This thesis explores the field of legged robots with reduced degree-of-freedom (DOF) leg mechanisms. Multi-legged robots have drawn interest among researchers due to their high level of adaptability on unstructured terrains. However, conventional legged robots require multiple degrees of freedom and each additional degree of freedom increases the overall weight and complexity of the system. Additionally, the complexity of the control algorithms must be increased to provide mobility, stabilization, and maneuvering. Normally, robotic legs are designed with at least three degrees of freedom resulting in complex articulated mechanisms, which limits the applicability of such robots in real-world applications. However, reduced DOF leg mechanisms come with reduced tasking capabilities, such as maintaining constant body height and velocity during locomotion. To address some of the challenges, this thesis proposes a novel bipedal robot with reduced DOF leg mechanisms. The proposed leg mechanism utilizes the Reuleaux triangle to generate the foot trajectory to achieve a constant body height during locomotion while maintaining a constant velocity. By using a differential drive, the robot is also capable of steering. In addition to the analytical results of the trajectory profile of each leg, the thesis provides a trajectory function of the Reuelaux triangle cam with respect to time such that the robot can maintain a constant velocity and constant body height during walking. An experimental prototype of the bipedal robot was integrated and experiments were conducted to evaluate the walking capability of the robot. Ongoing future work of the proposed design is also outlined in the thesis. / Master of Science / Bipedal robots are a type of legged robots that use two legs to move. Legs require multiple degrees of freedom to provide propulsion, stabilization, and maneuvering. Additional degrees of freedom of the leg result in a heavier robot, more complex control method, and more energy consumption. However, reduced degree of freedom legs result in a tradeoff between certain tasking capabilities for easier controls and lower energy consumption. As an attempt to overcome these challenges, this thesis presents a robot design with a reduced degree of freedom leg mechanism. The design of the mechanism is described in detail with its preliminary analysis. In addition, this thesis presents experimental validation with the robot which validates that the robot is capable of moving with constant body height at constant velocity while being of capable of steering. The thesis concludes with a discussion of the future work.

No description available.

This thesis aims to explain how the concepts of functional modeling are implemented in the development and validation of real-world hybrid dynamic systems. I also discuss how control theory is integrated with the design process in order to understand the significance of periodic orbits on a simple dynamic system. Two hybrid system applications with different levels of complexity will be considered in this thesis – an anthropomorphic Bipedal walking robot and a Double Pendulum with a mechanical stop. The primary objectives of this project are to demonstrate the phenomena of Zeno and zeno periodic orbits in hybrid dynamic systems involving impacts. Initially, I describe the salient features of the product design procedure and then explain the significance of functional modeling as a part of this process. We then discuss hybrid dynamic systems and the occurrence of Zeno behavior in their mathematical form. Also, the necessary conditions for existence of Zeno and zeno equilibrium points are provided. Then the theory of completed Lagrangian hybrid systems is explained in detail. We then examine the two hybrid dynamic systems being considered for this project. Prior research undertaken on bipedal walking is explored to understand their design and achievement of stable walking gaits with appropriate actuation mechanisms. Based on this insight, a suitable design procedure is employed to develop the bipedal robot model. The desired actuation mechanisms for all the configurations considered for this model as well as the challenges faced in employing optimal actuation will be discussed. However, due to the high level of complexity of the bipedal robot model, a simpler hybrid dynamic system is considered to simplify fabrication and control of the model. This is the motivation behind designing and building the Double Pendulum model with a mechanical stop in an attempt to observe zeno behavior in this system. We begin by formally demonstrating that the “constrained” double pendulum model displays Zeno behavior and complete this Zeno hybrid system to allow for solutions to be carried past the Zeno point. The end result is periods of unconstrained and constrained motions in the pendulum, with transitions to the constrained motion occurring at the Zeno point. We then consider the development of a real physical pendulum with a mechanical stop and introduce non-plastic impacts. Later, we verify through experimentation that Zeno behavior provides an accurate description of the behavior of the physical system. This provides evidence to substantiate the claim that Zeno behavior, while it does not technically occur in reality, provides an accurate method for predicting the behavior of systems undergoing impacts and that the theory developed to understand Zeno behavior can be applied to better understand these systems.

Indiana University-Purdue University Indianapolis (IUPUI) / Khakpour, Zahra M.S.M.E., Purdue University, May 2017. Multibody Dynamics Model of A Full Human Body For Simulating Walking, Major Professor: Hazim El-Mounayri. Bipedal robotics is a relatively new research area which is concerned with creating walking robots which have mobility and agility characteristics approaching those of humans. Also, in general, simulation of bipedal walking is important in many other applications such as: design and testing of orthopedic implants; testing human walking rehabilitation strategies and devices; design of equipment and facilities for human/robot use/interaction; design of sports equipment; and improving sports performance & reducing injury. One of the main technical challenges in that bipedal robotics area is developing a walking control strategy which results in a stable and balanced upright walking gait of the robot on level as well as non-level (sloped/rough) terrains. In this thesis the following aspects of the walking control strategy are developed and tested in a high-fidelity multibody dynamics model of a humanoid body model: 1. Kinematic design of a walking gait using cubic Hermite splines to specify the motion of the center of the foot. 2. Inverse kinematics to compute the legs joint angles necessary to generate the walking gait. 3. Inverse dynamics using rotary actuators at the joints with PD (Proportional-Derivative) controllers to control the motion of the leg links. The thee-dimensional multibody dynamics model is built using the DIS (Dynamic Interactions Simulator) code. It consists of 42 rigid bodies representing the legs, hip, spine, ribs, neck, arms, and head. The bodies are connected using 42 revolute joints with a rotational actuator along with a PD controller at each joint. A penalty normal contact force model along with a polygonal contact surface representing the bottom of each foot is used to model contact between the foot and the terrain. Friction is modeled using an asperity-based friction model which approximates Coulomb friction using a variable anchor-point spring in parallel with a velocity dependent friction law. In this thesis, it is assumed in the model that a balance controller already exists to ensure that the walking motion is balanced (i.e. that the robot does not tip over). A multi-body dynamic model of the full human body is developed and the controllers are designed to simulate the walking motion. This includes the design of the geometric model, development of the control system in kinematics approach, and the simulation setup.

The objectives of this study were to implement force sensors on the feet of a bipedal robot and analyze their response at different conditions. The data will be used to design a control strategy for the robot. The powered joints of the robot are driven by linear motors. A force sensor circuit was made and calibrated with different kinds of weight. A trajectory generator and inverse kinematics calculator for the robot were made to control the robot walking movement in an open-loop manner. The force data were taken at a certain period of time when the robot was in a standing position. Experiments with external disturbances were also performed on the robot. The ZMP position and mass of the robot were calculated by using the data of force sensors. The force sensor circuit was reliable in taking and handling the data from the sensor although the noise from the motors of the robot was present. / <p>Validerat; 20111115 (anonymous)</p>

Esta tese trata de um robô bípede em caminhar dinâmico. Neste robô, que normalmente é um sistema sub-atuado, fazemos uso de um disco de inércia que funciona num certo sentido como um atuador adicional. Através deste disco, obtém-se mais liberdade para a elaboração de passos repetitivos e um aumento na robustez. Por outro lado, o sistema de controle dos passos deve controlar, além do passo propriamente dito, também a velocidade do disco, de modo que não sejam saturados os atuadores (motores elétricos). Apresentamos então um controlador capaz de realizar estas ações simultaneamente. / This Thesis is about a bipedal robot in a dynamic walking gait. In this robot, which is usually a under-actuated system, a inertial wheel is employed and acts as an additional actuator. By using this wheel, one can design a cyclic walking gait with increased robustness and with more freedom. On the other hand, the control system must take care of the step itself, and also must ensure that the wheel speed does not exceed the actuators (motors) limits. We present a controller able to perform this tasks.

This work presents an alternative method for 3D bipedal gait design using independent controllers for the plane of motion frontal and sagittal. The use of virtual constraints to design a stable gait for the frontal system is fully developed and studied in this work and the resulting gait simulated. The results, although not definitive, are promising. / Esta tese apresenta um método alternativo de síntese de marcha bípede 3D usando controladores independentes projetados para os planos de movimento frontal e sagital. O uso de restrições virtuais no projeto de uma marcha estável para o plano frontal é completamente desenvolvido e estudado neste trabalho. A marcha resultante é simulada e os resultados, apesar de ainda não definitivos, são promissores.

Esta tese trata de um robô bípede em caminhar dinâmico. Neste robô, que normalmente é um sistema sub-atuado, fazemos uso de um disco de inércia que funciona num certo sentido como um atuador adicional. Através deste disco, obtém-se mais liberdade para a elaboração de passos repetitivos e um aumento na robustez. Por outro lado, o sistema de controle dos passos deve controlar, além do passo propriamente dito, também a velocidade do disco, de modo que não sejam saturados os atuadores (motores elétricos). Apresentamos então um controlador capaz de realizar estas ações simultaneamente. / This Thesis is about a bipedal robot in a dynamic walking gait. In this robot, which is usually a under-actuated system, a inertial wheel is employed and acts as an additional actuator. By using this wheel, one can design a cyclic walking gait with increased robustness and with more freedom. On the other hand, the control system must take care of the step itself, and also must ensure that the wheel speed does not exceed the actuators (motors) limits. We present a controller able to perform this tasks.

No description available.

No description available.