Freeform Fresnel surface, method for producing a freeform Fresnel surface and method for creating a design data set

Description

[0001] The present invention relates to a method for producing a freeform Fresnel surface by machining a starting material. The invention further relates to a method for creating a design data set for producing a freeform Fresnel surface and to a spectacle lens with a freeform Fresnel surface.

[0002] From CJ Li et al. "Ultra-precision machining of Fresnel lens mold by singlepoint diamond turning based on axis B rotation", Int. J. Adv. Manuf. Technol. (2015) 77, 907-913 and from J. Yan et al. "Micro grooving on single-crystal germanium for infrared Fresnel lenses", J. Micromech. Microeng. 15 (2005), 1925-1931, spherical Fresnel lenses are known.

[0003] A freeform Fresnel surface is defined as a freeform surface described by a polynomial, formed by multiple offsets along its z-axis by a preferably constant amount and by the respective clipping at a support surface on the one hand and a preferably parallel or preferably concentric surface on the other. An example of a freeform Fresnel surface 100 is shown in Figure 1 The figure shows the individual Fresnel facets 102 with their respective Fresnel segment surfaces 104 and back faces 106, as well as the intersection lines 108 with the support surface. The support surface can be planar or curved. Its origin coincides with the origin of the polynomial. The origin of the preferably parallel or preferably concentric surface is offset by a certain amount in the z-direction and generates the structural depth of the Fresnel segment surface.

[0004] Examples of freeform Fresnel surfaces are shown in DE 10 2009 010 537 A1 and DE 10 2009 010 538 A1, the latter of which also describes a method for manufacturing a freeform Fresnel surface. Freeform Fresnel surfaces are used, for example, in data glasses or similar devices, as described, for example, in US 5,369,415, US 6,204,974 B1, US 2010 / 0260455 A1, or WO 2006 / 013565 A1.

[0005] The production of the freeform Fresnel surface (either as an original part or as an injection mold, e.g., for industrial production) is carried out by advancing a cutting tool in the direction of the z-axis up to the z-value specified by the mathematical description for the respective xy-position.

[0006] A first object of the present invention is to provide an advantageous method for producing freeform Fresnel surfaces for a spectacle lens.

[0007] A second object of the invention is to provide a computer-implemented method for creating an advantageous design data set for manufacturing a freeform Fresnel surface for a spectacle lens. A third object of the invention is to provide an advantageous spectacle lens.

[0008] The first two problems are solved by a method for producing freeform Fresnel surfaces for a spectacle lens according to claim 1 and a computer-implemented method for creating an advantageous design data set for producing a freeform Fresnel surface for a spectacle lens according to claim 6, respectively. The third problem is solved by a freeform Fresnel surface according to claim 13. The dependent claims contain advantageous embodiments of the invention.

[0009] In the inventive method for producing a freeform Fresnel surface for a spectacle lens with a number of Fresnel facets, each having a Fresnel segment surface and a back flank, the freeform Fresnel surface is produced by machining a starting body based on design data for the freeform Fresnel surface. The design data for the freeform Fresnel surface is based on: a support surface of the freeform Fresnel surface, defined in a coordinate system with an x-direction, a y-direction, and a z-direction; a family of freeform surfaces staggered in the z-direction of the coordinate system and inclined to the xx-plane of the support surface, each of the freeform surfaces defining the Fresnel segment surface of a Fresnel facet; a family of intersection curves along which the freeform surfaces of the family of freeform surfaces intersect the support surface, the projection of the intersection curves onto the xy-plane not resulting in a circular arc; cylindrical surfaces or conical surfaces whose cylindrical axes or conical axes are perpendicular to the xy-plane of the coordinate system, each cylindrical surface or conical surface being defined by a specific angular dimension.The conical surface intersects a specific freeform surface from the family of freeform surfaces at the height of the support surface and also intersects the freeform surface located directly below the specific freeform surface in the z-direction, such that the intersection with the specific freeform surface defines an upper intersection line and the intersection with the freeform surface located directly below it in the z-direction defines a lower intersection line. The area of ​​the circular cylindrical surface or conical surface extending between the upper and lower intersection lines then defines the back face of the Fresnel facet belonging to the selected freeform surface. The production of the freeform Fresnel surface is then carried out by forming the Fresnel segment surfaces and the back flanks of the Fresnel facets by circular machining of the starting body based on the design data, whereby material is removed from the starting body until the Fresnel segment surface and the back flank are exposed for each Fresnel facet.

[0010] In the machining process of the surface, the movement of the tool used for production follows a circular path projected onto the xy-plane. . This is state of the art in

[0011] The area of ​​the Fresnel facet boundaries, and especially the back faces, cannot be machined in this way because the projection of the spatial intersection curves defining the shape onto the xy-plane does not result in a circular arc. In contrast, the inventive method, by using circular cylindrical or conical lateral surfaces to generate the design data, ensures that the projection of the Fresnel facet edges onto the xy-plane represents circular paths. This makes it possible to machine the Fresnel segment surfaces and the back faces with a tool guided on concentric circular paths. In other words, when machining the starting body in a circular path, the movement of the tool used can follow a circular path projected onto the xy-plane, which simplifies the control of the machine tool for machining the freeform Fresnel surface.The feed values ​​of the tool used for the circular machining of the starting body in the z-direction can be converted into cylindrical coordinates, taking into account the position of the circular cylinder axis or the cone axis.

[0012] Within the framework of the method according to the invention, it is advantageous if the origin of the coordinate system for describing the freeform Fresnel surface is defined such that it lies centrally in the support surface, so that a compensating plane defined by the freeform Fresnel surface is perpendicular to the z-axis of the system. Within the framework of the invention, the shape of the circular cylindrical surfaces or conical surfaces is designed such that the upper intersection lines approximate the shape of the intersection curve of the respective freeform surface with the support surface as closely as possible. In the case of circular cylindrical surfaces, this can be achieved by a suitable selection of the radius of the circular cylinder, and in the case of conical surfaces, by a suitable selection of the cone angle and the distance of the cone apex from the xy-plane.A good approximation of the upper intersection line to the shape of the intersection curve of the respective freeform surface with the support surface can be achieved if a selected circular cylindrical surface or conical surface is constructed such that it passes through the endpoints of the intersection curve of a selected intersection curve from the family of intersection curves and a point on the selected intersection curve that lies between the two endpoints of this intersection curve. It is advantageous if the point between the two endpoints of the selected intersection curve lies at least approximately midway between the two endpoints of the intersection curve. Furthermore, it is advantageous if the selected intersection curve is a central intersection curve within the family of intersection curves. The circular cylindrical or conical axes of all other circular cylindrical or conical surfaces are then chosen such that they coincide with the circular cylindrical or conical axis of the selected intersection curve.The cone axis of the selected circular cylindrical surface or conical surface coincides with the cone's lateral surface. Furthermore, for all freeform surfaces, the circular cylindrical surface or conical surface associated with a specific freeform surface passes through a point on the intersection curve of that particular freeform surface with the support surface. It is also advantageous if the point on the intersection curve of the specific freeform surface with the support surface lies at least approximately midway between the two endpoints of the respective intersection curve.

[0013] According to the invention, a computer-implemented method is also provided for creating a design data set for manufacturing a freeform Fresnel surface for a spectacle lens, comprising a number of Fresnel facets, each having a Fresnel segment surface and a back flank, and for controlling a machine tool for machining the freeform Fresnel surface in a circular path. This method comprises the following steps: Defining a support surface of the freeform Fresnel surface, defined in a coordinate system with an x-direction, a y-direction, and a z-direction; Defining a family of freeform surfaces staggered in the z-direction of the coordinate system, extending at an angle greater than 0 and less than 90 degrees to the support surface, each of the freeform surfaces defining the Fresnel segment surface of a Fresnel facet; Determining a family of intersection curves along which the freeform surfaces of the family of freeform surfaces intersect the support surface, the projection of the intersection curves onto the xy-plane not resulting in a circular arc; Determining circular cylindrical surfaces or conical lateral surfaces whose circular cylindrical axes orThe cone axes are perpendicular to the xy-plane of the coordinate system, with each circular cylindrical surface or conical surface intersecting a specific freeform surface from the family of freeform surfaces at the level of the support surface and also intersecting the freeform surface located directly below the specific freeform surface in the z-direction, such that the intersection with the specific freeform surface defines an upper intersection line and the intersection with the freeform surface located directly below it in the z-direction defines a lower intersection line. The area of ​​the circular cylindrical surface or conical surface extending between the upper and lower intersection lines then defines the back face of the Fresnel facet belonging to the selected freeform surface.

[0014] Typically, creating the design data set also includes determining cylinder coordinates for shaping the Fresnel segment surfaces and back flanks of the Fresnel facets by circular machining of the starting body using a cutting tool, whereby the required feed values ​​for the tool in the z-direction are determined taking into account the position of the circular cylinder axis or the cone axis.

[0015] Within the framework of the inventive method for creating a design data set, it is advantageous if the origin of the coordinate system for describing the freeform Fresnel surface is defined in such a way that it lies in the middle of the support surface.

[0016] Within the scope of the invention, the shape of the circular cylindrical or conical slant surfaces is designed such that the upper intersection lines approximate the shape of the intersection curve of the respective freeform surface with the support surface as closely as possible. This can be achieved, for example, by designing a selected circular cylindrical or conical slant surface by arranging it along the intersection curve endpoints of a selected intersection curve from the family of intersection curves and a point on the selected intersection curve that lies between the two intersection curve endpoints of this intersection curve. It is advantageous if the point between the two intersection curve endpoints of the selected intersection curve is placed at least approximately midway between the two intersection curve endpoints.Furthermore, it is advantageous if the selected intersection curve is one located centrally within the set of intersection curves. The circular cylinder axes or cone axes of all other circular cylinder surfaces or cone surfaces are then arranged such that they coincide with the circular cylinder axis or cone axis of the selected circular cylinder surface or cone surface. Additionally, the circular cylinder surface or cone surface associated with a specific freeform surface is arranged by passing through a point on the intersection curve of the specific freeform surface with the support surface. Here, too, it is advantageous if the point on the intersection curve of the specific freeform surface with the support surface lies at least approximately midway between the two endpoints of the respective intersection curve.

[0017] In both the inventive method for producing a free-form Fresnel surface and the inventive method for creating a design data set, if the circular cylindrical surfaces or conical surfaces are circular cylindrical surfaces, conical surfaces can be placed through the Fresnel segment surfaces after the construction of the Fresnel segment surfaces and the back flanks using the circular cylindrical surfaces, wherein the associated cones are dimensioned with respect to their cone angle and the position of their apexes above the xy-plane such that they each intersect two adjacent Fresnel segment surfaces completely, and wherein the section of the conical surface located between the intersection lines of a conical surface with the adjacent Fresnel segment surfaces forms the back flank between the adjacent Fresnel segment surfaces.In this embodiment of the process, the back faces do not run parallel to the z-direction, which simplifies the machining of the back faces. This further development is not necessary if the cylindrical or conical surfaces are conical surfaces.

[0018] According to the invention, a computer program product comprising software components for carrying out one of the methods according to the invention is also provided.

[0019] Furthermore, according to the invention, a spectacle lens with a freeform Fresnel surface is provided. The freeform Fresnel surface has a number of Fresnel facets, each with a Fresnel segment surface designed as a freeform surface that lacks mirror and rotational symmetry, and a back facet, as well as a structural depth defined in a coordinate system with an x-direction, a y-direction, and a z-direction along the z-direction. In the spectacle lens according to the invention, the Fresnel segment surfaces and the back facet are each bounded by lines whose projection onto the xy-plane of the coordinate system are circular segments in the xy-plane. This is advantageous for machining during the production of the freeform Fresnel surface, since the movement of the tool used for production can follow a circular path projected onto the xy-plane.This is advantageous with regard to the production of this surface in the spectacle lens, since the movement of the tool used to produce the freeform Fresnel surface can follow a circular path projected onto the xy-plane.

[0020] Further features, properties and advantages of the present invention will become apparent from the following description of exemplary embodiments with reference to the accompanying figures. Figure 1 shows an example of a prior art freeform Fresnel surface. Figure 2 shows a step in a prior art method for generating a prior art freeform Fresnel surface. Figure 3 shows a further step in the prior art method for generating a prior art freeform Fresnel surface. Figure 4 shows a first step of an embodiment of the inventive method for creating a design data set for manufacturing a freeform Fresnel surface. Figure 5 shows a further step of the embodiment of the inventive method. Figure 6 shows yet another step of the embodiment of the inventive method. Figure 7 shows yet another step of the embodiment of the inventive method. Figure 8 shows conical surfaces used to generate design data for inclined back faces of the Fresnel facets of a freeform Fresnel surface.Figure 9 shows a first illustration to explain the dimensioning of the cone lateral surfaces from . Figure 8 Figure 10 shows a second illustration to explain the dimensioning of the cone lateral surfaces. Figure 8 Figure 11 shows a freeform Fresnel surface with inclined back faces. Figure 12 shows a spectacle lens with a freeform Fresnel surface.

[0021] Before discussing an embodiment of the invention, the following will be discussed: Figure 2 and 3 An example of how to create a freeform Fresnel surface using a state-of-the-art method is explained.

[0022] As in Figure 2As shown, in the prior art method, the origin of the freeform Fresnel surface lies outside the utilized area (surface aperture). The curvatures of the support surface 110 and the concentric surface 112 are illustrated by equatorial lines 114 and 116. The distance h between the two surfaces 110 and 112 in the direction of the z-axis determines the structural depth and thus the width of the individual Fresnel segment surfaces 104.

[0023] The freeform Fresnel surface is mathematically described as follows: z = z F − h ⋅ floor z F − z T h with: z T = c T ⋅ r 2 1 + 1 − 1 + k T ⋅ c T 2 ⋅ r 2 z F = c F ⋅ r 2 1 + 1 − 1 + k F ⋅ c F 2 ⋅ r 2 + ∑ i = 1 N A i x y r 2 = x 2 + y 2

[0024] Here, the subscript "F" denotes the dimensions of the freeform Fresnel surface, while the subscript "T" indicates the dimensions of the support surface 110. The letter h denotes the structural depth of the Fresnel segment surface, c the curvature, and k the taper of the respective surface. A denotes the coefficients of the freeform surface.

[0025] The Figure 2Figure 1 shows the construction of the freeform Fresnel surface according to the mathematical description. Shown are staggered freeform surfaces 118 in the z-direction and the support surface 110 with the concentric surface 112. Each of the freeform surfaces 118 generates a spatial intersection curve 120, 122 with the support surface 110 and the concentric surface 112, the shape of which depends on the shape of the freeform surface 118 and the curvature of the support and concentric surfaces. (The uppermost and lowermost freeform surfaces each intersect only the support and concentric surfaces, respectively.) The generated intersection curves (120, 122) form the outer and inner boundaries of the individual Fresnel segment surfaces 104, respectively. Figure 3 The Fresnel segment surfaces 104 generated by the clipping of the freeform surfaces 118 are shown.

[0026] Up to the point in Figure 3The constructed surface corresponds to the mathematical description in the depicted state. However, a real surface, which, for example, is produced in a single piece of material using a machining process, also exhibits the following between the Fresnel segment surfaces: Figure 1 The recognizable back flanks 106 are shown. The back flanks 106 can be inclined relative to the xy-plane (e.g., for technological reasons). They follow, for example, the intersection curves on the concentric surface 112 and define the Fresnel segment surfaces before intersecting the support surface 110.

[0027] The following will be based on the Figures 4 to 7 An embodiment of the inventive method for creating a design data set for the production of a free-form Fresnel surface is described.

[0028] In the first step of the process, the origin 0 of the freeform Fresnel surface is approximately placed in the center of the used surface aperture, so that a compensating plane (xy-plane) defined by the freeform Fresnel surface is perpendicular to the z-axis of the system. This is in Figure 4 shown, which, in addition to the origin 0, also shows the support surface 2, the freeform surfaces 4 and the concentric surface 6.

[0029] In the inventive method, as in the prior art, the intersection curves 8 with the support surface 2 are determined for a set of freeform surfaces 4 staggered in the z-direction and inclined to the xy-plane of the support surface so that they intersect the support surface 2. The result is a set of intersection curves 8, each representing the intersection of a freeform surface 4 with the support surface 2, wherein each freeform surface 4 represents a subsequent Fresnel segment surface 10 (see Figure 7 ) defined.

[0030] The next step, which involves Figure 5 As shown graphically, a circular cylindrical surface 18 is defined by the endpoints 14a, 14b and a central point 16 of a selected – in this exemplary embodiment, the central – intersection curve 8. The axis A of this circular cylinder is perpendicular to the xy-plane. The position of the circular cylinder axis A relative to the origin 0 of the freeform Fresnel surface is described by the coordinates xz and yz. For reasons of space, the position of the circular cylinder axis A is shown in a foreshortened form in the figure.

[0031] Due to the described positioning of the circular cylinder surface 18, it intersects the freeform surface 4 belonging to the intersection curve 8 in the area of ​​the support surface 2 and forms an intersection line 20 that approximates the intersection curve 8 as closely as possible (see Figure 7), which is hereinafter referred to as the upper section line 20. The projection of the upper section line 20 onto the xy-plane then represents a segment of a circle that most closely approximates the projections of the intersection curves 8 onto the xy-plane. Furthermore, the cylindrical surface 18 also intersects the freeform surface located in the family of freeform surfaces 4 directly below the freeform surface 4 that generates the intersection curve 8. The section line 22 of the cylindrical surface 18 with this freeform surface is hereinafter referred to as the lower section line 22. The projection of the lower section line onto the xy-plane also represents a segment of a circle.

[0032] In the next step, which is in Figure 6As graphically represented, for each intersection curve 8 of a freeform surface 4 with the support surface 2, a circular cylindrical surface 18' is placed through a central point on the respective intersection curve 8, the axis of which coincides with the previously generated circular cylinder axis A. The result is a set of concentric circular cylindrical surfaces 18, 18', each of which intersects a specific freeform surface from the set of freeform surfaces 4 in the region of the support surface 2, forming an upper intersection line 20 in each case. Similarly, a lower intersection line 22 is formed for the intersection of the respective circular cylindrical surface 18' with the freeform surface located beneath the specific freeform surface.Both the upper section lines 20 and the lower section lines 22 represent sections of circles in the projection onto the xy-plane, whereby the projection of an upper section line 20 onto the xy-plane is as close as possible to the projection of the intersection curve 8 of the corresponding freeform surface 4 with the support surface 2 onto the xy-plane.

[0033] Within the scope of the invention, the upper section lines 20 and the lower section lines 22 define the outer and inner boundaries of the individual Fresnel segment surfaces 10, instead of the intersection curves of a freeform surface 4 with the support surface 2 and the concentric surface 6. A cylindrical surface 18, 18' simultaneously forms the outer boundary of a preceding and the inner boundary of a subsequent Fresnel segment surface 10, such that the surface section of the corresponding freeform surface 4 located between the upper section line 20 of a cylindrical surface 18, 18' and the lower section line 22 of the adjacent cylindrical surface 18, 18' forms the Fresnel segment surface 10 of a Fresnel facet 12. The surface section of a cylindrical surface 18, 18' located between the upper section line 20 and the lower section line 22 then forms the back face of the Fresnel facet 12.

[0034] As a result of the described construction of the freeform Fresnel surface, the bounding edges of the Fresnel segment surfaces 10 no longer lie exactly on the support surface 2 or the concentric surface 6, but are instead bounded by circular path segments when projected onto the xy-plane. Therefore, when machining a starting body to produce the freeform Fresnel surface, the movement of the tool used can follow a circular path projected onto the xy-plane. The movements of the tool required for the circular machining of the starting body can be specified in polar coordinates, whereby the tool feed values ​​in the z-direction can be expressed by the z-component of the cylindrical coordinates.

[0035] A free-form Fresnel surface manufactured according to the described embodiment for the inventive method would have back flanks perpendicular to the xy-plane. However, it is often technologically and functionally advantageous for the back flanks to be inclined relative to the xy-plane. Combined with the objective of guiding the machining tool along circular paths, this necessitates designing the back flanks as a section of a conical shell. The axes of the cones should preferably coincide with the axes of the circular cylinders described in the first embodiment.

[0036] In Figure 8The freeform Fresnel surface produced using the previously described method is shown together with a set of coaxial conical lateral surfaces 24. The associated cones are dimensioned with respect to their cone angle and the position of their apexes above the xy-plane such that they each define two adjacent Fresnel segment surfaces 10, 10' (see Figure 9 and 10 Cut continuously. Non-continuous cut lines would create undefined gaps in the finished freeform Fresnel surface.

[0037] A favorable dimensioning of the conical lateral surfaces 24 results when the intersection curve 26 of a conical lateral surface 24 is tangent to the lower intersection line 22 at the second of the adjacent Fresnel segment surfaces 10, 10', i.e., the Fresnel segment surface 10'. In the Figure 9 and 10 This dimensioning is illustrated using the example of a conical lateral surface 24 and the two Fresnel segment surfaces 10, 10' intersected by it. Figure 9The figure shows a conical surface and the two Fresnel segment surfaces 10, 10' intersected by it in a perspective view. Figure 10 Figure 1 shows the same arrangement viewed along the y-axis. The intersection lines created by the conical surface 24 on the Fresnel segment surfaces 10 and 10' are visible. The portion of the segments located above the intersection line of the first segment 10 in the z-direction and below the intersection line of the second segment 10' in the z-direction are truncated by the conical surface.

[0038] The complete freeform Fresnel surface is created by mutually clipping the Fresnel segment surfaces 10 and the conical lateral surfaces 24, whereby the remaining sections of the conical lateral surfaces 24 form the back flanks 28 of the Fresnel facets (12).

[0039] To produce the complete freeform Fresnel surface by circular movements of the tool, the respective feed values ​​zw of the tool in the z-direction, along which the structural depth of the freeform Fresnel surface is given, are converted from Cartesian coordinates of the mathematical description of the freeform Fresnel surface into polar coordinates of the machine tool, taking into account the position of the cone axis (xz; yz). Figure 11 The finished freeform Fresnel surface and the relationships between the coordinates are shown. The conversion is performed using the following formulas: z = z W = f x F y F = f α W r W α W = arctan y Z − y F / x Z − x F r W = x Z − x F 2 + y Z − y F 2

[0040] The subscript "F" denotes the dimensions of the freeform Fresnel surface, while the subscript "W" indicates the dimensions of the tool or machine. The subscript Z denotes the positional coordinates of the cone axis.

[0041] Freeform Fresnel surfaces, as described in the present application, are used, for example, in the field of smart glasses. Smart glasses typically comprise at least one lens through which an imaging beam path, originally originating from a display device, is guided, via multiple reflections at the lens surfaces, to an output structure, from which it is coupled out of the lens towards the user's eye. An example of such a lens 100 is shown in Figure 12 The 200 lens can, as shown in Fig. 12The lens 200 is shown to have an edge thickening region 206 in which the thickness of the lens is increased to achieve optimal guidance of the imaging beam path 202 to the output coupling structure 204. The coupling of the imaging beam path 202 into the lens 200 is achieved with the aid of a prism 208, which serves as a coupling device. By means of the prism 208, which is sometimes also called a tube, the imaging beam path 202 originating from a display (not shown) is coupled into the lens 200 at such an angle that it can reach the output coupling structure 204 after multiple reflections at the outer surface 201 and the inner surface 203 of the lens 200. In the present example, the output coupling structure 204 is designed as a freeform Fresnel surface, which was manufactured according to the described method.Therefore, the Fresnel segment surfaces and the back flanks of the freeform Fresnel surface are each bounded by lines whose projection onto the xy-plane of the coordinate system are circular segments in the xy-plane.

[0042] The present invention has been described in detail with reference to an exemplary embodiment for illustrative purposes. It is understood, however, that the invention is not limited to this exemplary embodiment. Rather, those skilled in the art will recognize that, within the scope of the invention as defined in the claims, deviations from the exemplary embodiments are also possible. For example, it is possible to use conical surfaces instead of circular cylindrical surfaces from the outset, whereby the construction of the upper and lower intersection lines of the conical surfaces with the freeform surfaces from the family of freeform surfaces can be designed as described for the circular cylindrical surfaces. The invention is therefore intended to be limited only by the appended claims. Reference symbol list

[0043] 0 Origin 2 Support surface 4 Freeform surface 6 Concentric surface 8 Intersection curve 10 Fresnel segment surface 12 Fresnel facet 14a,b Endpoint 16 Middle point 18, 18' Circular cylinder lateral surface 20 Upper section line 22 Lower section line 24 Conical lateral surface 26 Intersection curve 28 Back flank 102 Fresnel facet 104 Fresnel segment surface 106 Back flank 108 Intersection line 110 Support surface 112 Concentric surface 114 Equatorial line 116 Equatorial line 118 Freeform surface 120 Intersection curve 122 Intersection curve 200 Spectacle lens 201 Outer surface 202 Imaging beam path 203 Inner surface 204 Coupling structure 206 Edge thickening area 208 Prism

Claims

1. Method for producing a freeform Fresnel surface for a spectacle lens having a number of Fresnel facets (12) that each have a Fresnel segment surface (10) and a trailing edge (28), in which the freeform Fresnel surface is produced by way of machining a base body on the basis of construction data for the freeform Fresnel surface, wherein the construction data for the freeform Fresnel surface are based on: - a carrier surface (2) of the freeform Fresnel surface, which is defined in a coordinate system with an x-direction, a y-direction and a z-direction; - a family of freeform surfaces (4) which are staggered in the z-direction of the coordinate system and inclined with respect to the x-y plane of the carrier surface, wherein each of the freeform surfaces (4) defines in each case the Fresnel segment surface (10) of a Fresnel facet (12); - a family of intersection curves (8) along which the freeform surfaces (4) in the family of freeform surfaces (4) intersect the carrier surface (2), wherein the projection of the intersection curves onto the x-y plane does not result in any circular arcs; - circular cylinder surfaces (18, 18') or cone surfaces whose circular cylinder axes (A) or cone axes are perpendicular to the x-y plane of the coordinate system, wherein each circular cylinder surface (18, 18') or cone surface intersects in each case a specific freeform surface (4) from the family of freeform surfaces at the height of the carrier surface (2) and additionally intersects the freeform surface (4) arranged in each case in the z-direction immediately below the specific freeform surface (4), with the result that the intersection with the specific freeform surface (4) defines an upper intersection line (20) and the intersection with the freeform surface that is arranged in the z-direction immediately below it defines a lower intersection line (22), and wherein the region of the circular cylinder surface or cone surface extending between the upper intersection line (20) and the lower intersection line (22) defines the trailing edge of the Fresnel facet (12) belonging to the selected freeform surface (4), wherein the shape of the circular cylinder surfaces (18, 18') or cone surfaces is designed such that the upper intersection lines (20) are each approximated to the shape of the intersection curve (8) of the respective specific freeform surface (4) with the carrier surface (2); wherein for producing the freeform Fresnel surface, the Fresnel segment surfaces (10) and the trailing edges (28) of the Fresnel facets (12) are formed by circular-path-shaped machining of the base body based on the construction data, wherein material is removed from the base body until the Fresnel segment surface (10) and the trailing edge (28) are exposed for every Fresnel facet (12).

2. Method according to Claim 1, in which the origin (0) of the coordinate system for the description of the freeform Fresnel surface is defined such that it is located centrally in the carrier surface (2).

3. Method according to Claim 1 or Claim 2, in which - a selected circular cylinder surface (18) or cone surface is constructed such that it extends through the intersection curve end points (14a, 14b) of a selected intersection curve (8) in the family of intersection curves and a point (16) on the selected intersection curve (8) that is located between the two intersection curve end points (14a, 14b) of said intersection curve (8), - the circular cylinder axes (A) or cone axes of all other circular cylinder surfaces (18') or cone surfaces coincide with the circular cylinder axis (A) or cone axis of the selected circular cylinder surface (18) or cone surface, and - for all freeform surfaces (4), the circular cylinder surface (18, 18') or cone surface that is assigned to a specific freeform surface extends through a point on the intersection curve (8) of said specific freeform surface (4) with the carrier surface (2).

4. Method according to one of the preceding claims, in which the circular cylinder surfaces (18, 18') or cone surfaces are circular cylinder surfaces (18, 18'), and in which cone surfaces (24) are disposed through the Fresnel segment surfaces (10) after the construction of the Fresnel segment surfaces (10) and the trailing edges using the circular cylinder surfaces (18, 18'), with the associated cones being dimensioned with respect to their cone angle and the position of their tips above the x-y plane such that they continuously intersect in each case two adjacent Fresnel segment surfaces (10, 10') and with the section of the cone surface (24) located between the intersection lines of a cone surface (24) with the adjacent Fresnel segment surfaces (10, 10') forming the trailing edge (28) between the adjacent Fresnel segment surfaces (10, 10').

5. Method according to one of the preceding claims, in which, in the circular-path-shaped machining of the base body, the movement of the used tool follows a circular path that is projected onto the x-y plane.

6. Computer-implemented method for creating a construction data set for the production of a freeform Fresnel surface for a spectacle lens having a number of Fresnel facets (12) each having a Fresnel segment surface (10) and a trailing edge (28) and for the control of a machine tool for the circular-path-shaped machining of the freeform Fresnel surface, comprising the steps of: - defining a carrier surface (2) of the freeform Fresnel surface, which is defined in a coordinate system with an x-direction, a y-direction and a z-direction; - defining a family of freeform surfaces (4) which are staggered in the z-direction of the coordinate system and inclined with respect to the x-y plane of the coordinate system, wherein each of the freeform surfaces (4) defines in each case the Fresnel segment surface (10) of a Fresnel facet (12); - ascertaining a family of intersection curves (8) along which the freeform surfaces (4) in the family of freeform surfaces intersect the carrier surface (2), wherein the projection of the intersection curves onto the x-y plane does not result in any circular arcs; - ascertaining circular cylinder surfaces (18, 18') or cone surfaces whose circular cylinder axes (A) or cone axes are perpendicular to the x-y plane of the coordinate system, wherein each circular cylinder surface (18, 18') or cone surface intersects in each case a specific freeform surface (4) from the family of freeform surfaces at the height of the carrier surface (2) and additionally intersects the freeform surface (4) arranged in each case in the z-direction immediately below the specific freeform surface (4), with the result that the intersection with the specific freeform surface (4) defines an upper intersection line (20) and the intersection with the freeform surface (4) that is arranged in the z-direction immediately below it defines a lower intersection line (22), and wherein the region of the circular cylinder surface (18, 18') or cone surface extending between the upper intersection line (20) and the lower intersection line (22) defines the trailing edge (28) of the Fresnel facet (12) belonging to the selected freeform surface (4), wherein the shape of the circular cylinder surfaces (18, 18') or cone surfaces is designed such that the upper intersection lines (20) are each approximated to the shape of the intersection curve (8) of the respective specific freeform surface (4) with the carrier surface (2).

7. Method according to Claim 6, furthermore comprising: ascertaining cylinder coordinates for forming the Fresnel segment surfaces (10) and trailing edges (28) of the Fresnel facets by way of circular-path-shaped machining of the base body using a machining tool, wherein the required infeed values for the tool in the z-direction are ascertained taking into account the position of the circular cylinder axis (A) or the cone axis.

8. Method according to Claim 6 or Claim 7, in which the origin (0) of the coordinate system for the description of the freeform Fresnel surface is defined such that it is located centrally in the carrier surface (2).

9. Method according to any one of Claims 6 to 8, in which - a selected circular cylinder surface (18) or cone surface is constructed by being arranged such that it extends through the intersection curve end points (14a, 14b) of a selected intersection curve (8) in the family of intersection curves and a point (16) on the selected intersection curve (8) that is located between the two intersection curve end points (14a, 14b) of said intersection curve (8), - the circular cylinder axes (A) or cone axes of all other circular cylinder surfaces (18') or cone surfaces are arranged such that they coincide with the circular cylinder axis (A) or cone axis of the selected circular cylinder surface (18) or cone surface, and - for all freeform surfaces (4), the circular cylinder surface (18, 18') or cone surface that is assigned to a specific freeform surface (4) is arranged such that it extends through a point on the intersection curve (8) of said specific freeform surface (4) with the carrier surface (2).

10. Method according to any one of Claims 6 to 9, in which the circular cylinder surfaces (18, 18') or cone surfaces are circular cylinder surfaces (18, 18'), and in which cone surfaces (24) are disposed through the Fresnel segment surfaces (10) after the construction of the Fresnel segment surfaces (10) and the trailing edges using the circular cylinder surfaces (18, 18'), with the associated cones being dimensioned with respect to their cone angle and the position of their tips above the x-y plane such that they continuously intersect in each case two adjacent Fresnel segment surfaces (10, 10') and with the section of the cone surface (24) located between the intersection lines of a cone surface (24) with the adjacent Fresnel segment surfaces (10, 10') forming the trailing edge (28) between the adjacent Fresnel segment surfaces (10, 10').

11. Computer program product, having software components for performing a method according to any one of Claims 1 to 5 using a machine tool that cuts in a circular-path-shaped manner.

12. Computer program product, having software components for performing a method according to any one of Claims 6 to 10.

13. Spectacle lens having a freeform Fresnel surface having a number of Fresnel facets (12) that have in each case a Fresnel segment surface (10), which is in the form of a freeform surface that has no mirror and rotational symmetry, and a trailing edge (28) and also having a structure depth, which is defined along the z-direction of a coordinate system with an x-direction, a y-direction and a z-direction, characterized in that the Fresnel segment surfaces (10) and the trailing edge (28) are bounded in each case by lines (20, 22), the projections of which onto the x-y plane of the coordinate system are circle line sections in the x-y plane.