Nonlinear flexure coupling elements for precision control of multibody systems

Conventional multibody systems used in robotics and automated machinery contain bearing components that exhibit complex and uncertain tribological characteristics. These limit fundamentally the precision of the automated motion and also cause wear. Replacing traditional bearing joints with flexure couplings eliminates these tribological effects, together with wear, reducing necessary system maintenance and offering a potential for increased motion precision. A flexure-coupled multibody system is considered and a novel general solution technique is presented. Derivation of a large deflection flexure coupling model is provided and subsequently validated using an experimental facility. A focused study of a unique double-flexure-coupling rigid body system is given; the formulated nonlinear mathematical model can be used for feedforward control. Equivalent control is also applied to a corresponding system with traditional bearing joints. The feasibility of replacing bearing joints by flexure couplings is demonstrated in terms of accurate large displacement control and reduction of high-frequency disturbances.

Flexure Analysis of Laminated Plates Using Multiquadratic RBF Based Meshfree Method

The linear and nonlinear flexure analysis of laminated plates with twenty theories with the five variable higher order shear deformation theory (HSDT) is investigated using multiquadratic radial basis function based meshfree method. The mathematical formulation of the actual physical problem of the plate subjected to transverse loading is presented utilizing von Karman nonlinear kinematics. These non-linear governing differential equations of equilibrium are linearized using quadratic extrapolation technique. The different results for deflection and stresses are obtained for thin to a thick plate and compared with some published results. It is observed that some of the theories taken here are well suited for analysis of thin as well as a thick plate while some theories are suited only for thin plates.

Ring-Based Stiffening Flexure Applied as a Load Cell With High Resolution and Large Force Range

This paper applies linear elastic theory and Castigliano's first theorem to design nonlinear (stiffening) flexures used as load cells with both large force range and large resolution. Low stiffness at small forces causes high sensitivity, while high stiffness at large forces prevents over-straining. With a standard 0.1 μm deflection sensor, the nonlinear load cell may detect 1% changes in force over five orders of force magnitude. In comparison, a traditional linear load cell functions over only three orders of magnitude. We physically implement the nonlinear flexure as a ring that increasingly contacts rigid surfaces with carefully chosen curvatures as more force is applied. We analytically describe the load cell performance as a function of its geometry. We describe methods for manufacturing the flexure from a monolithic part or multiple parts. We experimentally verify the theory for two load cells with different parameters.

Nanomechanics of Peeling Studied Using the Atomic Force Microscope

Through adaptation of an atomic force microscope, we have developed a peel test at the micro- and nanoscale level that has the capability of investigating how long flexible nanotubes, nanowires, nanofibers, proteins, and DNA adhere to various substrates. This novel atomic force microscopy (AFM) peeling mode extends existing AFM “pushing” and “pulling” force spectroscopies by offering practical knowledge about the complex interplay of nonlinear flexure, friction, and adhesion when one peels a long flexible molecule or nanostructure off a substrate. The static force peeling spectroscopies of straight multiwalled carbon nanotubes suggest that a significant amount of the total peeling energy is channeled into nanotube flexure. Meanwhile dynamic force spectroscopies offer invaluable information about the dissipative physical processes involved in opening and closing a small “crack” between the nanotube and substrate.