Abstract:
A positioning device for positioning a load is provided. The positioning device includes a motor, a measuring device, and an evaluation device. The measuring device is associated with the motor, and is operable to ascertain measurement data that characterizes the motor current consumption by the motor in the positioning of the load. The evaluation device evaluates the measurement data that have been ascertained by the measuring device, so that in that way the loading of the positioning device by the load can be ascertained.

Description:
This application claims the benefit of DE 10 2007 026 114.6 filed Jun. 5, 2007, which is hereby incorporated by reference. 
     BACKGROUND 
     The present embodiments relate to positioning a load. 
     During particle therapy, a particle beam, for example, including protons or heavy ions, is generated in an accelerator. The particle beam is carried in a radiation channel from the accelerator to an exit window of the radiation channel. The particle beam enters an irradiation or treatment room through the exit window. The particle beam may be used to treat cancer. 
     The success of tumor treatment depends on the precision of the tumor positioning. Positioning a patient depends on a plurality of factors. For example, the precision of positioning depends on how the patient is supported and the rigidity of the patient support system. In positioning the patient, the weight of the patient may cause elastic deformation that leads to imprecise positioning. 
     A more-rigid construction may be used to avoid elastic deformation under the load of the patient. However, the more-rigid construction results in higher costs. 
     Alternatively, it is possible to compensate for elastic deformation, for example, by using known load data to compensate for a predictable deformation. The system cannot be used flexibly, since the load data have to be known prior to treatment. In particle therapy, the load data is not known because of the variability of the loading from one patient to another. 
     Another possibility is to use sensors, such as force-torque sensors, to ascertain the loading. However, such systems are comparatively expensive. 
     SUMMARY AND DESCRIPTION 
     The present embodiments may obviate one or more of the drawbacks or limitations inherent in the related art. For example, in one embodiment, a load is ascertained simply, flexibly, and economically. 
     In one embodiment, a positioning device for positioning a load includes a motor, measuring device, and an evaluation device. The motor moves the positioning device. The measuring device is associated with the motor and is operable to ascertain (determine) measurement data that characterizes the motor current consumption by the motor in the positioning of the load. The evaluation device may evaluate the measurement data, so that the loading of the positioning device by the load may be ascertained. 
     The motor current consumption, the force, and/or the torque that act on the motor may be ascertained. Using the geometry of the positioning device, the loading of the positioning device by the load may be attained, for example, without additional sensors. The load data of the load, such as the weight and/or the location of the load on the positioning device, may be ascertained at least in part with the positioning device. The load data of the load does not need to be known prior to treatment. 
     Based on the ascertained loading of the positioning device, an elastic deformation, for instance, may be quantitatively predicted from the loading. The elastic deformation may be predicated, for example, via a relationship based on empirical values and/or a relationship ascertained by calculation. The deviation in an actual position of the load from a desired set-point position may be ascertained. In static positioning of the load, for example, a warning signal may be output if the ascertained loading is above a threshold value, or if the expected elastic deformation exceeds a tolerance range. 
     In one embodiment, the positioning device further includes at least one further motor for moving the positioning device; and a further measuring device. The further measuring device is associated with the further motor and is operable to ascertain further measurement data that characterizes the motor current consumption by the further motor in the positioning of the load. 
     The evaluation device may take into account the further measurement data, in addition to the measurement data, during the evaluation. Because the motor current consumption of further motors is measured, the loading of the positioning device may be ascertained more precisely. For example, loading, or load data, may be ascertained redundantly. The loading may be ascertained more precisely, because variables whose ascertainment requires the measurement data of at least two different motors may be ascertained. 
     In one embodiment, the positioning device additionally has a control device for positioning the positioning device. The control device may use the ascertained loading to compensate for a deformation. 
     As a result, it is possible in particular upon static positioning of the load at a desired set-point position to reach the set-point position automatically, even if a deformation of the positioning device by the load occurs. Once the loading is ascertained, the elastic deformation of the positioning device can be determined from it. To that end, a relationship based for instance on experience and/or on calculation can be used. Next, a compensation signal can be ascertained, with which the control device corrects the position of the positioning device accordingly, so that the desired set-point position is reached. 
     In one embodiment, the evaluation device is operable to ascertain the weight of the load and/or the position of the center of gravity of the load. For example, the position of the load, relative to the positioning device, may be ascertained. 
     In one embodiment, the positioning device is a multiaxial robot arm with a plurality of joints. The load may be flexibly positioned. By measuring the motor current consumption of at least one motor, which is used to move one of the joints, the loading of the positioning device (e.g., a robot arm) may be ascertained. A deformation of the positioning device by the load may be compensated for. 
     During the evaluation of the measured measurement data, at least one joint position may be taken into account. At least one joint position may be taken into account whenever the robot arm used in the positioning includes different joint positions for one of the joints. The geometry of the robot arm may be ascertained using the joint position. The geometry of the robot arm may be used to ascertain the center of gravity of the load or the weight of the load. However, if the robot arm for positioning the load has similar joint positions that differ only slightly from one another, then the at least one joint position may not be considered when ascertaining the load, since the geometry of the robot arm varies only insignificantly. 
     The positioning device may be a patient positioning device for positioning a patient in a medical system, such as in a particle therapy system. This offers a solution to the problem of positioning a patient as precisely as possible in the medical system, and may increase the safety of the system. 
     In one embodiment, a method for operating a positioning device for positioning a load includes positioning the load by moving the positioning device with the aid of the at least one motor; ascertaining (determining) measurement data that characterize a motor current consumption by the at least one motor in the positioning of the load; evaluating the ascertained measurement data in such a way that loading of the positioning device by the load is ascertained. The method may further include controlling the positioning device using the ascertained loading of the positioning device in such a way that a deformation of the positioning device by the load is compensated for. 
     The method can be implemented, for example, based on software in a computer unit that is connected to the positioning device for controlling the positioning device. In ascertaining the loading, the weight of the load and/or the position of the center of gravity of the load may, for example be determined as load data. 
     The ascertained loading of the positioning device may be subjected to a plausibility check, and may increase the reliability of the method. 
     In one embodiment, the loading in a positioning device, such as a multiaxial robot arm having a plurality of joints may be ascertained. At least one joint position may be taken into account. 
     In one embodiment, if the positioning device has a plurality of motors, and measurement data is ascertained for each of the motors, the measurement data characterizing the respective motor current consumption in the positioning of the load, then the loading of the positioning device by the load may be ascertained redundantly. For example, an error signal may be output if in the redundant ascertainment a deviation is found that is outside a tolerance range. An error signal may indicate a malfunction of the positioning device, so that motion of the positioning device may be blocked, for example, for safety reasons. 
     In one embodiment, a medical diagnosis and/or treatment system includes a positioning device for a patient. The positioning device is located in a examination room or treatment room, and the positioning device may include the features discussed above or below. The medical diagnosis and/or treatment system may be used for radiation therapy, such as particle therapy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates one embodiment of a particle therapy system; 
         FIG. 2  illustrates one embodiment of a positioning device for a patient; and 
         FIG. 3  illustrates a flow chart for a method for ascertaining the loading of a patient positioning device. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a particle therapy system  10 . The particle therapy system  10  may be used to irradiate a body, such as tissue diseased by tumor, with a particle beam. 
     The particles may be ions, protons, pions, helium ions, carbon ions, or other types of ions. The particles may be generated in a particle source  11 . If, as shown in  FIG. 1 , there are two particle sources  11 , which generate different types of particles, then a fast switchover between these two types of particles is possible. A switching magnet  12  may be, for example, used for the fast switchover. The switching magnet  12  is located between the particle sources  11  and a preaccelerator  13 . For example, the particle therapy system  10  may, for example, be operated with protons and with carbon ions simultaneously. 
     The ions generated by the ion source or one of the particle sources  11 , and optionally selected with the switching magnet  12 , are accelerated to a first energy level in the preaccelerator  13 . The preaccelerator  13  is, for example, a linear accelerator (LINAC for “LINear ACcelerator”). The particles are fed into an accelerator  15 , such as a synchrotron or cyclotron. In the accelerator  15 , the particles are accelerated to radiation treatment energies. Once the particles leave the accelerator  15 , a high-energy beam transport system  17  carries the particle beam to one or more treatment rooms  19 . In the treatment room  19 , the accelerated particles are aimed at a body to be irradiated. The accelerated particles may be aimed at a body either from a fixed direction (e.g., in a “fixed beam” room) or from various directions via a movable gantry  21  that is rotatable about an axis  22  (e.g., in a “gantry-based” room). 
       FIG. 2  shows a positioning device as a robot arm  31 . The robot arm  31 , for a patient  55 , may be used in a treatment room of a particle therapy system. 
     The robot arm  31  has six different joints  33 ,  35 ,  37 ,  39 ,  41 ,  43 , which are moved by a motor  45 ,  47 . The motors  45 ,  47  are located behind the linings of the robot arm  31 . Measuring devices  49 ,  51  are located on (connected to) each of the motors  45 ,  47 , and with them, measurement data that characterizes the motor current consumption at the respective motor  45 ,  47  upon positioning a patient may be ascertained. The motors  45 ,  47  and the associated measuring devices  49 ,  51  are shown at only two joints  39 ,  41 , for the sake of simplicity. A measuring device  49 ,  51  associated with one of the motors  45 ,  47  does not need to be located in the immediate vicinity of a motor, as shown. For example, the measuring device  49 ,  51  may be located in a control unit for the motors  45 ,  47 . 
     The measurement data is carried to an evaluation device  53 . The evaluation device  53  may ascertain the load data for the positioning device. The load data for the positioning device may include the weight m of the patient  55  and the location l of the center of gravity  57  of the patient  55 . The load data may be used for oppositely controlling the joints  33 ,  35 ,  37 ,  39 ,  41 ,  43  of the robot arm  31  in such a way to compensate for the deformation caused by loading of the positioning device. Compensation may be done, for example, by the control device  59 , with which a compensatory motion of the robot  31  may be executed. 
     The evaluation device  53  and the control device  59  may be implemented, for example, in a computer unit  61  that is connected to the robot arm  31 . 
     The control device  59  may compensate for sagging of the components of the table system  63 . Sagging may include, for example, sagging of the tabletop  65 , sagging of the table pedestal, or sagging of the tabletop and of the accessories affixed to it. 
       FIG. 3  shows a flow chart of an embodiment of a method for ascertaining load of a positioning device  31 , for example, as shown in  FIG. 2 . 
     Proportionality exists between the motor current consumption I n  for a joint n and the torque M n  acting on the joint. The torque M n  is the result of the geometry of the robot arm (position of the individual joints  33 ,  35 ,  37 ,  39 ,  41 ,  43 ) and of the location of the center of gravity of the patient (“l”) and the weight of the patient (“m”). The location l and weight m may be unknown variables. Since the geometry (e.g., the position of the individual joints  33 ,  35 ,  37 ,  39 ,  41 ,  43 ) is known, and the motor current consumption may be ascertained with the measuring devices  49 ,  51 , the loading of the positioning device by a patient may be ascertained during the positioning  69 . 
     After declaration  71  and initialization  73  of the variables for ascertaining the loading, a first measurement  75  of the motor current consumption is made at two different joints. Using the first measurement  75 , a first calculation  77  of the weight of the patient m 1  and of the location of the center of gravity  11  of the patient may be performed. 
     Similar to this first measurement  75  and first calculation  77 , a second measurement  79  of the motor current consumption is made at two further, different joints. Analogously to the first calculation  77 , the weight of the patient m 2  and the location of the center of gravity  12  of the patient may be calculated in a second calculation  81 . 
     After this twofold, redundant calculation, a redundancy check  83  may be performed. If the variables calculated in the first calculation  77  and in the second calculation  81  differ too greatly, for example, if the difference between the associated torques is greater than a predetermined threshold value ε, this is an indication of a malfunction of the system. A first error signal  85  may be output. 
     The variables calculated may be subjected to a plausibility check  87 . The plausibility check  87  may generate a second error signal  89  whenever one of the two calculated values is outside a predetermined tolerance range. The error signal may indicate a malfunction of the system. 
     If the redundancy check  83  and the plausibility check  87  have not reported any errors, then an arithmetic averaging  91  of the weight m 1 , m 2 , calculated twice, of the patient and of the center of gravity  11 ,  12  of the patient, calculated twice, may be performed. 
     The averaged variables may be transferred as variables to a computer unit (value transfer  93 ). These variables may, for example, be used to perform a control  95  of the positioning system, in such a way that compensation for an elastic deformation of the positioning system in positioning the patient is performed. 
     In one embodiment, a quality check of the positioning system in the context of a quality assurance act, for example, is performed daily. During the quality check, the positioning system is loaded with a defined load, such as with load data known in advance. The method is performed, and the values transferred to the variables may be compared with reference values. When the transferred values are outside a predetermined tolerance range, a malfunction of the positioning device may have occurred. 
     Various embodiments described herein can be used alone or in combination with one another. The forgoing detailed description has described only a few of the many possible implementations of the present invention. For this reason, this detailed description is intended by way of illustration, and not by way of limitation. It is only the following claims, including all equivalents that are intended to define the scope of this invention.