JP2009009095A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can always produce an image with stable density by executing proper control of image formation conditions by correcting variation of VL based on an image formation time, an image formation stop time, a temperature of an atmosphere environment and an absolute humidity of the atmosphere environment. <P>SOLUTION: The image forming apparatus is equipped with a timer 24 measuring the image formation time t1 lapsed from start of rotation of a photosensitive drum 1 and the image formation stop time t2 lapsed from stop of the rotation of the photosensitive drum 1, and a temperature and humidity sensor 18 detecting the temperature Tc and the humidity of the atmosphere environment around the photosensitive drum 1. When the absolute humidity is low, a charging voltage is controlled based on a measured result of the timer 24 and detected results of the temperature and humidity sensor 18. When the absolute humidity is high, the charging voltage is controlled based on the measured result of the timer 24 and the temperature detected result of the temperature and humidity sensor 18 without using humidity information. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  2. Description of the Related Art Conventionally, a photoreceptor provided in an image forming apparatus using an electrophotographic method generally includes a photosensitive layer composed of a charge generation layer and a charge transport layer.

  When a print start signal is input, the photosensitive member is driven in a certain direction and starts rotating. By applying a bias to the charging device with respect to the surface of the photoconductor, the surface of the photoconductor is charged to a constant potential (hereinafter referred to as a charging step).

  The surface potential of the photosensitive member at this time is set as a dark portion potential VD. The surface of the photoconductor whose surface is charged to VD is irradiated with laser light or LED light that is on / off controlled based on a signal from the controller (hereinafter referred to as an exposure process).

  The potential of the exposed portion on the surface of the photoreceptor varies depending on the exposure process, and an electrostatic latent image having a potential different from that of the surrounding is formed on the surface of the photoreceptor. The description will be made assuming that the potential of the portion where the exposure is performed and the electrostatic latent image is formed is the bright portion potential VL.

  A developing voltage is applied to the developing device disposed opposite to the photosensitive member on the surface of which the electrostatic latent image is formed, and charged toner is supplied to the electrostatic latent image from the developing device. Thereby, the electrostatic latent image is developed as a toner image on the surface of the photoreceptor (hereinafter referred to as a developing step). Note that the developing voltage applied to the developing device in the developing process will be described as Vdev.

  The toner image developed on the surface of the photoreceptor is brought into contact with the transfer material as the photoreceptor rotates and is transferred to the transfer material (hereinafter referred to as a transfer process). In the transfer process, the transfer material is passed between a transfer member such as a transfer roller disposed adjacent to the photoconductor and rotating in the forward direction at substantially the same speed as the photoconductor, thereby transferring the transfer material to the transfer material. The toner image is transferred. Specifically, a bias having a polarity opposite to that of the toner is applied to the transfer member, and in this state, the transfer material is passed between the photoconductor and the transfer member, whereby a toner image is formed on the transfer material from the photoconductor. It is the structure which transcribe | transfers.

  By the way, even if the bias applied to the charging device in the charging step is constant and the exposure conditions are constant in the exposure step, VL may fluctuate by repeating image formation. As a cause of this, it is conceivable that residual charges are generated in the photoreceptor due to exposure, and VL fluctuates during image formation. In addition, the VL may fluctuate due to the temperature rise of the photosensitive member during rotation due to sliding friction with the charging member and the cleaning member that the photosensitive member contacts, heat radiation from the exposure member, the fixing device, or the like. Possible cause.

  Thus, when VL fluctuates due to the exposure process of the photoconductor and the temperature rise of the photoconductor, the development contrast, which is the difference between Vdev and VL, changes. A change in development contrast leads to a change in the amount of toner loaded on the photoreceptor, resulting in a change in image density on the transfer material. The following description will be made assuming that the development contrast is Vcont.

On the other hand, conventionally, in order to stabilize the image density, there is an image forming apparatus that performs image forming condition control such as detecting the VL of the photosensitive member in advance by a sensor and controlling the amount of toner supplied in accordance with the result. It has been proposed (see Patent Document 1).

  However, in this configuration, since a sensor for detecting the VL of the photosensitive member is newly installed, there arises a problem that the cost of the apparatus main body is increased and the size thereof is increased.

  In addition, when the number of rotations of the photoconductor performed before the exposure process is selected based on the temperature and humidity around the photoconductor for the purpose of discharging and charging the surface of the photoconductor, An image forming apparatus that suppresses fluctuations in image density has been proposed (see Patent Document 2).

  However, when the rotational speed of the photoconductor before image formation is increased based on the temperature and humidity around the photoconductor, there arises a problem that the printing speed is lowered and the productivity of the image forming apparatus is lowered.

On the other hand, in view of the above-described conventional problems, an image forming apparatus that predicts the VL of the photosensitive member from the temperature around the photosensitive member, the image forming time, and the image forming stop time, and controls the image forming conditions accordingly is proposed. (See Patent Document 3).
JP 2000-181158 A JP-A-2005-300745 JP 2002-258550 A

  However, it has been confirmed that the fluctuation of VL depends not only on the temperature of the photoconductor but also on the absolute humidity of the atmosphere environment of the photoconductor and the image forming time (time for driving the apparatus main body). Further, it has been confirmed that the fluctuation of VL has not only an increase in the absolute value of VL but also a behavior in which the absolute value of VL decreases.

  On the other hand, in the prior art disclosed in Patent Document 3, the absolute humidity of the atmosphere environment of the photoconductor and the image formation time are not taken into consideration, and fluctuations in VL can cause both an increase in VL and a decrease in VL. Since this is not assumed, fluctuations in VL cannot be accurately predicted.

  That is, in the image forming apparatus according to the above-described conventional example, it is impossible to accurately predict the fluctuation of VL and obtain a stable density image. Note that a phenomenon in which the absolute value of VL increases with the image formation time even when the conditions in the charging process and the exposure process are the same is referred to as VL up. A phenomenon in which the absolute value of VL decreases with image formation time is referred to as VL down.

  Here, with reference to FIG. 2 and FIG. 3, a process in which VL up and VL down occur with the image formation time will be described. FIG. 2 is a conceptual diagram of the surface potential of the photoconductor, and FIG. 3 is a diagram showing the variation of VL with the passage of the image formation time or the image stop time (FIG. 3D).

  As shown in FIG. 2, Vdev−VL, which is the difference between Vdev and VL, becomes Vcont. As this Vcont increases, the amount of toner developed on the photoconductor increases, so the image density increases.

  VL up is a phenomenon in which Vcont decreases and image density decreases because VL fluctuates in the direction of arrow A in FIG. 2 (in which the absolute value increases). On the other hand, VL down is a phenomenon in which Vcont increases and image density increases because VL fluctuates in the direction of arrow B (the direction in which the absolute value decreases) in FIG.

First, a phenomenon in which VL up occurs will be described. In an L / L environment (low temperature and low humidity environment), for example, an environment of 15 ° C./10% RH, even when several continuous images are formed, the VL increases as the image formation time elapses as shown in FIG. The phenomenon occurs.

  In addition, it has been confirmed that the rate of increase in VL per unit time is larger as the absolute humidity of the atmosphere of the photoreceptor is lower. That is, the lower the absolute humidity of the photoconductor atmosphere, the more remarkable the VL increase phenomenon.

  Further, VL up is affected by the time (image formation stop time) that the photoconductor has stopped before image formation is performed, and the longer this image formation stop time, the greater the increase in VL.

  For example, when the image formation stop time is long, VL rises to V1 as shown in FIG. 3A, but when the image formation stop time is short, VL is lower than V1 as shown in FIG. It only rises to a small V2.

  Such a VL-up phenomenon is considered to be mainly caused by an increase in the number of residual charges in the photosensitive layer due to exposure of the photosensitive member during image formation. In other words, in an environment where the absolute humidity of the atmosphere is low, the resistance of any layer in the photosensitive layer is high, so that it is difficult for the charge to move or inject smoothly in the photosensitive layer, and the residual in the photosensitive layer. The number of charges increases. As a result, VL up is considered to occur.

  Residual charges generated by the image formation gradually escape from the photosensitive layer to the ground when the image formation is completed. The longer the image formation stop time, the smaller the residual charge generated during the previous image formation. Therefore, the next time the image is formed, the residual charge tends to accumulate. Accordingly, as the image formation stop time is longer, the effect of VL increase appears more significantly when the next image formation is performed, and the amount of increase in VL increases.

  Next, a phenomenon in which VL down occurs will be described. In an environment where the temperature is not low and low humidity, for example, an environment of 23 ° C./50% RH, when continuous image formation is performed, the phenomenon of VL down occurs with the passage of image formation time as shown in FIG. On the other hand, the VL lowered by the VL down shows a tendency to recover to the original VL as the time during which image formation is not performed after image formation, that is, the image formation stop time is longer.

  For example, in FIG. 3C, when the VL at the previous image formation is reduced to V4 due to the VL down by the previous image formation, the initial VL at the next image formation is as shown in FIG. The longer the image formation stop time, the closer to the original VL, V3.

  Such a VL down phenomenon is considered to be mainly caused by a decrease in the number of residual charges in the photosensitive layer. That is, when an image is formed, the temperature of the photosensitive member rises and the resistance of the photosensitive layer decreases. Therefore, the residual charge trapped in the photosensitive layer moves to the outside of the photosensitive member, which is considered as the cause of the VL down. It is done.

  Note that the cause of the temperature rise of the photosensitive member as the image formation time elapses is friction with the developing member, charging member, cleaning member, etc., which are members in contact with the photosensitive member, and heat radiation from the exposure member, fixing device, etc. It is thought to be the main cause.

  Furthermore, based on the results of these experiments, the temperature of the photoconductor can be accurately predicted from the temperature of the atmosphere environment of the photoconductor that causes the temperature rise of the photoconductor, the image formation time, and the image formation stop time. It has been confirmed.

Note that the VL up and VL down phenomenon described above is caused by the temperature of the ambient environment of the photoconductor,
Depending on the absolute humidity of the atmospheric environment, only one of them may occur or it may occur simultaneously.

  For example, in an environment where the absolute humidity is low, the amount of increase in VL due to VL increase becomes very large, so there is a case where the influence of VL down is not seen and only the influence of VL up is noticeable. On the other hand, in an environment where the absolute humidity is high, the VL increase is unlikely to occur, so the influence of the VL decrease may be noticeable.

  In some environments, VL up and VL down may occur at the same time, and as shown in FIG. 3E, a phenomenon may occur in which VL once increases and then decreases. In another environment, as shown in FIG. 3F, a phenomenon may occur in which VL once decreases and then increases.

  From the above, it has been found that VL-up can be predicted according to absolute humidity, temperature, photoconductor stop time, and photoconductor rotation time. Further, it has been found that the VL down can be predicted according to the temperature, the photosensitive member stop time, and the photosensitive member rotation time without using the absolute humidity. And when the value of absolute humidity is high, since VL up does not generate | occur | produce, it turned out that VL can be accurately estimated only by considering VL down. The prediction of VL up and VL down will be described later.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that obtains an image with a stable density by performing appropriate control to change image forming conditions between when the absolute humidity is low and when the absolute humidity is high. .

  In order to achieve the above object, the present invention provides a rotatable photosensitive member, a charging device for applying a charging voltage to charge the surface of the photosensitive member, and exposing the surface of the photosensitive member after charging to a static state. An exposure apparatus for forming an electrostatic latent image; a developing apparatus to which a developing voltage is applied and a developer is attached to the electrostatic latent image to develop it as a developer image; and a time during which the photoconductor is rotating. A time measuring device that measures information related to the photosensitive member rotation time and information related to the photosensitive member stop time, which is the time during which the photosensitive member is stopped, information related to the temperature of the environment of the image forming apparatus, and information related to absolute humidity. When the first range is a range where the absolute humidity is low and the second range is a range where the absolute humidity is high, the environmental measurement device is measured by the environmental measurement device when the absolute humidity is the first range. Temperature information and information The image forming conditions are controlled according to the information on the humidity, the information on the photosensitive member rotation time measured by the time measuring device and the information on the photosensitive member stop time, and when the absolute humidity is in the second range, Without using information on absolute humidity measured by the environmental measuring device, information on temperature measured by the environmental measuring device, information on photosensitive member rotation time measured by the time measuring device, and information on photosensitive member stop time And a control device for controlling image forming conditions according to the above.

  According to the present invention, it is possible to provide an image forming apparatus that obtains an image with a stable density by performing appropriate control to change the image forming conditions when the absolute humidity is low and when the absolute humidity is high. .

  The best mode for carrying out the present invention will be exemplarily described in detail below based on the embodiments with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

[Overall configuration of image forming apparatus]
FIG. 4 shows a schematic configuration of the image forming apparatus according to the present embodiment. The image forming apparatus 100 is a laser beam printer that forms an image on a recording medium (transfer material) such as a recording sheet, an OHP sheet, or a cloth by an electrophotographic image forming process.

  The image forming apparatus 100 according to the present embodiment includes a cylindrical rotatable photosensitive drum 1 (photosensitive member) provided as an image carrier. Four photosensitive drums 1 are provided for each corresponding type of toner (developer), and each photosensitive drum 1 is driven to rotate in the direction of arrow A in FIG.

  When a signal for starting an image forming operation is input, the photosensitive drum 1 starts to rotate and the surface of the photosensitive drum 1 is uniformly charged to a negative charge by the charging roller 2 (charging device).

  When the surface of the photosensitive drum 1 is charged with a negative charge, the exposure device 3 emits a laser beam 4 based on the image information, scans and exposes the surface of the photosensitive drum 1, and forms an electrostatic latent image on the surface. As described above, the surface potential of the photosensitive drum 1 in the charging step is VD, and the surface potential of the exposed portion is VL.

  The developing device 5 develops the electrostatic latent image as a toner image (developer image) by attaching toner to the electrostatic latent image formed on the photosensitive drum 1. Note that a developing voltage applied to the developing device 5 in the developing step is Vdev, and a developing contrast that is a difference between Vdev and VL is Vcont.

  The toner image formed on the photosensitive drum 1 is transferred to the transfer material P carried on the transfer belt 9 between the photosensitive drum 1 and a transfer roller 7 provided as a transfer member. At this time, a toner image is transferred from the photosensitive drum 1 onto the transfer material P by applying a transfer bias to the transfer roller 7. A plurality of transfer materials P are stacked on a paper feed tray 11 disposed below the apparatus main body, and are conveyed to the transfer belt 9 via a feed roller 12 and a conveyance roller 13.

  On the other hand, toner remaining on the surface of the photosensitive drum 1 without being transferred to the transfer material P is removed by a cleaning blade 16 provided in contact with the surface of the photosensitive drum 1 and then stored in the waste toner storage unit 8. The

  The transfer belt 9 is stretched around four rollers 10a, 10b, 10c, and 10d. The transfer belt 9 rotates in the direction of arrow B in FIG. 4 and sequentially conveys the transferred transfer material P to the image forming stations SY to SBk. To do. Then, transfer from the photosensitive drum 1 to the transfer material P is performed at the stations SY, SM, SC, and SBk of the respective colors, whereby the toner images of the respective colors are superimposed on the transfer material P to form a desired image.

  When the image is transferred to the transfer material P, the transfer material P is conveyed to the fixing device 14, and the toner image transferred onto the surface of the transfer material P is melted and fixed and fixed on the transfer material P. Then, the transfer material P that has been fixed is discharged to a tray 15 disposed outside the color image forming apparatus 100.

  In addition to the above configuration, the image forming apparatus 100 is provided with a temperature / humidity sensor 18 as an environmental measurement device, and the temperature / humidity sensor 18 detects the temperature / humidity of the ambient environment of the photosensitive drum 1. In this embodiment, the temperature / humidity sensor is used as the environment measurement device, but the temperature and humidity may be provided as separate sensors.

The detected temperature and humidity are output to the CPU 22. The CPU 22 calculates the absolute humidity of the atmospheric environment based on the input temperature / humidity detection result. It is stored in the storage means 20 in units of 1 ° C. and 0.1 g / m ³ . The storage means 20 and the CPU 22 are both disposed in the engine control unit 17 provided below the apparatus main body.

The absolute humidity represents the amount of water vapor (g) contained per unit volume of the atmospheric environment, and the unit is g / m ³ . In the present embodiment, the absolute humidity is calculated in the CPU 22 based on the detection result of the temperature / humidity sensor 18. The place where the temperature / humidity sensor 18 is provided is not limited to this, and it may be provided around the photosensitive drum 1 or may be a place other than that.

Further, in the present embodiment, the temperature and absolute humidity information of the atmospheric environment is stored in the storage means 20 in units of 0.1 ° C. and 0.1 g / m ³ , respectively, but these units are particularly limited. It is not a thing and units other than these may be sufficient.

  In this embodiment, the one-component development method is used. However, the present invention is not limited to this, and a two-component development method may be used.

  As the toner used in the exemplary embodiment, a known toner used in electrophotography can be used, and an optimal toner is appropriately selected according to the development process. In this embodiment, a non-magnetic developer is used as the developer, but a configuration using a magnetic developer may be used.

[Configuration of photosensitive drum]
Next, the configuration of the photosensitive drum 1 used in the present embodiment will be described with reference to FIG. The photosensitive layer of the photosensitive drum 1 in the present embodiment is a laminated type in which a function is separated into a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material. Further, a surface protective layer is formed on the layered photosensitive layer. Hereinafter, each layer forming the photosensitive drum 1 will be described.

(Base layer 1a)
As the support for the photosensitive layer, a conductive material is used. For example, what shape | molded metals, such as aluminum, aluminum alloy, copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium, nickel, and indium, in the shape of a drum or a sheet | seat is mentioned.

  Moreover, it is also possible to use what laminated metal foil, such as aluminum and copper, to the plastic film, and what vapor-deposited aluminum, indium oxide, tin oxide, etc. on the plastic film.

  Alternatively, a metal, a plastic film, paper, or the like provided with a conductive layer by applying a conductive substance alone or together with a binder resin may be used.

  In the present embodiment, as shown in FIG. 5, the Al base 1a is provided on the base layer.

(Undercoat layer 1b)
As shown in FIG. 5, an undercoat layer 1b having a barrier function and an adhesive function is provided on the upper layer of the Al base 1a.

Examples of the material for the undercoat layer 1b used in the present embodiment include polyvinyl alcohol, polyethylene oxide, nitrocellulose, ethyl cellulose, methyl cellulose, ethylene-acrylic acid copolymer, and the like. Alcohol-soluble amides, polyamides, polyurethanes, caseins, glues, gelatins and the like can also be used.

  The undercoat layer 1b is formed by applying a solution obtained by dissolving these materials in an appropriate solvent on the Al substrate 1a and drying it.

(Positive charge injection preventing layer 1c)
In addition, an intermediate resistance positive charge injection preventing layer that serves to prevent the positive charge injected from the aluminum substrate 1a from canceling the negative charge charged on the surface of the photosensitive drum 1 is formed on the undercoat layer 1b. 1c is provided.

(Charge generation layer 1d)
Further, a charge generation layer 1d containing a charge generation material is provided on the positive charge injection prevention layer 1c.

  Examples of the charge generation material used for the charge generation layer 1d include azo pigments such as monoazo, disazo, and trisazo, phthalocyanine pigments such as metal phthalocyanine and nonmetal phthalocyanine, and indigo pigments such as indigo and thioindigo.

  It is also possible to use perylene pigments such as perylene anhydride and perylene imide, polycyclic quinone pigments such as anthraquinone and pyrenequinone, squarylium dyes, pyrylium salts and thiapyrylium salts, and triphenylmethane dyes. .

  Furthermore, inorganic substances such as selenium, selenium-tellurium, amorphous silicon, quinacridone pigments, azurenium salt pigments, cyanine dyes, xanthene dyes, quinoneimine dyes, styryl dyes, cadmium sulfide, zinc oxide, etc. are used. May be.

  However, among these, it is particularly preferable to use metal phthalocyanines such as oxytitanium phthalocyanine, hydroxygallium phthalocyanine, and chlorogallium phthalocyanine.

  The charge generation layer 1d can be formed by applying a charge generation layer coating solution obtained by dispersing a charge generation material together with a binder resin and a solvent and drying the coating solution.

  Examples of the method for dispersing the charge generation material include a method using a homogenizer, ultrasonic waves, a ball mill, a sand mill, an attritor, a roll mill, and the like. The ratio between the charge generating material and the binder resin is preferably in the range of 10: 1 to 1:10 (mass ratio), and more preferably in the range of 3: 1 to 1: 1 (mass ratio).

  The solvent used in the coating solution for the charge generation layer is selected from the solubility and dispersion stability of the binder resin and charge generation material used, and the organic solvents include alcohols, sulfoxides, ketones, ethers, esters, aliphatic halogens. Hydrocarbons and aromatic compounds.

  When applying the coating solution for the charge generation layer, for example, a coating method such as a dip coating method (a dip coating method), a spray coating method, a spinner coating method, a roller coating method, a Meyer bar coating method, or a blade coating method is used. be able to.

(Charge transport layer 1e)
A charge transport layer 1e containing a charge generation material is provided on the charge generation layer 1d. The charge transport layer 1e is formed of a suitable charge transport material, and examples thereof include triarylamine compounds, hydrazone compounds, styryl compounds, stilbene compounds, pyrazoline compounds, oxazole compounds, thiazole compounds, and triallylmethane compounds.

  Examples of the binder resin used for the charge transport layer 1e include acrylic resin, styrene resin, polyester resin, polycarbonate resin, polyarylate resin, and polysulfone resin. Further, polyphenylene oxide resin, epoxy resin, polyurethane resin, alkyd resin, unsaturated resin, or the like can be used.

  However, polymethyl methacrylate resin, polystyrene resin, styrene-acrylonitrile copolymer resin, polycarbonate resin, polyarylate resin, diallyl phthalate resin and the like are particularly preferable. These can be used singly or in combination of two or more as a mixture or copolymer.

  The charge transport layer 1e can be formed by applying a charge transport layer coating solution obtained by dissolving a charge transport material and a binder resin in a solvent, and drying it. The ratio between the charge transport material and the binder resin is preferably in the range of 2: 1 to 1: 2 (mass ratio).

  Examples of the solvent used in the charge transport layer coating solution include ketones such as acetone and methyl ethyl ketone, and esters such as methyl acetate and ethyl acetate. It is also possible to use ethers such as dimethoxymethane and dimethoxyethane, aromatic hydrocarbons such as toluene and xylene, hydrocarbons substituted with halogen atoms such as chlorobenzene, chloroform and carbon tetrachloride.

  When applying the coating solution for the charge transport layer, for example, a coating method such as a dip coating method (dip coating method), a spray coating method, a spinner coating method, a roller coating method, a Meyer bar coating method, a blade coating method, or the like is used. be able to.

(Surface protective layer 1f)
A surface protective layer 1f is provided as a surface layer on the charge transport layer 1e. The surface protective layer 1f is formed by applying a coating solution obtained by dissolving or diluting a curable phenol resin with a solvent or the like onto the photosensitive layer, thereby forming a cured layer by causing a polymerization reaction after coating. Is done.

[Control configuration of image forming condition control]
With reference to FIG. 1, a control configuration of image forming condition control of image forming apparatus 100 in the present embodiment will be described. FIG. 1 is a system block diagram of image forming condition control in the present embodiment.

  Part of image formation condition control is to keep the maximum density of each color constant (hereinafter referred to as Dmax control) and to maintain the halftone gradation characteristics linearly with respect to the image signal (hereinafter referred to as Dhalf control). Is done by.

  In the Dmax control, the maximum density of each color is affected by the film thickness of the photosensitive drum 1 and the atmospheric environment. The formation conditions are set.

On the other hand, the Dhalf control prevents a natural image from being formed due to an output density shift with respect to an input image signal due to a nonlinear input / output characteristic (γ characteristic) peculiar to electrophotography.
Image processing that cancels the characteristics and keeps the input / output characteristics linear is performed.

  Specifically, a plurality of toner patches having different input image signals are detected by an optical sensor to obtain a relationship between the input image signal and density. From this relationship, the image signal input to the image forming apparatus is converted so that a desired density is obtained with respect to the input image signal. This Dhalf control is performed after image forming conditions such as a charging voltage and a developing voltage are determined by Dmax control.

  When the density of the output image changes with the image formation time due to the change in VL, it is possible to suppress the color change by frequently performing Dmax control and Dhalf control, for example, every five printed sheets.

  However, frequently performing the Dmax control and the Dhalf control is not realistic because the printing speed is greatly reduced and the productivity of the image forming apparatus is significantly reduced.

  Therefore, in the present embodiment, Dmax control and Dhalf control are performed only once for every 1000 printed sheets. In the present embodiment, the Dmax control and the Dhalf control are set to timing once for every 1000 printed sheets, but the present invention is not limited to this.

  That is, another timing may be used, or a configuration in which Dhalf control is not performed at all may be used. In addition, the timing for performing Dmax control and Dhalf control may be determined based on toner consumption and the like instead of the number of printed sheets.

  In this embodiment, the Dmax control and the Dhalf control are performed only once for every 1000 printed sheets, so that the VL fluctuates greatly during that time. Therefore, if the image forming condition control is performed only by Dmax control and Dhalf control, a stable image density cannot be obtained.

  Therefore, in this embodiment, as an image forming condition control method other than Dmax control and Dhalf control, image forming condition control is performed so that the development contrast (Vcont) becomes constant by correcting the fluctuation of VL.

  Specifically, the development contrast (Vcont) is made constant by controlling at least one of the charging voltage determined by the Dmax control and the development voltage Vdev based on the VL fluctuation prediction.

  Such image forming condition control is performed by the control configuration shown in FIG. As shown in FIG. 1, the image forming condition control in the present embodiment includes a storage unit 20, a reading unit 21, a writing unit 26, and a CPU 22.

  These storage means 20, reading means 21, writing means 26, and CPU 22 are provided in the engine control unit 17 of the image forming apparatus 100 shown in FIG. Further, a well-known electronic memory can be suitably used as the storage means 20, but is not limited to this. In the present embodiment, a nonvolatile EEPROM is used as the storage means 20.

  Further, the CPU 22 calculates the image forming time and the image forming stop time by the calculating unit 25 for correcting the fluctuation of the VL, the control unit 23 for controlling the image forming condition based on the VL correction amount calculated by the calculating unit 25. A timer 24 as a possible time measuring means is provided.

  The timer 24 counts the image forming time in units of one second while the photosensitive drum 1 is driven. The timer 24 counts the image formation stop time in units of one second while the driving of the photosensitive drum 1 is stopped.

  In the present embodiment, the timer 24 counts in units of one second, but is not particularly limited, and may be in units other than one second. The image formation time and the image formation stop time measured by the timer 24 are stored in the storage unit 20 via the writing unit 26.

  In this embodiment, both the image formation time and the image formation stop time are measured by the timer 24. However, the two timers independently measure the image formation time and the image formation stop time. It may be.

  The image forming condition control configuration according to the present embodiment is provided with a reading unit 21 for reading information stored in the storage unit 20. The reading unit 21 sends information read from the storage unit 20 to the CPU 22.

  The calculation unit 25 in the CPU 22 calculates the correction amount of the VL fluctuation by a method described later based on the information stored in the storage unit 20. The control unit 23 sends information for controlling the image forming conditions to the image forming unit based on the VL correction amount calculated by the calculating unit 25.

[Control method of image forming condition control]
Based on the control configuration of the image forming condition control described above, (VL up correction amount calculation method) and (VL down correction amount calculation method) will be described, and the image forming condition control control method will be described. To do.

  In order to stabilize the image density when VL increases or decreases in VL, it is necessary to obtain a correction amount for correcting the VL variation and perform image forming condition control.

  Further, the image forming condition control includes controlling the developing voltage Vdev and controlling the charging voltage. In particular, in the present embodiment, a control method for controlling the charging voltage (image forming conditions) of the charging device 2 will be described.

Specifically, after obtaining the VL fluctuation amount due to VL down and VL up, the correction amount (VL down correction amount, VL up correction amount) that cancels the fluctuation is used as a reference charging voltage. In addition, image forming condition control is performed. In the present embodiment, the reference charging voltage is a charging voltage determined by Dmax control.

  Further, in this embodiment, there is no difference between the Y, M, C, and K stations as the characteristics of the photosensitive drum 1, and therefore the charging voltage control method described below is applied to all these stations. And

  FIG. 6 is a conceptual diagram of image formation condition control in the present embodiment. The process in which the control unit 23 controls the charging voltage in the charging device 2 based on the fluctuation of VL calculated by the calculation unit 25. It is shown.

In the present embodiment, the image forming time (hereinafter referred to as t1) represents a time elapsed since the stopped photosensitive drum 1 started to be driven. Further, the image formation stop time (hereinafter referred to as t2) represents the time that has elapsed since the drive of the photosensitive drum 1 was stopped. As will be described later, in this embodiment, the information is temporarily reset so that t1 = 0 is input at the start of one image formation (one unit of image formation job).

  Accordingly, the image formation time t1 corresponds to the photosensitive member rotation time from the start of image formation to the execution of control of image formation conditions by the control device. At the end of one image formation (one unit of image formation job), t2 = 0 and information is reset. Therefore, the image formation stop time t2 corresponds to the photosensitive member rotation stop time from the end of the previous image formation to the start of the next image formation. For the image forming time t1 and the image forming stop time t2, a method may be used in which integrated values from when the image forming apparatus is turned on are stored and VL fluctuations are obtained using the integrated values.

  In addition, the absolute humidity of the atmospheric environment is expressed as W, the temperature of the atmospheric environment is expressed as Tc, the amount of variation due to VL up is ΔU, and the amount of variation due to VL down is ΔD. The absolute humidity of the atmospheric environment is W, and the temperature of the atmospheric environment is Tc, which is the absolute humidity and temperature of the atmospheric environment when the Dmax control is executed.

  The image forming apparatus in the present embodiment enters a standby state by performing a multi-rotation operation before rotating the photosensitive drum 1 for an image formation preparation operation after turning on the power. Dmax control, absolute humidity, and temperature are measured and stored in the storage means during a period from when the image forming apparatus is turned on until it enters a standby state.

  In this embodiment, the negatively charged photosensitive drum 1 is used. For example, if the reference VL is −100V, it becomes −120V when VL up occurs, and −80V when VL down occurs. Therefore, ΔU is 0 or a negative value, and ΔD is 0 or a positive value.

  The calculation unit 25 calculates the first correction amount and the second correction amount from the fluctuation of VL, and the control unit 23 calculates the charging voltage to be applied to the charging device 2 so that Vcont becomes constant based on the prediction result. Control.

  First, in order to obtain the VL fluctuation, it is necessary to obtain both the fluctuation due to VL up and the fluctuation due to VL down.

  The calculating means 25 obtains the fluctuation of VL by calculating the fluctuation amount due to VL up and the fluctuation amount due to VL down, respectively. Further, the calculation means 25 calculates ΔU, which is a fluctuation amount due to VL up, from three parameters t1, t2, and W, and calculates ΔD, which is a fluctuation amount due to VL down, from the three parameters t1, t2, and Tc. .

  Further, the characteristics relating to the fluctuation of the VL are given to a table stored in the storage means 20, and the calculating means 25 calculates the fluctuation of the VL by referring to this table. Hereinafter, a method of calculating the correction amount (first correction amount, second correction amount) for VL fluctuation caused by VL down and VL up will be described.

(Calculation method of VL fluctuation correction amount (first correction amount) due to VL down)
First, a method for calculating the correction amount (first correction amount) of the VL fluctuation ΔD due to VL down will be described. The fluctuation due to the VL down is performed by referring to the VL down table 28 stored in the storage unit 20, as shown in FIG.

As shown in FIG. 8, the VL down table includes a table C, a table D, and a table E. Based on these tables, the fluctuation amount ΔD due to the VL down with respect to the image forming time is calculated.

  In this embodiment, as described above, since there is a correlation between the fluctuation amount ΔD due to VL down and the temperature of the photosensitive drum 1, the fluctuation amount ΔD due to VL down is calculated by predicting the temperature of the photosensitive drum 1. Yes.

  Specifically, the temperature of the photosensitive drum 1 at the time of image formation is calculated by referring to the table C, and the temperature of the photosensitive drum 1 at the time of image formation stop is calculated by referring to the table D.

  Further, the fluctuation amount due to the VL down is calculated by referring to the calculated temperature of the photosensitive drum 1 and the table E.

  Hereinafter, the predicted temperature of the photosensitive drum 1 is generally expressed as T, T at the start of image formation is expressed as Ti, and T at the time of image formation stop is expressed as Tk, and the VL down table 28 will be described.

  First, the table C will be described. The table C is composed of 21 tables, the temperature increase table 00 to the temperature increase table 20. The temperature increase table 00 to the temperature increase table 20 are tables showing the temperature of the photosensitive drum 1 with respect to the image formation time.

  However, in FIG. 8A, only three temperature increase tables (temperature increase table 00, temperature increase table 03, temperature increase table 08) are shown for the sake of space. Although FIG. 8A is not in the form of a table, actually, this graph is described in the table C as a table form.

  In the present embodiment, the temperature rise profile of the photosensitive drum 1 varies depending on the difference between the predicted temperature Ti of the photosensitive drum 1 and the ambient temperature Tc at the start of image formation, that is, Ti-Tc. That is, the smaller the Ti-Tc, the higher the temperature rise of the photosensitive drum 1 with respect to the image formation time.

  Therefore, the table used differs depending on Ti-Tc at the start of image formation. For example, as illustrated in FIG. 8A, when Ti-Tc is 0 ° C. and Ti and Tc are equal, the temperature raising table 00 is used. When Ti-Tc is 8 ° C., the temperature raising table 08 is used.

  As described above, the temperature of the photosensitive drum 1 can be accurately predicted by selecting an optimum temperature increase table from the 21 tables of the table C according to the value of Ti-Tc at the start of image formation. Can do.

  In the present embodiment, only 21 temperature rising tables are prepared as the table C. However, the present invention is not limited to this, and the number of increases required for accurately predicting the temperature of the photosensitive drum 1 is not limited thereto. A warm table should be prepared.

  In this embodiment, if the temperature of the photosensitive drum 1 can be predicted in units of 1 ° C., the accuracy is sufficient, and the temperature of the photosensitive drum 1 only rises up to 20 ° C. relative to the environmental temperature. Was configured as 21 tables.

  Next, the table D will be described. The table D is composed of 21 tables, a temperature decrease table 00 to a temperature decrease table 20. The temperature drop table 00 to the temperature drop table 20 is a table showing the temperature of the photosensitive drum 1 with respect to the image formation stop time.

However, FIG. 8B shows only three temperature lowering tables (temperature lowering table 02, temperature lowering table 09, and temperature lowering table 14) for the sake of space. Although FIG. 8B is not in the form of a table, this graph is actually described in the table D as a table form.

  In this embodiment, the temperature drop profile of the photosensitive drum 1 differs depending on the difference between the predicted temperature Tk and the environmental temperature Tc of the photosensitive drum 1 when the image formation is stopped, that is, Tk−Tc. The profile becomes saturated.

  For this reason, the larger the Tk−Tc, the larger the temperature drop of the photosensitive drum 1 with respect to the image forming time. That is, the table used differs depending on Tk-Tc when image formation is stopped. For example, referring to FIG. 8B, when Tk-Tc is 14 ° C., the temperature drop table 14 is used, and Tk-Tc is 2 ° C. In this case, the temperature drop table 02 is used.

  As described above, the temperature of the photosensitive drum 1 can be accurately predicted by selecting an optimal temperature-decreasing table from among the 21 tables D in accordance with the value of Tk−Tc when image formation is stopped. it can.

  In the present embodiment, only 21 temperature reduction tables are prepared as the table D. However, the present invention is not limited to this, and the number of temperature reduction tables necessary for accurately predicting the temperature of the photosensitive drum 1 is not limited thereto. Should be prepared.

  In this embodiment, if the temperature of the photosensitive drum 1 can be predicted in units of 1 ° C., the accuracy is sufficient, and the temperature of the photosensitive drum 1 only rises to 20 ° C. at the maximum with respect to the environmental temperature. Table D was configured as 21 tables.

By using the table C and the table D described above, it is possible to accurately predict the temperature of the photosensitive drum 1 in both cases of image formation and image formation stop.
The reason why the temperature of the photosensitive drum 1 is not directly measured by the temperature / humidity sensor is that even if the temperature / humidity sensor is brought close to the temperature of the photosensitive drum 1, the actual photosensitive member temperature and the measured temperature of the temperature / humidity sensor This is because an error occurs.

  The reason why the error occurs is that the temperature rise of the photoconductor not only affects the temperature in the vicinity of the photoconductor, but also the temperature rise due to rubbing with the charging member and the cleaning member with which the photoconductor contacts. Therefore, in this embodiment, the temperature of the photosensitive drum 1 is predicted with high accuracy by the photosensitive member rotation time and the photosensitive member stop time.

  In this embodiment, the fluctuation amount ΔD due to VL down is proportional to the difference between the predicted temperature T of the photosensitive drum 1 and the temperature Tc of the ambient environment, that is, T−Tc. The ambient temperature Tc here is the ambient temperature of the image forming apparatus when the Dmax control is performed to determine the reference charging voltage. This relationship is shown in Table E shown in FIG.

  That is, in the present embodiment, by predicting the temperature T of the photosensitive drum 1, it is possible to calculate the fluctuation amount ΔD due to VL down and to calculate the first correction amount so as to cancel the fluctuation amount. is there. That is, the first correction amount for correcting the fluctuation amount ΔD due to VL down is based on the temperature of the photosensitive drum 1 and the temperature of the ambient environment of the photosensitive drum 1.

For example, when T-Tc is 4 ° C., the fluctuation amount ΔD due to VL down is +5 V from Table E. Therefore, the first correction amount may be determined so as to cancel this. When ΔD becomes + 5V, if the charging voltage is left as it is, VL will be reduced by 5V in absolute value, so that correction is performed to increase the charging voltage by 5V in absolute value. Although FIG. 8C does not have a table shape, this graph is actually described in the table E as a table shape.

  In other words, the VL fluctuation amount ΔD due to the VL down increases as the temperature Tc of the atmosphere environment of the photosensitive drum 1 is lower than the table E in FIG. Further, as the image forming time t1 increases, the temperature T of the photosensitive member 1 increases (table C in FIG. 8), so that the amount of variation VL of VL due to VL down increases. Further, since the temperature of the photosensitive member 1 decreases as the image formation stop time increases (Table D in FIG. 8), the VL fluctuation amount ΔD due to VL down decreases (however, ΔD <0 is not satisfied).

  Then, as shown in FIG. 2, when the VL fluctuation amount ΔD due to the VL down increases (direction B in FIG. 2), the first correction amount that increases the absolute value of VD so as to cancel it is formed. In addition to the conditions.

  Further, if the VL fluctuation amount ΔD due to VL down decreases, a first correction amount that decreases the absolute value of VD accordingly may be added to the image forming conditions. Here, the value of VD has a positive correlation with the value of the charging voltage applied to the charging device, and VD increases as the charging voltage increases.

  That is, if the temperature of the photosensitive drum 1 is the same, the charging voltage is corrected so as to increase the absolute value of VD as the ambient temperature Tc of the photosensitive drum 1 is lower. Further, the charging voltage is corrected so that the absolute value of VD increases as the image forming time t1 increases. Further, the charging voltage is corrected so that the absolute value of VD decreases as the image formation stop time t2 increases.

  In the present embodiment, the VL down table 28 is used as a table for calculating the fluctuation amount ΔD due to the VL down. However, the present invention is not limited to this. Regarding the table C, the temperature of the photosensitive drum 1 with respect to the image forming time may be set to other values. Regarding the table D, the temperature of the photosensitive drum 1 with respect to the image formation stop time may be set to another value. Regarding the table E, other values may be used as long as the relationship between the temperature of the photosensitive drum 1 and the VL down is expressed.

  Further, the table C, the table D, and the table E are not described as table shapes, but may be described as equations as long as the temperature of the photosensitive drum 1 and the VL down characteristics can be expressed. Further, in the present embodiment, the predicted temperature of the photoreceptor 1 is obtained from the environmental temperature, the image formation time, and the image formation stop time. However, if it is possible to directly measure the temperature of the photoconductor 1 with high accuracy, the image forming conditions may be changed according to the temperature of the photoconductor 1 and the environmental temperature.

(Calculation method of VL fluctuation correction amount (second correction amount) due to VL up)
Next, a calculation method of the correction amount (second correction amount) of the VL fluctuation due to VL up will be described. The VL fluctuation ΔU due to the VL up is performed by referring to the VL up table 27 stored in the storage unit 20, as shown in FIG.

  As shown in FIG. 7, the VL up table 27 includes a table A and a table B. Based on these tables, the VL variation amount ΔU due to the VL up with respect to the image forming time is calculated.

As shown in FIG. 7A, the table A shows the amount of VL variation with respect to the image formation time, and the table B shows the conditions (absolute humidity and absolute humidity) at the start of image formation as shown in FIG. The coefficients selected based on (image formation stop time) are shown as a 3 × 3 matrix.

  The calculation of the fluctuation amount due to the VL-up with respect to the image formation time is performed by multiplying the table A by the coefficient selected from the table B. Although FIG. 7A is not in the form of a table, actually, this graph is described in the table A as the form of the table.

The reason why the table A is multiplied by the coefficient selected from the table B is that the fluctuation amount of VL depends on the absolute humidity and the image formation stop time. In the present embodiment, as the absolute humidity increases, the amount of increase in VL decreases, and in an environment where the absolute humidity is W ≧ 2.5 g / m ³ , no increase in VL occurs.

  In this embodiment, the VL variation amount ΔU during image formation becomes smaller as the image formation stop time from the end of the previous image formation to the start of the next image formation is shorter.

  As described above, the table B is given a coefficient reflecting the influence of the absolute humidity and the influence of the image formation stop time. That is, by multiplying the table A by the coefficient selected from the table B, it is possible to calculate the fluctuation amount due to the VL up with high accuracy under any condition.

  Then, the second correction amount may be calculated so as to cancel the VL fluctuation amount ΔU due to the VL up.

That is, the VL fluctuation amount ΔU due to the VL increase increases as the absolute humidity W in the atmospheric environment is lower than that in the table B. Further, it increases as the image formation stop time t2 increases. Further, as the image forming time t1 increases from the table A, the VL fluctuation amount ΔU due to the VL increase increases. Then, as shown in FIG. 2, when the VL fluctuation amount ΔU due to VL increase increases (FIG. 2).
Middle A direction), Vcont becomes small.

  As described above, the second correction amount may be corrected so as to cancel the increase in the VL fluctuation amount ΔU due to VL up. That is, when ΔU increases, correction for decreasing the absolute value of the charging voltage may be performed so that the absolute value of VD decreases. By doing so, Vcont can be made the original size (see FIG. 2).

  Specifically, the absolute value of the charging voltage decreases as the absolute humidity W in the atmosphere environment of the photosensitive drum 1 decreases, and the absolute value of the charging voltage decreases as the image formation time t1 increases, and the image formation stop time t2 increases. The absolute value of the charging voltage may be decreased as the value increases.

  In the present embodiment, the VL up table 27 is used as a table for calculating the fluctuation amount ΔU due to the VL up. However, the present invention is not limited to this. Regarding the table A, the VL-up variation amount ΔU with respect to the image formation time may be set to other values.

  Similarly, the values of the table B may be changed, or the matrix may be provided as a matrix having a different size instead of a 3 × 3 matrix. Further, the table A and the table B are not described as table shapes, but may be described as mathematical expressions as long as the VL-up characteristics can be expressed.

By the above method, the calculation means 25 calculates the amount of fluctuation due to the VL up 27 using the VL up table, and calculates the amount of fluctuation due to the VL down using the VL down table 28, thereby calculating the first and second corrections. It is possible to calculate the quantity. Then, the charging voltage VD is controlled based on these correction amounts. The first correction amount is calculated according to the temperature, the image formation time (the rotation time of the photoconductor 1), and the image formation stop time (the rotation stop time of the photoconductor 1).

  The second correction amount is calculated according to the absolute humidity, the image formation time (the rotation time of the photoconductor 1), and the image formation stop time (the rotation stop time of the photoconductor 1). Therefore, when the image forming conditions are controlled by the first correction amount and the second correction amount, that is, in the range where the absolute humidity is low (first range), the temperature, the absolute humidity, and the image forming time (of the photoconductor 1). Rotation time) and image formation stop time (rotation stop time of the photoreceptor 1) control the image formation conditions.

As described above, in the range where the absolute humidity is high (second range; in this embodiment, W ≧ 2.5 g / m ³ ), the VL increase phenomenon does not occur. Therefore, it is not necessary to calculate the second correction amount. Accordingly, in the range where the absolute humidity is high, the image forming conditions are controlled by the temperature, the image forming time (the rotation time of the photoconductor 1), and the image formation stop time (the rotation stop time of the photoconductor 1).

  In addition, the VL increase phenomenon does not occur in the range where the absolute humidity is high. Therefore, if conditions other than absolute humidity (temperature, image formation time, image formation stop time) are the same, the charging voltage or development voltage is higher when the absolute humidity is higher than when the absolute humidity is low. The absolute value becomes smaller.

  Then, the control unit 23 sends information for charging voltage control to the developing device 5 based on the information of the calculation results to the image forming unit. In the present embodiment, the charging voltage VD is controlled so that the development contrast (Vcont) is constant.

(Specific flow of image forming condition control)
Next, the flow of image forming condition control according to the present embodiment will be described with reference to the flowchart of FIG.

  When the start of image formation is instructed, the image formation time t1 is stored as 0 in the storage means 20 (S1), and the timer 24 starts counting time in units of 1 second (S2). Thereafter, the reading unit 21 reads the environmental temperature, absolute humidity, and image formation stop time from the storage unit 20 (S3).

  The calculation means 25 calculates the variation ΔU due to VL increase from the image formation time, the image formation stop time, and the absolute humidity by the method described above (S4).

  Further, the calculation means 25 calculates the fluctuation amount ΔD due to VL down that calculates the fluctuation amount due to VL up from the image forming time, the image formation stop time, and the environmental temperature by the method described above (S5).

  The calculating means 25 calculates the VL fluctuation amount as ΔU + ΔD from the VL up fluctuation amount ΔU and the VL down fluctuation amount ΔD calculated in S4 and S5. Based on the calculation result, the control means 23 controls the charging voltage applied to the charging device 2 so that Vcont becomes constant (S6).

  The CPU 22 determines whether or not the image formation is finished. When the image formation is continued (S7, No), the count of the image formation time t1 is increased by 1 second (S8), and the steps from S4 to S7 are repeated until the image formation is completed. When the image formation is completed (S7, Yes), the process proceeds to the calculation when the image formation is stopped.

  At the end of image formation, the CPU 22 stores the environmental temperature and absolute humidity input from the temperature / humidity sensor 18 in the storage unit 20 (S9).

  Then, the image forming time t2 is stored as 0 in the storage means 20 (S10), and the timer 24 starts counting time in units of 1 second (S11). Thereafter, the environmental temperature is read from the storage means 20 by the reading means 21 (S12).

  The calculating means 25 calculates the temperature of the photosensitive drum 1 when image formation is stopped by the method described above (S13).

  The CPU 22 determines whether or not image formation is started. If the image formation remains stopped (S14, No), the count of the image formation time t2 is increased by 1 second (S15), and the steps from S13 to S14 are repeated until the image formation is started. The calculation of the temperature of the photosensitive drum 1 is continued. When image formation is started (S14, Yes), the process proceeds to the calculation at the time of image formation from S1 (S16).

  In the present embodiment, the charging voltage is controlled as the image forming condition control. However, the developing voltage Vdev may be corrected and controlled. When controlling the development voltage Vdev, if VL increases, the absolute value of the development voltage is increased so that Vcont is kept constant.

  Further, when VL goes down, the absolute value of the developing voltage is caused to occur so that Vcont is kept constant. Furthermore, it may be configured to control both the charging voltage and the developing voltage Vdev.

  Next, the effects obtained by this embodiment will be described by comparing the case where the image forming condition control of this embodiment is performed and the case where it is not performed (comparative example). Here, a control method for controlling the development voltage Vdev is adopted. The conventional image forming apparatus is assumed to have the same configuration as the image forming apparatus 100 of the present embodiment except that the above-described image forming condition control is not performed.

FIG. 10 (a) shows the results after performing Dmax control and Dhalf control in both the comparative example and the present embodiment under N / N (23 ° C./15% RH, absolute humidity 8.87 g / m ³ ). , The transition of the development voltage (Vdev) and VL when the continuous image formation of up to 1000 sheets is performed is shown. Further, the image formation stop time (t2) before the start of image formation was 5000 seconds.

FIG. 10B shows the transition of the halftone density at that time. In FIG. 10B, the method for measuring the chromaticity of the printed matter is to use a toner patch on a transfer material (product name: color laser copier paper 81.4 g / m ² manufactured by Canon Inc.), and tones in 10 levels for each color. The one formed by was measured.

  Specifically, each toner patch after fixing was measured by GRETAG Spectrolino (manufactured by Gretag Macbeth). FIG. 10B shows, as an example, the result of the density transition of a magenta halftone (printing rate 50%) patch.

  As shown in FIG. 10A, in the image forming apparatus 100 according to the present embodiment, the VL is reduced by 28V per 1000 sheets in the N / N environment. In this way, in the N / N environment, the fluctuation due to the VL-up does not occur at all, and only the fluctuation due to the VL-down occurs. .

In the comparative example, since printing is always performed at the development voltage (−250 V) determined by the Dmax control, Vcont increases with the number of image formations, and the increase amount is 28 V per 1000 sheets. Therefore, in the comparative example, as shown in FIG. 10B, the image density increases with the number of images formed, and the increase amount is 0.154 per 1000 sheets.

  On the other hand, in the case where the present embodiment is performed, since the variation in VL is calculated from the development voltage (−250 V) determined by the Dmax control and the development voltage is sequentially changed, printing is performed regardless of the number of images formed. Vcont can be kept constant.

  As shown in FIG. 10A, the variation in Vcont is suppressed to 3 V per 1000 sheets passed. Therefore, in this embodiment, as shown in FIG. 10B, the image density is stable regardless of the number of images formed, and the density is from 0.410 to 0.430, and the density variation is 0.020, which is stable. It was confirmed that a concentration was obtained.

  FIG. 10B shows only the result of the magenta halftone (printing rate 50%) patch. However, when this embodiment is used, the patch density and other colors of other magenta tones are used. It was confirmed that the patch density of the sample was also stable. Further, it was confirmed that the density is stabilized when the present embodiment is used not only in continuous printing but also in intermittent printing.

FIG. 11 (a) shows the result of performing Dmax control and Dhalf control in both the comparative example and the present embodiment under L / L (15 ° C./10% RH, absolute humidity 1.06 g / m ³ ). , The transition of the development voltage (Vdev) and VL when the continuous image formation of up to 1000 sheets is performed is shown.

  FIG. 11B shows the transition of the halftone density at that time. The method for measuring the chromaticity of the printed material is the same as that in FIG. 10B in the N / N environment. FIG. 11B shows, as an example, the result of density transition of a magenta halftone (printing rate 50%) patch.

  As shown in FIG. 11A, in the image forming apparatus 100 according to the present embodiment, the VL is increased by 38 V per 1000 sheets in the L / L environment. In this way, in the L / L environment, the temperature of the photosensitive drum 1 is increased, so that the VL should be decreased. However, since the absolute humidity is low, the amount of fluctuation due to the increase in VL is very large. It is thought that the characteristics of the continual rise and eventually saturated.

  In the comparative example, since printing is always performed at the development voltage (−250 V) determined by the Dmax control, Vcont decreases with the number of images formed, and the amount of decrease is 38 V per 1000 sheets.

  Therefore, in the comparative example, as shown in FIG. 11B, the image density decreases with the number of images formed, and the amount of decrease is 0.159 per 1000 sheets.

  On the other hand, in the case where the present embodiment is performed, since the variation in VL is calculated from the development voltage (−250 V) determined by the Dmax control and the development voltage is sequentially changed, printing is performed. Instead, Vcont can be kept constant.

  As shown in FIG. 11A, the fluctuation of Vcont is suppressed to 2V per 1000 sheets. Therefore, in this embodiment, as shown in FIG. 11B, the image density is stable regardless of the number of images formed, and the density varies from 0.387 to 0.420, resulting in a density fluctuation of 0.033. It was confirmed that the obtained concentration was obtained.

  FIG. 11B shows only the result of a magenta halftone (printing rate 50%) patch. However, when this embodiment is used, patch densities and other colors of other magenta tones are used. It was confirmed that the patch density of the sample was also stable. Further, it was confirmed that the density is stabilized when the present embodiment is used not only in continuous printing but also in intermittent printing.

  As described above, according to the configuration of the present embodiment, even when printing is performed continuously or intermittently, the fluctuation of the VL of the photosensitive drum 1 is obtained, and the correction amount based on the result is added, so that it is always stable. An image having a high density can be obtained and a high-quality image can be provided.

  In addition, since the characteristics of VL fluctuation depending on the atmospheric environment (temperature, absolute humidity) can be accurately predicted, an image having a stable density can be obtained in accordance with the atmospheric environment fluctuation.

  In this embodiment, since there is no difference between the Y, M, C, and K stations as the characteristics of the photosensitive drum 1, the charging voltage control is performed in the same manner in all the stations. However, the charging voltage control method may be changed between stations.

  In this embodiment, the charging voltage is controlled based on the VL fluctuation result as the surface potential of the photosensitive drum 1. However, the charging voltage control is performed based on the prediction result of the potential fluctuation of the halftone image portion. May be performed.

  In this embodiment, the charging voltage is controlled in units of one second, but the charging voltage may be controlled in other units. For example, the charging voltage may be controlled in units of 0.5 seconds, or the charging voltage may be controlled in units of one page.

  In this embodiment, the charging voltage is controlled as an image forming condition for keeping Vcont constant. However, the developing voltage Vdev may be controlled.

  That is, a configuration may be adopted in which Vcont is made constant by obtaining fluctuations in VL while keeping the charging voltage VD constant and adding correction amounts (third and fourth correction amounts) to the development voltage Vdev.

  Specifically, after obtaining the VL fluctuation amount due to VL down and VL up, a correction amount for canceling those fluctuations (VL down correction amount: third correction amount, VL up correction amount: first 4) is added to the developing voltage to control the image forming conditions.

  For this purpose, a table showing the relationship between the development voltage and the predicted VL may be stored in the storage unit 20 and the development voltage may be controlled so that the VL is always constant.

  Since the third correction amount calculation method is not different from the first correction amount calculation method described above, the third correction amount is described with the description of the first correction amount calculation method. A description of the calculation method is omitted.

  Further, the fourth correction amount calculation method is not different from the second correction amount calculation method described above, and therefore the fourth correction amount is described with the description of the second correction amount calculation method. A description of the calculation method is omitted.

  Further, it may be configured to control both the charging voltage and the developing voltage Vdev based on the result of predicting the fluctuation of VL. Further, the VL fluctuation may be corrected by changing the exposure amount based on the predicted VL fluctuation.

  As described above, by correcting the fluctuation of VL based on the temperature, the absolute humidity, the image formation time, and the image formation stop time of the photosensitive drum 1, appropriate image formation condition control is performed, and an image having a stable density is always obtained. It is possible to provide an image forming apparatus capable of obtaining the above.

[Second Embodiment]
The second embodiment of the present invention is characterized in that the control for changing the image forming conditions is stopped when the temperature and humidity environment in which the image forming apparatus is placed changes greatly. Since the other points are the same as in the first embodiment, the description of the same parts is omitted, and only the parts different from the first embodiment are described.

  In the first embodiment, the environmental temperature Tc and the absolute humidity W are measured from when the image forming apparatus is turned on until it enters a standby state where image formation can be performed, and is stored in the storage unit. The correction amount is calculated according to the temperature and absolute humidity. However, if the environment in which the image forming apparatus is placed changes between the measurement of temperature and absolute humidity and the next measurement of temperature and absolute humidity, the correction amount may not be calculated properly. There is sex.

  Therefore, in the image forming apparatus according to the present embodiment, when the environmental temperature and the absolute humidity measured by the temperature / humidity sensor 18 change greatly, the control of correcting the image forming condition due to the fluctuation of VL is stopped. Yes.

  By doing so, it is possible to prevent the image forming conditions from becoming inappropriate due to a rapid change in the temperature and humidity environment.

Block diagram showing a control configuration of image forming condition control in the present embodiment Diagram showing the concept of the surface potential of the photoreceptor Diagram showing the relationship between image formation time and surface potential of photosensitive drum Schematic configuration diagram of an image forming apparatus according to the present embodiment Schematic configuration diagram of a photosensitive drum in the present invention Conceptual diagram of image forming condition control in the present invention The figure which shows the content of the VL up table in this invention The figure which shows the content of the VL down table in this invention The flowchart figure showing the image formation condition control which concerns on this invention The figure which shows the surface potential of the photosensitive drum with respect to the number of image formations in N / N environment, and the image density with respect to the number of image formations. The figure which shows the surface potential of the photosensitive drum with respect to the number of image formation, and the image density with respect to the number of image formation in the L / L environment.

Explanation of symbols

20 storage means 21 reading means 22 CPU
23 control means 24 timer 25 calculation means 26 writing means 27 VL up table 28 VL down table 100 image forming apparatus

Claims (9)

A rotatable photoreceptor,
A charging device for applying a charging voltage to charge the surface of the photoreceptor;
An exposure device that exposes the surface of the photoreceptor after charging to form an electrostatic latent image;
A developing device to which a developing voltage is applied, and a developer is attached to the electrostatic latent image to develop it as a developer image;
A time measuring device that measures information related to the photosensitive member rotation time, which is the time during which the photosensitive member is rotating, and information related to the photosensitive member stop time, which is the time during which the photosensitive member is stopped;
An environmental measurement device that measures information about temperature and information about absolute humidity;
When the range where the absolute humidity is low is the first range and the range where the absolute humidity is high is the second range,
When the absolute humidity is in the first range, information on the temperature measured by the environmental measurement device, information on the absolute humidity, information on the photoconductor rotation time measured by the time measurement device, and information on the photoconductor stop time And control the image forming conditions according to
When the absolute humidity is in the second range, the information on the temperature measured by the environmental measurement device and the photosensitivity measured by the time measurement device are used without using the information on the absolute humidity measured by the environmental measurement device. A control device for controlling image forming conditions in accordance with information relating to body rotation time and information relating to photoreceptor stop time;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the information about the temperature measured by the environment measuring apparatus is a temperature from when the image forming apparatus is turned on to when the image forming apparatus is in a standby state.   3. The image formation according to claim 1, wherein the information related to the absolute humidity measured by the environmental measurement device is an absolute humidity from when the power of the image forming apparatus is turned on to when the image forming apparatus enters a standby state. apparatus.   4. The photoconductor rotation time measured by the time measuring device is a photoconductor rotation time from the start of image formation to execution of control of image forming conditions by the control device. The image forming apparatus according to any one of the above.   5. The photoconductor stop time measured by the time measuring device is a photoconductor stop time from the end of the previous image formation to the start of the next image formation. An image forming apparatus according to claim 1. The image forming conditions are:
6. The image forming apparatus according to claim 1, wherein the image forming apparatus is at least one of the charging voltage and the developing voltage.   The absolute value of the charging voltage or the absolute value of the developing voltage is controlled by the control device to be smaller when the absolute humidity is in the second range than when the absolute humidity is in the first range. The image forming apparatus according to claim 6. A photoreceptor,
A charging device for applying a charging voltage to charge the surface of the photoreceptor;
An exposure device that exposes the surface of the photoreceptor after the charging to form an electrostatic latent image;
A developing device to which a developing voltage is applied, and a developer is attached to the electrostatic latent image to develop it as a developer image;
An environmental measuring device that measures temperature-related information;
A control device for controlling image forming conditions in accordance with information on the temperature of the photoconductor and information on the temperature of the environment;
An image forming apparatus comprising: The image forming conditions are:
The image forming apparatus according to claim 8, wherein the image forming apparatus is at least one of the charging voltage and the developing voltage.

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