Quasi-straightened Knee Walking for the Humanoid Robot

Most humanoid robots do not walk in a very human-like manner due to their style of bent knee walking. Typically for decoupling the motion in the sagittal and the coronal planes, the acceleration term in the zero moment point (ZMP) equation is set to zero, resulting in a constant height of the center of mass (COM). This constraint creates the bent knee profile that is fairly typical for walking robots,which particularly requires high torque transmission from motors. Hence, it is interesting to investigate an improved trajectory generator that produces a more straight knee walking which is more energy efficient and natural compared to those performed by the bent knee walking. This issue is addressed by adding a virtual spring-damper to the cart-table model. This strategy combines the preview control for generating the desired horizontal motions of the COM, and the virtual model for generating the vertical COM motion. The feasibility is evaluated by a mathematical investigation of the sensitivity of ZMP errors in MATLAB simulation of a multi-body humanoid model. The walking pattern is applied to the simulated humanoid iCub using the dynamic simulator OpenHRP3. The simulated iCub successfully performs walking gaits. Simulation results are presented and compared to the biomechanical study from human gaits. Both the knee joint torque and energy consumption of all joints required by the proposed strategy are reduced compared to that of the conventional cart-table scheme.

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