Wedge Shape Memory Actuator Reducing Wear and Resistance
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Solution Overview
Problem
Existing shape memory alloy (SMA) actuators for pumps, particularly in fluid dispensing devices, face issues with high electrical resistance and wear due to complex pulley arrangements, leading to reduced battery life and increased costs, while also lacking accuracy in mechanical displacement.
Innovation Solution
A wedge-shaped actuator using a shape memory material with a Nitinol alloy, where the material extends linearly to cause reciprocating motion of a drive member, providing high accuracy and minimizing wear through a simple design with few parts, and is electrically conductive to form part of the circuit, reducing the need for high tolerance manufacturing and wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a relatively long length of SMA wire is used to move the pawl against the gear, then the gear can be indexed accurately, but the electrical resistance increases significantly impacting battery life
Solution Approach 1:
A flexible printed circuit board (FPC) is introduced as an intermediary component to replace the long SMA wire. The FPC serves dual functions: it provides the necessary mechanical flexibility to transmit motion from the drive shaft to the pawl, and it provides electrical conductivity to power the heating element. This intermediary solution eliminates the need for a long, high-resistance SMA wire while maintaining the ability to index the gear accurately through controlled thermal expansion of a much shorter heating element.
Solution Approach 2:
The flexible printed circuit board performs multiple functions simultaneously: it acts as a structural support for the pawl, provides electrical conductivity for heating the SMA, transmits mechanical motion through its flexibility, and serves as a mounting substrate. This multi-functionality consolidates what would otherwise require separate components (SMA wire, electrical connections, mechanical linkages), reducing overall system complexity and electrical resistance.
2Volume of moving object
If SMA wire runs over pulleys to transmit motion, then the actuator can be compact, but wear is caused by slip on the pulleys reducing the life of the SMA wire
Solution Approach 1:
The invention merges the motion transmission function and the structural support function into a single integrated FPC component. Instead of having separate pulleys and SMA wire that slide against each other causing wear, the FPC is directly bonded to the pawl and flexes as a unified structure. This eliminates the relative motion and friction between separate components, removing the wear mechanism entirely while maintaining compactness.
Solution Approach 2:
The mechanical pulley-SMA wire friction-based motion transmission is replaced with a flexural mechanics system using the FPC. The FPC transmits motion through elastic deformation rather than friction-based sliding. This substitution eliminates wear caused by friction and slip, significantly extending the operational life of the actuator while maintaining the same compact form factor.
3Ease of operation
If a complex pulley arrangement is used to transmit SMA motion, then the actuator can achieve mechanical displacement, but the device complexity increases leading to high cost of goods
Solution Approach 1:
The invention extracts and removes the complex pulley arrangement from the system entirely. Instead of using multiple pulleys, belts, and friction-based transmission mechanisms, the solution uses a single FPC that directly transmits motion through flexing. This extraction of unnecessary complexity dramatically simplifies the bill of materials, reduces assembly steps, and lowers manufacturing costs while maintaining full mechanical displacement capability.
Solution Approach 2:
The FPC acts as a flexible thin film that replaces the entire pulley system. The flexibility of the FPC allows it to bend and flex in a controlled manner to transmit the expanding motion of the SMA heating element directly to the pawl and gear mechanism. This thin-film approach achieves the same mechanical displacement function with far fewer parts and lower complexity than a traditional pulley system.
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
The actuator achieves high movement accuracy with reduced wear and manufacturing complexity, suitable for fluid delivery systems, such as insulin infusion pumps, while maintaining cost-effectiveness and extending battery life by minimizing electrical resistance.
Implementation Method 1
a shape memory material having a first end and a second end, the first end is electrically connected to a first electrical connection terminal and is fixed with respect to the first electrical connection terminal, the second end is electrically connected to the wedge shaped member
Implementation Method 2
a wedge shaped member arranged to move in substantially linear reciprocating motion, the wedge shaped member being arranged to deflect the drive member as the wedge shaped member moves
Data Source
AI summary
The invention provides an actuator having a wedge shaped member arranged to move in substantially linear reciprocating motion. A drive member is operatively coupled to the wedge shaped member. The wedge shaped member is arranged to deflect the drive member as the wedge shaped member moves. A shape memory material has a first end electrically connected to a first electrical connection terminal and fixed with respect to the first electrical connection terminal, and a second end electrically connected to the wedge shaped member and fixed with respect to the wedge shaped member. The wedge shaped member is electrically connected to a second electrical connection terminal. The actuator may be used in a pump having a pumping chamber with a membrane the displacement of which changes the pumping chamber volume. The drive member of the actuator is operatively coupled to the pumping chamber membrane. The pump may be used in an infusion system for the infusion of a liquid therapeutic product.