Abstract
This paper aims to determine an optimal structure for a quadruped robot, which will allow the robot’s joint torque sum to be minimised. An animal’s characteristic limb length ratio is a vital part of its overall morphology and the one that enables it to travel easily through its environment. For the same reason, a robot’s structure needs to be suitably designed for locomotion in its working environment. Joint torques are necessary to maintain the posture of the robot and to accelerate joint angles during walking motion, hence, minimisation of joint torques reduces energy consumption. We performed a numerical simulation in which we analysed the joint torques for various limb lengths and slope angles in order to determine the optimal structure of a robot walking on a slope. Our investigation determines that the optimal Ratio of Rear Leg Length (RRL) can be derived by the use of a simulation designed to determine the physical structure of quadruped robot. Our analysis suggests that joint torque will increase as the slope angle becomes steeper if the rear legs of the robot are shorter than its forelegs, and that joint torque will decrease as the slope angle declines if the robot’s forelegs are shorter than its rear legs. Finally, experimental results validated our simulation analysis.
Highlights
There have been a number of research efforts involving robots that utilise locomotion techniques similar to those used by animals (Hirai et al 1998; Nakanishi et al 2000; Raibert et al 1986)
If we focus on a two-dimensional plane with the constant Rear Leg Length (RRL), it can be confirmed that the slope angle minimising Cs will be small as RRL is larger
Experimental results confirmed that Csex is close to Cs when the slope angle is −15◦ to 15◦
Summary
There have been a number of research efforts involving robots that utilise locomotion techniques similar to those used by animals (Hirai et al 1998; Nakanishi et al 2000; Raibert et al 1986). In conventional research of quadruped robots moving on a slope, gait planning aimed at maintaining high stability or optimisation of moving speed on a slope is discussed, and specialised robots are developed to work on such slopes. The purpose of this research is to determine the limb length ratio of a robot designed to require a minimum amount of total joint torque when walking on a slope. Since animals evolved their leg lengths and shapes based on their living environments, it can be granted that a robot should have an optimal link length for each slope angle. This paper reports further experimental results and considerations in order to supplement the previous weak results
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