Inspired by the advantages from natural birds' shape-morphing adapted flight performance, this work investigates how the bioinspired adaptative morph induced inertia variation affects the flight performance of a morphing quad-rotor. Extensive numerical and experimental evaluations on a custom-built morphing quad-rotor that is steered along a predefined path and hovers in the presence of constant wind disturbance were performed and analyzed. Simulation results demonstrate that the smaller quad-rotor exhibits better agility performance due to the compact volume/size and lower weight, while the bigger one appears more flight robustness in a disturbed environment such as windy testing area. Experimental studies further prove that by adaptatively altering its volume/size, our quad-rotor with the bioinspired in-flight morphing behavior can well execute path following tasks in a constrained space without deviating the trajectory when encountering obstacles, as well it can withstand external wind torque through morphing up its volume to therewith increase relevant moment-of-inertia for improving the flight robustness. Compared to the regular scaled aerial vehicles whose volumes' change follows a weight change proportionally, our results also indicate that our in-flight morphing aerial vehicle mechanism (i.e. the quad-rotor morphs the volume but without changing weight/mass) shows more advantages in power efficiency and morphologically adaptative flight capability.

This paper addresses the consensus issue of multiagent systems with both input amplitude and rate constraints. We propose simple yet effective distributed control algorithms that integrate a velocity damping term with nonlinear saturated functions for both undirected and directed graphs. Leveraging the interplay between Barbalat’s lemma and graph theory, we show that all agents can achieve consensus without violating predefined input amplitude and rate constraints through the presented control algorithms. Moreover, we employ the developed framework to solve the rendezvous control problem of quadrotor unmanned aerial vehicles (UAVs) with motion limits. To illustrate and validate our proposed approach, we conduct extensive simulations and comparative experiments. Note to Practitioners —Most existing control methods for multiagent systems achieve consensus but neglect the constraints on the amplitude and rate of the control signal. However, in practice, the control signals are invariably subject to limitations in their amplitude and rate due to factors such as actuator saturation, considerations for ride comfort, and actuator wear. This neglect leads to a degradation in system performance and in severe cases results in the loss of closed-loop stability. This work primarily focuses on developing new control methods that can achieve consensus without violating the predefined input amplitude and rate limitations. The experiments on rendezvous control of quadrotor UAVs show the practical applicability of the presented algorithms, which yield satisfactory control performance as verified by theoretical analysis. This research contributes to the advancement of distributed control for multiagent systems, particularly in scenarios where input constraints are a critical consideration.

Inspired by natural earthworms’ locomotion mechanism, this paper investigates how the earthworm’s muscle works and presents the approach to mimic segmental muscle by employing rigid elements-based morphing structures. Specifically, the proposed earthworm-like robot employs a class of 2D rigid elements and their array to achieve programable bidirectional 3D deformation, making the formed mechanism precisely controllable and work effectively, thus facilitating the robot’s peristaltic locomotion more efficient. To comprehensively investigate the morphing structure and its formed earthworm-like robot, the kinematics, mechanics, deformation-dependent locomotion framework with its adapted model, as well as the factors that affect the optimal velocity are developed and presented. Extensive simulations and experiments on the proposed robot are performed. The results verify the effectiveness of the morphing mechanism and it enabled earthworm-like robot and the consistency between the proposed locomotion model and the practical tests. The results also prove that regardless of the condition of the contact surface, the optimal phase shift angle can be achieved when each segment approximately contracts and relaxes once in one wavelength period. Our developed prototype achieves a speed of multiple body lengths per minute, which is very competitive compared with most developed earthworm-like robots.

Electrotactile displays can open a new sensory substitution channel to be utilized in a vast array of applications. But there are still challenges in different aspects of such systems. One of the most crucial concerns, is the effects of receptor fatigue. Our tests show that during prolonged exposure of receptors to the electrical signals, their sensitivity to the signal level changes gradually and adjustments in the signal's power are required to keep the receptors is the stimulated state. This was confirmed by monitoring the electrical current passing through the skin and calculating the corresponding impedance. More interestingly, the rates of the impedance changes are different for each part of the skin, indicating inconsistent rates of receptor fatigue for each region of the skin. These electrical properties of the skin were addressed in this research for the purpose of rendering consistent sensations for the users regardless of the person or skin conditions. To solve these challenges, two methods are employed: a voltage control system based on pulse-width modulation is used to adjust the signal power; and Kalman filtering is used to predict impedance changes in advance and supply the skin with the proper signal. The result is a self-contained automated system capable of managing the signal power for any user at any given time or skin condition.

This paper develops and experimentally validates a 3D-printed snake robot prototype. Its structure is designed to allocate limited room for each functional module (including an external power module, battery power module, the wireless control and transmission module and some detective sensors), so as to ensure the snake robot works in different environments. In order to control and track the snake robot, a low-cost MEMS-IMU (micro-electro-mechanical systems inertial measurement unit)-based snake robot motion tracking system is developed. Three algorithms (low-pass filter, baseline calibration, and Kalman filter) are used to eliminate noise from IMU’s acceleration data, thus minimizing the noise influence to tracking accuracy. Through signal processing, the IMU acceleration data can be effectively used for motion tracking. The result from the video tracking software is employed as a reference for comparison, so as to evaluate the motion tracking algorithm efficiency. The comparison results demonstrate high efficiency of the proposed IMU-based motion tracking algorithm.

This paper focuses on designing, kinematically and dynamically characterizing a novel deformable quad-rotor that is based on the scissor-like foldable mechanisms. Inspired by morphological adaptation of birds during flight, the quad-rotor allows that its volume can be varied to dynamically adapt complex environments and spaces. The advantages of such mechanism are twofold following the scenario, that is, the quad-rotor can stably fly with a big volume/size and can also switch to a smaller volume for a swift flight in response to the changes of the environments and spaces. It therefore is capable of efficiently avoiding obstacles, stably passing through narrow spaces, and resisting certain-extent wind effects. To generate the controllable deformation, the actuated angulated scissor elements in the structure play an important role. In this paper, the scissor element design, its actuation mechanism, and volume deformation of the new quad-rotor are presented in detail. Simulations and experiments are then conducted to validate the controlled deformation as well as to investigate the deformation elicited effects to the activated quad-rotor airframe and its aerodynamics. The results demonstrate the effectiveness of the proposed deformable quad-rotor, and prove that it enables excellent volume deformation performance, good flight adaptation, as well as minimal aerodynamics influences during deforming.