Trajectory generation of straightened knee walking for humanoid robot iCub

Abstract

Abstract-Most humanoid robots walk with bent knees, which particularly requires high motor torques at knees and gives an unnatural walking manner. It is therefore essential to design a control method that produces a motion which is more energy efficient and natural comparable to those performed by humans. In this paper, we address this issue by modeling the virtual springdamper based on the cart-table model. This strategy utilizes the preview control, which generates the desired horizontal motion of the center of mass (COM), and the virtual spring-damper for generating the vertical COM motion. The theoretical feasibility of this hybrid strategy is demonstrated in Matlab simulation of a multi-body bipedal model. Knee joint patterns, ground reaction force (GRF) patterns, COM trajectories are presented. The successful walking gaits of the child humanoid "iCub" in the dynamic simulator validate the proposed scheme. The joint torques required by the proposed strategy are reduced, compared with the one required by the cart-table model.

Control design to achieve dynamic walking on a bipedal robot with compliance

“…10(a) depicts Roboray's dynamic walking. Roboray performs fully knee stretched-walking compared to the conventional knee bent walkers requiring larger knee joint torques [17]. Fig.…”

Capture point trajectories for reduced knee bend using step time optimization

“…From the 3D feasible space, we can compute the 2D feasibility region, F 2D ⊂ R 2 , in the x-y plane where the CoM must be located, shown as the shaded green region in Figure 4. To do so, we assume that the distance from the CoM to each hip can be treated as a constant, a fairly common [10] and accurate assumption due to the mass distribution on most humanoid robots. This allows us to offset the sphere origins from the ankle locations, defining the blue circles in Figure 4 as s l and s r , enabling us to directly consider the CoM rather than the hip locations as in Figure 3.…”

“…Several works have attempted to address planning and control of appropriate height trajectories for straighter legs. In [10], the authors presented an approach for generating straightened-knee trajectories by combining model predictive control (MPC) of the ZMP to generate horizontal CoM trajectories with a spring-damper approach to generate vertical CoM trajectories. Alternatively, [11] used linear differential inclusion to incorporate these height trajectories directly into the MPC, resulting in relatively natural, cyclical motions of the CoM.…”

“…While some previous works are capable of generating kinematically feasible height trajectories [10], [11], these approaches, along with most others, typically rely on arbitrarily chosen single and double support phase durations. While kinematic feasibility of the CoM height plan is guaranteed, this has the fundamental limitation of ignoring the effects of step timing on the resulting horizontal CoM plans.…”

Straight-Leg Walking Through Underconstrained Whole-Body Control

“…The general objective becomes to design trajectories that result in the robot's legs being as straight as possible without violating the kinematics or the centroidal dynamics. In [10], the authors presented an approach for generating straightened-knee trajectories by modeling the legs as spring dampers to compute the CoM height after generating horizontal trajectories using model predictive control (MPC) of the ZMP. Alternatively, [11] used linear differential inclusion to incorporate these height trajectories directly into the MPC, resulting in relatively natural, cyclic motions of the CoM.…”