JPH0511645A - Image forming device - Google Patents

Abstract

PURPOSE:To control a transfer bias applied to a transfer roller to a bias state for using by converging a voltage-current characteristic with respect to the image carrier of the transfer roller on one point set in advance on a voltage- current curve. CONSTITUTION:On the voltage-current characteristic curves with respect to a photosensitive drum on the transfer rollers 1-4 having prescribed resistance, a voltage applied to a transfer roller core metal, is gradually increased, and a current flowing into the photosensitive drum is detected. A point P that the detected current is intersected with a transfer bias setting line set in advance and expressed by Itau=f(V), is obtained, and the voltage value Vtau at this time, is held and applied when a transfer sheet passes. The resistance of the transfer roller is detected during a pre-/multi-rotation, and then, the accurate P-point is detected during a rotation before printing, to obtain the transfer bias Vtau, with algorithm for requiring the point P. Therefore, a bias for flowing a large amount of currents to the transfer roller having low resistance, and a small amount of the currents to the transfer roller having high resistance, can be set when a paper passes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a toner image or the like on an image bearing member such as a photoconductive photosensitive member, a dielectric member or a magnetic member by an appropriate image forming process means such as electrophotography, electrostatic recording or magnetic recording. Of a transferable image is formed and carried, and the transfer material is passed through a transfer site between the image carrier and a contact transfer means such as a roller body or a belt body which is brought into contact with the image carrier to apply a transfer bias to the image carrier side. The present invention relates to a transfer type image forming apparatus such as a copying machine or a printer, which transfers a transferable image to a transfer material side to obtain an image formed product.

[0002]

2. Description of the Related Art In an image forming apparatus having a contact type transfer means, a transfer bias applied to the transfer means is usually controlled by a constant voltage or a constant current.

A transfer roller or the like used as the contact transfer means is usually one in which conductive particles are dispersed in rubber and the volume resistance is appropriately adjusted, but this kind of material is well known. Since the resistance value changes over several digits depending on the environment, it is difficult to always apply a stable transfer bias regardless of the environment.

[0004] To briefly describe this, when a transfer bias is set appropriately in a normal temperature and normal humidity environment (23 ° C, 60% RH, hereinafter referred to as N / N environment), a low temperature and low humidity environment (15 ° C, 10%). In RH (hereinafter, referred to as L / L environment), a transfer failure occurs because the resistance value of the transfer unit / transfer material is large. On the contrary, high temperature and high humidity environment (32
At 85 ° C., 85% RH, hereinafter referred to as H / H environment), the resistance value of the transfer means becomes small, so that an excessive bias is applied, and the excessive charge generated by this causes punch-through of the transfer material. As a part of the toner as the transfer bias is converted to the same polarity as the transfer bias and does not transfer to the transfer material, a transfer omission occurs, or an excessive current flows into the image bearing member (hereinafter referred to as a photoconductor drum) to transfer memory. Or occur.

On the other hand, the constant current control eliminates the above-mentioned inconvenience caused by the change in the resistance of the transfer means, and can secure the amount of electric charge required for continuous transfer. However, this type of image forming apparatus is large or small. Since various transfer materials can be used normally, when a small-sized transfer material is used, naturally, there is an area where the image carrier and the transfer means come into direct contact with each other. Therefore, if this direct contact area is large, most of the current will flow through this area, and especially under the L / L environment, the transfer charge will be insufficient and transfer failure will occur.

In order to avoid the above-mentioned inconvenience, constant current control is performed when the transfer material is not present at the transfer portion, and the voltage at this time is held, and when the paper is passed, the voltage is fixed at this voltage. A control method for controlling voltage (Active Transfer Voltage)
Control (hereinafter referred to as ATVC method) has been proposed (Japanese Patent Application No. 1-85189, etc.).

More specifically, a constant current is passed through the dark potential (V _D portion) of the photosensitive drum, the generated voltage is monitored, and the voltage is changed to. 1x ,. Coefficient times ,. Apply a constant voltage ,. In addition, the applied bias is controlled by performing other combinations, etc., and has a certain effect in preventing the occurrence of transferability variations due to environmental changes and transfer material size differences.

[0008]

However, the contact transfer means has the following drawbacks.

That is, the relationship between the current flowing through the photosensitive drum and the current flowing through the transfer material differs depending on the resistance value of the contact transfer means. FIG. 10 shows a voltage-current characteristic curve (VT characteristic) when the transfer roller is used as the contact transfer means when the paper is not passed and when the paper is passed. The low resistance transfer roller a and the high resistance transfer roller are shown. For b and V, the VI characteristics are shown when the sheet is not passed (to the photosensitive drum) and when the sheet is passed (to the transfer material + photosensitive drum). The solid line graph shows the characteristics when the paper is not passed, and the broken line graph shows the characteristics when the paper is passed.

That is, FIG. 10 shows VI with or without transfer material.
It shows that the characteristics are very different. Therefore, the contact transfer means such as a transfer roller has a drawback that it is directly vulnerable to fluctuations in the load impedance with respect to the photosensitive drum, such as the presence or absence of a transfer material and the transfer of small size paper.

Therefore, in order to set the transfer bias, it is necessary to consider the fluctuation of the load impedance. Specifically, it is required to control the current flowing through the transfer material to be constant regardless of the resistance of the transfer unit. When actually controlling the transfer bias, it is thought that constant current will always flow if constant current control is performed, but the drawback of constant current control is that when small size paper arrives, it is not the transfer material but the surface of the photoconductor with a small load impedance. A large amount of current flows into this, resulting in a transfer failure.

In the ATVC method, a current is made to flow on the photosensitive drum on the transfer material, the resistance of the contact transfer means is detected from the generated voltage, and the current flowing at the time of transfer is estimated and applied. There is a problem that the accuracy is low because the current value to be applied is one value. In addition, since the resistance of the contact transfer means actually has voltage dependence, it is not possible to make a sufficient estimation with the ATVC method. Therefore, when the resistance of the contact transfer means changes due to aging due to long-term use, environmental change, and voltage dependence, sufficient control cannot be performed and transfer failure is likely to occur.

According to the present invention, the transfer bias applied to the contact transfer means is varied during the manufacture of the resistance value of the contact charging means.
The purpose is to always be able to obtain good transferability regardless of environmental changes, etc. by always controlling the bias state that is most suitable for use by sufficiently responding to environmental changes, durability changes, and voltage changes. And

[0014]

The present invention is an image forming apparatus having the following configuration.

(1) A transferable image is formed and carried on the image carrier by the image forming process means, and a transfer material is passed between the image carrier and the contact transfer means to which a transfer bias is applied. In a transfer type image forming apparatus for transferring a transferable image on the image carrier side to a transfer material side, the voltage-current characteristic of the contact transfer means with respect to the image carrier is set to one point on a preset voltage-current curve. An image forming apparatus having a converging unit.

(2) The converging means uses the voltage-current characteristics of the contact transfer means with respect to the image carrier,
The image forming apparatus according to (1), characterized in that the image forming apparatus is divided into two modes, a rough adjustment and a fine adjustment.

(3) The image forming apparatus according to (1) or (2), wherein the preset voltage-current characteristic is a function of voltage and current.

[0018]

In other words, in the image forming sequence of the image forming apparatus,
For example, before the transfer operation, the intersection point of the voltage-current characteristic curve of the contact transfer means with respect to the image carrier and the transfer bias setting line represented by the preset relational expression of voltage and current is obtained, and the voltage at that time is passed through. By applying to the transfer material at the time of paper or by performing different measurement modes for measuring the resistance value of the contact transfer means a plurality of times before the transfer operation, the contact bias near the transfer bias finally applied to the contact transfer means is performed. By applying the transfer bias after obtaining the voltage-current characteristics, the contact transfer means having a relatively low resistance is applied with a bias such that a large current is caused to flow to the contact transfer means having a relatively low resistance when the contact transfer means having a relatively high resistance is applied. It is possible to set a bias such that a small amount of electric current flows when the paper is not passed when the paper is not passed.

As a result, when the transfer material is fed, almost the same amount of current always flows into the transfer material regardless of the resistance value state of the contact transfer means. High transfer efficiency and good transferability are always ensured without being affected by aging due to use, environmental changes, voltage changes, and the like.

In other words, it becomes possible to realize the transfer bias control which sufficiently copes with the manufacturing variation of the resistance value of the contact transfer means, the environmental variation / durability variation, and the voltage variation, and the L / L environment, the H / H environment, etc. Transfer failure can be solved and the transfer bias can be controlled to the bias most suitable for use of the transfer means, so that the latitude (margin) of the resistance value of the transfer means is widened, the yield at the time of manufacturing the transfer means is improved, and the cost is reduced. As a result, good transferability can be obtained in a wider resistance value range than before.

[0021]

【Example】

<Example 1> (Figs. 1 to 5) (1) Example of image forming apparatus Fig. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a laser printer using an electrophotographic process.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image bearing member. The photoconductor drum of this example is formed by forming an OPC photoconductor layer (organic photoconductor layer) on the outer peripheral surface of a conductive drum substrate such as Al. The process speed (circumferential direction) is 50 mm / sec in the clockwise direction indicated by the arrow. It is driven to rotate at a speed), and the maximum throughput of the printer is 8 sheets of A4 size.

Reference numeral 2 denotes a primary charging roller as a charging processing means for the photosensitive drum 1, which is brought into pressure contact with the photosensitive drum 1 with a predetermined pressing force and rotates following the rotation of the photosensitive drum 1. A bias voltage is applied to the charging roller 2 from the power source 3 to uniformly negatively charge the peripheral surface of the rotating photosensitive drum 1. The power supply 3 is subjected to constant voltage control / constant current control by the DC controller 10 having a CPU via the AD converter 9a and the DA converter 9b.

Scanning is performed by a laser beam 4 which is image-modulated and output from a laser scanner (not shown) corresponding to target image information on the surface of the rotary photosensitive drum 1 which is uniformly negatively charged by the charging roller 2. Upon exposure, the potential of the scanning exposed portion is attenuated and an electrostatic latent image corresponding to the target image information is formed on the surface of the rotary photosensitive drum 1. The electrostatic latent image is developed as a toner image by the negative toner of the reversal developing device 5.

Then, the toner image is transferred from a paper feeding unit (not shown) to a transfer portion between the photosensitive drum 1 and a transfer roller 6 as a contact transfer means through a conveying path 7 at the same timing as the rotation of the photosensitive drum 1. The transfer material P that has been fed is sequentially transferred. The transfer roller 6 is brought into pressure contact with the photosensitive drum 1 with a predetermined pressing force, is rotated in the forward direction of the rotation of the photosensitive drum 1 at substantially the same peripheral speed as the photosensitive drum 1, and the power source 3 The transfer bias is applied from.

The transfer material P that has passed through the transfer portion is sequentially separated from the rotary photosensitive drum 1 and conveyed to a fixing device (not shown) to be subjected to a fixing process of a transfer toner image.

The surface of the photosensitive drum 1 after the transfer of the toner image to the transfer material P is cleaned by a cleaner 8 to remove adhering residual contaminants such as transfer residual toner, and is repeatedly used for image formation.

The material of the transfer roller 6 as the contact transfer means used in this embodiment is urethane rubber, silicone rubber, EPR (ethylene propylene rubber), EPDM (terpolymer of ethylene propylene diene), IR (isoprene). Although a rubber material such as rubber) is used, EPDM is used in this embodiment. Examples of the conductive material dispersed in EPDM include carbon, zinc oxide, tin oxide, and the like. In this example, zinc oxide having a relatively high specific resistance was used. Then, EPDM in which zinc oxide is dispersed is foamed and formed in a roller shape with a thickness of 6 mm on a core metal 6a made of SUS φ8,
The foamed EPDM transfer roller 6 having an outer diameter of φ20 was used.

The resistance value of the transfer roller is determined from the relationship between the current measured under a load of about 300 g and a peripheral speed of about 50 mm / sec with respect to the ground, and a voltage of 1.0 KV. When the resistance value was measured, it was about 5 × 10 ^{7 to} 5 ×
Lot variation occurred at 10 ⁹ Ω. The primary charging potential on the photosensitive drum 1 is a dark potential V _D = −600V and an exposure potential (bright potential) V _L = −100V.

(2) Transfer Bias Control Method FIG. 2 shows each VI of the transfer rollers 1 to 4 having the following resistance values.
It is a characteristic curve. The measuring method of the resistance value is the above-mentioned measuring method.

Roller 1 = 3.0 × 10 ⁸ Ω Roller 2 = 5.5 × 10 ⁸ Ω Roller 3 = 1.1 × 10 ⁹ Ω Roller 4 = 3.0 × 10 ⁹ Ω The features of the present invention are mainly Since the transfer bias is set, the present embodiment will be described with reference to FIG. FIG. 2 shows VI characteristics of the rollers 1 to 4 with respect to the dark potential V _D portion on the photosensitive drum 1.

In the present embodiment, the voltage applied to the transfer roller core metal 6a is gradually increased in a digital or analog manner to detect the current flowing into the photosensitive drum 1. In other words, the resistance of the transfer roller 6 is being measured. Then, a point P that overlaps with a transfer bias setting line represented by I _T = f (V) set in advance by an experiment or the like is obtained, and the voltage value V _T at that time is held,
It is adapted to be applied when the transfer paper is passed. In this embodiment, the first-order function of I _T = −1.69V _T +7.29 is used. V _T is KV and I _T is a unit of μA.

There are many algorithms for obtaining the point P, and an example thereof is shown in FIG. In the laser printer used in this embodiment, after the power is turned on, the fixing device is first heated, and the drive of the photosensitive drum 1 is started several seconds before the end of the warm-up. This is to clean the surface of the photosensitive drum 1,
This is a sequence called "pre-multi-rotation", which is performed for the purpose of making the surface potential uniform.

The feature of this embodiment is that, in the transfer bias setting mode, the approximate resistance value of the transfer roller 6 is detected during this pre-multi-rotation (measurement mode 1: rough adjustment), and then during the pre-printing rotation, it is almost accurate. Detect point P (measurement mode 2:
Fine adjustment), the transfer bias V _T is to be obtained.

This will be described with reference to FIG.
In FIG. 3, sequences other than transfer, such as primary charging and developing bias, are omitted. As described above, the front multi-rotation starts before and after the fixing roller 6 is ready. At this time, the photosensitive drum 1 is prepared for printing and the primary charging by the charging roller 2 is performed.

A voltage of V _t = V ₀ is initially applied to the transfer roller 6 in order to carry out the above sequence. Here, V ₀ = 1 KV. The value of V ₀ is the transfer bias V
_It is preferable to be high in order to shorten the convergence time to _T , but considering the occurrence of overcurrent due to the use of a low resistance transfer roller, 0.8 to 1.2 KV is desirable. V
_t = current to V ₀ is applied from the transfer roller 6 to the photosensitive drum 1 is Iriryu, but compared to sample the current value I _t at that time and the transfer bias setting on line f (V _T).

The above sampling time does not have to cover one round of the transfer roller because this sequence is rough adjustment.
Considering the convergence time to V _T , the transfer roller 1/8
The circumference is about 1/4 circumference (0.15-0.25 sec). Then, the sampling error ΔI set in advance
₁ consideration was compared to the conditional expressions 1 f (V _T) - was set to increase the _{△ I 1 ≦ I t ≦ f} (V t) + △ applied voltage to satisfy I ₁ only △ V. Here, ΔI ₁ was 0.5 μA and ΔV was 200V. Sequentially voltage increases holds until reaching the pre-rotation hold a temporary V _t at the stage that satisfies the above conditions.

Since the pre-multi-rotation is also a sequence for automatically ejecting the paper after the jam, for example, the time for ejecting the transfer material P to the outside of the machine is set to be executed. Therefore, there is sufficient time to execute the above sequence. Even in the roller 4 which seems to take the longest time in this embodiment,
It was possible to obtain the final V _t within 0 seconds.

Next, the pre-rotation process during printing will be described. In the processing during the above-described pre-multi-rotation, V _t that flows a current I _t (FIG. 2) close to I _T on the transfer bias setting line
Therefore, the accuracy of the current value is further increased during the pre-rotation.

Conditional expression 2 during pre-rotation in FIG. 3 is for that purpose. When the V _t obtained during the pre-multi-rotation is applied over the entire circumference of the roller during the pre-rotation, there are many cases where the transfer roller 6 has circumferential irregularity and the current value fluctuates in the circumferential direction. Therefore I _t is _{f (V T) - △ I} 1 ≦ I t ≦ f (V t) + △ might be slightly deviated from the condition that I _1. Conditional expression 2 during the pre-rotation is set in consideration of that fact. Here, the current value I _T for setting the transfer bias is controlled with a margin of ΔI ₂ = 0.2 μA.

The applied voltage V _t is adjusted until the conditional expression is satisfied, and it branches in the directions of 1, 2, and 3 in the figure according to the judgment result, and when the condition is satisfied, V _t is the transfer bias V _T.
Is set as. Sampling at the applied voltage V _t during the pre-rotation is performed for a time period (0.6 to 1.2 sec) from the half circumference of the roller to the entire circumference in order to improve accuracy.
Be thus set a relatively long time to think, because starting from I _t is a value close to I _T, it is converged in a short time. In this experiment, when the rollers 1 to 4 were used and tested, they converged within 3 to 4 seconds.

Next, how the transfer bias setting line I _T = f (V _T ) used in this embodiment is obtained will be described. In the laser printer used in this example, how much current was applied to the transfer material P to obtain good print with high transfer efficiency was sought. FIG. 4 is a graph showing the relationship between the paper passing current (transfer current) and the transfer efficiency η when the resistance value of the transfer roller 6 is changed. The environment was N / N environment, the transfer material was 75 g / m ² paper (4024 manufactured by XEROX), and the transfer efficiency was measured by using a reflection densitometer.

From FIG. 4, in the laser printer used in this embodiment, there is a peak of transfer efficiency at a current of about 1.5 to 3.0 μA when the paper is passed. Regardless of the resistance of the transfer roller, the peak position is the same.
This proves that the transfer efficiency does not depend on the difference in resistance value or the applied voltage, but depends on the amount of current flowing through the transfer material.

Next, the current flowing through the dark potential V _D when a voltage which is the difference in the resistance of the transfer roller is applied, and the same voltage is applied to the transfer material after passing the paper to obtain the transfer efficiency at that time. I asked how it would change.

FIG. 5 shows the relationship between the current flowing in the dark potential V _D portion and the transfer efficiency η. In this graph, the transfer efficiency peaks of the rollers 1 and 4 deviate from each other. This is
As described above, in the roller 4 having a relatively high resistance, whether or not there is a transfer material between the transfer roller and the photosensitive drum, the resistance of the roller itself is dominant, so that the current flowing into the photosensitive drum is It becomes almost constant. Therefore, the peaks of the transfer efficiencies almost coincide with each other, as can be seen by paying attention to the roller 4 in the current graph when the paper is passed (FIG. 4) and the current graph when the paper is not passed (FIG. 5). It can be seen that the peak is at 1.5 to 3.0 μA.

On the contrary, in the case of a roller having a low resistance such as the roller 1, the resistance of the transfer material becomes more effective than the resistance of the roller itself, so that the current when the paper is not passed (I) at the same voltage. _VD ) becomes large. Therefore, in order to pass a current of 1.5 to 3.0 μA at which the transfer efficiency reaches a peak during sheet passing, it is necessary to apply a voltage such that a current of 4.0 to 6.0 μA flows to the non-sheet passing portion. I understand. In order to always keep the transfer efficiency at the peak regardless of the resistance of the transfer roller, it is desirable to perform constant current control with a transfer current of 1.5 to 3.0 μA when the paper is passed.

However, when the contact transfer means such as a transfer roller is controlled with a constant current, as described above, when transferring a small size paper, a larger current flows into the photosensitive member side than the transfer material, which causes a voltage drop. Occurs, which causes insufficient transfer of charges to the back surface of the transfer material, resulting in transfer failure. Therefore, it can be said that a stable transferred image cannot be obtained unless constant voltage control is performed during transfer. The function I _T = f (V _T ) takes the above-mentioned characteristics into consideration, and when a low resistance transfer roller is used, the current flowing to the dark potential V _D portion is relatively increased, and a high resistance roller is used. Sometimes it is set to be relatively small. By setting in this way, the value of the current flowing through the transfer material can be accurately controlled regardless of the resistance of the transfer roller used.

The reason why the rough adjustment is divided into the pre-multi-rotation and the fine adjustment is divided into the pre-rotation in this embodiment is that the pre-multi-rotation mode is executed only when the power is turned on. Resistance detection will be performed in an environment that can be said to be said. If the room temperature, humidity, etc. change every moment in the office, the transfer conditions may change, and the conditions may deviate from the one in the morning. In such a case, better transferability can be obtained by performing fine adjustment in the pre-rotation mode performed before the printing operation to set the bias.

In the laser printer of this embodiment, rollers 1 to 1 are used.
When each transfer roller of No. 4 was used and the above-mentioned control was performed and a long-term durability test, an environmental test, etc. were carried out, even if the resistance fluctuation of the roller itself occurs, the transfer bias which is always considered to be optimum can be obtained by the above-mentioned sequence. Therefore, no transfer failure occurred, and the transfer roller can be used in a wide resistance range.

<Embodiment 2> (FIGS. 6 and 7) FIG. 6 shows a schematic diagram of a control system according to a second embodiment of the present invention. The feature of this embodiment is that the transfer bias setting line V _T =
As a method of obtaining a fulcrum P between g (I _T ) and the VI characteristic of the transfer roller, the current I _T flowing into the photosensitive drum is variable.

In the voltage variable method described in the first embodiment, when the transfer roller having extremely low resistance is used,
Even at a relatively low voltage of 0 KV, an excessive current may flow into the photosensitive drum. In such a case, the photosensitive member may be charged or charged with a charge having a polarity opposite to that of the temporary charging, and the photosensitive member may be damaged. When this reverse charging cannot be recovered by the temporary charging of the next stage, it may be developed in the developing process and may cause a bad image as fog in the next printing.

In this embodiment, in order to avoid the above danger,
The current is changed within a practically useful transfer current range to detect the intersection point P.

Further, as described in the first embodiment, since there is a condition that a good transfer property can be obtained in a region where the transfer material sheet passing current is 1.5 to 3.0 μA, the minimum of the photoconductor inflow current I _T is 1. It was set to 5 μA. I _T was changed by setting the line of 1.5 μA as the lower limit line and the line of current amount 5 μA that does not damage the photosensitive drum as the upper limit line. The current value of 5 μA is the process speed,
The value is determined by the photosensitive material, and this value is the upper limit in the laser printer used in this embodiment. The direction for changing I _T is 1.5 → 5.0 μA, but 5.0 → 1.
Either 5 μA or either may be used, but in the present embodiment, it is 5.0 μA.
It was made to change gradually from μA.

FIG. 7 shows an example of the algorithm of this embodiment. Also in this embodiment, as in the first embodiment, a voltage is applied by detecting a substantially accurate resistance value as fine adjustment (measurement mode 2) during the previous multi-rotation.

[0055] transfer bias setting line V _T used in this Example V _T [KV], V in units of I _T [μA] _{T = g (I T) =} - a 0.59I _T +4.31.

During the pre-multi-rotation of FIG. 7, the detection current I _T is set to I _to = 5.0 μA and is decreased in steps of ΔI ₁ = 0.3 μA to obtain the generated voltage V _T. V _T is obtained by sampling and averaging one-fourth round of the roller. V
_T conditional expression _{1 g (I T) -ΔV 1} ≦ V T ≦ g (I T) + ΔV 1 (ΔV 1 = 250V) was roller one round sample with a current I _T at that time Once satisfied, the generated voltage V the next by averaging the _T held as V _ta, at the time of actual printing, the pre-rotation is determined by the condition 2 in rotation before the V _ta set to destination starts, when no match is again current I _T In order to change, the control is branched into 1 or 3 and fine adjustment is performed. Here, ΔI ₂ = 0.1 μA
The current is changed in steps, and one round of the roller is sampled by I _T to obtain V _ta .

When the conditional expression is satisfied, V _ta is directly applied to the transfer roller as the transfer bias V _T.

When the current I _T is below the 1.5 μA line, I _T = 1.5 μA is automatically set to obtain V _ta and become the transfer bias V _T.

Even when the current value was varied as in this example, the transfer bias V _T was set within a time period substantially equal to that in Example 1, and the same effect was obtained. In addition, since the current control is performed, there is no risk of damaging the photoconductor drum, and thus highly reliable control is possible.

<Embodiment 3> (FIGS. 8 and 9) As a third embodiment of the present invention, a case having a mode for cleaning the contact transfer means during the pre-multi-rotation will be described.

A laser printer or the like having a contact transfer means usually has a cleaning mode in consideration of the case where the transfer means is contaminated with toner when jammed. The cleaning mode is mainly performed at the time of drum rotation called post-rotation after completion of printing, and a bias having the same polarity as toner is usually applied to the contact transfer means. In addition, in the case of a jam, it is often performed during the pre-multi revolution in consideration of turning off the power of the main body once and restarting.

In such a case, for example, if the cleaning mode is performed and then the measurement mode 1 (coarse adjustment) as described in Embodiments 1 and 2 is performed, or the cleaning mode is performed after the measurement mode 1 is performed. If this happens, the front multi-rotation will take a very long time, and the wait time may take a long time.

In this embodiment, in order to avoid such a problem, the cleaning mode and the measurement mode 1 are simultaneously performed. This is possible because the discharge characteristics of the contact transfer means have almost no difference between positive and negative bias.

The laser printer shown in FIG. 1 has a cleaning mode in which a bias of -1.5 KV is applied to the transfer roller core metal 6a for 4 seconds.

The bias and time of the cleaning mode have an effect on the cleaning property as independent factors. If the bias is high, the cleaning will be completed in a short time, but if it is too high, the toner may be reversely charged and the cleaning may not be sufficiently performed. On the other hand, if it is too low, the amount of toner remaining on the transfer roller increases, and the toner is transferred to the back surface of the transfer material at the time of the next printing, causing a problem such as transfer back stain. A longer cleaning time is better, but a long cleaning time affects the above-mentioned throughput,
If it is too short, it is likely to cause transfer stain on the back. Therefore, there is an appropriate bias and time, and in this experiment -1.5K.
The cleaning mode such as V and 4 sec was the most efficient.

Next, the features of this embodiment will be described with reference to FIG. FIG. 8 shows the EPD described in the first and second embodiments.
5 is a VI characteristic curve of the M foam transfer roller with respect to the ground potential (OV) on the photosensitive drum. The line of I _T = f (V _T ) is the transfer bias setting line at this time, and is corrected so that a good bias can be obtained by controlling the transfer roller with the absolute value of the obtained V _T and I _T values. is there. The function of the corrected line _{I T = f (V T)} = 1.33V T -6.0 is (I _T [μA], V _T [KV]).

Therefore, even in the measurement mode 2, the control is performed with a negative bias, and finally the positive bias is converted into the transfer bias.

Next, the algorithm of this embodiment will be described with reference to FIG. In this embodiment, the applied voltage to the transfer roller core metal 6a is set to -2.0 KV, and I _t for one roller is sampled. At this point, most of the toner adhering to the transfer roller has retransferred onto the photosensitive drum. Even if I _t was sampled while the toner was attached to the transfer roller, and I _t was sampled when the toner was not attached, there was no significant difference in I _t . This is probably because when the toner is transferred to the drum by the electric field, it is transferred at the same time as the charge. After that, this algorithm is repeated by changing V _t with ΔV = 200 V until the conditional expression is satisfied, but at the time when the conditional expression is satisfied, toner has not already adhered to the transfer roller. This is probably because most of the toner was transferred onto the drum when I _t was sampled in the vicinity of V ₀ because the desired set potential V _b was set to a high value of −2.0 KV. Sampling time for this time I _t is a one round of the roller 4 minutes. If the condition is satisfied, the value of V _t at that time is held.

Since the description of the measurement mode 2 (fine adjustment) is almost the same as that of the first embodiment, a part of the description is omitted here, but the transfer bias V _T is obtained by applying the obtained applied bias V _t to a positive value. Converting.

By carrying out the present invention in the cleaning mode during the pre-multi-rotation as in the present embodiment, the pre-multi-rotation becomes long and the wait time is not affected. Since the effects as described in 1) are obtained at the same time, stable transferability can always be obtained.

[0071]

As described above, according to the present invention, a transferable image is formed and carried on the image carrier by the image forming process means.
A transfer-type image forming apparatus that transfers a transferable image on the image carrier side to the transfer medium side by passing a transfer material between the image carrier and the contact transfer means that is in contact with the image carrier and applies a transfer bias It becomes possible to realize the transfer bias control sufficiently corresponding to the manufacturing variation of the resistance value of the transfer means, the environmental change / durability change, and the voltage change, and it is possible to realize the L / L environment and the H / H.
Transfer defects in the environment etc. are solved, and the transfer bias can be controlled to the bias most suitable for use of the transfer means, so the latitude (margin) of the resistance value of the transfer means is widened, and the yield at the time of manufacturing the transfer means is improved. In addition, the cost can be reduced, and good transferability can be obtained in a wider resistance value range than in the past.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus (laser printer) according to a first embodiment.

FIG. 2 is a VT characteristic graph for explaining the principle of the resistance measurement mode of the first embodiment device.

FIG. 3 is an algorithm of the first embodiment device.

FIG. 4 is a graph of current and transfer efficiency when the transfer material is passed.

FIG. 5 is a graph showing the relationship between the current flowing in the dark potential portion and the transfer efficiency.

FIG. 6 is a VT characteristic graph for explaining the principle of the resistance measurement mode of the second embodiment device.

FIG. 7 Algorithm of the second embodiment device

FIG. 8 is a VT characteristic graph for explaining the principle of the resistance measurement mode of the third embodiment device.

FIG. 9 Algorithm of the second embodiment device

FIG. 10 is a voltage-current characteristic curve (VT characteristic) when a transfer roller is used as the contact transfer means when the paper is not passed and when the paper is passed.

[Explanation of symbols]

1 Image carrier (photosensitive drum) 2 Contact transfer means (transfer roller) 3 Bias application power supply 4 laser light 5 Developer 6 Contact transfer means (transfer roller) 8 cleaner P transfer material DC controller with 10 CPUs 9a AD converter 9b DA converter

Claims (3)

[Claims] 1. A transferable image is formed and carried on an image carrier by an image forming process means, and a transfer material is passed between the image carrier and the contact transfer means to which a transfer bias is applied. In a transfer type image forming apparatus for transferring a transferable image on the image carrier side to a transfer material side, the voltage-current characteristic of the contact transfer means with respect to the image carrier is converged to one point on a preset voltage-current curve. An image forming apparatus comprising: 2. The converging means is means for using the voltage-current characteristics of the contact transfer means with respect to the image carrier, and is divided into two modes of rough adjustment and fine adjustment. 1. The image forming apparatus according to 1. 3. The preset voltage-current characteristic is a function of voltage and current.
Alternatively, the image forming apparatus described in 2 above.