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A kinematic scheme is presented which allows for planning attitude manoeuvres of satellites after actuator failure. The scheme relies on the identification of admissible rotation axes around which the control system can deliver to...
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A kinematic scheme is presented which allows for planning attitude manoeuvres of satellites after actuator failure. The scheme relies on the identification of admissible rotation axes around which the control system can deliver torque components in spite of the failure. Two techniques discussed in the literature, based on a single rotation that either minimizes the angular displacement from a given target attitude or aims a sensor exactly along a prescribed direction, are compared with a new technique based on a two-step approach, which allows for achieving any prescribed attitude by means of a sequence of two feasible rotations. Dynamic simulation is used for analysing potential capabilities and limits of the considered kinematic approaches to manoeuvre planning of under-actuated satellites.
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The objective of this paper is to generate a desired flight path to be followed by an autonomous airship. The space is supposed without obstacles. As there are six degrees of freedom and only three inputs for the LSC AS200 airship...
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The objective of this paper is to generate a desired flight path to be followed by an autonomous airship. The space is supposed without obstacles. As there are six degrees of freedom and only three inputs for the LSC AS200 airship, three equality constraints appear due to the under-actuation.
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Control over landing posture can effectively prevent structural damage when a portable device is accidentally dropped. Given size and cost constraints, the number of actuators should be limited. This paper presents an optimal post...
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Control over landing posture can effectively prevent structural damage when a portable device is accidentally dropped. Given size and cost constraints, the number of actuators should be limited. This paper presents an optimal posture control method that allows an under-actuated system to land with the desired posture. A simplified model of a portable computer/telephone is considered, comprising two rigid bodies and an active joint. The objective is to minimize the input torque produced by the actuator to achieve the desired posture. A two-point boundary value problem is formulated; i.e., the initial and final angular positions and velocities are predetermined, and the inequality constraints are established on the basis of the capacity of the actuator and acceptable level of state variables. In the numerical analysis, the backward-sweep algorithm is applied to determine the appropriate Lagrange multiplier, and the falling dynamics are explored using Matlab. The optimal controller design is presented, together with simulation results confirming that the system is capable of performing landing posture control with minimum input torque.
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This paper presents an approach to damp out the oscillatory motion of the pendulum-like hanging platform on which a robotic manipulator is mounted. To this end, moving masses were installed on top of the platform. In this paper, a...
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This paper presents an approach to damp out the oscillatory motion of the pendulum-like hanging platform on which a robotic manipulator is mounted. To this end, moving masses were installed on top of the platform. In this paper, asymptotic stability of the platform (which implies oscillation damping) is achieved by designing reference acceleration of the moving masses properly. A main feature of this work is that we can achieve asymptotic stability of not only the platform, but also the moving masses, which may be challenging due to the under-actuation nature. The proposed scheme is validated by the simulation studies.
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This paper develops a mathematical analysis of contact forces for the under-actuated finger in a general under-actuated robotic hand during grasping. The concept of under-actuation in robotic grasping with fewer actuators than deg...
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This paper develops a mathematical analysis of contact forces for the under-actuated finger in a general under-actuated robotic hand during grasping. The concept of under-actuation in robotic grasping with fewer actuators than degrees of freedom (DOF), through the use of springs and mechanical limits, allows the hand to adjust itself to an irregularly shaped object without complex control strategies and sensors. Here the main concern is the contact forces, which are important elements in grasping tasks, based on the proposed mathematical analysis of their distributions of the n-DOF under-actuated finger. The simulation results, along with the 3-DOF finger from the ADAMS model, show the effectiveness of the mathematical analysis method, while comparing them with the measured results. The system can find magnitudes of the contact forces at the contact positions between the phalanges and the object.
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In this paper, we explore a novel multi-mode hybrid Unmanned Aerial Vehicle (UAV). We combine a tailless fixed-wing with a dual-wing monocopter such that the craft's propulsion systems and aerodynamic surfaces are fully utilized i...
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In this paper, we explore a novel multi-mode hybrid Unmanned Aerial Vehicle (UAV). We combine a tailless fixed-wing with a dual-wing monocopter such that the craft's propulsion systems and aerodynamic surfaces are fully utilized in both a horizontal cruising mode and a vertical hovering mode. This maximizes the structural efficiency across the flight envelope, thereby reducing drag and unused mass while airborne in either flight mode. This UAV is also designed such that the transition between the two flight modes can be executed in mid-air, using only its existing flight actuators and sensors — there are no transition specific actuators. Using two prototypes, the foundational design and control of the system is established; the first explores the hovering mode characteristics of the unique dual-wing monocopter configuration, while the second explores the full multi-mode capabilities of the combined platform. In addition to analytical simulations, the prototypes are experimentally evaluated and assessed to demonstrate the feasibility, viability and potential of this multi-mode aerial robot design.
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This paper proposes a robust three-dimensional (3-D) path-following controller for an under-actuated stratospheric airship in the presence of uncertainties. The resultant control system exhibits an inner-outer loop control structu...
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This paper proposes a robust three-dimensional (3-D) path-following controller for an under-actuated stratospheric airship in the presence of uncertainties. The resultant control system exhibits an inner-outer loop control structure. In the outer control loop, the path-following error dynamics is constructed in a moving Serret-Frenet frame and a new guidance law with the sideslip and attack angle compensation is designed, which decreases the path-following steady-state error. In the inner control loop, a disturbance observer based backstepping control law is proposed to achieve the desired dynamic behavior on the path. Furthermore, a new velocity tracking control strategy is developed which aligns the resultant velocity tangent to the path. Finally, numerical simulation results are shown to verify the effectiveness of the proposed controller.
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In this paper, a control strategy based on the optimal control and subspace stabilization approach is developed to solve the two-point boundary value problem of a highly under-actuated quadrotor. To facilitate the development, the...
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In this paper, a control strategy based on the optimal control and subspace stabilization approach is developed to solve the two-point boundary value problem of a highly under-actuated quadrotor. To facilitate the development, the dynamic model of the quadrotor is firstly presented. Then the boundary value problem is mathematically formulated based on the optimal control theory. According to the problem formulation and utilizing the subspace stabilization approach, the control strategy is proposed to suppress the state-trajectory tracking errors and manipulate the quadrotor from a known initial state to the desired final state in a finite time horizon. As there exist input delays in real-time flights, the Smith predictor is designed to enhance the performance of the developed control strategy. Finally, an indoor experimental platform of the quadrotor is built and real-time experiments of the ball-batting is conducted with a coefficient of restitution of approximate 0.7 and a racket with diameter of 0.13 m. The experimental results show that the quadrotor can well establish the desired final state and bat the ball towards its target location (the deviation of position is less than 0.15 m), which verify the feasibility of the proposed control strategy.
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This work fits into the emerging field of soft robotics and presents the implementation of an under-actuated approach to dynamic control of pneumatic systems. An insight about the control method is provided. Afterwards, the analys...
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This work fits into the emerging field of soft robotics and presents the implementation of an under-actuated approach to dynamic control of pneumatic systems. An insight about the control method is provided. Afterwards, the analysis of two case studies is conducted, in terms of conceptual design, mechanical design and experimental validation. The first example involves a worm-like robot for pipe inspection, made up of soft and rigid components, while the second one consists in a two-fingered gripper, realized through soft continuum bending actuators. Both these systems are composed of multiple silicone chambers connected in parallel to a single pressure source. The method is based on the co-design of the mechanical properties of the system and of the time profile of the input to achieve different dynamical responses within a given set of desired behaviours. It is shown that a proper design of the chambers stiffness and damping enables to change the dynamic behaviour of the overall system by simply modulating the pressurization rate.
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In this paper a dynamical model and the governing equations of motion of a micro-cantilever beam with rotating joint as an application of under-actuated systems will be developed. The model is based on the geometrically nonlinear ...
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In this paper a dynamical model and the governing equations of motion of a micro-cantilever beam with rotating joint as an application of under-actuated systems will be developed. The model is based on the geometrically nonlinear equations of motion of the microbeam, employing strain gradient elasticity theory. The Rayleigh-Ritz method is used to discretize partial differential equations to obtain a set of nonlinear ordinary differential equations of motion. Then, a controlled Lagrangian method as a robust procedure for controller design is employed to achieve an acceptable tracking on the hinge's angle of rotation of a micro-cantilever beam while undesirable vibration of the under-actuated flexible variable is damped. A stability analysis of the closed-loop system is also discussed. The advantages of the controlled Lagrangian method lie in its ability to find the Lyapunov function to prove the stability of the system and its capability of handling under-actuated devices. The performance of the designed control scheme is illustrated through several numerical simulation results and some comparisons are made in various situations.
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