Even after many technological advancements in wheeled and tracked vehicles, still, their mobility is limited to plain and less rough terrains. Even if we develop a one with the maximum capability to travel in rough terrain, speed is to be compromised heavily. In order to resolve this problem, we can look into the solution of nature. All the animals and humans are capable to access much of the earth’s landmass with the legs. Though it is less stable, slower and needs a complex blend of features, it has been the locomotion of almost all the creatures due to its phenomenal advantages.
Since 1960, many engineers of different disciplines have studied this, came to gather and built many vehicles that work on Legged Locomotion. Even though so many path-breaking experiments and simulations have been carried out, still, the technology has not reached up to the mark to be used extensively in prospective applications like defence, nuclear plants, assistance for disables etc. The reason behind this lag is due to its complex system design. Though Legged Robot can be of Two, Six or more Legs, Four Leg system is a good trade-off between stability and Complexity. Quadruped has high Load Carrying Capacity and better stability over Biped or Humanoid Robots and in comparison with Multi-Legged systems, it is having broader Leg Space, less Mechanism Redundancy and lower level of Complexity. As per one of the pioneer scientists in Quadruped Robot, Shigeo Hirose, “Quadruped Robot is the best form of Legged Robots from the aspects of stability, control difficulty and manufacturing cost”. Here in this report, an attempt is made to touch upon some of the aspects of Quadruped Locomotion.
In Quadruped Locomotion, Gait Planning is the centred aspect. Gait can be defined by the time and the location history of placement and lifting of each leg, which can ultimately lead to motion of the body in a Specific Pre-defined direction. To walk in different conditions, various gait patterns have been identified by the researchers mainly by observing the nature.
Most of the Quadruped Animals walk continuously when the path is clear. But in some conditions, the terrain where ‘Continuous Gait’ is not possible, and maintaining stability becomes important, the body moves while all four legs are on the ground. In this case, legs and body movement happens intermediately i.e. One after Another. Such ‘Discontinuous Gait’ is also a significant part of Legged Locomotion.
Most of the gait patterns are ‘Periodic’ in nature that means all the various motion happens at the same time in the cycle throughout the run. But, when terrain is highly irregular, the placement and lift of each foot are subject to the condition and the periodicity cannot be maintained in that case. Such a way, the Gait is classified in a second way i.e. ‘Periodic’ and ‘Non-Periodic’. These Non-Periodic’ Gaits are referred by many researchers as ‘Free Gaits’ which means, the Robot is free to choose the foothold and timing of each leg.
Based on the stability, the gaits can also be classified as Statically Stable Gait or ‘Static Gait’ which maintains stability by generating the gait such a way to keep the Gravity Centre always inside the Support Polygon and ‘Dynamic Gait’. Support Polygon is the polygon created by 3 or 4 leg foothold points.