The high deformability and compliance of soft robots allow safer interaction with the environment. On the other hand, these advantages bring along controllability and predictability challenges which result in loss of force and stiffness output. Such challenges should be addressed in order to improve the overall functional performance and to meet the requirements of real-scenario applications. In this paper, we present a bidirectional in-plane manipulator which consists of two unidirectional fiber-reinforced actuators (FRAs) and a hybrid soft-rigid stiffness control structure (SCS), all of them controlled by air pressure. Both controllability and predictability of the manipulator are enhanced by the hybrid soft-rigid structure. While the FRAs provide positioning and position dependent stiffness, the SCS increases the stiffness of the manipulator without position dependency. The SCS is able to increase the manipulator stiffness by 35%, 30%, and 18%, when one FRA is pressurized at 150 kPa, 75 kPa, and 0 kPa, respectively. Experiments are carried out to present the feasibility of the proposed manipulator.

A novel mechanism for actuating a miniature swimming robot is described, modeled, and experimentally validated. Underwater propulsion is obtained through the interaction of mobile internal permanent magnets that move a number of polymeric flaps arranged around the body of the robot. Due to the flexibility of the proposed swimming mechanism, a different range of performances can be obtained by varying the design features. A simple multiphysics dynamic model was developed in order to predict basic behavior in fluids for different structural parameters of the robot. In order to experimentally verify the proposed mechanism and to validate the model, a prototype of the swimming robot was fabricated. The device is 35 mm in length and 18 mm in width and thickness, and the forward motion is provided by four flaps with an active length of 20 mm. The model was able to correctly predict flap dynamics, thrust, and energy expenditure for magnetic dragging within a spindle-frequency range going from 2 to 5 Hz. Additionally, the model was used to infer robot-thrust variation related to different spindle frequencies and a 25% increase in flap active length. Concerning swimming performance, the proposed technical implementation of the concept was able to achieve 37 mm/s with 4.9% magnetic mechanism efficiency.

In this work, we propose a new concept for locomotion of a miniature jellyfish-like robot based on the interaction of mobile permanent magnets. The robot is 35 mm in length and 15 mm in width, and it incorporates a rotary actuator, a magnetic rotor, several elastic magnetic tails and a polymeric body embedding a wireless microcontroller and power supply. The novel magnetic mechanism is very versatile for numerous applications and can be tailored and adapted on the basis of different specifications. An analytical model of the magnetic mechanism allows to shape the robot design based on the specific application. The working principle of the robot together with the design, prototyping and testing phases are illustrated in this paper.