Underactuation

The underactuated fingers used in numerous robotic systems are evaluated by grasping force, configuration space, actuation method, precision of operation, compactness and weight. In consideration of all such factors a novel linkage based underactuated finger with a self-adaptive actuation mechanism is proposed to be used in prosthetics hands, where the finger can accomplish flexion and extension. Notably, the proposed mechanism can be characterized as a combination of parallel and series links. The mobility of the system has been analyzed according to the Chebychev-Grübler-Kutzbach criterion for a planar mechanism. With the intention of verifying the effectiveness of the mechanism, kinematics analysis has been carried out, by means of the geometric representation and Denavit-Hartenberg (D-H) parameter approach. The presented two-step analysis followed by a numerical study, eliminates the limitations of the D-H conversion method to analyze the robotics systems with both series and parallel links. In addition, the trajectories and configuration space of the proposed finger mechanism have been determined by the motion simulations. A prototype of the proposed finger mechanism has been fabricated using 3D printing and it has been experimentally tested to validate its functionality. The kinematic analysis, motion simulations, experimental investigations and finite element analysis have demonstrated the effectiveness of the proposed mechanism to gain the expected motions.

In this paper, stability analysis of walking gaits and robustness analysis are developed for a five-link and four-actuator biped robot. Stability conditions are derived by studying unactuated dynamics and using the Poincaré map associated with periodic walking gaits. A stable gait is designed by an optimization process satisfying physical constraints and stability conditions. Also, considering underactuation problem, a time-invariant control law is designed to track the stable motion of biped. Validation of proposed approach is achieved by numerical simulations. Moreover, the robustness of motion on the uneven surfaces and elastic contact model are investigated.

A new class of simple, adaptive, under-actuated and compliant robot hands has recently attracted the interest of the robotics community. The under-actuated mechanisms and the structural compliance used in these hands facilitate and robustify not only grasping but also the execution of dexterous, in-hand manipulation tasks. Another significant characteristic of the particular hands is that they are able to efficiently grasp a wide range of everyday life objects even under significant object pose uncertainties. However, these hands, are difficult to model due to kinematic constraints introduced by the under-actuation and the use of complex flexure joints. Moreover, adaptive hands tend to reconfigure upon contact with the object surface, imposing certain parasitic object motions. In this paper, we propose a learning scheme that uses the contact force measurements collected from tactile sensors to estimate the post-contact reconfiguration of the hand-object system and the imposed parasitic object motion. The learning scheme's estimates are compared with " ground truth " data that describe the actual motion of the object and that are collected using a vision based motion capture system. The proposed learning scheme can be used with any type of adaptive robot hand and its efficiency is experimentally validated using extensive paradigms involving different hand designs and various everyday life objects.

The autonomous underwater vehicle (AUV) mostly has fewer control inputs than the degree of freedoms (DOFs) in motion and be classified into underactuated system. It is difficult tasks to stabilize that system because of the highly nonlinear dynamic and model uncertainties. Hence, it usually required nonlinear control method and this paper presents the stabilization of an underactuated X4-AUV using backstepping based PID nonlinear control techniques. The X4-AUV system is executed by separating system into two parts subsystem which is translational and rotational subsystems. Integral backstepping control is applied for translational subsystem and PID backstepping control for the rotational subsystem. The effectiveness of the proposed control technique for an underactuated X4-AUV demonstrates through simulation.

Underactuated systems are very difficult to control and stabilize due to fewer number of control inputs as compared to degrees of freedom (DOF). Thus, this research manuscript presents a comparative analysis of two major control schemes for an underactuated air cushion vehicle (ACV) commonly known as hovercraft. By studying the translational and angular dynamics of proposed underactuated mechatronic system, the mathematical model had been derived using Newton Euler formalism. The validity and effectiveness of proportional integrated differentiator (PID) control design is compared with the Fuzzy based PID (F-PID) scheme. Thus, with provided simulation results, paper concludes that the proposed algorithm of fuzzy based PID (F-PID) is better solution for achieving robust transient and steady state performances than simple PID control scheme even in the availability of bounded uncertainties with quick convergence rate.

The control of underactuated Euler-Lagrange systems with uncertain and switched parameters is an important problem whose solution has many applications. The problem is challenging as standard adaptive control techniques do not extend to this class of systems due to structural constraints that lead to parametrization difficulties. This note proposes an adaptive switched control framework that handles the uncertainty and switched dynamics without imposing structural constraints. A case study inspired by autonomous vessel operations is used to show the effectiveness of the proposed approach.

ABSTRACT We consider design of coordinating controllers for a fleet of underactuated ships. Each ship is modeled as a mechanical system with 3 degrees of freedom and 2 control inputs, which are the propeller thrust and the angle of the rudder; presence of lumped environmental forces is assumed. The proposed motion planning procedure relies on properties of an auxiliary explicitly constructed second order dynamical system. We propose a procedure for motion planning for the whole fleet and for design of a coordinating feedback controller, which stabilizes the motion. In the case when geometric paths for ship motions are given, following our approach, we obtain a description of all feasible motions of the fleet along these paths. In addition, it is shown how to design controllers to counteract environmental forces while remaining on the paths. As a side result, we provide some modi.cations and give some insights into the weather optimal positioning control design, introduced in [1] for a fully actuated ship model.

In this paper a new PI+ PD fuzzy controller, which includes a dynamic switching fuzzy system (DFSFS), is applied to swing-up an underactuated mechanism: the pendubot. This mechanism consists of a double pendulum actuated only at the first joint. This new ...

Abstract—A new sensor-based homing integrated guidance and control law is presented to drive an underactuated autonomous un-derwater vehicle (AUV) toward a fixed target, in three dimensions, using the information provided by an ultrashort baseline (USBL) positioning ...