One Soft Step: Bio-Inspired Artificial Muscle Mechanisms for Space Applications

Soft robots, devices with deformable bodies and powered by soft actuators, may fill a hitherto unexplored niche in outer space. All space-bound payloads are heavily limited in terms of mass and volume, due to the cost of launch and the size of spacecraft. Being constructed from stretchable materials allows many possibilities for compacting soft robots for launch and later deploying into a much larger volume, through folding, rolling, and inflation. This morphability can also be beneficial for adapting to operation in different environments, providing versatility, and robustness. To be truly soft, a robot must be powered by soft actuators. Dielectric elastomer transducers (DETs) offer many advantages as artificial muscles. They are lightweight, have a high work density, and are capable of artificial proprioception. Taking inspiration from nature, in particular the starfish podia, we present here bio-inspired inflatable DET actuators powering low-mass robots capable of performing complex motion that can be compacted to a fraction of their operating size.

Structural material with designed thermal twist for a simple actuation

Materials with desired thermal deformation are very important for various engineering applications. Here, a material with the combination of chiral structure and TiNi shape memory alloy (SMA) sheets that performs a twist during heating is proposed. The thermo-mechanical properties of these materials are experimentally investigated. Inspired by this, a car-like material performing translational and rotational motion is designed, which illustrates the potential applications for the next-generation soft robotic devices. Based on this method, one can design remotely manipulated artificial muscles, nanorobots, revolute pairs, and thermal sensors or actuators in a noncontact fashion.

Design, analysis, and validation of an orderly recruitment valve for bio-inspired fluidic artificial muscles

Biological musculature employs variable recruitment of muscle fibers from smaller to larger units as the load increases. This orderly recruitment strategy has certain physiological advantages like minimizing fatigue and providing finer motor control. Recently fluidic artificial muscles (FAM) are gaining popularity as actuators due to their increased efficiency by employing these bio-inspired recruitment strategies such as active variable recruitment (AVR). AVR systems use a multi-valve system (MVS) configuration to selectively recruit individual FAMs depending on the load. However, when using an MVS configuration, an increase in the number of motor units in a bundle corresponds to an increase in the number of valves in the system. This introduces greater complexity and weight. The objective of this paper is to propose, analyze, and demonstrate an orderly recruitment valve (ORV) concept that enables orderly recruitment of multiple FAMs in the system using a single valve. A mathematical model of an ORV-controlled FAM bundle is presented and validated by experiments performed on an ORV prototype. The modeling is extended to explore a case study of a 1-DOF robot arm system consisting of an electrohydraulic pressurization system, ORV, and a FAM-actuated rotating arm plant and its dynamics are simulated to further demonstrate the capabilities of an ORV-controlled closed-loop system. An orderly recruitment strategy was implemented through a model-based feed forward controller. To benchmark the performance of the ORV, a conventional MVS with equivalent dynamics and controller was also implemented. Trajectory tracking simulations on both the systems revealed lower tracking error for the ORV controlled system compared to the MVS controlled system due to the unique cross-flow effects present in the ORV. However, the MVS, due to its independent and multiple valve setup, proved to be more adaptable for performance. For example, modifications to the recruitment thresholds of the MVS demonstrated improvement in tracking error, albeit with a sacrifice in efficiency. In the ORV tracking performance remained insensitive to any variation in recruitment threshold. The results show that compared to the MVS, the ORV offers a simpler and more compact valving architecture at the expense of moderate losses in control flexibility and performance.

DESIGN OF APPARATUS FOR EVALUATION OF TEMP-DEPENDENCE OF CREEP EFFECT IN PAM

The creep effect in relationship with the research of pneumatic artificial muscles represents a dynamic phenomenon characterized by slow changes in muscle displacement caused by the material's elasticity. However, the temperature of the environment in which the muscle works affects the temperature of the muscle. It also affects the creep effect itself; as a result, the process of identifying hysteresis models of muscle becomes difficult. The article contains a description and implementation of a measuring apparatus designed to measure the temperature dependence of the creep effect of fluid muscles. The apparatus was designed and constructed at the authors' workplace to analyze the creep effect and evaluate its impact on the accuracy of experimental models describing the dynamics of the drive.

Electrostatic Zipping Actuators—Analysis of the Pull-In Effect Depending on the Geometry Parameters

Continuous work on a new generation of actuators, referred to as artificial muscles, resulted in the initiation of work on electrostatic zipping actuators, the concept of which is derived from micro electro-mechanical devices. Despite partial knowledge of their basic operating parameters, a question remains whether electrostatic zipping actuators are able to meet the expectations in the context of generated forces and control possibilities. In order to get closer to the answer to this question, the authors of this work created a solution method using FEM, which allowed them to conduct a series of concentric contraction tests of the desired solution. In addition to the basic features of the actuators tested, such as their length, thickness and width, for the first time the size of the weld surface, to which the loading force was applied, was taken into account. The results of the investigations show the possibility of adjusting the supply voltage range to the application requirements, but most importantly, they present the variability of the pull-in strain parameter. In extreme configurations, its value increases from ~10% to ~26%. The results obtained emphasize the need for further analysis of electrostatic zipping actuators using FEM. It will make it possible to precisely define the characteristics of this technology as well as its limits. These activities will provide the ultimate answer to the potential of electrostatic zipping actuators as artificial muscles.