Gait Analysis of Quadruped Robot Using the Equivalent Mechanism Concept Based on Metamorphosis

Abstract

The previous research regarding the gait planning of quadruped robot focuses on the sequence for lifting off and placing the feet, but neglects the influence of body height. However, body height affects gait performance significantly, such as in terms of the stride length and stability margin. We herein study the performance of a quadruped robot using the equivalent mechanism concept based on metamorphosis. Assuming the constraints between standing feet and the ground with hinges, the ground, standing legs and robot body are considered as a parallel mechanism, and each swing leg is regarded as a typical serial manipulator. The equivalent mechanism varies while the robot moves on the ground. One gait cycle is divided into several periods, including step forward stages and switching stages. There exists a specific equivalent mechanism corresponding to each gait period. The robot's locomotion can be regarded as the motion of these series of equivalent mechanisms. The kinematics model and simplified model of the equivalent mechanism is established. A new definition of the multilegged robot stability margin, based on friction coefficient, is presented to evaluate the robot stability. The stable workspaces of the equivalent mechanism in the step forward stage of trotting gait under different friction coefficients are analyzed. The stride length of the robots is presented by analyzing the relationship between the stable workspaces of the equivalent mechanisms of two adjacent step forward stages in one gait cycle. The simulation results show that the stride length is larger with increasing friction coefficient. We herein propose a new method based on metamorphosis, and an equivalent mechanism to analyze the stability margin and stable workspace of the multilegged robot.

Leg Mechanism Design and Motion Performance Analysis for an Amphibious Crab-like Robot

“…Gait planning is also a necessary aspect that needs to be addressed. Xu et al proposed a new method based on metamorphosis and an equivalent mechanism to analyze the stability margin and stable workspace of multi-legged robots [12]. Chen et al proposed a novel gait planning method for six-legged robots to optimize terrain adaptability and walking speed [13].…”

Kinematics analysis of a four-legged heavy-duty robot with a force–position hybrid control servo actuator in a parallel-executed cylinder system

“…However, it is well known that tetrapods in nature usually twist, dive or bend their trunks to walk, run or crawl (Gonzalez-Luchena et al, 2016;Li et al, 2014;Gallant and Gosselin, 2018). The turning strategy of a four-legged robot based on leg gait was mentioned by Zhang and Dai (2018). The transition between a single supporting leg of the four-legged robot and a walking posture was studied by Pouya et al (2016).…”

Legged walking on inclined surfaces

“…Quadrupeds can be set to execute a variation of gaits based on desired overall speed, sequences and strides. The main idea is to contemplate trotting in form of a robot configuration with two contact points with its environment and adjust foot placement based on state feedback to maintain a stable periodic orbit [59].…”

“…Next, one leg is lifted off the ground entering its swing phase and comes back down instantiating the switching phase at which point it is back to stance and the next leg enters its swing phase. Through this, walking can be achieved in 4 switching periods and 8 total phases of each leg [59]. Though this produces a rather slow walking gait it requires less energy and is more stable than other gait cycles.…”

“…This involves two legs being in the swing phase and two in stance, making four periods in the gait within one switching phase. A trotting gait allows faster methods to cover distances [59].…”