JP2021028669A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that outputs a plurality of test charts for density adjustment, the image forming apparatus capable of preventing a situation where an area on a first test chart for density adjustment where a transfer property is reduced due to excess and deficiency of a transfer current repeatedly occurs on a second and subsequent test charts for density adjustment.SOLUTION: In an image forming apparatus that can control a voltage applied to a transfer member to a constant voltage, and can perform limiter control of controlling the voltage applied to the transfer member based on a result of detection performed by a current detection unit so that the result of detection performed by the current detection unit falls within a predetermined range, in a series of adjustment modes for outputting a first test chart for density adjustment and a second test chart subsequent to the first test chart to perform density adjustment, a control unit determines a predetermined voltage while the second test chart passes through a transfer unit based on the amount of change of voltage in the limiter control in the first test chart.SELECTED DRAWING: Figure 7

Description

The present invention relates to an image forming apparatus such as a copier, a printer, and a faxing apparatus using an electrophotographic system or an electrostatic recording system.

Conventionally, in an image forming apparatus using an electrophotographic method or the like, a toner image is electrostatically transferred from an image carrier such as a photoconductor or an intermediate transfer body to a recording material such as paper.

This transfer is often performed by applying a transfer voltage to a transfer member such as a transfer roller that comes into contact with the image carrier to form a transfer portion. If the transfer voltage is too low, "image density thinning (transfer omission)" may occur in which the desired image density cannot be obtained due to insufficient transfer. In addition, if the transfer voltage is too high, a discharge will occur in the transfer section, and the polarity of the toner charge in the toner image will be reversed due to the effect of the discharge, resulting in "white spots" in which the toner image is not partially transferred. It may occur. Therefore, in order to form a high-quality image, it is required to apply an appropriate transfer voltage to the transfer member.

The amount of charge required for transfer varies depending on the size of the recording material and the area ratio of the toner image. Therefore, the transfer voltage is often applied by constant voltage control in which a constant voltage corresponding to a predetermined current density is applied. When the transfer voltage is applied by constant voltage control, the transfer according to the predetermined voltage is performed on the part where the target toner image is present, regardless of the current flowing on the outside of the recording material or the part where there is no toner image on the recording material. This is because it is easy to secure the current. However, the electrical resistance of the transfer members that make up the transfer section changes according to product variations, member temperature, cumulative usage time, etc., and the electrical resistance of the recording material that passes through the transfer section also depends on the type of recording material and the surrounding environment. It changes according to (temperature / humidity). Therefore, when controlling the transfer voltage at a constant voltage, it is necessary to adjust the transfer voltage in response to fluctuations in the electrical resistance of the transfer member or recording material.

Patent Document 1 discloses the following transfer voltage control method in a configuration in which the transfer voltage is controlled at a constant voltage. Immediately before the start of continuous image formation, a predetermined voltage is applied to the transfer unit in a state where there is no recording material, a current value is detected, and a voltage value at which a predetermined target current can be obtained is obtained. Then, the recording material sharing voltage according to the type of recording material is added to this voltage value, and the transfer voltage value applied by constant voltage control at the time of transfer is set. By such control, the transfer voltage corresponding to the desired target current can be applied by constant voltage control regardless of the fluctuation of the electric resistance value of the transfer portion such as the transfer member and the fluctuation of the electric resistance value of the recording material. ..

Here, the types of recording materials include, for example, types due to differences in the surface smoothness of recording materials such as high-quality paper and coated paper, and types due to differences in the thickness of recording materials such as thin paper and thick paper. .. The recording material shared voltage can be obtained in advance according to, for example, the type of such recording material. However, there are many types of recording materials in circulation. In addition, the electrical resistance of the recording material differs depending on the wet state of the recording material (moisture content of the recording material), but the moisture content of the recording material is the time it was placed in the environment even if the environment (temperature / humidity) is the same. Varies depending on. Therefore, it is often difficult to accurately obtain the voltage shared by the recording material in advance. If the transfer voltage is not an appropriate value including the fluctuation of the electrical resistance of the recording material, image defects such as low image density (missing transfer) and white spots may occur as described above.

In response to such problems, in Patent Documents 2 and 3, in a configuration in which the transfer voltage is controlled at a constant voltage, the current (transfer current) supplied to the transfer unit when the recording material passes through the transfer unit is used. It has been proposed to set upper and lower limits. The passage of the recording material through the transfer section is also referred to as "paper passing". By such control, the transfer current supplied to the transfer unit during paper transfer can be set to a current in a predetermined range, so that the occurrence of image defects due to insufficient or excessive transfer current can be suppressed. In Patent Document 2, the upper limit value is obtained based on environmental information. In Patent Document 3, the upper limit value and the lower limit value are obtained according to the front and back of the recording material, the type of the recording material, and the size of the recording material in addition to the environment.

In the configuration in which the transfer voltage is controlled at a constant voltage, when the recording material passes through the transfer unit, when the current flowing through the transfer member deviates from a predetermined range, the transfer is performed so that the current falls within the predetermined range. The control that changes the target voltage of the constant voltage control of the voltage is also called "limiter control". Further, here, the magnitudes (high and low) of the voltage and current are those when compared in absolute values.

Japanese Unexamined Patent Publication No. 2004-117920 Japanese Patent No. 4161005 Japanese Unexamined Patent Publication No. 2008-275946

As described above, there is a limiter control that detects the transfer current during paper passing and controls the transfer voltage so that the transfer current is within a predetermined range (below the upper limit value, above the lower limit value). In the limiter control, after it is detected that the transfer current is out of the predetermined range, the transfer voltage is changed so that the transfer current is within the predetermined range. Therefore, in the region of the recording material that passes through the transfer section between the detection of the transfer current and the completion of the change of the transfer voltage, the transfer current is out of the appropriate range, and the concentration due to the excess or deficiency of the transfer current. Image defects such as deterioration may occur.

For example, in a region where the transfer current is below the lower limit in a low humidity environment, image density thinning (transfer omission) occurs due to insufficient transfer current.

By the way, with the use of the apparatus, the image density on the paper may deviate from the target density. Therefore, an adjustment mode may be executed in which a test chart for density adjustment is output and the image density on paper is automatically adjusted according to a user's instruction from the operation unit. In this adjustment mode, for example, a test chart in which a test image for adjusting the maximum density (so-called Dmax control) is transferred on paper may be output. In addition, a test chart to which a test image for adjusting gradation from the maximum density on paper to halftones and highlights is transferred may be output. As described above, the adjustment mode outputs a test chart in which a plurality of test images for density adjustment are formed based on a user's instruction, and a plurality of test charts may be output.

In an image forming apparatus that performs such automatic image adjustment, there are the following problems when the limiter control described above is performed. That is, when limiter control is performed, if there is a region where the transfer current is below the lower limit value as described above, the transferability is not stable in that section. Therefore, if a toner image for density adjustment is formed in a region where the transfer current is below the lower limit value, the accuracy of the image adjustment is lowered. For this reason, when the limiter control is executed on the first sheet when outputting a plurality of test charts, a region where the transferability is reduced that may occur at the tip of the first sheet is repeatedly generated on the second and subsequent sheets as well. There is a possibility of doing it.

The present invention relates to an image forming apparatus capable of executing an adjustment mode for outputting a plurality of test charts and adjusting the density on paper. Then, an object of the present invention is to make a test chart for the second and subsequent sheets even if a region where the transferability is lowered due to excess or deficiency of the transfer current occurs at the time of outputting the first test chart in the adjustment mode. It is to prevent the same trouble from occurring repeatedly.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention applies to an image carrier that carries a toner image, a transfer member to which a voltage is applied to transfer the toner image carried on the image carrier to a recording material at a transfer unit, and the transfer member. A power supply that applies a voltage, a current detector that detects the current flowing through the transfer member, and a voltage applied to the transfer member when the recording material passes through the transfer member are set to a predetermined voltage. A control unit that controls voltage, and a control unit that controls the voltage applied to the transfer member based on the detection result of the current detection unit so that the detection result of the current detection unit falls within a predetermined range, and image formation. In an image forming apparatus including an operation unit for operating the device, the control unit has a first test chart for adjusting an image density and the first test chart based on an instruction input to the operation unit. It is possible to execute a series of adjustment modes in which a second test chart output after the test chart of the above and a plurality of test charts including the test chart are output to adjust the image density, and the second test chart is The predetermined voltage applied to the transfer member when passing through the transfer unit is applied to the transfer member based on the detection result of the current detection unit when the first test chart passes through the transfer unit. It is characterized in that it is determined based on the amount of change of the voltage in control.

According to the present invention, even if a region where transferability is deteriorated due to excess or deficiency of transfer current occurs at the time of output of the first test chart in the adjustment mode, the same applies to the second and subsequent test charts. It is possible to suppress the repeated occurrence of defects.

It is a schematic sectional view of an image forming apparatus. It is a schematic diagram of the structure regarding secondary transcription. It is a schematic block diagram which shows the control mode of the main part of an image forming apparatus. It is a flowchart for demonstrating the outline of the secondary transfer voltage control. It is a schematic diagram which shows an example of the table data of the recording material shared voltage. It is a schematic diagram which shows an example of the table data of a predetermined current range. It is a flowchart for demonstrating the automatic image adjustment according to this invention. It is a chart figure for demonstrating the voltage change method of a limiter control. It is a schematic diagram of a chart diagram and an image for explaining a problem. It is a chart diagram and the schematic diagram of the image for demonstrating the effect of an Example. It is a schematic diagram of the test chart for the maximum concentration control. It is a schematic diagram which shows an example of the relationship between the exposure intensity and the image density. It is a schematic diagram of the test chart for automatic gradation control.

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

[Example 1]
1. 1. Overall configuration and operation of the image forming apparatus FIG. 1 is a schematic configuration diagram of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment has the functions of a tandem type multifunction device (copier, printer, facsimile apparatus) adopting an intermediate transfer method capable of forming a full-color image by using an electrophotographic method. ).

The image forming apparatus 100 has the first, second, third, and fourth image forming units SY, SM, which form images of each color of yellow, magenta, cyan, and black as a plurality of image forming units (stations), respectively. Has SC and SK. For elements having the same or corresponding functions or configurations in each image forming unit SY, SM, SC, SK, Y, M, C, K at the end of the code indicating that they are elements for any color are omitted. And there is a general explanation. In this embodiment, the image forming unit S includes a photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a primary transfer roller 5, and a drum cleaning device 6, which will be described later.

The photosensitive drum 1, which is a rotatable drum-shaped (cylindrical) photoconductor (electrophotographic photosensitive member) as the first image carrier that carries the toner image (toner image), is in the direction of arrow R1 (counterclockwise) in the drawing. It is rotationally driven (clockwise). The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative electrode property in this embodiment) by a charging roller 2, which is a roller-type charging member as a charging means. The surface of the charged photosensitive drum 1 is scanned and exposed by an exposure device (laser scanner device) 3 as an exposure means based on image information, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1. To.

The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by supplying toner as a developer by the developing apparatus 4 as a developing means, and a toner image is formed on the photosensitive drum 1. In this embodiment, the exposed portion (image portion) on the photosensitive drum 1 whose absolute potential value is lowered by being exposed after being uniformly charged is charged with the same polarity as the charging polarity of the photosensitive drum 1. Toner adheres (reversal development method). In this embodiment, the normal charging polarity of the toner, which is the charging polarity of the toner during development, is the negative electrode property. The electrostatic image formed by the exposure apparatus 3 is an aggregate of small dot images, and the density of the toner image formed on the photosensitive drum 1 can be changed by changing the density of the dot images. In this embodiment, the maximum density of each color toner image is about 1.5 to 1.7, and the amount of toner loaded at the maximum density is about 0.4 to 0.6 mg / cm ^2. It has become.

An intermediate transfer belt 7 which is an intermediate transfer body composed of an endless belt as a second image carrier that supports a toner image is arranged so that it can come into contact with the surfaces of the four photosensitive drums 1. ing. The intermediate transfer belt 7 is an example of an intermediate transfer body that conveys a toner image primaryly transferred from another image carrier for secondary transfer to a recording material. The intermediate transfer belt 7 is stretched on a drive roller 71 as a plurality of tension rollers, a tension roller 72, and a secondary transfer opposed roller 73. The drive roller 71 transmits a driving force to the intermediate transfer belt 7. The tension roller 72 controls the tension of the intermediate transfer belt 7 to be constant. The secondary transfer opposing roller 73 functions as an opposing member (opposing electrode) of the secondary transfer roller 8 described later. The intermediate transfer belt 7 is rotated (circumferentially moved) at a transport speed (peripheral speed) of about 300 to 500 mm / sec in the direction of arrow R2 (clockwise) in the figure by rotationally driving the drive roller 71. The tension roller 72 is subjected to a force that pushes the intermediate transfer belt 7 from the inner peripheral surface side to the outer peripheral surface side by the force of the spring as an urging means, and this force causes the intermediate transfer belt 7 to be conveyed in the transport direction. Is under tension of about 2 to 5 kg. On the inner peripheral surface side of the intermediate transfer belt 7, a primary transfer roller 5 which is a roller-type primary transfer member as a primary transfer means is arranged corresponding to each photosensitive drum 1. The primary transfer roller 5 is pressed toward the photosensitive drum 1 via the intermediate transfer belt 7 to form a primary transfer portion (primary transfer nip) N1 in which the photosensitive drum 1 and the intermediate transfer belt 7 come into contact with each other. .. The toner image formed on the photosensitive drum 1 is electrostatically transferred (primary transfer) on the rotating intermediate transfer belt 7 by the action of the primary transfer roller 5 in the primary transfer unit N1. .. During the primary transfer step, the primary transfer roller 5 receives a primary transfer voltage (primary transfer bias), which is a DC voltage opposite to the normal charging polarity of the toner, from the primary transfer power supply (not shown). Is applied. For example, when forming a full-color image, the toner images of each color of yellow, magenta, cyan, and black formed on each photosensitive drum 1 are sequentially transferred so as to be superimposed on the intermediate transfer belt 7.

On the outer peripheral surface side of the intermediate transfer belt 7, a secondary transfer roller 8 which is a roller-type secondary transfer member as a secondary transfer means is arranged at a position facing the secondary transfer facing roller 73. The secondary transfer roller 8 is pressed toward the secondary transfer opposed roller 73 via the intermediate transfer belt 7, and the secondary transfer portion (secondary transfer nip) in which the intermediate transfer belt 7 and the secondary transfer roller 8 come into contact with each other. ) Form N2. The toner image formed on the intermediate transfer belt 7 is a recording material that is sandwiched and conveyed between the intermediate transfer belt 7 and the secondary transfer roller 8 by the action of the secondary transfer roller 8 in the secondary transfer unit N2. (Sheet, transfer material) Electrostatically transferred (secondary transfer) to P. The recording material P is typically paper (paper), but is not limited to this, and synthetic paper made of resin such as water resistant paper, plastic sheets such as OHP sheets, and cloth are used. It may be done. During the secondary transfer step, the secondary transfer roller 8 receives a secondary transfer voltage (secondary transfer bias) from the secondary transfer power supply (high voltage power supply circuit) 20, which is a DC voltage having a polarity opposite to the normal charging polarity of the toner. ) Is applied. The recording material P is housed in a cassette (recording material or set) 11 or the like as a feeding unit (paper feeding unit, storage unit), and the feeding roller 12 is driven based on the feeding start signal to drive the cassette 11. It is fed (paper-fed) one by one from the above and sent to the registration roller 9. After being temporarily stopped by the resist roller 9, the recording material P is supplied to the secondary transfer unit N2 in time with the toner image on the intermediate transfer belt 7.

The recording material P to which the toner image is transferred is conveyed to the fixing device 10 as a fixing means by a conveying member or the like. The fixing device 10 fixes (melts, fixes) the toner image on the recording material P by heating and pressurizing the recording material P carrying the unfixed toner image. After that, the recording material P is discharged (output) to the outside of the apparatus main body of the image forming apparatus 100.

Further, the toner remaining on the surface of the photosensitive drum 1 after the primary transfer step (primary transfer residual toner) is removed from the surface of the photosensitive drum 1 by the drum cleaning device 6 as a photoconductor cleaning means and recovered. Further, deposits such as toner (secondary transfer residual toner) and paper dust remaining on the surface of the intermediate transfer belt 7 after the secondary transfer step are removed from the intermediate transfer belt 7 by the belt cleaning device 74 as an intermediate transfer body cleaning means. It is removed from the surface and recovered.

Here, in this embodiment, the intermediate transfer belt 7 is an endless belt having a three-layer structure of a resin layer, an elastic layer, and a surface layer from the inner peripheral surface side to the outer peripheral surface side. As the resin material constituting the resin layer, polyimide, polycarbonate or the like can be used. The thickness of the resin layer is preferably 70 to 100 μm. Further, as the elastic material constituting the elastic layer, urethane rubber, chloroprene rubber and the like can be used. The thickness of the elastic layer is preferably 200 to 300 μm. Further, as the surface layer material, a material that reduces the adhesive force of the toner to the surface of the intermediate transfer belt 7 and facilitates the transfer of the toner to the recording material P in the secondary transfer portion N2 is desirable. For example, one or more resin materials such as polyurethane, polyester, and epoxy resin can be used. Alternatively, one or more of elastic materials such as elastic materials (elastic rubber, elastomer) and butyl rubber can be used. In addition, these materials include one or more types of powders and particles such as fluororesin, or one or more types of these powders and particles, which reduce surface energy and enhance lubricity. Those having different particle sizes can be dispersed and used. The thickness of the surface layer is preferably 5 to 10 μm. The electrical resistance of the intermediate transfer belt 7 is adjusted by adding a conductive agent for adjusting the electrical resistance such as carbon black, and the volume resistivity is preferably 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm.

Further, in the present embodiment, the secondary transfer roller 8 is configured to have a core metal (base material) and an elastic layer formed of an ion conductive foam rubber (NBR rubber) around the core metal. Ru. In this embodiment, the outer diameter of the secondary transfer roller 8 is 24 mm, and the surface roughness Rz of the secondary transfer roller 8 is 6.0 to 12.0 (μm). Further, in this embodiment, the electric resistance value of the secondary transfer roller 8 is 1 × 10 ⁵ to 1 × 10 ⁷ Ω when measured by applying 2 kV at N / N (23 ° C., 50% RH), and the elastic layer. The hardness of Asker-C is about 30 to 40 °. Further, in this embodiment, the width in the longitudinal direction (rotational axis direction) of the secondary transfer roller 8 (the length in the direction substantially orthogonal to the transport direction of the recording material P) is about 310 to 340 mm. In this embodiment, the width of the secondary transfer roller 8 in the longitudinal direction is the maximum width of the width of the recording material P (the length in the direction substantially orthogonal to the transport direction) that the image forming apparatus 100 guarantees transport. Maximum width) longer. In this embodiment, since the recording material P is conveyed with reference to the center in the longitudinal direction of the secondary transfer roller 8, all the recording materials P guaranteed to be conveyed by the image forming apparatus 100 are in the longitudinal direction of the secondary transfer roller 8. Pass within the length range. As a result, it is possible to stably convey the recording material P of various sizes and to stably transfer the toner image to the recording material P of various sizes.

Further, an automatic document transfer device 91 and an image reading unit (image reading device) 90 as a reading means are arranged above the main body of the image forming device 100. The automatic document transfer device 91 automatically conveys the recording material P on which the image is formed to the image reading unit 90. The image reading unit 90 reads an image on the recording material P which is conveyed by the automatic document conveying device 91 or is arranged on the platen glass 92. The image reading unit 90 illuminates the recording material P transported by the automatic document transporting device 91 or arranged on the platen glass 92 with light from a light source (not shown). Then, the image formed on the recording material P by the image reading element (not shown) is configured to be read with a predetermined dot density. That is, the image reading unit 90 optically reads the image on the recording material P and converts it into an electric signal.

FIG. 2 is a schematic diagram of a configuration relating to secondary transcription. The secondary transfer roller 8 abuts on the secondary transfer opposed roller 73 via the intermediate transfer belt 7 to form the secondary transfer portion N2. A secondary transfer power supply 20 having a variable output voltage value is connected to the secondary transfer roller 8. The secondary transfer facing roller 73 is electrically grounded (connected to the ground). When the recording material P passes through the secondary transfer unit N2, a secondary transfer voltage, which is a DC voltage opposite to the normal charging polarity of the toner, is applied to the secondary transfer roller 8. By supplying the secondary transfer current to N2, the toner image on the intermediate transfer belt 7 is transferred onto the recording material P. In this embodiment, for example, a secondary transfer current of +20 to +80 μA is passed through the secondary transfer unit N2 during the secondary transfer. In addition, the roller corresponding to the secondary transfer facing roller 73 of this embodiment is used as a transfer member, and a secondary transfer voltage having the same polarity as the normal charging polarity of the toner is applied to the roller, and the secondary transfer roller of this embodiment is applied. A roller corresponding to 8 may be used as a counter electrode and electrically grounded.

In this embodiment, based on the information on the electrical resistance of the secondary transfer unit N2 (mainly the secondary transfer roller 8 in this example) acquired in the state where the secondary transfer unit N2 does not have the toner image and the recording material P, The secondary transfer voltage applied to the secondary transfer roller 8 is set by constant voltage control during the secondary transfer. That is, constant voltage control is performed so that the voltage applied to the secondary transfer roller 8 becomes a predetermined voltage. Further, in this embodiment, the secondary transfer current flowing through the secondary transfer unit N2 during paper passing is detected. Then, the secondary transfer power supply 20 is set so that the secondary transfer current is equal to or lower than a predetermined upper limit value and equal to or higher than a predetermined lower limit value (here, simply referred to as "predetermined current range (predetermined range)"). The secondary transfer voltage output by voltage control is controlled (limiter control). This predetermined current range can be set based on various information. The various types of information may include, for example, the following information. First, the conditions (recording) specified by the operation unit 31 (FIG. 3) provided in the main body of the image forming apparatus 100 and the external device 200 (FIG. 3) such as a personal computer communicatively connected to the image forming apparatus 100. Information about the type of material P, etc.). It is also information on the detection result of the environment sensor 32 (FIG. 3). Further, it is information on the electric resistance of the secondary transfer unit N2 (mainly the secondary transfer roller 8 in this embodiment) acquired without the toner image and the recording material P in the secondary transfer unit N2. For example, this predetermined current range can be changed based on information on the thickness and width of the recording material P used for image formation. Information regarding the thickness of the recording material P and the width of the recording material P can be acquired based on the information input from the operation unit 31 or the external device 200. Alternatively, it is also possible to provide a detecting means for detecting the thickness and width of the recording material P in the image forming apparatus 100 and perform control based on the information acquired by the detecting means.

In this embodiment, in order to perform such control, the secondary transfer power supply 20 has a current (secondary transfer current) flowing through the secondary transfer unit N2 (that is, the secondary transfer roller 8 or the secondary transfer power supply 20). ) Is connected to the current detection circuit 21 as a current detection means (current detection unit). Further, the secondary transfer power supply 20 is connected to a voltage detection circuit 22 as a voltage detecting means (voltage detection unit) for detecting the voltage (secondary transfer voltage) output by the secondary transfer power supply 20. The control unit 50 may function as a voltage detection unit and detect the voltage output by the secondary transfer power supply 20 from the indicated value of the voltage output from the secondary transfer power supply 20. In this embodiment, the secondary transfer power supply 20, the current detection circuit 21, and the voltage detection circuit 22 are provided in the same high-voltage substrate.

2. 2. Control mode FIG. 3 is a schematic block diagram showing a control mode of a main part of the image forming apparatus 100 of this embodiment. The control unit (control circuit) 50 as a control means includes a CPU 51 as an arithmetic control means which is a central element for performing arithmetic processing, a RAM 52 as a storage means, a memory (storage medium) such as a ROM 53, and the like. To. The RAM 52, which is a rewritable memory, stores information input to the control unit 50, detected information, calculation results, and the like, and the ROM 53 stores a control program, a data table obtained in advance, and the like. Data can be transferred and read from each other between the CPU 51 and the memories such as the RAM 52 and the ROM 53.

An image reading unit 90 provided in the image forming device 100 and an external device 200 such as a personal computer are connected to the control unit 50. Further, an operation unit (operation panel) 31 provided in the image forming apparatus 100 is connected to the control unit 50. The operation unit 31 is a display unit that displays various information to operators such as users and service personnel under the control of the control unit 50, and an input unit for the operator to input various settings related to image formation to the control unit 50. And are configured with. The operation unit 31 may be composed of a touch panel or the like having a function of a display unit and a function of an input unit. Job information including control commands related to image formation such as the type of recording material P is input to the control unit 50 from the operation unit 31 or the external device 200. The type of recording material P can be distinguished from the recording material P such as attributes, manufacturer, brand, product number, basis weight, thickness, etc. based on general characteristics such as plain paper, thick paper, thin paper, glossy paper, and coated paper. It contains arbitrary information. The control unit 50 can acquire information on the type of the recording material P by directly inputting the information, and for example, by selecting a cassette 11 for storing the recording material P, the cassette can be obtained in advance. It can also be obtained from the information set in association with 11. Further, the secondary transfer power supply 20, the current detection circuit 21, and the voltage detection circuit 22 are connected to the control unit 50. In this embodiment, the secondary transfer power supply 20 applies a secondary transfer voltage, which is a constant voltage controlled DC voltage, to the secondary transfer roller 8. The constant voltage control is a control so that the value of the voltage applied to the transfer unit (that is, the transfer member) becomes a substantially constant voltage value. An environment sensor 32 is connected to the control unit 50. In this embodiment, the environment sensor 32 detects the temperature and humidity of the atmosphere inside the housing of the image forming apparatus 100. The temperature and humidity information detected by the environment sensor 32 is input to the control unit 50. The control unit 50 can obtain the water content (moisture content, absolute water content) of the atmosphere in the housing of the image forming apparatus 100 based on the temperature and humidity detected by the environment sensor 32. The environment sensor 32 is an example of an environment detecting means for detecting at least one of the temperature and humidity of at least one of the inside and the outside of the image forming apparatus 100. The control unit 50 comprehensively controls each part of the image forming apparatus 100 based on the image information from the image reading unit 90 and the external device 200 and the control commands from the operating unit 31 and the external device 200 to perform the image forming operation. Let it run.

Here, the image forming apparatus 100 executes a job (printing operation) which is a series of operations of forming and outputting an image on a single or a plurality of recording materials P, which is started by one start instruction (printing instruction). To do. The job generally includes an image forming step, a pre-rotation step, a paper-to-paper step when forming an image on a plurality of recording materials P, and a back-rotating step. The image forming step is a period during which an electrostatic image of an image actually formed and output on the recording material P is formed, a toner image is formed, a primary transfer of the toner image is performed, and a secondary transfer is performed, and the image is formed (image). The formation period) means this period. More specifically, the timing at the time of image formation differs depending on the position where each of the steps of forming the electrostatic image, forming the toner image, and performing the primary transfer and the secondary transfer of the toner image is performed. The pre-rotation step is a period during which the preparatory operation before the image forming step is performed from the input of the start instruction to the actual start of forming the image. The inter-paper process is a period corresponding between the recording material P and the recording material P when image formation is continuously performed on the plurality of recording materials P (continuous image formation). The post-rotation step is a period during which the rearranging operation (preparation operation) is performed after the image forming step. The non-image forming period (non-image forming period) is a period other than the image forming period, and is from the pre-rotation step, the inter-paper step, the post-rotation step, and further, when the power of the image forming apparatus 100 is turned on or from the sleep state. It includes a pre-multi-rotation process, which is a preparatory operation at the time of recovery. In this embodiment, control for setting the initial value of the secondary transfer voltage, control for determining the upper limit value and the lower limit value (predetermined current range) of the secondary transfer current during paper passing are executed at the time of non-image formation. To. The sleep state means that when a predetermined time set in advance has elapsed from the output of the last image, power is supplied to the elements of the image forming apparatus 100 other than some elements such as a part of the control unit 50. Is in a stopped state. As will be described later, the adjustment mode for outputting a test image for density adjustment may be called a job as in the normal image formation job.

3. Outline of secondary transfer voltage control Next, an outline of secondary transfer voltage control will be described. FIG. 4 is a flowchart showing an outline of the procedure for controlling the secondary transfer voltage. FIG. 4 shows a simplified procedure for secondary transfer voltage control among the controls executed by the control unit 50 when the job is executed, and many other controls when the job is executed are not shown. Has been done. The same applies to the flowchart of FIG. 7 described later. Further, FIG. 4 shows an example of executing a job of forming an image on one recording material P.

First, when the control unit 50 acquires the job information from the operation unit 31 or the external device 200, the control unit 50 starts the operation of the job (S1). In this embodiment, the information of this job includes the following information. That is, the image information specified by the operator and the information regarding the recording material P forming the image. Information about the recording material P includes the size (width, length) of the recording material P, information related to the thickness of the recording material P (thickness or basis weight), and whether or not the recording material P is coated paper. Information related to the surface property of the material P (paper type category) can be mentioned. The control unit 50 writes the information of this job to the RAM 52.

Next, the control unit 50 obtains a basal voltage Vb, which is a voltage output from the secondary transfer power supply 20 in order to flow a predetermined target current Italy in the state where the secondary transfer unit N2 does not have the recording material P, and causes the RAM 52. Remember (S2). This base voltage Vb corresponds to the secondary transfer partial carrying voltage which is the transfer voltage corresponding to the electric resistance of the secondary transfer unit N2 (mainly the secondary transfer roller 8 in this embodiment). The ROM 53 stores information indicating the correlation between the environmental information and the target current Ittaget for transferring the toner image on the intermediate transfer belt 7 onto the recording material P. In this embodiment, this information is set as table data indicating the target current amount for each category of the moisture content of the atmosphere. This table data was obtained in advance by experiments or the like. The control unit 50 acquires environmental information (temperature / humidity) detected by the environment sensor 32. Further, the control unit 50 obtains the moisture content of the atmosphere based on the environmental information (temperature / humidity) detected by the environment sensor 32. Then, the control unit 50 obtains the target current Target corresponding to the environment from the information indicating the relationship between the environmental information and the target current Target. Further, the control unit 50 receives the toner image on the intermediate transfer belt 7 and the secondary transfer unit N2 (mainly in this embodiment) before the recording material P on which the toner image is transferred reaches the secondary transfer unit N2. Information on the electrical resistance of the secondary transfer roller 8) is acquired. Then, the basal voltage Vb corresponding to the target current Target is obtained based on the information. In this embodiment, the basal voltage Vb is obtained by the following ATVC control (Active Transfer Voltage Control). A predetermined voltage (test voltage) or current (test current) is supplied from the secondary transfer power source 20 to the secondary transfer roller 8 in a state where the secondary transfer roller 8 and the intermediate transfer belt 7 are in contact with each other. Then, the current value when a predetermined voltage is being supplied or the voltage value when a predetermined current is being supplied is detected. For example, a plurality of levels of test voltage or test current are supplied, the voltage-current characteristic which is the relationship between the voltage and the current is acquired, and the base voltage Vb corresponding to the target current Target is obtained based on the voltage-current characteristic. Alternatively, as the test current, for example, the target current Italy may be supplied, and the output voltage value of the secondary transfer power supply 20 at that time may be obtained as the basal voltage Vb.

Next, the control unit 50 obtains the recording material sharing voltage Vp, which is the voltage output from the secondary transfer power source 20 by adding the electric resistance component of the recording material P, and stores it in the RAM 52 (S3). The ROM 53 stores information for obtaining the recording material shared voltage Vp as shown in FIG. In this embodiment, this information is set as table data showing the relationship between the moisture content of the atmosphere and the recording material sharing voltage Vp for each category of the basis weight of the recording material P. The table data for obtaining the recording material shared voltage Vp is obtained in advance by an experiment or the like. The control unit 50 obtains the moisture content of the atmosphere based on the environmental information (temperature / humidity) detected by the environment sensor 32. Then, the control unit 50 obtains the recording material shared voltage Vp from the table data based on the information on the basis weight of the recording material P included in the job information acquired in S1 and the above environmental information. .. The voltage shared by the recording material (transfer voltage corresponding to the electrical resistance of the recording material P) Vp may change depending on the surface property of the recording material P as well as the information (basis weight) related to the thickness of the recording material P. is there. Therefore, the table data may be set so that the recording material shared voltage Vp changes depending on the information related to the surface property of the recording material P. Further, in the present embodiment, the information related to the thickness of the recording material P (further, the information related to the surface property of the recording material P) is included in the job information acquired in S1. However, the image forming apparatus 100 may be provided with a measuring means for detecting the thickness of the recording material P and the surface property of the recording material P, and the recording material sharing voltage Vp may be obtained based on the information obtained by the measuring means. ..

Next, the control unit 50 obtains an initial value of a target value (target voltage) of the secondary transfer voltage Vtr applied from the secondary transfer power supply 20 to the secondary transfer roller 8 during paper passing, and stores it in the RAM 52 ( S4). That is, the control unit 50 obtains Vb + Vp, which is the sum of the base voltage Vb and the recording material sharing voltage Vp, as the initial value of the secondary transfer voltage Vtr by the time the recording material P reaches the secondary transfer unit N2. And store it in RAM 52. Then, the recording material P is prepared for the timing when it reaches the secondary transfer unit N2.

Further, the control unit 50 determines the upper limit value and the lower limit value (predetermined current range) of the secondary transfer current during paper passing (S5). As shown in FIG. 6, the ROM 53 stores information for obtaining a range of current that can be passed through the secondary transfer unit N2 during paper transfer from the viewpoint of suppressing image defects. In this embodiment, this information is set as table data showing the relationship between the amount of water in the atmosphere and the upper and lower limits of the current that may be passed through the secondary transfer unit N2 during paper transfer. This table data was obtained in advance by experiments or the like. The control unit 50 obtains the moisture content of the atmosphere based on the environmental information (temperature / humidity) detected by the environment sensor 32. Then, the control unit 50 obtains a predetermined current range of the secondary transfer current during paper passing from the table data based on the environmental information.

The range of the current that can be passed through the secondary transfer unit N2 during paper transfer varies depending on the width of the recording material P. As an example, FIG. 6 shows table data set assuming a recording material P having a width (297 mm) corresponding to A4 size. A plurality of table data may be set according to the width of the recording material P. Alternatively, when the width of the recording material P is different from the width equivalent to the A4 size, the width equivalent to the A4 size is supported by the proportional calculation using the ratio of the width of the recording material P actually passed to the width equivalent to the A4 size. The value of the table data to be used may be corrected and used. Here, as the current flowing through the transfer section when the recording material P passes through the secondary transfer section N2, there are a paper-passing section current and a non-paper-passing section current. The paper-passing unit current is a current that flows in a region (“paper-passing portion”) through which the recording material P of the secondary transfer unit N2 passes in a direction substantially orthogonal to the transport direction of the recording material P. The non-paper-passing portion current is a current that flows in a region (“non-passing portion”) through which the recording material P of the secondary transfer unit N2 does not pass in a direction substantially orthogonal to the transport direction of the recording material P. The current that can be detected during paper passing is the sum of the paper-passing part current and the non-paper-passing part current. Therefore, the range of the current that can be passed through the paper-passing portion is set in advance in the same manner as in the above table data, and the current that flows through the non-paper-passing portion is obtained. A predetermined current range may be obtained by adding the range of the current that can be passed. The current flowing through the non-passing paper portion can be obtained, for example, as follows. Using the information (voltage-current characteristics) regarding the electrical resistance of the secondary transfer unit N2 acquired in S2, the current that flows when the secondary transfer voltage Vtr is applied is obtained. Then, the non-passing portion is calculated from the above-mentioned current by proportional calculation using the ratio of the width of the non-passing portion (the difference between the width of the secondary transfer roller 8 and the width of the recording material P) to the width of the passing portion. The current flowing through can be calculated. Further, the predetermined current range for suppressing image defects may change depending on the thickness and surface properties of the recording material P in addition to the environmental information. Therefore, the table data may be set so that the current range changes depending on the information (basis weight) related to the thickness of the recording material P and the information related to the surface property of the recording material P. The information in the predetermined current range may be set as a calculation formula. Further, the information in the predetermined current range may be set as a plurality of table data or calculation formulas for each size of the recording material P.

Next, the control unit 50 detects the secondary transfer current by the current detection circuit 21 during paper passing, and if the detected secondary transfer current is out of the predetermined current range determined in S5, the secondary transfer is performed. The voltage Vtr is changed (limiter control) (S6). That is, the transfer voltage is changed so that the secondary transfer current is within a predetermined range. At this time, the control unit 50 changes the secondary transfer voltage Vtr by applying the offset voltage ΔVp described later to Vb + Vp. In other words, this process corresponds to changing the Vp of Vb + Vp to change the secondary transfer voltage Vtr. In order to perform this operation, the high-voltage substrate that supplies the secondary transfer voltage can repeat the operation of detecting the current at a predetermined detection time and switching the high voltage at a predetermined response time based on the result. It has become.

To further explain, in the limiter control (current limiter control), after the detection time (first period) for detecting the transfer current and the signal for changing the transfer voltage based on the detection result of the transfer current at the detection time are output. The response time (second period) waiting for the response is repeated. FIG. 8 schematically shows an example of the transition of the transfer current and the transfer voltage in the limiter control. In this operation, the control unit 50 outputs a signal for changing the voltage output to the secondary transfer power supply 20 based on the signal indicating the current detection result input from the current detection circuit 21 during the detection period. Will be done. FIG. 8 shows an example in which the secondary transfer voltage is changed when the secondary transfer current detected during paper passing is below the lower limit value. As shown in FIG. 8, when the predetermined secondary transfer voltage is applied for 8 ms (response time + detection time) and the secondary transfer current is still below the lower limit, the secondary transfer voltage is as follows. Is changed. That is, the secondary transfer voltage is changed to the secondary transfer voltage obtained by adding a predetermined voltage fluctuation range (ΔV in the figure) to the predetermined secondary transfer voltage. Further, the change of the secondary transfer voltage is repeatedly executed until the secondary transfer current detected during paper passing reaches the lower limit value. The same applies when the secondary transfer current detected during paper passing exceeds the upper limit value. When the predetermined secondary transfer voltage is applied for 8 ms (response time + detection time) and the secondary transfer current still exceeds the upper limit value, the secondary transfer voltage is changed as follows. That is, the secondary transfer voltage is changed to the secondary transfer voltage obtained by subtracting the predetermined secondary transfer voltage by a predetermined voltage fluctuation range (ΔV in the figure). Further, the change of the secondary transfer voltage is repeatedly executed until the secondary transfer current detected during paper passing reaches the upper limit value. The detection time and response time are each about 10 msec, depending on the performance of the high-voltage substrate. In this embodiment, the detection time and the response time are 8 msec each.

Here, the voltage fluctuation width per time in the limiter control is defined as "voltage fluctuation width ΔVps". Further, in the limiter control, which is the cumulative value of the voltage fluctuation width ΔVps (when the voltage is increased, ΔVps which is a positive value is added, and when the voltage is decreased, ΔVps which is a negative value is added). Let the voltage change amount be "offset voltage ΔVp". This offset voltage ΔVp corresponds to the difference between the initial value of the secondary transfer voltage Vtr obtained by adding the base voltage Vb and the recording material sharing voltage Vp and the secondary transfer voltage Vtr after being changed by the limiter control. To do.

Then, the control unit 50 repeatedly performs the limiter control during notification until the output of the desired image of the job is completed, and ends the job when the output of the desired image of the job is completed.

4. Outline of automatic image adjustment Next, an outline of "automatic image adjustment" will be described. In this embodiment, automatic image adjustment (also referred to as (automatic image) adjustment mode) that automatically outputs a test chart to which a test image for adjusting image density is transferred is executed based on the input of the operation unit 31 is possible. Is. In this embodiment, "automatic image adjustment" adjusts "maximum density control (so-called Dmax control)" that adjusts the maximum density on paper and gradation from the maximum density on paper to halftones and highlights. "Automatic gradation control" is performed.

The automatic image adjustment is an adjustment mode that can be automatically performed by the user pressing a button from the screen on the UI at an arbitrary timing.

As shown in FIG. 3, when the automatic image adjustment button is pressed by the user from the operation unit 31, the control unit 50 executes the automatic image adjustment mode. The control unit 50 first executes "maximum concentration control". The control unit 50 acquires the charging potential of the photosensitive drum 1 set at the time of the previous maximum concentration adjustment or the charging potential of the photosensitive drum 1 determined according to the temperature and humidity detected by the environment sensor 32. Then, the control unit 50 controls the charging device so that the charging potential of the photoconductor drum 1 becomes the acquired charging potential. After that, the control unit 50 shakes the exposure intensity by 10 levels to form a test image (a plurality of patch images) for density adjustment on the photosensitive drum 1. Then, the formed patch image is transferred to a recording material, and a test chart for adjusting the maximum density as shown in FIG. 11 is output. The density of the plurality of patch images formed on the test chart for adjusting the maximum density is measured by the image reading unit 90, and the density result as shown in FIG. 12 is obtained. Based on the acquired density result, the control unit 50 determines the exposure intensity at which each color density becomes the target maximum density.

Next, the control unit 50 continuously executes the "automatic gradation control" after the maximum density adjustment is executed. The control unit 50 sets the charging potential and exposure intensity of the photosensitive drum determined by "maximum density control" to the charging potential and exposure intensity of the photosensitive drum 1. Then, the control unit 50 controls the exposure time of the exposure device 3 to form a plurality of patch images for gradation control on the photosensitive drum 1. Then, the patch image formed on the photosensitive drum 1 is transferred to the recording material, and a test chart for automatic gradation control as shown in FIG. 13 is output. In the test chart for automatic gradation control, a total of 20 patches are formed for each color in 12 to 240 sections in 12 increments for the image signals 0 to 255. The patch length in the transport direction for each signal was 19.5 to 20.5 mm. The paper used was A3 size. The test chart for automatic gradation control is measured by the image reading unit 90. Based on this measurement result, the control unit 50 corrects the exposure time by a predetermined amount with respect to the deviation amount when the density deviates from the target density for each image signal, and the gradation targeted for each color. Automatically adjusts to.

This automatic gradation control is performed on each of a plurality of types of screens such as a copy screen, a text screen, and an image screen. Therefore, the test chart for automatic gradation control shown in FIG. 18 is for one screen type, and the other screen types are subsequently output, the density measurement is read by the image reading unit 90, and the exposure time of the corresponding screen is corrected. The process is repeated.

When performing automatic gradation control, the larger the number of gradation patches, the higher the accuracy to obtain the target gradation. In this example, 20 screens of each color were used.

As described above, the user can instruct the automatic image adjustment from the operation unit 31 at an arbitrary timing to adjust (calibrate) the maximum density and the gradation density of the image output on the paper.

5. Taking over the offset voltage As described above, when the limiter control is performed, a predetermined current range in which image defects can be suppressed is predetermined for the secondary transfer current during paper passing. When the detected secondary transfer current is out of this predetermined current range, the transfer voltage is changed so as to fall within the predetermined current range.

However, as can be seen from the above-mentioned limiter control method, in the limiter control, a time lag occurs from the detection that the transfer current deviates from the predetermined range to the completion of the change of the transfer voltage. Therefore, as described above, in the region where the transfer current is out of the appropriate range, which passes through the transfer portion until the transfer voltage change is completed, image defects due to excess or deficiency of the transfer current occur. There is. Then, as described above, when such an image defect occurs in the first image, there is a high possibility that the same image defect will occur in the second and subsequent images. This is because the recording materials used for the concentration adjustment are likely to be the same type of recording materials, and it is considered that the recording materials are also left unattended.

FIG. 9 shows the transition of the secondary transfer voltage and the secondary transfer current when the test chart for automatic image adjustment is output, and the occurrence of image defects when the control of this embodiment described later is not performed. It is shown schematically. The first sheet is a test chart for adjusting the maximum density, and the second and subsequent sheets show a case where a test chart for gradation control is output. FIG. 9 shows a case where image adjustment control is performed using A3 size paper having a ^{basis weight of 90 g / m 2} as the recording material P in an environment of 23 ° C. and 5% RH (moisture content of 0.9 g / kg or less). Shown. Further, FIG. 9 shows an example in which the secondary transfer current detected during the first sheet of paper is less than the lower limit current. Regarding the recording material P, the image formed on the recording material P, and the like, the front end and the rear end are related to the transport direction of the recording material P.

In the example of FIG. 9, the lower limit value of the predetermined current range is 50 μA, the upper limit value is 70 μA, the target current Target of the secondary transfer current is 60 μA, and the initial value of the secondary transfer voltage Vtr determined according to the target current Target is It is assumed that the voltage is 2500V. This secondary transfer voltage Vtr is the total value of the basal voltage Vb (= 1500V) and the recording material sharing voltage Vp (= 1000V). The target current Target is determined according to the environmental information. The base voltage Vb is set to the target current based on the information on the electrical resistance of the secondary transfer unit N2 (mainly the secondary transfer roller 8 in this embodiment) acquired in the state where the secondary transfer unit N2 has no recording material. It will be decided accordingly. Further, the recording material sharing voltage Vp is determined according to the information on the basis weight of the recording material P. The recording material sharing voltage Vp is preset with a value relating to the standard recording material P as table data indicating the relationship with the environment.

The secondary transfer current detected when the secondary transfer voltage Vtr is applied to the tip of the first recording material P is 40 μA, which is lower than the lower limit of 50 μA. This is a case where the passing recording material P has the same basis weight as the standard recording material P when the table value of the recording material sharing voltage Vp is determined, but the electric resistance is extremely high due to drying. And so on.

Since the secondary transfer current detected at the tip of the first recording material P is below the lower limit of 50 μA, the secondary transfer voltage Vtr is changed to 2600 V (2500 V + voltage fluctuation width ΔVps (= 100 V)). Then, the secondary transfer current is detected again. After that, the secondary transfer voltage Vtr is changed so as to increase every voltage fluctuation width ΔVps (= 100V) until the secondary transfer current reaches the lower limit value. Then, when the secondary transfer voltage reaches 3200 V, the secondary transfer current reaches the lower limit of 50 μA. Therefore, the secondary transfer voltage Vtr is changed seven times. After the secondary transfer current reaches the lower limit, the change of the secondary transfer voltage Vtr is stopped, the secondary transfer voltage is maintained at 3200 V, and the toner image is directed toward the rear end of the first recording material P. Secondary transcription is performed.

That is, in the example of FIG. 9, in the section A from the tip of the first recording material P having the secondary transfer current of 40 μA until the secondary transfer current reaches the lower limit current of 50 μA, the image due to insufficient transfer current. Image defects such as low density (missing transfer) occur. Then, in the example of FIG. 9, since the secondary transfer voltage control is performed on the second image as well as on the first image, image defects such as image density thinning (transfer omission) due to insufficient transfer current are performed as in the first image. Will occur. This is because the recording material P used for the first sheet and the recording material P used for the second sheet are the same type of recording material P, and the left state of those recording materials P is also the same. is there. In FIG. 9, an image defect due to insufficient transfer current has been described as an example, but the same problem may occur with respect to an image defect due to an excessive transfer current.

Therefore, in this embodiment, when the automatic image control is executed, the offset voltage ΔVp in the limiter control of the first test chart is taken over and the secondary transfer voltage Vtr of the second and subsequent test charts is set. As a result, it is possible to prevent the region where the transferability is lowered due to the excess or deficiency of the transfer current in the first image of the automatic image control from being repeatedly generated in the second and subsequent images of the automatic image control.

In this embodiment, the secondary transfer voltage Vtr of the second and subsequent images of the automatic image control is set by using the offset voltage ΔVp substantially the same as the offset voltage ΔVp in the limiter control of the first image of the automatic image control. In particular, in this embodiment, the settings are as follows. The value of the secondary transfer voltage Vtr applied to the tip of the second test chart of the automatic image control is added to the voltage value obtained by adding the base voltage Vb and the recording material sharing voltage Vp, and one of the automatic image controls. It is a voltage value to which the offset voltage ΔVp in the limiter control of the eye is added. However, setting the secondary transfer voltage Vtr of the second image of the automatic image control by taking over the offset voltage ΔVp of the first limiter control of the automatic image control is not limited to the following configuration. That is, the setting is not limited to using the same offset voltage ΔVp as the offset voltage ΔVp of the first limiter control of the automatic image control. That is, when the secondary transfer voltage Vtr is changed by the limiter control on the first image of the automatic image control, the secondary transfer voltage Vtr of the second image of the automatic image control is controlled by the first limiter of the automatic image control. It can be determined based on the amount of change in the secondary transfer voltage Vtr according to. Here, for the sake of simplicity, determining the secondary transfer voltage Vtr of the second image of the automatic image control based on the amount of change of the secondary transfer voltage Vtr by the limiter control of the first image of the automatic image control is simply ". The offset voltage ΔVp is taken over. "

FIG. 7 is a flowchart showing an outline of the procedure of the secondary transfer voltage control in the present embodiment including the process of taking over the offset voltage ΔVp of the first sheet of the automatic image adjustment. Further, the description of the same procedure as that of FIG. 4 will be omitted as appropriate.

The processes of S101 to S105 in FIG. 7 are the same as the processes of S1 to S5 of FIG. 4, respectively.

When the automatic image adjustment JOB is started, the control unit 50 determines the secondary transfer bias and the transfer current range according to the flow of FIG. Then, as described above, the test chart for automatic image adjustment is sequentially output. First, when outputting the first sheet (n = 1) of the test chart for automatic image adjustment, the transfer voltage Vtr (= Vn = Vb + Vp) is applied (S106). In this embodiment, the first test chart for automatic image adjustment is a test chart for maximum density adjustment. The transfer current In is acquired when the test chart for adjusting the maximum concentration passes through the transfer section (S107). When the transfer current In when the test chart for adjusting the maximum concentration is passing through the transfer portion is out of the predetermined range (No in S108), the transfer voltage is corrected (S109). When the transfer current In does not deviate from the predetermined range (Yes in S108), the test chart for adjusting the maximum concentration is output without correcting the transfer voltage. In this way, the test chart for adjusting the maximum density is output, and the output test chart is read by the image reading unit 90, and the maximum density is adjusted. When the maximum density adjustment is executed, the control unit 50 outputs a gradation control test chart as the second test chart for automatic image adjustment (S110). Here, regarding the transfer voltage applied from the tip of the second sheet for automatic image adjustment, if the limiter control is performed during the passing of the first sheet (No in S108), the transfer voltage after correction is applied. Vn'is adopted (S111). That is, the offset voltage ΔVp is taken over and the secondary transfer voltage Vtr (= Vn') of the second and subsequent test charts is set. Hereinafter, the same applies to the case where the automatic gradation adjustment test chart of another screen is output as the third sheet of the test chart for automatic image adjustment. The same applies to the test charts after that.

In FIG. 10, under the same conditions as in FIG. 9, the secondary transfer voltage Vtr applied to the tip of the second test chart is set by taking over the offset voltage ΔVp of the first sheet when the automatic image adjustment is executed. It is the same figure as FIG. 9 in the case of this. In the example of FIG. 10, the secondary transfer voltage Vtr applied to the tip of the second test chart has substantially the same value as the secondary transfer voltage Vtr after being changed by the limiter control of the first sheet. .. In this case, in the first section A, as in the case of FIG. 9, a region in which the transferability is lowered due to insufficient transfer current is generated. However, in the second sheet, the secondary transfer voltage Vtr = 3200V, which is obtained by adding the offset voltage ΔVp stored in the first sheet to the voltage value obtained by adding the base voltage Vb and the recording material sharing voltage Vp (table value). Is applied from the tip of the recording material P. Therefore, image defects do not occur in the entire area from the front end to the rear end of the recording material P.

In this embodiment, the maximum density adjustment test chart is smaller than the number of patches in the automatic gradation adjustment test chart, and in the case of A3 size, the patch length in the transport direction is 20 mm x 10 so as to avoid the section A. It may be arranged. Here, the section A refers to an area where limiter control is performed. In this embodiment, it is within a predetermined area arranged at the front end of the test chart (a region sandwiched at a position advanced by a predetermined distance from the front end side of the test chart to the rear end side). In this embodiment, when the transfer current In is out of the predetermined range, the transfer voltage is changed by 100 V. The amount of change in the transfer voltage per step may be appropriately changed based on the transfer current In so that the change in the transfer voltage can be completed within the section A. On the other hand, in the second and subsequent test charts for gradation adjustment, the test image for gradation adjustment may be set so as to be formed in the region including the section A.

In this embodiment, the initial value of the secondary transfer voltage Vtr when outputting the second test chart is set to Vb + Vp + ΔVp (the coefficient of ΔVp is 1). That is, the offset voltage ΔVp itself when outputting the first test chart is inherited, but the present invention is not limited to this. For example, it may be set to Vb + Vp + ΔVp × first coefficient (the predetermined coefficient is a value other than 1).

7 Intermediate transfer belt 8 Secondary transfer roller 20 Secondary transfer power supply 21 Current detection circuit 22 Voltage detection circuit 50 Control unit

Claims (4)

An image carrier that supports a toner image and
A transfer member that transfers a toner image carried on the image carrier to a recording material at a transfer unit when a voltage is applied.
A power supply that applies a voltage to the transfer member and
A current detection unit that detects the current flowing through the transfer member, and
A control unit that controls a constant voltage so that the voltage applied to the transfer member becomes a predetermined voltage when the recording material passes through the transfer unit, and the detection result of the current detection unit is within a predetermined range. A control unit that controls the voltage applied to the transfer member based on the detection result of the current detection unit.
In an image forming apparatus including an operation unit for operating an image forming apparatus,
The control unit obtains a first test chart for adjusting the image density and a second test chart output after the first test chart based on an instruction input to the operation unit. It is possible to execute a series of adjustment modes in which a plurality of test charts including the test charts are output to adjust the image density, and the predetermined voltage when the second test chart passes through the transfer unit is set to the first voltage. When the test chart of 1 is passing through the transfer unit, it is characterized in that it is determined based on the amount of change in the voltage by controlling the voltage applied to the transfer member based on the detection result of the current detection unit. Image forming device. The first aspect of the present invention is characterized in that the control unit determines the predetermined voltage when the second test chart is passing through the transfer unit based on a value obtained by multiplying the change amount by a coefficient. The image forming apparatus described. The first test chart is a test chart for adjusting the maximum density, and the second test chart is a test chart for adjusting the gradation of density. The image forming apparatus according to 1 or 2. In the first test chart, a plurality of first test images for adjusting the maximum density are formed, and in the second test chart, a plurality of second tests for adjusting the gradation of the image are formed. When an image is formed and the first test chart passes through the transfer unit and the detection result of the current detection unit deviates from the predetermined range, the first test chart The predetermined voltage is changed within the predetermined region of the tip in the transport direction, the first test image is formed avoiding the predetermined region, and the second test image is formed in the region including the predetermined region. The image forming apparatus according to claim 3, wherein the image forming apparatus is formed.

Images