Abstract:
The lens is made by injection molding in a mold through the injection of molten plastic material in at least three injection shots using a multistep process. It includes a first outer lens part, a second outer lens part and a lens core part forming an interior of the lens. The lens core part is embedded between the first and second outer lens parts. The lens core part is divided into at least two subparts separated at least partially by at least one elongated slot extending across the lens core part between the first and second surfaces of the lens core part. The slot or slots made through the lens core part are filled and fused with the plastic material of the first outer lens part.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     The present case is a continuation of PCT patent application No. PCT/CA2014/050735 filed on 5 Aug. 2014. PCT patent application No. PCT/CA2014/050735 claims the benefits of U.S. patent applications Nos. 61/862,366 filed on 5 Aug. 2013 and 61/899,006 filed on 1 Nov. 2013. The contents of all these prior applications are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The technical field relates generally to lenses made by injection molding. 
     BACKGROUND 
     Illumination apparatuses for automotive vehicles often use powerful incandescent light sources that generate an intense heat. These light sources are generally optically coupled to optical glass lenses since glass can withstand the generated heat and will not deform in use. However, the heat from most incandescent light sources is generally too high for optical lenses made of plastic materials. 
     Solid state light sources generate considerably less heat than incandescent light sources having the same illumination power. White LEDs are increasingly used as light sources in illumination apparatuses for the automotive industry, for example in head lights. Such illumination apparatuses can thus include optical lenses made of plastic materials because heat is not as high as with incandescent light sources. 
     Illumination apparatuses for automotive vehicles generally use thick lenses to project the light in front of the vehicles. The light beam from the light sources is projected as a magnified image and the lens refracts the light beams accordingly. Thick lenses have a relatively high ratio between the thickness of the lens along the central optical axis and the thickness of the lens at the edges. These optical lenses are thus relatively thicker compare to optical lenses in other applications, as defined by the standard understanding in the industry in terms of the ratio between the key dimensions of optical lenses. 
     Thick lenses made of plastic materials are not easy to manufacture using usual injection molding methods because the injection molding process itself may cause deformations of the optical active surfaces. For instance, these lenses tend to shrink during cooling in a manner that reduces their accuracy and performances. Ultimately, the quality of thick lenses made of plastic materials can become an issue, particularly when high production volumes are required. One example of such context is the automotive and lighting industries. Using the known injection methods thus create challenges in terms of costs and complexities. Other injection molding issues can have a negative impact on the quality of thick lenses, particularly in terms of having a stable batch-to-batch consistency and surface accuracy. 
     Multistep injection methods for manufacturing plastic lenses have been used for several years. For instance, such method can include using rotary molds or shuttle molds to inject two or more layers of the same plastic material over one another with a clear boundary surface between each layer. However, several applications require stringent tolerances of the shape and the curvatures of optical lenses that can be difficult to obtain using these known methods, particularly for manufacturing thick lenses. 
     Clearly, room for improvements always exists in this area of technology. 
     SUMMARY 
     There is provided herein a thick lens for use with a light source, the lens being made by injection molding in a mold through the injection of a molten plastic material in at least three injection shots using a multistep process, the lens including: a first outer lens part having opposite first and second surfaces, the first surface of the first outer lens part defining a first optical active surface of the lens that refracts incoming light beams from the light source; a second outer lens part having opposite first and second surfaces, the first surface of the second outer lens part defining a second optical active surface of the lens that refracts the incoming light beams from the light source; and a lens core part forming an interior of the lens and that is embedded between the first outer lens part and the second outer lens part, the lens core part having opposite first and second surfaces, the lens core part being divided into at least two subparts separated at least partially by at least one elongated slot extending across the lens core part between the first and second surfaces of the lens core part; wherein the second surface of the first outer lens part and the first surface of the lens core part are fused together, the second surface of the second outer lens part and the second surface of the lens core part are fused together, and the at least one slot made through the lens core part is filled and fused with the plastic material of the first outer lens part, the lens having a lens body that is entirely filled with the plastic material in a gapless manner to prevent refraction inside the lens body of light beams from the light source. 
     There is also provided an illumination apparatus including: a solid state light source; and a thick lens through which light from the solid state light source is collected, the lens being constructed as previously defined. 
     Details on various aspects and features of the proposed concept will be apparent from the following detailed description and the appended figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is an isometric view illustrating an example of a generic thick lens as suggested herein; 
         FIG. 2  is a front view of the lens of  FIG. 1 ; 
         FIG. 3  is a cross-section view of the lens taken along line  3 - 3  in  FIG. 2 ; 
         FIG. 4  is a cross-section view of the lens taken along line  4 - 4  in  FIG. 2 ; 
         FIG. 5  is a semi-schematic isometric view of the lens of  FIG. 1 ; 
         FIG. 6  is a semi-schematic front view of the lens of  FIG. 1 ; 
         FIG. 7  is a first semi-schematic side view of the lens of  FIG. 1 ; 
         FIG. 8  is a second semi-schematic side view of the lens of  FIG. 1   
         FIG. 9  is a semi-schematic isometric view of the lens of  FIG. 1 ; 
         FIG. 10  is an exploded isometric view depicting the parts of the lens of  FIG. 1 ; 
         FIG. 11  is a view similar to  FIG. 10  but as viewed from another angle; 
         FIGS. 12A and 12B  are isometric views depicting two examples of the lens core part after the first injection shot of the molten plastic material; 
         FIG. 13  is an isometric view depicting an example of the first outer lens part after the second injection shot of the molten plastic material; 
         FIG. 14  is an isometric view depicting an example of the second outer lens part after the third injection shot of the molten plastic material; 
         FIGS. 15 and 16  are exploded isometric views depicting lenses having other examples of lens core parts; 
         FIG. 17  is a semi-schematic isometric view illustrating another kind of lens as suggested herein; 
         FIG. 18  is a semi-schematic isometric view of the lens of  FIG. 17 , as viewed from the another angle; 
         FIG. 19  is a semi-schematic top view of the lens of  FIG. 17 ; 
         FIG. 20  is a first semi-schematic side view of the lens of  FIG. 17 ; 
         FIG. 21  is a second semi-schematic side view of the lens of  FIG. 17 ; 
         FIG. 22  is a semi-schematic isometric view illustrating another kind of lens as suggested herein; 
         FIG. 23  is a top view of the lens of  FIG. 22 ; 
         FIG. 24  is a cross-section view taken along line  24 - 24  in  FIG. 23 ; and 
         FIG. 25  is an exploded view depicting the various parts of the lens of  FIG. 22 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an isometric view illustrating an example of a generic thick lens  100 . The illustrated lens  100  is only for the sake of illustration. Numerous other shapes and configurations are possible as well. 
     The composite lens  100  is made of a same transparent plastic resin material. Examples of plastic materials include polymethylmethacrylate (PMMA) and polycarbonate, to name just a few. Other plastic materials can be used, depending on the implementation. 
       FIG. 2  is a front view of the lens  100  of  FIG. 1 .  FIG. 3  is a cross-section view of the lens  100  taken along line  3 - 3  in  FIG. 2 .  FIG. 4  is a cross-section view of the lens  100  taken along line  4 - 4  in  FIG. 2 . 
     As can be seen, the lens  100  includes a lens body  102  having a first optical active surface  104  on its rear side and a second optical active surface  106  on its front side. The first optical active surface  104  also includes at least one curved surface. The curved surface portion can be for instance spherical, cylindrical, aspheric, parabolic or free form. Variants are also possible. 
     The first optical active surface  104  of the illustrated example includes a recessed portion  108  into the lens body  102 . The recessed portion  108  can be the location for a light source, for instance a solid state light source having one or more light emitting diodes (LED). Variants are possible as well. A solid state light source is schematically depicted in  FIGS. 3 and 4  at  110 . This can be an arrangement for an automotive headlamp. Other uses and applications are possible as well, including the ones outside the context of automotive vehicles such a general lighting, solar concentrators, etc. 
     In use, the solid state light source  110  is optically coupled to the lens  100 . Light beams emitted by the solid state light source  110  enter the lens body  102  through the first optical active surface  104  and then exit through the second optical active surface  106 . A generic example of a set of light beams  112  is shown in  FIG. 4 . 
     The second optical active surface  106  of the illustrated example includes a plurality of light diffusing elements to spread and orient the outgoing light in accordance with the requirements. They are shown as being concentrically disposed around a protruding curved portion  114  located at the center of the second optical active surface  106 . The area around the protruding curved portion  114  is also shown as being concave. However, the exact shape, configuration and arrangement of all the optical active surfaces  104 ,  106  of the lens  100  can vary from one implementation to another. The illustrated lens  100  is generic and for this reason, the light diffusing elements on the second optical active surface  106  are only illustrated in a semi-schematic manner. They can also be omitted in some implementations. 
     As can be seen in  FIG. 4 , at least some of the light beams inside the lens  100  are reflected through total internal reflection (TIR) on internal TIR surfaces located on what constitutes the lateral sides of the lens  100 . Some of the light beams also go through the lens body  102  without reflecting on the TIR surfaces. 
       FIG. 5  is a semi-schematic isometric view of the lens  100  of  FIG. 1 .  FIG. 5  shows that the lens  100  includes a core part  120  embedded between a first outer lens part  122  and a second outer lens part  124 . The core part  120  is shown in solid lines while the two outer lens parts  122 ,  124  are shown in stippled lines. The first optical active surface  104  is located on the first outer lens part  122  and the second optical active surface  106  is located on the second outer lens part  124 . 
     It should be noted that the core part  120  and the two outer lens parts  122 ,  124  are separately visible in  FIG. 5  only for the sake of illustration. 
     The core part  120  and the two outer lens parts  122 ,  124  are fused together during manufacturing so as to create the resulting lens  100 . The term “fused” means securing or bonding the lens layers together using heat coming from the hot molten plastic material during the manufacturing process to form a monolithic piece. The fused lens layers are generally made of the same plastic material but variants could be possible. The two outer lens parts  122 ,  124  have the same refractive index. The boundary between each of the outer lens parts  122 ,  124  and the core part  120  is not distinguishable or visible with naked eye, for example using the light coming from the solid state light source  110  ( FIG. 4 ) with which the lens  100  will be used. The lens body  102  ( FIGS. 3 and 4 ) is thus transparent to this light. There is thus no refraction of the light beams at the boundaries between the outer lens parts  122 ,  124  inside the lens  100 . However, the boundaries could be viewed using polarized light, phase contrast microscopy or other known visualization devices or instruments. 
     As can also be seen in  FIG. 5 , the illustrated lens  100  has a central axis  126  passing through the first and second optical active surfaces. This lens  100  has a plane of symmetry that is coincident with the central axis  126 . Variants are possible as well. 
       FIG. 6  is a semi-schematic front view of the lens  100 .  FIG. 7  is a first semi-schematic side view of the lens  100 .  FIG. 8  is a second semi-schematic side view of the lens  100 .  FIG. 9  is a semi-schematic isometric view of the lens  100 . The core part  120  and the two outer lens parts  122 ,  124  are separately visible in  FIGS. 6 to 9  only for the sake of illustration. 
       FIG. 10  is an exploded isometric view depicting the parts of the lens  100  of  FIG. 1 .  FIG. 11  is a view similar to  FIG. 10  but as viewed from another angle. As can be seen, the core part  120  of the lens  100  includes two elongated slots  130  intersecting at the center. The slots  130  are perpendicular to one another and are rectilinear. They divides the core part  120  in four subparts  132 , namely in four subparts  132  having a substantially similar volume. The four subparts  132  remain connected to one another by relatively small interconnecting portions. The core part  120  forms a monolithic piece over which the two outer lens parts  122 ,  124  are molded. The configuration is made of create smaller subparts that are easier to cool than a very thick one when the lens core  120  is manufactured. Various tabs  134  are also provided around the core part  120 , for instance for positioning of the core part  120  during manufacturing. 
     The lens  100  can be manufactured using, for instance, an injection molding device and/or a method as described in U.S. patent application No. 61/862,366 filed on 5 Aug. 2013, the entire contents of which are hereby incorporated by reference. Using other devices and/or methods can be possible as well. 
       FIGS. 12A and 12B  are isometric views depicting two examples of the lens core part  120  after the first injection shot of the molten plastic material. In  FIG. 12A , the lens core part  120  has cold runners on the side that are made of solidified material. These portions will be cut afterwards. However, they are on non-optical surfaces.  FIG. 12A  shows that the molten plastic material was injected from opposite sides, both coming from a common supply. 
     In  FIG. 12B , the lens core part  120  is shown with two hot runners. They are provided to inject the molten plastic material. 
       FIG. 13  is an isometric view depicting an example of the first outer lens part  122  after the second injection shot of the molten plastic material. The first outer lens part  122  is shown as if it is unconnected to the lens core part  120  but again, this is only for the sake of illustration. As can be seen, the first outer lens part  122  includes internal planar ribs  140  formed by the plastic material of the first outer lens part  122  filling the corresponding elongated slots  130  inside the core part  120 . The side walls of the slots  130  and these ribs  140  will be fused together during the manufacturing process. The side surfaces of the first outer lens part  122  also form the TIR surfaces that will reflect some of the light beams inside the lens  100  when they are emitted by the light source  110 , as shown in  FIG. 4 . The first outer lens part  122  has a cold runner on one side. 
       FIG. 14  is an isometric view depicting an example of the second outer lens part  124  after the third injection shot of the molten plastic material. The second outer lens part  124  is shown as if it is unconnected to the lens core part  120  but again, this is only for the sake of illustration. The second outer lens part  124  has a cold runner on one side. 
       FIGS. 15 and 16  are exploded isometric views depicting lenses  100  having other examples of core parts  120 . In  FIG. 15 , the core part  120  includes two slots  130  forming a T-shaped arrangement since one is shorter than the other. The core part  120  is thus divided in three subparts in this implementation. In  FIG. 16 , the core part  120  only has a single central slot  130 . The core part  120  is thus divided in two subparts. Other arrangements and configurations are possible as well. 
     In  FIGS. 5 to 16 , the slots  130  are substantially parallel to the major axes of the lens  100  (width and length). Each slot  130  includes opposite planar walls that are substantially parallel to one another. Variants are possible as well. 
       FIG. 17  is a semi-schematic isometric view illustrating another kind of lens  100 . The slots  130  of the core part  120  inside this lens  100  are disposed radially. They are also symmetrically disposed and connected together at the center where the central axis  126  is located. Like in  FIG. 5 , the core part and the outer lens parts  122 ,  124  of this lens  100  are distinctly visible only for the sake of illustration. 
       FIG. 18  is an isometric semi-schematic view of the lens  100  of  FIG. 17 , as viewed from the bottom.  FIG. 19  is a semi-schematic top view of the lens  100  of  FIG. 17 .  FIG. 20  is a first semi-schematic side view of the lens  100  of  FIG. 17 .  FIG. 21  is a second semi-schematic side view of the lens  100  of  FIG. 17 . 
       FIG. 22  is a semi-schematic isometric view illustrating another kind of lens  100 . The core part of this lens  100  includes three radially-disposed slots  130 . 
       FIG. 23  is a top view of the lens  100  of  FIG. 22 .  FIG. 24  is a cross-section view taken along line  24 - 24  in  FIG. 23 .  FIG. 25  is an exploded view depicting the various parts of the lens of  FIG. 22 . 
     The proposed concept is not limited to these examples and other implementations are possible as well. 
     The present detailed description and the appended figures are meant to be exemplary only, and a skilled person will recognize that variants can be made in light of a review of the present disclosure without departing from the proposed concept.