JP4865045B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus having a plurality of image forming units, for example, an electrophotographic color image forming apparatus, yellow, magenta, cyan, and black printing mechanisms are arranged along the traveling direction of the conveyor belt. Yes. FIG. 16 is a schematic view showing a conventional image forming apparatus having such a configuration. The image forming units 1a to 1d include a charging unit, an exposure unit, a developing unit, a transfer unit, an image carrier, and the like. The exposure units 3a to 3d form an electrostatic latent image on the image carrier, and the developing unit develops the electrostatic latent image to form a visible image, that is, a toner image. The adsorbing units 4a and 4b charge the conveyance belt 7 and adsorb the print medium 6 by electrostatic force. The driving rollers 5a-5c are rotationally driven by a driving source (not shown) to cause the conveyor belt 7 to travel in the arrow direction. The transfer units 2a-2d transfer the image on the image carrier to the medium 6.

  The image forming units 1a to 1d contain toners corresponding to black, yellow, magenta, and cyan. The print medium 6 conveyed to the suction means 4a and 4b by a paper feeding mechanism (not shown) is adsorbed by the conveyance belt 7, placed on the conveyance belt 7, and further conveyed. When the print medium 6 reaches the image forming units 1a to 1d, images on the image forming units 1a to 1d are sequentially transferred onto the print medium 6 by the transfer unit 2 at a timing controlled by a control unit (not shown). . The print medium 6 having all or part of the image formed by the image forming units 1a to 1d is then separated from the conveying belt 7 and thermally fixed by the fixing units 8a and 8b. Discharged.

  FIG. 17 shows the calibration of the density sensor 9 and the image density detection operation according to the prior art. The sensor used as the density sensor 9 has variations in characteristics. The cause of the variation may be a variation in the light emission amount of the light emitting element used in the sensor, a variation in the light receiving sensitivity of the light receiving element, a mounting state of the light emitting element and the light receiving element (such as a mutual mounting angle), or the like. If there are variations in characteristics of the density sensor 9, even if a density detection pattern having the same density is detected, the detection value differs for each sensor. As a result, a difference occurs in the print density between the image forming apparatuses.

  In order to solve this problem, a shutter 10 is provided between the density sensor 9 and the conveyor belt 7, and the density reference member 11 is mounted on the surface of the shutter 10 that faces the density sensor 9. When this density reference member 11 is detected, calibration (S1-S2 in FIG. 17) is performed to adjust the light emission amount of the density sensor 9 so that the same detection value can be obtained from any sensor. This calibration is performed prior to the later-described image density detection operation. The shutter 10 is opened and closed by being driven by a solenoid or motor (not shown).

The image density detection operation (S3-S8 in FIG. 17) is performed at a timing such as a preliminary operation different from the normal printing operation. During the density detection operation, the print medium 6 is not transported, and the density detection pattern formed by the image forming units 1 a to 1 d is directly transferred onto the transport belt 7. As the transport belt 7 travels, the density detection pattern is carried onto the density sensor 9. The density sensor 9 performs density detection during a period in which the density detection pattern printed on the transport belt 7 passes over the density sensor 9. The density sensor 9 includes a light emitting unit and a light receiving unit. The light emitting unit emits light to the density detection pattern printed on the conveyor belt 7 and the light receiving unit receives the reflected light, thereby detecting the density of the density detection pattern.
(For example, refer to Patent Document 1).

JP 2001-63191 A

  Prior to the image density detection operation, when the preliminary correction of the density sensor 9 is performed, the shutter 10 is moved to the closing position, and the density reference member 11 mounted on the shutter 10 is opposed to the density sensor 9. The density sensor 9 detects the density reference member 11. When detecting the density of the image, the density sensor 9 detects the density pattern formed on the conveyor belt 7 by moving the shutter 10 to a position where the shutter 10 is opened. However, the conventional apparatus has the following problems. That is, for some reason, (1) the shutter 10 does not close, (2) the shutter 10 does not open, and (3) the shutter 10 closes while detecting the density, there is a possibility that accurate density detection may not be performed. There was a possibility of incorrect density correction.

An image forming apparatus according to the present invention includes:
A plurality of image forming units each forming a toner image of a corresponding color, a toner image carrier capable of carrying a toner image formed by the image forming unit, and a toner image density of the toner image carrier being detected And is driven to be located at either the closed position or the open position, and is located between the toner image carrier and the density detector at the closed position, and at the open position. Has an open / close member that is not located between the toner image carrier and the density detector, and a controller that determines whether the open / close member is in the closed position,
In the step of changing the image forming condition after the control unit instructs the control unit to move the opening / closing member to the open position ,
Based on the first detection value detected at a timing when the image forming unit detects the first toner image generated on the toner carrier before the image forming condition is changed , and the first detection value. A second detection value detected at a timing at which the image forming unit detects a second toner image generated on the toner carrier after the image forming condition is changed ,
The control unit is a case where a difference between an expected value that would be detected from the second toner image and the second detected value is not within an allowable range, and the first detected value and the first detected value are When the detected value of 2 is substantially equal, it is determined that the opening / closing member is in the closed position,
When the difference between the expected value and the second detection value is within an allowable range, the image forming condition corresponding to each image forming unit is changed until all the image forming conditions of the plurality of image forming units are changed. The step of sequentially changing the process is continued.

  When detecting the density of the image, it is possible to detect a malfunction in the shutter 10 by detecting the difference in the detected value of the density (detected value) before and after changing the image forming condition. This increases the reliability of the detection result of the density sensor 9, enables more accurate density correction, and maintains stable print quality.

  By detecting the difference between the expected value of the predetermined density and the actual density value when detecting the density, it is possible to detect a malfunction of the image forming unit. Thereby, the reliability of the detection output of the density sensor 9 is increased, more accurate density correction is possible, and stable image quality can be maintained.

It is a control block diagram which shows the outline | summary of an apparatus. The positional relationship between the density reference member and the density sensor when the open / close member is closed is shown. The positional relationship between the density reference member and the density sensor when the open / close member is opened is shown. The change of the output by the drive current of a density sensor is shown. The relationship between the density of the image to be detected and the output of the density sensor is shown. 2 shows a schematic flow of a concentration detection operation according to the first embodiment. An example of a density detection pattern is shown. 10 is a flowchart showing a density detection operation according to the second embodiment. The density | concentration detection pattern by Embodiment 2 is shown. 10 is a flowchart illustrating a density detection operation according to the third embodiment. The density detection pattern by Embodiment 3 is shown. The relationship of density change when image forming conditions are changed is shown. 10 is a flowchart illustrating an outline of a density detection operation according to a fourth embodiment. Indicates the allowable range of image density. 10 is a flowchart illustrating an outline of a density detection operation according to a fifth embodiment. It is the schematic of the prior art and the image forming apparatus of this invention. The density sensor calibration and image density detection operation according to the prior art will be described.

Embodiment 1 FIG.
In the first embodiment, when the calibration operation (S1-S2 in FIG. 17) using the reflectance of the conventional density reference member is executed, the value of the drive current of the light emitting element is detected, and the shutter 10 It is characterized by determining whether the opening / closing operation is good or bad.

  The first embodiment will be specifically described below with reference to the drawings. The configuration of the apparatus according to the first embodiment is the same as the conventional example shown in FIG. FIG. 1 is a control block diagram showing an outline of the apparatus. FIG. 2 shows a state in which the shutter 10 is closed. FIG. 3 shows a state where the shutter 10 is opened.

  In FIG. 1, the control unit 21 drives the image forming units 1a to 1d, the high-voltage power supply 24, and the driving unit 25 according to the data transferred from the host device or the host controller 20 to form an image. A density detector described later detects the density of this image. The operator performs various settings of the image forming apparatus via the operation / display unit 22, and the operation / display unit 22 displays various types of information on the image forming apparatus. The shutter driving unit 27 is a driving unit for opening and closing the shutter.

  Reflection by the color toner is mainly diffuse reflection. Therefore, as the amount of color toner adhering to the conveyor belt increases, the amount of reflected light also increases due to diffuse reflection. On the other hand, reflection by the conveyor belt itself is mainly specular reflection. Therefore, when toner is not attached to the belt, the amount of reflected light due to the specular reflection of the belt is maximized. Since the black toner absorbs light, the amount of reflected light due to specular reflection decreases as the amount of black toner adhering to the belt increases.

  When the conveyance belt 7 itself diffuses and reflects, light that is diffusely reflected by the toner image formed on the conveyance belt 7 and light that is diffusely reflected by the conveyance belt 7 are incident on the density sensor 9. Only the light diffusely reflected by the image cannot be detected accurately. Therefore, the conveyor belt 7 is selected to have a surface that is difficult to diffusely reflect. Therefore, the transport belt 7 is configured by a uniform member, and the optical reflection characteristics of the surface thereof are uniform over the entire surface of the transport belt 7.

  FIG. 4 shows a change in output with respect to the driving current of the density sensor 9. A voltage V1 in FIG. 4 is a detection output of the density sensor 9 when there is no diffuse reflected light from the image whose density is to be detected. FIG. 5 shows the relationship between the density of an image to be subjected to density detection and the output of the density sensor 9. A voltage V2 in FIG. 5 is a detection output of the density sensor 9 when there is no specular reflection light from the image.

Here, calibration of the density sensor 9 will be described. As shown in FIG. 4, the detection output of the sensor used as the density sensor 9 varies from sensor to sensor. Possible causes of sensor variations include variations in the amount of light emitted from the light-emitting elements, variations in light-receiving sensitivity of the light-receiving elements, and mounting conditions (such as inclination during mounting) of the light-emitting elements and the light-receiving elements. If the detection output of the density sensor 9 varies, the detection output varies depending on the sensor even when detecting density detection patterns having the same density. Therefore, a difference in print density occurs between the image forming apparatuses. When detecting the same density reference member 11, the value of the drive current passed through the light emitting element is adjusted for each density sensor 9 so that the same detection output can be obtained from any density sensor. This is the calibration of diffuse reflection of the density sensor 9. This calibration is performed prior to the image density detection operation. Thus, in the diffuse reflection calibration of the density sensor 9, the calibration is performed with the shutter 10 closed to eliminate variations in sensitivity of the density sensor 9 related to color. On the other hand, in the calibration of the specular reflection of the density sensor 9, the density sensor 9 is calibrated with the shutter 10 opened to eliminate variations in sensitivity regarding black. The density sensor 9 includes a light receiving element for receiving diffuse reflection and a light receiving element for receiving specular reflection. These two light receiving elements have different mounting directions, and each of them easily receives the target reflected light.

  FIG. 6 shows a schematic flow of the calibration and density detection operation according to the first embodiment. FIG. 7 shows density detection patterns 12a-12d according to the first embodiment. The operation of the first embodiment will be described with reference to FIG. First, in S101, the shutter 10 is closed. In S102, the drive current of the light emitting element is set to zero. When the light emitting element of the density sensor is not emitting light, that is, when the value of the drive current is zero, dark output (voltage V1 in FIG. 4) appears on the output side of the density sensor 9. This dark output has a slight variation as shown in FIG.

  In S103, it is determined whether or not the detection output of the density sensor 9 in S102 is within a predetermined allowable range. If the detection output is not within the predetermined range, the process proceeds to S104, where it is determined that the density sensor 9 is defective, and the process is terminated without performing the subsequent density detection operation. Examples of the malfunction of the density sensor 9 include a malfunction and assembly failure of the light receiving element of the density sensor 9, or a signal path from the density sensor 9 to a control unit that detects the drive current of the density sensor 9 and the detection output voltage. A short circuit with the ground or the like at can be considered.

  In S103, if the detected output is within a predetermined allowable range, the process proceeds to S105, and diffuse reflection calibration is performed using the density reference member 11 provided facing the density sensor 9 of the shutter 10. This calibration is the same as the calibration of S1-S2 in FIG.

  In S105, when the calibration of diffuse reflection is performed, if the shutter 10 is not closed due to malfunction or the like, the conveyance belt 7 is used as a reference reflection member, and the calibration is automatically continued. Since almost no diffuse reflection is obtained from the conveyor belt 7, more drive current is required for the light emitting element of the density sensor than in the calibration using the density reference member 11. Therefore, a comparison with the normal current range in the case of executing the diffuse reflection calibration is performed. If the normal current range is exceeded, it is determined that there is an abnormality, and the process proceeds to S119, where the shutter remains open. The process is terminated without performing the subsequent density detection operation.

  Next, in S107, the shutter 10 is opened (FIG. 3). In S108, calibration of specular reflection (also referred to as regular reflection) is performed using the conveyance belt 7 instead of the density reference member.

  Next, in S109, it is determined whether or not the value of the drive current of the light emitting element is within a preset allowable range. In S109, if the value of the drive current is not within the preset allowable range, the process proceeds to S117, where it is determined that the shutter is still closed, and the subsequent processing is terminated.

  If the calibration is normally completed in S105 to S106 and S108 to S109, the shutter 10 is closed in S110, and the process proceeds to S111. In S111, the density detection mode is entered. That is, the image forming units 1a-1d and the conveyance belt 7 are driven to generate density detection patterns 12a-12d (FIG. 7) of cyan, magenta, yellow, and black, and the density detection patterns 12a-12d are transferred by the transfer unit 2. Are sequentially transferred onto the conveyor belt 7.

Next, in S112, the shutter 10 is opened by a solenoid or a motor (not shown) (FIG. 3). In step S113, the conveyance belt 7 is caused to travel, and the density detection patterns 12a-12d on the conveyance belt 7 are moved over the density sensor 9. In S114, the density of the density detection patterns 12a-12d is detected and stored. Further, the image density correction is performed by changing image forming conditions such as a developing energy amount such as a high voltage for development and an electrostatic latent image forming energy amount such as a light amount of an exposure device in accordance with the detected density. In S115, it is confirmed whether or not the density detection and density correction of the density detection patterns 12a to 12d for all colors have been completed. When density detection and density correction are completed, the shutter 10 is closed in S116 (FIG. 2), and the process is terminated. If a shutter malfunction occurs in the middle of density detection, the amount of development energy, such as a high voltage for development, or the amount of light from the exposure device is based on the density obtained by the detection operation until the shutter malfunction occurs. The image forming conditions such as electrostatic latent image forming energy are changed.

  In the first embodiment, in addition to the operation of the conventional apparatus, the output of the density sensor 9 in a state where no drive current is supplied to the light emitting element of the density sensor is confirmed before the calibration of the density sensor 9 is performed. As a result, it is possible to detect a malfunction of the concentration sensor itself, a short circuit of the wiring, or the like. Further, since the quality of the opening / closing operation of the shutter 10 can be determined based on the value of the drive current passed through the density sensor 9 at the time of calibration, erroneous detection of density due to the malfunction of the shutter 10 can be prevented. Thereby, the reliability of the detection output of the density sensor 9 is improved, more accurate density correction is possible, and stable print quality can be maintained.

Embodiment 2. FIG.
It is characterized in that at the time of density detection, the density of a density detection pattern having two different density values, low density and high density, is detected to detect a shutter malfunction.

  FIG. 8 is a flowchart showing the density detection operation according to the second embodiment. FIG. 9 shows a density detection pattern according to the second embodiment.

  In S201 of FIG. 8, the shutter 10 is closed. In S202, the diffuse reflection detection calibration is performed using the density reference member 11 provided on the surface of the shutter 10 so as to face the density sensor 9. This calibration is the same as the calibration of S1-S2 in FIG. In S203, it is determined whether or not the calibration has ended normally. If the calibration has ended normally, the process proceeds to S204. If the calibration has not ended normally, the process proceeds to S216, where it is determined that the shutter remains open. The subsequent processing is terminated.

  In S204, the shutter 10 is opened. Next, in step S <b> 205, specular reflection calibration is performed by the transport belt 7 instead of the density reference member 11. Next, in S206, it is confirmed whether the calibration is normally completed. Since the details of the determination are the same as those in the first embodiment, detailed description thereof is omitted. If it is determined that the process has not ended normally, the process proceeds to S217, and the process ends without performing the operation in the subsequent density detection mode, assuming that the shutter remains closed.

  In S206, it is determined whether or not the calibration is normally completed. If the calibration is normally completed, the process proceeds to S207, and the image forming units 1a to 1d and the conveyance belt 7 are driven, and cyan, magenta, yellow, and black 9 generate density detection patterns having a low density (12a-12d) and a high density (12A-12D) as shown in FIG. 9, and the density detection pattern is transferred onto the conveyance belt 7 by the transfer unit 2. To form.

  In step S <b> 208, the conveyance belt 7 is run to move the density detection pattern to above the density sensor 9. In S209, the density of the low density pattern 12a-12d is detected, and this density is stored. In S210, it is determined whether or not the density detection of the low density pattern of all colors is completed. S209 and S210 are repeated until the density detection and density storage of the low density patterns of all colors are completed.

  In S211, the density of the high density pattern 12A-12D of each color is detected, and this density is stored. In S212, the density values of the low density patterns 12a-12d and the high density patterns 12A-12D are compared. If the density value difference is lower than the predetermined reference value, the process proceeds to S218, where it is determined that the shutter 10 remains closed, and the process ends. In S212, if the difference in density of each color is equal to or greater than a predetermined reference value, it is determined that the color is normal, and the process proceeds to S213. In S213, it is determined whether or not the density detection of all colors has been performed normally. If not completed, S211 to S213 are repeated. In S213, if it is determined that the density detection of all colors has been performed normally, the process proceeds to S214, and electrostatic latent such as the development energy amount such as a high voltage for development and the light amount of the exposure device, depending on the detected density. Image forming conditions such as image forming energy are changed. In S215, the shutter 10 is closed and the process ends. If a shutter malfunction occurs in the middle of density detection, the amount of development energy, such as a high voltage for development, or the amount of light from the exposure device is based on the density obtained by the detection operation until the shutter malfunction occurs. The image forming conditions such as electrostatic latent image forming energy are changed.

Embodiment 3 FIG.
Embodiment 3 has the following features. That is, for each color, two density patterns of low density and high density form adjacent density detection patterns, and by detecting these densities, a malfunction of the shutter is detected. Further, when a malfunction of the shutter occurs during the density detection, the amount of development energy such as a developing high voltage or the exposure device is determined based on the density obtained by the detection operation until the malfunction of the shutter occurs. The image forming conditions such as the electrostatic latent image forming energy such as the amount of light are changed.

  FIG. 10 is a flowchart showing the density detection operation according to the third embodiment. FIG. 11 shows a density detection pattern according to the third embodiment.

  In S301 of FIG. 10, the shutter 10 is closed. In step S <b> 302, diffuse reflection calibration is performed using the density reference member 11 provided to face the density sensor 9 of the shutter 10. This calibration is the same as the calibration of S1-S2 in FIG. In S303, it is determined whether or not the diffuse reflection calibration is normally completed. If the calibration is normally completed, the process proceeds to S304. If the calibration is not completed normally, the process proceeds to S315, and the shutter remains open. It judges that it is a thing and complete | finishes subsequent processes.

  In S304, the shutter is opened. In step S <b> 305, calibration of specular reflection is performed using a conveyance belt instead of the density reference member 11. In step S306, it is confirmed whether the specular reflection calibration has been completed normally. Details of the determination are the same as those in the first embodiment, and a description thereof is omitted. If it is determined that the process has not been completed normally, the process proceeds to S316, where it is determined that the error has occurred while the shutter is closed, and the process ends without performing the subsequent density detection mode operations.

  In S306, if the specular reflection calibration is completed normally, the process proceeds to S307, where the image forming units 1a-1d and the belt 7 are driven, and each of cyan, magenta, yellow and black as shown in FIG. The density detection pattern in which the low density (12a-12d) and high density (12A-12D) patterns are adjacent to each other is generated, and the density detection pattern is formed on the transport belt 7 by the transfer unit 2. In step S <b> 308, the conveyance belt 7 is run to move the density detection pattern to above the density sensor 9.

  In step S309, for example, the density of the cyan low density pattern 12d is detected and stored. In step S310, the density of the cyan high density pattern 12D is detected. In S311, the density value of the low density pattern 12d is compared with the density value of the high density pattern 12D. If the density value difference is lower than the predetermined reference value, the process proceeds to S317, where it is determined that the shutter 10 remains closed, the subsequent density detection mode operation is not executed, and development such as development high voltage is performed. The processing ends without changing the image forming conditions such as the energy amount and the electrostatic latent image forming energy such as the light amount of the exposure device. S309 to S311 are repeated until the change of the image forming conditions is completed for all colors. Since the processing speed is sufficiently higher than the belt traveling speed, the density detection pattern shown in FIG. 11 can be processed only by passing the density sensor 9 once.

  In S311, if the density difference between the low density pattern and the high density pattern is equal to or greater than a predetermined reference value, it is determined that the density detection has ended normally, and the process proceeds to S312. In S312, corresponding to the density values detected in S309 and S310, image forming conditions such as a developing energy amount such as a developing high voltage and an electrostatic latent image forming energy such as a light amount of an exposure device are changed.

  Proceeding to S313, it is determined whether or not the density detection has been completed for all the colors. If not, S309 to S313 are repeated. If the detection of the density for all colors is completed in S313, the shutter 10 is closed in S314. As described above, in the third embodiment, a reliable concentration detection operation can be performed.

Embodiment 4 FIG.
The configuration of the image forming apparatus used in the fourth embodiment is the same as that of the conventional apparatus shown in FIG. The density detection operation according to the fourth embodiment will be described below. In the fourth embodiment, for the density detection patterns 12a to 12d, a step of detecting whether or not the operation of the shutter 10 is defective by detecting a difference in density value (detection value) before and after changing the image forming condition. The added point is different from the first embodiment.

  FIG. 12 shows the relationship between the expected value of density and the detected value when changing the image forming conditions according to the fourth embodiment. For example, when the density (detected value) detected in S409 in FIG. 13 described later is A in FIG. 12, the image forming conditions such as the development energy amount and the electrostatic latent image forming energy amount are increased in the direction of increasing the density. When changed, the expected value of the density after correction is B1 in FIG. Further, a range surrounded by two broken lines in FIG. 12 is an allowable error range from the expected value B1. In S412, it is confirmed whether or not the detected density value in S411 is within an allowable range.

  Here, when the detected value is B2 with respect to the expected value B1, B2 is outside the allowable range surrounded by the broken line, and the difference from the expected value B1 is B. B2 is substantially equal to A, which means that the shutter remains closed.

  When the image forming conditions are changed in the direction of decreasing the density, the expected density value after correction is C1 in FIG. A range surrounded by two broken lines is an allowable error range from the expected value C1 point. Here, when the detected value is the C2 point with respect to the expected density value C1, the C2 is outside the allowable range surrounded by the broken line, and the difference from the expected value C1 is C. C2 is substantially equal to A, which means that the shutter remains closed.

  FIG. 13 is a flowchart showing an outline of operations in the calibration mode and the density detection mode according to the fourth embodiment. The concentration detection operation of the fourth embodiment will be described in detail below with reference to FIGS. 13, 12, 2, 3, and 17. FIG.

  In S401 of FIG. 13, the shutter 10 is closed (FIG. 2). In S402, the drive current of the light emitting element is set to zero.

  In step S403, it is determined whether the detection output of the density sensor 9 in step S402 is within a predetermined allowable range. If the detected output is not within the predetermined allowable range, the process proceeds to S415, where it is determined that there is a problem with the density sensor 9, and the process is terminated without performing the subsequent density detection operation. In S403, if the detection output of the density sensor is within the predetermined allowable range, the process proceeds to S404. In S <b> 404, calibration is performed to detect diffusely reflected light from the density reference member 11 provided to face the density sensor 9 of the shutter 10. Here, the calibration of the density sensor 9 is the same as that described in the first embodiment, and therefore the description thereof is omitted.

  Next, in S405, it is determined whether the calibration has been completed normally. Since this determination is performed in the same manner as in the first embodiment, description thereof is omitted. If it is determined that there is an abnormality in S405, the process proceeds to S416, and the process is terminated without executing the subsequent density detection mode operation, assuming that the shutter 10 remains open. When the calibration is normally completed in S405, the process proceeds to S406, where the image forming units 1a-1d and the conveyance belt 7 are driven, and the density detection pattern 12a including each color of cyan, magenta, yellow, and black (FIG. 7). -12d is generated. These density detection patterns 12a to 12d are transferred onto the conveyor belt 7 by the transfer unit 2. Next, in S407, the shutter 10 is opened by a solenoid or a motor (not shown) (FIG. 3).

  In step S <b> 408, the conveyance belt 7 or the like is caused to travel to a position where the density pattern on the conveyance belt 7 faces the density sensor 9. In S409, the density detection patterns 12a-12d for the respective colors are detected, and the detected density values (detected values) are stored. In S410, it is confirmed whether or not the density detection of the density patterns 12a-12d for all colors has been completed. Until the density detection of all colors (detection of detection values) is completed, in S409-S410, the density detection patterns 12a-12d are sequentially moved to face the density sensor 9, density detection is performed, and the detected density value (detection) Value).

  In S411, after changing the image forming conditions such as the development energy amount such as a high voltage for development and the electrostatic latent image formation energy amount such as the light amount of the exposed portion based on the density (detected value) detected in S409. Then, the density detection pattern is printed again. The density of the density detection patterns 12a-12d is detected. If the detected density value (detected value) is not within the allowable range shown in FIG. 12, the determination result in S412 is N, and the process proceeds to S417. In S417, it is determined that the shutter remains closed. However, since control to open the shutter is still performed in S407, the process proceeds to S414, and the process is terminated after a command to close the shutter is issued. In S412, it is checked in S411 whether or not the detected value is within the allowable range of the expected value.

  If it is determined in S412 that the difference between the detected value of the density after changing the image forming conditions, that is, the density correction, and the expected value is within the allowable range, the process proceeds to S413. In S413, it is detected whether or not the detection of the density detection patterns 12a-12d for all colors is completed. S411 to S413 are repeated until the confirmation of the densities of all colors is completed. When all colors are finished, the process proceeds to S414, the shutter 10 is closed, and the process is finished.

  As described above, according to the fourth embodiment, when detecting the image density, the difference in the detected value of the density (detected value) before and after changing the image forming condition is detected to detect the malfunction of the shutter 10. It becomes possible. This increases the reliability of the detection result of the density sensor 9, enables more accurate density correction, and maintains stable print quality. If a shutter malfunction occurs in the middle of density detection, the amount of development energy, such as a high voltage for development, or the amount of light from the exposure device is based on the density obtained by the detection operation until the shutter malfunction occurs. The image forming conditions such as electrostatic latent image forming energy are changed.

Embodiment 5
The configuration of the apparatus used in the fifth embodiment is the same as that of the conventional apparatus shown in FIG. The operation of the calibration and density detection mode according to the fifth embodiment will be described below. In the fifth embodiment, it is possible to detect a malfunction of the image forming unit by detecting a difference between an expected value of a predetermined density and an actual density value at the time of density detection. Thereby, the reliability of the detection output of the density sensor 9 is increased, more accurate density correction is possible, and stable image quality can be maintained.

  FIG. 15 is a flowchart showing an outline of the density detection operation according to the fifth embodiment. The operation of the fifth embodiment will be described in detail below with reference to FIG. 15, FIG. 17, FIG. 2, and FIG.

  In S501 of FIG. 15, the shutter 10 is closed. In S502, the drive current of the light emitting element is set to zero.

  In step S503, it is determined whether the detection output of the density sensor in step S502 is within an allowable range. If the detection output is not within the allowable range, the process proceeds to S516, where it is determined that there is a problem (sensor error) in the density sensor 9, and the process ends without performing the subsequent density detection mode operation.

  In S503, if the detection output of the density sensor 9 is within the predetermined allowable range, the process proceeds to S504.

  In S <b> 504, calibration is performed to detect diffusely reflected light from the density reference member 11 provided so as to face the density sensor 9 of the shutter 10. Here, the calibration of the density sensor 9 is the same as that described in the first embodiment, and therefore the description thereof is omitted.

  Next, in step S505, it is determined whether the calibration has been completed normally. Since this determination is performed in the same manner as in the first embodiment, detailed description thereof is omitted. If it is determined that there is an abnormality in S505, the process proceeds to S517, and it is determined that the shutter 10 remains open, and the process ends without executing the subsequent density detection mode operation.

  When the calibration is normally completed in S505, the process proceeds to S506, and the image forming units 1a-1d and the conveyance belt 7 are driven, and density detection patterns 12a-12d having respective colors of cyan, magenta, yellow, and black (FIG. 7). ) Is generated. These density detection patterns 12a to 12d are printed on the conveyor belt 7 by the transfer means 2.

  Next, in S507, the shutter 10 is opened by a solenoid or a motor (not shown). In step S <b> 508, the conveyance belt 7 or the like is caused to travel, and the density detection pattern on the conveyance belt is moved to a position facing the density sensor 9.

  In S509, the density of each color density detection pattern 12a-12d is detected, and the detected density value is stored. In S510, it is determined whether or not the density value detected in S509 is within an allowable range. FIG. 14 shows the allowable range of the density value detected in S509 with two dotted lines. If the detected density value is outside these broken lines, the process proceeds to S518, where it is determined that the image forming unit is malfunctioning, and the process is terminated without performing subsequent density correction.

  In S510, if the detected density value is within the allowable range as shown in FIG. 14A, the process proceeds to S511. In step S511, it is determined whether or not density detection has been completed for all color density detection patterns. The processing from S509 to S511 is repeated until the detection of all colors is completed. In S511, when the density detection is completed for the density detection patterns of all colors, the process proceeds to S512.

  In S512, after changing the image forming conditions such as the development energy such as a high voltage for development and the electrostatic latent image formation energy such as the light amount of the exposure device based on the density detected in S509, the density detection pattern is printed again. And the density of the density detection pattern is detected as in S509.

  In step S513, density detection is performed after the image forming condition is changed, and it is determined whether or not the detected density is within a predetermined allowable range. If it is not within the allowable range, the process proceeds to S519, and it is determined that the shutter remains closed. However, since the control to open the shutter is still performed in S507, the process proceeds to S515, and after issuing a command to close the shutter, the process is terminated.

  In S513, if the detected density value is within the allowable range, the process proceeds to S514. In S514, it is determined whether or not the processing for all colors has been completed, and the processing in S512 and S513 is repeated until the processing is completed for the density detection patterns for all colors. In S514, when the processing is completed for the density detection patterns of all colors, the shutter 10 is closed in S515 and the processing is ended. If a shutter malfunction occurs in the middle of density detection, the amount of development energy, such as a high voltage for development, or the amount of light from the exposure device is based on the density obtained by the detection operation until the shutter malfunction occurs. The image forming conditions such as electrostatic latent image forming energy are changed.

  According to the fifth embodiment, it is possible to detect a malfunction of the image forming unit by detecting a difference between an expected value of a predetermined density and an actual density value when detecting the density. Thereby, the reliability of the detection output of the density sensor 9 is increased, more accurate density correction is possible, and stable image quality can be maintained.

  In the first to fifth embodiments, the developing devices for the respective colors are arranged in the order of black, yellow, magenta, and cyan from the upstream side of the medium conveyance direction, and the density detection patterns are formed in the order of black, yellow, magenta, and cyan. As described above, the arrangement order of the developing devices and density detection patterns of the respective colors is not limited to this. In the present invention, an example of termination as an error as soon as it is determined that the operation is defective has been described. However, the entire operation may be re-executed or may be executed a plurality of times. Further, in the present invention, two types of density are detected for each color, but may be three types and is not limited to two types.

  In the above embodiment, the shutter opening / closing determination is made based on the density detection value at the time of calibration of the density sensor or the density detection value of the toner image formed on the belt. It is also possible to determine whether the shutter is open or closed by detecting this.

7 Conveyor belt,
9 Concentration sensor,
11 Concentration reference member,
10 Shutter.

Claims (5)

A plurality of image forming units each forming a toner image of a corresponding color ;
A toner image carrier capable of carrying a toner image formed by the image forming unit;
A density detector for detecting the density of the toner image on the toner image carrier;
It is driven so as to be located at either the closed position or the open position, and is located between the toner image carrier and the density detector at the closed position, and at the open position, the toner image carrier and the density detector. An opening / closing member that is not located between the concentration detection unit and
A controller that determines whether or not the opening / closing member is in the closed position;
In the step of changing the image forming condition after the control unit instructs the control unit to move the opening / closing member to the open position ,
Based on the first detection value detected at a timing when the image forming unit detects the first toner image generated on the toner carrier before the image forming condition is changed , and the first detection value. A second detection value detected at a timing at which the image forming unit detects a second toner image generated on the toner carrier after the image forming condition is changed ,
The control unit is a case where a difference between an expected value that would be detected from the second toner image and the second detected value is not within an allowable range, and the first detected value and the first detected value are When the detected value of 2 is substantially equal, it is determined that the opening / closing member is in the closed position,
When the difference between the expected value and the second detection value is within an allowable range, the image forming condition corresponding to each image forming unit is changed until all the image forming conditions of the plurality of image forming units are changed. An image forming apparatus characterized by continuing the step of sequentially changing the image.   The image forming apparatus according to claim 1, wherein the expected value is set based on the first detection value.   The image forming apparatus according to claim 1, wherein the step of changing the image forming condition is a step of density correction. The image forming conditions, the image forming apparatus according to any one of claims 1 to 3, characterized in that the amount of developing energy amount or an electrostatic latent image formed energy level or exposure unit. The image forming apparatus according to any one of claims 1 to 4, characterized in that the concentration is different from the first toner image and the second toner image.

Images