JP2005189094A - Scanning optical device inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scanning optical device inspection apparatus which extends an inspection area in a scanning optical device to be inspected without decreasing detection accuracy for an optical defect. <P>SOLUTION: A laser beam emitted from a light source device 10 as a collimated light beam forms a line image on a diffraction branch element 20 through a cylindrical lens 11 and branches into three light beams to form a line image again on a reflection surface 13b of a polygon mirror 13 through a relay lens 12. The three light beams are reflected by the polygon mirror 13 and pass through the scanning optical device to be inspected at different heights in a sub scanning direction to form spots on a surface to be scanned spaced apart in a main scanning direction. While rotating the polygon mirror 13, a sensor section 15a of an inspection apparatus 15 is moved in the main scanning direction to detect a peak amount of light of each light beam for each position in the main scanning direction. It is then determined that there is an optical defect in a position where the peak amount of light extremely decreases. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a scanning optical element inspection apparatus for inspecting a scanning optical element included in a scanning optical apparatus used in a drawing apparatus such as a laser printer.

  This type of scanning optical device is used by being incorporated in a drawing device such as a laser printer or a digital copier, and the laser beam emitted from the light source device is successively applied by each reflecting surface of a polygon mirror that rotates at a constant speed. And having a basic configuration in which it is deflected within a certain angle range and focused as a spot to be scanned on the surface to be scanned by a scanning optical element (fθ lens) having fθ characteristics. Further, the surface tilt error caused by the rotation axis of the polygon mirror and the inclination of each reflecting surface, that is, the focusing position in the sub-scanning direction (direction perpendicular to the main scanning direction in which the spot is scanned) on the surface to be scanned. In order to cancel the deviation, the laser beam emitted as parallel light from the light source device is transmitted through the cylindrical lens, and once converged in the vicinity of the reflection surface of the polygon mirror in the sub-scanning direction, a line image is formed, and anamorphic A so-called surface tilt error in which the spot is always focused at the same height position in the sub-scanning direction on the scanned surface by conjugating the line image near the reflecting surface and the scanned surface through the configured scanning optical element. A scanning optical device having a correction function is also generally used.

  The scanning optical element used in such a scanning optical apparatus is a lens that is long in the main scanning direction, and the beam diameter of the laser beam incident is extremely small compared to the lens diameter. In many cases, the laser beam passes through only a small part of the scanning optical element. Therefore, if optical defects such as dust, scratches, and refractive index abnormality are present in each lens surface or inside of the scanning optical element in a part in the main scanning direction, the laser beam being scanned will Only at the moment of passing the target defect, the spot state on the surface to be scanned becomes abnormal (for example, the light amount is reduced, the spot diameter is enlarged or reduced, and the spot position is shifted). As a result, streak noise extending in the sub-scanning direction from a position corresponding to the optical defect in the main scanning direction is formed on the surface to be scanned moving in the sub-scanning direction.

  In order to avoid such deterioration in print quality, the scanning optical element incorporated in the scanning optical device must be inspected before the scanning optical device is completed. For this purpose, a conventional inspection technique is to perform a sensory inspection of a scanning optical element before being incorporated in a scanning optical device by human eyes. Further, for defects such as striae and distortion that may occur in plastic injection-molded lenses, a method of visualizing these defects with a strain gauge and performing a result by human visual observation has been adopted. Further, a technique of extracting optical defects by performing predetermined image processing on image data obtained by photographing a scanning optical element instead of human visual observation has been used.

  However, all of the optical defects present in the scanning optical element do not cause the print quality degradation described above. That is, when the scanning optical element is incorporated in the scanning optical apparatus and the laser light beam is actually scanned, only the optical defect existing in the region through which the laser light beam is transmitted causes the above-described print quality degradation. Nevertheless, according to the above-described method, optical defects that cause print quality degradation cannot be identified and inspected, so there is no problem with the print quality of the scanning optical device as a product. Do not overlook optical defects that can cause poor yields (thus increasing manufacturing costs) or cause problems with the printing quality of scanning optical devices due to being judged as defective. I couldn't. Furthermore, in the case of a method including a human visual process, it is unavoidable that the detection result is affected by a change in the judgment standard of the examiner or a judgment error due to the physical condition.

In view of this, there has been proposed an inspection apparatus that includes the entire configuration of the scanning optical device other than the scanning optical element and includes light receiving means that slides in the main scanning direction along the surface where the surface to be scanned should exist (Patent Document) 1). In order to inspect the scanning optical element using this inspection apparatus, the inspection target scanning optical element is arranged at a predetermined position in the inspection apparatus (the same position as when the inspection target optical element is incorporated in the scanning optical apparatus). In this state, the laser beam is scanned by actually rotating the polygon mirror, and the light amount of the spot formed after passing through the scanning optical element to be inspected is measured by this light receiving means at each position in the main scanning direction. is there. Then, the measurement result by the light receiving means shows the print quality itself by the scanning optical device that actually incorporates the scanning optical element to be inspected, so that there is no problem in the printing quality of the scanning optical device. It is possible to obtain inspection results that eliminate the influence of defects.
Japanese Patent Laid-Open No. 10-332534

  According to the inspection apparatus described above, only the region through which the laser beam passes through the scanning optical element is inspected as an inspection target region (only optical defects existing in this region are detected).

  However, once the inspection optical scanning element has been removed from the inspection apparatus, it is assembled again as a product in the scanning optical apparatus. Therefore, due to the mechanical error inherent in the scanning optical device and the assembling error when assembling the scanning optical element, the position where the laser beam is actually transmitted deviates from the inspection target area in the sub-scanning direction. May end up.

  This problem will be schematically described with reference to FIG. In FIG. 12, the solid line indicates the lens surface of the inspection target scanning optical element, the broken line indicates the inspection target region, and D indicates an optical defect (for example, a foreign object). As described above, if the optical defect D exists only outside the inspection target region, it is determined that the inspection target scanning optical element is a non-defective product. However, when this inspection target scanning optical element is incorporated into the scanning optical device, If there is any error, the actual transmission position of the laser beam may be shifted from the inspection target region in the sub-scanning direction and overlap the optical defect D. In this way, when the actual transmission position of the laser beam overlaps with the optical defect D, the scanning optical element product incorporating the scanning optical element, although the scanning optical element is determined to be non-defective As a result, the print quality will deteriorate.

  In order to cope with such a shift in the transmission position, the width of the inspection target area in the inspection target scanning optical element may be expanded in the sub-scanning direction to some extent in advance on the inspection apparatus. One possible method for this is to increase the width of the transmission region of the laser beam with respect to the scanning optical element to be inspected by expanding the beam diameter of the laser beam emitted from the light source device. If this method is adopted, as shown in FIG. 13, the width of the region to be inspected is widened. Therefore, when incorporated in the scanning optical apparatus, an optical error D that can overlap with the transmission position of the laser beam due to various errors is generated. Can also be included in the region to be inspected.

  However, if the beam diameter of the laser beam incident on the optical element to be inspected is enlarged, the ratio of the beam diameter to the size of the smallest optical defect that can affect the print quality increases. If this ratio increases, even if the laser beam hits such an optical defect, the ratio of the amount of light blocked by the optical defect to the entire laser beam (that is, the reduction rate of the light amount). Will become smaller. Therefore, there arises a problem that it becomes difficult to detect a change in the amount of light received by the light receiving means (that is, the detection sensitivity to an optical defect is lowered).

  Therefore, the present invention can widen the width of the inspection target region in the inspection target scanning optical element in the sub-scanning direction without reducing the detection sensitivity to the optical defect with a simple configuration. Providing a scanning optical element inspection apparatus capable of obtaining an inspection result corresponding to the print quality as a product of a scanning optical apparatus incorporating a scanning optical element to be inspected regardless of whether there is a mechanical error or an assembly error with respect to the scanning optical apparatus. Is an issue.

  The scanning optical element inspection apparatus according to the present invention devised to solve such a problem eliminates optical defects in a scanning optical element that converges dynamically deflected laser light on a predetermined surface to be scanned. An apparatus for inspecting a laser light source that emits a laser beam, an anamorphic lens that converges the laser beam emitted from the laser light source in the sub-scanning direction to form a line image, and a line formed by the anamorphic lens A diffraction branch element that is arranged at the position of the image and divides the laser beam into a plurality of beams in the sub-scanning direction; a relay lens that converges the plurality of laser beams branched by the diffraction branch element again as a line image; and A deflection unit that positions a deflection point at the position of the line image to be formed and dynamically deflects a plurality of laser beams along the main scanning direction; Same as the surface to be scanned with respect to the scanning optical element held by the deflecting means and the scanning optical element held at the predetermined position on the optical path of the laser beam dynamically deflected by the deflecting means Detecting means for measuring the state of the laser light beam converged by the scanning optical element held by the holder while moving in the main scanning direction on the surface assumed to be in a relative positional relationship; It is characterized by.

  If comprised in this way, it will become possible to test | inspect simultaneously the several position from which the height of the scanning optical element which is a test object differs in the subscanning direction with the some laser beam branched by the diffraction branching element. As described above, by dividing the laser beam into a plurality of parts, the inspection target region in the scanning optical element can be expanded in the sub-scanning direction without increasing the beam diameter of the laser beam transmitted through the scanning optical element.

  The relay lens is preferably composed of a first lens group and a second lens group. In that case, the front focal point of the first lens unit is matched with the position of the diffraction branch element, the rear focal point of the first lens unit is matched with the front focal point of the second lens unit, and the rear focal point of the second lens unit is deflected. It is desirable to arrange so as to coincide with the deflection point of the means.

  Further, it is desirable that the diffraction branch element is arranged so that the grating vector is inclined with respect to both the main scanning direction and the sub-scanning direction.

Further, when the wavelength of the laser light source is λ, the width of the light beam incident on the anamorphic lens is Dz, and the distance from the rear principal point of the anamorphic lens to the line image position is f _CL , the following condition (1 ) Is desirable.

Dz / f _CL > (λ / p) sinγ> Dz / 2f _CL (1)
Where p: pitch of the periodic structure of the diffraction element,
γ: angle with respect to the main scanning direction in the direction of the lattice vector.

  As the diffraction branching element, a phase type diffraction element in which a large number of non-linearly changing reference phase patterns are formed in parallel at an equal pitch, and incident light is diffracted and branched into a plurality of light beams of equal light quantity can be used.

  According to the scanning optical element inspection apparatus of the present invention, the width of the inspection target area in the inspection target scanning optical element can be increased without lowering the detection sensitivity for the optical defect. Regardless of whether there is an assembly error with respect to the optical device, an inspection result corresponding to the print quality as a product of the scanning optical device incorporating the inspection target scanning optical element can be obtained.

  Hereinafter, embodiments for carrying out the scanning optical element inspection apparatus according to the present invention will be described. FIG. 1 is a perspective view showing a configuration of a scanning optical element inspection apparatus (hereinafter simply referred to as “inspection apparatus”) 1 according to the present embodiment. FIG. 2 is an optical configuration diagram in the main scanning direction. These are optical configuration diagrams in the sub-scanning direction.

  This inspection apparatus 1 is intended to inspect a scanning optical element having a specific shape that is incorporated and used in a specific scanning optical apparatus. Specifically, as shown in FIGS. 1 to 3, the inspection apparatus 1 includes a light source device 10, a cylindrical lens 11, a diffraction branch element 20, a relay lens 12, and a polygon mirror along the traveling direction of the laser beam. 13, a scanning optical element holder 14 that holds an inspection target scanning optical element (fθ lens) L, and a detection device 15.

  The light source device 10 is a device that emits laser light as parallel light, and is configured by a gas laser device such as an argon laser, or a combination of a semiconductor laser and a collimator lens. Between the light source device 10 and the cylindrical lens 11, as shown in FIG. 2, opening means 10a for limiting the beam width of the laser beam which is a parallel beam is arranged. The opening shape of the opening means 10a is a rectangle that is long in the main scanning direction (direction parallel to the paper surface of FIG. 2) and short in the sub-scanning direction (direction orthogonal to the paper surface of FIG. 2). It may be oval or oval having a major axis in the main scanning direction.

  The cylindrical lens 11 is an anamorphic lens that converges a laser beam emitted from the light source device 10 as parallel light in the sub-scanning direction to form a line image. A diffraction branch element 20 is arranged at the position of the line image formed by the cylindrical lens 11. Although details of the diffraction branch element 20 will be described later, it has an action of branching the laser light in both the main scanning direction and the sub-scanning direction. In this example, the laser beam is branched into three.

  The relay lens 12 includes a first lens group 12a and a second lens group 12b each composed of a positive single lens, and has a function of conjugating the diffraction branch element 20 and the reflecting surface of the polygon mirror 13. In the scanning optical device configured as a product, the reflection surface of the polygon mirror 13 is disposed at the position of the line image formed by the cylindrical lens 11, whereas in the inspection device, the diffraction branch element 20 is disposed at the position of the line image. Therefore, the relay lens 12 is disposed between the diffraction branch element 20 and the polygon mirror 13 so that a line image is formed again on the reflection surface of the polygon mirror 13.

The arrangement of each element from the cylindrical lens 11 to the polygon mirror 13 is as shown in FIG. When the focal length of the cylindrical lens 11 is f _CL , the focal length of the first lens group 12a of the relay lens is f ₁ , and the focal length of the second lens group 12b is f ₂ , the distance between the cylindrical lens 11 and the diffraction branch element 20 Is f _CL , the distance between the diffractive branch element 20 and the first lens group 12 a is f ₁ , the distance between the first lens group 12 a and the second lens group 12 b is f ₁ + f ₂ , the second lens group 12 b and the polygon mirror 13. the distance between the reflecting surface of the f _2. That is, the diffraction branch element 20 is disposed at the focal position of the cylindrical lens 11 in the sub-scanning direction, the front focal point F ₁ of the first lens group 12a is made to coincide with the position of the diffraction branch element 20, and the rear side of the first lens group 12a. The focal point F ₁ ′ is arranged to coincide with the front focal point F ₂ of the second lens group 12 b, and the rear focal point F ₂ ′ of the second lens group 12 b is arranged to coincide with the deflection point of the polygon mirror 13.

  With such an arrangement, the parallel laser beam emitted from the light source device 10 is converged only in the sub-scanning direction by the cylindrical lens 11, is branched into three by the diffraction branch element 20, and enters the relay lens 12 at different angles. The line lens is again formed at the same position on the reflection surface of the polygon mirror 13 by the action of the relay lens 12.

  The polygon mirror 13 as the deflecting means has a flat regular hexagonal prism shape, and six reflecting surfaces are formed on the side surface. A motor (not shown) having a rotational axis connected coaxially to the central axis (symmetrical axis) 13a. 1 and FIG. 2 rotate at high speed in the clockwise direction. The polygon mirror 13 passes through a position where the optical axis of the collimator lens 22 is inside the circumscribed circle and offset from the central axis 13a, and the line image re-formed by the relay lens 12 is in the vicinity of the reflecting surface 13b. Are arranged in a positional relationship existing in As a result, the laser beam transmitted through the relay lens 12 enters the reflecting surface 13b of the polygon mirror 13 and is reflected (deflected). As the polygon mirror 13 rotates, each reflecting surface 13b sequentially enters the optical path of the laser beam and gradually changes its direction, so that the laser beam repeatedly repeats in one direction (that is, the main scanning direction). Scanned. At this time, the three laser beams remain parallel in the main scanning direction, but in the sub scanning direction, once converged on the reflecting surface 13b and then diverge.

  The scanning optical element holder 14 is a jig that detachably holds the inspection target scanning optical element L. The three laser light beams scanned by the polygon mirror 13 are incident on the inspection target scanning optical element L held by the scanning optical element holder 14 at three places having different heights in the sub-scanning direction. Move in the scanning direction. FIG. 11 is an explanatory diagram showing trajectories of three laser light beams that scan the inspection target scanning optical element L by the inspection apparatus 1 according to the embodiment.

  The scanning optical element L to be inspected is an anamorphic lens system for correcting a surface tilt error together with a cylindrical lens (corresponding to the cylindrical lens 11) in the scanning optical device as a product. That is, the inspection target scanning optical element L has a power in which the image-side focal point substantially coincides with the surface to be scanned in the main scanning direction, and the surface to be scanned with the reflecting surface of the polygon mirror 13 in the sub-scanning direction. It has the power to conjugate the surface. Therefore, the three laser beams deflected by the polygon mirror 13 pass through the inspection target scanning optical element L as long as they are not affected by the optical defect of the inspection target optical element L, and are thus incident on the surface to be scanned. Spots are formed at corresponding positions, and these spots move in the main scanning direction along a surface corresponding to the surface to be scanned. The three spots are separated from each other in the main scanning direction and are formed at the same position in the sub scanning direction. In FIG. 1, the trajectories of the three spots moving in this way are indicated by broken lines.

  The detection device 15 as detection means is composed of a sensor unit 15a and a drive unit 15b. The sensor unit 15a is a device that holds the light receiving surface of the light receiving element on the front surface thereof. The drive unit 15b is a device that moves the sensor unit 15a in the main scanning direction. The detection device 15 includes an encoder (not shown) for detecting the position of the light receiving surface of the sensor unit 15a in the main scanning direction.

  At the time of inspection, a laser beam is emitted from the light source device 10 and the polygon mirror 13 is rotated at a high speed, and the sensor unit 15a is moved in the main scanning direction from the start end to the end of the scanning range at a relatively low speed by the drive unit 15b. Thereby, the sensor unit 15a repeatedly receives three laser beams while changing the position in the main scanning direction. Then, the position information in the main scanning direction output from the encoder and the peak light quantity value received by the light receiving element of the sensor unit 15a at that position are input to a processing device (not shown). The three laser beams pass through the same height in the sub-scanning direction of the light receiving surface of the light receiving element, but are separated in the main scanning direction, so that the light receiving element of the sensor unit 15a differs from the three laser beams. Since the light is received at the timing, the processing apparatus can identify the position of the inspection target scanning optical element L through which the received laser light beam has passed.

  The processing device records the position information from the encoder in association with the peak light amount value of each laser beam at that position. If there is no defect in the scanning optical element L to be inspected, the peak light amount value continues smoothly, and if there is an optical defect, the peak light amount value at that position rapidly decreases. Therefore, the presence or absence of an optical defect can be inspected by monitoring the change in the peak light quantity value for each laser beam. In this manner, the optical defect can be detected by detecting the peak light quantity while moving the sensor unit 15a once over the scanning range. In the example of FIG. 11, since there is an optical defect D in the optical path of the laser beam passing through the lower side in the drawing, the peak light quantity value of this laser beam rapidly decreases at the portion corresponding to the optical defect. The processing device uses a threshold value set slightly lower than the peak light amount value when there is no optical defect in the inspection target region for each position in the main scanning direction, and the measured peak light amount value falls below the threshold value. In this case, it is determined that an optical defect exists in the portion in the inspection target area.

  The diffraction branching element 20 used in the above optical system is an element that is formed by arranging a large number of non-linearly changing reference phase patterns in parallel at an equal pitch, and diffracts incident light into a plurality of light beams of equal light quantity. For example, an element described in JP-A-10-332534 can be used. That is, as schematically shown in FIG. 5, the diffraction branch element 20 has a plurality of strip-like reference phase patterns P1, P2,... Extending in the x direction arranged in parallel in the y direction on the substrate B at an equal pitch. It is formed. The substrate B is made of a transparent resin material or glass material including the reference phase pattern.

  Each of the reference phase patterns P1, P2,... Is formed so that the phase difference given within the pitch in the y direction changes nonlinearly, that is, has a multivalued value instead of a binary value. And a smooth continuous shape having no phase gap between the reference phase patterns. By splitting the laser beam with a diffractive branching element instead of a reflection type, even when separating the light beam in the optical path of convergent and divergent light, the optical path length must be matched for all the light beams and the conjugate condition must be satisfied Can do. In addition, by using a diffraction branch element having no phase gap as described above, a plurality of diffracted lights can be generated efficiently.

  Table 1 below shows a numerical configuration of a reference phase pattern used for the three-divided beam splitting element 20 of the embodiment (corresponding to Example 2 of JP-A-10-332534). In this table, one pitch of the reference phase pattern is equally divided into 64 coordinates from 0 to 63 along the y direction in FIG. 5, that is, the parallel direction of the phase pattern, and the relative shape at each coordinate is the position of the light. It is shown as a phase difference (unit: radians). When the actual shape is expressed as a height from the point of coordinate 0, assuming use in the air, assuming that the wavelength used is λ and the refractive index of the element is n, the phase × λ / (2π (n− 1)). FIG. 6 is a graph showing the shape of the reference phase pattern of the light beam splitting element 20 shown in Table 1. The vertical axis represents the phase difference and the horizontal axis represents the coordinates.

以下の表２は、上述の光束分割素子２０の光束分割性能を示す数値であり、入射光の強度を１として、分割された各光束の光量を±１０次の範囲で次数毎に示している。回折効率は、目的とする分割数の回折光の強度和が入射光束の強度に占める割合を示す。なお、表２に示される回折光の強度分布は、図７のグラフに示されている。これらのグラフで、横軸は回折光の次数、縦軸は入射光の強度を１としたときの各次数の回折光の強度を示す。

Table 2 below is a numerical value showing the light beam splitting performance of the light beam splitting element 20 described above. The intensity of the incident light is 1, and the light amount of each split light beam is shown for each order within a range of ± 10th order. . The diffraction efficiency indicates the ratio of the intensity sum of the diffracted light of the target number of divisions to the intensity of the incident light beam. The intensity distribution of the diffracted light shown in Table 2 is shown in the graph of FIG. In these graphs, the horizontal axis represents the order of diffracted light, and the vertical axis represents the intensity of diffracted light of each order when the intensity of incident light is 1.

上記のように構成された回折分岐素子２０は、図８に示すように、入射光に垂直な面内で見たときに、その格子ベクトル(回折による光の分岐方向、角度を示すベクトルであり、基準位相パターンの向きに直交する図５のｙ方向に延びる)が主走査方向に対して角度γをなすように配置されている。したがって、分岐した光束は、図９に示すように副走査方向にも広がりつつ、図１０に示すように主走査方向にも広がる。分岐した光束は、図１０に示すように、主走査方向については平行光であるため、分岐してリレーレンズ１２を介してポリゴンミラー１３に入射する光束は、主走査方向では平行光の状態を保っている。３本の光束は、リレーレンズ１２を介してポリゴンミラー１３に対して同じ位置に入射するため、複数の光束を走査する場合にもポリゴンミラー１３の面のサイズを大きくする必要がない。

As shown in FIG. 8, the diffraction branch element 20 configured as described above is a grating vector (a vector indicating the direction and angle of light branching due to diffraction) when viewed in a plane perpendicular to the incident light. , Extending in the y direction of FIG. 5 orthogonal to the direction of the reference phase pattern) is arranged so as to form an angle γ with respect to the main scanning direction. Therefore, the branched light beam spreads in the sub-scanning direction as shown in FIG. 9 and also in the main scanning direction as shown in FIG. As shown in FIG. 10, since the branched light beam is parallel light in the main scanning direction, the light beam branched and incident on the polygon mirror 13 via the relay lens 12 has a parallel light state in the main scanning direction. I keep it. Since the three light beams enter the polygon mirror 13 at the same position via the relay lens 12, it is not necessary to increase the size of the surface of the polygon mirror 13 when scanning a plurality of light beams.

  By tilting the grating vector with respect to the main scanning direction, the spot can be separated in the main scanning direction on the surface to be scanned as described above, so that a single sensor detects three light beams in a time-sharing manner. Therefore, the configuration of the detection unit 15 is simplified.

  Further, by making the line image formed on the diffraction branch element 20 oblique with respect to the reference phase pattern of the diffraction branch element 20, the number of reference phase patterns where the light beams intersect can be increased. If the direction of the line image coincides with the direction of the reference phase pattern, when the line image is thin, the number of reference phase patterns included in the range of the line image decreases, and the diffraction efficiency decreases. By making the periodic structure oblique to the line image, the number of reference phase patterns intersecting the line image can be increased, and the diffraction efficiency can be increased.

  Further, it is desired that the inspection areas through which the three laser beams pass on the lens surface of the scanning target scanning optical element L are not separated from each other. For this purpose, it is necessary to reduce the branch angle in the sub-scanning direction. By tilting the grating vector of the diffraction branching element 20 with respect to the main scanning direction, the substantial branching angle in the sub-scanning direction can be reduced.

In order to appropriately set the inspection region by the three laser beams, the angle γ of the grating vector with respect to the main scanning direction and the pitch p of the periodic structure (reference phase pattern) of the diffraction branch element 20 determine the wavelength of the laser beam. It is desirable to satisfy the following condition (1), where λ is the width of the light beam incident on the anamorphic lens in the sub-scanning direction is Dz, and the distance from the rear principal point of the anamorphic lens to the line image position is f _CL .

Dz / f _CL > (λ / p) sinγ> Dz / 2f _CL (1)
If the upper limit of the above condition is exceeded, a gap is generated in the region through which a plurality of laser light beams pass, and the inspection is overlooked. On the other hand, below the lower limit, the overlap of the areas through which the plurality of laser beams pass is too large, which is disadvantageous for the enlargement of the inspection area.

  Specifically, the inspection apparatus 1 of the embodiment has the following specifications.

Laser beam wavelength (λ): 780 nm
Aperture size: 3.00mm in the main scanning direction
Sub-scanning direction (Dz) 0.77mm
Focal length (f _CL ) of cylindrical lens 11: 50 mm
Focal length (f ₁ ) of the relay lens first lens group 12a: 50 mm
Focal length (f ₂ ) of the second lens group 12b: 50 mm
Distance from cylindrical lens 11 to diffraction branch element 20: 50 mm
Distance from the diffraction branch element 20 to the first lens group 12a: 50 mm
Distance between the first lens group 12a and the second lens group 12b: 100 mm
Distance from the second lens group 12b to the polygon mirror 13: 50 mm
Pitch of reference phase pattern of diffraction branch element 20 (p): 44.7 μm
Angle between lattice vector and main scanning direction (γ): 45 °
When the reference phase pattern is formed at a pitch of 44.7 μm, the three light beams branched by the diffraction branch element 20 have an angle difference of 1 ° (2 ° as a whole). When the angle γ is 45 °, the angle difference between the main scanning direction and the sub-scanning direction is 0.707 °, and an overlap of 0.175 ° (20%) can be obtained in the sub-scanning direction.

  Further, when the focal length in the main scanning direction of the scanning optical element L to be inspected is 150 mm and the magnification in the sub scanning direction is −2.0 times, in the above design example, Fno in the main scanning direction of the light beam reaching the scanning surface is 50. Fno in the sub-scanning direction is 65. Further, the distance between the spots on the surface to be scanned in the main scanning direction is 1.85 mm.

  The components of the optical system are the same as those in the above embodiment, and when the angle γ of the diffraction branching element 20 with respect to the main scanning direction is changed from 45 ° to 30 °, the branching angle in the sub-scanning corresponding direction is 0.500 °. The branch angle in the scanning-corresponding direction is 0.866 °, and the inspection target scanning optical element L can be inspected with three laser beams while having an overlap of 0.382 ° (43%) in the sub-scanning direction. In this case, the interval between the spots on the surface to be scanned in the main scanning direction is 2.27 mm.

  Table 3 below shows the results of calculating the values of the terms in the above condition (1) for the embodiment in which the angle γ is 45 ° and the modified example of 30 °. In either case, the intermediate term is between the upper limit and the lower limit, and it can be seen that the condition (1) is satisfied.

このように、本実施形態によると、回折分岐素子２０によりレーザー光束を３本に分岐することにより、スポット位置（即ち、検出装置１５のセンサ部１５ａによる受光位置）を副走査方向に変位させることなく、検査対象走査光学素子Ｌに対するレーザー光束の入射位置及び透過位置（即ち、検査対象領域）を副走査方向の高さが異なる複数の領域に設定することができる。その結果、検査対象走査光学素子Ｌへの透過時におけるビーム径はそのままに、全体としての検査対象領域を拡げることができる。また、各レーザー光束は時間差を持ってセンサ部１５ａに入射するため、単一のセンサで検査が可能であり、検出装置１５としては、従来のものをそのまま用いることができるのである。

As described above, according to the present embodiment, the spot position (that is, the light receiving position by the sensor unit 15a of the detection device 15) is displaced in the sub-scanning direction by branching the laser beam into three beams by the diffraction branching element 20. Instead, the incident position and transmission position of the laser beam with respect to the inspection target scanning optical element L (that is, the inspection target area) can be set to a plurality of areas having different heights in the sub-scanning direction. As a result, it is possible to expand the entire inspection target region while maintaining the beam diameter during transmission to the inspection target scanning optical element L. Further, since each laser beam enters the sensor unit 15a with a time difference, the inspection can be performed with a single sensor, and the conventional detection device 15 can be used as it is.

  As described above, according to the present embodiment, since the beam diameter is not enlarged at all, the detection sensitivity does not deteriorate, but the inspection target area is expanded, so that the non-defective scanning optical in which no optical defect is detected by the inspection. If the element L is incorporated in a scanning optical device (not shown) after the inspection is completed, even if there is a mechanical error or an assembly error in the scanning optical device itself, it is caused by the scanning optical element. The print quality does not deteriorate. Even when the inspection target area is enlarged in this way, the enlargement ratio is about three times at maximum, and therefore, it is caused by an error of the scanning optical apparatus itself that can normally occur or an assembly error of the scanning optical element L to the scanning optical apparatus. The presence or absence of an optical defect outside the range in which the laser beam can deviate does not affect the inspection result.

  The optical configuration of the inspection apparatus according to the present embodiment is appropriately changed according to the optical configuration of the scanning optical apparatus in which the inspection target scanning optical element L is incorporated. Further, the sensor unit 15a of the detection device 15 measures the light amount of the laser beam, but may measure the beam diameter of the laser beam. In that case, a determination threshold value corresponding to the measured beam diameter may be set.

The perspective view which shows schematic structure of the scanning optical element inspection apparatus which is embodiment of this invention Optical configuration diagram in main scanning direction of scanning optical element inspection apparatus Optical configuration diagram of scanning optical element inspection apparatus in sub-scanning direction Optical configuration diagram showing details of arrangement from cylindrical lens to polygon mirror of scanning optical element inspection device A perspective view schematically showing the structure of a diffraction branch element Graph showing the phase distribution within one period of the reference phase pattern of the diffraction branch element Graph showing the intensity for each order of the light beam branched by the diffraction branch element Diagram showing the direction of the grating vector of the diffractive branching element when viewed in a plane perpendicular to the incident light Explanatory drawing in the sub-scanning direction showing the optical path of the light beam branched by the diffraction branch element Explanatory drawing in the main scanning direction showing the optical path of the light beam branched by the diffraction branching element The figure which shows the inspection object area | region in the inspection apparatus of embodiment The figure which shows the inspection object area | region in the conventional inspection apparatus The figure which shows the inspection object field at the time of expanding the beam diameter in the conventional inspection device

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light source device 10a Aperture means 11 Cylindrical lens 12 Relay lens 13 Polygon mirror 14 Scanning optical element holder 15 Inspection apparatus 20 Diffraction branch element 21 Semiconductor laser L Scanning target scanning optical element

Claims (5)

A scanning optical element inspection apparatus for inspecting an optical defect of a scanning optical element for converging dynamically deflected laser light on a predetermined surface to be scanned,
A laser light source that emits a laser beam;
An anamorphic lens that forms a line image by converging a laser beam emitted from the laser light source in a sub-scanning direction;
A diffractive branch element that is arranged at the position of a line image formed by this anamorphic lens and divides a laser beam into a plurality of parts in the sub-scanning direction;
A relay lens that converges a plurality of laser light beams branched by the diffraction branching element again as a line image;
A deflection means for locating a deflection point at a position of a line image formed by the relay lens and dynamically deflecting a plurality of laser beams along the main scanning direction;
A holder for holding the scanning optical element at a predetermined position on the optical path of the laser beam dynamically deflected by the deflecting means;
The scanning optical element held by the holder on a surface virtually assumed to have the same relative positional relationship as the scanned surface with respect to the scanning optical element held by the deflection unit and the holder And a detecting means for measuring the state of the laser beam converged by the laser beam while moving in the main scanning direction.   The relay lens includes a first lens group and a second lens group, the front focus of the first lens group is made to coincide with the position of the diffraction branch element, and the rear focus of the first lens group is the first lens group. 2. The scanning optical element inspection apparatus according to claim 1, wherein the front focal point of the two lens groups is made to coincide with the rear focal point of the second lens group to the deflection point of the deflecting means.   The scanning optical element inspection apparatus according to claim 1, wherein the diffraction branching element is arranged such that a grating vector thereof is inclined with respect to both a main scanning direction and a sub-scanning direction. When the wavelength of the laser light source is λ, the width of the light beam incident on the anamorphic lens is Dz, the distance from the rear principal point of the anamorphic lens to the line image position is f _CL , the following conditions ( The scanning optical element inspection apparatus according to claim 3, wherein 1) is satisfied.
Dz / f _CL > (λ / p) sinγ> Dz / 2f _CL (1)
Where p: pitch of the periodic structure of the diffraction branching element,
γ: angle with respect to the main scanning direction in the direction of the lattice vector. The diffractive branch element is a phase type diffractive element that is formed by arranging a large number of non-linearly changing reference phase patterns in parallel at an equal pitch, and diffracts incident light into a plurality of light beams of equal light quantity. The scanning optical element inspection apparatus according to claim 1.

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