Camera lens unit

Abstract

The present invention provides a camera lens unit that can suppress the reduction of optical performance even if the plastic lens absorbs water. The camera lens unit (1) has a lens barrel (2) formed of a resin material and a first plastic lens (10) to a seventh plastic lens (70) housed in the lens barrel (2). At least two adjacent plastic lenses among the first plastic lens (10) to the seventh plastic lens (70) have different water absorption rates. In these two plastic lenses with different water absorption rates, a conical interlocking inclined surface centered on the optical axis X is formed so as to be interlocked on the outside of the optically effective part of each lens. When forming the interlocking inclined surface, the interlocking inclined surface of the high water absorption side plastic lens on the side with high water absorption rate is formed on the outside of the interlocking inclined surface of the low water absorption side plastic lens on the side with low water absorption rate.

Description

Technical Field

[0001] The present invention relates to an imaging lens unit for forming an image of a subject on a solid-state imaging element such as a CCD sensor or a CMOS sensor. Background Art

[0002] Portable information devices such as smartphones, home appliances, and automobiles are equipped with imaging lens units for realizing camera functions. An imaging lens unit is a unit for forming an image of a subject on a solid-state imaging element such as a CCD sensor or a CMOS sensor, and has a plurality of lenses in a lens barrel. The optical performance of an imaging lens unit depends not only on the optical characteristics of a single lens, but also on the degree of consistency of the optical axes of the lenses housed in the lens barrel, the degree of inclination, the degree of deviation of the surface spacing from the design value, and the like.

[0003] As a method for adjusting the optical axis, inclination and lens surface interval between lenses, there is a method of forming a fitting structure at the edge of each lens and performing these adjustments by fitting the lenses using the fitting structure. For example, the camera lens unit described in Patent Document 1 has such a fitting structure. In the camera lens unit, a fitting inclined surface centered on the optical axis and a flat portion continuously provided on the fitting inclined surface are formed relative to the edge of each lens. When assembling the camera lens unit, first, the fitting inclined surface of the first lens is fitted with the fitting inclined surface of the second lens and the flat portion of the first lens is abutted against the flat portion of the second lens. Further, the fitting inclined surface of the second lens is fitted with the fitting inclined surface of the third lens and the flat portion of the second lens is abutted against the flat portion of the third lens. The optical axis of each lens is adjusted by fitting the fitting inclined surfaces, and the inclination and lens surface interval are adjusted by abutting the flat portions. According to the camera lens unit described in Patent Document 1, the position and posture of each lens can be controlled with high precision in the lens barrel.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: U.S. Patent Application Publication No. 2018 / 335607 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] In recent years, in addition to the lightness and cost reduction of camera lens units, plastic lenses are used in large quantities for the purpose of improving optical performance by using aspherical surfaces. Plastic lenses have a water absorption rate as a unique value. In the lens interlocking structure described in Patent Document 1, it is possible that the optical performance is reduced when the lenses with different water absorption rates are combined with each other. For example, when two plastic lenses with different water absorption rates are combined using the above interlocking structure, stress based on the difference in water absorption rates is generated inside each lens due to water absorption by each lens. The stress generated in the lens will affect the lens surface spacing and lens surface shape. Even if the lens absorbs water, as long as the water is discharged from the lens by subsequent placement, the impact on the optical performance is small. However, if the internal stress remains even after being placed after absorbing water, and the surface shape and surface spacing of the lens are changed due to the internal stress, the optical performance of the camera lens unit is reduced.

[0009] The present invention has been made in view of such problems, and an object of the present invention is to provide an imaging lens unit capable of suppressing a decrease in optical performance even when a plastic lens absorbs water.

[0010] Means used to solve problems

[0011] The camera lens unit of the present invention comprises a lens barrel formed of a resin material and a plurality of plastic lenses housed in the lens barrel. At least two adjacent plastic lenses among the plurality of plastic lenses have different water absorption rates and are formed to be able to engage with conical engaging inclined surfaces centered on the optical axis outside their respective optically effective parts. In addition, among the adjacent plastic lenses, the engaging inclined surface of the high water absorption side plastic lens on the side with a high water absorption rate is formed outside the engaging inclined surface of the low water absorption side plastic lens on the side with a low water absorption rate.

[0012] At least two adjacent plastic lenses among the plurality of plastic lenses are formed with conical interlocking inclined surfaces centered on the optical axis on the outer sides of their optically effective parts, i.e., the so-called edge parts. During assembly, the optical axes of the lenses can be made consistent by interlocking the interlocking inclined surfaces formed on the edge parts of the lenses. That is, the camera lens unit of the present invention has a structure that makes the optical axes of the plastic lenses consistent by interlocking the interlocking inclined surfaces. In addition, it is not necessary to set interlocking inclined surfaces for all the plastic lenses in the lens barrel, and for some of the plastic lenses, the optical axis can also be adjusted by interlocking the outer peripheral surface of the lens with the inner wall surface of the lens barrel.

[0013] In addition, the volume change of a plastic lens with a high water absorption rate due to water absorption is greater than the volume change of a plastic lens with a low water absorption rate due to water absorption. In the conventional camera lens unit, when plastic lenses with different water absorption rates are adjacent, the volume change of the plastic lens with a high water absorption rate in the outer direction, i.e., in the direction orthogonal to the optical axis, is limited by the interlocking inclined surface formed on the plastic lens with a low water absorption rate. Due to this limitation, stress based on the difference in water absorption rate is generated inside each lens, resulting in a reduction in the optical performance of the camera lens unit.

[0014] In the camera lens unit of the present invention, among at least two adjacent plastic lenses, the interlocking inclined surface of the plastic lens on the side with a higher water absorption rate is formed outside the interlocking inclined surface of the plastic lens on the side with a lower water absorption rate. According to such a structure, even if the volume of the plastic lens on the side with a higher water absorption rate changes due to water absorption, it will not be interfered by the interlocking inclined surface of the plastic lens on the side with a lower water absorption rate, so the stress generated inside the lens can be appropriately suppressed. In addition, in this specification, for convenience, among the plastic lenses with different water absorption rates, the plastic lens on the side with a higher water absorption rate is referred to as a "plastic lens on the side with a higher water absorption rate", and the plastic lens on the side with a lower water absorption rate is referred to as a "plastic lens on the side with a lower water absorption rate".

[0015] In the imaging lens unit of the above structure, when the water absorption rate of the plastic lens on the low water absorption side is set to β1 and the water absorption rate of the plastic lens on the high water absorption side is set to β2, it is preferable that the following conditional expressions (1) and (2) are satisfied:

[0016] β1<0.1% (1),

[0017] β2>0.2%(2).

[0018] The greater the difference between the water absorption rate of the high water absorption side plastic lens and the low water absorption side plastic lens, the greater the stress generated inside the plastic lens. The structure of the imaging lens unit of the present invention is particularly effective when plastic lenses satisfying conditional expressions (1) and (2) are adjacent.

[0019] In the imaging lens unit having the above structure, it is preferable that the water absorption rate of the lens barrel is higher than the water absorption rate of the plurality of plastic lenses.

[0020] When the water absorption rate of the lens barrel is lower than that of the plurality of plastic lenses, when the plastic lenses expand in volume due to water absorption, there is a concern that stress may be generated inside the lenses due to the contact between the outer peripheral surface of the plastic lenses and the inner wall surface of the lens barrel. By making the water absorption rate of the lens barrel higher than that of the plastic lenses, the generation of such stress inside the lenses can be avoided.

[0021] In the imaging lens unit of the above structure, when the water absorption rate of the lens barrel is set to β3, the following conditional expression (3) is preferably satisfied:

[0022] β3>0.4% (3).

[0023] In the imaging lens unit having the above structure, it is preferable that the linear expansion coefficient of the plastic lens on the high water absorption side is larger than the linear expansion coefficient of the plastic lens on the low water absorption side.

[0024] The volume expansion of the plastic lens due to water absorption is closely related to the linear expansion coefficient. When the linear expansion coefficient of the plastic lens on the side with high water absorption is larger than that of the plastic lens on the side with low water absorption, the structure of the imaging lens unit of the present invention becomes effective.

[0025] In the imaging lens unit having the above structure, it is preferable that at least one of the outer peripheral surfaces of the highly water-absorbent plastic lens is fitted to the inner wall surface of the lens barrel.

[0026] By fitting at least one of the outer peripheral surfaces of the highly water-absorbent plastic lens to the inner wall surface of the lens barrel, the optical axis of the plastic lens can be made to coincide with the central axis of the lens barrel.

[0027] Effects of the Invention

[0028] According to the imaging lens unit of the present invention, it is possible to provide an imaging lens unit capable of suppressing degradation of optical performance even when a plastic lens absorbs water. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a cross-sectional view schematically showing an imaging lens unit according to an embodiment of the present invention.

[0030] Figure 2 Is has Figure 1 An exploded cross-sectional view of the lens assembly portion of the imaging lens unit shown.

[0031] Figure 3 Is to show about Figure 2 An exploded cross-sectional view showing the second lens, the third lens, and the fourth lens in the lens mounting portion in comparison with a conventional structure.

[0032] Figure 4 Is to show about Figure 2 An exploded cross-sectional view showing the fourth lens, the fifth lens and the sixth lens in the lens mounting portion in comparison with a conventional structure.

[0033] Figure 5 Is to show about Figure 1 FIG. 1 is a graph showing the results of a simulation of the maximum stress generated in each lens when the temperature of the imaging lens unit shown is increased.

[0034] Figure 6 Is to show about Figure 1FIG. 1 is a graph showing the results of a simulation of the amount of change in the surface spacing between the lenses that occurs when the temperature of the imaging lens unit is lowered.

[0035] Description of Reference Numerals

[0036] 1: Camera lens unit,

[0037] 2: Lens barrel,

[0038] 3: Peripheral wall,

[0039] 4: front wall,

[0040] 4A: Opening,

[0041] 4B: receiving surface,

[0042] 10: First plastic lens,

[0043] 11: Lens part,

[0044] 12: Edge,

[0045] 13: abutment surface,

[0046] 14: Annular step portion,

[0047] 14A: Engagement inclined surface,

[0048] 14B: Annular plane,

[0049] 20, 120: second plastic lens,

[0050] 21: Lens part,

[0051] 22: Edge,

[0052] 23, 24: Annular step part,

[0053] 23A, 24A, 124A: Engagement inclined surface,

[0054] 23B, 24B, 124B: annular plane,

[0055] 30, 130: The third plastic lens,

[0056] 31: Lens part,

[0057] 32: Edge,

[0058] 33, 34: Annular step part,

[0059] 33A, 34A, 133A, 134A: Engagement inclined surface,

[0060] 33B, 34B, 133B, 134B: annular plane,

[0061] 40, 140: fourth plastic lens,

[0062] 41: Lens unit,

[0063] 42: Edge,

[0064] 43, 44: Annular step portion,

[0065] 43A, 44A, 143A, 144A: Engagement inclined surface,

[0066] 43B, 44B, 143B, 144B: annular plane,

[0067] 50, 150: Fifth plastic lens,

[0068] 51: Lens part,

[0069] 52: Edge,

[0070] 53: Annular step portion,

[0071] 53A, 153A, 154A: Engagement inclined surface,

[0072] 53B, 54, 153B, 154B: annular plane,

[0073] 60, 160: Sixth plastic lens,

[0074] 61: Lens unit,

[0075] 62: Edge,

[0076] 63, 64, 163B: Annular plane,

[0077] 163A: Engagement inclined surface,

[0078] 70: seventh plastic lens,

[0079] 71: Lens unit,

[0080] 72: Edge,

[0081] 73, 74: Annular plane,

[0082] 80, 81, 82, 83, 84, 85: shielding plate,

[0083] 90: Spacer ring,

[0084] 91: Pressure ring,

[0085] F: Infrared cut-off filter,

[0086] S: Camera sensor. DETAILED DESCRIPTION

[0087] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In addition, the structure described in the following embodiment is only an example, and its deformation and modification are free, and it is not intended to limit the technical scope of the present invention.

[0088] like Figure 1 As shown in FIG. 1 , the imaging lens unit 1 of this embodiment is combined with a solid-state imaging element S and an infrared cut filter F, and is mounted on a camera of a portable information device such as a smartphone. The imaging lens unit 1 includes a lens barrel 2 and a lens housed in the lens barrel 2. In the following description, for convenience, Figures 1 to 4 The left side in the diagram is defined as the front (or object side), and the right side is defined as the rear (or image side).

[0089] The lens barrel 2 is formed of a black and opaque resin material such as polycarbonate to which carbon is added. The lens barrel 2 has a substantially cylindrical peripheral wall portion 3 opened along the optical axis X and a front wall portion 4 formed integrally with the peripheral wall portion 3 in a manner that blocks the front opening. An opening portion 4A is formed at the center of the front wall portion 4, with the optical axis X as the center. A receiving surface 4B is formed at the rear of the front wall portion 4 and is perpendicular to the optical axis X.

[0090] In the imaging lens unit 1 of the present embodiment, seven plastic lenses are housed in the lens barrel 2. Specifically, a first plastic lens 10, a second plastic lens 20, a third plastic lens 30, a fourth plastic lens 40, a fifth plastic lens 50, a sixth plastic lens 60, and a seventh plastic lens 70 are housed in order from the object side toward the image side. In addition, although the present embodiment is configured as a structure in which seven plastic lenses are housed in the lens barrel 2, the present invention can be applied as long as it is a lens structure having at least two plastic lenses, and a glass lens may be included in a part of the lens structure.

[0091] A resin shading plate 80 to 85 is inserted between each lens of the first plastic lens 10 to the seventh plastic lens 70. The shading plates 80 to 85 have a disk shape with an opening at the center, and block unnecessary light between each lens. A spacer ring 90 is inserted between the sixth plastic lens 60 and the seventh plastic lens 70. The spacer ring 90 is a circular ring-shaped member having an opening whose diameter is larger than the diameter of the optically effective portion on the image side of the sixth plastic lens 60 and the diameter of the optically effective portion on the object side of the seventh plastic lens 70. The surface interval between the sixth plastic lens 60 and the seventh plastic lens 70 is determined by the shading plate 85 and the spacer ring 90. After the above first plastic lens 10 to the seventh plastic lens 70, the shading plates 80 to 85 and the spacer ring 90 are stored in the lens barrel 2, an annular pressing ring 91 is fixed to the peripheral wall portion 3 of the lens barrel 2 from the rear of the seventh plastic lens 70 by an adhesive or the like.

[0092] Figure 2 This is an exploded cross-sectional view of a lens assembly portion composed of the first plastic lens 10 to the seventh plastic lens 70 housed in the lens barrel 2, the light shielding plates 80 to 85, and the spacer ring 90. Figure 2 As shown, an annular step portion centered on the optical axis X is formed outside the optically effective portion, i.e., the so-called edge portion, of the first to fifth plastic lenses 10 to 50. By fitting the annular step portions of the plastic lenses, the position and posture of the plastic lenses can be accurately maintained in the lens barrel 2.

[0093] The first plastic lens 10 integrally comprises a lens portion 11 having a lens function and an edge portion 12 located at the periphery of the lens portion 11. On the object side of the edge portion 12, a contact surface 13 perpendicular to the optical axis X is formed. The contact surface 13 is formed at a position that contacts with the receiving surface 4B of the lens barrel 2. When the first plastic lens 10 is accommodated in the lens barrel 2, the contact surface 13 contacts with the receiving surface 4B of the lens barrel 2. On the other hand, on the image side of the edge portion 12, an annular step portion 14 is formed, which is composed of an inwardly conical fitting inclined surface 14A centered on the optical axis X and an annular plane 14B toward the image side connected to the outer periphery of the fitting inclined surface 14A. The annular plane 14B is formed to be perpendicular to the optical axis X.

[0094] The second plastic lens 20 integrally includes a lens portion 21 having a lens function and an edge portion 22 located at the periphery of the lens portion 21. An annular step portion 23 is formed on the object side of the edge portion 22, and the annular step portion 23 is composed of a conical fitting inclined surface 23A facing outward with the optical axis X as the center and an annular plane 23B connected to the outside from the end of the fitting inclined surface 23A. The fitting inclined surface 23A is formed at a position substantially equal to the vertical distance from the fitting inclined surface 14A of the first plastic lens 10 to the optical axis X. The annular plane 23B is formed to be perpendicular to the optical axis X. On the other hand, an annular step portion 24 is formed on the image side of the edge portion 22, and the annular step portion 24 is composed of a conical fitting inclined surface 24A facing outward with the optical axis X as the center and an annular plane 24B connected to the outside from the end of the fitting inclined surface 24A. Among them, the annular plane 24B is formed to be parallel to the annular plane 23B.

[0095] During assembly, the fitting inclined surface 23A of the second plastic lens 20 is fitted into the fitting inclined surface 14A of the first plastic lens 10, and the annular flat surface 23B of the second plastic lens 20 is abutted against the annular flat surface 14B of the first plastic lens 10. Thus, the optical axis of the first plastic lens 10 is aligned with the optical axis of the second plastic lens 20, and the surface interval between the first plastic lens 10 and the second plastic lens 20 is determined.

[0096] The third plastic lens 30 integrally includes a lens portion 31 having a lens function and an edge portion 32 located at the periphery of the lens portion 31. An annular step portion 33 is formed on the object side of the edge portion 32, and the annular step portion 33 is composed of a conical fitting inclined surface 33A facing inward with the optical axis X as the center and an annular plane 33B connected to the outside from the end of the fitting inclined surface 33A. The fitting inclined surface 33A is formed at a position substantially consistent with the vertical distance from the fitting inclined surface 24A of the second plastic lens 20 to the optical axis X. The annular plane 33B is formed to be perpendicular to the optical axis X. On the other hand, an annular step portion 34 is formed on the image side of the edge portion 32, and the annular step portion 34 is composed of a conical fitting inclined surface 34A facing inward with the optical axis X as the center and an annular plane 34B connected to the outside from the end of the fitting inclined surface 34A. Among them, the annular plane 34B is formed to be parallel to the annular plane 33B.

[0097] During assembly, the fitting inclined surface 33A of the third plastic lens 30 is fitted into the fitting inclined surface 24A of the second plastic lens 20, and the annular flat surface 33B of the third plastic lens 30 is abutted against the annular flat surface 24B of the second plastic lens 20. Thus, the optical axis of the second plastic lens 20 is aligned with the optical axis of the third plastic lens 30, and the surface interval between the second plastic lens 20 and the third plastic lens 30 is determined.

[0098] The fourth plastic lens 40 integrally includes a lens portion 41 having a lens function and an edge portion 42 located at the periphery of the lens portion 41. An annular step portion 43 is formed on the object side of the edge portion 42, and the annular step portion 43 is composed of a conical fitting inclined surface 43A facing outward with the optical axis X as the center and an annular plane 43B connected to the outside from the end of the fitting inclined surface 43A. The fitting inclined surface 43A is formed at a position substantially consistent with the vertical distance from the fitting inclined surface 34A of the third plastic lens 30 to the optical axis X. The annular plane 43B is formed to be perpendicular to the optical axis X. On the other hand, an annular step portion 44 is formed on the image side of the edge portion 42, and the annular step portion 44 is composed of a conical fitting inclined surface 44A facing outward with the optical axis X as the center and an annular plane 44B connected to the outside from the end of the fitting inclined surface 44A. Among them, the annular plane 44B is formed to be parallel to the annular plane 43B.

[0099] During assembly, the fitting inclined surface 43A of the fourth plastic lens 40 is fitted into the fitting inclined surface 34A of the third plastic lens 30, and the annular flat surface 43B of the fourth plastic lens 40 is abutted against the annular flat surface 34B of the third plastic lens 30. Thus, the optical axis of the third plastic lens 30 is aligned with the optical axis of the fourth plastic lens 40, and the surface interval between the third plastic lens 30 and the fourth plastic lens 40 is determined.

[0100] The fifth plastic lens 50 integrally includes a lens portion 51 having a lens function and an edge portion 52 located at the periphery of the lens portion 51. An annular step portion 53 is formed on the object side of the edge portion 52, and the annular step portion 53 is composed of a conical fitting inclined surface 53A facing inward with the optical axis X as the center and an annular plane 53B connected to the outside from the end of the fitting inclined surface 53A. The fitting inclined surface 53A is formed at a position substantially consistent with the vertical distance from the fitting inclined surface 44A of the fourth plastic lens 40 to the optical axis X. The annular plane 53B is formed to be perpendicular to the optical axis X. In addition, an annular plane 54 parallel to the annular plane 53B is formed on the image side of the edge portion 52. Furthermore, for the fifth plastic lens 50, its outer peripheral surface is formed to be able to fit with the inner wall surface of the peripheral wall portion 3 of the lens barrel 2.

[0101] During assembly, the fitting inclined surface 53A of the fifth plastic lens 50 is fitted into the fitting inclined surface 44A of the fourth plastic lens 40, and the annular flat surface 53B of the fifth plastic lens 50 is brought into contact with the annular flat surface 44B of the fourth plastic lens 40. Thus, the optical axis of the fourth plastic lens 40 is made to coincide with the optical axis of the fifth plastic lens 50, and the surface interval between the fourth plastic lens 40 and the fifth plastic lens 50 is determined. In addition, the fitting of the fifth plastic lens 50 with the lens barrel 2 makes the optical axes of the first to fifth plastic lenses 10 to 50 coincide with the central axis of the lens barrel 2.

[0102] The sixth plastic lens 60 integrally includes a lens portion 61 having a lens function and an edge portion 62 located at the periphery of the lens portion 61. An annular plane 63 perpendicular to the optical axis X is formed on the object side of the edge portion 62. An annular plane 64 parallel to the annular plane 63 is formed on the image side of the edge portion 62. In addition, the outer peripheral surface of the sixth plastic lens 60 is formed to be able to fit with the inner wall surface of the peripheral wall portion 3 of the lens barrel 2.

[0103] The seventh plastic lens 70 integrally includes a lens portion 71 having a lens function and an edge portion 72 located at the periphery of the lens portion 71. An annular plane 73 perpendicular to the optical axis X is formed on the object side of the edge portion 72. An annular plane 74 parallel to the annular plane 73 is formed on the image side of the edge portion 72. The pressure ring 91 abuts against the annular plane 74. The outer peripheral surface of the seventh plastic lens 70 is formed to be able to fit with the inner wall surface of the peripheral wall portion 3 of the lens barrel 2.

[0104] When the outer peripheral surface of the sixth plastic lens 60 and the outer peripheral surface of the seventh plastic lens 70 are respectively fitted into the inner wall surface of the peripheral wall portion 3 of the lens barrel 2, the optical axes of the two lenses are aligned. In addition, by sandwiching the shielding plate 84 between the fifth plastic lens 50 and the sixth plastic lens 60, the surface interval between the fifth plastic lens 50 and the sixth plastic lens 60 is determined. Similarly, by sandwiching the spacer ring 90 and the shielding plate 85 between the sixth plastic lens 60 and the seventh plastic lens 70, the surface interval between the sixth plastic lens 60 and the seventh plastic lens 70 can be determined.

[0105] As described above, by the interlocking and abutting of the annular step portions formed on the edge portions of each plastic lens and the interlocking of the outer peripheral surface of the lens with the inner wall surface of the lens barrel 2, the optical axes of the first plastic lens 10 to the seventh plastic lens 70 are consistent inside the lens barrel 2, and the surface spacing between the lenses is determined to be a constant value.

[0106] Next, the behavior of each lens in the imaging lens unit 1 of the present embodiment when each lens absorbs water will be described in comparison with a conventional imaging lens unit.

[0107] Figure 3 The following is a comparison between the structure of the edge of the second to fourth plastic lenses and the structure of the present embodiment. Figure 3 , the exploded view on the left shows the conventional second plastic lens 120, third plastic lens 130 and fourth plastic lens 140. The second plastic lenses 20, 120 and fourth plastic lenses 40, 140 are low water absorption side plastic lenses, and the third plastic lenses 30, 130 are high water absorption side plastic lenses.

[0108] In the conventional lens structure, the fitting inclined surface 124A of the second plastic lens 120 is fitted with the fitting inclined surface 133A of the third plastic lens 130, and the annular flat surface 124B of the second plastic lens 120 is in contact with the annular flat surface 133B of the third plastic lens 130. The fitting inclined surface 124A is an inwardly conical surface centered on the optical axis X, and the fitting inclined surface 133A is an outwardly conical surface centered on the optical axis X. Thus, in the relationship between the second plastic lens 120 and the third plastic lens 130, the fitting inclined surface 133A of the high water absorption side plastic lens is located at an inner side than the fitting inclined surface 124A of the low water absorption side plastic lens.

[0109] In addition, the fitting inclined surface 134A of the third plastic lens 130 is fitted with the fitting inclined surface 143A of the fourth plastic lens 140, and the annular flat surface 134B of the third plastic lens 130 is in contact with the annular flat surface 143B of the fourth plastic lens 140. The fitting inclined surface 134A is an inwardly conical surface centered on the optical axis X, and the fitting inclined surface 143A is an outwardly conical surface centered on the optical axis X. Thus, in the relationship between the third plastic lens 130 and the fourth plastic lens 140, the fitting inclined surface 134A of the high water absorption side plastic lens is located at a position further outward than the fitting inclined surface 143A of the low water absorption side plastic lens.

[0110] In such a structure, when the second plastic lens 120 to the fourth plastic lens 140 expand due to water absorption, the third plastic lens 130 tends to expand outward more than the other two plastic lenses on the low water absorption side. At this time, the fitting inclined surface 124A of the second plastic lens 120 restricts the expansion of the third plastic lens 130 in the outward direction. Therefore, stress is generated inside the second plastic lens 120 and the third plastic lens 130.

[0111] On the other hand, in the structure of the present embodiment, in the relationship between the second plastic lens 20 and the third plastic lens 30, the fitting inclined surface 33A of the high water absorption side plastic lens is located at the outer side than the fitting inclined surface 24A of the low water absorption side plastic lens. Therefore, even if the second plastic lens 20 to the fourth plastic lens 40 expand due to water absorption, the expansion of the third plastic lens 30 in the outer direction will not be restricted by the fitting inclined surface 24A. In this way, the second plastic lens 20 and the third plastic lens 30 will not be subjected to stress caused by interference between the low water absorption side plastic lens and the high water absorption side plastic lens as in the conventional lens structure.

[0112] Figure 4 FIG. 2 is a diagram showing the structure of the edge of the fourth to sixth plastic lenses, and a comparison between the conventional structure and the structure of the present embodiment. Figure 4 , the exploded view on the left shows a conventional fourth plastic lens 140, a fifth plastic lens 150, and a sixth plastic lens 160. The fourth plastic lenses 40 and 140 are low water absorption side plastic lenses, and the fifth plastic lenses 50 and 150 and the sixth plastic lenses 60 and 160 are high water absorption side plastic lenses.

[0113] In the conventional lens structure, the fitting inclined surface 144A of the fourth plastic lens 140 is fitted with the fitting inclined surface 153A of the fifth plastic lens 150, and the annular flat surface 144B of the fourth plastic lens 140 is in contact with the annular flat surface 153B of the fifth plastic lens 150. The fitting inclined surface 144A is an inwardly conical surface centered on the optical axis X, and the fitting inclined surface 153A is an outwardly conical surface centered on the optical axis X. Thus, in the relationship between the fourth plastic lens 140 and the fifth plastic lens 150, the fitting inclined surface 153A of the high water absorption side plastic lens is located at an inner side than the fitting inclined surface 144A of the low water absorption side plastic lens.

[0114] In addition, the fitting inclined surface 154A of the fifth plastic lens 150 is fitted with the fitting inclined surface 163A of the sixth plastic lens 160, and the annular flat surface 154B of the fifth plastic lens 150 is in contact with the annular flat surface 163B of the sixth plastic lens 160. The fitting inclined surface 154A is an inwardly conical surface centered on the optical axis X, and the fitting inclined surface 163A is an outwardly conical surface centered on the optical axis X. Therefore, in the relationship between the fifth plastic lens 150 and the sixth plastic lens 160, the fitting inclined surface 154A is located at a position further outward than the fitting inclined surface 163A.

[0115] In such a structure, when the fourth plastic lens 140 to the sixth plastic lens 160 expand due to water absorption, the fifth plastic lens 150 tends to expand further outward than the fourth plastic lens 140. At this time, the fitting inclined surface 144A of the fourth plastic lens 140 restricts the expansion of the fifth plastic lens 150 in the outward direction. Therefore, stress is generated inside the fourth plastic lens 140 and the fifth plastic lens 150.

[0116] On the other hand, in the structure of the present embodiment, in the relationship between the fourth plastic lens 40 and the fifth plastic lens 50, the fitting inclined surface 53A of the high water absorption side plastic lens is located at a position further outward than the fitting inclined surface 44A of the low water absorption side plastic lens. Therefore, even if the fourth plastic lens 40 to the sixth plastic lens 60 expand due to water absorption, the expansion of the fifth plastic lens 50 in the outward direction will not be restricted by the fitting inclined surface 44A. In this way, the fourth plastic lens 40 and the fifth plastic lens 50 will not be subjected to stress caused by interference between the low water absorption side plastic lens and the high water absorption side plastic lens as in the conventional lens structure.

[0117] Next, the results of simulation of stress caused by water absorption and the amount of change in the lens surface interval are described for each plastic lens of the camera lens unit 1. Here, nonlinear static analysis (thermal analysis) is used instead of material property values ​​in a high temperature and high humidity environment to pseudo-simulate water absorption of the lens. In addition, the content shown below is only the result of simulation under certain conditions, and various factors need to be considered for the phenomenon that occurs in each plastic lens in a real environment.

[0118] In this simulation, the temperature is raised from 25°C to 85°C, maintained at 85°C, and cooled from 85°C to 25°C, and the maximum stress generated in each lens and the change in the surface spacing between lenses under these environments are evaluated. The heating time, heat retention time, and cooling time are set to be the same. From the time of heating to the time of heat retention, the value obtained by adding the linear expansion coefficient converted from the volume expansion coefficient of water absorption to the linear expansion coefficient of the material is used, that is, the linear expansion coefficient of water absorption (hereinafter referred to as "converted linear expansion coefficient") is taken into account, and the linear expansion coefficient of the material is used when cooling. The volume expansion coefficient here is assumed to be the value when the volume expands to the equivalent of the saturated water absorption rate. Below, the linear expansion coefficient, the volume expansion coefficient of water absorption, and the converted linear expansion coefficient of the first plastic lens 10 to the seventh plastic lens 70 and the lens barrel 2 of this embodiment are shown. In addition, the first plastic lens 10 to the seventh plastic lens 70 and the first plastic lens to the seventh plastic lens in the previous lens structure are represented as L1 to L7.

[0119]

[0120] In the camera lens unit 1 of the present embodiment, the third plastic lens 30 (L3), the fifth plastic lens 50 (L5) and the sixth plastic lens 60 (L6) correspond to the high water absorption side plastic lens on the side with high water absorption rate, and the first plastic lens 10 (L1), the second plastic lens 20 (L2), the fourth plastic lens 40 (L4) and the seventh plastic lens 70 (L7) correspond to the low water absorption side plastic lens on the side with low water absorption rate. The linear expansion coefficient of the high water absorption side plastic lens is larger than the linear expansion coefficient of the low water absorption side plastic lens.

[0121] When the water absorption rate of the low water absorption side plastic lens is β1 and the water absorption rate of the high water absorption side plastic lens is β2, the first plastic lens 10 to the seventh plastic lens 70 satisfy the following conditional expressions (1) and (2):

[0122] β1<0.1% (1),

[0123] β2>0.2%(2).

[0124] In addition, when the water absorption rate of the lens barrel 2 is higher than the water absorption rates of the first plastic lens 10 to the seventh plastic lens 70 and the water absorption rate of the resin material of the lens barrel 2 is set to β3, the following conditional expression (3) is satisfied:

[0125] β3>0.4% (3).

[0126] The following shows the results of a simulation of the maximum stress generated inside the lens when the temperature rises.

[0127] Conventional lens structure

[0128]

[0129] Lens structure of this embodiment

[0130]

[0131] Figure 5 : is a graph showing the maximum stress inside the lens generated when the temperature rises. In the graph, the dotted line represents the maximum stress value in the conventional lens structure, and the solid line represents the maximum stress value in the lens structure of this embodiment. Figure 5 As shown, according to the lens structure of this embodiment, the stress generated inside each plastic lens can be reduced to substantially zero.

[0132] Next, the results of simulating the change in the lens surface spacing on the optical axis during temperature reduction are shown. In addition, the surface spacing between the first plastic lens and the second plastic lens is represented as "L1-L2", and the surface spacing between the second plastic lens and the third plastic lens is represented as "L2-L3", and the surface spacing between other plastic lenses is represented in the same manner.

[0133] Conventional lens structure

[0134]

[0135] Lens structure of this embodiment

[0136]

[0137] Figure 6 : is a graph showing the amount of change in the lens surface spacing on the optical axis when the temperature is lowered. In the graph, the dotted line shows the amount of change in the lens surface spacing in the conventional lens structure, and the solid line shows the amount of change in the lens surface spacing in the lens structure of this embodiment. Figure 6 As shown, according to the lens structure of this embodiment, the amount of change in the lens surface interval can be made smaller than that of the conventional lens structure.

[0138] Industrial Applicability

[0139] The present invention can be mounted on a camera built into a portable information device such as a smartphone, a home appliance, or a car, and can be applied to fields requiring stable optical performance.

Claims

1. A camera lens unit, characterized in that: The lens barrel is formed of a resin material and a plurality of plastic lenses are accommodated in the lens barrel. The lens barrel is made of black, opaque resin material. At least two adjacent plastic lenses among the plurality of plastic lenses have different water absorption rates and are formed to be able to fit into conical fitting inclined surfaces centered on the optical axis outside their respective optically effective portions. In the adjacent plastic lenses, the fitting inclined surface of the high water absorption side plastic lens on the side with high water absorption is formed outside the fitting inclined surface of the low water absorption side plastic lens on the side with low water absorption; When the water absorption rate of the low water absorption side plastic lens is set to β1, the water absorption rate of the high water absorption side plastic lens is set to β2, and the water absorption rate of the lens barrel is set to β3, the following conditions are satisfied: β1＜0.1％，β2＞0.2％，β3＞0.4％； The water absorption rate of the lens barrel is higher than the water absorption rate of the plurality of plastic lenses; The linear expansion coefficient of the high water absorption side plastic lens is greater than the linear expansion coefficient of the low water absorption side plastic lens; At least one of the outer peripheral surfaces of the highly water-absorbent plastic lens is fitted into the inner wall surface of the lens barrel.

Images