Mircea Neagoe

Modeling and Optimization of the Global Solar Irradiance Collecting Efficiency

This article presents a mathematical model for estimating the direction of the maximal global solar irradiance (MGSI) based on actual values of direct/beam and diffuse irradiance, model that can be used to determine a correct value of the global collecting efficiency of solar tracking systems. Using this model, the collecting efficiency can be improved by tracking the solar conversion surface to minimize its incidence angle with the maximal global irradiance instead of the beam irradiance. The analysis of the numerical results obtained using in-field data-based simulations showed a significant improvement of the real collecting efficiency, especially during cloudy days when the diffuse irradiance is preponderant.

Conceptual Design of a Chain Speed Increaser for Small Hydropower Stations

Most small hydropower stations drive trains include a gearbox to increase the speed of the turbine shaft to the generator. An increase in speed is needed because the hydro turbines shafts turn at a much lower speed than is required by most electrical generators. The range in which the input angular speed must be increased is 4–8. The speed increasers for this kind of applications must have an acceptable efficiency, reduced overall dimensions and complexity and, therefore, a reduced technological cost. The paper objective is to enlarge the base of speed increasers for small hydro stations with chain transmissions. The concept of the proposed chain transmission to be used as speed increaser is developed using a conceptual design algorithm. The algorithm is based on the VDI model and consists in the following steps: 1°. Requirements list establishment; 2° Global function establishment; 3°. Global function description by structures of sub-functions; 4°. Solving structures generation by: solving the sub-functions, sub-solutions composition and elimination of inadequate solution; 5°. The best solving structure selection by evaluation. The speed increaser function is detailed as part of a hydropower station. The sub-functions of the speed increaser are further analyzed in order to generate the solving structures. Sixteen distinct structural variants are presented in the paper. But only those structural variants, whose technical characteristics fulfill, quantitatively, the requirements, are considered as solving structures (for the speed increaser function). In order to select the solving structures, the synthesis of the sprockets teeth numbers for all the structural variants is performed and their efficiency is calculated. Then, their evaluation is made taking into account the technical-economic criteria; thus, the optimal solution that fulfils the requirements list (the principle solution) is found. The principle solution is an innovative concept of the chain speed increaser and represents an input data for the embodiment design phase.Copyright

Comparative Analysis of Two Wind Turbines with Planetary Speed Increaser in Steady-State

Planetary transmissions used as speed amplifiers in wind/hydro conversion systems typically rely on the conventional concept of mechanism with one input and one output. This concept is found in the most of the high power wind turbines; however, the need to implement in the built environment smaller wind turbines with speed amplifiers led to new turbine concepts such as counter-rotating rotors and classical generator. The paper presents a comparative analysis of two wind turbines with one rotor and respectively two counter-rotating rotors, which contain identical electrical generators and the same type of mechanical amplifier used as a 1 DOF mechanism and differential one respectively. With the assumption of maintaining the same electrical generator running point for both wind turbines, the steady-state behaviour of the considered turbines is identified and a comparative kinematic and static performance analysis is performed, aiming at highlighting the impact on efficiency and on constructive design and development of the two turbines.

Structural Synthesis of Parallel Linkages by Multibody Systems Method

A large variety of methods are mentioned in literature for the structural analysis and conception of parallel linkages, applicable to planar and/or spatial mechanisms developed for various applications as manipulators-robots, guiding mechanisms for car wheels and axle, solar tracking systems. Modern design requires today a unitary description of all the mechanisms in a product (including linkages) for complex simulation and optimization on software platforms. This paper proposes a seven steps general method for the parallel linkages’ structural analysis and synthesis, considered as Multibody Systems. The method is based on the concept that describes a mechanism by a minimum number of bodies. Using as input data the application area, the motion space, the mechanism mobility and the type of joints, all possible fundamental multibody chains are obtained and, based on, the corresponding mechanisms. The method is described in detail and applied for the geometrical constraints of rotational (R), spherical (S), translational (T) and their combinations types. As example, a tracking system for a solar thermal platform, based on a parallel linkage with two degrees of freedom with R, S and T joints is presented.

On New High Performance Systems with Linear Actuators for Diurnal Orientation of PV Platforms

The paper presents new mechatronic systems used to perform the diurnal orientation of photovoltaic (PV) platforms, aiming to achieve high angular strokes and also low cost, high precision, constructive simplicity and relative low pressure angles. Starting from the disadvantages of the existing tracking mechanism identified in the literature (patents, scientific articles, market documentation, etc.), new high performance linkages and gear mechanisms driven by linear actuators are proposed in the paper. Hence, four new tracking mechanisms, achieving high angular strokes (over 180o), are described: a) quadrilateral type, b) rhombus type, c) slider-crank type, and d) linkage with gears type. These mechanisms are designed especially for concentrating PV systems, which require high orientation precision on the entire angular stroke.

Rigid vs. flexible links dynamic analysis of a 3DOF parallel robot

The paper presents the dynamic modeling of a 3 DOF parallel robot of type 1PRRR+2PRPaR. Kinematical and dynamical analytical models using Lagrange formulation with multipliers in rigid links hypothesis are carried out, followed by numerical simulation of the rigid vs. flexible links robot models. The flexible links models are derived using AutoFlex module from ADAMS software. Finally, relevant conclusions regarding the dynamic behavior of the 3DOF parallel robot are presented.

Rigid versus Flexible Link Dynamic Analysis of a 3DOF Delta Type Parallel Manipulator

This paper presents a comparative kinematic and dynamic analysis of a Delta parallel robot based on numerical simulations of the rigid vs. flexible links robot models. The flexible links numerical models are derived using AutoFlex module of Adams software. Finally, the conclusions regarding the obtained results useful in manipulator constructive design are presented.

On a New Parallel Tracking System for Accurate Orientation of Concentrated Solar Convertors

The concentrated solar energy convertors (e.g. solar-thermal dish, concentrated photovoltaic) require high tracking accuracy to maintain low incidence angles of the solar ray in relation with the concentrator optical axis (e.g. tracking accuracy of 0.05°...0.1°). This functional requirement is currently ensured by the high performance dual-axis solar tracking systems, able to reach the imposed accuracy, including expensive rotary actuator solutions. This paper proposes a new high accuracy tracking system for diurnal orientation, integrating a 2 DOF parallel linkage driven by linear actuators, as a simple, accurate, and cost-effective solution. A kinematic and static approach used for optimisation of the driving programs of the two linear actuators is presented, following the requirements: a) ensure the imposed tracking accuracy and b) achieve advantageous transmitting angles and hence lowest driving forces. The performances of the system are analysed on large orientation strokes (over 130°); the results obtained confirm the viability of the new tracking system concept, with higher performances compared to other similar known solutions.

Dynamic analysis of a Triglide parallel robot

This paper presents the analytical dynamic modeling of a Triglide parallel robot and numerical simulation using Maple and Adams software. The Lagrange with multipliers method was successfully applied to develop the closed-form dynamic model using the Maple software. Next, an equivalent dynamic virtual model of the Triglide parallel robot was developed and simulated in ADAMS program on different task. The simulation of the theoretical dynamic models (closed-form model) and ADAMS numerical approach confirm the validity of the analytical dynamic model.

Comparative dynamic analysis of two parallel robots

The paper presents a comparative dynamic modeling and VR (virtual reality) simulation for two 3 DOF medical parallel robots: a three coupled motions structure (Orthoglide robot) versus two coupled motion parallel structure (robot of type 1PRRR+2PRPaR). Kinematical and dynamical models, followed by a VR application with control aspects are presented for these two parallel robots. The innovative user interface for high-level control of the two parallel robots, presented in the paper, was developed in MATLAB - Simulink and SimMechanics environment, while the closed form dynamic models were obtained in MAPLE program. This kind of parallel robots can be successfully applied for medical applications where accuracy and high dynamic behavior are required. This research will lay a good foundation for the development of medical parallel robots.