JP2009020252A - Electrophotographic image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic image forming apparatus suitably carrying out detection of an environment around each developer becoming a control factor when controlling the developing condition of each developing device in an image forming apparatus provided with a plurality of developing devices. <P>SOLUTION: The electrophotographic image forming apparatus provided with the plurality of developing devices for developing an electrostatic latent image formed on a photoreceptor drum with the developer is provided with: humidity sensor units 14a and 14b installed in at least two pieces of the developing devices 4Y and 4K among the plurality of developing devices 4Y, 4M, 4C and 4K; and a control means controlling image forming conditions according to the detection results. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention includes an electrophotographic image having a plurality of developing means for forming a toner image on an electrostatic image formed on an image carrier, the developing conditions of which are controlled by a humidity detecting means. The present invention relates to a forming apparatus.

  In an electrophotographic image forming apparatus such as a copying machine, a developing device is provided for developing an electrostatic image formed on a photosensitive drum as an image carrier. For example, in a tandem color image forming apparatus, the photosensitive drum and the developing device include a photosensitive drum and a developing device that form images of yellow (Y), magenta (M), cyan (C), and black (Bk) colors. is doing. The developing unit has toner of each color inside, and the toner is ejected from the developing sleeve to the paired photosensitive drum side during development, and the electrostatic image on the photosensitive drum is visualized as a toner image. .

  Here, the movement of the toner from the developing sleeve of the developing device to the photosensitive drum varies depending on the charging potential of the photosensitive drum and the magnitude of the developing bias voltage applied to the developing sleeve, but depends on the charge amount (tribo) of the toner itself. Also changes. That is, if the toner charge amount is large, an electric force is greatly applied, so that the toner is easily moved to the photosensitive drum side. Conversely, if the toner charge amount is small, the toner is photosensitive drum. It becomes difficult to move to the side.

  Various development techniques have been proposed in the past. For example, there are many methods such as a magnetic brush development method (see Patent Document 1), a powder cloud method (see Patent Document 2), a fur brush development method, and a liquid development method. Among these developing methods, a magnetic brush developing method using a two-component developer mainly composed of toner and carrier is widely used. While this method can provide a relatively stable and good image, it has problems due to the two-component developer, such as carrier deterioration and fluctuation in the mixing ratio of toner and carrier.

  In order to avoid such a problem, various development methods using a one-component developer composed only of toner have been proposed. According to this developing method, there is no need to control the mixing ratio of the toner with respect to the carrier, so that there is an advantage that the apparatus is simplified.

  However, even in a developing method using a one-component developer, the durability of the developer progresses depending on the image forming conditions, and the charged state of the toner cannot be denied due to a change in environment. When the developer deteriorates, the image density unexpectedly decreases, or a so-called “fogging” phenomenon occurs in which the developer adheres to the white background of the transfer material. That is, an appropriate density of the output image cannot be obtained.

  On the other hand, not only these one-component developer and two-component developer, but also the toner charge amount in the developing device that affects the image quality has been conventionally known to fluctuate depending on the surrounding humidity environment. It is proposed that when the ambient humidity is high, the charge amount of the toner tends to decrease, and by detecting the humidity in the vicinity of the developing device, the developing conditions are controlled to form a stable image. Yes. As a method for controlling the development conditions, for example, there is a method in which the charging potential to the photosensitive drum is changed to always set the appropriate development conditions. For example, there is a method of optimizing the development conditions according to the charge amount of the toner by changing the development bias voltage applied to the development sleeve. Furthermore, a method has been mainly proposed in which both the charging potential to the photosensitive drum and the developing bias voltage are controlled appropriately.

  For example, in Patent Document 3, temperature / humidity information of the surrounding environment is detected by a temperature / humidity detector installed in the apparatus, using the toner density level at normal temperature and humidity and the developing bias voltage as reference values. Then, proposals have been made to increase or decrease the toner density and the developing bias from the reference value according to the absolute humidity information that is the detection result.

U.S. Pat. No. 2,874,063 US Patent No. 221776 JP-A-9-146360

  However, in a conventional image forming apparatus, a sensor for detecting humidity is attached in the electrical board of the apparatus or in the vicinity of a specific developing unit in the apparatus. In this case, the humidity sensor detects the surroundings of the toner in the developing unit. Humidity may not be detected accurately.

  A method of attaching the humidity sensor inside the developing device has also been proposed. However, in this case, a proposal is made in consideration of the temperature around the toner in each color developing device depending on the temperature distribution state inside the device and the arrangement state of the developing device assuming a tandem color image forming apparatus having a plurality of developing devices. It wasn't. Therefore, it has been difficult to properly control the development conditions by a signal from the humidity sensor.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus having a plurality of developing units around each developer serving as a control factor when controlling the developing conditions of each developing unit. The present invention provides an electrophotographic image forming apparatus that appropriately detects the environment.

  A typical means in the present invention for solving the above-described problems is that a plurality of image forming means having developing means for developing an electrostatic image formed on an image carrier with a developer contained in a developing container. An electrophotographic image forming apparatus comprising: a detecting unit arranged in at least two developing units among the plurality of developing units, and detecting a humidity state in the developing container of the arranged developing unit; And a control unit that controls image forming conditions of the plurality of image forming units according to a detection result by the detecting unit.

  In the present invention, the humidity state of the developer contained in the developing means is detected by the detecting means, and the image forming conditions of the plurality of image forming means are controlled based on the result. For this reason, it is possible to obtain the humidity state in the plurality of developing containers by at least two detection means, thereby enabling proper image formation based on the detected humidity information, and a high-quality output image. Can be obtained.

[Entire configuration of electrophotographic image forming apparatus]
First, the overall configuration of an electrophotographic image forming apparatus (hereinafter referred to as “image forming apparatus”) of the present embodiment will be described with reference to FIGS. 1 and 2. 1 is an overall schematic explanatory diagram of the image forming apparatus according to the present embodiment, and FIG. 2 is a configuration explanatory diagram of an image forming unit.

  The image forming apparatus of this embodiment is a color laser printer having a maximum sheet passing size of A3 size using a transfer type electrophotographic process having a plurality of image forming means, a contact charging method, and a reversal developing method. Then, a full-color image is formed on a transfer material, for example, a sheet, an OHP sheet, a cloth, and the like according to image information from an external host device communicably connected to the image forming apparatus main body (apparatus main body) and output. Can do.

  The image forming apparatus includes image forming units PY, PM, PC, which respectively form yellow (Y), magenta (M), cyan (C), and black (Bk) images as image forming units serving as a plurality of image forming units. Has PBk. Then, the toner image is once and continuously transferred to the intermediate transfer member 91 by the process cartridge 8 (8Y, 8M, 8C, 8Bk) provided in each image forming unit. Thereafter, the toner image is transferred onto the transfer material S at a time to obtain a full-color print image, which is a quadruple drum type (tandem type) image forming apparatus. Four process cartridges 8Y, 8M, 8C, and 8Bk are arranged in order of yellow, magenta, cyan, and black in series in the moving direction of the intermediate transfer belt 91.

  In the present embodiment, the image forming portions P (PY, PM, PC, PBk) of the respective colors have the same configuration except that the color of the developer used is different. Therefore, in the following, when there is no particular need to distinguish, subscripts Y, M, C, and Bk that indicate elements of each image forming unit will be omitted, and a general description will be given.

  First, the overall operation when a four-color full-color image is formed will be described. A color-separated image signal is generated in accordance with a signal from an external host device communicably connected to the image forming apparatus. In response to this signal, each color toner image is formed in each process cartridge 8 of each image forming section P. In each process cartridge 8, a rotating drum type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 as an image carrier is charged by a charging roller 2 as a charging unit, and its uniformly charged surface is exposed by an exposure unit 3. An electrostatic image is formed on the photosensitive drum 1 by scanning exposure. A toner image is formed by supplying toner as a developer to the electrostatic image by the developing means 4.

  The toner images of the respective colors formed on the respective photosensitive drums 1 are sequentially superimposed and transferred onto an intermediate transfer belt 91 as an intermediate transfer member that is a second image carrier that moves by applying a bias to the primary transfer roller 92. The The full-color toner image formed on the intermediate transfer belt 91 is transferred onto the transfer material S that has been conveyed to the secondary transfer portion where the intermediate transfer belt 91 and the secondary transfer roller 10 as the secondary transfer means face each other. Are collectively transferred. Next, the transfer material S is conveyed to a fixing device 13 as fixing means, where the toner image is fixed and then discharged outside the apparatus.

  Here, each element of the image forming apparatus will be described in more detail sequentially with reference to FIG.

  The image forming apparatus includes a rotating drum type electrophotographic photosensitive member (photosensitive drum) 1 as an image carrier. In the present embodiment, the photosensitive drum 1 is an organic photoconductor (OPC) drum, and is driven to rotate in the counterclockwise direction indicated by an arrow in the drawing at a predetermined peripheral speed around the central support shaft.

  In this embodiment, the image forming apparatus includes a charging roller 2 that is a contact charger as a charging unit. By applying a voltage under a predetermined condition to the charging roller 2, the photosensitive drum 1 is uniformly charged to a negative polarity. The charging roller 2 holds both ends of the cored bar 2a rotatably by bearing members, and is urged toward the photosensitive drum 1 by a pressing spring so as to be pressed against the surface of the photosensitive drum 1 with a predetermined pressing force. I am letting. The charging roller 2 rotates following the rotation of the photosensitive drum 1. Then, a predetermined vibration voltage (charging bias voltage Vdc + Vac) obtained by superimposing an alternating voltage of a predetermined frequency on a direct current voltage is applied to the charging roller 2 via the metal core 2a from the power source 20 as a voltage applying means, and rotates. The peripheral surface of the drum 1 is charged to a predetermined potential. A contact portion between the charging roller 2 and the photosensitive drum 1 is a charging portion a.

  A charging roller cleaning member 2 f is provided for the charging roller 2. In the present embodiment, the charging roller cleaning member 2f is a flexible cleaning film, and the cleaning member 2f is disposed in parallel to the longitudinal direction of the charging roller 2, and the surface layer of the charging roller 2 is the cleaning member 2f. It is rubbed with. As a result, contaminants (fine toner, external additives, etc.) on the surface layer of the charging roller 2 are removed.

  The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2. After that, image exposure means (color separation / imaging exposure optical system for color original image, scanning exposure system by laser scanning that outputs a laser beam modulated in accordance with time-series electric digital pixel signal of image information, etc.) The image exposure L is received. As a result, electrostatic images of color components corresponding to the image forming portions PY, PM, PC, and PBk of the target color image are formed. In the present embodiment, a laser beam scanner using a semiconductor laser is used as the exposure unit 3. The laser beam scanner outputs a laser beam modulated in accordance with an image signal sent from a host apparatus such as an image reading apparatus (not shown) to the image forming apparatus side, and the rotating photosensitive drum 1 is uniform. The surface to be charged is subjected to laser scanning exposure (image exposure). By this laser scanning exposure, the potential irradiated with the laser light L on the surface of the photosensitive drum 1 is lowered, so that an electrostatic image corresponding to the scanned and exposed image information is formed on the surface of the rotating photosensitive drum 1. The The irradiation position of the image exposure L on the photosensitive drum 1 is the exposure part b.

  The electrostatic image formed on the photosensitive drum 1 is developed with toner by a developing device 4 as developing means. In the present embodiment, the developing device 4 is a two-component contact developing device (two-component magnetic brush developing device). The developing device 4 includes a developing container (developing device main body) 40, a developing sleeve 41 as a developer carrying member having a magnet roller fixedly disposed therein, and a developer regulating blade 42 as a developer regulating member. A two-component developer (developer) 46, which is a mixture of resin toner particles (toner) and magnetic carrier particles (carrier), is mainly contained in the developer container 40 and disposed on the bottom side in the developer container 40. Stirring screws 43 and 44 as developer stirring members are provided.

  The developing sleeve 41 is rotatably disposed in the developing container 40 with a part of its outer peripheral surface exposed to the outside, and the developer regulating blade 42 is opposed to the developing sleeve 41 with a slight gap. Yes. As the developing sleeve 41 rotates in the direction of the arrow in FIG. 2, a thin developer layer is formed on the developing sleeve 41. The developing sleeve 41 is rotationally driven with respect to the photosensitive drum 1 at a speed of a predetermined peripheral speed ratio in a direction opposite to the traveling direction of the photosensitive drum 1. The developer thin layer on the developing sleeve 41 comes into contact with the surface of the photosensitive drum 1 in the developing section c and rubs the photosensitive drum 1 appropriately. A predetermined developing bias voltage is applied to the developing sleeve 41 from a power source 24 as voltage applying means. In the present embodiment, the developing bias voltage applied to the developing sleeve 41 is an oscillating voltage obtained by superimposing a direct voltage (VDC) and an alternating voltage (VAC).

  As described above, the toner in the developer 46 coated as a thin layer on the surface of the developing sleeve 41 where the developer rotates and conveyed to the developing section c is formed on the photosensitive drum 1 by the electric field due to the developing bias voltage. Selectively adhere to the electrostatic image. As a result, the electrostatic image is developed as a toner image. In the present embodiment, toner adheres to the exposed bright portion on the photosensitive drum 1 and the electrostatic image is reversely developed. The developer thin layer on the developing sleeve 41 that has passed through the developing section c is returned to the developer reservoir in the developing container 40 as the developing sleeve 41 continues to rotate.

  Further, the developing device 4 is provided with stirring screws 43 and 44 as developer stirring members. The agitation screws 43 and 44 rotate in synchronization with the rotation of the developing sleeve 41, and have a function of agitating and mixing the supplied toner with a carrier to give the toner a predetermined charged charge. Further, the agitating screws 43 and 44 respectively convey the developer 46 in the opposite direction in the longitudinal direction, and supply the developer 46 to the developing sleeve 41. At the same time, the developer 46 having a reduced toner concentration (ratio of toner in the developer) by the developing process is transported to the toner replenishing section, and the developer 46 is circulated in the developing container 40.

  On the upstream side wall surface of the screw 44 of the developing device 4, a sensor 45 that detects a change in the magnetic permeability of the developer 46 and detects the toner concentration in the developer 46 is provided. A toner supply opening 47 is provided slightly downstream of the density sensor 45. After performing the developing operation, the developer 46 is carried to the toner density sensor 45, where the toner density is detected. Depending on the detection result, the toner concentration in the developer 46 is kept constant. For this purpose, toner is replenished from the toner replenishment unit 5 through the toner replenishment opening 47 of the developer 4 by the rotation of the screw 51 provided in the developer replenishment container (toner replenishment unit) 5 connected to the developer 4 as appropriate. The replenished toner is conveyed by the agitating screw 44, mixed with the carrier, given an appropriate charge, and then carried to the vicinity of the developing sleeve 41, where a thin layer is formed on the developing sleeve 41 for development. .

  An intermediate transfer unit 9 as a transfer unit is provided so as to face the photosensitive drums 1 of the image forming portions PY, PM, PC, and PBk. In the intermediate transfer unit 9, an endless intermediate transfer belt 91, which is an intermediate transfer member, is wound around a driving roller 94, a tension roller 95, and a secondary transfer counter roller 96 with a predetermined tension. Move in the direction of the arrow.

  The toner image formed on the photosensitive drum 1 enters a primary transfer nip portion (transfer portion) d that is a portion where the photosensitive drum 1 and the intermediate transfer belt 91 are opposed to each other. In the transfer portion d, the primary transfer roller 92 is lifted by springs provided at both ends thereof, and is brought into contact with the back side of the intermediate transfer belt 91 at a predetermined pressure. The primary transfer roller 92 is connected to a primary transfer bias power supply 93 as a voltage application unit so that the primary transfer bias voltage can be independently applied to each image forming unit PY, PM, PC, PBk. First, a yellow toner image formed on the photosensitive drum 1 by the above-described operation is transferred to the intermediate transfer belt 91 by the first color (yellow) image forming unit PY. Subsequently, magenta, cyan, and black color toner images are sequentially transferred in multiple by the image forming units PM, PC, and PBk from the photosensitive drums 1 corresponding to the respective colors that have undergone the same process.

  The four-color full-color image formed on the intermediate transfer belt 91 is then supplied from a transfer material feeding means (not shown) by a secondary transfer roller 10 as a secondary transfer means, and as a conveying means at a predetermined timing. Are transferred onto the transfer material S sent from the feeding roller 12.

  The transfer material S to which the toner image has been transferred is then conveyed to a fixing device 13 as a fixing unit, where the toner image is melted and fixed on the transfer material S by heat and pressure. Thereafter, the transfer material S is discharged out of the apparatus to obtain a color print image.

  A constant current power source may be used as a high voltage power source for primary transfer and secondary transfer. Even with such a configuration, the voltage applied from the power source to the primary transfer roller and the secondary transfer roller can be reduced, and control can be easily performed.

  In the above description, the roller-shaped primary transfer roller 92 and the secondary transfer roller 10 have been used.

  Further, the secondary transfer residual toner remaining on the intermediate transfer belt 91 is cleaned by a cleaning blade 11a as a cleaning unit provided in the intermediate transfer belt cleaner 11 to prepare for the next image forming process.

  As shown in FIG. 2, the developer charge amount control means 6 and the residual developer uniformizing means 7 are applied to the photosensitive drum 1 between the transfer portion d and the charging portion a along the rotation direction of the photosensitive drum 1. It is touched.

  Residual developer uniformizing means 7 and developer charge amount control means are located downstream of the transfer portion d in the rotational direction of the photosensitive drum 1 and upstream of the charging portion a and sequentially from the upstream of the photosensitive drum 1 in the rotational direction. 6 is arranged. A contact portion e between the residual developer uniformizing means 7 and the photosensitive drum 1 and a contact portion f between the developer charge amount control means 6 and the photosensitive drum 1 are formed.

  There is transfer residual toner on the surface of the photosensitive drum 1 after the transfer process in the transfer portion d, and the transfer residual toner affects the negative polarity toner of the image portion, the positive polarity toner of the non-image portion, and the positive polarity voltage of the transfer. Thus, the toner whose polarity is reversed to the positive polarity is included.

  In order to make the polarity of such a transfer residual toner have a negative polarity, developer charge amount control means 6 is provided. That is, in this embodiment, a negative DC voltage having the same polarity as the normal polarity of the toner is applied to the developer charge amount control unit 6 from the power source 21 as the voltage application unit.

  Further, in order to disperse a partial transfer residual toner and a large amount of transfer residual toner on the photosensitive drum 1, a residual developer uniforming means 7 is provided. A positive DC voltage having a polarity opposite to the normal polarity of the toner is applied to the residual developer uniformizing means 7 from a power source 22 as a voltage applying means. The residual developer uniformizing means 7 may be applied with an AC voltage or an AC voltage superimposed with a DC voltage.

  The toner on the photosensitive drum 1 is given a negative charge by the developer charge amount control means 6, and then, when passing through the charging portion a, the developing device 4 by the charge eliminating effect due to the AC voltage applied to the charging roller 2. The amount of charge can be reduced to an appropriate amount that can be recovered with The toner that has passed through the charging portion a is removed from the photosensitive drum 1 in the developing device 4 by simultaneous development cleaning.

  Note that voltage application means such as the power supplies 20, 21, 22, 24 and the primary transfer bias power supply 93 provided in the image forming apparatus are controlled by a control circuit unit 130 serving as a control means for controlling the overall operation of the image forming apparatus main body. Be controlled.

  In this embodiment, the photosensitive drum 1, the charging roller 2, the charging roller cleaning member 2 f, the developing device 4, the residual toner uniformizing unit 7, the toner charge amount control unit 6, and the like are integrated into a cartridge so that the process cartridge 8 is replaced. Constitute.

  The process cartridge 8 is detachably mounted on the image forming apparatus main body. Further, in a state where the process cartridge 8 is mounted on the image forming apparatus main body, a driving means (not shown) provided on the image forming apparatus main body and a driving transmission means on the process cartridge 8 side are connected, and the photosensitive drum 1 and the developing unit are connected. The device 4 and the charging roller 2 are ready to be driven. Further, in a state where the process cartridge 8 is mounted on the image forming apparatus main body, the various voltage applying means are electrically connected to the object via contacts provided on the process cartridge 8 side and the image forming apparatus main body side, respectively. . That is, various voltage applications such as power sources 20, 21 and 22 for applying a bias to the charging roller 2, the toner charge amount control unit 6 and the residual toner uniformizing unit 7, and a power source (not shown) for applying a bias to the developing sleeve 41. The means are electrically connected.

  On the other hand, the toner replenishing unit 5 is detachably attached to the developing device 4 and the image forming apparatus main body via an attaching unit.

[Humidity sensor unit]
The image forming apparatus according to the present embodiment is configured to control a developing bias applied in accordance with the humidity in the developing device. Next, a configuration for detecting humidity in the developing device for that purpose will be described.

  In an electrophotographic image forming apparatus, the toner charge amount in the developing device changes due to a change in humidity, and the amount of toner movement from the developing device to the photosensitive drum side also changes. Accordingly, it is necessary to detect the humidity in the vicinity of the developing device with the humidity detection sensor and control the development conditions with the detection signal so that an appropriate image can be formed on the photosensitive drum. In this case, if the humidity detected by the humidity detection sensor is different from that in the developing device, it is difficult to appropriately control the development conditions.

  On the other hand, in a tandem color image forming apparatus, the change in the ambient humidity of the toner inside each color developer differs depending on the arrangement state in the apparatus, so that the humidity around the toner is properly detected for each developer. There is a need to do. In this case, if the development conditions for each color are determined based on the humidity detection result of the only developer, there is a high possibility that it is different from the humidity state inside the developer for other colors, and appropriate control of the development conditions for all colors is not possible. .

  Therefore, in the present embodiment, humidity detection means is provided inside the developing device of at least two colors according to the apparatus temperature distribution state, and the humidity state inside the developing device that does not have humidity detection means based on two humidity detection signals is determined. By detecting the estimation, the development conditions are controlled to suit each color.

  A configuration diagram of the humidity sensor unit 14 and the developing device 4 is shown by a dotted line frame A in FIG. A developing device wall surface in the vicinity of the developer 46 in the developing device 4 is partially opened, a filter 61 is provided in the opening portion, and a humidity sensor unit 14 as detection means is provided outside the filter 61 and the wall surface. The humidity sensor unit 14 is fixedly disposed to the developing device 4 by a claw-shaped mold member. With this configuration, the humidity information in the developing container can be detected by the humidity sensor unit 14.

  The filter transmission hole is configured to be 1 μm or less so that the toner and the developer do not flow out from the filter 61 into the humidity sensor unit 14. For this reason, a pulverized toner having a particle size smaller than that of the developer is 7 μm or more in this embodiment. For this reason, the filter 61 cannot be transmitted. Further, the perforation hole of the filter 61 is formed so that the air current around the developer circulates and the same environmental condition as that of the inside of the developing device is quickly obtained.

  Inside the humidity sensor unit 14, a humidity element 60 and a temperature element 63 of a polymer foil capacitance detection type are arranged. Electrical conversion is performed based on the relative humidity of the surrounding environment from the humidity element 60 and the temperature information from the temperature element 63, and converted into an absolute humidity detection signal in the environment where each sensor unit 14 is arranged. A humidity conversion board 62 on which a conversion circuit (not shown) for mounting is mounted is included.

  The humidity element 60 is a polymer foil capacitive humidity sensor, and the capacitance varies depending on the wet and dry characteristics of the polymer foil inside the element in accordance with the relative humidity of the surrounding environment. The temperature element 63 is an NTC thermistor that is a thermistor whose resistance value decreases with increasing temperature. In this embodiment, the surface layer is coated to protect the polymer foil used for humidity elements that require airflow circulation with the external environment from the entry of fine particles such as toner and developer. It has a strong resistance structure.

  These humidity sensor units 14 are disposed only in the yellow process cartridge 8Y closest to the fixing device 13 and the black process cartridge 8Bk disposed farthest away. Then, the humidity detection signal of the humidity sensor unit 14a arranged in the yellow developing unit and the humidity sensor unit 14b arranged in the black developing unit is notified to the control circuit unit 130. The detection result is used as a control factor for a control amount such as a developing bias voltage and a charging bias voltage for each of yellow, magenta, cyan, and black supplied from a power source 22 as a voltage applying unit.

  Of the four process cartridges, the yellow process cartridge 8Y is in the highest temperature region, and the black process cartridge 8K is in the lowest temperature region. The humidity element 60, which is a detection unit of the humidity sensor units 14a and 14b, is disposed in the vicinity of the developer accommodated in each developer and is not covered with the developer. As a result, the humidity state of the developer accommodated in the developer unit in the highest temperature region and the humidity state of the developer accommodated in the developer unit in the lowest temperature region among the four developer units. It is something to detect.

[Humidity detection and development bias control]
Next, a configuration for controlling image forming conditions based on detection results from the humidity sensor units 14a and 14b will be described. Examples of the image forming conditions include development control for controlling the development bias DC, charging control for controlling the charging AC and charging DC, and the like. In the present embodiment, the control target factor is described with respect to the development bias DC.

  FIG. 3 is a simplified operation flow diagram relating to humidity detection and feedback control to the developing bias based on the detection result from when the image forming apparatus is in a standby state until image formation is completed. Each step will be described in detail, and will be described using other drawings as appropriate.

  In S701 shown in FIG. 3, the image forming apparatus is in a standby state for a user operation in a standby state or a print request from an external host connected via a network. Further, even in the low power mode and the sleep mode, even if the standby state and the operation state of this flow are replaced, the control flow substantially the same as that of the present embodiment is performed.

  When a user operation or a print request signal 411 (see FIG. 4) from the external host is input in S702, the image forming apparatus is returned from the standby state, and activation control of each image forming unit is performed.

  In this control flow, the start-up control related to the humidity sensor unit in the developing device and the accompanying bias control will be described.

(Humidity detection)
After returning from standby, humidity detection signals are input from humidity sensor units 14a and 14b arranged at the bottom of the yellow (Y) and black (Bk) developing units. In step S703, the input humidity detection signal is converted into a table to obtain humidity information. From the humidity information of yellow (Y) and black (Bk) acquired in step S704, the estimation unit calculates magenta (M) and cyan (C ) Estimate and control the internal humidity state of the developer.

  The estimation control of this embodiment will be described with reference to FIGS. 4 is a control block diagram around the control circuit unit 130, FIG. 5 is a frequency-relative humidity conversion table, and FIG. 6 is a transition diagram of the internal humidity of each developing device during the image forming operation.

  In the present embodiment, the table conversion process of the input detection signal in S703 and the estimation control of the developing unit internal humidity state in S704 are performed using the control means, conversion table, etc. shown in FIGS. .

  The detection results of the humidity element 60 and the temperature element 63 in the humidity sensor units 14a and 14b arranged together with the filters at the top of the developing unit of yellow (Y) and black (Bk) are displayed on the conversion board 62 (see FIG. 2). Converted into an electrical signal. As shown in FIG. 4, the converted humidity detection signals 401 and 402 are converted into an electrical frequency output from the humidity detection value by the conversion board 62 and output, and input to the CPU 404 in the control circuit unit 130. The

  The CPU 404 is an integrated circuit that performs processing by integrating control in image formation. The humidity detection signal input to the timer input unit of the CPU 404 measures a frequency by detecting a periodic signal change of the humidity detection signal by an internal timer circuit. The ROM 403 has a conversion table of detected humidity corresponding to the input frequency to the CPU 404 in accordance with the frequency measured internally, whereby the detected humidity of the humidity sensor units 14a and 14b is recognized. The conversion table is stored in advance in the ROM 403 based on the humidity-frequency detection specification of the humidity detection sensor unit, and the conversion table has frequencies of yellow (Y) and black (Bk) as shown in FIG. (S703).

  Thus, the remaining magenta and cyan developer internal humidity Hm and Hc are calculated by calculation using the yellow and black developer internal humidity Hy and Hbk subjected to table conversion. In the present embodiment, the calculation processing method based on the detected humidity Hy and Hbk of yellow and black reduces the humidity in a manner that the temperature / humidity change is inversely proportional to the relative distance from the fixing device 13 that is a heat source. Thus, the estimation is detected (S704).

  Hy−Hbk = A,

  Hm = Hy− (A ÷ 3), Hc = Hbk + (A ÷ 3)

  That is, of the four developing units, the humidity state in the other two developing units in which the humidity sensor unit 14 is not arranged is estimated from the humidity in the two developing units in which the humidity sensor unit 14 is arranged as follows. To do.

  First, among the four parallel developing devices, the closest to the fixing device 13, the yellow developing device humidity Hy having the highest developing device humidity among the four developing devices, and the farthest from the fixing device 13, The black developer inside humidity Hbk of the lowest developer inside humidity is detected. Then, a difference A between the two humidity Hy and Hbk is obtained, and it is estimated that the humidity A is uniformly reduced between the developing devices as the difference A moves away from the fixing device 13, and the magenta and cyan developing device humidity Hm existing in the middle. Calculate Hc.

  As a result, the humidity environment information Hy, Hm, Hc, and Hbk inside all the developing devices of yellow, magenta, cyan, and black are recognized.

  As an example of the humidity detection result inside the developing device of each color during the image forming operation, in the graph shown in FIG. 6, the print start T1 corresponds to S702 in FIG. Hereinafter, as a control flow result corresponding to S703, the humidity detection result (Hy) of the humidity sensor unit 14a arranged in the yellow developing device in time series, the humidity detection result (Hbk) of the humidity sensor unit 14b arranged in the black developing device. ) Is plotted. At the same time, the results of calculating and estimating the magenta (M) and cyan (C) internal humidity in S704 are plotted as the magenta humidity calculation estimation result (Hm) and the cyan humidity calculation estimation result (Hc). . In other words, as described above, the humidity environment inside the development of each color results in a low humidity environment in inverse proportion to the relative distance from the fixing device 13.

  In the image forming apparatus of this embodiment, the image forming conditions are controlled based on the humidity information detected and estimated as described above. That is, based on the humidity information of each color detected in S705, each development bias voltage is set to the HV (high voltage) control unit 405 according to the humidity information. The setting of the development bias voltage (VDC) based on the humidity information is determined based on the relationship of “absolute humidity−toner charge amount” shown in the graph a of FIG.

(Development bias control in low humidity environment)
As shown in graph a of FIG. 7, the toner charge amount tends to increase in a low-humidity environment, and therefore, when a development bias voltage is applied, there is an electrical influence on the photosensitive drum surface potential. growing. Therefore, when the same developing bias voltage as that in the normal humidity environment is applied, the amount of toner supplied to the electrostatic image portion on the photosensitive drum becomes smaller than that in the normal humidity environment. That is, the toner density is lowered with respect to the developed image at normal humidity. This is because the amount of charge per unit amount of toner supplied to the electrostatic image location on the drum is large, so that the amount of toner supplied to the electrostatic image location is small compared to the non-electrostatic image location compared to normal humidity. This is because the potential becomes the same.

  Therefore, as shown in the graph b in FIG. 7, it is necessary to control with a developing bias voltage corresponding to the toner charge amount. Specifically, the development bias voltage VDC = −500 V in the normal humidity environment (50% RH), whereas the development bias voltage VDC = −600 V in the low humidity environment (5% RH). .

  As a result, the amount of toner developed on the photosensitive drum is larger than that at normal humidity, but the toner charge amount is large, so that the problem that the amount of toner supplied to the photosensitive drum is excessive as described above is offset. Thus, it is possible to obtain a toner supply amount (toner concentration) equivalent to that at normal humidity.

(Development bias control in high humidity environment)
On the other hand, in a high humidity environment (80% RH), the toner charge amount tends to be lower than that in the normal humidity environment. Therefore, when the same development bias voltage as that in the normal humidity environment is applied, a predetermined toner concentration is obtained. In contrast, the toner supply amount is excessive. That is, the toner density becomes higher than the predetermined developed image density at normal humidity. Therefore, contrary to the case where the toner charge amount is high, VDC = −350V. As a result, as in the case of low humidity, the amount of toner developed on the drum due to the toner charge amount is substantially the same as in normal humidity. That is, the problem that the toner supply amount is excessive is offset and an appropriate toner density image can be obtained.

  As described above, the toner charge amount is estimated based on the internal humidity of the developing device for each color, and the development bias voltage set so as to be equivalent to the normal humidity environment based on the estimated toner charge amount is the detection result for each color. As a set value, the CPU 404 temporarily stores it in the RAM 410.

  In S706, when the image forming operation by the external host and the user is not executed, the flow of S703 to S705 is repeated every predetermined time, so that an appropriate development bias voltage corresponding to the change in the internal environment of each color developer is obtained. The set value is stored and updated in the RAM 410.

  On the other hand, when the image forming operation is executed, an image forming start signal is input to the control circuit unit 130. After inputting the image formation start signal, each control factor is executed at a predetermined control timing, and image formation is performed. An electrostatic image is formed by charge control and exposure control on the photosensitive drum, which is the image formation control described above. Thereafter, at the development control timing of each color of the image, the CPU 404 refers to the setting information of the development bias voltage of each color stored in the RAM 410 in S705 to the HV control unit 405 (S707). Each developing bias voltage is supplied from the HV control unit 405 to each developing device according to a predetermined control timing by the CPU (Y_developing HV406, M_developing HV407, C_developing HV408, Bk_developing HV409). (S708 to S710).

  As described above, the humidity state of the developer accommodated in the yellow and black developing devices is detected by the detection unit immediately before the image forming operation. Then, based on the result, the humidity state of the developer in the magenta and cyan developing devices in which the detecting means is not arranged is estimated. Thereby, the charge amount of the developer in each color developing device can be obtained with high accuracy by at least two detection means, and a development bias voltage output corresponding to the result can be obtained for each color. For this reason, it is always stable without being influenced by environmental fluctuations such as a low-humidity environment or a high-humidity environment, and development control with an appropriate output value can be performed, so that a high-quality output image can be obtained.

  In the present embodiment, an example is shown in which the detection unit detects the humidity state in the developing device and controls the image forming conditions. However, in addition to humidity detection, the temperature element 63 detects the developer temperature state in the yellow and black developing units, and the developer temperature state in the magenta and cyan developing units in which the temperature element 63 is not disposed. Is estimated. The image forming conditions may be controlled using both humidity and temperature. In this way, higher-definition image formation control can be performed.

  Further, in this embodiment, two locations (yellow and black) are used as humidity detection targets inside the developing device, but it is also possible to install humidity sensors at all four locations of each color and perform the same control. . In that case, control can be performed with higher accuracy than in the present embodiment.

  In this embodiment, an image forming apparatus including four developing units of yellow, magenta, cyan, and black is illustrated. However, in order to enable development with color toners such as light cyan and light magenta, the present invention can be similarly applied to an image forming apparatus including six developing devices. That is, if the image forming apparatus includes a plurality of developing units, the number of developing units need not be limited to four as in the above-described embodiment.

  Although feedback control to only the development bias voltage has been described, feedback control is performed for various bias values such as charging control (charging AC and charging DC) and developing bias voltage (developing AC) or image formation control factors. However, the same effect can be obtained.

  In this embodiment, a tandem color image forming apparatus using a two-component developer has been described as an example. However, even if the present invention is applied to a tandem type and one-drum type color image forming apparatus using a one-component developer, a high-quality image can be obtained by stable image formation.

1 is a schematic cross-sectional view of an example of an image forming apparatus to which the present invention can be applied. FIG. 2 is a schematic cross-sectional view showing a process cartridge mounted on the image forming apparatus in FIG. 1. It is a series of control flowcharts in this embodiment. FIG. 3 is a control block diagram showing the relationship between a humidity sensor, a control circuit, and development bias voltage control. It is an example of the humidity sensor output conversion table by CPU. FIG. 6 is a diagram illustrating a transition during image formation of a relative humidity output by a humidity sensor disposed inside a developing device of Y, M, C, and Bk. FIG. 5 is a diagram illustrating a relational expression of relative humidity, toner charge amount, and developing bias voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 2 ... Charging roller 4 ... Developing device 8 ... Process cartridge 9 ... Intermediate transfer unit
13… Fixer
14 Humidity sensor unit
40… Developing container
41… Development sleeve
42… Developer regulating blade
43, 44… stirring screw
45 ... Toner density sensor
60… Humidity element
61… Filter
62… Conversion board
63… Temperature element
93… Primary transfer bias power supply
130… Control circuit section

Claims (3)

In an electrophotographic image forming apparatus comprising a plurality of image forming means having developing means for developing an electrostatic image formed on an image carrier with a developer contained in a developing container.
A detecting unit disposed in at least two developing units among the plurality of developing units, and detecting a humidity state in the developing container of the arranged developing unit;
Control means for controlling image forming conditions of the plurality of image forming means according to a detection result by the detecting means;
An electrophotographic image forming apparatus comprising:   2. The electrophotographic image forming apparatus according to claim 1, wherein the detecting unit is disposed in a developing unit disposed in a highest temperature region and a lowest temperature region among the plurality of developing units.   3. The detection unit according to claim 1, wherein the detection unit is disposed in a region where the detection unit is in the vicinity of the developer accommodated in the developer container and is not covered with the developer. The electrophotographic image forming apparatus described.

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