Image forming apparatus and control method for image forming apparatus

Abstract

To provide an image forming apparatus that can define a control range of a developing bias without using a sensor that detects the concentration of toner, and thereby can prevent the occurrence of an abnormal image.SOLUTION: An image forming apparatus comprises: an image carrier 21 on which an electrostatic latent image is formed; developing means that has a developer carrier 33 facing the image carrier and carrying developer including toner, and develops the electrostatic latent image formed on the image carrier to form a toner image; voltage application means 16 that applies a developing bias to the developer carrier; current detection means 16 that detects a current output from the voltage application means when the image carrier is developed; a transfer body to which the toner image formed on the image carrier is transferred; toner adhesion amount detection means 19 that detects the amount of adhesion of toner in the toner image transferred to the transfer body; and a control unit 18 that calculates the amount of electrification of toner based on a result of detection performed by the current detection means and a result of detection performed by the toner adhesion amount detection means. The control unit calculates a predicted value of the distance between the image carrier and the developer carrier based on the amount of electrification of toner.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus and a control method for an image forming apparatus. [Background technology]

[0002] Conventionally, in image forming apparatuses using electrophotography, a technique has been known in which the development current during the development process is detected and the image forming conditions are controlled (process control) based on the detection results in order to stabilize the image quality of the output image.

[0003] Patent Document 1 discloses that when a toner image is formed, the current output from a voltage application means is detected, the amount of toner attached to the image carrier is detected, and the image forming conditions on the image carrier are adjusted based on the detection results. According to Patent Document 1, the image density of the output image is stabilized, and problems such as background smearing can be prevented.

[0004] For example, in an image forming device using a two-component developer, a development bias is applied to a development roller (developer carrier), and the electrostatic latent image on the image carrier is developed with toner that has been stirred and charged in the development device. Attempts are being made to prevent carrier adhesion and deviation from the target image density by controlling the development bias applied to the development roller according to the toner density. Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional technology, the control range of the development bias must be determined using toner concentration, which requires a sensor to detect toner concentration. In Patent Document 1, the amount of charge on the toner is calculated from the current that flows when the toner is developed and the amount of toner attached to the image carrier, and this is reflected in the image creation conditions. However, a sensor to detect toner concentration is required to determine the control range of the development bias. If an attempt is made to reduce the cost and size of the device by eliminating the sensor to detect toner concentration, the control range of the development bias cannot be varied, which increases the risk of abnormal images being generated.

[0006] Therefore, the present invention aims to provide an image forming apparatus that can specify the control range of the development bias applied to the developer carrier without using a sensor to detect toner concentration by predicting the distance between the developer carrier and the image carrier, thereby suppressing the occurrence of abnormal images. [Means for solving the problem]

[0007] In order to solve the above problem, the image forming apparatus of the present invention comprises an image carrier on which an electrostatic latent image is formed, a developer carrier facing the image carrier and carrying a developer containing toner, a developing means for developing the electrostatic latent image formed on the image carrier to form a toner image, a voltage application means for applying a development bias to the developer carrier, a current detection means for detecting the current output from the voltage application means when developing the image carrier, a transfer body onto which the toner image formed on the image carrier is transferred, a toner adhesion amount detection means for detecting the toner adhesion amount of the toner image transferred to the transfer body, and a control unit for calculating the toner charge amount based on the detection result of the current detection means and the detection result of the toner adhesion amount detection means, and is characterized in that the control unit calculates a predicted value of the distance between the image carrier and the developer carrier based on the toner charge amount. [Effects of the Invention]

[0008] According to the present invention, by predicting the distance between the developer carrier and the image carrier, it is possible to specify the control range of the development bias applied to the developer carrier without using a sensor to detect the toner concentration, thereby providing an image forming apparatus that can suppress the occurrence of abnormal images. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating an example of an image forming apparatus according to the present invention. [Figure 2] 1 is a schematic view showing a main part of an example of an image forming apparatus according to the present invention; [Figure 3] FIG. 2 is a schematic diagram of a main part of an example of an image forming unit. [Figure 4] FIG. 4 is a schematic diagram of a main part of FIG. 3. [Figure 5] FIG. 10 is a diagram showing an example of the relationship between development capability γ and toner charge amount, in the case of linear approximation. [Figure 6] 10 is an example of measurement results showing the relationship between development capability γ and toner charge amount. [Figure 7] 1 is an example of a control flow. [Figure 8] FIG. 10 is a diagram illustrating an example of the relationship between toner concentration and toner charge amount. DETAILED DESCRIPTION OF THE INVENTION

[0010] An image forming apparatus and a method for controlling an image forming apparatus according to the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following embodiments, and other modifications, additions, corrections, deletions, and other changes can be made within the scope of what a person skilled in the art can conceive. Any embodiment that achieves the functions and effects of the present invention is included in the scope of the present invention.

[0011] The image forming apparatus of the present invention comprises an image carrier on which an electrostatic latent image is formed, a developer carrier facing the image carrier and carrying a developer containing toner, a developing means for developing the electrostatic latent image formed on the image carrier to form a toner image, a voltage application means for applying a development bias to the developer carrier, a current detection means for detecting the current output from the voltage application means when developing the image carrier, a transfer body onto which the toner image formed on the image carrier is transferred, a toner adhesion amount detection means for detecting the toner adhesion amount of the toner image transferred to the transfer body, and a control unit for calculating the toner charge amount based on the detection results of the current detection means and the detection results of the toner adhesion amount detection means, and is characterized in that the control unit calculates a predicted value of the distance between the image carrier and the developer carrier based on the toner charge amount.

[0012] The control method for an image forming apparatus of the present invention includes a developing step of developing an electrostatic latent image formed on an image carrier using a developer carrier that faces the image carrier and carries a developer containing toner; a voltage application step of applying a developing bias to the developer carrier using a voltage application means; a current detection step of detecting a current output from the voltage application means when developing the image carrier; a transfer step of transferring a toner image formed on the image carrier to a transfer body; a toner adhesion amount detection step of detecting a toner adhesion amount of the toner image transferred to the transfer body; and a calculation control step of calculating a toner charge amount based on the detection results of the current detection step and the detection results of the toner adhesion amount detection step, wherein the calculation control step calculates a predicted value of the distance between the image carrier and the developer carrier based on the toner charge amount, and controls the voltage application means to control the upper and lower limits of the developing bias based on the calculated predicted value of the distance between the image carrier and the developer carrier.

[0013] According to the present invention, by predicting the distance between the developer carrier and the image carrier, it is possible to specify the control range of the development bias applied to the developer carrier without using a sensor to detect the toner concentration, thereby suppressing the occurrence of abnormal images.

[0014] First, the overall configuration and operation of the image forming apparatus will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes the main body of a color copier as an image forming apparatus, 2 denotes a writing unit that emits a laser beam based on image information, and 20Y, 20M, 20C, and 20BK denote process cartridges as image forming units corresponding to each color (yellow, magenta, cyan, and black). 21 denotes a photosensitive drum as an image carrier housed in each of the process cartridges 20Y, 20M, 20C, and 20BK. 22 denotes a charging unit that charges the photosensitive drum 21. 23 denotes a developing unit that develops the electrostatic latent image formed on the photosensitive drum 21. 24 denotes a transfer bias roller as a transfer unit that transfers the toner image formed on the photosensitive drum 21 to an intermediate transfer belt 27. 25 denotes a cleaning unit that collects untransferred toner from the photosensitive drum 21.

[0015] Further, 27 denotes an intermediate transfer belt (intermediate transfer body) as a second image carrier onto which the toner images of each color are transferred in an overlapping manner. 29 denotes a second transfer bias roller as a transfer section that transfers the toner image formed on the intermediate transfer belt 27 onto the transfer material P. 30 denotes a transfer belt that transports the transfer material P onto which the toner images of four colors are transferred in an overlapping manner. 32Y, 32M, 32C, and 32BK denote toner supply sections that supply toner of each color to the developing section 23 of each process cartridge 20Y, 20M, 20C, and 20BK. 61 denotes a paper feed section that stores the transfer material P such as transfer paper. 66 denotes a fixing section that fixes unfixed images on the transfer material P. 120 denotes a scanner that optically reads a placed original.

[0016] Here, each of the process cartridges 20Y, 20M, 20C, and 20BK integrates a photosensitive drum 21, a charging unit 22, a developing unit 23, and a cleaning unit 25. Images of each color (yellow, magenta, cyan, and black) are formed on the photosensitive drum 21 of each of the process cartridges 20Y, 20M, 20C, and 20BK. The process cartridges are an example of an image forming unit.

[0017] The following describes the operation of the image forming apparatus during normal color image formation. Each of the four photosensitive drums 21 rotates counterclockwise in FIG. 1. First, the surface of each photosensitive drum 21 is uniformly charged at a position facing the charging unit 22 (charging process). Then, the charged surface of each photosensitive drum 21 reaches the irradiation position of the respective laser beam.

[0018] On the other hand, when a color original is placed on the original placement section of scanner 120, the image information of the original is optically read by a reading section (not shown). That is, an illumination light source is scanned over the original, and an original image is formed on a color CCD (not shown). The original image is then photoelectrically converted by the color CCD to generate R, G, and B image signals. These image signals are sent to writing section 2. After that, in writing section 2, laser light corresponding to the image signals is emitted from the light source, one for each color. The laser light is incident on and reflected by polygon mirror 3, and then passes through lenses 4 and 5. After passing through lenses 4 and 5, the laser light passes through separate optical paths for each color component: yellow, magenta, cyan, and black (this is the exposure process).

[0019] The yellow laser light is reflected by mirrors 6 to 8 and then irradiated onto the surface of the photosensitive drum 21 of the first process cartridge 20Y from the right side of the drawing. At this time, the yellow laser light is scanned in the direction of the rotation axis of the photosensitive drum 21 (main scanning direction) by the polygon mirror 3 rotating at high speed. In this way, an electrostatic latent image of the yellow component is formed on the photosensitive drum 21 after it has been charged by the charging unit 22.

[0020] Similarly, the magenta laser light is reflected by mirrors 9-11 and then irradiated onto the surface of the photosensitive drum 21 of the process cartridge 20M, which is the second from the right on the paper, forming an electrostatic latent image of the magenta component. The cyan laser light is reflected by mirrors 12-14 and then irradiated onto the surface of the photosensitive drum 12 of the process cartridge 20C, which is the third from the right on the paper, forming an electrostatic latent image of the cyan component. The black laser light is reflected by mirror 15 and then irradiated onto the surface of the photosensitive drum 21 of the process cartridge 20BK, which is the fourth from the right on the paper, forming an electrostatic latent image of the black component.

[0021] Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent images of each color have been formed continues to rotate and reaches a position facing the developing unit 23. Then, the developing unit 23 supplies toner of each color onto the photosensitive drum 21, and the latent images on the photosensitive drum 21 are developed (this is the developing process).

[0022] Thereafter, the surfaces of the photosensitive drums 21 after the development step reach positions facing the intermediate transfer belt 27. Here, transfer bias rollers 24 are installed at each facing position so as to abut against the inner circumferential surface of the intermediate transfer belt 27. Then, at the positions of the transfer bias rollers 24, the images of each color formed on the photosensitive drums 21 are sequentially transferred onto the intermediate transfer belt 27 (first transfer step).

[0023] After the first transfer step, the surface of each photosensitive drum 21 reaches a position facing the cleaning unit 25. The cleaning unit 25 then collects untransferred toner remaining on the photosensitive drum 21 (this is the cleaning step). Thereafter, the surface of the photosensitive drum 21 passes through a charge removal unit (not shown), and a series of image forming processes on the photosensitive drum 21 is completed.

[0024] Meanwhile, the surface of the intermediate transfer belt 27 onto which the images (toner images) of each color on the photosensitive drum 21 are transferred and superimposed runs in the direction of the arrow in the figure and reaches the position of the second transfer bias roller 29. Then, at the position of the second transfer bias roller 29, the full-color image on the intermediate transfer belt 27 is secondarily transferred onto the transfer material P (secondary transfer process).

[0025] Thereafter, the surface of the intermediate transfer belt 27 reaches the position of an intermediate transfer belt cleaning unit (not shown), and the untransferred toner on the intermediate transfer belt 27 is collected by the intermediate transfer belt cleaning unit, completing the series of transfer processes on the intermediate transfer belt 27.

[0026] Here, the transfer material P at the position of the second transfer bias roller 29 has been transported from a paper feed section 61 via a transport guide 63, registration rollers 64, and the like. More specifically, transfer paper P is fed by paper feed roller 62 from paper feed unit 61, which stores transfer material P, and passes through conveyance guide 63, and is then guided to registration roller 64. Upon reaching registration roller 64, transfer material P is conveyed toward the position of second transfer bias roller 29 in synchronization with the toner image on intermediate transfer belt 27.

[0027] Thereafter, the transfer material P onto which the full-color image has been transferred is guided by the transfer belt 30 to the fixing unit 66. In the fixing unit 66, the color image is fixed onto the transfer material P at the nip between a heating roller 67 and a pressure roller 68. After the fixing process, the transfer material P is discharged as an output image to the outside of the apparatus main body 1 by a paper discharge roller 69, and a series of image forming processes is completed.

[0028] 2 is a schematic diagram illustrating the inside of an example of an image forming apparatus according to the present embodiment, which illustrates, for example, a photosensitive drum 21 (image carrier), a developing roller 33 (developer carrier), a process cartridge 20 (image forming unit), an intermediate transfer belt 27 (intermediate transfer member), a transfer roller 24, and a transport roller 28.

[0029] The process cartridge 20 has a photosensitive drum 21 and a developing roller 33, and is provided for each of black, cyan, magenta, and yellow. When describing the process cartridges 20K, 20C, 20M, and 20Y without distinguishing between black K, cyan C, magenta M, and yellow Y, they will be referred to as the process cartridge 20. The same applies to the photosensitive drums 21K, 21C, 21M, and 21Y and the developing rollers 33K, 33C, 33M, and 33Y.

[0030] In the image forming apparatus of this example, the electrostatic latent image on the photosensitive drum 21 is developed by the developing roller 33 to form a toner image on the photosensitive drum 21, and the toner image is then transferred to the intermediate transfer belt 27. The toner image transferred to the intermediate transfer belt 27 is then transferred to a recording medium and fixed, thereby forming an image. The intermediate transfer belt 27 is an example of an intermediate transfer body, and the intermediate transfer body is an example of a transfer body. The toner image on the photosensitive drum 21 may be transferred to a recording medium, but it is preferable to transfer it to the intermediate transfer body first and then to the recording medium.

[0031] The toner supplied to the surface of the developing roller 33 is developed in accordance with the pattern of the electrostatic latent image on the photosensitive drum 21. In this embodiment, in order to adjust the conditions of the developing bias, it is preferable to form an image of a detection pattern, detect the detection pattern, and adjust the control conditions.

[0032] The detection pattern can be changed as needed, for example, a patch of 60 mm in the main scanning direction and 10 mm in the sub-scanning direction can be used. Since the size of the detection pattern in the main scanning direction is proportional to the development current, the detection accuracy of the development current can be improved by increasing the size of the detection pattern. Note that the main scanning direction is the transport direction of the intermediate transfer belt 27, and the sub-scanning direction is the direction perpendicular to the main scanning direction.

[0033] When the electrostatic latent image on the photosensitive drum 21 is developed, toner moves from the developing roller 33 toward the photosensitive drum 21. The movement of the toner is shown schematically by the white arrow in the figure. At this time, a current corresponding to the total charge of the moved toner flows from the developing roller 33 toward the high-voltage board 17. This current is shown schematically by the black arrow in the figure. This current is also called the developing current. The developing current can also be said to be the current output from the voltage application means (developing power supply 16) when developing the image carrier.

[0034] In this example, the development power supply 16 corresponds to a voltage application means that applies a development bias to the developer carrier. The development power supply 16 is also provided with a current detection means (current detection circuit) that includes a resistor connected in the power supply circuit. In this example, the current detection means corresponds to the current detection circuit. The development bias may be a DC voltage or an AC voltage.

[0035] Using the detected development current, the toner charge amount Q [-μC] can be calculated using the following formula (1).

[0036]

number

[0037] In (Equation 1), the following is represented. Ave: Average calculation I_dev: Development current [A] T: Integral time [s]

[0038] T represents the integral time [s], which means the time required for development. Specifically, it is the time from when the developing roller 33 starts to rotate until it stops rotating. Furthermore, Ave(I_dev) means the average value of the development current, and since the development current I_dev is an AC value, the average value is calculated. The toner charge amount Q is obtained by multiplying Ave(I_dev) by T, and may therefore be referred to as the total toner charge amount.

[0039] The detection pattern developed on the photosensitive drum 21 is transferred onto the intermediate transfer belt 27. The transferred detection pattern 40 is transported toward a secondary transfer roller (not shown) by the intermediate transfer belt 27. At this time, when the detection pattern 40 passes by the optical sensor 19, the amount of toner attached to the detection pattern 40 is detected.

[0040] The optical sensor 19 is a toner adhesion amount detection means that detects the amount of toner adhesion on the toner image transferred to the transfer body, and is sometimes referred to as a P sensor. The optical sensor 19 irradiates light onto the detection pattern 40 on the intermediate transfer belt 27 and detects the reflected light. The irradiated light and reflected light are schematically indicated by arrows in the figure. The optical sensor 19 can determine the amount of toner adhesion by converting the amount of reflected light into the amount of toner adhesion.

[0041] The toner adhesion amount calculated in this embodiment is the amount of toner adhesion per unit area, and is expressed in g / mm 2 The toner adhesion amount is defined as M / A [g / mm 2 ]. Note that "A" stands for area.

[0042] The toner charge Q [-μC] calculated by the above formula (1) and the toner adhesion amount M / A [g / mm 2 ], the charge amount Q / M [-μC / g] of the toner can be calculated by the following formula (2).

[0043] In determining the following formula (2), the amount of adhered toner is detected, and then the toner mass M is calculated by multiplying the amount by the area of ​​the detection pattern. Toner mass M [g] = toner adhesion amount [g / mm 2 ] × detection pattern area [mm 2 ]

[0044] The toner charge amount is calculated using the toner mass M thus calculated. Toner charge amount Q / M [-μC / g] = Toner charge amount Q [-μC] / Toner mass M [g] This equation can also be said to correspond to the following equation (2).

[0045]

number

[0046] In (Equation 2), the following is represented. Ave: Average calculation I_dev: Development current [A] M / A: Toner adhesion amount per unit area [g / mm 2 ] Spd: Linear speed of intermediate transfer belt [mm / s] Width: Width of the detection pattern in the main scanning direction [mm] T1: Primary transfer rate [%] Tr: Reverse transcription rate [%] Q / M: Toner charge amount [-μC / g] T: Integral time [s]

[0047] T1 represents the primary transfer rate [%], which can be calculated by dividing the amount of toner adhered to the intermediate transfer belt by the amount of toner adhered to the photosensitive member. Tr represents the reverse transfer rate [%], and can be calculated by dividing the amount of toner transferred onto the photosensitive member of the downstream station (image forming unit) by the amount of toner on the intermediate transfer belt. The reason for using Ave(M / A), that is, the reason for calculating the average amount of toner adhesion per unit area, is that the amount of toner may fluctuate within the detection pattern, and the influence of such fluctuations must be reduced. Furthermore, the unit of the development current [A] is converted to [A] = [C / s], which is the charge amount per unit time. By applying this to equation (2), the unit of Q / M becomes [-μC / g].

[0048] In FIG. 1 and the above description, an example is described in which the toner charge amount is calculated for the cyan image forming unit, but in reality, it is possible to calculate the toner charge amount for each of the other image forming units.

[0049] FIG. 3 is a schematic diagram of the essential parts of the image forming apparatus of this embodiment, and is a schematic diagram of a process cartridge 20. The process cartridge 20 in the figure is shown to include a photosensitive drum 21, a developing roller 33, a developing section 23 (developing means), and a photosensitive unit 26. The photosensitive unit 26 is provided with the photosensitive drum 21, as well as other components such as a charging means and a cleaning means. The developing section 23 is provided with the developing roller 33, as well as other components such as a supply roller that supplies toner to the developing roller 33. In the figure, the process cartridge 20 is shown for one of black, cyan, magenta, and yellow, and the description thereof applies to the other process cartridges (image forming units) as well.

[0050] 4 is a schematic diagram of the main parts of FIG. 3, illustrating the distance between the photosensitive drum 21 and the developing roller 33. Hereinafter, the distance between the photosensitive drum 21 (image carrier) and the developing roller 33 (developer carrier) may be referred to as the PG (Photoconductor Gap), or may also be referred to as a gap. In the drawing, the PG is indicated by the reference numeral 34. The PG is the distance between the surface of the photosensitive drum 21 and the surface of the developing roller 33.

[0051] PG is known as a characteristic value related to development ability. Generally, as PG increases, development ability tends to decrease. Hereinafter, development ability will be expressed as γ, and development ability γ will be referred to as development γ. The unit of development ability γ is mg / cm 2 / -kV.

[0052] The predicted value of PG can be calculated based on the toner charge amount Q and the development capability γ. The development ability γ (development γ) is calculated, for example, as follows. In advance, in the image forming apparatus, a toner image is formed by gradually changing the development potential [-kV], and the toner adhesion amount [mg / cm ] of the toner image is measured. 2 ], and the development potential [-kV] and the toner adhesion amount [mg / cm 2], and linear approximation is performed on this relationship. The slope of the straight line obtained by linear approximation is used as the developing ability γ [mg / cm 2 / -kV].

[0053] The control unit forms a detection pattern to calculate the toner charge amount Q, and can calculate the predicted value of PG using this toner charge amount Q and the development γ that has been determined in advance. In this way, when the predicted value of PG is calculated using development γ, the development capability of the device is taken into consideration, so the predicted value of PG can be calculated with greater accuracy.

[0054] The toner image formed when determining the development γ is not particularly limited and can be appropriately selected, for example, an image like the detection pattern described above. The toner adhesion amount of this toner image can be measured using, for example, the optical sensor 19 described above. The development potential [-kV] is determined from the relationship between the development bias and the potential of the exposed portion of the photosensitive member.

[0055] FIG. 5 is a linear approximation diagram illustrating an example of the relationship between development γ and toner charge Q / M. Generally, development γ is used as a characteristic value that indicates the ease of development with toner. Development γ correlates with toner charge Q / M, and as shown in FIG. 5, it is known that the relationship changes depending on PG, which is the tolerance of the developing device. As shown in FIG. 5, the larger the PG, the smaller the development γ, even for the same toner charge Q / M. Also, the smaller the PG, the larger the development γ, even for the same toner charge Q / M. In other words, the larger the PG, the smaller the development γ, and the smaller the PG, the larger the development γ. Note that the PG center refers to the PG between when the PG is large and when the PG is small.

[0056] Figure 5 is a linear approximation of the relationship between development γ and toner charge amount Q / M, and in reality it is not a straight line but a curve as shown in Figure 6 below. The relationship between development γ and toner charge amount Q / M varies depending on PG, and because PG has a tolerance, the relationship will differ depending on the image forming unit.

[0057] Figure 6 shows an example of the results of measuring development γ and toner charge amount Q / M. Figure 6 also shows the results of acquiring the relationship between development γ and toner charge amount Q / M when PG is actually changed within the tolerance. The detection pattern of Example 1 above was created, and the results were plotted for each PG.

[0058] As shown in Figure 6, similar to Figure 5, the larger PG is, the smaller development γ is for the same toner charge amount Q / M, and the smaller PG is, the larger development γ is for the same toner charge amount Q / M. As shown in the figure, the relationship between development γ and toner charge amount Q / M is a curve, and this curve fits the measurement results well. The relationship between development γ and toner charge amount Q / M is a straight line in Figure 5, but a curve in Figure 6. This difference is due to the use of a simple linear approximation for control.

[0059] 5 and 6, the toner charge amount Q / M and the development γ at that time can be used to calculate an estimated value (predicted value) of PG of the image forming apparatus without using a sensor to detect the toner concentration. In this embodiment, when calculating the predicted value of PG, a linear approximation as shown in FIG. 5 can be used, or actual measurement results as shown in FIG. 6 can be used. Using FIG. 5 has the advantage that calculation can be performed simply in terms of control, and using FIG. 6 has the advantage that calculation can be performed with higher accuracy.

[0060] To elaborate on PG, even if the rough value of PG is known when assembling an image forming device, the PG value is, for example, on the order of tens to hundreds of micrometers (sometimes exceeding 1000 micrometers), making it difficult to determine the exact value. Furthermore, because PG has tolerances, it may differ from the design value, making it difficult to determine the exact value. Furthermore, if PG changes with repeated image formation, the expected development cannot be achieved, increasing the risk of abnormal images. Therefore, by detecting the development current and toner adhesion amount, calculating the toner charge, and estimating PG from the toner charge, the current PG value, or a value close to the current PG, can be predicted.

[0061] According to this embodiment, the upper and lower limits of the developing bias can be controlled by controlling the voltage application means based on the calculated predicted value of PG. Furthermore, the background potential can be controlled based on the calculated predicted value of PG. How the developing bias and background potential are controlled while taking into consideration factors will be described in the flow chart below. To briefly explain, for example, when PG is large, the developing ability is difficult to achieve, so increasing the upper and lower limit ranges of the developing bias can prevent the image density from becoming too low. When PG is small, the developing ability is easy to achieve, so lowering the upper and lower limit ranges of the developing bias can reduce the incidence of carrier adhesion and prevent the image density from becoming too high.

[0062] FIG. 7 is a diagram illustrating an example of the overall control flow. The following flow is performed by, for example, the control unit 18. The control unit 18 includes, for example, a CPU (Central Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory).

[0063] Furthermore, it is preferable to perform this control when the device is first turned on. By performing this control when the device is first turned on, it is possible to prevent the effects of developer deterioration and to accurately calculate the toner charge amount. Repeated image formation can cause the relationship between Q / M and γ to fluctuate due to, for example, developer deterioration or a decrease in the amount of developer being pumped, which can affect the calculation of the predicted value of PG.

[0064] In S11, a detection pattern is formed to detect the toner charge amount Q / M. As described above, an electrostatic latent image is formed on the photosensitive drum 21, and is developed by the developing means to form a toner image.

[0065] In S12, the development current during development is calculated from the amount of current detected by the current detection circuit. The total charge amount of the toner image is calculated from the development current. The formed toner image is transferred onto the intermediate transfer belt 27 as a detection pattern 40, and the amount of toner attached to the detection pattern 40 is detected by the optical sensor 19.

[0066] In S13, the toner charge amount Q / M is calculated from the total charge amount of the toner and the amount of toner adhesion. The toner charge amount Q / M can be calculated as described above.

[0067] In S14, the calculated toner charge amount Q / M and development capability γ are applied to the relationship between toner charge amount Q / M and development γ shown in, for example, Figures 5 and 6. In this way, a predicted value of PG can be calculated. The predicted value of PG is calculated for each image forming unit. Note that development γ is calculated in advance, for example, before performing S11.

[0068] In S15, it is determined which category the calculated predicted value of PG falls into. PG is divided into several categories, for example, three categories, based on the upper and lower limits of the tolerance, and it is determined which category the calculated predicted value of PG falls into. In this way, by dividing PG into categories and controlling the development bias and background potential according to each category, the risk of abnormal images occurring can be further reduced.

[0069] The number of divisions is not particularly limited, and may be three as described above, or any other number. Upper and lower limits of the developing bias and the background potential value corresponding to each division are set in advance. Although it is difficult to define the PG divisions in general, they can be divided into three divisions, for example, less than (300) μm, at least (300) μm and less than (400) μm, and at least (400) μm.

[0070] In S16, the upper and lower limits of the developing bias are controlled based on the calculated predicted value of PG. The expression "controlling the upper and lower limits of the developing bias" may be expressed as "expanding (releasing) the upper limit of the control range of the developing bias" or "expanding (releasing) the lower limit of the control range of the developing bias." It may also be expressed as "determining the upper and lower limits of the developing bias." It may also be expressed as "controlling the upper and lower limits of the output of the developing bias."

[0071] In this embodiment, it is determined which category the calculated predicted value of PG falls into (S15), and the upper and lower limits of the developing bias are controlled according to the category (S16). For example, if the calculated predicted value of PG is 0.33 mm or more, it is determined that it falls into category A (this is a description for explanatory purposes), and the upper limit of the control range of the developing bias is changed from an initial value of -600 V to -800 V after release.

[0072] As in S16, by controlling the upper and lower limits of the developing bias, it is possible to prevent the occurrence of abnormal images such as carrier adhesion. For example, if the developing bias is too high, carrier adhesion is more likely to occur, so the control range of the developing bias is prevented from becoming unnecessarily high. Also, if the developing bias is too low, the image density will fall below the lower limit of the standard, resulting in an image with low image density.

[0073] To control the upper and lower limits of the developing bias, for example, a voltage application means is controlled. The ranges of the upper and lower limits of the developing bias vary depending on the predicted PG and the device configuration, and are therefore difficult to define in general terms, but for example, when the PG is 300 μm to 400 μm, the upper limit of the developing bias is preferably set in the range of 600 V to 800 V, and the lower limit of the developing bias is preferably set in the range of 250 V to 450 V. Another way of defining the ranges of the developing bias is, for example, to change the upper limit from the initial value preferably to -100 V to +100 V, and to change the lower limit from the initial value preferably to -100 V to +100 V.

[0074] Furthermore, in this embodiment, it is possible to control the upper and lower limits of the developing bias for each process cartridge 20. In this way, by controlling the upper and lower limits of the developing bias for each process cartridge 20, it is possible to control the upper limit of the developing bias to be high only for a process cartridge 20 with low development capability, for example. This reduces the risk of abnormal images being produced in each process cartridge 20, and reduces the risk of abnormal images being produced overall.

[0075] In S17, the background potential is controlled based on the calculated predicted value of PG. The background potential is a bias for preventing toner adhesion to non-image areas, known as background scumming. Increasing the background potential can prevent background scumming, but if it is too high, carrier adhesion occurs, resulting in an abnormal image. PG and background scumming are correlated, and if the PG is wide (large), background scumming worsens. Therefore, if the PG is wide, increasing the background potential can suppress background scumming, and if the PG is narrow, decreasing the background potential can suppress carrier adhesion.

[0076] In this way, by controlling the background potential based on the calculated predicted value of PG, it is possible to suppress background smear and carrier adhesion, and to suppress the occurrence of abnormal images. Specifically, the background potential can be controlled, for example, by controlling a voltage application unit that applies a charging voltage to the photosensitive member. Note that the background potential in this embodiment is the potential difference between the charging potential of the photosensitive member and the developing bias.

[0077] How to control the surface potential varies depending on the predicted PG and the device configuration, so it is difficult to define in general terms, but for example, if the predicted PG is 300 μm to 400 μm, it is preferable to set the surface potential in the range of 50 V to 250 V.

[0078] As with the developing bias, it is preferable to determine which category the calculated predicted value of PG falls into (S15) and control the background potential according to the category (S17). Note that the term "control" may also be expressed as "determining the value of the background potential."

[0079] Like the developing bias, the background potential can be controlled for each process cartridge 20. By controlling the background potential for each process cartridge 20 in this way, even if the PG differs for each process cartridge 20, it is possible to suppress the occurrence of abnormal images for each process cartridge 20, and it is possible to suppress the occurrence of abnormal images overall.

[0080] In this embodiment, either S16 or S17 may be performed, but it is preferable to perform both S16 and S17. By performing both, the occurrence of abnormal images can be further suppressed. Also, either S16 or S17 may be performed first.

[0081] Thus, the control flow ends.

[0082] Next, the toner concentration will be described. In this embodiment, the toner concentration may be calculated based on the calculated toner charge amount. FIG. 8 shows an example of the relationship between toner concentration and toner charge amount. In two-component developers, there is a correlation between toner concentration and toner charge amount. Therefore, by using the toner charge amount Q / M detected as described above, it is possible to determine the toner concentration even in devices that do not have a sensor to detect toner concentration.

[0083] In this embodiment, the toner concentration is calculated and then used to perform control such as limiting the amount of toner replenishment, thereby making it possible to suppress toner scattering and background scumming.

[0084] As described above, the present invention provides a method for controlling an image forming apparatus. In the method for controlling an image forming apparatus of the present invention, by predicting the distance between the developer carrier and the image carrier, it is possible to define the control range of the development bias applied to the developer carrier without using a sensor for detecting toner concentration, and it is possible to suppress the occurrence of abnormal images. The following provides additional information.

[0085] The control method for the image forming apparatus includes, for example, a developing process, a voltage application process, a current detection process, a transfer process, a toner adhesion amount detection process, and a calculation control process.

[0086] In the developing step, the electrostatic latent image formed on the image carrier is developed by a developer carrier that faces the image carrier and carries a developer containing toner. In the voltage application step, a development bias is applied to the developer carrier by a voltage application means, which may be, for example, a development power source 16. In the current detection step, the current (development current) output from the voltage application means when developing the image carrier is detected. The development current can be detected by a current detection circuit provided in the development power supply 16, for example. In the transfer step, the toner image formed on the image carrier is transferred to a transfer body, preferably an intermediate transfer belt 27, for example. In the toner adhesion amount detection step, the amount of toner adhesion of the toner image transferred onto the transfer body is detected. The amount of toner adhesion can be detected by, for example, an optical sensor 19. The calculation control step calculates the toner charge amount based on the detection result of the current detection step and the detection result of the toner adhesion amount detection step. The calculation control step is performed by, for example, the control unit 18.

[0087] The calculation and control step calculates a predicted value of the distance between the image carrier and the developer carrier based on the toner charge amount, and controls the voltage application means to control the upper and lower limits of the developing bias based on the calculated predicted value of the distance between the image carrier and the developer carrier. In this way, it is possible to define the control range of the developing bias applied to the developer carrier without using a sensor that detects toner concentration.

[0088] The developing step, voltage application step, and transfer step correspond to, for example, S11 in Fig. 7. Any image may be used in the developing step, voltage application step, and transfer step, but it is preferable to form a detection pattern 40. The current detection step and toner adhesion amount detection step correspond to, for example, S12 in Fig. 7. The calculation control step corresponds to, for example, S13 to S16 in Fig. 7. It is preferable that the calculation control step controls the background potential (S17). [Explanation of symbols]

[0089] 6. Gap 16 Development power supply / current detection circuit 17 High-voltage board 18 Control Unit 19 Optical Sensor 20 Process cartridge 21 Photosensitive drum 23 Development section 26 Photoconductor unit 27 Intermediate transfer belt 33 Developing roller 40 Detection Pattern [Prior art documents] [Patent documents]

[0090] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-189790

Claims

1. an image carrier on which an electrostatic latent image is formed; a developer carrier facing the image carrier and carrying a developer containing toner; a developing means for developing the electrostatic latent image formed on the image carrier to form a toner image; a voltage applying means for applying a developing bias to the developer carrier; a current detection means for detecting a current output from the voltage application means when developing the image carrier; a transfer body onto which the toner image formed on the image carrier is transferred; a toner adhesion amount detecting means for detecting the amount of toner adhesion of the toner image transferred onto the transfer body; a control unit that calculates a toner charge amount based on the detection result of the current detection means and the detection result of the toner adhesion amount detection means, The image forming apparatus is characterized in that the control unit calculates a predicted value of the distance between the image carrier and the developer carrier based on the toner charge amount.

2. 2. The image forming apparatus according to claim 1, wherein the control unit calculates a predicted value of the distance between the image carrier and the developer carrier based on the toner charge amount and a development capability γ calculated as follows: [Development ability γ] In advance, in the image forming apparatus, a toner image is formed by gradually changing the development potential, the amount of toner adhesion of the toner image is detected, the relationship between the development potential and the amount of toner adhesion of the toner image is determined, a linear approximation is performed on this relationship, and the slope of the straight line determined by the linear approximation is defined as the development capability γ.

3. 3. The image forming apparatus according to claim 1, wherein the control unit calculates the toner charge amount based on the detection result of the current detection means and the detection result of the toner adhesion amount detection means when the detection pattern is formed, and calculates a predicted value of the distance between the image carrier and the developer carrier based on the toner charge amount.

4. The image forming apparatus according to any one of claims 1 to 3, characterized in that the control unit calculates a predicted value of the distance between the image carrier and the developer carrier when the image forming apparatus is turned on for the first time.

5. The image forming apparatus according to any one of claims 1 to 4, characterized in that the control unit controls the voltage application means to control the upper and lower limits of the development bias based on a predicted value of the calculated distance between the image carrier and the developer carrier.

6. 6. The image forming apparatus according to claim 1, wherein the control unit controls the background potential based on a predicted value of the calculated distance between the image carrier and the developer carrier.

7. 7. The image forming apparatus according to claim 6, wherein the control unit determines whether the calculated predicted value of the distance between the image carrier and the developer carrier is in a predetermined category, and determines upper and lower limit values ​​of the developing bias or the value of the background potential according to the predetermined category.

8. a plurality of image forming units each having the image carrier and the developing means; 7. The image forming apparatus, wherein the control section performs at least one of the control described in claim 5 and the control described in claim 6 for each of the image forming units.

9. 9. The image forming apparatus according to claim 1, wherein the control unit calculates the toner density based on the calculated toner charge amount.

10. 10. The image forming apparatus according to claim 1, wherein the transfer body is an intermediate transfer body.

11. a developing step of developing the electrostatic latent image formed on the image carrier by a developer carrier that faces the image carrier and carries a developer containing toner; a voltage application step of applying a development bias to the developer carrier by a voltage application means; a current detection step of detecting a current output from the voltage application means when developing the image carrier; a transfer step of transferring the toner image formed on the image carrier to a transfer member; a toner adhesion amount detecting step of detecting the amount of toner adhesion of the toner image transferred to the transfer body; a calculation control step of calculating a toner charge amount based on the detection result of the current detection step and the detection result of the toner adhesion amount detection step, a control method for an image forming apparatus, characterized in that the calculation and control step calculates a predicted value of the distance between the image carrier and the developer carrier based on the toner charge amount, and controls the voltage application means to control the upper and lower limits of the development bias based on the calculated predicted value of the distance between the image carrier and the developer carrier.

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