JP2019066695A - Image forming apparatus - Google Patents

Abstract

To provide a compact, low-price image forming apparatus, the image forming apparatus capable of preventing the occurrence of an abnormal image and obtaining a good image.SOLUTION: An image forming apparatus transfers a solid pattern onto an intermediate transfer belt being a transfer target member with a primary transfer bias as a set transfer condition with which an afterimage can be prevented, on the basis of the distance of travel of a photoreceptor and a charging bias being a charging condition, and detects the amount of attachment of the transferred solid pattern with an optical sensor unit as an attachment amount detection member. When the attachment amount is outside a target range, the image forming apparatus corrects the set primary transfer bias and charging bias.SELECTED DRAWING: Figure 9

Description

  The present invention relates to an image forming apparatus.

A charging member such as a charging roller for charging the surface of a photosensitive member such as an image carrier, an exposure member for forming a latent image on the photosensitive member, a transfer belt to which a toner image formed on the surface of the image carrier is transferred There is known an image forming apparatus provided with a transfer receiving member.
Image forming apparatuses are widely used in home offices and general user areas, and downsizing of the main unit and long life have been required. It is known to use a small-sized LED light source as an exposure member for forming a latent image on a photosensitive member in order to miniaturize the main body. When an LED light source is used, a phthalocyanine-based pigment is used for the charge generation layer of the photosensitive member in view of the characteristics of the LED light source, and the charge transport layer is made thicker to increase the life of the photosensitive member.
However, photoreceptors using phthalocyanine-based pigments tend to contain charges inside the photoreceptor, and the thick charge transport layer reduces the capacitance of the photoreceptor, resulting in charges generated by the application of the transfer bias in the transfer process. Was easy to include. As a result, the potential unevenness (history) of the first rotation of the photoconductor remains on the photosensitive member, and the potential unevenness can not be reliably eliminated in the charging step of the second rotation of the photoconductor, and the toner image with unevenness formed on the surface of the photoconductor As a result, the image is transferred, resulting in image unevenness, and an abnormal image (residue image) is easily generated on the paper as the printing medium.

In order to make it difficult to generate such an abnormal image (afterimage), Patent Document 1 includes a surface potentiometer which detects the surface potential on the photosensitive member, and when the surface potential difference is out of the specified value, the charging current is It is described that the charging current is corrected if it is within the set value, and the transfer current is corrected if the transfer current is outside the set value and the transfer current is within the set value. Furthermore, a photosensor is provided to detect the amount of toner adhesion on the photosensitive member, and if the difference in the amount of adhesion on the photosensitive member is outside the specified value, the charging current is corrected if the charging current is within the set value, and the charging current is out of the set value. If the transfer current is within the set value, it is described that the transfer current is corrected.
However, a surface voltmeter for measuring the surface potential of a photosensitive member occupies a large volume compared to a photo sensor, and is not suitable for downsizing of an image forming apparatus. In addition, surface potentiometers are much more expensive than photosensors and are not suitable for cost reduction.
On the other hand, although the photosensor for detecting the amount of toner adhesion on the photosensitive member can detect the amount of toner adhesion on the photosensitive member, it can not detect the surface potential itself on the photosensitive member. That is, it has been impossible to accurately grasp the potential unevenness on the surface of the photosensitive member from the photo sensor. Although the amount of toner adhesion on the photosensitive member is affected by the surface potential on the photosensitive member, the abnormal image on the paper additionally includes the consumption condition of the photosensitive member, the toner charge condition, the use condition of the device and the environment (temperature and humidity And other factors had an impact.

  Therefore, an object of the present invention is to provide an image forming apparatus capable of suppressing generation of an abnormal image and obtaining a good image, with a compact and inexpensive image forming apparatus.

  In order to solve the above problems, according to the present invention, an image carrier, a charging member for charging the surface of the image carrier, and a transfer member to which a toner image formed on the surface of the image carrier is transferred An image forming apparatus comprising: a film thickness detection member for detecting a film thickness of the image carrier; and an adhesion amount detection member for detecting an adhesion amount of toner on the transfer target member; Based on the charging condition for charging the surface of the image carrier and the transfer condition for transferring the toner image on the surface of the image carrier from the detection result of the film thickness detection member, the charging condition is set. The toner adhesion amount of the toner pattern formed on the transfer member is detected by the adhesion amount detection member under the transfer conditions set as above, and the toner adhesion amount detected by the adhesion amount detection member is out of a predetermined range, Said transfer conditions and before The corrects the charging condition in which the features.

  According to the present invention, it is possible to provide an image forming apparatus capable of suppressing generation of an abnormal image and obtaining a good image with a small-sized and low-cost image forming apparatus.

FIG. 1 is a schematic configuration diagram of a color laser printer that is an image forming apparatus according to the present embodiment. FIG. 6 is a view for explaining the arrangement of primary transfer rollers when a metal roller is used as the primary transfer roller 5; FIG. 2 is a block diagram showing a part of an electric circuit in the printer. Control flow of image density control. FIG. 5 is a diagram showing a time series of the photosensitive member surface potential when a negative afterimage is generated. FIG. 6 is a diagram showing a time series of the photosensitive member surface potential when a positive afterimage is generated. The graph which shows the relationship between transfer efficiency and negative afterimage rank to primary transfer bias. FIG. 6 is a view showing an example of the relationship between the charging bias, the photosensitive member traveling distance, and the primary transfer bias when the negative afterimage and the transfer efficiency fall within an allowable range. Control flow diagram of afterimage countermeasure control. FIG. 6 is a graph showing the relationship between the amount of adhesion of a solid pattern on the intermediate transfer belt and the transfer bias. The figure which shows the relationship between the residual potential and the transfer bias. An example of the image pattern created at the time of negative afterimage check. The figure which shows the afterimage evaluation image used by this verification experiment. FIG. 2 is a schematic configuration diagram of a tandem-type direct transfer image forming apparatus. FIG. 1 is a schematic diagram of a monochrome image forming apparatus. FIG. 2 is an enlarged view of the vicinity of a primary transfer nip in a monochrome image forming apparatus.

  FIG. 1 is a schematic configuration diagram of a color laser printer (hereinafter, simply referred to as a printer) which is an image forming apparatus according to the present embodiment. Although a color laser printer will be described as an embodiment, the image forming apparatus may be a mono-laser printer or an electrophotographic apparatus such as a copying machine or an MFP (Multi Function Printer).

  The printer shown in FIG. 1 is provided with four process units 10Bk, 10Y, 10M and 10C detachably mounted on the printer main body 100 at the center of the printer main body 100. Each of the process units 10Bk, 10Y, 10M and 10C contains developers of different colors of black (Bk), yellow (Y), magenta (M) and cyan (C) corresponding to color separation components of a color image. It has the same configuration as the above. Therefore, when the colors are not particularly distinguished, the description of Bk, Y, M, C, etc. is omitted after the reference numerals of the respective members.

  Each process unit 10 includes a photosensitive member 1 as a latent image carrier, a charging device 2 for charging the surface of the photosensitive member, a developing device 4, a cleaning device 7 for cleaning the surface of the photosensitive member, and a step for removing residual potential on the photosensitive member surface. It comprises a static eliminator 8 or the like which is a static eliminator for irradiating a light. The photosensitive member 1 is a cylindrical drum having a diameter of 24 mm. The photosensitive member 1 uses a phthalocyanine-based pigment for the charge generation layer to make the charge transport layer thicker than the charge generation layer. The latent image carrier may be a photosensitive belt having a photosensitive layer.

  The developing device 4 is a two-component developing device, and has a developing roller which is a developing member disposed opposite to the photosensitive member 1, and a developer having inside thereof toner and carrier having normal negative charge polarity. Is stored. The developing device may be a one-component developing device using toner of negative polarity.

  The cleaning device 7 has a cleaning blade 6 counter-contacting the photosensitive member 1. Cleaning is performed by scraping the transfer residual toner on the photosensitive member 1 by the cleaning blade 6. Instead of the blade cleaning method, an electrostatic method such as an electrostatic brush method or an electrostatic roller method can be mounted.

  Above each process unit 10, an exposure device 3 which is a latent image forming unit that exposes the surface of each photosensitive member 1 is provided. The exposure device 3 has an LED which is a light source as an exposure member. The exposure apparatus may be configured to include a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like. The surface of each photosensitive member 1 is exposed to laser light L based on the image data.

  Below each process unit 10, an intermediate transfer belt 15 as a transfer member is provided. The intermediate transfer belt 15 is an endless belt, and is stretched by a secondary transfer opposite roller 21, a cleaning backup roller 16, a primary transfer roller 5, and a tension roller 20. In the present embodiment, an intermediate transfer belt 15 is provided below each process unit 10. An intermediate transfer belt 15 may be provided above each process unit 10.

Examples of materials used for the intermediate transfer belt 15 include PVDF (vinyl fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), TPE (thermoplastic elastomer), etc. And the like are used as a resin film endless belt. In the present embodiment, as the intermediate transfer belt 15, an endless belt having a laminated structure in which carbon black is added to TPE with a tensile elastic modulus of 1000 [Mpa] to 2000 [Mpa] is used. In addition, a belt having a thickness of 90 [μm] to 160 [μm] and a width of 230 [mm] was used. Moreover, as electrical resistance, volume resistivity 10 ⁸ [Ω · cm] to 10 ¹¹ [Ω · cm] and surface resistivity 10 ^8.5 [Ω / □] to 10 ^{11 in} an environment of 23 ° C. and 50% RH. [Ω / □] (both measured by HirestaUP MCP-HT450 manufactured by Mitsubishi Chemical Corporation, applied voltage 500 V, applied time 10 seconds) was used.

When the volume resistivity of the intermediate transfer belt 15 facing the photosensitive member 1 having the potential exceeds 10 ¹¹ [Ω · cm], the transfer of the toner becomes insufficient. Even if the surface resistivity exceeds 10 ¹¹ [Ω / □], transfer of toner becomes insufficient. On the other hand, when the volume resistivity is less than 10 ⁸ [Ω · cm], toner scattering occurs. Even if the surface resistivity is less than 10 ^8.5 [Ω / □], toner scattering occurs. Therefore, an intermediate transfer belt with a volume resistivity of 10 ⁸ [Ω · cm] to 10 ¹¹ [Ω · cm] and a surface resistivity of 10 ^8.5 [Ω / □] to 10 ¹¹ [Ω / □] Is preferred. When the toner transfer is insufficient, a primary transfer bias is applied to increase transfer efficiency. In addition, since the toner scattering is further generated by applying the primary transfer bias, it is necessary to control the primary transfer bias. Since the intermediate transfer belt 15 tends to have a higher potential as it goes downstream in the image forming order, the primary transfer biases corresponding to each process unit 10 are higher in each primary transfer bias as they go downstream in the image forming order. Individual control is required. At this time, if the primary transfer bias is made too high, an afterimage easily occurs.

  In the present embodiment, the intermediate transfer belt 15 is rotated in the direction indicated by the arrow in the figure by rotationally driving the secondary transfer opposing roller 21 by the belt drive motor 114 (see FIG. 3). Further, both axial end portions of the tension roller 20 which is a dependent roller accompanying the rotation of the intermediate transfer belt 15 are pressed by a spring to apply tension to the intermediate transfer belt 15 and a drive roller to which the drive of the drive motor is transmitted. The intermediate transfer belt 15 is reliably transmitted to the intermediate transfer belt 15 via a certain secondary transfer opposing roller 21.

  In the present embodiment, a photosensitive member drive motor 119 (see FIG. 3) for driving the photosensitive member 1 and a belt drive motor 114 (see FIG. 3) for rotationally driving the secondary transfer facing roller 21 are provided. Although the drive source of the process unit for driving the image forming apparatus and the drive source for driving the secondary transfer facing roller 21 are independently provided, the drive source of the process unit for driving the photosensitive member 1 etc. and the secondary transfer facing roller 21 are The drive source to drive the rotation may be common. By sharing the drive source for driving the process unit 10 and the intermediate transfer belt 15, the printer main body can be miniaturized and the cost can be reduced. In addition, it is desirable to simultaneously turn on / off the drive of the process unit 10Bk for Bk and the intermediate transfer belt 15 at the same time, to make the printer main body compact and cost-effective.

The four primary transfer rollers 5 are sponge rollers appropriately set within a range of φ 8 to 20 [mm], and the intermediate transfer belt 15 is sandwiched between the four primary transfer rollers 5 and the respective photosensitive members 1, respectively, A primary transfer nip is formed between the transfer belts 15.
Further, a primary transfer high voltage power supply 116 (see FIG. 3) is connected to each primary transfer roller 5, and a primary transfer bias of a predetermined DC voltage of +100 [V] to +2000 [V] is applied from this high voltage power supply. By doing this, a transfer electric field is formed.
As the sponge roller of the primary transfer roller 5, an ion conductive roller (urethane + carbon dispersion, NBR, hydrin rubber) adjusted to a resistance value of 10 ⁶ to 10 ⁸ Ω, a roller of an electron conductive type (EPDM), etc. are used. Be

Further, a metal roller can be used as the primary transfer roller 5.
FIG. 2 is a view for explaining the arrangement of the primary transfer roller 5 when a metal roller is used as the primary transfer roller 5 of FIG.
By using a metal roller for the primary transfer roller 5, there is an advantage that the cost can be reduced compared to the case of using a sponge roller. However, when the primary transfer roller 5 is a metal roller, when the primary transfer roller 5 is brought into contact with the photosensitive member 1 via the intermediate transfer belt 15, the photosensitive member 1 may be worn out prematurely. This is because if the photosensitive member 1 or the primary transfer roller 5 is eccentric, the contact pressure between the photosensitive member 1 and the primary transfer roller 5 is not constant. As a result, a portion that is higher than the predetermined contact pressure is generated. As a result of the contact pressure becoming higher than a predetermined value, the progress of the wear of the photosensitive member 1 is accelerated, and the deterioration of the photosensitive member 1 is accelerated.
As shown in FIG. 2, when a metal roller is used as the primary transfer roller 5, the primary transfer roller 5 is disposed downstream of the photosensitive member 1 in the moving direction of the intermediate transfer belt 15. Then, the intermediate transfer belt 15 is pressed to the photosensitive member side, and the intermediate transfer belt 15 is wound around the circumferential surface of each photosensitive member 1 to form a primary transfer nip N. The primary transfer roller 5 downstream of the primary transfer nip N in the moving direction of the intermediate transfer belt 15 can be arranged not to be in contact with the photosensitive member 1 via the intermediate transfer belt 15. Since the photosensitive member 1 and the primary transfer roller 5 do not contact at the same time at the opposing portion, the deterioration of the photosensitive member 1 can be suppressed without being affected by the eccentricity of the photosensitive member 1.

  Further, the intermediate transfer belt 15 comes into contact with the photosensitive member 1 by the tension of the intermediate transfer belt 15, and the transfer pressure is stabilized. As a result, the cohesion between the toners becomes high at the primary transfer nip, and image defects such as hollow defects are eliminated. Further, since the primary transfer roller 5 is disposed downstream of the primary transfer nip in the transfer belt movement direction, the distance between the inlet of the primary transfer nip and the surface of the primary transfer roller is increased. As a result, the primary transfer bias of the primary transfer roller 5 does not act on the primary transfer nip inlet (upstream side in the belt movement direction), and toner scattering due to the gap discharge between the photosensitive member 1 and the intermediate transfer belt 15 at the nip inlet is prevented. be able to. Also in the sponge roller of FIG. 1, the primary transfer roller 5 is slightly shifted to the downstream side of the transfer belt moving direction with respect to the primary transfer nip. The center of the primary transfer nip and the center of the nip between the primary transfer roller 5 and the intermediate transfer belt 15 do not match, and toner scattering due to gap discharge at the inlet of the primary transfer nip can be prevented.

The secondary transfer roller 25 of FIG. 1 sandwiches the intermediate transfer belt 15 with the secondary transfer counter roller 21 to form a secondary transfer nip. The secondary transfer roller 25 is a sponge roller having a diameter of 16 to 25 [mm], and an ion conductive roller (urethane + carbon dispersion, NBR, hydrin) or an electron adjusted to a resistance value of 10 ⁶ to 10 ⁹ [Ω] A conductive type roller (EPDM) or the like is used.

In the present embodiment, as the secondary transfer counter roller 21, a urethane coating roller (thickness 0.05 [mm], 変 化 19 [mm]) having a small change in diameter due to temperature is used. The electric resistance value was set to 10 ⁶ Ω or less so as to be lower than that of the secondary transfer roller 25. The secondary transfer counter roller 21 is a urethane coating roller and has a thickness of 0.05 mm, but polyurethane rubber (thickness 0.3 to 1 mm), thin layer coating roller (thickness 0.03 to 0) .1 mm or the like may be used.

  In addition, a secondary transfer high voltage power supply 117 (see FIG. 3) is connected to the secondary transfer roller 25, and a predetermined secondary transfer bias is applied from the secondary transfer high voltage power supply to obtain a transfer electric field. Form.

As the secondary transfer bias, an attraction transfer method was used, and a predetermined current of +5 to 100 [μA] was applied as constant transfer control as the transfer bias at the time of sheet passing. The attractive transfer method is a method of forming a secondary transfer electric field by applying a positive bias to the secondary transfer roller 25 and grounding the secondary transfer opposing roller 21.
Besides the attractive transfer method, there is a repulsive transfer method. The repulsive transfer method is a method of forming a secondary transfer electric field by applying a negative bias to the secondary transfer opposing roller 21 and grounding the secondary transfer roller 25. Instead of the attractive transfer method, a repulsive transfer method may be used.

The belt cleaning device 32 for cleaning the intermediate transfer belt 15 is performed by a method having a cleaning blade 31 which is in counter contact with the intermediate transfer belt 15. Cleaning is performed by scraping the transfer residual toner on the intermediate transfer belt 15 by the cleaning blade 31.
Instead of such a blade cleaning method, an electrostatic method such as an electrostatic brush method or an electrostatic roller method can also be mounted. In the case of the electrostatic method, instead of the cleaning blade 31, a cleaning brush / roller to be biased is disposed. As a result, according to the use condition of the image forming apparatus, the pre-charging of the transfer residual toner is required, the cleaning unit itself needs to be enlarged, the high voltage power supply is added, and the extra operation for the bias cleaning is required. The blade cleaning method is preferable from the viewpoint of downsizing, cost reduction, and cleanability.

  On the other hand, at the lower portion of the printer main body 100, a paper feed tray 22 accommodating transfer paper P as a recording medium, a paper feed roller 23 for carrying out the transfer paper P from the paper feed tray 22, and the like are provided. Here, the recording medium includes, in addition to the plain paper, thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, etc. In addition, it has a manual feed port 42 through which the transfer paper set in the manual feed tray is conveyed.

  In the printer main body 100, there is provided a transport path for discharging the transfer sheet P from the sheet feed tray 22 or the manual feed tray through the secondary transfer nip to the outside of the apparatus. In the present configuration, the sheet feeding takes a vertical path. On the conveyance path, on the upstream side of the transfer sheet conveyance direction below the position of the secondary transfer roller 25, a pair of registration rollers 24 as conveyance means for conveying the transfer sheet P to the secondary transfer nip is disposed.

  Further, on the downstream side of the transfer sheet conveyance direction above the position of the secondary transfer roller 25, a fixing device 40 for fixing the unfixed image transferred to the transfer sheet P is disposed.

The basic operation of the image forming apparatus having the above configuration is as follows.
In FIG. 1, when the image forming operation is started, each photosensitive member 1 in each process unit 10 has a circumferential speed of 60 [mm / s] to 350 [mm] clockwise in FIG. / S] is rotationally driven at an appropriately set peripheral speed within the range.
A charging device 2 having a charging roller, which is a charging member in the form of a roller, is in pressure contact with the surface of each photosensitive member 1 at the charging opposing portion, and the charging device 2 rotates following the rotation of the photosensitive member 1. Then, a bias of DC voltage is applied to the charging device 2 by a high voltage power source, whereby the surface of the photosensitive member 1 is uniformly charged to -500 [V] or the like to a predetermined polarity by the charging device 2. Note that a bias in which an AC voltage is superimposed on a DC voltage may be used.

  Writing light is irradiated (exposed) from the exposure device 3 onto the surface of each charged photosensitive member 1, and an electrostatic latent image is formed on the surface of each photosensitive member 1. The exposure apparatus 3 uses a small LED light source as an exposure member for the purpose of downsizing. At this time, the image information to be exposed on each photosensitive member 1 is monochrome image information in which a desired full color image is separated into color information of yellow, magenta, cyan and black. The exposure may be performed by a laser beam scanner using a laser diode or the like. The surface potential of the exposed portion of the photosensitive member 1 is usually −50 [V].

  By supplying the toner carried on the developing roller of each developing device 4 to the electrostatic latent image formed on each photosensitive member 1 in this manner, the electrostatic latent image is visualized as a toner image ( Visualization). In the development to be developed into a toner image, a predetermined development bias of DC voltage -200 [V] is applied from a high voltage power source to the developing roller of the developing device 4. Note that a bias in which an AC voltage is superimposed on a DC voltage may be used.

  Further, when the image forming operation is started, the secondary transfer opposing roller 21 is rotationally driven in the counterclockwise direction in the drawing, and the intermediate transfer belt 15 is caused to travel in the direction shown by the arrow in the drawing. Then, a predetermined primary transfer bias (+100 [V] to +2000 [V]) is applied to each primary transfer roller 5 by the primary transfer high voltage power supply 116 (refer to FIG. 3), whereby each photoreceptor 1 and the intermediate transfer belt A transfer field is formed at the primary transfer nip between 15 and 15.

  Thereafter, when the toner image of each color on the photosensitive member 1 reaches the primary transfer nip as the photosensitive member 1 rotates, the toner image on each photosensitive member 1 is generated by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 15. In this way, a full-color toner image is carried on the surface of the intermediate transfer belt 15.

  Further, the toner on each photosensitive member 1 that can not be transferred to the intermediate transfer belt 15 is removed by the cleaning blade 6 that is in contact with the counter of the cleaning device 7. Thereafter, the surface of each photosensitive member 1 is irradiated with the charge removing light by the charge removing device 8 so that the surface of each photosensitive member 1 is removed, and the surface potential is initialized.

  The cleaning device may not be provided around the photosensitive member 1 and the developing device 4 may use a cleanerless method for collecting the transfer residual toner. Further, in the printer of this embodiment, a cleaning method for electrostatically cleaning the surface of the photosensitive member may be employed.

  At the lower portion of the printer main body 100, the sheet feeding roller 23 is rotationally driven, and the transfer sheet P is sent out from the sheet feeding tray 22 to the conveyance path. The transfer paper P delivered to the conveyance path is resisted so that the toner image portion on the surface of the intermediate transfer belt 15 reaches the secondary transfer nip between the secondary transfer roller 25 and the secondary transfer opposing roller 21. The sheet is sent to the secondary transfer nip by the roller pair 24. At this time, a transfer bias of the reverse polarity to the toner charge polarity of the toner image on the intermediate transfer belt 15 is applied to the secondary transfer roller 25, whereby a transfer electric field is formed in the secondary transfer nip. There is.

  Thereafter, when the toner image on the intermediate transfer belt 15 reaches the secondary transfer nip as the intermediate transfer belt 15 rotates, the transfer electric field formed in the secondary transfer nip causes the toner image on the intermediate transfer belt 15 to The toner images are collectively transferred onto the transfer paper P.

  At this time, the residual toner on the intermediate transfer belt 15 which can not be transferred to the transfer paper P is removed by the cleaning blade 31 of the belt cleaning device 32 above the intermediate transfer belt 15. The removed toner passes through a toner conveyance path communicating with the belt cleaning device 32, and is conveyed to a waste toner container 33 disposed between the intermediate transfer belt 15 and the paper feed tray 22 and collected.

The transfer sheet P is separated from the intermediate transfer belt 15 by the curvature of the secondary transfer facing roller 21 and conveyed to the fixing device 40, and the toner image on the transfer sheet P is fixed to the transfer sheet P by heat and pressure by the fixing device 40. Be done. Then, the transfer sheet P is discharged from the discharge port 41 to the outside of the apparatus.
Thus, a series of image forming processes in the printer according to the present embodiment are completed.

Further, in the printer according to the present embodiment, the speed of the image forming process (image forming operation) is changed according to the type of transfer sheet P. Specifically, when a relatively thick transfer paper having a basis weight of 100 [g / m ² ] or more is used, the image forming process speed is set to be a half speed, and the transfer material is a fixing nip composed of a fixing roller pair. It passes over twice the normal imaging process speed. Thereby, the fixability of the toner image can be secured.

  Further, in the printer of the present embodiment, a belt contact / separation mechanism for contacting and separating the intermediate transfer belt 15 with the photosensitive members 1 of the process units (10C, 10M, 10Y) other than the Bk color process unit (10Bk) is used. Have. At the time of full color image formation, the belt contact / separation mechanism is controlled such that the intermediate transfer belt 15 is in contact with each photosensitive member 1. On the other hand, at the time of monochrome image formation, the belt contact / separation mechanism is controlled so that the intermediate transfer belt 15 is separated from the photosensitive members 1 of process units other than the Bk color process unit. Specifically, the belt contact / separation mechanism includes an intermediate transfer contact / disengagement clutch 115 (see FIG. 3), and the intermediate transfer contact / disengagement clutch 115 is controlled to perform contact / disengagement of the intermediate transfer belt 15 .

  Further, an optical sensor unit 118 is disposed downstream of the intermediate transfer belt surface movement direction downstream of the process unit 10C for C, which is disposed at the most downstream side of the intermediate transfer belt surface movement direction among the plurality of process units. It is disposed so as to face the front surface with a predetermined gap. In the optical sensor unit 118, reflection type photo sensors, which are three adhesion amount detection members, are arranged at predetermined intervals in the main scanning direction (the width direction of the intermediate transfer belt). The light emitted from the light emitting element is reflected by the toner image on the front surface or the belt of the intermediate transfer belt 15, and the amount of reflected light is detected by the light receiving element. The control unit 110 (see FIG. 3) detects a toner image on the intermediate transfer belt 15 based on the output voltage value from the optical sensor unit 118, and detects the toner adhesion amount per unit area of the toner image. To

FIG. 3 is a block diagram showing a part of an electric circuit in the printer.
The printer includes a control unit 110 that controls the operation of each unit in the printer main body 100 that requires operation control and the devices included in each unit. The control unit 110 includes a central processing unit (CPU), a memory including a ROM and a RAM, an I / O port for input and output, and the like. One I / O port is connected to the operation unit 111. The other I / O port is a transfer paper position detection unit 112, a temperature and humidity sensor 113, a belt drive motor 114, an intermediate transfer contact clutch 115, a transfer high voltage power supply 116, 117, an optical sensor unit 118, a photoconductor drive motor It is connected with 119 and so on.

  Here, the transfer sheet position detecting means 112 calculates the position of the transfer sheet P from the timing when the registration roller pair 24 (see FIG. 1) starts to rotate. In addition, the temperature and humidity sensor 113 acquires environmental information in the printer main body 100. The operation unit 111 also includes a touch panel display and various keys, and displays an image on the display or receives various information input by a key operation of the operator.

In the present printer, image density control for optimizing the image density of each color is executed every time the power is turned on or whenever printing of a predetermined number of sheets is performed.
FIG. 4 is a control flowchart of image density control of the printer of FIG. 1, which is controlled by the control unit 110 of FIG.
In the image density control, first, a gradation pattern of each color is formed on the intermediate transfer belt 15 at a position facing the reflection type photo sensor which is the adhesion amount detection member of the optical sensor unit 118 (S1). The gradation pattern of each color comprises a plurality of toner patches having different image densities.

  The gradation pattern of each color is different from the uniform charging potential on the photosensitive member 1 in the printing process (image forming operation), the absolute value (minus value) of the charging bias is gradually increased, and the absolute value of the charging potential Increase (negative value) gradually. Then, while forming a plurality of patch electrostatic latent images for forming a gradation pattern image by power exposure in which the surface potential of the photosensitive member is about −50 [V], each of them is formed on the photosensitive member 1 of each color. To develop by the developing device 4 of FIG. During this development, the value of the developing bias applied to the Y, M, C, K developing rollers is gradually increased. A tone pattern image of Y, M, C, K is formed on each photosensitive member 1 by such development. These are primarily transferred to the intermediate transfer belt 15.

  The gradation pattern of each color formed on the intermediate transfer belt 15 passes the position facing the optical sensor unit 118 as the intermediate transfer belt 15 moves endlessly. At this time, the optical sensor unit 118 receives light of an amount according to the toner adhesion amount per unit area of the toner patch of each gradation pattern.

  Next, the adhesion amount of each toner patch of the toner pattern of each color is calculated from the relationship between the toner adhesion amount and the output voltage of the optical sensor unit 118 when each color toner patch is received. That is, the toner adhesion amount of each toner patch is detected (S2).

  Next, the imaging conditions are adjusted based on the detected adhesion amount. Specifically, the development γ characteristic line (y = ax + b), which linearly approximates the relationship between the result of detecting the toner adhesion amount on the toner patch and the development potential when forming each toner patch, is calculated by regression analysis . Then, an appropriate developing bias value to be a target toner adhesion amount is calculated from the developing γ characteristic, and the developing bias value as the developing condition for Y, M, C, K is determined by the control unit 110 (see FIG. 3). To do (S3).

  After the development bias value is determined, the charging potential of the photosensitive member 1 is determined by adding the background potential α for the purpose of suppressing the occurrence of background stains to the determined development bias value. Then, the charging bias which is the charging condition is determined from the determined charging potential and the charging characteristic information (the relationship between the charging potential of the photosensitive member 1 and the charging bias) in the memory in the control unit 110 obtained in advance (S4) ). In the present embodiment, the charging change is a charging bias, but may be a fluctuation of a gap between a member such as a charging roller and the photosensitive member.

  Here, there are two types of abnormal images (after images) due to potential unevenness, negative afterimages and positive afterimages. The negative afterimage is a phenomenon in which the potential of the unexposed area (non-image area) after primary transfer is higher than that of the exposed area (image area), and the positive afterimage has the potential of the exposed area (image area) after primary transfer This phenomenon is higher than the unexposed area (non-image area). Whether a negative afterimage or a positive afterimage occurs depends on the imaging process conditions. Among the image forming process conditions, when the transfer bias is high (a positive value is large), a negative afterimage occurs, and when it is low (a small positive value), a positive afterimage tends to occur.

FIG. 5 is a diagram showing a time series of the photosensitive member surface potential when a negative afterimage is generated.
FIG. 5I shows the surface potential of the photosensitive member after charging by the charging device 2 for the first rotation of the photosensitive member. The charging bias is a negative voltage, and the surface of the photoreceptor after charging is uniformly charged to a predetermined negative potential (in this example, -500 [V]).
FIG. 5 (ii) shows the surface potential of the photosensitive member after the exposure for the first rotation of the photosensitive member. A positive charge is induced from the inside of the photosensitive member on the exposed portion of the photosensitive member surface irradiated (exposed) with the laser light L by the exposure device 3 and neutralized with the negative charge on the photosensitive member surface (in this example, -50 [V ]. Therefore, the potential of the exposed portion becomes higher than the potential of the unexposed portion after charging (in this example, -500 [V]).

  FIG. 5 (iii) shows the photoreceptor surface potential after primary transfer. The primary transfer bias is a positive voltage. Therefore, the photosensitive member surface after the primary transfer becomes a positive potential by the primary transfer bias. When the primary transfer bias is applied, the potential difference between the unexposed area and the primary transfer bias is larger than the potential difference between the exposed area and the primary transfer bias, so the unexposed area is more likely to be injected with the primary transfer current than the exposed area. . As a result, the surface potential after primary transfer in the exposed area is 100 [V], the surface potential after primary transfer in the unexposed area is 150 [V], and the photoreceptor surface potential in the exposed area is unexposed Lower than the potential of

FIG. 5 (iV) shows the surface potential of the photosensitive member after charging by the charging device 2 for the second rotation of the photosensitive member.
As shown in FIG. 5 (iii), since the surface potential of the photosensitive member in the exposed area is lower than the potential of the unexposed area, in the second cycle, the first unexposed area having a high charging potential is not sufficiently recharged. . When the portion which is not sufficiently recharged becomes the unexposed portion also in the second round, the toner adheres to the portion and becomes a negative afterimage.

FIG. 6 is a diagram showing a time series of the photosensitive member surface potential when a positive residual image is generated.
6 (i) and 6 (ii) are the same as FIGS. 5 (i) and 5 (ii), and after charging and exposure, the photosensitive member surface potential is the potential of the exposed portion (image portion) of -50 [V]. The potential of the unexposed area (non-image area) becomes -500 [V].
When the primary transfer bias is applied under various conditions such as a low primary transfer bias of positive voltage, as shown in FIG. 6 (iii), the surface of the photosensitive member becomes negative even after the primary transfer. As a result, after the primary transfer, the potential of the exposed area becomes higher than the potential of the unexposed area. Therefore, as shown in FIG. 6 (iV), the portion which was the exposed portion can not be sufficiently recharged to -500 [V] by the charging bias, and the potential is higher than the portion which is the unexposed portion. Get higher. Therefore, in the second round, when the first round exposed portion having a high charging potential is not exposed and becomes the unexposed portion in the second round, the toner adheres to that portion and a positive residual image is formed.

As shown in FIG. 6, in the case of a positive residual image, the surface of the photosensitive member after primary transfer has a negative potential as shown in FIG. 6 (iii), so that the charge can be removed by the charge removal light of the charge removing device 8 (see FIG. Specifically, by irradiating (exposing) the photosensitive member surface with charge removing light, a positive charge is induced from the inside of the photosensitive member, and the surface of the photosensitive member is removed by neutralizing the negative charge on the photosensitive member surface. be able to. Therefore, the photosensitive member surface potential after the charge removal can be made uniform, and the residual image can be suppressed.
However, as shown in FIG. 5 (iii), in the case where a negative afterimage occurs in which the photosensitive member potential of the unexposed area of the positive potential is higher than that of the exposed area. The photosensitive member 1 can not be removed by the discharge light of the discharging device 8. Therefore, in order to suppress the afterimage, it is necessary to separately provide a charge removing device capable of removing the surface of the photosensitive member of positive potential.

  By reducing the primary transfer bias (reducing the positive value), the residual charge on the surface of the photosensitive member after transfer is reduced, so that the residual image is suppressed. However, if the primary transfer bias is lowered in order to suppress the afterimage, the transfer efficiency may be lowered and the image density may be insufficient. Even if the primary transfer bias is set so that the transfer efficiency falls within the allowable range due to the toner charge state, the electrical resistance of the primary transfer roller 5, the tolerance of the primary transfer nip, the electrical resistance of the intermediate transfer belt 15, etc. It was lower than the default and there was a possibility that the image density shortage might occur.

  Therefore, in the present embodiment, it is possible to set image forming conditions so as to suppress an afterimage and a decrease in transfer efficiency while suppressing an increase in cost. The details will be described below.

FIG. 7 is a graph showing the relationship between transfer efficiency and negative afterimage rank with respect to primary transfer bias.
The transfer efficiency shown on the left vertical axis in the figure is the rate at which the toner on the photosensitive member is transferred to the intermediate transfer belt 15. Generally, when the primary transfer bias of positive polarity is low, the toner is negatively charged on the photosensitive member Since the force for electrostatically attracting the toner to the intermediate transfer belt 15 is weak, the transfer efficiency is lowered.
When the primary transfer bias is high, the discharge in the primary transfer nip weakly charges the toner, resulting in low transfer efficiency. As a result, usually, the transfer efficiency changes in a parabolic curve as the primary transfer bias increases, as shown by the solid line in FIG.
In the present embodiment, the transfer efficiency Y or more is set in the transfer efficiency allowable range, and the primary transfer bias falling within the transfer efficiency allowable range is Z1 or more and Z2 or less.

On the other hand, the negative afterimage rank shown on the right vertical axis in the figure is obtained by ranking the degree of negative afterimage by sensory evaluation.
In the drawing, a two-dot chain line (A) indicates the relationship between the negative residual image rank and the primary transfer bias at the initial stage of use of the photosensitive member. Also, the higher the negative afterimage rank, the better the degree of negative afterimage. As can be seen from FIG. 5 (iii), the potential of the non-image area after the primary transfer step tends to be larger than that of the image area as the primary transfer bias is higher (plus value is larger). Therefore, as shown in FIG. 7, the higher the primary transfer bias, the worse the negative afterimage rank (as shown by the graph, the graph goes down to the right).
In the present embodiment, the afterimage rank X or more is set in the negative afterimage allowable range.
The primary transfer bias falling within the negative afterimage allowable range is Z3 or less.

  As understood from the relationship between the negative afterimage rank and the primary transfer bias, when the primary transfer bias is set to less than Z1 at the initial stage of using the photosensitive member, the positive charge on the surface of the photosensitive member is suppressed after the primary transfer, and the negative afterimage Is suppressed. However, the transfer efficiency is lowered, and the image density on the transfer paper is lower than the specified image density. When the primary transfer bias is set to S1 of Z1 or more and Z3 or less, positive charge on the surface of the photosensitive member is suppressed after primary transfer, and negative afterimage is suppressed. In addition, the transfer efficiency is increased, and the image density on the transfer sheet is not reduced below the specified image density. If the toner adhesion amount of the toner image on the photosensitive member is increased by adjusting the charging bias and the developing bias in order to avoid the lowering of the image density due to the lowering of the transfer efficiency, the cleaning device 7 is better than the transfer to the intermediate transfer belt. As a result, the amount of waste toner is increased, and the yield of toner is reduced. As described above, even if the charging bias and the developing bias are simply adjusted, the transfer efficiency is not improved, and a good image can not be obtained.

  In addition, since the initial photosensitive member having a larger film thickness tends to contain positive charge generated by the positive transfer bias than the time-lapse photosensitive member whose film thickness is reduced due to abrasion or the like, the negative residual image is deteriorated. . Therefore, in the initial stage of use of the photosensitive member 1, as indicated by a two-dot chain line (a) in the figure, Z1 in a state in which the primary transfer bias is lowered (plus value is decreased) in order to keep the negative afterimage within the allowable range. Set S1 to Z3 or less. However, since it becomes difficult to contain positive charge in the photoreceptor used over time, the relationship between the primary transfer bias and the negative afterimage rank changes from the two-dotted line (A) in the figure to the one-dotted line (A) in the figure. As a result, even if the transfer efficiency is increased in S2 from the range where there is a margin of Z1 or more and Z4 or less in the state where the primary transfer bias can be made high (larger positive value), the negative residual image can be contained within the allowable range.

  Therefore, when the photosensitive member 1 is in the initial stage of use and the film thickness is large, as shown by the set value S1 in FIG. 7, the transfer efficiency is set to the primary transfer bias near the lower limit value of the transfer efficiency allowable range. On the other hand, when the film thickness of the photosensitive member 1 is thin due to the use of the photosensitive member 1 over time, as shown by the setting value S2 of FIG. As a result, a negative residual image can be suppressed, and a primary transfer bias that can suppress a decrease in transfer efficiency can be obtained. As described above, it is possible to set the primary transfer bias in which the afterimage is suppressed by using the photosensitive member traveling distance as the photosensitive member film thickness information.

Further, in the present embodiment, as shown in FIG. 4, the charging bias is determined and changed each time by the image density control. It is also possible to change to an appropriate primary transfer bias by this changed charging bias.
When the charging bias is low (the negative value is large), the amount of discharge between the photosensitive member and the charging roller is larger than when the charging bias is high (the negative value is small), and the negative charge from the charging roller to the photosensitive member The injection amount of the toner increases and the effect of uniformly charging the surface of the photosensitive member to the negative polarity becomes high. As a result, the potential difference between the unexposed area after charging and the exposed area can be reduced, the residual potential after charging can be reduced, and negative afterimage can be suppressed.
Therefore, when the charging bias set in the image density control described above is low (the negative value is large), the negative residual image rank is within the allowable range even if the primary transfer bias is increased (plus value is increased) to enhance the transfer efficiency. Can be On the other hand, when the charging bias set in the image density control is high (the negative value is small), the effect of uniformly charging the surface of the photosensitive member to the negative polarity is reduced, so the primary transfer bias is lowered (the positive value is reduced). Thus, by reducing the potential difference between the unexposed area and the exposed area after transfer, the negative residual image can be contained within the allowable range.

FIG. 8 is a view showing an example of the relationship between the charging bias, the photosensitive member traveling distance, the negative afterimage, and the primary transfer bias where the transfer efficiency is within the allowable range. The charging bias has three selection values of -500V, -600V, and -700V, and the photosensitive member traveling distance consists of three sections up to less than 40 [km].
In the example shown in FIG. 8, the photosensitive member travel distance is used as the film thickness information of the photosensitive member 1. The photosensitive member travel distance can be determined, for example, from the cumulative driving time of the photosensitive member drive motor 119 as a film thickness detection member and the circumferential speed of the photosensitive member 1. That is, in the present embodiment, the photosensitive member drive motor 119 has a function as a part of the film thickness detection device. Further, as the film thickness information of the photosensitive member 1, the number of formed images may be used.
In the example shown in FIG. 8, when the photosensitive member travel distance is 0 [km] or more and less than 10 [km] and the charging bias is -500 V, -600 V, -700 V, transfer is performed as an afterimage countermeasure primary transfer bias. Set the primary transfer bias for maximum efficiency at 600V, 650V, 700V.
When the photosensitive member travel distance is 25 km or more and less than 40 km and the charging bias is -500 V, the afterimage countermeasure primary transfer bias is set to 750 V, but when the charging bias is -600 V and -700 V As an afterimage countermeasure primary transfer bias, the primary transfer bias (800 V) at which the transfer efficiency is maximized is particularly set.
As described above, in the present embodiment, it is possible to set the primary transfer bias which suppresses the afterimage, using the photosensitive member traveling distance as the photosensitive member film thickness information and the charging bias.

  However, the relationship between the transfer efficiency and the primary transfer bias is that the toner charge state, the electrical resistance of the primary transfer roller 5, the electrical resistance of the intermediate transfer belt 15, the tolerance of the primary transfer nip, the photoreceptor and the intermediate transfer belt It is affected by fluctuations in the eccentricity of the primary transfer roller and drive jitter.

When the relationship between the transfer efficiency and the primary transfer bias is shifted to the right as shown by the broken line in FIG. 7, for example, the residual image countermeasure primary transfer bias set based on the relationship shown in FIG. It becomes less than the lower limit value, and the image density may be lowered.
In particular, at the initial stage of using the photosensitive member, as shown in the set value S1 of FIG. 7, the afterimage countermeasure primary transfer bias is set near the lower limit value of the transfer efficiency allowable range. As a result, as shown by the broken line in the figure, when the relationship between the transfer efficiency and the primary transfer bias shifts to the right with respect to the solid line in the figure due to other factors, the set afterimage countermeasure primary transfer bias is within the transfer efficiency allowable range. It becomes less than the lower limit value.

  Therefore, in the present embodiment, a test pattern is formed on the intermediate transfer belt 15 with the after image countermeasure primary transfer bias set, and the adhesion amount of the formed toner pattern is detected by the optical sensor unit 118. As a result of the detection, if the toner adhesion amount is less than the predetermined value, the transfer efficiency is less than the allowable range with the set residual image countermeasure primary transfer bias, so the primary transfer bias is increased (plus value is increased). Further, as a result of raising the primary transfer bias, a negative residual image is generated, and accordingly, the charging bias is lowered by about 100 V (a negative value is increased). Such control will be described in a control flow diagram.

FIG. 9 is a control flow diagram of afterimage countermeasure control.
Although the afterimage countermeasure control is executed after the image density control of FIG. 4, the control start timing of the afterimage countermeasure control from the image density control is not after a predetermined time. Afterimage countermeasure control is performed, for example, every 5 km of the photosensitive member travel distance.
First, an afterimage countermeasure primary transfer bias, which is a transfer condition, is determined from the relationship shown in FIG. 8 based on the photosensitive member traveling distance, the charging bias, and the above (S11). For example, a non-volatile storage device such as a memory or an HDD provided in the control unit 110 (see FIG. 3) is an approximate expression showing the relationship between the primary transfer bias and the charging bias obtained based on the relationship shown in FIG. Are stored in every traveling distance of the photosensitive member 1 (approximation corresponding to 0 to 10 km, approximation corresponding to 10 to 25 km, approximation corresponding to 25 to 40 km).
In the present embodiment, the transfer condition change is a transfer bias such as a residual image countermeasure primary transfer bias, but a gap between the photosensitive member and the intermediate transfer belt 15 (primary transfer nip) or the intermediate transfer belt 15 and the primary transfer roller 5 It may be a change of the gap (nip) of Further, as shown in FIG. 2, in the configuration in which the primary transfer roller 5 and the photosensitive member 1 are not in contact with the photosensitive member 1 via the intermediate transfer belt 15, the axial center-to-center distance between the primary transfer roller and the photosensitive member May be changed.

  Further, even if the primary transfer bias is the same, the residual potential on the surface of the photosensitive member differs depending on the use environment (temperature and humidity) of the apparatus. As a result, the relationship between the afterimage rank and the primary transfer bias shown in FIG. 7 differs depending on the use environment of the apparatus, and the relationship between the primary transfer bias and the charging bias shown in FIG. 8 also changes. For this reason, three approximate expressions for each traveling distance of the photosensitive member 1 are provided for each environment.

  Furthermore, the residual potential on the photoreceptor surface also varies depending on the process speed (image forming speed). As a result, the relationship between the afterimage rank and the primary transfer bias shown in FIG. 7 differs depending on the process speed, and the relationship between the primary transfer bias and the charging bias shown in FIG. 8 also changes. Therefore, in an apparatus that changes the process speed (image forming speed) based on the paper thickness etc., three approximate expressions of the traveling distance of the photosensitive member 1 set for each environment are stored for each process speed. . For example, if the process speed is 2 patterns, the environmental conditions are high temperature and humidity, 3 patterns of normal temperature and humidity, 3 patterns of low temperature and low humidity, and the photoreceptor travel distance is divided into 3 sections, a total of 2 × 3 × 3 Eighteen approximations will be stored. These approximate expressions are obtained in advance by experiments.

  The control unit 110 specifies an approximate expression to be used from environmental information (temperature and humidity) obtained from the detection result of the temperature and humidity sensor 113, the process speed, and the traveling distance of the photosensitive member 1, and the specified approximate expression And the charging bias to determine an afterimage countermeasure primary transfer bias. Also, a table as shown in FIG. 8 is stored in the non-volatile storage device for each combination of process speed and environment, and the primary transfer bias is determined from the photosensitive member traveling distance, the charging bias, and the table. You may

  As described above, in the present embodiment, a surface voltmeter for measuring the surface potential of the photosensitive member 1 is provided by setting the afterimage countermeasure primary transfer bias using an approximate expression obtained in advance. The apparatus can be made inexpensive as compared with the case of setting the afterimage countermeasure primary transfer bias based on the measurement result. Further, the afterimage countermeasure primary transfer bias can be set without forming a pattern for afterimage detection, and toner consumption can be suppressed, and control time can be shortened.

Next, the control unit 110 transfers the solid patterns of Y, M, C, Bk colors to the intermediate transfer belt 15 with the determined afterimage countermeasure primary transfer bias, and applies the toner adhesion amounts of these solid patterns to the optical sensor unit It detects in 118 (S12).
The solid pattern of each color may be a single solid patch in order to reduce toner consumption, and in order to improve measurement accuracy, a plurality of solid patches are formed in the sub scanning direction (intermediate transfer belt surface movement direction). The average value of the toner adhesion amount may be used as the toner adhesion amount of the solid pattern.

  Further, in the optical sensor unit 118, three reflection type photosensors are arranged at predetermined intervals in the main scanning direction (the width direction of the intermediate transfer belt), and the toner adhesion amount is detected at three locations in the main scanning direction. can do. Therefore, the solid pattern may be formed at three locations in the main scanning direction. By forming the solid pattern at three locations in the main scanning direction, deviation of the transfer efficiency in the main scanning direction can be detected.

  As shown in FIG. 1, the solid patterns of the respective colors are transferred to the intermediate transfer belt 15 in the order from the process units 10C on the downstream side of the process units 10Bk, 10Y, 10M and 10C. That is, on the intermediate transfer belt, a solid pattern is formed in the order of C, M, Y and Bk in the moving direction of the intermediate transfer belt 15. This is because when the solid patterns of C color, M color, Y color, and Bk color are transferred to the intermediate transfer belt 15 at the same position in the moving direction of the intermediate transfer belt 15 with different positions in the width direction. It is because a malfunction arises. That is, when the solid pattern transferred from the upstream process unit to the intermediate transfer belt 15 passes the primary transfer nip of the downstream process unit, it is reversely transferred to the photosensitive member 1 of the downstream process unit, and the upstream process unit This is a defect that the adhesion amount of the solid pattern is reduced. In addition, in the downstream process unit, there is also a problem that the solid pattern of the upstream process unit affects the transfer efficiency.

  When the solid patterns of the respective colors are transferred to the intermediate transfer belt in the order of arrangement from the upstream side of the process unit, that is, Bk, Y, M, and C, the intermediate transfer belt 15 in the order of arrangement from the downstream side of the process unit As compared with the case of transferring to the case, it is not preferable because the time for afterimage countermeasure control becomes longer.

  As described above, in the present embodiment, in order from the downstream side of the process unit (in order of C, M, Y, and Bk), in the present embodiment, from the viewpoint of shortening the time for afterimage countermeasure control and detecting transfer efficiency favorably from solid patterns. A solid pattern of each color is formed on the intermediate transfer belt 15. The solid patterns of the respective colors are sequentially transferred from the respective process units to the intermediate transfer belt 15. However, since the photosensitive member traveling distances are different for the respective process units, they can be separately transferred to the intermediate transfer belt 15.

  Next, the control unit 110 checks whether the toner adhesion amount of the solid pattern of each color detected in FIG. 9 is within the target range (S13). When the detected toner adhesion amount is within the target range (Y in S13), since the transfer efficiency is within the allowable range, the residual image countermeasure primary transfer bias set at the time of solid pattern creation is set. As a result, transfer conditions can be set with high accuracy in which transfer defects such as residual images and reduction in transfer efficiency can be suppressed, and a good image can be obtained.

  On the other hand, when the detected toner adhesion amount is not within the target range (N in S13), the transfer efficiency is below the allowable range, and therefore the afterimage countermeasure primary transfer bias is changed. In the case of FIG. 7, the change of the afterimage countermeasure primary transfer bias is a change that is normally increased (the positive value is increased) (S14).

FIG. 10 is a view showing the relationship between the adhesion amount of the solid pattern on the intermediate transfer belt and the transfer bias.
As can be seen from FIG. 10, the relationship between the adhesion amount of the solid pattern on the intermediate transfer belt and the primary transfer bias is the same as the relationship between the transfer efficiency and the primary transfer bias shown in FIG. It changes to draw a parabola of mountains. Further, the primary transfer bias to be set is set to a low position of the parabola at a peak (a location where the adhesion amount increases with respect to the increase of the primary transfer bias) in order to set low for preventing the residual image. The rising portion is approximated by a linear function, and the slope A of the approximated linear function is stored in the non-volatile storage device (memory) of the control unit 110, and the stored slope A and the detected adhesion amount Determine the primary transfer bias to be changed.

  Specifically, first, the difference ΔM between the detected adhesion amount M and the lower limit value Mi of the adhesion amount allowable range is calculated, and based on this ΔM and the inclination A, the correction amount of the primary transfer bias (increase amount ) Calculate ΔB (ΔM / A = ΔB). Then, the primary transfer bias to be changed is obtained by adding the obtained correction amount ΔB to the residual image countermeasure primary transfer bias B at the time of solid pattern formation (B + ΔB). Then, the primary transfer bias determined in this way is changed.

  As described above, in the present embodiment, the solid pattern is transferred onto the intermediate transfer belt with the set residual image countermeasure primary transfer bias, and the primary transfer bias is corrected from the amount of adhesion of the solid pattern to obtain the toner charge state, the primary charge. Reduction of transfer efficiency caused by various factors such as electrical resistance of transfer roller 5, electrical resistance of intermediate transfer belt 15, tolerance of primary transfer nip, eccentricity of photoreceptor, intermediate transfer belt and primary transfer roller, drive jitter, etc. Transfer defects can be suppressed. This makes it possible to suppress abnormal images on paper such as image density shortage.

  When the slope of the rising portion in the relationship between the transfer efficiency and the primary transfer bias changes due to the environment, the process speed, etc., the slope A is stored for each environment and each process speed. Then, based on the detection result of the temperature and humidity sensor 113 and the process speed, the inclination A used for the calculation is specified. As a result, it is possible to suppress a transfer failure such as a decrease in transfer efficiency due to factors such as the use condition of the apparatus such as the process speed and the environment (temperature and humidity). This makes it possible to suppress abnormal images on paper such as image density shortage.

  By changing (increasing) the primary transfer bias, the afterimage rank falls below the allowable range. Therefore, as shown in FIG. 9, the charging bias is changed based on the changed primary transfer bias (S15). The charging bias to be changed is calculated using the modified primary transfer bias and an approximate expression showing the relationship between the primary transfer bias and the charging bias used to calculate the afterimage countermeasure primary transfer bias set at the time of solid pattern formation.

FIG. 11 is a diagram showing the relationship between the residual potential and the transfer bias.
The solid line in FIG. 11 shows the relationship between the residual potential when the charging bias is -600 V and the primary transfer bias, and the broken line shows the relationship between the residual potential when the charging bias is -700 V and the primary transfer bias. ing. The higher the primary transfer bias (the larger the positive value), the larger the potential difference with the surface of the photosensitive member, and the amount of discharge between the photosensitive member and the primary transfer roller increases, resulting in unexposed and exposed areas after transfer. The potential difference between the Further, as can be seen from FIG. 11, the lower the charging bias (the larger the negative value), the greater the amount of discharge between the photosensitive member and the charging roller, so the effect of uniformly charging the photosensitive member surface is high. The potential difference between the exposed portion and the exposed portion can be reduced, and the residual potential after charging can be reduced. Therefore, in the primary transfer bias, when the charging bias is -600 V, the residual potential is above the allowable range, and even if the residual image rank is below the allowable range, the residual potential is below the allowable range by setting the charging bias to -700 V. And the afterimage rank can be made into an acceptable range.
As a result, it is possible to set the transfer condition and the charging condition with high accuracy which can suppress the occurrence of an abnormal image on paper such as an afterimage or an image density shortage.

  In FIG. 9, when the charging bias is changed, the surface potential of the photosensitive member after charging is changed, the background potential (the potential difference between the non-dew potential and the developing bias) is changed, and there is a possibility that background contamination may occur. Therefore, the developing bias is changed based on the changed charging bias (S16). Specifically, in the above-described image density control, the developing bias is determined in the reverse order to the case of determining the charging bias. That is, the drum charging potential is obtained from the charging characteristic information (the relationship between the drum charging potential and the charging bias) obtained in advance and the changed charging bias. Next, the developing condition which is the developing bias to be changed from the drum charging potential and the background potential α for the purpose of suppressing the generation of the background stain is determined.

  Further, by changing the developing bias, the developing potential (the potential difference between the exposed portion potential and the developing bias) is changed, and the image density is changed. Therefore, the exposure condition which is the exposure amount to the photosensitive member of the exposure device 3 is changed (S17). Specifically, the exposure amounts are made different from each other by the changed charging bias and the changed developing bias, and gradation patterns having different adhesion amounts are created. Then, the gradation pattern formed on the photosensitive member 1 is transferred to the intermediate transfer belt 15 by the changed primary transfer bias, and the amount of toner adhesion of each patch of the gradation pattern is detected by the optical sensor unit 118. Then, the exposure amount is adjusted based on the detection result. As a result, it is possible to suppress the afterimage and to set an image forming condition under which a prescribed image density can be obtained.

  The charging bias determined in step S4 of the image density control of FIG. 4 and the after image countermeasure primary transfer bias determined in step S11 of the afterimage countermeasure control of FIG. . However, in the present embodiment, the charging bias is set from the toner pattern on the intermediate transfer belt 15 in the image density control. Then, in the afterimage countermeasure control, the afterimage countermeasure primary transfer bias is set from the previous charging bias (and traveling distance), a toner pattern is created on the intermediate transfer belt 15, and the transfer amount is outside the target range By correcting the conditions and the charging conditions, it is possible to suppress an afterimage and a transfer failure, and to improve the accuracy of the transfer conditions and the charging conditions. As described above, the control timings of the image density control and the afterimage countermeasure control are not linked (the former is performed every time the power is turned on or every time printing is performed for a predetermined number of sheets, while the latter is performed every photosensitive distance (5 km)). And the suppression of the afterimage and the improvement of the transfer efficiency are solved by using the margin of the transfer condition (the margin which can be changed from S1 to S2 in FIG. 7).

  Further, since the solid pattern formed in the afterimage countermeasure control of the present embodiment is detected by the optical sensor unit 118 which detects the gradation pattern formed by the image density control, a dedicated sensor for detecting this solid pattern is Compared with the separately provided invention, afterimage countermeasure control can be performed with an inexpensive configuration.

Further, when the image density control of FIG. 4 is executed, the gradation pattern may be transferred to the intermediate transfer belt 15 with the primary transfer bias at which the transfer efficiency is the highest. As a result, the gradation pattern having the highest transfer efficiency is transferred to the intermediate transfer belt 15, and the charge bias and the development bias can be set such that the image density failure due to factors other than the transfer efficiency is suppressed.
Then, a solid pattern in the afterimage countermeasure control is created with the charging bias and the developing bias set in the image density control. As a result, based on the result of the adhesion amount of the solid pattern transferred to the intermediate transfer belt 15, the residual image countermeasure primary transfer bias set from the film thickness of the photosensitive member 1 and the charging bias is corrected to achieve accurate transfer efficiency. You can get a good image.

  Further, in the afterimage countermeasure control, when the afterimage countermeasure primary transfer bias is changed, the charging bias and the developing bias are not desired to be changed as much as possible. This is because the charging bias and the developing bias determined by the image density control are to be changed, which may affect the image density. Therefore, when the afterimage countermeasure primary transfer bias is changed, an image may be actually created, and the generation state of the negative afterimage of the created image may be checked as follows to change the charging bias.

FIG. 12 is an example of an image pattern created at the time of negative residual image check.
As shown in FIG. 12, the image pattern created at the time of negative afterimage check is composed of a solid pattern consisting of a plurality of solid patches and a halftone pattern consisting of halftone images. The length of a solid pattern composed of a plurality of solid patches is the length of one round of the photosensitive member. The negative afterimage appears relatively clearly in the halftone pattern formed after the pattern of the plurality of solid patches. The control unit 110 causes the optical sensor unit 118 to grasp a negative afterimage based on the toner adhesion amount of the halftone image. If the negative afterimage is within the allowable range, the charging bias is not changed. On the other hand, when the negative afterimage is less than the allowable range, the charging bias is changed based on the negative afterimage.

  Also, for example, when there is a photosensitive member film thickness deviation, the appearance of an afterimage is different in the main scanning direction. In the present embodiment, in the optical sensor unit 118, three reflective photosensors are arranged at predetermined intervals in the main scanning direction (the width direction of the intermediate transfer belt). Therefore, three solid patterns of the image pattern created at the time of negative afterimage check may be formed in the main scanning direction corresponding to the three reflective photosensors. As a result, it is possible to grasp a negative afterimage from three points in the main scanning direction from the halftone pattern. By changing the charging bias on the basis of the negative afterimage of the worst result among the detection results of the negative afterimage in the three main scanning directions, the generation of the negative afterimage in the main scanning direction can be suppressed.

  Further, in the afterimage countermeasure control described above, the primary transfer bias is changed from the detection result of the solid pattern and the relationship between the primary transfer bias and the transfer efficiency previously obtained by experiment, and the changed transfer bias is obtained. Although the charging bias is changed from the relationship between the afterimage and the charging bias, it is not limited thereto. For example, as described above, first, a solid pattern is created with a primary transfer bias set based on the thickness of the photosensitive member and the charging bias. If the adhesion amount is lower than the target, the primary transfer bias is increased by a predetermined value. Next, the image pattern shown in FIG. 12 is created, and the adhesion amount of the solid pattern and the adhesion amount of the halftone pattern are respectively confirmed. If the adhesion amount of the solid pattern does not reach the target adhesion amount, the predetermined value transfer bias is increased. On the other hand, when it is determined from the adhesion amount of the halftone image that a negative afterimage is generated, the charging bias is increased by a predetermined value. Such operation may be repeated to determine the primary transfer bias and the charging bias. As a result, the use environment of the image forming apparatus is different from the assumption, and the relationship between the primary transfer bias and the transfer efficiency, and the relationship between the charge bias and the afterimage rank are different from the relationships obtained in advance by experiments. Even in the case where the image is shattered, it is possible to set an optimal transfer bias and a charging bias in which a reduction in negative afterimage and image density is suppressed, and a good image can be obtained.

Next, verification experiments conducted by the applicant will be described.
Environment, process speed and afterimage countermeasure control were made different from each other to investigate afterimage and image density.
In the verification experiment, the image forming apparatus of the intermediate transfer system shown in FIG. 1 was used. The intermediate transfer belt 15 used a traveling distance of 30 km, and the photosensitive member 1 used a traveling distance of 15 km. Further, as shown in FIG. 2, the primary transfer roller of the metal roller was used, and was disposed in non-contact with the photosensitive member. Further, a charge removing lamp was disposed between the cleaning blade 6 and the charging device 2 as a charge removing device. The electrical resistance of the intermediate transfer belt 15 is 10.0 [log Ω].

FIG. 13 is a view showing an afterimage evaluation image used in the present verification experiment.
As shown in FIG. 13, the residual image evaluation image has characters on the right of the front end of the image and white characters on the left. Behind that, it has a halftone pattern. When an afterimage occurs, the character occurs at a position one round back of the photosensitive member from the position of the character. Furthermore, in the afterimage evaluation image, a solid (painted) image is provided behind the halftone pattern in order to determine whether the primary transfer bias is appropriate from the viewpoint of transfer efficiency. When the primary transfer bias is low, the amount of toner transferred from the photosensitive member 1 to the intermediate transfer belt 15 decreases and the density decreases. The left and right margins of the halftone pattern and solid image formed on the sheet are 2 mm. The afterimage and the image density were evaluated based on the afterimage evaluation image formed on the sheet.

<Evaluation: Afterimage>
The residual image was visually confirmed as to the halftone pattern of the residual image evaluation image formed on the sheet, and it was judged as “x” when the residual image was confirmed, and “o” when not.

<Evaluation: Concentration>
The image density is determined by measuring the solid (painted) image of the residual image evaluation image formed on the sheet with a reflection densitometer, and determining the image density as “x” when the image density is less than ID 1.3 or otherwise as “o”. did.

<Evaluation: Overall>
When either "afterimage" or "density" occurred, it was determined as "x", and when not so, it was determined as "o".

Example 1
Verification tests were conducted at a linear velocity of 300 mm / sec and an environment of 23 ° C. and 50%. After execution of image density control, afterimage countermeasure control was performed, and then the above-mentioned image evaluation image was formed, and the afterimage and image density were evaluated. The primary transfer bias at the time of gradation pattern formation in image density control (the primary transfer bias with the highest transfer efficiency obtained in advance by experiment) was 900V. Further, the charging bias set by the image density control was -500V. Further, based on the environment of the apparatus, the process speed, the charging bias, and the traveling distance of the photosensitive member 1, an afterimage countermeasure primary transfer bias at the time of forming a solid patch toner image was set. The afterimage countermeasure primary transfer bias set was 700V. Further, in Example 1, the toner adhesion amount of the solid pattern falls below the specified range, and the afterimage countermeasure primary transfer bias is changed. The primary transfer bias after change is 800V. Also, the charging bias was changed based on the change of the primary transfer bias. The charge bias after change was -550V.

Example 2
A verification test was conducted under the same conditions as in Example 1 except that the environment was 27 ° C. and 80%. In Example 2, the primary transfer bias at the time of gradation pattern formation was 800 V, and the residual image countermeasure primary transfer bias at the time of solid pattern formation was 600 V. Further, in Example 2, the adhesion amount of the solid pattern is within the specified range, the afterimage countermeasure primary transfer bias is not changed, and the afterimage countermeasure control is 600V.

[Example 3]
The verification test was performed under the same conditions as in Example 1 except that the process speed was 60 mm / sec. In Example 3, the primary transfer bias at the time of gradation pattern formation was 700 V, and the afterimage countermeasure primary transfer bias at the time of solid pattern formation was 600 V. Also in the third embodiment, the adhesion amount of the solid pattern is within the specified range, the afterimage countermeasure primary transfer bias is not changed, and the primary transfer bias after the afterimage countermeasure control is 600V.

Comparative Example 1
The verification test was conducted under the same conditions as in Example 1 except that the afterimage countermeasure control was not performed after the execution of the image density control. The primary transfer bias at the time of gradation pattern formation was 900 V, and the primary transfer bias set for anti-image measures was 600 V.

Comparative Example 2
Countermeasures against residual image when creating a solid pattern Verification was performed under the same conditions as in Example 1 except that the primary transfer bias was used as the primary transfer bias (primary transfer bias that maximizes transfer efficiency) when forming gradation patterns in image density control. The test was done. The primary transfer bias at the time of gradation pattern formation and the afterimage countermeasure primary transfer bias were 900V. Further, since the primary transfer bias set in the afterimage measure is the primary transfer bias at which the transfer efficiency is maximum, the adhesion amount of the solid pattern is within the allowable range, and the primary transfer bias set after the afterimage measure control is also 900V. there were.

Comparative Example 3
A verification test was conducted under the same conditions as in Example 2 except that the afterimage countermeasure primary transfer bias was set based on the process speed, the charging bias, and the traveling distance of the photosensitive member 1 without using the environment. The primary transfer bias at the time of gradation pattern formation was 800 V, and the afterimage countermeasure primary transfer bias set based on the process speed, the photosensitive member travel distance, and the charging bias was 700 V without taking environmental conditions into consideration. In Comparative Example 3, the adhesion amount of the solid pattern was within the specified range, the primary transfer bias was not changed, and the primary transfer bias after anti-image countermeasure control was 700 V.

Comparative Example 4
A verification test was conducted under the same conditions as in Example 3 except that the afterimage countermeasure primary transfer bias was set based on the environment, the charging bias, and the traveling distance of the photosensitive member 1 without using the process speed. The primary transfer bias at the time of gradation pattern formation was 700 V, and the afterimage countermeasure primary transfer bias set based on the environment, the photosensitive member travel distance, and the charging bias was 700 V without considering the process speed. In Comparative Example 4, the adhesion amount of the solid pattern was within the specified range, the primary transfer bias was not changed in the afterimage countermeasure control, and the primary transfer bias after the afterimage countermeasure control was also 700V.

  The results of each Example and Comparative Example are shown in Table 1.

  As shown in Table 1, in Comparative Example 1, afterimage countermeasure control was not performed, the transfer efficiency fell below the allowable range, and the image density became "x".

  In Comparative Example 2, the afterimage countermeasure primary transfer bias set at the time of solid pattern formation is a primary transfer bias in which the afterimage is not considered. Therefore, an afterimage was generated on the image, and the afterimage became “x”.

  In Comparative Example 3, since the afterimage countermeasure primary transfer bias set at the time of solid pattern formation was not taken into consideration in the environment, an afterimage was generated on the image, and the afterimage became “x”.

  Further, in Comparative Example 4, since the afterimage countermeasure primary transfer bias set at the time of solid pattern formation did not take into consideration the process speed, an afterimage was generated on the image, and the afterimage became “x”.

  On the other hand, in Examples 1 to 3 in which the afterimage countermeasure control is performed, good results can be obtained for both afterimage and image density. Further, as can be seen from Examples 2 and 3, the afterimage countermeasure primary transfer bias set at the time of solid pattern formation is set based on the environment, process speed, charging bias and traveling distance of the photosensitive member 1. Therefore, even if the process speed and the environment changed, an image in which the generation of an afterimage was suppressed could be obtained.

Next, a modification of the image forming apparatus will be described.
FIG. 14 is a schematic configuration diagram of a tandem direct transfer type image forming apparatus.
The image forming apparatus shown in FIG. 14 includes a sheet conveying belt 51 for conveying the transfer sheet P, and the sheet conveying belt 51 contacts the photoreceptors 1Y, 1M, 1C, and 1K, respectively, and outputs Y, M, C, and K. Form a primary transfer nip. The primary transfer nip for Y, M, C, K in the process of transporting the transfer sheet P from the left side to the right side in the drawing along with its own endless movement while holding the transfer sheet P on its own surface Sequentially into As a result, the Y, M, C, and K toner images are superimposed on the transfer sheet P and primarily transferred. Further, the optical sensor unit 118 is disposed to face the front surface of the paper conveyance belt 51 via a predetermined gap. In the case where the primary transfer roller of each color is a metal roller, as shown in FIG.

  In the image forming apparatus shown in FIG. 14, the gradation pattern or solid pattern is transferred to the paper conveyance belt 51, and the adhesion amount of the gradation pattern or solid pattern transferred to the paper conveyance belt 51 is the optical sensor unit. It is detected by 118. That is, in the tandem type direct transfer type image forming apparatus, the paper conveyance belt 51 has a function as a transfer member to which the toner image is transferred from the photosensitive member.

FIG. 15 is a schematic block diagram of a monochrome image forming apparatus.
Also in this image forming apparatus, the transfer sheet P is conveyed to the primary transfer nip, and the toner image on the photosensitive member is directly transferred to the transfer sheet P.
FIG. 16 is an enlarged view of the vicinity of the primary transfer nip in the monochrome image forming apparatus.
The primary transfer roller 5 is a sponge roller, and the primary transfer roller is deformed directly to the photosensitive member to form a primary transfer nip of a desired width. Further, the optical sensor unit 118 is disposed to face the outer peripheral surface of the primary transfer roller 5 with a predetermined gap.

  The gradation pattern and the solid pattern are transferred to the primary transfer roller 5, and the adhesion amount of the gradation pattern and the solid pattern transferred to the primary transfer roller 5 is detected by the optical sensor unit 118. That is, in this monochrome image forming apparatus, the primary transfer roller 5 also has a function as a transferred member to which the toner image is transferred from the photosensitive member.

The above-described one is an example, and the following effects can be obtained.
(Aspect 1)
An image carrier such as a photosensitive member 1 or the like, a charging member such as a charging roller of a charging device 2 for charging the surface of the image carrier, an intermediate transfer belt 15 to which a toner image formed on the surface of the image carrier is transferred And an optical sensor unit for detecting an adhesion amount of toner on the transfer member, and a film thickness detection member (photosensitive member drive motor 119) for detecting the film thickness of the image carrier. The image carrier is provided with charging conditions (in the present embodiment, charging bias) for charging the surface of the image carrier by the charging member including the adhesion amount detection member such as the photo sensor 118, and the detection result of the film thickness detection member. The transfer conditions (primary transfer bias in this embodiment) for transferring the toner image on the surface to the transfer member are set, and the toner adhesion amount of the toner pattern formed on the transfer member under the set transfer conditions is the adhesion amount Out it is detected by members, from the detection result of the adhering amount detection member to correct the transfer condition and the charging condition.
As described in the embodiment, the likelihood of occurrence of an afterimage differs depending on charging conditions such as the charging bias of the charging device and the film thickness of the image carrier. Therefore, based on the charge condition and the detection result of the film thickness detection member, it is possible to set the transfer condition capable of suppressing an afterimage. As a result, transfer conditions that can suppress an afterimage can be set without using a potential sensor, and downsizing of the apparatus and cost reduction of the apparatus can be achieved.
Further, by setting the transfer condition using the detection result of the film thickness detection member, it is possible to set the transfer condition optimum for the consumption condition of the image carrier.
However, due to various factors such as the toner charge state, the use condition of the apparatus, and the environment (temperature and humidity), under the set transfer conditions, transfer failure such as a decrease in transfer efficiency may occur and an abnormal image on paper may occur.
Therefore, in the first aspect, the toner pattern is transferred to the transfer receiving member under the transfer conditions that can suppress the set residual image, and the adhesion amount of the toner pattern transferred to the transfer receiving member is detected. As a result, it can be determined whether the transfer condition set to suppress the afterimage is a transfer condition such as a transfer failure such as a decrease in transfer efficiency. Then, with the transfer bias set to suppress the residual image, if the toner adhesion amount is out of the predetermined range due to various factors described above and a transfer failure occurs and an abnormal image on paper occurs, the transfer bias should be corrected. Thus, it is possible to use a transfer bias that can suppress transfer failure.
In addition, since there is a possibility that an afterimage may occur by correcting the transfer condition in this way, the occurrence of the afterimage can also be suppressed by correcting the charging condition.
As a result, it is possible to suppress the occurrence of abnormal images on paper such as residual images and transfer defects while achieving downsizing and cost reduction of the devices, and good images can be obtained.

(Aspect 2)
In the first aspect, an exposure member such as a light source of the exposure device 3 for forming an electrostatic latent image on the charged surface of the image carrier such as the photosensitive member 1 and a development for developing the electrostatic latent image on the surface of the image carrier An exposure condition (in the present embodiment, an exposure amount) for forming a latent image by the exposure member, provided with a developing member such as a developing roller of the apparatus 4 and when the charging condition (in the present embodiment, the charging bias) is corrected The developing conditions (in the present embodiment, the developing bias) for developing the electrostatic latent image by the developing member are adjusted.
According to this, as described in the embodiment, when the charging condition (charging bias) is corrected, the target background potential can be maintained by adjusting the developing condition (development bias), and the non-exposed portion It is possible to suppress the occurrence of ground contamination to which toner adheres. In addition, by adjusting the exposure conditions, it is possible to maintain the target development potential.
Thereby, an afterimage is suppressed and a good image can be obtained.

(Aspect 3)
In the aspect 1 or 2, the charging condition used when setting the transfer condition is a toner pattern of the charging condition setting toner pattern formed by forming a charging condition setting toner pattern such as a gradation pattern on the transfer member. The adhesion amount is detected by the adhesion amount detection member such as the optical sensor unit 118, and the charging condition is set based on the detection result of the adhesion amount detection member.
Thereby, the influence of the charging failure is suppressed on the adhesion amount of the toner pattern such as the solid pattern. Therefore, the transfer failure can be well grasped from the adhesion amount of the toner pattern.

(Aspect 4)
In any one of the first to third aspects, the charging device is provided from a contact portion such as a primary transfer nip where the image carrier and a transfer member such as the intermediate transfer belt 15 contact in the surface movement direction of the image carrier such as the photosensitive member 1 A charge removing member such as a light source of the charge removing device 8 for removing the charge by irradiating the surface of the image bearing member with light is disposed between the charge opposing portion where the charge member such as the charge roller is opposed.
According to this, as described in the embodiment, it is possible to suppress a positive afterimage that is generated when the negative potential remains after transfer.

(Aspect 5)
In any one of the embodiments 1 to 4, the transfer member such as the intermediate transfer belt 15 is a belt member, and the outer peripheral surface of the belt member is an image bearing member such as the photosensitive member 1 while in contact with the inner peripheral surface of the belt member. A contact member such as a primary transfer roller 5 to be brought into contact with the body is provided, and the contact member is disposed downstream of the contact point between the belt member and the image carrier in the surface movement direction of the belt member.
According to this, as described in the embodiment, the contact member such as the primary transfer roller 5 is not brought into contact with the image carrier such as the photosensitive member 1 via the transferred member such as the intermediate transfer belt 15 It can be arranged, and it is possible to suppress the premature deterioration of the image carrier.

(Aspect 6)
In the fifth aspect, the contact member such as the primary transfer roller 5 is a metal roller.
According to this, as described in the embodiment, the cost can be reduced compared to the case of using a sponge roller.

(Aspect 7)
In any one of the first to sixth aspects, a temperature / humidity detection member such as a temperature / humidity sensor 113 for detecting the temperature and humidity in the apparatus main body is provided, and the transfer condition at the time of forming the toner pattern is the charging condition; According to the detection result of the film thickness detection member and the temperature and the humidity detected by the temperature and humidity detection member, as described in the embodiment, it is possible to set the optimum transfer conditions in which the residual image is suppressed. it can.

(Aspect 8)
In any one of the aspects 1 to 7, the transfer condition at the time of forming the toner pattern is set from the charging condition, the detection result of the film thickness detection member, and the image forming speed.
According to this, as described in the embodiment, it is possible to set an optimal transfer condition in which an afterimage is suppressed.

(Aspect 9)
In any one of the aspects 1 to 8, the transferred member such as the intermediate transfer belt 15 is a conductive belt having a surface resistance of 8.5 [log Ω / □] or more and 11.0 [log Ω / □] or less.
According to this, as described in the embodiment, it is possible to perform good transfer with a low transfer bias, to suppress generation of an afterimage, to suppress the flow of transfer current in the surface direction, and to suppress toner scattering. it can.

1: photoconductor 2: charging device 3: exposure device 4: developing device 5: primary transfer roller 6: cleaning blade 7: cleaning device 8: cleaning device 8: process unit 15: intermediate transfer belt 16: cleaning backup roller 51: paper Conveying belt 100: Printer main unit 110: Control unit 111: Operation unit 113: Temperature and humidity sensor 114: Belt drive motor 115: Intermediate transfer contact clutch 116: Primary transfer high voltage power supply 117: Secondary transfer high voltage power supply 118: Optical sensor unit 119 : Photoconductor drive motor

Patent No. 5084225

Claims (9)

An image carrier,
A charging member for charging the surface of the image carrier;
An image forming apparatus comprising: a transfer member to which a toner image formed on the surface of the image bearing member is transferred;
A film thickness detection member for detecting the film thickness of the image carrier;
An adhesion amount detection member for detecting an adhesion amount of toner on the transfer target member;
Set the transfer conditions to transfer the toner image on the surface of the image carrier from the charging condition to charge the surface of the image carrier by the charging member and the detection result of the film thickness detection member to the transfer target member And
The toner adhesion amount of the toner pattern formed on the transfer target member under the transfer condition set as the charging condition is detected by the adhesion amount detection member,
The image forming apparatus, wherein the correction of the transfer condition and the charging condition is performed when the toner adhesion amount detected by the adhesion amount detecting member is out of a predetermined range. In the image forming apparatus according to claim 1,
An exposure member for forming an electrostatic latent image on the charged surface of the image carrier;
And a developing member for developing the electrostatic latent image on the surface of the image carrier.
An image forming apparatus, wherein when the charging condition is corrected, an exposure condition for forming a latent image by the exposure member and a developing condition for developing the electrostatic latent image by the developing member are adjusted. In the image forming apparatus according to claim 1 or 2,
The charging condition used when setting the transfer condition forms a charging condition setting toner pattern on the transfer target member, and detects the amount of toner adhesion of the formed charging condition setting toner pattern with the adhesion amount detecting member. An image forming apparatus characterized in that the charging condition is set based on the detection result of the adhesion amount detection member. The image forming apparatus according to any one of claims 1 to 3.
The surface of the image carrier is irradiated with light from the contact portion where the image carrier and the transfer member are in contact to the charge opposing portion where the charging member is opposed in the surface movement direction of the image carrier. An image forming apparatus comprising a charge removing member for removing charges. The image forming apparatus according to any one of claims 1 to 4.
The transfer target member is a belt member,
It has an abutment member which abuts on the inner circumferential surface of the belt member and causes the outer circumferential surface of the belt member to abut on the image carrier.
An image forming apparatus, wherein the contact member is disposed downstream of the contact point between the belt member and the image carrier in the surface movement direction of the belt member. In the image forming apparatus according to claim 5,
The image forming apparatus, wherein the contact member is a metal roller. The image forming apparatus according to any one of claims 1 to 6.
Has a temperature and humidity detection member to detect the temperature and humidity in the device body,
2. The image forming apparatus according to claim 1, wherein the transfer conditions for forming the toner pattern are set from the charging condition, the detection result of the film thickness detection member, and the temperature and humidity detected by the temperature and humidity detection member. The image forming apparatus according to any one of claims 1 to 7.
2. The image forming apparatus according to claim 1, wherein the transfer conditions for forming the toner pattern are set from the charging condition, the detection result of the film thickness detection member, and the image forming speed. The image forming apparatus according to any one of claims 1 to 8.
The image forming apparatus, wherein the transfer member is a conductive belt having a surface resistance of 8.5 [log Ω / □] or more and 11.0 [log Ω / □] or less.