JP2005321714A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can stably suppress the production of image memory. <P>SOLUTION: When continuous printing is to be performed, a table setting a transfer bias to decrease the voltage to be applied on primary intermediate transfer drums 20A, 20B for the first sheet of printing with respect to the target transfer voltage is preliminarily memorized in a table memory part 50; and the table is read out by a controlling unit 40 from the table memory section 50 to set the transfer voltage to form an image. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having an intermediate transfer member that transfers toner from a photoreceptor to a recording medium.

  In general, an image forming apparatus such as an electrophotographic copying machine or a laser beam printer uses a charging unit to charge the surface of a photosensitive drum, and after performing exposure based on image data using an exposure unit, the surface of the photosensitive drum. A toner image is formed on the surface. Then, the toner image is transferred to a recording medium using a transfer unit, and the transferred toner image is fixed by a fixing unit, thereby forming an image on the recording medium.

  In recent full-color copying machines, full-color laser beam printers, and the like, a toner image formed on a photosensitive drum is primarily transferred to an intermediate transfer member, and yellow, cyan, magenta, and black are transferred onto the intermediate transfer member. After the color toner images are superimposed, a full-color image is formed by performing secondary transfer on the recording medium at once.

  In recent image forming apparatuses such as printers, there is an increasing demand for cost reduction, and a direct current power source is used without superimposing alternating current by charging and transfer. The merit of using a DC power supply has advantages such as suppression of ozone generation, suppression of resonance phenomenon caused by AC power supply, and suppression of photoconductor surface deterioration and wear in addition to cost merit. There are disadvantages such as inferior to the superimposed system, and when the transfer member and the charging member are in contact with the photoreceptor, they are vulnerable to contamination of the member surface.

  In particular, the weak charging ability of DC charging means that the potentials are uniformly aligned when the charging history is not sufficient enough to cancel the potential history corresponding to the image pattern one round before the photoreceptor during the next charging process. The image history becomes apparent as the image memory of the photoconductor.

  In the transfer process, a potential is applied between the photosensitive member and the transfer member. At this time, when the potential polarity applied to the transfer member is the same as the polarity of the charging member, the transfer member functions as an auxiliary charging device. On the other hand, when the polarity is reverse, it functions as an erase device that cancels the potential of the photoreceptor after the charging process. That is, the current flowing through the transfer member affects the surface potential of the photosensitive member, causing a halftone density change. In a system in which the polarity of the transfer voltage applied to the transfer member is opposite to the polarity of the charge voltage applied to the charging member, if the transfer current is small, an increase in transfer residue and image memory are generated, and the current is kept constant. On the contrary, a thin image memory tends to be generated. That is, since the charging capability of DC charging is low, an image memory is generated depending on the transfer current.

  In a DC charging system, even when the charging member is stable without being contaminated and deteriorated, the image memory may be generated sensitively due to fluctuations in the amount of current flowing through the transfer member. In order to prevent this, it is desirable to keep the amount of current flowing through the transfer member constant.

  On the other hand, not only image memory countermeasures, but various techniques have been proposed to make the transfer current constant for the purpose of stabilizing transfer efficiency (for example, Patent Documents 1 to 4).

  In the technique described in Patent Document 1, constant current control for making the current constant has been studied. However, a constant current power source requires a highly accurate power source and increases costs, and is required for a small printer. Contrary to low cost.

  Further, Patent Documents 2 to 4 have been proposed as techniques related to a constant voltage power supply with cost merit.

  In the technique disclosed in Patent Document 2, transfer voltage control means that performs resistance detection of a transfer member a plurality of times and determines a different transfer constant voltage bias for each resistance detection process when the detected resistance of the transfer member is lower than a predetermined value. Has been proposed.

  In the technique described in Patent Document 3, when printing is performed a plurality of times, a transfer voltage is detected and an average value is calculated. Then, it has been proposed to determine the target value of the transfer voltage at the time of the next printing based on the average value.

In the technique described in Patent Document 4, it is proposed to estimate the optimum transfer voltage by measuring the number of printed sheets and the use environment.
U.S. Pat. No. 3,781,105 Japanese Patent Laid-Open No. 2000-075694 JP 11-309901 A Japanese Patent Laid-Open No. 10-301344

  By the way, since the transfer member is semiconductive, immediately after application of a voltage, a large amount of displacement current flows for charging the capacitance. In particular, a large amount of transfer current is generated on the first sheet printed from a state where there has been no printing for a while.

  Further, in recent printers, as a method of collecting the residual toner remaining on the photosensitive member or the charging member or the transfer member without being transferred to the recording sheet, each of the charging voltage and the transfer voltage applied during normal printing is used. A cleaning method that collects toner by applying a voltage having a polarity opposite to the polarity or applying a potential difference different from a normal potential difference has been proposed. A state of being charged with a charge having a polarity opposite to that at the time of printing or a state having a surface potential of a magnitude different from that at the time of normal printing. When printing is performed after this cleaning, as described above, a displacement potential that flows to charge the capacitance is transiently generated during the initial printing.

  In the conventional technology as described above, it is mentioned that a stable current supply is provided against a resistance increase with time of energization of the transfer member and a resistance change of a semiconductive material such as a transfer member due to a temperature / humidity change. However, the displacement current at the time of printing the first sheet is not considered, and there is a concern about the stability of the transfer current in the constant voltage DC power source at the time of continuous printing.

  Further, since the stability of the transfer current is lost due to the displacement current in this way, there is a problem that the occurrence of the image memory appears remarkably.

  The present invention has been made in consideration of the above-described facts, and an object of the present invention is to provide an image forming apparatus that can stably suppress the occurrence of an image memory.

  In order to achieve the above object, an invention according to claim 1 includes an intermediate transfer member that transfers toner from a photoreceptor to a recording medium, and an image that forms an image by applying a transfer bias to the intermediate transfer member. The forming apparatus includes a control unit that controls a displacement current flowing through the intermediate transfer member at the start of applying the transfer bias.

  As described above, since the transfer member is semiconductive, when the image formation is started from a state where the image formation has not been performed for a while, the capacitance of the transfer member is charged when the image is formed on the first recording medium. Therefore, a transition current flows transiently through the intermediate transfer member.

  Therefore, in the first aspect of the invention, the displacement current flowing through the intermediate transfer member is controlled by the control means at the beginning of applying the transfer voltage (for example, when forming the first sheet, the second sheet, or the like). As a result, the displacement current that flows transiently as described above can be suppressed. That is, since it is possible to prevent the transfer current from being lost due to the displacement current, it is possible to stably suppress the occurrence of the image memory.

  The control means is, for example, a transfer bias control means for controlling a displacement current that flows transiently to the intermediate transfer member by setting a transfer bias lower than a predetermined target transfer bias, as in the invention described in claim 2. Or a timing control means for controlling the displacement current flowing in the intermediate transfer member transiently by setting the image formation timing based on the image information as in the invention of claim 3. May be applied.

  In addition, since there is a change in characteristics due to deterioration with time or the like, the control means may control the displacement current based on the cumulative number of image formations on the recording medium, as in the fourth aspect of the invention. For example, a table for controlling the displacement current in the initial state and a table for controlling the displacement current after the lapse of time may be provided, and a table to be used may be selected according to the cumulative image formation.

  Further, since the displacement current changes depending on the surrounding environment, as in the invention described in claim 5, the detecting means for detecting at least one of ambient ambient temperature and humidity is further provided, and the control means detects the detecting means. The target transfer bias may be controlled based on the result.

  As a means for charging the photoconductor, a DC power source can be used as in the invention described in claim 6.

  As described above, according to the present invention, since the control means for controlling the displacement current flowing through the intermediate transfer member at the beginning of applying the transfer bias can be provided, the displacement current flowing transiently can be suppressed. Thus, there is an effect that generation of the image memory can be suppressed.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. In the present embodiment, the present invention is applied to a full-color laser beam printer.

  FIG. 1 is a diagram showing a schematic configuration of a full-color printer according to an embodiment of the present invention. The arrows in FIG. 1 indicate the rotation direction of each rotating member.

  As shown in FIG. 1, the full-color laser printer 10 according to the embodiment of the present invention includes photosensitive drums 12Y, 12M for yellow (Y), magenta (M), cyan (C), and black (K). 12C, 12K, charging rolls 14Y, 14M, 14C, 14K for primary charging that come into contact with these photosensitive drums 12Y, 12M, 12C, 12K, and an optical unit 16Y that emits laser light for forming images of the respective colors. , 16M, 16C, 16K, the developing devices 18Y, 18M, 18C, 18K, and the first photosensitive drums 12Y, 12M that are in contact with two of the four photosensitive drums 12Y, 12M, 12C, 12K described above. A primary intermediate transfer drum 20A, a second primary intermediate transfer drum 20B in contact with the remaining two photosensitive drums 12C and 12K, and the first and second Primary intermediate transfer drum 20A, those in contact with the secondary intermediate transfer drum 22 to 20B, in a final transfer roll 24 abuts on the secondary intermediate transfer drum 22, and the main part is configured.

  Among these configurations, the photosensitive drums 12Y, 12M, 12C, 12K, charging rollers 14Y, 14M, 14C, 14K, developing units 18Y, 18M, 18C, 18K, first and second primary intermediate transfer drums 20A, The 20B and the secondary intermediate transfer drum 22 are integrated as a single image forming unit 26. For example, when the image quality deteriorates due to deterioration of the photosensitive drum, the image forming unit 26 is replaced as it is. It is possible to do.

  The photoconductor drums 12Y, 12M, 12C, and 12K have a common contact plane M and are arranged at regular intervals. Further, the first primary intermediate transfer drum 20A and the second primary intermediate transfer drum 20B have their rotational axes parallel to the axes of the photosensitive drums 12Y, 12M, 12C, and 12K and with a predetermined symmetry plane as a boundary. Are arranged so as to be in the relationship of the plane object. Further, the secondary intermediate transfer drum 22 is arranged so that the rotation axis thereof is parallel to the photosensitive drums 12Y, 12M, 12C, and 12K.

  When forming a full-color image, a signal corresponding to image information for each color is rasterized by an image processing unit (not shown) and input to the laser optical units 16Y, 16M, 16C, and 16K. In the laser optical units 16Y, 16M, 16C, and 16K, the laser light for forming an image corresponding to each color of Y, M, C, and K is modulated, and the corresponding photosensitive drums 12Y, 12M, 12C, and 12K. It comes to be irradiated. As a result, latent images corresponding to the respective colors are formed on the photosensitive drums 12Y, 12M, 12C, and 12K.

  Around the photosensitive drums 12Y, 12M, 12C, and 12K, an image forming process for each color is performed by a known electrophotographic method. For example, an OPC photoconductor can be used as the photoconductor drums 12Y, 12M, 12C, and 12K, and the surface of these photoconductor drums 12Y, 12M, 12C, and 12K is a charging roll to which a DC voltage of about 800 V is applied. 14Y, 14M, 14C, and 14K are uniformly charged to about 300V, for example. In the present embodiment, only the DC component is applied as the charging rolls 14Y, 14M, 14C, and 14K.

  An electrostatic latent image corresponding to input image information (image data) for each color is predetermined on the surfaces of the photosensitive drums 12Y, 12M, 12C, and 12K having a surface potential that is uniformly charged in this way. Formed with timing. By writing the electrostatic latent images with the laser optical units 16Y, 16M, 16C, and 16K, the surface potentials of the image exposure portions of the photosensitive drums 12Y, 12M, 12C, and 12K are neutralized to about 60 V or less.

  The electrostatic latent images corresponding to the respective colors formed on the surfaces of the photosensitive drums 12Y, 12M, 12C, and 12K are developed by the developing units 18Y, 18M, 18C, and 18K for the corresponding colors, and the photosensitive drums 12Y. , 12M, 12C, and 12K are visualized as toner images of respective colors. Developers 18Y, 18M, 18C, and 18K are filled with developers composed of different Y, M, C, and K color toners and carriers, respectively. When the toner is supplied from a toner supply device (not shown) to the developing units 18Y, 18M, 18C, and 18K, the supplied toner is sufficiently agitated with the carrier by the auger 28 and frictionally charged. Inside the developing roll 30, a magnet roll (not shown) having a plurality of magnetic poles arranged at a predetermined angle is fixed. The amount of developer conveyed to the vicinity of the surface of the developing roll 30 is regulated by the developer amount regulating member 34 by the paddle 32 that conveys the developer to the developing roll 30.

  The toner supplied onto the developing roll 30 is in the form of a magnetic brush composed of a carrier and toner by the magnetic force of a magnet roll (not shown), and this magnetic brush contacts the photosensitive drums 12Y, 12M, 12C, and 12K. It touches. AC and DC (AC + DC) developing bias voltages are applied to the developing roll 30 to develop the toner on the developing roll 30 into electrostatic latent images formed on the photosensitive drums 12Y, 12M, 12C, and 12K. As a result, a toner image is formed. In the present embodiment, the developing bias voltage is about 4 kHz, 1.5 Vpp for alternating current, and about 230 volts for direct current.

  Next, the toner images of the respective colors Y, M, C, and K formed on the photosensitive drums 12Y, 12M, 12C, and 12K are transferred onto the first primary intermediate transfer drum 20A and the second primary intermediate transfer drum 20B. The primary transfer is electrostatically performed.

  Cyan and magenta toner images formed on the photosensitive drums 12Y and 12M are cyan and magenta toner images formed on the first primary intermediate transfer drum 20A and cyan and black toner images formed on the photosensitive drums 12C and 12K, respectively. And transferred onto the second primary intermediate transfer drum 20B. By shifting the writing start timing of the electrostatic latent image on the photosensitive drums 12Y, 12M, 12C, and 12K for each color, the yellow and magenta toner images that are primarily transferred on the first primary intermediate transfer drum 20A are appropriately obtained. A superimposed dual color image is formed. Also, a double color image in which cyan and black toner images are appropriately superimposed is formed on the second primary intermediate transfer drum 20B.

The surface potential necessary for electrostatically transferring the toner images from the photosensitive drums 12Y, 12M, 12C, and 12K onto the first and second primary intermediate transfer drums 20A and 20B is about + 250V to 500V. The optimum surface potential varies depending on the charged state of the toner, the ambient temperature, and the humidity. However, when the toner charge amount is in the range of −20 to −35 μC / g and is in a normal temperature and humidity environment, the first surface potential is the first. The surface potential of the second primary intermediate transfer drums 20A and 20B is preferably about + 380V. The resistance values of the first and second primary intermediate transfer drums 20A and 20B are set to about 10 ⁸ Ω, and a metal pipe made of Fe, Al, or the like is made of a low resistance elastic layer (such as conductive silicon rubber). R = 10 ² to 10 ³ Ω). Further, a fluorine rubber layer having a thickness of 3 to 100 μm is provided on the surface of the low resistance elastic layer as a high release layer, and is bonded with a silane coupling adhesive (primer). The resistance value of the high release layer is about R = 10 ⁵ to 10 ⁹ Ω. A voltage is applied to the first and second primary intermediate transfer drums 20A and 20B from a constant voltage power source.

  Thereafter, the dual-color toner images formed on the first and second primary intermediate transfer drums 20A and 20B are electrostatically secondary-transferred onto the secondary intermediate transfer drum 22. Accordingly, a final toner image in which the four colors Y, M, C, and K are overlapped is formed on the secondary intermediate transfer drum 22.

  The toner image formed on the secondary intermediate transfer drum 22 is transferred by the transfer roller 24 to the paper P conveyed by the conveyance roller 36 or the like, and then fixed by the fixing unit 38, whereby the toner image is formed on the paper P. An image is formed.

  The developer of each color developing device 18Y, 18M, 18C, 18K may be a two-component developer in which toner and a carrier are mixed, or a single-component developer containing only toner.

  The toner used here is an emulsion aggregation coalescence method (EA method) formed by agglomerating and coalescing styrene acrylic resin fine particles and pigment fine particles of Y, M, C, and K, respectively, to an average particle diameter of about 6 μm. The toner produced in (1) was used. The particle size distribution index (GSD) was 1.23. The average particle diameter is a value of a volume average particle diameter measured with a Coulter counter (manufactured by Coulter). Then, by adjusting the heating time and heating temperature during polymerization, four types (four colors) of toner having the same average particle size and particle size distribution were prepared.

  The toner shape (toner shape factor) was calculated by the following equation by performing image analysis on an enlarged photograph of the toner obtained with an optical microscope (Microphoto FXA: manufactured by Nikon Corporation) using an image analyzer Luzex3 (manufactured by NIRECO). Value.

  The toner shape factor is expressed as a ratio of the projected area of the toner and the area of a circle circumscribing the toner, and is 100 in the case of a true sphere, and increases as the shape collapses. The toner shape factor is calculated for a plurality of toner particles, and the average value is used as a representative value. In this embodiment, spherical toner having a shape factor of 100 to 125 is used, but toner having a shape factor of 100 to 140 may be used.

  Further, an appropriate amount of silica and titania inorganic fine particles having an average particle diameter of 10 to 100 nm is externally added to the toner and mixed with a carrier made of ferrite beads having an average particle diameter of 50 μm to form a developing roll of −25 to −35 μC. / G charge amount was obtained.

In addition to the emulsion aggregation and coalescence method, a spherical toner formed by a suspension polymerization method, a dissolution suspension method, an emulsion polymerization method, a kneading and pulverization method, or the like may be used as the toner.
[First Embodiment]
Next, the configuration of the control system of the full color laser printer 10 according to the first embodiment of the present invention will be described.

  FIG. 2 is a block diagram showing the configuration of the control system of the full color laser printer according to the first embodiment of the present invention.

  The full-color laser printer includes a control unit 40, and the entire device is controlled by the control unit 40.

  A transfer drum driver 42, a photoconductor driver 44, a paper transport system 46, a laser light source unit 16, an environment sensor 48, and a table storage unit 50 are connected to the control unit 40.

  The transfer drum driver 42 is connected to the first primary transfer drum 20A, the second primary transfer drum 20B, and the secondary transfer drum 22, and is applied by the transfer drum driver 42 during rotation driving and transfer of each transfer drum. The transfer bias to be controlled is controlled. The transfer bias applied to the transfer drum is supplied from a DC power supply 52 that is a constant voltage power supply connected to the transfer drum driver 42.

  The photosensitive drum 44 and the charging roll 14 corresponding to each color are connected to the photosensitive drum driver 44. The driving of the photosensitive drum 12 is controlled by the photosensitive drum driver 44, and charging for charging the photosensitive drum 12 is performed. Drive control of the roll 14 is performed. The charging roll 14 is applied with a voltage for charging by a DC power source 52 connected to the photoconductor driver 44.

  The paper transport system 46 includes a transport roller 36, and transports the paper P to the transfer position by driving the transport roller 36.

  The laser light source unit 16 modulates a laser beam based on image data representing an image to be formed and is input to the control unit 40, and irradiates each photosensitive drum 12 with the modulated laser beam. A latent image is formed on the drum 12.

  For example, the environmental sensor 48 detects the ambient temperature and humidity of the full-color laser printer 10 and outputs the detection result to the control unit 40.

  The table storage unit 50 stores a table of transfer voltages applied to the primary intermediate transfer drums 20A and 20B according to the detection result of the environment sensor 48, and a transfer voltage applied to the primary intermediate transfer drums 20A and 20B according to the number of images formed. Are stored.

  The table stored in the table storage unit 50 is, for example, a transfer voltage table as shown in FIGS.

  FIG. 3 is a diagram illustrating an example of a transfer voltage table corresponding to the environment stored in the table storage unit 50, and FIG. 4 is a diagram illustrating an example of a transfer voltage table according to the number of image formations in the initial state. FIG. 5 is a diagram illustrating an example of a transfer voltage table corresponding to the number of image formations over time (after a predetermined number of image formations).

  That is, the control unit 40 selects a target transfer voltage corresponding to the environment as shown in FIG. 3 as the transfer voltage applied to the primary intermediate transfer drums 20A and 20B. Further, as shown in FIGS. 4 and 5, correction of the target transfer voltage according to the page on which the image is formed is added, and the correction of the target transfer voltage is further changed as time passes. ing. Specifically, in the present embodiment, the control unit 40 controls the transfer bias so that the output is 92% to 97% with respect to the target transfer voltage when performing image formation for the first page in the initial state. The transfer bias is controlled so that the output becomes 96% to 100% with respect to the target transfer voltage with the change with time. If the transfer bias is set to be lower than the target transfer voltage at the start of applying the transfer voltage, the value is not limited to the above numerical range.

  Next, the flow of processing performed by the control unit 40 of the full-color laser printer 10 according to the embodiment of the present invention configured as described above will be described. FIG. 6 is a flowchart showing an example of the flow of processing performed by the control unit 40 of the full-color laser printer 10 according to the embodiment of the present invention.

  First, in step 100, it is determined whether or not the control unit 40 has received image data to be printed, and the process waits until the determination is affirmed and the process proceeds to step 102.

  In step 102, the environment by the environment sensor 48 is detected and input to the control unit 40, the process proceeds to step 104, and a transfer voltage table corresponding to the detection result of the environment sensor 48 is read. That is, the target transfer voltage for each environment shown in FIG. 3 is read.

  Next, in step 106, the control unit 40 determines whether the total number of prints is equal to or greater than a predetermined number. That is, whether or not a change with time has occurred is determined based on the total number of prints. If the determination is affirmative, the process proceeds to step 108, and if the determination is negative, the process proceeds to step 110. .

  In step 108, a transfer voltage table corresponding to the number of image formations over time is read. In step 110, a transfer voltage table corresponding to the number of image formations in the initial state is read. That is, in step 108, a table as shown in FIG. 5 is read, and in step 110, a table as shown in FIG. 4 is read.

  Subsequently, in step 112, it is determined whether or not there is a correction page. In this determination, it is determined whether or not the page has a transfer voltage set low according to the read table. If the determination is negative, the process proceeds to step 114, and if the determination is affirmative. Proceeds to step 116.

  In step 114, a target voltage corresponding to the environment is set. In step 116, a transfer voltage (correction voltage) corresponding to the number of image formations is set.

  Next, in step 118, the transfer bias is controlled so as to achieve the set transfer voltage, and image forming processing is performed. That is, the transfer voltage set as described above is set in the transfer drum driver 42 by the control unit 40, whereby the transfer voltage set to the first and second primary intermediate transfer drums 20A and 20B is applied. After the laser light source unit 16 is controlled based on the image data and a latent image is formed on each photosensitive drum 12, the sheet is passed through the first and second primary intermediate transfer drums 20 </ b> A and 20 </ b> B and the secondary transfer drum 22. An image is formed on P.

  In step 120, the control unit 40 determines whether the image formation is completed. This determination is made by determining whether or not image formation has been completed for all image data received by the control unit 40. If the determination is negative, the process returns to step 106 and the above-described processing is repeated. When the determination in step 120 is affirmed, the series of processing by the control unit 40 is terminated.

  Here, the processing (transfer voltage control) performed by the control unit 40 of the full-color laser printer 10 as described above will be described in detail.

  FIG. 7 shows the amount of current flowing through the first and second primary transfer drums 20A and 20B when the voltage applied to the first and second primary intermediate transfer drums 20A and 20B is swung from 320 V to 600 V, and at that time. The generation level of the generated image memory is shown. The surface of each photosensitive drum 12 is uniformly charged to about 300 V by a charging roll 30 to which a DC voltage of about 800 V is applied, and the environment shows the result at 22 ° C. and 55% humidity.

  In this evaluation of the image memory, image formation is performed with a single color image of magenta color with the laser light emitted from the laser light source unit 16, and when the sign of this image memory is positive, the photosensitive member goes round one revolution. In the pattern consisting of the image portion and the non-image portion, the portion corresponding to the image portion is a positive image memory that appears as a dark history in the second round of the photoconductor. Conversely, if the sign of the image memory is negative, the image This is a negative image memory in which the portion corresponding to the portion becomes thinner in the second round of the photoreceptor.

  The generation level of the image memory in FIG. 7 is a value based on the evaluation standard of the ghost grade shown in FIG. 8, where 0 is a ghost has not occurred and 1 is a level that cannot be discerned at first glance. Level at which it can be seen that the history of the image before the photosensitive drum has become darker, 2 is the level at which the image before the photosensitive drum has appeared as the history is a level where there is not much contrast, and 3 is the image before the photosensitive drum Is clearly visible as a dark history and is a level that can be discriminated even from a distance, and -1 is a level that cannot be discerned at first glance, but if you look closely, the history of the image around the photoconductor drum is thin (like white spots) ), 2 indicates that the image before the photoconductor circle appears as a history level, and there is not much difference in light and shade, 3 indicates that the image before the photoconductor circle is clear and light (white spots are clear) To the level that can be discriminated even from a distance, expressed as 0.5, the intermediate level of each level is represented as 0.5, the level of the ghost level slightly worse than ± 3 is ± 3.5, If the degree is in the range of ± 2, it is difficult to identify with the naked eye unless staring.

  As shown in FIG. 7, the image memory changes from positive to zero and negative as the amount of current flowing through the primary intermediate transfer drums 20A and 20B increases.

  Further, as shown in FIG. 9, when five continuous prints are performed under the condition that the applied voltage to the primary intermediate transfer drums 20A and 20B is fixed to 440V, the current amount of the primary intermediate transfer drums 20A and 20B. The relationship between the number of pages and the number of pages shows that a large amount of displacement current is generated in the first sheet.

  Although voltage is applied to the primary intermediate transfer drums 20A and 20B from a constant voltage power source, the voltage flows to charge the capacitance of the primary intermediate transfer drum during a period until the surface potential of the primary intermediate transfer drum is stabilized. Displacement current is generated, and in particular, a large amount of displacement current is transiently generated on the first sheet when continuous printing is performed.

  FIG. 10 shows that the applied voltage supplied from the constant voltage power source to the first and second primary intermediate transfer drums 20A and 20B is output 100% of the target transfer voltage from the first sheet, and the environment is 22 ° C. and 55% RH. It is a figure which shows the result of having conducted the experiment regarding an image memory below. As an image memory evaluation method at this time, a ghost grade was confirmed by printing five continuous prints in a single magenta color.

  When the applied voltage supplied from the constant voltage power source to the first and second primary intermediate transfer drums 20A and 20B is 440V, as shown in FIG. 10, the first and second primary intermediate transfer drums 20A and 20B. The current value of the first image was about 22 μA, and the image memory was generated as a ghost grade-1 negative image memory. On the second and subsequent sheets, the value of the current flowing to the first and second primary intermediate transfer drums 20A and 20B was within the range of 17.5 ± 1.0 μA, and no image memory was generated. When the target transfer voltage is set to output 100% from the first sheet in this way, the first and second primary intermediate transfer drums 20A and 20B on the first sheet are output during the period until the surface potential is stabilized. Displacement current that flows to charge the capacitance of the first and second primary intermediate transfer drums 20A and 20B is generated, resulting in the generation of a negative image memory.

  Therefore, in this embodiment, for example, when performing continuous printing in a new initial state, there is a table in which the voltage applied to the primary intermediate transfer drums 20A and 20B for only the first sheet is set smaller than the target transfer voltage. It is stored in the table storage unit 50, and the controller 40 reads the table from the table storage unit 50 and sets the transfer voltage. Accordingly, as shown in FIGS. 11 and 12, the displacement current generated in the first primary intermediate transfer drums 20A and 20B can be controlled. FIG. 11 is a table showing the displacement current for each page with respect to each target transfer voltage, the corrected transfer voltage, and the corrected displacement current. FIG. 12 shows the corrected current for each target transfer voltage. It is a graph which shows the displacement current (primary intermediate transfer drum current) of each page.

  For example, as shown in FIG. 11, when the target surface potential of the primary intermediate transfer drums 20A and 20B is 440V and the applied voltage supplied from the constant voltage power source to the primary intermediate transfer drums 20A and 20B is 440V, In the initial state (for example, until 0 to 1000 sheets are printed), only the first sheet is set to 414 V, which is 94% output of 440 V. As a result, as shown in FIGS. 11 and 13, when continuous printing is performed, the transfer current is kept in the range of 17.5 ± 1.0 μA through one to five sheets, and the image memory is not generated all the time. Can do.

  In the present embodiment, as described above, the table storage unit 50 stores a table that can derive an optimum value in accordance with the total number of prints of the full-color laser printer 10, the temperature and humidity in the apparatus, and the like, regardless of the number of pages. Therefore, it is possible to perform high-quality image formation in which generation of a stable image memory is suppressed according to changes in temperature and humidity. Further, stable high-quality image formation can be performed by changing the transfer voltage according to an appropriate number of sheets as well as the first sheet as necessary.

  In this embodiment, when the deterioration of the transfer members such as the first and second primary intermediate transfer drums 20A and 20B and the secondary intermediate transfer drum 22 has progressed with time, a table corresponding to the deterioration with time is used. Since it is stored in the table storage unit 50, as shown in FIG. 14, even when deterioration with time progresses, high-quality image formation in which generation of a stable image memory is suppressed can be performed as in the initial state. . That is, in the present embodiment, it is possible to perform high-quality image formation in which the generation of a stable image memory is suppressed from the initial stage over time.

For example, when the deterioration with time progresses, the applied voltage supplied from the constant voltage power source to the first and second primary intermediate transfer drums 20A and 20B is set to 440V, and as shown in FIG. For the first and second prints, the transfer voltage is output to 421V, which is 96% output of 440V. As a result, when continuous printing is performed, the transfer current is kept in the range of 17.5 ± 1.0 μA through one to five sheets, and the image memory can be kept from occurring all the time.
[Second Embodiment]
Next, a full color laser printer according to a second embodiment of the present invention will be described. Note that the schematic configuration of the full-color laser printer is the same as that of the first embodiment, and a description thereof will be omitted.

  The configuration of the control system of the full-color laser printer according to the second embodiment is the same as that of the control system 40 except that the function of the control unit 40 and the table stored in the table storage unit 50 are different. Description of is omitted.

  In the control unit 40 of the full-color laser printer 10 according to the first embodiment, the displacement current flowing in the first and second primary intermediate transfer drums 20A and 20B is controlled by controlling the transfer voltage. The control unit 41 (see FIG. 2) of the full-color laser printer 10 according to the second embodiment controls the pre-transfer time from when the transfer voltage is applied to when the image forming operation is started (exposure is started by the laser light source unit 16). It has become.

  In the table storage unit 51 (see FIG. 2) of the full-color laser printer according to the second embodiment, the transfer applied to the primary intermediate transfer drums 20A and 20B according to the detection result of the environmental sensor 48, as in the first embodiment. A voltage table is stored, and a pre-transfer time table corresponding to the number of formed images is stored. That is, the table storage unit 51 has a pre-transfer time table corresponding to the number of image formations instead of the transfer voltage table applied to the primary intermediate transfer drums 20A and 20B corresponding to the number of image formations in the first embodiment. Based on the pre-transfer time table, the control unit 41 controls the pre-transfer time from when a voltage is applied to the primary intermediate transfer drums 20A and 20B until exposure is started. Specifically, the control unit 41 analyzes the image data and controls the pre-transfer time by controlling the timing of applying a voltage to the primary intermediate transfer drums 20A and 20B with respect to the image formation start position. It has become.

  Next, the flow of processing performed by the control unit 41 of the full color laser printer 10 according to the second embodiment will be described. FIG. 15 is a flowchart showing an example of the flow of processing performed by the control unit 41 of the full-color laser printer 10 according to the second embodiment of the present invention.

  First, in step 200, it is determined whether or not the control unit 41 has received image data to be printed. The process waits until the determination is affirmed, and the process proceeds to step 202.

  In step 202, the environment by the environment sensor 48 is detected and input to the control unit 41, the process proceeds to step 204, and a transfer voltage table corresponding to the detection result of the environment sensor 48 is read. That is, the target transfer voltage for each environment shown in FIG. 3 is read.

  Next, in step 206, a pre-transfer time table is read, and the process proceeds to step 208.

  In step 208, the image data input to the control unit 41 is analyzed, an image formation start position (image writing position on the paper P) is detected, the process proceeds to step 210, and the read pre-transfer time table is read. Then, a transfer voltage is applied based on the detected image formation start position. That is, the application timing of the transfer voltage to be applied is controlled.

  Subsequently, the process proceeds to step 212, and an image forming process is performed. That is, after each laser light source unit 16 is controlled based on the image data and a latent image is formed on each photosensitive drum 12, the first and second primary intermediate transfer drums 20A and 20B and the secondary transfer drum 22 are moved. Thus, an image is formed on the paper P.

  In step 214, the control unit 41 determines whether or not the image formation is completed. This determination is made by determining whether or not image formation has been completed for all image data received by the control unit 41. If the determination is negative, the process returns to step 212 and the above-described processing is repeated. When the determination in step 214 is affirmed, the series of processing by the control unit 41 is terminated.

  Here, the processing (pre-transfer time control) performed by the control unit 41 of the full-color laser printer as described above will be described in detail.

  FIG. 7 shows the first and second primary transfer drums 20A when the voltage applied to the first and second primary transfer drums 20A and 20B is swung from 320V to 600V, as described in the first embodiment. The amount of current flowing through 20B and the generation level of the image memory generated at that time are shown.

  As shown in FIG. 7, the image memory changes from positive to zero and negative as the amount of current flowing through the primary intermediate transfer drums 20A and 20B increases.

  As shown in FIG. 9, when five continuous prints are performed under the condition that the applied voltage to the primary intermediate transfer drums 20A and 20B is fixed to 440V, the current of the primary intermediate transfer drums 20A and 20B From the relationship between the amount and the number of pages, it can be seen that a large amount of displacement current is generated in the first sheet.

  As described above, voltage is applied to the primary intermediate transfer drums 20A and 20B from a constant voltage power source, but the capacitance of the primary intermediate transfer drum during the period until the surface potential of the primary intermediate transfer drum is stabilized is set. Displacement current flowing for charging is generated, and a large amount of displacement current is generated transiently on the first sheet, particularly when continuous printing is performed.

  FIG. 16 is a diagram in which the number of pages in FIG. 9 is replaced with the elapsed time after the application of the primary transfer voltage, and the amount of displacement current decreases with the passage of time and stabilizes at about 4.6 sec. If the image is transferred to the primary transfer drum after the displacement current immediately after monitoring during continuous printing disappears and the current stabilizes, generation of an image memory can be prevented.

  Table 1 below shows that when the time from when the voltage starts to be applied to the primary intermediate transfer drums 20A and 20B to the time when the leading edge of the sheet reaches the primary intermediate transfer drums 20A and 20B from the photosensitive member is fixed at 1.4 sec. The results of an experiment relating to an image memory in a 22 ° C. 55% RH environment in which continuous printing is performed when the image position is at the leading edge of the sheet and when the image position is at the center of the sheet are shown. In the image memory evaluation method, as in the first embodiment, the ghost grade was confirmed by printing five continuous sheets in a single magenta color.

  As in the example described in the first embodiment, when the applied voltage supplied from the constant voltage power source to the first and second primary intermediate transfer drums 20A and 20B is 440V and the image position is at the leading edge of the sheet, The current value to the first and second primary intermediate transfer drums 20A and 20B was about 22 μA for the first sheet, and the image memory was generated as a ghost grade negative image memory (Comparative example in Table 1). 1). On the second and subsequent sheets, the value of the current flowing to the first and second primary intermediate transfer drums 20A and 20B was within the range of 17.5 ± 1.0 μA, and no image memory was generated. The surface potential of the primary intermediate transfer drums 20A and 20B that can be placed on the first sheet is generated, resulting in the generation of a negative image memory (see Comparative Example 1 in Table 1).

  Similarly, when the applied voltage supplied from the constant voltage power source to the first and second primary intermediate transfer drums 20A and 20B is 440 V and the image position is in the center of the sheet, the first first sheet In the image memory, a negative image memory of ghost grade -0.5 was generated (see Comparative Example 2 in Table 1), and no image memory was generated for the second and subsequent sheets.

  Therefore, in the present embodiment, the time from when the voltage starts to be applied to the primary intermediate transfer drums 20A and 20B until the toner at the leading edge of the image portion reaches the primary intermediate transfer drums 20A and 20B from the respective photosensitive drums 12 is pre-processed. By controlling the transfer time, the amount of current can be stabilized, thereby preventing the occurrence of image memory.

  For example, when the target surface potential of the primary intermediate transfer drums 20A and 20B is 440V and the applied voltage supplied from the constant voltage power source to the primary intermediate transfer drums 20A and 20B is 440V under the environmental condition of 22 ° C. and 55% RH. When the image position is at the leading edge of the sheet, the pre-transfer time is set to 4.6 sec (4.6 sec until the leading edge of the first sheet), and as a result of continuous printing, the transfer current is 1 to 5 sheets. The image memory can be kept from occurring all the time within the range of 17.5 ± 1.0 μA (see Example 1 in Table 1).

  In addition, when the image position is in the center, the pre-transfer time is set to 4.6 sec (3.6 sec until the leading edge of the first sheet of paper), and when continuous printing is performed, the transfer current is at the leading edge of the first sheet of paper. 19.2 μA and displacement current still remained, but after the center position of the first image with the image, it is within the range of 17.5 ± 1.0 μA, and the image memory can be kept from occurring all the time (Table 1). Example 2).

  In the second embodiment, a pre-transfer time table corresponding to a change with time may be provided as in the first embodiment. As a result, it is possible to form a high-quality image without generating a stable image memory regardless of temperature and humidity fluctuations from the beginning to the passage of time.

  In the second embodiment, in order to control the pre-transfer time, image data is analyzed to control the timing of applying a voltage to the primary intermediate transfer drums 20A and 20B with respect to the image formation start position. However, the present invention is not limited to this as long as the pre-transfer time can be controlled. For example, the conveyance start timing of the paper P may be controlled.

1 is a diagram illustrating a schematic configuration of a full-color laser printer according to an embodiment of the present invention. 1 is a block diagram illustrating a configuration of a control system of a full color laser printer according to a first embodiment of the present invention. It is a table | surface which shows an example of the transfer voltage table according to the environment memorize | stored in the table memory | storage part of the full-color laser printer concerning 1st Embodiment of this invention. 3 is a table showing an example of a transfer voltage table corresponding to the number of image formations in an initial state stored in a table storage unit of the full-color laser printer according to the first embodiment of the present invention. 4 is a table showing an example of a transfer voltage table corresponding to the number of image formations over time (after a predetermined number of image formations) stored in the table storage unit of the full-color laser printer according to the first embodiment of the present invention. It is a flowchart which shows an example of the flow of the process performed in the control part of the full-color laser printer concerning 1st Embodiment of this invention. The amount of current flowing through the first and second primary transfer drums when the voltage applied to the first and second primary intermediate transfer drums is swung from 320 V to 600 V, and the generation level of the image memory generated at that time are shown. It is a graph. It is a table | surface which shows the evaluation criteria of a ghost grade. FIG. 6 is a diagram illustrating a current value flowing through the first and second primary intermediate transfer drums for each page when an applied voltage supplied from a constant voltage power source to the first and second primary intermediate transfer drums is 440V. . The voltage applied from the constant voltage power source to the first and second primary intermediate transfer drums is output 100% of the target transfer voltage from the first sheet, and an experiment relating to the image memory is performed at 22 ° C. and 55% RH. It is a figure which shows the result of having performed. It is a table | surface which shows the transfer current value for every page in each target transfer voltage, and the transfer current value for every page at the time of transfer voltage correction | amendment. It is a graph which shows the displacement current of each page after correction | amendment for every target transfer voltage. When the applied voltage supplied from the constant voltage power source to the first and second primary intermediate transfer drums is 440 V, the value of the current flowing through the first and second primary intermediate transfer drums for each page before and after correction is calculated. FIG. It is a table | surface which shows the transfer current value for every page in each target transfer voltage after time, and the transfer current value for every page at the time of transfer voltage correction | amendment. It is a flowchart which shows an example of the flow of the process performed in the control part of the full-color laser printer concerning 2nd Embodiment of this invention. The value of current flowing through the first and second primary intermediate transfer drums with respect to the elapsed time after the application of the primary intermediate transfer voltage when the applied voltage supplied from the constant voltage power supply to the first and second primary intermediate transfer drums is 440V FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Full color laser printer 12 Photosensitive drum 14 Charging roll 20A 1st primary transfer drum 20B 2nd primary transfer drum 40, 41 Control part 42 Transfer drum driver 44 Photoconductor driver 48 Environmental sensor 50, 51 Table memory | storage part 52 DC power supply

Claims (6)

An image forming apparatus that includes an intermediate transfer member that transfers toner from a photoreceptor to a recording medium, and that forms an image by applying a transfer bias to the intermediate transfer member,
An image forming apparatus comprising: control means for controlling a displacement current flowing through the intermediate transfer member at the start of applying the transfer bias.   The image forming apparatus according to claim 1, wherein the control unit includes a transfer bias control unit that controls the displacement current by setting a transfer bias lower than a predetermined target transfer bias.   The image forming apparatus according to claim 1, wherein the control unit includes a timing control unit configured to control the displacement current by setting an image formation timing based on image information.   The image forming apparatus according to claim 1, wherein the control unit controls the displacement current based on a cumulative number of image formations on a recording medium.   5. The apparatus according to claim 1, further comprising a detection unit that detects at least one of an ambient atmosphere temperature and a humidity, wherein the control unit controls a target transfer bias based on a detection result of the detection unit. The image forming apparatus according to any one of the above.   6. The image forming apparatus according to claim 1, further comprising a direct current power source for charging the photosensitive member.

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