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In material handling, numerous solutions have been proposed to enhance the flexibility and adaptability of transport systems. Among these solutions, smart surfaces stand out as one of the most interesting responses, utilizing an array of actuators for common feeding tasks. The current paper focuses on a novel system within this category, notable for its distinguishing factor of being underactuated. With this characteristic, the concept leads to a simplified cost-effective design and a not actively driven functioning, leveraging gravity or object own velocity to manipulate the material flow maintaining top class performances, as the sorting rate reaches 4000 pcs/h. Specifically, the article begins with an introduction of the concept design and its digital model, followed by a description of the experimental setup built to test the surface's functionality and evaluate the predictions of the virtual counterpart. On top of that, a method to determine the essential parameters for the surface simulation is proposed and applied. As a result, the prototype successfully completed the three main intralogistic tasks experimented, i.e., sorting, slowing, and stopping of packages. Lastly, the digital model outcomes of the same operations were computed and compared with the measured results, demonstrating an accuracy of prediction with displacements and time errors below 7%. [ABSTRACT FROM AUTHOR]

On-Orbit Servicing is increasingly crucial with the growing number of spacecraft. The foundation for On-orbit servicing is space docking mechanisms. As On-Orbit Servicing tasks become more complex, the demands for docking capture mechanisms increase in both function and performance. Therefore, it is crucial to design a docking mechanism with a large tolerance. Among various docking capture mechanisms, the multi-claw capture mechanism has the advantages of low impact and reliable capture. This paper analyzes the Common Berthing Mechanism and a docking mechanism with an underactuated two-degree-of-freedom claw-type capture mechanism as its core is proposed. Subsequently, this paper provided a detailed design of the mechanism based on the principle of underactuated capture. Furthermore, this article conducts numerical analyses of key mechanisms such as the capture mechanism and guide mechanism in the design process, verifying the functionality of the mechanisms. After completing the analysis of capturing dynamics, the tolerance ability of the mechanism was also verified, various key parameters were determined, and the parameters of components such as the torsion spring were also determined. Finally, the prototype of the proposed docking mechanism is developed, and the experiment is completed to validate its functional principle and tolerance capability. • This paper presents a docking mechanism for large spacecraft (weighing over 8 tons). • The mechanism employs an underactuated two-degree-of-freedom claw-type capture mechanism. • Simulations and simple laboratory tests were performed for design and validation. • The maximum lateral tolerance of this mechanism reaches 220 mm. • The developed port has reached a TRL of about 4. [ABSTRACT FROM AUTHOR]

The snake-like robot has superior flexibility in complex and extreme environments due to its long and narrow robotic arm and redundant degrees of freedom. Based on the structure of the underactuated snake-arm robot, two trajectory tracking algorithms based on equivalent rod length and equivalent virtual joint are proposed to realize the tracking of the target curve by the snake-arm robot and meet the motion control requirements of the snake-arm robot. Finally, a snake-like robot prototype with an arm length of 1 075 mm and seven joint units is designed and the trajectory tracking experiment is carried out. The results show that the snake-like robot can easily pass through a narrow pipe with a diameter of more than 90 mm. The smooth and vibration-free motion process verifies the correctness of the trajectory control algorithm and the rationality of the structural design. [ABSTRACT FROM AUTHOR]

Differential flat underactuated robots have fewer actuators than degrees of freedom (DOFs). This characteristic makes it possible to design light and cost-effective robots with great dexterity. The primary challenge associated with these robots lies in effectively controlling the passive joint, in particular, when collisions with obstacles in the workspace have to be avoided. Most of the previous research focused on point-to-point motions without any control on the actual robot trajectory. In this work, a new method is presented to plan trajectories that include one or more via points. In this way, the underactuated robot can avoid the obstacles in the workspace, similarly to traditional fully actuated robots. First, a trajectory planning strategy is analytically described; then, numerical results are presented. The numerical results show the effects of the via points and of the order of the polynomials adopted to define the motion laws. In addition, experimental tests performed on a two-DOF underactuated robot are presented, and their results validate the proposed method. [ABSTRACT FROM AUTHOR]

Humanoid grasping is a critical ability for anthropomorphic hand, and plays a significant role in the development of humanoid robots. In this article, we present a deep learning-based control framework for humanoid grasping, incorporating the dynamic contact process among the anthropomorphic hand, the object, and the environment. This method efficiently eliminates the constraints imposed by inaccessible grasping points on both the contact surface of the object and the table surface. To mimic human-like grasping movements, an underactuated anthropomorphic hand is utilized, which is designed based on human hand data. The utilization of hand gestures, rather than controlling each motor separately, has significantly decreased the control dimensionality. Additionally, a deep learning framework is used to select gestures and grasp actions. Our methodology, proven both in simulation and on real robot, exceeds the performance of static analysis-based methods, as measured by the standard grasp metric Q^. It expands the range of objects the system can handle, effectively grasping thin items such as cards on tables, a task beyond the capabilities of previous methodologies. [ABSTRACT FROM AUTHOR]

This paper investigates the attitude controller design for an underactuated reusable launch vehicle (RLV) with nonminimum phase property. To address the nonminimum phase problem, a zero dynamic active suppression control (ZDASC) method based on Byrnes-Isidori (B-I) standard model transformation is proposed. First, a computable criterion for the nonminimum phase property of RLVs is presented, by which we can effectively determine the nonminimum phase property based on aerodynamic parameters in the RLV model. Second, an augmented system consisting of internal dynamics and dynamic compensator is constructed, and a ZDASC method is proposed for the RLV attitude control system with nonminimum phase property, which can enable adaptive stabilization of the RLV’s zero dynamics under different operating conditions and uncertainties. ZDASC achieves output accurate tracking without solving the ideal internal dynamics, which reduces the computational complexity and enhances system robustness. Finally, simulation results of the RLV attitude control are provided to verify the effectiveness and robustness of the proposed controller in tracking the guidance commands as well as stabilizing the internal dynamics.

Bipedal robots have long been a focal point of robotics research with an unwavering emphasis on platform stability. Achieving stability necessitates meticulous design considerations at every stage, encompassing resilience against environmental disturbances and the inevitable wear associated with various tasks. In pursuit of these objectives, here, the bipedal L04 Robot is introduced. The L04 Robot employs a groundbreaking approach by compactly enclosing the hip joints in all directions and employing a coupled joint design. This innovative approach allows the robot to attain the traditional 6 degrees of freedom in the hip joint while using only four motors. This design not only enhances energy efficiency and battery life but also safeguards all vulnerable motor reducers. Moreover, the double-slider leg design enables the robot to simulate knee bending and leg height adjustment through leg extension. This simulation can be mathematically modeled as a linear inverted pendulum (LIP), rendering the L04 Robot a versatile platform for research into bipedal robot motion control. A dynamic analysis of the bipedal robot based on this structural innovation is conducted accordingly. The design of motion control laws for forward, backward, and lateral movements are also presented. Both simulation and physical experiments corroborate the excellent bipedal walking performance, affirming the stability and superior walking capabilities of the L04 Robot. [ABSTRACT FROM AUTHOR]

In a competitive scenario, to effectively utilise the resources and battery power, the communication and control update has to be minimised to a great extent. In this work, an event-triggered coupled controller with linearly varying event threshold is proposed for setpoint tracking of USV, which optimally utilises the resources with the help of a simple interactive control loop in a classical control framework. The gains of coupled controller are optimised using differential evolution (DE) algorithm. This research analyses the effect of various classes of event thresholds on the number of triggering instants and proposes a linear event threshold (LET) for a reduced number of control triggers. In addition, the relative percentage difference in energy consumption of the USV for different cases of event-triggered control are compared with that of the USV without event-triggered control. The simulation results establish the superiority of the linear event-triggered control in reducing the control update significantly with satisfactory performance in setpoint tracking without compromising stability. [ABSTRACT FROM AUTHOR]

In order to solve the problem of poor flexibility of existing picking manipulators, a picking manipulator with a wrist joint has been designed, the wrist is capable of rotating 45° forward and backward around the x and y axes. Firstly, ANSYS was used to simulate the performance of different hoses under different conditions, and finally a 4*6mm PVC hose was selected to replace the internal cardan joint as the transmission component. Secondly, the wrist structure was optimized using genetic algorithm to reduce the tendon rope variation differences to 0.31mm and 0.24mm. Finally, the results of orchard picking experiments indicate that the endeffector rotation of 720° can ensure that the fruit stalks can be unscrewed, the time required to complete the picking is 1.6s, and the overall picking success rate was 100%. After 9 days of placing the harvested fruit, both the flesh and skin are intact, indicating that the manipulators can complete the non-destructive picking operation. [ABSTRACT FROM AUTHOR]

Differential flat underactuated robots have fewer actuators than degrees of freedom (DOFs). This characteristic makes it possible to design light and cost-effective robots with great dexterity. The primary challenge associated with these robots lies in effectively controlling the passive joint, in particular, when collisions with obstacles in the workspace have to be avoided. Most of the previous research focused on point-to-point motions without any control on the actual robot trajectory. In this work, a new method is presented to plan trajectories that include one or more via points. In this way, the underactuated robot can avoid the obstacles in the workspace, similarly to traditional fully actuated robots. First, a trajectory planning strategy is analytically described; then, numerical results are presented. The numerical results show the effects of the via points and of the order of the polynomials adopted to define the motion laws. In addition, experimental tests performed on a two-DOF underactuated robot are presented, and their results validate the proposed method.

Granular environments, such as sand, are one of the most challenging substrates for robots to move within due to large depth‐dependent forces, unpredictable fluid/solid resistance forces, and limited sensing capabilities. An untethered robot is presented, inspired by biological diggers like sea turtles, which utilize underactuated appendages to enable propulsion and obstacle sensing in granular environments. To guide the robot's design, experiments are conducted on test appendages to identify the morphological and actuation parameters for forward thrust generation. Obstacle sensing is observed in granular media by measuring the increased force on the moving appendage caused by changes in the granular flow around it. These results are integrated into an untethered robot capable of subsurface locomotion in a controlled granular bed like natural, loosely packed sand. The robot achieves subsurface "swimming" at a speed of 1.2 mm s−1, at a depth of 127 mm, faster than any other reported untethered robot at this depth, while also detecting obstacles during locomotion via force sensors embedded in the appendages. Finally, subsurface robot locomotion in natural sand at the beach is demonstrated, a feat no other robot has accomplished, showcasing how underactuated structures enable movement and sensing in granular environments with limited limb control. [ABSTRACT FROM AUTHOR]

Today, most humanoid mechanical fingers use an underactuated mechanism driven by linkages or tendons, with only a single and fixed grasping trajectory. This paper proposes a new multi-mode humanoid finger mechanism based on linkage and tendon fusion transmission, which is embedded with an adjustable-length tendon mechanism to achieve three types of grasping mode. The structural parameters of the mechanism are optimized according to the kinematic and static models. Furthermore, a discussion was conducted on how to set the speed ratio of the linkage driving motor and the tendon driving motor to adjust the length and tension of the tendon, in order to achieve the switching of the shape-adaptive, coupled-adaptive, and variable coupling-adaptive grasping modes. Finally, the multi-mode functionality of the proposed finger mechanism was verified through multiple grasping experiments. [ABSTRACT FROM AUTHOR]

Since its introduction in the late 1980s, passivity-based control (PBC) has proven to be successful in controlling many robotic systems. The connection between stability and passivity theory is the most attractive feature of controllers designed using this methodology. However, the need to solve nonlinear partial differential equations (PDE) in closed-form has been a major challenge in applying PBC to general robotic systems. Here, we introduce a systematic approach to design controllers for a class of underactuated mechanical systems based on interconnection and damping assignment. Exploiting the universal approximation capability of neural networks, we formulate a data-driven optimisation problem that discovers solutions to the required PDEs automatically. Our approach does not destroy the passivity structure, preserving the inherent stability properties. We demonstrate the efficacy of our framework on two benchmark problems: the inertia wheel pendulum and the ball and beam system. [ABSTRACT FROM AUTHOR]

Designing a controller for the cooperative transport of a payload using quadcopter-type unmanned aerial vehicles (UAVs) is a very challenging task in control theory because these vehicles are underactuated mechanical systems. This paper presents a novel robust adaptive formation control design for the cooperative transport of a suspended payload by ropes using two underactuated quadcopters in the presence of external disturbances and parametric uncertainties. The structure of the proposed controller is divided into two subsystems: fully actuated and underactuated. An integral sliding mode adaptive control strategy is proposed for the fully actuated subsystem, and for the underactuated subsystem, an adaptive control strategy based on the combination of Backstepping and sliding mode is proposed. Then, the control parameters of the sliding surfaces of both control subsystems are adaptively tuned by a neural network. In addition, to improve the robustness of the proposed controller, a disturbance observer is incorporated to estimate and compensate for the lumped disturbances. The asymptotic stability of the cooperative transport system is verified with the Lyapunov theorem. Finally, numerical simulations are performed in MATLAB/Simulink environment, and the results show that the proposed controller successfully transports the payload safely and without oscillations. Moreover, the desired formation pattern is maintained throughout the flight task, even with external disturbances and parametric uncertainties.

The study presents an adaptive robust control method for the Pendubot subjects to matched and mismatched uncertainty. First, the control task is formatted as a reduced-dimension equality constraint of the system states. To handle the matched and mismatched uncertainties, an orthogonal decomposition method is employed to make the mismatched part disappear after decomposition. Based on the above, an adaptive robust control law based on constraint-following is devised. By the Lyapunov approach, it is rigorously proven that the proposed approach ensures the uniform boundedness and uniform ultimate boundedness of the closed-loop control system and thus renders approximate constraint-following, regardless of uncertainty. Simulation and experimental results are provided and discussed, demonstrating the good performance of the proposed approach. [ABSTRACT FROM AUTHOR]

Featured Application: The research presented herein could be used mostly in warehouse logistics transport activities in smart manufacturing. A proposed optimized model for the trajectory tracking control of a wheeled inverted pendulum robot (WIPR) system is presented in this study, which addresses the problem of poor trajectory tracking performance in the presence of unknown disturbances due to the nonlinear and underactuated characteristics of the system. First, a kinematic controller was used to track a reference trajectory and generate a control law that specifies the desired forward and rotation speeds of the system. Next, a nonlinear disturbance observer (NDO) was designed to enhance the system's robustness to external disturbances and improve its tracking performance. Then, the coupled system state variables were decoupled into two subsystems: a forward rotation subsystem and a tilt angle velocity subsystem. An improved hierarchical sliding mode controller was designed to control these subsystems separately. Finally, simulation experiments were conducted to compare the proposed method with a common sliding mode control approach. The simulation results demonstrate that the proposed method achieves better tracking performance in the presence of unknown disturbances. [ABSTRACT FROM AUTHOR]

Granular environments, such as sand, are one of the most challenging substrates for robots to move within due to large depth‐dependent forces, unpredictable fluid/solid resistance forces, and limited sensing capabilities. An untethered robot is presented, inspired by biological diggers like sea turtles, which utilize underactuated appendages to enable propulsion and obstacle sensing in granular environments. To guide the robot's design, experiments are conducted on test appendages to identify the morphological and actuation parameters for forward thrust generation. Obstacle sensing is observed in granular media by measuring the increased force on the moving appendage caused by changes in the granular flow around it. These results are integrated into an untethered robot capable of subsurface locomotion in a controlled granular bed like natural, loosely packed sand. The robot achieves subsurface “swimming” at a speed of 1.2 mm s−1, at a depth of 127 mm, faster than any other reported untethered robot at this depth, while also detecting obstacles during locomotion via force sensors embedded in the appendages. Finally, subsurface robot locomotion in natural sand at the beach is demonstrated, a feat no other robot has accomplished, showcasing how underactuated structures enable movement and sensing in granular environments with limited limb control.

Bipedal robots have long been a focal point of robotics research with an unwavering emphasis on platform stability. Achieving stability necessitates meticulous design considerations at every stage, encompassing resilience against environmental disturbances and the inevitable wear associated with various tasks. In pursuit of these objectives, here, the bipedal L04 Robot is introduced. The L04 Robot employs a groundbreaking approach by compactly enclosing the hip joints in all directions and employing a coupled joint design. This innovative approach allows the robot to attain the traditional 6 degrees of freedom in the hip joint while using only four motors. This design not only enhances energy efficiency and battery life but also safeguards all vulnerable motor reducers. Moreover, the double-slider leg design enables the robot to simulate knee bending and leg height adjustment through leg extension. This simulation can be mathematically modeled as a linear inverted pendulum (LIP), rendering the L04 Robot a versatile platform for research into bipedal robot motion control. A dynamic analysis of the bipedal robot based on this structural innovation is conducted accordingly. The design of motion control laws for forward, backward, and lateral movements are also presented. Both simulation and physical experiments corroborate the excellent bipedal walking performance, affirming the stability and superior walking capabilities of the L04 Robot.

Modern industrial applications of robotics such as small-series production and automated warehousing require versatile grippers, i.e., grippers that can pick up the widest possible variety of objects. These objects must often be grasped or placed inside a container, which limits the size of the gripper. In this article, we propose to combine the two most popular gripper technologies in order to maximise versatility: finger grippers and suction-cup (vacuum) grippers. Many researchers and a few companies have followed this same idea in the past, but their gripper designs are often overly complex or too bulky to pick up objects inside containers. Here, we develop a gripper where the suction cup is lodged inside the palm of a two-finger robotic hand. The suction cup is mounted on a retractile rod that can extend to pick up objects inside containers without interference from the two fingers. A single actuator drives both the finger and sliding-rod motions so as to minimise the gripper complexity. The opening and closing sequence of the gripper is achieved by using a planetary gear train as transmission between the actuator, the fingers and the suction cup sliding mechanism. Special attention is paid to minimise the overall gripper size; its diameter being kept to 75 mm, which is that of the end link of the common UR5 robot. A prototype of the gripper is built and its versatility is demonstrated in a short accompanying video.

As the working tool of the robot, the importance of the gripper becomes more prominent with the extensive use of the robot. This paper proposes a new type of underactuated universal gripper that can be applied to handle lightweight parts of any shape. It integrates a crank train and a four-bar mechanism to grasp objects. The kinematics and statics analysis of the proposed gripper were carried out; and in this paper, we briefly introduce the concept and control system design. Then, the motion characteristics and grasping ability of the underactuated gripper are presented. A prototype of the gripper was designed and manufactured based on the simulation analysis, and relevant grasping experiments were carried out. The experimental results verify that the proposed universal gripper has the advantages of safe design, easy manufacturing, effective gripping, and stable holding of objects. [ABSTRACT FROM AUTHOR]

An investigation of the auto-berthing problem for underactuated surface vessels is presented, considering dynamic uncertainties, finite time, transmission load, and environmental disturbance constraints. It is proposed to integrate the finite time control technology with the event-triggered mechanism input algorithm to develop a novel control scheme. Applying the differential homeomorphism coordinate method transforms the vessel into a standard integral cascade form to solve the underactuated problem. A finite-time technology and an event-triggered technology are then used to save time for the berthing vessel, decrease the transmission burden between the controller and vessel, and reduce the acting frequency of the actuator. Furthermore, the radial basis function network(RBF) is employed to approximate unknown nonlinear functions, and minimum learning parameters(MLP) are introduced to reduce computational complexity. Based on the Lyapunov stability theory, a sufficient effort has been made to verify the stability of the closed-loop system. The simulation results demonstrate the effectiveness of the proposed scheme.

This article dwells on two technical aspects, the design and implementation of an upgraded version of the differential shape-memory alloy–based revolute actuator/rotary actuating mechanism for stabilization and position control of a two-degree-of-freedom centrally hinged ball on beam system. The actuator is configured with differential and inclined placement of shape-memory alloy springs to provide bidirectional angular shift. The shape-memory alloy spring actuator occupies a smaller space and provides more extensive reformation with justifiable actuation force than an equally able shape-memory alloy wire. The cross or diagonal architecture of shape-memory alloy springs provides force amplification and reduces the actuator's control effort. The shape-memory alloy spring–embodied actuator's function is exemplified by the highly dynamic underactuated custom-designed ball balancing system. The ball position control is experimentally demonstrated by cascade control using the control laws that have been unattempted for shape-memory alloy actuated systems; the ball is positioned with linear (integer-order and fractional-order) proportional–integral–derivative controllers optimized with genetic algorithm and particle swarm optimization at the outer/primary loop. Angular control of the shape-memory alloy actuated beam is obtained with nonlinear (integer-order and fractional-order sliding mode control) control algorithms in the inner/secondary loop. [ABSTRACT FROM AUTHOR]

The loss of hand functions in upper limb amputees severely restricts their mobility in daily life. Wearing a humanoid prosthetic hand would be an effective way of restoring lost hand functions. In a prosthetic hand design, replicating the natural and dexterous grasping functions with a few actuators remains a big challenge. In this study, a function-oriented optimization design (FOD) method is proposed for the design of a tendon-driven humanoid prosthetic hand. An optimization function of different functional conditions of full-phalanx contact, total contact force, and force isotropy was constructed based on the kinetostatic model of a prosthetic finger for the evaluation of grasping performance. Using a genetic algorithm, the optimal geometric parameters of the prosthetic finger could be determined for specific functional requirements. Optimal results reveal that the structure of the prosthetic finger is significantly different when designed for different functional requirements and grasping target sizes. A prosthetic finger was fabricated and tested with grasping experiments. The mean absolute percentage error between the theoretical value and the experimental result is less than 10%, demonstrating that the kinetostatic model of the prosthetic finger is effective and makes the FOD method possible. This study suggests that the FOD method enables the systematic evaluation of grasping performance for prosthetic hands in the design stage, which could improve the design efficiency and help prosthetic hands meet the design requirements. [ABSTRACT FROM AUTHOR]

Today, most humanoid mechanical fingers use an underactuated mechanism driven by linkages or tendons, with only a single and fixed grasping trajectory. This paper proposes a new multi-mode humanoid finger mechanism based on linkage and tendon fusion transmission, which is embedded with an adjustable-length tendon mechanism to achieve three types of grasping mode. The structural parameters of the mechanism are optimized according to the kinematic and static models. Furthermore, a discussion was conducted on how to set the speed ratio of the linkage driving motor and the tendon driving motor to adjust the length and tension of the tendon, in order to achieve the switching of the shape-adaptive, coupled-adaptive, and variable coupling-adaptive grasping modes. Finally, the multi-mode functionality of the proposed finger mechanism was verified through multiple grasping experiments.

• An under-actuated snake robot is designed based on cable traction. • The motion of the under-actuated snake robot is controlled based on iterative tractrix. • Realize the whole process trajectory control for the under-actuated snake robot. • The algorithm can satisfy the online or offline control of snake robots. This article proposes an adaptive trajectory control method for under-actuated snake robots by simplifying the control and actuation systems of hyper-redundant robots. The under-actuated joints are formed by controlling the spatial rotation angles of multiple rigid joints in the joint group in order for them to synchronize. Based on the under-actuated configuration, a trajectory control algorithm is proposed and includes the following parts: (i) A control principle based on variable rod length is adopted so that the snake robot can track into a small working space; (ii) a trajectory planning of the snake robot in a fixed state at one end is realized by an iterative tractrix principle minimizing the joint displacement; and (iii) a fast return tracking control of the snake robot in any posture is realized by adopting the principles of the variable rod-length tractrix and the forced return iteration. A snake robot with an arm 2300 mm in length is designed and fabricated. The trajectory control simulation and experiments validate the correctness of the trajectory control algorithm and the rationality of the structural design. [ABSTRACT FROM AUTHOR]

This study addresses the control problem of simultaneous tracking control and stabilization for underactuated unmanned surface vessels (USVs) with only two available inputs in the surge and yaw directions. Firstly, two velocity modifications are introduced to transform the error dynamics into two decoupled subsystems. Then, a novel error transforming scheme is presented to reduce the complexity of controller expressions and overcome the difficulties caused by underactuated dynamics. Based on the above transforming scheme and the event-triggered control (ETC) mechanism, a unified control method is designed to guarantee that the error states converge to a bounded neighborhood of the origin while excluding the Zeno behavior of the controllers. In addition, two radial basis function neural networks (RBFNNs) are applied to approximate the unknown dynamics and additional control errors caused by the ETC mechanism. Finally, comparative simulation experiments are performed to validate the effectiveness of the proposed controller. • A novel error transforming scheme is presented to simplify the designing procedure. • An ETC based simultaneous tracking and stabilization control strategy is designed. • Some complementary variables are involved to deal with the input saturation constraints. [ABSTRACT FROM AUTHOR]

A proposed optimized model for the trajectory tracking control of a wheeled inverted pendulum robot (WIPR) system is presented in this study, which addresses the problem of poor trajectory tracking performance in the presence of unknown disturbances due to the nonlinear and underactuated characteristics of the system. First, a kinematic controller was used to track a reference trajectory and generate a control law that specifies the desired forward and rotation speeds of the system. Next, a nonlinear disturbance observer (NDO) was designed to enhance the system’s robustness to external disturbances and improve its tracking performance. Then, the coupled system state variables were decoupled into two subsystems: a forward rotation subsystem and a tilt angle velocity subsystem. An improved hierarchical sliding mode controller was designed to control these subsystems separately. Finally, simulation experiments were conducted to compare the proposed method with a common sliding mode control approach. The simulation results demonstrate that the proposed method achieves better tracking performance in the presence of unknown disturbances.

This paper proposes a novel type of grasping strategy that draws inspiration from the role of touch and the importance of wrist motions in human grasping. The proposed algorithm, which we call Sequential Contact-based Adaptive Grasping, can be used to reactively modify a given grasp plan according to contacts arising between the hand and the object. This technique, based on a systematic constraint categorization and an iterative task inversion procedure, is shown to lead to synchronized motions of the fingers and the wrist, as it can be observed in humans, and to increase grasp success rate by substantially mitigating the relevant problems of object slippage during hand closure and of uncertainties caused by the environment and by the perception system. After describing the grasping problem in its quasi-static aspects, the algorithm is derived and discussed with some simple simulations. The proposed method is general as it can be applied to different kinds of robotic hands. It refines a priori defined grasp plans and significantly reduces their accuracy requirements by relying only on a forward kinematic model and elementary contact information. The efficacy of our approach is confirmed by experimental results of tests performed on a collaborative robot manipulator equipped with a state-of-the-art underactuated soft hand. [ABSTRACT FROM AUTHOR]

Surface-vehicle berthing is a complex and challenging task. It involves complicated ship dynamics owing to a large drift angle and the time-varying environmental disturbances induced by wind, wave, and current. Therefore, berthing requires state processing at each step and a controller that can respond to the non-linear behavior of the unmanned surface vehicle (USV). Herein, a systematic approach for the autonomous berthing of a USV is proposed. A state-machine approach is proposed to solve state transitions in the berthing step. A model reference adaptive controller was adopted to cope with the uncertainty of USV dynamics during berthing. Herein, the theoretical background and design of the adaptive controller are described. Simulation for the validation of the proposed method was conducted using the robot operating system Gazebo-based simulator. Finally, the respective performances of the proposed method and conventional controller were compared. Using the proposed berthing approach, an accurate and stable docking of small USVs became achievable. [ABSTRACT FROM AUTHOR]

This paper focuses on the autonomous recovery maneuvers of an unknown underactuated practical catamaran, which returns to its initial position corresponding to the man overboard (MOB) by simply adjusting the rate of turn. This paper investigates the completion of model-based path following control for not only the traditional Williamson turn, but also complex recovery routes under time-varying disturbances. The main difficulty of model-based path following control for predicting the hydrodynamic derivatives of a practical catamaran was solved by the approximated calculation of a diagonal matrix. The second key problem of differential calculation for an underactuated model in the case of complex reference trajectories under severe disturbances was investigated. Even though this paper employs a diagonal matrix with unknown nonlinear terms, the experimental test using a small craft with payloads by remote control demonstrated the sway force per yaw moment in turning cases. Adaptive backstepping mechanisms with unknown parameters were proven by the Lyapunov theory as well as the passive-boundedness of the sway dynamics, guaranteeing the stability of sway motion in the case of unavailable sway control. The effectiveness of the algorithms of the guiding concept and error dynamics is demonstrated by the numerical simulations. [ABSTRACT FROM AUTHOR]

The attitude control of an underactuated reusable launch vehicle (RLV) in the reentry phase involving nonminimum phase problem and control input constraints is investigated in this article. To address the nonminimum phase problem, an approach combining output redefinition and robust backstepping is proposed, where a synthetic output is constructed using the combination of the original output and the internal states to obtain stable zero dynamics, and then robust backstepping is performed on the new output. Besides, the ideal internal dynamics are obtained by using optimal bounded inversion, which are incorporated into the controller as the reference trajectories for the internal states to improve the output tracking accuracy. To cope with the control input constraints, a simple and useful anti-windup strategy is proposed by using feedback error clipping, which is shown to be very effective in mitigating control input saturation. Numerical simulations are given to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this study, we propose a fully automatic dishwashing and arranging system. The user simply places the used dishes on the worktop, and the system automatically arranges them in the dish basket and cleans the dishes in the dishwasher. The washed dishes are automatically arranged on the worktop by the system. This eliminates the need to manually load and unload dishes. To realize this system, we develop a novel underactuated robotic hand for grasping multiple shaped dishes stably. The motion of the underactuated mechanism used in the robotic hand for the dishes is modeled, and stability is analyzed. The dimensions of the link used for the underactuated mechanism are determined based on the results. In addition, we conduct grasp experiments for dishes of various shapes, and an experiment on arranging dishes to confirm the effectiveness of the proposed system. The proposed hand is expected to contribute to the full automation of the dishwashing process in restaurants and other commercial kitchens as well as in the standard home. [ABSTRACT FROM AUTHOR]

A new type of hand rehabilitation training device based on shape memory alloy spring is proposed for the existing hand rehabilitation training device with complex structure and poor portability. The device realizes miniaturization， portability and easy operation of hand rehabilitation training device through underactuation mode， driven by single memory alloy spring and multiple common springs. The relationship between the output force and the output stroke of the shape memory alloy spring is investigated and experimentally verified. The influencing factors of knuckle output force are analyzed. By comparing PID control and fuzzy control， the control efficiency of the device is improved. The simulation and experiment on the device verify the rationality of the device， and provide a research basis for the optimization of the device in the next step.

This paper presents the control modelling and synthesis using a coupled multivariable under-actuated nonlinear adaptive U-model approach for an unmanned marine robotic platform. A nonlinear marine robotics model based on the dynamic equation using the Newtonian method and derivation with respect to the kinematics equations and rigid-body mass matrixes are explained. This nonlinear marine robotics model represents the underwater thruster dynamics, marine robotics dynamics and kinematics related to the earth-fixed frame. Coupled multivariable nonlinear adaptive control synthesis using a U-model approach for the Remotely Operated Vehicle (ROV) and Unmanned Surface Vessel (USV) represent an unmanned marine robotics application. A comparison is presented for the proposed nonlinear control approach between the U-model control approach with nonlinear Fuzzy Logic Control and Sliding Mode Control for the ROV and USV platforms. The results show minimum mean square error values and tracking performance between the plant or system model with the proposed method. Lastly, robustness and stability analysis for the proposed U-Model nonlinear control approach are presented by implementing an adaptive learning rate value.

This paper presents the development of unmanned marine robotic control modelling and control synthesis using a coupled multivariable underactuated nonlinear adaptive U-model approach. The proposed controller was developed using thru an open source robot operating system (ROS) platform. The new adaptive coupled U-model based internal model control (IMC) node was successfully developed and tested. The proposed controller demonstrated the simplicity of the control synthesis process and the implementation of the mathematical algorithm in real-time. The controller was compared with the proven existing GIRONA 500 UUV for real-time performance. The ROS environment provides fast and reliable controller design and development compared to conventional software architecture. Simulation and real-time experiment were conducted using ROS via the GIRONA 500 UUV platform and compared with a PID mission controller. A new ROS node of nonlinear adaptive U-model based IMC was developed using ROS. The results showed good control signal convergence and tracking performance between the plant or system model with the proposed method.

As the working tool of the robot, the importance of the gripper becomes more prominent with the extensive use of the robot. This paper proposes a new type of underactuated universal gripper that can be applied to handle lightweight parts of any shape. It integrates a crank train and a four-bar mechanism to grasp objects. The kinematics and statics analysis of the proposed gripper were carried out; and in this paper, we briefly introduce the concept and control system design. Then, the motion characteristics and grasping ability of the underactuated gripper are presented. A prototype of the gripper was designed and manufactured based on the simulation analysis, and relevant grasping experiments were carried out. The experimental results verify that the proposed universal gripper has the advantages of safe design, easy manufacturing, effective gripping, and stable holding of objects.