JP2020012930A - Image forming apparatus - Google Patents

Abstract

To make it possible to accurately determine the state of deterioration of a carrier in an image forming apparatus to which a two-component developing system is applied.SOLUTION: A mode control unit 984 changes the frequency of the AC voltage of a developing bias while maintaining constant the potential difference of the DC voltage between a developing roller 231 and a photoreceptor drum 20. The mode control unit 984 determines the state of deterioration of a carrier on the basis of the relationship between a change in the amount of the frequency and the amount of change in the value of a current measured by a current measuring unit 973 when a latent image absence area where an electrostatic latent image is not formed faces the developing roller 231 on the surface of the photoreceptor drum 20, the value of the current flowing between an image carrier and developing roller.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus to which a two-component developing method is applied.

  2. Description of the Related Art Conventionally, an image forming apparatus that includes a photosensitive drum (image carrier), a developing device, and a transfer member and forms an image on a sheet is known. In such an image forming apparatus, the electrostatic latent image formed on the photosensitive drum is visualized by the developing device, and a toner image is formed on the photosensitive drum. Then, the toner image is transferred to the sheet by the transfer member. Further, as a developing technique for making a latent electrostatic image visible and forming a toner image, a two-component developing technique using a developer containing a toner and a carrier is known.

  In the two-component development, a phenomenon is seen in which the developer is deteriorated under the influence of the number of prints, environmental fluctuation, print mode (continuous number of prints per job), print ratio, and the like. As a result, problems such as a decrease in image density, occurrence of toner fog, and an increase in toner scattering occur. To cope with such problems, conventionally, the deterioration state of the developer is predicted from the number of printed sheets, environmental fluctuations, printing mode, printing rate, etc., and the toner density, the developing bias, the surface potential of the photoconductor, the rotation speed of the developing roller, In addition, a technique has been employed in which the output of a suction fan that collects scattered toner is adjusted to suppress a decrease in image density, deterioration of toner fogging, and deterioration of toner scattering.

  However, these techniques are only combinations of predictions under the respective conditions of the number of prints, environmental fluctuations, print mode, and print ratio, and when a plurality of conditions change in a complex manner, the deterioration state of the developer is reduced. It was difficult to predict accurately.

  For this reason, a technique for accurately predicting the charge amount of the toner has been proposed as an indicator of the state of deterioration of the developer. For example, in Patent Documents 1 to 3, when a developing bias is applied to a developing roller carrying a developer, a current value of a current flowing between the photosensitive drum and the developing roller (hereinafter referred to as a developing current) is measured. Is done. Then, the measured current value of the developing current is calculated as the amount of charge of the toner moved to the photosensitive drum. Further, the amount of developed toner is calculated from the measurement result of the image density of the developed toner layer. Then, the charge amount of the toner is calculated from the charge amount of the toner and the development amount of the toner.

Japanese Patent No. 5024192 Patent No. 5273542 Patent No. 4480066

  However, in the above-described conventional technology, when an area where an electrostatic latent image is not formed (hereinafter, a latent image-free area) is opposed to the developing roller, a current flowing through a carrier in which toner does not move (hereinafter, referred to as a current). , The carrier current) may be measured as the current value of the developing current. For this reason, the current value of the measured development current is erroneously calculated as being the charge amount of the toner transferred from the developing roller to the photosensitive drum, and the toner charge amount is calculated using the erroneously calculated charge amount of the toner. There is a possibility that the charge amount is incorrectly calculated.

  Here, if the current value of the carrier current is a constant value, a current value obtained by excluding the fixed value from the measured current value of the developing current may be calculated as the toner charge amount. However, when the opportunity for development increases and the opportunity for transporting the developer to the developing roller increases, the toner may rub against the carrier, so that the carrier may be abraded or deteriorated due to contamination. As a result, a change occurs in the resistance value and the impedance of the carrier, and the current value of the carrier current may not be constant.

  As described above, in the conventional technique, the deterioration state of the carrier is not accurately grasped, and the current value of the carrier current is not accurately excluded from the measured current value of the developing current. Therefore, the charge amount of the toner is accurately calculated. It was difficult. For this reason, the charge amount of the toner cannot be accurately predicted, and the deterioration state of the developer may not be accurately grasped.

  SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and an object of the present invention is to enable a deterioration state of a carrier to be accurately determined in an image forming apparatus to which a two-component developing method is applied.

  An image forming apparatus according to an aspect of the present invention includes an image carrier that is rotated to form an electrostatic latent image on a surface thereof, and that carries a toner image in which the electrostatic latent image is made visible, An exposure device that forms the electrostatic latent image on the surface of a body; and an exposure device that is disposed to face the image carrier, is rotated, carries a developer including a toner and a carrier on a peripheral surface, and includes a toner on the image carrier. A developing roller that forms the toner image by supplying the developing roller, a developing bias applying unit that can apply a developing bias in which an AC voltage is superimposed on a DC voltage to the developing roller, and the image carrier and the developing roller. A current measuring unit that measures a current value of a current flowing therebetween, and changing a frequency of an AC voltage of the developing bias while maintaining a constant potential difference of a DC voltage between the developing roller and the image carrier, The circumference A carrier which is a current value measured by the current measuring unit when the amount of change in the number and a latent image-free area where the electrostatic latent image is not formed on the surface of the image carrier is opposed to the developing roller. A determination unit configured to determine a deterioration state of the carrier based on a relationship between the amount of change in the current value and the amount of change in the current value.

  When the developing roller and the latent image-free area on the surface of the image carrier are opposed to each other, the developing is applied to the developing roller while maintaining a constant DC voltage potential between the developing roller and the latent image-free area. It is assumed that the frequency of the bias AC voltage is changed. In this case, the relationship between the amount of change in the frequency and the amount of change in the carrier current value, which is the current value of the current flowing between the non-latent image area and the developing roller, differs according to the deterioration state of the carrier. Found that.

  Specifically, the carrier can be represented by a parallel circuit in which a resistor and a capacitor are connected in parallel. When the frequency of the developing bias increases, the impedance of the capacitor included in the parallel circuit decreases, so that the impedance of the carrier decreases. Therefore, the carrier current value increases as the frequency increases. When the frequency of the developing bias decreases, the impedance of the capacitor increases, and the impedance of the carrier increases. Therefore, the carrier current value decreases as the frequency decreases. From these facts, the inventors have found that the relationship between the amount of change in the frequency and the amount of change in the carrier current value can be approximated by a straight line having a positive slope.

  Further, as the carrier is removed, the resistance value of the resistor included in the parallel circuit decreases, and the carrier current value increases. For this reason, the inventor has found that the inclination of the straight line increases as the carrier is removed. On the other hand, as the carrier becomes contaminated, the resistance value of the resistor included in the parallel circuit increases, and the carrier current value decreases. For this reason, the inventor has found that the inclination of the straight line decreases as the carrier becomes contaminated.

  Therefore, according to this configuration, as the inventor has found, when the developing roller and the latent image-free area are opposed to each other, the potential difference of the DC voltage between the developing roller and the image carrier is kept constant. When the frequency of the AC voltage of the developing bias is changed in this state, the relationship between the amount of change in the frequency and the amount of change in the carrier current value can be approximated by a straight line with a positive slope, and the slope of the straight line is the carrier. Utilizing the fact that it differs depending on the deterioration state of the carrier, the deterioration state of the carrier can be accurately determined.

  The determining unit may determine whether the carrier has deteriorated according to whether a slope of a measurement straight line indicating a relationship between a change amount of the carrier current value and a change amount of the frequency is larger than a predetermined reference slope. You may decide.

  According to this configuration, the deterioration state of the carrier is regularly determined according to whether or not the slope of the measurement straight line indicating the relationship between the amount of change in the carrier current value and the amount of change in the frequency is greater than a predetermined reference slope. can do.

  Further, the determination unit may determine that the greater the inclination of the measurement straight line is greater than the reference inclination, the greater the deterioration of the carrier due to scraping.

  According to this configuration, it is possible to appropriately determine that the greater the inclination of the measurement straight line is greater than the reference inclination, the greater the deterioration of the carrier due to abrasion, utilizing the knowledge of the inventor described above.

  When the inclination of the measurement straight line is larger than a predetermined first inclination larger than the reference inclination, the determination unit may determine that the life of the carrier due to scraping has come.

  According to this configuration, using the knowledge of the inventor described above, when the inclination of the measurement straight line is larger than the first inclination that is larger than the reference inclination, the degree of carrier deterioration due to scraping corresponds to the first inclination. It is possible to appropriately determine that the life of the carrier due to scraping has come.

  In addition, first life expectancy information indicating a relationship between a first difference calculated by subtracting the inclination of the measurement straight line from the first inclination and a life expectancy until the carrier comes to life due to scraping is stored in advance. The determination unit calculates the first difference when the inclination of the measurement straight line is greater than the reference inclination and equal to or less than the first inclination, and the carrier reaches its life due to scraping. It may be determined that the life expectancy up to is the life expectancy associated with the calculated first difference in the first life expectancy information.

  According to this configuration, using the first life expectancy information stored in advance in the storage unit, the inclination of the measurement straight line is calculated from the first inclination used to determine whether the life of the carrier due to scraping has come. However, the remaining life until the life of the carrier due to abrasion can be properly grasped depending on how small it is.

  Further, the determination unit may determine that the deterioration of the carrier due to contamination is greater as the inclination of the measurement straight line is smaller than the reference inclination.

  According to this configuration, it is possible to appropriately determine that the deterioration of the carrier due to contamination is greater as the inclination of the measurement straight line is smaller than the reference inclination, utilizing the knowledge of the inventor described above.

  The determining unit may determine that the life of the carrier due to contamination has come when the inclination of the measurement straight line is smaller than a predetermined second inclination that is smaller than the reference inclination.

  According to this configuration, using the knowledge of the inventor described above, when the inclination of the measurement straight line is smaller than a second inclination smaller than the reference inclination, the degree of carrier deterioration due to contamination corresponds to the second inclination. And it is possible to appropriately judge that the life of the carrier due to contamination has come.

  Further, second life expectancy information indicating a relationship between a second difference calculated by subtracting the second slope from the slope of the measurement straight line and a life expectancy until the carrier reaches the life due to contamination is stored in advance. The determination unit calculates the second difference when the inclination of the measurement straight line is smaller than the reference inclination and equal to or greater than the second inclination, and the carrier reaches its life due to contamination. It may be determined that the life expectancy up to is the life expectancy associated with the calculated second difference in the second life expectancy information.

  According to this configuration, using the second life expectancy information stored in advance in the storage unit, the inclination of the measurement straight line is calculated from the second inclination used to determine whether the life of the carrier due to contamination has come. However, the life expectancy until the life of the carrier due to the contamination can be properly grasped depending on how large the carrier is.

  Further, the reference slope may be previously determined to be a slope of the measurement straight line obtained when the carrier is not deteriorated.

  According to this configuration, it is determined whether or not the slope of the measurement straight line indicating the relationship between the change amount of the carrier current value and the change amount of the frequency is larger than the slope of the measurement straight line obtained when the carrier is not deteriorated. In this case, it is possible to appropriately determine the deterioration state of the carrier.

  The image forming apparatus further includes a transfer device that transfers the toner image formed on the image carrier to a sheet, and the determination unit determines the deterioration state of the carrier by the transfer device. This may be performed at a time corresponding to a sheet interval between one sheet and another succeeding sheet when an image is transferred.

  According to this configuration, when a toner image is continuously transferred to a plurality of sheets by the transfer device, a region without a latent image corresponding to a space between one sheet and another subsequent sheet faces the developing roller. Utilizing the time period, it is possible to efficiently determine the deterioration state of the carrier.

  Alternatively, the image carrier further includes an image condition adjustment unit that executes a calibration operation for adjusting a parameter that determines the image quality of the toner image transferred to the sheet, wherein the calibration operation includes changing the developing bias. The operation of forming the plurality of toner images is included in the operation, and the determination of the deterioration state of the carrier by the determination unit is performed during the execution of the calibration operation at the time of forming one toner image and the subsequent toner image. May be performed at a time corresponding to the time between the formation.

  According to this configuration, during the execution of the calibration operation by the image condition adjusting unit, the latent image-free area corresponding to between the time of forming one toner image and the time of forming another subsequent toner image is a developing roller. By using the period in which the carrier is facing, it is possible to efficiently determine the deterioration state of the carrier.

  Further, according to this configuration, the deterioration state of the carrier is determined during the adjustment of the parameter that determines the image quality of the toner image transferred to the sheet by the calibration operation. For this reason, the deterioration state of the carrier can be appropriately determined using the adjusted parameters, and the unadjusted parameters can be appropriately adjusted using the determination result of the deterioration state of the carrier. .

  According to the present invention, in an image forming apparatus to which a two-component developing method is applied, the deterioration state of a carrier can be accurately determined.

FIG. 1 is a cross-sectional view illustrating an internal structure of an image forming apparatus according to an embodiment of the present disclosure. FIG. 1 is a cross-sectional view of a developing device according to an embodiment of the present invention and a block diagram illustrating an electrical configuration of a control unit. FIG. 3 is a schematic diagram illustrating a developing operation of the image forming apparatus according to the embodiment of the present disclosure. FIG. 3 is a schematic diagram illustrating a magnitude relationship between potentials of an image carrier and a developing roller according to an embodiment of the present invention. 6 is a flowchart of a deterioration prediction mode executed in the image forming apparatus according to the embodiment of the present disclosure. FIG. 7 is a diagram illustrating an example of changes in the frequency of an AC voltage of a developing bias and a carrier current value in a deterioration prediction mode. FIG. 7 is a diagram illustrating an example of a relationship between a slope of an approximate straight line, a reference slope, and a first slope. FIG. 9 is a diagram illustrating an example of a relationship between a slope of an approximate straight line, a reference slope, and a second slope.

  Hereinafter, an image forming apparatus 10 according to an embodiment of the present invention will be described in detail with reference to the drawings. In the present embodiment, a tandem type color printer will be described as an example of the image forming apparatus. The image forming apparatus may be, for example, a copying machine, a facsimile machine, or a multifunction peripheral thereof. Further, the image forming apparatus may form a single color (monochrome) image.

  FIG. 1 is a sectional view showing an internal structure of the image forming apparatus 10. The image forming apparatus 10 includes an apparatus main body 11 having a box-shaped housing structure. In the apparatus main body 11, a sheet feeding section 12 for feeding a sheet P, an image forming section 13 for forming a toner image to be transferred onto the sheet P fed from the sheet feeding section 12, and the toner image is primarily transferred. An intermediate transfer unit 14 (transfer device), a toner replenishing unit 15 for replenishing toner to the image forming unit 13, and a fixing unit 16 for performing processing for fixing an unfixed toner image formed on the sheet P to the sheet P. It is decorated. Further, at the upper part of the apparatus main body 11, there is provided a paper discharge unit 17 for discharging the sheet P subjected to the fixing processing by the fixing unit 16.

  An operation panel 18 for inputting output conditions and the like for the sheet P is provided at an appropriate position on the upper surface of the apparatus main body 11. The operation panel 18 is provided with a power key, a touch panel for inputting output conditions, and various operation keys.

  In the apparatus main body 11, a sheet conveying path 111 extending vertically is formed at a position on the right side of the image forming section 13. The sheet conveying path 111 is provided with a pair of conveying rollers 112 for conveying a sheet to an appropriate position. Further, a pair of registration rollers 113 for performing skew correction of the sheet and feeding the sheet at a predetermined timing to a nip portion for secondary transfer described later is provided on the sheet conveying path 111 on the upstream side of the nip portion. The sheet transport path 111 is a transport path that transports the sheet P from the paper supply unit 12 to the paper discharge unit 17 via the image forming unit 13 and the fixing unit 16.

  The paper supply unit 12 includes a paper supply tray 121, a pickup roller 122, and a paper supply roller pair 123. The paper feed tray 121 is removably mounted below the apparatus main body 11, and stores a sheet bundle P1 in which a plurality of sheets P are stacked. The pickup roller 122 feeds out the uppermost sheet P of the sheet bundle P1 stored in the sheet feeding tray 121 one by one. The paper feed roller pair 123 sends out the sheet P fed by the pickup roller 122 to the sheet transport path 111.

  The paper feeding unit 12 includes a manual paper feeding unit attached to the left side of the apparatus main body 11 shown in FIG. The manual sheet feeding unit includes a manual tray 124, a pickup roller 125, and a sheet feeding roller pair 126. The manual feed tray 124 is a tray on which sheets P to be manually fed are placed, and is opened from the side of the apparatus body 11 as shown in FIG. The pickup roller 125 feeds out the sheet P placed on the manual feed tray 124. The sheet feeding roller pair 126 sends out the sheet P fed by the pickup roller 125 to the sheet conveying path 111.

  The image forming unit 13 forms a toner image to be transferred to the sheet P, and includes a plurality of image forming units that form toner images of different colors. In this embodiment, the image forming units of magenta (M) color are sequentially arranged from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 141 (from left to right in FIG. 1). A magenta unit 13M using a developer, a cyan unit 13C using a cyan (C) developer, a yellow unit 13Y using a yellow (Y) developer, and a black (Bk) developer are used. A black unit 13Bk is provided. Each of the units 13M, 13C, 13Y, and 13Bk includes a photosensitive drum 20 (image carrier), a charging device 21, a developing device 23, a primary transfer roller 24, and a cleaning device 25 disposed around the photosensitive drum 20. Is provided. An exposure device 22 common to the units 13M, 13C, 13Y, and 13Bk is disposed below the image forming unit.

  The photoreceptor drum 20 is driven to rotate around its axis to form an electrostatic latent image on the surface thereof, and carries a toner image in which the electrostatic latent image has been revealed. As the photosensitive drum 20, for example, a known amorphous silicon (α-Si) photosensitive drum or an organic (OPC) photosensitive drum is used. The charging device 21 uniformly charges the surface of the photosensitive drum 20 to a predetermined charging potential. The charging device 21 includes a charging roller and a charging cleaning brush for removing toner attached to the charging roller. The exposure device 22 is disposed downstream of the charging device 21 in the rotation direction of the photosensitive drum 20, and has various optical devices such as a light source, a polygon mirror, a reflection mirror, and a deflection mirror. The exposure device 22 forms an electrostatic latent image by irradiating the surface of the photosensitive drum 20 uniformly charged to the charged potential with light modulated based on image data.

  The developing device 23 is disposed downstream of the exposure device 22 in the rotation direction of the photosensitive drum 20. The developing device 23 includes a developing roller 231. The developing roller 231 is arranged to face the photosensitive drum 20 at a predetermined developing nip portion NP (FIG. 3). The developing roller 231 is rotated to carry the developer including the toner and the carrier on the peripheral surface and supply the toner to the photosensitive drum 20 to form the toner image.

  The primary transfer roller 24 forms a nip with the photosensitive drum 20 with the intermediate transfer belt 141 provided in the intermediate transfer unit 14 interposed therebetween. Further, the primary transfer roller 24 primarily transfers the toner image on the photosensitive drum 20 onto the intermediate transfer belt 141. The cleaning device 25 cleans the peripheral surface of the photosensitive drum 20 after the transfer of the toner image.

  The intermediate transfer unit 14 is disposed in a space provided between the image forming unit 13 and the toner replenishing unit 15, and includes an intermediate transfer belt 141, a drive roller 142 rotatably supported by a unit frame (not shown), and , A driven roller 143 and a backup roller 146. The intermediate transfer belt 141 is an endless belt-shaped rotating body, and is stretched over the driving roller 142 and the driven rollers 143 and 146 such that the peripheral surface thereof comes into contact with the peripheral surface of each of the photosensitive drums 20. I have. The intermediate transfer belt 141 is driven to rotate by rotation of the driving roller 142. A belt cleaning device 144 that removes toner remaining on the peripheral surface of the intermediate transfer belt 141 is disposed near the driven roller 143.

  A secondary transfer roller 145 is disposed outside the intermediate transfer belt 141 so as to face the drive roller 142. The secondary transfer roller 145 is pressed against the peripheral surface of the intermediate transfer belt 141 to form a transfer nip with the driving roller 142. The toner image primarily transferred on the intermediate transfer belt 141 is secondarily transferred to a sheet P supplied from the paper supply unit 12 at a transfer nip. That is, the intermediate transfer unit 14 and the secondary transfer roller 145 function as a transfer unit that transfers the toner image carried on the photosensitive drum 20 to the sheet P. The drive roller 142 is provided with a roll cleaner 200 for cleaning the peripheral surface thereof.

  The toner replenishing unit 15 stores toner used for image formation. In the present embodiment, the toner replenishing unit 15 includes a magenta toner container 15M, a cyan toner container 15C, a yellow toner container 15Y, and a black toner container 15Bk. These toner containers 15M, 15C, 15Y, and 15Bk store replenishment toner of each color of M / C / Y / Bk. The toner of each color is supplied to the developing devices 23 of the image forming units 13M, 13C, 13Y, and 13Bk corresponding to each color of M / C / Y / Bk from the toner discharge port 15H formed on the bottom surface of the container.

  The fixing unit 16 includes a heating roller 161 having a heating source therein, a fixing roller 162 disposed to face the heating roller 161, a fixing belt 163 stretched between the fixing roller 162 and the heating roller 161, a fixing belt 163. And a pressure roller 164 that is arranged to face the fixing roller 162 with the fixing roller 162 interposed therebetween to form a fixing nip portion. The sheet P supplied to the fixing unit 16 is heated and pressed by passing through the fixing nip. As a result, the toner image transferred to the sheet P at the transfer nip is fixed to the sheet P.

  The paper discharge unit 17 is formed by recessing the top of the apparatus main body 11, and a paper discharge tray 171 that receives the discharged sheet P is formed at the bottom of the concave. The sheet P on which the fixing process has been performed is discharged to a discharge tray 151 via a sheet conveyance path 111 extending from an upper portion of the fixing unit 16.

<About the developing device>
FIG. 2 is a cross-sectional view of the developing device 23 according to the present embodiment and a block diagram illustrating an electrical configuration of the control unit 980. The developing device 23 includes a developing housing 230, a developing roller 231, a first screw feeder 232, a second screw feeder 233, and a regulating blade 234. The developing device 23 employs a two-component developing method.

  The developing housing 230 is provided with a developer accommodating portion 230H. The developer accommodating section 230H accommodates a two-component developer composed of a toner and a carrier. Further, the developer accommodating portion 230H transports the developer in a first transport direction (a direction perpendicular to the plane of FIG. 2, a direction from the rear to the front) from one end of the developing roller 231 toward the other end in the axial direction. And a second transport unit 230B which is communicated with the first transport unit 230A at both ends in the axial direction and in which the developer is transported in a second transport direction opposite to the first transport direction. Including. The first screw feeder 232 and the second screw feeder 233 are rotated in the directions indicated by arrows D22 and D23 in FIG. 2, and transport the developer in the first transport direction and the second transport direction, respectively. In particular, the first screw feeder 232 supplies the developer to the developing roller 231 while transporting the developer in the first transport direction. The toner contained in the developer is frictionally charged with the carrier while being circulated and transported in the first transport direction and the second transport direction. On the other hand, the carrier contained in the developer may be scraped or contaminated by friction with the toner while being circulated and transported in the first transport direction and the second transport direction.

  The developing roller 231 is arranged to face the photosensitive drum 20 at the developing nip portion NP (FIG. 3). The developing roller 231 includes a sleeve 231S that is rotated, and a magnet 231M that is fixed and disposed inside the sleeve 231S. The magnet 231M has S1, N1, S2, N2 and S3 poles. The N1 pole functions as a main pole, the S1 pole and the N2 pole function as carrier poles, and the S2 pole functions as a peeling pole. The S3 pole functions as a pumping pole and a regulating pole. As an example, the magnetic flux densities of the S1, N1, S2, N2, and S3 poles are set to 54 mT, 96 mT, 35 mT, 44 mT, and 45 mT. The sleeve 231S of the developing roller 231 is rotated in the direction of arrow D21 in FIG. The developing roller 231 is rotated, receives the developer in the developing housing 230, carries the developer layer, and supplies toner to the photosensitive drum 20. In this embodiment, the developing roller 231 rotates in the same direction (with direction) at a position facing the photosensitive drum 20.

  The regulating blade 234 (layer thickness regulating member) is arranged at a predetermined interval on the developing roller 231, and regulates the layer thickness of the developer supplied from the first screw feeder 232 onto the peripheral surface of the developing roller 231.

  The image forming apparatus 10 including the developing device 23 further includes a developing bias applying unit 971, a driving unit 972, a current measuring unit 973, and a control unit 980. The control unit 980 includes a CPU (Central Processing Unit), a ROM (Read Only Memory) for storing a control program, a RAM (Random Access Memory) used as a work area of the CPU, and the like.

  The developing bias applying unit 971 includes a DC power supply and an AC power supply, and applies a developing bias in which an AC voltage is superimposed on a DC voltage to the developing roller 231 based on a control signal from a bias control unit 982 described later.

  The driving unit 972 includes a motor and a gear mechanism for transmitting the torque thereof. In response to a control signal from a driving control unit 981 described below, the developing unit 231 in addition to the photoconductor drum 20 and the developing roller 231 in the developing device 23 during the developing operation. And the first screw feeder 232 and the second screw feeder 233 are rotationally driven.

  The current measuring unit 973 includes an ammeter, and measures a current value of a current flowing between the photosensitive drum 20 and the developing roller 231 when the developing bias is applied to the developing roller 231 by the developing bias applying unit 971. I do. The current value measured by the current measuring unit 973 is referred to by the control unit 980.

  The control unit 980 functions as the drive unit 981, the bias control unit 982, the storage unit 983, the mode control unit 984, and the image condition adjustment unit 985 by the CPU executing the control program stored in the ROM. I do.

  The drive control unit 981 controls the drive unit 972 to rotationally drive the developing roller 231, the first screw feeder 232, and the second screw feeder 233. Further, the drive control unit 981 controls a drive mechanism (not shown) to rotate the photosensitive drum 20.

  The bias control unit 982 controls the developing bias applying unit 971 during the developing operation to provide a potential difference between a DC voltage and an AC voltage between the photosensitive drum 20 and the developing roller 231. The toner is moved from the developing roller 231 to the photosensitive drum 20 by the potential difference.

  The storage unit 983 stores various types of information referred to by the drive control unit 981, the bias control unit 982, the mode control unit 984, and the image condition adjustment unit 985. For example, the storage unit 983 stores the value of the developing bias adjusted according to the rotation speed of the developing roller 231 and the environment.

  Further, the storage unit 983 stores the first difference calculated by subtracting the slope of the approximate line (measurement straight line) L (FIGS. 7 and 8) described later from the predetermined first slope larger than the predetermined reference slope. And first life expectancy information indicating the relationship between the life expectancy of the carrier and the life expectancy until the end of life is stored in advance. The reference slope is previously determined to be a slope of an approximate straight line L (FIGS. 7 and 8) described later obtained when the carrier is not deteriorated. Life expectancy until the carrier reaches the end of life due to scraping is, for example, the number of times and time during which the developing operation can be performed normally, the number of sheets (number of prints) on which a toner image can be transferred, and And / or the number of print jobs.

  In addition, the storage unit 983 stores a second difference calculated by subtracting a predetermined second slope smaller than the reference slope from the slope of an approximate straight line L (FIGS. 7 and 8) described later, Second life expectancy information indicating the relationship between the life expectancy until the end of the life is stored in advance. Life expectancy until the carrier reaches the life due to contamination includes, for example, the number of times and time during which the developing operation can be performed normally, the number of sheets (the number of prints) on which the toner image can be transferred, and And / or the number of print jobs.

  The mode control unit 984 (determination unit) executes the deterioration prediction mode. In the deterioration prediction mode, the mode control unit 984 changes the frequency of the AC voltage of the developing bias while keeping the potential difference of the DC voltage between the developing roller 231 and the photosensitive drum 20 constant. The mode control unit 984 determines the amount of change in the frequency and the current measurement unit 973 when the latent image-free area on the surface of the photosensitive drum 20 where no electrostatic latent image is formed faces the developing roller 231. And the amount of change in the measured current value (hereinafter referred to as the carrier current value), the deterioration state of the carrier is determined.

  The image condition adjusting unit 985 executes a calibration operation for adjusting a parameter that determines the image quality of the toner image transferred to the sheet. The parameters include a rotation speed of the photosensitive drum 20, a charging potential when the charging device 21 charges the surface of the photosensitive drum 20, a developing bias applied to the developing roller 231, and a developing bias when the exposure device 22 is irradiated with light. Includes light quantity and the like.

<About two-component development>
Hereinafter, two-component development will be described. FIG. 3 is a schematic diagram of the developing operation of the image forming apparatus 10 according to the present embodiment, and FIG. 4 is a schematic diagram showing the magnitude relationship between the potentials of the photosensitive drum 20 and the developing roller 231.

  As shown in FIG. 3, a developing nip NP is formed between the developing roller 231 and the photosensitive drum 20. The toner TN and the carrier CA carried on the developing roller 231 form a magnetic brush. In the developing nip portion NP, the toner TN is supplied from the magnetic brush to the photosensitive drum 20 side, and a toner image TI is formed.

  As shown in FIG. 4, the surface potential of the photosensitive drum 20 is charged by the charging device 21 to the background portion potential V0 (V). Thereafter, when exposure light is irradiated by the exposure device 22, the surface potential of the photosensitive drum 20 is changed from the background portion potential V0 to the image portion potential VL (V) at the maximum according to the image to be printed. On the other hand, a DC voltage Vdc of a developing bias is applied to the developing roller 231, and an AC voltage (not shown) is superimposed on the DC voltage Vdc.

  In this case, the potential difference between the surface potential V0 and the DC component Vdc of the developing bias is a potential difference that suppresses toner fogging on the surface of the photosensitive drum 20 where no latent image exists. On the other hand, the potential difference between the surface potential VL after the exposure and the DC component Vdc of the developing bias is a developing potential difference that moves the positive polarity toner to the electrostatic latent image formed on the surface of the photosensitive drum 20. Further, the movement of the toner from the developing roller 231 to the photosensitive drum 20 is promoted by the AC voltage applied to the developing roller 231.

  Each toner is frictionally charged with a carrier while being circulated and transported in the developing housing 230. The amount of charge of each toner affects the amount of toner (developing amount) that moves toward the photosensitive drum 20 due to the above-described developing bias. Therefore, if it becomes possible to accurately predict the charge amount of the toner in the image forming apparatus 10, by adjusting the developing bias and the toner density according to the number of prints, environmental fluctuation, print mode, print ratio, etc. Image quality can be maintained. For this reason, techniques for accurately predicting the charge amount of toner have been proposed, for example, as described in Patent Documents 1 to 3 described above.

<Regarding problems in the prior art>
It is assumed that the proposed technique is applied to the image forming apparatus 10. In this case, the current value of the current flowing between the photosensitive drum 20 and the developing roller 231 (hereinafter referred to as “developing current”) measured by the current measuring unit 973 is the value of the toner moved from the developing roller 231 to the photosensitive drum 20. It is assumed to be the amount of charge. Further, a density sensor is provided in the image forming apparatus 10, and the density sensor measures the image density of the toner image formed on the photosensitive drum 20. Then, the toner development amount is calculated from the measurement result, and the toner charge amount is calculated from the calculated toner development amount and the assumed toner charge amount.

  In this case, when the latent image-free area is facing the developing roller, the current value (hereinafter, the carrier current value) of the current (hereinafter, the carrier current value) flowing in the carrier in which the toner does not move is measured. There is a possibility that the current value of the developing current (hereinafter, a developing current value) may be measured by the unit 973. Therefore, the measured current value of the developing current is erroneously calculated as being the charge amount of the toner moved from the developing roller 231 to the photosensitive drum 20, and the toner amount is calculated using the erroneously calculated toner charge amount. May be incorrectly calculated.

  Here, if the current value of the carrier current is a constant value, a current value obtained by excluding the measured developing current value by the fixed value may be calculated as the toner charge amount. However, when the opportunity for development increases and the opportunity for the developer to be circulated and conveyed to the developing roller 231 increases, the toner may rub against the carrier, and the carrier may be abraded or deteriorated due to contamination. As a result, a change occurs in the resistance value and impedance of the carrier, and the current value of the carrier current may not be constant.

  As described above, when the above-described proposed technology is applied, the deterioration state of the carrier is not accurately grasped, and the carrier current value is not accurately excluded from the measured development current value. It is difficult to calculate accurately. For this reason, the charge amount of the toner cannot be accurately predicted, and the deterioration state of the developer may not be accurately grasped.

  Further, as described above, even if there is no problem in the charge amount of the toner and no problem occurs in the toner image formed on the photosensitive drum 20, the carrier may be deteriorated due to scraping or contamination. In this case, if the developing operation is repeated without considering that the carrier has deteriorated, the life of the carrier may come soon. As a result, suddenly, the toner cannot be normally moved, and a desired toner image may not be formed. For this reason, it is desired to accurately grasp the state of deterioration of the carrier so that preventive maintenance such as replacement of the developer before the life of the carrier can be performed.

<About judgment of carrier deterioration state>
Therefore, the inventor has made intensive studies on accurately determining the deterioration state of the carrier. Specifically, the present inventor changes the frequency of the AC voltage of the developing bias applied to the developing roller 231 in a state where the potential difference of the DC voltage between the developing roller 231 and the latent image-free area is kept constant. Was. As a result, the present inventor has found that the relationship between the amount of change in the frequency and the amount of change in the carrier current value measured by the current measuring unit 973 when the developing roller 231 faces the region without a latent image is determined. It has been found that it differs depending on the deterioration state of the carrier.

  Specifically, the present inventors have found the following about the characteristics of the carrier. The carrier can be represented by a parallel circuit in which a resistor and a capacitor are connected in parallel. When the frequency of the developing bias increases, the impedance of the capacitor included in the parallel circuit decreases, so that the impedance of the carrier decreases. Therefore, the carrier current value increases as the frequency increases. On the other hand, when the frequency of the developing bias decreases, the impedance of the capacitor increases, so that the impedance of the carrier increases. Therefore, the carrier current value decreases as the frequency decreases. From these facts, the inventors have found that the relationship between the amount of change in the frequency and the amount of change in the carrier current value can be approximated by a straight line having a positive slope (hereinafter, an approximate line).

  Further, as described above, when the opportunity for development increases and the opportunity for the developer to be circulated and conveyed to the developing roller 231 increases, the toner and the carrier rub against each other, and the carrier may be abraded or deteriorated by contamination. . As the carrier is removed, the resistance value of the resistor included in the parallel circuit decreases, and the carrier current value increases. For this reason, the inventor has found that the slope of the approximate straight line increases as the carrier is removed. On the other hand, as the carrier becomes contaminated, the resistance value of the resistor included in the parallel circuit increases, and the carrier current value decreases. For this reason, the inventor has found that as the carrier becomes contaminated, the slope of the approximate line becomes smaller.

  Therefore, the inventor recalls that the degraded state of the carrier is accurately determined based on the slope of the approximate straight line when the frequency of the AC voltage of the developing bias is changed using the characteristics of the carrier that have been found. did.

<Carrier degradation prediction mode>
Hereinafter, a deterioration prediction mode, which is an operation of determining the deterioration state of a carrier based on the above knowledge, will be described. FIG. 5 is a flowchart of the deterioration prediction mode executed in the image forming apparatus 10 according to the present embodiment. FIG. 6 is a diagram illustrating an example of changes in the frequency f of the AC voltage of the developing bias and the carrier current value Ic in the deterioration prediction mode. FIG. 7 is a diagram illustrating an example of the relationship between the slope of the approximate straight line L, the reference slope, and the first slope. FIG. 8 is a diagram illustrating an example of the relationship between the slope of the approximate straight line L, the reference slope, and the second slope.

  As shown in FIGS. 5 and 6, when starting the deterioration prediction mode, the mode control unit 984 sets a variable n for changing the frequency f of the AC voltage of the developing bias to n = 1 (step S01).

  The mode control unit 984 controls the drive control unit 981 and the bias control unit 982 to rotate the photosensitive drum 20 and to rotate the developing roller 231 by one or more rotations while applying a preset reference developing bias. After the rotation, the frequency f of the AC voltage of the developing bias is set to the n-th frequency fn (n = 1) (step S02).

  The reference developing bias is set so that the deterioration prediction mode is not affected by the history of the immediately preceding image formation. Normally, a bias used for printing (image formation) is applied to the reference developing bias condition. Further, if only a DC voltage is applied as the reference developing bias, the effect of eliminating the above history is weak. Therefore, it is desirable that the DC voltage and the AC voltage are applied in a superimposed manner. However, in step S02, the operation of rotating the developing roller 231 by one or more rotations with the reference developing bias applied is not essential and may be omitted.

  Next, when the developing roller 231 faces the no-image region in a state where the developing bias in which the frequency of the AC voltage is set to the n-th frequency fn is applied to the developing roller 231, Then, the current measuring unit 973 measures the carrier current value Icn for a certain period T (step S03).

  Then, the mode control unit 984 stores the value of the n-th frequency fn in the storage unit 983 in association with the representative value of the carrier current value Icn measured during the certain period T (step S04). Here, the representative value of the carrier current value Icn is, for example, an average value, a maximum value, a minimum value, or the like of the carrier current value Icn measured during the certain period T.

  Next, the mode control unit 984 determines whether or not the variable n relating to frequency is equal to a preset specified number N (step S05). If the variable n is not equal to the specified number N (NO in step S05), the value of n is counted up by one (n = n + 1, step S06), and steps S02 to S04 are repeated. In order to increase the accuracy of the measurement, the prescribed number N is preferably set to 2 or more, and more preferably 3 or more. In this embodiment, the specified number N is set to 4.

  On the other hand, when the variable n is equal to the specified number N (YES in step S05), the mode control unit 984 sets the approximate straight line indicating the relationship between the change amount of the frequency f of the AC voltage of the developing bias and the change amount of the carrier current value Ic. The inclination of L is calculated (step S07).

  Specifically, in step S07, as shown in FIG. 7 or FIG. 8, the mode control unit 984 stores the two-dimensional coordinate system in which the horizontal axis represents the value of the frequency f and the vertical axis represents the carrier current value Ic. The N points indicated by the value of each frequency fn and the representative value of the carrier current value Icn associated with the value of each frequency fn stored in the unit 983 are plotted. Then, the mode control unit 984 derives an approximate straight line L passing in the vicinity of the N points, and calculates a slope of the derived approximate straight line L.

  The mode control unit 984 determines the deterioration state of the carrier according to whether or not the slope of the approximate straight line L calculated in step S07 is larger than the slope of the predetermined reference straight line L0 (reference slope) (step S08). ). Thereby, the deterioration state of the carrier can be determined regularly.

  Here, the reference straight line L0 is set to the approximate straight line L obtained in step S07 by performing steps S01 to S07 when the carrier is not deteriorated, for example, immediately after replacing the developer with a new one. Just do it. The reference straight line L0 is not limited to this, and may be determined in advance in a test operation or the like by performing the same operation as in steps S01 to S07. In this case, the inclination of the reference straight line L0 may be stored in advance in a ROM or the like and used in step S08.

  For example, it is assumed that the approximate straight line L shown in FIG. 7 has been calculated in step S07. In this case, in step S08, the mode control unit 984 determines that the carrier is deteriorated due to scraping because the slope of the approximate straight line L is larger than the slope of the reference straight line L0 (hereinafter, reference slope). In addition, the mode control unit 984 determines that the larger the slope of the approximate straight line L is than the reference slope, the greater the deterioration of the carrier due to scraping. That is, the mode control unit 984 determines the absolute value of the difference between the slope of the approximate straight line L and the reference slope as the degree of carrier deterioration due to scraping.

  On the other hand, it is assumed that the approximate straight line L shown in FIG. 8 has been calculated in step S07. In this case, in step S08, the mode control unit 984 determines that the carrier has deteriorated due to contamination because the slope of the approximate straight line L is smaller than the reference slope. In addition, the mode control unit 984 determines that the smaller the slope of the approximate straight line L is than the reference slope, the greater the deterioration of the carrier due to contamination. That is, the mode control unit 984 determines the absolute value of the difference between the slope of the approximate straight line L and the reference slope as the degree of carrier deterioration due to contamination.

  After step S08, the mode control unit 984 determines whether or not the lifetime has reached the carrier (step S09).

  For example, suppose that the approximate straight line L shown in FIG. 7 is calculated in step S07, and it is determined in step S08 that the carrier is deteriorated due to scraping. In this case, in step S09, the mode control unit 984 determines the carrier of the carrier due to scraping based on the slope of the approximate straight line L and the slope of the first straight line L1 having a slope larger than the reference slope (hereinafter, the first slope). Determine if the life has expired.

  Here, the first straight line L1 is determined in advance in a test operation or the like by using the carrier whose life due to shaving has come to pass from step S01 to step S07, and thereby the approximate straight line L obtained in step S07. The inclination of the first straight line L1 is stored in advance in a ROM or the like and used in step S09.

  For example, as shown in FIG. 7, when the slope of the approximate straight line L is larger than the reference slope but equal to or smaller than the first slope, the mode control unit 984 determines that the life of the carrier due to the scraping has not come ( (NO in step S09). On the other hand, when the slope of the approximate straight line L is larger than the reference slope and larger than the first slope, the mode control unit 984 determines that the life of the carrier due to scraping has come (YES in step S09). As a result, the degree of deterioration of the carrier due to scraping becomes greater than the degree corresponding to the first inclination, and it is possible to appropriately determine that the life of the carrier due to scraping has come.

  On the other hand, it is assumed that the approximate straight line L shown in FIG. 8 is calculated in step S07, and it is determined in step S08 that the carrier is deteriorated due to contamination. In this case, in step S09, the mode control unit 984 determines the carrier due to contamination based on the slope of the approximate straight line L and the slope of a predetermined second straight line L2 having a slope smaller than the reference slope (hereinafter, the second slope). It is determined whether or not the end of the life has been reached.

  Here, the second straight line L2 is defined in advance as an approximate straight line L obtained in step S07 by performing steps S01 to S07 in a test operation or the like using a carrier whose life due to contamination has come. . The inclination of the second straight line L2 is stored in advance in a ROM or the like and used in step S09.

  For example, as illustrated in FIG. 8, when the slope of the approximate straight line L is smaller than the reference slope but equal to or greater than the second slope, the mode control unit 984 determines that the life of the carrier due to contamination has not come. (NO in step S09). On the other hand, when the slope of the approximate straight line L is smaller than the reference slope and smaller than the second slope, the mode control unit 984 determines that the life of the carrier due to contamination has come (YES in step S09). As a result, the degree of deterioration of the carrier due to contamination becomes smaller than the degree corresponding to the second inclination, and it is possible to appropriately determine that the life of the carrier due to contamination has come.

  If the mode control unit 984 determines in step S09 that the life of the carrier due to scraping has come, or determines that the life of the carrier due to contamination has come (YES in step S09), the operation panel 18 displays A message prompting replacement of the device 23 and replacement of the developer is displayed (step S10), and the deterioration prediction mode is ended.

  On the other hand, if the mode control unit 984 determines in step S09 that the life of the carrier due to scraping has not come, or determines that the life of the carrier due to contamination has not come (NO in step S09), the operation panel At 18, a message indicating the life expectancy until the life of the carrier is reached is displayed (step S 11), and the deterioration prediction mode is ended.

  For example, as shown in FIG. 7, the slope of the approximate straight line L calculated in step S07 is larger than the reference slope and equal to or less than the first slope, and in step S09, the life of the carrier due to scraping has not come. It is assumed that it is determined. In this case, in step S11, the mode control unit 984 calculates a first difference that is a result of subtracting the slope of the approximate straight line L from the first slope. Then, the mode control unit 984 determines that the life expectancy until the life of the carrier due to scraping is associated with the calculated first difference in the first life expectancy information stored in the storage unit 983. And a message indicating the remaining life is displayed on the operation panel 18.

  Thus, using the first life expectancy information stored in advance in the storage unit 983, the inclination of the approximate straight line L is more than the first inclination used to determine whether or not the life of the carrier due to scraping has come. The life expectancy until the life of the carrier due to the scraping is reached can be appropriately grasped depending on whether the life is small.

  On the other hand, as shown in FIG. 8, the slope of the approximate straight line L calculated in step S07 is smaller than the reference slope and equal to or greater than the second slope, and in step S09, the life of the carrier due to contamination has not come. It is assumed that it is determined. In this case, the mode control unit 984 calculates a second difference that is a result of subtracting the second slope from the slope of the approximate straight line L in step S11. Then, the mode control unit 984 determines that the life expectancy until the carrier reaches the life due to contamination is the life expectancy associated with the calculated second difference in the second life expectancy information stored in the storage unit 983. And a message indicating the remaining life is displayed on the operation panel 18.

  Thus, using the second life expectancy information stored in advance in the storage unit 983, the slope of the approximate straight line L is more than the second slope used to determine whether the life of the carrier due to contamination has come. The life expectancy until the life of the carrier due to contamination reaches can be appropriately grasped depending on whether the degree is large.

  As described above, in the deterioration prediction mode, as the inventor has found, when the developing roller 231 faces the area without a latent image, the DC voltage between the developing roller 231 and the photosensitive drum 20 is reduced. The relationship between the amount of change in the frequency f and the amount of change in the carrier current value Ic when the frequency f of the AC voltage of the developing bias is changed with the potential difference kept constant is approximated by an approximate straight line L having a positive slope. By making use of the fact that the slope of the approximate straight line L differs depending on the deterioration state of the carrier, the deterioration state of the carrier can be accurately determined.

<Execution timing of deterioration prediction mode>
Hereinafter, the execution timing of the deterioration prediction mode will be described. The deterioration prediction mode is manually started in accordance with an instruction input using the operation panel 18. Alternatively, the deterioration prediction mode is automatically started at a predetermined timing. For example, the deterioration prediction mode is desirably performed at a time corresponding to a sheet interval between one sheet and another succeeding sheet when a toner image is continuously transferred to a plurality of sheets by the intermediate transfer unit 14. .

  In this case, when a toner image is continuously transferred to a plurality of sheets by the intermediate transfer unit 14, a region without a latent image, which corresponds to a space between one sheet and another subsequent sheet, faces the developing roller 231. Utilizing the time period, it is possible to efficiently determine the deterioration state of the carrier.

  The present invention is not limited thereto, and the deterioration prediction mode may be performed during the execution of the calibration operation by the image condition adjusting unit 985. The calibration operation includes an operation of forming a plurality of toner images on the photosensitive drum 20 by changing the developing bias. Specifically, it is desirable that the deterioration prediction mode is performed at a time corresponding to between the time of forming one toner image and the time of forming another subsequent toner image during the execution of the calibration operation.

  In this case, during the execution of the calibration operation, a period during which the non-latent image area is opposed to the developing roller 231 corresponds to the time between the formation of one toner image and the formation of another subsequent toner image. Utilization can be used to efficiently determine the deterioration state of the carrier.

  Further, the determination of the deterioration state of the carrier is performed during the adjustment of the parameter that determines the image quality of the toner image transferred to the sheet by the calibration operation. For this reason, the deterioration state of the carrier can be appropriately determined using the adjusted parameters, and the unadjusted parameters can be appropriately adjusted using the determination result of the deterioration state of the carrier. .

  Further, the deterioration prediction mode may be executed when the image forming apparatus 10 is shipped from a factory after manufacturing and when the main body is set up at the place where the image forming apparatus 10 is used. In this case, it is possible to grasp the deterioration state of the carrier that has changed during the idle period of the image forming apparatus 10.

<About the modified embodiment>
As described above, the embodiment of the present invention has been described, but the present invention is not limited to this. For example, the following modified embodiment can be adopted.

  (1) The surface of the developing roller 231 may be, for example, one subjected to knurl processing, one having a concave shape (dimple), or one subjected to blast processing.

  (2) The storage unit 983 may not store the first life expectancy information and / or the second life expectancy information. If the first life expectancy information is not stored in the storage unit 983, the life expectancy until the life of the carrier due to scraping may not be displayed in step S11. If the second life expectancy information is not stored in the storage unit 983, the life expectancy until the carrier reaches the life due to contamination may not be displayed in step S11. When the first life expectancy information and the second life expectancy information are not stored in the storage unit 983, step S11 may be omitted.

  (3) It is assumed that the mode control unit 984 determines in step S08 that the carrier has deteriorated due to scraping. In this case, step S09 and subsequent steps may be omitted, and a message indicating the degree of deterioration of the carrier due to scraping determined in step S08 may be displayed on the operation panel 18. Similarly, in step S08, when the mode control unit 984 determines that the carrier has deteriorated due to contamination, the step S09 and subsequent steps are omitted, and a message indicating the degree of deterioration of the carrier due to contamination determined in step S08. May be displayed on the operation panel 18.

  (4) In step S08, the mode control unit 984 may not determine the degree of carrier deterioration due to contamination and / or contamination.

  (5) When the image forming apparatus 10 includes a plurality of developing devices 23 as shown in FIG. It may be used in.

10 Image forming device 14 Intermediate transfer unit (transfer device)
20 Photoconductor drum (image carrier)
Reference Signs List 22 Exposure device 23 Development device 231 Development roller 971 Development bias application unit 972 Drive unit 973 Current measurement unit 980 Control unit 981 Drive control unit 982 Bias control unit 983 Storage unit 984 Mode control unit (judgment unit)
985 Image condition adjustment unit Ic Carrier current value L Approximate straight line (straight line for measurement)
L0 Reference straight line L1 First straight line L2 Second straight line f Frequency

Claims (11)

Rotated, an electrostatic latent image is formed on the surface, and an image carrier that carries a toner image in which the electrostatic latent image has been revealed;
An exposure device that forms the electrostatic latent image on the surface of the image carrier,
A developing roller that is arranged to face the image carrier, is rotated, and carries a developer including a toner and a carrier on a peripheral surface and supplies the toner to the image carrier to form the toner image;
A developing bias applying unit that can apply a developing bias in which an AC voltage is superimposed on a DC voltage to the developing roller;
A current measuring unit that measures a current value flowing between the image carrier and the developing roller,
The frequency of the AC voltage of the developing bias is changed in a state in which the potential difference of the DC voltage between the developing roller and the image carrier is kept constant, and the amount of change in the frequency and the surface of the image carrier are changed. The carrier based on a relationship between a carrier current value, which is a current value measured by the current measuring unit when a latent image-free area where an electrostatic latent image is not formed is opposed to the developing roller. A determination unit for determining the deterioration state of
An image forming apparatus comprising: The determination unit determines a deterioration state of the carrier according to whether or not a slope of a measurement straight line indicating a relationship between a change amount of the carrier current value and a change amount of the frequency is larger than a predetermined reference slope. The image forming apparatus according to claim 1. The image forming apparatus according to claim 2, wherein the determination unit determines that the greater the inclination of the measurement straight line is greater than the reference inclination, the greater the deterioration of the carrier due to scraping. 4. The image forming apparatus according to claim 2, wherein the determination unit determines that the life of the carrier due to scraping has come when the inclination of the measurement straight line is greater than a predetermined first inclination that is greater than the reference inclination. 5. apparatus. A storage in which first life expectancy information indicating a relationship between a first difference calculated by subtracting the inclination of the measurement straight line from the first inclination and life expectancy until the carrier reaches the end of life due to shaving is stored in advance. Part,
When the inclination of the measurement straight line is greater than the reference inclination and equal to or less than the first inclination, the determination unit calculates the first difference, and the remaining life until the carrier reaches the life due to shaving is the remaining life. The image forming apparatus according to claim 4, wherein it is determined that the life expectancy is associated with the calculated first difference in the first life expectancy information. The image forming apparatus according to claim 2, wherein the determination unit determines that deterioration of the carrier due to contamination is greater as the inclination of the measurement straight line is smaller than the reference inclination. The said judgment part judges that the lifetime of the said carrier by contamination has come when the inclination of the said measurement straight line is smaller than the predetermined 2nd inclination smaller than the said reference inclination. An image forming apparatus according to claim 1. A memory for storing in advance second life expectancy information indicating a relationship between a second difference calculated by subtracting the second slope from the slope of the measurement straight line and a life expectancy until the carrier reaches the life due to contamination. Part,
When the inclination of the measurement straight line is smaller than the reference inclination and equal to or greater than the second inclination, the determination unit calculates the second difference, and the life expectancy until the carrier reaches the life due to contamination is The image forming apparatus according to claim 7, wherein the image forming apparatus determines that the life expectancy is associated with the calculated second difference in the second life expectancy information. 9. The image forming apparatus according to claim 2, wherein the reference inclination is set in advance to an inclination of the measurement straight line obtained when the carrier is not deteriorated. 10. A transfer device that transfers the toner image formed on the image carrier to a sheet,
The determination of the deterioration state of the carrier by the determination unit is performed when the toner image is continuously transferred to a plurality of sheets by the transfer device and corresponds to a sheet interval between one sheet and another succeeding sheet. The image forming apparatus according to claim 1, wherein the image forming is performed. An image condition adjustment unit that executes a calibration operation for adjusting a parameter that determines the image quality of the toner image transferred to the sheet,
The calibration operation includes an operation of changing the developing bias to form the plurality of toner images on the image carrier,
The determination of the deterioration state of the carrier by the determination unit is performed at a time corresponding to a time between the formation of one toner image and the formation of another subsequent toner image during the execution of the calibration operation. The image forming apparatus according to any one of claims 1 to 10.