Patent Number: 
Section: description

FIG. 1 shows a first embodiment of a leaf 22 of a multi-leaf collimator 23 configured in accordance with the invention. A displacement detecting element 1 formed as potentiometer comprising electrical functional elements, i.e. measuring resistance 2 or 15, voltage pick-off 4, conductor path 13 and slide contact path 16, is disposed in a region 33, 33xe2x80x2 of a leaf 22 which is not subjected to the main radiation 34 of a radiation source 45 since this region 33, 33xe2x80x2 is located in the shadow of a pre-collimator 36 which delimits the main radiation 34 corresponding to the lines 46 and 46xe2x80x2 or another linexe2x80x94depending on the setting. Another setting of the leaf 22 is shown with dashed lines in which the front edge 44 was adjusted through an adjusting motion 38. To safeguard the shielding region 33xe2x80x2, the pre-collimator 36 must also be displaced corresponding to the adjusting motion 39 (shown with dashed lines). In this embodiment, the housing 9 must be shielded in regions where no electrical functional elements are provided since the shielding material should not be weakened in areas where only the leaves 22 shield the main radiation 34. Of course, a fixed delimitation of the main radiation 36 could be provided instead of the pre-collimator 36. The displacement-detecting element 1 should then be arranged such that no electrical functional element of the displacement-detecting element 1 can move into this main radiation 46. This embodiment also shows that the housing 9 of the displacement-detecting element 1 has a dovetailed outer contour 31, which is inserted into a complementary recess 32 of the leaf 22. The housing 9 of the displacement detecting element 1 is rigidly connected to the leaf 22 by screwing it into a recess 37 and surrounds a tongue 11 which is fixed to the collimator housing by means of a mounting 43 at its bore 27. The housing 9 may e.g. also be glued, soldered, riveted or mounted in a different fashion. In this manner, the tongue 11 can move in the housing 9 when the leaf 22 performs the adjusting motion 38 to produce, as described in detail below, a signal that is converted into displacement information through a means 5 and is processed by the control of a multileaf collimator 23. Clearly, the latter can also effect the displacement information conversion. The illustration also shows the guidance 41 of the leaf 22 and a drive 42, which is indicated by a bar and a double arrow. The leaf 22 has an adjustment path with indicated maximum length 7.7xe2x80x2 thereby shows the position on the adjusting path to be detected. It is thereby advantageous to be able to adjust the leaf 38 past the centerline 40 of the multi-leaf collimator 23 to produce desired shapes. The functional principle of shaping using the multi-leaf collimator 23 is also explained below. The front edge 44 of the leaf 22 is advantageously inclined parallel to the main radiation 34. The corresponding device is, however, not subject matter of this application. FIG. 1a shows the leaf 22 in section Ixe2x80x94I. The leaf 22 is a thin plate (shown in larger scale than in FIG. 1). One sees that the displacement-detecting element 1 must be extremely flat. It preferably has an extremely flat housing 9 to permit insertion of the housing 9 of the displacement-detecting element 1 into a recess 37 laterally disposed in the leaf 22. The housing 9 should not protrude since the next leaf borders at that location although it could also partially extend in a groove in the neighboring leaf. FIG. 1b schematically shows a multi-leaf collimator 23 in plan view, opposite to the direction of irradiation, wherein the delimitation 24 is shown within which the leaves 22 set the opening 25 for the radiation 34. This is effected by the drives 42 of the leaves 22 with precise positioning being obtained by the inventive displacement-detecting element 1. Since the leaves 22 are formed as densely packed lamellas of minimum width, it is important that the displacement detecting elements 1 detect the positions of the leaves 22 while having an extremely flat construction. They can be disposed e.g. in a recess 37 on the side of the leaves 22, above or below the material required for shielding. In this fashion, their positions can be directly detected and they can be protected from the main radiation 34 thereby avoiding error sources and obtaining an inexpensive solution requiring little space. FIG. 1c shows an embodiment with an alternative arrangement of a displacement-detecting element 1 on a leaf 22. In this case, the housing 9 of the displacement detecting element 1 is disposed on the lower side of the leaf 22 so that it is completely shielded by the leaf 22 and therefore positioned in a region 33xe2x80x2 where the main radiation 34 is largely shielded for each position of the leaf 22. FIG. 2 shows an embodiment of the inventive displacement-detecting element 1. This displacement-detecting element 1 comprises a housing 9 and a tongue 11, wherein the housing 9 has a recess 10 extended along the housing 9 in which the tongue 11, formed in correspondence with the recess 10, is displaceably disposed. The housing 9 can be mounted to the structural component 22 being measured via bores 28 and the bore 27 fixes the tongue 11. In this fashion, the housing 9 is displaced relative to the tongue 11 corresponding to the position changes of the leaf 22 to which the housing 9 is mounted. To detect the position changes, the tongue 9 has a measuring resistance 2 formed as resistance strip 6. The irregular edge of the resistance strip 6 constitutes a compensation 8, which is provided by removing part of the material from the resistance strip 6 to serve for precise adjustment of the displacement-detecting element 1. The measuring resistance 2 has a terminal 12 at one end and its other end is connected to a conductor path 13 which extends parallel to the resistance strip 6 to the second terminal 14 of the measuring resistance 2, disposed next to the first terminal 12. The voltage source 3 is connected to these terminals 12 and 14. A second slide contact path 16 is disposed on the tongue 11 which extends parallel to the resistance strip 6 and the conductor path 13 and which has a terminal 17. The resistance strip 6 serves as first slide contact path 15. The voltage pick-off 4 is effected in that the housing 9 has a first wiper 18 and a second wiper 19 which are electrically connected to thereby produce an electrical connection between the measuring resistance 2 and the second slide contact path 16 at the respective position. For this reason, all the terminals 12, 14 and 17 are located on the fixed tongue 11. This avoids cable connections subjected to motion, which could cause cable breakage. To increase the reliability of the contact, the wipers 18, 19 are fork-shaped and have several contact zones. In the position detected herein, the wipers 18, 19 are disposed on the partial length 7xe2x80x2 of the full displacement path 7 of a leaf 22 to be detected. Advantageously, the first and second wiper 18 and 19 pass through a window 21 of the housing 9. The two wipers 18 and 19 can be resiliently disposed without requiring too much height. This embodiment permits flat construction of the displacement-detecting element 1 and mounting to very flat leaves 22. The voltage pick-off 4 permits measurement between the terminal 17 and one of the terminals 12 or 14 by means of which the length of the respective displacement 7xe2x80x2 and therefore the position of a leaf 22 can be determined. The measurement can be effected by disposing a resistance 20 between the terminals 17 and 12 or 14 where the voltage is picked off using a means for converting the signal into displacement information 5. This may be a voltage meter calibrated to the displacement. The resistance 20, the means 5 for converting a signal into displacement information and the voltage source 3 are symbolically drawn here. This or a corresponding function is generally integrated in the overall electronics of the device. The signals of the displacement detecting elements of all leaves are advantageously passed on to the control device of the multi-leaf collimator to thereby form the desired contours in a rapid and exact fashion. FIG. 2 shows a conducting layer 26, which is mounted on the housing 9 for shielding. A further conducting layer 26xe2x80x2 serves for soldering on the wipers 18 and 19. This layer 26xe2x80x2 is very thin. FIG. 3 shows a housing 9 of the inventive displacement-detecting element 1 which must be sufficiently long to permit a pushing motion of the tongue 11 relative to the housing 9, which corresponds, to the length of maximum displacement 7 of the leaf 22 to be detected. The other structural components correspond to those already described in FIG. 2. FIG. 4 shows a tongue 11 of the embodiment shown in FIG. 2 wherein the measuring resistance 2 must have the above-mentioned length of displacement 7. Compensation 8 of the measuring resistance 2 was effected within this region. The figure also shows the connection between the end of the resistance strip 6 opposite to the terminal 12 and the conductor path 13, which leads to the other terminal 14. The second slide contact path 16 must also have the same length 7. FIG. 5 shows advantageous embodiments of the displacement-detecting element 1. In one embodiment, electrical functional elements such as the measuring resistance 2, the conductor path 13 and the second slide contact path 16 are disposed in a gap 29 between the housing 9 and the tongue 11 to protect them from wear and soiling. Such a gap 29 can be realized e.g. by two steps 30 in the recess 10. A further advantageous embodiment has the above-mentioned dovetailed outer contour 31 of the housing 9 to be able to insert the housing 9 into the leaf 22 to be detected. In this manner, a very flat displacement-detecting element 1 can be mounted to very flat leaves 22 of multi-leaf collimators 23. This embodiment is of course only one possible realization of the invention. Depending on the design of the leaves 22, it is also possible to dispose the electrically insulated measuring resistance 2 directly on a leaf 22 and make the voltage pick-off 4 stationary. The housing 9 and tongue 11 can also have other designs. The functional elements 2 and 4 may also be disposed vice versa. Other shapes are also feasible. One leaf can have several displacement detecting elements 1 to increase the operating safety through a checking measurement and/or via increased precision of displacement detection. LIST OF REFERENCE NUMERALS 1 displacement-detecting element (potentiometer) 2 measuring resistance (functional element) 3 voltage source 4 voltage pick-off (functional element) 5 means for converting the signal into displacement information 6 resistance strip 7 maximum length 7xe2x80x2 part of the displacement (displacement to be detected) 8 balance 9 housing 10 recess 11 tongue 12 terminal of the measuring resistance 13 conductor path 14 connection of the measuring resistance (via conductor path) 15 first slide contact path (measuring resistance) 16 second slide contact path 17 terminal of the second slide contact path 18 first wiper (at the measuring resistance) 19 second wiper (at the second slide contact path) 20 resistance 21 window 22 leaf 23 multi-leaf collimator 24 delimitation 25 opening for radiation 26, 26xe2x80x2 conducting layers 27 bore for mounting the tongue 28 bore for mounting the housing 29 gap 30 steps 31 dovetailed outer contour 32 complementary recess for dovetailed outer contour 33, 33xe2x80x2, 33xe2x80x3 region of the leaves, which is not subjected to main radiation 33 region shielded by the pre-collimator 33xe2x80x2 region of shielding in a different position of the pre-collimator 33xe2x80x3 region shielded by the leaves 34 main radiation 35 side of the leaves facing away from radiation 36 pre-collimator 37 recess on the leaves for insertion of the housing 9 38 double arrow: adjusting motion of the leaf 39 double arrow: adjusting motion of the pre-collimator 40 center line of the multi-leaf collimator 41 guidance of the leaf 42 drive of the leaf 43 mounting of the tongue 44 front edge of the leaves 45 radiation source 46, 46xe2x80x2 delimitation of the main radiation