1,721,579 research outputs found
Singularity-free evolution from one configuration to another in serial and fully-parallel manipulators
No full textAmong the several ways adopted for the characterization of manipulator performances is identification of the typologies of maneuvers allowed by the manipulator kinematic arrangement. The multiplicity of configurations corresponding to a given hand position for serial manipulators, or to a given set of input values for fullyparallel manipulators, makes one wonder whether a manipulator can perform the maneuver of changing its configuration without meeting singularities. The paper shows that singularity-free configuration change is possible both for general-geometry serial and fully-parallel architectures. Results are reported that shed light on potential performances of manipulators and allow, in perspective, a deeper exploitation of their structural peculiarities. © 1998 by ASME
Analytical form solution of the direct kinematics of a 4-4 fully in-parallel actuated six degree-of-freedom mechanism
No full textThis paper presents the direct position analysis in analytical form of a six-degree-of-freedom 4-4 fully-parallel mechanism. For a given set of actuator displacements the mechanism becomes a structure and the analysis finds all the possible closures of the structure. The analysis is performed in two steps. First, the two closures of the tetrahedron-like subchain of the structure are found. Then, for each tetrahedron closure, two transcendental equations are determined that represent the closure of the remaining part of the 4-4 structure. The two equations can he reduced to algebraic equations and, after eliminating the unwanted unknowns, a final 8th order equation in only one unknown is obtained. Hence, the maximum number of possible real closures of the 4-4 structure is sixteen. Numerical examples are reported which illustrate and confirm the new theoretical result
Kinematics of a family of translational parallel mechanisms with three 4-DOF legs and rotary actuators
No full textThis paper focuses on the kinematics of a family of translational parallel mechanisms equipped with three 4-DOF legs and rotary actuators. The direct and the inverse position problems are solved in analytical form, the velocity analysis is carried out, the workspace is determined and the loci of both kinematic singularities and isotropic configurations are derived. Furthermore, the problem of singularity avoidance by means of actuator redundancy is addressed and some solutions are proposed. Two special architectures are finally considered as case studies: in the first, the three actuation axes are mutually orthogonal; in the second, two actuation axes are parallel to each other and the third is perpendicular to them. The comparison of the two architectures on the basis of kinematic considerations allows for the selection of the second one as a preferable solution. © 2003 Wiley Periodicals, Inc
Singularity-free evolution from one configuration to another in serial and fully-parallel manipulators
No full textAmong the several ways adopted for the characterization of manipulator performances is identification of the typologies of maneuvers allowed by the manipulator kinematic arrangement. The multiplicity of configurations corresponding to a given hand position for serial manipulators, or to a given set of input values for fully-parallel manipulators. makes one wonder whether a manipulator can perform the maneuver of changing its configuration without meeting singularities. The paper shows that singularity-free configuration change IS possible both for general-geometry serial and fully-parallel architectures. Results are reported that shed light on potential performances of manipulators and allow. in perspective. a deeper exploitation of their structural peculiarities
A new kinematic model for the closure equations of the generalized Stewart platform mechanism
No full textThe paper deals with the direct position analysis of the six degrees of freedom parallel manipulator known as generalized Stewart Platform Mechanism. When a set of actuator displacements is given the mechanism becomes a statically determined structure and the analysis solves for the closure of the structure. The governing equations are non-linear and many solutions are possible. Kinematic models reported in the literature relate to systems of six equations in six unknowns, which are solved numerically because of their complexity. Based on a novel approach, a new kinematic model of the structure is presented in this paper. It leads to a system of three equations in three unknowns that greatly reduces the computational burden. Finally, a case study has been reported. © 1991 Kluwer Academic Publishers
Echelon form solution of direct kinematics for the general fully-parallel spherical wrist
No full textThis paper presents the echelon form direct position analysis of a class of fully in-parallel actuated mechanisms for the orientation of a rigid body with a fixed point. The mechanisms have a structure which is the most general one for manipulator spherical wrists with three degrees of freedom and fully-parallel arrangement. The analysis results in a two-equation system in echelon form; the first equation is of 8th order and the remaining is linear. As a consequence, when a set of actuator displacements is given, eight configurations of the mechanism are possible. A numerical example confirms the new theoretical result. © 1993
Position analysis of a new family of 3-DOF translational parallel manipulators
No full textThis article presents the position analysis of a new family of 3-limbed 3-dof parallel manipulators, whose output links exhibit a motion of pure translation with respect to the base. Each limb contains four passive revolute joints and an active prismatic pair, which can be mounted anywhere along the kinematic chain or replaced by a fifth revolute one. A univariate polynomial has been found that solves the direct position problem wherever the actuators are placed. The inverse analysis has been carried out in closed-form for all possible locations of the actuated joints. Finally, numerical examples are provided
Closed-form direct position analysis of a 5-5 parallel mechanism
No full textThe paper presents the closed form direct displacement analysis for a class of Stewart platform-type parallel mechanisms whose general feature consists of six legs which meet five distinct points both in the base and in the movable output link. Out of the two possible arrangements, only one is here analyzed in detail. Given a set of actuator displacements the analysis provides all the possible locations of the platform relative to the base. The analysis results in a 40th degree polynomial equation in one unknown. The roots of the equation provide in the complex field forty closures of the mechanism. This new result has been numerically verified by the inverse displacement analysis. © 1993 by ASME
Forward displacement analysis of parallel mechanisms: Closed form solution of prr-3s and ppr-3s structures
No full textThe forward displacement analysis (FDA) in closed form of two classes of new parallel mechanisms derived from the Stewart Platform Mechanism (SPM) is presented in this paper. These mechanisms, when a set of actuator displacements is given, become multiloop structures of type PRR-3S and PPR-3S, with P, R and S for prismatic, revolute and spherical pairs, whereas the SPM has the structure RRR- 3S. Solving the FDA in closed form means finding all the possible positions and orientations of the output controlled link when a set of actuator displacements is given, or equivalently, finding all possible closures of the corresponding structure. The closed form analysis of the PRR-3S and PPR-3S structures here presented results in algebraic equations in one unknown of degreee 16 and 12, respectively. Hence 16 and 12 closures of the corresponding structures can be obtained. Numerical examples confirm these new theoretical results. © 1992 by ASME
A family of 3-DOF translational parallel manipulators
No full textThis article addresses parallel manipulators with fewer than six degrees of freedom, whose use may prove valuable in those applications in which a higher mobility is uncalled for. In particular, a family of 3-dof manipulators containing only revolute joints or at the most revolute and prismatic ones is studied. Design and assembly conditions sufficient to provide the travelling platform with a pure translational motion are determined and two sub-families that fulfill the imposed constraint are found: one is already known in the literature, while the other is original. The new architecture does not exhibit rotation singularities, i.e., configurations in which the platform gains rotational degrees of freedom. A geometric interpretation of the translation singularities is provided
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