Robot Hands

The majority of the works on grasping consider
both object as well as robot hand parameters to be accurately
known and do not take into account the constraints imposed
by the robot hand. In this paper, a complete methodology is
proposed that handles the grasping problem under a wide range
of uncertainties. Initially, we search for an acceptable posture
that provides robustness against positioning inaccuracies and
maximizes the ability of the robot hand to exert forces on the
object. Subsequently, in order to secure the grasp stability, we
also deal with the determination of sufficient contact forces.
Finally, an appropriate tactile sensor setup, mounted on the
robot hand, allow us to reduce the magnitude of uncertainty
regarding the grasping parameters. The efficiency of our approach
is validated through extensive experimental paradigms
using a 15 DoF DLR/HIT II robotic hand attached at the end
effector of a 7 DoF Mitsubishi PA10 robotic manipulator.

This thesis presents the design, modeling, and development of adaptive robot hands that are capable of performing dexterous, in-hand manipulation. The robot hand comprises of anthropomorphic robotic fingers, which employ an adaptive actuation mechanism. The mechanism achieves both flexion/extension and adduction/abduction, on the finger’s metacarpophalangeal joint, by using two actuators. Moment arm pulleys are employed to drive the tendon laterally, such that an amplification on the abduction motion occurs, while also maintaining the flexion motion. Particular emphasis has been given to the modeling and the analysis of the actuation mechanism. Also, a model for spatial motion is provided that relates the actuation modes with the finger motion and the tendon force with the finger characteristics. For the hand design, the use of differential mechanisms simplifies the actuation scheme, as we utilize only two actuators for four fingers, achieving affordable dexterity. A design optimization framework assess the results of hand anthropometry studies to derive key parameters for the bio-inspired actuation design. The model assumptions are evaluated with the finite element method. The proposed finger has been fabricated with the Hybrid Deposition Manufacturing technique and the actuation mechanism’s efficiency has been validated with experiments that include the computation of the finger workspace, the assessment of the force exertion capabilities, the demonstration of the feasible motions, and the grasping and manipulation capabilities. Also, the hand design is fabricated with off-the-shelf materials and rapid prototyping techniques while its efficiency has been validated using an extensive set of experimental paradigms that involved the execution of grasping and in-hand manipulation tasks with everyday objects.