Abstract:
An apparatus for movable weight-compensating suspension of a focusing objective of a laser system comprises a force generation device to generate a counterforce component  G  which counteracts the weight of the focusing objective, a transmission device which transmits the counterforce component  G  onto the focusing objective and permits upward/downward compensatory movement of the focusing objective, in such a way that in the case of an upward/downward compensatory movement of the focusing objective, an optical axis (O) of the focusing objective maintains at least its orientation in space, and preferably its position in space.

Description:
FIELD OF THE INVENTION 
     The invention concerns movable weight-compensating suspension of a focussing objective of a laser system. The laser system preferably provides pulsed laser radiation, which is focussed by means of the focussing objective onto a desired location where the radiation is to act. 
     BACKGROUND OF THE INVENTION 
     Movable weight-compensating suspension of the focussing objective is desired, not exclusively but above all, where treatment of living tissue is involved, and there is direct contact between the tissue and the laser system. Such direct contact is often produced, for example, in the case of operations on the human eye using laser surgery, when incisions in the cornea or other parts of the eye are to be made using ultra-short pulses of laser radiation. In this case, direct contact is intended to ensure precise positioning of the eye to be treated relative to the laser system in the direction of propagation of the radiation. Usually, a suitable interface unit (patient adapter) is connected in front of the focussing objective, and effects the physical coupling of the eye to the laser system. The interface unit usually has a holder, which is coupled to the focussing objective, for a contact element which is to be brought into contact with the eye and is made of a material which is transparent to the laser radiation. The contact element can, for example, be a plane underside for applanation of the cornea. 
     Focussing objectives in laser systems are often multi-lens systems, which can put considerable weight on the scales. Several kilograms are not unusual for such focussing objectives. Obviously, in an eye operation the full weight of the focussing objective must not rest on the eye being treated. Weight-compensating suspension for the focussing objective is therefore provided. The force which the focussing objective still exerts on the eye in the case of such a weight-compensating solution is reduced to a few newtons (e.g. 1 to 2 N), for example. This makes it possible to deflect the focus-sing objective upward, gently and not dangerously to the eye, if the patient suddenly happens to raise his or her head involuntarily, e.g. in a panic reaction. 
     An example of weight-compensating suspension of a focussing objective is given in U.S. Pat. No. 5,336,215. There the weight of the objective is compensated for by a spring system, by means of which the objective is movably suspended in a frame relative to the latter. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to give a reliably and precisely functioning solution for weight compensation of a focussing objective in a laser system. 
     According to the invention, for this purpose movable weight-compensating suspension of a focussing objective of a laser system is provided, comprising:
         a force generation device to generate a counterforce component which counteracts the weight of the focussing objective,   a transmission device which transmits the counterforce component onto the focussing objective and permits upward/downward compensatory movement of the focussing objective, and   a guidance device for movable guidance of the focussing objective, in such a way that in the case of an upward/downward compensatory movement of the focussing objective, an optical axis of the focussing objective maintains at least its orientation in space, and preferably its position in space.       

     Guidance of the focussing objective through the guidance device prevents undesired tilting of the optical axis of the objective in the case of an upward/downward compensatory movement of the objective. “Upward/downward compensatory movement” is understood here as a movement of the focussing objective upward or downward relative to the laser system. Thus despite a compensatory movement of the objective, the optical axis remains in a specified orientation to the object which is being treated, e.g. to the optical axis of a human eye which is being treated. It should be pointed out here that the invention can in principle be used with laser systems for any application purposes, and in particular for working on any materials (including dead matter), and is by no means restricted to ophthalmological application purposes. 
     The force generation device can include a counterweight, the mass of which is used to generate at least part, and in particular the whole, of the counterforce component. The counterweight can consist of a single counterweight member, or alternatively can consist of multiple (at least two) individual weight members, which for example can be used in changeable numbers or/and in changeable position relative to each other. The individual weight members can also be combined into a single total weight, and taken individually out of the total weight. By such variabilities of the counterweight, specially precise taring of the weight compensation is possible. 
     Moreover, within the invention, generating part of the counterforce component by means of at least one elastic element should not be excluded. Because of the disadvantage, which is often associated with elastic elements, that the effective force depends on the distance (the elasticity depends on the state of deformation of the elastic element), the force generation device preferably does not generate the counterforce component exclusively by means of elastic elements. However, combining one or more elastic elements with a counterweight is also conceivable, e.g. to implement a desired force-distance dependency intentionally. The transmission device is preferably in the form of a rocker, on one side of which the counterforce component acts, and on the other side of which the weight of the focussing objective acts. Functionally, the rocker can be compared with a weighing beam. 
     For example, the rocker is formed of at least one lever body, one lever arm of which is connected to the focussing objective, and the other lever arm of which is connected to the force generation device. It is understood that two or more such lever bodies can be provided adjacently, parallel and at a distance, to form the rocker. A force application point of the force generation device on the lever body can be adjustable along it, so as to adjust the torque acting on the lever body. In general, preferably at least one force application point of the force generation device on the rocker can be adjusted with respect to its distance from a swivelling axis of the rocker. 
     Use of a counterweight which is applied on one side of the rocker (i.e. on one lever arm) to generate at least part of the counterforce component has the advantage of the maximum possible constancy of the generated counterforce component over the whole operationally required movement travel of the focussing objective. By intentional displacement of the centre of gravity of the counterweight relative to the rocker, the force-distance characteristic curve of the suspension apparatus can be set definitively. This makes taring possible even with an indivisible counterweight. On the other hand, if the force generation device includes at least one elastic element, the force-distance characteristic curve of the suspension apparatus can be set in addition to the typically spring-like force-distance characteristic of the elastic element, because the force application point of the elastic element is movable along the lever or along the rocker. 
     The focussing objective is preferably supported on the rocker so that it can rotate relative to the rocker around an axis of rotation which runs parallel to a swivelling axis of the rocker at a distance. It is recommended, for spatial positional stability of the optical axis of the objective, that the support of the focussing objective on the rocker is at a variable distance to the swivelling axis of the rocker. If the rocker is tilted, the focussing objective can then carry out a simultaneous movement, meaning a change of distance from the rocker axis. In this way the objective can move up and down along a straight line instead of along a circular path, i.e. it maintains its trans-verse position (transverse means orthogonal to the objective axis) relative to the object being worked on. 
     The swivelling bearing of the rocker is preferably of low-friction form, and can for example be implemented by means of a plastic sliding bearing or a rolling bearing. Low friction is a desirable aim, to avoid, as far as possible, falsification of the effective force-distance characteristic of the suspension apparatus by overlaid friction forces. 
     In a preferred embodiment, the focussing objective is supported on a supporting surface arrangement of the rocker so that it can move freely. In particular, the sup-porting surface arrangement can be in such a form that the objective can be placed loosely on the rocker. The supporting surface arrangement can, for example, be formed of at least one longitudinal recess—into which the objective can be inserted with a suitable supporting pin or other supporting formation—of at least one lever body of the rocker. For example, the recess can be open upward, or/and it can—in relation to the longitudinal extent of the relevant lever arm, on which the objective grips—be open to the front or rear, so that the supporting formation of the objective can be inserted from the front or rear into the recess. 
     It is understood that the supporting surface arrangement can alternatively, for example, be in the form of an arrangement of one or more enclosed long holes, the objective engaging with each long hole by a suitable supporting projection. It is also understood that according to a modification, the supporting surface arrangement can be formed on the objective, and suitable supporting formations for support on the supporting surface arrangement can be formed on the rocker. 
     In any case, the support of the objective on the rocker is preferably such that not only rotation of the objective relative to the rocker in the course of a swivelling movement of the rocker is made possible, but also a radial change of the distance between the axis of rotation of the objective and the rocker axis (radially in relation to the rocker axis). 
     The guidance device is preferably in the form of a linear guide with a parallel guidance direction to the optical axis of the focussing objective. It preferably has guidance formations which prevent movements of the focussing objective transversely to the optical axis in the case of an upward/downward compensatory movement of the focussing objective. This is useful for stabilising the position of the objective in space. 
     For example, the guidance device can include a linear bearing and a slide which is guided in it. The slide can be fixed on the focussing objective. The linear bearing can also include at least one guidance groove. The slide can also include at least one guidance projection, which is set up to work with the guidance groove in such a way that movement of the slide in a horizontal direction is avoided. In this way, guidance of the focussing objective in a vertical direction is made possible, the optical axis of the focussing objective being able to maintain its alignment and position in the case of a compensatory movement of it relative to an initial position. For this purpose, the guidance groove can be formed with an undercut, into which the guidance projection engages. 
     According to another point of view, the invention provides a laser system, comprising:
         a laser radiation source, preferably of pulsed laser radiation,   a focussing objective for focussing the laser radiation the focussing objective having an optical axis,   an interface unit, which is arranged on the radiation exit side of the focussing objective and is preferably separably coupled to it, with a contact element, which is transparent to the laser radiation, for placing on an object on which work is to be done using the laser radiation,   a suspension apparatus, in particular of the type described above, for movable weight-compensating suspension of the focussing objective, this apparatus having a rocker, with two rocker arms, which is supported on a housing member so that it can be swivelled around a rocker axis of the laser system, the focussing objective being supported on one of the rocker arms so that it can rotate relative to the rocker around a parallel axis of rotation to the rocker axis, and on the other rocker arm a counterweight to generate a counterforce component which compensates for at least a predominant part of the weight of the focussing objective being attached, and the apparatus also having a guidance system for linearly movable guidance of the focus-sing objective along the optical axis thereof.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a weight compensating suspension apparatus according to one aspect of the invention. 
     
    
    
     The invention is further explained below, on the basis of the attached drawing.  FIG. 1  shows, schematically and not at all to scale, an embodiment of a laser system for making incisions in the cornea or other tissue parts of a human eye. 
     DETAILED DESCRIPTION 
     Of the laser system, which as whole is marked with  10 , only the “output stage” is shown in the drawing, i.e. essentially only a focussing objective  12  with a patient adapter  13  arranged on the radiation exit side of it. The focussing objective  12  is weight-compensated and movably suspended by a suspension apparatus  14 . If “weight compensation” is mentioned here, it means compensation for at least a pre-dominant part of the weight of the objective  12 . A particularly small residual part of the objective weight can remain without compensation, e.g. of the order of magnitude of a few newtons of weight. The focussing objective  12  focusses, in a way which is not shown in more detail, an afocal beam of rays of the laser radiation pro-vided by the laser system  10  onto a focus location within the eye tissue to be cut. The laser radiation which is used has, for example, pulse durations in the femtosecond range, and a wavelength in the low infrared range (e.g. between approx. 1000 and approx. 1100 nm), or in the UV range, preferably above about 300 nm. 
     The suspension apparatus  14 , in the shown embodiment of  FIG. 1 , has a force generation arrangement with a counterweight  16 , which generates a vertically directed weight component  G , with which it is intended that the weight of the focussing objective  12  should be at least partly compensated for. The suspension apparatus  14  also includes a transmission arrangement in the form of a rocker  18 , which at its right-hand end in  FIG. 1  is separably joined to the counterweight  16 , whereas at its other, left-hand end in  FIG. 1  it has a bearing seat  20  for separable coupling with the focussing objective  12 . The counterweight  16  can be shifted along the appropriate lever arm of the rocker, so that the effective force application point K of the counterweight, and thus the effective counterforce moment, can be changed. 
     The rocker  18  is carried by a bearing  22  so that it can rotate around a swivelling axis X at a distance between the points of application of the objective  12  and of the counterweight  16 . The bearing  22  supports the rocker  18 , via one or more connecting cheeks  21 , on a schematically indicated supporting part  23 , which itself can be arranged stationarily or movably relative to other components of the laser system  10 . 
     The rocker  18  can have, for example, an oblong, in particular essentially straight lever rod  19 , which at one of its ends is coupled to the objective  12 , and at its other end is coupled to the counterweight  16 . Purposefully, two such lever rods  19  are provided, parallel to each other, on both sides of the objective  12  (i.e. behind and in front of the objective  12  in the viewing direction of  FIG. 1 ). However, in the further description only one lever rod will be mentioned, but the following explanations apply analogously to both lever rods. 
     In the shown example the above-mentioned bearing seat  20  is formed by a laterally made recess  24  of the lever rod  19  (indicated by a dotted line), which is open on more than one side, that is upward and to the left in the FIGURE. The floor  24   a  of this recess  24  forms a supporting surface for a vertical journal  26  which stands laterally away from the objective  12  and projects into the recess. The focussing objective  12  rests loosely on the lever rod  19  via its vertical journal  26 . If the rocker  18  is swivelled, not only is the objective  12  rotated around the journal axis relative to the rocker  18 , but also the vertical journal  26  is displaced within the bearing seat  20 . With this displacement, the radial distance of the vertical journal  26  from the swivel-ling axis X changes. This makes it possible, despite upward or downward movement of the objective  12 , to keep the position and orientation of an optical objective axis O in space unchanged. So that the displacement of the vertical journal  26  in the bearing seat  20  takes place without friction as far as possible, for example the vertical journal  26  can carry a ring  28 , which can roll on the floor  24   a  of the recess  24 , on a sliding or rolling bearing. 
     The suspension apparatus  14  also includes a guidance system for vertical linear guidance of the focussing objective  12 . Whereas the possibility of displacing the vertical journal  26  in the bearing seat  20  creates the precondition for a constant position in space of the objective axis O when the objective  12  moves, the guidance system ensures that the objective axis O is actually not tilted or displaced transversely (to the axis O). 
     The guidance system, in the shown embodiment, includes a linear bearing  30  which is fixed relative to the focussing objective  12 , and a slide  32  which is guided on it and fixed on the focussing objective  12 . The linear bearing  30  is provided with a guidance groove  34 , which is in the form of an undercut and engages with a guidance projection  36  of the slide  32 . The guidance projection  36  is T-shaped in cross-section in the embodiment shown in  FIG. 1 , the two T side arms  36   a  of the guidance projection  36  engaging with the undercut guidance groove  34  in such a way that a horizontal (transverse) movement of the focussing objective  12  away from the linear bearing  30  (to the right in  FIG. 1 ) is prevented. Additionally, the engagement of the T side arms  36   a  with the undercut guidance groove  34  ensures that the focussing objective  12  does not tilt. It is always held by the guidance arrangement in a specified orientation. 
     The engagement of the guidance projection  36  with the guidance groove  34  provides sufficient vertical play to ensure the necessary movement travel of the focussing objective  12  in the vertical direction. 
     If the focussing objective  12 , with its patient adapter  13 , is placed on the eye (not shown) to be treated, the focussing objective  12  can be deflected vertically upward by a slight counter-pressure caused by the eye. In the case of this compensatory movement of the focussing objective  12 , the vertical journal  26  shifts by rolling (or alternatively sliding) along the floor  24   a  of the recess  24 , while the rocker  18  rotates clockwise around the rocker axis X, and simultaneously the objective  12  rotates relative to the rocker  18  around the axis of the vertical journal  26 . In contrast, if, in an imaginary hypothetical case, the focussing objective  12  was joined rigidly to the rocker  18 , an upward or downward movement of the focussing objective  12  would result in tilting the optical axis O. However, in the shown embodiment, such tilting is excluded, because of the movable support of the objective  12  on the rocker  18 , and because of the linear guidance of the objective  12  by the linear bearing  30 .