JP2014048633A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust sensitivity of a detection part which detects the density of an image after an image forming apparatus is shipped.SOLUTION: A control part executes a balance adjustment operation for adjusting sensitivity of an IDC sensor when an image forming apparatus is shipped or the IDC sensor is replaced. A baseline correction is first operated (S100) followed by transfer of a high density image on an intermediate transfer belt (S110). The high density image whose density is higher than an image patch at the time of image correction operation is formed by increasing a developing bias voltage or increasing a laser power at the time of exposure. Then, it is determined whether or not that a specific period has lapsed after shipment of the image forming apparatus (S120), and when the specific period has lapsed, the high density image is formed by overlapping a plurality of images (S130). Finally, the IDC sensor radiates light on the high density image, a P wave and an S wave reflected on the high density image is received, and a P/S calculation is performed to calculate a correction value for adjusting the sensitivity of an S wave reception part (S140).

Description

  The present invention relates to an image forming apparatus that forms an image by transferring toner onto an image carrier.

  In recent years, image forming apparatuses such as copiers having multiple functions such as printers, scanners, and facsimiles have been widely used. The image forming apparatus is, for example, a four-color image forming unit composed of yellow (Y), magenta (M), cyan (C), and black (K) arranged in tandem along the belt rotation direction of the intermediate transfer belt. It has. Each of the four color image forming units develops the latent image on the photosensitive drum with the color toner of the developing unit based on the image data to form a toner image, and then superimposes these toner images on the intermediate transfer belt. And transcribe. The toner image superimposed on the intermediate transfer belt is transferred onto a sheet, and the sheet onto which the toner image is transferred is discharged onto a sheet discharge tray.

  In such an image forming apparatus, the amount of toner attached to each color and the position of the toner image may vary depending on the use frequency and use environment in each image forming unit. Therefore, in order to obtain a high-quality color image by preventing variations in the toner adhesion amount, image stability such as image adjustment and resist adjustment is performed according to the environmental changes in the image forming apparatus and the frequency of use of each image forming unit. Is being processed. By this image stabilization processing, the optimum state of the image forming process can be maintained.

  In the image stabilization process described above, the following process is performed. First, a patch image (toner mark) composed of a plurality of gradations for density correction is formed on the intermediate transfer belt, and the patch image is read by an optical sensor. Subsequently, based on the detection signal corresponding to the patch image read by the optical sensor, the development bias voltage, the intensity of the drive signal to the LED or LD constituting the exposure unit, the output timing, and the like are adjusted, and the four-color toner The image density and the like are optimized.

  For example, Patent Document 1 discloses that light reflected from a toner image on a photosensitive drum is separated into P wave (P polarized light) and S wave (S polarized light) using a polarizing filter, and the separated P wave is converted into P wave. By receiving light by the light receiving part (P light receiving element) and receiving S wave by the S wave light receiving part (S light receiving element), and subtracting the output of the S wave light receiving part from the output of the P wave light receiving part, the amount of toner adhesion A toner adhesion amount measuring device that accurately measures the toner is disclosed.

JP-A-6-250480

  However, the conventional toner adhesion amount measuring device disclosed in Patent Document 1 has the following problems. That is, in the conventional toner adhesion amount measuring apparatus, the P wave light reflected by the toner image on the photosensitive drum is irregularly reflected on the toner image and becomes random light. Here, the random light usually has a characteristic that when the intermediate transfer belt is completely covered with toner, the P wave component and the S wave component are ideally mixed one-to-one.

  FIG. 11 shows an example of the relationship between random light and toner adhesion amount. The vertical axis in FIG. 11 is the PS output, and the horizontal axis in FIG. 11 is the toner adhesion amount. As shown by the solid line in FIG. 11, when the toner adhesion amount reaches the adhesion amount that completely covers the intermediate transfer belt, the difference result by the calculation of (PS output) becomes zero. However, in practice, P−S = 0, that is, P = S is not often obtained as shown by the broken line in FIG.

  In order to cope with such variations in the light receiving elements and the like, conventionally, the light receiving circuit is configured so that the difference between the P wave received by each light receiving unit and the S wave is zero before the actual device is loaded (before the device is shipped). The sensitivity is adjusted. For example, using a device including an S wave light receiving circuit, a P wave light receiving circuit, a differential amplifier circuit, a variable resistor, and the like, light is irradiated onto a film having characteristics similar to toner, and light reflected on the film ( P wave and S wave) are received by each of the S wave light receiving circuit and the P wave light receiving circuit. Then, while watching the differential amplification output of the received P wave and S wave, the sensitivity is adjusted by adjusting a variable resistor provided in the S wave light receiving circuit, for example, so that PS = 0. Is going.

  However, since the conventional apparatus described above is assumed to be used before the actual machine is turned on, it is difficult to adjust the balance after the actual machine is turned on. For this reason, if the sensor characteristics have changed due to replacement of the toner adhesion amount measuring device (density detection sensor) after the actual machine has been introduced, or if there are variations in the polarizing plate of the density detection sensor after the actual machine has been introduced, There was a problem that the sensitivity could not be adjusted.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of adjusting the sensitivity of a detection unit that detects the density of an image after the actual machine is introduced. is there.

  In order to solve the above problems, an image forming apparatus according to the present invention includes an image forming unit that forms an image on an image carrier, and an image on the image carrier formed by the image forming unit. The detection unit that detects the reflected light reflected by the image, the image correction operation that corrects the image density based on the reflected light detected by the detection unit, and the sensitivity of the detection unit And a control unit that performs a balance adjustment operation. The detection unit receives a first light receiving unit that receives a P wave among the reflected light reflected by the image, and receives an S wave among the reflected light reflected by the image. And a second light receiving unit, and the control unit outputs a high density image having a higher density than the highest density image formed on the image carrier during the image correction operation during the balance adjustment operation. The image forming unit is controlled to form a high density formed on the image carrier. The first light receiving unit so that the level of the P wave reflected by the image and received by the first light receiving unit is the same as the level of the S wave reflected by the high density image and received by the second light receiving unit. And the sensitivity of at least one of the second light receiving part is adjusted.

  According to the present invention, the control unit causes the first light receiving unit and the first light receiving unit so that the levels of the P wave received by the first light receiving unit and the S wave received by the second light receiving unit are the same. Since the sensitivity of at least one of the two light receiving units is adjusted, a balance adjustment operation can be performed in the apparatus. As a result, the balance of the detection unit can be adjusted even after the device is shipped.

1 is a diagram illustrating a configuration example of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a diagram for explaining a patch image formed on an intermediate transfer belt during an image correction operation. FIG. 6 is a diagram for explaining a high density image formed on an intermediate transfer belt during a balance adjustment operation. It is a figure which shows the structural example of an IDC sensor. It is a figure which shows the example of a relationship between a toner adhesion amount and a P wave / S wave. FIG. 6 is a diagram for describing reflection of light emitted from an IDC sensor when there is no toner on an intermediate transfer belt. 1 is a diagram illustrating a block configuration example of an image forming apparatus. It is a figure which shows the structural example of a P wave light-receiving part and a S wave light-receiving part. 6 is a flowchart illustrating an operation example of the image forming apparatus during a balance adjustment operation. 6 is a flowchart illustrating an operation example of the image forming apparatus during an image correction operation. It is a figure which shows the example of a relationship between toner adhesion amount and P wave output-S wave output.

Hereinafter, the best mode for carrying out the invention (hereinafter referred to as an embodiment) will be described.
[Configuration example of image forming apparatus]
The image forming apparatus 100 according to the present invention has a function of performing an image correction operation for performing image density correction and the like, and a balance adjustment operation for adjusting variation of the light receiving elements of the IDC sensor 120 used for the image correction operation. It has. In the balance adjustment operation, the P-wave component or the S-wave component received by the P-wave light receiving unit 130 by irradiating the high-density image 160 formed of the toner image formed on the intermediate transfer belt 8 with the light of the P-wave component or S-wave, By adjusting the sensitivity of at least one of the P-wave light receiving unit 130 and the S-wave light receiving unit 140 so that the level of the S wave received by the unit 140 is the same, the balance adjustment is performed in the apparatus after the actual machine is introduced. Is possible.

  FIG. 1 shows an example of the configuration of an image forming apparatus 100 according to the present invention. In addition, the dimension ratio of drawing is expanded on account of description and may differ from an actual ratio. As shown in FIG. 1, the image forming apparatus 100 is called a tandem type image forming apparatus, and includes an automatic document feeder 80 and an apparatus main body 102. The automatic document conveyance unit 80 is attached to the upper part of the apparatus main body 102 and sends out the paper set on the conveyance table to the image reading unit 90 of the apparatus main body 102 by a conveyance roller or the like.

  The apparatus main body 102 includes an image reading unit 90, an image forming unit 10, an intermediate transfer belt 8 that is an example of an image carrier, an IDC sensor 120 that is an example of a detection unit, a paper feeding unit 20, a fixing unit 44, and automatic paper reversal conveyance. And a unit 60 (Auto Duolex Unit: hereinafter referred to as ADU). The image reading unit 90 scans and exposes a document placed on a document table by an optical system of a scanning exposure device, photoelectrically converts an image of the document scanned by a CCD (Charge Coupled Devices) image sensor, and outputs an image information signal. Generate. The image information signal is output to the image forming unit 10 after being subjected to analog processing, analog / digital (hereinafter referred to as A / D) conversion processing, pseudo correction, image compression processing, and the like by an image processing unit (not shown).

  The image forming unit 10 forms an image by electrophotography, and includes an image forming unit 10Y that forms a yellow (Y) image, an image forming unit 10M that forms a magenta (M) image, The image forming unit 10C forms a cyan (C) color image, and the image forming unit 10K forms a black (K) color image. In this example, common function names, for example, Y, M, C, and K indicating colors to be formed are added to the back of the reference numeral 10.

  The image forming unit 10Y includes a photosensitive drum 1Y, a charging unit 2Y, an exposure unit (optical writing unit) 3Y, a developing unit 4Y, and a cleaning unit 6Y disposed around the photosensitive drum 1Y. The image forming unit 10M includes a photosensitive drum 1M, and a charging unit 2M, an exposure unit 3M, a developing unit 4M, and a cleaning unit 6M disposed around the photosensitive drum 1M. The image forming unit 10C includes a photosensitive drum 1C, and a charging unit 2C, an exposure unit 3C, a developing unit 4C, and a cleaning unit 6C disposed around the photosensitive drum 1C. The image forming unit 10K includes a photosensitive drum 1K, and a charging unit 2K, an exposure unit 3K, a developing unit 4K, and a cleaning unit 6K disposed around the photosensitive drum 1K.

  Respective photosensitive drums (image carriers) 1Y, 1M, 1C, and 1K in the image forming units 10Y, 10M, 10C, and 10K, charging units 2Y, 2M, 2C, and 2K, exposure units 3Y, 3M, 3C, and 3K, development The parts 4Y, 4M, 4C, and 4K and the cleaning parts 6Y, 6M, 6C, and 6K have a common content configuration. In the following description, Y, M, C, and K are not used unless particularly distinguished.

  The charging unit 2 charges the surface of the photosensitive drum 1 almost uniformly. The exposure unit 3 is composed of, for example, an LPH (LED Print Head) having an LED array and an imaging lens, or a polygon mirror type laser exposure scanning device, and the photosensitive drum 1 is irradiated with laser light based on an image information signal. Scan to form an electrostatic latent image. The developing unit 4 develops the electrostatic latent image formed on the photosensitive drum 1 with toner. As a result, a toner image which is a visible image is formed on the photosensitive drum 1.

  The intermediate transfer belt 8 is stretched by a plurality of rollers and supported so as to be able to run. When the primary transfer roller operates, the intermediate transfer belt 8 travels, and the toner image formed on each photosensitive drum 1 is transferred to the image transfer position of the intermediate transfer belt 8 (primary transfer). A plurality of patch images 150 having a plurality of gradations (densitys) are formed on the surface of the intermediate transfer belt 8 opposite to the surface on which the toner image is transferred (see FIG. 2). During the balance adjustment operation, a high-density image 160 having a higher density than the patch image 150 is formed (see FIG. 3).

  The IDC sensor 120 is composed of, for example, an optical sensor, and is disposed on the surface opposite to the surface on which the photosensitive drum 1 and the like of the intermediate transfer belt 8 are disposed. The IDC sensor 120 irradiates light on the surface of the intermediate transfer belt 8 during image correction operation or balance adjustment operation, and detects the amount of reflected light (toner adhesion amount) reflected on the surface. Depending on the density of the toner image on the intermediate transfer belt 8 detected by the IDC sensor 120, the light amount (laser power, etc.) is controlled by the exposure unit 3, the development bias voltage in the development unit 4 is controlled, and the like. Correction etc. are performed. Details of the IDC sensor 120 will be described later.

  The paper feed unit 20 includes a plurality of paper feed trays 20A and 20B that accommodate paper sizes such as A3 and A4. The paper M transported from the paper feed trays 20 </ b> A and 20 </ b> B by the transport rollers 22, 24, 26, 28 and the like is transported to the registration roller 32 via the loop creation roller 30. Note that the number of paper feed trays is not limited to three. In addition, a single or a plurality of large capacity sheet feeding devices capable of accommodating a large capacity sheet M may be connected as necessary.

  The registration roller 32 has a driving roller and a driven roller, and corrects skew of the paper M by forming a loop when the leading edge of the paper M is abutted by the loop creation roller 30. The sheet M is conveyed to the secondary transfer unit 34 at a predetermined timing. In the secondary transfer unit 34, the color image transferred to the image forming position of the intermediate transfer belt 8 is collectively transferred onto the surface of the paper M conveyed from the paper supply unit 20 (secondary transfer). The sheet M that has been secondarily transferred is conveyed to the fixing unit 44.

  The fixing unit 44 is provided downstream of the secondary transfer unit 34 in the paper conveyance direction, and includes a pressure roller and a heating roller. The fixing unit 44 fixes the toner image on the surface of the paper M to the paper M by performing pressure and heat treatment on the paper M on which the toner image is transferred by the secondary transfer unit 34.

  On the downstream side of the fixing unit 44 in the sheet conveyance direction, a conveyance path switching unit 48 for switching the conveyance path of the sheet M to the discharge path side or the ADU 60 side is provided. The conveyance path switching unit 48 includes, for example, a solenoid and a motor, and performs conveyance path switching control based on a selected printing mode (single-sided printing mode, double-sided printing mode).

  The paper M on which single-sided printing has been completed in the single-sided printing mode or the paper M on which double-sided printing has been completed in the double-sided printing mode is subjected to a fixing process in the fixing unit 44 and then is more in the paper transport direction than the fixing unit 44. The paper is discharged onto a paper discharge tray by a paper discharge roller 46 provided on the downstream side.

  Further, when the paper M is fed again to the image forming unit 10 in the duplex printing mode, the paper M on which the image is formed on the front side is transported to the ADU 60 via the transport path switching unit 48. The sheet M transported to the ADU 60 is transported to the switchback path via the transport roller 62 and the like. In the switchback path, the reverse rotation control of the ADU roller 64 causes the trailing edge of the sheet M to be conveyed to the U-turn path section, and the sheet is transferred to the registration roller 32 by the transport rollers 66 and 68 provided in the U-turn path section. The paper is fed again in a state where M is turned upside down. The paper M re-fed to the registration roller 32 is subjected to the same image forming process as that on the front side of the paper M. The sheet M on which the image has been transferred to the back surface by the image forming unit 10 is subjected to a fixing process by the fixing unit 44, and then is discharged onto the paper discharge tray via the conveyance path switching unit 48 and the paper discharge roller 46.

[Patch image configuration example]
Next, the patch image 150 formed on the intermediate transfer belt 8 during the image correction operation will be described. FIG. 2 shows an example of the configuration of the patch image 150 formed on the intermediate transfer belt 8 at the time of image operation correction. As shown in FIG. 2, a plurality of patch images 150 </ b> A to 150 </ b> E correspond to (oppose) the IDC sensor 120 on the surface of the intermediate transfer belt 8 opposite to the surface on which the photosensitive drum 1 and the like are disposed. And along the belt rotation direction D1.

  The plurality of patch images 150A to 150E are formed with different gradation patterns with different development bias voltages. For example, the patch image 150A is formed so that the toner density (toner adhesion amount) becomes the highest, and the toner density decreases toward the patch images 150B, 150C,. For the patch image 150, for example, a dither pattern can be used.

[Configuration example of high density image]
Next, the high density image 160 formed on the intermediate transfer belt 8 during the balance adjustment operation will be described. FIG. 3 shows an example of the configuration of the high density image 160 formed on the intermediate transfer belt 8 during the balance adjustment operation. As shown in FIG. 3, a high density image 160 is formed at a position corresponding to (opposed to) the IDC sensor 120 on the surface of the intermediate transfer belt 8 opposite to the surface on which the photosensitive drum 1 and the like are disposed.

  The high density image 160 is formed so as to have a density higher than the density of the patch image 150A having the highest toner density among the patch images 150 formed on the intermediate transfer belt 8 at the time of image operation correction. Thereby, the surface of the intermediate transfer belt 8 can be completely covered with the toner. In this example, an example in which a single high-density image 160 is formed on the intermediate transfer belt 8 has been described. However, a plurality of high-density images 160 such as a patch image 150 may be formed. If a plurality of high density images 160 are formed, the balance adjustment operation can be performed a plurality of times, so that the accuracy of the balance adjustment operation can be increased.

[Configuration example of IDC sensor]
Next, a configuration example of the IDC sensor 120 will be described. FIG. 4 shows an example of the configuration of the IDC sensor 120. As shown in FIG. 4, the IDC sensor 120 includes a light emitting unit 122, a polarizing plate 124, and an S wave light receiving unit 126 on the light emitting side, and a P wave light receiving unit 130, an S wave light receiving unit 140, and a polarizing plate 128 on the light receiving side. It has.

  First, the light emission side will be described. The light emitting unit 122 is composed of, for example, a light emitting diode that is a light emitting element, and obliquely strikes the surface of the intermediate transfer belt 8 through the polarizing plate 124 using infrared light or visible light having an intensity corresponding to the input current as irradiation light. Irradiate from. The polarizing plate 124 separates the P wave and the S wave included in the irradiation light emitted from the light emitting unit 122, allows the P wave to pass (straight forward) among the separated irradiation light, and transmits the S wave to the S wave light receiving unit 126. Reflect to the side. In this manner, the intermediate transfer belt 8 is irradiated with a single polarized light. In this example, the case where the P wave is irradiated as a single polarized light is described, but an S wave may be used as long as it is a single polarized light. The S wave light receiving unit 126 is composed of, for example, a photodiode as a light receiving element, and receives the S wave component reflected (polarized) by the polarizing plate 124.

  Next, the light receiving side will be described. Irradiated light emitted from the light emitting unit 122 via the polarizing plate 124 is reflected on a predetermined image formed on the intermediate transfer belt 8. FIG. 4 illustrates a case where a high density image 160 used during the balance adjustment operation is formed as an image. The polarizing plate 128 separates the P wave and the S wave of the reflected light reflected on the predetermined image of the intermediate transfer belt 8, passes the P wave out of the separated irradiation light, and transmits the S wave to the S wave receiving unit. Reflected to the 140 side. The P-wave light receiving unit 130 is composed of, for example, a photodiode that is a light-receiving element, and receives the P-wave component that has passed through the polarizing plate 128. The S wave light receiving unit 140 is composed of, for example, a photodiode that is a light receiving element, and receives the S wave component reflected by the polarizing plate 128. The P-wave light receiving unit 130 constitutes an example of a first light receiving unit, and the S-wave light receiving unit 140 constitutes an example of a second light receiving unit.

[Example of relationship between toner adhesion amount and P wave / S wave]
Next, an example of the relationship between the toner adhesion amount of the image transferred onto the intermediate transfer belt 8 and the light (P wave / S wave) reflected from the image or the like will be described. FIG. 5 shows an example of the ratio between the toner adhesion amount and the P wave / S wave. As shown in FIG. 5, when the toner adhesion amount on the intermediate transfer belt 8 is small or when there is no toner, the irradiated P wave component light is specularly reflected on the belt surface, so that it reflects as the P wave component. All are received by the P-wave light receiving unit 130.

  FIG. 6 shows a case where there is no toner on the intermediate transfer belt 8. As shown in FIG. 6, when there is no toner on the intermediate transfer belt 8, the intermediate transfer belt 8 has a beautiful mirror surface, so that the reflected light reflected on the surface of the intermediate transfer belt 8 changes its polarization axis. Without being performed, the light is received by the P-wave light receiving unit 130 as it is. Therefore, in this case, since the P wave component is increased, the value of the P wave / S wave is also increased.

  On the other hand, when the toner adhesion amount on the intermediate transfer belt 8 is large, that is, when the density of the toner adhesion amount is high, the irradiated light is irregularly reflected on the image and the P wave component and the S wave component are separated. Since the random light is included, the value of the P wave / S wave is reduced by reducing the P wave component. That is, the higher the density of the toner image formed on the intermediate transfer belt 8, the closer the P wave and S wave contained in the reflected light approach the same amount.

Here, the patch image 150A (see FIG. 2) having the highest density among the patch images 150 formed on the intermediate transfer belt 8 during the image correction operation has a toner adhesion amount of about 4.0 g / second as shown in FIG. It has become a m ^2. For example, by setting the developing bias to −393V, the charging voltage to −601V, and the laser output (light intensity) to 131, a patch image 150A having a toner adhesion amount of 4.0 g / m ² can be obtained. Can be formed.

In contrast, the high density image 160 (see FIG. 3) formed on the intermediate transfer belt 8 during the balance adjustment operation has a toner adhesion amount of 7.0 g / m ² or more, and is formed during the image correction operation. The toner density is higher than that of the highest density patch image 150A. For example, the development bias is set to -700 V, the charging voltage is set to -908 V, and the laser output (light intensity) is set to twice that of the image correction operation (244), so that 8.5 g / m ² A high-density image 160 with a toner adhesion amount can be formed. Thus, if the toner adhesion amount is about 7.0 g / m ² or more, the ratio of P wave to S wave is 1 (PS = 0) as shown in FIG. Even if the toner adhesion amount cannot be accurately controlled, the balance adjustment operation can be performed.

[Block Configuration Example of Image Forming Apparatus]
Next, a block configuration example of the image forming apparatus 100 according to the present invention will be described. FIG. 7 shows an example of a block configuration of the image forming apparatus 100. The image forming apparatus 100 includes a control unit 50 that controls the overall operation of the apparatus. The control unit 50 includes a CPU (Central Processing Unit) 52, a ROM (Read Only Memory) 54 that stores control software and data, and a RAM 56 (Random Access Memory) that constitutes a work area of the CPU 52. ing. The CPU 52 executes the balance adjustment operation, the image correction operation, and the image forming operation by developing the software and data read from the ROM 54 on the RAM 56 and starting the software to control each part of the image forming apparatus 100.

  An IDC sensor 120, an operation display unit 70, a memory unit 72, and an image forming unit 10 are connected to the control unit 50, respectively. FIG. 8 shows an example of a circuit configuration on the light receiving unit side of the IDC sensor 120. The IDC sensor 120 includes a light emitting unit 122, a P wave light receiving unit 130, and an S wave light receiving unit 140. As shown in FIGS. 7 and 8, the light emitting unit 122 emits light toward the intermediate transfer belt 8 based on the control of the control unit 50 during the balance adjustment operation and the image correction operation.

  As shown in FIG. 8, the P-wave light receiving unit 130 includes a photodiode 132 and a differential amplifier circuit 134. The photodiode 132 receives the P wave component of the reflected light reflected by the predetermined image on the intermediate transfer belt 8, converts the received P wave into an electric signal, and outputs the electric signal to the differential amplifier circuit 134. The differential amplifier circuit 134 amplifies the electrical signal input from the photodiode 132 and outputs an output signal to the control unit 50. In this example, a P-wave signal obtained during the balance adjustment operation is called an output signal Pbal, and a P-wave signal obtained during the image correction operation is called an output signal P.

  As shown in FIG. 8, the S-wave light receiving unit 140 includes a photodiode 142 and a differential amplifier circuit 144. The photodiode 142 receives the S wave component of the reflected light reflected by the predetermined image on the intermediate transfer belt 8, converts the received S wave into an electric signal, and outputs the electric signal to the differential amplifier circuit 144. The differential amplifier circuit 144 amplifies the electrical signal input from the photodiode 142 and outputs an output signal to the control unit 50. In this example, the S wave signal obtained during the balance adjustment operation is referred to as an output signal Sbal, and the S wave signal obtained during the image correction operation is referred to as an output signal S. In addition, since a well-known differential amplifier circuit is used for the differential amplifier circuits 134 and 144, detailed description is omitted.

  During the balance adjustment operation, the control unit 50 divides the output signal Pbal input from the P-wave light receiving unit 130 and the output signal Sbal input from the S-wave light receiving unit 140, and uses the value obtained by this division as the S-wave. The correction value (correction coefficient) for adjusting the sensitivity of the light receiving unit 140 is stored in the memory unit 72. Further, the control unit 50 adjusts the sensitivity of the S wave light receiving unit 140 by multiplying the output signal S output from the S wave light receiving unit 140 by the correction value calculated during the balance adjustment operation during the image correction operation, and then P Gamma correction (density correction) is performed by calculating the difference between the output signal P output from the wave light receiving unit 130 and the output signal S of the S wave light receiving unit 140 that has been subjected to sensitivity adjustment.

  The operation display unit 70 is composed of a touch panel in which a display unit composed of a liquid crystal display or the like and an input unit composed of a capacitance method, a resistance film method, or the like are combined. Hard keys including numeric keys and a start button are provided on the periphery of the touch panel. The operation display unit 0 displays, for example, an operation screen for selecting a balance adjustment operation or selecting an image forming condition such as a paper size or a paper type, or accepts input information selected by the user on this operation screen and operates it. The signal is supplied to the control unit 50.

  The memory unit 72 is configured by, for example, a nonvolatile semiconductor memory, an HDD (Hard Disk Drive), or the like. In the memory unit 72, for example, a correction value for adjusting the sensitivity of the light receiving unit of the IDC sensor 120 calculated during the balance adjustment operation, and a reference value (threshold value) of each image patch used for density determination during the image correction operation. Is stored.

  The image forming unit 10 includes an exposure unit 3 and a developing unit 4. When the exposure unit 3 forms the high density image 160 during the balance adjustment operation, the exposure unit 3 outputs a laser under the condition of a higher laser power than that during the image correction operation under the control of the control unit 50. When the developing unit 4 forms a high density image 160 during the balance adjustment operation, the developing bias between the developing unit 4 and the photosensitive drum 1 under the condition of a higher developing bias voltage than that during the image correction operation is controlled under the control of the control unit 50. Apply voltage.

[Example of operation during balance adjustment]
Next, an operation example of the image forming apparatus 100 during the balance adjustment operation according to the present invention will be described. FIG. 9 is a flowchart illustrating an example of the operation of the image forming apparatus 100 during the balance adjustment operation. The balance adjustment operation is executed, for example, when the image forming apparatus 100 is shipped or when the IDC sensor 120 is replaced. The balance adjustment operation can be selected on the display screen of the operation display unit 70, or can be automatically selected and executed by determining that the IDC sensor 120 has been replaced, for example.

  As shown in FIG. 9, when the balance adjustment operation is selected in step S100, the control unit 50 performs baseline correction. In the base line correction, light is irradiated onto a region where the toner is not attached (hereinafter referred to as a base line) on the intermediate transfer belt 8, and the reflected light reflected on the base line is received by the P wave light receiving unit 130 or the like. Based on the characteristics of the entire circumference of the baseline according to the result of receiving the reflected light of the IDC sensor 120, the control unit 50 controls the light amount of the light emitting unit 122 so that the amplitude of the output voltage of the IDC sensor 120 is within a predetermined range. Adjust to a constant. Further, the toner adhesion amount may be kept constant by appropriately variably controlling the peripheral speed ratio of the developing unit.

When the baseline correction is completed, the image forming unit 10 transfers the high density image 160 (highly adhered toner) onto the intermediate transfer belt 8 based on the control of the control unit 50 in step S110. As described above, the toner adhesion amount of the high density image is, for example, 7.0 g / m ² or more. When the toner adhesion amount is less than 7.0 g / m ² , the P wave and S wave of the reflected light (random light) irradiated from the IDC sensor 120 and reflected by the high density image 160 on the intermediate transfer belt 8 This is because the component ratio is not necessarily 1: 1 (PS = 0). In order to form the high density image 160, the control unit 50 controls, for example, the operation of the developing unit 4 so as to increase the developing bias voltage, or the operation of the exposing unit 3 so that the laser power during exposure is increased, The operation of the charging unit is controlled so that the charging voltage of the photosensitive drum 1 is increased.

  The above-described high density image 160 is formed by controlling three image forming conditions of developing bias, charging voltage, and laser output, but the high density image 160 is controlled by controlling at least one or more image forming conditions. May be formed.

When the transfer of the high density image is completed, in step S120, the control unit 50 determines whether or not a certain period has elapsed since the image forming apparatus 100 was shipped. This is due to the use of the developing unit 4 and the exposure unit 3 for a certain period of time, which deteriorates with time. This is because it may not be possible to completely cover 8. That is, when the developing unit 4 or the like is deteriorated with time, a high density image of 7.0 g / m ² or more may not be formed. Examples of the case where the balance adjustment operation is performed when a certain period of time has elapsed from the time of shipment include a case where the IDC sensor 120 is replaced after shipment. If the control unit 50 determines that the certain period of time has elapsed from the time of shipment, the control unit 50 proceeds to step S130. On the other hand, if the image forming apparatus 100 determines that a certain period has not elapsed since shipment, the process proceeds to step S140.

When a certain period of time has passed since the shipment, the image forming unit 10 forms a high density image 160 formed on the intermediate transfer belt 8 by superimposing a plurality of images in step S130. That is, the high density image 160 is formed by performing an image forming operation a plurality of times and superimposing and laminating a plurality of images. The number of times to superimpose the image may be determined by the control unit 50 in consideration of the elapsed time from the shipment so that the toner adhesion amount of the image is 7.0 g / m ² or more. May be set. At this time, the high-density image 160 can be formed by superimposing a plurality of images made of toner of a single color, or can be formed by superposing a plurality of images made of toner of a plurality of colors. As a result, even if the developing unit 4 or the like deteriorates with time, the intermediate transfer belt 8 can be completely covered with toner, and a highly adhered toner image can be reliably formed.

  When the transfer of the high-density image 160 is completed, the control unit 50 performs a balance adjustment operation in step S140. In the balance adjustment operation, light is applied to the high density image 160 formed on the intermediate transfer belt 8. The P wave light receiving unit 130 receives the P wave among the reflected light reflected on the high density image 160 and outputs an output signal Pbal to the control unit 50. The S wave light receiving unit 140 receives the S wave of the reflected light reflected on the high density image 160 and outputs an output signal Sbal to the control unit 50.

The control unit 50 outputs the P wave so that the output of the P wave output signal Pbal input from the P wave light receiving unit 130 is the same as the output of the S wave output signal Sbal input from the S wave light receiving unit 140. The sensitivity of the light receiving unit 130 and the S wave light receiving unit 140 is adjusted. Specifically, the sensitivity of the P-wave light receiving unit 130 and the S-wave light receiving unit 140 is adjusted so that the difference between the P-wave output signal P and the S-wave output signal S becomes 0 during the image correction operation. The correction value for this is calculated. For example, when adjusting the sensitivity of the S wave light receiving unit 140, a correction value for adjusting the sensitivity of the S wave light receiving unit 140 is calculated by the following equation (1).
Correction value = output signal Pbal / output signal Sbal (1)

  After calculating the correction value by the above equation (1), the control unit 50 stores the calculated correction value in the memory unit 72. Such a series of operations is performed when the image forming apparatus 100 is shipped or when the IDC sensor 120 is replaced. In this example, the case where the sensitivity of the S wave light receiving unit 140 is adjusted has been described. However, the sensitivity on the P wave light receiving unit 130 side may be adjusted, or the P wave light receiving unit 130 side and the S wave light receiving unit 140 may be adjusted. You can also adjust both sensitivities.

[Operation example during image correction]
Next, an operation example of the image forming apparatus 100 during the image correction operation according to the present invention will be described. FIG. 10 is a flowchart illustrating an example of the operation of the image forming apparatus 100 in the image correction operation. The timing for executing the image correction operation includes a preset timing and a timing forcibly performed by a user or a service person. The former includes, for example, when the image forming apparatus 100 is turned on, when returning from the energy saving mode, when the temperature change or temperature change in the apparatus after the previous image correction operation has exceeded each threshold, or Or when the cumulative number of printed sheets exceeds a threshold.

  As shown in FIG. 10, in step S200, the control unit 50 performs baseline correction. In the base line correction, the base line on the intermediate transfer belt 8 is irradiated with light, and the reflected light reflected on the base line is received by the P wave light receiving unit 130 or the like. Based on the characteristics of the entire circumference of the baseline according to the result of receiving the reflected light of the IDC sensor 120, the control unit 50 controls the light amount of the light emitting unit 122 so that the amplitude of the output voltage of the IDC sensor 120 is within a predetermined range. Adjust to a constant.

  When the baseline correction is completed, the image forming unit 10 creates a patch image 150 including a plurality of gradation patterns on the intermediate transfer belt 8 based on the control of the control unit 50 in step S210. The control unit 50 sequentially sets the developing unit 4 of the image forming unit 10 to different developing bias voltages, and each of the plurality of patch images 150A to 150E having different densities based on the set different developing bias voltages on the intermediate transfer belt 8. (See FIG. 2).

  When the creation of the patch image 150 is completed, the control unit 50 executes gamma correction in step S220. In the gamma correction, a P wave is applied to the patch image 150 formed on the intermediate transfer belt 8 via the polarizing plate 124. The P-wave light receiving unit 130 receives a P-wave among the reflected light reflected on the patch image 150 and outputs an output signal P to the control unit 50. The S wave light receiving unit 140 receives the S wave of the reflected light reflected on the patch image 150 and outputs an output signal S to the control unit 50.

Subsequently, the control unit 50 reads out a correction value for correcting the sensitivity of the S wave light receiving unit 140 calculated during the balance adjustment operation from the memory unit 72, and outputs the output signal P and S wave received from the P wave light receiving unit 130. Using the output signal S acquired from the unit 140 and the correction value (Pbal / Sbal), density correction is executed by the following equation (2).
Output signal P-Output signal S × (Pbal / Sbal) (2)

  As shown in the above equation (2), first, the output signal S acquired from the S-wave light receiving unit 140 is multiplied by the correction value (Pbal / Sbal), so that the photodiode 142 and the polarizing plate 128 of the S-wave light receiving unit 140 are obtained. A balance error caused by variations due to the above is corrected. Next, the density state of the patch image 150 formed on the intermediate transfer belt 8 is acquired by obtaining the difference between the output signal P and the output signal S after balance adjustment. The control unit 50 calculates a density correction value based on the acquired density state of the patch image 150 and a reference value set in advance for each patch image 150, and based on the calculated density correction value, the charging voltage, Adjust the development bias voltage, the amount of laser power, etc. The image correction operation is performed by such a series of processes.

  As described above, according to the present embodiment, the sensitivity of the P wave light receiving unit 130 and the S wave light receiving unit 140 is adjusted using the toner image so that the P wave output and the S wave output are the same. Therefore, even after the image forming apparatus 100 is shipped, the balance of the IDC sensor 120 can be adjusted in the apparatus. That is, the balance can be adjusted according to the conditions in the apparatus. This eliminates the need for adjustment parts such as a film as compared with the case of external adjustment using a film or the like similar to the toner, so that the cost can be reduced. In addition, since the balance adjustment operation can be performed using actual toner or the like, the adjustment accuracy can be made higher than that of the external adjustment. Furthermore, according to the present embodiment, for example, even if the IDC sensor 120 is replaced after the image forming apparatus 100 is shipped and the image forming conditions change, the balance of the IDC sensor 120 is adjusted again in the apparatus. Can do.

  Further, according to the present embodiment, when an image is formed on the intermediate transfer belt 8 during the balance adjustment operation, the laser power of the exposure unit 3 is increased or the development bias voltage of the development unit 4 is increased. Therefore, a high density image 160 having a high toner density (toner adhesion amount) can be reliably formed on the intermediate transfer belt 8. In addition, when a certain period of time has elapsed since the shipment of the image forming apparatus 100, the images are superimposed several times or images of a plurality of colors are superimposed in consideration of deterioration over time of the exposure unit 3 and the like. Thus, the high-density image 160 having a high toner density (toner adhesion amount) can be reliably formed on the intermediate transfer belt 8. Thereby, the balance adjustment operation can be performed with high accuracy.

  It should be noted that the technical scope of the present invention is not limited to the above-described embodiments, and includes those in which various modifications are made to the above-described embodiments without departing from the spirit of the present invention. For example, in the above-described embodiment, the balance adjustment operation is performed when the device is shipped or when the IDC sensor 120 is replaced. However, the present invention is not limited to this. The balance adjustment operation may be performed after the shipment of the apparatus and when the temperature change in the image forming apparatus 100 exceeds a certain level. This is because the characteristics of each component may change due to temperature changes. In this case, for example, a temperature sensor is installed in the image forming apparatus 100, and it is determined whether or not to execute the balance adjustment operation based on the detection result of the temperature sensor.

  Further, the image carrier to be subjected to density control is not limited to the intermediate transfer belt 8 as described above, and may be the photosensitive drum 1 as long as the toner images are superimposed. .

8 Intermediate transfer belt (image carrier)
DESCRIPTION OF SYMBOLS 10 Image forming part 50 Control part 100 Image forming apparatus 120 IDC sensor (detection part)
130 P-wave light receiving part (first light receiving part)
140 S wave receiver (second receiver)
160 High density image

Claims (6)

An image forming unit that forms an image on the image carrier;
A detection unit that irradiates an image on the image carrier formed by the image forming unit with P-wave or S-wave light and detects reflected light reflected by the image;
An image correction operation for correcting the density of the image based on the reflected light detected by the detection unit, and a control unit for performing a balance adjustment operation for adjusting the sensitivity of the detection unit,
The detector is
A first light receiving unit that receives a P wave among the reflected light reflected by the image;
A second light receiving unit that receives S waves of the reflected light reflected by the image,
The controller is
During the balance adjustment operation, the image forming unit is controlled so as to form a high density image having a higher density than the highest density image formed on the image carrier during the image correction operation,
The P wave reflected by the high density image formed on the image carrier and received by the first light receiving unit, and the S wave reflected by the high density image and received by the second light receiving unit. An image forming apparatus, wherein the sensitivity of at least one of the first light receiving unit and the second light receiving unit is adjusted so that the level of the wave is the same. The image forming apparatus according to claim 1, wherein the image forming unit includes a developing unit, and forms the high density image under a condition in which a developing bias voltage of the developing unit is increased. The image forming apparatus according to claim 1, wherein the image forming unit includes an exposure unit, and forms the high-density image under a condition in which a laser power of the exposure unit is increased. The image forming apparatus according to claim 1, wherein the image forming unit forms the high-density image by superimposing a plurality of images. The image forming apparatus according to claim 1, wherein the image forming unit forms the high-density image by superimposing two or more color images. The image forming unit forms the high-density image by superposing a plurality of images in addition to setting a condition for increasing the developing bias voltage when the developing unit is used for a certain period of time. The image forming apparatus according to claim 2.