JP2017146589A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can accurately detect the amount of developer even when the amount of developer per unit area is increased.SOLUTION: An image forming apparatus 200 has a high density mode of changing a peripheral speed ratio between a photoreceptor drum 201 and a developing roller to increase the amount of toner per unit area to be developed compared with that during normal image formation, and a detection mode for forming a toner patch for detection on the photoreceptor drum 201 while reducing the peripheral speed ratio between the photoreceptor drum 201 and developing roller compared with that in the high density mode and for detecting the amount of toner per unit area of the toner patch for detection with an optical sensor 220. When the image forming apparatus detects the amount of toner on the photoreceptor drum 201 in the high density mode, the detection accuracy may be reduced, and thus the image forming apparatus predicts (estimates) the amount of toner on the photoreceptor drum 201 in the high density mode on the basis of a result of detection of the amount of toner on the photoreceptor drum 201 in the detection mode.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrophotographic or electrostatic recording image forming apparatus.

  2. Description of the Related Art Conventionally, as an image forming apparatus such as a laser beam printer, an in-line color image forming apparatus configured by arranging a plurality of image forming stations in the rotation direction of an intermediate transfer member is known. The image forming station of this image forming apparatus has an image carrier and develops an electrostatic latent image formed on the image carrier by a developing means. The developed developer image is primarily transferred from the image carrier to the intermediate transfer member. This process is repeated at a plurality of image forming stations to form a color developer image on the intermediate transfer member. Thereafter, the color developer image is secondarily transferred to a recording material such as paper, and the color developer image is fixed to the recording material by a fixing unit.

  The image on the recording material created by a series of image forming operations needs to output an image and density intended by the user. Further, in a full-color image (color developer image) created at a plurality of image forming stations, color reproducibility and stability are required.

  Therefore, in Patent Document 1, by changing the rotational speed of the developing sleeve variously, a plurality of patches are formed on the photosensitive drum, which is an image carrier, and a patch reaching a necessary density is detected from the plurality of patches. It has been proposed to determine the rotational speed of the developing sleeve.

  Patent Document 2 proposes changing the developing bias and changing the rotation speed of a developer carrying member such as a developing roller for the purpose of expanding the selection range of colors.

JP-A-11-38750 JP-A-8-227222

  Here, the invention of Patent Document 2 has a configuration in which the amount of developer supplied from a developer carrier such as a developing roller to an image carrier such as a photosensitive member is increased in order to widen the selection range of colors.

  When the selection range of the color is expanded by increasing the amount of developer per unit area on the image carrier, the amount of developer may not be detected accurately by the detection unit that detects the amount of developer. all right.

The image forming apparatus of the present invention includes:
An image carrier for carrying a developer image;
A developer carrier for carrying the developer;
A detector for detecting the amount of developer on the image carrier;
An image forming mode for forming the developer image on the image carrier by supplying the developer carried on the developer carrier to the image carrier;
A detection mode in which a developer image for detection is formed on the image carrier and the amount of developer in the developer image for detection is detected by the detection unit; and
A circumferential speed ratio v11 / v12 between the circumferential speed v11 of the developer carrier and the circumferential speed v12 of the image carrier in the detection mode is Δv1,
When the peripheral speed ratio v21 / v22 between the peripheral speed v21 of the developer carrier and the peripheral speed v22 of the image carrier in the image forming mode is Δv2,
The developer amount on the image carrier in the image forming mode is estimated based on the detection result of the developer amount on the image carrier in the detection mode in a state where Δv1 <Δv2. To do.

Another image forming apparatus according to the present invention includes:
An image carrier for carrying a developer image;
An intermediate transfer member to which a developer image on the image carrier is transferred;
A developer carrier for carrying the developer;
A detector for detecting the amount of developer on the intermediate transfer member;
An image forming mode for forming the developer image on the intermediate transfer member by transferring the developer supplied from the developer carrier to the image carrier to the intermediate transfer member;
A detection mode in which a developer image for detection is formed on the image carrier and the amount of developer in the developer image for detection is detected by the detection unit; and
wherein, the peripheral speed ratio v11 / v12 between the peripheral speed v11 of the developer carrier and the peripheral speed v12 of the image carrier in the detection mode is Δv1,
When the peripheral speed ratio v21 / v22 between the peripheral speed v21 of the developer carrier and the peripheral speed v22 of the image carrier in the image forming mode is Δv2,
The developer amount on the intermediate transfer member in the image forming mode is estimated based on the detection result of the developer amount on the image carrier in the detection mode in a state where Δv1 <Δv2. To do.

  According to the present invention, by changing the peripheral speed ratio, the developer amount per unit area on the image carrier or intermediate transfer member can be changed, so that the developer amount can be accurately detected.

1 is a schematic diagram of an image forming apparatus according to a first embodiment. Schematic diagram of a process cartridge according to Example 1 and Example 2 Schematic of the optical sensor unit according to Example 1 and Example 2. Relationship between the output from the optical sensor unit and the toner amount according to the first and second embodiments. Flowchart of a detection mode for detecting the amount of toner on the photosensitive drum according to the first embodiment. A flowchart of a detection mode for detecting the amount of toner on the photosensitive drum according to the first comparative example. Schematic diagram of an image forming apparatus according to Embodiment 2.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

  In the present specification, terms are used as follows.

  An image forming apparatus refers to an apparatus that forms an image on a recording material.

  The process cartridge means a cartridge having at least an image carrier. In many cases, the charging unit, the developing unit, the cleaning unit, and the image carrier are integrally formed into a cartridge, and this cartridge is a cartridge that can be attached to and detached from the main body of the image forming apparatus.

  Further, the developing device means a device having at least a developer carrying member. In many cases, this means a device that integrates a developer carrier, a developing frame that supports the developer carrier, and components related thereto, and is detachable from the main body of the image forming apparatus.

  The apparatus main body refers to an apparatus configuration portion excluding at least the process cartridge from the configuration of the image forming apparatus. Further, the developing device may be configured to be detachable from the apparatus main body alone. In this case, the apparatus constituent portion excluding the developing device from the configuration of the image forming apparatus is used as the apparatus main body.

[Example 1]
In the first embodiment, an embodiment in which the amount of developer on the image carrier (the mass of developer per unit area) is predicted and detected with high accuracy using a regular reflection type optical sensor unit as a detection unit will be described. In particular, even when an image is formed such that a plurality of toner layers as a developer are formed on a photosensitive drum as an image carrier, it is possible to accurately detect and detect.

  The first embodiment has a detection mode in which a developer image such as a toner image for detecting the amount of developer is formed on an image carrier such as a photosensitive drum, and the formed developer image is detected by a detection unit.

  In the first embodiment, a toner amount that is a developer amount on the photosensitive drum at the time of image formation is predicted. Therefore, the peripheral speed ratio of the detection mode (moving speed of the developing roller in the detection mode / photosensitive drum) is more than the peripheral speed ratio of the photosensitive drum to the developing roller (moving speed of the developing roller / moving speed of the photosensitive drum) during image formation. (Moving speed) is reduced. In Example 1, the moving speed of the photosensitive drum is not changed, but the moving speed of the developing roller is decreased to reduce the peripheral speed ratio. The moving speed is, for example, a speed at which the surface of the developing roller moves in the case of the developing roller. In this embodiment, the moving speed is such that the outer surface of the developing roller that rotates about the rotation axis rotates.

  In a state where the peripheral speed ratio is reduced, the amount of toner per unit area on the photosensitive drum is detected by an optical sensor unit which is a detection unit. In the detection mode, since the peripheral speed ratio is reduced, the toner amount per unit area on the photosensitive drum is smaller than the toner amount per unit area on the photosensitive drum at the time of image formation. Therefore, [1] the peripheral speed ratio in the image forming mode at the time of image formation and [2] the peripheral speed ratio in the detection mode are compared, and [3] the toner amount per unit area of the photosensitive drum in the detection mode, The amount of toner per unit area on the photosensitive drum at the time of formation is predicted. The peripheral speed ratio is controlled so that the toner amount per unit area on the photosensitive drum in the detection mode falls within the range of the toner amount per unit area that can be accurately detected by the detection unit. For this reason, it becomes possible to detect the toner amount with higher accuracy than directly measuring the toner amount per unit area at the time of image formation.

  The detection mode is executed when the image forming apparatus is turned on or at an appropriate timing when the image forming conditions should be reviewed. Various setting conditions can be changed within a necessary range by using information on the toner amount per unit area on the photosensitive drum obtained by the detection mode. For example, based on information on the amount of toner per unit area on the photosensitive drum, the amount of toner on the paper is calculated and the fixing temperature is changed, used for color matching image processing, the amount of toner per unit area on the developing roller Can be predicted. Therefore, hereinafter, the detection mode for detecting the toner amount on the photosensitive drum is simply referred to as a detection mode.

  In the first exemplary embodiment, the detection unit detects the amount of toner per unit area on the photosensitive drum. However, the detection unit may detect the amount of toner per unit area transferred onto an intermediate transfer member described later. .

  Details of the process cartridge and the image forming apparatus according to this embodiment will be described below. FIG. 1 is a schematic cross-sectional view of an image forming apparatus 200 of this embodiment. The image forming apparatus 200 of this embodiment is a full-color laser printer that employs an inline method and an intermediate transfer method. The image forming apparatus 200 can form a full-color image on a recording material (for example, recording paper) according to the image information. The image information is transmitted as a signal from an image reading device connected to the image forming device 200 or a host device (not shown) such as a personal computer connected to the image forming device so as to be communicable. The transmitted signal is input to the CPU 215 which is a control unit (control unit) provided in the engine controller 214 in the image forming apparatus 200.

  The image forming apparatus 200 includes first, second, and third images for forming images of yellow (Y), magenta (M), cyan (C), and black (K), respectively, as a plurality of image forming units. And fourth image forming units SY, SM, SC, and SK. Here, the image forming unit includes a process cartridge 208 and a primary transfer roller 212 disposed on the opposite side via the intermediate transfer belt 205. In the present embodiment, the first to fourth image forming units SY, SM, SC, and SK are arranged in a line in a direction that intersects the vertical direction (an oblique direction with respect to the horizontal direction). In the present embodiment, the configurations and operations of the first to fourth image forming units are substantially the same except that the colors of the images to be formed are different. Therefore, in the following, unless there is a particular distinction, the subscripts Y, M, C, and K given to the reference numerals to indicate that they are elements provided for any color are omitted, and generally explain. However, depending on the configuration, the shape, configuration, and operation of the image forming unit may be different. For example, since the black capacity is increased, the outer shape of the process cartridge becomes larger than that of other process cartridges, and as a result, the black image forming unit may be enlarged.

  The image forming apparatus 200 according to the present exemplary embodiment includes four drum-type electrophotographic photosensitive members (hereinafter referred to as photosensitive drums 201) arranged in parallel in a direction intersecting the vertical direction (oblique with respect to the horizontal direction) (hereinafter referred to as a photosensitive drum 201). FIG. 1). The photosensitive drum 201 is driven to rotate in the direction indicated by the arrow A (clockwise) by a driving force (driving source) received by a gear serving as a driving force transmission unit. This driving means can be controlled within a necessary range with respect to the rotational driving speed (moving speed) of the photosensitive drum. A charging roller 202 is disposed around the photosensitive drum 201 as a charging unit that uniformly charges the surface of the photosensitive drum 201. Also, a scanner unit (exposure device) 203 is disposed as an exposure unit that irradiates a laser based on image information to form an electrostatic image (electrostatic latent image) on the photosensitive drum 201. Around the photosensitive drum 201, a developing unit (developing device) 204 as a developing unit that develops an electrostatic image as a toner image, and an optical sensor unit 220 that is a detection unit that detects the amount of toner on the photosensitive drum 201 are arranged. ing. Further, a cleaning blade 206 as a cleaning unit for removing toner remaining on the surface of the photosensitive drum 201 after transfer (transfer residual toner), and a pre-exposure LED 216 for discharging the potential on the photosensitive drum 201 are arranged. Further, an intermediate transfer belt 205 as an intermediate transfer member for transferring the toner image on the photosensitive drum 201 to the recording material 207 is disposed facing the four photosensitive drums 201. In the process cartridge 208, a photosensitive drum 201, a charging roller 202 as a process unit for the photosensitive drum 201, a developing unit 204, and a cleaning blade 206 are integrally configured, and can be attached to and detached from the image forming apparatus 200. In this embodiment, the process cartridges 208 for each color all have the same shape, and the process cartridges 208 for each color have yellow (Y), magenta (M), cyan (C), and blank (K). Each color toner is stored. In this embodiment, a toner having a negative charge characteristic is used as a developer. However, depending on the configuration, a positively chargeable toner may be used, and it may be magnetic or nonmagnetic. A two-component developer may be used depending on the configuration.

  An intermediate transfer belt 205 formed of an endless belt as an intermediate transfer member abuts on all the photosensitive drums 201 and rotates in the direction indicated by an arrow B (counterclockwise). The intermediate transfer belt 205 is wound around a driving roller 209, a secondary transfer counter roller 210, and a driven roller 211 as a plurality of support members. On the inner peripheral surface side of the intermediate transfer belt 205, four primary transfer rollers 212 as primary transfer units are arranged in parallel so as to face each photosensitive drum 201. The primary transfer roller 212 is supplied with a bias (positive polarity in this embodiment) having a polarity opposite to the normal charging polarity of the toner (negative polarity in this embodiment as described above) from a primary transfer bias power source (not shown). Applied. As a result, the toner image on the photosensitive drum 201 is transferred onto the intermediate transfer belt 205. A secondary transfer roller 213 as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 210 on the outer peripheral surface side of the intermediate transfer belt 205. A bias having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 213 from a secondary transfer bias power source (not shown). As a result, the toner image on the intermediate transfer belt 205 is transferred to the recording material 207. The recording material 207 onto which the toner image has been transferred is thermally fixed by passing through the fixing device 230, and is discharged outside the apparatus to obtain a final print (recording material on which the toner image is printed).

  In this embodiment, the primary transfer roller is disposed in each image forming unit, but the configuration may be such that the number of primary transfer rollers is shared from four to one. Alternatively, the toner image may be transferred by eliminating the primary transfer roller itself and giving a potential difference to the surface of the photosensitive drum opposite to the surface of the intermediate transfer member with the current from the secondary transfer roller.

  Next, FIG. 2 shows the overall configuration of the process cartridge 208 mounted on the image forming apparatus 200 of this embodiment. FIG. 2 is a schematic cross-sectional view of the process cartridge 208 of this embodiment as viewed from the longitudinal direction (rotation axis direction) of the photosensitive drum 201. In the present embodiment, the configuration and operation of the process cartridge 208 for each color are the same except for the type (color) of the developer stored therein. The process cartridge 208 includes a photosensitive unit 301 having a photosensitive drum 201 and the like, and a developing unit 204 having a developing roller 302 and the like. The photosensitive unit 301 has a cleaning frame 303 as a frame that supports various elements in the photosensitive unit 301. A photosensitive drum 201 is rotatably attached to the cleaning frame 303 via a bearing (not shown). In the photosensitive drum 201, a driving force of a driving motor (not shown) as a driving unit (driving source) is transmitted to a gear provided in the photosensitive unit 301, so that an arrow A direction (clockwise direction) shown in the drawing corresponds to an image forming operation. Is driven to rotate. The photosensitive drum 201 that is the center of the image forming process uses an organic photoreceptor in which an outer peripheral surface of an aluminum cylinder is coated with a functional undercoat layer, a carrier generation layer, and a carrier transport layer in this order. Further, a cleaning member 206 and a charging roller 202 are arranged in the photosensitive unit 301 so as to come into contact with the peripheral surface of the photosensitive drum 201. The transfer residual toner removed from the surface of the photosensitive drum 201 by the cleaning member 206 falls into the cleaning frame 303 and is stored.

  The charging roller 202 as charging means is driven to rotate by bringing the roller portion of conductive rubber into pressure contact with the photosensitive drum 201. Here, a predetermined DC voltage is applied to the core of the charging roller 202 to the photosensitive drum 201 as a charging process, and thereby, a uniform dark portion potential (Vd) is applied to the surface of the photosensitive drum 201. It is formed. The above-described scanner unit 203 exposes the photosensitive drum with laser light emitted corresponding to the image data. The exposed photosensitive drum loses its surface charge by the carrier from the carrier generation layer, and the potential is lowered. As a result, an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 201 in which the exposed portion has a predetermined bright portion potential (Vl) and the unexposed portion has a predetermined dark portion potential (Vd). The developing unit 204 includes a developing roller 302 that is a developer carrying member (rotation direction is an arrow D direction), a developing blade 309 that is a regulating member, a toner supply roller 304 that is a developer supply member (the rotation direction is an arrow E direction), A toner 305 which is a developer is included. Further, a stirring member 307 that is also a toner 305 conveying member and a toner storage chamber 306 that stores the toner 305 are provided. The toner 305 moves in the container by the movement of the stirring member 307 (the rotation direction is the direction of arrow G), and a part of the toner 305 is conveyed from the toner storage chamber 306 to the developing chamber 308. The rotational driving speed of the developing roller 302 can be controlled within a necessary range. In this embodiment, a predetermined developing bias Vdc (developing voltage, developing potential) is applied to the developing roller 302. By applying a bias (voltage), toner is transferred only from the potential difference to the bright portion potential at the developing portions 201a and 302a where the photosensitive drum 201 and the developing roller 302 are in contact with each other. The electrostatic latent image is visualized to form a toner image.

  Next, an optical sensor unit (hereinafter referred to as an optical sensor) 220, which is a detection unit that detects the amount of toner on the photosensitive drum 201, will be described with reference to FIG. The optical sensor 220 is connected at a light spot diameter of 0.8 mm on the photosensitive drum 201 by an LED 221 light transmission system that irradiates light to a detection patch, a lens (not shown), a pinhole (not shown), and a photodiode 222. It is constituted by a light receiving system to be imaged. In this embodiment, the irradiated light is imaged on the photosensitive drum 201 by a lens, and the regular reflection light quantity of a detection patch (toner image) passing through this portion is received by a photodiode as a light receiving element. Based on this, the toner amount is detected. FIG. 4 shows the relationship between the detected toner output (kg / m ^ 2) per unit area on the photosensitive drum 201 and the detected signal output when a specular reflection type optical sensor is used. The absolute value of the signal output of the background portion (the surface of the image carrier when there is no toner) when there is no toner varies depending on the mounting accuracy of the sensor and the surface property of the image carrier such as a photosensitive drum. For this reason, by using the normalized value obtained by dividing the output signal when there are a plurality of layers of toner by the output signal of the background portion, the toner concentration (toner mass) is detected with high accuracy regardless of these disturbance factors. It becomes possible. The output signal correction of the detection unit itself such as the optical sensor is not necessarily performed every detection mode because the signal output varies depending on the mounting accuracy of the optical sensor and the surface property of the image carrier. In many cases, it is sufficient to correct the output signal of the detection unit once at an appropriate timing such as before the first image formation (before the first development) in a new cartridge. In addition, after a new process cartridge is mounted on the image forming apparatus, a signal detected by the detection unit before the first image formation may be used as a correction value for a signal detected by the detection unit in the detection mode. The control unit may correct the detection signal of the detection unit in the detection mode for the process cartridge before performing the first image forming operation after the process cartridge is mounted on the main body of the image forming apparatus. Specifically, for example, when a density correction command is input by the user or when the high density mode is selected, the detection signal may be corrected.

  In the specular reflection type optical sensor used in this example and the comparative example, the detection accuracy is the toner mass (kg / m ^ 2) per unit area on the photosensitive drum 201, and the results shown in Table 1 below are obtained. It was. [1] Practical whether the difference in mass (kg / m ^ 2) between the detection result of toner mass per unit area (kg / m ^ 2) and the actual weight measurement result falls within 0.0005 In-range and out-of-use range were distinguished. This was determined based on whether or not the toner mass per unit area where the fixing temperature should be changed can be distinguished by the secondary color of the toner on the recording material 207 in this embodiment and the comparative example.

  It was found from observation with an optical microscope that the toner layer on the photosensitive drum 201 is one layer when the toner mass (kg / m ^ 2) per unit area is 0 to 0.0030 (kg / m ^ 2). . Similar observations confirmed that the toner layer on the photosensitive drum 201 has a plurality of layers at 0.0045 (kg / m ^ 2) or more. Since the optical sensor 220 uses a regular reflection type, the amount of toner is detected by a decrease in the amount of light caused by the specular reflection light from the target surface being hidden by the toner. Therefore, the detection accuracy is high when the toner layer is in the range of approximately one layer, and detection is generally possible in the range of one to two layers, and there are cases where the three layers are detectable depending on the density of the toner layer. However, when the toner layer is four or more layers, the detection accuracy is lowered. The reason why it is substantially one layer instead of one layer is to reduce the specular reflected light from the target surface in order to fill the gap between the toner and the toner even when the toner is placed slightly above the one layer, This is because the detection accuracy has a good range.

  Next, the toner mass per unit area in which the detection accuracy is high will be described. First, the maximum toner mass per unit area forming one layer is M (kg / m ^ 2), the average radius of the toner is R (m), the specific gravity of the toner is ρ (kg / m ^ 3), and the closest density on the plane Let H be the filling area ratio. The close-packed area ratio H on the plane is the ratio of the maximum projected area and the area of the plane that can be arranged in one layer on a certain plane, assuming that the toners are all spheres of the same size. The arrangement of the spheres is called a hexagonal packing arrangement, and the area ratio H is π / 12≈0.9069. Assuming that the toner is a collection of average radii, (the maximum number of toners entering the unit plane) = H / (πR ^ 2). That is, the theoretical maximum toner mass per unit area when the toner is one layer is M = (toner volume) × ρ × (maximum number of toners entering the unit plane) = (4/3 × πR ^ 3). ) × ρ × (H / (πR ^ 2)) = 4/3 × R × ρ × H. Actually, since the toner has a radius distribution, the filling area ratio on the plane is smaller than the closest packing area ratio H on the plane. Therefore, the toner mass per unit area of one layer or less is expected to be smaller than 4/3 × R × ρ × H. When actually examined, at least in the range where the toner mass per unit area is 4/3 × R × ρ × H or less, highly accurate detection could be performed. As a result, it was shown that the toner can be detected with high accuracy when the toner is one layer or less. Further, since the actual filling area ratio on the plane of the toner is smaller than the closest packing area ratio H on the plane, it is shown that there is a range that can be detected with high accuracy even when the toner is loaded more than one layer. Therefore, (toner mass per unit area in which detection accuracy is high) ≦ 4/3 × R × ρ × H. In this embodiment, 4/3 × R × ρ × H = 0.00302. The average radius in this example was 2.5 μm (2.5 × 10 ^ −6 [m]), and the specific gravity was 1 × 10 ^ 3 (kg / m ^ 3). The average particle diameter was measured using a Multisizer 3 manufactured by BECKMAN COULTER, and the specific gravity was measured using a true density meter.

  In the configuration described above, although image formation is performed, the amount of toner to be developed may vary due to potential variation or the like. When it fluctuates, images such as density unevenness and color unevenness may occur. For this reason, in this embodiment, a sufficient latent image electric field is formed with respect to the charge amount of the toner formed on the developing roller, and in the high print image pattern such as a solid black image, all of the toner image from the developing roller is formed. (Or almost all) toner was developed on the photosensitive drum. The so-called “100% development setting” is adopted. Therefore, there is almost no toner on the developing roller 302 after development. By forming a sufficient latent image, it is possible to obtain a developed image that is a stable toner image even when developability varies due to factors such as potential fluctuations.

  In recent color LBP (color laser beam printer), in order to obtain a richer image, it is desired to increase the image density, expand the selection range of the color, increase the color, and the like. In order to achieve that purpose, in addition to the mode for obtaining general image density, the peripheral speed ratio between the photosensitive drum and developing roller is changed to increase the amount of toner to be developed in order to increase density and color. Proposals have been made for technology to be applied. The peripheral speed ratio is controlled by a signal from a CPU that is a control unit. Hereinafter, a mode in which the toner amount per unit area to be developed is increased as compared with the normal image forming mode (normal image forming mode) by changing the peripheral speed ratio between the photosensitive drum 201 and the developing roller 302 is referred to as “high density mode”. Call. The high density mode is also a kind of image forming mode. Here, the peripheral speed ratio is defined as follows. (Relative speed ratio [%] between photosensitive drum and developing roller) = {(rotational speed of developing roller surface) / (rotating speed of photosensitive drum surface)} × 100 [%]. In the following, the peripheral speed ratio between the photosensitive drum and the developing roller is simply expressed as “peripheral speed ratio”.

  However, it has been found that if the toner amount is detected in this high density mode, the detection accuracy may be lowered. In view of this, the inventors have intensively studied and found a detection method for accurately detecting the toner amount even in an image forming apparatus that forms an image in a high density mode (which constitutes the “image forming mode” of the present invention). The detection method will be described below.

  This detection method uses the result of a detection mode for detecting the amount of toner on the photosensitive drum (which constitutes the “detection mode” of the present invention), and per unit area on the photosensitive drum in the high density mode (image formation mode). The amount of toner is estimated (estimated).

  In this embodiment, the image forming mode and the detection mode are executed by the control unit.

  First, the operation in the detection mode will be described with reference to FIG. When the detection mode execution request (S101) is issued from the engine controller 214, the detection mode is performed. In the detection mode, first, the photosensitive drum 201 and the developing roller 302 are started to rotate at a peripheral speed ratio of 80% (S102). In this embodiment, the circumferential speed ratio is set such that the rotational speed of the photosensitive drum 201 is the same (not changed) as that during normal image formation (in the non-high density mode), and the rotational speed of the developing roller 302 is changed. The speed ratio was set. Details regarding the peripheral speed ratio, the developing bias, and the latent image setting in the detection mode are shown below. The peripheral speed ratio in the detection mode is 80%, which is smaller than that in normal image formation (in the non-high density mode) and in the high density mode. For example, if the peripheral speed ratio in normal image formation is set to 150% and the peripheral speed ratio in the high density mode is set to 250% (Δv2), the peripheral speed ratio in the detection mode is 80% (Δv1). Smaller than in the density mode or high density mode. That is, the relationship of Δv1 <Δv2 is established. Conceptually, the circumferential speed ratio between the developer carrier and the image carrier in the detection mode (moving speed of the developer carrier / moving speed of the image carrier) is Δv1.

  Here, the toner amount per unit area on the photosensitive drum 201 during normal image formation in this embodiment is set to 0.0028 (kg / m ^ 2). As described above, since the toner amount per unit area on the photosensitive drum 201 needs to be 4/3 × R × ρ × H = 0.00302 or less, the peripheral speed ratio is set to 80% in this embodiment. . When the peripheral speed ratio is Δv and the toner amount per unit area on the developing roller 302 is G (kg / m ^ 2), the peripheral speed ratio satisfies Δv ≦ (4/3 × R × ρ × H) / G. There is a need to. That is, if the circumferential speed ratio in the detection mode is Δv1, Δv1 ≦ (4/3 × R × ρ × H) / G. In other words, Δv1 is set so that the toner amount per unit area on the photosensitive drum is theoretically one layer or less. As for the lower limit of the peripheral speed ratio, it is sufficient that the peripheral speed ratio is equal to or greater than the peripheral speed ratio at which the toner amount per unit area on the photosensitive drum 201 is equal to or greater than the lower limit amount detectable by the optical sensor unit 220. In this embodiment, the peripheral speed ratio during normal printing is 150%, and the peripheral speed ratio during high density mode is 250%. In the high concentration mode, the relationship of Δv2> (4/3 × R × ρ × H) / G is established, where the peripheral speed ratio in the high concentration mode is Δv2. The development contrast in the detection mode is -200V. Here, the development contrast is (development bias Vdc) − (light portion potential Vl on the photosensitive drum) and indicates a potential difference for developing the toner from the developing roller 302 to the photosensitive drum 201. In the detection mode, the solid black toner portion is set to be developed from the developing roller 302 to the photosensitive drum 201 almost entirely. The development contrast is −200 V during normal printing and −350 V during the high density mode, and is a setting in which almost all toner is developed onto the photosensitive drum 201 as in the detection mode.

  Here, the condition for developing almost all the toner onto the photosensitive drum 201 will be described in detail. The toner on the developing roller 302 is developed onto the photosensitive drum 201 by the developing contrast at the developing nip formed by the electrostatic latent image formed on the photosensitive drum 201 and the developing bias applied to the developing roller 302. . The developable amount of toner developed based on the development contrast is determined by the product of the electrostatic capacity (C) of the photosensitive drum and the development contrast (ΔVc) with respect to the total amount of charged charge of the supplied toner. That is, C (capacitance) × ΔVc (development contrast) represents the total amount of charged charge of toner per unit area that can be developed from the developing roller to the photosensitive drum in the developing nip portion. Further, the total amount of charged charge of the toner supplied to the photosensitive drum is determined according to the charged charge amount per unit area (Q / S) on the developing roller and the peripheral speed ratio (Δv) with respect to the photosensitive drum. It is expressed as a product of × Δv.

  From the above, the amount of toner that can be developed relative to the development contrast is represented by the relational expression of Q / S (charge amount) × Δv (peripheral speed ratio) = C (electrostatic capacity) × ΔVc (development contrast). . That is, when Q / S × Δv ≦ C × ΔVc, the total charge amount of toner supplied from the developing roller is smaller than the charge amount that can be received by the photosensitive drum. All or all are developed.

Actually, when ΔVc = −200 [V], M / S on the photosensitive drum is slowed down under the condition of Δv = 210 [%], and Q / S × Δv is −0.32 × 10. ^{It is} about ⁻³ (Q / S = −0.15 × 10 ⁻³ q / m 2). From the above result and the relationship of Q / S × Δv = C × ΔVc, the photosensitive drum capacity C = 1.6 × 10 ⁻⁶ [F]. Q / S was measured using a suction type small charge amount measuring device (MODEL 212HS) manufactured by TREK.

  Subsequently, an electrostatic latent image for toner detection is formed on the photosensitive drum 201 in the development setting described above, and a toner patch for detection is formed on the electrostatic latent image by developing toner from the developing roller 302 (S103). ). The toner amount for the detection toner patch is detected by the optical sensor 220 (S104). When the detection is completed, the detected information is recorded in the nonvolatile memory 901 (S105), and the operation on the photosensitive drum toner amount detection mode is ended (S106).

  Next, prediction of the toner amount on the photosensitive drum 201 in the high density mode will be described. The peripheral speed ratio in the high concentration mode of this embodiment is 250%, and the peripheral speed ratio in the detection mode is 80%. Therefore, by multiplying the toner amount information obtained in the toner amount detection mode on the photosensitive drum by (250% / 80%) = 3.125 times, the toner per unit area on the photosensitive drum 201 in the high density mode. Predict the amount. Actually, using the toner amount information recorded in the non-volatile memory 901, the CPU 215 as the control unit performs the calculation. As described above, by reducing the peripheral speed ratio between the photosensitive drum 201 and the developing roller 302 and detecting the toner amount per unit area on the photosensitive drum 201 with high accuracy, the toner amount in the high density mode can be accurately detected. It becomes possible to predict. In this embodiment, the peripheral speed ratio is set by changing the rotation speed (drive speed) of the developing roller 302 without changing the rotation speed (drive speed) of the photosensitive drum 201 during normal printing (in the non-high density mode). Set up. However, the present invention is not limited to this, and the rotational speed of the photosensitive drum may be changed while keeping the rotational speed of the developing roller constant. Further, the peripheral speed ratio may be changed by changing the rotational speeds of both the developing roller and the photosensitive drum. The rotational speed (driving speed) of the photosensitive drum 201 during normal printing (in the non-high density mode) is such that the moving speed of the surface of the photosensitive drum 201 is 200 mm / sec. Therefore, in this embodiment, when the peripheral speed ratio is 80%, the moving speed of the surface of the developing roller is 160 mm / sec, and when the peripheral speed ratio is 250%, the moving speed of the surface of the developing roller is 500 mm / sec. sec.

  In this way, the peripheral speed ratio v11 / v12 between the peripheral speed v11 of the developer carrier and the peripheral speed v12 of the image carrier in the detection mode is Δv1, and the peripheral speed v21 of the developer carrier and the image carrier in the image forming mode. When the peripheral speed ratio v21 / v22 to the peripheral speed v22 of the body is set to Δv2, the control means sets the image based on the detection result of the developer amount on the image carrier in the detection mode in a state where Δv1 <Δv2. The amount of developer on the image carrier in the formation mode can be estimated.

(Comparative Example 1)
Next, the operation of the detection mode in the high concentration mode in the comparative example will be described with reference to FIG. When the detection mode execution request (S201) is issued from the engine controller 214, the detection mode is performed. In the detection mode in the high density mode, the photosensitive drum 201 and the developing roller 302 start rotating at a peripheral speed ratio of 250% (= peripheral speed ratio in the high density mode) (S202). The development contrast in the detection mode in the high density mode is −350V. As in the first embodiment, the solid black portion is set to develop almost all toner from the developing roller 302 onto the photosensitive drum 201. Next, a detection toner patch is formed in the same manner as in the first embodiment (S203), and the toner amount is detected by the optical sensor 220 (S204). When the detection is completed, the detected information is recorded in the nonvolatile memory 901 (S205), and the detection mode operation in the high density mode is ended (S206).

<Examination of detection accuracy>
Example 1 and Comparative Example 1 were carried out over a plurality of peripheral speed ratios, and the detection accuracy was examined. As a method for measuring the toner amount, an electrostatic latent image for detection is formed on the photosensitive drum 201, a toner patch for detection is formed, and the toner mass per unit area on the photosensitive drum 201 (kg / m ^ 2). ) Was measured by collecting the toner that actually adhered. By comparing the measurement results with the detection results, the following indices were used for evaluation.
○: The difference between the detection result and the actual measurement result is within 0.0005 (kg / m ^ 2) ×: The difference between the detection result and the actual measurement result exceeds 0.0005 (kg / m ^ 2) <Detection accuracy result>
Table 2 shows the result of comparing the detection accuracy (prediction accuracy) of the comparative example and the present example by changing some peripheral speed ratios. The toner mass (kg / m ^ 2) per unit area on the photosensitive drum 201 having a circumferential speed ratio of 150% was 0.0043. The toner mass (kg / m ^ 2) per unit area on the photosensitive drum 201 having a peripheral speed ratio of 200% was 0.0057. The toner mass (kg / m ^ 2) per unit area on the photosensitive drum 201 having a peripheral speed ratio of 250% was 0.0075.

  In Example 1, good detection accuracy was obtained over the range of the peripheral speed ratio of 150% to 250%. Even in the high density mode such as 200% or 250%, the peripheral speed ratio between the photosensitive drum 201 and the developing roller 302 is lowered during the detection mode, and the toner amount per unit area on the photosensitive drum is detected with high accuracy. doing. This is because the toner amount in the high density mode can be predicted with high accuracy.

  In Comparative Example 1, the peripheral speed ratio is 200% and 250% even in the detection mode, so that the toner layer on the photosensitive drum 201 becomes three or more layers, and the detection accuracy by the optical sensor is reduced, resulting in a decrease in detection accuracy. I have.

  Thus, the use of the present embodiment can improve the accuracy of prediction in the high concentration mode. In this embodiment, a peripheral speed ratio of 80%, which is within approximately one layer at the time of detection, is used. However, by reducing the peripheral speed ratio with respect to the time of image formation, the toner amount can be reduced to a range that can be accurately detected by the detection unit. If possible, a general detection is possible.

  Further, in the present embodiment, when determining the peripheral speed ratio for obtaining the necessary density, the necessary peripheral speed can be accurately predicted from the toner amount on the developing roller. This is because the toner amount on the developing roller is almost entirely transferred to the photosensitive drum, and the toner amount on the developing roller is substantially constant. Therefore, it is not necessary to detect a plurality of patches while swinging a plurality of peripheral speeds. Therefore, detection time and toner consumption can be reduced compared to a detection method in which a plurality of patches are detected while swinging a plurality of peripheral speeds.

  In this embodiment, the peripheral speed ratio is changed by changing the driving speed of the developing roller 302. This is because in this embodiment, it has been confirmed that the toner amount per unit area on the developing roller 302 does not depend on the rotation speed (drive speed). In many cases, the amount of toner on the developing roller does not depend on the rotational speed (driving speed) under the restriction of the contact type developing blade in the one-component nonmagnetic developing system. In order to detect the amount of toner on the photosensitive drum in the high density mode with higher accuracy, a method of changing the driving speed of the photosensitive drum 201 so as to obtain a desired peripheral speed ratio with respect to the driving speed of the developing roller 302 in the high density mode. There is also.

  The peripheral speed ratio and the bias in the present embodiment are examples, and are not limited to the present embodiment. Also, as an example of changing printing conditions using information on the amount of toner on the photosensitive drum, the fixing temperature and image processing have been taken as examples, but other bias and latent image settings, inter-paper distance, toner remaining amount detection, etc. You may feed back to the change of setting conditions.

  As described above, in the first exemplary embodiment, the toner on the photosensitive drum 201 in the high density mode is detected by reducing the peripheral speed ratio of the developing roller 302 to the photosensitive drum 201 and detecting the toner amount on the photosensitive drum with high accuracy. The quantity can be predicted with high accuracy.

[Example 2]
In the first embodiment, the toner amount is detected on the “photosensitive drum 201” by the optical sensor 220 serving as a detection unit.

  In the second embodiment, the optical sensor 220 which is disposed on the photosensitive drum 201 in the first embodiment so as to face the photosensitive drum 201 of each image forming station is disposed so as to face the intermediate transfer belt 205 which is an intermediate transfer member. Has been. That is, in this embodiment, the amount of toner on the “intermediate transfer member” is detected by the optical sensor as the detection unit. According to the present embodiment, the number of optical sensors 220 can be reduced and the cost can be reduced.

  Other than that, there are many parts that overlap with the first embodiment, and portions that overlap with the first embodiment are omitted in the description of the second embodiment.

  Details of the process cartridge and the image forming apparatus according to this embodiment will be described below. FIG. 7 is a schematic sectional view of the image forming apparatus 200 of this embodiment. The image forming station includes a process cartridge 208 and a primary transfer roller 212 disposed on the opposite side via an intermediate transfer belt 205 as an intermediate transfer member. In this embodiment, the optical sensor 220 is disposed downstream of the process cartridge 208 in the movement direction of the intermediate transfer belt 205 and upstream of the secondary transfer counter roller 210 in the movement direction of the intermediate transfer belt 205.

<Toner Amount Detection Method of Example 2>
A method for detecting the toner amount of the intermediate transfer member in the high density mode in the second embodiment will be described. The printing conditions (image forming conditions) are the same as those in Example 1 and Comparative Example 1. The peripheral speed ratio in the high density mode is 250% while the peripheral speed ratio in normal image formation is 150%. Yes.

  Each latent image is set such that the development contrast during normal image formation is -200 V and the development contrast in the high density mode is -350 V. This development contrast is a setting in which almost all toner from the developing roller 302 is developed onto the photosensitive drum 201.

  First, in this embodiment, a mode for detecting the amount of toner per unit area on the intermediate transfer member is performed (hereinafter referred to as a detection mode). By performing this detection mode, the toner amount per unit area on the intermediate transfer member in the high density mode is predicted and detected. The detection mode will be described in this embodiment. In the detection mode of this embodiment, a detection patch latent image (development contrast: −200 V) is formed on the photosensitive drum 201, and toner is supplied from the developing roller 302 to the latent image at a peripheral speed ratio of 80%. Thus, a detection toner patch is formed. A detection toner patch is formed on the intermediate transfer belt 205 by primarily transferring the formed detection toner patch to the intermediate transfer belt 205. The detection toner patch on the intermediate transfer belt 205 is detected using an optical sensor 220 as a detection unit. The development contrast of the detection patch latent image is set so that almost all toner is developed from the developing roller 302 onto the photosensitive drum 201, and the latent image potential of the patch latent image is not filled with the toner charge. is there. In this embodiment, the primary transfer efficiency was 94 to 98%. Therefore, when the toner on the photosensitive drum 201 is transferred onto the intermediate transfer belt 205, the toner amount is reduced to 96%, which is an average value of primary transfer efficiency. Then, by multiplying the toner amount detection information on the intermediate transfer belt 205 by the reciprocal of the transfer efficiency, the toner amount on the photosensitive drum 201 is estimated, and information on the toner amount per unit area on the developing roller is obtained. Thereafter, the method for predicting the toner amount of the photosensitive drum 201 in the high density mode from the toner amount information on the developing roller is the same as in the first embodiment. Table 3 shows the results of detection accuracy when several peripheral speed ratios are changed.

  As shown in Table 3, it can be seen that the use of this example improves the prediction accuracy when the peripheral speed ratio is large. In addition, since the number of optical sensors 220 can be reduced from four to one with respect to the first embodiment, cost and main body space can be reduced.

  The peripheral speed ratio and the bias in the present embodiment are examples, and are not limited to the present embodiment. Examples of changing the printing conditions (image forming conditions) using information relating to the toner amount per unit area on the intermediate transfer member include the following. There are setting conditions such as bias for development and charging, latent image, distance between papers, and toner remaining amount detection.

  As described above, by reducing the peripheral speed ratio between the photosensitive drum 201 and the developing roller 302 and detecting the toner amount on the intermediate transfer belt 205 with high accuracy, the toner amount on the photosensitive drum 201 in the high density mode is increased. Can be predicted with accuracy.

  That is, also in this embodiment, the circumferential speed ratio v11 / v12 between the circumferential speed v11 of the developer carrying member and the circumferential speed v12 of the image carrying body in the detection mode is Δv1, and the circumferential speed of the developer carrying body in the image forming mode is set. When the peripheral speed ratio v21 / v22 between v21 and the peripheral speed v22 of the image carrier is Δv2, the control means detects the developer amount on the image carrier in the detection mode in a state where Δv1 <Δv2. Based on the above, it is possible to estimate the amount of developer on the intermediate transfer member in the image forming mode. Further, the developer amount on the image carrier can be predicted based on the estimated value of the developer amount on the intermediate transfer member in the image forming mode.

(Other)
In the above embodiments, the peripheral speed ratio of the detection mode and the peripheral speed ratio of the image forming mode are different from each other. However, when there are a plurality of image forming modes, the peripheral speed ratio of one image forming mode is described. And the peripheral speed ratio in the detection mode may be the same peripheral speed ratio. For example, there are a first image forming mode and a second image forming mode. The first image forming mode is a peripheral speed ratio (Δv2) of 250%, the second image forming mode is a peripheral speed ratio (Δv3) of 80%, and the detection mode is a peripheral speed ratio. A setting such that the speed ratio (Δv1) is 80% is also possible. In this case, the relationship of Δv3 <Δv2 and Δv1 = Δv3 is established.

  That is, the image forming mode further includes a first image forming mode and a second image forming mode. In the first image forming mode, the peripheral speed of the developer carrier is v21, and the peripheral speed of the image carrier is v22, and the peripheral speed ratio v21 / v22 between the peripheral speed v21 of the developer carrier and the peripheral speed v22 of the image carrier is Δv2, and the peripheral speed of the developer carrier in the second image forming mode is v31 and the image carrier. When the circumferential speed ratio v31 / v32 to the circumferential speed v32 is Δv3, Δv3 <Δv2. Note that Δv1 = Δv3.

  Further, in the embodiments so far, a regular reflection type optical sensor is used, but an irregular reflection type optical sensor may be used depending on the configuration. However, the diffuse reflection type detects light scattered from the light source to the density patch as scattered light in all directions. The reflected light is weak and the reflectivity varies depending on the spectral sensitivity of the toner. There is a need to.

  On the other hand, the specular reflection type described so far has a so-called specular reflection in which, as shown in FIG. 3, the angle between the optical axis of light applied to the patch from a light source such as an LED and the optical axis of the reflected light is equal to the target surface. It detects light. When detecting specularly reflected light, the amount of toner is detected by reducing the amount of light caused by the specularly reflected light from the target surface being hidden by the toner. For this reason, when detecting regular reflection light, there is a feature that the absolute value of the light intensity is high regardless of the spectral sensitivity of the toner. Therefore, it was found that in a state where the toner has two or more layers, the specular reflection light becomes weak, and as a result, the detection accuracy is lowered.

  In the above embodiments, the description has been made on the assumption that all the toner on the developing roller is transferred to the photosensitive drum. However, such an apparatus configuration is not necessarily required. If the peripheral speed ratio is changed so that the amount of toner per unit area can be detected by the detection unit, the present invention can be used. In the present invention, the transfer belt 205 may not be provided.

  As described above, according to the present invention, it is possible to accurately detect the developer amount by changing the amount of developer per unit area by changing the peripheral speed ratio.

201 Photosensitive drum (image carrier)
202 Charging roller 205 Intermediate transfer belt (intermediate transfer member)
206 Cleaning member 208 Process cartridge 212 Primary transfer roller 213 Secondary transfer roller 214 CPU (control unit)
220 Optical sensor unit (detector)
222 Photodiode 302 Developing roller (developer carrier)

Claims (13)

An image forming apparatus,
An image carrier for carrying a developer image;
A developer carrier for carrying the developer;
A detector for detecting the amount of developer on the image carrier;
An image forming mode for forming the developer image on the image carrier by supplying the developer carried on the developer carrier to the image carrier;
A detection mode in which a developer image for detection is formed on the image carrier and the amount of developer in the developer image for detection is detected by the detection unit; and
A circumferential speed ratio v11 / v12 between the circumferential speed v11 of the developer carrier and the circumferential speed v12 of the image carrier in the detection mode is Δv1,
When the peripheral speed ratio v21 / v22 between the peripheral speed v21 of the developer carrier and the peripheral speed v22 of the image carrier in the image forming mode is Δv2,
The developer amount on the image carrier in the image forming mode is estimated based on the detection result of the developer amount on the image carrier in the detection mode in a state where Δv1 <Δv2. Image forming apparatus. An image forming apparatus,
An image carrier for carrying a developer image;
An intermediate transfer member to which a developer image on the image carrier is transferred;
A developer carrier for carrying the developer;
A detector for detecting the amount of developer on the intermediate transfer member;
An image forming mode for forming the developer image on the intermediate transfer member by transferring the developer supplied from the developer carrier to the image carrier to the intermediate transfer member;
A detection mode in which a developer image for detection is formed on the image carrier and the amount of developer in the developer image for detection is detected by the detection unit; and
wherein, the peripheral speed ratio v11 / v12 between the peripheral speed v11 of the developer carrier and the peripheral speed v12 of the image carrier in the detection mode is Δv1,
When the peripheral speed ratio v21 / v22 between the peripheral speed v21 of the developer carrier and the peripheral speed v22 of the image carrier in the image forming mode is Δv2,
The developer amount on the intermediate transfer member in the image forming mode is estimated based on the detection result of the developer amount on the image carrier in the detection mode in a state where Δv1 <Δv2. Image forming apparatus. The capacitance of the image carrier is C,
The development contrast formed by the light portion potential of the image carrier and the development potential of the developer carrier is ΔVc,
When the charge amount per unit area of the developer carried on the developer carrying body is Q / S,
The image forming apparatus according to claim 1, wherein (Q / S) × Δv1 ≦ C × ΔVc in the detection mode. G is the mass per unit area of the developer carried on the developer carrying body in the detection mode,
The average radius of the developer is R,
The specific gravity of the developer is ρ,
When the area ratio of the closest packing on the plane is H,
4. The image forming apparatus according to claim 1, wherein Δv <b> 1 ≦ (4/3 × R × ρ × H) / G in the detection mode. 5.   5. The image forming apparatus according to claim 4, wherein Δv <b> 2> (4/3 × R × ρ × H) / G in the image forming mode.   6. The image forming apparatus according to claim 1, wherein (Q / S) × Δv ≦ C × ΔVc in the image forming mode.   The image forming apparatus according to claim 1, wherein the detection unit includes an optical sensor unit that receives regular reflection light.   The Δv1 is set so that the developer amount per unit area of the developer image on the image carrier is theoretically 1 layer or less. The image forming apparatus described in 1. The image forming mode further includes a first image forming mode and a second image forming mode,
In the first image forming mode, the peripheral speed of the developer carrier is v21, the peripheral speed of the image carrier is v22, the peripheral speed v21 of the developer carrier and the peripheral speed of the image carrier. The circumferential speed ratio v21 / v22 with respect to the speed v22 is Δv2, and
When the circumferential speed ratio v31 / v32 between the circumferential speed v31 and the circumferential speed v32 of the image carrier is Δv3 in the second image forming mode,
9. The image forming apparatus according to claim 1, wherein Δv <b> 3 <Δv <b> 2.   The image forming apparatus according to claim 9, wherein Δv1 = Δv3 in the image forming mode. Having the image carrier and the developer carrier, and having a process cartridge attachable to an image forming apparatus;
The signal detected in the detection mode is corrected based on the signal detected by the detection unit before performing the first image forming operation after the process cartridge is mounted on the main body of the image forming apparatus. The image forming apparatus according to any one of claims 1 to 10.   The image forming apparatus according to claim 2, wherein the developer amount on the image carrier is predicted based on an estimated value of the developer amount on the intermediate transfer member in the image forming mode. The image forming apparatus according to claim 1, further comprising a control unit capable of executing the image forming mode and the detection mode.

Images