Method for producing a vehicle tire

Abstract

The invention relates to a method for producing a vehicle tire, comprising the steps of providing an unprofiled green tire (1) and applying a tire profile (11) to the circumference by means of a laser (2), wherein the laser (2) is arranged in a stationary manner and is guided within a working area (21) in accordance with a section of the tire profile (11) in order to remove material from the green tire (1), wherein the entire circumference of the green tire (1) is divided into adjacent working areas (10) that can be covered by the working area (21), and all working areas (10) of the tire circumference are successively positioned in the working area (21) of the laser (2) and processed by the laser to remove material, wherein the processing of all working areas (10) of the tire circumference is repeated until the desired profile depth of the tire profile (11) is achieved in all working areas (10).wherein after each complete machining of all working fields (10) of the tire circumference, each working field (10) is displaced relative to the previously determined position by a predetermined amount and a predetermined direction and then the machining of the working fields (10) is carried out again.

Description

The invention relates to a method for producing a vehicle tire, comprising the steps of providing an unprofiled raw tire and introducing a tire profile on the circumferential side by means of a laser, wherein the laser is arranged in a fixed position and is guided within a working region in accordance with a cutout of the tire profile in order to remove material of the raw tire, wherein the entire circumference of the raw tire is divided into mutually adjacent working fields which can be covered by the working region and successively all working fields of the tire circumference are positioned in the working region of the laser and processed by the latter in a material-removing manner, wherein the processing of all working fields of the tire circumference is repeated until the desired profile depth of the tire profile is reached in all working fields.In the course of the development and testing of vehicle tires, it is necessary to create prototypes which are intended to have a construction which corresponds as exactly as possible to the later series tire and a configuration of the tire profile which corresponds as exactly as possible. Since the production method customary in series production using vulcanization molds having the tire profile in the negative is much too expensive for such prototype production, a method is frequently used for producing prototype tires, in which the desired profile is cut into an unprofiled raw tire (patch tire) by means of cutting blades, as has become known, for example, from DE 2238090 A1.In recent times, besides such a cutting of patch tires, processing by means of a laser is also considered, in which a tire is positioned under a laser using a handling robot, as is known, for example, from U.S. Pat. No. 4,564,737 A. However, the guidance of the laser is associated with great effort.EP 0 714 724 A2 discloses a method and a device for producing profiling, such as markings, inscriptions, patterns in vehicle tires, in which a laser assembly having an adjustable laser head and a control unit for generating targeted relative movements between the laser head and the vehicle tire are used. The introduction of a tire profile into the circumference of the processed vehicle tire is not described in this publication.A suitable laser processing station for circumferentially introducing a tyre profile into an unprofiled raw tyre comprises a stationary or stationary laser which can be guided, for example, by means of a suitable mirror optical system within a spatially limited working region in accordance with a section of the tyre profile. The green tyre, which is still unprofiled at the start of the machining, is positioned with a handling robot so as to guide the workpiece under the stationary laser, which now removes material layer by layer from the green tyre in accordance with the desired tyre profile. Since the laser has only a limited working range with respect to the entire circumference of the green tyre to be processed, the green tyre is divided into a plurality of working fields which adjoin one another and together enclose the complete circumference of the green tyre, each working field being dimensioned such that it can be covered by the working range of the laser. It is thus possible, by continuously repositioning the raw tire, to successively bring all the working fields successively into the working range of the laser and to process them in accordance with the desired tire profile. In this case, the entire circumference of the raw tire is processed multiple times, for example up to 60 times, completely over all working fields until the desired profile depth of the tire profile is reached. A usual machining depth in the working range of the laser is, for example, approximately 0.1 mm, so that a profile depth of 6 mm can be achieved with 60 machining operations.During the successive or successive machining of the work fields adjoining one another, it is to be ensured that the work fields do not overlap one another in order to avoid double machining with a corresponding increase in the machining depth. This has been ensured hitherto by leaving small boundary regions, so-called field boundaries, between the adjoining working fields, which boundary regions have not been processed by the laser. These field limits are shown in the completely lasered tire profile as webs which have previously had to be removed manually with great effort, since such a tire is otherwise not suitable for testing. The effort required for this purpose was about one to two days per tire, which seems to be in need of improvement. In addition, the visual impression of such a lasered tire is in particular highly improved for use as a measuring tire.It is an object of the invention to propose a method for producing a vehicle tire of the type mentioned at the beginning, which overcomes the disadvantages of the prior art and enables the processing of an unprofiled raw tire with a laser in mutually adjoining working fields without forming undesired field boundaries.To achieve the object set, according to the invention, a method according to the features of claim 1 is proposed.Advantageous embodiments and developments of the invention are the subject matter of the dependent claims.To achieve the object set, it is proposed according to the invention that after each complete machining of all working fields of the tire circumference, each working field is displaced from the previously defined position by a predetermined amount and a predetermined direction and then the machining of the working fields is carried out again, wherein the displacement and the re-execution of the machining are repeated until the desired profile depth of the tire profile is reached.By the displacement of all working fields in accordance with the invention with respect to the previously defined and processed position, the field boundaries are eliminated, since they are no longer located one above the other in the vertical projection, but are instead formed at always different positions in accordance with the displacement carried out, whereby the field boundaries quasi become blurred. A field limit remaining in the last machined layer is only a fraction of a millimeter high at the usual machining depths and can be neglected.According to one proposal of the invention, the work fields each have a substantially, preferably exactly rectangular circumference, and each work field is displaced along a diagonal through the work field and processed again. The amount and direction of the displacement is preferably selected to be the same for all working fields.If working fields come to lie partially outside the circumference of the vehicle tire in the edge region transversely to the circumferential direction of the vehicle tire, in particular during the gradual displacement per circumferential processing, the part of the working field no longer lying on the tire circumference is continued according to a proposal of the invention on the opposite circumferential edge of the vehicle tire, so that the entire outer circumference of the vehicle tire can always be processed and is wrapped with working fields.According to a further proposal of the invention, the amount or length by which each working field is displaced following complete processing of the circumference of the vehicle tire is dependent on the number of repetitions of the circumferential processing of all working fields on the vehicle tire. Accordingly, it is proposed that each working field is displaced through the working field by a factor of 1 / n, multiplied by the length of the diagonals, where n is the number of complete machinings of all working fields of the tire circumference carried out by the laser until the desired profile depth of the tire profile is reached. If, for example, the machining of all working fields of the tire circumference is carried out 60 times until the desired profile depth of the tire profile is reached, in order to arrive at an average machining depth of 0.1 mm to 6 mm profile depth, each working field is displaced by 1 / 60 of the length of the diagonals of the working fields after completion of a complete machining of all working fields of the tire circumference, in particular along the diagonal through the working field.As a result, a laser-machined vehicle tire provided with a tire tread is obtained, the field boundaries of which between the individual working fields are eliminated, so that no further work is required to remove the field boundaries. Also visually, the result obtained is much more homogeneous and for tire tests, for example with respect to aquaplaning properties, water can be displaced unimpeded via the lasered grooves or depressions in the tire tread.In order to achieve the desired machining depth per complete machining of a working field, for example the already mentioned 0.1 mm per complete machining, it is proposed according to a further proposal of the invention to operate the laser at a preset power at the beginning of the removal, i.e. preferably during the first complete machining of all working fields of the tire circumference. This power is selected by the skilled person to the effect that, taking into account the material combination prevailing in the raw tire, the desired machining depth can be expected under the application of the preset power to the laser, which is estimated in particular by adding empirically determined values. After a preset number of complete machining operations of all working fields of the tire circumference, for example after one to four complete machining operations and subsequent displacement of all working fields, the actually ablated profile depth is measured in at least one working field and compared with the predetermined setpoint value of the desired machining depth, wherein the power of the laser is increased or decreased accordingly in the event of deviations of the ablated and measured profile depth from the setpoint value.According to a further proposal of the invention, this increase or decrease in the power of the laser can be determined from a stored regression curve in which the machining depths are brought into a relationship with the laser power.In this way, the actually effected material removal can be determined directly with the method according to the invention as a function of the laser power, whereby the method according to the invention reliably adjusts to the desired machining depth per working step within a short time and the desired profile depth of the tire profile is achieved with the highest accuracy at the conclusion of the last machining.The measurement of the profile depth can be effected in particular with a three-dimensional depth sensor.The substantial advantage of the regulation of the laser power effected in this way is that even when multicompound layers are used in the initially still unprofiled raw tire, the material removal dependent on the laser power and the processing depth resulting therefrom are adjusted within a short time without additional tire pattern as a test reference on the actual workpiece, i.e. the raw tire to be processed, whereby further working time and costs are saved.Further embodiments and details of the method according to the invention are explained below with reference to an exemplary embodiment in the drawing. The following are shown: FIG. 1 shows a schematic side view of a green tyre processed by means of a laser; FIG. 2 shows the displacement according to the invention of a working field during several successive machining operations; FIG. 3 is a schematic view of two adjacently arranged work fields and their displacement during several successive machining operations; FIG. 4 shows a graphical representation of the material removal effected by the laser in a work field in a setpoint / actual comparison; FIG. 5 shows a regression curve of the material removal effected by the laser in a working field as a function of the laser power.FIG. 1 shows a greatly simplified schematic representation of the production of a tire prototype from an initially unprofiled green tire 1, which is processed in the region of its outer circumference by a laser 2 and a laser beam 20 emitted by the latter in a working region 21 accessible by the laser 2, in that material of the green tire 1 is evaporated at a processing depth proceeding from the outer circumference by the action of the laser beam 20 and is thus removed.The laser 2 is arranged in a fixed position and is capable, by means of optical devices, in particular lenses and mirrors, which are not shown in detail, of machining the spatially limited working region 21, which covers only a fraction of the entire outer surface of the green tyre 1 to be machined.In order nevertheless to ensure complete processing of the entire outer surface of the raw tyre 1, this outer periphery is virtually occupied by a multiplicity of directly adjoining working fields 10 or divided into these, which can be effected, for example, by appropriate software of a controller of the laser 2. An example of such a work field 10 is shown in FIG. 2.A rectangular shape of the working field 10 can be seen, wherein the size of the working field 10 is dimensioned such that it can be completely covered by the working region 21 of the laser 2. If the entire outer circumference or the outer surface of the green tire 1 is divided into a plurality of such directly adjoining work fields 10, a positioning device can position the green tire in each case in the work region 21 of the laser 2 in such a way that all the work fields 10 are successively processed by the laser 2 in a material-removing manner until complete processing of the entire tire circumference has taken place. In this way, the tire profile indicated in FIG. 2 by reference numeral 11 can be introduced in all working fields 10 from corresponding subsection in the individual working fields 10 into the initially unprofiled raw tire 1.However, within the scope of a single machining of all work fields 10, the desired machining depth is usually not achieved, which is required for producing the tire profile 11 at the desired profile depth of, for example, 6 mm. Accordingly, the machining of all work fields 10 is repeated several times until the desired profile depth is reached. With a usual machining depth of about 0.1 mm per operation, 60 successive machining operations of all the work fields 10 are consequently required until the desired profile depth is reached.As can be seen in particular from the illustration in FIG. 3, with continued unchanged positioning of the adjacent work fields 10 between the adjacent work fields 10, field boundaries would remain unprocessed, since the work areas 10 must not overlap. This would result in double machinings and correspondingly higher machining depths in the overlapping areas.Therefore, as can be seen from FIGS. 2 and 3, after each complete machining of all the work fields 10, a slight displacement of the work fields 10 from their previously machined position is carried out before the renewed machining of all the work fields 10 on the tire circumference of the raw tire 1 is carried out. In the exemplary embodiment shown, the displacement takes place along the diagonal running through the individual work fields 10 by an amount of 1 / n of the length of the diagonal, wherein n is the number of operations of all work fields 10 until the desired profile depth is reached.If, in this respect, for example, 60 complete machining operations are necessary in order to arrive at a profile depth of 6 mm at a machining depth of 0.1 mm per operation, each working field 10 is displaced in the direction of the diagonal of the working field 10 by 1 / 60 of the length of the diagonals of the working field 10 after completion of each complete machining of the tire circumference and of all working fields 10.As a result, this causes the field boundaries present between adjacent working fields 10 to become blurred, so that in the finished tire profile no longer webs along the field boundaries have to be removed manually or impair the visual appearance.It should be noted incidentally with respect to the illustration according to FIGS. 2 and 3 that adjacent work fields 10 can be arranged not only one above the other, as illustrated in FIG. 3, i.e. in the circumferential direction, but also transversely with respect to the circumferential direction of the green tyre 1.In order to achieve the desired machining depth per operation for forming the tire profile 11, the laser 2 is initially operated at a preset laser power at the beginning of the machining, which is determined empirically from a regression curve as a function of the material properties of the raw tire.After each or more complete machining operations of all working fields of the tire circumference, for example, a comparison of the machining depth actually achieved in at least one working field 10 with the expected machining depth is then carried out in the manner of a setpoint / actual comparison, and the laser power is correspondingly tracked, i.e. increased or decreased, if deviations of the actually achieved machining depth from the expected machining depth are detected.As is apparent from the graphical representation according to FIG. 4, in this way the actual machining depth or the measured removal 4 already converges after a few passes or complete machinings of all working fields 10 of the tire circumference and without significant over-oscillations with the set value specification or the expected removal 3.The regression curve shown in FIG. 5, which represents a polynomial function of 1stgrade, moreover shows the ablation interpolation 5, which results from the actually measured ablation, which is plotted in the form of individual measurement points 6 as a function of the applied laser power.The measurement of the actual ablation can be carried out, for example, with a three-dimensional depth sensor after each complete machining of all working fields 10 of the tire circumference. The more depth measurement points exist, the more characteristic the regression curve maps the material properties.As a result, the material removal is adjusted to the desired setpoint value within the shortest time due to the applied laser power. This is of great advantage in particular in the case of raw tires 1 made of different materials, for which no ablation information of the laser 2 is yet available.It is understood that the method explained above can be used not only in the introduction of profile depressions of a tire profile into a raw tire but also in other fields of application in which material removal is to take place on larger surfaces which are not completely covered by the field of operation of the laser.List of reference numbers:1 Raw tire 2 Laser 3 Expected removal (target value) 4 Measured removal (actual value) 5 Removal interpolation 6 Measured removal 10 Working field 11 Tire profile 20 Laser beam 21 Working regionReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 2238090 A1

[0002] U.S. Pat. No. 4,564,737 A

[0003] EP 0 714 724 A2

[0004]

Claims

Method for producing a vehicle tyre, comprising the steps of providing an unprofiled green tyre (1) and introducing a tyre profile (11) on the circumferential side by means of a laser (2), wherein the laser (2) is arranged in a fixed position and is guided within a working region (21) in accordance with a cutout of the tyre profile (11) in order to remove material of the green tyre (1), wherein the entire circumference of the green tyre (1) is divided into mutually adjoining working fields (10), which can be covered by the working region (21) and successively all working fields (10) of the tyre circumference are positioned in the working region (21) of the laser (2) and processed by said working region in a material-removing manner, wherein the processing of all working fields (10) of the tyre circumference is repeated as many times as possible, A method for the production of a desired tread depth of the tyre tread (11) in all working fields (10), characterised in that after each complete machining of all working fields (10) of the tyre periphery, each working field (10) is displaced relative to the previously defined position by a predetermined amount and a predetermined direction and then the machining of the working fields (10) is carried out again.Method according to claim 1, characterised in that the work fields (10) have a substantially rectangular periphery and each work field (10) is displaced along a diagonal through the work field (10) and is processed again.Method according to Claim 1 or 2, characterized in that each working field (10) is displaced through the working field (10) by an amount of 1 / n of the length of the diagonals, wherein n is the number of repetitions of the complete machining of all working fields (10) of the tyre circumference carried out by the laser (2) until the desired profile depth of the tyre profile (11) is reached.Method according to one of Claims 1 to 3, characterized in that, at the start of the removal, the laser (2) is operated with a preset power and, after a preset number of complete machining operations of all working fields (10) of the tyre circumference, the removed profile depth is measured in at least one working field (10) and compared with a predefined setpoint value, wherein, in the event of deviations of the removed profile depth from the setpoint value, the power of the laser (2) is increased or decreased accordingly.Method according to Claim 4, characterized in that the increase or decrease in the power of the laser (2) is determined from a stored regression curve.Method according to one of claims 4 or 5, characterised in that the measurement of the profile depth is effected with a three-dimensional depth sensor.

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