Compliant Leg Architectures and a Linear Control Strategy for the Stable Running of Planar Biped Robots

Abstract

This paper investigates two fundamental structures for biped robots and a control strategy to achieve stable biped running. The first biped structure contains straight legs with telescopic springs, and the second one contains knees with compliant elements in parallel with the motors. With both configurations we can use a standard linear discrete-time state-feedback control strategy to achieve an active periodic stable biped running gait, using the Poincare map of one complete step to produce the discrete-time model. In this case, the Poincare map describes an open-loop system with an unstable equilibrium, requiring a closedloop control for stabilization. The discretization contains a stance phase, a flight phase and a touch-down. In the first approach, the control signals remain constant during each phase, while in the second approach both phases are discretized into a number of constant-torque intervals, so that its formulation can be applied easily to stabilize any active biped running gait. Simulation results with both the straight-legged and the kneed biped model demonstrate stable gaits on both horizontal and inclined surfaces.

Finite-time control strategy for the running of a telescopic leg biped robot

“…To design a finite-time controller, a desired trajectory is needed for the generalized coordinates. It has been shown that, for any arbitrary forward speed, the considered biped model has passive periodic running gaits which are unstable [4]. These gaits can be stabilized using some linear event-based controllers [4].…”

“…It has been shown that, for any arbitrary forward speed, the considered biped model has passive periodic running gaits which are unstable [4]. These gaits can be stabilized using some linear event-based controllers [4]. In this research, we synthetize a finite-time controller to generate stable running gaits around the passive gaits.…”

“…Furthermore, similarities of biped robots to human kind make them ready to help people in many tasks of modern life. Another important aspect of legged robots is that they can have high degrees of freedom (DOF) making them able to cover a larger workspace [3][4][5][6]. These characteristics lead to a wide spectrum of applications such as hazardous inspection, giving service in crowded hospitals, companion and entertainment jobs at home.…”

“…The gait dynamics in various biped robot structures have already been investigated by researchers [4][5][6][7]. Raibert [3] designed and built spring-loaded inverted pendulum (SLIP)like one-legged robots for 2D and 3D hopping gaits.…”

“…Hu et al [12] studied generating passive running gaits for a telescopic springy leg biped model with three point masses and then designed an event-based controller to stabilize it. Dadashzadeh et al [4] generalized this control method to active running gaits of telescopic and kneed biped models on even and sloped terrains. The controller was a discrete state feedback controller on Poincare map.…”