1 Multi-objective optimization of a tripod parallel mechanism for a robotic leg Matteo Russo 1 , Saioa Herrero 2 , Oscar Altuzarra 2 , Marco Ceccarelli 1 1 LARM – Lab. of Robotics and Mechatronics, Univ. of Cassino and South Latium, Italy e-mail: matteo.russo@unicas.it, ceccarelli@unicas.it 2 Mechanical Eng. Dept., UPV/EHU University of the Basque Country, Spain e-mail: saioa.herrero@ehu.es, oscar.altuzarra@ehu.es Abstract. This paper presents the multi-objective optimization of a three-degree-of-freedom parallel manipulator. First, the geometry of the mechanism is described and its kinematic and static performance is characterized with closed-form expressions of workspace volume and force efficiency. These indices are used as objective functions of the optimization, which is then conduced in order to compute the optimal design of the manipulator. Finally, the results of the multi-objective optimization are reported and discussed. Keywords: Multi-objective Optimization, Robot Design, Leg Mechanisms, Parallel Robots. 1 Introduction Parallel mechanisms in robotic legs are seldom used, since they usually have a smaller workspace than serial mechanisms of the same size. However, parallel ar- chitectures perform better in accuracy and payloads [1,2] and therefore they can substitute serial mechanisms when they fulfil workspace requirements. Some ex- amples of parallel mechanisms used as robot legs can be found in [3-6]. The novel tripod architecture that is analysed in this paper is proposed in [7-9] while its kine- matics is briefly described in section 2. In order to find an optimal design for the mechanism, a multi-objective optimization is proposed in this work. The objective functions for the optimization of parallel mechanisms are discussed in many re- search works, such as [10-16]. In these studies, several indices have been proposed in order to characterize the workspace of the manipulator, its kinematic and dynamic performance and its stiffness. Among them, the workspace volume and the effi- ciency in force transmission are the most relevant ones for a robotic leg mechanism. Therefore, these two functions are evaluated in their closed-form expressions in section 3 for the proposed structure, while section 4 shows the multi-objective op- timization solution by mapping the objective functions in the parameter space and discussing the results in order to find an optimal design. Author's version