A general method for the design and fabrication of shape memory alloy active spring actuators

Shape memory alloys have been widely proposed as actuators, in fields such as robotics, biomimetics and microsystems: in particular spring actuators are the most widely used, due to their simplicity of fabrication. The aim of this paper is to provide a general model and the techniques for fabricating SMA spring actuators. All the steps of the design process are described: a mechanical model to optimize the mechanical characteristic for a given requirement of force and available space, and a thermal model for the estimation of the electrical power needed for activation. The parameters of both models are obtained by experimental measurements, which are described in the paper. The models are then validated on springs manufactured manually, showing also the fabrication process. The design method is valid for the dimensioning of SMA springs, independently from the external ambient conditions. The influence on the actuator bandwidth was investigated for different working environments, providing numerical indications for the utilization in underwater applications. The spring characteristics can be calculated by the mechanical model with an accuracy of 5%. The thermal model allows one to calculate the current needed for activation under different ambient conditions, in order to guarantee activation in the specific loading conditions. Moreover, two solutions were found to reduce the power consumption by more than 40% without a dramatic reduction of bandwidth

Bioinspired Soft Actuation System Using Shape Memory Alloys

Soft robotics requires technologies that are capable of generating forces even though the bodies are composed of very light, flexible and soft elements. A soft actuation mechanism was developed in this work, taking inspiration from the arm of the Octopus vulgaris, specifically from the muscular hydrostat which represents its constitutive muscular structure. On the basis of the authors’ previous works on shape memory alloy (SMA) springs used as soft actuators, a specific arrangement of such SMA springs is presented, which is combined with a flexible braided sleeve featuring a conical shape and a motor-driven cable. This robot arm is able to perform tasks in water such as grasping, multi-bending gestures, shortening and elongation along its longitudinal axis. The whole structure of the arm is described in detail and experimental results on workspace, bending and grasping capabilities and generated forces are presented. Moreover, this paper demonstrates that it is possible to realize a self-contained octopus-like robotic arm with no rigid parts, highly adaptable and suitable to be mounted on underwater vehicles. Its softness allows interaction with all types of objects with very low risks of damage and limited safety issues, while at the same time producing relatively high forces when necessary

Design of a compact bistable mechanism based on dielectric elastomer actuators

Bistable mechanisms are widely used in the applications where two stable positions must be held for long time without energy consumption. The main advantage of bistable mechanisms is a sensible reduction in bulkiness and energy cost. Among the possible active triggering systems, dielectric elastomer actuators (DEAs) are gaining attention, for their efficiency and strain rate, as a viable alternative to traditional technologies. In the present work, a novel design of a bistable system is proposed, counting on a cross-like shape bistable element coupled with two axially arranged conical DEAs. Analytical and FEM models have been used to implement and analyze the behavior of the single components and the final coupled system. The obtained results confirm the feasibility of the switching process between the equilibrium points and the capability to capture and numerically describe the interactions between the actuators and the bistable beams. A specific device has been finally envisaged to exemplify the possibility to develop a light-weight and compact system able to sustain and passively maintain a linear displacement which equals the 46 % of its own total length

Development of the functional unit of a completely soft octopus-likerobotic arm

In the presented paper the realization of an artificial functional unit of muscular hydrostat inspired by the octopus is shown. The octopus has been chosen because it shows high manipulation capabilities and dexterity without a skeletal support, thus it is a good example of Embodied Intelligence. Inspiration from Nature concerns the features that are interesting from a robotic point of view for the development of an artificial muscular hydrostat: in particular actuators arrangement and their antagonistic mechanism. The main focus was on the two key elements of the unit: soft actuators and support structure. Shape memory alloys (SMA) has been chosen for actuation technology, whereas the support structure is a braided sleeve, that provides spatial continuity to the action of the actuators. Two contiguous units have been built and tested in water. Capabilities of shortening, elongation and bending have been observed and their performances evaluated. A maximum elongation of 43% has been recorded from shortened to elongated condition, with a diameter variation of 25%, finding a good match with the expected results from the support structure models. Relative angle between extremities has been measured during bending in two conditions and their efficiency has been compared

Design and development of a soft robotic octopus arm exploiting embodied intelligence

The octopus is a marine animal whose body has no rigid structures. It has eight arms mainly composed of muscles organized in a peculiar structure, named muscular hydrostat, that can change stiffness and that is used as a sort of a modifiable skeleton. Furthermore, the morphology of the arms and the mechanical characteristics of their tissues are such that the interaction with the environment, namely water, is exploited to simplify the control of movements. From these considerations, the octopus emerges as a paradigmatic example of embodied intelligence and a good model for soft robotics. In this paper the design and the development of an artificial muscular hydrostat are reported, underling the efforts in the design and development of new technologies for soft robotics, like materials, mechanisms, soft actuators. The first prototype of soft robot arm is presented, with experimental results that show its capability to perform the basic movements of the octopus arm (like elongation, shortening, and bending) and demonstrate how embodiment can be effective in the design of robots

Soft Robot Arm Inspired by the Octopus

The octopus is a marine animal whose body has no rigid structures. It has 8 arms composed of a peculiar muscular structure, named muscular hydrostat. The octopus arms provide it with both locomotion and grasping capabilities, thanks to the fact that their stiffness can change over a wide range and it can be controlled through combined contractions of the muscles. The muscular hydrostat can better be seen as a modifiable skeleton. Furthermore, the morphology the arms and the mechanical characteristics of their tissues are such that the interaction with the environment, namely water, is exploited to simplify control. Thanks to this effective mechanism of embodied intelligence, the octopus can control a very high number of degrees of freedom, with relatively limited computing resources. From these considerations, the octopus emerges as a good model for embodied intelligence and for soft robotics. The prototype of a robot arm has been built based on an artificial muscular hydrostat inspired to the muscular hydrostat of the Octopus vulgaris. The prototype presents the morphology of the biological model and the broad arrangement of longitudinal and transverse muscles. Actuation is obtained with cables (longitudinally) and with SMA springs (transversally). The robot arm combines contractions and it can show the basic movements of the octopus arm, like elongation, shortening, and bending

The Application of Embodiment Theory to the Design and Control of an Octopus-like Robotic Arm

This paper examines the design and control of a robotic arm inspired by the anatomy and neurophysiology of Octopus vulgaris in light of embodiment theory. Embodiment in an animal is defined as the dynamic coupling between sensorymotor control, anatomy, materials, and the environment that allows for the animal to achieve effective behaviour. Octopuses in particular are highly embodied and dexterous animals: their arms are fully flexible, can bend in any direction, grasp objects and modulate stiffness along their length

Octopus-Inspired Innovative Suction Cups

Octopus show great adhesion capabilities thanks to their suckers covering their ventral side of their arms. Starting from biological investigation, we identified preliminary specifications for the design of innovative artificial suction cups, which could be used in the field of soft robotics. The main features of the biological sucker are maintained as leading criteria for the choice of the actuation technology and mechanism. In this preliminary work, we focused on the imitation of the functionality of the specific muscle bundles which generate suction to obtain adhesion. Dielectric Elastomers Actuators (DEA) were identified as a suitable solution. A study on materials and manufacturing techniques was made. Different possible solutions in the use of DEA are also described