231 research outputs found
Stiffness Analysis of Parallel Manipulators with Preloaded Passive Joints
The paper presents a methodology for the enhanced stiffness analysis of
parallel manipulators with internal preloading in passive joints. It also takes
into account influence of the external loading and allows computing both the
non-linear "load-deflection" relation and the stiffness matrices for any given
location of the end-platform or actuating drives. Using this methodology, it is
proposed the kinetostatic control algorithm that allows to improve accuracy of
the classical kinematic control and to compensate position errors caused by
elastic deformations in links/joints due to the external/internal loading. The
results are illustrated by an example that deals with a parallel manipulator of
the Orthoglide family where the internal preloading allows to eliminate the
undesired buckling phenomena and to improve the stiffness in the neighborhood
of its kinematic singularities
Enhanced stiffness modeling of manipulators with passive joints
The paper presents a methodology to enhance the stiffness analysis of serial
and parallel manipulators with passive joints. It directly takes into account
the loading influence on the manipulator configuration and, consequently, on
its Jacobians and Hessians. The main contributions of this paper are the
introduction of a non-linear stiffness model for the manipulators with passive
joints, a relevant numerical technique for its linearization and computing of
the Cartesian stiffness matrix which allows rank-deficiency. Within the
developed technique, the manipulator elements are presented as pseudo-rigid
bodies separated by multidimensional virtual springs and perfect passive
joints. Simulation examples are presented that deal with parallel manipulators
of the Ortholide family and demonstrate the ability of the developed
methodology to describe non-linear behavior of the manipulator structure such
as a sudden change of the elastic instability properties (buckling)
Stiffness modeling of non-perfect parallel manipulators
The paper focuses on the stiffness modeling of parallel manipulators composed
of non-perfect serial chains, whose geometrical parameters differ from the
nominal ones. In these manipulators, there usually exist essential internal
forces/torques that considerably affect the stiffness properties and also
change the end-effector location. These internal load-ings are caused by
elastic deformations of the manipulator ele-ments during assembling, while the
geometrical errors in the chains are compensated for by applying appropriate
forces. For this type of manipulators, a non-linear stiffness modeling
tech-nique is proposed that allows us to take into account inaccuracy in the
chains and to aggregate their stiffness models for the case of both small and
large deflections. Advantages of the developed technique and its ability to
compute and compensate for the compliance errors caused by different factors
are illustrated by an example that deals with parallel manipulators of the
Or-thoglide famil
Nonlinear Effects in Stiffness Modeling of Robotic Manipulators
The paper focuses on the enhanced stiffness modeling of robotic manipulators
by taking into account influence of the external force/torque acting upon the
end point. It implements the virtual joint technique that describes the
compliance of manipulator elements by a set of localized six-dimensional
springs separated by rigid links and perfect joints. In contrast to the
conventional formulation, which is valid for the unloaded mode and small
displacements, the proposed approach implicitly assumes that the loading leads
to the non-negligible changes of the manipulator posture and corresponding
amendment of the Jacobian. The developed numerical technique allows computing
the static equilibrium and relevant force/torque reaction of the manipulator
for any given displacement of the end-effector. This enables designer detecting
essentially nonlinear effects in elastic behavior of manipulator, similar to
the buckling of beam elements. It is also proposed the linearization procedure
that is based on the inversion of the dedicated matrix composed of the
stiffness parameters of the virtual springs and the Jacobians/Hessians of the
active and passive joints. The developed technique is illustrated by an
application example that deals with the stiffness analysis of a parallel
manipulator of the Orthoglide family.Comment: ISSN 2070-372
Stiffness Modeling of Robotic-Manipulators Under Auxiliary Loadings
International audienceThe paper focuses on the extension of the virtual-joint-based stiffness modeling technique for the case of different types of loadings applied both to the robot end-effector and to manipulator intermediate points (auxiliary loading). It is assumed that the manipulator can be presented as a set of compliant links separated by passive or active joints. It proposes a computationally efficient procedure that is able to obtain a non-linear force-deflection relation taking into account the internal and external loadings. It also produces the Cartesian stiffness matrix. This allows to extend the classical stiffness mapping equation for the case of manipulators with auxiliary loading. The results are illustrated by numerical examples
Stiffness modeling for perfect and non-perfect parallel manipulators under internal and external loadings
International audienceThe paper presents an advanced stiffness modeling technique for perfect and non-perfect parallel manipulators under internal and external loadings. Particular attention is paid to the manipulators composed of non-perfect serial chains, whose geometrical parameters differ from the nominal ones and do not allow to assemble manipulator without internal stresses that considerably affect the stiffness properties and also change the end-effector location. In contrast to other works, several types of loadings are considered simultaneously: an external force applied to the end-effector, internal loadings generated by the assembling of non-perfect serial chains and external loadings applied to the intermediate points (auxiliary loading due to the gravity forces and relevant compensator mechanisms, etc.). For this type of manipulators, a non-linear stiffness modeling technique is proposed that allows to take into account inaccuracy in the chains and to aggregate their stiffness models for the case of both small and large deflections. Advantages of the developed technique and its ability to compute and compensate the compliance errors caused by the considered factors are illustrated by an example that deals with parallel manipulators of the Orthoglide family
Actuators for a space manipulator
The robotic manipulator can be decomposed into distinct subsytems. One particular area of interest of mechanical subsystems is electromechanical actuators (or drives). A drive is defined as a motor with an appropriate transmission. An overview is given of existing, as well as state-of-the-art drive systems. The scope is limited to space applications. A design philosophy and adequate requirements are the initial steps in designing a space-qualified actuator. The focus is on the d-c motor in conjunction with several types of transmissions (harmonic, tendon, traction, and gear systems). The various transmissions will be evaluated and key performance parameters will be addressed in detail. Included in the assessment is a shuttle RMS joint and a MSFC drive of the Prototype Manipulator Arm. Compound joints are also investigated. Space imposes a set of requirements for designing a high-performance drive assembly. Its inaccessibility and cryogenic conditions warrant special considerations. Some guidelines concerning these conditions are present. The goal is to gain a better understanding in designing a space actuator
STABILITY OF MANIPULATOR CONFIGURATION UNDER EXTERNAL LOADING
International audienceThe paper is devoted to the analysis of robotic manipulator behavior under internal and external loadings. The main contributions are in the area of stability analysis of manipulator configurations corresponding to the loaded static equilibrium. In contrast to other works, in addition to usually studied the end-platform behavior with respect to the disturbance forces, the problem of configuration stability for each kinematic chain is considered. The proposed approach extends the classical notion of the stability for the static equilibrium configuration that is completely defined the properties of the Cartesian stiffness matrix only. The advantages and practical significance of the proposed approach are illustrated by several examples that deal with serial kinematic chains and parallel manipulators. It is shown that under the loading the manipulator workspace may include some specific points that are referred to as elastostatic singularities where the chain configurations become unstable
- …