JP2001051527A - Transfer controlling device for image forming device, and monitor processing device used for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely execute a transfer control so that uneven transfer may not occur in an image part at the leading end part of a transfer material, even for the transfer material having different resistance. SOLUTION: The device is provided with a current detecting means 5 for detecting a current flowing between an image carrier 1 and a contact transfer means 2, a current change monitor processing means 6 for monitoring the change in the current flowing between the image carrier 1 and the contact transfer means 2 in a monitoring section (k) before and after the leading end part of the transfer material 3 rushes into a nip area between the image carrier 1 and the contact transfer means 2 at the stage before the transfer bias is applied, and a transfer bias setting means 7 for setting the transfer bias to be applied between the image carrier 1 and the contact transfer means 2 based on information monitored by the means 6. Besides, a monitoring condition setting means 8 for setting the monitoring condition by the means 6 is added. Besides, the monitor processing device which is adaptable to the means 6 is intended.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged color material (toner, etc.) formed on an image carrier in a copying machine, a laser printer, or another image forming apparatus employing an electrophotographic system or an electrostatic recording system. Control device used when a visible image is transferred to a transfer material by an image forming apparatus, and in particular, an image forming apparatus effective in a mode including a contact transfer unit arranged in contact with an image carrier via a transfer material And a monitor processing device used for the same.

[0002]

2. Description of the Related Art As a conventional image forming apparatus, for example, an electrophotographic system will be described. An electrostatic latent image is formed on an image bearing drum such as a photosensitive drum, and the electrostatic latent image is developed. There is known a device in which a visualized image is formed (a toner image is formed) by a device, and then the visualized toner image is transferred to a sheet as a transfer material by a transfer device. As this type of transfer device, a non-contact type device such as a corotron, which is not in contact with the image bearing drum, may be used.However, due to the advantages of easy position adjustment and easy maintenance, the image bearing drum has In many cases, a contact-type device such as a transfer roll that is close enough to make contact or contact via paper is used. When the latter contact type transfer device is used, for example, a transfer bias is applied to the transfer roll, a transfer current flows between the transfer roll and the image bearing drum, and the toner image on the image bearing drum is transferred to the paper side. Is transferred to

Here, the transfer bias application method is roughly classified into a constant current control method for controlling the current to be constant and a constant voltage control method for controlling the voltage to be constant. At this time, the constant current control method can maintain an appropriate transfer voltage according to the sheet resistance when the sheet width is substantially the same as the transfer roll width, but the sheet width is smaller than the transfer roll width. When the transfer current is small (in the case of a small-size sheet), the transfer current escapes outside the sheet, and a desired transfer voltage cannot be obtained. Therefore, there is a problem that a transfer failure is easily caused. To solve this problem, specify the paper size and change the current value for each size (manual specification by the user), or detect the paper size and change the current value for each size (automatic correction). ), And in both cases,
A variable constant current control method in which the constant current is variably set.

On the other hand, the constant voltage control method has good adaptability to sheets of different sizes because the transfer current can be ensured even for small-size sheets. Transfer current cannot be maintained. To solve such a problem,
Specify high-resistance paper, change the transfer voltage (user manual specification), monitor the transfer current in the paper,
When the current is small, the transfer bias may be increased (automatic correction). In either case, the variable constant voltage control method is used.

[0005]

However, even when a variable constant voltage control method is employed as a transfer bias application method, in particular, a transfer failure to an image near the leading end of a sheet tends to occur. Challenges were found.
To explain this point in detail, transfer voltage (transfer bias)
The rise time varies because the load characteristics vary depending on the load and the like. Therefore, if the current is monitored during the rise of the transfer voltage, the voltage is unstable, and the monitored value is not reliable. Therefore, in order to detect the sheet resistance, it is necessary to monitor the current after the transfer voltage has risen. For this reason, when the high-resistance paper passes, as shown in FIG. 17, the voltage rise time t1 + transfer monitor time t2 + the voltage rise time t3 for correcting the high-resistance paper transfer voltage must be obtained before the appropriate transfer current is obtained. Is generated, and in the section M excluding the non-image area from this delay time, the transfer current is too small, resulting in poor transfer. In FIG. 17, the page gap voltage means a voltage applied between the image bearing drum and the transfer roll before the transfer voltage is applied, and the page gap current means the image bearing drum and the transfer roll when the page gap voltage is applied. Indicates the current flowing between them.

[0006] Under such circumstances, the transfer failure section is extremely small in a low-speed machine, so that the delay time is not particularly bothersome. However, in recent high-speed machines, the transfer failure area becomes large, so that the delay time cannot be ignored. In order to reduce the delay time, it is conceivable to reduce the voltage rise time and the monitor time. Here, if the voltage rise times t1 and t3 are to be shortened, the overshoot becomes large and a transfer memory is easily generated, and if this is to be suppressed, the cost increases. Further, as shown in FIG. 18, if the transfer voltage is raised before the paper arrives at the transfer roll in order to gain the rising portion of the transfer voltage, the area M1 before the paper reaches the transfer roll is obtained. The transfer current flows too much to the image bearing drum,
There is a concern that this may become a transfer memory. On the other hand, if a high-resistance paper transfer voltage is raised across the image area of the paper when the high-resistance paper passes, the transfer current is increased in the area M2 where the transfer voltage is rising. Is too small to cause transfer failure.

Further, if the monitor time t2 is to be shortened, the resistance of the paper may not be accurately determined, and the reliability may be impaired. That is, when the transfer current is monitored, it usually has periodicity as shown in FIG. This is due to the fact that the transfer roll and the image-carrying drum have resistance irregularities in the circumferential period. In many cases, the resistance unevenness of the transfer roll is larger than the resistance unevenness of the image bearing drum. Here, the description will be made assuming that the resistance unevenness of the transfer roll is dominant. Further, the resistance unevenness of the sheet is often smaller than the resistance unevenness of the transfer roll, and is assumed to be a constant here. In FIG. 19, the upper side (dotted line) is a current monitor for normal paper, and the lower side (solid line) is a current monitor for high-resistance paper. At this time, in order to detect a high-resistance sheet, an average resistance value cannot be obtained unless a monitor having a length equal to or longer than the transfer roll circumference is performed in section A, for example. If the section B is used to reduce the monitoring time, a significant difference may occur depending on whether the section is an X point or a Y point. In other words, it may be determined that the sheet is a high-resistance sheet even though it is a normal sheet, or that the sheet is a normal sheet even though the sheet is a high-resistance sheet. In this case, it cannot be said that high-resistance paper is judged.
Low reliability. In some cases, a transfer memory due to an excessively large transfer current may occur.

[0008] Such a technical problem can actually occur in the prior art as described below, for example. For example, in Japanese Patent Application Laid-Open No. 8-123211, when there is a sheet between an image carrier (corresponding to an image carrier drum) and a transfer member (corresponding to a transfer roll), a transfer current is monitored and a transfer voltage is corrected. Is described. In this prior art, in order to increase the reliability of discriminating special paper such as high-resistance paper, it is necessary to lengthen the current monitor section,
At the leading edge of the paper, the transfer voltage may not be corrected in time, resulting in poor transfer. Conversely, if the current monitor section is shortened,
The reliability of the special paper discrimination is low, and there is a risk of erroneous detection. Japanese Patent Application Laid-Open No. 8-314295 discloses a technique in which a transfer current is monitored outside the image area of a sheet and reflected on the image area. Also in this prior art, since the monitor section is short, there is a possibility of erroneous detection of special paper discrimination. In addition, it is described that the difference between the current monitor value inside the first sheet and the current monitor value outside the sheet is reflected on the second sheet. It is often used in the sheet mode, and it is difficult to accurately control the transfer current for a sheet in the single sheet mode in real time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and is intended to perform transfer control without causing uneven transfer to the leading end image area of a transfer material even for transfer materials having different resistances. An object of the present invention is to provide a transfer control device of an image forming apparatus that can be reliably realized and a monitor control device used for the transfer control device.

[0010]

That is, according to the present invention, as shown in FIGS. 1A and 1B, an image carrier 1 on which a visible image is formed and supported by a charged color material, and the image carrier 1 is provided. 1. A contact transfer unit 2 that is arranged in contact with a transfer material 3 via a transfer material 3 and transfers a visible image on an image carrier to the transfer material 3. A bias including at least a transfer bias between the image carrier 1 and the contact transfer unit 2 In an image forming apparatus provided with a bias applying unit 4 for applying a voltage, a current detecting unit 5 for detecting a current flowing between the image carrier 1 and the contact transfer unit 2, and a transfer bias is set using the current detecting unit 5. Before the application, the current flowing between the image carrier 1 and the contact transfer unit 2 in the monitor section k before and after the leading end of the transfer material 3 enters the nip area between the image carrier 1 and the contact transfer unit 2 Current change monitor processing means for monitoring change If this current change monitoring process means 6
And a transfer bias setting unit 7 for setting a transfer bias to be applied between the image carrier 1 and the contact transfer unit 2 based on the information monitored by the control unit.

In such technical means, the image carrier 1 may be an image carrier such as a photoreceptor, a dielectric, or the like, as long as the image carrier 1 forms and carries a visible image by a charged color material. The image forming carrier and the intermediate transfer body are arranged such that the intermediate transfer body is brought into contact with the image forming carrier, and the image on the image forming carrier is once transferred to the intermediate transfer body and then collectively transferred to a transfer material. May be combined. As for the contact transfer means 2, not only those contacting the image carrier 1 but also the image carrier 1 via the transfer material 3.
And those arranged close enough to make contact. Further, the bias applying unit 4 may be any unit which applies at least a transfer voltage (transfer bias) VTR. It is preferable that the bias voltage can be variably adjusted over a wide range, not limited to the variable range of the transfer voltage, so that the page gap voltage Vpg applied before the transfer material 3 reaches can be applied.

Further, the current detecting means 5 includes a means for directly detecting the current and a means for detecting a physical quantity (resistance or voltage) accompanying the current and indirectly detecting the current.
Further, the current change monitor processing means 6 includes a means for continuously monitoring a current change in addition to monitoring a current change at predetermined intervals. If the transfer bias setting means 7 has a requirement to set the transfer bias based on the monitor information from the current change monitor processing means 6, the transfer bias setting means 7 may be provided with other requirements, such as a standard transfer bias described later. This includes a temporary setting mode and a mode in which a confirmation mode is added to the transfer bias setting.

In order to improve the monitoring accuracy of the current change monitor processing means 6, the current change monitor processing means 6 needs to be provided before the transfer material 3 enters the nip region between the image carrier 1 and the contact transfer means 2. It is preferable to add monitor condition setting means 8 for setting monitor conditions. The “monitor condition” here mainly means a bias voltage (for example, a page gap voltage) applied by the bias applying unit 4 during the monitoring process, but is not limited thereto, and includes various conditions.

As a specific mode of the monitor condition setting means 8, for example, an initial current flowing between the image carrier 1 and the contact transfer means 2 in a state where a predetermined initial bias V 0 is applied by the bias applying means 4. Is monitored, and environmental conditions are estimated based on the initial current information to set the monitoring conditions by the current change monitor processing means 6. According to this aspect, it is possible to reduce the number of components by using the current detection means 5. Also,
As another specific mode, there is provided an apparatus having an environment detecting means for detecting an environmental condition, and setting a monitoring condition by the current change monitoring processing means 6 based on environment detecting information from the environment detecting means.

Further, from the viewpoint of improving the setting accuracy of the transfer bias, the transfer bias setting means 7 sets the image before the transfer material 3 enters the nip area between the image carrier 1 and the contact transfer means 2. The current flowing between the carrier 1 and the contact transfer means 2 is monitored, and a standard transfer bias is provisionally set based on the monitor information.
In which the final transfer bias is permanently set based on the monitor information according to the above. Furthermore, since the transfer condition changes for each environmental condition, as a mode for optimizing for each environmental condition, it is preferable that the transfer bias setting means 7 sets the transfer bias individually for each environmental condition. . For example, in the method of temporarily setting the standard transfer bias described above, the standard transfer bias may be temporarily set for each environmental condition, and then the final transfer bias may be permanently set. The environmental condition may be considered in at least one of the steps of finally setting the final transfer bias. Here, the “environmental condition” refers to monitoring an initial current flowing between the image carrier 1 and the contact transfer unit 2 in a state where a predetermined initial bias is applied by the bias applying unit 4. Widely include those that are estimated based on the information and those that are detected by the environment detection unit. Further, since the transfer conditions also change for each transfer material size, as a mode for optimizing for each transfer material size, the transfer bias setting means 7 sets the transfer bias individually for each transfer material size. Is preferred. For example, in the method of temporarily setting the standard transfer bias described above, it is only necessary to temporarily set the standard transfer bias for each transfer material size and then permanently set the final transfer bias. In this case, for example, After temporarily setting the standard transfer bias irrespective of the transfer material size, temporarily setting the standard transfer bias, such as a mode in which the final transfer bias is permanently set for each transfer material size, the final transfer bias The transfer material size condition may be considered in at least any one of the steps of the main setting.

Further, in the above-described method of temporarily setting the standard transfer bias, from the viewpoint of simplifying the processing when the transfer material 3 is a standard sheet, the transfer bias setting means 7 is provided with a current change monitoring processing means. The standard transfer bias may be changed under the condition that the difference of the current change due to 6 exceeds a predetermined threshold. As a simple method for setting the final transfer bias, for example, the transfer bias setting means 7 sets the standard transfer bias to a standard transfer bias by a constant multiple determined according to the difference in current change by the current change monitor processing means 6. What is necessary is just to set the final transfer bias by multiplication.

Further, for example, in a situation where the transfer material 3 partially contains water, if the transfer bias is once set, a transfer failure or the like may occur at a partially water-containing portion. There are concerns that will happen. In order to avoid such a situation effectively, the transfer bias setting unit 7 sets the transfer bias based on, for example, current change information from the current change monitor processing unit 6 and then sets the image carrier 1 and the contact transfer unit 2. Any method may be used as long as the current flowing therebetween is monitored and the transfer bias is changed based on the monitor current information under the condition that the monitor current exceeds a predetermined threshold value with respect to the transfer current by the set transfer bias.

Further, the present invention is directed to the transfer control device of the image forming apparatus shown in FIGS. 1A and 1B, but is applied to the current change monitor processing means 6 used in the transfer control device. The present invention is also applicable to a monitor processing device that is effective for a computer. Here, as a typical mode of the monitor processing apparatus according to the present invention, a physical quantity change (current change or the like) in a predetermined monitor section including a sudden physical quantity change point (corresponding to the edge of the transfer material 3) is determined. In a monitor processing apparatus that monitors a plurality of times at intervals, a change in physical quantity is calculated based on monitor values of remaining monitor points excluding a monitor point located near the physical quantity change point. In this embodiment, since monitor points near a sudden physical quantity change point are not used, unstable monitor values can be removed, which is preferable in that monitor accuracy can be improved accordingly.

Another aspect of the monitor processing apparatus according to the present invention is a monitor processing apparatus which monitors a physical quantity change in a predetermined monitor section including a sudden physical quantity change point a plurality of times at a predetermined interval. The monitor values of the monitor points are sequentially compared, and a physical quantity change is calculated based on each monitor value difference. According to this aspect, even if the sudden physical quantity change point itself is displaced, if the monitor interval is made sufficiently small, the displacement can be absorbed. Further, as a development of this method, the monitor values of the preceding and following monitor points are sequentially compared, and the monitor value difference between certain monitor points exceeds a predetermined threshold value, and
Under the condition that the monitor value difference between the next monitor points does not exceed the predetermined threshold value, the manner in which the physical quantity change is calculated, the monitor values of the preceding and following monitor points are sequentially compared, and each monitor value difference and a plurality of monitor value differences The physical quantity change is calculated by the sum of Here, the former advanced type is preferable in that erroneous detection due to noise can be prevented, and the latter advanced type is preferable in that it can cope with a situation where the monitor value changes gradually (for example, skew of the transfer material).

Next, the operation of the above technical means will be described. As shown in FIGS. 1 (a) and 1 (b), the current change monitor processing means 6 uses the current detecting means 5 to nip the image carrier 1 and the contact transfer means 2 before the transfer bias is applied. In a monitor section k before and after the leading end of the transfer material 3 enters the area, a change in current flowing between the image carrier 1 and the contact transfer means 2 is monitored. Then, the transfer bias setting means 7 determines the transfer bias VTR to be applied between the image carrier 1 and the contact transfer means 2 based on the information monitored by the current change monitor processing means 6 (for example, the difference ΔI of the monitor current).
Set. At this time, at the leading end of the transfer material 3, there is a delay time corresponding to the sum of the maximum time of about half of the monitor section k and the rising time t of the transfer bias VTR before the appropriate transfer current flows. Compared with the conventional method of monitoring the transfer current after the transfer bias is applied, there is no first rise at the time of the normal transfer bias application, and
Since there is no need to monitor over the circumferential period of the contact transfer means 2, the delay time itself can be kept very short. For this reason, even if the transfer material 3 has a high resistance, the transfer bias VTR
Is set within the leading end portion of the transfer material 3 that does not reach the image area, and accordingly, transfer failure in the leading end image area of the transfer material 3 cannot occur.

In the embodiment in which the monitor condition setting means 8 is added, it is possible to set monitor conditions (for example, the page gap voltage Vpg) in consideration of environmental conditions. The fluctuation component of the environmental condition and the like are excluded from the monitoring processing by (i.e., a wide monitoring width can be used), and the monitoring processing accuracy is improved accordingly.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings. FIG. 2 is an explanatory diagram showing an embodiment of an image forming apparatus (a printer in the present embodiment) to which the present invention is applied. In FIG.
Denotes a printer main body.
1, an image processing unit 12 that performs predetermined image processing on image information input from the outside, and outputs an image based on image information that has been subjected to predetermined image processing by the image processing unit 12 An image output unit 13 is provided. The image processing unit 12 in the printer body 11 reads image information sent from a host computer such as a personal computer (not shown), a communication line such as a telephone line or a LAN, or an image reading device (not shown). Image information or the like is input.

The image output unit 1 in the printer body 11
Reference numeral 3 denotes a ROS 14 for performing image exposure based on image information on which predetermined image processing has been performed by the image processing unit 12.
(Raster Output Scanner) is located.
In the OS 14, image exposure with the laser light LB is performed according to the image information. In the ROS 14, a laser beam LB is emitted from a semiconductor laser (not shown) according to gradation data of image information. The laser beam LB emitted from the semiconductor laser is deflected and scanned by the rotating polygon mirror 15, and is scanned on the photosensitive drum 18 as an image bearing drum via the reflection mirrors 16 and 17.

Here, as the photosensitive drum 18 on which the laser beam LB is scanned and exposed by the ROS 14, for example, a negatively charged photosensitive body using an organic photoconductive substance (OPC) is used. The photosensitive drum 18 is driven to rotate at a predetermined speed in a direction indicated by an arrow by driving means (not shown). This photosensitive drum 18
Is charged uniformly to a predetermined potential by the charging roll 19 in advance, and then a laser beam LB is scanned and exposed according to image information to form an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum 18 is developed by the developing device 20 to become a toner image. The toner image formed on the photosensitive drum 18 is transferred onto a sheet 23 as a transfer material by a transfer roll 22 arranged so as to be in contact with the photosensitive drum 18, and the toner image is transferred. The discharged paper 23 is discharged from the photosensitive drum 18 by a charge removal unit 24 composed of a needle electrode. In the present embodiment, the transfer roll 22 is formed of an ion conductive material, while an AC voltage or an AC voltage obtained by superimposing a DC voltage is applied to the separation charger 24 formed of the needle electrode. It has become so.

Further, the paper 23 is provided in the printer main body 11.
Paper is fed from a paper cassette 25 disposed at a lower portion of the inside in a state of being separated one by one by a feed roll 26. The fed paper 23 is conveyed to the surface of the photosensitive drum 18 by the registration roll 27 at a predetermined timing. The printer main body 11 includes a manual feed tray 28 provided on the right side surface so as to be openable and closable. The manual feed tray 28 is rotated clockwise to a substantially horizontal position to stop the manual feed tray 28. From the manual feed tray 28, not only fixed-size sheets but also transfer materials having different materials and sizes, such as OHP sheets and postcards, can be fed via a feed roll 29 having a large diameter and a retard pad 30.

Further, the paper 23 on which the toner image has been transferred from the photosensitive drum 18 is discharged by the separating charger 24 composed of a needle-shaped electrode and separated from the surface of the photosensitive drum 18 as described above. Thereafter, the sheet is transported to the fixing unit 32 via the transport chute 31. The sheet 23 separated from the surface of the photosensitive drum 18 passes between the heating roll 33 and the pressure roll 34 of the fixing unit 32, and the toner image is fixed on the sheet 23 by the heat and pressure at the time of passing. Thereafter, the sheet is discharged onto a discharge tray 36 provided on the upper part of the printer main body 11 by the discharge roll 35, and the image forming process is completed. On the other hand, the residual toner is removed from the surface of the photosensitive drum 18 after the toner image transfer process is completed by a cleaning device 38 having a cleaner blade 37, so that the surface is ready for the next image forming process.

Further, in the present embodiment, the photosensitive drum 18 and the developing device 20 and the cleaning device 38 around the photosensitive drum 18 are integrally unitized as a process cartridge 40 in order to improve maintenance. The process cartridge 40 can be lifted above the printer main body 11 by partially opening the upper cover also serving as the discharge tray 36, and is detachably attached to the printer main body 11. ing. In FIG. 2, reference numeral 41 denotes a process cartridge 40.
Shutter that covers the photosensitive drum 18 when the
2 is a low voltage power supply (LVPS).

In particular, in the present embodiment, as shown in FIG. 3A, a transfer control device 100 for controlling the transfer conditions of the transfer roll 22 is provided. This transfer control device 10
0 denotes a transfer voltage variable output circuit 101 for applying a transfer bias (transfer voltage) and other bias voltages between the photosensitive drum 18 and the transfer roll 22, and a transfer current and other current flowing between the photosensitive drum 18 and the transfer roll 22 Transfer current detecting circuit 102 for detecting
The control unit 10 executes the transfer condition control process shown in FIG. 4 by using the current information detected at step 02, and controls the transfer bias.
3 is provided.

Next, the operation of the image forming process transfer control device of the image forming apparatus according to this embodiment will be described with reference to FIGS. In the following description, it is assumed that the image forming process speed is about 100 mm / sec and the surface potential of the photosensitive drum 18 is about 400V. First, the control unit 103 starts the charging process of the photosensitive drum 18 in the image forming process, and then determines the initial bias V0 determined by the transfer voltage variable output circuit 101, specifically, the resistance of the transfer roll 22 for detecting the resistance. A voltage (for example, 500 V) is applied. Thereafter, in a state where the initial bias V0 has completely risen, the control unit 103 selects a monitor section k1 of one or more rounds of the transfer roll 22 in order to absorb a variation in resistance of the transfer roll 22, and sends it to the transfer current detection circuit 102. The detected current value I0 is monitored every several tens msec. (For example, 40 msec.).

The ion-conductive transfer roll 22 generally has a large environmental dependency, and usually has an environment of N / N (22 ° C./5
5% RH), a high temperature and high humidity environment H
/ H (28 ° C./85% RH), the current flows too much and becomes insufficient in a low temperature and low humidity environment L / L (10 ° C./15% RH). Therefore, it is necessary to detect the resistance of the transfer roll 22, and the above-described resistance detection processing of the transfer roll 22 (corresponding to the environment detection processing) is performed. It should be noted that the initial bias V0 is selected so that it does not become a transfer memory under any environment and a relatively large value can be obtained as the detected current value I0.

Then, the control unit 103 operates, for example, as shown in FIG.
A table such as that shown in FIG.
Environmental classification (classification: H / H,
(Section: N / N, section: L / L), and determines the page gap voltage Vpg corresponding to the environmental section, and then applies the determined page gap voltage Vpg. The page gap voltage Vpg is set before the paper 23 reaches the nip area between the photosensitive drum 18 and the transfer roll 22 (hereinafter, referred to as a transfer nip area as needed in the present embodiment), in other words, the paper 23 This is a voltage applied between the photosensitive drum 18 and the transfer roll 22 in a state where it does not exist, and is selected so that a predetermined range of current flows in any environment. In particular, in the present embodiment, under the condition that such a page gap voltage Vpg (set according to the environmental category) is applied, the transfer voltage VTR determination and the transfer current monitoring before and after the leading edge of the sheet described later are performed. Therefore, in any environment, the monitor accuracy for determining the transfer voltage VTR and for monitoring the front and rear ends of the sheet is improved.

Thereafter, the control unit 103 monitors the monitor section k2 for one or more rounds of the transfer roll 22 in order to absorb uneven resistance of the transfer roll 22 in a state where the page gap voltage Vpg has completely risen when the page gap voltage Vpg is applied. Is selected, and the transfer current detection circuit 102 monitors the detection current value Ipg every several tens msec. (For example, 40 msec.). Then, the control unit 103 searches a table such as that shown in FIG. 5B, for example, and determines the standard transfer voltage (transfer bias) based on the detected current value Ipg and the environmental classification corresponding to the previously detected detected current value I0. ) Determine VTR1 as the transfer voltage VTR.

Thereafter, the control unit 103 monitors a change in current before and after the front end of the paper every several milliseconds (for example, 4 msec) in a monitor section k3 before and after the front end of the paper enters the transfer nip area. The current difference Δ before and after is detected. At this time, if the monitor interval is made shorter and the monitor section k3 is made shorter, it is advantageous for delay until the transfer bias rises, and the resistance unevenness of the transfer roll 22 can be ignored. That is, as shown in FIG.
Is the transfer current monitor value when there is no paper, and the lower side (solid line) is the transfer current monitor value when paper is present. I do. However, the transfer roll 2
Regardless of where the resistance variation of No. 2 is monitored, only the resistance of the paper is detected from the short-term current value difference Δ. FIG. 14 shows a specific example of a change state of the transfer current monitor value in the monitor section k3. According to FIG. 14, at the boundary point between the paper area (Paper Aera) and the non-paper area (Non Paper Aera). It is understood that the transfer current monitor value changes abruptly, and a current value difference occurs between the two. The details of the monitoring process in the present embodiment will be described later.

Thereafter, as shown in FIG. 4, the control unit 103 checks whether or not the current value difference Δ exceeds a predetermined threshold value TH1, and if the current value difference Δ exceeds the threshold value TH1, the sheet is a high-resistance sheet. Judge that there is, change the transfer voltage VTR to VTR2,
If the threshold value TH1 is not exceeded, it is determined that the sheet has normal resistance, and the process of changing the transfer voltage VTR is skipped. At this time, the process of changing the transfer voltage VTR is as follows: VTR = VTR
2 = R1 * VTR (R1: constant), where "R1" is determined uniformly according to the current value difference Δ, for example, as shown in FIG. 6 (a). In the example of FIG. 6A, TH1 is set to 1.0 μA. Here, the threshold value TH1 may be common to all sections, or may be divided for each environmental section to.

In this state, the control section 103
As shown in (1), a transfer voltage VTR determined 2 mm after the leading end of the sheet is applied. Then, after the transfer voltage VTR has completely risen, the control unit 103 sets a predetermined monitor section k4 in the image area (usually one round of the transfer roll 22 in order to absorb the resistance unevenness of the transfer roll 22). Of the transfer current detecting circuit 10).
2, the detected current value ITR is set to several tens msec.
0 msec.) To detect the current value ITR in the paper. Thereafter, the control unit 103 sets the ITR to a predetermined threshold value TH2.
It is checked whether or not it exceeds the threshold value TH2. If it exceeds the threshold value TH2, it is determined that the paper is partially water-containing and the transfer voltage V
TR is changed to VTR3, and if it does not exceed the threshold value TH2, the process of changing the transfer voltage VTR is skipped, assuming that there is no partial water content phenomenon on the paper.

Here, the threshold value TH2 may be common to all sections, but, for example, as shown in FIG.
You may make it separate for every. As the process of changing the transfer voltage VTR, VTR = VTR3 = R2 * VTR (R2: constant) is performed.
As shown in (b), it is determined according to the detected current value ITR and the environmental category.

Thereafter, as shown in FIG. 4, the control unit 103 applies a voltage to be applied to the transfer roll 22 when the rear end of the sheet reaches a transfer nip area by 2 mm before the page gap voltage Vpg.
After that, the transfer voltage VTR is reset to VTR1 (VTR = VTR1). After that, until continuous printing is completed,
Each step from the process of detecting the current value difference Δ before and after the leading edge of the sheet to the process of resetting the transfer voltage VTR to VTR1 is repeated.

Here, a specific example of the transfer control processing in the present embodiment will be described. Assume that V0 = 500 V is applied and a current of 4 μA flows at this time (FIG. 5).
(A)). This determines that Vpg = 1000V,
Monitor current value Ipg at the time of application of page gap voltage is 5.6
Suppose that it became μA. Assume that the first transfer voltage VTR1 is determined to be 1080 V in response to the current value (see FIG. 5B). If the monitor current difference △ before and after the leading edge of the sheet at this time is 3 μA, the constant is determined to be 1.4, and VTR2 =
1.4 * 1080 = 1510V etc. (FIG. 6 (a)
reference).

Next, a specific example of the monitor process in the monitor section k3 will be described. Example of Monitor Processing As shown in FIG. 15 (a), this is for monitoring the time ± 2 mm of the time aimed at the leading edge of the paper by timing the ON signal of the registration roll 27, for example, as shown in FIG. It discards subtle monitor values and takes the difference between the first few averages and the second several averages. Specific processing in the control unit 103 is performed according to, for example, a flowchart shown in FIG. In FIG. 8, the image forming process speed is 100 mm / sec. And the transfer roll outer diameter is φ20.
The same applies to FIGS. 9 to 11. In FIG. 8, the control unit 103 starts a transfer monitor aiming at a position 2 mm ahead of the paper, monitors 11 times at intervals of 4 msec., For example, 11 times, and deletes an average obtained by deleting the monitor having the smallest current value among the four monitors from the beginning. And the average of three of the last four monitors excluding the monitor with the largest current is Iba
After ck, the current value difference Δ (Iforward−Iback) is calculated, and it is further checked whether the current value difference Δ exceeds the threshold value TH1. If the current value difference Δ exceeds the threshold value TH1, the transfer voltage (transfer bias) VTR is calculated. Change to VTR2 (VTR = VTR2 = R
1 * VTR).

In this system, the monitor section k3 is
The time is 40 msec. And the length is about 4 mm. Since it is about 6% with respect to the circumference of the transfer roll 22 of about 63 mm, the transfer roll 22 is hardly affected by uneven resistance. Further, in this processing example, a delicate monitor value that is inside or outside the paper is discarded. For example, three monitor values out of 11 monitor values are discarded, and several monitor values before and after (in this example, four monitor values) are used. ) Averaged, so relatively resistant to noise. Further, in this processing example, in order to accurately detect even if the registration is displaced, the monitor having the smallest current value is discarded on the portion corresponding to the outside of the sheet, and the portion corresponding to the inside of the sheet is discarded.
The one with the largest current value is discarded.

Example of Monitor Processing This is a process of registering the registration roll 2 as shown in FIG.
7, a timing is set to the ON signal, and the vicinity of the leading edge of the paper is monitored by shortening the monitoring interval without severely considering the leading edge of the paper. For example, the N-th and (N +
1) The first time is always compared, and if the (N + 1) th monitor value is smaller than the Nth time by a certain degree or more, it is determined that the sheet is a high-resistance sheet. Specific processing in the control unit 103 is performed according to, for example, a flowchart shown in FIG. In FIG. 9, the control unit 103
The transfer monitor is started with an aim of m times before, and is monitored from N = 0 to 15 every 4 msec, for example, and the monitor values of the Nth and (N + 1) th times are compared. Then, it is always checked whether or not the current value difference Δ exceeds the threshold value TH1, and if the current value difference Δ exceeds the threshold value TH1, it is determined that the sheet is a high-resistance sheet, and the transfer voltage (transfer bias) VTR is changed to VTR2 (VTR = VTR2 = R1 *
VTR).

This processing example is an example in which at least the monitor section is set so as to straddle the leading edge of the sheet, and is capable of coping with misregistration (an example resistant to misregistration). That is, since the current monitor is always compared with the previous monitor, even if the leading end position of the paper is shifted, the detection accuracy of the high resistance paper does not decrease. However, it is necessary to set the monitor section within a range in which detection of high-resistance paper cannot be detected due to registration deviation. Also, in this processing example, the front end of the sheet 3 m
It is assumed that N> 15, assuming 2 mm after m. While the voltage is applied to the transfer roll 22, if the monitoring interval is constantly shortened and the monitoring is performed, the load on the CPU of the control unit 103 increases. Load is not a big deal. Further, in this processing example, since the effective monitor section is as short as 4 msec., It is not affected by the uneven resistance of the transfer roll 22.

Monitor processing example This is a development of the monitor processing example, and is an example that is resistant to registration deviation and noise. Specific processing in the control unit 103 is performed according to, for example, a flowchart shown in FIG. In FIG. 10, the control unit 103 goes through the same steps as in FIG. 9, for example, when the current value difference Δ between the monitor point N and (N−1) exceeds the threshold value TH1 (for high-resistance paper. ), The transfer monitor of the next monitor point (N + 1) is further performed, and the current value difference モ ニ タ between the monitor point (N + 1) and N is within the allowable range (A <▲ <B in this example). It is checked whether or not the monitor values of the monitor point (N + 1) and N are substantially the same. If the value falls within the allowable range, it is determined that the sheet is a high-resistance sheet because it is not erroneous detection due to sudden noise, and the transfer voltage (transfer bias) VTR is changed to VTR2 (VTR = VTR2 = R1 * VT).
R).

In this processing example, after determining that the sheet is a high-resistance sheet, a step of confirming that this is not an erroneous detection due to noise is added. At this time, A and B may be constants, but are preferably functions of the current difference Δ. Also in this processing example, the effective monitor section is 8 msec.
Therefore, the transfer roller 22 is not affected by uneven resistance.

Monitor processing example This is a development of the monitor processing example, and is an example that is strong against registration deviation and also strong against paper skew. The specific processing in the control unit 103 is described in, for example, FIG.
Is performed according to the flowchart shown in FIG. In FIG. 11, the control unit 103 goes through the same steps as in FIG.
For example, it is checked whether the current value difference ΔN (= IN−1−IN) between the monitor point N and (N−1) exceeds the threshold value TH1, and if the current value difference ΔN exceeds the threshold value TH1, a high-resistance sheet is used. It is determined that there is, and the transfer voltage (transfer bias) VTR is set to VTR2.
(VTR = VTR2 = R1 * VTR). If the threshold T
Even under the condition not exceeding H1, the current value difference ΔN−
It is checked whether or not the sum S (ΔN−1 + ΔN) with 1 (= IN−2−IN−1) exceeds the threshold value TH1, and if it exceeds the threshold value TH1, it is determined that the sheet is a high-resistance sheet. Change the transfer voltage (transfer bias) VTR to VTR2 (VTR = VTR2 = R
1 * VTR).

This processing example aims to accurately detect the skew of the sheet. This is a method for relieving a situation where a monitor is performed in a situation where the paper is skewed and only one side of the transfer roll 22 is nipped. In such a case, the difference between two monitors may be small even for high-resistance paper. During skew, the monitor value gradually changes, so that the difference of one time is not so large, but the sum of the differences of a plurality of times may increase. Even when the sum of a plurality of differences is large (twice in this processing example), the transfer voltage (transfer bias) VTR is changed by determining that the sheet is a high-resistance sheet in the same manner as when the difference is large once. It is.

In the present embodiment, the environmental condition is estimated by using the transfer current detecting circuit 102. However, the present invention is not limited to this. For example, FIG.
As shown by a virtual line, an environment detecting device 104 such as a temperature sensor or a humidity sensor may be provided, and the page gap voltage Vpg corresponding to the environmental classification may be determined based on information from the environment detecting device 104. .

Further, as shown in FIG. 16, even for the same high-resistance paper, the profile of the transfer current monitor value differs between the large paper size and the small paper size.
That is, when the transfer current monitor value difference before and after the leading edge of the paper is captured, in the case of a large-size paper,
The difference in paper resistance is counted as the difference. On the other hand, in the case of a small-size sheet such as a postcard, there is no difference in current before and after the leading end of the sheet in a portion where the transfer roll and the photosensitive drum are in direct contact. Therefore, for small size paper,
The difference is calculated to be smaller than that of a large-size sheet having the same resistance. Therefore, for small size paper,
To further increase the detection sensitivity of high-resistance paper, for example, FIG.
As shown in (b), the paper size detection device 105 may be provided to change the detection sensitivity of the high-resistance paper for each detected paper size. As an example, FIG.
In the embodiment shown in FIG. 6, when the transfer voltage (transfer bias) VTR is changed to VTR2, VTR2 = R1 * VTR is calculated. As a table for determining the constant R1 at this time, for example, FIG. As shown in (1), the constant R1 is determined for each paper size by taking into account the paper size information (for example, large size and small size) in addition to the current value difference Δ and the environmental category. Then, the transfer voltage VTR2 may be optimized.

[0049]

As described above, according to the transfer control device of the image forming apparatus according to the present invention, before the transfer bias is applied, the image carrier and the contact member are monitored in the monitor section before and after the leading end of the transfer material. The current flowing between the transfer units is monitored, and the transfer bias is set based on the monitor information. Therefore, even if a high-resistance transfer material is used, the transfer bias can be appropriately adjusted at the leading end that does not reach the image area of the transfer material. Transfer bias setting can be realized. For this reason, even if transfer materials having different resistances are used, it is possible to always apply an appropriate transfer bias to the image area of the transfer material, and there is no concern that a transfer failure occurs over the entire transfer material. . Further, according to the present invention, it is only necessary to devise the monitoring process itself by software, and it is not necessary to add a new device. Therefore, there is no concern that the cost of the device itself is unnecessarily increased.

In particular, in the present invention, if the monitor condition setting means is provided, the monitor processing by the current change monitor processing means can be optimized.
The monitoring processing accuracy can be improved, and the setting of the transfer bias can be realized with high accuracy.

Further, according to the monitor processing apparatus of the present invention, the state of the physical quantity change can be accurately determined in monitoring the physical quantity change in a monitor section having a sudden physical quantity change point. Accuracy can be greatly improved.

[Brief description of the drawings]

FIG. 1A is an explanatory diagram showing an outline of a transfer control device of an image forming apparatus according to the present invention, and FIG. 1B is an explanatory diagram showing an outline of an operation state thereof.

FIG. 2 is an explanatory diagram illustrating an overall configuration of an embodiment of an image forming apparatus to which the present invention has been applied.

FIG. 3A is an explanatory diagram illustrating an outline of a transfer control device of the image forming apparatus according to the embodiment, and FIG. 3B is an outline diagram of a transfer control device of the image forming apparatus according to a modification of the embodiment. FIG.

FIG. 4 is a flowchart illustrating an overall process of the transfer control device according to the embodiment.

5A is an explanatory diagram showing a table when V0 is applied, and FIG. 5B is an explanatory diagram showing a table when Vpg is applied.

FIGS. 6A and 6B are explanatory diagrams each showing an example of a table for determining a constant R1.

FIG. 7A is an explanatory diagram showing an example of a TH2 table;
(B) is an explanatory view showing an example of a table for determining the constant R2.

FIG. 8 is an explanatory diagram showing an example of a monitor process used in the present embodiment.

FIG. 9 is an explanatory diagram showing an example of a monitor process used in the present embodiment.

FIG. 10 is an explanatory diagram showing an example of a monitor process used in the present embodiment.

FIG. 11 is an explanatory diagram showing an example of a monitor process used in the present embodiment.

FIG. 12 is an explanatory diagram schematically showing a process of determining a transfer bias according to the embodiment;

FIG. 13 is an explanatory diagram showing a change state of a transfer current monitor value in the present embodiment.

FIG. 14 is an explanatory diagram showing a change state of a transfer current monitor value in a monitor section in the present embodiment.

FIG. 15A is an explanatory diagram schematically illustrating an example of a monitor process used in the present embodiment, and FIG. 15B is an explanatory diagram schematically illustrating an example of the monitor process used in the present embodiment.

FIG. 16 is an explanatory diagram showing a change state of a transfer current monitor value in a monitor section when using sheets of different sizes according to the present embodiment.

FIG. 17 is an explanatory view schematically showing an example of a transfer bias setting process performed using a transfer control device of a conventional image forming apparatus.

FIG. 18 is an explanatory diagram schematically showing another example of the transfer bias setting process performed using the transfer control device of the conventional image forming apparatus.

FIG. 19 is an explanatory diagram showing an example of a conventional transfer current monitor profile.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Contact transfer means, 3 ... Transfer material, 4 ... Bias applying means, 5 ... Current detection means, 6 ... Current change monitoring processing means, 7 ... Transfer bias setting means, 8 ... Monitor condition setting means

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA01 DA14 DC02 DC19 DE09 EA03 EC06 ED24 2H032 AA05 BA12 BA13 CA02 CA12 CA14

Claims (14)

[Claims] 1. An image carrier on which a visible image is formed and carried by a charged color material, and a visible image on the image carrier, which is disposed in contact with the image carrier via a transfer material, is transferred to the transfer material. In an image forming apparatus including a contact transfer unit and a bias applying unit that applies a bias voltage including at least a transfer bias between the image carrier and the contact transfer unit, a current flowing between the image carrier and the contact transfer unit is detected. Current detecting means, and using the current detecting means, before the transfer bias is applied, in the monitor section before and after the leading end of the transfer material enters the nip area between the image carrier and the contact transfer means. Current change monitor processing means for monitoring a change in current flowing between the body and the contact transfer means; and a transfer to be applied between the image carrier and the contact transfer means based on information monitored by the current change monitor processing means. A transfer control device for an image forming apparatus, comprising: a transfer bias setting unit for setting a shooting bias. 2. A transfer control device for an image forming apparatus according to claim 1, wherein a monitoring condition is set by a current change monitor processing unit before a transfer material enters a nip area between the image carrier and the contact transfer unit. A transfer control device for an image forming apparatus, comprising a monitor condition setting unit. 3. The transfer control device for an image forming apparatus according to claim 2, wherein the monitor condition setting means is configured to apply a predetermined initial bias by the bias applying means between the image carrier and the contact transfer means. A transfer control device for an image forming apparatus, wherein an initial current flowing is monitored, and environmental conditions are estimated based on the initial current information to set monitor conditions by a current change monitor processing unit. 4. The transfer control device for an image forming apparatus according to claim 2, wherein said monitor condition setting means includes environment detection means for detecting environmental conditions, and based on environment detection information from said environment detection means. A transfer control device for an image forming apparatus, wherein a monitor condition is set by a current change monitor processing means. 5. The transfer control device for an image forming apparatus according to claim 1, wherein the transfer bias setting unit is configured to control the image holding before the transfer material enters a nip area between the image bearing member and the contact transfer unit. The current flowing between the body and the contact transfer means is monitored, the standard transfer bias is provisionally set based on the monitor information, and the final transfer bias is finally set based on the monitor information by the current change monitor processing means. A transfer control device for an image forming apparatus. 6. The image forming apparatus according to claim 1, wherein the transfer bias setting unit sets the transfer bias individually for each environmental condition. Transfer control device. 7. The image forming apparatus according to claim 1, wherein the transfer bias setting means sets a transfer bias individually for each transfer material size. Transfer control device of the device. 8. The transfer control device for an image forming apparatus according to claim 5, wherein the transfer bias setting unit is configured to control the transfer bias under a condition in which a difference in current change by the current change monitor processing unit exceeds a predetermined threshold. A transfer control device for an image forming apparatus, wherein a standard transfer bias is changed. 9. The transfer control device for an image forming apparatus according to claim 5, wherein the transfer bias setting means is standardized by a constant multiple determined according to a difference in current change by the current change monitoring processing means. A transfer control device for an image forming apparatus, wherein a final transfer bias is set by multiplying the transfer bias. 10. The transfer control device for an image forming apparatus according to claim 1, wherein the transfer bias setting means sets a transfer bias based on current change information from the current change monitor processing means.
Monitor the current flowing between the image carrier and the contact transfer means,
A transfer control device for an image forming apparatus, wherein a transfer bias is changed based on monitor current information under a condition where the monitor current exceeds a predetermined threshold value with respect to a transfer current by a set transfer bias. 11. A monitor processing apparatus for monitoring a physical quantity change in a predetermined monitor section including a sudden physical quantity change point a plurality of times at a predetermined interval, the monitor processing apparatus excluding a monitor point located near the physical quantity change point. A monitor processing device wherein a physical quantity change is calculated based on a monitor value of a monitor point. 12. A monitor processing apparatus for monitoring a physical quantity change in a predetermined monitor section including a sudden physical quantity change point a plurality of times at a predetermined interval, wherein the monitor values of preceding and following monitor points are sequentially compared, and each monitor value is compared. A monitor processing device for calculating a physical quantity change by a difference. 13. A monitor processing apparatus for monitoring a physical quantity change in a predetermined monitor section including a sudden physical quantity change point a plurality of times at a predetermined interval, wherein the monitor values of preceding and following monitor points are sequentially compared, and a certain monitor point is compared. A monitor processing device for calculating a physical quantity change under a condition that a monitor value difference between the monitor points exceeds a predetermined threshold value and a monitor value difference between the next monitor points does not exceed the predetermined threshold value. 14. A monitor processing device for monitoring a physical quantity change in a predetermined monitor section including a sudden physical quantity change point a plurality of times at a predetermined interval, wherein the monitor values at the preceding and following monitor points are sequentially compared, and each monitor value is compared. A monitor processing device for determining a physical quantity change by a sum of a difference and a plurality of monitor value differences.