Note: Descriptions are shown in the official language in which they were submitted.
CA 02791803 2012-08-31
Apparatus for the weight-compensating movable suspension
of a focussing objective of a laser device
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.
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
ele-
ment 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 focussing 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 US 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.
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It is an object of the invention to give a reliably and precisely functioning
solu-
tion for weight compensation of a focussing objective in a laser system.
According to the invention, for this purpose movable weight-compensating sus-
s pension of a focussing objective of a laser system is provided,
comprising:
- a force generation device to generate a counterforce component which coun-
teracts 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 unde-
sired tilting of the optical axis of the objective in the case of an up-
ward/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 com-
pensatory 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 hu-
man 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 com-
bined 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.
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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 deforma-
tion 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 intention-
ally.
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
zo 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 ad-
vantage of the maximum possible constancy of the generated counterforce com-
ponent over the whole operationally required movement travel of the focussing
objective. By intentional displacement of the centre of gravity of the counter-
weight relative to the rocker, the force-distance characteristic curve of the
sus-
pension 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.
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The focussing objective is preferably supported on the rocker so that it can
ro-
tate 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
posi-
tional stability of the optical axis of the objective, that the support of the
focus-
sing 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
simul-
taneous 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 transverse position (transverse means
orthogo-
io nal 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
supporting surface arrangement can be in such a form that the objective can be
placed loosely on the rocker. The supporting surface arrangement can, for ex-
ample, 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 up-
ward, 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.
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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.
Certain exemplary embodiments can provide a laser system comprising: a source
of 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 includes 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, an
apparatus 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
of the laser system so that it can be swivelled around a rocker axis, the
focussing objective
being supported on one of the rocker arms so that it can rotate relative to
the rocker around
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a parallel axis of rotation to the rocker axis, and a force generation device
acting on the
other rocker arm for generating a counterforce component, which counteracts
the weight of
the focussing objective, the force generation device including a
counterweight, the mass of
which is used to compensate for at least a predominant part of the weight of
the focussing
objective, and the apparatus also having a guidance device for linearly
movable guidance of
the focussing objective along the optical axis thereof, wherein the guidance
device is
arranged to guide the focussing objective in such a way that in the case of an
upward/downward compensatory movement of the focussing objective, the optical
axis of
the focussing objective maintains its orientation and position in space.
Another embodiment 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
CA 02791803 2012-08-31
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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 ob-
jective being attached, and the apparatus also having a guidance system for
linearly movable guidance of the focussing objective along the optical axis
thereof.
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.
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
objec-
tive 12 is weight-compensated and movably suspended by a suspension appara-
tus 14. If "weight compensation" is mentioned here, it means compensation for
at least a predominant 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 provided 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 -6, with which it is intended that the weight of the
focussing objective 12 should be at least partly compensated for. The suspen-
sion 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
coun-
terweight 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
effec-
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tive 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).
How-
ever, 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 24a 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
jour-
nal 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 dis-
placed within the bearing seat 20. With this displacement, the radial distance
of
the vertical journal 26 from the swivelling 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 0 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 24a 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
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position in space of the objective axis 0 when the objective 12 moves, the
guid-
ance system ensures that the objective axis 0 is actually not tilted or
displaced
transversely (to the axis 0).
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 36a of the guidance projection 36 engaging with the undercut guid-
ance 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 36a with the under-
cut 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 com-
pensatory movement of the focussing objective 12, the vertical journal 26
shifts
by rolling (or alternatively sliding) along the floor 24a 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
ob-
jective 12 was joined rigidly to the rocker 18, an upward or downward move-
ment 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.
