Proximal Actuation of an Elastically Loaded Scissors Mechanism for the Leg Design of a Quadruped Robot

Muhammad Hamza Asif Nizami,Muhammad Jawad Khan,Darren Dancey,Sara Ali,Yasar Ayaz,Muhammad Naveed,Zaid Ahsan Shah,Raheel Nawaz,Khalid Akhtar

doi:10.1109/access.2020.3037250

Abstract

Spring Loaded Pantographs (SLPs) are frequently used in designing lightweight limbs for multi-legged robots. Quadruped robots that incorporate cable-pulled SLP legs have proven to be agile, robust and capable of conserving energy during their gait cycle. In such designs, the extension of the distal segments via the knee joint is dependent upon the length of the cable. In this article we propose the use of an Elastically Loaded Scissors Mechanism (ELS Mechanism or ELSM), which is a variant of the SLP. Driven by 'pulling' onto the proximal joint of the scissors as opposed to the distal joint, this proposed leg utilizes the increased mechanical advantage of the scissors mechanism to 'amplify' input angles to larger output displacement by the knee joint. Analysis and Simulations reveal that the proposed mechanism achieves increased motion speed as compared to the SLP mechanism. This, however, comes at the cost of higher load on the actuator which serves as an engineering trade-off. This is validated by experimentation using motion capture and load motor techniques of the SLP and ELS configurations in a physical quadruped robot.

Highlights

Legged locomotion is widely considered a prime candidate for handling uneven terrains since it requires comparatively sparse interaction with ground than its wheeled or tracked locomotion alternatives
In this paper we propose the use of an Elastically Loaded Scissors Mechanism (ELS Mechanism or ELSM), which is a variant of the Spring Loaded Pantographs (SLPs)
As it had been pointed out that in small sized quadrupeds, the major hindrance to achieve bio-inspired locomotion is the inability of servo motors actuating the knee joint to reach beyond their saturation velocity to achieve higher stepping frequency, we propose the usage of scissors mechanisms instead of pantograph mechanism

Summary

Introduction

Legged locomotion is widely considered a prime candidate for handling uneven terrains since it requires comparatively sparse interaction with ground than its wheeled or tracked locomotion alternatives. From [8] who demonstrated the application of the Spring Mass model in the design of a family of dynamically stable robots ranging from single legged hoppers to quadruped robots, to the design of SCOUT II [9], BigDog [10], StarlETH [11] and ATRIAS [12], ATLAS and PETMAN [13] and other such dynamically stable robots. These models govern the planning and control of most modern walking robots. The main aim is to either simplify or ( i ) (iii) ( v ) ( a )

Objectives

Discussion

Conclusion