Simulation and Optimization For Inchworm Like-Robot Locomotion

The intent of this work was to develop an optimized design for inchworm locomotion. Different works found in the literature imitate inchworm locomotion using different methods in order to grip the surface of the ground such as pads, magnets or wheels. On the other hand, this inchworm like-robot uses controlled friction by changing water between the end bodies. This water, moved by a miniature pump, is part of the weight of the bodies in contact with the floor. A prototype of the robot was built and recorded at 60 frames per second in order to obtain experimental results. A model in Matlab for the study of inchworm locomotion, was defined by three different theories (Multibody constraint equations, impulse and momentum analysis of impact, and variable system of particles) used in conjunction to obtain the equations of motion of the system. It was imperative to perform an initial experiment without changeable mass and a similar one with changeable mass in order to compare the effectiveness of the robot’s motion with and without water. Optimization theory was used as a tool to evaluate the dynamic behavior of the robot and find a more appropriate solution. The solutions of the optimization are not to claim perfection but for now they show improvement in the behavior of the robot. INTRODUCTION Requiring both propulsive and control mechanisms, animals involve a contractile structure (muscles in most cases) to generate movement and a nervous system to coordinate locomotion. Two types of locomotion, axial and appendicular, achieve animal motion. In this paper we have a special interest in axial locomotion where the animal’s body changes its shape and the interaction with the environment provides the propulsive force. Inchworms are members of the phylum Annelida (i.e. segmented worms). Inchworms move by a process known as peristaltic contraction. A worm's body is a fluid filled tube divided into separate segments. There are circular muscles that surround each segment and longitudinal muscles running from segment to segment along the length of the worm. Contraction of the longitudinal muscles shortens and widens the segments of the worm’s body. Circular muscle contraction lengthens and narrows the segments. By alternating these processes in wave-like motion the worm moves forward or backward. This type of locomotion is important because of the adaptation to the surrounding environment. The inchworm doesn’t need the whole body to move. Because it uses just a small part of its body to have enough frictional resistance along the surface, it can adapt easily to difficult terrains. Overall, an inchworm biomimetic robot can be used in different tasks where human life is in danger. For instance deactivating footmines, military espionage, urban search and rescue, cleaning or repairing oil tubes, or just helping humans to take pictures or record different elements from nature in hostile terrains. Even though most of today’s mobile robots have wheels or legs, other classes of robots, such as hyper-redundant (i.e. snake-like or inchworm-like robots), are becoming more and more popular [1]. Snake-like robots have been studied before and a variety of robots and analysis have been developed. One of the related works is a robot capable of propelling itself forward using internal torques only. The robot consisted of a long chain of serially connected segments. The lead segment defines the path to be traced, and the additional segments are constrained to follow this lead [2]. There are other ways to achieve the motion of a snake as in Klaassen [3] in which the mechanism consists of different sections with surface sensors. Each section has three motors to control the position of one universal joint by way of ropes. In Ohno [4], the robot is composed of serially connected pneumatic modules. Each module had pneumatic actuators, valves, displacement sensors, springs, and a microprocessor inside its body. Each module had three degrees of freedom. In order to generate friction between the belly of the machine and the ground, passive wheels were installed into the robot preventing lateral slipping. Other studies of hyper-redundant robots, more specifically inchworm-like robots, have been studied before. One of the previous works presented actuators with binary actions (on/off) that were used in the design of grippers and extensors in order to change the shape of the robot to generate the motion. The grippers created friction when they were turned “on” or in