In logistics applications, the vision-based technology for grasping target objects in the air is relatively mature. However, when operating across the air and water such as grasping marine products from the water, the visual information collected by the camera will be disturbed by ripples and bubbles on the water surface, resulting in low grasping efficiency. Therefore, we introduce a grasping strategy based on single-visual mapping for multi-step (SVMMS) strategy to achieve cross-medium operations involving stacked objects. Specifically, we design a multifunctional integrated Deep Q-learning-based network model to extract visual features from the scene to effectively detect stacked objects and outputs their hierarchical relationships. Moreover, we quantify the underlying relationship between motion logic during action execution and changes in RGB-D during action execution to help the robot achieve efficient and collision-free operations. Our approach also incorporates a time-series design with prioritized experience replay to globally optimize the action sequence. Additionally, we propose a novel sim2real method by combining domain randomization to address the difference in object sizes between the simulation and the real world. Extensive experiments in both simulation and physical environments show that SVMMS-Grasp significantly outperforms existing methods in terms of task success rate, stability, and operational efficiency.

High maneuverability is essential to the autonomous operation of underwater robots. To achieve real-time maneuvering motion, the control strategy must take into account nonlinear hydrodynamic effects, which are extremely difficult to accurately capture during motion and therefore a balance must be struck between accuracy and real-time computational efficiency. Therefore, this paper proposes a data-driven approach to model the dynamics of the underwater robot using Sparse Identification of Nonlinear Dynamics (SINDy). Compared with existing works, our method does not require any physical prior knowledge and only uses a short period of onboard sensor data. Subsequently, the learned dynamic model is incorporated into a model predictive controller (MPC) to enable precise attitude control. Finally, the proposed method is implemented on our developed fully vectored propulsion underwater robot, and a series of attitude tracking experiments are conducted in an indoor water tank. Experimental results reveal that our approach significantly improves the model accuracy and reduces the attitude tracking errors by over 79% at a control frequency of 20 Hz, which proves the effectiveness and real-time performance of the method.

Morphing quadrotors that can be potentially applied to confined spaces such as warehouses, tanks, and pipelines have flourished in recent years. Most work has focused on the mechanical feasibility of the morphing systems and high-level flight controller design, with limited discussions on low-level control. In this paper, a constrained model predictive control (MPC) is proposed and applied to solve the attitude control problem of a morphing quadrotor. Prior to controller design, a custom-built morphing quadrotor is introduced with the kinematic and dynamic models established and corresponding issues and challenges presented. In the controller, to eliminate the steady-state error, an embedded integrator is adopted by exploiting the differential variables; then, the constraints of the morphing quadrotor are incorporated into the MPC formulation to simulate real flight conditions, and an orthonormal function is employed to approximate the control input sequences in the controller to alleviate the computational burden. In the comparative studies, several scenarios are considered to demonstrate the effectiveness of the proposed control strategy in attitude control.

Due to the low motion efficiency and maneuver-ability of underwater robots with six degrees of freedom, it is challenging for them to respond quickly to the attitude requirements during underwater autonomous manipulation. This paper presents a novel autonomous underwater robot with fully vectored propulsion and a model predictive control method to achieve more agile and efficient movements autonomously. In detail, we first design a robot with eight vector-distributed thruster layouts for fully vectored propulsion and construct the software architecture based on the robot operating system (ROS). Then, we establish the hydrodynamic model by adopting the Fossen approach and construct a 13-dimensional system state-space equation, which is discretized using the explicit fourth-order Runge-Kutta method. To achieve autonomous manipulation, model predictive control is employed along with physical constraints of the custom-built robot to enable real-time prediction and optimization of the robot’s states for control purposes. Finally, numerical simulations and experiments of the Point-to-Point Motion are conducted to test the robot’s performance. Experimental results reveal that the average error of each direction is 0.0027 m, 0.0031 m, and 0.0368 m in the x-axis, y-axis, and z-axis, respectively, and 0.8502°, 2.1941°, 0.2408° corresponding to three attitude angles, which verify the performance of employing MPC to control an autonomous underwater robot with fully vectored propulsion.

Current multi-modal hybrid robots with flight and wheeled modes have fallen into the dilemma that they can only avoid obstacles by re-taking off when encountering obstacles due to the poor performance of wheeled obstacle-crossing. To tackle this problem, this paper presents a novel multi-modal hybrid robot with the ability to actively adjust the wheel’s size, which is inspired by the behavior of the turtle’s legs when it encounters obstacles, to enhance the traversal performance. In detail, we describe the hardware design that allows the robot to achieve a modal switch between flight and wheeled modes through foldable structures and variable wheel diameters; then, we present the architecture to control these two morphing mechanisms. After that, we establish the theoretical kinematic models for both the foldable arm and variable wheel and carry out extensive experiments to test the performance of the foldable arm, the variable-diameter wheel, as well as the traversal performance of the robot. Experimental results show that the proposed multimodal robot can realize the function of a quadrotor, respond quickly with full-scale folding within 0.9 s, climb a maximum slope of 36°, and traverse narrow passageways, which exhibit superior mobility and environmental adaptability.

This paper presents our comparative study on how the flight performances of an in-flight morphing quad-rotor are affected by the morph induced inertia variation. A custom-built in-flight morphing quad-rotor was employed in numerical and experimental tests for the study and analysis. In these tests, the quad-rotor is controlled to follow a predefined path and/or to hover in an environment with the constant wind disturbance. Our numerical results indicate that the morphing-size-down quad-rotor exhibits more agile in flight attributed to the compact volume/size, while the big-size one shows more flight stability in a disturbed and windy environment. Compared to regular scaled aerial vehicles whose volume/size changes follow a weight change proportionally, the numerical results reveal that our morphing quad-rotor that changes its volume with identical mass can acquire more merits towards high flight performances. Experimental validations further prove that through adaptatively transform its size in a complex and constrained environment, the in-flight morphing quad-rotor is not only capable of well performing path following tasks when encountering obstacles on the path or nearby the path, but also enhances the flight performance of withstanding external torques by extending its size so as to increase its moment-of-inertia. In summary, our in-flight morphing quad-rotor can acquire higher flight performances by adaptatively morphing when flying in complex environments.

In this paper, we investigate the consensus problem of multiple unmanned aerial vehicles (UAVs) in the presence of environmental constraints under a general communication topology containing a directed spanning tree. First, based on a position transformation function, we propose a novel dynamic reference position and yaw angle for each UAV to cope with both the asymmetric topology and the constraints. Then, the backstepping-like design methodology is presented to derive a local tracking controller for each UAV such that its position and yaw angle can converge to the reference ones. The proposed protocol is distributed in the sense that, the input update of each UAV dynamically relies only on local state information from its neighborhood set and the constraints, and it does not require any additional centralized information. It is demonstrated that under the proposed protocol, all UAVs reach consensus without violation of the environmental constraints. Finally, simulation and experimental results are provided to demonstrate the performance of the protocol.

In this paper, a simple tracking control scheme is proposed for quadrotor systems with uncertain dynamics. It precludes the necessity for prohibitive analytic computation of the derivatives of the desired (virtual) attitude that is typically employed in controlling quadrotor systems. Moreover, this control scheme is approximation-free in the sense that it does not incorporate any adaptive laws, observers, or command filters to compensate for unknown parameters in the dynamics and the absence of the analytic differentiation, thus exhibiting remarkably low complexity levels and making its implementation straightforward. The thrust saturation is approached in the position control design which also enables the singularity in desired attitude extraction to be avoided entirely. It is demonstrated that based on the proposed scheme, the tracking errors can be made arbitrarily small by appropriately selecting design parameters. Extensive simulations and experiments are performed to verify the effectiveness of our scheme.

Inspired by the inchworm locomotion mechanism, this paper presents our recently developed self-deformable capsule-like robot. The robot has the actuated deformation capability that relies on a novel rigid elements-based morphing structure (REMS) and its soft actuation mechanisms. When the robot deforms, it generates the crawling locomotion behavior and thus friction waves between the robot and contact surface to facilitate the inchworm-like crawling movement. The paper starts reviewing the deformable properties of natural biological entities like capsules, presents state of the art of the current capsule-like robots, and details the bio-inspired design of the self-deformable capsule-like robot by describing the model of robot kinematics and its locomotion mechanism. Both simulation and experimental results validate the excellent performance of this capsule-like robot. The developed self-deformable capsule-like robot has the advantage of crawling on varied surfaces and it also has the capabilities to crawl in a variety of narrow pipes based on the deformation elicited locomotion nature of the robot.

The paper presents the development of a novel deformable quad-rotor enabled aerial gripper. The mechanism of our deformable quad-rotor is based on simultaneous expansion or contraction of the quad-rotor body, which is generated by controlling a rigid elements based morphing structure (REMS). Such deformation results in a highly deformable quad-rotor that can not only perform morphological adaptation in response to environmental changes and obstacles, but also improve the flight performance by contracting to facilitate the agility/maneuverability or by expanding to enhance the stability. Meanwhile, inspired by the wasp grasping behavior, such controllable expansion and contraction from the REMS ingeniously enable a new function of aerial gripper. In this paper, we start to detail the mechanism and design of the REMS based deformable quad-rotor, then present the quad-rotor deformation enabled aerial gripper design, its dynamics modeling, the grasping function and analysis. The simulation was conducted in order to graphically show the elicited aerodynamic flow situation during expansion or contraction of the quad-rotor with and without carrying payload. Experiments were further implemented to validate the grasping function of the gripper and the flight performance of the quad-rotor. Finally, two case studies on the new aerial gripper were performed. All results demonstrate the excellent performance of the deformable quad-rotor enabled aerial gripper, that is, it has the advantages of both flight maneuverability and grasping capability during performing tasks.

Inspired by natural earthworm locomotion behavior and segmental muscle motion mechanism, this paper presents our recently developed compliant modular earthwormlike robot with the novel segmental muscle-mimetic design unit that is capable of efficiently mimicking earthworms' segmental muscle contraction and extension functions. The new class of segmental muscle-mimetic design unit relies on the curvature of scissor mechanisms that can be extended and contracted smoothly through controlled servo motors. The paper starts reviewing natural earthworm locomotion behavior, details the bio-inspired concept and design of both the segmental muscle-mimetic unit and the multi-segment earthworm-like robot prototype, and then presents the robot's locomotion models and analysis of the locomotion efficiency of the robot. Simulation and experimental results validate that both the design and the prototyped multi-segment earthworm-like robot have the excellent performance such as its muscle-like contractions behavior, peristaltic locomotion behavior, and highly competitive moving speed.

To improve the obstacle surmounting performance of the quad-rotor vehicle, this paper focuses on designing, kinematically and dynamically characterizing a novel deformable quad-rotor that is based on the scissor-like foldable structures. The foldable structure allows that the volume of the quad-rotor can be tuned to dynamically adapt variously sized obstacles and small spaces. To generate the controllable deformation, the actuated angulated elements that are the essential components of the scissor-like foldable structure play an important role. The element design, its actuation mechanism and the corresponding configuration patterns for the new quad-rotor are presented in the paper in detail. The simulations on deformation properties and obstacle surmounting ability are then performed to verify the deformation capability of the structure. In addition, experiments were extensively conducted to test the controlled deformation of the structure as well to investigate the deformation induced effects to the activated quad-rotor airframe and its aerodynamics. All implementation results validate the effectiveness of the proposed deformable quad-rotor design, that is, it enables the new quad-rotor having excellent obstacle surmounting performance, adaptability, flight maneuverability, as well as minimal aerodynamics influences during deforming.