Bistable Shape Memory Actuator Without Return Springs
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Solution Overview
Problem
Existing actuator devices using shape memory wires require permanent restoring forces, leading to energy inefficiency, stress on the wires, and large construction space, especially when maintaining positions over time.
Innovation Solution
An actuator device with a bistable elastic bending element, held at attachment points, uses shape memory wires to apply switching torques for deformation between actuator positions, eliminating the need for restoring springs and allowing for compact design with small deflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a return spring is used to restore the shape memory wire to its previous length, then the wire can be reset to its initial state, but this leads to permanent load on the wire, critical stresses, and accelerated aging
Solution Approach 1:
The patent removes the return spring from the system entirely, replacing it with a bistable mechanism that uses the shape memory wire's own properties to achieve both actuation and restoration. The wire is stretched between two attachment points on a movable element, and when heated, it naturally returns to its original length, pulling the element to the opposite position without requiring any external restoring force.
Solution Approach 2:
The shape memory wire serves dual functions: it acts as both the actuator (when heated to contract) and the restorer (when cooled to elongate). The bistable mechanism allows the wire to maintain positions without continuous energy input, and the alternating heating/cooling cycles enable the wire to automatically switch between states without external assistance.
2Duration of action of moving object
If the shape memory wire is electrically energized to maintain a position over time, then the actuator device can hold its position, but this results in very high energy consumption
Solution Approach 1:
Instead of continuous electrical energization, the system uses periodic thermal cycles. The shape memory wire is heated only temporarily to trigger a state change, then allowed to cool naturally. Once in the desired position, no further energy input is required to maintain that position, as the bistable mechanism holds it passively until the next activation cycle.
3Length of moving object
If a long shape memory wire is used to achieve appreciable deflections, then the actuator can produce sufficient movement, but this requires large construction space
Solution Approach 1:
The patent transforms the linear motion problem into a rotational or angular displacement problem. By mounting the shape memory wire at an offset from the pivot point of the movable element, a small linear contraction of the wire produces a large angular rotation of the element. This leverages the moment arm principle, where the perpendicular distance from the pivot to the wire attachment point amplifies the effect of the wire's short stroke.
4Stability of the object's composition
If the shape memory wire is continuously loaded by the restoring force, then the wire maintains tension, but this leads to accelerated aging due to permanent load
Solution Approach 1:
The wire experiences tension only during the brief heating phase when it contracts. During the cooling phase and while holding positions, the wire is relaxed or under minimal load. This intermittent loading pattern, rather than continuous stress, significantly reduces fatigue accumulation and extends the wire's operational life.
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
Enables bistable actuator positions without permanent load on shape memory wires, reducing energy consumption and physical stress, while achieving significant deflections with shorter shape memory wires, resulting in a more efficient and space-saving design.
Implementation Method 1
a force resulting from the length reduction of a previously stretched wire made of shape memory material (shape memory wire) when exposed to heat
Implementation Method 2
When the heating element 20 is energized, the shape memory wire 10 is heated
Data Source
AI summary
The invention relates to a bistable actuator device (1) for providing at least two actuator positions comprising:an elastic bending element (2) supported at at least one attachment point (31, 32, 34) such that, by applying a switching torque at the attachment point (31, 32, 34), elastic deformation of the bending element (2) results in a change from a first actuator position to a second actuator position; andat least one actuator element (41, 42) formed with a shape memory wire, the shape memory wire causing a pulling force by heating and being coupled to a portion of the bending element (2) at the attachment point (31, 32, 34) so that the pulling force causes the switching torque at the attachment point (31, 32, 34) to move the bending element (2) from the first actuator position to the second actuator position.