OPTIMIZATION OF A FUZZY CONTROL DESIGN WITH RESPECT TO A PARALLEL MECHANISM WORKSPACE

Disertační práce je zaměřena na využití fuzzy logiky při návrhu řízení paralelního mechanismu založeného na Stewartově platformě. Hlavním cílem je navrhnout řídicí systém, který zabezpečí provádění biomedicínských experimentů. K tomuto účelu je nezbytné zařízení, které zajistí simulaci fyziologických pohybů lidského těla charakteristickým danému implantátu, včetně silového zatížení. Uzavřený kinematický řetězec paralelních manipulátorů výrazně zvyšuje tuhost mechanismu. Manipulátory s paralelní kinematickou strukturou dosahují lepší přesnosti a opakovatelnosti dosažení požadované polohy efektoru a mohou vyvozovat větší sílu než běžné manipulátory se sériovou kinematickou strukturou. Obecnou nevýhodou paralelních mechanismů bývá jejich relativně malá pracovní oblast oproti sériovým, složitější struktura a komplikované řešení přímé kinematické úlohy. Předkládaná práce přináší efektivní řešení přímé kinematické úlohy pomocí simulačního modelu s fuzzy inferenčním systémem typu Takagi-Sugeno. Navržený systém řízení využívá stavových a fuzzy regulátorů typu Takagi-Sugeno, které jsou odvozeny od stavových regulátorů s integrací na vstupu. Pro návrh a optimalizaci fuzzy regulátorů byla použita technika anfis (adaptive neuro-fuzzy inference system), která emuluje trénovací data pomocí trénování s použitím metody nejmenších čtverců v kombinaci s metodou zpětného šíření. Navržené fuzzy regulátory jsou použity pro řízení jednotlivých ramen manipulátoru. Vlastnosti navrženého systému řízení jsou dokumentovány testovacím experimentem.The Ph.D. thesis is focused on using the fuzzy logic for control of a parallel manipulator based on a Stewart platform. The proposed mechanism makes possible to simulate the physiological movements of the human body and observe degradation processes of the cord implants. Parallel manipulators such as a Stewart platform represent a completely parallel kinematic mechanism that has major differences from typical serial link robots. However, they have some drawbacks of relatively small workspace and difficult forward kinematic problems. Generally, forward kinematic of a parallel manipulators is very complicated and difficult to solve. This thesis presents a simple and efficient approach to design simulation model of forward kinematic based on Takagi-Sugeno type fuzzy inference system. The control system of the parallel manipulator id based on state-space and fuzzy logic controllers. The proposed fuzzy controller uses a Sugeno type fuzzy inference system (FIS) which is derived from discrete position state-space controller with an input integrator. The controller design method is based on anfis (adaptive neuro-fuzzy inference system) training routine. It utilizes a combination of the least-squares method and the backpropagation gradient descent method for training FIS membership function parameters to emulate a given training data set. The proposed fuzzy logic controllers are used for the control of a linear actuator. The capabilities of the designed control system are shown on verification experiment.

An Overview of Kinematic and Calibration Models Using Internal/External Sensors or Constraints to Improve the Behavior of Spatial Parallel Mechanisms

This paper presents an overview of the literature on kinematic and calibration models of parallel mechanisms, the influence of sensors in the mechanism accuracy and parallel mechanisms used as sensors. The most relevant classifications to obtain and solve kinematic models and to identify geometric and non-geometric parameters in the calibration of parallel robots are discussed, examining the advantages and disadvantages of each method, presenting new trends and identifying unsolved problems. This overview tries to answer and show the solutions developed by the most up-to-date research to some of the most frequent questions that appear in the modelling of a parallel mechanism, such as how to measure, the number of sensors and necessary configurations, the type and influence of errors or the number of necessary parameters

Modeling and Control of the Cooperative Automated Fiber Placement System

The Automated Fiber Placement (AFP) machines have brought significant improvement on composite manufacturing. However, the current AFP machines are designed for the manufacture of simple structures like shallow shells or tubes, and not capable of handling some applications with more complex shapes. A cooperative AFP system is proposed to manufacture more complex composite components which pose high demand for trajectory planning than those by the current APF system. The system consists of a 6 degree-of-freedom (DOF) serial robot holding the fiber placement head, a 6-DOF revolute-spherical-spherical (RSS) parallel robot on which a 1-DOF mandrel holder is installed and an eye-to-hand photogrammetry sensor, i.e. C-track, to detect the poses of both end-effectors of parallel robot and serial robot. Kinematic models of the parallel robot and the serial robot are built. The analysis of constraints and singularities is conducted for the cooperative AFP system. The definitions of the tool frames for the serial robot and the parallel robot are illustrated. Some kinematic parameters of the parallel robot are calibrated using the photogrammetry sensor. Although, the cooperative AFP system increases the flexibility of composite manufacturing by adding more DOF, there might not be a feasible path for laying up the fiber in some cases due to the requirement of free from collisions and singularities. To meet the challenge, an innovative semi-offline trajectory synchronized algorithm is proposed to incorporate the on-line robot control in following the paths generated off-line especially when the generated paths are infeasible for the current multiple robots to realize. By adding correction to the path of the robots at the points where the collision and singularity occur, the fiber can be laid up continuously without interruption. The correction is calculated based on the pose tracking data of the parallel robot detected by the photogrammetry sensor on-line. Due to the flexibility of the 6-DOF parallel robot, the optimized offsets with varying movements are generated based on the different singularities and constraints. Experimental results demonstrate the successful avoidance of singularities and joint limits, and the designed cooperative AFP system can fulfill the movement needed for manufacturing a composite structure with Y-shape