JP6614871B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus having a function of forming an image on a recording medium such as a sheet, such as a copying machine, a printer, or a facsimile machine.

  Consumables used in an electrophotographic image forming apparatus eventually reach the lifetime to be replaced with the frequency of use. In the case of the toner cartridge, when the toner to be supplied is exhausted in the container, in the case of the development unit, when the durability of the developer is deteriorated, in the case of the drum unit, the drum is deteriorated and an image defect may occur. In the case of a waste toner container, the case where the container is filled with waste toner is applicable. In general, an image forming apparatus has a configuration in which when a consumable item reaches the end of its life, it is detected and the user is prompted to replace it.

  One of the configurations is to provide a new / old detection mechanism for identifying whether a consumable is a new product or an old product. As a method of providing a new and old detection mechanism to detect the life of a consumable, it is conceivable to provide an electric memory on the consumable and write information on it. However, since the semiconductor memory is very expensive, there is a problem that the consumables are expensive and the running cost is increased.

  In order to solve this problem, there has been disclosed an image forming apparatus using an old and new detection mechanism having a relatively inexpensive configuration without using an expensive member such as a semiconductor memory in the old and new detection mechanism (see Patent Document 1).

  In particular, for drum units and development units, the initial image density of the drum unit is used to absorb the solid variation of the drum unit by giving information to the main unit that it is the initial drum unit, regardless of whether the user or the service person is replaced. The initial operation of the drum unit, which detects the initial state of the drum and the initial state such as the film thickness of the drum, is essential. In other words, the drum that carries the parts of the drum unit has a solid variation in film thickness, so it is necessary to detect the initial film thickness and perform control according to the film thickness. Since there is a solid variation in resistance, it is necessary to detect the initial image density and perform control in accordance with the image density.

  Further, since the toner is not supplied to the photosensitive drum cleaning member at the time of initial installation, the slippage between the drum and the cleaning member is lost when used in this state, and so-called blade squealing or blade swell A fatal symptom occurs as a system. Accordingly, means for forcibly supplying toner to the cleaning member is taken at the time of initial installation.

  An electrophotographic image forming apparatus is provided with a photoconductor, and when image formation is performed, a charging process is performed to uniformly charge the surface of the photoconductor to a predetermined potential. For this charging process, for example, a contact charging method is used in which a charging roller is brought into contact with the surface of the photosensitive member and a voltage is applied to the charging roller to charge the surface of the photosensitive member. In the contact charging method, a DC voltage having a voltage value Vd + Vth is applied to the charging roller in order to charge the surface of the photoreceptor to a desired potential Vd.

  Here, the voltage value Vth is a discharge start voltage to the photosensitive member that is a member to be charged when a DC voltage is applied to the charging roller. Further, a charging method called an AC charging method is used in order to further uniform the charge on the photosensitive member. In this AC charging method, a charging voltage obtained by superimposing an AC voltage having a peak-to-peak voltage value (pp voltage value) twice or more of the voltage value Vth on a DC voltage having a voltage value corresponding to a desired potential Vd is applied. This is a method of applying to the charging roller. In the case of this AC charging method, by superimposing the AC voltage, discharge to the plus side and minus side occurs alternately, and the surface of the photoreceptor can be uniformly charged.

  In the AC charging method, the relationship between the voltage value Vc of the AC voltage and the current value Ic of the AC voltage flowing through the charging roller is not always constant, the thickness of the photosensitive layer of the photoconductor, the degree of deterioration due to long-term energization of the charging roller, It varies depending on the environmental temperature. For example, when the impedance of the charging roller increases due to the long-term use of the charging roller, the current value Ic of the AC voltage flowing through the charging roller becomes small with respect to the same voltage value Vc. In a low-temperature and low-humidity environment (L / L), the material dries and the resistance value increases, making it difficult to discharge. Therefore, in order to obtain uniform charging, the voltage value Vc (amplitude) of the AC voltage is increased. There is a need to.

  On the contrary, in a high temperature and high humidity environment (H / H), the material absorbs moisture and the resistance value decreases, so that the same voltage value Vc causes more discharge than necessary between the charging roller and the photoreceptor. Become. Therefore, in order to stably supply a high-quality image over a long period of time, the voltage value of the AC voltage applied to the charging roller and the charging roller so that uniform charging can be performed without causing excessive discharge. It is necessary to control the current value of the AC voltage flowing through the. The discharge of the charging roller and the photosensitive member accelerates the deterioration of the photosensitive member by scraping the photosensitive member, and an abnormal image such as an image flow in a high-temperature and high-humidity environment due to a discharge product is generated.

  Therefore, the surface of the photoconductor is cleaned with a cleaning blade and the surface of the photoconductor is scraped off very slightly to prevent an image flow due to a discharge product. As described above, the photoconductor is scraped in the process of discharging and cleaning at the time of charging, and as the use proceeds, the film thickness of the photoconductive layer of the photoconductor becomes thinner. Therefore, a technique has been proposed in which the photosensitive layer thickness of the photoconductor is detected by measuring a direct current flowing when the photoconductor is charged to determine the life of the photoconductor or change the image forming conditions. Yes.

  As the photosensitive layer thickness decreases, the capacitance on the surface of the photoconductor increases, and the DC current required to charge the photoconductor from the neutralized state to the specified charging potential increases. By doing so, the degree of film thickness reduction can be detected. As the phenomenon of drum cartridge replacement time, there are many image defects such as streaks and unevenness due to the above-mentioned photoconductor drum scraping, so the degree of decrease in film pressure is detected from DC current and the time when the life of the photoconductor drum is reached is predicted. In addition, a system for displaying on a display is implemented. As for what is mounted, only the direct current component flowing from the charging roller to the photosensitive drum is detected and the film thickness of the photosensitive drum is judged, but the alternating current also depends on the thickness of the photosensitive drum. It is known that the current changes, and it is possible to similarly predict the change in the film thickness of the photosensitive drum by detecting an alternating current.

  Further, in order to accurately predict the change in the film thickness of the photosensitive drum, a method of detecting a relative change in DC current from the initial state of the photosensitive drum is desirable. This is because the method of simply predicting the film thickness of the photosensitive drum from the detected direct current takes into account the environment in which the main body is placed during the detection of the direct current and the resistance variation of the charging roller. Therefore, if the environment where the main unit is placed is not the expected environment, or if the charging roller has high or low resistance, the drum cartridge will be randomly selected. When assembled, the amount of current flowing from the charging roller to the photosensitive drum is very likely to fluctuate, and the film thickness of the photosensitive drum is often erroneously detected.

  Therefore, a method of detecting the amount of direct current flowing from the charging roller in the initial stage of the drum cartridge to the photosensitive drum and calculating the change in film thickness of the photosensitive drum according to the difference current from the initial current value with reference to the initial current value. Is not good. It is possible to greatly suppress the false detection factors such as the environmental factors where the main body is placed and the resistance variation factors of the charging roller.

JP 2003-316227 A

  For products that detect the film thickness of the photosensitive drum, as described above, the main body recognizes that the drum cartridge is new and unused, and matches the variations in the photosensitive drum film thickness and charging roller resistance. Initialization operation, so-called acquisition of information on the initial state of the DC current flowing through the drum, or acquisition of information on the initial state of image density, reset of the counter value indicating the usage status of the drum cartridge, supply of toner to the initial photosensitive drum cleaning It is necessary to perform the mode, etc., but as described above, in order to recognize that the drum cartridge is unused, the old and new detection members that affect the cost are mounted on the drum cartridge. Or, after the unused drum cartridge is inserted by the user and service person, it is not used in the main unit. Tasks such as inputting information of a certain effect directly at present, have been implemented.

  There is a demand for an initialization operation to be automatically started when an unused drum cartridge is mounted without mounting an old or new detection member.

  An image forming apparatus according to the present invention includes an image carrier, a charging member that charges the image carrier, and an exposure unit that exposes the image carrier charged by the charging member to form an electrostatic image. Developing means for developing the electrostatic image formed on the image carrier with toner, transfer means for transferring the developed toner image to the intermediate transfer body, and a direct current flowing between the charging member and the image carrier An image forming apparatus comprising: a charging current detecting unit that detects the density of the toner patch image; a density detecting unit that detects a density of a toner patch image formed on the intermediate transfer member; and a counting unit that counts the usage amount of the image carrier. When the difference between the detected current amount by the charging current detecting means and the previous detected current amount is smaller than a predetermined current amount, the count of the counting means is maintained, and when the detected current amount difference is equal to or larger than the predetermined current amount. The detected density of the toner patch image by the density detecting means is compared with the previous detected density, and if the detected density difference is smaller than a predetermined density, the count of the counting means is maintained, and the detected density difference When the value is equal to or higher than a predetermined concentration, the counting means resets the count.

  The present invention proposes a method capable of accurately determining whether a drum cartridge is new or old without using a new / old detection member that has been mounted to determine whether a drum cartridge is new or old. As a new and old detection method, the conventional drum film thickness detection control is simply used as it is, so that the deterioration of the drum can be carried out without any deterioration.

6 is a flowchart illustrating a flow of detecting whether a drum cartridge is new or old using the photosensitive drum film thickness detection described in the first embodiment. It is the schematic which shows the cross section of the image carrier as described in Examples 1-9. It is a figure which shows the concept of the discharge current control which determines the charging alternating voltage employ | adopted in the Example. It is a block diagram which shows the application path | route of the charging high voltage as described in Examples 1-9. 6 is a graph showing the relationship between the film thickness of the photosensitive drum described in Examples 1 to 9 and the direct current flowing from the charging roller to the photosensitive drum. It is the flowchart which showed the control flow about the conventional general photoreceptor drum film thickness detection used as the premise of an Example. 5 is a flowchart showing a detailed control flow of conventional photosensitive drum film thickness detection which is a premise of the embodiment. 6 is a sequence chart showing a sequence relating to photoconductor drum film thickness detection which is a premise of the embodiment. FIG. 10 is a schematic diagram showing a relationship of a direct current flowing from a charging roller to a photosensitive drum when unused drum cartridges of Examples 1 to 9 are put into the main body. 10 is a graph showing the relationship between the film thickness of the photosensitive drum and the differential current γ described in Examples 1 to 9. 1 is a schematic configuration diagram of a four-drum type color electrophotographic copying apparatus described in Embodiments 1 to 9 of the image forming apparatus according to the present invention. It is a circuit diagram which shows the main body control method of Examples 1-9. FIG. 10 is a circuit diagram illustrating a toner ATR patch control method of Examples 1 to 9. FIG. 6 is a diagram showing the relationship between the output of an image density sensor 77 and the density of an output image when the density of a toner patch formed on the photosensitive drum 1 is changed stepwise by the area gradation of each color. 6 is a flowchart illustrating a flow of detecting whether a drum cartridge is new or old using the photosensitive drum film thickness detection described in the first embodiment.

Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.
FIG. 11 is a longitudinal sectional view showing a schematic configuration of an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 has four colors in which four image forming units are arranged in tandem along the moving direction of an end-lease belt type intermediate transfer material (hereinafter referred to as an intermediate transfer belt) that is a toner support material. This is a full-color image forming apparatus.

  The image output unit 1P is roughly divided into an image forming unit 10 (four stations a, b, c, and d are arranged in parallel, and the configuration is the same), a paper feeding unit 20, an intermediate transfer unit 30, a fixing unit. It consists of a unit 40 and a control unit (not shown). Further, each unit will be described in detail. Photosensitive drums 11a, 11b, 11c, and 11d as image carriers are pivotally supported at their centers and are driven to rotate in the direction of the arrow. The primary chargers 12a, 12b, 12c, and 12d, the laser scanner units 13a, 13b, 13c, and 13d, and the developing devices 14a, 14b, 14c, and 14d are arranged in the rotation direction facing the outer peripheral surfaces of the photosensitive drums 11a to 11d. ing.

  The primary charging rollers 12a to 12d give a uniform charge amount to the surfaces of the photosensitive drums 11a to 11d. Next, the laser scanner units 13a to 13d expose the photosensitive drums 11a to 11d with light beams such as laser beams modulated according to the recording image signal, thereby forming electrostatic latent images thereon. Details of the operation of the laser scanner unit will be described later.

  Further, the electrostatic latent images are visualized by developing devices 14a to 14d each containing developer of four colors such as yellow, cyan, magenta and black (hereinafter referred to as toner). On the downstream side of the image transfer regions N1a, N1b, N1c, and N1d where the visualized visible image is transferred to the intermediate transfer member, the image carrier is not transferred to the transfer material by the cleaning devices 15a, 15b, 15c, and 15d. The image carrier is cleaned by scraping off the toner remaining on 11a to 11d.

  By the process described above, image formation by each developer is sequentially performed. As the image carriers 11a to 11d, negative OPC photosensitive drums were used. Specifically, a negative organic semiconductor in which an azo pigment is used as a CGL layer (carrier generation layer) as a photoreceptor layer, and a mixture of hydrazone and resin is laminated thereon to a thickness of 29 μm as a CTL layer (carrier transport layer). Layer (OPC layer).

  Next, the cleaning devices 15a, 15b, 15c and 15d will be described. As the cleaning device, a counter blade method is used, and the free length of the cleaning blade is 8 mm. The cleaning blade is an elastic blade mainly composed of urethane, and is brought into contact with the image carrier with a pressure of about 35 g / cm.

  The sheet feeding unit 20 includes cassettes 21a and 21b and a manual feed tray 27 for storing the recording material P, pickup rollers 22a and b and 26 for feeding the recording material P one by one in the cassette or from the manual feed tray, and each pickup roller. A pair of paper feed rollers 23 and a paper feed guide 24 for conveying the recording material P sent out from the recording roller to the registration rollers, and for feeding the recording material P to the secondary transfer region Te in accordance with the image forming timing of the image forming unit. It consists of registration rollers 25a and 25b.

  The intermediate transfer unit 30 will be described in detail. The intermediate transfer belt 31 (for example, PET [polyethylene terephthalate] or PVdF [polyvinylidene fluoride] is used as its material) is energized by a drive roller 32 that transmits driving to the intermediate transfer belt 31 and a spring (not shown). As a result, the intermediate transfer belt 31 is wound around a tension roller 33 that applies an appropriate tension, and a driven roller 34 that faces the secondary transfer region Te across the belt. Among these, a primary transfer plane A is formed between the driving roller 32 and the tension roller 33.

  The drive roller 32 is coated with rubber (urethane or chloroprene) having a thickness of several millimeters on the surface of the metal roller to prevent slippage with the belt. The drive roller 32 is rotationally driven by a pulse motor (not shown). Primary transfer rollers 35 a to 35 d are arranged behind the intermediate transfer belt 31 in the primary transfer regions Ta to Td where the image carriers 11 a to 11 d and the intermediate transfer belt 31 face each other. A secondary transfer roller 36 is disposed so as to face the driven roller 34, and a secondary transfer region Te is formed by a nip with the intermediate transfer belt 31. The secondary transfer roller 36 is pressed with an appropriate pressure against the intermediate transfer member.

  A brush roller (not shown) for cleaning the image forming surface of the intermediate transfer belt 31 and a waste toner box (not shown) for storing collected toner are disposed on the intermediate transfer belt and downstream of the secondary transfer region Te. Is provided. A cleaning device 100 for cleaning the secondary transfer residual toner is provided on the intermediate transfer belt. The fixing unit 40 includes a fixing roller 41a having a heat source such as a halogen heater inside, a pressure roller 41b to which the roller is pressed (this roller may also have a heat source), and a transfer material to the nip portion of the roller pair. A guide 43 for guiding P, and an inner discharge roller 44 and an outer discharge roller 45 for further guiding the transfer material P discharged from the roller pair to the outside of the apparatus.

  The control unit includes a control board and a motor drive board (not shown) for controlling the operation of the mechanism in each unit. Further, the temperature / humidity sensor 50 is disposed at the illustrated position so that the environmental temperature and humidity around the apparatus can be accurately measured without being affected by the fixing unit 40 serving as a heat source in the apparatus. Various controls are performed based on the output. By the way, as a characteristic of the color toner, a weight average particle diameter of 5 to 8 μm is preferable for forming a good image.

Next, the configuration of the charging roller 12 will be described. It is formed of two layers of an electric resistance adjusting layer called a middle layer of the charging roller 12 and a surface layer in order to protect it from contamination such as a developer.
The electrical resistance adjusting layer is formed of a thermoplastic resin composition in which a polymer type ion conductive material is dispersed. The volume resistivity of the electric resistance adjusting layer is preferably 10 ⁻⁶ to 10 ⁻⁹ Ωcm. If it exceeds 10 ⁻⁹ Ωcm, charging ability and transfer ability are insufficient, and if the volume resistivity is lower than 10 ⁻⁶ Ωcm, leakage due to current concentration on the entire photosensitive drum 11 occurs.

  The electrical resistance adjusting layer is preferably made of polypropylene (PP), polymethyl methacrylate (PMMA), polystyrene (PS), and their copolymers (AS, ABS), polyamide, polycarbonate (PC), etc. It is composed of a thermoplastic resin. As the polymer type ion conductive material dispersed in these thermoplastic resins, a polymer compound containing a polyether ester amide component is preferable. Polyether ester amide is an ion conductive polymer material, and is uniformly dispersed and immobilized at a molecular level in a matrix polymer.

  Therefore, there is no variation in resistance value due to poor dispersion as seen in a composition in which an electron conductive conductive agent such as metal oxide or carbon black is dispersed. In addition, when a high applied voltage is applied as the charging roller 12, in the case of an electron conductive conductive agent, a path through which electricity easily flows is formed, so that a leakage current to the image carrier 11 is generated and charging is performed. In the case of the roller 12, a white / black spot image that is an abnormal image is generated. Since polyether ester amide is a polymer material, bleeding out hardly occurs. About a compounding quantity, since it is necessary to make resistance value into a desired value, it is necessary to make a thermoplastic resin into 20 to 70 weight% and a polymeric ion conductive agent to 80 to 20 weight%.

  Furthermore, an electrolyte (salt) can be added to adjust the resistance value. Examples of salts include alkali metal salts such as sodium perchlorate and lithium perchlorate, lithium imide salts such as lithium bisimide and lithium trismethide, ethyltriphenylphosphonium / tetrafluoroborate, tetraphenylphosphonium / bromide and the like. Grade phosphonium salts. The conductive agent may be used alone or in combination as long as the physical properties are not impaired.

  In order to uniformly disperse the conductive material in the matrix polymer at the molecular level, by adding a compatibilizing agent, micro-dispersion in the charging material becomes possible. Therefore, a compatibilizing agent may be appropriately used. Examples of the compatibilizing agent include those having a glycidyl methacrylate group which is a reactive group. In addition, an additive such as an antioxidant may be used as long as the physical properties are not impaired. There is no restriction | limiting in particular regarding the manufacturing method of a resin composition, It can manufacture easily by mixing each material, melt-kneading with a biaxial kneader, a kneader, etc.

  Moreover, the formation on the conductive support (core metal) as the electric resistance adjusting layer can be easily performed by coating the conductive resin composition on the conductive support by means of extrusion molding or injection molding. Can be done.

In this embodiment, the volume resistivity of the surface layer is made larger than the volume resistivity of the electric resistance adjusting layer. As described above, when the volume resistivity of the surface layer is larger than the volume resistivity of the electric resistance adjusting layer, it is possible to prevent voltage concentration at the defective portion of the image carrier 11 and occurrence of abnormal discharge. However, if the electric resistance value of the surface layer is too high, the charging ability will be insufficient, and therefore the difference in electric resistance value between the surface layer and the electric resistance adjusting layer is preferably 10 ³ Ωcm or less. As a material for forming the surface layer, a fluorine-based resin, a silicone-based resin, a polyamide resin, a polyester resin, and the like are excellent in non-adhesiveness and are preferable in terms of cleaning properties.

  Further, the surface layer is formed on the electric resistance adjusting layer by dissolving the constituent material of the surface layer in an organic solvent to prepare a coating material, and performing various coating methods such as spray coating, dipping and roll coating. The film thickness is preferably 10 to 30 μm.

  The surface layer material can be either one-component or two-component, but it can improve environmental resistance, non-adhesiveness, and releasability by using a two-component paint that also uses a curing agent. . In the case of a two-component paint, a method of crosslinking and curing the resin by heating the coating film is common. However, since the electrical resistance adjusting layer is made of a thermoplastic resin, it cannot be heated at a high temperature. As the two-component paint, it is effective to use a main component having a hydroxyl group in the molecule and an isocyanate resin that causes a crosslinking reaction with the hydroxyl group. By using an isocyanate resin, a crosslinking / curing reaction occurs at a relatively low temperature of 100 ° C. or lower.

  As a result of investigations from the non-adhesiveness of the toner, it was confirmed that the resin is a silicone-based resin having a high non-adhesiveness of the toner, and an acrylic silicone resin having an acrylic skeleton in the molecule is particularly good.

  The charging member (charging roller) 12 has an important electrical characteristic (electrical resistance value), so the surface layer needs to be conductive. As a method for making the surface layer conductive, there is a method of dispersing a conductive agent in a resin material constituting the surface layer. Such a conductive agent is not particularly limited. For example, conductive carbon such as ketjen black EC and acetylene black, rubber such as SAF, ISAF, HAF, FEF, GPF, SRF, FT, and MT. Carbon, color carbon with oxidation treatment, pyrolytic carbon, indium-doped tin oxide (ITO), tin oxide, titanium oxide, zinc oxide, copper, silver, germanium and other metals, and metal oxides, polyaniline , Conductive polymers such as polypyrrole and polyacetylene.

  In addition, there are ionic conductive materials as conductivity imparting materials, inorganic ionic conductive materials such as sodium perchlorate, lithium perchlorate, calcium perchlorate, lithium chloride, and further ethyltriphenylphosphonium tetrafluoroborate And organic ionic conductive substances such as quaternary phosphonium salts such as tetraphenylphosphonium bromide, modified fatty acid dimethylammonium ethosulphate, ammonium stearate acetate, and laurylammonium acetate.

  The charging device 12a, the image carrier 11a, and the image carrier cleaning unit 15a exist as an integral cartridge. By replacing the cartridge, the charging device 12a, the image carrier 11a, and the image carrier The body cleaning unit 15a can be replaced as a consumable at once. There are various types of cartridges, from those that can be replaced by service personnel to those that can be replaced by the user, but the cartridge used in this embodiment has a mechanism that can be replaced by the user. The exchange procedure is a mechanism displayed on a display installed in the main body.

  As described above, this image forming apparatus is a four-color full-color image forming apparatus in which four image forming units are arranged in tandem along the moving direction of an end-lease belt type intermediate transfer material that is a developer support material. However, the image forming units 10a, 10b, 10c, and 10d indicate yellow, magenta, cyan, and black, respectively. Images are formed on the intermediate transfer belt in the order of yellow, magenta, cyan, and black.

  As shown in FIG. 2, 11a, 11b, and 11c are yellow, magenta, and cyan image carriers, respectively, but an undercoat layer B, a charge generation layer C, and a charge transport layer D are formed on the support A, respectively. The organic photoconductors are laminated in the order of.

  The support A of the electrophotographic photosensitive member can be used without particular limitation as long as it has conductivity and does not affect the measurement of hardness. For example, a metal or alloy such as aluminum, copper, chromium, nickel, zinc and stainless steel formed into a drum shape can be used.

  The undercoat layer B is used for improving the adhesion of the photosensitive layer, improving the coating property, protecting the support, coating defects on the support, improving the charge injection from the support, or protecting the photosensitive layer from electrical breakdown. Formed for. Materials for the undercoat layer B include polyvinyl alcohol, poly-N-vinylimidazole, polyethylene oxide, ethyl cellulose, ethylene-acrylic acid copolymer, casein, polyamide, N-methoxymethylated 6 nylon, copolymer nylon, glue and Gelatin or the like can be used. These are dissolved in a suitable solvent and coated on a support. At that time, the thickness of the undercoat layer B is preferably 0.1 to 2 μm.

  Next, a photosensitive layer is formed on the undercoat layer B. In the case of forming a laminated photosensitive layer in which the charge generation layer C and the charge transport layer D are functionally separated and laminated, the charge generation layer C and the charge transport layer D are laminated on the undercoat layer B in this order.

  Here, as the charge generation material used for the charge generation layer C, selenium-tellurium, pyrylium, thiapyrylium dyes, various central metals and crystal systems, more specifically, for example, α, β, γ, ε, and X type Phthalocyanine compounds having a crystal form such as, anthanthrone pigments, dibenzpyrenequinone pigments, pyranthrone pigments, trisazo pigments, disazo pigments, monoazo pigments, indigo pigments, quinacridone pigments, asymmetric quinocyanine pigments, quinocyanine and JP-A No. 54-143645 Examples thereof include amorphous silicones described in the publication. In this example, a charge generation layer using a phthalocyanine compound capable of increasing sensitivity to achieve high image quality was used.

  In the case of this laminated type photoreceptor, the charge generation layer C comprises the above charge generation material in a 0.3 to 4 times amount of binder resin and solvent, homogenizer, ultrasonic dispersion, ball mill, vibration ball mill, sand mill, attritor, roll mill, etc. And the dispersion is applied on the undercoat layer and dried, or a film composed of a single composition of the charge generating material is used for the undercoat layer B by vapor deposition or the like. Form on top. The film thickness of the charge generation layer C is preferably 5 μm or less, and particularly preferably in the range of 0.1 to 2 μm.

  Examples of the binder resin include polymers and copolymers of vinyl compounds such as styrene, vinyl acetate, vinyl chloride, acrylic acid ester, methacrylic acid ester, vinylidene fluoride, trifluoroethylene, polyvinyl alcohol, polyvinyl acetal, polyvinyl Butyral, polycarbonate, polyester, polysulfone, polyphenylene oxide, polyurethane, cellulose resin, phenol resin, melamine resin, silicon resin, epoxy resin, and the like can be used.

  Next, the charge transport layer D is formed as follows. Suitable charge transport materials, for example, heterocyclic compounds such as poly-N-vinylcarbazole and polystyrylanthracene, polymer compounds having condensed polycyclic aromatics, heterocyclic compounds such as pyrazoline, imidazole, oxazole, triazole and carbazole, Low molecular weight compounds such as triarylalkane derivatives such as phenylmethane, triarylamine derivatives such as triphenylamine, phenylenediamine derivatives, N-phenylcarbazole derivatives, stilbene derivatives, hydrazone derivatives, etc. A resin similar to that described for the generation layer can be applied) and dispersed / dissolved in a solvent, and the solution is applied onto the charge generation layer C and dried using the above-mentioned known method.

  In this case, the ratio of the charge transport material to the binder resin is preferably 20 to 100, more preferably 30 to 100, when the total weight of both is 100. If the amount of the charge transporting material is less than that, the charge transporting ability is lowered, and problems such as a decrease in sensitivity and an increase in residual potential occur. The thickness of the charge transport layer D in the multilayer photoreceptor having the protective layer is preferably 1 to 50 μm, more preferably 3 to 30 μm. In this embodiment, the charge transport layer D is a photoreceptor having a thickness of 29 μm.

Next, the block circuit of the charging bias application system of this embodiment will be described. FIG. 4 is a block circuit diagram of a charging bias application system for the charging roller 12 used in this embodiment.
A predetermined vibration voltage (bias voltage Vdc + Vac) obtained by superimposing an AC voltage having a frequency f on a DC voltage from the power source S1 is applied to the charging roller 12 via a cored bar, whereby the peripheral surface of the rotating photosensitive drum 11 is predetermined. Is charged to a potential of. A power supply S1 that is a voltage application means for the charging roller 12 includes a direct current (DC) power supply 101 and an alternating current (AC) power supply 102.

  Reference numeral 103 denotes a control circuit which controls the DC power source 101 and the AC power source 102 of the power source S1 to be turned on and off so as to apply a DC voltage, an AC voltage, or a superimposed voltage of both to the charging roller 12. And a function of controlling the DC voltage value applied to the charging roller 12 from the DC power supply 1001 and the peak-to-peak voltage value of the AC voltage applied from the AC power supply 102 to the charging roller 12. Reference numeral 104 denotes an alternating current value measuring circuit as means for measuring the alternating current value flowing through the charging roller 12 via the photosensitive member 11. The AC current value information measured from the circuit 10 4 is input to the control circuit 10 3.

  Reference numeral 50 denotes an environmental sensor as a means for detecting the environment where the printer is installed. The detected environmental information is input from the environmental sensor 50 to the control circuit 103. The environmental information input to the control circuit 103 is temperature information and relative humidity information. The control circuit 103 calculates the absolute moisture amount from the input temperature and humidity information, and changes the setting of the charging high-pressure condition, the setting of the development high-pressure condition, the setting of the transfer high-pressure condition, and the like based on the calculated absolute moisture amount. . The charging high-voltage conditions can be changed by changing the charging high-voltage conditions during direct image formation or by changing the control conditions used for the control for determining the charging AC peak voltage applied during image formation, which will be described later. .

  If it is necessary to determine a suitable charging condition under the condition where the main body is placed, it is better to change the control condition used for the control to determine the charging AC peak voltage applied during the latter image formation. preferable. Then, the control circuit 103 uses the AC current value information input from the AC current value measurement circuit 104, and also the environmental information input from the environmental sensor 50, to the appropriate peak interval of the AC voltage applied to the charging roller 12 in the charging process of the printing process. It has a function of executing a voltage value calculation / determination program. Next, a general AC voltage control method for making the discharge current amount described in this embodiment constant will be described.

  Conventionally, the amount of discharge current quantified according to the following definition has been substituted for the actual amount of AC discharge, and has a strong correlation with the photoconductor drum scraping, image flow, and charging uniformity. Has been found.

  That is, as shown in FIG. 3, the alternating current Iac is in a linear relationship with respect to the peak-to-peak voltage Vpp, less than the charging start voltage Vth × 2 (V) (undischarged region), and gradually increases from that point toward the discharge region. In the direction of increasing current. In a similar experiment in a vacuum where no discharge occurs, a straight line is maintained, so this is considered to be the increment ΔIac of the current involved in the discharge.

Therefore, when the ratio of the current Iac to the peak-to-peak voltage Vpp less than the discharge start voltage Vth × 2 (V) is α, AC current such as current flowing to the contact portion (hereinafter referred to as nip current) other than current due to discharge The current becomes α · Vpp, and the difference between Iac measured when a voltage higher than the discharge start voltage Vth × 2 (V) is applied, and this α · Vpp,
ΔIac = Iac−α · Vpp Equation 1
To ΔIac is defined as a discharge current amount that indicates the amount of discharge instead.

  The amount of discharge current changes as the environment and durability are increased when charging is performed under the control of a constant voltage or a constant current. This is because the relationship between the peak-to-peak voltage and the discharge current amount and the relationship between the alternating current value and the discharge current amount are fluctuating. In the AC constant current control method, control is performed with the total current flowing from the charging member to the member to be charged.

  As described above, the total current amount is the sum of the nip current α · Vpp and the discharge current amount ΔIac that flows by discharging at the non-contact portion. In constant current control, the charged object is actually charged. In addition to the discharge current, which is the current required for the control, the nip current is controlled. For this reason, the amount of discharge current cannot actually be controlled. Even if the constant current control is performed with the same current value, the discharge current amount naturally decreases as the nip current increases due to the environmental variation of the charging member material, and the discharge current amount increases as the nip current decreases. Even with the current control method, it is impossible to suppress the increase / decrease in the amount of discharge current, and it has been difficult to realize both the shading of the photosensitive drum and the charging uniformity when aiming for a long life.

  Therefore, in this embodiment, the peak-to-peak voltage necessary for obtaining the predetermined discharge current amount D during the printing process is calculated every printing preparation rotation operation, and the obtained peak-to-peak voltage is set to a constant voltage during the printing process. The AC current is applied to the charging roller 12 while being controlled, and when the AC current value during the printing process is applied in the continuous printing mode and the peak-to-peak voltage (Vpp), which is an undischarged area, is applied to the charging roller 12 during the paper-to-paper process. Is used to correct the peak-to-peak voltage applied during the next printing process.

  This not only absorbs fluctuations in resistance values due to manufacturing variations of the charging roller 12 and environmental variations of the materials and high-pressure variations in the main unit, but also counters fluctuations in the resistance values of the charging roller 12 due to continuous printing. By making correction for each sheet, it is possible to reliably control with a desired discharge current amount. The control method as described above is hereinafter referred to as discharge current amount control.

  In this embodiment, charging AC setting to be applied to the charging roller is determined by the above-described discharge current control, and charging is performed as much as possible within a range in which halftone unevenness that is a poorly charged image, sand, fog, and the like can be prevented. The setting of the charging AC voltage is determined within a setting range in which the discharge amount from the roller can be reduced, thereby preventing the occurrence of image flow.

  In addition, since the image flow occurs in an environment where the amount of absolute moisture is particularly large, in this embodiment, the above-mentioned in-machine temperature / humidity sensor calculates the absolute amount of moisture inside the main body, and according to the absolute amount of moisture, The setting of the discharge current amount during the discharge current control is changed.

  In other words, in an environment with a large amount of absolute moisture, image flow is likely to occur, but charging failure is unlikely to occur, so the discharge current amount is set to be extremely small. However, even when the appropriate amount of discharge current is controlled as described above, when image formation with the low-duty image continues, or when the multi-rotation control is performed before returning from sleep when the main power is turned on, Since the supply amount of the abrasive in the developer supplied to the cleaning blade is reduced, and the ability to remove the discharge products adhering to the photosensitive drum is lowered, the image flow is likely to occur.

  The film thickness detection control of the photosensitive drum, which is a premise of the present invention, will be described. As shown in FIG. 4, as a life detecting means for detecting the film thickness of the photosensitive drum 11 between the photosensitive drum 11 and the ground, a DC bias and an AC bias are used as charging biases by contacting the photosensitive drum 11. A resistance R for measuring a direct current flowing from the charging roller 12 to which the superposed voltage is applied to the photosensitive drum 11 and a capacitor bypassing the alternating current are provided, and the resistance R is provided. Is measured by the control circuit 103, the current film thickness of the photosensitive layer of the photosensitive drum 11 is detected by the control circuit 103 based on the measured value, and the current film thickness of the photosensitive drum 11 is detected by the control circuit 103. It is configured to make a judgment.

FIG. 5 is a graph showing changes in the direct current flowing through the photosensitive drum 11 when the film thickness of the photosensitive drum 11 changes with the charging potential kept constant.
As can be seen from FIG. 5, the direct current flowing through the photosensitive drum 11 increases as the photosensitive layer thickness decreases. Generally, the drum thickness detecting means is used to calculate the life of the photosensitive drum 11. That is, by measuring the change in film thickness of the photosensitive drum 11, the limit until the image defect of the cartridge including the photosensitive drum 11 is predicted.

  However, the relationship between the thickness of the photosensitive drum 11 and the DC current value as shown in FIG. 5 differs depending on the material of the photosensitive drum 11, the rotational speed of the photosensitive drum of the image forming apparatus, and the like.

  In the present embodiment, as a means for detecting the film thickness of the photosensitive drum, the case where the DC current detection circuit 103 as the lifetime detecting means is provided between the photosensitive drum 11 and the ground has been described. The aforementioned DC current detection circuit 103 may be provided between the charging roller 12 and the charging bias application power source S1 or between the charging bias application power source S1 and the ground.

  Here, with respect to the photosensitive drum film thickness prediction control to be calculated by obtaining a differential current from the initial reference current, which is performed in order to increase the prediction accuracy of the film thickness change of the photosensitive drum according to the present embodiment, Details will be described.

  In the conventional method, as shown in the flowchart and the control circuit diagram of FIG. 6 and FIG. 12, the main body CPU 201 applies a direct current to the charging roller 12 by the charging DC high voltage applying means 205 and the charging AC voltage applying means 203. The application of the voltage and the AC voltage is instructed, and the DC current amount flowing from the charging roller 12 to the photosensitive drum 11 at the time of application is detected by the DC current detecting means 210. Based on the detected DC current amount, as shown in FIG. Based on the relationship between the direct current and the film thickness of the photosensitive drum, the current film thickness of the photosensitive drum is predicted, and image control and life prediction of the drum cartridge have been performed according to the predicted film thickness.

  In this embodiment, in order to more accurately predict the film thickness of the photosensitive drum, the reference current is detected in the initial state of the photosensitive drum as described below, and the photosensitive member is detected based on the difference current from the reference current. Control is performed to predict the film thickness of the drum. The conventional photosensitive drum film thickness detection control will be described in more detail with reference to FIGS. 7 and 12. As shown in the flowchart of FIG. 7, the photosensitive drum film thickness detection control is executed (A1). Then, the main body CPU 201 causes the charging DC high voltage applying means 205 and the charging AC high voltage applying means 206 to apply a high voltage to the charging roller 12 so that the photosensitive drum has a predetermined drum potential (A2).

  Subsequently, the amount of direct current flowing from the charging roller 12 to the photosensitive drum 11 is detected by the charging direct current detecting means 210 (A3). After detecting the direct current, the CPU determines whether the drum cartridge is in an unused initial state or in use (A4). A method for determining whether or not a drum cartridge is unused is a feature of the present invention. Conventionally, there are generally two methods for detecting whether or not a drum cartridge is used.

  First, there is a method in which the main body CPU recognizes that the drum cartridge is in an initial state by pressing a switch for prompting an initial initialization operation on the drum cartridge present on the operation unit. Also, the second is equipped with a fuse on the side of the drum cartridge to determine whether it is new or old.When the main power is turned on with the drum cartridge in the main body, the fuse is blown off. The CPU recognizes the timing when the fuse is blown as the initial state of the drum cartridge. When the fuse is already blown in advance, it is generally determined that the drum cartridge is in use.

  When determining that the drum cartridge is in the initial state, the main body CPU stores the amount of direct current flowing from the charging roller 12 detected above to the photosensitive drum 11 in the memory 202 as the initial reference current α (A5). In this case, the photosensitive drum film thickness detection control is terminated (A10). On the other hand, if the drum cartridge is in use, the amount of direct current flowing from the charging roller 12 detected above to the photosensitive drum 11 is stored in the memory 202 as β (A6).

  Subsequently, the main body CPU 201 calculates a differential current γ between the initial reference current α stored in the memory 202 and the detected DC current amount β when the drum cartridge is in the initial state (A7). Here, FIG. 10 shows the relationship of the differential current γ between the initial reference current α related to the present embodiment and the detected DC current amount β. The main body CPU 201 predicts the photosensitive drum film thickness of the drum cartridge from the relationship between the calculated differential current γ and the photosensitive drum film thickness in FIG. 10 (A8). The main body CPU feeds back to the image control conditions according to the predicted film thickness of the photosensitive drum, laser exposure means 204, charging DC high voltage application means 205, charging AC voltage application means 203, development high voltage application means 206, and 1 The setting of the next transfer high voltage applying means 208 and the like is changed.

  Generally, as the film thickness of the photosensitive drum decreases, the developability improves, so the difference between the light and dark potentials on the photosensitive drum, which is determined by the charging DC high voltage, the amount of laser light, etc., so-called latent image contrast. Therefore, it is desirable to change the conditions of the charging direct current high voltage means and the laser exposure means. In addition, it is desirable to reduce the charging AC voltage according to the film thickness of the photosensitive drum. If the charging AC voltage is not changed, an overcurrent is generated, which promotes the wear and scratches of the photosensitive drum. It might be. Similarly, the primary transfer high pressure is preferably reduced according to the film thickness of the photosensitive drum.

  Next, with respect to the photosensitive drum film thickness detection control according to the present embodiment, details of the control will be described using the sequence chart of FIG. As shown in the sequence chart of FIG. 8, the photosensitive drum film thickness control is performed after the control in the preparation stage after the main power is turned on (so-called pre-multi-rotation control), or when the predetermined number of drums or the predetermined number of drum rotations is reached. In general, the control is performed by intervening between the sheets, and from the viewpoint of productivity, the control is performed only after the previous multiple rotations at the time of the main power supply. It has been devised to make it larger so that control does not enter too often.

  In this embodiment, the photosensitive drum film thickness detection control is set so that the control is performed after the pre-multi-rotation control after the main power is turned on and by interruption every 1000 sheets. The main body CPU 201 sequentially turns off the charging DC high voltage 205, the charging AC high voltage 203, the development high voltage 206, and the primary transfer high voltage 208 after the pre-multi-rotation control and 1000 sheets passed. After all the high voltages are turned off, the primary transfer high voltage 208, the charging DC high voltage 205, the charging AC voltage 203, and the development high voltage 206 are applied in this order.

  Only when the charging DC high voltage 205 and the charging AC voltage 203 are superimposed can be held at a predetermined drum potential, it is desirable that the charging DC high voltage 205 and the charging AC voltage 203 are applied at substantially the same timing. As described above, in order to stabilize the photosensitive drum potential, it is desirable to set the charging AC voltage 203 to about twice or more of the charging DC voltage 201. In many cases, discharge current control is performed. Further, the charging DC high voltage 205 at the time of detecting the photosensitive drum film thickness is generally set under conditions different from normal image forming conditions.

  Since the setting of the charging DC high voltage 205 at the time of normal image formation is determined by conditions determined by image density control or the like, it changes randomly depending on the environment, the number of sheets used, and the like. However, when the photosensitive drum film thickness is detected, it is necessary to calculate the difference current γ between the DC current reference current α and the DC current β at that time, as described above. Therefore, the reference current α and the DC current β The potential conditions must be the same. That is, when the photosensitive drum potential changes, the direct current β greatly changes. Therefore, in order to control the photosensitive drum with a constant potential, the charging DC voltage 205 must be kept constant. .

  Further, in this embodiment, a pre-exposure neutralization unit is provided, and the pre-exposure neutralization unit is ON during control. The pre-exposure neutralizing means is selected so that it emits light sufficiently and the photosensitive drum potential can be sufficiently eliminated. In general, 10 to 50 μW is preferable, but in this embodiment, it is set to 30 μW. If the pre-exposure means does not perform static elimination, the drum potential after passing through the primary transfer section is not neutralized, and the drum after passing through the primary transfer section depends on the primary transfer high-pressure conditions and environmental conditions. Since the potential fluctuates, a stable DC current cannot be detected.

  The DC current is stabilized by emitting pre-exposure until the photosensitive drum potential is neutralized and canceled to 0V. In this embodiment, the development high voltage 206 is applied almost simultaneously with the charging DC high voltage 205 and the charging AC high voltage 203. This is because the potential difference between the photosensitive drum potential and the development potential is the same as that at the time of image formation. The purpose is to keep the potential difference. If the potential difference between the photosensitive drum potential and the developing potential, so-called Vback, becomes too large, the carrier in the developer adheres to the photosensitive drum, so-called carrier adhesion occurs. However, unlike the present embodiment, this method may be used because carry-off can be prevented if rotation of the developing sleeve is stopped even when the development high voltage 206 is not applied.

Example 1
With reference to the control flow of FIG. 1, a method for determining whether or not the usage status of the drum cartridge is unused by the photosensitive drum film thickness detection control of the present invention will be described.
As shown in the flowchart of FIG. 1, when the photosensitive drum film thickness detection control is executed (B1), the main body CPU 201 causes the charging direct current high voltage applying means 205 to set the photosensitive drum at a predetermined drum potential. The charging AC high voltage applying means 206 applies a high voltage to the charging roller 12, and the charging DC current detecting means 210 detects the DC current amount β (μA) flowing from the charging roller 12 to the photosensitive drum 11 (B2).

  The CPU calculates a difference current value γ = α−β which is a difference between the direct current value α (μA) detected at the previous film thickness detection control and the direct current amount β (μA) detected at B2 (B3 ). When the value of γ is γ ≧ 20, after the film thickness detection control is finished (B4), it is determined that a new drum cartridge is unused, and the initial installation counter is reset (B5 ). Counters that should be reset when a new cartridge is inserted include the drum rotation time integrated value, the charging high voltage application time integrated value, the sheet passing number integrated value, etc. since the previous drum cartridge replacement. Therefore, it is desirable to start a new integration from the current timing of inserting the drum cartridge. Since the number of sheets to be passed depends on the size of the paper, it is generally integrated by A4 size conversion.

  If the value of γ is γ ≧ 20, adjustment control and special mode are executed (B6). As the adjustment control, toner patch density control, which is control related to image density, color shift correction control, update of initial current value of drum film thickness detection control, and the like should be performed. For toner patch control, a digitally created patch image is transferred onto the intermediate transfer belt, the density of the patch formed on the intermediate transfer belt is detected, charging potential setting, development potential setting, transfer potential setting, laser There are image density control that appropriately adjusts the density by reflecting it in power settings and the like, and development density control that adjusts the ratio of toner and carrier in the developing device, so-called T / D ratio.

  These may be the case when the drum cartridge is new and the photosensitive drum film thickness is suddenly reset to the initial state, or the charging roller surface contamination state changes abruptly and the resistance is drastically reduced to the initial state. If reset, the image density will fluctuate greatly if the charging potential setting, development potential setting, transfer potential setting, and laser power setting before the new drum cartridge is inserted. It is extremely important to carry out the image control and the development density control.

  As for color misregistration correction, when the drum changes to a new drum and the drum film thickness increases, the outer diameter of the drum changes, which may affect color misregistration. It is desirable to implement the deviation correction control.

  Regarding drum film thickness detection control, if the initial current value set at the initial state of the previous drum is maintained, fluctuations in the current value corresponding to the solid variation of the drum film thickness cannot be absorbed. There is a risk that detection will not be possible. Therefore, when the drum becomes new, it is desirable to reset the initial current value again and store it again.

  What should be implemented as the special mode is implementation of the toner supply mode. As described above, since no toner is supplied to the photosensitive drum cleaning member of the initial drum cartridge, the initial drum cartridge is likely to cause a phenomenon such as blade squealing or blade wobbling. Therefore, it is preferable to implement a mode in which toner is supplied to the blade.

  If the value of γ is γ <20, the CPU determines that there is no evidence that the drum cartridge has been replaced with a new one, performs the film thickness detection control as normal, and terminates (B7). Subsequently, the normal image forming operation is started (B8).

  FIG. 9 shows a schematic diagram of a direct current value flowing from the charging roller to the drum when an unused drum cartridge is inserted into the main body, used for a while, and then an unused drum cartridge is again inserted into the main body. It can be seen that the DC current value greatly changes when the drum cartridge is changed to a new one.

  Of course, in this embodiment, the value of the difference current value γ, which is the difference between the DC current value α detected at the previous film thickness detection control and the DC current amount β detected by B2, is 20 μA or more, and it is new. Although it was determined whether or not the cartridge was inserted, the relationship between the drum film thickness change and the DC current change also varies depending on the film thickness and material of the drum and the type of the charging roller as shown in FIG. It is necessary to determine a threshold value for determining whether or not a new cartridge has been inserted in the above configuration. In the configuration of the present embodiment, the threshold value for determining whether or not a new cartridge has been inserted is appropriately 15 to 30 μA, but in order to reliably determine that it is a new drum cartridge, 20 μA is used. did.

  As described above, it is possible to determine whether or not a new drum cartridge has been inserted into the main body from the amount of change in the DC current value flowing from the charging roller to the drum that can be detected during drum film thickness detection control. Therefore, it is possible to automatically determine whether a drum cartridge is new or old without adding a new fuse or new detection member such as a special fuse to the drum cartridge, and to perform necessary counter reset, control, special mode, etc. became.

(Example 2)
Here, the toner density control by the patch detection ATR related to the present case will be described. As shown in the circuit diagram of FIG. 12, the CPU 201 of the image forming apparatus according to the present embodiment is sandwiched between the trailing edge of the latent image of the preceding image and the leading edge of the latent image formed thereafter during continuous image formation. In addition, an electrostatic latent image (patch latent image) of the toner patch is formed in the non-image area (hereinafter referred to as “between images”). The patch latent image is developed with toner to form a toner patch (toner pattern) for controlling the toner density.

  The printer control unit is provided with a toner patch signal generation circuit (pattern generator) 212 that generates a toner patch signal so that a toner patch having a predetermined density is formed. The toner patch signal from the pattern generator 212 is supplied to the pulse width modulation circuit 213 to generate a laser driving pulse having a pulse width corresponding to the above-described predetermined density. The laser driving pulse is supplied to the semiconductor laser of the laser scanner, and the semiconductor laser is caused to emit light for a time corresponding to the pulse width, and the photosensitive drum 11 is scanned and exposed.

  As a result, a patch latent image corresponding to the predetermined density is formed on the photosensitive drum 11. Next, the patch latent image is developed by the developing device 14 and transferred onto the intermediate transfer belt 30 to form a toner patch on the intermediate transfer belt 30. When the density of the toner patch is higher than the predetermined density, the CPU 201 determines that the toner density is high and decreases the toner supply amount. When the toner density is low, the CPU 201 determines that the toner density is low and the toner supply amount. Increase. The above is the general patch detection ATR.

  As shown in the control circuit diagram of FIG. 13, the amount of reflected light from the toner patch formed on the intermediate transfer belt 30 is measured by the image density sensor 77. The image density sensor 77 includes a light emitting unit including a light emitting element such as an LED, and a light receiving unit including a light receiving element such as a photodiode (PD). The image density sensor 77 measures the amount of reflected light at the timing when the toner patch formed between “images” on the photosensitive drum 11 passes under the image density sensor 77. A signal related to the measurement result is input to the CPU 201. Thereafter, the CPU 201 obtains a correction amount (described later) of the replenishment toner amount estimated to obtain a desired constant density (amount of reflected light).

  In more detail below, the reflected light (near infrared light) from the photosensitive drum 11 input to the image density sensor 77 is converted into an electrical signal. The electric signal of 0 to 5V is converted into an 8-bit digital signal by an A / D conversion circuit 78 provided in the control unit. The digital signal is converted into density information by a density conversion circuit 79 provided in the control unit.

  FIG. 14 is a diagram showing the relationship between the output of the image density sensor 77 and the density of the output image when the density of the toner patch formed on the photosensitive drum 1 is changed stepwise by the area gradation of each color. Note that the output of the image density sensor 77 in a state where the toner is not attached to the photosensitive drum 11 is set to 5 V, that is, 255 level.

  As shown in FIG. 14, the area coverage by each toner increases, and the output of the image density sensor 77 decreases as the image density increases. Based on the characteristics of the image density sensor 77, a table 79a dedicated to each color for converting the output of the image density sensor 77 into a density signal is prepared in advance. The table 79a is stored in the storage unit of the density conversion circuit 79. Thereby, the density conversion circuit 79 can accurately read the image density for each color. The density conversion circuit 79 outputs the density information to the CPU 102.

  The toner patch density signal is set to 128 levels out of 255 levels (density 0.8) by toner density control by the patch detection ATR method. Therefore, the toner patch density should be 0.8. However, the image characteristics of the image forming apparatus may always change. Therefore, the measurement result of the toner patch density by the image density sensor 77 is not always 0.8. For example, when a toner patch is formed in a state where the toner charge amount immediately after the power supply of the image forming apparatus is turned on, the toner patch is formed at a density higher than 0.8 (for example, 0.9).

  On the other hand, when a toner patch having an increased toner charge amount due to a change in humidity or the like is formed, the toner patch is formed at a density lower than 0.8 (for example, 0.7) depending on how the humidity changes. Therefore, the CPU 102 is based on the difference ΔD (± 0.1 in the above case) between the reference density signal (predetermined density 0.8) of the toner patch obtained at the initial setting and the measurement result (toner patch density). The amount of toner supplied into the developing device 14 is controlled. As a result, although there is a certain amount of ripple, the toner density in the developing device 14 has a good and constant density transition. This is patch ATR control.

Next, a method for determining whether or not the drum cartridge is used by the photosensitive drum film thickness detection control of the present invention will be described using the control flow of FIG.
In the configuration in the present embodiment, the threshold value for determining whether or not a new cartridge has been inserted is appropriately 15 to 30 μA. In the first embodiment, in order to reliably determine that the cartridge is a new drum cartridge. 20 μA, but 15 μA or 30 μA can also be determined. However, if the threshold value is too small, there is a possibility that detection may be erroneously detected, for example, when a foreign object exists in the charging roller and a low current flows instantaneously.

  If the threshold value is too large, the possibility of erroneous detection by detecting even when leakage from the charging roller to the photosensitive drum due to drum spots or the like occurs is not zero. Therefore, in this embodiment, the determination threshold is set to 15 μA, and the double check method based on the toner patch density is used in order to minimize the possibility of erroneous detection.

  As shown in the flowchart of FIG. 15, when the photosensitive drum film thickness detection control is executed (C1), the main body CPU 201 sets the charging DC high voltage applying means 205 so that the photosensitive drum has a predetermined drum potential. The charging AC high voltage applying means 206 applies a high voltage to the charging roller 12, and the charging DC current detecting means 210 detects the DC current amount β (μA) flowing from the charging roller 12 to the photosensitive drum 11 (C2).

  The CPU calculates a difference current value γ = α−β which is a difference between the direct current value α (μA) detected at the previous film thickness detection control and the direct current amount β (μA) detected at C2 (C3 ). When the value of γ is γ ≧ 15, after the film thickness detection control is finished (C4), the patch toner image is further transferred onto the intermediate transfer belt 30 by the same method as the patch ATR control method as described above. And the density of the formed patch toner image is detected by the image density sensor 77.

  The density of the toner patch detected this time is detected from the relationship between the output of the image density sensor 77 in FIG. 14 and the density of the output image, and the detection result is stored in the CPU 102 as Y (0 to 255). The CPU calculates the relationship between the previous toner patch density detection result X (0 to 255) and the currently detected toner patch density detection result Y. Specifically, the value of W = XY, which is the difference between the previous toner density detection result X and the current toner density detection result Y, is calculated. If W ≧ 20, a new drum cartridge is unused. It is judged that it has been turned on, and the counter at the time of initial installation is reset (C6).

  As the deterioration of the drum progresses due to exposure, the sensitivity of the charge generation layer becomes dull, and it is common that the latent image contrast cannot be obtained even when exposed with the same amount of laser light. In other words, when the deterioration of the drum progresses due to use of the drum, the density of the toner patch imaged under the same image forming conditions is lowered. However, as in this embodiment, when a new drum cartridge is inserted, the deterioration of the drum is reset, so even if the toner patch density is created under the same imaging conditions as described above, the density is It becomes high at a stretch.

  Therefore, if the value of W = XY, which is the difference between the previous toner density detection result X and the current toner density detection result Y, is calculated as in this embodiment, if the difference is large due to the difference, unused It can be detected that a new drum cartridge is inserted. Counters that should be reset when a new cartridge is inserted include the drum rotation time integrated value, the charging high voltage application time integrated value, the sheet passing number integrated value, etc. since the previous drum cartridge replacement. Therefore, it is desirable to start a new integration from the current timing of inserting the drum cartridge. Since the number of sheets to be passed depends on the size of the paper, it is generally integrated by A4 size conversion.

  When the value of γ is γ ≧ 15, the adjustment control is executed and the special mode is executed (C7). As the adjustment control, toner patch density control, which is control related to image density, color shift correction control, update of initial current value of drum film thickness detection control, and the like should be performed.

  In this embodiment, the toner patch control is executed during the control flow of FIG. The detected patch density is reflected in the charging potential setting, development potential setting, transfer potential setting, laser power setting, etc., and the density is adjusted appropriately to adjust the toner / carrier ratio in the developer, the so-called T / D ratio. It is desirable to do.

  These may be the case when the drum cartridge is new and the photosensitive drum film thickness is suddenly reset to the initial state, or the charging roller surface contamination state changes abruptly and the resistance is drastically reduced to the initial state. If reset, the image density will fluctuate greatly if the charging potential setting, development potential setting, transfer potential setting, and laser power setting before the new drum cartridge is inserted. It is extremely important to carry out the image control and the development density control.

  As for color misregistration correction, when the drum changes to a new drum and the drum film thickness increases, the outer diameter of the drum changes, which may affect color misregistration. It is desirable to implement the deviation correction control.

  Regarding drum film thickness detection control, if the initial current value set at the initial state of the previous drum is maintained, fluctuations in the current value corresponding to the solid variation of the drum film thickness cannot be absorbed. There is a risk that detection will not be possible. Therefore, when the drum becomes new, it is desirable to reset the initial current value again and store it again.

  What should be implemented as the special mode is implementation of the toner supply mode. As described above, since no toner is supplied to the photosensitive drum cleaning member of the initial drum cartridge, the initial drum cartridge is likely to cause a phenomenon such as blade squealing or blade wobbling. Therefore, it is preferable to implement a mode in which toner is supplied to the blade.

  If W <20, it is determined that there was a deficiency in the calculation of the differential current value γ = α-β, because a new unused drum cartridge was not inserted. No film thickness detection is performed (C8).

  Similarly to Example 1, when the value of γ is γ <15, the CPU determines that there is no evidence that the drum cartridge has been replaced with a new one, and performs film thickness detection control as normal, End (C8). Subsequently, the normal image forming operation is started (C9).

  As described above, it is possible to determine whether or not a new drum cartridge has been inserted into the main body from the amount of change in the DC current value flowing from the charging roller to the drum that can be detected during drum film thickness detection control. Therefore, it is possible to automatically determine whether a drum cartridge is new or old without adding a new fuse or new detection member such as a special fuse to the drum cartridge, and to perform necessary counter reset, control, special mode, etc. became. In the second embodiment, the toner patch density is measured and a change in the density is detected, thereby enabling a double check to be performed to improve the accuracy of determining whether or not the drum cartridge has been changed to a new one. Yes.

205 charging DC high voltage applying means, 206 charging AC high voltage applying means, 12 charging roller,
210 Charging DC current detection means, 11 photosensitive drum

Claims (2)

An image carrier, a charging member that charges the image carrier, an exposure unit that exposes the image carrier charged by the charging member to form an electrostatic image, and an image carrier formed on the image carrier. Developing means for developing the electrostatic image with toner, transfer means for transferring the developed toner image to the intermediate transfer member, charging current detection means for detecting a direct current flowing between the charging member and the image carrier, In an image forming apparatus comprising: a density detecting unit that detects a density of a toner patch image formed on the intermediate transfer member; and a counting unit that counts the amount of use of the image carrier .
When the difference between the detected current amount detected by the charging current detecting means and the previous detected current amount is smaller than the predetermined current amount, the count of the counting means is maintained, and when the detected current amount difference is equal to or larger than the predetermined current amount, The detected density of the toner patch image by the density detecting means is compared with the previous detected density, and when the detected density difference is smaller than a predetermined density, the count of the counting means is maintained, and the detected density difference is The image forming apparatus according to claim 1, wherein the count unit resets the count when the density is equal to or higher than a predetermined density. The image forming apparatus according to claim 1, wherein the counting unit counts a usage amount of the image carrier and a usage amount of the charging member.