Optimal design of a three dimensional 4 dof cobot with differential gears

Cobots are passive robots that share their work space with a human. They are safe for whom manipulates them and facilitate the task execution which increase productivity. Also they take advantage of the human vision, intelligence and dexterity because their goal is to guide the operator who moves the robot. They can execute transport or precision tasks at low cost, reducing the operator training time. This work presents a COBOT which has four rotational degrees of freedom (DOF) and its work space is a sphere. The design is optimized for one trajectory. The optimal criterion is specialized for COBOTs because the objective is to transmit the biggest blocking force in a forbidden direction. The COBOT posseses CVT which are based on differential gears because they can support high load, they have high efficiency and their assembly to the links is the simplest. The optimization problem needs to model the link´s stresses, to solve the direct and inverse kinematic problem and the transmission ratio. Also a trajectory, based on virtual wall, defines the optimal design. The design process is simplified to the minimization problem. Every design criterions are expressed mathematically to be programmed. This method can be reproduced for any system.