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.

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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 e�ciency, the goal has been to use variable leg sti�ness to obtain variable walking gait while combining these two aspects. In contrast, most existing systems are either energy e�cient or robust. The thesis consists mainly of two papers; the �rst investigates the use of variable leg sti�ness to obtain variable gait on the Spring-Loaded Inverted Pendulum (SLIP) model. The parameter space in which gaits of a desired velocity exist is �rst explored and a normalised unique descrip- tion of a SLIP gait is developed. Based on the control of variable leg sti�ness, 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 di�erent from the SLIP model in that it has legs with torsional sti�ness knees, which is more realistic as compared to existing robot designs, which use knees and leg retraction to avoid food scu�ng. 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 Sti�ness Ac- tuators (VSAs) to control the knee sti�ness. 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 sti�ness. The variable knee sti�ness 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)
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