JP4480662B2 - Method for creating image pattern for evaluation and evaluation chart - Google Patents

Description

The present invention relates to a method for creating an evaluation image pattern and an evaluation chart.

  Conventionally, in response to the demand for high-speed image output, many image forming apparatuses including so-called multi-beam optical scanning devices that simultaneously scan an image carrier with light beams comprising a plurality of light sources have been developed and commercialized. . In an image forming apparatus equipped with this multi-beam optical scanning device, it is important to stably maintain the beam pitch between the light beams in the sub-scanning direction in the manufacturing / market in order to obtain a stable output image.

Further, as a prior art document relating to the detection of the displacement of the beam pitch, it consists of an image pattern in which n dot lines (n ≧ 2) formed in the main scanning direction repeat in the sub-scanning direction with a period that is an integral multiple of the number of light beams. , An evaluation chart including an image evaluation pattern formed by combining a plurality of image patterns formed by combining a plurality of different light beams in the main scanning direction, and an image evaluation pattern output function for outputting the image evaluation pattern Has been disclosed and proposed (for example, see Patent Document 1).
JP-A-10-62705

  Certainly, with the evaluation chart and the image recording apparatus disclosed in Patent Document 1, it is possible to detect the deviation of the beam pitch from the image density difference by viewing the output image evaluation pattern. .

  However, in the evaluation chart and the image recording apparatus disclosed in Patent Document 1, it is considered that the image evaluation pattern is output from the line-shaped electrostatic latent image formed on the photosensitive member by continuous light beam emission. Therefore, there is a possibility that the image density of the image evaluation pattern becomes high. Therefore, there is a possibility that a minute beam pitch shift in the sub-scanning direction cannot be detected from the image evaluation pattern formed on the paper. In addition, as the resolution of the output image increases further, defects in the output image are likely to occur even with a small change in the beam pitch. Therefore, it is not possible to detect a slight beam pitch deviation in the sub-scanning direction from the image evaluation pattern. Conceivable.

In view of the above-described problems, the present invention provides an evaluation image pattern creation method and an evaluation chart capable of outputting an evaluation image pattern for detecting a minute beam pitch change in the sub-scanning direction of a light beam. The purpose is to provide.

In order to achieve the above object, an image forming apparatus according to the present invention mainly deflects n light beams respectively emitted from n (n ≧ 2) light sources by a deflecting unit so as to be mainly on an image carrier. By scanning in the scanning direction, n electrostatic latent images are separately formed at a predetermined pitch in the sub-scanning direction of the image carrier, and electrostatic latent images are formed in the main scanning direction. In a method for creating an image pattern for evaluation in which a two-dimensional electrostatic latent image is formed on the image carrier by driving the image carrier in the sub-scanning direction at a predetermined pitch, an image for evaluation is generated. During the first scanning at the time of pattern output , two adjacent light beams from the first and second light beams to the (n-1) th and nth among the n light beams are arranged in the sub-scanning direction. The dot is shifted by a predetermined pitch in the main scanning direction on the image carrier. Are sequentially formed for each of a plurality of discontinuous predetermined dots with a predetermined pulse light emission time shorter than the light emission time, and then, the nth light beam is formed in a predetermined direction shorter than the one dot pulse light emission time in the main scanning direction. During the pulse emission time, the first micro dot electrostatic latent image formed on a plurality of discontinuous predetermined dots and the first scan during the second scan different from the first scan by a predetermined pitch in the sub-scan direction. The first plurality of dots are formed at a position corresponding to the nth plurality of dots during the scanning of the first plurality of dots with a predetermined pulse emission time shorter than the one dot pulse emission time, and then first in the main scanning direction. Two light beams adjacent to the (n−1) th and nth light beams from the second light beam are shifted by a predetermined pitch in the sub-scanning direction, and shorter than the one-dot pulse emission time in the main scanning direction on the image carrier. Predetermined pal In the light emission time, it is characterized by outputting the evaluation image pattern having an electrostatic latent image of the second fine dots formed in this order for each discrete predetermined plurality of dots, the. With such a configuration, it is possible to output an evaluation image pattern in which the minimum detection accuracy with respect to a change in pitch between light beams is improved as compared with the conventional image forming apparatus. By observing the output evaluation image pattern, it is possible to detect a minute beam pitch change of several nanometers as a significant density difference / visual density difference.

The evaluation chart according to the present invention is configured to be a recording material to which the evaluation image pattern is output by the evaluation image pattern creation method having the above-described configuration. By adopting such a configuration, by observing the evaluation image pattern output as an image on the evaluation chart, a change in the pitch of a minute beam such as several nm is detected as a significant density difference / visual difference. It becomes possible.

  Further, the image forming apparatus according to the present invention deflects the first light beam and the second light beam respectively emitted from the first light source and the second light source by the deflecting unit and simultaneously scans the image carrier. Two electrostatic latent images are simultaneously formed at a predetermined pitch in the sub-scanning direction of the image carrier, the electrostatic latent image is formed in the main scanning direction, and the image carrier is further moved in the sub-scanning direction. By driving at a predetermined pitch, a two-dimensional electrostatic latent image is formed on the image carrier to output an image, and at the time of image output, the first light beam and the second light beam are emitted for one dot pulse emission time. Then, a one-dot electrostatic latent image is simultaneously formed on the image carrier at the predetermined pitch in the sub-scanning direction, and the first light beam and the second light beam are output when the evaluation image pattern is output. When one dot pulse is emitted by a light beam A first period in which an electrostatic latent image of minute dots is formed at the predetermined pitch simultaneously in the sub-scanning direction on the image carrier with a shorter predetermined pulse emission time, and after the first period, the second light A second period in which an electrostatic latent image of minute dots is formed in the main scanning direction on the image carrier by the beam in the predetermined pulse emission time; and an electrostatic latent image of minute dots formed in the second period A third period in which an electrostatic latent image of minute dots is formed in the main scanning direction on the image carrier in the main scanning direction by the first light beam at the predetermined pitch in the sub-scanning direction, and An image pattern for evaluation is output from the electrostatic latent image formed in Step 1, and the electrostatic latent images of minute dots respectively formed in the first period, the second period, and the third period are further converted in the main scanning direction. The first predetermined number, the second predetermined number and And it is configured as one formed by a second predetermined number of discontinuous. With such a configuration, it is possible to output an evaluation image pattern in which the minimum detection accuracy with respect to a change in pitch between the first light beam and the second beam is improved as compared with the conventional image forming apparatus. By observing the output evaluation image pattern, it is possible to detect a minute beam pitch change of several nanometers as a significant density difference / visual density difference.

  The evaluation chart according to the present invention is configured to be a recording material to which the evaluation image pattern is output by the image forming apparatus including the first light source and the second light source. By adopting such a configuration, by observing the evaluation image pattern output as an image on the evaluation chart, a change in the pitch of a minute beam such as several nm is detected as a significant density difference / visual difference. It becomes possible.

As described above, with the evaluation image pattern creation method and evaluation chart according to the present invention, it is possible to detect a minute beam pitch change in the sub-scanning direction of the light beam.

  Hereinafter, a case where the present invention is applied to a copying machine will be described as an example. FIG. 1 is a block diagram showing a main configuration of a copying machine according to the present invention. As shown in FIG. 1, a copying machine 1 according to this embodiment includes a central processing unit 10 (hereinafter referred to as a CPU [Central Processing Unit] 10) that controls the operation of the entire apparatus, and a document transport that automatically transports a document. Unit 11, a document take-in unit 12 that takes in a document transported from document transport unit 11 and generates image data, and an operation display unit 13 that includes operation means (such as a numeric keypad or touch panel) and display means (such as a liquid crystal display). A multi-beam optical scanning unit, which will be described later, and an image forming unit 14 that outputs an image on a sheet based on image data, and a fixing unit that fixes the image output obtained on the sheet by the image forming unit 14 on the sheet 15, a sheet feeding unit 16 that feeds the image forming unit 14, a ROM [Read Only Memory] in which various control programs are stored, and a RAM [Random Access Memor used as a work area] y] and the like.

  In addition to controlling the operation of the entire apparatus, the CPU 10 performs processing related to image output control of an evaluation chart, which will be described in detail later.

  FIG. 2 is a schematic diagram showing a multi-beam optical scanning unit and a photosensitive drum provided in the image forming unit 14 of the copying machine 1. The image forming unit 14 irradiates a first light beam and a second light beam together on a surface of a later-described photosensitive drum 142 that is uniformly charged to a predetermined potential by a charger (not shown). The image forming apparatus includes a multi-beam optical scanning unit 141 capable of forming a latent image, and an image bearing member photosensitive drum 142 on which a toner image is formed on the drum surface based on image data. Although not shown, the image forming unit 14 naturally includes a charger, a transfer roller, a developing device, a static eliminator, and the like used for image formation.

  The multi-beam light scanning unit 141 receives the first light beam and the light beam toward the prism 145 provided with a collimator lens (not shown) according to the pulse current input from the pulse generator (not shown) based on the image data. A first light source 143 and a second light source 144 of a semiconductor laser that emits a second light beam (that is, laser light), and a first light beam and a second light beam incident from the first light source 143 and the second light source 144, respectively. A prism 145 for converting the first and second light beams incident through the collimator lens (not shown) into a predetermined beam pitch, and a prism 145. A cylinder lens 146 for condensing the passed first and second light beams on a polygon mirror 147, which will be described later, and a cylinder lens The first and second light beams incident from 46 are reflected by the polygon mirror 147 that scans the first and second light beams by rotating at a predetermined speed, and scanned by the polygon mirror 147. A scanning lens 148 that guides the first light beam and the second light beam to a condensing lens 149 described later, and the first light beam and the second light beam incident from the scanning lens 148 are condensed on a reflecting plate 150 described later. The condenser lens 149 includes a reflecting plate 150 that reflects the first light beam and the second light beam incident from the condenser lens 149 and enters the surface of the photosensitive drum 142.

  The first light beam and the second light beam emitted from the first light source 143 and the second light source 144, respectively, are incident on the polygon mirror 147 via the prism 145 and the cylinder lens 146. The first light beam and the second light beam are scanned by the polygon mirror 147, and the photosensitive drum 142 is uniformly charged at a predetermined potential via the scanning lens 148, the condenser lens 149, and the reflection plate 150. An electrostatic latent image is formed on the surface at a predetermined pitch P at the same time in the sub-scanning direction, and an electrostatic latent image in the main scanning direction is further formed along with the scanning.

  As shown in FIG. 3, the memory unit 17 stores image pattern data 171 for outputting an image pattern for evaluation. The image pattern data 171 includes dot data for emitting the first light beam and the second light beam from the first light source 143 and the second light source 144, respectively, at a predetermined pulse light emission time T2 shorter than the one dot pulse light emission time T1. 172 is recorded with the following pattern configuration.

  Note that the 1-dot pulse time T1 is the time when the first light beam and the second light beam are emitted from the first light source 143 and the second light source 144, respectively, at the time of image output to a normal sheet based on image data. The first light beam and the second light beam are sub-scanned on the surface of the photosensitive drum 142 through the prism 145, the cylinder lens 146, the polygon mirror 147, the scanning lens 148, the condenser lens 149, and the deflecting unit 150. This is the emission time of the first light beam and the second light beam necessary for simultaneously forming an electrostatic latent image of one dot (for example, 30 nm) at a predetermined pitch P in the direction. Further, the predetermined pulse emission time T2 is 1/2 to 1/3 of the one dot pulse emission time T1, and preferably 1/3 to 1/4. Thereby, it is possible to output an image pattern for evaluation that makes it possible to evaluate a shift in pitch between the first light beam and the second light beam.

  As shown in FIG. 3, the image pattern data 171 includes a one-dot pulse emission time T1 by the first light beam and the second light beam emitted from the first light source 143 and the second light source 144, respectively, in the first period. An electrostatic latent image of two minute dots simultaneously formed at a predetermined pitch P in the sub-scanning direction on the photosensitive drum 142 with a predetermined pulse emission time T2 shorter than that in the main scanning direction on the photosensitive drum 142. Each of the first period data 173 for discontinuously forming six (corresponding to the first predetermined number) and the second light beam in the second period after the first period from the one-dot pulse emission time T1 A second period for forming six electrostatic latent images of micro dots discontinuously (corresponding to a second predetermined number) in the main scanning direction on the photosensitive drum 142 in a short predetermined pulse emission time T2. In the third period, after the photosensitive drum 142 is driven by a predetermined pitch P in the third period, the first light beam is applied to the electrostatic latent image of minute dots formed in the second period. Six electrostatic latent images of minute dots (corresponding to a second predetermined number) are discontinuously formed in the main scanning direction on the photosensitive drum 142 in a predetermined pulse light emission time T2 shorter than the one dot pulse light emission time T1. The third period data 175 to be included is included for two cycles.

  Next, the document copying operation in the copying machine 1 configured as described above will be described. In the document copying operation in the copying machine 1, first, a document is transported from the document transport unit 11 to the document capture unit 12, and the document capture unit 12 captures the document (generates image data). The generated image data is temporarily stored in the memory unit 17, read out again, and sent to the image forming unit 14. Then, image output based on the image data in the copying machine 1 is performed as follows.

  In the image forming unit 14, pulse currents are input from a pulse generation unit (not shown) to the first light source 143 and the second light source 144 based on the image data, so that the first light source 143 and the second light source 144 respectively receive the first current. The one light beam and the second light beam are emitted and enter the polygon mirror 147 via the prism 145 and the cylinder lens 146. The first light beam and the second light beam scanned by the polygon mirror 147 are uniformly charged to a predetermined potential by a charger (not shown) through the scanning lens 148, the condenser lens 149, and the reflection plate 150. On the surface of the photosensitive drum 142, an electrostatic latent image is simultaneously formed at a predetermined pitch P in the sub-scanning direction, and an electrostatic latent image in the main scanning direction is further formed along with the scanning. The photosensitive drum 142 is scanned again based on the image data after being rotated by the pitch P in the sub-scanning direction from the first incident position of the first light beam and the second light beam onto the photosensitive drum 142. An electrostatic latent image is formed on the photosensitive drum 142 by the first light beam and the second light beam. By repeating such an operation, a two-dimensional electrostatic latent image based on the image data is formed on the photosensitive drum 142. Then, toner is attached to the electrostatic latent image by a developing device (not shown) and development is performed, and a toner image is formed on the photosensitive drum 142. Thereafter, the toner image on the photosensitive drum 142 is transferred to the sheet conveyed from the sheet feeding unit 16. The fixing unit 15 heats and presses the toner image and fixes the toner image on the paper, and then the printed paper is discharged.

  Note that the copying machine 1 according to the present embodiment is configured to output an evaluation image pattern that can detect minute changes in the beam pitch in the sub-scanning direction of a plurality of light beams incident on the photosensitive drum 142. It has characteristics. Therefore, in the following, referring to the drawings, it is possible to detect a minute change in beam pitch in the sub-scanning direction of a plurality of light beams incident on the photosensitive drum 142 in the copying machine 1 of the present embodiment. The output operation of the evaluation image pattern will be described. FIG. 4 is a diagram showing an electrostatic latent image formed on the photosensitive drum 142 when the copying machine 1 outputs the evaluation image pattern. FIG. 5 is a diagram showing an evaluation image pattern output from the electrostatic latent image shown in FIG. 4 by the copying machine 1. First, the case where there is no deviation in the predetermined pitch P between the first light beam and the second light beam in the copying machine 1 will be described.

  First, when an evaluation chart button (not shown) for executing printing of an evaluation chart on the operation display unit 13 is pressed, a signal accompanying the pressing is input to the CPU 10, and the CPU 10 starts printing an evaluation image pattern. Be recognized. Then, the photosensitive drum 142 is uniformly charged to a predetermined potential by a charger (not shown).

  Subsequently, the CPU 10 reads the image pattern data 171 shown in FIG. 3 from the memory unit 17, and the electrostatic latent image shown in FIG. 4 is formed on the surface of the photosensitive drum 142 by the control of the CPU 10 based on the image pattern data 171. It is formed as follows.

  As shown in FIG. 4, in the first scan, the pulse current is not input to the first light source 143 and the second light source 144 for a predetermined time and a predetermined pulse light emission time T2 shorter than the one-dot pulse light emission time T1. After the input is repeated and input six times in a discontinuous manner, the pulse current is not input to the second light source 144 for a predetermined time and input for a predetermined pulse light emission time T2 shorter than the 1-dot pulse light emission time T1. Are repeated and input 6 times in a discontinuous manner.

  With the input of such a pulse current, as shown in FIG. 4, the first light beam and the second light beam from the first light source 143 and the second light source 144, respectively, for a predetermined period of time as shown in FIG. The emission and the emission of the predetermined pulse emission time T2 shorter than the one-dot pulse emission time T1 are repeated, and the emission is discontinuously and 6 times at the same time, and the prism 145, the cylinder lens 146, the polygon mirror 147, the scanning lens 148, and the light collection. The electrostatic latent image 21 of two micro dots is deflected and scanned by the deflecting means including the lens 149 and the reflecting plate 150 at the same time in the sub scanning direction on the photosensitive drum 142 at a predetermined pitch P in the main scanning direction. (Corresponding to the first predetermined number) are formed discontinuously.

  Then, as shown in FIG. 4, in the second period, the second light beam from the second light source 144 is not emitted for a predetermined time and emitted for a predetermined pulse emission time T2 shorter than the one-dot pulse emission time T1. , And is discontinuously emitted six times, and is deflected and scanned by a deflecting means including a prism 145, a cylinder lens 146, a polygon mirror 147, a scanning lens 148, a condensing lens 149, and a reflecting plate 150. 6 electrostatic latent images 21 of minute dots are discontinuously formed (corresponding to a second predetermined number) in the main scanning direction.

  In the second scan, first, the photosensitive drum 142 is rotationally driven so as to be shifted by the pitch P in the sub-scanning direction. Then, a non-input of a predetermined time and an input of a predetermined pulse light emission time T2 shorter than the 1-dot pulse light emission time T1 are repeated and input to the first light source 143 six times discontinuously. Then, the pulse current is repeatedly applied to the first light source 143 and the second light source 144 by non-input for a predetermined time and input for a predetermined pulse light emission time T2 shorter than the 1-dot pulse light emission time T1, and simultaneously. Input 6 times. Further, a non-input for a predetermined time and an input for a predetermined pulse light emission time T2 shorter than the one-dot pulse light emission time T1 are repeated and the pulse current is input discontinuously six times to the second light source 144.

  With the input of such a pulse current, in the third period, the first light beam from the first light source 143 is not emitted for a predetermined time and has a predetermined pulse emission time T2 shorter than the one-dot pulse emission time T1. The light is repeatedly emitted and discontinuously emitted six times, and is deflected and scanned by a deflecting unit including a prism 145, a cylinder lens 146, a polygon mirror 147, a scanning lens 148, a condensing lens 149, and a reflecting plate 150. Six electrostatic latent images 21 of minute dots are formed discontinuously (corresponding to a second predetermined number).

  Then, in the next first period, the first light beam and the second light beam from the first light source 143 and the second light source 144 are not emitted for a predetermined time and predetermined pulse emission shorter than the one-dot pulse emission time T1. The emission at time T2 is repeated, and the emission is discontinuously 6 times at the same time, and is deflected and scanned by the deflecting means including the prism 145, the cylinder lens 146, the polygon mirror 147, the scanning lens 148, the condensing lens 149 and the reflecting plate 150. The electrostatic latent images 21 of two micro dots formed at the same time in the sub scanning direction on the photosensitive drum 142 at the pitch P are formed discontinuously in the main scanning direction.

  Then, in the next second period, the second light beam from the second light source 144 repeats non-emission for a predetermined time and emission for a predetermined pulse emission time T2 shorter than the one-dot pulse emission time T1, The light is emitted six times in succession, deflected and scanned by a deflecting unit including a prism 145, a cylinder lens 146, a polygon mirror 147, a scanning lens 148, a condensing lens 149, and a reflecting plate 150, and in the main scanning direction on the photosensitive drum 142. Six electrostatic latent images 21 of minute dots are formed discontinuously.

  In the third scan, first, the photosensitive drum 142 is rotationally driven so as to be shifted by the pitch P in the sub-scanning direction. Then, a non-input of a predetermined time and an input of a predetermined pulse light emission time T2 shorter than the 1-dot pulse light emission time T1 are repeated and input to the first light source 143 six times discontinuously.

  With the input of such a pulse current, in the next third period, the first light beam from the first light source 143 is not emitted for a predetermined time, and a predetermined pulse emission time shorter than the one-dot pulse emission time T1. T2 is repeatedly emitted and discontinuously emitted six times, and is deflected and scanned by a deflecting unit including a prism 145, a cylinder lens 146, a polygon mirror 147, a scanning lens 148, a condensing lens 149, and a reflecting plate 150 to be photosensitive. Six electrostatic latent images 21 of minute dots are formed discontinuously on the body drum 142 in the main scanning direction.

  The predetermined pulse emission time T2 shorter than the 1 dot pulse emission time T1 is 1/2 to 1/3 of the 1 dot pulse emission time T1, and preferably 1/3 to 1/4. By setting the predetermined pulse emission time T2 to 1/2 to 1/3 of the one-dot pulse emission time T1, as shown in FIGS. 5 and 7 to be described later, the first light beam and the second light beam It is possible to output the evaluation image pattern 22 that can evaluate the deviation of the pitch P.

  As shown in FIG. 4, the electrostatic latent images 21 of the minute dots adjacent in the sub-scanning direction formed on the photosensitive drum 142 are partially overlapped, and the first light beam and the first light beam If there is no deviation in the pitch P of the two light beams, this overlap amount is constant in the electrostatic latent images 21 of all the minute dots adjacent in the sub-scanning direction.

  As described above, the electrostatic latent image formed on the photoconductor drum 142 has a predetermined pulse emission time shorter than the one dot pulse emission time by the first light beam and the second light beam. An electrostatic latent image of two minute dots is simultaneously formed in the sub-scanning direction on the drum 142 at a predetermined pitch P, and the electrostatic latent image of these minute dots is a first predetermined number (in the main scanning direction ( In this embodiment, six) the first period formed discontinuously, and after the first period, the main light on the photosensitive drum 142 has a predetermined pulse emission time shorter than the one dot pulse emission time by the second light beam. The electrostatic latent image of one minute dot in the scanning direction is formed in the second period in which the second predetermined number (six in this embodiment) is discontinuous in the main scanning direction, and in the second period. Place in the sub-scanning direction with respect to the electrostatic latent image of minute dots. The electrostatic latent image of one minute dot on the photosensitive drum 142 in the main scanning direction with a predetermined pulse emission time shorter than the one dot pulse emission time by the first light beam at the pitch P of the second predetermined number ( In this embodiment, it is formed in 6) the third period formed discontinuously.

  That is, the electrostatic latent image formed on the photosensitive drum 142 is predetermined in the sub-scanning direction of the photosensitive drum 142 with a predetermined pulse emission time shorter than the one-dot pulse emission time by adjacent light beams during the same scanning. And the electrostatic latent image of the first minute dots formed discontinuously by a predetermined number (six in this embodiment) in the main scanning direction and the sub-scanning direction during different scanning In the sub-scanning direction on the photosensitive drum 142 with a predetermined pulse emission time shorter than the one-dot pulse emission time by the front-end and rear-end light beams (in this embodiment, the first light beam and the second light beam, respectively) And electrostatic latent images of second minute dots formed at a predetermined pitch and discontinuously by a predetermined number (six in this embodiment) in the main scanning direction. An evaluation image pattern is output from the electrostatic latent image formed as described above as follows.

  Next, as shown in FIG. 4, in the electrostatic latent image 21 of a plurality of micro dots formed on the photosensitive drum 142, an overlapping region of the electrostatic latent image 21 of micro dots adjacent in the sub-scanning direction is displayed. Since the difference between the combined potential and the surrounding potential becomes large, toner is attached to the overlapping region of the electrostatic latent image 21 of minute dots by a developing device (not shown) to form a toner image. Thereafter, the toner image is transferred to the sheet conveyed from the sheet feeding unit 16, and the fixing unit 15 fixes the toner image on the sheet. Then, the sheet on which the evaluation image pattern shown in FIG. 5 is printed (that is, the evaluation chart) is discharged from the electrostatic latent image shown in FIG. For the sake of easy understanding of the invention, FIG. 5 shows an electrostatic latent image 21 of minute dots indicated by broken lines for convenience.

  As described above, when there is no deviation in the pitch P between the first light beam and the second light beam, the evaluation image pattern 22 on the evaluation chart is between four evaluation image patterns 22 as shown in FIG. With no difference in density. By visually observing the evaluation chart and observing the density difference between the evaluation image patterns 22, it is possible to determine whether or not there is a deviation in the pitch P between the first light beam and the second light beam.

  Next, when there is a deviation in the pitch P between the first light beam and the second light beam in the copying machine 1, the electrostatic latent image formed on the photosensitive drum 142 and the printing result from the electrostatic latent image are described. A description will be given below. FIG. 6 is a diagram showing an electrostatic latent image formed on the photosensitive drum 142 when the pitch P between the first light beam and the second light beam is shifted. FIG. 7 is a diagram showing an evaluation image pattern output from the electrostatic latent image shown in FIG. 6 by the copying machine 1. Note that the electrostatic latent image shown in FIG. 6 and the evaluation image pattern output from the electrostatic latent image shown in FIG. 7 have no deviation in the pitch P of the first light beam and the second light beam described above. Are formed by the copying machine 1 in the same manner as in FIG. Further, the case where the pitch P in the sub-scanning direction between the first light beam and the second light beam is shifted by ΔP will be described as an example. Further, it is assumed that there is no deviation in the rotational driving of the photosensitive drum 142 by the pitch P in the sub-scanning direction.

  As shown in FIG. 6, since the pitch P in the sub-scanning direction between the first light beam and the second light beam is shifted by ΔP, the photosensitive member is simultaneously used by the first light beam and the second light beam in the first scan. The electrostatic latent image 21 of the minute dots formed on the drum 142 in the first period includes the electrostatic latent image 21 of the minute dots formed by the first light beam and the static of the minute dots formed by the second light beam. The overlapping area with the electrostatic latent image 21 is increasing. Also, the electrostatic latent image 21 of minute dots formed on the photosensitive drum 142 by the second light beam at the first scan and the first light beam at the second scan. The overlapping area of the minute dots with the electrostatic latent image 21 in the third period is reduced. Further, in the second scan, the electrostatic latent image 21 of the minute dots of the first period formed on the photosensitive drum 142 at the same time by the first light beam and the second light beam was formed by the first light beam. The overlapping area between the electrostatic latent image 21 of minute dots and the electrostatic latent image 21 of minute dots formed by the second light beam is increased. Further, the electrostatic latent image 21 of the minute dots formed on the photosensitive drum 142 by the second light beam in the third scan and the first light beam in the second scan. The overlapping area of the minute dots with the electrostatic latent image 21 in the third period is reduced.

  As described above, the area of the overlapping area of the electrostatic latent images 21 of the minute dots adjacent to each other in the sub scanning direction formed on the photosensitive drum 142 by the first light beam and the second light beam has six in the main scanning direction. The increase and decrease are repeated for each electrostatic latent image of minute dots. This means that the combined potential of the electrostatic latent images of the minute dots adjacent in the sub-scanning direction is not constant for every six minute electrostatic latent images in the main scanning direction.

  Further, as shown in FIG. 7, the density of the evaluation image pattern 22 on the evaluation chart is such that the pitch P in the sub-scanning direction between the first light beam and the second light beam is shifted by ΔP. Since the combined potential of the electrostatic latent images 21 of the minute dots adjacent to each other is not constant for each of the six latent electrostatic images of the six minute dots in the main scanning direction, , It will be a repeating shade. That is, the evaluation image pattern 22 corresponding to a large overlapping area of electrostatic latent images of minute dots adjacent to the sub-scanning direction light formed on the photosensitive drum 142 by the first light beam and the second light beam is as follows. Since the combined potential due to the electrostatic latent image of the minute dots adjacent in the sub-scanning direction becomes large, it becomes dark. Conversely, the evaluation image pattern 22 corresponding to a small overlapping area of electrostatic latent images of minute dots adjacent to the sub-scanning direction light formed on the photosensitive drum 142 by the first light beam and the second light beam. Is thinner because the combined potential of the electrostatic latent images of minute dots adjacent in the sub-scanning direction becomes smaller. In FIG. 7, for the sake of easy understanding of the invention, an electrostatic latent image 21 of minute dots indicated by a broken line is shown for convenience.

  Thus, when there is a deviation in the pitch P between the first light beam and the second light beam, the evaluation image pattern 22 on the evaluation chart is between the four evaluation image patterns 22 as shown in FIG. There will be a difference in density. By visually observing the evaluation chart and observing the density difference between the evaluation image patterns 22, it is possible to determine whether or not there is a deviation in the pitch P between the first light beam and the second light beam. Further, as shown in FIG. 7, if there is a density difference between the evaluation image patterns 22 on the evaluation chart, it is possible to detect a minute beam pitch change of several nm as a visual density difference.

  As described above, the copying machine 1 according to the present embodiment does not cause the first light source 143 and the second light source 144 to emit light continuously at the time of outputting the evaluation image pattern, but is shorter than the one-dot pulse emission time. Of the first light beam and the second light source 144 are suppressed by forming the first light beam and the second light beam adjacent to each other in the sub-scanning direction. The difference in the pitch P between the first light beam and the second light beam emitted from each of the light beams is such that a difference in density and a difference in visual density between the image patterns for evaluation 22 appear greatly. For this reason, it is possible to increase the minimum detection accuracy with respect to the change in the pitch P between the first light beam and the second light beam as compared with the conventional image forming apparatus. As a result, it is possible to detect a change in the pitch P of a minute beam as small as several nm as a significant density difference / visual density difference.

  The evaluation image pattern printed on the sheet from the electrostatic latent image formed on the photosensitive drum in the copying machine having the first light source, the second light source, and the third light source in the multi-beam light scanning unit is also as described above. Similar effects can be obtained. This will be described below. FIG. 8 is a view showing an electrostatic latent image formed on a photosensitive drum in a copying machine having a first light source, a second light source, and a third light source in a multi-beam light scanning unit. FIG. 9 is a diagram showing an evaluation image pattern output from the electrostatic latent image shown in FIG. Note that the copying machine 1 has a configuration in which a third light source is added to the multi-beam optical scanning unit 141 shown in FIG. 2, and therefore detailed description of the configuration is omitted. Further, each part of the copying machine 1 is denoted by the same reference numeral as above, and the description thereof is omitted unless particularly necessary. The light beam emitted from the third light source is referred to as a third light beam.

  Further, in the copier 1 of the present embodiment, as described above, the CPU 10 reads the image pattern for the evaluation chart stored in the memory unit 17 and controls the CPU 10 based on the image pattern data as shown in FIG. The electrostatic latent image shown is formed on the photosensitive drum 142 as follows. In the first scan, in the fourth period, the first light beam and the second light beam from the first light source 143 and the second light source 144, respectively, are not emitted for a predetermined time and are shorter than the one dot pulse emission time T1. The pulse emission time T2 is repeatedly emitted and discontinuously emitted six times, and is deflected and scanned by a deflecting unit including a prism 145, a cylinder lens 146, a polygon mirror 147, a scanning lens 148, a condensing lens 149, and a reflecting plate 150. As a result, the electrostatic latent images 21 of two micro dots formed simultaneously at the pitch P in the sub-scanning direction on the photosensitive drum 142 are discontinuously formed in the main scanning direction. Then, in the fifth period, the second light beam and the third light beam respectively from the second light source and the third light source are emitted for a predetermined time and have a predetermined pulse light emission time T2 shorter than the one dot pulse light emission time T1. The light is repeatedly emitted and discontinuously emitted six times, and is deflected and scanned by the deflecting means by the deflecting means including the prism 145, the cylinder lens 146, the polygon mirror 147, the scanning lens 148, the condensing lens 149, and the reflecting plate 150, Six electrostatic latent images 21 of two minute dots formed simultaneously at the pitch P in the sub scanning direction on the photosensitive drum 142 are formed discontinuously in the main scanning direction. Then, in the sixth period, the third light beam from the third light source repeats non-emission for a predetermined time and emission of a predetermined pulse emission time T2 shorter than the one-dot pulse emission time T1, thereby discontinuously 6 The light is emitted once and deflected and scanned by a deflecting unit including a prism 145, a cylinder lens 146, a polygon mirror 147, a scanning lens 148, a condensing lens 149, and a reflecting plate 150, so that it is minute in the main scanning direction on the photosensitive drum 142. Six electrostatic latent images 21 of dots are formed discontinuously.

  In the second scan, first, the photosensitive drum 142 is rotationally driven so as to be shifted by the pitch P in the sub-scanning direction. In the seventh period, the first light beam from the first light source repeats non-emission for a predetermined time and emission of a predetermined pulse emission time T2 shorter than the one-dot pulse emission time T1, and is discontinuous 6 The light is emitted once and deflected and scanned by a deflecting unit including a prism 145, a cylinder lens 146, a polygon mirror 147, a scanning lens 148, a condensing lens 149, and a reflecting plate 150, so that it is minute in the main scanning direction on the photosensitive drum 142. Six electrostatic latent images 21 of dots are formed discontinuously. Then, in the eighth period, the first light beam and the second light beam are emitted from the first light source 143 and the second light source 144, respectively, and the predetermined pulse emission time shorter than the one-dot pulse emission time T1. T2 is repeatedly emitted and discontinuously emitted six times, and is deflected and scanned by a deflecting unit including a prism 145, a cylinder lens 146, a polygon mirror 147, a scanning lens 148, a condensing lens 149, and a reflecting plate 150 to be photosensitive. The electrostatic latent images 21 of minute dots formed at the same time in the sub scanning direction on the body drum 142 at the pitch P are formed discontinuously in the main scanning direction.

  The predetermined pulse emission time T2 shorter than the 1 dot pulse emission time T1 is 1/2 to 1/3 of the 1 dot pulse emission time T1, and preferably 1/3 to 1/4. By setting the predetermined pulse emission time T2 to 1/2 to 1/3 of the one-dot pulse emission time T1, as shown in FIG. 9 described later, the first light beam, the second light beam, and the third light It is possible to output the evaluation image pattern 22 that can evaluate the deviation of the beam pitch P.

  Subsequently, as shown in FIG. 8, the composite potential of the overlapping region in the electrostatic latent image 21 of the minute dots adjacent on the photosensitive drum 142 in the sub-scanning direction is greatly different from the surrounding potential. Therefore, toner is attached to the overlapping area of the electrostatic latent image 21 of minute dots by a developing device (not shown) to form a toner image. Thereafter, the toner image is transferred to the sheet conveyed from the sheet feeding unit 16, and the fixing unit 15 fixes the toner image on the sheet. Then, the sheet on which the evaluation image pattern 22 shown in FIG. 9 is printed (ie, the evaluation chart) is discharged from the electrostatic latent image shown in FIG. In FIG. 9, for the sake of easy understanding, the electrostatic latent image 21 of minute dots indicated by broken lines is shown for convenience.

  As described above, when there is no deviation in the pitch P between the first light beam, the second light beam, and the third beam, the evaluation image pattern 22 on the evaluation chart has four evaluation images as shown in FIG. There is no density difference between the image patterns 22. In addition, when the pitch P between the first light beam, the second light beam, and the third beam is shifted, the evaluation image pattern 22 on the evaluation chart has a density difference between the four image patterns. Become. Therefore, by visually observing the evaluation chart and observing the difference in density between the evaluation image patterns 22, it is determined whether or not there is a deviation in the pitch P between the first light beam, the second light beam, and the third beam. can do. Further, if there is a density difference in the evaluation image pattern 22 on the evaluation chart, a minute change in the pitch P of the beam, such as several nm, can be grasped as a visual contrast difference.

  In the above embodiment, the output operation of the evaluation image pattern has been described by taking as an example the case where the multi-beam light scanning unit 141 of the copying machine 1 is provided with two or three light sources. The number of light sources provided in the light beam scanning unit 141 is not limited to two or three, but may be n (n ≧ 2) light sources, and the same effects as described above can be obtained. It is.

  In the above embodiment, the description has been given by taking the configuration in which the evaluation image pattern is printed on the paper as an example. However, the configuration of the present invention is not limited to this, and the evaluation image pattern is printed. Any recording material can be used.

  In the above embodiment, the copying machine has been described as an example. However, the configuration of the present invention is not limited to this, and can be widely applied to image forming apparatuses such as printers and facsimiles. It is.

  The configuration of the present invention can be variously modified within the scope of the present invention in addition to the above embodiment.

  The present invention can be widely applied to image forming apparatuses such as printers and facsimiles and evaluation charts in addition to copying machines, and is a technique useful for detecting pitch deviation between light beams.

FIG. 2 is a block diagram showing a main configuration of a copier according to the present invention. FIG. 2 is a schematic diagram showing a multi-beam optical scanning unit and a photosensitive drum provided in the image forming unit 14 of the copying machine 1. FIG. 4 is a diagram schematically illustrating image pattern data for output of an evaluation image pattern stored in a memory unit 17. FIG. 4 is a diagram showing an electrostatic latent image formed on the photosensitive drum 142 during the operation of outputting the evaluation image pattern of the copying machine 1. FIG. 5 is a diagram showing an evaluation image pattern output from the electrostatic latent image shown in FIG. 4 by the copying machine 1. FIG. 6 is a diagram showing an electrostatic latent image formed on the photosensitive drum 142 when there is a deviation in the pitch P between the first light beam and the second light beam. FIG. 7 is a diagram showing an evaluation image pattern output from the electrostatic latent image shown in FIG. 6 by the copying machine 1. These are diagrams showing an electrostatic latent image formed on a photosensitive drum in a copying machine having a first light source, a second light source, and a third light source in a multi-beam light scanning unit. These are figures which show the image pattern for an evaluation output from the electrostatic latent image shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Copy machine 10 Central processing unit 11 Document conveying part 12 Document taking-in part 13 Operation display part 14 Image forming part 141 Multi-beam optical scanning unit 142 Photosensitive drum 143 First light source 144 Second light source 145 Prism 146 Cylinder lens 147 Polygon Mirror 148 Scan lens 149 Condenser lens 150 Reflector 15 Fixing unit 16 Paper feed unit 17 Memory unit 171 Image pattern data 172 Dot data 173 First period data 174 Second period data 175 Third period data 21 Electrostatic latent of minute dots Image 22 Image pattern for evaluation T1 1 dot pulse emission time T2 Predetermined pulse emission time

Claims (2)

By simultaneously deflecting n light beams respectively emitted from n (n ≧ 2) light sources by the deflecting means and scanning the image carrier in the main scanning direction, in the sub-scanning direction of the image carrier. The n electrostatic latent images are separately formed at a predetermined pitch, the electrostatic latent image is formed in the main scanning direction, and the image carrier is further driven at the predetermined pitch in the sub scanning direction. In the method of creating an evaluation image pattern in which a two-dimensional electrostatic latent image is formed on an image carrier and image output is performed,
During the first scanning at the time of outputting the evaluation image pattern, two light beams adjacent from the first and second light beams to the (n−1) th and nth among the n light beams are obtained. A predetermined pitch emission time is shorter than a one-dot pulse emission time in the main scanning direction on the image carrier with a predetermined pitch shift in the sub-scanning direction, and is sequentially formed for each of a plurality of discontinuous predetermined dots. , An electrostatic latent image of first micro dots formed on a predetermined plurality of discontinuous dots with a predetermined pulse emission time shorter than the one dot pulse emission time in the main scanning direction of the nth light beam;
During the second scanning, which differs from the first scanning by a predetermined pitch in the sub-scanning direction, the first light beam is applied to the position corresponding to the nth plurality of dots in the first scanning from the one-dot pulse emission time. The predetermined plurality of dots are formed in a short predetermined pulse emission time, and then two adjacent light beams from the first and second light beams to the (n−1) th and nth in the main scanning direction are arranged in the sub-scanning direction. The electrostatic discharge of the second minute dots that are formed in order for each of a plurality of discontinuous predetermined dots with a predetermined pulse emission time shorter than the one-dot pulse emission time in the main scanning direction on the image carrier by shifting a predetermined pitch. Latent image,
A method for creating an image pattern for evaluation, comprising: outputting an image pattern for evaluation having

An evaluation chart, wherein the evaluation image pattern is output by the evaluation image pattern creating method according to claim 1.

Images