Patent Publication Number: US-2007102175-A1

Title: Surgical apparatus capable of converting rotary motion to rectilinear motion

Description:
RELATED APPLICATIONS  
      Not applicable  
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
      Not applicable  
     TECHNICAL FIELD  
      This invention relates to a surgical motor used for sawing and the like and includes mechanism for converting rotary motion to linear motion. In particular, this invention is characterized as utilizing a drive shaft and eccentric shaft that are parallel to the driven shaft.  
     BACKGROUND OF THE INVENTION  
      There are a sundry of motor mechanisms in the medical field as well as the construction field that are designed to convert rotary motion to linear or rectilinear motion necessary to operate a motorized saw. The mechanism for making the conversion in both the medical and non-medical field typically use a wobble plate or an angularly mounted drive shaft that converts the rotary motion of the motor to the linear motion necessary to power the saw blade. While such mechanism are generally efficient, they have the propensity of wearing prematurely and inducing a great deal of vibratory motion. Obviously, the reciprocating electric saw used for non-medical purposes need not concern itself over the vibratory motion, size and feel of the mechanism. On the other hand these conditions and characteristics of the non-medical saws are far different than the parameters necessary for the power saws utilized by surgeons. In accordance with this invention, we have provided conversion mechanism that is characterized as providing less vibrations and noise hereto known in both the prior art medical power saws and commercial power saws. We have found that by virtue of this invention the power saw enhances the feel of the motor in the hands of a surgeon, is small and light weight and has an increased life. It is quite apparent that a motor that generates less noise and vibration provides an improved feel in the hands of a surgeon who typically is performing intricate work during the surgical procedure performed on a patient. Of course, in the interest of economy it is abundantly important to increase the useable life of the motor.  
      U.S. Pat. No. 5,555,626 granted to Fuchs on Sep. 17, 1996 entitled RECIPROCATING DRIVE MECHANISM exemplifies a motion conversion motor that utilizes a wobble plate which as is typical in these designs uses an angularly or oblique angle mechanism disposed shaft between the driving and driven members. Such devices are capable of being hand held and are portable.  
      Saws for medical purposes are exemplified in U.S. Pat. Nos. 4,827,615, 5,916,218, 5,606,603, and 6,302,406 granted to Graham on May 9, 1989, entitled MICROSURGERY SAW DRIVE, granted to Hagen et al on Jun. 29, 1999 entitled SAW FOR SURGICAL PURPOSES, granted to Linden on Mar. 11, 1997 entitled SURGICAL CUTTING DEVICE WITH SAFETY INTERLOCK, granted to Ventura on Oct. 16, 2001 entitled CONNECTOR ASSEMBLY FOR A SURGICAL SAW BLADE. As in the teachings of these patents and the non-medical patents the mechanism for converting the rotary motion developed by the motor is obtain by mechanism that includes a member that is angularly disposed relative to the driving and or driven mechanism. We have found that the problem with the converting mechanism is that it adversely affects the life of the medical saw. Moreover, typically these heretofore known devices are prone to have vibrations in the handle and produce unwanted noise.  
      We have found that we can obviate the problems alluded to in the above paragraph by disposing the driving, driven and conversion mechanism parallel to each other. Not only has this arrangement shown to enhance the longevity of the instrument, it also provides an improved “feel” to the surgeon as it eliminates or reduces vibrations and eliminates or at least lowers the noise level.  
     SUMMARY OF THE INVENTION  
      An object of this invention is to provide an improved saw for use in medical procedures.  
      Another object of this invention is to provide mechanism that converts rotary motion to linear motion with the use of parallel shafts for a saw or other medical instrument and is characterized as reducing noise levels, reducing vibrations, is lighter in weight and increasing the useful life of the saw.  
      The foregoing and other features of the present invention will become more apparent from the following description and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of the medical attachment mechanism for converting rotary motion into linear or oscillating motion to provide rectilinear motion imparted to a saw or other surgical instrument;  
       FIG. 2  is an exploded view of the conversion mechanism of this invention and details the parts of the mechanism depicted in  FIG. 1 ; and  
       FIG. 3  is a sectional view of the assembled mechanism of the apparatus depicted in  FIGS. 1 and 2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      This invention details, in the preferred embodiment, mechanism for converting rotary motion to linear motion for driving a saw used in medical procedures. While in the preferred embodiment the mechanism powers the saw in a rectilinear motion, as one skill in this art will appreciate, the actuating mechanism can be designed by relocating the cam and with minor changes to the structure to produce an oscillating motion for medical instruments where an up and down motion, rather than in and out motion is desired.  
      As best seen in  FIGS. 1, 2  and  3  the medical apparatus for converting rotary motion to linear motion is generally illustrated by reference numeral  10  having a main body  12  that serves as a handle for the surgeon, a lock adapter  14  for attaching to a motor (not shown) for producing rotary motion and collet mechanism generally illustrated by reference numeral  16  for attaching a surgical instrument, say a saw blade (not shown). As noted in  FIG. 3  the reduced diameter portion  18  of lock adapter extending outwardly at the aft end of the main body  12  removably fits into the motor securing chuck (not shown) at the aft end  20  of the offset shaft  22  disposed in the reduced diameter bore section  24  of the central through bore  26  of the lock adapter  14 . A dowel pin  28  extending through a hole ( 29 ) in the end of shaft  22  serves to connect to the motor drive (not shown) by inserting a slotted portion of the drive mechanism to engage the dowel pin  28 . It will be noted that the length of dowel pin  28  is less than the diameter of the bore  24  so that the edges of dowel pin  28  are spaced from the wall of bore  24 . The chuck portion of the motor which are commercially available and are well known are omitted here from for the sake of simplicity and convenience. A pair of commercially available ball bearings  26  separated by the wave washer  36  are disposed in the larger diameter bore portion  30  of the lock adapter  14  for supporting the offset shaft  22  for rotary motion.  
      The lock adapter  14  is secured to the main body or casing  12  by the threaded bushing  32  that threaded to the inner surface enlarged bore  34  formed in the casing  12 . The lock adapter carries flange  40  that extends outwardly toward the inner diameter of the enlarged bore portion  42  formed on the aft end of the casing  12 . This flange is forced against the shoulder  42  and bears there against and is locked into position by the threaded bushing  32 .  
      The stub shaft portion  50  is formed on fore end of the offset shaft  22  and is oriented eccentrically relative but parallel thereto. Bearing  52  is snugly fitted to the end of stub shaft  50  which in turn is mounted in the yoke  54  between the bifurcated arms  56  and  58 . Yoke  54  is rotatably mounted to casing  12  by pin  60  that fits through the opposed drilled holes  62  formed in the casing  12  and is rotary supported by a pair of bearings  52  made from a ceramic material and includes roller or bushing  59  mounted therein. The yoke  54  carries a laterally extending projection  66  that serves as a cam as will be explained in detail herein below. Mechanically connected to the yoke  54  is the drum  68  that carries enlarged hollow portion  70  formed on the end thereof and may be formed integrally therewith or mechanically coupled thereto. Aperture  72  formed on the end of the enlarged portion  70  serves to receive the projection  66  and the dynamics of the system serves to convert the rotary motion of the offset shaft  22  to a linear motion of the drum  68  by virtue of the action between the rotary motion of bearing  52 , yoke  54 , projection  66  and drum  68 . To assure a smooth transition from the rotary motion to the linear motion, the spherical ring  74  is fitted between the bearing  52  and arms  56  and  58  of yoke  54 .  
      Drum  68  is supported to casing  12  by the linear bearing  76  which consists of a cylindrical cage  78  and a plurality of balls  80  fitted into predetermined holes  82 . Obviously, the drum rides on the inner surface of the balls so as to effectually provide a smooth and efficient rectilinear motion. The collet  16  is threadably fitted on the end of drum  68  by virtue of the threads  84  formed on the drum  68  and the inner threads  86  formed on the aft end of collet nut  88 . The fore end of drum  86  includes the axial slot  90  that serves to receive the removably mounted saw blade (not shown). The inner surface  92  of the collet nut  88  is conically shaped so that as the nut is threaded on the drum  84  in an aft direction, the end of the collet nut  88  drives the gap in the slot  90  toward a closed position, urging the surfaces of the slot  90  against the saw blade for securing the same to the drum for rectilinear movement. Snap ring  94  serves to prevent the collet nut  88  from inadvertently become dislodged by overturning the collet nut.  
      Pin  96  serves to orient the lock adapter  14  to casing  12  and fits into hole  98  in lock adapter  14  and the slot  100  formed on the inner surface of the casing  12 . Retaining ring  102  serves to hold the linear bearing  76  securely in place in the casing  12  as does the snap rings  104  and  106  that support the offset shaft  22  in place.  
      In operation the rotary motion imparted to the offset shaft  22  is converted to linear motion of the drum  86  by virtue of the dynamics of the eccentric stub shaft driving the bearings and spherical ring against the arms  56  and  58  of the yoke  54  rotating the same about the pin  60 .  
      The projection  66  of yoke  54  defines a cam that drives the drum  68  that defines the follower.  
      The back and forth motion of the cam essentially defines the linear motion that is ultimately carried to the collet  16 . It will be appreciated that the offset shaft  22 , the stub shaft  50 , and drum  68  are all parallel to each other. It has been found that this arrangement not only effectively produces a surgical saw that has improved the operating life of those heretofore known surgical saws, but also operates with virtually no vibratory motion and noiseless which provides a better feel in the hands of the surgeon.  
      Although this invention has been shown and described with respect to detailed embodiments thereof, it will be appreciated and understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the disclosed invention.