1,720,979 research outputs found
Mapping human hand fingertips motion to an anthropomorphic robotic hand
No full textThe mapping of the human intention to a dexterous
anthropomorphic robotic hand is still an open issue among
researchers. The complexity behind this problems comes mainly
from three factors: the kinematics differences between the users
and the robotic hand(s); the differences in size and motion
capabilities among different users hands; and the high number
of degrees of freedom present in an anthropomorphic hand.
In this work, we present a procedure for the determination of
a linear transformation capable to interface the user and the
robot kinematics and therefore to allow a precise and natural
control of the mechanical device. The main assumption that
we make is that different human hand kinematics differ -with
a good approximation- for a scaling factor only, whereas the
proportions between the phalanges lengths and the relative
orientation of the fingers are kept almost constant in healthy
people [1]. We also assume that, being the considered robotic
hand highly anthropomorphic, this condition holds also between
the user and the robotic hand. In addition, while for a robotic
hand the definition of a reference frame fixed to the palm
is a free choice, for the human hand tracked with some
external system it is completely software dependent. Therefore
additional rotational and translational corrective terms have
to be introduced to compensate for the different placement
of the palm reference frame with respect to the fingers. We
have applied this approach to control the UB-Hand IV using
a commercial device called Leap Motion, able to track with a
good accuracy the pose of the palm and the positions of the
key points of the human hand, i.e. the end points of the hand
bones [2]
An Underwater Robotic Gripper with Embedded Force/Torque Wrist Sensor
No full textIn this paper, a three-finger underwater gripper with force/torque sensor integrated in the wrist interface is presented. The actuation is based on electric servo motors and cable transmission. The gripper is characterized by 8 Degrees of Freedom (DOFs) actuated by only three motors. The coupling among the DOFs of the fingers is implemented by means of multiple pulleys connected to the motor output shaft. The solutions adopted to make the system at the same time simple enough and suitable for marine applications are discussed and analyzed along with the integration of the sensors needed for handling complex manipulation and cooperation tasks. The effectiveness of the device is tested in a pool where the gripper is part of a complex robotic system composed of an Autonomous Underwater Vehicle (AUV) and a dexterous 7-DOFs arm. The goal of the benchmark experiments is the autonomous search of a known object and its recovery and transportation
Modeling, design, and experimental evaluation of rotational elastic joints for underactuated robotic fingers
No full textIn this paper, a novel 3D printed Rotational Joint (RJ) embedding an integrated elastic element is presented. The RJ, produced as a single piece by means of an FDM printer, comprises a traditional pin hinge coupled with a pair of spiral torsion springs, providing the desired compliance for the application at hand. Benefits of the proposed design include monolithic manufacturing and possibility to be successfully employed in robotic articulated devices requiring joint elasticity for their functioning. On the other hand, the sub-optimal RJ behavior, mainly caused by the unavoidable friction between 3D printed mating surfaces, must be accurately taken into account for design purposes. In this context, preliminary reliability tests have been performed showing promising results in terms of lifetime and negligible fatigue effects. Then, a mathematical model of the system is derived, which comprises the spring elasticity along with any frictional effects that may be due to either the pin hinge itself or the tendon transmission (frequently employed in underactuated robotic devices). The model parameters have been empirically evaluated by comparing simulated and experimental data. In addition, the last part of the paper describes how the proposed RJ can be effectively employed for the design of modular, underactuated fingers, providing three degrees of freedom and a single tendon transmission. To this end the model of the joint module proposed in this work will be the starting point for the geometry dimensioning of a finger with a desired free closure motion
Design of a Beam-Based Variable Stiffness Actuator via Shape Optimization in a CAD/CAE Environment
No full textIndustrial robots are commonly designed to be very fast and stiff in order to achieve extremely precise position control capabilities. Nonetheless, high speeds and power do not allow for a safe physical interaction between robots and humans. With the exception of the latest generation lightweight arms, purposely design for human-robot collaborative tasks, safety devices shall be employed when workers enter the robots workspace, in order to reduce the chances of injuries. In this context, Variable Stiffness Actuators (VSA) potentially represent an effective solution for increasing robot safety. In light of this consideration, the present paper describes the design optimization of a VSA architecture previously proposed by the authors. In this novel embodiment, the VSA can achieve stiffness modulation via the use of a pair of compliant mechanisms with distributed compliance, which act as nonlinear springs with proper torque-deflection characteristic. Such elastic elements are composed of slender beams whose neutral axis is described by a spline curve with non-trivial shape. The beam geometry is determined by leveraging on a CAD/CAE framework allowing for the shape optimization of complex flexures. The design method makes use of the modeling and simulation capabilities of a parametric CAD software seamlessly connected to a FEM tool (i.e. Ansys Workbench). For validation purposes, proof-concept 3D printed prototypes of both non-linear elastic element and overall VSA are finally produced and tested. Experimental results fully confirm that the compliant mechanism behaves as expected
Optimal design of 3D printed spiral torsion springs
No full textSpiral Torsion Springs (STS) are generally manufactured employing medium/high-carbon steel alloys shaped as thin rods with rectangular cross section. Meanwhile, plastic materials (e.g. ABS or PLA), currently used in freeform manufacturing processes, may not be suited for several applications, owing to the low material yield strength and the rather poor fatigue life. Despite the above-mentioned limitations, the main advantages of a 3D printing process, as compared to more traditional manufacturing techniques, are the design flexibility and the possibility to directly integrate elastic components within a joint mechanism produced as a single (monolithic) part. In particular, provided that the external forces acting on the spring coils are maintained within a certain threshold and that the spring geometry is suitably optimized, a reliable 3D-printed STS alternative to traditional steel springs is actually feasible. Given these premises, the main purpose of the present paper is to propose a model-based optimization algorithm that allows to optimally size STS for user-specified torque-deflection characteristics. Optimal STS geometries are then realized in ABS via Fused Deposition Manufacturing, and subsequently tested with a purposely-designed experimental set-up. Furthermore, the behavior of each STS sample (in terms of stiffness and equivalent Von Mises stress) is evaluated by means of non-linear finite elements analysis, in order to check the correspondence with the expected behavior. Finally, numerical and experimental results are provided, which demonstrate the prediction capabilities of the proposed modeling/optimization techniques, and confirm that well-behaved STS can be conceived and produced. Envisaged applications concern the development of smart structures for robot design, such as multi-articulated compliant robotic chains that can be used as low-cost manipulators (i.e. arm) or as mini-manipulators (i.e. fingers). The proposed approach effectively simplifies the production and the assembly of the mechanism, also allowing for an easier integration of embedded sensory-actuation systems
Development of an haptic interface based on twisted string actuators
No full textIn this paper, a cable-driven haptic interface able to move in the six-dimensional space, suitable for applications in various robotic scenarios is presented. The device takes advantage of four force-controlled twisted string actuators to generate a linear force along the three Cartesian space dimensions while providing a considerable force-weight ratio and low inertia. The system consists of a frame fixed to the ground, where the twisted string actuation modules are arranged, and by a mechanical interface devoted to the physical connection of the actuators with the forearm of the human operator. This mechanical interface allows to secure the forearm of the user while leaving to her/him the freedom to use the hand to accomplish other tasks, such as teleoperating a robotic gripper. The four twisted string actuators allow to control the three linear DoF of the haptic interface, allowing both Cartesian position and a force regulation. Both the design, the simulation and the preliminary implementation of the haptic interface are presented in this work
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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