JP2015176071A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of an image density shift due to unsuitable imaging conditions in each color of Y, C, M, K and the occurrence of a transfer failure due to the wear of a photoreceptor, as well as to suppress the increase of a downtime in an image forming apparatus.SOLUTION: A printer includes a control unit that carries out a process control for determining imaging conditions of each imaging unit 1Y, 1C, 1M, 1K based on detection results by an optical sensor unit 20 about a toner adhesion amount to a test toner image (patch image) formed by the imaging units 1Y, 1C, 1M, 1K under predetermined imaging conditions. The control unit is configured to carry out a transfer condition determination process to determine transfer conditions of a toner image from photoreceptors 2Y, 2C, 2M, 2K onto an intermediate transfer belt 7 based on a transfer current value or a transfer voltage value while the process control is carried out.

Description

  The present invention relates to an image forming apparatus that performs an image forming condition determining process for determining an image forming condition of an image forming unit based on a result of detecting a toner adhesion amount with respect to a test toner image formed by an image forming unit. It is.

  In general, an image forming apparatus that forms an image by an electrophotographic process includes a photosensitive member as a latent image carrier, a charging device that uniformly charges the photosensitive member, and an optical writing device that optically writes a latent image on the charged photosensitive member. The image forming apparatus includes a developing device that develops a latent image to obtain a toner image. In such a configuration, if the image forming conditions such as the optical writing intensity of the latent image and the development potential are not suitable for the environment, the target image density cannot be obtained and an image density shift occurs.

  As an apparatus capable of suppressing the occurrence of such image density deviation, an image forming apparatus described in Patent Document 1 is known. This image forming apparatus periodically performs process control processing as image forming condition determination processing as described below. That is, a gradation pattern image is formed and transferred from the photoreceptor to the surface of the intermediate transfer belt. The gradation pattern image includes a plurality of test toner images having different image densities, and these test toner images are arranged along the belt moving direction. The control unit of the image forming apparatus sets the target image density for the image forming conditions such as the optical writing intensity of the latent image and the developing potential based on the result of detecting the toner adhesion amount of the test toner image by the reflection type photo sensor. Determine possible values. By periodically executing such process control processing, it is possible to suppress the occurrence of image density deviation due to environmental fluctuations.

  On the other hand, it is known that the photosensitive layer (surface layer) of the photoconductor wears with time, and depending on the amount of wear, the image can have various adverse effects. Therefore, the image forming apparatus described in Patent Document 2 estimates the thickness of the photosensitive layer as follows, and reflects the result in setting the image forming conditions. That is, when a transfer bias having a predetermined voltage value is applied to the transfer roller, the transfer current value flowing between the transfer roller and the photosensitive member becomes a value corresponding to the thickness of the photosensitive layer of the photosensitive member. The thickness of the photosensitive layer is estimated based on the result of detecting the transfer current value.

  As a result of experiments, the inventors have also determined, in addition to the transfer current value, the output value (transfer voltage value) of the transfer bias from the power supply when a transfer bias having a predetermined current value is applied to the transfer roller by constant current control. It has been found that the value depends on the thickness of the photosensitive layer of the photoreceptor. Therefore, it is possible to predict the thickness of the photosensitive layer not only by the transfer current value but also by referring to the result of detecting the transfer voltage value.

  In addition, the present inventors have shown through experiments that the value of the transfer current flowing between the transfer roller and the photoconductor increases as the thickness of the photoconductive layer decreases as the photoconductor wears. It has also been found that if the transfer performance is not improved by changing the transfer conditions, transfer defects will be caused. Therefore, in order to suppress the occurrence of such a transfer failure, the thickness of the photosensitive layer of the photoconductor is estimated based on the result of detecting the transfer current value or the transfer voltage value, and the process for determining the transfer conditions based on the result is periodically performed. An image forming apparatus is being developed.

  This image forming apparatus can suppress the occurrence of transfer failure due to wear of the photosensitive layer of the photosensitive member by periodically performing the above-described processing, but increases the downtime of the apparatus. It has caused the problem of end. Specifically, in a configuration in which image formation condition determination processing such as process control processing is periodically performed in order to suppress the occurrence of image density deviation due to environmental fluctuation, the charging potential (charging bias) of the photoconductor is determined by the execution. Will be changed regularly. When the charging potential is changed, even if the thickness of the photosensitive layer does not change, the transfer current value and the transfer voltage value change, so the photosensitive layer based on the detection result of the transfer current value and the transfer voltage value is changed. Thickness cannot be estimated. For this reason, it is necessary to detect the transfer current value or the transfer voltage value while charging the photosensitive member at a predetermined charging potential when the print job is not being performed, and during that time, the print job cannot be performed. As a result, downtime is increased.

  The present invention has been made in view of the above background, and an object thereof is to provide the following image forming apparatus. That is, the image forming apparatus can suppress an increase in downtime of the apparatus while suppressing occurrence of image density deviation due to improper image forming conditions and occurrence of transfer failure due to wear of the latent image carrier.

  To achieve the above object, the present invention provides a latent image carrier that carries a latent image, charging means for charging the surface of the latent image carrier, and writing a latent image on the surface of the latent image carrier after charging. A latent image writing means; an image forming means having a developing means for developing the latent image to obtain a toner image; a transfer means for transferring the toner image on the surface of the latent image carrier to a transfer body; An adhesion amount detection means for detecting a toner adhesion amount with respect to a toner image formed by the image means; and a toner adhesion amount with respect to a test toner image formed on the imaging means under a predetermined image forming condition. And an image forming apparatus including a control unit that performs an image forming condition determining process for determining an image forming condition of the image forming unit based on a result detected by the image forming unit. Of the entire area in the direction of body surface movement, A transfer condition determination process is performed for determining the transfer condition of the transfer unit based on the transfer current value or the transfer voltage value when the region charged under the charging condition is moved to a position facing the transfer unit. As described above, the control means is configured.

  According to the present invention, it is possible to suppress an increase in downtime of an apparatus while suppressing occurrence of image density deviation due to improper image forming conditions and occurrence of transfer failure due to wear of a latent image carrier. There is an effect.

1 is a schematic configuration diagram illustrating a configuration of a printer according to an embodiment. FIG. 3 is a configuration diagram illustrating a main configuration of an image forming unit of the printer. FIG. 2 is a block diagram showing a main part of an electric circuit of the printer. FIG. 3 is a partial perspective view illustrating a part of an intermediate transfer belt of the printer. The graph which shows the relationship between a primary transfer rate and a primary transfer current. 6 is a graph showing a relationship among a charging potential Vd, a developing bias Vb, a primary transfer voltage, and a toner adhesion amount when forming a patch image. 6 is a graph showing a relationship between a primary transfer voltage and a charging potential Vd under constant current control conditions. The graph which shows the relationship between the output target value of a primary transfer current, and a primary transfer rate. 3 is a data table showing the relationship between the thickness d of the photosensitive layer, the environment, and the primary transfer voltage under constant current control conditions. The graph which shows the relationship between thickness d and the primary transfer voltage in the conditions of constant current control. FIG. 3 is a configuration diagram showing belt resistance detection means in the printer according to the embodiment. The graph which shows the relationship between the primary transfer bias on the conditions of constant current control, and correction | amendment of the detection result of the charging potential Vd. 6 is a graph for explaining an improvement in primary transfer rate when a linear velocity difference is provided between a photoconductor and an intermediate transfer belt. The graph which shows the relationship between thickness d and a preferable linear velocity difference.

  Hereinafter, an electrophotographic printer will be described as an example of an embodiment of an image forming apparatus to which the present invention is applied. First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram showing the configuration of the printer. As shown in FIG. 1, this printer has four image forming units 1Y, 1C, 1M for forming images of yellow (Y), cyan (C), magenta (M), and black (K). , 1K. Hereinafter, the subscripts Y, C, M, and K of the respective symbols indicate members for yellow, cyan, magenta, and black, respectively. The color order of Y, C, M, and K is not limited to the order shown in FIG. 1, and may be another order of arrangement.

  FIG. 2 is a configuration diagram showing a configuration of an image forming unit for Y in the printer. As shown in FIG. 2, there are a charging roller 3Y as a charging means, a developing device 4Y as a developing means, a cleaning device 5Y, and the like around a drum-shaped photoconductor 2Y as a latent image carrier provided in the image forming unit 1Y. Is arranged. The charging roller 3Y made of a rubber roller rotates while being in contact with the surface of the photoreceptor 2Y. In this printer, a charging bias is applied to the charging roller 3Y by a charging power source (not shown) to generate a discharge between the charging roller 3Y and the photosensitive member 2Y, thereby charging the surface of the photosensitive member 2Y with toner. It is designed to be uniformly charged to the same polarity as the polarity.

  A two-component developer containing Y toner and a magnetic carrier is accommodated in the developing device 4Y. The developing device 4Y includes a developing roller 4aY that is a developer carrying member facing the photosensitive member 2, a screw that conveys and stirs the developer, a toner concentration sensor (not shown), and the like. The developing roller 4aY is composed of a hollow and rotatable sleeve and a magnet roller included so as not to be rotated.

  The image forming unit 1Y is configured as a process cartridge in which a photosensitive member 2Y, a charging roller 3Y, a developing device 4Y, and a cleaning device 5Y disposed around the photosensitive member 2Y are supported by a common support as a unit. . And, it can be attached to and detached from the printer main body, and consumable parts can be replaced at the same time when the lifetime is reached. The other image forming units 1C, 1M, and 1K use C toner, M toner, and K toner as toners, but the other configurations are the same as those of the Y image forming unit.

  Below the image forming units 1Y, 1C, 1M, and 1K, an optical writing unit 6 serving as a latent image writing unit is disposed. The optical writing unit 6 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and performs optical scanning with laser light L on the surfaces of the photoreceptors 2Y, 2C, 2M, and 2K of each color based on image data. I do. By this optical scanning, electrostatic latent images for yellow, cyan, magenta, and black are formed on the uniformly charged surfaces on the photoreceptors 2Y, 2C, 2M, and 2K.

  Above the image forming units 1Y, 1C, 1M, and 1K, an intermediate transfer unit that transfers the toner images of the respective colors from the photoconductors (2Y, 2C, 2M, and 2K) of the respective colors to the recording sheet S via the intermediate transfer belt 7. 8 is arranged. The intermediate transfer belt 7 is endlessly moved in the counterclockwise direction in the figure by the rotational drive of at least one of the rollers while being stretched by a plurality of rollers.

  The endless intermediate transfer belt 7 as a transfer body is a smooth layer made of a base layer made of fluorine resin, PVD, polyimide resin or the like with little elongation, and a fluorine-based resin coated on the front side. The belt comprises a multilayer structure having at least a good coat layer. In addition to the intermediate transfer belt 7, the intermediate transfer unit 8 includes a cleaning device 10 including a primary transfer roller 9Y, 9C, 9M, 9K, a brush roller, a cleaning blade, and the like, a secondary transfer backup roller 11, and an optical sensor unit 20. Etc.

  Primary transfer rollers 9Y, 9C, 9M, and 9K as transfer bias members sandwich the intermediate transfer belt 7 between the photoreceptors 2Y, 2C, 2M, and 2K. As a result, primary transfer nips for Y, M, C, and K in which the photoreceptors 2Y, 2M, 2C, and 2K contact the front surface of the intermediate transfer belt 7 are formed. The intermediate transfer unit 8 includes a secondary transfer roller 12 positioned on the outer side of the belt loop in the vicinity of the secondary transfer backup roller 11 on the downstream side in the belt movement direction from the image forming unit 1K. The secondary transfer roller 12 is sandwiched between the intermediate transfer belt 7 and the secondary transfer backup roller 11 to form a secondary transfer nip.

  A fixing unit 13 is disposed above the secondary transfer roller 12. The fixing unit 13 includes a fixing roller and a pressure roller that contact each other while rotating to form a fixing nip. The fixing roller has a built-in halogen heater, and electric power is supplied to a heater from a power source (not shown) so that the surface of the fixing roller has a predetermined temperature, and a fixing nip is formed between the fixing roller and the pressure roller.

  At the bottom of the printer main body, paper feed cassettes 14a and 14b for storing a plurality of recording sheets S as recording media on which output images are recorded, a paper feed roller (not shown), a resist roller pair 15 and the like are disposed. . Further, a manual feed tray 14c for manually feeding paper from the side is provided on the side of the printer main body. Further, on the right side of the intermediate transfer unit 8 and the fixing unit 13 in the drawing, a double-sided unit 16 is provided for transporting the recording sheet S to the secondary transfer nip again during double-sided printing.

  At the upper part of the printer main body, toner supply containers 17Y, 17C, 17M, and 17K for supplying toner to the developing devices of the image forming units 1Y, 1C, 1M, and 1K are disposed. The printer main body is also provided with a waste toner bottle, a power supply unit, etc. (not shown).

  Next, the operation of the printer will be described. First, the photoreceptor 2Y is driven to rotate while a predetermined charging bias is applied to the charging roller 3Y by a charging power source (not shown). The surface of the photoreceptor 2Y is uniformly charged as it passes through a position facing the charging bias. The surface of the photosensitive member 2Y charged to a predetermined potential is scanned with the laser light L based on the image data by the optical writing unit 6, whereby an electrostatic latent image is written on the photosensitive member 2Y. When the surface of the photoconductor 2Y carrying the electrostatic latent image reaches the developing device 4Y as the photoconductor 2Y rotates, the electrostatic latent image on the surface of the photoconductor 2Y is developed by the developing roller 4aY arranged to face the photoconductor 2Y. Y toner is supplied to the image. Thereby, a Y toner image is formed on the surface of the photoreceptor 2Y. An appropriate amount of Y toner is supplied from the toner supply container 17Y into the developing device 3Y in accordance with the output of a toner density sensor (not shown).

  Similar operations are performed at predetermined timings in the image forming units 1C, M, and K. As a result, Y, C, M, and K toner images are formed on the surfaces of the photoreceptors 2Y, 2C, 2M, and 2K. These Y, C, M, and K toner images are primarily transferred to the front surface of the intermediate transfer belt 7 in order at the primary transfer nip for Y, C, M, and K. This primary transfer is performed by applying a voltage having a polarity opposite to that of the toner to the primary transfer rollers 9Y, 9C, 9M, and 9K by a transfer power source (not shown).

  The recording sheet S is conveyed from one of the paper feed cassettes 14 a and 14 b or the manual feed tray 14 c and stops once when it reaches the registration roller pair 15. Then, the registration roller pair 15 is rotated in accordance with a predetermined timing to send the recording sheet S toward the secondary transfer nip.

  The Y, C, M, and K toner images superimposed on the intermediate transfer belt 7 are secondarily transferred to the recording sheet S at the secondary transfer nip where the secondary transfer roller 12 and the intermediate transfer belt 7 abut. This secondary transfer is performed by applying a voltage having a polarity opposite to that of the toner to the secondary transfer roller 12 by a secondary transfer power source (not shown). After leaving the secondary transfer nip, the recording sheet S is conveyed toward the fixing unit 13 and is sandwiched between the fixing nips. The toner image on the recording sheet S is heated and fixed by heat from the fixing roller at the fixing nip. In the case of single-sided printing, the recording sheet S on which the toner image is fixed is discharged out of the apparatus by the respective transport rollers. In the case of duplex printing, the recording sheet S is conveyed to the duplex unit 16 by each conveyance roller and reversed, and an image is formed on the surface opposite to the surface on which the image has been previously formed as described above. After that, it is discharged out of the machine.

  In this printer, an imaging condition determination process called process control is performed at a predetermined timing in order to stabilize image quality over time and environmental fluctuations. In the process control process, a Y gradation pattern image composed of a plurality of patch-like Y toner images (test toner images) is formed on the photoreceptor 2 </ b> Y and transferred to the intermediate transfer belt 7. Similarly, C, M, and K gradation pattern images are formed on the photoreceptors 2C, 2M, and 2K. Then, the toner adhesion amount of each toner image in those gradation pattern images is detected by the optical sensor unit 20, and based on the detection result, a developing bias applied to the developing sleeve, a charging bias applied to the charging roller, etc. Adjust the image forming conditions.

  FIG. 3 is a block diagram showing the main part of the electric circuit of the printer. As shown in the figure, the control unit 30 includes image forming units 1Y, 1C, 1M, and 1K, an optical writing unit 6, a paper feed motor 81, a registration motor 82, an intermediate transfer unit 8, an optical sensor unit 20, and the like. Are electrically connected. The control unit 30 includes a CPU 30a that executes arithmetic processing and various programs, a RAM 30b that stores data, and a nonvolatile memory 30c. The paper feed motor 81 is a drive source for the paper feed rollers of each paper feed cassette and paper feed tray. The registration motor 82 is a driving source for the registration rollers.

  The optical sensor unit 20 has an optical sensor composed of a plurality of reflective photosensors arranged at a predetermined interval in the belt width direction of the intermediate transfer belt 7. Each optical sensor is configured to output a signal corresponding to the light reflectance of an intermediate transfer belt 7 or a patch image (patch toner image) described later on the intermediate transfer belt 7. Four optical sensors are provided. Three of them capture both the regular reflection light and the diffuse reflection light on the belt surface so that the output according to the Y, M, C toner image and the Y, C, M adhesion toner can be performed. Output according to. The remaining one captures only the specularly reflected light on the belt surface and performs output according to the amount of light so as to perform output according to the K toner image and K adhering toner.

  The control unit 30 performs process control processing at a predetermined timing, such as when a main power supply (not shown) is turned on, when waiting after a predetermined time has elapsed, or when waiting after outputting a predetermined number of prints or more. Specifically, when this predetermined timing arrives, the photosensitive members 2Y, 2C, 2M, and 2K are uniformly charged while being rotated. This charging is different from a uniform value (for example, −700 V) during normal printing as the charging bias Vc, and its absolute value is increased. Electrostatic latent images for Y patch images, C patch images, M patch images, and K patch images are formed on the photoreceptors 2Y, 2C, 2M, and 2K by scanning the laser beam L with the optical writing unit 6, respectively. By developing them with the developing devices 12Y, 12C, 12M, and 12K, Y, C, M, and K gradation pattern images are formed on the photoreceptors 2Y, 2C, 2M, and 2K. During development, the controller 30 gradually increases the absolute value of the developing bias Vb applied to the developing roller (4a) for each color. The development bias Vb and the charging bias Vc are both negative DC biases.

  As shown in FIG. 4, the Y, C, M, and K gradation pattern images are transferred so as to be aligned in the belt width direction without overlapping on the intermediate transfer belt 7. Specifically, the Y gradation pattern image Sy is transferred to one end in the width direction of the intermediate transfer belt 7. The C gradation pattern image Sc is transferred to a position slightly shifted to the center side from the Y gradation pattern image in the belt width direction. The M gradation pattern image Sm is transferred next to the C gradation pattern image in the width direction of the intermediate transfer belt 7. The K gradation pattern image Sk is transferred to the other end in the belt width direction.

  The optical sensor unit 20 includes a Y optical sensor 21Y, a C optical sensor 21C, an M optical sensor 21M, and a K optical sensor 21K that detect light reflection characteristics of the belt at different positions in the belt width direction. Yes. Of these four optical sensors, the K optical sensor 21K employs a sensor that detects only regular reflection light so as to detect a change in light reflection characteristics of the belt surface caused by adhesion of K toner. On the other hand, other optical sensors are of a type that detects both regular reflection light and diffuse reflection light so as to detect a change in light reflection characteristics of the belt surface caused by adhesion of Y, C, or M toner. Is.

  The Y optical sensor 21Y is disposed at a position for detecting the Y toner adhesion amount of the Y patch image of the Y gradation pattern image Sy formed at one end of the intermediate transfer belt 7 in the width direction. The C optical sensor 21C is disposed at a position for detecting the C toner adhesion amount of the C patch image of the C gradation pattern image Sc located near the Y gradation pattern image Sy in the belt width direction. . Further, the M optical sensor 21M is disposed at a position for detecting the M toner adhesion amount of the M patch image of the M gradation pattern image Sm located near the C gradation pattern image Sc in the belt width direction. ing. The K optical sensor 21K is disposed at a position for detecting the K toner adhesion amount of the K patch image of the K gradation pattern image Sk formed at one end portion in the width direction of the intermediate transfer belt 7.

  The control unit 30 calculates the light reflectance of each color patch image based on output signals sequentially sent from the four optical sensors of the optical sensor unit 20, and obtains the toner adhesion amount based on the calculation result to obtain the RAM 30a. To store. The gradation pattern images of the respective colors that have passed through the position facing the optical sensor unit 20 as the intermediate transfer belt 7 travels are cleaned from the front surface of the belt by the cleaning device 10.

The toner adhesion amount of the patch image in the Y, M, C, K gradation pattern images (Sk, Sm, Sc, Sy) is 0.1 [mg / cm ² ] at the minimum and 0.55 [mg / cm at the maximum. cm ² ]. Further, when the Q / d distribution of the toner is measured, it is almost aligned with the normal charging polarity.

  The control unit 30 determines image forming conditions of the image forming apparatuses 1Y, 1C, 1M, and 1K based on the toner adhesion amount of each patch image in each color gradation pattern image. Specifically, a function (y = ax + b) indicating a straight line graph is calculated by regression analysis based on the result of detecting the toner adhesion amount in the patch image and the development potential when each patch image is formed. Then, an appropriate development bias value is calculated by substituting the target value of the image density into this function.

  In the nonvolatile memory 30c of the control unit 30, image forming condition data in which several tens of development bias values and appropriate photosensitive member charging potentials (hereinafter referred to as charging potentials Vd) corresponding to the developing bias values are associated in advance. The table is stored. For each of the image forming apparatuses 1Y, 1C, 1M, and 1K, the control unit 30 develops the development bias value closest to the calculation result of the development bias value from the image formation condition table, and the corresponding charging potential Vd. And specify. In subsequent print jobs, image formation is performed under the same image formation conditions as the specific result, so that stable image formation can be performed with an image density close to the target value even when the installation environment and toner deterioration with time occur. .

The transfer power supply unit 52 individually outputs primary transfer biases for Y, C, M, and K to be applied to the primary transfer rollers 9Y, 9C, 9M, and 9K by constant current control. As described above, in the configuration in which the primary transfer bias is output by constant current control, as the photosensitive layer of the photosensitive member is scraped over time, the electrostatic capacitance C of the photosensitive member increases accordingly. As a result, the primary transfer voltage V decreases.
“Q = C × V = Sε / d × V”

  In this equation, Q is the charge amount of the photoreceptor, C is the capacitance, V is the primary transfer voltage, S is the area of the photoreceptor, ε is the dielectric constant of the photoreceptor, and d is the thickness of the photosensitive layer. . When the thickness d of the photosensitive layer decreases with time, the primary transfer voltage V decreases under the condition that the primary transfer bias is output by constant current control (the condition that the constant charge amount Q is output). . That is, as the photosensitive layer thickness d decreases, the primary transfer electric field strength decreases. As a result, as shown in FIG. 5, the graph showing the relationship between the primary transfer rate and the primary transfer current is shifted to the high current side, and the desired primary transfer rate cannot be obtained with the set current value. For this reason, it becomes impossible to provide a stable image over time.

  In this printer, as described above, the process control process is performed when the power is turned on or whenever a predetermined number of images are formed. At this time, the development bias value and the charging bias value are gradually increased in order to form ten patch images having different toner adhesion amounts for each color. The gradation pattern image is transferred onto the intermediate transfer belt 7 while outputting a primary transfer bias having a constant current value by constant current control. However, since the image area ratio of the gradation pattern image is relatively low, The output voltage value (primary transfer voltage) of the transfer bias greatly depends on the charging potential Vd. For this reason, as shown in FIGS. 6 and 7, the patch images formed under different charging potential Vd conditions are primarily transferred under different primary transfer voltage conditions. The transfer power supply unit 52 has voltage detectors for Y, C, M, and K that individually detect the output voltage value of each primary transfer bias. Thereby, the primary transfer voltages in Y, C, M, and K can be individually detected.

  The control unit 30 performs a transfer condition determination process in the process control process. In this transfer condition determination process, the output target value of the primary transfer current from the transfer power supply unit 52 is determined as the transfer condition for each color. Specifically, a thickness data table indicating the relationship between the combination of the primary transfer voltage and the charging bias and the thickness d of the photosensitive layer is stored in the nonvolatile memory 30c. Then, for each of the Y, C, M, and K patch images, the transfer power supply unit 52 detects the value of the primary transfer voltage when entering the primary transfer nip. Then, the thickness d corresponding to the combination of the detection result and the charging bias value at the time of patch image formation is specified from the thickness data table. Thereafter, it is determined whether or not the specified thickness d is smaller than a predetermined threshold value. If not, the same value as before is determined as the output target value of the primary transfer current. On the other hand, when the thickness is smaller than the threshold value, as shown in FIG. 8, a larger value than before is determined as the output target value. Thus, by increasing the value of the primary transfer voltage, it is possible to ensure a desired primary transfer rate and output a stable image even under conditions where the thickness d is smaller than the threshold value.

  As a patch image used for predicting the thickness d, an image formed from a plurality of patch images, for example, under a charging bias condition of 600 [V] is used. The timing at which the patch image enters the primary transfer nip is determined by a time measurement process, and the detection result of the primary transfer voltage when the timing arrives is acquired from the transfer power supply unit 52. Then, the thickness d corresponding to the obtained result is specified from the thickness data table, and when the specified result is smaller than the threshold value, a value larger than usual is determined as the output target value of the primary transfer current. For example, when the initial thickness d is 40 [μm], it is assumed that the transfer voltage is 1.5 [kV] when a charging bias of 600 [V] is applied in an intermediate temperature and humidity environment (MM). Assume that the threshold is set to 35 [μm]. When the primary transfer voltage when the patch image enters the primary transfer nip is 1.2 [kV], the photosensitive layer thickness d is predicted to be 34 [μm] as shown in FIGS. Is done. Since the prediction result of the thickness d is smaller than the threshold value, the output target value of the primary transfer current is raised by 2 [μA] than before. However, in order to increase the prediction accuracy of the thickness d, the output target value is obtained only when the detection result of more than half of the ten patch images (ten-step charging bias values) is smaller than the threshold value. You may make it raise.

  The example in which the threshold value of the thickness d is set to 35 [μm] or less and the output target value is increased by 2 [μA] when the threshold value is smaller than that is described. However, the present invention is not limited to this. It is good also as a structure which raises each output target value. In the printer according to the embodiment, the process line speed 120 [mm / sec] is set. However, in the configuration in which the process line speed is changed according to a user command, the output target value is set according to the process line speed. The correction amount may be changed.

  Next, a printer according to an example in which a more characteristic configuration is added to the copier according to the embodiment will be described. Unless otherwise specified below, the configuration of the printer according to the example is the same as that of the embodiment.

  In the printer according to the embodiment, the detection result of the primary transfer voltage when the patch image enters the primary transfer nip is used to predict the thickness d. The detection result depends on the electrical resistance of the intermediate transfer belt 7. Change. The electrical resistance of the intermediate transfer belt 7 changes with time according to environmental fluctuations and the degree of deterioration. Therefore, when the thickness d is predicted based solely on the detection result of the primary transfer voltage, depending on the electrical resistance of the intermediate transfer belt 7, a large error may occur between the predicted value of the thickness d and the actual thickness. is there.

  Therefore, the printer according to the embodiment includes a belt resistance detection unit that measures the electrical resistance of the intermediate transfer belt 7. As shown in FIG. 12, the belt resistance detection unit includes a first metal roller 71, a second metal roller 72, a current detection unit 73, a power source 74, and the like. The first metal roller 71 disposed outside the loop of the intermediate transfer belt 7 and the second metal roller 72 disposed inside the loop sandwich the intermediate transfer belt 7 therebetween. The first metal roller 71 is grounded, while a predetermined bias is applied to the second metal roller 72 by the power source 74.

  When a predetermined bias is applied to the second metal roller 72 by the power source 74, a current corresponding to the electric resistance of the intermediate transfer belt 7 flows to the current detection unit 73. That is, the current detection result by the current detection unit 73 has a value corresponding to the electric resistance of the intermediate transfer belt 7. The control unit 30 stores an algorithm indicating the relationship between the detection result and the electrical resistance in the nonvolatile memory 30c. And the electrical resistance value corresponding to a detection result is specified from the above-mentioned algorithm.

  FIG. 12 is a graph showing the relationship between the primary transfer voltage when the patch image enters the primary transfer nip and the charging potential Vd of the photoreceptor. This graph changes according to the electric resistance of the intermediate transfer belt 7. Specifically, the higher the electrical resistance of the intermediate transfer belt 7, the lower the height position of the graph and the lower the primary transfer voltage. Therefore, the control unit 30 corrects the detection result of the primary transfer voltage according to the detection result of the electrical resistance. As a result, the primary transfer voltage used for the prediction of the thickness d is corrected to a value closer to the thickness d, thereby avoiding deterioration of the prediction accuracy of the thickness d due to fluctuations in the electrical resistance of the intermediate transfer belt 7.

  This printer has a contact / separation mechanism (not shown) that makes the first metal roller 71 and the second metal roller 72 contact and separate from the intermediate transfer belt 7 respectively. The control unit 30 controls the driving of the contact / separation mechanism so that the first metal roller 71 and the second metal roller 72 are brought into contact with the intermediate transfer belt 7 only when the electric resistance of the intermediate transfer belt 7 is measured. Let When the electrical resistance is not measured, the two metal rollers are separated from the intermediate transfer belt 7 respectively. Thereby, the sliding time between the intermediate transfer belt 7 and the metal roller is reduced, and the burden on the intermediate transfer belt 7 is reduced as compared with the case where the intermediate transfer belt 7 is always in contact with each other, thereby suppressing the life of the intermediate transfer belt 7 from deteriorating. Can do.

  Next, a printer according to a modified example in which a part of the configuration of the printer according to the embodiment is changed to another configuration will be described. Unless otherwise specified, the configuration of the printer according to the modification is the same as that of the embodiment.

  In the printer according to the modification, instead of determining the output target value of the primary transfer current as the transfer condition in the transfer condition determination process, the linear velocity difference between the photoconductor and the intermediate transfer belt 7 is determined. Specifically, the linear velocity of the photosensitive member is increased as the photosensitive layer thickness d decreases. As the linear velocity of the photosensitive member is increased, a larger shearing force is applied to the toner image in the primary transfer nip, so that the primary transfer rate can be improved.

  When the predicted result of the thickness d is equal to or greater than a predetermined threshold, the control unit 30 determines a standard value as the linear velocity (and hence the linear velocity difference) of the photoconductor. Then, the drive motor of the photosensitive member is controlled so that the standard value is obtained. On the other hand, when the predicted result of the thickness d is smaller than the threshold value, the linear velocity of the photosensitive member is determined to be a value that is higher by 0.5 [%] than the standard value. As a result, the shear force of the toner image in the primary transfer nip is increased to improve the primary transfer rate as shown in FIG. 13, thereby suppressing the occurrence of transfer failure due to the decrease in the thickness d.

  In this printer, if the rate of increase of the linear velocity of the photosensitive member is made larger than 0.5% with respect to the standard value, image deterioration due to banding due to vibration is likely to occur. Therefore, the linear velocity is increased within a range not exceeding 0.5 [%].

  However, in order to improve the prediction accuracy of the thickness d, the prediction result of the thickness d is smaller than the threshold value for more than half of the ten patch images (ten-stage charging bias value). Only the linear velocity of the photosensitive member may be increased by 0.5 [%] from the standard value. Further, as shown in FIG. 14, a plurality of threshold values may be set, and the linear velocity increase rate may be varied in accordance with each threshold value.

  Note that a method of increasing the toner amount of the photoconductor for the purpose of suppressing the image density shortage accompanying the decrease in the thickness d is also conceivable, but in this case, when the toner image is primarily transferred from the photoconductor to the intermediate transfer belt 7. This increases the possibility of generating dust by scattering toner. From the viewpoint of suppressing the image density shortage without generating image dust, a method of making the linear velocity difference between the photosensitive member and the intermediate transfer belt different as in this printer is effective. In addition, if a linear speed difference is provided from the beginning and a method of constantly increasing the primary transfer efficiency is employed, a load on the photosensitive member and the belt due to the linear speed difference is always applied. Therefore, it is desirable to provide the linear velocity difference only when the thickness d is below the threshold value.

  As a method of providing the linear velocity difference, a method is adopted in which the linear velocity of the photosensitive member is increased as the thickness d decreases. However, the linear velocity of the intermediate transfer belt 7 is increased as the thickness d decreases. May be. However, in the latter case, it is desirable to advance the writing start timing of the latent image by the optical writing unit 6 as the linear velocity increases in order to suppress the expansion of the output image on the recording sheet.

  The image forming apparatus to which the present invention can be applied is not limited to a multifunction peripheral, and the present invention can also be applied to a copying machine, a printer, a facsimile, a plotter, and the like using a general electrophotographic process.

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]
A latent image carrier (eg, photoconductors 2Y, 2C, 2M, 2K) that carries a latent image, a charging means (eg, charging roller 3Y) that charges the surface of the latent image carrier, and the latent image carrier after charging. Image forming means (for example, image forming apparatus) having latent image writing means (for example, optical writing unit 6) for writing a latent image on the surface and developing means (for example, developing device 4Y) for developing the latent image to obtain a toner image 1Y, 1C, 1M, 1K) and transfer means (for example, primary transfer rollers 9Y, 9C, 9M, 9K) for transferring the toner image on the surface of the latent image carrier to a transfer body (for example, intermediate transfer belt 7). An adhesion amount detection means (for example, the optical sensor unit 20) for detecting a toner adhesion amount with respect to the toner image formed by the image formation means, and a test toner image formed on the image formation means under a predetermined image formation condition. Toner adhesion to In an image forming apparatus comprising: a control unit (for example, the control unit 30) that performs an image forming condition determination process for determining an image forming condition of the image forming unit based on a result of detecting the adhesion amount detecting unit. In the image forming condition determination process, a transfer current value when an area charged under a predetermined charging condition out of the entire area in the surface movement direction of the latent image carrier is made to enter a position facing the transfer unit, or The control unit is configured to perform a transfer condition determination process for determining a transfer condition of the transfer unit based on a transfer voltage value.

In such a configuration, it is possible to suppress the occurrence of an image density shift due to improper image forming conditions by executing the image forming condition determination process and optimizing the image forming conditions.
Also, transfer condition determination processing is performed to determine conditions according to the amount of wear of the latent image carrier as transfer conditions based on electrical characteristics recognized around the transfer means, such as changes in transfer voltage and transfer current. By doing so, it is possible to suppress the occurrence of transfer failure due to wear of the latent image carrier.
Furthermore, the occurrence of downtime of the apparatus can be suppressed for the reason described below. That is, in the general image forming condition determination process, the latent image carrier is used regardless of the setting of the charged potential of the latent image carrier in a normal print job in order to accurately grasp the image forming performance of the image forming means. Is provided with a timing for charging the at a predetermined charging potential. For example, when forming a gradation pattern image composed of 10 test toner images, the latent image for each test toner image is written on a latent image carrier charged at a predetermined charging potential. An image forming apparatus is known. In this configuration, the latent image writing area of the test toner image on the latent image carrier is charged at a predetermined charging potential during the image forming condition determination process, regardless of the setting of the latent image carrier charging potential in a normal print job. I am letting. Although the latent image writing areas of the individual test toner images on the latent image carrier are charged with different charging potentials, the latent image writing area of the first test toner image is always charged with the predetermined first charging potential. An image forming apparatus is also known. In this configuration, the latent image writing area of the first test toner image on the latent image carrier is set to a predetermined value during the image formation condition determination process regardless of the setting of the charging potential of the latent image carrier in a normal print job. Charging is performed at the first charging potential. As described above, in the image forming condition determination process, it is common to provide a timing for charging the latent image carrier at a predetermined charging potential regardless of the setting of the charging potential of the latent image carrier in a normal print job. is there. In the aspect A, in the image forming condition determination process, when the area charged under the predetermined charging condition is entered into the position facing the transfer unit in the entire area in the surface movement direction of the latent image carrier. To determine the transfer current value or transfer voltage. Thereby, without increasing the downtime of the apparatus, the transfer current value or the transfer voltage value when the region charged with the predetermined charging potential in the latent image carrier is made to enter the position facing the transfer means is grasped. As a result, the occurrence of downtime of the apparatus can also be suppressed.

[Aspect B]
Aspect B is a transfer bias member (for example, primary transfer rollers 9Y, 9C, 9M, and 9K) that is disposed at a position facing the latent image carrier and to which a transfer bias is applied. The transfer power supply (for example, the transfer power supply unit 52) that outputs the transfer bias is used, and the transfer power output by the constant current control is used as the transfer power supply (for example, the transfer power supply unit 52). The control is performed so that the output voltage value from the transfer power supply when the transfer bias of the current value of the output is output is grasped as the transfer voltage value, and the transfer condition is determined based on the grasped result. It is characterized by comprising means. In such a configuration, the wear amount of the latent image carrier can be predicted based on the output voltage value of the transfer power supply.

[Aspect C]
Aspect C, in aspect A or B, in the transfer condition determination process, estimates the thickness of the surface layer of the latent image carrier based on the transfer current value or the transfer voltage value, and based on the estimation result, The control means is configured to perform processing for determining transfer conditions. In this configuration, the transfer condition can be corrected to an appropriate one based on the estimation result of the thickness of the surface layer (for example, the photosensitive layer).

[Aspect D]
In the aspect D, in the aspect B, in the transfer condition determination process, the control unit is configured to execute a process of determining an output target value of a current used for constant current control of the transfer bias as the transfer condition. It is characterized by comprising. In such a configuration, it is possible to suppress deterioration of transfer efficiency due to wear of the latent image carrier by correcting the output current target value.

[Aspect E]
In the aspect E, in any of the aspects A to C, in the transfer condition determination process, as the transfer condition, a process of determining a linear velocity difference between the latent image carrier and the transfer body is performed. The control means is configured. In such a configuration, it is possible to suppress deterioration in transfer efficiency due to wear of the latent image carrier by correcting the linear velocity difference.

[Aspect F]
In aspect F, in any one of aspects A to E, as the transfer unit, a transfer bias is applied in a state where the intermediate transfer belt is sandwiched between the endless intermediate transfer belt and the latent image carrier and itself. Belt resistance detecting means (for example, the first metal roller 71, the second metal roller 71, the second metal roller 71, the second transfer roller 9Y, 9C, 9M, and 9K). A metal roller 72, a current detection unit 73, etc.), and in the transfer condition determination process, in addition to the transfer current value or transfer voltage value, based on the detection result by the belt resistance detection means, the transfer The control means is configured to perform a process for determining a condition. With such a configuration, it is possible to suppress improper determination conditions regarding the transfer conditions due to the temporal variation of the electrical resistance of the intermediate transfer belt 7.

[Aspect G]
An aspect G is the aspect F according to the aspect F, wherein the belt resistance detecting means includes a first roller (for example, a first metal roller 71) that contacts the front surface of the intermediate transfer belt and a back surface of the intermediate transfer belt. Two rollers (second metal roller 72), voltage applying means for applying a voltage to the first roller or the second roller, and a current for detecting a current value flowing between the first roller and the second roller It has a detecting means (for example, a current detecting unit 73), and uses the one that calculates the electric resistance of the intermediate transfer belt based on the current value. With this configuration, the electric resistance of the intermediate transfer belt 7 can be calculated based on the current detection result by the current detection means.

[Aspect H]
Aspect H is the aspect G according to aspect G, wherein the belt resistance detection means is provided with contact / separation means for contacting and separating the first roller and the second roller with respect to the intermediate transfer belt, respectively. The control means is configured to perform a process of separating the first roller and the second roller from the intermediate transfer belt by the contact / separation means when the detection is not performed. With such a configuration, it is possible to suppress deterioration of the intermediate transfer belt due to sliding with the first roller and the second roller.

1Y, 1C, 1M, 1K: Image forming device (image forming means)
2Y, 2C, 2M, 2K: photoconductor (latent image carrier)
3Y: charging roller (charging means)
4Y: developing device (developing means)
6: Optical writing unit (latent image writing means)
9Y, C, M, K (primary transfer means, transfer bias member)
20: Optical sensor unit adhesion amount detection means)
30: Control unit (control means)
52: Transfer power supply unit (transfer power supply)
71: First metal roller (first roller)
72: Second metal roller (second roller)
73: Current detection unit (current detection means)

JP 2014-6471 A JP 2003-76101 A

Claims (8)

A latent image carrier for carrying a latent image, a charging means for charging the surface of the latent image carrier, a latent image writing means for writing a latent image on the surface of the latent image carrier after charging, and developing the latent image An image forming means having a developing means for obtaining a toner image, a transfer means for transferring the toner image on the surface of the latent image carrier to a transfer body, and toner adhesion to the toner image formed by the image forming means Based on the result of detecting the amount of toner adhesion to the test toner image formed on the image forming means under a predetermined image forming condition, the image forming means detects the amount of toner attached to the test toner image. An image forming apparatus comprising: a control unit that performs an image forming condition determination process for determining an image forming condition of the unit;
In the image forming condition determination process, a transfer current value when an area charged under a predetermined charging condition out of the entire area in the surface movement direction of the latent image carrier is made to enter a position facing the transfer unit, or An image forming apparatus, wherein the control unit is configured to perform a transfer condition determination process for determining a transfer condition of the transfer unit based on a transfer voltage value. The image forming apparatus according to claim 1.
As the transfer means, a transfer bias member disposed at a position facing the latent image carrier and applied with a transfer bias is used.
As a transfer power supply for outputting the transfer bias, a power supply that outputs the transfer bias with constant current control,
In the transfer condition determination process, an output voltage value from the transfer power supply when a transfer bias having a predetermined current value is output from the transfer power supply is grasped as the transfer voltage value, and the transfer voltage value is determined based on the grasped result. An image forming apparatus characterized in that the control means is configured to perform a process for determining a condition. The image forming apparatus according to claim 1 or 2,
In the transfer condition determination process, the thickness of the surface layer of the latent image carrier is estimated based on the transfer current value or the transfer voltage value, and the transfer condition is determined based on the estimation result. An image forming apparatus comprising the control means. The image forming apparatus according to claim 2.
In the transfer condition determination process, the control unit is configured to perform a process of determining an output target value of a current used for constant current control of the transfer bias as the transfer condition. Forming equipment. The image forming apparatus according to any one of claims 1 to 3,
In the transfer condition determination process, the control unit is configured to perform a process of determining a linear velocity difference between the latent image carrier and the transfer body as the transfer condition. apparatus. The image forming apparatus according to claim 1,
As the transfer means, an endless intermediate transfer belt, and a transfer bias member to which a transfer bias is applied in a state where the intermediate transfer belt is sandwiched between the latent image carrier and itself are used,
A belt resistance detecting means for detecting an electric resistance of the intermediate transfer belt is provided;
And, in the transfer condition determination process, in addition to the transfer current value or the transfer voltage value, a process for determining the transfer condition based on a detection result by the belt resistance detection unit is performed. An image forming apparatus comprising a control means. The image forming apparatus according to claim 6.
As the belt resistance detection means, a voltage is applied to the first roller that contacts the front surface of the intermediate transfer belt, the second roller that contacts the back surface of the intermediate transfer belt, and the first roller or the second roller. Voltage applying means for applying, and current detecting means for detecting a current value flowing between the first roller and the second roller, and calculating an electric resistance of the intermediate transfer belt based on the current value. An image forming apparatus using the apparatus. The image forming apparatus according to claim 7.
Contacting / separating means for contacting and separating the first roller and the second roller with respect to the intermediate transfer belt is provided in the belt resistance detecting means,
When the belt resistance detection unit does not detect the electrical resistance, the control unit is configured to perform a process of separating the first roller and the second roller from the intermediate transfer belt by the contact / separation unit. An image forming apparatus.

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