JP2017097255A - Image forming apparatus and image correction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus and an image correction method, capable of suppressing the occurrence of deviation of the writing start position of an image formed on the front surface and rear surface of a medium.SOLUTION: An image forming apparatus 100 and the image correction method include an image forming part 20 which develops a developer image, a conveyance part which conveys the medium to the image forming part and re-conveys the medium whose second surface is used as the front surface by reversing the first surface on which the developer image is transferred to the image forming part, a detection sensor which detects the developer image formed on the first and second surfaces of the medium, and a control part which controls the image forming part according to a first mode for performing the correction of image formation by the image forming part and a second mode for performing normal image formation. The control part controls the image forming part so as to form a correction developer image on the first and second surfaces of a transparent medium in the first mode and corrects the image formation on the basis of a detection result corresponding to a deviation amount between a first correction developer image and a second correction developer image detected by the detection sensor.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus having a double-sided printing function and an image correction method.

  2. Description of the Related Art Some conventional image forming apparatuses have a double-sided printing function in which an image is formed on the surface of a medium and then a reversal operation is performed to form an image on the back surface of the medium (see, for example, Patent Document 1).

JP 2012-181387 A

  However, in the prior art, there is a case where a deviation occurs in the writing start position of the image formed on the front surface and the back surface of the medium.

  The present invention has been made in view of such a situation, and an object of the present invention is to form an image that can suppress the occurrence of deviation in the writing start position of the image formed on the front surface and the back surface of the medium. An apparatus and an image correction method are provided.

In order to solve the above problems, an image forming apparatus according to the present invention develops a developer image by attaching a developer to an electrostatic latent image formed by exposure of an exposure unit based on print data. When,
A transport unit that transports the medium to the image forming unit and re-transports the medium having the second surface as a surface by reversing the first surface on which the developer image is transferred; A detection sensor that detects the developer images formed on the first surface and the second surface of the medium, a first mode for correcting image formation by the image forming unit, and normal image formation. A control unit that controls the formation of the developer image by the image forming unit in accordance with a second mode for performing the first mode of the transparent medium when the control unit is in the first mode. The image forming unit is controlled to form a correction developer image on the second surface, and the first correction developer image on the first surface and the second surface on the second surface detected by the detection sensor. Against the deviation from the developer image for correction Based on the detection result, it is characterized by correcting the image formation by the image forming unit.

  The image correction method according to the present invention includes a second surface that is the back surface of the first surface after an image forming unit that performs image formation forms a first correction developer image on the first surface of the transparent medium. Forming a second correction developer image, and detecting a value corresponding to a shift amount between the first correction developer image and the second correction developer image with a transmission type detection sensor; And a step of correcting image formation by the image forming unit based on a detection result by the detection sensor.

  According to the present invention, it is possible to provide an image forming apparatus and an image correction method capable of suppressing the occurrence of a shift in the writing start position of an image formed on the front surface and the back surface of a medium.

1 is a schematic configuration diagram illustrating a main configuration of a printer according to an embodiment. FIG. 2 is a schematic configuration diagram illustrating a main configuration of an image forming unit according to the present embodiment. FIG. 2 is a block diagram illustrating a control configuration of a printer according to the present embodiment. It is the schematic explaining the conveyance path | route of the medium using the double-sided printing unit which concerns on this embodiment. 6 is a flowchart illustrating an operation for correcting a printing position deviation according to the present embodiment. It is a figure explaining the printing position shift detection pattern which concerns on this embodiment. It is a figure explaining the medium on which the printing position shift detection pattern based on this embodiment was printed. It is a figure which shows the result of having read the medium which printed the printing position shift detection pattern with the permeation | transmission sensor. FIG. 9 is a result of representing the reading result of FIG. 8 by analog data. FIG. 10 is a diagram illustrating a result of executing the averaging process illustrated in FIG. 9. It is a figure which shows an example of the reading result of the permeation | transmission sensor in case printing position deviation generate | occur | produces. It is a figure explaining the method of calculating a printing position shift adjustment value. FIG. 6 is a diagram for explaining a printing position misalignment correction operation. It is a figure explaining the printing position shift detection pattern which concerns on this embodiment. It is a figure explaining the medium on which the printing position shift detection pattern based on this embodiment was printed. It is a figure explaining the method of calculating a printing position shift adjustment value. FIG. 6 is a diagram for explaining a printing position misalignment correction operation.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably.

  FIG. 1 is a schematic configuration diagram illustrating a main configuration of a printer 100 as an image forming apparatus according to the present embodiment. The printer 100 according to this embodiment is a color electrophotographic image that forms a color image by superimposing toners as four types of developers of black (K), yellow (Y), magenta (M), and cyan (C). A configuration as a printer is provided.

  The printer 100 is formed in a substantially S-shape starting from the medium storage tray 10 that stores the medium P and starting from the transport rollers 40 to 42, the transfer unit 30, the fixing unit 35, the transport roller 43, and the stacker 36. An image forming unit 20 is provided along the medium conveyance path S indicated by the middle dotted line.

  The medium storage tray 10 stores the medium P in a stacked state, and is detachably attached to the lower part of the printer 100. The pickup roller 11 is configured to be able to come into contact with the medium P when the medium storage tray 10 is mounted on the printer 100. The pickup roller 11 picks up the medium P one by one from the uppermost part and feeds it to the transport roller 40. Feed paper. The conveyance rollers 40 to 42 correct the skew of the medium P and convey the medium P along the medium conveyance path S to the image forming unit 20.

  The image forming unit 20 includes four image forming units 21K, 21Y, 21M, and 21C that are detachably disposed along the paper conveyance path S, and an LED (Light Emitting Diode) head 27K that serves as an exposure device. 27Y, 27M, and 27C, and a transfer unit 30 that transfers the toner image formed by each image forming unit onto the medium P by Coulomb force. The four image forming units 21K, 21Y, 21M, and 21C arranged in series on the paper conveyance path S have the same member configuration, and only the toner used is different.

  Here, the main configuration of the image forming units 21K, 21Y, 21M, and 21C according to the present embodiment will be described with reference to FIG. As described above, the image forming units 21K, 21Y, 21M, and 21C differ only in the toner used, and the other configurations can be the same. Therefore, in the following description, the image forming units are identified. In the following description, the symbols K, Y, M, and C are removed. FIG. 2 is a main part configuration diagram schematically illustrating the configuration of the image forming unit 21 together with the LED head 27, the transfer roller 34, and the transfer belt 31.

  The image forming unit 21 includes a photosensitive drum 22 as an image carrier, a charging roller 23 as a charging member, a developing roller 24 as a developer carrier, a supply roller 25 as a supply member, and a development containing toner. And a toner cartridge 26 as an agent container. The image forming unit 21 is detachably mounted at a predetermined position of the image forming unit 20 shown in FIG. 1, and the toner cartridge 26 is configured to be detachable from the image forming unit 21 itself.

  The photosensitive drum 22 is, for example, an inorganic photosensitive drum provided with a photosensitive layer such as selenium or amorphous silicon on a conductive substrate roller such as aluminum, or a charge generating agent or charge transporting agent dispersed in a binder resin. An organic photosensitive drum provided with an organic photosensitive layer can be used. The photosensitive drum 22 forms an electrostatic latent image on its surface by light based on image information irradiated by the LED head 27.

  The charging roller 23 is a roller member that is provided in contact with the peripheral surface of the photosensitive drum 22 and is constituted by, for example, a metal shaft and semiconductive epichlorohydrin rubber. The charging roller 23 uniformly charges the surface of the photosensitive drum 22 with a charging voltage applied from a charging roller voltage power source 109 described later.

  The developing roller 24 is provided in contact with the peripheral surface of the photosensitive drum 22. For example, a semiconductive urethane rubber layer in which carbon black is dispersed is disposed on the outer periphery of a metal shaft such as stainless steel, and the surface thereof is subjected to an isocyanate treatment. It is a roller member. The developing roller 24 charges the toner with a developing voltage applied from a developing roller voltage power source 110 described later, and develops the toner image by attaching the charged toner to the electrostatic latent image formed on the surface of the photosensitive drum 22.

  The supply roller 25 is, for example, a roller member configured by disposing a semiconductive foamed urethane sponge layer as an elastic layer on the outer periphery of a metal shaft such as stainless steel. The supply roller 25 charges the toner with a supply voltage applied from a supply roller voltage power source 111 described later, and supplies the charged toner to the developing roller 24.

  The toner cartridge 26 is a box-shaped member having a storage space for storing unused toner. At the bottom of the toner cartridge 26, the toner can be supplied to the supply roller 25 when the image forming unit 21 is mounted. A shutter member that can slide in a predetermined direction to form an opening is formed.

  The LED head 27 includes, for example, a light emitting element such as an LED element and a lens array, and is disposed so that light emitted from the LED element is formed on the surface of the photosensitive drum 22 based on image information. ing.

  The transfer unit 30 is made of, for example, polyamideimide, polyamide, and the like. The transfer unit 30 electrostatically attracts and conveys the medium P, a transfer roller 31 that drives the transfer belt 31 by rotating, and a drive roller 32. The tension roller 33 that stretches the transfer belt 31 and the photosensitive drums 22K, 22Y, 22M, and 22C provided in the image forming units 21K, 21Y, 21M, and 21C, respectively, are positioned via the transfer belt 31. And transfer rollers 34K, 34Y, 34M, and 34C that transfer toner images to the medium P based on a transfer voltage applied from a transfer roller power source 112, which will be described later.

  Returning to FIG. 1 again, the fixing unit 35 includes at least a fixing roller 35a and a pressure roller 35b. The fixing roller 35a is formed by, for example, covering a hollow cylindrical cored bar made of aluminum or the like with a heat-resistant elastic layer such as silicone rubber and covering the same with a PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) tube. It is formed by. In the cored bar, for example, a heater (not shown) such as a halogen lamp is provided. The pressure roller 35b is configured, for example, by covering a cored bar made of aluminum or the like with a heat-resistant elastic layer such as silicone rubber and covering the same with a PFA tube. The pressure roller 35b is disposed so that a pressure contact portion is formed between the pressure roller 35b and the fixing roller 35a. The medium P on which the toner image has been transferred in the transfer unit 30 passes through a pressure contact portion composed of a fixing roller 35a and a pressure roller 35b maintained at a predetermined temperature, whereby heat and pressure are applied to the toner on the medium P. The applied toner melts and the toner image is fixed.

  The transport roller 43 transports the medium P that has passed through the fixing unit 35 to a stacker 36 that is formed using the apparatus housing.

  The medium sensors 50 to 54, 67 and 68 detect the position of the medium P on the medium transport paths S and T. The control unit 101 described later detects a conveyance delay of the medium P, a paper jam, and the like based on the detection results of the medium sensors 50 to 54, 67, and 68 via the medium sensor control unit 114. As the medium sensors 50 to 54, 67, and 68, for example, a combination of an actuator that is a lever member configured to be rotatable by being in contact with the medium P and a transmissive or reflective photosensor is used. it can.

  The double-sided printing unit 60 includes a separator 61 and a reverse separator 62, and is indicated by solid arrows x, y, and z in FIG. In addition, the medium P is transported along a medium transport path T formed in a substantially arc shape including transport rollers 64 to 66. The reversing operation of the medium P by the duplex printing unit 60 will be described later.

  The transmission sensor 70 reads a printing position deviation detection pattern as a correction developer image formed on both surfaces of the medium P. The reading result obtained by the transmission sensor 70 is used to calculate the amount of deviation of the image forming position between the front surface as the first surface and the back surface as the second surface. The transmission sensor 70 includes a projector having a light projecting element that projects light, and a light receiver having a light receiving element that is disposed to face the light projector and receives the projection light through the detection target. If it is the structure of this, it may be a transmission type, a groove shape, or a U-shape. Further, as a detection member for reading the print position shift detection pattern, not only a transmission type sensor but also a retroreflection type sensor, a diffuse reflection type sensor, a narrow visual field reflection type sensor, or a limited reflection type sensor may be used.

  Next, a control configuration of the printer 100 according to the present embodiment will be described with reference to FIGS. 1, 2, and 3. FIG. 3 is a block diagram illustrating the control configuration of the printer 100.

  The control unit 101 shown in FIG. 3 includes, for example, a microprocessor, a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output port, a timer, and the like, and receives print data and control commands from a host device (not shown). Then, the entire printer 100 is controlled in sequence, and the printing operation is comprehensively controlled. Then, the control unit 101 performs toner image formation by the image forming unit 20 in accordance with the first mode for correcting image formation by the image forming unit 20 and the second mode for performing normal image formation. Control.

  The charging roller power control unit 102 controls the charging roller voltage power source 109 based on an instruction from the control unit 101 so as to apply a voltage (charging bias) to the charging roller 23 and uniformly charge the surface of the photosensitive drum 22. The applied voltage is controlled.

  Based on an instruction from the control unit 101, the LED head control unit 103 performs control to form an electrostatic latent image by exposing the charged photosensitive drum 22 to light by irradiating light based on print data.

  The developing roller power supply control unit 104 controls the developing roller voltage power supply 110 to control the developing roller 24 in order to attach toner to the electrostatic latent image formed on the surface of the photosensitive drum 22 based on an instruction from the control unit 101. The applied voltage is controlled to apply a voltage (development bias).

  The supply roller power control unit 105 applies a voltage (supply bias) to the supply roller 25 by controlling the supply roller voltage power supply 111 in order to supply toner to the developing roller 24 based on an instruction from the control unit 101. Control applied voltage.

  The transfer roller power supply control unit 106 controls the transfer roller power supply voltage 112 to transfer the toner image formed on the surface of the photosensitive drum 22 to the medium P based on an instruction from the control unit 101. Application voltage control for applying a transfer bias) is performed.

  The medium transport control unit 107 controls the transport operation of the medium P inside the printer 100 based on an instruction from the control unit 101. The medium conveyance control unit 107 controls the pickup roller 11 and the conveyance rollers 40 to 43 and 63 to 66 by controlling the conveyance roller control unit 113, and controls the medium sensors 50 to 54 and 67 by controlling the medium sensor control unit 114. 68, by controlling the separator controller 115 to drive / stop the separator 61 and the reverse separator 62, the transport operation including the reverse operation of the medium P is controlled.

  Based on the reading result of the transmissive sensor 70 via the transmissive sensor control unit 116, the calculation unit 108 determines the amount of deviation of the image forming position between the front surface as the first surface and the rear surface as the second surface of the medium P as the print position displacement adjustment amount. Calculate as

  Here, the conveyance path of the medium P using the duplex printing unit 60 will be described with reference to FIG. FIG. 4 is a schematic diagram for explaining the conveyance path of the medium P during double-sided printing.

  First, the medium P is fed from the medium storage tray 10 by the pickup roller 11. The medium P is transported to the image forming unit 20 along the medium transport path S indicated by the dotted line in FIG. 4 via the transport rollers 40 to 42 (step S1). In the case of single-sided printing, the medium P that has passed through the image forming unit 20, the transmission sensor 70, and the fixing unit 35 is conveyed by the conveyance roller 43 in the direction of the arrow w in FIG.

  On the other hand, in the case of duplex printing, the medium P that has passed through the fixing unit 35 is transported along a medium transport path T indicated by a solid line in FIG. Specifically, the medium P that has passed through the fixing unit 35 has its transport path switched by the separator 61, and is transported into the duplex printing unit 60 indicated by arrows x and y in FIG. 4 (step S2). Then, the medium P is reversely conveyed by the conveyance (reverse) roller 63 and the reverse separator 62 to the conveyance path indicated by the arrow z in FIG. 4 (step S3).

  The medium P whose front and back surfaces are reversed by the reverse conveyance is conveyed again to the image forming unit 20 by the conveyance rollers 64 to 66 in the duplex printing unit 60. After image formation by the image forming unit 20, the medium P passes through the transmission sensor 70 and the fixing unit 35, is conveyed by the conveyance roller 43 in the direction of the arrow w in FIG. 4, and is discharged to the stacker 36.

  Next, the operation for correcting the printing position deviation according to the present embodiment will be described. FIG. 5 is a flowchart for explaining the operation of correcting the printing position deviation. In the present embodiment, it is assumed that a transmissive medium that can be read by the transmissive sensor 70 is used as the medium P on which the printing position deviation detection pattern is formed.

  In step S <b> 10, the control unit 101 instructs the medium conveyance control unit 107 to convey the medium P in order to print the printing position deviation correction pattern on the medium P. Upon receiving the instruction, the medium conveyance control unit 107 drives the pickup roller 11 via the conveyance roller 113 to start feeding the medium P (step S10).

  Next, the control unit 101 causes the printing position misalignment correction pattern to be printed on the medium P via the image forming unit 20. That is, the control unit 101 controls the charging roller control unit 102, the LED head drive control unit 103, the developing roller power control unit 104, the supply roller power control unit 105, the transfer roller power control unit 106, etc. A printing position deviation correction pattern, which will be described later, is printed on the first surface (step S20).

  When printing of the printing position deviation correction pattern on the front surface is completed, the control unit 101 instructs the medium conveyance control unit 107 to reversely convey the medium P. Upon receiving the instruction, the medium conveyance control unit 107 reversely conveys the medium P via the conveyance roller control unit 113, the medium sensor control unit 114, and the separator control unit 115 (step S30).

  Next, the control unit 101 causes the printing position deviation detection pattern to be printed on the back surface of the medium P whose front and back surfaces are reversed. The control unit 101 controls the second roller of the medium P by controlling the charging roller control unit 102, the LED head drive control unit 103, the developing roller power control unit 104, the supply roller power control unit 105, the transfer roller power control unit 106, and the like. A printing position misalignment correction pattern, which will be described later, is printed on the back surface (step S40).

  In step S <b> 50, the control unit 101 gives an instruction to the transmission sensor control 116 to read the print position deviation detection pattern using the transmission sensor 70 via the calculation unit 108. Upon receiving the instruction, the transmission sensor control unit 116 causes the transmission sensor 70 to read the print position deviation detection pattern.

  Next, the control unit 101 instructs the calculation unit 108 to average the sensor output value obtained from the transmission sensor 70 and to calculate the print position deviation adjustment amount. Receiving the instruction, the calculation unit 108 averages the sensor output values obtained from the transmission sensor 70 (step S60), and calculates the print position deviation adjustment amount (step S70).

  Next, a printing position deviation detection turn, a printing position deviation detection pattern detection method, and a printing position deviation adjustment amount calculation method according to the present embodiment will be described based on experimental data.

  First, a print position deviation detection pattern used for correcting a print position deviation in the medium longitudinal direction (vertical direction deviation of the medium P) will be described. The control unit 101 prints the printing position deviation detection pattern as shown in FIG. 6 on the surface of the medium P as the first detection pattern group via the black (K) image forming unit 21K of the image forming unit 20. Further, the control unit 101 causes the printing position deviation detection pattern to be printed as the second detection pattern group on the back surface of the medium P as shown in step S40 of FIG.

  As described above, the print position misalignment detection pattern shown in FIG. 6 is used for correcting the print position misalignment in the vertical direction of the medium. (1) No print xmm (A), (2) Print yes ymm (B), (3) No printing This is a pattern in which zmm (C) is repeated. The values shown in Table 1 are the values of (A), (B), and (C) corresponding to the print position deviation detection patterns printed on the front surface and the back surface, respectively.

  When the printing position deviation detection pattern shown in FIG. 6 is transferred to the front and back surfaces of the transmissive medium P at intervals (A), (B), and (C) shown in Table 1, the printing position deviation as shown in FIG. The detection pattern becomes a printed medium. Here, in the printing position deviation detection pattern on the back surface, the interval of (C) is 15.04 mm, and therefore the deviation of the back surface pattern from the front surface pattern to 15.04 mm-14.10 mm = 0.94 mm for each pattern. Will occur.

  Next, a method for detecting the print position deviation detection pattern will be described. In this embodiment, the transmittance when the patterns overlap on both the front and back surfaces, the transmittance when there is a pattern on only one of the front and back surfaces, and the patterns on both the front and back surfaces do not overlap In this case, the printing position deviation is evaluated by measuring the transmittance in this case with the transmission sensor 70.

Specifically, when the patterns are overlapped on both the front and back surfaces, the transmittance of the medium P is low (the sensor output value of the transmission sensor 70 is high), and the patterns on both the front and back surfaces are not overlapping. In this case, the transmittance of the medium P increases (the sensor output value of the transmission sensor 70 decreases). That is, in the above three cases, the relationship between the sensor output values of the transmission sensor 70 is expressed by the following equation (1).
Transmittance when the patterns on both sides of the front and back surfaces do not overlap <Transmittance when there is a pattern on only one side of the front and back surfaces <When the patterns overlap on both the front and back surfaces Formula (1)

  FIG. 8 shows a result of reading the medium P on which the printing position deviation detection pattern is printed by the transmission sensor 70. As shown in FIG. 8, the sensor output value is high in the portion where the pattern overlaps on both the front and back surfaces of the medium P (light shielding).

  Next, a method for sampling the sensor output value of the transmission sensor 70 will be described. In general, there is a possibility that various noises are on the sensor output value. Therefore, in this embodiment, the sensor output value (reading value) is calculated by sequentially calculating the average value of the sampling results for five times, and the three points excluding the maximum value and the minimum value of the five points taking the average. The average value of is sequentially calculated.

  FIG. 9 shows the result of the reading of FIG. 8 expressed in analog data, and FIG. 10 shows the result of executing the averaging process in FIG. FIG. 11 shows an example of the reading result of the transmission sensor 70 when the printing position deviation occurs. As shown in FIG. 11, it can be seen that when the print position shift occurs in the vertical direction of the medium P, the reading results on the front surface and the back surface of the medium P are different (the print position is relatively ± 0.8 mm on the front surface and the back surface). Gap).

Next, a method for calculating the print position deviation adjustment value from the sensor output value from the transmission sensor 70 will be described. In the present embodiment, the print position deviation adjustment value is calculated by specifying the light-shielding portion (the portion with the highest sensor output value) of the sensor output result. Specifically, the calculation unit 108 divides the print position deviation detection pattern shown in FIG. 7 into blocks as shown in FIG. 12, and specifies the block in which the portion with the highest sensor output value is recorded. Then, the calculation unit 108 applies the specified number of blocks to the following equation (2) to calculate the print position deviation adjustment amount.
Print position misalignment adjustment amount = (11−Int (number of blocks−1) / 92) * 4 (Expression 2)
(Int means the integer part)

  When the value obtained by the expression (2) is a positive number, it indicates that the printing position on the back surface is shifted to the upper side of the medium, and conversely, when the value obtained is a negative number, the printing position on the back surface. Is shifted to the lower side of the medium. From these results, as shown in FIG. 13, the control unit 101 controls the LED head control unit 103 to adjust the exposure timing of the LED head 27 at the time of printing on the back surface, thereby performing a printing position misalignment correction operation.

  That is, when the printing position on the back side is shifted to the upper side of the medium, the control unit 101 delays the printing timing on the back side. Conversely, when the printing position on the back side is shifted to the lower side of the medium, the control unit 101 prints on the back side. Control to advance the timing.

  Next, a print position deviation detection pattern used for correcting the print position deviation in the medium short direction (left and right direction deviation of the medium P) will be described. The control unit 101 prints a print position shift detection pattern as shown in FIG. 14 on the surface of the medium P as a third detection pattern group via the black (K) image forming unit 21K of the image forming unit 20. Further, as shown in step S40 of FIG. 5, the control unit 101 causes the printing position shift detection pattern to be printed on the back surface of the medium P as the fourth detection pattern group.

  As described above, the print position misalignment detection pattern shown in FIG. 14 is used for correcting the print position misalignment in the left-right direction of the medium. (1) Printing present (front end) xdot (A ′), (2 ) No print ydot (B ′), (3) Print present zdot (C ′), (4) Print present (rear end) This pattern repeats wdot (D ′). The values shown in Table 2 are the values of (A), (B), (C), and (D) corresponding to the print position deviation detection patterns printed on the front surface and the back surface, respectively.

  14 is transferred to the front and back surfaces of the transmissive medium P at intervals (A), (B), (C), and (D) shown in Table 2 as shown in FIG. This is a medium on which a printing position deviation detection pattern is printed.

  The method for detecting the printing position deviation detection pattern can be the same as the method using the printing position deviation detection pattern in the vertical direction of the medium P. Similarly, the transmittance of the medium P is measured by using the transmission sensor 70. This can be achieved.

  Next, the method for calculating the print position deviation adjustment value from the sensor output value by the transmission sensor 70 can be the same as the method using the print position deviation detection pattern in the vertical direction of the medium P. In the present embodiment, the print position deviation adjustment value is calculated by specifying the light-shielding portion (the portion with the highest sensor output value) of the sensor output result. Specifically, the calculation unit 108 divides the print position deviation detection pattern shown in FIG. 14 into blocks as shown in FIG. 16, and specifies the block in which the portion with the highest sensor output value is recorded. Then, the calculation unit 108 applies the specified number of blocks to the above equation (2), and calculates the print position deviation adjustment amount.

  If the value obtained by equation (2) is a positive number, it indicates that the printing position on the back side is shifted to the left side of the medium, and conversely if the value obtained is a negative number, the printing position on the back side. Is shifted to the right side of the medium. From these results, as shown in FIG. 17, the control unit 101 controls the LED head control unit 103 to adjust the print data position of the LED head 27 at the time of printing on the back side, thereby performing a print position misalignment correction operation. .

  That is, when the print position on the back side is shifted to the left side, the control unit 101 adds dummy data to the left side of the print data to shift the print data position to the right, and conversely, the print position on the back side is shifted to the right side. If there is, the control unit 101 performs control to add dummy data to the right side of the print data and shift the print data position to the left side.

  As described above, according to the present embodiment, printing of the printing position deviation detection pattern, reading of the printing position deviation detection pattern, and calculation of the printing position deviation adjustment amount can be completed within the printer apparatus. Is not bothered. Furthermore, since the printing position deviation adjustment amount as the correction value is calculated and applied in the apparatus, it is possible to expect a reduction in “setting deviation” due to a user's manual setting. Furthermore, in the present embodiment, a pattern using the same toner (black (K) in the present embodiment) is printed on the front and back surfaces of the medium. Can be corrected.

  In the description of the present invention, a direct transfer type printer has been described as an example of an image forming apparatus. However, the present invention is not limited to this, for example, an intermediate transfer type printer, a copying machine, a FAX, an MFP, and the like. It is applicable to.

10 Media storage tray 11 Pickup roller 20 Image forming units 21K, 21Y, 21M, 21C Image forming units 22, 22K, 22Y, 22M, 22C Photosensitive drum 23 Charging roller 24 Developing roller 25 Supply roller 26 Toner cartridges 27, 27K, 27Y, 27M, 27C LED head 30 Transfer section 31 Transfer belt 32 Drive roller 33 Tension rollers 34, 34K, 34Y, 34M, 34C Transfer roller 35 Fixing section 35a Fixing roller 35b Pressure roller 36 Stackers 40-43, 63-66 Conveying roller 50 ˜54, 67, 68 Medium sensor 60 Duplex printing unit 61 Separator 62 Reverse separator 70 Transmission sensor 101 Control unit 102 Charging roller power control unit 103 LED head control unit 104 Developing roller power control unit 105 Roller power source control unit 106 Transfer roller power source control unit 107 Medium conveyance control unit 108 Calculation unit 109 Charging roller voltage power source 110 Development roller voltage power source 111 Supply roller voltage power source 112 Transfer roller voltage power source 113 Conveyance roller control unit 114 Media sensor control unit 115 Separator Control unit 116 Transmission sensor control unit

Claims (7)

An image forming unit that develops a developer image by attaching a developer to an electrostatic latent image formed by exposure of an exposure unit based on print data;
A transport unit that transports the medium to the image forming unit and re-transports the medium having the second surface as a surface by reversing the first surface to which the developer image has been transferred;
A detection sensor for detecting the developer image formed on the first surface and the second surface of the medium;
A control unit that controls the formation of the developer image by the image forming unit according to a first mode for correcting image formation by the image forming unit and a second mode for performing normal image formation; With
When the control unit is in the first mode, the control unit controls the image forming unit to form a correction developer image on the first surface and the second surface of the transparent medium, and is detected by the detection sensor. Further, based on a detection result corresponding to a deviation amount between the first correction developer image on the first surface and the second correction developer image on the second surface, the image forming unit corrects the image formation. An image forming apparatus characterized by that. Correction of image formation by the image forming unit is to correct a shift amount of an image forming position on the first surface and the second surface of the medium,
The control unit is based on a detection result corresponding to a shift amount between the first correction developer image on the first surface and the second correction developer image on the second surface detected by the detection sensor. The image forming apparatus according to claim 1, wherein a shift amount of the image forming position is calculated. The image forming apparatus according to claim 1, wherein the shift amount of the image forming position is adjusted by an exposure timing of the exposure unit or a shift amount of the print data. The first correction developer image and the second correction developer image each include a plurality of detection patterns for detecting the presence or absence of image formation formed at predetermined intervals in the longitudinal direction of the medium as detection pattern groups,
The second detection pattern group on the second surface has at least one of the detection patterns formed at a predetermined interval different from the first detection pattern group on the first surface. 4. The image forming apparatus according to any one of items 3. The first correction developer image and the second correction developer image each include a plurality of detection patterns for detecting the presence or absence of image formation formed at predetermined intervals in the short direction of the medium,
The fourth detection pattern group on the second surface has at least one of the detection patterns formed at a predetermined interval different from that of the third detection pattern group on the first surface. 5. The image forming apparatus according to any one of 4 above. A calculation unit that calculates a shift amount between the first correction developer image and the second correction developer image;
The calculation unit calculates the shift amount based on a transmittance according to an overlap between the detection pattern group on the first surface and the detection pattern group on the second surface detected by the detection sensor. The image forming apparatus according to claim 4 or 5. An image forming unit that performs image formation forms a first correction developer image on the first surface of the transparent medium, and then forms a second correction developer image on the second surface that is the back surface of the first surface. Steps,
Detecting a value corresponding to a deviation amount between the first correction developer image and the second correction developer image with a transmission type detection sensor;
And a step of correcting image formation by the image forming unit based on a detection result by the detection sensor.