This thesis focuses on mechanical design and simulation studies of a quadruped robot motion control system, targeting at designing an autonomous legged robot. The designed quadruped robot with ``X"-configuration is developed for traversing rocky and sloped terrain with a static walking gait. The mechanical design of the quadruped robot is illustrated in Chapter 2, including the main body design, leg design and component selection. In the design process, appropriate mechanical structures are utilized to minimize the energy consumption. To improve energy efficiency, a set of principles is proposed. Corresponding implementations are also concretely introduced in this chapter. In addition, to simplify the mechanical structure of the quadruped robot, the mass is symmetrically distributed about the frontal and lateral planes. To improve the leg agility, the leg mass is minimized. On the one hand, the lightweight design is implemented by optimizing the mass distribution of the leg mechanism. On the other hand, the key components are assembled in the body part instead of the legs as many as possible. A sufficient leg length is also selected not only to allow the robot to step on or over obstacles, but also to avoid the leg getting caught by objects. Particularly, the leg structure is demonstrated, including the hip joint, thigh part, knee joint and limb part with a telescoping joint. When the robot sustains extensive payload, the deformed shape in joints may lead to structural failures, thereby influencing the quadrupedal locomotion. Finite element analysis (FEA) is performed when designing the structural components in reasonable structures. The design processes of the shoulder part and brass rod are demonstrated as examples. Based on the setup of loads and fixtures, the maximum deformed shape of these structural components are analyzed. From FEA simulation results, the yield strength is two orders of magnitude larger than the maximum of von Mises stress. Hence, these components are suitable to be incorporated in the quadruped robot. Based on the designed mechanical structure, simulation studies of the quadruped robot motion control system are analyzed in Chapter 3, including the modeling for a robotic leg and animated simulation. Since the quadrupedal locomotion is executed by manipulating the postures of four legs, the leg model is significant to the motion control system, thereby being analyzed mathematically. Two links kinematic conversion is implemented between the foot-end trajectory and joint angles. The dynamic model of the leg is also computed to discovery the relationship between the actuating torques and joint angles. To animate the quadrupedal locomotion, a CAD robot model is converted into MATLAB. Following the predefined footfall pattern, four legs move in sequence to execute the creeping gait. The segment of the desired trajectory of the foot-end fits a fifth order polynomial and does not include the set of singular configurations. Then, the PD control is utilized to adjust the leg posture to track the desired path. Furthermore, the actual joint angles are calculated in the MATLAB/SimMechanics quadruped robot by using Euler-Lagrange equations. Lastly, simulation results are presented to analyze the tracking performance in the joint angles and foot-ends. Finally, conclusions of the thesis are summarized, and future work is presented in Chapter 4. / Graduate / 2019-03-07

Quadruped robots offer distinct advantages in navigating challenging terrains due to their flexible and shock-absorbing characteristics. This flexibility allows them to adapt to uneven surfaces, enhancing their maneuverability. In contrast, rigid robots excel in tasks that require speed and precision but are limited in their ability to navigate complex terrains due to their restricted motion range. Another category of robots, known as soft robots, has gained attention for their unique attributes. Soft robots are characterized by their lightweight and cost-effective design, making them appealing for various applications. Recent advancements have made significant strides in practical control strategies for soft quadruped robots, particularly in diverse and unpredictable environments. An emerging approach in enhancing the autonomy of robots is through reinforcement learning. While this approach shows promise in enabling robots to learn and adapt to their surroundings, it necessitates rigorous training and must exhibit robustness in real-world scenarios. Moreover, a significant hurdle lies in bridging the gap between simulations and reality, as models trained in idealized virtual environments often struggle to perform as expected when deployed in the physical world. This thesis aims to address these challenges by optimizing the control of soft quadruped robots using a model-based reinforcement learning approach. The primary goal is to refine the gait control of these robots, taking into account the complexities encountered in real-world environments. The report covers the implementation of model-based reinforcement learning, including simulation setup, reward design, and policy refinement. Results show improved training efficiency and autonomous behavior, confirming the method’s effectiveness in enhancing soft quadruped robot capabilities.It is important to note that this report provides a concise summary of the thesis results due to the word limit imposed by the Department of Machine Design. For a comprehensive understanding of the research and its implications, the complete version is attached separately here. / Fyrbenta robotar är tack vare deras flexibla och stötdämpande egenskaper är väl lämpade att navigera utmanande terräng. Deras struktur möjliggör anpassning till ojämnheter i underlaget och bidrar till att öka deras rörelseförmåga. I kontrast utmärker sig stela robotar som det bästa valet för uppgifter som kräver snabbhet och precision, men deras förmåga att navigera komplex terräng är begränsad av deras rörelseomfång. En annan typ av robot, så kallade mjuka robotar, har nyligen uppmärksammats för sina unika egenskaper. Dessa robotar kännetecknas av en kostnadseffektiv lättviktsdesign, vilket gör dem attraktiva för många olika användningsområden. Nyligen har betydelsefulla framsteg gjorts inom kontroll av mjuka fyrbenta robotar, framför allt vad gäller kontroll i varierade miljöer. En av de huvudsakliga utmaningarna för att öka robotars autonomi är förstärkningsinlärning. Även om denna teknik är lovande för att ge robotar förmågan att lära sig och anpassa sig efter sin omgivning, kräver den omfattande träning samt måste uppvisa robusthet i verkliga scenarion. Ett större hinder är dessutom klyftan mellan simulation och verklighet, då modeller som tränats i ideella simuleringar ofta presterar sämre än väntat i den fysiska världen. Detta examensarbete behandlar dessa utmaningar genom att implementera en modellbaserad förstärkningsinlärningsmetod för kontroll av fyrbenta robotar, med det primära målet att förfina gångkontrollen för dessa robotar med hänsyn till de komplexa beteenden som uppstår i verkliga miljöer. Denna rapport behandlar implementeringen av modellbaserad förstärkningsin lärning samt simulering, belöningsdesign och policyförfining. Resultat visar på en förbättrad inlärningsförmåga och bättre autonomt beteende, vilket gör metoden lämplig för att förbättra prestandan av mjuka fyrbenta robotar. Var god att notera att denna rapport endast ger en nedkortad sammanfattning av forskningen och dess resultat på grund av krav från institutionen för maskinkonstruktion. En fullständig version innehållande mer detaljer kring studien och dess konsekvenser bifogas här.

Quadruped robots can traverse a multitude of terrains with greater ease when compared to wheeled robots. Traditional rigid quadruped robots possess severe limitations as they lack structural compliance. Most of the existing soft quadruped robots are tethered and are actuated using pneumatics, which is a low grade energy source and lacks viability for long endurance robots. The work in this thesis proposes the development of a continuum actuator driven quadruped robot which can provide compliance while being un-tethered and electro-mechanically driven. In this work, continuum actuators are developed using mostly 3D printed parts. Additionally, the closed loop control of continuum actuators for walking is developed. Linear Quadratic Regulator (LQR) and pole placement based methods for controller synthesis were evaluated and LQR was determined to be better when minimizing the actuator effort and deviation from set-point. These continuum actuators are composed together to form a quadruped. Gait analyses on the quadruped were conducted and legs of the quadruped were able to trace the gaits for walking and galloping. / Fyrfotarobotar kan lättare korsa en mängd olika terränger jämfört med hjulrobotar. Traditionella styva fyrfotarobotar har kraftiga begränsningar då de saknar strukturell följsamhet. De flesta befintliga mjuka fyrbenta robotar är kopplade till en eller flera kablar och drivs av pneumatik, vilket är en lågkvalitativ energikälla och lämpar sig inte för robotar med lång uthållighet. Arbetet i denna avhandling föreslår utvecklingen av en continuum ställdonsdriven fyrfotarobot, som ger följsamhet samtidigt som den ¨ar frånkopplad och elektromekaniskt driven. I detta arbete framställs continuum ställdon med mestadels 3D-printade delar. Dessutom utvecklas dessa ställdons slutna kontrolloop för gång. Linjärkvadratisk regulator (LQR) och metoder baserade på polplacering utvärderades för styrsyntes, och det fastställdes att LQR presterade bättre när man minimerar ställdonets ansträngning samt avvikelse från referensvärde. Continuum ställdon sammansattes för att bilda en fyrbent robot. Gånganalyser utfördes på roboten och dess ben kunde följa gång- och galopprörelser.