The present invention relates to a polishing tool for polishing a spectacle lens in a surface machining process. The present invention relates also to a system and a method with said polishing tool. Technical background

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. Figure 2 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 (Li). The contour of the back surface (Li) 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 Figure 2, which indicates the contour of the back surface (Li) 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.

Figures 5 and 6 illustrate exemplarily a typical polishing process known in the prior art. In these Figures, a lens (L) is supported by a lens support unit (220) with a spindle (221) and a lens holder (222). Polishing of the lens (L) is performed with a soft polishing tool (510) and a polishing liquid (521) (often referred to as “slurry”) that is supplied through an external nozzle (520). Typically, the polishing liquid (521) 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 (510) is rotated about a rotational axis (indicated by arrow (513)) and linearly movable (indicated by arrow (512)). Further, the polishing tool (510) is covered by a soft coating (515), 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 (221) and the polishing tool (510) may rotate about its own axis and may be tilted and/or moved across the optical surface (Li) of the lens (L). The polishing process illustrated in Figure 6 relies on the presence of polishing liquid (521) between lens surface (Li) and soft coating (515). In addition, it was found that the effectiveness, quality and heat management of the polishing process depends on a film of polishing liquid (521), which may form between lens surface (Li) and soft coating (515)? having a defined thickness.

For example, if the thickness of the film is too high, the abrasive particles of the polishing liquid (521) do not come sufficiently into contact with the polishing tool (510). Thereby, the necessary mechanical interaction between polishing tool (510) and particles (and subsequently, between particles and optical lens surface (Li)) cannot be effected. Accordingly, the result from the polishing process maybe insufficient. In comparison, if the thickness of the film is too low, the surfaces of the lens (L) and the polishing tool (510) 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 (510) being damaged or deformed. Additionally, not enough heat may be transported away from the lens (L) by the polishing liquid (521) 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 (520) pointing onto the moving parts from different directions and projecting vast amounts of polishing liquid (521) towards lens (L) and polishing tool (510) to ensure a sufficient amount of polishing liquid (521) entering the gap between lens (L) and polishing tool (510). Therein, also the pressure, by which the polishing liquid (521) is fed through the nozzle (520), was adapted to increase the output of polishing liquid (521) through the nozzles (520). 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 (521) in the working chamber while the film thickness cannot be controlled. Accordingly, a high quantity of polishing liquid (521) 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 (521). Furthermore, the polishing liquid (521) has to be cooled in a chiller prior to being dispensed through the nozzle (520) to ensure sufficient cooling during the polishing process. Typically, the temperature of the polishing liquid (521) is kept at about 14 °C. Thus, the effectiveness, efficiency and resourcefulness of the polishing process of known prior art solutions is low, respectively.

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. Summary of the invention

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 Figures 7 and 8. In the undisclosed experiments, different rotatable polishing tools (610, 620) were used having a tool body (611, 621) with a polishing surface (615, 625) being outwardly exposed at a first axial end of the tool body (611, 621), the polishing surface (615, 625) being axially bulged convexly or concavely with respect to their rotational axis for polishing an optical surface (Li, L2) of a spectacle lens (L). The tool body (611, 621) further comprised one or more channels (614, 624) extending axially through the tool body (611, 621) from one (or more) inlets (612, 622). The inlet(s) (612, 622) were provided at a second axial end being opposite to the first axial end with respect to the rotational axis. The channel(s) (614, 624) extended to one or more outlets (613, 623), which is/are provided at the first axial end, to supply the polishing surface (615, 625) with a polishing agent (521). The one or more outlets (613, 623) were distributed uniformly across the polishing surface (615, 625) (e.g. like a showerhead). For example, Figure 7 illustrates a configuration of the polishing tool (610) that was used in the experiments and had only a single outlet (613), the single outlet (613) was arranged centrally on the polishing surface (615). Unfortunately, the quality and results of the polishing process in the undisclosed experiments with such polishing tool (610) were unsatisfactory. This is because the mere provision of an opening (613) for the polishing agent (521) on the polishing surface (615) leads during operation to a localized increase of pressure in the area around the opening (613). Subsequently, the material of the polishing surface (615) around the opening (613) deforms locally and a free space (FS) or pocket filled with polishing agent (521) is formed leading to a blind spot of the polishing surface (615) that cannot effect any polishing interaction with the lens surface (Li). Figure 8 exemplarily illustrates an alternative configuration of a polishing tool (620) used in the experiments. Therein it was found that also the provision of multiple, distributed openings (623) in the polishing surface (625) 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 (6io, 620) 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 50%, 60%, 70%, 80% 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 o.imm to i.omm, or from 0.2mm to 0.8mm, or from 0.4mm to 0.6mm, or of 0.5mm. Alternatively or additionally, the groove may have a depth ranging from 0.1mm to 1.0mm, or from 0.2mm to 0.8mm, or from 0.4mm to 0.6mm, or of 0.5mm.

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 crosssection 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 0.5mm to 2.5mm, or from 0.8mm to 2.0mm, or of 1.3mm. 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 40 ShA up to 90 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 50 MPa to too MPa. More preferred, the base portion may have a thickness (i.e. extension along the rotational axis) between 5 mm and 15 mm. Preferably, the base portion may be relatively stiff in comparison to other sections of the tool body. The base portion maybe 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 maybe 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 2 MPa and i2MPa. More preferred, the holder portion may have a thickness (i.e. extension along the rotational axis) between 10 mm and 25 mm. 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 0.1mm to 100mm, preferably 1.0mm to 20mm, most preferred 10mm. Preferably, the tool body (preferably the base portion (if present)) may comprise a port for fluidly connecting the channel with a polishing agent IO 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 Figure 2) 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 maybe 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 o.oimicrometers to 0.5mm. 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 maybe 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 maybe 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 1 to 2 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.

4. Brief description of drawings

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.

Figure 1 shows schematically a lens in a front view and a side view.

Figure 2 shows schematically a customized lens in a side view at the end of a surface machining process.

Figure 3 shows schematically a side view of the connection between a lens and a lens support at the beginning of a surface machining process.

Figure 4 shows schematically a side view of a customized lens in a lens support during a surface machining process.

Figures 5 and 6 show schematically a side view of a customized lens in a lens support being polished in a surface machining process of the prior art.

Figures 7 and 8 show schematically a side view of an experimental setup for testing polishing tools for polishing a customized lens in a lens support, respectively.

Figure 9 shows a schematic sectional view of an embodiment of a polishing tool according to the present invention.

Figure 10 shows a schematic front view of an embodiment of a polishing tool according to the present invention.

Figure 11 shows a schematic view of an embodiment of a system according to the present invention with the polishing tool of Figure 9. Detailed description

Figure 1 shows exemplary a profile of a lens L before the start of a surface machining process. Figure 2 shows an example of a customized lens L at the end of a surface machining process. Figures 3 and 4 show different steps of a lens generating process. Figures 5 and 6 highlight known problems existing in the prior art. Each of Figures 7 and 8 illustrates an experimental setup for identifying problems existing in polishing processes. Figures 9 to 11 show different views and aspects of embodiments of the invention.

For instance, a first aspect of the invention relates to a polishing tool 100 for polishing a spectacle lens L in a surface machining process. Embodiments of the polishing tool 100 are exemplarily illustrated in Figures 7 to 9.

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. Figures 1 and 2 show examples for the lens L. The lens L may have two opposite optical (side) surfaces Li, L2 and a circumferential edge L3. The optical (side) surfaces Li, L2 may be convex and/ or concave. Typically, the lenses L maybe 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 Li, L2 may be processed while the other one of the two side surfaces Li, L2 of the lens L is supported by a lens support unit 220. This is exemplarily illustrated in Figures 3 to 6 and 11. Naturally, either or both of the two side surfaces Li, 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 Figure 1, with a front surface L2 most suitable for the vision enhancing application, which may remain unchanged. In comparison, the rear surface Li of the lens blank L may be processed to generate a customized (progressive) lens L, as exemplarily shown in Figure 2.

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 Li, L2 to the approximate curvature and thickness), smoothing (i.e. grinding one of the optical surfaces Li, 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 100 is suitable (and configured) for being used in such a surface machining process, for example. Further, the polishing tool 100 is suitable (and configured) for polishing spectacle lenses; consequently, the polishing tool too may be suitable for following curvatures typically existing with spectacle lenses and for processing typical materials used for spectacle lenses.

The polishing tool too comprises a tool body 110 for being rotatably supported about a rotational axis RA1. This is exemplarily indicated in Figures 9 and 11. The rotational axis RAi may be a body axis or a symmetry axis of the tool body 110 and/or an axis offset from the polishing tool too.

The tool body 110 comprises a first axial end 101 and a second axial end 102, which is provided opposite to the first axial end 101 with respect to the rotational axis RAi. Preferably, the tool body 110 may extend (continuously) along (with) the rotational axis RAi from the first axial end 101 to the second axial end 102. Figures 9 and 11 show this exemplarily. The tool body 110 may have any shape or form, such as a cylindrical shape. For example, the tool body 110 maybe coaxial with the rotational axis RAi.

The tool body 110 may comprise a layered and/or a continuous structure, for example. In Figures 9 and 11, the tool body 110 is exemplarily shown as being composed of different layers. The tool body 110 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 101, the tool body 110 comprises a polishing surface 130, which is exposed to the outside. Figure 11 illustrates exemplarily how the outwardly exposed configuration of the polishing surface 130 can facilitate an interaction between the polishing tool too and the lens surface Li. The polishing surface 130 is axially bulged convexly or concavely with respect to the rotational axis RAi for polishing an optical surface Li, 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 130 may have a curved (round) shape projecting outwardly (convex) or retracting inwardly (concave). Figures 9 and 11 show the polishing surface 130 exemplarily being axially bulged convexly with respect to the rotational axis RAi. Preferably, the polishing surface 130 may be bulged such that the polishing surface 130 may have a curvature at least similar or higher than the optical surface Li, L2. More preferred, the polishing surface 130 maybe smaller in size than the optical surface Li, L2 of the lens L. For example, the polishing surface 130 may cover 1/50, 1/20, 1/10, 1/8, 1/5, or 1/4 of the (entire) area of the optical surface Li, L2. The polishing surface 130 may form an (axial) end face of the polishing tool 100. Further, the polishing surface 130 may face in a direction away from the second axial end 102. The polishing surface 130 may have any shape or form. For example, the polishing surface 130 may be circular or oval when seen along the rotational axis RAi. However, these are only examples and not a complete enumeration.

Preferably, the polishing surface 130 may be formed by a polishing film 113 of the tool body 110. The polishing film 113 may form the first axial end 101. The polishing film 113 may be one of the layers of the tool body 110. For example, the polishing film 113 may be made of soft a material to avoid damaging the optical surface Li, L2 of the lens L in a polishing process. For instance, the polishing film 113 may be made of polyurethane. Naturally, other materials can be used for forming the polishing film 113. The polishing film 113 may be provided as a coating or a film. Preferably, the polishing film 113 may have a thickness ranging from 0.5mm to 2.5mm, or from 0.8mm to 2.0mm, or of 1.3mm. The polishing film 113 may comprise a projecting edge 133 that protrudes radially from the tool body 110 as exemplarily illustrated in Figure 9. Thereby, excessive operational forces when by entering the optical surface Li in the polishing process can be avoided.

The second axial end 102 of the tool body 110 may preferably be formed by a base portion 111. The base portion 111 may be one of the layers of the tool body 110. The base portion 111 may be suitable (or configured) for rotatably supporting the polishing tool 100, for example, in a tool holder of a lens generator for a surface machining process. This is exemplarily indicated in the schematic illustration of Figure 11. For this, the base portion 111 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 110 may also comprise a holder portion 112, which may be arranged between the polishing film 113 and the base portion 111. The holder portion 112 may be one of the layers of the tool body 110. The holder portion 112 may be capable of adapting axially to the contour of the optical surface Li, L2 of the lens L. For this, the holder portion 112 may be configured to be reversibly deformable under pressure. For example, the holder portion 112 maybe made of plastic, e.g. a closed cell rubber material, such as neoprene, EPDM or NBR. The tool body 110 further comprises a channel 140, which extends axially (along or coaxially with the rotational axis RA1) through the tool body 110. Therein, the channel

140 may penetrate the polishing film 113, the base portion 111 and the holder portion 112, respectively, as exemplarily illustrated in Figures 9 and 11. The channel 140 may have a constant, stepwise or continuously increasing/decreasing diameter along its extension direction. Preferably, the channel 140 may have a cross-section of any shape or form, for example a circular or rectangular cross-section. The channel 140 may be formed by the passages formed in the respective sections of the tool body 110 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 140 comprises an inlet 142, preferably for feeding a polishing agent into the channel 140. This is exemplarily illustrated in Figures 9 and 11. The inlet 142 is provided at the second axial end 102. Preferably, the base portion 111 may comprise the inlet 142. More preferred, the inlet 142 maybe formed as an opening, for example in (the tool body 110 or) the base portion 111. The inlet 142 may have a cross-section with the same or a different shape as the channel 140. The channel 140 may expand radially towards or at the inlet 142. Figures 9 and 11 show this exemplarily.

The tool body 110 (or the base portion 111) may further comprise a port 143 for fluidly connecting the channel 140 with a polishing agent supply unit 240 (such as illustrated in Figure 11). This is exemplarily illustrated in Figures 9 and 11. The port 143 may be a valve, hose connector, pipe or hose. Preferably, the port 143 may have the same size as the inlet 142. More preferred, the port 143 may be removeably connected to the inlet 142. The port 143 may be press-fitted into the inlet 142. Preferably, the port 143 may comprise a gasket 144 for radially sealing against the polishing agent supply unit 240 (cf. Figure 11) to prevent the polishing agent from leaking and to enable only the polishing agent entering the channel 140 via the inlet 142. This is exemplarily shown in Figures 9 and 11. The gasket 144 may be made of rubber and/or may be an O-ring. However, these are only examples and not a complete enumeration.

The channel 140 further comprises an (preferably a single) outlet 141 to supply the polishing surface 130 with a polishing agent (preferably, the polishing agent fed through the inlet 142). The outlet 141 is provided at the first axial end 101. Preferably, the outlet

141 may be provided at the centre of the polishing surface 130 (such as exemplarily illustrated in Figures 9 to 11). Preferably, the outlet 141 maybe coaxial with the rotational axis RAi. However, it is also conceivable to provide the outlet 141 at a different position. For example, the outlet 141 may be provided in a section immediately (e.g. radius <iomm) surrounding the rotational axis RA1 (or the centre of the polishing surface 130). Preferably, the polishing film 113 may comprise the outlet 141. This is exemplarily illustrated in Figures 9 to 11. The outlet 141 may have any shape or form. For example, the outlet 141 may be circular, and/ or may expand or reduce in diameter towards the first axial end 101. Preferably, the outlet 141 may be formed (to provide the same functionality) as a nozzle or throttle. The outlet 141 may have a diameter significantly smaller than the diameter of the polishing surface 130 (delimited by the perimeter), i.e. 1/100, 1/80, 1/50, 1/20, 1/10, 1/8, or 1/5 of the diameter of the polishing surface 130.

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 maybe made of metal (e.g. aluminium oxide), silicon or plastic. Preferably, the solid particles may have a grain size ranging from 1 to 2 micrometres.

The polishing surface 130 comprises at least one groove 150. Preferably, the polishing film 113 may comprise the groove 150. Figures 9 to 11 show this exemplarily.

As indicated exemplarily in Figure 10, the polishing surface 130 may comprise a plurality of said grooves 150 (i.e. more than one of the groove 150). If in the following reference is made to “the groove 150”, the respective description also applies to the “plurality of grooves 150” unless specified otherwise. The grooves 150 may have the same or a different configuration. For example, the grooves 150 maybe identical or they may have at least partially a different shape and/or cross-section.

The groove 150 extends radially away from the outlet 141 to the perimeter of the polishing surface 130 to distribute the polishing agent across the polishing surface 130. The groove 150 may have any shape or form. For instance, the groove 150 may extend radially along a main extension direction. Therein, the groove 150 may extend such that its path does not turn back in a radial direction towards the outlet 141 (but instead, the groove 150 may proceed extending radially outwards). The groove 150 may extend in a linear, straight, curved and/ or arcuate manner.

Alternatively or additionally, as exemplarily shown in Figure 10, the groove 150 may extend in a wave or zigzag manner. Therein, the groove 150 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 150 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 Figure 10, where the groove 150 is exemplarily illustrated as comprising a straight first section 151 that connects the outlet 141 with a curved second section 152, and a third section 153 that extends straight from the curved second section 152 to the perimeter of the polishing surface 130 (polishing film 113). It is further conceivable that the groove 150 may have branches and/or may diverge into other (neighbouring) groove(s) 150.

The groove 150 may have a circular or rectangular cross-section when seen along the main extension direction and/or along a flow direction. Preferably, the groove 150 may have a width W ranging from 0.1mm to 1.0mm, or from 0.2mm to 0.8mm, or from 0.4mm to 0.6mm, or of 0.5mm (cf. Figure 10). Alternatively or additionally, the groove 150 may have a depth T ranging from 0.1mm to 1.0mm, or from 0.2mm to 0.8mm, or from 0.4mm to 0.6mm, or of 0.5mm (cf. Figure 9).

Different grooves 150 may preferably be provided on the polishing surface 130 as radially diverging. Alternatively or additionally, the plurality of grooves 150 may be (evenly) distributed about the outlet 141 (or the rotational axis RAi). For example, based on the arrangement and/or configuration of the grooves 150 (e.g. circumferential orientation, curved sections etc.), the polishing tool 100 may be used only in one rotational direction about the rotational axis RAi in order to work properly.

A further aspect of the present invention relates to a system 200 for polishing of at least one of the optical surfaces Li, L2 of the spectacle lens L. Figure 11 shows this exemplarily.

The system 200 comprises a surface processing unit 210 for processing the optical surface Li, L2 of the spectacle lens L. Therein, the surface processing unit 210 comprises the above described polishing tool too. For example, it is also conceivable that the surface processing unit 210 may comprise a linearly movable (indicated by arrows 410, 420) cutter 400, such as illustrated exemplarily in Figure 4.

The surface processing unit 210 comprises further a polishing agent supply unit 240 to supply the polishing surface 130 with a polishing agent. The polishing agent supply unit 240 is fluidly connected to the channel 140 (through the port 143) via the inlet 142 of the polishing tool 100 to supply the groove(s) 150 with polishing agent through the outlet 141. Preferably, the above described gasket 144 may radially seal the connection to prevent the polishing agent from leakage and to enable the polishing agent entering the channel 140 only via the inlet 142. Thus, for example, the polishing agent may be pumped by a pump 241 of the polishing agent supply unit 240 from a voluminous tank 242 of the polishing agent supply unit 240 through a pipe 213 to the port 143 and, subsequently, to the inlet 142. From the inlet 142, the polishing agent may flow through the channel 140 to the outlet 141 and to the groove(s) 150. For example, in the state of rotating the polishing tool too about the rotational axis RA1, the polishing agent is pushed radially outwards towards the perimeter of the polishing surface 130. Simultaneously existing circumferential forces may drive the polishing agent out of the grooves 150 so that the polishing agent is distributed across the (entire) polishing surface 130. The different configuration of the sections of the grooves 150 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 150 that are radially further away from the outlet 141. Thus, effects of the centrifugal acceleration can be reduced.

The system 200 comprises further a lens support unit 220 (mentioned before in relation to Figures 3 to 6) for supporting the lens L during the polishing process. For this, the lens support unit 220 may comprise a lens holder 222 that may apply a suction force onto the lens L. Additionally, the lens support unit 220 may comprise a spindle 221 that rotates about a second rotational axis RA2 (indicated by arrow 223). Figures 3 to 6 and 11 show this exemplarily.

The system 200 comprises also a drive unit to apply a relative motion between the polishing tool too and the lens support unit 220. Therein, the relative motion comprises at least rotating the polishing tool too about the rotational axis RAi to facilitate polishing of the optical surface Li, L2 with the polishing tool too. This is exemplarily indicated by arrow 213 of Figure 11. Additionally, the relative motion may comprise tilting, pivoting and/ or linearly moving (as indicated by arrows 211 and 212 in Figure 11) the polishing tool too relatively to the lens support unit 220 to apply the relative motion. Preferably, the drive unit may be adapted to displace the polishing tool too relative to the lens support unit 220 in order to obtain a defined distance therebetween.

It is also conceivable that the drive unit comprises and/or drives the spindle 221. Therein, the drive unit may be preferably adapted to rotate the lens support unit 220 about the second rotational axis RA2 to effect the (additional) relative motion (e.g. arrow 223). The drive unit maybe part of the surface processing unit 210 or vice versa. Figure 11 shows this exemplarily.

The system 200 may further comprise a control unit 230 for controlling the relative motion by the drive unit and/or the surface processing unit 210. The control unit 230 may control the system 200 based on processing features, like the lens type, form and thickness, the polishing tool type, the polishing agent type. Therein, the control unit 230 preferably may be configured to adapt a relative rotational speed between the optical surface Li, L2 and the polishing tool 100. Alternatively or additionally, the control unit 230 may be configured to adapt a pressure for supplying the polishing agent to the polishing tool too and/or a flow rate of the polishing agent (through the channel 140).

A further aspect of the present invention relates to a process of polishing at least one of the optical surfaces Li, L2 of the (spectacle) lens L. In the process, the above system 200 is provided. Alternatively, it is also conceivable to provide a different system for surface processing having the above described polishing tool too.

The (spectacle) lens L is seated in said (or a) lens support unit 220. The polishing tool too is relatively rotated with respect to the lens L. A polishing agent is delivered through the channel 140 to the polishing surface 130, which faces an optical surface Li, L2 of the lens L to be polished. Through the rotation, for example, the polishing agent is delivered through the grooves 150 radially outwards from the outlet 141 so that the polishing agent is distributed across the polishing surface 130 for polishing the optical surface Li, L2.

For example, in a surface machining process, typically the lens L and the polishing tool too (with the polishing film 113) may be rotated relatively to each other in opposite directions from each other. By supplying polishing agent through the channel 140 into the grooves 150, the polishing agent can be transported (and squeezed) between the polishing surface 130 (the polishing film 113) and the optical surface Li, 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 Li, L2/polishing surface 130). For example, it maybe advantageous to provide a plurality of grooves 150 across the polishing surface 130 so that the polishing agent can be distributed uniformly. Generally, by directing/routing the polishing agent through the (pathway of the) grooves 150, it may be possible to control the exposure of the polishing agent to circumferential and radial acceleration (depending on its position in the groove 150). Thereby, the distribution of the polishing agent across the polishing surface 130 may be improved as it becomes possible to control how the polishing agent travels across the polishing surface 130 (i.e. where and when it travels with respect to being dispensed from the outlet 141).

The process may further comprise the step of controlling a thickness of a layer (film) of the polishing agent between the optical surface Li, L2 and the polishing surface 130 by adapting a flow rate and/or a supply pressure of the polishing agent based on a rotational speed of the polishing tool 100 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. All the features of the embodiments described hereinabove can be combined in any possible way and be provided interchangeably.

For example, it is also conceivable that the tool body 110 may comprise a plurality of channels 140 extending through the tool body 110. The plurality of channels 140 may connect one or more of the inlet 142 with one or more of the outlet 141. For example, each of the plurality of channels 140 may correspond with one inlet 142 and one outlet 141. However, each of the plurality of channels 140 may extend between the same inlet 142 and a plurality of outlets 142 that may be provided on the polishing surface 130. Each of the plurality of outlets 141 may be provided with one or more grooves 150 extending therefrom radially away to the perimeter of the polishing surface 130 to distribute the polishing agent across the polishing surface 130. For example, the plurality of outlets 141 may be distributed uniformly across the polishing surface 130. For instance, (larger) gaps between the grooves 150 as shown exemplarily in Figure 10, maybe provided with additional outlets 141 and additional grooves 150 (not illustrated).