Towards the Design and Evaluation of Robotic Legs of Quadruped Robots

Legged systems have potentials of better mobility than traditional wheeled and tracked vehicles on rough terrain. The reason for the superior mobility of legged systems has been studied for a long period and plenty of robots using legs for locomotion have been developed during recent few decades. However the built legged robots still exhibit insufficiency of expected locomotive ability comparing with their counterparts in nature with similar size. The reason may be complicated and systematic associated with several aspects of the development such as the design, key components, control & planning and/or test and evaluation. The goal of this thesis is to close the gap between legged robots research & development and practical application and deployment. The research presented in this thesis focuses on three aspects including morphological parameters of quadruped robots, optimal design for knee joint mechanism and the development of a novel test bench— Terrain Simulator Platform. The primary motivation and target for legged robots developing is to overcome the challenging terrain. However few legged robots take the feature of terrain into consideration when determining the morphological parameters, such as limb length and knee orientation for robots. In this thesis, the relationship between morphological parameters of quadruped robots and terrain features are studied by taking a ditch/gap as an example. The influence of diverse types of morphological parameters including limb length, limb mass, the center-of-mass position in limbs and knee configuration on the ditch crossing capability are presented. In order to realize extended motion range and desired torque profile, the knee joint of HyQ2max adopts a six-bar linkage mechanism as transmission. Owing to the complexity of closed-loop kinematic chain, the transmission ratio is difficult to design. In this thesis, I used a static equilibrium based approach to derive the transmission relationship and study the singularity conditions. Further desired torque profile of knee joint are realized by a multi-variable geometric parameters optimization. For the test and performance evaluation of robotic leg, I designed and constructed a novel test bench— Terrain Simulator Platform (TSP). The main function of the TSP is to provide sufficient test conditions for robotic leg by simulating various terrain features. Thus working status of robotic leg can be known before the construction of the whole robot. The core of the TSP is a 3-PRR planar parallel mechanism. In this thesis, the structure design and implementation, the kinematics including singularity, workspace etc, and dynamics of this 3-PRR mechanism are presented.