Distance measurement optical device

Abstract

Provided is a distance measurement optical device with which a high distance measurement accuracy can easily be achieved. A light projecting optical system (10) and a light receiving optical system (20) of a distance measurement optical device (1) each comprise, in order from a measurement target object side, a first lens group (G11, G21) having a negative refractive power, a second lens group (G12, G22) having a positive refractive power, and a third lens group (G13, G23) having a positive refractive power. A number n of lenses constituting the light receiving optical system (20) is larger than a number m of lenses constituting the light projecting optical system (10). With the exception of n-m lenses from the measurement target object side of the first lens group (G11, G21) of the light receiving optical system (20), the positivity and negativity of the refractive powers of the lenses are arranged in the same order from the measurement target object side in the light projecting optical system (10) and the light receiving optical system (20)

Description

Optical device for distance measurement

[0001] The present invention relates to a distance measuring optical device that can easily achieve high distance measurement accuracy.

[0002] A distance measuring device is known that projects light emitted from a plurality of light-emitting elements arranged one-dimensionally or two-dimensionally onto a measurement object, and calculates the distance to the measurement object from the time it takes for the reflected light from the measurement object to be detected by a plurality of light-receiving elements arranged one-dimensionally or two-dimensionally.The distance measuring optical device provided in this distance measuring device includes a light-projecting optical system that projects light emitted from the plurality of light-emitting elements onto the measurement object, a light-receiving optical system that collects reflected light from a wide area of ​​the measurement object and makes it incident on the light-receiving elements, and a holding member that holds both the light-projecting optical system and the light-receiving optical system.

[0003] In the distance measuring optical device disclosed in Patent Document 1, the number and shape of lenses are substantially the same in the light projecting optical system and the light receiving optical system. This makes it easy to align the projection methods of the light projecting optical system and the light receiving optical system, and also makes the projection characteristics (details described later) in the lens design values ​​similar. This makes it possible to suppress a decrease in the distance measuring accuracy of the distance measuring device caused by differences in the projection characteristics of the light projecting optical system and the light receiving optical system.

[0004] Japanese Patent Application Laid-Open No. 2021-148667

[0005] However, in the above-described conventional technology, the light projected from the light-projecting optical system is diffusely reflected by the surface of the measurement object, so the amount of reflected light incident on the light-receiving element via the light-receiving optical system is likely to be reduced compared to the amount of light projected onto the measurement object via the light-projecting optical system. To compensate for this reduction in light amount, it is conceivable to use different lens configurations for the light-projecting optical system and the light-receiving optical system so as to increase the aperture ratio of the light-receiving optical system. However, in this case, it becomes difficult to approximate the projection characteristics of the lenses at the design values ​​of the light-projecting optical system and the light-receiving optical system to similarity, making it difficult to ensure distance measurement accuracy.

[0006] SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a distance measuring optical device that can easily achieve high distance measurement accuracy.

[0007] To achieve this object, the present invention provides a distance measuring optical device for projecting light emitted in an optical axis direction from a plurality of light-emitting elements arranged one-dimensionally or two-dimensionally in a direction perpendicular to the optical axis direction onto a measurement object, and calculating a distance to the measurement object from the time it takes for the light reflected from the measurement object to be detected by a plurality of light-receiving elements arranged one-dimensionally or two-dimensionally in a direction perpendicular to the optical axis direction, the distance measuring optical device comprising: a light-projecting optical system that projects the light emitted from the plurality of light-emitting elements onto the measurement object, a light-receiving optical system that collects the light reflected from the measurement object and makes it incident on the light-receiving elements, and a holding member that holds both the light-projecting optical system and the light-receiving optical system. Both the light-projecting optical system and the light-receiving optical system are composed of a plurality of lenses held in a lens barrel, and, in order from the measurement object side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power. The number n of lenses constituting the light-receiving optical system is greater than the number m of lenses constituting the light-projecting optical system, and except for nm lenses from the measurement object side of the first lens group of the light-receiving optical system, the positive and negative refractive powers of the lenses are arranged in the same order from the measurement object side in the light-projecting optical system and the light-receiving optical system.

[0008] According to the distance measuring optical device of claim 1, the refractive powers of the first lens group, the second lens group, and the third lens group in both the light projecting optical system and the light receiving optical system are negative, positive, and positive, respectively. This allows the light projecting optical system to project light onto a wide area of ​​the measurement object, and the light receiving optical system to collect reflected light from a wide area of ​​the measurement object. Furthermore, because the refractive powers of each lens group in the light projecting optical system and the light receiving optical system are the same, it is easy to align the projection methods of both systems.

[0009] The number n of lenses constituting the light-receiving optical system is greater than the number m of lenses constituting the light-projecting optical system. Except for the nm lenses from the side of the first lens group of the light-receiving optical system facing the object to be measured, the positive and negative refractive powers of the lenses are arranged in the same order from the side of the object to be measured in the light-projecting optical system and the light-receiving optical system. In this way, by making most of the lens configurations the same in the light-projecting optical system and the light-receiving optical system, it is easy to make the projection characteristics at the lens design values ​​similar. Therefore, the distance measurement accuracy of a distance measuring device using this distance measuring optical device can be ensured.

[0010] Furthermore, nm lenses are added to the light-receiving optical system on the side closer to the object to be measured, so that the first lens group maintains negative refractive power relative to the light-projecting optical system. This makes it possible to easily correct various aberrations while maintaining the similarity of projection characteristics and increasing the aperture of the light-receiving optical system relative to the light-projecting optical system, and to easily ensure the amount of reflected light incident on the light-receiving element. As a result, high distance measurement accuracy can be easily achieved in the distance-measuring optical device.

[0011] According to the distance measuring optical device of claim 2, in the light projection optical system, a value calculated based on a projection method from the difference between the real image height at the lens design value and the real image height resulting from the actually manufactured lens is defined as the light projection-side angular error. Similarly, in the light receiving optical system, a value calculated based on a projection method from the difference between the real image height at the lens design value and the real image height resulting from the actually manufactured lens is defined as the light reception-side angular error. The maximum absolute value of the final light reception position deviation calculated based on the projection method from the difference between the light projection-side angular error and the light reception-side angular error calculated for each half angle of view and azimuth angle is less than half the size of the short side of the rectangular minimum detection area in the distance measuring device. This prevents reflected light that should be incident on a specific detection area from being incident on another detection area, thereby improving the distance measurement accuracy of a distance measuring device using the distance measuring optical device in addition to the effect of claim 1.

[0012] According to the distance measuring optical device of claim 3, since both the light projecting optical system and the light receiving optical system are of the equidistant projection type, the image height is proportional to the angle of view, and therefore, in addition to the effect of claim 1, the resolution with respect to the distance to the measurement object and the angle of view can be made uniform between the center (low angle of view side) and the periphery (high angle of view side).

[0013] According to a distance measuring optical device described in claim 4, the lens barrel of at least one of the light projecting optical system and the light receiving optical system is rotatably fitted into a fitting hole provided in the holding member. In each of the light projecting optical system and the light receiving optical system, the amount of deviation of the projection characteristics of the actually manufactured lens from the design value projection characteristics of the lens (manufacturing error in the projection characteristics) may vary depending on the azimuth angle. By rotating the lens barrel relative to the fitting hole, the orientation of the light projecting optical system and the orientation of the light receiving optical system can be easily combined so that the manufacturing error in the projection characteristics cancels out. As a result, in addition to the effect of claim 1, the distance measuring accuracy of a distance measuring device using the distance measuring optical device can be further improved.

[0014] According to a fifth aspect of the distance measuring optical device, at least one of the light projecting optical system and the light receiving optical system includes a focal length adjustment mechanism for adjusting a focal length. In each of the light projecting optical system and the light receiving optical system, manufacturing errors in the projection characteristics vary depending on the respective focal lengths. Therefore, by adjusting the focal length of at least one of the light projecting optical system and the light receiving optical system using the focal length adjustment mechanism, the manufacturing errors in the projection characteristics of the light projecting optical system and the light receiving optical system can be made closer to each other. As a result, the manufacturing errors in the projection characteristics of the light projecting optical system and the light receiving optical system can be more easily canceled out, thereby further improving the distance measurement accuracy of a distance measuring device using the distance measuring optical device, in addition to the effects of any one of the first to fourth aspects.

[0015] According to a sixth aspect of the distance measuring optical device, the lens barrel of at least one of the light projecting optical system and the light receiving optical system, which is provided with a focal length adjustment mechanism, is formed by axially connecting a first lens barrel holding a first lens group and a second lens barrel holding a second and third lens group. The focal length adjustment mechanism includes a male thread provided on the outer peripheral surface of one of the first and second lens barrels and a female thread provided on the inner peripheral surface of the other of the first and second lens barrels, into which the male thread fits. By adjusting the length of the fitting between the male thread and the female thread, the distance between the first and second lens groups changes, making it easy to adjust the focal length. Therefore, in addition to the effect of the fifth aspect, the focal length adjustment mechanism can be simplified.

[0016] According to a seventh aspect of the distance measuring optical device, the lens barrel of at least one of the light projecting optical system and the light receiving optical system, which is provided with a focal length adjustment mechanism, is formed by axially connecting a first lens barrel holding a first lens group and a second lens barrel holding a second and third lens group. The focal length adjustment mechanism includes a spacer sandwiched axially between the first and second lens barrels. By adjusting the thickness of this spacer (the axial dimension), the distance between the first and second lens groups changes, making it easy to adjust the focal length. Therefore, in addition to the effect of the fifth aspect, the focal length adjustment mechanism can be simplified.

[0017] 1A is a schematic diagram showing the projection characteristics of the light projection optical system, and FIG. 1B is a schematic diagram showing the projection characteristics of the light receiving optical system.

[0018] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a perspective view of a distance measuring optical device 1 according to one embodiment. Fig. 2 is a cross-sectional view of the distance measuring optical device 1. Fig. 3 is a cross-sectional view of a light projecting optical system 10 excluding a lens barrel 12. Fig. 4 is a cross-sectional view of a light receiving optical system 20 excluding a lens barrel 22. Note that hatching indicating lens cross sections has been omitted in each drawing. Furthermore, each drawing schematically shows a two-dimensionally arranged light emitting element 2 and a light receiving element 4.

[0019] The cross-sectional views of Figures 2 and 3 are cross-sectional views including the optical axis A1 of the light-projecting optical system 10. The cross-sectional views of Figures 2 and 4 are cross-sectional views including the optical axis A2 of the light-receiving optical system 20. In Figure 3, of the optical paths passing through the light-projecting optical system 10, the optical path along the optical axis A1 is shown by a dashed line, and the optical path at the position farthest from the optical axis A1 is shown by a two-dot chain line. Note that in Figure 3, to make the optical path of the two-dot chain line easier to see, the optical path when light is emitted from point 3 outside the light-emitting element 2 is shown. In Figure 4, of the optical paths passing through the light-receiving optical system 20, the optical path along the optical axis A2 is shown by a dashed line, and the optical path at the position farthest from the optical axis A2 is shown by a two-dot chain line.

[0020] 1 and 2, the distance measuring optical device 1 constitutes a part of a distance measuring device. The distance measuring device projects light emitted from a light emitting element 2 onto an object to be measured, and calculates (measures) the distance from the distance measuring device to the object to be measured based on the time it takes for the reflected light from the object to be detected by a light receiving element 4.

[0021] In this specification, the side of the distance measuring optical device 1 that faces the object to be measured in the optical axis direction will be referred to as the front side (forward), and the side of the light emitting element 2 and the light receiving element 4 will be referred to as the rear side (rear). Furthermore, in the vertical direction perpendicular to the front-to-rear direction (optical axis direction), the upper side of the paper in Fig. 2 will be referred to as the top side, and in the horizontal direction perpendicular to the front-to-rear and vertical directions, the far side of the paper in Fig. 2 will be referred to as the left side. However, the vertical direction does not necessarily coincide with the vertical direction, and the front-to-rear and horizontal directions do not necessarily coincide with the horizontal direction.

[0022] The light-emitting element 2 is an element for emitting light forward, and in this embodiment, emits laser light. A plurality of light-emitting elements 2 are arranged two-dimensionally, vertically and horizontally, to form a single light source. This light source is called a vertical cavity surface-emitting laser (VCSEL). However, the light source is not limited to a surface-emitting laser, and may be formed by arranging light-emitting elements 2 such as laser diodes (LDs) or light-emitting diodes (LEDs) one-dimensionally in either the vertical or horizontal direction. Furthermore, the light-emitting element 2 may emit light other than laser light.

[0023] The light receiving element 4 is an element that detects light incident on the light receiving element 4, converts the light into an electrical signal, and sends it to the control circuit of the distance measuring device. A plurality of light receiving elements 4 are arranged two-dimensionally vertically and horizontally to form one light receiving section. The distance measuring device measures the distance depending on the timing when the light receiving element 4 detects light, the position of the light receiving element 4 that detected the light, etc.

[0024] The light receiving section may be formed by arranging the light receiving elements 4 one-dimensionally, either vertically or horizontally. One of the plurality of light emitting elements 2 and the plurality of light receiving elements 4 may be arranged two-dimensionally, and the other one-dimensionally. Also, both the light emitting elements 2 and the light receiving elements 4 may be arranged one-dimensionally. In this case, it is preferable that the arrangement directions are parallel to each other.

[0025] The optical distance measuring device 1 is configured to cause reflected light emitted from a plurality of light emitting elements 2 to be incident on a plurality of light receiving elements 4 corresponding vertically and horizontally. For example, the optical distance measuring device 1 is configured to cause reflected light emitted from the upper leftmost light emitting element 2 to be incident on three light receiving elements 4 vertically and horizontally from the upper leftmost light emitting element 2.

[0026] The distance measuring optical device 1 comprises a light projection optical system 10 that projects light emitted from multiple light-emitting elements 2 onto the object to be measured, a light receiving optical system 20 that collects reflected light from the object to be measured and makes it incident on multiple light receiving elements 4, and a holding member 30 that holds both the light projection optical system 10 and the light receiving optical system 20.

[0027] The holding member 30 is a plate-like member that forms part of the housing of the distance measuring device. An upper fitting hole 31 and a lower fitting hole 32 are formed through the holding member 30 in the thickness direction. A cylindrical tube portion 33 protrudes from the front surface of the holding member 30 so as to extend the inner circumferential surface of the fitting hole 31 forward, and a cylindrical tube portion 34 protrudes from the front surface of the holding member 30 so as to extend the inner circumferential surface of the fitting hole 31 forward.

[0028] The projection optical system 10 is configured by holding multiple optical elements (lenses, etc.) in a cylindrical lens barrel 12 that is fitted from the front into a fitting hole 31 (tubular portion 33) of a holding member 30. The optical axis A1 of the projection optical system 10 is the same as the central axis of the lens barrel 12 and the central axis of the fitting hole 31. Therefore, the lens barrel 12 can be rotated around the optical axis A1 relative to the fitting hole 31.

[0029] The lens barrel 12 comprises a cylindrical first lens barrel 13 that constitutes a portion of the front side of the lens barrel 12, and a cylindrical second lens barrel 14 that constitutes the remainder of the lens barrel 12. The second lens barrel 14 is the part that fits into the fitting hole 31. A step 14a that comes into contact with the front end of the cylindrical portion 33 is formed on the outer circumferential surface of the second lens barrel 14. The contact between the front end of the cylindrical portion 33 and the step 14a positions the second lens barrel 14 axially relative to the holding member 30.

[0030] A male thread 15 is formed on a rear portion of the outer circumferential surface of the first lens barrel 13. A female thread 16 is formed on a front portion of the inner circumferential surface of the second lens barrel 14. The male thread 15 fits into this female thread 16, thereby connecting the first lens barrel 13 and the second lens barrel 14 in the axial direction.

[0031] By adjusting the length of the mating portion between the male thread portion 15 and the female thread portion 16, the first lens barrel 13 can be positioned in the axial direction (front-to-back direction) relative to the second lens barrel 14, which is positioned on the holding member 30. This changes the spacing between the multiple optical elements held in the lens barrel 12, making it possible to easily adjust the focal length f1 of the projection optical system 10. Therefore, the male thread portion 15 and the female thread portion 16 simplify the focal length adjustment mechanism for adjusting the focal length f1.

[0032] The focal length adjustment mechanism also includes an annular spacer 28 that is sandwiched around the entire periphery between the first lens barrel 13 and the second lens barrel 14 in the front-to-rear direction. By adjusting the thickness (front-to-rear dimension) of the spacer 28, the first lens barrel 13 can be positioned in the front-to-rear direction relative to the second lens barrel 14, and the focal length f1 can be easily adjusted. Therefore, the spacer 28 simplifies the focal length adjustment mechanism for adjusting the focal length f1.

[0033] The focal length adjustment mechanism may be configured using only either the engagement between the male thread portion 15 and the female thread portion 16 or the spacer 28. However, by combining these, when the spacer 28 is sandwiched between the first lens barrel 13 and the second lens barrel 14, an axial force is generated in the male thread portion 15 and the female thread portion 16. As a result, it becomes easier to maintain the position of the first lens barrel 13 relative to the second lens barrel 14, and unintentional fluctuations in the focal length f1 can be suppressed.

[0034] The light-receiving optical system 20 is configured such that multiple optical elements (lenses, etc.) are held in a lens barrel 22 that is fitted into a fitting hole 32 (cylinder portion 34) of the holding member 30, and does not have a focal length adjustment mechanism. A step 22a that comes into contact with the front end of the cylinder portion 34 is formed on the outer circumferential surface of the lens barrel 22. The lens barrel 22 is positioned axially (in the front-to-rear direction) relative to the holding member 30 by contact between the front end of the cylinder portion 34 and the step 22a.

[0035] The length in the front-to-rear direction from the rear end of barrel 12 of light-projecting optical system 10 to step 14a is longer than the length in the front-to-rear direction from the rear end of barrel 22 of light-receiving optical system 20 to step 22a. Correspondingly, the length in the front-to-rear direction of tube portion 33 into which barrel 12 fits is longer than the length in the front-to-rear direction of tube portion 34 into which barrel 22 fits. This makes it easier for workers to recognize that, when assembling distance-measuring optical device 1, barrel 12 should be fitted into tube portion 33 and barrel 22 should be fitted into tube portion 34.

[0036] The optical axis A2 of the light receiving optical system 20 is the same as the central axis of the lens barrel 22 and the central axis of the fitting hole 32. Therefore, the lens barrel 22 can be rotated around the optical axis A2 relative to the fitting hole 32. The optical axes A1 and A2 are parallel to each other.

[0037] The mechanism by which the lens barrel 12 of the light projecting optical system 10 and the lens barrel 22 of the light receiving optical system 20 are rotatably fitted into the fitting holes 31, 32 of the holding member 30 is referred to as a rotation mechanism. The rotation mechanism is not limited to a case in which both the light projecting optical system 10 and the light receiving optical system 20 are configured to be rotatable relative to the holding member 30, and may be a case in which only one of the light projecting optical system 10 and the light receiving optical system 20 is configured to be rotatable.

[0038] The engagement between the fitting holes 31, 32 and the lens barrels 12, 22 is a transition fit. This allows the lens barrels 12, 22 to rotate relative to the holding member 30 by applying force, while the rotation of the lens barrels 12, 22 can be stopped by not applying force. However, the engagement between the fitting holes 31, 32 and the lens barrels 12, 22 may also be a clearance fit. In this case, threaded holes opening onto the inner circumferential surfaces of the fitting holes 31, 32 may be formed through the holding member 30, and the tip of a screw fitted into the threaded hole may be pressed against the lens barrels 12, 22 to stop the rotation of the lens barrels 12, 22 relative to the fitting holes 31, 32.

[0039] 2 and 3, the optical elements of the projection optical system 10 will be described. The optical elements of the projection optical system 10 are composed of, in order from the front side toward the light-emitting element 2, a first lens group G11 having negative refractive power, a second lens group G12 having positive refractive power, an aperture stop 11, and a third lens group G13 having positive refractive power.

[0040] Each of the lens groups G11 to G13 is composed of one or more lenses, which are arranged symmetrically about the optical axis A1. The aperture stop 11 is used to appropriately cut off the portion of the light passing through the projection optical system 10 that is far from the optical axis A1, and is composed of a part of the lens barrel 12 (second lens barrel 14).

[0041] The first lens group G11 is composed of a single first lens L11 having negative refractive power and is held by the first lens barrel 13. The first lens L11 is a meniscus lens that is convex toward the front. This allows light passing through the first lens L11 to be greatly spread outward in the direction perpendicular to the axis toward the front, thereby increasing the maximum angle of view of the projection optical system 10 (maximum value of the half angle of view θ1).

[0042] The second lens group G12 is composed of one second lens L12 having positive refractive power and is held by the second lens barrel 14. The second lens L12 is a biconvex lens. This second lens L12 makes it easier to focus light traveling toward the first lens L11.

[0043] The third lens group G13 is composed of, in order from the front, a third lens L13, a fourth lens L14, and a fifth lens L15, and is held by the second lens barrel 14. The third lens L13 is a biconcave lens with negative refractive power. Note that the front lens surface of the third lens L13 is substantially flat, approximating a plano-concave lens.

[0044] The fourth lens L14 is a meniscus lens having negative refractive power and convex toward the rear. The fifth lens L15 is a biconvex lens having positive refractive power. This third lens group G13 can condense the light emitted from each light-emitting element 2 while bending the light toward the optical axis A1 so that the light spreads in front of the aperture stop 11.

[0045] The projection optical system 10 described above is a retrofocus type that can project light from a plurality of light-emitting elements 2 over a wide range, and is composed of a total of five lenses. The projection optical system 10 forms the light beams emitted from the light-emitting elements 2 that are two-dimensionally arranged vertically and horizontally into spots, and projects them onto the object to be measured with increased vertical and horizontal spacing.

[0046] The second lens group G12 and the third lens group G13 are configured to correct various aberrations occurring in the first lens group G11. The focal length adjustment mechanism adjusts the focal length f1 of the projection optical system 10 by varying the distance between the first lens group G11 and the second and third lens groups G12 and G13. Therefore, the focal length adjustment mechanism makes it possible to adjust the focal length f1 by moving the first lens group G11 while ensuring the ability to correct various aberrations without changing the distance between the second lens group G12 and the third lens group G13.

[0047] 2 and 4, the optical elements of the light receiving optical system 20 will be described. The optical elements of the light receiving optical system 20 are composed of, in order from the front side toward the light receiving element 4, a first lens group G21 having negative refractive power, a second lens group G22 having positive refractive power, an aperture stop 21, and a third lens group G23 having positive refractive power.

[0048] Each of the lens groups G21 to G23 is composed of one or more lenses, which are arranged symmetrically about the optical axis A2. The aperture stop 21 is used to adjust the amount of light and the resolution, and is composed of a part of the lens barrel 22.

[0049] The light receiving optical system 20 may have a glass filter or a cover glass provided at a predetermined position. The glass filter is a parallel plate with almost no refractive power and functions as a visible light cut filter, bandpass filter, ultraviolet cut filter, polarizing filter, etc. The cover glass is a parallel plate with almost no refractive power and is provided to protect the light receiving element 4 and the like. The glass filter and cover glass are not essential. Multiple glass filters may be provided.

[0050] The first lens group G21 is composed of, from the front side, an additional lens LA and a first lens L21. Both the additional lens LA and the first lens L21 have negative refractive power and are meniscus lenses convex toward the front side. The outer diameter and effective diameter of the additional lens LA are larger than those of the first lens L21, respectively. As a result, light incident on the additional lens LA is adjusted so that the angle it forms with the optical axis A2 gradually becomes gentler before exiting the first lens L21. As a result, the maximum angle of view of the light receiving optical system 20 (maximum value of the half angle of view θ2) can be increased.

[0051] The second lens group G22 is composed of a single second lens L22 having positive refractive power. The second lens L22 is a biconvex lens. This second lens L22 makes it easier to focus light traveling toward the third lens group G23.

[0052] The third lens group G23 is composed of, from the front side, a third lens L23, a fourth lens L24, and a fifth lens L25. The third lens L23 is a plano-concave lens with negative refractive power and a flat front surface. The fourth lens L24 is a meniscus lens with negative refractive power and a convex rear surface. The fifth lens L25 is a biconvex lens with positive refractive power.

[0053] The third lens group G23 can condense light heading toward each light receiving element 4, while bending, toward the optical axis A1, light that tends to spread outward in the axis-perpendicular direction behind the aperture stop 21. In addition, the second lens group G22 and the third lens group G23 are configured to correct various aberrations generated in the first lens group G21.

[0054] The light receiving optical system 20 described above is a retrofocus type that can allow reflected light from a wide range of the measurement object to be incident on the light receiving element 4, and is composed of a total of six lenses. The light receiving optical system 20 narrows the intervals between the reflected light beams that are generated by the multiple light beams projected by the light projection optical system 10 so that the vertical and horizontal intervals are widened, and causes them to be incident on the corresponding vertical and horizontal light receiving elements 4, respectively.

[0055] Since the positive and negative refractive powers of the lens groups G11 to G13 and G21 to G23 are the same in the light projecting optical system 10 and the light receiving optical system 20, it is easy to align the projection methods of both. Furthermore, with the exception of one additional lens LA from the front side of the first lens group G21 of the light receiving optical system 20, the number of lenses is the same in the light projecting optical system 10 and the light receiving optical system 20, and the positive and negative refractive powers of the lenses are arranged in the same order from the front. In this way, by making most of the lens configurations the same in the light projecting optical system 10 and the light receiving optical system 20, it is easy to make the projection characteristics at the lens design values ​​similar.

[0056] First, the projection method related to the projection characteristics will be described. The projection method is a method in which an ideal image height y is expressed by a focal length f and a half angle of view θ. When distinguishing between these, the projection optical system 10 will be referred to as an ideal image height y1, a focal length f1, and a half angle of view θ1, while the light receiving optical system 20 will be referred to as an ideal image height y2, a focal length f2, and a half angle of view θ2.

[0057] The ideal height y1 of the projection optical system 10 is the height of an ideal image formed by the projection optical system 10 when the image plane is made up of the multiple light-emitting elements 2, and zero is set on the optical axis A1. The focal length f1 of the projection optical system 10 is the composite focal length of the entire projection optical system 10. The half angle of view θ1 of the projection optical system 10 is the angle between the chief ray passing through the front surface of the first lens L11 and the optical axis A1.

[0058] The ideal image height y2 of the light-receiving optical system 20 is the height of an ideal image formed by the light-receiving optical system 20 when the image plane is the multiple light-receiving elements 4, and is set to zero on the optical axis A2. The half angle of view θ2 of the light-receiving optical system 20 is the angle between the chief ray passing through the front surface of the additional lens LA and the optical axis A2.

[0059] The focal length f1 of the light-projecting optical system 10 and the focal length f2 of the light-receiving optical system 20 may be the same or different. When the vertical and horizontal dimensions of the two-dimensionally arranged multiple light-emitting elements 2 (light source) are smaller than the vertical and horizontal dimensions of the two-dimensionally arranged multiple light-receiving elements 4 (light-receiving unit), the focal length f1 can be made smaller than the focal length f2. When the vertical and horizontal dimensions of the light source are larger than the vertical and horizontal dimensions of the light-receiving unit, the focal length f1 can be made larger than the focal length f2. Furthermore, when the vertical and horizontal dimensions of the light source and the light-receiving unit are the same, the focal length f1 and the focal length f2 can be made approximately the same.

[0060] In this embodiment, both the light-projecting optical system 10 and the light-receiving optical system 20 are of the equidistant projection type, where y = f · θ. Note that an equidistant projection optical system is an optical system designed based on y = f · θ, and often refers to an optical system in which the offset angles dθ1 and dθ2, described below, are 5° or less. With the equidistant projection type, the ideal image height y is proportional to the half angle of view θ, so the resolution for the distance to the measurement object and the angle of view can be made uniform between the center (low angle of view) and the periphery (high angle of view).

[0061] Examples of projection methods include the central projection method represented by y = f tan θ, the stereographic projection method represented by y = 2f tan(θ / 2), the orthogonal projection method represented by y = f sin θ, and the equisolid angle projection method represented by y = 2f sin(θ / 2). The light-projecting optical system 10 and the light-receiving optical system 20 may be designed based on each formula to adopt the respective projection methods.

[0062] Furthermore, by using the same projection method in the light-projecting optical system 10 and the light-receiving optical system 20, the light that is converted by the light-projecting optical system 10 and travels from the light-emitting element 2 toward the object to be measured is reconverted by the light-receiving optical system 20 so as to return to its original state before being incident on the light-receiving element 4. As a result, in a distance measuring device using the distance-measuring optical device 1, the correspondence between the multiple light-receiving elements 4 and the object to be measured becomes easier to understand, and distance measurement accuracy can be improved.

[0063] FIG. 5A is a schematic diagram showing the projection characteristics of the projection optical system 10. In the graph of FIG. 5A, the vertical axis represents the half angle of view θ1, and the horizontal axis represents the deviation angle dθ1. The deviation angle dθ1 is a value obtained by dividing the difference dy1 between the real image height, which is the height of the actual image formed by the projection optical system 10 at a predetermined half angle of view θ1, and the ideal image height y1 calculated by y1 = f1 · θ1, by the focal length f1 based on the projection method. In other words, the deviation angle dθ1 is a value obtained by converting the difference dy1 between the ideal image height y1 and the real image height into an angle. The deviation angle dθ1 is a positive value when the real image height deviates outward in the axis-perpendicular direction relative to the ideal image height y1, and a negative value when the real image height deviates toward the optical axis A1.

[0064] This calculation method for the deviation angle dθ1 is used when the projection optical system 10 is an equidistant projection system. In any projection system, the deviation angle dθ1 is calculated by substituting the difference dy1 for y in the corresponding equation. For example, in the case of the central projection system, the deviation angle dθ1 is calculated from the difference dy1 based on dy1 = f1 tan(dθ1).

[0065] The projection characteristic of the projection optical system 10 is the way in which the deviation angle dθ1 varies depending on the half angle of view θ1. The projection characteristic B1 shown by the solid line in FIG. 5A is a characteristic calculated from the design values ​​of each lens of the projection optical system 10.

[0066] Similarly, FIG. 5B is a schematic diagram showing the projection characteristics of the light receiving optical system 20. In the graph of FIG. 5B, the vertical axis represents the half angle of view θ2, and the horizontal axis represents the deviation angle dθ2. The deviation angle dθ2 is the difference dy2 between the real image height, which is the height of the actual image formed by the light receiving optical system 20 at a predetermined half angle of view θ2, and the ideal image height y2 calculated by y2 = f2 θ2, divided by the focal length f2. The deviation angle dθ2 is a positive value when the real image height deviates outward in the axis-perpendicular direction relative to the ideal image height y2, and a negative value when the real image height deviates toward the optical axis A2. In any projection method, not just the equidistant projection method, the deviation angle dθ2 is the value of θ obtained when the difference dy2 is substituted for y in the equation indicating the method.

[0067] The projection characteristic of the light receiving optical system 20 is the way in which the deviation angle dθ2 varies depending on the half angle of view θ2. The projection characteristic B2 shown by the solid line in FIG. 5B is a characteristic calculated from the design values ​​of each lens of the light receiving optical system 20.

[0068] 5A and 5B, the projection characteristics B1 and B2 of the lens design values ​​are similar between the light projecting optical system 10 and the light receiving optical system 20, which have most of the same lens configuration. Therefore, even if there are deviations dθ1 and dθ2 from the ideal projection method, the light converted by the light projecting optical system 10 toward the measurement object from the light emitting element 2 is reconverted by the light receiving optical system 20 so as to return to its original state before being incident on the light receiving element 4. As a result, a distance measuring device using the distance measuring optical device 1 can ensure distance measurement accuracy.

[0069] Furthermore, in this embodiment, except for one additional lens LA, the number of lenses and the order of positive and negative refractive powers of the lenses are the same between the light projecting optical system 10 and the light receiving optical system 20, and the lens shapes (for example, meniscus lenses convex to the front, biconvex lenses, etc.) are also substantially the same. As a result, the projection characteristics B1 and B2 in the lens design values ​​can be made more similar between the light projecting optical system 10 and the light receiving optical system 20, thereby improving distance measurement accuracy.

[0070] Furthermore, since one additional lens LA is added to the front side of the light-receiving optical system 20 so that the first lens group G21 maintains negative refractive power relative to the light-projecting optical system 10, it is possible to easily correct various aberrations while maintaining the similarity of the projection characteristics B1 and B2 and increasing the diameter of the light-receiving optical system 20 relative to the light-projecting optical system 10. Furthermore, since the additional lens LA is a negative meniscus lens that is convex toward the front, it is easy to further increase the effective diameter of the light-receiving optical system 20. This makes it easy to ensure the amount of reflected light that enters the light-receiving element 4 via the light-receiving optical system 20, even if light from the light-projecting optical system 10 is diffusely reflected by the surface of the measurement object.

[0071] As a result of the above, according to the distance measurement optical device 1, by making most of the lens configurations of the light projection optical system 10 and the light receiving optical system 20 the same, and by providing an additional lens LA in the light receiving optical system 20, high distance measurement accuracy can be easily achieved.

[0072] Although the projection characteristics B1 and B2 of the lens design values ​​have been described for each of the light-projecting optical system 10 and the light-receiving optical system 20, the projection characteristics of actually manufactured lenses often deviate from the projection characteristics B1 and B2 due to manufacturing errors. Furthermore, lenses actually manufactured are not necessarily perfectly symmetrical with respect to the optical axes A1 and A2, and the projection characteristics often vary depending on the azimuth angle. The azimuth angle is the angle between the principal ray and a reference position about the optical axes A1 and A2 when viewed in the axial direction of the optical axes A1 and A2.

[0073] The projection characteristic C1α indicated by the dashed line in Fig. 5A is a characteristic calculated by measuring the real image height and focal length f1 at the azimuth angle α for the projection optical system 10 using an actually manufactured lens. The projection characteristic C1β indicated by the two-dot chain line in Fig. 5A is a characteristic calculated by measuring the real image height and focal length f1 at the azimuth angle β different from the azimuth angle α for the projection optical system 10 using an actually manufactured lens. The difference between the projection characteristic C1α and the projection characteristic B1 is the manufacturing error D1α of the projection characteristic at the azimuth angle α. The difference between the projection characteristic C1β and the projection characteristic B1 is the manufacturing error D1β of the projection characteristic at the azimuth angle β.

[0074] The projection characteristic C2α shown by the two-dot chain line in Fig. 5(b) is a characteristic calculated by measuring the real image height and focal length f2 at the azimuth angle α for the light receiving optical system 20 using an actually manufactured lens. The projection characteristic C2β shown by the two-dot chain line in Fig. 5(b) is a characteristic calculated by measuring the real image height and focal length f2 at the azimuth angle β for the light receiving optical system 20 using an actually manufactured lens. The difference between the projection characteristic C2α and the projection characteristic B2 is the manufacturing error D2α of the projection characteristic at the azimuth angle α. The difference between the projection characteristic C2β and the projection characteristic B2 is the manufacturing error D2β of the projection characteristic at the azimuth angle β.

[0075] 5A and 5B, the manufacturing errors D1α, D1β, D2α, and D2β of the projection characteristics vary depending on the azimuth angles α and β in the light projection optical system 10 and the light receiving optical system 20, respectively. For example, in this embodiment, the manufacturing error D1α of the projection characteristics of the light projection optical system 10 at the azimuth angle α is closer to the manufacturing error D2β of the projection characteristics of the light receiving optical system 20 at the azimuth angle β than the manufacturing error D2α of the projection characteristics of the light receiving optical system 20 at the azimuth angle α. Therefore, when reflected light of light projected from the light projection optical system 10 at the azimuth angle α is incident on the light receiving optical system 20 at the azimuth angle β, the manufacturing errors D1α and D2β of the projection characteristics tend to cancel each other out.

[0076] The distance measuring optical device 1 is provided with a rotation mechanism (fitting holes 31, 32, lens barrels 12, 22) that rotates at least one of the light projecting optical system 10 and the light receiving optical system 20 relative to the holding member 30, so that the azimuth angle α of the light projecting optical system 10 and the azimuth angle β of the light receiving optical system 20 can be easily combined so that the manufacturing errors D1α and D2β of the projection characteristics cancel each other out. As a result, the distance measuring accuracy of a distance measuring device using the distance measuring optical device 1 can be further improved.

[0077] Furthermore, because the projection characteristics of the light-projecting optical system 10 vary depending on the focal length f1 in both the design value and the manufactured product, the manufacturing errors D1α and D1β of the projection characteristics also vary depending on the focal length f1. Therefore, by adjusting the focal length f1 using the focal length adjustment mechanism (external thread portion 15, internal thread portion 16, spacer 28), the manufacturing errors D1α, D1β, D2α, and D2β of the projection characteristics can be made closer to each other in the light-projecting optical system 10 and the light-receiving optical system 20. This makes it easier for the manufacturing errors D1α, D1β, D2α, and D2β of the projection characteristics to cancel each other out in the light-projecting optical system 10 and the light-receiving optical system 20, thereby further improving the distance measurement accuracy of the distance measuring device using the distance measuring optical device 1.

[0078] Here, the manufacturing errors D1α and D1β of the projection characteristics of the projection optical system 10 can also be considered as manufacturing errors (projection-side angular errors) of the deviation angle dθ1, which varies depending on the half angle of view θ1 and the azimuth angle. In other words, the projection-side angular error is a value calculated based on the projection method from the difference between the real image height of the lens at the design value and the real image height of the lens actually manufactured in the projection optical system 10. For example, in the case of the equidistant projection method, it is calculated using the formula "(manufactured real image height) - (design real image height) = f1 (projection-side angular error)."

[0079] Similarly, the manufacturing errors D2α and D2β of the projection characteristics of the light-receiving optical system 20 can also be considered as manufacturing errors of the deviation angle dθ2 (light-receiving-side angle error) that vary depending on the half angle of view θ2 and the azimuth angle. In other words, the manufacturing error of the deviation angle dθ2 is a value calculated based on the projection method from the difference between the real image height of the lens at the design value and the real image height of the lens that is actually manufactured in the light-receiving optical system 20. For example, in the case of the equidistant projection method, it is calculated using the formula "(manufactured real image height) - (design real image height) = f2 · (light-receiving-side angle error)."

[0080] To further improve the distance measurement accuracy, first, for each half angle of view θ and azimuth angle, the final light-receiving position deviation is calculated based on the projection method from the difference between the light-projection-side angular error and the light-receiving-side angular error. For example, in the case of the equidistant projection method, this is calculated using the formula "(final light-receiving position deviation) = f2 · ((light-projection-side angular error) - (light-receiving-side angular error))." It is preferable that the maximum absolute value MA of the multiple calculated final light-receiving position deviations is equal to or less than half the size of the short side of the rectangular minimum detection area of ​​the distance measurement device of the distance measurement optical device 1.

[0081] The distance measuring device of the distance measuring optical device 1 measures distance for each rectangular minimum detection area. This minimum detection area may be rectangular with short and long sides, or may be square with two sides of the same size. In this specification, even if the minimum detection area is square, the size of one of the sides will be referred to as the "size of the short side."

[0082] If the maximum value MA is equal to or less than half the size of the short side of the minimum detection area, reflected light that should be incident on a specific detection area can be prevented from being incident on another detection area, thereby improving the distance measurement accuracy of a distance measuring device that uses the distance measuring optical device 1.

[0083] If the maximum value MA is not less than half the size of the short side of the minimum detection area, the manufacturing errors can be easily cancelled out by using a rotation mechanism or focal length adjustment mechanism, and adjustment can be made until it is less than half.

[0084] The above has been explained based on the above embodiment, but the present invention is not limited to the above embodiment, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0085] In the above embodiment, the number n of lenses constituting the light-projecting optical system 10 is five, and the number m of lenses constituting the light-receiving optical system 20 is six. However, these numbers n and m may be changed as appropriate under predetermined conditions. One of the predetermined conditions is that the refractive powers of the first lens group G11, G21, the second lens group G12, G22, and the third lens group G13, G23 in both the light-projecting optical system 10 and the light-receiving optical system 20 are negative, positive, and positive, respectively.

[0086] The second predetermined condition is that the number n is greater than the number m. The third predetermined condition is that, except for the n-m lenses from the front of the first lens group G21 of the light-receiving optical system 20, the positive and negative refractive powers of the lenses are arranged in the same order from the front in the light-projecting optical system 10 and the light-receiving optical system 20. As long as these predetermined conditions are met, even if the numbers n and m of lenses are changed, the distance measuring optical device 1 can easily make the projection characteristics at the design values ​​of the lenses similar, as described above.

[0087] In the above embodiment, the projection systems of the light projecting optical system 10 and the light receiving optical system 20 are the same and are the equidistant projection system, but this is not limiting. For example, the projection systems of the light projecting optical system 10 and the light receiving optical system 20 may be the same and be a projection system other than the equidistant projection system. Furthermore, the projection system of the light projecting optical system 10 and the projection system of the light receiving optical system 20 may be different. Note that even if the projection systems of the light projecting optical system 10 and the light receiving optical system 20 are different, as long as most of the lens configuration is the same, it is easy to make the projection characteristics of the lens design values ​​similar.

[0088] In the above embodiment, the case where the rotation mechanism and the focal length adjustment mechanism are provided in the distance measurement optical device 1 has been described, but this is not limiting. For example, at least one of the rotation mechanism and the focal length adjustment mechanism may be omitted from the distance measurement optical device 1.

[0089] Furthermore, the rotation mechanism is not limited to that described in the above embodiment, as long as it can rotate at least one of the light-projecting optical system 10 and the light-receiving optical system 20 about the respective optical axes A1, A2. For example, in a case where the lens barrels 12, 22 are non-rotatably attached to the cylindrical portions 33, 34 (fitting holes 31, 32), a rotation mechanism that rotates the cylindrical portions 33, 34 themselves may be provided in the holding member 30.

[0090] The focal length adjustment mechanism is not limited to being provided only in the light projecting optical system 10, but may be provided only in the light receiving optical system 20, or may be provided in both the light projecting optical system 10 and the light receiving optical system 20. The focal length adjustment mechanism is not limited to that described in the above embodiment, as long as it can adjust the focal lengths f1, f2 of at least one of the light projecting optical system 10 and the light receiving optical system 20.

[0091] For example, the focal length adjustment mechanism may change the distance between the second lens group G12, G22 and the third lens group G13, G23. The focal length adjustment mechanism may also change the distance between the lenses in each of the lens groups G11 to G13 and G21 to G23. The focal length adjustment mechanism may be configured by fitting a female thread formed on the inner circumferential surface of the first lens barrel 13 with a male thread formed on the outer circumferential surface of the second lens barrel 14. The focal length adjustment mechanism may be configured by configuring the first lens barrel 13 to be axially slidable relative to the second lens barrel 14, and by switching between a state that allows the sliding and a state that locks the sliding.

[0092] REFERENCE SIGNS LIST 1 Distance measuring optical device 2 Light emitting element 4 Light receiving element 10 Light projecting optical system 12, 22 Lens barrel 13 First lens barrel 14 Second lens barrel 15 Male threaded portion 16 Female threaded portion 20 Light receiving optical system 28 Spacer 30 Holding member 31, 32 Fitting hole G11, G21 First lens group G12, G22 Second lens group G13, G23 Third lens group

Claims

1. A distance measuring optical device provided in a distance measuring device for calculating the distance to a measurement object from the time until the light emitted from a plurality of light emitting elements arranged one-dimensionally or two-dimensionally in a direction perpendicular to the optical axis direction is projected onto the measurement object and the reflected light from the measurement object is detected by a plurality of light receiving elements arranged one-dimensionally or two-dimensionally in a direction perpendicular to the optical axis direction, the distance measuring optical device comprising: a projection optical system that projects the light emitted from the plurality of light emitting elements onto the measurement object; a light receiving optical system that condenses the reflected light from the measurement object and makes it incident on the light receiving elements; and a holding member that holds both the projection optical system and the light receiving optical system, wherein both the projection optical system and the light receiving optical system are each composed of a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, in this order from the measurement object side, by a plurality of lenses held in a lens barrel, the number n of lenses constituting the light receiving optical system is larger than the number m of lenses constituting the projection optical system, and except for n - m lenses from the measurement object side of the first lens group of the light receiving optical system, the positive and negative of the refractive power of the lenses are arranged in the same order from the measurement object side in the projection optical system and the light receiving optical system.

2. In the projection optical system, a value calculated based on the projection method from the difference between the actual image height at the design value of the lens and the actual image height by the actually manufactured lens is defined as the projection-side angular error, in the light receiving optical system, a value calculated based on the projection method from the difference between the actual image height at the design value of the lens and the actual image height by the actually manufactured lens is defined as the light receiving-side angular error, and the maximum value of the absolute value among the displacements of the final light receiving positions calculated based on the projection method from the difference between the projection-side angular error and the light receiving-side angular error calculated for each half angle and azimuth angle is equal to or less than half of the size of the short side of the rectangular minimum detection region in the distance measuring device. The distance measuring optical device according to claim 1.

3. The distance measuring optical device according to claim 1, wherein both the projection optical system and the light receiving optical system are equidistant projection methods.

4. The distance measuring optical device according to claim 1, wherein at least one of the lens barrels of the projection optical system and the light receiving optical system is rotatably fitted into a fitting hole provided in the holding member.

5. The distance measuring optical device according to any one of claims 1 to 4, wherein at least one of the light projecting optical system and the light receiving optical system includes a focal length adjusting mechanism for adjusting the focal length.

6. The lens barrel of at least one of the light projecting optical system and the light receiving optical system in which the focal length adjusting mechanism is provided is formed by axially connecting a first lens barrel that holds the first lens group and a second lens barrel that holds the second lens group and the third lens group. The focal length adjusting mechanism includes a male screw portion provided on an outer peripheral surface of one of the first lens barrel and the second lens barrel, and a female screw portion provided on an inner peripheral surface of the other of the first lens barrel and the second lens barrel and into which the male screw portion is fitted. The distance measuring optical device according to claim 5.

7. The lens barrel of at least one of the light projecting optical system and the light receiving optical system in which the focal length adjusting mechanism is provided is formed by axially connecting a first lens barrel that holds the first lens group and a second lens barrel that holds the second lens group and the third lens group. The focal length adjusting mechanism includes a spacer sandwiched axially between the first lens barrel and the second lens barrel. The distance measuring optical device according to claim 5.

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