JP2007171541A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing a transfer defect caused under the influence of toner sticking on the transfer body in a transfer stage for toner from an image carrier to a recording material on the transfer body or to the transfer body by detecting the toner on the transfer body with simple constitution. <P>SOLUTION: The image forming apparatus includes: the image carrier 1 carrying a toner image; the transfer body 51 carrying and conveying the recording material P; a transfer means 55 of transferring the toner image on the image carrier 1 to the recording material P on the transfer body 51; a transfer bias output means 56 of outputting a bias for the transfer to the transfer means 55; an optical sensor 9 which detects reflected light when the transfer body 51 is irradiated with light; and a control means 110 of controlling the bias for the transfer output by the transfer bias output means. The control means 110 is configured to control the bias for the transfer output by the transfer bias output means 56 according to the result of detection of the quantity of the reflected light from the transfer body 51 by the optical sensor 9. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that forms an image by using an electrophotographic system or an electrostatic recording system.

  2. Description of the Related Art Conventionally, for example, in an electrophotographic image forming apparatus, an electrostatic image (latent image) formed on an electrophotographic photosensitive member (photosensitive member) generally used as an image carrier is developed as a toner image. The toner image is finally electrostatically transferred to a recording material such as recording paper. Thereafter, the toner image on the recording material is typically fixed on the recording material by heating and pressing.

  As a color image forming apparatus using an electrophotographic system, for example, the following system is known. That is, a method of directly transferring toner images formed on a plurality of photosensitive members onto a recording material conveyed by an electrostatic transportation belt (ETB) as a transfer member (hereinafter referred to as “direct transfer method”). .) Further, the toner images on the plurality of photosensitive members are temporarily transferred (primary transfer) to an intermediate transfer belt as a transfer member, and then the toner images are transferred from the intermediate transfer belt onto a recording material (secondary transfer). System (hereinafter referred to as “intermediate transfer system”). At present, these two types of color image forming apparatuses are mainstream. An image forming apparatus in which a plurality of photoconductors are arranged along the surface movement direction of the conveyance belt or the intermediate transfer belt is generally called a tandem type or inline type image forming apparatus.

  Of the two methods described above, in the former direct transfer method, a plurality of photoconductors are individually charged by the charging unit, and electrostatic images are individually formed on the plurality of photoconductors by the exposure unit. Then, the electrostatic image on each photoconductor is developed as a toner image by, for example, negatively charged toner adhered by a developing unit. This toner image is directly transferred to a recording material conveyed by an electrostatic conveyance belt (hereinafter simply referred to as “conveyance belt”).

  In the latter intermediate transfer system, the intermediate transfer belt is in contact with the photosensitive member at the primary transfer portion, and the toner image formed on the photosensitive member is temporarily transferred onto the intermediate transfer belt at the primary transfer portion. Transcribed. Thereafter, the toner image is transferred (secondary transfer) from the intermediate transfer belt to the recording material in the secondary transfer portion.

  The direct transfer method requires only one transfer for each color toner, and therefore has an advantage that an image that is essentially superior to character scattering or the like can be obtained compared to the intermediate transfer method.

  On the other hand, in the intermediate transfer method, unlike the direct transfer method, there is no need to adsorb the recording material to the transfer body, and a plurality of toner images formed on the intermediate transfer belt are transferred to the recording material in a lump. Therefore, there is an advantage that a thumbtack can be formed without selecting a recording material.

For example, as an image forming apparatus that employs a direct transfer method, Patent Document 1 discloses an apparatus that detects an electrical resistance of a recording material by an adsorption roller that electrostatically attracts the recording material to a conveyance belt. According to this method, even when recording materials or transport belts that have elements that are unstable in terms of electrical resistance due to changes in the environment (temperature / humidity) are used, the electrical resistance of the recording materials and transport belts is directly measured. It can be detected well and the transfer bias corresponding to it can be obtained.
JP 2001-209233 A JP 2001-147632 A JP 2000-305379 A

  In general, the toner deteriorates as the durability of the image forming unit including the photosensitive member, the charging unit, the developing unit, and the like progresses. The toner thus deteriorated is likely to be transferred to a non-image portion on the photosensitive member (a portion where the toner on the photosensitive member should not adhere: a dark portion potential portion) to cause a phenomenon of fogging. Hereinafter, the toner that moves to the photoconductor due to the fogging phenomenon is referred to as “fogging toner”.

  If the fog toner is a direct transfer system, for example, the fog toner is transferred to the transport belt and stains the transport belt. Similarly, in the case of the intermediate transfer system, the image is transferred to the intermediate transfer belt, and the intermediate transfer belt is soiled.

  In the direct transfer method, if fog toner is present on the conveyance belt, the adhesion between the recording material and the conveyance belt is lowered. In the intermediate transfer method, the adhesion between the photosensitive member and the intermediate transfer belt is lowered.

  For this reason, if fog toner is present, the transfer bias may be insufficient under normal control, and transfer defects may occur. That is, when the adhesion is lowered by the fog toner, in the direct transfer system, the contact resistance between the recording material and the conveyance belt is increased as compared with the case where the fog toner is not present. Similarly, in the intermediate transfer method, the contact resistance between the photosensitive member and the intermediate transfer belt is increased as compared to when no fog toner is present. Therefore, in order to transfer the toner on the photoreceptor normally, it is desired to apply a higher transfer bias.

  Typically, the fogging toner as described above causes the conveyance belt or the intermediate transfer belt to become soiled with toner over time. May get dirty.

  However, conventionally, it has not been possible to detect the presence of fog toner directly on the conveyance belt 51 with a simple configuration. Therefore, for example, even if the transfer bias is obtained according to the electrical resistance values of the recording material P and the conveyance belt 51, a transfer bias sufficient to transfer the toner on the photosensitive drum 1 to the recording material P can be given. In some cases, transfer defects may occur.

  By the way, the toner adhering to the conveyance belt or the intermediate transfer belt is generally removed and collected from the conveyance belt or the intermediate transfer belt by contacting a cleaning member such as a cleaning blade or a brush provided in the belt cleaning unit. .

  On the other hand, conventionally, as disclosed in Patent Document 2, there is a method in which the toner on the conveyance belt or the intermediate transfer belt is reversely transferred to the photosensitive member, and the toner is collected by the cleaning means of the photosensitive member. Hereinafter, such a belt cleaning method is referred to as “electrostatic cleaning”. According to the electrostatic cleaning, there is an advantage that the space for the waste toner container of the belt cleaning unit becomes unnecessary.

  However, the execution interval of electrostatic cleaning of such a conveyance belt or intermediate transfer belt is usually about once after printing about 100 pages. For this reason, the conveyance belt or the intermediate transfer belt may be contaminated with fog toner or the like in the latter half of the electrostatic cleaning execution interval. As a result, for example, there is a possibility that the transfer failure as described above may occur. Such electrostatic cleaning of the conveying belt or the intermediate transfer belt may be performed every time a print job (image forming operation on one or a plurality of recording materials in response to one image forming start instruction) is started. However, there is a possibility that the time that the user must wait for the image output becomes long and the usability is lowered.

  Here, Patent Document 3 discloses a method of detecting the amount of dirt on the rubbing means for rubbing the intermediate transfer member with an optical reflection sensor and changing the voltage applied to the secondary transfer means according to the detection result. To do. However, the method disclosed in Patent Document 3 does not control the bias transferred from the photoreceptor to the belt side based on the detection result of the optical reflection sensor. Further, in the above method described in Patent Document 3, the amount of toner adhesion on the intermediate transfer member is not directly detected, and providing the rubbing means as described above leads to a complicated configuration of the image forming apparatus. .

  Accordingly, an object of the present invention is to detect toner on a transfer member with a simple configuration and generate an image from the image carrier to the recording material or transfer member on the transfer member, which is generated by the influence of the toner attached on the transfer member. An object of the present invention is to provide an image forming apparatus capable of suppressing transfer failure in toner transfer.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the first aspect of the present invention provides an image carrier that carries a toner image, a transfer member that carries and conveys a recording material, and a toner image on the image carrier as a recording material on the transfer member. A transfer means for transferring; a transfer bias output means for outputting a bias for the transfer to the transfer means; an optical sensor for detecting reflected light when light is irradiated on the transfer body; and the transfer And a control unit that controls the bias for transfer output from the bias output unit. The control unit is configured to detect the amount of light reflected from the transfer body by the optical sensor. The image forming apparatus controls the bias for the transfer output by the transfer bias output means.

  According to the second aspect of the present invention, an image carrier that carries a toner image, a transfer member to which toner on the image carrier is transferred, and a transfer unit that transfers the toner image on the image carrier to the transfer member. A transfer bias output means for outputting a bias for the transfer to the transfer means, an optical sensor for detecting reflected light when light is irradiated on the transfer body, and the transfer bias output means. Control means for controlling the bias for transfer to be output, secondary transfer means for secondary transfer of the toner image on the transfer member to a recording material, and for the secondary transfer with respect to the secondary transfer means And a secondary transfer bias output means for outputting the bias of the transfer bias output means according to a result of detecting the amount of reflected light from the transfer body by the optical sensor. Image forming apparatus is provided, which comprises controlling a bias for the transfer to be output.

  According to a third aspect of the present invention, an image carrier that carries a toner image, a transfer member that carries and transports a recording material, and a transfer that transfers a toner image on the image carrier to a recording material on the transfer member. A transfer bias output means for outputting a bias for the transfer to the transfer means, an optical sensor for detecting reflected light when light is irradiated on the transfer body, and before the transfer A detection means for detecting a voltage generated in the transfer body when a detection current is applied to the transfer body or a current flowing in the transfer body when a detection voltage is applied to the transfer body; and a detection result of the detection means And a control unit that controls the bias for transfer output from the transfer bias output unit based on the result of detecting the amount of reflected light from the transfer body by the optical sensor. The control unit controls that the relationship between the bias value for transfer output from the transfer bias output unit differs from the detection result of the voltage or current by the detection unit when the detection current or the detection voltage is applied. An image forming apparatus is provided.

  According to the fourth aspect of the present invention, an image carrier that carries a toner image, a transfer member to which toner on the image carrier is transferred, and a transfer unit that transfers the toner image on the image carrier to the transfer member. A transfer bias output unit that outputs a bias for the transfer to the transfer unit, an optical sensor that detects reflected light when light is irradiated on the transfer body, and the transfer sensor before the transfer Based on a detection means for detecting a voltage generated in the transfer body when a detection current is applied to the transfer body or a current flowing in the transfer body when a detection voltage is applied to the transfer body, and a detection result of the detection means Control means for controlling the bias for the transfer output by the transfer bias output means, secondary transfer means for secondary transfer of the toner image on the transfer member to the recording material, and the secondary transfer means For the secondary transfer In the image forming apparatus having a secondary transfer bias output unit that outputs a bias, when the result of detecting the amount of reflected light from the transfer body by the optical sensor is different, the detection current or the detection voltage is applied. There is provided an image forming apparatus that controls that the relationship of the bias value for transfer output from the transfer bias output unit differs from the detection result of the voltage or current by the detection unit at the time .

  According to the present invention, the toner on the transfer member is detected with a simple configuration, and the toner from the image carrier to the recording material on the transfer member or the transfer member is generated due to the influence of the toner attached on the transfer member. Transfer defects in transfer can be suppressed.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
[Overall Configuration and Operation of Image Forming Apparatus]
FIG. 1 shows a schematic cross section of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus 100 according to the present exemplary embodiment can form a full color image corresponding to an image information signal on a recording material (recording medium) P, for example, a recording sheet, an OHP sheet, or the like, using an electrophotographic method. It is a laser beam printer. The image information signal is sent to the apparatus main body A from an external device such as a personal computer that is communicably connected to the image forming apparatus main body (apparatus main body) A. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type direct transfer type multicolor image forming apparatus.

  The image forming apparatus 100 includes four image forming units, that is, first to fourth stations Sa, Sb, Sc, and Sd. Each station Sa, Sb, Sc, Sd is for forming an image of each color of yellow, magenta, cyan, and black, respectively.

  In the present embodiment, the configurations and operations of the stations Sa to Sd are substantially the same except that the color of the toner used is different. Therefore, in the following, when there is no particular need to distinguish, subscripts a, b, c, and d given to the reference numerals are omitted to indicate that they are elements provided for any color, and a general description will be given. To do.

  The station S has a photosensitive drum 1 as an image carrier that carries a toner image. Around the photosensitive drum 1, a charging roller 2 as primary charging means, an exposure device (laser scanner device) 3 as exposure means, a developing device 4 as developing means, and a drum cleaner 6 as cleaning means are provided. Yes.

  In this embodiment, the four independent stations S including the photosensitive drum 1, the charging roller 2, the developing device 4, the exposure device 3, and the drum cleaner 6 are arranged in a vertical line. Further, a transfer unit 5 provided with a conveyance belt (recording material carrier) 51 as a transfer body is arranged so as to face each station S. For example, a full color image can be formed by adsorbing and conveying the recording material P to the conveying belt 51 and transferring the toner from the photosensitive drum 1 of each station S.

  Here, in this embodiment, the photosensitive drum 1 and the charging roller 2, the developing device 4, and the drum cleaner 6 as process means acting on the photosensitive drum 1 are integrally formed into a cartridge, and the apparatus body A A removable process cartridge B is formed.

  The photosensitive drum 1 as an image carrier is a rotary drum type electrophotographic photosensitive member that is repeatedly used, and is rotationally driven at a predetermined peripheral speed (process speed) v1 [mm / s] in a clockwise direction indicated by an arrow in the drawing. The In this embodiment, the photosensitive drum 1 is a negatively charged OPC photosensitive member having a diameter of 30 mm.

The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2 during the rotation process. A DC voltage of −1.2 kV is applied to the charging roller 2 as a charging bias from a charging bias power source (not shown) as a charging bias output unit. In this embodiment, the charging roller 2 is a roller having an actual resistance of 1 × 10 ⁶ Ω, and is in contact with the photosensitive drum 1 with a total pressure of 9.8 N and is driven to rotate. As a result, the surface of the photosensitive drum 1 is charged to −600 V by the DC contact charging method.

  Next, the charged surface of the photosensitive drum 1 is subjected to image exposure by the exposure device 3. Thereby, an electrostatic image (latent image) corresponding to the color component image of the target color image is formed on the photosensitive drum 1 of each station S. The exposure device 3 includes a laser diode, a polygon scanner, a lens group, and the like, and forms an electrostatic image by forming an image of the laser beam modulated by the image signal on the photosensitive drum 1.

  In the main scanning direction (a direction orthogonal to the progress of the recording material P), writing of laser exposure is performed with a predetermined time delay from a position signal in a polygon scanner called BD for each scanning line. Further, in the sub-scanning direction (advancing direction of the recording material P), it is delayed by a predetermined time from a TOP signal starting from a switch in the paper conveyance path. As a result, each station S can always perform exposure at the same position on the recording material P.

  Next, the electrostatic image on the photosensitive drum 1 is developed by the developing device 4. The developing device 4 develops an electrostatic image as a toner image by a one-component developer that does not include a magnetic material as a developer, that is, a one-component contact development method using toner. In this embodiment, the charging polarity of the toner is negative.

  The developing device 4 has a developing roller disposed as a developer carrying member facing the photosensitive drum. The developing roller is coated with toner with a developing blade as a developer regulating member. The developing roller is rotationally driven at substantially the same speed as the photosensitive drum 1 to supply toner to the photosensitive drum 1. A developing bias power source (not shown) as a developing bias output means is connected to the developing roller, and a DC voltage of about −500 V is applied as a developing bias during the developing operation. Thereby, the electrostatic image on the photosensitive drum 1 is developed by the reversal development method.

  In this embodiment, the toner is a spherical toner having a two-layer structure manufactured by a polymerization method, and a resin binder layer called a shell is surrounded around a wax at the center.

  The transfer unit 5 has a transport belt 51 that moves endlessly. The conveyor belt 51 is stretched around three rollers, a driving roller 52 and driven rollers 53 and 54. The conveyor belt 51 is disposed to face all the photosensitive drums 1. The conveyor belt 51 is driven by a driving roller 52 and is driven to rotate at a predetermined peripheral speed v2 [mm / s] in the direction indicated by an arrow in the drawing. As a material for forming the conveyance belt 51, a dielectric resin such as a polyethylene terephthalate resin (PET resin), a polyvinylidene fluoride resin, a polyurethane resin, or a polyimide resin can be preferably used. In this embodiment, the peripheral speed v1 of the photosensitive drum 1 and the peripheral speed v2 of the transport belt 51 are substantially the same 181 [mm / s].

  Inside the transport belt 51, a transfer roller 55 that is in contact with the inner peripheral surface of the transport belt 51 is provided so as to face the respective photosensitive drums 1. The transfer roller 55 is in contact with the photosensitive drum 1 via the transport belt 51, and forms a transfer portion (transfer nip) N between the transfer roller 55 and the photosensitive drum 1. Each transfer roller 55 is connected to a transfer bias power source (high voltage power source) 56 as a transfer bias output unit. During the transfer process, the transfer bias output from the transfer bias power source 56 is applied to the transfer roller 56. In this embodiment, a positive transfer bias having a polarity opposite to the normal charging polarity of the toner is applied. The toner image on the photosensitive drum 1 is transferred to the recording material P in contact with the photosensitive drum 1 by an electric field that directs the toner from the photosensitive drum 1 to the conveying belt 51 side formed by the transfer bias.

As the transfer roller 55, an elastic roller made of a blend of epichlorohydrin rubber and NBR rubber capable of applying a high voltage adjusted to a volume resistivity of 1 × 10 ⁷ Ωcm was used. The transfer roller 5 is in contact with the nip portion N between the back surface of the conveyor belt 51 and the photosensitive drum 1 with a transfer pressure of 2.94 [N].

  The recording material P is supplied from the cassette in a recording material supply unit (not shown), passes through the registration roller, and then contacts the conveying belt 51 via the transfer inlet guide.

  In this embodiment, the process cartridge B is arranged vertically, and the apparatus main body A is divided between the transport belt 51 and the process cartridge B. As a result, the installation area of the image forming apparatus 100 can be minimized, or a desired object can be achieved by opening and closing only the front door for the replacement of the process cartridge B and jam processing. With such a configuration, since the recording material P is conveyed upward against gravity, the recording material P and the conveyance belt 51 are sufficiently adsorbed.

  That is, in this embodiment, the recording material P is sandwiched with the conveyance belt 51 near the contact point between the recording material P and the conveyance belt 51, and the adsorption as the adsorption means for adsorbing the recording material P to the transfer belt 51 is performed. A roller 57 is provided. The suction roller 57 sandwiches the conveyance belt 51 between the driven roller 54 and forms a suction portion (suction nip) Q.

  The suction roller 57 is connected to a suction bias power source 58 as suction bias output means. When the recording material P is conveyed, the suction bias voltage output from the suction bias power source 58 is applied to the suction roller 57, so that the recording material P is in contact with the driven roller 54 as an electrically grounded facing member facing the suction roller 57. An electric field is formed between them. As a result, dielectric polarization is generated between the conveyance belt 51 and the recording material P, and an electrostatic attracting force is generated on both. In this embodiment, during image formation, a voltage of +1 kV is applied as the suction bias to the suction roller 57 from the suction bias power source 58 and charges are applied to the recording material P, thereby generating suction transport force.

The suction roller 57 is a solid rubber roller having a diameter of 12 mm in which carbon black is dispersed in EPDM rubber for resistance adjustment, and a high pressure bias for suction can be applied to the core metal. The electric resistance value of the suction roller 57 is adjusted so that the resistance value becomes 1 × 10 ⁶ Ω when a metal foil having a width of 1 cm is wound around the outer periphery of the roller and a voltage of 500 V is applied between the metal core. .

  In the present embodiment, in the suction portion Q, a bias is applied to the suction roller 57 that contacts the outer peripheral surface of the transport belt 51, and the driven roller 54 that contacts the inner peripheral surface of the transport belt 51 is electrically grounded. . However, on the contrary, the suction roller 57 may be electrically grounded by applying a suction bias to the driven roller 54. In this case, the polarity of the applied suction bias is opposite to the above. Further, the suction bias is not limited to the suction means that is in contact with the conveyance belt 51, but may be applied to the suction means that is disposed in non-contact with the conveyance belt 51, such as a corona charger.

  In a recording material supply unit (not shown), the recording material P which is supplied from the cassette and passes through the transfer inlet guide and the suction roller 57 and obtains the suction force with the transport belt 51 is transported by the transport belt 51. And enters the transfer section Na of the first station Sa. In the transfer portion Na, the toner image is transferred from the photosensitive drum 1a onto the recording material P by the transfer roller 55a provided on the back surface of the conveyance belt 51.

  Here, in this embodiment, the transfer bias applied to the transfer roller 55 when the toner is transferred to the recording material P is calculated from the current flowing through the suction roller 57 during the sheet passing prior to the transfer process. And the impedance of the recording material P. In the present embodiment, in one-sided printing in a normal environment, a DC bias controlled at a constant voltage of about +1.1 kV to +1.5 kV is applied from the transfer bias power source 56 to the transfer roller 55 of each station S.

  The method itself of detecting information related to the electrical resistance value of the conveyance belt 51 and the recording material P and determining the transfer bias value according to the detection result is an arbitrary method such as the method described in Patent Document 1. The method can be adopted.

  More specifically, for example, the suction bias power source 58 includes a suction bias output unit that outputs a bias to the suction roller 57. Further, the suction bias power supply 58 includes a detection unit that detects an output voltage value or an output current value when the suction bias output unit outputs a bias controlled by constant current control or constant voltage control. Then, when there is no recording material P in the suction portion Q or when it is present, a predetermined constant current control or constant voltage controlled bias is output to the suction roller 57 from the suction bias output portion of the suction bias power source 58. To do. As a result, a bias under constant current control or constant voltage control, that is, a detection current or a detection voltage is applied to the transport belt 51 via the suction roller 57.

  The detection unit detects a voltage or current generated between the input side and output side terminals of the suction bias output unit at this time. And the said detection part outputs the electric signal which concerns on a detection result with respect to CPU110 as a control means. The CPU 110 can obtain the electrical resistance value of the transport belt 51 from the detection result of the output voltage value or the output current value of the suction bias output unit when the recording material P is not in the suction unit Q. Further, the CPU 110 can obtain the electrical resistance values of the conveyance belt 51 and the recording material P from the detection result of the output voltage value or the output current value of the suction bias output when the recording material P exists in the suction portion Q. Therefore, the CPU 110 controls the transfer bias value applied to the transfer roller 55 from the transfer bias power source 56 of each station S according to the electric resistance value of the conveyance belt 51 and the recording material P based on the detection result of the detection unit. can do. The detection unit may be connected to the suction bias power source 58 instead of being built in the suction bias power source 58.

  For example, when detecting an output voltage value when a constant current controlled bias is output from an adsorption bias output as in this embodiment, the detected voltage value is increased linearly or nonlinearly by a predetermined arithmetic expression. This value can be used as the transfer bias value at each station S. In addition, table data relating the current or voltage detection result by the detection unit and the transfer bias value at each station S is set, and the CPU 110 determines the transfer bias value by referring to this table data. It may be. Information such as these arithmetic expressions and table data can be stored in advance in a ROM 112 as storage means electrically connected to the CPU 110.

  In the present embodiment, the suction roller 57 and the suction bias power source 58 constitute detection means for detecting a voltage generated in the transport belt 51 when a detection current is applied to the transport belt 51 before transfer. The detection means may be configured to detect a current flowing through the conveyor belt 51 when a detection voltage is applied to the conveyor belt 51. In the present embodiment, in particular, the detection means applies the detection current or detection voltage in the region of the transfer member 51 carrying the recording material P, and detects the voltage or current value at that time. The CPU 110 constitutes a control means for controlling the bias for transfer output from the transfer bias power supply 55 based on the detection result of the detection means.

  In this embodiment, as described above, a predetermined detection bias is applied to the suction roller 57 as detection means for detecting information related to the electrical resistance values of the conveyance belt 51 and the recording material P. However, the present invention is not limited to this. For example, when the suction bias is applied to the driven roller 54 in the suction portion Q as described above, the driven roller 54 may be used as a detection unit. it can.

  Alternatively, a transfer roller 55 that is a transfer unit can be used as a detection unit for detecting information related to the electrical resistance values of the conveyance belt 51 and the recording material P. For example, in each transfer portion N, when the recording material P is not present or is present (such as a non-image portion at the leading end of the recording material P), the detection current or detection voltage is applied, and the voltage or current value at that time is calculated. Can be detected. Further, among the transfer portions N of the plurality of stations S, in the transfer portion N on the upstream side in the conveying direction of the recording material P, when the recording material P is not present or present in the transfer portion N, the detection current or the detection voltage is set. It may be applied to detect the voltage or current value at that time. Then, the transfer bias in the transfer portion N downstream from the transfer portion N may be obtained.

  Further, as another method, the detection means may be provided separately from the suction roller 57, the driven roller 54, or the transfer roller 55.

  As described above, a more appropriate transfer bias can be obtained by obtaining the transfer bias according to the electrical resistance values of the recording material P and the conveying belt 51, but the present invention is not limited to this. If desired, the transfer bias may be predetermined as a predetermined value.

  For example, when a full-color image is formed, toner images are formed on the photosensitive drums 1a to 1a at the stations Sa to Sd as described above. Each time the recording material P passes through the transfer portions Na to Nd of the stations Sa to Sd, toner images of different colors are sequentially transferred onto the recording material P from the photosensitive drum 1.

  The recording material P is separated from the conveyance belt 51 by using the curvature of the driving roller 52 after the transfer of the toner images of all colors is completed after passing through the transfer portion Nd of the fourth station S. Thereafter, the recording material P is conveyed to a heating / pressure fixing device 7 as a fixing unit.

  The fixing device 7 includes, as a fixing member, a fixing roller 71 (heating fixing member) 71 having a heating unit disposed inside, and a pressure roller (pressure fixing member) 72. The fixing device 7 melts and mixes the unfixed toner image by applying heat and pressure to the recording material P in a fixing portion (fixing nip) formed by the fixing roller 71 and the pressure roller 72, and also performs recording. It is fixed on the material P. Thereby, for example, a full-color image is formed as a recorded image.

  The recording material P on which the image is fixed is discharged out of the apparatus via a transport unit (not shown). A final print is thus obtained.

  Further, the toner (transfer residual toner) remaining on the photosensitive drum 1 after the transfer process is removed and collected by the drum cleaner 6.

[Optical sensor]
Next, the optical sensor P provided in the image forming apparatus 100 of this embodiment will be described.

  The density of the toner image formed on the photosensitive drum 1 may change with time and / or temperature, humidity, etc. in the apparatus. Therefore, in this embodiment, a density detection toner image (patch image) having a predetermined density is formed on the photosensitive drum 1 at a predetermined timing, and this is transferred to the conveyance belt 51. The density (toner adhesion amount) of this batch image is detected by the reflective optical sensor 9. An electrical signal corresponding to the density detected by the optical sensor 9 is sent to the CPU 110. In accordance with this signal, the CPU 110 controls the amount of toner replenished into the developing device 4 in this embodiment. This density control sequence is performed for each station S.

  In addition, due to an assembly error of the apparatus, replacement of the transfer unit 5 including the conveyance belt 51, replacement of the process cartridge B, and the like, the color toner images may not be properly superimposed on the recording material P, and color misregistration may occur. Therefore, in the present embodiment, in order to prevent this in advance, the color misregistration correction control sequence may be performed every predetermined period or at a predetermined time. First, a predetermined toner image (patch image) for color misregistration correction control is formed on the photosensitive drum 1, and this is transferred to the transport belt 1. The optical sensor 9 detects this patch image and sends an electrical signal to the CPU 110. The CPU 110 can detect information related to the position on the conveying belt 51 of a predetermined toner image for color misregistration control using an electrical signal from the optical sensor 9. This sequence is performed for each station S. The CPU 110 determines the color misregistration status, and controls the image formation start timing in each station S in this embodiment.

  As shown in FIG. 2, in this embodiment, the reflective optical sensor 9 includes a light emitting element 91 such as an LED having a wavelength of 950 nm, a light receiving element 92 such as a photodiode, and a holder 93. In this embodiment, the optical sensor 9 is provided to face the conveyance belt 51 at the position of the driven roller 54.

  For example, when the density detection of a patch image for density detection is described as an example, the optical sensor 9 irradiates the patch image on the conveyor belt 51 with light from the light emitting element 91 (in this embodiment, infrared light). Then, the reflected light is measured by the light receiving element 92. Thereby, the density of the patch image is measured. The reflected light from the patch image includes a regular reflection component and an irregular reflection component. Basically, the regular reflection component is light reflected by the conveyor belt 51 as a base, and the amount of reflected light decreases as the amount of toner increases. On the other hand, the irregular reflection component is light scattering by toner, and the amount of reflected light increases as the amount of toner increases. However, for example, when infrared light having a wavelength of 950 nm is used, the black toner exceptionally absorbs this infrared light, so that the amount of reflected light decreases as the toner amount increases. The optical sensor 9 outputs a signal corresponding to the amount of light received by the light receiving element 92 to the CPU 110.

  In the following description, the detection result of the optical sensor 9 may refer to the magnitude of the “reflectance” to be detected or the difference value thereof. However, this does not mean that in the control using the optical sensor 9, the detection result of the optical sensor 9 is converted into a reflectance form and used. The detection result of the optical sensor 9 is processed in the form of any signal corresponding to the amount of reflected light received when the optical sensor 9 irradiates light onto the belt, substantially corresponding to the reflectance of the detection target. Also good. For example, as will be readily understood by those skilled in the art, a voltage output value, a current output value associated with the reflectance of the detection target, or a digital signal in which these are A / D converted, as described below. It is possible to compare the values in magnitude or calculate the difference value.

  The toner amount can be detected regardless of whether the regular reflection light amount or the irregular reflection light amount is measured (detected). In this embodiment, a method of measuring (detecting) a regular reflection component is adopted. When detecting the color misregistration correction patch image, the CPU 110 detects the presence or absence (corresponding to density information) of a toner image having a predetermined pattern on the conveyance belt 51 from the change in the amount of light received by the light receiving element 92. Information relating to the timing at which the toner image is detected can be detected.

[Electrostatic cleaning]
Next, the fog toner adhering to the conveyance belt 71, or the toner of the toner image for density detection and the toner image for color misregistration control (hereinafter, these toners may be collectively referred to as “unnecessary toner”). The cleaning method will be described.

  As described above, fog toner easily adheres to the conveyor belt 51, for example, when the toner deteriorates due to durability. As described above, the fog toner may cause a transfer failure in the transfer portion N.

  In this embodiment, unnecessary toner on the conveyor belt 51 is electrostatically reversely transferred to the photosensitive drum 1 and the reversely transferred unnecessary toner is collected by the drum cleaner 6 (electrostatic cleaning). As the electrostatic cleaning method itself, any available method such as the method described in Patent Document 2 can be employed. For example, in this embodiment, the electrostatic cleaning of the conveyor belt 51 is performed as follows.

  In the present embodiment, there are cases where both positive and negative toners are present in the unnecessary toner adhering to the transport belt 51. Therefore, the polarity of the voltage applied to the transfer rollers 55a to 55d is appropriately switched to change the photosensitive toner. Cleaning is performed by reverse transfer to the drums 1a to 1d. More specifically, in this embodiment, during cleaning, the first and fourth transfer rollers 55a and 55d have a positive voltage, and the second and third transfer rollers 55b and 55c have a negative voltage. Applied. As a result, the toner charged to positive polarity is reversely transferred to the first and fourth photosensitive drums 1a and 1d, and charged negatively to the second and third photosensitive drums 1b and 1c. The toner being transferred is reversely transferred.

  More specifically, a voltage of 1.0 KV having the same polarity as that during normal image formation (in this embodiment, positive polarity) is applied to the first transfer roller 55a, and the polarity is opposite to the normal charging polarity of the toner. The transferred toner is transferred to the first photosensitive drum 1a. Then, this toner is collected in a waste toner container of the first drum cleaner 6a. At this time, some of the toner that passes through the first photosensitive drum 1a without being collected is one whose polarity is reversed. Here, the polarity of the voltage applied to the first transfer roller 55a is opposite to the normal charging polarity of the toner because the charging polarity is reversed positively to the unnecessary toner on the conveying belt 51. Because there are few things. With such a configuration, it is possible to prevent unnecessary toner from being offset and collected in the waste toner container of the first drum cleaner 6a. Therefore, it is possible to prevent the first process cartridge Ba from being replaced abnormally earlier than the other process cartridges Bb to Bd.

  Next, a voltage of -1.5 KV having a polarity opposite to that at the time of normal image formation (positive polarity in this embodiment) is applied to the second transfer roller 55b, so that the negative polarity that has not been collected on the first photosensitive drum 1a is applied. The charged toner is transferred to the second photosensitive drum 1b. Then, the toner is collected in a waste toner container of the second drum cleaner 6b. However, if the amount of unnecessary toner on the transport belt 51 is large, it may not be possible to collect all negatively charged toner.

  Thereafter, the toner remaining on the conveyance belt 51 is charged with the original negative polarity when it passes between the negative toner remaining without being collected and the second photosensitive drum 1b and the second transfer roller 55b. Is a toner that has been reversed to a reverse polarity (positive polarity).

  Similarly, a voltage of -1.5 KV having a polarity opposite to that at the time of normal image formation (positive polarity in this embodiment) is applied to the third transfer roller 55c, so that the negative polarity that has not been collected on the second photosensitive drum 55b is applied. The charged toner is transferred to the third photosensitive drum 1c. Then, the toner is collected in a waste toner container of the third drum cleaner 6c. Nearly all of the unnecessary toner charged to the negative polarity on the conveyance belt 51 is collected, and after that, what remains on the conveyance belt 51 is a small amount of toner charged to the positive polarity.

  A voltage of 1.0 KV having the same polarity as that during normal image formation (positive polarity in this embodiment) is applied to the fourth transfer roller 55d. As a result, toner having a polarity (positive polarity) opposite to the original charged polarity, which has not been transferred to the first to third photosensitive drums 1a to 1c and remains on the conveying belt 51, is transferred to the fourth photosensitive drum 1d. Let them transcribe. Then, this toner is collected in a waste toner container of the fourth drum cleaner 6d, and cleaning of unnecessary toner on the transport belt 51 is completed.

  As described above, normally, unnecessary toner of positive and negative polarities on the conveyor belt 51 is efficiently and quickly passed through the photosensitive drums 1a to 1d while the conveyor belt 51 makes one revolution. Each can be collected in a container. However, in the electrostatic cleaning sequence, the conveying belt 51 may be rotated twice or more.

  Accordingly, it is not necessary to provide a dedicated cleaning device (cleaning blade, waste toner container) for the transport belt 51, so that the degree of freedom in designing the device can be increased, the number of waste toner containers can be reduced, and the user can The number of parts to be replaced can be reduced.

Here, during normal image formation, the peripheral speeds of the conveyance belt 51 and the photosensitive drum 1 in each transfer portion N may not be completely coincident due to variations in mechanical accuracy of components. Therefore, in order to prevent the phenomenon that the transferred toner image is lost, or to improve the stability of the conveyance speed of the recording material P by the conveyance belt 51, the peripheral speed of the conveyance belt 51 in each transfer portion N is increased. There may be a slight difference in peripheral speed between the photosensitive drum 1 and the peripheral speed. In this case, the ratio R of the peripheral speed difference of the peripheral speed (B) of the conveying belt 51 to the peripheral speed (A) of the photosensitive drum 1 represented by the following formula is preferably 3% or less.
R = ((B−A) / A) × 100 (%)
This is to prevent the toner image transferred to the recording material P from being excessively expanded with respect to the original image, and preventing the toner from being fused to the photosensitive drum 1 or the conveyance belt 51. However, during the normal image formation, this peripheral speed difference is not necessarily provided, and may be zero.

  In electrostatic cleaning, the speed difference between the peripheral speed of the conveyor belt 51 and the peripheral speed of the photosensitive drum 1 can be made larger than that in the normal image formation. In this case, generally, the peripheral speed of the conveyor belt 51 is made higher than that during normal image formation. With such a configuration, the toner whose charging ability on the conveyance belt 51 has decreased, the density detection toner image laminated on the conveyance belt 51 at the time of jam, the toner image for color misregistration control, etc. The photosensitive drum 1 can perform transfer in a shorter time. That is, by providing a larger peripheral speed difference than that at the time of image formation, transfer efficiency can be improved and cleaning ability can be improved.

  As described above, when a larger peripheral speed difference is provided during electrostatic cleaning than during normal image formation, the peripheral speed difference ratio R is preferably 6% or more. As a result, the unnecessary toner on the transport belt 51 can be cleaned efficiently and stably in a short time. Further, in order to perform the cleaning satisfactorily, the peripheral speed difference ratio is desirably 10% or more. In general, deterioration due to rubbing between the surface of the photosensitive drum 1 and the surface of the conveyor belt 51 cannot be ignored. Therefore, the ratio of the peripheral speed difference is preferably 200% or less. For example, by separately providing a drive source for rotating the photosensitive drum 1 and a drive source for rotating the conveyance belt 51, the ratio of the peripheral speed difference during image formation and electrostatic cleaning can be made different. it can.

  As described above, by providing a peripheral speed difference between the conveyance belt 51 and the photosensitive drum 1 during cleaning, the toner on the conveyance belt 51 can be forcibly moved by a frictional force. As a result, the influence of the van der Waals force between the transport belt 51 and the toner is weakened, and the non-polar toner can be reduced by applying the charge by the transfer roller 55. Since the toner is more strongly affected by the electric field, the cleaning ability is dramatically improved, and the cleaning can be performed efficiently and stably in a short time.

  This electrostatic cleaning sequence is performed during a so-called end rotation (post-rotation) operation after a normal image formation and before a next image formation start signal is input at predetermined intervals or at predetermined times. Is called. Further, when the above-described density control sequence or color shift control sequence is performed, after the sequence is completed, the above-described transport belt 51 is electrostatically cleaned as necessary, and after the cleaning is completed, the next image formation start signal is awaited. The so-called standby mode is entered. In this embodiment, the electrostatic cleaning sequence of the transport belt 51 is executed as one operation in the startup sequence when the image forming apparatus 100 is turned on.

  By the way, in a state where the image forming apparatus is activated, the electrostatic cleaning of the transport belt 51 is normally performed about once after printing about 100 pages.

  However, if the configuration is such that the surface of the conveyor belt 51 is cleaned every predetermined period as described above, the conveyor belt 51 may be contaminated with fog toner or the like in the latter half of the cleaning execution interval as described above.

  If fog toner is present on the conveying belt 51, the adhesion between the recording material P and the conveying belt 51 is lowered. For this reason, if fog toner is present, the transfer bias may be insufficient under normal control, and transfer defects may occur. However, as described above, conventionally, it has not been possible to detect the presence of fog toner directly on the conveyance belt 51 with a simple configuration. Therefore, for example, even if the transfer bias is obtained according to the electrical resistance values of the recording material P and the conveyance belt 51, a transfer bias sufficient to transfer the toner on the photosensitive drum 1 to the recording material P can be given. In some cases, transfer defects may occur.

  It is also conceivable that the electrostatic cleaning of the transport belt 51 as described above is performed every time a print job is started. However, as described above, this may lead to a decrease in usability.

  Therefore, in the present embodiment, during the electrostatic cleaning execution timing of the conveyor belt 51, the degree of contamination of the conveyor belt 51 is detected using the optical sensor 9, and the transfer bias value is corrected according to the detection result. Control. That is, the execution interval of the electrostatic cleaning of the conveying belt 51 is increased as much as possible, and a decrease in transferability due to contamination of the conveying belt 51 is compensated by correcting the transfer bias value. As a result, it is possible to minimize the time during which the user cannot output an image because the electrostatic cleaning of the conveyor belt 51 is performed, improve usability, and always obtain good transfer performance. This will be described in more detail below.

  The optical sensor 9 provided for density detection or color misregistration detection is used for detection of fog toner on the conveyor belt 51, thereby directly detecting the toner on the conveyor belt 51. In addition, the apparatus configuration can be simplified. However, if desired, a special optical sensor may be separately provided for detecting fog toner on the transport belt 51.

[Detection of fog toner]
Next, the fog toner detection means will be described in more detail.

  In this embodiment, the optical sensor 9 reads the reflectance R1 on the conveyance belt 51 after the start-up sequence when the power of the image forming apparatus 100 is turned on. At this time, the conveyor belt 51 is cleaned in the startup sequence, and the reflectance of the conveyor belt 51 when the fog toner is not substantially present on the conveyor belt 51 can be measured. The optical sensor 9 outputs a signal related to the detection result at this time to the CPU 110.

  CPU110 memorize | stores the detection result of the optical sensor 51 obtained at this time in the memory (RAM) 111 as a memory | storage means as reference | standard reflectance R1. The CPU 110 updates this reference value every time the conveyor belt 51 is electrostatically cleaned.

  Next, the reflectance R2 on the conveyance belt 51 is read by the optical sensor 9 during the preparatory rotation operation that is performed before the start of the image forming operation at the time of non-image formation. The CPU 110 reads the reference reflectance R 1 stored in the memory 111, that is, the reflectance R 1 when no fog toner is present on the transport belt 51. Then, the CPU 110 obtains a difference value | R1-R2 | between the reference reflectance R1 and the reflectance R2.

  The reflectances R1 and R2 are subjected to appropriate statistical processing such as averaging with respect to the output of the optical sensor 9 within a certain period of time or a certain section on the conveyor belt 51 (along the moving direction of the conveyor belt 51). It may be a given value.

  The difference value | R1-R2 | of the reflectance detection result indicates the amount of toner remaining on the conveyance belt 51. In other words, in this embodiment, the optical sensor measures the specular reflection component. When the amount of toner adhering to the conveyor belt 51 increases, the reflectance R2 on the conveyor belt 51 is greater than the reference reflectance R1. Get smaller. Therefore, the difference value | R1-R2 | increases as the amount of toner adhering to the transport belt 51 increases. Therefore, the CPU 110 can detect the degree of contamination of the conveyor belt 51 with toner by obtaining the difference value | R1-R2 |.

  Then, the CPU 110 controls the transfer bias in accordance with the difference value | R1-R2 | obtained as described above. In this embodiment, the transfer bias value obtained by the control 9 using the suction roller 57 is corrected as described above. This makes it possible to suppress transfer defects caused by fog toner.

  More specifically, in this embodiment, table data as shown in Table 1 is stored in advance in the ROM 112 as a storage unit as information relating the difference value | R1-R2 | and the correction value of the transfer bias value in advance. Has been. This transfer bias correction value corrects the transfer bias value so that an appropriate transfer efficiency can be obtained when an amount of fog toner indicating the corresponding difference value | R1-R2 | is attached on the conveyance belt 51. The value to get. In this embodiment, the correction value is a voltage value added to the transfer bias obtained by the above-described control using the suction roller 57.

  Then, the CPU 110 refers to the table data stored in the ROM 112 to determine a transfer bias correction value corresponding to the obtained difference value | R1-R2 |. Then, the transfer bias value obtained by the above-described control using the suction roller 57 is corrected by the correction value obtained here, and determined as a transfer bias value applied from the transfer bias power source 56 to the transfer roller 55.

  In other words, when the result of detecting the amount of light reflected from the conveyor belt 51 by the optical sensor 9 is different, the transfer to the detection result of the voltage or current by the detection means when the detection current or the detection voltage is applied. Bias value relationship is different. This is because a correction value corresponding to the result of detecting the amount of reflected light from the conveyor belt 51 is added to the transfer bias value obtained from the detection result of the detection means.

  Table 2 shows a difference value | R1-R2 | of the reflectance detection result indicating the amount of fog toner, a transfer bias correction amount according to the result, and a transfer defect occurrence state depending on whether or not the transfer bias is corrected. The result of investigating the relationship is shown. Note that the environment at this time was a temperature of 23 ° C. and a humidity of 50%, and recording paper X × 4024 (basis weight 75 g) was used as the recording material P.

  As shown in Table 2, when the difference value | R1−R2 | is 0, fog toner is not present on the conveyance belt 51, and thus the transfer bias is not corrected. On the other hand, when the amount of fog toner on the transport belt 51 increases, the transfer defect is worsened when the transfer bias correction control is not performed. On the other hand, in this embodiment, as the difference value | R1−R2 | increases, the correction amount is sequentially increased to + 100V, + 200V, and + 300V, and the transfer bias is corrected, so that no transfer failure occurs. A good image was obtained.

  This is because the presence of fog toner increases the contact resistance between the recording material P and the conveyance belt 51, and a higher transfer bias is required to transfer the toner on the photosensitive drum 1 normally. This is probably because the bias was corrected appropriately.

  In this embodiment, as described above, table data as shown in Table 1 is stored in advance in the ROM 112 as information relating the difference value | R1-R2 | and the correction value of the transfer bias. However, as information indicating the above relationship, a predetermined arithmetic expression for converting the difference value | R1-R2 | into a correction value for the transfer bias is stored in the ROM 112, and the CPU 110 performs transfer using the arithmetic expression. A bias correction value may be calculated. This arithmetic expression may be a linear expression or a curved expression.

  As described above, according to the present embodiment, the amount of fog toner on the conveyance belt 51 is detected during the preparatory rotation operation performed before the start of the image forming operation, and the transfer bias is corrected according to the detection result. Add. As a result, it is possible to suppress the occurrence of transfer failure due to the influence of fog toner without increasing the number of cleaning sequences of the conveyor belt 51.

  In this embodiment, the amount of fog toner on the transport belt 51 is detected during the preparatory rotation operation that is performed before the start of the image forming operation as during non-image formation. On the other hand, the amount of fog toner on the conveyance belt 51 is detected during the end rotation operation performed after the end of the image formation operation as during non-image formation, and the transfer bias is corrected in the next image formation operation. Also good. This also provides substantially the same effect.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration of the image forming apparatus of the present embodiment is the same as that of the first embodiment. Therefore, elements having the same or equivalent functions and configurations as those of the first embodiment are denoted by the same reference numerals and detailed description thereof is omitted, and characteristic points in the present embodiment are mainly described.

  In the first exemplary embodiment, the detection timing of the fog toner on the conveyance belt 51 is only the end rotation operation performed during the preparation rotation operation performed before the start of the image forming operation or after the end of the image forming operation.

  On the other hand, in this embodiment, during non-image formation, during a series of continuous image forming operations on a plurality of recording materials P, a conveyance belt corresponding to a non-image forming area between image forming operations, that is, between paper sheets. The optical sensor 9 detects the reflectance at the location on 51. As a result, the amount of fog toner on the transport belt 51 is detected, and is always fed back to the transfer bias control. This point is different from the first embodiment.

  As in the first embodiment, the amount of fog toner may be detected during the preparatory rotation operation before the start of the image forming operation or during the end rotation operation after the end of the image forming operation.

  More specifically, FIG. 5 shows the relationship between the number of prints and the amount of fog toner on the conveyor belt 51. As can be seen from FIG. 5, the amount of fog toner on the conveyor belt 51 changes according to the number of prints.

  Therefore, in this embodiment, the optical sensor 9 reads the reflectance of the non-image forming area between image forming operations, that is, the portion on the conveying belt 51 corresponding to the interval between sheets, so that the conveying belt is formed during continuous image formation. The amount of fog toner adhering to 51 is detected. Then, the transfer bias is corrected according to the detection result.

  More specifically, first, similarly to the first embodiment, the optical sensor 9 reads the reflectance R1 on the transport belt 51 after the start-up sequence is completed. Then, the detection result of the optical sensor 9 at this time is stored in a memory (RAM) 111 as storage means as a reference reflectance R1.

  Next, at the time of continuous printing, the optical sensor 9 reads the reflectance R2 of the non-image forming area during the image forming operation, that is, the portion on the conveying belt 51 corresponding to the space between the sheets. The CPU 110 reads the reference reflectance R1 stored in the memory 111. Then, the CPU 110 obtains a difference value | R1-R2 | between the reference reflectance R1 and the reflectance R2.

  FIG. 6 schematically shows a region on the conveyor belt 51. In this embodiment, in the surface movement direction of the conveyor belt 51, a section (inter-sheet area) 51a between the trailing edge of the nth image forming area on the conveyor belt 51 and the leading edge of the (n + 1) th image forming area. The optical sensor 9 detects the reflectance. In the direct transfer type image forming apparatus 100, the image forming area on the conveyance belt 51 corresponds to the carrying area of the recording material P, and the non-image forming area corresponds to the area other than the carrying area of the recording material P.

  In the same manner as described in the first embodiment, the reflectance R2 detected in the inter-paper area on the conveyor belt 51 is equal to the output of the optical sensor 9 in the inter-paper area for a certain period of time or in a certain section. It may be a value obtained by performing appropriate statistical processing such as averaging processing.

  The CPU 110 determines a correction value of the transfer bias corresponding to the obtained difference value | R1-R2 | by referring to the table data as shown in Table 1 stored in the ROM 112. Then, the transfer bias value obtained by the above-described control using the suction roller 57 is corrected by the correction value obtained here, and determined as the transfer bias value applied from the transfer bias power source 56 to the transfer roller 55.

  In this way, the transfer bias is corrected for each page in accordance with the difference value | R1-R2 |. Thereby, even when the amount of fog toner on the conveyor belt 51 changes during continuous printing, it is possible to suppress transfer defects.

  As shown in FIG. 4, for example, when the transfer portion Nd of the fourth station Sd is used as a reference, in this embodiment, the position of the optical sensor 9 is the position of the transfer portion N of the fourth station Sd. Therefore, the position of the conveyor belt 51 is shifted by about a half circumference. Therefore, the timing at which the optical sensor 9 is turned on is delayed by a half circumference of the transport belt 51 from the time when the sheet interval is located at the transfer portion Nd of the fourth station Sd.

  Table 3 shows a difference value | R1-R2 | of the reflectance detection result indicating the amount of fog toner, a transfer bias correction amount according to the result, and a transfer defect occurrence state depending on whether or not the transfer bias is corrected. The result of investigating the relationship is shown. Note that the environment at this time was a temperature of 23 ° C. and a humidity of 50%, and recording paper X × 4024 (basis weight 75 g) was used as the recording material P.

  As shown in Table 3, when the difference value | R1−R2 | is 0, no fog toner is present on the conveyance belt 51, and thus the transfer bias is not corrected. On the other hand, when the amount of fog toner on the transport belt 51 increases, the transfer defect is worsened when the transfer bias correction control is not performed. On the other hand, in this embodiment, as the difference value | R1−R2 | increases, the correction amount is sequentially increased to + 100V, + 200V, and + 300V, and the transfer bias is corrected, so that no transfer failure occurs. A good image was obtained.

  As described above, according to the present exemplary embodiment, the amount of fog toner on the conveyance belt 51 that is constantly changed by continuous printing is detected in the non-image forming area during the image forming operation, and the amount of fog toner is always changed according to the detection result. Correction is applied to the transfer bias. As a result, it is possible to suppress the occurrence of transfer failure due to the influence of fog toner without increasing the number of cleaning sequences of the conveyor belt 51.

Example 3
Next, another embodiment of the present invention will be described. The basic configuration of the image forming apparatus of the present embodiment is the same as those of the first and second embodiments. Therefore, elements having the same or equivalent functions and configurations as those of the first and second embodiments are denoted by the same reference numerals and detailed description thereof is omitted, and characteristic points in the present embodiment are mainly described.

  In Examples 1 and 2, the detection timing of the fog toner on the conveyance belt 51 was only during non-image formation.

  In particular, in the second exemplary embodiment, as illustrated in FIG. 6, the conveyance belt 51 in the non-image forming area 51 a during the image forming operation so that the amount of fog toner on the conveyance belt 51 can always be detected during continuous image formation. The amount of fog toner above was detected.

  On the other hand, in this embodiment, as shown in FIG. 6, the amount of fog toner on the conveyance belt 51 is detected in the non-image forming area 51b during the image forming operation. That is, the recording material P on the conveyor belt 51 is a section between the leading edge and the trailing edge of the image forming area on the conveyor belt 51 in the surface movement direction of the conveyor belt 51 and in the direction orthogonal to the movement direction. The optical sensor 9 detects the reflectance of the region 51b outside the edge of the optical sensor. Then, the transfer bias is corrected according to the detection result.

  As a result, as in the second embodiment, for example, the amount of fog toner on the conveyor belt 51 that changes during continuous printing can be detected at all times, and the degree of freedom in the reflectance detection position is increased.

  In addition to the reflectance detection area on the conveyor belt 51 in the present embodiment, the area outside the end in the width direction (direction perpendicular to the moving direction) of the recording material P in the inter-paper area is also the reflectance detection area. Can be included. Thereby, for example, during continuous printing, the reflectance can be detected at an arbitrary position in the surface movement direction of the conveyor belt 51, and the degree of freedom of the reflectance detection position is further increased. That is, if the optical sensor 9 detects the reflectance of the area other than the image forming area on the conveyor belt 51, for example, the amount of fog toner on the conveyor belt 51 can always be detected during continuous printing. Become.

Example 4
Next, still another embodiment of the present invention will be described.

[Overall Configuration and Operation of Image Forming Apparatus]
FIG. 3 shows a schematic cross section of the image forming apparatus 200 of this embodiment. The image forming apparatus 200 according to the present exemplary embodiment can form a full-color image corresponding to an image information signal on a recording material (recording medium) P, such as a recording sheet or an OHP sheet, using an electrophotographic method. It is a laser beam printer. The image information signal is sent to the apparatus main body A from an external device such as a personal computer that is communicably connected to the image forming apparatus main body. The image forming apparatus 200 of the present embodiment is a tandem type intermediate transfer type multicolor image forming apparatus. The intermediate transfer type image forming apparatus 200 is excellent in that good images can be obtained on various recording materials. In FIG. 3, elements having the same or corresponding functions and configurations as those of the image forming apparatus 100 shown in FIG.

  The image forming apparatus 200 includes four image forming units, that is, first to fourth stations Sa, Sb, Sc, and Sd. These four stations Sa to Sd are arranged in a line at regular intervals. Has been placed. Each station Sa, Sb, Sc, Sd is for forming an image of each color of yellow, magenta, cyan, and black, respectively.

  In the present embodiment, the configurations and operations of the stations Sa to Sd are substantially the same except that the color of the toner used is different. Therefore, in the following, when there is no particular need to distinguish, subscripts a, b, c, and d given to the reference numerals are omitted to indicate that they are elements provided for any color, and a general description will be given. To do.

  In the station S, a photosensitive drum 1 as an image carrier is installed. Around the photosensitive drum 1, a charging roller 2, an existing device 4, a primary transfer roller 55, and a drum cleaner 6 are installed. An exposure device (laser scanner device) 3 is installed above the charging roller 2 and the developing device 4.

  The photosensitive drum 1 is a negatively charged organic photosensitive drum. The photosensitive drum 1 has an outer diameter of 30.0 mm, and has an OPC photosensitive layer on a drum base such as aluminum.

  The charging roller 2 as a contact charging means is in contact with the photosensitive drum 1 with a predetermined pressure contact force.

  The developing device 4 employs a two-component developing method using a two-component developer mainly including non-magnetic resin toner particles (toner) and magnetic toner particles as a developer. The developing devices 4a, 4b, 4c, and 4d contain yellow toner, magenta toner, cyan toner, and black toner, respectively. In this embodiment, the developing device 4 develops the electrostatic image on the photosensitive drum 1 as a toner image by reversal development.

  An intermediate transfer unit 10 is provided so as to face the photosensitive drums 1a to 1d of the stations Sa to Sd. The intermediate transfer unit 10 has an intermediate transfer belt (intermediate transfer member) 11 that moves endlessly as a transfer member. The intermediate transfer belt 11 can be formed of the same material as the conveyance belt 51 in the first to third embodiments. A primary transfer roller 15 as a primary transfer unit is disposed on the inner peripheral side of the intermediate transfer belt 11. A primary transfer roller 55 as a contact transfer unit is in contact with the surface of each photosensitive drum 1 with a predetermined pressing force via an intermediate transfer belt 11 as an intermediate transfer member. Thus, a primary transfer portion (primary transfer nip) N1 where the photosensitive drum 1 and the intermediate transfer belt 11 are in contact with each other is formed at each station S.

  The intermediate transfer belt 11 is stretched around a driving roller 12, a secondary transfer counter roller 13, and a driven roller 14. The intermediate transfer belt 11 is stretched in a state where a predetermined tension is applied to the driven roller 14 by a pressure unit. In this embodiment, a load of 98 N is applied so that the intermediate transfer belt 11 and the driving roller 12 do not slip. The driving roller 11, the secondary transfer counter roller 13 and the driven roller 14 are electrically grounded.

  Further, a secondary transfer roller 21 is provided as a secondary transfer unit that contacts the outer peripheral surface of the intermediate transfer belt 11 at the position of the secondary transfer roller 13. The secondary transfer roller 21 as a contact transfer unit is in contact with the secondary transfer counter roller 13 through the intermediate transfer belt 11 with a predetermined pressing force. Thus, a secondary transfer portion (secondary transfer nip) N2 in which the secondary transfer roller 21 contacts the intermediate transfer belt 11 is formed.

  Further, the fixing device 7 is arranged on the downstream side in the transport direction of the recording material P from the secondary transfer portion N2. The fixing device 7 includes a fixing roller 71 and a pressure roller 72.

  In addition, a reflective optical sensor 9 is disposed opposite the intermediate transfer belt 11 at the position of the driving roller 12.

  When an image forming operation start signal is issued from a host computer connected to the apparatus main body, the photosensitive drum 1 of the station S is rotationally driven by a driving device (not shown). The photosensitive drum 1 is rotationally driven at a predetermined moving speed v1 [mm / s] in the arrow direction (counterclockwise direction) in the drawing (v1 [mm / s] is about 117 mm / s in this embodiment).

  Then, the charging roller 2 to which a charging bias is applied from a charging bias power source (not shown) uniformly charges the surface of the photosensitive drum 1 to a predetermined negative potential (in this embodiment, about −650 V). .

  The exposure apparatus 3 converts the color-separated image signal input from the host computer into an optical signal. The exposure device 3 scans and exposes the charged photosensitive drum 1 with laser light, which is a converted optical signal, and forms an electrostatic image corresponding to image information on the photosensitive drum 1.

  For example, when forming a full-color image, first, in the first station Sa, the electrostatic image formed on the photosensitive drum 1a is visualized as a toner image with yellow toner attached thereto by the developing device 4a. The developing device 4 has a developing sleeve as a developer carrying member. A magnet as a magnetic field generating means is disposed in the developing sleeve. A negative developing bias is applied to the developing sleeve from an existing bias power source. In this embodiment, a bias in which an AC voltage is superimposed on a DC voltage having a DC component of −400 V, an AC component having a peak-to-peak voltage of 1.5 kVpp, a frequency of 3 kHz, and a rectangular waveform is used as the developing bias.

  This yellow toner image is transferred (primary transfer) onto the intermediate transfer belt 11 by the primary transfer roller 15a at the primary transfer portion N1a of the first station Sa. At this time, the primary transfer roller 15a is supplied with a primary transfer bias of positive polarity under constant voltage control from a primary transfer bias power source 16a as a primary transfer bias output means (in this embodiment, about + 500V to + 650V). Is applied. At this time, the intermediate transfer belt 11 is moved (rotated) at a predetermined moving speed v2 [mm / s] in the direction of the arrow in synchronization with the rotation of the photosensitive drum 1 by the drive roller 12 being driven to rotate. is doing. In this embodiment, the circumferential speed v1 of the photosensitive drum 1 and the circumferential speed v2 of the transport belt 51 are substantially the same.

  As in the first to third embodiments, the image forming apparatus 200 generates a voltage generated in the intermediate transfer belt 11 when a detection current is applied to the intermediate transfer belt 11 before the toner is transferred to the intermediate transfer belt 11. It may have a detecting means for detecting The detection unit may detect a current flowing through the intermediate transfer belt 11 when a detection voltage is applied to the intermediate transfer belt 11. The control unit may control the bias for primary transfer output from the primary transfer bias power source 16 based on the detection result of the detection unit. In the present embodiment, for example, the primary transfer roller 15 can be used as the detection means. As an alternative method, the detection means may be specially provided separately from the primary transfer roller 15. Moreover, CPU110 can be used as a control means. The method for obtaining the primary transfer bias is substantially the same as the method for obtaining the transfer bias described in the first embodiment, except that the recording material P is not carried on the intermediate transfer belt 11.

  As described above, a more appropriate primary transfer bias can be obtained by obtaining the primary transfer bias according to the electric resistance value of the intermediate transfer belt 11, but the present invention is not limited to this. If desired, the primary transfer bias may be predetermined as a predetermined value.

  The yellow toner image transferred onto the intermediate transfer belt 11 is driven by the drive roller 11 and moved to the second station Sa side. Similarly, in the second station Sb, the magenta toner image formed on the photosensitive drum 1b is superimposed on the yellow toner image on the intermediate transfer belt 11 at the primary transfer portion N1b. Is transcribed.

  Thereafter, similarly, a cyan toner image and a black toner image respectively formed on the photosensitive drums 1c and 1d of the third and fourth stations Sc and Sd are sequentially superimposed on the primary transfer portions N1c and N1d, respectively. It is transferred together. As a result, a full-color toner image is formed on the intermediate transfer belt 11.

  The recording material P is conveyed to the secondary transfer portion N2 in accordance with the timing at which the front end of the full color toner image on the intermediate transfer belt 11 is moved to the secondary transfer portion N2.

  In the secondary transfer portion N2, the full-color toner image on the intermediate transfer belt 11 is collectively transferred (secondary transfer) onto the recording material P. At this time, the secondary transfer roller 21 is applied with a secondary transfer bias of positive polarity (in this embodiment, +20 μA) controlled at a constant current from a secondary transfer bias power source 22 as a secondary transfer bias output means. .

  The recording material P carrying a full-color toner image is conveyed to the fixing device 7. The fixing device 7 heats and presses a full-color toner image at a fixing portion (fixing nip) between the fixing roller 71 and the pressure roller 72 to fix it on the surface of the recording material P. Thereafter, the recording material P is discharged to the outside of the apparatus, and a series of image forming operations is completed.

  The toner remaining on the photosensitive drum 1 after the primary transfer process (primary transfer residual toner) is removed and collected by the drum cleaner 6.

  The toner remaining on the surface of the intermediate transfer belt 11 after the secondary transfer may be removed and collected by a belt cleaner 17 as a belt cleaning means. Alternatively, unnecessary toner on the intermediate transfer belt 11 may be periodically removed and collected by electrostatic cleaning similar to that performed on the conveyance belt 51 in the first to third embodiments.

  In the same manner as described in the first exemplary embodiment, the image forming apparatus 200 according to the present exemplary embodiment performs intermediate transfer of a density detection toner image and a color shift correction toner image (patch image) at a predetermined timing. It is formed on the belt 11 and this is detected by the optical sensor 9. The optical sensor 9 is also used for detecting fog toner on an intermediate transfer belt 11 described later.

[Detection of fog toner]
In the intermediate transfer type image forming apparatus 200 as well, as in the case of the direct transfer type, fog toner easily adheres to the intermediate transfer belt 11 when, for example, the toner deteriorates due to durability. As described above, the fog toner may cause a transfer failure in the primary transfer portion N1.

  For example, the transition of the amount of fog toner on the intermediate transfer belt 11 during continuous printing is the same as that of the conveyance belt 51 described above with reference to FIG.

  Therefore, in this embodiment, in the same manner as described in the second embodiment, the reflectance of the non-image forming area between image forming operations, that is, the portion on the intermediate transfer belt 11 corresponding to the gap between the sheets is optical. Read by sensor 9. Thus, the amount of fog toner on the intermediate transfer belt 11 that constantly changes according to the number of prints is detected, and the primary transfer bias is always corrected.

  More specifically, first, as the reflectance R1 when no fog toner exists on the intermediate transfer belt 11, the reflectance R1 on the intermediate transfer belt 11 after the start-up sequence is completed, for example, as in the first to third embodiments. Is read by the optical sensor 9. Then, the detection result of the optical sensor 9 at this time is stored in a memory (RAM) 111 as storage means as a reference reflectance R1.

  Next, at the time of continuous printing, the optical sensor 9 reads the reflectance R2 of a non-image forming area between image forming operations, that is, a portion on the intermediate transfer belt 11 corresponding to the space between sheets. The CPU 110 reads the reference reflectance R1 stored in the memory 111. Then, the CPU 110 obtains a difference value | R1-R2 | between the reference reflectance R1 and the reflectance R2.

  Then, the CPU 110 determines the correction value of the primary transfer bias corresponding to the obtained difference value | R1-R2 | by referring to table data as shown in Table 4 stored in the ROM 112. Then, as described above, the primary transfer bias value obtained or set in advance before the primary transfer process is corrected by the correction value obtained here, and the primary transfer roller 16 is supplied with the primary transfer roller. 15 is determined as a transfer bias value to be applied.

  For example, if the primary transfer bias is required before the primary transfer process as described above, in other words, the following occurs. That is, when the result of detecting the amount of light reflected from the intermediate transfer belt 11 by the optical sensor 9 is different, the primary for the detection result of the voltage or current by the detection means when the detection current or the detection voltage is applied. The relationship of the transfer bias value is different.

  Thus, the primary transfer bias is corrected for each page in accordance with the difference value | R1-R2 |. As a result, even when the fog toner amount changes due to continuous printing, it is possible to suppress transfer defects in the primary transfer portion N1.

  As in the second embodiment, for example, when the primary transfer portion N1d of the fourth station Sd is used as a reference, the position of the optical sensor 9 is the position of the primary transfer portion N1d of the fourth station Sd. It is out of position. Therefore, the timing at which the optical sensor 9 is turned on is delayed from the time when the sheet interval is located at the primary transfer portion N1d of the fourth station Sd.

  As shown in Table 5, the difference value | R1-R2 | of the reflectance detection result indicating the amount of fog toner, the correction amount of the primary transfer bias according to the result, and whether or not the primary transfer bias is corrected The result of investigating the relationship with the occurrence of transfer failure is shown. The environment at this time is a temperature of 23 ° C. and a humidity of 50%.

  As shown in Table 5, when the difference value | R1−R2 | is 0, no fog toner is present on the intermediate transfer belt 11, and thus the transfer bias is not corrected. On the other hand, when the amount of fog toner on the intermediate transfer belt 11 increases, the transfer defect deteriorates when the primary transfer bias correction control is not performed. On the other hand, in this embodiment, as the difference value | R1−R2 | increases, the correction amount is sequentially increased to + 40V, + 80V, and + 120V, and the primary transfer bias is corrected, thereby correcting the transfer failure. A good image that did not occur was obtained.

  As described above, according to the present exemplary embodiment, even in the intermediate transfer type image forming apparatus 200, the amount of fog toner on the intermediate transfer belt 11 is detected by the optical sensor 9 and corrected to the primary transfer bias. In addition, the occurrence of transfer defects can be suppressed.

  In addition, when the image forming apparatus 200 includes an electrostatic cleaning sequence for the intermediate transfer belt 11, it is possible to suppress the occurrence of transfer failure due to the influence of fog toner without increasing the number of cleaning sequences.

  In this embodiment, in particular, the amount of fog toner is detected at a non-image forming area between image forming operations, that is, at a position on the intermediate transfer belt 11 corresponding to the space between sheets, and primary transfer is always performed according to the detection result. Feedback to bias control. Thereby, even when the fog toner amount increases during continuous printing, it is possible to always obtain a good primary transfer efficiency.

  In the intermediate transfer type image forming apparatus 200, in addition to or in place of the detection of the fog toner amount between the sheets, during the preparatory rotation operation before the image forming operation or during the end operation after the end of the image forming operation. Of course, it is also possible to detect the amount of fog toner. Similarly to the case of the conveyance belt 51 described in the third embodiment, the reflectance on the intermediate transfer belt 11 may be detected in the non-image forming area during the image forming operation. In other words, if the optical sensor 9 detects the reflectance of the area other than the image forming area on the intermediate transfer belt 11, for example, the amount of fog toner on the intermediate transfer belt 11 can always be detected during continuous printing. It becomes possible.

  As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned embodiment. For example, in each of the above embodiments, the roller is used as the transfer unit or the primary transfer unit. However, the present invention is not limited to this, and a blade, a brush, or a corona charger that is a non-contact charger may be used. Note that a contact charger such as a roller, a blade, or a brush is preferably used as a transfer means in order to perform electrostatic cleaning satisfactorily by bringing the conveyance belt or the intermediate transfer belt into close contact with the photosensitive drum.

  Further, the image forming apparatus 100 shown in FIG. 1 has a belt cleaner that removes and collects toner on the surface of the conveyor belt 51 as a cleaning unit for the conveyor belt 51, similarly to the image forming apparatus 200 shown in FIG. Also good.

  The reference value R1 corresponding to the reflectance on the belt when the fog toner is not substantially present on the belt is limited to information that is updated each time the belt is cleaned and stored in the storage means. It is not something. For example, a device that is detected by an initial setting operation at the time of installation of the apparatus and stored in the storage unit, or a unit that is stored in advance in the storage unit may be used.

  In each of the embodiments described above, a plurality of transfer bias correction values are set in association with the difference value | R1-R2 | as table data or the like. However, the method for setting the transfer bias correction value is limited to this. Is not to be done. For example, whether to set the threshold value of the detection result of the optical sensor and switch the correction value of the transfer bias or correct the transfer bias depending on whether the detection result of the optical sensor is less than or equal to the threshold value. It can also be determined whether or not. In this case, as in the above embodiments, for example, threshold value and transfer bias correction value information is stored in the storage means provided in the apparatus main body, and the control means of the apparatus main body controls the transfer bias using the information. You just have to do it.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. It is a schematic block diagram of an example of an optical sensor. It is a schematic sectional drawing of the other Example of the image forming apparatus which concerns on this invention. It is a timing chart for demonstrating the detection timing of an optical sensor. 7 is a graph for explaining the relationship between the number of continuous prints and the amount of fog toner on the belt. FIG. FIG. 5 is a schematic diagram illustrating a non-image forming area during an image forming operation and a non-image forming area during the image forming operation.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging roller (charging means)
3 Exposure equipment (exposure means)
4 Developer (Developer)
5 Transfer unit 6 Drum cleaner (cleaning means)
9 Optical sensor 10 Intermediate transfer unit 11 Intermediate transfer belt (transfer body, intermediate transfer body)
51 Conveyor belt (transfer body, recording material carrier)
55 Transfer roller (transfer means)
56 Transfer bias power supply (transfer bias output means)
P Recording material

Claims (12)

An image carrier that carries a toner image, a transfer member that carries and conveys a recording material, a transfer unit that transfers a toner image on the image carrier to a recording material on the transfer member, and the transfer unit A transfer bias output means for outputting a bias for the transfer, an optical sensor for detecting reflected light when light is irradiated on the transfer body, and the transfer bias output by the transfer bias output means. An image forming apparatus having a control means for controlling a bias;
The image forming apparatus characterized in that the control means controls the transfer bias output from the transfer bias output means in accordance with a result of detecting the amount of reflected light from the transfer body by the optical sensor. . An image carrier that carries a toner image, a transfer member to which toner on the image carrier is transferred, a transfer unit that transfers a toner image on the image carrier to the transfer member, and the transfer unit Transfer bias output means for outputting a bias for the transfer, an optical sensor for detecting reflected light when light is irradiated on the transfer body, and a bias for the transfer output by the transfer bias output means Control means for controlling the toner image, secondary transfer means for secondary transfer of the toner image on the transfer member to the recording material, and secondary transfer for outputting a bias for the secondary transfer to the secondary transfer means. An image forming apparatus having a bias output unit;
The image forming apparatus characterized in that the control means controls the transfer bias output from the transfer bias output means in accordance with a result of detecting the amount of reflected light from the transfer body by the optical sensor. .   3. The image forming apparatus according to claim 1, wherein the detection of the amount of light reflected from the transfer body by the optical sensor is performed on the transfer body during non-image formation.   The detection of the amount of reflected light from the transfer body by the optical sensor is the transfer body during the preparation rotation operation performed before the start of the image formation operation, the transfer body during the end rotation operation performed after the end of the image formation operation, or The image forming apparatus according to claim 3, wherein the transfer is performed on the transfer body corresponding to a non-image forming area between image forming operations.   3. The image forming apparatus according to claim 1, wherein detection of the amount of reflected light from the transfer body by the optical sensor is performed on the transfer body corresponding to a non-image forming area during image formation. .   The said control means controls the bias for the said transfer based on the difference value between the detection result of the said optical sensor, and a reference value, The one of Claims 1-5 characterized by the above-mentioned. Image forming apparatus.   A cleaning sequence for cleaning the transfer body, wherein the reference value is a detection result of the optical sensor immediately after the cleaning sequence is executed, and storage means for storing information relating to the reference value is provided. The image forming apparatus according to claim 6.   The image forming apparatus according to claim 7, wherein information on the reference value stored in the storage unit is updated each time the cleaning sequence is executed.   The image forming apparatus according to claim 6, wherein the reference value is a predetermined value, and has a storage unit in which information corresponding to the reference value is stored in advance.   10. The toner according to claim 1, wherein in the cleaning sequence, the toner on the transfer body is electrostatically transferred onto the image carrier and removed from the transfer body. The image forming apparatus described. An image carrier that carries a toner image, a transfer member that carries and conveys a recording material, a transfer unit that transfers a toner image on the image carrier to a recording material on the transfer member, and the transfer unit A transfer bias output means for outputting a bias for the transfer, an optical sensor for detecting reflected light when light is irradiated on the transfer body, and a detection current to the transfer body before the transfer. Detection means for detecting a voltage generated in the transfer body when applied or a current flowing in the transfer body when a detection voltage is applied to the transfer body; and the transfer bias output means based on a detection result of the detection means An image forming apparatus comprising: a control unit that controls a bias for the transfer to be output;
When the result of detecting the amount of light reflected from the transfer body by the optical sensor differs, the transfer bias output for the detection result of the voltage or current by the detection means when the detection current or the detection voltage is applied An image forming apparatus that controls that the relationship of the bias values for transfer outputted by the means is different. An image carrier that carries a toner image, a transfer member to which toner on the image carrier is transferred, a transfer unit that transfers a toner image on the image carrier to the transfer member, and the transfer unit Transfer bias output means for outputting a bias for the transfer, an optical sensor for detecting reflected light when the transfer body is irradiated with light, and applying a detection current to the transfer body before the transfer Detecting means for detecting a voltage generated in the transfer body or a current flowing in the transfer body when a detection voltage is applied to the transfer body, and the transfer bias output means outputs based on a detection result of the detection means. Control means for controlling the bias for the transfer, secondary transfer means for secondary transfer of the toner image on the transfer member to the recording material, and for the secondary transfer with respect to the secondary transfer means 2 to output the bias A transfer bias output unit, an image forming apparatus having,
When the result of detecting the amount of light reflected from the transfer body by the optical sensor differs, the transfer bias output for the detection result of the voltage or current by the detection means when the detection current or the detection voltage is applied An image forming apparatus that controls that the relationship of the bias values for transfer outputted by the means is different.

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