Journal of Engineering and Thermal Sciences
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A distributed control for a grasping function of a hyperredundant arm
Get PDFThe paper focuses on the control problem of a tentacle robot that performs the coil function of grasping. First, the dynamic model of a hyperredundant arm with continuum elements produced by flexible composite materials in conjunction with active-controllable electro-rheological fluids is analyzed. Secondly, both problems, i.e. the position control and the force control are approached. The difficulties determined by the complexity of the non-linear integraldifferential equations are avoided by using a basic energy relationship of this system. Energy-based control laws are introduced for the position control problem. A force control method is proposed, namely the DSMC method in which the evolution of the system on the switching line by the ER fluid viscosity is controlled. Numerical simulations are also presente
Fiber-optic sensors for nanometric displacement and vibration measurement in mechatronics
Get PDFFiber-optic sensors are widely used for displacement and vibration measurements in mechatronic systems. Sensors can be of very small size and operate in blast danger conditions and strong electromagnetic interference environment. In this work modeling and experimental investigation of the characteristics U-h of fiber-optic sensor of displacement have been accomplished with a view to obtain the maximal sensitivity in the displacement and vibration measurements. The modeling and experimental results were perfectly coincidental, therefore the limit sensitivity of sensors can be predicted by modeling. Configurations of non-contact fiber optic sensors of the maximal possible sensitivity have been found, the metrological parameters of which do not depend either on the degradation of the light source, intensity or on the elements used in the mechatronics system measurements as well as on the value of the mirror reflection coefficient and changes with the aging process. All that increases the reliability of mechatronics system monitoring, which is of utmost importance for their exploitatio
Development of electropneumatic servo system with reference model based signal adaptive force controller
Get PDFDue to pneumo-mechanical power conversion process nonlinearities and process parameters (volumes and initial pressures of pneumatical cylinder working chambers) on line change it is problematic to ensure satisfactory control quality of pneumatic proportional servo drive. Considering that all nonlinearities are concentrated in the force generation stage, application of adaptive force control mode is suggested. Electropneumatic servo drive with reference model based signal adaptive force controller is developed and investigated in this paper. It is presented the strategies of reference model choice and are given control quality investigation results of electropneumatic servo syste
Determination of rational sizes of leg prosthetics manufacturing errors and their links resilience
Get PDFPaper presents rational values of manufacturing and assembly summary errors appointed according to hip and its joint, knee and tarsus motion trajectories, angular analysis, also research results of step asymmetry and variation of shoulder’s and head’s tilt angles, either the anthropometrical parameters were evaluated. The analysis of possibilities of manufacture and assembly errors and inter-compensation of leg prosthesis elastic links was made. The results showed that disabled person gait will be smoother and he will not get tired so soon, when values of elastic deformations will be two times bigger than the summary value of manufacturing and assembly errors. Besides, the essential condition of disabled smooth gait is that the value of manufacturing and assembly errors of leg prosthesis links would be positiv
CFAR vibration signal change test and its applications to real-time recognition of developing cracks in jet engine rotors
Get PDFThis paper introduces a new technique for early identification of fatigue cracks, namely the constant false alarm rate (CFAR) test. This test works on the null hypotheses that a target vibration signal is statistically similar to a reference vibration signal. In effect, this is a time-domain signal processing technique that compares two signals, and returns the likelihood whether the two signals are similar or not. The system monitors the vibration signal of the rotor as it cycles, and compares that vibration signal with, say, the original vibration signal. The difference vector reflects the change in vibration over time. As a crack develops, the vector changes in a characteristic way. Thus, it is possible, during CFAR test, to determine whether the two signals are similar or not. Therefore, by comparing a given vibration signal to a number of reference vibration signals (for several crack scenarios) it is possible to state which is the most likely condition of the rotor under analysis. The CFAR test not only successfully identifies the presence of the fatigue cracks but also gives an indication related to the advancement of the crack. This test, despite its simplicity, is an extremely powerful method that effectively classifies different vibration signals, allowing for its safe use as another condition monitoring techniqu
Study of robot actuator operating as a system on air films
Get PDFThe paper analyzes the dynamics of a robot pneumatic actuator. The mechanical system motion is described by a differential equation system when the air flow is expressed by a non-dimensional Prandtl formula. The findings of the digital study are presented. The zones of self-exciting vibrations of the vibrotransducer have been determined, as well as the dependences of amplitudes and frequency upon the supply air pressure. The dependence of the linear movement of the actuator’s gripper device and its velocity on the geometric parameters of the vibrating transducer of the mechanical system is presente
Researches of temperature influence on parameters of rotor rotation of rotary system
Get PDFRotary systems with bearings of sliding friction are analyzing in this paper. It is researching influence of temperature change on characteristics of work of searching system. It had done experimental researches trying to ascertain how temperatures change is doing influence on parameters of work of rotary systems with bearings of sliding. Experimental measurements are doing by methodology that is making specially, using different transducers of measurement. It is describing and giving principal system of measurement and analysis, its photo, scheme of measurement and methodology of experiments performance. It is getting primary signals of measurement of rotor vibrations, temperature changes and results of analysis are giving in graphs. It is doing analysis of getting results and it is establishing interdependences of searching parameters, their consistent patterns of changes and influence on quality of work of searching syste
Meaningful finite element discretization scheme: a case for circular disk subjected to four radial loads
Get PDFIn finite element (FE) modelling, apart from proper element selection, selection of an appropriate discretization scheme is crucial in correctly evaluating the intended variables. Photoelasticity plays an effective role in selecting an appropriate discretization scheme for modelling problems in stress analysis. A meaningful FE discretization is very important in evaluating the desired parameters in FE analysis. The adaptive mesh refinement emphasizes the need for a meaningful discretization of domain. This paper presents a discretization strategy for meaningful discretization of the circular disk subjected to four equal radial loads. The work evolved the generation of software for the disk subjected to four radial loads perpendicular to each other. Due to symmetry of the problem only quarter of the disk is discretized
Parametric and non parametric characterization of a shear mode magnetorheological damper
Get PDFMR (magnetorheological) dampers are versatile devices whose design is aimed to take the best of magnetorheological fluids: high yield strength, low power requirements, insensitivity to contaminants and hence, low cost. MR dampers have proven to be a good option for the mitigation of uncomfortable and hazardous vibrations in systems such as vehicles, buildings, bridges, etc. However, MR dampers are highly nonlinear devices that exhibit a hysteretic force-velocity loop. Their extensive applications in vibration control systems demand an accurate mathematical model. In this paper, two models for an MR damper operated in shear mode are presented: a parametric approach (Bouc-Wen model) and a non parametric one (neural network model
Possibilities of assessment of reliability of an anthropotechnical system
Get PDF"Reliability and safety characteristics [7] of an anthropotechnical system are the basic information about the correctness of relation between a man (e.g. pilot) and a helicopter (machine). Methods of defining them are still an open problem. The article presents an innovative way of definition of reliability characteristics of a pilot and a helicopter engine as well as an entire anthropotechnical system. Described are theoretical bases of this method, which are various configurations of the ""equation of state"" describing relations pilot – helicopter and helicopter – pilot [8, 9]. Defined was the set of ""numbers of limit state violations"" of the parameter of pilot’s physical condition aP and technical state of the helicopter aS, which as ""premises of damage"" were used for calculation of estimators of reliability characteristics. It is noteworthy that these characteristics could be particularly useful in the process of comparing different pilots and helicopters in various situations appearing in the course of utilisation