JP2014071330A - Transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer device configured to set a proper amount of separation between an image carrier and a transfer member, to prevent shock jitters, and to provide an image forming apparatus including the transfer device.SOLUTION: A transfer device includes: an image carrier 5 of an endless belt rotatably stretched by a plurality of stretching members; a transfer member 14 that comes in contact with a top surface, which is an outer peripheral surface of the image carrier, to form a transfer nip; and contact/separation means 20 for bringing the image carrier and the transfer member close to/away from each other by a preset amount of separation. The transfer device transfers a toner image carried on the top surface to a transfer material P held in the transfer nip. The transfer device includes speed detection means 21 for detecting speed of the image carrier, and separation amount changing means for changing the set separation amount according to the detection result of the speed detection means. The transfer material is conveyed toward the transfer nip, and the separation amount changing means changes the set separation amount value on the basis of the detection result of the speed detection means, in a separation amount setting change mode.

Description

  The present invention relates to a transfer device used in an image forming apparatus such as a printer, a facsimile machine, and a copying machine, and an image forming apparatus including the transfer device.

  2. Description of the Related Art Conventionally, in an image forming apparatus, when a sudden speed change occurs in an intermediate transfer belt, which is an image carrier of an endless belt that is endlessly moved while being stretched by a plurality of stretching rollers, the primary transfer nip is transferred from the photoreceptor. As a result, the image transferred onto the intermediate transfer belt expands and contracts. For this reason, light and shade occurs in a portion of the image that should have a constant image density, and an abnormal image called a shock jitter occurs.

  The sudden change in the speed of the intermediate transfer belt described above is caused by the transfer paper passing through the secondary transfer nip formed by the secondary transfer roller, which is a transfer member that contacts the front surface of the intermediate transfer belt, and the intermediate transfer belt. Occurs when paper is used.

  In the image forming apparatus described in Patent Document 1, the transfer paper is transported toward the secondary transfer nip, and before the transfer paper enters the secondary transfer nip, the rotation cam of the contact / separation mechanism is driven, The secondary transfer roller is forcibly moved away from the intermediate transfer belt. Thereby, a minute gap is formed between the secondary transfer roller and the intermediate transfer belt, and the occurrence of shock jitter when the transfer paper enters the secondary transfer nip can be suppressed. Immediately after the leading edge of the transfer paper enters the minute gap, the secondary transfer roller is released from the forced movement of the secondary transfer roller by driving the rotating cam, and the secondary transfer roller is moved to the intermediate position by the biasing force of the spring of the contact / separation mechanism. Press toward the transfer belt. As a result, the secondary transfer roller comes into contact with the intermediate transfer belt, and a sufficient transfer pressure is exerted at the secondary transfer nip during the transfer process to suppress the occurrence of transfer failure.

  The greater the distance between the secondary transfer roller and the intermediate transfer belt relative to the paper thickness, the smaller the impact when the transfer paper enters the transfer nip, and the greater the effect of reducing the speed fluctuation of the intermediate transfer belt.

  However, when the secondary transfer roller and the intermediate transfer belt are brought into contact with each other, the secondary transfer roller collides against the intermediate transfer belt due to the biasing force of the spring, and an impact is generated. End up.

  The impact generated when the secondary transfer roller and the intermediate transfer belt are brought into contact with each other increases as the distance between the secondary transfer roller and the intermediate transfer belt increases. For this reason, if the separation amount is increased too much in order to reduce the impact when the transfer material enters the transfer nip, the impact at the time of contact between the secondary transfer roller and the intermediate transfer belt will be large, and the speed fluctuation of the intermediate transfer belt will change. It grows and shock jitter occurs.

  In order to reduce the impact generated when the secondary transfer roller and the intermediate transfer belt are brought into contact with each other, if the distance between the secondary transfer roller and the intermediate transfer belt is too small, There is a risk that a large impact may occur when the transfer material enters.

  The present invention has been made in view of the above problems, and its purpose is to optimally set the distance between the image carrier and the transfer member and to suppress the occurrence of shock jitter, and An object of the present invention is to provide an image forming apparatus provided with the transfer device.

  In order to achieve the above object, an invention according to claim 1 is directed to an image carrier of an endless belt that is rotatably supported by a plurality of tension members, and a front surface that is an outer peripheral surface of the image carrier. A toner image carried on the front surface, comprising: a transfer member that forms a transfer nip in contact with the image bearing member; and contact / separation means that contacts and separates the image carrier and the transfer member by a predetermined separation amount. In a transfer device that transfers the image to a transfer material sandwiched in a transfer nip, a speed detection unit that detects the speed of the image carrier, and a separation amount that changes the set value of the separation amount based on the detection result of the speed detection unit A separation amount setting change mode in which a transfer material is conveyed toward the transfer nip, and the setting value of the separation amount is changed by the separation amount changing unit based on a detection result of the speed detection unit. Characterized by having A.

  In the present invention, the separation amount setting change mode is executed, so that the separation amount reduces the speed fluctuation of the image carrier that occurs when the transfer material enters the transfer nip, based on the detection result of the speed detection unit. As described above, the set value of the separation amount can be changed by the separation amount changing means. As a result, the image carrier and the transfer member can be separated with an optimum separation amount without the separation amount being too small or too large. Therefore, after the separation amount setting change mode is executed, before the transfer material enters the transfer nip, the image carrier and the transfer member are separated by the changed setting value, so that the transfer material enters the transfer nip or The impact generated when the image carrier and the transfer member come into contact with each other can be reduced. Since the impact can be reduced in this way, the speed fluctuation of the image carrier can be reduced, and the occurrence of shock jitter can be suppressed.

  As described above, according to the present invention, there is an excellent effect that the amount of separation between the image carrier and the abutting member can be set optimally and the occurrence of shock jitter can be suppressed.

The flowchart which concerns on the control which sets the separation amount to an appropriate value automatically. FIG. 2 is a schematic explanatory diagram of a main part in a full color mode of the printer according to the embodiment. FIG. 2 is a schematic explanatory diagram of a main part in a monochrome mode of the printer according to the embodiment. The schematic diagram for demonstrating shape factor SF-1. The schematic diagram for demonstrating shape factor SF-2. The figure explaining the separation mechanism which separates a secondary transfer roller and a drive roller. The graph which showed the state of the process linear velocity fluctuation | variation of an intermediate transfer belt. The graph which shows the relationship between separation amount and the maximum deceleration amount of process linear velocity. The graph which showed the relationship between the rotation angle of an eccentric cam, and a separation amount.

  Hereinafter, an embodiment in which the present invention is applied to an electrophotographic color printer (hereinafter simply referred to as a printer) as an image forming apparatus will be described with reference to the drawings. First, an overall outline of the printer according to this embodiment common to the respective configuration examples will be described.

  Here, FIG. 2 is a schematic explanatory diagram of main parts when the printer according to the present embodiment is in the full color mode, and FIG. 3 is a schematic explanatory diagram of main parts when the printer according to the present embodiment is in the monochrome mode.

  As shown in FIG. 2, the printer of this embodiment includes four process units 120Y, 120M, and 120C for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. 120K. Further, an intermediate transfer unit 32, a fixing device 50, a registration roller pair (not shown), an optical writing unit, a paper feed cassette, and the like are also provided.

  The process units 120Y, 120M, 120C, and 120K are provided with photosensitive drums 1Y, 1M, 1C, and 1K, respectively, that are image carriers, and are disposed to face the intermediate transfer belt 5. Around each photosensitive drum 1, a photosensitive member cleaning device 6 using a cleaning blade, a charge eliminating device (not shown), a charging device 2, a developing device 4, and the like are provided.

  Further, an optical writing unit (not shown) is provided above each process unit 120, and includes a laser diode, a polygon mirror, various lenses, and the like. Then, the photosensitive drums 1Y, 1M, 1C, and 1K of the process units 120Y, 120M, 120C, and 120K are optically scanned with scanning light that is emitted based on image information sent from an external personal computer or the like.

  Specifically, the photosensitive drums 1Y, 1M, 1C, and 1K of the process units 120Y, 120M, 120C, and 120K are rotationally driven in the clockwise direction in the drawing by driving means (not shown). The optical writing unit irradiates the rotationally driven photosensitive drums 1Y, 1M, 1C, and 1K while deflecting the scanning lights Ly, Lm, Lc, and Lk in the rotation axis direction, respectively, thereby performing optical scanning processing. I do. As a result, electrostatic latent images based on image information of each color of Y, M, C, and K are formed on the photosensitive drums 1Y, 1M, 1C, and 1K.

  The developing devices 4Y, 4M, 4C, and 4K use toners of yellow, magenta, cyan, and black, respectively, and electrostatic latent images formed on the photosensitive drums 1Y, 1M, 1C, and 1K, respectively. A toner is attached to form a visible image. When forming a full-color image, each developing device 4 forms a visible image with toner in the order of arrangement in the moving direction of the intermediate transfer belt 5, and the visible images of the respective colors are sequentially transferred onto the intermediate transfer belt 5. Thus, a full color image is formed.

  The intermediate transfer belt 5 is stretched by stretching rollers such as a driving roller 7 and a driven roller 8, and rotates when the driving roller 7 is driven by a driving motor (not shown). The process speed of the intermediate transfer belt 5 is adjusted to 150 [mm / sec]. An optical sensor 41 for detecting a toner pattern for adjusting image forming conditions formed on the intermediate transfer belt 5 is provided at a position facing the driven roller 8 via the intermediate transfer belt 5.

  Inside the intermediate transfer belt 5, primary transfer rollers 9Y, 9M, 9C, and 9K, a belt cleaning counter roller 14, and the like are arranged. Each roller is supported by bearings and arms by unit side plates (not shown) provided on both sides of the intermediate transfer unit 32 in the width direction of the intermediate transfer belt. Here, the drive roller 7 serves as a counter roller of the secondary transfer roller 15 and also serves as a secondary transfer bias roller.

  The primary transfer rollers 9Y, 9M, 9C, and 9K are arranged at the contact portions between the respective photosensitive drums 1 and the intermediate transfer belt 5, and a predetermined primary transfer bias voltage is applied during the primary transfer. Become. In the present embodiment, +1800 [V] is set to be applied.

The intermediate transfer belt 5 is made of polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer (ETFE), polyimide (PI), polycarbonate (PC) or the like in a single layer or a plurality of layers, and is made of a conductive material such as carbon black. Is distributed. The volume resistivity is adjusted to be in the range of 10 ⁸ to 10 ¹² [Ωcm], and the surface resistivity is adjusted to be in the range of 10 ⁹ to 10 ¹³ [Ω / □].

  If necessary, a release layer may be coated on the surface of the intermediate transfer belt 5. Examples of the material used for the coating include the following. That is, ethylene-tetrafluoroethylene copolymer (ETFE), polytetrafluoroethylene (PTFE), vinylidene fluoride, perfluoroalkoxy fluororesin (PEA), tetrafluoroethylene-hexafluoropropylene copolymer Fluororesin such as (FEP) and vinyl fluoride (PVF) can be used. The material used for the coating is not limited to this.

  The method of manufacturing the intermediate transfer belt 5 includes a casting method, a centrifugal molding method, and the like, and the surface thereof may be polished as necessary. If the volume resistivity of the intermediate transfer belt 5 exceeds the above-described range, the bias voltage required for transfer increases, which increases the power supply cost. Further, since the charging potential of the intermediate transfer belt 5 becomes high in the transfer process, the transfer paper peeling process, and the like, and self-discharge becomes difficult, it is necessary to provide a static elimination means. Also, if the volume resistivity and surface resistivity are below the above ranges, the charge potential decays faster, which is advantageous for static elimination by self-discharge, but toner scattering occurs because the current during transfer flows in the surface direction. End up. Therefore, the volume resistivity and the surface resistivity of the intermediate transfer belt 5 in this embodiment must be within the above ranges.

  In addition, the measured value measured as follows was used for the measured value of volume resistivity and surface resistivity. That is, an HRS probe (inner electrode diameter 5.9 [mm], ring electrode inner diameter 11 [mm]) is connected to a high resistivity meter (manufactured by Mitsubishi Chemical Corporation: Hiresta), and 100 [ V] (surface resistivity of 500 [V]) was applied, and the measured value after 10 seconds was used.

  The intermediate transfer belt 5 is provided with a belt cleaning blade 10 that removes residual toner, paper dust, and the like on the intermediate transfer belt 5. The belt cleaning blade 10 is made of urethane rubber, and is configured to dam and clean the toner so as to be pressed against the intermediate transfer belt 5 toward the belt cleaning counter roller 14.

  A brush roller 12 for applying the solid lubricant 11 to the intermediate transfer belt 5 is disposed in contact therewith. A brush facing roller 13 is disposed at a position facing the brush roller 12 via the intermediate transfer belt 5. The reason why the solid lubricant 11 is applied to the intermediate transfer belt 5 by the brush roller 12 is to facilitate cleaning by the belt cleaning blade 10.

  As the lubricant molded as the solid lubricant 11, a fatty acid metal salt having a linear hydrocarbon structure is used. Examples of the fatty acid metal salt include the following. That is, a fatty acid containing at least one fatty acid selected from stearic acid, palmitic acid, myristic acid, and oleic acid, and containing at least one metal selected from zinc, aluminum, calcium, magnesium, and lithium Metal salts are mentioned. In particular, zinc stearate is the most preferable material in terms of cost, quality stability, and reliability because it is produced on an industrial scale and has been used in many fields.

  However, the higher fatty acid metal salts that are generally used industrially are not the simple substance composition of the name, but include other fatty acid metal salts, metal oxides, and free fatty acids that are more or less similar. The fatty acid metal salt used in the form is no exception.

  These lubricants are supplied in the form of powder in small amounts. As a specific method, the lubricant is solidly formed into a block shape by a brush such as the brush roller 12 as in this embodiment. There are a method of scraping and applying the agent, a method of supplying the toner by external addition, and the like. However, when the lubricant is supplied externally to the toner, the supply amount depends on the output image area and cannot always be supplied to the entire surface of the intermediate transfer belt. For this reason, when the lubricant is to be stably supplied to the entire surface of the intermediate transfer belt with a simple apparatus configuration, the solid lubricant 11 is scraped off by the brush roller 12 as in the present embodiment, and the intermediate transfer belt 5 is removed. The method of applying to is good.

  In order to scrape off the solid lubricant 11 with the brush roller 12, the solid lubricant 11 is pressed against the brush roller 12 with a force of 1 [N] to 4 [N] by a lubricant pressurizing means such as a spring. .

  Since the width of the solid lubricant 11 needs to be set wider than the width of the image formed on the intermediate transfer belt 5, it is set to 304 [mm] or more in this embodiment. Further, the width of the brush roller 12 needs to be larger than the width of the solid lubricant 11 in order to scrape the solid lubricant 11 uniformly.

  A brush facing roller 13 is provided at a position facing the brush roller 12 via the intermediate transfer belt 5. Further, a belt urging roller 17 that urges the intermediate transfer belt 5 is provided downstream of the brush roller 12 in the intermediate transfer belt rotation direction and upstream of the photosensitive drum 1Y in the intermediate transfer belt rotation direction. By urging the intermediate transfer belt 5 with the belt urging roller 17 in this way, vibration of the intermediate transfer belt 5 due to the brush roller 12 is suppressed. In the present embodiment, the belt urging roller 17 is provided on the outer side of the intermediate transfer belt 5, but the same effect can be obtained even if it is provided on the inner side.

  Of the primary transfer rollers 9K, 9C, 9M, and 9Y, the color primary transfer rollers 9C, 9M, and 9Y can be brought into contact with and separated from the intermediate transfer belt 5 by a conventionally known contact and separation mechanism (not shown). Yes. In the full color mode, the primary transfer rollers 9C, 9M, and 9Y that are separated from the intermediate transfer belt 5 in the monochrome mode shown in FIG. 3 are brought into contact with the intermediate transfer belt 5 as shown in FIG. . As a result, the intermediate transfer belt 5 is brought into contact with and wound around the respective photosensitive drums 1 in a state where the intermediate transfer belt 5 is extended by the primary transfer rollers 9. The primary transfer roller 9K is in contact with and wound around the intermediate transfer belt 5 regardless of whether in the full color mode or the monochrome mode.

The secondary transfer roller 15 is configured by coating a metal core such as stainless steel with an elastic body such as urethane adjusted to a resistance value in a range of 10 ⁶ to 10 ¹⁰ [Ω] with a conductive material. Has been.

  Here, if the resistance value of the secondary transfer roller 15 exceeds the above range, it becomes difficult for the current to flow. Therefore, a higher voltage must be applied in order to obtain a required transfer property, resulting in an increase in power supply cost. . In addition, since a high voltage is applied, a discharge occurs in the gap before and after the transfer portion nip, so that white spots are lost due to the discharge on the halftone image.

  On the contrary, if the resistance value of the secondary transfer roller 15 is below the above range, the transferability between the multi-color image portion (for example, three-color superimposed image) and the single-color image portion existing on the same image cannot be achieved. This is because the resistance value of the secondary transfer roller 15 is low, so that a sufficient current flows to transfer the monochrome image portion at a relatively low voltage. However, it is optimal for the monochrome image portion to transfer the multiple color image portion. A voltage value higher than the voltage is required. Therefore, if the voltage is set such that the multi-color image portion can be transferred, the transfer current becomes excessive in a single-color image, and the transfer efficiency is reduced.

  The resistance value of the secondary transfer roller 15 was measured as follows. That is, in a state where the secondary transfer roller 15 is installed on a conductive metal plate and a load of 4.9 [N] on one side (total of 9.8 [N] on both sides) is applied to both ends of the core metal, It calculated from the electric current value which flows when a voltage of 1000 [V] is applied between a metal core and the metal plate.

  The rotational driving of the secondary transfer roller 15 is provided with a driving force by a driving gear (not shown), and the peripheral speed thereof is adjusted to be substantially the same as the peripheral speed of the intermediate transfer belt 5. The secondary transfer is controlled by a constant current, and in this embodiment, the set value is set to +30 [μA].

  Further, the transfer paper P, which is a transfer material, reaches the secondary transfer position by the feed roller (not shown), the transfer paper transport roller, and the registration roller pair so that the leading end of the four-color superimposed image on the intermediate transfer belt 5 reaches the secondary transfer position. Paper is fed according to the timing. The four-color superimposed image transferred onto the transfer paper P is discharged by a discharging means (not shown), then conveyed along the fixing inlet guide to the fixing device 50, and after fixing, a pair of discharge rollers (not shown). Is discharged.

  The toner used in this embodiment is a polymerized toner produced by a polymerization method. FIG. 4 is a schematic diagram for explaining the shape factor SF-1, and FIG. 5 is a schematic diagram for explaining the shape factor SF-2.

  The shape factor SF-1 indicates the ratio of the roundness of the toner shape and is expressed by the following formula 1. This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.

  When the value of the shape factor SF-1 is 100, the shape of the toner is a true sphere, and becomes irregular as the value of the shape factor SF-1 increases. The shape factor SF-1 of the toner used in this embodiment is preferably in the range of 100 to 180.

  The shape factor SF-2 indicates the ratio of the unevenness of the toner shape, and is expressed by the following formula 2. A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner onto the two-dimensional plane by the figure area AREA and multiplying by 100 / 4π.

  When the value of the shape factor SF-2 is 100, unevenness does not exist on the toner surface, and as the shape factor SF-2 increases, the unevenness of the toner surface becomes more prominent. The shape factor SF-2 of the toner used in this embodiment is preferably in the range of 100 to 180.

  Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzing it. Calculated. When the shape of the toner is close to a sphere, the contact state between the toner and the toner or between the toner and the photosensitive drum 1 becomes a point contact, so that the attractive force between the toners becomes weak. For this reason, the fluidity is increased, the adsorption force between the toner and the photosensitive drum 1 is also weakened, and the transfer rate is increased. If either of the shape factor SF-1 or the shape factor SF-2 exceeds 180, the transfer rate is lowered, and the cleaning property when attached to the transfer unit is also not preferred.

  The toner particle size is preferably in the range of 4 [μm] to 10 [μm] in terms of volume average particle size. When the particle size is smaller than this range, it becomes a cause of background stains at the time of development, fluidity is deteriorated, and further, aggregation tends to occur, so that voids are likely to occur. On the other hand, when the particle diameter is larger than the above range, a high-definition image cannot be obtained due to toner scattering and resolution deterioration. In this embodiment, a toner having a volume average particle diameter of 6.5 [μm] is used.

  Here, as described above, the intermediate transfer belt 5 rotates when the drive motor drives the drive roller 7. Usually, the intermediate transfer belt 5 rotates at a constant linear velocity. When the intermediate transfer belt 5 rotates, an inertia acts on the driven roller 8 driven by the intermediate transfer belt 5, and a force for continuing to rotate the driven roller 8 is applied. In order to transfer the toner image on the intermediate transfer belt 5 to the transfer paper P, the printer transfers the toner image to the secondary transfer nip formed between the drive roller 7 and the secondary transfer roller 15 via the intermediate transfer belt 5. The sheet P is transferred by the transfer bias and pressure applied to the secondary transfer roller 15. At this time, when the transfer paper P enters the secondary transfer nip, the rotation of the intermediate transfer belt 5 is hindered, and the speed fluctuation of the intermediate transfer belt 5 occurs.

  Next, the contact / separation mechanism 20 that contacts and separates the secondary transfer roller 15 and the drive roller 7 will be described with reference to FIG. FIG. 6 is a view of the vicinity of the secondary transfer nip as viewed from the lower side of the apparatus. A contact / separation mechanism using the stepping motor 22, the eccentric cam 19, the biasing spring 23, and the like will be described.

  As shown in FIG. 6, the secondary transfer roller 15 and the drive roller 7 are disposed so as to face each other with the intermediate transfer belt 5 interposed therebetween. The secondary transfer roller 15 and the intermediate transfer belt 5 (drive roller 7) can be freely contacted and separated within a certain range by the contact / separation mechanism 20.

  A biasing force is applied to the secondary transfer roller 15 toward the drive roller 7 by a biasing spring 23 that is a biasing means. Thereby, a desired transfer pressure can be applied to the transfer paper P at the secondary transfer nip. The urging spring 23 includes a compression spring and a tension spring.

  Eccentric cams 19 are provided coaxially with the drive roller 7 at both axial ends of the drive roller 7. The eccentric cam 19 is abutted against ball bearings 24 of the secondary transfer roller 15 attached to both ends in the axial direction of the secondary transfer roller 15 so as not to prevent the rotation of the secondary transfer roller 15.

  The shape of the eccentric cam 19 is such that the shortest distance between the rotation center of the eccentric cam 19 and the outer shape is shorter than the diameter of the drive roller 7 and the longest distance between the rotation center of the eccentric cam 19 and the outer shape. The portion is longer than the diameter of the drive roller 7.

  When the rotary shaft 29 to which one eccentric cam 19 is attached rotates, the eccentric cam 19 is also attached to each other by a D-cut groove or the like so as to rotate at the same timing and at the same angle. Further, the rotation shaft 29 to which the eccentric cam 19 is attached is configured such that the rotation can be freely controlled by the stepping motor 22.

  In FIG. 6, a timing belt 27 is rotatably stretched between a gear 25 attached to the drive shaft 28 of the stepping motor 22 and a gear 26 attached to the side opposite to the eccentric cam 19 of the rotary shaft 29. Yes. The rotation of the stepping motor 22 is transmitted to the rotating shaft 29 attached to the eccentric cam 19 via the timing belt 27. Note that the rotation of the stepping motor 22 can be controlled at a step angle of 1.8 [°].

  The eccentric cam 19 is rotated by the stepping motor 22 before the transfer paper P enters the secondary transfer nip. The eccentric cam 19 is abutted against the ball bearing 24. By rotating the eccentric cam 19, the secondary transfer roller resists the urging force from the urging spring 23 when the following equation 3 is satisfied. 15 is pushed down in a direction away from the intermediate transfer belt 5.

  With such a configuration, when the transfer sheet enters the secondary transfer nip, the secondary transfer roller 15 and the intermediate transfer belt 5 are separated from each other, and the impact when the transfer sheet enters is suppressed. Process linear velocity fluctuations can be reduced.

  When the leading edge of the transfer paper P begins to pass through the secondary transfer nip, the eccentric cam 19 starts to rotate again by the stepping motor 22. When the following relationship 4 is satisfied, the secondary transfer roller 15 and the driving roller 7 come into contact with each other via the intermediate transfer belt 5 and application of a desired transfer pressure to the transfer paper P is started.

  Similarly, when the transfer paper P comes out of the secondary transfer nip, the eccentric cam 19 is rotated by the stepping motor 22, and the secondary transfer roller before the trailing edge of the transfer paper P finishes passing through the secondary transfer nip. 15 and the intermediate transfer belt 5 are separated from each other. Thereby, the impact when the transfer paper P passes through the secondary transfer nip can be reduced.

  FIG. 7 shows the process linear velocity fluctuation of the intermediate transfer belt 5. The intermediate transfer belt 5 is usually driven at a process linear velocity within a certain range around a preset process linear velocity. However, when the transfer paper P enters the secondary transfer nip or the secondary transfer roller 15 and the intermediate transfer belt 5 come into contact with each other, the process linear velocity is reduced by the impact and torque load generated at that time ( The valley of the graph of FIG. After that, when the transfer paper P passes through the secondary transfer nip, the torque load factor due to the transfer paper P is removed, so that the process linear velocity of the intermediate transfer belt 5 is accelerated (the peak portion in the graph of FIG. 7).

  If the impact due to the transfer paper entering the secondary transfer nip or the contact between the secondary transfer roller 15 and the intermediate transfer belt 5 is large, the degree of deceleration of the intermediate transfer belt 5 also increases accordingly. For this reason, the drop in the valley of the graph of FIG. As a result, an abnormal image called a horizontal line appears in the printed image called shock jitter.

  As shown in FIG. 6, an encoder and a speed detection device 21 are attached to the intermediate transfer belt 5, and the process linear velocity of the intermediate transfer belt 5 can always be monitored. The process linear velocity detection information detected by the speed detection device 21 is transmitted to a control unit (not shown) that controls the stepping motor 22.

  FIG. 8 is a graph showing how the maximum deceleration amount of the process linear speed is changed by changing the distance between the secondary transfer roller 15 and the intermediate transfer belt 5.

  Here, the maximum deceleration of the process linear velocity is the difference between the average value of the process linear velocity in the graph of FIG. 7 and the minimum value of the process linear velocity in the valley portion of the graph. It shows how far the speed has decelerated from the set speed.

  As shown in the graph of FIG. 8, when the distance between the secondary transfer roller 15 and the intermediate transfer belt 5 is small, the transfer paper P collides with the secondary transfer roller 15 or the intermediate transfer belt 5 at the secondary transfer nip, An impact due to the transfer paper entering the secondary transfer nip and a torque load on the intermediate transfer belt 5 are generated. Therefore, the maximum deceleration amount of the process linear speed is also increased, and shock jitter is generated.

  On the other hand, when the separation amount is large, the transfer paper P hardly collides with the secondary transfer roller 15 or the intermediate transfer belt 5 at the secondary transfer nip, and the impact due to the transfer paper entering the secondary transfer nip can be suppressed. . However, since the impact when the secondary transfer roller 15 and the intermediate transfer belt 5 come into contact with each other increases, the maximum deceleration amount of the process linear speed increases and shock jitter occurs.

  Therefore, it is necessary to set the separation amount so that the fluctuation amount (maximum deceleration amount) of the process linear speed of the intermediate transfer belt 5 is minimized, but the optimum value of the separation amount is the thickness, rigidity, and humidity of the transfer paper P. It changes with things.

  FIG. 9 is a graph showing the relationship between the rotation angle of the eccentric cam 19 and the separation amount. As shown in the graph of FIG. 9, the amount of separation can be changed by changing the rotation angle of the eccentric cam 19.

  FIG. 1 shows a flowchart relating to control for automatically setting the separation amount performed by the control unit to an appropriate value.

  First, monitoring of the process linear velocity of the intermediate transfer belt 5 is started by the encoder and speed detector 21 attached to the intermediate transfer belt 5 (S1). Then, printing of the first transfer sheet P is started (S2). Before the first transfer sheet P enters the secondary transfer nip, the eccentric cam 19 is rotated by a preset angle by the stepping motor 22, and the secondary transfer roller 15, the intermediate transfer belt 5 (drive roller 7), Are separated by an arbitrary amount. The separation amount by the set angle is set as a separation amount default (S3). When the leading edge of the transfer paper P passes through the secondary transfer nip, the eccentric cam 19 is returned to the original position by the stepping motor 22.

  Before the trailing edge of the transfer paper P is separated from the secondary transfer nip, the eccentric cam 19 is rotated by the stepping motor 22 to separate the secondary transfer roller 15 and the intermediate transfer belt 5 from each other. Then, the maximum deceleration amount of the process linear velocity of the intermediate transfer belt 5 detected by the encoder and speed detection device 21 is stored in the storage unit as the deceleration amount 1 (S4).

  Subsequently, printing of the second transfer sheet P is started (S5). Before the second transfer sheet P enters the secondary transfer nip, the eccentric cam 19 is rotated by a specified angle by the stepping motor 22. At this time, the angle at which the eccentric cam 19 is rotated is the angle obtained by rotating the eccentric cam 19 in the first sheet + α (α is an arbitrary angle), and the distance between the secondary transfer roller 15 and the intermediate transfer belt 5 is The distance is different from that of the first sheet. The separation amount by this angle is set as the separation amount default + α (S6). Then, similarly to the first transfer paper P, the maximum deceleration amount of the process linear velocity of the intermediate transfer belt 5 detected by the encoder and speed detection device 21 is stored in the storage unit as the deceleration amount 2 (S7).

  Subsequently, printing of the third transfer sheet P is started (S8). Before the third transfer sheet P enters the secondary transfer nip, the eccentric cam 19 is rotated by a specified angle by the stepping motor 22. At this time, an angle at which the eccentric cam 19 is rotated is an angle −β (β is an arbitrary angle) by which the eccentric cam 19 is rotated by the first transfer sheet P, and the secondary transfer roller 15, the intermediate transfer belt 5, and the like. Is set to be different from the first and second transfer sheets P. The separation amount by this angle is set as a separation amount default -β (S9). Then, similarly to the first and second transfer sheets P, the maximum deceleration amount of the process linear velocity of the intermediate transfer belt 5 detected by the encoder and the speed detector 21 is stored in the storage unit as the deceleration amount 3 ( S10).

  Then, the deceleration amount 1, the deceleration amount 2, and the deceleration amount 3 are compared, and the angle for rotating the eccentric cam 19 that becomes the separation amount with the smallest deceleration amount is set as a new separation amount default (S12). Next, the deceleration amount 1, the deceleration amount 2 and the deceleration amount 3 are compared with a preset target deceleration amount, and any of the deceleration amount 1, the deceleration amount 2 and the deceleration amount 3 is less than the target deceleration amount. If it is lower (YES in S13), a series of separation amount setting change control is terminated. As a result, it is possible to automatically set the separation amount so that the deceleration amount of the intermediate transfer belt 5 is less than the target deceleration amount.

  On the other hand, when all of the deceleration amount 1, the deceleration amount 2 and the deceleration amount 3 are larger than the target deceleration amount (NO in S13), the process returns to the top of the flowchart and the separation amount is adjusted again according to the flowchart. Even if this loop is repeated n times (n can be set arbitrarily), if none of the deceleration amount 1, deceleration amount 2 and deceleration amount 3 falls below the target deceleration amount, the loop is aborted and set last. The default distance is used as the setting value.

  In the flowchart shown in FIG. 1, three sheets of transfer paper P are passed and the amount of change in the process linear speed of the intermediate transfer belt 5 is detected and compared. You can choose any number.

  Also, the average value of the fluctuation amount of the process linear velocity of the first to nth sheets, the average value of the fluctuation amount of the process linear velocity of the (n + 1) th to mth sheets, and the (m + 1) th to pth sheets It is possible to compare not only from one sheet but also from an average value of an arbitrary number of sheets, such as an average value of variation in process linear velocity.

  A series of separation amount setting change control in the flowchart shown in FIG. 1 is set as a separation amount setting mode, and this separation amount setting mode is incorporated in the image forming apparatus main body so that it can be executed at an arbitrary timing.

  For example, by setting the transfer sheet P that the user desires before printing in the paper feed unit and executing the separation amount setting mode, the optimum separation amount can be set for the transfer sheet P that the user desires to print. It is performed automatically, and abnormal images due to shock jitter can be reduced.

  When executing the separation amount setting mode, image formation using toner is not performed, and heat generation of the fixing device that fixes the toner to the transfer paper P is stopped, so that the separation amount setting mode is executed. The used transfer paper P can be reused for normal image formation. In addition, the amount of power used can be reduced.

  Further, the separation amount setting mode may be performed within a normal image forming operation. That is, a plurality of transfer sheets P of the same type are conveyed toward the secondary transfer nip, and image formation is performed on, for example, the previous three transfer sheets P, and the separation amount is set as shown in FIG. Change control is performed to change the setting value to the optimum separation amount. For the fourth and subsequent transfer sheets P, image formation is performed, and the secondary transfer roller 15 and the intermediate transfer belt 5 are separated by the set value of the separation amount changed by the separation amount setting change control. Let This may cause shock jitter on the transfer paper P used for the separation amount setting change control, but suppresses the occurrence of shock jitter on the transfer paper P after the separation amount setting change control is executed. Can do. Therefore, when forming an image on a plurality of transfer sheets P of the same type, the number of abnormal images can be reduced as compared with the case where the separation amount setting change control is not performed.

  Here, changes in the diameters of the secondary transfer roller 15 and the eccentric cam 19 occur due to wear due to use over time and differences in processing accuracy. For this reason, even if an optimal separation amount is set for each transfer sheet P in advance, the separation amount between the secondary transfer roller 15 and the intermediate transfer belt 5 is different from the target value, and the shock jitter is deteriorated.

  On the other hand, in this embodiment, even if the diameters of the secondary transfer roller 15 and the eccentric cam 19 change due to wear and processing accuracy, the separation amount between the secondary transfer roller 15 and the intermediate transfer belt 5 is as follows. The optimum value is automatically set. For this reason, it is possible to suppress shock jitter when the transfer paper P enters the secondary transfer nip.

  Further, the amount of separation between the secondary transfer roller 15 and the intermediate transfer belt 5 varies depending on conditions such as the thickness, size, surface property, rigidity, and humidity of the transfer paper P. Therefore, it is necessary to set an enormous amount as the separation amount, or when the transfer paper P that is not set by the user is used, the optimum separation amount cannot be set and a shock jitter may occur. .

  On the other hand, in this embodiment, the optimum separation amount is automatically set by detecting the process linear velocity of the intermediate transfer belt 5. Therefore, compared with the case where the separation amount is individually set in advance and stored in the storage unit according to the difference in the thickness, rigidity, environment, etc. of the transfer paper P, the man-hours and set values for necessary settings are reduced. It can be greatly reduced. Also, as described above, by executing the separation amount setting mode, the optimum separation amount is automatically set for the transfer paper P that the user desires to print, and abnormal images due to shock jitter are reduced. be able to.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
An image carrier of an endless belt such as an intermediate transfer belt 5 that is rotatably supported by a plurality of tension members, and a front surface that is an outer peripheral surface of the image carrier, and a secondary transfer nip or the like A transfer member such as a secondary transfer roller 15 that forms a transfer nip, and contact / separation means such as an contact / separation mechanism 20 that contacts and separates the image carrier and the transfer member by a predetermined separation amount. In the transfer device for transferring the toner image carried on the surface to a transfer material such as transfer paper P sandwiched in the transfer nip, speed detection means such as a speed detection device 21 for detecting the speed of the image carrier, and speed detection means And a separation amount changing means such as a control unit for changing the set value of the separation amount based on the detection result of the sheet, transporting the transfer material toward the transfer nip, and separating based on the detection result of the speed detection means. The amount of separation is set by the amount changing means. Having a distance amount setting change mode for changing a. According to this, as described in the above embodiment, the amount of separation between the image carrier and the transfer member can be set optimally, and the occurrence of shock jitter can be suppressed.
(Aspect B)
In (Aspect A), the separation amount changing unit changes the setting value of the separation amount in accordance with the fluctuation amount of the speed fluctuation of the image carrier. According to this, as described in the above embodiment, the setting value of the separation amount can be changed so as to reduce the speed fluctuation of the image carrier in accordance with the fluctuation amount of the speed fluctuation of the image carrier. .
(Aspect C)
In (Aspect A) or (Aspect B), it has storage means such as a storage unit for storing the speed detected by the speed detection means, and transports a plurality of transfer materials toward the transfer nip, The amount of separation is changed for each transfer material, and the amount of change in the speed fluctuation is stored in the storage means. According to this, as described in the above embodiment, it is possible to detect or store how the variation amount of the speed variation has changed by changing the separation amount.
(Aspect D)
In (Aspect C), the fluctuation amount of each speed fluctuation stored in the storage means is compared, and the set value of the separation amount is changed to an arbitrary value. According to this, as described in the above embodiment, by comparing the fluctuation amount of the speed fluctuation stored in the storage means, the separation amount can be changed to an arbitrary value and the shock jitter can be reduced.
(Aspect E)
In (Aspect C), the fluctuation amounts of the respective speed fluctuations stored in the storage unit are compared, and the separation amount that minimizes the fluctuation quantity of the speed fluctuation is set as a set value. According to this, as described in the above embodiment, the shock jitter can be reduced by reducing the fluctuation amount of the speed fluctuation.
(Aspect F)
In (Aspect C), an average value is acquired from the variation amount of each speed variation stored in the storage unit and stored in the storage unit. According to this, as described in the above embodiment, it is possible to acquire the fluctuation amount that is less affected by the error than the fluctuation amount acquired with only one transfer material.
(Aspect G)
In (Aspect C), the variation amount of each speed variation stored in the storage unit is compared with a target variation amount that is set in advance, and the variation amount of each speed variation is equal to or greater than the target variation amount. If there is, again, the plurality of transfer materials are conveyed toward the transfer nip, and the separation amounts different from the above-described separation amounts when the plurality of transfer materials are conveyed toward the transfer nip. The separation amount is changed for each transfer material, and the setting value of the separation amount is repeatedly changed. According to this, as described in the above-described embodiment, by repeating the setting change of the separation amount until the variation amount of the speed variation reaches the target value, the separation is automatically performed so that the variation amount is less than the target variation amount. The amount is set.
(Aspect H)
In the (Aspect A), (Aspect B), (Aspect C), (Aspect D), (Aspect E), (Aspect F) or (Aspect G), the separation amount changed and set by the separation amount changing means Can be stored in the storage means for each transfer material, and the separation amount stored in the storage means can be recalled at an arbitrary timing. According to this, as described in the above embodiment, the separation amount for each transfer material that has been adjusted once is stored separately, so that the setting of the separation amount is executed the next time the same transfer material is used. Even if you do not, you can call the separation amount set in the past. Therefore, it is possible to set the separation amount so that the variation amount of the speed variation is less than the target variation amount without taking time.
(Aspect I)
A toner image forming unit such as a process unit 120 that forms a toner image on an image carrier such as the photosensitive drum 1, and a transfer unit such as an intermediate transfer unit 32 that transfers the toner image on the image carrier to a transfer material. In the image forming apparatus provided, as the transfer unit, (Aspect A), (Aspect B), (Aspect C), (Aspect D), (Aspect E), (Aspect F), (Aspect G) or (Aspect H) ) Transfer device. According to this, as described in the above-described embodiment, it is possible to optimally set the distance between the image carrier and the transfer member, suppress the generation of shock jitter, and perform good image formation.

DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Charging device 4 Developing device 5 Intermediate transfer belt 6 Photoconductor cleaning device 7 Drive roller 8 Driven roller 9 Primary transfer roller 10 Belt cleaning blade 11 Solid lubricant 12 Brush roller 13 Brush counter roller 14 Belt cleaning counter roller 15 Secondary transfer roller 17 Belt urging roller 19 Eccentric cam 20 Contact / separation mechanism 21 Detection device 22 Stepping motor 23 Biasing spring 24 Ball bearing 25 Gear 26 Gear 27 Timing belt 28 Drive shaft 29 Rotating shaft 32 Intermediate transfer unit 41 Optical sensor 50 Fixing device 120 Process unit

JP 2011-133653 A

Claims (9)

An image carrier of an endless belt stretched rotatably by a plurality of stretching members;
A transfer member that forms a transfer nip in contact with a front surface that is an outer peripheral surface of the image carrier;
Contact and separation means for contacting and separating the image carrier and the transfer member by a predetermined separation amount;
In the transfer device for transferring the toner image carried on the front surface to the transfer material sandwiched in the transfer nip,
Speed detecting means for detecting the speed of the image carrier;
A separation amount changing means for changing the setting value of the separation amount from the detection result of the speed detection means,
Transfer having a separation amount setting change mode in which a transfer material is conveyed toward the transfer nip, and the setting value of the separation amount is changed by the separation amount changing unit based on a detection result of the speed detection unit. apparatus. The transfer device according to claim 1.
The transfer apparatus according to claim 1, wherein the separation amount changing unit changes a set value of the separation amount in accordance with a variation amount of a speed variation of the image carrier. The transfer device according to claim 1 or 2,
Having storage means for storing the speed detected by the speed detection means;
A transfer apparatus characterized in that a plurality of transfer materials are conveyed toward a transfer nip, the separation amount is changed for each transfer material, and the amount of change in the speed fluctuation is stored in the storage means. The transfer device according to claim 3.
A transfer device characterized in that the amount of change in each speed variation stored in the storage means is compared and the set value of the separation amount is changed to an arbitrary value. The transfer device according to claim 3.
A transfer apparatus characterized in that the amount of fluctuation of each speed fluctuation stored in the storage means is compared, and the separation amount at which the fluctuation amount of the speed fluctuation is the smallest is set as a set value. The transfer device according to claim 3.
A transfer apparatus, wherein an average value is acquired from each speed variation stored in the storage means and stored in the storage means. The transfer device according to claim 3.
The variation amount of each speed variation stored in the storage means is compared with a target variation amount that is a preset target.If the variation amount of each speed variation is equal to or greater than the target variation amount, Again, the plurality of transfer materials are conveyed toward the transfer nip, and the separation amounts are different for each transfer material with a separation amount different from the separation amount when the previous plurality of transfer materials are conveyed toward the transfer nip. A transfer apparatus characterized by repeatedly changing the set value of the separation amount by changing the amount. The transfer device according to claim 1, 2, 3, 4, 5, 6 or 7.
The setting value of the separation amount changed and set by the separation amount changing unit is stored in the storage unit for each transfer material, and the separation amount stored in the storage unit can be called at an arbitrary timing. Characteristic transfer device. Toner image forming means for forming a toner image on the image carrier;
In an image forming apparatus comprising transfer means for transferring a toner image on the image carrier to a transfer material,
An image forming apparatus using the transfer device according to claim 1, 2, 3, 4, 5, 6, 7, or 8 as the transfer means.

Images