JP4968913B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus having a patch sensor for performing image density control and gradation control.

  Conventionally, an image forming apparatus uniformly charges the surface of a photosensitive member such as a drum as an image carrier, and performs exposure corresponding to an image signal on the surface with an exposure device such as a laser, An electrostatic latent image is formed. The electrostatic latent image is developed by a developing device having toner as a developer to form a visible image (toner image).

   Further, the toner image is transferred to a recording paper or an intermediate transfer member using a transfer unit, and finally the image is fixed on the recording paper using a fixing device. In an image forming apparatus such as a color copying machine, the processes until the unfixed toner image is formed are performed for different colors such as yellow, magenta, cyan, and black.

  For example, each color toner image is formed on a separate drum, and each toner image is superposed on the same intermediate transfer member carried by the means for conveying the recording paper. There are various methods such as a method of superimposing one color for each rotation on one photoconductor.

  However, in the color image, even if the image density of each color changes slightly, the variation in color is easy to understand. Therefore, it is necessary to control the density of each color to be constant.

  The following method is known as one of the density controls.

  In the non-image area of the photoconductor, a patch image of a predetermined density of each color such as yellow, magenta, cyan, and black is formed, and the density is read by a patch sensor arranged toward the photoconductor. Based on the density Measure the excess and deficiency of the developed toner.

As a result of this measurement, for example, when the toner is insufficient, the amount of toner supplied to the developing device of the corresponding color is increased, and the image density of each color is kept constant. On the other hand, if the patch is dark, the amount of toner supplied to the developing device is reduced, or the number of times of supply is limited to keep the image density constant.

The non-image area is an area where toner on the upstream side or downstream side of the toner image formed by the image forming apparatus is not carrying toner, or the rotation direction of the photoconductor. A region between a plurality of adjacent toner images can be considered. In Patent Document 1, the toner agent adheres to the transfer roller by the transfer bias by switching the high-voltage bias of the transfer means when the toner image formed in the non-image area passes the transfer point, and finally, Prevents the recording paper from getting dirty. By this control, it is possible to switch the bias according to the color and density of the patch image, and this is a very effective means against dirt.

  However, a patch sensor that measures the density of a toner image drawn in a non-image region is generally an optical sensor (LED), and the wavelength of the LED is used in the 600 nm to infrared region.

  Since the charged state of the photoreceptor is changed by light, the charged state may be changed by the LED of the patch sensor. When the charged state changes, the toner does not get on only the exposed portion, or the density becomes high.

  The exposure by the LED of the patch sensor generally starts before the toner image enters the field of view of the patch sensor, and the LED is generally turned off after the toner image is sufficiently out of the field of view. Therefore, exposure by the LED of the patch sensor is performed in a wider range than the toner image, and a state in which the charged state of the photoconductor is different from other portions is created.

In the case of an OPC drum generally used in a copying machine, if the transfer bias is applied in the vicinity of the patch sensor, the potential on the photoreceptor varies in the exposure area of the LED of the patch sensor depending on the magnitude of the transfer bias.

  After that, when the residual charge is removed by an LED array or the like and the photosensitive member is uniformly charged by the primary charger, the charged state is not uniform only in the portion irradiated with the LED of the patch sensor. When it is used in the case, the band-like image unevenness occurs.

  On the other hand, since the number of readings of the patch sensor varies due to the occurrence of noise at the time of reading, it is better to read the sensor value multiple times and perform an averaging process. It is necessary to increase the number of reading of density.

However, when performing density control between paper when an image is formed on a plurality recording paper, copy sheets per minute of the image forming apparatus is the time between the recording paper and multi Ihodo recording sheet is shortened, detecting the number of patches Ru few kuna.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of preventing strip-shaped charging unevenness on a photosensitive member due to exposure of an LED of a patch sensor and performing highly accurate density control.

In order to achieve the above object, an image forming apparatus according to claim 1 includes a photosensitive member that carries a toner image and is driven to rotate, an image forming unit that forms a toner image on the photosensitive member, and a transfer voltage. A transfer unit that transfers the toner image formed on the photoconductor by the image forming unit to a transfer body that is in contact with the photoconductor, and the transfer voltage is applied to the transfer unit. After transferring the toner image on the photosensitive member to the transfer member, a transfer voltage applying unit for lowering the transfer voltage, and a toner image formed on the photosensitive member by the image forming unit on the rotating direction of the photosensitive member And a detected image forming unit that forms the detected toner image on the image forming unit, and a downstream side of the image forming unit and an upstream side of the transfer unit. At the side position Irradiating means for irradiating light, and the image forming means based on a light reception result of light emitted from the irradiating means and reflected by the detected toner image formed by the detected image forming means. In the image forming apparatus to be controlled, the irradiating unit emits light toward the photoconductor after the transfer voltage is lowered to a predetermined voltage after the transfer voltage applying unit starts to decrease the transfer voltage. Irradiating . According to another aspect of the present invention, there is provided an image forming apparatus comprising: a photoconductor that carries a toner image and is driven to rotate; an image forming unit that forms a toner image on the photoconductor; A detected image forming means for forming a detected toner image preceding the rotation direction of the photosensitive member on the toner image formed on the body by the image forming means and a transfer voltage; A transfer means for transferring a toner image formed on the photoconductor by an image forming means to a transfer body in contact with the photoconductor; a transfer voltage applying means for applying the transfer voltage to the transfer means; and the photoconductor In the rotation direction, light is applied to the toner image to be detected formed on the photoconductor at a position downstream from the image forming unit and upstream from the transfer unit, and then the irradiation is performed. Irradiating means for turning off the light, In the image forming apparatus for controlling the image forming unit based on the light reception result of the light irradiated from the irradiation unit and reflected by the toner image to be detected, the transfer voltage applying unit is configured such that the irradiation unit emits light. After the light is extinguished, the transfer voltage to be applied to the transfer unit is raised after the amount of light emitted from the irradiation unit becomes smaller than a predetermined value.

  According to the present invention, the LED of the patch sensor is turned on after the transfer bias when transferring from the photosensitive member to the transfer medium is sufficiently lowered. As a result, it is possible to prevent the belt-shaped charging unevenness from occurring on the photosensitive member due to the exposure of the LED of the patch sensor, and it is possible to turn on the patch LED at an optimal timing and to take as many readings as possible. . As a result, highly accurate density control can be performed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged view of a main part of the image forming apparatus of FIG.

  Since the full-color image forming apparatus itself shown in FIGS. 1 and 2 has a well-known structure, the description of the structure and operation will be simplified.

  1 and 2, a primary charger 2, a laser scanner unit 3, a developing rotary 4, an intermediate transfer member 5, and a cleaning device 6 are disposed around a drum-shaped photosensitive member 1, and further downstream in the vicinity thereof. An exposure device 12 for removing residual charges is arranged.

Each developing unit of yellow, magenta, cyan, and black is housed in the developing rotary 4 , and the developing rotary 4 can be rotated in the direction of an arrow by a developing rotary drive motor (not shown). In the present embodiment, the developing devices are for four colors, but are not limited to four colors.

  A three-stage sheet feeding unit 7 is provided at the lower portion of the apparatus main body, and a secondary transfer charger 8 and a separation charger 13 (FIG. 2) are in contact with the lower portion of the intermediate transfer member 5. Further, a primary transfer roller 14 is provided inside the intermediate transfer member 5 and in a contact portion with the photosensitive member 1.

A conveyance belt 9 is provided downstream of the separation charger 13 in the recording paper conveyance direction, and a fixing device 10 is provided further downstream thereof. A paper discharge tray 11 (FIG. 1) is provided on the downstream side of the fixing device 10 and outside the main body of the apparatus.

  As shown in FIG. 2, a patch sensor 15, which is a main part of the present invention, is provided between the developing rotary 4 and the intermediate transfer member 5 so as to face the photoreceptor 1.

  Each color toner image on the photoreceptor 1 is sequentially transferred onto the intermediate transfer member 5 by a known electrophotographic process, and a full-color image is formed on the intermediate transfer member 5. Thereafter, the recording paper is fed from the paper feeding unit 7 at a predetermined timing, and is fed into the nip portion between the secondary transfer charger 8 and the intermediate transfer member 5 in synchronism with the toner image. Then, the toner image on the intermediate transfer member 5 is collectively transferred to the recording paper by the action of the secondary transfer charger 8.

  The recording paper is then separated from the intermediate transfer member 5 by the separation charger 13 and conveyed to the fixing device 10 by the conveying belt 9, where the unfixed toner image is fixed, and the recording paper is discharged to the discharge tray 11. The paper is discharged.

  Next, a toner density control patch will be described.

  FIG. 3 is a configuration diagram of the patch sensor in FIG.

  In FIG. 3, the patch sensor 15 includes an LED 301, optical sensor elements 302 and 303, and a beam splitter 304.

  The LED 301 has a wavelength in the 600 nm to infrared region. An LED on signal (not shown) is given from the main body, and the LED can be turned on / off. The light emitted from the LED 301 hits the surface of the patch image 305 formed on the photosensitive member 1 and is reflected. The reflected light passes through a beam splitter 304 that can separate wavelengths matched to the LED 301 and is separated into transmitted light and scattered light. The transmitted light is detected by the optical sensor element 302 and the scattered light is detected by the optical sensor 303. The toner density is determined by the ratio of the transmitted light and scattered light.

  As shown in FIG. 4, the patch toner image 305 is formed on the photoreceptor 1 between the image area T1 and the image area T2 (between sheets). A patch image 305 is formed for each color between sheets.

For example, a yellow-only patch image Yp is formed between the image region T1 and the image region T2, and a magenta-only patch image Mp is formed between the next image region T2 and the image region T3. When images are formed in the image areas T1, T2, and T3, a primary transfer bias is applied, and the image is copied onto the intermediate transfer member 5 .

  FIG. 5 is a diagram showing a generation principle of a memory on the photosensitive member generated by exposure by the LED of the patch sensor of FIG.

(1) in FIG. 5 shows the photoreceptor potential Vd after the initial primary charging by the primary charger 2. The surface of the photoreceptor 1 is uniformly charged to Vd = −600V. (2) is a diagram showing the potential when the patch image 305 is latently formed on the photosensitive member 1 by laser exposure from the laser scanner unit 3 . The photoreceptor potential is lowered by the patch latent image.

  (3) is a view in which a negatively charged toner is placed on the patch latent image of (2) by the developing device to form a visible image. Thereafter, when the LED of the patch sensor 15 is turned on, a deeper latent image is formed around the area where the LED is lit around the patch latent image as shown in (4).

  In this embodiment, the potential is about -50V. At this time, when the primary transfer bias is applied, the potential is uniformly lowered as shown in (5). The photoconductor potential at this time is due to the photoconductor characteristics and the magnitude of the transfer bias.

The toner on the latent image is copied onto the intermediate transfer member 5 by the primary transfer, and when the pre-exposure LED (exposure device 12) is turned on to make the potential of the photosensitive member 1 uniform again, as shown in (6). In addition, there is no charge in the region where the LED of the patch sensor 15 is lit. Thereafter, when laser exposure from the laser scanner unit 3 is performed, the potential is not uniform only in a region where no charge is placed. Even if the toner is developed here, the desired density is not obtained, and image unevenness occurs.

  A voltage of about 2 KV to 4 KV is applied to the primary transfer roller 14 as a primary transfer bias.

  FIG. 6 is a diagram illustrating a first example of the primary transfer bias circuit applied to the primary transfer roller in FIG.

  The voltage supplied from the power supplies 403 and 404 is boosted via the transformer 401 or 402 when the TR (transistor) 1 or TR2 is switched by the control signal A or B. Here, when the control signal A outputs an ON signal, a positive voltage is output by the transformer 401, and when the control signal B outputs an ON signal, a negative voltage is output by the transformer 402.

  C1, C2 and R1, R2 are constants in the primary transfer bias circuit, and Ct and Rt are capacitance and resistance determined by the arrangement of the primary transfer roller 14 and the main body. For example, when TR1 is turned on and a positive voltage is output, C1 and CT in the circuit are charged, and the voltage is applied to the primary transfer roller 14. Conversely, when TR1 is turned off, the charges charged in C1 and CT are discharged through R1, RT and R2, and the voltage applied to the primary transfer roller 14 becomes zero.

  That is, the primary transfer bias has time required for charging / discharging C1, C2, and CT, and the rising time is called Ton and the falling time is called Toff. CT depends on the model, because it depends on the material of the primary transfer roller 14, the connector material of the power supply unit, and the arrangement in the main body. Therefore, the rise time and fall time of the primary transfer bias are almost uniquely determined if the bias value is constant.

  A CPU (not shown) that controls the main body stores the rise time and can control the control signals A and B of the primary transfer bias.

In this embodiment, as shown in FIG. 7 , the primary transfer bias (primary transfer voltage) Vtr is lowered by turning off the control signal A. In the present embodiment, the voltage at this time falls from 2 KV to 4 KV to around 0 to 100 V. At this time, the off time of the primary transfer bias takes Toff depending on the discharge time of C1 and CT.

  In this embodiment, it takes about several ms to 10 ms. By turning on the LED 301 of the patch sensor 15 after Toff, the primary transfer voltage Vtr and the LED are prevented from overlapping. Since the LED 301 of the patch sensor 15 can be turned on in the order of ns when an ON signal is input, only the fall time Toff of the primary transfer bias needs to be considered.

The primary transfer bias Vtr during image formation can be changed by the environmental temperature or humidity. Fall time Toff of the primary transfer bias, as shown in FIG. 8, the primary transfer bias Vtr is lower nearly as short Kunar.

  As the number of readings by the patch sensor 15 increases, the density of the patch image 305 can be accurately detected without being affected by noise or the like by the averaging process. Therefore, since it is better to light the patch LED 301 immediately after the primary transfer bias falls, the lighting time can be made sufficiently long by changing the Toff value according to the transfer bias value (not shown) and lighting the LED 301. it can.

  FIG. 9 is a diagram illustrating a second example of the primary transfer bias circuit applied to the primary transfer roller in FIG.

  The basic operation is the same as that of the circuit shown in FIG. In the circuit of FIG. 9, there is voltage detection means 405 that can monitor the voltage applied to the primary transfer roller 14, and the detection output is input to a main body CPU (not shown).

  The threshold value Va is set in the CPU, and the LED 301 of the patch sensor 15 is activated when the primary transfer bias Vtr is equal to or lower than the threshold value Va as shown in FIG. Va does not have to be zero. Depending on the sensitivity of the photosensitive member 1 to the wavelength, Va> 0 can be set and the LED 301 of the patch sensor 15 can be started up quickly, so that the number of detections can be increased accordingly.

  When the patch operation is performed between recording sheets or the like, the primary transfer bias is once lowered, and the LED 301 of the patch sensor 15 is raised to detect the patch density. Thereafter, in order to form an image again, it is necessary to lower the LED 301 of the patch sensor 15 and raise the primary transfer bias. At this time, if the primary transfer bias is not applied after the light quantity of the LED 301 of the patch sensor 15 has sufficiently decreased, similar charging unevenness occurs on the photosensitive member 1.

  In order to prevent this, as shown in FIG. 11, the primary transfer bias is raised after the light quantity of the LED 301 of the patch sensor 15 has fallen sufficiently. The light quantity of the LED 301 of the patch sensor 15 takes about several μsec after the OFF signal of the LED 301 is given, and the value is uniquely determined by the LED 301. A timer is operated by the CPU of the main body for the fall time Tled, and then a primary transfer bias control signal is given.

  The image forming apparatus of the present invention described above includes the patch sensor 15 that detects the density of the patch image formed in the non-image area of the photoreceptor, and the toner image is detected when the patch sensor 15 detects the density of the patch image. The high pressure of the transfer means for transferring the toner from the photoreceptor to the transfer medium is lowered. And it controls so that lighting of LED301 of the patch sensor 15 may be started after it becomes below a predetermined voltage.

  The image forming apparatus of the present invention changes the lighting timing of the LED 301 according to the voltage applied to the transfer unit.

  The image forming apparatus of the present invention further includes a voltage detection unit 405 that detects a voltage applied to the transfer unit. When the voltage detection unit 405 detects that the voltage is equal to or lower than a predetermined voltage, the LED 301 of the patch sensor 15 is turned on. Start.

  In the image forming apparatus of the present invention, the high voltage of the transfer unit is raised again after a predetermined time since the LED 301 of the patch sensor 15 is turned off.

1 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged view of a main part of the image forming apparatus in FIG. 1. It is a block diagram of the patch sensor in FIG. FIG. 2 is a timing chart showing patch toner images formed in an image area and a non-image area of the photoconductor in FIG. 1. It is a figure which shows the generation | occurrence | production principle of the memory on the photoreceptor which arises by exposure by LED of the patch sensor of FIG. FIG. 3 is a diagram illustrating a first example of a primary transfer bias circuit applied to a primary transfer roller in FIG. 2. It is a figure which shows the ON timing of primary transfer bias and LED of a patch sensor (1). It is a figure which shows the relationship between the OFF time of a primary transfer bias and a primary transfer bias. FIG. 6 is a diagram illustrating a second example of a primary transfer bias circuit applied to the primary transfer roller in FIG. 2. It is a figure which shows the ON timing of primary transfer bias and LED of a patch sensor (2). It is a figure which shows the OFF timing of primary transfer bias and LED of a patch sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 5 Intermediate transfer body 14 Primary transfer roller 15 Patch sensor 301 LED
305 patch image

Claims (6)

A photoreceptor that carries a toner image and is driven to rotate;
Image forming means for forming a toner image on the photoreceptor;
A transfer unit configured to transfer a toner image formed on the photoconductor by the image forming unit to a transfer body in contact with the photoconductor by applying a transfer voltage;
A transfer voltage applying means for lowering the transfer voltage after transferring the toner image on the photoconductor to the transfer body by applying the transfer voltage to the transfer means;
Detected image forming means for causing the image forming means to form a detected toner image subsequent to the toner image formed on the photosensitive member by the image forming means in the rotation direction of the photosensitive member;
An irradiating unit that irradiates light toward the photoconductor at a position downstream of the image forming unit and upstream of the transfer unit in the rotation direction of the photoconductor;
In the image forming apparatus for controlling the image forming unit based on a light reception result of the light irradiated from the irradiation unit and reflected by the detected toner image formed by the detected image forming unit,
The irradiating unit irradiates the photosensitive member with light after the transfer voltage has dropped to a predetermined voltage after the transfer voltage applying unit starts to lower the transfer voltage. Image forming apparatus. The irradiating means is directed toward the photoconductor after a lapse of time from when the transfer voltage applying means starts to lower the transfer voltage until the transfer voltage becomes smaller than the predetermined voltage. The image forming apparatus according to claim 1, wherein the image forming apparatus irradiates light. The image forming apparatus includes: a transfer voltage value applied to the transfer unit when the toner image is transferred to a transfer body; and the transfer voltage after the transfer voltage application unit starts to lower the transfer voltage. Having storage means for storing data indicating a correspondence relationship with the time required until the voltage becomes smaller than the predetermined voltage,
The irradiating means includes the transfer voltage value and the data stored in the storage means when the toner image is transferred to the transfer body after the transfer voltage applying means starts to lower the transfer voltage. 3. The image forming apparatus according to claim 2, wherein light is emitted toward the photoconductor after a time specified based on the time elapses. The image forming apparatus includes a voltage detection unit that detects a transfer voltage applied to the transfer unit by the transfer voltage application unit,
The irradiating means is directed toward the photoconductor after the voltage detected by the voltage detecting means becomes smaller than the predetermined voltage after the transfer voltage applying means starts to decrease the transfer voltage. The image forming apparatus according to claim 1, wherein the image forming apparatus irradiates light. A photoreceptor that carries a toner image and is driven to rotate;
Image forming means for forming a toner image on the photoreceptor;
Detected image forming means for causing the image forming means to form a detected toner image preceding the toner image formed on the photosensitive member by the image forming means in the rotation direction of the photosensitive member;
A transfer unit configured to transfer a toner image formed on the photoconductor by the image forming unit to a transfer body in contact with the photoconductor by applying a transfer voltage;
Transfer voltage applying means for applying the transfer voltage to the transfer means;
Irradiating light on the toner image to be detected formed on the photoconductor at a position downstream of the image forming unit and upstream of the transfer unit in the rotation direction of the photoconductor; An irradiation means for turning off the light to be irradiated thereafter;
In an image forming apparatus that controls the image forming unit based on a light reception result of light irradiated from the irradiation unit and reflected by the toner image to be detected,
The transfer voltage applying unit sets a transfer voltage to be applied to the transfer unit after the amount of light irradiated from the irradiation unit becomes smaller than a predetermined value after the irradiation unit turns off the light. An image forming apparatus characterized by being raised. The transfer voltage applying unit is configured to transfer the light to the transfer unit after a time required for the amount of light emitted from the irradiation unit to become smaller than the predetermined value after the irradiation unit turns off the light. 6. The image forming apparatus according to claim 5, wherein a transfer voltage to be applied is raised.

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