Mobile Robots

General Concepts

This chapter presents the fundamental general concepts of mobile robots that can move from one place to another autonomously within a predefined workspace to achieve their desired goals. Specifically, the chapter (i) provides a list of the main historical landmarks of general robotics and mobile robots, (ii) discusses the locomotion issues of ground (wheeled, legged) mobile robots, (iii) investigates the wheel and drive types of mobile robots (nonholonomic, omnidirectional) and, (iv) introduces the concepts of mobile robot degree of mobility, degree of steerability, and maneuverability.

Keywords

Wheeled mobile robot; maneuverability; fixed wheel; castor wheel; universal wheel; mecanum wheel; differential drive; bicycle drive; tricycle drive; omnidirectional drive; Ackerman steering; skid steering

1.1 Introduction

Mobile robots are robots that can move from one place to another autonomously, that is, without assistance from external human operators. Unlike the majority of industrial robots that can move only in a specific workspace, mobile robots have the special feature of moving around freely within a predefined workspace to achieve their desired goals. This mobility capability makes them suitable for a large repertory of applications in structured and unstructured environments. Ground mobile robots are distinguished in wheeled mobile robots (WMRs) and legged mobile robots (LMRs) Mobile robots also include unmanned aerial vehicles (UAVs), and autonomous underwater vehicles (AUVs). WMRs are very popular because they are appropriate for typical applications with relatively low mechanical complexity and energy consumption. Legged robots are suitable for tasks in nonstandard environments, stairs, heaps of rubble, etc. Typically, systems with two, three, four, or six legs are of general interest but many other possibilities also exist. Single-leg robots find rare applications because they can only move by hopping. Mobile robots also include mobile manipulators (wheeled or legged robots equipped with one or more light manipulators to perform various tasks).

The objective of this chapter is to present the fundamental general concepts of WMRs. In particular, the chapter

 provides a list of the main historical landmarks of general robotics and mobile robots;

 discusses the locomotion issues of ground (wheeled, legged) mobile robots;

 investigates the wheel and drive types of mobile robots (nonholonomic, omnidirectional); and

 introduces the concepts of mobile robot degree of mobility, degree of steerability, and maneuverability.

1.2 Definition and History of Robots

1.2.1 What Is a Robot?

The term "robot" (robota) was used for the first time in 1921 by the Czech writer Karel Capek and means slave servant or forced labor. In science and technology there is not a global or unique definition of a robot. When Joseph Engelberger, the father of modern robotics, was asked to define a robot he said: "I can't define a robot but I know one when I see one." The Robotics Institute of America (RIA) defines an industrial robot as "a reprogrammable multi-functional manipulator designed to move materials, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks which also acquire information from the environment and move intelligently in response." This definition does not capture mobile robots.

The definition adopted in the European Standard EN775/1992 is as follows: "Manipulating industrial robot is an automatically controlled reprogrammable multi-purpose, manipulative machine with several degrees of freedom (DOF), which may be either fixed in place or mobile for use in industrial automation applications.

Ronald Arkin says: "An intelligent robot is a machine able to extract information from its environment and use knowledge about its work to move safely in a meaningful and purposive manner."

Rodney Brooks says: "To me a robot is something that has some physical effect on the world, but it does it based on how it senses the world and how the world changes around it."

In summary, a robot is referred in the literature as a machine that performs an intelligent connection between perception and action. An autonomous robot is programmed to work without human intervention, and with the aid of embodied artificial intelligence can perform and live within its environment. Today's mobile robots can move around safely in cluttered surroundings, understand natural speech, recognize real objects, locate themselves, plan paths, and generally think by themselves. Intelligent mobile robot design employs the methodologies and technologies of intelligent, cognitive, and behavior-based control. Mobile robots must maximize flexibility of performance subject to minimal input dictionary and minimal computational complexity.

1.2.2 Robot History

The history of robots can be divided in two general periods [1,2]:

 Ancient and preindustrial period

 Industrial and robosapien period

1.2.2.1 Ancient and Preindustrial Period

The first robot in the worldwide history (around 2500-3000 BC) is the Greek mythodological mechanical creature called Talos ("?????") [3]. This name is attributed both to a human being (the son of Daedalus' sister Perdika) and a mechanical artificial entity constructed by Hephaestus, under the order of Zeus, with bronze body and a single vein from the neck up to the ankle, where a copper nail blocked it out. Talos was gifted by Zeus to Europe who afterward gave him to her son Minos to guard Crete. Talos died when the Argonaut Poas removed the copper nail from his heel. This resulted in the spilling out of the ichor ("the blood of the immortals") flowing in the Poas' vein. The name Talos was given to Asteroid 5786 discovered by Robert McNaught, on September 31, 1991 at Siding Spring Observatory in Coonabarabran, New South Wales (Australia). Around 350 BC the friend of Plato Archytas of Tarentum constructed a mechanical bird ("pigeon") which was propelled by steam. This represents one of the earlier historic studies of flight or airplane model:

Around 270 BC: Ktesibios ("?t?sß???") has discovered the water clock that involves movable parts, and wrote his book "About Pneumatics" (?e? ??e?µat???) where he has shown that air is a material entity.

Around 200 BC: Chinese artisans design and construct mechanical automata, such as orchestra, etc.

Around 100 AD: Heron of Alexandria designs and constructs several regulating mechanisms, such as the odometer, the steam boiler (aclopyle), the automatic opening of temples, and automatic distribution of wine.

Around 1200 AD: The Arab author Al Jazari writes "Automata" which is one of the most important texts in the study of the history of technology and engineering.

Around 1490: Leonardo Da Vinci constructs a device that looks as an armored knight. This seems to be the first humanoid robot in Western civilization.

Around 1520: Hans Bullman (Nuernberg, Germany) builds the first real android in robot history imitating people (e.g., playing musical instruments).

1818: Mary Shelley writes the famous novel Frankenstein based on an artificial life creature (robot) developed by Dr. Frankenstein. All robots in this novel turned eventually against human kind in a frightening way.

1921: The Chzech dramatist Karel Capek coins the term robota (robot) in his play named "Rossum's Universal Robots" meaning compulsory or slavery work.

1940: The science fiction writer Isaac Asimov used for the first time the terms "robot" and "robotics." In 1942, he wrote "Runaround" a story that involved his three laws of robotics (known as Asimov's laws).

1.2.2.2 Industrial and Robosapien Period

This period starts in 1954 when George Devol, Jr patented his multijoined robotic arm (the first modern robot). In 1956, together with Joseph Engelberger founded the world's first robot company called Unimation (from Universal Automation):

1961: The first industrial robot called Unimate joined a die-casting production line at General Motors.

1963: The RanchoArm, the first computer controlled robotic arm, was put in operation at the Rancho Los Amigos Hospital (Downey, CA). This was a prosthetic arm designed to aid the handicapped.

1969: The first truly flexible arm, known as the, Stanford Arm, was developed in the Stanford Artificial Intelligence Laboratory by Victor Scheinman. This arm soon became a standard, and is still influencing the design of today's robotic manipulators.

1970: This is the starting year of mobile...