Power transmission device

A power transmission device for converting rotational movement of a rotation shaft having a rotation shaft axis and a top end, into oscillatory movement having a primary component of movement in a direction perpendicular to the rotation shaft axis in a plane parallel to or containing the rotation shaft axis, includes a recessed portion formed in the top end of the rotation shaft, a bearing with an outer race rockably mounted in the recessed portion, an inner race positioned within the outer race, and balls positioned between the outer race and the inner race for permitting relative rotation between the outer race and the inner race, an extending link having a first end fit in the inner race such that rotation of the rotating shaft causes rotation of the outer race therewith about the inner race, the link also having a second, opposite end, a rotary plate, a pin for connecting the rotary plate to the second end of the extending link, the pin having a central axis, and a supporting mechanism for providing that the rotary plate moves with the oscillatory movement in a direction such that the component of the oscillatory movement is perpendicular to the rotation shaft axis and is perpendicular to the axis of the pin.

BACKGROUND OF THE INVENTION 
The present invention relates to a cutting device which is suitable for 
cutting and/or amputating fine bones of hands and feet of humans and 
animals. 
In dental treatment, tooth cutting is carried out by using cutting tools to 
be driven by a micromotor rotating at high speed. In recent years, with 
the progress of subdivision of medical areas and specialization of medical 
technology, there have appeared specialists, for example, for the medical 
treatment of hands or feet only. In medical treatment of hands or feet it 
is also necessary to carry out operations such as bone amputation or 
cutting, but no cutting device which is suitable for use in medical 
treatment of hands or feet, has been developed. Every specialist feels 
inconvenienced not having it. 
SUMMARY OF THE INVENTION 
It is the primary object of the present invention is to provide a cutting 
device which is suitable for amputating or cutting fine bones of hands or 
feet of humans and animals. 
It is another object of the present invention to provide a power 
transmission device which converts rotation of a rotation shaft into 
reciprocal movement along the axis of the rotation shaft. 
It is still another object of the present invention to provide a power 
transmission device which converts rotation of a rotation shaft into 
reciprocal turning movement about the same axis as that of the rotation 
shaft. 
It is a further object of the present invention to provide a power 
transmission device which converts rotation of a rotation shaft into 
reciprocal turning movement in the direction perpendicular to the axis of 
the rotation shaft in a plane parallel to the axis of the rotation shaft. 
The above-mentioned features and other advantages of the present invention 
will be apparent from the following detailed description which goes with 
the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a sectional view for explaining an embodiment of a power 
transmission device for converting rotational movement of a rotation shaft 
into reciprocal movement along the rotation shaft's axis. In FIG. 1, 
numeral 1 denotes a rotation shaft connected to a rotation shaft to be 
driven by, for example, a micromotor known (not shown) for use in dental 
treatment, 2 a bevel gear mounted on the top of the rotation shaft 1, 3 a 
second rotation shaft being rotatable about an axis perpendicular to the 
axis of the rotation shaft 1 by means of a second bevel gear 4 mounted on 
the second rotation shaft and meshing the bevel gear 2. The rotation shaft 
3 is provided with two eccentric shafts 3a and 3b arranged 180.degree. 
apart from each other about the axis of the rotation shaft 3. A link 4 at 
its one end engages the eccentric shaft 3a and at its opposite end engages 
a pin 5 whereto a first-reciprocating member 6 is connected. A guide pin 7 
is provided so as to assure smooth movement of the reciprocating member 6. 
A chucking member 8 threadedly engages the reciprocating member 6. A 
sawing plate 9 is inserted into the chucking member 8 in loosened state 
and secured to the second reciprocating member 6 by tightening the 
chucking member 8. A link 10 engages at its one end with the eccentric 
shaft 3b and at its opposite end with a pin 11 whereon the second 
reciprocating member 12 is mounted. 
Accordingly, when the rotation shaft 1 rotates, its rotational movement is 
transmitted to the second rotation shaft 3 through the bevel gears 2 and 
4, whereby the eccentric shafts 3a and 3b revolve. The eccentric 
revolution of the eccentric shaft 3a in the direction perpendicular to the 
shown section of FIG. 1 is absorbed by the pin 5 and only its reciprocal 
movement in the lateral direction, i.e. the axial direction of the 
rotation shaft 1 is transmitted to the first reciprocating member 6, 
whereby the sawing plate 9 reciprocates along the axis indicated by arrows 
A to cut a bone or the like by its cutting teeth. At the same time, 
revolution of the eccentric shaft 3b through the link 10 and the pin 11 is 
transmitted to the second reciprocating member 12 which reciprocally moves 
along the same axis but in the opposite direction in relation to the 
reciprocating member 6 because the eccentric shafts 3a and 3b are located 
180.degree. apart in relation to the axis of rotation shaft 3. Namely, 
while the first reciprocating member 6 moves to the left (or the right), 
the second reciprocating member 12 moves to the right (or the left). The 
second reciprocating member 12 acts as a damping member for the first 
reciprocating member 6. In other words, it serves as a balancer of the 
rotating shaft 3, which makes rotation of the shaft 3 stabilized so as to 
ensure smooth reciprocation of the sawing plate 9. 
As apparent from the foregoing description, according to the present 
invention it is possible to provide the power transmission device which is 
capable of converting rotational movement of a rotation shaft into 
reciprocal movement along the axis of the rotation shaft, assuring more 
smooth reciprocation. 
However, since the above-mentioned cutting tool is of such a type which 
moves reciprocally in the direction indicated by arrows A and the rotation 
shaft 1 is coupled with a conventional handpiece for use in dental 
treatment, it is feared that the reciprocating portion may be disconnected 
from the rotation shaft portion during operation of the device. 
FIG. 2 is a sectional view for explaining an embodiment of a connecting 
portion of the device, by which the above-mentioned problem was solved. In 
FIG. 2, a rotation shaft side and reciprocating portion side are indicated 
by numerals I and II respectively. A rotation shaft 20 in a dental 
handpiece is driven by a micromotor (not shown) mounted in a power section 
and located in a center of a sleeve 21 having a peripheral groove 21a 
formed externally thereon. A mechanism for converting rotational movement 
of the rotation shaft 20 into the reciprocal movement in the axial 
direction of the shaft 20 comprises a connecting sleeve 30 that 
accommodates therein the rotation shaft 1 connected at its one end to the 
rotation shaft 20 and has a plurality of through holes 30a arranged in the 
circumferential direction thereof. The sleeve 21 is slidably inserted in 
the axial direction in the connecting sleeve 30. A ball 40 is placed in 
each through-hole 30a of the connecting sleeve 30. The connecting sleeve 
30 is accommodated in a sliding sleeve 50 which is slidable in its axial 
direction along the external surface of the connecting sleeve 30 and can 
be located at any of two positions 50a and 50b. This sliding sleeve 50 has 
an internally concaved portion 50c having an inner diameter D1 larger than 
an outer diameter D0 of the connecting sleeve 30. The sliding sleeve 50 is 
positioned at the first fixing position 50b (see the lower half of FIG. 2) 
with a concaved portion placed opposite to the balls 40 (see the lower 
half of FIG. 2), and the sleeve 21 is inserted into the connecting sleeve 
30 in such a way that the balls 40 are fitted in the circular groove 21a 
of the sleeve 21 (see the upper half of FIG. 2). Then, the sliding sleeve 
50 is located at the second fixing position 50a in such way that the ball 
40 is placed in the circular groove 21a under the pressure of the inner 
wall surface of the sliding sleeve 50 (see the upper half of FIG. 2). This 
eliminates the possibility of disconnection of the connecting sleeve 30 
from the sleeve 21. 
As mentioned above, in this embodiment the rotation shaft portion I and 
reciprocating portion II are securely connected with each other by means 
of the balls 40 and the sliding sleeve 50 so as not to cause the 
reciprocating portion II to slip off from the rotor shaft portion I during 
operation of the device for converting the rotational movement of the 
rotation shaft 20 into reciprocal movement along the axis of the rotor 
shaft 20. 
FIG. 3 is a view of a principal part of a power transmission device 
embodying the present invention, which is capable of converting rotational 
movement of a rotation shaft into reciprocal turning movement about the 
same axis as that of the rotator shaft. In FIG. 3, numeral 1 designates a 
rotation shaft to be connected to a rotation shaft driven by, for example, 
a micromotor for use in dental treatment. 
Rotation of the rotation shaft 1 is transmitted through inclined rotation 
transmitting device 61 to a second rotation shaft 62 eccentrically 
positioned in relation to the rotation shaft 1. This rotation shaft 62 at 
its front end has a bearing 63 which rotates with an eccentricity to the 
second rotation shaft 62 as shown in FIG. 3(b) and causes rocking of a 
rockable member 64 which at its side opposite to the bearing 63 has a 
concaved portion 64a having the same width in the X--X direction as the 
diameter of the bearing 63 and of the width in the Y--Y direction larger 
than the maximum eccentricity of the bearing 63. The bearing 63a is fitted 
in the concaved portion 64a. Accordingly, when the second rotation shaft 
62 rotates, the rockable member 64 reciprocally revolves about the axis 
64b in the X--X direction. The rockable member 64 is supported by 
supporting member 65, for example, as fitted in a hollow hole 65a thereof. 
The supporting member 65 is rotatably mounted in a fixing member 67 by 
means of a bearing 66. 
In FIG. 3, 68 is a bearing fixing side member, 69 is a washer, 70 is a 
fixing bolt and 9 is a sawing plate. The supporting member 65 has the 
hollow hole 65a with a thread 65b for threadedly engaging fixing bolt 70. 
The sawing plate 9 can be secured at its end between the bearing fixing 
member 68 and the washer 69 by tightening the bolt 70. While the rotation 
shaft 1 rotates, the sawing plate 9 together with the supporting member 65 
reciprocally moves in the direction perpendicular to the section shown in 
FIG. 3. 
As is apparent from the foregoing description, the preferred embodiment 
makes it possible to transmit rotation of the rotation shaft 1 to the 
coaxially therewith mounted rotary supporting member 65 which in turn 
coaxially and reciprocally moves. Accordingly, when the sawing plate 9 
having cutting teeth is secured to the rotary supporting member 65 of the 
device, the sawing blade can reciprocally move at a high speed so as to 
easily cut bones and the like. 
FIG. 4 is a sectional construction view (a section taken on line IV--IV of 
FIG. 5) of the principal part of an embodiment of the power transmission 
device for converting rotational movement of a rotation shaft effectively 
into reciprocal turning movement in the direction perpendicular to the 
axis of the rotation shaft in a plane parallel thereto, and FIG. 5 is a 
section taken on line V--V of FIG. 4, wherein numeral 1 designates a 
rotation shaft adapted to be connected with a rotation shaft driven by a 
conventional micromotor, for example, for use in dental treatment. 
A rotation shaft 1 has a recess 1b eccentrically formed in its top end 1a, 
wherein a single-shielded bearing 81 is rockably fitted at its outer race 
81a and has a link 82 secured in its inner race 81b. When the rotation 
shaft 1 rotates, the recessed potion 1b eccentrically revolves to spin the 
link 82 being supported at its end in inner race 81b of the bearing 81. 
The link 82 is connected at its other end with a pin 83 to a rotatable 
plate 84 which is connected to a rotatable rod 85 in such a way to be 
rotated as one unit. A pressure plate 86 is connected to the top end of 
the link 82 so as to be rockable as one unit. 87 is a fixing nut and 9 is 
a sawing plate having cutting teeth 9a at its top end. The rotatable rod 
85 has a driver groove 85a formed in its head for turning the rotatable 
rod 85 and has a lower portion threaded for engaging the fixing nut 87 
which can be firmly locked with its projection 87a fitted in a groove 
formed at the lower portion of rotatable plate 84. When the rotatable rod 
85 is turned in the tightening direction by using, e.g. a coin inserted in 
the groove 85a of the rod 85, the rod 85 moves the fixing nut 87 upward to 
clamp the sawing plate 9 between the rotatable plate 84 and the pressure 
plate 86. When the rotatable rod 85 is turned in the opposite direction, a 
gap between the rotatable plate 84 and the pressure plate 86 is widened to 
allow removal of the sawing plate 9. 
In the embodiment described above, the rotating shaft 1, the pin 83 and the 
rotatable rod 85 have their axes at right angles to each other, so that 
the rockable plate 84 is prevented from moving upward and downward (in 
direction A of FIG. 4) by the rotatable rod 85 and movement in this 
direction (A) can be absorbed by the eccentric movement of the link 82 
which is pivotally connected to the rotatable plate 84 with the pin 83. 
Movement in the direction perpendicular to the section of FIG. 4, i.e. in 
direction B shown in FIG. 5, can not be absorbed by the pin 83 and be 
fully transmitted to the rotatable plate 84. However, the rotatable plate 
84 rotates in ball bearings 90 and 91 together with rotatable rod 85 in a 
supporting portion 89, whereby the sawing plate 9 rotates about the 
rotatable rod 85. It will therefore be appreciated that, although there is 
oscillatory movement of plate 84 about the axis of rotatable rod 85, such 
oscillatory movement consists primarily of a component of such movement in 
the direction of arrow B in FIG. 5, with an additional minor component of 
such movement in the horizontal direction of FIG. 5, that is, parallel to 
the axis of shaft 1. Thus, an effectively reciprocatory movement is 
obtained, which is perpendicular to the axis of pin 83 and perpendicular 
to the axis of shaft 1. 
As be apparent from the foregoing, in the embodiment described it is 
possible to convert rotational movement of the rotation shaft effectively 
into reciprocal movement in a direction perpendicular to the rotation 
shaft axis and in a plane parallel to or containing the rotation shaft 
axis. Consequently, by using the device in which a plate having cutting 
teeth at its top end is mounted, it is possible to cut or cut off a bone 
or the like with the cutting plate by moving the device as if a vertical 
line is drawn with a pencil. The cutting plate 9 can be mounted in the 
device at a desired angle as shown in FIG. 5.