Patent Description:
It is an advantage of custom-made lenses that the optical power of such lens can locally vary to correspond more accurately with a person's actual needs for visual assistance. For example, a person may require a lens that improves near and far distance vision while little to no visual correction is required for distances in-between. <FIG> shows an example for a custom-made lens (L) with such properties. Therein, the lens (L) is illustrated with a front surface (L2) and a specifically machined back surface (L1). The contour of the back surface (L1) follows a customized power map to facilitate different prescription values for different sections of the lens (L). For example, lower section (L13) comprises comparatively more material than other sections of the lens (L). Thereby, vision of objects in close proximity can be improved for a person looking through the lower section (L13). For reference, a dashed line (L15) is shown in <FIG>, which indicates the contour of the back surface (L1) of a lens without a localized power variation.

Generally, different methods of producing corrective lenses exist, such as an injection moulding, a casting or a machining process. Typically, in the casting process, a mould is used to produce stock lenses having a low to middle power range. The optical surfaces generated in this process are already polished. In comparison, in a machining process, individually calculated lenses are generated by a machine referred to as "lens generator". This process requires special tools for milling, turning and polishing to generate optical surfaces with a localized power variation and high quality.

As described, an important part of every lens generating process is the polishing step, in which the surface roughness of the lens is significantly reduced since surface roughness can have undesirable effects, such as scattering of light and specular reflection.

<FIG> illustrate exemplarily a typical polishing process known in the prior art. In these Figures, a lens (L) is supported by a lens support unit (<NUM>) with a spindle (<NUM>) and a lens holder (<NUM>). Polishing of the lens (L) is performed with a soft polishing tool (<NUM>) and a polishing liquid (<NUM>) (often referred to as "slurry") that is supplied through an external nozzle (<NUM>). Typically, the polishing liquid (<NUM>) comprises a liquid with abrasive particles of defined particle sizes. Generally, polishing involves drawing polishing particles (grains) over the surface to be polished with or without the application of pressure. Thereby, roughness peaks of the surface can be abraded and thus levelled out. The polishing tool (<NUM>) is rotated about a rotational axis (indicated by arrow (<NUM>)) and linearly movable (indicated by arrow (<NUM>)). Further, the polishing tool (<NUM>) is covered by a soft coating (<NUM>), which is provided on a surface that comes into contact with the lens (L). During the polishing process, the lens (L) rotates about the rotation axis (RA2) of a spindle (<NUM>) and the polishing tool (<NUM>) may rotate about its own axis and may be tilted and/or moved across the optical surface (L1) of the lens (L). The polishing process illustrated in <FIG> relies on the presence of polishing liquid (<NUM>) between lens surface (L1) and soft coating (<NUM>). In addition, it was found that the effectiveness, quality and heat management of the polishing process depends on a film of polishing liquid (<NUM>), which may form between lens surface (L1) and soft coating (<NUM>), having a defined thickness.

For example, if the thickness of the film is too high, the abrasive particles of the polishing liquid (<NUM>) do not come sufficiently into contact with the polishing tool (<NUM>). Thereby, the necessary mechanical interaction between polishing tool (<NUM>) and particles (and subsequently, between particles and optical lens surface (L1)) cannot be effected. Accordingly, the result from the polishing process may be insufficient. In comparison, if the thickness of the film is too low, the surfaces of the lens (L) and the polishing tool (<NUM>) are at risk of coming into direct contact with each other so that rotational energy is converted into heat instead of surface abrasion. However, this poses a risk of the lens (L) or the polishing tool (<NUM>) being damaged or deformed. Additionally, not enough heat may be transported away from the lens (L) by the polishing liquid (<NUM>) during the polishing process so that there is a risk of the lens (L) being deformed or damaged due to thermal overload.

In the prior art, attempts were made to address these problems by providing a multitude of nozzles (<NUM>) pointing onto the moving parts from different directions and projecting vast amounts of polishing liquid (<NUM>) towards lens (L) and polishing tool (<NUM>) to ensure a sufficient amount of polishing liquid (<NUM>) entering the gap between lens (L) and polishing tool (<NUM>). Therein, also the pressure, by which the polishing liquid (<NUM>) is fed through the nozzle (<NUM>), was adapted to increase the output of polishing liquid (<NUM>) through the nozzles (<NUM>). However, these known solutions are disadvantageous for various reasons: For example, the high rotational speeds of the moving components lead to an uncontrolled distribution of polishing liquid (<NUM>) in the working chamber while the film thickness cannot be controlled. Accordingly, a high quantity of polishing liquid (<NUM>) is needed for the polishing process while maintenance and cleaning times of the so configured machines are increased. Also, the size of the machines has to be increased as a large tank and a suitable pump are needed for assuring necessary flow rates and quantities of polishing liquid (<NUM>). Furthermore, the polishing liquid (<NUM>) has to be cooled in a chiller prior to being dispensed through the nozzle (<NUM>) to ensure sufficient cooling during the polishing process. Typically, the temperature of the polishing liquid (<NUM>) is kept at about <NUM>. Thus, the effectiveness, efficiency and resourcefulness of the polishing process of known prior art solutions is low, respectively.

<CIT> shows a polishing tool according to the preamble of claim <NUM> with an additional polishing cover <NUM>. <CIT> shows a polishing tool with a flat polishing pad for large optical elements, such as an optical mirror for space applications.

Therefore, it is an object of the present invention to provide a polishing tool, system and method that overcome the aforementioned disadvantages of the prior art, respectively. Therein, it is a particular object of the invention to ensure a sufficient supply of polishing fluid in a region between the lens to be polished and the polishing tool throughout the polishing process. In addition, it is an object of the invention to reduce the amount of polishing liquid required in the polishing process while ensuring sufficient cooling in the polishing process and increasing the achievable quality of the finished lens.

These and other objects, which become apparent upon reading the description, are solved by the subject-matter of the independent claims. The dependent claims refer to preferred embodiments of the invention.

A first aspect of the invention relates to a polishing tool for polishing a spectacle lens in a surface machining process. The polishing tool comprises a tool body for being rotatably supported about a rotational axis. The tool body comprises a polishing surface being outwardly exposed at a first axial end of the tool body. The polishing surface is axially bulged convexly or concavely with respect to the rotational axis for polishing an optical surface of the spectacle lens. The tool body further comprises a channel extending axially through the tool body. The channel extends from an inlet to an outlet to supply the polishing surface with a polishing agent. The outlet (of the channel) is provided at the first axial end. The inlet (of the channel) is provided at a second axial end, which is
opposite to the first axial end with respect to the rotational axis. The polishing surface comprises at least one groove that extends radially away from the outlet to the perimeter of the polishing surface to distribute the polishing agent across the polishing surface.

With other words, a tool for being used in a process of smoothening an optical surface of a spectacle lens by removing material therefrom can be provided. The polishing tool comprises a tool body that is suitable (configured) for being supported such that the tool body can be rotated about a rotational axis (e.g. its own axis or an axis offset thereto), for instance. The tool body comprises a first axial end and a second axial end, which is opposite to the first axial end with respect to the rotational axis. At the first axial end, the tool body comprises a polishing surface, such as, for example, an exterior (outside layer) that is accessible from (open to) the outside. The polishing surface is suitable for polishing a (typically curved) optical surface of the spectacle lens and, for example, forms a (with respect to the rotational axis) concavely or convexly curved shape sticking axially out from the tool body. The tool body comprises a(n internal) passage for delivering a polishing agent (e.g. a liquid, a suspension of solids and of a fluid or paste) to the polishing surface, which extends axially in (or inside) the tool body from an inlet to an outlet. The outlet is provided at the first axial end and is suitable (configured) for releasing the polishing agent onto the polishing surface. The polishing surface comprises at least one groove, such as a canal, passage or indentation, for example. The groove extends radially away from the outlet to the perimeter of the polishing surface (e.g. to an edge encompassing or surrounding the polishing surface) to deliver (and/or to administer) the polishing agent across the polishing surface. Preferably, the groove may be open to the outside and/or may be open on the side facing the lens surface during polishing.

The provision of an outlet and a groove in the polishing surface as well as making the polishing tool rotatable facilitate a uniform distribution of the polishing agent across the polishing surface. The polishing agent can enter the polishing surface directly through the outlet where centrifugal forces can drive the polishing agent through the groove to the outer edges of the polishing surface. Thereby, the polishing agent can be supplied directly where it is needed, i.e. onto and across the polishing surface, i.e. the surface of the polishing tool that effects smoothing of the optical surface of the lens (for example by entering into mechanical interaction therewith), so that the polishing agent can be used more effectively and efficiently. For example, it is possible to reduce the overall slurry displacement significantly and thereby, to reduce the amount of energy, consumption of polishing agent and generation of wastewater significantly. This allows designing machine components, such as pumps, pipes and tanks, considerably smaller. Also, the overall maintenance and cleaning times can be reduced by using this polishing tool. Further, the curved shape of the polishing surface supports the polishing effectiveness and efficiency of the lens surface.

Further, it can be ensured that a film of polishing agent forms between the polishing surface and the lens surface to be polished. This increases not only the life span of the polishing tool but also facilitates reliable cooling of the lens surface and the polishing tool with the polishing agent without having to provide an additional cooler for the polishing agent. Therein, it was found that the inventors managed to overcome a prejudice of the prior art that the formation of a film of suitable thickness would be incompatible with a fast rotation of the polishing tool relative to the lens as centrifugal forces would transport the polishing agent too quickly away from the polishing surface.

In addition, it was found that the quality and results of the polishing process can be improved with this polishing tool while maintaining rotational speeds at a high level. In experiments not disclosed to the public, it was found that the mere provision of one or more outlets on the polishing surface without the provision of the groove leads to polishing imprecisions and irregular lens surfaces. This is exemplarily illustrated in <FIG>. In the undisclosed experiments, different rotatable polishing tools (<NUM>, <NUM>) were used having a tool body (<NUM>, <NUM>) with a polishing surface (<NUM>, <NUM>) being outwardly exposed at a first axial end of the tool body (<NUM>, <NUM>), the polishing surface (<NUM>, <NUM>) being axially bulged convexly or concavely with respect to their rotational axis for polishing an optical surface (L1, L2) of a spectacle lens (L). The tool body (<NUM>, <NUM>) further comprised one or more channels (<NUM>, <NUM>) extending axially through the tool body (<NUM>, <NUM>) from one (or more) inlets (<NUM>, <NUM>). The inlet(s) (<NUM>, <NUM>) were provided at a second axial end being opposite to the first axial end with respect to the rotational axis. The channel(s) (<NUM>, <NUM>) extended to one or more outlets (<NUM>, <NUM>), which is/are provided at the first axial end, to supply the polishing surface (<NUM>, <NUM>) with a polishing agent (<NUM>). The one or more outlets (<NUM>, <NUM>) were distributed uniformly across the polishing surface (<NUM>, <NUM>) (e.g. like a showerhead). For example, <FIG> illustrates a configuration of the polishing tool (<NUM>) that was used in the experiments and had only a single outlet (<NUM>), the single outlet (<NUM>) was arranged centrally on the polishing surface (<NUM>). Unfortunately, the quality and results of the polishing process in the undisclosed experiments with such polishing tool (<NUM>) were unsatisfactory. This is because the mere provision of an opening (<NUM>) for the polishing agent (<NUM>) on the polishing surface (<NUM>) leads during operation to a localized increase of pressure in the area around the opening (<NUM>). Subsequently, the material of the polishing surface (<NUM>) around the opening (<NUM>) deforms locally and a free space (FS) or pocket filled with polishing agent (<NUM>) is formed leading to a blind spot of the polishing surface (<NUM>) that cannot effect any polishing interaction with the lens surface (L1). <FIG> exemplarily illustrates an alternative configuration of a polishing tool (<NUM>) used in the experiments. Therein it was found that also the provision of multiple, distributed openings (<NUM>) in the polishing surface (<NUM>) could not overcome this issue but lead to the formation of multiple free spaces (FS) or pockets instead. When comparing these experimental and undisclosed polishing tools (<NUM>, <NUM>) to the polishing tool according to the present invention, it can be found that with the additional provision of a groove, as suggested by the invention, the formation of a free space or pocket can be avoided and a film of polishing agent with uniform thickness can be established across the polishing surface, leading to higher quality and consistency of the polishing process.

According to a preferred embodiment, the groove may extend radially along a main extension direction. For example, the main extension direction may be a direction that may (primarily, i.e. to at least <NUM>%, <NUM>%, <NUM>%, <NUM>% or more) correspond with a direction pointing from the groove's starting point (e.g. the outlet) to the groove's end-point (a point on the perimeter). Preferably, the groove may extend radially always in directions having the same radial orientation. More preferred, the groove may extend (along the main extension direction) in a linear, straight, curved and/or arcuate manner, more preferred in a wave or zigzag manner.

Thereby, it is possible to tailor the flow rate and distribution of the polishing agent across the polishing surface to the specific polishing application. Accordingly, the thickness of the film of the polishing agent can be adapted to the individual application, such as the lens material, the rotational speeds, and/or the polishing agent used. Thus, the polishing result and efficiency can be improved even further.

According to a further preferred embodiment, the groove may comprise different sections (or differently configured sections). For example, the groove may comprise straight, angled, arcuate and/or curved sections.

Thus, by providing the groove with dissimilar sections the flow speed of the polishing agent can be different in each of the respective sections. Thereby, the design of the polishing tool can take effects of centrifugal or other dynamic operational forces into consideration.

Preferably, adjoining sections may extend circumferentially in opposite directions. Preferably, the sections may have the same radial orientation.

By alternating the extension direction of adjoining sections (only) circumferentially, flow of the polishing agent can be decelerated and thus, a constant film thickness can be ensured across the polishing surface during operation.

The adjoining sections may preferably be connected to each other by an arcuate portion that more preferred may form a gradual transition between the respective adjoining sections. For example, the groove may comprise a straight first section that connects the channel opening with a curved second section, and a third section that extends straight (or in a linear manner) from the second section to the perimeter of the polishing surface.

By avoiding sharp edges or corners at a transition between different sections of the groove, the accumulation of solid material (e.g. abrasion particles or abraded lens material) contained in the polishing agent can be prevented and thus, the risk of blockage of the groove during the polishing process can be reduced.

According to a preferred embodiment, the groove may have a width ranging from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or of <NUM>. Alternatively or additionally, the groove may have a depth ranging from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or of <NUM>.

By providing the cross-section of the groove with the above dimensions, the thickness of the film of polishing agent between the polishing surface and the lens surface is advantageous. Thereby, the results and quality of the polishing process can be improved.

According to a further preferred embodiment, the polishing tool may comprise a plurality of said grooves. Preferably, the grooves may radially diverge. Alternatively or additionally, the grooves may be (evenly) distributed about the outlet or the rotational axis. The grooves may preferably have the same or at least partially a different shape and/or cross-section (as seen along the main extension direction). Preferably, the cross-section may be triangular, rectangular, rounded and/or any other suitable shape. Preferably, the polishing tool (or the groove(s)) may be configured such that, in operation, the polishing agent may be distributed differently depending on the rotational direction.

By providing the polishing surface with a multitude of differently orientated and configured grooves, the thickness of the film of polishing agent between polishing surface and lens surface can be adjusted and the polishing tool can be optimized for specific applications. Hence, the quality of the polishing process can be improved.

According to a preferred embodiment, the tool body may comprise a layered structure and/or may comprise different components that preferably may be integrally provided. Alternatively or additionally, the different components (namely a below described base portion, holder portion and polishing film) may be connected to each other by gluing. For instance, the tool body may comprise one or more (different) sections, for example, a base portion, a holder portion and/or a polishing film. Preferably, the (three) sections may be arranged in the aforementioned order.

Thereby, portions (layers) of the polishing tool can be provided from different materials and with different characteristics while maintaining the polishing tool as a unit.

Preferably, the tool body may comprises a polishing film forming the first axial end of the tool body. More preferred, the polishing film may form the polishing surface. The polishing film may be configured to enter into contact with the optical surface of the lens. For example, during the surface machining process, the polishing tool may be pressed against the lens with the polishing film. Typically, in a surface machining process the lens and the polishing tool (with the polishing film) may be rotated in opposite directions to each other. By squeezing the polishing agent between polishing film and optical surface of the lens, mechanical abrasion may be effected due to the relative movement between the two surfaces (e.g. lens/polishing film). Preferably, the polishing film may comprise the outlet and the groove. The polishing film may preferably have a thickness ranging from <NUM> to <NUM>, or from <NUM> to <NUM>, or of <NUM>. The polishing film may be provided as a coating and/or may be made of a soft material, such as plastic, e.g. polyurethane. Preferably, the polishing film may have a surface hardness ranging from <NUM> ShA up to <NUM> ShA. Therein, the numerical values with the unit "ShA" relate to the Shore A Hardness Scale.

Thereby, the polishing surface can be provided with properties required in a polishing process of a lens surface, like material flexibility, abrasion resistance and low adhesion.

For instance, the polishing film may correspond to a portion of prior art polishing tools that is commonly referred to as "carrier". However, this is only an example.

Alternatively or additionally, the tool body may comprise a base portion for rotatably supporting the polishing tool. The base portion may preferably form the second axial end and/or it may comprise the inlet. For example, the base portion may be made of a rigid material, such as metal or hard plastic, e.g. nylon. Preferably, the base portion may have a tensile strength between <NUM> MPa to <NUM> MPa. More preferred, the base portion may have a thickness (i.e. extension along the rotational axis) between <NUM> and <NUM>. Preferably, the base portion may be relatively stiff in comparison to other sections of the tool body. The base portion may be made of a rigid plastic or metal.

Thereby, the polishing tool can be provided with a rigid base that can be coupled to a motor for operating the polishing tool. In addition, the polishing tool can be provided with sufficient rigidity, e.g. to apply, if required, pressure onto the surface of the lens.

Preferably, the tool body may further comprise a holder portion. The holder portion may be attached to at least one of the polishing film and the base portion. Preferably, the holder portion may be sandwiched between the polishing film and the base portion. The holder portion may be deformable for adapting to the optical surface of the spectacle lens. For example, the holder portion may be made of a soft material, such as plastic. For instance, it is conceivable that the holder portion may be made of polyurethane or a closed cell rubber material, such as neoprene, EPDM (ethylene propylene diene monomer) or NBR (nitrile butadiene rubber). Preferably, the holder portion may have a modulus of elasticity ranging between <NUM> MPa and 12MPa. More preferred, the holder portion may have a thickness (i.e. extension along the rotational axis) between <NUM> and <NUM>. The holder portion may be relatively flexible in comparison to the base portion. Preferably, the holder portion may have a layered structure. For example, the holder portion may be made of different materials. Alternatively or additionally, the holder portion may comprise layers of the same material but different material configuration (e.g. density, air permeability, pore size).

Thereby, it is possible to provide the polishing tool with a barrier layer that prevents the polishing tool from absorbing polishing agent and protects the base portion from corroding. Further, the polishing tool can be provided with a layer from material having a balanced ratio between rigidity and flexibility to adapt to the shape (curvature) of the lens surface while maintaining the capability of the polishing tool of exerting pressure on the lens surface.

According to a further preferred embodiment, the channel may extend along the rotational axis of the polishing tool. Preferably, the channel may be coaxial with the rotational axis. More preferred, the outlet may be at the centre of the polishing surface. Alternatively or additionally, (as so far present) the channel may penetrate at least one, preferably each of the polishing film, the base portion and the holder portion. Preferably, the channel may have a diameter ranging from <NUM> to <NUM>, preferably <NUM> to <NUM>, most preferred <NUM>. Preferably, the tool body (preferably the base portion (if present)) may comprise a port for fluidly connecting the channel with a polishing agent supply unit. More preferred, the port may comprises a gasket for radially sealing against the polishing agent supply unit to prevent the polishing agent from leakage and/or to enable only the polishing agent entering the channel via the inlet. The port may be a hose connector or a valve, for example.

Thereby, a sufficient and consistent supply of the polishing surface with polishing agent can be ensured. Furthermore, it is possible to connect the polishing tool removably with a polishing apparatus so that differently configured polishing tools can be used with the same polishing apparatus. Thus, this configuration improves the flexibility and applicability of the polishing tool.

A further aspect of the present invention relates to a system for polishing at least one optical surface of a spectacle lens. The system comprises a surface processing unit for processing the optical surface of the spectacle lens. Therein, the surface processing unit comprises the polishing tool as described above. Further, the surface processing unit comprises a polishing agent supply unit that is fluidly connected to the channel via the inlet of the polishing tool to supply the groove (or grooves) of the polishing surface with a polishing agent via the channel and the outlet. The system further comprises a lens support unit for supporting the spectacle lens during the polishing process. The system also comprises a drive unit to apply a relative motion between the polishing tool and the lens support unit at least by rotating the polishing tool about the rotational axis to allow polishing of the optical surface.

The system comprises all advantages and benefits that were described in detail above for the polishing tool. In addition, with the above described system, a highly customized spectacle lens having a customized power map (such as shown in <FIG>) can be generated and polished with the required accuracy and quality.

According to a preferred embodiment, the relative motion may comprise tilting, pivoting and/or linearly moving the polishing tool relatively to the lens support unit to apply the relative motion. Alternatively or additionally, the drive unit may be adapted to rotate the lens support unit about a second rotational axis (e.g. of a spindle) to apply the relative motion. Alternatively or additionally, the drive unit may be preferably adapted to displace the polishing tool relative to the lens support unit to obtain a defined distance between the polishing tool and the lens support unit (or preferably (the optical surface of) the spectacle lens). Preferably, the distance may be between <NUM>. 01micrometers to <NUM>. More preferred, the size of the distance may depend on (or correspond with) the size of the particles in the polishing agent. However, it is also conceivable that the drive unit may be preferably adapted to displace the polishing tool relative to the lens support unit so that there is no gap (i.e. distance equal to or even below zero) between the polishing tool and the lens support unit (or preferably (the optical surface of) the spectacle lens). For example, it is conceivable that the polishing tool may be set to be in contact or in pressurized contact with the lens surface.

Thereby, it is possible to adjust movements of the polishing tool with high precision and flexibility as the thickness of the film of polishing agent forming between the lens surface and the polishing surface can be ensured in the system. Also, it is not necessary to reduce the velocity of the respective moving system components so that the polishing time can be maintained or even reduced while improving the quality of the polishing result. Further, it is not necessary to increase the size of pumps, pipes or a tank for delivering a sufficient amount of polishing agent between the polishing tool and the lens surface.

According to a further embodiment, the system may further comprise a control unit for controlling the relative motion by the drive unit. Preferably, the control unit may be suitable and/or configured to control said relative motion based on processing features. Such processing features may comprise, for example, type of lens to be generated, form and/or thickness of the lens, type of polishing tool, and/or type of polishing agent. Naturally, further processing features may be possible. Preferably, the control unit may be configured to adapt a relative rotational speed between the optical surface and the polishing tool. Alternatively or additionally, the control unit may be configured to adapt a pressure for supplying the polishing agent through the polishing tool and/or it may be configured to adapt a flow rate of the polishing agent.

Thereby, it is possible to accurately adjust the thickness of the film between the lens surface and the polishing surface in correlation with the relative position and/or movement of the polishing tool to the lens surface. Thus, polishing can be completed without undue kinematic constraints and with high quality.

Preferably, the polishing agent may comprise a fluid (preferably comprising water and/or a cooling agent,) and solid (metal (e.g. aluminium), diamond powder, minerals, silicon or plastic) particles with a grain size ranging from <NUM> to <NUM> micrometres.

Thereby, it is possible to smooth and level the surface of the lens with high precision so that scattering of light through the lens and specular reflection can be reduced.

According to a preferred embodiment, the polishing agent supply unit may be fluidly connected to the polishing tool through the port (of the tool body, preferably provided at the base portion). Therein, a or said gasket may radially seal against the polishing agent supply unit to prevent the polishing agent from leakage and to enable the polishing agent entering the channel only via the inlet. Preferably the polishing agent supply unit may comprise a pump and a tank for supplying the polishing agent.

Thereby, fast processing times can be achieved as the polishing tool can be quickly and reliably connected and disconnected from the surface processing unit.

A further aspect of the present invention relates to a process of polishing an optical surface of a spectacle lens. The process comprises the step of providing a system for surface processing having a polishing tool as described above. Alternatively or additionally, the process comprises the step of providing the system described above. A spectacle lens is seated in a lens support unit of the system (either of the aforementioned systems). The polishing tool is relatively rotated with respect to the spectacle lens. A polishing agent is delivered through the channel (of the polishing tool) to the polishing surface (of the polishing tool), which faces an optical surface of the spectacle lens to be polished, so that the polishing agent is delivered through the grooves radially outwards from the outlet (of the polishing tool) to distribute the polishing agent across the polishing surface for polishing the optical surface.

Preferably, the process further comprises the step of controlling a thickness of a layer of the polishing agent between the optical surface and the polishing surface (with the control unit) by adapting one or more processing parameters. The processing parameters may be a flow rate or a supply pressure of the polishing agent. The processing parameters may be preferably (additionally) one or more of the group of distance between the polishing surface and the optical surface, rotational velocities of the lens and polishing tool, and/or the polishing tool's translational moving speed(s) relative to the lens. The processing parameters may be adapted based on a rotational speed of either or both of the polishing tool and the spectacle lens.

With such configurations of the method, it is possible to achieve all advantages and benefits that were described in detail above. Also, it is possible to improve the quality and accuracy of the lens generated in the polishing process.

A further aspect of the present invention relates to a use of a polishing tool as described above for polishing an optical surface of a spectacle lens with a polishing agent. Preferably, the spectacle lens is a progressive lens.

Further features, advantages and objects of the invention will become apparent for the skilled person when reading the following detailed description of embodiments of the invention and when taking in conjunction with the figures of the enclosed drawings. In case numerals have been omitted from a figure, for example for reasons of clarity, the corresponding features may still be present in the figure.

<FIG> shows exemplary a profile of a lens L before the start of a surface machining process. <FIG> shows an example of a customized lens L at the end of a surface machining process. <FIG> show different steps of a lens generating process. <FIG> highlight known problems existing in the prior art. Each of <FIG> illustrates an experimental setup for identifying problems existing in polishing processes. <FIG> show different views and aspects of embodiments of the invention.

For instance, a first aspect of the invention relates to a polishing tool <NUM> for polishing a spectacle lens L in a surface machining process. Embodiments of the polishing tool <NUM> are exemplarily illustrated in <FIG>.

Generally, a "lens" may be understood, for example, as any transmissive optical device that is adapted to change the course of light by refraction. For example, the lens L may be an ophthalmologic lens, such as corrective or prescription lenses. <FIG> show examples for the lens L. The lens L may have two opposite optical (side) surfaces L1, L2 and a circumferential edge L3. The optical (side) surfaces L1, L2 may be convex and/or concave. Typically, the lenses L may be made of a transparent and/or translucent material, e.g. a plastic material for spectacle lenses, such as polycarbonate, or glass.

In a surface machining process, typically only one of the two optical surfaces L1, L2 may be processed while the other one of the two side surfaces L1, L2 of the lens L is supported by a lens support unit <NUM>. This is exemplarily illustrated in <FIG> and <FIG>. Naturally, either or both of the two side surfaces L1, L2 of the lens L may be processed in the surface machining process.

The surface machining process may be started by choosing a lens blank, such as the lens L exemplarily shown in <FIG>, with a front surface L2 most suitable for the vision enhancing application, which may remain unchanged. In comparison, the rear surface L1 of the lens blank L may be processed to generate a customized (progressive) lens L, as exemplarily shown in <FIG>.

The surface machining process may typically comprise, for example, any surfacing or manufacturing step(s) for the generation of optical devices, such as cribbing (i.e. reducing an outer diameter of the lens blank L in a milling process), roughing (i.e. grinding one of the optical surfaces L1, L2 to the approximate curvature and thickness), smoothing (i.e. grinding one of the optical surfaces L1, L2 to the exact curvature and thickness), bevelling (i.e. cutting the lens L to the shape of eyeglass frames) and polishing (i.e. making the lens L smooth; providing regular transmission and reduce specular reflection). However, these are only examples and not a complete enumeration.

The polishing tool <NUM> is suitable (and configured) for being used in such a surface machining process, for example. Further, the polishing tool <NUM> is suitable (and configured) for polishing spectacle lenses; consequently, the polishing tool <NUM> may be suitable for following curvatures typically existing with spectacle lenses and for processing typical materials used for spectacle lenses.

The polishing tool <NUM> comprises a tool body <NUM> for being rotatably supported about a rotational axis RA1. This is exemplarily indicated in <FIG> and <FIG>. The rotational axis RA1 may be a body axis or a symmetry axis of the tool body <NUM> and/or an axis offset from the polishing tool <NUM>.

The tool body <NUM> comprises a first axial end <NUM> and a second axial end <NUM>, which is provided opposite to the first axial end <NUM> with respect to the rotational axis RA1. Preferably, the tool body <NUM> may extend (continuously) along (with) the rotational axis RA1 from the first axial end <NUM> to the second axial end <NUM>. <FIG> and <FIG> show this exemplarily. The tool body <NUM> may have any shape or form, such as a cylindrical shape. For example, the tool body <NUM> may be coaxial with the rotational axis RA1.

The tool body <NUM> may comprise a layered and/or a continuous structure, for example. In <FIG> and <FIG>, the tool body <NUM> is exemplarily shown as being composed of different layers. The tool body <NUM> may comprise any number of layers. The respective layers may be connected to each other by adhesive bond, like gluing, or by a mechanical connection, such as a screw. However, these are only examples and not a complete enumeration.

At the first axial end <NUM>, the tool body <NUM> comprises a polishing surface <NUM>, which is exposed to the outside. <FIG> illustrates exemplarily how the outwardly exposed configuration of the polishing surface <NUM> can facilitate an interaction between the polishing tool <NUM> and the lens surface L1. The polishing surface <NUM> is axially bulged convexly or concavely with respect to the rotational axis RA1 for polishing an optical surface L1, L2 of the lens L. For example, depending on the type of the lens L, e.g. a converging or diverging lens, the polishing surface <NUM> may have a curved (round) shape projecting outwardly (convex) or retracting inwardly (concave). <FIG> and <FIG> show the polishing surface <NUM> exemplarily being axially bulged convexly with respect to the rotational axis RA1. Preferably, the polishing surface <NUM> may be bulged such that the polishing surface <NUM> may have a curvature at least similar or higher than the optical surface L1, L2. More preferred, the polishing surface <NUM> may be smaller in size than the optical surface L1, L2 of the lens L. For example, the polishing surface <NUM> may cover <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, or <NUM>/<NUM> of the (entire) area of the optical surface L1, L2. The polishing surface <NUM> may form an (axial) end face of the polishing tool <NUM>. Further, the polishing surface <NUM> may face in a direction away from the second axial end <NUM>. The polishing surface <NUM> may have any shape or form. For example, the polishing surface <NUM> may be circular or oval when seen along the rotational axis RA1. However, these are only examples and not a complete enumeration.

Preferably, the polishing surface <NUM> may be formed by a polishing film <NUM> of the tool body <NUM>. The polishing film <NUM> may form the first axial end <NUM>. The polishing film <NUM> may be one of the layers of the tool body <NUM>. For example, the polishing film <NUM> may be made of soft a material to avoid damaging the optical surface L1, L2 of the lens L in a polishing process. For instance, the polishing film <NUM> may be made of polyurethane. Naturally, other materials can be used for forming the polishing film <NUM>. The polishing film <NUM> may be provided as a coating or a film. Preferably, the polishing film <NUM> may have a thickness ranging from <NUM> to <NUM>, or from <NUM> to <NUM>, or of <NUM>. The polishing film <NUM> may comprise a projecting edge <NUM> that protrudes radially from the tool body <NUM> as exemplarily illustrated in <FIG>. Thereby, excessive operational forces when by entering the optical surface L1 in the polishing process can be avoided.

The second axial end <NUM> of the tool body <NUM> may preferably be formed by a base portion <NUM>. The base portion <NUM> may be one of the layers of the tool body <NUM>. The base portion <NUM> may be suitable (or configured) for rotatably supporting the polishing tool <NUM>, for example, in a tool holder of a lens generator for a surface machining process. This is exemplarily indicated in the schematic illustration of <FIG>. For this, the base portion <NUM> may be made of a preferably rigid material, such as metal or hard plastic, like nylon. However, this is only an example and it is conceivable to use other materials.

Preferably, the tool body <NUM> may also comprise a holder portion <NUM>, which may be arranged between the polishing film <NUM> and the base portion <NUM>. The holder portion <NUM> may be one of the layers of the tool body <NUM>. The holder portion <NUM> may be capable of adapting axially to the contour of the optical surface L1, L2 of the lens L. For this, the holder portion <NUM> may be configured to be reversibly deformable under pressure. For example, the holder portion <NUM> may be made of plastic, e.g. a closed cell rubber material, such as neoprene, EPDM or NBR.

The tool body <NUM> further comprises a channel <NUM>, which extends axially (along or coaxially with the rotational axis RA1) through the tool body <NUM>. Therein, the channel <NUM> may penetrate the polishing film <NUM>, the base portion <NUM> and the holder portion <NUM>, respectively, as exemplarily illustrated in <FIG> and <FIG>. The channel <NUM> may have a constant, stepwise or continuously increasing/decreasing diameter along its extension direction. Preferably, the channel <NUM> may have a cross-section of any shape or form, for example a circular or rectangular cross-section. The channel <NUM> may be formed by the passages formed in the respective sections of the tool body <NUM> or it may be formed by providing a tube or hose extending through these passages. However, these are only examples and not a complete enumeration.

The channel <NUM> comprises an inlet <NUM>, preferably for feeding a polishing agent into the channel <NUM>. This is exemplarily illustrated in <FIG> and <FIG>. The inlet <NUM> is provided at the second axial end <NUM>. Preferably, the base portion <NUM> may comprise the inlet <NUM>. More preferred, the inlet <NUM> may be formed as an opening, for example in (the tool body <NUM> or) the base portion <NUM>. The inlet <NUM> may have a cross-section with the same or a different shape as the channel <NUM>. The channel <NUM> may expand radially towards or at the inlet <NUM>. <FIG> and <FIG> show this exemplarily.

The tool body <NUM> (or the base portion <NUM>) may further comprise a port <NUM> for fluidly connecting the channel <NUM> with a polishing agent supply unit <NUM> (such as illustrated in <FIG>). This is exemplarily illustrated in <FIG> and <FIG>. The port <NUM> may be a valve, hose connector, pipe or hose. Preferably, the port <NUM> may have the same size as the inlet <NUM>. More preferred, the port <NUM> may be removeably connected to the inlet <NUM>. The port <NUM> may be press-fitted into the inlet <NUM>. Preferably, the port <NUM> may comprise a gasket <NUM> for radially sealing against the polishing agent supply unit <NUM> (cf. <FIG>) to prevent the polishing agent from leaking and to enable only the polishing agent entering the channel <NUM> via the inlet <NUM>. This is exemplarily shown in <FIG> and <FIG>. The gasket <NUM> may be made of rubber and/or may be an O-ring. However, these are only examples and not a complete enumeration.

The channel <NUM> further comprises an (preferably a single) outlet <NUM> to supply the polishing surface <NUM> with a polishing agent (preferably, the polishing agent fed through the inlet <NUM>). The outlet <NUM> is provided at the first axial end <NUM>. Preferably, the outlet <NUM> may be provided at the centre of the polishing surface <NUM> (such as exemplarily illustrated in <FIG>). Preferably, the outlet <NUM> may be coaxial with the rotational axis RA1. However, it is also conceivable to provide the outlet <NUM> at a different position. For example, the outlet <NUM> may be provided in a section immediately (e.g. radius <<NUM>) surrounding the rotational axis RA1 (or the centre of the polishing surface <NUM>). Preferably, the polishing film <NUM> may comprise the outlet <NUM>. This is exemplarily illustrated in <FIG>. The outlet <NUM> may have any shape or form. For example, the outlet <NUM> may be circular, and/or may expand or reduce in diameter towards the first axial end <NUM>. Preferably, the outlet <NUM> may be formed (to provide the same functionality) as a nozzle or throttle. The outlet <NUM> may have a diameter significantly smaller than the diameter of the polishing surface <NUM> (delimited by the perimeter), i.e. <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, or <NUM>/<NUM> of the diameter of the polishing surface <NUM>.

The polishing agent may be a mixture between a liquid and solid particles, for example. The liquid may comprise water and/or a cooling agent. The solid particles may be made of metal (e.g. aluminium oxide), silicon or plastic. Preferably, the solid particles may have a grain size ranging from <NUM> to <NUM> micrometres.

The polishing surface <NUM> comprises at least one groove <NUM>. Preferably, the polishing film <NUM> may comprise the groove <NUM>. <FIG> show this exemplarily.

As indicated exemplarily in <FIG>, the polishing surface <NUM> may comprise a plurality of said grooves <NUM> (i.e. more than one of the groove <NUM>). If in the following reference is made to "the groove <NUM>", the respective description also applies to the "plurality of grooves <NUM>" unless specified otherwise. The grooves <NUM> may have the same or a different configuration. For example, the grooves <NUM> may be identical or they may have at least partially a different shape and/or cross-section.

The groove <NUM> extends radially away from the outlet <NUM> to the perimeter of the polishing surface <NUM> to distribute the polishing agent across the polishing surface <NUM>. The groove <NUM> may have any shape or form. For instance, the groove <NUM> may extend radially along a main extension direction. Therein, the groove <NUM> may extend such that its path does not turn back in a radial direction towards the outlet <NUM> (but instead, the groove <NUM> may proceed extending radially outwards). The groove <NUM> may extend in a linear, straight, curved and/or arcuate manner.

Alternatively or additionally, as exemplarily shown in <FIG>, the groove <NUM> may extend in a wave or zigzag manner. Therein, the groove <NUM> may comprise different sections. The different sections may be connected to each other to form a continuous flow path for the polishing agent. Preferably, adjoining sections may be connected to each other by an arcuate portion. More preferred, the connecting portions, e.g. the arcuate portions, may form a gradual transition between the respective adjoining sections. Thereby, a continuous flow in the groove <NUM> can be achieved and blockages can be avoided. Preferably, the respective section (one of the different sections) may be straight, angled, arcuate and/or curved. Adjoining sections may extend circumferentially in opposite directions. An example for the different sections is provided in <FIG>, where the groove <NUM> is exemplarily illustrated as comprising a straight first section <NUM> that connects the outlet <NUM> with a curved second section <NUM>, and a third section <NUM> that extends straight from the curved second section <NUM> to the perimeter of the polishing surface <NUM> (polishing film <NUM>). It is further conceivable that the groove <NUM> may have branches and/or may diverge into other (neighbouring) groove(s) <NUM>.

The groove <NUM> may have a circular or rectangular cross-section when seen along the main extension direction and/or along a flow direction. Preferably, the groove <NUM> may have a width W ranging from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or of <NUM> (cf. Alternatively or additionally, the groove <NUM> may have a depth T ranging from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or of <NUM> (cf.

Different grooves <NUM> may preferably be provided on the polishing surface <NUM> as radially diverging. Alternatively or additionally, the plurality of grooves <NUM> may be (evenly) distributed about the outlet <NUM> (or the rotational axis RA1). For example, based on the arrangement and/or configuration of the grooves <NUM> (e.g. circumferential orientation, curved sections etc.), the polishing tool <NUM> may be used only in one rotational direction about the rotational axis RA1 in order to work properly.

A further aspect of the present invention relates to a system <NUM> for polishing of at least one of the optical surfaces L1, L2 of the spectacle lens L. <FIG> shows this exemplarily.

The system <NUM> comprises a surface processing unit <NUM> for processing the optical surface L1, L2 of the spectacle lens L. Therein, the surface processing unit <NUM> comprises the above described polishing tool <NUM>. For example, it is also conceivable that the surface processing unit <NUM> may comprise a linearly movable (indicated by arrows <NUM>, <NUM>) cutter <NUM>, such as illustrated exemplarily in <FIG>.

The surface processing unit <NUM> comprises further a polishing agent supply unit <NUM> to supply the polishing surface <NUM> with a polishing agent. The polishing agent supply unit <NUM> is fluidly connected to the channel <NUM> (through the port <NUM>) via the inlet <NUM> of the polishing tool <NUM> to supply the groove(s) <NUM> with polishing agent through the outlet <NUM>. Preferably, the above described gasket <NUM> may radially seal the connection to prevent the polishing agent from leakage and to enable the polishing agent entering the channel <NUM> only via the inlet <NUM>. Thus, for example, the polishing agent may be pumped by a pump <NUM> of the polishing agent supply unit <NUM> from a voluminous tank <NUM> of the polishing agent supply unit <NUM> through a pipe <NUM> to the port <NUM> and, subsequently, to the inlet <NUM>. From the inlet <NUM>, the polishing agent may flow through the channel <NUM> to the outlet <NUM> and to the groove(s) <NUM>. For example, in the state of rotating the polishing tool <NUM> about the rotational axis RA1, the polishing agent is pushed radially outwards towards the perimeter of the polishing surface <NUM>. Simultaneously existing circumferential forces may drive the polishing agent out of the grooves <NUM> so that the polishing agent is distributed across the (entire) polishing surface <NUM>. The different configuration of the sections of the grooves <NUM> may cause the polishing agent to flow with different speeds. In particular, gradual transitions between adjoining sections may be useful for lowering the speed of flow of the polishing agent flowing through parts of the groove <NUM> that are radially further away from the outlet <NUM>. Thus, effects of the centrifugal acceleration can be reduced.

The system <NUM> comprises further a lens support unit <NUM> (mentioned before in relation to <FIG>) for supporting the lens L during the polishing process. For this, the lens support unit <NUM> may comprise a lens holder <NUM> that may apply a suction force onto the lens L. Additionally, the lens support unit <NUM> may comprise a spindle <NUM> that rotates about a second rotational axis RA2 (indicated by arrow <NUM>). <FIG> and <NUM> show this exemplarily.

The system <NUM> comprises also a drive unit to apply a relative motion between the polishing tool <NUM> and the lens support unit <NUM>. Therein, the relative motion comprises at least rotating the polishing tool <NUM> about the rotational axis RA1 to facilitate polishing of the optical surface L1, L2 with the polishing tool <NUM>. This is exemplarily indicated by arrow <NUM> of <FIG>. Additionally, the relative motion may comprise tilting, pivoting and/or linearly moving (as indicated by arrows <NUM> and <NUM> in <FIG>) the polishing tool <NUM> relatively to the lens support unit <NUM> to apply the relative motion. Preferably, the drive unit may be adapted to displace the polishing tool <NUM> relative to the lens support unit <NUM> in order to obtain a defined distance therebetween.

It is also conceivable that the drive unit comprises and/or drives the spindle <NUM>. Therein, the drive unit may be preferably adapted to rotate the lens support unit <NUM> about the second rotational axis RA2 to effect the (additional) relative motion (e.g. arrow <NUM>). The drive unit may be part of the surface processing unit <NUM> or vice versa. <FIG> shows this exemplarily.

The system <NUM> may further comprise a control unit <NUM> for controlling the relative motion by the drive unit and/or the surface processing unit <NUM>. The control unit <NUM> may control the system <NUM> based on processing features, like the lens type, form and thickness, the polishing tool type, the polishing agent type. Therein, the control unit <NUM> preferably may be configured to adapt a relative rotational speed between the optical surface L1, L2 and the polishing tool <NUM>. Alternatively or additionally, the control unit <NUM> may be configured to adapt a pressure for supplying the polishing agent to the polishing tool <NUM> and/or a flow rate of the polishing agent (through the channel <NUM>).

A further aspect of the present invention relates to a process of polishing at least one of the optical surfaces L1, L2 of the (spectacle) lens L. In the process, the above system <NUM> is provided. Alternatively, it is also conceivable to provide a different system for surface processing having the above described polishing tool <NUM>.

The (spectacle) lens L is seated in said (or a) lens support unit <NUM>. The polishing tool <NUM> is relatively rotated with respect to the lens L. A polishing agent is delivered through the channel <NUM> to the polishing surface <NUM>, which faces an optical surface L1, L2 of the lens L to be polished. Through the rotation, for example, the polishing agent is delivered through the grooves <NUM> radially outwards from the outlet <NUM> so that the polishing agent is distributed across the polishing surface <NUM> for polishing the optical surface L1, L2.

For example, in a surface machining process, typically the lens L and the polishing tool <NUM> (with the polishing film <NUM>) may be rotated relatively to each other in opposite directions from each other. By supplying polishing agent through the channel <NUM> into the grooves <NUM>, the polishing agent can be transported (and squeezed) between the polishing surface <NUM> (the polishing film <NUM>) and the optical surface L1, L2 of the lens L. Thereby, mechanical abrasion can be effected as the abrasive particles contained in the polishing agent can be moved due to the relative movement between the two surfaces (e.g. optical surface L1, L2/polishing surface <NUM>). For example, it may be advantageous to provide a plurality of grooves <NUM> across the polishing surface <NUM> so that the polishing agent can be distributed uniformly. Generally, by directing/routing the polishing agent through the (pathway of the) grooves <NUM>, it may be possible to control the exposure of the polishing agent to circumferential and radial acceleration (depending on its position in the groove <NUM>). Thereby, the distribution of the polishing agent across the polishing surface <NUM> may be improved as it becomes possible to control how the polishing agent travels across the polishing surface <NUM> (i.e. where and when it travels with respect to being dispensed from the outlet <NUM>).

The process may further comprise the step of controlling a thickness of a layer (film) of the polishing agent between the optical surface L1, L2 and the polishing surface <NUM> by adapting a flow rate and/or a supply pressure of the polishing agent based on a rotational speed of the polishing tool <NUM> and/or the spectacle lens L. However, it is also conceivable to consider (in addition) other parameters, such as the desired smoothness of the lens L or the consistency and composition of the polishing agent.

The invention is not limited by the embodiments as described hereinabove, as long as being covered by the appended claims.

Claim 1:
A polishing tool (<NUM>) for polishing a spectacle lens (L) in a surface machining process, comprising a tool body (<NUM>) for being rotatably supported about a rotational axis (RA1),
wherein the tool body (<NUM>) comprises a polishing surface (<NUM>) being outwardly exposed at a first axial end (<NUM>) of the tool body (<NUM>), the polishing surface (<NUM>) being axially bulged convexly or concavely with respect to the rotational axis (RA1) for polishing an optical surface (L1, L2) of the spectacle lens (L),
wherein the tool body (<NUM>) comprises a channel (<NUM>) extending axially through the tool body (<NUM>) from an inlet (<NUM>), which is provided at a second axial end (<NUM>) being opposite to the first axial end (<NUM>) with respect to the rotational axis (RA1), to an outlet (<NUM>), which is provided at the first axial end (<NUM>), to supply the polishing surface (<NUM>) with a polishing agent,
characterized in that
the polishing surface (<NUM>) comprises at least one groove (<NUM>) that extends radially away from the outlet (<NUM>), the outlet (<NUM>) being the groove's (<NUM>) starting point, to the perimeter of the polishing surface (<NUM>) to distribute the polishing agent across the polishing surface (<NUM>).