Safety needle syringe braking system

Abstract

A braking mechanism for a retractable safety syringe is disclosed herein. In a first embodiment, the braking mechanism is disposed about the distal end of a piston. The braking mechanism may comprise a friction material about a post attached to a piston. The friction material is displaced from a seat to a landing when the piston is traversed to a fully extended position to disengage the braking mechanism. In a second embodiment, the braking mechanism is disposed at a proximal end of a syringe body. The braking mechanism has a friction member which engages an outer surface of a rigid shaft of a plunger. The friction member is selectively pivotable to disengage the braking mechanism.

What is claimed is: 
     
         1 . A retractable safety syringe for preventing syringe reuse and accidental needle pricking, the syringe comprising:
 a syringe body defining a distal end, proximal end and inner surface;   a plunger having a piston disposed within the syringe body, a rigid shaft extending through the proximal end of the syringe body, and a thumb platform attached to the rigid shaft which is operative to traverse the piston between a retracted position and a fully extended position, the piston further having a braking mechanism comprising;
 a protuberance having a seat and a landing, an outer periphery of the seat being larger than the outer periphery of the landing; 
 a friction material disposable about the seat or the landing, a maximum friction force between the friction material and the inner surface of the body being greater than or about equal to a retraction force of to retraction mechanism when the friction material is disposed about the seat, and the friction force between the friction materials and the inner surface of the body being less than the retraction force when the friction material is disposed about the landing; and 
 a punch attached to the distal end of the body and operative to displace the friction material from the seat to the landing when the piston is traversed to the fully extended position. 
   
     
     
         2 . The syringe of  claim 1 , wherein the protuberance of the braking mechanism has two tines, an outer periphery of the seat being larger than an inner periphery of the friction material in a relaxed state, the tines being bendable to fit the friction material about the seat. 
     
     
         3 . The syringe of  claim 2 , wherein the two tines further define the landing, the landing outer periphery being sufficiently smaller than the friction material inner periphery such that the frictional force between the friction material and the inner surface of the syringe body is smaller than the retraction force when the friction material is disposed about the landing. 
     
     
         4 . The syringe of  claim 2 , wherein distal ends of the tines have an under cut groove to receive the inner periphery of the friction material. 
     
     
         5 . The syringe of  claim 4 , wherein the two tines are inwardly displaceable to release the friction material. 
     
     
         6 . The syringe of  claim 5 , wherein the punch has a frusto-conical surface aligned to distal ends of the tines for receiving the distal ends of the tines and inwardly displacing the tines. 
     
     
         7 . The syringe of  claim 6 , wherein the punch has a fulcrum aligned to an interface between the friction material and the seat for separating the friction material from the seat as the piston is traversed to the fully extended position. 
     
     
         8 . The syringe of  claim 1  wherein the retraction mechanism is a variable vacuum compartment. 
     
     
         9 . The syringe of  claim 1  wherein the retraction mechanism is a spring. 
     
     
         10 . A retractable safety syringe for preventing syringe reuse and accidental needle pricking, the syringe comprising:
 a syringe body defining a distal end and a proximal end;   a plunger having a piston disposed within the syringe body, a rigid shaft extending through the proximal end of the syringe body and a thumb platform attached to the rigid shaft which is operative to traverse the piston between a retracted position, a first extended position, and a second extended, the plunger being biased toward the retracted position via a retraction mechanism;   a braking mechanism adjacent the proximal end of the syringe body, the braking mechanism comprising:
 a friction member having a through hole, the rigid shaft slidably disposed through the through hole, the friction member having an up position and a down position, an inner edge of the through hole frictionally engages the rigid shaft to resist a retraction force of the retraction mechanism that urges the plunger to the retracted position when the friction member is in the up position and the inner edge of the through hole frictionally disengages the rigid shaft when the friction member is in the down position to permit the retraction force to urge the plunger to the retracted position. 
   
     
     
         11 . The syringe of  claim 10  wherein the friction member is rotatable between the up position and the down position. 
     
     
         12 . The syringe of  claim 10  wherein the friction member further comprises a pawl for retaining the friction member in the down position when the pawl engages the proximal end of the syringe body and the inner edge of the through hole frictionally disengages the rigid shaft. 
     
     
         13 . The syringe of  claim 12  further comprising a base member, the friction member being pivotably attached to the base member and the pawl being selectively attachable to the base member. 
     
     
         14 . The syringe of  claim 13  wherein the pawl has a J shape. 
     
     
         15 . The syringe of  claim 10  wherein a maximum frictional force between the friction member and the rigid shaft is greater than or equal to about the retraction force of the retraction mechanism.