Syringe Binary Attachment Mechanism for Dead Space Reduction
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Solution Overview
Problem
Existing syringe assemblies with replaceable needle assemblies face issues with dead space variations due to inconsistent torque application, leading to medication wastage and potential leakage, as they either leak if not tightened enough or over-tighten and compromise the fitting over time.
Innovation Solution
A syringe and needle assembly with binary attachment features, including a lug and ramp mechanism that provides tactile feedback and ensures proper attachment with less than 180° rotation, preventing further tightening after secure engagement, thus minimizing dead space and ensuring consistent sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a frusto-conical syringe tip is used to frictionally engage the needle hub, then an excellent seal is provided, but dead space varies significantly due to tolerance variations in the tapered surfaces
Solution Approach 1:
The patent changes the geometric parameters of the engagement interface from a frusto-conical shape with an acute angle to a flat seal surface perpendicular to the longitudinal axis. This parameter change eliminates the sensitivity to angle and diameter variations, providing consistent dead space while maintaining effective sealing through the flat-to-flat engagement between the syringe tip and needle hub.
2Manufacturing precision
If a flat seal perpendicular to the longitudinal axis is used, then dead space is reduced, but the sealed condition is reached abruptly without gradual tightening feedback
Solution Approach 1:
The patent incorporates a ratchet mechanism that provides tactile feedback during the attachment process. As the needle hub is rotated onto the syringe barrel, the ratchet engages at specific intervals to provide audible and tactile signals, guiding the user to apply the correct amount of torque and indicating when proper engagement has been achieved, thus preventing both under-tightening and over-tightening.
3Manufacturing precision
If threaded engagement is used to allow consistent torque application in manufacturing, then proper attachment is achieved, but over-tightening can occur leading to creep and loss of preload over time
Solution Approach 1:
The patent employs a self-limiting engagement mechanism where the flat seal surfaces make contact at a predetermined position, automatically preventing further tightening. The geometry of the flat-to-flat engagement interface ensures that once the surfaces are in contact, additional rotation is mechanically blocked, eliminating the risk of over-tightening and the associated long-term problems of creep and preload loss.
4Adaptability or versatility
If no attachment limitation is provided, then strong users can attach the needle assembly, but weak users may not apply sufficient torque leading to leakage
Solution Approach 1:
The ratchet mechanism provides progressive tactile and audible feedback during rotation, making it easy for users of all strengths to understand when proper engagement is achieved. The feedback signals guide users to continue rotating until the ratchet engages, ensuring sufficient torque is applied without requiring the user to estimate the correct amount of force, thus accommodating both strong and weak users while maintaining seal integrity.
Data Source
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AI summary
A syringe and detachable needle assembly having binary attachment features include an elongate syringe barrel having a longitudinal axis, an open proximal end and an open distal end including a collar. The collar includes the cylindrically shaped sidewall. A needle assembly includes the hub having a body portion including a proximal end, a distal end and a conduit therethrough. A cannula having a distal end, a proximal end and a lumen therethrough is attached to the distal end of the hub so that the lumen is in fluid communication with the chamber. A lug is provided on one of the collar and the hub and a ramp and a rest surface is provided on the other of the collar and the hub. The ramp is oriented at an acute angle with respect to longitudinal axis for guiding the lug during needle assembly attachment, to the rest surface forcing the hub to contact the barrel to form a seal the hub and the barrel.