JP2003107810A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which can always keep image density proper in spite of a rise in the surface temperature of a photosensitive body of a circulation type both-surface recording system image forming device. SOLUTION: On a paper feed conveyance path L1 of a paper feeding conveyance mechanism 21, a temperature sensor 53 which comes into contact with a conveyed recording medium is arranged to detect the temperature of the recording medium P. The surface temperature of the photosensitive body is estimated from the correlation between photosensitive body surface temperature which is previously found by an experiment and the temperature detected by the temperature sensor 53 on the basis of the temperature of the recording medium P detected by the temperature sensor 53. According to the estimated photosensitive body surface temperature, image formation parameters of an image formation part 10, i.e., at least one of the developing bias voltage of a developing unit 13, a voltage applied to an electrostatic charger 12, and the exposure output of a laser device 15 to the photosensitive body 11 is adjusted to always maintain proper image density.

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,
In particular, it relates to an image forming apparatus capable of forming images on both sides of a recording medium.

[0002]

2. Description of the Related Art Today, image forming apparatuses such as copying machines and printers have become widespread, but recently, further downsizing and speeding up have been achieved, and environmental problems and office expenses have been reduced. In particular, in response to an increasing demand for reducing the number of recording media used, a double-sided image forming apparatus for recording images on both sides of the recording medium has been developed even in a small printer or the like.

In such an image forming apparatus of double-sided recording type, when the recording and fixing processing of the first image on the first surface of the recording medium, that is, the front surface, is completed in the image forming section, the front and back of the recording medium are immediately reversed. And convey it again to the image forming unit,
There is an image forming apparatus called a cyclic double-sided recording system, which is configured to record and fix a second image on the second surface, that is, the back surface, of a recording medium.

[0004]

In the above-mentioned image forming apparatus of the circulating type double-sided recording system, the recording medium heated by the fixing process of the toner image by the fixing device is not cooled sufficiently and the recording medium of the image forming unit is again cooled. Because it is transported to the photoconductor,
The photoreceptor is heated by the heat of the re-fed high temperature recording medium.

The amount of heat received by the photosensitive member is larger in a high-speed image forming apparatus, and is larger in a case where a large number of recording media are continuously processed. Therefore, in a small-sized apparatus in which sufficient heat dissipation cannot be expected, an image forming operation is performed. As it continues, the temperature of the photoconductor gradually increases, and as a result, the image density also gradually increases.

When a large number of recording media are continuously processed, the gradually increasing image density of the recording media not only deteriorates the image quality but also increases the toner consumption amount, which is not preferable. .

As a countermeasure against this, a density sensor for measuring the image density formed on the photosensitive member, for example, an automatic image density control sensor (ADIC) is arranged, and a developing bias or the like is operated so as to keep the image density constant. Although it can be solved by controlling the image parameter, the following problems have been pointed out.

That is, in a small-sized image forming apparatus, in order to downsize the apparatus and facilitate the handling, an integrated image forming unit (imaging cartridge) in which a photoconductor, a charger and a developing device are integrally formed is provided. Although many are adopted, there is no space for installing a density sensor or the like for measuring the density of toner formed on the photoconductor in this configuration. Further, it is difficult to use the above-mentioned density sensor in the case where the transfer roller is used to transfer the toner image formed on the photoconductor to the recording medium.

Further, the correlation between the surface temperature of the photosensitive member and the image density is previously examined by an experiment, and the experimental result is made into data and stored in the control means, and the surface temperature of the photosensitive member is stored when the image forming operation is executed. A method is conceivable in which the image density is estimated based on the correlation between the measured image temperature and the imaged surface temperature stored in the control means.

At this time, when the method of directly measuring the surface temperature by directly contacting the temperature sensor with the surface of the photoconductor is adopted, the influence of frictional heat generated by the frictional contact between the photoconductor and the temperature sensor is eliminated. There is a need. Further, the reflection type temperature sensor that measures the surface temperature of the photoconductor in a non-contact manner is not affected by the frictional heat described above, but since this type of temperature sensor is expensive, it increases the manufacturing cost of the device and reduces the size. The image forming apparatus cannot be used.

Further, a method of estimating the surface temperature of the photoconductor by measuring the air temperature (ambient temperature) in the space around the photoconductor is conceivable, but in this method, the paper passing mode (single-sided recording mode, double-sided recording mode) is used. Etc.), the air temperature fluctuates depending on the image forming conditions such as the type of recording medium and the length of waiting time, and the correlation with the photoconductor surface temperature cannot be accurately grasped. Cannot be accurately estimated.

Further, when the switch of the image forming apparatus is turned on to start the image forming operation in the state of being cooled to the ambient temperature, the rise of the surface temperature of the photoconductor with the passage of time is based on the experimental data. It can be predicted to some extent, and the image density can be controlled. But,
If there is a situation where the surface temperature of the photoconductor decreases once due to a short stop of the image forming operation after the surface temperature of the photoconductor rises, the surface temperature of the photoconductor with the passage of time is It does not always change as predicted based on the data, and even with this method, the surface temperature of the photoconductor cannot be accurately estimated.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and the invention of claim 1 provides a charging device for imparting an electric charge to at least the image carrier and the surface of the image carrier. An image forming unit including an exposure unit that exposes an image on the image carrier, a developing device that develops an image latent image formed on the image carrier, and a toner formed on the image carrier. A transfer unit for transferring an image to a recording medium, a paper feeding / conveying mechanism having a paper feeding / conveying path for conveying the recording medium supplied from the paper feeding unit to the image forming unit, and a recording medium having an image formed on one side thereof. In a double-sided image forming apparatus having a re-feeding conveyance mechanism having a re-feeding conveyance path for reversing the front and back of the sheet and re-feeding it to the image forming unit, Temperature detecting means for detecting the temperature of the recording medium conveyed and conveyed; Further comprising a control means for controlling the imaging parameters of the image forming unit based on the detected by detection means temperature is a double-sided image forming apparatus according to claim.

The temperature detecting means is a temperature detecting means for detecting, as the temperature of the recording medium, the temperature of the metal plate arranged on the sheet passing side surface of the conveying guide arranged on the sheet feeding conveying path.

The metal plate may be made of the same material as the base material of the image carrier of the image forming section.

Further, it is preferable that the metal plate is arranged at a position closest to the image carrier of the image forming section on the sheet feeding and conveying path.

Further, the image forming parameter is at least one of a developing bias voltage, a voltage applied to the charging charger, and an exposure output to the image carrier.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 shows an image forming section of a double-sided image forming apparatus according to an embodiment of the present invention, and a sheet feeding / conveying mechanism including a sheet feeding / conveying path for conveying a recording medium supplied from a sheet feeding section to the image forming section. FIG. 4 is a cross-sectional view illustrating a configuration of a re-feeding / conveying mechanism including a re-feeding / conveying path for re-feeding a recording medium having an image formed on one surface to an image forming unit.

In FIG. 1, reference numeral 10 designates a known electrophotographic image forming section. The image forming section 10 includes a photoconductor 11, a charger 12 arranged around the photoconductor 11, a developing device 13, and a cleaner 14. Image forming unit 10 configured
a, and a laser device 15 for projecting the laser light modulated by the image signal toward the photoconductor 11.

A transfer roller 16 is arranged at a position facing the photoconductor 11, and the recording medium is directed toward the photoconductor 11 at a predetermined timing on the upstream side of the photoconductor 11 in the recording medium conveyance direction. A pair of registration rollers 17 for conveying the sheet is arranged.

The developing device 13 is loaded with toner inside, and develops the latent image of the image formed on the photoconductor 11 by the laser device 15 with the toner to visualize it.

A sheet feeding section 20 and a sheet feeding and transporting mechanism 21 are arranged on the upstream side of the image forming section 10 in the recording medium transporting direction. The paper feed unit 20 is the paper feed tray 2 in this embodiment.
2 and paper feed roller 23, paper feed cassette 24 and paper feed roller 2
However, it is not limited to this.

The paper feeding / transporting mechanism 21 is a mechanism for transporting the recording medium P supplied from the paper feeding tray 22 or the recording medium P supplied from the paper feeding cassette 24 to the registration roller pair 17, and the transportation roller pair. 26, 27, a transport guide 28, a transport guide 29, and the like, and a paper feed transport path L1 for the recording medium P is formed.

A fixing device 30 includes a heating roller 31 and a pressure roller 32 each having a heater therein, and the surface temperature of the heating roller 31 is controlled to a predetermined temperature suitable for the fixing process by a temperature control device (not shown). It A re-feeding / transporting mechanism 40 is arranged downstream of the fixing device 30 in the recording medium transporting direction.

The re-feeding / conveying mechanism 40 is a mechanism for ejecting the recording medium on which the image recording is completed to the ejection tray 49, or re-feeding the recording medium having an image recorded on one side thereof to the image forming section 10. , Switching claw 41 for switching the conveyance direction of the recording medium
And a discharge roller 42, which is disposed on the downstream side thereof and is rotatable in the forward and reverse directions, a recording medium sensor SE, a pair of transport rollers 43, a transport guide 44, a transport guide 45, and the like, and the re-feed transport path L2. Are formed. The switching operation of the switching claw 41 and the forward and reverse rotation of the discharge roller 42 are
It is controlled by a control circuit (not shown).

Registration roller pair 17 of sheet feeding / conveying mechanism 21
The metal plate 51 is fixed to the transport guide 29 close to, and a temperature sensor 53 for detecting the temperature of the metal plate 51 is arranged. Since the temperature of the conveyed recording medium P cannot be directly detected, the recording medium P is conveyed by the conveying guide 29.
The metal plate 51 is made of synthetic resin so that the heat of the recording medium P is transferred to the metal plate 51 while being in contact with the metal plate 51 when being conveyed along the metal plate 51.
It is fitted and attached to the curved part of.

The metal plate 51 may be made of the same material as the metal cylinder which is the base of the photoconductor 11, and the metal plate 51
It is preferable that the heat capacity of the metal plate 51 be substantially equal to the heat capacity of the photoconductor 11 and that the temperature variation characteristics of the metal plate 51 and the photoconductor 11 with respect to time during heating and heat radiation be the same.

The mounting position of the metal plate 51 on the transport guide 29 is within the width of the minimum recording medium through which the paper can pass, and the mounting position of the temperature sensor 53 with respect to the metal plate 51 is the metal plate 5.
The center of 1 is to stabilize the temperature change during heating and heat radiation.

With the above configuration, the detection value (temperature) detected by the temperature sensor 53 is the temperature of the metal plate 51, not the temperature of the recording medium P itself, but the metal plate in contact with the recording medium P. Since the temperature of 51 can be regarded as a temperature that substantially matches the temperature of the recording medium P, in the following description,
The detection value detected by the temperature sensor 53 will be described as the temperature of the recording medium P.

The operation of the above configuration will be described. First, the case of the single-sided recording mode will be described. Single-sided recording mode is set in the image forming apparatus by operating an operation panel (not shown),
It is assumed that the image forming operation is started.

Laser light modulated by an image signal is projected from the laser device 15 toward the photoconductor 11 and the image latent image formed on the photoconductor 11 is developed by the developing device 13 to be formed on the photoconductor 11. Forms a toner image.

On the other hand, the recording medium P supplied from the paper feed tray 22 of the paper feed unit 20 or the paper feed cassette 24 is fed by the feed roller pair 26, 27 of the feed feed mechanism 21 and the feed guide 2.
8. The sheet is conveyed to the registration roller pair 17 via the sheet feeding conveyance path L1 including the conveyance guide 29 and the like, and is temporarily stopped.

As the photoconductor 11 rotates, the registration roller pair 17 rotates at the timing when the toner image formed on the photoconductor 11 reaches the transfer position, and the recording medium P is conveyed to the transfer position. The toner image on the photoconductor 11 is transferred to the recording medium P by the action of the transfer roller 16 at the transfer position.
The recording medium P on which the toner image is transferred onto the recording medium P is fixed by the fixing device 30 and then conveyed to the re-feeding conveyance mechanism 40.

Since the single-sided recording mode is set in the image forming apparatus, the control circuit of the re-feeding / conveying mechanism 40 controls the discharge roller 42 so as to keep rotating in the forward direction. The recording medium is directly discharged to the paper discharge tray 49 by the forward rotation of the discharge roller 42, and the image forming operation is completed.

Next, the case of the double-sided recording mode will be described.
It is assumed that the double-sided recording mode is set in the image forming apparatus by the operation of the operation panel (not shown) and the image forming operation is started.

Since the transfer of the toner image to the recording medium P from the formation of the first image on the photoconductor 11 is the same as that in the one-sided recording mode, the description thereof will be omitted. After being formed and fixed on the first surface (front surface) of the recording medium P, the recording medium P is conveyed to the re-feeding conveyance mechanism 40.

Since the double-sided recording mode is set in the image forming apparatus, the control circuit of the re-feeding and conveying mechanism 40 controls the discharge roller 42 and the switching claw 41 as follows. That is, when the recording medium P in which the image is formed only on the first surface (front surface) and the second surface (rear surface) is blank, the discharge roller 42 is rotated in the forward direction to fix the recording medium P. Are conveyed in the direction of the paper discharge tray 49.

When the trailing edge of the recording medium P is detected by the recording medium sensor SE (at this point, the trailing edge of the recording medium P has not yet passed the discharge roller 42), the switching claw 41 is moved to the re-feeding conveyance path. While switching to the L2 side, the discharge roller 42 is rotated in the opposite direction.

The recording medium P includes a pair of transport rollers 43, a transport guide 44, a transport guide 45, etc., and a re-feed transport mechanism 4
0 through the sheet re-feeding / conveying path L2, and further through the sheet feeding / conveying path L1 of the sheet feeding / conveying mechanism 21 including the pair of conveying rollers 26 and 27, the conveying guide 28, the conveying guide 29, and the registration roller pair 17 Is transported to and stopped.

A second image is formed on the photoreceptor 11,
A second toner image is formed. As the photoconductor 11 rotates, the registration roller pair 17 rotates at the timing when the second toner image on the photoconductor 11 reaches the transfer position, and the second toner image is re-fed at the transfer position. The image is transferred onto the second surface (back surface) of the recording medium P.

The recording medium P on which the second toner image is transferred is fixed by the fixing device 30, and then the re-feeding / conveying mechanism 40.
However, at this point, the control circuit of the re-feeding / transporting mechanism 40 controls the discharge roller 42 to continue rotating in the forward direction, so that the recording medium on which the fixing process has been performed does not move to the discharge roller 42. The output tray 49 is directly rotated by the normal rotation.
And the image forming operation is completed.

The relationship between the temperature of the recording medium P detected by the temperature sensor 53 of the paper feed / transport mechanism 21 and the surface temperature of the photoconductor 11 will be described.

The temperature sensor 53 detects the temperature of the metal plate 51 provided on the conveyance guide 29 near the registration roller pair 17 of the paper feed / conveyance mechanism 21, but as described above, the temperature of the metal plate 51 is detected. Can be regarded as a temperature that substantially matches the temperature of the recording medium P, so the detected value of the temperature sensor 53 is treated as the temperature of the recording medium P.

FIG. 2 is a diagram showing the results of an experiment comparing the surface temperature of the photoconductor with the value detected by the temperature sensor. The experiments were conducted in three-sided recording mode and double-sided recording in three cases: the environment temperature in which the image forming apparatus is installed is in the standard temperature range, is higher than the standard temperature range, and is lower than the standard temperature range. I went with mode.

The surface temperature of the photoconductor 11 is precisely measured by using a thermocouple to obtain a measured value. In addition, the temperature sensor 53
1 are arranged at a point A near the registration roller pair 17 in FIG. 1 and a point B on the upstream side of the point A in the recording medium conveyance direction for comparison, and the detection value is obtained. In addition, for reference, the environmental temperature in which the transport guide 29 is arranged and the external environmental temperature in which the apparatus is arranged were measured.

The numerical values in FIG. 2 will be described. When the surface temperature of the photoconductor is in the standard temperature range, the surface temperature of the photoconductor is 27.3 ° C. in the single-sided recording mode, the measured value of the temperature sensor at the point A is 34.2 ° C., and the surface temperature of the photoconductor is Was 6.9 ° C. Further, the value detected by the temperature sensor at point B was 34.4 ° C., and the difference from the surface temperature of the photoconductor was 7.1.
The outside temperature was 26 ° C. In the double-sided recording mode, the surface temperature of the photoconductor was 38.8 ° C, the value detected by the temperature sensor at point A was 47.6 ° C, and the difference from the surface temperature of the photoconductor was 8.8 ° C. Further, the detection value of the temperature sensor at point B was 48.2 ° C., and the difference from the surface temperature of the photosensitive member was 9.4.
The outside temperature was 26 ° C.

When the surface temperature of the photoconductor is higher than the standard temperature range, the surface temperature of the photoconductor is 3 in the single-sided recording mode.
Detection value of temperature sensor at point A at 6.3 ° C, 41.0
C., and the difference from the surface temperature of the photoreceptor was 4.7.degree. Further, the detection value of the temperature sensor at point B was 41.6 ° C., the difference from the surface temperature of the photosensitive member was 5.3 ° C., the air temperature near the conveyance guide was 48.3 ° C., and the outside air temperature was 32 ° C. Also, in the double-sided recording mode, the surface temperature of the photoconductor is 47.0 ° C.
The value detected by the temperature sensor at that point was 55.3 ° C, and the difference from the surface temperature of the photoconductor was 8.3 ° C. Further, the detection value of the temperature sensor at the point B is 55.3 ° C., the difference from the surface temperature of the photosensitive member is 8.3 ° C., the air temperature near the conveyance guide is 58.2 ° C.,
The outside air temperature was 32.5 ° C.

When the surface temperature of the photoconductor is lower than the standard temperature range, the surface temperature of the photoconductor is 1 in the single-sided recording mode.
Temperature sensor detection value at point A, point A 24.5
C., and the difference from the surface temperature of the photoconductor was 6.4.degree. Further, the detection value of the temperature sensor at point B was 25.5 ° C., the difference from the surface temperature of the photosensitive member was 7.4 ° C., the air temperature near the conveyance guide was 32.0 ° C., and the outside air temperature was 10.7 ° C. . In the double-sided recording mode, the surface temperature of the photoconductor is 26.7.
The temperature sensor detected a value of 35.2 ° C. at point A and point A, and the difference from the surface temperature of the photoconductor was 8.5 ° C. Further, the detection value of the temperature sensor at point B is 36.0 ° C., the difference from the surface temperature of the photoconductor is 9.3 ° C., and the air temperature near the conveyance guide is 38.
The temperature was 6 ° C and the outside air temperature was 11.7 ° C.

As is clear from the above description, the temperature sensor 53 is arranged at the point A near the registration roller pair 17 of the sheet feeding / conveying mechanism 21 and the detected value of the temperature sensor 53 and the surface temperature of the photosensitive member. The difference from the measured value is small, and it can be seen that the position is desirable.

As described above, since the detected value of the temperature sensor 53 has a certain correlation with the surface temperature of the photoconductor 11, the surface temperature of the photoconductor is calculated from the detected value of the temperature sensor based on a large number of experimental data. A numerical table for obtaining the values is created or compiled into a form of an arithmetic expression and stored in a storage device of a control circuit configured by a microprocessor (CPU) which is a control means for controlling the image forming parameters of the image forming unit. .

When executing the image forming operation,
The surface temperature of the photoconductor is estimated from the detected value detected by the temperature sensor 53, and based on the estimated surface temperature of the photoconductor, the image forming parameters of the image forming unit, that is, the developing bias voltage, the voltage applied to the charger, and the image. At least one exposure output to the carrier shall be adjusted. As a result, the image density of the recorded image can be always maintained at an appropriate density even when the image forming operation for a large number of sheets is executed.

In the above description, in the image forming apparatus capable of recording images on both sides of the recording medium, the change of the image density based on the rise of the surface temperature of the photoconductor by the recording medium re-fed is controlled. However, the present invention is not limited to coping with the rise in the surface temperature of the photoconductor due to the recording medium that is re-fed in such double-sided recording work, and is based on a normal change in environmental temperature. It goes without saying that the present invention can also be applied to control when the surface temperature of the photoconductor rises and the image density changes.

[0053]

As described in detail above, according to the present invention, in an image forming apparatus capable of recording an image on both sides of a recording medium, a temperature detecting means arranged on a paper feed conveying path of a paper feed conveying mechanism conveys the image. The temperature of the recording medium is detected, the surface temperature of the photoconductor is estimated based on the detected value, and the image forming parameter of the image forming unit is based on the estimated surface temperature of the photoconductor,
That is, the developing bias voltage, the voltage applied to the charger,
Since at least one of the exposure outputs to the image carrier is adjusted, an image forming apparatus that does not require a complicated image density detecting means and can always maintain an appropriate image density with a simple configuration. Can be provided.

Since no special image density detecting means is required, it can be applied to a small-sized double-sided image forming apparatus using an image forming unit such as an imaging cartridge in which a photoconductor and a developing device are integrally formed. .

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating an image forming unit, a sheet feeding / conveying mechanism of a recording medium, and a sheet refeeding / conveying mechanism of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a comparison result between a photosensitive member surface temperature and a temperature sensor detection value (recording medium temperature).

[Explanation of symbols]

10 Image forming section 11 photoconductor 12 Charger 13 Developer 14 cleaner 15 Laser device 16 Transfer roller 17 Pair of registration rollers 20 paper feeder 21 Paper feed transport mechanism 22 Paper tray 23 Paper feed roller 24 paper cassettes 25 paper feed rollers 26, 27 Conveyor roller pair 28, 29 Transport guide 30 fixing device 31 heating roller 32 pressure roller 40 Refeeding and transporting mechanism 41 Switching claw 42 discharge roller 43 Conveyor roller pair 44, 45 Transport guide 49 Output tray 51 metal plate 53 Temperature sensor L1 paper feed transport path L2 Refeeding conveyance path

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/02 102 G03G 15/02 102 3F048 15/04 15/06 101 3F100 15/043 21/00 384 3F101 15/06 101 15/04 120 21/00 384 F term (reference) 2H027 DA11 DA13 DA32 DE04 DE07 DE09 EA01 EA02 EA05 EC06 EC18 EC19 ED03 ED06 ED09 ED17 EE01 EE06 EF09 FA13 FA35 ZA07 2H028 BA16 BB02 BD03 276073 AA01 DA06 DA07 DA22 2H200 FA01 GA10 GA23 GA28 GA29 GA30 GA34 GA44 GA56 GA60 GB22 GB25 HA02 HA12 HA28 HB03 HB12 HB22 JA02 JA28 JA29 LA12 LA21 NA01 PA02 PA18 PA22 PB07 PB12 PB27 PB38 PB40 3F048 AA05 AB01 BA01 BA15 DA01 BA14 BA15 BB02 BB02 3F101 FB08 FD01 LA07 LB03

Claims (5)

[Claims] 1. An image carrying member, a charging device for applying an electric charge to the surface of the image carrying member, an exposure unit for exposing an image on the image carrying member, and an image latent image formed on the image carrying member. An image forming unit having a developing device for developing, a transfer unit for transferring the toner image formed on the image carrier to a recording medium, and a recording medium supplied from a paper feeding unit to the image forming unit. A paper feeding / conveying mechanism having a paper feeding / conveying path, and a paper re-feeding / conveying path for reversing the front and back of a recording medium having an image formed on one side and re-feeding it to the image forming unit. An image forming apparatus including a mechanism, a temperature detecting unit that is disposed on a sheet feeding / conveying path of the sheet feeding / conveying mechanism and detects a temperature of a recording medium conveyed, and a temperature detecting unit based on the temperature detected by the temperature detecting unit. Means for controlling image forming parameters of the image forming unit An image forming apparatus comprising the. 2. The temperature detecting means is a temperature detecting means for detecting, as the temperature of a recording medium, a temperature of a metal plate arranged on a sheet passing side surface of a conveying guide arranged on the sheet feeding conveying path. The double-sided image forming apparatus according to claim 1, which is characterized in that. 3. The double-sided image forming apparatus according to claim 2, wherein the metal plate is made of the same material as the base material of the image carrier of the image forming unit. 4. The double-sided image forming apparatus according to claim 2, wherein the metal plate is arranged at a position closest to the image carrier of the image forming unit on the sheet feeding and conveying path. 5. The double-sided image forming method according to claim 1, wherein the image forming parameter is at least one of a developing bias voltage, a voltage applied to a charging charger, and an exposure output to an image carrier. apparatus.