WO2015179989A1

WO2015179989A1 - Apparatus and method for laser processing of a workpiece on a three-dimensional surface area

Info

Publication number: WO2015179989A1
Application number: PCT/CH2014/000074
Authority: WO
Inventors: Ivan Sergio CALDERON MOSCOSO; Mathieu BONNY
Original assignee: Unitechnologies Sa
Priority date: 2014-05-30
Filing date: 2014-05-30
Publication date: 2015-12-03

Abstract

The invention relates to an apparatus for laser processing of a workpiece (81) on a three-dimensional surface area (82), the apparatus comprising a positioning assembly (31) and a laser assembly (4) to direct a laser beam (8) to an incidence position such that the laser beam (8) comprises a spot area (84) inside the surface area (82). The invention further relates to a corresponding method. To meet high precision requirements of the processing, the invention suggests a control unit configured to operate the incidence position along an incidence trajectory (83) on the surface area (82) and to provide a controlled energy density of the laser beam (8) along the incidence trajectory (83).

Description

Apparatus and method for laser processing of a workpiece on a three- dimensional surface area

The present invention relates to an apparatus for laser processing on a three- dimensional surface area of a workpiece. The invention further relates to a method for laser processing on a three-dimensional surface area of a workpiece.

Laser irradiation is increasingly used in the field of surface processing. Typical application areas include ablation, cutting, engraving, polishing or other surface treatments or machining methods of the workpiece surface. In these areas, a laser is employed to produce surface modifications on a surface layer of the workpiece and/or volume modifications extending from the surface to an essential part of the inner volume of the workpiece. A significant problem, however, is the processing of parts comprising an uneven surface, such as a surface curvature, or other three-dimensional surface structures, including inner volume structures, of a high complexity. An intricate handling is required during laser processing of those parts which is even more challenging when a high precision of the processing is needed, in particular during the processing on a micrometer scale. During such a micro-processing a surface treatment in a range below 100 μιη, in particular below 10 μιτι or even in a range of 1 μιτι and below, is often desired. For example, during micro-polishing a processing of a surface depth below 1 0 μιη is often required. In consequence, an elaborate automatized manipulation technique must be provided to comply, on the one hand, with the handling of a rather complex workpiece geometry, and, on the other hand, with high precision demands. In the face of those technical difficulties, a small space consumption of such a laser processing apparatus is aspired. At the same time, an automatized processing at a fast speed and a reproducible production quality would be desirable. It is an object of the present invention to propose a laser processing apparatus and method having the capability to meet high precision requirements, such that laser processed surfaces and/or laser processed volumes can be manufactured in a reproducible way. It is another object to propose such an apparatus that is capable to manage at least one of the surrounding processing environment, the workpiece, the laser beam, and the contact region in between the laser beam and the workpiece in an efficient way, in particular in view of processing costs and/or at least one of time, space, and energy consumption. It is another object to propose an apparatus and method with an applicability for laser-micro- processing, in particular capable to produce surface features at a size ranging below 10 μηη or to 1 μηι and below, and/or for the processing of three

dimensional surface structures and/or volume structures, in particular curved surfaces and/or volumes. It is yet another object to provide such an apparatus and method with a low space consumption and/or a high processing speed and/or low manufacturing costs.

At least one of these objects is achieved by the apparatus according to claim 1 and/or the method according to claim 28. The dependent claims define preferred embodiments.

Accordingly, the invention suggests a processing apparatus comprising

- a positioning assembly configured to position a surface area of a workpiece in a working space;

- a laser assembly configured to direct a laser beam to an incidence position on the surface area such that the laser beam comprises a spot area inside the surface area; and

- a control unit configured to operate the incidence position along an incidence trajectory substantially extending over the surface area. At least one of the positioning assembly and the laser assembly is configured to provide a relative movement of the workpiece with respect to the laser beam such that the incidence position of the laser beam is continuously shifted from a previous spot area to a following spot area along the incidence trajectory. The control unit is configured to operate the laser assembly to provide a controlled energy density of the laser beam along the incidence trajectory.

Due to the controlled relative movement of the workpiece with respect to the laser beam under simultaneous control of the energy density of the laser beam on each spot area, high precision requirements of the processed workpiece can be met.

An according processing method comprises the steps of

- directing a laser beam to an incidence position on said surface area such that the laser beam comprises a spot area within said surface area; and

- providing a relative movement of the workpiece with respect to the laser beam along an incidence trajectory such that the incidence position of the laser beam is subsequently shifted from a previous spot area to a following spot area within said surface area. A controlled energy density of the laser beam is provided along the incidence trajectory.

Further advantageous features and preferred embodiments of the invention are described below and can be correspondingly applied to the apparatus and to the method according to the invention.

Preferably, the controlled energy density at the spot area is provided by a predetermination and/or monitoring and/or adjustment of at least one parameter. Preferably, the adjustable parameters comprise at least one of the laser intensity, the laser movement speed, the laser frequency, the laser pulse duration, and the angle of incidence of the laser beam relative to the surface area at the incidence position along the incidence trajectory. Preferably, the control unit is configured to operate the laser assembly to provide a controlled energy density of the laser beam at substantially each spot area along the incidence trajectory. More preferred, a substantially constant energy density of the laser beam is provided at least for a plurality of adjacent spot areas, in particular corresponding to a discrete surface and/or volume structure of the processing. Most preferred, a substantially constant energy density of the laser beam is provided at substantially each spot area along the incidence trajectory. According to a preferred implementation, the substantially constant energy density applied on two respective spot areas does not deviate by more than 5%, more preferred by more than 1 %, and most preferred by more than 0.1 %.

Preferably, the control unit is configured to automatically operate the processing method on the processing apparatus. To this end, the control unit is preferably operatively connected with the laser assembly and positioning assembly.

Preferably, the control unit is configured to predetermine the incidence trajectory and/or to operate the laser beam along a predetermined incidence trajectory.

Preferably, the spot areas are equally spaced. The control unit is preferably configured to operate the incidence position along the incidence trajectory in such a way that the relative movement along the incidence trajectory produces an overlapping area of adjacent spot areas. Preferably, the overlapping area corresponds to at least 20%, more preferred at least 50% and most preferred at least 80%, of the size of each of two adjacent spot areas. In this way, a high quality of the processing can be provided. Preferably, the angle of incidence of the laser beam does not deviate by more than 60°, more preferred by more than 30 °, from the normal vector of said surface area on the incidence position of substantially each spot area on the incidence trajectory. Most preferred, the laser beam angle does not deviate by more than 15 ° from this normal vector. Accordingly, the laser assembly is preferably adapted to provide such an angle of incidence of the laser beam. This can further contribute to a high quality of the processing, in particular due to a good and reproducible condition of the laser spot such as the value of the energy density in each spot area. According to a preferred configuration, the angle of incidence of the laser beam may deviate from the normal vector of said surface area on the incidence position of at least one spot area on the incidence trajectory. Such a deviation may be caused by a curved surface area during the movement of the workpiece with respect to the laser beam. Preferably, the power of the laser beam is varied in between at least two different spot areas to provide a substantially constant energy density at different spot areas. Accordingly, the control unit is preferably configured to adjust the output power of the laser beam in order to provide the substantially constant energy density at different spot areas, more preferred at substantially each spot area. In particular, the control unit is preferably configured to adjust the output power of the laser beam when the angle of incidence of the laser beam on said surface area changes from the previous spot area to the following spot area.

Preferably, the control unit is configured with logic to determine the incidence trajectory in dependence of at least one of geometrical and material properties of the workpiece. In particular, a datafile comprising three dimensional properties of the workpiece is preferably used to deduce the incidence trajectory. Preferably, the control unit is also configured to determine the angle of incidence of the laser beam in each spot area along the incidence trajectory. Preferably, the control unit is further configured to determine the normal vector of the surface area in each spot area and/or a deviation of the angle of incidence of the laser beam from the normal vector. Preferably, corresponding movement parameters for the positioning assembly and/or the laser assembly, in particular a scanner, are also determined by the control unit. Preferably, laser parameters are also determined by the control unit, such as an adjustment of the laser intensity depending on the respective angle of incidence.

Preferably, the control unit is provided with a memory to store the incidence trajectory previously determined for a specific type of the workpiece. In particular, the incidence trajectory may be determined by the control unit for a prototype of the workpiece and subsequently stored in the memory. In a following step, the processing method is executed on a plurality of workpieces of that type based on the stored information. Preferably, the working space is defined by a limited space in which the laser assembly is adapted to provide the laser beam, in particular a focal point of the laser beam. This may comprise a one-dimensional, two-dimensional, or three- dimensional space. Preferably, the size of the working space in at least one dimension is at least the spot size of the laser beam, more preferred at least 1 mm, and most preferred at least 1 cm. Preferably, the size of the working space in at least one dimension is at most 1 m, more preferred at most 1 dm.

Preferably, the laser assembly is adapted to provide a movement of the laser beam within the working space.

Preferably, the laser assembly is adapted to provide a translational movement of the laser beam, in particular of a focusing point of the laser beam, in at least two dimensions, more preferred three dimensions. Preferably, the laser assembly comprises a beam shape converter adapted to change the intensity profile of the laser beam before it is directed to the incidence position. Preferably, the laser assembly is configured to provide a laser beam with a spot diameter of at most 250 μιη, more preferred at most 100 μηι and most preferred at most 50 μιη, in each spot area. Preferably, the positioning assembly is adapted to provide a translational movement of the workpiece in at least one dimension, more preferred in at least two dimensions, most preferred in three dimensions. Preferably, the positioning assembly is adapted to provide a rotational movement of the workpiece in at least one dimension, more preferred at least two dimensions. Preferably, at least one rotational axis, more preferred at least two rotational axes, for the workpiece is provided. Preferably, at least two rotational axes have a substantially perpendicular orientation with respect to each other. Accordingly, the relative movement of the workpiece with respect to the laser beam preferably comprises a rotational movement of the workpiece. Such a rotational movement is in particular advantageous with respect to a processing of a three-dimensional surface area in order to provide substantially equivalent processing conditions on different surface portions. Preferably, the positioning assembly is configured to provide a movement of the workpiece and the laser assembly is configured to simultaneously provide a movement of the laser beam. Thus, the relative movement of the workpiece with respect to the laser beam preferably comprises a simultaneous movement of the workpiece and the laser beam. In this way, high processing speeds can be achieved within a comparatively small working space. Preferably, the positioning assembly and the laser assembly are configured such that the angle between the surface area and the direction in which the laser beam is directed substantially remains unaltered during said simultaneous movement of the workpiece and the laser beam. Thus, during the relative movement of the workpiece with respect to the laser beam by the simultaneous movement of the workpiece and the laser beam the laser beam direction with respect to the surface area preferably remains substantially unaltered. This can further contribute to the reliability of the processing.

According to a preferred configuration, the laser assembly is adapted to provide a faster movement of the laser beam as compared to the movement of the workpiece provided by the positioning assembly. In particular, the movement provided by the laser assembly is preferably at least 1 0 times, more preferred at least 100 times, faster. In this way, the movement of the laser beam can be used for a fast processing of geometrically substantially equivalent surface portions on the three-dimensional surface area. The positioning assembly is then preferably applied to provide a repositioning of a subsequent geometrically equivalent surface portion to the laser beam at its incidence position. Such a geometrically equivalent surface portion may be characterized by a surface portion at which the angle of incidence of the laser beam only deviates within a certain angular range during a translational movement of the laser beam along this surface portion, even if the surface portion is kept stationary. In particular, an angular range of at most 60 °, more preferred 30 ° and most preferred at most 1 5 °, may be applied.

Preferably, the positioning assembly comprises a plurality of kinematic chains, wherein each kinematic chain is arranged in between a static base and a movable part comprising a support for the workpiece. Preferably, the kinematic chains extend in a lateral direction from the base. Preferably, at least two of the kinematic chains have a different spacing from the surface of the earth.

Preferably, at least one kinematic chain comprises a front arm having at least two spaced parallel arm sections pivotally secured to the movable part. The parallel arm sections preferably form part of a parallelogram linkage with the movable part. Preferably, the kinematic chain comprises a rear portion actuated by a motor, wherein the front arm is pivotally secured to the rear portion. Such a positioning assembly can offer the advantage of providing a rigid, fast and precise movement of the workpiece at a relatively large movement distance in at least one dimension.

Preferably, the positioning assembly is configured to pick up the workpiece from a position outside the working space. Preferably, the positioning assembly is configured to move the workpiece from a position outside the working space to a position inside the working space and/or to move the workpiece from a position inside the working space to a position outside the working space. Preferably, the positioning assembly comprises at least one kinematic chain adapted to move the workpiece from the position outside the working space to the position inside the working space, in particular before the processing, and adapted to provide a movement of the workpiece with respect to the laser beam, in particular during the processing.

Preferably, the positioning assembly is configured to move the workpiece from a position outside the enclosure to a position inside the enclosure and/or to move the workpiece from a position inside the enclosure to a position outside the enclosure. Preferably, the positioning assembly comprises at least one kinematic chain adapted to move the workpiece from the position outside the enclosure to the position inside the enclosure, in particular before the processing, and adapted to provide a movement of the enclosure with respect to the laser beam, in particular during the processing. Preferably, the at least one kinematic chain is also adapted to move the workpiece from the position inside the enclosure to the position outside the enclosure, in particular after the processing. Thus, the positioning assembly is preferably configured to subsequently perform various movement tasks of the workpiece by using the same at least one kinematic chain. This can contribute to a low space consumption and low manufacturing costs of the apparatus. This can further contribute to a high precision during the execution of subsequent processing tasks on a plurality of workpieces by employing the same kinematic chain such that no coordination mismatch during a task sharing of different kinematic chains can occur.

Preferably, the positioning assembly comprises at least one kinematic chain adapted to provide a movement of the workpiece inside the enclosure with respect to the laser beam, in particular during the processing. Preferably, the movement provided inside the enclosure comprises a rotational movement.

Preferably, the rotational movement of the workpiece inside the enclosure is independent from a translationai movement of the enclosure and/or workpiece outside the enclosure. In this way, a coordination mismatch in between the different kinematic chains employed for the translationai and rotational movement can be avoided.

Preferably, the positioning assembly is configured to pick the workpiece from a feeder system and/or from an entry port. The feeder system may comprise at least one of a conveyor, tray, and band. The entry port may comprise at least one of an operator, conveyor, tray, band, or manipulator. Preferably, the positioning assembly is configured to position the workpiece in the working space, in particular at a starting position for the processing, in particular before the processing has started. Preferably, the positioning assembly is configured to move the workpiece within the working space during the processing. Thus, the positioning assembly can contribute to the processing. Preferably, the positioning assembly is configured to place the workpiece back to the feeder system and/or to the exit port from the working space, in particular after the processing. Preferably, the apparatus comprises a protection assembly configured to survey and/or control the surrounding environment of at least one of the workpiece, the laser beam, and the region in which the interaction of both occurs. Preferably, the protection assembly is configured in such a manner that it will efficiently contribute to the laser processing performance. Preferably, it is adapted to keep the volume surrounding the processing fully compliant to the processing needs, in particular by providing at least one of an anti oxidation environment, a sterile environment, laminar flow of a medium, in particular a fluid and/or gas and/or mist and/or suspension, to be provided at the incidence position of the laser beam, a catalysing environment, a chemically active environment, and a vacuum environment.

Preferably, the protection assembly comprises a medium, in particular gas and/or liquid and/or mist and/or suspension, surrounding the incidence position of the laser beam on the workpiece. Preferably, the protection assembly is configured to a monitoring and control of the medium.

The protection assembly is preferably linked to the control unit in a way that the surrounding environment remains continuously monitored and controlled with respect to processing demands. In particular, the control unit may comprise at least two subunits, wherein one subunit is configured to operate the relative movement of the laser beam and the workpiece and/or the laser parameters and the other subunit is configured to monitor and/or control the processing environment. Preferably the monitoring and/or controlling is carried out in such a way that the surrounding environment remains adapted to at least one of the following : the workpiece, the laser beam and the region where the laser beam and the workpiece are found themselves in contact. Accordingly, the surrounding environment is moved over the whole space and its features remain constantly monitored and controlled. Preferably, the protection assembly is adapted to provide the controlled surrounding environment and is configured to constantly follow all the motion of the workpiece over the whole space.

Preferably, the processing apparatus comprises an enclosure for the workpiece, in particular a box having an inner volume to receive the workpiece. Preferably, the enclosure is comprised in the protection assembly. Preferably, the workpiece - ii - is arranged inside an inner volume of the enclosure. The enclosure preferably comprises a wall section through which the laser beam is transmittable. In particular, one transmittable wall section or a plurality of transmittable wall sections may be provided.

Preferably, the positioning assembly is configured to provide a movement of the enclosure during which the angle in between the direction in which the laser beam is directed and the wall section is substantially unaltered. Preferably, the laser beam is substantially directed perpendicular to the wall section. Preferably, the positioning assembly is adapted to provide a movement of the enclosure substantially in parallel to a surface of the wall section. In this way, the orientation of the wall section with respect to the direction of the laser beam preferably remains substantially unaltered during the movement of the incidence position on the workpiece along the incidence trajectory. This can contribute to a high quality of the processing.

Preferably, the enclosure comprises an inlet for a medium, in particular a gas. Preferably, the medium is provided in an inner volume of the enclosure in such a way, that it is surrounding the position of incidence of the laser beam on the surface area. Preferably, the medium is supporting the laser processing on the surface area, in particular a protective medium such as a protective gas.

Preferably, the enclosure is adapted to follow at least a translational movement of the workpiece during the shifting of the incidence position of the laser beam. More preferred, the enclosure is configured to follow the work piece motion in all space directions. According to a preferred configuration, the enclosure and the workpiece are mechanically connected in such a way, that a translational movement of the enclosure generates a corresponding translational movement of the workpiece. More preferred, the workpiece is provided with at least one additional degree of freedom, in particular a rotational degree of freedom, that is independent from the movement of the enclosure. Thus, a processing environment inside the enclosure is preferably carried jointly with the working piece during a respective movement in between the laser beam and the working piece. In this way, parasitic influences on the laser processing, such as medium turbulences, can be effectively avoided and a processing environment of equal quality can be provided at substantially each surface region of the processing during the movement of the workpiece. Beyond that, the movement of the enclosure allows to keep an inner volume of the enclosure comparatively small, preferably in the same range as the volume of the

workpiece. This can further contribute to a simplification to provide and to maintain a processing environment of a desired quality. For instance, this can result in cost savings and/or quality improvements of the processing

environment.

In particular, it has been realized during the present invention that a crucial parameter for the quality of the processing is the environment surrounding the impact zone at which the laser beam acts on the respective surface area of the workpiece. An adequate medium such as a protection gas can be used to avoid a contamination of the processing environment and to increase the accuracy and reproducibility of the processing. The application of such a medium, however, can lead to an undesired perturbation of the processing environment. For instance, gaseous currents or turbulences in the processing environment may be caused which have a negative impact on the processing. The apparatus according to the invention can reduce or prevent those perturbations, in particular by a movement of the processing environment within the enclosure and/or an adequate size of the inner volume of the enclosure.

Preferably, the enclosure is sealed. Preferably, the sealing of the enclosure comprises at least a substantially airtight sealing of the enclosure's inner volume from the external environment and/or a tight sealing for the medium inside the enclosure's inner volume in order to avoid leakage of the medium. Preferably, the inner volume of the enclosure is at most 10 dm³, more preferred at most 0.5 dm³. Preferably, the control unit, in particular a subunit of the control unit, is configured to control the flow of the medium. In particular, the control unit is preferably configured to control physical and/or chemical properties of the medium flowing through the inlet and/or through an outlet of the enclosure. In this way, a processing environment is preferably provided by the control unit. Preferably, the enclosure is configured to heat the processing environment contained therein, in particular to a temperature of at least 300 K, more preferred at least 500 K.

Preferably, the control unit, in particular a subunit of the control unit, is thus adapted to control the processing environment inside the enclosure surrounding the workpiece during the shifting of the incidence position along the incidence trajectory, wherein the environment preferably substantially follows the trajectory of the workpiece. In this way, turbulences within the environment can be effectively avoided and the processing environment can comply with high standards and advantageously contribute to the quality of the processing.

Preferably, the environment remains suitably configured for shifting conditions of a subsequent laser processing.

According to a preferred implementation, the control unit, in particular a subunit of the control unit, is configured to control the flow and/or concentration of the medium in such a way that substantially no medium is inserted inside the enclosure during said shifting of the incidence position along the incidence trajectory. Thus, substantially no flow of the medium inside the enclosure preferably occurs during the surface processing. In this way, turbulences can be effectively avoided. Moreover, a high quality of the processing environment can still be maintained due to the sealing of the enclosure and/or its comparatively small inner volume, such that a low leakage of the medium from the enclosure preferably occurs. Moreover, a comparatively low amount of the medium can be applied during the processing, in particular due to the comparatively small inner volume of the enclosure and/or the temporal restriction of the medium flow when no processing takes place. This can advantageously contribute to the economy of the processing.

Preferably, the enclosure substantially has a cylindrical shape, such as a cylinder with a circular or oblong profile. Preferably, the positioning assembly is configured to establish a mechanical connection with the enclosure, in particular to grab the enclosure. Preferably the enclosure comprises a connector adapted to provide a mechanical connection with the positioning assembly. Preferably, the mechanical connection is detachable such that the positioning assembly can grab and/or release the enclosure. Preferably, the connector is a pneumatic and/or electromagnetic locking means. Preferably, the positioning assembly is configured to insert the workpiece inside the enclosure before the processing and/or to remove the workpiece from the enclosure after the processing. The positioning assembly is preferably configured to grab the workpiece from a fixture and/or to receive the workpiece from another manipulation device, in particular a robot, a conveyor system, a manipulator system, a feeding system. In this way, an advantageous automation of the processing can be achieved, in particular for a subsequent processing of a number of workpieces. According to a preferred configuration, the positioning assembly is adapted to provide a translational movement of the enclosure, in particular with the

workpiece arranged inside the enclosure. Preferably, the positioning assembly is adapted to provide a rotational movement of the workpiece inside the enclosure. To this end, the positioning assembly preferably comprises at least one rotational axis extending inside the inner volume of the enclosure to rotate the workpiece independent from the enclosure walls.

According to an alternative configuration, the positioning assembly is preferably adapted to provide a translational movement of the workpiece inside the enclosure. Preferably, the positioning assembly is adapted to provide a rotational movement of the workpiece inside the enclosure.

According to another alternative configuration, the positioning assembly is preferably adapted to provide a rotational movement of the enclosure. Preferably, the positioning assembly is also adapted to provide a translational movement of the enclosure. In order to be adapted to execute a translational and/or rotational movement of the enclosure, the positioning assembly preferably comprises a connector, in particular a pneumatic locking, on the enclosure walls. Preferably, a wall section of the enclosure, in particular a rear wall, is mechanically fixed to the positioning assembly. Preferably, at least a member of the connector is provided on the wall section that is mechanically fixed to the enclosure and/or at least a member of the connector is provided on the a wall section that is not mechanically fixed to the enclosure. Preferably, the apparatus is provided as an independent working station.

Preferably, the apparatus is integrated as part of a production line, in particular at least one apparatus or a plurality of the apparatuses, for instance repeatedly arranged along a feeder system. Preferably, the apparatus is integrated as a subsystem in a higher-ranking working assembly, in particular as an off-line working station within a production equipment.

According to a first preferred application, polishing, in particular micro-polishing, is performed within the surface area. Correspondingly, the control unit is preferably configured to provide a substantially constant energy density of the laser beam at substantially each spot area such that irregularities on the surface area are reduced by the impact of the laser beam. Preferably, the surface area has a surface roughness with an average depth of at most 100 μιη, more preferred at most 10 μιη. Preferably, the laser beam produces a melted surface layer in each spot area, wherein the depth of the melted surface layer has a depth of at most 10 μηη, more preferred at most 5 μηπ, most preferred at most 1 μιη. In this way, micro- polishing can be performed. Correspondingly, the properties of the laser beam are preferably provided such that an according melting depth can be achieved, in particular output power and/or spot size and/or beam shape and/or pulse width and/or pulse frequency. Alternatively or additionally, the laser beam is preferably configured to ablate material from the surface area. Preferably, polishing at a surface roughness above 10 μηπ is performed this way, in particular in a processing step preceding a micro-polishing. Correspondingly, the properties of the laser beam are preferably provided such that an according ablation depth can be achieved.

According to a second preferred application, engraving is performed within the surface area or an inner volume. Correspondingly, the properties of the laser beam are preferably provided such that a desired engraving depth can be achieved along the surface area, in particular by ablation and/or melting of a surface layer within each spot area extending inside the inner volume of the workpiece. The control unit is preferably configured to provide a substantially constant energy density of the laser beam at substantially each spot area such that a desired engraving depth is provided.

According to a third preferred application, cutting is performed along the surface area extending through a portion or the complete volume of the workpiece.

Correspondingly, the properties of the laser beam are preferably provided such that a desired cutting depth can be achieved along the surface area, in particular by ablation and/or melting of a surface layer within each spot area extending inside the inner volume of the workpiece. The control unit is preferably configured to provide a energy density required for the cutting.

According to a first preferred implementation, the surface area corresponds to a continuous area on the surface of the workpiece. Preferably, the continuous area has the size of at least one tenth, more preferred at least one fifth, of the total size of the surface of the workpiece on at least one face of the workpiece. For instance, the continuous area may correspond to substantially the total area of at least one face of the workpiece. Preferably, polishing and more preferred micro- polishing is applied in this implementation.

According to a second preferred implementation, the surface area corresponds to at least a pattern and/or at least a symbol provided on the surface of the workpiece. Preferably, the pattern and/or symbol is visible to the human eye. Preferably, polishing and/or engraving is applied in this implementation. More preferred, micro-polishing and/or micro-engraving is employed in order to yield a better homogeneity of the pattern and/or symbol.

According to a third preferred implementation, the surface area corresponds to at least a marking structure. Preferably, the marking structure is suitable to designate and/or recognize the workpiece. Preferably, the marking structure is readable by a recognition device and/or from the human eye. Preferably, polishing and/or engraving is applied in this implementation. More preferred, micro-polishing and/or micro-engraving is employed in order to yield a better homogeneity of the marking structure.

Preferably, the three-dimensional area section comprises at least one curved and/or graded and/or uneven area portion. Preferred materials of the surface area on the workpiece include metals, metallic alloys, glass, sapphire, crystalline materials, ceramics, semiconductor materials, composites, biological tissues and cells, and polymers. The invention is explained in more detail hereinafter by means of preferred embodiments with reference to the drawings which illustrate further properties and advantages of the invention. The figures, the description, and the claims comprise numerous features in combination that one skilled in the art may also contemplate separately and use in further appropriate combinations. In the drawings:

Fig. 1 is a perspective view of an apparatus for processing a surface area of a workpiece; Fig. 2 is a detailed view of a positioning assembly of the apparatus shown in Fig. 1 ; Fig. 3 is a detailed view of elements contained inside and outside of a sealed enclosure of the apparatus shown in Fig. 1 ;

Fig. 4 is a perspective view of a workpiece with a surface area to be

polished by the processing apparatus shown in Fig. 1 ; and

Fig. 4A is a schematic enlarged view of a portion of the surface area to be polished shown in Fig. 4.

Fig. 1 depicts an apparatus 1 for processing a surface area of a workpiece.

Apparatus 1 comprises a stable bottom platform 2 on which various components for an automatized micro-processing process are mounted. To achieve a very high working precision of these components, platform 2 ensures vibration- resistance of apparatus 1 allowing the application of laser irradiation of a high quality at an accurately determined incidence position on the surface portion of the workpiece to be polished and at the same time a very precise manipulation of the workpiece along an incidence trajectory of the laser irradiation over this surface portion.

In an upper region of apparatus 1 , a laser assembly 4 is arranged. Laser assembly 4 comprises a laser source 6 generating a raw laser beam and a beam transfer assembly 7 adapting the raw laser beam to required properties and directing the adapted laser beam 8 to the surface area of the workpiece. Beam transfer assembly 7 is disposed on an upper platform 9 rigidly mounted on bottom platform 2. Laser source 6 is disposed on another upper platform 10 rigidly mounted on bottom platform 2.

Laser source 6 is preferably constituted by a C0₂ laser, in particular comprising a lasing wavelength in a range of approximately 10 μιη, or a fibre laser, in particular comprising a wavelength range between 1 μιη and 1 .5 μιη, or a picosecond laser, in particular comprising a wavelength around 1 064 nm, 532 nm, or 355 nm. The output power of laser source 6 preferably ranges from 1 W to 1 kW. Preferably, the type of laser source 6 is chosen based on at least one of the material properties of the workpiece and/or the desired type of processing and/or the shape of the surface area. In all cases, a laser source with a high beam quality is applied with a value of M² that is smaller than 2, more preferred smaller than 1 .8, wherein M² denotes the ratio of the beam parameter product (BPP) of the actual beam to that of an ideal Gaussian beam at the same wavelength. The laser irradiation emitted from laser source 6 is preferably fiber coupled and/or directly coupled by means of optical lenses and/or mirrors into beam transfer assembly 7.

Beam transfer assembly 7 comprises a waveguide 12 delivering the laser beam from laser source 6 to a scanner 1 1 . In the optical path of waveguide 12, a collimator 16 is arranged, followed by a beam shaper 13. Beam shaper 13 comprises an alignment assembly including several mirrors required for a precise alignment of the laser beam to the beam entrance of scanner 1 1 .

Beam shaper 13 further comprises a beam shape converter that is adapted to convert the intensity profile of the raw beam emitted from laser source 6 from an initial approximate Gaussian beam profile with the above described M² value to another beam profile, in the case that such a different beam shape is desired for the processing. Possible beam shapes include a cylindrical top hat profile, a square top hat profile, and a ring shaped profile.

Beam shaper 13 is arranged at a 90 degrees deflection point in waveguide 12 at which waveguide 12 extends from a side region of apparatus 1 to an upper center region of apparatus 1 in which scanner 1 1 is arranged. In this way, scanner 1 1 is disposed above a working space 15 of apparatus 1 located at a medium width and at a medium height of apparatus 1 . Within working space 15, the processing procedure is carried out on the surface area of the workpiece.

Scanner 1 1 is adapted to deflect laser beam 8 towards working space 1 5 below, in a direction substantially perpendicular to the surface of platform 2. Scanner 1 1 is also adapted to provide a translational movement of laser beam 8, in particular of a focal point of laser beam 8, in three dimensions within working space 15. This translational movement of laser beam 8 is indicated by the coordinate system 30 depicted in Fig. 1 . Thus, laser beam 8 can be selectively moved along a u-direction substantially in parallel to the surface of platform 2, a v-direction substantially in parallel to the surface of platform 2, and w-direction substantially perpendicular to the surface of platform 2. The speed of the beam movement ranges in between 0.5 m/s and 5 m/s. At the same time, beam shaper 13 is configured to keep laser beam 8 substantially perpendicular to the surface of platform 2 corresponding to the orientation of the surface of the earth.

Scanner 1 1 further comprises a focusing optics, in particular a f theta optics, at its optical output. The focusing optics allows to reach a focusing of the laser beam at a spot area with a diameter of at least 250 μηι, more preferred at least 100 μηη, or below. Next to scanner 1 1 , a camera 17 is arranged. Camera 17 is employed for referencing and on line viewing of the processing inside working space 15, in particular to test and monitor the process quality.

A sealed enclosure 21 is arranged inside working space 1 5 below scanner 1 1 and above a lower platform 27 rigidly mounted on bottom platform 2. Enclosure 21 has a substantially circular-cylindrical shape comprising a circular side wall 22 and a flat front wall 23 and a flat rear wall 29. At its top side, side wall 22 comprises a flat top portion 24 extending substantially in parallel with respect to the surface of platform 2. Flat top portion 24 comprises a transmission window 25 below scanner 1 1 through which laser beam 8 can be transmitted. Transmission window 25 is arranged such that laser beam 8 is substantially directed

perpendicular to its surface. The upper surface of transmission window 25 is substantially arranged in parallel with respect to the u-direction and v-direction of the translational movement of laser beam 8 according to coordinate system 30. Transmission window 25 is formed by a borofloat glass. The workpiece is positioned inside an inner volume of enclosure 21 with the surface area to be polished being arranged such that it faces transmission window 25 during the processing. An inlet 76 is provided at the rear side of enclosure 21 , as depicted in Fig. 3, which allows the filling of a protection gas inside an inner volume 51 of enclosure 21 . Preferably, at least one of Helium, Argon, C02, and nitrogen are used as a protection gas. A control unit is preferably employed to manage the gas flow and/or to monitor the oxygen content inside enclosure 21 .

Thus, a protection assembly for the processing environment surrounding the incidence position of laser beam 8 is provided comprising enclosure 21 and a control equipment monitoring the processing environment inside enclosure 21 and being linked to a gas control unit. The protection assembly and/or gas control unit are adapted to provide a processing environment inside enclosure 21 surrounding the workpiece during the shifting of the incidence position along the incidence trajectory. This environment substantially follows the trajectory of the workpiece such that turbulences within the environment are avoided.

Gas flow management is preferably carried out such that gas speeds between 0 mm/s and 50 mm/s are ensured in proximity to the workpiece and a positive pressure of about 50 mbar is kept inside enclosure 21 . A sensor 26 for the monitoring of the oxygen content inside inner volume 51 of enclosure 21 is provided in front wall 23. Oxygen content monitoring is applied such that an oxygen concentration level below 900 ppm is provided inside enclosure 21 .

Inner volume 51 of enclosure 21 is smaller than 5 dm³. The relatively small inner volume and an airtight sealing of enclosure 21 allow that a desired gas concentration of the protection gas in inner volume 51 can be maintained over a long period without any refilling of the protection gas inside inner volume 51 . Thus, the processing can be carried out without any additional gas flow through inlet 76. In this way, any gas flow perturbations inside inner volume 51 can be effectively avoided during the processing. This is highly beneficial for the quality and reproducibility of the surface processing which is carried out by the application of laser beam 8 on the surface area of the workpiece inside inner volume 51 of enclosure 21 . Another advantage lies in a very low gas consumption that is required for each processing. Another advantage is the small productions costs of such an enclosure.

Fig. 2 depicts a detailed view on positioning assembly 31 of processing apparatus 1 . Positioning assembly 31 comprises three kinematic chains 32, 33, 34. Each kinematic chain 32, 33, 34 is mounted on a rear end 35, 36, 37 to the front side of a base plate 38. Base plate 38 is perpendicular to bottom platform 2 and rigidly mounted thereon. Kinematic chains 32, 33, 34 extend in a lateral direction from base plate 38, substantially in parallel to each other and in parallel to bottom platform 2. At the front end of each kinematic chain 32, 33, 34 a movable support plate 50 is mounted.

Kinematic chains 32, 33, 34 are circularly arranged such that they face a virtual central axis. First kinematic chain 32 is facing bottom platform 2. Kinematic chains 32, 33, 34 are equally spaced from each other by a respective separation angle of 120°. First kinematic chain 32 is arranged at a larger distance from bottom platform 2 as compared to second and third kinematic chain 33, 34.

Second and third kinematic chain 33, 34 are arranged at an equal distance from bottom platform 2.

Each kinematic chain 32, 33, 34 comprises a rear portion 39, 40, 41 and a front portion 42, 43, 44. Each rear portion 39, 40, 41 comprises a linear bearing 45 for a carriage 46 actuated by a respective motor. Linear bearing 45 is mounted on base plate 38 at its rear end and on a front plate 48 at it its front end and extends perpendicular between the two plates 38, 48. In this way, rear portion 39, 40, 41 of kinematic chains 32, 33, 34 is adapted to provide an actuation in a direction substantially in parallel to bottom platform 2.

Each linear bearing 45 of rear portions 39, 40, 41 comprises a hollow bar 66 with on open inner flank. Inside bar 66, a roller bearing 67 is arranged longitudinally extending in between base plate 38 and front plate 48. Roller bearing 67 provides a suspension for carriage 46 and further comprises a tensioning system for carriage 46. The tensioning system, in particular comprising several springs, provides an adaptable force in between carriage 46 and movable support plate 50. In this way it is accomplished that the balls of roller bearing 67 can fall out from hollow bar 66 in case of any external shock on apparatus 1 , wherein a damage of respective hollow bar 66 is avoided and the main structure of apparatus 1 remains operable. The tensioning system is arranged in between carriage 46 and movable support plate 50. It allows the parallel bars to be always under compression, except in a case of shock. In a case of shock, the tensioning system allows parallel bars 51 , 52 to dismount. In this way, any huge damage can be avoided while the tensioning system still holds movable support plate 50.

The front portions of kinematic chains 32, 33, 34 are constituted by a respective front arm 42, 43, 44. Each front arm 42, 43, 44 is pivotally secured at its rear end to carriage 46 of respective rear portion 39, 40, 41 . At its front end, each front arm 42, 43, 44 is pivotally secured to support plate 50 thus constituting a part that is movable by the actuation of kinematic chains 32, 33, 34. Support plate 50 is surrounded by kinematic chains 32, 33, 34. Front arms 42, 43, 44 extend from carriage 46 of rear portion 39, 40, 41 towards the front at which movable support plate 50 is located. Each front arm 42, 43, 44 comprises two respective arm sections 51 , 52. Arm sections 51 , 52 are spaced from each other and extend in parallel to each other. Each arm section is pivotally secured to the respective carriage 46 of rear portion 39, 40, 41 at its rear end and to movable support plate 50 at its front end. In this way, a parallelogram linkage is provided in between arm sections 51 , 52, carriage 46, and movable support plate 50. The parallelogram linkage of movable support plate 50 to front arms 42, 43, 44 ensures that a translationai movement of support plate 50 in three dimensions can be provided under the actuation through kinematic chains 32, 33, 34 in such a way that no rotational movement of support plate 50 is caused by such an actuation.

A schematic illustration of this movement is depicted in Fig. 2 by coordinate system 60. Support plate 50 can be selectively moved along a x-direction substantially in parallel to the surface of platform 2, a y-direction substantially in parallel to the surface of platform 2, and z-direction substantially perpendicular to the surface of platform 2. The respective movement along each axis of

coordinate system 60 is carried out in increments by means of absolute

encoders. Absolute encoding of the movement is an important feature allowing to avoid a repeatability of the respective encoder at each initialization. In this way, a time consuming initialisation of the encoders can be avoided.

The above described positioning assembly 31 bears an analogy to a delta type robot in that it includes a base 38 where a first kinematic part 39, 40, 41 has a degree of freedom in a first x-direction and is only pivotally secured to the base 38. A second kinematic part 42, 43, 44 is a parallelogram type linkage that is pivotally secured in a manner to provide a further degree of freedom to the first kinematic part 39, 40, 41 such that the second kinematic part 42, 43, 44 can pivot relative to the first kinematic part 39, 40, 41 in a second y-direction and in a third z-direction, due to the parallelogram type linkage. The parallelogram type linkage, however, prevents a resulting rotative movement of the movable end plate 50 with respect to a plane in the y-z directions. The above described positioning assembly 31 , however, is different from a common delta type robot in that the kinematic chains 32, 33, 34 are not arranged in such a way that they hang down from base 38, but they substantially project laterally from base 38. Such an arrangement of laterally extending parallel kinematic chains 32, 33, 34 in a delta like architecture has been found to be particular useful in the context of an ultraprecise manipulation of a workpiece that is required in particular during micro-processing of a curved surface area, wherein the laser beam is provided substantially perpendicular to the lateral extension direction of kinematic chains 32, 33, 34. On the one hand, a high robustness and stability of the desired movement with respect to laser beam 8 can be achieved in this way, due to the lateral parallel arrangement of several chains 32, 33, 34, contributing to a high precision and reliability of the movement. In particular, vibrational disturbances occurring after each increment step of the movement due to the resulting mass acceleration can be largely reduced. On the other hand, comparatively high movement speeds of the processed workpiece with respect to the incidence position of laser beam 8 can be provided by such an arrangement. For instance, movement speeds of 3 m/s and movement accelerations of 100 m/s² or even higher are feasible.

Typically, the movement speed during normal operation is in a range of 0.1 to 0.5 m/s.

A third advantage lies in the fact that a particular large distance of possible movement is provided along the x-direction substantially parallel with respect to base plate 38 and perpendicular to laser beam 8, corresponding to the degree of freedom offered by first kinematic part 39, 40, 41 . The particularly large degree of freedom of the motion in this direction is particularly advantageous in that it allows an easy initial positioning of the workpiece to a desired position inside working space 15 at which the processing of the workpiece takes place.

It has been realized in the course of the present invention, however, that the lateral arrangement of kinematic chains 32, 33, 34 in positioning assembly 31 can be advantageously applied in association with many other industrial applications, in particular to generally automate the movement of a workpiece with respect to the incidence position of a laser beam substantially perpendicular to the earth's surface.

The resolution of movement of support plate 50 provided by kinematic chains 32, 33, 34 is preferably less than 200 nm per increment in each translational direction of coordinate system 60. At the front end of kinematic chains 32, 33, 34, two rotational axes are provided in addition to the three translational degrees of freedom according to coordinate system 60, as further described below. Fig. 3 depicts a detailed view on enclosure 21 of processing apparatus 1 , wherein circular side wall 22 and a flat front wall 23 are not shown. Rear wall 29 of enclosure 21 is mounted to movable support plate 50 of positioning assembly 31 . At the center of rear wall 29, a first rotation axis 61 is arranged extending from the outside through rear wall 29 to inner volume 51 of enclosure 21 . At the front end of rotation axis 61 and in front of rear wall 29, a second rotation axis 62 is arranged extending perpendicular with respect to first rotation axis 61 . At an end side of second rotation axis 62, a gripper 63 is arranged adapted to carry a workpiece 81 to be processed inside enclosure 21 .

Thus, movable support plate 50, rear wall 29, first rotation axis 61 , second rotation axis 62, and gripper 63 form a movable end part 79 of kinematic chains 32, 33, 34 that can be moved in the translational three dimensions according to coordinate system 60 by positioning assembly 31 . Moreover, movable end part 79 is rotatable around the direction of extension of first rotation axis 61 substantially extending perpendicular to base plate 38 at an angle φ, offering a first rotational degree of freedom 65. Furthermore, movable end part 79 is rotatable around the direction of extension of second rotation axis 62

substantially extending perpendicular to bottom platform 2 at an angle γ, offering a second rotational degree of freedom 66. Respective motors to selectively actuate a rotation of movable end part 79 along first rotational degree of freedom 65 and/or second rotational degree of freedom 66 are comprised in positioning assembly 31 . First rotational degree of freedom 65 comprises a resolution of about 1 mdeg/increment, wherein mdeg denotes a thousandth part of a degree. Second rotational degree of freedom 66 comprises a resolution of about 10 mdeg/increment.

During a movement of enclosure 21 by positioning assembly 31 , the upper surface of transmission window 25 substantially remains parallel with respect to the u-direction and v-direction of the translational movement of laser beam 8 according to coordinate system 30. Furthermore, the upper surface of transmission window 25 substantially remains parallel with respect to the x- direction and y-direction of the translational movement of enclosure 21 by positioning assembly 31 . Before the beginning of the actual processing, workpiece 81 is disposed on gripper 63 such that the surface area to be polished points away from first rotation axis 61 . Subsequently, movable end part 79 is moved by positioning assembly 31 into working space 1 5 to a position on top of lower platform 27 at which front wall 23 and side wall 22 of enclosure 21 are mounted until rear wall 29 is located at the rear side of enclosure 21 . Enclosure 21 is then grabbed by positioning assembly 31 by means of an actuation of pneumatic fingers 74, 75 disposed on the rear side of enclosure 21 which act together with corresponding slots 77, 78 protruding from the rear edge of lateral side wall 22.

Thus, a pneumatic locking mechanism is provided by pneumatic fingers 74, 75 and corresponding slots 77, 78 by which enclosure 21 can be locked to kinematic chains 32, 33, 34 of positioning assembly 31 . In this way, fingers 74, 75 and corresponding slots 77, 78 constitute a respective member of a connector adapted to provide a detachable mechanical connection in between enclosure 21 and positioning assembly 31 . In consequence, enclosure 21 can be moved by positioning assembly 31 along the translational degrees of freedom illustrated in coordinate system 60. In this way, enclosure 21 is configured to follow the motion of the workpiece in all translational space directions 60 of kinematic chains 32- 34.

Rotational axes 61 , 62, however, are not locked to enclosure 21 but extend inside inner space 70 of enclosure 21 . Thus, workpiece 81 can be rotated along rotational degrees of freedom 65, 66 inside inner space 70 without an according rotation of enclosure 21 . In this way, transmission window 25 has a substantially perpendicular orientation with respect to laser beam 8 irrespective of any movement of the workpiece along translational degrees of freedom 60 and/or rotational degrees of freedom 65, 66.

Lower platform 27 comprises an adjustment means 52 on top of its rear end to ensure the correct positioning of enclosure 21 . Adjustment means 52 comprises a wall section 59 having a semicircular cut-out 53 at its upper edge substantially corresponding to the shape of rear wall 29 arranged on top. At each upper end of semicircular cut-out 53, an indentation 54, 55 is provided. Corresponding bolts 56, 57 are provided at opposed ends on the circumference of rear wall 29. In this way, a correct positioning of enclosure 21 on lower platform 27 with respect to a correct height can be ensured, corresponding to a correct position with respect to a translational movement in the z-direction.

Adjustment means 52 further comprises a longitudinal bar 58 arranged at a central bottom portion of wall section 59 protruding therefrom in a direction perpendicular to base plate 38. Longitudinal bar 58 allows to ensure a correct positioning of enclosure 21 with respect to a correct orientation in the y-direction.

Fig. 4 depicts a detailed view on a specific example of workpiece 81 . In this case, the workpiece is provided as a watchcase or watchcase-like object 81 on which a conical surface area 82 surrounding the clock face shall be subject of a processing performed with apparatus 1 . In particular, a polishing process shall be applied on surface area 82.

Fig. 4A shows a schematic view of an enlarged portion of surface area 82. During the laser processing, a relative movement in between laser beam 8 and curved surface area 82 is provided such that the incidence position of laser beam 8 directed on surface area 82 is moved along an incidence trajectory 83. In the example, incidence trajectory 83 commences with a path of the laser spot on conical surface area 82 around the center of watchcase 81 at a certain radius and is then continued at a larger radius in the inverse direction.

Along incidence trajectory 83 of laser beam 8, equidistant spot areas 84 are generated on surface area 82 at the respective incidence positions of laser beam 8. Spot areas 84 correspond to an energy density of laser beam 8 to which surface area 82 is exposed within the respective spot area 84. The energy density is kept substantially constant for each spot area 84, wherein melting of a surface layer of surface area 82 occurs in each spot area due to the impact of laser beam 8. Preferably laser beam 8 is directed substantially perpendicular on surface area 82, such that an angle of incidence a of laser beam 8 does substantially not deviate from the normal vector of surface area 82 at the center of the respective spot area 84. Due to the movement along curved surface area 82, however, an angle of incidence β of laser beam 8 deviating from the normal vector of surface area 82 at the center of the respective spot area 84 may also occur. In this case, the intensity of laser beam 8 is advantageously adjusted in apparatus 1 such that the energy density at the respective spot area 84 remains substantially identical with respect to the energy density in other spot areas 84. In this way,

substantially homogenous properties of the melted surface layer in different spot areas 84 are provided.

The equidistant spacing in between subsequent spot areas 84 on incidence trajectory 83 corresponds to a predefined increment in the relative motion in between laser beam 8 and surface area 82 and/or to a temporal interval in between subsequent pulses of laser beam 8. Thereby, the relative movement is provided at such a movement velocity that adjacent spot areas 84 comprise an overlapping area section 85.

Overlap 85 corresponds to at least 50% of the area size of each spot area 84 of the two adjacent spot areas 84, more preferred at least 80% of each adjacent spot area 84. Overlap 85 between adjacent spot areas 84 has substantially a constant size for different adjacent spot areas 84 along incidence trajectory 83. Overlaps 85 provide a more homogenous application of the energy of laser beam 8 on surface area 82 along incidence trajectory 83 leading to a higher polishing quality substantially without remaining artifacts. For instance, an inhomogeneous energy distribution of the laser beam profile within each spot area 84 can be compensated this way. Moreover, the repeated exposure of area section 82 to laser beam 8 within each overlap 85 produces an increased depth of the respected melted surface layer in that area also contributing to a better polishing quality. Apparatus 1 further comprises a control unit operationally connected to beam transfer assembly 7, positioning assembly 31 , and the gas flow control of enclosure 21 . In addition, the control unit comprises a memory for storing the coordinates of incidence trajectory 83 for a specific processing, in particular depending on a respective type of workpiece 81 and/or area section 82.

Beyond that, the control unit is configured with logic to determine the coordinates of incidence trajectory 83 for a specific processing, in particular depending on a respective type of workpiece 81 and/or area section 82. The logic comprises a reader of three dimensional data, in particular CAD data, of geometrical properties of the workpiece.

The logic is further adapted to calculate the coordinates of spot areas 84 along incidence trajectory 83 and to determine a respective actuation scheme for positioning assembly 31 to provide a corresponding movement of workpiece 81 . The logic is also adapted to determine a respective movement scheme for scanner 1 1 . The logic is further adapted to determine a possible deviation of the angle of incidence of laser beam 8 from the normal vector in each spot area 84. In case of such a deviation is determined, the logic is further adapted to determine corresponding adjustment parameters for the laser intensity.

An example for a process operated by the control unit is subsequently presented on the example of a polishing procedure: At first, the incidence trajectory on the surface area for a prototype of a specific workpiece is determined by the control unit, and the corresponding movement and synchronisation parameters for positioning assembly 31 and scanner 1 1 as well as adjustment parameters for inherent properties of laser beam 8, such as a varying laser intensity depending on the respective angle of incidence.

Subsequently, these parameters are stored in the memory of the control unit.

After determination of the process parameters for the specific type of workpiece, the polishing process on workpiece 81 is initiated. At first, workpiece 81 is indexed on a pick position located outside working space 15 by means of actuators or an operator. In a following step, positioning assembly 31 grabs workpiece 81 on a fixture with gripper 63. Subsequently, workpiece 81 is moved by positioning assembly 31 towards working space 15 such that rear wall 29 is positioned at a designated position at which it is surrounded by side wall 22 of enclosure 21 . Then, rear wall 29 is locked to side wall 22 by actuation of fingers 74. A correct initial position of enclosure 21 is ensured by its alignment on adjustment means 52. During the positioning of workpiece 81 and/or enclosure 21 to the initial processing position, enclosure 21 is filled with a protective gas. After reaching a oxygen concentration below a desired level inside inner volume 70, the injection of the protective gas through inlet 76 is stopped.

After the above initiation steps, the polishing on surface area 82 is started. If the surface roughness of surface area 82 exceeds a critical value, a pre-polishing routine is performed first. To this end, laser beam 8 is generated from a cw laser source and set to a relatively high emission power such that polishing by abrasion occurs on surface area 82 on a macroscopic scale during a relative movement of laser beam 8 with respect to surface area 82 along incidence trajectory 83.

When the surface roughness of surface area 82 is below a critical value, the actual micro-polishing process is executed. To this end, laser beam 8 is generated from a pulsed laser source and set to an emission power at which remelting of a surface layer occurs on surface area 82 within spot areas 84 at the incidence position of laser beam 8 which is moved along incidence trajectory 83.

The movement is performed simultaneously by a movement of laser beam 8 by scanner 8 and by a movement of workpiece 81 by positioning assembly 31 . Scanner 8 allows a higher processing speed within working space 15 wherein positioning assembly 31 ensures a continuous delivery of a respective portion of surface area 82 to be processed into working space 1 5. Rotational degrees of freedom 65, 66 are exploited to provide an angle of incidence of laser beam 8 substantially corresponding to a normal vector on curved surface area 82 at the momentary incidence position. In this way, the energy density of laser beam 8 within spot areas 84 can be kept substantially constant and a homogenous polishing can be achieved. In a case in which the angle of incidence of laser beam 8 inside a spot area 84 deviates from the calculated normal vector on curved surface area 82, corresponding adjustments of the laser power are provided by the control unit, such that the energy density of laser beam 8 in this spot area 84 substantially remains constant with respect to the energy density of laser beam 8 in the other spot areas 84. After the relative movement of the incidence position of laser beam 8 along incidence trajectory 83, the polishing procedure is finished. Enclosure 21 is moved back to the initial position on adjustment means 52 on top of lower platform 27. Then pneumatic locking 74, 75 of enclosure 21 is opened and workpiece 81 is moved back to the initial fixture outside working space 1 5. A next workpiece of the same type as workpiece 81 is picked up by positioning assembly 31 and a subsequent polishing process is initiated with the same process parameters that have been predetermined by the control unit for the prototype. From the foregoing description, numerous modifications of the processing apparatus and method are apparent to one skilled in the art without leaving the scope of protection of the invention that is solely defined by the claims.

Claims

1 . An apparatus for laser processing on a three-dimensional surface area (82) of a workpiece (81 ), the apparatus comprising

- a positioning assembly (31 ) configured to position said surface area (82) in a working space (15); and

- a laser assembly (4) configured to direct a laser beam (8) to an incidence position on said surface area (82) such that the laser beam (8) comprises a spot area (84) inside said surface area (82);

characterized by

- a control unit configured to operate the incidence position along an incidence trajectory (83) substantially extending over said surface area (82),

wherein at least one of the positioning assembly (31 ) and the laser assembly (4) is configured to provide a relative movement of the workpiece (81 ) with respect to the laser beam (8) such that the incidence position of the laser beam (8) is continuously shifted from a previous spot area (84) to a following spot area (84) along the incidence trajectory (83), and the control unit is configured to operate the laser assembly (4) to provide a controlled energy density of the laser beam (8) at substantially each spot area (84).

2. The apparatus according to claim 1 , characterized by a sealed enclosure (21 ) for the workpiece (81 ), the enclosure (21 ) comprising a wall section (25) through which the laser beam (8) is transmittable. 5

3. The apparatus according to claim 2, characterized in that the enclosure (21 ) comprises an inlet (76) to insert a medium inside an inner volume (79) of the enclosure (21 ).

4. The apparatus according to claim 2 or 3, characterized in that the inner o volume (79) of the enclosure (21 ) is at most 10 dm³, more preferred at most 1 dm³.

5. The apparatus according to ciaim 3 or 4, characterized in that the control unit is configured to survey physical and/or chemical properties of the medium inside the enclosure (21 ).

6. The apparatus according to one of the claims 3 to 5, characterized in that the control unit is configured to control the flow of the medium through the inlet (76) in such a way that substantially no medium is inserted inside the enclosure (21 ) during said shifting of the incidence position along the incidence trajectory (83).

7. The apparatus according to one of the claims 2 to 6, characterized in that the positioning assembly (31 ) is configured to provide a movement of the enclosure (21 ) during which the angle in between the direction in which the laser beam (8) is directed and the wall section (25) is substantially unaltered.

8. The apparatus according to one of the claims 2 to 7, characterized in that the positioning assembly (31 ) is configured to provide a rotational movement of the workpiece (81 ) inside the enclosure (21 ).

9. The apparatus according to one of the claims 2 to 8, characterized in that the enclosure (21 ) is adapted to follow a translational movement of the workpiece (81 ) during the shifting of the incidence position of the laser beam (8).

10. The apparatus according to one of the claims 2 to 9, characterized in that the positioning assembly (31 ) is configured to establish a mechanical connection with the enclosure (21 ).

1 1 . The apparatus according to one of the claims 2 to 10, characterized in that the enclosure (21 ) comprises a connector (74, 75, 77, 78) adapted for a detachable mechanical connection with the positioning assembly (31 ).

12. The apparatus according to one of the claims 1 to 1 1 , characterized in that the positioning assembly (31 ) is adapted to provide a translational movement of the workpiece (81 ) in at least two dimensions (60).

13. The apparatus according to one of the claims 1 to 12, characterized in that the positioning assembly (31 ) is adapted to provide a rotational movement of the workpiece (81 ) in at least one dimension (65, 66).

14. The apparatus according to one of claims 1 to 13, characterized in that the positioning assembly (31 ) is configured to provide a movement of the workpiece (81 ) and the laser assembly (4) is configured to simultaneously provide a movement of the laser beam (8).

15. The apparatus according to claim 14, characterized in that the positioning assembly (31 ) and the laser assembly (4) are configured such that the angle between the workpiece (81 ) surface and the direction in which the laser beam (8) is directed substantially remains unaltered during said simultaneous movement of the workpiece (81 ) and the laser beam (8).

1 6. The apparatus according to one of the claims 1 to 15, characterized in that the positioning assembly (31 ) comprises a plurality of kinematic chains (32, 33, 34), wherein each kinematic chain (32, 33, 34) is arranged in between a static base (38) and a movable part (79) comprising a support (63) for the workpiece

(81 ).

1 7. The apparatus according to claim 16, characterized in that the kinematic chains (32, 33, 34) extend in a lateral direction from the base (38).

18. The apparatus according to claim 1 6 or 17, characterized in that at least one kinematic chain (32, 33, 34) comprises a front arm (42, 43, 44) having at least two spaced parallel arm sections (51 , 52) pivotally secured to the movable part (79).

19. The apparatus according to claim 18, characterized in that the kinematic chain (32, 33, 34) comprises a rear portion (39, 40, 41 ) actuated by a motor, wherein the front arm (42, 43, 44) is pivotally secured to the rear portion (39, 40, 41 ).

20. The apparatus according to one of claims 1 to 19, characterized in that the laser assembly (4) is adapted to provide a translational movement of the laser beam (8) in at least two dimensions (30).

21 . The apparatus according to one of claims 1 to 20, characterized in that the laser assembly (4) is adapted to provide the laser beam (8) with an angle of incidence on said surface area (82) deviating at most 60° from the normal vector of said surface area (82) on the incidence position of substantially each spot area (84) on the incidence trajectory (83).

22. The apparatus according to one of claims 1 to 21 , characterized in that the laser assembly (4) comprises a beam shape converter (13) adapted to change the intensity profile of the laser beam (8) before it is directed to the incidence position.

23. The apparatus according to one of the claims 1 to 22, characterized in that the control unit is configured to adjust the output power of the laser beam (8) in order to provide the substantially constant energy density at substantially each spot area (84).

24. The apparatus according to one of the claims 1 to 23, characterized in that the control unit is configured to adjust the output power of the laser beam (8) when the angle of incidence of the laser beam (8) on said surface area (82) changes from the previous spot area (84) to the following spot area (84).

25. The apparatus according to one of claims 1 to 24, characterized in that the control unit is configured to operate the incidence position along the incidence trajectory (83) in such a way that adjacent spot areas (84) are overlapping.

26. The apparatus according to one of claims 1 to 25, characterized in that the control unit is configured with logic to determine the incidence trajectory (83) in dependence of at least one of geometrical and material properties of the workpiece (81 ).

27. The apparatus according to one of the claims 1 to 26, characterized in that the control unit is provided with a memory to store the incidence trajectory

(83) previously determined for a specific type of the workpiece (81 ).

28. A method for laser processing on a three-dimensional surface area (82) of a workpiece (81 ) comprising the step of

- directing a laser beam (8) to an incidence position on said surface area (82) such that the laser beam (8) comprises a spot area (84) within said surface area (82) ;

characterized by the step of

- providing a relative movement of the workpiece (81 ) with respect to the laser beam (8) along an incidence trajectory (83) such that the incidence position of the laser beam (8) is subsequently shifted from a previous spot area (84) to a following spot area (84) within said surface area (82), wherein a controlled energy density of the laser beam (8) is provided at substantially each spot area

(84) such that irregularities on said surface area (82) are reduced by the impact of the laser beam (8).

29. The method according to claim 28, characterized in that the relative movement along the incidence trajectory (83) produces an overlapping area (85) of adjacent spot areas (84).

30. The method according to claim 29, characterized in that the overlapping area (85) corresponds to at least 20%, more preferred at least 50%, of the size of the adjacent spot areas (84).

31 . The method according to one of the claims 28 to 30, characterized in that the angle of incidence of the laser beam (8) does not deviate by more than 60 ° from the normal vector of said surface area (82) on the incidence position of substantially each spot area (84) on the incidence trajectory (83).

32. The method according to one of the claims 28 to 31 , characterized in that the angle of incidence of the laser beam (8) deviates from the normal vector of said surface area (82) on the incidence position of at least one spot area (84) on the incidence trajectory (83).

33. The method according to one of the claims 28 to 32, characterized in that the relative movement of the workpiece (81 ) with respect to the laser beam (8) comprises a simultaneous movement of the workpiece (81 ) and the laser beam (8).

34. The method according to one of the claims 28 to 33, characterized in that the laser beam (8) produces a melted surface layer in each spot area (84), wherein the depth of the melted surface layer has a depth of at most 10 μητι.