Lens design and manufacturing method

Abstract

The present invention discloses a lens comprising a central portion comprising a first polymer; and a peripheral portion comprising a second polymer; wherein the peripheral portion surrounds the central portion; and wherein the peripheral portion has a skeletal density greater than its bulk density. The present invention also discloses a method of manufacturing a lens and an article containing the lens, the method comprising injecting a molten polymer into a mold to produce the lens; wherein the lens comprises a central portion; and a peripheral portion; wherein the peripheral portion surrounds the central portion; and wherein the peripheral portion has a skeletal density greater than its bulk density.

Description

Technical Field

[0001] The present invention discloses a lens design and a manufacturing method thereof, and in particular, discloses a lens capable of adapting to mismatched thermal expansion coefficients and a manufacturing method thereof. Background Art

[0002] Advanced Driver Assistance Systems (ADAS) are used in vehicles to assist drivers while driving. When designed with a safe human-machine interface, they aim to improve automotive safety and, more generally, road safety.

[0003] Advanced driver assistance systems (ADAS) are systems developed to automate, adapt, and enhance vehicle systems for safer and better driving. The automated systems ADAS provide vehicles have been proven to reduce road accidents by mitigating the human errors that often cause them. Safety features are designed to prevent collisions and accidents by providing technologies that warn the driver of potential problems or by implementing protective measures and taking control of the vehicle to avoid a collision. Adaptive features can automatically illuminate, provide adaptive cruise control and collision avoidance, pedestrian collision avoidance (PCAM) mitigation, incorporate satellite navigation / traffic warnings to warn the driver of other vehicles or hazards, lane departure warning systems, automatic lane centering, display blind spots, or connect to a smartphone for navigation instructions. ADAS relies on input from multiple data sources, including automotive imaging, light detection and ranging (LiDAR), radar, image processing, computer vision, and in-vehicle networking.

[0004] To facilitate automotive imaging, ADAS systems often incorporate lenses as part of their optical equipment. To make ADAS systems accessible to a wider audience, there is a desire to reduce costs while improving performance. However, lower-cost lenses have drawbacks that must be overcome to make them suitable for use in ADAS systems. Summary of the Invention

[0005] In one exemplary embodiment, a lens includes a central portion comprising a first polymer and a peripheral portion comprising a second polymer, the peripheral portion surrounding the central portion, and having a skeleton density greater than a bulk density of the peripheral portion.

[0006] In another exemplary embodiment, the composite coefficient of thermal expansion of the peripheral portion is lower than the composite coefficient of thermal expansion of the central portion.

[0007] In another exemplary embodiment, the first polymer and the second polymer are the same.

[0008] In another exemplary embodiment, the first polymer is different from the second polymer.

[0009] In yet another exemplary embodiment, the peripheral portion includes a cavity.

[0010] In yet another exemplary embodiment, the cavities are evenly distributed throughout the entire peripheral portion.

[0011] In yet another exemplary embodiment, the peripheral portion comprises foam.

[0012] In yet another exemplary embodiment, the central portion extends to the peripheral portion, and opposing faces of the peripheral portion are parallel to each other.

[0013] In yet another exemplary embodiment, the curved surface of the central portion surrounds the peripheral portion, and the peripheral portion of the lens has no parallel surfaces.

[0014] In yet another exemplary embodiment, the cross-sectional geometry of the cavity as viewed in a plane parallel to the paper is square, rectangular, circular, elliptical, polygonal, or a combination thereof.

[0015] In yet another exemplary embodiment, areas of the peripheral portion that contain cavities are larger than those areas that do not contain cavities.

[0016] In yet another exemplary embodiment, the first polymer and the second polymer include cyclic olefin polymers.

[0017] In yet another exemplary embodiment, the cyclic olefin polymer comprises a cyclic olefin copolymer.

[0018] In yet another exemplary embodiment, an article includes a lens comprising a central portion and a peripheral portion, wherein the peripheral portion surrounds the central portion and has a skeletal density greater than a bulk density.

[0019] In another exemplary embodiment, the article is an automobile.

[0020] In one exemplary embodiment, a method of manufacturing a lens includes injecting a molten polymer into a mold to form the lens. The lens includes a central portion and a peripheral portion. The peripheral portion surrounds the central portion. The peripheral portion has a skeletal density greater than its bulk density.

[0021] In another exemplary embodiment, the molten polymer comprises a polyolefin.

[0022] In yet another exemplary embodiment, the polyolefin comprises a cyclic olefin copolymer.

[0023] In yet another exemplary embodiment, the lens is disposed in a fixture.

[0024] In yet another exemplary embodiment, the lens is arranged in a fixture arranged in a car.

[0025] The above features and advantages and other features and advantages of the present disclosure will be apparent from the following detailed description when considered in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Additional features, advantages, and details appear, by way of example only, in the following detailed description, which refers to the accompanying drawings, in which:

[0027] FIG. 1(A) is a depiction of a side view of a prior art lens;

[0028] FIG. 1(B) is a depiction of a top view of the prior art lens of FIG. 1(A);

[0029] FIG2(A) is a depiction of a side view of an exemplary schematic diagram of a lens disclosed herein;

[0030] FIG2(B) is a view of a cross section taken along line YY′ of FIG2(A);

[0031] FIG2(C) is another view of a cross section taken along line YY′ of FIG2(A);

[0032] FIG3(A) is a depiction of a side view of an exemplary schematic diagram of a lens disclosed herein;

[0033] FIG3(B) is a view of a cross section taken along line YY′ of FIG3(A);

[0034] FIG4(A) is a depiction of a lens having a circular cavity in the peripheral portion;

[0035] FIG4(B) is a depiction of a lens having a rectangular cavity in the peripheral portion;

[0036] FIG4(C) is a depiction of a lens having an S-shaped cavity in the peripheral portion;

[0037] FIG4(D) is a depiction of a lens having a circular cavity in the peripheral portion;

[0038] FIG4(E) is a depiction of a lens having a circular cavity in the peripheral portion;

[0039] FIG5(A) depicts another embodiment of a lens having a plurality of cavities in a peripheral portion;

[0040] FIG5(B) depicts a cross-sectional view of the lens of FIG5(A);

[0041] FIG5(C) depicts an isometric view of the lens of FIG5(A);

[0042] FIG5(D) depicts an isometric view of the lens of FIG5(B);

[0043] FIG6(A) depicts another embodiment of a lens having a plurality of cavities in a peripheral portion;

[0044] FIG6(B) is a cross-sectional view taken along section XX' of FIG6(A); and

[0045] FIG. 6(C) is an isometric view of the lens of FIG. 6(A). DETAILED DESCRIPTION

[0046] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0047] Bulk density is defined as the mass of an object divided by the volume it occupies. The volume occupied by an object is calculated without considering any pores or cavities. For example, consider an object with a mass of M, a width of W, a height of H, and a length of L. This object also has three circular channels of radius R drilled through it over a length of L. The bulk density of this object is calculated by dividing its mass (M) by its volume (W × H × L). In other words, the volume of the pores is not considered when calculating bulk density.

[0048] Bone density is defined as the mass of an object divided by the total volume it occupies. In other words, bone density is the density of a material without any pores or cavities. The skeletal density of an object with mass (M) as detailed above would be calculated by dividing the mass (M) by the volume (W × H × L – 3 × πR 2 L). In other words, the volume of the three circular channels with radius R and length L is subtracted from the volume (W × H × L) to give the bone density. This is sometimes called the true density.

[0049] Description of Embodiments

[0050] Disclosed herein are polymer-containing lenses for use in automotive ADAS systems. This disclosure presents a novel approach to minimizing radial stresses in polymer lenses caused by mismatched coefficients of thermal expansion (CTE) and other environmental stresses. The lenses are designed to accommodate forces caused by CTE mismatch with the supporting device, thereby preventing damage to the lenses and mitigating the effects of providing erroneous signals to the driver of the car containing the ADAS system. The polymer lenses are designed to have cavities around the periphery of the lenses. By positioning these cavities around the periphery of the lenses, the field of view of the lenses is not disturbed, and the lenses can expand and contract without temporary or permanent deformation. The performance of the lenses is thus stabilized while minimizing the cost of the lenses used in ADAS systems.

[0051] Polymer lenses are also much cheaper than lenses containing glass. However, the coefficient of thermal expansion (CTE) of these polymer lenses is higher than that of glass lenses, and the CTE mismatch with the supporting device (containing the polymer lens) often leads to undesirable deformation. The high-performance lenses currently used in ADAS systems are made of a metal barrel and all glass elements to minimize aberrations. These lenses differ from the lenses used to display video to the driver in that the fidelity of the image produced by the lens is used by the algorithms trained to perform perception and modeling. When the user of the video is a human, such small aberrations are insignificant and lower performance lenses can be used.

[0052] Figures 1(A) and 1(B) depict a conventional lens 100. The lens includes a peripheral portion 102 surrounding a central portion 104. Light enters the lens through the central portion 104. The light entering the lens is ultimately transmitted to an image sensor (not shown), etc. The lens 100 is placed in a support device (not shown) that provides support and maintains its position during vehicle operation. In one embodiment, the peripheral portion and the central portion form a solid, integral piece. Neither the central portion nor the peripheral portion contains any cavities.

[0053] The central portion 104 is generally circular with a radius R2, while the peripheral portion 102 is also circular, with a radius R1 greater than R2. When the lens 100 is subjected to temperature changes, the peripheral portion 102 expands and contracts most circumferentially (as indicated by arrow R3). The maximum expansion (which occurs when the temperature rises) generally promotes an increase in the outer circumference of the lens 100. However, because the lens 100 is constrained in a support device (not shown) that contacts the lens 100 at its periphery 102, the material at the periphery of the lens 100 is subject to compressive forces.

[0054] Similarly, when the lens 100 is subjected to a decrease in temperature, the circumferential length of the lens 100 will decrease. However, because the lens 100 is constrained in a support device (not shown) that contacts the lens 100 at its periphery 102, the material at the periphery of the lens 100 will be subjected to elongation forces.

[0055] Over time, these continuous compressive and elongation forces will promote deformation of the lens. Furthermore, if any of these forces become too great, they may cause temporary deformation of the lens prescription, leading to aberrations. To overcome these aberrations, it is desirable to modify the periphery of the lens by including cavities in the peripheral portion, thereby accommodating expansion or contraction of the lens's periphery without causing any temporary or permanent deformation of the lens and without any distortion of the field of view. In other words, the skeleton density of the peripheral portion of the lens is higher than its bulk density.

[0056] Figures 2(A) and 2(B) illustrate an exemplary schematic diagram of a lens 200 that can accommodate compressive or elongation stresses without any deformation because the peripheral portion has a higher bone density than its bulk density. Lens 200 includes a peripheral portion 202 surrounding a central portion 204. The peripheral portion is in continuous contact with the central portion. In one embodiment, the peripheral portion and the central portion form a single, solid, integral piece. Peripheral portion 202 includes a plurality of cavities 206 distributed therethrough. Some of the cavities in the peripheral portion are not used to accommodate fasteners, such as screws, bolts, nuts, rivets, etc., which are typically used to secure the lens to a support device. Some of the cavities in the peripheral portion are used to accommodate fasteners, such as screws, bolts, nuts, rivets, etc., which are typically used to secure the lens to a support device. The support device is a structure that secures the lens in place during use. Figure 2(A) is a front view of the lens of the present invention, which includes cavities 206 distributed throughout the peripheral portion 202, while Figure 2(B) is a cross-sectional view taken along line YY′ of Figure 2(A). In one embodiment, some of the cavities may be used to accommodate both increases or decreases in size due to temperature changes and to accommodate fasteners such as screws, bolts, nuts, rivets, etc., which are typically used to secure the lens to the support.

[0057] 3(A) and 3(B) are depictions of another exemplary embodiment of a lens 200. The difference between the lenses in FIG2(A) and 3(A) lies in the change in the shape of the lens, and therefore the shape of the corresponding cavity. In FIG2(A), the lens 200 includes a central portion 204 whose curvature terminates when it contacts a peripheral portion 202 (which has parallel opposing faces or sides 210 and 212) (see FIG2(B)). In FIG3(A), the curved surface of the central portion of the lens surrounds the peripheral portion 202. The peripheral portion 202 of the lens in FIG3(B) does not have parallel surfaces.

[0058] 2(A), 2(B), 3(A), and 3(B), it can be seen that the peripheral portion 202 is concentric with the central portion 204. In one embodiment, the peripheral portion 202 is coaxial with the central portion 204. It should also be noted that while the lenses shown in FIG2(A), 2(B), 3(A), and 3(B) have opposing convex surfaces, the lenses may also have opposing concave surfaces, or alternatively, have one convex surface and opposing concave surfaces.

[0059] The cavity 206 present in the peripheral portion absorbs the forces generated by the CTE mismatch with the support device (not shown). The support device contacts the lens 200 at its periphery, and most of the heat transfer occurs between the peripheral portion and the support device. The presence of the cavity 206 allows the polymer material in the peripheral portion 202 to expand into the cavity, thereby minimizing the forces transferred from the peripheral portion to the central portion. In addition, if the solid portion 202 forms an angle greater than zero with R1, the stress will be further reduced due to the spring action. This prevents deformation of the central portion and minimizes the aberration of the object being imaged. This also prevents the lens from being constantly replaced due to permanent deformation (sometimes called permanent fixation). In one embodiment, the peripheral portion includes multiple cavities surrounding the entire central portion of the lens. In another embodiment, the peripheral portion includes multiple cavities extending around only a portion of the central portion of the lens.

[0060] The number of cavities depends on the size of each cavity, the radius of the lens, and the area occupied by the peripheral portion of the lens. In one embodiment, the peripheral portion includes 3 or more cavities, 4 or more cavities, 5 or more cavities up to 100 or fewer cavities, 75 or fewer cavities, and 50 or fewer cavities.

[0061] In one embodiment, referring now to FIG. 2(A), cavity walls 208 are closer together at outer radius R1 than at inner radius R2. Because greater strain is more likely to be encountered as one moves further from the center of the lens, this feature better absorbs CTE mismatches with surrounding materials (e.g., support fixtures). The cavities in FIG. 2(B) extend from one surface 210 to the opposing surface 212 of the peripheral portion (i.e., they extend through the thickness of the peripheral portion). Note that the cavities do not have to extend from surface 210 to the opposing surface 212; they can be positioned internally within the peripheral portion 202 and surrounded on all sides by polymer, as shown in FIG. 2(C). FIG. 2(C) is another cross-section taken along line YY′ of FIG. 2(A). In this case, the internal cavity 206 can be filled with a cooling fluid or phase transfer material capable of absorbing some of the heat experienced by the lens. Note that in this embodiment, the cooling fluid or phase transfer material is permanently trapped within the cavity.

[0062] The cavity 206 can have a variety of geometric shapes. The geometry can be regular (having a shape defined by Euclidean geometry) or irregular (having a non-Euclidean shape). For example, the cross-sectional area of ​​the cavity along the plane around line YY′ (in Figures 2(A) and 3(A)) can be rectangular, circular, square, elliptical, polygonal, or a combination thereof. Similarly, the cross-sectional area of ​​the cavity along the plane perpendicular to the plane around line YY′ can be rectangular, circular, square, elliptical, polygonal, or a combination thereof. The cavities 206 can be uniformly or non-uniformly distributed along the peripheral portion. They can be periodic or non-periodic. In a preferred embodiment, the cavities have a regular shape and are uniformly distributed in the peripheral portion.

[0063] In one embodiment, an equivalent cavity-like structure can be created in the peripheral portion by foaming a portion of the polymer. The foamed portion is present only in the peripheral portion and ensures that the skeletal density of the peripheral portion is greater than the bulk density of the same area. The foamed portion can include open-cell foam, closed-cell foam, or a combination thereof. It can extend in a band around the entire lens, or alternatively, only in a portion of the peripheral portion.

[0064] Figures 4(A), 4(B), 4(C), 4(D), and 4(E) depict isometric views of various cavities that may be used in the peripheral region 202 to provide CTE matching characteristics to the lens 200. Figure 4(A) is an exemplary depiction of a lens 200 having cavities with a circular cross-sectional profile (in a plane parallel to the paper) distributed along the peripheral portion 202, while Figure 4(B) is an exemplary depiction of a lens 200 having cavities with a rectangular cross-sectional profile (in a plane parallel to the paper) distributed along the peripheral portion 202. Figure 4(C) is an exemplary depiction of a lens 200 having cavities with an S-shaped cross-sectional profile (in a plane parallel to the paper) distributed along the peripheral portion 202.

[0065] Figures 4(D) and 4(E) are exemplary depictions of a lens 200 having cavities that are evenly distributed but spaced farther apart than the cavities depicted in Figures 4(A) to 4(C). In Figures 4(D) and 4(E), it can also be observed that the areas having cavities have a larger radius than the rest of the peripheral portion 202 that does not have cavities.

[0066] While Figures 4(A) through 4(E) depict a lens having a peripheral region with opposing parallel surfaces extending outward from a central portion 104 (similar to the lenses in Figures 2(A) and 2(B)), these features may also be incorporated into lenses (not shown) in which the curvature extends to the outer boundaries of the lens (i.e., in which the curved surfaces of the lens surround the peripheral portion (similar to the lenses in Figures 3(A) and 3(B))).

[0067] Figures 5(A), 5(B), 5(C) and 5(D) depict another embodiment of a lens 200. In Figure 5(A), it can be seen that the peripheral portion 202 (which surrounds the central portion 204) contains a cavity in the form of a slot 214 and extends from the inner radius (R2) (see Figure 5(B)) to the outer radius (R1) of the peripheral portion. In addition, the peripheral portion 202 is angled relative to an axis (LL') passing through the center of mass of the lens and the outer corner 216 where the central portion 204 intersects the peripheral portion. Figure 5(B) is a depiction of a cross-section of the lens taken along section XX' of Figure 5(A). It can be seen that the peripheral portion is angled relative to the axis LL'. The angle θ can vary between 5 degrees and 60 degrees, preferably between 15 degrees and 45 degrees. At least a portion of the plurality of slots is not used to accommodate fasteners such as screws, bolts, nuts, rivets, etc., which are typically used to secure the lens to a support device. At least some of the slots may be used to receive fasteners such as screws, bolts, nuts, rivets, etc., which are typically used to secure the lens to the support means.

[0068] Figures 5(C) and 5(D) are isometric views of the lenses of Figures 5(A) and 5(B), respectively. When the lens is subjected to temperature changes, the cavity 214 in the peripheral portion 202 absorbs some of the differential expansion that occurs between the central portion 204 and the peripheral portion 202, thereby preventing distortion of the field of view.

[0069] FIG6(A) is another exemplary depiction of a lens 200 in which the peripheral portion 202 is significantly larger at the location of cavity 214 than elsewhere around the lens. In other words, the radius at the location of cavity 214 is larger than the radius of the rest of the peripheral portion 202. The cavity can have an elongated cross-sectional area (with the elongated axis YY′ parallel to a tangent to the circumference), so that it can accommodate changes in material dimensions due to temperature changes. The elongated cross-sectional area of ​​the cavity also allows for a chamber to accommodate fasteners such as screws, bolts, nuts, rivets, etc., which are typically used to secure the lens to a supporting device. FIG6(B) is a cross-sectional view of the lens of FIG6(A). As can be seen in FIG6(B), the peripheral portion 202 of the lens 200 is surrounded by the curvature of the central portion 204 of the lens. FIG6(C) depicts an isometric view of the lens 200 of FIG6(A). As can also be seen in FIG6(C), the radius of the area surrounding cavity 214 is significantly larger than the radius of the rest of the peripheral portion 202.

[0070] As described above, the skeleton density of the peripheral portion of the lens is greater than the bulk density. The skeleton density of the peripheral portion can be equal to the bulk density of the central portion of the lens. It should also be understood that the coefficient of thermal expansion of the peripheral portion is lower than the coefficient of thermal expansion of the central portion. The coefficient of thermal expansion of the peripheral portion is a composite of the coefficients of thermal expansion of the material in the cavity (air) and the lens construction materials, while the coefficient of thermal expansion of the central portion is solely the coefficient of thermal expansion of the lens construction materials.

[0071] The material used in the lens is an optically transparent polymer. In one embodiment, the polymer is preferably a water-resistant, UV-radiation-resistant and abrasion-resistant polymer. If desired, a water-resistant and / or abrasion-resistant coating may be provided on the lens. UV-resistant coatings, heat stabilizers, UV absorbers, infrared-resistant coatings, etc. may also be used in or on the lens. It is desirable that the transmittance of the polymer material be greater than 85%, preferably greater than 90%, and more preferably greater than 95% when measured according to ASTM D1003. The refractive index of the polymer used in the lens may be between 1.1 and 1.7, preferably between 1.2 and 1.65, and more preferably between 1.45 and 1.58. If desired, a higher refractive index coating, such as a coating containing titanium dioxide or zirconium oxide, may be provided on the lens.

[0072] In one embodiment, a single polymer may be used throughout the lens. In another embodiment, a first polymer may be used in the central portion of the lens, while a second polymer may be used in the peripheral portion. In one embodiment, the first polymer may be the same as the second polymer. In another embodiment, the first polymer may be different from the second polymer.

[0073] The polymer used in the lens can be selected from a variety of thermoplastic polymers, blends of thermoplastic polymers, thermosetting polymers, or blends of thermoplastic polymers and thermosetting polymers. The polymer is preferably an organic polymer. The polymer may include a blend, copolymer, terpolymer, or a combination thereof of polymers. The polymer may also be an oligomer, a homopolymer, a copolymer, a block copolymer, an alternating block copolymer, a random copolymer, a graft copolymer, a star block copolymer, a dendrimer, a polyelectrolyte (a polymer having some repeating groups, which contains an electrolyte), a polyampholyte (a polyelectrolyte having cationic and anionic repeating groups), an ionomer, or the like, or a combination thereof. The number average molecular weight of the organic polymer is greater than 10,000 g / mol, preferably greater than 20,000 g / mol, and more preferably greater than 50,000 g / mol. The upper limit of the number average molecular weight of the polymer may be 1,000,000 g / mol.

[0074] Examples of organic polymers that can be used in the lenses are polyolefins, polyacrylates, polyacrylates, polymethacrylates, polycarbonates, polystyrenes, polyesters, polyimides, polyetherimides, and the like, or combinations thereof. Polyolefin lenses are preferred.

[0075] The polyolefin is preferably a polyolefin that has low ultraviolet (UV) absorption when exposed to ambient light. Suitable examples of polyolefins are cyclic olefin polymers. In one embodiment, the cyclic olefin polymer comprises a cyclic olefin copolymer. Cyclic olefin copolymers are obtained by combining cyclic monomers such as 8,9,10-trinorbornene-2-ene (norbornene) or 1,2,3,4,4a,5,8,8a-octahydro-1,4:5,8-dimethylnaphthalene (tetracyclododecene) with ethylene (e.g., TOPAS Advanced Polymer). Mitsui Chemical ) chain copolymerization or by ring-opening metathesis polymerization of various cyclic monomers followed by hydrogenation (Japan Synthetic Rubber Zeon Chemical and ) manufactured.

[0076] In one embodiment, in a method of making the disclosed lens, a suitable polymer (e.g., one or more of the cyclic olefin copolymers listed above) is fed into an injection molding machine, where it is formed into a mold having a negative image of the lens shown in the figure. The polymer is injected into the mold at a suitable flow temperature that prevents the formation of pinholes and other defects. The walls of the mold are cooled with a coolant, causing the melt to solidify, at which point it is ejected from the mold. Large quantities of lenses can be produced in this manner.

[0077] In one embodiment, the lenses may also be manufactured by methods such as compression molding, vacuum forming, blow molding, etc. In another embodiment, additive manufacturing may be used to manufacture the lenses disclosed herein. In yet another embodiment, a combination of one or more of injection molding, vacuum forming, blow molding, compression molding may be used in conjunction with additive manufacturing.

[0078] In one embodiment, the molding operation for making the mold is prepared in a two-step process. In another embodiment, when the lens includes a foamed peripheral portion, the foamed peripheral portion can be first injection molded in a first molding step. A suitable foaming agent, such as liquid carbon dioxide, liquid nitrogen, etc., can be used to produce the foam. The molded foamed peripheral portion is then placed in a second mold, and the central portion is subsequently injected into the mold and fused with the peripheral portion during the second molding operation. The polymer used in the central portion (first polymer) can be the same or different from the polymer used in the peripheral portion (second polymer). The mold is then cooled, and the molded lens with the foamed peripheral portion and the optically clear central portion is ejected.

[0079] The lenses can be processed to remove any mold lines and then placed in structural devices used in automobiles, medical devices inserted into the body such as catheters, and downhole drilling tools to measure excavation progress.

[0080] Although the present invention has been described with reference to some embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for its elements without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope of the present disclosure. Therefore, it is intended that the present disclosure is not limited to the specific embodiments disclosed as the best mode intended for carrying out the present disclosure, but that the present disclosure will include all embodiments falling within the scope of the appended claims.

Claims

1. A lens comprising: a central portion comprising a first polymer; and a peripheral portion comprising a second polymer; wherein the peripheral portion surrounds the central portion; and Wherein the skeleton density of the peripheral portion is greater than its bulk density; wherein the peripheral portion comprises a cavity; the cavity being disposed internally within the peripheral portion and surrounded on all sides by the second polymer. 2 . The lens according to claim 1 , wherein the composite thermal expansion coefficient of the peripheral portion is lower than the thermal expansion coefficient of the central portion.

3. The lens of claim 1, wherein the first polymer is the same as the second polymer.

4. The lens of claim 1, wherein the first polymer is different from the second polymer.

5. The lens of claim 4, wherein the cavities are evenly distributed throughout the peripheral portion. The lens of claim 1 , wherein the peripheral portion comprises foam.

7. The lens of claim 1, wherein the central portion extends to the peripheral portion, and wherein opposing faces of the peripheral portion are parallel to each other.

8. The lens of claim 1, wherein the curved surface of the central portion surrounds the peripheral portion, and wherein the peripheral portion of the lens has no parallel surfaces.

9. The lens of claim 1, wherein the cross-sectional geometry of the cavity as viewed on a plane parallel to the paper is square, rectangular, circular, elliptical, polygonal, or a combination thereof.

10. The lens of claim 1, wherein areas of the peripheral portion that contain cavities are larger than those areas that do not contain cavities.

11. The lens of claim 3, wherein the first polymer and the second polymer comprise cyclic olefin polymers.

12. The lens of claim 11, wherein the cyclic olefin polymer comprises a cyclic olefin copolymer.

13. An article comprising the lens of claim 1.

14. The article of claim 13, wherein the article is an advanced driver assistance system.

15. A method for manufacturing a lens, suitable for manufacturing the lens according to any one of claims 1 to 14, the method comprising: injecting a molten polymer into a mold to produce the lens; The lens comprises: central portion; and a peripheral portion; wherein the peripheral portion surrounds the central portion; and wherein the peripheral portion has a skeletal density greater than its bulk density.

16. The method of claim 15, wherein the molten polymer comprises a polyolefin.

17. The method of claim 16, wherein the polyolefin comprises a cyclic olefin copolymer.

18. The method of claim 15, further comprising placing the lens in a fixture.

19. The method of claim 18, wherein the lens arranged in the fixture is arranged in an advanced driver assistance system.

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