JP2009169311A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which suppresses influence due to irregular sensitivity of a photoreceptor and an S-D Gap and which achieves improvement of quality of an image by a test patch without increasing manufacture cost of the photoreceptor and a developer carrier. <P>SOLUTION: Based on information from a photoreceptor phase detection means for detecting a phase of the photoreceptor 31 from a reference position determined in advance and a developer carrier phase detection means for detecting a phase of the developer carrier 62 in a developing device 33 from a reference position determined in advance, the test patch image is formed on a predetermined position of the photoreceptor 31 by using developer carried on a predetermined position of the developer carrier 62, and then the density of the test patch image is detected by a patch image density detection means 70. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a developer that is a rotating member that carries the developer and conveys the developer to a developing portion that faces the photosensitive member in order to develop an electrostatic latent image formed on the photosensitive member that is a rotating member. The present invention relates to an image forming apparatus that includes a developing device including a carrier and performs image density adjustment.

  In recent years, there has been a growing demand for direct imaging printers that do not require plates. Many companies employ direct imaging printers due to the shortage of finishing time, service to each customer, and the environmental problems of mass production and disposal. Among direct imaging printers, the power of electrophotographic printers that are highly productive and close to the finish of offset printing is on the rise.

  In such situations, color stability is the most important alternative to conventional offset printing and photography.

  In order to ensure color stability, each company implements stabilization control that closes in the printer. More specifically, in Patent Document 1, a test patch image for toner density detection formed on a photoconductor is read by a density sensor and fed back to a toner density control unit in a developing device to control to an appropriate density. The technology is described.

  When a patch image is formed for the toner density detection and the image density of the patch image is detected, it is affected by sensitivity unevenness of the photoconductor. Although the charging potential, the developing potential, and the potential of the exposed portion are kept constant in terms of control, the same density may not be formed because the sensitivity characteristics of the photoconductor are different. Since the detection result changes, the density correction result differs for each correction, and a color difference (control variation) occurs.

  In the apparatus described in Patent Document 2, in order to suppress the influence of the sensitivity unevenness of the photoconductor, a drum home position mark and a detection body are provided, and patches are always printed at a predetermined timing, thereby suppressing control variations. .

  Furthermore, in the apparatus described in Patent Document 3, unevenness in the potential of the photoconductor is avoided by changing the amount of exposure light. Further, it is disclosed that a potential is measured at the time of shipment of a photosensitive member and a two-dimensional characteristic table is stored.

  However, it is not only the sensitivity unevenness (potential unevenness) that the density change occurs in the image forming apparatus as in Patent Document 2 and Patent Document 3. In particular, density unevenness occurs when a gap (interval: hereinafter referred to as “SD gap”) between the developing device and the photosensitive member varies.

Patent Document 4 discloses a technique for reducing the deflection of the cylindrical surface of the cylindrical member.
Japanese Patent Laid-Open No. 1-309082 JP 2006-162745 A JP 2002-67387 A Japanese Patent Laid-Open No. 9-50179

  However, according to the technique described in Patent Document 4, the amount of eccentricity varies depending on the member to be processed. In particular, when a plastic member or the like is used as a drum-shaped photosensitive member, that is, a flange of the photosensitive drum, the wear due to durability is also affected, and a vibration of several tens of μm occurs.

  As shown in FIG. 14 attached to the present application, the density change also occurs with this fluctuation. FIG. 14 is an excerpt of a highlight portion having gradation characteristics with dot growth of 170 lines, and the horizontal axis indicates the dot area% and the vertical axis indicates the relative density value when the paper density is zero. When attention is paid to about 13% in halftone dot area%, it can be seen that a density difference of about 0.1 occurs even with a difference of about 50 μm in SD gap. Like the sensitivity unevenness, this unevenness has also affected the density correction.

  For fine processing of a developer carrier (hereinafter referred to as “developing sleeve”) that is a drum flange of a photosensitive drum or a rotating body in a developing device, and for creating a two-dimensional photosensitive member characteristic table, many The man-hours and measuring instruments and cutting machines are necessary. In any case, the cost will increase significantly.

  Further, in Patent Document 2, when a patch image for correction is printed, the patch image is always formed after a certain time on the basis of the drum home position of the photosensitive drum. When printing is performed on a portion where the sensitivity unevenness of the photosensitive drum is steep, or when printing is performed on the peak or bottom of the sensitivity, overcorrection or undercorrection occurs, and the desired density is not necessarily met.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the image quality of a test patch image without suppressing the sensitivity unevenness of the photoconductor and the effect of SD gap, and without increasing the manufacturing cost of the photoconductor and the developer carrier. An image forming apparatus is provided.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a photoconductor that is a rotating body on which an electrostatic latent image is formed,
A developing device including a developer carrying member that is a rotating member that carries a developer for developing an electrostatic latent image on the photosensitive member and conveys the developer to a developing unit facing the photosensitive member;
Patch image density detection means for detecting the density of the test patch image;
Photoconductor phase detection means for detecting the phase of the photoconductor from a predetermined reference position;
Developer carrier phase detection means for detecting a phase from a predetermined reference position of the developer carrier in the developing device;
In an image forming apparatus having
Based on information from the photoconductor phase detection means and the developer carrier phase detection means, a developer carried at a predetermined position of the developer carrier is used, and a predetermined position of the photoconductor is determined. Form a test patch image on the
Detecting the density of the test patch image by the patch image density detecting means;
An image forming apparatus characterized by the above.

  According to the present invention, it is possible to improve the quality of an image based on a test patch image without suppressing the sensitivity unevenness of the photoconductor and the SD gap, and without increasing the manufacturing cost of the photoconductor and the developer carrier. As a result, the accuracy of density control can be improved.

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

Example 1
FIG. 1 shows a schematic cross-sectional configuration of an electrophotographic image forming apparatus which is a first embodiment of an image forming apparatus according to the present invention. First, the overall configuration of the image forming apparatus of this embodiment will be described.

[overall structure]
Referring to FIG. 1, an image forming apparatus 100 according to the present exemplary embodiment includes a scanner unit 1, a laser exposure unit 2, an image forming unit 3 including a photosensitive drum 31, a fixing unit 4, a paper feeding / conveying unit 5, and the like. It is comprised by the engine control part 300 (refer FIG. 3) which controls.

  The scanner unit 1 is a step of creating image data by optically reading a document image by applying illumination 13 to a document 12 placed on a document table 11 and converting the image into an electrical signal.

  The laser exposure unit 2 causes a light beam such as a laser beam modulated according to the image data to enter a rotating polygon mirror (polygon mirror) 21 that rotates at a constant angular velocity, and as a reflected scanning light, a drum-shaped rotating body. The electrophotographic photosensitive member, that is, the photosensitive drum 31 is irradiated.

  The image forming unit 3 executes a series of electrophotographic processes. That is, the photosensitive drum 31 is rotationally driven, charged by the charger 32, and the electrostatic latent image formed on the photosensitive drum 31 by the laser exposure unit 2 is developed with toner by the developing device 33. Thereafter, the toner image is transferred to the sheet S as a transfer material by the transfer / separation device 34 and separated from the photosensitive drum 31. At this time, the minute toner remaining on the photosensitive drum 31 without being transferred is collected by the cleaning device 36.

  The fixing unit 4 is configured by a combination of a roller and a belt, and includes a heat source such as a halogen heater, and melts and fixes the toner on the sheet onto which the toner image has been transferred by the image forming unit 3 by heat and pressure.

  The sheet feeding / conveying unit 5 has at least one sheet storage 51 represented by a sheet cassette or a paper deck, and a plurality of sheets stored in the sheet storage 51 according to an instruction from the printer control unit 300. One sheet is separated from S and conveyed to the image forming unit 3 and the fixing unit 4. When forming an image on both sides of the sheet, control is performed so that the sheet S that has passed through the fixing unit 4 passes through a conveyance path for conveying the sheet S to the image forming unit 3 again.

  The engine control unit 300 communicates with a controller 200 (see FIG. 3) that controls the entire image forming apparatus, and executes control according to the instruction. Then, while managing the states of the scanner unit 1, the laser exposure unit 2, the image forming unit 3, the fixing unit 4, and the paper feeding / conveying unit 5, an instruction is given so that the whole can operate smoothly in harmony. Do.

  FIG. 2 is a cross-sectional view of the image forming unit 3. Along with the output instruction information, the photosensitive drum 31 rotates in the clockwise direction (arrow direction). The cleaner unit, which is the cleaning device 36, collects the toner adhering to the photosensitive drum 31 and cleans the drum surface.

  The primary charger 32 has a discharge device called a grid, and brings the drum surface potential to a specified state. The potential sensor 37 measures the surface potential of the portion (Vl) irradiated with the laser of the photosensitive drum 31 and the primary charging potential (Vd) that is not exposed. After the power is turned on, the surface potential is measured at a timing such as when a certain number of sheets are output, and the laser light quantity, charging bias, developing bias, etc. are changed as appropriate.

  The developing device 33 includes a developing container 61 that contains a developer. In the developing container 61, a developer carrier 62 that is a rotating body, that is, a developing sleeve can be rotated in an opening facing the photosensitive drum 31. Carrying. In this embodiment, a magnetic one-component developer is used as the developer. Further, the developing sleeve 62 is formed of a nonmagnetic cylindrical member, and a magnet roller 63 that is a magnetic field generating means having a plurality of magnetic poles therein is fixedly arranged.

  Accordingly, when the developing sleeve 62 rotates, the developer is carried on the developing sleeve 62, and the developer is conveyed to the developing portion A facing the photosensitive drum 31. The photosensitive drum 31 and the developing sleeve 62 are separated from each other by a predetermined gap, that is, SD gap, and so-called jumping development is performed. Of course, as the developer, a two-component developer including a toner and a magnetic carrier can be adopted, and a magnetic brush developing system can also be adopted.

  The developing device 33 is provided with a replenishing toner cartridge 60a and a hopper 60b serving as a primary storage location, so that the developer can be replenished into the developing container 61 via the toner cartridge 60a and the hopper 60b. It is configured. The replenished developer is stirred and mixed with the developer in the developing container 61 by the stirring blades 64 a, 64 b and 64 c serving as the stirring and conveying means 64, and is supplied to the developing sleeve 62.

  The developing sleeve 62 visualizes the electrostatic latent image formed on the photosensitive drum 31 by the laser at the developing unit A, and forms a toner image.

  A dust collection roller 71 is disposed on the downstream side of the developing device 33 in the rotation direction of the photosensitive drum 31. The dust collecting roller 71 electrostatically attracts and collects toner scattered from the vicinity of the developing position A.

  A pre-transfer charger 72 disposed further downstream than the dust collecting roller 71 assists transferability by applying a charge to the toner image formed on the photosensitive drum 31. The pre-transfer exposure LED 73 assists the separation of the transfer material (sheet) S from the photosensitive drum 31 by lowering the potential of the photosensitive drum 31.

  Thereafter, the paper is conveyed at a predetermined timing, passed through the transfer guide 74, electrostatically transferred by the transfer charger 34a in a stable state, and separated by the separation charger 34b. The transfer material S onto which the toner image has been transferred is sent to the fixing device 4 (see FIG. 1) by the conveying device 35, and is pressurized and heated. After the toner image is fixed, the transfer material S is discharged out of the main body.

  A density detection sensor 70 as a patch image density detection unit is disposed between the transfer / separation charging device 34 and the cleaning unit 36. A test patch image is formed at a specified timing and detected by the sensor 70. The sensor output value is sent to the printer control unit 350.

  The photosensitive drum 31 is provided with a drum home position mark 31M indicating a reference position, and a sensor 31S (see FIG. 6) as a photosensitive member phase detecting means for detecting this mark is disposed in proximity to the photosensitive drum 31. Has been.

  Similarly, a home position mark 62M indicating a reference position is also provided on the developing sleeve 62 of the developing device 33, and a sensor 62S as a developer carrier phase detecting means for detecting the mark 62M (see FIG. 7). Is disposed in proximity to the developing sleeve 62. Each sensor will be described later.

[Engine control unit]
FIG. 3 is an exemplary block diagram of the controller unit 200, the engine control unit 300, and the printer engine unit 350 according to this embodiment.

  The image forming apparatus 100 is divided into a controller unit 200, an engine control unit 300, and a printer engine unit 350.

  The engine control unit 300 mainly includes the following units.

  That is, the engine control unit 300 includes a video interface 301 that is an interface circuit for connecting to the controller unit 200. Furthermore, for example, it has a main control unit 310 including a main control CPU 311, an image processing gate array 312, and an image forming unit 313.

  The main control CPU 311 is a control circuit that controls the respective units of the printer unit as a whole and controls the mechanical control CPU 320 as a sub CPU. The image processing gate array 312 is an image processing circuit that performs γ correction and the like on the image data received by the interface 301. The image forming unit 313 controls the laser exposure amount and the light emission time.

  The mechanical control CPU 320 controls the drive unit 351, the sensor unit 352, the paper feed control unit 353, the high voltage control unit 354, and the like.

  The drive unit 351 is a motor, a clutch, a fan, or the like. The sensor unit 352 is a position detection sensor for the transfer material S or the like. The paper feed control unit 353 controls the supply of the transfer material S. The high voltage controller 354 controls the charge amount of the photosensitive drum 103, the transfer bias of the transfer charger 34a, and the like.

[Density detection sensor]
FIG. 4 is a diagram illustrating an example of the concentration detection sensor 70 in the present embodiment. It is assumed that the concentration detection sensor 70 is included in the second sensor unit 355.

  The density detection sensor 70 includes a light emitting unit 400 such as an LED (light emitting diode) and a light receiving unit 401 such as a PD (photo detector). The light Io emitted from the light emitting unit 400 to the photosensitive drum 31 is reflected by the surface of the photosensitive drum 31. The reflected light Ir is received by the light receiving unit 401, and the amount of received light is output from the light receiving unit 401. The amount of reflected light Io measured by the light receiving unit 401 is monitored by the LED light amount control unit 403. Further, the LED light quantity control unit 403 notifies the main control CPU 311 of the light quantity of the reflected light Io. The main control CPU 311 calculates the density of the patch image based on the emission intensity of the irradiation light Io and the received light amount (measured value) of the reflected light Ir. When the image is not output, the shutter drive control unit 407 is controlled to operate the shutter unit 408.

  Stabilization control is so-called Dmax control for controlling the maximum density described in, for example, Japanese Patent Application Laid-Open No. 8-9158. First, while changing the exposure amount, the development voltage, and the charging voltage, the patch is changed. Create an image on a trial basis. The density of each created patch image is measured, and the exposure amount, development voltage, and charging voltage value corresponding to the target maximum density are calculated based on the measured value.

  The maximum concentration condition of this embodiment will be described by taking a certain environment (temperature 23 ° C., humidity 50%) as an example.

  In the patch image, the charging potential is kept constant (−500 V), the developing bias is kept constant (−350 V, etc.), the contrast potential (Vcont) is changed by laser power (hereinafter referred to as “LPW”), and the density sensor 70 is changed. To detect.

  As shown in FIG. 5, the LPW set value that leads to the maximum density condition (for example, reflection density on paper 1.6, drum loading 0.5 mg / cm 2) is derived.

  The contrast potential (Vcont) is a potential difference between the surface potential of the image area on the photosensitive drum and the potential of the developing sleeve (developing bias).

[Drum home position mark and sensor]
FIG. 6 shows a drum home position mark 31M as a reference position, and a photosensitive member phase detection means for detecting the drum home position mark 31M and detecting the phase (ie, position) of the photosensitive drum 31 based on the detected information. The relationship of the sensor 31S is shown. In this embodiment, a conventional technique for detecting a speed fluctuation of a drum called a drum encoder is used.

  In other words, according to the present embodiment, as shown in FIG. 6, the photosensitive drum 31 is provided with drum flanges 31c on both sides of the drum-shaped photosensitive member 31a. The drum shaft 31b, which is a drum rotation shaft, protrudes outward. ing. In FIG. 6, only the drum flange 31c on one side is shown.

  The drum home position mark 31M is located at a part of any one of the drum flanges 31c and has a structure penetrating the flange 31c. That is, only that part is a hole (hollow).

  In order to detect the mark 31M, a drum home position sensor 31S as a photoconductor phase detecting means is located. The drum home position sensor 31S is an optical sensor composed of an infrared LED 31Sa and a photodiode (hereinafter referred to as “PD”) 31Sb, and is configured such that specularly reflected light is incident on the drum flange 31c. In FIG. 6, the drum home position sensor 31S detects a region 31d indicated by dots on the flange 31c and a drum home position mark 31M.

  The detection area 31d in FIG. 6 represents the area with dots for easy understanding, but is not specially processed and is the same as the other areas of the flange, the same material and the same surface as the flange member. Property (irregularity and color).

  The photosensitive drum 31 whose center is supported by the drum shaft 31b is in a rotatable state. The drum home position sensor 31S has a large detection value because regular reflection light is reflected and incident on the PD 31Sb in the normal detection region 31d. On the other hand, since the drum home position mark 31M is hollow, incident light is not reflected. That is, the detection value is small because no light is incident on the PD 31Sb. Using this signal difference, the position of the drum can be grasped.

  The detection signal of the drum home position sensor 31S is sent to the image processing GA 312 and the main control CPU 311 via the sensor unit 355 of FIG. The drum diameter is 80 mm. It rotates at a speed of 200 mm / sec during image formation and patch detection.

[Sleeve home position mark and sensor]
In FIG. 7, the sleeve home position mark 62M as a reference position and the sleeve home position mark 62M are detected. Then, the relationship of the sensor 62S as the developer carrier phase detection means for detecting the phase (ie, position) of the developing sleeve 62 based on the detection information is shown.

  According to the present embodiment, as shown in FIG. 7, the developing sleeve 62 is a sleeve-like cylindrical body, and the developing operation area is a blasted area 62a except for both ends. The sleeve rotation shaft 62b protrudes outward on both sides of the cylindrical body. FIG. 7 shows only one side of the developing sleeve 62.

  As shown in FIG. 7, the sleeve home position mark 62M is a convex portion provided at the end of the sleeve. A transmissive sensor 62S is arranged so as to sandwich the convex portion 62M. The sensor 62S is a sleeve home position sensor and constitutes a developer carrier phase detection means.

  The sleeve home position sensor 62S irradiates the infrared LED 62Sa from below and makes light incident on the upper PD 62Sb. Except for the sleeve home position, light enters the PD and the detection value increases. When the sleeve home position mark 62M is detected, the detected value is small because the light is blocked. The position of the sleeve can be grasped using this signal difference.

  The sleeve diameter is 30 mm.

[flow]
FIG. 8 shows a flowchart of this embodiment.

  Upon receiving the print instruction, the image forming apparatus determines whether it is time to generate a density patch for density adjustment (S1). In this embodiment, adjustment is performed every 1000 sheets.

  When the detection timing is reached (YES in S1), the developing sleeve drive motor (not shown) is stopped immediately after the developing sleeve 62 is detected using the sleeve home position sensor 62S. As a stopping method, deceleration control as shown in FIG. 9 is performed.

  That is, the rotational speed is gradually decreased (100, 50 mm / sec) from the first home position detection (HP1), and controlled to be 10 mm / sec from the third home position detection (HP3). And it stops after a fixed time (9.4 seconds later) after the third home position detection (HP4) (S2).

  In this way, in this embodiment, the stop operation is performed so that the mark 62M is always applied to the sensor 62S. Normally, the developing device is filled with toner and is in a compressed state, so if it is about 10 mm / sec, it can be stopped without rotating due to inertia.

  FIG. 10 is a schematic timing diagram until the patch image is printed.

  The image forming apparatus in which the developing sleeve 62 is stopped at a predetermined position starts preparation for patch printing.

  With the developing sleeve 62 stopped, the photosensitive drum 31 starts to rotate. The sensor 31S ignores the first home position detection and waits for the sensor 31S to detect the second home position that has reached the stable rotational speed. In this embodiment, the sensor 31S detects the second home position after about 1.2 seconds after a predetermined time has elapsed, and sends an instruction to rotate the sleeve 62 (S3). As in the drum, the developing sleeve is rotated at 200 mm / sec, and after a predetermined time has elapsed, in this embodiment, a patch image is formed using the second sleeve home position detection as a trigger. Is detected (S4).

  With the above operation, the phases of the developing sleeve 62 and the photosensitive drum 31 can be matched.

  The patch image is detected by the density sensor 70 while keeping the charging potential constant and the developing bias constant, changing Vcont with LPW (S5).

  Every time the LPW is changed (S6), the position of the sleeve and the drum is returned to the reference position before the patch printing until a predetermined number of times, i = 5 in this embodiment, (the operation of FIG. 9). Returning to (S2), patch printing under the following conditions is started from there. In this manner, a total of five (i = 5) patch images are printed under the same conditions (in the same place), and the patch image density is detected (S4). As a result, adjustments that are not affected by drum sensitivity or SD gap are possible.

  A desired image forming condition is calculated from the five levels of density values, and the calculation result is registered (S7, S8). Then, the process proceeds to a normal image forming operation (S9), and then the image forming operation is terminated.

  If it is not time to generate a density patch for adjustment in step 1 (S1) (NO in S1), the process immediately proceeds to a normal image forming operation (S9), and then the image forming operation is performed. finish.

  According to the present embodiment, with the above configuration, the sensitivity irregularity of the photosensitive drum 31 and the influence of the SD gap are suppressed, and the image quality of the test patch image is improved without increasing the manufacturing cost of the photosensitive drum 31 and the developing sleeve 62. Can be improved. As a result, the accuracy of density control can be improved.

Example 2
Next, a second embodiment of the image forming apparatus according to the present invention will be described. Since the overall configuration of the image forming apparatus of the present embodiment is the same as that of the image forming apparatus described in the first embodiment, the description of the first embodiment is used and the description thereof is omitted here.

  However, in the first exemplary embodiment, the developing sleeve 62 stops rotating, and at the same time, the photosensitive drum 31 starts rotating, and then the photosensitive drum home position sensor 31S has passed a predetermined time, that is, 1.2 seconds later. The second home position position (reference position) is detected. At that time, the developing sleeve 62 starts to rotate again, and forms a test patch image when the developing sleeve home position sensor 62S detects the second home position (reference position) after a predetermined time has passed. It was.

  On the other hand, in this embodiment 2, it is determined which position on the drum is optimal for patch detection, and a patch image is printed at a location offset from the location printed in the first embodiment. There is a feature in how to determine the offset amount. The flow of Example 2 is shown in FIG.

  Referring to the flowchart of FIG. 11, after the power is turned on (S11), the background profile on the drum is re-registered (S12). This profile is used as correction data when a dynamic range difference occurs due to a scratch on the drum or the like.

  Next, a uniform test pattern (test pattern) is formed on the drum for one revolution, and the image density is detected by the density detection sensor 70 (S13). The concentration detection result is shown in FIG.

  Thus, a density gradient appears despite the fact that the same pattern is printed. The present embodiment is characterized in that a patch is printed in an area where there is little change, and the patch printing position is offset so that there is no influence of the density gradient in the surface of the patch image.

  What is necessary is just to obtain | require what is called a gradient for a density | concentration gradient. It can be seen that the closer to the slope 0, the more stable the region. FIG. 12 shows the stable region. Since the patch image is printed at a portion where the change is smaller than when the patch image is printed at a mountain or valley portion, the density change in the patch image is small. Therefore, the detected density is stabilized and the calibration accuracy is improved.

  The inclination is calculated every 20 msec, the position where the inclination is continuously in the range of 0.9 to 1.1 is calculated (S14), and the specified position of the calculation result is registered (S15). Then, the offset amount is changed so that the test patch image is formed at that position.

  Then, the process proceeds to the image forming operation (S1 to S9) according to the same process as the flow shown in FIG. However, in step 4 (S4), not the home position of the developing sleeve 62 but an offset from the home position, that is, a position where there is little change in density of the patch image.

  Further, it is desirable to optimize the continuous amount and the condition of 20 msec according to the size of the patch image and the process speed (200 mm / sec in this embodiment).

  In the description of the present embodiment, the eccentricity of the sleeve 62 has been ignored. However, by averaging the density profiles of several drums, the profile of only the drum can be easily obtained. The inclination may be calculated from the profile thus obtained, and the patch print position offset amount may be changed.

  Also in this embodiment, the same effects as those of the first embodiment can be obtained. That is, it is possible to improve the image quality of the test patch image without suppressing the sensitivity unevenness of the photosensitive drum 31 and the influence of the SD gap and increasing the manufacturing cost of the photosensitive drum 31 and the developing sleeve 62. As a result, the accuracy of density control can be improved.

Example 3
Next, a third embodiment of the image forming apparatus according to the present invention will be described. Since the overall configuration of the image forming apparatus of the present embodiment is the same as that of the image forming apparatus described in the first embodiment, the description of the first embodiment is used and the description thereof is omitted here.

  However, in the first exemplary embodiment, the developing sleeve 62 stops rotating, and at the same time, the photosensitive drum 31 starts rotating, and then the photosensitive drum home position sensor 31S has passed a predetermined time, that is, 1.2 seconds later. The second home position position (reference position) is detected. At that time, the developing sleeve 62 starts to rotate again, and forms a test patch image when the developing sleeve home position sensor 62S detects the second home position (reference position) after a predetermined time has passed. It was.

  In the second embodiment, the density detection sensor 70 is used to detect the density change of the test patch image, and the position of the photosensitive drum 31 with the smallest density change is registered as a predetermined position. Next, the rotation of the developing sleeve 62 is stopped, and at the same time, the rotation of the photosensitive drum 31 is started. Thereafter, when the photosensitive drum home position sensor 31S detects the reference position of the photosensitive drum 31 after a predetermined time has elapsed, the developing sleeve 62 is detected. Rotate. Then, the test patch image is formed at a predetermined position of the photosensitive drum with the smallest density change of the photosensitive drum 31 calculated based on the detection information of the reference position of the photosensitive drum home position sensor 31S.

  On the other hand, in this embodiment, it is detected which position on the drum has the in-plane average density, and the patch is detected at that position. FIG. 13 shows a flowchart of this embodiment.

  In Patent Document 2, variations in calibration due to drum factors are suppressed. In the first embodiment (embodiment 1), it was possible to suppress the calibration variation occurring between the sleeve and the drum. In the second embodiment (embodiment 2), it is possible to perform more stable calibration by printing on a portion with less unevenness of the drum.

  However, in the above three examples, only a certain part has a desired density, but the other parts do not have a desired density. Furthermore, if correction is performed using uneven peaks and bottoms, an image that is overcorrected or significantly undercorrected is formed as the density of the entire drum.

  In the present embodiment, the offset amount is changed based on the first embodiment as in the second embodiment. In this change method, the density gradient of the drum is obtained in the second embodiment. In this embodiment, the position where the average density is obtained is calculated, and the offset amount is changed so that the patch image is formed at the position.

  That is, the flowchart of the present embodiment shown in FIG. 13 is the same as the flowchart of the second embodiment shown in FIG. 11, and at step 3 (S3), as in the second embodiment, at least one rotation of the photosensitive drum 31. A test pattern is formed over a minute, and the image density is detected by the density sensor 70.

  However, in this embodiment, in step 14 (S14), the average density position is calculated, and the specified position of the calculation result is registered (S15). This is different from the second embodiment. Then, the offset amount is changed so that a patch image is formed at that position.

  The inclination is calculated every 20 msec, the position where the inclination is continuously in the range of 0.9 to 1.1 is calculated (S14), and the specified position of the calculation result is registered (S15).

  The average value can be calculated by a method well known to those skilled in the art. Detailed description is omitted.

  That is, in the third embodiment, the density detection sensor 70 is used to detect the density change of the test patch image, and the position of the photosensitive drum 31 that is the average value of the density change is registered as a predetermined position. Next, the rotation of the developing sleeve 62 is stopped, and at the same time, the rotation of the photosensitive drum is started. Thereafter, when the photosensitive drum home position sensor 31S detects the reference position of the photosensitive drum after a predetermined time has elapsed, the developing sleeve 62 is rotated. Then, the test patch image is formed at the predetermined position of the photosensitive drum, which is the average value of the density change of the photosensitive drum, calculated based on the detection information of the reference position of the photosensitive drum home position sensor 31S. The

  Also in this embodiment, the same operational effects as those of Embodiments 1 and 2 can be obtained. That is, it is possible to improve the image quality of the test patch image without suppressing the sensitivity unevenness of the photosensitive drum 31 and the influence of the SD gap and increasing the manufacturing cost of the photosensitive drum 31 and the developing sleeve 62. As a result, the accuracy of density control can be improved.

In the second and third embodiments, the position on the photosensitive drum on which the patch is to be printed has been determined. However, it may be determined which position on the developing sleeve 62 is to be used for printing. This is particularly effective when the developing sleeve diameter is large. For example, it is effective when the developing sleeve has a circumferential length longer than the circumferential length of the photosensitive drum 31 or a belt-like developer carrier.

  That is, according to the first method of the present modification, as in the second embodiment, a test pattern is formed on the photosensitive drum 31 for at least one turn, and the density sensor 70 detects a change in density of the test pattern. . Then, the position of the developing sleeve 62 with the smallest density change is registered as the specified position.

  Next, the rotation of the developing sleeve 62 is stopped, and at the same time, the rotation of the photosensitive drum 31 is started. Thereafter, when the photosensitive drum home position sensor 31S detects the reference position of the photosensitive drum 31 after a predetermined time has elapsed, the developing sleeve 62 is rotated, and the predetermined position of the developing sleeve 62 with the smallest density change of the developing sleeve 62 is used. Then, a test patch image is formed.

  According to the second method of this modification, as in the third embodiment, a test pattern is formed on the photosensitive drum 31 for at least one turn, and the density change of the test pattern is detected by the density sensor 70. Then, the position of the developing sleeve 62 that becomes the average value of the density change is registered as a specified position.

  Next, the rotation of the developing sleeve 62 is stopped, and at the same time, the rotation of the photosensitive drum 31 is started. Thereafter, when the photosensitive drum home position sensor 31S detects the reference position of the photosensitive drum 31 after a predetermined time has elapsed, the developing sleeve 62 is rotated, and the predetermined position of the developing sleeve 62 that becomes the average value of the density change of the developing sleeve 62 is detected. To form a test patch image.

  Furthermore, when it is desired to grasp only the SD gap, the profile of the SD gap can be grasped by applying only the developing bias. This method may be used to determine which position on the developing sleeve is to be printed.

  In other words, in the above embodiment, the test pattern formed on the photosensitive drum 31 is charged and exposed to the photosensitive drum 31 to form an electrostatic latent image of a predetermined pattern, and the electrostatic latent image is developed. As a result, a test pattern was formed.

  On the other hand, a test pattern is formed by applying only the developing bias without forming an electrostatic latent image and, in some cases, applying only the developing bias after uniformly charging the photosensitive drum 31. .

  Therefore, in this case, a test pattern of the toner image is formed not only on the patch forming portion having a predetermined shape but on the entire surface of the photosensitive drum 31. For this reason, from the viewpoint of toner consumption, it is desirable to perform the maintenance only once a month, or only at the time of factory shipment, development device, or drum replacement.

  As described above, according to the present invention, the test patch image for calibration can be printed at the same SD gap and the same photosensitive drum position in consideration of the home position of the developing sleeve 62. It was possible to reduce the variation of each calibration.

  Further, the position of the photosensitive drum or the position of the developing sleeve to be used to form the test patch image can be more closely matched to the desired density by using the gradient and average value of the patch image density change. Stable calibration is now possible.

  In each of the above embodiments, the present invention has been described with respect to a direct-type black and white image forming apparatus that directly transfers a toner image onto a transfer material, but the present invention is not limited to this. The present invention may be an image forming apparatus using an intermediate transfer member or a color image forming apparatus.

  Further, the photosensitive member and the developer carrying member as the rotating member do not need to be a photosensitive drum and a developing sleeve, respectively, but are a belt-like photosensitive belt and a developing member that are stretched around a support roller and movable in a certain direction. It can also be a belt.

1 is an overall configuration cross-sectional view of an embodiment of an image forming apparatus according to the present invention. 1 is a configuration cross-sectional view of an image forming unit in an embodiment of an image forming apparatus according to the present invention. 1 is a block diagram of an engine control unit and a printer engine unit in an embodiment of an image forming apparatus according to the present invention. It is a schematic block diagram of one Example of a density sensor. FIG. 3 is a conceptual diagram of calculation of a maximum density condition in an embodiment of an image forming apparatus according to the present invention. FIG. 3 is a relationship diagram between a drum home position sensor and a mark in an embodiment of the image forming apparatus according to the present invention. FIG. 3 is a relationship diagram between a sleeve home position sensor and a mark in an embodiment of the image forming apparatus according to the present invention. 3 is a flowchart in an embodiment of an image forming apparatus according to the present invention. It is explanatory drawing of one Example of a sleeve stop operation | movement. It is explanatory drawing of one Example of patch printing timing. 6 is a flowchart in another embodiment of the image forming apparatus according to the present invention. It is explanatory drawing of one Example of the density profile on a drum. 6 is a flowchart in another embodiment of the image forming apparatus according to the present invention. It is a figure for demonstrating the subject of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Scanner part 2 Laser exposure part 3 Image forming part 4 Fixing part 5 Paper supply / conveyance part 31 Photosensitive drum (photosensitive body)
31M Drum home position mark 31S Drum home position sensor (photoconductor phase detection means)
33 Developing Device 62 Developing Sleeve (Developer Carrier)
62M Sleeve home position mark 62S Sleeve home position sensor (developer carrier phase detection means)
100 Image forming apparatus

Claims (6)

A photoreceptor that is a rotating body on which an electrostatic latent image is formed;
A developing device including a developer carrying member that is a rotating member that carries a developer for developing an electrostatic latent image on the photosensitive member and conveys the developer to a developing unit facing the photosensitive member;
Patch image density detection means for detecting the density of the test patch image;
Photoconductor phase detection means for detecting the phase of the photoconductor from a predetermined reference position;
Developer carrier phase detection means for detecting a phase from a predetermined reference position of the developer carrier in the developing device;
In an image forming apparatus having
Based on information from the photoconductor phase detection means and the developer carrier phase detection means, a developer carried at a predetermined position of the developer carrier is used, and a predetermined position of the photoconductor is determined. Form a test patch image on the
Detecting the density of the test patch image by the patch image density detecting means;
An image forming apparatus.   2. The test patch image is formed when the developer carrying member and the photoconductor are rotated and a phase between the developer carrying member and the photoconductor reaches a specified position. Image forming apparatus. A test pattern is formed on the photoconductor over at least one turn, and the density change of the test pattern is detected using the patch image density detection means, and the position of the photoconductor having the smallest density change is set as a specified position. Register,
Next, after the photoconductor phase detecting means detects the reference position of the photoconductor, a test patch image is formed at the specified position of the photoconductor where the density change of the photoconductor is the smallest. The image forming apparatus according to claim 1. A test pattern is formed on the photoconductor over at least one turn, and the density change of the test pattern is detected using the patch image density detection means, and the position of the photoconductor that is an average value of the density change is defined. Register as location,
Next, after the photoconductor phase detecting means detects the reference position of the photoconductor, a test patch image is formed at the specified position of the photoconductor that is an average value of the density change of the photoconductor. The image forming apparatus according to claim 1. A test pattern is formed on the developer carrier over at least one turn, and the density change of the test pattern is detected using the patch image density detection unit, and the position of the developer carrier with the smallest density change is detected. As the default position,
Next, after the developer carrier phase detection means detects the reference position of the developer carrier, the specified position of the developer carrier with the least density change of the developer carrier is used. The image forming apparatus according to claim 1, wherein a test patch image is formed. A test pattern is formed on the developer carrying member for at least one turn, and the density change of the test pattern is detected by using the patch image density detecting means to obtain an average value of the density change. Is registered as the specified position,
Next, after the developer carrier phase detection means detects the reference position of the developer carrier, the specified position of the developer carrier that is an average value of the density change of the developer carrier is used. The image forming apparatus according to claim 1, wherein a test patch image is formed.

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