<Figure: Observation of locomotion of a dog in (a) the walk phase, (b) the trot phase, and (c) the gallop phase.>
<Video: experiment and simulation on automatic multiple gait-phase transition
A simple and effective method to realize the locomotion of legged robots is by the design of appropriate jointangle trajectories. Due to the complicated nature of legged locomotion, the desired joint-angle trajectories are often inspired from those of animals. The locomotion of quadruped animals exhibits multiple gait phases, such as walk, trot, canter, and gallop, which may necessitate for the trajectory generation algorithm of a quadruped robot to be able to generate joint-angle trajectories in multiple gait phases. In the gait of animals, each gait phase is optimal for a certain speed, and thus transition of the gait phases is necessary for effective increase or decrease of the locomotion speed. The classification of the gait phases, however, is discrete, and thus the resultant jointangle trajectories may be discontinuous due to the transition. The smooth and continuous transition of gait phases is shown in upper video.
B. Bio-Inspired Actuation System An actuation system for high-speed running robots is required to exhibit back-drivability, high-power-capacity, high efficiency, etc. For this reasoning, the gear train is not desirable in the actuation system. In our laboratory, we have developed a new direct-driven linear actuator for the development of a running robot.
<Figure: The mechanical design of a linear DC motor for the hip joint of Cheetaroid; A-B: moving forcers, C: a trail with magnets, D: permanent magnets, E: pairs of brushes and electrodes, F: cores with electromagnetic coils.>
The whole body dynamics is simulated by Newtonian mechanics. The numerical simulation is used for the design of gait controllers.
<Figure: Schematic for the simulation of a rear leg>
<Video: simulation of the rear legs with the actual dimensions>
<Figure: The previous version of Cheetaroid-I>
<Video: The latest version of Cheetaroid-I>
<Video: Gait motion from a trot phase using the Cheetaroid-II>
Many approaches have been introduced to improve the gait stability and the locomotion speed of legged robots. In this project, a quadruped robot, called Cheetaroid-II, the gait motions of which are generated by mechanical link systems, is introduced. The robot has four legs that propel the robot body by mimicking the leg motions of an animal running fast. For the
easiness in control and the minimal weight of the overall robot system, all the four legs are connected by mechanical links and actuated by only one actuator. In addition to the actuated leg joints, the proposed robot also has compliant feet for enhancing gait efficiency. The parameters of the mechanical link system are selected by an optimization process such that the simulated link motion is close to the leg motions of the animal. The actuator, however, is subjected to large disturbance forces due to
the whole body actuation. Therefore, a set of a worm-gear and a worm-wheel is used as a transmission system for improved mechanical impedance and disturbance rejection performance.