JP5088562B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  For example, as described in Patent Document 1, a so-called tandem image forming apparatus is conventionally known. In this configuration, the photosensitive member is provided for each of yellow, magenta, cyan, and black, for example, and these are arranged along the circumferential direction of the belt for conveying the paper. Each color image carried by each photoconductor is transferred to a sheet on the belt.

By the way, in such a tandem image forming apparatus, if the image forming position of each color with respect to the paper is shifted, a color image in which the color shift has occurred is formed. Therefore, the image forming position alignment of each color is important. Therefore, conventionally, an image forming apparatus that detects and corrects an image forming position shift of each color has been disclosed. Specifically, this image forming apparatus forms a registration pattern (positioning pattern) including a plurality of marks corresponding to each color of yellow, magenta, cyan, and black on the belt. This registration pattern is a pattern in which the marks of the respective colors are arranged at intervals along the circumferential movement direction. The position of each color mark on the belt changes according to the shift of the image forming position of each color. Therefore, the position of each color mark on the belt is detected by an optical sensor, and the deviation of the image forming position of each color is corrected based on the detected position.
JP-A-6-137812

  By the way, the belt does not always move uniformly over the entire circumference, and variation may occur in each part. Therefore, the correction result of the image forming position may be different depending on where the registration pattern is formed on the belt. In some cases, it is desired to correct the image forming position not only in the moving direction of the belt but also in a direction orthogonal to the moving direction and parallel to the belt plane. Here, in Patent Document 1, it is described that the registration pattern should be as long as possible. However, from the description in Patent Document 1, the movement direction of the belt and the influence of variations in belt fluctuations are suppressed. It is not possible to know how to correct the image forming position in the direction orthogonal thereto.

  The present invention has been completed based on the above circumstances, and its object is to form an image in the moving direction of the image carrier and a direction perpendicular thereto while suppressing the influence of fluctuation variation of the image carrier. An object of the present invention is to provide an image forming apparatus capable of correcting the position.

As a means for achieving the above object, an image forming apparatus according to a first aspect of the present invention is a first image carrier for detecting rotational displacement of an image carrier that is rotationally driven and an image forming position in the rotational direction of the image carrier. One pattern and a second pattern for detecting a shift in image forming position in a direction orthogonal to the rotation direction are formed on the image carrier, and formed on the image carrier. A detecting unit configured to detect the first pattern and the second pattern; and a correcting unit configured to correct an image forming position in the forming unit based on a detection result of the detecting unit. And then the second operation is performed. The first operation corresponds to at least one of the first pattern and the second pattern corresponding to a half circumference on the image carrier. An operation of forming in one region and forming at least the other pattern in a second region corresponding to the remaining half circumference different from the first region, wherein the second operation is the first operation. In this operation, the second pattern is formed in the region where the first pattern is formed, and the first pattern is formed in the region where the second pattern is formed in the first operation.
According to the present invention, the first pattern for detecting the shift of the image forming position in the rotation direction of the image carrier (hereinafter referred to as “first direction”) is the image carrier in the first operation and the second operation. Formed in different regions above. Further, the second pattern for detecting the deviation of the image forming position in the direction orthogonal to the first direction (hereinafter referred to as “second direction”) is also different on the image carrier between the first operation and the second operation. Formed in the region. Therefore, compared to a configuration in which the first pattern and the second pattern are formed at the same position in the first operation and the second operation, it is possible to suppress the influence due to the variation variation on the image carrier. In addition, since the first pattern forming area and the second pattern forming area are switched in the first operation and the second operation, the correction of the image forming position in the first direction and the image forming position in the second direction are performed. Differences in accuracy from correction can be suppressed.

In a second aspect based on the first aspect, the correction means includes a first correction based on detection results of the detection means in both the first operation and the second operation, and the first operation and the second operation. It is configured to be able to perform the second correction based on the detection result of the detection means in any one of the operations, and determine which of the first correction and the second correction is to be executed by the correction means. A determination means is provided.
According to this invention, depending on the situation, correction is performed using the detection results in the first operation and the second operation, or correction is performed using the detection results in only one of the first operation and the second operation. Can be switched.

According to a third invention, in the second invention, the forming means is configured to perform the forming operation of the first pattern and the second pattern when an execution condition is satisfied, and the correcting means is configured to perform the second correction. In this case, a change means is provided for changing the execution condition to a condition that causes the next forming operation to be performed earlier than in the case where the first correction is performed.
Since the first correction uses more detection results than the second correction, the correction accuracy is higher. Therefore, when the second correction is executed, it is desirable to perform the next forming operation earlier than when the first operation is executed by relaxing the execution conditions of the forming means.

According to a fourth aspect of the present invention, in the second or third aspect of the present invention, the determination means finally determines whether to perform the first correction or the second correction before the second operation. The forming unit does not execute the second operation when the determining unit determines the second correction based on the detection result of the detecting unit in the first operation.
According to the present invention, it is possible to prevent the second operation from being performed unnecessarily.

According to a fifth invention, in the second or third invention, the determining means determines based on a remaining amount of the colorant in the forming means.
According to this invention, appropriate pattern formation and correction can be performed according to the remaining amount of the colorant.

According to a sixth invention, in any one of the second to fifth inventions, there is provided a recovery means for recovering the colorant adhering to the image carrier, and the determining means is a method for determining the colorant by the recovery means. Determine based on the amount collected.
According to this invention, appropriate pattern formation and correction can be performed according to the amount of colorant recovered.

In a seventh aspect based on any one of the second to fourth aspects, the determining means determines based on an operation by a user.
According to the present invention, it is possible to switch between the first correction and the second correction based on the user's judgment.

According to an eighth invention, in any one of the second to seventh inventions, there is provided judgment means for judging whether or not the detection result of the detection means is normal, and the correction means is the judgment means by the judgment means. When it is determined that the detection result corresponding to the second operation is not normal, the correction based on the detection result in the first operation is performed among the second corrections.
According to the present invention, when the detection result in the second operation is not normal, it is possible to perform correction quickly using the detection result for the first operation without performing the second operation again.

  According to the present invention, it is possible to correct the image forming position in the direction of movement of the belt and the direction orthogonal thereto while suppressing the influence due to the fluctuation variation of the image carrier.

An embodiment of the present invention will be described with reference to FIGS.
(Entire printer configuration)
FIG. 1 is a side sectional view showing a schematic configuration of a printer 1 according to the present embodiment. In the following description, the right side (right side) in FIG. 1 is the front side (front side) of the printer 1.

  As shown in FIG. 1, a printer 1 (an example of an image forming apparatus) is a direct transfer tandem color laser printer and includes a casing 3. A supply tray 5 is provided at the bottom of the casing 3, and a recording medium (for example, a sheet material such as paper) 7 is stacked on the supply tray 5.

  The recording medium 7 is pressed toward the pickup roller 11 by the pressing plate 9 and is sent to the registration roller 13 by the rotation of the pickup roller 11. The registration roller 13 corrects the skew of the recording medium 7 and then sends the recording medium 7 onto the belt unit 15 at a predetermined timing.

  The image forming unit 17 includes a belt unit 15 as an example of a conveyance unit, a scanner unit 19 as an example of an exposure unit, a process unit 21, a fixing unit 23, and the like. In the present embodiment, the scanner unit 19 and the process unit 21 are examples of “forming unit”.

  The belt unit 15 includes an endless belt 29 (an example of an image carrier) provided between a pair of support rollers 25 and 27 (an example of a moving mechanism). The belt 29 circulates in the counterclockwise direction in FIG. 1 when the rear support roller 27 is driven to rotate, and conveys the recording medium 7 placed on the belt 29 backward.

  A cleaning roller 31 (an example of a collecting unit) for removing toner (including a registration pattern 91 described later), paper dust, and the like attached to the belt 29 is provided below the belt unit 15. .

  The scanner unit 19 includes a laser light emitting unit (not shown) that is on / off controlled based on image data, and performs high-speed scanning while irradiating the surface of the photosensitive drum 33 corresponding to each color with the laser light L of each color image. .

  Four process units 21 are provided corresponding to the respective colors of black, cyan, magenta, and yellow. Each process unit 21 has the same configuration except for the color of toner (an example of a colorant). In the following description, when it is necessary to distinguish each color, subscripts of K (black), C (cyan), M (magenta), and Y (yellow) are attached to the codes of the respective parts, and it is not necessary to distinguish them. In this case, the subscript is omitted.

  Each process unit 21 includes a photosensitive drum (an example of a photosensitive member) 33, a charger 35, a developing cartridge 37, and the like.

  The developing cartridge 37 includes a toner storage chamber 39, a supply roller 41, a developing roller 43 (an example of a developer image carrier), and a layer thickness regulating blade 45 (an example of a layer thickness regulating unit).

  The toner is supplied to the developing roller 43 by the rotation of the agitator 47 (an example of a stirring unit) and the supply roller 41. Further, the toner supplied onto the developing roller 43 enters between the layer thickness regulating blade 45 and the developing roller 43 and is carried on the developing roller 43 as a thin layer having a constant thickness.

  The surface of the photosensitive drum 33 is uniformly positively charged by the charger 35. Thereafter, exposure is performed with the laser light L from the scanner unit 19, and electrostatic latent images corresponding to the respective color images to be formed on the recording medium 7 are formed.

  Next, the toner carried on the developing roller 43 is supplied to the electrostatic latent image formed on the surface of the photosensitive drum 33. As a result, the electrostatic latent image on the photosensitive drum 33 is visualized as a toner image for each color.

  A negative transfer bias is applied to the transfer roller 49 while the recording medium 7 conveyed by the belt 29 passes through each transfer position between the photosensitive drum 33 and the transfer roller 49 (an example of a transfer unit). Is done. As a result, the toner images carried on the surface of each photosensitive drum 33 are sequentially transferred to the recording medium 7. The recording medium 7 onto which the toner image has been transferred in this way is conveyed to the fixing device 23.

  The fixing device 23 heat-fixes the toner image on the recording medium 7 by heating the recording medium 7 carrying the toner image while being conveyed by the heating roller 51 and the pressure roller 53. Then, the heat-fixed recording medium 7 is discharged onto a paper discharge tray 57 by a paper discharge roller 55.

  Further, as shown in FIG. 1, the printer 1 is provided with an optical sensor 81 at the lower rear side of the belt 29. The optical sensor 81 is a reflective sensor including a light projecting unit and a light receiving unit. The light projecting unit irradiates light on the surface of the belt 29 from an oblique direction, and the light receiving unit receives reflected light from the surface of the belt 29, and will be described later in an irradiation area on the belt 29 by the light projecting unit. A binarized signal corresponding to whether or not there are marks 93 and 95 of the registration pattern 91 is output.

  Further, the printer 1 is provided with a first toner sensor 83 that detects the remaining amount of toner in the toner storage chamber 39 of each process unit 21. Specifically, a light transmissive window (not shown) is provided in the toner storage chamber 39, and the first toner sensor 83 has a light projecting unit and a light receiving unit disposed facing each other through the window. A signal corresponding to the remaining amount of toner in the toner storage chamber 39 is output.

  Further, the printer 1 is provided with a second toner sensor 87 that detects the amount of toner collected in the collection box 85 by the cleaning roller 31. Specifically, the collection box 85 is provided with a light-transmitting window (not shown), and the second toner sensor 87 has a light projecting unit and a light receiving unit arranged to face each other through the window. A signal corresponding to the amount of toner collected in the collection box 85 is output.

(Electrical configuration of printer)
FIG. 2 is a block diagram showing an electrical configuration of the printer 1 described above.
The printer 1 includes a CPU 61, a ROM 63, a RAM 65, an EEPROM (nonvolatile memory) 67, an operation unit 69, a display unit 71, the image forming unit 17, the network interface 73, an optical sensor 81, and the like.

  Various programs for controlling the operation of the printer 1 are recorded in the ROM 63, and the CPU 61 controls the operation of the printer 1 while storing the processing results in the RAM 65 and the EEPROM 67 according to the program read from the ROM 63. .

  The operation unit 69 includes a plurality of buttons, and various input operations such as an instruction to start printing can be performed by the user. The display unit 71 includes a liquid crystal display and a lamp, and can display various setting screens and operation states. The network interface 73 is connected to an external computer (not shown) or the like via a communication line 75, and mutual data communication is possible.

(Position correction processing)
In the printer 1, if the image forming position (transfer position) of each color with respect to the recording medium 7 is shifted, a color image having a color shift is formed. Therefore, it is important to align the image forming positions of each color. A process for correcting this color misregistration is a misregistration correction process. 3 to 6 are schematic diagrams showing patterns on the belt 29 in each operation process. In each figure, a top view, a side view, and a bottom view of the belt 29 are shown in this order from the top.

1. Registration Pattern FIGS. 4 to 6 show a first registration pattern (hereinafter simply referred to as “first pattern 91 </ b> A”). The first pattern 91A is used to detect a deviation amount of the image forming position in the rotation direction of the belt 29 (hereinafter referred to as “sub-scanning direction”). Specifically, the first pattern 91 </ b> A has a configuration in which a plurality of bar-shaped marks 93 extending in the left-right direction are arranged along the moving direction of the belt 29. In addition, a mark group in which a black mark 93K, a yellow mark 93Y, a magenta mark 93M, and a cyan mark 93C are arranged in this order is arranged in one or more sets along the sub-scanning direction. It has become.

  3, 4 and 6 show a second registration pattern (hereinafter simply referred to as “second pattern 91B”). The second pattern 91B is used to detect a shift amount of the image forming position in a direction orthogonal to the sub-scanning direction (hereinafter referred to as “main scanning direction”). Specifically, the second pattern 91 </ b> B has a configuration in which a plurality of pairs of marks 95 including a pair of bar-shaped marks that are at different angles with respect to the main scanning direction are arranged along the moving direction of the belt 29. It has become. The plurality of pairs of marks 95 include a black mark 95K, a yellow mark 95Y, a magenta mark 95M, and a cyan mark 95C, one pair or a plurality of pairs. For example, the EEPROM 67 stores the first pattern data and the second pattern data.

2. Control Content of Misalignment Correction Processing The CPU 61 executes misalignment correction processing shown in FIG. First, in S1, it is determined whether or not the execution condition is satisfied. Here, as an example of the execution condition, the elapsed time from the previous misregistration correction process or the number of recording media on which image formation has been performed has reached a certain reference value.

  When the CPU 61 determines that the execution condition is satisfied (S1: Y), the CPU 61 reads the data of the second pattern 91B and the data of the first pattern 91A from the EEPROM 67 and supplies them to the image forming unit 17 in this order. Thereby, the image forming unit 17 executes the first operation.

  This first operation is executed while the belt 29 rotates approximately one and a half times. Specifically, the first operation is started when a predetermined reference point P on the belt 29 is on the support roller 27 side, for example, and is completed until the reference point P rotates approximately one and a half times.

  FIG. 3 is a diagram showing the belt 29 in which the reference point P has rotated approximately one turn from the start of the first operation, and FIG. 4 shows the belt 29 in which the reference point P has rotated approximately one and a half turns from the start of the first operation. It is a figure. As shown in FIG. 3, in the first operation, the second pattern 91B is formed on the first region 29A of the belt 29, and then, the first pattern 91A is formed on the second region 29B of the belt 29 as shown in FIG. Is formed. The first region 29A is a region of the belt 29 that is substantially half the circumference of the belt 29 from the reference point P, and the second pattern 91B is a length that extends over substantially the entire length of the first region 29A. A maximum number of marks 95 are arranged in the first area 29A. Here, the maximum number is a mark when four sets of a black mark 95K, a yellow mark 95Y, a magenta mark 95M, and a cyan mark 95C are arranged as a set on the first area 29A. Number 95.

  The second area 29 </ b> B is an area for the remaining substantially half circumference other than the first area 29 </ b> A on the surface of the belt 29. The first pattern 91A has a length that extends over substantially the entire length of the second region 29B, and has a configuration in which the maximum number of marks 93 are arranged in the second region 29B. Here, the maximum number is a mark when four sets of a black mark 93K, a yellow mark 93Y, a magenta mark 93M, and a cyan mark 93C are arranged as a set on the second area 29B to the maximum. The number 93.

  The CPU 61 obtains the binarized signal sequentially sent from the optical sensor 81 during the first operation in S3, and in S4, based on the binarized signal, the measured values (black values) of the marks 93 and 95 are obtained. It is determined whether or not the misregistration amounts of the marks 93C, 93M, and 93Y of other colors with respect to the mark 93K are normal values. At this time, the CPU 61 functions as a determination unit.

  Specifically, when each pulse width of the binarized signal is extremely smaller or larger than a predetermined value, it is determined that the measured values at the positions of the marks 93 and 95 are not normal. Such a case may occur when temporary noise is generated in the optical sensor 81, for example. Here, when it is determined that the measured values of the positions of the marks 93 and 95 are not normal (S4: N), for example, the display unit 71 displays that the positional deviation correction has failed (S5). At this time, the configuration may be such that the process returns to S2 and the first operation is performed again.

When the CPU 61 determines that the measured values of the positions of the marks 93 and 95 are normal (S4: Y), the CPU 61 sets a condition for correcting the image forming position (second correction) using only the measured values of the first operation in S6. It is determined whether the condition is satisfied, in other words, whether the second operation is executed. This condition includes the following. At this time, the CPU 61 functions as a determination unit.
(1) A case where the user has set the correction of the image forming position with the measurement value of only the first operation on the operation unit 69.
(2) The user has set the speed emphasis mode among the speed emphasis mode and the image quality emphasis mode on the operation unit 69.
(3) When the CPU 61 detects based on the detection signal from the first toner sensor 83 that there is a toner storage chamber 39 in which the remaining amount of toner is below a predetermined amount. At this time, it is desirable to perform the second correction in order to suppress the amount of toner used in the positional deviation correction process.
(4) When the CPU 61 detects based on the detection signal from the second toner sensor 87 that the amount of toner collected in the collection box 85 is greater than or equal to a predetermined amount. At this time, the amount of toner used in the misregistration correction process should be reduced to suppress the amount of toner collected in the collection box 85 so that the toner collection amount does not exceed the storage limit of the collection box 85. Therefore, it is desirable to perform the second correction.

  In S6, “Y” may be determined in S6 when any one of the above conditions (1) to (4) is satisfied, or the above (1) to (4 ) May be determined as “Y” in S6 when two or more of the above conditions are satisfied.

[First correction]
When it is determined that the above condition is not satisfied (S6: N), the measured value of the first operation is temporarily stored in the RAM 65 in S7, and the cleaning roller is rotated while the belt 29 is rotated once or twice in S8. 31 is activated to remove the first pattern 91A and the second pattern 91B from the belt 29.

  Next, in S9, the CPU 61 reads the data of the first pattern 91A and the data of the second pattern 91B from the EEPROM 67 and supplies them to the image forming unit 17 in this order (the order opposite to that in the first operation). The image forming unit 17 performs the second operation at the timing when the reference point P of the belt 29 reaches the same position as that in the first operation (the same position as in FIG. 3). This timing can be set in advance by calculating from the start timing of the first operation and the set speed of the belt 29.

  In the second operation, similar to the first operation, the belt 29 is executed during approximately one and a half revolutions. Specifically, the second operation is started when the reference point P on the belt 29 is on the support roller 27 side, for example, and is completed until the reference point P rotates approximately one and a half times. The first pattern 91A has a length that covers substantially the entire length of the first area 29A, and has a configuration in which the maximum number of marks 95 are arranged in the first area 29A.

  FIG. 5 is a view showing the belt 29 in which the reference point P has rotated approximately one turn from the start of the second operation, and FIG. 6 shows the belt 29 in which the reference point P has been rotated approximately one and a half turns from the start of the second operation. It is a figure. As shown in FIG. 5, in the second operation, the first pattern 91A is formed on the first region 29A of the belt 29, and then, as shown in FIG. 6, the second pattern 91B is formed on the second region 29B of the belt 29. Is formed. The first pattern 91A has a length that covers substantially the entire length of the first region 29A, and has a configuration in which the maximum number of marks 95 are arranged in the first region 29A. The second pattern 91B has a length that covers substantially the entire length of the second region 29B, and has a configuration in which the maximum number of marks 93 are arranged in the second region 29B.

  In short, in the second operation, the second pattern 91B is formed in the region where the first pattern 91A is formed in the first operation, and the first pattern 91A is formed in the region where the second pattern 91B is formed in the first operation. .

  The CPU 61 acquires the binarized signal sequentially sent from the optical sensor 81 during the second operation in S10, and the measured values of the positions of the marks 93 and 95 are normal based on the binarized signal in S11. Determine if it is a value. Note that the determination content at this time is the same as in S4. When it is determined that the measured values at the positions of the marks 93 and 95 are normal (S11: Y), the image forming position (first correction) is performed with the measured values of both the first operation and the second operation. First, in S12, an average value of measured values of both the first operation and the second operation is calculated.

  Specifically, the CPU 61, based on the measurement values of the first pattern 91A in both the first operation and the second operation, averages the measurement values of the yellow marks 93Y and the measurement values of the magenta marks 93M. Value, and the average value of the measured values of the cyan marks 93C. Further, based on the measured values of the second pattern 91B of both the first operation and the second operation (the distance between the two bar-shaped marks of each mark 95), the average value of the measured values of the yellow marks 95Y, the magenta mark 95M The average value of the measured values of each other and the average value of the measured values of the cyan marks 95C are calculated. Next, in S14, a correction value (hereinafter referred to as “first correction value”) of the image forming position in the sub-scanning direction of each color is calculated from the average value based on the measurement value of the first pattern 91A. Further, a correction value (hereinafter referred to as “second correction value”) of the image forming position of each color in the main scanning direction is calculated from the average value based on the measurement value of the second pattern 91B.

  In step S15, the two correction values are stored in the EEPROM 67. In step S16, the belt 29 is cleaned in the same manner as in step S8, and the positional deviation correction process is terminated. In the subsequent image forming operations, the image forming unit 17 forms each color image on the recording medium at the image forming position corrected by the first correction value and the second correction value. Specifically, the color shift correction in the sub-scanning direction and the main scanning direction is performed by adjusting the timing at which the scanner unit 19 emits the laser light corresponding to each color according to the first correction value and the second correction value. Do. At this time, the optical sensor 81 and the CPU 61 function as detection means. The CPU 61 functions as a correction unit.

  When it is determined in S11 that the measured values at the positions of the marks 93 and 95 are not normal (S11: N), it is determined whether or not the second operation is performed again in S17. For example, it is displayed on the display unit 71 that the positional deviation correction has failed, and it is determined whether or not the second operation is performed again according to the operation of the operation unit 69 by the user. If it is determined that the second operation is to be performed again (S17: Y), the process returns to S8 and the second operation is performed again after the belt 29 is cleaned.

  If it is determined in S17 that the second operation is not performed again (S17: N), it is determined in S18 whether or not to use the measurement value of the first operation that has already been temporarily stored in the RAM 65 in S7. For example, the user is inquired through the display unit 71 as to whether or not the measurement value of the first action is to be used, and whether or not the measurement value of the first action is to be used according to the user's operation at the operation unit 69 in response to this. to decide.

  When it is determined that the measurement value of the first operation is used (S18: Y), based on the measurement value of the first pattern 91A of the first operation in S19, the average value of the measurement values of the yellow marks 93Y, the magenta value The average value of the measured values between the marks 93M and the average value of the measured values between the cyan marks 93C are calculated. Further, based on the measurement values of the second pattern 91B in the first operation, the average value of the measurement values of the yellow marks 95Y, the average value of the measurement values of the magenta marks 95M, and the average of the measurement values of the cyan marks 95C Each value is calculated. This average value calculation process is performed, for example, after “Y” in S4 of FIG. 7 and before S6, and is stored in the RAM 65 or the like, and the average value is read from the RAM 65 or the like in S19. It may be.

  Next, in S20, the execution condition in S1 is changed to a milder condition. Specifically, by setting the reference value of the execution condition to a value smaller than the initial value, the next positional deviation correction process is executed earlier than before the change of the execution condition. Thereafter, the execution condition is returned to the initial condition in S13, and the process proceeds to S14. If it is determined in S18 that the measurement value of the first operation is not used (S18: N), the process proceeds to S5.

[Second correction]
When the condition of S6 is satisfied (S6: Y), the process proceeds to S19 to perform the second correction based on the measured value of only the first operation. At this time, since the second operation is not performed, it is possible to prevent wasteful consumption of toner.

(Effect of this embodiment)
According to the present embodiment, the first pattern 91A is formed at different positions on the belt 29 in the first operation and the second operation. The second pattern 91B is also formed at different positions on the belt 29 in the first operation and the second operation. Therefore, it is possible to suppress the influence due to the variation in fluctuation of the belt 29 as compared with the configuration in which the first pattern 91A and the second pattern 91B are formed at the same position in the first operation and the second operation. In addition, since the formation position of the first pattern 91A and the formation position of the second pattern 91B are switched between the first operation and the second operation, the correction of the image formation position in the sub-scanning direction and the image formation in the main scanning direction are performed. Position correction can be performed with substantially uniform accuracy.

  Whether the first correction using the measured values (detection results) in the first operation and the second operation is performed according to the user's judgment, the status of the printer 1 such as the remaining amount of toner and the amount of collected toner. It is possible to switch whether to perform the second correction using only the measurement value in the operation.

  Since the first correction uses more detection results than the second correction, the correction accuracy is higher. Therefore, when the second correction is executed, the execution condition of the misalignment correction process is relaxed (S20 in FIG. 7), and the next misalignment correction process is performed earlier than when the first operation is executed. Like to do.

  When the measurement value in the second operation is not normal (S11: N in FIG. 7), the detection result for the first operation can be quickly corrected without performing the second operation again (S17). : N).

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.
(1) In the above embodiment, a direct transfer type color laser printer is shown as the image forming apparatus. However, the present invention can also be applied to, for example, an intermediate transfer type laser printer. It can also be applied to a printer. Further, a printer having two, three, five or more colorants may be used. Even if the printer is a monochrome printer, by applying the present invention, an image can be formed at an accurate position with respect to the recording medium.

  (2) In the above embodiment, the “image carrier” is the belt 29 for conveying the recording medium. However, if the image forming apparatus adopts an intermediate transfer system, an intermediate transfer belt may be used. Good.

  (3) In the above embodiment, when the measured values of the positions of the marks 93 and 95 are not normal values (S4: N in FIG. 7), the configuration may proceed to S8 instead of S5 in the same drawing. That is, the second operation is executed when a normal measurement value is not obtained in the first operation. In this case, if a normal measurement value is obtained in the second operation, correction is performed based on the measurement value in the second operation.

  (4) In the said embodiment, it is good also as a structure which does not skip 2nd operation | movement without performing S6 of FIG. In this case, the second operation is always executed when the first operation ends.

  (5) In the above embodiment, the maximum number of marks 93 and 95 is formed in each of the regions 29A and 29B of the belt 29. However, the maximum number is not necessarily formed, and the distance between the marks is further increased. It may be. However, with the configuration of the embodiment, it is possible to improve the accuracy of image forming position deviation correction by offsetting variation variations in substantially the entire circumference of the belt 29.

  (6) Unlike the above embodiment, the first pattern 91A is first formed in the first operation, then the second pattern 91B is formed first, the second pattern 91B is formed first in the second operation, and then The first pattern 91A may be formed.

  (7) Unlike the above embodiment, a pattern including the first pattern 91A or the second pattern 91B may be formed in each of the regions 29A and 29B. For example, as shown in FIG. 8, in the first operation, first, the second pattern 91B and the first pattern 91A are first formed in the first area 29A, and then the first pattern 91A and the second pattern are formed in the second area 29B. They are formed in the order of the pattern 91B. In the second operation, first, the first pattern 91A and the second pattern 91B are formed in the first area 29A in this order, and then the second pattern 91B and the first pattern 91A are formed in the second area 29B in this order. In short, in the second operation, the second pattern 91B may be formed at the position where the first pattern 91A is formed in the first operation, and the first pattern 91A may be formed at the position where the second pattern 91B is formed in the first operation. . In other words, in the second operation, the first pattern and the first pattern 91A and the second pattern 91B in the first operation are reversed with respect to the reference point in the rotation direction of the belt 29 with respect to the first pattern and the second pattern 91B. A second pattern may be formed.

1 is a side sectional view showing a schematic configuration of a printer according to an embodiment of the present invention. Block diagram showing the electrical configuration of the printer Schematic showing the pattern on the belt when the belt makes one revolution in the first operation Schematic showing the pattern on the belt when the first operation is completed Schematic showing the pattern on the belt when the belt makes one revolution in the second operation Schematic showing the pattern on the belt when the second operation is completed Flow chart showing misalignment correction processing Schematic showing the pattern on the belt of the modified example

Explanation of symbols

1. Printer (image forming device)
19 ... Scanner part (formation means)
21. Process part (formation means)
29 ... belt (image carrier)
29A ... first area 29B ... second area 31 ... cleaning roller (collecting means)
61 ... CPU (formation means, detection means, judgment means, correction means, determination means)
81. Optical sensor (detection means)
91A ... first pattern 91B ... second pattern

Claims (7)

A rotationally driven image carrier;
At least one of a first pattern for detecting a shift in the image forming position in the rotation direction of the image carrier and a second pattern for detecting a shift in the image forming position in a direction orthogonal to the rotation direction . A pattern is formed in a first area corresponding to the half circumference on the image carrier, and at least the other pattern is formed in a second area corresponding to the remaining half circumference that is different from the first area. One operation is performed, and then the second pattern is formed in a region where the first pattern is formed in the first operation, and the first pattern is formed in a region where the second pattern is formed in the first operation. Forming means for performing a second operation for forming
Detection means for detecting the first pattern and the second pattern formed on the image carrier;
Based on the detection results of the detection means in both the first action and the second action, a first correction for correcting an image forming position in the forming means, and in any one of the first action and the second action A correction unit capable of performing a second correction for correcting the image forming position based on a detection result of the detection unit;
It said determining means for determining whether to perform one of the first correction and the second correction to the correction means, the image forming apparatus Ru comprising a. The image forming apparatus according to claim 1 ,
The forming means is configured to perform the forming operation of the first pattern and the second pattern when an execution condition is satisfied,
An image forming apparatus comprising: a changing unit that changes the execution condition to a condition that causes the next forming operation to be performed earlier when the correction unit performs the second correction than when the first correction is performed. An image forming apparatus according to claim 1 or claim 2,
The determining means is configured to finally determine before the second operation whether to perform the first correction or the second correction,
The image forming apparatus that does not execute the second operation when the determining unit determines the second correction based on the detection result of the detecting unit in the first operation by the determining unit . An image forming apparatus according to claim 1 or claim 2,
The determining unit is an image forming apparatus that determines based on a remaining amount of the colorant in the forming unit . An image forming apparatus according to any one of claims 1 to 4,
A recovery means for recovering the colorant adhering to the image carrier;
The determination unit is an image forming apparatus that determines based on a recovery amount of the colorant by the recovery unit . An image forming apparatus according to any one of claims 1 to 3,
The determination unit is an image forming apparatus that determines based on an operation by a user. An image forming apparatus according to any one of claims 1 to 6,
A determination means for determining whether the detection result of the detection means is normal;
When the determination unit determines that the detection result corresponding to the second operation is not normal, the correction unit performs correction based on the detection result in the first operation out of the second correction. .

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