Injection Device Drive Coupling for Complete Syringe Discharge
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Solution Overview
Problem
Existing injection devices face challenges in ensuring complete discharge of syringe contents due to manufacturing difficulties and reliability issues with flexible latch arms, which require both stiffness for shock loads and flexibility for unlatching, and may result in incomplete or excessive discharge.
Innovation Solution
A releasable drive coupling with a first drive element having a flexible arm and a second drive element with a drive surface, where inward flexing of the second flexible arm causes it to disengage from the first flexible arm, allowing the drive elements to slide relative to each other, and an actuator-driven decoupling component that automatically disengages the coupling when the drive elements reach a nominal position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If flexible latch arms are made stiff to withstand shock loads, then strength is improved, but flexibility for unlatching deteriorates
Solution Approach 1:
The drive coupling is divided into two separate drive elements (first and second) that can move independently relative to each other. The flexible arms are segmented into multiple components (first flexible arm on first drive element, second flexible arm on second drive element) that work together but can flex independently, allowing each component to be optimized for its specific function.
Solution Approach 2:
The flexible arms act as intermediary elements between the two drive elements. The first flexible arm engages with the second flexible arm, which in turn engages with the drive surface. This intermediary arrangement allows the system to transmit axial loads while providing a controlled flexing mechanism for automatic unlatching.
2Reliability
If safety margin is increased to ensure complete discharge, then reliability is improved, but device complexity increases due to multiple unlatching mechanisms
Solution Approach 1:
The invention merges the driving function and the unlatching function into a single integrated drive coupling mechanism. The same flexible arms that transmit drive also automatically unlatch when the syringe reaches its retracted position, eliminating the need for separate unlatching mechanisms and fluid damping systems.
Solution Approach 2:
The drive coupling is designed to automatically unlatch itself based on the syringe's position. When the syringe is fully retracted, the second flexible arm automatically disengages from the first flexible arm, causing the drive elements to slide relative to each other and release the syringe without requiring additional mechanisms or user intervention.
3Ease of manufacture
If manufacturing precision is relaxed to simplify production, then ease of manufacture is improved, but reliability of latch arm engagement deteriorates
Solution Approach 1:
The invention changes the engagement parameter from precise point-contact (as in conventional latch arms) to surface-contact engagement. The second flexible arm engages with a drive surface on the first drive element, providing a larger contact area that is more tolerant of manufacturing variations while maintaining reliable engagement.
Data Source
AI summary
An injection device (210) is described. A housing (212) receives a syringe and includes a return spring (226) for biasing the syringe from an extended position in which its needle (218) extends from the housing (212) to a retracted position in which the it does not. A drive spring (230) acts on a first drive element (232) and a second drive element (234) acts upon the syringe to advance it from its retracted position to its extended position and discharge its contents through the needle. The first drive element (232) is capable of movement relative to the second (234) once a nominal decoupling position has been reached. A release mechanism is activated when the first drive element (234) is further advanced to a nominal release position, to release the syringe (214) from the action of the drive spring (230), whereupon the return spring (226) restores the syringe (214) to its retracted position. Decoupling of the drive elements is achieved with a particular form of releasable drive coupling using two pairs of overlying flexible arms (235, 247). A particular form of release mechanism that also uses flexible arms (233) is also envisaged.