JP2780043B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Industrial Application Field) The present invention relates to an image forming apparatus using an electrostatic transfer process, such as an electrostatic transfer machine and the same printer.

(Problems to be Solved with Conventional Technique) An image carrier and a transfer unit that comes into contact with the image carrier, such as a transfer roller and a transfer belt, which come into contact with the image carrier, are provided at a transfer portion formed as a nip portion between the two. A known image forming apparatus includes a step of inserting a transfer material such as paper, applying a transfer bias to the transfer means, and transferring the toner image on the image carrier to the transfer material. It is known that there are a constant current control method and a constant current control method as the transfer bias for causing the transfer bias.

However, in this type of apparatus, since the transfer means is in contact with the image carrier, and the resistance value of the transfer means greatly changes depending on the environment, the following disadvantages were unavoidable.

That is, when performing the constant voltage control, the normal temperature and the normal humidity (23
℃, 60% RH: below N / N) Even if the appropriate transfer bias value is selected, low temperature and low humidity (15 ℃, 10% RH: below L)
(/ L) environment, the resistance of the transfer roller or the like as the transfer means is increased, so that sufficient charge cannot be applied to the transfer material, resulting in poor transfer.

Further, in an environment of high temperature and high humidity (32 ° C., 85% RH: hereinafter referred to as “H / H”), the resistance of the transfer means is reduced and an excessive bias is applied, so that the image quality is inevitably deteriorated.

When constant current control is performed, a fixed amount of electric charge can be applied to the transfer material without being affected by fluctuations in the resistance of the transfer unit due to the environment.For example, by setting an appropriate current in an N / N environment However, if a small transfer material such as a postcard is used in an L / L environment, most of the current will flow through the non-paper passing area where the image carrier and the transfer means are in direct contact. , And a problem such as occurrence of transfer failure occurs.

The present invention has been made to cope with such a situation, and in an image forming apparatus using a contact-type transfer unit such as a transfer roller, a transfer material exists between the transfer unit and the image carrier. When the transfer is not performed, a bias having the same polarity as that of charging the image carrier is applied to the transfer unit, and a transfer bias at the time of passing the next transfer material is set based on the bias. It is an object of the present invention to provide an image forming apparatus capable of always performing good transfer stably without being affected by the change of the image forming apparatus.

(2) Configuration of the Invention (Technical Means for Solving the Problems, Action of the Invention) In order to achieve the above object, the present invention provides an image carrier,
An image forming unit for forming an image on the image carrier, an image forming unit including a charging unit for charging the image carrier, and a transfer member for forming a nip between the image carrier and the nip, A transfer member for transferring the image of the image carrier to the transfer material sent to the transfer unit, and a voltage applied to the transfer member when transferring the image to the transfer material has a polarity opposite to the charging polarity of the charging unit. In one image forming apparatus, when the transfer material is not present in the nip portion, the transfer member performs constant current control,
A constant voltage control is performed on the transfer member when transferring an image to a transfer material at a voltage corresponding to a voltage applied to the transfer member during the constant current control, and a voltage applied to the transfer member during the constant current control Is an image forming apparatus (1) having the same polarity as the charging polarity of the charging means, or an image carrier, and image forming means for forming an image on the image carrier, An image forming unit including a charging unit that charges a body, and a transfer member that forms a nip portion with the image carrier, and a transfer member that transfers an image of the image carrier to a transfer material sent to the nip portion Wherein the voltage applied to the transfer member at the time of image transfer to the transfer material is opposite in polarity to the charging polarity of the charging means, wherein the transfer is performed when the transfer material is not present in the nip portion. The first member
The second constant voltage control is performed on the transfer member at the time of transferring an image to a transfer material with a voltage corresponding to the current flowing through the transfer member during the first constant voltage control, and the first constant voltage control is performed. Wherein the voltage applied to the transfer member during the constant voltage control is the same polarity as the charging polarity of the charging means, or any of the above (1) or (2). In things
The image forming apparatus according to claim 3, wherein the transfer member is a rotating body, or the image forming apparatus according to (3), wherein the transfer member has a roller shape. ).

With this configuration, in an image forming apparatus provided with a contact-type transfer unit such as a transfer roller, stable transferability can be always obtained regardless of the environment.

(Explanation of Embodiment) FIG. 1 is a schematic side view of a main part showing a configuration of a laser beam printer suitable for applying the present invention. A rotating cylindrical image carrier (hereinafter referred to as a photoconductor) has a photosensitive layer made of an organic semiconductor on its surface, and the photosensitive layer is a primary charger 2.
To be uniformly negatively charged.

Next, the charged surface is irradiated with a laser beam 7 image-modulated by a laser scanner 5, and the potential of the irradiated portion is attenuated to form an electrostatic latent image.

Next, when the latent image reaches a developing site facing the developing device 9, negatively charged toner is supplied from the developing device and adheres to the latent image portion to form a toner image.

Further, when the photosensitive member 1 rotates and this latent image reaches a transfer portion where the photosensitive member 1 and the chargeable transfer roller 2 come into contact with each other to form a transfer portion, the latent image is transferred to the transfer material at the same time. P is guided to the transfer site, and at the same time, a transfer bias is applied to the transfer roller 2 by the bias applying unit 4 to transfer the toner image on the photoconductor to the transfer material.

Thereafter, the transfer material is separated from the photoreceptor 1 and reaches a fixing portion (not shown). After the toner image is fixed and fixed to the transfer material, the transfer material is discharged outside the machine. The residual toner is eliminated by the cleaner 10 and the residual charge is eliminated by the pre-electrification lamp 8, so that the photoreceptor 1 is ready for the next step.

By the way, in the illustrated apparatus, the transfer roller 2 is obtained by dispersing carbon in EPDM on a core metal having a diameter of 8 mm,
A medium resistance material adjusted to a volume resistance of 10 ⁷ to 10 ¹⁰ Ωcm and a hardness of 25 to 30 ° (Asker C hardness) was formed to have an outer diameter of 20 mm.

However, as described above, this transfer roller is also susceptible to the effects of environmental humidity. Specifically, a 220 mm long roller is pressed against a conductive flat plate so as to have a nip width of 2 mm, and 1 KV is applied between the two. When the resistance value is measured by applying a voltage of approximately 10 ⁹ Ω under the L / L environment, approximately 4 × 10 ⁸ Ω under the N / N environment, H / H
Under the environment, it was found that the value greatly changed to approximately 5 to 10 × 10 ⁷ Ω.

Of course, this value slightly changes depending on the material, manufacturing method, and the like, but it is difficult to largely change the above-described characteristic change by such means.

The present embodiment has been achieved in view of such a situation. At the time of pre-rotation, a voltage having the same polarity as that of the primary charger 3 between adjacent transfer materials (referred to as a sheet interval) during continuous printing. Is applied to the transfer roller 2 and the resistance value of the roller is estimated based on the current value at that time, whereby the optimum bias voltage is applied at the time of the next sheet passing.

FIG. 2 shows the current-voltage characteristics between the photosensitive member 1 and the transfer roller 2 in each environment, and the figures A, B, and C are good under L / L, N / N, and H / H environments, respectively. Shows the range in which transferability can be obtained.

In this case, the current value when a negative voltage is applied to the transfer roller is small because the photosensitive member is previously negatively charged (usually -600 V
), And the photoreceptor and the transfer roller have some rectifying properties.

FIG. 3 shows the current value when a voltage of -3 KV is applied to the transfer roller on the horizontal axis, and the optimum transfer voltage value at the time of transfer for this value on the vertical axis.

That is, even if the resistance value of the transfer roller changes due to environmental fluctuations, an appropriate bias setting period is provided between sheets during pre-rotation, and a predetermined voltage having the same polarity as that of the charger is applied to the transfer roller. The optimum transfer bias can be set at the time of the next transfer depending on the value.

FIG. 4 is a schematic diagram of an apparatus which makes the above possible, in which the bias applying means 4 comprises a variable constant voltage power supply 13, a current source 14 and a controller unit 15, as shown in the timing chart of FIG. And the transfer roller 2 during the pre-rotation
A voltage of −3 KV is applied to the current, the current value at this time is obtained by the ammeter 14, a voltage corresponding thereto is obtained from FIG. 3, and this voltage is applied as a transfer bias at the time of the first transfer. I do.

The reading of the ammeter may be an average value in the entire region to which -3 KV is applied, or may be sampled in sections. In addition, in order to synchronize with the surface of the photoconductor, the transfer bias is switched by Δt from the laser exposure.

Similarly, -3 KV is also applied between the first and second sheets, and the transfer bias for the second sheet is determined from the current value at this time.

In this case, the voltage from the read current i _T the control unit
To determine the V _T, the linear operation circuit analog, V _T =
−i _T × α + β (α and β are constants), or may be calculated by a computer or by a lookup table.

According to the present invention, since a bias having the same polarity as that of the charger is applied between papers or the like, transfer memory does not occur. In particular, in a laser beam printer, it is common to perform APC control in which laser exposure is performed to control the amount of light to be constant between papers or the like. Light potential,
When the transfer roller attenuates the voltage to approximately -100 V and charges the portion with a positive potential, a transfer memory is more likely to occur than in a dark potential portion (approximately -600 V) where no exposure is performed. Deterioration of image quality such as fog and excessive density in a halftone portion can be prevented.

Of course, even when the APC control is not performed, it is needless to say that the effect of preventing the generation of the transfer memory is obtained.

Further, by applying a voltage having a polarity opposite to that at the time of transfer to the transfer roller, an effect of returning the toner adhered to the surface of the roller to the photoconductor occurs, that is, there is an effect of cleaning the transfer roller.

FIG. 6 is a timing chart showing another embodiment of the present invention.

Although the application of the present invention has already been described as having an effect of cleaning the toner adhered to the transfer roller, it is sufficiently possible that the transfer roller is extremely contaminated, particularly when a jam occurs. And
This embodiment is suitable for such a case.

As shown in the figure, after the main switch is turned on, the preparatory rotation is performed as appropriate, and at this time, the charger 3 is turned off, and the photoconductor surface potential is maintained at substantially zero potential (at this time, in synchronization with the main motor). It is preferable to turn on the pre-exposure lamp 8).

In addition, the preparatory rotation is started when the former roller of the fixing device including the roller having the normal heat source and the roller pressed against the former has reached an appropriate temperature, thereby heating the latter roller.

By applying a voltage of −3 KV to the transfer roller 2 at the start of the preparation rotation, the photosensitive member is in a non-charged state (almost
0V), the transfer roller can be effectively cleaned.

Next, the charge applied to the transfer roller is switched to +3 KV.
As a result, the reverse fog toner (the positively charged toner in this case) existing in the toner also transfers to the photoconductor 1, and the transfer roller surface is sufficiently cleaned.

In this process, the resistance value of the transfer roller may be estimated while the negative voltage is being applied to the transfer roller, and the optimum transfer voltage may be determined based on the estimated value.

In this case, since the surface of the photoconductor 1 is at zero potential,
The transfer current value when a negative voltage is applied to the transfer roller becomes larger than in the case of the above-described embodiment, and the estimation accuracy of the optimum transfer voltage is improved.

FIG. 7 shows still another embodiment of the present invention. In this apparatus, a bias applying means 16 to the transfer roller 2 is used.
Sets a constant voltage power supply 17 having a positive polarity, a constant current power supply 18 having a negative polarity, and a current value of the constant current power supply 18, and detects a voltage of the power supply 18, thereby detecting a voltage value of the constant voltage power supply 17. And a switch 20 for switching between the two power supplies.

When the power supply 18 is set so as to obtain a constant current of −10 μA, the voltage at this time varies from −3.5 KV to −2 KV depending on the environment according to the graph of FIG. In this case, the optimal voltage for the transfer is the hatched portion in the positive voltage region of FIG. 2, and varies between +3.7 and +1.7 KV depending on the environment.

 This is shown by the solid line D in FIG.

In the figure, the horizontal axis is the output voltage V _T1 (minus voltage) of the constant current power supply 18, and the vertical axis is the optimum transfer voltage estimated from this value.
V _T2 (positive voltage).

The dotted line E is an approximation line of the solid line D. If this is used, the controller 19 uses the output voltage V _T1 of the constant current power supply 18 to obtain V _T2 = −α × V _T1 (α is a constant ), The applied voltage of the constant voltage power supply 17 can be easily determined.

Detection timing of the V _T1, as shown in FIG. 8,
At the time of the pre-rotation, a constant current is applied between the sheets, the voltage at this time is detected and set as V _T1, and V _T2 is obtained as described above and applied at the next transfer.

As can be seen from FIG. 2, the optimal transfer bias value is the voltage
Although V _T changes considerably due to environmental changes, the current i _T
Are generally concentrated around 20 μA, in other words,
It can be said that the current value is more appropriate as a guideline for optimizing the transfer bias.

Therefore, it can be said that the method of setting the appropriate voltage by performing the constant current control as in this embodiment can obtain higher reliability.

Although the present invention has been described with reference to the embodiment using the transfer roller, the present invention is not limited to this, and it is needless to say that the present invention can be applied to a device using a transfer belt as a transfer unit. The charging means for the body is not limited to the corona discharger type, and it goes without saying that a charging roller, a contact type charging means, that is, a blade-shaped charging means can also be used.

In this case, when a direct current is superimposed on an alternating current and applied as a charging power source, the polarity of the charging means is that of the direct current.

(3) Effects of the Invention As described above, according to the present invention, in an image forming apparatus having an image carrier and a transfer member forming a nip portion, a voltage applied to the transfer member when no transfer material exists in the nip portion Is the same polarity as the charging polarity of the charging means for charging the image carrier, and by setting the transfer voltage accordingly, stable transferability is always obtained regardless of the environment, and a good quality image is obtained. Has a remarkable effect.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a main part of an image forming apparatus suitable for applying the present invention, FIG. 2 is a graph showing a difference in current-voltage characteristics due to a difference in environment, and FIG. FIG. 4 is a schematic diagram showing the configuration near the transfer site of the apparatus of FIG. 1, FIG. 5 is a timing chart showing the operation of the above, and FIG. 6 shows another embodiment. FIG. 7 is a schematic diagram showing a configuration in the vicinity of a transfer site showing still another embodiment, FIG. 8 is a timing chart showing the operation of the above, and FIG. 9 is a graph for explaining the operation of the above. It is. 1, photoreceptor, 2, transfer roller, 3, charger, 4,
16 ... bias applying means, 13 ... constant voltage power supply, 14 ... ammeter, 15, 19 ... controller, 17 ... constant voltage power supply, 19
.... Constant current power supply.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koichi Tanikawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yasumasa Otsuka 3-30-2, Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-2-123385 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 15/16

Claims (4)

(57) [Claims] An image forming means for forming an image on the image carrier, the image forming means including a charging means for charging the image carrier; and a nip portion provided with the image carrier. A transfer member for forming, the transfer member for transferring the image of the image carrier to the transfer material sent to the nip portion, the voltage applied to the transfer member at the time of image transfer to the transfer material is In the image forming apparatus having a polarity opposite to a charging polarity of the charging unit, a constant current control is performed on the transfer member when there is no transfer material in the nip portion, and a constant current is applied to the transfer member during the constant current control. A constant voltage control is performed on the transfer member when transferring an image to a transfer material with a voltage corresponding to a voltage, and a voltage applied to the transfer member during the constant current control is the same polarity as the charging polarity of the charging unit. An image forming apparatus comprising: 2. An image forming apparatus comprising: an image carrier; and an image forming unit for forming an image on the image carrier, the image forming unit including a charging unit for charging the image carrier. A transfer member for forming, the transfer member for transferring the image of the image carrier to the transfer material sent to the nip portion, the voltage applied to the transfer member at the time of image transfer to the transfer material is In the image forming apparatus having a polarity opposite to a charging polarity of the charging unit, a first constant voltage control is performed on the transfer member when no transfer material is present in the nip portion, and the first constant voltage control is performed during the first constant voltage control. A second constant voltage control is performed on the transfer member at the time of image transfer to a transfer material with a voltage corresponding to a current flowing through the transfer member, and the voltage applied to the transfer member during the first constant voltage control is the charge Image forming apparatus having the same polarity as the charging polarity of the means. Place. 3. An image forming apparatus according to claim 1, wherein said transfer member is a rotating body. 4. The image forming apparatus according to claim 3, wherein said transfer member has a roller shape.