Design and implementation of a novel hybrid quadruped spherical mobile robot

Abstract

Spherical mobile robots are a novel type of mobile robots having some advantages in motion over other ordinary mobile robots. The advantages can be related to their symmetric spherical shape. Despite many works being conducted in recent years on spherical mobile robots, it seems that finding the best driving mechanism with higher efficiency still needs much research. In this article, a novel type of spherical mobile robot is introduced. This robot has a hybrid structure of the spherical robots and ordinary four legged or quadruped robots. Adding legs to the spherical robot reduces some disadvantages of its behavior. After introduction of the mentioned robot, its dynamic model based on Lagrange equations is obtained. The accuracy of the developed dynamic model in tracking a trajectory is verified through a dynamic simulation. Experimental results in tracking a square trajectory is presented to show the verification.

Introduction

The research on robotics engineering has grown tremendously in recent years. Many researchers and scientists all over the world have made an attempt to achieve novel motion and control mechanisms for robots in various applications. The field of mobile robots which can move freely unlike the manipulators is one of the most important fields in robotics engineering. Car like robots, humanoid robots and nature-inspired robots such as snake or fish robots are some kinds of mobile robots. One can name many types of mobile robots, each of them with advantages and disadvantages and therefore, they can be used in some applications considering their advantages. The spherical mobile robot is a novel type of robot having found a remarkable place among the other mobile robots in recent years [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. It has some specific characteristics over other types such as higher stability in motion, easy and rapid recovery of situation when the robot collides with obstacles [1], [2], and ability to follow the path with the least resistance [3]. These characteristics are due to the external spherical shape of the robot. The spherical mobile robot is often made of two essential parts. The internal driving unit is usually called IDU, whose task is the mobilization of the robot. It contains several pieces of equipment for power storage and control and driving units. The robot’s outer spherical shell is the second essential part usually made of plastics or glass or other similar materials letting the radio connection between the internal unit and the outside master computer [1]. Yet, many researches on the spherical robots have been about the improvement of their propulsion mechanism. So far, several mechanisms have been proposed for the propulsion system of the spherical robots, and we are going to review some of them here.

Halme et al. offered a propulsion system for their spherical robot made of a motor driven wheel whose turning disturbed the mass center equilibrium. Hence, mobility of their robot was based on disturbing the robot mass center position by IDU motion. They also modeled their spherical mobile robot kinematically and dynamically [1]. BHQ-1 was presented by Zhan et al. [2]. They studied the dynamic modeling of their robot using a simplified Boltzmann–Hamel equation. They showed experimentally that their deduced equations could govern the behavior of their proposed robot. “August” was a new design of an omnidirectional spherical mobile robot designed by Javadi, et al. [3]. They used the well-known Newton method for its dynamic modeling and discussed its trajectory planning. Joshi et al. made a new mechanism for their spherical robot consisting of two DC motors and worked on the principle of conservation of angular momentum [4]. They applied Euler parameters to establish the mathematical formulation of the robot. Jia et al. developed a gimbal counter-weight pendulum for their studied spherical robot, with two driving and steering motors [5]. The driving motor connected gimbal and outer shell produced the driving torque about the lateral rotation axis of the gimbal. The steering motor located on the longitudinal axis of the gimbal, produced the leaning torque for steering of the robot. They developed the dynamic model of the robot using the constrained Lagrangian method and presented simulation results. The literature review on the similar researches related to spherical robots shows that there are mainly two essential principles for their movement, disturbing the center of gravity and angular momentum conservation. In addition, it can be found that many spherical mobile robots are based on the principles of center of gravity offset [6]. Shu et al. presented a novel kind of spherical robot whose motion was based on conservation of angular momentum [6]. This robot was made of a ball-shaped outer shell containing an IDU of the robot. The IDU of the robot composed of two motors and a counter-weight. Motor 1 was in the horizontal position and its shaft was fixed to the shell. Its role was driving the robot. Motor 2 was in the vertical position w.r.t the surface and its role was steering the robot. They used Lagrange equations to study the dynamic model of their robot. Then they discussed the mechanism of controlling the robot. Michaud invented “Roball” whose IDU was composed of a $T$ shaped-structure mounting all components on it [15]. Two DC motors were mounted horizontally between the IDU and outer shell whose motion made the center of gravity of the robot move forward and backward to produce the robot’s movement. The steering role of the robot was for the third motor on the vertical position of the frame. Bicchi et al. designed a spherical robot with a small car with two wheels as an IDU [17], [18]. From the motion of this car, the center of gravity of the robot was changed, thereupon the robot moved on the surface. Phipps et al. studied the “Rolling Disk Biped” hybrid robot named RDB [20]. RDB was able to walk, climb and roll. They developed the quasi-static rolling controller for their robot. Then after a comparison between the rolling and walking of the robot, they concluded that rolling can improve energy efficiency over walking.