Patent Number: 
Section: claims

1. A multi-leaf collimator comprising:a guide frame,a plurality of metal plates arranged in the guide frame in a displaceable fashion,a plurality of piezoelectric motors, each piezoelectric motor including:at least two piezoelectric actuators,an internally toothed driving ring that is excited by a stroke of the at least two piezoelectric actuators to a circulating displacement movement, andan externally toothed shaft attached to the driving ring such that the shaft is rotated by the displacement movement of the driving ring. 2. The multi-leaf collimator according to claim 1, comprising a motor housing that houses a number of the piezo-electric actuators, drive rings and shafts. 3. The multi-leaf collimator according to claim 1, wherein a toothed coupling between each externally toothed shaft and a toothed portion of a corresponding metal plate converts a rotation of the shaft into a linear movement of the metal plate. 4. The multi-leaf collimator according to claim 1, wherein the positioning of the metal plates can be controlled electrically. 5. The multi-leaf collimator according to claim 1, comprising electrical linear transducers for monitoring the position of each metal plate. 6. The multi-leaf collimator according to claim 5, wherein the positioning of the metal plates is electrically controlled, with a signal of the electrical linear transducer of each metal plate being used as a control signal. 7. The multi-leaf collimator according to claim 1, wherein a control electronics system is remote from the electrical motor such that it is arranged in a region with a radiation dose which is lower compared to that of the electrical motor. 8. A method for operating a multi-leaf collimator comprising a guide frame with a plurality of metal plates arranged in a displaceable fashion, and a plurality of piezoelectric motors, each piezoelectric motor including at least two piezoelectric actuators, an internally toothed driving ring that is excited by a stroke of the at least two piezoelectric actuators to a circulator displacement movement, and an externally toothed shaft attached to the driving ring such that the shaft is rotated by the displacement movement of the driving ring, the method comprising:controlling the plurality of piezoelectric motors such that at least one of the metal plates is movable both individually and simultaneously according to individual movement profiles. 9. A method for operating a multi-leaf collimator comprising a guide frame with a plurality of metal plates arranged in a displaceable fashion, and a plurality of piezoelectric motors, each piezoelectric motor including at least two piezoelectric actuators, an internally toothed driving ring that is excited by a stroke of the at least two piezoelectric actuators to a circulating displacement movement, and an externally toothed motor shaft attached to the driving ring such that the motor shaft is rotated by the displacement movement of the driving ring, the method comprising:for each piezoelectric motor, controlling the at least two piezoelectric actuators using a sine/cosine voltage to control the position of the motor shaft, wherein the at least two piezoelectric actuators are arranged at right angles to one another and operate according to a longitudinal effect.