The invention relates to a method of three-dimensionally shaping at least a portion of a plate like object, whereby material is heated and deformed by means of a force exerted on said portion by a medium. The invention relates to a method of manufacturing a mould for producing a lens, such as a customized contact lens, to a method of producing a contact lens and to a device for carrying out the method of shaping.

US-A 5147437, discloses a method of shaping a mould for producing an eye glass lens whereby a part of a mould for producing eyeglass lenses is placed on a ceramic platform having a shape corresponding to the mould shape, except for a recess in the surface of the ceramic platform. After the platform, with the part of the mould on it, is heated in a furnace, the air is sucked out of the recess, so that the material of the mould sags into the recess. After cooling down, the relevant part of the mould is locally shaped according to the shape of the recess. The locally deformed mould can be used for manufacturing eyeglass lenses containing a flat top bifocal segment. This method requires direct contact between the mould part and the ceramic platform, whereby any disturbance of the surface of the platform is transferred to the mould. Because of the use of a ceramic platform, this method is furthermore not flexible, costly and not suitable for manufacturing a customized mould. A customized mould is understood to mean a mould that is designed for producing a product for a specific purpose or for a specific user, such a spectacle or contact lens wearer.

A conventional method of manufacturing a contact lens is based on curing an UV hardening polymer between a concave half and a convex half of a composed mould.

Often, the mould is made of a plastic material. The plastic mould can be made by a process of injection moulding by means of a metal mould.

A contact lens has a concave surface, which should abut the human eye and is called the base surface, and a convex surface, which is called the front surface. Such a lens should correct the human eye for a/o for spherical and cylindrical aberrations. The amount of correction the contact lens should provide, thus the surface profile, or shape, varies from eye

to eye. Therefore, the conventional manufacturing method requires a large number of predefined mould shapes to choose from in order to obtain the desired eye correction.

Furthermore, besides correction of spherical and cylindrical aberrations it is desired to correct also for higher order aberrations, whereby in fact a customized lens, has to be manufactured, i. e. a lens which is appropriate for only one person. The manufacturing of a customized lens requires a special customized mould and that mould can only be used for manufacturing a number of lenses for that one person.

A mould for manufacturing a customized contact lens, a customized mould, can be obtained by modifying by re-shaping a mould having a base shape. A base shape is understood to mean a shape that approximates the required, customized shape to a certain degree so that only limited modifications are needed to obtain the required shape. can be modified. That mould having the base shape can be chosen from a limited number of standard moulds which are produced in a conventional way, for example by injection molding with a metal mould. The'base shape'means that only limited modifications are required to obtain the final shape. The modification of the mould comprises the modification of the shape of one or of both surfaces, the concave surface and the convex surface respectively, each abutting a side of the lens during the molding operation of the contact lens.

The said modification can be performed by mechanically removing material However, this method is time consuming method. Moreover, the machined area of the mould surface must undergo a finishing operation to achieve the required smooth surface of the mould. Another method of modification, which is disclosed in WO 02/0559169, is based on sagging, under controlled conditions, of the mould resting on an array of individually controlled actuators to deform the surface of the mould into the desired shape during the molding process. This method requires a complicated device, especially in case fine modifications are required.

It is an object of the present invention is to provide a flexible, a relative simple, low cost and fast method of three-dimensionally shaping at least a portion of a plate like object, in particular of a mould for producing a contact lens. This method is characterized in that different forces are exerted on a first surface and an opposite surface, respectively of said portion and in that this portion is locally heated, which results in a deformation of said portion..

The locally heating results in a local plastic deformation of the object material, because of the difference in forces exerted on the two surfaces. By heating a predetermined portion of the plate like object, the material of that portion will be deformable by relative low forces, while the surrounding of that portion will not deform so easily. Therefore, when the difference of the forces at both sides of the portion is sufficient, the heated material will be forced by the larger force towards the side where the lower force is present, and the object will thereby locally deform. Thereby, the surface of the object will maintain its smooth shape, so that after shaping of the object no subsequent finishing treatment of the object surface is needed.

One of the forces exerted on the opposite surfaces of the object may be zero, which means that in one of said chambers there is no medium, but vacuum.

The method according to the invention is especially suitable for the manufacture of the mould half's of a composed mould for producing a customized contact lens, of which only a small number, from one to a few, has to be produced and for which it is important that the method is flexible, fast and cheap. However the method can be used for manufacturing moulds for other purposes, in general for producing an optical surface. An optical surface is understood to mean a surface of an optical element, such as a lens an correction plate etc, which surface changes the wave front of a beam of radiation passing the surface. A customized optical surface is understood to mean a surface that is especially designed for a specific purpose or for a specific user, such as a spectacle or contact lens wearer.

A preferred embodiment of the method is characterized in that locally heating is performed by means of a laser beam.

A laser beam is an excellent means for locally heating the object, because laser radiation can be concentrated very well on a predetermined portion of the object and can heat that portion fast, so that the required deformation can be realized before the heat is spread out in the object material outside the exposed area.

Preferably the method is characterized in that use is made of a laser beam, which intensity distribution and or cross-section at the surface of the object is adapted to the required deformation.

In this way the extent and the amount of deformation can be controlled with high precision so that a fine and detailed deformation becomes possible. The intensity distribution across the cross section of the laser beam may be such that different discrete areas of the object portion are heated simultaneously, which areas ay overlap each other.

The method may be further characterized in that an annular region of said portion is exposed.

Material of the annular region is then displaced from the side subjected to the larger force to the opposite side, to form an elevated platform. at the latter side.

A preferred embodiment of the method is characterized in that the temperature of the material of the object is set to predetermined value before local heating within said portion is started.

This temperature setting can be realized by cooling or heating the material by means of the medium at the sides of the object. Setting the object at a predetermined temperature will affect the heat spreading of the local heating operation and thereby the deforming process. In case the predetermined temperature is close to the temperature at which the deformation starts, the heat spreading of the local heating will be relative small, which means that larger deformations can be realized.

An embodiment of the method is characterized in that the force-exerting medium is a fluid and in that the force on the object portion is controlled by supplying fluid to or discharge fluid from at least one side of the object.

The medium can be a liquid or a gas, for example air. The application of gas has the advantage that its pressure can be easily controlled. Air has the advantage that it is available everywhere. Using a liquid for the medium has the advantage that the amount of deformation can be controlled by supplying or discharging liquid, rather than by controlling the pressure of liquid. However, supplying or discharging liquid in a controlled way requires more complicated equipment.

A further embodiment of the method is characterized in that the combined step of exerting force and locally heating is repeated at least once, thereby using for each combined step different values for at least one the parameters: force difference, size and position of the heated area within said portion, energy distribution across the heated area and heating time.

Now the deformation, or shaping of the plate like object is performed in more, successive, steps, whereby each step realizes an amount of deformation that is smaller than the amount of deformation realized by the preceding step. This allows fine-tuning of the deformation.

This embodiment may be further characterized in that in successive steps at least partly overlapping areas are heated.

The local heating operation can be repeated at the same area or at a different area within the object portion to be shaped. The different area may overlap the previous heated area. In this way, the surface of the processed object can be given a relative complex predetermined shape.

The embodiment of the method wherein two or more successive combined steps of locally heating and exerting force are used may be further characterized in that between two successive combined steps the object shape realized so far in measured interferometrically.

The intermediate shape of the object can be measured very accurately, which allows accurate determining the parameter values for the next combined step.

A main application of the invention is use of the method for manufacturing a mould for producing a customized optical surface. For this application the method is characterized in that the object is a base mould.

The terms optical surface, customized and base mould are defined herein above.

As a further step, the method can be used for manufacturing a composed mould for producing a lens, which composed mould comprises a first and second mould half for forming a first and a second lens surface, respectively of the lens. For this application the method is characterized in that at least one of the mould half's is manufactured by means of the method of three-dimensionally shaping as described herein before.

For other applications the method may be characterized by the further steps of : flattening one of the surfaces of the shaped object so that a plate like object having a thickness variation is obtained.

For this application one starts with a flat plate as the object. After three- dimensionally shaping the object in the way described above, one of the main surfaces is flattened by removing material from that surface, for example by a grinding operation, which - if required-is followed by a polishing operation. Thereby a plate is obtained that shows thickness variation. This plate introduces phase variations in a beam of radiation passing through it and may be used as a customized optical correction plate to correct for wave front aberration in a beam which travels through an optical device or system.

By deforming the flat surface of this plate again by means of the present method, a plate can be obtained that shows different surface relief at its two sides and a thickness variation.

The invention also relates to a method of producing a lens having a first lens surface and a second lens surface, which method comprises the steps of : providing a composed mould comprising a first mould half having a mould surface, which is the negative of the first lens surface, and a second mould half having a mould surface, which is the negative of the second lens surface; filling the space between the mould surfaces with a polymer material; exposing the polymer material to UV radiation, thereby hardening the material and shaping it to a lens having the said first and second lens surface. This method is characterized in that use is made of a composed mould manufactured according to the method described herein above for the composed mould.

The lens produced in this way may be a spectacle or binocular or telescope lens, but also a lens for an optical instrument or system.

The invention specifically relates to, and is most advantageously used in, a method for producing a contact lens. This method is characterized in that use is made of a composed mould comprising a first mould half having a concave mould surface and a second mould half having a convex mould surface.

A suitable base mould to be used with the method of manufacturing a mould forms also part of the invention. This mould is characterized in that it has a base shape surface that can be re-shaped by a combined step of heating and exerting force.

An embodiment of this mould is characterized in that the material of the mould is a plastic material..

If this material is transparent, the mould may be further characterized in that the mould material comprises a radiation absorber.

Such an absorber stimulates the required heating of the mould The invention also relates to a device for use with the method as described herein above. This device is characterized in that it comprises: a first chamber for containing, during the shaping process, a medium at a first pressure and a second chamber for containing a fluid at a second pressure, different from the first pressure holding means arranged between the first and second chamber and for holding a mould to be shaped such that, during the shaping process, the mould forms a wall between the to chambers, and -means for controlled heating a portion of the mould.

A preferred embodiment of this device is characterized in that the means for heating is constituted by an exposure unit comprising a laser.

The use of a laser allows ell-defined heating of the object, both with respect to the location of the heated area and with respect to the amount of heating.

This embodiment is preferably further characterized in that the laser exposure unit comprises means for controlling the intensity distribution and or the cross-section of the laser beam at the location of the object to be shaped.

With this embodiment the heating and thus the shaping process can be refined.

A specific embodiment of the device is characterized in that the laser beam supplied by the laser exposure unit has an annular cross-section.

Well-defined shapes of the object can be obtained with an embodiment of the device, which is characterized by computer means for controlling and adjusting shaping- process parameters, such as pressure difference, shape and intensity distribution of the laser beam and laser exposure time.

These and other aspects of the invention are apparent from and will be elucidated, by way of non-limitative example, with reference to an embodiment of the method of manufacturing a mould for producing a contact lens. In the drawings: Fig. 1 shows a sectional view of a mould for producing a contact lens; Fig. 2 shows a sectional view of an embodiment of the device for deforming a portion of a base mould; Figs. 3 and 4 show a first deforming operation; Fig. 5 shows the result of this operation; Fig. 6 and Fig. 7 show a second deforming operation; Fig. 8 shows the result of this operation; Fig. 9 shows a more complex deformation process; and.

Fig. 10 shows an embodiment of an interferometer that can be used with the method for measuring intermediate obtained plate shapes.

The Figures are only schematic representations, showing only those elements, which are relevant for understanding the invention.

Fig. 1 shows a composed mould for producing a contact lens. The mould comprises two mould parts, or-half s, a mould half 1 having a concave mould surface 1', which is used for shaping the convex front surface of the contact lens, and mould half 2 having a convex mould surface 2'for shaping the concave back surface of the contact lens.

The back surface abuts the eye when the contact lens is placed on the eye and is also called base side of the contact lens. Both mould half s 1,2 are provided with a circular edge portion 4, by means of which the mould half s can be clamped to keep them in a predetermined position during the production of a contact lens.

Mould half s 1 and 2 may both be made of a transparent plastic material and are manufactured, for example by a mould operation with a metal mould. The concave surface of mould half 1 and the convex surface of mould half 2 must be smooth, so that the surfaces of the contact lens produced by means of these mould half's do not need an additional finishing operation after the mould process..

To produce a contact lens, a hard able material, for example a UV hardening polymer, is brought in the space 3 between the two transparent plastic mould half s 1 and 2.

Subsequently the composed mould with the polymer is subjected to UV radiation for curing the polymer, so that the polymer is cured, or hardened. The result is a contact lens having a convex lens surface, which shape is defined by mould surface 1', and a concave lens surface, which shape is defined by mould surface 2'. This generally known method for producing a contact lens is relative simple and can be performed at low costs.

Fig. 2 shows schematically a portion of an embodiment of a device 10 according to the invention for manufacturing a mould such as mould half 1 or 2, by means of local deformation only of a base mould 30. The device comprises a first chamber 12 having a first wall 14 and a second chamber 16 having a second wall 18. The walls fit to each other as is shown in Fig. 2. During the deformation process the base mould 30 is placed between the two chambers and separates these chambers. First wall 14 has a circular recess in which the circular edge 32 of the base moulds fits. Circular edge 4 provides for a gas tight sealing between the chambers 12 and 16. Air, or another gas or a liquid, can be supplied through conduit 20 to chamber 12 and through conduit 22 to chamber 16, so that the pressure in each of the chambers 12 and 16, and thus the force exerted on the two surfaces of the base mould 30 can be controlled independently. Means for controlling gas-or fluid pressure are well- known to the person skilled in the art and thus need not to be described here and are not shown in Fig. 2.

An embodiment of the method will be described by means of which the base mould is deformed twice, in two steps, to obtain the required shape of a mould that can be used, for example, for producing a customized contact lens.

Fig. 3 shows the start of the first deforming operation. Thereby air is blown through conduit 9, as indicated by arrow 28, in order to increase the air pressure in chamber 12 to a predetermined level. In chamber 16 the environment air pressure is maintained, so that a downward force, which is determined by the pressure difference, is exerted on the upper side of the base mould 30. This mould is exposed to a laser beam from a laser exposure unit 34, which beam is denoted by arrow 24. The base mould is made of a transparent material, such as a glass or a transparent plastic, so that the laser beam passes through the mould and heats it locally, at the exposed area The area is heated above a temperature at which the mould material weakens and becomes deformable at relative low force. This allows the downward force resulting from the pressure difference in the two chambers deforming the mould at the area where the laser beam is incident. The deformation operation stops as soon as the laser beam is switched off, because the temperature at the exposed area rapidly falls down due to spread of the generated heat in the mould material. The heat that is spread to the surrounding of the exposed area is small enough to prevent the surrounding from reaching the weakening temperature.

The laser exposure unit may, in addition to the laser source, comprise beam shaping optical elements for shaping the beam, i. e. the size and the shape of its cross-section at the location of base mould 30 and for setting the intensity distribution within the cross- section. These optical elements, such as spherical and cylindrical lenses, diaphragms, conical shaped (axicon) elements etc and their functions are well known in the optical technique and need not to be described here and are not shown in Fig. 2. The said optical elements allows imparting the heating laser beam any cross-section shape and size and any intensity distribution so that the heated area and thus the deformation can be controlled very well. The shaping, or deforming device this is very flexible and allows making of any required deformation.

Fig. 4 shows the result of the first deformation operation. The deformed mould 40 shows a sunken area 42 at then location where the laser beam was incident. The size of the deformation 42 depends on a number of parameters, such as the difference between the pressure in chamber 12 and the pressure in chamber 16, the shape and size of the cross section of laser beam 24, the energy distribution over the heated area, the exposure time, and the energy absorption by the material of the base mould 30. The values these parameters

should have to realize deformations having predetermined sizes and profiles can easily be obtained from experiments and stored in a library, for example in a memory of a computer which controls the shaping device 10.

In case the material of the base mould 30 is a transparent plastic, which is normally used as material for moulds for contact lenses, the method can be improved by adding a laser radiation absorbing component to the mould material so that its absorption capability is increased and its heating is speed up. The heating of the relevant portion of the material of mould 30 should be fast enough, so that the deformation can take place before the heat is spread out too much over the remainder of the mould material.

The force on the object, or the different pressures at its two sides may also be realized by using a liquid instead of a gas, like air, as the medium in the chambers 12 and 16.

The force on the object portion is then controlled by supplying fluid to or discharging fluid from at least one of the chambers. The said pressure difference can also be realized by filling one chamber with a gas and vacuum pumping the other chamber.

If the mould 40 obtained from the first deformation operation should be further deformed a second, or even a third or more, deformation operation (s) can be carried out to obtain the final, required, shape of the mould. In the successive deformation operations, values for the parameters: location of the exposure beam, intensity of this beam, force exerted on the mould etc, are used, which are different from those values used during the preceding deformation operation (s) t values. Figs. 5-7 show such a second deformation step.

Fig. 5 represents the start of this step; a mould 40 with a first deformation 42 is placed in the device 10. As shown in Fig. 6 chamber 12 has an open connection with the environment so that the pressure in this chamber is equal to the air pressure. The pressure in chamber 16 is now increased by blowing air or pressing a liquid through conduit 22, as indicated by arrow 50. Thus, an upwardly directed force is exerted on the lower surface of mould 40. A laser beam denoted by arrow 24'and having border rays 26'is directed at the left edge of the deformation 42. This laser beam has a cross-section which is different from, for example smaller than, the cross-section of the laser beam 24 used during the first deformation operation. As shown in Fig. 7, an area of the mould 40 will be deformed, which is smaller than the area of mould 30 that was deformed during the first deformation operation. The laser beam 24'used during the second deformation operation may also have another cross-sectional shape and/or intensity distribution than the laser beam 24 used during the first deformation operation.

Fig. 8 shows the result of the second deformation operation. Due to the position of the exposing laser beam 24'with respect to the mould 40 and the size of the cross-section of this beam and due to the upward force exerted at the lower side of the mould, on the location of the said force and the local heating of part 1 by the laser beam 13 a mould 44 is obtained, which has, besides a sunken portion 42, a raised portion 46 at the edge of the portion 42.

After the mould, or another object, has been deformed, in one or more deformation operation (s), to the required shape, the walls 14 and 18 can be separated and the mould can be removed from the device.

The process time for shaping an object by plastic deformation as described herein above depends on the material of the object and the used equipment, the process conditions and the required accuracy, but this time will remain within the order of seconds.

As a large range of heating temperatures and heated area sizes as well as forces can be used, the shaping process is very flexible and allows providing objects with very different shapes.

In case a composed mould for production of a contact lens is to be manufactured, each of the two mould half's can be manufactured as described at the hand of Fig. 2-4 and, when needed, at the hand of Figs. 5-8.

In a shaping process for a plate-like object the deformation step (s) described herein above may be combined with a shaping step of another type, such as grinding. This will be illustrated at the hand of Figs. 9a-9d.

Fig. 9a shows a vertical cross-section of a part 60 of a plate-like object having an upper surface 62 and a lower surface 64. As shown in Fig. 9b, this object is first subjected to a first deformation step, whereby local heating of a surface area 70 and an downwards force on the upper surface are used. The downwards is indicated by the different pressures pi and p2, pi being larger than p2, at the upper and lower surface. This step results in a sunken portion 66 in the plate, which lower surface 64'has a raised portion 68.

In a next process step, the lower surface 64'is flattened, for example by means of grinding. The result of this step is shown in Fig. 9c: the raised portion 66 has been removed and the lower surface 64"is flat again. In the deformed area 70 the thickness of the plate has been decreased.

Then a second deformation step is carried out, this time with an upwards force on the lower surface by making pressure p2 larger than pressure pi. The plate is heated now over an area 72, which partly overlaps with the area 70. This results in a second deformation

in the form of a raised portion 76 at the location of the area 72 and in a complex shape of the final plate 78, as shown in Fig. 9d.

By combining on or more of the described deforming operations and one or more material removing operations a plate like object can be given a very complex shape.

The shape process of Figs. 9a-9d is a direct process, i. e. no mould is used. The plates of Fig.

9c and Fig. 9d, have a varying thickness across their surface and thus introduces phase shifts across the cross-section of a beam passing through this plate. The process of Figs. 9a-9d is very suitable for manufacturing a customized optical correction plate for use in a specific optical apparatus or instrument to correct for residual aberrations in the optical path of such apparatus or instrument.

Between successive deformation operations, as shown in Figs. 2-4 and Figs.

5-8 respectively and/or material removing steps, as shown in Fig. 9c, the intermediate shape of the object can be measured to determine the next deformation and thus the values of the process parameters to be used. required information. An instrument for such measurement is an interferometer an embodiment of which is shown in Fig. 10.

This interferometer comprises a laser source 82 supplying a laser beam b and a beam splitter 84, for example a semi-transparent mirror, which splits the laser beam b into a measuring beam bm and a reference beam br. The object 90 to be measured is arranged in the path of the measuring beam, whilst a reference object 92 is arranged in the path of the reference beam. In the path of the measuring beam and of the reference beam a lens system 86 and 88, respectively may be arranged, for example comprising a single lens, for suitable illumination of the object 90 and the reference object 92. The measuring beam bm and the reference beam br are reflected and travel along the same path back to the beam splitter 84, which reflects the reflected measuring beam and transmits the reflected reference beam to a detector 96. This detector may be a camera having an electronic sensor array, like a CCD or a CMOS sensor. Between the beam splitter 84 and the detector a lens system, for example comprising a single lens, may be arranged for proper imaging on the sensor array.

In the embodiment of Fig. 10 the distance between the beam splitter 84 and the object 90 to be measured is equal to the distance between the beam splitter and the reference object 92 and the measurement is based on determining differences between the object 90 and the reference object 92. The reference object 92 has the required shape the object 90 should have. If the shape of an area of the object 90 differs from the shape of the corresponding area of the reference object 92, the measuring beam portion from the object 90 area will have another phase than the measuring beam portion from the reference object 92

area. This phase difference can be detected by the camera 96, because the reflected measuring beam and reference beam interfere at the sensor of this camera.

The interferometer allows very accurate measuring of the said phase differences and contributes to the final accuracy with which the mould are another object can be shaped.

In the embodiment of Fig. 10 the intermediate object 90 to be measured is reflective, for example a phase correcting mirror. In that case the reference object is also a mirror so that the required reflection is obtained without further measures. Also an intermediate mould surface can be made reflective to allow measuring in this way. In case a transparent intermediate mould or object is to be measured another type of interferometer can be used, wherein the measuring and the reference beam pass through the object to be measured and the reference object, respectively and are then combined to interfere at the detector surface.

The invention has been described at the hand of the manufacture of a customized composed mould for producing a contact lens, but may also be used for manufacturing a mould for producing a spectacle lens or a lens for an optical apparatus or device. it has also been mentioned that the invention can be used for the direct production of a phase correcting plate. In addition to these application, the shaping method can be used for the manufacture of other optical components, such as a micro-lens array and, in general for three dimensionally shaping of glass or metal sheets. The most innovative is still the use of the method for the manufacture of moulds for customized contact lenses, because practically it is the only method to manufacture such moulds in an easy, cheap, simple and flexible way.