JP2011170025A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, which can suppress an error of detection of a toner concentration on an image carrier even when time passes. <P>SOLUTION: Based on the detection value of regularly-reflected light detected by an optical sensor 160 about the surface of a base-surface portion on which toner image from an intermediate transfer belt 7 is not carried, an input current set value for the light-emitting element 161 of the optical sensor 160 is adjusted. Based on the adjusted input current set value, output conversion information, indicating a relation between the detection value of diffused light and toner density after correction, is determined. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  Conventionally, an optical detection means (optical sensor) that can detect both regular reflection light and diffuse reflection light at the same time immediately after the power is turned on or at a predetermined timing such as when the number of printouts reaches a predetermined number. There is known an image forming apparatus that performs image forming condition adjustment control such as process control by using (see, for example, Patent Documents 1 and 2). This image forming condition adjustment control is performed as follows, for example. First, the light emitted from the light emitting element of the optical detection means is reflected by the background portion (the portion where no toner is attached) of the surface of the intermediate transfer belt as the image carrier, and the reflected light is reflected by the light receiving element of the optical sensor. Receives light and outputs an output value corresponding to the reflected light. Next, a reference toner image having a predetermined shape is formed on the surface of the photoconductor, the reference toner image is transferred onto the intermediate transfer belt, and the light emitted from the light emitting element is reflected by the reference toner image. The reflected light is received by the light receiving element, and an output value corresponding to the reflected light is output. Then, using the output value in the background portion of the intermediate transfer belt surface as a reference value, the reference value is compared with the output value in the reference toner image, and the toner density of the reference toner image (toner adhesion amount per unit area) is obtained. To grasp. Based on the toner density thus grasped, control of the uniform charging potential of the photosensitive member, the developing bias, the optical writing intensity to the photosensitive member, and the toner concentration of the developer so that the toner density becomes a desired density. Adjust imaging conditions such as target values. Such image forming condition adjustment control makes it possible to perform a printout with a stable image density over a long period of time.

  When the detection value of diffuse reflected light is used as in the conventional image forming apparatus described above, the toner image (particularly the color toner image) is not affected by the belt surface characteristics such as the surface roughness and glossiness of the intermediate transfer belt. Since the detection value monotonously increases with an increase in toner density (toner adhesion amount), the toner density can be detected up to a high toner density range. However, since the diffuse reflected light is almost zero for the background portion on the surface of the intermediate transfer belt, the detection sensitivity of the diffuse reflected light cannot be calibrated using the background portion on the surface of the intermediate transfer belt. Therefore, the image forming apparatus detects the regular reflection light of the background portion of the surface of the intermediate transfer belt and calibrates the detection sensitivity of the diffuse reflection light with respect to the toner image based on the detection value of the regular reflection light of the background portion. Yes. By using the detection value of the specular reflection light detected on the background portion of the intermediate transfer belt surface in this way, the detection sensitivity of the diffuse reflection light with respect to the toner image can be calibrated without using the reference inspection plate (calibration plate). it can.

  Further, since the surface of the image carrier such as the intermediate transfer belt, which is the detection target of the optical detection means, changes with time according to the usage situation, the light reflection characteristic of the surface of the image carrier changes. Conventionally, even if the light reflection characteristics of the surface of the image carrier change over time, the optical detection means emits light so that the detection result of the regular reflection light on the surface of the image carrier surface is maintained at a predetermined output value. It has been done to adjust the input current value supplied to the means.

  However, when the present inventors diligently conducted experiments on the image forming apparatus provided with the conventional optical detection means, even if the input current value is adjusted, it takes time from the start of use of the image forming apparatus. It has been found that the detection error of the toner density may increase when the time elapses. In particular, such an increase in toner density detection error over time is likely to occur in the case of a color toner image. If the toner density detection error increases in this way, the image formation conditions cannot be controlled properly. For example, when the toner density detection error increases, it is determined that the toner density is gradually lower than the actual density, and the image density is controlled to be higher.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of suppressing a detection error of toner density on an image carrier over time.

In order to achieve the above object, an invention according to claim 1 includes an image carrier that carries a toner image on a surface thereof, a light emitting unit that irradiates light to the surface of the image carrier and the toner image carried on the surface, and An optical detection means having light receiving means for receiving specular reflection light and diffuse reflection light irradiated from the light emitting means and reflected by the toner image, and the optical detection means based on a predetermined input current setting value; A current supply means for supplying an input current to be input to the light emitting means; a detection value detected by the optical detection means for the toner image carried on the surface of the image carrier; and a relationship between the detected value and the toner density Control means for calculating the toner density of the toner image based on the output conversion information indicating, and controlling the image forming conditions based on the calculated toner density, the image forming apparatus comprising: The toner image on the image carrier Input current adjusting means for adjusting the input current set value based on the detected value of the specularly reflected light detected by the optical detecting means on the surface of the background portion that is not, and the input current set value after the adjustment And output conversion information determining means for determining output conversion information used for calculation of the toner density.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the control means detects the surface of the background portion where the toner image of the image carrier is not carried by the optical detection means. Based on the detection value of the reflected light, the detection value of the diffused light detected by the optical detection means is corrected for the toner image carried on the surface of the image carrier, and the detection value of the diffused light after the correction is corrected. The toner density of the toner image is calculated based on output conversion information indicating the relationship between the detected value of the diffused light and the toner density.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, when the output conversion information determining unit adjusts the input current set value by the input current adjusting unit, the input after the adjustment is adjusted. The output conversion information used for the calculation of the toner density is determined based on the current setting value.
According to a fourth aspect of the present invention, the image forming apparatus according to the first or second aspect further comprises storage means for storing a plurality of different types of output conversion information that can be used for the calculation of the toner density. The determining means selects one output conversion information from the plurality of types of output conversion information based on the adjusted input current set value, and determines the output conversion information to be used for calculating the toner density. It is a feature.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, a plurality of the optical detection means are provided at different detection locations, and the input current adjusting means is the plurality of optical The input current set value is adjusted for each detection means, and the output conversion information determination means determines the output conversion information for each of the plurality of optical detection means.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the light used by the optical detection means is infrared light.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the toner image carried on the image carrier is a color toner image of a plurality of colors having different colors, and the output The conversion information can be commonly used for the color toner images of a plurality of colors.

  According to the present invention, based on the detection value of the specularly reflected light detected by the optical detection means for the surface of the background portion on which the toner image of the image carrier is not carried, the light is input to the light emission means of the optical detection means. By adjusting the input current set value, the amount of light applied to the toner image on the image carrier by the light emitting means can be set to a predetermined amount. Then, based on the adjusted input current set value correlated with the change in the surface characteristics of the image carrier, appropriate output conversion information used for calculating the toner density is determined. By using the output conversion information determined in this way, even when the surface characteristics of the image carrier change over time and the relationship between the detection value detected by the optical detection means and the toner density changes, the optical characteristics can be changed. An error in the toner density calculated from the detection value of the detection means can be kept low. Therefore, the detection error of the toner density on the image carrier can be suppressed even with time.

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 3 is a schematic configuration diagram of an image forming unit. FIG. 3 is an enlarged schematic configuration diagram in the vicinity of an intermediate transfer belt showing a pattern formation position and an optical sensor arrangement position. The cross-sectional view of an optical sensor. FIG. 3 is a block diagram illustrating a main part of a control system of the printer. 6 is a graph showing the relationship between the specular reflection light output value of the optical sensor and the toner adhesion amount. The graph which shows the relationship between the diffuse reflected light output value of an optical sensor, and the toner adhesion amount. The graph which shows the result of the reflected light integration measurement which measured the spectral characteristic which integrated | accumulated all the reflected light from the surface of an intermediate transfer belt. 6 is a graph showing diffuse reflection characteristics on the surface of an intermediate transfer belt. 6 is a graph showing a relationship between a development potential and a regular reflection normalization value Rn of an optical sensor that receives regular reflection from an intermediate transfer belt. The graph which shows the result of having monitored the input current setting value of the optical sensor. Explanatory drawing which shows the example of a conversion table.

Hereinafter, an embodiment in which the present invention is applied to a full-color printer (hereinafter referred to as a printer) 100 as an image forming apparatus will be described.
FIG. 1 is a configuration diagram showing a schematic configuration of the printer 100. As shown in FIG. 1, the printer 100 includes an apparatus main body that is fixed in position for storing each component as an image forming unit, and a drawable sheet cassette 21 that stores a transfer material S. An image forming unit 1Y, 1C, 1M, 1K for forming toner images of each color of yellow (Y), cyan (C), magenta (M), and black (K) is provided at the center of the apparatus main body. Yes. Hereinafter, the subscripts Y, C, M, and K of the respective symbols indicate members for yellow, cyan, magenta, and black, respectively.

  FIG. 2 is a configuration diagram showing a schematic configuration of the image forming means. As shown in FIGS. 1 and 2, in the present embodiment, drum-shaped photoreceptors 2Y, 2C, 2M, and 2K as image carriers, charging rollers 3Y, 3C, 3M, and 3K as charging means, and image writing As a unit having at least a laser exposure device 20 as a means (exposure means), developing devices 4Y, 4C, 4M, and 4K as developing means, and cleaning devices 6Y, 6C, 6M, and 6K that remove transfer residual toner on the surface of the photoreceptor. The image forming units 1Y, 1C, 1M, and 1K for each color are configured as a plurality of sets (four in this embodiment), and the above-described colors for yellow (Y), magenta (M), cyan (C), and black (K) are described above. The image forming units 1Y, 1C, 1M, and 1K are opposed to the horizontal stretching surface of the intermediate transfer belt 7 as an image carrier that runs in a loop shape, and Y, C, M, It is disposed of in the order. Also, the four image forming units 1Y, 1C, 1M, and 1K for each color have the same configuration.

  The charging rollers 3Y, 3C, 3M, and 3K charge the photoconductors 2Y, 2C, 2M, and 2K by charging with the same polarity as the toner held at a predetermined potential (in this embodiment, negative charging). And uniform potentials are applied to the photoreceptors 2Y, 2C, 2M, and 2K. The charging means is not limited to the charging roller, and various devices such as a charging brush and a charging charger can be used as appropriate.

  The laser exposure device 20 exposes the upstream sides of the developing devices 4Y, 4C, 4M, and 4K to the charging rollers 3Y, 3C, 3M, and 3K on the downstream side in the rotation direction of the photoreceptors 2Y, 2C, 2M, and 2K. Further, the laser exposure device 20 is arranged so as to perform exposure scanning in the main scanning direction in parallel with the rotation axes of the photoreceptors 2Y, 2C, 2M, and 2K.

The laser exposure apparatus 20 includes, for example, a light source composed of a semiconductor laser (LD), a coupling optical system (or beam shaping optical system) composed of a collimating lens, a cylindrical lens, and the like, an optical deflector composed of a rotating polygon mirror, and the like. The image data of each color (or the image data (or the image data) read by an image reading device (not shown) provided in a separate configuration and recorded in the memory, or the like. Photosensitive layers 2Y, 2C, 2M, and 2K for the respective colors are formed by laser beams L _Y , L _C , L _M , and L _{K that} are intensity-modulated in accordance with image data of each color input from an external device such as a personal computer. Image exposure is performed to form an electrostatic latent image for each color. As the image writing means (exposure means), in addition to the laser exposure apparatus 20 described above, an LED writing apparatus combining a light emitting diode array (LED array) and a lens array can be used.

  The photoreceptors 2Y, 2C, 2M, and 2K are, on the undercoat layer formed on the surface of the conductive cylindrical support, in the order of the charge generation layer (lower layer) and the charge transport layer (upper layer) as the photosensitive layer, or These photosensitive layers are laminated in the reverse order. Further, a known surface protective layer such as an overcoat layer mainly composed of a thermoplastic or thermosetting polymer may be formed on the surface of the charge transport layer or the charge generation layer. In this embodiment, the conductive cylindrical supports of the photoreceptors 2Y, 2C, 2M, and 2K are grounded.

  The developing devices 4Y, 4C, 4M, and 4K are formed of a cylindrical non-magnetic stainless steel or aluminum material that maintains a predetermined gap with respect to the peripheral surface of the photoconductor 2 and rotates in the forward direction and the rotation direction of the photoconductor 2. Development sleeves 41Y, 41C, 41M, and 41K, and one or two components of yellow (Y), magenta (M), cyan (C), and black (K) in the developing device 4 according to the development color of each color. Contains component developer. In the present embodiment, as an example, a two-component developer (toner is negatively charged in the present embodiment) composed of toner and a magnetic carrier t is accommodated in the developing device 4. A plurality of fixed magnets or magnet rolls magnetized with a plurality of magnetic poles are disposed. Further, the developing devices 4Y, 4C, 4M, and 4K for each color are provided with a stirring / conveying member 42 that transports the developer in the container while stirring, and a replenishing unit 43 that replenishes toner from each color toner bottle 37. It has been. Further, the developing devices 4Y, 4C, 4M, and 4K for the respective colors are provided with toner concentration sensors 44Y, 44C, 44M, and 44K that detect the toner concentration of the developer in the container as necessary.

  The developing sleeves 41Y, 41C, 41M, and 41K of the developing devices 4Y, 4C, 4M, and 4K for the respective colors are placed on the drum surface of the photoreceptors 2Y, 2C, 2M, and 2K with a predetermined gap, for example, 100 [ [mu] m] to 500 [[mu] m] is maintained in a non-contact state, and by applying a developing bias in which a DC voltage and an AC voltage are superimposed on the developing sleeves 41Y, 41C, 41M, and 41K, Contact or non-contact reversal development is performed to form toner images on the surfaces of the photoreceptors 2Y, 2C, 2M, and 2K.

  The cleaning devices 6Y, 6C, 6M, and 6K include, for example, a cleaning blade 61 and a cleaning roller (or cleaning brush) 62, and the cleaning blade 61 is provided in contact with the counter surface of the photoreceptor surface.

The intermediate transfer belt 7 that is an intermediate transfer member and an image carrier is stretched in contact with the driving roller 8 that also serves as a secondary transfer backup roller, the support roller 9, the tension rollers 10a and 10b, and the backup roller 11 to be intermediate transfer. The belt 7 is provided so that the rotation direction thereof is counterclockwise as indicated by an arrow in the drawing.
Further, a secondary transfer roller 14 is provided through the intermediate transfer belt 7 so as to face the driving roller 8. A cleaning blade 12 a of the belt cleaning device 12 is provided in contact with the intermediate transfer belt 7 at the position of the support roller 9 in the counter direction. Similarly, primary transfer rollers 5Y, 5C, 5M, and 5K for each color are provided to face the photoreceptors 2Y, 2C, 2M, and 2K with the intermediate transfer belt 7 interposed therebetween.

This intermediate transfer belt 7 is an endless belt having a volume resistance of 10 ⁶ [Ω · cm] to 10 ¹² [Ω · cm]. For example, polycarbonate (PC), polyimide (PI), polyamideimide (PAI), polyvinylidene Conductive fillers such as carbon are dispersed in resin materials such as fluoride (PVDF), tetrafluoroethylene-ethylene copolymer (ETFE), and rubber materials such as EPDM, NBR, CR, polyurethane, etc. A material containing a material is used, and the thickness is set to about 50 [μm] to 200 [μm] in the case of a resin material and about 300 [μm] to 700 [μm] in the case of a rubber material. preferable. A rubber layer may be provided on the resin belt, and a coating layer may be provided on the surface layer. Further, in order to prevent the toner from adhering to the surface of the intermediate transfer belt 7 or to improve the cleaning property, a means for applying a release agent such as a fluorine-based resin or a lubricant may be provided on the belt surface. .

  The intermediate transfer belt 7 is driven by rotation of the drive roller 8 by a drive motor (not shown). The drive roller 8 is a conductive or semi-conductive material in which a conductive filler such as carbon is dispersed in a circumferential surface of a conductive metal bar (not shown) such as stainless steel, or a rubber or resin material such as polyurethane, EPDM, or silicon. A material coated with a conductive material is used.

  The primary transfer rollers 5Y, 5C, 5M, and 5K are provided to face the photoreceptors 2Y, 2C, 2M, and 2K across the intermediate transfer belt 7, and the intermediate transfer belt 7 and the photoreceptors 2Y, 2C, 2M, and 2K are provided. A transfer zone is formed between the two. The primary transfer rollers 5Y, 5C, 5M, and 5K are applied with a DC voltage having a polarity opposite to that of the toner (a positive polarity in the present embodiment) from a DC power source (not shown) to form a transfer electric field in the transfer area. The toner images of the respective colors formed on the photoreceptors 2Y, 2C, 2M, and 2K are transferred onto the intermediate transfer belt 7.

The primary transfer rollers 5Y, 5C, 5M, and 5K, which are the first transfer means for each color, are made of polyurethane on the peripheral surface of a conductive metal core (not shown) such as stainless steel having an outer diameter of 8 [mm], for example. , EPDM, silicon, or other rubber material is dispersed with a conductive filler such as carbon or an ionic conductive material, so that the volume resistance is from 10 ⁵ [Ω · cm] to 10 ⁹ [Ω · cm. A semi-conductive elastic rubber (not shown) having a thickness of 5 [mm] and a rubber hardness of 20 [°] to 70 [°] (Asker-C) in a solid or foamed sponge state. Formed.

  The secondary transfer roller 14 that performs transfer onto the surface of the transfer material S is provided opposite to the drive roller 8 that is grounded with the intermediate transfer belt 7 interposed therebetween, and is a direct current having a polarity opposite to that of the toner (in this embodiment, a positive polarity). A voltage is applied by a direct current power source, and the superimposed toner image carried on the intermediate transfer belt 7 is transferred to the surface of the transfer material S via the secondary transfer roller 14.

The secondary transfer roller 14 serving as a second transfer unit that re-transfers the color toner image on the intermediate transfer belt 7 onto the transfer material S has a circumference of a conductive metal core such as stainless steel having an outer diameter of 16 [mm]. On the surface, a volume resistance is 10 ⁵ [Ω · cm] to 10 ⁹ by dispersing a conductive filler such as carbon in a rubber material such as polyurethane, EPDM, silicon, or containing an ionic conductive material. Semiconductive elastic rubber (not shown) having a thickness of 7 [mm] and a rubber hardness of about 20 [°] to 70 [°] (Asker-C) in a solid state or foamed sponge state of about [Ω · cm] ). Unlike the primary transfer rollers 5Y, 5C, 5M, and 5K, the secondary transfer roller 14 may come in contact with toner and may coat the surface with a good releasability such as semiconductive fluorine resin or urethane resin. Further, as described above, the driving roller 8 has a conductive core such as stainless steel dispersed on a peripheral surface of a conductive core metal such as polyurethane, EPDM, or silicon, or a conductive filler such as carbon, or an ionic property. A semiconductive material containing a conductive material is coated to a thickness of about 0.05 [mm] to 0.5 [mm].

  The cleaning blades 61 and 12a in contact with the surfaces of the photoreceptors 2Y, 2C, 2M, and 2K and the intermediate transfer belt 7 have a thickness of 1 [mm] to 3 [mm] and a JIS-A hardness of 60 [°] on the sheet metal holder. To 80 [°] plate-like urethane rubber is bonded so that the free length becomes about 5 [mm] to about 12 [mm], and is sensitive to a load of about 5 [gf] to about 50 [gf]. It is in contact with the bodies 2Y, 2C, 2M, 2K and the intermediate transfer belt 7. Further, a fluorine coating may be applied to the blade tip so that the blade does not rise, or conductive urethane rubber may be used so that the other side is not charged.

  The transfer material S such as transfer paper is conveyed one by one by a paper feed roller 27 from the paper feed cassette 21 or the like, and is superimposed on the intermediate transfer belt 7 sandwiched between the secondary transfer roller 14 and the drive roller 8 via the registration roller 13. The toner image is transferred from the intermediate transfer belt 7 at the secondary transfer portion and sent to the fixing device 15 as fixing means, and is fixed by heat welding between the fixing roller 15a and the pressure roller 15b of the fixing device 15. Is discharged to the paper discharge unit 18.

  In the present embodiment, the charging rollers 3Y, 3C, 3M, and 3K are used as charging means for the photoreceptors 2Y, 2C, 2M, and 2K, and the primary transfer rollers 5Y, 5C, 5M, and 5K are used as primary transfer members. However, it is preferable from the viewpoint of suppressing the generation of harmful ozone, but is not limited to this, and the corotron discharger can be used as a charging means or a primary transfer means in a non-contact state.

  Further, the intermediate transfer belt 7 is opposed to the portion where the intermediate transfer belt 7 is wound around the driving roller 17 from the front surface side through a predetermined gap on the downstream side in the rotation direction of the intermediate transfer belt 7 from the secondary transfer portion. An optical sensor unit 16 provided with a plurality of optical sensors 160 as optical detection means is disposed (see FIG. 3). The optical sensor unit 16 detects a gradation pattern, which will be described later, formed on the intermediate transfer belt 7. Specifically, as shown in FIG. 3, the optical sensor unit 16 includes an optical sensor 160K that detects a K-color gradation pattern Sk, an optical sensor 160M that detects an M-color gradation pattern Sm, and a C-color image. An optical sensor 160C for detecting the gradation pattern Sc and an optical sensor 160Y for detecting the Y gradation pattern Sy are provided. (In the following description, when the optical sensors of the respective colors are not distinguished, the description will be made with the color code deleted.)

  FIG. 4 is a schematic configuration diagram of the optical sensor 160 according to the present embodiment. The optical sensor 160 in the present embodiment includes a light emitting element 161 as a light emitting means, and a first light receiving element 162 and a second light receiving element 163 as light receiving means for receiving reflected light. Each element 161, 162, 163 is mounted on a printed circuit board 164. Each element 161, 162, 163 is enclosed in an upper case 165. In the upper case 165, incident light irradiated from the light emitting element 161 is transferred to a toner image (hereinafter, a target image) on the intermediate transfer belt 7 or the intermediate transfer belt. A path 402 for securing an emission optical path to the detection target) and an incident optical path for the reflected light reflected by the detection target to reach the first light receiving element 162 and the second light receiving element 163. Passages 401 and 403 are respectively formed. The space formed by the light emitting element 161 and the passage 402 and the space formed by the first light receiving element 162 and the passage 403 are separated by a light shielding wall 405, so that the light from the light emitting element 161 can be directly transmitted. The incident to one light receiving element 162 is suppressed. In addition, a space formed by the light emitting element 161 and the passage 402 and a space formed by the second light receiving element 163 and the passage 404 are separated by a light shielding wall 404, and light from the light emitting element 161 is directly transmitted to the first light emitting element 161. The incident light to the two light receiving elements 163 is suppressed. A condensing lens 167 b is disposed on the exit optical path of the upper case 165. Further, condensing lenses 167a and 167c are also disposed on the incident optical path. The upper case 165 is fixed on the printed circuit board 164 by fitting with the lower case (not shown) via the printed circuit board 164.

  The emitted light that has traveled from the light emitting element 161 along the surface of the printed circuit board 164 is refracted by the condenser lens 167b and collected on the surface of the detection target (the intermediate transfer belt 7 or the toner image). Then, the specularly reflected light reflected from the detection target moves along the surface of the printed circuit board 164 through the condenser lens 167a, enters the first light receiving element 162, and is diffusely reflected light reflected from the toner image. Moves along the surface of the printed circuit board 164 through the condensing lens 167 c and enters the second light receiving element 163. The condensing lenses 167a to 167c may be omitted, and a member such as a dust-proof transmission sheet or a transmission film may be used instead of the condensing lens. Further, not a lens but a filter for selecting a wavelength may be used.

  As the light emitting element 161, an infrared light emitting diode (LED) is often used because it detects the amount of color toner attached. In the present embodiment, the light emitting element 161 using an LED having a wavelength of 950 [mn] is used. The light emission amount of the LED can be adjusted by a forward current If as an input current flowing through the LED. However, the adjustment parameter of the light emission amount is not limited to the forward current If, and any adjustment parameter corresponding thereto may be used. Further, when these characteristic values depend on current, constant current control is desirable. Note that constant current control may be performed by PWM (pulse width modulation) control.

  As the light receiving elements 162 and 163, a photodiode (PD), a phototransistor (PTr), a photo IC, or the like can be used. Each of the light receiving elements 162 and 163 receives regular reflection light and diffuse reflection light, which is reflected from a detection target (in this embodiment, an intermediate transfer belt), from the light emitted from the light emitting element 161, and outputs a light reception signal. Then, the received light signal is converted into an electrical signal, and the optical sensor unit 16 obtains the converted signal as an output value of the detection result.

  The optical sensor 160 also includes a current supply circuit as current supply means for supplying a supply current If as an input current necessary for light emission from the light emitting element 161 to the light emitting element 161.

  FIG. 5 is a block diagram showing the main part of the control system of the printer 100. In the figure, a control unit 200 as a control means is composed of, for example, a microcomputer, a CPU (Central Processing Unit) 201 as an arithmetic processing means, a RAM (Random Access Memory) 202 of a nonvolatile memory as a storage means, and a ROM ( Read Only Memory) 203 and the like. The control unit 200 is electrically connected to the image forming units 1Y, 1M, 1C, 1K, the laser exposure device 20, the optical sensor 160, and the like. The control unit 200 is also electrically connected to notification means such as the display unit 112 and the speaker 111. And the control part 200 controls these various apparatuses based on the control program memorize | stored in RAM202. The RAM 202, which is a non-volatile memory, outputs output conversion data (conversion table) and output conversion formula (algorithm) described later as output conversion information used when calculating the toner density (toner adhesion amount) from the detection value of the optical sensor 160. Is remembered.

Further, as will be described later, the control unit 200 performs the control of the optical sensor 160 based on the detection value of the specularly reflected light detected by the optical sensor 160 on the surface of the background portion where the toner image of the intermediate transfer belt 7 is not carried. It functions as an input current adjusting means for adjusting the input current set value of the light emitting element. Furthermore, the control unit 200 determines output conversion information such as output conversion data (conversion table) and output conversion formula (algorithm) used for calculation of toner density based on the adjusted input current set value. It also functions as a determination means.

  The control unit 200 also controls image forming conditions for forming an image. Specifically, the control unit 200 performs control to individually apply a charging bias to each charging member in the image forming units 1Y, 1M, 1C, and 1K. As a result, the photoreceptors 2Y, 2M, 2C, and 2K of each color are uniformly charged to the Y, M, C, and K drum charging potential. The control unit 200 individually controls the powers of the four semiconductor lasers corresponding to the image forming units 1Y, M, C, and K of the laser exposure apparatus 20. In addition, the control unit 200 performs control to apply the developing bias of the developing bias values for Y, M, C, and K to the developing rollers in the image forming units 1Y, M, C, and K. As a result, a developing potential for electrostatically moving the toner from the sleeve surface side to the photosensitive member side acts between the electrostatic latent images of the photosensitive members 2Y, 2M, 2C, and 2K and the developing sleeve. Develop.

  The control unit 200 executes image density control for optimizing the image density of each color when the power is turned on or whenever a predetermined number of prints are performed. This image density control is performed as follows, for example. First, the control unit 200 calibrates the optical sensors 160Y, 160M, 160C, and 160K. In the calibration of the optical sensor 160, first, light is applied to the background portion on the surface of the intermediate transfer belt 7 where the toner image is not carried, and the regular reflection light is received by the first light receiving element 162. Then, it is checked whether or not the output voltage of the first light receiving element 162 is within a predetermined range. When it is outside the predetermined range, the supply current If as the input current supplied to the light emitting element 161 of the optical sensor 160 is adjusted so that the output voltage of the first light receiving element 162 falls within a predetermined range. The light emission intensity of the light emitting element 161 is adjusted. By this adjustment, it is possible to suppress variations in output voltages of the light receiving elements 162 and 163 due to variations in light emission intensity such as individual differences in light emission efficiency of the light emitting elements 161, temperature fluctuations and temporal fluctuations, and accurately measure the toner image density. can do. On the other hand, when the output voltage of the first light receiving element 162 is within a predetermined range, the calibration process of the optical sensor 160 is finished as it is. As described above, the control unit 200 changes the value of the current supplied to the light emitting element 161 while referring to the output voltage from the first light receiving element 162 that receives the specularly reflected light from the background portion, and the light emitting element 161 emits light. It has a function as a light emission amount adjusting means for adjusting the amount of light.

  After calibration of the optical sensor 160, for example, process control is executed as follows. First, gradation patterns Sk, Sm, Sc, and Sy of each color as shown in FIG. 3 are automatically formed on the intermediate transfer belt 7 at positions facing the optical sensors 160Y, M, C, and K. Specifically, the photoconductors 2Y, 2M, 2C, and 2K are uniformly charged while rotating. The charging potential at this time is gradually increased, unlike the uniform drum charging potential in the printing process. Then, while forming a plurality of patch electrostatic latent images for forming a gradation pattern image on the photoconductors 2Y, 2M, 2C, and 2K by scanning with laser light, they are used for Y, M, C, and K, respectively. Develop with a developing device. During this development, the control unit 200 gradually increases the value of the developing bias applied to the Y, M, C, and K developing rollers. By such development, Y, M, C, and K gradation pattern images are formed on the photoreceptors 2Y, 2M, 2C, and 2K. These are primarily transferred so as to be arranged at a predetermined interval in the main scanning direction of the intermediate transfer belt 7.

  Each gradation pattern (Sk, Sm, Sc, Sy) formed on the intermediate transfer belt 7 passes through a position facing the optical sensor 160 as the intermediate transfer belt 7 moves endlessly. At this time, the optical sensor 160 receives reflected light of an amount corresponding to the toner adhesion amount per unit area with respect to the toner patch of each gradation pattern. In the case of the K color toner, the irradiated light is absorbed by the toner surface, so that the diffuse reflection light component is hardly included and can be ignored. Therefore, the K-color optical sensor 160K detects the amount of adhesion using the output voltage of the first light receiving element 162 that receives the specularly reflected light. On the other hand, in the case of color toners of Y, M, and C colors, the light irradiated on the toner surface is diffusely reflected, so that the first light receiving element 162 of the optical sensor 160 includes a lot of diffusely reflected light in addition to the regular reflected light. It is. Therefore, the optical sensors 160Y, 160M, and 160C detect the amount of adhesion using the output voltage of the second light receiving element 163 that receives diffusely reflected light. Note that the output voltage of each of the optical sensors 160Y, 160M, 160C, and 160K obtained by detecting the toner patch of each gradation pattern includes a crosstalk voltage, and thus cannot be said to be a highly accurate detection value. There are cases. Therefore, the control unit 200 may execute an output value correction process for removing the crosstalk voltage component on the output voltage of the optical sensor 160 obtained by detecting the toner patch of each gradation pattern.

  Next, based on the output voltage of the optical sensor 160, the toner adhesion amount corresponding to the toner density of each toner patch is calculated. The RAM 202 stores a conversion table as output conversion information indicating the relationship between the output voltage value from the optical sensor 160 and the corresponding toner adhesion amount. The output voltage of the first light receiving element 162 that receives the specularly reflected light (the specularly reflected light output value of the optical sensor 160) and the toner adhesion amount have a relationship as shown in FIG. 6, and the RAM 202 has an output value of the optical sensor. And a conversion table for regular reflection light in which the toner adhesion amount has a relationship as shown in FIG. Further, the output value of the second light receiving element (diffuse reflected light output value of the optical sensor) and the toner adhesion amount have a relationship as shown in FIG. 7, and the RAM 202 has an output value of the optical sensor and the toner adhesion amount. A conversion table for diffuse reflection light having a relationship as shown in FIG. 7 is stored. Then, from the output voltage of the first light receiving element 162 when the K color toner patch is detected and the above-described conversion table for regular reflection light, the adhesion amount in each toner patch of the K color gradation pattern is calculated. The Y, M, and C color gradation patterns are determined from the output voltage of the second light receiving element 163 when the Y, M, and C color toner patches are detected and the above-described conversion table for diffuse reflection light. The toner adhesion amount in each toner patch is calculated.

  After calculating the toner adhesion amount for each toner patch in each color gradation pattern, image forming conditions (image forming conditions) are adjusted based on each toner patch in each color gradation pattern. In each of the colors Y, M, C, and K, the plurality of toner patches in the gradation pattern (Py, m, c, k) are developed with different combinations of drum charging potentials and developing biases. The toner adhesion amount (image density) per unit area gradually increases. Since the toner adhesion amount is correlated with the developing potential which is the difference between the drum charging potential and the developing bias, the relationship between the two becomes a substantially linear graph on the two-dimensional coordinates.

  The control unit 200 calculates a function (y = ax + b) indicating a straight line graph by regression analysis based on the result of detecting the toner adhesion amount in each toner patch and the development potential when each toner patch is imaged. . Then, an appropriate development bias value is calculated by substituting the target value of the image density into this function, and stored in the RAM 202 as corrected development bias values for Y, M, C, and K.

  The RAM 202 stores an image forming condition data table in which several tens of development bias values and appropriate drum charging potentials individually corresponding to the values are associated in advance. The control unit 200 selects a developing bias value closest to the corrected developing bias value from the image forming condition table for each of the image forming units 1Y, 1M, 1C, and 1K, and sets a drum charging potential associated therewith. Identify. The identified drum charging potential is stored in the RAM 202 as Y, M, C, and K correction drum charging potentials. When all the corrected development bias values and corrected drum charging potentials are stored in the RAM 202, the Y, M, C, and K development bias value data are corrected to the same values as the corresponding corrected development bias values. Store again. Also, the drum charging potentials for Y, M, C, and K are corrected to values equivalent to the corresponding correction drum charging potentials and stored again. By such correction, the image forming conditions for forming an image are corrected to conditions capable of forming a toner image having a desired image density.

Next, switching of the conversion table used when calculating the toner adhesion amount from the output voltage value of the optical sensor 160 in the image density control will be described.
In the printer having the above-described configuration, when the present inventors investigated image density control over time from the start of use in a new state, the optical sensor 160 is based on the detection result of regular reflection on the surface of the background portion of the intermediate transfer belt 7. It has been found that a phenomenon that the toner density (toner adhesion amount) of the toner image on the intermediate transfer belt 7 cannot be detected correctly occurs only by adjusting the input current (supply current If) supplied to the light emitting element 161.

  Table 1 shows development γ calculated by carrying a toner image developed by the same developing device for each of the new and time-lapse intermediate transfer belts and detecting the toner image with an optical sensor. “Development γ” indicates the developing ability of the developer, and should have the same value if the developing ability is the same. However, in the color toner image, the development γ was slightly lower by 20%. As a result, in the case of a time-lapse intermediate transfer belt, it is determined that the intermediate transfer belt is thinner than the actual one, and the image density is controlled to be high.

  Conventionally, the aging of the surface of the intermediate transfer belt is mainly that the surface shape changes and the surface roughness changes due to the surface being worn (including flaws) or the adhering of some substance. I thought it might be the main factor. However, when it was visually observed (visible light region), it seemed that some substance had adhered, and when the characteristics of the substance were analyzed, it was inferred that a phenomenon that had not been assumed previously occurred as shown below. Results were obtained.

  FIG. 8 shows the result of the reflected light integrated measurement in which the surface of the intermediate transfer belt is irradiated with light and the spectral characteristics obtained by integrating all the reflected light are measured. In the figure, the horizontal axis represents wavelength [nm], and the vertical axis represents reflectance [%]. From the result of FIG. 8, it is possible to know how much light of which wavelength is absorbed. Overall, the reflectance is very small, and it can be said that it is a substance that is difficult to reflect originally. In addition, the specification of the optical sensor 160 used for this measurement was that light having a light emission peak at a wavelength of 950 nm was irradiated and a light receiving sensitivity peak was at a wavelength of 800 nm. When paying attention, it was found that the reflected light was weakened by about half in the time-lapse product compared to the new product. From this, it can be presumed that the substance attached over time absorbs light.

  FIG. 9 shows diffuse reflection characteristics on the surface of the intermediate transfer belt. If the irregularities on the surface of the intermediate transfer belt are disturbed over time, the light (incident light) emitted from the optical sensor 160 may be diffusely reflected on the surface of the intermediate transfer belt, and the optical sensor 160 may not be able to receive light. Therefore, how much the light diffuses when irradiated at a wavelength of 950 nm at an incident angle of 45 ° was measured by changing the angle of the light receiving element. The horizontal axis in FIG. 9 is the angle of the light receiving element (0 ° is an absolute reflection angle), and the vertical axis is the reflectance [%]. As can be seen from FIG. 9, there is almost no difference in the width of the peak, no difference in the diffuse reflection characteristics between the new product and the time-lapse product, and it was found that the influence of the surface roughness of the intermediate transfer belt is small. When the thickness of the substance adhering to the intermediate transfer belt was actually measured, it was about several tens of nanometers, which is unlikely to affect the surface roughness. It has also been confirmed that the substance attached to the intermediate transfer belt does not transmit light with a wavelength of 950 nm.

  Table 2 shows the quantitative measurement results of the transmittance and the reflectance of the substance attached to the intermediate transfer belt measured at a wavelength of 900 nm. From Table 2, it can be seen that the time-lapsed product has a reflectivity as low as 57% compared to the initial new product, and since no transmission or diffuse reflection occurs, the adhered substance is in the infrared region. It was inferred that it was absorbing light. Based on this result, the calculation mechanism of the toner density (toner adhesion amount) in the image forming apparatus having the above configuration was analyzed. As a result, the output of the detected value of the specularly reflected light changed between the initial new and time-lapse intermediate transfer belts. I found out.

  FIG. 10 shows a reference with an output value of an optical sensor that receives regular reflection from the intermediate transfer belt when the developing potential (which can be treated as the same as the toner adhesion amount under the same developing ability) is on the horizontal axis. A normalized value for the surface (hereinafter referred to as “regular reflection normalized value Rn”) is shown. According to the result of FIG. 10, the regular reflection normalized value of the time-lapse product is smaller than the initial new product at the same development potential. This means that the reflected light is less likely to return to the optical sensor as the product becomes aged. Since the output value of the optical sensor is normalized, the value should not change due to factors other than the toner concentration. Therefore, the characteristics shown in FIG. 10 are affected by the surface of the background portion of the intermediate transfer belt. It is estimated that

  On the other hand, the diffused light output characteristics when the diffused light is detected by the optical sensor hardly change between the initial time and the time. In black toner detection, there is no detection error of toner density (toner adhesion amount). (As shown in Table 1 above, development γ is almost unchanged.)

The results of the above experiment and analysis are summarized as follows (1) to (4).
(1) Some material adheres to the surface of the intermediate transfer belt over time.
(2) The substance adhering to the intermediate transfer belt does not change the surface roughness.
(3) The substance adhering to the intermediate transfer belt absorbs the wavelength of the detection region of the optical sensor.
(4) The detection value of regular reflection of the optical sensor that detects the background portion of the intermediate transfer belt has a great influence. The detection value of the diffused light of the optical sensor that detects the toner density of the toner image on the intermediate transfer belt has little influence.

  In other words, the specular reflection output characteristic (normalized value) of the optical sensor, which should originally depend only on the toner adhesion amount, changes with the aging of the intermediate transfer belt. The detected value (correction value) of the diffused light of the optical sensor calibrated with the detected value has changed. For this reason, the relationship between the detection value (correction value) of the diffused light of the optical sensor and the toner concentration (toner adhesion amount) deviates from the correct relationship, and the output conversion data set when it is new is inappropriate over time. It is thought that it has become. If the output conversion data becomes incorrect, the toner adhesion amount of the toner image using the optical sensor cannot be detected correctly over time.

  Therefore, based on the results of the above experiment and analysis, in the printer of the present embodiment, as shown below, based on the adjusted input current setting value, the corrected diffused light detection value and the toner density are calculated. A conversion table indicating the relationship is determined.

  As shown in the image density control described above, the toner adhesion amounts of the gradation patterns Sk, Sm, Sc, and Sy of each color are measured by outputting the specular reflection detection value of the optical sensor 160 to the surface of the background portion of the intermediate transfer belt 7. Is based on. Therefore, it is a set value of the input current supplied to the light emitting element (LED) of the optical sensor 160 so that the output of the regular reflection detection value of the optical sensor 160 to the surface of the background portion of the intermediate transfer belt 7 becomes a predetermined output. The input current set value is adjusted. Here, when the surface state of the intermediate transfer belt 7 changes due to aging of the intermediate transfer belt 7, the output of the regular reflection detection value of the optical sensor 160 decreases. Therefore, the input current set value of the optical sensor 160 is adjusted to be high, and the output level of the regular reflection detection value of the optical sensor 160 with respect to the surface of the background portion of the intermediate transfer belt 7 is maintained at a predetermined output level.

  FIG. 11 shows the result of monitoring the input current set value of the optical sensor 160 in the printer having the above configuration. The results of FIG. 11 are obtained in the full color mode with an image area ratio of 0.5% and 1 ppj. The horizontal axis in FIG. 11 is the number of sheets, and the vertical axis is the ratio of the input current set value over time adjusted so as to obtain the output level of the predetermined regular reflection detection value relative to the initial input current set value (hereinafter referred to as “input current”). "Initial ratio"). A to D in the figure are the results of different photosensors used for measurement and the arrangement of the photosensors in the printer. Although the degree varies depending on the difference in characteristics of the optical sensor and the surface state of the intermediate transfer belt 7 (how the substance is attached, etc.), it can be seen that the ratio of the input current set value increases according to the number of sheets to be passed. . Further, there is a correlation between the initial ratio of the input current and the surface state of the intermediate transfer belt 7, and this correlation characteristic can be used to suppress the detection error of the toner adhesion amount by the optical sensor 160.

  Due to the surface change of the intermediate transfer belt 7, the conversion table indicating the relationship between the output (correction value) of the diffused light detection value of the optical sensor 160 and the toner adhesion amount is shifted. In the conventional image forming apparatus, only one conversion table is held. On the other hand, in the printer of this embodiment, a plurality of different types of conversion tables illustrated in FIG. 12 are stored in the RAM 202 which is a nonvolatile memory, and the input current set value (current initial value after adjustment) described above is stored. Depending on the ratio, a conversion table is selected from a plurality of types of conversion tables, and control is performed to switch to an appropriate conversion table. By this switching control, as shown in Table 3, it was possible to suppress the detection error of the toner density (toner adhesion amount) for color toner images (particularly, C and M toner images).

Although it is conceivable to prevent substances from adhering to the surface of the intermediate transfer belt 7 over time, there are many disadvantages and it is not practical as a countermeasure.
For example, if a lubricant such as zinc stearate is applied to the surface of the intermediate transfer belt 7, such a substance tends to be difficult to adhere. However, in this case, a new part is added to the printer, resulting in a cost.
It is also conceivable that the environment (temperature / humidity) is an environment in which the above substances are difficult to adhere to the intermediate transfer belt 7. However, in this case, the use environment of the user is limited, which is not preferable.
In addition, when the image area is high or the volume is high (high printer job), the substance tends not to adhere to the intermediate transfer belt 7. In this case, restrictions are imposed on the use situation of the user. It is not preferable.

  Next, a more specific embodiment of switching the conversion table based on the adjusted input current set value (current initial ratio) will be described. First, data indicating the relationship between the diffused light detection value (correction value) of the optical sensor 160 and the toner concentration (toner adhesion amount) is obtained in advance for a plurality of states having different current initial ratios. The data acquired for the plurality of characteristics is stored in the RAM 202, which is a non-volatile memory of the control unit 200, for example, as a conversion table shown in FIG.

The plurality of types of states are divided into, for example, an initial current ratio of (1) a state of 100% to less than 200%, (2) a state of 200% to less than 300%, and (3) a state of 300% or more. be able to. Here, the state (1) is a new intermediate transfer belt 7, the state (2) is an intermediate transfer belt 7 having an initial current ratio of 200%, and the state (3) is an intermediate transfer belt having an initial current ratio of 300%. 7 can be used. Then, a toner image is actually created on each intermediate transfer belt 7, the specular reflection output and the diffuse reflection output are read by the optical sensor 160 based on a predetermined control algorithm, and the diffused light detection value immediately before the conversion to the toner density is performed. Up to the correction value. The toner adhesion amount (toner amount per unit area: mg / cm ² ) of the toner image on the intermediate transfer belt 7 at that time is measured using a sack-in method or the like. The relationship between the correction value of the diffused light detection value and the toner adhesion amount of the toner image is obtained, and a conversion table as shown in FIG. 12 is created. Since it is only necessary to know the relationship between the correction value of the diffused light detection value and the toner adhesion amount of the toner image, a conversion formula or algorithm may be created as output conversion information instead of the conversion table.

  The number of divisions in the above state (three divisions in the present embodiment) and the state of the reference data may be set appropriately based on the required specifications of each image forming apparatus. If the number of divisions is large, the accuracy can be increased, but the memory capacity required for storing the conversion table increases.

  Further, the relationship between the correction value of the diffused light detection value and the toner adhesion amount of the toner image is desirably changed according to the change in the surface of the intermediate transfer belt 7. For example, when the input current set value is adjusted and determined, the current initial ratio is calculated at the same timing as the adjustment, and in which range of (1) to (3) the current initial ratio value falls. According to the determination result, it is selected and determined which of the diffused light detection value correction values (1) to (3) is used and the relationship (conversion table or the like) between the toner adhesion amount of the toner image. .

  Further, when a plurality of optical sensors 160 are mounted as in the printer of the present embodiment, the degree of temporal change in the surface state of the intermediate transfer belt differs depending on the detection location of the optical sensor 160. There are some locations where the change in the surface state of the intermediate transfer belt with time is large, and some locations are small. Therefore, when determining the input current setting value for each optical sensor, the current initial ratio is calculated at the same time, and it is determined to which range of (1) to (3) the calculated current initial ratio value applies. Depending on the determination result, it is possible to select and determine which of the diffused light detection value correction values (1) to (3) is used and the relationship (conversion table or the like) between the toner adhesion amount of the toner image. Good.

  Further, the detection characteristics of the optical sensor 7 do not depend on the color of the toner in the infrared light region. Therefore, in the surface condition of one intermediate transfer belt, that is, at one detection position, the relationship (conversion table etc.) between the correction value of the diffused light detection value and the toner adhesion amount of the toner image is a common 1 for each color. I only need one. However, when the toner particle shape and lightness are different for each color, the relationship (conversion table etc.) between the correction value of the diffused light detection value and the toner adhesion amount of the toner image can be held for each color. However, using a correction coefficient for each color, etc., correction is made so that there is no color difference at the stage of correcting the diffused light detection value of the optical sensor 160, and the correction value of the diffused light detection value and the toner adhesion amount of the toner image The relationship (conversion table etc.) can be reduced as much as possible.

As described above, according to the image forming apparatus of the present embodiment, the optical sensor 160 is based on the detection value of the regular reflection light detected by the optical sensor 160 on the surface of the background portion on which the toner image of the intermediate transfer belt 7 is not carried. By adjusting the input current setting value input to the light emitting element, the light amount irradiated to the toner image on the intermediate transfer belt 7 by the light emitting element can be set to a predetermined light amount. Then, output conversion information such as an appropriate conversion table used for calculating the toner density is determined based on the adjusted input current setting value correlated with the change in the surface characteristics of the intermediate transfer belt 7. By using the output conversion information determined in this way, even when the surface characteristics of the intermediate transfer belt 7 change with time and the relationship between the detected value detected by the optical sensor 160 and the toner density changes, the optical sensor The toner density error calculated from the 160 detection values can be kept low. Therefore, the detection error of the toner density on the intermediate transfer belt 7 can be suppressed even over time.
Further, according to the image forming apparatus of the present embodiment, the intermediate transfer belt 7 is based on the detection value of the specularly reflected light detected by the optical sensor 160 on the surface of the background portion where the toner image of the intermediate transfer belt 7 is not carried. The diffused light detection value detected by the optical sensor 160 is corrected for the toner image carried on the surface 7, and the corrected diffused light detection value and the relationship between the diffused light detection value and the toner density are expressed as follows. The toner density of the toner image is calculated based on the output conversion information shown. By using the detected value of the diffused light after correction, the toner density (toner of the toner image (particularly the color toner image) is not affected by the belt surface characteristics such as the surface roughness and glossiness of the intermediate transfer belt 7. Adhesion amount) can be accurately detected up to the high toner concentration range.
Further, according to the image forming apparatus of the present embodiment, when the input current set value is adjusted, output conversion information used for calculating the toner density is determined based on the adjusted input current set value. The output conversion information used for calculating the toner density can be changed in accordance with the change in the surface of the intermediate transfer belt 7.
The image forming apparatus according to the present embodiment further includes a storage unit (RAM 202 of the control unit 200) that stores a plurality of different types of output conversion information that can be used for the calculation of the toner density. Based on the input current setting value, any one of the plurality of types of output conversion information is selected and determined as output conversion information used for calculating the toner density. In this case, the output conversion information can be determined by a simple process of selecting from a plurality of types of output conversion information.
Also, according to the image forming apparatus of the present embodiment, a plurality of optical sensors 160 are provided at different detection locations, and the input current set value is adjusted for each of the plurality of optical sensors 160 and the output conversion information is determined. By doing so, even if the change over time of the surface of the intermediate transfer belt 7 differs at the detection location where the optical sensor 160 is provided, the detection error of the toner density on the intermediate transfer belt 7 over time is suppressed at each detection location. Can do.
Further, according to the image forming apparatus of the present embodiment, the light used by the optical sensor 160 is infrared light whose detection characteristics (sensitivity) do not depend on the color of the toner. It becomes possible to detect the toner density of the toner.
Further, according to the image forming apparatus of the present embodiment, the toner image carried on the intermediate transfer belt 7 is a plurality of color toner images having different colors, and the output conversion information such as the conversion table includes a plurality of colors. The color toner image may be used in common. In this case, the capacity of the memory for storing the output conversion information such as the conversion table can be reduced as compared with the case where the output conversion information such as the conversion table is used for each of a plurality of colors.

  In this embodiment, the case where the toner density (toner adhesion amount) of the toner image on the intermediate transfer belt 7 is detected by the optical sensor 160 has been described. However, the present invention is applicable to other image carriers such as a photoconductor. The same applies to the case where the optical sensor 160 detects the toner density (toner adhesion amount) of the toner image carried on the surface.

7 Intermediate transfer belt 160 Optical sensor 200 Control unit

JP 2004-279664 A JP 2004-354623 A

Claims (7)

An image carrier that carries a toner image on the surface;
A light emitting means for irradiating light on the surface of the image carrier and a toner image carried on the surface; and a light receiving means for receiving specular reflection light and diffuse reflection light reflected from the surface and the toner image. An optical detection means comprising:
Current supply means for supplying an input current to be input to the light emitting means of the optical detection means based on a predetermined input current setting value;
Based on the detection value detected by the optical detection means for the toner image carried on the surface of the image carrier and the output conversion data indicating the relationship between the detection value and the toner density, the toner of the toner image An image forming apparatus comprising: a control unit that calculates density and controls image forming conditions based on the calculated toner density;
An input current adjusting means for adjusting the input current set value based on the detected value of the specularly reflected light detected by the optical detecting means for the surface of the background portion on which the toner image of the image carrier is not carried;
An image forming apparatus comprising: output conversion information determining means for determining output conversion information used for calculating the toner density based on the adjusted input current set value. The image forming apparatus according to claim 1.
The control means is carried on the surface of the image carrier based on the detected value of the specularly reflected light detected by the optical detection means for the surface of the background portion where the toner image of the image carrier is not carried. The detected value of diffused light detected by the optical detection means is corrected for the toner image, the detected value of diffused light after the correction, and the output conversion information indicating the relationship between the detected value of diffused light and the toner density And calculating the toner density of the toner image based on the above. The image forming apparatus according to claim 1 or 2,
The output conversion information determining means determines output conversion information used for calculating the toner density based on the adjusted input current setting value when the input current setting value is adjusted by the input current adjusting means. An image forming apparatus. The image forming apparatus according to claim 1 or 2,
Storage means for storing a plurality of different types of output conversion information that can be used for calculating the toner density;
The output conversion information determination unit selects any one of the plurality of types of output conversion information based on the adjusted input current set value, and outputs the conversion information used for calculating the toner density. An image forming apparatus characterized by determining. The image forming apparatus according to claim 1,
A plurality of the optical detection means are provided at different detection locations,
The input current adjustment means adjusts the input current set value for each of the plurality of optical detection means,
The output conversion information determination unit determines the output conversion information for each of the plurality of optical detection units. The image forming apparatus according to claim 1,
An image forming apparatus characterized in that light used in the optical detection means is infrared light. The image forming apparatus according to claim 1,
The toner image carried on the image carrier is a color toner image of a plurality of colors different from each other,
The image forming apparatus, wherein the output conversion information can be used in common for the color toner images of the plurality of colors.

Images