University of Twente Student Theses


Control strategy for variable gait using variable knee stiffness in a bipedal robot model

Roozing, W. (2014) Control strategy for variable gait using variable knee stiffness in a bipedal robot model.

[img] PDF
Abstract:The work described in this master thesis investigates the control of bipedal walking robots based on the principle of passive dynamic walking. Inspired by the high performance of human walking, which combines high robustness with high energy efficiency, the goal has been to use variable leg stiffness to obtain variable walking gait while combining these two aspects. In contrast, most existing systems are either energy efficient or robust. The thesis consists mainly of two papers; the first investigates the use of variable leg stiffness to obtain variable gait on the Spring-Loaded Inverted Pendulum (SLIP) model. The parameter space in which gaits of a desired velocity exist is first explored and a normalised unique description of a SLIP gait is developed. Based on the control of variable leg stiffness, a gait switching strategy is proposed that controls the system from one limit cycle walking gait to another in order to change the walking speed. The strategy is shown to be able to control the system to another gait within a limited number of steps, after which control action converges to zero. The second paper investigates the Segmented Spring-Loaded Inverted Pendulum (S-SLIP) model, which is different from the SLIP model in that it has legs with torsional stiffness knees, which is more realistic as compared to existing robot designs, which use knees and leg retraction to avoid food scuffing. It is shown that the S-SLIP model exhibits walking gait, and a control strategy is developed that is able to stabilise the system after a disturbance. The gait switching strategy is applied to this model and it is shown that the system can be controlled from one limit cycle walking gait to another. Furthermore, a realistic bipedal robot model is designed that uses Variable Stiffness Actuators (VSAs) to control the knee stiffness. The control is based on the strategy developed for the S-SLIP model, and is extended with additional components to facilitate hip swing and leg retraction, which arise due to the additional dynamics of this model. A reference gait is obtained by using this model with constant leg stiffness. The variable knee stiffness is then used to stabilise the system into this gait and to inject energy losses generated by foot impacts. It is shown that this results in a stable limit cycle walking gait. The thesis concludes with a discussion of results obtained and recommendations for future work.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:52 mechanical engineering
Programme:Mechatronics MSc (60027)
Link to this item:
Export this item as:BibTeX
HTML Citation
Reference Manager


Repository Staff Only: item control page