In this paper, the problem of impedance control of dual-arm cooperative manipulators is studied. A general impedance control scheme is adopted, which encompasses a centralized impedance control strategy, aimed at conferring a compliant behavior at the object level, and a decentralized impedance control, enforced at the end-effector level, aimed at avoiding large internal loading of the object. Remarkably, the mechanical impedance behavior is defined in terms of geometrically consistent stiffness. The overall control scheme is based on a twoloop arrangement, where a simple proportional integral derivative inner motion loop is adopted for each manipulator, while an outer loop, using force and moment measurements at the robots wrists, is aimed at imposing the desired impedance behaviors. The developed control scheme is experimentally tested on a dual-arm setup composed of two 6-DOF industrial manipulators carrying a common object. The experimental investigation concerns the four different controller configurations that can be achieved by activating/deactivating the single impedance controllers.

This paper presents the design, control, and experimental validation of a novel fully-actuated aerial robot for physically interactive tasks, named Tilt-Hex. We show how the Tilt-Hex, a tilted-propeller hexarotor is able to control the full pose (position and orientation independently) using a geometric control, and to exert a full-wrench (force and torque independently) with a rigidly attached end-effector using an admittance control paradigm. An outer loop control governs the desired admittance behavior and an inner loop based on geometric control ensures pose tracking. The interaction forces are estimated by a momentum based observer. Control and observation are made possible by a precise control and measurement of the speed of each propeller. An extensive experimental campaign shows that the Tilt-Hex is able to outperform the classical underactuated multi-rotors in terms of stability, accuracy and dexterity and represent one of the best choice at date for tasks requiring aerial physical interaction

In this paper a novel hierarchical motion control scheme for quadrotor aerial vehicles equipped with a manipulator is proposed. The controller is organized into two layers: in the top layer, an inverse kinematics algorithm computes the motion references for the actuated variables; in the bottom layer, a motion control algorithm is in charge of tracking the motion references computed by the top layer. A simulation case study is developed to demonstrate the effectiveness of the approach in the presence of disturbances and unmodeled dynamics.

Impedance control is a well-established framework to manage the interaction of the end effector of a robot manipulator with the environment, For the execution of six-degree-of-freedom (DOF) tasks, both the end-effector position and orientation must be handled. The operational space control schemes typically utilize minimal representations of end-effector orientation; however, such representations do not lead to a physically meaningful definition of the rotational part of the impedance equation, and they suffer from the occurrence of representation singularities. In this work a new approach to six-DOF impedance control is proposed, where the end-effector orientation displacement is derived from the rotation matrix expressing the mutual orientation between the compliant frame and the desired frame, An alternative Euler angles-based description is proposed which mitigates the effects of representation singularities. Then, a class of angle/axis representations are considered to derive the dynamic equation for the rotational part of a six-DOF impedance at the end effector, using an energy-based argument. The unit quaternion representation is selected to further analyze the properties of the rotational impedance, The resulting impedance controllers are designed according to an inverse dynamics strategy with contact force and moment measurements, where an inner loop acting on the end-effector position and orientation error is adopted to confer robustness to unmodeled dynamics and external disturbances. Experiments on an industrial robot with open control architecture and force/torque sensor have been carried out, and the results in a number of case studies are discussed

This paper presents a novel paradigm for physical interactive tasks in aerial robotics allowing reliability to be increased and weight and costs to be reduced compared with state-of-the-art approaches. By exploiting its tilted propeller actuation, the robot is able to control the full 6D pose (position and orientation independently) and to exert a full-wrench (force and torque independently) with a rigidly attached end-effector. Interaction is achieved by means of an admittance control scheme in which an outer loop control governs the desired admittance behavior (i.e., interaction compliance/stiffness, damping, and mass) and an inner loop based on inverse dynamics ensures full 6D pose tracking. The interaction forces are estimated by an inertial measurement unit (IMU)-enhanced momentum-based observer. An extensive experimental campaign is performed and four case studies are reported: a hard touch and slide on a wooden surface, called the sliding surface task; a tilted peg-in-hole task, i.e., the insertion of the end-effector in a tilted funnel; an admittance shaping experiment in which it is shown how the stiffness, damping, and apparent mass can be modulated at will; and, finally, the fourth experiment is to show the effectiveness of the approach also in the presence of time-varying interaction forces.