Traction Modeling and Control of a Differential Drive Mobile Robot to Avoid Wheel Slip

The motion of a differential drive mobile robot with consideration of slip at contact between the wheels and the ground is studied in this work. Traction forces between the wheel and the ground are derived by considering a rigid wheel, rigid ground interaction model and a caster wheel which provides support to the mobile robot during motion. The motion governing equations are determined by incorporating the traction forces. Numerical simulations are conducted to learn the motion behavior of the robot with wheel slip for a range of wheel input torques. Based on the traction force model and observations from numerical simulations, a slip avoidance controller that limits the input torques is developed. Experiments are conducted to verify the characteristics of the dynamic model with slip and the control strategy used to avoid slip. Models that describe the dynamics of a differential drive mobile robot with and without slip are presented and discussed. A traction force model is developed by considering a simple Coulomb friction model. The caster wheel plays an important role in determining the traction forces. The longitudinal and lateral velocities of the wheel are used to compute the longitudinal and lateral forces. Wheel slip occurs if the reaction force exerted by the applied torque is greater than the static frictional force, which is calculated by the proposed model and this limit is used to implement a slip avoidance controller. Numerical simulations and experiments of the system using the proposed traction model reveal that the angular velocity of the wheels is greater than the corresponding linear velocity when slip occurs. The proposed torque limiting controller to avoid slip is also implemented in numerical simulations and experiments. Experimental results show a good correlation with the numerical simulations, thus verifying the approach and the developed dynamic model with wheel slip.Mechanical Engineerin

5to. Congreso Internacional de Ciencia, Tecnología e Innovación para la Sociedad. Memoria académica

El V Congreso Internacional de Ciencia, Tecnología e Innovación para la Sociedad, CITIS 2019, realizado del 6 al 8 de febrero de 2019 y organizado por la Universidad Politécnica Salesiana, ofreció a la comunidad académica nacional e internacional una plataforma de comunicación unificada, dirigida a cubrir los problemas teóricos y prácticos de mayor impacto en la sociedad moderna desde la ingeniería. En esta edición, dedicada a los 25 años de vida de la UPS, los ejes temáticos estuvieron relacionados con la aplicación de la ciencia, el desarrollo tecnológico y la innovación en cinco pilares fundamentales de nuestra sociedad: la industria, la movilidad, la sostenibilidad ambiental, la información y las telecomunicaciones. El comité científico estuvo conformado formado por 48 investigadores procedentes de diez países: España, Reino Unido, Italia, Bélgica, México, Venezuela, Colombia, Brasil, Estados Unidos y Ecuador. Fueron recibidas un centenar de contribuciones, de las cuales 39 fueron aprobadas en forma de ponencias y 15 en formato poster. Estas contribuciones fueron presentadas de forma oral ante toda la comunidad académica que se dio cita en el Congreso, quienes desde el aula magna, el auditorio y la sala de usos múltiples de la Universidad Politécnica Salesiana, cumplieron respetuosamente la responsabilidad de representar a toda la sociedad en la revisión, aceptación y validación del conocimiento nuevo que fue presentado en cada exposición por los investigadores. Paralelo a las sesiones técnicas, el Congreso contó con espacios de presentación de posters científicos y cinco workshops en temáticas de vanguardia que cautivaron la atención de nuestros docentes y estudiantes. También en el marco del evento se impartieron un total de ocho conferencias magistrales en temas tan actuales como la gestión del conocimiento en la universidad-ecosistema, los retos y oportunidades de la industria 4.0, los avances de la investigación básica y aplicada en mecatrónica para el estudio de robots de nueva generación, la optimización en ingeniería con técnicas multi-objetivo, el desarrollo de las redes avanzadas en Latinoamérica y los mundos, la contaminación del aire debido al tránsito vehicular, el radón y los riesgos que representa este gas radiactivo para la salud humana, entre otros

New Spatially Dependent Models for Web Lateral Dynamics and Model-Based Designs for Control of Web Lateral Position and Slope

The control of web lateral behaviour is important to obtain quality products and enable new technologies in R2R manufacturing. In this work, regulation of web lateral position and slope at any point within the span is investigated. For this, a new model for the web lateral behaviour rep­resented by spatially dependent lateral transfer functions was obtained, by including the entry rule directly in the boundary conditions and then applying a one dimensional (1-D) temporal Laplace transform to both the governing equations and boundary conditions. The proposed approach over­comes one of the key limitations of the existing methods which provide web lateral position only on the rollers. Determination of slope, moments, and shear forces within the span are also readily obtained by the proposed method, which was not the case in prior models. The approach also significantly simplifies the consideration of shear (relevant for short spans), in addition to bending, which has been found to be difficult to handle in the past model development studies. The new governing equations provide mechanisms to analyze web lateral behavior within spans, study prop­agation of lateral disturbances, and aid in the development of closed loop lateral control systems in emerging applications that require precise lateral positioning of the web. As an example of their application, common guide configurations are analyzed using the new model, and their influence in the span is presented. The determination of moments and shear may be useful for the research to study and predict wrinkles and other web failures. Using the proposed model several controllers were developed and analyzed, and it is concluded that controlling the web lateral position and slope requires controlling the rotation and translation of the guide roller independently. Further, it is concluded that web slope is required as feedback. Currently available commercial web guides have only one control action that simultaneously con­trols the translation and rotation through a kinematic chain, thus incapable of web slope control. Since there are no available sensors to measure web slope directly, observers to estimate not only the web slope, but also the disturbances were developed. For this, it was assumed that only edge sensors (that measure web lateral position) are available; as results of this analysis conditions for observability, controllability, and determination of the minimum number of edge sensors and their location are also presented. The edge sensor location is based in a new approach that search for the minimum norm of the observer gains along the span. It is shown that less sensors than the estab­lished by previous studies are required for the slope estimation. Finally, a model based controller to obtain web lateral position and slope regulation that actively rejects the lateral disturbances in the system is developed. Results from numerical simulations of representative situations to support the developments and discussions are provided. An experimental platform and a device capable to displace and rotate a roller independently was developed. This new guide system was employed to validate the proposed spatially dependent lateral transfer functions, the effectiveness of the ob­servers, and verify that adding the the web slope as feedback in the controllers improves the web lateral behaviour. This study is particularly relevant for high-precision lateral regulation within the span that may be required for emerging R2R applications in flexible and hybrid electronics, such as nanoimprint­ing, printing, and deposition processes