The present embodiments relate to a device and a method to determine the position of a component that is moveable in a linear manner along an assigned axis according.
In many technical applications, the position of moveable components is to be determined precisely. This may be achieved by integration over the movement trajectory of assigned drives (e.g., stepper motors or linear drives). For many applications such as, for example, in medical technology, measurement technology, optics or the like, the accuracy of such measurement methods is not sufficient.
An example of the need for precise position determinations in medical technology may be found in the field of multi-leaf collimators.
Multi-leaf collimators are used to shape the beam of an X-ray beam that may be generated by a linear accelerator in therapeutic radiation therapy. Such a collimator encompasses a plurality of leaves of a radio-opaque material (e.g., tungsten). The leaves are arranged in a moveable manner such that, by the positioning the leaves, the cross-sectional profile of the beam may be adjusted to match contours of the perimeter of an area of tissue located in the X-ray beam that is to be treated. This provides that the tissue to be treated (e.g., a tumor) receives the desired dose of radiation, while the surrounding tissue is exposed to as little radiation as possible.
In modern methods of radiation therapy such as, for example, in dynamic arc irradiation, the position of the leaves is to be constantly adjusted since the beam moves in relation to the patient, and the contour of the perimeter of the tissue that is to be irradiated therefore changes as a function of an angular position of the beam to the patient. In intensity-modulated treatment, the aim of which is to distribute the radiation as regularly as possible in the zone to be irradiated and thus to make up for imbalances in the passage of radiation through the body, a constant adjustment of the position of the collimator leaves is provided.
In order to provide a reliable operation of such a multi-leaf collimator, each position of the leaves is to be known precisely at all times. From the prior art, this may be achieved by installing a piezo transducer in direct contact with an edge of a respective leaf and generating surface waves in the leaf by using the piezo transducer. Such surface waves (e.g., edge waves) then run along the edge of the leaf and are reflected on a defined obstacle (e.g., on a corner of the leaf). The relative position of the leaf may be determined from a signal propagation time for the signal that has been transmitted or reflected.