6D interaction control with aerial robots: The flying end-effector paradigm

Abstract

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.

Nonlinear Model Predictive Control with Enhanced Actuator Model for Multi-Rotor Aerial Vehicles with Generic Designs

“…6, is a fully-actuated MDT platform with six non-collinear tilted rotors, from which it inherits the name 'Tilt-Hex'. In this case, the prototype has been completely designed and manufactured in our laboratory, and has already been presented in some of our previous contributions [2,31]. The values of the physical parameters used in the MRAVs models are summarized in Tables 4 and 5.…”

“…3 in [60], the larger the angle α, the larger the set of body-frame lateral forces. This translates also into the possibility of decoupling the control of the body force and moment in a larger extent, which becomes particularly useful in many realistic scenarios, ranging from 6D trajectory tracking, see [31], to aerial physical interaction tasks, see [2,3], and disturbance rejection in general. On the other hand, the increase of the tilting angle implies also an increment in the energy consumption.…”

“…A subset of this class is represented by the so-called fully-actuated systems, for which the control force can be varied in all directions, disregarding the actuator constraints. Vehicles of this kind have been demonstrated to be particularly suitable for the accomplishment of aerial physical interactions tasks [2,3], i.e., operations which require an active contact and a consequent exchange of energy between the robots and the surrounding environment. Examples of such operations are grasping, transportation and manipulation of loads, contact-based inspection tasks, and building/decommissioning of structures.…”

Design and optimal control of a tiltrotor micro-aerial vehicle for efficient omnidirectional flight

“…We compare capabilities of the two optimized tiltrotor OMAV results to other state-of-the-art OMAVs. Morphologies selected for comparison are the fixed rotor tilt-hex realized for aerial interaction applications (Ryll et al, 2019) and the fixed rotor omnidirectional platforms derived and realized by Brescianini and D'Andrea (2016) and Park et al (2016). Morphological representations for these systems are shown in the far right column of Figure 4 For fairness of comparison, the lack of tilting motors and related components for fixed rotor morphologies are reflected in reduced mass and rotational inertia, as seen in Table 3.…”

Omni-Plus-Seven (O7+): An Omnidirectional Aerial Prototype with a Minimal Number of Unidirectional Thrusters

“…To decouple the platform's forces from its orientation, multiple designs in the literature presented platforms that exploit the full six-dimensional wrench space. [5] and [6] use tilted uni-directional thrusters to apply 3 forces independently from the applied moment. However, these platforms cannot apply forces in any direction, and are usually limited to force directions in the upper hemi-sphere.…”