Bioinspired sprawling robotic leg and a path-planning procedure

Abstract

This article shows the characteristics of a sprawling robotic leg inspired by the limb postures of certain reptilian animals known as sprawling-legged creatures. The main part of the robotic limb is based on the eight-bar Peaucellier–Lipkin linkage, and its main attribute is the ability to trace a true straight line, due to the rotational motion of the input link. However, when the eight-bar linkage is modified, it is capable of tracing true circular concave or convex arcs, when two of its constitutive links have distinct and precise lengths. This gives rise to the concepts of concavity and convexity, related to a robotic leg based on the Peaucellier–Lipkin mechanism, such as the one described herein. Our bioinspired robotic leg can trace concave or convex curves, as well as straight lines, making it a reptile-like robotic limb that is very similar to the natural one. We also introduce the concept of rotation center tuning, which refers to the ability of the leg to adapt its posture to the center of rotation of the entire walking machine, resulting in an easy and suitable gait process. The theoretical information is illustrated through the simulation of an example that provides a path-planning procedure, focusing on the rotation center tuning process and a walking gait. The example also includes the design of an elliptical path projected onto the cylindrical workspace and followed by the reptilian foot.

Hexapod with legs based on Peaucellier–Lipkin mechanisms

“…The second one, written by Núñez-Altamirano et al, 3 formulates the dynamics of a single PL-based leg when it executes the swing phase along a straight path. The third one, reported by Juárez-Campos et al, 4 explains the origins of conception of the PL-based leg. It was inspired by the sprawling leg postures of some reptilian animals.…”

“…The contribution of this research concerns the bioinspired design of long legs relative to its body, created in the likeness of the arthropod known as harvestman. 20 The five-DoF robotic leg presented in this article and in other works [2][3][4]7 was conceived from the one-DoF PL mechanism, which is commonly referred to as Straight Line Mechanism because it uses a rotation of the input link to create a straight line motion of the output point. 21 It was invented by Peaucellier (1864), an officer of the French army, and by Lipkin (1871), a Russian mathematician.…”

“…According to equations (1) and (2), d AB and d BC can be expressed as function of r c and k AC , see equations (3) and (4)…”

“…Each leg performs its own particular RCT. 4 After the RCT process, the geometric center of the walking machine, denoted by point G, moves along the arc length a G , given in Table 5, coincident with the circular path shown in Figure 21. Its coordinates are given by equation 40, when varies from min to max , given in Table 6, where U c r is the center of rotation generated byê 1 U andê 2 U , see Table 5.…”

“…Once the leg is configured, only the remaining two DoFs are driven to provide the walking travel in agreement to the support and transfer phases exerted on foot during the gait. 4 This process of walking is different from the one exerted by traditional mechanical architectures, which ordinarily requires three DoFs, which are coordinately controlled, to move the whole leg and position its foot.…”