Patent Description:
More precisely the invention relates to a method for manufacturing an optical lens by additive manufacturing.

The invention also relates to an intermediate optical element manufactured by additive manufacturing.

Using additive manufacturing technology to manufacture an optical lens is of interest because the obtained optical lens is directly shaped to fit the frame that shall carry it and/or the obtained optical lens complies with the wearer's ophthalmic prescription.

The additive manufacturing process needs to be precisely performed; in particular a new layer needs to be positioned very accurately on the already polymerised layer to correctly manufacture the optical lens.

The major drawback of such a technology is that the obtained articles do not have a good surface quality due to the asperities formed by the edges of the layers.

There are two main methods for improving the surface quality of the lenses in additive manufacturing. A first method consists in decreasing the thickness of the layers thereby minimizing the asperities; however this method increases the manufacturing time since more layers have to be deposited. A second method consists in post-processing the surface of the lens by polishing the asperities; however a precise polishing increases the manufacturing time.

There is a need to find a method that produces optical lenses with good surface quality without increasing the manufacturing time.

<CIT> is a comparative example related to 3D printing of an optical lens.

Therefore one object of the invention is to provide a method for manufacturing an optical lens by additive manufacturing according to claim <NUM>.

In general, the smoothing of an asperity depends not only on its thickness (which depends on the thickness of the layer), but also on its location in the intermediate optical element. It is generally easier and faster to remove an asperity situated at the periphery of the intermediate optical element, than an asperity situated at its apex.

Hence, for an intermediate optical element whose layers have the same thickness, the smoothing will be achieved faster at the periphery than at the center. The smoothing step then has to take this difference into account. This may be a complicated process and increase the manufacturing time.

Here, the thickness of each layer is determined based on the position of the layer in the intermediate optical element and in order to simplify the smoothing step.

For example, by having thicker layers near the periphery and thinner layer near the apex, it is possible to remove all the asperities at the same rate. Thanks to the method of the invention, the smoothing step is simplified, and the manufacturing time is reduced.

Other advantageous and non-limiting features of the method according to the invention are set by the dependent method claims.

The invention also relates to an intermediate optical element manufactured by additive manufacturing according to claim <NUM>.

Other advantageous and non-limiting features of the intermediate optical element according to the invention are set by the dependent apparatus claims.

Each thickness (and/or exposed length) mentioned above may be a thickness (or an exposed length) in at least a plane of the intermediate optical element, in particular in a radial plane of the intermediate optical element when the intermediate optical element is rotation symmetrical.

The method and intermediate optical element according to the invention will be described next, in reference with the appended drawings.

<FIG> shows a system <NUM> for manufacturing an optical lens <NUM>. The system includes an additive manufacturing machine <NUM> for producing an intermediate optical element <NUM>. The system includes a smoothing machine <NUM> for smoothing intermediate element <NUM> into optical lens <NUM>.

Additive manufacturing machine <NUM> comprises a depositing device <NUM>. Depositing device <NUM> is suitable for manufacturing intermediate optical element <NUM> using an additive manufacturing technology. The expression "additive manufacturing technology" refers to processes that manufacture solid objects by juxtaposing volume elements or voxels. In the case of the present invention, intermediate optical element <NUM> is thus manufactured volume element by volume element, layer by layer. The additive manufacturing technology may be in practice stereolithography (SLA) or polymer jetting or continuous liquid interface production (CLIP) technology.

In the illustrated example, depositing device <NUM> comprises a nozzle or a bank of nozzles to deposit the layers.

In the examples described below, a subsequent layer is deposited on a previous layer, thereby defining a deposition axis A. The deposition axis A is thus here perpendicular to the main surfaces of each deposited layer, or, said differently, extends along the thickness of each deposited layer.

Additive manufacturing machine <NUM> also comprises a first control unit <NUM> to control depositing device <NUM>. First control unit <NUM> includes a first microprocessor <NUM> and a first memory <NUM>. First memory <NUM> stores instructions that allow additive manufacturing machine <NUM> to implement a method for manufacturing intermediate optical element <NUM> as described below, when these instructions are executed by first microprocessor <NUM>.

Smoothing machine <NUM> includes a smoothing device <NUM> and a second control unit <NUM>.

Smoothing machine <NUM> is configured to smooth the surface of intermediate optical element <NUM> in order to produce optical lens <NUM>.

Smoothing device <NUM> includes a polishing device able to subtract a volume of material from intermediate optical element <NUM>.

Smoothing device <NUM> includes, for example, a spindle bearing polishing tool, for example a polishing pupil having a predetermined diameter.

Alternatively, smoothing device <NUM> may include a vibratory finishing device <NUM>. Vibratory finishing device includes a tub wherein intermediate optical element <NUM> is placed along with some abrasive material, for example sand. When the tub is vibrated, the sand will rub against the surface of intermediate optical element <NUM> thereby polishing it.

Alternatively, smoothing device <NUM> includes a coating deposition machine able to add a volume of material to intermediate optical element <NUM>.

Second control unit <NUM> includes a second microprocessor <NUM> and a second memory <NUM>. Second memory <NUM> stores parameters that allow smoothing machine <NUM> to implement a method for smoothing intermediate optical element <NUM> as described below when these instructions are executed by second microprocessor <NUM>.

In the case of a polishing pupil, the parameters include, for example, the trajectory of the polishing pupil over the surface of intermediate optical element <NUM>, the number of scans to carry out, the rotational speed of the polishing pupil and/or the rotational speed of intermediate optical element <NUM>, and an angle of a polishing pupil axe with the surface of intermediate optical element <NUM>.

In the case of a vibratory bowl, the parameters include the duration of the smoothing and the kind of abrasive material and its average size in case of a vibratory finishing device <NUM>.

In case of a thin film deposition machine, the parameters include the volume of coating or the average thickness of the coating.

<FIG> schematically illustrates intermediate optical element <NUM>. In the present example, intermediate optical element <NUM> has a body provided with a first face <NUM> that is here convex, and a second face <NUM> that is here concave. Intermediate optical element <NUM> has a peripheral edge connecting first face <NUM> to second face <NUM>.

Intermediate optical element <NUM> is here formed by a plurality of predetermined volume elements that are juxtaposed and superposed to form a stack of superposed layers <NUM> of material.

These predetermined volume elements have a different geometry and a different volume from each other. These volume elements may also consist of the same material, or as a variant may consist of at least two different materials, for example having distinct refractive indices.

<FIG> also indicates with dotted lines a target first face <NUM> and a target second face <NUM>. Target first face <NUM> corresponds to a first face <NUM> of optical lens <NUM>, as illustrated on <FIG>. Target second face <NUM> corresponds to a second face <NUM> of optical lens <NUM>.

Target surfaces <NUM> and <NUM> are determined beforehand, for example in view of the ophthalmic prescription of the wearer of the lens.

First face <NUM> and second face <NUM> of intermediate optical element <NUM> have asperities <NUM> formed by the edges of layers <NUM> where the first face <NUM> and second face <NUM> depart from the target faces <NUM>, <NUM>.

A center or apex of the intermediate optical element <NUM> may thus be defined as corresponding to the uppermost point of the target first face <NUM> along deposition axis A. The layer of the intermediate optical element <NUM> defining the center or apex is thus here the layer deposited last. When the intermediate optical element <NUM> is rotation-symmetrical (and the axis of the rotation symmetry is parallel to the deposition axis), this center or apex is situated on the axis of the rotation symmetry.

In the example of <FIG>, the periphery of the intermediate optical element <NUM> corresponds to the lowermost regions of the intermediate optical element <NUM> along the deposition axis (i.e. to the regions deposited first).

<FIG> illustrates a detail of first face <NUM> of a first embodiment of intermediate optical element <NUM>.

Superposed layers <NUM> form "stair-step" at the interface between a lower layer and the end of the upper juxtaposed layer in the direction of an axis A which is, here, a deposition axis A. The "stair-step" has an exposed surface <NUM> which is not covered by the upper juxtaposed layer.

Each layer <NUM> is here provided with a peak <NUM>, also called a high point, which is located at the free end of the layers <NUM>, and a depression <NUM>, also called a low point, that is located at the junction between the end of an upper layer and the lower layer immediately below.

Each layer <NUM> is furthermore provided with a shoulder <NUM> arranged between the peak <NUM> and the depression <NUM> and substantially representative of the thickness h of the layer <NUM>.

Each layer <NUM> further has a length I. The superposed layers <NUM> illustrated here, have different lengths l in order to form first face <NUM> and second face <NUM>.

Each layer further has an exposed length r which corresponds to the length of exposed surface <NUM>.

The superposed layers <NUM> illustrated here, have different lengths I in order to form first face <NUM> and second face <NUM>.

An asperity <NUM> is formed at the free ends of two adjacent layers <NUM>. As explained below, the volume or cross-sectional surface (in a given plane) of an asperity <NUM> may be estimated by considering the volume or cross-sectional surface of the corresponding depression <NUM>, or, as a variation, by considering the volume or cross-sectional surface of the corresponding peak <NUM>.

A first layer <NUM>, a second layer <NUM>, a third layer <NUM> and a fourth layer <NUM> are illustrated in <FIG>.

First layer <NUM> has a first thickness h<NUM>, a first length l<NUM> and a first exposed length r<NUM>.

Second layer <NUM> lies on top of first layer <NUM>. Second layer has a second thickness h<NUM>, a second length l<NUM> and a second exposed length r<NUM>. The exposed surfaces of first layer <NUM> and second layer <NUM> form a first asperity <NUM>.

Third layer <NUM> has a third thickness h<NUM>, a third length l<NUM> and a third exposed length r<NUM>. In the example illustrated by <FIG>, third layer <NUM> lies on top of second layer <NUM>. Alternatively, third layer <NUM> and second layer <NUM> may not be adjacent. There could be one or more intermediate layers between third layer <NUM> and second layer <NUM>.

Fourth layer <NUM> lies on top of third layer <NUM>. Fourth layer <NUM> has a fourth thickness h<NUM>, a fourth length l<NUM> and a fourth exposed length r<NUM>. The exposed surfaces of third layer <NUM> and fourth layer <NUM> form a second asperity <NUM>.

Since in this example, third layer <NUM> lies on top of second layer <NUM>, the exposed surfaces of second layer <NUM> and third layer <NUM> form a third asperity <NUM>.

Intermediate optical element <NUM> also has a first end layer <NUM> and a second end layer <NUM> (which is, in this represented example, first layer <NUM>). Second end layer <NUM> is the layer deposited first along a deposition axis A. First layer <NUM> is the layer deposited last along deposition axis A.

In this example, as first face <NUM> is convex, first length l<NUM> is greater than second length l<NUM> which is itself greater than third length l<NUM>, which is itself greater than fourth length l<NUM>. First end layer <NUM> is the shortest layer; in some embodiments, second end layer <NUM> may be the longest layer of intermediate optical element <NUM>.

Each layer <NUM> has a substantially constant thickness h over their length I. The various layers <NUM> have, however, respective thicknesses that are different from each other.

In the first embodiment of intermediate optical element <NUM> illustrated by <FIG>, first layer <NUM> has a first thickness h<NUM> greater than second thickness h<NUM> of second layer h<NUM>. Second thickness h<NUM> is itself greater than third thickness h<NUM> of third layer <NUM>. Third thickness h<NUM> is itself greater than fourth thickness h<NUM>.

In other words, in this first embodiment, thickness h increases from first end layer <NUM> to second end layer <NUM>.

In other words, layers whose free end is further away from deposition axis A have greater thickness h than layers whose free end is closer to deposition axis A.

First layer <NUM> extends further than second layer <NUM> over first exposed length r<NUM>. Second layer <NUM> extends further than third layer <NUM> over second exposed length r<NUM>. Third layer extends further than fourth layer <NUM> over third exposed length r<NUM>.

In other words, in this first embodiment, exposed length r decreases from first end layer <NUM> to second end layer <NUM>.

In other words, layers whose free end is further away from deposition axis A have shorter exposed length r than layers whose free end is closer to deposition axis A.

As illustrated on <FIG>, the intermediate optical element <NUM> may not have a rotational symmetry. In this case, the exposed length r of a layer <NUM> may vary over the layer <NUM>.

For example, exposed length r<NUM> of second layer <NUM> may determined by: <MAT> where r<NUM> may be the minimum exposed length for the second layer <NUM> and Δr is a variation of exposed length in a direction radial with respect to deposition axis A.

In other embodiments, the intermediate optical element <NUM> has a rotational symmetry. The layers <NUM> of such an intermediate optical element <NUM> each have a constant exposed length r.

In a second embodiment of the intermediate optical element (not represented), thickness h is constant from the first end layer to a first transition layer. Thickness h then increases from the first transition layer to the second end layer.

In this second embodiment, exposed length r of the layers increases from first end layer to a second transition layer. Exposed length is then constant from second transition layer to second end layer.

In an example of the second embodiment, first transition layer and second transition layer are the same layer. In another example of the second embodiment, first transition layer and second transition layer are different layers.

<FIG> illustrates optical lens <NUM> obtained after smoothing intermediate optical element <NUM>. First face <NUM> and second face <NUM> of optical lens <NUM> are smoothed to comply with ophthalmic requirements.

The method for manufacturing an optical lens by additive manufacturing is based on the deposition of layers <NUM> of optical material and on their subsequent smoothing.

<FIG> is a schematic representation of the steps of the method for manufacturing an optical lens by additive manufacturing.

In a step S0, the manufacturing settings for the additive manufacturing of optical lens <NUM> are determined. Step S0 is implemented by first control unit <NUM>. The manufacturing settings include, for example, the number of layers <NUM> to be deposited, the thickness h, the length l and the exposed length r of each layer <NUM>, the material to be deposited.

In a step S01, first control unit <NUM> receives a file containing prescription values for a wearer of optical lens <NUM> to be manufactured. First control unit <NUM> also receives complementary fitting and personalization data relating to the wearer and/or to a frame intended to receive ophthalmic lens <NUM>. These complementary fitting and personalization data correspond, for example, geometrical values that especially characterize the frame and the visual behavior of the wearer. Complementary fitting and personalization data include, for example, an eye-lens distance, a position of the rotation center of the eye etc..

In a step S02, first control unit <NUM> determines a corrective optical function tailored to the wearer from the wearer prescription values and the complementary fitting and personalization data.

In a step S03, first control unit <NUM> determines target geometric characteristics for the optical lens <NUM> to be manufactured from the optical function.

Target geometric characteristics include, for example coordinates (x, y, z) of a finite number of points of optical lens <NUM>. Alternatively, target geometric characteristics include a surface function z = f(x, y) defining target first face <NUM> and target second face <NUM>.

In a step S04, first control unit <NUM> also receives a file containing smoothing data. Smoothing data includes, for example, the diameter of the polishing pupil, the speed of rotation, the speed of the scan, the pressure the pupil exerts on the surface of the intermediate optical element <NUM>.

In a step S05, first control unit <NUM> determines geometric characteristics of intermediate optical element <NUM> based on the smoothing data and on the target geometric characteristics. First control unit <NUM> then generates a file containing the determined geometric characteristics of intermediate optical element <NUM>.

The geometric characteristics may take the form of, for example coordinates (x, y, z) of a finite number of points of intermediate optical element <NUM>. Alternatively, the geometric parameters may take the form of a surface function z = f(x, y) defining first face <NUM> and second face <NUM> intermediate optical element <NUM>.

<FIG> illustrate how the geometrical characteristics may be determined.

This explanation is given by considering a particular plane across the intermediate optical element <NUM>, here a radial plane of a rotational-symmetric intermediate optical element <NUM> (i.e. a plane containing the axis of the rotation symmetry). The solution also applies however to intermediate optical element <NUM> that are not rotation-symmetric either by determining the geometrical characteristics separately in several distinct planes crossing the intermediate optical element <NUM> (and possibly by determining the geometric characteristics outside these planes by interpolation), or by determining the geometrical characteristics in a particular plane crossing the intermediate optical element <NUM> as described below and by using the determined characteristics in other planes. These solutions make it possible to homogenize the volume of asperities optical lenses generally have a shape that is nearly rotation-symmetric.

<FIG> illustrates intermediate optical element <NUM> and its envelope curve C. Curve C passes by every peak <NUM> of the layers <NUM>. In the embodiment shown in <FIG>, intermediate optical element <NUM> has a spherical envelope, and curve C is a circle of center I. Other types of curve are possible. In order to determine the geometrical characteristics of the layers, curve C is approximated by lines joining adjacent peaks <NUM>. As shown in the detail view included in <FIG>, a line d joins the two adjacent peaks <NUM> represented. <FIG> also illustrates deposition axis A.

Angle θ represents the angle between the free end of a layer <NUM> (i.e. the exposed surface <NUM> of layer <NUM>) and straight line d. The further the free end is from deposition axis A, the greater the angle θ.

Angle θ is thus also the angle between deposition axis A (orthogonal to the exposed surface of layer <NUM>) and a straight line N normal to straight line d and passing by depression <NUM>. As curve C is a circle in the present example and straight line d approximate curve C, angle θ (between deposition axis A and straight line N) corresponds to the angle between deposition axis A and a the radius R of circle C passing through depression <NUM> and angle θ is then representative of the position of a point (depression <NUM>) on the first face <NUM> of intermediate element <NUM>.

Since a triangle formed by shoulder <NUM>, exposed surface <NUM> and straight line d is a right angle triangle, angle θ can be determined with the formula: <MAT>.

This formula establishes a relationship between the thickness h and the exposed length r of a layer <NUM> and its position in the intermediate optical element <NUM>.

As it is now explained, to facilitate the smoothing step and improve the quality of resulting optical lens <NUM>, not all the thicknesses h and exposed lengths r are desirable.

Boundaries conditions used to determine the thickness h and the exposed length r of the layers <NUM> are now described.

<FIG> represents a graph of the variation of the exposed length r as a function of angle θ at a constant thickness hc for a point of intermediate optical element <NUM>.

As the value of angle θ increases, the value of exposed length r decreases. In other words, the layers <NUM> extending further away from deposition axis A have shorter exposed lengths r than shorter layers.

As a consequence, the asperities <NUM> become easier to smooth with increasing angle θ. In other words, for one scan of the pupil, the asperities <NUM> further from deposition axis A are removed faster than the asperities closer to deposition axis A. In other words, the smoothing is achieved faster at the periphery than near the center (here, the apex) of intermediate optical element <NUM>.

If the number of scans is set based on the smoothing of the asperity <NUM> at the periphery, then the asperity near the center will not have reached target at the end of the smoothing step.

If the number of scans is set based on the smoothing of the asperity <NUM> at the center, then too much material will have been removed at the periphery at the end of the smoothing step.

Hence, it is not desirable that all the layers <NUM> have the same thickness h.

In addition, there exists a maximum exposed length rmax beyond which the difficulty of the smoothing of the asperities is considered difficult (for example, the optical lens produced is not of ophthalmic quality). Hence, it is not desirable for the layers to have an exposed length r greater than the maximum exposed length rmax. The maximum exposed length rmax may be determined experimentally.

<FIG> represents a graph of the variation of the thickness h as a function of angle θ at a constant exposed length rc for a point of intermediate optical element <NUM>.

The value of constant exposed length rc is determines by the geometrical requirements of first end layer <NUM>.

As the value of angle θ increases, the value of thickness h also increases.

As a consequence, the asperities <NUM> become harder to smooth with increasing angle θ. In other words, for one scan of the pupil, the asperities <NUM> closer to deposition axis A are removed faster than the asperities further from deposition axis A. In other words, the smoothing is achieved faster near the center than at the periphery of intermediate optical element <NUM>.

If the number of scans is set based on the smoothing of the asperity <NUM> at the periphery, then too much material will have been removed at the center at the end of the smoothing step.

If the number of scans is set based on the smoothing of the asperity <NUM> near the center, then the asperity at the periphery will not have reached target at the end of the smoothing step.

Hence, it is not desirable that all the layers <NUM> have the same exposed length r.

In addition, there exists a maximum thickness hmax beyond which the difficulty of the smoothing of the asperities is increased. Hence, it is not desirable for the layers <NUM> to have a thickness greater than maximum thickness hmax. Maximum thickness hmax may be determined experimentally.

On the graph of <FIG> a second line L2 illustrates the variation of thickness h as a function of angle θ for point of a common intermediate optical element <NUM> and for a constant exposed length rc.

A common value for the diameter of intermediate optical element <NUM> is <NUM>. A common value for the radius of curvature of intermediate optical element <NUM> is <NUM>. A common value for the refractive index of intermediate optical element <NUM> is <NUM>.

As a result, a common value for angle θ at the periphery of intermediate optical element <NUM> is π/<NUM>.

A common value for the exposed length of top layer <NUM> is <NUM>,<NUM>, it is, here, the value of the constant exposed length rc.

A current minimum thickness hmin, as determined by the current state of additive manufacturing technologies, is <NUM>. The minimum thickness hmin is illustrated by a third line L3.

A shaded area S indicates a set of points of coordinates (h, θ) for which smoothing is considered difficult. The set of points is, for example, determined experimentally. For example a test intermediate optical element of geometrical characteristics comprised to in the set of points does not provide an optical lens of ophthalmic quality.

The shaded area S has a lower limit represented by a fourth line L4. The lower limit corresponds to maximum thickness hmax. A common value for maximum thickness hmax is, for example, <NUM>.

As it is visible on the graph of <FIG>, for a constant exposed length rc, the maximum thickness hmax is reached for an angle θ smaller than the desired π/<NUM>.

In other words, it is not possible to achieve an intermediate optical element <NUM> of angle π/<NUM> with a constant exposed length rc.

To determine thicknesses h and exposed length r that are well adapted for the subsequent smoothing, a first embodiment of the method is to vary the value of the thickness h and of the exposed length r over the whole intermediate optical element <NUM>. The first embodiment of the method produces the first embodiment of intermediate optical element <NUM> (represented on <FIG>).

On the graph of <FIG>, first line L1 represents the variation of thickness h as a function of angle θ wherein the thickness h increases with increasing angle θ, and wherein the exposed length r decreases with increasing angle θ. Second line L2 represents the variation of thickness h as a function of angle θ for a constant exposed length r.

Third line L3 represents the minimum thickness value (for example, <NUM>).

A fourth line L4 represents the minimum thickness value of the shaded area S, i.e. the maximum thickness hmax (for example <NUM>).

Angle θp represents the angle at the periphery of intermediate optical element <NUM>.

To achieve an optimal smoothing, all the points of coordinates (h, θ) (and their corresponding exposed length r) situated in the zone delimited by first line L1, second line L2, third line L3 and fourth line L4 may be used to determine the parameters of intermediate geometrical element <NUM>, including the thickness h and the exposed length r of the layers <NUM>.

A variant of the first embodiment of the method is to determine the parameters, including the thickness t and the exposed length r of the layers <NUM>, such that cross sectional area of the asperity <NUM> in a radial plane remains constant for all layers <NUM>.

This variant, represented on the graph of <FIG>, facilitates the smoothing of the intermediate optical element <NUM> as the polishing pupil approximatively polishes the same volume for each asperity <NUM> during the scanning of intermediate optical element <NUM>.

The graph of <FIG> represents another graph of the variation of the thickness h as a function of angle θ for a varying exposed length r. The graph of <FIG> includes the variant of the first embodiment of the method.

Second line L2 represents the variation of thickness h for a constant exposed length (as represented in <FIG>).

Fifth line L5 represents the variation of thickness h when keeping the cross sectional area of the asperities <NUM> constant as proposed above.

The surface Sasp279 of the asperity of top layer <NUM>, evaluated in the present case by considering the cross section of depression <NUM>, is given by: <MAT> where, as seen previously: <MAT> then: <MAT> where: <MAT>.

To achieve an optimal smoothing, all the points comprised between second line L2 and fifth line L5 may be used to determine the geometric file of intermediate optical element <NUM>. However, to keep the surface of the asperity constant during the polishing step, the points near fifth line L5 should be selected.

On the graph of <FIG>, a sixth line L6 represents the variation of thickness h when keeping the section of the surface of the asperities <NUM> constant for a constant exposed length rc. However, it is visible that the maximum thickness hmax is reached for angles θ below the desired π/<NUM>. Hence it is not desirable to select points on sixth line L6.

A second embodiment of the method is illustrated on <FIG>. The second embodiment of the method produces the second embodiment of intermediate optical element <NUM>.

The graph of <FIG> illustrates the variation of thickness h in function of angle θ for a second possibility for determining the parameters of intermediate optical element <NUM>.

In this case, thickness h is constant over a first range of angles θ comprised between <NUM> and a first transition angle θ<NUM>. First transition angle θ<NUM> corresponds to the angle between deposition axis A and the first transition layer of the second embodiment of the intermediate optical element.

Then, for a second range comprising angles greater than first transition angle θ<NUM>, thickness h increases. The thickness h reaches the maximum thickness hmax for a maximum angle θmax.

Exposed length r increases over another first range of angles comprised between <NUM> and a second transition angle θ<NUM>. Second transition θ<NUM> angle corresponds to the angle between deposition axis A and the second transition layer of the second embodiment of the intermediate optical element.

Exposed length r is then constant over another second range comprising angles greater than second transition angle θ<NUM>.

In the present example, first transition angle θ<NUM> and second transition angle θ<NUM> are equal.

In a variant of the second embodiment of the method, first transition angle θ<NUM> and second transition angle θ<NUM> are different.

To achieve an optimal smoothing, all the points of coordinates (h, θ) (and their corresponding exposed length r) situated in the zone delimited by first line L1, second line L2, third line L3 and fourth line L4 may be used to determine the parameters of intermediate geometrical element <NUM>.

In a step S06, first control unit <NUM> generates a manufacturing file corresponding to the manufacturing settings of intermediate optical element <NUM> based on the geometry characteristics of intermediate optical element <NUM>.

This "settings" file is similar to the geometry file of intermediate optical element <NUM> previously generated , the difference being that is reflects a transcribed description of the geometry desired for this intermediate optical element <NUM> to be manufactured, with, in practice, an arrangement of the predetermined volume elements of the one or more materials, relative to a frame of reference of the additive manufacturing machine, and an order of deposition of the volume elements relative to one another.

Alternatively, step S0 may be implemented partly or in total by an external calculating unit that subsequently transmits the parameters to first control unit <NUM>.

In a step S1, the layers <NUM> are deposited by additive manufacturing machine <NUM>. First microprocessor <NUM> implements the manufacturing settings received from first control unit <NUM>.

In a step S11 a first layer <NUM> of first thickness h<NUM> and first length l<NUM> is deposited.

In a step S12, a second layer <NUM> of second thickness h<NUM> and second length l<NUM> is deposited onto first layer <NUM>. Second layer <NUM> is located so as to respect the first exposed length r<NUM> of first layer <NUM>.

In a step S13, a third layer <NUM> of third thickness h<NUM> and length l<NUM> is deposited onto second layer <NUM>. Third layer <NUM> is located so as to respect the second exposed length r<NUM> of second layer <NUM>.

Alternatively, an intermediate layer (not represented) may be deposited onto second layer <NUM>. The intermediate layer is located so as to respect the second exposed length r<NUM> of second layer <NUM>.

Third layer <NUM> is then deposited onto the intermediate layer. Third layer <NUM> is located so as to respect the exposed length of the intermediate layer.

Alternatively, a plurality of other intermediate layers may be deposited on top of the intermediate layer. Each intermediate layer is located so as to respect the exposed length of the intermediate layer immediately below.

In a step S14, a fourth layer <NUM> of fourth thickness h<NUM> and length l<NUM> is deposited onto third layer <NUM>. Fourth layer <NUM> is located so as to respect the third exposed length r<NUM> of third layer <NUM>.

The deposition steps are implemented until all the layers <NUM> are deposited.

Intermediate optical element <NUM> is then placed into smoothing machine <NUM>.

In a step S2, smoothing device <NUM> smooths the surface of intermediate optical element <NUM>. Smoothing instructions are determined or received by second control unit <NUM>.

In the case of a polishing device containing a polishing pupil, smoothing instructions contain the data previously mentioned, such as scan speed, rotational speed of the pupil, number of scan. The smoothing instructions are determined so that the surface of each face <NUM>, <NUM> of the intermediate optical element <NUM> need to be submitted to the same number of scans to smooth the asperities <NUM>.

Second microprocessor <NUM> implements the smoothing instructions and the polishing pupil scans the surface of intermediate optical element <NUM>, thereby smoothing first asperity <NUM>, second asperity <NUM> and third asperity <NUM>.

According to a variant, the smoothing includes applying a coating onto the surface of the intermediate optical element <NUM>. A first volume of coating is applied onto first asperity <NUM>. A second volume of coating is applied onto the second asperity <NUM>).

The method optionally comprises a step of treating first face <NUM> and second face <NUM> of optical lens <NUM> by adding thereto one or more predetermined functional coatings. The functional coatings include, for example, anti-fog, antireflection, tinted, anti-scratch coatings.

Alternatively, before the step of deposition, a cylinder of optical material is provided to additive manufacturing machine <NUM>. The cylinder forms a core of intermediate optical element <NUM>. Layers <NUM> are then deposited around the cylinder to obtain intermediate optical element <NUM>.

Claim 1:
Method for manufacturing an optical lens (<NUM>) by additive manufacturing, comprising steps of:
- depositing a first layer (<NUM>) having a first thickness (h<NUM>),
- depositing a second layer (<NUM>), having a second thickness (h<NUM>), onto the first layer (<NUM>), said second layer (<NUM>) forming a first asperity (<NUM>) with the first layer (<NUM>),
- depositing a third layer (<NUM>) having a third thickness (h<NUM>),
- depositing a fourth layer (<NUM>) having a fourth thickness (h<NUM>) onto the third layer (<NUM>), thereby forming an intermediate optical element (<NUM>), said fourth layer (<NUM>) forming a second asperity (<NUM>) with the third layer (<NUM>),
- smoothing the first asperity (<NUM>) and the second asperity (<NUM>) on the intermediate optical element (<NUM>), thereby forming the optical lens (<NUM>),
wherein said second thickness (h<NUM>) and said fourth thickness (h<NUM>) are different,
wherein the intermediate optical element (<NUM>) has a first end layer (<NUM>), a second end layer (<NUM>) and a plurality of layers situated between the first end layer (<NUM>) and the second end layer (<NUM>), each layer having a thickness (h) and an
exposed length (r),
characterized in that
the thickness (h) increases with the layers from the first end layer (<NUM>) to the second end layer (<NUM>) and in that
the exposed length (r) decreases from the first end layer (<NUM>) to the second end layer (<NUM>).