Oscillation Damping Control of Pendulum-like Manipulation Platform using Moving Masses

This paper presents an approach to damp out the oscillatory motion of the pendulum-like hanging platform on which a robotic manipulator is mounted. To this end, moving masses were installed on top of the platform. In this paper, asymptotic stability of the platform (which implies oscillation damping) is achieved by designing reference acceleration of the moving masses properly. A main feature of this work is that we can achieve asymptotic stability of not only the platform, but also the moving masses, which may be challenging due to the under-actuation nature. The proposed scheme is validated by the simulation studies.Comment: IFAC Symposium on Robot Control (SYROCO) 201

Compliant aerial manipulation.

The aerial manipulation is a research field which proposes the integration of robotic manipulators in aerial platforms, typically multirotors – widely known as “drones” – or autonomous helicopters. The development of this technology is motivated by the convenience to reduce the time, cost and risk associated to the execution of certain operations or tasks in high altitude areas or difficult access workspaces. Some illustrative application examples are the detection and insulation of leaks in pipe structures in chemical plants, repairing the corrosion in the blades of wind turbines, the maintenance of power lines, or the installation and retrieval of sensor devices in polluted areas. Although nowadays it is possible to find a wide variety of commercial multirotor platforms with payloads from a few gramps up to several kilograms, and flight times around thirty minutes, the development of an aerial manipulator is still a technological challenge due to the strong requirements relative to the design of the manipulator in terms of very low weight, low inertia, dexterity, mechanical robustness and control. The main contribution of this thesis is the design, development and experimental validation of several prototypes of lightweight (<2 kg) and compliant manipulators to be integrated in multirotor platforms, including human-size dual arm systems, compliant joint arms equipped with human-like finger modules for grasping, and long reach aerial manipulators. Since it is expected that the aerial manipulator is capable to execute inspection and maintenance tasks in a similar way a human operator would do, this thesis proposes a bioinspired design approach, trying to replicate the human arm in terms of size, kinematics, mass distribution, and compliance. This last feature is actually one of the key concepts developed and exploited in this work. Introducing a flexible element such as springs or elastomers between the servos and the links extends the capabilities of the manipulator, allowing the estimation and control of the torque/force, the detection of impacts and overloads, or the localization of obstacles by contact. It also improves safety and efficiency of the manipulator, especially during the operation on flight or in grabbing situations, where the impacts and contact forces may damage the manipulator or destabilize the aerial platform. Unlike most industrial manipulators, where force-torque control is possible at control rates above 1 kHz, the servo actuators typically employed in the development of aerial manipulators present important technological limitations: no torque feedback nor control, only position (and in some models, speed) references, low update rates (<100 Hz), and communication delays. However, these devices are still the best solution due to their high torque to weight ratio, low cost, compact design, and easy assembly and integration. In order to cope with these limitations, the compliant joint arms presented here estimate and control the wrenches from the deflection of the spring-lever transmission mechanism introduced in the joints, measured at joint level with encoders or potentiometers, or in the Cartesian space employing vision sensors. Note that in the developed prototypes, the maximum joint deflection is around 25 degrees, which corresponds to a deviation in the position of the end effector around 20 cm for a human-size arm. The capabilities and functionalities of the manipulators have been evaluated in fixed base test-bench firstly, and then in outdoor flight tests, integrating the arms in different commercial hexarotor platforms. Frequency characterization, position/force/impedance control, bimanual grasping, arm teleoperation, payload mass estimation, or contact-based obstacle localization are some of the experiments presented in this thesis that validate the developed prototypes.La manipulación aérea es un campo de investigación que propone la integración de manipuladores robóticos in plataformas aéreas, típicamente multirotores – comúnmente conocidos como “drones” – o helicópteros autónomos. El desarrollo de esta tecnología está motivada por la conveniencia de reducir el tiempo, coste y riesgo asociado a la ejecución de ciertas operaciones o tareas en áreas de gran altura o espacios de trabajo de difícil acceso. Algunos ejemplos ilustrativos de aplicaciones son la detección y aislamiento de fugas en estructura de tuberías en plantas químicas, la reparación de la corrosión en las palas de aerogeneradores, el mantenimiento de líneas eléctricas, o la instalación y recuperación de sensores en zonas contaminadas. Aunque hoy en día es posible encontrar una amplia variedad de plataformas multirotor comerciales con cargas de pago desde unos pocos gramos hasta varios kilogramos, y tiempo de vuelo entorno a treinta minutos, el desarrollo de los manipuladores aéreos es todavía un desafío tecnológico debido a los exigentes requisitos relativos al diseño del manipulador en términos de muy bajo peso, baja inercia, destreza, robustez mecánica y control. La contribución principal de esta tesis es el diseño, desarrollo y validación experimental de varios prototipos de manipuladores de bajo peso (<2 kg) con capacidad de acomodación (“compliant”) para su integración en plataformas aéreas multirotor, incluyendo sistemas bi-brazo de tamaño humano, brazos robóticos de articulaciones flexibles con dedos antropomórficos para agarre, y manipuladores aéreos de largo alcance. Puesto que se prevé que el manipulador aéreo sea capaz de ejecutar tareas de inspección y mantenimiento de forma similar a como lo haría un operador humano, esta tesis propone un enfoque de diseño bio-inspirado, tratando de replicar el brazo humano en cuanto a tamaño, cinemática, distribución de masas y flexibilidad. Esta característica es de hecho uno de los conceptos clave desarrollados y utilizados en este trabajo. Al introducir un elemento elástico como los muelles o elastómeros entre el los actuadores y los enlaces se aumenta las capacidades del manipulador, permitiendo la estimación y control de las fuerzas y pares, la detección de impactos y sobrecargas, o la localización de obstáculos por contacto. Además mejora la seguridad y eficiencia del manipulador, especialmente durante las operaciones en vuelo, donde los impactos y fuerzas de contacto pueden dañar el manipulador o desestabilizar la plataforma aérea. A diferencia de la mayoría de manipuladores industriales, donde el control de fuerzas y pares es posible a tasas por encima de 1 kHz, los servo motores típicamente utilizados en el desarrollo de manipuladores aéreos presentan importantes limitaciones tecnológicas: no hay realimentación ni control de torque, sólo admiten referencias de posición (o bien de velocidad), y presentan retrasos de comunicación. Sin embargo, estos dispositivos son todavía la mejor solución debido al alto ratio de torque a peso, por su bajo peso, diseño compacto y facilidad de ensamblado e integración. Para suplir estas limitaciones, los brazos robóticos flexibles presentados aquí permiten estimar y controlar las fuerzas a partir de la deflexión del mecanismo de muelle-palanca introducido en las articulaciones, medida a nivel articular mediante potenciómetros o codificadores, o en espacio Cartesiano mediante sensores de visión. Tómese como referencia que en los prototipos desarrollados la máxima deflexión articular es de unos 25 grados, lo que corresponde a una desviación de posición en torno a 20 cm en el efector final para un brazo de tamaño humano. Las capacidades y funcionalidades de estos manipuladores se han evaluado en base fija primero, y luego en vuelos en exteriores, integrando los brazos en diferentes plataformas hexartor comerciales. Caracterización frecuencial, control de posición/fuerza/impedancia, agarre bimanual, teleoperación de brazos, estimación de carga, o la localización de obstáculos mediante contacto son algunos de los experimentos presentados en esta tesis para validar los prototipos desarrollados por el auto

Development of didactic physics experiments using a miniaturized wireless acquisition board

This work intends to utilize a miniaturized data acquisition board, with wireless communication, to modernize labs of introductory physics classes, namely in Mechanics, Thermodynamics, and Electromagnetism, as well as to develop low cost solutions for these labs. The acquisition board used was BITalino, developed by the company PLUX. The selected experiments were the real pendulum and the Faraday induction. The real pendulum experiment uses a built-in accelerometer, while for the Faraday Induction a pre-amplifier was built in order to measure and recorded the induced voltage. A digital thermometer was also built, with the intent of being used in Thermodynamics experiments. The design philosophy of this project is to use, as much as possible, off the shelf components - both electronic and physical. The real pendulum experiment proved a success, it allowed finding of the damping time constant of the motion, as well as how the period of a real pendulum depends on the angle of oscillation. The pre-amplifier built to measure induced voltage in 10 300 V range and the digital thermometer were tested and both showed good results

Effects of a thermal inversion experiment on STEM students learning and application of damped harmonic motion

There are diverse teaching methodologies to promote both collaborative and individual work in undergraduate physics courses. However, few educational studies seek to understand how students learn and apply new knowledge through open-ended activities that require mathematical modeling and experimentation focused on environmental problems. In this work, we propose a novel home experiment to simulate the dynamics of a particulate under temperature inversion and model it as damped harmonic motion. Twenty six first year students enrolled in STEM majors answered six qualitative questions after designing and developing the experiment. These questions helped analyze the students epistemological beliefs about their learning process of physics topics and its applications. Results showed that this type of open-ended experiments could facilitate the students understanding of physics phenomena. In addition, this experiment showed that it could help physics professors to promote students epistemological development by giving their students the opportunity to search for different sources of knowledge and becoming self-learners instead of looking at the professor as the epistemological authority. At the end, students described this activity as a positive experience that helped them realize alternative ways to apply physics topics in different contexts of their environment.Comment: 23 pages, 5 figure

Passive Compliance Control of Aerial Manipulators

This paper presents a passive compliance control for aerial manipulators to achieve stable environmental interactions. The main challenge is the absence of actuation along body-planar directions of the aerial vehicle which might be required during the interaction to preserve passivity. The controller proposed in this paper guarantees passivity of the manipulator through a proper choice of end-effector coordinates, and that of vehicle fuselage is guaranteed by exploiting time domain passivity technique. Simulation studies validate the proposed approach.Comment: IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) 201

Implementation and Control of an Inverted Pendulum on a Cart

An Inverted Pendulum on a Cart is a common system often used as a benchmark problem for control systems. The system consists of a cart that can move in one direction on the horizontal plane and a pendulum attached to the cart through a hinge point. The pendulum can rotate 360° on the plane made up of the vertical direction and the direction the cart can move. The system is controlled by applying a force to the cart, to make it move. This thesis consists of two goals. The first goal is to build a lab model of the Inverted Pendulum on a Cart system. The second goal is to create a controller that can swing the pendulum from a pendulum down position to a pendulum up position, and balance it in this position. The lab model is built using a track that the cart can move along, a stepper motor for applying force to the cart and a microcontroller for controlling the system. The pendulum angle and the cart position are measured using incremental encoders. A Mathematical model of the system have been derived. This forms the basis for the design of the controller and is also used for simulating and testing the system and controller in MATLAB/Simulink before it is implemented on the real system. The controller consists of three parts. An extended Kalman filter is implemented to estimate the non-measurable state. An energy-based controller is used to swing the pendulum from the down position to the up position. This controller regulates the energy in the pendulum to be close to the energy the pendulum should have when it is balanced in the upright position. When the pendulum is close to the upright position the controller will switch to a linear quadratic regulator to balance the pendulum. This controller is based on a linearized version of the mathematical system model. The lab model and the controllers have been successfully built and implemented

Vibration attenuation by mass redistribution

A nontraditional approach for active structural vibration attenuation was proposed using mass redistribution. The focus was on pendulum structures where the objective was to examine the effectiveness of mass reconfiguration along or within a structure to attenuate its vibrational energy. The mechanics associated with a translating mass along a rotating structure give rise to a Coriolis inertia force which either opposes or increases angular oscillations, thereby producing positive or negative damping, respectively. A strategy of cycling the mass to maximize attenuation and minimize amplification required the mass be moved at twice the frequency of the structural vibrations and be properly coordinated with the angular oscillations. The desired coordination involved moving the mass away from the pivot as the pendulum nears its vertical position and moving the mass towards the pivot when the pendulum nears its maximum angular excursion. System mass reconfiguration was analyzed by studying various mass displacement profiles including sinusoidal, piece-wise constant velocity and modified proportional and derivative action patterns. These strategies were optimized for various time intervals to maximize the rate of energy attenuation or minimize the final energy state. For small amplitude oscillations with sinusoidal mass motion, the dynamic behavior was modeled by Mathieu-Hill equations to explain the beating phenomenon that occurred when the frequency of the mass motion remained constant. Several control systems were designed to generate aforementioned mass reconfiguration profiles. The methodologies included human operator, modified proportional and derivative action, knowledge or rule based and artificial neural network controllers. The human operator system improved with experience and was the most effective. Other systems depended on the chosen parameterization or the implementation of self-adjusting parameters. Several unique tools were developed during the course of this research, as referenced herein

The effect of leg muscle activation state and localized muscle fatigue on tibial response during impact.

The purpose of this study was to examine the effects of activation state, localized muscle fatigue (LMF), gender, and muscle on the tibial response parameters (TRPs) measured at the knee during heel impacts. A human pendulum apparatus delivered consistent impacts to the unshod, right (dominant) heel of 15 females and 15 males (m age 22.6 +/- 1.4 years, body mass 71.7 +/- 15.1 kg, and height 1.74 +/- 0.11 m). The tibialis anterior (TA: Session 1) and lateral gastrocnemius (LG: Session 2) muscles were examined using electromyography to allow voluntary contraction of various activation states [baseline, 15%, 30%, 45%, 60% of the maximum activation state (MAS)], and to assess LMF. Subjects were successfully able to voluntarily contract their muscle to the required activation states. (Abstract shortened by UMI.) Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2005 .H65. Source: Masters Abstracts International, Volume: 44-03, page: 1354. Thesis (M.H.K.)--University of Windsor (Canada), 2005

Dynamic model of a spherical robot from first principles

Department Head: Allan Thomson Kirkpatrick.2010 Summer.Includes bibliographical references (pages 77-78).A prototype of a pendulum driven spherical robot has been developed during previous research and shown to exhibit unique dynamic behavior. Starting from first principles, a mathematical model for this spherical robot rolling on flat ground was developed in order to determine if this unique behavior was inherent to spherical robots in general or simply peculiar to this prototype. The complete equations of motion were found using Lagrangian methods, and numerically integrated using computer tools. A 3D simulation program was written to animate the results of integrating the equations. The dynamics apparent in the simulations were found to closely match the observed dynamics of the physical prototype

Rotating potential of a stochastic parametric pendulum

The parametric pendulum is a fruitful dynamical system manifesting some of the most interesting phenomena of nonlinear dynamics, well-known to exhibit rather complex motion including period doubling, fold and pitchfork bifurcations, let alone the global bifurcations leading to chaotic or rotational motion. In this thesis, the potential of establishing rotational motion is studied considering the bobbing motion of ocean waves as the source of excitation of a oating pendulum. The challenge within this investigation lies on the fact that waves are random, as well as their observed low frequency, characteristics which pose a broader signi cance within the study of vibrating systems. Thus, a generic study is conducted with the parametric pendulum being excited by a narrow-band stochastic process and particularly, the random phase modulation is utilized. In order to explore the dynamics of the stochastic system, Markov-chain Monte-Calro simulations are performed to acquire a view on the in uence of randomness onto the parameter regions leading to rotational response. Furthermore, the Probability Density Function of the response is calculated, applying a numerical iterative scheme to solve the total probability law, exploiting the Chapman-Kolmogorov equation inherent to Markov processes. A special case of the studied structure undergoing impacts is considered to account for extreme weather conditions and nally, a novel design is investigated experimentally, aiming to set the ground for future development