JP2006289790A - Method of determining optimum conjugate length of lens array, printing head, its manufacturing method, and apparatus of determining optimum conjugate length of lens array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing head which prevents streak irregularities in images resulting from variation of optical characteristics and is superior in printing image quality. <P>SOLUTION: A light beam ejected from a lens array 17 is imaged while the lens array 17 is moved along a direction of light axis. Along with this, an imaging point 32 when an X-direction beam diameter A1 or Y-direction beam diameter A2 obtained from a two-dimensional shape of the imaged light beam becomes a minimum value is obtained (step S290). A distance between the obtained imaging point 32 and a light emitting point is determined as an optimum conjugate length of the lens array 17 (step S300). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a print head used in an electrophotographic copying machine, a printer, and the like, a manufacturing method thereof, a method for determining an optimum conjugate length of a lens array provided in the print head, and an optimum lens array used for determining an optimum conjugate length of a lens array. The present invention relates to a conjugate length determination device.

  In general, an electrophotographic apparatus such as a copying machine or a printer includes an image forming apparatus, and a print head is known as an important part constituting the image forming apparatus. In recent years, there has been a demand for downsizing of the apparatus, and for this purpose, an LED print head using a light emitting diode (hereinafter abbreviated as LED) as a light emitter has attracted attention. The LED print head plays a role of forming an electrostatic latent image on the outer peripheral surface of the photosensitive body by irradiating the light of the LED onto a drum-shaped photosensitive body uniformly charged to perform image exposure. Then, toner is attached to the electrostatic latent image and developed, and the developed toner image is transferred and fixed on a recording medium such as paper to form a printed image.

  Such LED print heads usually form an LED array in which LEDs corresponding to the number of pixels of an image formed on a recording sheet are arranged in a row and the light emitted from each LED is imaged on the outer peripheral surface of the photoreceptor. And a lens array in which rod lenses are arranged (see, for example, Patent Document 1). FIG. 16 illustrates a conventional LED print head 51. The LED print head 51 includes a print head main body 52. A lens array 54 and an LED array 53 are fixed at different positions in the print head main body 52, respectively. A plurality of LEDs 55 are arranged in the LED array 53, and a plurality of rod lenses are arranged in the lens array 54.

  Incidentally, the light emitting point 57 of the LED array 53 and the image forming point 59 on the outer peripheral surface of the photosensitive member 56 are in a so-called conjugate relationship. In this case, the distance between the light emitting point 57 and the image forming point 59 is the conjugate length. (TC). Usually, after determining the optimum value of the conjugate length (TC) by a predetermined method, the lens array 54 and the photoconductor 56 are positioned based on the LED array 53 based on the value.

  Here, the conventional method for determining the optimum conjugate length is introduced. First, the center point 58 of the lens array 54 is arranged at a position separated by about TC / 2 with respect to the light emitting point 57. A light quantity measuring means using a photodiode or the like is arranged at a position separated by about TC with respect to the light emitting point 57. Next, in a state where the position of the center point 58 is maintained at a height that is ½ of the position of the imaging point 59, the light amount measuring means and the lens array 54 are moved along the optical axis direction (the direction of arrow F1 in FIG. 16). To move. At that time, the change of the light quantity with respect to the change of the TC value is measured by the light quantity measuring means, and an average value of MTF (Modulation Transfer Function) is obtained based on this measurement. The average value of MTF (hereinafter abbreviated as MTFave) is an average value obtained from measured values obtained at a plurality of points along the longitudinal direction of the lens array 54 (in the vicinity of a plurality of imaging points 59 shown in FIG. 17). Refers to that. FIG. 18 is a graph with the TC value (mm) on the horizontal axis and MTFave (%) on the vertical axis, and the upwardly convex curve is a curve showing the change in MTFave. If the TC value at the position where MTFave is maximum in this curve is MTF-TC, this MTF-TC value is determined as the optimum conjugate length.

Based on the MTF-TC value determined in this way, the lens array 54 and the photoconductor 56 are positioned as follows. That is, with the position of the light emitting point 57 of the LED array 53 as a reference, the center point 58 of the lens array 54 is fixed together at a position spaced apart by MTF-TC / 2 (mm). Further, with the position of the light emitting point 57 of the LED array 53 as a reference, the outer peripheral surface of the photoconductor 56 is fixed together at a position spaced apart by MTF-TC (mm). Conventionally, image forming apparatuses using the LED print head 51 have strict requirements for high image quality. For this reason, the positioning operation as described above needs to be performed severely.
JP-A-6-320790 (FIG. 1 and the like)

  By the way, it is desirable that the optical characteristics of the lens array 54 are always constant among the manufacturing lots. However, in practice, there is a possibility that the optical characteristics vary when compared between a plurality of manufacturing lots. Therefore, even if an attempt is made to assemble another production lot by applying the MTF-TC value determined based on a specific production lot, the lens array 54 and the photoconductor 56 may not be fixed at appropriate positions. For this reason, for example, the size of the beam diameter at the imaging point 59 varies for each manufacturing lot, and this causes unevenness in the electrostatic image on the photoconductor 56. Then, this unevenness appears as a streak unevenness of the image formed on the recording paper, and the print image quality is deteriorated.

  The present invention has been made in view of the above problems, and an object thereof is to provide a print head that is less likely to cause image streak unevenness due to variations in optical characteristics and has excellent print image quality, and a method for manufacturing the same. It is in. Another object of the present invention is to provide a method for determining the optimum conjugate length of a lens array and a lens array optimum conjugate length determining apparatus suitable for manufacturing such an excellent print head.

  In order to solve the above-mentioned problem, a first invention is a method for determining an optimum conjugate length of a lens array formed by arranging a plurality of rod lenses, and a light beam is emitted from a light emitting point of a light emitter to one end of the lens array. The light beam emitted from the other end of the lens array is imaged while moving the lens array along the optical axis direction, and a predetermined geometry obtained from the two-dimensional shape of the imaged light beam. A method for determining an optimum conjugate length of a lens array, comprising: determining an imaging point of a light beam when a physical parameter is a minimum value, and determining a distance between the imaging point and the light emitting point as an optimum conjugate length. The gist.

  A second invention is a method of manufacturing a print head by fixing a lens array formed by arranging a plurality of rod lenses to a print head main body to which a light emitter is fixed. The center point in the optical axis direction of the lens array is aligned with a position separated from the light emitting point of the light emitter by a distance of ½ of the optimum conjugate length determined by the method, and in this state, the lens array is The gist of the method is a method of manufacturing a print head, which is fixed to the print head body.

  Furthermore, a third invention includes a print head body, a light emitter fixed to the print head body, and a lens array in which a plurality of rod lenses are arranged and fixed to the print head body. A center point in the optical axis direction of the lens array is arranged at a position separated from the light emitting point of the light emitter by a distance of 1/2 of the optimum conjugate length determined by the method of the first invention. The gist of the print head is as follows.

  In these inventions, the image point of the light beam when the predetermined geometric parameter obtained from the two-dimensional shape of the imaged light beam is the minimum value is obtained, and the distance between the calculated image point and the light emitting point is obtained. Is determined as the optimum conjugate length. For this reason, for example, even if there is a variation in optical characteristics for each production lot, the optimum conjugate length can be determined without being affected by it. Therefore, if the arrangement position of the lens array is determined based on the optimum conjugate length, it is possible to reduce the influence of variations in the optical characteristics of each production lot, and the lens array is placed at an ideal position compared to the conventional case. Arrangement becomes possible. If the lens array is positioned and fixed at the arrangement position, image streak unevenness is less likely to occur, and the print image quality can be improved.

  The lens array refers to a lens having a structure in which rod lenses (rod lenses) are arranged. As an example of a suitable lens array, there is a SELFOC lens array having a structure in which optical fibers having a parabolic refractive index distribution from the center to the periphery are used as a rod lens. Selfoc lens array (hereinafter abbreviated as “SLA”) is a registered trademark of Nippon Sheet Glass Co., Ltd.

  The “predetermined geometric parameters obtained from the two-dimensional shape of the imaged light beam” are 1) the beam diameter of the imaged light beam, 2) the beam cross-sectional area of the imaged light beam, and 3) the image formed. For example, the outer peripheral length of the light beam. That is, when these geometric parameters take the minimum value, the imaged light beam is usually in the most focused state. Among these geometrical parameters, it is preferable to determine the optimum conjugate length using the beam diameter of the imaged light beam in 1). According to this, compared with the case where the optimal conjugate length is determined using other geometric parameters, the burden of calculation processing can be reduced.

  Here, when the beam diameter is adopted as the predetermined geometric parameter, the following may be performed. That is, the beam diameters in two directions orthogonal to each other in the two-dimensional shape of the formed light beam are defined as an X direction beam diameter and a Y direction beam diameter, respectively. Then, the rate of change when the position of the lens array is changed by the same distance is compared. The larger change rate at this time is adopted as the “beam diameter” used as a predetermined geometric parameter. According to this method, the minimum value of the beam diameter can be obtained more easily and accurately, and as a result, the optimum conjugate length can be obtained with higher accuracy. This surely contributes to the improvement of print image quality.

  When the beam cross-sectional area of the imaged light beam of 2) is adopted as a predetermined geometric parameter, for example, a virtual circle circumscribing or inscribed is approximated based on the shape of the imaged light beam, and the virtual cross section is approximated. The area of the circle may be obtained and defined as the beam cross-sectional area. In this case, however, it is allowed to approximate to another shape (for example, a rectangle) instead of a circle. Alternatively, the X-direction beam diameter and the Y-direction beam diameter may be obtained based on the shape of the imaged light beam, and a value obtained by integrating them may be defined as the beam cross-sectional area.

  When the beam outer peripheral length of the imaged ray of 3) is adopted as a predetermined geometric parameter, for example, a virtual circle that circumscribes or circumscribes it is approximated based on the shape of the imaged ray, and then You may obtain | require the outer periphery length of a virtual circle, and define it as a beam outer periphery length.

  When the position of the light emitting point of the light emitter is offset in the width direction from the longitudinal center line of the lens array, the optimum conjugate is calculated by adding a correction value calculated based on the offset amount. It is preferable to correct the length. In this way, the minimum value of the geometric parameter can be intentionally increased. Therefore, even if the position of the light emitting point is offset in the width direction, the change in the amount of light incident on the rod lens and the unevenness in the amount of light generated in the imaging light can be alleviated. it can.

  In order to solve the above-mentioned problems, a fourth invention is an apparatus for determining an optimum conjugate length of a lens array formed by arranging a plurality of rod lenses, and receives a light beam emitted from the lens array. A light receiving means for imaging, a light receiving means driving means for driving the light receiving means along an optical axis direction of the lens array, a lens array driving means for driving the lens array in synchronization with the light receiving means driving means, By calculating based on the output from the light receiving means, the image point of the light beam when the predetermined geometric parameter obtained from the two-dimensional shape of the light image formed by the light receiving means becomes the minimum value is obtained. The gist of the lens array optimum conjugate length determination apparatus is characterized by comprising a calculation means for determining the distance between the imaging point and the light emitting point as the optimum conjugate length.

  According to the present invention, the computing means obtains an imaging point when the predetermined geometric parameter obtained from the two-dimensional shape of the imaged light beam is the minimum value, and determines the obtained imaging point and light emitting point. Is determined as the optimum conjugate length. For this reason, for example, even if there is a variation in optical characteristics for each production lot, the optimum conjugate length can be determined without being affected by it. Therefore, if the arrangement position of the lens array is determined based on the optimum conjugate length, it is possible to reduce the influence of variations in the optical characteristics of each production lot, and the lens array is placed at an ideal position compared to the conventional case. Arrangement becomes possible. If the lens array is positioned at the arrangement position, it is difficult for image streak unevenness to occur, and the print image quality can be improved.

  As described above in detail, according to the invention described in claims 1 to 4, even if there is a variation in the optical characteristics causing the occurrence of image streak unevenness, a conjugate length that can reduce the influence of the lens array is provided. It can be determined as the optimal conjugate length of. According to the fifth aspect of the present invention, it is possible to provide a manufacturing method capable of obtaining a print head that is less likely to cause image streak unevenness due to variations in optical characteristics and has excellent print image quality. According to the sixth aspect of the present invention, it is possible to obtain a print head which is less likely to cause image streak unevenness due to variations in optical characteristics and has excellent print image quality. According to the seventh aspect of the present invention, even if there is a variation in the optical characteristics that causes streak unevenness in the image, the conjugate length that can reduce the influence is determined as the optimum conjugate length of the lens array. It is possible to provide a lens array optimum conjugate length determination device that can be used.

  Hereinafter, an embodiment embodying the present invention will be described in detail with reference to the drawings.

  As shown in FIGS. 1 and 2, the LED print head 11 (print head) irradiates light onto a uniformly charged photosensitive drum 21 having a substantially cylindrical shape, so that the outer peripheral surface of the photosensitive drum 21 is irradiated. This is a part for forming an electrostatic latent image. The print head main body 12 that constitutes the LED print head 11 is a member that is substantially L-shaped when viewed from the longitudinal direction of the print head main body 12, and is disposed in parallel to the rotation axis of the photosensitive drum 21. . The print head main body 12 includes a base portion 13 and a protruding portion 14 that protrudes from a part of the upper surface 19 of the base portion 13. In addition, an elongated rectangular LED substrate is fixed to the upper surface 19 of the base portion 13 with an adhesive or the like, and a plurality of LED arrays 15 (light emitter arrays) are mounted on the LED substrate. The LED array 15 is configured by arranging a plurality of LED elements 16 (light emitters) along the array longitudinal direction. Note that the longitudinal direction of the array is also referred to as “X direction” for convenience.

  As shown in FIG. 1, a lens array 17 is fixed to the side surface of the protruding portion 14 with an adhesive or the like. The lens array 17 has a function of forming incident light from the light emitting point 31 (see FIG. 3) of the LED element 16 on the outer peripheral surface of the photosensitive drum 21. The lens array 17 according to the present embodiment is a so-called SLA configured by arranging a plurality of rod lenses 18 in a zigzag pattern along the longitudinal direction of the array between a pair of side plates 20. The side plate 20 is a plate made of glass epoxy resin having a substantially rectangular shape, and the rod lens 18 is a rod-like member made of optical fiber having a circular cross section. Further, a gap between the side plates 20 and the rod lenses 18 is filled with silicone resin.

  Further, a pair of photosensitive member positioning pins 22 (photosensitive member positioning members) are implanted at positions near both ends of the LED substrate on the upper surface 19 in a state of protruding toward the photosensitive drum 21 side. The photoconductor positioning pin 22 is a member for positioning the LED print head 11 and the photoconductor drum 21 by bringing the outer peripheral surface of the photoconductor drum 21 into contact with the tip.

  Next, a lens array positioning and fixing device used for determining the optimum conjugate length of the lens array 17 will be described.

  As shown in FIG. 2, the lens array positioning and fixing device 1 includes a camera position adjusting device 9, a lens array driving device 10 (lens array driving means), and a control unit 24. The camera position adjusting device 9 includes a CCD (Charge Coupled Device) camera 2 as a light receiving means and a camera moving actuator 3 as a light receiving means driving means. The CCD camera 2 is a means for receiving a light beam emitted from the lens array 17, that is, a light beam from the LED element 16 to form an image and outputting image data. Each LED element 16 emits light by driving the light emission control circuit 41. In addition, you may comprise so that each LED element 16 may be made to light without depending on the drive of the light emission control circuit 41. FIG. The CCD camera 2 is attached to the camera moving actuator 3 in a downward state. The camera moving actuator 3 moves along the longitudinal direction of the lens array 17 (that is, the X direction, the thickness direction in FIG. 2) by driving the first driver 44. The camera moving actuator 3 moves along the optical axis direction of the lens array 17 (that is, the Z direction, the vertical direction in FIG. 2) by driving the second driver 45.

  The lens array driving apparatus 10 includes a base 6, a first slider 7, a second slider 8, and a lens array holder 5. The first slider 7 is supported by the base 6 and is moved in the horizontal direction by driving the first slider driving driver 42. The second slider 8 is supported by the first slider 7 and is moved in the vertical direction by the driving of the second slider driving driver 43.

  As shown in FIG. 2, the lens array holder 5 has a proximal end portion connected to the second slider 8 and a distal end portion disposed below the CCD camera 2. The lens array holder 5 is configured to hold or release the lens array 17 by driving a holder driving driver (not shown). The lens array 17 may be held and released by vacuum suction or the like. The lens array holder 5 is moved in a direction (horizontal direction in FIG. 2) in which the gripped lens array 17 is brought into contact with or separated from the side surface of the projecting portion 14 by driving the first slider driving driver 42. . The lens array holder 5 is moved along the optical axis direction of the lens array 17 by driving the second slider driving driver 43. Further, the lens array 17 held by the lens array holder 5 moves in synchronization with the camera moving actuator 3. For example, when the camera moving actuator 3 (and the CCD camera 2) moves a predetermined distance along the optical axis direction of the lens array 17 by driving the second driver 45, the lens array 17 is driven by the second slider driving driver 43. Is moved by a distance that is half the predetermined distance.

  As shown in FIG. 2, the control unit 24 controls the entire lens array positioning / fixing device 1. The control unit 24 includes a CPU 25, and a ROM 26, a RAM 27, and an input / output port (I / O port) 28 are connected to the CPU 25. The CPU 25 executes various processes for controlling the entire lens array positioning / fixing device 1 and outputs the processing results as a predetermined control signal. For example, the CPU 25 drives and controls the light emission control circuit 41 and the drivers 42, 43, 44, and 45. The ROM 26 stores a control program for controlling the lens array positioning / fixing device 1. The RAM 27 temporarily stores various types of information necessary for the operation of the lens array positioning / fixing device 1. Specific examples of such information include imaging data output from the CCD camera 2 by photographing a light beam emitted from the LED element 16. Further, the CCD camera 2, the light emission control circuit 41, and the drivers 42, 43, 44, 45 are electrically connected to the input / output port 28. Further, the imaging data output from the CCD camera 2 is input to the CPU 25 via the input / output port 28.

  Next, the relationship between the positional deviation between the lens array 17 and the LED array 15 and the unevenness in the amount of light generated in the imaging light will be described.

  4 to 6 are diagrams for explaining a problem when the position of the light emitting point 31 of the LED element 16 constituting the LED array 15 is offset in the width direction of the lens array 17. When the LED element 16 is caused to emit light, a light beam emitted from the light emitting point 31 of the LED element 16 enters the lens array 17. However, as shown in FIGS. 5 and 6, if the light emission position of each LED element 16 is shifted in the width direction (that is, the Y direction) from the longitudinal center line L <b> 1 of the lens array 17, the light enters the rod lens 18. The amount of light changes. As a result, the unevenness in the amount of light generated in the imaging light becomes large, and unevenness occurs in the electrostatic image at the location exposed corresponding to that portion. When printing is performed in this state, the unevenness appears as streak unevenness formed on the recording paper at a pitch approximately equal to the diameter of the rod lens 18, and the print image quality is deteriorated. The above problem does not occur if each light emitting point 31 is assembled so that the position of each light emitting point 31 is not shifted in the width direction of the lens array 17, but in reality, the position of the light emitting point 31 is offset due to variations in component accuracy and assembly accuracy. The print image quality deteriorates. This causes the yield of the LED print head 11 to decrease.

  Therefore, in the present embodiment, as shown in FIG. 6, the distance from the light emitting point 31 of the LED element 16 to the image forming point 32 on the photosensitive drum 21 is set to TCopt + ΔTC. Here, ΔTC indicates an arbitrary minute length (correction value). By this ΔTC, the X-direction beam diameter A1 and the Y-direction beam diameter A2 can be intentionally increased. Therefore, even if fluctuations in the width direction of the lens array 17 occur, streak unevenness can be reduced. . In this case, the center point 33 in the optical axis direction of the lens array 17 is arranged at a position separated from the light emitting point 31 by a distance of ½ of TCopt + ΔTC (see FIG. 3).

  Next, a method for manufacturing the LED print head 11 using the lens array positioning and fixing device 1 will be described based on the flowchart of FIG.

  First, the LED substrate on which the LED array 15 is mounted is fixed to the upper surface 19 of the base portion 13 of the print head body 12 using an adhesive or the like. Next, the print head body 12 to which the LED array 15 is fixed is placed and fixed in a predetermined area on the side of the base 6. And CPU25 performs a preparatory process in step S100 shown by FIG. Specifically, the CPU 25 drives the holder driving driver to cause the lens array holder 5 to hold the lens array 17. Then, the CPU 25 drives the first slider driving driver 42 and the second slider driving driver 43 to temporarily determine the position of the lens array 17. Specifically, the lens array 17 is brought into contact with the side surface of the projecting portion 14 and at a position separated from the light emitting point 31 of the LED element 16 by a distance ½ of the conjugate length in the optical axis direction of the lens array 17. A center point 33 is arranged. The conjugate length here is MTF-TC.

  Next, in step S110, the CPU 25 performs a process of determining the optimum conjugate length (TCopt) of the lens array 17 using the beam diameter as a predetermined geometric parameter. Specifically, the CPU 25 executes a subroutine shown in the flowchart of FIG. The subroutine of FIG. 8 includes the processes of steps S210 to S300. In step S210, the CPU 25 drives the light emission control circuit 41 to cause each LED element 16 on the print head body 12 to emit light. As a result, the light beam emitted from each LED element 16 enters one end of the lens array 17.

  Next, in step S220, the CPU 25 performs processing for measuring the X-direction beam diameter A1 (see FIG. 3) as follows. That is, the CPU 25 forms an image on the CCD camera 2 with light rays emitted from the other end of the lens array 17 while moving the CCD camera 2 and the lens array 17 along the optical axis direction (Z direction). At that time, the CPU 25 takes in the imaging data output from the CCD camera 2 and performs a predetermined image analysis process, thereby changing the X-direction beam diameter A1 with respect to changes in the positions of the CCD camera 2 and the lens array 17. Measure.

  Specifically, the CPU 25 changes the position of the CCD camera 2 and the lens array 17 in the Z direction a plurality of times, moves the CCD camera 2 along the longitudinal direction (X direction) of the lens array 17 at each position, etc. The average value is calculated based on the measured value of the X-direction beam diameter A1 at the measurement points provided at the interval. Here, FIG. 9 is a graph in which the horizontal axis is a TC value (mm) and the vertical axis is a beam diameter (μm), and a curve C1 indicating a change in the X-direction beam diameter A1 is drawn in the graph. Yes. This curve C1 is a downward convex curve, and the average value of the X-direction beam diameter A1 takes the minimum value at the convex portion.

  In step S230, the CPU 25 executes substantially the same process as in step S220, and calculates the average value of the Y-direction beam diameter A2. In the graph of FIG. 9, a curve C2 indicating a change in the Y-direction beam diameter A2 is drawn. This curve C2 is a downward convex curve, and the average value of the Y-direction beam diameter A2 takes the minimum value at the convex portion. Further, the CPU 25 calculates the change rate of the X-direction beam diameter A1 (change rate when the position of the lens array 17 is changed by the same distance) in step S240, and calculates the change rate of the Y-direction beam diameter A2 in step S250. To do.

  In step S260, the CPU 25 determines whether or not the rate of change of the X direction beam diameter A1 is larger than the rate of change of the Y direction beam diameter A2. When the rate of change of the X-direction beam diameter A1 is larger than the rate of change of the Y-direction beam diameter A2 (step S260: Y), the CPU 25 uses the minimum value of the X-direction beam diameter A1 to determine the optimum conjugate length TCopt. This is adopted as the beam diameter (step S270). On the other hand, when the rate of change of the X direction beam diameter A1 is smaller than the rate of change of the Y direction beam diameter A2 (step S260: N), the CPU 25 determines the optimum conjugate length TCopt with the minimum value of the Y direction beam diameter A2. This is adopted as the beam diameter for this (step S280).

  In step S290, the CPU 25 obtains the image point 32 of the light beam when the adopted beam diameter becomes the minimum value. Further, in step S300, the CPU 25 determines the calculated distance between the imaging point 32 and the light emitting point 31 as the optimal conjugate length (TCopt), and stores the determined optimal conjugate length in the RAM 27. Accordingly, the CPU 25 determines a position separated by a distance of ½ of TCopt as an arrangement position of the lens array 17 (see FIG. 3), stores data indicating the arrangement position in the RAM 27, and this subroutine. Exit.

  Here, when the subroutine shown in FIG. 8 ends, the CPU 25 proceeds to the process of step S120 shown in FIG. In step S120, the CPU 25 performs a process for measuring the offset amount L2 (see FIGS. 5 and 6). Here, a method of measuring the offset amount L2 by the CPU 25 is exemplified below. That is, the CPU 25 drives the first slider driving driver 42 to separate the lens array 17 from the side surface of the projecting portion 14 and retract from the lower side of the CCD camera 2. Then, based on the imaging data output from the CCD camera 2, the CPU 25 uses the position of the longitudinal center line L1 (see FIGS. 4 and 5) of the lens array 17 in the fixed state as a reference to offset the predetermined light emitting point 31. The quantity L2 is measured. Note that the offset amount L2 may be measured by other methods. If the offset amount L2 is known in advance, this step S120 may be omitted.

  Next, in step S130, the CPU 25 calculates a correction value (ΔTC) based on the measured offset amount L2. If the measured offset amount L2 is 0, the calculated correction value is 0. In step S140, the CPU 25 corrects the optimum conjugate length by adding the correction value (ΔTC) to the optimum conjugate length (TCopt), and the process proceeds to step S150.

  In step S150, the CPU 25 drives the second slider driving driver 43 to move the lens array 17 up and down to thereby reduce the distance ½ of the corrected optimum conjugate length ((TCopt + ΔTC) / 2). Only the center point 33 in the optical axis direction of the lens array 17 is aligned with the position away from the light emitting point 31 of the LED element 16. In this state, the lens array 17 is fixed to the side surface of the protruding portion 14. Specifically, an ultraviolet curable adhesive is applied between the side wall of the lens array 17 and the side surface of the protrusion 14. Then, the applied ultraviolet curable adhesive is irradiated with ultraviolet rays for a predetermined time to cure the ultraviolet curable adhesive. Then, after the ultraviolet curable adhesive is cured, the holding of the lens array 17 by the lens array holder 5 is released. As a result, the lens array 17 is positioned and fixed, and the LED print head 11 shown in FIG. 1 is completed.

  Therefore, according to the present embodiment, the following effects can be obtained.

  (1) In the method for determining the optimum conjugate length of the lens array 17 in this embodiment, the result when the X-direction beam diameter A1 or the Y-direction beam diameter A2 becomes the minimum value (beam diameter min shown in FIGS. 11 to 13). An image point 32 is obtained. The distance between the imaging point 32 and the light emitting point 31 at that time is determined as the optimum conjugate length (TCopt: described as “beam diameter TC” in FIGS. 9 to 13 and 15). On the other hand, in the comparative example (conventional example), the conjugate length when the MTF becomes the maximum value (MTFmax shown in FIGS. 11 to 13) is determined as the optimum conjugate length (MTF-TC shown in FIG. 10). Yes. The magnitude relationship between the beam diameter TC and the MTF-TC varies depending on the lens array 17, but varies greatly depending on the manufacturing lot of the lens array 17 (for example, lots A, B, and C). For example, the graph of FIG. 11 shows the MTF change curve and the beam diameter change curve in the lot A where the beam diameter TC <MTF−TC. The graph of FIG. 12 shows the MTF change curve and the beam diameter change curve in the lot B where the beam diameter TC≈MTF−TC. The graph of FIG. 13 shows the MTF change curve and the beam diameter change curve in the lot C in which the beam diameter TC> MTF−TC.

  Therefore, if the optimum conjugate length is determined using MTF-TC and the LED print head 11 is assembled, the beam diameter varies depending on the production lot, and the optimum conjugate length cannot be determined with high accuracy. On the other hand, as in this embodiment, when the optimum conjugate length is determined using the beam diameter TC and the LED print head 11 is assembled, the beam diameter is stabilized regardless of the production lot. Therefore, the optimum conjugate length can be determined with high accuracy. Therefore, if the arrangement position of the lens array 17 is determined on the basis of the optimum conjugate length, it is possible to reduce the influence of the variation in optical characteristics for each production lot, and the lens array is positioned at an ideal position compared to the conventional case. 17 can be disposed. If the lens array 17 is positioned and fixed at the arrangement position, image streak unevenness due to variations in the optical characteristics of each production lot is less likely to occur, and the print image quality can be improved.

  Note that the value of MTFmax when the beam diameter TC is used is lowered in the case other than the lot B. However, the standard MTFmax value is 60-70%. In comparison with this, the amount of decrease in MTFmax when a product other than lot B is selected is at most several points. Even if the value of MTFmax is reduced to this extent, there is no practical problem in resolution.

  (2) Let us consider a case where the LED print head 11 is assembled by correcting the optimum conjugate length by adding ΔTC to the MTF-TC value in the comparative example shown in FIG. For example, in the lot A where the beam diameter TC <MTF-TC, the beam diameter min becomes too large and the print image quality is greatly deteriorated (see FIG. 14). On the other hand, in the present embodiment, ΔTC is added to the beam diameter TC (see FIG. 10) to correct the optimum conjugate length, and the LED print head 11 is assembled. In this case, even in the lens array 17 of lot A, the beam diameter min does not increase so much (see FIG. 15), so that stable print image quality can be obtained.

  In addition, you may change embodiment of this invention as follows.

  In the above embodiment, of the X-direction beam diameter A1 and the Y-direction beam diameter A2, the beam diameter having the larger change rate when the position of the lens array 17 is changed by the same distance is set to the optimum conjugate length (TCopt). It was adopted as a geometric parameter to determine. Instead, one of the X direction beam diameter A1 and the Y direction beam diameter A2 may be adopted as a geometric parameter. Further, an average value of the X-direction beam diameter A1 and the Y-direction beam diameter A2 may be adopted as a geometric parameter.

  In the above embodiment, the minimum values of geometric parameters such as the X-direction beam diameter A1 and the Y-direction beam diameter A2 may be obtained by the following method, for example. First, three or more measurement points are selected from measurement points arranged at equal intervals along the longitudinal center line L1 of the lens array 17 (see FIGS. 4 and 5). Next, the values of the geometric parameters at the selected measurement points are obtained, and a predetermined curve equation is derived from the obtained values by, for example, the least square method. Then, the minimum value of the derived expression is adopted as the “minimum value of the geometric parameter”.

  In the process for determining the optimum conjugate length of the lens array 17 (see FIG. 8), the measurement of the Y direction beam diameter A2 (step S230) may be performed before the measurement of the X direction beam diameter A1 (step S220). Good. Similarly, the calculation of the change rate of the Y-direction beam diameter A2 (step S250) may be performed prior to the calculation of the change rate of the X-direction beam diameter A1 (step S240). Alternatively, after measuring the X-direction beam diameter A1 and calculating the rate of change (steps S220 and S240), the Y-direction beam diameter A2 may be measured to calculate the rate of change (steps S230 and S250). After measuring the direction beam diameter A2 and calculating the rate of change, the rate of change may be calculated by measuring the X direction beam diameter A1.

  In step S260 (see FIG. 8) of the above embodiment, it is determined whether or not the rate of change of the X-direction beam diameter A1 is larger than the rate of change of the Y-direction beam diameter A2. It may be determined whether or not the rate of change is larger than the rate of change of the X-direction beam diameter A1. In this way, when the determination in step S260 is “YES”, the minimum value of the Y-direction beam diameter A2 is adopted as the beam diameter for determining the optimum conjugate length (step S280), and the determination in step S260 is performed. Is “NO”, the minimum value of the X-direction beam diameter A1 is adopted as the beam diameter for determining the optimum conjugate length (step S270).

  Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the embodiment described above are listed below.

  (1) An apparatus for determining an optimum conjugate length of a lens array in which a plurality of rod lenses are arranged, which receives light rays emitted from the lens array, forms an image, and outputs image formation data A light receiving means driving means for driving the light receiving means along the optical axis direction of the lens array; a lens array driving means for driving the lens array in synchronization with the light receiving means driving means; The beam diameters in two directions orthogonal to each other in the two-dimensional shape of the light beam imaged by the light receiving means are defined as an X-direction beam diameter and a Y-direction beam diameter, respectively. When the position of the array is changed by the same distance, the image forming point of the light beam when the beam diameter having the larger rate of change becomes the minimum value is obtained, and the distance between the image forming point and the light emitting point is Lens array optimal conjugation length determination apparatus characterized by comprising a calculating means for determining a suitable conjugation length.

The schematic perspective view which shows the LED print head in one Embodiment which actualized this invention. Schematic which shows a lens array positioning fixing device. The figure for demonstrating the determination method of the optimal conjugate length of a lens array. The figure for demonstrating the light quantity nonuniformity in the lens array of a comparative example. The figure for demonstrating the correction method of optimal conjugate length. The figure for demonstrating the correction method of optimal conjugate length. The flowchart which shows the process which manufactures an LED print head. The flowchart which shows the optimal conjugate length determination process of a lens array. The graph which shows the relationship between conjugate length and beam diameter. Schematic which shows the relationship between beam diameter TC and MTF-TC. The graph which shows the relationship between conjugate length and a beam diameter, and the relationship between conjugate length and MTF. The graph which shows the relationship between conjugate length and a beam diameter, and the relationship between conjugate length and MTF. The graph which shows the relationship between conjugate length and a beam diameter, and the relationship between conjugate length and MTF. The graph for demonstrating the relationship between MTF-TC + (DELTA) TC and a beam diameter. The graph for demonstrating the relationship between beam diameter TC + (DELTA) TC and a beam diameter. Schematic which shows the LED print head in a prior art. The figure for demonstrating the measuring method of MTF. The graph which shows the relationship between conjugate length and MTFave.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Camera moving actuator 8 as a light-receiving means drive means ... CCD camera 10 as a light-receiving means ... Lens array drive device 11 as a lens array drive means ... LED print head 12 as a print head ... Print head main body 16 ... Light emitter LED element 17 as lens array 18 rod lens 25 CPU as arithmetic means
31 ... Light emitting point 32 ... Imaging point 33 ... Center point A1 ... X-direction beam diameter A2 ... Y-direction beam diameter L1 ... Longitudinal center line L2 ... Offset amount TCopt ... Optimum conjugate length ΔTC ... Correction value

Claims (7)

A method for determining an optimum conjugate length of a lens array formed by arranging a plurality of rod lenses,
A light beam is incident on one end of the lens array from a light emitting point of the light emitter,
While moving the lens array along the optical axis direction, while imaging the light beam emitted from the other end of the lens array,
Find the image point of the ray when the predetermined geometric parameter obtained from the two-dimensional shape of the imaged ray is the minimum value,
A method for determining an optimum conjugate length of a lens array, wherein a distance between the imaging point and the light emitting point is decided as an optimum conjugate length.   2. The method for determining the optimum conjugate length of a lens array according to claim 1, wherein the predetermined geometric parameter is a beam diameter of an imaged ray.   The beam diameter in two directions orthogonal to each other in the two-dimensional shape of the formed light beam is defined as the X direction beam diameter and the Y direction beam diameter, respectively, and the rate of change when the lens array position is changed by the same distance is larger. The method according to claim 1, wherein the beam diameter of the lens array is adopted as the predetermined geometric parameter.   When the position of the light emitting point of the light emitter is offset in the width direction from the longitudinal center line of the lens array, the optimum conjugate length is obtained by adding a correction value calculated based on the offset amount. 4. The method for determining the optimum conjugate length of a lens array according to claim 1, wherein correction is performed. A method of manufacturing a print head by fixing a lens array formed by arranging a plurality of rod lenses to a print head body to which a light emitter is fixed,
5. A central point in the optical axis direction of the lens array at a position separated from the light emitting point of the light emitter by a distance of ½ of the optimum conjugate length determined by the method according to claim 1. And the lens array is fixed to the print head body in this state. The printhead body,
A light emitter fixed to the print head body;
5. A lens array comprising a plurality of rod lenses arranged and fixed to the print head body, and having a half of the optimum conjugate length determined by the method according to claim 1. A print head, wherein a center point in the optical axis direction of the lens array is disposed at a position separated from the light emitting point of the light emitter by a distance. An apparatus for determining an optimum conjugate length of a lens array formed by arranging a plurality of rod lenses,
A light receiving means for receiving and forming a light beam emitted from the lens array;
A light receiving means driving means for driving the light receiving means along the optical axis direction of the lens array;
Lens array driving means for driving the lens array in synchronization with the light receiving means driving means;
An image forming point of a light beam when a predetermined geometric parameter obtained from a two-dimensional shape of the light beam imaged by the light receiving device is a minimum value by performing an operation based on an output from the light receiving device. And a calculation means for determining the distance between the image forming point and the light emitting point as the optimum conjugate length.

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