Lead Screw Contact Detection in Pen Injectors
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Solution Overview
Problem
Current medicament delivery devices, such as pen-type injectors, lack a reliable mechanism to ensure that medicament delivery only begins once the plunger has made contact with the piston, preventing accidental or premature medicament expulsion.
Innovation Solution
A lead screw design with a shaft and head portion, featuring a fixed and displaceable part, biasing means, and a sensor to detect contact between the parts, utilizing resilient fingers and openings for precise engagement and a sensor to prevent inadvertent actuation, integrated with a drive mechanism for medicament expulsion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple lead screw design is used, then device complexity is reduced, but reliability of medicament delivery control deteriorates
Solution Approach 1:
The lead screw head is divided into a fixed part and a displaceable part, allowing independent sensing of contact events. The resilient fingers are segmented to provide both mechanical retention and tactile sensing capability. This segmentation enables reliable contact detection without adding complex external sensing systems.
Solution Approach 2:
The resilient fingers serve dual functions: mechanically retaining the displaceable part during normal operation and sensing contact events through their deflection. The system uses its own structural elements for both mechanical function and sensing, eliminating the need for separate complex sensing mechanisms.
2Reliability
If contact detection mechanism is added, then reliability of delivery control is improved, but device complexity increases
Solution Approach 1:
The sensing function is merged with the mechanical retention structure. The resilient fingers that hold the displaceable part during normal operation also serve as the contact sensing elements. This consolidation achieves reliable contact detection without adding separate complex sensing subsystems.
Solution Approach 2:
The structural elements of the lead screw (resilient fingers) perform the sensing function as part of their normal operation. The system uses its own mechanical components to detect contact events, eliminating the need for external sensing devices and reducing overall system complexity.
3Measurement precision
If resilient fingers with sensor are used, then measurement precision of contact detection is improved, but device complexity increases
Solution Approach 1:
The resilient fingers serve as both mechanical retention elements and contact sensing elements. Their elastic deflection naturally provides precise contact detection without requiring separate sensing electronics, maintaining simplicity while achieving accurate measurement.
Solution Approach 2:
The physical state of the resilient fingers (deflection angle, contact force) changes predictably with lead screw position and contact events. This parameter change provides a natural, precise sensing mechanism that leverages the mechanical properties of the structure itself rather than adding complex electronic sensing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Ensures accurate and controlled medicament delivery by detecting contact between the lead screw and piston, preventing premature expulsion and allowing for precise calculation of medicament quantity remaining in the cartridge.
Implementation Method 1
one of the fixed part and the displaceable part is provided with a plurality of resilient fingers extending axially with respect to the lead screw
Implementation Method 2
biasing means acting normally to urge the displaceable part away from the fixed part
Data Source
AI summary
The present invention relates to a medicament delivery device such as a pen type injector used to expel medicament from a medicament cartridge under the action of a lead screw. The medicament cartridge typically comprises a cylinder having a displaceable piston at one end displacement causing medicament contained within the cartridge to be expelled. It is of advantage to know when the plunger contacts the displaceable piston since no delivery of medicament can occur before this point. A delivery device is disclosed in which a lead screw for a medicament delivery device comprises a shaft portion and a head portion, the head portion further comprising a fixed part, a displaceable part movable with respect to the fixed part, biasing means acting normally to urge the displaceable part away from the fixed part and a sensor to detect when the displaceable part moves towards the fixed part, one of the fixed part and the displaceable part being provided with a plurality of resilient fingers extending axially with respect to the lead screw, and the other of the fixed part and the displaceable part being provided with a plurality of opening, each of the resilient fingers extending within a corresponding opening.