In this paper, we present the ADAPT, a novel reconfigurable force-balanced parallel manipulator for spatial motions and interaction capabilities underneath a drone. The reconfigurable aspect allows different motion-based 3-DoF operation modes like translational, rotational, planar, and so on, without the need for disassembly. For the purpose of this study, the manipulator is used in translation mode only. A kinematic model is developed and validated for the manipulator. The design and motion capabilities are also validated both by conducting dynamics simulations of a simplified model on MSC ADAMS, and experiments on the physical setup. The force-balanced nature of this novel design decouples the motion of the manipulator's end-effector from the base, zeroing the reaction forces, making this design ideally suited for aerial manipulation applications, or generic floating-base applications.

This paper introduces a novel parallel architecture that provides 6 DOF motion and 1 DOF grasping capabilities while all the motors are located at the base. Parallel robotic devices are widely used now in haptic applications, thanks to their high stiffness and low inertia, which improve the mechanical bandwidth of the device. Classical parallel haptic devices usually do not provide grasping capabilities since all motors are located on the base. Grasping capabilities is sometime desirable to allow the operator to feel the shape and stiffness of the manipulated objects. Thanks to a novel configurable platform, the grasping capability of this haptic device is part of the mechanical architecture itself and can be fully controlled by base-located motors.

This paper investigates the possibility of increasing the robustness of underactuated grasping through the use of variable transmission ratios. We propose a 4-step procedure to investigate and improve the robustness of an underactuated finger on a fixed object. This procedure maximizes the robustness against random force disturbances to the maximum obtainable value under given circumstances. A simulation study is presented that analyzes the disturbance robustness, followed by an experimental study to confirm the effect. The variable transmission ratio is a promising means to increase grasp robustness and has great application potential.

The ability of underactuated hands to grasp small objects is very limited, because the precision grasp is normally unstable. The goal of this paper is to achieve stable precision grasps by means of simple design modifications of the distal phalanges of the fingers. These modifications comprise the curving of the contact area of the distal phalanx, the application of a mechanical limit to prevent hyperextension of the distal phalanx, and the application of a compliant joint between the proximal and distal phalanges. A model is developed to calculate the limits of the finger dimensions in order to achieve stable precision grasps for different object sizes. An experimental setup is used to test the grasp stability and to verify the calculated results. It is concluded that stable precision grasps exist for the combination of concavely curved distal phalanges with a mechanical limit or with a compliant joint, if the limits to the finger dimensions are satisfied.

To evaluate and optimize the mechanical design of underactuated hands, a benchmark test is defined that quantifies the ability to hold grasped objects subject to force disturbances as occurs during for instance pick and place operations. The ability to hold is quantified by the magnitude of the maximum permitted static force on the center of a cylindrical object of known radius at which it can still be hold within the underactuated hand. A static grasp model is developed to efficiently calculate the effect of design parameters of the hand on this maximum force. This model is applied to a planar, underactuated hand with six degrees of freedom, calculating the maximum force while the rotational joint stiffnesses and distance between the fingers was varied. We demonstrated that the rotational joint stiffness has no effect on this force, while decreasing the distance between the fingers has a negative effect. These results were validated by measurements in an experimental setup. These preliminary results show that the developed benchmark test can be effective to evaluate and optimize the performance of underactuated hands to hold objects in pick and place operations.