JP2008151847A - Scanning optical system and measurement apparatus for optical deflector using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a measurement apparatus capable of simultaneously detecting the wobbling and eccentricity of the deflection surface of a rotating polygon mirror. <P>SOLUTION: The scanning optical system has: a light source means; an incident optical system which guides a luminous flux from the light source means to an optical deflector; the optical deflector which is provided with the rotating polygon mirror having a plurality of deflection surfaces which deflect the guided luminous flux; and an imaging optical system which images the deflected luminous flux onto a surface to be scanned. In the scanning optical system, an incident optical system is arranged at a limited angle with respect to a reference surface perpendicular to the rotation axis of the rotating polygon mirror in a subscanning cross section, and the optical deflector is so arranged that the deflection surface, on which the variation in the radiated position of the luminous flux generated on the surface to be scanned due to the eccentricity which is caused by the differences among the distances of the respective deflection surfaces of the rotating polygon mirror from the rotation center becomes maximum, and the deflection surface, on which the variation in the radiated position of the luminous flux generated on thesurface to be scanned due to the wobbling which is caused by the differences among the angles of the respective deflection surfaces of the rotating polygon mirror with respect to the rotation center becomes maximum, are different from each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a scanning optical system and an optical deflector measuring apparatus using the scanning optical system. In particular, it is most suitable for surface tilt measurement and surface eccentricity measurement of an optical deflector used in a scanning optical device that performs optical writing using a laser beam in an electrophotographic apparatus such as an LBP, a digital copying machine, or a digital FAX.

  2. Description of the Related Art Conventionally, in a scanning optical device such as a laser beam printer, a light beam modulated and emitted from a light source unit according to an image signal is periodically deflected by, for example, a polygon mirror (light deflector). An image forming optical system (fθ lens system) having fθ characteristics converges in a spot shape on the surface of a photosensitive recording medium (photosensitive drum), and optical recording is performed on the recording medium surface to perform image recording.

  FIG. 12 is a schematic view of the main part of a conventional scanning optical apparatus. In the figure, the divergent light beam emitted from the light source means 91 is converted into a parallel light beam by the collimator lens 92. Then, the light beam (light quantity) is shaped by the aperture stop 93 and is incident on the cylindrical lens 94 having refractive power only in the sub-scanning direction. Of the light beam incident on the cylindrical lens 94, the light exits as it is in the main scanning section, converges in the sub-scanning section and converges in the sub-scanning section, and the deflection surface of the polygon mirror (rotating polygon mirror) 95 of the drive motor (motor) unit 81. An image is formed as a line image at 95a.

  The light beam reflected and deflected by the deflecting surface 95a of the polygon mirror 95 is guided onto a photosensitive drum surface 97 as a surface to be scanned through an imaging optical system (fθ lens system) 96 having fθ characteristics. Then, by rotating the polygon mirror 95 in the arrow A direction, the photosensitive drum surface 97 is optically scanned in the arrow B direction (main scanning direction) to record image information.

  FIG. 13 is a cross-sectional view of a principal part showing a motor unit for rotating a polygon mirror in the conventional scanning optical apparatus shown in FIG. In the figure, the same elements as those shown in FIG.

  In the figure, a polygon mirror 95 is disposed on a polygon mirror seating surface 82 and is attached to a motor shaft 83 by a fixing means such as a C ring through elastic means such as a wave washer. A small amount of fitting backlash is provided between the mounting hole 84 of the polygon mirror 95 and the motor shaft 83 so that no galling occurs at the time of mounting. A difference in distance from the center of rotation to the deflection surface (hereinafter referred to as “surface eccentricity”) occurs. Further, the distance from the center of the mounting hole 84 to the deflection surface 95 usually varies by 5 to 30 μm depending on the processing accuracy, and this is also surface eccentricity.

  In an oblique incidence optical system in which a light beam is incident at a specific angle with respect to a deflection scanning surface (in a main scanning section) on which a light beam is scanned by a polygon mirror 95, pitch unevenness may occur on the scanned surface 97 due to this surface decentering. Known (see Patent Documents 1 and 2).

  On the other hand, the perpendicularity between each deflection surface 95a of the polygon mirror 95 and the polygon mirror seating surface 82 is different for each surface with machining accuracy, or the perpendicularity machining accuracy between the motor shaft 83 and the polygon mirror seating surface 82 is insufficient. There is a case where For example, there is a case where foreign matter such as dust is sandwiched between the polygon mirror 95 and the polygon mirror seating surface 82 and assembled. In this case, an angle between the deflection surfaces of the polygon mirror 95 with respect to the rotation center of the polygon mirror 95, that is, a relative difference in bow between the deflection surfaces (hereinafter referred to as surface tilt) is generated.

  Surface tilt also causes uneven pitch on the scanned surface. This problem has been pointed out in many documents. In general, it is possible to reduce pitch unevenness to some extent by using a surface tilt correction optical system in which a polygon mirror surface (deflection surface) and a surface to be scanned are optically conjugate in the sub-scan section.

  Note that the pitch unevenness is a fluctuation amount of the height of the irradiation position of the light beam on the surface to be scanned when the optical deflector rotates once.

  In recent color image forming apparatuses, since various types of screen angles and lines are used for halftone expression, it is a problem that moire due to pitch unevenness occurs in a specific pattern. Reduction is required.

  For this reason, the surface eccentricity accuracy and surface tilt accuracy required for the polygon mirror are becoming stricter year by year.

  In order to meet this demand, there is a method of arranging a position detection sensor around the rotary polygon mirror. Among these, in a state where the rotary polygon mirror is stationary using the grip adjustment means, the relative distances to the rotation center axes of the plurality of mirror surface portions (deflection surfaces) of the rotary polygon mirror using the surrounding position detection sensor are substantially equal. It is known to position and adjust (so as to eliminate so-called eccentricity). (See Patent Document 3).

  Patent Document 3 describes that the position detection sensor may be provided at only one position by rotating the grip adjustment means.

Furthermore, it is known to adjust the surface tilt of the polygon mirror so that the distance from each deflection surface to the center of rotation is equal on the adjustment tool, or to adjust the surface tilt so that the surface tilt angles of each deflection surface are equal. (See Patent Document 4).
Japanese Patent Laid-Open No. 10-327302 JP 2001-51226 A JP 11-119140 A JP 2004-102006 A

  In Patent Document 3, assuming that the polygon mirror is stationary, the same number of position detection sensors as the deflection surface are arranged. Therefore, it is necessary to increase or decrease the number of position detection sensors according to the number of surfaces of the polygon mirror. Therefore, when measuring polygon mirrors with different specifications, it is necessary to review the number and arrangement of sensors.

  In each of Patent Documents 3 and 4, the surface eccentricity adjustment that makes the surface eccentricity between the deflection surfaces equal (that is, the relative difference approaches zero) and the surface tilt amount between the deflection surfaces become equal (that is, the relative difference). The tilting adjustment is performed individually.

  To adjust the surface eccentricity between the deflection surfaces to be equal, the polygon mirror may be shifted by two axes with respect to the rotation axis in a plane perpendicular to the rotation axis. To adjust the amount of surface tilt between the deflection surfaces to be equal, the polygon mirror may be tilted biaxially with respect to the rotation axis. Since both are two-axis adjustments, adjustments such that the amount of surface tilt and the amount of surface eccentricity are equal between the deflection surfaces are possible only when the number of polygon mirrors is four or less. In the case of more than 4 surfaces, for example, 6 or 8 or more polygon mirrors, in principle, it is difficult to make adjustments so that the amount of surface tilt and the amount of surface eccentricity are equal between the deflection surfaces. Therefore, for example, in a polygon mirror having six surfaces or more than eight surfaces, the amount of surface tilt or the amount of surface eccentricity remains even with the adjustment method of the conventional example. Due to the remaining surface tilt and surface eccentricity, pitch unevenness also remains when incorporated in the scanning optical device.

  In addition to Patent Document 3, there are a laser length measuring device and a three-dimensional measuring device as a method for measuring surface eccentricity. As a method of measuring surface tilt, a method of observing the deflection surface with an autocollimator while rotating the polygon mirror, a method of measuring the deflection of the reflected light beam by rotating the polygon mirror while causing the collimated light beam to enter the polygon deflection surface, etc. There is.

  However, each method measures surface eccentricity and surface tilt individually. As a result, it is necessary to individually distribute tolerances for the pitch unevenness of the surface tilt factor and the pitch unevenness of the surface eccentricity factor, and it becomes necessary to more strictly set the allowable values for surface eccentricity and surface tilt as the pitch unevenness increases. Yes. As a result, there is a problem that the yield is lowered and the production efficiency is lowered.

  An object of the present invention is to provide a measuring apparatus capable of simultaneously detecting surface tilt and surface eccentricity of a deflecting surface of an optical deflector.

  Another object of the present invention is to provide a scanning optical system in which an optical deflector is appropriately adjusted and arranged in the scanning optical system to perform high-precision optical scanning.

The scanning optical system of the present invention is
A light source means, an optical deflector having a rotating polygon mirror that deflects and scans the light beam emitted from the light source means, an incident optical system that guides the light beam emitted from the light source means to the rotating polygon mirror,
A scanning optical system comprising: an imaging optical system that forms an image of a light beam deflected and scanned by a deflection surface of the rotary polygon mirror on a surface to be scanned;
The light beam incident on the deflecting surface of the rotary polygon mirror is incident at a finite angle with respect to a plane perpendicular to the rotation center of the rotary polygon mirror in the sub-scan section.
The optical deflector has a deflection surface that maximizes the amount of fluctuation in the irradiation position of the light beam generated on the scanned surface due to surface eccentricity that is a difference in distance from each deflection surface of the rotary polygon mirror to the rotation center,
The rotating polygon mirror is arranged so as to be different from the deflection surface where the variation amount of the irradiation position of the light beam generated on the surface to be scanned is maximized due to the surface tilt which is a difference in angle with respect to the rotation center of each deflection surface. It is a feature.

The measuring device of the present invention comprises:
A surface decentering amount that is a difference in distance between each deflecting surface and the rotation center of the optical deflector of the optical deflector including the rotating polygon mirror having a plurality of deflecting surfaces, and a rotation center of each deflecting surface of the rotating polygon mirror A measuring device for measuring the amount of surface tilt that is the difference in angle with respect to
An incident optical system for guiding a light beam to the deflection surface of the rotary polygon mirror;
A detection optical system that forms an image of the light beam reflected by the deflecting surface on the imaging surface;
Detecting means for detecting information on the irradiation position of the light beam incident on the imaging surface of the detection optical system;
Comprising at least one measuring optical system for detecting, by the detecting means, the amount of fluctuation of the irradiation position on the imaging plane of the light beam sequentially reflected by each deflecting surface by rotating the rotary polygon mirror;
One of the measurement optical systems is configured such that the incident optical system is connected to the optical deflector within the sub-scan section formed by the rotation center of the optical deflector and the normal line of the deflection surface of the rotary polygon mirror. It is arranged at a finite angle with respect to a plane perpendicular to the center of rotation, and the light beam is incident on the deflecting surface of the rotary polygon mirror so as to form a line image parallel to the plane.
The detection optical system forms the line image on the imaging plane,
The position of the line image and the position of the deflection surface of the rotary polygon mirror are set so as not to coincide with each other.

The measurement method of the present invention includes:
A surface decentering amount that is a difference in distance between each deflecting surface and the rotation center of the optical deflector of the optical deflector including the rotating polygon mirror having a plurality of deflecting surfaces, and a rotation center of each deflecting surface of the rotating polygon mirror A method of measuring the amount of surface tilt that is the difference in angle with respect to
In a sub-scan section formed by the rotation center of the optical deflector and the normal line of the deflection surface of the rotary polygon mirror, the light beam has a finite angle with respect to a plane perpendicular to the rotation center of the optical deflector. An incident optical system that guides the light beam to the deflection surface of the rotary polygon mirror and forms the light beam as a line image at a position that does not coincide with the deflection surface of the rotary polygon mirror, and the line image reflected by the deflection surface. Using a measurement optical system having a detection optical system that forms an image on an image formation surface and a detection unit that detects an irradiation position of a light beam formed on the image formation surface,
By rotating the rotary polygon mirror, light beams from the incident optical system are sequentially irradiated to the respective deflection surfaces, reflected by the respective deflection surfaces, and the amount of variation in the irradiation position of the light beams formed on the imaging surface is detected. It is characterized in that the amount of surface eccentricity and the amount of surface tilt of each deflecting surface are obtained using the signal measured by the means and using the signal obtained by the detecting means at this time.

The adjustment method of the present invention includes:
In an optical deflector used in a scanning optical system that scans a surface to be scanned using a light deflector including a rotary polygon mirror having a plurality of deflection surfaces with a light beam from an incident optical system,
A surface decentering measurement optical system for measuring a surface decentering amount that is a difference in distance between each deflection surface of the rotary polygon mirror and the rotation center of the optical deflector;
A surface tilt measuring optical system for measuring a surface tilt amount that is a difference in angle with respect to the rotation center of each deflection surface of the rotary polygon mirror;
The surface eccentricity measurement optical system and the surface tilt measurement optical system simultaneously detect the surface eccentricity and surface tilt amount of any deflection surface, and the deflection surface with the largest surface eccentricity amount and the deflection surface with the largest surface tilt amount are different. And adjusting the optical deflector.

  ADVANTAGE OF THE INVENTION According to this invention, the measuring apparatus which can detect the surface fall and surface eccentricity of the deflection surface of an optical deflector simultaneously can be achieved.

  In addition, it is possible to achieve a scanning optical system in which an optical deflector is appropriately adjusted and arranged in the scanning optical system to perform high-precision optical scanning.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 14 is a sectional view (main scanning sectional view) of an essential part of Embodiment 1 of the scanning optical system according to the present invention.

  In the following description, the main scanning direction is a direction perpendicular to the rotation axis of the rotating polygon mirror and the optical axis of the imaging optical system (the direction in which the light beam is reflected and deflected (deflected and scanned) by the rotating polygon mirror). The sub-scanning direction is a direction parallel to the rotation axis of the rotary polygon mirror. The main scanning section is a plane including the main scanning direction and the optical axis of the imaging optical system. The sub-scanning section is a section perpendicular to the main scanning section.

  In FIG. 14, reference numeral 141 denotes a light source means, which is composed of, for example, a semiconductor laser. Reference numeral 142 denotes a condensing lens (collimator lens) as a condensing optical system, which converts a light beam emitted from the light source means 141 into a parallel light beam. Reference numeral 143 denotes an aperture stop which shapes the beam shape by limiting the passing light flux.

  A lens system (cylindrical lens) 144 has a specific power only in the sub-scan section (sub-scan direction). The cylindrical lens 144 forms the light beam that has passed through the condenser lens 142 as a line image on or near the deflection surface (deflection surface) 145a of a rotary polygon mirror (polygon mirror) 145, which will be described later, in the sub-scan section.

  Note that the condensing lens 142 and the cylindrical lens 144 may be configured by one optical element. Each element such as the condenser lens 142, the aperture stop 143, and the cylindrical lens 144 constitutes one element of the incident optical system (first imaging optical system) LA.

  Reference numeral 145 denotes a rotating polygon mirror as a deflecting means, which is composed of, for example, an eight-sided polygon mirror (rotating polygon mirror), and is rotated at a constant speed in the direction of arrow A in the figure by a driving means (not shown) such as a motor. ing.

  The rotary polygon mirror 145, the driving means, the holding means for rotating and holding the rotary polygon mirror 145, etc. constitute an element of the optical deflector.

  Reference numeral 146 denotes an imaging optical system (second imaging optical system) having a condensing function and an fθ characteristic, which is composed of a single imaging lens or a plurality of imaging lenses (anamorphic lenses) and is deflected by a rotating polygon mirror 145. A light beam based on image information is imaged on a photosensitive drum surface 148 as a surface to be scanned. In addition, the imaging lens 146 compensates for the surface tilt of the deflecting surface by making a conjugate relationship between the deflecting surface 145a of the rotary polygon mirror 145 or its vicinity and the photosensitive drum surface 148 in the sub-scan section.

  Reference numeral 148 denotes a photosensitive drum surface as a surface to be scanned.

  In this embodiment, the light beam emitted from the semiconductor laser 141 is converted into a parallel light beam by the condenser lens 142, the light beam (light quantity) is limited by the aperture stop 143, and is incident on the cylindrical lens 144. Out of the parallel light flux incident on the cylindrical lens 144, it is emitted as it is in the main scanning section. In the sub-scan section, a line image (a line image elongated in the main scanning direction) is formed on the deflection surface 145a of the rotary polygon mirror 145.

  The light beam reflected and deflected by the deflecting surface 145 a of the rotary polygon mirror 145 is imaged in a spot shape on the photosensitive drum surface 148 via the imaging lens 146. By rotating the rotary polygon mirror 145 in the direction of arrow A, optical scanning is performed on the photosensitive drum surface 148 in the direction of arrow B (main scanning direction) at a constant speed. As a result, an image is recorded on the photosensitive drum surface 148 as a recording medium.

  In the scanning optical system of the present embodiment, the first imaging optical system LA is disposed at a finite angle with respect to a reference plane perpendicular to the rotation center of the rotary polygon mirror 145 in the sub-scan section.

  A difference in distance from each deflection surface 145a of the rotary polygon mirror 145 and the rotation center is referred to as surface eccentricity. A difference in angle with respect to each deflection surface 145a of the rotary polygon mirror 145 and the rotation center is referred to as surface tilt.

  The optical deflector composed of the rotary polygon mirror 145 used at this time is determined as a non-defective product by a measuring apparatus described later.

  The optical deflector has the maximum fluctuation amount of the irradiation position of the light beam generated on the scanned surface 148 due to the surface decentering and the maximum fluctuation amount of the irradiation position of the light beam generated on the scanned surface 148 due to the surface tilt. It is arranged so that the deflection surface becomes different.

  In this embodiment, the rotation axis of the optical deflector and the rotary polygon mirror 145 have an adjustment mechanism (not shown) that can adjust the position relatively. At this time, the optical deflector has a deflection surface in which the deviation of the irradiation position of the light beam on the scanned surface caused by surface eccentricity is maximized and a deflection in which the deviation of the irradiation position of the light beam on the scanned surface caused by surface tilt is maximized. The surface is adjusted to be different.

  FIG. 1 is a schematic view of a measuring apparatus according to a second embodiment of the present invention, and shows surface eccentricity measurement and surface tilt measurement of a deflection surface of a rotary polygon mirror (polygon mirror) of an optical deflector.

  FIG. 1 shows a sub-scan sectional view of a measurement optical system used for surface eccentricity measurement and surface tilt measurement.

  The laser diffused light emitted from the semiconductor laser (light source means) 1 is collimated by a collimator lens (first optical element) 2, and a laser beam formed by a circular diaphragm 3 disposed thereafter is taken out. Thereafter, the light is condensed only in the sub-scanning direction of the polygon mirror (rotating polygonal mirror) by the cylindrical lens (first anamorphic optical element) 4 </ b> A and enters the deflection surface 52 of the polygon mirror 51. At this time, a line image is formed at a position where the deflection surface 52 of the polygon mirror 51 does not coincide. The light beam reflected by the deflecting surface 52 enters the second cylindrical lens (second anamorphic optical element) 4B while slightly diverging in the sub-scanning direction. Since the front focal point of the cylindrical lens 4B is arranged so as to coincide with the position of the line image (that is, the front focal point does not coincide with the deflection surface 52), the reflected light is returned to parallel light. Thereafter, since the parallel light is imaged at the rear focal position of the jig lens (second optical element) 6, the V slit 7 is arranged at this imaging position.

  In conjunction with the second anamorphic optical element 4B, the first anamorphic optical element 4A is provided so as to be movable in the optical axis direction.

  The beam that has passed through the V slit 7 is received by the photodiode 8 and the amount of light is monitored. The drive motor (motor) 54 has a rotation shaft 55 and is fitted in the fitting hole 53 of the polygon mirror 51. The optical deflector 5 is constituted by the motor 54 and the polygon mirror 51. A rotation center 56 of the rotation shaft 55 is used.

  The semiconductor laser 1 to the cylindrical lens 4A constitute an incident optical system, the cylindrical lens 4B and the jig lens 6 constitute a detection optical system, and the V slit 7 and the photodiode 8 constitute detection means. Detection means is provided at an image forming point of the detection optical system. A measurement optical system is constituted by the incident optical system, the detection optical system, and the detection means. The measuring device is constituted by holding means (not shown) for holding these measuring optical systems (measuring devices) and electric signal processing means (not shown) for processing electric signals from the detecting means.

  As shown in FIG. 1, a plane perpendicular to the rotation shaft 55 and perpendicular to the sub-scanning section (paper surface) is taken as a reference plane. The incident optical system (from the semiconductor laser 1 to the cylindrical lens 4A) is incident at a specific incident angle θi with respect to the reference surface. Further, the detection optical system (the cylindrical lens 4B and the jig lens 6) is also arranged at a specific reflection angle θo with respect to the reference surface. It is desirable to set θi and θo so that the absolute values are equal and the directions are different.

  In this embodiment, the amount of surface eccentricity, which is the difference in distance between each deflecting surface 52 of the optical deflector 5 having the rotating polygon mirror 51 having a plurality of deflecting surfaces and the rotation center 56 of the optical deflector 5, and the rotational polygon mirror 51. This is a measuring device that measures the amount of surface tilt that is the difference in angle with respect to the rotation center 56 of each deflection surface 52.

  The measuring apparatus according to this embodiment includes incident optical systems 1 to 4A that guide a light beam to the deflecting surface 52 of the rotary polygon mirror 51, and detection optical systems 4B and 6 that image the light beam reflected by the deflecting surface 52 on the imaging surface. And detection means 7 and 8 for detecting information on the irradiation position of the light beam incident on the imaging plane of the detection optical system.

  The rotating polygon mirror 51 is rotated to include one or more measuring optical systems configured to detect the amount of variation of the irradiation position on the imaging surface of the light beams sequentially reflected by the deflecting surfaces 52 by the detecting means.

  One of the measurement optical systems is a sub-scan section formed by the rotation center 56 of the optical deflector 5 and the normal line of the deflection surface 52 of the rotary polygon mirror 51, and the incident optical system is the optical deflector. 5 is arranged at a finite angle with respect to a reference plane (XY plane) perpendicular to the center of rotation 56.

  The light beam from the incident optical system is incident on the deflecting surface 52 of the rotary polygon mirror 55 so as to form a line image parallel to the reference surface.

  The detection optical system forms a line image on the imaging plane. The position of the line image and the position of the deflecting surface 52 of the rotary polygon mirror 51 are set to be inconsistent.

  A measuring method for obtaining the surface eccentricity and surface tilt amount of each deflecting surface 52 of the polygon mirror 51 of the optical deflector 5 using the measuring apparatus of the present embodiment is as follows.

  In the measurement method of the present embodiment, the surface eccentricity and the rotational polyhedron, which are the difference in distance from each deflecting surface 52 of the optical deflector 5 having the rotating polygon mirror 51 having a plurality of deflecting surfaces and the rotational center 56 of the optical deflector 5. A surface tilt amount that is a difference in angle with respect to the rotation center 56 of each deflection surface 52 of the mirror 51 is measured.

  In the incident optical system, the light beam is perpendicular to the rotation center 56 of the optical deflector 5 in the sub-scan section formed by the rotation center 56 of the optical deflector 5 and the normal line of the deflection surface 52 of the rotary polygon mirror 51. It is led to the deflection surface 52 of the rotary polygonal mirror 51 at a finite angle with respect to a simple reference surface. The incident optical system forms a light beam as a line image at a position where the light beam does not coincide with the deflection surface 52 of the rotary polygon mirror 51.

  The detection optical system forms an image of the line image reflected by the deflection surface 52 on the imaging surface. The detection means detects the irradiation position of the light beam formed on the imaging surface. A measurement optical system having such means is used.

  Then, by rotating the rotary polygon mirror 51, the light beams from the incident optical system are sequentially irradiated onto the respective deflection surfaces, and the variation amount of the irradiation position of the light beams reflected by the respective deflection surfaces 52 and imaged on the imaging surface is detected. It is measured by means. At this time, the amount of surface eccentricity and the amount of surface tilt of each deflecting surface 52 are obtained using signals obtained by the detecting means.

  Numerical examples in the present embodiment are shown in Table 1. The incident optical system (semiconductor laser 1 to cylindrical lens 4A) assumes an incident angle θi = −20 ° with respect to the reference plane. The detection optical system (cylindrical lens 4B and jig lens 6) also assumes a reflection angle θo = + 20 ° with respect to the reference surface. The surface spacing in the table is a dimension measured on the optical axis of the incident optical system and the detection optical system.

  DXc in the table indicates the amount of movement of the cylindrical lenses 4A and 4B.

  The distance between the polygon deflection surface 52 and the line image is dX. In the measuring apparatus according to the present embodiment, the movement amount dXc and the distance dX coincide with each other. This is because in the configuration shown in Table 1, the light beam incident on the cylindrical lens 4A is parallel light. Note that when the light beam incident on the cylindrical lens 4A is divergent light or convergent light, the movement amount dXc and the distance dX do not match.

  When dX = 0, the polygon deflection surface 52 and the V slit 7 are in an optically conjugate relationship by the detection optical system (the cylindrical lens 4B and the jig lens 6). In other words, the polygon deflecting surface 52 and the V slit 7 are arranged so as to satisfy a perfect surface tilt correction relationship by the detection optical system. At this time, the rear focal position of the cylindrical lens 4A coincides with the polygon deflection surface 52. Further, the front focal position of the cylindrical lens 4B and the polygon deflection surface 52 coincide with each other.

  In contrast, in this embodiment, dX ≠ 0, that is, the detection optical system is arranged so as not to satisfy the surface tilt correction relationship between the polygon deflection surface 52 and the V slit 7. The state of the optical path at that time is shown in FIGS. FIG. 2 shows the case of dX> 0, and FIG. 3 shows the case of dX <0.

  Since dX> 0 in FIG. 2, the light beam forms a line image behind the polygonal deflection surface 52 and forms an image once. The distance between the polygon deflection surface 52 and the line image is dX. Then, by matching the front focal point of the cylindrical lens 4B with the position of the line image, it can be seen that the light beam emitted from the cylindrical lens 4B becomes parallel light. Thereafter, since the parallel light is imaged at the rear focal position of the jig lens 6, the V slit 7 is disposed at this imaging position.

  Since dX <0 in FIG. 3, the light beam forms a line image in front of the polygon deflection surface 52 and forms an image once. The distance between the polygon deflection surface 52 and the line image is dX. Then, by matching the front focal point of the cylindrical lens 4B with the position of the line image, it can be seen that the light beam emitted from the cylindrical lens 4B becomes parallel light. Thereafter, since the parallel light is imaged at the rear focal position of the jig lens 6, the V slit 7 is arranged at this imaging position.

  In the measurement optical system as described above, when the polygon mirror 51 of the actual light deflector 5 is decentered and tilted, that is, how the posture information of each deflection surface of the rotary polygon mirror works. 4 and FIG.

  The optical deflector 5 performs measurement while rotating. It is desirable to measure the rotation speed at the rotation speed when the optical deflector is used in the scanning optical system. The light beam guided from the incident optical system to the optical deflector 5 by the rotation operation of the optical deflector 5 is deflected and scanned. Then, before and after the normal line of the deflection surface 52 comes into the sub-scan section (paper surface) of FIG. 1, the detection light beam scans on the V slit 7 in the direction perpendicular to the paper surface through the detection optical system.

FIG. 4 shows a case where the deflection surface 52 of the polygon mirror 51 is assembled with the rotational axis 55 of the optical deflector 5 being eccentric. When assembled with the surface being decentered, the surface enters and exits for each deflecting surface as the polygon mirror 51 rotates. In FIG. 4, for example, it is assumed that the deflection surface 52 ′ when the surface is decentered by p, θi = θ (arbitrary angle). The reflection point of the light beam originally reflected by the deflecting surface 52 is ΔZ = p × tan θ in the deflecting surface 52 ′.
Shift upwards only. As a result, the irradiation position on the V slit 7 has a fluctuation amount dZp of dZp = 2 × ΔZ × cos θ × β = 2 × P × sin θ × β (2)
It becomes. However,
P: Deflection plane surface eccentricity θ: Oblique incident angle with respect to the reference plane in the sub-scan section of the incident optical system (finite angle)
β is a lateral magnification in the sub-scan section of the detection optical system.

  Next, FIG. 5 shows a case where the deflecting surface 52 of the polygon mirror 51 is assembled with the rotation axis 55 of the optical deflector 5 tilted. If the surface is tilted and assembled, the bow (tilt) of the surface is generated for each deflection surface as the polygon mirror 51 rotates. In FIG. 5, for example, a deflection surface 52 'is obtained when the surface is decentered by ε. In this embodiment, since the detection optical system (the cylindrical lens 4B and the jig lens 6) is arranged so as not to satisfy the surface tilt correction relationship between the polygon deflection surface 52 and the V slit 7, an optical path as shown in FIG. 5 is taken.

The details of the optical path are as follows. By shifting the cylindrical lens 4B in the optical axis direction by dXc, the front focal position of the cylindrical lens 4B is shifted by dXc from the deflection surface 5. Therefore, the conjugate point (shown in FIG. 5) with respect to the deflection surface 52 across the detection optical system is a position shifted by dX × β ² from the V slit 7. At this time, when the deflecting surface 52 is tilted to become the deflecting surface 52 ′, the reflected light beam is incident on the cylindrical lens 4B at an angle of 2 × ε with respect to the optical axis, and is further conjugated after passing through the jig lens 6. Pass the point and reach the V-slit. The light beam emitted from the jig lens 6 has an angle of 2 × ε / β with respect to the optical axis. In such an optical path, the variation dZε of the arrival position on the V slit 7 is
dZε = (β ² × dX) × tan (2 × ε / β) Equation 3
Can be expressed.

  As described above, in the measuring apparatus of the present embodiment, when the optical deflector is tilted or decentered, the light beam scanned on the V slit 7 causes irradiation position fluctuations. The fluctuation amounts dZp and dZε are expressed by Equation 2 below. And Equation 3 can be used.

  The surface eccentricity P may be defined as PP of the relative distance from the rotation center of all the deflection surfaces, and the surface tilt amount ε is PP of the bowing amount (angle with respect to the rotation center) of all the deflection surfaces. It may be defined.

  In this embodiment, the V slit 7 and the photodiode 8 are used as means for measuring the irradiation position fluctuations dZp and dZε of the scanning light beam. The V slit 7 has a V-shaped aperture so that the width w in the direction in which the light beam scans changes with the irradiation position (height) h, and the time that the beam crosses the aperture depends on the irradiation position (height). Configured differently. By providing the photodiode 8 behind the V slit 7, the irradiation position (height) is associated with the time for receiving light. Such a V-slit method is a technique disclosed in many documents.

  In the present invention, a V-slit method is described. For example, a one-dimensional line CCD is arranged perpendicularly (within the paper surface of FIG. 1) to the scanning direction of the light beam, and irradiation is performed by detecting a CCD pixel crossed by the light beam. A known technique such as a method for measuring the position may be employed.

  In this embodiment, the relative position between the rotation center 56 of the optical deflector 5 and the rotary polygon mirror 51 is adjusted so that the fluctuation amount of the irradiation position of the light beam on the imaging surface by the detection optical system is not more than a specific value. An adjustment mechanism (not shown) is included.

  Next, a specific method for setting the distance dX will be described. The maximum pitch unevenness allowable in the design of the scanning optical system is determined from the print image of the image forming apparatus. Usually, the maximum pitch unevenness Bmax is about 5 μm. In recent years, the maximum pitch unevenness may be suppressed to about 2 μm for higher image quality. The surface tilt amount and surface eccentricity amount of the optical deflector are calculated for the required maximum pitch unevenness. First, assuming that there is no surface eccentricity, the surface unevenness (allowable surface inclination amount) εo is determined by accumulating the pitch unevenness tolerance caused by the surface inclination and totaling Bmax.

  Next, assuming that there is no surface tilt at all, the pitch unevenness tolerance caused by the surface eccentricity is accumulated, and the surface eccentricity (allowable surface eccentricity amount) Po is determined to be Bmax in total. Note that Po is also a relative fluctuation range between the deflection surfaces of the polygon mirror of εo.

  FIG. 6 shows an allowable area for surface eccentricity and surface tilt. The horizontal axis represents surface eccentricity, the vertical axis represents surface tilt, and a line connecting (Po, 0) and (0, εo) is drawn. Since Po and εo are determined as described above, the pitch unevenness becomes Bmax when the combination is (Po, 0) or (0, εo). In the combination inside the region connecting the two points, the pitch unevenness becomes smaller than Bmax.

  However, when measuring surface eccentricity and surface tilt with an individual measuring machine as in the prior art, it is necessary to allocate the Bmax to cause the surface tilt and cause the surface eccentricity to determine an allowable value. For example, if Bmax / 2 is allocated to Bmax / 2 due to surface tilt and the remaining Bmax / 2 is allocated due to surface eccentricity, the allowable value of surface deflection of the optical deflector is εo / 2, and the allowable surface eccentricity is Po / 2. It was. As a result, the combination of the shaded areas in FIG.

  On the other hand, in this embodiment, since the measurement of the surface eccentricity and the surface tilt can be performed simultaneously by using the measuring device of FIG. 1, all combinations of the hatched and halftone dot regions of FIG. Can do.

At that time, the distance dX is important. The method of setting the distance dX is such that the variation of the irradiation position with the measuring instrument in FIG. 1 shows almost the same value when the combination of surface eccentricity and surface tilt is both (Po, 0) and (0, εo). You only have to set it. In other words, in order for the light flux fluctuation dZ on the sensor to be substantially the same at Po and εo, the ratio of dZp and dZε in the above equations 2 and 3 is
0.8 ≦ | dZp / dZε | ≦ 1.2 Formula 4
It is necessary to become.

Here, the same is true when dZp / dZε = 1. Therefore,
0.8 ≦ (β ² × dX × tan (2 × εo / β)) / 2 × Po × sin θ × β) ≦ 1.2
From
0.8 ≦ | (dX / (2 × Po × sin θ / (β × tan (2 × εo / β)))) | ≦ 1.2
Is guided. If you need more sophisticated measurements
0.9 ≦ | (dX / (2 × Po × sin θ / (β × tan (2 × εo / β)))) | ≦ 1.1
Is desirable.

  Specifically, in an optical deflector that requires the specifications of Po = 0.033 mm and εo = 1.6 ′ (minutes), dX = ± 24.25 mm, and the tolerance is calculated as ± 0.49 mm. When this optical deflector is evaluated by the measurement optical system shown in Table 1, the cylindrical lenses 4A and 4B are moved by dXc = dX = ± 24.25 mm.

  By the way, dX always has two values, plus and minus. The reason is that, in the scanning optical device in which the optical deflector is assembled, even if the optical deflector having the same surface tilt amount is used, the variation direction of the irradiation position may be reversed due to other component accuracy variations.

  For example, if the focal length in the sub-scanning direction of the fθ lens of the scanning optical device is shorter than the design value, the irradiation position varies downward when the deflection surface of the polygon mirror faces upward. Conversely, if the focal length in the sub-scanning direction of the Fθ lens of the scanning optical device is longer than the design value, the irradiation position changes upward when the deflection surface of the polygon mirror is directed upward. The inspection method assuming the former is dX> 0, and the inspection method assuming the latter is dX <0. Regarding the surface eccentricity, the direction of the irradiation position variation dZ is the same whether dX> 0 or dX <0.

  Specifically, in the configuration of the measurement optical system shown in Table 1, when dXc = + 24.25 mm, the direction of the surface eccentricity P in FIG. 4 is negative, and the irradiation position is dZ = − with respect to P = −0.033 mm. It swings 45.23 μm (dZp direction in FIG. 4). Further, assuming that the direction of surface tilt in FIG. 5 is positive, the irradiation position deviates by dZ = −45.23 μm (direction dZε in FIG. 5) with respect to the deflection surface of ε = + 1.6 ′.

  On the other hand, when dXc = -24.25 is set, the irradiation position fluctuates by dZ = −45.23 μm with respect to P = −0.033 mm. Further, the irradiation position deviates by dZ = + 45.23 μm with respect to the deflection surface of ε = + 1.6 ′.

In the optical system shown in Table 1, P ₀ = 0.033 mm and pitch unevenness is 5 μm, and ε ₀ = 1.6 ′ and pitch unevenness is 5 μm.

  For the above reasons, in this embodiment, in order to measure the optical deflector 5, the cylindrical lenses 4A and 4B are moved and arranged by the movement amount dXc corresponding to the two patterns of dX> 0 and dX <0. In order to change the arrangement smoothly, a stage may be provided so that the cylindrical lenses 4A and 4B can be moved in the optical axis direction in conjunction with each other.

  In addition, the relative position of the rotation center of the optical deflector and the rotary polygon mirror is adjusted by an adjustment mechanism so that the fluctuation amount of the irradiation position of the light beam in the detection means is less than a specific value.

  Next, numerical examples of what pitch irregularities and detection results appear when there is actual surface tilt or surface eccentricity will be described with reference to FIGS. 7A to 7C and Tables 2 to 7. FIG.

  7A to 7C are views of polygon mirrors having 8, 6 and 4 deflection surfaces as viewed from the direction of the rotation axis. For convenience, an XY Cartesian coordinate system is defined, and the origin coincides with the rotation axis. The rotation axis is the Z axis, and the front side of the paper is the plus direction. Further, the surface in the plus direction of the X axis is defined as the first surface, and the second surface... Nth surface is determined clockwise.

  Next, detection example 1 is shown.

  Assume that surface tilting surface eccentricities as shown in Tables 2A and 2B occur in the optical deflector assembled with the 8-sided polygon mirror of FIG. 7A. This example shows a case where a single polygon mirror machined with zero machining accuracy and zero eccentricity is shifted by 8.25 μm in the Y-axis direction relative to the center of the rotation axis when attached to the drive motor. Further, it shows a case where a right rotation (rotation in which the Y-axis plus side turns to the front of the paper) 0.4 'occurs around the X axis.

  The scanning optical system in the table of FIG. 2 has uneven pitch when an optical deflector with surface decentering Po = 0.033 mm or surface tilt εo = 1.6 ′ is mounted (scanned surface (photosensitive member) when the deflector rotates once). It is assumed that the image forming performance is such that the height variation amount of the irradiation position at 5 μm. In addition, surface tilt (1) in the table is a manufacturing variation of the scanning optical system, and it is assumed that the focal length of the Fθ lens in the sub-scanning direction is shorter than the design value, and surface tilt (2) is a manufacturing variation of the scanning optical system. It is assumed that the focal length of the fθ lens in the sub-scanning direction is longer than the design value.

  Total (1) is the sum of pitch unevenness due to surface tilt (1) and pitch unevenness due to surface eccentricity. Total (2) is the sum of pitch unevenness due to surface tilt (2) and pitch unevenness due to surface eccentricity.

  According to Table 2A, pitch unevenness due to surface tilt causes maximum and minimum pitch unevenness on the third and seventh surfaces, and pitch unevenness due to surface eccentricity causes maximum and minimum pitch unevenness on the third and seventh surfaces. As a result, the total pitch unevenness of the scanning optical system takes the maximum and minimum values on the third surface and the seventh surface when the focal length of the fθ lens in the sub-scanning direction is shorter than the design value (total (1)). When the focal length in the sub-scanning direction of the Fθ lens is longer than the design value (total (2)), the pitch unevenness due to the surface tilting factor and the pitch unevenness due to the surface eccentricity cancel each other, and the total pitch unevenness of the scanning optical system becomes zero. .

  Next, when this optical deflector is measured by the measuring optical system (inspection apparatus) shown in Table 1, the vibration of the light beam on the V slit 7 is shown in Table 2B. As described above, the measurement optical system has a variation in irradiation position on the V slit 7 (one turn of the deflector) when an optical deflector with surface decentering Po = 0.033 mm or surface tilt εo = 1.6 ′ is assembled. The imaging performance is 45.23 μm.

  Further, the surface tilt (1) in the table is the case where the moving distance dXc = -24.25 mm of the cylindrical lens 4B of the measuring optical system, and the surface tilt (2) is the moving distance dXc = + 24.25 of the cylindrical lens 4B of the measuring optical system. This is the case for mm. Total (1) is the sum of the variation in irradiation position due to surface tilt (1) and the variation in irradiation position due to surface eccentricity. Total (2) is the sum of the variation in irradiation position due to surface tilt (2) and the variation in irradiation position due to surface eccentricity.

  According to Table 2B, the variation in the irradiation position due to the surface tilt causes the maximum and minimum of the variation in the irradiation position on the third surface and the seventh surface, and the variation in the irradiation position due to the surface eccentricity also occurs on the third surface and the seventh surface. The maximum and minimum of the variation of the irradiation position is generated. As a result, the variation of the total irradiation position of the measurement optical system takes the maximum and minimum values on the third surface and the seventh surface at dXc = −24.25 mm (total (1)). In addition, in the case of dXc = + 24.25 mm (total (2)), the fluctuation of the irradiation position due to the surface tilting factor and the fluctuation of the irradiation position due to the surface eccentricity cancel each other, and the fluctuation of the total irradiation position of the measurement optical system becomes zero.

  According to Tables 2A and 2B, it can be seen that the measuring device can detect the surface tilt and surface eccentricity of the optical deflector that causes pitch unevenness of 5 μm or less in the scanning optical system as 45.23 μm. Therefore, it is possible to select only non-defective optical deflectors by inspecting the optical deflectors using the measuring device before the step of assembling the scanning optical system. In the measurement apparatus of the present invention having the configuration shown in Table 1, as shown in Tables 2A and 2B, irradiation position fluctuations due to surface tilt and surface eccentricity are simultaneously detected.

  Here, the scanning optical system is a system in which an optical deflector that has been determined to be non-defective after inspection is incorporated.

  In the optical deflector shown in Table 2A, the deflection surface where the pitch unevenness due to surface tilt is maximized and the surface where the pitch unevenness due to surface eccentricity is maximized are the same surface, and the phase is the same. The permissible pitch unevenness Bmax = 5 μm is allocated in half by the factor of surface tilt and the factor of surface eccentricity. This corresponds to εo / 2 and Po / 2 in FIG.

  When the surface tilt and the surface eccentricity are separately measured and inspected, it is necessary to use a tolerance distribution in which εo / 2 = 0.8 ′ and Po / 2 = 16.5 μm are acceptable standard values for the respective measurements. However, when measuring tilt and surface eccentricity at the same time as in this example, it is not necessary to set the irradiation position fluctuation of the surface tilt factor and the surface eccentricity separately, and the allowable standard value for measurement by adding the irradiation position fluctuation Can be decided.

  Next, detection example 2 is shown.

  Assume that surface tilting surface eccentricity as shown in Tables 3A and 3B occurs in the optical deflector assembled with the 8-sided polygon mirror of FIG. 7A. This example shows a case where the polygon mirror is processed with zero machining accuracy and zero eccentricity and is shifted by -8.25 μm in the Y-axis direction with respect to the center of the rotation axis when it is attached to the drive motor. Further, it shows a case where a right rotation (rotation in which the Y-axis plus side turns to the front of the paper) 0.4 'occurs around the X axis. At this time, the first and fifth surfaces are free of surface tilt and surface eccentricity.

  In Tables 3A and 3B, notations such as the scanning optical system, surface tilt (1) and (2), and total (1) and (2) are the same as Tables 2A and 2B. According to Table 3A, the total pitch unevenness of the scanning optical system takes the maximum and minimum values on the third surface and the seventh surface when the focal length of the Fθ lens in the sub-scanning direction is longer than the design value (total (2)). Further, when the focal length of the fθ lens in the sub-scanning direction is shorter than the design value (total (1)), the pitch unevenness due to the surface tilting factor and the pitch unevenness due to the surface eccentricity cancel each other, and the total pitch unevenness of the scanning optical system becomes zero. .

  Next, when this optical deflector is measured by the measurement optical system (inspection apparatus) shown in Table 1, the vibration of the light beam on the V slit 7 is shown in Table 3B. According to Table 3B, the variation of the total irradiation position of the measurement optical system takes the maximum and minimum values on the third surface and the seventh surface at dXc = + 24.25 mm (total (2)). For dXc = −24.25 mm (total (1)), the fluctuation of the irradiation position due to the surface tilting factor and the fluctuation of the irradiation position due to the surface eccentricity cancel each other, and the fluctuation of the total irradiation position of the measurement optical system becomes zero.

  According to Tables 3A and 3B, it can be seen that the measuring device can detect the surface tilt and surface eccentricity of the optical deflector that cause the pitch unevenness of 5 μm or less in the scanning optical system as 45.23 μm. Therefore, it is possible to select only non-defective optical deflectors by inspecting the optical deflectors using the measuring device before the step of assembling the scanning optical system. In the measuring apparatus of the present invention having the configuration shown in Table 1, as shown in Tables 3A and 3B, irradiation position fluctuations due to surface tilt and surface eccentricity are simultaneously detected.

  In the optical deflector of Table 3A, the deflection surface where the pitch unevenness due to the surface tilt is maximized and the surface where the pitch unevenness due to the surface eccentricity is maximum are the same surface and have the same phase. The permissible pitch unevenness Bmax = 5 μm is allocated in half by the factor of surface tilt and the factor of surface eccentricity. This corresponds to (εo / 2, Po / 2) in FIG.

  When the surface tilt and the surface eccentricity are separately measured and inspected, it is necessary to use a tolerance distribution in which εo / 2 = 0.8 ′ and Po / 2 = 16.5 μm are acceptable standard values for the respective measurements. However, when measuring tilt and surface eccentricity at the same time as in this example, it is not necessary to set the irradiation position fluctuation of the surface tilt factor and the surface eccentricity separately, and the allowable standard value for measurement by adding the irradiation position fluctuation Can be decided.

  Next, detection example 3 is shown.

  Assume that surface tilting surface eccentricity as shown in Tables 4A and 4B occurs in the optical deflector assembled with the 8-sided polygon mirror of FIG. 7A. This example shows a case where a polygon mirror with a single machining accuracy of zero tilted surface and eccentricity is shifted by +8.25 μm in the Y-axis direction with respect to the center of the rotation axis when attached to the drive motor. Further, it shows a case where a right rotation (rotation in which the X axis plus side turns to the front of the paper) 0.4 'occurs around the Y axis. At this time, the first and fifth surfaces are free of surface tilt and surface eccentricity.

  The notations such as the scanning optical system, surface tilt (1) (2), and total (1) (2) in Tables 4A and 4B are the same as Tables 2A and 2B. According to Table 4A, the total pitch unevenness of the scanning optical system takes the maximum and minimum values on the second surface and the sixth surface when the focal length of the fθ lens in the sub-scanning direction is shorter than the design value (total (1)). When the focal length of the fθ lens in the sub-scanning direction is longer than the design value (total (2)), the pitch unevenness due to the surface tilting factor and the pitch unevenness due to the surface eccentricity take the maximum and minimum values on the fourth and eighth surfaces.

  Next, when this optical deflector is measured by the measurement optical system (inspection apparatus) shown in Table 1, the vibration of the light beam on the V slit 7 is shown in Table 4B. According to Table 4B, the variation of the total irradiation position of the measurement optical system takes the maximum and minimum values on the second surface and the sixth surface at dXc = -24.25 mm (total (1)). For dXc = + 24.25 mm (total (2)), the variation of the irradiation position due to the surface tilt factor and the variation of the irradiation position due to the surface eccentricity are the maximum and minimum values on the fourth and eighth surfaces.

  According to Tables 4A and 4B, it can be seen that the measuring device can detect surface tilt and surface eccentricity of the optical deflector that cause pitch unevenness of 3.54 μm or less in the scanning optical system as 31.98 μm. Therefore, it is possible to select only non-defective optical deflectors by inspecting the optical deflectors using the measuring device before the step of assembling the scanning optical system. In the measurement apparatus of the present invention in Table 1, as shown in Tables 4A and 4B, fluctuations in the irradiation position due to surface tilt and surface eccentricity are simultaneously detected.

  In the optical deflector of Table 4A, the deflection surface where the pitch unevenness due to surface tilt is maximized is different from the surface where the pitch unevenness due to surface eccentricity is maximized, and the phase is different. Even if the amount of surface tilt and the amount of surface eccentricity are the same as the cases in Tables 2A and 3A (16.5μm, 0.8 '), the total pitch unevenness B = 3.54μm, which is less than PP = 5.00μm in Tables 2A and 3A. it can. Therefore, the optical performance of the scanning optical system is improved.

  In the scanning optical system, when the polygon mirror is assembled to the rotation axis of the optical deflector, the variation of the irradiation position caused by the surface decentering is maximized and the variation of the irradiation position caused by the surface tilt. It is good to arrange so that the deflection surfaces (1 surface, 5 surfaces) that maximize the amount are different. The deflection surface may be varied depending on the assembling process, or may be assembled so as to differ depending on the adjusting process by the position adjusting means.

  Tables 2 to 4 show cases where the surface eccentricity = 16.5 μm and the surface tilt = 0.8 ′. In particular, Table 4 describes an example in which pitch unevenness can be reduced when incorporated in a scanning optical system, compared to Tables 2 and 3. The following Tables 5 to 7 show examples in which the surface eccentricity is reduced to 25.4 to 33.0 μm, the surface tilt amount is reduced to 1.07 to 1.6 ′, and the pitch unevenness Bmax of the scanning optical system is achieved to be 5.00 μm.

  Example 4 of detection is shown.

  Assume that surface tilting surface eccentricities as shown in Tables 5A and B occur in the optical deflector assembled with the 8-sided polygon mirror of FIG. 7A. This example shows a case in which a polygon mirror with a single machining accuracy of zero tilted surface and eccentricity is shifted by +16.5 μm in the Y-axis direction with respect to the center of the rotation axis when attached to the drive motor. Further, it shows a case where a clockwise rotation (rotation such that the X-axis plus side turns to the front of the paper) 0.8 'occurs around the Y-axis.

  The notations such as the scanning optical system, surface tilt (1) (2), and total (1) (2) in Tables 5A and 5B are the same as Tables 2A and 2B. According to Table 5A, the total pitch unevenness of the scanning optical system shows the maximum and minimum values on the first, third, fifth and seventh surfaces when the focal length of the Fθ lens in the sub-scanning direction is shorter than the design value (total (1)). Take. Further, when the focal length of the fθ lens in the sub-scanning direction is longer than the design value (total (2)), the pitch unevenness due to the surface tilting factor and the pitch unevenness due to the surface eccentricity take the maximum and minimum values on the first, third, fifth and seventh surfaces. .

  Next, when this optical deflector is measured by the measurement optical system (inspection apparatus) shown in Table 1, the fluctuation of the light beam on the V slit 7 is shown in Table 5B. According to Table 5B, the variation of the total irradiation position of the measurement optical system has the maximum and minimum values on the first, third, fifth, and seventh surfaces when dXc = −24.25 mm (total (1)). For dXc = + 24.25 mm (total (2)), the variation of the irradiation position due to the surface tilting factor and the variation of the irradiation position due to the surface eccentricity take the maximum and minimum values on the first, third, fifth and seventh surfaces.

  According to Tables 5A and 5B, it can be seen that the measuring device can detect the surface tilt and surface eccentricity of the optical deflector that cause the pitch unevenness of 5.00 μm or less in the scanning optical system as 45.23 μm. Therefore, it is possible to select only non-defective optical deflectors by inspecting the optical deflectors using the measuring device before the step of assembling the scanning optical system. In the measuring apparatus of the present invention having the configuration shown in Table 1, as shown in Tables 5A and 5B, variations in irradiation position due to surface tilt and surface eccentricity are simultaneously detected.

  In the optical deflector of Table 5A, the deflection surface where the pitch unevenness due to the surface tilt is maximized is different from the surface where the pitch unevenness due to the surface eccentricity is maximized, and the phases are different. Even if the amount of surface tilt and surface eccentricity is larger than the cases in Table 2A and Table 3A (33.0μm, 1.6 '), the total pitch unevenness PP = 5.00μm, and the amount of surface tilt and surface eccentricity from Table 2A and Table 3A. Is greatly acceptable. Therefore, the assembly workability of the scanning optical system is improved. When assembling the polygon mirror 51 with respect to the rotation shaft 55 of the optical deflector 5, the deflection surface (3 surface, 7 surface) that maximizes the irradiation position variation caused by surface eccentricity, and the irradiation position variation caused by surface tilt. It is good to arrange so that the deflection surface where the maximum value is different. The deflection surfaces (1 surface, 5 surfaces) may be varied depending on the assembly process, or may be assembled so as to differ depending on the adjustment process by the adjustment mechanism.

  Example 5 of detection is shown.

  Assume that surface tilting surface eccentricities as shown in Tables 6A and 6B occur in the optical deflector assembled with the 6-sided polygon mirror of FIG. 7B. This example shows a case where the polygon mirror single product processed with zero surface tilt and eccentricity is shifted by +12.7 μm in the Y-axis direction with respect to the center of the rotation axis when attached to the drive motor. Further, a case is shown in which a right rotation (rotation such that the X-axis plus side turns to the front of the sheet) 0.53 'occurs around the Y-axis.

  The notations such as scanning optical system, surface tilt (1) (2), and total (1) (2) in Tables 6A and 6B are the same as Tables 2A and 2B. According to Table 6A, the total pitch unevenness of the scanning optical system takes the maximum and minimum values on the second and fifth surfaces when the focal length of the fθ lens in the sub-scanning direction is shorter than the design value (total (1)). When the focal length of the fθ lens in the sub-scanning direction is longer than the design value (total (2)), the pitch unevenness due to the surface tilting factor and the pitch unevenness due to the surface eccentricity take the maximum and minimum values on the third and sixth surfaces.

  Next, when this optical deflector is measured by the measurement optical system (inspection apparatus) shown in Table 1, the fluctuation of the light beam on the V slit 7 is shown in Table 5B. According to Table 6B, the variation of the total irradiation position of the measurement optical system takes the maximum and minimum values on the second and fifth surfaces at dXc = -24.25 mm (total (1)). For dXc = + 24.25 mm (total (2)), the variation of the irradiation position due to the surface tilt factor and the variation of the irradiation position due to the surface eccentricity are the maximum and minimum values on the third and sixth surfaces.

  According to Table 6A and Table 6B, it can be seen that the measuring device can detect the surface tilt and surface eccentricity of the optical deflector that cause the pitch unevenness of 5.00 μm or less in the scanning optical system as 45.23 μm. Therefore, it is possible to select only non-defective optical deflectors by inspecting the optical deflectors using the measuring device before the step of assembling the scanning optical system. In the measurement apparatus of the present invention having the configuration shown in Table 1, as shown in Tables 6A and 6B, fluctuations in irradiation position due to surface tilt and surface eccentricity are simultaneously detected.

  In the optical deflector of Table 6A, the deflection surface where the pitch unevenness due to surface tilt is maximized is different from the surface where the pitch unevenness due to surface eccentricity is maximized, and the phases are different. Even if the surface tilt amount and surface eccentricity are larger than those in Table 2A and Table 3A (22.0μm, 1.07 '), the total pitch unevenness PP = 5.00μm, and the surface tilt amount and surface eccentricity from Tables 2A and 3A. Is greatly acceptable. Therefore, the assembly workability of the scanning optical system is improved. When the polygon mirror 51 is assembled to the rotating shaft 55 of the optical deflector 5, the deflection surface that maximizes the irradiation position variation caused by surface eccentricity is different from the deflection surface that maximizes the irradiation position variation caused by surface tilt. It is good to arrange like this. The deflection surface may be varied depending on the assembly process, or may be assembled differently depending on the adjustment process.

  Example 6 of detection is shown.

  Assume that surface tilted surface eccentricities as shown in Tables 7A and B occur in the optical deflector assembled with the four-surface polygon mirror in FIG. 7C. This example shows a case where a polygon mirror with a machining accuracy of zero tilted surface and zero eccentricity is shifted by +16.5 μm in the Y-axis direction with respect to the center of the rotation axis when attached to the drive motor. Further, it shows a case where a right rotation (rotation such that the X-axis plus side turns toward the front of the paper) 0.8 'occurs around the Y-axis.

  The notations such as the scanning optical system, surface tilt (1) (2), and total (1) (2) in Tables 5A and 5B are the same as those in Tables 2A and 2B. According to Table 7A, the total pitch unevenness of the scanning optical system takes the maximum and minimum values on the second and fourth surfaces when the focal length of the Fθ lens in the sub-scanning direction is shorter than the design value (total (1)). When the focal length of the fθ lens in the sub-scanning direction is longer than the design value (total (2)), the pitch unevenness due to the surface tilting factor and the pitch unevenness due to the surface eccentricity take the maximum and minimum values on the second and fourth surfaces.

  Next, when this optical deflector is measured by the measurement optical system (inspection apparatus) shown in Table 1, the fluctuation of the light beam on the V slit 7 is shown in Table 5B. According to Table 7B, the variation of the total irradiation position of the measurement optical system takes the maximum and minimum values on the second and fourth surfaces at dXc = -24.25 mm (total (1)). In addition, when dXc = + 24.25 mm (total (2)), the variation of the irradiation position due to the surface tilt factor and the variation of the irradiation position due to the surface eccentricity take the maximum and minimum values on the second and fourth surfaces.

  According to Tables 7A and 7B, it can be seen that the measuring device can detect the surface tilt and surface eccentricity of the optical deflector that cause the pitch unevenness of 5.00 μm or less in the scanning optical system as 45.23 μm. Therefore, it is possible to select only non-defective optical deflectors by inspecting the optical deflectors using the measuring device before the step of assembling the scanning optical system. In the measurement apparatus of the present invention having the configuration shown in Table 1, as shown in Tables 7A and 7B, irradiation position fluctuations due to surface tilt and surface eccentricity are simultaneously detected.

  In the optical deflector of Table 7A, the deflection surface where the pitch unevenness due to surface tilt is maximized and the surface where the pitch unevenness due to surface eccentricity is maximum are different and have different phases. Even if the amount of surface tilt and the amount of surface eccentricity are larger than those in Tables 2A and 3A (33.0μm, 1.6 '), the total pitch unevenness PP is 5.00μm, and the amount of surface tilt and surface eccentricity is larger than Tables 2A and 3A. Largely acceptable. Therefore, the assembly workability of the scanning optical system is improved. When the polygon mirror 51 is assembled to the rotating shaft 55 of the optical deflector 5, the deflection surface that maximizes the irradiation position variation caused by surface eccentricity is different from the deflection surface that maximizes the irradiation position variation caused by surface tilt. It is good to arrange like this. The deflection surface may be varied depending on the assembly process, or may be assembled differently depending on the adjustment process.

  8 and 9 are schematic views of the main part of the measuring apparatus according to the third embodiment of the present invention. FIG. 8 and FIG. 9 each show a surface eccentricity measuring device and a surface tilt measuring device of the optical deflector.

  FIG. 8 is a sub-scan sectional view of a measurement optical system that includes two measurement optical systems of the embodiment of FIGS. 1 to 3 and is used for surface eccentricity measurement and surface tilt measurement. FIG. 9 shows an apparatus for analyzing measurement signals obtained from the two measurement optical systems in FIG.

  In FIG. 8, the measurement optical systems of FIGS. 2 and 3 are arranged on the left and right of the optical deflector 5, and the opposing deflection surfaces of the polygon mirror 51 are detected simultaneously. Therefore, the optical axes of the two measurement optical systems are arranged in the sub-scan section (paper surface) including the rotation center 56 of the deflector.

  Each of the two measurement optical systems causes a light beam to be incident on different deflecting surfaces of the rotary polygon mirror, and detects a variation amount of the irradiation position of the light beam by a detecting unit.

  In the first measurement optical system of FIG. 8, the laser diffused light emitted from the semiconductor laser 11 is collimated by the collimator lens 12, and the laser beam formed by the circular aperture 13 disposed thereafter is taken out. Thereafter, the light is condensed only in the sub-scanning direction of the polygon mirror 51 by the cylindrical lens 14 </ b> A and enters the deflection surface 521 of the polygon mirror 51. At this time, a line image is formed at a position where the deflection surface 521 of the polygon mirror 51 does not coincide. The light beam reflected by the deflecting surface 521 enters the second cylindrical lens 14B while slightly diverging in the sub-scanning direction. Since the front focal point of the cylindrical lens 14B is arranged so as to coincide with the position of the line image (that is, the front focal point does not coincide with the deflection surface 521), the reflected light is returned to parallel light. Thereafter, since the parallel light is imaged at the rear focal position of the jig lens 16, the V slit 17 is disposed at this imaging position.

  In the second measurement optical system of FIG. 8, the laser diffused light emitted from the semiconductor laser 21 is collimated by a collimator lens 22 and a laser beam shaped by a circular diaphragm 23 disposed thereafter is taken out. Thereafter, the light is condensed only in the sub-scanning direction of the polygon mirror by the cylindrical lens 24 </ b> A and is incident on the deflection surface 522 of the polygon mirror 51. At this time, a line image is formed at a position where the deflection surface 522 of the polygon mirror 51 does not coincide. The light beam reflected by the deflecting surface 522 is incident on the second cylindrical lens 24B while slightly diverging in the sub-scanning direction. Since the front focal point of the cylindrical lens 24B is arranged to coincide with the position of the line image (that is, the front focal point does not coincide with the deflection surface 522), the reflected light is returned to parallel light. After that, since the parallel light is imaged at the rear focal position of the jig lens 26, the V slit 27 is arranged at this imaging position.

  The beams that have passed through the V slits 17 and 27 are received by the photodiodes 18 and 28, and the amount of light is monitored. The monitored light quantity is transferred as an electric signal to an analysis device 9 as an electric signal processing means shown in FIG. 9 for analysis.

  The motor 54 has a rotation shaft 55 and is fitted in the fitting hole 53 of the polygon mirror 51. The optical deflector 5 is constituted by the motor 54 and the polygon mirror 51. A rotation center 56 of the rotation shaft 55 is used.

  In the first measurement optical system, the semiconductor laser 11 to the cylindrical lens 14A constitute an incident optical system, the cylindrical lens 14B and the jig lens 16 constitute a detection optical system, and the V slit 17 and the photodiode 18 serve as detection means. Constitute. Detection means is provided at an image forming point of the detection optical system. A measurement optical system is constituted by the incident optical system, the detection optical system, and the detection means. Further, the measuring device is constituted by an analysis device 9 as a holding means (not shown) for holding the measurement optical system and an electric signal processing means for processing an electric signal from the detecting means.

  In the second measurement optical system, the semiconductor laser 21 to the cylindrical lens 24A constitute an incident optical system, the cylindrical lens 24B and the jig lens 26 constitute a detection optical system, and the V slit 27 and the photodiode 28 serve as detection means. Constitute. Detection means is provided at an image forming point of the detection optical system. A measurement optical system is constituted by the incident optical system, the detection optical system, and the detection means. Further, the measuring device is constituted by an analysis device 9 as a holding means (not shown) for holding the measurement optical system and an electric signal processing means for processing an electric signal from the detecting means.

  In this embodiment, the amount of fluctuation of the irradiation position of the light beams by the detection means of the two measurement optical systems is converted into the surface eccentricity amount and the surface tilt amount of each deflection surface by the calculation means.

  A plane perpendicular to the rotation shaft 55 as shown in FIG. The incident optical system (semiconductor laser to cylindrical lens) is incident at a specific incident angle θi with respect to the reference plane. This θi may be the same position in the first measurement optical system and the second measurement optical system, or may be a different value.

  The detection optical system (cylindrical lens and jig lens) is also arranged at a specific reflection angle θo with respect to the reference plane. It is desirable to set θi and θo so that the absolute values are equal and the directions are different.

  Numerical examples in the present embodiment are the same as those in Table 1. The incident optical system assumes an incident angle θi = −20 ° with respect to the reference plane. The detection optical system also assumes a reflection angle θo = + 20 ° with respect to the reference surface. The surface spacing in the table is a dimension measured on the optical axis of the incident optical system and the detection optical system.

  DX1c in the table indicates the amount of movement of the cylindrical lenses 14A and 14B. dX2c represents the amount of movement of the cylindrical lenses 24A and 24B. dX1 and dX2 are distances between the polygon deflection surface and the line image, respectively. When dX1 = dX2 = 0, the polygon deflection surface 521 and the V slit 17 are in an optically conjugate relationship by the detection optical system (the cylindrical lens 14B and the jig lens 16). Further, the polygon deflection surface 522 and the V slit 27 are in an optically conjugate relationship by the detection optical system (the cylindrical lens 24B and the jig lens 26). That is, the polygon deflection surface 521 and the V slit 17, and the polygon deflection surface 522 and the V slit 17 satisfy a perfect surface tilt correction relationship by the detection optical system. At this time, the rear focal position of the cylindrical lens 14A coincides with the polygon deflection surface 521, and the rear focal position of the cylindrical lens 24A coincides with the polygon deflection surface 522. Further, the front focal position of the cylindrical lens 14B and the polygon deflection surface 521 coincide, and the front focal position of the cylindrical lens 24B and the polygon deflection surface 522 coincide with each other.

  In contrast, in this embodiment, dX ≠ 0, that is, the detection optical system is arranged so as not to satisfy the surface tilt correction relationship between the polygon deflection surface 521 and the V slit 17 and the surface tilt correction relationship between the polygon deflection surface 522 and the V slit 27. Further, when dX1 of the first measurement optical system is dX1, and dX of the second measurement optical system is dX2, dX1 = −dX2> 0.

  That is, the position of the line image in the first measurement optical system and the position of the line image in the second measurement optical system are opposite to the position of the deflection surface of the rotary polygon mirror.

  In FIG. 8, since the first measurement optical system has dX1> 0, the light beam forms a line image behind the polygonal deflecting surface 521 and forms an image once. The distance between the polygon deflection surface 521 and the line image is dX1. Then, by matching the front focal point of the cylindrical lens 14B with the position of the line image, it can be seen that the light beam emitted from the cylindrical lens 14B becomes parallel light. Thereafter, since the parallel light is imaged at the rear focal position of the jig lens 16, the V slit 17 is disposed at this imaging position.

  Further, in FIG. 8, since dX2 <0 is set in the second measurement optical system, the light beam forms a line image in front of the polygon deflection surface 522 and forms an image once. The distance between the polygon deflection surface 522 and the line image is dX2. Then, by matching the front focal point of the cylindrical lens 24B to the position of the line image, it can be seen that the light beam emitted from the cylindrical lens 24B becomes parallel light. After that, since the parallel light is imaged at the rear focal position of the jig lens 26, the V slit 27 is disposed at this imaging position.

  As described above, the position of the focal line (line image) with respect to the polygon deflection surface is arranged so that the first measurement optical system is behind the deflection surface and the second measurement optical system is in front of the deflection surface. It has become a relationship.

  In this embodiment, when the line image is formed at at least two different positions with respect to the deflection surface of the rotary polygon mirror, the surface eccentricity and the surface tilt amount of the deflection surface are obtained.

  In particular, there are two measurement optical systems, and the position of the line image in the first measurement optical system and the position of the line image in the second measurement optical system are opposite to the position of the deflection surface of the rotary polygon mirror. Measured so that

In this embodiment, dX1 = −dX2, but approximately −1.2 ≦ dX1 / dX2 ≦ −0.8 Equation 8
By setting as above, the object of the present embodiment can be achieved.

  In this embodiment, the irradiation position of the light beam is simultaneously detected with respect to the opposing deflection surfaces 521 and 522, and the fluctuation of the irradiation position is simultaneously detected with respect to different deflection surfaces.

  In this embodiment, there is an arithmetic means for converting the amount of deviation of the irradiation position of the light beam by the detecting means in the two measurement optical systems into the surface eccentricity amount and the surface tilt amount of each deflection surface.

  In the measurement optical system as described above, how the polygon mirror 51 of the actual light deflector 5 operates when the surface is decentered or tilted will be described with reference to FIGS. 4 and 5 above. It is the same as that.

  As described above, in the measuring apparatus according to the present embodiment, when the optical deflector has the surface tilt ε and the surface eccentricity p, the light beam scanning on the V slits 17 and 27 causes the irradiation position to fluctuate, and its fluctuation amount dZp. And dZε can be expressed by the above formulas 2 and 3.

  In this embodiment, the relative positions of the rotation center of the optical deflector and the deflection surface of the rotary polygon mirror are set so that the fluctuation amount of the irradiation position of the light beam at the detection means in the two measurement optical systems is less than or equal to a specific value. An adjustment mechanism for adjustment is provided.

  In this embodiment, V slits 17 and 27 and photodiodes 18 and 28 are used as means for measuring fluctuations dZp and dZε of the irradiation position of the scanning light beam. The V-slit has a V-shaped aperture so that the width w in the direction in which the light beam scans changes with the irradiation position (height) h, and the time that the beam crosses the aperture varies depending on the irradiation position (height). It is configured as follows. The photodiodes 18 and 28 are provided behind the V slits 17 and 27 to associate the irradiation position (height) with the time for receiving light. Such a V-slit method is a technique disclosed in many documents.

  In this embodiment, the V-slit method is described. For example, a one-dimensional line CCD is arranged perpendicularly to the scanning direction of the light beam (in the plane of FIG. 8), and a CCD pixel crossed by the light beam is detected. A known technique such as a method of measuring the irradiation position may be employed.

  Next, a specific method for setting the distances dX1 and dX2 will be described. The maximum pitch unevenness allowable in the design of the scanning optical system is determined from the print image of the image forming apparatus. Usually, the maximum pitch unevenness Bmax is about 5 μm.

  In recent years, the maximum pitch unevenness may be suppressed to about 2 μm for higher image quality. The surface tilt amount and surface eccentricity amount of the optical deflector are calculated for the required maximum pitch unevenness. First, assuming that there is no surface eccentricity, the pitch unevenness εmax is determined by accumulating the pitch unevenness tolerance caused by the surface tilt and totaling Bmax.

  Next, assuming that there is no surface tilt at all, the pitch unevenness tolerance caused by the surface eccentricity is accumulated, and the surface eccentricity Pmax is determined so that the total becomes Bmax. Pmax is also a relative fluctuation range between the deflection surfaces of the polygon mirror of εmax.

  Specifically, in the optical deflector which is applied to the above formulas 2 and 3 and the standards of Po = 0.033 mm and εo = 1.6 ′ (min) are required, dX1 = + 24.25 mm and dX2 = −24.25 mm. When this optical deflector is evaluated by the measurement optical system shown in Table 8, the cylindrical lenses 14A, 14B, 24A, and 24B are moved by dX1c = + 24.25 mm and dX2c = -24.25 mm.

  By the way, the reason for providing two measurement optical systems constituted by plus and minus dX1, dX2 is as follows.

  In a scanning optical device in which an optical deflector is assembled, even if an optical deflector having the same surface tilt amount is used, the variation direction of the irradiation position may be reversed due to variations in the accuracy of other components. For example, if the focal length in the sub-scanning direction of the fθ lens of the scanning optical device is shorter than the design value, the irradiation position varies downward when the deflection surface of the polygon mirror faces upward. Conversely, if the focal length in the sub-scanning direction of the Fθ lens of the scanning optical device is longer than the design value, the irradiation position changes upward when the deflection surface of the polygon mirror is directed upward. The inspection method assuming the former is dX1> 0, and the inspection method assuming the latter is dX2 <0. Regarding the surface eccentricity, the direction of the irradiation position variation dZ is the same whether dX1> 0 or dX2 <0.

  Specifically, in the configuration of the first measurement optical system, when moving with dX1c = + 24.25 mm, the direction of the surface eccentricity P in FIG. 4 is negative, and the irradiation position is dZ with respect to P = −0.033 mm. = −45.23 μm (dZp direction in FIG. 4) Further, assuming that the direction of surface tilt in FIG. 5 is positive, the irradiation position is deviated by dZ = −45.23 μm (direction dZε in FIG. 5) with respect to the deflection surface of ε = + 1.6 ′.

  On the other hand, when the second measuring optical system is moved with dX2c = −24.25, the irradiation position is deviated by dZ = −45.23 μm with respect to P = −0.033 mm. Further, the irradiation position deviates by dZ = + 45.23 μm with respect to the deflection surface of ε = + 1.6 ′.

  For the above reasons, in this embodiment, in order to measure the optical deflector 5, the cylindrical lenses 14A and 14B may be moved to two patterns of dX1c> 0 and the cylindrical lenses 24A and 24B may be moved to dX2c <0. You may arrange from the beginning. In the embodiment of FIG. 1, the positions of the cylindrical lenses 4A and 4B are moved so that these two types of measurement optical systems can be covered by one optical system. In the present embodiment, since the measurement and inspection can be performed without moving the position of the cylindrical lens, the inspection assembly process can be speeded up easily.

Further, as described above, in the first measurement optical system and the second measurement optical system, the irradiation position variation due to surface decentration is the same direction, and the irradiation position variation due to surface tilt is in the opposite direction. This can be expressed as follows: dZ1 (n) = dZ (Pn) + dZ (εn)
dZ2 (n) = dZ (Pn) -dZ (εn) Equation 10
However,
Pn ··· Surface eccentricity of the nth surface of the polygon mirror εn · · Surface tilt amount of the nth surface of the polygon mirror dZ (Pn) · · Irradiation position fluctuation caused by surface eccentricity dZ (εn) · · Caused by surface eccentricity Irradiation position fluctuation dZ1 (n) ·· Irradiation position fluctuation when the nth surface of the polygon mirror is measured with the first measurement optical system dZ2 (n) ·· The nth surface of the polygon mirror is the second measurement optics This is the irradiation position variation when measured by the system.

  Next, a case where the irradiation position fluctuation amounts dZ1 (n) and dZ2 (n) of the first measurement optical system and the second measurement optical system are analyzed and determined by the analysis device 9 of FIG. 9 will be described.

In a normal inspection process, irradiation position variation information obtained by the first measurement optical system and the second measurement optical system for the test deflector 5 is sent to the analysis device 9. here
MAX (dZ1 (n)) − MIN (dZ1 (n)) ≦ 45.23μm
MAX (dZ2 (n)) − MIN (dZ2 (n)) ≦ 45.23μm
If both of the above are satisfied, it is determined that the pitch unevenness that combines the surface tilt and surface eccentricity of the test deflector is good (the pitch unevenness when assembled to the scanning optical system is 5 μm or less).

Further, in the analysis device 9 of the present embodiment, the surface tilt and surface eccentricity of each surface of the deflector to be measured are calculated from the irradiation position variation information obtained by the first measurement optical system and the second measurement optical system. Is possible. Specifically, the sum and difference of Equations 9 and 10 may be taken. From the sum of Equation 9 and Equation 10,
dZ (Pn) = (dZ1 (n) + dZ2 (n)) / 2 Formula 11
Also, due to the difference, dZ (εn) = (dZ1 (n) −dZ2 (n)) / 2
It becomes. From this result, since the surface tilt and surface eccentricity of each surface of the test deflector are shown as in Equations 11 and 12, the surface tilt amount (total deflection surface) of the test deflector is determined from the different dX values. And the amount of surface eccentricity (PP of surface eccentricity of all deflection surfaces) can also be calculated by the calculation means.

  In the measuring apparatus of FIG. 8, in order to determine which deflection surface of the deflector to be detected is detected, marking may be performed on the upper surface of the polygon mirror 51 and the motor 54, and the determination may be performed. . Alternatively, it may be performed by an existing technique that detects a current waveform flowing through the motor or an electromagnetic pulse emitted from the motor. In FIG. 8, since the first measurement optical system and the second measurement optical system are arranged opposite to the polygon mirror 51 and detect different deflection surfaces, dZ1 (n) and dZ2 (n) is detected at different timings. Therefore, it is necessary to calculate the variation information of the irradiation position taken into the analysis device 9 by shifting the phase timing so that the detected deflection surfaces are the same.

  Next, a method for adjusting the relative position of the motor 54 and the polygon mirror 51 based on the analysis result of the analysis device 9 will be described with reference to FIG. 7A, FIG. 7B, Table 9, and Table 10.

  7A and 7B are views of a polygon mirror having 8 and 6 deflection surfaces as seen from the direction of the rotation axis. For convenience, an XY Cartesian coordinate system is defined, and the origin coincides with the rotation axis. The rotation axis is the Z axis, and the front side of the paper is the plus direction. Further, the surface in the plus direction of the X axis is defined as the first surface, and the second surface... Nth surface is determined clockwise.

(Example 1 of adjustment method)
Assume that surface tilting surface eccentricity as shown in Tables 9A and 9B occurs in the optical deflector assembled with the 6-sided polygon mirror of FIG. 7B. This example shows a case in which a polygon mirror with a single machining accuracy is tilted and the machining accuracy varies with both eccentricity and eccentricity is attached to a drive motor. The amount is shown in Table 9A.

  In the scanning optical system in Table 9A, when an optical deflector with surface decentering Po = 0.033 mm or surface tilt εo = 1.6 ′ is assembled, pitch unevenness (amount of fluctuation in irradiation position when the deflector makes one rotation) ) Has an imaging performance of 5 μm. In addition, surface tilt (1) in the table is a manufacturing variation of the scanning optical system, and it is assumed that the focal length of the fθ lens in the sub-scanning direction is shorter than the design value, and surface tilt (2) is a manufacturing variation of the scanning optical system. It is assumed that the focal length of the fθ lens in the sub-scanning direction is longer than the design value. Total (1) is the sum of pitch unevenness due to surface tilt (1) and pitch unevenness due to surface eccentricity. Total (2) is the sum of pitch unevenness due to surface tilt (2) and pitch unevenness due to surface eccentricity.

  According to Table 9A, the pitch unevenness caused by the surface tilt causes the maximum pitch unevenness on the first surface, and the pitch unevenness caused by the surface eccentricity causes the maximum pitch unevenness on the second surface. As a result, the total pitch unevenness of the scanning optical system takes the maximum and minimum values on the first surface and the third to sixth surfaces when the focal length of the fθ lens in the sub-scanning direction is shorter than the design value (total (1)). Further, when the focal length of the fθ lens in the sub-scanning direction is longer than the design value (total (2)), the pitch unevenness due to the surface tilt factor and the pitch unevenness due to the surface eccentricity are the maximum and minimum values on the first surface and the second surface. In the worst case, 7.42 μm pitch unevenness occurs.

  Next, when this optical deflector is measured by the measurement optical system (inspection apparatus) shown in Table 8, the vibration of the light beam on the V slit 7 is shown in Table 9B. As described above, when the optical deflector with the surface eccentricity Po = 0.033 mm or the surface tilt εo = 1.6 ′ is assembled, the measurement optical system changes the irradiation position on the V slit 7 (the deflector rotates once). The imaging performance is 45.23 μm. Further, the surface tilt (1) in the table is the detection result of the first measurement optical system, and the surface tilt (2) is the detection result of the second measurement optical system.

  According to Table 9B, the second measurement optical system dZ ≧ 45.23 μm, which exceeds the detection criterion. Therefore, this test deflector is determined to be defective.

  Next, the relative position of the polygon mirror 51 and the motor 54 is adjusted. A clearance is provided between the fitting hole 53 of the polygon mirror and the rotating shaft 55 of the motor 54, and eccentricity adjustment and surface tilt adjustment can be performed by an adjustment mechanism. The adjustment may be left in the measuring device or may be removed and performed on another tool. Specifically, a 16 μm shift adjustment is performed in the Y direction in FIG. 7B, and then a propeller adjustment of 0.8 ′ around the Y axis is performed. For easy adjustment, the polygon mirror may be held with a holder and finely moved. After this adjustment, the results of measurement with the measurement optical system (inspection apparatus) in Table 8 are shown in Table 9C. The measurement results of the first measurement optical system and the second measurement optical system are both dZ ≦ 45.23 μm, which satisfies the above detection criterion. Therefore, this test deflector is determined as a non-defective product.

  Table 9D shows the occurrence of pitch unevenness when the optical deflector 5 determined to be non-defective is assembled in the scanning optical system.

  According to Table 9D, it can be understood that the pitch unevenness was 5 μm or less in the scanning optical system, and improvement was achieved. As described above, the optical deflector is inspected by using the measuring device at a stage prior to the step of assembling the scanning optical system, and the defective optical deflector finely adjusts the positional relationship between the polygon mirror 51 and the motor by the adjusting mechanism. I do. By assembling only the optical deflector that is determined to be a non-defective product through this adjustment process, the pitch unevenness of the scanning optical system can be improved.

  In the measuring method using the measuring apparatus shown in FIG. 8 and FIG. 9, the light deflection is performed by the adjusting mechanism so that the fluctuation amount of the irradiation position of the light beam by the detecting means in the two measuring optical systems is equal to or smaller than the specific value. The relative position of the rotation center of the instrument and the deflection surface of the rotary polygon mirror is adjusted.

  10 and 11 are schematic views of Embodiment 4 of the present invention. 10 and 11 show an apparatus for measuring surface eccentricity and surface tilt of an optical deflector.

  FIG. 10 is a perspective view of a measurement optical system that has two measurement optical systems of the embodiment of FIGS. 1 to 3 and is used for surface eccentricity measurement and surface tilt measurement. FIG. 11 shows an apparatus for analyzing measurement signals obtained from the two measurement optical systems in FIG.

  In the first measurement optical system of FIG. 10, the laser diffused light emitted from the semiconductor laser 11 is collimated by a collimator lens 12 and a laser beam formed by a circular diaphragm 13 disposed thereafter is taken out. Thereafter, the light is condensed only in the sub-scanning direction of the polygon mirror by the cylindrical lens 14 </ b> A and is incident on the deflection surface 52 of the polygon mirror 51. At this time, a line image is formed at a position where the deflection surface 52 of the polygon mirror 51 does not coincide. The light beam reflected by the deflecting surface 52 enters the second cylindrical lens 14B while being slightly diverged in the sub-scanning direction. Since the front focal point of the cylindrical lens 14B is arranged so as to coincide with the position of the line image (that is, the front focal point does not coincide with the deflection surface 52), the reflected light is returned to parallel light. Thereafter, since the parallel light is imaged at the rear focal position of the jig lens 16, the V slit 17 is disposed at this imaging position.

  In the second measurement optical system of FIG. 10, the laser diffused light emitted from the semiconductor laser 21 is collimated by a collimator lens 22 and a laser beam shaped by a circular diaphragm 23 disposed thereafter is taken out. Thereafter, the light is condensed only in the sub-scanning direction of the polygon mirror by the cylindrical lens 24 </ b> A and enters the deflection surface 52 of the polygon mirror 51. At this time, a line image is formed at a position where the deflection surface 52 of the polygon mirror 51 does not coincide. The light beam reflected by the deflecting surface 52 is incident on the second cylindrical lens 24B while slightly diverging in the sub-scanning direction. Since the front focal point of the cylindrical lens 24B is arranged to coincide with the position of the line image (that is, the front focal point does not coincide with the deflecting surface 52), the reflected light is returned to parallel light. After that, since the parallel light is imaged at the rear focal position of the jig lens 26, the V slit 27 is arranged at this imaging position.

  The beams that have passed through the V slits 17 and 27 are received by the photodiodes 18 and 28, and the amount of light is monitored. The monitored light quantity is transferred as an electrical signal to an analysis device 9 as an electrical signal processing means for analysis.

  The motor 54 has a rotation shaft 55 and is fitted in the fitting hole 53 of the polygon mirror 51. The optical deflector 5 is constituted by the motor 54 and the polygon mirror 51. A rotation center 56 of the rotation shaft 55 is used.

  In the first measurement optical system, the semiconductor laser 11 to the cylindrical lens 14A constitute an incident optical system, the cylindrical lens 14B and the jig lens 16 constitute a detection optical system, and the V slit 17 and the photodiode 18 serve as detection means. Constitute. Detection means is provided at an image forming point of the detection optical system. A measurement optical system is constituted by the incident optical system, the detection optical system, and the detection means. Further, the measuring device is constituted by an analysis device 9 as a holding means (not shown) for holding the measurement optical system and an electric signal processing means for processing an electric signal from the detecting means.

  In the second measurement optical system, the semiconductor laser 21 to the cylindrical lens 24A constitute an incident optical system, the cylindrical lens 24B and the jig lens 26 constitute a detection optical system, and the V slit 27 and the photodiode 28 serve as detection means. Constitute. Detection means is provided at an image forming point of the detection optical system. A measurement optical system is constituted by the incident optical system, the detection optical system, and the detection means. Further, the measuring device is constituted by an analysis device 9 as a holding means (not shown) for holding the measurement optical system and an electric signal processing means for processing an electric signal from the detecting means.

  As shown in FIG. 10, a plane perpendicular to the rotation shaft 55 is defined as a horizontal reference plane. The incident optical system (semiconductor laser to cylindrical lens) is incident at a specific incident angle θi with respect to the reference plane. This θi may be the same position in the first measurement optical system and the second measurement optical system, or may be a different value.

  Further, the first measurement optical system is incident at an incident angle α1 and the second measurement optical system is incident at an incident angle α2 with respect to a vertical reference plane including the rotation center 56 of the rotation shaft 55 (XZ plane in FIG. 1). I am letting. Ideally, α1 = −α2 is desirable, but this is not necessarily the case.

  The arrangement of the first and second measurement optical systems in FIG. 10 will be described as follows with reference to FIG. For example, the first measurement optical system is incident at an angle α1 from the front side with respect to the paper surface of FIG. The second measurement optical system is made incident at an angle α2 from the rear side with respect to the paper surface of FIG. 1 (the sign is negative because it is the rear side with respect to the paper surface).

  Further, the detection optical system (cylindrical lens and jig lens) is also arranged at a specific reflection angle θo with respect to the reference surface as in FIG. The incident angles α1 and α2 and the reflection angle θo are desirably set so that the absolute values are equal and the directions are different.

  In both the first measurement optical system and the second measurement optical system, a light beam is incident on the same deflecting surface 52 and simultaneously detected.

  As described above, in the fourth embodiment, the two measurement optical systems cause the light beam to enter the same deflection surface of the rotary polygon mirror, and the detection unit detects the amount of variation in the irradiation position of the light beam.

  Numerical examples in the present embodiment are the same as those in Table 8. The difference is that the measuring device is opposed to the deflector so that the light beam is incident on different deflecting surfaces, and symmetrical with respect to the sub-scanning reference surface so that the light beams enter the same deflecting surface. It is arranged. Therefore, the surface distance measured along the optical axis, the positional relationship between the focal lines, and the detected irradiation position fluctuation amount are the same.

  As described above, according to each embodiment, it is possible to simultaneously measure the surface eccentricity accuracy and surface tilt accuracy of an arbitrary deflection surface of the optical deflector. Further, it is possible to evaluate the deviation (pitch unevenness) in the height of the irradiation position of the scanning beam caused by surface decentering and surface tilt when the optical deflector that has been inspected and measured is assembled in a scanning optical device, on the same scale. . Further, when adjusting either or both of the surface eccentricity and the surface tilt, it is not necessary to require a more precise adjustment than before. Alternatively, it is possible to adjust pitch unevenness with higher accuracy than before.

  Furthermore, it is possible to measure the surface eccentricity and surface tilt of the deflecting surface while rotating the optical deflector at a high speed.

  In the scanning optical system of the present invention, the optical deflector used in the scanning optical system that scans the surface to be scanned using the optical deflector provided with the rotary polygon mirror having a plurality of deflecting surfaces. The method of adjusting the position of and setting to a specific position is as follows.

  A surface decentering measurement optical system that measures a surface decentering amount that is a difference in distance between each deflecting surface 52 of the rotating polygon mirror 51 and the rotation center 56 of the optical deflector 5, and a rotation center of each deflecting surface 52 of the rotating polygon mirror 51. The surface tilt measuring optical system for measuring the surface tilt amount which is a difference in angle with respect to 56 is used. The surface eccentricity measuring optical system and the surface tilt measuring optical system simultaneously detect the surface eccentricity and surface tilt amount of any deflection surface, and the deflection surface having the largest surface eccentricity and the deflection surface having the largest surface tilt amount are different. Thus, the optical deflector 5 is adjusted.

Layout of Example 2 of the present invention Optical path diagram of Example 2 of the present invention Optical path diagram of Example 2 of the present invention The figure explaining generation | occurrence | production of the pitch nonuniformity by the surface eccentricity of Example 2 of this invention. The figure explaining generation | occurrence | production of the pitch nonuniformity by the surface inclining of Example 2 of this invention. The figure which shows the tolerance | permissible_range of the surface eccentricity and surface inclination of Example 2 of this invention The figure explaining the polygon mirror of Example 2 of this invention The figure explaining the polygon mirror of Example 2 of this invention The figure explaining the polygon mirror of Example 2 of this invention Layout of Example 3 of the present invention Conceptual diagram of the detection device of Example 3 of the present invention Layout of Example 4 of the present invention Conceptual diagram of the detection device of Example 4 of the present invention Schematic diagram of main parts of a conventional optical scanning device Schematic diagram of main parts of optical deflector Schematic diagram of the main part of the first embodiment of the scanning optical system of the present invention

Explanation of symbols

1,11,21 laser light source
2,12,22 Collimator lens
3,13,23 aperture
4,14,24 Cylindrical lens
5 Optical deflector
6, 16, 26 jig lens
7,17,27 V slit
8,18,28 Light receiving sensor

Claims (23)

A light source means, an optical deflector having a rotating polygon mirror that deflects and scans the light beam emitted from the light source means, an incident optical system that guides the light beam emitted from the light source means to the rotating polygon mirror,
A scanning optical system comprising: an imaging optical system that forms an image of a light beam deflected and scanned by a deflection surface of the rotary polygon mirror on a surface to be scanned;
The light beam incident on the deflecting surface of the rotary polygon mirror is incident at a finite angle with respect to a plane perpendicular to the rotation center of the rotary polygon mirror in the sub-scan section.
The optical deflector has a deflection surface that maximizes the amount of fluctuation in the irradiation position of the light beam generated on the scanned surface due to surface eccentricity that is a difference in distance from each deflection surface of the rotary polygon mirror to the rotation center,
The rotating polygon mirror is arranged so as to be different from the deflection surface where the variation amount of the irradiation position of the light beam generated on the surface to be scanned is maximized due to the surface tilt which is a difference in angle with respect to the rotation center of each deflection surface. A characteristic scanning optical system. The rotating shaft of the optical deflector and the rotary polygon mirror have an adjustment mechanism that can adjust the position relatively,
The optical deflector includes a deflection surface that maximizes the deviation of the irradiation position of the light beam on the surface to be scanned, which is caused by surface eccentricity that is a difference in distance between each deflection surface of the rotary polygon mirror and the rotation center of the optical deflector. ,
The rotating polygon mirror is mounted so as to be adjusted to be different from the deflecting surface where the deviation of the irradiation position of the light beam on the surface to be scanned caused by the surface tilt which is a difference in angle with respect to the rotation center of the deflecting surface of the rotating polygon mirror is different. The scanning optical system according to claim 1. A surface decentering amount that is a difference in distance between each deflecting surface and the rotation center of the optical deflector of the optical deflector including the rotating polygon mirror having a plurality of deflecting surfaces, and a rotation center of each deflecting surface of the rotating polygon mirror A measuring device for measuring the amount of surface tilt that is the difference in angle with respect to
An incident optical system for guiding a light beam to the deflection surface of the rotary polygon mirror;
A detection optical system that forms an image of the light beam reflected by the deflecting surface on the imaging surface;
Detecting means for detecting information on the irradiation position of the light beam incident on the imaging surface of the detection optical system;
Comprising at least one measuring optical system for detecting, by the detecting means, the amount of fluctuation of the irradiation position on the imaging plane of the light beam sequentially reflected by each deflecting surface by rotating the rotary polygon mirror;
One of the measurement optical systems is configured such that the incident optical system is connected to the optical deflector within the sub-scan section formed by the rotation center of the optical deflector and the normal line of the deflection surface of the rotary polygon mirror. It is arranged at a finite angle with respect to a plane perpendicular to the center of rotation, and the light beam is incident on the deflecting surface of the rotary polygon mirror so as to form a line image parallel to the plane.
The detection optical system forms the line image on the imaging plane,
A measuring apparatus, wherein the position of the line image and the position of the deflection surface of the rotary polygon mirror are set to be inconsistent. dX is the distance between the position of the line image and the position of the deflection surface of the rotary polygon mirror,
Po is the allowable amount of surface eccentricity of the deflection surface,
θ is a finite angle with respect to the plane in the sub-scan section of the incident optical system,
εo is the allowable amount of surface tilt of the deflection surface,
When β is a lateral magnification in the sub-scan section of the detection optical system,
0.8 ≦ | (dX / (2 × Po × sinθ / (β × tan (2 × εo / β)))) | ≦ 1.2
The measurement apparatus according to claim 3, wherein the following condition is satisfied. The incident optical system includes a first optical element that converts the light beam from the light source means into parallel light in the sub-scanning section, and a first anamorphic optical element that forms parallel light into a line image in the sub-scanning section. Have
The detection optical system includes a second anamorphic optical element that converts the line image into parallel light in a sub-scan section and a second optical element that forms parallel light in the sub-scan section. The measuring apparatus according to claim 3.   The measurement apparatus according to claim 5, wherein the first anamorphic optical element is provided so as to be movable in the optical axis direction in conjunction with the second anamorphic optical element.   The distance dX has calculation means for calculating a surface eccentricity amount and a surface tilt amount of the deflection surface from a variation amount of the irradiation position of the light beam detected by the detection means at two different distance dX values. The measuring apparatus according to claim 4.   An adjustment mechanism is provided for adjusting a relative position between a rotation center of the optical deflector and the rotary polygon mirror so that a fluctuation amount of a light beam irradiation position on the imaging surface is a specific value or less. Item 4. The measuring device according to Item 3.   There are two measurement optical systems, and the position of the line image in the first measurement optical system and the position of the line image in the second measurement optical system are opposite to the position of the deflection surface of the rotary polygon mirror. The measuring device according to claim 3, wherein the measuring device is located. The distance between the position of the line image in the first measurement optical system and the position of the deflection surface of the optical deflector is dX1,
When the distance between the position of the line image in the second measurement optical system and the position of the deflection surface of the optical deflector is dX2,
−1.2 ≦ dX1 / dX2 ≦ −0.8
The measurement apparatus according to claim 9, wherein the following condition is satisfied.   11. The two measurement optical systems make a light beam incident on the same deflecting surface of the rotary polygon mirror, and detect the variation amount of the irradiation position of the light beam by the detecting means. The measuring device described in 1.   11. The two measuring optical systems respectively cause a light beam to be incident on different deflection surfaces of the rotary polygon mirror, and the amount of fluctuation of the irradiation position of the light beam is detected by the detection means. The measuring device described in 1.   13. The apparatus according to claim 9, further comprising an arithmetic unit that converts a variation amount of a light beam irradiation position at the detection unit in the two measurement optical systems into a surface eccentric amount and a surface tilt amount of the deflecting surface. The measuring device according to any one of the above.   The relative position of the rotation center of the optical deflector and the deflection surface of the rotary polygon mirror is set so that the amount of fluctuation of the irradiation position of the light beam at the detection means in the two measurement optical systems is less than or equal to a specific value. The measuring apparatus according to claim 9, further comprising an adjusting mechanism for adjusting. A surface decentering amount that is a difference in distance between each deflecting surface and the rotation center of the optical deflector of the optical deflector including the rotating polygon mirror having a plurality of deflecting surfaces, and a rotation center of each deflecting surface of the rotating polygon mirror A method of measuring the amount of surface tilt that is the difference in angle with respect to
In a sub-scan section formed by the rotation center of the optical deflector and the normal line of the deflection surface of the rotary polygon mirror, the light beam has a finite angle with respect to a plane perpendicular to the rotation center of the optical deflector. An incident optical system that guides the light beam to the deflection surface of the rotary polygon mirror and forms the light beam as a line image at a position that does not coincide with the deflection surface of the rotary polygon mirror, and the line image reflected by the deflection surface. Using a measurement optical system having a detection optical system that forms an image on an image formation surface and a detection unit that detects an irradiation position of a light beam formed on the image formation surface,
By rotating the rotary polygon mirror, light beams from the incident optical system are sequentially irradiated to the respective deflection surfaces, reflected by the respective deflection surfaces, and the amount of variation in the irradiation position of the light beams formed on the imaging surface is detected. A measuring method characterized in that a surface eccentric amount and a surface tilt amount of each deflecting surface are obtained by using a signal obtained by the detecting means at this time. dX is the distance between the position of the line image and the position of the deflection surface of the rotary polygon mirror,
Po is the allowable amount of surface eccentricity of the deflection surface,
θ is a finite angle with respect to a reference plane in the sub-scan section of the incident optical system,
εo is the allowable amount of surface tilt of the deflection surface,
When β is a lateral magnification in the sub-scan section of the detection optical system,
0.8 ≦ | (dX / (2 × Po × sinθ / (β × tan (2 × εo / β)))) | ≦ 1.2
The measurement method according to claim 15, wherein the following condition is satisfied.   The measurement according to claim 15, wherein when the line image is formed at at least two different positions with respect to the deflection surface of the rotary polygon mirror, a surface eccentricity amount and a surface tilt amount of the deflection surface are obtained. Method.   There are two measurement optical systems, and the position of the line image in the first measurement optical system and the position of the line image in the second measurement optical system are opposite to the position of the deflection surface of the rotary polygon mirror. The measurement method according to claim 15, wherein the measurement is performed so as to be positioned.   19. The two measurement optical systems make a light beam incident on the same deflecting surface of the rotary polygon mirror, and detect a variation amount of an irradiation position of the light beam by the detecting unit. Measuring method.   19. The two measurement optical systems each cause a light beam to be incident on different deflection surfaces of the rotary polygon mirror, and the amount of variation in the irradiation position of the light beam is detected by the detection unit. Measuring method.   21. The method according to any one of claims 18 to 20, wherein the amount of fluctuation of the irradiation position of the light beam at the detection means of the two measurement optical systems is converted into a surface eccentricity amount and a surface tilt amount of each deflection surface by a calculation means. The measuring method according to item.   In an adjustment mechanism, the rotation center of the optical deflector and the deflection surface of the rotary polygon mirror are relative to each other so that the fluctuation amount of the irradiation position of the light beam at the detection means in the two measurement optical systems is less than or equal to a specific value. The measurement method according to any one of claims 18 to 21, wherein the position is adjusted. In an optical deflector used in a scanning optical system that scans a surface to be scanned using a light deflector including a rotary polygon mirror having a plurality of deflection surfaces with a light beam from an incident optical system,
A surface decentering measurement optical system for measuring a surface decentering amount that is a difference in distance between each deflection surface of the rotary polygon mirror and the rotation center of the optical deflector;
A surface tilt measuring optical system for measuring a surface tilt amount that is a difference in angle with respect to the rotation center of each deflection surface of the rotary polygon mirror;
The surface eccentricity measurement optical system and the surface tilt measurement optical system simultaneously detect the surface eccentricity and surface tilt amount of any deflection surface, and the deflection surface with the largest surface eccentricity amount and the deflection surface with the largest surface tilt amount are different. And adjusting the optical deflector.