Modeling and Control of a Flexible Structure Incorporating Inertial Slip-Stick Actuators

Shape and vibration control of a linear flexible structure by means of a new type of inertial slip-stick actuator are investigated. A nonlinear model representing the interaction between the structure and a six-degree-of-freedom Stewart platform system containing six actuators is derived, and closed-loop stability and performance of the controlled systems are investigated. A linearized model is also derived for design purposes. Quasistatic alignment of a payload attached to the platform is solved simply by using a proportional controller based on a linear kinematic model. The stability of this controller is examined using a dynamic model of the complete system and is validated experimentally by introducing random thermal elongations of several structural members. Vibration control is solved using an H∞ loop-shaping controller and, although its performance is found to be less satisfactory than desired, the nonlinear model gives good predictions of the performance and stability of the closed-loop system

Experimental Validation of a Sliding Mode Control for a Stewart Platform Used in Aerospace Inspection Applications

The authors introduce a new controller, aimed at industrial domains, that improves the performance and accuracy of positioning systems based on Stewart platforms. More specifically, this paper presents, and validates experimentally, a sliding mode control for precisely positioning a Stewart platform used as a mobile platform in non-destructive inspection (NDI) applications. The NDI application involves exploring the specimen surface of aeronautical coupons at different heights. In order to avoid defocusing and blurred images, the platform must be positioned accurately to keep a uniform distance between the camera and the surface of the specimen. This operation requires the coordinated control of the six electro mechanic actuators (EMAs). The platform trajectory and the EMA lengths can be calculated by means of the forward and inverse kinematics of the Stewart platform. Typically, a proportional integral (PI) control approach is used for this purpose but unfortunately this control scheme is unable to position the platform accurately enough. For this reason, a sliding mode control (SMC) strategy is proposed. The SMC requires: (1) a priori knowledge of the bounds on system uncertainties, and (2) the analysis of the system stability in order to ensure that the strategy executes adequately. The results of this work show a higher performance of the SMC when compared with the PI control strategy: the average absolute error is reduced from 3.45 mm in PI to 0.78 mm in the SMC. Additionally, the duty cycle analysis shows that although PI control demands a smoother actuator response, the power consumption is similar.This research was funded by the Basque Government through the project SMAR3NAK (ELKARTEK KK-2019/00051), by the Ministerio de Economía y Competitividad (RTI2018-094669-B-C31) and by Aernnova and the Diputación Foral de Álava (DFA) through the project CONAVAUTIN 2 (Collaboration Agreement)

Advanced Strategies for Robot Manipulators

Amongst the robotic systems, robot manipulators have proven themselves to be of increasing importance and are widely adopted to substitute for human in repetitive and/or hazardous tasks. Modern manipulators are designed complicatedly and need to do more precise, crucial and critical tasks. So, the simple traditional control methods cannot be efficient, and advanced control strategies with considering special constraints are needed to establish. In spite of the fact that groundbreaking researches have been carried out in this realm until now, there are still many novel aspects which have to be explored

Design and implementation of a six-degree of freedom robotic platform for measuring the forces of flying objects

The purpose of this project was to research, design and build a six-degree of freedom platform that measures the forces of flying animal robotics. The platform had to have an embedded force sensing mechanism and should be able to move in response to forces detected and measured. The platform had to measure the forces in six different orthogonal axes. The course of action and focus of the thesis was to research, design, build and control the robotic platform and it was an individual project

Design, Development, and Evaluation of a Teleoperated Master-Slave Surgical System for Breast Biopsy under Continuous MRI Guidance

The goal of this project is to design and develop a teleoperated master-slave surgical system that can potentially assist the physician in performing breast biopsy with a magnetic resonance imaging (MRI) compatible robotic system. MRI provides superior soft-tissue contrast compared to other imaging modalities such as computed tomography or ultrasound and is used for both diagnostic and therapeutic procedures. The strong magnetic field and the limited space inside the MRI bore, however, restrict direct means of breast biopsy while performing real-time imaging. Therefore, current breast biopsy procedures employ a blind targeting approach based on magnetic resonance (MR) images obtained a priori. Due to possible patient involuntary motion or inaccurate insertion through the registration grid, such approach could lead to tool tip positioning errors thereby affecting diagnostic accuracy and leading to a long and painful process, if repeated procedures are required. Hence, it is desired to develop the aforementioned teleoperation system to take advantages of real-time MR imaging and avoid multiple biopsy needle insertions, improving the procedure accuracy as well as reducing the sampling errors. The design, implementation, and evaluation of the teleoperation system is presented in this dissertation. A MRI-compatible slave robot is implemented, which consists of a 1 degree of freedom (DOF) needle driver, a 3-DOF parallel mechanism, and a 2-DOF X-Y stage. This slave robot is actuated with pneumatic cylinders through long transmission lines except the 1-DOF needle driver is actuated with a piezo motor. Pneumatic actuation through long transmission lines is then investigated using proportional pressure valves and controllers based on sliding mode control are presented. A dedicated master robot is also developed, and the kinematic map between the master and the slave robot is established. The two robots are integrated into a teleoperation system and a graphical user interface is developed to provide visual feedback to the physician. MRI experiment shows that the slave robot is MRI-compatible, and the ex vivo test shows over 85%success rate in targeting with the MRI-compatible robotic system. The success in performing in vivo animal experiments further confirm the potential of further developing the proposed robotic system for clinical applications

Sliding-Mode control for high-precision motion control systems

In many of today's mechanical systems, high precision motion has become a necessity. As performance requirements become more stringent, classical industrial controllers such as PID can no longer provide satisfactory results. Although many control approaches have been proposed in the literature, control problems related to plant parameter uncertainties, disturbances and high-order dynamics remain as big challenges for control engineers. Theory of Sliding Mode Control provides a systematic approach to controller design while allowing stability in the presence of parametric uncertainties and external disturbances. In this thesis a brief study of the concepts behind Sliding Mode Control will be shown. Description of Sliding Mode Control in discrete-time systems and the continuous Sliding Mode Control will be shown. The description will be supported with the design and robustness analysis of Sliding Mode Control for discrete-time systems. In this thesis a simplified methodology based on discrete-time Sliding Mode Control will be presented. The main issues that this thesis aims to solve are friction and internal nonlinearities. The thesis can be outlined as follows: -Implementation of discrete-time Sliding Mode Control to systems with nonlinearities and friction. Systems include; piezoelectric actuators that are known to suffer from nonlinear hysteresis behavior and ball-screw drives that suffer from high friction. Finally, the controller will be implemented on a 6-dof Stewart platform which is a system of higher complexity. -It will also be shown that performance can be enhanced with the aid of disturbance compensation based on a nominal plant disturbance observer

Advanced Control of Piezoelectric Actuators.

168 p.A lo largo de las últimas décadas, la ingeniería de precisión ha tenido un papel importante como tecnología puntera donde la tendencia a la reducción de tamaño de las herramientas industriales ha sido clave. Los procesos industriales comenzaron a demandar precisión en el rango de nanómetros a micrómetros. Pese a que los actuadores convencionales no pueden reducirse lo suficiente ni lograr tal exactitud, los actuadores piezoeléctricos son una tecnología innovadora en este campo y su rendimiento aún está en estudio en la comunidad científica. Los actuadores piezoeléctricos se usan comúnmente en micro y nanomecatrónica para aplicaciones de posicionamiento debido a su alta resolución y fuerza de actuación (pueden llegar a soportar fuerzas de hasta 100 Newtons) en comparación con su tamaño. Todas estas características también se pueden combinar con una actuación rápida y rigidez, según los requisitos de la aplicación. Por lo tanto, con estas características, los actuadores piezoeléctricos pueden ser utilizados en una amplia variedad de aplicaciones industriales. Los efectos negativos, como la fluencia, vibraciones y la histéresis, se estudian comúnmente para mejorar el rendimiento cuando se requiere una alta precisión. Uno de los efectos que más reduce el rendimiento de los PEA es la histéresis. Esto se produce especialmente cuando el actuador está en una aplicación de guiado, por lo que la histéresis puede inducir errores que pueden alcanzar un valor de hasta 22%. Este fenómeno no lineal se puede definir como un efecto generado por la combinación de acciones mecánicas y eléctricas que depende de estados previos. La histéresis se puede reducir principalmente mediante dos estrategias: rediseño de materiales o algoritmos de control tipo feedback. El rediseño de material comprende varias desventajas por lo que el motivo principal de esta tesis está enfocado al diseño de algoritmos de control para reducir la histéresis. El objetivo principal de esta tesis es el desarrollo de estrategias de control avanzadas que puedan mejorar la precisión de seguimiento de los actuadores piezoeléctricos comerciale