Nicu George Bizdoaca

Dynamic control for a tentacle manipulator with SMA actuators

The control problem of the spatial tentacle manipulator with SMA control is presented. The difficulties determined by the complexity of the nonlinear integral-differential equations are avoided by using a very basic energy relationship of this system. A PD controller is discussed and a control coefficient selection procedure is introduced. Numerical simulations for planar and spatial tentacle models are presented and an experimental model is discussed.

Frequency criteria for the grasping control of a hyper-redundant robot

The paper focuses on hyper-redundant arms with continuum elements that perform the grasping function by coiling. First, there is concern with the dynamic model of the continuum arm for the position control during non-contact operations with the environment. A frequency stability criterion based on the Kahman - Yakubovich - Popov Lemma and P and PD control algorithms is proposed. Then, the grasping control of the arm in contact with a load is analyzed. The dynamics of the system are discussed and an extension of the Popov criterion is endorsed. The control algorithms based on SMA actuators are introduced. Numerical simulations and experimental results of the arm motion toward an imposed target are presented.

Condition monitoring of transformer oil using thermal analysis and other techniques

Any transformer oil undergoes continuous degradation because of all electric, thermal, mechanical, and climatic stresses it suffers while operating in the transformer. Therefore, the oil has to be checked on regular basis in order to decide whether it is necessary to regenerate or replace it, avoiding thus a sudden failure of the transformer. This article presents results of in-the-laboratory-performed experiments on transformer mineral oil samples. Those samples came from a power transformer that works in the Romanian power network. There were three monitoring stages conducted over four-and-a-half years. We used two measuring techniques: (i) measurement of the state parameters of transformer oil (breakdown voltage, loss factor, water contents, acidity index, interfacial tension, number of particles larger than 5 microns, and gas contents) in order to describe the oil condition during the monitoring period and to anticipate any severe fault. This enables the user to take preventive action before a severe fault might eventually occur; (ii) thermal analysis (TA) and Fourier transform infrared spectroscopy (FTIR), in order to determine the stability of oil samples. By using TA and FTIR, and by evaluating each and every significant parameter, it has been proven that the tested oil is still adequate for further employment in the power transformer.

Control Strategy of a 3-DOF Walking Robot

The paper presents the mathematical model of a walking robot where the active pair of legs has three free joints. The mathematical model of the robot is determined considering a systemic approach of the robot as variable causality dynamic systems (VCDS). Taking into account a possible symmetrical structure, only the vertical xz-plane evolution is considered. The results can be extended to three-dimensional space. The approach is best on variable dynamic systems, considering that each leg of the pair can change the state depending of the causality order. It is considered that the first leg has both joints free and the second leg has the second joint free. The model is implemented in MATLAB environment and some evolutions examples are presented.

Active solar panel tracking system actuated by shape memory alloy springs

The unique properties (e.g. Shape memory effects) exhibited by shape memory alloys (SMAs) offer the possibility of producing Smart Sun Tracking Mechanisms (SSTMs) for photovoltaic panels. The paper presents an experimental model of an active solar panel tracking system, conceived by authors. This model uses SMA springs as actuators. The SMA springs work as linear actuators by contracting with great strength and speed when heated. The SMA springs attached to this structure can be activated to accurately change the position of the solar panel, following, this way, the motion of the sun throughout the day (appropriately tilted to directly face the sun during the day time). The active shape-change control of SMA spring, the possibilities for miniaturization, easy integration in system structure can effectively increase the efficiency of such SSTM.

Shape memory alloy-based smart module structure working under intense thermo-mechanical stress

The paper presents a complete model for a modular mechatronic structure actuated by a one-way memory effect shape memory alloy actuator. In order to claim the complete attribute of the model, the austenite transformation temperature evolution of actuator was evaluated in relation with the precision and repeatability related capabilities of the mechatronic structure. The evolution of austenite transformation temperature was obtained through determinations based on DSC method. Those determinations were performed on the shape memory alloy wire used as actuator in the modular mechatronic structure. The wire is subject of intense and repetitive operating mode. All determinations are performed on the SMA wire used as actuator system after 5,000, and 1,003,600 cycles, respectively. The results indicate a shift in both As and Af temperatures, a trend that is heavily dependent on the operating history of the system. Using experimental results, authors built a graph (surface) that is based on heating time schedule, heating current, and austenite finish temperature. Also, the results lead to the conclusion that for any desired heating time, it can be identified (in a restricted but relatively wide range), at least a pair of both austenite finish temperature and heating current. If the control algorithm modifies the electrical current in accordance with the number of working cycles and austenite transformation temperature evolution, the time response and, by default, the structure repeatability are assured even after over 1 million working cycles.

A two level hierarchical fuzzy controller for hyper-redundant cooperative robots

A hierarchical fuzzy controller with two levels is proposed to solve the control for a multi-chain robotic system formed by tentacle manipulators grasping a common object with hard point contacts. The control system contains two parts: the first component is a conventional controller which implements a control strategy based on the Lyapunov stability, and the second one is an adaptive fuzzy controller which adjusts the control parameters by the output of the first level controller. The stability and robustness is investigated and the fuzzy rules are established. Simulation results are presented and discussed.

Control of Snake Type Biomimetic Structure

Robotic cooperative tasks impose, in many cases, a grasping action. Grasping by coiling it is one of the most versatile action. The present article propose a frequency stability criterion based on the Kahman – Yakubovich – Popov Lemma for the hyper-redundant arms with continuum element that performs the grasping function by coiling. Dynamics of the biomimetical robot during non-contact and contact operations, for the position control, is studied. An extension of the Popov criterion is developed. The P control algorithms based on SMA snake-type robot actuators are introduced. Numerical simulations and experimental results of the snake type robot motion toward an imposed target are presented.

Biomimetic control architecture for robotic cooperative tasks

This article proposes some control algorithms to be applied to the MIROSOT robot league architecture. The MIROSOT league soccer game concept is fairly simple: two teams of robots, with 3–5 robots per side, play football autonomously. The ball that the teams play with is an orange golf ball. Above the pitch is a machine vision camera running at 60 frames per second. This camera is linked to a server, which calculates the positions and velocities of each of the robots and the ball, and then determines what each robot should be doing. These instructions are then communicated to the robots over wireless links. In order to develop an efficient control strategy and architecture, the robots have to use strategies from the real human soccer game. Using the software Simi Scout, a suitable analysis of tactics can be extracted from the games. After analyzing the soccer game, a number of attributes are specified and then embedded at different levels. The specified attributes are interconnected, and the analysis of the game is processed for optimization. Using this information, the robot program is adapted and experimental tests/games are played. We comment on the results, and propose an improved control architecture based on practical results.

Modeling and Analysis of Soccer Robot Tasks Using Generalized Stochastic Petri Nets

Robot soccer competition provides an excellent opportunity for robotics research. In particular, the soccer robots must perform real-time visual recognition, navigate in a dynamic field, avoid the obstacle, collaborate with teammates, and kick the ball in the correct direction. All these tasks demand robots that are autonomous (sensing, thinking, and acting as independent creatures), efficient (functioning under time and resource constraints), cooperative (collaborating with each other robot to accomplish tasks that are beyond individual’s capabilities), and intelligent (reasoning and planing actions and perhaps learning from experience). This paper proposes a method of defining and analysing the attacking robot tasks using Petri nets. Attacking soccer robot behaviors are modeled using the generalized stochastic Petri nets. Using Petri nets allows qualitative and quantitative analysis of the task execution. Petri net model is implemented in Petri Net Toolbox under MATLAB environment. Therefore, it is validated the net topology, the evolution of (their dynamics), the structural and behavioral properties (corresponding to checking if resources usage is stable and the model have no deadlocks), as well as the stochastic performance.