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Chapter 8 — Motion Control

Wan Kyun Chung, Li-Chen Fu and Torsten Kröger

This chapter will focus on the motion control of robotic rigid manipulators. In other words, this chapter does not treat themotion control ofmobile robots, flexible manipulators, and manipulators with elastic joints. The main challenge in the motion control problem of rigid manipulators is the complexity of their dynamics and uncertainties. The former results from nonlinearity and coupling in the robot manipulators. The latter is twofold: structured and unstructured. Structured uncertainty means imprecise knowledge of the dynamic parameters and will be touched upon in this chapter, whereas unstructured uncertainty results from joint and link flexibility, actuator dynamics, friction, sensor noise, and unknown environment dynamics, and will be treated in other chapters. In this chapter, we begin with an introduction to motion control of robot manipulators from a fundamental viewpoint, followed by a survey and brief review of the relevant advanced materials. Specifically, the dynamic model and useful properties of robot manipulators are recalled in Sect. 8.1. The joint and operational space control approaches, two different viewpoints on control of robot manipulators, are compared in Sect. 8.2. Independent joint control and proportional– integral–derivative (PID) control, widely adopted in the field of industrial robots, are presented in Sects. 8.3 and 8.4, respectively. Tracking control, based on feedback linearization, is introduced in Sect. 8.5. The computed-torque control and its variants are described in Sect. 8.6. Adaptive control is introduced in Sect. 8.7 to solve the problem of structural uncertainty, whereas the optimality and robustness issues are covered in Sect. 8.8. To compute suitable set point signals as input values for these motion controllers, Sect. 8.9 introduces reference trajectory planning concepts. Since most controllers of robotmanipulators are implemented by using microprocessors, the issues of digital implementation are discussed in Sect. 8.10. Finally, learning control, one popular approach to intelligent control, is illustrated in Sect. 8.11.

Different jerk limits of robot-arm trajectories

Author  Torsten Kröger

Video ID : 760

This video displays the motions of a 6-DOF industrial- robot arm controlled in joint space. The first reference trajectory is not jerk-limited. The second trajectory features a joint jerk limit of 400 deg/s^3 for all six joints, and the third trajectory has a jerk limit of 20 deg/s^3 for all robot joints.

Chapter 56 — Robotics in Agriculture and Forestry

Marcel Bergerman, John Billingsley, John Reid and Eldert van Henten

Robotics for agriculture and forestry (A&F) represents the ultimate application of one of our society’s latest and most advanced innovations to its most ancient and important industries. Over the course of history, mechanization and automation increased crop output several orders of magnitude, enabling a geometric growth in population and an increase in quality of life across the globe. Rapid population growth and rising incomes in developing countries, however, require ever larger amounts of A&F output. This chapter addresses robotics for A&F in the form of case studies where robotics is being successfully applied to solve well-identified problems. With respect to plant crops, the focus is on the in-field or in-farm tasks necessary to guarantee a quality crop and, generally speaking, end at harvest time. In the livestock domain, the focus is on breeding and nurturing, exploiting, harvesting, and slaughtering and processing. The chapter is organized in four main sections. The first one explains the scope, in particular, what aspects of robotics for A&F are dealt with in the chapter. The second one discusses the challenges and opportunities associated with the application of robotics to A&F. The third section is the core of the chapter, presenting twenty case studies that showcase (mostly) mature applications of robotics in various agricultural and forestry domains. The case studies are not meant to be comprehensive but instead to give the reader a general overview of how robotics has been applied to A&F in the last 10 years. The fourth section concludes the chapter with a discussion on specific improvements to current technology and paths to commercialization.

An autonomous cucumber harvester

Author  Elder J. van Henten, Jochen Hemming, Bart A.J. van Tuijl, J.G. Kornet, Jan Meuleman, Jan Bontsema, Erik A. van Os

Video ID : 308

The video demonstrates an autonomous cucumber harvester developed at Wageningen University and Research Centre, Wageningen, The Netherlands. The machine consists of a mobile platform which runs on rails, which are commonly used in greenhouses in The Netherlands for the purpose of internal transport, but they are also used as a hot- water heating system for the greenhouse. Harvesting requires functional steps such as the detection and localization of the fruit and assessment of its ripeness. In the case of the cucumber harvester, the different reflection properties in the near infrared spectrum are exploited to detect green cucumbers in the green environment. Whether the cucumber was ready for harvest was identified based on an estimation of its weight. Since cucumbers consist 95% of water, the weight estimation was achieved by estimating the volume of each fruit. Stereo-vision principles were then used to locate the fruits to be harvested in the 3-D environment. For that purpose, the camera was shifted 50 mm on a linear slide and two images of the same scene were taken and processed. A Mitsubishi RV-E2 manipulator was used to steer the gripper-cutter mechanism to the fruit and transport the harvested fruit back to a storage crate. Collision-free motion planning based on the A* algorithm was used to steer the manipulator during the harvesting operation. The cutter consisted of a parallel gripper that grabbed the peduncle of the fruit, i.e., the stem segment that connects the fruit to the main stem of the plant. Then the action of a suction cup immobilized the fruit in the gripper. A special thermal cutting device was used to separate the fruit from the plant. The high temperature of the cutting device also prevented the potential transport of viruses from one plant to the other during the harvesting process. For each successful cucumber harvested, this machine needed 65.2 s on average. The average success rate was 74.4%. It was found to be a great advantage that the system was able to perform several harvest attempts on a single cucumber from different harvest positions of the robot. This improved the success rate considerably. Since not all attempts were successful, a cycle time of 124 s per harvested cucumber was measured under practical circumstances.

Chapter 22 — Modular Robots

I-Ming Chen and Mark Yim

This chapter presents a discussion of modular robots from both an industrial and a research point of view. The chapter is divided into four sections, one focusing on existing reconfigurable modular manipulators typically in an industry setting (Sect. 22.2) and another focusing on self-reconfigurable modular robots typically in a research setting (Sect. 22.4). Both sections are sandwiched between the introduction and conclusion sections.

This chapter is focused on design issues. Rather than a survey of existing systems, it presents some of the existing systems in the context of a discussion of the issues and elements in industrial modular robotics and modular robotics research. The reader is encouraged to look at the references for further discussion on any of the presented topics.

SMORES

Author  Jay Davey

Video ID : 1

SMORES robot showing self-reconfiguration. Reference: J. Davey, N. Kwok, M. Yim: Emulating self-reconfigurable robots - Design of the SMORES system, Proc. IEEE/RSJ Int. Conf. Intell. Robot. Syst. (IROS), Vilamoura (2012), pp. 4464-4469

Chapter 76 — Evolutionary Robotics

Stefano Nolfi, Josh Bongard, Phil Husbands and Dario Floreano

Evolutionary Robotics is a method for automatically generating artificial brains and morphologies of autonomous robots. This approach is useful both for investigating the design space of robotic applications and for testing scientific hypotheses of biological mechanisms and processes. In this chapter we provide an overview of methods and results of Evolutionary Robotics with robots of different shapes, dimensions, and operation features. We consider both simulated and physical robots with special consideration to the transfer between the two worlds.

Coevolved predator and prey robots

Author  Dario Floreano

Video ID : 38

Coevolved predator and prey robots engaged in a tournament. The predator and prey robot (from left to right) are placed in an arena surrounded by walls and are allowed to interact for several trials starting at different, randomly-generated orientations. Predators are selected on the basis of the percentage of trials in which they are able to catch (i.e., to touch) the prey, and prey on the basis of the percentage of trials in which they were able to escape (i.e., to not be touched by) predators. Predators have a vision system, whereas the prey have only short-range distance sensors, but can go twice as fast as the predator. Collision between robots is detected by a conductive belt at the base of the robots.

Chapter 34 — Visual Servoing

François Chaumette, Seth Hutchinson and Peter Corke

This chapter introduces visual servo control, using computer vision data in the servo loop to control the motion of a robot. We first describe the basic techniques that are by now well established in the field. We give a general overview of the formulation of the visual servo control problem, and describe the two archetypal visual servo control schemes: image-based and pose-based visual servo control. We then discuss performance and stability issues that pertain to these two schemes, motivating advanced techniques. Of the many advanced techniques that have been developed, we discuss 2.5-D, hybrid, partitioned, and switched approaches. Having covered a variety of control schemes, we deal with target tracking and controlling motion directly in the joint space and extensions to under-actuated ground and aerial robots. We conclude by describing applications of visual servoing in robotics.

2.5-D VS on a 6-DOF robot arm (1)

Author  Francois Chaumette, Seth Hutchinson, Peter Corke

Video ID : 64

This video shows a 2.5-D VS on a 6-DOF robot arm with (x_g, log(Z_g), theta u) as visual features. It corresponds to the results depicted in Figure 34.12.

Chapter 51 — Modeling and Control of Underwater Robots

Gianluca Antonelli, Thor I. Fossen and Dana R. Yoerger

This chapter deals with modeling and control of underwater robots. First, a brief introduction showing the constantly expanding role of marine robotics in oceanic engineering is given; this section also contains some historical backgrounds. Most of the following sections strongly overlap with the corresponding chapters presented in this handbook; hence, to avoid useless repetitions, only those aspects peculiar to the underwater environment are discussed, assuming that the reader is already familiar with concepts such as fault detection systems when discussing the corresponding underwater implementation. Themodeling section is presented by focusing on a coefficient-based approach capturing the most relevant underwater dynamic effects. Two sections dealing with the description of the sensor and the actuating systems are then given. Autonomous underwater vehicles require the implementation of mission control system as well as guidance and control algorithms. Underwater localization is also discussed. Underwater manipulation is then briefly approached. Fault detection and fault tolerance, together with the coordination control of multiple underwater vehicles, conclude the theoretical part of the chapter. Two final sections, reporting some successful applications and discussing future perspectives, conclude the chapter. The reader is referred to Chap. 25 for the design issues.

Two underwater Folaga vehicles patrolling a 3-D area

Author  Gianluca Antonelli, Alessandro Marino

Video ID : 94

This video records one of the final experiments for the European project Co3AUV (http://www.Co3-AUVs.eu). It was conducted successfully during February 2012 in collaboration with GraalTech at the NURC (NATO Undersea Research Center) site.

Chapter 19 — Robot Hands

Claudio Melchiorri and Makoto Kaneko

Multifingered robot hands have a potential capability for achieving dexterous manipulation of objects by using rolling and sliding motions. This chapter addresses design, actuation, sensing and control of multifingered robot hands. From the design viewpoint, they have a strong constraint in actuator implementation due to the space limitation in each joint. After briefly introducing the overview of anthropomorphic end-effector and its dexterity in Sect. 19.1, various approaches for actuation are provided with their advantages and disadvantages in Sect. 19.2. The key classification is (1) remote actuation or build-in actuation and (2) the relationship between the number of joints and the number of actuator. In Sect. 19.3, actuators and sensors used for multifingered hands are described. In Sect. 19.4, modeling and control are introduced by considering both dynamic effects and friction. Applications and trends are given in Sect. 19.5. Finally, this chapter is closed with conclusions and further reading.

UBH2, University of Bologna Hand, ver. 2 (1992)

Author  Claudio Melchiorri

Video ID : 756

This hand, developed at the University of Bologna at the beginning of the 1990s, was the first to implement the "whole-hand-manipulation" capability. It was equipped with intrinsic tactile force/torque sensors in each phalange and in the palm.

Chapter 25 — Underwater Robots

Hyun-Taek Choi and Junku Yuh

Covering about two-thirds of the earth, the ocean is an enormous system that dominates processes on the Earth and has abundant living and nonliving resources, such as fish and subsea gas and oil. Therefore, it has a great effect on our lives on land, and the importance of the ocean for the future existence of all human beings cannot be overemphasized. However, we have not been able to explore the full depths of the ocean and do not fully understand the complex processes of the ocean. Having said that, underwater robots including remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) have received much attention since they can be an effective tool to explore the ocean and efficiently utilize the ocean resources. This chapter focuses on design issues of underwater robots including major subsystems such as mechanical systems, power sources, actuators and sensors, computers and communications, software architecture, and manipulators while Chap. 51 covers modeling and control of underwater robots.

Preliminary experimental result of the ROV iTurtle

Author  Hyun-Taek Choi

Video ID : 797

This video shows the preliminary experimental result of an underwater robot named iTurtle developed by KRISO (Korea Research Institute of Ships and Ocean Engineering). iTurtle is especially designed for underwater-structure inspection as an observation class ROV. It has dimming and direction controllable LED and halogen lights and a HD underwater camera, all of which are positioned by four horizontal thrusters. More importantly, its system software architecture is implemented using the structure explained in Fig. 25.7. The motion in this video is controlled by a human operator.

Chapter 7 — Motion Planning

Lydia E. Kavraki and Steven M. LaValle

This chapter first provides a formulation of the geometric path planning problem in Sect. 7.2 and then introduces sampling-based planning in Sect. 7.3. Sampling-based planners are general techniques applicable to a wide set of problems and have been successful in dealing with hard planning instances. For specific, often simpler, planning instances, alternative approaches exist and are presented in Sect. 7.4. These approaches provide theoretical guarantees and for simple planning instances they outperform samplingbased planners. Section 7.5 considers problems that involve differential constraints, while Sect. 7.6 overviews several other extensions of the basic problem formulation and proposed solutions. Finally, Sect. 7.8 addresses some important andmore advanced topics related to motion planning.

Simulation of a large crowd

Author  Dinesh Manocha

Video ID : 21

Motion-planning methods can be used to simulate a large crowd which is a system with a very high degree of freedom. This video illustrates an approach that uses an optimization method to compute a biomechanically energy-efficient, collision-free trajectory for each agent. Many phenomena arise such as lane formation.

Chapter 15 — Robot Learning

Jan Peters, Daniel D. Lee, Jens Kober, Duy Nguyen-Tuong, J. Andrew Bagnell and Stefan Schaal

Machine learning offers to robotics a framework and set of tools for the design of sophisticated and hard-to-engineer behaviors; conversely, the challenges of robotic problems provide both inspiration, impact, and validation for developments in robot learning. The relationship between disciplines has sufficient promise to be likened to that between physics and mathematics. In this chapter, we attempt to strengthen the links between the two research communities by providing a survey of work in robot learning for learning control and behavior generation in robots. We highlight both key challenges in robot learning as well as notable successes. We discuss how contributions tamed the complexity of the domain and study the role of algorithms, representations, and prior knowledge in achieving these successes. As a result, a particular focus of our chapter lies on model learning for control and robot reinforcement learning. We demonstrate how machine learning approaches may be profitably applied, and we note throughout open questions and the tremendous potential for future research.

Learning motor primitives

Author  Jens Kober, Jan Peters

Video ID : 355

The video shows recent success in robot learning for two basic motor tasks, namely, ball-in-a-cup and ball paddling. The video illustrates Section 15.3.5 -- Policy Search, of the Springer Handbook of Robotics, 2nd edn (2016). Reference: J. Kober, J. Peters: Imitation and reinforcement learning - Practical algorithms for motor primitive learning in robotics, IEEE Robot. Autom. Mag. 17(2), 55-62 (2010)