1,721,007 research outputs found
Design of Compliant Mechanisms Approximating Straight and Circular Paths
No full textCompliant mechanisms are extensively employed in many fields due to their advantages over their rigid-body counterparts. They transmit force, motion, and energy through the elastic deformations of their flexible parts, that often consist of beams with uniform or variable cross-section, with straight or initially-curved axis. Although extensive efforts have been made in the analysis of the deflections, fewer studies dealt with the kinematic aspects associated to the deflection problem. Recently, some investigations focused on the behavior of the pole of the displacements, which characterizes the rigid displacements or on the inflection circle for developing pseudo-rigid-body models. In this paper, the instantaneous geometric invariants are applied to the description of the motion generated by straight flexures. The developed analytical formulation gives kinematic insights on the geometric characteristic of motion up to the fourth order. The invariants lead to the determination of fundamental geometric entities, that are the inflection circle, the cubic of stationary curvature and its derivative, the Ball's point, and the Burmester's points. In particular, Ball's and Burmester's points identify the special points on the plane that approximate straight paths to the third order, and circular paths to the fourth order, respectively. A possible implementation of the geometric invariants to the design of compliant mechanisms is briefly discussed
A Proportional Control Strategy for Stiffness Tuning of Parallel Manipulators
No full textThis article presents a control strategy for the stiffness regulation of parallel manipulators based on the implementation of a simple proportional controller. Starting from the assignment of the stiffness or compliance matrix in the task space, defined by the application-specific requirements, a proper control action is calculated by considering the translational and rotational compliances of the end effector. The proposed approach is applied in SE(2) and SE(3), addressing the analysis of the 3RRR planar parallel manipulator and the 6UPS Stewart-Gough platform. The proposed control scheme decouples the effects of the applied force and moment on the end effector displacement and rotation. Numerical examples are presented, with multibody simulations performed to verify the effectiveness of the proposed approach. The effect of friction in the active and passive joints is also investigated
Dynamic model and performance assessment of the natural motion of a SCARA-like manipulator in pick-and-place tasks
No full textThe energy efficiency of manipulators performing cyclic motions can be enhanced by utilizing the so-called natural motion, namely, the natural oscillations that occur when elastic elements are placed in series or parallel with the actuators. In this paper, the natural motion of the RR-4R-R robot is discussed. This manipulator exhibits a 4-DOF mobility similar to that of the widespread SCARA robot, but the vertical prismatic joint is replaced by a four-bar mechanism. This modification, along with the adoption of a direct-drive actuator for the four-bar mechanism, makes it easier to achieve the elastic balancing of the robot, allowing the exploitation of its natural motion. The robot dynamics is analysed using the Lagrangian approach. Two types of elastic balancing are considered: one using a torsional spring and one using a linear coil spring. A simplified model of the vertical motion is then proposed, decoupled from the inertial effects of the horizontal motion, and used to estimate the vertical natural period. The behaviour of the manipulator with natural elastic balancing is compared with that obtained with exact elastic balancing, which provides an indifferent equilibrium in any robot position. This comparison is first carried out in the time domain, and then the space of the robot operating conditions is sampled through multibody simulations, performed to investigate the threshold of convenience between exact and natural balancing. Simulation results indicate that exploiting the natural motion of the RR-4R-R manipulator can significantly reduce energy consumption in a wide range of industrial applications involving pick-and-place tasks
BISTURI AD ATTUAZIONE REMOTA PER TRATTAMENTI ENDOLUMINALI
No full textLa presente invenzione è relativa a un bisturi con attuazione remota per trattamenti endoluminali. Il bisturi oggetto della presente invenzione rientra nell’ambito della chirurgia mini invasiva che, come è noto, rimane promettente ma ancora non sufficientemente esplorata proprio a causa di una ancora non propriamente adeguata strumentazione. In particolare, il bisturi oggetto della presente invenzione trova una preferita e vantaggiosa applicazione nella chirurgia della stenosi carotidea e nella polipectomia endoscopica, senza per questo perdere in generalità
Isotropic compliance in RRP planar manipulators
No full textIn the present paper, the isotropic compliance property is investigated, specifically focusing on RRP plane manipulators. The property is achieved by means of active stiffness regulation, considering three different control strategies, dependent on the joint exerting the control action. For each case, the analytical solutions and the corresponding workspace subsets are presented. To compare the three methods, the active and overall stiffness coefficients are evaluated in the postures defining the isotropic compliance subsets. The feasibility of the methods is also evaluated, considering the passive and active stiffness coefficients
Natural Motion of the RR-4R-R Manipulator: Effects of Trajectory Types and Parameters
No full textIn robotics, it is possible to exploit the Natural Motion, or Free Vibration Response, of a manipulator equipped with elastic elements to reduce the energy consumption in cyclic motions, such as pick-and-place tasks. In [1], this approach has been applied to the RR-4R-R manipulator, a SCARA-like robot in which the vertical prismatic joint is replaced with a four-bar mechanism lying in a vertical plane, to facilitate the introduction of balancing elastic elements. While exact elastic balancing of the vertical four-bar provides indifferent equilibrium, suitable for slow movements, a linear elastic balancing obtained by linear torsional springs gives rise to a Natural Motion, which can be exploited to reduce energy consumption in fast cyclic motions, in which inertial forces become prevalent. The threshold of convenience between Exact Balancing (EB) and Natural Balancing (NB) has been evaluated for the RR-4R-R robot by means of a multibody model in [1] in terms of Integral Control Effort (ICE) and maximum values of the actuation torques. A wider simulation campaign has been carried out, with different trajectory types and parameters, and also considering the influence of finite stop phases, to assess the proposed architecture's energy-saving effectiveness more exhaustively
Isotropic compliance in E(3): Feasibility and workspace mapping
No full textA manipulator control system, for which isotropic compliance holds in the Euclidean
space Eð3Þ, can be significantly simplified by means of diagonal decoupling. However,
such simplification may introduce some limits to the region of the workspace where the
sought property can be achieved. The present investigation reveals how to detect which
peculiar subset, among four different classes, a given manipulator belongs to. The paper
also introduces the concept of control gain ratio for each specific single-input/single-output
joint control law in order to limit the maximum gain required to achieve the isotropic
compliance condition
MEMS-based conjugate surfaces flexure hinge
No full textThis paper presents a new concept flexure hinge for MEMS applications and reveals how to design, construct, and experimentally test. This hinge combines a curved beam, as a flexible element, and a pair of conjugate surfaces, whose contact depends on load conditions. The geometry is conceived in such a way that minimum stress conditions are maintained within the flexible beam. A comparison of the new design with the other kind of revolute and flexible joints is presented. Then, the static behavior of the hinge is analyzed by means of a theoretical approach, based on continuum mechanics, and the results are compared to those obtained by means of finite element analysis (FEA) simulation. A silicon hinge prototype is also presented and the construction process, based on single step lithography and reactive ion etching (RIE) technology, is discussed. Finally, a crucial in–SEM experiment is performed and the experimental results are interpreted through the theoretical models
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