Journal of Engineering and Thermal Sciences
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Finite element analysis of thermo-elastical modal damping of mems vibrations
Get PDFThe paper deals with finite element analysis of damped modal vibrations Q-factor values determined by thermal-elastic damping in micro-electrical-mechanical systems (MEMS). Mathematically the problem is formulated as a complex eigenvalue problem. Verification problems have been solved by using several computational environments and different presentations of model equations in order to comprehend and reduce the influence of rounding errors. The analysis of damped modal properties of selected real MEMS resonator revealed the main features of thermal-elastic damping by taking into account 3D geometry of the resonator and anchoring (clamping) structur
Vibration control of cantilever beam
Get PDFThe paper describes two approaches to problem of active damping of vibrations of cantilever beam. First one uses standard LTI (linear time invariant) mathematical model of the system and state feedback with the state observer designed by pole placement method. The incomplete pole assignment method is used instead of the standard full assignment. The second one is based on experimental identification of the first mode shape and design dynamic compensator. Experimental results of both methods are compared. The problem of robustness of the compensator by frequency domain method based on the unstructured uncertainty of the model is also addresse
The influence of friction on the dynamic model for a 6-DOF parallel robot with triangular platform
Get PDFThe dynamic analysis is an important element of the mechanical design and control of parallel mechanisms. This paper presents a method for the dynamical modeling of the guided in three points parallel robots with six degrees of freedom having triangular platform, including the friction. The evaluation of the full generalized forces is performed in two stages. In the first stage, the drive generalized forces are established, based on the dynamical equations without friction. Using the Newton-Euler equations, the reactions from each joint are computed. In the second stage the additional drive generalized forces due to the frictions from the active and passive joints are computed by means of two approaches. The first approach considers the whole mechanism. The generalized additional forces which include the friction effect from the corresponding drive joints and the friction effect from all passive joints are calculated using principle of virtual power and the mechanism Jacobi matrices. The second approach treats the kinematic chains as independent. The generalized additional forces are evaluated using the virtual work principle. In both approaches the passive joints are approximated with compliant joints whose momentum are equal to the friction torques of these joint
ERF valves controlled by plane capacitor electric field
Get PDFHoles filled with electrorheological fluid (ERF) are used to form the Braille symbols or relief in Array Manipulators. Matrix of holes is made in the fabric-based copper laminate. Voltage applied to coppered upper and lower surfaces of the plate creates electric field, which controls ERF viscosity. Three methods to form a relief are investigated: (a) using an elastic membrane, covering the holes, (b) dielectric pins moving in the holes, (c) metallic pins moving in the holes. Electric field in a hole of the matrix was calculated as electric field in a hole of plane capacitor. In the case of metallic pins, the mean electric field near the electrodes is considerably stronger than in the case of dielectric pins. The controlling voltage can be decreased using multilayer copper laminate valves, composed of some fabric-based plates with opposite directions of electric field in neighbouring plate
Computerized posturography for data analysis and mathematical modelling of postural sway during different two-legged and one-legged human stance
Get PDFMechanisms of balance control are investigated on computerized posturography data on vertical two-legged and uncomfortable one-legged stance measured on healthy subjects. Oscillations of the centre of mass in the course of 30 s standing and the corresponding trajectories for a step forward off the force platform have been computed. Spectral analysis of the time series revealed three main harmonics for the studied postures. When a volunteer was balancing standing on one leg, all the harmonics were shifted towards the high frequencies and the sway amplitude was twice increased in comparison with comfortable two-legged vertical stance. Decomposition of the sway trajectories into the rambling and trembling components has been carried out. It was shown that in the course of the one-legged stance the balance control strategy includes ‘scanning’ of the larger area with bigger sway amplitudes in the vicinity of the stable state as compared to two-legged stance. A mathematical model of the body as a multi-link system is considered. Mass and inertia of each body segment and torques in joints are taken into consideration. The calculated own and forced frequencies of the model correspond to the spectral analysis of the posturography data. One-legged stance is proposed as an excellent tool for revealing the balance problems. It is shown that investigation of the oscillations and trajectories of the centre of mass for the step forward off the force platform is perspective for medical diagnostics to distinguish between the spine and joint pathologie
Measurement of sportsman‘s jump psychomotoric reaction
Get PDFFor representatives of sport games are very important components of physical abilities – spring and rate of psychomotoric reaction. For the following sportsman’s especially important is the rate of psychomotoric reaction, which defines reaction to the constantly changing ambience, similar to the sport action. Testing system, which simulates the situation of sports game, was created in the department of Informatics and biomechanics of LKKA. This system allows estimating the physical capabilities of player – spring and the speed of psychomotoric reaction. The speed of psychomotoric reaction is evaluated by making the jump-up. The influence of the height of jump-up on the spring and speed of reaction of sportsman is investigated. Considering the results of experiments and statistical analysis some recommendations are given and conclusions withdraw
Research of artificial heart ventricle based on the principle of travelling waves driven by piezoelectric actuation
Get PDFThe present article deals with the piezoelectrically-induced travelling wave that arises in periodically loaded tube and it drives blood through tube intended for application as an artificial heart ventricle. However, frequencies of piezoelectrically actuated running waves lie in ultrasonic frequency band and such big frequencies cannot be used for the blood transfer in an artificial heart. Using finite element method the forms of oscillations in the tube of the artificial heart ventricle, natural frequencies and the characteristics of blood flow through the tube (rate of flow-through, flow and pressure) were calculated. Blood pressure and flow dependencies on different tube characteristics such as tube diameter, wall thickness and frequency and magnitude of systolic driving force were studied. The calculation method allows estimating rational parameters of the artificial heart ventricle
Validation of vibration analysis using photo-elastic coatings
Get PDFThe analysis of vibrations is performed using a plate bending element assuming that a coating has no effect to the motion of the plate. The stresses in the coating are calculated by using the procedure of conjugate approximation. Then the relative error norms for the finite elements are determined. They are represented graphically and serve for validation of the results of calculations in hybrid experimental - numerical procedures
Analysis of insertion process for robotic assembly
Get PDFInsertion process of cylindrical parts with clearance for robotic assembly using vibratory excitation is analyzed in the paper. Mathematical model of vibratory parts insertion process, which determines peg contact with the chamfer of the bush, peg one point and two point contact with the bush hole, was formed. Simulation of cylindrical parts insertion process was performed. The influence of vibrations on the insertion process, when mobile based peg is kinematically excited in axial direction, was determined. The combinations of excitation and system parameters, under which insertion process duration is the shortest and the process is the most reliable, were detecte
Characteristics of porous implant steel 316L for orthopedic applications
Get PDFThe porous materials are recently considered to be the prospective biomaterials for restorative medicine. The Young’s modulus of porous metallic biomaterials is much lower than those of non-porous and comparable to modulus of hard tissues, which can improve the conditions of bone remodeling and heading. The porous structure is also interesting from tribological point of view. The usage of porous material for friction elements of joint endoprostheses changes the wear mechanisms and causes decrease of resistance to motion and material wear loss. The aim of present research was to analyze the structure of porous 316L implant steel and its influence on main functional properties of sinters. Samples with porosity of 26, 33, and 41% were made of the 316 stainless steel by the powder metallurgy method. Microstructure was described using conventional image analysis techniques. The mechanical properties were determined in static compressing tests. Fatigue tests were conducted under the fully reversed strain controlled mode. A good correlation has been found between structural parameters and tribological as well as mechanical properties. The low-cyclic fatigue investigations confirm the steady properties of porous materials in the certain range of strai