Coordinate measuring machine with linear guide and method for producing coordinate measuring machine

Abstract

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 linear guide comprising:-a guide element, which extends in a linear direction,-a support structure, which extends in the linear direction, the guide element is fastened to the load-bearing structure,-a carriage which can be moved along the guide element in a linear direction and is guided by the guide element during movement, the guide element being in the form of a hollow body, the outer wall of which is formed from a wall material having a first coefficient of thermal expansion, the wall material has a first thermal expansion coefficient, and the hollow body is filled with a filling material having a second thermal expansion coefficient, as a result of which the filling material forms the hollow body, the load-bearing structure has a third thermal expansion coefficient which is higher than the first thermal expansion coefficient of the wall material, and the second thermal expansion coefficient of the filling material is also higher than the first thermal expansion coefficient.

Description

Technical Field

[0001] The invention relates to a coordinate measuring machine having a linear guide for guiding a first part of the coordinate measuring machine to move relative to a second part of the coordinate measuring machine. The invention also relates to a method for producing such a coordinate measuring machine. Background Art

[0002] Coordinate measuring machines with linear guides have been known for a long time. DE 10 2009 039353 A1 describes such a coordinate measuring machine, for example. The present invention relates in particular to a linear guide with a carriage mounted in rolling bearings, i.e. the movement of the carriage relative to the linear guide is achieved using at least one rolling bearing.

[0003] In the case of a slide mounted in rolling bearings of a coordinate measuring machine (CMM), recirculating ball guides are usually used. The guide rails are bulky and are made of steel. Since the CMM should deform as little as possible during temperature changes, the support structure (also called load-bearing construction) to which the guide rails are fastened is made of a material having approximately the same thermal expansion coefficient as the guide rails. The support structure therefore consists of steel or iron and has a correspondingly high weight. This problem still exists even if spherical guide bushings (e.g., sold by Bosch Rexroth AG, Lohr am Main, Germany) are used instead of guides with profile rails, because the guide rails with a rounded cross-section are also made of solid steel. Summary of the invention

[0004] The object of the present invention is to provide a coordinate measuring machine having a linear guide with rolling bearings which is wear-resistant and enables a precise determination of the coordinates of a workpiece, but is lightweight.

[0005] The term "coordinate measuring machine" includes any type of machine that can be used to determine the coordinates of a workpiece, regardless of whether the linear movement guided by the linear guide is driven by a motor or manually by a user. In one type of coordinate measuring machine, the coordinates are surface coordinates, that is, the coordinates of points on the surface of the workpiece are determined. Another type of coordinate measuring machine is alternatively or additionally capable of determining the coordinates inside the workpiece. This type includes coordinate measuring machines that utilize invasive radiation that penetrates into the material of the workpiece and, in particular, measure the intensity of the radiation transmitted through the workpiece. Typically, radiation is transmitted through the workpiece from different directions, and the scanned workpiece is subjected to, in particular, computer-assisted reconstruction based on the results of the radiation transmission. This process is also known as computed tomography (CT). However, the term "coordinate measuring machine" also includes conventional coordinate measuring machines, such as machines with a gantry design or a gantry design, as well as coordinate measuring machines with a movable bridge, articulated arm machines, and machines with a hexapod mechanism, in particular, a quill with a sensor that can be moved relative to the bridge is mounted on the movable bridge. Coordinate measuring machines also include machines in which at least one sensor is fixedly positioned relative to at least one degree of freedom of relative movement of sensor and measured object, and in which case the workpiece to be measured can be moved relative to the at least one sensor, for example in the case of a machine with a movable measuring table. The term "coordinate measuring machine" also covers machines which, although not primarily designed as coordinate measuring machines, are arranged to work like coordinate measuring machines. In particular, these machines have at least one measuring sensor for determining coordinates. For example, robots are known, such as robot arms with rotary joints, to which sensors for capturing the surface of the workpiece (e.g. structured light sensors) are fastened instead of or in addition to the tool, or machine tools are known to which measuring sensors (e.g. tactile sensors) are fastened instead of or in addition to the machining tool. For example, hexapods are also known to which sensors for capturing the surface of the workpiece (e.g. tactile sensors) are fastened instead of or in addition to the machining tool.

[0006] The invention also does not restrict the type of sensor used by the coordinate measuring machine to determine the coordinates. Tactile sensors have been mentioned as examples, which can be, for example, tactile sensors of the switch type or the measuring type. The tactile sensor can in particular be a passive sensor or an active sensor. The active sensor can be configured to generate a detection force, with which the tactile probe detects the surface of the workpiece to be measured. Optical sensors are often used alternatively or in addition, for example, projection sensors, in particular structured light sensors, laser triangulation sensors, line scan cameras, cameras for capturing two-dimensional images, cameras for capturing three-dimensional images, arrangements with at least two cameras or confocal color sensors. There are also, for example, capacitive sensors and inductive sensors.

[0007] Therefore, the term "coordinate measuring machine" also includes 3D scanners. As mentioned above, systems based on triangulation, such as laser scanners and projection sensors, are particularly advantageous here because they can generate many measuring points with 3D coordinates in a short time. The projection sensor projects a pattern (e.g. a stripe pattern) onto the surface area of ​​the measured object and uses at least one image capture unit (camera) to capture the image of the measured object and the projected pattern. The 3D coordinates of the surface points of the measured object can be determined by evaluating the image record. In order to completely capture the measured object or the surface of the measured object, only one measuring position is usually not enough, so the relative position of the 3D scanner relative to the measured object is usually changed repeatedly. This positioning can be done manually (in a handheld manner) or semi-automatically or automatically, for example by using a robot to guide the 3D scanner. The position change can also or additionally be achieved by moving the object relative to the 3D scanner, for example by a rotating table.

[0008] It is proposed to produce the load-bearing construction of the linear guide, to which the guide element is fastened, and the surface of the guide element from various materials. In particular, the material forming the surface of the guide element can thus be made wear-resistant over a long period of time, so that the carriage of the linear guide can move along the surface mounted in the rolling bearing without causing any associated wear to the surface. Possible materials are therefore in particular steel, preferably hardened steel. In contrast, the load-bearing construction can comprise or be manufactured from, in particular, a light metal, such as magnesium or aluminum, or an alloy containing magnesium and / or aluminum. As a result, the load-bearing construction, which is usually more cumbersome than the guide element, can have a relatively low weight.

[0009] Especially with the material combination steel / light metal, these materials expand to different degrees when the temperature rises. The thermal expansion coefficient of light metal, especially aluminum, is about twice that of steel. This can lead to considerable mechanical stresses and to deformations of the guide element. As a result, the carriage can be guided along the guide element in a curved path instead of a straight line.

[0010] Therefore, it is proposed to design the guide element as a hollow body and to fill it with a filling material in such a way that the guide element as a whole retains a higher coefficient of thermal expansion than the wall material of the hollow body. The wall material can therefore be particularly wear-resistant and be, for example, steel. However, the resulting coefficient of thermal expansion of the filled hollow body can / has been adapted to the coefficient of thermal expansion of the load-bearing construction. In the present description, the corresponding coefficient of thermal expansion is understood to refer in particular to the longitudinal coefficient of expansion, since what is important is the thermal expansion in the linear direction in which the linear guide guides the movement of the carriage. The filler and the outer wall are connected to each other. As a result of this connection, the outer wall and the filler expand and contract in the same way in the longitudinal direction when the temperature changes. Since the filler is inside the outer wall extending around the filler, no relevant bending of the guide element occurs at least in the longitudinal direction.

[0011] In particular, the following is proposed: A coordinate measuring machine having a linear guide for guiding a first part of the coordinate measuring machine to move relative to a second part of the coordinate measuring machine, wherein the linear guide comprises:

[0012] - a guide element extending in a linear direction,

[0013] a carrying structure to which the guide element is fastened,

[0014] a carriage which is movable along the guide element in the linear direction and is guided by the guide element during the movement,

[0015] wherein the guide element is in the form of a hollow body, the outer wall of which is formed by a wall material having a first coefficient of thermal expansion and the hollow body is filled with a filling material having a second coefficient of thermal expansion, as a result of which a filling of the hollow body is formed,

[0016] wherein the load-bearing structure has a third coefficient of thermal expansion, which is higher than the first coefficient of thermal expansion of the wall material, and

[0017] The second thermal expansion coefficient of the filling material is also higher than the first thermal expansion coefficient.

[0018] The following is also proposed: A method for producing a coordinate measuring machine, the coordinate measuring machine comprising a linear guide for guiding a first part of the coordinate measuring machine to move relative to a second part of the coordinate measuring machine, and wherein the method comprises:

[0019] - produce guide elements extending in a linear direction,

[0020] - fastening the guide element to the load-bearing structure,

[0021] - arranging the carriage so that it can move along the guide element in the linear direction and is guided by the guide element during the movement,

[0022] wherein the guide element is in the form of a hollow body, the outer wall of which is formed by a wall material having a first coefficient of thermal expansion and the hollow body is filled with a filling material having a second coefficient of thermal expansion, as a result of which a filling of the hollow body is formed,

[0023] wherein the load-bearing structure has a third coefficient of thermal expansion, which is higher than the first coefficient of thermal expansion of the wall material, and

[0024] The second thermal expansion coefficient of the filling material is also higher than the first thermal expansion coefficient.

[0025] Embodiments of the coordinate measuring machine described in this specification correspond to embodiments of the production method and vice versa.

[0026] Therefore, the hollow body has an outer wall. The outer surface of the wall interacts with the carriage in order to guide the carriage to move in a linear direction defined by the linear guide. Although in many cases the wall material is homogeneous, i.e. the inner side and the outer surface of the wall are formed from the same material with the same material structure, the outer surface of the wall can also be hardened additionally. For example, a laser beam hardening device can be used to harden the outer surface of the wall. It can also be advantageous, in particular when filling the hollow body, that the wall has been heated and / or has been subjected to mechanical loading. This mechanical loading can optionally be followed by mechanical reprocessing of the outer surface (e.g. sanding) so that it meets the requirements desired for the linear guide. In particular, the outer surface can be hardened after this mechanical reprocessing.

[0027] In many cases, the hollow body can be referred to as a tube, the shape of which is not limited to a hollow cylindrical shape. Instead, the tube can have, for example, constrictions on two oppositely positioned sides, in which correspondingly shaped protrusions of the carriage engage when the carriage 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-section of the outer wall and the cross-section of the filler are constant in the linear direction over the entire profile of the linear guide, in which the guide element is able to guide the carriage to move. Of course, the guide element usually has a plurality of fastening devices or one continuous fastening device, which extends in the linear direction and fastens the guide element to the load-bearing structure. Due to one or more fastening devices, in particular the cross-section of the wall and the cross-section of the filler may change at certain points, for example a screw or bolt may pass through the cross-section. However, the cross-section can be referred to as constant.

[0028] It is also preferred that the filler is connected to the outer wall of the hollow body at the inner surface of the outer wall. This connection can / has been achieved in various ways according to the configuration. For example, the filler material can be cast into the inner space of the hollow body defined by the outer wall. In the case of metal, the filler material is therefore melted, cast into the hollow body and allowed to solidify. In particular, if the inner surface of the outer wall is rough, the casting of the filler material makes it possible to form a shape-fitting connection with the outer wall. Optionally, before casting, the surface of the outer wall can be machined, such as roughened and / or provided with a recess, such as by carving a recess in the form of an internal thread (i.e., forming a spiral recess extending continuously in a linear direction). As an alternative or in addition, a protrusion can be formed on the inner surface of the outer wall, such as by pressing into a ring. For this purpose, the outer wall can be heated, for example, and the corresponding ring can be introduced into the hollow body, while its temperature is lower than that of the outer wall. After the ring has been introduced, the outer wall cools and shrinks, with the result that the ring is pressed in / pressed in. The roughening of the inner surface can be achieved, for example, by particle blasting, particularly sandblasting.

[0029] As an alternative to casting the filler material, the filler material can be pressed in, for example, by preheating the outer wall of the hollow body, introducing the unheated filler material, and allowing the outer wall to cool. This method also makes it possible to establish a good connection between the filler material and the inner surface of the outer wall, especially a frictional connection.

[0030] Another possibility is to use an adhesive between the inner surface of the outer wall of the hollow body and the filler for integral bonding. In particular, the fiber composite material can be bonded into the hollow body (for example, using an adhesive). In some cases, the adhesive not only produces an integral bond, but also a frictional engagement or even a force-fit connection. Particularly contemplated fibers are one or more of the following: 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, such as a thermosetting plastic, an elastomer or a thermoplastic.

[0031] As described above, the third thermal expansion coefficient of the load-bearing construction and the second thermal expansion coefficient of the filling material are higher than the first thermal expansion coefficient of the outer wall of the hollow body, or the materials are selected accordingly. Thus, the resulting expansion coefficient of the filled hollow body is at least similar to the thermal expansion coefficient of the load-bearing construction.

[0032] In certain embodiments, the resulting coefficients of thermal expansion preferably reach the same value. In this case, the second coefficient of thermal expansion of the filling material is higher than the third coefficient of thermal expansion of the load-bearing construction. This preferred embodiment has the advantage that the influence of the different thermal expansions of the load-bearing construction and the guide element is minimized. However, when the resulting coefficient of thermal expansion of the hollow body does not have / does not reach the same value as the coefficient of thermal expansion of the load-bearing construction, the second coefficient of thermal expansion of the filling material can also be higher than the third coefficient of thermal expansion of the load-bearing construction. In this case, the resulting coefficient of thermal expansion is at least very similar to the coefficient of thermal expansion of the load-bearing construction.

[0033] For each embodiment and configuration, it is correct that the coefficient of thermal expansion can be based on a defined temperature value, such as 20 or 22 degrees Celsius, or alternatively can be based on a temperature range, such as the allowed operating temperature range of the coordinate measuring machine. The allowed operating temperature range starts with a value of at least 15 degrees Celsius in many cases, and is lower in some cases, such as 10 degrees Celsius. The allowed operating temperature range ends with a value of at most 35 degrees Celsius in many cases, and is higher in some cases, such as 40 degrees Celsius.

[0034] In particular, the thermal expansion coefficient of the filled hollow body can / has been matched with the third thermal expansion coefficient of the bearing structure, which is derived from the first thermal expansion coefficient and the second thermal expansion coefficient and the size of the outer wall and the size of the filler. Preferably, therefore, in addition to the thermal expansion coefficient of the material used or to be used, the size of the outer wall and the size of the filler are also considered in the design, in particular its cross-sectional area in the cross section extending perpendicular to the linear direction. Therefore, suitable materials for the outer wall and the filler can be selected and the corresponding thermal expansion coefficient can be selected accordingly, and in addition the cross-sectional area of ​​the outer wall and the filler can be selected / established. This makes it possible to adapt or match the resulting thermal expansion coefficient of the filled hollow body to the thermal expansion coefficient of the bearing structure. However, in the design of the linear guide, the thermal expansion coefficient of the bearing structure can also be selected alternatively or additionally by selecting the corresponding material or the corresponding material combination, so that the resulting expansion coefficient of the bearing structure and the thermal expansion coefficient of the filled hollow body are adapted or matched to each other.

[0035] Matching the coefficients of thermal expansion is understood to mean in particular that they are identical at a defined temperature (e.g. room temperature, such as 20 or 22 degrees Celsius), or are identical on average over a temperature range that may be less than the permissible operating range of the coordinate measuring machine or may be the operating range. However, in another embodiment, matching is understood to mean that the coefficients of thermal expansion are approximately identical, in particular under the temperature conditions mentioned in the previous sentence, and for example at a defined temperature or on average over a temperature range that deviates from each other by less than ten percent, preferably less than eight percent, in particular less than five percent.

[0036] In particular, the filler can be made of a metal, a metal alloy or of a fiber composite material. Possible metals are, for example, zinc, optionally also a metal alloy. Zinc can be easily processed, in particular melted at a relatively low melting point, in order to fill the hollow body with it. In addition, zinc has a quite suitable coefficient of thermal expansion of about 29 micrometers per Kelvin, in particular when steel is used as the material for the outer wall of the hollow body and light metal is used as the material of the load-bearing construction. This second coefficient of thermal expansion of zinc as a filler material is higher than the first coefficient of thermal expansion of steel as a wall material (depending on the type, about 11 to 16 micrometers per Kelvin) and also higher than the third coefficient of thermal expansion of the load-bearing construction, for example in the case of aluminum (about 23 to 24 micrometers per Kelvin). BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention is not limited to these exemplary embodiments. In the various figures of the accompanying drawings:

[0038] Figure 1 An exemplary embodiment of a coordinate measuring machine is shown, the coordinate measuring machine comprising a linear guide for guiding a linear movement of two parts of the coordinate measuring machine relative to each other,

[0039] Figure 2 A simplified illustration of an exemplary embodiment of a linear guide is shown, which comprises two guide elements and a carriage which is guided linearly movably on these guide elements, and

[0040] Figure 3 Shown is a section through a guide element of a linear guide and through a fastening element for fastening the guide element to a load-bearing construction. DETAILED DESCRIPTION

[0041] Figure 1 An example of a coordinate measuring machine 28 is shown, which has a base 1, to which a measuring table 2 is fastened. In the particular embodiment shown, the substructure of the measuring table 2 and the part standing upright behind the measuring table 2 form an L-shaped part 8, which, for example, also serves as a housing for a controller for controlling the operation of the coordinate measuring machine 28. The L-shaped part 8 can, for example, be a casting. A linear guide is arranged on the top side of the L-shaped part 8, along which the measuring carriage 5 can be moved in the horizontal direction indicated by the arrow x. In accordance with Figure 1 The linear guide is not shown in the illustration because it is covered by the bellows 9. The end of the linear guide is provided with a drive 7 ( Figure 1Only the cover is shown in the figure). The drive 7 makes it possible to drive the measuring carriage 5 of the linear guide in the direction of the arrow x. In addition, a scale is provided below the bellows for capturing the corresponding position of the measuring carriage 5 in the direction indicated by x. The measuring carriage 5 itself is also provided with a linear guide so that the vertically aligned measuring carriage 6 can be moved in the horizontal direction indicated by the arrow y. The measuring carriage 6 is also provided with a drive 10 for movement ( Figure 1 Here again only the cover is shown) and a scale which makes it possible to measure the position of this measuring carriage in the horizontal direction indicated by the arrow y. The measuring carriage 6 itself also has a linear guide inside, by means of which another measuring carriage 36 can be mounted so as to be linearly movable in the vertical direction indicated by the arrow z, although only its lower end (in the form of a quill 3) is shown here. The sensor 4 is fastened to the lower end of the measuring carriage 36, that is to say at the lower end of the quill 3.

[0042] The measuring carriage 36 can be moved via the drive 11 in the direction indicated by the arrow z (in this case, in Figure 1 Only the cover of the drive 11 is shown in the figure). In addition, a scale which is also not shown and can be used to determine the exact position of the measuring carriage 36 is arranged inside the measuring carriage 6. The sensor 4 is in the form of a measuring sensor, in the case of which a probe needle 30 for probing the workpiece 31 is mounted so as to be deflectable in all three coordinate directions x, y and z (corresponding to the arrows x, y, z and to the Cartesian coordinate system) relative to the sensor housing. When probing the workpiece 31, the probe needle 30 is deflected from its non-operating position relative to the housing of the sensor 4 in the coordinate directions x, y and z, and this deflection is determined by the corresponding detectors in the coordinate directions x, y and z. The measured deflection of the probe needle 30 is then mathematically combined with the position of the measuring carriages 5, 6 and 36 measured via the scale, so that the position of the probed point on the surface of the workpiece 31 can be accurately calculated. The controller 8 is used to actuate the drives 7, 10 and 11 to read out the scale values ​​of the measuring carriages 5, 6 and 36 and to read out the probe needle deflection of the probe needle 30 of the sensor 4 in the coordinate direction. For this purpose, the controller has, for example, a plurality of microprocessors so as to be able to perform control tasks in real time. Figure 1 A control panel (not shown in detail in the figure and which can be used to set the CNC measurement sequence and further process the measurement results) and a control panel (which can also be used to manually operate the coordinate measuring machine via corresponding operating elements) are connected to the microprocessor controller. At least one of the above-mentioned linear guides can be designed in a manner according to the invention.

[0043] 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 can be mounted linearly displaceable in one or more coordinate directions, for example. Other configurations of the coordinate measuring machine are also basically possible. Some examples have already been mentioned above. For example, a coordinate measuring machine with a receiving seat (for example, a linear guide in a kinematic chain of two successive rotational degrees of freedom) can have only a rotational degree of freedom of movement. According to another example, a coordinate measuring machine with a rotational degree of freedom of movement can additionally be movable relative to a fixed base along a linear guide.

[0044] The sensor 4 is also only one of a number of possible exemplary embodiments. Instead of the measuring sensor 4, a switch sensor can also be used, which triggers an electrical pulse when its probe tip contacts the workpiece, or an optical sensor, such as a digital camera or a laser triangulation sensor. The coordinate measuring machine can also include a plurality of sensors.

[0045] therefore, Figure 1 Thus, a coordinate measuring machine 28 is shown, which comprises a sensor 4 for capturing the surface of a workpiece 31, a workpiece support (here: workpiece table 2) for receiving the workpiece 31 to be measured, and a mechanism (here with measuring carriages 5, 6 and 36) for moving the sensor 4 relative to the workpiece 31. In particular, in other embodiments of the coordinate measuring machine, these structural elements of the coordinate measuring machine can be configured differently. Only in the case of the coordinate measuring machine 28 shown and possibly in the case of some other configurations, in which the mechanism has at least one vertically movable measuring carriage 36, which is guided on a vertical linear guide that is movable relative to a part of the mechanism that is stationary relative to the measuring carriage, the sensor 4 is fastened to the lower end of the measuring carriage.

[0046] Figure 2 An isometric view of a linear guide with two tubular, mutually parallel guide elements 24 is shown. The guide elements 24 movably guide the movement of a carriage 22 which has four slotted ball bearing bushings 23. For the ball bearing bushings and guide elements, only one is denoted by the reference numerals 23 and 24, respectively, in each case. The guide elements 24 are each fastened to the carrier construction 21 via a fastening element 26 extending parallel to the guide elements 24.

[0047] Figure 2The linear guides shown in are only exemplary embodiments and may differ therefrom if the invention is implemented differently. For example, there may be only a single guide element or there may be more than two guide elements. Furthermore, it is possible for the respective guide element to be fastened directly to the load-bearing structure not indirectly via a fastening element, but for example via a plurality of bolts or in another way. Furthermore, Figure 2 Compared to the one shown in FIG. 1 , the load-bearing structure may not be a one-piece structure such as a base plate, but may have any other load-bearing structure, such as a structure having a plurality of pillars connected to each other. The cross-sectional profile of at least one guide element may also not be as shown in FIG. Figure 2 , but any other cross-sectional profile suitable for the corresponding linear guide. For example, Bosch Rexroth (as already mentioned in the introduction) in addition to Figure 2 In addition to spherical guide bushings of the type shown in the drawings, spherical guide rails and roller guide rails as well as roller runner guides are also produced, in which case the guide elements have the same Figure 2 The cross-sectional profiles of different shapes are shown in FIG. , for example an X-shaped profile with two oppositely positioned lateral constrictions. According to the invention, these guide elements, referred to as rails, can also be made in the form of hollow bodies with a filler. Figure 2 Another possible modification of the linear guide shown in relates to the spherical bushing 23 which can be formed differently and / or replaced by other elements mounted in rolling bearings.In particular, the above-mentioned possible modifications can be realized individually or in any desired combination.

[0048] Figure 3 shows that passing through a Figure 2 24 and the fastening element 26. However, it is mainly the cross-sectional shape of the fastening element 26 that is different from Figure 2 The cross-sectional shapes shown in are different.

[0049] The guide element 24 has a hollow body with an outer wall 41 and a filling 42. In addition to the hollow body, the guide element 24 may also have further components, such as respective terminations at opposite ends. The guide element 24 may also have cutouts for fastening means.

[0050] To produce the filling 42 of the hollow body, in a specific exemplary embodiment, a metallic filling material has been melted and cast into the inner space of the hollow body. Optionally, the inner surface of the outer wall has been roughened beforehand by sandblasting. Here, the material of the wall is steel, preferably hardenable steel. In this exemplary embodiment, the filling material is zinc. The load-bearing construction in the exemplary embodiment is also made of aluminum. Alternatives and variants of the design of the linear guide have been discussed.

[0051] An exemplary embodiment of how the coefficient of thermal expansion of the materials and the size of the cross-sectional area of ​​the outer wall and the filler of the guide element can be configured is described below. The calculation assumes that, upon temperature changes, the wall material and the filler material of the hollow body expand / contract to different degrees in the linear direction (direction of the guide linear movement), and therefore exerts corresponding longitudinal forces on the outer wall and the filler in the linear direction (hereinafter also referred to as the longitudinal direction). Assuming that the connection between the outer wall and the filler remains in place, so that there is no relative movement in the longitudinal direction, the following balance of forces holds:

[0052] F1+F2=0 (1)

[0053] In this respect, F1 represents the force acting on the outer wall in the longitudinal direction and F2 represents the force acting on the filler in the longitudinal direction. Due to the balance of forces, these forces act in opposite directions. The following relationship is used:

[0054] F=σ·A (2)

[0055] The above forces can be expressed by the product of the mechanical stress σ and the cross-sectional area A of the outer wall and the filler. The mechanical stress σ can be expressed by the elastic modulus E and the expansion ε sp . Later, the indices 1 and 2 are at least partially reused for the notation. They then again refer to the outer wall and the filling, respectively. In equation 3, the index Sp represents the mechanical stress causing the expansion. Now, in addition, the thermal expansion is also introduced and is represented by the symbol ε th This thermal expansion can be expressed as the product of the thermal expansion coefficient α and the temperature difference Δθ according to the following equation 4:

[0056] σ=E·ε Sp (3)

[0057] ε th =α·Δθ (4)

[0058] By using the expressions on the right hand side of Equation 2 and Equation 3, Equation 5 and Equation 6 are generated in turn from Equation 1:

[0059] σ1·a1+σ2·A2=0 (5)

[0060]

[0061] Rearranging Equation 6 yields:

[0062]

[0063] Total expansion ε ges are the sum of the thermal expansion and mechanical expansion of the outer wall and the filler, respectively. Since the expansion of the outer wall and the expansion of the filler are also the same because they are fixedly connected to each other, the result is as follows:

[0064]

[0065] Rearranging equation 8 gives:

[0066]

[0067] Using the expression on the right hand side of equation 4 in equation 9 gives:

[0068]

[0069] The equation can be rearranged and then the expression on the right hand side of Equation 7 can be used for the mechanical expansion on the left hand side of Equation 7. The mechanical expansion of the filler can then be calculated based on To rearrange and solve the resulting equation:

[0070]

[0071] Now, the thermal expansion coefficient α ver It can be expressed as follows. Here we use Equation 8:

[0072]

[0073] The index ver represents the thermal expansion coefficient α ver is related to the combination of outer wall and filling. Now, the expressions on the right-hand side of equation 4 and equation 14 can be used in each case in equation 15 to give:

[0074]

[0075] Fractionating the temperature difference Δθ on the right hand side of Equation 16 gives the following:

[0076]

[0077] Thermal expansion coefficient α ver Therefore, the expression on the right hand side of equation 17 is derived, which involves the thermal expansion coefficient α1 of the outer wall of the hollow body, the thermal expansion coefficient α2 of the filler, the elastic moduli E1 and E2 of the outer wall and the filler, respectively, and the cross-sectional areas A1 and A2 of the outer wall and the filler, respectively. If the thermal expansion coefficient α1 of the filled hollow body (i.e., the combination of the hollow wall and the filler) verThe design prescription for the thermal expansion coefficients and cross-sections of the outer wall and the filler of the hollow body is obtained by being equal to the thermal expansion coefficients of the load-bearing construction. In particular, if suitable materials are initially selected for the outer wall and the filler, their thermal expansion coefficients are established. Then, the ratio (quotient) of the cross-sectional area of ​​the outer wall of the hollow body to the cross-sectional area of ​​the filler can be selected so that equation 17 is satisfied. Since only the ratio of the cross-sectional areas must obtain a value that satisfies equation 17, the total cross-sectional area of ​​the filled hollow body can still be varied and can be selected in particular so that the desired mechanical stiffness of the hollow body as a whole is obtained.

[0078] In particular, when producing a linear guide, it is therefore possible to proceed as follows:

[0079] a) determining and / or establishing the values ​​of the coefficient of thermal expansion of the load-bearing structure, the value of the coefficient of thermal expansion of the outer wall of the hollow body and the value of the coefficient of thermal expansion of the filling of the hollow body, in particular by selecting suitable materials in each case; it should be noted that if the total coefficient of thermal expansion of the hollow body should be at least approximately the same as the coefficient of thermal expansion of the load-bearing structure, the value of the coefficient of thermal expansion of the load-bearing structure must be between the value of the coefficient of thermal expansion of the outer wall and the value of the coefficient of thermal expansion of the filling;

[0080] b) determining and / or establishing a value for the ratio of the cross-sectional area of ​​the outer wall of the hollow body to the cross-sectional area of ​​the filling, in particular presupposing that the cross-sectional area of ​​the outer wall of the hollow body and the cross-sectional area of ​​the filling in a linear direction are of equal size;

[0081] c) Determine the cross-sectional area of ​​the hollow body.

[0082] In particular, the values ​​determined and / or established by steps a) and b) are determined and / or established in dependence on one another such that the resulting coefficient of thermal expansion of the hollow body is identical to the coefficient of thermal expansion of the load-bearing construction.

[0083] The order of steps a) to c) is not fixed here and can vary depending on the embodiment. Thus, for example, it is possible to start with step c). In principle, step b) can also be carried out before step a). However, the results of steps a) and b) depend on each other. Steps a) and b) can also be carried out partially in parallel. For example, the material of the load-bearing structure and therefore the thermal expansion coefficient can be established first, then the size of at least one of the cross-sectional area of ​​the outer wall of the hollow body and the cross-sectional area of ​​the filler can be established, and then the residual value of the thermal expansion coefficient and the cross-sectional area can be determined.

[0084] The coordination according to steps a) to c) can also be carried out iteratively. For example, the two materials for the outer wall of the hollow body and the filling can first be selected, as a result of which 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 ratio of the cross-sectional areas is not suitable for practical implementation, optionally also taking step c) into account. 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 step b) being carried out again.

Claims

1. A coordinate measuring machine having a linear guide for guiding a first part of the coordinate measuring machine to move relative to a second part of the coordinate measuring machine, wherein: The linear guide comprises: - a guide element (24) extending in a linear direction, a carrying structure (21) to which the guide element (24) is fastened, a carriage (22) which is movable in the linear direction along the guide element (24) and is guided by the guide element (24) during the movement, wherein the guide element (24) is in the form of a hollow body, the outer wall (41) of which is formed by a wall material having a first thermal expansion coefficient (α1), and the hollow body is filled with a filling material having a second thermal expansion coefficient (α2), as a result of which a filling (42) of the hollow body is formed, wherein the support structure (21) has a third thermal expansion coefficient which is higher than the first thermal expansion coefficient (α1) of the wall material, and The second thermal expansion coefficient (α2) of the filling material is also higher than the first thermal expansion coefficient (α1).

2. The coordinate measuring machine according to claim 1, wherein: The second thermal expansion coefficient (α2) of the filling material is higher than the third thermal expansion coefficient of the supporting structure (21).

3. The coordinate measuring machine according to claim 2, wherein: The thermal expansion coefficient of the filled hollow body matches the third thermal expansion coefficient of the supporting structure (21), and the thermal expansion coefficient of the filled hollow body is obtained from the first thermal expansion coefficient (α1) and the second thermal expansion coefficient (α2) as well as the dimensions of the outer wall (41) and the dimensions of the filler (42).

4. A coordinate measuring machine according to any one of the preceding claims, wherein: The filler (42) is connected to the outer wall (41) of the hollow body at the inner surface of the outer wall (41).

5. A coordinate measuring machine according to any one of the preceding claims, wherein: The cross-section of the outer wall (41) and the cross-section of the filler (42) are constant in the linear direction over the entire contour of the linear guide, and the guide element (24) is capable of guiding the carriage (22) to move in the linear direction.

6. A coordinate measuring machine according to any one of the preceding claims, wherein: The wall material of the outer wall (41) of the hollow body is steel.

7. A coordinate measuring machine according to any one of the preceding claims, wherein: The supporting structure (21) is made of light metal.

8. A coordinate measuring machine according to any one of the preceding claims, wherein: The filler (42) is made of metal, metal alloy or fiber composite material.

9. A method for producing a coordinate measuring machine, the coordinate measuring machine comprising a linear guide for guiding a first part of the coordinate measuring machine to move relative to a second part of the coordinate measuring machine, and wherein: The method includes: - producing a guide element (24) extending in a linear direction, - fastening the guide element (24) to the carrying structure (21), - arranging the carriage (22) so that the carriage (22) can be moved in the linear direction along the guide element (24) and is guided by the guide element (24) during the movement, The guide element (24) is in the form of a hollow body, the outer wall (41) of which is formed by a wall material having a first thermal expansion coefficient (α1), and the hollow body is filled with a filling material having a second thermal expansion coefficient (α2), as a result of which a filling (42) of the hollow body is formed, wherein the support structure (21) has a third thermal expansion coefficient which is higher than the first thermal expansion coefficient of the wall material, and The second thermal expansion coefficient (α2) of the filling material is also higher than the first thermal expansion coefficient (α1).

10. The method according to claim 9, wherein: The second coefficient of thermal expansion (α2) of the filler material is selected to be higher than the third coefficient of thermal expansion of the load-bearing structure (21).

11. The method according to claim 10, wherein: By selecting a material having the first thermal expansion coefficient (α1) and the second thermal expansion coefficient (α2) and by configuring the size of the outer wall (41) and the size of the filler (42), the thermal expansion coefficient of the filled hollow body is matched to the third thermal expansion coefficient of the supporting structure (21), and the thermal expansion coefficient of the filled hollow body is obtained from the first thermal expansion coefficient and the second thermal expansion coefficient as well as the size of the outer wall (41) and the size of the filler (42).

12. The method according to any one of claims 9 to 11, wherein: The filler (42) is connected to the inner surface of the outer wall (41) of the hollow body.

13. The method according to any one of claims 9 to 12, wherein: The cross-section of the outer wall (41) and the cross-section of the filler (42) remain constant in the linear direction over the entire contour of the linear guide, and the guide element (24) is capable of guiding the carriage (22) to move in the linear direction.

14. The method according to any one of claims 9 to 13, wherein: The wall material of the outer wall (41) of the hollow body is steel, the supporting structure (21) is made of light metal, and / or the filler (42) is made of metal, a metal alloy or a fiber composite material.

15. The method according to any one of claims 9 to 14, comprising the following steps: a) determining and / or establishing the value of the thermal expansion coefficient of the support structure (21), the value of the thermal expansion coefficient of the outer wall (41) of the hollow body, and the value of the thermal expansion coefficient of the filling (42) of the hollow body; b) determining and / or establishing a value for the ratio between the cross-sectional area of ​​the outer wall (41) of the hollow body and the cross-sectional area of ​​the filling (42); c) establishing the cross-sectional area of ​​the hollow body; in, The values ​​determined and / or established by steps a) and b) are determined and / or established in dependence on one another such that the resulting coefficient of thermal expansion of the hollow body is identical to the coefficient of thermal expansion of the carrier construction.

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