Online Recognition of Environment Properties by Using Bilateral Control

The topic of this thesis is identification of the mechanical impedance of an unknown environment. Through the use of bilateral control based on DOB and RFOB structures, position, speed and force information are gathered and analyzed while performing continuous contact with the environment. The nonlinear Hunt-Crossley model is preferred over the classic Kelvin-Voigt model. Particular attention is given to the precise recognition of contact and the detection of an occurring deformation.ope

Volume 3 – Conference

We are pleased to present the conference proceedings for the 12th edition of the International Fluid Power Conference (IFK). The IFK is one of the world’s most significant scientific conferences on fluid power control technology and systems. It offers a common platform for the presentation and discussion of trends and innovations to manufacturers, users and scientists. The Chair of Fluid-Mechatronic Systems at the TU Dresden is organizing and hosting the IFK for the sixth time. Supporting hosts are the Fluid Power Association of the German Engineering Federation (VDMA), Dresdner Verein zur Förderung der Fluidtechnik e. V. (DVF) and GWT-TUD GmbH. The organization and the conference location alternates every two years between the Chair of Fluid-Mechatronic Systems in Dresden and the Institute for Fluid Power Drives and Systems in Aachen. The symposium on the first day is dedicated to presentations focused on methodology and fundamental research. The two following conference days offer a wide variety of application and technology orientated papers about the latest state of the art in fluid power. It is this combination that makes the IFK a unique and excellent forum for the exchange of academic research and industrial application experience. A simultaneously ongoing exhibition offers the possibility to get product information and to have individual talks with manufacturers. The theme of the 12th IFK is “Fluid Power – Future Technology”, covering topics that enable the development of 5G-ready, cost-efficient and demand-driven structures, as well as individual decentralized drives. Another topic is the real-time data exchange that allows the application of numerous predictive maintenance strategies, which will significantly increase the availability of fluid power systems and their elements and ensure their improved lifetime performance. We create an atmosphere for casual exchange by offering a vast frame and cultural program. This includes a get-together, a conference banquet, laboratory festivities and some physical activities such as jogging in Dresden’s old town.:Group 8: Pneumatics Group 9 | 11: Mobile applications Group 10: Special domains Group 12: Novel system architectures Group 13 | 15: Actuators & sensors Group 14: Safety & reliabilit

Contact force and torque estimation for collaborative manipulators based on an adaptive Kalman filter with variable time period.

Contact force and torque sensing approaches enable manipulators to cooperate with humans and to interact appropriately with unexpected collisions. In this thesis, various moving averages are investigated and Weighted Moving Averages and Hull Moving Average are employed to generate a mode-switching moving average to support force sensing. The proposed moving averages with variable time period were used to reduce the effects of measured motor current noise and thus provide improved confidence in joint output torque estimation. The time period of the filter adapts continuously to achieve an optimal trade-off between response time and precision of estimation in real-time. An adaptive Kalman filter that consists of the proposed moving averages and the conventional Kalman filter is proposed. Calibration routines for the adaptive Kalman filter interpret the measured motor current noise and errors in the speed data from the individual joints into. The combination of the proposed adaptive Kalman filter with variable time period and its calibration method facilitates force and torque estimation without direct measurement via force/torque sensors. Contact force/torque sensing and response time assessments from the proposed approach are performed on both the single Universal Robot 5 manipulator and the collaborative UR5 arrangement (dual-arm robot) with differing unexpected end effector loads. The combined force and torque sensing method leads to a reduction of the estimation errors and response time in comparison with the pioneering method (55.2% and 20.8 %, respectively), and the positive performance of the proposed approach is further improved as the payload rises. The proposed method can potentially be applied to any robotic manipulators as long as the motor information (current, joint position, and joint velocities) are available. Consequently the cost of implementation will be significantly lower than methods that require load cells

Human-Robot Collaboration for Kinesthetic Teaching

Recent industrial interest in producing smaller volumes of products in shorter time frames, in contrast to mass production in previous decades, motivated the introduction of human–robot collaboration (HRC) in industrial settings, as an attempt to increase flexibility in manufacturing applications by incorporating human intelligence and dexterity to these processes. This thesis presents methods for improving the involvement of human operators in industrial settings where robots are present, with a particular focus on kinesthetic teaching, i.e., manually guiding the robot to define or correct its motion, since it can facilitate non-expert robot programming.To increase flexibility in the manufacturing industry implies a loss of a fixed structure of the industrial environment, which increases the uncertainties in the shared workspace between humans and robots. Two methods have been proposed in this thesis to mitigate such uncertainty. First, null-space motion was used to increase the accuracy of kinesthetic teaching by reducing the joint static friction, or stiction, without altering the execution of the robotic task. This was possible since robots used in HRC, i.e., collaborative robots, are often designed with additional degrees of freedom (DOFs) for a greater dexterity. Second, to perform effective corrections of the motion of the robot through kinesthetic teaching in partially-unknown industrial environments, a fast identification of the source of robot–environment contact is necessary. Fast contact detection and classification methods in literature were evaluated, extended, and modified to use them in kinesthetic teaching applications for an assembly task. For this, collaborative robots that are made compliant with respect to their external forces/torques (as an active safety mechanism) were used, and only embedded sensors of the robot were considered.Moreover, safety is a major concern when robotic motion occurs in an inherently uncertain scenario, especially if humans are present. Therefore, an online variation of the compliant behavior of the robot during its manual guidance by a human operator was proposed to avoid undesired parts of the workspace of the robot. The proposed method used safety control barrier functions (SCBFs) that considered the rigid-body dynamics of the robot, and the method’s stability was guaranteed using a passivity-based energy-storage formulation that includes a strict Lyapunov function.All presented methods were tested experimentally on a real collaborative robot

Modeling and Control of Reluctance Actuators

Los actuadores de reluctancia son dispositivos que se caracterizan por una elevada densidad de fuerza, buena eficiencia, gran tolerancia frente a fallos y un coste reducido. Estas características hacen que estén siendo considerados como una alternativa muy prometedora frente a otro tipo de actuadores electromagnéticos en ciertas aplicaciones que requieren gran velocidad y precisión. Por otro lado, los actuadores de reluctancia también son la solución ideal para algunos dispositivos electromecánicos que requieren unas prestaciones modestas, lo cual es debido principalmente a que son compactos, tienen un bajo coste y consumen relativamente poco. En concreto, los relés electromecánicos y las válvulas de solenoide son dispositivos cuya operación está basada en la fuerza creada por un pequeño actuador de reluctancia.A pesar de sus ventajas, los actuadores de reluctancia son sistemas complejos cuya dinámica es no lineal. Una de sus características más distintivas es que la fuerza magnética que provoca el movimiento es siempre de atracción y, además, depende fuertemente de la posición de la armadura. Básicamente, el comportamiento de esta fuerza es lo que explica que dispositivos como los relés y las electroválvulas sufran fuertes impactos y desgaste cada vez que son activados. Adicionalmente, algunos fenómenos electromagnéticos como la histéresis magnética o las corrientes inducidas hacen que el modelado dinámico de los actuadores de reluctancia sea bastante complejo. El trabajo realizado en esta tesis doctoral está enfocado en estudiar las posibilidades que ofrecen estos actuadores y, en concreto, en analizar el comportamiento dinámico y proponer algoritmos de estimación y control para relés electromecánicos y válvulas de solenoide.El primer objetivo de la investigación es el desarrollo de modelos dinámicos para actuadores de reluctancia, es decir, modelos de orden reducido que puedan ser utilizados para realizar simulaciones transitorias lo más precisas posibles con un bajo coste computacional. Para ello, lo primero que se ha estudiado es el comportamiento electromagnético de estos sistemas. El método de modelado más usado en la tesis es el de los circuitos magnéticos equivalentes (MEC, por sus siglas en inglés). No obstante, también se han realizado algunas simulaciones con modelos de elementos _nitos, en concreto para validar las aproximaciones del método MEC o para calcular la reluctancia del entrehierro. Se han estudiado los principales fenómenos electromagnéticos que aparecen en los actuadores de reluctancia, lo que ha llevado a la obtención de expresiones analíticas para modelar la dispersión de flujo, las corrientes inducidas y la saturación e histéresis magnéticas. Por otra parte, la expresión de la fuerza magnética que produce el movimiento se ha obtenido mediante un balance energético del sistema.El movimiento de la armadura también se ha estudiado en la tesis. Dado que los actuadores de reluctancia tienen generalmente un recorrido físicamente acotado, se han propuesto dos técnicas diferentes que permiten modelar los límites del movimiento y los rebotes de la armadura. Una vez estudiado el movimiento, el modelo mecánico se ha combinado con las ecuaciones electromagnéticas para poder analizar el comportamiento dinámico del actuador en su conjunto. Se han desarrollado cinco modelos dinámicos distintos, desde el más sencillo posible hasta uno que incluye todos los fenómenos electromagnéticos citados con anterioridad, y posteriormente se han comparado teniendo en cuenta su precisión y coste computacional.Las medidas experimentales son fundamentales a la hora de analizar y caracterizar cualquier sistema dinámico. Por ello, otro de los objetivos de la tesis ha sido la evaluación de distintas técnicas de medida que pudieran ayudar a mejorar la comprensión sobre el comportamiento dinámico de los actuadores de reluctancia y, en caso de que fuera posible, formar parte de un bucle de control realimentado. En este sentido, se ha intentado grabar el movimiento de uno de los dispositivos estudiados mediante tres instrumentos ópticos distintos. Los resultados indican que, a pesar de que en ciertas situaciones sí sería posible medir la trayectoria del dispositivo durante su movimiento, ninguno de los instrumentos podría aplicarse en la práctica por su baja flexibilidad y alto coste. Por este motivo, también se ha explorado el uso de otras variables que puedan ser medidas mucho más fácilmente.Otra parte importante de la investigación ha estado centrada en técnicas de estimación. Se han desarrollado dos algoritmos que son capaces de estimar, en tiempo real, el flujo magnético, la resistencia y la inductancia de un actuador dado. Los algoritmos utilizan únicamente medidas de tensión y corriente, lo cual representa una clara ventaja ya que no se necesita utilizar sensores o equipamiento añadido. Las prestaciones de ambos estimadores han sido analizadas mediante simulación y experimentos reales. El problema de estimar la posición de la armadura también se ha abordado en la tesis. En concreto, se ha prestado especial atención en resaltar los efectos que la histéresis magnética produce en la estimación, algo que no había sido estudiado con anterioridad.Finalmente, se han propuesto distintas técnicas de control para actuadores de reluctancia. En concreto, el objetivo principal es lograr que estos sigan un movimiento con aterrizaje suave, es decir, un movimiento que no dé lugar a impactos o rebotes. Como un primer paso, se han estudiado las propiedades básicas de los sistemas de control, es decir, la estabilidad, controlabilidad y observabilidad. Después se ha explorado la técnica de linealización por realimentación como un posible método para diseñar un bucle de control realimentado para la trayectoria de la armadura. Los resultados obtenidos demuestran que el control por realimentación es capaz de controlar el movimiento con gran precisión, siempre y cuando haya disponibles medidas o estimaciones precisas de la posición en tiempo real. Como esta situación es difícil que se dé en la práctica, se ha estudiado el uso de técnicas de control óptimo en bucle abierto para aquellos casos en los que la posición de la armadura no se pueda obtener. En particular, se han obtenido distintas soluciones tiempo óptimo y de energía óptima para un actuador nominal y, posteriormente, se ha analizado su robustez utilizando un método de Montecarlo.Como alternativa a los métodos clásicos, se ha estudiado la aplicabilidad de los métodos Run-to-Run (R2R) en actuadores de relutancia. Estas técnicas están diseñadas específicamente para sistemas que realizan un proceso repetitivo y, por lo tanto, son idóneas para dispositivos como los relés y las válvulas. En concreto, los métodos R2R implícitos se basan en la idea de construir una función que evalúe el desempeño del sistema al final de cada repetición. De esta forma, es posible mejorar el comportamiento dinámico del actuador a lo largo de las repeticiones utilizando un algoritmo de búsqueda.Las posibilidades para diseñar un controlador R2R son prácticamente infinitas, así que en la tesis se dan consejos prácticos sobre cómo elegir y parametrizar la señal de entrada, cómo usar las medidas disponibles para evaluar el comportamiento del sistema o cómo comparar distintos algoritmos de búsqueda. Los experimentos realizados demuestran que el algoritmo R2R diseñado es capaz de mejorar enormemente el comportamiento de un relé electromecánico y que, después de unos pocos ciclos, ,los resultados son incluso mejores que con cualquier estrategia presente en la literatura.Reluctance actuators are characterized by having a high force density, good efficiency, high fault tolerance and reduced cost. These features make them a promising alternative to other electromagnetic actuators for high-speed and high-precision applications. In addition, reluctance actuators are also ideal for small switch-type devices that require a modest performance because of their compactness, low cost, reduced mass and low energy dissipation. In particular, electromechanical switches and solenoid valves are devices whose operation is based on the force created by a small reluctance actuator. Despite their advantages, reluctance actuators are systems with highly nonlinear dynamics. One of their most distinctive features is that the magnetic force that produces the motion is always attractive and varies greatly with the position of the armature. In essence, the nature of this force explains why switch-type devices like relays and valves are subject to strong impacts and wear each time they are operated. In addition to that, electromagnetic phenomena such as magnetic hysteresis and eddy currents make the dynamic modeling of reluctance actuators even more difficult. The work of this thesis aims to investigate the capabilities of reluctance actuators and, in particular, to analyze the dynamic behavior and propose estimation and control algorithms for electromechanical switches and solenoid valves. The first objective of the investigation is the development of control-oriented dynamical models for reluctance actuators, i.e., low-order models that can be used to perform accurate transient simulations with low computational requirements. For that, the electromagnetic behavior of these systems is firstly studied. The magnetic equivalent circuit (MEC) methodology is selected as the primary modeling technique. Simulations from finite element models are also used for some specific purposes, e.g., to verify the assumptions of the MEC approach or to calculate the reluctance of the air gap. Then, the main electromagnetic phenomena that occur in reluctance actuators are studied. Analytic expressions are derived to model magnetic saturation, hysteresis, flux fringing and eddy currents, and an energy balance is used to obtain the expression for the magnetic force that produces the motion. After that, the motion of the armature is incorporated to the analysis. Given that reluctance actuators usually have a limited range of motion, two different techniques are proposed to model the limits of the armature stroke and the bouncing phenomenon. Then, the electromagnetic equations and the mechanical models are combined to describe the overall dynamic behavior of the actuator. Five different dynamical models are presented, ranging from a computationally inexpensive structure to a comprehensive model that includes saturation, hysteresis, eddy currents and flux fringing. The models are compared in terms of accuracy and computational requirements. Measurements play an important role in the analysis and characterization of dynamical systems. Thus, another objective of this thesis is the evaluation of different measurement methodologies that may improve the understanding of the dynamic behavior of reluctance actuators and, if possible, be used as part of a feedback controller. In this regard, three optical instruments are explored in order to record the motion of switch-type actuators. The results show that, even though in some cases it is possible to measure the position of several components of the device, none of the instruments could be applied in a practical situation due to their low flexibility and high cost. For that reason, other variables that are much more easily obtainable are also explored. Another significant part of the research is devoted to estimation in reluctance actuators. Two different algorithms are proposed to estimate the magnetic flux, the resistance and the inductance of the device, both of which can be implemented in real time. The algorithms rely only on measurements of the coil voltage and current, which represents a clear advantage because no additional hardware is required. Simulation and experiments are presented to show the performance of the estimators. Furthermore, the estimation of the armature position is also investigated in this work. In particular, special focus is put on highlighting the effects of magnetic hysteresis on the performance of different estimation approaches. Control strategies are then proposed to achieve soft landing in reluctance actuators, i.e., a controlled motion without impacts or bounces. As a first step, the basic properties of control systems theory---stability, controllability and stability---are investigated for a nominal actuator. Then, feedback linearization is explored as a method to design a trajectory tracking controller for the armature position. The obtained results show that soft landing can be accomplished by means of feedback control provided that accurate measurements or estimates of the position are available. Since this situation is rare in practice, open-loop optimal control is proposed as an alternative technique when the position is not accessible. Different time-optimal and energy-optimal solutions are derived for a nominal actuator and then compared in terms of robustness using a Monte Carlo analysis. Finally, Run-to-Run (R2R) control is explored as another method that may be used to improve the performance of reluctance actuators. These techniques are specifically designed for systems that perform a repetitive operation and, hence, they are very well suited to being applied to switch-type devices. In particular, implicit R2R methods are based on the idea of building a function that evaluates the performance of the system at the end of each repetition. In this way, the dynamic behavior of the actuator can be gradually improved along the repetitions by conducting a black-box search. Considering that the possibilities to design a R2R controller are almost endless, practical advice is given on how to select and parameterize the input profile, how to use measurements to evaluate the system performance and how to compare different search algorithms. The performed experiments show that the designed R2R controller is able to improve greatly the behavior of a switch-type device and that, after a few cycles, it outperforms other methodologies in the literature.<br /

Second International Symposium on Magnetic Suspension Technology, part 2

In order to examine the state of technology of all areas of magnetic suspension and to review related recent developments in sensors and controls approaches, superconducting magnet technology, and design/implementation practices, the 2nd International Symposium on Magnetic Suspension Technology was held at the Westin Hotel in Seattle, WA, on 11-13 Aug. 1993. The symposium included 18 technical sessions in which 44 papers were presented. The technical sessions covered the areas of bearings, bearing modelling, controls, vibration isolation, micromachines, superconductivity, wind tunnel magnetic suspension systems, magnetically levitated trains (MAGLEV), rotating machinery and energy storage, and applications. A list of attendees appears at the end of the document

Development of PVDF tactile dynamic sensing in a behaviour-based assembly robot

The research presented in this thesis focuses on the development of tactile event sig¬ nature sensors and their application, especially in reactive behaviour-based robotic assembly systems.In pursuit of practical and economic sensors for detecting part contact, the application ofPVDF (polyvinylidene fluoride) film, a mechanical vibration sensitive piezo material, is investigated. A Clunk Sensor is developed which remotely detects impact vibrations, and a Push Sensor is developed which senses small changes in the deformation of a compliant finger surface. The Push Sensor is further developed to provide some force direction and force pattern sensing capability.By being able to detect changes of state in an assembly, such as a change of contact force, an assembly robot can be well informed of current conditions. The complex structure of assembly tasks provides a rich context within which to interpret changes of state, so simple binary sensors can conveniently supply a lot more information than in the domain of mobile robots. Guarded motions, for example, which require sensing a change of state, have long been recognised as very useful in part mating tasks. Guarded motions are particularly well suited to be components of assembly behavioural modules.In behaviour-based robotic assembly systems, the high level planner is endowed with as little complexity as possible while the low level planning execution agent deals with actual sensing and action. Highly reactive execution agents can provide advantages by encapsulating low level sensing and action, hiding the details of sensori-motor complexity from the higher levels.Because behaviour-based assembly systems emphasise the utility of this kind of quali¬ tative state-change sensor (as opposed to sensors which measure physical quantities), the robustness and utility of the Push Sensor was tested in an experimental behaviourbased system. An experimental task of pushing a ring along a convoluted stiff wire is chosen, in which the tactile sensors developed here are aided by vision. Three differ¬ ent methods of combining these different sensors within the general behaviour-based paradigm are implemented and compared. This exercise confirms the robustness and utility of the PVDF-based tactile sensors. We argue that the comparison suggests that for behaviour-based assembly systems using multiple concurrent sensor systems, bottom-level motor control in terms of force or velocity would be more appropriate than positional control. Behaviour-based systems have traditionally tried to avoid symbolic knowledge. Considering this in the light of the above work, it was found useful to develop a taxonomy of type of knowledge and refine the prohibition

NASA SBIR abstracts of 1991 phase 1 projects

The objectives of 301 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1991 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 301, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1991 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

Tactile mapping of harsh, constrained environments, with an application to oil wells

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. [110]-114).This work develops a practical approach to explore rough environments when time is critical. The harsh environmental conditions prevent the use of range, force/torque or tactile sensors. A representative case is the mapping of oil wells. In these conditions, tactile exploration is appealing. In this work, the environment is mapped tactilely, by a manipulator whose only sensors are joint encoders. The robot autonomously explores the environment collecting few, sparse tactile data and monitoring its free movements. These data are used to create a model of the surface in real time and to choose the robot's movements to reduce the mapping time. First, the approach is described and its feasibility demonstrated. Real-time impedance control allows a robust robot movement and the detection of the surface using a manipulator mounting only position sensors. A representation based on geometric primitives describes the surface using the few, sparse data available. The robustness of the method is tested against surface roughness and different surrounding fluids. Joint backlash strongly affect the robot's precision, and it is inevitable because of the thermal expansion in the joints. Here, a new strategy is developed to compensate for backlash positioning errors, by simultaneously identifying the surface and the backlash values. Second, an exploration strategy to map a constraining environment with a manipulator is developed. To maximize the use of the acquired data, this work proposes a hybrid approach involving both workspace and configuration space. The amount of knowledge of the environment is evaluated with an approach based on information theory, and the robot's movements are chosen to maximize the expected increase of such knowledge. Since the robot only possesses position sensors, the location along the robot where contact with the surface occurs cannot be determined with certainty. Thus a new approach is developed, that evaluates the probability of contact with specific parts of the robot and classifies and uses the data according to the different types of contact. This work is validated with simulations and experiments with a prototype manipulator specifically designed for this application.by Francesco Mazzini.Ph.D