Process for machining a lens

Abstract

A process for machining a lens includes the steps of holding a semi-finished product through a suction holding force which is active during an entire surface machining cycle of the semi-finished product; carrying out the surface machining cycle on a surface to be machined of the semi-finished product; and activating a pressure holding force depending on the level of the mechanical stresses exerted on the semi-finished product during the surface machining cycle on said surface.

Claims

1. A process for machining a lens, the process comprising the steps of: holding a semi-finished product through a suction holding force which is active during an entire surface machining cycle of the semi-finished product, wherein said semi-finished product comprises a convex front surface, a concave rear surface to be machined opposite to the front surface and a perimeter surface, wherein the suction holding force acts on the front surface; carrying out the surface machining cycle only on said rear surface to be machined of the semi-finished product by a machine tool; and activating a pressure holding force depending on a magnitude of mechanical stresses exerted on the rear surface of the semi-finished product during the surface machining cycle on said rear surface, the pressure holding force acting on said rear surface, wherein the surface machining cycle on said rear surface comprises a first step in which the semi-finished product is held by the application of both the suction holding force on said front surface and the pressure holding force on said rear surface and the machine tool machines the rear surface of the semi-finished product moving from the outer edge of the rear surface towards the central portion of the rear surface, and a subsequent step in which the semi-finished product is held by application of just the suction holding force on said front surface and the machine tool has reached the central portion of the rear surface.

2. The process for machining a lens according to claim 1, wherein the pressure holding force is activated depending on an instantaneous position taken up by the machine tool on the rear surface in the surface machining cycle.

3. The process for machining a lens according to claim 2, wherein the pressure holding force is kept active when the machine tool is close to the outer edge of the rear surface to be machined.

4. The process for machining a lens according to claim 2, wherein the pressure holding force is not active when the machine tool is close to a central portion of the rear surface to be machined.

5. The process for machining a lens according to claim 1, wherein the step of holding through a suction holding force comprises activating a suction unit when the front surface rests against a Suction chamber arranged in a first rotary shaft.

6. The process for machining a lens according to claim 1, wherein the process comprises, before the step of holding through a suction holding force, the step of adapting a deformable support element to the shape of the front surface.

7. The process for machining a lens according to claim 6, wherein the step of adapting the deformable support element comprises: resting the front surface against the deformable support element in order to give such a deformable support element a shape matching the shape of the front surface; and locking in position the support element in such a matching shape.

8. The process for machining a lens according to claim 1, wherein the step of holding through a suction holding force comprises activating a suction unit when the front surface rests against a suction chamber arranged in a first rotary shaft, and wherein the step of activating the pressure holding force comprises bringing a second rotary shaft, parallel to the first rotary shaft, to an operative position thereof in contact with the rear surface and exerting a pressure on said rear surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further characteristics and advantages of the present invention will become clearer from the following detailed description of some preferred embodiments thereof, made with reference to the attached drawings. The different characteristics in the single configurations can be combined as desired according to the previous description, if it should be necessary to benefit from the advantages resulting specifically from a particular combination.

(2) In such drawings,

(3) FIG. 1 is a schematic view of a first operative configuration of a first embodiment of a holding group of a semi-finished product for implementing the process for machining a lens according to the present invention;

(4) FIG. 2 is a schematic view of the holding group of FIG. 1 in a second operative configuration;

(5) FIG. 3 is a schematic view of a second embodiment of the holding group of a semi-finished product for implementing the process for machining a lens according to the present invention.

DETAILED DESCRIPTION

(6) In the following description, in order to illustrate the figures identical reference numerals will be used to indicate constructive elements with the same function.

(7) With reference to the figures, a holding group of a semi-finished product for implementing the process for machining a lens according to the present invention is shown and it is wholly indicated with 10.

(8) Going into the detail of the example embodiment illustrated, the semi-finished product 20 is a block of semi-finished material intended to become a lens.

(9) Such a semi-finished product 20 comprises a first surface 20a that is already machined, called front or convex surface, and at least one second surface, like for example the rear surface 20b, opposite the front surface 20a, and/or a perimeter side surface 20c.

(10) The rear surface 20b is generally intended to be surface machined.

(11) The holding group 10 comprises a suction holding device 10a. Such a device preferably comprises a first rotary shaft or rear mandrel 11 ending with a suction chamber 12 at the end intended to come into contact with the front surface 20a.

(12) The suction chamber 12 is connected to a suction unit 12b for generating the vacuum and comprises a gasket 13 or other type of sealing elements capable of making a fluid tight coupling once such sealing elements are rested onto the front surface 20a.

(13) The holding group 10 also comprises a pressure holding device 10b. Such a device preferably comprises a second rotary shaft or front mandrel 14, arranged parallel to the first rotary shaft 11, suitable for exerting a pressure on the rear surface 20b.

(14) The second rotary shaft 14 is mobile between a first operative position, illustrated in FIG. 1, in which it is in contact with the rear surface 20b, thus being able to exert a pressure directly on such a surface 20b, and a second operative position, illustrated in FIG. 2, in which it is distant from the rear surface 20b, therefore leaving free access to a machine tool of the surface 20b, for example a cutting tool 30 such as a turning plate or a milling cutter. The figures show a turning plate, purely as an example.

(15) In FIG. 1, the second rotary shaft 14 is illustrated resting against an appendage 20d of the semi-finished product 20 remaining at the end of a first perimeter rough machining step carried out by the cutting tool 30.

(16) The movement of the rotary shaft 14 between the first and the second operative position and the pressure exerted on the surface to be machined 20b are controlled through an actuator (not illustrated), for example of the pneumatic or hydraulic type.

(17) In alternative embodiments that are not illustrated, the pressure holding device is such as to exert a radial pressure on the perimeter surface 20c of the semi-finished product 20, therefore comprising elements that are mobile between a first operative position in which they are in contact with such a perimeter surface 20c and exert a radial pressure on it, and a second operative position in which such elements are not in contact with the perimeter surface 20c.

(18) According to a preferred, but not limiting, embodiment illustrated in FIG. 3, the holding group 10 also comprises a deformable support element 16, preferably of the self-locking type, made in the suction chamber 12.

(19) Advantageously, the deformable support element 16 comprises a plurality of concentric rings 16a that rest against the base 12a of the suction chamber 12 through interposition of elastic means 16b, like for example a plurality of springs. The concentric rings 16a terminate, at their free end adapted to rest against the lens 20, with circular gaskets 16c. For the sake of clarity of illustration, reference numerals 16a and 16b are associated in FIG. 3 with just a few of the aforementioned concentric rings and elastic means.

(20) Thanks to the structure described above the support element 16 is able to adapt its shape so as to make a support surface of the front surface 20a of the semi-finished product 20, the shape of which perfectly matches the shape of the front surface 20a.

(21) In particular, when initially the semi-finished product 20 is loaded onto the holding group 10, it still has a thickness and therefore a strength that is sufficient to counteract the action of the elastic means 16b without the force of such elastic means 16b resulting in the breaking of the semi-finished product 20.

(22) By resting the front surface 20a of the semi-finished product 20 against the free ends of the concentric rings 16a, they take up an axial position determined by the particular shape of such a front surface 20a.

(23) Once the shape matching the front surface 20a has been reached, the plurality of concentric rings 16a is locked in position through the action of a locking device 17, for example of the mechanical or hydraulic type.

(24) In this way the support element 16 is able to keep the shape initially set even once the thickness of the lens has undergone a substantial reduction, also providing a counter-thrust evenly distributed over the entire front surface 20a.

(25) Alternative embodiments foresee the use of deformable support elements 16 of the fluid or semifluid type as an alternative to the spring support element.

(26) The process for machining a lens according to the invention will be described hereafter with reference, as a non-limiting example, to a process for generating lenses. Such a process for machining a lens comprises the following steps.

(27) Once a semi-finished product 20 intended to become a lens is loaded onto the holding group 10, the suction holding device 10a is activated, keeping it operative during the entire machining cycle. In this way, the semi-finished product 20 is held through a suction holding force during the entire machining cycle.

(28) Thereafter, the machining cycle is started, which in the specific case of generating lenses comprises firstly the rough machining or rough surface cutting of the surface to be machined 20b of the semi-finished product 20, starting from a machining close to the edge, to then pass to the machining of the central portion of such a surface 20b.

(29) During the rough machining step close to the edge of the surface to be machined 20b, in addition to the suction holding device 10a, the pressure holding device 10b is also activated.

(30) In the specifics of the illustrated embodiment, the suction unit of the holding device 10a is activated when the front surface 20a of the semi-finished product 20 rests against the suction chamber 12 arranged in the first rotary shaft 11.

(31) Thereafter, the actuator of the pressure holding device 10b is activated so as to bring the second rotary shaft 14 into its operative position in contact with the surface to be treated 20b of the semi-finished product 20, placing it in a condition to exert a pressure on such a surface to be machined 20b.

(32) It is therefore possible to carry out the rough machining operations of the surface to be machined 20b close to the edge of the semi-finished product 20 since the combined suction holding and pressure holding action also allows the higher mechanical stresses to which the lens is subjected during such operations to be counteracted as well.

(33) Once the rough machining operations of the surface to be machined 20b close to the edge of the semi-finished product 20 have ended, the pressure holding device 10b is deactivated so as to give free access to the central part of the surface to be machined 20b.

(34) Once the second rotary shaft 14 has been brought into its operative position distant from the surface to be machined 20b, the advancing speeds of the semi-finished product 20 can in fact be kept high, therefore involving a minimal loss in terms of cycle time.

(35) Indeed, advantageously, the cutting tool 30 now operates close to the centre of the semi-finished product 20, involving low cutting forces that can be counteracted with just the vacuum holding force.

(36) It is thus possible to end the rough cutting operations close to the centre of the semi-finished product 20.

(37) In such a configuration it is also possible to proceed to the finishing and polishing cutting steps of the surface 20b through the relative tools. Such operations indeed also generate low stresses that can be counteracted through just the action of the suction holding device 10a.

(38) In the preferred embodiment illustrated in FIG. 3, before the step of activating the suction holding device 10a there is a step of adapting the deformable support element 16 to the shape of the front surface 20a of the semi-finished product 20.

(39) Such a step comprises resting the front surface 20a of the semi-finished product 20 against the support element 16 in order to give the support element a configuration adapted to and matching the shape of the front surface 20a and locking in position of the support element 16 in such a configuration.

(40) From the description that has been made the characteristics of the process for machining a lens of the present invention are clear, just as the relative advantages are also clear.

(41) In particular, the process for machining a lens according to the invention is perfectly able to ensure both precision of positioning, and reliability of holding of the semi-finished product during the entire machining cycle, this moreover in the absence of a reference block, in this way avoiding all of the drawbacks deriving from the use of such a block.

(42) Further variants of the embodiments described above are possible, without departing from the teaching of the invention.

(43) In particular, the description refers as a non-limiting example to a process for generating lenses. However, the process according to the present invention can be actuated in any application for machining lenses where it is necessary to effectively hold a semi-finished product in order to be able to simultaneously proceed to machine it.

(44) Moreover, the sequence of the activation steps of the suction holding force and of the pressure holding force is not restricted to that described purely as an example. Differently, the inventive concept also extends to machining processes that foresee a first machining step with low stresses in which just the suction holding force operates and a second machining step with high stresses in which the pressure holding force also additionally operates or to any combination of such steps.

(45) Finally, it is clear that the process for machining a lens thus conceived can undergo numerous modifications and variants, all of which are covered by the invention; moreover, all of the details can be replaced with technically equivalent elements. In practice, the materials used, as well as the sizes, can be whatever according to the technical requirements.