BLOCKING PIECE AND METHOD FOR VACUUM BLOCKING A LENS BLANK

Abstract

A blocking piece for vacuum blocking a lens blank is disclosed. The blocking piece includes a blank contacting element formed of a rigid fluid-permeable material having an upper surface for contacting the lens blank. The blocking piece further includes a support element having an upper part tightly enclosing the blank contacting element on a peripheral surface of the blank contacting element and a lower part adapted to engage with a clamping device for clamping the blocking piece. The lens blank is fixed to the upper surface of the blank contacting element by applying a vacuum within the blocking piece to provide suction through essentially the entire upper surface of the blank contacting element. The disclosure further relates to a method for blocking a lens blank and a use of an element formed of a rigid fluid-permeable material as a part of a blocking piece.

Claims

1. A blocking piece for vacuum blocking a lens blank, the blocking piece comprising: a blank contacting element formed of a rigid fluid-permeable material having an upper surface for contacting the lens blank; and a support element having an upper part tightly enclosing the blank contacting element on a peripheral surface of the blank contacting element and a lower part configured to engage with a clamping device for clamping the blocking piece, wherein the blocking piece is configured to fix the lens blank to the upper surface of the blank contacting element by applying a vacuum within the blocking piece to provide a suction through essentially the entire upper surface of the blank contacting element to suck the lens blank to the upper surface of the blank contacting element.

2. The blocking piece according to claim 1, wherein the rigid fluid-permeable material comprises or consists of a rigid porous material having an open porosity.

3. The blocking piece according to claim 1, wherein the rigid fluid-permeable material comprises or consists of one or more of the following materials: ceramic materials, carbide materials, in particular silicon carbide, oxide materials, in particular aluminum oxide, and aluminum foam.

4. The blocking piece according to claim 1, wherein the upper surface of the blank contacting element is spherically shaped according to a target shape of a front surface of the lens blank to be contacted with the upper surface of the blank contacting element.

5. The blocking piece according to claim 1, wherein outer dimensions of a peripheral surface and optionally a lower surface of the blank contacting element essentially correspond to inner dimensions of the upper part of the support element tightly enclosing the blank contacting element, and wherein the blank contacting element optionally is adhesively attached to an inner surface of the upper part of the support element.

6. The blocking piece according to claim 1, wherein the support element comprises a vacuum reservoir being in fluidic communication with a lower surface and optionally with a peripheral surface of the blank contacting element, and wherein the support element comprises a valve for carrying out one or more of the following actions: evacuating the vacuum reservoir, and venting the vacuum reservoir.

7. The blocking piece according to claim 6, wherein the valve is configured as a spring-loaded valve remaining in a closed state unless being activated by counteracting a spring force of the spring-loaded valve.

8. The blocking piece according to claim 1, wherein the lower part of the support element comprises an engagement element for engaging the support element with a clamping device, and wherein the engagement element optionally comprises a conical protrusion having a peripheral recess for providing a tight fitting and form fitting engagement of the engagement element with the clamping device.

9. The blocking piece according to claim 1, wherein the upper part and the lower part of the support element are provided as a single piece or as separate parts attached to each other; and wherein the support element is at least partly made of one or more of the following metallic material: aluminum, an aluminum alloy, and stainless steel.

10. The blocking piece according to claim 1, wherein the support element further comprises an identification element providing information for identifying the blocking piece, wherein the information provided by the identification element is accessible from outside the blocking piece, and wherein optionally the identification element may comprise or consist of one or more of the following items: a bar code, a QR-code, a human-readable label, and an RFID chip.

11. The blocking piece according to claim 1, further comprising a sealing lip at a periphery of the blocking piece to assist with providing the vacuum within the blocking piece and between the lens blank and the upper surface of the blank contacting element.

12. A method for blocking a lens blank to a blocking piece, the method comprising: providing a blocking piece having a blank contacting element formed of a rigid fluid-permeable material, the blank contacting element having an upper surface for contacting the lens blank, wherein the blank contacting element is tightly enclosed by a support element on a peripheral surface of the blank contacting element; arranging a lens blank at the upper surface of the blank contacting element such that the lens blank entirely covers the upper surface; and applying a vacuum within the blocking piece to provide a suction through the rigid fluid-permeable material sucking the lens blank to the entire upper surface of the blank contacting element.

13. The method according to claim 12, wherein a suction force of the applied vacuum sucking the lens blank to the upper surface of the blank contacting element has a strength of at least 80 N.

14. The method according to claim 12, wherein the lens blank is provided with a protective foil at the front surface facing the blank contacting element, the protective foil increasing a friction coefficient as compared to the friction coefficient of the front surface of the lens blank not having the protective foil.

15. A use of a blocking piece according to claim 1 for blocking a lens blank by applying a vacuum within the blocking piece to suck the lens blank to the blank contacting element formed of a rigid fluid-permeable material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The disclosure will now be described with reference to the drawings wherein:

[0048] FIGS. 1A and 1B show a blocking piece according to an exemplary embodiment in a perspective view and in a cross-sectional view.

[0049] FIG. 2 depicts a blocking piece according to an exemplary embodiment in a bottom view.

[0050] FIGS. 3A and 3B depict a blocking piece according to an exemplary embodiment with and without a lens blank blocked to it.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0051] In the drawings the same reference signs are used for corresponding or similar features in different drawings.

[0052] FIGS. 1A and 1B show a perspective view (FIG. 1A) and a cross-sectional view (FIG. 1B) of a blocking piece 10 according to an optional exemplary embodiment for vacuum blocking a lens blank. The blocking piece 10 comprises a blank contacting element 12 formed of a rigid fluid-permeable material and having an upper surface 12a for contacting a front surface of a lens blank. The blocking piece 10 further comprises a support element 14 having an upper part 14a and a lower part 14b. The upper part 14a of the support element 14 tightly encloses the peripheral blank contacting element 12, wherein the upper part 14a is partly covered by a sealing lip 16 of the blocking piece 10. The lower part 14b of the support element 14 is adapted to engage with a clamping device and comprises for this purpose an engagement element 18. The engagement element 18 is adapted to engage a respective counter part of a clamping device of a machine for machining the back side of the lens blank. A peripheral recess 20 of the engagement element provides a form-fitting and force-fitting engagement with the clamping device (not shown). According to this exemplary embodiment, the engagement element 18 is identical to an engagement element of a conventional blocking piece to ensure full compatibility with conventional clamping devices and/or blocking devices. This allows replacing conventional blocking pieces with a blocking piece 10 according to the presented exemplary embodiment.

[0053] According to the presented exemplary embodiment, the upper surface 12a has a radius of curvature which is adapted to the radius of curvature of a lens blank to be blocked. If the lens blanks to be blocked are typically equipped with a protective foil or coating on their front surface, the thickness of the protective foil or coating may be considered at the radius of curvature of the upper surface 12a.

[0054] The blank contacting element 12 is made of a rigid and fluid-permeable material. According to the presented exemplary embodiment the blank contacting element 12 is formed of a porous material, such as aluminum oxide, having an open porosity between 10% and 15%. This choice of material ensures a sufficient rigidity to avoid a deformation of the blank contacting element 12 when applying a vacuum and sucking a lens blank to the upper surface 12a. On the other hand, the open porosity ensures the ability of the blank contacting element 12 to enable a fluid flow, i.e., a fluid permeability, required for generating the suction to suck the lens blank to the upper surface.

[0055] FIG. 1B shows a cross-sectional view of the blocking piece 10 revealing inter alia a peripheral wall 12b and a lower surface of the blank contacting element 12. The peripheral wall 12b is tightly enclosed by the upper part 14a of the support element 14 to prevent a fluid stream entering or exiting the peripheral wall 12b. Also, the lower surface 12c of the blank contacting element 12 is enclosed by the upper part 14a of the support element 14, wherein the upper part 14a comprises one or more through holes to enable a fluidic connection between the lower surface 12c of the blank contacting element 12 and a vacuum reservoir 22 arranged underneath the upper part 14a of the support element 14. Via the one or more through holes and the open porosity of the blank contacting element 12 a suction can be generated from the upper surface 12a of the blank contacting element 12 through the bulk body of the blank contacting element 12 to the vacuum reservoir 22 and a vacuum source (not shown), which may be connected to the vacuum reservoir 22. For the sake of illustration, the blank contacting element 12 may be considered as a diffusor for the suction generated by a vacuum source underneath the upper part 14a of the support element.

[0056] The blocking piece moreover comprises a valve 24 attached to the vacuum reservoir 22 allowing evacuating the vacuum reservoir 22 by opening the valve 24 and connecting it to a vacuum source (not shown). The valve 24 is a spring-loaded valve prevailing in a closed state unless the spring force is overcome by a force impact for opening the valve 24. The spring 24a of the spring-loaded valve 24 is exemplarily indicated. Similarly, the valve 24 may be used for venting the vacuum reservoir 22 to break the vacuum and unblocking a blocked lens blank. This may be achieved by opening the valve while the blocking piece 10 and in particular the valve 24 is disconnected from the vacuum source 24.

[0057] The sealing lip 16 is attached at the periphery of the upper part 14a of the support element 14 enclosing the blank contacting element 12. The sealing lip 16 assists contacting the lens blank in an airtight manner to facilitate the establishment of a vacuum in the void formed by the vacuum reservoir 22, the through holes(s) in the support element 14, the open pores of the blank contacting element 12 and a possible remaining local gap between the front surface of the lens blank and the periphery of the blank contacting element 12. However, the sealing lip 16 merely serves the purpose of assisting an airtight sealing but does not refrain the lens blank from contacting the entire upper surface 12a of the blank contacting element 12.

[0058] FIG. 1B further illustrates that the support element 14 according to the presented exemplary embodiment is made of several separate parts. These parts comprise the upper part 14a, the lower part 14b and the valve 24. Such a composition of several elements facilitates the manufacturing of various different blocking pieces, such as blocking pieces having different blank contacting elements 12. For this purpose, different upper parts 14a may be provided, which are each adapted to one or more of the various different blank contacting elements 12.

[0059] FIG. 2 depicts a perspective bottom view of the blocking piece 10 according to the blocking piece 10 presented in FIGS. 1A and 1B. The bottom view reveals the valve 24 arranged in the center of the support element 14 and concentrically with the engagement element 18. In addition, FIG. 2 reveals an identification element 26 attached at the lower surface 14c of the support element 14. The identification element may comprise a transponder, such as a RFID transponder, which may be read or written with a conventional RFID sender and receiver. The identification element 26 may be used for storing information concerning the blocking piece 10 and/or concerning a lens blank blocked to the blocking piece 10, such as prescription data to be applied to the lens blank and/or information for identifying the order or serial number of the spectacle lens to be manufactured. Alternatively, or additionally the identification element may comprise other kinds of identification means, such as a bar code and/or a QR code and/or an inscription readable for humans. Moreover, the bottom view depicts several screws 28 fixing the upper and lower part 14a, 14b of the support element to each other.

[0060] FIGS. 3A and 3B depict a blocking piece according to the optional exemplary embodiment shown in FIGS. 1A and 1B without a lens blank blocked to the blocking piece 10 (FIG. 3A) and with a lens blank 30 being blocked to the blocking piece 10. As can be seen in FIG. 3B, the blocked lens blank 30 is blocked to the blocking piece such that the front surface 100 of the lens blank is in contact with the entire upper surface 12a of the blank contacting element 12. The lens blank 30 is blocked to the blocking piece 10 by a vacuum provided in the vacuum reservoir 22, which generates a suction force to the lens blank 30 through the porous blank contacting element against the upper surface 12a of the blank contacting element 12.

[0061] FIG. 3A further illustrates the reference directions used throughout this document regarding the blocking piece 10 and the lens blank 30. These are the front surface 100 and the back surface 102 of the lens blank 30, the upper side 104 and lower side 106 of the blocking piece 10, the upper part 14a and the lower part 14b of the support element 14, as well as the upper surface 12a, the peripheral surface 12b and the lower surface 12c of the blank contacting element 12. These directions and parts shall be indicated by the respective names although, depending on the orientation of the blocking piece 10 in the three-dimensional space, may not always result in the upper side being oriented in an upward direction according to the common understanding. The directions in this description are merely provided for illustrative purposes.

[0062] In the following, a method according to an optional exemplary embodiment of the disclosure for blocking a lens blank to a blocking piece according to a preferred exemplary embodiment is exemplary illustrated.

[0063] For blocking a lens blank, a clamping device is used to which the vacuum blocking piece is mechanically clamped. The valve is opened automatedly during the clamping process. The blocking device has a centering stop suitable for the respective blank diameter. The vacuum may be generated by means of a Venturi nozzle connected to a compressed air system, such as a compressed air system commonly used in industry delivering air at a pressure of about 6 bar. This allows generating a vacuum of about 0.8 bar, which corresponds to an absolute pressure of about 0.2 bar. The spherical front surface of the lens blank, which may have been cast or machined, is covered with a protective foil or a coating, is placed on the spherical upper surface of the blank contacting element of the blocking piece clamped in the clamping device, centered with the aid of a centering stop, and the vacuum is then switched on. The vacuum causes the lens blank to contact the upper surface of the blank contacting element, moving it onto the sealing lip on the peripheral side of the blocking piece and thus sealing the system from the outside, wherein the lens blank is tightly attached to essentially the entire upper surface of the blank contacting element. A spring-loaded mechanism then closes the valve of the blocking piece. The blocked lens blank is not fixed to the blocking piece and can now be removed from the clamping device together with the blocking piece. In the event of an unforeseen loss of vacuum, for example due to long downtimes in the production environment, rest periods at the weekend or similar, the vacuum can simply be replenished in a processing machine or in a special device made for this purpose.

[0064] To detach, i.e., to unblock the spectacle lens processed from the lens blank from the vacuum blocking piece, the valve of the blocking piece is opened inside an unblocking device, thus ventilating the vacuum reservoir of the blocking piece. This process of ventilation can be forced by supplying compressed air. It is also possible to detach the spectacle lens from the block piece by blowing focused compressed air from the outside between the front surface of the spectacle lens and the sealing lip and upper surface using a nozzle. In principle, the unblocking process described can also be carried out in the same device that is used for the blocking process. In this case, in addition to the “evacuate” function, a “ventilate” function can be provided, which can then be activated by means of a pneumatic switching device.

[0065] The foregoing description of the exemplary embodiments of the disclosure illustrates and describes the present invention. Additionally, the disclosure shows and describes only the exemplary embodiments but, as mentioned above, it is to be understood that the disclosure is capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the concept as expressed herein, commensurate with the above teachings and/or the skill or knowledge of the relevant art.

[0066] The term “comprising” (and its grammatical variations) as used herein is used in the inclusive sense of “having” or “including” and not in the exclusive sense of “consisting only of.” The terms “a” and “the” as used herein are understood to encompass the plural as well as the singular.

[0067] All publications, patents and patent applications cited in this specification are herein incorporated by reference, and for any and all purposes, as if each individual publication, patent or patent application were specifically and individually indicated to be incorporated by reference. In the case of inconsistencies, the present disclosure will prevail.

LIST OF REFERENCE SIGNS

[0068] 10 blocking piece [0069] 12 blank contacting element [0070] 12a upper surface of blank contacting element [0071] 12b peripheral surface of blank contacting element [0072] 12c lower surface of blank contacting element [0073] 14 support element [0074] 14a upper part of support element [0075] 14b lower part of support element [0076] 14c lower surface of support element [0077] 16 sealing lip [0078] 18 engagement element [0079] 20 peripheral recess of engagement element [0080] 22 vacuum reservoir [0081] 24 valve [0082] 24a spring of the spring-loaded valve [0083] 26 identification element [0084] 28 screw [0085] 30 lens blank [0086] 100 front surface of lens blank [0087] 102 back surface of lens blank [0088] 104 upper side of blocking piece [0089] 106 lower side of blocking piece