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CPG를 이용한 ZMP 기반 이족 로봇의 무릎 핀 보행 궤적 생성 (Stretched knee walking trajectory generation for ZMP-based biped robot using Central Pattern Generators)

Abstract : 

       This article suggests a combination of CPG neural networks and kinetic trajectory planning for stretched-knee walking of a biped robot. Furthermore, this paper suggests ZMP compensation for stable walking. Instability when a foot swings during SSP(single support phase) and when the center of mass moves to another point was decreased by calculating the real ZMP coordinate with the slope of the base body with respect to the pivot point. Using the calculated ZMP and applying compensation for the forward and lateral directions at the knees and ankles in real time make it possible to maintain the stability of robot. Especially, how much the robot leans laterally toward the supporting foot can he determined by the ZMP in the lateral direction. From this, it is possible to get toward motions of the ankles in the roll direction. Recently, researches on biped robots using CPG have been intensified. The biggest merit of using CPG is that it can get a stable walking posture to overcome uncertainty and disturbance easily. Since a single unit of CPG generates a limit cycle, the movement can be easily stabilized. The neural network among CPGs also connects the walking posture smoothly. The robot only with CPG but nothing, however, determines the period time with combination of lots of unknown variables. Changing direction and velocity according to the initially determined period time like a mechanical doll or applying to free movement like jumping are very difficult. Furthermore, it needs trial and error to determine unknown variables for desired posture and velocity. However, there is no certain value needed for CPG model even though former researchers have been determining with lots of experiments. So, in the thesis, CPG model is used only to each pitch direction of waist and knees. Inverted pendulum model and waist pendulum model were used for generating joint and pitch torque. Simultaneously, yaw torque of waist is applied. Stretched knee walking has been succeeded with the combination of CPGs of knee and waist. As a result, the singularity problem of the legs has been resolved. The robot body movement was to be natural with the neural communication between trajectory generation and CPG pattern. The movements at the waist with IP movement was to make the locomotion stride wider. However, simulation of biped locomotion based on the trajectory failed due to the instability of locomotion could not be controlled.