The Experts below are selected from a list of 20544 Experts worldwide ranked by ideXlab platform

V A Lubarda - One of the best experts on this subject based on the ideXlab platform.

  • Equilibrium Position of screw dislocation near circular inhomogeneity at the tip of an elastic wedge
    Meccanica, 2018
    Co-Authors: V A Lubarda
    Abstract:

    The image force on a screw dislocation at the distance $$\rho =\alpha a\,(\alpha >1)$$ from the tip of an isotropic wedge of shear modulus G with a circular inhomogeneity of radius a and shear modulus $$G'$$ at its end is determined by the method of image dislocations. If the wedge angle is $$\pi /n$$ , for an integer $$n\ge 1$$ , $$4n-1$$ image dislocations are needed to achieve the required traction-free boundary conditions and the interface continuity conditions. It is shown that for the positive values of the inhomogeneity parameter $$\kappa =(G'-G)/(G'+G)$$ , there is an Equilibrium Position of the dislocation along the plane of symmetry of the wedge, specified by the parameter $$\alpha _\mathrm{eq}=\left[ 2n\kappa +\left( 1+4n^2\kappa ^2\right) ^{1/2}\right] ^{1/2n}$$ . The Equilibrium Position is stable relative to disturbances of the dislocation Position along the plane of symmetry, but unstable for other disturbances. If the edges of the wedge and the inhomogeneity are fixed, rather than traction free, the Equilibrium Position of the dislocation along the plane of symmetry is specified by $$\alpha _\mathrm{eq}=\left[ 1-4n\kappa /(2n-1)\right] ^{1/4n}$$ , provided that the inhomogeneity is softer than the matrix material ( $$\kappa <0$$ ). The Equilibrium Position is unstable relative to disturbances of the dislocation Position along the plane of symmetry. In the case of homogeneous wedges ( $$\kappa =0$$ ), the image force in the plane of symmetry for a wedge with fixed edges depends on the wedge angle and is given by $$f=(2n-1)k/2\rho$$ (away from the tip), while for a wedge with free edges the image force is independent of the wedge angle ( $$f=-k/2\rho$$ ).

  • Equilibrium Position of screw dislocation near circular inhomogeneity at the tip of an elastic wedge
    Meccanica, 2017
    Co-Authors: V A Lubarda
    Abstract:

    The image force on a screw dislocation at the distance $$\rho =\alpha a\,(\alpha >1)$$ from the tip of an isotropic wedge of shear modulus G with a circular inhomogeneity of radius a and shear modulus $$G'$$ at its end is determined by the method of image dislocations. If the wedge angle is $$\pi /n$$ , for an integer $$n\ge 1$$ , $$4n-1$$ image dislocations are needed to achieve the required traction-free boundary conditions and the interface continuity conditions. It is shown that for the positive values of the inhomogeneity parameter $$\kappa =(G'-G)/(G'+G)$$ , there is an Equilibrium Position of the dislocation along the plane of symmetry of the wedge, specified by the parameter $$\alpha _\mathrm{eq}=\left[ 2n\kappa +\left( 1+4n^2\kappa ^2\right) ^{1/2}\right] ^{1/2n}$$ . The Equilibrium Position is stable relative to disturbances of the dislocation Position along the plane of symmetry, but unstable for other disturbances. If the edges of the wedge and the inhomogeneity are fixed, rather than traction free, the Equilibrium Position of the dislocation along the plane of symmetry is specified by $$\alpha _\mathrm{eq}=\left[ 1-4n\kappa /(2n-1)\right] ^{1/4n}$$ , provided that the inhomogeneity is softer than the matrix material ( $$\kappa

Yuzhuang Zhao - One of the best experts on this subject based on the ideXlab platform.

  • height adjustment of vehicles based on a static Equilibrium Position state observation algorithm
    Energies, 2018
    Co-Authors: Sizhong Chen, Yuzhuang Zhao
    Abstract:

    In this paper, a static state observer algorithm based on the static Equilibrium Position is proposed, which can realize accurate control of electric vehicle height adjustment with existing road excitation. The existence of road excitation can lead to deflection variation of the electronically controlled air suspension (ECAS). The use of only dynamic deflection as the reference for the electric vehicle height adjustment will produce great errors. Therefore, this paper provides an observation algorithm, which can realize the accurate control of vehicle height. Firstly, the static Equilibrium Position equation of suspension is derived according to the theory of hydrodynamics and characteristics of pneumatic chamber. Secondly, a vehicle dynamics model with seven degrees of freedom (7-DOF) is established and the kinetic equations are discretized. Then, the unscented Kalman filter (UKF) algorithm is used to obtain the static Equilibrium Position of vehicle. According to the vehicle static Equilibrium Position obtained by UKF, the height of the vehicle is adjusted by using a fuzzy controller. The simulation and experimental results show that this proposed algorithm can realize the control of vehicle height with an accuracy of over 96%, which ensures the excellent driving performance of vehicles under different road conditions.

Abhinav Dahiya - One of the best experts on this subject based on the ideXlab platform.

  • Positive–Negative Stiffness Actuators
    IEEE Transactions on Robotics, 2019
    Co-Authors: David J Braun, Vincent Chalvet, Abhinav Dahiya
    Abstract:

    Compliant actuators are typically designed to possess a tunable positive stiffness characteristic in order to generate restoring force upon displacement. These actuators either require two independent motor units or closed-loop control to change both their Equilibrium Position and output stiffness. The introduction of negative stiffness, in combination with tunable positive stiffness, may reduce the complexity and extend the capability of these actuators in unexpected ways. In this paper, we present a compliant actuator that employs a passive negative stiffness mechanism in conjunction with an effectively tunable positive stiffness mechanism. We show that such actuator enables open-loop stiffness modulation and Equilibrium Position control using a single motor unit, as opposed to more conventional variable stiffness and series elastic actuators. The paper presents the theoretical foundation of positive-negative stiffness actuators and demonstrates low-power stiffness modulation and Equilibrium Position control achievable with a prototype positive-negative stiffness actuator.

  • Efficiently tunable positive-negative stiffness actuator
    Proceedings - IEEE International Conference on Robotics and Automation, 2017
    Co-Authors: Abhinav Dahiya, David J Braun
    Abstract:

    — Compliant actuators have found their place in ar-eas of prosthetics, rehabilitation and robot locomotion because they enable safe human-robot and stable robot-environment interaction, both non-trivial to achieve using conventional rigid actuation. These actuators are capable of varying their Equilibrium Position and apparent output stiffness in a way humans change the resting Position and compliance of their limbs. Just like antagonistically actuated human joints, these actuators require two motor units to provide control over the Equilibrium Position and the positive joint stiffness. Here we present a novel compliant actuation concept which affords control over the Equilibrium Position and joint stiffness using a single motor unit. In order to achieve this unconventional functionality, the actuator combines a passive positive feed-back (negative stiffness) mechanism with an efficiently tunable negative feedback (positive stiffness) mechanism. This provides a novel design with two distinct operation modes, one leading to unprecedented stiffness tunability, while the other enabling Equilibrium point controllability. We present the first practical implementation of this actuator using a prototype prosthetic limb design along with experimental data testifying the range of tunability, covering compliant to rigid behaviour, without paying much on the power input.

Peter J Halling - One of the best experts on this subject based on the ideXlab platform.

  • solvent effects on biocatalysis in organic systems Equilibrium Position and rates of lipase catalyzed esterification
    Biotechnology and Bioengineering, 1991
    Co-Authors: Rao H Valivety, Grant A Johnston, Colin J Suckling, Peter J Halling
    Abstract:

    : Porcine pancreatic lipase immobilized on celite particles has been employed as a catalyst for the esterification of dodecanol and decanoic acid in a predominantly organic system. Solvent influence on the Equilibrium Position and on the catalyst activity has been studied using 20 solvents, including aliphatic and aromatic hydrocarbons, ethers, ketones, nitro- and halogenated hydrocarbons, and esters. The Equilibrium constant for esterification correlates well with the solubility of water in the organic solvent, which in turn shows a good relationship with a function of Guttman's donor number and the electron pair acceptance index number of the solvent. This may be rationalized in terms of the requirements for solvation of water and of the reactants. The catalyst activity, measured as the initial rate of the esterification reaction, is best correlated as a function of both n-octanol-water partition coefficient (log P) and either the electron pair acceptance index or the polarizability.

  • solvent selection for biocatalysis in mainly organic systems predictions of effects on Equilibrium Position
    Biotechnology and Bioengineering, 1990
    Co-Authors: Peter J Halling
    Abstract:

    Predictions may be made for the influence of solvent choice on the Equilibrium Position of biocatalyzed reactions, based on data for the liquid–liquid distribution of the reactants. The most reliable predictions are probably for dilute systems, based on partition coefficients or correlations derived from them. The effective Equilibrium constant for esterification reactions is predicted to alter by more than four orders of magnitude on changing between different water-immiscible solvents. The Equilibrium constant correlates well with the solubility of water in the solvent, and is most favorable for synthesis in the least polar solvents (aliphatic hydrocarbons). Similar effects seem to apply for other reactions, including oxidation of alcohols and hydrolysis of chlorides. Predictions can be made for nondilute systems using the UNIFAC system of group contributions, but the reliability of these is more questionable.

D. Lefeber - One of the best experts on this subject based on the ideXlab platform.

  • maccepa the mechanically adjustable compliance and controllable Equilibrium Position actuator design and implementation in a biped robot
    Robotics and Autonomous Systems, 2007
    Co-Authors: B. Vanderborght, M. Van Damme, B. Verrelst, D. Lefeber
    Abstract:

    In this paper a rotational actuator with a novel adaptable compliance (inverse of stiffness) is presented. First, a number of comparable designs are given with their possible drawbacks. The MACCEPA concept and design is then described in detail. The equation to calculate the generated torque is derived. Depending on the design parameters, it is shown that the torque is a quasi linear function with respect to the angle between the Equilibrium Position and the actual Position. Also, the change of the pre-tension has a quasi linear effect on the torque. Another advantage is that the actuator can be built with standard components, e.g. electrical servo motors. Experiments show independent control of the Equilibrium Position and compliance. The use of the MACCEPA in the Controlled Passive Walking biped Veronica is described. Controlled Passive Walking is an approach that combines the advantages of actively controlled robots and passive walkers. By adapting the compliance of the joints, natural motions can be chosen in order to obtain a controllable and energy efficient walking motion. To test the concept, the biped Veronica is built, actuated by six MACCEPAs.

  • maccepa the mechanically adjustable compliance and controllable Equilibrium Position actuator a 3dof joint with two independent compliances
    International Applied Mechanics, 2007
    Co-Authors: M. Van Damme, B. Vanderborght, B. Verrelst, D. Lefeber
    Abstract:

    The MACCEPA is a straightforward and easy to construct rotational actuator in which the compliance can be controlled separately from the Equilibrium Position. A 3DOF joint with adaptable compliance is presented. The generated torque is a linear function of the compliance and of the angle between the Equilibrium Position and actual Position. This makes this actuator perfectly suitable for dynamic walking, human-robotic interfaces, and robotic rehabilitation devices

  • MACCEPA: the mechanically adjustable compliance and controllable Equilibrium Position actuator for 'controlled passive walking'
    Proceedings 2006 IEEE International Conference on Robotics and Automation 2006. ICRA 2006., 2006
    Co-Authors: B. Vanderborght, M. Van Damme, B. Verrelst, D. Lefeber
    Abstract:

    In this paper a novel rotational actuator with adaptable compliance is presented. First the importance of adaptable compliance for bipedal walking is explained, and then a number of comparable designs are given with their possible drawbacks. The MACCEPA concept and design is described in detail. The formula to calculate the generated torque is derived. It is shown, depending on the design parameters, that the torque is a quasi linear function with respect to the angle between Equilibrium Position and actual Position. Also the change of the pre-tension has a quasi linear effect on the torque. Another advantage is that the actuator can be built with standard components, e.g. electrical servo motors. Experiments show the independent control of Equilibrium Position and compliance. Finally, the concept of controlled passive walking is explained, which is a combination of the control strategies of active and passive walking robots. Controlled passive walking requires actuators with adaptable compliance, preferably where the control of Equilibrium Position and compliance are independent

  • ICRA - MACCEPA: the mechanically adjustable compliance and controllable Equilibrium Position actuator for 'controlled passive walking'
    Proceedings 2006 IEEE International Conference on Robotics and Automation 2006. ICRA 2006., 2006
    Co-Authors: B. Vanderborght, M. Van Damme, B. Verrelst, D. Lefeber
    Abstract:

    In this paper a novel rotational actuator with adaptable compliance is presented. First the importance of adaptable compliance for bipedal walking is explained, and then a number of comparable designs are given with their possible drawbacks. The MACCEPA concept and design is described in detail. The formula to calculate the generated torque is derived. It is shown, depending on the design parameters, that the torque is a quasi linear function with respect to the angle between Equilibrium Position and actual Position. Also the change of the pre-tension has a quasi linear effect on the torque. Another advantage is that the actuator can be built with standard components, e.g. electrical servo motors. Experiments show the independent control of Equilibrium Position and compliance. Finally, the concept of controlled passive walking is explained, which is a combination of the control strategies of active and passive walking robots. Controlled passive walking requires actuators with adaptable compliance, preferably where the control of Equilibrium Position and compliance are independent

  • Controlled Passive Walker Veronica Powered by Actuators with Independent Control of Equilibrium Position and Compliance
    2006 6th IEEE-RAS International Conference on Humanoid Robots, 2006
    Co-Authors: B. Vanderborght, M. Van Damme, B. Verrelst, D. Lefeber
    Abstract:

    This paper presents the biped Veronica actuated with the MACCEPA actuator. The MACCEPA is an electrical actuator of which the compliance and Equilibrium Position are fully independent and both are set by a dedicated servo motor. 6 such actuators are used to power the planar biped Veronica. The control concept is based on "controlled passive walking". Instead of continuously controlling the biped, the control parameter sets for each joint are only changed a few times during walking. Between the discrete control actions the motion is passive due to the compliant actuators. So this robot behaves like an actuated passive walker. Because the compliance is adaptable, different natural frequencies can be selected. This means that the walking motion is not restricted to a fix walking speed