JP6343969B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile.

  2. Description of the Related Art A transfer device using a transfer member such as a transfer roller or a transfer belt brought into contact with the surface of an image carrier when transferring a toner image formed on the image carrier onto a transfer material such as paper is known. Yes.

  In an image forming apparatus equipped with such a transfer device, a toner image is formed on the image carrier with charged toner, the transfer member is pressed against the image carrier, and the pressure nip portion between the two is set as a transfer position. Insert the transfer material. At that time, a transfer bias having a polarity opposite to that of the toner is applied to the transfer member, and the toner image on the image carrier is transferred to the transfer material by the action of the electric field formed thereby.

  Such a contact transfer system can reliably hold the transfer material as compared with a transfer unit that uses a known corona discharger, and therefore, a transfer deviation of the toner image at the transfer position is less likely to occur. In addition, since the transfer bias may be a relatively low voltage, the entire apparatus can be made compact and compact, and there are various advantages such as no generation of ozone.

  In an image forming apparatus that employs the contact transfer method, the bias applied to the transfer member is controlled by constant voltage control or constant current control. However, since the transfer member is made of a semiconductor rubber material, the resistance value of the transfer member varies greatly depending on the environment. For example, the resistance value increases in a low temperature and low humidity environment, and the resistance value decreases in a high temperature and high humidity environment. Such a resistance change of the resistance member causes a transfer defect.

  Such a problem due to the environment will be described by taking as an example an embodiment in which transfer is performed directly from a photoconductor as an image carrier to a transfer material such as paper by being applied to a charging roller as a charging member. At the time of printing, that is, at the time of image formation, the surface of the photosensitive member is charged by the charging roller. At this time, in the configuration of the contact transfer system, a current called an inflow current flows from the transfer roller to the photosensitive member. The inflow current is applied from the transfer roller to the charged photosensitive member after the start of laser beam irradiation by the optical writing unit and before the toner image of the electrostatic latent image formed at the laser beam irradiation position reaches the transfer site. It is a flowing current. The magnitude of the inflow current varies depending on the impedance of the transfer roller, the surface potential of the photosensitive member controlled to adjust the image density, and the like, and varies depending on the environmental conditions in which the image forming apparatus is installed.

  When a transfer output power source that applies a transfer current or voltage to the transfer roller is activated when a flow-in current is generated, a start-up failure occurs unless the transfer output power source is activated with a current larger than the flow-in current. Moreover, even if it starts, it may overshoot with respect to the setting of aim. If a start-up failure occurs, a transfer failure occurs because a sufficient transfer bias is not ensured. Also, overshooting results in overtransfer, generating an abnormal image due to discharge, leaving an electrostatic history on the photoconductor, generating streaks on the image, or damaging the photoconductor itself. As a result, abnormal images may be generated, and stable image quality may not be obtained.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses that a detection unit that detects output voltages or currents of the transfer output power supply unit and the cleaning bias power supply unit can be provided for the purpose of preventing a start failure of the transfer output power supply unit due to a flowing current. . With such a configuration, the output is adjusted according to the detected output voltage or current to normalize the startup. However, the configuration disclosed in Patent Document 1 detects and controls the transfer output value, and it is necessary to provide detection means for detecting the transfer output, and the apparatus is complicated. Furthermore, depending on the control conditions, the output at the time of start-up becomes too large, and there is a possibility that density unevenness is generated while leaving an electrostatic history on the photoreceptor. For example, when a negatively charged toner is used, in the direct transfer method, the surface potential of the photosensitive member is negatively charged, and a transfer current (or voltage) is applied with a positive value. At this time, if the transfer output at start-up becomes too large, the surface potential of the photoreceptor after transfer corresponding to the output at start-up is close to zero with respect to other potentials or is charged to the plus side. The charged photoreceptor surface potential shifts to the plus side with respect to other locations, and density unevenness occurs.

  An object of the present invention is to control the transfer current value at start-up to an appropriate value different from the image portion current with a simple configuration with respect to the inflow current, thereby suppressing the start-up failure of the transfer output power supply unit. It is to obtain stable image quality in various environments.

An object of the present invention is to provide an image carrier that carries a toner image, a transfer member that faces the image carrier, and a transfer power source that applies a transfer current or voltage so as to form an electric field between the image carrier and the transfer member. In the image forming apparatus including the environment detection unit, after the irradiation of the image carrier charged by the charging member with the writing member, the irradiation position is between the image carrier and the transfer member. The threshold value of the output at the start of transfer of the current or voltage at the time of starting up the transfer power supply until reaching the transfer site is set according to the detection value of the environment detecting means, and the detection of the environment detecting means based on the results, after the transfer start time of the output is activated at least the threshold value set in accordance with the detected value of said environment detection means, is solved by switching to the transfer start time of a low image area output than the output The

According to the present invention , the transfer power source from the start of irradiation of the image carrier charged by the charging member with the writing member to the time when the irradiation position reaches the transfer portion between the image carrier and the transfer member. The threshold value of the current or voltage transfer start-up output is set according to the detection value of the environment detection means, and the transfer start output is detected by the environment detection means based on the detection result of the environment detection means. After starting at the threshold value set according to the value, the output is switched to an image portion output lower than the output at the time of transfer start-up. An excessive increase in output is prevented.

1 is a conceptual front sectional view of an image forming apparatus. FIG. 3 is an enlarged front view showing a configuration around a photoconductor of a printer engine. It is a timing chart which shows the sequence of the transfer output at the time of continuous printing which concerns on one Embodiment of this invention. It is a timing chart which shows the design sequence of the transfer output at the time of the continuous printing in the past. FIG. 5A is a schematic diagram illustrating an actual output example in the prior art. FIG. 5A is an example in which a transfer power supply is poorly activated, and FIG. 5B is an example in which an overshoot is generated.

Embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a front sectional view showing a copying machine as an image forming apparatus according to the present embodiment. The copying machine 1 includes a scanner device 2 disposed on the upper side and a printer device 3 that forms an image of a document read by the scanner device 2 on a sheet as a transfer material.

  In the printer device 3, a sheet from a sheet feeding tray 4 that stacks and holds sheet-like sheets, or a manual tray 5 that receives manually fed sheets, to a sheet discharge stacker unit 8 through a printer engine 6 and a fixing unit 7. A conveyance path is formed.

  FIG. 2 is an enlarged front view showing an extracted configuration around the drum-shaped photoconductor 10 of the printer engine 6. Around the photosensitive member 10 which is an image carrier that carries a toner image, there are a charging roller 11, an irradiation exposure position of writing light P by an optical writing device 12 (FIG. 1), a developing device 13, and a transfer means of a contact transfer system. A transfer roller 14 and a cleaning blade 15 are arranged in this order. The developing device 13 includes a developing sleeve 16 and a toner sensor 17. Reference numeral 18 denotes a so-called P sensor for detecting the toner density of the toner image formed on the photoconductor 10, and reference numeral 19 denotes a transfer position (transfer nip) which is a region where the photoconductor 10 and the transfer roller 14 face each other. This is a registration roller for controlling the sheet feeding / conveying timing. Reference numeral 20 denotes a temperature / humidity sensor which is an environment detection means.

  In such a configuration, the charging roller 11 is in contact with the photosensitive member 10 and applies a bias to the charging roller 11 to supply a uniform charge to the surface of the photosensitive member 10 and uniformly charge to a constant potential. A latent image is formed by irradiating the charged photosensitive member 10 with writing light P by a laser from the optical writing device 12, and a toner image is formed on the photosensitive member 10 when passing through the developing device 13. The paper fed from the paper feed tray 4 or the like and fed to the photoconductor 10 through the resist roller 19 is subjected to the action of a transfer electric field by the transfer roller 14 when passing through the transfer position, so that the toner image on the photoconductor 10. Is transferred onto the sheet and further melted and fixed in the fixing unit 7.

In such a basic configuration, a contact transfer method that is also adopted in this embodiment will be described. The resistance value of the transfer roller 14 used in this embodiment is 10 ⁶ to 10 ⁹ Ω when DC 1000 V is applied in a room temperature and humidity environment of 23 ° C. and 50% Rh. In a transfer device that performs constant current control, the transfer bias applied to the transfer roller 14 is adjusted so that the value of the current that flows during paper feeding is constant. As a basic characteristic of the transfer, the toner image on the photoreceptor 10 is electrically attracted to the paper surface by applying a reverse charge to the toner on the back surface of the paper.

  Untransferred toner that has not been transferred to the paper at the time of transfer is collected from the photoreceptor 10 by the cleaning blade 15. The collected residual toner is conveyed through a recycle toner path (not shown) provided in the vicinity of the blade, and is supplied again to the developing device together with new toner and recycled.

  Next, the transfer output sequence will be described with reference to FIG. The output is described as current, but the same applies to voltage. When printing is started, a negative current is first applied from a cleaning bias portion of a transfer power supply (not shown), and the negatively charged toner accumulated on the transfer roller 14 is cleaned to the photosensitive member by an electric force (pre-job cleaning). ). That is, a cleaning bias having the same polarity as the toner is applied in the cleaning before transfer. Thereafter, the output once becomes zero, and thereafter, application of a positive starting current is started from the transfer output portion of the transfer power supply for transfer. In the present invention, a threshold is provided for the output at the time of start-up (output at the time of transfer start-up; output at the time of start-up from the state where the transfer output is zero), and the start-up is performed at an output exceeding the threshold (HVP start-up current). ). As described later, the threshold value related to the output at the time of startup is set according to the environment detected by the temperature / humidity sensor 20. After that, before the transfer material (paper) arrives at the transfer position, switching to the image part output (image part current) for toner transfer generates abnormal images such as discharge images (white spots) due to overtransfer. Is avoided. After the transfer material leaves the transfer position (between sheets), it switches to non-image part output. Non-image area output modes include applying positive current so as not to attract reverse polarity ground toner on the photoconductor to the transfer roller, or setting both output to zero and negative toner. May not be attracted. Alternatively, there may be a case where the negatively charged toner is electrically splashed by applying a minus. When the non-image part is set to zero or minus output, the transfer output becomes zero once. Therefore, it is necessary to activate the positive output again as the image part output. It will be. FIG. 3 shows an example in which the non-image portion output is set to zero, and the image is output once above the threshold value of the transfer activation output at the time of activation even before application of the second image portion output. As a result, it is possible to prevent problems due to transfer output start failure.

  As a comparative example, FIG. 4 and FIG. 5 show an example of starting up below a threshold at the time of transfer activation. FIG. 4 shows a target sequence, and FIGS. 5-1 and 5-2 show schematic diagrams of outputs when a start-up failure occurs. FIG. 5A is a pattern in which a start failure occurs and no output is generated, and is a pattern generated under a condition where the difference between the threshold and the start current is large. On the other hand, FIG. 5-2 shows a pattern that occurs when an overshoot occurs during startup and the threshold and the startup current are close. When an overshoot occurs, a considerably large current flows with respect to the target output, which may leave a positive electrostatic history (change in surface potential) on the photoconductor. In this case, the charge removal lamp cannot remove the charge but remains as a history, and there is a possibility that a defect such as a decrease in the density of only that portion of the photosensitive member may occur.

  The impedance of the transfer roller is greatly affected by the environment because the resistance decreases in a high temperature and high humidity environment. For this reason, the inflow current is also affected by the environment, and the inflow current increases as the temperature and humidity become higher. On the other hand, in transfer, if the transfer bias is low, toner dust and blur are generated due to insufficient transfer, and if it is too high, white spots due to discharge occur due to excessive transfer, so an optimal current setting is required. Since the transfer property is affected not only by the impedance of the transfer roller but also by the impedance change of the paper as the transfer material, the optimum transfer current value changes not only from the transfer member but also from the point of the transfer material. For this reason, there may be a difference between the output necessary for suppressing the start failure of the transfer output power supply and the optimum output for transfer. In conventional image forming apparatuses as well, environmental sensors (temperature / humidity sensors) that can detect environmental information such as temperature / humidity are provided in order to ensure that the image part output is an appropriate transfer output. It is known to correct to an appropriate transfer output at. As shown in Table 1, in the present invention, the transfer start output is also controlled based on the environment detection result. In Table 1, the threshold for the output at start-up is set only from the point of absolute humidity, but it is naturally assumed that the threshold for output at start-up is specified from the point of temperature alone or from both points of temperature and humidity.

By using an environmental sensor that adjusts the output of the image portion, it is not necessary to provide new detection means, and it is possible to cope with the start-up failure problem of the output power supply with a simple configuration.
In order to determine the output threshold value at the time of start-up, an inflow current that causes a start-up failure of the transfer output power supply is measured in advance. At this time, the measurement is performed under the condition that the inflow current becomes large (mainly the lower limit of the transfer roller impedance and the upper limit of the surface potential of the photosensitive member), and the threshold value of the output at startup in each environment is set. Start-up with higher output than the measured inflow current will not cause start-up failure. Further, in the present invention, even if the start-up output is considerably larger than the image portion output, the transfer material is switched to the image portion output before reaching the transfer nip after the start-up output is applied. Will not occur.

  In a general contact transfer type image forming apparatus, "bias cleaning" is performed to apply a bias to the transfer roller and return it to the photoconductor to clean the dirt that has moved from the photoconductor to the transfer roller during image formation. There is. The stain includes, for example, toner developed outside the copy area at the time of reading the scanner and developed outside the transfer material (paper) area, and non-image area dirt toner. In bias cleaning, a negative bias is applied to the transfer roller in order to return the normally charged negative toner, and a positive bias is applied in order to clean the positively charged reversely charged toner. In pre-job cleaning performed before image formation (before transfer) after printing is started, a negative bias is often applied in order to prevent backside contamination of the paper due to negative toner in the transfer roller during transfer. In this case, in order to apply the positive output after applying the negative output, it is necessary to zero the output once, but in order to shorten the first copy time, it is necessary to activate the transfer output immediately before the start of transfer. There is a high risk of starting the output. The start-up output of the present invention can suppress a start-up failure by applying a short time of about 10 ms and does not extremely increase the first copy time.

  In the direct transfer method, the surface potential of the photosensitive drum may be controlled in order to adjust the image density and the like, and the flowing current may change at that time. There are various timings for controlling the surface potential, but when an adjustment operation is performed during printing, the flowing current changes during the printing operation. When the start-up output is adjusted based on the surface potential change, the control becomes complicated. However, since the present invention sets a value that is considered in advance, the start-up failure can be suppressed with simple control.

  In an image forming apparatus in which the control of reducing the linear speed with respect to the normal process linear speed in the high image mode corresponding to thick paper under low temperature fixing, it is necessary to set an output at startup corresponding to the linear speed. Since the impedance of the transfer roller increases as the linear velocity decreases, the inflow current tends to decrease. On the other hand, if the normal linear speed startup output is set, the output will be excessive at low linear speeds, leaving a positive electrode history on the photoconductor and lowering the development potential. May cause abnormal images such as streaks and bands. For this reason, when the low linear velocity mode is set with respect to the normal linear velocity, it is necessary to set the output at startup smaller than the normal linear velocity. If there are a plurality of linear velocities, as shown in Table 2, the output setting at the start corresponding to each process linear speed is set, and it is possible to prevent both the start failure of the transfer output power supply and the abnormal image.

  Although the transfer roller method has been described above as an example, the same control can be applied to the transfer belt method to obtain the same effect.

6 Printer Engine 10 Photoreceptor 11 Charging Roller 13 Developer 14 Transfer Roller 15 Cleaning Blade 17 Toner Sensor 18 P Sensor 19 Registration Roller

JP 2008-225029 A

Claims (6)

An image carrier that carries a toner image, a transfer member that faces the image carrier, a transfer power source that applies a transfer current or voltage to form an electric field between the image carrier and the transfer member, and environmental detection An image forming apparatus comprising:
After the irradiation of the image carrier charged by the charging member by the writing member with the writing member, the transfer power source until the irradiation position reaches the transfer site between the image carrier and the transfer member. The threshold value of the current or voltage transfer start output at the start is set according to the detection value of the environment detection means ,
Based on a detection result of said environment detection means, said transfer after startup output is activated in the above the threshold value set in accordance with the detected value of said environment detection means, to the transfer start time of a low image area output than the output An image forming apparatus, wherein the image forming apparatus is switched . The image forming apparatus according to claim 1, wherein the transfer start output is output in a state where the transfer output is zero. The image forming apparatus according to claim 1 or 2, the image forming apparatus, wherein said environment detection means is a temperature and humidity sensor. The image forming apparatus according to any one of claims 1 to 3 transfer startup output image forming apparatus characterized by output after application of the cleaning bias. The image forming apparatus according to any one of claims 1-4, wherein the image bearing member is a photosensitive member, an image forming apparatus, characterized in that said transfer member is in contact with the photosensitive member. The image forming apparatus according to any one of claims 1 to 5, the image forming apparatus characterized by the threshold of the transfer start time of output are provided respectively in accordance with the process linear velocity.

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