JP2017111376A - Image formation device and image density adjustment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device capable of making real density of a print image proper density regardless of a print condition in a previous period.SOLUTION: An image formation device comprises: an image formation part for forming a developer image on a medium; a printing counter (320) which serves as a print number detection part for detecting a print number (J); a dot counter (330) which serves as a printing rate detection part for detecting a printing rate (d); an environment detection part (340) for detecting an environment detection value which contains at least one of temperature (T) and humidity (h); a density detection part (350) for detecting density of the developer image formed by the image formation part, and outputting a density detection value (G) indicating the detected density; and a control part (301) for controlling the whole device. The control part (301) corrects the density detection value (G) output from the density detection part (350) according to the print number (J), the printing rate (d), and the environment detection value (T, h).SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus using an electrophotographic process and an image density adjusting method in the image forming apparatus.

  In general, an image forming apparatus using an electrophotographic process has a function of adjusting the density of a printed image (developer image) (see, for example, Patent Document 1). In the apparatus of Patent Document 1, when adjusting the image density, a reference pattern for density detection is formed on the medium, the density of the reference pattern is detected by the density detection unit, and the density detection value generated by the density detection unit is determined in advance. A difference from a target value (reference value) indicating the obtained target density is calculated, and based on this difference, either the developing bias voltage (developing energy) of the developing roller or the exposure amount (exposure energy) of the exposure unit is adjusted. .

JP 2011-13397 A (for example, paragraphs 0047 to 0052)

  However, in an image forming apparatus using an electrophotographic process, the reference pattern may be different depending on printing conditions in a period before the present such as the number of printed sheets, a printing rate (printing duty), and a printing environment (for example, temperature and humidity). In some cases, the density is not formed at an appropriate density (for example, a reference pattern having a density higher than the appropriate value is formed). If the development bias voltage or the exposure light amount is adjusted based on the difference between the density detection value for the reference pattern that is not appropriate and a predetermined target value, the actual density of the printed image based on the input image data deviates from the appropriate density. There was a thing.

  The present invention has been made to solve the above-described problems of the prior art, and an image forming apparatus capable of setting an actual density of a printed image to an appropriate density regardless of printing conditions in a period prior to the present, and An object is to provide an image density adjustment method.

  An image forming apparatus according to the present invention is an image forming apparatus that prints an image by an electrophotographic process, an image forming unit that forms a developer image on a medium, a print number detection unit that detects the number of prints, and a print A print rate detection unit for detecting a print rate in the printer, an environment detection unit for detecting an environment detection value including at least one of temperature and humidity, and a density of the developer image formed by the image forming unit. A density detection unit that outputs a density detection value indicating the detected density, and a control unit that controls the entire apparatus, the control unit according to the number of printed sheets, the printing rate, and the environment detection value The density detection value output from the density detection unit is corrected.

  An image density adjustment method according to the present invention is an image density adjustment method in an image forming apparatus including an image forming unit that forms an image on a medium by an electrophotographic process, and a density detection unit that detects the density of the image. The image forming unit forms at least one of a step of forming a reference pattern made of a developer on the medium (133), a step of acquiring the number of printed sheets, a step of detecting a printing rate, and temperature and humidity. An environment detection value including: a step in which the density detection unit detects a density of the reference pattern and outputs a density detection value indicating the detected density; the number of printed sheets; the print rate; and Correcting the density detection value output from the density detection unit according to the environment detection value; and a correction density generated by correcting the density detection value Based on the detection value, characterized by a step of adjusting the density of the image formed by the image forming unit.

  According to the present invention, by appropriately correcting the density detection value output from the density detection unit in accordance with the printing conditions in the period prior to the present, the print image can be printed regardless of the printing conditions in the period prior to the present. The actual density can be set to an appropriate density.

1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram illustrating an enlarged image forming unit in FIG. 1. (A) is a figure which shows the density | concentration detection part (state in which the sensor shutter was opened) of FIG. 1, (b) is a figure which shows the density | concentration detection part (state in which the sensor shutter was closed). It is a circuit diagram which shows the density | concentration detection part of FIG. 2 is a block diagram schematically showing a configuration of a control system of the image forming apparatus according to the present embodiment. FIG. It is a diagram showing an example of a patch pattern formed on a transfer belt of the image forming apparatus according to the present embodiment. It is a figure which shows the relationship (gamma curve about the printing image of black toner) with the density | concentration detection value which is a density | concentration detection value output from a density | concentration detection part, and the actual density | concentration (OD value) measured with the spectral densitometer. It is a figure which shows the relationship (gamma curve about the printing image of a magenta toner) with the density | concentration detection value which is a density | concentration detection value output from a density | concentration detection part, and the actual density | concentration (OD value) measured with the spectral densitometer. It is a figure which shows the change of the relationship (gamma curve about the printing image of a magenta toner) with a density detection value and an actual density (OD value) by the number of printed sheets (after leaving and after mass printing). It is a figure which shows the change of the relationship (gamma curve about the printing image of a magenta toner) with a density detected value and an actual density (OD value) by printing duty (low duty, middle duty, high duty). It is a figure which shows the change of the relationship (gamma curve about the print image of a magenta toner) of a density detected value and an actual density (OD value) by printing environment (HH environment, NN environment, LL environment). 6 is a flowchart showing a calculation process of a print sheet number coefficient (Px) in the image forming apparatus according to the present embodiment. FIG. 4 is a diagram illustrating an average print duty coefficient (Dx) of each color for each average print duty (d) in the image forming apparatus according to the present embodiment in a tabular format. FIG. 3 is a table showing a relationship between an environmental detection value (temperature T and humidity h) and an environmental value (Fx) around or inside the image forming apparatus according to the present embodiment. FIG. 6 is a diagram illustrating an environmental coefficient (Ex) of each color for each environmental value (Fx) in the image forming apparatus according to the present embodiment in a table format. FIG. 5 is a diagram showing a correction value (B) of a γ curve correction coefficient (A) for each color for each density detection value in the image forming apparatus according to the present embodiment in a table format. FIG. 6 is a table showing γ curve correction coefficients (A100, A85, A70, A50, A30, A15) corrected for each color for each density detection value in the image forming apparatus according to the present embodiment in a table format. It is a figure which shows correction | amendment of the gamma curve using the corrected gamma curve correction coefficient (A100, A85, A70, A50, A30, A15) in the image forming apparatus which concerns on this Embodiment. It is a figure which shows the (gamma) curve correction coefficient (A) by which each color was correct | amended for every density | concentration detection value in the image forming apparatus of a comparative example in a table format. It is a figure which shows correction | amendment of the gamma curve of the comparative example using the gamma curve correction coefficient (A) of FIG. 5 is a flowchart showing a density correction operation in the image forming apparatus according to the present embodiment.

<1> Image forming apparatus 100
Hereinafter, an image forming apparatus 100 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 5. The image forming apparatus 100 is an apparatus that can perform the image density adjustment method according to the embodiment of the present invention.

  FIG. 1 is a schematic configuration diagram showing an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 is a tandem direct transfer printer. As shown in FIG. 1, the image forming apparatus 100 has image forming units 110K, 110Y, 110M, and 110C that form a developer (toner) image on a recording medium 10 such as paper by an electrophotographic process as a main configuration. A medium supply unit (paper feeding unit) 120 that supplies the recording medium 10 to the image forming units 110K, 110Y, 110M, and 110C, a conveyance unit (transfer belt unit) 130 that conveys the recording medium 10, and an image forming unit 110K. , 110Y, 110M, and 110C, a transfer roller 140 serving as a transfer portion, and a fixing device 150 serving as a fixing device that fixes the toner image transferred onto the recording medium 10 onto the recording medium 10. And a discharge roller pair 125 as a medium discharge unit for discharging the recording medium 10 that has passed through the fixing device 150 to the outside of the image forming apparatus 100. Having. 1 shows a printer having four image forming units 110K, 110Y, 110M, and 110C, the number of image forming units that the image forming apparatus 100 has is three or less, or five or more. Also good. FIG. 1 shows a case where the image forming apparatus 100 is a color printer. However, the present invention is an apparatus that forms an image on a recording medium by an electrophotographic process. The present invention can also be applied to a monochrome printer having one.

  As shown in FIG. 1, the medium supply unit 120 includes a medium cassette (paper cassette) 121, a paper feed roller (hopping roller) 122 that feeds the recording media 10 loaded in the medium cassette 121 one by one, a medium A roller 123 that transports the recording medium 10 fed out from the cassette 121 and a roller pair 124 that transports the recording medium 10 toward the image forming units 110K, 110Y, 110M, and 110C are provided.

  The image forming units 110K, 110Y, 110M, and 110C display a black (K) toner image, a yellow (Y) toner image, a magenta (M) toner image, and a cyan (C) toner image on the recording medium 10. Form each one. The image forming units 110K, 110Y, 110M, and 110C are arranged along the medium conveyance path from the upstream side to the downstream side in the medium conveyance direction (the arrow direction from right to left in FIG. 1). The image forming units 110K, 110Y, 110M, and 110C have image forming units 112K, 112Y, 112M, and 112C for respective colors that are detachably formed. The image forming units 112K, 112Y, 112M, and 112C arranged in series are provided corresponding to the respective colors of the image forming units 110K, 110Y, 110M, and 110C, and the image forming unit 112C forms an image with cyan toner, The image forming unit 112M forms an image with magenta toner, the image forming unit 112Y forms an image with yellow toner, and the image forming unit 112K forms an image with black toner. The image forming units 112K, 112Y, 112M, and 112C basically have the same structure except that the toner colors are different.

  The image forming units 110K, 110Y, 110M, and 110C have exposure devices (exposure units) 111K, 111Y, 111M, and 111C as exposure optical units for the respective colors, respectively.

  Each of the image forming units 112K, 112Y, 112M, and 112C uniformly charges the photosensitive drum 113 as an image carrier that is rotatably supported around the rotation center axis, and the surface of the photosensitive drum 113. An electrostatic latent image is formed on the surface of the photosensitive drum 113 by exposure by a charging roller 114 as a charging member and an exposure device (any one of 111K, 111Y, 111M, and 111C), and then toner is applied to the surface of the photosensitive drum 113. And a developing device 115 for forming a toner image corresponding to the electrostatic latent image, and a cleaning blade 119a (shown in FIG. 2) as a cleaning member for the surface of the photosensitive drum 113.

  FIG. 2 is a schematic configuration diagram illustrating the image forming unit 110C of FIG. 1 in an enlarged manner. The image forming units 110M, 110Y, and 110K basically have the same structure as the image forming unit 110C. As shown in FIG. 2, the cleaning blade 119a scrapes off the toner remaining on the surface of the rotating photosensitive drum 113 and the residue such as the external additive peeled off from the toner, and puts the residue into the recovery container 119b. to recover.

  As shown in FIG. 2, the developing device 115 includes a toner storage portion as a developer storage portion that forms a developer storage space for storing toner, and a developer carrier that supplies toner to the surface of the photosensitive drum 113. A developing roller 116 as a developer, a supply roller 117 as a developer supplying member for supplying the toner stored in the toner storage portion to the developing roller 116, and a toner regulating member for regulating the thickness of the toner layer on the surface of the developing roller 116. And a developing blade 118. The image forming apparatus 100 also includes a power supply unit 173 that applies a bias voltage to the developing roller 116, a power supply unit 174 that applies a bias voltage to the supply roller 117, a power supply unit 171 that applies a bias voltage to the charging roller 114, And a power supply unit 172 that applies a bias voltage to the transfer roller 140.

  In the present embodiment, the toner charge amount is about −23 [μC / g] on average, and the toner is negatively charged. Further, a negative bias voltage is applied to the charging roller 114, the developing roller 116, and the supply roller 117. In the present embodiment, for example, a bias voltage of −1000 [V] is applied to the charging roller 114, −200 [V] is applied to the developing roller 116, and −300 [V] is applied to the supply roller 117. .

  Exposure by each of the exposure devices 111K, 111Y, 111M, and 111C is executed on the surface of the uniformly charged photosensitive drum 113 based on image data for printing. Each of the exposure apparatuses 111K, 111Y, 111M, and 111C is an LED head including an LED array in which a plurality of LED (light emitting diode) elements are arranged in the axial direction of the photosensitive drum 113. However, a laser scanning unit having a laser irradiation unit and a polygon mirror (scanning rotary polygon mirror) may be employed as the exposure apparatus instead of the LED head.

  As shown in FIG. 1, the transport unit (transfer belt unit) 130 is driven by the transfer unit (transport belt) 133 that electrostatically attracts and transports the recording medium 10, and is driven by the drive unit to drive the transfer belt 133. A driving roller 131 and a tension roller (driven roller) 132 that forms a pair with the driving roller 131 and stretches the transfer belt 133 are provided.

  As shown in FIG. 1, the transfer roller 140 is disposed to face the photosensitive drum 113 of each of the image forming units 112K, 112Y, 112M, and 112C with the transfer belt 133 interposed therebetween. The developer image (toner image) formed on the surface of the photosensitive drum 113 of each of the image forming units 112K, 112Y, 112M, and 112C by the transfer roller 140 is transported in the arrow direction along the medium transport path. The image is sequentially transferred onto the upper surface of the medium (print medium) 10 to form a color image in which a plurality of toner images are superimposed. Below the transfer belt 133, a movable (open / close) sensor shutter 354, a density detector (density sensor) 350, and a transfer cleaning device 134 are provided. When detecting the density of the print image, the image forming units 112K, 112Y, 112M, and 112C use a toner image of a patch pattern (reference pattern) having a predetermined density on the transfer belt (density adjustment medium) 133. , And the density of the image on the transfer belt 133 is detected by the density detector 350.

  The fixing device 150 includes a pair of rollers 151 and 152 that are pressed against each other. The roller 151 is a heat roller with a built-in heater, and the roller 152 is a pressure roller (backup roller) pressed against the roller 151. The recording medium 10 having an unfixed developer image (toner image) passes between a pair of rollers 151 and 152 of the fixing device 150. At this time, the unfixed toner image is heated and pressurized and fixed on the recording medium 10.

  When forming an image in the image forming apparatus 100 according to the present embodiment, first, the surface of the photosensitive drum 113 is uniformly charged by the charging roller 114 to which a negative voltage is applied. Next, light corresponding to an image to be printed is irradiated onto the photosensitive drum 113 from an LED head as an exposure device, and an electrostatic latent image is formed on the photosensitive drum 113. For example, the toner in the toner container is negatively charged by friction between the developing roller 116 to which a voltage of about −200 [V] is applied and the supply roller 117 to which a voltage of about −300 [V] is applied. Then, the toner is supplied to the developing roller 116 by the potential difference between the developing roller 116 and the supply roller 117 and the physical conveying force of the roller, and the layer pressure of the toner is adjusted by the developing blade 118 and brought into contact with the photosensitive drum 113. The toner in contact with the photosensitive drum 113 receives a force due to the electric field generated by the difference between the potential of the photosensitive drum 113 and the potential of the developing roller 116, and in the exposure region, the toner moves to the photosensitive drum 113 and is not exposed. In the area, the toner remains on the developing roller 116. In this way, development for changing the electrostatic latent image into a visible image is performed.

  Next, the recording medium 10 is conveyed by the transfer belt 133, and when the recording medium 10 passes between the image forming units 110 </ b> K, 110 </ b> Y, 110 </ b> M, and 110 </ b> C and the transfer roller 140, the transfer roller 140 receives the voltage from the voltage control unit 310. A positive bias voltage is applied, and the toner image on the surface of the photosensitive drum 113 is transferred to a medium (the recording medium 10 or the transfer belt 133). The recording medium 10 is conveyed to the fixing device 150 and is sandwiched from both sides by a rotating heat roller, and is pressurized while being heated. The toner constituting the toner image is melted by the heat of the heat roller, and the melted toner is pressurized and penetrates between the fibers of the recording medium 10 to fix the toner image. Thereafter, the recording medium 10 is discharged out of the image forming apparatus 100 by the discharge roller pair 125. The toner remaining on the photosensitive drum 113 after the transfer process is scraped off and collected by the cleaning blade 119a.

<< 2 >> Concentration detector 350
3A and 3B are schematic configuration diagrams illustrating the density detection unit 350 of the image forming apparatus 100 according to the present embodiment. FIG. 3A is a diagram showing a state where the sensor shutter 354 is opened, and FIG. 3B is a diagram showing a state where the sensor shutter 354 is closed. The density detection unit 350 includes a light emitting element 351 that emits light, a light receiving element 352 that receives specularly reflected light (a black sensor), and a light receiving element 353 that receives diffusely reflected light (a color sensor). Yes. The color sensor is a sensor for cyan, magenta, and yellow other than black. The light emitting element 351 is, for example, an LED. When the light emitting element 351 emits light, regular reflection light from the transfer belt 133 is received by the light receiving element 352 (black sensor), and diffuse reflection light from the transfer belt 133 is received by the light receiving element 353 (color sensor).

  The density detector 350 is provided so as to face the transfer belt 133, and the light emitting element 351 irradiates the toner image formed on the transfer belt 133 with light (for example, infrared rays) and reflects the reflected light. The toner density on the transfer belt 133 is detected by the light receiving elements 352 and 353.

  As shown in FIG. 3A, when the sensor shutter 354 is in the open state, the density detection unit 350 causes the light emitting element 351 to emit light, and the regular reflection light from the transfer belt 133 is received by the light receiving element 352. As shown in FIG. 3B, when the sensor shutter 354 is in the closed state, the density detector 350 receives diffuse reflected light on the back surface of the sensor shutter 354 made of, for example, ABS resin by the light receiving element 353. Receive light.

  FIG. 4 is a circuit diagram of a drive circuit of the density detector 350 of the image forming apparatus 100 according to the present embodiment. The output of the light receiving element 352 is input to the input terminal of an A / D (analog / digital) converter 365 through the resistance elements R3 and R4, the operational amplifier 363, and the resistance element R5. Similarly, the output of the light receiving element 353 is input to the other input terminal of the A / D converter 365 through the resistance elements R6 and R7, the operational amplifier 364, and the resistance element R8. The A / D converter 365 includes a circuit that converts analog data into digital data, and has an input terminal to which the analog data is input from the density detection unit 350. The output of the light receiving element 352 is input to the input terminal of the 10-bit A / D converter 365 through the operational amplifier 363. The output of the light receiving element 353 is input to the input terminal of the 10-bit A / D converter 365 through the operational amplifier 364.

  The D / A converter 361 includes a circuit that converts digital data into analog data, and has an output terminal that outputs analog data to the density detection unit 350. The D / A (digital / analog) converter 361 sets the output level of the output terminal to. The light emitting current of the light emitting element 351 is controlled by a circuit that can be varied in the range of 0 to 3.3 [V] and is configured by a FET (field effect transistor) 362 and resistors R1 and R3. By controlling the current flowing through the FET 362 and controlling the current flowing through the light emitting element 351, the light emission level becomes variable.

  When the light emitting element is turned on, light from the light emitting element is irradiated onto the transfer belt 133 as shown in FIGS. The light irradiated by the light emitting element is regularly reflected and diffusely reflected. Here, the amount of specularly reflected light attenuates according to the toner density of the black toner image formed on the transfer belt 133. Therefore, the density of the black toner image can be detected from the amount of specularly reflected light received by the light receiving element 352.

  Further, the amount of diffuse reflected light increases according to the toner density thickness of the color (cyan, magenta, yellow) formed on the transfer belt 133. Therefore, the color (cyan, magenta, yellow) toner density can be detected based on the amount of diffusely reflected light received by the light receiving element 353.

  The transfer belt 133 has a glossy black surface. The transfer belt 133 is protected from toner contamination scattered in the image forming apparatus by the sensor shutter 354 except during the density correction operation. As shown in FIG. 3A, the density detection unit 350 performs black toner calibration using the surface of the belt on which the toner image is not formed with the sensor shutter 354 open. Further, as shown in FIG. 3B, calibration for cyan, yellow, and magenta toner image detection is performed using the back surface of the sensor shutter 354 with the sensor shutter 354 closed.

  The calibration measures the values of the light receiving element 352 and the light receiving element 353 using the sensor output voltage with the light emitting element 351 turned off as a dark potential. The dark potential output of the light receiving element 352 is stored in the storage unit as Vie2d, and the dark potential output of the light receiving element 353 is stored in the storage unit. The dark potential is approximately 0.5 [V] to 1.0 [V] although it varies depending on the individual difference of the sensor.

  Next, the irradiation level of the light emitting element 351 is increased stepwise, and the potential difference between the dark potential and the output of the light receiving element 352 and the light receiving element 353 at that time is amplified by the operational amplifiers 363 and 364 is 2.0 [V. ] To adjust. The predetermined voltage 2.0 [V] is converted by the A / D converter 365 when the voltage at the input terminal of the A / D converter 365 is converted by the A / D converter 365 and when the Vie3d and Vie2d are detected. Judgment is based on the difference between the values.

  The A / D converter 365 holds a range of 3.3 [V]. The control value of the D / A converter 361 that controls the current flowing through the light emitting element 351 at this time is held, and is used in subsequent density detection operations. This control value is different when cyan, magenta, and yellow toner images are detected and when a black toner image is detected.

  The density of the toner image can always be detected stably by the calibration operation. Further, when the toner image is detected, a value obtained by subtracting the dark potential from the sensor output voltage is used. In the following description, the concentration detection value output from the concentration detection unit is a voltage obtained by amplifying the sensor output voltage with an operational amplifier, and the sensor output voltage at the irradiation level of the light emitting element 351 determined by calibration. Is a value obtained by subtracting the sensor output voltage in a state where the light emitting element 351 is turned off.

<< 3 >> Control System of Image Forming Apparatus 100 FIG. 5 is a block diagram schematically showing the configuration of the control system of the image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 stores a control parameter, a control unit 301, an interface unit 302 that receives image data from the host device 200, an image signal processing unit 303 that processes image data to obtain image data for printing, and a control parameter. A storage unit 304, a calculation unit 305 that calculates a printing rate, a timer 306 that measures time, and a print control unit 307 that controls the image forming units 110K, 110Y, 110M, and 110C. In addition, the image forming apparatus 100 includes a voltage control unit 310 that controls a voltage supplied to each roller of the image forming units 110K, 110Y, 110M, and 110C, a print counter (printed sheet number detecting unit) 320 that counts the number of printed sheets, A dot counter (print rate detection unit) 330 that counts dots of printing image data, and an environment detection value (T, h) including at least one of the temperature T and humidity h of the environment around or inside the image forming apparatus 100 Density detection that detects the density of the developer image formed by the environment detection unit 340 that performs measurement and the image forming unit (110C,...), And outputs a density detection value (detection voltage value) G indicating the detected density. Part 350. A control unit 301 controls the entire image forming apparatus 100. The control unit 301 displays an average print duty as a printing rate J in a predetermined period (for example, a predetermined time) and a printing rate in a predetermined period (for example, a period from the previous printing stop to the current printing start). The density detection value G output from the density detection unit 350 is corrected according to (Duty) d and the environment detection value (temperature T, humidity h) at a certain time. The environment detection value may be a single measurement, but is preferably an average value of a plurality of detection values. Note that a part of the control system in FIG. 5 (for example, the control unit) includes a memory as a storage device (storage unit) that stores a program as software and an information processing device that executes the program stored in the memory. (For example, by a computer).

  In the image density adjustment method in the image forming apparatus 100 according to the present embodiment, the image forming unit (110C,...) Forms a patch pattern (reference pattern) made of a developer on the transfer belt 133 as a medium. The print counter 320 is a step of obtaining the number of printed sheets J in a predetermined period (period before the present), and the dot counter 330 is the printing rate in the predetermined period (period before the present). The step of detecting the printing duty d and the environment detection value (T, h) including at least one of the temperature T and the humidity h in a predetermined period (period before the present) are acquired by the environment detection unit 340. And a step in which the density detector 350 detects the density of the reference pattern and outputs a density detection value G indicating the detected density. To. Further, in the image density adjustment method, the control unit 301 corrects the density detection value G output from the density detection unit 350 according to the number of printed sheets J, the print duty d, and the environment detection value (T, h). And a step in which the control unit 301 adjusts the density of an image formed by the image forming unit (110C,...) Based on the corrected density detection value Ga generated by correcting the density detection value G. In the step of adjusting the image density, the exposure amount is controlled by the exposure unit (111C,...) That forms an electrostatic latent image on the photosensitive drum 113 of the image forming unit (110C,. At least one of bias voltage control in the developing roller 116 that supplies toner to 113 is performed.

<4> Correction of Relationship (γ Curve) Between Detected Density Value and Actual Density (OD Value) FIG. 6 is a patch composed of a toner image formed on the transfer belt 133 of the image forming apparatus 100 according to the present embodiment. It is a figure which shows the example of a pattern (reference pattern). When the image forming apparatus 100 executes density adjustment, a predetermined bias voltage is applied to the image forming units 110K, 110Y, 110M, and 110C of the respective colors, and the density is transferred onto the transfer belt 133 as shown in FIG. Patch patterns 371, 372, and 373 for detection are formed. Here, on the transfer belt 133, patch patterns 371, 372, and 373 composed of solid images of black (K), yellow (Y), magenta (M), and cyan (C) are formed for each print duty. The patch pattern 371 includes solid images K1, Y1, M1, and C1 having a printing duty of 100%. The patch pattern 372 includes solid images K2, Y2, M2, and C2 having a print duty of 70%. The patch pattern 373 includes solid images K3, Y3, M3, and C3 having a printing duty of 30%.

  The sensor shutter 354 is opened, the patch patterns 371, 372, and 373 are moved to positions opposite to the density detection unit 350, and the density detection unit 350 detects the patch patterns 371, 372, and 373, and the density detection values at that time (detection) Voltage value) G is measured. Here, density detection value information indicating the relationship between the density detection value G output from the density detection unit 350 and the actual density (OD value) of the patch patterns 371, 372, and 373 is stored in the storage unit 304 in advance. Therefore, by referring to the density detection value information stored in the storage unit 304, the actual density (OD value) of the patch patterns 371, 372, and 373 is calculated from the density detection value G detected by the density detection unit 350. be able to. Then, density correction is performed by adjusting at least one of the developing bias of the image forming units 110K, 110Y, 110M, and 110C and the light amount of the exposure device 111C so that the difference between the target density and the calculated density approaches 0. .

FIG. 7 is a diagram showing the relationship between the actual image density (OD value) of the black (K) toner on the medium and the density detection value (actual measurement value) G [V] output from the density detection unit 350 as a white circle. is there. FIG. 8 shows the actual image density (OD value) of the color toner on the medium (that is, yellow toner, magenta toner, cyan toner) and the density detection value (actual measurement value) G [ V] is a diagram showing white circles. 7 and 8, the horizontal axis indicates the detected density value G [V], and the vertical axis indicates the actual density (OD value). The actual concentration (OD value) was measured with a spectral densitometer “X-rite 528” manufactured by X-rite. The media used is “Hammermill 241b” paper. The OD value is an optical density (Optical Density) value. 7 and 8, a curve representative of the distribution of white circles indicating the density detection value is called a γ curve indicating γ characteristics. The OD value and the density detection value G [V] can be approximated by an exponential function (OD = G ^γ ) when γ is a gamma value.

  As shown in FIG. 7, in the case of black toner, the OD value tends to be higher as the density detection value G [V] is lower. Further, as shown in FIG. 8, in the case of color toner (that is, yellow toner, magenta toner, cyan toner), the higher the density detection value G [V], the higher the OD value tends to be.

  FIG. 9 shows the relationship (γ curve) between the actual image density (OD value) of magenta toner on the medium and the density detection value (actual measurement value) G [V] output from the density detection unit 350 as white circles and black triangles. It is a figure shown by. In FIG. 9, the horizontal axis indicates the density detection value G [V], and the vertical axis indicates the actual density (OD value). In FIG. 9, white circles indicate measured values of the density detection value G [V] when the printing operation has not been performed for 8 hours since the previous printing (after leaving for a long time). A black triangle indicates an actual measurement value of the density detection value G [V] when printing 2000 sheets (that is, 2k sheets) is executed from a state after being left for a long time (after 2k printing). The data in FIG. 9 was actually measured in a printing environment having a printing duty of 0.5% and an intermediate temperature / humidity environment (NN environment) (temperature 23 ° C., humidity 55%). FIG. 9 shows the actual measurement values for the magenta toner, but the actual measurement values for the yellow and cyan toners, which are other color toners, show the same tendency as the actual measurement values for the magenta toner. Further, the relationship (γ curve) between the OD value of the image using black toner and the density detection value G is generally a shape obtained by reversing the right and left of the relationship (γ curve) for magenta toner.

  As shown in FIG. 9, the γ curve indicated by the actual measurement value (black triangle) after mass printing changes compared to the γ curve indicated by the actual measurement value after standing for a long time (white circle). The actual concentration is higher than that after standing for a long time (OD value is increased). The cause of this is that when high-volume printing with a low toner consumption and a low duty (printing rate 0.5%) is performed, damaged toner increases around the developing roller 116, and the deteriorated toner is used for subsequent printing. It is thought to be done. In other words, the cause of this is thought to be that the deteriorated toner tends to peel off the external additive, and as a result, the toner is agglomerated and the toner adhesion amount increases, resulting in a high density. In addition, it is considered that the deteriorated toner has a higher density due to an increase in charge amount and a higher transfer efficiency.

  FIG. 10 shows the relationship (γ curve) between the actual image density (OD value) of magenta toner on the medium and the density detection value (actual measurement value) G [V] output from the density detection unit 350 as white triangles and white circles. It is a figure shown by a black circle. In FIG. 10, the horizontal axis indicates the detected density value G [V], and the vertical axis indicates the actual density (OD value). In FIG. 10, the white triangle indicates the density detection value G [V] when printing 2000 sheets is performed with a low duty (printing rate 0.5%) from the state after being left for a long time (after a large amount of printing). A white circle indicates an actual measurement value, and the white circle indicates an actual measurement value of the density detection value G [V] when printing 2000 sheets from a state after being left for a long time with a medium duty (printing rate 10%) (after a large amount of printing). A black circle indicates an actually measured value of the density detection value G [V] when printing 2000 sheets is performed with a high duty (printing rate 60%) from a state after being left for a long time (after a large amount of printing). . The data in FIG. 10 was actually measured in a printing environment that is an NN environment (temperature 23 ° C., humidity 55%). FIG. 10 shows the actual measurement values for the magenta toner, but the actual measurement values for the yellow and cyan toners, which are other color toners, show the same tendency as the actual measurement values for the magenta toner.

  As shown in FIG. 10, the γ curve indicated by the low-duty measured value after large-scale printing (white triangle) indicates the measured value after medium-duty and high-duty mass printing (γ curve indicated by white circles and γ curve indicated by black circles). It can be seen that the actual density increases (OD value increases) after mass printing with low duty. The reason for this is that when a large amount of printing with a low toner consumption and a low duty (printing rate of 0.5%) is performed, damaged toner increases around the developing roller 116, and the deteriorated toner is included in the subsequent printing. It is thought to be used. In other words, the deteriorated toner is considered to be caused by the density becoming high because the external additive is easily peeled off, and as a result, toner aggregation occurs and the amount of toner adhesion increases. On the other hand, in medium duty and high duty printing, the toner around the developing roller 116 is consumed in a relatively large amount, so that the deteriorated toner hardly remains and is not easily used for printing. it is conceivable that.

  FIG. 11 shows the relationship (γ curve) between the actual density (OD value) of the image of magenta toner on the medium and the density detection value (actual measurement value) G [V] output from the density detection unit 350 as a black circle, white circle, It is a figure shown with a white triangle. In FIG. 11, the horizontal axis indicates the density detection value G [V], and the vertical axis indicates the actual density (OD value). In FIG. 11, black circles indicate the density when printing with a low duty (printing rate 0.5%) of 2000 printed sheets is performed in a low-temperature and low-humidity environment (LL environment) (after mass printing) after being left for a long time. The measured value of the detection value G [V] indicates the measured value, and the white circle indicates that when printing with a low duty (printing rate 0.5%) of 2000 printed sheets is performed in the NN environment after being left for a long time (after mass printing) ) Shows the measured value of the density detection value G [V], and the white triangle shows a low duty (printing rate of 0.5%) printing of 2000 sheets from a state after being left for a long time, in a high temperature and high humidity environment (HH). The measured value of the density detection value G [V] when executed in (Environment) (after mass printing) is shown. Here, the LL environment has a temperature of 10 ° C. and a humidity of 20%, the NN environment has a temperature of 23 ° C. and a humidity of 55%, and the LL environment has a temperature of 28 ° C. and a humidity of 80%. FIG. 11 shows the actual measurement values for the magenta toner, but the actual measurement values for the yellow and cyan toners, which are other color toners, show the same tendency as the actual measurement values for the magenta toner.

  As shown in FIG. 11, the actual measurement value after mass printing in the HH environment (γ curve indicated by white triangles) is the actual measurement value after mass printing in the LL environment (γ curve indicated by black circles) and after mass printing in the NN environment. It can be seen that the actual density is higher (the OD value is higher) than the actually measured value (γ curve indicated by the white circle). This is because, in the HH environment, the temperature and humidity in the image forming apparatus 100 are higher than in the NN environment and the LL environment, so that the toner in the developing container is likely to accumulate damage and toner aggregation occurs. It is considered that the amount of adhesion increases.

  From the actual measurement results shown in FIG. 9 to FIG. 11, the density detection output from the density detection unit 350 according to the number of printed sheets, the printing duty, and the printing environment, which are the printing conditions of the apparatus in the period before the current time based on the current time. It can be seen that the relationship (γ curve) between the value G [V] and the actual concentration (OD value) changes. As described above, when the γ curve changes depending on the printing conditions in the period before the present, when the print density (actual density) adjustment (density correction) is executed, the actual density (OD value) corresponding to the change in the γ curve. Deviates from the target density. Therefore, in the present embodiment, even when the γ curve changes due to the printing conditions (the number of printed sheets, the printing duty, and the printing environment) in the period before the present, it is caused by the printing conditions in the period before the present. The print density does not deviate from the target density by correcting the γ curve by an amount corresponding to the change amount of the γ curve, that is, canceling the change of the γ curve due to the printing conditions in the period before the present. Like that.

  The correction of the γ curve is performed by the following procedure, for example. The control unit 301 calculates the print number coefficient Px from the number of printed sheets within a predetermined period (for example, the predetermined time immediately before) based on the present (FIG. 12 described later), and the predetermined period The average print duty coefficient Dx is calculated from the average value of the print ratio (average print duty d) (FIG. 13 described later), and the environment value Fx based on the environment detection value (T, h) detected by the environment detection unit 340 Is used to calculate the environmental coefficient Ex (FIGS. 14 and 15 to be described later), and the γ curve correction coefficient A is calculated from the print number coefficient Px, the average print duty coefficient Dx, and the environmental coefficient Ex (formula 1 to be described later). Using the “corrected γ curve correction coefficient” Ax (= A100, A85, A70, A50, A30, A15) obtained by correcting the curve correction coefficient A with the correction value (FIG. 16 described later), the γ curve To correct

  FIG. 12 is a flowchart showing a calculation process of the print number coefficient Px in the present embodiment. Here, the initial value of the print number coefficient Px is, for example, 0. As shown in FIG. 12, when the power of the image forming apparatus 100 is turned on, time measurement starts (step S1), and counting of the number of printed sheets is started (step S2). When a preset time (for example, 30 minutes) elapses (step S3), the number of printed sheets executed in the 30 minutes is counted (step S4), and the control unit 301 determines that the number of printed sheets is 200 sheets or more. It is determined whether or not there are less than 200 sheets (step S4).

  If the counted number of printed sheets is 200 sheets or more (200 or more in step S4), 1 is added to the printed sheet number coefficient Px (step S5). Here, it is determined whether the print number coefficient Px is 4 or more (step S6). If the print number coefficient Px is 4 or more (YES in step S6), the print number coefficient Px is set to 4 (step S7). Write to the storage unit (step S8). If the print number coefficient Px is smaller than 4 (NO in step S6), the print number coefficient Px is directly written in the storage unit 304 (step S8).

  If the number of printed sheets counted in step S4 is less than 200 (less than 200 in step S4), 0.5 is subtracted from the printed sheet number coefficient Px to calculate updated Px (step S9). Here, it is determined whether the print number coefficient Px is 0 or less (step S10). If the print number coefficient Px is 0 or less (YES in step S10), the print number coefficient Px is set to 0 (step S11). ), And writes in the storage unit 304 (step S8). If the print number coefficient Px is greater than 0 (NO in step S10), the print number coefficient Px is directly written in the storage unit 304 (step S8). When the process of step S8 ends, the process returns to step S1 and the above process is repeated.

  According to the processing of FIG. 12, the print number coefficient Px is determined in the range of 0 to 4, and approaches 4 as the number of prints per predetermined time increases, and the number of prints per predetermined time decreases. It approaches 0. Therefore, the print number coefficient Px is an index indicating the number of prints per predetermined time. The closer the printed sheet number coefficient Px is to 4, the greater the influence on the γ curve, and the closer the printed sheet number coefficient Px is to 0, the smaller the influence on the γ curve.

  The average print duty d is an average value of the print duty in a predetermined period. The print duty is calculated from a dot count per sheet, for example, a count value of the number of light emission of the exposure device (111C,...). The predetermined period is, for example, a period from receiving a density correction instruction to receiving a next density correction instruction. The printing duty when printing a solid black on one sheet is 100%, and the printing duty when printing a blank sheet is 0%.

  FIG. 13 is a diagram showing the relationship between the average print duty d and the average print duty coefficient Dx in a tabular format. The average print duty coefficient Dx is calculated according to the average print duty d. The average printing duty coefficient Dx is determined in the range of −0.15 to 0, for example. When the average print duty d is 5% or more, the average print duty coefficient Dx is zero. When the average print duty d is 3% or less, the average print duty coefficient Dx decreases as the average print duty d approaches zero. Here, the smaller the average print duty coefficient Dx (closer to −0.15) is, the greater the influence on the γ curve is. The larger the average print duty coefficient Dx (closer to 0) is, the greater the influence is given to the γ curve. The impact is small.

  The environmental value Fx is determined by the temperature T and humidity h around or inside the image forming apparatus 100 detected by the environment detection unit 340. FIG. 14 is a diagram showing the relationship between the detected temperature T and humidity h and the environmental value Fx in a tabular format. As shown in FIG. 14, the environmental value Fx is determined in the range of 1 to 8 by dividing the temperature into 6 levels and the humidity into 10 levels. As the temperature T and the humidity h are higher, the environmental value Fx is closer to 1. As the temperature T and the humidity h are lower, the environmental value Fx is closer to 8.

  The environmental coefficient Ex is calculated according to the environmental value Fx. FIG. 15 is a diagram showing the relationship between the environmental value Fx and the environmental coefficient Ex in a tabular format. The environmental coefficient Ex is calculated in the range of 0.80 to 1.20 based on the environmental value Fx. The larger the environmental value Fx, the larger the environmental coefficient Ex, and the smaller the environmental value Fx, the smaller the environmental coefficient Ex. The closer the environmental coefficient Ex is to 1.0, the smaller the influence on the γ curve is. The closer the environmental coefficient Ex is 0.80 or 1.20, the larger the influence on the γ curve is. With the environmental value Fx being 4 and 5 (NN environment) as a reference, when the environmental value Fx is 1 (HH environment), the γ curve is corrected so that the density becomes light, and when the environmental value Fx is 8 (LL environment), the density It shows that the γ curve is corrected so that becomes darker.

The control unit 301 calculates the γ curve correction coefficient A from the print number coefficient Px, the average print duty coefficient Dx, and the environment coefficient Ex obtained as described above, and stores them in the storage unit 304. The γ curve correction coefficient A is a coefficient for correcting a deviation from the reference γ curve, and is calculated by the following equation 1, for example.
A = Ex + (Dx * Px / 4) Formula 1
In the present embodiment, Px has a value in the range of 0 to 4, Dx has a value in the range of −0.15 to 0, and Ex is in the range of 0.80 to 1.20. And A has a value in the range of 0.1 to 1.0. From this equation, in this embodiment, when Ex = 0.80, Dx = −0.15, and Px = 4, A = 0.65 (minimum value), and Ex = 1.20, Dx When = 0 or Px = 0, A = 1.20 (maximum value).

  When the γ curve correction coefficient A is 1.0, it means that correction from the reference γ curve is not performed. When the γ curve correction coefficient A is a value larger than 1.0, for example, 1.2, it means that the γ curve is corrected so that the density becomes 20% higher. When the γ curve correction coefficient A is smaller than 1.0, for example, 0.8, it means that the γ curve is corrected so that the density is 20% thinner.

  The γ curve correction coefficient A is corrected by a correction value B (FIG. 16) corresponding to the density of the patch pattern. FIG. 16 shows the correction value B of the γ curve correction coefficient A with respect to the density of the patch pattern for density detection. The density of the patch pattern is the density of the patch pattern having a printing rate (print duty) of 100%, 85%, 70%, 50%, 30%, 15% formed on the transfer belt 133 at the time of density correction. The γ curve correction coefficient A is corrected by a correction value B for each density of the patch pattern shown in FIG.

FIG. 17 is a table of “corrected γ curve correction coefficients” Ax (= A100, A85, A70, A50, A30, A15) for each color for each density detection value G in the image forming apparatus 100 according to the present embodiment. It is a figure shown by. “Corrected γ curve correction coefficient” Ax (= A100, A85, A70, A50, A30, A15) is calculated by the following equation 2 using the correction value (B) of FIG.
Ax = 1 + (A−1) × B Equation 2

As an example, for magenta toner, A = AM = 0.9, and using the correction value B in FIG. 16, “corrected γ curve correction coefficient” Ax (= A100, A85, A70, A50, A30, A15) Is obtained as follows.
A100 = 1 + (AM-1) * 1.0 = 1 + (0.9-1) * 1.0 = 0.90
A85 = 1 + (AM−1) × 0.8 = 1 + (0.9−1) × 0.8 = 0.92
A70 = 1 + (AM−1) × 0.6 = 1 + (0.9−1) × 0.6 = 0.94
A50 = 1 + (AM-1) * 0.4 = 1 + (0.9-1) * 0.4 = 0.96
A30 = 1 + (AM−1) × 0.2 = 1 + (0.9−1) × 0.2 = 0.98
A15 = 1 + (AM−1) × 0.1 = 1 + (0.9−1) × 0.1 = 0.99
In this way, by using the correction value B of FIG. 16, the “corrected γ curve correction coefficient” Ax is obtained, and this “corrected γ curve correction coefficient” Ax is multiplied by the OD value (= G ^γ ). In the high density region, the correction amount by the “corrected γ curve correction coefficient” Ax is increased, and in the low density region, the correction amount by the “corrected γ curve correction coefficient” Ax is decreased.

FIG. 18 is a diagram illustrating correction of a γ curve using “corrected γ curve correction coefficient” Ax (= A100, A85, A70, A50, A30, A15) in the image forming apparatus 100 according to the present embodiment. is there. FIG. 18 shows the case of magenta toner, for example. As described with reference to FIG. 17, in this embodiment, “corrected γ curve correction coefficient” Ax (A100, A85, A70, A50, A30, A15) for each color for each of a plurality of density detection values G. And the γ curve (OD = G ^γ ) is corrected using these values. The “corrected γ curve correction coefficient” Ax (A100, A85, A70, A50, A30, A15) increases as the density increases and decreases as the density decreases. The length of the downward arrow in FIG. The correction amount by the γ curve correction coefficient Ax indicated by is smaller as the density is lower. As can be seen from FIG. 9, FIG. 10, and FIG. 11, the larger the density detection value G, the greater the effect of mass printing on the actual density, the effect of the lower printing rate on the actual density, and the environmental detection value (HH (Environment) has a larger influence on the actual density, and the smaller the density detection value G, the greater the influence of mass printing on the actual density, the lower printing rate on the actual density, and the environment detection value (HH environment) on the actual density. This is because the influence is small. Therefore, by using the “corrected γ curve correction coefficient” Ax (= A100, A85, A70, A50, A30, A15), as shown in FIG. 18, the corrected γ curve is corrected and corrected. The γ curve can be brought close to the target γ curve. The yellow toner and cyan toner are the same as in the case of magenta toner. Further, the relationship (γ curve) between the OD value of the image using black toner and the density detection value G is generally a shape obtained by reversing the right and left of the relationship (γ curve) for magenta toner.

  FIG. 19 is a table showing the γ curve correction coefficients A (= AK, AY, AM, AC) of the respective colors in the image forming apparatus of the comparative example. In this comparative example, the γ curve correction coefficient A is a constant value for each color. FIG. 20 is a diagram illustrating correction of the γ curve of the comparative example using the γ curve correction coefficient A (= AK, AY, AM, AC) of FIG. FIG. 20 shows the case of magenta toner, for example. As described with reference to FIG. 19, in the comparative example, the γ curve correction coefficient A is calculated for each color, and the measured γ curve is corrected using these values as shown in FIG. The later γ curve (broken line) is used. In this case, in the region where the density detection value G is high, the measured γ curve can be brought close to the target γ curve, but in the region where the density detection value G is low, the correction amount is too large and deviation occurs. There is. As can be seen from FIGS. 9, 10, and 11, the larger the density detection value G is, the larger the effect of mass printing on the actual density, the lower print rate on the actual density, and the environmental detection value (HH environment). ) Has a greater effect on the actual density, and the smaller the density detection value G, the greater the effect of mass printing on the actual density, the effect of the low printing rate on the actual density, and the effect of the environmental detection value (HH environment) on the actual density. Is small.

  As described above, in the image forming apparatus 100 according to the present embodiment, for a region where the density of the solid image constituting the patch pattern is high, the correction amount of the γ curve is increased and the density of the solid image constituting the patch pattern is increased. For regions with low γ, the correction amount of the γ curve is reduced to correct the γ curve appropriately.

<< 5 >> Print Density Adjustment FIG. 21 is a flowchart showing the density correction operation in the image forming apparatus 100 according to the present embodiment. In density correction, first, the control unit 301 calculates a print number coefficient Px from the print number J by the process shown in FIG. 12 (step S21).

  Next, when there is an instruction for density correction (YES in step S22), the control unit 301 obtains the environmental value Fx shown in FIG. 14 from the environmental detection values (temperature T and humidity h), and the environmental value Fx. From FIG. 15, the environmental coefficient Ex shown in FIG. 15 is calculated (step S23).

  Next, the control unit 301 calculates the average print duty coefficient Dx shown in FIG. 13 from the print duty d (step S24).

  Next, the control unit 301 calculates a γ curve correction coefficient A (for each color for each density detection value G from the print number coefficient Px in FIG. 12, the environment coefficient Ex in FIG. 15, and the average print duty coefficient Dx in FIG. 13. = AK, AY, AM, AC) is determined (step S25).

  Next, the control unit 301 corrects the γ curve correction coefficient A by using the correction value B (FIG. 16), and “corrected γ curve correction coefficient” Ax (= A100, A85, A70,. A50, A30, A15) are calculated (step S26).

  Next, the control unit 301 corrects the γ curve using the “corrected γ curve correction coefficient” Ax (= A100, A85, A70, A50, A30, A15) of each color for each density, and is corrected. The print density is adjusted based on the γ curve (corrected density detection value Ga) (step S27).

  Note that the order of steps S21 to S24 is not limited to the order shown in FIG. 21, and the order of steps S21 to S24 may be other orders.

<6> Effect As described above, according to the present embodiment, the γ curve correction coefficient A is calculated according to the number of printed sheets, the print duty, and the past printing conditions of the printing environment, and this γ curve correction coefficient A is used as the density. Each of the colors is corrected with the correction value B for each color, and the “corrected γ curve correction coefficient” Ax (= A100, A85, A70, A50, A30, A15) is used to correct the γ curve. Conversion from the density detection value G output from 350 to the density can be performed accurately. For this reason, it is possible to perform density adjustment that brings the print density close to the target density regardless of the printing conditions in the period before the present time.

<< 7 >> Modifications In the above embodiment, an example in which the present invention is applied to a printer as an image forming apparatus has been described. However, the present invention is not limited to printing such as an MFP (multifunctional peripheral device), a facsimile, and a copying machine. The present invention can be applied to other devices having functions.

  In the above embodiment, the tandem direct transfer type image forming apparatus that directly transfers the developer image on the photosensitive drum to the paper as the recording medium has been described. The present invention can also be applied to other types of image forming apparatuses such as a tandem intermediate transfer system that transfers to an intermediate transfer belt and transfers a developer image on the intermediate transfer belt to a sheet as a recording medium.

  In the above-described embodiment, the case where a pattern including three types of solid images of 30%, 70%, and 100% is used as the patch pattern. However, there are three types of solid images included in the patch pattern. It is not limited to the type. By increasing the number of solid images having different printing rates included in the patch pattern, it is possible to perform density detection with higher accuracy.

  In the above embodiment, as shown in FIG. 16, the correction values B at six different densities are used for each color. However, the number of correction values B for each color toner is not limited to six. Further, the density of the correction value B is not limited to 100%, 85%, 70%, 50%, 30%, and 15%.

  In the above embodiment, the count time and the count number when calculating the printed sheet number coefficient Px are 30 minutes and 200 counts, respectively, but these are only examples, and other count times and count numbers are adopted. Also good. It is desirable to select appropriate values according to the characteristics of the image forming apparatus.

  10 recording medium (medium), 100 image forming apparatus, 110K, 110Y, 110M, 110C image forming unit, 111K, 111Y, 111M, 111C exposure apparatus, 112K, 112Y, 112M, 112C image forming unit, 113 photoconductor drum (image) Carrier), 114 charging roller, 115 developing device, 116 developing roller (developer carrier), 117 supply roller, 118 developing blade, 119a cleaning blade, 119b collection container, 120 paper feeding device, 130 transfer belt unit (conveying unit) 133, transfer belt (medium), 140 transfer roller, 150 fixing device, 171 power supply unit for charging roller, 172 power supply unit for transfer roller, 173 power supply unit for developing roller, 174 power supply for supply roller Unit, 200 host device, 301 control unit, 302 interface unit, 303 image signal processing unit, 304 storage unit, 305 calculation unit, 306 timer, 307 print control unit, 310 voltage control unit, 320 print counter (print number detection unit) , 330 dot counter (print rate detection unit), 340 environment detection unit, 350 density detection unit, 351 light emitting element, 352 light receiving element (black sensor), 353 light receiving element (color sensor), 354 sensor shutter, 361 D / A converter, 362 FET, 363, 364 operational amplifier, 365 A / D converter.

Claims (8)

In an image forming apparatus that prints an image by an electrophotographic process,
An image forming unit for forming a developer image on the medium;
A print number detection unit for detecting the number of prints;
A print rate detector for detecting a print rate in printing;
An environment detection unit for detecting an environment detection value including at least one of temperature and humidity;
A density detection unit that detects a density of the developer image formed by the image forming unit and outputs a density detection value indicating the detected density;
A control unit for controlling the entire apparatus;
With
The image forming apparatus, wherein the control unit corrects the density detection value output from the density detection unit according to the number of printed sheets, the printing rate, and the environment detection value.   The correction of the density detection value is correction of a γ curve representing the relationship between the actual density indicating the actual density of the developer image to be detected by the density detection unit and the density detection value output from the density detection unit. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the number of printed sheets is a number of printed sheets within a predetermined period.   The image forming apparatus according to claim 1, wherein the printing rate is an average printing rate within a predetermined period.   5. The environment detection value according to claim 1, wherein the environment detection value includes at least one of a temperature and a humidity around or inside the image forming apparatus within a predetermined period. Image forming apparatus. The image forming unit controls an image carrier, an exposure unit that forms an electrostatic latent image on the image carrier, a developer carrier that visualizes the electrostatic latent image with a developer, and a printing operation. A printing control unit that
The print control unit performs at least one of exposure amount control by the exposure unit and bias voltage control in the developer carrier based on the corrected density detection value generated by correcting the density detection value. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. An image density adjustment method in an image forming apparatus, comprising: an image forming unit that forms an image on a medium by an electrophotographic process; and a density detection unit that detects the density of the image,
The image forming unit forming a reference pattern made of a developer on a medium; and
Obtaining the number of prints;
Detecting the printing rate; and
Obtaining an environmental detection value including at least one of temperature and humidity;
The density detector detects the density of the reference pattern and outputs a density detection value indicating the detected density;
Correcting the density detection value output from the density detection unit according to the number of printed sheets, the printing rate, and the environment detection value;
Adjusting the density of an image formed by the image forming unit based on the corrected density detection value generated by correcting the density detection value.   In the step of adjusting the density of the image, the exposure amount control by the exposure unit that forms an electrostatic latent image on the image carrier of the image forming unit, and the developer carrier that supplies the developer to the image carrier 8. The image density adjustment method according to claim 7, wherein at least one of bias voltage control in the body is performed.

Images