Coordinate measuring machine with a linear guide and method for manufacturing a coordinate measuring machine

Abstract

Coordinate measuring machine with a linear guide for guiding a movement of a first part of the coordinate measuring machine relative to a second part of the coordinate measuring machine, the linear guide comprising: - a guide element (24) extending in a straight line, - a supporting structure (21) to which the guide element (24) is attached, - a carriage (22) which is movable in a straight line along the guide element (24) and is guided during movement by the guide element (24), wherein the guide element (24) is designed as a hollow body, the outer wall (41) of which is formed by a wall material with a first thermal expansion coefficient (α1) and which is filled with a filling material with a second thermal expansion coefficient (α2), so that a filling (42) of the hollow body is formed, wherein the supporting structure (21) has a third thermal expansion coefficient which is higher than the first thermal expansion coefficient (α1) of the wall material, and wherein the second thermal expansion coefficient (α2) of the filler material is also higher than the first thermal expansion coefficient (α1).

Description

The invention relates to a coordinate measuring machine having a linear guide for guiding a movement of a first part of the coordinate measuring machine relative to a second part of the coordinate measuring machine. The invention further relates to a method for producing such a coordinate measuring machine.Coordinate measuring machines with linear guides have been known for a long time. For example, DE 10 2009 039 353 A1 describes such a coordinate measuring machine. The present invention relates in particular to linear guides with rolling-contact carriages, i.e. the movement of the carriage relative to the linear guide is realized using at least one rolling bearing.Usually, in the case of rolling-bearing slides of coordinate measuring machines (CMM), ball circulation guides are used. The guide rail is made massively of steel. Since a CMM is to deform as little as possible during temperature changes, the supporting structure (also referred to as supporting construction) to which the guide rail is fastened is produced from a material having approximately the same coefficient of thermal expansion as the guide rail. Therefore, the supporting structures consist of steel or iron and have a correspondingly high weight. This problem also exists when using ball bush guides (e.g. offered by Bosch Rexroth AG, Lohr am Main, Germany) instead of guides with a profile rail, since the guide rails which are round in cross section are likewise made of solid steel.DE 31 25 681 A1 describes, with respect to a coordinate measuring machine, that a base frame consists of at least one synthetic resin concrete shaped part, that a steel guide is inserted into the shaped part, and that the composition of the synthetic resin concrete at least in the region adjoining the steel guide is selected such that its coefficient of thermal expansion is approximately equal to that of the steel guide. Epoxy resin or acrylic resin may be used as the synthetic resin. By selecting the mixing ratio of synthetic resin to stone granules, desired properties of the concrete can be adjusted in a targeted manner. In particular, a suitable mixed-particle ratio allows a thermal expansion coefficient of the hardened synthetic resin concrete to be achieved which is approximately equal to that of steel.US 2005 / 0 097 766 A1 discloses a coordinate measuring machine having an element and a structure which are movable with respect to one another along rails, wherein the rails have a different thermal expansion coefficient than the structure to which they are fastened. In one embodiment, a rail is arranged on the structure opposite the rails. This web has a coefficient of thermal expansion, a stiffness, a distance from the neutral axis of the structure, and a cross-sectional dimension such that the web compensates for any thermal stresses in the structure caused by differential expansion or contraction of the structure and rails upon temperature changes to minimize any deflection of the structure.CN 1 09 556 547 A describes a composite guide rail structure for a measuring machine. The structure consists of a guide rail body and grit patches. The guide rail body has a cylindrical structure made of a composite material having a carbon fiber matrix, and serves as a guide rail body of the guide rail structure. The granules are attached to the outer surfaces of the guide rail body to make direct contact with a movable member. Both end surfaces of the guide rail body are each provided with a connecting plate.It is an object of the present invention to specify a coordinate measuring machine with a linear guide with rolling bearings which is robust with respect to wear, enables precise determination of the coordinates of a workpiece and can nevertheless be realized with low weight.The term coordinate measuring machine includes any types of devices with which coordinates of workpieces can be determined, regardless of whether the linear movement guided by the linear guide is motor-driven or manually driven by a user. In a class of coordinate measuring machines, the coordinates are surface coordinates, i.e. coordinates of surface points of workpieces are determined. Another class of coordinate measuring machines is alternatively or additionally capable of ascertaining coordinates in the interior of workpieces. These include coordinate measuring machines which use invasive radiation penetrating into the material of the workpiece and in particular measure the intensity of the radiation passing through the workpiece. Typically, the workpiece is irradiated from different directions and, on the basis of the results of the irradiation, an in particular computer-assisted reconstruction of the detected workpiece is carried out. Such methods are also referred to as computer tomography (CT). However, the term coordinate measuring machine also includes classic coordinate measuring machines, for example, devices of portal construction or gantry construction and coordinate measuring machines with a movable bridge, on which in particular a spindle sleeve with a sensor movable relative to the bridge is mounted, articulated arm devices and devices with a hexapod mechanism. Furthermore, this includes devices whose at least one sensor is fixedly positioned with respect to at least one degree of freedom of the relative movement of sensor and measurement object and in which the workpiece to be measured is movable relative to the at least one sensor, such as e.g. in the case of a device with a movable measurement table. The term coordinate measuring machine also includes machines which, although not primarily designed as coordinate measuring machines, are configured to operate like a coordinate measuring machine. In particular, these machines have at least one measurement sensor which is used for determining the coordinates. Known are, for example, robots, for example robot arms with rotary joints, to which a sensor for detecting the workpiece surface (for example a strip projection sensor) is fastened instead of a tool or in addition to a tool, or machine tools to which a measurement sensor (for example a tactile sensor) is fastened instead of a machining tool or in addition to a machining tool. Hexapod mechanics are also known, for example, to which a sensor for detecting the workpiece surface (for example a tactile sensor) is fastened instead of a machining tool.Also, with respect to the types of sensors used by a coordinate measuring machine for detecting the coordinates, the invention is not limited. Tactile sensors have already been mentioned as an example, which may be, for example, those of the switching type or of the measuring type. The tactile sensors can be passive or active sensors in particular. Active sensors can be configured to generate a probing force with which a tactile probe probes a surface of a workpiece to be measured. Optical sensors are often used alternatively or additionally, for example a projection sensor, in particular a strip projection sensor, a laser light sensor, a line camera, a camera for capturing two-dimensional images, a camera for capturing three-dimensional images, an arrangement having at least two cameras or a confocal chromatic sensor. Further, there are, for example, capacitive sensors and inductive sensors.The term coordinate measuring machine therefore also includes 3D scanners. Here, as mentioned above, triangulation-based systems, such as laser scanners and projection sensors, for example, are particularly advantageous since they can generate many measurement points with their 3D coordinates in a short time. Projection sensors project a planar pattern, e.g. a stripe pattern, onto the measurement object and record images of the measurement object together with the projected pattern with at least one image recording unit (camera). By evaluating the image recordings, the 3D coordinates of surface points of the measurement object can be determined. In order to completely capture a measurement object or the measurement object surface, often not only one measurement position is sufficient, so that the relative position from the 3D scanner to the measurement object is usually changed multiple times. This positioning can be effected manually (held by hand), or else semi-automatically or automatically, for example by guiding the 3D scanner with a robot. The change in position can also or additionally be realized by a movement of the object relative to the 3D scanner, for example by a rotary table.It is proposed to produce the supporting construction of the linear guide to which the guide element is fastened and the surface of the guide element from different materials. In particular, the material which forms the surface of the guide element can therefore be designed to be permanently abrasion-resistant, such that the carriage (also referred to as carriage) of the linear guide can be moved along the surface in a rolling-contact manner without causing relevant wear on the surface. Steel and preferably hardened steel are therefore particularly suitable as material. The load-bearing construction, on the other hand, can be / are manufactured in particular from light metal, such as magnesium or aluminum or an alloy with magnesium and / or aluminum. The load-bearing construction which is generally more bulky than the guide element can therefore have a relatively low weight.In particular, in the case of the steel / light metal material combination, the materials expand differently when the temperature is increased. The coefficient of thermal expansion of light metal, in particular of aluminum, is approximately twice as high as that of steel. This can lead to considerable mechanical stresses and to deformation of the guide element. As a result, the carriage can be guided not rectilinearly along the guide member but along a curved path.It is therefore proposed to construct the guide element as a hollow body and to fill it with a filling material in such a way that the guide element overall receives a thermal expansion coefficient which is higher than that of the wall material of the hollow body. The wall material can therefore be abrasion-resistant in particular and can be steel, for example. The resulting thermal expansion coefficient of the filled hollow body can, however, be / can be adapted to that of the supporting construction. In this description, the respective coefficient of thermal expansion is understood to mean in particular the coefficient of linear expansion, since the thermal expansion in the straight direction in which the movement of the carriage is guided by the linear guide is important. The filling and the outer wall are connected to one another. A consequence of this connection is that the outer wall and the filling expand or contract in the longitudinal direction in the same way when the temperature changes. Due to the fact that the filling is located inside the outer wall extending around the filling, at least no relevant bending of the guide element in the longitudinal direction thereby occurs.In particular, it is proposed: a coordinate measuring machine having a linear guide for guiding a movement of a first part of the coordinate measuring machine relative to a second part of the coordinate measuring machine, wherein the linear guide has:a guide element extending in a rectilinear direction,a supporting structure to which the guide element is fastened,a carriage movable in the linear direction along the guide element and guided by the guide element during a movement,wherein the guide element is designed as a hollow body, the outer wall of which is formed by a wall material having a first coefficient of thermal expansion and which is filled with a filling material having a second coefficient of thermal expansion, such that a filling of the hollow body is formed, wherein the load-bearing construction has a third coefficient of thermal expansion which is higher than the first coefficient of thermal expansion of the wall material, and wherein the second coefficient of thermal expansion of the filling material is likewise higher than the first coefficient of thermal expansion.Furthermore, the following is proposed: A method for producing a coordinate measuring machine, which has a linear guide for guiding a movement of a first part of the coordinate measuring machine relative to a second part of the coordinate measuring machine, and wherein the method has:producing a guide element extending in a rectilinear direction,fastening the guide element to a supporting structure,arranging a carriage such that the carriage is movable in the rectilinear direction along the guide element and is guided by the guide element during a movement,wherein the guide element is designed as a hollow body, the outer wall of which is formed by a wall material having a first coefficient of thermal expansion and which is filled with a filling material having a second coefficient of thermal expansion, so that a filling of the hollow body is formed,wherein the supporting structure includes a third thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermal thermalhaving an expansion coefficient that is higher than the first thermal expansion coefficient of the wall material, andwherein the second coefficient of thermal expansion of the filler material is likewise higher than the first coefficient of thermal expansion.Configurations of the coordinate measuring machine described in this description correspond to configurations of the production method and vice versa.The hollow body therefore has an outer wall. The outer surface of this wall cooperates with the carriage to guide its movement in the rectilinear direction defined by the linear guide. While in many cases the wall material is homogeneous, i.e. the interior of the wall and the outer surface are formed by the same material with the same material structure, it is also possible that the outer surface of the wall is additionally hardened. For example, it is possible to cure the outer surface of the wall using a laser beam curing device. This can be advantageous in particular also when the wall has been heated during the filling of the hollow body and / or has been subjected to a mechanical load. Such a mechanical load can optionally be followed by a mechanical post-processing (e.g. grinding) of the outer surface, so that this corresponds to the requirements desired for a linear guide. In particular after such a mechanical finishing, the outer surface can be hardened.In many cases, the hollow body may be referred to as a tube, and the shape of the tube is not limited to the hollow cylinder shape. Instead, the tube can have, for example, restrictions on two mutually opposite sides, in which correspondingly shaped projections of the slide engage while the latter is guided by the guide element. In any case and regardless of whether the hollow body can be referred to as a tube, it is preferred that the cross sections of the outer wall and of the filling are constant over an entire course of the linear guide in the rectilinear direction, in which the movement of the carriage can be guided by the guide element. Of course, the guide element generally has a plurality of fastenings or a continuous fastening running in the rectilinear direction, by means of which it is fastened to the supporting construction. Due to the fastening or fastenings, the cross section, in particular of the wall, but also of the filling, can be changed in places, for example penetrated by a screw or a bolt. Nevertheless, the cross section can be referred to as constant.Furthermore, it is preferred that the filling is / is connected to the outer wall on the inner surface of the outer wall of the hollow body. Depending on the configuration, the connection can / can be realized in various ways. For example, the filling material can be cast into the interior space of the hollow body delimited by the outer wall. In the case of metals, the filling material is therefore melted, poured into the hollow body and allowed to solidify. In particular, if the inner surface of the outer wall is rough, a form-fit connection to the outer wall is produced by the pouring in of the filling material. Optionally, the surface of the outer wall can be mechanically processed, for example roughened and / or provided with depressions, for example by cutting depressions in the manner of an internal thread, i.e. a helical depression running continuously along the rectilinear direction is formed. Alternatively or additionally, protrusions may be formed on the inner surface of the outer wall, for example, by press-fitting rings. For this purpose, the outer wall can be heated, for example, and the respective ring can be introduced into the hollow body, while it has a lower temperature than the outer wall. After the ring has been introduced, the outer wall cools and shrinks, so that the ring is / is pressed in. Roughening of the inner surface can be achieved, for example, by particle blasting, in particular sandblasting.As an alternative to casting in the filler material, the filler material can be pressed in, for example, by prior heating of the outer wall of the hollow body, by introducing the non-heated filler material and by allowing the outer wall to cool. This method also makes it possible to produce a good connection of the filler material to the inner surface of the outer wall, in particular a frictional connection.A further possibility is a cohesive connection by using an adhesive between the inner surface of the outer wall of the hollow body and the filling. In particular, a fiber composite material can be glued (e.g. using an adhesive) into the hollow body. Under certain circumstances, the adhesive not only produces a cohesive connection, but also a frictional connection or even a force-fit connection. In particular, suitable fibers are one or more of glass fibers, carbon fibers, ceramic fibers, aramid fibers, boron fibers, basalt fibers, steel fibers, natural fibers and nylon fibers. The matrix is in particular a polymer, for example a thermoset, an elastomer or a thermoplastic.As mentioned, the third coefficient of thermal expansion of the supporting construction and the second coefficient of thermal expansion of the filling material are higher than the first coefficient of thermal expansion of the outer wall of the hollow body, or the materials are selected accordingly. The resulting coefficient of expansion of the filled hollow body is / is therefore at least approximated to the coefficient of thermal expansion of the supporting construction.Preferably, the resulting coefficient of thermal expansion reaches the same value in certain configurations. In this case, the second coefficient of thermal expansion of the filling material is higher than the third coefficient of thermal expansion of the supporting construction. The preferred embodiment has the advantage that effects of different thermal expansion of supporting construction and guide element are minimized. However, the second coefficient of thermal expansion of the filler material may be higher than the third coefficient of thermal expansion of the supporting structure even if the resulting coefficient of thermal expansion of the hollow body does not have / reach the same value as that of the supporting structure. In this case, at least a good approximation of the resulting coefficient of thermal expansion to the coefficient of thermal expansion of the supporting construction takes place.For each configuration and embodiment, the coefficients of thermal expansion may be related to a defined temperature value such as 20 or 22 degrees Celsius, or alternatively may be related to a temperature range such as the permissible operating temperature range of the coordinate measuring machine. The allowable operating temperature range often starts at a value that is at least 15 degrees Celsius, and in some cases is below, for example 10 degrees Celsius. The allowable operating temperature range often ends at a value that is at most 35 degrees Celsius, and in some cases is above, for example at 40 degrees Celsius.In particular, a thermal expansion coefficient of the filled hollow body resulting from the first and the second thermal expansion coefficients and from the dimensions of the outer wall and the filling can be / are matched to the third thermal expansion coefficient of the supporting construction. Therefore, in addition to the thermal expansion coefficients of the materials used or to be used, the dimensions of the outer wall and of the filling and in particular the cross-sectional areas thereof in a cross-section running perpendicular to the rectilinear direction are preferably taken into account in the design. It is therefore possible to choose suitable materials for the outer wall and filling and thus the corresponding coefficients of thermal expansion and also to choose / define the cross-sectional areas of the outer wall and filling. As a result, the resulting coefficient of expansion of the filled hollow body can be adapted or adapted to the coefficient of thermal expansion of the supporting construction. However, it is also possible, alternatively or additionally, to select the thermal expansion coefficient of the supporting construction by selecting a corresponding material or a corresponding material combination when designing the linear guide in such a way that the resulting expansion coefficient of the supporting construction and the thermal expansion coefficient of the filled hollow body are / are adapted to one another or are matched to one another.The adaptation of the thermal expansion coefficients is understood in particular to mean that they are the same at a defined temperature, for example room temperature, such as 20 or 22 degrees Celsius, or on average in a temperature range that can be smaller than the permissible operating range of the coordinate measuring machine or this operating range. In another embodiment, however, the adaptation is understood to mean that the coefficients of thermal expansion are approximately the same, in particular under the temperature conditions mentioned in the preceding sentence, and deviate from one another by less than ten percent, preferably less than eight percent and in particular less than five percent, for example at the defined temperature or on average in the temperature range.In particular, the filling can consist of a metal, a metal alloy or of a fiber composite material. Zinc, for example, is suitable as metal, optionally also for the metal alloy. Zinc can be processed well and, in particular, melted at a relatively low melting point in order to fill it into the hollow body. In addition, zinc, especially when steel is used as the material for the outer wall of the hollow body and when a light metal is used for the load-bearing construction, has a well-suited coefficient of thermal expansion of about 29 micrometers per kelvin. This second coefficient of thermal expansion of zinc as filling material is higher than the first coefficient of thermal expansion of steel (depending on the type about 11-16 micrometers per kelvin) as wall material and is also higher than the third coefficient of thermal expansion of the supporting construction, for example in the case of aluminum (about 23-24 micrometers per kelvin).Referring now to the accompanying drawings, embodiments of the invention will be described. However, the invention is not limited to these embodiments. The individual figures of the drawing show: FIG. 1 shows an exemplary embodiment of a coordinate measuring machine which has linear guides for guiding rectilinear movement of two parts of the coordinate measuring machine relative to one another, FIG. 2 shows an exemplary embodiment of a linear guide, which is illustrated in a simplified manner and has two guide elements and a carriage guided on the guide elements in a linearly movable manner, and FIG. 3 shows a cross section through a guide element of a linear guide and through a fastening element which serves for fastening the guide element to a supporting structure.FIG. 1 shows, as an example, a coordinate measuring machine 28 which has a base 1 on which a measurement table 2 is fastened. In the specific embodiment shown, the substructure of the measuring table 2 and a part projecting behind the measuring table 2 form an L-shaped part 8, which also serves, for example, as a housing for a control for controlling the operation of the coordinate measuring machine 28. The L-shaped part 8 can be, for example, a cast part. On the upper side of the L-shaped part 8 a linear guide is arranged, along which a measuring slide 5 can be moved in the horizontal direction denoted by the arrow x. The linear guide cannot be seen in the illustration according to FIG. 1, since it is covered by a bellows 9. At the end of the linear guide, a drive 7 is provided, of which only the cover can be seen in FIG. 1. By means of the drive 7, a movement of the measuring slide 5 of said linear guide can be driven in the direction of the arrow x. In addition, a scale is also provided under the bellows, with which scale the respective position of the measuring slide 5 in the direction denoted by x can be detected. A linear guide is likewise arranged on the measuring slide 5 for its part, so that the vertically oriented measuring slide 6 can be moved in the horizontal direction denoted by the arrow y. For this measuring slide 6 as well, a drive 10 for the movement is provided (here too only the cover can be seen in FIG. 1 ), as well as a scale with which the position of the measuring slide in the horizontal direction denoted by the arrow y can be measured. The measuring slide 6 in turn also has a linear guide in its interior, by means of which a further measuring slide 36 is mounted in a linearly movable manner in the vertical direction denoted by the arrow z, of which however only the lower end can be seen here in the form of a spindle sleeve 3. A sensor 4 is fastened to the lower end of the measuring slide 36, i.e. to the lower end of the spindle sleeve 3.The measuring slide 36 can be moved by a drive 11 in the direction designated by the arrow z (here too only the cover of the drive 11 can be seen in FIG. 1 ). In addition, a scale, which is likewise not visible, is arranged within the measuring slide 6, by means of which scale the precise position of the measuring slide 36 can be determined. The sensor 4 is designed as a measuring sensor, in which a stylus 30, with which the workpiece 31 is scanned, is mounted so as to be deflectable relative to the sensor housing in all three coordinate directions x, y and z (corresponding to the arrows x, y, z and corresponding to a Cartesian coordinate system). When touching the workpiece 31, the stylus 30 is deflected from its rest position relative to the housing of the sensor 4 in the coordinate directions x, y and z, this deflection being determined by corresponding sensors in the coordinate directions x, y and z. By calculating the measured deflection of the stylus 30 with the positions of the measuring slides 5, 6 and 36 measured via the scales, it is then possible to calculate exactly the position of a scanned point on the surface of the workpiece 31. The actuation of the drives 7, 10 and 11 and the readout of the scale values of the measuring slides 5, 6 and 36 and the readout of the stylus deflection of the stylus 30 of the sensor 4 in the coordinate directions are effected by the controller 8, which for this purpose has, for example, a plurality of microprocessors, in order to be able to carry out the control tasks in real time. Connected to this microprocessor control is a measurement computer, not shown in detail in FIG. 1, with which CNC measurement sequences can be produced and the measurement results can be further processed, and an operator console with which the coordinate measuring machine can also be manually operated via corresponding operator control elements. At least one of the linear guides mentioned can be configured in the manner according to the invention.Of course, the coordinate measuring machine 28 shown here is only one of many possible exemplary embodiments. For example, the linear axes can be arranged differently. For this purpose, the measuring table 2 could be mounted linearly displaceably, for example, in one or more coordinate directions. Basically, other constructions of coordinate measuring machines are also possible. Examples have already been mentioned above. For example, a coordinate measuring machine with one exception, for example a linear guide in the kinematic chain of two successive rotational degrees of freedom, can have exclusively rotational degrees of freedom of movement. According to a further example, a coordinate measuring machine with rotational degrees of freedom of movement can additionally be movable relative to a fixed base along a linear guide.The sensor 4 is also only one of several possible exemplary embodiments. Instead of a measuring sensor 4, a switching sensor can also be used which triggers an electrical pulse when the workpiece is touched by its stylus, or an optical sensor, such as a digital camera or a laser triangulation sensor. The coordinate measuring machine can also have a plurality of sensors.FIG. 1 thus shows a coordinate measuring machine 28 comprising a sensor 4 for detecting the surface of a workpiece 31, a workpiece support (here: workpiece table 2) for receiving a workpiece 31 to be measured, and a mechanism (here with measurement slides 5, 6 and 36) for moving the sensor 4 relative to the workpiece 31. In particular, these structural elements of a coordinate measuring machine can be embodied in a different manner in other embodiments of coordinate measuring machines. Only in the coordinate measuring machine 28 shown and possibly in some other constructions, the mechanism has at least one measuring slide 36 movable in the vertical direction, which is guided on a vertical linear guide movably relative to a part of the mechanism fixed relative to the measuring slide, wherein the sensor 4 is fastened to the lower end of this measuring slide.FIG. 2 shows an isometric view of a linear guide with two tubular guide elements 24 running parallel to one another. The movement of a slide 22, which has four slotted ball bearings 23, is guided movably by the guide elements 24. Of the ball bearings and the guide elements, only one is designated by the reference numerals 23 and 24, respectively.The guide elements 24 are each fastened to a supporting structure 21 via a fastening element 26 extending parallel to the guide element 24.The linear guide shown in FIG. 2 is merely an exemplary embodiment from which it is possible to deviate in various ways in the realization of the invention. For example, only a single guide member may be present, or more than two guide members may be present. Furthermore, the respective guiding element may not be indirectly fastened to the supporting structure via a fastening element, but e.g. directly via a plurality of threaded bolts or in another way. In addition, unlike the one illustrated in FIG. 2, the supporting structure may not be a monolithic body such as e.g. a base plate, but any other supporting structure, such as a structure with a plurality of struts connected to each other. The cross-sectional profile of the at least one guide element can also not be circular, as shown in FIG. 2, but can be any other cross-sectional profile suitable for the respective linear guide. For example, as already mentioned above, Bosch Rexroth AG, in addition to ball bush guides of the type shown in FIG. 2, also produces ball rail guides and roller rail guides and roller guides in which the guide element has a differently shaped cross-sectional profile than shown in FIG. 2, for example a profile with two mutually opposite lateral restrictions of the type of an X. These guide elements, which are designated as rails, can also be / are designed according to the invention as hollow bodies with filling. A further possible modification of the linear guide shown in FIG. 2 relates to the ball bushings 23, which can be shaped differently and / or can be replaced by other rolling-bearing elements. In particular, the aforementioned possible modifications can be realized individually or in any combination.FIG. 3 shows a cross section through an arrangement with a guide element 24 and a fastening element 26 similar to that shown in FIG. 2. Above all, however, the cross-sectional shape of the fastening element 26 differs from that shown in FIG. 2.The guide element 24 has a hollow body which has an outer wall 41 and a filling 42. In addition to the hollow body, the guide element 24 can also have further components, such as, for example, a termination at the opposite ends. Furthermore, the guide element 24 can have recesses for fastening means.In order to produce the filling 42 of the hollow body, in the specific exemplary embodiment, the metallic filling material has been melted and poured into the interior of the hollow body. Previously, optionally, the inner surface of the outer wall has been roughened by sandblasting. The material of the wall is a steel, preferably a hardenable steel. The filler material is zinc in the exemplary embodiment. Furthermore, the supporting construction in the exemplary embodiment is made of aluminum. Alternatives and variants of the embodiment of a linear guide have already been discussed.An exemplary embodiment is described below for how the coefficients of thermal expansion of the material and the sizes of the cross-sectional areas of the outer wall and filling of the guide element can be designed. The calculations assume that the wall material and the filling material of the hollow body expand / contract differently in the rectilinear direction (the direction in which the linear movement is guided) upon a change in temperature and therefore a longitudinal force is exerted in each case on the outer wall and the filling in the rectilinear direction, also referred to below as the longitudinal direction. As long as the connection between the outer wall and the filling remains and therefore no relative movement occurs in the longitudinal direction, a force equilibrium applies:Here, F 1 denotes the force acting on the outer wall in the longitudinal direction, and F 2 denotes the force acting on the filling in the longitudinal direction. Due to the equilibrium of forces, these forces are directed in opposite directions to each other. Utilizing the relationship: the above-mentioned. Forces are expressed by the product of the mechanical stress σ and by the cross-sectional area A of the outer wall or the filling. The stress σ can be expressed again by the product of the modulus of elasticity E and the strain ε Sp. The indices 1 and 2 are later used again at least partially for the symbols. These then again designate the outer wall or the filling. In Equation 3, the index Sp denotes the mechanical stress that results in the strain. Also introduced is the thermal expansion denoted by the symbol ε th which can be expressed by the product of the thermal expansion coefficient α and the temperature difference Δθ according to the following equation 4.Substituting the terms on the right of Equation 2 and Equation 3 yields Equation 5 and Equation 6 in sequence from Equation 1.The following results from reshaping equation 6:The total strain ε ges is the sum of the thermal strain and the mechanical strain for both the outer wall and the filling. Since, furthermore, the expansion of the outer wall and the expansion of the filling are of the same magnitude because of their firm connection to one another, the following results:By transforming equation 8, one obtains:Substituting the expression on the right side of Equation 4 into Equation 9, one obtains:This equation can be transformed and then the expression on the right side of equation 7 can be used for the mechanical strain on the left side of equation 7. The resulting equation can then be transformed and resolved after the mechanical strain ε 2Sp of the filling:Now, the thermal expansion coefficient α ver can be expressed as follows. Equation 8 is used here:The index ver expresses that the coefficient of thermal expansion α ver relates to the composite of outer wall and filling. Now, the expressions on the right side of Equation 4 and Equation 14 in Equation 15 can be respectively used, and it is found that:After shortening the fraction on the right-hand side of equation 16 by the temperature difference Δθ, the following results:The coefficient of thermal expansion α ver is therefore obtained from the expression on the right-hand side of equation 17, which includes the coefficients of thermal expansion α 1 of the outer wall of the hollow body, the coefficient of thermal expansion α 2 of the filling, the moduli of elasticity E 1 and E 2 of the outer wall or of the filling and the cross-sectional areas A 1 and A 2 of the outer wall or of the filling. If the coefficient of thermal expansion α ver of the filled hollow body (i.e. of the composite of outer wall and filling) is made equal to the coefficient of thermal expansion of the supporting construction, a design specification for the coefficients of thermal expansion and cross sections of the outer wall and of the filling of the hollow body is obtained. In particular, if suitable materials are first selected for the outer wall and the filling, then their thermal expansion coefficients are fixed. Subsequently, the ratio (the quotient) of the cross-sectional areas of outer wall and filling of the hollow body can be selected such that equation 17 is fulfilled. Since only the ratio of the cross-sectional areas has to result in a value which satisfies equation 17, the total cross-sectional area of the filled hollow body can still be varied and can in particular be selected such that a desired mechanical stiffness of the hollow body is achieved overall.In particular, the following can therefore be adopted when a linear guide is produced: a) Determination and / or establishment of the values of the coefficient of thermal expansion of supporting construction, outer wall of the hollow body and filling of the hollow body, in particular by selection of suitable materials in each case; it should be noted that the value of the coefficient of thermal expansion of the supporting construction must lie between the values of the coefficients of thermal expansion of the outer wall and the filling if the total coefficient of thermal expansion of the hollow body is to become at least approximately equal to the coefficient of thermal expansion of the supporting construction; b) In particular, assuming constant-sized cross-sectional areas of the outer wall and filling of the hollow body in the straight-line direction, Determination and / or establishment of the value of the ratio of the cross-sectional areas of the outer wall and filling of the hollow body; c) Establishment of the cross-sectional area of the hollow body.In particular, the values determined and / or defined by steps a) and b) are determined and / or defined as a function of one another in such a way that the resulting coefficient of thermal expansion of the hollow body is equal to the coefficient of thermal expansion of the supporting construction.The order of steps a) to c) is not fixed here and can be varied depending on the embodiment. Thus, it is possible, for example, to begin with step c). Step b) can also be carried out in principle before step a). However, the results of steps a) and b) depend on each other. Also, steps a) and b) may be partially performed in parallel. For example, the material and thus the coefficient of thermal expansion of the supporting construction can first be determined, then the size of at least one of the cross-sectional areas of the outer wall and filling of the hollow body can be determined, and then the remaining values of the coefficients of thermal expansion and of the cross-sectional area can be determined.The configuration according to steps a) to c) can also be carried out iteratively. For example, the two materials of the outer wall and the filling of the hollow body can first be selected, whereby step a) is carried out, and then the ratio of the cross-sectional areas can be determined in step b). However, as a result of step b), it can be established that the aspect ratio is unsuitable for practical implementation, optionally also taking into account step c). This in turn can lead to at least one of the materials selected in step a) being replaced by another. This in turn leads to a renewed execution of step b).

Claims

Coordinate measuring machine having a linear guide for guiding a movement of a first part of the coordinate measuring machine relative to a second part of the coordinate measuring machine, wherein the linear guide has: - a guide element (24) extending in a rectilinear direction, - a supporting construction (21) to which the guide element (24) is fastened, - a carriage (22) which is movable in the rectilinear direction along the guide element (24) and is guided by the guide element (24) during a movement, wherein the guide element (24) is designed as a hollow body, the outer wall (41) of which is formed by a wall material having a first coefficient of thermal expansion (α 1) and which is filled with a filling material having a second coefficient of thermal expansion (α 2) such that a filling (42) of the hollow body is formed, wherein the supporting structure (21) has a third coefficient of thermal expansion higher than the first coefficient of thermal expansion (α 1) of the wall material, and wherein the second coefficient of thermal expansion (α 2) of the filling material is also higher than the first coefficient of thermal expansion (α 1).The coordinate measuring machine according to claim 1, wherein the second coefficient of thermal expansion (α 2) of the filling material is higher than the third coefficient of thermal expansion of the supporting structure (21).Coordinate measuring machine according to Claim 2, wherein a thermal expansion coefficient of the filled hollow body resulting from the first (α 1) and the second (α 2) thermal expansion coefficients and from the dimensions of the outer wall (41) and the filling (42) is matched to the third thermal expansion coefficient of the supporting construction (21).Coordinate measuring machine according to one of the preceding claims, wherein the filling (42) is connected to the outer wall (41) on the inner surface of the outer wall (41) of the hollow body.Coordinate measuring machine according to one of the preceding claims, wherein the cross sections of the outer wall (41) and of the filling (42) are constant over an entire course of the linear guide in the rectilinear direction, in which the movement of the carriage (22) can be guided by the guide element (24).Coordinate measuring machine according to one of the preceding claims, wherein the wall material of the outer wall (41) of the hollow body is a steel.Coordinate measuring machine according to one of the preceding claims, wherein the load-bearing construction (21) is manufactured from light metal.Coordinate measuring machine according to one of the preceding claims, wherein the filling (42) consists of a metal, a metal alloy or of a fiber composite material.Method for producing a coordinate measuring machine, which has a linear guide for guiding a movement of a first part of the coordinate measuring machine relative to a second part of the coordinate measuring machine, and wherein the method has: - producing a guide element (24) extending in a rectilinear direction, - fastening the guide element (24) to a supporting structure (21), - arranging a slide (22) such that the slide (22) is movable in the rectilinear direction along the guide element (24) and is guided during a movement by the guide element (24), wherein the guide element (24) is designed as a hollow body, the outer wall (41) of which is formed by a wall material having a first coefficient of thermal expansion (α 1) and which is filled with a filling material having a second coefficient of thermal expansion (α 2), forming a filling (42) of the hollow body, wherein the supporting structure (21) has a third coefficient of thermal expansion which is higher than the first coefficient of thermal expansion of the wall material, and wherein the second coefficient of thermal expansion (α 2) of the filling material is likewise higher than the first coefficient of thermal expansion (α 1).Method according to claim 9, wherein the second coefficient of thermal expansion (α 2) of the filling material is chosen to be higher than the third coefficient of thermal expansion of the supporting structure (21).Method according to claim 10, wherein a thermal expansion coefficient of the filled hollow body resulting from the first (α 1) and the second (α 2) thermal expansion coefficients and from the dimensions of the outer wall (41) and the filling (42) is adapted to the third thermal expansion coefficient of the supporting construction (21) by selecting materials having the first and the second thermal expansion coefficients and by shaping the dimensions of the outer wall (41) and the filling (42).Method according to any of claims 9-11, wherein the filling (42) is connected to the inner surface of the outer wall (41) of the hollow body.Method according to one of Claims 9-12, wherein the cross sections of the outer wall (41) and of the filling (42) are made constant over an entire course of the linear guide in the rectilinear direction, in which the movement of the carriage (22) can be guided by the guide element (24).Method according to one of claims 9 - 13, wherein the wall material of the outer wall (41) of the hollow body is a steel, the load-bearing construction (21) is manufactured from light metal and / or the filling (42) is manufactured from a metal, a metal alloy or from a fiber composite material.Method according to one of Claims 9-14, having the following steps: a) determining and / or defining the values of the coefficient of thermal expansion of supporting structure (21), outer wall (41) of the hollow body and filling (42) of the hollow body; b) determining and / or defining the value of the ratio of the cross-sectional areas of the outer wall (41) and of the filling (42) of the hollow body; c) defining the cross-sectional area of the hollow body; wherein the values determined and / or defined by steps a) and b) are determined and / or defined as a function of one another in such a way that the resulting coefficient of thermal expansion of the hollow body is equal to the coefficient of thermal expansion of the supporting structure.

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