The considered echography robot Fig.1 manipulates an echography probe controlled remotely by an operator. During its operation, the robot is placed on the patient and held by an assistant. Therefore, robot must be light enough to be held without fatigue. At the same time, deformation of the robot must be limited in order to obtain a good precision. Robot architecture is based on a parallel structure with pantographs that has good kinematic properties but that gave a too heavy system. That's why we investigate here the shape optimization of the structure to lighten it while maintaining a minimum stiffness for precision of the probe positioning. In this first study, only most challenging articulated pantographs are shape optimized.