WO2019235372A1

WO2019235372A1 - Optical system, and imaging device and imaging system equipped with same

Info

Publication number: WO2019235372A1
Application number: PCT/JP2019/021656
Authority: WO
Inventors: 吉田　博樹; 木村　一己; 工藤　源一郎; ▲寛▼人加納
Original assignee: キヤノン株式会社
Priority date: 2018-06-07
Filing date: 2019-05-31
Publication date: 2019-12-12

Abstract

An optical system 10 comprising a front group 11, a light-shielding member 4 and a rear group 12 which are positioned in this order from the object side to the image side, wherein: the light-shielding member 4 is provided with an opening which is long in a first direction; the front group 11 forms an intermediate image of an object in the opening in a second cross-section perpendicular to the first direction, without forming an image of the object in the opening in a first cross-section parallel to the first direction; the rear group 12 has a diffractive surface 5 for diffracting beams of light which have passed through the opening into a plurality of beams of light which have different wavelengths from one another in the second cross-section, and focuses the plurality of beams of light at different locations in the second cross-section; and the beams of light which are emitted by the front group 11 and are incident on the opening are not parallel in the first cross-section.

Description

Optical system, imaging apparatus and imaging system including the same

The present invention relates to an optical system used in an imaging apparatus that obtains image information by splitting a light beam from an object, and is suitable for inspection and evaluation in industrial fields such as manufacturing, agriculture, and medicine.

Conventionally, there has been known an optical system in which a light beam from a test object (object) is split into a plurality of light beams having different wavelengths, and the light beams are condensed at different positions. Patent Document 1 describes an optical system having cylindrical mirrors disposed on both sides of a slit that is long in one direction and a diffraction grating that splits a light beam from the cylindrical mirror.

US Pat. No. 7,1998,877

However, since the optical system described in Patent Document 1 employs a cylindrical mirror, the light beam incident on the slit and the light beam dispersed by the diffraction grating become parallel light in a cross section including the longitudinal direction of the slit. ing. Therefore, in order to collect the light beam in the cross section, it is necessary to dispose a lens on the image side of the diffraction grating. Furthermore, in order to realize a wide angle of view, it is necessary to arrange more optical elements, and the entire system becomes large.

An object of the present invention is to provide an optical system capable of realizing a wide angle of view while being small, an imaging apparatus including the optical system, and an imaging system.

In order to achieve the above object, an optical system according to one aspect of the present invention is an optical system including a front group, a light shielding member, and a rear group arranged in order from the object side to the image side. A long opening is provided in the first direction, and the front group does not form an object on the opening in the first cross section parallel to the first direction, and the first group extends in the first direction. In the second vertical section, an intermediate image of the object is formed on the opening, and the rear group splits the light beam that has passed through the opening in the second cross section into a plurality of light beams having different wavelengths. The plurality of light beams are condensed at different positions in the second cross section, and the light beams that exit from the front group and enter the aperture are not in the first cross section. An optical system characterized by parallel light.

The principal part schematic in the XY cross section of the optical system which concerns on embodiment. The principal part schematic in the ZX cross section of the optical system which concerns on embodiment. FIG. 3 is a diagram illustrating an MTF of the optical system according to the first embodiment. FIG. 6 is a schematic diagram of a main part of an optical system according to a second embodiment. FIG. 6 is a diagram showing an MTF of an optical system according to Example 2. FIG. 6 is a schematic diagram of a main part of an optical system according to Example 3. FIG. 6 is a diagram showing an MTF of an optical system according to Example 3. FIG. 7 is a schematic diagram of a main part of an optical system according to a fourth embodiment. FIG. 10 is a diagram showing an MTF of an optical system according to Example 4. The principal part schematic of the imaging system as the usage example 1 of the optical system which concerns on embodiment. The principal part schematic of the imaging system as the usage example 2 of the optical system which concerns on embodiment.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Each drawing may be drawn on a different scale for the sake of convenience. Moreover, in each drawing, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted.

In the following description, an XYZ coordinate system is defined as an absolute coordinate system, and an xyz coordinate system is defined as a local coordinate system for each optical surface. In the local coordinate system, the x axis is the normal axis (optical axis) at the apex (origin) of each optical surface, the y axis is parallel to the Y axis and orthogonal to the x axis at the origin, the z axis is the x axis, and It is an axis orthogonal to the y-axis. Further, the Y direction and the y direction are the first direction (reading direction), the Z direction and the z direction are the second direction (spectral direction), the XY cross section and the xy cross section are the first cross section (read cross section), the ZX cross section, and The zx cross section is also referred to as a second cross section (spectral cross section).

FIG. 1 and FIG. 2 are main part schematic views of an optical system 10 according to an embodiment of the present invention, FIG. 1 shows a first cross section, and FIG. 2 shows a second cross section. 1 and 2 show the shape of each member in a cross section including the optical axis. In FIG. 1, each member is shown in the same sheet for convenience. In FIGS. 1 and 2, the diffraction grating on the diffraction surface is omitted for convenience. In the present embodiment, the test object is disposed at a position near Z = 0 on the object plane parallel to the YZ plane, and the light receiving surface 7 of the image sensor is disposed on the image plane of the optical system 10. To do. In addition, it is assumed that the test object is illuminated with white light (light having a plurality of wavelength components) such as sunlight.

The optical system 10 according to this embodiment includes a front group 11, a light shielding member (slit member) 4, and a rear group 12 arranged in order from the object side to the image side. The optical system 10 forms an image of the test object on the light receiving surface (image surface) 7 by collecting a light beam from a test object (not shown) located on the −X side. The front group 11 includes a diaphragm 1, a first reflection surface 2, and a second reflection surface 3. The rear group 12 has a third reflecting surface (diffraction surface) 5 and a fourth reflecting surface 6. Note that a cover glass G is disposed immediately before the light receiving surface 7, but this is treated as not contributing to image formation.

The diaphragm 1 is a member for regulating the width of the light beam from the test object in the second direction, and is arranged so that the opening surface thereof is perpendicular to the X direction. However, the diaphragm 1 may be provided outside the optical system 10. As shown in FIGS. 1 and 2, it is desirable that the light beam entrance (aperture 1) and the light exit (light receiving surface 7) in the optical system 10 be disposed on opposite sides of each optical surface. Thereby, when the optical system 10 is applied to an imaging device, it is possible to easily avoid that the light beam from the test object is blocked by the imaging element, wiring, or the like.

The light shielding member 4 has a long opening (slit) in the first direction. The light shielding member 4 serves as a stop for restricting the width of the light beam in the first direction while restricting the angle of view in the second cross section of the optical system 10 to shield unnecessary light. Note that the width of the opening of the light shielding member 4 is determined according to the required light quantity, resolution, and the like. The width of the opening of the light shielding member 4 in the second direction is preferably shorter than the width (several mm) in the first direction and is several μm to several hundred μm. If the width of the opening of the light shielding member 4 in the second direction is too large, the resolution on the light receiving surface 7 is lowered, and if it is too small, the effective light beam contributing to image formation is easily shielded. More preferably, it is 10 μm or more and 0.2 mm or less.

The region other than the aperture in the aperture stop 1 and the light shielding member 4 is a light shielding surface that does not transmit light in at least the use wavelength band (design wavelength band) of the optical system 10. As the diaphragm 1 and the light shielding member 4, it is possible to employ one having a hole in a sheet metal or one having a chromium vapor deposited on the surface of a glass plate. By adopting such a light shielding member 4, the optical system 10 can form an image of a linear reading region (test region) that is long in the first direction.

The first reflection surface 2, the second reflection surface 3, and the fourth reflection surface 6 are reflection surfaces obtained by applying a reflection coating to a base surface having a free-form surface shape. The base surface of each reflecting surface is formed by processing (cutting, polishing, molding with a mold, etc.) a block material made of glass, resin, metal or the like. The reflective coating desirably has a spectral reflection characteristic that can realize sufficient energy efficiency (light utilization efficiency) in the used wavelength band. When the base surface has a sufficient reflectance in the used wavelength band, the reflective coating may be omitted.

In the present embodiment, each of the first reflecting surface 2, the second reflecting surface 3, and the fourth reflecting surface 6 is an aspherical surface, and specifically, the curvature (power) between the first cross section and the second cross section. Are different anamorphic optical surfaces (anamorphic reflecting surfaces). Thereby, different optical actions can be generated in the first cross section and the second cross section. Each reflective surface of the front group 11 may not be an anamorphic optical surface. For example, each reflective surface may be a spherical surface, and an anamorphic refractive surface may be provided instead. However, in order to reduce the number of optical surfaces in the front group 11, it is desirable that at least one of the first reflecting surface 2 and the second reflecting surface 3 is an anamorphic optical surface.

The rear group 12 only needs to have at least one diffractive surface. For example, the base surface of the diffractive surface 5 is made an aspherical surface (anamorphic surface), and the fourth reflecting surface 6 is made spherical or removed. May be. However, in order to satisfactorily correct coma aberration and the like generated for each wavelength generated by the diffractive surface 5, it is desirable to provide an optical surface other than the diffractive surface 5 in the rear group 12, and the diffractive surface 5 as in the present embodiment. It is more preferable to dispose an anamorphic optical surface on the image side. When the diffractive surface 5 is provided in the front group 11, only a part of the light beams having a certain wavelength can pass through the opening of the light shielding member 4. Therefore, the diffractive surface 5 needs to be provided in the rear group 12.

Further, in the optical system 10, in order to suppress the occurrence of aberration by sharing power between the optical surfaces, it is more preferable that all the optical surfaces of the front group 11 and the rear group 12 are anamorphic optical surfaces. The configurations of the front group 11 and the rear group 12 are not limited to those described above, and the optical surfaces in each group may be increased or decreased. However, in order to realize downsizing of the entire system and reduction in the number of parts, it is desirable that each of the front group 11 and the rear group 12 is constituted by two reflecting surfaces as in this embodiment.

In the present embodiment, by making all the optical surfaces reflective surfaces, the optical path is bent to realize the miniaturization of the optical system 10 while suppressing the occurrence of chromatic aberration. At this time, in order to reduce the size of the optical system 10, as shown in FIG. 2, the reflecting surfaces are arranged so that the optical paths intersect in each of the front group 11 and the rear group 12 (so that it becomes a character of 4). It is desirable to arrange. If necessary, a prism or an internal reflection mirror may be used as a reflection member including a reflection surface. However, in order to suppress the occurrence of chromatic aberration as described above, the reflection member is an external reflection mirror, and the reflection surface is It is desirable to be configured to be adjacent to air. Further, if necessary, at least one optical surface may be a refractive surface (transmission surface).

However, particularly in the rear group 12, since holding members and wirings (not shown) are arranged around the light shielding member 4 and the light receiving surface 7, it is difficult to secure a sufficient space for arranging the refractive optical element. . Even if a sufficient space can be secured, it is necessary to arrange a plurality of refractive optical elements in order to correct chromatic aberration satisfactorily, so that the entire system becomes large. Therefore, it is desirable that at least all optical surfaces included in the rear group 12 are reflective surfaces. Furthermore, it is more preferable that all the optical surfaces included in the front group 11 are reflecting surfaces.

The third reflecting surface 5 is a diffractive surface 5 composed of a base surface and a diffraction grating provided on the base surface. The base surface in the diffractive surface 5 has a free-form surface shape like the other reflecting surfaces. The diffraction grating is composed of a plurality of gratings (convex portions) arranged at a pitch on the order of submicron to micron, and the height of each grating is on the order of submicron to micron. As the diffraction grating, one having a stepped shape, a rectangular uneven shape, a blazed shape, a SIN wave shape or the like in the zx cross section can be adopted. The shape of the diffraction grating is selected in consideration of the required diffraction efficiency and ease of manufacture.

In the present embodiment, a blazed shape is employed that is relatively easy to achieve both improvement in diffraction efficiency and ease of manufacture. In a blazed diffraction grating, the portion farthest from the base surface in the x direction is the lattice apex, the portion that reflects (diffracts) incident light is the blazed surface (lattice surface), and does not contribute to diffraction adjacent to the blazed surface. The part is called a lattice wall surface. The diffractive surface 5 according to this embodiment is arranged so that the blaze surface faces the light receiving surface 7 side (image side) and the grating wall surface faces the object side. As a result, a short wavelength light beam is incident on the + Z side of the light receiving surface 7 in FIG. 2, and a long wavelength light beam is incident on the −Z side.

The base surface is formed in the same manner as the other reflective surfaces described above. The diffraction grating can be formed by machining the base surface by cutting or polishing, but the diffraction grating may be formed at the same time as the base surface is formed. For example, a diffractive optical element in which a fine concavo-convex structure is provided on the surface of a mirror piece constituting a mold and a diffraction grating is provided by molding using the mold may be manufactured.

In order to improve the diffraction efficiency of the diffraction surface 5, a reflective coating may be applied to the surface of the diffraction grating. The base surface of the diffractive surface 5 is preferably an anamorphic surface having different curvatures in the xy section and the zx section. This makes it possible to share power with other anamorphic optical surfaces, thus facilitating correction of aberrations. In the present embodiment, the base surface of the diffractive surface 5 is an anamorphic surface. However, the base surface may be a flat surface or a spherical surface with emphasis on the ease of manufacturing the diffraction grating.

The operation of the optical system 10 will be described with reference to FIGS.

The light beam emitted from the test object passes through the aperture of the diaphragm 1, is reflected by the first reflecting surface 2 and the second reflecting surface 3, and reaches the light shielding member 4. At this time, the front group 11 does not image the test object on the opening of the light shielding member 4 in the first cross section (XY cross section), and on the opening of the light shielding member 4 in the second cross section (ZX cross section). An intermediate image of the test object is formed in That is, the front group 11 is configured such that the focal position does not coincide with the object plane in the first cross section. Thus, a line-shaped intermediate image (line image) that is long in the first direction is formed on the opening of the light shielding member 4. Here, “on the opening” is not limited to the exact position of the opening, but also includes the vicinity (substantially above the opening) of the opening slightly separated from the position of the opening in the optical axis direction.

The light beam that has passed through the opening of the light shielding member 4 is split into a plurality of light beams having different wavelengths by the diffraction surface 5 in the second cross section. At this time, since the diffraction grating on the diffraction surface 5 is composed of a plurality of gratings (ridge lines) arranged in the z direction, the light beam incident on the diffraction surface 5 is subjected to spectral action only in the z direction and spectral action in the y direction. I do not receive it.

The plurality of light beams from the diffractive surface 5 are reflected by the fourth reflecting surface 6 and enter the light receiving surface 7 disposed on the image surface. At this time, a plurality of light beams having different wavelengths are condensed at different positions on the light receiving surface 7 in the second cross section. That is, according to the optical system 10 according to the present embodiment, since a plurality of images for each wavelength can be formed on the light receiving surface 7, the light receiving surface 7 can acquire a plurality of image information for each wavelength.

As described above, the optical system 10 according to the present embodiment generates different optical actions in the first cross section including the reading direction and the second cross section including the spectral direction. Specifically, in the first cross section, the test object is imaged on the light receiving surface 7 without being imaged once on the opening of the light shielding member 4, but in the second cross section, the test object is imaged on the light shielding member 4. The image is once formed on the aperture and then re-imaged on the light receiving surface 7. That is, the test object is imaged once in the first cross section, while the test object is imaged twice in the second cross section.

According to this configuration, since the convergence state of the light beam (light beam incident on the opening) passing through the opening of the light shielding member 4 is not limited in the first cross section, the degree of freedom in designing the optical system 10 can be improved. it can. Accordingly, the front group 11 and the rear group 12 can appropriately share the power to form an image of the test object on the light receiving surface 7, and various aberrations can be easily corrected. Wide area) and high definition of captured images.

Specifically, by configuring the front group 11 such that the focal position in the first cross section does not coincide with the object plane, the light beam passing through the opening of the light shielding member 4 can be made non-parallel light. Thereby, it becomes easy to realize a wide angle of view in the first cross section. If the light beam passing through the opening of the light shielding member 4 is parallel light, it is necessary to arrange a large number of optical elements in the rear group 12 in order to increase the angle of view of the optical system 10. The system becomes larger. In the present embodiment, a wide angle of view is realized by using a divergent light as a light beam passing through the opening of the light shielding member 4. However, a light beam passing through the opening of the light shielding member 4 as necessary. May be convergent light.

Also, in the first cross section, when the test object is once imaged on the opening of the light shielding member 4, each of the front group 11 and the rear group 12 must independently correct the aberration. Therefore, it is necessary to increase the power of each optical surface, for example, the degree of freedom in designing each optical surface is lowered, and it is difficult to increase the angle of view of the optical system 10. On the other hand, in the second cross section, since it is not necessary to widen the angle of view, it is possible to increase the NA by once imaging the test object on the opening of the light shielding member 4.

In the configuration described above, each of the front group 11 and the rear group 12 has different powers in the first cross section and the second cross section. In order to realize this configuration, it is necessary to provide an anamorphic optical surface for each of the front group 11 and the rear group 12. At this time, the anamorphic optical surface included in the front group 11 should be positively given power not only to the second cross section but also to the first cross section (make the absolute value of curvature larger than 0). desirable. It is more preferable that the power code of the front group 11 and the power code of the rear group 12 are different from each other.

Specifically, in the second cross section, a positive power is applied to the front group 11 and the rear group 12 in order to form an image once on the opening of the light shielding member 4 and then re-image the light receiving surface 7. It is necessary to have. On the other hand, in the first cross section, since it is not necessary to once form an image of the test object on the opening of the light shielding member 4, in order to realize a further wide angle of view, the front group 11 is given negative power. It is desirable to give the rear group 12 positive power. Thereby, since the optical system 10 becomes a retro focus type in the first cross section, the focal length of the entire system is shortened, and a wide angle of view can be realized. However, when the test object is sufficiently separated from the optical system 10, the optical system 10 is made a telephoto optical system by giving the front group 11 positive power and giving the rear group 12 negative power. Also good.

The manner in which the light beam is split by the diffraction surface 5 will be described with reference to FIG. Here, a case is considered in which a white light beam emitted from one point of the test object is split into light beams having respective wavelengths of λ1 [nm], λ2 [nm], and λ3 [nm] (λ2 <λ1 <λ3). . However, in FIG. 2, only the chief ray and the marginal ray are shown among the light beams.

The chief ray L1P and the marginal rays L1U and L1L in the white light beam emitted from the test object are line-shaped intermediately on the opening of the light shielding member 4 via the stop 1, the first reflecting surface 2, and the second reflecting surface 3. Form an image. The principal ray L2P and the marginal rays L2U, L2L that have passed through the opening of the light shielding member 4 are caused by the diffraction surface 5 to have rays L3P, L3U, L3L of wavelength λ1, rays L4P, L4U, L4L of wavelength λ2, and rays of wavelength λ3. Spectroscopy into L5P, L5U, and L5L. Then, each of the light beams having the wavelength λ1, the wavelength λ2, and the wavelength λ3 is condensed at the first position 73, the second position 74, and the third position 75 on the light receiving surface 7.

As described above, according to the optical system 10 according to the present embodiment, it is possible to achieve both a reduction in size and a wide angle of view of the entire system.

[Example 1]
The optical system 10 according to Example 1 of the present invention will be described below. The optical system 10 according to the present example has the same configuration as the optical system 10 according to the above-described embodiment.

In this embodiment, the distance from the test object to the diaphragm 1 (object distance) is 300 mm, the width of the reading region in the first direction is 300 mm, and the angle of view in the first section is ± 24.17 °. In the present embodiment, the wavelength band used is 400 nm to 1000 nm, and the width of the image forming area (incident area) of the light beam on the light receiving surface 7 in the second direction is 2.7 mm.

The composite focal lengths in the first cross section of the front group 11 and the rear group 12 according to this embodiment are -16.27 mm and 28.30 mm, respectively, and the composite focal lengths in the second cross section of the front group 11 and the rear group 12 are respectively. The focal lengths are 19.99 mm and 25.76 mm, respectively. As described above, the optical system 10 according to the present embodiment improves the imaging performance by performing the intermediate in the second cross section, while widening the angle of view (reading) by adopting the retrofocus type in the first cross section. Realization of wide area).

Here, an expression of the surface shape of each optical surface of the optical system 10 according to the present embodiment will be described. In addition, the expression of the surface shape of each optical surface is not limited to that described later, and each optical surface may be designed using another expression as necessary.

The shape (bus shape) of the first reflecting surface 2, the second reflecting surface 3, the third reflecting surface (diffraction surface) 5, and the fourth reflecting surface 6 in the first cross section of the first reflecting surface 2, the second reflecting surface 3, and the fourth reflecting surface 6 according to the present embodiment. Is expressed by the following expression in each local coordinate system.

Here, R _y is a radius of curvature (bus curvature radius) in the xy section, and K _y , B ₂ , B ₄ , and B ₆ are aspheric coefficients in the xy section. The numerical values of the aspheric coefficients B ₂ , B ₄ , and B ₆ may be different from each other on both sides of the x axis (−y side and + y side) as necessary. As a result, the bus shape can be asymmetric in the y direction with respect to the x axis. In the present embodiment, secondary to sixth-order aspheric coefficients are used, but higher-order aspheric coefficients may be used as necessary.

Further, the shape (sub-wire shape) in the second cross section at an arbitrary position in the y direction of each base surface of each optical surface according to the present embodiment is expressed by the following expression.

However, K _z and M _jk are aspheric coefficients in the zx section. Further, r ′ is a radius of curvature (sub-wire curvature radius) in the zx section at a position separated by y from the optical axis in the y direction, and is represented by the following equation.

Here, r is the radius of curvature of the strand on the optical axis, and E ₂ and E ₄ are the strand changing coefficients. When r = 0 in Expression (Expression 3), the first term on the right side of Expression (Expression 2) is treated as zero. Note that the numerical values of the child line change coefficients E ₂ and E ₄ may be different from each other on the −y side and the + y side as necessary. This makes it possible to make the aspherical amount of the child wire shape asymmetric in the y direction. Moreover, although the equation (Equation 3) includes only even terms, odd terms may be added as necessary. Further, a higher order strand change coefficient may be used as necessary.

Note that the first-order term of z in the equation (Equation 2) is a term that contributes to the tilt amount (child tilt amount) of the optical surface in the zx section. Therefore, by setting M _jk to different values on the −y side and the + y side, it is possible to change the amount of subordinate tilt asymmetrically in the y direction. However, the amount of sub-line tilt may be changed asymmetrically by using odd terms. In addition, the quadratic term of z in the equation (Equation 2) is a term that contributes to the radius of curvature of the optical surface. Therefore, in order to simplify the design of each optical surface, the subsurface curvature radius may be given to the optical surface using only the quadratic term of z in Expression (Expression 2) instead of Expression (Expression 3).

The shape of the diffraction grating on the diffraction surface 5 is not particularly limited as long as it is expressed by a phase function based on a known diffractive optical theory. In this embodiment, when the fundamental wavelength (design wavelength) is λ [mm] and the phase coefficient in the zx section is C1, the shape of the diffraction grating on the diffraction surface 5 is defined by the following phase function φ. However, in this embodiment, it is assumed that the diffraction order of the diffraction grating is 1.
φ = (2π / λ) × (C1 × z)

Note that the fundamental wavelength here is a wavelength for determining the height of the diffraction grating, the spectral characteristics of the illumination light with respect to the object to be examined, the spectral reflectance of the reflective surface other than the diffraction surface 5, and the imaging including the light receiving surface 7. It is determined based on the spectral light receiving sensitivity of the element, the required diffraction efficiency, and the like. In other words, the fundamental wavelength corresponds to a wavelength that is desired to be emphasized during detection by the light receiving surface 7. In this embodiment, by setting the fundamental wavelength λ to 542 nm, the visible range in the used wavelength band can be intensively observed. However, for example, by setting the fundamental wavelength to about 850 nm, the near infrared region can be intensively observed, or by setting the fundamental wavelength to about 700 nm, the near infrared region can be observed in a balanced manner from the visible region. Also good.

Table 1 shows the position of the vertex of each optical surface of the optical system 10 according to the present embodiment, the direction of the normal at the vertex, and the radius of curvature at each cross section. In Table 1, the position of the vertex of each optical surface is indicated by the distance X, Y, Z [mm] from the origin in the absolute coordinate system, and the direction of the normal line (x axis) is the X axis in the ZX section including the optical axis. Is represented by an angle θ [deg]. Further, d [mm] represents an interval (surface interval) between optical surfaces, d ′ [mm] represents an interval between reflection points of chief rays on each optical surface, and R _y and R _z are principal components. The curvature radii in the XY cross section and the ZX cross section at the reflection point of the light beam are shown. In addition, when the value of the radius of curvature of each reflecting surface is positive, it indicates a concave surface, and when it is negative, it indicates a convex surface.

Table 2 shows the surface shapes of the optical surfaces of the optical system 10 according to this example.

Table 3 shows the aperture [1] in the y direction and the z direction of the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the light receiving surface 7. In the present embodiment, all of the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the light receiving surface 7 are rectangular.

FIG. 3 shows an MTF (Modulated Transfer Function) of the optical system 10 according to the present embodiment. In FIG. 3, the MTF for each wavelength of 700 nm (frq1), 400 nm (frq2), and 1000 nm (frq3) is obtained when the object height [mm] in the reading region is Y = 0, 30, 60, 90, 120, 150. Shows about each of them. As shown in FIG. 3, the spatial frequency [lines / mm] for each wavelength of the imaging element including the light receiving surface 7 is 27.8, 41.7, and 55.6. As can be seen from FIG. 3, the aberration is satisfactorily corrected over the entire reading region, and a sufficient depth of focus is ensured.

[Example 2]
Hereinafter, the optical system 10 according to Embodiment 2 of the present invention will be described. In the optical system 10 according to the present embodiment, the description of the configuration equivalent to that of the optical system 10 according to Embodiment 1 described above is omitted.

FIG. 4 is a schematic diagram of a main part in the first and second cross sections of the optical system 10 according to the embodiment of the present invention. The optical system 10 according to the present embodiment has a shorter optical path length from the stop 1 to the light receiving surface 7 than the optical system 10 according to the first embodiment, thereby realizing further downsizing of the entire system.

In this embodiment, the distance from the test object to the diaphragm 1 is 300 mm, the width of the reading region in the first direction is 300 mm, and the angle of view in the first section is ± 24.46 °. In this embodiment, the used wavelength band is 400 nm to 1000 nm, and the width of the imaging region in the second direction on the light receiving surface 7 is 2.7 mm. The composite focal lengths in the first cross section of the front group 11 and the rear group 12 according to the present embodiment are respectively -14.21 mm and 16.69 mm, and the composite focal lengths in the second cross section of the front group 11 and the rear group 12 are respectively. The focal lengths are 19.33 mm and 11.01 mm, respectively.

As in Example 1, Table 4 shows the position of the vertex of each optical surface of the optical system 10 according to this example, the direction of the normal line at the vertex, and the radius of curvature at each cross section, and Table 5 shows each optical surface. Table 6 shows the diameter of the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the diameter of the light receiving surface 7. However, as for the shape of the third reflecting surface 5 in the second cross section, the local line that differs from position to position so that the normal line at each position on the generatrix represented by the equation (Equation 1) matches the x axis. After defining the coordinate system, it is expressed by the above equation (Equation 2). The reason why the values of the curvature radii _Ry do not match between Table 4 and Table 5 is that the values of the curvature radii in Table 4 consider the tilt angle in the second cross section.

FIG. 5 shows the MTF of the optical system 10 according to the present embodiment, as in FIG. As can be seen from FIG. 5, the aberration is satisfactorily corrected over the entire reading region, and a sufficient depth of focus is ensured.

[Example 3]
The optical system 10 according to Example 3 of the present invention will be described below. In the optical system 10 according to the present embodiment, the description of the configuration equivalent to that of the optical system 10 according to Embodiment 1 described above is omitted.

FIG. 6 is a main part schematic diagram in the first and second cross sections of the optical system 10 according to the embodiment of the present invention. The optical system 10 according to the present embodiment has a smaller (brighter) F value on the image side (exit side) than the optical system 10 according to the first embodiment. Specifically, the F value on the image side of the optical system 10 according to Example 1 is 4.7 and 4.0 in the first and second cross sections, respectively, whereas the optical value according to this example is shown. The image side F values of the system 10 are 4.1 and 3.5 in the first and second cross-sections, respectively.

In this embodiment, the distance from the test object to the diaphragm 1 is 300 mm, the width of the reading region in the first direction is 300 mm, and the angle of view in the first section is ± 24.44 °. In this embodiment, the wavelength band used is 400 nm to 1000 nm, and the width of the imaging region in the second direction on the light receiving surface 7 is 2.64 mm. The composite focal lengths in the first cross section of the front group 11 and the rear group 12 according to the present embodiment are -14.46 mm and 26.85 mm, respectively, and the composite focal lengths in the second cross section of the front group 11 and the rear group 12 are respectively. The focal lengths are 19.34 mm and 24.98 mm, respectively.

As in Example 1, Table 7 shows the position of the vertex of each optical surface of the optical system 10 according to this example, the direction of the normal at the vertex, and the radius of curvature at each cross section. Table 8 shows each optical surface. Table 9 shows the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the diameter of the light receiving surface 7.

FIG. 7 shows the MTF of the optical system 10 according to the present embodiment, as in FIG. As can be seen from FIG. 7, the aberration is satisfactorily corrected over the entire reading region, and a sufficient depth of focus is ensured.

[Example 4]
The optical system 10 according to Example 4 of the present invention will be described below. In the optical system 10 according to the present embodiment, the description of the configuration equivalent to that of the optical system 10 according to Embodiment 1 described above is omitted.

FIG. 8 is a schematic diagram of a main part in the first and second cross sections of the optical system 10 according to the embodiment of the present invention. The optical system 10 according to the present embodiment has a shorter optical path length from the stop 1 to the light receiving surface 7 than the optical system 10 according to the first embodiment, thereby realizing further downsizing of the entire system.

In this embodiment, the distance from the test object to the diaphragm 1 is 300 mm, the width of the reading region in the first direction is 300 mm, and the angle of view in the first section is ± 24.49 °. In this embodiment, the wavelength band used is 400 nm to 1000 nm, and the width of the imaging region in the second direction on the light receiving surface 7 is 2.37 mm. The combined focal lengths in the first cross section of the front group 11 and the rear group 12 according to the present embodiment are −13.23 mm and 16.78 mm, respectively, and the combined focal lengths of the front group 11 and the rear group 12 in the second cross section are respectively. The focal lengths are 17.53 mm and 11.25 mm, respectively.

As in Example 1, Table 10 shows the position of the vertex of each optical surface of the optical system 10 according to this example, the direction of the normal line at the vertex, and the radius of curvature at each cross section. Table 11 shows each optical surface. Table 12 shows the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the diameter of the light receiving surface 7. The reason why the values of the curvature radii _Ry do not match between Table 10 and Table 11 is that the values of the curvature radii in Table 10 take into account the tilt angle in the second cross section.

In the present embodiment, the sub-wire shapes of the first reflecting surface 2, the second reflecting surface 3, the third reflecting surface 5, and the fourth reflecting surface 6 are the following formulas instead of the above formula (Equation 3). It is expressed using Further, the shape of the sub-line of the third reflecting surface 5 is expressed by the above formula (Equation 2) after defining a different local coordinate system for each position on the bus line as in the second embodiment.

FIG. 9 shows the MTF of the optical system 10 according to the present embodiment as in FIG. As can be seen from FIG. 9, the aberration is satisfactorily corrected over the entire reading region, and a sufficient depth of focus is ensured.

[Imaging apparatus and imaging system]
Hereinafter, an imaging apparatus (spectral reading apparatus) and imaging system (spectral reading system) as examples of use of the optical system 10 according to the above-described embodiment will be described.

FIGS. 10 and 11 are schematic views of main parts of the

imaging systems

100 and 200 according to the embodiment of the present invention. The

imaging systems

100 and 200 are configured to change the relative positions of the

imaging system

101 and 201 having an optical system 10 and an imaging device that receives an image formed by the optical system 10, and the imaging apparatus and the test objects 103 and 203.

Sections

102 and 202. Each imaging system desirably has an image processing unit that generates an image based on image information obtained from the imaging element. The image processing unit is a processor such as a CPU, for example, and may be provided inside or outside each imaging apparatus.

According to the

imaging devices

101 and 201, a plurality of pieces of image information (one-dimensional images) corresponding to a plurality of wavelengths are obtained by imaging the

linear reading regions

104 and 204 that are long in the first direction (Y direction) once. Can be obtained. At this time, it is desirable to configure each imaging device as a multispectral camera that can acquire image information corresponding to four or more types of wavelengths more than a general camera. Furthermore, it is more preferable to configure each imaging device as a hyperspectral camera that can acquire image information corresponding to 100 or more wavelengths.

As the image pickup element in each image pickup apparatus, a CCD (Charge Coupled Device) sensor, a CMOS (Complementary Metal Oxide Semiconductor) sensor, or the like can be employed. The imaging device may be configured to photoelectrically convert not only visible light but also infrared light (near infrared light or far infrared light). Specifically, an image sensor using a material such as InGaAs or InAsSb may be employed according to the wavelength band used. In addition, the number of pixels of the image sensor is desirably determined based on the resolution required in the reading direction and the spectral direction.

As shown in FIG. 10, the transport unit 102 in the imaging system 100 is means for moving the test object 103 in the second direction (Z direction). A belt conveyor or the like can be employed as the transport unit 102. On the other hand, as illustrated in FIG. 11, the conveyance unit 202 in the imaging system 200 is a unit that moves the imaging device 201 in the second direction. As the transport unit 202, a multicopter, an airplane, an artificial satellite, or the like can be employed. By using the transport unit 202, it is possible to perform imaging at a plurality of positions in the second direction even for a large test object that cannot be transported by a belt conveyor or the like that is difficult to move. .

According to the

imaging systems

100 and 200, a plurality of positions in the second direction can be obtained by causing each imaging device to sequentially image the reading area while changing the relative position of each imaging device and each test object in each transport unit. A plurality of pieces of image information corresponding to can be acquired. A two-dimensional image corresponding to a specific wavelength can be generated by performing rearrangement or arithmetic processing of the plurality of captured images by the image processing unit. In addition, since each image information represents the light and shade information in the first direction, the image processing unit generates a spectrum distribution (spectrum information) based on the light and shade information for each wavelength at a specific position in the second direction. Also good.

In addition, you may comprise each conveyance part so that both each imaging device and each test object may be moved. Moreover, you may enable it to adjust the relative position in the optical axis direction (X direction) of each imaging device and each test object by each conveyance part. Alternatively, an optical member (focusing member) that can be driven inside or outside the optical system 10 is arranged, and the position of the optical member may be adjusted so that the object can be focused.

[Inspection method and manufacturing method]
Hereinafter, an object (test object) inspection method and article manufacturing method using the optical system 10 according to the above-described embodiment will be described. The optical system 10 is suitable for inspection (evaluation) in industrial fields such as manufacturing, agriculture, and medicine.

In the first step (imaging step) in the inspection method according to the present embodiment, the image information of the object is acquired by imaging the object via the optical system 10. At this time, an imaging apparatus or an imaging system as described above can be used. That is, it is possible to acquire image information of the entire object by imaging the object while changing the relative positions of the object and the imaging device. In addition, image information of a plurality of objects can be acquired sequentially (continuously). In the first step, a plurality of pieces of image information corresponding to the wavelengths of the plurality of light beams emitted from the optical system 10 may be acquired.

In the next second step (inspection step), the object is inspected based on the image information acquired in the first step. At this time, for example, the user (inspector) confirms (determines) the presence or absence of foreign matter or scratches in the image information, or the control unit (image processing unit) detects foreign matter or scratches in the image information and notifies the user. May be. Or you may employ | adopt the control part which controls the manufacturing apparatus of the articles | goods mentioned later according to the determination result of the presence or absence of a foreign material or a crack.

In the second step, the object may be inspected based on the spectrum distribution of the object acquired using a plurality of pieces of image information for each wavelength. By using the image information acquired via the optical system 10, it is possible to detect unique spectral information of the object to be inspected, and thereby to identify the component of the object. For example, the image processing unit may generate image information in which coloring or the like is enhanced for each spectrum distribution, and the user may perform inspection based on the image information.

The inspection method according to the present embodiment can be applied to a manufacturing method for articles such as foods, pharmaceuticals, and cosmetics. Specifically, the material (object) for manufacturing the article can be inspected by the inspection method described above, and the article can be manufactured using the inspected material. For example, when it is determined in the second step that the material has foreign matter or scratches, the user (manufacturer) or the manufacturing apparatus removes the foreign matter from the material or discards the foreign matter or scratched material. can do.

Further, the above inspection method may be used for detecting an abnormality in the manufacturing apparatus. For example, the presence or absence of an abnormality may be determined based on the image information of the manufacturing apparatus, and the driving of the manufacturing apparatus may be stopped or the abnormality may be corrected according to the determination result.

The present invention is not limited to the above embodiment, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, in order to make the scope of the present invention public, the following claims are attached.

The present application claims priority based on Japanese Patent Application No. 2018-109857 filed on June 7, 2018 and Japanese Patent Application No. 2019-042881 filed on March 11, 2019, All the descriptions are incorporated herein.

Claims

An optical system composed of a front group, a light shielding member, and a rear group arranged in order from the object side to the image side,
The light shielding member is provided with a long opening in the first direction,
The front group does not image an object on the opening in a first cross section parallel to the first direction, and the object on the opening in a second cross section perpendicular to the first direction. An intermediate image of
The rear group has a diffractive surface for splitting the light beam that has passed through the opening in the second cross section into a plurality of light beams having different wavelengths, and the plurality of light beams are collected at different positions in the second cross section. Light
In the first cross section, an optical system that emits light from the front group and enters the aperture is non-parallel light.
2. The optical system according to claim 1, wherein in the first cross section, the sign of the power of the front group and the sign of the power of the rear group are different from each other.
3. The optical system according to claim 2, wherein, in the first cross section, the front group has a negative power and the rear group has a positive power.
4. The optical system according to claim 1, wherein in the first cross section, a light beam emitted from the front group and incident on the opening is divergent light. 5.
5. The optical system according to claim 1, wherein, in the second cross section, the front group and the rear group have a positive power.
6. The optical system according to claim 1, wherein a sign of power in the first section and a sign of power in the second section of the front group are different from each other.
The optical system according to any one of claims 1 to 6, wherein a base surface of the diffractive surface is an aspherical surface.
The optical system according to any one of claims 1 to 7, wherein the diffractive surface is a reflective surface.
The optical system according to any one of claims 1 to 8, wherein the light shielding member regulates a width of the light beam from the object in the first direction.
The optical system according to any one of claims 1 to 9, wherein the front group includes a diaphragm that regulates a width of a light beam from the object in a second direction perpendicular to the first direction. system.
The optical system according to any one of claims 1 to 10, wherein all optical surfaces included in the front group and the rear group are reflection surfaces.
An image pickup apparatus comprising: the optical system according to any one of claims 1 to 11; and an image pickup element that receives an image formed by the optical system.
An imaging system comprising: the imaging device according to claim 12; and a conveyance unit that changes a relative position between the imaging device and the object.
A first step of acquiring image information of the object by imaging the object via an optical system;
And a second step of inspecting the object based on the image information,
The optical system is composed of a front group, a light shielding member, and a rear group arranged in order from the object side to the image side,
The light shielding member is provided with a long opening in the first direction,
The front group has an aspherical surface, and in the first cross section parallel to the first direction, the object is not imaged on the opening, and in the second cross section perpendicular to the first direction. Forming an intermediate image of the object on the aperture;
The rear group has a diffractive surface for splitting the light beam that has passed through the opening in the second cross section into a plurality of light beams having different wavelengths, and the plurality of light beams are collected at different positions in the second cross section. Light
The inspection method according to claim 1, wherein a tilt angle of the aspheric surface in the second cross section changes in the first direction.
15. The inspection method according to claim 14, wherein the first step includes a step of imaging the object while moving the object in a direction perpendicular to the first direction.
The inspection method according to claim 14 or 15, wherein the first step includes a step of acquiring a plurality of pieces of image information corresponding to wavelengths of the plurality of light beams.
17. The method according to claim 14, wherein the second step includes a step of inspecting the object based on a spectral distribution of the object acquired using the plurality of pieces of image information. Inspection method described in 1.
The inspection method according to any one of claims 14 to 17, wherein the second step includes a step of determining the presence or absence of foreign matter in the object.
Inspecting the object by the inspection method according to any one of claims 14 to 18,
And a step of manufacturing an article using the object inspected in the step.
The manufacturing method according to claim 19, wherein the step of manufacturing the article includes a step of removing foreign matter from the object.