Lightweight design optimization for legs of bipedal humanoid robot

Minimizing the mass and moment of inertia is a crucial objective in robot design. Especially for the biped humanoid robots, leg mass and moment of inertia severely affect the robot’s ultimate speed, motion stability, and interaction safety. The lightweight design for the legs of biped humanoid robots has been a hot but difficult research topic in recent decades. This paper will propose a new optimization approach for achieving lightweight design of biped humanoid robot legs. Firstly, the joint drivetrain dynamic model will be established, followed by the process of determining the selection criteria of motors and gearbox, and clarifying the calculation method of joint mass attributes. Secondly, the minimal total mass of the robot’s legs is taken as the goal to optimize, and the parameters related to the motor and gearbox models are the design variables. As the robot walks stably, the maximal walking speed that is close to the target speed is regarded as the constraint. A complex method is then implemented in a commercial mathematical software, the model to simulate robot dynamics is established in commercial dynamic software, and the dynamic simulation is completed using the three-dimensional linear inverted pendulum gait planning method. Finally, the Walker robot is used as an example to demonstrate the effectiveness of the proposed design optimization approach. The results show that the design optimization method can significantly reduce the total mass of the robot’s legs, reduce the torque requirements of the robot’s leg joints, and improve the stability of the robot’s motion. The optimization approach presented in this study is also important and applicable to the lightweight design of other categories of robots.