Note: Descriptions are shown in the official language in which they were submitted.
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Elastically flexible coupling body
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The invention relates to an elastically flexible coupling
body for high-frequency tools, according to the preamble
of Claim 1.
The term `high-frequency' in the claims and in the
lo description is to be understood to mean a frequency that
amounts to from a few kHz up to 40 kHz and more. For
common dental applications, it may preferentially lie
within the range from 15 kHz to 25 kHz.
A high-frequency tool for dental purposes is described in
DE 42 38 384 Al. Said tool includes an ultrasonic drive
unit which includes an extended stack of piezoelectric
discs in series. This stack of discs is accommodated in
a handle of the tool. The coupling body takes the form
of a ring oscillator which exhibits four oscillation
maxima equally distributed in the circumferential
direction. One of the oscillation maxima is connected to
the ultrasonic drive unit; an oscillation maximum that is
offset by 90 relative thereto is connected to the tool.
The latter consequently executes a motion, the direction
of which is tilted by 90 in relation to the direction of
the driven motion of the ultrasonic drive unit.
Tools of the type considered above find application, in
particular, in the dental field, in order to clean tooth
surfaces or alternatively to generate cavities in teeth.
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In this connection the coupling bodies have to exhibit
relatively small dimensions, in order to enable a dentist
to have a good view of the respective working site even
under the cramped conditions in the mouth of a patient.
The annular coupling bodies according to the state of the
art, exhibiting small diameters, work reliably only when
they have been worked in highly precise manner and have
been produced from special, expensive materials. if
these conditions are not adhered to, fractures in the
coupling body - and hence a failure of the tool - may
occur.
By means of the present invention, a coupling body
according to the preamble of Claim 1 is to be developed
further in such a way that it can be produced more easily
and is less inclined towards material fractures.
In accordance with the invention, this object is achieved
by means of a coupling body having the features specified
in Claim 1.
In the case of the coupling body according to the
invention, excitation of the natural oscillations is
effected by virtue of the fact that a torque is caused to
act at a predetermined point on the flexural arms. This
torque is generated by a force which acts on the driven
flexural arm or arms under a lever arm.
Advantageous further developments of the invention are
specified in dependent claims.
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According to Claim 2, a particularly effective excitation
of the natural oscillations of the flexural arms is
obtained, since the driving tilting motion is fed in at a
point on the flexural arm at which the latter exhibits a
node of a natural oscillation.
The further development of the invention according to
Claim 3 is advantageous with regard to symmetrical
oscillation conditions and symmetrical loads of the
lo driven flexural arm or arms.
With the further development of the invention according
to Claim 4, it is ensured that a non-driven flexural arm
also oscillates and is loaded symmetrically in relation
to a transverse median plane of the arm.
A coupling body according to Claim 5 has two flexural
arms with drive bodies mounted in the same direction of
rotation and acting as mass bodies, the centres of
gravity of which are in each instance remote from the
neutral fibre of the flexural arm carrying them. If the
flexural arms have a force applied to them in the
longitudinal direction, the drive bodies mounted with
spacing and acting as mass bodies result, by reason of
their inertia, in flexures, in the same direction of
rotation, of the two flexural arms.
Since the two driven ends and the two free, driving ends
of the flexural arms are connected by connecting arms, at
the driving ends of the flexural arms a motion of the
connecting arm situated there is obtained that is
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perpendicular to the longitudinal direction of the two
flexural arms and hence also perpendicular to the drive
motion, parallel hereto, which is imposed on the
connecting arm connecting the driven ends of the flexural
arms.
A coupling body according to Claim 2 can consequently be
regarded as a frame with flexible parallel sides which
carry drive bodies which are mounted with spacing from
io the edges of the frame and which act as mass bodies. The
coupling body consequently forms an elastically
deformable parallelogram linkage with mounted drive
bodies acting as mass bodies, which have the result that
a high-frequency imposed linear reciprocating input
motion is converted into a substantially linear
reciprocating output motion having the same frequency,
which is tilted relative to said input motion.
The further development of the invention according to
Claim 6 is advantageous with regard to adjusting the
loads and conditions of movement in both flexural arms to
be the same.
In the case of a coupling body according to Claim 7, for
the moment of inertia generated by one of the drive
bodies it is possible to profit from the transverse
dimension of the frame spanned by the various arms. The
mass of the one drive body can therefore be chosen to be
somewhat smaller.
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In this connection, according to Claim 8 the torques that
the drive bodies acting as mass bodies exert on the
flexural arms when the frame constituted by flexural arms
and connecting arms is accelerated can be adapted to one
another, despite differing masses of the drive bodies.
The further development of the invention according to
Claim 9 is advantageous with regard to compact dimensions
of the coupling body.
The further development of the invention according to
Claim 10 is advantageous with regard to smooth boundary
surfaces of the coupling body.
A coupling body according to Claim 11 is distinguished in
that accelerations of the frame constituted by flexural
arms and connecting arms in the direction of the axes of
the flexural arms are converted particularly effectively
into flexural oscillations.
In this connection, according to Claim 12 particularly
large dimensions can be given to the drive body situated
inside the frame.
The further development of the invention according to
Claim 13 is also advantageous with regard to a strong
generation of flexural oscillations. Correspondingly
strong are the drive motions derived therefrom in the
direction of the tool axis, which are provided by the
tool-side connecting arm.
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Claim 14 specifies a particularly simple and reliable
possibility for the connection of sonotrode and coupling
body.
A coupling body according to Claim 15 permits the unit
constituted by coupling body and driven end of the
sonotrode to be of particularly short construction in the
direction perpendicular to the plane of the frame.
The further development according to Claim 16 also serves
for a uniform distribution of the mechanical loads on
both flexural arms.
The further development of the invention according to
is Claim 17 is advantageous with regard to a precise and
reliable initiation of the drive motion and with regard
to a precise and safe movement of the tool.
This applies to an increased extent to a coupling body
according to Claim 18.
In the case of a coupling body according to Claim 19, the
geometry assumed in the force-free state is a rectangle.
The deflections of the flexural arms take place
symmetrically towards both sides of the rectangle edges
constituted by them, as a result of which a residual
motion component parallel to the input motion, which
remains in the case of a relatively large deflection of
the flexural arms, can be kept very small or, in the case
of small deflections such as are of interest here, is
practically zero.
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The further development of the invention according to
Claim 20 is advantageous with regard to the avoidance of
local stresses in the material of the coupling body.
In the case of a coupling body according to Claim 21, the
mass bodies and the connecting arms may be situated
substantially in the same plane, without the drive body
situated inside the frame impeding the deformation of the
frame. In consequence, a coupling body can be produced
in a straightforward manner starting from a plane-
parallel blank.
The further development of the invention according to
Claim 22 is advantageous with regard to a simple and
secure fastening of the tool to the driving part of the
coupling body.
With the further development of the invention according
to Claim 23, it is ensured that the coupling body is of
particularly slender construction in the vicinity of the
tool. This is advantageous with regard to good visual
contact with the working site.
According to Claim 24, a simple and loadable connection
of the coupling body to the drive unit is obtained. The
latter may be constituted, for example, simply by an
ultrasonic generator or by an ultrasonic generator with
downstream sonotrode.
The further development of the invention according to
Claim 25 is once again advantageous with regard to
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favourable ergonomics of the tool that has been realised
with the coupling body.
The further development of the invention according to
Claim 26 is advantageous from a like the regard to the
producibility of the coupling body from a plane-parallel
blank. Furthermore, the rectangularly prismatic basic
geometry of the flexural arm permits the frequencies of
oscillation to be calculated precisely in advance.
Lastly, the flexural oscillations are accurately
predetermined by the rectangular shape: the oscillations
induced in the flexural arms are largely free from
torsions with respect to the longitudinal axis of the
flexural arms.
The aforementioned advantages apply to an increased
extent to a coupling body according to Claim 27 and to
one according to Claim 28.
The further development of the invention according to
Claim 29 is advantageous with regard to compact
construction of the coupling body and of a handpiece
containing it in the vicinity of the working site. This
facilitates both the handling under spatially cramped
conditions and the visual contact with the working site.
A coupling body according to Claim 30 is distinguished by
particularly long service life.
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The invention will be elucidated in more detail below on
the basis of exemplary embodiments with reference to the
drawing. Shown therein are:
Figure 1: a side view of a dental ultrasonic handpiece,
in which the various principal components of
the handpiece are indicated schematically;
Figure 2: a side view of a coupling body that can be
used in an ultrasonic handpiece according to
Figure 1;
Figure 3: a schematic view of the coupling body
according to Figure 2 in a motion phase in
which a pulling force directed towards the
right in the drawing is exerted on the
coupling body;
Figure 4: a view similar to that of Figure 3, wherein,
however, a pushing force directed towards the
left in the drawing is exerted on the
coupling body;
Figure 5: a perspective view of a practical embodiment
of a coupling body for a tool according to
Figure 1;
Figure 6: a longitudinal section through the coupling
body according to Figure 6;
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Figure 7: a perspective view of a further modified
coupling body;
Figure 8: a median section through the coupling body
according to Figure 7 together with the
driven end a sonotrode; and
Figure 9: a view similar to that of Figure 7, in which
a coupling body that has again been modified
lo is reproduced.
Denoted overall by 10 in Figure 1 is an ultrasonic
handpiece that serves for driving a tool 12.
In the case of the tool 12, it may be a question, for
example, of a lancet-shaped flat tool with which the
lateral faces of a tooth are to be machined. The tool 12
is moving in the direction of the arrow 14 which is
indicated in the drawing. During working with the tool
12, a jet 18 of a working fluid is directed onto said
tool through a nozzle 16, said fluid containing an
abrasive medium suspended in water.
For the purpose of generating the vertical to-and-fro
motion of the tool 12 in Figure 1, the amplitude of which
amounts to a few 10 pm to 100 pm, use is made of an
ultrasonic generator 20 which is accommodated inside a
handle 22 of the handpiece 10. The ultrasonic generator
20 includes a plurality of piezoelectric discs stacked in
succession in the axial direction and is connected at its
driven end, situated on the left in Figure 1, to a
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sonotrode 24. The latter serves to concentrate the
ultrasonic energy by `funnel action' and to make a
correspondingly enlarged amplitude of motion available at
the output.
The end of the sonotrode 24 is connected to a coupling
body 26. The latter converts the driven motion of the
.sonotrode 24, which is directed in the axial direction of
the handle 22 and which is horizontal in the drawing,
into a motion of the tool 12 that is perpendicular to the
axis of the handle 22 and vertical in the drawing.
Figure 2 shows schematic structure of the coupling body
26. Said body has two equally long flexural arms 28, 30,
parallel to one another, which each have a rectangular
cross-section, the long side of the cross-section being
perpendicular to the plane of the drawing of Figure 2.
The ends of the flexural arms 28, 30 are closed by
connecting arms 32, 34 so as to form a rectangular frame
36, the inner edge of which exhibits quadrant-shaped
roundings 38 at the corners.
Perpendicular to the plane of the drawing of Figure 2 the
connecting arms 32, 34 have the same dimensions as the
flexural arms 28, 30 but have a width B which is
distinctly greater than the width b of the flexural arms.
The connecting arms 32, 34, which incidentally are also
shorter, may therefore be regarded as being substantially
rigid in comparison with the flexural arms 28, 30.
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The connecting arms 32, 34 carry at their middle
identical drive bodies 40, 42 acting as mass bodies, the
centres of gravity of which are remote from the neutral
fibres of the flexural arms 28, 30 by the same spacing D
in the upward direction. The drive bodies 40, 42
likewise have the same dimension perpendicular to the
plane of the drawing of Figure 2 as the flexural arms 28,
30 and the connecting arms 32, 34. The entire coupling
body 26 can consequently be produced by being sawn out of
a plane-parallel blank.
The drive bodies 40, 42 acting as mass bodies have
substantially the shape of axially short cylinders and
are connected to the adjacent connecting arms 32, 34 via
transition portions 44, 46.
The transition portions 44, 46 are connected at their two
sides to the flexural arms 28, 30, in each instance via
roundings 48, 50.
Under operational conditions the connecting arm 32 which
is situated on the left in the drawing is connected to
the tool 12 via a collet chuck which is not represented,
whereas the connecting arm 34 which is situated on the
right in the drawing is connected to the driven portion
of the sonotrode 24 via a connecting head which is not
represented in Figure 2.
In Figures 3 and 4 it is shown how the coupling body is
deformed when a pulling force directed to the right, and
a pushing force directed to the left, respectively, is
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exerted on the connecting arm 34 which is situated on the
right in the drawing.
If, as represented in Figure 3, a force directed to the
right is exerted on the connecting arm 34, the inertia of
the drive bodies 40, 42 has the result that the flexural
arms 28, 30 become curved downwards. Since the drive
bodies 40, 42 are exactly the same as far as their
geometry, their material and their weight are concerned,
the two flexural arms 28, 30 are bent downwards in the
same way. Since their lengths remain constant and their
free ends move identically, the connecting arm 32
situated on the left in the drawing is moved downwards
parallel to the connecting arm 34.
If, on the other hand, a force directed to the left is
exerted on the right-hand connecting arm 34, then on
account of the inertia of the drive bodies 40, 42, in a
manner similar to that described above, a flexure - in
the same direction of rotation and of the same magnitude
- of the flexural arms 28, 30 occurs upwards, and hence a
motion of the connecting arm 32 upwards in a direction
exactly parallel to the extent of the connecting arm 34.
It will be discerned that the coupling body 26
consequently converts a reciprocating motion exerted on
the driven connecting arm 34 situated on the right, which
takes place in the axis of the sonotrode 24 and hence in
the axis of the ultrasonic generator 20 and of the handle
22), into a motion of the tool that takes place
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perpendicular to the axis of the sonotrode 24 and hence
to that of the handle 22.
From Figures 2 to 4 it is evident that the drive body 40,
which is situated inside the frame 36 and is carried by
the lower flexural arm 32, is so far removed from the
upper flexural arm 34 situated outside the frame 36 that
the flexural motion thereof is not impaired. Since, as
stated, both flexural arms 28, 30 are deflected in the
same direction and by the same amounts, this spacing
between the drive body 40 and the flexural arm 30 does
not need to be large.
Figures 5 and 6 show a practical exemplary embodiment of
a coupling body 26. Parts of the coupling body 26 that
correspond, from the point of view of function, to
corresponding parts already above with reference to
Figures 2 to 4 are again provided with the same reference
symbols and do not need to be described again in detail
in terms of their basic properties.
The coupling body 26 according to Figure 5 can be
produced from a plane-parallel blank by two elongated
holes, which are each terminated at their ends by a
semicylindrical surface 48, being produced in it in the
region of the flexural arms 28, 30. In the web remaining
between the two elongated holes a slot 52 is then
produced by milling, as a result of which a lower drive-
body base 40 is obtained.
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Similarly, in an upper portion of the blank two further
elongated holes are generated which are terminated by
flattened semicylindrical surfaces 50 and of which the
left-hand one is opened upwards and to the left in such a
way that the bottom surface of the elongated hole is
continued as far as the free horizontal end of the
coupling body 26 and the elongated hole is opened upwards
shortly before the right-hand end face of the elongated
hole.
Similarly, the upper portion of material above the right-
hand elongated hole of Figure 5 is also milled away, in
such a manner that a substantially T-shaped drive body 42
is obtained.
Moulded on the connecting arm 34, situated on the right,
of the coupling body is a connecting head 54 which
exhibits a threaded bore 56 which is open towards the
right and into which an end portion of the sonotrode 24,
which is provided with thread, can be screwed.
An upper boundary surface of the connecting head 54 and a
lower boundary surface of this connecting head are
situated in such a way that the bore 56 situated
centrally in the connecting head is situated
approximately at the height of the upper flexural arm 30.
The transition surfaces of these upper and lower boundary
surfaces to the actual coupling body are curved, as
indicated at 58 and 60 in the drawing. The edges of the
connecting head 54 are broken by bevels 62.
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The end portion of the coupling body 26 that is situated
on the left in Figure 5 exhibits a central vertical slot
64 which leads to a vertical bore 66. In the region
situated on the left, the outside of the connecting arms
32, 34 are each provided, symmetrically in relation to
the longitudinal median plane, with a chamfer 68, so that
clamping portions 70, 72 of the connecting arm 34
situated on the left are obtained.
Parallel to the bore 66, an axially slotted receiving
sleeve 74 is inserted into the connecting arm 32, into
which the shaft of a tool can be inserted.
By means of a clamping screw, which is not represented,
the clamping portions 70, 72 can be moved towards one
another, contrary to their spring force, in order to
clamp the shaft of a tool firmly in the receiving sleeve
74.
The upper drive body 42 has a central vertical slot 78
which is open in the direction towards its upper end
face, in the bottom of which a through-bore 80 is
provided. The latter is flush with a fastening bore 82
in the drive-body base 40.
The shaft of a mass rod 84 which extends, with lateral
clearance, through the through-bore 80 and the slot 78 is
firmly inserted (welded) into the fastening bore 82, so
that the mass rod 84 does not impinge laterally even when
the coupling body 26 is subjected to ultrasound.
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The end face of the mass rod 84 and the upper side of the
drive body 42 are substantially coplanar.
The geometry and mass of the drive-body base 40 and of
the mass rod 84 are so chosen that the common moment of
inertia with respect to the region of attachment to the
flexural arm 28 is substantially equal to the moment of
inertia of the drive body 42 in relation to its region of
attachment to the flexural arm 30.
In terms of function, the coupling body 26 according to
Figures 5 and 6 corresponds to that according to
Figures 2 to 4.
Titanium is used as material for the coupling body 26 and
where appropriate, its parts.
Figures 7 and 8 show a modified coupling body 26 which is
of more compact construction in the direction
perpendicular to the axis of the flexural arms 28, 30.
Components that have already been described with
reference to the preceding Figures are provided with the
same reference symbols, even when they are geometrically
somewhat differently shaped, provided that they
correspond functionally.
The drive body 42 protruding outwards beyond the frame of
the coupling body 26 is reduced in size and projects only
quite slightly into the interior of the frame. The drive
body 40 projecting into the interior of the frame is
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continued with its flat end face up until a short
distance before the inside of the flexural arm 30.
The drive body 40 serves as coupling portion for a
sonotrode. To this end, the threaded bore 56 is provided
in it. Furthermore, a through-bore 86 is provided in the
connecting arm 32, through which a drive portion 88 of
the sonotrode 24 is able to extend with clearance.
The axis of the bore 86 runs parallel to the flexural
arms 28, 30 and centrally between the latter, so that the
driven portion 88 acts on the flexural arm 28 under a
lever arm (via the drive body 40). On account of this
geometry of the application of force, a good stimulation
of oscillation of the coupling-body frame constituted by
the flexural arms 28, 30 and the connecting arms 32, 34
is guaranteed, although the drive bodies 40, 42 exhibit
distinctly reduced mass in comparison with the other
exemplary embodiments.
The coupling body 26 according to Figures 7 and 8 is
distinguished by particularly compact structure and good
redirection of the input motion into a driven motion
extending inclined at 90 in relation to said input
motion.
The coupling body according to Claim 9 largely resembles
that according to Figure 7.
But the drive body 42 has now disappeared, and the end
face of the drive body 40 has once again moved closer to
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the inner surface of the flexural arm 30, as close as is
possible in terms of manufacturing engineering.
Production is effected in such a way that a plate-like
blank is milled with the desired outer contour, and two
apertures with the roundings 38, 48 are generated in it,
whereby firstly a central continuous web remains which
later forms the drive body 40. Into the intermediate
product obtained in such a way, the shape of which
substantially corresponds to an 18', the through-bore 86
is then drilled, and the threaded bore 56 which is
aligned therewith is sunk.
Then the slot 52 is produced by milling, as closely as
is possible in terms of manufacturing engineering, at the
inside of the flexural arm 30 with a narrow disc-milling
cutter.
The flexural arm 28 has, by reason of the drive body 40
carried by it, a different oscillatory behaviour from
that which a flexural arm exhibiting an identical cross-
section without mounted drive body would have.
In order to compensate for this difference, the flexural
arm situated at the bottom in Figure 9 is approximately
25 percent wider (dimension in the vertical direction in
Figure 9) than the flexural arm 28. In this way, both
flexural arms 28, 30 have the same natural frequency and
oscillate with their ends adjacent to the connecting arm
34 in phase with identical amplitude.
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In a practical exemplary embodiment, the coupling body
26, measured in the longitudinal direction (in the
drawing, in the horizontal direction), has an overall
dimension of 24.2 mm; measured in the transverse
direction (in the drawing, the vertical direction), the
lower boundary surface of the coupling body 26 has a
spacing from the longitudinal axis of the same that
amounts to 4 mm, whereas the upper outer surface of the
coupling body 26 exhibits a spacing from the longitudinal
lo axis of only 3.6 mm. The difference in spacing
corresponds to the enlarged transverse dimension of the
flexural arm 30 which is situated at the bottom in
Figure 9.
In this practical exemplary embodiment the thickness of
the plate from which the coupling body 26 has been
produced amounts to 5 mm, the diameter of the through-
bore 86 amounts to 4 mm, and the diameter of the threaded
bore 56 amounts to 3.5 mm.
Titanium serves as material for the coupling body 26.
