CA1060303A

CA1060303A - Medical saw

Info

Publication number: CA1060303A
Application number: CA273,162A
Authority: CA
Inventors: Hans E. Harder; Erich Blumberg
Original assignee: Howmedica International Inc
Current assignee: Stryker Ireland Ltd
Priority date: 1976-03-11
Filing date: 1977-03-03
Publication date: 1979-08-14
Also published as: CH597839A5; FR2343468A1; FR2343468B3; SE7702405L

Abstract

ABSTRACT OF THE DISCLOSURE

A medical saw for particular application to dental work, which comprises a frameless saw blade clamped at one end and driven through an eccentric by a pneumatic motor at a relatively high speed, the high frequency of the stroke enabling accurate and fast cuts to be obtained.

Description

-This invention relates to a medical saw having a slidably mounted, motor driven clamping device for an elonga-ted saw blade to be reciprocated in its longitudinal direc-tion.
Saws are required in many fields of medicine, for " example in surgery, and particularly in the dental field, i.e. in dental technical laboratories. In the latter, a frequently occurring task consists of sawing stumps out of saw cut models made of plaster, cement or plastics. This work is often carried out by hand with the aid of a hacksaw, which is relatively time consuming and often entails diffi-culties, since the hacksaw mounting opposite the grip is a nuisance. Moreover, the task often requires a precise narrow cut, which can only be ensured with difficulty by lS hand, particularly when there is only a short travel avail-able on account of interfering model parts.
The aim of the invention is to provide a medical saw with structural features which ensure exact cuts with minimum sawing time.
The present invention achieves this aim by clamping - a frameless saw blade in a clamping device which is recipro-cably driven by a rotary pneumatic motor via an eccentric device.
According to the invention, there is provided a medical saw comprising an elongated cylindrical housing in

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106()303 which a pneumatic motor is mounted having a rotatable output shaft axially aligned with and coupled to a first bevel gear in meshed engagement with a second bevel gear, ~aid second bevel gear being secured to one end of a rotatable shaft having eccentrically mounted at its other end a ball bearing member receiving an upstanding pin of a connecting rod linked in driving relationship with the stock of a saw blade chuck the blade-clamping head of which together with an ad-jacent minor length of said stock lies outside of said hoùsing, the remaining length of said stock being slidably received in a guide bushing which limits the stock to linear reciprocal driven movement in a direction parallel to the longitudinal axis of said cylindrical housing upon actuation ` of said pneumatic motor, said guide bushing being mounted in and substantially coextensive with a bore of a projection which extends from said housing as an integral nose-like portion thereof having a reduced cross-sectional dimension and length relative thereto, said housing having a coupling connection for a compressed air supply which leads to a valve arrangement within the housing for controlling the com-pre~sed air current from said coupling connection to an inlet channel of said pneumatic motor, said valve arrangement being operable by a hand lever extending alongside the outer periphery of said housing in position to be operated by the palm of a hand gripping the housing during a sawing opera-tion.
By reciprocat~ng the saw blade chuck at a high frequency, there i8 produced a stabilization of the blade, comparable to that obtainëd by mounting the blade in a frame, slnce the blade ls by itsel~ stabilized by the high

-3-frequency and consequently permits exact cuts within theshortest time. ~he eccentric mounting of the ball bearing member used in driving the stock of the saw blade chuck enables the chuck to be guided accurately in the direction of the stroke, so that there is practically no wandering of the blade from the direction of the stroke and the accuracy of the cut is increased further.
Our use of a pneumatic motor permits very high stroke speeds, as such motors normally permit rotational speeds between 10,000 and 30,000 rpm and above. We prefer-ably use a stroke frequency which lies in the region of 15,000 strokes per minute and approximately matches a corresponding motor rotational speed. It is thus not neces-sary to insert a speed changing drive between the motor and the eccentric mounting means for the ball bearing member, which considerably simplifies the overall construction of the saw according to the invention. The eccentric mounting means, pneumatic motor and control means for the motor are advantageously accommodated in a common housing.
Preferably the eccentric mounting means is designed in such a way that the length of stroke amounts to only a few millimeters, more specifically in the region of 4 mm.
The high stroke frequency permits a comparatively short stroke, so that the pattern of the work, or of other model parts as the case may be, does not impair the cutting opera-tion. There is furthermore the advantage that the eccentri-city does not lead to particularly large moments of imbalance, which might possibly result in undesirable vibration of the entire saw or of its mounting. Additional measures for damp-ing or compensating for imbalance do not, therefore, need to ~,,' be provided.
The construction of the saw according to the inven-tion also allows mobile employment of the saw, which is thus not tied to a stationary arrangement; rather, by means of a compressed air hose which is connected to a source of com-pressed air, it can be employed wherever desired, and it is also easy to handle because of its small overall size.
The connecting rod and the stock of the chuck are preferably connected by means of a coupling.
The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:
Figure l shows a side view schematically of a medical saw embodying the invention;
Figure 2 shows partly in section and enlarged the saw according to Figure l.
The medical saw according to Figure 1 is parti-cularly for dental use and features a longish housing 10 having at the rear end a coupling connection ll for a com-pressed air supply, as well as a pivotally connected end ofan elongated hana lever 12. As seen in Figure l, hand lever 12 extends alongside the outer periphery of housing lO in positlon to be operated by the palm of a hand gripping the housing during a sawing operation. At its front end, housing lO extends into a flattened projection 13 in which, as will be described more fully below, is carried a stock 14 of a`
chuck 15 for a saw blade which is not illuætrated here. The saw blade 18 a simple elongated flat part whiah is shaped at one end in such a manner as to be easily insertable in the head of the chuck lS.

_5_ ~' - ~060303 A pneumatic motor 16, controlled through a valve arrangement 17 which, for its part, is operated by hand lever 12, is located in the housing 10. The valve arrangement 17 controls the compressed air current from the coupling con-nection 11 to the inlet channel 18 of the motor 16. Theoutput shaft 19 of motor 16 is coupled to a transmis~ion shaft 20 which is rotatably mounted in two radial bearings 21, 22. The transmission shaft 20 is joined at the end facing away from the motor to a bevel gear 23 which engages with a bevel gear 24 secured on a shaft 25. The shaft 25 runs transversely to the transmission shaft 20 and is mounted in two radial bearings 26 so as to be rotatable. At its low-er end the shaft 25 has an eccentric plate 27, carrying another radial bearing 28 in which is mounted a pin 29 connec-ted to a connecting rod 30. Connecting rod 30 is linkedthrough a coupling 31 with the stock 14 of the chuck 15.
The stock 14 is carried with precision in a guide bushing 32 in the projection 13 of the hou~ing 10. The eccentricity of the eccentric plate 27 is selected in such a way that the stroke lies in the region of 4 mm. In this way, even at high rotational rates, only a comparatively small moment of imbalance is produced so that no impairment of the user or in respect of the precision of the cut is caused .
To carry out a sawing operation, a saw blade is clamped in the chuck 15. The hand lever 12 is then operated, it being necessary for a locking plate 33 to be in a given po~ition, ~ince otherwise operation of the lever 12 does not lead to a shift in the valve arrangement 17. The actuated valve arrangement 17 permit~ compressed air to be fed to the ~` 1060303 pneumatic motor 16, which runs at approximately 15,000 rpm.
Motor 16 drives shaft 25 and eccentric plate 27 through the transmission consisting of bevel gear~ 23 and 24, so that the chuck and consequently the saw blade clamped in it attain a stroke frequency of approximately 15,000 strokes per minute.
It is possible in this way to make accurate cut~ in a mini-mum working time, the saw blade being guided with the utmost stability because of the high stroke frequency.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A medical saw comprising an elongated cylindrical housing in which a pneumatic motor is mounted having a rotatable output shaft axially aligned with and coupled to a first bevel gear in meshed engagement with a second bevel gear, said second bevel gear being secured to one end of a rotatable shaft having eccentrically mounted at its other end a ball bearing member receiving an upstanding pin of a connecting rod linked in driving relationship with the stock of a saw blade chuck the blade-clamping head of which together with an adjacent minor length of said stock lies outside of said housing, the remaining length of said stock being slidably received in a guide bushing which limits the stock to linear reciprocal driven movement in a direction parallel to the longitudinal axis of said cylindrical hous-ing upon actuation of said pneumatic motor, said guide bush-ing being mounted in and substantially coextensive with a bore of a projection which extends from said housing as an integral nose-like portion thereof having a reduced cross-sectional dimension and length relative thereto, said housing having a coupling connection for a compressed air supply which leads to a valve arrangement within the housing for controlling the compressed air current from said coupl-ing connection to an inlet channel of said pneumatic motor, said valve arrangement being operable by a hand lever extending alongside the outer periphery of said housing in position to be operated by the palm of a hand gripping the housing during a sawing operation.

2. A medical saw according to claim 1, wherein the pneumatic motor, coupling connection, valve arrangement and a pivot connection for the hand lever are disposed at one end of the cylindrical housing, whilst the bevel gears, connecting rod and saw blade chuck are disposed at the other end of said housing.

3. A medical saw according to claim 1 or 2, wherein the guide bushing is removably mounted in said bore of the projection and is held therein by a set screw threaded into the wall of said projection.