Abstract
For quadruped robots with springy legs, a successful jump usually requires both suitable elastic parts and well-designed control algorithms. However, these two problems are mutually restricted and hard to solve at the same time. In this study, we attempt to solve the problem of controller design with the help of a robot without any elastic mounted parts, in which the untethered robot is made to jump on a trampoline. The differences between jumping on hard surfaces with springy legs and jumping on springy surfaces with rigid legs are briefly discussed. An intuitive control law is proposed to balance foot contact forces; in this manner, excessive pitch oscillation during hopping or bounding can be avoided. Hopping height is controlled by tuning the time delay of the leg stretch. Together with other motion generators based on kinematic law, the robot can perform translational and rotational movements while hopping or bounding on the trampoline. Experiments are conducted to validate the effectiveness of the proposed control framework.
Highlights
Hopping or bounding, which is one of the fundamental abilities of quadruped robots, can help these robotsReceived April 28, 2019; accepted July 12, 2019✉ Boxing WANG, Chunlin ZHOU ( ), Ziheng DUAN, Qichao ZHU, Jun WU Binhai Industrial Technology Research Institute of Zhejiang University, Tianjin 300301, China overcome obstacles and increase movement speed
Berkemeier [7] analyzed the stability of quadrupedal bounding and pronking through a simplified spring-damper model and proved that the linearized bound of the unperturbed model is always neutrally stable if the dimensionless body inertia is greater than 1
Experiments are performed on a untethered servo-actuated quadruped robot and a commercial adult-used trampoline (Fig. 1)
Summary
Hopping or bounding, which is one of the fundamental abilities of quadruped robots, can help these robots. Various approaches have been proposed to achieve stable hopping or bounding. A position-controlled robot may be able to jump by mounting elastic elements, subsequently reducing energy loss during touchdown impact. Unlike in typical serial elastic actuation, a passive springloaded leg mechanism with multiple segments was proposed by Spröwitz et al [19] to increase the robustness of a quadruped robot during trotting and stepping down events. We attempt to solve the above problems by proposing a control framework that can achieve stable quadrupedal hopping, bounding, and translational/rotational motion control on a trampoline (Fig. 1). The control algorithms can be designed initially for the trampoline tests and used to select and mount the suitable elastic components.
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