Abstract:
A board apparatus for balance exercises and balance games having a platform that tiltable on a base part, freely rotatable around a vertical axis, and mounted movably along the vertical axis. A restoring part generates restoring forces that counteract motions of the platform and can be modified by the user. The restoring part includes four elastomer springs that are arranged at a distance from the center of the base part. The elastomer springs can be offset inward or outward with respect to the center of the base part, enabling accurate adaptation of the restoring forces. When twisting the platform around the vertical axis, the restoring part always returns the support part into one of two initial positions that are located 180 degree opposite to one another.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is filed under 35 U.S.C. §371 as a national stage application of International Application No. PCT/EP10/04279 filed Jul. 14, 2010, claiming priority from German Application No. 10 2009 033 440.8 filed Jul. 16, 2009. 
     FIELD OF THE INVENTION 
     The invention relates to an apparatus for balance exercises and balance games of a user, encompassing a base part, a support part for the user&#39;s body which is tiltable relative to the base part around a longitudinal axis X and a transverse axis Y, and a restoring apparatus for generating a restoring force that counteracts a tilt of the support part. An apparatus of this kind is also referred to as a “balance board.” 
     BACKGROUND OF THE INVENTION 
     The balance boards known from the existing art serve, inter alia, as input devices for computer games. These balance boards are often used, for example, in computer games in which sports such as skateboarding, snowboarding, or surfing are simulated. 
     A further application sector of balance boards is utilization as a training or rehabilitation device with which users can practice balance and the coordination of certain motion sequences. These training or rehabilitation devices are usually not designed for use in conjunction with a computer, and therefore also do not possess sensor apparatuses for the generation of sensor signals that can be further processed by a computer. 
     Apparatuses for balance exercises and balance games (balance boards) are sufficiently known in the existing art. The following documents are closest to the invention presented here: 
     US 2008/0261696 A1 discloses an apparatus for sensing weight displacements and jumping motions of a user. It encompasses a support surface that is mounted on four supporting feet. Beam-shaped spring elements are arranged respectively between the support surface and the four supporting feet. In the context of the greatly limited deformability of these spring elements, the support surface is tiltable relative to the supporting feet around two horizontal, mutually orthogonal spatial axes X and Y, and mounted movably along a vertical spatial axis Z orthogonal to the spatial axes X and Y. 
     Attached onto each of the beam-shaped spring elements are strain gauges that sense the deformation of the spring elements. Weight displacements and jumping motions of the user are sensed indirectly via the deformation of the spring elements. 
     U.S. Pat. No. 7,008,359 B2 discloses an apparatus for balance exercises. It encompasses a base part, a support surface, and a central spring element that is arranged between the base part and support surface and is fixedly connected to each of them. The support surface can be tilted and rotated in relation to the base part, the spring element generating restoring forces that counteract those motions. The apparatus possesses an adjusting mechanism with which said restoring forces can be modified. The adjusting mechanism encompasses four wedge-like locking apparatuses that can simultaneously be shifted radially (relative to a central and vertical axis Z). When the locking apparatuses are shifted inward, the space for elastic deformation of the central spring element becomes smaller, bringing about an increase in the restoring force and at the same time a limitation of the maximum tilt angle. 
     EP 0 966 724 B1 discloses an apparatus for sensing weight displacements, rotational motions, and jumping motions of a user. A support surface is mounted on a base part, tiltably around two horizontal, mutually orthogonal spatial axes X and Y, as well as rotatably around a vertical spatial axis Z orthogonal to spatial axes X and Y and movably along said spatial axis Z. The restoring forces that counteract a tilt and a vertical motion of the support surface are generated by an air tube, and can be adjusted by modifying the inflation pressure in the air tube. The air tube is arranged between the base part and an intermediate part that is mounted nontiltably but rotatably relative to the support surface. A sensor apparatus senses the motions of the support surface and generates corresponding sensor signals. 
     All these balance boards have in common the fact that they comprise a support surface, tiltable on a base part, for the user&#39;s body, and a restoring apparatus for generating a restoring force counteracting the tilt. If the balance boards are designed to be used to control computer games, they furthermore possess a sensor apparatus that senses weight displacements on the support surface. 
     The disadvantage of the apparatus described in US 2008/0261696 A1 is that the tiltability of the support surface is so greatly limited that a tilt is barely perceptible by the user. This is disadvantageous because the user does not obtain direct feedback regarding the motions performed by him or her. Feedback instead occurs only indirectly via the respective computer program and the signal which is outputted again after processing the input signal. If, conversely, the support surface of the apparatus described in US 2008/0261696 A1 were to tilt perceptibly in the context of a weight displacement, the user would obtain direct physical feedback regarding the motions performed by him or her. The user would thereby be substantially better able to calibrate his or her weight displacements, which as a result would make a computer game easier to control. 
     A further disadvantage of the greatly limited tiltability of the support surface of the apparatus described in US 2008/0261696 A1 emerges when it is used to control computer games that simulate sports such as skateboarding, snowboarding, or surfing. In these sports, the corresponding items of sporting equipment (skateboards, snowboards, or surfboards) in reality execute pronounced motions, in which context the user obtains, by way of the change in the spatial position of the item, important feedback as to its interaction with the environment. 
     Because the support surface of the apparatus described in US 2008/0261696 A1 does not modify its spatial position in a manner similar to, for example, the item of sporting equipment that the apparatus represents in a computer game, the user does not obtain the impression that he or she is interacting, by way of the apparatus described in US 2008/0261696 A1, with the virtual environment of the computer game. This negatively affects the impression of a virtual reality, and disrupts the user&#39;s game experience. 
     A further disadvantage of the greatly limited tiltability of the support surface of the apparatus described in US 2008/0261696 A1 is lastly that this apparatus can be used to only a very limited extent as a training or rehabilitation device. The reason for this is that the strength and coordination of specific muscle groups such as, for example, the ankle musculature can be improved only when the user or patient is standing on a definitely tiltable support surface and must compensate for that tilt with his or her locomotor system. 
     A further disadvantage of the apparatus described in US 2008/0261696 A1 is that the restoring forces cannot be modified by the user. Given that the tiltability of the support surface of the apparatus described in US 2008/0261696 A1 is in any case very greatly limited, however, this disadvantage is acceptable, since the need for an adaptation of restoring forces increases only with an increasingly pronounced tiltability of the support surface. The reason is that as the tilting motions of the support surface become greater, it becomes that much more difficult for the user to maintain his or her balance when no restoring forces, or only small ones, are counteracting a tilt of the support surface. 
     The magnitude of the restoring forces experienced by a user as appropriate depends, however, not only on his or her skill and preferences, but also very substantially on his or her weight. In the context of a balance board conceived for the mass market, it would therefore be desirable if its restoring forces could be adapted both to the forces exerted on the balance board by a small child weighing 15 kg, and to the forces exerted on the balance board by a large adult weighing 150 kg. 
     The apparatus described in U.S. Pat. No. 7,008,359 B2 offers a definitely perceptible tiltability of the support surface, which is also absolutely necessary for the use, intended by the inventors, as a training and rehabilitation device. In the case of the apparatus described in U.S. Pat. No. 7,008,359 B2, the restoring forces can consequently be modified. The restoring forces are increased by the fact that the so-called locking mechanism decreases the space for an elastic deformation of the central rubber spring element, the result being to bring about a preload on the spring element. 
     A disadvantage of the apparatus described in U.S. Pat. No. 7,008,359 B2 is, however, that the increase in the restoring forces is accompanied by an increasing limitation of the tiltability of the support surface. It has already been mentioned, however, that certain training effects can be produced for the user only if he or she must compensate for pronounced tilting motions of a support surface. As a design constraint, therefore, not every user will be able to achieve the same training effect with this apparatus. 
     A further disadvantage of the apparatus described in U.S. Pat. No. 7,008,359 B2 is that the restoring forces cannot be modified independently of one another for different tilt directions. The central rubber spring element is indeed designed so that it generates smaller restoring forces in the context of a tilt around the longitudinal axis of the device than in the context of a tilt around the transverse axis. This takes into account the fact that the forces a user standing on the support surface is capable of exerting on the support surface by means of a weight displacement between his or her forefoot and heel are smaller than those produced by a weight displacement between his or her left and right foot, at least when the user is standing on the support surface with his or her feet comfortably at shoulder width. 
     But because the locking mechanism of the apparatus described in U.S. Pat. No. 7,008,359 B2 always engages simultaneously at four points on the central rubber spring element, and thus also simultaneously modifies the restoring forces in the context of a tilt around the longitudinal axis and a tilt around the transverse axis, the ratio of the restoring forces for the longitudinal and the transverse axis is defined as a result of the design and is not modifiable. 
     On the basis of experience, however, it is not the case that two users who prefer, for example, the same restoring forces in the context of a tilt around the transverse axis (i.e. in the context of a weight displacement between the left and right foot, and vice versa) will also always find the same restoring forces in the context of a tilt around the longitudinal axis (i.e. a weight displacement between the forefoot and heel) to be appropriate. This is especially not the case when these two users have feet of different sizes, since when the foot sizes are different, energy is introduced at different points, resulting in turn in non-identical lever ratios. 
     Optimally, however, it should be possible not only to modify the ratio between the restoring forces for the longitudinal axis and the transverse axis. For certain exercises, for example for rehabilitation in a context of unilateral injuries, it may be desirable for greater restoring forces to be generated with a displacement of weight onto the left foot than with a displacement of weight onto the right foot, and vice versa, or for greater restoring forces to be able to be generated with a displacement of weight onto the forefoot than with a displacement of weight onto the heel, and vice versa. 
     In the case of the apparatus described in EP 0 966 724 B1, the restoring forces can be modified with no limitation on the tiltability of the support surface, since here the increase in restoring force is achieved solely by way of an increase in the pressure in the air tube and not, as in the case of the apparatus described in U.S. Pat. No. 7,008,359 B2, by reducing the space for elastic deformation of the spring element. 
     The air cushioning technology of the apparatus described in EP 0 966 724 B1 also has disadvantages, however. In order for the air cushioning system not to have too highly progressive a spring characteristic, which would cause the cushioning to be perceived by the user as too hard, the air tube must have comparatively large dimensions. The components between which the air tube is arranged and against which it engages (which in EP 0 966 724 B1 are the base part and the intermediate part) must be designed to be similarly large. The result is large overall dimensions and heavy weight for the apparatus as a whole, making its handling in turn impractical. In addition, the comparatively high material usage has an unfavorable effect on manufacturing costs. 
     A further disadvantage is the fact that an accessory, for example an air pump with a pressure gauge, is needed in order to adapt the pressure in the air tube. This in turn increases the cost of the apparatus as a whole. In addition, a user may find that dealing with the accessory or filling the air tube is in itself inconvenient. 
     It is also the case that in the case of the apparatus described in EP 0 966 724 B1, the ratio of the restoring forces in the various tilt directions is defined in terms of physical design by the arrangement of the air tube, and is not modifiable. The disadvantages explained above with reference to U.S. Pat. No. 7,008,359 B2 are thus also relevant to EP 0 966 724 B1. 
     Yet another disadvantage arises when the apparatus described in EP 0 966 724 B1 is also used for computer simulation of certain sports such as snowboarding or surfing. Here a better impression of a virtual reality would be achievable if the return forces could, for example, be adjusted so that the support part is less easy to tilt forward than to tilt back, although this is also not possible with EP 0 966 724 B1. 
     SUMMARY OF THE INVENTION 
     It is consequently an object of the present invention, which the inventors call DYNAMIC BOARD, to make available a safe, compact, and economically manufacturable balance board having a restoring apparatus that enables maximally flexible and simple adaptation of the restoring forces to different users&#39; needs without thereby limiting functionality, in particular the tiltability of the support surface. 
     According to a first aspect of the invention, this object is achieved in an apparatus of the species in that the restoring apparatus is designed to use replaceable spring elements having different dimensions or having a different spring force; that the restoring apparatus encompasses at least four individual spring elements; and that of the at least four spring elements, at least two are arranged parallel to the longitudinal axis X and at least two parallel to the transverse axis Y. 
     For purposes of the invention, a restoring apparatus is designed to use replaceable spring elements having different dimensions or having a different spring force if spring elements can be exchanged with no need for irreversible modifications to the apparatus as a whole. “No modification” in this context exists when, for example, the spring elements that are present are to be replaced with spring elements of smaller dimensions and, for example, a compensator piece must be used for that purpose. A restoring apparatus is therefore always designed to use replaceable spring elements having different dimensions or having a different spring force when the apparatus makes it possible to undo the exchange of one spring element for a different spring element having different dimensions or having a different spring force. 
     Designing the restoring apparatus so that replaceable spring elements having different dimensions or having a different spring force can be used offers substantial advantages as compared with certain restoring apparatuses known in the existing art that permit an adaptation of restoring forces to the differing needs of users. 
     One possibility, already mentioned above and known in the existing art, for increasing restoring forces involves putting the spring element under preload by means of an adjusting apparatus. The preloading of a spring element necessarily results, however, in a shortening of the spring travel that is still available for restoring a tilt. The consequence of this can be that heavier users, who prefer greater restoring forces, cannot achieve the tilt angles they actually desire, since the maximum spring compression has already been previously reached. An alternative would be to use a spring element whose spring travel is so long that even with a corresponding preload, sufficient spring travel is still available for achieving the desired tilt angle. This would, however, also increase the overall height of the apparatus. In addition, for users who need little or no preload, the support surface would then be mounted at a greater height above the floor than actually necessary, thereby increasing the danger of injury in the event of slippage off the support surface. 
     If provision is therefore made for adapting the return forces by way of an increase in preload, this always has a disadvantageous effect either on overall height or on the maximum tilt angle of the support surface. If, conversely, the restoring apparatus is designed to use replaceable spring elements having different dimensions or having a different spring force, then for each user there will be spring elements having the restoring force desired by him or her, which on the one hand have enough spring travel to achieve the desired tilt angles but on the other hand also do not have too long a spring travel that would result in an unnecessarily large overall height and also an increased risk of injury. 
     Another possibility, known in the existing art, for adapting the restoring forces that counteract a tilt of the support surface to the different needs of users is the use of spring elements whose spring force can be modified, e.g. an air cushioning system. As already set forth above, however, the use of an air cushioning system is complex in terms of design, and the components of an air cushioning system are comparatively expensive to manufacture. A restoring apparatus having replaceable spring elements is, conversely, substantially easier and more economical to manufacture. 
     The restoring apparatus of the apparatus according to the present invention furthermore encompasses not a one-piece spring element but instead at least four individual spring elements. This is advantageous in that the number of adaptation possibilities is also multiplied by the combination of multiple spring elements. 
     In contrast to the one-piece spring element, four individual spring elements also do not need to be arranged at the center of the apparatus (defined by the intersection of tilt axes X and Y). This proves to be favorable when the user is, as intended, standing on the support surface with his or her feet comfortably at shoulder width. In this case, in accordance with the lever principle, the shorter the spacing of the user&#39;s feet from the spring elements, the lower the force exerted by him or her on the spring elements. 
     Because of the more favorable lever ratios, four spring elements that are arranged at a certain distance from the center of the apparatus thus need to generate, in total, lower restoring forces than one central spring element. This has the advantage that the spring elements can be of smaller dimensions, which in turn has a favorable effect on manufacturing costs. 
     A further advantage as compared with one central spring element is that the at least four individual, decentrally arranged spring elements do not additionally need to take on the function of fixedly connecting the support part and base part to one another. It is therefore possible to provide, at the center of the apparatus, a separate mount or connection between the support part and base part. There is thus no need in this case to create a fixed connection between the spring elements and the base part and between the spring elements and the support part (or a part connected nontiltably to the support part); this substantially simplifies replacement of the spring elements. 
     This is not to be understood to mean, however, that for purposes of the invention only those restoring apparatuses that possess a separate mount or connection between the support part and base part are designed to use replaceable spring elements having different dimensions or having a different spring force. It is also entirely possible to dispense with a separate mount and to connect the support part fixedly to the base part by way of the four spring elements. Even if the four spring elements were, for example, bolted to the support part and/or base part, this would nevertheless be an apparatus according to the present invention provided said spring elements can be exchanged for other spring elements having different dimensions or having a different spring force with no need to make irreversible modifications to the apparatus as a whole. 
     In addition, in the apparatus according to the present invention, of the at least four spring elements, at least two are arranged parallel to the longitudinal axis X and at least two parallel to the transverse axis Y. This is advantageous in particular because users who prefer, for example, the same restoring forces in the context of a weight displacement between the left and right foot (i.e. in the context of a tilt around the transverse axis Y) do not also always find the same restoring forces to be appropriate in the context of a weight displacement between the forefoot and heel (i.e. in the context of a tilt around the longitudinal axis X). 
     Specifically, if the spring elements are not aligned at the tilt axes X and Y, it is then thereby possible also to generate different restoring forces in the context of weight displacements between the left foot and right foot, and between the forefoot and heel. The ratio between the restoring forces upon a tilt around the longitudinal axis and the restoring forces upon a tilt around the transverse axis is then, however, defined by the physical design, specifically by the distances at which the spring elements are located respectively from tilt axes X and Y. 
     If, on the other hand, in a context of four spring elements, two are arranged parallel to the longitudinal axis X and two parallel to the transverse axis Y, this has the advantage that essentially only one spring element in each case counteracts the tilting of the support surface when the support surface is tilted exclusively around the longitudinal axis X or around the transverse axis Y. For example, if the support surface is tilted exclusively around the longitudinal axis X, essentially only one of the two spring elements that are arranged parallel to the transverse axis Y is counteracting the tilt of the support surface (leaving aside the comparatively small restoring forces that are simultaneously also generated by the two spring elements that are arranged parallel to the tilt axis X). 
     With this arrangement of the spring elements it is consequently possible not only to generate different restoring forces for weight displacements between the left foot and right foot, and between the forefoot and heel, but also to modify the ratio between the restoring forces in the context of a tilt around the longitudinal axis and the restoring forces in the context of a tilt around the transverse axis. This arrangement thus guarantees maximum flexibility in adapting the restoring forces to the various needs of users. 
     In a refinement of the apparatus according to the present invention, it is proposed that the spring elements be embodied as elastomer springs; this is to be understood as all spring elements whose elasticity is based very predominantly on the effect of entropy elasticity (in contrast to energy elasticity). 
     Elastomer springs are particularly well suited for use in an apparatus according to the present invention because, as compared e.g. to compression springs made of metal, they can establish relatively high spring forces over short spring travel lengths. This is, however the prerequisite for minimizing the overall height of the apparatus according to the present invention as a function of the predefined tilt angles. A minimized overall height is desirable in order to keep the risk of injury as low as possible, in the event of slippage off the support surface. 
     An optimal relationship between overall height and predefined tilt angles is achieved when the tilt of the support surface is limited not by the maximum spring compression of the spring elements, but instead because the support part comes to a stop against the floor or the base part. The reason is that in this case the maximum tilt angle of the support surface depends exclusively on the length of the support surface and the height at which it is mounted above the floor. In order for the tilt of the support surface no longer to be limited by the maximum spring compression of the spring elements, however, it is in turn necessary to arrange the spring elements relatively close to the center of the apparatus (defined by the intersection of the tilt axes). 
     An arrangement of the spring elements at only a short distance from the center of the apparatus places particular demands on the spring elements, however, for the following reasons: On the one hand, the spring travel that is available for establishing the desired restoring force becomes smaller, the closer to the center of the apparatus a spring element is arranged. On the other hand, however, the necessary restoring force also becomes larger, the closer to the center of the apparatus the spring element is arranged—at least when the user is, as intended, standing on the support surface with his or her feet comfortably at shoulder width. Specifically, in the context of a weight displacement, the farther away the user&#39;s foot (and therefore the force introduction point) is from the center of the apparatus, the greater (in accordance with the lever principle) the force the user is exerting on the spring element. 
     It is thus apparent that an apparatus optimized in terms of overall height requires that the spring elements that are used be able to establish relatively large spring forces with short spring travels. These requirements are met particularly well by elastomer springs. 
     In addition, however, elastomer springs are also particularly well suited for use in an apparatus according to the present invention because of their slightly progressive spring characteristic, since experience indicates that users perceive it as advantageous when the restoring force increases slightly with increasing tilt, since this makes it easier for users to maintain balance even at larger tilt angles. 
     It is further proposed that the elastomer springs be slipped onto holding apparatuses. This allows a user to exchange the elastomer springs conveniently and without tools if he or she wishes to adapt the restoring forces to a different user weight or if the elastomer springs need to be exchanged as a result of fatigue or settling. 
     It is furthermore advantageous to use elastomer springs produced from chloroprene rubber or polyurethane, which preferably are standardized in accordance with an industry standard, e.g. DIN 9835. This is advantageous because standardized elastomer springs made of chloroprene rubber or polyurethane are comparatively inexpensive to manufacture. These spring elements also can be exchanged economically if settling or fatigue of the spring elements should occur after extended use of the apparatus according to the present invention. 
     It is moreover proposed that the elastomer springs have a height of between 40 mm and 60 mm. The reason is that because elastomer springs of this height can on the one hand be arranged so that the support surface can achieve a tilt angle of approximately 15° that is desirable from the standpoint of sports medicine, and so that the tilt is limited not by the maximum spring compression of the elastomer springs but by contact between the platform and the floor. This is, however, as already explained, the prerequisite for an optimized overall height. Although the elastomer springs must, for this purpose, be arranged relatively close to the center of the apparatus, and (as also already explained) although rather unfavorable lever ratios result therefrom, elastomer springs of the proposed height on the other hand also generate sufficiently large restoring forces to adapt the apparatus to the needs of very heavy users. Elastomer springs of the proposed overall height therefore prove to be particularly advantageous for achieving the smallest possible overall height for the apparatus as a whole at tilt angles of up to approx. 15°, and thus minimizing the risk of injury to the user. 
     In a refinement of the apparatus according to the present invention, it is further proposed that the spring elements be capable of being offset parallel to the longitudinal axis X and/or parallel to the transverse axis Y, since in this manner the restoring forces can be adapted even more flexibly and accurately to users&#39; needs. 
     When a spring element is offset outward from the center of the apparatus (said center being defined by the intersection of the tilt axes), the spring travel when the support surface tilts toward that spring element becomes longer; when the spring element is offset inward, the spring travel becomes shorter. The longer the spring travel, the greater the restoring force that is generated by the spring element and counteracts the tilt of the support surface, and vice versa. 
     Offsetting of the spring elements inward or outward has another effect as well, however, namely a change in lever ratios. The weight force exerted on the spring elements by a user standing on the support surface is greater, the farther inward the spring element is offset, and smaller, the farther outward it is offset. 
     For example, a heavy user who exerts large weight forces on the support surface can offset the spring elements outward, thereby at the same time achieving the result that on the one hand he or she exerts less of a weight force on the spring elements, and on the other hand the spring elements generate a greater restoring force. 
     The result of this dual effect, i.e. the shortening or lengthening of the spring travel in conjunction with the lengthening or shortening, respectively, of the lever, is that the spring elements need to be offset over only a relatively short distance in order to enable adaptation of the restoring forces over a wide spectrum. 
     If the restoring forces are adapted by offsetting the spring elements inward or outward, and not (as, for example, in the case of the apparatus described in U.S. Pat. No. 7,008,359 B2) by an increase or decrease, respectively, in the space for elastic deformation of the spring element, this also does not produce any disadvantageous restriction on tiltability, at least not when the spring elements are not offset so far outward that maximum spring compression is achieved as a result of the tilt. 
     If the apparatus according to the present invention is therefore designed not only to use replaceable spring elements having different dimensions or having a different spring force, but also to offset the spring elements parallel to the longitudinal axis X and/or parallel to the transverse axis Y, the result is that far fewer replaceable spring elements need to be available in order to permit adaptation of the restoring forces within a very wide spectrum. 
     If elastomer springs are used, for example, it is possible with elastomer springs having dimensions of 25×40 mm (parallel to transverse axis Y) and 32×50 mm (parallel to longitudinal axis X) to generate, by corresponding offsetting, restoring forces that are commensurate with a user weight in the range from approx. 15 kg to approx. 60 kg. With elastomer springs having dimensions of 32×50 mm (parallel to transverse axis Y) and 40×50 mm (parallel to longitudinal axis X), restoring forces that are appropriate for a user weight in the range from approx. 40 kg to approx. 150 kg are generated by corresponding offsetting. It is thus possible, by combining three pairs of standardized elastomer springs, to cover in simple and economical fashion a utilization range, in terms of user weight, from approx. 15 kg to approx. 150 kg, provided the elastomer springs can additionally be offset inward or outward. 
     Lastly, it is further advantageous if all four spring elements can be offset inward or outward independently of one another. That is because it is thereby possible to modify the ratio of the restoring forces in the various tilt directions not only by corresponding replacement of the spring elements, but also by a corresponding offset of the spring elements. Independent offsetting of the four spring elements thus on the one hand allows the restoring forces to be adjusted differently for weight displacements between the left foot and right foot, and between the forefoot and heel. On the other hand, the ratio between the restoring forces in the context of a tilt around the longitudinal axis and the restoring forces in the context of a tilt around the transverse axis can also be modified, which is advantageous in particular for users having the same weight but different foot sizes. 
     It is further proposed that the spring elements each be capable of being shifted in a guide groove in the base part. In this embodiment, the individual spring elements can be steplessly offset, the result being to allow very exact adaptation of the restoring forces to the individual requirements of the individual user. 
     According to a further aspect, the apparatus according to the present invention encompasses an adjusting apparatus with which all the spring elements can be offset simultaneously, the adjusting apparatus preferably being embodied as a rotatable adjusting disk having circular eccentric elongated holes. 
     An adjusting apparatus is advantageous when, for example, the apparatus is used on a frequently changing basis by various people who prefer different settings of the restoring apparatus. It is then possible, by means of an adjusting apparatus that simultaneously offsets all the spring elements, to perform an adaptation to user specifications easily and quickly. Use of an adjusting disk has, however, the disadvantage that the ratio between the restoring forces in the context of a tilt around the longitudinal axis and the restoring forces in the context of a tilt around the transverse axis is determined by the adjusting apparatus and is not modifiable. 
     If the adjusting apparatus is embodied as an adjusting disk having circular eccentric elongated holes, an exact adjustment of the restoring apparatus can be performed because of the reduction ratio with which a rotation of the adjusting disk effects an offset of the spring elements. Use of the adjusting disk is further advantageous because as a result of the self-locking of the adjusting disk, separate immobilization of the spring elements is no longer necessary. 
     The apparatus according to the present invention moreover preferably encompasses a sensor apparatus for sensing weight displacements of the user&#39;s body, so that the apparatus can be used not only as a training and rehabilitation device but also as an input device for a computer or a game console. 
     Displacements of the user&#39;s weight can be sensed in simple fashion if the sensor apparatus measures the tilt direction and tilt angle of the support surface, since the user can bring about a tilt of the support surface only via a weight displacement, provided the user is not holding onto anything (although that may be assumed when the apparatus is being used for balance exercises or balance games). It is understood that this sensing method relates only to a relative sensing of a user&#39;s weight displacements, since the tilt angle of the support surface depends not only on the force exerted on the support surface, but also on the restoring forces that have been set by the user by means of the restoring apparatus. Displacements of the user&#39;s weight can of course, however, be sensed not only via a measurement of the tilt angle of the support surface but also, for example, using force meters that are incorporated into the supporting feet of the apparatus according to the present invention. 
     In a refinement of the apparatus according to the present invention, it is further proposed that the support part be movable vertically along a vertical axis Z; that the apparatus according to the present invention encompass a restoring apparatus for generating a restoring force that counteracts a vertical motion of the support part; and that the apparatus according to the present invention encompass a sensor apparatus that senses vertical accelerations of the user&#39;s body. 
     If the apparatus according to the present invention encompasses a sensor apparatus with which not only weight displacements but also vertical accelerations of the user&#39;s body are sensed, this expands the potential applications of the apparatus according to the present invention as an input device for a computer or a game console. In the simulation of sports such as skateboarding, snowboarding, or surfing, for example, jumping motions in the virtual environment can be controlled by actual jumping motions of the user, making the simulation more realistic and intensifying the impression of a virtual reality. 
     Vertical accelerations of the user can be sensed in simple fashion if the support part is movable vertically along a vertical axis Z and if the apparatus according to the present invention encompasses a restoring apparatus for generating a restoring force that counteracts a vertical motion of the support part. In this case the sensor apparatus can measure the vertical motion of the support surface along the vertical axis Z and thereby indirectly sense vertical accelerations of the user&#39;s body. This is because the user can bring about a change in the vertical location of the support surface only by way of a vertical acceleration of his or her body&#39;s center of gravity, provided the user is not holding onto anything (although that may be assumed when the apparatus is being used for balance exercises or balance games). It is understood that this sensing method refers only to a relative sensing of a user&#39;s vertical accelerations, since the vertical motion of the support surface depends not only on the force exerted on the support surface, but also on the restoring forces that are generated by the restoring apparatus. Vertical accelerations of the user&#39;s body can of course, however, be sensed not only via a measurement of the vertical motion of the support surface but also, for example, using force meters that are incorporated into the supporting feet of the apparatus according to the present invention. 
     In a refinement of the apparatus according to the present invention, it is further proposed that the support part be rotatable around a vertical axis Z; that the apparatus according to the present invention encompass a rotational restoring apparatus for generating a restoring force that counteracts a rotation of the support part; and that the apparatus according to the present invention encompass a sensor apparatus that senses rotational motions of the user. 
     This embodiment firstly expands the potential applications of the apparatus as a training and rehabilitation device, since a rotation of the support surface, while overcoming a rotational restoring force counteracting the rotation, utilizes additional muscle groups of the user. 
     If the apparatus according to the present invention furthermore encompasses a sensor apparatus for sensing the rotational motions of the user, this also expands the potential applications of the apparatus according to the present invention as an input device for a computer or a game console. In the simulation of sports such as skateboarding, snowboarding, or surfing, for example, rotational motions in the virtual environment can be controlled by actual rotational motions of the user, making the simulation more realistic and intensifying the impression of a virtual reality. 
     It is further proposed that the support part be rotatable 360° clockwise and counter-clockwise as often as desired. This is in turn advantageous if the apparatus is used to simulate sports such as skateboarding, snowboarding, or surfing, since in these sports the respective items of sporting equipment can likewise be twisted 360° clockwise and counter-clockwise as often as desired. A platform that is freely rotatable in this fashion thus makes the simulation even more realistic, and further intensifies the impression of a virtual reality. Even when the apparatus is used as a training and rehabilitation device, however, a freely rotatable platform makes greater demands on the user and can be used in more versatile fashion than a platform that can be rotated only up to a certain angle. 
     It is further proposed that the rotational restoring apparatus generate a restoring force that returns the support part, when twisted, to an initial position; and that the restoring force reach its maximum when the support part is twisted half a revolution clockwise or counter-clockwise out of that initial position. This is particularly advantageous in turn if the apparatus according to the present invention serves as an input device for computer simulation of sports such as skateboarding or snowboarding. In this case the user will set up the apparatus as a whole in such a way that its longitudinal axis X is oriented perpendicular to the plane of the screen of the computer or the game console, since this orientation corresponds to the orientation of the simulated item of sporting equipment when traveling straight ahead. 
     If the user exerts on the platform a torque that does not exceed the maximum restoring force that is established in the context of a 180-degree twist, the platform is returned to the initial position by the restoring force, oppositely to the rotation direction initiated by the user. If, on the other hand, the user exerts on the platform a torque that exceeds the maximum restoring force at 180°, the restoring force that is established (and any excess torque of the user) will return the platform to the initial position in the rotation direction initiated by the user, with the result that the user has then completed one 360-degree revolution. The user will therefore, after execution of a rotational motion and once restoring is complete, always find him- or herself in the same position with respect to the screen as before execution of the rotational motion, the result being that control of the computer simulation is made easier. In addition, this embodiment of the rotational restoring apparatus contributes to the impression of a realistic simulation, since in reality skateboards or snowboards likewise exhibit a tendency to align themselves along the direction of travel. 
     Alternatively, it is proposed that the rotational restoring apparatus generate a restoring force that returns the support part, when twisted, to one of two initial positions that are located 180° opposite to one another; and that the restoring force reach its maximum when the support part is rotated one-quarter revolution clockwise or counter-clockwise out of those two initial positions. 
     With this embodiment, if the user exerts on the platform a torque that does not exceed the maximum restoring force that is established in the context of a 90-degree twist, the platform is returned to the first initial position by the restoring force oppositely to the rotation direction initiated by the user. If, on the other hand, the user exerts on the platform a torque that exceeds the maximum restoring force at 90°, the restoring force that is established (and any excess torque of the user) will direct the platform to the second initial position, which is located 180° opposite to the first initial position, in the rotation direction initiated by the user. The user will therefore, after execution of a rotational motion and once restoring is complete, always find him- or herself in the same position with respect to the screen as before execution of the rotational motion, or in a position that is mirror-reversed with respect thereto. 
     As compared with the approach described previously, with only one initial position, this is advantageous in that for many users it might be too difficult to maintain balance in the context of 360-degree revolutions. The impression of a realistic simulation would furthermore also be supported by this embodiment with two initial positions, since in reality skateboards or snowboards can, for example, likewise be used in two different positions (these positions being referred to as “regular” or “goofy” depending on which foot is toward the front in the direction of travel). 
     A rotational restoring apparatus having the aforementioned properties can be manufactured economically and at the same time compactly, since it encompasses a counterelement that takes the form of a straight cylinder and is connected nonrotatably to the platform, as well as at least one spring element that engages against the enveloping surface of said cylindrical counterelement. 
     If the bottom surface of the cylindrical counterelement has a symmetrical oval shape, this implements in simple fashion a rotational restoring apparatus which returns the support part, when twisted, to an initial position, and the restoring force of which reaches its maximum when the support part is twisted half a revolution clockwise or counter-clockwise out of that initial position. 
     If the symmetrical oval basic shape of the cylindrical counterelement is moreover modified in such a way that an indentation is provided at at least one vertex of the oval basic shape, the spring element that engages against the enveloping surface of said cylindrical counterelement can latch into said indentation. This latching prevents the support part from moving out of the initial position when the user, while tilting the standing surface by means of weight displacements on the standing surface, also inadvertently executes smaller rotational motions, as may occur, for example, when a user moves his or her arms in order to regain his or her balance. If a rotation of the standing surface were also initiated in this case, this could cause the user to lose his or her balance entirely and no longer be able to remain on the standing surface. The latching in the initial position according to the present invention thus serves for user safety. 
     If, on the other hand, the bottom surface of the cylindrical counterelement has an elliptical shape, this implements in simple fashion a rotational restoring apparatus which returns the support part, when twisted, into one of two initial positions that are located 180° opposite to one another and whose restoring force reaches its maximum when the support part is rotated clockwise or counter-clockwise one-quarter revolution out of said two initial positions. 
     The elliptical basic shape of the cylindrical counterelement is preferably modified in such a way that an indentation is provided at two vertices of the elliptical basic shape, preferably at the two secondary vertices, i.e. at the two points closest to the center of the ellipse. It is thereby possible to achieve a latching of the support part in two initial positions located 180 degrees opposite to one another. This has, for the safety of the user, the same advantages that have already been explained previously in the context of the apparatus according to the present invention with latching in only one initial position. 
     It is further proposed that the spring element encompass a contact element whose contact surface is in rolling contact against the enveloping surface of the cylindrical counterelement. This rolling contact minimizes friction between the spring element and the counterelement, thereby ensuring that even in angular positions with unfavorable lever ratios, the support part is reliably directed back into its initial position. This is advantageous because it makes handling of the apparatus according to the present invention easier and safer if the user, after executing a rotational motion, always finds him- or herself back in the same orientation with respect to his or her environment. 
     It is furthermore advantageous if, when the support part is in the initial position, said contact element rests in partially positive fashion in the indentation of the cylindrical counterelement, since in this manner comparatively little noise occurs when the support part latches in the initial position. 
     According to a further aspect of the invention, the restoring force that counteracts a twist of the support surface is adjustable. This is advantageous because, for example, a child can exert a very much smaller torque on the platform with his or her rotational motion than can an adult. If the rotational restoring force were not adjustable, the rotational restoring force would thus need to be designed to be very low so that children would also be capable of initiating a complete twist of the support part. This would, however, have critical disadvantages for adult users. As already explained, smaller torques are often inadvertently exerted on the platform, especially due to motion of the arms. If the rotational restoring force is very low, then especially adults with a large body mass would often trigger rotational motions of the support part even though they had intended only to tilt the platform by way of a weight displacement. This would make handling of the apparatus according to the present invention much more difficult especially for heavier adults, and in the worst case might result in falls and injuries if a user can no longer control an inadvertently initiated rotational motion. In a safe balance board that is as easy as possible to handle, the rotational restoring forces should therefore also be adjustable. 
     In a refinement of the apparatus according to the present invention, it is further proposed that a button area having at least two buttons be provided on the platform of the support part. This is advantageous in that a user, when utilizing the apparatus according to the present invention as an input device for a computer game, requires no further input devices in order, for example, to navigate in the computer game&#39;s menu. 
     It is further proposed that upon actuation of the buttons, a signal is triggered only when the surface of the buttons is located below the surface of the platform. This embodiment ensures that the buttons are actuated only deliberately with the toe area, and not inadvertently with the sole of the foot during a balance exercise or a balance game. 
     According to a further aspect, the apparatus according to the present invention lastly encompasses a vibration apparatus that transfers vibrations to the support part and is controlled by signals of a computer program. The apparatus can in this fashion convey to the user, by way of the vibrations, a haptic feedback regarding specific events occurring in a computer game. In the training sector, warnings can also thereby be conveyed to the user, for example when a specific tilt angle that should not be exceeded from a therapeutic standpoint, or because of a risk of injury, is exceeded. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The apparatus according to the present invention for balance exercises and balance games having modifiable restoring forces, hereinafter also referred to as a DYNAMIC BOARD, will be explained in more detail below with reference to the appended drawings, in which 
         FIG. 1  is a perspective overall view of the DYNAMIC BOARD according to the present invention; 
         FIG. 2  is an exploded perspective view of the apparatus; 
         FIG. 3  is a plan view of the platform with section A-A labeled; 
         FIG. 4  is an enlarged sectional view of detail II; 
         FIG. 5  is an enlarged sectional view of detail II in a tilted position; 
         FIG. 6  is an enlarged depiction of sectional view B-B; 
         FIG. 7  is an enlarged depiction of sectional view C-C; 
         FIG. 8  is an enlarged depiction of sectional view C-C for an alternative embodiment; 
         FIG. 9  depicts a carrier plate for an alternative embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The DYNAMIC BOARD is labeled very generally with the number  1  in  FIG. 1  and  FIG. 2 . It is made up of three main assemblies, namely support part  10 , restoring apparatus  20 , and base part  30  (see  FIG. 2 ). 
     Support part  10  encompasses platform  13 , button unit  11 , electronics unit  12 , and carrier plate  14  with bearing pin  14   b . Carrier plate  14  with bearing pin  14   b  is made up of an elliptically shaped carrier plate  14   a  and the bearing pin  14   b  fixedly connected thereto, bearing pin  14   b  being aligned at the center point of the elliptical carrier plate  14   a . The center point of the elliptical carrier plate  14   a  is defined by the intersection of the two axes of symmetry of the ellipse. Platform  13  is bolted to carrier plate  14   a.    
     Electronics unit  12  is made up of motion sensor unit  12   a , processor unit  12   b , interface unit  12   c  for wireless data exchange, and the battery (not depicted). Motion sensor unit  12   a  involves commercially usual electronic measurement systems, preferably microelectromechanical (MEM) gyroscopes and accelerometers. Electronics unit  12  is located in a central depression in platform  13 , and is bolted to platform  13 . 
     Button unit  11  (see also  FIG. 4 ) is likewise fitted into the central depression in platform  13 , above electronics unit  12 . The four movable buttons  11   a  of button unit  11  each have associated with them a switch element  12   e , located therebelow, on electronics unit  12 . Buttons  11   a  are held under compression by eight compression springs  11   b , as seen in  FIG. 4 , inside retaining ring  11   c  and retaining plate  11   d . Retaining ring  11   c  is bolted to platform  13 . The bolts for securing retaining plate  11   d  are bolted to carrier plate  14   a  through four spacer sleeves  11   e , as seen in  FIG. 4 . Spacer sleeves  11   e  pass through four cutouts  12   f  in electronics unit  12 . The top surface of the four buttons  11   a  is largely flush with the top surface of platform  13 . Contact between movable buttons  11   a  and switch elements  12   e  located respectively therebeneath occurs only when the buttons  11   a  have been pushed downward sufficiently far that the top surface of the buttons  11   a  is located below the top surface of platform  13 . 
     Support part  10  and base part  30  are connected via carrier plate  14  with bearing pin  14   b , by the fact that bearing pin  14   b  is guided through pivot bearing  32  fastened in basic frame  31  and secured by means of screw  15   b  (see  FIG. 4 ). Spacer sleeve  15   a  is inserted between the head of the screw  15   b  and the movable part of pivot bearing  32  so that the movability of pivot bearing  32  is not limited. Pivot bearing  32  is preferably embodied in accordance with DIN 648, and with a permissible tilt angle of at least 15°. As a result of this arrangement, support part  10  can be tilted around two horizontal and mutually orthogonal axes X and Y, and rotated around a vertical axis Z, relative to base part  30 . In addition, support part  10  can be moved in translation in the direction of vertical axis Z. 
     The movements of support part  10  that are recited above are sensed by way of motion sensor unit  12   a  of electronics unit  12  that is connected fixedly to the support part  10  (see  FIG. 2 ). Specific motions of the user that he or she executes on platform  13 , for example weight displacements, rotational motions, and jumping motions, can be indirectly sensed by way of the motions of support part  10 . 
     Restoring part  20  (see  FIG. 2 ) encompasses a rotational restoring unit  21  and tilt restoring unit  22  as subassemblies. Rotational restoring unit  21  is made up of intermediate carrier  21   a , axial bearing  21   d , and two leaf spring units  21   c . Intermediate carrier  21   a  rests in planar fashion on spring elements  22   b  and  22   c  of tilt restoring unit  22 . The underside of intermediate carrier  21   a  is stiffened by means of cross members  21   b  (see  FIG. 4 ) connected fixedly thereto. Cross members  21   b  extend in parallel fashion over almost the entire length of the underside of intermediate carrier  21   a , the spacing between them being selected so that the two longitudinal spring elements  22   b  fit in the center between the cross members  21   b . This prevents intermediate carrier  21   a  from twisting with reference to tilt restoring unit  22  and base part  30 . The two leaf spring units  21   c  are fastened on the upper side of intermediate carrier  21   a.    
     Carrier plate  14  with bearing pin  14   b  is mounted, via bearing pin  14   b , rotatably relative to intermediate carrier  21 . Axial bearing  21   d  is located between carrier plate  14  with bearing pin  14   b  and intermediate carrier  21   a . To minimize overall height, axial bearing  21   d  is preferably embodied as an axial bearing in accordance with DIN 711 or DIN 722. Support part  10  can thus be rotated as desired, with little friction, with respect to restoring part  20 . Upon a rotation of support part  10  of up to 90° in each case, the two leaf spring units  21   c  are preloaded by the engagement of the elliptically shaped carrier plate  14   a , and thereby bring about a restoration to the original position. Upon a rotation of support part  10  of more than 90°, the above-described arrangement brings about a rotation of support part  10  to a new initial position located 180° opposite to the original position. 
     Tilt restoring unit  22  encompasses two longitudinal spring elements  22   b , two transverse spring elements  22   c , and four spring element holders  22   d  (see  FIG. 4  and  FIG. 6 ). The two longitudinal spring elements  22   b  and the two transverse spring elements  22   c  are each slipped from above onto the four spring element holders  22   d . The four spring element holders  22   d  are each inserted into an elongated hole  31   a  in basic frame  31 , and secured below basic frame  31  each with two flat nuts  22   e . Of the four elongated holes  31   a  in the basic frame, two extend parallel to longitudinal axis X, and two parallel to transverse axis Y (see  FIG. 1  and  FIG. 6 ). By means of spring element holders  22   d  guided in elongated holes  31   a , all the spring elements  22   b  and  22   c  are thus shiftable individually and steplessly on base part  30 , the shift occurring parallel to longitudinal axis X and to transverse axis Y, respectively. 
     A tightening of screw  15   b  reduces the spacing between support part  10  and base part  30 , and thus also the spacing of the components against which spring elements  22   b  and  22   c  engage (see  FIG. 4 ). Spring elements  22   b  and  22   c  can thus be pre-tensioned by tightening screw  15   b . It is also possible in this fashion to compensate for an aging-related settling (shrinkage) of spring elements  22   b  and  22   c . A loosening of screw  15   b , conversely, allows any pre-tensioning of spring elements  22   b  and  22   c  to be released, in order to facilitate shifting of spring element holders  22   d  on the base part  30 . 
     Tilt restoring unit  22  can selectably be used in combination with adjusting disk  22   a  (see  FIG. 6 ). This makes it possible, by rotating the adjusting disk  22   a , to shift all spring elements  22   b  and  22   c  simultaneously and at a specific ratio. In this context, spring element holders  22   d  simultaneously project through the circular elongated holes  22   f , arranged eccentrically with respect to vertical axis Z, of adjusting disk  22   a , and elongated holes  31   a  in basic frame  31 . The shifting of spring elements  22   b  and  22   c  occurs, steplessly and with little energy expenditure, by way of the gated guide thereby realized. 
     Base part  30  encompasses basic frame  31 , pivot bearing  32 , and four rubber plates  34 . Basic frame  31  comprises four supporting feet, arranged symmetrically with respect to section axis A-A of  FIG. 3 , on which rubber plates  34  are respectively attached. The position of the four supporting feet on basic frame  31  is selected so that secure stability of the DYNAMIC BOARD is guaranteed in the context of any displacement of the center of gravity of a user&#39;s body on platform  13 . 
     A vibration apparatus (not shown), which is activated by electronics unit  12 , is optionally incorporated into platform  13 . The vibration apparatus is a commercially available signal transducer that generates vibrations using asymmetrical weight driven by electric motors and that is known, for example, from manual control devices for video game consoles (called “game pads”). 
       FIG. 8  shows the rotational restoring apparatus of an alternative embodiment of the DYNAMIC BOARD, in a depiction analogous to  FIG. 7 . The rotational restoring apparatus corresponds in substantial portions to the embodiment according to  FIG. 7 , for which reason analogous parts are labeled in  FIG. 8  with the same reference characters but incremented by 100. In addition, the alternative embodiment in accordance with  FIG. 8  is described below only insofar as it differs from the one in accordance with  FIG. 7 . 
     In the embodiment in accordance with  FIG. 8 , rotational restoring unit  121  encompasses intermediate carrier  121   a  having fixed cross members  121   b  (not depicted) and a tension spring unit as a sub-group. The tension spring unit sub-group encompasses two carriages  121   c   1  made of polyacetal or polyformaldehyde, two tension springs  121   c   2 , four threaded rods  121   c   3 , two deep groove ball bearings  121   c   4  per DIN 625, and two holding plates  121   c   5  with bearing shaft. 
     Intermediate carrier  121   a  is embodied as a rectangular plate. As is also the case in the embodiment in accordance with  FIG. 7 , the underside of intermediate carrier  121   a  rests in planar fashion on spring elements  22   b  and  22   c  of tilt restoring unit  22 , and is stiffened by two respective cross members  21   b  connected fixedly thereto. Exactly as in the case of the original embodiment, this prevents intermediate carrier  121   a  from becoming twisted with reference to tilt restoring unit  22  and base part  30  (see  FIG. 4 ). 
     The two carriages  121   c   1  are mounted on intermediate carrier  121   a  by means of a linear slide guide. For this purpose, intermediate carrier  121   a  is machined flat on both sides. The two carriages  121   c   1  are connected at both ends via the tension spring  121   c   2  in each case. The preload of the two tension springs  1212  can be steplessly adjusted by way of threaded rods  121   c   3  at each end of said tension springs  121   c   2 . The respectively deep groove ball bearing  121   c   4  is rotatably mounted and centered on the inner side of the carriages  121   c   1 . Deep groove ball bearings  121   c   4  are retained by the holding plate  121   c   5  with the bearing shaft that is bolted to the carriage  121   c   1 . 
     Carrier plate  114   a  has an elliptical basic shape that is interrupted by two indentations. The indentations are recessed into the elliptical basic shape at the location of the two secondary vertices of that ellipse, i.e. the two points closest to the center point of the ellipse. The radius of the indentations corresponds to the radius of the two deep groove ball bearings  121   c   4 . Carrier plate  114   a  is arranged with a 90° twist as compared with the variant embodiment according to  FIG. 7 . Linear sliding guidance of the two carriages  121   c   1  occurs along the longitudinal axis of the apparatus as a whole. 
     As a result of the preload of tension springs  121   c   2  and the positive seating of deep groove ball bearings  121   c   4  in the indentations of carrier plate  114   a , support part  10  is retained, in two initial positions, to prevent twisting relative to intermediate carrier  121   a  and base part  30 . In these two initial positions, located 180° opposite to one another, platform  13  is oriented lengthwise with respect to base part  30 . The retention can be released by the user by introducing a torque via platform  13  into carrier plate  114   a  fixedly connected thereto. 
     The excursion of the two carriages  121   c   1 , and thus also the force exerted by tension springs  121   c   2  via the two deep groove ball bearings  121   c   4  on carrier plate  114   a , changes depending on the degree of twisting of platform  13  and thus of carrier plate  114   a . When twisting occurs, the two deep groove ball bearings  121   c   4  make rolling contact against the lateral surface of carrier plate  114   a . This rolling contact minimizes the friction between carriages  121   c   1  and the carrier plate, thereby ensuring that even in angular positions with unfavorable lever ratios, support part  10  is reliably directed back into one of the two initial positions. 
     In the context of a 90° twist, deep groove ball bearings  121   c   4  abut against the two principal vertices of the elliptical carrier plate  114   a , i.e. against the points farthest away from the rotation point of carrier plate  114   a . In this position carriages  121   c   1  have the greatest possible excursion, and tension springs  121   c   2  the greatest possible tension, with the result that the restoring force reaches its maximum. If the user exerts on platform  13  a torque that does not overcome this maximum restoring force at 90°, support part  10  is returned by the restoring force, opposite to the rotation direction initiated by the user, to the first initial position and is latched therein. If, on the other hand, the user exerts on platform  13  a torque that exceeds the maximum restoring force at 90°, the restoring force that is established (and any excess torque of the user) will direct support part  10 , in the rotation direction initiated by the user, to the second initial position that is located 180° opposite to the first initial position, and latch it therein. 
     In  FIG. 9  an alternative embodiment of carrier plate  14   a / 114   a  of the DYNAMIC BOARD is depicted and is labeled  214   a . When this carrier plate  214   a  is used, the rotational restoring apparatus in accordance with  FIG. 8  must be modified in such a way that the tension spring unit encompasses only one carriage  121   c   1  having a deep groove ball bearing  121   c   4 , and that the two tension springs  121   c   2  at the other end are connected not to a second carriage  121   c   1  but instead fixedly to intermediate carrier  121   a.    
     Carrier plate  214   a  has a symmetrical oval basic shape. The rotation point of carrier plate  214   a  is arranged so that it is at identical distances from two oppositely located vertex points of the oval basic shape, and at non-identical distances from the other two oppositely located vertex points. The oval basic shape of carrier plate  214   a  is interrupted by an indentation. The indentation is recessed into the oval basic shape at the point at which the vertex point is closest to the rotation point. 
     In the context of a 180° twist, the one deep groove ball bearing  121   c   4  rests against that point on the oval carrier plate  114   a  that is farthest from its rotation point. In this position carriage  121   c   1  then has the greatest possible excursion, and tension springs  121   c   2  have the greatest possible tension, with the result that the restoring force reaches its maximum. If the user exerts on platform  13  a torque that does not overcome this maximum restoring force at 180°, support part  10  is returned by the restoring force, oppositely to the rotation direction initiated by the user, to the first initial position, and is latched therein. If, on the other hand, the user exerts on platform  13  a torque that exceeds the maximum restoring force at 180°, the restoring force that is established (and any excess torque of the user) will return support part  10 , in the rotation direction initiated by the user, to the initial position and latch it therein.