Title of Invention

SPINDLE DRIVE FOR DIAGNOSTIC OR THERAPEUTIC DEVICE

Abstract

The invention relates to a spindle drive for a diagnostic or therapeutic device. In an advantageous embodiment, the spindle drive comprises a drive (20) , a spindle nut (19) driven by the drive (20), a spindle (18) circled by the spindle nut (19), and a catch nut (10) . The catch nut (10) is constructed such that, while the spindle nut (19) is intact, it is not in mutual engagement with the spindle (18) and assumes a predefined distance to the drive (20) . If the spindle nut (19) fails, however, it is brought by axial movement of the spindle (18) into mutual engagement with the spindle (18). Further, a switching element is included, which is fixedly connected to the catch nut (10) . The catch nut (10) can be moved axially within predefined motional limits. In addition, an emergency off switch (5) is included, which can be activated by a switching sensor, the switching element actuating the switching sensor when the catch nut (10) is moved axially relative to the drive (20) by axial movement of the spindle (18).

Full Text

2005P17747IN Description Spindle drive for diagnostic or therapeutic device The invention relates to a spindle drive with threaded spindle and spindle nut and having a catch nut. The invention further relates to a diagnostic and/or therapeutic device and a patient positioning system which comprises such a spindle drive. Spindle drives with threaded spindle are used in applications in which, for example, loads or system components have to be moved and precisely positioned. Apart from industrial applications such as machine tools and end user applications such as garage door openers, other systems in which spindle drives are used can include medical diagnostic and/or therapeutic devices (DT devices). Here, for example, X-ray tube assemblies, X-ray image receivers or patient positioning systems for such equipment, as well as for computer tomography equipment, magnetic resonance equipment or nuclear medicine and radiation therapy equipment, are moved and positioned. Unidentified wear or even mechanical failure of the spindle drive poses considerable risks of injury and endangerment for the user or for other persons entering into contact with the spindle-driven apparatus, for example in X-ray devices for the doctor or the patient. In spindle drives with threaded spindle, wear rising to complete failure can stem from the fact that a spindle nut revolving on the threaded spindle, where appropriate with epicyclic gearing, for example, recirculating ball gear, fails. If the balls of the recirculating ball gear are destroyed by wear, for example, then the recirculating ball gear is no longer in mutual engagement with the threaded spindle. The form closure between the spindle and the mass to be moved is thus lost. The recirculating ball gear is then no longer supported by means of the balls in the thread of the threaded spindle, but instead becomes almost freely movable. In 2005P17747IN - 2 - a vertical drive, the mass to be moved can then, in the worst scenario, fall down. In order to avert the risk of danger due to an unforeseeable failure of the spindle drive, recirculating ball gears with so-called catch nuts or safety nuts are used. The catch nut is fixedly connected to the spindle nut and has a thread which, just like the balls of the recirculating ball gear, is in mutual engagement with the thread of the threaded spindle. The pitch of the thread of the catch nut here corresponds to the pitch of the thread of the spindle nut and to that of the thread of the threaded spindle, so that the catch nut can revolve jointly with the recirculating ball gear around the threaded spindle. The thread of the catch nut can be constructed such that it revolves frictionlessly around the threaded spindle as long as the spindle nut, or, where appropriate, its recirculating ball gear, revolves truly, i.e. within predefined tolerances. The catch nut comes into effect, however, if the spindle nut is no longer revolving truly, for example owing to excessive bearing play of the recirculating ball gear or even destruction of the balls. If, in such a wear situation, the force closure between threaded spindle and recirculating ball gear is lost, then the force closure between catch nut and threaded spindle is established instead. An uncontrolled self-movement of the mass to be moved is then prohibited by the catch nut. The mass to be moved is thereby prevented, for example, from falling down. Since the thread of the catch nut substantially corresponds to that of the spindle nut, an operation of the spindle drive despite failure of the spindle nut is conceivable. The catch nut steps in for the spindle nut and replaces it in its function. In a spindle drive which is arranged such that it is not necessarily visible to a user, but is hidden, for example, behind panels or cladding parts, this is not readily apparent. This gives rise, however, to the critical situation in which, if the spindle nut fails and the operation is continued on the 2005P17747IN - 3 - basis of the catch nut, no further safeguard exists, so that, should the catch nut subsequently fail, the complete failure of the spindle drive ensues and, for example, a height-adjusting device falls down. In spindle drives with fixed spindle nut and therein rotating spindle, it is therefore customary to check the mutual connection of catch nut and spindle nut, for example by electrical means. If the spindle nut fails and if, for example, in a height-adjusting device, the catch nut falls down onto the latter, then a mutual contact is formed which is electrically or mechanically detectable. This mutual contact is detected and can be used to activate an emergency off switch. In spindle drives with fixed spindle, in which the spindle nut is driven and revolves around the spindle, such checking of the contact between spindle nut and catch nut is not readily possible, however, since a, for example, electrical contact to the two rotating nuts would here be necessary. To create a contact to rotating parts is complicated, however. Moreover, standard contact types, e.g. sliding contacts, are, for their part, subject to wear and thus prone to error. In GB 8 96 914 C, an apparatus is described for indicating an admissible wearing of a first nut, which bears a load and, as a result of wearing, is subject to displacement along a threaded spindle. The apparatus contains a second nut, which bears no load and in which said threaded spindle engages, and means which allow only a relative axial displacement between the two nuts. The second nut has an adjustable stopper, which actuates a switch on the first nut whenever the relative axial distance between the two nuts falls below a value corresponding to the admissible wearing of the thread of the first nut. The switch is connected to a display means, which is switched on when the switch is actuated. The object of the invention consists in defining a system by which, in a spindle drive with fixed spindle and revolving, 2005P17747IN - 4 - driven spindle nut and catch nut, a failure of the spindle nut can be identified. A further object of the invention consists in defining a patient positioning system and a diagnostic and/or therapeutic device having such a spindle drive. The invention achieves this object through a spindle drive having the features of the first patent claim and through a patient positioning system having the features of the seventh patent claim and through a diagnostic and/or therapeutic device having the features of the ninth patent claim. A fundamental concept of the invention consists in defining a spindle drive having a drive, having a spindle nut driven by the drive, having a spindle circled by the spindle nut, and having a catch nut which is constructed such that, while the spindle nut is intact, it is not in mutual engagement with the spindle and assumes a predefined distance to the drive and, if the spindle nut fails, is brought by axial movement of the spindle into mutual engagement with the spindle. The spindle drive comprises a switching element, which is fixedly connected to the catch nut, and the catch nut can be moved axially within predefined motional limits. An emergency off switch is further included, which can be activated by a switching sensor, and the switching element actuates the switching sensor when the catch nut is moved axially relative to the drive by axial movement of the spindle. This yields the advantage that the mutual contact of the spindle nut and catch nut, i.e. of two moving parts, does not have to be checked, but only an axial displacement of the catch nut relative to the drive, as a non-movable fixed part, has to be checked. An uncomplicated solution is obtained, in which, for example, error-prone sliding contacts can be dispensed with. An advantageous illustrative embodiment provides that the switching element is constructed as a switching tube lying 2005P17747IN - 5 - concentrically over the spindle nut. The tubular construction offers, on the one hand, the advantage that the switching element is thus rotation invariant. On the other hand, an additional cladding of the spindle drive is thereby obtained, which offers an optical protection and protection against unintended engagement in moving mechanical parts of the spindle drive. A further advantageous illustrative embodiment provides that the spindle drive is vertically orientated in such a way that a height adjustment of the spindle is realized by revolution of the spindle nut. Such a spindle drive can be used, for example, as the lifting device for a patient positioning system, for an X-ray stand or an equipment component such as a C-arm. The load to be lifted here weighs heavily on the spindle, which therefore, in the event of failure of the spindle nut, falls down together with the load. This embodiment provides that the catch nut is disposed in such a way above the spindle that the catch nut, in the event of failure of the spindle nut, falls down in mutual engagement with the spindle onto the spindle nut and is stopped by the latter. As a result of the spindle and load having fallen down, the switching element connected to the catch nut is simultaneously jointly moved, so that an instant and automatic actuation of the emergency off switch is guaranteed. In a further advantageous embodiment, the emergency off switch of the spindle drive is connected to a drive such that the drive is stopped and/or switched off by activation of the emergency off switch. This ensures that a further operation of the spindle drive, following failure of the spindle nut, i.e. in a generally unsafe operating situation, is prohibited. Further advantageous embodiments emerge from the dependent patent claims and from the following figures and figure description, in which: 2005P17747IN - 6 - figure 1 shows a lifting unit with spindle drive, figure 2 shows a spindle drive with component of the lifting unit, figure 3 shows a spindle drive with emergency off switch, figure 4 shows a construction diagram with non-activated emergency off switch, figure 5 shows a construction diagram with activated emergency off switch, and figure 6 shows a diagnostic and/or therapeutic apparatus. In figure 1, a lifting unit with spindle drive is represented schematically. The lifting unit can be a component part of a patient positioning system and serve for the height adjustment thereof, but it can also be a component part of a C-arm apparatus or of another DT device and serve for the height adjustment, for example, of a C-arm or of a radiation source. The lifting unit comprises a bottom base plate 23, on which both a double scissors and the spindle drive are mounted. A lifting plate 22 can be linearly transported by the double scissors and the spindle drive relative to the base plate 23, i.e. in the chosen embodiment can be adjusted in height. The spindle drive comprises a drive 20, which drives the spindle nut 19. The spindle nut 19 revolves around the spindle 18, so that a recirculating ball spindle is formed. As a result of the revolution of the spindle nut 19 around the non-rotating spindle 18, the latter is transported axially, in the figure, therefore, up or down. The spindle 18 runs at its top end in an immersion tube 6 0 (it intrudes into the immersion tube 60). The immersion tube 60 is connected to the spindle 18 and prevents this from being able 2005P17747IN - 7 - to rotate. It is transported up or down by the movement of the spindle 18. In addition, it is fixedly connected to the cross bar 64 of the double scissors. If the immersion tube 60 is transported up or down, then the cross bar 64 is therefore also transported up or down. The cross bar 64, in turn, is a component part of the double scissors and is integrated in an axis of the scissors construction. The up or down movement of the cross bar 64 therefore causes a shortening or lengthening of the double scissors and thus a height adjustment of the lifting plate 22. In order to allow the lifting plate 22 to be lowered as far as possible, the inner diameter of the immersion tube 6 0 is here wider than the outer diameter of the spindle nut 19, so that, upon lowering, the immersion tube 60 can slide over the spindle nut 19 or the spindle nut 19 can intrude into the immersion tube 60. In figure 2, the same spindle drive as in the preceding figure 1 is represented, yet without lifting unit. The spindle drive is driven by a drive 20, which rotates the spindle nut 19. The spindle nut 19 revolves around the spindle (not discernible in the figure), which is thereby moved up or down. The spindle is seated in the immersion tube 60 and is connected thereto in such a way that it is prevented from rotating. Otherwise, the spindle nut 19 would transport the spindle along with it. The immersion tube 60 is fixedly connected to the cross bar 64, which, for its part, forms an axis of the scissors construction of the lifting unit. The spindle drive thus adjusts the height of the scissors construction via the cross bar 64. In figure 3, the same spindle drive as in the preceding figure is represented, without immersion tube, cross bar and without switching element. The drive 2 0 rotates the spindle nut 19, which revolves around the spindle 18. The spindle nut 19 is seated on a spindle tube 8, to which it is fixedly connected and which is driven by the drive 20. The catch nut 10 is 2005P17747IN - 8 - disposed in the spindle nut 19 in such a way that, when the spindle nut 19 is rotated, it is transported along with it. While the spindle nut 19, as long as it is intact, is in mutual engagement with the spindle 18, for example as a recirculating ball spindle via balls disposed in the thread, the catch nut 10 is normally not in mutual engagement with the spindle 18. A touching contact between spindle 18 and catch nut 10 is avoided as far as possible in order to prevent unintended wearing of the catch nut 10. The catch nut 10, in contrast to the spindle nut 19, is therefore constructed as a standard screw nut without friction-reducing ball recirculation. Fitted to the drive 20 or in the immediate vicinity of the spindle tube 8 is an emergency off switch 5. The emergency off switch 5 has a push button 6, which is facing the spindle tube 8 but does not touch it. The push button 6 is designed to be actuated by the switching tube (not represented in the figure) should the spindle nut 19 fail. In figure 4, a construction diagram of the spindle drive with all necessary components is represented. The drive 20 drives the spindle tube 8 via a worm gear (not to be described in detail). Fixedly connected to the spindle tube 8 is the spindle nut 19, which revolves by means of a ball recirculation around the spindle 18. The spindle 18 reaches through the spindle tube and the drive and is provided at the top end with a bolt eye. In the mounted state, the top end of the spindle 18 bears the load to be raised or lowered, the spindle 18 being connected to the load such that it is prevented from rotating. Depending on the construction, the bolt eye may be used for this purpose. Above the spindle nut 19 there is disposed the catch nut 10, which is connected to the spindle nut 19 such that, when this is rotated, it is transported along with it. The catch nut 10 has an inner thread, which fits into the thread of the spindle 18. The threading and arrangement of the catch nut 10 are chosen such that this is in no or only slight contact with the 2005P17747IN - 9 - spindle 18, so that friction-induced wear is precluded. Nor is it necessary, therefore, for the catch nut 10 to have a friction-reducing ball recirculation. The catch nut 10 is disposed at a predefined distance to the spindle nut 19. It is fixedly connected to the switching tube 7, the switching tube 7 lying concentrically over the spindle nut 19 and the spindle tube 8. The switching tube 7 is connected such that it can be moved at least axially relative to the spindle nut 19 and the spindle tube 8, and not fixedly to the latter. On the drive 20, in the immediate vicinity of the spindle tube 8, there is disposed the emergency off switch 5 with the push button 6. The push button 6 is constructed as a ball. In the chosen representation, the switching tube 7 does not actuate the push button 6, i.e. the emergency off switch 5 is not activated. This constellation is not obtained as long as the spindle nut 19 is intact and is working correctly. In figure 5, the same spindle drive as in the preceding figure 4 is described, yet in the constellation which is obtained in the event of failure of the spindle nut 19. The same reference symbols are used as in the preceding figure description. Should the spindle nut 19 fail, the form closure to the spindle 18 is abolished, for example because the balls of the ball recirculation of the spindle nut 19 have burst or the threads are worn. This means that the spindle 18 is no longer held by the spindle nut 19, but falls down. Should the spindle nut 19 fail, the catch nut 10 comes into action however. As a result of the spindle 18 having fallen down, the thread of the spindle 18 enters into mutual engagement with the inner thread of the catch nut 10. The falling-down spindle therefore weighs heavily on the catch nut 10 by resting on the inner thread thereof. When the spindle falls down, the catch nut 10 is therefore transported along 2005P17747IN - 10 - with it. The fall distance for the catch nut 10 is limited, however, by the spindle nut 19, which remains fixedly seated on the spindle tube 8. Spindle 18 and catch nut 10 thus fall precisely such a way down until the catch nut 10 hits the spindle nut 19. The fall distance is thus obtained from the distance between spindle nut 19 and catch nut 10 in the intact state. If the catch nut 10 falls down, the switching tube 7 connected thereto is transported along with it. The switching tube 7 thus falls just as far down with it. Consequently, it enters into contact at the lower end, however, with the push button 6 and actuates this. The push button 6 is pressed by the switching tube 7 to the emergency off switch 5 and activates this. At the emergency off switch 5 a signal is thus present, which indicates the failure of the spindle nut 19. The signal can be used to display an error report on a control unit, to prompt an automatic recording of the error report in a log file or to stop or switch off the drive 20 immediately. Immediate switching-off of the drive 2 0 ensures that the spindle drive, following failure of the spindle nut 19, cannot inadvertently continue to be operated, for example because the failure has not been spotted by the operator. In fig. 6, a DT device 3 with a patient positioning system 1 is represented schematically. The DT device 3 comprises a C-arm 31, which bears a beam source 33 and an image detector 34. It can be used, for example, to produce X-ray images, in the case of lower-energy X-ray radiation, or for therapeutic radiation, for example in the case of higher-energy X-ray radiation. The C-arm 31 is mounted in a C-arm holder 32. This can be constituted by a construction standing freely in the room or by a construction embedded in a wall or ceiling of the room. The C-arm 31 allows the X-ray tube assembly 33 and the X-ray detector 34 to be positioned in such a way that a patient 2005P17747IN - 11 - positioned with the aid of the patient positioning system 1 can be scanned by the X-ray beam. The patient positioning system 1 comprises a couch 11 onto which a patient can be laid. The couch 11 can be displaced in the horizontal direction, which is intended to be indicated by a horizontally orientated double arrow. For this purpose, it is mounted in floating arrangement on a base 12. In addition, the height of the couch can be adjusted. For this purpose, the base 12 comprises a lifting system (not represented in detail in the figure). The height adjustability is indicated by a vertically orientated double arrow. The height adjustment of the couch 11 is achieved by a lifting unit with spindle drive, as has been described in connection with the preceding figures. Similarly, a height adjustment of the C-arm 31 can be realized by such a spindle drive. 2005P17747IN - 12 - Patent claims 1. A spindle drive having a drive (20), having a spindle nut (19) driven by the drive (20), having an axially transportable spindle (18) circled by the spindle nut (19), and having a catch nut (10) constructed such that, while the spindle nut (19) is intact, it is not in mutual engagement with the spindle (18) and assumes a predefined distance to the drive (20) and, if the spindle nut (19) fails, is brought by axial movement of the spindle (18) into mutual engagement with the spindle (18) , characterized in that a switching element is included, which is fixedly connected to the catch nut (10), in that the catch nut (10) can be moved axially within predefined motional limits, in that an emergency off switch (5) is included, which can be activated by a switching sensor, and in that the switching element actuates the switching sensor when the catch nut (10) is moved axially relative to the drive (20) by axial movement of the spindle (18). 2. The spindle drive as claimed in claim 1, characterized in that the spindle nut (19) comprises a recirculating ball spindle. 3. The spindle drive as claimed in one of the preceding claims, characterized in that the switching element is constructed as a switching tube (7) lying concentrically over the spindle nut (19). 4. The spindle drive as claimed in one of the preceding claims, characterized in that the switching sensor is constructed as a push button (6). 5. The spindle drive as claimed in one of the preceding claims, characterized in that it is vertically orientated in such a way that a height adjustment of the spindle (18) is realized by revolution of the spindle nut (19), in that the spindle (18) , in the event of failure of the spindle nut (19) , 2005P17747IN - 13 - falls down, and in that the catch nut (10) is disposed in such a way above the spindle nut (19) that the catch nut (10) , in the event of failure of the spindle nut (19) , falls down in mutual engagement with the spindle (18) onto the spindle nut (19) and is stopped by the latter. 6. The spindle drive as claimed in one of the preceding claims, characterized in that the spindle nut (19) is driven by a drive (20) , and in that the emergency off switch (5) is connected to the drive (20) in such a way that the drive (20) is stopped and/or switched off by activation of the emergency off switch (5). 7. The spindle drive as claimed in one of the preceding claims, characterized in that the drive (20) comprises a drive motor and a worm gear. 8. A patient positioning system (1) having a lifting unit which comprises a spindle drive as claimed in claims 1 to 7. 9. The patient positioning system (1) as claimed in claim 8, characterized in that the spindle (18) is fixedly fastened to a component of the lifting unit. 10. A diagnostic and/or therapeutic device (3) having a lifting unit which comprises a spindle drive as claimed in one of the preceding claims 1 to 7.

Documents:

01029-kol-2006-abstract.pdf

01029-kol-2006-claims.pdf

01029-kol-2006-correspondence others.pdf

01029-kol-2006-correspondence-1.1.pdf

01029-kol-2006-correspondence-1.2.pdf

01029-kol-2006-description(complete).pdf

01029-kol-2006-drawings.pdf

01029-kol-2006-form-1.pdf

01029-kol-2006-form-2.pdf

01029-kol-2006-form-3.pdf

01029-kol-2006-form-5.pdf

01029-kol-2006-g.p.a.pdf

01029-kol-2006-other.pdf

1029--KOL-2006-(11-12-2014)-CLAIMS.pdf

1029--KOL-2006-(11-12-2014)-CORRESPONDENCE.pdf

1029-KOL-2006-(01-04-2013)-CORRESPONDENCE.pdf

1029-KOL-2006-ABSTRACT-1.1.pdf

1029-KOL-2006-CANCELLED PAGES.pdf

1029-KOL-2006-CLAIMS-1.1.pdf

1029-kol-2006-correspondence 1.1.pdf

1029-KOL-2006-DESCRIPTION (COMPLETED)-1.1.pdf

1029-KOL-2006-DRAWINGS-1.1.pdf

1029-KOL-2006-FORM 1-1.1.pdf

1029-KOL-2006-FORM 2-1.1.pdf

1029-KOL-2006-PETITION UNDER RULE 137.pdf

1029-KOL-2006-REPLY TO EXAMINATION REPORT.pdf

1029-KOL-2006-SCHEDULE.pdf

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