor incorporated in the drum and the drum heater is activated or deactivated by comparing the output value of the thermistor with a preset reference value, the drum heater can be driven only either at a 100% output or at a 0% output in response to the thermistor output. Therefore, whether the output value is higher or lower than the reference set value, the drum surface temperature is apt to overshoot the set temperature, so that it is difficult to control the temperature so as to be maintained constant with a high precision.
During copying, since the sheet is in contact with the drum surface and deprives the drum of its heat, the surface temperature is influenced by the sheet size. Likewise, the influence of environmental factors such as the sheet temperature and the atmospheric temperature on the drum surface temperature is not ignorable in the drum using the amorphous silicon material. According to the conventional control method, it is impossible to reflect these factors in the drum heater output.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an image forming apparatus which realizes a highly precise drum surface temperature control employable for a photoreceptor drum using an amorphous silicon material by controlling the amount of output to a drum heater by a fuzzy reasoning based on factors such as the environment, the drum temperature, the operation state and the sheet size in controlling the surface temperature of the photoreceptor drum.
To achieve the above-mentioned object, according to the present invention, an image forming apparatus is provided with a photoreceptor drum incorporating a drum heater and a temperature controlling means for controlling an output to the drum heater by a fuzzy reasoning using a membership function based on a condition associated with the surface temperature of the photoreceptor drum. The temperature controlling means is capable of performing control with different amounts of output to the drum heater between in a transferring operation state where a sheet of paper is brought into contact with the surface of the photoreceptor drum to transfer a toner image formed on the drum surface to the sheet of paper and in a waiting state where the execution of the transferring operation is possible.
Preferably, the condition of the fuzzy reasoning for controlling the output to the drum heater in the temperature controlling means includes the room temperature and the size of the transfer sheet in addition to the surface temperature of the photoreceptor drum.
In an image forming apparatus arranged as described above, the amount of output to the drum heater is regulated by a fuzzy reasoning based on the drum surface temperature, the room temperature and the sheet size, so that the surface temperature of the photoreceptor drum can be maintained at a predetermined temperature with a high precision. In particular, by using the size of the sheet which deprives the drum surface of its heat during transferring as a condition for the fuzzy reasoning, the drum surface temperature during transferring is maintained with a high precision.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other objects and features of this invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanied drawings in which:

Fig. 1 is a front view showing the arrangement of a relevant portion of a copying machine employing the present invention;
Fig. 2 is a cross-sectional view showing an internal structure of a photoreceptor drum;
Fig. 3 shows an electric circuit which supplies the power to a drum heater;
Fig. 4 is a block diagram showing the arrangement of a temperature controlling means which controls the temperature of the photoreceptor drum by a fuzzy reasoning;
Fig. 5 is a flowchart showing a control operation by a central processing unit (CPU);
Fig. 6A shows a membership function of a condition portion according to Rule 1 in the fuzzy reasoning;
Fig. 6B shows a membership function of a conclusion portion according to Rule 1 in the fuzzy reasoning;
Fig. 7A shows a membership function of the condition portion according to Rule 2;
Fig. 7B shows a membership function of the conclusion portion according to Rule 2;
Fig. 8A shows a membership function of the condition portion according to Rule 3;
Fig. 8B shows a membership function of the conclusion portion according to Rule 3;
Fig. 9A shows a membership function of the condition portion according to Rule 4;
Fig. 9B shows a membership function of the conclusion portion according to Rule 4;
Fig. 10A shows a membership function of the condition portion according to Rule 5;
Fig. 10B shows a membership function of the conclusion portion according to Rule 5;
Fig. 11A shows a membership function of the condition portion according to Rule 6;
Fig. 11B shows a membership function of the conclusion portion according to Rule 6;
Fig. 12A shows a membership function of the condition portion according to Rule 7;
Fig. 12B shows a membership function of the conclusion portion according to Rule 7;
Fig. 13A shows a membership function of the condition portion according to Rule 8; and
Fig. 13B shows a membership function of the conclusion portion according to Rule 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment where an image forming apparatus according to the present invention is employed in an electrographic copying machine will be described with reference to the drawings. Referring to Fig. 1, there is schematically shown the arrangement of an electrographic copying machine according to this embodiment. Reference numeral 1 represents a photoreceptor drum which rotates in a clockwise direction of the figure at a constant speed. Along the periphery of the photoreceptor drum 1, the following are arranged in this order in its rotation direction (moving direction): a charging section A, an exposing section B, a developing section C, a transferring section D, a separating section E, a cleaning section F, and a charge removing section G.
In the charging section A, a charger 2 is arranged. The charger 2 is a corona discharger such as a corotron. To its main wire 2a, a high voltage of approximately 4kV to 6kV is typically applied. When a high voltage is applied to the charger 2, a corona discharge is generated, so that a charge is supplied to the drum surface. Typically, the surface potential of the drum 1 thus charged is approximately 900V.
When the charged portion of the surface of the drum 1 reaches the exposing section B as the drum 1 rotates, a reflection light beam L₁ from an original image is irradiated to the charged portion through a non-illustrated optical system to expose the portion. In this case, only the surface potential of the exposed portion is decreased by optical attenuation in correspondence with the exposure amount, so that an electrostatic latent image is formed on the drum surface.
A surface electrometer 3 is arranged just in front of the developing section C in the rotation direction of the drum 1. The surface electrometer 3 measures the charging potential of the drum surface when the drum surface reaches the developing section C. Since the potential of the drum surface charged at the charging section A is dark-decayed before the drum surface reaches the developing section C, the surface potential is reduced to approximately 820V when the drum surface reaches the developing section C. In other words, it is necessary for the drum surface potential at the developing section C to be approximately 820V, and the voltage applied to the charger 2 at the charging section A is set at a value (900V) allowing for the dark decay.
Reference numeral 4 represents an image erasing blank lamp arranged adjacent to the surface electrometer 3. The blank lamp 4 is constituted by light emitting diode (LED) arrays. When an erasure of a part of an electrostatic latent image is intended for a purpose such as specifying an image area, the blank lamp 4 selectively turns on necessary LEDs so that the portion of the electrostatic latent image irradiated by the LEDs which have been turned on is optically attenuated and erased. This lamp 4 is not used during normal copying.
In the developing section C, a developer unit 5 and a toner hopper 6 for supplying toner to the developer unit 5 are arranged. In this arrangement, toner contained in the toner hopper 6 is supplied into the developer unit 5 by a necessary amount through a sponge roller 7. The toner and carrier (iron powder) are agitated by an agitating roller 8 in the developer unit 5, and the toner held by the carrier adheres to the surface of a developing roller 9. When the portion of the drum 1 on which an electrostatic latent image is formed reaches the developing section C, the toner in the developer unit 5 electrically adheres to the drum surface through the developing roller 9 according to the electrostatic latent image, thereby forming a toner image.
In the transferring section D, a transfer charger 10 comprising a corona discharger is arranged. When the drum 1 reaches the transferring section D, a sheet P is fed onto the drum surface through a paper feeding roller pair 11 arranged in a paper feeding section, and a voltage of a polarity reverse to that of the toner is applied to the transfer charger 10 to transfer the toner image formed on the drum surface to the sheet P.
In the separating section E, a separating charger 12 comprising a corona discharger like the transfer charger 10 is arranged. The separating charger 12 applies an alternating current electrical field to the drum surface to thereby release the sheet P from being attracted to the drum 1, so that the sheet P to which the toner image has been transferred is separated from the drum 1.
In the cleaning section F, a cleaner 13 is arranged. The cleaner 13 removes things such as toner adhering to the drum surface by scrubbing the drum surface. The residual toner on the drum surface reaches the cleaning section F and is removed by the cleaner 13. Then, in the charge removing section G, a charge removing light beam L₂ is irradiated from a charge removing lamp 14 to the drum surface to optically attenuate the surface potential of the drum 1, so that the charge is removed. Thereafter, the drum 1 returns to the charging section A to be ready for the next copying operation.
Referring to Fig. 2, the photoreceptor drum 1 includes a drum base 15 made of a metal such as aluminum on which a photosensitive layer 16 is formed by depositing an amorphous silicon photosensitive material. A flange 17 is attached to each end of the drum base 15 and a drum shaft 18 is attached to connect the flanges 17. Further, a drum heater 19 is provided in the drum base 15.
The drum heater 19 includes a substrate 20, a cotton cloth 21, and a heat generator 22 arranged on one surface of the substrate 20. Both ends of the heat generator 22 extend outside the substrate 20, and a connecting terminal is attached to each of the ends of the heat generator 22. Reference numeral 23 represents a drum surface temperature sensor comprising a thermistor. The sensor 23 is fixed at an appropriate position between the substrate 20 and the cotton cloth 21 of the drum heater 19. The terminals of the drum surface temperature sensor 23 both extend outside the substrate 20.
One of the connecting terminals of the heat generator 22 and one of the terminals of the drum surface temperature sensor 23 are connected to a common rotational connection (not shown) and the other terminals thereof are connected to different rotational connections, respectively, so that power is supplied to the heat generator 22 and that a temperature sensing signal of the drum surface temperature sensor 23 is transmitted to a microcomputer 24 (see Fig. 3) serving as a temperature controlling means.
Referring to Fig. 3, there is shown a circuit for controlling the power supply to the drum heater 19. In the power supply controlling circuit, a series circuit including the drum surface temperature sensor 23 and a resistor 25 is connected between power terminals, and a node 26 between the drum surface temperature sensor 23 and the resistor 25 is connected to an input port of the microcomputer 24 serving as a temperature controlling means. The drum heater 19 and a switching device 27a are connected between the power terminals and the switching device 27a is connected to the microcomputer 24 through a pulse width modulator (PWM) 27b. Activation and deactivation of the switching device 27a is controlled by a pulse signal from the pulse width modulator 27b. When the switching device 27a is activated, power is supplied to the drum heater 19. The microcomputer 24 supplies the pulse width modulator 27b with a control signal to modulate the pulse width.
The microcomputer 24 controls the output of the drum heater 19 by a fuzzy reasoning using membership functions based on conditions associated with the surface temperature of the photoreceptor drum 1. Referring to Fig. 4, there is shown a control system including the microcomputer 24. Reference numeral 28 represents a CPU of the microcomputer 24 provided with a function to actually perform the fuzzy reasoning. Reference numeral 29 represents a read only memory (ROM) for storing fuzzy rules and membership functions necessary for the fuzzy reasoning. Reference numeral 30 represents a random access memory (RAM) used as a working storage for the fuzzy reasoning.
Reference numeral 31 represents a sheet size sensor arranged at an appropriate position in the paper feeding section. Reference numeral 32 represents a room temperature sensor for measuring the temperature of the room in which the copying machine is placed. Information from the sheet size sensor 31, the drum surface temperature sensor 23 and the room temperature sensor 32 is supplied to the CPU 28. The CPU 28 determines whether the copying machine is in a copying state or in an initial calibration state or in a waiting state where copying is possible, and performs control with a different amount of output to the drum heater 19 according to the state of the copying machine.
Specifically, in the temperature controlling means of the above-described arrangement, the amount of output to the drum heater 19 is calculated by a fuzzy reasoning based on factors including the room temperature, the drum temperature, the copying operation condition and the sheet size used for copying. The output of the pulse width modulator 27b is controlled based on the output amount to thereby control the drum surface temperature so as to be maintained at a preset appropriate temperature. Thereby, the precision of the surface temperature control of the drum 1 provided with the amorphous silicon made photosensitive layer 16 is improved.
Referring to Fig. 5, there are shown the details of the drum surface temperature controlling operation by the CPU 28. The CPU 28 performs control in accordance with each of the following states of the copying machine: a state where the copying machine is performing a copying operation; a state where copying is possible and the copying machine is waiting for the execution of a copying operation; and a state where the copying machine is performing the initial calibration, i.e. a state where the copying machine is performing various initial settings including the increase of the drum surface temperature after the start of the power supply to the copying machine.
First, at step #5, the voltage between the drum surface temperature sensor 23 and the resistor 25 (voltage at the node 26) are measured to judge the drum surface temperature corresponding the measured voltage. Then, at step #10, whether the copying machine is in the copying state or in the initial calibration state or in the waiting state is determined. When the copying machine is in the waiting state, the process proceeds to step #45 to execute a corresponding fuzzy control while the copying machine is in the waiting state.
In the fuzzy control for the waiting state, the following two fuzzy rules are used:

Rule 1: The output to the drum heater 19 is slightly decreased when the drum surface temperature is slightly higher than an appropriate value (45°C). The membership functions of the condition portion and the conclusion portion of the fuzzy reasoning according to Rule 1 are shown in Figs. 6A and 6B, respectively.
Rule 2: The output to the drum heater 19 is slightly increased when the drum surface temperature is slightly lower than the appropriate value. The membership functions of the condition portion and the conclusion portion according to Rule 2 are shown in Fig. 7A and 7B, respectively.

In this case, the membership functions of the conclusion portions are obtained from the drum surface temperature read out by the CPU 28 and the membership functions of the condition portions of the rules. Then, the membership functions thus obtained of the conclusion portions of the Rules 1 and 2 are superposed by a center of gravity (CG) method to obtain the center of gravity which is set as the value of the output to the drum heater 19.
When it is determined at step #10 that the copying machine is in the copying state, the process proceeds to step #15 to judge the size of sheets to be fed, i.e. the selected sheet size based on a detection signal transmitted from the sheet size sensor 31. Then, at step #20, a corresponding fuzzy control is executed while copying is performed.
In the fuzzy control for the copying state, the following three fuzzy rules are used:

Rule 3: The output to the drum heater 19 is decreased when the sheet size is small. The membership functions of the condition portion and the conclusion portion according to Rule 3 are shown in Figs. 8A and 8B, respectively.
Rule 4: The output to the drum heater 19 is slightly decreased when the drum surface temperature is slightly higher than the appropriate value (45°C). The membership functions of the condition portion and the conclusion portion according to Rule 4 are shown in Figs. 9A and 9B, respectively.
Rule 5: The output to the drum heater 19 is slightly increased when the drum surface temperature is slightly lower than the appropriate value. The membership functions of the condition portion and the conclusion portion according to Rule 5 are shown in Figs. 10A and 10B, respectively.

In this case, the membership functions of the conclusion portions are obtained from the membership functions of the condition portions of the rules based on the drum surface temperature and the sheet size read out by the CPU 28. Then, the membership functions thus obtained of the conclusion portions of the three Rules 3, 4 and 5 are superposed by the CG method to obtain the center of gravity which is set as the value of the output to the drum heater 19.
The control is thus performed with different amounts of output to the drum heater between in the waiting state and in the copying state in order to cope with whether the heat of the drum surface is deprived of by the sheet or not. In the copying state, since the sheet P is directly in contact with the drum surface, the drum surface is deprived of its heat by the sheet P to decrease the drum surface temperature. On the contrary, in the waiting state, since the sheet P is not supplied, no factor is present associated with the variation in drum surface temperature. Therefore, it is necessary for the amount of output to the drum heater 19 to be higher in the copying state than in the waiting state.
The reason why the sheet size is used as a fuzzy reasoning factor in the copying state in addition to the drum surface temperature is that the amount of deprival of the drum surface heat by the sheet depends on the sheet size. The larger the sheet size is, the more the drum surface is deprived of its heat. To compensate therefor, it is necessary to increase the amount of output to the drum 19.
When it is determined at step #10 that the copying machine is in the initial calibration state, the process proceeds to step #35 to judge the room temperature based on the measurement data transmitted from the room temperature sensor 32. Then, at step #40, a fuzzy control corresponding to the initial calibration is executed.
In the fuzzy control for the initial calibration state, the following three fuzzy rules are used:

Rule 6: The output to the drum heater 19 is decreased when the room temperature is high. The membership functions of the condition portion and the conclusion portion according to Rule 6 are shown in Figs. 11A and 11B, respectively.
Rule 7: The output to the drum heater 19 is slightly decreased when the drum surface temperature is slightly higher than the appropriate value (45°C). The membership functions of the condition portion and the conclusion portion according to Rule 7 are shown in Figs. 12A and 12B, respectively.
Rule 8: The output to the drum heater 19 is slightly increased when the drum surface temperature is slightly lower than the appropriate value. The membership functions of the condition portion and the conclusion portion according to Rule 8 are shown in Figs. 13A and 13B, respectively.

In this case, the membership functions of the conclusion portions are obtained from the drum surface temperature and the room temperature read out by the CPU 28 and the membership functions of the condition portions of the rules. Then, the membership functions thus obtained of the conclusion portions of the three Rules 6, 7 and 8 are superposed by the CG method to obtain the center of gravity which is set as the value of the output to the drum heater 19.
In any of the waiting state, the copying state and the initial calibration state, the amount of output to the drum heater 19 obtained by the fuzzy reasoning is inputted to the pulse width modulator 27b at step #25. By activating or deactivating the switching device 27a according to the pulse width modulated output, the power supply to the drum heater 19 is controlled with a high precision at step #30, thereby maintaining the drum surface temperature at the preset appropriate temperature (45°C).
While the room temperature is not used as a condition for the fuzzy reasoning in the copying state and in the waiting state in the above-described example, the condition associated with the room temperature shown in Rule 6 may be included in the reasoning in the copying state and in the waiting state like in the initial calibration state.
As described above, according to the present invention, the amount of output of the drum heater is varied according to the state of the copying machine, and the sheet size and the room temperature as well as the drum surface temperature are considered as conditions for the fuzzy reasoning to decide the amount of output of the drum heater, so that the drum surface temperature can be maintained at a predetermined temperature with a high precision. Consequently, the drum surface can always be charged at a constant potential, so that the density of the transferred image is stable. As a result, a high quality copy image cam be provided. The present invention is advantageous, particularly, to the use in an image forming apparatus employing a photoreceptor drum using an amorphous silicon photosensitive material having a high temperature dependency.
Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.

Claims

An image forming apparatus comprising:
a photoreceptor drum (1) incorporating a drum heater (19); and
temperature controlling means (24) for controlling an output to the drum heater (19) by a fuzzy reasoning using a membership function based on a condition associated with a surface temperature of the photoreceptor drum (1),
wherein said temperature controlling means (24) performs control with a different amount of output to the drum heater (19) between in a transferring operation state where a sheet of paper is brought into contact with the surface of the photoreceptor drum (1) to transfer a toner image formed on the drum surface to the sheet of paper and in a waiting state where the transferring operation is possible.
An image forming apparatus according to claim 1, wherein the condition for the fuzzy reasoning for controlling the output to the drum heater (19) in the temperature controlling means (24) includes a size of the sheet of paper in addition to the surface temperature of the photoreceptor drum (1).
An image forming apparatus according to claim 1, wherein a photosensitive layer (16) formed on the surface of the photoreceptor drum (1) is made of an amorphous silicon photosensitive material.
An image forming apparatus comprising:
a photoreceptor drum (1) on an outer surface of which an image is formed, said photoreceptor drum (1) transferring said image to a sheet of paper;
a drum heater (19) provided on an inner surface of the photoreceptor drum (1), said drum heater (19) generating a heat by an electric power;
power supplying means (27a, 27b) for supplying the electric power to the drum heater (19);
a drum temperature sensor (23) which detects a temperature of the outer surface of the photoreceptor drum (1);
a room temperature sensor (32) which detects a room temperature; and
power amount regulating means (24) for regulating an amount of the electric power supplied from the power supplying means (27a, 27b) to the drum heater (19) based on a temperature detected by the drum temperature sensor (23) and a temperature detected by the room temperature sensor (32).
An image forming apparatus according to claim 4, wherein said power amount regulating means (24) decides the amount of the electric power supplied from the power supplying means (27a, 27b) to the drum heater (19) by a fuzzy reasoning based on the temperature detected by the drum temperature sensor (23) and the temperature detected by the room temperature sensor (32).
An image forming apparatus according to claim 5, wherein a sheet size sensor (31) is provided which detects a size of the sheet of paper, and wherein said photoreceptor drum (1) transfers the image to the sheet of paper with its outer surface being in contact with the sheet of paper, and wherein said power amount regulating means (24) decides the amount of the electric power supplied from the power supplying means (27a, 27b) to the drum heater (19) by a fuzzy reasoning based on the temperature detected by the drum temperature sensor (23), the temperature detected by the room temperature sensor (32) and a sheet size detected by the sheet size sensor (31).
An image forming apparatus according to claim 4, wherein said power supplying means (27a, 27b) intermittently supplies the electric power to the drum heater (19) by alternately repeating a state where the electric power is outputted and a state where the electric power is not outputted, and wherein said power amount regulating means (24) regulates the amount of the electric power supplied from the power supplying means (27a, 27b) to the drum heater (19) by changing a length of a time during which the power supplying means (27a, 27b) outputs the electric power.
An image forming apparatus according to claim 4, wherein said power amount regulating means (24) changes the amount of the electric power supplied from the power supplying means (27a, 27b) to the drum heater (19) between while the image forming apparatus is executing an operation to form an image on the outer surface of the photoreceptor drum (1) and to transfer the image to the sheet of paper and while the image forming apparatus is waiting for an execution of said operation.
An image forming apparatus according to claim 4, wherein said power amount regulating means (24) changes the amount of the electric power supplied from the power supplying means (27a, 27b) to the drum heater (19) among while the image forming apparatus is executing an operation to form an image on the outer surface of the photoreceptor drum (1) and to transfer the image to the sheet of paper; while an execution of said operation is possible and the image forming apparatus is waiting for the execution of said operation; and in a period of time from when a state of the image forming apparatus is changed from a no power supplied state to a power supplied state to when the execution of said operation becomes possible.