JP2010054987A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that the accuracy of reading a patch image formed on a belt member deteriorates in a state that a tension is small, because the tension of the belt member is made small so as to make the belt member durable. <P>SOLUTION: An image forming apparatus is constituted so as to read the patch image on the belt member in a state that the tension is made larger than the tension applied to the belt member when forming an image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic system or an electrostatic recording system. More specifically, the present invention relates to an image forming apparatus having a movable belt member disposed in contact with an image carrier on which a toner image is formed on the surface.

  Conventionally, as a color image forming apparatus capable of forming a full-color image, the following direct transfer type and intermediate transfer type image forming apparatuses are known. In the direct transfer method, a toner image formed on one or more photosensitive drums is transferred to a recording material carried on a movable belt member (hereinafter referred to as “transfer belt”) as a recording material carrier. In the intermediate transfer method, a toner image formed on one or more photosensitive drums is transferred to a movable belt member (hereinafter referred to as “intermediate transfer belt”) as an intermediate transfer member. Thereafter, the toner image on the intermediate transfer belt is transferred to the recording material (secondary transfer). In the intermediate transfer method, it is easy to form an image on various recording materials, and the selectivity of the transfer material can be improved.

  FIG. 12 shows an outline of an image forming apparatus using a conventional intermediate transfer system. In this figure, the process unit as an image forming unit is provided corresponding to each color of yellow, magenta, cyan, and black. 1a to 1d are photosensitive drums, 2a to 2d are charging units, 3a to 3c are exposure units, 4a to 4d are developing devices, 51 is an intermediate transfer belt, 53a to 53d are primary transfer members, and 6a to 6d are photosensitive units. Drum cleaning devices 56 and 57 are secondary transfer members.

  First, in the case of forming a full-color image, the photosensitive drums 1a to 1d are uniformly charged by the charging devices 2a to 2d, and then exposure according to the image signal is performed by the exposure means 3a to 3d. An electrostatic latent image is formed on 1a-1d. Thereafter, the toner images are developed by the developing devices 4a to 4d, and the toner images on the photosensitive drums 1a to 1d are applied to the intermediate transfer belt 51 by applying a transfer bias to the transfer members 53a to 53d from a transfer high-voltage power supply (not shown). Sequentially transferred. The untransferred toner remaining on the photosensitive drums 1a to 1d is collected by the cleaning units 6a to 6d. The images sequentially transferred from the respective photosensitive drums onto the intermediate transfer belt 51 in the above-described manner are transferred onto the recording material P by applying a secondary transfer bias between the secondary transfer members 56 and 57. The The toner image on the recording material P is fixed by the fixing device 7 to obtain a full color image.

  In such a color image forming apparatus, an optical sensor 30 is provided for detecting the density of the patch image formed on the belt member. The optical sensor 30 detects the density of the patch image to control the image density of each color by toner replenishment control of the developer, etc., or the registration shift is detected by the optical sensor 30. Yes. This configuration is not limited to the intermediate transfer system shown in FIG. 12, but is the same for the transfer belt system.

  As shown in FIG. 3, the optical sensor 30 emits light from the light emitting element 30 a to the patch image on the belt member 51. The amount of light reflected by regular reflection and / or irregular reflection on the surface of the belt member 51 in the patch image portion is received by the light receiving element 30b. Based on the obtained image density signal, the image density is fed back to control the image density by controlling the toner replenishment to the developer and controlling the latent image exposure and development bias. To do.

However, when the density of the patch image on the intermediate transfer belt 51 is detected using the optical sensor 30, if the belt member 51 vibrates, the optical sensor 30 picks up the vibration error, and the density is accurately measured. There was a problem that it could not be detected well. Further, in Patent Document 1, an optical sensor is installed as close to the opposing roller as possible to detect this problem, but this is not sufficient. Further, when an optical sensor is provided immediately above the opposing roller, there is a problem that the outer diameter fluctuation of the roller is picked up and accuracy is not obtained.
JP-A-14-72574

  Therefore, in order to improve the detection accuracy of the optical sensor 30, a configuration in which the vibration of the belt member is reduced by increasing the tension of the belt member can be considered.

  However, in the configuration in which the tension is always increased, the life of the intermediate transfer belt 51 is shortened because it is applied to the intermediate transfer belt 51.

  Accordingly, an object of the present invention is to improve the accuracy of detecting the density of a patch image in spite of extending the life of the intermediate transfer belt.

  An image carrier, a toner image forming unit for forming a toner image on the image carrier, a belt member in contact with the image carrier, a plurality of tension members for stretching the belt member, and a belt member on the belt member. A toner image detecting member for detecting the formed control toner image, and an adjustment for adjusting a toner image forming condition when an image is formed on a recording material by the toner image forming unit based on an output of the toner image detecting member. A changing means for changing the tension of the belt member by the tension member, and when the toner image detecting member detects a control toner image formed on the belt member. And an execution unit that executes a function of making the tension of the belt member by the stretching member larger than the tension at the time of image formation for forming an image on a recording material.

  According to the present invention, it is possible to improve the accuracy of patch image density detection without shortening the life of the intermediate transfer belt.

  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]
First, the overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described. FIG. 1 shows a schematic cross-sectional configuration of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 according to the present exemplary embodiment is a full-color electrophotographic image forming apparatus that includes four photosensitive drums and uses an intermediate transfer method.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units (process units) Sa, Sb, Sc, and Sd as a plurality of image forming units. The image forming portions Sa, Sb, Sc, and Sd are for forming colors of yellow, magenta, cyan, and black, respectively.

  In this embodiment, the configuration of each of the image forming units Sa to Sd is substantially the same except that the color of the toner used is different. Therefore, in the following, unless there is a particular distinction, the subscripts a, b, c, and d given to the reference numerals in the drawing are omitted to indicate that they are elements provided for any color, and are summarized Explained.

  The image forming unit S includes a photosensitive drum 1 as an image carrier. Around the photosensitive drum 1, toner image forming means is provided. Specifically, a charging roller 2 as a primary charging unit, a laser scanner 3 as an exposure unit, a developing device 4 as a developing unit, a cleaning unit 6 as a cleaning unit, and the like along the rotation direction of the photosensitive drum 1. They are arranged sequentially. A rotatable belt member, that is, an intermediate transfer belt 51 in this embodiment, is disposed adjacent to the photosensitive drums 1a to 1d of the image forming units Sa to Sd.

  The intermediate transfer belt 51 is stretched around a driving roller 52, a stretching roller 55, a secondary transfer inner roller 56, and an upstream regulating roller 58a as a plurality of stretching members. The intermediate transfer belt 51 is rotated in the direction of the arrow R3 in the figure by the driving force transmitted by the driving roller 52 as belt driving means. Further, primary transfer rollers 53a to 53d as primary transfer members are disposed at positions facing the respective photosensitive drums 1a to 1d on the inner peripheral surface side of the intermediate transfer belt 51. The primary transfer rollers 53a to 53d urge the intermediate transfer belt 51 toward the photosensitive drums 1a to 1d, and the primary transfer portions (primary transfer portions) in which the photosensitive drums 1a to 1d and the intermediate transfer belt 51 come into contact with each other. Nip) N1a to N1d are formed. That is, the primary transfer member forms a contact portion between the photosensitive drum and the intermediate transfer belt 51. Further, a secondary transfer outer roller 57 as a secondary transfer member is disposed at a position facing the secondary transfer inner roller 56 on the outer peripheral surface side of the intermediate transfer belt 51. The secondary transfer outer roller 57 contacts the outer peripheral surface of the intermediate transfer belt 51 to form a secondary transfer portion (secondary transfer nip) N2.

  The images on the photosensitive drums 1a to 1d formed by the respective image forming units Sa to Sd are sequentially multiplex-transferred onto the intermediate transfer belt 51 that moves and passes adjacent to the photosensitive drums 1a to 1d. Thereafter, the image transferred onto the intermediate transfer belt 51 is further transferred onto a recording material P such as paper at the secondary transfer portion N2.

  FIG. 2 shows the image forming unit S in more detail. Further description will be made with reference to FIG. 2 as well. The photosensitive drum 1 is rotatably supported by the image forming apparatus main body. The photosensitive drum 1 is a cylindrical electrophotographic photosensitive member that basically includes a conductive substrate 11 such as aluminum and a photoconductive layer 12 formed on the outer periphery thereof. The photosensitive drum 1 has a support shaft 13 at the center thereof. The photosensitive drum 1 is rotationally driven about a support shaft 13 in the direction of an arrow R1 by a driving unit (not shown). In this embodiment, the charging polarity of the photosensitive drum 1 is negative.

  Above the photosensitive drum 1 in the figure, a charging roller 2 as a primary charging means is disposed. The charging roller 2 is in contact with the surface of the photosensitive drum 1 and uniformly charges the surface of the photosensitive drum 1 to a predetermined polarity and potential. The charging roller 2 includes a conductive core 21 disposed in the center, a low resistance conductive layer 22 formed on the outer periphery thereof, and a medium resistance conductive layer 23, and is configured in a roller shape as a whole. Yes. The charging roller 2 is disposed in parallel with the photosensitive drum 1 while both ends of the cored bar 21 are rotatably supported by bearing members (not shown). The bearing members at both ends are urged toward the photosensitive drum 1 by pressing means (not shown). As a result, the charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force. The charging roller 2 is driven to rotate in the direction indicated by the arrow R2 as the photosensitive drum 1 rotates in the direction indicated by the arrow R1. A charging bias voltage is applied to the charging roller 2 by a charging bias power source 24 as a charging bias output unit. Thereby, the surface of the photosensitive drum 1 is uniformly charged by contact.

  The laser scanner 3 performs scanning while turning off / on laser light based on image information, and exposes the charged photosensitive drum 1. As a result, an electrostatic latent image corresponding to the image information is formed on the photosensitive drum 1.

  The developing device 4 includes a developing container 41 that contains a two-component developer including non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. A developing sleeve 42 as a developer carrying member is rotatably installed in an opening of the developing container 41 facing the photosensitive drum 1. In the developing sleeve 42, a magnet roller 43, which is a magnetic member, is fixedly disposed so as not to rotate with respect to the rotation of the developing sleeve 42. The two-component developer is carried on the developing sleeve 42 by the magnetic field of the magnet roller 43. Further, a regulating blade 44 as a developer regulating member that regulates the two-component developer carried on the developing sleeve 42 and thins it is installed at a position below the developing sleeve 42 in the drawing. The developing container 41 is divided into a developing chamber 45 and an agitating chamber 46, and a replenishing chamber 47 containing replenishing toner is provided in the upper portion of the drawing. The replenishing chamber 47 is used for toner replenishment control for replenishing toner to the agitating chamber 46 and maintaining the toner concentration of the developer in the developing container 41 at a predetermined value during image density control by the patch detection method.

  A thin layer of the two-component developer on the developing sleeve 42 is conveyed to a developing area facing the photosensitive drum 1 as the developing sleeve 42 rotates. The two-component developer on the developing sleeve 42 rises in the developing region by the magnetic force of the developing main pole of the magnet roller 43 located in the developing region, and a magnetic brush for the two-component developer is formed. The surface of the photosensitive drum 1 is rubbed by the magnetic brush, and a developing bias voltage is applied to the developing sleeve 42 by a developing bias power source 48 as a developing bias output means. Thereby, the toner adhering to the carrier constituting the ears of the magnetic brush adheres to the exposed portion of the electrostatic image on the photosensitive drum 1 to form a toner image. In this embodiment, a toner image is formed on the photosensitive drum 1 by reversal development.

  The primary transfer roller 53 includes a cored bar 531 and a conductive layer 532 formed in a cylindrical shape on the outer peripheral surface thereof. Both ends of the primary transfer roller 53 are urged toward the photosensitive drum 1 by a pressing member (not shown) such as a spring. As a result, the conductive layer 532 of the primary transfer roller 53 is pressed against the surface of the photosensitive drum 1 via the intermediate transfer belt 51 with a predetermined pressing force. Further, a primary transfer bias power source 54 as a primary transfer bias output means is connected to the cored bar 531. A primary transfer portion N1 is formed between the photosensitive drum 1 and the primary transfer roller 53. An intermediate transfer belt 51 is sandwiched between the primary transfer portion N1. The primary transfer roller 53 contacts the inner peripheral surface of the intermediate transfer belt 51 and rotates as the intermediate transfer belt 51 moves. At the time of image formation, the primary transfer roller 53 is supplied with a primary transfer bias power supply 54 by a reverse polarity (second polarity) of the normal charging polarity of the toner (first polarity: negative polarity in this embodiment). : Positive transfer in this embodiment) is applied. An electric field is formed between the primary transfer roller 53 and the photosensitive drum 1 in such a direction that the toner of the first polarity moves from the photosensitive drum 1 toward the intermediate transfer belt 51. As a result, the toner image on the photosensitive drum 1 is transferred (primary transfer) to the surface of the intermediate transfer belt 51.

  Deposits such as toner (primary transfer residual toner) remaining on the surface of the photosensitive drum 1 after the primary transfer process are cleaned by the cleaning device 6. The cleaning device 6 includes a cleaning blade 61 as a cleaning member, a conveying screw 62, and a drum cleaning device housing 63. The cleaning blade 62 is brought into contact with the photosensitive drum 1 at a predetermined angle and pressure by a pressurizing unit (not shown). Thus, the toner remaining on the surface of the photosensitive drum 1 is scraped and removed from the photosensitive drum 1 by the cleaning blade 62 and is collected in the drum cleaning device housing 63. The collected toner or the like is transported by the transport screw 62 and discharged to a waste toner container (not shown).

  In FIG. 1, below the photosensitive drums 1a to 1d in the figure, there are an intermediate transfer belt 51, primary transfer rollers 53a to 53d, a secondary transfer inner roller 56, a secondary transfer outer roller 57, and an intermediate transfer belt cleaning device 59. Etc., the intermediate transfer unit 5 is configured. The secondary transfer inner roller 56 is electrically grounded. Further, a secondary transfer bias power source 58 as a secondary transfer bias output means is connected to the secondary transfer outer roller 57 which is a transfer member. The secondary transfer inner roller 56 contacts the inner peripheral surface of the intermediate transfer belt 51 and rotates as the intermediate transfer belt 51 moves.

  For example, when a full-color image is formed, toner images of the respective colors are formed on the photosensitive drums 1a to 1d of the first to fourth image forming units Sa to Sd. The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 51 by receiving a primary transfer bias from the primary transfer rollers 53 facing the photosensitive drums 1a to 1d with the intermediate transfer belt 51 interposed therebetween (primary transfer). ) This toner image is conveyed to the secondary transfer portion N2 as the intermediate transfer belt 51 rotates.

  The recording material P to which the toner image formed on the intermediate transfer belt 51 is transferred is conveyed to the secondary transfer portion N2 by the recording material supply unit 8 at a predetermined timing. That is, in the transfer material supply means 8, the recording material P taken out one by one by the pickup roller 82 from the cassette 81 as the recording material storage unit is conveyed to the secondary transfer unit N2 by the conveying roller 83 and the like.

  In this embodiment, during image formation, the secondary transfer outer roller 57 is charged by a secondary transfer bias power source 58 with a polarity opposite to the normal charging polarity of the toner (first polarity: negative polarity in this embodiment) ( A secondary transfer bias voltage having a second polarity (positive polarity in this embodiment) is applied. Then, an electric field is formed between the secondary transfer inner roller 56 and the secondary transfer outer roller 57 in a direction in which the toner having the first polarity moves from the intermediate transfer belt 51 toward the recording material P. As a result, the toner image on the intermediate transfer belt 51 is transferred (secondary transfer) onto the recording material P. The recording material P onto which the toner image has been transferred in the secondary transfer portion N2 is conveyed to a fixing device 7 as a fixing unit.

  Note that deposits such as toner remaining on the intermediate transfer belt 51 after the secondary transfer step are removed and collected by the intermediate transfer belt cleaning device 59. The intermediate transfer belt cleaning device 59 has the same configuration as the drum cleaning device 6.

  The fixing device 7 includes a fixing roller 71 that is rotatably arranged, and a pressure roller 72 that rotates while being pressed against the fixing roller 71. A heater 73 such as a halogen lamp is disposed inside the fixing roller 71. The surface temperature of the fixing roller 71 is adjusted by controlling the voltage supplied to the heater 73 and the like. When the recording material P is conveyed to the fixing device 7, the recording material P is nipped and conveyed by a nip portion formed by the fixing roller 71 and the pressure roller 72 that rotate at a constant speed. The toner on the recording material P is fixed on the recording material by pressure and heat. Thus, a full color image is formed on the recording material P.

  In this embodiment, the process speed corresponding to the moving speed of the photosensitive drum 1 and the intermediate transfer belt 51 is 200 mm / sec.

Here, the intermediate transfer belt 51 is made of a dielectric resin such as PC (polycarbonate), PET (polyethylene terephthalate), or PVDF (polyvinylidene fluoride). In this embodiment, the intermediate transfer belt 51 has a surface resistivity of 10 ¹² Ω / □ (using a probe conforming to the JIS-K6911 method, an applied voltage of 100 V, an applied time of 60 sec, 23 ° C./50% RH), and a PI ( A polyimide resin was used. However, the present invention is not limited to this, and other materials, volume resistivity, and thickness may be used.

The primary transfer roller 53 is constituted by a core metal 531 having an outer diameter of 8 mm and a conductive urethane sponge layer 532 having a thickness of 4 mm. The electric resistance value of the primary transfer roller 53 was about 10 ⁵ Ω (23 ° C./50% RH). The electrical resistance value of the primary transfer roller 53 is such that the primary transfer roller 53 in contact with a metal roller grounded under a load of 500 g is rotated at a peripheral speed of 50 mm / sec and the core metal 531 is rotated. It is obtained from a current value measured by applying a voltage of 100V.

The secondary transfer inner roller 56 includes a cored bar 561 having an outer diameter of 18 mm and a conductive and solid silicone rubber layer 562 having a thickness of 2 mm. The electrical resistance value of the secondary transfer inner roller 56 was about 10 ⁴ Ω in the same measurement method as that for the primary transfer roller 53. Further, the secondary transfer outer roller 57 includes a core metal 571 having an outer diameter of 20 mm and a conductive EPDM rubber sponge layer 572 having a thickness of 4 mm. The electrical resistance value of the secondary transfer outer roller 57 was about 10 ⁸ Ω when the applied voltage was 2000 V in the same measurement method as the primary transfer roller 53.

[About patch detection optical sensor]
In the present invention, in the rotation direction of the intermediate transfer member, the toner is located downstream of the secondary transfer portion of the image forming apparatus and the primary transfer portion for black of the final color, and upstream of the secondary transfer portion. One optical sensor 30 which is an image detection member was installed. According to the present invention, the optical sensor 30 measures the density of the patch image formed by the yellow, magenta, cyan, and black toners formed on the photosensitive drums 1a, 1b, 1c, and 1d and transferred onto the intermediate transfer belt 51. It can be detected.

  As shown in FIG. 3, the optical sensor 30 irradiates the patch image on the intermediate transfer belt 51 with light from the light emitting element 30a, and regular reflection and / or irregular reflection on the surface of the intermediate transfer belt 51 in the patch image portion. The amount of reflected light is received by the light receiving element 30b. The generated electric signal (image density signal) is amplified to a predetermined reference value by the signal processing unit and stored as an amplification factor.

  First, the developer concentration is initially set. The initial setting of the developer concentration is usually performed when the image forming apparatus main body is installed or when the developer is replaced.

  Next, a procedure for reading the patch image by the optical sensor 30 will be described.

  The optical sensor 30 measures the amount of reflected light from the intermediate transfer belt 51 and adjusts the output value of the optical sensor 30 at that time to a predetermined value, for example, 0.5V. Next, a patch image, which is a control toner image, is formed on the photosensitive drum 1 on the photosensitive drum 1, and the optical sensor 30 detects the density of the patch image formed on the intermediate transfer belt 51. The image density signal is read as an initial set value and stored in the storage unit.

  Next, a patch image is formed at a predetermined timing, specifically, every predetermined number of image formations, the patch image density is measured by the optical sensor 30, and the obtained image density signal adjusts the toner image formation conditions. Is input to the adjustment unit. In this adjusting unit, the control unit has this function.

  The adjustment unit compares the obtained image density signal with the initial value, and feeds back the comparison result to the image forming conditions, and the toner such as the condition of toner replenishment to the developer, the exposure of the latent image, and the developing bias The image density is controlled by controlling the image forming conditions.

  In this embodiment, the optical sensor 30 is a specular reflection type, but the present invention is not limited to the specular reflection type optical sensor.

[About flapping of intermediate transfer belt]
Control for changing the tension of the belt member will be described. In the image forming apparatus of FIG. 1, when a patch image is formed and the density of the patch image is measured by the optical sensor 30 to obtain a density signal, the belt member is rotating. Along with the rotation, it vibrates in a direction perpendicular to the belt surface of the rotating intermediate transfer belt 51. Due to this vibration, the distance between the optical sensor, the bell, and the surface is not stable, and the vibration due to the vibration is included in the density signal, and the image density detection accuracy is lowered.

  On the other hand, it was confirmed that by increasing the tension applied to the belt member, the amplitude of the belt member is reduced and the error of the density signal is reduced.

  In this embodiment, the tension during image formation for forming an image on a recording material is 5 kg · f. By increasing the tension when the patch image is read by the optical sensor from 5 kg · f to 8 kg · f, vibration due to flapping of the intermediate transfer belt can be suppressed by about 30 μm.

  In this embodiment, the distance between the detection surface of the optical sensor and the intermediate transfer belt is set to 4.5 mm. In this case, FIG. 10 shows the relationship between the amount of deviation (mm) from 4.5 mm and the sensor output voltage (V) corresponding thereto. When the tension was 5 kg · f, the vibration was 60 μm. That is, the output of the optical sensor at this time was 1.0 V ± 0.02 V. On the other hand, when the tension is 8 kg · f, the vibration can be 30 μm, and the output of the optical sensor is 1.0 V ± 0.01 V. As described above, when the vibration was suppressed by 30 μm, the fluctuation of 0.01 V as the sensor output voltage could be suppressed.

  FIG. 11 shows the relationship between the sensor output voltage and the density signal level. When the tension is 5 kg · f, the sensor output voltage is 0.98 V. However, when the tension is 8 kg · f, the sensor output voltage can be 0.99 V. As a result, from the respective density signal levels shown in FIG. 11, it was possible to suppress a blur of 3 to 4% as the density signal level.

  In this embodiment, a mechanism for changing the tension applied by the stretching roller is employed as a changing means for increasing the tension applied to the belt member when detecting the patch image density. That is, as shown in FIG. 4, the cam structure 90 is used to change the expansion / contraction width of the spring 91 that is an elastic member. A driving force is transmitted to the cam by the driving unit 92. The state of the cam 90 in FIG. 4A is a state when an image is formed, and the tension applied to the intermediate transfer belt is small. When the patch image is detected by the optical sensor, as shown in FIG. 4B, the spring 91 is contracted by rotating the cam 90 by 90 ° to increase the tension applied to the intermediate transfer belt.

  Regarding the procedure for increasing the tension applied to the tension roller using the cam structure, the following is preferable. That is, when the patch image is formed and the patch image density is measured by the optical sensor 30 to obtain the image density signal, the cam shown in FIG. Rotate from state to state (b). Thereby, the tension applied to the stretching roller 55 is increased via the spring 91. Thereafter, by obtaining the patch image density signal, the vibration shake caused by the intermediate transfer belt entering the density signal can be reduced.

  An electric block diagram of this embodiment is shown in FIG. First, the optical sensor 30 is connected to the control unit 200, and data read by the optical sensor 30 is stored in the storage unit 201 via the control unit 200. Then, the data stored in the storage unit 201 and the newly read data are compared, and the control unit (adjusting unit) outputs a signal for changing the image forming conditions of the image forming unit S. On the other hand, the control unit 200 has a function of controlling the operation of a cam that is a changing means. Further, the control unit 200 determines the tension of the intermediate transfer belt by the cam mechanism when the toner image detection member detects the control toner image formed on the intermediate transfer belt, when forming an image on the recording material. It has the function of the execution part which performs the function made larger than the tension | tensile_strength in.

  Next, control when a patch image is formed will be described with reference to the flowchart of FIG.

  First, when the control starts (S001), the output of the patch image formation signal from the control unit is determined (S002). Here, the output of the patch image forming signal is performed at a predetermined timing such as when it is performed during the continuous image forming operation or during the preparation period for starting up the image forming apparatus to the image formable state (standby state). If no patch image forming signal is output, the standby or image forming operation is continued (S010). Next, when the patch image forming signal is output, it is determined whether the cam position is at the image forming position (S003). If the cam position is not at the image forming position, the cam position is the image forming position. (S004). Next, a patch image forming operation is started on the photosensitive drum of the image forming unit where the patch image is to be formed (S005). The patch image is formed on the photosensitive drum 1 of the image forming unit that forms the patch image, and it is determined whether the patch image is formed on the intermediate transfer belt (S006). When the patch image is not completely formed on the intermediate transfer belt, the patch image forming operation is continued. When the patch image formed on the photosensitive drum for forming the patch image has been transferred onto the intermediate transfer belt, the cam 91 moves to the patch image read-only position (FIG. 4B) (S007). In this embodiment, for example, when a signal indicating that a patch image is to be formed in all the image forming units is output, until the patch images of all the image forming units are transferred to the intermediate transfer belt, The tension is not changed. Then, it is determined whether or not the reading operation of the patch image formed on the intermediate transfer belt by the optical sensor is completed (S008), and when the reading operation is completed, the cam moves to the 90 home position. (S009). If the patch image is formed during the continuous image forming operation, the image forming operation is continuously performed. If the patch image is performed during the preparation period of the image forming apparatus, the operation toward the standby state is performed. (S010). Then, the control for forming the patch image ends (S011).

  As described above, the present invention is configured such that when a patch image is detected by an optical sensor, the tension of the belt member is made larger than the tension at the time of image formation and is made smaller again after the detection is completed. The reason why the tension applied to the belt portion is weakened is that when the tension is always kept strong, there are problems such as breakage and elongation of the intermediate transfer belt itself.

  As described above, according to this embodiment, it is possible to improve the accuracy of patch image density detection without shortening the life of the intermediate transfer belt.

Example 2
First, the overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described. FIG. 7 shows a schematic cross-sectional configuration of the image forming apparatus 100 of the present embodiment. The image forming apparatus 100 according to the present exemplary embodiment is a full-color electrophotographic image forming apparatus that includes four photosensitive drums and uses an intermediate transfer method. In the first embodiment, the changing means for changing the tension of the belt member has a configuration using a cam mechanism. However, in this embodiment, a movable tension member for changing the tension is provided. Different from 1.

  In this embodiment, when the tension applied to the belt member is increased, the tension roller 110 as a new tension member other than the tension roller comes into contact with and presses down the intermediate transfer belt (FIG. 8). . As the place to be pressed by the tension roller, an angle is generated between the belt member and the optical sensor surface between the rollers before and after the place to be detected by the optical sensor, and the belt cannot be detected accurately. Therefore, it is provided not between the rollers before and after the optical sensor, but between the stretching roller 52 and the secondary transfer portion beyond the stretching roller 52 immediately downstream of the optical sensor.

  The procedure for abutting and pressing the tension roller 110 against the intermediate transfer belt to apply tension is the same as the operation of the cam mechanism of the first embodiment.

  That is, since it is necessary to reduce the tension of the belt member at the time of image formation, the tension roller 110 and the belt member are in a non-contact state (FIG. 7). This state is the home position, which corresponds to the state of FIG. When the tension of the belt member is increased, the tension roller 110 is moved to a preset position where it comes into contact with the belt member as shown in FIG.

  In this way, even if a new tension member for tensioning the belt member is newly provided and separated into a contact state and a non-contact state with respect to the belt member, the life of the intermediate transfer belt is shortened. Therefore, it is possible to improve the accuracy of patch image density detection.

Example 3
[Overall Configuration and Operation of Image Forming Apparatus]
First, the overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described. FIG. 9 shows a schematic cross-sectional configuration of the image forming apparatus 100 of the present embodiment. The image forming apparatus 100 according to the present exemplary embodiment is a full-color electrophotographic image forming apparatus that includes four photosensitive drums and uses an intermediate transfer method.

  Next, a mechanism for attaching / detaching the belt member to / from the image carrier will be described.

  The image forming apparatus of the present embodiment has a full color mode and a black single color mode, and performs an operation of bringing the intermediate transfer belt into contact with and separating from the photosensitive drum accordingly.

  FIG. 9 shows the arrangement of the intermediate transfer belt when the image forming apparatus according to the present embodiment performs the image forming operation in the black monochrome mode. In the black monochrome mode, the intermediate transfer belt 51 contacts only the photosensitive drum 1d to form the transfer nip N1d, and only the black monochrome image is transferred to the intermediate transfer belt. In order to regulate the position of the intermediate transfer belt 51 at this time, the upstream regulating roller 58 (broken line position 58a in the figure) is retracted to the position of the upstream regulating roller 58 (solid line position 58b in the figure).

  On the other hand, in the full color mode, the upstream regulating roller 58 moves to the position of the broken line position 58a, so that the intermediate transfer belt 51 moves to the position indicated by the broken line.

  In this embodiment, when a black patch image is formed in the black monochrome mode, the tension of the belt member is increased by moving the upstream regulating roller. That is, in this embodiment, the tension of the belt member in the full color mode is larger than the tension of the belt member in the black monochrome mode.

  Further, when a patch image of each color is formed in the full color mode, the tension of the belt member is increased by moving the tension roller 110 shown in the second embodiment.

  In the present embodiment, a plurality of changing means for changing the tension are received, and a different part is moved in accordance with the image forming mode, thereby adjusting the tension of the belt member.

  Even in such a configuration having a plurality of changing portions, it is possible to improve the accuracy of patch image density detection without shortening the life of the intermediate transfer belt.

  In the present embodiment, the details of the operation in the black single-color mode have been described in the apparatus for forming four-color images of yellow, magenta, cyan, and black. However, this configuration can also be applied to an image forming apparatus using colors other than the above four colors, or an image forming apparatus using light color toner.

  In the above embodiments, the intermediate transfer belt is used. However, the direct transfer method in which an image is formed on a recording material carried and transported by the transfer belt can achieve the effects of the present invention. Can do.

  In the above-described embodiment, the timing at which the changing means for changing the tension of the belt member increases the tension of the belt member is performed after the patch image has been transferred from the image carrier to the belt member. However, the present invention is not limited to this configuration. When a patch image formation signal is input, the patch image is formed on the image carrier while the tension of the belt member is increased by the changing means. May be.

  As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned embodiment.

1 is a schematic cross-sectional configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional configuration diagram illustrating an image forming unit of the image forming apparatus in FIG. 1 in more detail. FIG. 2 is a schematic cross-sectional configuration diagram of a patch image density detection optical sensor of the image forming apparatus of FIG. 1. FIG. 2 is a schematic cross-sectional configuration diagram of a cam structure for changing a tension applied to a stretching roller of the image forming apparatus in FIG. 1. 1 is a block diagram in Embodiment 1. FIG. FIG. 3 is a flowchart of the first embodiment. FIG. 2 is a schematic cross-sectional configuration diagram in which a second tension roller for further applying tension to the intermediate transfer belt of the image forming apparatus in FIG. 1 is added. FIG. 8 is a schematic cross-sectional configuration diagram when tension is further applied to the intermediate transfer belt by a second tension roller in the image forming apparatus of FIG. 7. FIG. 2 is a schematic cross-sectional configuration diagram of an image forming apparatus that separates another color drum from one transfer portion of an intermediate transfer belt in a monochrome single-color mode. It is a displacement graph of the sensor output voltage when the focal distance between the optical sensor and the intermediate transfer belt changes. It is a change graph of the density signal level with respect to the change of the sensor output voltage. It is a schematic cross-sectional block diagram of the conventional image forming apparatus.

Explanation of symbols

1 Photosensitive drum (image carrier)
30 Optical sensor 51 Intermediate transfer belt (belt member)
58 Upstream restriction roller 90 Cam mechanism 110 Tension roller

Claims (5)

An image carrier, a toner image forming unit for forming a toner image on the image carrier, a belt member in contact with the image carrier, a plurality of tension members for stretching the belt member, and a belt member on the belt member. A toner image detecting member for detecting the formed control toner image, and an adjustment for adjusting a toner image forming condition when an image is formed on a recording material by the toner image forming unit based on an output of the toner image detecting member. An image forming apparatus having:
Changing means for changing the tension of the belt member by the tension member, and tension of the belt member by the tension member when the toner image detection member detects a control toner image formed on the belt member And an execution unit that executes a function of making the tension larger than the tension at the time of image formation for forming an image on a recording material.   The changing unit has an execution unit that executes a function of making the tension of the belt member larger than the tension at the time of image formation after the control toner image formed on the image carrier is transferred onto the belt member. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the belt member is an intermediate transfer belt that carries a toner image formed on a recording material.   A transfer member that forms a transfer portion that transfers a toner image formed on the intermediate transfer belt onto a recording material, and the toner image detection member includes: the image carrier; the belt member; The image forming apparatus according to claim 3, wherein the image forming apparatus is provided at a position downstream of the contact portion and upstream of the transfer portion.   2. The apparatus according to claim 1, wherein after the toner image detecting member detects a control toner image, the changing unit changes the tension of the belt member to a tension at the time of image formation for forming an image on a recording material. The image forming apparatus according to claim 4.

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