Abstract:
The present application relates to devices for determining inertia properties of an object, said devices comprising a support and a measuring platform which are arranged relative to each other in such a way that movements between two and five degrees of freedom are possible.

Description:
PRIORITY CLAIM TO RELATED APPLICATIONS 
     This application is a U.S. national stage application filed under 35 U.S.C. §371 from International Application Serial No. PCT/EP2014/059787, which was filed 13 May 2014, and published as WO2014/184201 on 20 Nov. 2014, and which claims priority to Germany Application No. 10 2013 208 875.2, filed 14 May 2013, which applications and publication are incorporated by reference as if reproduced herein and made a part hereof in their entirety, and the benefit of priority of each of which is claimed herein. 
     TECHNICAL FIELD 
     The subject-matter of the present invention is a device according to the independent claims, as well as a method according to the further independent claims. 
     BACKGROUND OF THE INVENTION 
     Inertia measurements for determining inertia characteristics of an object with a spatial mass distribution (in contrast to point masses) serve for the simulation or prediction of the dynamic behaviour of the object, such as a car for example. Information for example concerning the dynamic handling of a car is provided by way of determining the inertia characteristics, i.e. the mass, the centre of gravity as well as the moments (moments of inertia and/or moments of deviation) of the inertia tensor. Numerous industrial applications for determining inertia characteristics are known in the state of the art. 
     One device which is known in the state of the art for example is the device “Resonic 100” or “Resonic 350” of Resonic GmbH. The device comprises a carrier as well as a measurement platform and a plurality of spring elements which are arranged between the measurement platform and the carrier. The object to be measured is placed on the measuring platform and the measurement platform is deflected [out] by a random knock, so that the measurement platform subsequently freely oscillates. The inertia characteristics of the object placed on the measurement platform can be subsequently determined by way of the measuring of the frequency spectrum of the free oscillations. A measurement platform is hereinafter to be understood as a rigid receiver for the object to be measured. 
     A further device for determining inertia characteristics is known from US 2012/0324991. The device comprises a carrier, a measurement platform and a spherical joint which is arranged between the measurement platform and the carrier. The measurement platform is then actively moved (by way of actuators) and the forces which thereby act are determined via force sensors. Inertia characteristics of the object to be measured can then be determined from the force measurements and the measurement of the movement of the platform. 
     SUMMARY 
     It is the object of the present invention, to provide a device for determining inertia characteristics, which offers an alternative and/or an improvement with respect to the devices which are already known from the state of the art. This object is achieved by the devices of the independent claims and by way of the method of the further independent claims. 
     A first aspect of the invention encompasses a device with a carrier, with a measurement platform for arranging the object, as well as with a plurality of restoring elements arranged between the measurement platform and the carrier. The measurement platform is movable in up to five degrees of freedom with respect to the carrier (but not in six degrees of freedom) and a bearing arrangement and/or joint arrangement is arranged between the carrier and the measurement platform, in a manner such that this permits a movement of the measurement platform with respect to the carrier in at least two degrees of freedom, preferably at least three degrees of freedom. 
     The bearing arrangement and/or joint arrangement permits a movement of the measurement platform with respect to the carrier in between two and five degrees of freedom. The restoring elements are arranged between the carrier and the measurement platform, in a manner such that the measurement platform can freely oscillate about an equilibrium position. The restoring elements hereby are therefore to be understood as passive restoring elements, and not as actuators which transmit an active movement upon the measurement platform. The device according to the application oscillates freely as soon as this has been deflected once for example. The measurement of the frequency spectra of the free oscillations provides information on the inertia characteristics. A permanent, forced oscillation is not necessary. With n degrees of freedom, the natural frequencies and amplitudes of the n oscillations are preferably detected at least at n measurement points when measuring an object. 
     The bearing arrangement and/or joint arrangement (hereinafter bearing arrangement) is suitable for accommodating the static load of the object which is to be arranged on the measurement platform and is to be measured. The position or orientation of the measurement platform is independent of the object to be measured due to the arrangement of the object directly above the bearing arrangement. The effect of the stiffness and inertia of the restoring elements which permit the free oscillations is thus essentially the same for each object to be measured. Moreover, the static load of the object, which is to say the weight, bears on the bearing arrangement and/or joint arrangement and not on the restoring elements as is the case for example with the hitherto existing devices of Resonic GmbH. The restoring elements can be selected infinitely soft or hard since the load of the object to be measured from now is carried by the bearing arrangement and/or joint arrangement, so that highly elastic test objects, such as satellites for example, can be measured, since the natural frequencies of the free oscillations can be set almost infinitely low. 
     A calibration of the device, which is to say the evaluation of the total stiffness matrix of the restoring elements together with the combined mass matrix of restoring elements and measurement platform is moreover possible for example by way of a one-off calibration measurement. The mathematical model of the suspension of the measurement platform is not dependent on the object to be measured, since the calibration can be carried out independently of the test object and the orientation or position of the measurement platform is independent of the object to be measured, provided that the load of this lies above the bearing arrangement. This is in contrast to earlier devices, with which the calibration could not be carried out independently of the object to be measured, but had to be computed from the characteristics of the individual springs. Hereby, the modelling was only possible or practical for certain springs. Thus for example it is no longer necessary to exclusively apply tension springs with the present device, but one can likewise also fall back on other passive restoring elements. 
     In contrast to the state of the art, in which tension springs are applied as passive restoring elements, with the device of the present application it is no longer necessary to exclusively apply these, but other restoring elements are also possible. The space around the measurement platform is restricted with the application of tension springs according to the state of the art, since the tension springs suspend the measurement platform and thus the centre of gravity of the measurement platform lies below the upper suspension point of the tension springs. The size of the object to be measured however by way of this is essentially limited to a dimension which is smaller than the dimension of the measurement platform. The object can be formed larger than the measurement platform, and a centre of gravity of the measurement platform, in particular a centre of gravity of the object to be measured can lie above the suspension points of the restoring elements due to the fact that the present invention also permits other types of restoring elements. Measurement platforms which have a small inertia compared to the object to be measured can be applied on account of this, and thus the inertia characteristics of the object can be measured more accurately. 
     With regard to the restoring elements, it can be the case for example of compression springs, tension springs, leaf springs, helical springs, conical springs, torsion springs, spiral springs, disc springs, or similar springs which are known from the state of the art. Other passive restoring elements however are also possible, such as for example air-filled cylinders, in which a piston is led, wherein a loading of the piston/plunger compresses the air mass held in the cylinder and pressure oscillations occur in the cylinder. Further restoring elements can be deduced from the state of the art. 
     With regard to the carrier, for example it can be the case of a floor of a room or of a frame which is separate from the room and which can be connected to parts of a room or on account of its mass can be arranged in a spatially fixed manner during a measurement of inertia characteristics. 
     With regard to the measurement platform for arranging the object, it can be the case for example of a frame or a mount, which is connected to the carrier via the restoring elements and, in this aspect, preferably independently thereof via the bearing arrangement and/or joint arrangement. I.e. the restoring elements connect the measurement platform to the carrier in a direct manner, so that the restoring elements are not connected to the bearing arrangement and/or joint arrangement. In one variant, the carrier itself can be connected to a further carrier or the room, via further bearing arrangements and/or joint arrangements or restoring elements, wherein the further carrier is preferably arranged below the carrier. The restoring elements between the carrier and the measurement platform are thereby arranged in a manner such that each individual restoring element can effect a restoring in more than one degree of freedom. In a further variant there are exclusively restoring elements between the further carrier and the measurement platform. 
     The measurement platform or the carrier can be manufactured of metals, composite materials (e.g. glass-fibre-reinforced plastic, carbon, aramide or Kevlar) or other sufficiently stiff materials and can be manufactured from hollow elements, solid carriers or components constructed in a sandwiched construction manner. The measurement platform as a whole is designed in a rigid manner, so that this forms a rigid body. 
     A plurality here is to be understood as a number of restoring elements which is equal to two or more than two. 
     Further embodiments of the first aspect of the application are disclosed in the dependent claims as well as the embodiment examples. 
     In an embodiment, the plurality of restoring elements is spring elements. Spring elements are comparatively simple to manufacture and can be made available for a wide field of application. The spring hardness can be selected according to the mass of the object to be measured, so that stiffer springs or additional springs can prevent an object arranged on the measurement platform from flipping over, for example given an object with a large product of mass and height of the centre of gravity. Objects, whose centre of gravity lies almost infinitely above the measurement platform can be measured in this manner. The natural frequencies of the free oscillations can be infinitely reduced by way of matching the springs to the mass and height of centre of gravity, so that extremely elastic test objects can be measured. 
     In a further embodiment, the bearing arrangement and/or joint arrangement is designed in a manner such that the measurement platform is fixed in a preferable vertical translatory movement direction with respect to the carrier, i.e. the measurement platform is mounted in a manner such that the measurement platform has a spatially fixed point given a deflection of this. The measurement platform as a whole cannot be translatorily displaced along the z-axis in the case of a fixation in the z-direction. As long as the measurement platform for example is fixed with respect to the carrier in the translatory movement direction, in the z-direction, which is to say in the direction of gravity, the bearing arrangement and/or joint arrangement is particularly suited for accommodating the static load of the object to be measured. The calibration of the system is simplified by way of this, as initially mentioned. 
     In a further embodiment, the plurality of restoring elements is selected in a manner such that the plurality is larger than or equal to a number of degrees of freedom, in which the measurement platform is freely movable. In this manner, it can be ensured that the restoring elements reliably prevent a flipping of the measurement platform. 
     In a further embodiment, the device comprises a plurality of restoring elements which accommodate vertical as well as horizontal forces. 
     In a further embodiment, the plurality of restoring elements comprises a first and a second group of restoring elements, wherein the first group of restoring elements is arranged in a manner such that these predominantly accommodate vertical forces, and the second group of restoring elements is arranged in a manner such these predominantly accommodate horizontal forces. The different groups of restoring elements are in the position of restricting different degrees of freedom of the movement of the measurement platform, due to the fact that the restoring elements can accommodate different forces. Thus vertical restoring elements are preferably suitable for accommodating degrees of freedom of rotation which are directed about the x-direction and y-direction which is to say about the plane perpendicular to gravity. Horizontal restoring elements are suitable for accommodating a translatory movement in the plane as well as rotations about the z-axis. A translatory movement which is directed in the z-direction as the case may be is likewise restricted by the first group. 
     In a further embodiment, the carrier is preferably arranged completely below the measurement platform. The carrier in this manner does not limit the size of the object to be measured, which can project beyond the measurement platform. It is possible to measure comparably large objects by way of this, so that the applications possibilities of the device are increased. 
     The measurement platform in one variant is connected to the bearing arrangement and/or joint arrangement in a manner such that the movement is simultaneously effected in the two to five degrees of freedom. I.e. several consecutive measurements, with which different degrees of freedom are excited in each case, are not necessary. 
     In a further embodiment, the bearing arrangement and/or joint arrangement comprises at least one air bearing. Air bearings amongst other things have the advantage that operated by way of compressed air for example, they can represent a low-friction bearing. They are moreover inexpensively obtainable on the market and have a high stiffness, so that the kinematics of the free oscillations reflects the characteristics of the object to be measured, in an essentially unadulterated manner. With regard to the air bearings, it can be the case for example of a plane air bearing or a spherical air bearing. 
     In a further embodiment, the bearing arrangement and/or joint arrangement comprises at least one spherical bearing and/or joint, a torsion bearing, a ball bearing, and/or cardanic bearing, which is arranged between the carrier and the measurement platform, in manner such that the measurement platform is movable in at least two degrees of freedom. It is possible for example to permit a rotation about the x-axis and y-axis, on account of the bearings mentioned above. Moreover, that point of the measurement platform, on which the bearing engages, serves as a support of the weight of the object to be measured, since the bearing or joint mentioned above prevents a movement for example along the z-axis. 
     In a further embodiment, the bearing arrangement and/or joint arrangement comprises a plane sliding bearing which is arranged in a manner such that the measurement platform is movable in at least three degrees of freedom. Thereby, it can be the case of two translatory directions within the plane and a rotation about the z-axis. However, plane sliding bearings which only permit a single translatory direction or exclusively a rotation about the z-axis are also possible. 
     Hereby, it is to be mentioned that the different bearings can be combined with one another, so that between two and five degrees of freedom of the measurement platform are available for the measurement of the inertia characteristics of the object to be measured. 
     In another embodiment, the bearing arrangement and/or joint arrangement comprises a device for adjustment, so that the bearing arrangement can be fixed in a predefined position with respect to the carrier and/or the measurement platform. The predefined position is preferably a “zero position” which is to say a certain alignment of the components of the bearing arrangement with respect to the measurement platform or the carrier is given in this position. In this manner, it is ensured that the above-mentioned calibration of the device can be applied out of this “zero position”. The provision of the “zero position” is thus a hardware calibration. 
     In a further embodiment, the bearing arrangement and/or joint arrangement is designed in a manner such that a centre of gravity of the measurement platform is arranged directly above or below the centre of gravity of the measurement platform. 
     In a further embodiment, a gravity pendulum arrangement is arranged on the measurement platform, and this can add further degrees of freedom, additionally to the degrees of freedom which can be present by way of the movements between the carrier and the measurement platform. However, the limitation of the measurement platform being limited in at least one degree of freedom with respect to the carrier continues to be present. 
     In a further embodiment, the device comprises a multitude of sensors, in order, with regard to measurement technology, to detect a movement of the measurement platform with respect to the carrier. The frequency spectrum of the oscillations can be determined by way of the detection of the movement of the measurement platform with respect to the carrier, and thus the centre of gravity as well as the mass can be preferably determined from the natural frequencies and amplitudes, of the oscillation of the inertia tensor. 
     Only a subset of ten parameters (six parameters of the inertia tensor, three parameters of the centre of gravity, and the mass) can be determined if the number of degrees of freedom, in which the measurement platform can be moved, is reduced to less than five degrees of freedom, and one must have a prior knowledge concerning the object or several measurements must be carried out, wherein the object must be aligned differently with respect to the carrier, between two measurements. 
     Preferably, the sensors are arranged on the carrier or on the measurement platform or extend on the measurement platforms well as on the carrier. Suitable sensors for example are laser distance sensors which by way of triangulation determine the distance of certain points of the carrier and of the measurement platform to one another and thus determine frequency spectra and amplitudes. 
     Although force sensors, accelerations sensors or gyroscope sensors can be applied, these however are not necessary and are also not envisaged for numerous embodiments. 
     The data of the sensors is preferably led further to a data bus arranged on the device, wherein the data bus is configured in a manner such that a wireless or wired connection channel to a data processing installation can be built up. The data bus is provided for coupling the device to a data processing installation, wherein the data of the sensors is transferred to the data processing installation by the data bus. In alternative embodiment, parts of the signal processing can be arranged in the device itself. This for example comprises an A/D converter. 
     The plurality of sensors can be selected in a manner such the number is larger than or equal to a number of degrees of freedom, in which the measurement platform is freely movable. The different natural frequencies and oscillation amplitudes can be well resolved by way of this. 
     A second aspect of the present invention relates to a device for determining inertia characteristics of an object, wherein the device comprises a carrier, a measurement platform for arranging the object, as well as a bearing arrangement and/or joint arrangement, which is arranged between the carrier and the measurement platform, in a manner such that the bearing arrangement and/or joint arrangement permits a movement of the measurement platform with respect to the carrier in at least two degrees of freedom. 
     In this aspect of the invention, the carrier is arranged above the measurement platform and the measurement platform is designed in a manner such that the object is arranged below the measurement platform. The bearing arrangement and/or joint arrangement is moreover connected to the carrier via a plurality of restoring elements, in a manner such that the bearing arrangement and/or joint arrangement is movable with respect to the carrier perpendicularly to a direction of the weight force in two degrees of freedom. 
     The arrangement or device of the second aspect with this thereby corresponds to a gravity pendulum, which can either oscillate in one or two degrees of freedom, wherein the suspension point of the gravity pendulum is movable in at least one additional degree of freedom. At least two degrees of freedom can be utilised by way of this, in order to determine the inertia characteristics of an object arranged below the platform. The bearing arrangement similarly to the first aspect of the application can comprise a ball joint bearing or cardanic bearing, which can be moved in at least two degrees of freedom. The restoring elements in a variant of the second aspect create a direct connection between the carrier and the bearing arrangement and/or joint arrangement, so that the bearing arrangement and/or joint arrangement for example is led in the x-y plane, i.e. the plane perpendicular to the gravity force, and by way of the restoring elements can be restored into an idle position within the x-y plane. A direct connection between the restoring elements and the measurement platform is not necessary in this variant and is not envisaged in numerous embodiment examples, since in this embodiment, with which the measurement object is arranged below the measurement platform, the gravity permits a restoring of the measurement object into the idle position. 
     It should be mentioned that analogously to the first aspect, not only can the carrier be a separate component, but also can also be formed by a room ceiling or likewise. Guides of the restoring elements are then fastened on the ceiling or likewise. 
     A third aspect of the invention concerns a method for calibrating a device described above, wherein a mass matrix of the measurement platform and of the plurality of restoring elements and a total stiffness matrix of the restoring elements are determined in a calibration method. Different measurements with different calibration objects which have known inertia characteristics are carried out for the calibration measurement. The calibration can be carried out as a one-off after the construction or manufacture of the device on account of this, and subsequently only needs to be carried out at regular, larger time intervals. 
     In a further embodiment of the invention, the carrier and/or the measurement platform each comprise an adapter which is designed in a manner such that this comprises a receiver in each case for at least one restoring element. The adapter is preferably designed in a manner such that a different number of restoring elements can be arranged. The adapter can thereby for example receive one, two, three or more restoring elements. This is of great use if the device is to be used for determining inertia characteristics of different objects, in particular of a large different mass and objects with large centre of gravity heights. The device can achieve the desired total stiffness suitable for the object to be measured, by way of adding restoring elements. A restoring element for example can be added for each adapter and in each case the total stiffness matrix can be determined within the framework of calibration measurement, for the different restoring elements. The device in this manner can be applied over a large parameter range of masses, centre of gravity heights and size of the object. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further embodiments of the invention are explained in more detail by way of the subsequent embodiment examples. 
       There are shown in: 
         FIG. 1  a first embodiment of the device of the first aspect with tension springs; 
         FIGS. 2 a  and 2 b    an illustration of an embodiment of compression springs, and the adaptation possibilities of the device; 
         FIGS. 3 a  to 3 c    embodiments of a bearing arrangement and/or joint arrangement; 
         FIGS. 4 a  to 4 h    further embodiments of a bearing arrangement and/or joint arrangement; 
         FIGS. 5 a  to 5 d    embodiments of a device with an adjustment mechanism; 
         FIGS. 6 a  to 6 d    further embodiments of a device; 
         FIGS. 7 a  and 7 b    embodiment of a device with a gravity pendulum arrangement; 
         FIGS. 8 a  to 8 d    further embodiments of a device; 
         FIG. 9  an embodiment of a device according to the second aspect of the application; 
         FIGS. 10 a   / 10   b  illustration of the calibration of a device according to the first or second aspect. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a device  1  which comprises a measurement platform  2 , a bearing arrangement and/or joint arrangement  3  (hereinafter also only called bearing arrangement), as well as a plurality of restoring elements  4 . The bearing arrangement  3  is furthermore connected to a “carrier”  5  which in the present case is merely a floor. The restoring elements  4  are likewise arranged on a wall  5 ′ which can be part of the room, in which the carrier  5  is located. Alternatively, the bearing arrangement  3  can be arranged on a mount which likewise comprises the suspensions for the restoring elements  4 . 
     An object  6  to be measured is arranged on the measurement platform  2 , wherein the object  6  is arranged on the measurement platform  2  in a manner such that its centre of gravity runs along the line  7 . Additionally, an additional mass  8  is arranged on or at the measurement platform and is moved in a manner until the centre of gravity lies directly above the bearing arrangement  3 , in order to achieve a precise adjustment of the centre of gravity above the joint arrangement  3 . 
     In the present embodiment, the restoring elements  4  are tension springs. If the measurement platform is knocked, for example in the drawn z-direction, then the measurement platform  2  oscillates about the rotation degrees of freedom of the x-axis and y-axis, since the bearing arrangement  2  permits the movement in two degrees of freedom, as is schematically represented. As will be explained in more detail by way of the following embodiment examples, the bearing arrangement  3  can also be designed in a manner such that it can be moved in up to five degrees of freedom (then preferably three rotation degrees of freedom and two translatory degrees of freedom in the x-direction and y-direction). A periodic or repeated excitation of the system is not necessary. The restoring elements which are designed as tension springs in the drawn condition are located in the so-called zero position, in which the measurement platform is perpendicular to the z-direction. If the measurement platform is deflected out of this zero position, then the system begins to freely oscillate about the zero position. The natural frequencies and amplitudes of the system, which are effected by the free oscillations, together with the calibration matrix of the device  1  provide information on the nature of the inertia characteristics of the object  6 . The natural frequencies and/or amplitudes of the free oscillations can generally be measured. 
     The adaptation possibilities of the device are dealt with in the  FIGS. 2 a  and 2 b   . The same device  10  with a measurement platform  12  and with a bearing arrangement  13  which is identical in each case is represented in each of the  FIGS. 2 a  and 2 b      
     An object  16  which compared to the object  16 ′ of  FIG. 2 b    has a smaller mass and in the z-direction has a lower centre of gravity and smaller dimension is held on the platform  12  in  FIG. 2 a   . With the represented restoring elements, it is the case of compression springs  14  which are connected between the carriers  15  which is given by a mount which is not drawn in more detail. In this embodiment, the restoring elements  14  are not connected to the bearing arrangement  13 . Identical restoring elements  14 ′ which increase the total stiffness of the device  10  compared to the embodiment example represented in  FIG. 2 a    are additionally added to the restoring elements  14 , in order to adapt the device  10  for the measurement of a larger object  16 ′. In this manner, the system can be adapted to the object to be measured and be accordingly scaled. The restoring elements are preferably inserted, screwed or hooked, into an adapter. The natural frequencies of the system can be reduced by way of this and preferably minimised, without compromising the stability of the system. Particularly elastic bodies can be measured by way of this. 
     The measurement platform is arranged above the carrier in  FIGS. 2 a  and 2 b   . In this manner, is possible, as is represented in  FIG. 2 b    for example, to measure an object  16 ′ which has dimensions projecting beyond the measurement platform  12 . 
     As to how different bearing arrangements and/or joint arrangements can guide a movement in a multitude of degrees of freedom of the measurement platform is to be explained by way of  FIG. 3 . 
     A device  20  which comprises a measurement platform  22 , a bearing arrangement  23  and restoring elements  24  designed as compression springs is shown in  FIG. 3 a   . The bearing arrangement  23  and in each case an end of the restoring elements  24  is connected to a frame  25  serving as a carrier. With the bearing arrangement  23 , the bearing has a spherical air bearing, so that the measurement platform can be moved in three rotation degrees of freedom about the x-axis, y-axis and z-axis. The measurement platform  22  can move in these three rotation degrees of freedom with respect to the carrier, when the measuring platform  22  is deflected into free oscillation. Other spherical bearings, such as oil-mounted spherical forms, universal (cardan) joints (with two degrees of freedom about the x-axis and y-axis) or likewise can also be applied alternatively to the spherical air bearing. The spherical air bearing although being comparatively expensive, however has a very good (i.e. low) friction, which is to say that the measurement platform can be oscillated about the two rotation degrees of freedom essentially without friction. 
     A device  30  with a measurement platform  32 , as well as a bearing arrangement  33  and restoring elements  34  is shown in  FIG. 3 b   . A carrier  35  is moreover present. The measurement platform  32 , the restoring elements  34  as well as the carrier  35  can be compared to the elements described in  FIG. 3 a   . The bearing arrangement  33  comprises at least one plane air bearing which has a high stiffness and permits translatory movements within the x-y plane. Moreover, it permits a movement about the z-axis, so that the represented bearing arrangement  33  permits the movement of the measurement platform with respect to the carrier in three degrees of freedom. In the present embodiment, the bearing arrangement  3  comprises plane air bearings which are arranged at regular distances on the lower side of the measurement platform  32  which faces the carrier. 
     The bearing represented in  FIG. 3 a    as well as the bearing represented in  FIG. 3 b    is operated by way of compressed air. The carrier in many embodiments comprises compressed air feeds conduits for this, and these for example can be connected to an internal or external compressor. In a variant, the arrangement of  FIG. 3 a    can be arranged on an arrangement of  FIG. 3 b   , wherein the measurement platform which is mentioned in the description concerning  FIG. 3 b    would then be the carrier of the total arrangement, and the carrier mentioned in the description concerning  FIG. 3 b    would be the further carrier. The carrier mentioned in the description concerning  FIG. 3 a    would then correspond to the measurement platform of  FIG. 3 b   . The restoring elements of the total arrangement would independently run between the further carrier and the carrier, as well as between the carrier and the measurement platform. 
     A device  40  which comprises a measurement platform  42 , a bearing arrangement  42 , restoring elements  44  and a carrier  45  is shown in  FIG. 3 c   . The bearing arrangement  43  comprises a spherical bearing  46  as is described in the context of the bearing arrangement  23  of  FIG. 3 a   . The bearing arrangement  43  moreover comprises a plurality of plane air bearings  47  as described within the framework of  FIG. 3 b   . The bearing arrangement  43  combines the spherical bearing  46  and the plane air bearing  47  into a single bearing arrangement. In the present embodiment example, the spherical bearing  46  connects the measurement platform  42  to an intermediate pate  48  of the bearing arrangement  43 . The plane air bearings  47  are arranged on the lower side of the intermediate pate  48  and permit a movement along the x/y plane. The measurement platform  42  can now be moved in three rotation degrees of freedom and in two translatory degrees of freedom within the x/y-plane due to the combination of the spherical bearing  46  and the plane air bearing  47 . If the measurement platform  42  is deflected, then the measurement platform oscillates about a zero position due to the restoring elements and can execute movements in the five above mentioned degrees of freedom. 
     An evaluation of the inertia characteristics of the object to be measured is possible in a single measurement, for example from the measurement of the natural frequencies and the oscillation shapes. It is to be noted here, that although the device until now has been mentioned in combination with a carrier, in one embodiment the device can also be understood to the extent that this only encompasses restoring elements which are connectable to a carrier, and the bearing arrangement is likewise connectable to the carrier. Thus for example the unit shown in  FIG. 3 c    already forms independent subject-matter of the application, independently of the applied bearing arrangement. 
     Further variants of bearing arrangements are to be explained by way of the  FIG. 4 . A device  50  which comprises a measurement platform  52 , a bearing arrangement  53  as well as restoring elements  54  is disclosed in  FIG. 4 a   . The same arrangement is represented rotated by 90° about the z-axis in  FIG. 4 b   . As is shown in  FIG. 3 c   , the bearing arrangement  53  comprises a multitude of plane air bearings  55  which permit a sliding of the measurement platform  52  on the carrier. The plane bearings are connected to an intermediate plate  56 . A further bearing arrangement  57  which permits a movement in the two rotation degrees of freedom about the x-axis and y-axis is arranged on the intermediate plate. The bearing device  57  comprises a first half-cylinder  59  which extends along the y-axis, and which is arranged with its flat side on the measurement platform  52 . The half-cylinder is thus suitable for permitting a movement of the measurement platform about the y-axis. This can be schematically seen in  FIG. 4 c   , with which on the one hand the cylinder  58  is represented in the zero position (cylinder marked with an unbroken line) and deflected out of the zero position (cylinder marked with dashed line). The cylinder  58  is arranged on a plate  59  which for example is a ground or hardened plate. A further half-cylinder  60  which extends along the x-axis is arranged on the lower edge of the plane. Although not being absolutely necessary, for the purpose of simplicity it is assumed that the half-cylinder with its flat side is arranged on the lower side of the plate  59  and has a length comparable to the cylinder  58  and a comparable radius of curvature. The half-cylinder rolls on the plate  59  if the flat side of the half-cylinder is arranged on the plate  56 , so that only this plate  59  needs to be hardened. 
     The movement about the cylinder  60  permits a rotation of the measurement plate  52  about the x-axis. Thus the bearing arrangement  57  permits a movement about the two rotation degrees of freedom x and y. Oval or ellipsoidal shapes or several half-spheres arranged in a row can be selected instead of the circular cylinder shape. The bearing arrangement  57  has huge advantages compared to blade bearings, since the surface pressing of the bearing arrangement is significantly reduced compared to blade bearings. The rolling behaviour of the half-cylinder is modelled in the measurement algorithm. 
     Hardened metals, ceramics or diamond-like composite materials are considered as materials for the bearing arrangement  57 . The basic principle of the half-cylinders (or other arcuate shapes) arranged on one another in the bearing arrangement corresponds to that of a universal joint, since it permits a rotation about two rotation degrees of freedom. The bearing arrangement  57  can also be applied without a further plane bearing, as an independent bearing arrangement, in a device according to the application. 
       FIGS. 4 d  to 4 h    show further bearing arrangements. A device  61  with a measurement platform  62 , a bearing arrangement  63 , restoring elements  64  and a carrier frame  65  is represented in  FIG. 4 d   . The restoring elements connect the lower side of the measurement platform to the upper side of the carrier frame  65 . The same applies to the bearing device  63  which supports the measurement platform  62  in its middle, which is to say its centre of gravity. With the bearing arrangement  63 , it is the case of an elastic rod, which permits the three rotation degrees of freedom and translatory movements of the x/y plane. The rod is connected to the measurement platform and the carrier without further joints. One advantage of this solution is the simple design of the bearing arrangement  63 , with which however movements in up to five decrees of freedom are mad possible, but a disadvantage is the fact that one must fall back on an adapted calibration method. Metals, plastics or composite materials are considered as a material for the rods. 
     A device  70  which similarly to the  FIG. 4 d    comprises a measurement platform  72 , a bearing arrangement  73 , restoring elements  74  and a carrier frame  75  is represented in  FIG. 4 a   . The carrier frame  75  is thereby stationary with respect to the floor and cannot move along this. The bearing arrangement  73  comprises a rigid rod  76  which is connected to the measurement platform or the carrier frame via two ball joints  77  and  78 . A movement in five degrees of freedom is possible in this manner. One advantage of this solution is the simple construction of the bearing arrangement, but a disadvantage however is the fact that the geometric stiffness of the bearing arrangement must be taken into consideration. 
     A further embodiment of a device is represented in  FIG. 4 f   . The device  80  comprises a measurement platform  82 , a bearing arrangement  83 , and restoring elements  84  which are connected to the floor  85 . The bearing arrangement  83  comprises a multitude of plane air bearings which permit a movement of the measurement platform  82  with respect to the base  85  in the x/y direction and about the z-axis. The bearing arrangement moreover comprises a plate  87 , on which a further bearing arrangement  88  is placed. The bearing device  88  is a bearing based on flexure hinges. The bearing arrangement  8  thereby comprises a plate  89 , in which four flexure hinges  90  to  93  are arranged in the present embodiment example, as is also shown in  FIG. 4 g   . Thereby, the flexure hinges  90  and  91  are connected to the plate  87  via bearing blocks, and the flexure hinges  92  and  93  are connected to the measurement platform  82  via rods. A movement about the y-axis is possible about the joints  92  and  93 , and a movement about the x-axis is possible about the joints  90  and  91 . As flexural hinges, one can for example fall back on so-called “flexural pivots” which comprise a casing divided into two parts and the two casing parts can be twisted to one another via a mechanism. 
     A further alterative of a bearing arrangement is schematically represented in  FIG. 4 h   . A spherical cap  103  which is mounted on three balls  105  held in a spherical-segment-shaped shell  104 , is arranged on a measurement platform  102 , at the lower end. The platform can thereby undergo a movement about the three rotation degrees of freedom. The hemispherical shell  104  can thereby be arranged on a further plate, on which an additional bearing device for the movement within the plane is arranged, or can be assembled directly on a carrier. 
     Further bearing arrangements are possible, although a multitude of possible bearing arrangements has already been discussed. Thus for example the half-cylinder explained in  FIG. 4 a    can be replaced in each case by a multitude of hemispheres or mounted solid balls. Moreover, the cylinder could be replaced by a radial segment air bearing. Moreover, the different represented bearings can be combined with one another in a manner such that a movement of the measurement platform with respect to the carrier is possible in two to five degree of freedom in each case. 
     A mechanism for the adjustment of the device is explained by way of  FIG. 5 . A detail of the arrangement represented in  FIG. 4 a    (and  FIG. 4 b   ) is shown in the  FIG. 5 .  FIGS. 5 a  and 5 c   , as well as  5   b  and  5   d  in each case show representations of a device for determining inertia characteristics, in each case rotated by 90° about the z-axis. The measurement platform  52  is arranged on a bearing arrangement  57  which, as described in  FIG. 4 , comprises a cylinder  58 , a ground plate  59  and a second cylinder  60  which is arranged at a 90° angle to the first cylinder  58 . The cylinder  60  rolls on a further plate  56 . Although the measurement platform  52  in the ideal case only carries out rolling movements about the zero position, a lateral offset for example of the cylinder  58  with respect to the plate  59  can occur. The device comprises a mechanism  110  for the adjustment of the measurement platform  52  in the zero position, in order to carry out a hardware calibration of the device before a measurement. The adjustment can be carried out for example by way of at least one, preferably two ball heads  111  and a corresponding device  112  for engaging upon the ball head. The device  112  for example can have a cone shape which engages on the ball head for the self-adjustment of the measurement platform. A force is firstly exerted upon the left side of the measurement platform  52  for the calibration of the device. By way of this, the device  112  lowers onto the ball head  111  until the cylinder  58  releases from the plate  59 . One succeeds in the measurement platform  52  being aligned with respect to the plate  59  and the plate  56  due to the calibration of the device on the ball head. This can be recognised in  FIG. 5 b    for example. 
     It can be clearly recognised by way of the  FIGS. 5 c  and 5 d    that the device for adjustment  110  also effects an alignment along the y-axis, since a plurality of devices, in this case two devices are present. Likewise recognisable in  FIG. 5 d    is the fact that an adjustment of the bearing device  57  is achieved by locking the devices  112  on the ball heads  111 . The measurement platform is calibrated with respect to the plate  56  and the measurement can be initiated. 
     A further variant of a device is to be explained by way of  FIG. 6 . The device  120  comprises a measurement platform  122 , a bearing device  123  as well as restoring elements  124  which are not represented in more detail. The bearing device  123  apart from a plane bearing  125  comprises a plate  126 , on which a single cylinder  127  lies, so that a rotation about an axis is possible. A plan view of the plate  126  is represented in  FIG. 6 a   . Three grooves  128 ,  129  and  130 , in which the cylinder  120  is held can be recognised. Now, in  FIGS. 6 b  to 6 d   , the cylinder  127  is successively arranged in the grooves  128 ,  129  and  130 , so that in each case different degrees of freedom of the object which is stationarily fixed with respect to the measurement platform  122  can be excited into oscillation. All inertia characteristics of the object to be measured can be analysed bit by bit on account of this. 
     A further variant of a device  150  is represented in the  FIGS. 7 a  and 7 b   . The device comprises a measurement platform  152 , a bearing device  153  as well as restoring elements  154  which are fastened on a carrier  155 . With regard to the bearing arrangement, it is the case of plane air bearings which permit a movement within the x/y plane and a rotation about the z-axis. Additionally, a gravity pendulum arrangement  156  is arranged on the measurement platform  152 , with which arrangement an adapter  157  can be pendulated at two suspension points  158  on suspension surfaces  159  of the measurement platform, about a pendulum axis which is drawn as a dashed line. A rotation of the body  160  to be measured, for example about the x.-axis is possible due pendulating movement. Thus a measurement of four degrees of freedom can be carried out simultaneously with the present device. The suspension points  158  are designed as ball caps. The contact surfaces  159  as well as the multitude of suspension points  158  are represented in  FIG. 7 b   . A rotation of the adapter  157  clockwise or anticlockwise can now be carried out, in order to suitably measure the body  160 , so that different contacts points come to lie on the contact surfaces  159 . A complete measurement of the object is possible in this manner. 
     A further embodiment of a device is to be explained by way of  FIG. 8 .  FIG. 8 a    shows a device  200  in a lateral view, whereas  FIG. 8 b    shows a section through the device  200 .  FIGS. 8 c  and 8 d    show different detailed views of the device  200 . 
     The device  200  comprises a measurement platform  201  and a carrier  202 , wherein the measurement platform  201  and the carrier  202  in each case are a six-cornered metal mount with struts to the middle point of the hexagon. A bearing device  203  which can comprise different bearings or joints, in order to permit a movement of the measurement platform  201  with respect to the carrier  202  in two to five degrees of freedom is present between the measurement platform  201  and the carrier  202 . Further restoring elements  204  and  206  are present, in order to counteract a deflection of the measurement platform  201 . The restoring elements  204  belong to a first group of restoring elements which essentially accommodate vertically acting forces between the carrier and the measurement platform. With regard to the restoring elements  204 , it is the case of compression springs which are connected in each case to the carrier and the measurement platform, i.e. the restoring elements are arranged on the carrier and the measurement platform in a direct manner. The carrier as well as the measurement platform moreover comprises an adapter  205 , into which additional restoring elements can be hung/suspended. Only one restoring element is present for each adapter  205  in the represented case, wherein the total stiffness of the device or of the restoring elements can be adapted by way of simply adding or additionally suspending further restoring elements. The adding of restoring elements accommodating vertical forces also permits the measurement of objects with a relatively high centre of gravity. 
     The restoring elements  206  form a second group of restoring elements which here are designed as tension springs. The restoring elements  206  run essentially horizontally such as can be recognised by way of  FIG. 8 c    for example. Thereby, the second group of restoring elements  206  accommodate forces acting essentially in the plane, between the measurement platform  21  and the carrier  202 . Restoring forces can be provided for example with translatory movements or a rotation about the z-axis. 
     The bearing device  203  permits a movement about five degrees of freedom. Only plane air bearings  207  are represented in the section of  FIG. 8 b   , wherein the device moreover comprises two cylinders rolling on one another, as is show in  FIG. 4 a   . The carrier  202  moreover comprises height-adjustable feet  208 , in order to effect an alignment of the carrier parallel to the plane. Thereby, the feet for example can be adjusted in their height by way of screwing in or out. The device  200  moreover comprises a data bus or an air feed  209 , which is connected to the bearing device  203  as well as the sensors  210 . The device can be connected via the data bus  209  to a data processing installation which evaluates the data detected by the sensors  210  and thus determines the inertia characteristics of the object to be measured. With regard to the sensors  210 , it is the case of laser distance sensors which for example with the help of mirrors  211  as represented in  FIG. 8 d   , carry out distance measurements and thus render the movement of the measurement platform  201  with respect to the carrier  202  detectable. An object can be completely measured from an evacuation of the frequencies. However, other surfaces can also be applied, e.g. surfaces of aluminium or matt, non-mirroring surfaces, alternatively to the mirrors. 
     Further sensors are conceivable despite the fact that only distance sensors for detecting the frequency are used in the present embodiment. Force sensors can also be used despite the fact that they are more complicated, but this is not envisaged in numerous embodiments. 
     A further embodiment of a device is to be illustrated by way of  FIG. 9 . With regard to the device  300 , a carrier  301  which can be formed by a mount or for example a room ceiling is present. The device  300  moreover comprises a measurement platform  302 , on which an object  306  to be measured can be suspended. The measurement platform  302  is connected to the carrier  301  via a bearing arrangement and/or joint arrangement  303  and via restoring elements  304 . A movement along the z-axis is not possible since the restoring elements or the bearing arrangement  303  are or is led in guides  305 , but the bearing arrangement is movable within the x/y plane and can carry out a rotation about the z-axis. With regard to the bearing arrangement itself, it is the case of a universal joint which permits the movement about two rotation degrees of freedom. In the present embodiment example, one can make do without restoring elements between the measurement platform  302  and the carrier  301  since the restoring elements  304  counteract a movement within the x/y plane or a rotation about the z-axis of the bearing device  303  and the centre gravity on pendulating the measurement platform  302  about two degrees of freedom of the bearing arrangement  303  forms a “restoring force”. 
     As to the nature of the bearing arrangement  303 , this can be essentially analogously deduced from the bearing arrangements of the preceding embodiment examples. Thereby, cardanic bearings can be applied. The plane bearings can also be applied. With regard to the device  300  it is therefore essentially the case of a gravity pendulum, with which the suspension point can be moved by up to three degrees of freedom. 
     A calibration method is dealt with by way of  FIGS. 10 a  and 10 b   . The device  400  corresponds essentially to one of the embodiment examples of the device as described beforehand. The total stiffness of the restoring elements as well as a mass matrix of the measurement platform and of the restoring elements can be precisely determined by way of the application of calibration masses  402 . Different objects whose inertia characteristics are known are placed on the platform and inertia measurements carried out for this. The characteristics of the device are known after the total stiffness matrix and the mass matrix have been determined, as long as the object to be measured is placed on the platform in a manner such that its mass centre of gravity lies essentially precisely above the bearing arrangement and thus is carried or supported by this. The measurement platform with “real” measurements of an object thus has the same static zero position as with the calibration measurements.