fig1 by way of example shows a therapy system in the form of a lithotripsy device . this comprises a therapy source in the form of a shock wave transducer . a patient rest 4 is moreover provided , on which a patient to be treated comes to lie and which can be displaced and positioned relative to the therapy source 2 . an x - ray c - arm 6 with any x - ray image intensifier 8 is moreover provided in this embodiment example . the therapy source 2 comprises an ultrasound probe which is not shown in detail in fig1 and which is pivotable along an arcuate guide path 10 about an axis which extends parallel to the longitudinal axis of the patient rest and thus to the longitudinal axis of a patient on the patient rest 4 . the ultrasound probe is connected to an ultrasound control apparatus 11 which comprises an ultrasound screen 12 . the patient rest 4 or its surface are displaceable relative to the therapy source 2 in spatial coordinates x , y and z which are at right angles to one another , in order to be able to position a patient on the patient rest 4 relative to the therapy source . for this , a multi - axis positioning system is provided , and this comprises three independent drives for realising the displacement movement along the axes x , y and z . the drives here are not shown in detail , and can be designed in the usual manner and are represented here by the axes x , y and z . with the embodiment example described here , the patient rest is envisaged to be displaced with the outlined drives in the direction of the three axes . however , it is to be understood that accordingly the therapy source 2 could also be displaced relative to the patient rest . it would also be conceivable to realise the relative movement by way of a superposition of movements of the patient rest 4 and the therapy source 2 . the control of the drives is thereby effected according to the subsequent description . as is schematically shown in fig2 , the complete therapy source 2 together with the ultrasound probe 14 , which is arranged in it , is pivotable along an arcuate path 10 about the angle β . the ultrasound probe 14 is moreover rotatable within the therapy source 2 about an axis s about the angle α . the axis s thereby extends through the therapy focus 16 of the therapy source 2 . the patient 18 can be moved with the patient rest 4 in the x , y and z coordinates relative to the therapy source 2 via the drives . suitable angle sensors are provided for positional detection of the therapy source 2 as well as the ultrasound source 14 about the pivot angles α and β . the ultrasound picture 20 which is recorded by the ultrasound probe 14 is a section picture through the body of the patient . the plane of the ultrasound picture 20 is thereby rotatable about the axis s and about the angle α . moreover , it can pivot together with the therapy source 2 about the angle β along the arcuate path 10 . a stone 22 which is distanced to the therapy focus 16 is schematically shown here in the ultrasound picture 20 . it is thus necessary to move the patient 18 with the patient rest 4 such that the stone 22 comes to coincide with the therapy focus 16 , for treating the stone . since the ultrasound picture 20 can be rotated about the angle with respect to the axis s , the ultrasound picture 20 thereby does not necessarily extend in the plane which is spanned by the coordinate axes x and z of the drives . thus , a displacement movement of all three axes x , y and z is necessary as the case may be . thereby , the difficulty arises of not losing the stone 22 from the ultrasound picture 20 . fig3 by way of example shows the representation of the ultrasound picture 20 on the ultrasound screen 12 . in this picture , the position of the therapy focus 16 is characterized , and the stone 22 can be recognized . direction keys 24 as touch - sensitive fields are represented on the screen , with which keys a movement of the patient rest 4 can be initiated , so that the patient with the stone 22 can be displaced into the therapy focus 16 . a movement path b in the form of a vector connecting the stone 22 and the therapy focus 16 in the ultrasound picture 20 is necessary for this . a displacement movement precisely in the current plane , i . e . the section plane of the ultrasound picture 20 is thus necessary . the necessary movements can be selected by the user at the ultrasound screen 12 by way of direction keys 24 . according to the invention , a control device 26 is now provided , and this is connected to the ultrasound control apparatus 11 and receives the commands of the direction keys 24 . the control device 26 moreover via suitable angle sensors as input variables receives the above mentioned angles α and β , about which the section plane of the ultrasound picture 20 is pivoted . the control device 26 , taking into account these angles , transforms the movement path or the movement vector b into the three spatial coordinates x , y and z of the drives of the patient rest 4 . the drives x , y and z thereby obtain distance information with regard to the distance which the drives have to cover along the respective coordinate axis , as well as speed information which is adapted to these distances , from the control device 26 . i . e ., the control device 26 activates the drives of the axes x , y and z such that these are simultaneously displaced with adapted speeds . thereby , the drive which has the greatest distance to cover is moved the quickest , and the drive which has to cover the shortest distance is driven the slowest . if for example the distance between the therapy focus 16 and the stone 22 along the z - axis in the coordinate system of the patient rest 4 is three cm , along the y - axis is two cm and along the x - axis is one cm , then the drive of the z - axis is operated at triple the speed of the drive of the x - axis and the drive of the y - axis is operated at double the speed of the drive of the x - axis . thus , one succeeds in these three drives carrying out a resulting movement of the patient rest 4 precisely along the spatial direction of the movement vector b , along the axes x , y and z with a simulators drive . thus , one succeeds in the patient being moved exactly in the plane of the ultrasound picture 20 , and the stone 22 thus remaining in the ultrasound picture 20 during the complete movement , so that a visual control by the user is possible during the movement . as is to be recognized by way of fig5 , the y um coordinate in the two - dimensional ultrasound picture 20 on the ultrasound screen 12 extends in the same direction as the y us axis of the ultrasound probe 14 . thereby , the ultrasound probe 14 is rotatable about the angle α about the y us axis . the coordinate y um in the ultrasound picture 20 and which is at right angles to the y um coordinate always goes in the same direction as the x us axis of the ultrasound probe 14 . the angles α and β are to be compensated in the control device 26 for the transformation of the movement vector b into the cartesian coordinate system with the axes x , y and z of the patient rest 4 . thus , a first vector transformation , in which the angle α is compensated takes place . the angle β is compensated in a second vector transformation . the axis y us of the ultrasound picture 20 extends parallel to the movement axis x of the patient rest , and the axis x us of the ultrasound probe 14 extends parallel to the axis z of the coordinate system of the drives of the patient rest 4 , if the ultrasound probe 14 is located in its middle position along the angle β and which is shown in fig5 and it is located in the middle position shown in fig5 , in the direction of the pivot angle α . thus , a movement direction in the y - z plane results from the transformation of the angle α into the coordinate system x , y and z , and a movement direction in the z - x plane of this coordinate system results from the transformation of the angle β . thus , movement coordinates for the drives in the coordinate system x , y and z of the patient rest 4 result from the position of the movement vector 22 along the axes x us and y us together with the angles α and β . the drives are simultaneously displaced along the axes x , y and z with suitably adapted speeds , in order to then be able to move the patient rest 4 exactly along the vector 22 . it is to be understood that the therapy source 2 could also be moved along the axes x , y and z relative to the patient rest 4 , instead of a movement of the patient rest 4 . for example , it would also be conceivable to move the patient rest 4 along only one or two of the axes x , y and z , for example along the y and x , whereas the therapy source is movable along the other axes , for example along the z - axis . it is merely a question of the relative movement between the therapy source 2 and the patient rest 4 in the cartesian coordinate system x , y and z . the therapy source 2 is provided with a water - filled transmission path 28 which bears with a membrane 30 on the skin of the patient 18 , in order to be able to couple the shock waves produced by the therapy source 2 into the body of the patient 18 . if now the patient rest 4 is displaced along the axis x relative to the therapy source 2 , then the patient 18 is thus moved away from the therapy source 2 , and the membrane 30 would no longer lie in a surfaced manner on the surface of the body of the patient 18 as desired . a pressure control is provided in the transmission path 28 , in order to compensate this . for this , a pressure sensor 32 which detects the pressure in the inside of the transmission path 28 is provided in the transmission path 28 or is coupled to this . fluid can be led into the transmission path 28 or led out of this via suitable pumps or valves . by way of this , it is possible to keep the pressure in the inside of the transmission path 28 essentially constant . the control device 26 for this is preferably designed such that the pressure in the inside of the transmission path 28 is detected via the pressure sensor 32 after the therapy source 2 has been positioned with the transmission path 28 and the membrane 30 on the patient 18 in the desired manner , and then , with the movement of the patient 18 on the patient rest 4 relative to the therapy source 2 , the pressure in the transmission path 28 is subsequently kept constant or is held within predefined limits , by way of fluid being led or pumped into the transmission path 28 as the case may be , or being let off in the case of a pressure which is too high . thus , the bearing contact of the membrane 30 on the skin of the patient 18 can always be ensured in a defined manner , even with a movement of the patient 18 , be it by way of displacing the patient rest 4 or due to the patient &# 39 ; s own movements . while specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention , it will be understood that the invention may be embodied otherwise without departing from such principles .
a therapy system includes a therapy source emitting radiation or waves , an ultrasound probe , a patient rest as well as a multi - axis positioning system with several drives , by way of which the patient rest and the therapy source can be moved to one another in all three spatial directions . a control device is coupled to the ultrasound probe and configured such that in at least one operating mode , the control device simultaneously activates the drives of the multi - axis positioning system such that the patient rest is moved relative to the therapy source along a selectable movement path which lies within the plane of an ultrasound picture which is currently recorded by the ultrasound probe . a method for positioning a patient rest relative to a therapy source is also provided .