Topic
Direct stiffness method
About: Direct stiffness method is a research topic. Over the lifetime, 2584 publications have been published within this topic receiving 53131 citations.
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05 Dec 2011
TL;DR: This work improves the previous general approach, combining a residual-based flexibility torque estimator that uses also a kinematic Kalman filter to handle discretization and quantization errors with an enhanced recursive least squares algorithm that does not suffer from lack of persistent excitation.
Abstract: We consider the problem of estimating on line the nonlinear stiffness of flexible transmissions in robot joints, with special reference to actuation devices with adjustable stiffness in serial configuration. These joints are characterized by a principal motor for controlling the link motion and secondary motor for adjusting the stiffness. In this actuation configuration, the flexible transmission undergoes relatively small deformations and the stiffness estimation problem is more challenging due to poor excitation conditions. We improve our previous general approach, combining a residual-based flexibility torque estimator that uses also a kinematic Kalman filter to handle discretization and quantization errors with an enhanced recursive least squares algorithm that does not suffer from lack of persistent excitation. As a result, stiffness is estimated in a more robust way using only position measurements on the motor sides and motor dynamic parameters. The performance of the proposed estimation method is illustrated through simulations and experiments on the AwAS joint developed at IIT.
15 citations
25 Jun 2006
TL;DR: In this article, the stiffness model for a compliant parallel manipulator (CPM) with orthogonally mounted actuators is presented, which provides three spatial translational DOF for nano-scale manipulation.
Abstract: The stiffness modeling for a compliant parallel manipulator (CPM) is very important since it provides a basis for the characterization of static, modal, and dynamic behavior of the CPM. This paper presents the stiffness modeling of a three-prismatic-universal-universal (3-PUU) CPM with orthogonally mounted actuators, that is designed to provide three spatial translational DOF for nano-scale manipulation. Considering the compliance of each compliant element, the analytical stiffness model for a spatial CPM is established by a straightforward approach, which is then applied to stiffness modeling of the 3-PUU CPM. In addition, the finite element analysis is carried out to validate the developed model, and as a further application, the influence of architectural parameters on stiffness factors are derived based on the stiffness model, which is valuable for a cost-effective design of the CPM.
15 citations
TL;DR: In this paper, the effect of fiber curvature on the overall material stiffness of fiber-reinforced composites is discussed using the formalism of stiffness contribution tensor for the special case of a continuous sinusoidal fiber.
15 citations
TL;DR: In this article, an analytical representation for the solution of the neutron point kinetics equation, free of stiffness and assuming that reactivity is a continuous or sectionally continuous function of time, is presented.
14 citations
TL;DR: In this paper, a Bernoulli-Euler plane beam was used to construct templates for the beam material stiffness, geometric stiffness, and mass matrices, which can be used to design high performance elements.
Abstract: Teaches by example the application of finite element templates in constructing high performance elements. The example discusses the improvement of the mass and geometric stiffness matrices of a Bernoulli‐Euler plane beam. This process interweaves classical techniques (Fourier analysis and weighted orthogonal polynomials) with newer tools (finite element templates and computer algebra systems). Templates are parameterized algebraic forms that uniquely characterize an element population by a “genetic signature” defined by the set of free parameters. Specific elements are obtained by assigning numeric values to the parameters. This freedom of choice can be used to design “custom” elements. For this example weighted orthogonal polynomials are used to construct templates for the beam material stiffness, geometric stiffness and mass matrices. Fourier analysis carried out through symbolic computation searches for template signatures of mass and geometric stiffness that deliver matrices with desirable properties when used in conjunction with the well‐known Hermitian beam material stiffness. For mass‐stiffness combinations, three objectives are noted: high accuracy for vibration analysis, wide separation of acoustic and optical branches, and low sensitivity to mesh distortion and boundary conditions. Only the first objective is examined in detail.
14 citations