Patent Grant
8543236
This application is the National Stage of International Application No. PCT/EP2008/059095, filed on Jul. 11, 2008, which claims the priority of European Application No. 07290884.1, filed on Jul. 13, 2007 and European Application No. 07301237.9, filed on Jul. 16, 2007. The content of these applications is hereby incorporated by reference in its entirety.
This invention relates to a method for blocking an optical lens in a reference position on a molding block.
The process of preparing optical or ophthalmic lenses begins with an unfinished or semi-finished glass or plastic optical lens. Typically, semi-finished optical lens has a finished polished front surface and an unfinished back surface. By grinding away material from the back surface of the optical lens, the required corrective prescription is generated. Thereafter, the surface having had the corrective prescription imparted thereto is polished. The peripheral edge of the processed optical lens is then provided with a final desired contour. Thereby establishing a finished optical or ophthalmic lens. The optical lens can be, for example, made of plastic or glass material.
It is necessary during these various processing operations to securely maintain the optical lens in accurate alignment as well as in place on a molding block. This procedure is often referred to as “lens blocking”.
During the processing operation a desired prism may be introduced. The desired prism may be either a prescription prism or a non-prescription prism. The manufacturing of such desired prism requires that the lens be oriented in a desired specific orientation with respect to the manufacturing tools. The introduced prism may be different from one lens to another.
U.S. Pat. No. 5,919,080, describes an ophthalmic lens blocker for blocking a lens blank onto a support block. The lens is placed on three non moveable pins and moved trough a measuring device to measure the convex surface of the lens and finally moved to a blocking station to block the lens.
Various blocking materials are employed to secure the optical lens to the molding block. These blocking materials include glues, pitch and low temperature fusible metal alloys.
U.S. Pat. No. 6,036,313 discloses examples of compound families suitable for lens blocking with thermoplastic materials
In this blocking device, different types of lens holding units 12 and blocking rings 13 are prepared to correspond to the types of the optical lens 10. When blocking an optical lens 10, a lens holding unit 12 and a blocking ring 13 corresponding to the optical lens 10 are selected and used to position the optical lens 10. When the optical lens 10 is blocked by the lens holding unit 12, the center of the optical lens 10 must accurately coincide with the center of the lens holding unit 12.
For this purpose, in the centering devices, the optical lens 10 is clamped and centered with respect to the lens holding unit 12.
Such centering devices require a large number of components, for example a cylindrical member, a ring member, three rollers, three lever members, biasing means, holding portion releasing means, and the like. Accordingly, the structure of such centering devices has the disadvantage of leading to a high manufacturing cost. Such centering devices are thus not practical.
The accuracy of the molding block directly influences the lens machining accuracy, therefore high accuracy for the molding block is required.
Conventionally, the blocking operation is manually performed by the operator. Hence, high accuracy with regard to the molding block cannot be obtained.
When blocking the optical lens 10, the height of the optical surface to be blocked changes depending on the thickness of the peripheral edge of the lens 1.
Thus, a blocking ring 13 matching the thickness of the peripheral edge of the lens 10 is required. As a result, the number of types of the blocking rings 13 increases, and storage and management of the blocking rings 13 are cumbersome.
Conventionally, the optical lens 10 is placed on the blocking ring 13 in advance. A predetermined gap is set between the optical lens 10 and lens holding unit 12. The blocking material 14 is provided into the gap and cooled to solidify.
If the gap at the center is excessively narrow, the blocking material 14 can not reach the center readily, thus causing a dioptric power error.
On the contrary, if the gap is excessively wide, the use amount of blocking material 14 increases inevitably. The influence of heat shrinkage thus increases, and leading to an instability of the lens dioptric power.
The melting temperature and the amount of the blocking material 14 must be controlled highly accurately. Indeed, if the blocking material 14 is deprived of heat by the lens holding unit 12 or the optical lens 10 and is cooled to solidify, it cannot cover the entire surface of the lens holding unit 2. Hence, a sufficient bonding strength can not be obtained.
If the blocking material 14 starts to solidify before its supply operation has not been ended yet, bubbles are generated in the blocking material 14. In this case as well, the blocking material 14 does not cover the entire surface of the lens holding unit 12. Therefore, a sufficient bonding strength can not be obtained.
During the step of supplying the blocking material 14 into the gap between the optical lens and lens holding unit, the operator presses a button to provide the blocking material 14 into the gap. The operator stops supplying the blocking material 14 after he or she visually confirms that the provided blocking material 14 has reached a predetermined amount. This increases burden to the operator. Moreover, the supply amount of blocking material is not stable. However, if the supply amount of blocking material is excessively large, the blocking material 14 overflows from the gap between the optical lens 10 and lens holding unit 12. In this case the blocking material 14 also attaches to the peripheral surface or concave surface of the optical lens 10. If the supply amount is excessively small, sufficient bonding power can not be obtained.
Accordingly, there remains a need for improving blocking an optical lens. Thus, the goal of the present invention is to improve the blocking method of optical lens by providing a method for blocking an optical lens which is more easy to use and which enables to position the optical lens in a more reliable manner so as to ensure a more accurate machining of the lens.
According to an object of the invention a method for blocking an optical lens comprising:
According to the blocking method of the invention, the optical lens can be blocked in the second reference position which is function of the first reference position. Thus the lens, when being blocked in the second reference position is blocked in a more accurate manner with respect to the manufacturing tools.
In addition and unlike the blocking device disclosed in U.S. Pat. No. 5,919,080, as the pins are moveable in a vertical direction the blocking method according to the invention allows the blocking of the lens in an even more accurate position so as to introduce a desired prism and thereby limiting the modifications of the existing manufacturing tools and/or of the existing manufacturing process. Furthermore, the invention advantageously avoids the change of the entire existing manufacturing tools of a lens manufacturing lab.
According to further embodiments which can be considered alone or in combination:
According to another aspect, the invention relates also to a method of machining an optical lens comprising a blocking step in which the optical lens is blocked in a machining position according to a method of the invention and a machining step in which the optical lens is machined.
The machining of the surface may comprise generating a corrective prescription one or both of the surface of the optical lens, for example the sphere and/or the cylinder and/or a progressive additional surface.
The invention relates also to a computer program product for a data processing device, the computer program product comprising a set of instructions which, when loaded into the data processing device, causes the data processing device to perform at least one, for example all, of the steps, for example the calculating step, of the method according to the invention.
In addition, the present invention provides a computer-readable medium carrying one or more set of instructions of a computer program product of the invention.
The invention relates also to a blocking system comprising means to carry out the handling steps of a method according to the invention.
Non limiting embodiments of the invention will now be described with reference to the accompanying drawing wherein:
Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention.
The wording “upper” indicates a position relative to the optical lens surface when it is arranged so as the molding block 16 is substantially situated in a horizontal plane.
In an embodiment of the invention the blocking method of an optical lens comprises:
a) a orienting step,
b) a first blocking step,
c) a moving step,
d) a providing step,
e) a cooling step,
f) a placing step, and
g) a second blocking step.
The blocking method according to the invention can be used to block in a given position an optical lens. The optical lens can be, for example but not limited to, an ophthalmic lens, in particular an unfinished or semi-finished ophthalmic lens. More generally the optical lens can also be any optical component to be used, for example, in a camera or in a telescope.
It has to be understood that the machining method according to the invention can be used at different stage of the manufacturing process of an optical lens. The machining step can be, for example but not limited to, a cribbing step, a surfacing step, a roughing step, a fining step, a coating or spin coating step, an edging step, a grinding step, a polishing step.
For the purpose of the invention, “the prism” of the optical lens can be defined by the vector (αf, βf, Zf) which is perpendicular to the tangential plan at the prism reference point (PRP) of the optical lens; whereby αf corresponds to the prism amplitude as illustrated on
As is illustrated in
The pre-located pins 18 can have various geometry. As illustrated in
As illustrated in
The design data DES according to the invention may be calculated or selected taking into account wearer's parameters such as the wearer's prescription and/or a chosen spectacle frame and/or esthetical criteria and/or morphologic criteria.
The preset positions Z1, Z2, Z3 of the pins 18 are computed such that, when the optical lens 10 is placed on the pins 18 in their preset position Z1, Z2, Z3; the prism of the optical lens 10 correspond to the desired prism (αf, βf, Zf).
The software SOFT is thus arranged to first calculate the resulting prism (αr, βr, Zr), corresponding to the center of the optical lens 10 when being placed on the pre-located pins 18 and when the center of the spherical surface head of the pre-located pins 18 are aligned on the same horizontal line Z0. The resulting prism (αr, βr, zr) can be, for example, calculated by the software SOFT using the design data DES, the pin data PIN and the positioning data POS.
Then the software SOFT is arranged to calculate the desired vertical position (Z1, Z2, Z3) of each of the pins 18 by using the resulting prism (αr, βr, zr) and the prescription data PRES.
The desired vertical position (Z1, Z2, Z3) of the pins 18 corresponds to position of each of the pre-located pins 18 so as to have the prism of the optical lens which is equal to the desired prism (αr, βf, Zf).
Therefore, as illustrated on
When the pins 18 are in the pre-located position the surface of the optical lens, for example the convex surface can be placed on the pre-located pins 18.
More specifically, the optical lens 10 can be placed on the pre-located pins 18, by adjusting the position of the optical lens 10 such that the periphery of the optical lens 10 image-sensed by a CCD camera coincides with the reference line displayed on the same monitor that displays the optical lens 10, thus securing the positioning accuracy.
After the orienting step a), the method according to this embodiment further comprises a first blocking step b) illustrated on
During the first blocking step b), the first reference position (αf, βf, Zf), in which the optical lens was placed during the orienting step a), can be measured so as to obtain the first reference position (αf, βf, Zf).
The first reference position (αf, βf, Zf) of the optical lens 10 can be measured, for example, by using a measuring device 20 comprising a plurality of pins 22.
The pins 22 are put in contact with the free surface FS of the optical lens 10, which is the surface of the optical lens 10 opposite to the one that is in contact with the pre-located pins 18. Once the pins 22 are in contact with the free surface FS of the lens, they are, for example individually, blocked in position by a blocking mechanism (not shown on
The blocking mechanism may comprise any reversible blocking means well known from the person skilled in the art.
The first blocking step b) may comprise a contacting step, in which the pins 22 simply come in contact with the free surface FS of the lens in order to hold the optical lens 10 in the first reference position (αf, βf, Zf). Additionally, during the first blocking step b), the optical lens 10 is hold and blocked in the first reference position by a blocking system 24, for example a vacuum creating device.
After the first blocking step b) the method according to this embodiment further comprises a moving step c) illustrated on
During the moving step, the optical lens 10 is moved from the first reference position P1, (αf, βf, Zf) to a second reference position P2, (α2, β2, Z2), the second reference position P2, (α2, β2, Z2) being a function of the first reference position P1, (αf, βf, Zf). For example, the second reference position P2, (α2, β2, Z2) is substantially the same as the first reference position P1, (αf, βf, Zf).
For the purpose of the invention “the second reference position P2, (α2, β2, Z2) is substantially the same as the first reference position P1, (αf, βf, Zf)” means that the vector (αf, βf) of the optical lens 10 in its first reference position is substantially parallel to the vector (α2, β2) of the optical lens 10 in its second reference position. In a particular embodiment of the invention, additionally, the vertical position Zf of the PRP of the optical lens 10 in its first reference position is substantially the same as the vertical position Z2 of the PRP of the optical lens 10 in its second reference position.
The optical lens 10 is moved from its first reference position on the pre-located pins 18 to a position which allows putting the lens in contact with a blocking material 14.
During steps a) to c), the method according to the present embodiment, for example, comprises a providing step d) illustrated on
In an alternative embodiment, before pouring the blocking material 14 in to the molding block 16 a holding unit 12 can be inserted in the molding block 16.
As illustrated on
The blocking material 14 may include glues, pitch, low temperature fusible metal alloys and for example thermoplastic materials as disclosed in U.S. Pat. No. 6,036,313.
According to the present invention, a “thermoplastic material” is a material which comprises at least a thermoplastic material.
The thermoplastic materials have many advantages over traditional metal alloy materials. For example, the blocking materials 14 are non-toxic, environmentally safe, and for example biodegradable. The thermoplastic materials can be used with existing processing equipment and may be recycled. A molding block 16 comprising a solidified mass of a blocking material 14 can be used. The blocking material 14 may comprise a homopolymer or copolymer of epsilon-caprolactone, and for example has a number average molecular weight of at least 3,000, a mean bending modulus of at least 69 MPa at 21° C., or a mean flexural strength of at least 1 MPa at 21° C. The composition is solid at 21° C. and has a sufficiently low melting or softening point such that the composition may be placed adjacent to an ophthalmic lens blank at its melting or softening point without damaging the lens blank. The composition also has sufficient adhesion to an optical lens 10 or to an optical lens coating or tape to hold the optical lens 10 during a machining procedure.
The blocking material 14 is provided at a first state temperature, the first state temperature being for example above its melting or softening temperature, for example it is a temperature at which at least part of the blocking material 14 will flow under moderate pressure.
The blocking material 14 may be poured in the molding block 16 as illustrated on
For example, the amount of blocking material 14 in its intermediate state is measured to be adapted to the optical lens 10. In the sense of the invention “adapted to the optical lens” shall mean that the amount of blocking material 14 provided in the molding block 16, in its intermediate state, is calculated so that the volume defined by the internal surface of the molding block 16 and the surface of the optical lens 10 and taking into account is substantially equal to the volume of the blocking material 14 in its solid state. Of course if in an alternative embodiment holding unit 12 is inserted in the molding block 16 the geometry of the holding unit 12 should be taken into account for measuring the adapted amount of blocking material to be poured.
Advantageously, after the previous providing step d), the method according to the present embodiment further comprises a cooling step e), in which the blocking material 14 cools from its first state temperature to an intermediate state temperature, for example the intermediate state temperature being noticeably equal to the melting or softening temperature of the blocking material.
The cooling of the blocking material may be active, for example using water cooling, or passive, for example heat exchange with ambient air.
Thus, the cooling step e) avoids the thermal shock due to the contact between the optical lens 10 and the blocking material 14 when the temperature of the blocking material is too high. For example, the intermediate state temperature is below 54° C., or below 53° C.
For example, the blocking material is chosen in order to have its molding temperature below 54° C., or below 53° C.
After the cooling step e), when the blocking material 14 is in the intermediate state, the method according to the present embodiment comprises a placing step f) in which a surface of the optical lens 10, for example the convex surface, in the first reference position is placed in contact with the blocking material 14 as illustrated on
The blocking material is then cooled to a blocking state temperature. The final state temperature being close to room temperature, for example around 21° C.
The final state temperature is chosen so that the blocking material is solid at such temperature.
After, the placing step f), the method according to the present embodiment comprises a second blocking step g) in which the optical lens is blocked in its second reference position, as illustrated on
After the second blocking step g), the blocking system 24 releases the optical lens.
Thus, the optical lens 10 can be blocked in its second reference position and its free surface FS, can be machined.
In the above-mentioned description, the first reference position P1 and the second reference position P2 were defined with respect to the vector (α, β, Z) which is perpendicular to the tangential plan at the prism reference point (PRP). It has to be understood, that other point of the optical lens, different from the prism reference point (PRP), can also be used as reference point in order to define the first reference position P1 and the second reference position P2 of the optical lens.
The invention also relates to a blocking system comprising means to carry out the handling steps of a method according to the invention.
An example of such a blocking system as illustrated on
The first machining station A comprises an incoming conveyor 34, convoying the empty molding blocks 16, and a first handling device 26. The first handling device 26, moves the empty molding blocks 16 from the incoming conveyor 34 onto the carousel 25.
The carousel 25 may have a clockwise rotating movement, therefore moving the empty molding block 16 to the second machining station B.
The second machining station B comprises a providing device 32, so as to provide the adapted amount of blocking material 14 in the molding block 16.
The providing device 32 can be a poring device 32 arranged to pour the adapted amount of blocking material 14, at a temperature above its melting temperature, into the molding block 16.
The second machining station B can carry out the providing step d) of the blocking method as described previously.
The molding block 16 with the adapted amount of blocking material 14, is moved by the carousel 25 to the third machining station C.
A blocking system according to the invention may comprise means for cooling the blocking material 14 (not shown on
The third machining station C comprises orienting means 18 and a second handling device 28.
The orienting means 18 comprises pre-located pins 18 so as to orient the optical lens 10 according to the orienting step a) of the blocking method as described previously.
The second handling device 28 comprises a blocking system 24 so as to move the lens 10 from a first reference position (P1) to a second reference position (P2), so as to be in contact with a blocking material 14, the blocking material being in a molding block 16, the second reference position (P1) being a function of the first reference position (P2).
The second handling device 28 may also carry out the first blocking b), the moving c), the placing f) and the second blocking g) steps of the blocking method as described previously.
The fourth machining station D comprises an outgoing conveyor 36, convoying the molding blocks 16 with the optical lens 10 blocked in its second reference position, and a third handling device 30. The third handling device 30, moves the molding block 16 from the carousel 25 on to the outgoing conveyor 36. Each of the steps comprised in the method according to the previous embodiments can be carried out by a computer program comprising one or more stored sequence of instruction that is accessible to a processor and which, when executed by the processor, causes the processor to carry out each of the steps of the method.
The invention has been described above with the aid of an embodiment without limitation of the general inventive concept.
In particular the present invention provides for a method for blocking all kinds of lenses and substrates, particularly ophthalmic lenses, e.g. single vision (spherical, torical), bi-focal, progressive, aspherical, etc. and semi-finished lenses.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07290884 | Jul 2007 | EP | regional |
| 07301237 | Jul 2007 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/059095 | 7/11/2008 | WO | 00 | 7/12/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/010466 | 1/22/2009 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5341604 | Wood | Aug 1994 | A |
| 5919080 | Savoie et al. | Jul 1999 | A |
| 6036313 | Benjamin et al. | Mar 2000 | A |
| 20030214058 | Belly et al. | Nov 2003 | A1 |
| 20050122470 | Perrott et al. | Jun 2005 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20100297919 A1 | Nov 2010 | US |
