JP2003263042A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which such a paper hardly separable can easily be separated that a recycled paper which has tendency to curl and is hardly separable from a photoreceptor and also a paper for color copy whose resistance is high and which is hardly separable. <P>SOLUTION: A transfer current applied to a transfer charger is controlled at two levels of a first current A21 and a second current A22. The first relatively low current A21 is applied (refer to (c) in figure 2) corresponding to the top end area (area for instance to 7 mm from top end) of the paper, so that a negative electric charge charged to the top end area of the paper is reduced. Force by which the top end area of the paper is attracted by the photoreceptor is weakened, so that the top end of the paper is easily separated from the photoreceptor. It is returned to the second current A22 relatively high in a remaining area, so that normal transfer performance is secured. <P>COPYRIGHT: (C)2003,JPO

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 that visualizes an electrostatic image formed on a photoconductor into a toner image and then transfers the toner image onto a sheet.

[0002]

2. Description of the Related Art As an apparatus for forming an image by an electrophotographic method, there are a printer and a copying machine. In these devices, the surface of the photoconductor is uniformly charged to a predetermined high potential by, for example, positive discharge from the charger, and then selectively exposed to form an electrostatic latent image. This electrostatic latent image is
The toner image is developed by the developing device. After that, the toner image is transferred onto the paper by the transfer device, and finally the toner particles are fixed on the paper to form the image.

The toner image on the surface of the photosensitive member is transferred to the sheet of paper that is fed when it comes to a position facing the transfer charger. That is, in the transfer charger, a discharge opposite to that of the charging charger, for example, a negative discharge is performed. Negative charges discharged from the transfer charger are charged on the paper. As a result, the toner attached to the low potential portion on the photoconductor is electrostatically attracted to the paper. On the other hand, a separation charger is arranged immediately downstream of the transfer charger in the sheet conveying direction, and in this separation charger, a predetermined bias voltage is added to the positive side of a predetermined AC high voltage for discharging. As a result, the electric charge charged on the paper is removed, and the separation of the paper from the photoconductor is promoted.

[0004]

By the way, the paper on which the image is once fixed may be reused once. For example,
When copying on both sides of paper with a double-sided copying machine, 2
This is a case where the face is copied. In addition, an image may be formed on the second surface of the sheet having the image transferred on the first surface. Further, there are cases in which composite copying is performed by feeding paper from a manually fed paper tray. In these cases, since the paper has passed through the fixing device once and is exposed to the high heat of the fixing device, the edge of the paper tends to curl. For this reason, when it is attempted to separate the paper after transfer from the photoconductor, the paper is difficult to separate, and transfer failure is likely to occur.

Further, in the case of a paper for color copying or the like, the surface is very smooth and dense, and the paper resistance is high, so that it tends to be difficult to separate from the photoconductor. The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of easily separating a sheet that tends to be difficult to separate from a photoreceptor.

[0006]

In order to achieve the above object, the invention according to claim 1 provides a transfer current control means for applying a predetermined current to the transfer means when a sheet passes through. The predetermined current is a first current corresponding to when the leading end region of the sheet in the transport direction passes the transfer unit, and a second current corresponding to when the remaining region of the sheet passes the transfer unit. And the first current is smaller than the second current.

According to the present invention, the transfer current applied to the front end region of the paper, for example, a region of about 7 mm from the front end of the paper, which is usually free of an image, is relatively low, so that the front end region of the paper is loaded. Reduce the negative charge relatively. As a result, the force with which the leading end region of the paper is attracted to the photoconductor is weakened, and the leading end of the paper can be easily separated from the photoconductor. Further, in the remaining area of the paper, that is, the image area, the transfer current is returned to the original value, and thus normal transfer becomes possible.

According to a second aspect of the present invention, in the first aspect, the transfer current control means is provided on the condition that the sheet on which the image is fixed at least once passes through the transfer means.
The first current and the second current are used as the predetermined current. In this case, it is effective to accelerate the separation of the paper from the photoconductor by controlling the transfer current to be applied in two steps for the paper that has a curled tip and is difficult to be separated from the photoconductor after the transfer. It can be.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the first and second aspects are set according to at least one of the humidity of the environment in which the image forming apparatus is placed, the size of the sheet, and the type of sheet. It is characterized by comprising a correction means for correcting at least one of the currents. For example, when the humidity is high, the amount of moisture absorbed by the paper is large, so the paper has low resistance. Further, when the size of the paper is small, the amount of transfer current initially received at the front end of the paper becomes large in area ratio, and it is difficult to attenuate the transfer current. In the case of using an unused sheet and the case of using a so-called backing sheet, the latter has once passed through the high temperature fixing device, so that the amount of moisture absorption is small and therefore the resistance is high. Further, the paper for color copying has a high resistance. In this way, if the resistance value and size of the paper are different, even if the same transfer current is applied, the amount of charge and the charging area ratio at which the paper is actually charged are different, and as a result, the attraction force between the paper and the photoconductor different. Therefore, in the present invention, the attraction force between the paper and the photoconductor is adjusted by correcting the transfer current in consideration of conditions related to the resistance value and size of the paper, and the paper after transfer is separated from the photoconductor. I made it easier.

According to a fourth aspect of the present invention, there is provided separation voltage control means for applying a predetermined separation voltage to the separation means when the sheet passes, and the predetermined separation voltage is a predetermined AC voltage. A shift bias is added, and the predetermined shift bias corresponds to the first shift bias when the leading end region of the sheet in the transport direction passes through the separating unit, and the remaining region of the sheet passes through the separating unit. And a second shift bias corresponding to the first shift bias, and the first shift bias has a higher voltage than the second shift bias.

In the present invention, by relatively increasing the shift bias for separation applied to the leading end region of the paper, for example, a region up to about 7 mm from the leading end of the paper, the electric charge in the leading end region of the paper is relatively high. The positive direction (the charge has the same polarity as the photoconductor). This allows
It is possible to increase the repulsive force of the leading edge region of the paper from the photoconductor to facilitate separation of the leading edge of the paper from the photoconductor. In the remaining area of the paper, that is, the image area, the second shift bias is adopted to restore the bias voltage to the original value. This is because if the bias voltage for separation is increased as a whole, the paper may be easily separated from the photoconductor, but transfer defects may easily occur.To prevent this, the shift bias corresponding to the image area is prevented. (That is, the second shift bias) is lowered. Further, this bias shift may be used together with the control of the transfer current in claims 1, 2, and 3.

According to a fifth aspect of the present invention, in the fourth aspect, the first and second shifts are performed according to at least one of the humidity of the environment in which the image forming apparatus is placed, the size of the paper, and the type of the paper. It is characterized in that it comprises a correction means for correcting at least one of the biases. Even if the same shift bias is applied, the amount of charge actually charged on the paper and the decay rate of the charge differ depending on the humidity, the size of the paper, and the type of paper, and as a result, the repulsive force between the paper and the photoconductor differs . Therefore, in the present invention, the repulsive force between the paper and the photoconductor is adjusted by correcting the separation shift bias in consideration of the conditions relating to the resistance value and size of the paper,
The paper after transfer is made to be easily separated from the photoconductor.

According to a sixth aspect of the present invention, in the fourth or fifth aspect, the separation voltage control means responds to the fact that the leading end of the sheet in the sheet conveying direction reaches the conveying means adjacent to the separating means downstream in the sheet conveying direction. , A cut-off mode for making the predetermined separation voltage or shift bias zero. When the separation shift bias is applied, for example, when the paper absorbs moisture, the density of the toner transferred to the paper tends to decrease. Further, in gray scale and the like, black stripes tend to occur along the lateral direction of the paper. Therefore, in the present invention, by appropriately adopting the cut-off mode for cutting the shift bias or the entire separation voltage, it is possible to prevent the decrease in toner density and the occurrence of black streaks. Further, the timing at which the shift bias or the entire separation voltage is set to zero is the time when the separation of the paper from the photoconductor becomes reliable. That is, it is the time when the leading edge of the sheet in the transporting direction reaches the transporting means adjacent to the downstream of the separating means in the sheet transporting direction, and the leading edge of the sheet is pulled downstream by the transporting means.

According to a seventh aspect of the present invention, in the sixth aspect, there is further provided a control section for inputting a signal from the operation panel and outputting the signal to the separation voltage control means, the control section being provided by a user or a serviceman. It is characterized in that it includes means for setting the cut-off mode by an operation. For example, when the cutoff mode is used in a low humidity environment, the amount of moisture absorbed by the paper is small and the paper resistance is large, so that reverse transfer (toner moves from the paper to the photoconductor: so-called (Transmission omission) may occur, and the image may become scaly. Therefore, in the present invention,
For example, in consideration of the humidity environment and the like, the user or the service man operates the operation panel to set the cut-off mode or cancel the setting.

According to an eighth aspect of the present invention, in the sixth aspect, the separation voltage control means cuts in accordance with at least one of humidity of an environment in which the image forming apparatus is placed, paper size, and paper type. It is characterized by setting to the off mode. At the time when the separation of the paper from the photosensitive member becomes reliable, it is preferable to set the bias voltage or the separation voltage to zero in order to improve the transferred image.
For small size paper, the conveyance distance from the time when the separation of the paper becomes reliable until the trailing edge of the paper passes through the separating means is short, and setting the cut-off mode is not very effective. In addition, if the paper has passed through the fixing device once, there is a situation in which the paper has a high resistance and is likely to cause transfer omission. Therefore, in such a case, the cutoff mode should not be set. Not a good idea. Further, in an environment where the humidity is less than 30%, the resistance value of the paper becomes high, and when the cut-off mode is set, the transfer omission may easily occur. Therefore, in the present invention, the cutoff mode is automatically set in consideration of the humidity, the paper size, and the paper type.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing an internal configuration of a copying machine 1 as an image forming apparatus according to an embodiment of the present invention. Referring to FIG. 1, this copying machine 1
Is for copying an original image by the so-called electrophotographic method, and is provided with an exposure unit 2, an image forming unit 3, a sheet conveying mechanism 4, and a fixing device 5.

The exposure unit 2 is for exposing the surface of a photosensitive member 6 of the image forming unit 3 which will be described later with light corresponding to an original image, and includes an optical system (not shown) including a light source and a lens. I have it. The light source irradiates the document placed on the contact glass with light, and the reflected light is condensed by the optical system and guided to the surface of the photoconductor. The image forming unit 3 includes a drum-shaped photoconductor 6 for forming an electrostatic latent image. The photoconductor 6 is rotatable along a rotation direction R indicated by an arrow. Image forming unit 3
Is also provided with a charging device 7, a developing device 8, a transfer charger 9, a separation charger 10, a charge eliminating device 11 and a cleaning device 12 which are arranged around the periphery in the rotation direction R.

The sheet conveying mechanism 4 feeds the sheet 30 from a sheet feeding cassette or a manual sheet feeding tray in which the sheet 30 is accommodated, supplies the sheet 30 to the photoconductor 6, and transfers the sheet 30 after transfer.
Is discharged to the outside of the machine via the fixing device 5. The sheet conveyance mechanism 4 conveys the registration roller 13 for adjusting the timing of the sheet 30 fed from a sheet feeding cassette or the like and sending it to the photoconductor 6, and the sheet 30 separated from the photoconductor 6 after transfer to the fixing device 5 side. And a transport belt 14 for The registration roller 13 transmits the power from a drive mechanism (not shown) through the registration clutch 13a, and when the registration clutch 13a is turned on, the registration roller 13 exposes the sheet 30 which has stopped moving until then. It will be supplied to the body 6 side.
The control unit 1 which will be described later turns on / off the registration clutch 13a.
Controlled by 7.

The fixing device 5 is for fixing the image formed on the sheet 30 after transfer, and includes a fixing roller (not shown) including a heater. During image formation, the photoconductor 6 is rotationally driven in the rotational direction R. At this time, the surface of the photoconductor 6 is uniformly charged to a predetermined potential (for example, a positive potential) by the charging device 7. In this state,
When the surface of the photoconductor 6 is exposed by the exposure device 2, the photoconductor 6 is exposed.
An electrostatic latent image corresponding to the original image is formed on the surface of the. The electrostatic latent image is visualized (visualized) as a toner image by the developing device 8. Specifically, the toner accumulated in the toner hopper is supplied to the surface of the photoconductor 6 by the developing roller, and the toner adheres to the surface of the photoconductor 6 corresponding to the electrostatic latent image.

The toner images formed on the photoconductor 6 are fed out one by one from a paper feed cassette or the like to be registered by the registration rollers 13.
Is transferred to the paper 30 whose timing is adjusted and fed by the function of the transfer charger 9. After that, the sheet 30 on which the toner image is formed is separated from the photoconductor 6 by the separation charger 10, and is guided to the fixing device 5 by the transport mechanism including the transport belt 14. The transfer charger 9 and the separation charger 10 are respectively the discharge wires 9a.
And 10a.

In the fixing device 5, the toner image transferred onto the sheet 30 is fixed onto the sheet 30 by the action of the fixing roller. The sheet 30 after fixing is discharged to the outside of the machine by a predetermined discharging mechanism. On the surface of the photoconductor 6 after the transfer of the toner image, charges and transfer failure toner are usually left. The residual charge is removed by the charge removing device 11. The defective transfer toner is removed by the blade 12a of the cleaning device 12. This prepares for the next image forming operation.

Next, a configuration for controlling the transfer charger 9 and the separation charger 10, which is a feature of this embodiment, will be described. As a configuration for applying a direct current to the transfer charger 9, the control unit 17 controls the variable resistor 16 arranged in parallel in the supply line from the constant current direct current power supply 15 to the transfer charger 9, whereby the transfer charger 9 is controlled. It controls the supplied current.

An AC power supply 18, a DC bias power supply 19, and a normally closed switch 26 are connected in series to the line for applying the separation voltage to the separation charger 10. By controlling the bias voltage from the bias power supply 19 by the control unit 17, a predetermined AC voltage (for example, 13K) from the AC power supply 18 is applied to the separation charger 10.
A separation voltage obtained by adding a predetermined bias voltage (eg, 1.4 KV) to V) is applied. Further, the control unit 17 turns off (opens) the switch 26 under a predetermined condition,
The separation voltage is set to zero.

The copying machine 1 is provided with the above-mentioned control section 17 for controlling the operation of each section. Control unit 17
Includes a CPU 22 to which memories such as a ROM 20 and a RAM 21 are connected. The CPU 22 of the control unit 17 is connected to the variable resistor 16 and the bias power source 19, and controls the current application to the transfer charger 9 and the voltage application to the separation charger 10. An operation panel 23 is connected to the CPU 22, and the operation panel 23
A paper mode selection signal corresponding to the paper mode selected and set by the user is given. The paper mode includes a plain paper mode, a back paper mode, and a high resistance paper mode.

The plain paper mode is a mode in which OA paper (unused product) for normal copying is used. The back paper mode is a mode in which the paper used for one copy is used again. This is the case when the paper is set in the manual feed tray and the composite copy is performed, or when the back side of the paper with the image copied on the front side is used. The high resistance paper mode is a mode in which a paper having a smooth surface and a high paper resistance, such as a color copying paper, is used.

A document size detection sensor 24 for detecting the size of the document placed on the contact glass is connected to the CPU 22, and a signal from the document size detection sensor 24 is supplied. There is. Further, the CPU 22 is provided with a signal relating to the paper size set by the user on the operation panel 23. Specifically, the paper 30 of the size selected on the operation panel 23 is supplied to the photoconductor 6. When the automatic paper setting is selected and the same size setting is made on the operation panel 23, the paper 3 of the size detected by the document size detecting sensor 24 is selected.
0 is supplied to the photoconductor 6.

A humidity detecting sensor 25 arranged inside the copying machine 1 is connected to the CPU 22, and a signal from the humidity detecting sensor 25 is given to the CPU 22. The CPU 22 is configured to change and set each control pattern for transfer and separation based on the paper mode, paper size, humidity and the like. As a transfer current control pattern, as shown in FIGS. 2A to 2D, there are four patterns P1, P1A, P2, and P2A. Referring to FIG. A constant current A1 is adopted as the current, and referring to FIG. 2B, in the pattern P1A, the pattern P1A is used.
The current A1a that is smaller than the current A1 at 1 by a predetermined amount (for example, 60 μA) is adopted as the transfer current.

Here, t0 is a timing at which the registration clutch 13a is turned on and the sheet 30 registered by the registration roller 13 starts to be fed to the photoconductor 6 side. Timing ta is the leading edge 3 of the sheet 30 in the conveying direction.
1 (see FIG. 1) is the timing of passing directly above the discharge wire 9a of the transfer charger 9, and at the timing tb, the trailing edge 32 (see FIG. 1) of the sheet 30 passes directly above the discharge wire 9a of the transfer charger 9. It's timing.

Further, in these patterns P1 and P1A, the transfer current is corrected (environmental correction) according to the humidity environment. That is, as shown in FIG. 3, the humidity H detected by the humidity detection sensor 25 is Ha (for example, 5
0%) or more, a predetermined amount d (for example, 30 μA) is added to the transfer current A1 or A1a for correction (steps S1 and S2). That is, A1 is replaced by (A1 + d), or A1a is replaced by (A1a + d).
Replace with and correct.

Further, referring to FIGS. 2 (c) and 2 (d),
In the patterns P2 and P2A, the first and second currents are used as the transfer current to control in two steps. That is,
As shown in FIG. 2C, in the pattern P2, as the transfer current, the leading end region 34 of the paper 30 (refer to FIG.
The first region corresponding to the so-called non-image region, which is the region from the tip 31 of 0 to the region 33 of, for example, 7 mm.
Current A21 and a second current A22 corresponding to the remaining area 35 of the sheet 30 (the area excluding the leading edge area 34 with reference to FIG. 1 and mainly corresponding to the image area) are adopted.
Current A21 is set to be lower than the second current A22 by a predetermined amount (for example, 40 μA).

Timing tc is, for example, 7 from the leading edge of the paper.
This is the timing when the portion 33 of mm passes immediately above the discharge wire 9a of the transfer charger 9. The first current A21 is controlled in the section between the timing ta and the timing tc, and the second current is controlled in the section between the timing tc and the timing tb.
Is controlled by the current A22. In addition, referring to FIG. 2D, in the pattern P2A, the transfer current corresponds to the first current A21 corresponding to the leading end region 34 of the sheet 30 and the remaining region 35 (tc to tb) of the sheet 30. ) Corresponding to the second current A22a is adopted. The patterns P2 and P2A have the same first current A21. The second current A22a of the pattern P2A is larger than the second current A22 of the pattern P2 by a predetermined amount (for example, 40%).
μA) It is set low.

Further, as shown in FIG. 4, in the patterns P2 and P2A in which the transfer currents are controlled in stages, when the humidity (absolute humidity) detected by the humidity detecting sensor 25 is 50% or more, the remaining Area 35 (tc to t
second current A22 or A2 corresponding to the section b))
The correction is performed by subtracting a predetermined amount e (for example, 60 μA) from 2a (steps S31 and S2). That is, A22 is replaced with (A22-e), or A22a
Is replaced with (A22a-e) to correct.

On the other hand, the control patterns for separation are the following five patterns Q1, Q2, Q2A, Q3 and Q3A.
There is. As shown in FIGS. 5A to 5E, in each of the patterns Q1, Q2, Q2A, Q3 and Q3A, a shift bias for separation is applied from the timing t0 when the registration clutch 13a is turned on. ing. In the pattern Q1, as shown in FIG. 5A, as the shift bias composed of the DC voltage added to the main AC voltage, the first shift bias v1 corresponding to the leading end region 34 of the paper 30 and the paper 30 are used. The second shift bias v2 corresponding to the remaining area 35 is adopted, and the first shift bias v1 is set higher than the second shift bias v2 by a predetermined amount (for example, 0.2 KV). That is, it is a two-step control in which the shift bias corresponding to the tip region 34 is increased.

Here, the timing td is the timing at which the front end 31 (see FIG. 1) of the paper 30 in the transport direction passes just above the discharge wire 10a of the separation charger 10, and the timing te is the rear end 32 of the paper 30 (see FIG. 1). 1) is the timing of passing directly above the discharge wire 10a of the separation charger 10. At timing tf, for example, a portion 33 of 7 mm from the leading edge of the paper is separated by the discharge wire 1 of the charger
It is the timing to pass directly above 0a. Therefore,
The section between the timing td and the timing tf is the sheet 3
The tip region 34 of 0 is the discharge wire 1 of the separation charger 10.
Although it is a section passing immediately above 0a, it is actually a section from the timing t0 when the registration clutch 13a is turned on to the timing tf, which is controlled by the first shift bias V1 and is between the timing tc and the timing tb. Is controlled to the second shift bias V2.

Referring to FIG. 5B, in pattern Q2, when the humidity H detected by the humidity detecting sensor 25 is a predetermined value Ha (for example, 50%) or more (H ≧ Ha), it is similar to pattern Q1. When the humidity H is less than a predetermined value Ha (for example, 50%) (Ha> H), the second pattern of the pattern Q1 is used.
Constant shift bias v equal to the shift bias v2 of
2 is adopted. Referring to FIG. 5C, the pattern Q2
In A, if the humidity is H ≧ Ha, the first pattern is the same as in the pattern Q1.
And two-stage control using the second shift biases v1 and v2 are performed, and when Ha> H, a constant shift bias v2
Further, when the humidity is H ≧ Hb (where the predetermined value Hb is 30%, for example), the entire separation voltage including the shift bias and the AC voltage is set to zero in the section from the timing tg to the timing te. Add off mode. In the cutoff mode, only the shift bias of the separation voltage may be set to zero and the AC voltage may be left.

Here, the timing tg is the timing at which the leading edge 31 of the sheet 30 reaches the adjacent conveyor belt 14 downstream in the conveying direction of the separation charger 10 (the leading edge 3 of the sheet 30).
1 to 70 mm, for example, corresponds to the timing of passing through the discharge wire 10a of the separation charger 10),
After the timing Tg, the paper 30 is pulled by the conveyor belt 14, so that the paper 30 is reliably separated from the photoconductor 6. Therefore, even if the separation voltage is cut off after this timing Tg, it is considered that the separation performance will not be affected anymore. However, the cut-off mode setting is adopted when the conditions described later are satisfied.

Further, in these patterns Q2 and Q2A, the entire shift bias is corrected (environmental correction) according to the humidity environment. That is, as shown in FIG. 6, when the humidity H (absolute humidity) detected by the humidity detection sensor 25 is Ha (for example, 50%) or more, each shift bias v1 or v2 has a predetermined amount f (for example, 0. 1K
V) is added for correction (step S
1, S2). That is, v1 is replaced by (v1 + f), or v2 is replaced by (v2 + f) for correction.

Referring to FIG. 5D, the pattern Q3 is
First shift bias v1 and second shift bias v3
To adopt. Pattern Q3 is the same as pattern Q1
Although it is a step control pattern, the second shift bias v3 in the pattern Q3 is set lower than the second shift bias v2 in the pattern Q1 by a predetermined amount (for example, 0.1 KV). With reference to FIG. 5E, in the pattern Q3A,
The first and second shift biases v similar to the pattern Q3
Two-step control using 1, v3 is performed. Furthermore, when the humidity is H ≧ Hb (the predetermined value Hb is, for example, 30%) and the humidity is high, the two-step control using the first and second shift biases v1 and v3 is performed until the timing tg, and from the timing tg. In the section of timing te, a cutoff mode is added to make the entire separation voltage including the shift bias and the AC voltage zero. In the cutoff mode, only the shift bias of the separation voltage may be set to zero and the AC voltage may be left.

Next, a flow for determining each control pattern of transfer and separation will be described with reference to FIG. First, the paper mode selected by the user on the operation panel 23 is determined (step S1). Plain Paper Mode In the plain paper mode, it is determined whether the paper size is small or large (step S2). The large size is, for example, A3, B4, and A4 vertically passed (transported with the longitudinal direction along the transport direction), and the small size is a sheet smaller than the large size described above. In the A4 horizontal thread, the edge on the long side of the paper first receives the transfer current as the leading end in the transport direction, and the area that first receives the transfer current is larger than the area of the entire paper. Since the length of the sheet in the sheet transport direction is short, the upstream end of the sheet in the sheet transport direction does not come into contact with a conductive sheet guide or the like, so that it is difficult for electric charges to escape, and the sheet is included in the small size category.

That is, the paper has the transfer current exposed to
It also escapes in the surface direction of the paper, and it leaks to the transport guide and the like upstream of the transfer charger 9 in the transport direction.
When a transfer current is applied to the leading edge of a large-size paper, the current diffuses to a wide paper surface and leaks to a guide plate or the like, so that the exposure charge due to the transfer is attenuated in a relatively short time. However, for small size paper, the transfer current received at the leading edge of the paper immediately spreads over the entire narrow paper, and because the paper is short in the transport direction, the area that is in conductive contact with the guide plate upstream of the transfer site is small. Are considerably reduced (especially the guide plate before transfer is insulated) or none. Therefore, the transfer current received at the leading edge of the paper is attenuated slowly, and the separability is deteriorated accordingly. Also,
This relationship applies not only to "paper size" but also to "environmental humidity" and "paper quality" in terms of "ease of diffusion of electric charges in the paper surface direction". Introducing up means will also be carried out accordingly. For the above reasons (in short, because the exposed area ratio is large and the paper is short in the transport direction, and the conduction to the guide plate is likely to be insufficient), the A4 horizontal thread described above is put in a small size. It is determined whether the first surface or the second surface (steps S3 and S6). On the first side of the small size,
The pattern P1 [see FIG. 2 (a)] is adopted for the transfer and the pattern Q2 [see FIG. 5 (b)] is adopted for the separation (step S4), and the pattern P2 [see the FIG. 2 (b)] is adopted and the pattern Q1 [see FIG. 5 (a)] is adopted for separation (step S5).

On the first side of the large size, the pattern P1 is used for transfer and the pattern Q2A [see FIG. 5 (c)] is used for the separation (step S7). On the second side of the large size, the pattern P1 is used for transfer. The pattern P2 is adopted and the pattern Q1 is adopted for separation (step S8). In the case of copying the second side regardless of the sheet size, since the sheet 30 once passes through the fixing device 5, the leading end is curled, so that it is difficult to separate the sheet and a transfer failure is likely to occur. Therefore, for the second side, the leading edge region 3 of the sheet 30
4A, the transfer current is decreased as shown in FIG. 2C, and the separation shift bias (that is, the first shift bias v1) is increased as shown in FIG. After the separation, the separation is performed with a low shift bias (that is, the second shift bias v2) thereafter.

If the whole separation shift bias is increased, the separation performance itself is improved, but on the contrary, there is a risk of defective transfer. Therefore, the second shift bias v2 corresponding to the image area is set low. . Further, regarding the first side, the transfer is not subjected to step control. Large size 1
On the surface side, the pattern Q2A is adopted for separation, and the cut-off mode is applied conditionally (humidity H is, for example, 30% or more) because the leading edge 31 of the paper 30 is pulled by the conveyor belt 14 and separated. This is because, in a state in which is almost certain, particularly in a large size, there is no hindrance to the subsequent separation.

Backing Paper Mode In the backing paper mode, it is determined whether the paper size is small or large (step S9). When the size is small, the pattern P2 is adopted for transfer and the pattern Q3 [see FIG. 5 (d)] is adopted for separation (step S10). In the case of a large size, the pattern P1 is adopted for transfer and the pattern Q3A is used for separation.
[See FIG. 5 (e)] is adopted.

In the backing paper mode, since the paper sheet that has once passed through the fixing device 5 is used, basically, the pattern on the second side of the plain paper mode is used as a reference. That is, the transfer current is reduced to facilitate separation, the image area of the paper can be separated even with a low separation shift bias, and the transfer failure at the leading end of the paper 30 is less likely to occur than in the plain paper mode. Is. In the backing paper mode, when the size is small, the transfer current is controlled in two steps as shown in FIG.
The reason why the transfer current is constant as shown in FIG. 2A when the size is large is as follows. In other words, for small sizes where the transfer current received at the leading edge of the paper is slow to decay, the transfer current is lowered only at the leading edge of the paper, which is generally outside the image area, eliminating the difficulty of separation and reaching the image area. Then, a two-step control for returning the transfer current to an appropriate value is performed, and it is not difficult to separate a large size in which the transfer current received by the leading edge of the paper is rapidly attenuated, so that the transfer current is kept constant.

In the backing paper mode, the separation shift bias is set to 2 as shown in FIG. 5 (d) or FIG. 5 (e).
Shift bias v controlled in stages and corresponding to the image area
3 is set lower than the separation bias v2 corresponding to the image area in the plain paper mode. Further, in the large size of the backing paper mode, the cut-off mode is applied conditionally for separation for the same reason as described above.

High Resistance Paper Mode In the high resistance paper mode, the paper size is determined (step S12). Next, it is determined whether the first surface or the second surface (steps S13 and S16). On the first surface of a small size, the pattern P1A [see FIG. 2 (b)] is adopted for transfer and the pattern Q2 [see FIG. 5 (b)] for separation.
Is adopted (step S14), and the pattern P2A [see FIG. 2 (d)] is adopted for transfer and the pattern Q2 is adopted for separation on the second small-sized surface (step S15).

On the first side of the large size, the pattern P1 is used for transfer and the pattern Q2A [see FIG. 5 (c)] is used for separation (step S17), and on the second side of the large size, transfer is performed. The pattern P2 is adopted and the pattern Q1 is adopted for separation (step S1).
8). High resistance paper tends to be difficult to separate from the photoconductor 6.
Therefore, in a small size, the patterns P1A and P2A are adopted, and the transfer current is set to be lower than that in the plain paper mode to facilitate the separation.
The pattern Q2 is adopted for both sides.

Further, in the case of a large size, the transfer and separation are controlled in the same manner as the first and second sides of the plain paper mode. In case of high resistance paper, even if the transfer current is lowered a little,
There is almost no effect on the density of the transferred toner. Cut-off mode In the large-sized first side of each paper mode (plain paper mode, back paper mode, and high-resistance paper mode), a shift bias (or separation) for separation corresponding to, for example, 70 mm or more from the leading end 31 of the paper 30. The significance of adopting the cutoff mode for cutting the entire voltage) is as follows.

That is, for example, in an environment of high humidity of 30% or more, for example, transfer deviation (black streaks extending in the lateral direction) occurs, or the density of the toner transferred to the paper is lowered in the moisture-absorbed paper. In addition, reverse transfer (toner transfer from the paper to the photoconductor: so-called transfer omission) may occur at both ends of the paper, and the image may become scaly.
Therefore, by adopting the cut-off mode, it is possible to suppress the occurrence of the above-mentioned transfer deviation, obtain a good toner density even on a paper that has absorbed moisture, and suppress the occurrence of reverse transfer. When the cutoff is set in an environment where the humidity is less than 30%, for example, transfer omission occurs conversely, so the cutoff may be canceled and a predetermined separation voltage may be applied.

Further, in the above embodiment, the cutoff mode is automatically set according to the conditions, but the cutoff mode is set and set together with the operation of associating the paper feed cassette and the paper type. The canceling operation may be performed manually. That is, a service person (or user) operates the operation panel 23 to select ON / OFF of the cutoff mode in consideration of usage conditions such as humidity environment. Specifically, as shown in FIG. 8, the display 4 including, for example, a liquid crystal display unit of the operation panel 23.
When the machine initial setting button 42 is pressed on the zero initial setting screen 41 so that it is highlighted, a machine initial setting screen 43 is displayed as shown in FIG.

The left half of the machine initial setting screen 43 is associated with setting items and setting values. That is, as setting items, display 51 to 5 of paper types (cassettes 1 to 4)
4 and the cutoff mode display 55 are displayed, and each display 51
The display buttons 61 to 65 are laid out as set values corresponding to each of the display buttons 61 to 55, and corresponding to the display buttons 61 to 65, for example, "plain paper", "plain paper", "Recycled paper", "High resistance paper",
"On" is displayed.

In the right half of the machine initial setting screen 43, display buttons 71 to 78 corresponding to the type of paper and a set value change button 79 are laid out. Here, for example, when the display button 61 called "plain paper" next to the display 51 of the paper type (cassette 1) is pressed, the display of "plain paper" of the display button 61 is reversed. Here, for example, when the high resistance paper button 73 on the right side of the screen is pressed, the display button 61
The display of "plain paper" is replaced with the display of "high resistance paper". Next, by pressing the set value change button 79, the display of “high resistance paper” on the display button 61 is confirmed. Accordingly, at the time of copying, it is possible to recognize the paper type and set the corresponding paper mode according to which paper cassette is fed.

Further, the cutoff mode display button 65
Each time is pressed, the display is alternately switched between “ON” and “OFF”, and by further pressing the set value change button 79, the content of the display is fixed, and in the separation control patterns Q2A and Q3A, the cut is performed. Whether to apply the off mode is set. As described above, in the present embodiment, the paper mode, the paper size, the first side or the second
By properly controlling the transfer current and the separation shift bias in consideration of the surface, the humidity environment, etc., it is possible to prevent the separation failure, the transfer failure, etc. from the photoconductor 6 of the paper 30.

The present invention is not limited to the above embodiment, and for example, a part of the transfer or separation control pattern may be omitted and another similar pattern may be used instead. In addition, various modifications can be made within the scope of the present invention.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an internal configuration of a copying machine as an image forming apparatus according to an embodiment of the present invention.

2A to 2D are diagrams showing a temporal change of a transfer current in each control pattern of the transfer current.

FIG. 3 is a flowchart for environment correction in controlling transfer current.

FIG. 4 is a flowchart relating to environmental correction of transfer current.

5 (a) to 5 (e) are diagrams showing a temporal change of a shift bias in each control pattern of a separation voltage.

FIG. 6 is a flowchart relating to environment correction of separation shift bias.

FIG. 7 is a flowchart showing a process for determining a control pattern for a transfer current and a separation shift bias.

FIG. 8 is a diagram showing an initial setting screen of a display of an operation panel.

FIG. 9 is a diagram showing a machine initial setting screen.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Copier (image forming apparatus) 6 Photoconductor 9 Transfer charger 10 Separation chargers 9a, 10a Discharge wire 13 Registration roller 13a Registration clutch 14 Conveying belt (conveying means) 15 DC power supply 16 Variable resistance 17 Controller 18 AC power supply 19 Bias power supply 22 CPU 23 Operation Panel 24 Original Size Detection Sensor 25 Humidity Detection Sensor 26 Normally Closed Switch 30 Paper 31 Front End 32 Rear End 34 Front End Area 35 Remaining Area 41 Initial Setting Screen 43 Machine Initial Setting Screen 79 Set Value Change Button 81 ON / OFF Button (button for setting cut-off mode)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takahisa Nakaue             1-2-2 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka Prefecture             Kyocera Mita Co., Ltd. (72) Inventor Tadashi Umeda             1-2-2 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka Prefecture             Kyocera Mita Co., Ltd. (72) Takashi Nagashima, the inventor             1-2-2 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka Prefecture             Kyocera Mita Co., Ltd. F term (reference) 2H027 DA13 DA14 DB09 DC01 DC02                       DC04 EA03 EC02 ED16 ED24                       EE07 FA04 FA05 FA13 FB06                       FB07 FB19 GA12 GA28 GA34                       GA47 GA56 GB04 HB06                 2H028 BA06 BB02 BB04                 2H200 FA01 FA06 FA12 FA18 GA02                       GA03 GA04 GA23 GA32 GA44                       GB12 GB25 HA12 HA28 HB03                       HB48 JA28 JA29 JA30 JB06                       JB18 KA02 KA07 KA28 KA29                       KA30 NA02 NA06 PA03 PA04                       PA10 PA25 PA26 PA27 PB12                       PB25 PB27 PB28

Claims (8)

[Claims] 1. A transfer current control means for applying a predetermined current to a transfer means when a sheet passes, wherein the predetermined current is applied when a leading end region of the sheet in the transport direction passes the transfer means. Image formation, characterized in that it includes a corresponding first current and a corresponding second current when the remaining area of the sheet passes through the transfer means, the first current being smaller than the second current. apparatus. 2. The transfer current control means according to claim 1, wherein the predetermined current is the first current and the second current, provided that a sheet on which an image has been fixed at least once passes through the transfer means. An image forming apparatus using a current of 2. 3. The method according to claim 1, wherein at least one of the first and second currents is set in accordance with at least one of humidity of an environment where the image forming apparatus is placed, paper size, and paper type. An image forming apparatus comprising a correction unit for correcting. 4. A separation voltage control means for applying a predetermined separation voltage to the separation means when a sheet passes through, wherein the predetermined separation voltage is obtained by adding a predetermined shift bias to a predetermined AC voltage. The predetermined shift bias corresponds to the first shift bias corresponding to the leading end area of the sheet in the transport direction passing through the separating means and the second shift bias corresponding to the remaining area of the sheet passing through the separating means. And the first shift bias has a higher voltage than the second shift bias. 5. The method according to claim 4, wherein at least one of the first and second shift biases is corrected according to at least one of humidity of an environment in which the image forming apparatus is placed, paper size, and paper type. An image forming apparatus, comprising: 6. The separation voltage control means according to claim 4, wherein the separation voltage control means determines that the predetermined separation voltage is reached when the leading end of the paper in the paper conveyance direction reaches a conveyance means adjacent downstream of the separation means in the paper conveyance direction. Alternatively, the image forming apparatus includes a cut-off mode that makes the shift bias zero. 7. The control unit according to claim 6, further comprising a control unit for inputting a signal from the operation panel and outputting the signal to the separation voltage control unit, the control unit being in a cutoff mode by an operation of a user or a serviceman. An image forming apparatus comprising means for setting. 8. The cutoff mode according to claim 6, wherein the separation voltage control means sets the cutoff mode in accordance with at least one of humidity of an environment in which the image forming apparatus is placed, paper size, and paper type. An image forming apparatus characterized by.