Issue 4

JTAM, Sofia, vol. 43 Issue 4 (2013)

Propulsion System with Pneumatic Artificial Muscles for Powering Ankle-Foot Orthosis

Ivanka Veneva1, Bram Vanderborght2, Dirk Lefeber2, Pierre Cherelle2
1Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria
2Vrije Universiteit Brussel, Brussels, Belgium

The aim of this paper is to present the design of device for control of new propulsion system with pneumatic artificial muscles. The propulsion system can be used for ankle joint articulation, for assisting and rehabilitation in cases of injured ankle-foot complex, stroke patients or elderly with functional weakness. Proposed device for control is composed by microcontroller, generator for muscles contractions and sensor system. The microcontroller receives the control signals from sensors and modulates ankle joint flexion and extension during human motion. The local joint control with a PID (Proportional-Integral Derivative) position feedback directly calculates desired pressure levels and dictates the necessary contractions.The main goal is to achieve an adaptation of the system and provide the necessary joint torque using position control with feedback.

JTAM, Sofia, vol. 43 Issue 4 pp. 03-16 (2013), [Full Article]

Calculating the Right-Eigenvectors of a Special Vibration Chain by Means of Modified Laguerre Polynomials

Wolfgang Weber1, Bernd W. Zastrau1, Bernd Anders
1Institut für Mechanik und Flächentragwerke, Technische Universität Dresden, D-01069 Dresden, Germany
2Bienertstr. 29, 01187 Dresden, Germany

This contribution deals with the identification of the right eigenvectors of a linear vibration system with arbitrary n degrees of freedom as given in [1]. Applying the special distribution of stiffnesses and masses given in [1] yields a remarkable sequence of matrices for arbitrary n. For computing the (right-) eigenvectors a generalised approach allowing the use of Laguerre polynomials is performed.

JTAM, Sofia, vol. 43 Issue 4 pp. 17-28 (2013), [Full Article]

On Faraday Instability in Magnetic Liquids: Ince-Erdelyi Approach Applied to the Hill Equation Describing Oscillations of a Ferrofluid Free Surface

M. Hennenberg1, S. Slavtchev2, G. Valchev2
1Microgravity Research Center, Fac. Sc. Appl., Universit´e Libre de Bruxelles, Av. F.D. Roosevelt 50, Brussels 1050, Belgium
2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

When an isothermal ferrofluid is submitted to an oscillating magnetic field, the initially motionless liquid free surface can start to oscillate. This physical phenomenon is similar to the Faraday instability for usual Newtonian liquids subjected to a mechanical oscillation. In the present paper, we consider the magnetic field as a sum of a constant part and a time periodic part. Two different cases for the constant part of the field, being vertical in the first one or horizontal in the second one are studied. Assuming both ferrofluid magnetization and magnetic field to be collinear, we develop the linear stability analysis of the motionless reference state taking into account the Kelvin magnetic forces. The Laplace law describing the free surface deformation reduces to Hill’s equation, which is studied using the classical method of Ince and Erdelyi. Inside this framework, we obtain the transition conditions leading to the free surface oscillations.

JTAM, Sofia, vol. 43 Issue 4 pp. 29-48 (2013), [Full Article]

Elastic Plastic Properties of Multiphase Composite Based on Non Homogeneous Metal Matrix – Modelling and Simulation

Ludmila Parashkevova, Nikolina Bontcheva
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

A new approach for estimating the mechanical properties of multiphase composite is proposed. The Representative Volume Element (RVE) of the material consists of two different metal matrices and arbitrary number of elastic hardening phases. Multistep homogenization procedures are applied, accounting for influence of the constituent properties, sizes, volume fractions and microstructural distributions. Modified Mori-Tanaka homogenization technique for micropolar media and Budiansky self-consistent method are used for estimation the overall properties of the composite. The theoretical model is applied to description of the properties of precipitation hardening rapidly solidified alloy of the system AlFeVSi with high content of Fe and Si.

JTAM, Sofia, vol. 43 Issue 4 pp. 49-60 (2013), [Full Article]

Theoretical Study of the Effect of Probe Shape on Adhesion Force between Probe and Substrate in Atomic Force Microscope Experiment

Li Yang, Junhui Hu, Lingjiang Kong
College of Physics Science and Technology, Guangxi Normal University, Guilin, 541004, China

The quantitative description of adhesion force dependence on the probe shape is of importance in many scientific and industrial fields. We performed a theoretical study on the influences of the probe shape (the sphere and parabolic probe) on the adhesion force at different humidity in order to elucidate how the adhesion force varied with the probe shape in atomic force microscope manipulation experiment. We found that the combined action of the triple point and the Kelvin radius is the guiding trend of the adhesion force, and these two fundamental parameters are closely related to the probe shape. Meanwhile, the theoretical results demonstrated that the adhesion force are in a good agreement with the experiment data if the van der Waals force is take into account.

JTAM, Sofia, vol. 43 Issue 4 pp. 61-72 (2013), [Full Article]

The First Bulgarian Industrial Robot “PROBO” 1987

Galia V. Tzvetkova
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

The paper presents the first Bulgarian industrial robot “PROBO” build up entirely on elements, tools and human efforts at the former “Precision mechanics” laboratory within the Bulgarian Academy of Sciences. The robot was publicly demonstrated at Plovdiv exposition in 1987. The place of the robot in the world timeline is shown. A definition of “robot” is proposed, as well.

JTAM, Sofia, vol. 43 Issue 4 pp. 73-76 (2013), [Full Article]

Corrigendum to “Nonlinear Dynamics and Stability of Thin Films with Insoluble Surfactants” (Journal of Theoretical and Applied Mechanics, Sofia, 2011, vol. 41, No. 3, pp. 43–58)

S. Tabakova1,2
1Department of Mechanics, TU – Sofia, branch Plovdiv, 25, Tzanko Djustabanov, 4000 Plovdiv, Bulgaria
2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

JTAM, Sofia, vol. 43 Issue 4 pp. 77-78 (2013), [Full Article]

Corrigendum to “Diagnosis of Type, Location and Size of Cracks by Using Generalized Differntial Quadrature and Rayleigh Quotient Methods” (Journal of Theoretical and Applied Mechanics, Sofia, 2013, vol. 43, No. 1, pp. 61–70)

Majid Akbarzadeh Khorshidi1, Delara Soltani2
1School of Mechanical Engineering, College of Engineering, University of Tehran, Iran
2School of Mechanical Engineering, Mazandaran Institute of Technology, Iran

JTAM, Sofia, vol. 43 Issue 4 pp. 79-80 (2013), [Full Article]