Pneumatic actuators have gained huge popularity in the field of soft robotics. A class of this kind of devices exploits inflatable thin membranes which generate a desired displacement upon inflation, but often without providing sufficient force/torque to perform their task. In this paper, we propose a novel actuator combining a membrane and a rigid foldable structure. Experimental tests show that such INFlatable ORigami Actuator (INFORA) is characterized by relatively high stiffness compared to other actuators of the same class. We provide a mathematical model to be used for design purposes and we describe the fabrication process. In addition, we show how the INFORA can be used to build a tendril-like structure capable of performing grasping tasks.

Nowadays, robots can navigate complex and dynamic environments such as air, water, and different terrain. However, moving into the underground, and especially into the soil, is still a challenge. Soil is a complex environment, and its exploration and monitoring is a crucial aspect in different engineering fields. Although some robotic solutions for mapping the soil are available, none of them can navigate into it. In this work, we propose a new solution for dynamic obstacles detection by embedding a 6-axis force torque sensor into a plant-inspired robot for soil exploration. We measured the forces acting on the apical part of the robot while it penetrates the soil by growing. We tested the system in different configurations, and at different depths. Results show that it is possible to identify the relative position of the obstacle before touching it with the robot. By using the proposed method as control feedback it is possible to move toward the development of novel robotic systems for navigating in complex and dynamic environments, such as the soil.

This paper presents a new material deposition strategy for developing a growing robot capable of building its own body. The growing robot is inspired by plant growth and is based on a 3D printer-like mechanism. The plotting of a filament near the tip allows the forward movement of the robot and results in building a tubular body. A material deposition process is introduced to perform a straight continuous growth as well as a turning behavior in order to permit the navigation of the robot in the environment. Bending is achieved by controlling the filament height in each position of the plotting, lowering or increasing plotting velocity with a position PID control algorithm. We demonstrate that the continuous deposition of the filament allows to obtain homogeneous and robust structures, with a significant improvement of the robot's performance compared to our previous version of the system (i.e., more than 100 N pulling force and 200 N shear force). The current version of the robot can sustain its weight, move efficiently by growing in the environment - both air and soil - and penetrate hard medium (up to 60kPa).

In this paper, we present a study on peculiar plant root movements, named circumnutations, adopted by plants as an efficient strategy to penetrate the soil and implemented in robotic roots to improve their performance in exploration tasks. The robotic root is able to bend and interact with soil owing to a soft actuation mechanism based on the translation of rotary to linear motion by means of helical compression springs. The robotic root integrates a stimulus-oriented behavior combined with circumnutation movements, which leads to an extraordinarily large reduction (more than 80 times) of the force needed for penetration in artificial soil (sawdust) while performing circumnutations with respect to a straightforward movement.

In this paper we propose a soil penetration robotic system inspired by low friction penetration strategies in plant roots. Growth of cells at the root tip deforms soil, while sloughing cells in the cap create an interface between root and soil to reduce root-soil friction during penetration. A simple prototype, inspired by these root features and based on a tubular shaft and a soft continuum skin, was developed. The skin is kept inside the shaft and slips out and slides on its external body. This outward movement of the skin opens the soil in front of the tip and helps the system to penetrate. The skin covering the external body of shaft imitates the role of sloughing cells and provides low-friction interface between soil and shaft. Interaction between the external skin and soil gives to the system self-anchorage capabilities for the penetration. The performances of our robotic system were characterized during penetration in granular soils. The skin-soil interaction was found to be fundamental for 1) displacing the soil in front of the tip and 2) preventing backward movements of the robot by anchoring the posterior body to the soil. In order to exploit these effects some artificial hairs were added along the skin. The increased hair density (0.012 hairs/mm2) resulted in higher penetration depth of robot (about 30%).

Electro-rheological (ER) fluids are smart fluids which can transform into solid-like phase by applying an electric field. This process is reversible and can be strategically used to build fluidic components for innovative soft robots capable of soft locomotion. In this work, we show the potential applications of ER fluids to build valves that simplify design of fluidic based soft robots. We propose the design and development of a composite ER valve, aimed at controlling the flexibility of soft robots bodies by controlling the ER fluid flow. We present how an ad hoc number of such soft components can be embodied in a simple crawling soft robot (Wormbot); in a locomotion mechanism capable of forward motion through rotation; and, in a tendon driven continuum arm. All these embodiments show how simplification of the hydraulic circuits relies on the simple structure of ER valves. Finally, we address preliminary experiments to characterize the behavior of Wormbot in terms of actuation forces.