Unilateral Dexterity Research Articles

Unilateral Manipulability Quality Indices: Generalized Manipulability Measures for Unilaterally Actuated Robots

The study of the relationship between the desired system dynamics and the actuation wrench producing those dynamics is important for robotic system analysis. For traditionally actuated robots, the quality indices of dexterity and manipulability quantify this relationship. However, for unilaterally actuated robots (UARs), such as grasping hands and cable-driven parallel robots (CDPRs), these indices cannot be applied due to the unilateral actuation constraint. In this paper, the quality indices of unilateral dexterity (UD) and unilateral maximum force amplification (UMFA) are established for UARs with arbitrary number of actuators. It is shown that these quality indices provide task-independent quantifications of the physical properties of robustness and force amplification for UARs, and they can measure the mechanism’s capability both in singular and nonsingular poses. With these indices, manipulability ellipsoid-derived measures can be applied to arbitrary UARs. The significance of the quality indices for robot synthesis and motion generation analysis is illustrated through two case studies: a five-fingered grasp selection problem and the workspace analysis of a spatial CDPR.

A Robotic Ball for Upper-Extremity Training in Stroke Patients: A New Approach in Neurorehabilitation

Abstract Background Technology-supported therapy can contribute to the rehabilitation of distinctive upper-extremity symptoms resulting from stroke as neurons have the ability to reorganize. The robotic ball “Sphero 2.0”, an innovative therapeutic exergaming tool, was found to be suitable and hence used in neurorehabilitation for the first time. Objective The aim of this study was to evaluate the robotic-ball therapy concept and assess possible effects on motor parameters. Patients’ statements regarding the effects on rehabilitation after implementing the therapy concept over several weeks were included in the testing procedure. Furthermore, the study aimed to rate the technical suitability of the robotic ball. Methods 12 stroke patients (62.3±11.8 years, 170.8±10.9 cm, 82.5±16.6 kg, 6.37±5.53 months post-stroke) underwent 45-min training with the robotic ball, twice a week, over a period of 12 weeks. Regular therapy was complemented with this intervention. Pre and post intervention, grip strength, unilateral dexterity, self-reported disabilities of the arm, shoulder and hand and impairment, cognitive status and technical affinity were assessed. Results 10 patients were able to complete the training program and achieved significant improvement in grip strength (p=0.007, d=0.51) and unilateral dexterity (p=0.002, d=0.44) along with reduced self-reported disabilities of the arm, shoulder and hand and impairment (p=0.002, d=−1.12). The robotic ball was rated as excellent with 92.3±2.5 out of a maximum 100 points. Conclusions Patients severely or slightly impaired seemed to benefit less than moderately affected stroke patients. Specific improvements in dealing with activities of daily living contributed to a high motivation for the robotic-ball training. The training content can be adapted to users with heterogeneous impairments. The results of the present study should be confirmed with more patients in a future study with a crossover-design. Keywords: Stroke, motor function, robotic ball, upper extremities, exergaming

Dexterity measures with unilateral actuation constraints: the n+1 case

The study of the instantaneous kinematics and statics aims at capturing the properties of mechanisms in terms of the mapping of forces, velocities and error propagation. Dexterity measures have been developed to quantify these properties with a view to analysis and design. Tendons and cables may be viewed as unilateral actuators because they require tensioning for normal operation. When power grasping is abstracted to a set of forces acting at discrete points on the surface of an object, it can be analyzed in terms of unilateral statics. It is also used to analyze magnetic levitation resulting from forces caused by variable reluctance magnetic circuits, as is the case of a vehicle propelled by reaction jets. For all these cases, a new set of measures based on the unilateral statics is developed when n + 1 forces act on a n d.o.f. mechanism and force mapping properties are studied. It is proposed to replace the ordinary concepts of dexterity, singularity, isotropy, maximum force amplification and maximum dexterity gradient by unilateral dexterity, unilateral singularity, unilateral isotropy, unilateral maximum force amplification and unilateral maximum dexterity gradient, respectively. As an example of their application, the geometric optimization of a 3 d.o.f. tendon mechanism is performed.