Abstract:
A locking member is positionable within an opening in the arm and is likewise engageable with a post and slidable jointly with the arm along the axis of the post to initiate a clamping force. A shaft having a handle assembly on one end is threadable in the locking member and hand rotatable to move the locking member laterally relative the post to secure the arm and post together at selected positions relative each other. A spring means in the handle assembly provides increased turning torque as the lock is tightened and at a preselected designing load, a brake member overrides the washer to prevent further hand tightening.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a sliding arm lock assembly particularly adapted for use in a cardiac compressor having a base platform assembly, support pillar or post and a compressor arm slidably supported by the post. 
     FIG. 1 of the drawings illustrates in perspective such a unit and the lock assembly 10 is adapted to be manually controlled to permit positioning the arm 12 at different positions relative post 14 and platform assembly 16. One prior art embodiment is illustrated and described in commonly assigned U.S. Pat. No. 3,364,924 issued Jan. 23, 1968. In the type of prior art embodiment described in the above identified patent, the compression arm includes a peripheral collar which is rotatable on the support post and vertically slidable when the locking means is loosened. The locking means includes either a pair of generally cylindrical abutting elements or a single cylindrical element with a threaded stud extending therefrom having a handle or the like attached to one end for manual loosening and tightening. The cylindrical element or elements include a saddle-shaped seat portion for abutment with the periphery of the post to bind the assembly when the knob or handle is tightened. To bind the assembly, the knob is rotated so that the collar presses the cylindrical element toward the post to secure and bind the assembly. While this type of lock assembly works adequately, there are several disadvantages that are significantly overcome by the subject invention. To begin with, the prior art tightening mechanisms were subject to overtightening which resulted in reduced effectiveness or failure in the threaded shaft requiring replacement of the lock assembly. Too much torque could be applied resulting in repeated over stressing of the assembly. The assembly of course has to be manipulated by a variety of different types of persons and hence too little torque advantage could easily result in certain people not being able to tighten the assembly up adequately enough under certain uses. A second distinct drawback was the propensity when adjusting the compressor arm relative the post to unintentionally lift the compressor arm up sufficiently high enough toward the upper end of the post such that the locking assembly became displaced or misaligned relative the post therefore preventing further operation until the parts were carefully aligned once more. Thus, there is a need in this art for an improved sliding arm lock assembly. 
     SUMMARY OF THE INVENTION 
     The subject invention is described with particular reference to a cardiac compressor that includes a base platform assembly; an upstanding support post and compressor arm which extends radially from the post and includes a collar surrounding the post. The arm includes an opening in association with the collar for receipt of a locking or clamping member having a seat formed thereon configurated for cooperation with the post such that when the locking member is aligned within the opening and the seat is aligned with the post, the locking member is positionable between a released position wherein the arm can be slidingly moved along the axis of the post and a lock position wherein the arm is securely held rigidly relative the post. 
     In accordance with the invention, the locking member includes a threaded shaft and handle assembly on one end for rotation thereof. The handle assembly includes a spring means which cooperates with the arm increasing the turning torque required as the force between the locking member and post is increased. At a preselected torque, a brake means on the handle assembly seats relative the arm restricting further manual manipulation of the handle assembly to avoid excess stress or failure of the locking assembly. Preferably, a thrust washer is positioned intermediate the spring means and arm so that when the handle is rotated, the washer abuts the arm causing the locking member to move relative the post into a locked position. The spring means may comprise a conical washer which becomes more flattened as the locking member is tightened. 
     In more narrower aspects of the invention, means are provided to prevent unintentional removement and misalignment of the locking member while positioned in the compressor arm opening and adjustment means are provided in order to neutralize tolerance variation in parts. 
     The subject invention is extremely advantageous over the prior art in that it now provides a facile locking assembly which can be hand tightened by a variety of people of different physical strengths without varying the degree of tightness in the locking assembly. The leverage provided by the locking assembly of the subject invention permits almost any person to hand tighten easily to the varied desired level of torque at which point the lock assembly is adequately and safely tightened for operation of the cardiac compressor. The improved operation and ease with which it can be manipulated permits faster adjustment under conditions of emergency thereby increasing the overall speed and utility with which the cardiac compressor can be utilized by different skilled people. The locking means preventing unintentional removal or misalignment of the locking member adds further utility and speed of operation. The various adjustment means provided to neutralize tolerance variation in parts provides a better more economically feasible commercial product at lower cost. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing a cardiac compressor utilizing the subject sliding arm lock assembly; 
     FIG. 2 is an exploded view in perspective of the lock assembly; and 
     FIG. 3 is a fragmentary cross-sectional planned view of the subject invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now specifically to the drawings, a cardiac compressor assembly 1 includes the base platform subassembly 16, support pillar or post 14 extending upwardly from one edge of the rigid platform 16a of subassembly 16 and a compressor arm 12 extending out over the base plate or platform 16a. The compressor arm 12 has a plunger subassembly 18 mounted to the other end of arm 12 over the platform. The operation of the cardiac compressor illustrated need not be described in detail since it is well known in the art. A principal function is to depress the plunger subassembly 18 on the chest of a patient positioned over platform 16a to provide external cardial compression. Since the size of patients varies considerably, it is desirable to adjust the relative heights of compressor arm 12 over platform 16a and in furtherance thereof, compressor arm 12 includes a collar 20 at one end which surrounds post 14 and although closely fit thereover, includes internal clearance permitting easy movement of compressor arm axially relative post 14 as well as in positions of rotation thereabout. The sliding arm lock assembly 10 of the subject invention can be tightened to rigidly secure compressor arm 12 at any desired position relative post 14 and alternatively can be loosened to permit adjustment to any desired position. While the subject invention is described in particular detail with reference to a cardiac compressor, it will be appreciated that it could be utilized in a variety of different environments. 
     Referring now specifically to FIGS. 2 and 3, the particular details of lock assembly 10 will be described. Compressor arm 12 includes a lateral opening 22 extending through arm 12 and also having an exposed opening 23 opening into collar 20 at the transition between collar 20 and the one end of arm 12. The sliding lock assembly 10 includes a cylindrical locking member 24 having a generally saddle-shaped seat 25. The seat 25 has a radius of curvature corresponding generally to that of post 14 (FIG. 3) although relative movement is permitted between the parts when loosened. Locking member 24 includes an internal threaded passageway 26 extending axially through locking member 24. Preferably, passageway 26 is formed in a shrink fit insert 28 which extends from one end 30 of locking member 24 but not quite through to the opposite end 32 for reasons which will be explained hereinafter. The inner end 24a of locking member 24 does not extend to the surface 12a of arm 12 to permit a handle assembly 44 to bear up against arm 12 (or surface 12a) thus providing the relative clamping movement of locking member 24 and post 14. An internal opening 36 is formed in locking member 24 and at end 32, includes a stepped interior wall forming a stop 38 which prevents insert 28 from being positioned completely to end 32. Internal passageway 28 is threaded for receipt of a shaft 40 which includes a nut 42 anchored to one end by set screws 42a. A handle assembly 44 is secured to the opposite end 48 of shaft 40 and includes a hub portion 52 secured to end 48 by set screws 50, 50 extending radially through the hub. Hub 52 includes radially projecting thumb portions 54 formed integrally therewith. The hub also includes an axially extending annular shell 46 defining a stepped inner cross-sectional portion comprising: a first portion 60 in which shaft 48 is secured; a second portion 62 of greater cross-sectional width which houses an antifrictional thrust roller bearing 64, selected shims 66, and at least part of a thrust washer 68 which fetches up against or bears against bearing 62; and a third portion 76 of yet greater cross-sectional width which houses the remainder of thrust washer 68 and conical washer. Thrust washer 68 includes a stepped down portion 70 which bearing 62 seats on and a diametrically opposite reduced portion 72 in which is seated the conical washer 74. Conical washer 74 when positioned within hub portion 76 extends in its expanded position slightly beyond the plane of the terminal end 78 of hub shell 46. A large thrust washer 80 is biased into abutment against conical washer 74 and spaced from the terminal ends 78 of hub member 52 by conical washer 74. This spacing defined as gap &#34;g&#34; can be reduced to zero by applying appropriate compression force to conical washer 74 by rotation of handle assembly 44. The large thrust washer 80 is designed for abutment on the opposite side against compressor arm 12. The washer 80 is biased against conical washer 74 during a loosened condition of the assembly by a spring 82 positioned about shaft 48 held against the recessed end of insert 28. 
     OPERATION 
     Having described the basic elements of the sliding arm lock assembly 10, its operation should be well understood. With the locking assembly 10 positioned in opening 22 in compressor arm 12, and aligned relative post 14 such that the saddle-shaped seat 25 is in tongue and groove relationship with post 14. In order to tighten the compressor arm 12 to post 14, knob 46 is rotated causing handle assembly 66 to advance toward compressor arm 12 until the large thrust washer 80 comes into abutment with the side of compressor arm 12. Further tightening will then cause reactionary movement of locking member 24 toward handle assembly 44 causing the locking wedge engagement between seat 25 and post 14. As the torque increases due to this tightening, conical washer 74 will flex inwardly within the third portion 76 of the internal handle hub member 52. This will cause the turning torque required to increase slightly but still provide relatively easy manipulation due to the cooperation between large washer 80, conical washer 74 and thrust roller bearing 64. Continued tightening however eventually causes the terminal annular end portion 78 of shell 46 to come into physical contact with and seat on large washer 80 completely destroying the mechanical advantage of the assembly due to rubbing friction at a relatively large moment arm introduced by such physical contact. This restricts further flattening of conical washer 72 and the direct loading in this position acts as a brake to further manual tightening thereby limiting the force between seat 25 and post 14. By appropriately designing the force factor in the conical washer 74, the brake will take effect at the very preselected load desired for the lock assembly. The brake will thus prevent overstressing of the lock assembly. In order to compensate for tolerance variation in the parts, shims 66 are utilized to adjust to the different axial variations. Also, nut 42 is adjustable along shaft 40 to limit excessive loosening of handle assembly 44. Loosening of set screws 42a permits this adjustment. 
     An ancillary feature to the subject invention is the provision of a slot 90 (FIG. 2) for receipt of a screw 92 threaded into the arm assembly after locking member 24 is properly inserted and aligned with post 14. Screw 92 is threaded into a tapped hole 94 at the top of arm 12 next to post 14 and extends loosely into slot 90. When in place, screw 92 will prevent accidental removal, or excessive rotation, of the arm lock assembly 10 should the arm ever be raised above the end of the column. This greatly facilitates complete utilization of the cardiac compressor without causing unnecessary delay due to inadvertent misalignment of the locking member when the cardiac compressor arm 12 is either removed from post 14 or rotated thereabout at its upper end. 
     Although but one embodiment has been shown and described in detail, it will be obvious to those having ordinary skill in this art that the details of construction of this particular embodiment may be modified in a great many ways without departing from the unique concepts presented. It is therefore intended that the invention is limited only by the scope of the appended claims rather than by particular details of construction shown, except as specifically stated in the claims.