Innovative modular SMA actuator

A modular design for a shape memory actuator is proposed. The actuator is able to perform linear movements, while the modularity allows force and/or stroke improvements. Experimental results show how the behavior of the proposed implementation is sufficient for a wide class of problems and can be improved with proper developments

Model-based Design Framework for Shape Memory Alloy Wire Actuation Devices.

While Shape Memory Alloys (SMAs) have exceptional actuation characteristics such as high energy density, silent operation, flexible packaging, etc., they have not found widespread use in commercial applications because of the significant learning curve required of engineers before they are capable of designing actuation devices using this unique material. An SMA actuation device design framework consisting of grammar, design methods, and design process enables engineers of different backgrounds to make efficient and appropriate design decisions in different stages of the design process. A reference SMA actuation device structure built on a generalized actuation device hierarchical structure using the actuation device grammar works as a reference structure to identify and populate device design options, and to model and analyze the device actuation performance as well as to enlighten non-expert engineers about the essential elements of SMA actuation devices. Design methods consisting of modular modeling, model aggregation and performance prediction, and visualization approaches support design decisions to serve diverse stakeholders of actuation device design by exposing the effects of individual device elements not only for SMA actuation devices, but also for a wide range of actuation devices. A multi-stage design process is formalized to help engineers create a detailed design including a three-step decoupled equilibrium design procedure which prevents potential iteration by decoupling the force and deflection of actuation output behavior, and hides the complexity of material and SMA architectural models from engineers while still exposing the impact of design parameters. The design framework makes SMA design knowledge more accessible to engineers with different levels of expertise and roles in device development by systematically organizing and presenting the device grammar, design methods, and design process. A design tool software platform based on the framework enables the creation of computer-aided design tools to support a variety of design tasks, which were demonstrated in two use case examples. By having the SMA actuation device design framework, the acceptance of the SMA actuation technology into both research and commercial applications can be increased to utilize promising SMA actuation benefits, and the device development cycle leading to these applications can be streamlined.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120684/1/wonhekim_1.pd

Utilizing Systematic Design and Shape Memory Alloys to Enhance Actuation of Modular High-Frequency Origami Robots

Shape memory alloys (SMAs) describe a group of smart metallic materials that can be deformed by external magnetic, thermal, or mechanical influence and then returned to a predetermined shape through the cycling of temperature or stress. They have several advantages, such as having excellent mechanical properties, being low cost, and being easily manufactured, while also providing a compact size, completely silent operation, high work density, and requiring less maintenance over time. SMAs can undergo sold-to-solid phase transformations, and it is because of these phase transformations that they can experience shape memory effect (SME); or the ability to recover from a deformed shape to an initially determined shape through the cycling of temperature. However, since SME requires the cycling of temperature to actuate SMAs, the actuation frequency of these materials has been slow for small-scale applications, as actuation speed is limited by the time it takes to transition from a higher temperature (actuated, pre-determined state) to a lower temperature (flexible, reconfigurable state). While SMAs are known to be highly advantageous, their main drawback is that they are one of the slowest actuation methods in the field of origami robotics. SMAs cannot actuate quickly enough cyclically due to the long cooling times required to get from their austenite (higher temperature, actuated, pre-determined state) phase to their martensite (lower temperature, flexible, reconfigurable state) phase. Researchers have attempted to achieve a higher actuation speed in previous projects by using active cooling agents. However, this study investigated the use of SMAs to initiate high-frequency cyclic movement through a small-scale origami fold without an active cooling source. This study used a combination of different system design parameters to mechanically hasten the actuation speed of a folding hinge with no cooling component present. Through only design and a complete understanding of the SMAs, this study achieved consistent and relatively high results (\u3e1.5 Hz) of an actuation speed for a system of this size. This study discovered knowledge regarding the composition, material properties, and actuation limits of SMAs, and a new systematic design method was proposed for creating origami robots

Low power consumption mini rotary actuator with SMA wires

Shape memory alloys (SMAs) are smart materials widely used as actuators for their high power to weight ratio despite their well-known low energy efficiency and limited mechanical bandwidth. For robotic applications, SMAs exhibit limitations due to high power consumption and limited stroke, varying from 4% to 7% of the total length. Hysteresis, during the contraction and extension cycle, requires a complex control algorithm. On the positive side, the small size and low weight are eminently suited for the design of mini actuators for robotic platforms. This paper describes the design and construction of a light weight and low power consuming mini rotary actuator with on-board contact-less position and force sensors. The design is specifically intended to reduce (i) energy consumption, (ii) dimensions of the sensory system, and (iii) provide a simple control without any need for SMA characterisation. The torque produced is controlled by on-board force sensors. Experiments were performed to investigate the energy consumption and performance (step and sinusoidal angle profiles with a frequency varying from 0.5 to 10 Hz and maximal amplitude of 15?). We describe a transient capacitor effect related to the SMA wires during the sinusoidal profile when the active SMA wire is powered and the antagonist one switched-off, resulting in a transient current time varying from 300 to 400 ms

Experimental testing of a modular flexible actuator based on sma wires

A flexible finger made up of three actuator modules based on shape memory wires (SMA) is experimentally studied in this research. A module is composed by few simple components: a plastic body and SMA wires. The body is a thin cylinder with a lower and upper base and two intermediate disks. Three equidistant SMA wires are longitudinally placed and allow the module to bend in any direction when one or more wires are actuated. The motion of the module is performed with the heating and cooling of the wire and the central rod exerts bias force, necessary to the stretching of the wire to the original length. Two test benches were built to perform both positioning tests and force tests. To evaluate the actuator workspace different tests were performed, with different power supply, heating and cooling time, actuation sequence. Force tests were performed with different distance between the undeformed finger and the obstacle. The results achieved with this first prototype are encouraging since the finger shows stable and correct operation. The planar projection of the workspace is a circle of about 30-40 mm of radius and exerted force is similar to mathematical model results (about 1 N at 5 mm). These results are encouraging, even though, probably due to manufacturing imperfections and frictions, the movement is not very regular along the various directions

Synergistic Smart Morphing Aileron

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106472/1/AIAA2013-1512.pd

Design of a 2 DOFs Mini Hollow Joint Actuated with SMA Wires

Shape memory alloys (SMAs) are smart materials used in robotics because of its light weight and high force-to-weight ratio. The low energy efficiency, up to 5%, has limited their use for large actuators. However, they have shown advantages in the design of mini-robots because of the limited volume required for the actuation system. The present study reports the design and construction of a mini compliant joint (MCJ) with a 2 degrees of freedom (DOFs) intersecting axis. The MCJ prototype has a 20 mm external diameter surrounding a cavity of 8 mm, weighs 2 g, is 20 mm high and can perform an angle rotation of 30 ∘ in less than 260 ms. It uses SMA NiTi wires in antagonistic configuration and springs to reduce the energy consumption and minimise heat production. The design methods and experimental results of the manufactured prototype are reported and discussed

Towards enduring autonomous robots via embodied energy.

Autonomous robots comprise actuation, energy, sensory and control systems built from materials and structures that are not necessarily designed and integrated for multifunctionality. Yet, animals and other organisms that robots strive to emulate contain highly sophisticated and interconnected systems at all organizational levels, which allow multiple functions to be performed simultaneously. Herein, we examine how system integration and multifunctionality in nature inspires a new paradigm for autonomous robots that we call Embodied Energy. Whereas most untethered robots use batteries to store energy and power their operation, recent advancements in energy-storage techniques enable chemical or electrical energy sources to be embodied directly within the structures and materials used to create robots, rather than requiring separate battery packs. This perspective highlights emerging examples of Embodied Energy in the context of developing autonomous robots