Chattering Eliminated and Stable Gait Planning of Biped Robots Using a Fuzzy Sliding Mode Controller

Control of biped walking robots based on designated smooth and stable trajectories is a challenging problem that is the focus of this article. Because of highly nonlinear dynamics of biped robots, minor uncertainties in systems parameters may drastically affect the system performance, leading to a chattering phenomenon. To tackle this, a new Sliding Mode Control (SMC) approach is proposed privileging a chattering elimination method based on Fuzzy logic to regulate the switching gain. To this end, first a desired trajectory for the lower body will be designed to alleviate the impacts due to contact with the ground. This is obtained by fitting proper polynomials at appropriate break points. Then, the upper body motion is planned based on the Zero Moment Point (ZMP) criterion to provide a stable motion for the biped robot. Next, dynamics equations will be obtained for both single support phase (SSP) and double support phase (DSP). Finally, the SMC approach is applied for both the SSP and the DSP, while a new chattering elimination method using Fuzzy logic will be proposed based on regulating a constant switching gain. Obtained simulation results show that the performance of the system is properly accurate in terms of the tracking errors even in the presence of considerable uncertainties and exerted disturbances. Furthermore, the new proposed method substantially reduces chattering effects and avoids the instability of the biped robot due to this phenomenon, resulting in stable smooth motion control of this complicated system.