METHOD AND ARRANGEMENT FOR HIGH-ACCURATE CALIBRATION OF PARALLEL CINEMATICS

Description

[0001] The invention relates to a method and an arrangement for the high-precision calibration of a parallel kinematic system.

[0002] So-called parallel kinematics, especially hexapods, also known as Stewart platforms, are used, among other things, for the high-precision positioning of parts in production processes, and their range of applications has expanded dramatically in recent years. Newly developed application areas, such as semiconductor technology and the manufacturing of integrated circuits, demand the highest accuracy. At the same time, these applications are also subject to intense cost pressure, so that the option of consistently high-precision manufacturing of the individual components of the parallel kinematics is ruled out for cost reasons.

[0003] For materials used in the construction of ultra-precise mechanisms, it is particularly advantageous if they have a very low coefficient of thermal expansion, such as ceramics. However, these materials require complex machining. It must be taken into account that the machine tools used for machining them have a significantly higher coefficient of thermal expansion, and the resulting ceramic bodies exhibit length errors due to the vastly different thermal expansion, which is why they require subsequent calibration.

[0004] There are several approaches to improving the accuracy of parallel kinematics assembled from parts manufactured with moderate accuracy. For further information, see: https: / / www.uni-due.de / mechatronik / forschung / pkm.de, "PKM-Parallelkinematikmaschinen", Parallel Robots: Open Problems, Jean-Pierre Merlet INRIA, BP 93, 06902 Sophia-Antipolis, France, E-mail: Jean-Pierre.Merlet@sophia.inria.fr and Gottlieb, J.: Non-parametric Calibration of a Stewart Platform, in: Proceedings of 2014, Workshop on Fundamental Issues and Future Research Directions for Parallel Mechanisms and Manipulators, July 7-8, 2014, Tianjin, China.

[0005] A method according to the preamble of claim 1 is known from WO 99 / 28097 A1, JP 2010 207 967 A, EP 1 698 954 A1 and GB 2 505 558 A. Similar methods are also disclosed in DE 100 27 106 A1 and DE 198 58 154 A1.

[0006] The invention is based on the objective of providing an alternative and cost-efficient method and a corresponding arrangement for the high-precision calibration of parallel kinematics.

[0007] This problem is solved in its method aspect by a method with the features of claim 1 and in its apparatus aspect by an arrangement with the features of claim 7. Advantageous developments of the inventive concept are the subject of the respective dependent claims.

[0008] The invention aims to increase the accuracy of a parallel kinematic system manufactured and assembled to standard precision requirements by referencing it to a reference body. The reference body is a rigid body with highly precisely defined parameters, i.e., parameters determined during manufacturing or measured using metrology.

[0009] The geometric parameters are measured and manufactured with considerable effort and correspondingly high costs. However, its suitability and use for calibrating a large number of parallel kinematic systems ensures a reasonable distribution of its manufacturing costs and thus enables the cost-effective provision of correspondingly highly calibrated parallel kinematic products. Reference bodies are known in large numbers and for various applications, but to the inventors' knowledge, none have yet been used to solve the existing problem, particularly not in the configurations and methods described here.

[0010] A further aspect of the invention is that the position of the parts of the parallel kinematics or an outer contour spanned by them can be optimally adjusted to the reference body by adjusting adjustable parts.

[0011] The reference body is adapted. Finally, the invention includes the idea that the associated adjustment parameters of the adjusted part or parts are stored as zero-state product parameters of the parallel kinematics.

[0012] Specifically, the parallel kinematic system is a hexapod comprising six adjustable legs arranged on an optional base and a platform supported by the legs. The base (or base plate) can be an integral part of the hexapod, meaning its legs can be attached to the base. However, the invention is also applicable to a hexapod whose legs rest on a high-precision external base without being connected to it. In principle, the proposed method is also applicable to other types of parallel kinematic systems with extremely high accuracy requirements.

[0013] During the execution of the process, highly precise engagement elements are created or attached to the platform and / or the base. These elements are designed to engage with calibration reference elements provided on the reference body. The engagement elements are brought into contact with the calibration reference elements by adjusting the legs, and the leg adjustment parameters are stored as zero-state product parameters.

[0014] In one embodiment, the engagement elements are sleeve-shaped and the calibration reference elements are pin-shaped, adapted to the dimensions of the sleeves. Alternatively, the reverse is true: calibration reference elements are sleeve-shaped and engagement elements have a pin shape adapted to the dimensions of the sleeves. In the embodiments outlined below, sleeve-shaped engagement elements are also referred to as calibration sleeves, and these, in an identical design, also serve for the precise positioning of various components relative to each other during the assembly of the hexapod.

[0015] The aforementioned shapes, namely sleeve and pin shapes, are merely exemplary and, from the current perspective, advantageous geometric embodiments of the engagement elements and the calibration reference elements; other shapes, such as truncated cone, prism, or pyramid shapes and corresponding complementary shapes for the engagement elements or the calibration reference elements, are equally possible. In a further embodiment of the invention, the reference body has the shape of a right prism with a base having several vertices. This base is simultaneously a lower end face of the prism, and an upper end face of the prism, which is arranged parallel to the lower end face, has a shape identical to the lower end face.A first plurality of calibration reference elements is provided on one of the end faces of the prism and a second plurality of calibration reference elements is provided on the other end face of the prism, wherein during or within the calibration process the first plurality of calibration reference elements is brought into engagement with the platform and the second plurality of calibration reference elements with the base or a calibration support of the hexapod.

[0016] In particular, a reference body in the shape of a triangular prism with a triangular base and a calibration reference element at each corner of its two end faces appears suitable. However, reference bodies with bases having more than three corners or with curved edges can also be used. It is not essential that the reference body be in the shape of a prism. Furthermore, the arrangement of the calibration reference elements on parallel end faces of a reference body is not mandatory, as alternative arrangements, such as lateral or side face arrangements, are also possible.

[0017] In a version adapted to the prismatic reference body, the platform and / or the base of the hexapod has an opening adapted to the shape of the reference body's base. For calibration, the reference body is inserted through this opening into the leg section of the hexapod located between the platform and the base, and removed again after calibration. This design is also possible with a non-prismatic reference body, provided the contour of the opening corresponds to the largest circumference of the reference body, i.e., is slightly larger. In parallel kinematic systems that do not have the characteristics of a hexapod and where there is sufficient space between the legs or struts for laterally inserting a reference body, the aforementioned opening can be omitted.

[0018] As an alternative to the method described above, which can be simplified as calibration with an internal reference body, the method can also be carried out with an external reference body. Such a method is characterized by the fact that the platform and the base of the hexapod have a polygonal shape, the reference body has a continuous or upper and lower cutout adapted to the shape of the platform or base, and the hexapod is calibrated by the

[0019] The reference body is inserted through a breakthrough or breakthroughs and removed from it after calibration. Specifically, a first and second plurality of calibration reference elements are provided on the parallel upper and lower end faces of the reference body, wherein during or within the calibration process the first plurality of calibration reference elements engages with the platform and the second plurality of calibration reference elements engages with the base or a calibration support of the hexapod.

[0020] The latter alternative may offer the designer greater design freedom. Furthermore, it is not limited to hexapods with polygonal platforms or bases, but can also be used – by employing a reference body with appropriately adapted continuous or upper and lower cutouts or protrusions, or cutouts and / or protrusions on the base and / or platform of the hexapod – for parallel kinematics with entirely differently shaped platforms or bases.

[0021] According to the invention, the engagement elements on the platform are generated and positioned with high precision using a platform master template. This represents an important step in increasing the accuracy of parallel kinematics, since the platform and base, with all their kinematically relevant geometric parameters, are difficult and costly to manufacture with high relative accuracy.

[0022] If individual parts of the hexapod are made of ceramic or a similar material, the use of master templates and / or a ceramic reference body would be advantageous for the calibration process.

[0023] The master template(s) must be manufactured with high precision. If the desired accuracy is not achievable during its manufacture, the coordinates of reference elements supported by the master template(s) will be measured with high precision. An orientation blind hole serves to distinguish the individual reference elements and also defines the orientation of the master template(s) relative to the orientation blind holes on the base or platform.

[0024] For hexapods with an integrated base, a base master template is used to generate and precisely position the engagement elements on the base. If the platform (gondola) and base have identical geometry and dimensions, the same master template can be used for both.

[0025] With regard to the exemplary embodiments outlined below, a distinction must be made between two identical types of engagement elements: The first type of engagement element serves to align the hexapod for defining the zero-state product parameters. The calibration reference elements of the reference body engage with these engagement elements.

[0026] The second type of engagement element serves to position the so-called pedestals of adjustable struts (hereinafter referred to as strut pedestals). Pins, such as dowel pins, located on the strut pedestals, engage with these engagement elements. The positioning of the strut pedestals indirectly defines the coordinates of the ball joints. The coordinates of the strut pedestals and the ball joints are geometric parameters of a hexapod that define its kinematics and are predetermined by its design. The accuracy of the positioning therefore significantly determines the accuracy of the hexapod. However, with a different parallel kinematic design or a different definition of the hexapod's geometric parameters, the engagement elements of the second type can also be placed at other design-relevant reference points on the platform or base.

[0027] In the aforementioned configuration, it is advantageous to select the shape of the reference elements on the master template(s) to match the shape of the engagement elements of the platform, the base, or a comparable element of the parallel kinematics, and thus in turn to correspond with the calibration reference elements on the reference body. In particular, pin-shaped reference elements are provided for sleeve-shaped engagement elements, or conversely, sleeve-shaped reference elements are provided for the platform master template.

[0028] In a further embodiment of the method, the engagement elements are fixed by inserting and bonding sleeves or pins into pre-drilled holes in the platform or base that are larger than the sleeves or pins. In principle, in addition to adhesives, cement, or possibly a soft solder or similar proven materials for bonding parts are also suitable. During the bonding process, the position of the sleeves or pins is defined by a master template.

[0029] The apparatus aspects of the invention largely arise from the aforementioned process aspects, so they will not be fully elaborated upon here. However, it should be noted that the proposed arrangement includes at least the aforementioned reference body, in one embodiment additionally the master template(s) already mentioned, and in a further embodiment also a device for introducing a means for the material-bonded fixation of the high-precision engagement elements in bores of the platform or base, in particular an adhesive injection device.

[0030] The advantages and expediencies of the invention will become apparent from the following description of exemplary embodiments with reference to the figures. These show: Figs. 1-9 show different views of a hexapod as an example of a parallel kinematic system to which the proposed method can be applied; Figs. 10-19 show different views of a platform or a corresponding base of the hexapod according to [the proposed method]. Figs. 1-9 Figs. 20-22: Top view, side view, and bottom view of a platform master template; Figs. 23-28: Views of calibration sleeves as an example of engagement elements to be attached to the platform (or base); Figs. 29-37: Views of the so-called strut pedestals, with which the struts of the hexapod are attached to the platform and the base; Figs. 38-46: Views of the fully assembled base (strut support) of the hexapod. Figs. 1-9 Figs. 47-55: Views of an exemplary reference body in the form of a triangular prism with calibration reference elements on both end faces. Figs. 56-64: Illustrations explaining the design of the calibration reference elements. Figs. 65-73: Views of the hexapod according to... Figs. 1-9with reference body inserted during calibration, Figs. 74 and 75 synoptic representations to illustrate the two phases of an exemplary calibration process, Figs. 76 and 77 a perspective view or side view of another example of a hexapod, Figs. 78 to 86 various views of a hexapod used for calibration according to Figs. 76 and 77 adapted reference body Fig. 87 a representation showing the hexapod according to Figs. 76 and 77 with the reference body pushed over it.

[0031] The following example of a hexapod illustrates the method for increasing accuracy in parallel kinematics.

[0032] In Figs. 1 to 9The illustrations show a hexapod suitable for calibration according to the invention with a reference body and master templates. To highlight the essential features, cables, cable connections, and the drive motors inside the struts are not shown, while the ball joints of the legs are only indicated; the length adjustability of the struts is not apparent.

[0033] In Fig. 1 The platform (gondola) 1 to be moved or adjusted and the base 2 are shown. Fig. 3 The struts 3, 4, 5, 6, 7, and 8 are shown, which, through their change in length of gondola 1, create a pose. A pose is the description of the position of a rigid body in space. It refers to a freely selectable pivot point and quantitatively defines the rotation of the rigid body around this pivot point, as well as the spatial displacement of this pivot point. Fig. 4The strut platforms 9, 10, 11, 12, 13, and 14 of base 2 are shown. A strut with its two associated strut platforms is called a leg. In Fig. 9 The strut platforms 15, 16, 17, 18, 19 and 20 of gondola 1 are illustrated.

[0034] In this embodiment, without loss of generality, the base and the movable platform are constructed identically. The basic body of the base 2 and the gondola 1, i.e., the unmounted and freestanding individual body of the base 2 and the gondola 1, is hereinafter also referred to as the plate. Construction of the two identical plates

[0035] In Figs. 10 to 19 is a plate depicted in its projections; in Fig. 19 The plate is marked with the number 100.

[0036] In Fig. 19 are blind holes 102-107 for receiving intervention elements in the form of calibration sleeves (see Figs. 23-28) shown. The calibration sleeves serve as docking points for a reference body and allow the correct leg lengths to be determined in the initialization pose. In Fig. 19 Blind holes 108-119 are also shown. These blind holes also serve to accommodate engagement elements in the form of calibration sleeves, with the corresponding calibration sleeves being provided for defining the position of the strut platforms. All blind holes in the plates used for calibration have the same depth and diameter. Fig. 19 Holes 120-131 with internal threads are also shown. These are used to screw the strut platforms in place. Fig. 19An orientation notch 101 is also shown. This orientation notch 101 serves solely to break the symmetries with respect to rotation, in order to ensure a defined orientation of the plates relative to each other during assembly of the hexapod and a defined orientation of the hexapod when the reference body, which also breaks its symmetry, engages. To break the symmetry of the reference body 300 to be used according to Fig. 47 An orientation blind hole 301, located on the top side of the reference body 300, serves this purpose. The underside of the reference body 300 according to Fig. 47 It does not have such an orientation blind hole. Defined orientations are also required if the master templates and / or the reference body cannot be manufactured with the desired accuracy as mentioned below and therefore need to be measured.

[0037] In Fig. 19A triangular mounting opening 132 is also shown. It allows the prism-shaped reference body to be used to be positioned according to Fig. 47 to bring it inside the hexapod for adjustment. The triangle of the mounting opening is isosceles. Design and manufacture of the master template(s)

[0038] Fig. 20 shows a master template 200 for highly accurate positioning of the calibration sleeves in the plates from above, Fig. 21 from the side, and Fig. 22 The image shows the master template from below; its underside is unmachined. The basic body of the master template is a circular disc with a diameter identical to that of the plate.

[0039] Reference elements in the form of reference cylinders 202 to 219 protrude from the master template for the precise determination of the position of the calibration sleeves in the plates 100 according to Figs. 10-18These reference cylinders are precisely shaped and are all intended to protrude from the circular disk by the same predetermined length. If the side of the circular disk from which the reference cylinders protrude can be manufactured extremely flat, this flat surface can be used as a reference plane for the protrusion of the reference cylinders. Otherwise, the end faces of all reference cylinders should lie on an imaginary plane that is as parallel as possible to the surface of the circular disk.

[0040] The master template also has an orientation hole 201. This orientation hole 201 serves only to break the symmetry with respect to a rotation and makes it possible to orient the master template and the plate relative to each other in a defined way.

[0041] The master template(s) is / are a highly precise artifact. This artifact is / are produced only once. The necessary expertise to produce such artifacts lies with standards institutes such as the PTB.

[0042] If technically feasible and cost-effective, each reference cylinder is positioned within the required accuracy, without deviation from the design specifications. It is not essential that the positioning be highly precise relative to the disk; what matters is that the coordinates of the centers of the reference cylinder end faces are positioned with high accuracy relative to each other. For clarification, a slight displacement and / or rotation affecting all reference cylinders in the same way with respect to the supporting disk is acceptable.

[0043] If it proves impossible or too costly to position all reference cylinders precisely against each other in the desired manner, the reference cylinders are positioned as precisely as possible relative to each other, but the position of the reference cylinders relative to each other is then measured with high accuracy. Preparing the master template for the impression

[0044] The calibration sleeves are placed onto the 18 reference cylinders of the master template. The bases of the calibration sleeves rest on the circular disc of the cylinder caps. The edges of the calibration sleeves do not touch the surface of the master template, as the depth of the calibration sleeves is less than the length of the cylinders. Preparing the plates

[0045] The calibration sleeves are glued into the blind holes. For this purpose, the blind holes are filled with a defined amount of glue, but in such a small amount that no glue will ooze over the edge of the calibration sleeves.

[0046] If two or three calibration sleeves are later used to position another mechanical part during the assembly of a hexapod, then at most one of these calibration sleeves should be bonded with a hard adhesive such as cement or a hardening resin. The other calibration sleeves, on the other hand, should be attached with a slightly elastic adhesive that retains some deformability under pressure. This is particularly important because of the small tolerances of the calibration sleeves on the calibration reference elements of the reference body. It is crucial to prevent dimensional deviations and thermal expansion from interlocking all calibration sleeves and reference cylinders, and thus from preventing the zero-state product parameters from being set. Furthermore, it is essential to prevent dimensional deviations and thermal expansion from making assembly of the hexapod impossible.Furthermore, slightly elastic adhesives can be used that allow for complete curing.

[0047] Alternatively, assembly may also be possible without the use of an elastic adhesive by achieving a fit through different, suitable temperature control of the individual components.

[0048] Since the plate and master template each have an orientation blind hole, which breaks the symmetry with respect to the rotation, it can be clearly defined which blind holes are treated with which adhesive. Impression of the master template into the plates

[0049] The master template and plate are now fitted together, taking care to align the orientation holes. The circular disc surfaces should lie flat and flush against each other. The parts can be separated once the adhesive has cured. Assembly of the strut platforms

[0050] In the application example, for the sake of simplicity and clarity, the legs consist of three parts: two strut platforms and the strut itself, which varies in length.

[0051] The strut platforms are first attached to the plates, then later the struts themselves are attached to the balls of the strut platforms, the balls being part of a ball joint. A strut platform 9 with bores 9.1-9.4 and a ball joint part 9.5, 9.6 for engaging a (not shown) ball joint cup of a strut is shown in Figs. 29 to 37 depicted.

[0052] The in Fig. 30The strut platform 9 shown has two blind holes 9.1 and 9.2, each accommodating a dowel pin. The dowel pins are cylindrical in shape. Two dowel pins are required for the defined alignment of a strut platform. During adjustment and assembly, one end of each dowel pin is inserted into a blind hole in the strut platform, while the other end is inserted into the hole of the corresponding calibration sleeve, which is glued into the base plate. The dowel pins are therefore cylindrical pins that align the blind holes and calibration sleeves laterally with each other.

[0053] Since the strut platforms are geometrically small in relation to the dimensions of the entire hexapod, this embodiment assumes that the strut platforms can be manufactured with high precision using conventional methods. The required relative accuracies in the manufacturing of these parts are relative to the size of the entire hexapod and increase accordingly. Alternatively, the strut platforms can be manufactured in a manner analogous to the construction of the plates. This involves providing blind holes in both the strut platforms and the plates, into which calibration sleeves are glued using a further, specially manufactured master template. The sphere is then positioned in a similar manner relative to these sleeves.

[0054] The positioning of the spheres on the strut platforms can be achieved using calibration sleeves and dowel pins. The strut platform has one calibration sleeve, the cylinder supporting the sphere has two calibration sleeves, and the sphere itself has one calibration sleeve. The sphere's position can then be defined laterally using two dowel pins. The positioning of the calibration sleeves on the calibration platform, the cylinder supporting the sphere, and the sphere itself can be achieved using special master templates. A high-performance adhesive can be used to attach the cylinder to the strut platform and the sphere to the cylinder.

[0055] After inserting the dowel pins into the strut bases, the strut bases are screwed to the plate. Two holes, 9.3 and 9.4, are provided in the strut base 9 for the screws to pass through.

[0056] The mounting method described above does not define an exact installation height for the strut platforms, as their bases rest flat on the plate. Without loss of generality, this simplified approach is used in the present embodiment. This simplified procedure is also a recommended practical approach, as the plates are later aligned with the reference body. An error analysis reveals that errors in the height of the strut platforms result in a lower-order error, since the leg lengths are defined by zero-state product parameters with the reference body. The residual error affecting the accuracy of the poses arises because, due to the height error, the legs have a slightly different kinematic configuration than specified in the design. This effect of the error decreases the smaller the design-specified distance of the spheres to the surface of the plate.

[0057] The dowel pins mentioned for aligning the strut platforms are circular cylinders of the appropriate size; a corresponding construction drawing has been omitted from the figures.

[0058] The plates with all the fully assembled strut platforms are called strut supports. The hexagonal heads of the machine screws are visible in... Fig. 38 .

[0059] A strut support is in Figs. 38 to 46 shown. Preparations for inserting the reference body

[0060] If the hexapod's struts do not have absolute sensors, they must first be referenced. To do this, they are deflected into a position where a reference switch is activated, and the incremental length sensor is zeroed. After this zeroing, the corresponding strut lengths can be obtained by reading the strut's incremental length sensor. Referencing is not necessary for struts equipped with absolute sensors.

[0061] The gondola is then moved upwards to allow the reference body to be inserted into the interior of the hexapod. The mounting opening is provided for this purpose. Structure of the reference body

[0062] An exemplary reference body 300 is in Figs. 47 to 55 shown.

[0063] Reference solid 300 has the shape of a right prism with three vertices. Its base has the shape of an isosceles triangle. The side length of this triangle is chosen to be slightly smaller than that in Fig. 19 The triangular mounting opening 132 shown. This allows the reference body 300 to be inserted through the mounting opening 132.

[0064] Protruding from the prism are six identically constructed calibration reference elements in the form of calibration pins. These are shaped like circular cylinders, each with a base, hereinafter referred to as calibration pin bases. The diameter of the circular cylinders is dimensioned so that they fit precisely into the calibration sleeves.

[0065] The height of the prism-shaped base is the vertical difference between the upper and lower leg endpoints, reduced by twice the base height. It is assumed here that in the initialization pose, all upper and lower leg endpoints lie in the same plane, with these two planes being parallel to each other. For clarification, the essential geometric parameters of a hexapod can be simplified and defined by the coordinates of these 12 leg endpoints. The upper and lower leg endpoints are rigidly connected, and these points are kinematically relevant because they contain ball-and-socket joints or universal joints. The coordinates of these joints are also defined—indirectly—by the leg endpoints.

[0066] A calibration pin base has the same outer diameter as the corresponding calibration sleeve. If a calibration pin is flush with its calibration sleeve, meaning the calibration pin base rests on the edge of the calibration sleeve, then the coordinates of the calibration sleeve define a set of three Cartesian coordinates on which the calibration pins are positioned.

[0067] The prism surface is located due to the calibration pin base, which is particularly noticeable in Fig. 61 , never on the surface of the circular disc of the strut support.

[0068] In Figs. 56 to 64 A calibration pen is shown. It is simplified here and attached to a cube, and, as an example, fixed in a blind hole by gluing.

[0069] The reference body must be manufactured with high precision, as its accuracy is reflected in the accuracy of the alignment in the hexapod's initialization pose. If the desired accuracy is not achievable in its manufacture, the coordinates of the calibration pins are measured with high precision. The orientation blind hole 301 serves to distinguish the individual calibration pins. Fig. 47 . Fitting the reference body and the subsequent adjustment

[0070] The reference body enters through the triangular mounting opening 132. Fig. 19 into the interior of the hexapod to be calibrated. The three lower calibration pins of the reference body are inserted into the corresponding calibration sleeves of the base. It should be noted that the reference body 300 has an orientation blind hole 301 to break the symmetry, as do the base and the platform (reference numeral 101 in Fig. 19 The reference body is therefore inserted in a defined manner.

[0071] The hexapod with the inserted reference body is in the Figures 65 to 73 shown. The reference body is positioned opposite both triangular mounting holes in Fig. 19 rotated by 30°.

[0072] The hexapod is now brought into a de-energized and therefore manually movable state; then the gondola is moved in such a way that the calibration pins engage in the upper calibration sleeves.

[0073] Once this is done, the strut lengths are read and recorded according to the hexapod's serial number. When these strut lengths are later commanded, the hexapod will be in precisely this defined position.

[0074] After the strut lengths have been read out, the gondola is moved upwards, and the reference body can be removed.

[0075] After this calibration process, the strut lengths to be commanded are known, which belong to the initialization pose defined in this way.

[0076] If the reference body or master template was manufactured in such a way that relevant manufacturing deviations occurred after its production, the geometric parameters of the reference body or master template(s) are converted in such a way that the actual geometric parameters of the hexapod are obtained, in particular those of all engagement elements. Thus, all actual geometric parameters of the hexapod are known, and the hexapod is calibrated.

[0077] The geometric parameters of the hexapod, known or defined through calibration, are used as a model for the kinematic control of the hexapod. Calibration references to poses of a world coordinate system

[0078] Following the calibration process described above, the actual geometric parameters of the hexapod correspond to the geometric parameters intended by the design; the hexapod is therefore error-free within the error limits, or at least its actual geometric parameters are known, since they can be calculated from the actual geometric parameters of the master template(s) and the reference body. This also applies to the position of those engagement elements into which the calibration reference elements engaged.

[0079] If the hexapod is standing on an uneven surface, or if the disc-shaped plates are not ideally shaped, then the measured poses are affected by these factors. This is because pose measurements are usually based on probing the gondola or a body attached to it in relation to an external coordinate system that has no connection to the kinematically relevant geometric parameters of the hexapod.

[0080] Ultimately, the goal is to position a so-called Tool Center Point (TCP). TCP refers to the coordinates and orientation of that part of a kinematic system for whose positioning and movement the kinematic system is designed, and for whose precise coordinates and orientation the calibration measures are aimed.

[0081] To establish a true relationship between the TCP's poses and a world coordinate system, the calibration sleeves that served as the reference body's interface remain accessible. Their coordinates are defined by the geometric parameters of the master template(s) and the geometric parameters of the reference body. To achieve highly accurate positioning with the hexapod, the coordinates of these calibration sleeves must be referenced to the world coordinate system. Alternatively, the coordinates of the gondola's calibration sleeves can also be referenced to the world coordinate system if the hexapod is calibrated and in its initialization pose. The position of a TCP itself is referenced to the position of the gondola's calibration sleeves that served as the interface for the reference body.

[0082] Deviations in secondary geometric parameters, such as a lack of shape fidelity of the plates, then no longer play a role.

[0083] Fig. 74and 75 Figure 1 summarizes Phase I and Phase II of the proposed method for the embodiment described above and schematically shows the arrangement components used. It should be noted that both illustrations are purely schematic and not to scale.

[0084] In Fig. 74The figure shows that, as a first step S1, a prefabricated plate 100 of a hexapod is provided using standard manufacturing processes and with the inherent accuracy of these processes. This plate has blind holes for attaching the calibration sleeves or engagement elements (not specifically designated here) with a slightly enlarged diameter. In step S2, the platform master template 200, described in more detail above, is provided, and in step S3, calibration sleeves suitable for the reference cylinders of the master template are provided. In step S4, the calibration sleeves are attached to the reference cylinders.

[0085] In step S5, adhesive is injected into the blind holes using an adhesive injection device 400 to fix the calibration sleeves in the blind bores in the exact orientation specified by the master template. Then, in step S6, the master template 200 is aligned with the underside of the plate 100 so that the reference cylinders of the master template, with the sleeves attached, are seated in the corresponding blind holes of the plate 100. The adhesive must then be allowed to cure.

[0086] In step S7, the strut platforms 9 are provided for attaching the struts and fitted with dowel pins, and in step S8, the dowel pins arranged in the strut platforms are inserted into the calibration sleeves or engagement elements of the plate, and then the strut platforms are screwed to the plate 100, thus producing a platform (gondola) 1 or base 2 with high accuracy.

[0087] Next comes the assembly of the struts. Here, attention must be paid to the orientation of the base and the platform using the orientation holes.

[0088] Fig. 75 shows that in step S9 a complete hexapod is formed according to Figs. 1-9The reference body 300 is provided in a pre-assembled state. In step S10, a reference body 300 is provided, and in step S11, the reference body 300 is inserted through the opening 132 of platform 1 of the hexapod into its interior and rotated there until its calibration reference elements are positioned close to three (not visible here) calibration sleeves on platform 1 on one side and base 2 on the other. The orientation of the reference body relative to the hexapod must be observed, with the orientations being distinguishable by the orientation blind holes.

[0089] After deactivating the motorized adjustment mechanism of the hexapod's struts, the struts are adjusted manually—or by a designated external adjustment mechanism—so that the calibration reference elements of the reference body 300 engage with the calibration sleeves on the platform and base, which constitutes step S12 of the procedure. In step S13, a sensor device 500 records the corresponding adjustment parameters of the legs, and in step S14, these are stored as zero-state product parameters of the specific product for its use.

[0090] Figs. 76 to 87 In various views to illustrate a further embodiment of the method according to the invention, a further hexapod is shown, which has a platform (gondola) 871 and base 872 shaped differently compared to the first embodiment above (see Fig. 87The platform 871 and the base 872 are hexagonal in shape and, unlike the first embodiment, have no opening. The structure is otherwise identical to the hexapod described above, so it will not be explained again here.

[0091] To calibrate such a hexapod, an "external" reference body is used, which corresponds to reference body 300 according to Fig. 47 with number 300' (see Fig. 86) is designated. In a manner somewhat reversed of the procedure described above, in the associated method the hexapod (from below or above) is inserted through the openings 303, 304 in the upper plate 310 and lower plate 320 of the reference body, which are adapted to the basic shape of the platform 871 and the base 872 of the hexapod. Subsequently, to perform the calibration, the hexapod is slightly rotated within the reference body, which is located on the outside here, and then pushed apart until the corresponding calibration sleeves of the hexapod (not separately designated) and the calibration reference elements of the reference body engage. For further details of this process step, reference is made to the above explanations of the first embodiment.

[0092] In Fig. 76 Three intervention elements or calibration sleeves 761, 762, and 763 of the base 872 are visible in this perspective.

[0093] The implementation of the invention is not limited to these examples, but is also possible in a multitude of variations that are within the scope of professional practice.

Claims

1. Method for high-precision calibration of a parallel kinematic mechanism comprising several parts, at least one of which is movable and adjustable with defined adjustment parameters, wherein the position of the parts or an outer contour defined by them is determined by means of a reference body manufactured or measured with high precision (300) manufactured or measured with high precision, and the associated adjustment parameters of the or each adjusted part are stored as zero-state product parameters of the parallel kinematics, wherein the parallel kinematics is a hexapod comprising six legs (3-8) arranged, in particular attached, on an optional base (2) and a platform (1) carried by the legs, wherein high-precision engagement elements (761, 762, 763) are produced or attached to the platform and / or the base of the hexapod, which are designed to engage calibration reference elements provided on the reference body, the engagement elements are brought into engagement with the calibration reference elements by adjusting the legs, and the adjustment parameters of the legs are stored as zero-state product parameters, characterized in that the high-precision engagement elements are generated on the platform and / or the base by means of a master template (200) which has reference elements for both the engagement elements and the articulation points of the legs of the hexapod, and the positions of both the engagement elements for calibration and the articulation points of the legs are determined by means of the reference elements of the master template, wherein, in particular, in the case of sleeve-shaped engagement elements, pin-shaped reference elements are provided in the master template, and in the case of pin-shaped engagement elements, sleeve-shaped reference elements are provided in the master template.

2. Method according to claim 1, wherein the engagement elements are sleeve-shaped and the calibration reference elements are pin-shaped, adapted to the dimensions of the sleeves, or vice versa.

3. Method according to claim 1 or 2, wherein the reference body has the shape of a straight prism, the platform and / or the base of the hexapod has / have an opening adapted to the shape of the base surface of the reference body and, in particular, a first and second plurality of calibration reference elements are provided on the parallel upper and lower end faces of the reference body, wherein during the calibration process the first plurality of calibration reference elements are provided with the platform and the second plurality of calibration reference elements are provided with the base of the hexapod, and wherein during the calibration process the first plurality of calibration reference elements are provided with the platform and the second plurality of calibration reference elements are provided with the base of the hexapod.reference elements are provided on the parallel upper and lower end faces of the reference body, wherein during the calibration process the first plurality of calibration reference elements is brought into engagement with the platform and the second plurality of calibration reference elements is brought into engagement with the base or with a calibration base of the hexapod, wherein the reference body is inserted into the leg area of the hexapod for calibration through the opening and is removed from it again after calibration.

4. Method according to claim 1 or 2, wherein the platform and the base of the hexapod have a polygonal basic shape, and the reference body has a continuous or an upper and lower cutout adapted to the basic shape of the platform and the base, and in particular a first and second plurality of calibration reference elements are provided on the parallel upper and lower end faces of the reference bodyreference elements are provided on the parallel upper and lower end faces of the reference body, wherein during the calibration process the first plurality of calibration reference elements is brought into engagement with the platform and the second plurality of calibration reference elements is brought into engagement with the base or with a calibration base of the hexapod, and the hexapod is inserted through the opening or openings in the reference body for calibration and removed from it again after calibration.

5. Method according to one of the preceding claims, wherein the engagement elements and / or the articulation points of the legs are fixed by inserting and mechanically securing, in particular gluing, sleeves or pins into prefabricated holes in the platform and / or the base that are larger than the sleeves or pins.

6. Method for manufacturing a parallel kinematic mechanism, wherein the parts are pre-assembled to form a basic parallel kinematic mechanism and the parallel kinematic mechanism is completed by applying the method according to one of the preceding claims.

7. Arrangement for carrying out the method according to one of the preceding claims, which has a high-precision reference body (300) for determining the position of the parts of the parallel kinematics and which additionally has at least one master template (200) with reference elements (202-219) for determining the position of the high-precision engagement elements (761, 762, 763) on the platform and / or the base and the pivot points of the legs of the hexapod.

8. Arrangement according to claim 7, wherein the reference body has the shape of a straight prism with two end faces arranged parallel to each other, and in particular a plurality of calibration reference elements are provided on each of the two end faces.

9. Arrangement according to claim 8, wherein the calibration reference elements have a pin or sleeve shape adapted to the engagement elements of the platform and / or the base.

10. Arrangement according to one of claims 7 to 9, wherein both the calibration reference elements of the reference body and the reference elements of the master template are pin- or sleeve-shaped.

11. Arrangement according to one of claims 7 to 10, further comprising a device for introducing a means for the material-locking fixation of the high-precision engagement elements in bores of the platform, in particular an adhesive injection device.