JP2015135408A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to read an electrostatic latent image scale.SOLUTION: An antenna 101a is configured to at least partially overlap an electrostatic latent image scale 110b in a main-scanning direction. When the electrostatic latent image scale 110b and the antenna 101a relatively move in a sub-scanning direction, an induction current is generated in the antenna 101a. A control section detects the electrostatic latent image scale, on the basis of the induction current. The antenna and the electrostatic latent image scale are formed so that a position of an intersection thereof may be changed in the main-scanning direction when they relatively move.

Description

  The present invention relates to an image forming apparatus that detects a latent image graduation formed on an image carrier using a conductor.

  In general, an electrophotographic color image forming apparatus has a plurality of image forming units for speeding up, and sequentially transfers images of different colors (for example, yellow, magenta, cyan, and black) onto an intermediate transfer belt. A so-called tandem type color image forming apparatus is known.

  However, although the tandem type color image forming apparatus can increase the processing speed, the speed variation of the photosensitive drum and the intermediate transfer belt due to the mechanical accuracy and the like varies for each color image forming unit. Will occur. For this reason, the amount of movement between the outer peripheral portion of the photosensitive drum and the surface of the intermediate transfer belt at the transfer position differs for each image forming unit, and when the images formed in the respective image forming units are superimposed on the intermediate transfer belt, 100 to There was a problem that a color shift of each color of 150 μm occurred.

  Therefore, conventionally, an image forming apparatus has been proposed in which an electrostatic latent image scale having a striped pattern is written on the surface of the photosensitive drum, and the image formed in each of the image forming units is aligned using the electrostatic latent image scale. (See Patent Documents 1 to 3).

  More specifically, in Patent Documents 1 to 3, the electrostatic latent image graduation is formed in a rectangular shape that is long in the main scanning direction orthogonal to the sub-scanning direction that is the traveling direction of the drum or belt, and A linear conductive wire is provided as a sensor for detecting the electrostatic latent image scale. Then, the electrostatic latent image graduation is read by detecting the induced current generated when the electrostatic latent image graduations and the conductive wires formed so as to be parallel and overlap with each other in the main scanning direction are relatively moved. It is like that.

JP 2009-134264 A Japanese Patent No. 3706725 JP 2010-2111197 A

  The electrostatic latent image graduation and detection sensor arranged in parallel with the main scanning direction can detect the electrostatic latent image graduation with high accuracy by the rectangular electrostatic latent image graduation and detection sensor having a short width. On the other hand, in order to ensure design variations, methods other than the combination of the rectangular electrostatic latent image graduation parallel to the main scanning direction and the detection sensor have been required.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of reading an electrostatic latent image graduation by a method other than a combination of a rectangular electrostatic latent image graduation parallel to the main scanning direction and a detection sensor. .

  An image forming apparatus according to the present invention includes an exposure unit, an image carrier having an electrostatic latent image graduation formed by the electrostatic latent image formed by the exposure unit, and a rotation direction of the image carrier. In the main scanning direction orthogonal to a certain sub-scanning direction, at least a part of the electrostatic latent image graduation of the image carrier overlaps, and the electrostatic latent image graduation and the A conductor that relatively moves in the sub-scanning direction; and a control unit that detects the electrostatic latent image graduation based on an induced current generated in the conductor by the relative movement, the conductor and the electrostatic latent image graduation Is formed so that the position of the intersection changes in the main scanning direction when the relative movement is performed.

  According to the present invention, the conductor and the electrostatic latent image graduation are formed such that the intersection position thereof changes in the main scanning direction when the conductor and the electrostatic latent image graduation are relatively moved in the sub scanning direction. For this reason, the electrostatic latent image graduation can be read by a method other than the combination of the rectangular electrostatic latent image graduation parallel to the main scanning direction and the detection sensor. In addition, since the intersection position is formed so as to change in the main scanning direction, even if the attachment position of the conductor is shifted due to secular change or the like, for example, the relative positional relationship between the conductor and the electrostatic latent image graduation is shifted. The influence on the detection signal can be reduced.

1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. 1A is a schematic diagram illustrating an image forming unit in the image forming apparatus of FIG. 1, FIG. 1B is a schematic diagram illustrating another example of the electrostatic scale transfer structure, and FIG. 1C is a positional relationship between the latent image sensor and the electrostatic scale. Pattern diagram. FIG. 4 is a schematic diagram showing a relationship between a latent image sensor and a latent image scale on a photosensitive drum. (A) Schematic diagram showing configuration of latent image sensor, (b) Side view of FIG. 4 (a), (c) Schematic diagram showing connection relationship between latent image sensor and control unit, (d) Data processing circuit The schematic diagram which shows a structure. (A)-(e) The schematic diagram which shows the transition of the relative positional relationship of a latent image sensor and an electrostatic scale, (f) The graph which shows the sensor output in that case. (A)-(c) The figure explaining the difference in the electric current value to detect by the difference in the overlap amount of the main scanning direction of a latent image sensor and an electrostatic scale, (d) In FIG.6 (a)-(c). A graph in which the detected current values are superimposed. (A)-(c) The figure which shows the case where the electric current value of Fig.6 (a)-(c) is integrated, (d) The graph which accumulated the integrated value of Fig.7 (a)-(c). (A) The graph which shows the state in which the noise is riding on the electric current value which the latent image sensor detected the electrostatic scale, (b) The graph which shows the integrated value of the electric current value of Fig.8 (a). (A)-(c) The figure explaining the difference of the electric current value detected when the relative positional relationship of a latent image sensor and an electrostatic scale inclines, and its integral value. (A)-(g) The figure which shows the variation of the shape of the electrostatic graduation which has a linear part. (A)-(d) The figure which shows the variation of the shape of the electrostatic graduation which has a curve part. (A)-(c) In the electrostatic scale which has a curve part, The figure explaining the difference of the electric current value detected by the difference in the amount of overlaps of the latent image sensor and an electrostatic scale in the main scanning direction, and its integral value. (A) to (c) In the case where the conductor portion is inclined in the sub-operation direction, the difference between the detected current value and the integral value due to the difference in the overlap amount in the main scanning direction between the conductor portion and the electrostatic scale. Illustration to explain. (A)-(c) The figure explaining the difference of the detected electric current value and the integral value by the difference in the amount of overlaps of a conductor part and an electrostatic scale in the main scanning direction, when making a conductor part into a triangle shape. (A) Schematic diagram showing photosensitive drum surface defect, (b) Current waveform when photosensitive drum surface defect is detected by conductor, (c) Schematic diagram showing external noise, (d) Detecting external noise by conductor Current waveform when (A) The theoretical waveform of the rhomboid electrostatic latent image scale, (b) The waveform indicating the difference between the detected waveform of the rhombus electrostatic latent image scale and the theoretical waveform of FIG. 16 (a), (c) Photosensitive drum surface defect 16 (a) shows the difference between the detected waveform and the theoretical waveform shown in FIG. 16 (a), (d) shows the difference between the detected external noise waveform and the theoretical waveform shown in FIG. 16 (a), and (e) shows the waveform shown in FIG. The figure which shows the area inside the waveform of (), (f) The figure which shows the area inside the waveform of FIG.16 (c), (g) The figure which shows the area inside the waveform of FIG.16 (d). (A) The figure which shows the state in which the photosensitive drum surface defect exists between round type | mold electrostatic latent image graduations, (b) The electric current waveform which detected Fig.17 (a), (c) of FIG.17 (b) The figure which converted the zero cross timing into the pulse waveform. The schematic diagram which shows the control part which concerns on the 4th Embodiment of this invention. The flowchart figure which shows the detection control of the photosensitive drum surface defect. (A) Schematic diagram showing conductor part and electrostatic latent image graduation according to the fifth embodiment of the present invention, (b) State in which noise is placed on detection waveform of electrostatic latent image graduation in FIG. 20 (a) (C) The figure which shows the waveform after performing a low-pass process to the waveform of FIG.20 (b). The schematic diagram which shows a low-pass circuit.

<First Embodiment>
<Schematic configuration of image forming apparatus>
The image forming apparatus according to the first embodiment of the present invention will be described below. As shown in FIG. 1, a color laser printer 1 as an image forming apparatus according to this embodiment includes a recording material feeding unit 2 that feeds a recording material, and a recording material supplied from the recording material feeding unit 2. An image forming unit 3 for forming an image is provided. In addition, a fixing unit 4 for fixing the toner image formed by the image forming unit 3 by heating and pressing is provided.

  The recording material feeding unit 2 stores a recording material cassette 30 that stores the recording material to be fed, a feeding roller 31 that feeds the recording material one by one from the recording material cassette 30, and a recording fed by the feeding roller 31. Conveying rollers 32 and 33 for conveying the material toward the secondary transfer portion T2 are provided.

  The image forming unit 3 is a tandem type, and includes a plurality of yellow, magenta, cyan, and black image forming units 10PY, 10PM, 10PC, and 10PK arranged along an intermediate transfer belt (conveyance body) 20. . In the image forming unit 10PY, a charging unit 12Y, an exposure unit 13Y, a developing unit 14Y, a primary transfer roller (transfer unit) 15Y, and a cleaning unit 16Y are arranged around a photosensitive drum (image carrier, first photosensitive drum) 11Y. Configured. In the image forming unit 10PY, the photosensitive drum 11Y rotates in the direction of arrow A, and the surface is charged to a uniform potential by the charging unit 12Y.

  The exposure unit 13Y is a laser exposure unit that exposes image data for each pixel obtained by developing a yellow color separation image, and scans laser light using a polygon mirror (not shown). Thereby, an electrostatic image is written on the surface of the charged photosensitive drum 11Y. The electrostatic image on the photosensitive drum 11Y is developed as a toner image by the developing unit 14Y, carried and conveyed along with the rotation of the photosensitive drum 11Y, and then a bias voltage is applied to the primary transfer roller 15Y, whereby the primary transfer unit Primary transfer is performed on the intermediate transfer belt 20 in TY. Further, the cleaning unit 16Y slides the cleaning blade against the photosensitive drum 11Y to remove the transfer residual toner remaining on the surface of the photosensitive drum 11Y after passing through the primary transfer portion TY.

  Further, the image forming units 10PM, 10PC, and 10PK basically have the same configuration as the image forming unit 10PY, and magenta is provided for each of the photosensitive drums (image carrier, second photosensitive drum) 11M, 11C, and 11K. A toner image, a cyan toner image, and a black toner image are formed. The magenta toner image, the cyan toner image, and the black toner image formed on each of the photosensitive drums 11M, 11C, and 11K are primarily transferred to the intermediate transfer belt 20 so as to be sequentially superimposed on the yellow toner image. The In the present embodiment, the alphabets at the end of the reference numerals are changed for the corresponding configurations of the image forming units 10PY, 10PM, 10PC, and 10PK.

  The intermediate transfer belt 20 onto which each toner image is primarily transferred is supported by being supported by a drive roller 24, a tension roller 23, and a backup roller 21, and is rotated in the direction of arrow B. The four color toner images carried on the intermediate transfer belt 20 are collectively transferred by the registration roller 33 onto the recording material conveyed in time with the toner image at the secondary transfer portion T2. It has become. The residual transfer toner remaining on the intermediate transfer belt 20 after passing through the secondary transfer portion T2 is removed by the intermediate transfer belt cleaning unit 25.

<Schematic configuration of alignment mechanism>
Next, an alignment mechanism for aligning the toner images of the respective colors will be described with reference to FIGS. In the following description, the rotation direction of the intermediate transfer belt 20 and the photosensitive drums 11Y to 11K is referred to as a sub-scanning direction, and the direction orthogonal to the sub-scanning direction is referred to as a main scanning direction.

  As shown in FIG. 2A, the image forming unit 3 includes photosensitive drums 11Y, 11M, 11C, and 11K, exposure units 13Y to 13K that form electrostatic latent image graduations 110a to 110d on the photosensitive drums, An intermediate transfer belt 20 having a transfer region 20a. The image forming unit 3 includes electrostatic latent image graduation reading sensors (hereinafter simply referred to as latent image sensors) 100a to 100c, 200a to 200c, and a control unit 140 (FIG. 4) that read the electrostatic latent image graduations 110b to 110d and 210. (See (c)). In the present embodiment, the exposure means 13Y to 13K, the latent image sensors 100a to 100c, 200a to 200c, and the control unit 140 that form the electrostatic latent image graduation constitute an alignment mechanism that aligns images. Yes. Further, the image forming unit 3 serves as a mechanism for erasing the electrostatic latent image scale 210 transferred from each photosensitive drum to the transfer area 20a at the end of the intermediate transfer belt 20 in the sub-scanning direction. A roller 41 and an erasing counter roller 42 are provided.

  More specifically, in the image forming unit 3, the first latent image sensors 100a to 100c that read the electrostatic latent image graduations 110b to 110d formed on the photosensitive drums 11M to 11K correspond to the photosensitive drums 11M to 11K. Is provided. Further, second latent image sensors 200a to 200c for reading the electrostatic latent image scale 210 transferred to the transfer area 20a of the intermediate transfer belt 20 are provided between the photosensitive drums (11Y and 11M, 11M and 11C, 11C and 11K). Between).

  As shown in FIGS. 2C and 3, the first latent image sensor 100a is installed on the surface of the corresponding photosensitive drum 11M and as close as possible to the nip position (position where the photosensitive drum and the intermediate transfer belt are in contact). ing. The second latent image sensor 200a is installed on the surface of the intermediate transfer belt 20 and as close as possible to the nip position. The first and second latent image sensors 100a and 200a are arranged so that their distances to the nip position are equal. However, if the distances are known, they may not necessarily be equal. The first latent image sensors 100b and 100c are arranged in the same manner at the first latent image sensor 100a, and the second latent image sensors 200b and 200c are arranged at the same positions in the second latent image sensor 200a.

Next, the image alignment operation by the image forming unit 3 will be described. First, when an image is formed in the first image forming unit _10PY that is first primarily transferred to the intermediate transfer belt 20, a latent image that becomes a print image is formed in the effective image area by the exposure unit 13Y. Further, the electrostatic latent image graduation 110a is formed outside the effective image area (the end of the photosensitive drum in the main scanning direction).

  Next, the electrostatic latent image in the effective image area is developed by the developing unit 14Y and is primarily transferred to the intermediate transfer belt 20. Further, the electrostatic latent image graduation 110a is transferred to the transfer target areas 20a provided at both ends of the intermediate transfer belt 20 without development, and the electrostatic latent image graduation 210 is formed.

  In the first image forming unit 10PY, the primary transfer roller 15Y for toner transfer is formed to extend to the transferred area 20a so that the electrostatic latent image graduation 110a can be transferred to the transferred area 20a. ing. However, when it is desired to individually set the applied voltages for toner transfer and electrostatic latent image scale transfer, as shown in FIG. 2B, the primary transfer roller 15Y and the toner image forming roller 15Y1 are electrostatically charged. It may be divided into a latent image graduation 110a transfer roller 15Y2.

  On the other hand, on the photosensitive drum 11M of the second image forming unit 10PM, the electrostatic latent image graduation 110b is formed together with the latent image serving as the print image by the exposure unit 13M. The position of the electrostatic latent image graduation 210 on the intermediate transfer belt 20 is read by the second latent image sensor 200a, and the position of the electrostatic latent image graduation 110b on the photosensitive drum 11M is read by the first latent image sensor 100a.

  The control unit 140 shown in FIG. 4C determines the position of the electrostatic latent image graduation 210 from the position of the electrostatic latent image graduation 210 on the intermediate transfer belt 20 and the position of the electrostatic latent image graduation 110b on the photosensitive drum 11M. The amount of displacement of the position of the electrostatic latent image graduation 110b with respect to is calculated. The shift amount corresponds to the shift amount between the image on the photosensitive drum 11Y and the image on the photosensitive drum 11M on the intermediate transfer belt 20 as it is. Therefore, the control unit 140 corrects the drive control of the photosensitive drum 11M so as to eliminate the calculated shift amount, that is, so that the positions of the electrostatic latent image graduations 210 and 110b coincide. In other words, the detection timing of the electrostatic latent image graduation 210 by the antenna (first conductor portion) 201a of the latent image sensor 200a and the electrostatic latent image graduation by the antenna (second conductor portion) 101a of the latent image sensor 100a. The drive control of the photosensitive drum 11M is performed based on the detection timing of 110b. Then, the images formed on the photosensitive drum are matched on the intermediate transfer member.

  Accordingly, the toner image formed on the intermediate transfer belt 20 from the photosensitive drum 11M of the second image forming unit 10PM is color-matched with the toner image formed on the intermediate transfer belt 20 by the first image forming unit 10PY. Color misregistration is prevented.

  Similarly, in the third and fourth image forming units 10PC and 10PK, the positions of the electrostatic latent image graduations 210, 110c, and 110d are detected by the first and second latent image sensors 100b, 100c, 200b, and 200c. . Then, the deviation amount is calculated from the read positions of the electrostatic latent image graduations 210, 110c, and 110d, and the rotational speeds of the photosensitive drums 11C and 11K are corrected so as to eliminate the deviation amount. Accordingly, the positions of the color toner images of the second image forming unit 10PM, the third image forming unit 10PC, and the fourth image forming unit 10PK with respect to the toner image transferred to the intermediate transfer belt 20 by the first image forming unit 10PY. Can be precisely matched.

  When the image alignment operation is performed, the belt potential of the transfer area 20a on the intermediate transfer belt 20 is applied by the erasing roller 41 and the erasing counter roller 42, which can apply the AC potential and the DC potential in a superimposed manner. Initialization is performed, and the electrostatic latent image index 210 is erased. Note that a sine wave, a rectangular wave, a pulse wave, or the like can be used to smooth and smooth the potential unevenness on the belt and erase the electrostatic latent image graduation 210.

Further, in the present embodiment, the erasing roller 41 and the erasing counter roller 42 are configured to reduce the possibility that the potential state of the belt surface changes due to the influence of external noise or the like during the conveyance of the intermediate transfer belt 20. It is disposed immediately before the first image forming unit 10PY. However, the fourth image forming unit 10 _PK later, where it may be disposed of until before the first image forming unit 10PY. Further, the electrostatic latent image graduation 210 may be formed on the back side of the intermediate transfer belt 20, and other means such as a corona charger may be used to erase the electrostatic latent image graduation 210.

  In the above description, the image is aligned by controlling the rotation speed of the photosensitive drum. However, for example, the control unit 140 may correct the exposure timing for writing an image on the photosensitive drum by laser irradiation. It is possible to correct the deviation amount. Further, correction may be made by moving the laser irradiation light using a reflection mirror of the exposure means. It is possible to correct the deviation in the main scanning direction by detecting the deviation in the main scanning direction by devising the shape of the electrostatic latent image graduation described later, and controlling the exposure unit as described above.

  Further, on the photosensitive drum 11Y, the electrostatic latent image graduations 110a may be formed only at one end portion without being formed at both ends in the main scanning direction of the photosensitive drum.

<Configuration of latent image sensor and control unit>
Next, the configuration of the latent image sensor and the control unit will be described with reference to FIGS. FIG. 3 is a schematic diagram showing the photosensitive drum 11M and the first latent image sensor 100a of the second image forming unit 10PM. Hereinafter, the structure of the latent image sensor will be described using the first latent image sensor 100a, but the basic configuration of the latent image sensor is the same as that of the other first latent image sensors 100b and 100c, and The same applies to the two latent image sensors 200a to 200c.

  As shown in FIG. 3, the first latent image sensor 100 a includes a conductor portion 101 constituted by a conductor, and a flexible substrate 102 as an insulator that houses the conductor portion 101. More specifically, as shown in FIGS. 4A and 4B, the conductor 101 includes a signal detection unit (hereinafter also referred to as an antenna or a conductor) 101a and a signal transmission unit 101b. It is configured. The flexible substrate 102 is formed by bonding a base material 106 made of polyimide having a thickness of 25 μm and a cover material 103 made of polyimide having a thickness of 12 μm by an adhesive 104 made of epoxy having a thickness of 15 μm. . On the base member 106, a conductor portion 101 and a ground 105 made of a copper foil having a thickness of 9 μm are provided around the conductor portion 101 at a predetermined interval. 103. Note that the ground 105 may have any constant potential, and is not necessarily a ground potential.

  Further, as shown in FIG. 4C, the signal transmission unit 101 b that transmits the signal detected by the antenna 101 a is connected to the control unit 140. The control unit 140 includes a signal amplification circuit 120, a data processing circuit 121, an arithmetic unit 130, and the like. The signal amplifying circuit 120 is a circuit that takes out the position of the electrostatic latent image graduation 110b as an electric signal by detecting, amplifying and outputting the induced current flowing in the electric circuit up to the antenna 101a, and the data processing circuit 121 It is a circuit that processes an input signal. The arithmetic unit 130 includes an arithmetic unit 131 mainly composed of a CPU and a storage unit 132 mainly composed of RAM and ROM. A signal is input via the signal amplification circuit 120 and the data processing circuit 121, and is connected to each image forming unit in a controllable manner.

<Electrostatic latent image scale detection principle>
Next, the principle of detection of the electrostatic latent image graduation by the latent image sensor will be described with reference to FIGS. In the following description, the principle is described using the latent image sensor 100a, but the principle is the same for the other latent image sensors 100b, 100c, and 200a to 200c. The shape of the antenna 101a and the shape of the electrostatic latent image graduations 110a to 110d and 210 are the same in each image forming unit.

  FIGS. 5A to 5E are views showing the relative positional relationship between the antenna 101a of the latent image sensor 100a and the electrostatic latent image scale 110b when the photosensitive drum 11M rotates. Since the position of the latent image sensor 100a is fixed in the apparatus, when the photosensitive drum 11M rotates, the antenna 101a and the electrostatic latent image graduation 110b relatively move in the sub-scanning direction (arrow direction in the figure). When the electrostatic latent image graduation 110b is moved, the antenna 101a remains at a certain distance from the surface of the photosensitive drum 11M.

  As shown in FIG. 5A, the antenna 101a is a linear conductor extending in parallel with the main scanning direction orthogonal to the sub-scanning direction, and at least one of the electrostatic latent image graduation 110b in the main scanning direction. It extends until the parts overlap. That is, the antenna 101a is formed in a rectangular shape that is long in the main scanning direction and short in the sub scanning direction in plan view.

  Further, the electrostatic latent image graduation 110b has a triangular shape, more specifically, an isosceles triangular shape, and is arranged so that its base 1103 is parallel to the sub-scanning direction. Also, a first equilateral side (hereinafter referred to as a first straight line portion or a first conductor straight line portion) 1101 that is an equilateral side on the downstream side in the sub scanning direction and a second equilateral side (hereinafter referred to as a second straight line) that is the equilateral side on the upstream side in the sub scanning direction 1102 (referred to as a section or a second conductor straight line section) intersects with the antenna 101a.

  Here, since the electrostatic latent image graduation 110b is formed by an electrostatic latent image, it is recorded on the surface of the photosensitive drum 11M as the potential level. In this embodiment, the electrostatic latent image graduation 110b is negative. 100V, the surface of the surrounding photosensitive drum is minus 500V. For this reason, when the electrostatic latent image graduation 110b having a potential difference from the surroundings passes below the antenna 101a arranged slightly away from the surface of the photosensitive drum 11M (for example, several μm to several tens μm), the antenna 101a An induced current is generated. Then, the control unit 140 detects the electrostatic latent image graduation 110b based on the induced current. Note that, as described above, the potential of the electrostatic latent image graduation 110b is higher than those of the other photosensitive drum surfaces, and is therefore referred to as a positive potential in the following description.

  FIG. 5F shows an induced current generated in the antenna 101a when the electrostatic latent image graduation 110b moves from FIG. 5A to FIG. 5E (that is, electric wiring between the antenna 101a and the signal amplification circuit 120). 6 is a graph in which the signal amplification circuit 120 amplifies and outputs the induced current generated therein. As shown in FIG. 5A, when the electrostatic latent image graduation 110b approaches the antenna 101a, free electrons in the electric wiring are attracted to the antenna 101a side, and the flow of free electrons becomes an induced current. The amount of free electrons attracted to the antenna 101a by the electrostatic latent image graduation 110b increases as the area where the electrostatic latent image graduation 110b and the antenna 101a overlap increases. Therefore, the amount of free electrons in the antenna 101a increases along the inclination of the first linear portion 1101 between FIGS. 5A to 5C where the first linear portion 1101 and the antenna 101a intersect. It becomes the maximum at 5 (c). Since the induced current is a flow of free electrons, the induced current at this time rises at a time point a when the first linear portion 1101 and the antenna 101a begin to overlap as shown in FIG. Until a time point c, a constant current is detected. The reason why the current value between time point a and time point c is constant is that the current is the amount of electrons passing per unit time. That is, from the time point a to the time point c, the free electrons attracted to the antenna 101a increase at a constant rate according to the inclination of the first linear portion 1101. Here, since the current is the amount of electrons passing per unit time, if the rate of increase (electron flow) is constant, the current value is detected as a constant value.

  On the other hand, after the state of FIG. 5C, the antenna 101a intersects with the second straight portion 1102 until the state of FIG. 5E. Since the second straight line portion 1102 is inclined in the direction away from the antenna 101a opposite to the first straight line portion 1101, the electrostatic latent image between the antenna 101a and the electrostatic latent image is shown in FIGS. 5C to 5E. The overlap with the scale 110 b decreases according to the inclination of the second straight line portion 1102. For this reason, the number of free electrons attracted to the antenna 101b also starts to decrease, and the current value detected at the time point c is also inverted and becomes negative, as shown in FIG. 5 (f). After that, until the time point e, the free electrons attracted to the antenna 101a decrease according to the inclination of the second linear portion 1102, and the current value becomes constant at a predetermined negative value. When the antenna 101a and the electrostatic latent image graduation 110b do not overlap at the time point e, the current value becomes zero.

  Here, when the current value is reversed at the time point c and the current value of the induced current becomes zero (zero cross point 500), the electrostatic latent image graduation 110b is located immediately below the antenna 101a. The controller 140 can accurately detect the position of the electrostatic latent image graduation 110b by detecting the zero cross point 500.

  In detecting the zero cross point 500, the first straight line portion (first conductor straight line portion) 1101 and the second straight line portion (second conductor straight line portion) are smaller as the width of the electrostatic latent image graduation 110b in the sub-scanning direction is narrower. ) The inclination of 1102 can be made steep. Then, since the detected waveform intersects with the origin position at an angle closer to a right angle, the zero cross point 500 can be detected more accurately, which is desirable for detecting the electrostatic latent image graduation 110b.

  Next, the relationship between the overlap amount in the main scanning direction between the antenna 101a and the electrostatic latent image graduation 110b and the detected induced current waveform will be described. 6A to 6C are diagrams showing the relative positional relationship and the current value at that time when the overlap amount in the main scanning direction between the antenna 101a and the electrostatic latent image graduation 110b is changed. . Note that the overlap amount in the main scanning direction between the antenna 101a and the electrostatic latent image graduation 110b is the same as that in FIG. 5 in the case of FIG. 6A, and FIGS. 6B and 6C. Each time, the amount of overlap is reduced.

  FIG. 6D is a diagram in which the output signals (output waveforms) 501 to 503 output in FIGS. 6A to 6C are superimposed. As can be seen from FIG. 6D, when the overlap amount of the antenna 101a and the electrostatic latent image graduation 110b in the main scanning direction is reduced, the period in which the antenna 101a and the electrostatic latent image graduation 110b overlap is shortened, and the induced current is reduced. It can be seen that the detection times 601 to 603 are shortened. Therefore, by detecting the length of the detection times 601 to 603, the overlap amount in the main scanning direction between the antenna 101a and the electrostatic latent image graduation 110b, that is, the main scanning between the antenna 101a and the electrostatic latent image graduation 110b. It becomes possible to detect a shift in direction. In any of the output waveforms 501 to 503, since the slope of the linear portion of the electrostatic latent image graduation 110b is the same, the induced current value of the portion where the constant induced current continues is the same.

  7A to 7C show signals (integrated waveforms) 504 to 506 when the output signals 501 to 503 in FIGS. 6A to 6C are integrated, and FIG. ) Is a graph in which these integrated output signals 504 to 506 are superimposed. In this case, as shown in FIG. 7 (d), the passage times when the electrostatic latent image graduation 110b passes below the antenna 101a are represented as passage times 604 to 606, respectively. The shift amount in the main scanning direction can be detected from the difference. Further, in the integrated waveforms 504 to 506, the peak value is taken as the zero cross point 500, and the peak value (height) 607 to 609 is proportional to the amount of deviation in the main scanning direction. The amount of deviation in the main scanning direction can also be detected from the height of the value.

  The integration processing is performed by the data processing circuit 121 shown in FIG. 4C, and an example of the integration processing circuit included in the data processing circuit 121 is shown in the integration processing circuit 122 of FIG. Yes. The integration processing circuit 122 operates based on “an expression representing the input / output relationship” shown in the lower part of FIG. Further, the data processing circuit 121 is configured to perform A / D conversion on the detection signal and to perform digital integration processing.

  By the way, in the case of the output signal 507 in FIG. 8A in which noise is superimposed on the output signal detected by the antenna 101a, it is difficult to accurately detect the zero cross point 500. In this case, the points at both ends of the output signal necessary for detecting the shift amount in the direction of inspection (that is, the dotted line a and the dotted line e of the output signal 507) can be accurately detected under the influence of noise. It becomes difficult.

  Therefore, in this embodiment, in this case, the output processing 507 is integrated by the data processing circuit 121 as described above, and the zero cross point 500 and the main scanning direction deviation amount are based on the signal 508 after the integration processing. Detection is to be performed.

  Specifically, when the section from the dotted line a to the dotted line c in FIG. 8A that overlaps the first straight line portion 1101 is integrated, a right shoulder like the section from the dotted line a to the dotted line c in FIG. It goes up. Further, when the section from the dotted line c to the dotted line e in FIG. 8A that overlaps the second straight line portion 1102 is integrated, the section falls from the dotted line c to the dotted line e in FIG. 8B. . Since the integrated waveform 508 shown in FIG. 8B includes random noise, the control unit 140 draws approximate straight lines 613 and 614 of the rising waveform portion that rises to the right and the inclined waveform portion that drops to the right. Ask. Then, the intersection of these approximate lines 613 and 614 is detected as the zero cross point 500, and the deviation amount in the main scanning direction is detected from the peak value 612. In this way, the signal detected by the antenna 101a is integrated, and an approximate line is drawn on the sloped waveform portion of the acquired integrated waveform, so that the zero cross point 500 and the antenna 101a in the main scanning direction and the electrostatic latent image graduation are accurately measured. The amount of deviation from 110b can be detected. The approximate line is obtained by subjecting the signal digitized by the data processing circuit 121, which also functions as an A / D converter, to digital processing (a general method for generating an approximate straight line in statistics such as the least square method). Can be acquired.

  FIGS. 9A to 9C show a state in which the electrostatic latent image graduation 110b is tilted with respect to the antenna 101a and an output waveform at that time, and as it goes from FIG. 9A to FIG. 9C. The amount of overlap in the main scanning direction is reduced. The dotted lines in the figure are shown for comparison, and the electrostatic latent image graduations in FIG. 6 (a) in which the electrostatic latent image graduations 110b are not tilted, and the current in FIG. 6 (a). Waveform and integral waveform.

  As shown in FIGS. 9A to 9C, when the electrostatic latent image graduation 110b is tilted, the output waveforms 509, 511, 513 and the integrated waveforms 510, 512, 514 are distorted. However, in this embodiment, the antenna 101a and the electrostatic latent image graduation 110b are scanned at the intersection positions (for example, the intersection points CP1 and CP2 between the antenna 101a and the first and second linear portions 1101 and 1102) by the relative movement of both. It is configured to change in direction. For this reason, even if distortion occurs in the detection waveforms 509, 511, and 513 and the integration waveforms 510, 512, and 514, the influence on the detection of the zero cross point 500 and the deviation amount in the main scanning direction is small. That is, in the case of the present embodiment, even if the electrostatic latent image graduation 110b is tilted, the intersection point CP of the antenna 101a with the electrostatic latent image graduation 110b moves from the first linear portion 1101 to the second linear portion 1102. To do. Since this switching does not become much gentler due to the inclination, the zero cross point 500 can be accurately detected. That is, even if the parallelism between the antenna 101a and the electrostatic latent image graduation 110b is slightly deviated, the antenna 101a still has an overlapping portion from the first straight portion 1101 to the second straight portion 1102 for a short period. Switch. For this reason, in any of FIGS. 9A to 9C, the detected waveforms 509, 511, and 513 cross the origin position with a steep slope when the current value is reversed, and the zero cross point 500 can be easily specified. There is little influence on the detection accuracy by the deviation in parallelism. Further, since the amount of change of each waveform with respect to the positional deviation in the main scanning direction changes linearly, it is also possible to calculate the positional deviation amount.

  As described above, in the case of the printer 1 according to the present embodiment, the position detection accuracy of the electrostatic latent image graduation 110b is substantially lowered due to the shift in parallelism between the electrostatic latent image graduation 110b and the latent image sensor 100a. It can be lost. In addition, this makes it possible to give a margin to the mounting accuracy at the time of manufacturing the device. Furthermore, the detection accuracy can be maintained even when the parallelism is relatively shifted due to secular change or the like. In addition, the adjustment work of the parallelism can be omitted even when the photosensitive drum and the intermediate transfer belt are replaced.

  Moreover, the influence of noise can be reduced by performing integration processing of the current waveform. Therefore, the detection accuracy can be ensured without taking strict noise countermeasures, so that a noise canceling sensor for monitoring the noise level, a countermeasure such as a shield, and the like are not required. In addition, since the detection accuracy of the position of the electrostatic latent image graduation is improved, the color misregistration can be accurately corrected by the alignment mechanism (color misregistration correction system). A printed image is obtained.

  In the above-described embodiment, the electrostatic latent image graduation 110b has an isosceles triangular shape formed so that the base 1103 is parallel to the sub-scanning direction, but the shape of the electrostatic latent image graduation 110b is It is not limited to this.

  For example, as shown in FIGS. 10A to 10G, the electrostatic latent image graduation extends in the sub-scanning direction with a certain inclination in the main scanning direction and is a straight line portion intersecting with the antenna 101a. Any shape may be used as long as it has a shape. More specifically, as shown in FIG. 10A, a rhombus-shaped electrostatic latent image graduation 110b1 whose at least one side intersects the antenna 101a may be used. In this case, each of the sides L1 to L4 forming the outer edge is a straight line portion. Further, as shown in FIG. 10B, when only the sides L1 and L3 of the electrostatic latent image graduation 110b1 intersect with the antenna 101a, these sides L1 and L3 become straight portions.

  Furthermore, as shown in FIG. 10C, a parallelogram-shaped electrostatic latent image graduation 110b2 may be used. In this case, the sides L4 and L5 are straight portions. Further, as shown in FIG. 10 (d), an electrostatic latent image graduation 110b3 having an isosceles triangle shape whose base is arranged in parallel with the main scanning direction may be used. In this case, the side L6 is a straight line portion. Further, in FIG. 10D, the top portion facing the bottom side is arranged facing the direction of the antenna 101a, but it may be reversed as shown in FIG. In this case, the sides L7 and L8 are straight portions.

  Furthermore, as shown in FIG. 10 (f), a V-shaped electrostatic latent image graduation 110b5 whose top is directed in the main scanning direction may be used. In this case, the sides L9 to L12 are straight portions. Further, as shown in FIG. 10G, the electrostatic latent image graduation 110b6 may have a shape in which the shape of FIG. 10F is partially widened in the main scanning direction. In this case, the sides L13 to L16 are straight portions.

  As described above, in this embodiment, various shapes such as a triangle, a diamond shape, and a parallelogram can be adopted, and each shape can be used by being rotated at various angles. Furthermore, the electrostatic latent image graduations 110b5 and 110b6 having concave portions may be used as long as the antenna has a hypotenuse having a constant rate of change.

  Even when the zero cross point cannot be determined from the integral shape of the integrated waveform as shown in FIG. 10F, the approximate line of the inclined waveform portion is obtained as described above, and the intersection of the approximate lines is set as the zero cross point. Thus, the position of the electrostatic latent image graduation can be detected.

  Further, as shown in FIGS. 11A to 11D, the shape of the electrostatic latent image graduation 110b is a curved portion extending in the sub-scanning direction in which the inclination changes at a constant change rate in the main scanning direction. It may have a shape. For example, as shown in FIG. 11A, a circular electrostatic latent image graduation 110b7 may be used, and in this case, the circumferential edge (periphery) L17 is the curved portion.

  Furthermore, as shown in FIG. 11 (b), it may be a semicircular electrostatic latent image graduation 110b8. In this case, an arc (periphery) L18 is a curved portion. Furthermore, as shown in FIG. 11C, the electrostatic latent image graduation 110b9 may be a semi-ring shape (a shape having a concave portion). In this case, the outer arc L19 and the inner arc L20 are curved portions. Further, as shown in FIG. 11D, an electrostatic latent image graduation 110b10 having curved portions L21 and L22 having a shape with a change in curvature (sissoid shape) may be used.

  Each of the curved portions is formed such that the inclination is reversed at the position where the electrostatic latent image graduation is divided in the sub-scanning direction, and the curved portions L17 to L17 in FIGS. L20 is formed by a single curve having a constant slope change rate. Further, FIG. 11D shows a first curved line portion L21 having a constant slope, and extends in the sub-scanning direction so as to be continuous with the first curved line portion L21. The first curved line portion L21 has a direction opposite to that of the first curved line portion L21. It is formed by combining the second curved line portion L22 inclined in the main scanning direction with a change rate of inclination.

  As described above, even when the electrostatic latent image graduations 110b7 to 110b10 formed with a curved portion are used, the zero cross point where the current waveform intersects the origin position becomes the electrostatic latent image graduation detection position. . When the electrostatic latent image graduation has a curved portion, the slope of the detected current waveform changes as long as the curved portion and the antenna intersect. Therefore, by measuring the change, it is also possible to detect where the electrostatic latent image graduation is in the process of passing through the antenna other than the zero cross point. The method for detecting the zero cross point from the integrated waveform is the same as that when the electrostatic latent image graduation has a shape having a straight line portion.

  Also, as shown in FIGS. 12A to 12C, even when the shape of the electrostatic latent image graduation 110b has a curved portion, the amount of deviation in the main scanning direction between the antenna 101a and the electrostatic latent image graduation 110b is as follows. , Based on the detection times 815 and 816 of the current waveform and the integrated waveform. Further, the same is true in that the shift amount in the main scanning direction between the antenna 101a and the electrostatic latent image graduation 110b can be detected based on the peak value (height) 818 of the integrated waveform.

  Note that when a semicircular shape is used, since it has a nonlinear rate of change with respect to the antenna 101a, the peak value of the current value can be detected as a steeper change with respect to the shift amount in the main scanning direction. Needless to say, the same effect can be obtained even in the case of a circular shape.

<Second Embodiment>
Next, a second embodiment according to the present invention will be described. In the first embodiment, the case where the antenna is a linear member parallel to the main scanning direction has been described. In the second embodiment, the antenna is formed as a linear member that is inclined with a predetermined inclination with respect to the main scanning direction and extends in the sub-scanning direction. Different from form. In the following description, only differences from the first embodiment will be described, and descriptions of other configurations will be omitted.

  FIGS. 13A to 13C show a case where the antenna 101a1 is inclined at a predetermined inclination with respect to the main scanning direction. In the present embodiment, the angle of inclination of the antenna 101a1 with respect to the main scanning direction is about 45 °. However, a different angle may be used, and the shape of the electrostatic latent image graduation 110b11 is rectangular. It has become.

  An induced current output generated when the electrostatic latent image graduation 110b11 passes through the antenna 101a1 is an output waveform 715. The integrated value is as an integrated waveform 716. At this time, the amount of deviation between the antenna 101a1 in the main scanning direction and the electrostatic latent image graduation 110b11 is similar to the passage time (for example, passage times 821 and 822 in the case of FIG. 13A) as in the first embodiment. Can be detected on the basis. Further, the passage time in the integrated waveform is specified accurately from the intersection of the approximate line 819 and the X axis (origin position) and the intersection of the approximate line 820 and the X axis.

  FIG. 14 shows another example in which the shape of the antenna is changed. The antenna 101a2 and the electrostatic latent image scale 110b have a triangular area. The induced current generated by the movement of the electrostatic latent image graduation 110 b becomes an output waveform 717. The result of integrating the induced current is an integrated waveform 718. The amount of deviation with respect to the main scanning direction can be detected using any of the passage times 823 and 824 and the peak values 825 and 826 of the current waveform or the integrated waveform.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. This embodiment is different from the first and second embodiments in that the electrostatic latent image graduation and noise are distinguished by pattern matching. In the following description, these other embodiments are different. Only the different parts will be described.

  FIG. 15A is a diagram showing the photosensitive drum surface defect 300, and the waveform in FIG. 15B is an output signal waveform in which the photosensitive drum surface defect 300 is detected by the antenna 101a. The photosensitive drum surface defect 300 is a portion where the photosensitive drum surface cannot be charged for some reason, and is considered to be almost circular, and is detected as if a circular electrostatic latent image graduation exists. Is done.

  FIG. 15C is a diagram schematically illustrating the external noise 301 generated in the antenna 101a. The waveform in FIG. 15D is an output signal waveform when the antenna 101a detects the external noise 301. FIG. The external noise 301 is mainly pulsed or has a random waveform.

  The control unit 140 distinguishes the photosensitive drum surface defect 300 and the external noise 301 from the electrostatic latent image scale 110b by using pattern matching. The pattern matching is to determine whether or not the shapes are similar, and a certain waveform A (sample) is compared with certain waveforms B, C, and D (detected values). Various calculation methods for determining the same are devised), and it is a method for determining that the result is the same.

  FIG. 16A shows a “theoretical output signal waveform (sample)” in which the diamond-shaped electrostatic latent image graduation 110b is detected by the antenna 101a. When the antenna 101a detects the output signal, the data processing circuit 121 of the control unit 140 performs pattern matching by comparing the output signal with the theoretical output signal waveform shown in FIG.

  Specifically, in the present embodiment, the data processing circuit 121 compares the waveforms using “sum of squares of differences”. The procedure by “sum of squares of differences” will be described. The waveform obtained by subtracting “theoretical waveform, FIG. 16 (a)” from “detected waveform, FIG. 10 (a), FIG. 15 (b), FIG. 15 (d)”. “Difference waveform, FIG. 16 (b), (c), (d)”. A waveform obtained by squaring the difference waveform is “square waveform of difference, FIGS. 16 (e), (f), (g)”. Then, the areas of the “square waveform of difference, FIGS. 16E, 16F, and 16G” are respectively obtained and compared with a predetermined determination value (for example, 1/10 of the area when there is no signal). It is determined that “FIG. 16E, ie, the detected waveform FIG. 10A”, which is less than the determination value, has the same shape as “theoretical waveform, FIG. 16A”. Also, “FIGS. 16 (f) and (g), that is, detected waveforms, FIGS. 15 (b) and 15 (d)”, which are equal to or higher than the determination value, are different in shape from “theoretical waveforms, FIG. Judge that there is.

  Thus, by determining, the detection waveform in FIG. 10A is an output signal waveform in which the electrostatic latent image graduation is detected, and the detection waveforms in FIG. 15B and FIG. It can be determined that the output signal waveform is not a detected electrostatic latent image graduation. In the above description, the description has been made based on the rhombic electrostatic latent image graduation 110b1, but the above-described pattern matching can be applied to the combination of the electrostatic latent image graduations having various shapes and the antenna described above. The unique signal waveform obtained from various electrostatic latent image graduation shapes facilitates separation from noise.

<Fourth embodiment>
Next, a fourth embodiment of the present invention will be described. This embodiment is different from the other embodiments in that a round electrostatic latent image graduation and a photosensitive drum surface defect are distinguished using the periodicity of the graduation. Therefore, in the following description, only parts different from those of the other embodiments will be described.

  The round electrostatic latent image graduation 110b7 shown in FIG. 11A has an advantage that the accuracy of the mounting angle of the linear antenna 101a is not required for the round electrostatic latent image graduation 110b7. On the other hand, the round electrostatic latent image graduation shown in FIG. 11A and the photosensitive drum surface defect 300 shown in FIG. 15A have similar detection waveform shapes, and are almost distinguishable even if pattern matching is used. There is no problem.

  Therefore, in the present embodiment, as shown in FIG. 17A, this round electrostatic latent image is obtained by utilizing the fact that the round electrostatic latent image graduation 110b7 is written on the surface of the photosensitive drum at regular intervals. The photosensitive drum surface defect 300 existing between the scales 110b7 is detected. Hereinafter, the method for detecting the photosensitive drum surface defect 300 will be described in detail with reference to the flowcharts of FIGS. 17, 18, and 19.

  Specifically, in the present embodiment, the data processing circuit 121 has a pulsing circuit as shown in FIG. As shown in FIG. 17C, the data processing circuit 121 is configured to pulse the zero cross timings 541, 542, 543... In the detection waveform of FIG. .

  Here, when printing of the first page is started (S1 in FIG. 19), the arithmetic unit 130 sets the variable i = 1 (S2) and monitors the output pulse output from the data processing circuit 121 (S3). When the output pulse is detected (Yes in S3), the time measurement counter 133 (see FIG. 18) starts counting the count time T1 (see FIG. 17 (c)). When the next output pulse is detected (Yes in S5), the output pulse detected in step S5 is set to P1 (S6), and the measurement of the count time T1 is ended.

  Simultaneously with the end of the measurement of the count time T1, the time measurement counter 133 starts measuring the count time T2, and records this count time T1 as the time from zero cross timings 541 to 542 (S7).

  When the count time T1 is recorded, the arithmetic unit 130 performs the following processing to determine whether the output pulse P1 is the round scale 110b7 or the photosensitive drum surface defect 300. That is, the determination is made based on whether or not the count time T1 coincides with a fixed period (hereinafter referred to as Tcycle) in which the round electrostatic latent image graduation 110b7 is written on the surface of the photosensitive drum (S8).

  That is, the arithmetic unit 130 determines that the output pulse P1 is the round electrostatic latent image scale 110b7 when the count time T1 is larger than “Tcycle−Terr” and smaller than “Tcycle + Terr” (Yes in S8). (S9). In other cases (No in S8), the photosensitive drum surface defect 300 is determined (S10). Note that Terr is an allowable error, and in the present embodiment, a value of 5% of Tcycle is used.

  When the output pulse P1 is determined, the arithmetic unit 130 adds 1 to the variable i (S11), and determines whether printing for one page has been completed (S12). If the printing for one page has not been completed (No in S12), the steps from Step S5 to S12 are repeated. If the printing has been completed (Yes in S12), the printing for one page is terminated. (S13). In FIG. 17C, when the variable i is 3, the count time T3 is smaller than Tcycle, so the arithmetic unit 130 determines that the output pulse P3 is noise.

  By the way, when the variable i is 4, the count time T4 may be smaller than Tcycle, and even though the output pulse P4 is an electrostatic latent image scale, it may be determined as noise. Therefore, in this embodiment, in order to avoid such an erroneous determination, for example, in step S8, when the time interval T4 does not match Tcycle, the previous time interval T3 is set to the time interval T4. Add to. Then, it is determined again whether the time interval “T3 + T4” matches Tcycle. If the time interval “T3 + T4” matches Tcycle, the output pulse P4 may be determined to be an electrostatic latent image scale. .

  When the timing at which the electrostatic latent image graduation is detected as described above is outside the predetermined allowable range, the detection of the electrostatic latent image graduation is determined to be noise, so that these round electrostatic latent image graduations It is possible to accurately distinguish the photosensitive drum surface defect.

<Fifth embodiment>
Next, a fifth embodiment of the present invention will be described. This embodiment is different from the other embodiments in that the position of the electrostatic latent image graduation is accurately detected by low-pass processing. Therefore, in the following description, only parts different from those of the other embodiments will be described.

  FIG. 20B shows a state in which noise is superimposed on an output signal obtained by detecting the electrostatic latent image graduation 110b11 of FIG. 20A with the antenna 101a. In this state, it is difficult to accurately detect the zero cross point 550 necessary for detecting the position of the electrostatic latent image graduation 110b11 due to the influence of noise.

  Here, in the present embodiment, the noise component is removed by utilizing the fact that the frequency band of the noise component and the output signal waveform are different from each other in the waveform of FIG. Specifically, in the present embodiment, the low-pass circuit 123 shown in FIG. 21 is mounted on the data processing circuit 121, and low-pass processing is performed on the waveform of FIG. Then, the noise which is a high frequency component is removed, and the waveform of FIG. 20C is obtained, and the zero cross point 550 can be detected based on the current waveform of FIG. The electrostatic latent image index 110b11 can be detected.

  Note that the inventions described in the above-described embodiments may be combined in any way. Further, when correcting the alignment of the image on the intermediate transfer belt based on the detection of the electrostatic latent image scale, in this embodiment, the control unit controls the rotational speed of the photosensitive drum and the exposure unit. Alignment in the main and sub-scanning directions was performed. However, the alignment in the main and sub-scanning directions may be performed only by the exposure unit, and the image in the sub-scanning direction may be performed by driving control of the intermediate transfer belt instead of the photosensitive drum.

  11Y to 11K, 20: image carrier (photosensitive drum, intermediate transfer belt), 13Y to 13K: exposure means (exposure device), 101a: conductor (antenna), 140: control unit

Claims (15)

Exposure means;
An image carrier on the surface of which an electrostatic latent image graduation comprising an electrostatic latent image formed by the exposure means is provided;
In the main scanning direction orthogonal to the sub-scanning direction that is the rotation direction of the image carrier, at least a part of the electrostatic latent image graduation of the image carrier overlaps and the image carrier rotates. A conductor that moves relative to the electrostatic latent image graduation in the sub-scanning direction;
A controller that detects the electrostatic latent image graduation based on an induced current generated in the conductor by the relative movement; and
The conductor and the electrostatic latent image graduation are formed so that the intersection position thereof changes in the main scanning direction when the relative position is moved.
An image forming apparatus. The electrostatic latent image graduation is a shape having a straight portion that extends in the sub-scanning direction with a certain inclination in the main scanning direction and intersects the conductor.
The image forming apparatus according to claim 1. The straight portion is a first straight portion;
The electrostatic latent image graduation extends in the sub-scanning direction so as to be continuous with the first straight line portion and the first straight line portion, and has an inclination in a direction opposite to the first straight line portion. A second linear portion intersecting with the conductor inclined in the scanning direction,
The image forming apparatus according to claim 2. The electrostatic latent image graduation has a triangular or rhombus shape whose at least one side intersects the conductor.
The image forming apparatus according to claim 1. The electrostatic latent image graduation is a shape having a curved portion extending in the sub-scanning direction in which the inclination changes at a constant change rate in the main scanning direction
The image forming apparatus according to claim 1. The curved portion is a first curved portion,
The electrostatic latent image graduation extends in the sub-scanning direction so as to be continuous with the first curved portion and the first curved portion, and has a rate of change in inclination in a direction opposite to the first curved portion. And a second curved portion inclined in the main scanning direction.
The image forming apparatus according to claim 5. The electrostatic latent image graduation is a circular or semicircular shape whose periphery intersects the conductor.
The image forming apparatus according to claim 5. The conductor is a linear member formed to extend in parallel to the main scanning direction.
The image forming apparatus according to claim 1. The conductor is a linear member that is inclined with a predetermined inclination with respect to the main scanning direction and extends toward the sub-scanning direction.
The image forming apparatus according to claim 1. The conductor has a shape having a linear conductor portion that extends in the sub-scanning direction with a certain inclination in the main scanning direction and intersects the electrostatic latent image graduation.
The image forming apparatus according to claim 1. The conductor straight line portion is a first conductor straight line portion;
The conductor extends in the sub-scanning direction so as to be continuous with the first conductor straight line portion and the first conductor straight line portion, and the main scan has an inclination in a direction opposite to the first conductor straight line portion. A second conductor straight line section intersecting with the latent image graduation inclined in the direction,
The image forming apparatus according to claim 10. The conductor has a triangular or rhombus shape whose at least one side intersects the latent image graduation,
The image forming apparatus according to claim 10 or 11. The control unit integrates the waveform of the induced current and detects the electrostatic latent image graduation based on the integrated waveform.
The image forming apparatus according to claim 1. The control unit determines that the detection of the electrostatic latent image graduation is noise when the timing at which the electrostatic latent image graduation is detected is outside a predetermined allowable range.
The image forming apparatus according to claim 1. The image carrier includes first and second photosensitive drums, and an intermediate transfer body to which the electrostatic latent image scale formed on the surface of the first photosensitive drum is transferred.
The conductor is disposed between the first and second photosensitive drums, and detects the electrostatic latent image graduation transferred to the intermediate transfer member, and on the surface of the second photosensitive drum. Having a second conductor for detecting the formed latent image graduation,
The control unit is arranged on the first and second photosensitive drums based on the detection timing of the electrostatic latent image graduation by the first conductor and the detection timing of the electrostatic latent image graduation by the second conductor. Controlling at least one of the image carrier and the exposure means so that the formed image matches on the intermediate transfer member;
The image forming apparatus according to claim 1.

Images